Hemolysis Mechanism of Dental Adhesive …...136 Dental Materials Journal 9 (2): 136-146, 1990...

136 Dental Materials Journal 9 (2): 136-146, 1990

Hemolysis Mechanism of Dental Adhesive Monomer (Methacryloyl-oxydecyl Dihydrogen Phosphate) Using a Phosphatidylcholine Liposome System as a Model for Biomembranes

Seiichiro FUJISAWA*, Yoshinori KADOMA** and Yasuo KOMODA*** School of Dentistry , Tokyo Medical and Dental University, 1-5-45, Yushima, Bunkyou-Ku, Tokyo, 113 Japan

** Institute for Medical and Dental Engineering , Tokyo Medical and Dental University, 2-3-10. Kanda-Surugadai, Chiyoda-Ku, Tokyo 101, Japan

Received on July 2, 1990

Accepted on September 3, 1990

To clarify the mechanism of interaction of dental adhesive monomers with biological membranes at the molecular level, we studied the interaction of methacryloyloxydecyl dihydrogen phosphate (MDP) and methacrylic acid (MAA) with the dipalmitoylphosphatidylcholine (DPPC) liposome system using NMR and DSC. MDP-DPPC interaction became apparent through broadening of the DPPC phase transition as pH decreased, finally the enthalpy of MDP-DPPC (1:1mol ratio) reduced to zero at pH 2.5. Proton chemical shifts of MDP enhanced shielding and proton signals due to the phosphatidylcholine polar group (O-CH2-CH2-N bond) of DPPC were observed . MAA-DPPC interaction was smaller than that of MDP-DPPC, even at low pH. It was concluded that the strong hemolytic activity of MDP may be due to its interation with the

phospholipid bilayers of erythrocyte membranes.

Key words: Phosphate Monomer, Hemolytic Activity, Phospholipid Liposomes.

INTRODUCTION

Bonding agents are widely used in dentistry for pit and fissure sealants, restorative

materials, orthodontic and prosthetic devices1,2). To bond composite resins to dentin, bonding

agents must be directly applied to dentin and then the agents must penetrate or react with

the dentin structure. In particular, acid etching of dentin is liable to cause injury to dental

pulp due to the increase in dentin permeability3). Hence, dentin bonding agents in the

restorative system may directly affect the dental pulp. Thus, residual monomers, initiators

and other small molecules in bonding agents may be involved in pulpal responses. Recently,

phosphate monomers (phenyl-P) were used as one of components of the enamel and dentin

bonding agents4). This adhesive resin-system was found to be biocompatible with the dental

pulp when the infected outer layer of carious dentin was removed and then the phosphate

monomer system was placed upon the etched dentin5)6). However, this adhesive system

induced severe cytotoxicity7). The in-vivo usage test for restorative resin-system only

provides a rough measure of pulp irritation and the clinical histopathologic experimentation

does not allow quantification8). Therefore, it is important to evaluate the biological prop-

erties of materials before clinical application7,8). On the other hand, it appears that the

cause-and-effect relationship between restorative resin materials and pulpal responses is not

clearly correlated with biological properties of materials, microleakage, bacterial contamina-

tion, or any other single factor or multiple factors and that the absence of the •gtoxicity•h in

HEMOLYSIS MECHANISM OF MDP 137

a material does not make it biocompatible9).

The mechanism or components of the dentin-pulp complex which afford protection to the

dental pulp from resin systems have not been clarified. Dental pulp is a complex tissue

consisting of cells and abundant extracellular matrix. Components in dentinal tubules may

create a barrier against the diffusion of toxic substances of dental materials10-12). Dentin

permeability may be an important factor of pulpal responses caused by dental materials. Dentin and pulp tissues which are derived from mesoderm are known to be very sensitive to

acids13). Hydrophilic acid monomer, MAA used in self-curing methyl methacrylate (MMA)

resin-system was known to be toxic in the dental pulp3). Also, this showed the high degree

of acute toxicity in mice and of tissue toxicity14,15) MDP which has been used in the

commercial resin-system as a new bonding agent, is also an acid monomer16). The bonding

agents with MDP showed a larger cytotoxicity compared with those without MDP17) and had

an adverse effect on the dental pulp18). Therefore, it is of particular interest to determine how

the molecular structure of phospholipids in biological membranes is modified by interaction

with MDP compared to MAA.

In the present study, we examined the hemolytic activity caused by MDP, MAA and

MMA. NMR and DSC were used to investigate the degree and nature of interaction of MDP

or MAA with the DPPC liposome system as a model for biomembranes. The mechanism of

the interaction of MDP with erythrocyte membranes was discussed.

MATERIALS AND METHODS

L-ƒ¿-dipalmitoylphosphatidylcholine (DPPC)#, 3-(trimethylsilyl) propionic acid sodium

salts-D4 (TMSPA)## and deuterium oxide (D2O)## were used without purification. Metha-

crylic acid (MAA)* and methyl methacrylate (MMA)* were used after purification by means

of high performance liquid chromatography (HPLC)**.

Synthesis of MDP19). 10-Hydroxydecyl methacrylate was prepared from 1, 10-decanediol

and methacryloyl chloride. The product was isolated by column chromatography on silica

gel. The purified alcohol and triethylamine were slowly added to phosphorous oxychlor-

ide. After the termination of the reaction, the mixture was extracted with ether and the

solvent was evaporated. The resulting viscous MDP was washed with n-hexane several times

and dried (yield about 74%). The purity of MDP was examined by HPLC, indicating a single

peak. The structure of MDP was identified by NMR and infrared spectra.

Hemolysis studies. Human erythrocytes from normal male donors were isolated from

blood anticoagulated with EDTA by centrifugation (x1000) for 10min. The plasma and buffy

coat were then removed and erythrocytes were washed three times with PBS (phosphate

buffer solution 100mM, pH 7.4) before being dispersed in PBS. An appropriate concentration

of MAA, MDP and MMA were prepared in PBS. One ml of the solution obtained was placed

in each assay tube and 1ml of the cell suspension was added to it and incubated at 37•Ž for

# Sigma Chemical Co., St. Louis, MO., USA.## Merck Chemical Co. Darmstadt, Germany.

* Tokyo Kasei Chemical Co . Tokyo, Japan. ** Nippon Millipore Ltd . Waters Chromatography Division, Tokyo, Japan.

138 S. FUJISAWA, Y. KADOMA and Y. KOMODA

an appropriate time. After incubation, the tubes were centrifuged at 2000rpm 10min and the

absorbance of supernatant at a wave length of 545nm was measured by using a UV-210A

spectrometer.+ The hemolysis percentage was calculated on the basis of the measured

absorbance for the original cell suspension after hemolyzing had taken place by freezing and

thawing.

Preparation of the liposomes for NMR. An appropriate amount of DPPC was dissolved

in chloroform and dried under vacuum. The test monomer (MAA or MDP) was added to the

dried lipid film and was dispersed in D2O by vortexing on a Vortex shaker at 45•Ž for 2-3min

and then was sonicated under a nitrogen atmosphere for 30min at 45•Ž. The molar ratio of

DPPC to test compound was 1:1. Suspensions containing approximately 10% DPPC

liposomes were prepared.

NMR spectroscopy. Proton NMR spectra were measured at 30•Ž and 52•Ž under JEOL

JNM-GX 270 spectrometer***, at 270MHz. The chemical shifts (ƒÂH) of MDP, and MAA are

reported in ppm downfield from the external standard, TMSPA, as previously described12).

DSC studies. The DPPC liposome system was prepared in a manner similar to that

described above. All samples for DSC studies were 75mM DPPC, 140mM sodium phosphate

and the appropriate concentration of MDP and MAA. Each 10ƒÊl sample of both DPPC and

test compound was sealed in a DSC container. Also, some samples of MAA and MDP were

sealed in a container with D2O. The sample was then allowed to equilibrate for 14h at 5•Ž

and finally shaken again for 1min by hand at 25•Ž. The sample (20ƒÊl) was scanned in a sealed

calorimetric container on a DSC-Rigaku calorimeter### operating at a heating rate of 5•Ž/

min with a range setting of 0.5mcal/s20). The transition enthalpy (ƒ¢H) was calculated from

the area under the curve which was determined by cutting out the DSC-curves and weighing

the chart paper. Enthalpy measurements of the DPPC liposome system were run at least in

triplicate. Error limits on enthalpy are given as •}1 standard deviation.

Since in general, the enthalpy of pretransition is small and has a behavior similar to that

of the main transition, we discuss only the main transition21).

p H measurement of solution. pH was determined with a COM-8 pH meter++ at 23•Ž.

RESULTS

Hemolysis studies. The percentage of hemolysis caused by MDP, MAA and MMA is

shown in Table 1. In case of MDP, the time and concentration required to produce about 50

% hemolysis were 10min with 19mM and 60min with 2.4mM, respectively. MAA and MMA also showed a small degree of hemolysis (1-2%) at the same time and concentration.

From this, it is clear that the hemolytic activity of MDP was stronger than MAA. MAA

induced the denaturalization of hemoglobin at the concentration of 290-580mM due to its acid

reaction. At 75mM, however, the hemolysis of MAA was 6.4% for 60min.

NMR studies. The structure of MAA and MDP and DPPC are shown in Figs. 1 and 2,

*** JEOL , Tokyo, Japan.### Rigaku Denki Co. Ltd., Tokyo, Japan.

+ Shimadz Mfg . Co., Kyoto, Japan.++ Denki Kagaku Keiki Co. Ltd., Tokyo, Japan.


Table 1 Percentage of hemolysis caused by MDP, MAA and MMA at 37•Ž

MDP Methacryloyoxydecyl dihydrogen phosphate, MAA Methacrylic acid, MMA Methyl methacrylate, * 4% human erythrocytes in phosphate buffer solution at pH 7.4, # pH 3.9, + pH 4.4., DN Denaturalization of hemoglobin after hemolysis. and () SD for three

samples.

A

B

Fig. 1 1H NMR spectra of DPPC liposomes/MAA in D2O and structure of MAA. (A)

30•Ž; (B) 52•Ž.


MDP

DPPC

Fig. 2 Structures of MDP (methacryloyoxydecyl dihydrogen phosphate) and DPPC (dipalmitoylphosphatidylcholine).

A

B

C

Fig. 3 1H spectra of MDP, DPPC liposomes/MDP and DPPC liposomes in D2O at 52•Ž.

(A) MDP, (B) DPPC liposomes/MDP, and (C) DPPC liposomes.


respectively. The 1H NMR spectra of both MAA and MDP in the DPPC liposomes are shown

also in Figs. 1 and 3, respectively. Signals from MAA were broad at 52•Ž compared with

those at 30•Ž, indicating that its interaction with DPPC increased at 52•Ž. Signals at 0.92, 1.

34 and 3.28ppm were resulting from terminal methyls (H1), (CH2)14 chains (H2), and N+(CH3)3

choline (H3) of DPPC, respectively. In the case of MAA, the signal (3.67ppm) resulting from

the CH2N choline (H4) of DPPC was due to the hydrogen bonding at pH 2.7 at 52•Ž.

Chemical shifts (ƒÂH) and chemical shift differences (ƒ¢ƒÂH) of the DPPC liposomes/MAA

are shown in Table 2. The ƒ¢ƒÂH value of MAA is in the order: Ha (minus 0.02-minus 0.03

ppm)>Hc (0.00ppm)>Hb (0.00-0.02ppm). The upfield shift of Ha and the downfield shift

of Hb may indeed indicate their average orientation relative to the double-bond of MAA.

From this, we concluded that the double-bond portion of MAA is close to the lipid bilayers

of DPPC. The change at 52•Ž was larger than that at 30•Ž, being due to the fact that the

DPPC liposomes existed in a liquid phase at 52•Ž. The accuracy of proton chemical shift

was +0.01ppm in this experiment.

The 1H NMR spectra of MDP, DPPC liposomes/MDP and DPPC liposomes are shown

in Fig. 3, while ƒÂH and ƒ¢ƒÂH are shown in Table 3. No signal due to Ha and Hb was noted.

The intensity of Hc markedly decreased in the DPPC liposome/MDP system. Experimen-

tally, the signals due to H3, H4 and H5(POCH2) of DPPC appeared at 3.23, 3.67 and 4.32ppm,

respectively (Fig. 3C). The signals of H4 and H5 did not appear in the DPPC liposome system

without MDP. This indicates that the stabilization of intermolecular electrostatic interaction

between the positively charged ammonium group and anion phosphate oxygen group of

DPPC was disturbed by the addition of MDP. As shown in Table 3, the ƒ¢ƒÂH of Hf and Hc

were minus 0.15 and minus 0.03, respectively. Large upfield shifts were observed for Hf

whereas downfield shifts occured for Hc. The ƒ¢ƒÂH of H1 and H2, and H3 were 0.00ppm and

minus 0.05ppm, respectively. Upfield shifts occured for H3. Proton resonances for Hf and

H3 enhanced shielding (upfield shifts). This indicates the close proximity of the phosphate

groups of MDP and the N+(CH3)3 of DPPC. This interaction of MDP was markedly stronger

than that of MAA. The signals for H4 and H5 were observed at 30•Ž. Their chemical shifts

Table 2 Chemical shifts (ƒÂH) and chemical shift differences (ƒ¢ƒÂH) of methacrylic acid (MAA) in

the DPPC liposome system (1:1mol ratio) in D2O.

The ƒÂH values are in ppm downfield from TMSPA used external reference in D2O, and *: see

Figure 1.


Table 3 Chemical shifts (ƒÂH) and chemical shift differences (ƒ¢ƒÂH) of MDP, DPPC liposomes/MDP

(1:1mol ratio) and DPPC liposomes in D2O at 52•Ž

The ƒÂH value are in ppm downfield from TMSPA used as external reference in D2O, * see Figure

2., A: saturated MDP in D2O, ** Chemical shifts of DPPC in CDCl3-CD3OD

(2:1v/v) are expressed in ppm downfield from tetramethylsilane.23), and N non signal.

Fig. 4 Typical DSC curves for DPPC liposomes induced by MDP and MAA. (A) DPPC liposomes without any additives (control) at pH 6.8, (B) 75mM MDP at pH 2. 5 in D2O, (C) 75mM MDP at pH 6.3 in phosphate buffer solution, (D) 75mM MAA at pH 2.7 in D2O, and (E) 75mM MAA at pH 5.0 in phosphate buffer solution.


Table 4 Changes in phase transition temperature (Tm) and half-width (WH) and transition enthalpy

(ƒ¢H) of DPPC liposomes induced by MDP and MAA

* in sodium phosphate buffer solution at pH 6.8., ** in D2O, () SD for three samples, and DPPC 75mM.

were similar to those at 52•Ž.

DSC studies. The DSC thermograms of DPPC liposomes caused by MAA and MDP

addition are shown in Fig. 4. The changes in phase transition temperature (Tm), half-width

(WH) and transition enthalpy (ƒ¢H) of DPPC liposomes caused by compounds are shown in

Table 4. The transition profile for DPPC liposomes without additives (control) was ƒ¢H 8.72

kcal/mol at Tm 40.5•Ž (curve A). It was not pH-dependent between pH 2-pH 7.75mM MDP

caused the broadening of the DSC curve of DPPC liposomes by a decrease in pH from 6.3

(curve C) to pH 2.5 (curve B). The ƒ¢H of 75mM MDP at pH 2.5 was zero, indicating that

MDP caused the complete disruption of the DPPC liposomes. In MAA, the DSC curve was

slightly broadened by a decrease in pH from 5.0 (curve E) to pH 2.7 (curve D). The Tm and

ƒ¢H of 75mM MAA at pH 5.0 were 37•Ž and 8.45kcal/mol, respectively whereas those of

MDP at the same concentration at pH 6.3 were 32•Ž and 5.63kcal/mol, respectively. The

values observed for 38mM MAA at pH 5.5 were 39.5•Ž and 8.20kcal/mol, respectively,

whereas those for MDP at pH 6.3 were 35.5•Ž and 7.95kcal/mol, respectively. The ƒ¢H of

MDP was 1.65kcal/mol at pH 2.5 and 7.95kcal/mol at pH 6.3, indicating that the phase

transition properties induced by MDP were pH-dependent. In the case of MAA, effects of

pH on the Tm and ƒ¢H were small. MDP largely shifted Tm to a lower temperature and

produced a larger decrease in the ƒ¢H compared with MAA. This suggested that the

interaction of MDP with acyl chains of DPPC is stronger than MAA.

DISCUSSION

It is clear from the present NMR studies that MDP was markedly incorporated into the

DPPC liposome system and that the phosphatidylcholine polar group (O-C-C-N bond) of

DPPC was affected by the addition of MDP. Furthermore, in the DSC studies, the interaction

of MDP with the DPPC liposome system became apparent through broadening of the lipid

phase transition as pH decreased, and the final disappearance of the DSC peak resulting from


the liposomes alone. This may suggest that mixed MDP-DPPC micelles or other aggregates

are formed at pH 2.5, indicating that the attractive force for MDP-DPPC interaction may

arise from (1) hydrogen bonding involving un-ionized phosphate groups of MDP and phos-

phodiester head groups of DPPC and (2) the hydrophobic interaction between the hydrocar-bon portion (decyl group) of MDP and acyl chains of DPPC. As an additional observation

consistent with the suggestion of hydrogen bonding, it has been reported that the phosphodies-

ter group serves as H-bond acceptor in crystals of lipid hydrates22). It was concluded that the

strong hemolytic activity of MDP was caused by its impregnation into lipid and/or lipo-

protein layers of erythrocyte membranes.Also, the interaction of MAA appears to be due to the hydrogen bonding between

un-ionized carboxylate molecules and phosphodiester head group at pH 2.7. Comparing with

MDP, MAA had a smaller interaction with DPPC, even at a low pH. This was due to smaller

hydrophobicity of MAA.

Our results obtained from NMR and DSC suggest that MDP probably has a stronger interaction with the hydrophobic components containing lipids in biological membranes, than

compared with MAA and it possesses a high potential for causing membrane damage. In this

experiment, a pH-dependent interaction as a result of a cooperative hydrogen bonding was observed. Therefore, the degree of the interaction of acid monomers may be smaller as pH

increases in the tissue fluid.

Change in dentin-including secondary dentin formation induced by the interaction of

adhesive monomer may afford protection to the dental pulp from the resin systems, when

orifices of dentinal tubules can be perfectly sealed by the adhesive resin systems6,24).

However, unpolymerized surface-active monomers such as MDP in bonding agents may

cause injury to the pulp due to their high ability of membrane-damage when they directly

penetrate into the pulp18). MDP is used with other dimethacrylates in commercial bonding agents16). Some dimethacrylates such as Bis-GMA showed a larger degree of hemolysis than

MMA25). The degree of interaction of Bis-GMA with DPPC liposomes was smaller than that

of MDP (Data not shown). Our present studies suggested that since MDP interacts strongly

with the phospolipid bilayers, MDP is likely to interact with the lipid bilayers of membranes

of odontoblasts, nerve fibers and pulp cells in the dentin-pulp complex. Additional experi-

ments are required to clarify the mechanism of protection to the dental pulp from the

adhesive resin-systems.

CONCLUSION

1. MDP induced a stronger hemolytic activity than MAA.

2. In DSC studies, changes in Tm and enthalpy of DPPC liposomes induced by MDP were

larger than those of MAA.

3. Proton chemical shifts of MDP enhanced shielding due to the large interaction between

MDP and DPPC. MAA-DPPC interaction was smaller than that of MDP-DPPC.


REFERENCES

1) Tyas, M.J., Alexander, S.B., Beech, D.R., Brockhurs, P.J., and Cook, W.D: Bonding-retrospect and

prospect, Aus. Dent. J. 33: 364-374, 1988.2) Masuhara, E.: A dental adhesive and its clinical applications, Quitessence Publisher Co., Tokyo, 1982,

pp 11-22. (in Japanese)3) Stanley, H.R., Going, R.E., and Chancey, H.H.: Human pulp reponse to acid pretreatment of dentin

and composite restoration, J Am Dent Assoc 91: 817-825, 1975.4) Yamauchi, J., and Nakabayashi, N.: Adhesive agents for hard tissue containing phosphoric acid

monomer, Polymer Preprints 20: 59, 1979.5) Inokoshi, S.: Pulp responce to a new adhesive restorative resin, J Stomat Soc Japan 47: 410-426, 1980.

(in Japanese)6) Fusayama, T.: The problems preventing progress in adhesive restorative dentistry. J Dent Res 2: 158

-161, 1988.7) Kato, M., Nishida, T., Kataoka, Y., Yokoyama, M., Ogitani, Y., Nakamura, M. Kawahara, H.:

Saudies on the cytotoxic action of new restorative resin (in vitro), J Japan Soc Dent Appar Mat 20: 20-49, 1979. (in Japanese)

8) Spangberg, L, Rodrigues, H., Langeland, L. and Langeland, K.: Biologic effects of dental materials. 2. Toxicity of anterior tooth restorative materials on Hela cells in vitro, Oral Surgery 36: 713-724, 1973.

9) Cotton, W.R.: Guest editorial: How can a frog jump? A current assessment of pulp biology research,

J Dent Res 67: 1251, 1988.10) Meryon, S.D., and Jakeman, K.J.: An in vitro study of the role of dentine in moderating the

cytotoxicity of zinc eugenol cement, Biomaterials 7: 363-372, 1986.11) Fujisawa, S., Kadoma, Y. and Komoda, Y.: 1H and 13C NMR studies of the interaction of eugenol,

phenol, and triethyleneglycol dimethacrylate with phospholipid liposomes as a model system for odontoblast membranes, J Dent Res 67, 1438-1441, 1988.

12) Fujisawa, S., Kadoma, Y. and Komoda, Y.: Nuclear magnetic resonance spectroscopic studies of the interaction of methyl methacrylate and ethylene dimethacrylate with phosphatidylcholine liposomes as a model for biomembranes, Biomaterials 10: 51-55, 1989.

13) Roydhouse, R.H.: Silicate cements and pulpal degeneration J Am Dent Assoc 62: 670-675, 1961.14) Lawrence, H., Dillingham, E., Malik, M. and Autian, J.: Development of standard toxicity testing for

dental materials/products and explorating dental toxicology, PB Report 205740, 1971.15) Lawrence, W.H., Bass, G.E., Purcell, W.P., and Autian, J.: Use of mathematical models in the study

of structure-toxicity relationships of dental compounds. I. Esters of acrylic and methacrylic acids, J Dent Res 51: 526-535, 1972.

16) Fujisawa, S., Kadoma, Y. and Komoda, Y.: HPLC Separation of methacryloyloxydecyl dihydrogen

phosphate (MDP) from dental bonding agents, J J Den Mater, in press. (in Japanese)17) Taki, E., Yamamoto, K., Asai, S., Satou,, (M.,) Tsuchiya, H., Nakahashi, T., Kondo, M. and Kimura,

K.: Studies on the cytotoxicity of bonding agents by means of cell culture, Japan J Conserv Dent 32: 579-589, 1989. (in Japanese)

18) Otsuki, M.: Histopathological study on pulpal response to restorative composite resins and their ingredients, J Stomat Soc Japan, 55, 203-236, 1988. (in Japanese)

19) JPN patent, SHO58-21687, 1983.20) Fujisawa,. S, Kadoma, Y., and Masuhara, E.: A calorimetric study of the interaction of synthetic

phospholipid liposomes with vinyl monomers, acrylates and methacrylates, J Biomed Mater Res 18: 1105-1114, 1984.

21) Ladbrooke, B.D. and Chapman, D.: Thermal analysis of lipids, proteins and biological membranes. A review and summary of some recent studies, Chem Phys Lipids 3: 304-367, 1969.

22) Hauser, H., Pascher, I., Peasons, R.H. and Sundell, S.: Preferred conformation and molecular packing of phosphatidylethanolamine and phosphatidylcholine, Biochim Biophys Acta 650: 21-51, 1981.

23) Hauser, H., Guyer, W. Pascher, I., Skrabal, P. and Sundel, S. (1980): Polar group conformation of

phosphatidylcholine. Effect of solvent and aggregation Biochemistry 19: 366-377, 1980.


24) Fujisawa, S. Fujisawa, H. Atsuta, M. Masuhara, E., Komori, A. and Ishikawa, G.: Studies on dental self-curing resin (12) Effect of the new dental self-curing resin (F1) activated by tri-n-butyl borane on the pulp of the dog. Reports of the Institute for Medical and Dental Engineering 4: 129-139, 1970.

25) Fujisawa, S. and Kadoma, Y.: Effect of Bis-GMA analogs on hemolytic activity and DSC phase transition of phospholipid liposomes, J J Dent Mater 6: 592-599, 1987.

227

本号掲載論文の和文抄録

りん脂質リポソームを生体膜もモデルとして用いた歯科用接着性モノマー

(メタクリロイルオキシデシルジハイドロジエンホスフエート)の

溶血メカニズムの研究

藤沢盛一郎＊,門磨義則＊＊,菰田泰夫＊＊

＊東京医科歯科大学歯学部

＊＊東京医科歯科大学医用器材研究所

酸性モノマー(メタクリロイルオキシデシルジハイド

ロジエンホスフエート,MDP)は市販歯科用接着システ

ムの重要な成分として使用されている。この化合物はメ

タクリル酸(MAA)と比べ強い溶血作用を示した。歯科

用接着モノマーの生体膜との相互作用のメカニズムを分

子レベルで明らかにするため,我々はジパルミトイルホ

スファチジルコリン(DPPC)リポソームシステムと

MDP及びMAAの相互作用を,核磁気共鳴装置(NMR)

と示査走査熱量計(DSC)で研究した。DSCでMDP-

DPPC相互作用をみると,pHが減少するにつれて

DPPCリポソームの相転移のブロード化がおこり,最終

的にはpH 2.5でエントロピーが零になった(MDP-

DPPC 1:1モル比)。NMRでみると,MDPのプロト

ンケミカルシフトは遮蔽が高まり,DPPCリポソームの

流動性が高まるためのホスファチヂルコリン極性基

(OCH2CH2N)のプロトンシグナルが新たに観察され

た。MAA-DPPC相互作用は低いpH値でもMDP-

DPPCより小さかった。MDPの溶血活性は赤血球のり

ん脂質膜との相互作用に基づくものと結論づけられた。

Hemolysis Mechanism of Dental Adhesive …...136 Dental Materials Journal 9 (2): 136-146, 1990...

Documents

Transcript of Hemolysis Mechanism of Dental Adhesive …...136 Dental Materials Journal 9 (2): 136-146, 1990...