Glutathione S-transferase activity and isoenzyme concentrations in obese Avy/a and lean a/a mice

Effects of rosiglitazone treatment on the pentose phosphate pathway and glutathione-dependent enzymes in liver and kidney of rats fed a high-fat diet

BACKGROUND

Animals fed high-fat diets have been shown to develop hyperglycemia, insulin resistance, hyperlipidemia, and moderate obesity, which resemble the human metabolic syndrome. Obesity, the metabolic syndrome, and some thiazolidinediones, which act as insulin sensitizers, may increase oxidative stress, and/or influence the levels of cellular reducing equivalents and homeostasis.

OBJECTIVE

This study investigated the effects of a high-fat diet, rosiglitazone, or a high-fat diet plus rosiglitazone on metabolic syndrome parameters and crucial liver and kidney enzyme activities in rats.

METHODS

Male Wistar rats were assigned to 4 groups (n = 6 per group): (1) the fat (F) group was fed a rodent diet comprising 45 kcal% fat, (2) the rosiglitazone (R) group was fed a standard rat chow comprising 4.97 kcal% fat plus rosiglitazone (3 mg/kg.d), (3) the fat + rosiglitazone (FR) group was fed a rodent diet comprising 45 kcal% fat (as lard, product D12451) plus rosiglitazone (3 mg/kg.d), and (4) the control (C) group was fed a standard rat chow comprising 4.97 kcal% fat. Animals were housed for 4 weeks, at which time the liver and kidney were isolated for spectrophotometric determination of enzyme activities. Body weight was measured before treatment (baseline) and then weekly throughout the study. Adiposity was measured at the end of the 4 weeks.

RESULTS

The activities of glucose-6-phosphate dehydrogenase (G6PD), 6-phosphogluconate dehydrogenase (6-PGD), glutathione reductase (GR), and glutathione-S-transferase (GST) were significantly reduced in the livers of groups F, R, and FR compared with group C (all P < 0.05). Kidney G6PD, 6-PGD, and GR were found to be significantly lower in group R compared with the other groups (all P < 0.05). Kidney GST was similar in all groups. Plasma glucose, triglyceride, and insulin concentrations were significantly higher than in group F versus the other groups (all P < 0.05). Adiposity was increased in groups F and FR compared with groups C and R (all P < 0.05). Serum cholesterol concentrations were similar in all groups.

CONCLUSIONS

In this study, high-fat diet in rats decreased the enzyme activities responsible for pentose phosphate pathway and glutathione-dependent metabolism in liver but not in kidney. Similarly, these enzyme activities were inhibited with rosiglitazone treatment alone in both organs.

Increased glutathione conjugate transport: a possible compensatory protection mechanism against oxidative stress in obesity?

OBJECTIVE

To compare glutathione S-conjugate transport in obese and nonobese persons, and how glutathione S-conjugates are involved in the antioxidant status in obesity.

MATERIALS AND METHODS

The efflux of glutathione conjugates and malondialdehyde (MDA) levels were measured in erythrocytes of obese (N = 33) and nonobese (N = 28) persons at every 30 min during a 120 min incubation time in vitro. 2,4-dinitrophenyl-S-glutathione (DNP-SG) represented the glutathione S-conjugate.

RESULTS

The efflux of conjugate in erythrocytes from obese subjects (708 +/- 147 DNP-SG efflux nmol/ml erythrocytes/h) was significantly higher than that of control group (490 +/- 105 DNP-SG efflux nmol/ml erythrocytes/h) (P < 0.05). At all time points measured (30-120 min), there was an increase in DNP-SG efflux in obese group (P < 0.05). This is manifested by a decrease in cellular DNP-SG levels. The susceptibility of erythrocytes to in vitro 1-chloro-2,4-dinitrobenzene (CDNB)-induced oxidative stress were greater for cells of control group (P < 0.05), although hemolysis sensitivity of these cells are not different between both groups (P > 0.05). Following CDNB pretreatment, incubation of erythrocyte with vanadate, a DNP-SG transport inhibitor, resulted in an increase of MDA in both groups. However, in this case, the difference in susceptibility was not related to obesity. On the other hand, while erythrocyte glutathione level was lower in obese subjects (79% of control) than in controls (P < 0.05), the adenosine 5'-triphosphate (ATP) levels, the enzyme activities of glutathione S-transferase (GST) and the conjugation capacities of the erythrocytes were not different between groups (P>0.05).

CONCLUSION

Obesity may increase erythrocyte glutathione conjugate transport independent from ATP and GST activity that may protect against MDA formation in vitro.