Protection of rats by clofibrate against the hypoglycaemic and toxic effects of hypoglycin and pent-4-enoate. An ultrastructural and biochemical study

Abstract

An ultrastructural and biochemical study of the toxic and hypoglycaemic effects of hypoglycin and pent-4-enoate was made on the livers of normal and clofibrate-fed rats. Injection of hypoglycin to rats doubles (from 22% to 44%) the volume fraction of mitochondria and decreases (from 1.05% to 0.26%) the volume fraction of peroxisomes in hepatocytes. The fast-acting toxin pent-4-enoate causes few ultrastructural changes except for the accumulation of lipids. In male adult rats fed with 0.5% clofibrate in their diet for 1-2 months, the volume fraction occupied by peroxisomes and mitochondria in hepatocytes rose to 6.26% and 29.5% respectively. Clofibrate feeding apparently protected the animals against the toxic, hypoglycaemic and hypothermic effects of hypoglycin and of pent-4-enoate, and completely prevented the ultrastructural damage caused by hypoglycin. After hypoglycin administration, hepatic mitochondrial butyryl-CoA dehydrogenase activity was inhibited by more than 90% and, surprisingly, the activity of the peroxisomal enzymes studied was largely preserved. When hypoglycin was given to rats fed on a clofibrate-containing diet, the oxidation of decanoylcarnitine, which was incomplete after hypoglycin treatment alone, remained incomplete with uncoupled mitochondria, but became apparently complete with coupled mitochondria. In the latter condition, there was a slowing of the rate during the last quarter of the pulse of oxygen uptake. Further, butyryl-CoA dehydrogenase activity was much less affected by hypoglycin in clofibrate-fed animals. Pent-4-enoate does not inhibit beta-oxidation in coupled mitochondria from clofibrate-treated rats.

Presence of thiamine pyrophosphate in mammalian peroxisomes

“…In the fraction that, based on the catalase measurement, was mostly enriched in peroxisomes, TPP increased to 177 ± 2 pmol/mg protein (mean ± SEM of three experiments), about twofold more in comparison with the L-fraction (79.4 ± 11 pmol/mg protein). Assuming that the peroxisomal compartment accounts for 2–2.5% of the total hepatic protein content [11,12] and occupies approximately 10 μl per ml of liver [13,14], one can estimate the intraperoxisomal TPP concentration at approximately 65–85 μM. As part of the TPP may leak out of peroxisomes during the fractionation procedure, this value represents a minimal estimation, but appears to be higher than the cytosolic concentration, estimated at 15–20 μM assuming that the cytosol accounts for 80% of the hepatocyte volume [13].…”

Organic aciduria in rats made resistant to hypoglycin toxicity by pretreatment with clofibrate

“…The effects of feeding with clofibrate on rat liver are complex, including a 6-10-fold increase in peroxisomal f-oxidation, a 2-3-fold increase in mitochondrial fl-oxidation, a 2-fold increase in the fatty-acid-binding Z-protein (Renaud et al, 1978) and a 3-fold increase in total contents of CoASH and carnitine (Mannaerts et al, 1978). Van Hoof et al (1985) showed that the virtually complete inactivation of butyryl-CoA dehydrogenase activity caused by administration of hypoglycin in untreated rats was partly prevented by Vol. 246 pretreatment with clofibrate.…”

“…The significant organic aciduria in clofibrate-fed rats given hypoglycin indicates that the metabolic disturbances were only partly prevented, but, in this mode, those remaining were not enough to cause hypoglycaemia, hypothermia or death (see Van Hoof et al, 1985). This protection may be due to both a decrease in the extent of the inhibitions after administration of hypoglycin and an increased resistance to these inhibitions by clofibrate.…”

Phytol and Peroxisome Proliferation

“…Selective accumulation of one or several intermediates of phytanic acid catabolism in infantile Refsum's disease cannot be definitely ruled out. As in the case of hypoglycin (25), such metabolites might be toxic for peroxisomes. Overload of the entire set of reactions leading to phytanic acid breakdown has been achieved by exogenous administration of high doses of phytol to mice.…”

“…The ultrastructural and biological findings reported in infantile Refsum's disease have not yet been examined in adult-onset Refsum's disease; peroxisomes were studied in cultured fibroblasts from adult-onset Refsum patients, but not in other cell types (24). It was recently demonstrated that certain metabolites (hypoglycin) can have a destructive effect on rat liver peroxisomes (25). We now investigate the effect of phytanic acid accumulation following enhanced dietary supply of phytol on peroxisomal abundance and enzymology in several organs from mice.…”