Refsum's Disease: Characterization of

the Enzyme Defect in Cell Culture

JAmESH. HERNDON,J^i, DANm STEINBERG, B. WIuLI UnD oRF, andHEINR M. FALES

From the Molecular Disease Branch, National Heart Institute and theLaboratory of Viral Immunology, Division of Biologics Standards, NationalInstitutes of Health, Bethesda, Maryland 20014

A B S T R A C T Refsum's disease (heredopathia atacticapolyneuritiformis, HAP) is an inherited neurologicaldisorder associated with storage of the branched-chainfatty acid, phytanic acid (3,7,11,15-tetramethylhexa-decanoic acid). Cultured fibroblasts derived from skinbiopsies of HAPpatients did not contain elevated levelsof phytanate, yet showed rates of phytanate-C-14C oxi-dation less than 3% of those seen in cells from controlsubjects. Cells of control subjects converted phytanateto a-hydroxyphytanate, to pristanate (the [n-i] homo-logue of phytanate) and to 4,8,12-trimethyltridecanoate,compounds previously identified as intermediates on themajor pathway for phytanate metabolism in animals,providing the first direct evidence that this same oxi-dative pathway is operative in human cells. None ofthese breakdown products could be found after incuba-tion of phytanate with HAP cells. Labeled a-hydroxy-phytanate and labeled pristanate were oxidized at normalrates by HAP cells. Oxidation of the latter proceededat normal rates both when added to the medium at verylow tracer levels and at levels 100 times greater. Phy-tanate was incorporated into and released from lipidesters at normal rates by HAP cells. Elevated levels offree phytanate in the medium were no more toxic toHAP cells than to control cells over the 48- to 72-hrexposures involved in these studies, as evidenced bymorphologic criteria and by ability to oxidize labeledpalmitate. These findings are consistent with the hy-pothesis that the cells from HAPpatients are deficient ina single enzyme involved in the a-hydroxylation of

Dr. Herndon's address is Section of Dermatology, De-partment of Medicine, Yale University School of Medicine,New Haven, Conn. 06510. Dr. Steinberg's address is Di-vision of Metabolic Disease, Department of Medicine, Uni-versity of California, San Diego, La Jolla, Calif. 92037.

Received for publication 1 November 1968 and in revisedform 3 February 1969.

phytanate, while the enzymes involved in later steps arepresent at normal or near-normal levels.

INTRODUCTION

Heredopathia atactica polyneuritiformis (HAP) was de-fined as a clinical entity by Refsum in 1946 (1). Con-stant features of the syndrome include retinitis pigmen-tosa, peripheral polyneuropathy, cerebellar ataxia, andelevated cerebrospinal fluid protein without pleocytosis.Cardiac conduction abnormalities, pupillary changes,nerve deafness, anosmia, ichthyosis, and bony abnor-malities occur in a large proportion of cases (2). Anautosomal recessive pattern of inheritance was proposedby Refsum, and additional genetic data support this(3). In 1963, Klenk and Kahlke showed that the syn-drome was associated with accumulation of phytanic acid(3,7,11,15-tetramethylhexadecanoic acid) in blood andtissues (4). Studies by Steinberg and coworkers (5-8)have shown that phytanic acid is not synthesized en-dogenously but originates in the diet and that the pa-tients with HAPhave a defect in the oxidative pathwayfor degradation of phytanic acid. With the recent eluci-dation of a major pathway for phytanic acid oxidation inanimals (9-11), it became possible to further localizethe defect by testing the ability of patients to oxidizemetabolic products of phytanate.

The results presented below show that the enzymedefect in phytanic acid oxidation persists in fibroblastcultures derived from the skin of patients with HAP.Data are presented showing that the alpha-oxidative path-way for phytanate oxidation established by animal stud-ies is present also in human tissues, the first degradationproducts being a-hydroxyphytanic acid and pristanicacid (2,6,10,14-tetramethylpentadecanoic acid). Finally,it is shown that the rate of oxidation of pristanic acid

The Journal of Clinical Investigation Volume 48 1969 1017

and of a-hydroxyphytanic acid is unimpaired in the pa- a-hydroxyphytanic acid-U-14C was prepared from phytanictients' cultured cells, indicating that the principal enzyme acid-U-~C by bromination and hydrolysis in aqueous metha-defect lies in the production of a-hydroxyphytanic acid, nol. The product after methylation behaved as a single com-' ponent on GLCand its mass spectrum, determined using thepresumably the first step in phytanic acid oxidation. LKB-9000 combined GLC-mass spectrometer, was charac-Preliminary reports of some of these findings have ap- teristic for the methyl ester of an a-hydroxy acid (17). Onpeared (12-14). the other hand, two distinct bands were resolved by TLC

(ethyl acetate-hexane, 10: 90; Rf values, 0.38 and 0.33).METHODS The hydroxyphytanate radioactivity was equally divided be-tween the two bands (upper band, 51%; lower band 49%).

Sources and preparation of labeled compounds. Phytol- Actually four stereoisomeric compounds are expected in theU-j4C was purified as previously described (15) from the synthesis of a-hydroxyphytanate from phytol (see Fig. 1).nonsaponifiable lipid fraction of algae grown in 'CO2. After Natural phytol (from chlorophyll) has been shown (18, 19)addition of carrier phytol, radiopurity was checked by thin- to have the D configuration at carbon-7 and -11. The absolutelayer chromatography (TLC) of phytol itself, TLC after configuration was shown by Kates et al. (20) to be R. Noderivative formation (aldehyde and acetyl ester), and by changes at these two asymmetric centers should occur duringradioassay of fractions collected from a gas-liquid chro- the synthesis from phytol, and their designation is omittedmatography (GLC) column (16) (17% ethylene glycol suc- in the following discussion. Reduction of the 2,3-doublecinate [EGS] on Chromosorb W, Applied Science Labora- bond of phytol (followed by oxidation of the alcohol func-tories Inc., State College, Pa.). tion) should give equal amounts of 3-D- and 3-L-phytanic

Phytanic acid-U-"C was prepared from labeled phytol acid. Each of these then gives rise to equal amounts ofeither as described in detail previously (15) or by the fol- 2-D-hydroxy and 2-L-hydroxy acid. Thus the four a-hydroxy-lowing procedure: phytol-U-j4C was reduced to dihydrophy- phytanate species expected are: (2-D, 3-D), (2-D, 3-L), (2-L,.tol-U-14C by hydrogenation with platinum oxide in ethanol.' 3-D), and (2-L, 3-L). Separation by TLC into two bands canThe dihydrophytol-U-1`C was then oxidized to phytanic acid- be best explained on the basis of interactions between theU-14C with chromic acid in glacial acetic acid (2 hr). Purity 2-hydroxyl and the 3-methyl groups affecting polarity. Thusof the phytanic acid (>95%) was confirmed by cochroma- one band might be expected to contain (2-D, 3-L) plus (2-L,tography of its methyl ester with authentic methyl phytanate 3-D), while the other would contain (2-D, 3-D) plus (2-L,on several GLC liquid phases and by gas-liquid radiochro- 3-L). Resolution of the latter pair certainly would not bematography (16). Unless otherwise stated, radiopurity of anticipated. In confirmation of this interpretation, the opticaleach of the labeled compounds used was similarly confirmed rotations of both bands at 589 m/u were essentially zero.by gas-liquid radiochromatography. Neither band exhibited a true Cotton effect from 250 to 217

Pristanic acid-U-j'C was prepared from phytanic acid- m/A, but the lower band showed (a)m' = + 1950 ± 20° and aU-14C by a Barbier-Wieland degradation and purified by sudden sharp rise before extinction at 215 m~u.- The upperthin-layer and gas-liquid chromatography (9). Homophy- zone was very weakly positive at the same wavelengthtanic acid-U-j'C was prepared from labeled phytanic acid (a)22g = + 520 ±300. Additional confirmation of the natureby the Arndt-Eistert procedure-treatment of phytanoyl of the two bands was obtained through the hydroxylationchloride with ethereal diazomethane and rearrangement of of 3D, 7D, 1iD phytanic acid kindly supplied by Dr. M. Kates.the diazoketone with a methanolic suspension of silver oxide. This material was converted to its 2-hydroxy derivative andRadiopurity of both pristanic and homophytanic acids was separated as the methyl ester into two bands on TLC identi-over 95%. cal in Rf with those obtained from the (3-D, 3-L) mixture.

Each zone exhibited the same mass spectral pattern, as ex-'For reasons which remain obscure, some batches of PtO. pected with diastereoisomers, and they may be tentatively as-

were associated with extensive hydrogenolysis and low signed the 2D, 3D, 7D, 11D and 2L, 3D, 7D, 111i configurations.vields of the reduced compound. Insufficient material was available for optical rotation studies.

NUMBEROF ISOMERSCH3 CH3 CH3 CH3

XV~~~~~~CCH20HC H3 2

PHYTOL

H2,03

PHYTANIC ACID

CH3%%" COOH 2 (3D, 3L)

'Br2,H20 CH3

ALPHA HYDROXY I' HC COH

PHYTANIC ACID OHOH

4 (3D , 3L )2D 2L 2D 2L

FIGURE 1 Formation of four isomeric forms of a-hydroxyphytanic acid inthe chemical synthesis from natural phytol (from chlorophyll).

[018 J. H. Herudon, Jr., D. Steinberg, B. W. Uhlend4qrf, and Ht M.Fales

The labeled a-hydroxyphytanate mixtures in the upper andlower TLC bands were used separately as substrates in thetissue culture system, testing for differences between refer-ence cultures and HAPcultures. In the absence of determina-tion of absolute configuration, they are arbitrarily designated"less polar isomers" and "more polar isomers," respectively.

Palmitic acid-9,10-8H and palmitic acid-1-"C were pur-chased from the New England Nuclear Corp., Boston,Mass. These and all other radioactive fatty acids, with theexception of a-hydroxyphytanate, were purified by GLC ofmethyl esters before use, as previously described (15).After hydrolysis of the methyl esters, labeled free acidswere converted to potassium soaps with KOHand added to aswirling aqueous solution containing albumin. The amountsof fatty acid used did not exceed the binding capacity of thealbumin present, and all solutions were clear when added tothe tissue culture media. The methyl ester of a-hydroxy-phytanic acid-U-"C was purified by TLC as described above.Trimethyl silyl ethers were prepared (21) from the eluteda-hydroxyphytanate isomers and subjected to analyticalGLC (17% EGSon Chromosorb W) with collection of frac-tions for radio-assay (16). Radiopurity greater than 93%was demonstrated. GLC of the nonsilylated a-hydroxyphy-tanyl methyl ester was unsatisfactory due to adsorptive losseson the column.

Human serum albumin labeled with "'I was obtained fromE. R. Squibb & Sons, New York, and used without furtherpurification.

Patient material and initiation of tissue cultures. Threepatients with HAP, all of whom had elevated plasma phy-tanate concentrations, served as donors of tissue for culture.Two, J. S. and K. S., are Irish siblings, first reported indetail by Ashenhurst, Millar, and Milliken (22), and sub-sequently studied at the Clinical Center (8). M. G. is a 23year old French female whose case history has been reportedby Bonduelle and coworkers (23). Control cultures werederived from four normal volunteers, one patient each withamyloidosis, Niemann-Pick disease, Hurler's syndrome,homocystinuria, and several with as yet undiagnosed storagediseases involving complex lipids.

Methods used in initiating and maintaining fibroblast tis-sue cultures have been previously described (24). Biopsiestaken in the Clinical Center at NIH were immediately mincedand placed in sterile culture medium. Biopsies taken abroadwere placed in a vial containing a few milliliters of sterilemedium, packed in ice, and shipped air express to Bethesda(48-72 hr en route). Monolayer cultures were establishedin 200-ml milk dilution bottles containing 10 ml of mediumgassed with 5%o CO2 in air. In each culture, cells having thespindle shape characteristic of fibroblasts overgrew the earlyoutgrowth of flattened epithelial elements. When studieswere performed (during the third through twentieth pas-sage in culture) all the cells appeared fibroblastic.

Cultures were initiated and maintained in Eagle's minimalessential medium, modified to contain 0.16%o sodium bi-carbonate and supplemented with nonessential amino acids(25), neomycin (50 /g/ml), and phenol red (0.01%o). Fetalbovine serum (not heat inactivated) was incorporated in allmedia. Final serum concentration was 10%o except in incuba-tions with radioactive fatty acids, when serum concentrationvaried from 1 to 5%o, depending on the amount of substrateused. Medium pH was adjusted to between 7.3 and 7.4 andincubations were carried out at 36.5'C in 32-oz prescriptionbottles containing 20 ml of medium and between 1 X 107 and2 X 107 cells in a stationary growth phase. Labeled fattyacids were either added directly to the serum-containing

medium just before Millipore filtration or were first com-plexed with fetal bovine serum or human serum albumin,sterilized by filtration through prewashed Millipore filters,and then added to the culture. In all cases, the final prepara-tion was clear, indicating completeness of complex formationwith albumin.

Measurement of fatty acid oxidation. At the end of the in-cubation, "CO2 was released from the medium by acidifyingto pH 2 with HCl. An aliquot of medium was withdrawnthrough the rubber serum cap for determination of aqueoustritium (released from palmitic acid-3H). During with-drawal of medium, the bottle was oriented so that thesurface covered with cells remained uppermost and thus wasnot exposed to the acidified medium. The gas phase in thebottle was drawn slowly through 10 ml of 5.1 N NaOHwhile being displaced by saline, which entered through asecond needle. With approximately 80% of the atmospherecollected, the bottle's liquid content was returned to neu-trality with NaOH and the remaining gas was collected.The cell sheet was then washed three times with Ca'+- andMg++-free Dulbecco's saline (26), dispersed and collectedusing a small volume of 0.05%o trypsin, 0.005% ethylenedia-minetetraacetate (EDTA), and 0.2% methyl cellulose. Analiquot of the cell suspension was removed for enumerationin a Coulter counter. The remainder was washed in Dul-becco's saline and sonically disrupted before determinationof total protein (27) and lipid radioactivity.

The NaOHcontaining Na2"COs was slurried with 3.000 gof highly purified anthracene crystals (Fluorescence Grade,X 480, Eastman Kodak Company, Rochester, N. Y.) and0.2 ml of a solution of Triton, GR-5, diluted 1:10 v/v (Lot5729, Rohm & Haas Co., Philadelphia, Pa.) and counted ina liquid scintillation spectrometer (Packard Tri-Carb, model314 EX) (28). The rate of oxidation of palmitic acid wasalso determined in each of the cultures studied. In our earli-est experiments, one bottle of cells was incubated with pal-mitic acid-1-'C, while a duplicate bottle was incubated withthe branched-chain acid under study. In later studies, palmi-tate oxidation was determined simultaneously with that ofthe "C-labeled branched-chain compounds by including pal-mitic acid-9,10-3H in the same medium. Duplicate aliquots ofmedium withdrawn at the end of the incubation period wereneutralized and lyophilized; the tritium content of the waterdistilled off was determined in a dioxane-containing scintil-lation mixture (29).

Analysis of cell lipid radioactivity. Lipids were extractedfrom aqueous suspensions of sonically disrupted cells andfrom medium using chloroform-methanol 2:1 (25 ml/ml).After addition of one-fifth volume of 0.02 N H2S04, chloro-form and aqueous phases were separated. In some cases, freefatty acids (FFA) were extracted from the total lipid samplebefore saponification (30) ; in others, the total lipid fraction(including FFA) was heated at about 80'C for 1-2 hr in 2%NaOH in 95% ethanol (at least 2 ml/mg lipid). An equalvolume of distilled water was added and the nonsaponifiablelipids were extracted by shaking three times with equal vol-umes of hexane. The residual alkaline aqueous phase wasacidified and the saponifiable fraction similarly extracted,occasionally with an additional final diethyl ether extraction.

The FFA fraction and the esterified fatty acid fractionfrom each culture were converted to methyl esters by heat-ing overnight at 600C in 2%o H2SO4 in anhydrous methanol.Radioactivity in individual fatty acid methyl esters was as-sayed by gas-liquid radiochromatography (16). Resolutionof branched-chain and straight-chain fatty acids was achievedusing a mixed liquid phase (7%o EGS plus 1.5% SE-30 on

Refsum's Disease: Characterization of Enzyme Defect in Cell Culture 1019

Gaschrom Q) at 175'-1850C with N2 carrier gas flow of 80ml/min.

Labeled a-hydroxyphytanic acid in cell extracts was firstpartially purified by TLC of the total fatty acid methyl es-ters after addition of carrier methyl a-hydroxyphytanate(silica gel containing 0.1% Rhodamine 6G; developing sol-vent: benzene-hexane, 2: 1; R2 of a-hydroxyphytanate, ap-proximately 0.2). The radioactivity specifically associatedwith a-hydroxyphytanate was then determined by gas-liquidradiochromatography (17% EGS on Chromosorb W).

RESULTS

Time course of fatty acid oxidation in tissuecultureThe time course of 'CO2 evolution from labeled fatty

acids in tissue culture was examined in two ways. Inone experiment gas in individual culture bottles was re-peatedly sampled at 8- or 12-hr intervals over a 72 hrperiod. While minor losses of "CO2 with this procedurecould not be excluded, results of two experiments, shownin Fig. 2, indicate that production of "CO2 from la-beled palmitate and pristanate is linear for at least the1st 48 hr both in control and HAP cultures.

Using a second approach, bottles were removed at in-tervals from a group of replicates in which approximatelyequal numbers of cells of the same strain and at thesame stage of growth had been incubated with identical

10

0x X

2

0.0 64

cr0 4~

0

00 /

0 "

/\/~~~~~~-A--

-

12 24 36 48 60 72TIME (hr)

FIGURE 2 Time course of "CO2 production from pristanate-U-J'C (OA) and palmitate-1-'C (-,A) measured by re-peated sampling from individual flasks. Two HAP strains(0,O) and two control strains (A,A) were used. In oneexperiment 0.007 uimoles of pristanate-U-"C (SA = 33 ac/,gm) was added to an HAP (0) and to a control (A)strain in medium with pristanate: albumin molar ratio of0.02. In the second experiment 2.7 /moles of palmitate-1-"'C(SA=0.06 /Ac//Am) was added to an HAP (0) and to acontrol (A) strain in medium with palmitate:albumin mo-lar ratio of 6.0. See text for details of incubation and sam-pling procedure.

Qo304e

0

0

-

So

op

/

7

7/07/

I/7/

/

/

I

24 48 72TIME (hr)

FIGURE 3 Time course of 14CO2 production from homophy-tanate-U-"C by replicate control cultures. 0.6 nmoles ofhomophytanate-U--"C (SA = 0.18 /%c/gm) was added to eachof four cultures in media with homophytanate: albumin molarratio of 2.0. See Methods for details of incubation proce-dure.

aliquots of labeled fatty acid. Results of one such study,in which the (n + 1) homologue of phytanic acid, homo-phytanic acid, was added to a control cell strain, areshown in Fig. 3. A constant rate of production of 'CO2was observed in this study also.

In further studies, 48 hr was chosen as the standardincubation time. Several conditions must be observed inorder to maintain constant rates of oxidation. The ini-tial ratio of FFA to albumin in the medium must not betoo low; evidently uptake falls off as the FFA: albuminmolar ratio falls to very low values during the incubation,as reported by Spector and Steinberg for studies withascites tumor cells (31). The cell culture must be in astationary phase, since the cell count at the end of the 48hr incubation period is used as the basis for expressingresults. At albumin concentrations less than 1%, non-linear rates of oxidation were observed, possibly becausethe total amount of fatty acid that could be added (andstill keep all of the FFA bound to albumin) was so lowthat a significant fraction of it was utilized in the courseof the 48 hr incubation period, causing the substrateconcentration to fall over the course of the incubation.

Fatty acid oxidation in control and HAPcultures

Table I summarizes the comparative rates of oxida-tion in control and HAP cultures of labeled phytanate,pristanate, a-hydroxyphytanate, and palmitate. In eachcase the medium used was exactly the same for the con-trol and HAP cells. The defect in phytanate oxidationis apparent. The rate in HAP cultures was on the av-erage less than 3% of the rate in control cultures. In no

1020 J. H. Herndon, Jr., D. Steinberg, B. W. Uhlendorf, and H. M. Fales

TABLE IOxidation of Branched-Chain and Straight-Chain Fatty Acids by Control and HAPCell Cultures

a-OH-phytanate-Phytanate-U-14C Pristanate-U-4C U-14C Palmitate-1-'4C

A. Oxidation of labeled fatty acids (percentage of added radioactivity convertedto 14C02/48 hr per 107 cells)

HAPcultures 0.04 4:0.02 (8)* 6.7 =4:0.2 (13) 0.20 ±0.08 (6) 10.9 ±0.96 (27)Control cultures 3.4 ±0.79 (14) 6.4 4:0.85 (11) 0.19 :410.12 (4) 11.6 :4:1.6 (27)

(P < 0.001)

B. Oxidation of 14C-labeled substrates relative to simultaneously measured 3H-palmitate oxidation,(percentage added 14C in 14C02)/(percentage added 3H in 3H20) X 100

HAPcultures 0.39 ±0.11 (12)* 39 41:6.1 (9) 1.8 ±i0.9 (6)Control cultures 15.0 44.1 (11) 49 ±6.2 (8) 1.2 ±0.4 (3)

(P < 0.002)

* Results represent means 4SEM; No. of observations in parentheses.

case did the rate in HAP cultures exceed 5% of the rates of palmitate oxidation does not affect the con-control rate. clusions.

In contrast, pristanate, previously shown to be anearly intermediate on-the pathway of phytanate degrada- Oxidation of a-hydroxyphytanate isomerstion, was oxidized at the same high rate in both control As discussed under Methods, the synthesis of a-hy-and HAP cultures. There was no significant difference droxyphytanate-U-14C is expected to yield four isomericbetween control cultures and HAP cultures in the rate products based on stereoisomerism at the 2-position (hy-of oxidation of a-hydroxyphytanate. In control cultures, droxyl group D or L) and at the 3-position (methylhowever, the rate of oxidation of a-hydroxyphytanate group D or L) (see Fig. 1). One of the two bands re-was considerably slower than that of either phytanate or solved by TLC is assumed to include (2-D, 3-D) pluspristanate. This slow oxidation may reflect difficulty in (2-L, 3-L), while the other includes (2-D, 3-L) pluspenetration into mitochondrial sites of oxidation. Recent (2-L, 3-D) a-hydroxyphytanate. Which mixture is repre-studies' show that oxidation of a-hydroxyphytanate by sented in the less polar and which in the more polarisolated rat liver mitochondria is slower than that of TLC band is not known. In Table II is shown a com-phytanate but is strongly stimulated by addition of carni- parison of the rates of oxidation of these isomeric mix-tine. In Table I, the data for both less polar and more tures. In both control and HAP cultures the less polarpolar isomers have ben pooled. The separate results with mixture was oxidized more rapidly than the more polareach isomeric fraction are discussed below. mixture. The less polar mixture is also oxidized more

Finally, as shown in Table I, palmitate was oxidized rapidly by rat liver mitochondria.' When the results areat comparable high rates in control and HAP cultures. 'S. C. Tsai, J. Avigan, and D. Steinberg. UnpublishedAs shown in Table I B normalizing results to equal results.

TABLE I IOxidation of Isomers of Alpha-Hydroxyphytanate- U-14C by HAPand Control Cells

14CO2 or 3H20 (percentage of added radioactivity/48 hr per 107 cells)

A B C D Relative rates ofoxidation of

Origin of 14c-hydroxyphytanate. 1C-hydroxyphytanate, hydroxyphytanateculture less polar isomers 'H-palmitate more polar isomers 'H-palmitate isomers (corrected)*

HAP, 0.059 7.8 0.038 11.8 2.4HAP2 0.13 7.0 0.048 10.0 3.9Control 0.059 5.0 0.035 7.1 2.4

* 14CO2 produced from each isomer was normalized to equal palmitate-9, 10-3H oxidation (A/B and C/D), and a corrected ratiowas then calculated for expressing the relative rates of oxidation of the hydroxyphytanate isomers. This procedure may be inter-preted as correcting for differences in cell number and metabolic activity of cells.

Refsum's Disease: Characterization of Enzyme Defect in Cell Culture 1021

expressed relative to the simultaneously measured rateof palmitate oxidation (last column in Table II), it isseen that the less polar isomers were oxidized two tothree times more rapidly. Evidently there is some degreeof stereospecificity but no absolute specificity in the en-zymatic handling of a-hydroxyphytanate, and this issimilar in control and in HAPcells. The important pointin the present context is that the HAPcultures oxidizedboth isomeric fractions at least as well as did the controlcultures.

Analysis of cell lipid radioactivityTo establish first that analyses of cell lipid radioac-

tivity were measuring only firmly bound or incor-porated lipid and to evaluate the contribution from ad-sorbed albumin-bound fatty acid, 'I-labeled human se-rum albumin (HSA) was incubated with a culture for48 hr and the washed cells were examined for retainedradioactivity. Table III shows that the cell pellet con-tained only about 0.01% of the initial medium radio-activity. Thus, a culture containing 2 X 10' cells wouldhave irreversibly adsorbed or incorporated only about1 m/Amole of albumin in 48 hr or, assuming a constantrate, 6 X 10' molecules/cell per hr. This figures agreesclosely with results of published studies on the rate ofalbumin uptake by human and animal tumor cells in cul-ture (32, 33). Uptake of FFA attributable to uptake oradsorption of albumin is insignificant, then, relative tothe observed over-all rates of fatty acid uptake and

TABLE IIIUptake of 1311-labeled Human Serum Albumin

by Normal Fibroblasts*

Percentage ofmedium radio-

Total radioactivity activity presentSample in sample in cell pellet

cPm %Cell pellet 533

Incubated medium, 4,880,000 0.011(1 ml)

Unincubated medium, 4,630,000 0.012(1 ml)

* 8 Mc of 131I-HSA (SA = 185 uc/mole) were added to 25 ml ofmedium containing 0.02% albumin. Final albumin concentra-tion in the 20-ml portion incubated with the culture was0.032%, equivalent to 1.6% serum having an albumin con-centration of 2%. At the end of 48 hr, the cells were washed,dispersed, and collected in conventional fashion. Radioactivitywas measured in the medium that had been incubated withthe cells, in an aliquot of unincubated medium, and in the cellpellet. Each value represents the mean of three 1-min countsin a Nuclear-Chicago well-type gamma counter, model 183.

Oxidation and CellTABLE IV

Uptake of Phytanic acid- U-14C in Controland HAPCultures*

Percentage of added radio-activity per 107 cells in:

PercentageC02 + of total lipid

Origin of Total total radioactivityculture C02 lipid lipid in FFA

HAP1 0.124 17.9 18.0 302 0.075 22.1 22.2 203 0.003 21.2 21.2 254 0.06 14.3 14.4 19

Control1 5.2 7.7 12.9 242 7.9 7.3 15.2 30

* Analysis after 48-hr incubations. Each line represents resultsobtained with a single culture.

oxidation, which were two to three orders of magnitudegreater.

Uptake of labeled phytanate and oxidation to C02 weredetermined in 48-hr incubations. Typical experimentalresults are shown in Table IV. As already noted, oxi-dation to CO by HAP cultures was drastically reduced.However, there was a much greater accumulation ofphytanic acid radioactivity in the HAP cultures. Thetotal taken up ("4CO2 plus 14C-lipid) was thus virtuallythe same in control and HAP cultures. As shown inthe last column of Table IV, 20-30% of the cell lipidradioactivity was in the FFA fraction in both controland HAPcells. These findings suggest that the low yieldof '4CO2 from phytanate-U-14C was not due to impaireduptake from the medium.

TABLE VComparison of Palmitate-1-"4C and Phytanate- U-14C Oxidation

and Uptake by Control Cultures*

Percentage of added radio-activity per 107 cells in:

PercentageC02 + of total lipid

Total total radioactivityFA added C02 lipid lipid in FFA

Phytanate-U-14C 5.8 3.4 9.2 49

5.4 3.2 8.6 43

Palmitate-1-14C 6.8 30.0 36.8 63

5.5 25.7 31.2 61

* Analysis after 72-hr incubation. Each line represents resultsobtained with a single culture.

1022 J. H. Herudon, Jr., D. Steinberg, B. W. Uhlendorf, and H. M. Fales

rmF CONTROL CULTURE INCUBATED

3000k650k

600k

300k

250k

200

15t4 8,/2-Tlimelhy/-r.idecunooue

-(08z)100

50[

WITH PHYTANATE-U- C4

P~,voanue .FPh81onott~o/%X

Aris/antle(2.3

LJU,>

C]

CLcn

Uj

C-)

REFERENCESTANDARDGLC RUN

TIME

FIGuRE 4 Gas-liquid radiochromatogram of methylated fatty acids derived froma control culture incubated 48 hr with phytanic acid -U-14C. Radioactivity assayedin collected fractions is shown in upper part of figure. A standard fatty acid methylester mixture run under the same conditions is shown in lower part. The columnwas composed of a mixed liquid phase (7% EGSand 1-1/2% SE-30 on Gas ChromQ). Carrier gas flow was 80 ml/min, column temperature 1750C. The radioactivepeaks corresponding to phytanate, pristanate and 4,8,12-trimethyltridecanoate arelabeled and the percent each contributed to the total collected radioactivity given.

Oxidation and uptake of branched-chain acids (phy-tanate and pristanate) were compared with that ofpalmitate (Tables V and VI). The branched-chain acidswere oxidized as rapidly as palmitate, but were incor-porated much less rapidly into the lipid stores of thecells. The comparability in oxidation rates suggests that

discrimination was not at the level of entry into the cellbut rather at the level of esterification.

The distribution of radioactivity among the cell fattyacids at the end of 48 or 72 hr of incubation was deter-mined by gas-liquid radiochromatography of methylesters. A representative analysis of a control culture is

Refsum's Disease: Characterization of Enzyme Defect in Cell Culture

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LA-

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0C-)

1023

TABLE VIComparison of Palmitate-1-14C and Pristanate- U-14C Oxidation

and Uptake by HAPand Control Cultures*

Percentage of added radio-activity per 107 cells in:

Origin of TotalSubstrate culture C02 lipid

Pristanate-U-14C HAP 12.0; 17.5 4.8; 3.7

Control 9.3; 10.6 1.2; 2.2

Palmitate-1-14C HAP 13.8 18.5

Control 8.8 34

* Analyses after 48-hr incubation. Each value representsresults obtained in a single culture, either of HAPor controlcells.

shown in Fig. 4. In addition to the added substrate phy-tanate-"C, there was significant radioactivity in prista-nate and in 4,8,12-trimethyltridecanoate. The latter twofatty acids have been identified previously as degrada-tion products on a major pathway for phytanic acidcatabolism in animals (9-11). Quantitative results infour cell cultures of different origin are shown inTable VII. The present findings provide the first evi-dence that this same pathway is operative also in hu-man cells. The appreciable incorporation of radioactivityinto the normal 16-and 18-carbon fatty acids presumablyoccurred by breakdown of phytanate and reincorporationof labeled fragments.

The fatty acids extracted from an HAPculture simi-larly incubated with labeled phytanate showed, in strik-ing contrast, only the parent phytanate peak (Fig. 5).Thus, there was no evidence either of breakdown intoshorter branched-chain intermediates or of reincorpo-ration of phytanate-"C into straight-chain fatty acids.

Control cultures yielded in addition a small GLC

peak of radioactivity with a retention time about twicethat of phytanate (Fig. 4). This radioactive componentcochromatographed with authentic carrier a-hydroxy-phytanate on both a polar (EGS) and a nonpolar sili-cone liquid phase (OV-1). It accounted for 0.3-1.3% oftotal fatty acid radioactivity added to the control cul-tures (Table VII). None was detected in HAP cul-tures. As a further check on the identification of thisradioactive component, the mixture of fatty acids (asmethyl esters) derived from total lipids of two controlcultures incubated with phytanate-14C were fractionatedby TLC after addition of carrier methyl a-hydroxyphy-tanate (benezene-hexane, 2: 1; Ri of hydroxyphytanate,0.2). The material of the a-hydroxyphytanate zone waseluted from the silicic acid and then fracionated byGLC. 70-80% of the total radioactivity in the TLCband cochromatographed on GLCwith the carrier methyla-hydroxyphytanate.

Studies to rule out a metabolic block subsequentto formation of pristanic acidThe striking contrast between the relative inability of

HAP cultures to oxidize phytanate and their almostnormal ability to oxidize pristanate and a-hydroxyphy-tanate indicated a metabolic block before the formationof the latter two metabolites. On the other hand, westill had to consider the possibility that the block laydistal to pristanate. The results could be compatiblewith this possibility on the following basis. The sub-strate concentrations of pristanate used when testingfor its oxidation were probably considerably higherthan those presented to the cell when pristanate was be-ing generated by breakdown of substrate phytanate.Thus, for example, the cells might contain enzymes forpristanate oxidation that had a higher than normal Kmvalue. When presented with a high concentration ofpristanate in the medium, such an altered enzyme sys-tem might yield an over-all normal net rate of substrateutilization yet be unable to oxidize pristanate normally

TABLE VIIDistribution of Radioactivity among Cell Fatty Acids after 48- or 72-hr Incubations of

Control Cultures with Phytanate- U-14C*

Straight-chain4,8, 12- 16- and 18-

Time of a-Hydroxy- Trimethyl- carbon fattyincubation Origin of Culture Phytanate phytanate Pristanate tridecanoate acids

(hr)

48 A. B. (Hurler's syndrome) 85.5 0.7 1.6 0.9 6.848 A. H. (retinitis pigmentosa) 96.6 0.3 1.2 0.3 1.072 V. WV. (undiagnosed lipidosis) 60.3 0.8 1.9 0.6 23.872 R. D. (rheumatic heart disease) 66.5 1.3 4.3 0.3 18.6

* Values represent percentage of total radioactivity recovered from the GLCcolumn cochromatographing with the componentsindicated. Small quantities of radioactivity were associated with unidentified peaks.

1024 J. H. Herndon, Jr., D. Steinberg, B. W. Uhlendorf, and H. M. Fales

HAP CULTURE INCUBATED WITH PHYTANATE-U-C'4

4700

600 r-

Fkytr/onueJ

(.QOO*j

5001

400k

300k

200j

100F

uj

cn

C-)

Lu

REFERENCE STANDARDGLC RUN

Ofeuae -

Prs/noncle

TIME

FIGURE 5 Gas-liquid radiochromatogram of methylated fatty acids derived from HAPculture incubated 48 hr with phytanic acid-U-14C. See Fig. 4 for details.

when presented at low concentrations. Two approacheswere taken to test this possibility.

(a) Comparisons at low substrate concentrations ofpristanate. Control and HAP cultures were incubatedwith pristanate-U-"C at two widely different concentra-tions: 0.0018 mpamole/ml and 1.56 mpmole/ml. Thestudy with the lower concentration required the syn-

thesis of very high specific radioactivity pristanate-U-14C. The low concentration of pristanate used approxi-mated the concentration of pristanate calculated to be inthe cells at the end of a 48 hr incubation with phytanatein the medium. As shown in Table VIII, the fractionaloxidation of pristanate at the low concentration was

only slightly less than that at the high concentration.Oxidation of palmitate-5H in the presence of the highconcentration of pristanate was comparable to that seen

at the lower level, i.e., the high FFA concentration was

not noticeably toxic. The essential point here is thatthere was no important difference in the rate of prista-

TABLE VIIIComparison of Oxidation of Pristanic Acid- U-14C in HAPand

Control Cultures Incubated with High and withLow Levels of Substrate

l4COs or 1H20 recovered(per cent of added Pristanate

radioactivity per 48 hr oxidationper 107 cells) as per-

centage of14C-pristanate Origin of 14C-pris- $H-palmi- palmitateconcentration culture tanate tate oxidation

Low (0.0018mpmole/ml)* HAP 1 7.1 21.3 33

HAP2 4.3 10.0 43Control 8.6 32.5 27

High (1.56mumole/ml)* HAP 1 7.8 19.8 39

HAP2 5.7 13.3 43Control 9.5 29.7 32

* Pristanate-U-14C of SA = 33 ;pc/pm was used in lower level cultures;SA = 1 gc/pm in higher level cultures.

Refsum's Disease: Characterization of Enzyme Defect in Cell Culture

0L.CO

.->

Act

z

0

C-

4800r

1025

nate oxidation in HAPcells and in control cells. Indeed,if the data are normalized to equal rates of palmitateoxidation, the rate of pristanate oxidation in the HAPcells was somewhat greater than that in the control cells.

(b) Oxidation of homophytanic acid, the next higherhomologue of phytanic acid. As discussed later, themetabolic error in HAP apparently involves the a-oxi-dation system, whereas the /-oxidation system appearsto be intact, as evidenced by the normal rates of oxida-tion of pristanic acid. If this interpretation is correct,HAP cells might be expected to oxidize the next higherhomologue of phytanic acid, homophytanic acid, at anormal rate. In homophytanic acid (Fig. 6), the firstbranch-methyl group is in the gamma position and thebeta position is available for oxidative attack as in clas-sical beta oxidation. The product of such beta oxidationwould be pristanic acid. Thus, the use of homophyta-nate-"C as substrate provides a test of whether it isspecifically the beta methyl group that makes phytanatedifficult for HAP cells to metabolize. If oxidation ofhomophytanate were normal, it would also indicate thatpristanate generated within the cells is in fact oxidizedat a normal rate (see discusion above). As shown inTable IX, there was no difference between control andHAP cells in the rate of oxidation of homophytanate-U-14C nor in its total uptake into cell lipids.

Release of phytanate from ester formsAnother explanation considered for the poor rate of

phytanate oxidation in HAP cells was that there might

New RepositionCH3 not blocked

CCon CHC CH2R CH2 CH2 COOH

HOMOPHYTANICACID

? 10,-oxidation

CH3I

CH2 { CH/ \ /C\

R CH2 COOH

PRISTANIC ACID

+ CH3COOH

Successivef-oxidations

OXIDATION TO CO2AT NORMALRATE ?

FIGURE 6 Oxidation of homophytanic acid, the next higherhomologue of phytanic acid.

TABLE IXOxidation and Uptake of Homophytanate- U-1"C and Palmitate-

9, 10-'H by HAPand Control Cultures

Percentage of addedradioactivity per 107

cells in:

Origin of C02 or TotalSubstrate culture 3H20* lipid

Homophytanate-U-14CI HAP 3.1; 3.2 7.2; 9.2

Control 3.4; 3.4 6.0; 6.9

Palmitate-9, 10-3H HAP 15.0; 13.7 51; 44

Control 24.5; 21.0 44; 47

* Analysis after 48-hr incubation. Each value represents resultsobtained with a single culture.4 Prepared from phytanate-U-14C; thus the carboxyl carbonwas not labeled, but the remaining 20 carbons were uniformlylabeled.

be a slow rate of release of phytanate from lipid esters.In other words, phytanate might be taken up and esteri-fied normally but could not then be released and madeavailable for oxidation, i.e., it might be "trapped" inester forms. The following experiment was carried outin an attempt to detect differences in release of phyta-nate from previously labeled cells. Control and HAPstrains were incubated for 48 hr with 'C-labeled phy-tanate and palmitate-8H in the usual way. The cellswere then washed free of labeled medium and fresh me-dium was added. The cells were next incubated for anadditional 24 hr in the unlabeled medium. 'CO2 wascollected, 'H20 determined, and lipids were extractedfrom the medium by the method of Dole (34) and as-sayed for radioactivity. Cells were collected and celllipid radioactivity measured. Intracellular radioactivityat the beginning of the second incubation was taken asthe sum of cell lipid radioactivity and lipid radioactivityreleased to the medium. As shown in Table X, controland HAP cells released nearly identical percentages oflabeled endogenous material in 24 hr.

Other aliquots of medium were extracted similarlyand separated into lipid classes by TLC (hexane-diethyl ether-HAC, 90:10:2). Approximately 40% ofthe released radioactivity was .in the free fatty acidzone. Gas-liquid radiochromatography showed that es-sentially all of this radioactivity was in phytanic acid inboth HAPand control cultures. The TLC bands repre-senting cholesterol and complex lipid esters each con-tained radioactivity, suggesting that membrane debrissuspended in the medium contributed to the total lipidor that there was exchange with the lipoprotein lipids ofthe medium.

1026 J. H. Herndon, Jr., D. Steinberg, B. W. Uhlendorf, and H. M. Fales

TABLE XRelease of Radioactivity from HAPand Control Cells Previously

Labeled with Phytanate- U-14C*

Percentage of cell lipid radioactivityreleased to medium in 24 hr$

Origin ofculture 14C 'H

HAP 1 48 10HAP2 34 16.8Control 43 6

* Cells were labeled by incubation for 48 hr with phytanate-U-14C, washed, and then incubated for 24 hr in fresh, unlabeledmedium. The latter contained unlabeled pristanic acid (addedin an attempt to trap released fatty acids). See text for detailsof procedure.t 14C and 3H as percentage of calculated total cell lipid radio-activity present at beginning of second incubation. The latterwas taken to be the sum of lipid radioactivity released andthat extracted from cells at the end of the second incubation.

Toxicity of branched-chain fatty acids

Because fatty acid anions are known to be damagingto cell membranes under some circumstances, the pos-sible contribution of such effects had to be considered.Two specific questions were tested experimentally. First,is phytanic acid more toxic to cultured fibroblasts thanstraight-chain fatty acids? Second, are fatty acids, inparticular phytanic acid, more toxic to HAP cells thanto normal cells in culture? One strain of control cellsand two HAPstrains were grown in medium containingfree fatty acids over a wide range of concentrations.These concentrations were chosen to correspond toFFA: albumin molar ratios ranging from 0.025 to 6.4.The effects of phytanic acid, pristanic acid, and palmiticacid were compared. Duplicate cultures exposed to eachconcentration of FFA were examined unstained underthe light microscope after 24 and 48 hr for the pres-ence of cytoplasmic granulation and vacuolation, loss ofcellular attachment to the glass surface, and disorgani-zation of the cell sheet. Below FFA: albumin molar ra-tios of 3.2 there was no evidence of a toxic effect bythese criteria. The abnormalities noted above were pres-ent in mild form at a molar ratio of 3.2 and were severeat a molar ratio of 6.4. However, there was no evi-dent difference in toxicity among the three fatty acidstested, nor were there any evident differences in toxicityin control and HAPcells.

DISCUSSIONThese tissue culture experimental results support andcomplement the conclusion drawn from clinical studiesreported previously from this laboratory (13, 35),namely, that there is a primary block in phytanate degra-

dation in HAP. In those reports and in a companionpaper (36), it was shown that HAP patients convertedorally administered phytolj'C or intravenously adminis-tered phytanic acid-j4C to '4CO2 at much slower ratesthan did normal controls. Phytanic acid radioactivityalso persisted at much higher levels and for longer pe-riods in the patients' plasma than in that of the controls.Although a metabolic block in the oxidation of phytanicacid seemed a likely explanation for these findings, thisinterpretation was complicated by the presence in thepatients of large pools of unlabeled phytanate. Whileseveral lines of indirect evidence suggested that thefractional turnover of phytanic acid would not begrossly depressed by even large increases in pool size(8, 15), some dilutional effects could not be ruled out.In the present studies in cultured cells the problem ofisotope dilution does not arise. GLC analyses of theHAPcell lipids after three to five pasages showed neg-ligibly low phytanate levels. Both control and HAPcellsshowed traces of phytanate (probably attributable to thepresence of phytanate in the fetal bovine serum used inthe medium, less than 0.2% of total fatty acids). How-ever, there was no difference between HAPand controlcells in this regard. Accordingly, the greatly depressedrate of phytanic acid oxidation in HAP cultures, innone of which appreciable phytanate pools could bedemonstrated, leaves little doubt that there is a primarydefect. Preliminary results in fibroblast cultures from11 additional documented cases of HAP have shownrates of phytanate oxidation less than 5% of the ratesin control cultures.!

The present results lead us to conclude further thatthe defect lies in the conversion of phytanate to a-hy-droxyphytanate. This conclusion draws in part on ourpreviously reported results in animals showing that amajor oxidative pathway involves initial alpha-oxidation,to yield the (n-1) fatty acid (pristanic acid), followedby successive beta oxidations to yield lower degradationproducts as shown in Fig. 7 (9, 10). That this is infact a major pathway was shown by the very highyields of pristanic acid-'4C after injection of phytanicacid-1'C. Moreover, after feeding of large doses of phy-tanic acid, GLC-mass spectrometry failed to reveal ac-cumlation of any intermediates other than those shownin Fig. 7 even though spectra were obtained on allpeaks. Nor, after injection of phytanate-"C, was radio-activity found in any branched-chain acids other thanthose shown in Fig. 7. Hansen, Shorland, and Priorhave confirmed the accumulation of pristanate and4,8,12-trimethyltridecanoate in phytanic acid-fed rats(37, 38). More recently we showed that a-hydroxyphy-tanate-jC is formed from phytanate-j4C in rat liver

'Herndon, J. H., Jr., B. W. Uhlendorf, and D. Steinberg.Unpublished results.

Refsum's Disease: Characterization of Enzyme Defect in Cell Culture 1027

COOH

16

3,7,11,1S-tetramethylhexadecanoic acid (phytanic acid)

15 COOH

2,6,10,10,14-tetramethylpentadecanoic acid (pristanic acid)

13 COOH4,8,12.trimethyltridecanoic acid

112,6,10-trimethylundeconoic acid

COOH

TotaICarbonAtoms

20

19

16

14

119 COOH

4,8.dimethylnonanoic acid

FiGuRE 7 Identified intermediates of phytanic acid degradation. Breakdownproducts in a major oxidative pathway for phytanic acid, involving an ini-tial a-hydroxylation followed by oxidative removal of the first carbon; thisloss results in formation of pristanic acid. Alternate removal of 3- and2-carbon fragments by j3-oxidation could then produce the lower inter-mediates.

mitochondria and accumulates in livers of phytanic acid-fed mice (11).

Having established the major pathway for degrada-tion, we tested the capacity of HAPfibroblasts to oxidizethe presumed metabolic products of phytanate. The rateof oxidation of a-hydroxyphytanate->C and of prista-nate-1C were comparable in HAP and normal cells.If, and only if, these compounds are intermediates in theoxidation of phytanate, as they appear to be in the mouseand rat, do the results localize the metabolic error atthis initial alpha hydroxylation step. Thus the analysesof labeled products of phytanate oxidation in the celllipids are of central importance.

a-hydroxyphytanate-1'C, pristanate-"C and 4,8,12-tri-methyltridecanoate-1'C were all identified in normal fibro-blasts after incubation with phytanate-1C. No other la-beled compounds could be detected. These findings pro-vide the first direct evidence that the alpha-oxidativepathway for phytanic acid oxidation described in ani-mals occurs also in human cells. In contrast, the celllipids in HAP cultures contained none of these com-pounds, only the added substrate phytanate-14C beingdemonstrable. All of these findings taken together ap-

pear to justfy the conclusion that the HAP cells lacksome component of an alpha-hydroxylating system(Fig. 8).

The results with homophytanate-14C provided im-portant additional support for the localization of theenzymatic block. This (n + 1) homologue, as nearlysimilar as possible to phytanate with regard to physicaland chemical properties was, like pristanate, oxidizedand esterified by HAP cells at rates indistinguishablefrom those seen in control cells. In homophytanate themethyl substituent no longer blocks the beta carbon,but rather the gamma carbon. Consequently, homophy-tanate is susceptible to normal beta oxidation. The ex-pected product, pristanic acid, has the methyl substituenton the alpha carbon and is also susceptible to normalbeta oxidation. Thus, the next higher and the next lowerhomologues of phytanate are oxidized normally by HAPcells while phytanate itself is oxidized at only about 3%of the normal rate. Evidently it is specifically the beta-substitution that makes phytanate unavailable as a sub-strate in HAP cells.

Eldjarn and coworkers have approached the problemof identifying the enzyme error in HAP indirectly, by

1028 J. H. Herndon, Jr., D. Steinberg, B. W. Uhlendorf, and H. M. Fales

PHYTANIC ACID

+ SITE OF PRIMARY BLOCKIN REFSUM'S DISEASE

a-HYDROXYPHYTANIC ACID

PRISTANIC ACID

4,8,12-TRIMETHYLTRIDECANOIC ACID

2,6,10-TRIMETHYLUNDECANOIC ACID

CO2

FIGURE 8 Proposed localization of the enzymatic block indegradation of phytanic acid in HAPpatients.

using a variety of "model" compounds. The chain lengthand branching pattern of the "model" compounds usedhas not matched closely those of phytanate. Until morestudies have been done on the substrate specificity of theenzymes involved in oxidation of branched-chain acids,the interpretation of results of these studies remainsuncertain. Originally, Eldjarn concluded that patientswith HAPaccumulated phytanate because of a defect inomega oxidation, because after a loading dose of tri-caprin they excreted a lower than normal amount ofsebacic acid (the dicarboxylic acid resulting fromomega oxidation of capric acid) (39). Further stud-ies, however, showed that omega oxidation of a num-ber of other compounds, including 2,2-dimethylstearicacid, was normal (40). Recently, Try and Eldjarn re-peated the tricaprin loading test in two of the HAPpatients after their plasma phytanate levels had beenmarkedly reduced by dietary therapy (41). Now thetricaprin loading tests were within normal limits. It wasconcluded that the previous results reflected inhibition ofomega oxidation by the accumulated stores of phytanate.On the other hand, the same laboratory showed that themain degradation products from orally administered 3,6-dimethyloctanoic acid-8-14C were omega oxidation prod-ucts and that these were formed in comparable amountsby HAP patients and by controls (42). Neither in ourearlier studies in vivo or in vitro (9-11, 15), nor in thepresent human cell culture studies have we been able tofind evidence for formation of dicarboxylic acids de-rived from phytanate. Moreover, if it is assumed that theenzyme defect demonstrated here affects only alpha oxi-dation, one would have to conclude that the rate ofomega oxidation of the compound occurs at less than 5%

of the rate of alpha oxidation. It is of interest that An-tony and Landau have recently presented evidence fromingenious isotope experiments indicating that omegaoxidation of straight-chain acids is quantitatively un-important in rat liver-less than 4% the rate of betaoxidation (43).

Because of the more or less close analogy in struc-ture between phytanate and farnesoic acid, the latterbeing one isoprenoid unit shorter and being triply un-saturated, the possibility arose that C02 fixation mightbe involved as it is in the mechanism described by Seu-bert and Remberger (44). An apparent C02 requirementfor oxidation of a "model" compound (3,6-dimethylac-tanoate) was noted by Eldjarn, Try, and Stokke (45),but this was subsequently attributed to changes in oxy-gen tension (42). Neither in the present studies nor inprevious animal studies has there been evidence of theintermediate expected from an analogous pathway forphytanate degradation (9-11, 37, 38). After administra-tion of 3,6-dimethyloctanoate-8-14C to man, most of theurinary metabolites were omega oxidation products, asdiscussed above, but about 1.5% of the total was foundin the (n-1) acid (42, 46). HAP patients, on the otherhand, excreted none of the alpha oxidation product andproduced little or no "4CO2. These results and recentstudies by Stokke (47) provide confirmatory evidencefor the presence of an alpha-oxidative pathway. Theyare also compatible with our conclusion regarding thenature of the metabolic error in HAP if this "model"compound is indeed oxidized by the same enzyme systemsthat oxidize phytanate. Because so large a fraction of3,6-dimethyloctanoate is handled by omega oxidation,whereas this appears to be a minor pathway for phyta-nate oxidation, the validity of it as a model compoundshould be directly checked.

Try (48) has compared oxidation of 3,6-dimethyloc-tanoate-8-14C and of randomly labeled 3,14,14-trimethyl-pentanoic acid in controls and in two HAP patientswhose phytanate stores had been reduced by dietarymeans (49). The results indicated that the patients oxi-dized these compounds at one-third to one-half the nor-mal rates. Labeled metabolites were excreted in amountstoo low to be fully characterized. In view of the ap-parently very large capacity of the normal organism tometabolize phytanate (15), it is not certain that this de-gree of impairment would lead to phytanate accumula-tion. One cannot exclude the possibility that phytanatemay be oxidized relatively more rapidly in vivo than infibroblast cultures due to contributions of other organand cell types. However, as reported in the accompany-ing paper (36), in vivo oxidation of phytanate itself inthe three HAP patients studied here was impaired toan extent comparable to that seen in fibroblast cultures.

The present results demonstrate marked loss of phy-

Refsum's Disease: Characterization of Enzyme Defect in Cell Culture 1029

tanic acid-a-hydroxylase activity, but do not differenti-ate among several possible explanations for it (suppres-sion of enzyme protein synthesis, synthesis of an alteredenzyme protein, impairment of a cofactor regener-ating system, or other secondary basis for low activity).Assay of activity in cell-free systems with control of co-factor concentrations and, ultimately, isolation and char-acterization of the enzyme protein would be desirable.Recent studies in the rat have shown that the enzyme ispredominantly intramitochondrial and suggest a role forNADPHand ferric ion (50). However, attempts tosolubilize activity have thus far been unsuccessful.

The possibility has been raised that failure to hydro-lyze phytanic acid contained in lipid esters may be in-volved in the pathogenesis of HAP (35). AlthoughLaurell has shown that synthetic glyceryl triphytanateis resistant to hydrolysis by lipoprotein lipase obtainedfrom healthy subjects after heparin injection (51), theenzymatic capacity of HAP patients, particularly withregard to release from tissue stores, has not been di-rectly investigated. The present experiments with cul-tured human cells attempted to provide a direct test ofthe hypothesis. The finding that HAP and controlstrains released equivalent amounts of labeled phytanateafter being washed and reincubated in unlabeled mediummakes it seem unlikely that a defect in ester hydrolysisplays a major role in HAP.

The relationship between phytanate accumulation andthe symptoms of HAP remains uncertain. Malfunctionof lipid membranes into which phytanate is unavoidablyincorporated represents the most straightforward hy-pothesis linking the two (7, 8, 52). However, repeatedattempts to induce neurological abnormalities in ex-perimental animals by feeding phytol or phytanic acid,often at toxic levels and beginning during gestation(53, 54,') have been unsuccessful. In the present study,short-term exposure of fibroblasts to moderate levels ofunlabeled phytanic acid produced identical morphologicalchanges in HAP and normal strains. These changesbegan at the same threshold level as did similar effectswith palmitate. Subsequent studies extending overlonger periods' have provided suggestive evidence for aselective growth inhibitory effect of phytanic acid onHAP cultures. Consistent with this observation are re-ports of marked growth retardation in two cases ofHAP presenting an unusually early onset soon afterbirth (55, 56). The possibility remains that displace-ment of normal structural fatty acids by excess phytanatemay be responsible for the manifestations of HAP.

Another hypothesis would suppose that the alphahydroxylating enzyme absent in HAP, in addition to

' Steinberg, D., and J. Avigan. Unpublished data.'Herndon, J. H., Jr., D. Steinberg, and B. W. Uhlendorf.

Manuscript in preparation.

disposing of phytanate, normally plays a second andmore crucial metabolic role in nervous tissue. Consider-able evidence exists for the occurrence of alpha oxida-tion and the participation of long-chain alpha hydroxyfatty acids in brain and nerve metabolism (57-59).However, attempts to demonstrate oxidation of phyta-nate in nervous tissue or alpha hydroxylation of ligno-cerate in cultured fibroblasts6 have so far been negative.Further, the phytanate oxidizing system has now beenshown to have properties quite different from those ofthe brain alpha oxidizing system (60). Finally, twoindependent studies on postmortem tissue have failedto demonstrate abnormal patterns or concentrations oflong-chain, straight-chain alpha hydroxy acids in HAPnervous tissue (61, 62).

A third possibility is that phytanic acid interfereswith the function of fat-soluble vitamins such as A, E,or K, or with other essential cofactors with closely re-lated side chains. However, large doses of these ma-terials or of unsaturated fatty acids failed to protectexperimental animals against toxic effects of oral phytol(53,7)

Finally, it remains possible that deletion of phytanatehydroxylation is separate from the defect responsible forthe clinical manifestations of HAPbut closely linked toit on the same chromosome. The proposal that on thisor some other basis phytanate storage is not directlythe cause of the clinical changes may also explain thediscovery of patients who are clinically indistinguishablefrom those with HAP but who have normal phytanatelevels, oxidize phytanate normally in vivo, and whosecultured fibroblasts oxidize phytanic acid at normal rates(63,8). If further clinical observations confirm the previ-ously noted improvement on phytanic acid-low diets(49), however, a simple cause and effect relationshipcan be accepted.

ACKNOWLEDGMENTWeare indebted to Dr. Philippe Laudat for making it pos-sible to obtain a skin biopsy for culture from the patientM. G. in Paris.

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Acta Psychiat. Scand. Suppl. 38: 9.2. Kahlke, W. 1967. Heredopathia atactica polyneuriti-

formis (Refsum's disease). In Lipids and Lipidoses.G. Schettler, editor. Springer-Verlag New York Inc.,New York.

3. Richterich, R., S. Rosin, and E. Rossi. 1965. Refsum'sdisease (Heredopathia atactica polyneuritiformis): an

'Blass, J. P., and J. H. Herndon, Jr. Unpublished data.7Baxter, J. H. Unpublished data.8Kayden, H. J., D. Steinberg, C. E. Mize, and J. H. Hern-

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1030 J. H. Herndon, Jr., D. Steinberg, B. W. Uhlendorf, and H. M. Fales

inborn error of lipid metabolism with storage of 3,7,11,15-tetramethyl hexadecanoic acid: formal genetics. Human-genetik. 1: 333.

4. Klenk, E., and W. Kahlke. 1963. Uber das Vorkommender 3.7.11 .15-Tetramethylhexadecansaure (Phytansaure)in den Cholesterinestern und anderen Lipoidfraktionender Organe bei einem Krankheitsfall unbekannter Genese(Verdacht auf Heredopathia atactica polyneuritiformis-Refsum's Syndrome). Hoppe-Seyler's Z. Physiol.Chem. 333: 133.

5. Steinberg, D., J. Avigan, C. E. Mize, L. Eldjarn, K. Try,and S. Refsum. 1965. Conversion of U-C14-phytol tophytanic acid and its oxidation in heredopathia atacticapolyneuritiformis. Biochem. Biophys. Res. Commun. 19:783.

6. Steinberg, D., C. E. Mize, J. Avigan, H. M. Fales, L.Eldjarn, K. Try, 0. Stokke, and S. Refsum. 1966. Onthe metabolic error in Refsum's disease. J. Clin. Invest.45: 1076. (Abstr.)

7. Steinberg, D., C. E. Mize, J. Avigan, H. M. Fales, L.Eldjarn, K. Try, 0. Stokke, and S. Refsum. 1966. Onthe metabolic error in Refsum's disease. Trans. Amer.Neurol. Ass. 91: 168.

8. Steinberg, D., F. Q. Vroom, W. K. Engel, J. Cammer-meyer, C. E. Mize, and J. Avigan. 1967. Refsum's dis-ease-a recently characterized lipidosis involving thenervous system. Ann. Intern. Med. 66: 365.

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1032 J. H. Herndon, Jr., D. Steinberg, B. W. Uhlendorf, and H. M. Fales