Exercise in the management of non-insulin-dependent diabetes mellitus

[Epidemiology of diabetes and its non-coronary complications]

Diabetes mellitus is among the diseases with great impact on health and society, not only for its high prevalence but also for its chronic complications and high mortality. The most precise method to investigate the prevalence of diabetes is by oral glucose tolerance testing. In Spain, the prevalence of diabetes in the 30-65 year-old population is estimated to be 6.5% among 30-to-65- year old, and 10.3% among the 30-to-89 year-old population. The ratio of known to unknown diabetes ranges from 1:3 to 2:3. The incidence of diabetes mellitus type 2 in Spain is 8/1000 persons per year, and the incidence of type 1 is 11 to 12 cases per 100,000 persons per year. The prevalence of chronic complications varies according to type of diabetes, time since onset and degree of metabolic control: neuropathy 25%, retinopathy 32% and nephropathy 23%. Diabetes is one of the most important causes of death in Spain, occupying third place for women and seventh for men.

Total physical activity in relation to age, body mass, health and other factors in a cohort of Swedish men

BACKGROUND

Despite a large public health interest in physical activity and its role in obesity and other chronic diseases, only a few reports to date have addressed total levels of physical activity in relation to age, body mass, health and other lifestyle factors.

OBJECTIVE

To investigate whether levels of total physical activity among men are associated with age, body mass, self-rated health and other lifestyle factors in a cross-sectional setting.

METHODS

In a population-based cohort of 33 466 men aged 45-79 y in central Sweden, we collected information about physical activity through a self-administered questionnaire. Level of total physical activity was assessed quantitatively based on six questions on different activities: work/occupation, housework, walking/bicycling, exercise, inactive leisure time and sleeping. The physical activity levels were measured as metabolic equivalents, MET-h/day. The relation between age, body mass index, smoking, education, marital status and self-rated health, and total physical activity was studied in a cross-sectional analysis, using multivariate regression.

RESULTS

Total daily physical activity was decreasing systematically between age 45 and 79 (-4.1%, 95% CI -4.6, -3.6). Obese men reported -2.6% (95% CI -3.0, -2.1) lower physical activity than normal weight men. Those with high education had -7.0% (95%CI -7.3, -6.7) lower total physical activity than those with elementary school. Men with self-rated poor health had -11.3% (95%CI -12.1, -10.6) lower physical activity than those reporting very good health. The cross-sectionally observed decrease with age was greatest among obese men (-8.7%), current smokers (-7.9%), low-educated men (-5.6%) and those with poor health (-9.8%); the subgroups with very good health reported almost the same level of total physical activity (-0.6%) for age 74-79 as for age 45-49.

CONCLUSIONS

The observed decreasing levels of total physical activity with age to large degree depend on health status and other factors. The characterization of subjects with low total physical activity levels is of importance for understanding observed worldwide trends in increasing prevalence of obesity. The better understanding of these phenomena might also facilitate a better planning of public health interventions with messages specifically adjusted for subgroups of population with lower physical activity.

Exercise training eliminates age-related differences in skeletal muscle insulin receptor and IRS-1 abundance in rats

Insulin resistance is common in old age, and exercise training can improve insulin sensitivity. The purpose of this study was to determine the influence of age (6 vs 26 months) and exercise training (10 weeks of treadmill running) on insulin signaling protein abundance in skeletal muscle from male Fisher 344 rats. Muscle levels of insulin receptor (IR), insulin receptor substrate-1 (IRS-1), phosphatidylinositol 3-kinase (PI3K), and Akt1, a serine-threonine kinase, were determined. IRS-1 was reduced with aging, IR and PI3K abundance was greater in old rats, and Akt1 was unchanged. IRS-1 was increased by training in old but not young rats, and IR was increased by training in young but not old rats. PI3K tended to increase and Akt1 did not change with training, regardless of age. Aging does not uniformly affect insulin signaling protein abundance, and exercise differentially alters IR and IRS-1 in young and old rats, thereby eliminating age-related differences in these proteins.

Energy-sensing and signaling by AMP-activated protein kinase in skeletal muscle

AMP-activated protein kinase (AMPK) is emerging as an important energy-sensing/signaling system in skeletal muscle. This kinase is activated allosterically by 5'-AMP and inhibited allosterically by creatine phosphate. Phosphorylation of AMPK by an upstream kinase, AMPK kinase (also activated allosterically by 5'-AMP), results in activation. It is activated in both rat and human muscle in response to muscle contraction, the extent of activation depending on work rate and muscle glycogen concentration. AMPK can also be activated chemically in resting muscle with 5-aminoimidazole-4-carboxamide-riboside, which enters the muscle and is phosphorylated to form ZMP, a nucleotide that mimics the effect of 5'-AMP. Once activated, AMPK is hypothesized to phosphorylate proteins involved in triggering fatty acid oxidation and glucose uptake. Evidence is also accumulating for a role of AMPK in inducing some of the adaptations to endurance training, including the increase in muscle GLUT-4, hexokinase, uncoupling protein 3, and some of the mitochondrial oxidative enzymes. It thus appears that AMPK has the capability of monitoring intramuscular energy charge and then acutely stimulating fat oxidation and glucose uptake to counteract the increased rates of ATP utilization during muscle contraction. In addition, this system may have the capability of enhancing capacity for ATP production when the muscle is exposed to endurance training.

Health benefits of physical activity with special reference to interaction with diet

Regular physical activity causes numerous and substantial performance-improving and health-enhancing effects. Most of them are highly predictable, dose-dependent and generalizable to a wide range of population groups. Many of the biological effects of regular, moderate physical activity translate into substantially reduced risk of coronary heart disease, cerebrovascular disease, hypertension, maturity onset diabetes, overweight and obesity, and osteoporosis. These effects also substantially reduce the risk of deterioration of functional capacity. In the genesis of these conditions, a lack of physical activity and inadequate nutrition act synergistically and in part additively, and they operate largely through the same pathways. It is conceivable to suggest that the prevalence of, e.g, the above mentioned metabolic diseases is so high in Europe largely because of the high prevalence of sedentariness and inadequate nutrition. Thus, both physical activity and nutrition have to be given strong emphasis in policies, strategies and programmes that will be developed and implemented for improving the health of Europeans.

Relationships between physical activity, obesity and diabetes mellitus in a French elderly population: the POLA study. Pathologies Oculaires lieés á l' Age

OBJECTIVE

To analyse the relationships between body mass index, waist circumference, waist-to-hip ratio, physical activity and the risk of type 2 diabetes in a French elderly population.

DESIGN AND SUBJECTS

We conducted a cross-sectional study on 1113 men and 1419 women aged 60 y or more, participating in the POLA Study.

RESULTS

The prevalence of diabetes was two-fold higher in men than in women (19.1% and 9.3%, respectively). The anthropometric variables studied-body mass index (BMI), waist circumference (WC) and the waist/hip ratio (WHR)-were all positively related to the prevalence of type 2 diabetes. The strongest relationships were found for BMI in men and WHR in women. In both genders, sport activity and diabetes were inversely linked whereas no relationship was shown between the amount of household activity and diabetes mellitus.

CONCLUSION

In the elderly, overall obesity in men and abdominal fat accumulation in women appeared strongly related to diabetes. Sport activity was negatively and independently associated with the prevalence of diabetes mellitus.

Exercise-induced changes in expression and activity of proteins involved in insulin signal transduction in skeletal muscle: differential effects on insulin-receptor substrates 1 and 2

Level of physical activity is linked to improved glucose homeostasis. We determined whether exercise alters the expression and/or activity of proteins involved in insulin-signal transduction in skeletal muscle. Wistar rats swam 6 h per day for 1 or 5 days. Epitrochlearis muscles were excised 16 h after the last exercise bout, and were incubated with or without insulin (120 nM). Insulin-stimulated glucose transport increased 30% and 50% after 1 and 5 days of exercise, respectively. Glycogen content increased 2- and 4-fold after 1 and 5 days of exercise, with no change in glycogen synthase expression. Protein expression of the glucose transporter GLUT4 and the insulin receptor increased 2-fold after 1 day, with no further change after 5 days of exercise. Insulin-stimulated receptor tyrosine phosphorylation increased 2-fold after 5 days of exercise. Insulin-stimulated tyrosine phosphorylation of insulin-receptor substrate (IRS) 1 and associated phosphatidylinositol (PI) 3-kinase activity increased 2.5- and 3. 5-fold after 1 and 5 days of exercise, despite reduced (50%) IRS-1 protein content after 5 days of exercise. After 1 day of exercise, IRS-2 protein expression increased 2.6-fold and basal and insulin-stimulated IRS-2 associated PI 3-kinase activity increased 2. 8-fold and 9-fold, respectively. In contrast to IRS-1, IRS-2 expression and associated PI 3-kinase activity normalized to sedentary levels after 5 days of exercise. Insulin-stimulated Akt phosphorylation increased 5-fold after 5 days of exercise. In conclusion, increased insulin-stimulated glucose transport after exercise is not limited to increased GLUT4 expression. Exercise leads to increased expression and function of several proteins involved in insulin-signal transduction. Furthermore, the differential response of IRS-1 and IRS-2 to exercise suggests that these molecules have specialized, rather than redundant, roles in insulin signaling in skeletal muscle.

AMP-activated protein kinase: possible target for treatment of type 2 diabetes

A considerable amount of data have accumulated showing that contraction of muscle has an acute insulin-like effect, triggering the uptake of glucose. Chronic muscle contraction, as seen in endurance training has effects on insulin sensitivity, enhancing the effect of insulin on glucose uptake. Endurance training results in an increase in levels of GLUT4 in the muscle. This increase in GLUT4 is thought to be responsible in part for the enhancement of insulin sensitivity. Recent experiments have demonstrated that acute and chronic effects of muscle contraction on glucose uptake and the increase in GLUT4 may be due to activation of a protein kinase, AMP-activated protein kinase (AMPK). This kinase is activated by the increase in 5'-AMP and the decline in creatine phosphate that occur during muscle contraction. Phosphorylated AMPK then presumably phosphorylates undefined target proteins, which in turn increase glucose uptake and transcription of the GLUT4 gene. Experiments have demonstrated that this kinase, normally activated during exercise, can be activated artificially in muscle by injecting non-exercising rats with 5-aminoimidazole-4-carboxamide-riboside (AICAR), an adenosine analog. AICAR is taken up into muscle and phosphorylated to form an analog of 5'-AMP. Acute (stimulation of glucose uptake into muscle) and chronic (increase in GLUT4) effects of exercise can be reproduced by injection of this drug. These observations open the door to the possibility of treatment of patients with type 2 diabetes with AMPK activators.

Effects of physical activity on insulin action and glucose tolerance in obesity

PURPOSE

The purpose of this paper is to examine the effect of physical activity on glucose tolerance in relation to obesity.

METHODS

We reviewed current literature, with particular emphasis on randomized clinical trials, to prepare an evidence-based evaluation of the effects of physical activity on glucose intolerance in obesity.

RESULTS

This literature review indicates that physical activity has favorable effects on reducing insulin resistance in obesity and among patients with type 2 diabetes mellitus. Improvement in glucose tolerance is less consistently observed and is related to intensity of exercise, collateral changes in adiposity, the interval between exercise and testing of glucose tolerance, and the baseline severity of glucose intolerance.

CONCLUSION

A review of currently published clinical trial data supports the conclusion that physical activity can reduce insulin resistance and improve glucose intolerance in obesity.

Chronic activation of 5'-AMP-activated protein kinase increases GLUT-4, hexokinase, and glycogen in muscle

This study was designed to determine whether chronic chemical activation of AMP-activated protein kinase (AMPK) would increase glucose transporter GLUT-4 and hexokinase in muscles similarly to periodic elevation of AMPK that accompanies endurance exercise training. The adenosine analog, 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR), has previously been shown to be taken up by cells and phosphorylated to form a compound (5-aminoimidazole-4-carboxamide ribonucleotide) that mimics the effect of AMP on AMPK. A single injection of AICAR resulted in a marked increase in AMPK in epitrochlearis and gastrocnemius/plantaris muscles 60 min later. When rats were injected with AICAR (1 mg/g body wt) for 5 days in succession and were killed 1 day after the last injection, GLUT-4 was increased by 100% in epitrochlearis muscle and by 60% in gastrocnemius muscle in response to AICAR. Hexokinase was also increased approximately 2. 5-fold in the gastrocnemius/plantaris. Gastrocnemius glycogen content was twofold higher in AICAR-treated rats than in controls. Chronic chemical activation of AMPK, therefore, results in increases in GLUT-4 protein, hexokinase activity, and glycogen, similarly to those induced by endurance training.

AMP-activated protein kinase, a metabolic master switch: possible roles in type 2 diabetes

Adenosine 5'-monophosphate-activated protein kinase (AMPK) now appears to be a metabolic master switch, phosphorylating key target proteins that control flux through metabolic pathways of hepatic ketogenesis, cholesterol synthesis, lipogenesis, and triglyceride synthesis, adipocyte lipolysis, and skeletal muscle fatty acid oxidation. Recent evidence also implicates AMPK as being responsible for mediating the stimulation of glucose uptake induced by muscle contraction. In addition, the secretion of insulin by insulin secreting (INS-1) cells in culture is modulated by AMPK activation. The net effect of AMPK activation is stimulation of hepatic fatty acid oxidation and ketogenesis, inhibition of cholesterol synthesis, lipogenesis, and triglyceride synthesis, inhibition of adipocyte lipolysis and lipogenesis, stimulation of skeletal muscle fatty acid oxidation and muscle glucose uptake, and modulation of insulin secretion by pancreatic beta-cells. In skeletal muscle, AMPK is activated by contraction. Type 2 diabetes mellitus is likely to be a disease of numerous etiologies. However, defects or disuse (due to a sedentary lifestyle) of the AMPK signaling system would be predicted to result in many of the metabolic perturbations observed in Type 2 diabetes mellitus. Increased recruitment of the AMPK signaling system, either by exercise or pharmaceutical activators, may be effective in correcting insulin resistance in patients with forms of impaired glucose tolerance and Type 2 diabetes resulting from defects in the insulin signaling cascade.