Insulin resistance in the offspring of parents with type 2 diabetes

Biomolecular Mechanisms of Cardiorenal Protection with Sodium-Glucose Co-Transporter 2 Inhibitors

Diabetes mellitus (DM) is a metabolic disorder characterized by chronic hyperglycemia and associated with an increased risk of morbidity and mortality, primarily from cardiovascular and renal diseases. Sodium-glucose cotransporter 2 inhibitors (SGLT2-Is) are novel drugs for the treatment of type 2 DM and heart failure (HF). SGLT2-Is mediate protective effects on both the renal and cardiovascular systems. This review addresses the current knowledge on the biomolecular mechanisms of the cardiorenal protective effects of SGLT2-Is, which appear to act mainly through non-glucose-mediated pathways. Cardiorenal protection mechanisms lead to reduced chronic renal disease progression and improved myocardial and coronary endothelial function. Concomitantly, it is possible to observe reflected changes in biomarkers linked with diabetic kidney disease and HF.

Do static and dynamic insulin resistance indices perform similarly in predicting pre-diabetes and type 2 diabetes?

AIMS

We designed a study to compare the predictive power of static and dynamic insulin resistance indices for categorized pre-diabetes (PDM)/type 2 diabetes (DM).

METHODS

Participants included 1134 adults aged 18-60 years old with normal glucose at baseline who completed both baseline and 6-years later follow-up surveys. Insulin resistance indices from baseline data were used to predict risk of PDM or DM at follow-up. Two static indices and two dynamic indices were calculated from oral glucose tolerance test results (OGTT) at baseline. Area under the receiver operating characteristic curve (AROC) analysis was used to estimate the predictive ability of candidate indices to predict PDM/DM. A general estimation equation (GEE) model was applied to assess the magnitude of association of each index at baseline with the risk of PDM/DM at follow-up.

RESULTS

The dynamic indices displayed the largest and statistically predictive AROC for PDM/DM diagnosed either by fasting glucose or by postprandial glucose. The bottom quartiles of the dynamic indices were associated with an elevated risk of PDM/DM vs. the top three quartiles. However, the static indices only performed significantly to PDM/DM diagnosed by fasting glucose.

CONCLUSIONS

Dynamic insulin resistance indices are stronger predictors of future PDM/DM than static indices. This may be because dynamic indices better reflect the full range of physiologic disturbances in PDM/DM.

Physical activity is the key determinant of skeletal muscle mitochondrial function in type 2 diabetes

CONTEXT

Conflicting data exist on mitochondrial function and physical activity in type 2 diabetes mellitus (T2DM) development.

OBJECTIVE

The aim was to assess mitochondrial function at different stages during T2DM development in combination with physical exercise in longstanding T2DM patients.

DESIGN AND METHODS

We performed cross-sectional analysis of skeletal muscle from 12 prediabetic 11 longstanding T2DM male subjects and 12 male controls matched by age and body mass index.

INTERVENTION

One-year intrasubject controlled supervised exercise training intervention was done in longstanding T2DM patients.

MAIN OUTCOME MEASUREMENTS

Extensive ex vivo analyses of mitochondrial quality, quantity, and function were collected and combined with global gene expression analysis and in vivo ATP production capacity after 1 yr of training.

RESULTS

Mitochondrial density, complex I activity, and the expression of Krebs cycle and oxidative phosphorylation system-related genes were lower in longstanding T2DM subjects but not in prediabetic subjects compared with controls. This indicated a reduced capacity to generate ATP in longstanding T2DM patients only. Gene expression analysis in prediabetic subjects suggested a switch from carbohydrate toward lipid as an energy source. One year of exercise training raised in vivo skeletal muscle ATP production capacity by 21 ± 2% with an increased trend in mitochondrial density and complex I activity. In addition, expression levels of β-oxidation, Krebs cycle, and oxidative phosphorylation system-related genes were higher after exercise training.

CONCLUSIONS

Mitochondrial dysfunction is apparent only in inactive longstanding T2DM patients, which suggests that mitochondrial function and insulin resistance do not depend on each other. Prolonged exercise training can, at least partly, reverse the mitochondrial impairments associated with the longstanding diabetic state.

Comparison of in vivo postexercise phosphocreatine recovery and resting ATP synthesis flux for the assessment of skeletal muscle mitochondrial function

(31)P magnetic resonance spectroscopy (MRS) has been used to assess skeletal muscle mitochondrial function in vivo by measuring 1) phosphocreatine (PCr) recovery after exercise or 2) resting ATP synthesis flux with saturation transfer (ST). In this study, we compared both parameters in a rat model of mitochondrial dysfunction with the aim of establishing the most appropriate method for the assessment of in vivo muscle mitochondrial function. Mitochondrial dysfunction was induced in adult Wistar rats by daily subcutaneous injections with the complex I inhibitor diphenyleneiodonium (DPI) for 2 wk. In vivo (31)P MRS measurements were supplemented by in vitro measurements of oxygen consumption in isolated mitochondria. Two weeks of DPI treatment induced mitochondrial dysfunction, as evidenced by a 20% lower maximal ADP-stimulated oxygen consumption rate in isolated mitochondria from DPI-treated rats oxidizing pyruvate plus malate. This was paralleled by a 46% decrease in in vivo oxidative capacity, determined from postexercise PCr recovery. Interestingly, no significant difference in resting, ST-based ATP synthesis flux was observed between DPI-treated rats and controls. These results show that PCr recovery after exercise has a more direct relationship with skeletal muscle mitochondrial function than the ATP synthesis flux measured with (31)P ST MRS in the resting state.

Impaired microvascular perfusion: a consequence of vascular dysfunction and a potential cause of insulin resistance in muscle

Insulin has an exercise-like action to increase microvascular perfusion of skeletal muscle and thereby enhance delivery of hormone and nutrient to the myocytes. With insulin resistance, insulin's action to increase microvascular perfusion is markedly impaired. This review examines the present status of these observations and techniques available to measure such changes as well as the possible underpinning mechanisms. Low physiological doses of insulin and light exercise have been shown to increase microvascular perfusion without increasing bulk blood flow. In these circumstances, blood flow is proposed to be redirected from the nonnutritive route to the nutritive route with flow becoming dominant in the nonnutritive route when insulin resistance has developed. Increased vasomotion controlled by vascular smooth muscle may be part of the explanation by which insulin mediates an increase in microvascular perfusion, as seen from the effects of insulin on both muscle and skin microvascular blood flow. In addition, vascular dysfunction appears to be an early development in the onset of insulin resistance, with the consequence that impaired glucose delivery, more so than insulin delivery, accounts for the diminished glucose uptake by insulin-resistant muscle. Regular exercise may prevent and ameliorate insulin resistance by increasing "vascular fitness" and thereby recovering insulin-mediated capillary recruitment.

Graded occlusion of perfused rat muscle vasculature decreases insulin action

Insulin increases capillary recruitment in vivo and impairment of this may contribute to muscle insulin resistance by limiting either insulin or glucose delivery. In the present study, the effect of progressively decreased rat muscle perfusion on insulin action using graded occlusion with MS (microspheres; 15 mum in diameter) was examined. EC (energy charge), PCr/Cr (phosphocreatine/creatine ratio), AMPK (AMP-activated protein kinase) phosphorylation on Thr(172) (P-AMPKalpha/total AMPK), oxygen uptake, nutritive capacity, 2-deoxyglucose uptake, Akt phosphorylation on Ser(473) (P-Akt/total Akt) and muscle 2-deoxyglucose uptake were determined. Arterial injection of MS (0, 9, 15 and 30 x 10(6) MS/15 g of hindlimb muscle, as a bolus) into the pump-perfused (0.5 ml x min(-1) x g(-1) of wet weight) rat hindlimb led to increased pressure (-0.5+/-0.8, 15.9+/-2.1, 28.7+/-4.6 and 60.3+/-9.4 mmHg respectively) with minimal changes in oxygen uptake. Nutritive capacity was decreased from 10.6+/-1.0 to 3.8+/-0.9 micromol x g(-1) of muscle x h(-1) (P<0.05) with 30 x 10(6) MS. EC was unchanged, but PCr/Cr was decreased dose-dependently to 61% of basal with 30 x 10(6) MS. Insulin-mediated increases in P-Akt/total Akt decreased from 2.15+/-0.35 to 1.41+/-0.23 (P<0.05) and muscle 2-deoxyglucose uptake decreased from 130+/-19 to 80+/-12 microg x min(-1) x g(-1) of dry weight (P<0.05) with 15 x 10(6) MS; basal P-AMPKalpha in the absence of insulin was increased, but basal P-Akt/total Akt and muscle 2-deoxyglucose uptake were unaffected. In conclusion, partial occlusion of the hindlimb muscle has no effect on basal glucose uptake and marginally impacts on oxygen uptake, but markedly impairs insulin delivery to muscle and, thus, insulin-mediated Akt phosphorylation and glucose uptake.

Integration of the metabolic and cardiovascular effects of exercise

Most of the essays in this volume have adopted a reductionist approach and have focused on the biochemistry either in skeletal muscle or in the vascular wall. There is however a complex interaction between the biochemistry in the endothelium of the microvascular wall, the vascular smooth muscle and the skeletal muscle fibres involving signalling pathways in the three tissues and an intense exchange of signal molecules between them. In the present essay an integrative overview is given of this complex metabolic interaction and the impairments in it that lead to type 2 diabetes and cardiovascular disease.A reduced nitric oxide production by the (micro)vascular endothelium is identified as the key event and is reversible by regular exercise and a reduced calorie intake. The chapter also contains a description of the complex metabolic network controlled by the inducible transcription factor nuclear factor-kappaB, that is activated in more advanced stages of the chronic diseases, and either leads to repair of the microvascular wall or to irreversible damage and the severe complications of end stage cardiovascular disease and type 2 diabetes.