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Hepatic Glucose Output (hepatic + glucose_output)

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Medical Sciences	100%

Selected Abstracts

Effects of insulin resistance on endothelial function: possible mechanisms and clinical implications

DIABETES OBESITY & METABOLISM, Issue 10 2008
D Tousoulis
Insulin resistance (IR) is defined as a reduced responsiveness of peripheral tissues to the effects of the hormone, referring to abated ability of insulin in stimulating glucose uptake in peripheral tissues and in inhibiting hepatic glucose output. Insulin has both a vasodilatory effect, which is largely endothelium dependent through the release of nitric oxide, and a vasoconstrictory effect through the stimulation of the sympathetic nervous system and the release of endothelin-1. IR and endothelial dysfunction (ED) are not only linked by common pathogenetic mechanisms, involving deranged insulin signalling pathways, but also by other, indirect to the hormone's actions, mechanisms. Different treatment modalities have been proposed to affect positively both the metabolic effects of insulin and ED. Weight loss has been shown to improve sensitivity to insulin as a result of either altered diet or exercise. Exercise has favourable effects on endothelial function in normal states and in states of disease, in men and women, and throughout the age spectrum and, hence, in IR states. Metformin improves sensitivity to insulin and most likely affects positively ED. Studies have shown that inhibitors of the renin,angiotensin system alter IR favourably, while Angiotensin converting enzyme (ACE) inhibitors and Angiotensin receptor type II (ATII) inhibitors improve ED. Ongoing studies are expected to shed more light on the issue of whether treatment with the thiazolidinediones results in improvement of endothelial function, along with the accepted function of improving insulin sensitivity. Finally, improved endothelial function by such treatments is not in itself proof of reduced risk for atherosclerosis; this remains to be directly tested in clinical trials. [source]

Hepatic dysfunction and insulin insensitivity in type 2 diabetes mellitus: a critical target for insulin-sensitizing agents

DIABETES OBESITY & METABOLISM, Issue 9 2008
P. D. Home
The liver plays an essential role in maintaining glucose homeostasis, which includes insulin-mediated processes such as hepatic glucose output (HGO) and uptake, as well as in clearance of insulin itself. In type 2 diabetes, the onset of hyperglycaemia [itself a potent inhibitor of hepatic glucose output (HGO)], alongside hyperinsulinaemia, indicates the presence of hepatic insulin insensitivity. Increased HGO is central to the onset of hyperglycaemia and highlights the need to target hepatic insulin insensitivity as a central component of glucose-lowering therapy. The mechanisms underlying the development of hepatic insulin insensitivity are not well understood, but may be influenced by factors such as fatty acid oversupply and altered adipocytokine release from dysfunctional adipose tissue and increased liver fat content. Furthermore, although the impact of insulin insensitivity as a marker of cardiovascular disease is well known, the specific role of hepatic insulin insensitivity is less clear. The pharmacological tools available to improve insulin sensitivity include the biguanides (metformin) and thiazolidinediones (rosiglitazone and pioglitazone). Data from a number of sources indicate that thiazolidinediones, in particular, can improve multiple aspects of hepatic dysfunction, including reducing HGO, insulin insensitivity and liver fat content, as well as improving other markers of liver function and the levels of mediators with potential involvement in hepatic function, including fatty acids and adipocytokines. The current review addresses this topic from the perspective of the role of the liver in maintaining glucose homeostasis, its key involvement in the pathogenesis of type 2 diabetes and the tools currently available to reduce hepatic insulin insensitivity. [source]

Combination therapy using metformin or thiazolidinediones and insulin in the treatment of diabetes mellitus

DIABETES OBESITY & METABOLISM, Issue 6 2005
Suzanne M. Strowig
The biguanide, metformin, sensitizes the liver to the effect of insulin, suppressing hepatic glucose output. Thiazolidinediones such as rosiglitazone and pioglitazone enhance insulin-mediated glucose disposal, leading to reduced plasma insulin concentrations. These classes of drugs may also have varying beneficial effects on features of insulin resistance such as lipid levels, blood pressure and body weight. Metformin in combination with insulin has been shown to significantly improve blood glucose levels while lowering total daily insulin dose and body weight. The thiazolidinediones in combination with insulin have also been effective in lowering blood glucose levels and total daily insulin dose. Triple combination therapy using insulin, metformin and a thiazolidinedione improves glycaemic control to a greater degree than dual therapy using insulin and metformin or insulin and a thiazolidinedione. There is insufficient evidence to recommend the use of metformin or thiazolidinediones in type 1 diabetic patients. Although these agents are largely well tolerated, some subjects experience significant gastrointestinal problems while using metformin. Metformin is associated with a low risk of lactic acidosis, but should not be used in patients with elevated serum creatinine or those being treated for congestive heart failure. The thiazolidinediones are associated with an increase in body weight, although this can be avoided with careful lifestyle management. Thiazolidinediones may also lead to oedema and are associated with a low incidence of hepatocellular injury. Thiazolidinediones are contraindicated in patients with underlying heart disease who are at risk of congestive heart failure and in patients who have abnormal hepatic function. The desired blood glucose-lowering effect and adverse event profiles of these agents should be considered when recommending these agents to diabetic patients. The potential for metformin or the thiazolidinediones to impact long-term cardiovascular outcomes remains under investigation. [source]

Dorothy Hodgkin Lecture 2008 Gastric inhibitory polypeptide (GIP) revisited: a new therapeutic target for obesity,diabetes?

DIABETIC MEDICINE, Issue 7 2008
P. R. Flatt
Abstract There is increasing realization that gastric inhibitory polypeptide (GIP) has actions outside of the pancreas and gastrointestinal tract. Most significant is the presence of functional GIP receptors on adipocytes and the appreciation that GIP, secreted strongly in response to fat ingestion, plays a role in the translation of excessive amounts of dietary fat into adipocyte tissue stores. Such effects open up the possibility of exploiting GIP receptor antagonism for the treatment of obesity and insulin resistance. This is borne out by studies in high-fat-fed mice or ob/ob mice with either genetic knockout of GIP receptor or chemical ablation of GIP action using the GIP receptor antagonist, (Pro3)GIP. By causing preferential oxidation of fat, blockade of GIP signalling clears triglyceride deposits from liver and muscle, thereby respectively restoring mechanisms for suppression of hepatic glucose output and cellular glucose uptake. Further studies are needed to determine the applicability of this research to human obesity,diabetes. However, proof of concept is provided by emerging evidence that rapid cure of diabetes in grossly obese subjects undergoing Roux-en-Y bypass surgery is mediated in part by surgical bypass of GIP-secreting K-cells in the upper small intestine. [source]

Disturbed hepatic carbohydrate management during high metabolic demand in medium-chain acyl,CoA dehydrogenase (MCAD),deficient mice,

HEPATOLOGY, Issue 6 2008
Hilde Herrema
Medium-chain acyl,coenzyme A (CoA) dehydrogenase (MCAD) catalyzes crucial steps in mitochondrial fatty acid oxidation, a process that is of key relevance for maintenance of energy homeostasis, especially during high metabolic demand. To gain insight into the metabolic consequences of MCAD deficiency under these conditions, we compared hepatic carbohydrate metabolism in vivo in wild-type and MCAD,/, mice during fasting and during a lipopolysaccharide (LPS)-induced acute phase response (APR). MCAD,/, mice did not become more hypoglycemic on fasting or during the APR than wild-type mice did. Nevertheless, microarray analyses revealed increased hepatic peroxisome proliferator-activated receptor gamma coactivator-1, (Pgc-1,) and decreased peroxisome proliferator-activated receptor alpha (Ppar ,) and pyruvate dehydrogenase kinase 4 (Pdk4) expression in MCAD,/, mice in both conditions, suggesting altered control of hepatic glucose metabolism. Quantitative flux measurements revealed that the de novo synthesis of glucose-6-phosphate (G6P) was not affected on fasting in MCAD,/, mice. During the APR, however, this flux was significantly decreased (,20%) in MCAD,/, mice compared with wild-type mice. Remarkably, newly formed G6P was preferentially directed toward glycogen in MCAD,/, mice under both conditions. Together with diminished de novo synthesis of G6P, this led to a decreased hepatic glucose output during the APR in MCAD,/, mice; de novo synthesis of G6P and hepatic glucose output were maintained in wild-type mice under both conditions. APR-associated hypoglycemia, which was observed in wild-type mice as well as MCAD,/, mice, was mainly due to enhanced peripheral glucose uptake. Conclusion: Our data demonstrate that MCAD deficiency in mice leads to specific changes in hepatic carbohydrate management on exposure to metabolic stress. This deficiency, however, does not lead to reduced de novo synthesis of G6P during fasting alone, which may be due to the existence of compensatory mechanisms or limited rate control of MCAD in murine mitochondrial fatty acid oxidation. (HEPATOLOGY 2008.) [source]

Estimating gluconeogenesis by NMR isotopomer distribution analysis of [13C]bicarbonate and [1- 13C]lactate

NMR IN BIOMEDICINE, Issue 4 2008
Tiago Cardoso Alves
Abstract The gluconeogenic contribution to glucose production in livers isolated from rats fasted for 24,h was determined by 13C-NMR isotopomer distribution analysis of secreted glucose enriched from 99% [13C]bicarbonate (n,=,4) and 99% [1- 13C]lactate (n,=,4). Experiments with 3% 2H2O were also performed, allowing the gluconeogenic contribution to be measured by the relative 2H enrichments at positions 5 and 2 of glucose. From 13C-NMR analyses, the contribution of gluconeogenesis to glucose output was estimated to be 93,±,3% for [13C]bicarbonate perfusion and 91,±,3% for [1- 13C]lactate perfusion, in good agreement with the 2H-NMR analysis of the gluconeogenic contribution to glucose production (100,±,1% and 99,±,1%, respectively) and consistent with the expected negligible contribution from glycogenolysis. These results indicate that 13C-NMR analysis of glucose 13C-isotopomer distribution from either [13C]bicarbonate or [1- 13C]lactate precursor provides realistic estimates of the gluconeogenic contribution to hepatic glucose output. Copyright © 2007 John Wiley & Sons, Ltd. [source]