Azadirachta indica leaf extract modulates initiation phase of murine forestomach tumorigenesis.

The effects of aqueous Azadirachta indica leaf extract (AAILE) on benzo(a)pyrene [B(a)P]-induced forestomach tumorigenesis, B(a)P-DNA adduct formation and certain parameters of carcinogen biotransformation system in mice have been reported earlier from our laboratory. In this study, the effects of AAILE on the enzymes of B(a)P biotransformation, which play crucial role in initiation of chemical carcinogenesis - aryl hydrocarbon hydroxylase (AHH) and uridinediphosphoglucuronosyltransferase (UDP-glucuronosyltransferase) have been evaluated in murine forestomach and liver. In addition, lipid peroxidation (LPO) levels in forestomach as well as liver and the activities of tissue injury marker enzymes - lactate dehydrogenase, aspartate aminotransferase and alkaline phosphatase in the serum have also been evaluated. Oral administration of AAILE (100 mg/kg body wt for 2 weeks) reduces the AHH activity and enhances the UDP-glucuronosyltransferase activity in both the tissues, suggesting its potential in decreasing the activation and increasing the detoxification of carcinogens. The LPO levels decrease upon AAILE treatment in the hepatic tissue, suggesting its antioxidative and hence anti-carcinogenic effects. Non-significant alterations have been observed in tissue injury marker enzymes upon AAILE treatment, suggesting its safety at the given dose. In conclusion, AAILE appears to modulate initiation phase of carcinogenesis and may be suggested as safe and an effective agent for chemoprevention.

Effect of a fatty acid moiety of phospholipid and ceramide on purified GalT-3 (UDP-Gal:GM2 beta 1-3 galactosyltransferase) activity from embryonic chicken brain.

Galactosyltransferase, GalT-3 (UDP-Gal:GM2 beta 1-3 galactosyltransferase) has been characterized and solubilized from 19-day-old embryonic chicken brain, and purified to over 2000-fold using mixed-modal chromatography on a omega-aminohexyl Sepharose column and affinity chromatography on a UDP-hexanolamine Sepharose column. The activity of purified GalT-3 was modulated by phospholipids in vitro with stimulation observed specifically with dipalmitoyl phosphatidylethanolamine (PE). All natural phospholipids tested (PE, PC and PI) inhibited GalT-3 activity. Enzyme activity was affected by the structure of the phospholipid vesicle. It was stabilized by the hexagonal (dipalmitoyl PE) structure and inhibited by the bilayer (dielaidoyl PE) structure. The long-chain fatty acid moiety of the glycosphingolipid substrate, GM2, was found to be necessary for optimum enzyme activity. In the absence of fatty acid, the modified substrates, lyso-GM2 and acetyl-GM2, had a 10-fold increased Km and a 4-8 fold decreased Vmax compared to the normal substrate. We postulate that GalT-3 belongs to a group of glycosyltransferases having recognition for both the carbohydrate as well as the hydrophobic domains (HY-CARS) of their substrates and that the fatty acid moiety of either the substrate (GM2) or a heterotropic effector (phospholipid) plays an important role in regulating the activity of this enzyme.