INHIBITION OF GLUTHATION S TRANSFERASES BY CURCUMIN AND ITS DERIVATIVES MOLECULAR MECHANISM AND QUALITATIVE STRUCTURE-ACTIVITY RELATIONSHIPS
| Main Author: | Perpustakaan UGM, i-lib |
|---|---|
| Format: | Article NonPeerReviewed |
| Terbitan: |
[Yogyakarta] : Universitas Gadjah Mada
, 2000
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| Subjects: | |
| Online Access: |
https://repository.ugm.ac.id/23020/ http://i-lib.ugm.ac.id/jurnal/download.php?dataId=5948 |
Daftar Isi:
- ABSTRACT: Curcumin and dimethylcurcumin were commercially unavailable, therefore, it was synthesized by condensation of acetylacetone and aromatic aldehyde with catalyst of triethylamine. These compounds were subsequently used for synthesizing of their glutathione (GSH)- and mercapturic acid conjugates, chemically and enzymatically. Chemically synthesis via intermediate N-acetyl-S-L-alanyl methyl ester sulfenyl chloride was successful to get mercapturic acid of dimethyl curcumin,but not of curcumin [based on the proton nuclear magnetic resonance (H-NMR) and mass spectral data]. Unfortunately, from several chemical syntheses of the mercapturic acids of curcumin at different conditions: room temperature, 50 °C and at 60° C and at different solvents/reaction medium, viz dimethylsulfoxide, acetone, toluene, and chloroform and with bases, viz triethylamine and sodium methoxide, it was concluded that the synthesis of mercapturic acids of curcumin was not successful. Also, enzymatic synthesis of GSH-conjugate of curcumin with S-9 or cytosolic fractions of rat liver failed to get the mercapturic acid of curcumin (based on the thin layer chromato-graphic methods). Because the study failed to get the GSH-conjugate of curcumin and the mercapturic acid of curcumin, the research was directed to study the inhibition of GSH-conjugation to 1-chloro-2,4-dinitrobenzene (CDNB) catalyzed by glutathione S-transferases (GSTs) from cytosolic rat liver fraction. It seemed that curcumin inhibited the GSTs-activity in that conjugation. During the research progress, curcumin was found to be unstable, especially in alkaline solution. In the next studies, GSH conjugation to 1-chloro-2,4-dinitrobenzene (CDNB) or GSH conjugation to (ethacrynic acid) EA were performed in the medium of 0.1 M phosphate buffer pH 6.5, while in conjugation of GSH to 1,2-dichloro-4-nitrobenzene (DCNB) at pH 7.5. Curcumin and its derivatives (as inhibitors) were added to these incubations media. Because of the reason, the stability of curcumin and its derivatives in the absence and in the presence of GSH and cytosolic fractions of rat liver in the medium of phosphate buffer pH 6.5 and 7.5 was investigated first. The stability study of the solutions of curcumin and its derivatives was performed by UV-Vis scanning overlay every 5 minutes between 190-550 nm using a Hitachi 150-20 spectrophotometer. From the results of the stability studies, it was observed that curcumin and its derivatives resulted in different stabilities in the incubation media studied (based on the overlay UV-Vis spectra). In general, it can be concluded that curcumin and its derivatives showed a good stability in 0.I M phosphate buffer, pH 6.5. At higher pH values (pH 7.5), however, the stability of some curcumin derivatives was low. However, addition of GSH and cytosolic fraction of rat liver to the incubation mediaimproved their stability. The effects of curcumin and its derivatives on the conjugation of GSH to: I-chloro-2,4-dinitrobenzene (CDNB) (to represent the all classes of GSTs) and ethacrynic acid (EA) (to represent the pi class of GSTs) with the catalyst of rat liver cytosolic fractions of uninduced rat liver, phenobarbital (PB)-, p-naphthoflavone (pNF)-, and pyrazole (Pyr)-pretreated rat liver was performed. The GSH-conjugationto 1,2-dichloro-4- nitroben2ene (DCNB) (to represent the mu class of GSTs) with catalyst of GSTs from cytosolic fractions of uninduced rat liver was also performed. From the study with a substrates CDNB to estimate the activity of all classes of GSTs, it can be concluded that different of rat liver induced with PB, pNF, and Pyr, resulted in strong but different GST activities toward CDNB as a "general substrate" when compared to each other and to GST activities in uninduced rat liver. The type of inhibition of GST-activity in rat liver cytosols induced with different compounds is different. This observation may be due either to structural differences between curcumin and its derivatives and/or to a different composition of GST isoenzymes. Using DCNB as a substrate, it can be concluded that curcumin and itsderivatives showed different inhibitory effects on GSTs activity. Seven out of eight curcumin derivatives studied showed a competitive type of inhibition, with K) values ranging between 0.90 pM and 7.45 gM. In the study using a substrate EA, it can be concluded that when compared with uninduced rats, different induction of rats with PB, {3NF, and Pyr did not result in significantly different GST activities. Curcumin and its derivatives showed different inhibitory activities on GSTs. On GST activities from PB- and Pyr¬induced rats, all curcumin derivatives studied showed a non-competitive inhibitory effects. From the stucture-activity relationship study, it can be concluded that the inhibition of GSH-conjugation to CDNB, DCNB and EA catalyz.ed by GSTs from rat liver cytosolwith the inhibitors curcumin and its derivatives resulted in different types of inhibition. Based on the overall results of the research it can be concluded that the syntheses of mercapturic acids of curcumin and dimethylcurcumin [expected as end product in the metabolism of glutathione (GSH) conjugates of curcumin and dimethylcurcumin] were unsuccessful. Syntheses of GSH conjugates of curcumin was unsuccessful. Curcumin and its derivatives showed a good stability at low pH in a phosphate buffer. At high pH values, some of curcumin derivatives showed instability. Addition of glutathione (GSH) or cytosolic fraction of rat liver improved the stability of curcumin and curcumin 4 but not of curcumin I and 2. Curcumin and its derivatives showed different inhibitory activities towards GSTs from different inductions for GSH-conjugation to: CDNB, EA, and DCNB. The presence of different substituents in the aromatic benzene rings in the structure of curcumin resulted in a various type of inhibition on GSH conjugations to substrates studied. GENERAL CONCLUSIONS a.The present research resulted in novel insights the inhibitory potency of curcumin and a number of synthetic analogues. b.With the aid of the Stnicture-Activity Relationships (SARs) in this dissertation, it should be possible to more rationally design safer analogues of curcumin for specific purposes, e.g. food additives or therapeutic agents.