Peroxisomal proteins in rat gametes.

Peroxisomes are essential subcellular organelles, which appear to be derived from pre-existing organelles. This biogenetic mechanism assumes the presence of peroxisomes in either or both mammalian gametes (sperms and/or oocytes). In order to test the presence and subcellular localization of peroxisomal proteins in rat sperms and oocytes, the authors carried out fractionation and immunofluorescence experiments. The results showed that rat oocytes contain peroxisome-like structures, which were detected by indirect immunofluorescence, using an antisera against total peroxisomal proteins. In contrast, such structures were not detected in rat sperms, which appear to contain catalase localized in the cell cytosol. The results reported herein show evidence for the first time of the presence of peroxisome-like structures in mammalian oocytes, and provide evidence for the peroxisome biogenesis hypothesis, by division of pre-existing organelles.

Insulin antagonism: a novel role for human serum transferrin.

We have purified alpha2-glycoprotein (alpha2-GP), an insulin antagonist from human plasma which is induced by growth hormone (GH), and shown that pure alpha2-GP is a potent antagonist of severe insulin-induced hypoglycemia, producing acute hyperglycemia in intact rats and ketonuria in diabetic rats. The N-terminal amino acid sequence of alpha2-GP and the reactivity of alpha2-GP with an antitransferrin monoclonal antibody show that alpha2-GP is identical to human serum transferrin. Furthermore, pure human serum transferrin and non-glycosylated recombinant human transferrin reproduce the insulin antagonist effects of alpha2-GP in rats, whereas ovotransferrin shows no such effect. The neutralization of the insulin antagonism of human serum transferrin by an anti-transferrin monoclonal antibody shows that transferrin has a new function as a potent insulin antagonist. This novel role for human serum transferrin in the regulation of glucose metabolism provides a reasonable mechanism for the diabetogenic effect of GH, and has important implications for the etiology and progression of diabetes.

Characterization of human peroxisomal membrane proteins.

The peroxisomal membrane appears to play a crucial role in transporting proteins into the organelle. Some human genetic disorders involving peroxisome biogenesis, such as Zellweger syndrome, may be caused by genetic defects of the import machinery located in the peroxisomal membrane. In order to characterize the proteins of the human peroxisomal membrane, we isolated peroxisomes from human liver. We obtained their membranes using various procedures and analyzed their proteins by SDS-polyacrylamide gel electrophoresis and silver staining. We compared the protein composition of peroxisomal membranes with membranes derived from mitochondria and microsomes. The main peroxisomal membrane proteins (PMPs) have apparent molecular masses of 147, 112, 95, 87, 81, 79, 74, 69(70), 53-52 (double band), 47, 45, 43, 37, 31, 28, 22, and 17 kDa. The following PMPs of 147, 112, 79, 69(70), 53-52 (double band), 47, 43, 31, 28, 22, and 17 kDa fit the criteria for integral membrane proteins. We then produced rabbit polyclonal and mouse monoclonal antibodies that recognized some human PMPs. One of these antibodies detected mainly PMP43. We used this antiserum to evaluate the presence and subcellular distribution of the PMP43 in fibroblasts derived from patients affected by Zellweger syndrome. These results represent new information about the protein composition of the human peroxisomal membrane and provide biological tools for further characterization of the human PMPs and their genes in normal and pathological conditions.

Stress-induced hyperglycemia and hypoinsulinemia are suppressed by sulfonylurea. Predominant role of insulin.

Based on the in vitro blockade of adrenal catecholamines release by sulfonylurea, we searched for an anti-stress activity of this drug. Stress-induced hyperglycemia and insulin inhibition were employed as adrenergic stress indicators. A standard dose of the oral sulfonylurea glipizide (200 micrograms/100 g), administered 15 min before a 1-h restraint stress to intact or 80% pancreatectomized rats, produced total suppression of the stress-induced hyperglycemia-hypoinsulinemia, an effect followed by a significant post-stress hypoglycemia of 1 h duration. The latter effect was elicited by all the sulfonylureas assayed. In the 80% pancreatectomized rats, glipizide nearly halved the increases in plasma catecholamines at 30 min of stress, but did not modify those attained at 60 min, when glycemia was decreasing and insulinemia was still increasing. Moreover, behavioral experiments in intact stressed rats showed that the adrenergic overt behavior inhibition caused by propranolol was not produced either by glipizide or insulin, reinforcing that glipizide affect was not mediated by catecholamine inhibition. These findings suggest a blockade of catecholamines hepatic receptors by the anticipated insulin release induced by sulfonylurea. Thus, insulin fully dominated when insulin and catecholamines were administered in a stress-like sequence. A confirmation of these findings in diabetic patients subjected to surgical stress would allow a new therapeutic application of sulfonylurea. It is concluded that an anticipated insulin release plus an insulin dominant role over catecholamines activity might explain the anti-stress effect of sulfonylurea.

Isolation of peroxisomes from frozen human liver samples.

This paper shows the successful isolation of peroxisomes from human liver samples that were kept frozen at -70 degrees C. Purification of these peroxisomes was obtained by a combination of two subcellular fractionation techniques: differential centrifugation and isopycnic fractionation in Nycodenz density gradients. Peroxisome integrity was evaluated by latency measurements and by ultrastructural observation. The procedure described here may be useful for the isolation of other subcellular organelles from frozen human samples.

Induction of peroxisomal fatty acyl-coenzyme A oxidase and total carnitine acetyl-coenzyme A transferase in primary cultures of rat hepatocytes by garlic extracts.

Garlic has been proposed as a natural hypolipidemic substance. Most hypolipidemic compounds induce peroxisomal proliferation and increase enzyme activities associated with peroxisomal beta-oxidation in rat liver. Here we report that garlic methanol-extracts behave as hypolipidemic drugs, increasing the activity of peroxisomal fatty acyl-coenzyme A oxidase and of total carnitine acetyl-coenzyme A transferase in primary cultures of rat hepatocytes. Both enzymes are considered markers associated with increased peroxisomal beta-oxidation. As in the case of hypolipidemic peroxisome proliferators, garlic extracts partially prevented the decrease in fatty acyl-coenzyme A oxidase as the culture aged. No changes were observed in the activity of microsomal NADPH cytochrome c reductase or of mitochondrial glutamate dehydrogenase.

Adrenal and liver participation in the rat's post-stress diabetic response.

Sixty minutes of restraint stress, preceded by chlorpromazine administration which stimulates somatotrophic hormone secretion (STH), produced an acute post-stress diabetic response (PDR) in normal-intact rats as well as in adrenalectomized rats. This PDR lasted 3 to 4 hours and was evaluated by glucemia and glucosuria determination and by the appearance of an insulin antagonist, alpha2-glycoprotein STH-dependent, called alpha2-inhibitor, which inhibits glucose uptake by isolated tissues. When tested in the suprahepatic blood of animals after stress it showed increased activity, both in normal and in adrenalectomized rats. This result permits us to state that alpha2-inhibitor may be produced in the liver by and action of STH and without primary glucocorticoid participation. The post-stress hyperglucemic response of adrenalectomized rats had a similar tendency to that of the control, although with initial and final values of glucemia significantly below the control. This response supports the diea that postadrenalectomy gluconeogenesis was evoked during and after the systemic stress.