Insulin and glucagon degradation in liver are not affected by hepatic cirrhosis

Precision-cut liver slices as an ex vivo model to assess impaired hepatic glucose production

Fasting hypoglycemia is a severe and incompletely understood symptom of various inborn errors of metabolism (IEM). Precision-cut liver slices (PCLS) represent a promising model for studying glucose production ex vivo. This study quantified the net glucose production of human and murine PCLS in the presence of different gluconeogenic precursors. Dihydroxyacetone-supplemented slices from the fed mice yielded the highest rate, further stimulated by forskolin and dibutyryl-cAMP. Moreover, using 13C isotope tracing, we assessed the contribution of glycogenolysis and gluconeogenesis to net glucose production over time. Pharmacological inhibition of the glucose 6-phosphate transporter SLC37A4 markedly reduced net glucose production and increased lactate secretion and glycogen storage, while glucose production was completely abolished in PCLS from glycogen storage disease type Ia and Ib patients. In conclusion, this study identifies PCLS as an effective ex vivo model to study hepatic glucose production and opens opportunities for its future application in IEM research and beyond.

Hepatic Insulin Clearance in Regulation of Systemic Insulin Concentrations-Role of Carbohydrate and Energy Availability

Hyperinsulinemia is the hallmark of insulin resistance in obesity, and the relative importance of insulin clearance, insulin resistance, and insulin hypersecretion has been widely debated. On the basis of recent experimental evidence, we summarize existing evidence to suggest hepatic insulin clearance as a major and immediate regulator of systemic insulin concentrations responding within days to altered dietary energy and, in particular, carbohydrate intake. Hepatic insulin clearance seems to be closely associated with opposite alterations in hepatic lipid content and glucose production, providing a potential mechanistic link to hepatic insulin sensitivity. The molecular regulation of insulin clearance in the liver is likely to involve changes in insulin binding and receptor internalization in response to the dietary alterations, the molecular mechanisms of which await further research.

Insulin Clearance Is Associated with Hepatic Lipase Activity and Lipid and Adiposity Traits in Mexican Americans

Reduction in insulin clearance plays an important role in the compensatory response to insulin resistance. Given the importance of this trait to the pathogenesis of diabetes, a deeper understanding of its regulation is warranted. Our goal was to identify metabolic and cardiovascular traits that are independently associated with metabolic clearance rate of insulin (MCRI). We conducted a cross-sectional analysis of metabolic and cardiovascular traits in 765 participants from the Mexican-American Coronary Artery Disease (MACAD) project who had undergone blood sampling, oral glucose tolerance test, euglycemic-hyperinsulinemic clamp, dual-energy X-ray absorptiometry, and carotid ultrasound. We assessed correlations of MCRI with traits from seven domains, including anthropometry, biomarkers, cardiovascular, glucose homeostasis, lipase activity, lipid profile, and liver function tests. We found inverse independent correlations between MCRI and hepatic lipase (P = 0.0004), insulin secretion (P = 0.0002), alanine aminotransferase (P = 0.0045), total fat mass (P = 0.014), and diabetes (P = 0.03). MCRI and apolipoprotein A-I exhibited a positive independent correlation (P = 0.035). These results generate a hypothesis that lipid and adiposity associated traits related to liver function may play a role in insulin clearance.

Decreased expression of insulin and increased expression of pancreatic transcription factor PDX-1 in islets in patients with liver cirrhosis: a comparative investigation using human autopsy specimens

BACKGROUND

Glucose intolerance in patients with liver cirrhosis (LC), known as hepatogenous diabetes, is thought to be distinct from type 2 diabetes (T2DM) in some aspects. Hyperinsulinemia and/or insulin resistance in liver disease is associated with hepatocarcinogenesis, growth of hepatocellular carcinoma, and poor prognosis. However, the pathophysiological processes in islets that are responsible for hyperinsulinemia in LC are still not precisely known. Therefore, we investigated the histopathological differences in islets of Langerhans cells between LC and T2DM.

METHODS

A total of 35 human autopsy pancreatic tissue samples were used in this study (control, n = 18; T2DM, n = 6; LC, n = 11). The expression of insulin, glucagon, somatostatin, pancreatic duodenal homeobox-1 (PDX-1), proliferating cell nuclear antigen (PCNA), and Ki-67 was examined using immunohistochemistry and quantitated by image analysis.

RESULTS

Islet hypertrophy and a significant increase in PCNA-positive cells in islets were observed in the tissues from LC cases. The insulin-positive areas in islets were significantly decreased in LC cases compared with control and T2DM cases (P = 0.001, P = 0.035, respectively), whereas the PDX-1-positive area was significantly increased in LC cases (P = 0.001) compared with the control. Furthermore, disorganization of pancreatic endocrine cells and nucleocytoplasmic translocation of PDX-1 were both seen in the LC subjects.

CONCLUSIONS

In LC, islets undergo hypertrophy and exhibit paradoxical expression of insulin and PDX-1. In the subjects autopsied, insulin expression was decreased, whereas expression of the pancreatic transcription factor PDX-1 was increased in LC. These results point to important distinctions between LC and T2DM.

Insulin degradation: progress and potential

Insulin degradation is a regulated process that plays a role in controlling insulin action by removing and inactivating the hormone. Abnormalities in insulin clearance and degradation are present in various pathological conditions including type 2 diabetes and obesity and may be important in producing clinical problems. The uptake, processing, and degradation of insulin by cells is a complex process with multiple intracellular pathways. Most evidence supports IDE as the primary degradative mechanism, but other systems (PDI, lysosomes, and other enzymes) undoubtedly contribute to insulin metabolism. Recent studies support a multifunctional role for IDE, as an intracellular binding, regulatory, and degradative protein. IDE increases proteasome and steroid hormone receptor activity, and this activation is reversed by insulin. This raises the possibility of a direct intracellular interaction of insulin with IDE that could modulate protein and fat metabolism. The recent findings would place intracellular insulin-IDE interaction into the insulin signal transduction pathway for mediating the intermediate effects of insulin on fat and protein turnover.

Plasma somatostatin response to an oral test meal in liver transplant patients

Ten liver transplant patients were studied in basal conditions and after ingestion of a standard mixed test meal. Control groups included 10 normal subjects, 10 patients with nonalcoholic liver cirrhosis, and seven kidney transplant patients. Plasma somatostatin, blood glucose, and plasma insulin, C-peptide, and glucagon were determined before and 15, 30, 45, 60, 90, 120, and 180 minutes after the start of the meal. In liver transplant patients, basal somatostatin and insulin levels were significantly lower than in cirrhotics and were comparable to those recorded in controls and in kidney transplant patients. The time course of the somatostatin secretory response after the meal was similar in any group, but the increase, evaluated as the incremental area above baseline, was significantly higher in liver transplant patients than in controls and cirrhotics and comparable to that recorded in kidney transplant patients. Insulin incremental areas were also lower than in cirrhotics and comparable to those recorded in controls and kidney transplant patients. The data suggest that in liver transplant patients an increased somatostatin response to a meal may be related to a relative beta-cell secretory defect, which in turn seems consequent to immunosuppressive treatment.

Insulin secretion in pancreatic islets from rats with cirrhosis

Cirrhosis was induced in rats by subcutaneous injections of CCl4 for 13 or 17 weeks. The morphology of the pancreatic islets from the CCl4-treated rats was found to be normal. The CCl4-treated rats had lower fasting serum glucose levels and higher serum insulin levels than the controls. After an oral glucose load (3 g/kg body weight), glucose levels in CCl4-treated rats stayed within the normal range, whereas the serum insulin levels remained higher with a delayed decline of insulin with time. In vitro perifusion of islets from the CCl4-treated rats showed that the response to 16.7 mmol/l glucose was reduced with both lower total insulin output and stimulated insulin output, whereas the patterns of first and second phase of insulin release did not differ. The insulin content of the perifused islets was not affected by 13 weeks of CCl4 treatment. Islets from rats treated with CCl4 for 17 weeks showed normal secretory response to 20 mmol/l L-arginine. Taken together, the results, showing normal or reduced capacity for insulin secretion, suggest that the hyperinsulinemia accompanying CCl4-induced cirrhosis is not due to increased secretion of the pancreatic islets. It may rather be associated with decreased insulin degradation by the liver with cirrhosis.

Splanchnic and peripheral glucose metabolism in cirrhosis

The effects of glucose and insulin administration on splanchnic and leg exchange of glucose were investigated in seven patients with cirrhosis and six sex- and age-matched healthy controls using the catheter technique. After a basal period, glucose infusion (1 mg.kg-1.min-1) was given for 45 min, followed by a 2-h euglycemic insulin clamp (1 mU.kg-1.min-1). In the basal state insulin levels were significantly higher in patients than in controls (25 +/- 4 vs. 7 +/- 2 microU/ml). Net splanchnic glucose output tended to be lower in patients than in controls (0.50 +/- 0.16 vs 0.73 +/- 0.11 mmol/min nonsignificant), as did leg glucose uptake (0.06 +/- 0.01 vs 0.08 +/- 0.02 mmol/min, non-significant). Glucose infusion resulted in a significant rise in leg glucose uptake, while net splanchnic glucose output decreased in both groups. During the euglycemic insulin clamp, insulin concentrations rose to 110 +/- 10 and 80 +/- 8 microU/ml in patients and controls, respectively. C-peptide concentrations decreased in the healthy controls but were unchanged from the basal level in patients with cirrhosis. Glucose disposal during the last half hour of the clamp was 1.12 +/- 0.08 and 3.19 +/- 0.04 mmol/min in patients and controls, respectively (p < 0.001). Glucose was taken up by the splanchnic region in both groups but this uptake was significantly greater in patients than in controls (0.42 +/- 0.05 vs. 0.25 +/- 0.06 mmol/min, p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)