G. Carrera

Changes in activity of rat brush border enzymes incubated with a homologous series of aliphatic alcohols.

Abstract The effects of some aliphatic alcohols on the activity of several brush border enzymes have been investigated. At the concentrations used we found strong inhibition of(Na+ + K+)-APTase, and Mg2+-APTase while alkaline phosphatase and arylamidase activity was little influenced. The half-maximal ATPase inhibitory concentrations of alcohols were closely correlated with the length of the carbon chain and the interaction with the enzyme appeared to be hydrophobic. The change in free energy due to addition of one CH2 group is estimated at −620 cal for (Na+ + K+-ATPase and −730 cal for Mg2+-ATPase. The relationship between intestinal pharmacological activity of the alcohols and active transport is discussed.

II. Evaluation of the toxic risk of accumulated DDT in the rat: During fat mobilization

The effects of greatly reduced food intake were investigated in rats which had accumulated three times as much DDT as rats killed with a single dose approaching LD50. DDT and its metabolites mobilized more quickly than the fat deposits. The hypertrophy of the liver due to DDT decreased during food restriction and demonstrated the existence of a large detoxication capacity shown through the high metabolism of the pesticide. The disappearance ofp,p′ DDE was most rapid, followed byp,p′ DDD thenp,p′ DDT; they did not accumulate in the fat reserves. The half-life of the pesticide, which is normally three months in the rat, was reduced to five days under the experimental conditions. In spite of rapid mobilization, no major toxic signs were detected from either nutritional, physiopathological, or biochemical examinations.

I. Evaluation of the toxic risk of DDT in the rat: During accumulation

An investigation was undertaken on the accumulation of DDT and its metabolites in the rat. Rats received 14.5 mg DDT/kg b.w. every day for 52 days. Growth, food intake, body composition, and the activities of various enzymes were little affected. However, the level of total lipids fell 30% and the weight of the liver rose 20% due to cellular hypertrophy induced by the DDT. The quantity of DDT and its metabolites found in the carcass was 24 mg/rat i.e. three times that found in rats dead after a single dose of 200 mg/kg. Liver and brain contained 130 Μg/rat and 10 Μg/rat, respectively i.e. five times lower than those found in the rats which died from an acute dose of DDT. In the carcass,p,p′ DDT accumulates more thanp,p′ DDE orp,p′ DDD; the latter is preponderant in the liver.

Cadmium accumulation and cytotoxicity in rat hepatocytes co-cultured with a liver epithelial cell line

Cadmium accumulation and cytotoxicity were compared in hepatocytes in primary culture (HPC) or co-cultured (COC) with a rat liver epithelial cell line (RLEC). Cells were exposed for a 15-day period at 0, 0.045, 0.45 and 0.9 mum-Cd in the incubation medium. Cadmium uptake in COC was always linearly Cd dose and time dependent. In contrast, at the two highest doses for RLEC and only at the highest dose for HPC, a plateau in Cd uptake was observed. In viable cells 95% of the intracellular Cd was found in the cytosol, entirely protein bound. In the three types of culture the amount of Cd-metallothionein (MT) complex was proportional to Cd uptake and was in the order: COC > HPC > RLEC. Lactate dehydrogenase release in the medium and the DNA content of the plated cells at the end of exposure accounted for a marked Cd-induced cytotoxic effect in RLEC and a lesser effect in HPC. In contrast, no significant cytolysis was observed in COC. This suggests that although greater Cd accumulation was observed in COC than in HPC and RLEC, the detoxification procedure, dependent on Cd-MT complex formation, was more efficient and longer preserved in COC owing to a greater maintenance of hepatocyte specific functions, as evidenced by albumin secretion. This COC model offers a powerful tool for studying long-term accumulation and cytotoxicity of Cd in vitro at low exposure levels.

Mechanism of cadmium-decreased glucuronidation in the rat

In isolated rat hepatocytes, cadmium (0-200 microM) decreased the overall glucuronidation of both isopropyl N-(3-chloro-4 hydroxyphenyl)carbamate (4-hydroxychlorpropham, 4-OHCIPC) and 4-nitrophenol in a concentration-dependent manner. In contrast, in native rat liver microsomes, glucuronidation of 4-OHCIPC was increased by cadmium through activation of microsomal 4-OHCIPC glucuronosyl transferase. In addition, in rat microsome incubations, the net amount of 4-OHCIPC glucuronide was also indirectly increased by cadmium through a reduction in the activity of beta-glucuronidase. As the effect of cadmium on the activity of 4-OHCIPC glucuronosyl transferase could not account for the decrease in glucuronide formation in intact hepatocytes, the influence of cadmium on the availability of UDP-glucuronic acid (UDPGA) was investigated further. In isolated rat hepatocytes, cadmium depleted the UDPGA content in a dose-dependent manner without a change in the UDP glucose (UDPG) content. Cadmium did not increase the breakdown of UDPGA by microsomal UDPGA pyrophosphatase but strongly decreased (30-66%) the synthesis of the cofactor in the cytosol by inhibiting UDP-glucose dehydrogenase (UDPGDH). Cadmium (10-50 microM) was found to inhibit the purified enzyme from bovine liver (EC 1.1.1.22) non-competitively. In vivo in the absence of a substrate undergoing glucuronidation, cadmium administration, 1.5 and 2.5 mg Cd/kg i.v., to normally fed rats resulted in a 15 and 30% decrease of hepatic UDPGA, respectively. However, in the liver, neither the NAD+/NADH ratio nor the UDPG content was significantly changed following cadmium treatment. Both in vitro and in vivo results support the conclusion that in intact cells the reduction in overall 4-OHCIPC glucuronidation caused by cadmium was due to a decrease in UDPGA availability which results from the inhibiting effect of cadmium on UDPGDH.

Determination of 2-carboxy thiazolidine-4-carboxylic acid in biological fluids by ion-exchange chromatography.

A column ion-exchange chromatographic method for the determination of 2-carboxy thiazolidine-4-carboxylic acid (TDCA) in blood and urine is described. After elimination of endogenous thiols, alkaline hydrolysis of the compound yields cysteine which is determined spectrophotometrically. The described method is specific for intact TDCA. Using a 3-ml aliquot of sample it allows the linear determination of this hepatoprotective drug from 5 micrograms TDCA ml-1 with a detection limit of 3 micrograms ml-1. The method was applied to study the time course of plasma levels and urinary excretion. An in vitro metabolism study showed that TDCA has a potential as a cysteine donor for glutathione synthesis.

The action and interaction of three alimentary substances (ethanol, tannic acid and sodium sulfite) on the activity of the ATPases in enterocyte brush borders.

Abstract A 2 × 2 × 2 factorial study of interactions among three substances present in some alcoholic beverages (ethanol, tannic acid and sodium sulfite) on brush border ATPase activity indicated an interaction between sodium sulfite and tannic acid. Sodium sulfite decreased the inhibitory effect of tannic acid. A statistical analysis of the influence of these three substances on the kinetic parameters of brush border ATPases indicated that ethanol and tannic acid are non competitive inhibitors of (Na + + K + ) and Mg 2+ -ATPase activity while sodium sulfite inhibits competitively.

Cadmium-induced alterations of chlorpropham metabolism in isolated rat hepatocytes

In order to investigate the various steps of chlorpropham (CIPC) metabolism which could be influenced by cadmium, isolated rat hepatocytes were incubated in the presence of CIPC (0.1 mM) and of increasing Cd concentrations (0-180 microM). The results showed that Cd accumulation in hepatocytes was in good correlation to its concentration in the incubation medium. At 90 microM Cd, hydroxylation of CIPC was only slightly decreased by 30%, while CIPC hydrolysis into 3-chloraniline was unaffected by the presence of Cd. Accordingly, unchanged CIPC increased in hepatocytes. At 27 microM Cd, free 4-hydroxychlorpropham (4-OHCIPC) increased in the intracellular medium as a consequence of a strong suppression of both sulfation and glucuronidation which was related to the strong depletion of the intracellular ATP level under the combined influences of both cadmium and free 4-OHCIPC. Acetylation of 3-chloroaniline, which represents a minor pathway of CIPC metabolism, was already markedly suppressed (43%) with the lowest Cd concentration (27 microM). These in vitro results suggest that Phase II reactions are more sensitive to Cd than Phase I processes and that Cd enhanced the CIPC cytotoxicity as shown by alterations of the membrane integrity.

Hypertrophie du foie provoquée par l'oxythioquinox: Influence du taux de lipides de la ration alimentaire

The relationship between the level of lipid calories in the diet and the effects of oxythioquinox, administered at 200 mg/kg fresh food, for 35 days, wa studied on the liver enlargement of rat. The results show that the level lipid calories itself have no effect since, in the treated animals, the liver enlargement is due part to an increase of the water content and part to an increase of the size of the cells.

Etat nutritionnel du rat au cours d'une réalimentation faisant suite à une mobilisation massive du DDT par le jeûne

Rats were subjected to fasting-induced mobilization of a quantity of DDT equivalent to 45% of the LD50. They were then fed for 1 week for a nutritional and toxicological study. Mobilization