Inhibition characteristics of hypericin on rat small intestine glutathione-S-transferases

Chem Biol Interact. 2010 Oct 6;188(1):59-65. doi: 10.1016/j.cbi.2010.07.007. Epub 2010 Jul 14.

Abstract

Glutathione-S-transferases constitute a family of enzymes involving in the detoxification of xenobiotics, signalling cascades and serving as ligandins or/and catalyzing the conjugation of various chemicals and drugs. The widely expressed cytosolic GST-pi is a marker protein in various cancers and its increased concentration is linked to drug resistance. GST-pi is autoregulated by S-glutathionylation and it catalyzes the S-glutathionylation of other proteins in response to oxidative or nitrosative stress. S-glutathionylation of GST-pi results in multimer formation and the breakage of ligand binding interactions with c-Jun NH(2)-terminal kinase (JNK). Another widely expressed GST enzyme, GST-alpha is assumed as a marker in hepatocellular damage, is implicated in cancer, asthma, cardiovascular disease and response to chemotherapy. Although, it was shown that hypericin binds and inhibits GST-alpha and GST-pi, the inhibition characteristics have not been investigated in detail. The aim of this study was to investigate the effects of hypericin on major GSTs; GST-alpha and GST-pi purified from rat small intestine. When GSH used as varied substrate the inhibition pattern with hypericin was uncompetitive for GST-alpha (K(i)=0.16 + or - 0.02 microM) and noncompetitive for GST-pi (K(i) = 2.46 + or - 0.43 microM). While using CDNB (1-chloro-2,4-dinitrobenzene) as the varied substrate, the inhibition patterns were noncompetitive for GST-alpha and competitive for GST-pi; K(i) values for GST-alpha and GST-pi were 1.91 + or - 0.21 and 0.55 + or - 0.07 microM, respectively. Since hypericin accumulated in cancer cells and important in photodynamic therapy (PDT), inhibition of GST-alpha and GST-pi by hypericin might increase the effectivity of the treatment. Considering that GST-pi is responsible for the drug resistance its inhibition might increase the benefit obtained from chemotherapy.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Chromatography, Liquid
  • Electrophoresis, Polyacrylamide Gel
  • Glutathione Transferase / metabolism*
  • Intestine, Small / drug effects*
  • Intestine, Small / enzymology
  • Kinetics
  • Perylene / analogs & derivatives*
  • Perylene / pharmacology
  • Rats
  • Rats, Sprague-Dawley

Substances

  • Perylene
  • hypericin
  • Glutathione Transferase