Glaucia Regina Borba-Murad

Rat liver responsiveness to gluconeogenic substrates during insulin-induced hypoglycemia

Hepatic responsiveness to gluconeogenic substrates during insulin-induced hypoglycemia was investigated. For this purpose, livers were perfused with a saturating concentration of 2 mM glycerol, 5 mM L-alanine or 5 mM L-glutamine as gluconeogenic substrates. All experiments were performed 1 h after an ip injection of saline (CN group) or 1 IU/kg of insulin (IN group). The IN group showed higher (P<0.05) hepatic glucose production from glycerol, L-alanine and L-glutamine and higher (P<0.05) production of L-lactate, pyruvate and urea from L-alanine and L-glutamine. In addition, ip injection of 100 mg/kg glycerol, L-alanine and L-glutamine promoted glucose recovery. The results indicate that the hepatic capacity to produce glucose from gluconeogenic precursors was increased during insulin-induced hypoglycemia.

Changes in blood metabolic parameters during the development of Walker-256 tumour-induced cachexia in rats are not caused by decreased food intake

Blood metabolic parameters of Walker‐256 tumour‐bearing rats, on days 5, 8, 11 and 14 after implantation of tumour, were compared with those of rats without tumour fed ad libitum (free‐fed control) or with reduced feeding (pair‐fed control), similar to the anorexic tumour‐bearing rats. Cachexia parameters and tumour mass also were investigated. In general, especially on day 14 after implantation of tumour, there was reduction of body mass, gastrocnemius muscle mass, food intake and glycemia and increase of blood triacylglycerol, free fatty acids, lactate and urea, compared with free‐fed controls rats. These changes did not occur in pair‐fed control, except a slight reduction of glycemia. Pair‐fed control showed no significant changes in blood cholesterol and glycerol in comparison with free‐fed control, although there was reduction of cholesterol and increase of blood glycerol on day 14 after tumour implantation compared with pair‐fed control. The results demonstrate that, besides the characteristic signs of the cachexia syndrome such as anorexia, weight loss and muscle catabolism, Walker‐256 tumour‐bearing rats show several blood metabolic alterations, some of which begin as early as day 5 after implantation of tumour, and are accentuated during the development of cachexia. Evidence that the alterations of blood metabolic parameters of tumour‐bearing rats were not found in pair‐fed control indicate that they were not caused by decreased food intake. These changes were probably mediated by factors produced by tumour or host tissue in response to the presence of tumour. Copyright

Effect of infliximab on metabolic disorders induced by Walker-256 tumor in rats

BACKGROUND The purpose of this study was to investigate the effect of infliximab, an anti-tumor necrosis factor α (TNFα) monoclonal antibody, on the progression of cachexia and several metabolic parameters affected by the Walker-256 tumor in rats. METHODS Infliximab (0.5 mg/kg) was ip administered, twice a day, beginning at the day in which the Walker-256 tumor cells were inoculated. After 12 days of treatment, the tumor growth, some parameters of cachexia/anorexia, the blood levels of triacylglycerol, glucose, lactate and urea, the peripheral response to insulin and the hepatic glycolysis and gluconeogenesis were investigated. The peripheral response to insulin was evaluated by the insulin tolerance test and the glycolysis and gluconeogenesis in isolated perfused liver. RESULTS The treatment with infliximab did not alter the growth of the Walker-256 tumor, but attenuated (p < 0.05) the reduction of body weight and prevented (p < 0.05) the loss of retroperitoneal adipose tissue induced by the tumor. Moreover, treatment with infliximab tended to minimize the loss of gastrocnemius muscle, the reduction in food intake, the peripheral response to insulin and the liver gluconeogenesis from alanine, as well as the increased blood triacylglycerol, caused by the tumor. In contrast, treatment with infliximab did not attenuate the reduction in hepatic glycolysis and glycemia, nor did it minimize the rise in blood levels of lactate and urea induced by the tumor. CONCLUSION The treatment with infliximab ameliorated some changes associated with cachexia, such as the reduction of adipose tissue and body weight, suggesting that TNFα plays a significant role in mediating these changes induced by the tumor. In addition, infliximab tended to improve or had no effect on other metabolic parameters affected by the Walker-256 tumor, suggesting that other mediators or tumor-related events are involved in these disorders.

Tumor necrosis factor alpha abolished the suppressive effect of insulin on hepatic glucose production and glycogenolysis stimulated by cAMP

BACKGROUND Tumor necrosis factor alpha (TNFα) is implicated in the development of insulin resistance in obesity, type 2 diabetes and cancer. However, its ability to modulate the action of insulin on glycogen catabolism in the liver is controversial. The aim of the present study was to investigate whether TNFα acutely affects the suppression by insulin of hepatic glucose production (HGP) and glycogenolysis stimulated by cyclic adenosine monophosphate (cAMP). METHODS TNFα (10 μg/kg) was injected intravenously to rats and, 1 or 6h later, their livers were subjected to in situ perfusion with cAMP (3 μM), in the presence or absence of physiological (20 μU/mL) or supraphysiological (500 μU/mL) concentrations of insulin. RESULTS The injection of TNFα, 1 or 6h before liver perfusion, had no direct effect on the action of cAMP in stimulating HGP and glycogenolysis. However, when TNFα was injected 1h, but not 6h, before liver perfusion it completely abolished (p<0.05) the suppressive effect of 20 μU/mL insulin on HGP and glycogenolysis stimulated by cAMP. Furthermore, the injection of TNFα 1h or 6h before liver perfusion did not influence the suppression of cAMP-stimulated HGP and glycogenolysis by 500 μU/mL insulin. CONCLUSION TNFα acutely abolished the suppressive effect of physiological, but not supraphysiological, levels of insulin on HGP and glycogenolysis stimulated by cAMP, suggesting an important role of this mechanism to the increased HGP in several pathological states.

Investigation of the acute effect of leptin on the inhibition of glycogen catabolism by insulin in rat liver perfused in situ

Leptin, a cytokine secreted by adipose tissue, has been implicated in the insulin resistance associated with obesity. Here we examined the acute influence of leptin at physiological (10 ng/ml) and supraphysiological (50 ng/ml and 100 ng/ml) concentrations on the inhibition of glycogen catabolism promoted by insulin in rat liver perfusion experiments. Perfusion of the liver with insulin (20 microU/ml) decreased the activation of glucose production (p < 0.05) and glycogenolysis by cAMP (3 microM). However, the infusion of leptin, at concentrations similar to those found in non-obese (10 ng/ml), obese (50 ng/ml), and morbidly obese (100 ng/ml) individuals did not influence the acute inhibitory effect of insulin (20 microU/ml) on glucose production and glycogenolysis stimulated by cAMP (p > 0.05).We conclude that neither physiological nor supraphysiological concentrations of leptin directly influence the inhibition of glycogen catabolism promoted by insulin in rat liver perfused in situ.

Changes in liver gluconeogenesis during the development of Walker-256 tumour in rats

Few studies have investigated liver gluconeogenesis in cancer and there is no agreement as to whether the activity of this pathway is increased or decreased in this disease. The aim of this study was to evaluate gluconeogenesis from alanine, pyruvate and glycerol, and related metabolic parameters in perfused liver from Walker‐256 tumour‐bearing rats on days 5 (WK5 group), 8 (WK8 group) and 12 (WK12 group) of tumour development. There was reduction (P < 0.05) of liver glucose production from alanine and pyruvate in WK5, WK8 and WK12 groups, which was accompanied by a decrease (P < 0.05) in oxygen consumption. Moreover, there was higher (P < 0.05) pyruvate and lactate production from alanine in the WK5 group and a marked reduction (P < 0.05) of pyruvate and urea production from alanine in the WK12 group. In addition, liver glucose production and oxygen consumption from glycerol were not reduced in WK5, WK8 and WK12 groups. Thus the, the results show inhibition of hepatic gluconeogenesis from alanine and pyruvate, but not from glycerol, on days 5, 8 and 12 of Walker‐256 tumour development, which can be attributed to the metabolic step in which the substrate enters the gluconeogenic pathway.

Instant coffee extract with high chlorogenic acids content inhibits hepatic G‐6‐Pase in vitro, but does not reduce the glycaemia

Coffee is the main source of chlorogenic acid in the human diet, and it contains several chlorogenic acid isomers, of which the 5‐caffeoylquinic acid (5‐CQA) is the predominant isomer. Because there are no available data about the action of chlorogenic acids from instant coffee on hepatic glucose‐6‐phosphatase (G‐6‐Pase) activity and blood glucose levels, these effects were investigated in rats. The changes on G‐6‐Pase activity and liver glucose output induced by 5‐CQA were also investigated. Instant coffee extract with high chlorogenic acids content (37.8%) inhibited (p < 0.05) the G‐6‐Pase activity of the hepatocyte microsomal fraction in a dose‐dependent way (up to 53), but IV administration of this extract did not change the glycaemia (p > 0.05). Similarly, 5‐CQA (1 mM) reduced (p < 0.05) the activity of microsomal G‐6‐Pase by about 40%, but had no effect (p > 0.05) on glucose output arising from glycogenolysis in liver perfusion. It was concluded that instant coffee extract with high content of chlorogenic acids inhibited hepatic G‐6‐Pase in vitro, but failed to reduce the glycaemia probably because the coffee chlorogenic acids did not reach enough levels within the hepatocytes to inhibit the G‐6‐Pase and reduce the liver glucose output. Copyright