Metabolic effects of glucose-insulin infusions: myocardium and whole body

α-Lipoic acid attenuates cardiac fibrosis in Otsuka Long-Evans Tokushima Fatty rats

Background

Hyperglycemia leads to cardiac oxidative stress and an imbalance in glucose homeostasis. Diabetic cardiomyopathy is characterised by cardiac hypertrophy and fibrosis. However, the underlying mechanisms of diabetic cardiomyopathy are not fully understood. This study aimed to investigate the effects of alpha-lipoic acid (ALA) on cardiac energy metabolism, antioxidant effect, and fibrosis in the hearts of Otsuka Long-Evans Tokushima fatty (OLETF) rats.

Methods

Animals were separated into non-diabetic Long-Evans Tokushima Otsuka (LETO) rats and diabetes-prone OLETF rats with or without ALA (200 mg/kg/day) administration for 16 weeks. Diabetic cardiomyopathy was assessed by staining with Sirius Red. The effect of ALA on AMPK signalling, antioxidant enzymes, and fibrosis-related genes in the heart of OLETF rats were performed by Western blot analysis or immunohistochemistry.

Results

Western blot analysis showed that cardiac adenosine monophosphate-activated kinase (AMPK) signalling was lower in OLETF rats than in LETO rats, and that ALA treatment increased the signalling in OLETF rats. Furthermore, the low antioxidant activity in OLETF rats was increased by ALA treatment. In addition to increased Sirius red staining of collagen deposits, transforming growth factor-β1 (TGF-β1) and connective tissue growth factor (CTGF) were expressed at higher levels in OLETF rat hearts than in LETO rat hearts, and the levels of these factors were decreased by ALA.

Conclusions

ALA enhances AMPK signalling, antioxidant, and antifibrogenic effect. Theses findings suggest that ALA may have beneficial effects in the treatment of diabetic cardiomyopathy.

Intraoperative Management of Hyperglycemia in the Cardiac Surgical Patient

The stress response of cardiac surgery leads to hyperglycemia, and undergoing cardiopulmonary bypass magnifies this response greatly. Counter-regulatory hormones, the cytokine response, and the automatic nervous system are all part of the coordinated host response that can lead to hyperglycemia. Postoperative hyperglycemia is associated with worsened perioperative outcomes, and there are data demonstrating this to also be true for the intraoperative period. Many factors affect intraoperative glucose control, including cardiopulmonary pump (CPB) prime fluid composition, temperature while on CPB, and medications such as catecholamines and glucocorticoids. Intraoperative glucose control has a significant impact on postoperative outcomes. No optimal intraoperative insulin regimen has been identified, but continuous intravenous infusions appear to be superior to intermittent sliding scale dosing. In addition, the technique of hyperinsulinemic glucose clamp shows the greatest promise of achieving normoglycemia while on CPB.

Pre-operative oral carbohydrate loading in colorectal surgery: a randomized controlled trial

OBJECTIVE

Surgery induces a catabolic response with stress hormone release and insulin resistance. The aim of this study was to assess the effect of pre-operative carbohydrate administration on grip strength, gastrointestinal function and hospital stay following elective colorectal surgery.

METHODS

Thirty-six patients undergoing elective colonic resection were randomized into one of three groups. Group 1 were fasted; Group 2 were given pre-operative oral water, Group 3 received equivalent volumes of a Maltodextrin drink. Time to first flatus, first bowel movement and hospital stay were recorded. Muscle strength was measured pre-operatively, and on alternate days thereafter until discharge using a grip strength dynamometer.

RESULTS

Patients in the carbohydrate group had a median postoperative hospital stay of 7.5 days compared with 13 days in the water group (P > 0.01) and 10 days in the fasted group (P = 0.06). The median time postsurgery to first flatus was 3 days for both the fasted and water groups compared with 1.5 days in the carbohydrate group (P = 0.13). First bowel movement occurred on day 3 in the carbohydrate group, day 4 in the fasting group and day 5 in the water group. The fasted group showed a significant reduction in postoperative grip strength (P < 0.05) with a median drop of 10% at discharge. Neither the water nor the carbohydrate groups showed significant reductions in muscle strength.

CONCLUSION

We found that pre-operative administration of oral carbohydrate leads to a significantly reduced postoperative hospital stay, and a trend towards earlier return of gut function when compared with fasting or supplementary water.

Unraveling the temporal pattern of diet-induced insulin resistance in individual organs and cardiac dysfunction in C57BL/6 mice

Type 2 diabetes is a heterogeneous disease characterized by insulin resistance and altered glucose and lipid metabolism in multiple organs. To understand the complex series of events that occur during the development of obesity-associated diabetes, we examined the temporal pattern of changes in insulin action and glucose metabolism in individual organs during chronic high-fat feeding in C57BL/6 mice. Insulin-stimulated cardiac glucose metabolism was significantly reduced after 1.5 weeks of high-fat feeding, and cardiac insulin resistance was associated with blunted Akt-mediated insulin signaling and GLUT4 levels. Insulin resistance in skeletal muscle, adipose tissue, and liver developed in parallel after 3 weeks of high-fat feeding. Diet-induced whole-body insulin resistance was associated with increased circulating levels of resistin and leptin but unaltered adiponectin levels. High-fat feeding caused insulin resistance in skeletal muscle that was associated with significantly elevated intramuscular fat content. In contrast, diet-induced hepatic insulin resistance developed before a marked increase in intrahepatic triglyceride levels. Cardiac function gradually declined over the course of high-fat feeding, and after 20 weeks of high-fat diet, cardiac dysfunction was associated with mild hyperglycemia, hyperleptinemia, and reduced circulating adiponectin levels. Our findings demonstrate that cardiac insulin resistance is an early adaptive event in response to obesity and develops before changes in whole-body glucose homeostasis. This suggests that obesity-associated defects in cardiac function may not be due to insulin resistance per se but may be attributable to chronic alteration in cardiac glucose and lipid metabolism and circulating adipokines.

The beneficial effect of insulin, glucose, and dipyridamole on regional left ventricular function early after acute myocardial infarction

BACKGROUND

High-dose glucose-insulin-potassium (GIK) solution has beneficial effects on reducing mortality in acute myocardial infarction. Dipyridamole (DIP) is a powerful antioxidant and increases adenosine concentration. Experimentally, GIK and DIP have additive protective effects in ischemia-reperfusion injury.

AIM

This work aims to assess the acute effects of DIP alone, GIK alone, and GIK+DIP on left ventricular function in patients evaluated early after an acute myocardial infarction.

METHODS

Ten male patients (age 63+/-11 years) with uncomplicated acute myocardial infarction were evaluated within 3 days after admission. All had been treated with systemic thrombolysis and were on full therapy (including beta-blockers) at the time of testing. They underwent stress echocardiography [2D echo, with wall motion score index (WMSI) evaluated in a 16-segment model of the left ventricle, with each segment scored from 1=normal to 4=dyskinetic] during low-dose DIP alone (0.28 mg/kg in 4 min); GIK alone (4-h infusion of glucose 30%, 25 insulin units, and 40 mEq of KCl, at an infusion rate of 1.5 ml/kg/h); and GIK+DIP.

RESULTS

Regional systolic function (baseline WMSI=1.69+/-0.2) improved after DIP (1.54+/-0.1), GIK (1.54+/-0.1), and, to a greater extent, after GIK+DIP (1.33+/-0.2; p<0.001 vs. baseline; p<0.05 vs. DIP; p<0.05 vs. GIK).

CONCLUSION

High-dose GIK has an acute beneficial effect on regional left ventricular function in patients with acute myocardial infarction. This beneficial effect is potentiated by low-dose DIP coadministration.

Insulin therapy in people who have dysglycemia and type 2 diabetes mellitus: can it offer both cardiovascular protection and beta-cell preservation?

Mounting evidence suggests that insulin therapy may reduce risk for CV events while preserving beta-cell function, and several continuing long-term CV trials are testing these hypotheses explicitly.

Preoperative oral carbohydrate nutrition: an update

Insulin resistance is a central feature of the metabolic response after elective surgery as well as other trauma, and has been shown to be a predictor of the length of stay after surgery. Carbohydrate treatment instead of overnight fasting before surgery has been shown to reduce postoperative insulin resistance and to reduce hospital stay approximately 20% after elective surgery. For potential use as a clinical routine before surgery, a carbohydrate-rich drink was developed. Gastric emptying of a 50 g oral carbohydrate load using this drink is complete within 90 min after intake. Oral carbohydrate loading before surgery has confirmed previous data, using glucose and insulin infusions, that postoperative insulin resistance is reduced compared with overnight fasted patients before surgery, and this is associated with improved well-being before and after surgery.