Utjecaj progesterona na toksičnost benzena u štakora

Benzene is a frequently used industrial solvent. Its toxic manifestations could be modified by sex hormones, but mechanisms of their action are poorly understood. We have examined the influence of progesterone on lipid peroxidation (malondialdehyde), reduced glutathione (GSH), and cytochrome P450 2E1 (CYP2E1) in the liver and kidneys of female rats. Progesterone applied to benzene-treated rats inhibited the formation of reactive oxygen species (ROS), but in ovariectomised benzene-treated rats it significantly increased GSH in the liver. No improvement in CYP2E1 activity was observed in progesterone treated rats. Our results evidence that progesterone changes benzene toxicity (generation of ROS, oxidative stress). However, the probable antioxidative effect of progesterone needs to be confirmed by further studies.Benzen se u industriji često rabi kao otapalo. Zna se da na njegovu toksičnost mogu utjecati spolni hormoni, ali su mehanizmi njihova djelovanja još uvijek slabo poznati. Ispitali smo utjecaj progesterona na peroksidaciju lipida (malondialdehida), pad razina glutationa te aktivnost citokroma P450 2E1 (CYP2E1) u jetri i bubrezima štakorica. Primjena progesterona u štakorica koje su prethodno primile benzen inhibirala je stvaranje reaktivnih molekula kisika (engl. reactive oxygen species, krat. ROS), ali je u štakorica s ovariektomijom koje su također primile benzen doveo do značajnoga rasta glutationa u jetri. U štakorica koje su primile progesteron nije zamijećena poboljšana aktivnost izoeznima CYP2E1. Naši rezultati potvrđuju da progesteron utječe na toksičnost benzena (stvaranje ROS-a i oksidativni stres). Međutim, tek u budućim istraživanjima valja potvrditi djeluje li progesteron antioksidativno

Selenium effects and species differences in hepatic metabolism of pyrrolizidine alkaloids and other xenobiotics

The metabolism of pyrrolizidine alkaloids and other drugs was studied with regard to nutritional status and species differences. Pyrrolizidine alkaloids which are biotransformed to severely toxic metabolites were isolated from tansy ragwort (Senecio jacobaea). Semi-purified alkaloid crystals containing five alkaloids (senecionine, seneciophylline, jacobine, jacoline, and jacozine) were prepared and found to be free of N-oxide and dihydropyrrolizidine bases. Liver changes occurring with time resulting from a single administration (i.p.) of the alkaloidal preparation were studied. Of the mixed-function oxidases, alkaloid dehydrogenase was inhibited immediately (one hour) and recovered slowly. Inhibition coincided well with levels of liver bound pyrrole. On the other hand, cytochrome P-450, N-demethylase, and microsomal protein all were significantly depressed after one day but were normal by six days. N-demethylase activity was significantly elevated and liver pyrrole negligible by 57 days. A transient enlargement (six days) of the spleen was also observed. In a second experiment, one hour after a subacute dose of alkaloid, liver sulfhydryls were mildly depleted. A wide range of alkaloid dehydrogenase activities in different species was demonstrated. Nonogastric herbivores (4amster and rabbit) were highest followed by monogastric species (mouse and rat), ruminant species (cattle and sheep), and avian species (chickens and Japanese quail). With the exception of rabbits and chickens, pyrrole production in vitro generally correlates to the susceptibility of the species resulting from the fed plant. Chronic administration (12 days) of excess levels of selenium, copper, and vitamin A was studied using rats. High selenium caused a significant increase in liver weight, but had no effect on microsomal oxidases. Similarly, high copper had no effect on the oxidases. High vitamin A increased alkaloid dehydrogenase, aniline hydroxylas,:, and liver weight although the effects were not significant. In a separate experiment, rats pretreated with above-normal levels of selenium for five days were less susceptible to acute intoxication from tansy alkaloids. However, fewer of the pretreated animals survived (three weeks) the overall effect. In second-generation-selenium (SGS) deficient rats, low blood glutathione peroxidase (GPXase), poor growth, alopecia, and cataracts were observed. In males, low plasma testosterone and low microsomal protein were concurrent with low levels of microsomal N-demethylase, hydroxylase, and reductase. Alkaloid dehydrogenase was not affected by the deficiency. In SGS-deficient females, neither microsomal protein nor mixed-function oxidase activity was affected. However, phenobarbital treatment (induction) resulted in a greater increase in liver weight and a lesser increase in microsomal protein and alkaloid dehydrogenase in deficient animals. Pentobarbital sleeping time was not different in SGS-deficient males and females. In male rats fed a selenium-deficient diet for 11 months, body weight and blood GPXase were significantly lower. Mild alopecia, immotile sperm, and lower plasma testosterone were observed in some animals. N-demethylase (significantly) and hydroxylase (nonsignificantly) were less active. Phenobarbital treatment of deficient animals resulted in a greater increase in liver size and a substantially lesser increase in alkaloid dehydrogenase and cytochrome P-450 activity. Mixed-function oxidase activity was studied in selenium-deficient chickens and white-muscle diseased lambs. In chickens, the torula yeast diet produced poor growth and diarrhea. The selenium deficiency was without effect on the microsomal oxidases. All the oxidases were consistently less active in chickens fed a standard diet. In lambs receiving comparable levels of selenium and demonstrating similar GPXase activity, some were stricken with whitemuscle disease. Microsomal oxidases were consistently lower in the diseased individuals

Cytochrome P-450-Substrate Interaction and Hepatic Drug Metabolism in the Mouse

A drug which has entered the circulation, may be eliminated as such by the kidney and excreted in the urine. This depends on the lipid-solubility (lipophilicity) of the drug. In the kidney, lipid-soluble drugs are reabsorbed by the tubules, whereas water-soluble (hydrophilic) compounds cannot cross the tubular membrane. Upon passing through the liver some lipophilic drugs can be modified by conjugation with polar molecules, in order to be excreted in the bile or the urine, for example in the form of glucuronides. A large number of drugs, however, do not possess reactive groups for conjugation, They might tend to remain in the body, which is, in many cases, undesirable. In the liver, however, an enzyme system is present, which is capable of metabolizing these compounds by introducing polar groups with the aid of molecular oxygen, The metabolites produced may be excreted either directly or after subsequent conjugation

SEX-DEPENDENT DIFFERENCES IN DRUG METABOLISM IN THE RAT III. Temporal Changes in Type I Binding and NADPH-Cytochrome, P-450 Reductase during Sexual Maturation

ABSTRACT Microsomal ethylmorphine N-demethylase activity increased with age in male rats, but decreased with age in female rats. Relative to the cytochrome P-450 content of microsomes

The effects of some Chinese herbs on liver functions.

by Frankie Tat-kwong Lau.Bibliography: leaves 63-70Thesis (M.Ph.)--Chinese University of Hong Kong, 198

Role of Lipids in the Control of Sex Differences in the Phase I Metabolism of Drugs

Hepatic microsomal preparations from male and female rats were delipidated by column chromatography following cholate solubilisation. The enzyme activity was assayed using lignocaine as the substrate for the mixed function oxidase. The N-deethylation of lignocaine catalysed by delipidated microsomal proteins from male and female rat liver is greater when reconstituted in microsomal lipid than in dilauroylphosphatidylcholine (DLPC). The 3-hydroxylation of lignocaine is unaffected by this treatment. The above effect is mimicked by incorporation of dilauroylethanolamine (DLPE) into the DLPC vesicles with male- but not the female-derived enzymes. Microsomal lipids derived from the male were more effective than female-derived lipids in reconstituting enzyme activities with both male- and female-derived enzymes. There is, thus, a sex- and pathway dependent effect of the lipids: the male-specific N-deethylase pathway is more affected by lipid composition and then more so in the male-derived enzyme. It is possible, therefore, that some of the sex differences in drug metabolism may be related to changes in lipid composition. In addition, the sex-dependence of the metabolism of lignocaine was maintained in the reconstituted system, indicating that this is a suitable system for investigating the role of lipids in maintaining sex-specific drug metabolism. We have extended this work with the isolation of the isozyme of cytochrome P-450 responsible for the N-deethylation of lignocaine. The male-specific cytochrome P-450 isozyme, lignocaine N-deethylase, was purified to electrophoretic homogeneity from liver microsomes of untreated male rats with high retention of bioactivity. The purified N-deethylase was an efficient catalyst of the 16alpha-hydroxylation of androst-4 ene3,17-dione (specific activity of 10 nmole product/min/ nmole cytochrome P-450). The isozyme, together with purified NADPH-cytochrome P-450 reductase, was reconstituted using known lipids and the drug-metabolising activity assayed using lignocaine as substrate. The results showed that the purified isozyme only N-deethylated lignocaine and led to the following conclusion, (I) Mixed dilauroylphosphatidylcholine (DLPC)/dilauroylphosphatidylethanolamine (DLPE) vesicles gave a higher N-deethylase activity than DLPC vesicles. (II) The N-deethylation of lignocaine catalysed by a purified male-specific cytochrome P-450 from rat liver is greater when reconstituted in microsomal lipid than in DLPC. (III) Microsomal lipids derived from male were more effective than female-derived lipids in reconstituting enzyme activities. These data indicated that it is a direct interaction of the lipid with the enzyme (s) or an alteration of the protein-protein interactions caused by the lipid which leads to the change in enzyme activity and that it is the isozyme responsible for the N-deethylation that is particularly affected in this way. In order to assess which portion of the microsomal lipid causes these changes, the microsomal lipid has been fractionated into phospholipid and neutral lipid. Using delipidation and subsequent relipidation of microsomal lipid preparation, we have confirmed that the phospholipid is the most effective portion for the maintenance of the drug metabolism and the sex differences in drug metabolism. It is clear that the male-derived phospholipid was more efficient than the female-derived phospholipid when incorporated into both male- and female-derived delipidated microsomes. The mixture of phospholipid and neutral lipid fractions was very effective, indeed it restored the N-deethylase activity to the level of the microsomes. Experiments were carried out using the male-specific isozyme responsible for the N-deethylation of lignocaine and again it was shown that the phospholipid fraction was the most effective fraction when reconstituted with this isozyme, but it was less effective than the whole microsomal lipid. It is only when the combination of phospholipid and neutral lipid was used that the control activity was achieved. Again the male derived phospholipid was more effective than the female-derived phospholipid. We analysed the phospholipid composition and our analysis shows sex differences in microsomal phospholipid composition and in fatty acid acyl chain of the microsomal phospholipid. Also the analysis of the phospholipid from the diabetic animals showed that the streptozotocin treatment does alter the phospholipid composition and the ratio of acyl chains found. All these changes might be associated with differences in enzyme activity. (Abstract shortened by ProQuest.)