Bile acid abnormalities in peroxisomal disorders

Sacha Ferdinandusse

Lab. Genetic Metabolic DiseasesAcademic Medical Center

Amsterdam

Peroxisomes play an important role in bile acid biosynthesis

Bile acid biosynthesis involves:

• Modification of the ring structure of cholesterol

• Oxidation of the side chain

• Shortening of the side chain------Peroxisome

• Conjugation------Peroxisome

Cholesterol

Ring modifications

Side chain oxidation

3α,7α-dihydroxycholestanoic acid 3α,7α,12α-trihydroxycholestanoic acid(DHCA) (THCA)

Side chain shortening via peroxisomal β-oxidation

Chenodeoxycholic acid Cholic acid(CDCA) (CA)

Peroxisomal C27-bile acid intermediates

Peroxisomal functions

• Bile acid biosynthesis

• Fatty acid α- and β-oxidation

• Plasmalogen biosynthesis

• Glyoxylate metabolism

• L-pipecolic acid oxidation

• Very long-chain fatty acids (≥C24:0)

• Branched-chain fatty acids (phytanic acid, pristanic acid)

• Bile acid intermediates (DHCA, THCA); Biosynthesis bile acids

• Long-chain dicarboxylic acids

• Polyunsaturated fatty acids;Biosynthesis C22:6ω3 and C22:5ω6

Fatty acid oxidation in peroxisomes

OOH

OHOH

OH

OH

O

Fatty acid oxidation in peroxisomes

β-oxidation

Peroxisomal disorders associated with bile acid abnormalities

Peroxisomal disorders associated with bile acid abnormalities

• Peroxisome deficiency disorders (Zellweger spectrum)

• α-methylacyl-CoA racemase deficiency (AMACR)

• D-bifunctional protein deficiency (DBP)

• Sterol carrier protein X (SCPx)

Zellweger syndrome spectrum: • Zellweger syndrome • Neonatal adrenoleukodystrophy• Infantile Refsum disease

Characterized by the absence of functional peroxisomes.

Deficiency of multiple peroxisomal metabolic pathways.

Caused by mutations in one of the 12 human PEX genes involved in peroxisome assembly.

Peroxisome deficiency disorders

Clinical presentation:

• Neonatal hypotonia

• Seizures

• Impaired vision, impaired hearing

• Psycho-motor retardation

• Dysmorphic features

• Steatorrhea, fat-soluble vitamin deficiency

• Liver disease

Peroxisome deficiency disorders

Clinical presentation:• Liver disease

• Hepatomegaly

• Increased serum liver enzymes

• Cholestasis

• Proliferation of bile ducts

• Fibrosis (eventually cirrhosis)

• Steatosis

• Hemosiderosis

• Inflammation

• Lesions of cholangioles

Peroxisome deficiency disorders

Peroxisome deficiency disorders↓ Plasmalogens

↑ VLCFAs

↑ Pristanic acid and phytanic acid (diet and age dependent)

↑ DHCA , THCA, C29-dicarboxylic acid

- Sum of DHCA, THCA, C29-dicarboxylic acid as a % of total bile acids ranges from 5-90%.

- Pool size CDCA and CA is markedly reduced.

- C27-bile acid intermediates only partly conjugated, whereas C24-bile acids normally conjugated.

- C29-dicarboxylic acid poorly excreted in urine and bile.

Peroxisome deficiency disorders• Urine

Taurine conjugate of OH-THCA and di-OH-THCA (m/z 572 and 588)

5β-cholestanepentol and 27-nor- 5β-cholestanepentol glucuronide (m/z 627 and 613)

↓↓

α-methylacyl-CoA racemase (AMACR) deficiency

Two clinical presentations:

• The bile acid biosynthesis defect causes symptoms in childhood.

• The accumulation of branched-chain fatty acids caused symptoms in adulthood.

α-methylacyl-CoA racemase (AMACR) deficiency

α-methylacyl-CoA racemase (AMACR) deficiency

Clinical presentation in children:

• Fat-soluble vitamin deficiency (K, E, D)

• Cholestatic liver disease

α-methylacyl-CoA racemase (AMACR) deficiency

Clinical presentation in adult patients:

• Adult-onset sensory motor neuropathy

• Encephalopathy

• Seizures

• Postural and intention tremor

• Retinitis pigmentosa, Cataracts

α-methylacyl-CoA racemase (AMACR) deficiency

• Plasma

↑ Pristanic acid and phytanic acid (diet and age dependent)

↑ (25R)-DHCA and (25R)-THCA

S R S R

PBD

AMACR

D-bifunctional protein (DBP) deficiency

Clinical presentation:

• Neonatal hypotonia

• Seizures

• Impaired vision, impaired hearing

• Psycho-motor retardation

• Liver disease • Hepatomegaly• Cholestasis• Proliferation of bile ducts• Fibrosis• Steatosis• Hemosiderosis

D-bifunctional protein (DBP) deficiency

D-bifunctional protein (DBP) deficiency

• Plasma

↑ VLCFAs

↑ Pristanic acid and phytanic acid (diet and age dependent)

↑ DHCA and THCA (in most but not all patients)

Three subgroups of DBP deficiency:

• Type I: Combined DBP hydratase+dehydrogenase deficiency

• Type II: Isolated DBP enoyl-CoA hydratase deficiency

• Type III: Isolated DBP 3-hydroxyacyl-CoA dehydrogenase deficiency

D-bifunctional protein (DBP) deficiency

Bile acid abnormalities and DBP deficiencyType I + II: DHCA, THCA, 24-ene-THCA, (24S,25S)-24-OH-THCA

Type III: (24R,25R)-24-OH-THCA, (24R,25S)-24-OH-THCA, (24S,25S)-24-OH-THCA, DHCA, THCA, 24-ene-THCA

D-bifunctional protein (DBP) deficiency

Patients with a longer survival tend to accumulate less DHCA and THCA, suggesting that residual DBP activity contributes to the extent of bile acid abnormalities in patients.

D-bifunctional protein (DBP) deficiency

• Urine

Taurine conjugate of OH-24-ene-THCA and di-OH-24-ene-THCA (m/z 570 and 586)

Sterol carrier protein X (SCPx) deficiency

Clinical presentation:

• Spasmodic torticollis with dystonic head tremor• Hyposmia, hypoacusis, nystagmus• No abnormalities upon ophthalmologic investigations • Sensory motor neuropathy• Slight cerebellar ataxia

Sterol carrier protein X (SCPx) deficiency

Sterol carrier protein X (SCPx) deficiency

• Plasma

↑ Pristanic acid and phytanic acid

↑ DHCA and THCA

• Urine

Excretion of abnormal bile alcohol glucuronides

Glucuronide conjugates:•m/z 611 cholestanetetrol, ofpentahydroxy-27nor-cholestan-24one•m/z 613 27-nor-cholestanepentol•m/z 627 cholestanepentol, ofhexahydroxy-27nor-cholestan-24one•m/z 629 27-nor-cholestanehexol

Sterol carrier protein X (SCPx) deficiency

Conclusion

Bile acid abnormalities in peroxisomal disorders:

• C24-bile acids are reduced → reduced bile flow →cholestasis

• Accumulation of C27-bile acid intermediates → more hydrophobic, especially toxic, poorly conjugated, poorly excreted → cholestasis + liver injury

• Bile acid therapy successful in relatively mild patients

AcknowledgmentsThanks to many people at the laboratory

Genetic Metabolic Diseases, AMC.

Ronald J.A. WandersRies Duran

Simone DenisHenk OvermarsAlbert BootsmaHenny Rusch

Emma’s Children Hospital, AMCBwee-Tien Poll The

Peter Barth