Fluorescence spectroscopic investigation of competitive interactions between ochratoxin A and 13 drug molecules for binding to human serum albumin

Ochratoxin A (OTA) is a highly toxic mycotoxin found worldwide in cereals, foods, animal feeds and different drinks. Based on previous studies, OTA is one of the major causes of the chronic tubulointerstitial nephropathy known as Balkan endemic nephropathy (BEN) and exerts several other adverse effects shown by cell and/or animal models. It is a well‐known fact that OTA binds to various albumins with very high affinity. Recently, a few studies suggested that reducing the bound fraction of OTA might reduce its toxicity. Hypothetically, certain drugs can be effective competitors displacing OTA from its albumin complex. Therefore, we examined 13 different drug molecules to determine their competing abilities to displace OTA from human serum albumin (HSA). Competitors and ineffective chemicals were identified with a steady‐state fluorescence polarization‐based method. After characterization the competitive abilities of individual drugs, drug pairs were formed and their displacing activity were tested in OTA‐HSA system. Indometacin, phenylbutazone, warfarin and furosemide showed the highest competing capacity but ibuprofen, glipizide and simvastatin represented detectable interaction too. Investigations of drug pairs raised the possibility of the presence of diverse binding sites of competing drugs. Apart from the chemical information obtained in our model, this explorative research might initiate future designs for epidemiologic studies to gain further in vivo evidence of long‐term (potentially protective) effects of competing drugs administered to human patients. Copyright © 2012 John Wiley & Sons, Ltd.     

Effects of astaxanthin supplementation on chemically induced tumorigenesis in Wistar rats

ABSTRACT: BACKGROUND: Astaxanthin (ASTA) is a fat-soluble xanthophyll with powerful antioxidant functions. It is extracted from e.g. salmon, an important food source for certain human populations known to have a reduced risk of tumor development. It is possible that ASTA plays a role in cancer chemoprevention in such populations. The purpose of this study was to investigate the effects of dietary ASTA on chemically induced mammary tumorigenesis using N-methyl-N-nitroso-urea (MNU) in immature Wistar rats. METHODS: Thirty-six 37 days old juvenile female Wistar rats were at random allocated to 4 groups of which Groups 1 and 2 received a single dose of 55 mg MNU/kg body weight. The effects of ASTA was evaluated by giving rats of Groups 2 and 4 a dose of 50 mg ASTA/kg/day for the entire duration of the study. Group 3 rats received feed added alimentary oil.Necropsy and histopathological examinations were carried out on each rat 14 months after the administration of MNU. Haematological values and antioxidative status were determined. Oxidative stress was evaluated by monitoring superoxide dismutase (SOD) and glutathione peroxidase (GPx) activities in hepatic tissue. Lipid peroxidation and carbonylation of proteins was determined in protein extracts from the liver. RESULTS: Tumor development occurred only in rats of Groups 1 and 2, i.e. MNU exposed animals. Frequency of tumor development in general and average number of tumors per animal were insignificant between these two groups. Mammary gland tumors developed in equal frequencies in Group 1 and 2 rats, respectively. Although only rather few tumors were found in the mammary glands, a substantial number of other tumors were found in Group 1 and 2 rats, but at equal rates.Biochemical analyses showed significant higher levels of GPx, malondialdehyde and dinitrophenylhydrazine in Group 1 rats that for rats in all other groups thus indicating protective effects of ASTA on MNU induced hepatic oxidative stress. CONCLUSIONS: Supplementation with ASTA did not reduce tumorigenesis induced by MNU in Wistar rats. However, supplementation with ASTA seemed to have anti-inflammatory effects.     

Interaction of cholesterol with conformationally restricted phospholipids in vesicles.

The interaction of cholesterol with conformationally restricted analogs of dipalmitoylphosphatidylcholine (DPPC) and dipalmitoylphosphatidylglycerol (DPPG) in the liquid-crystalline phase has been studied in vesicles. These analogs contain one of three cyclopentane triols in place of the glycerol moiety found in natural phospholipids and make possible an analysis of whether a limitation of the conformational mobility in the glycerol backbone region affects the interaction with cholesterol. When cholesterol was incorporated into vesicles from cyclopentanoid phospholipids in which the acyl group vicinal to the head group is trans, the first-order rate constant for Cl- efflux is decreased similarly to that in vesicles from 'natural' DPPC or DPPG (about 50%). However, when the head group is in the unnatural 2 position, cholesterol has a much smaller effect on the rate of Cl- efflux (a decrease of about 20%). Cholesterol decreased the rate constants for valinomycin-mediated 86Rb+ efflux from vesicles of the cyclopentanoid PC analogs and of DPPC to a similar extent. The half-time values for spontaneous intervesicle cholesterol exchange were not markedly different using vesicles prepared with the natural glycerophospholipids and with the cyclopentano-phospholipids, suggesting that the geometrical orientation of the acyl chains or the head group has little influence on cholesterol desorption from the lipid/water interface.     

Oxidation of pyrazole by reconstituted systems containing cytochrome P-450 IIE1

Rat liver microsomes oxidize pyrazole to 4-hydroxypyrazole and this oxidation is increased in microsomes isolated from rats treated with inducers of cytochrome P-450 IIE1, such as pyrazole or ethanol. A reconstituted system containing the P-450 IIE1, purified from pyrazole-treated rats, oxidized pyrazole to 4-hydroxypyrazole in a time- and P-450-dependent manner. Oxidation of pyrazole was dependent on the concentration of pyrazole over the range of 0.15 mM to 1.0 mM. In isolated microsomes, glycerol inhibited pyrazole oxidation by about 50% under concentration conditions which occur in the reconstituted system; hence, the values for pyrazole oxidation by the reconstituted systems are underestimated because of the presence of glycerol. Oxidation of pyrazole was inhibited by competitive substrates for P-450 IIE1, such as 4-methylpyrazole, aniline and ethanol, as well as by an antibody raised against the pyrazole-induced P-450 IIE1. Thus, pyrazole is an effective substrate for oxidation by purified P-450 IIE1, extending the substrate specificity of this isozyme to potent inhibitors of alcohol dehydrogenase.