Diabetes. Dialogue between muscle and fat

Red rice koji extract alleviates hyperglycemia by increasing glucose uptake and glucose transporter type 4 levels in skeletal muscle in two diabetic mouse models

Background

Red rice koji (RRK), prepared by growing Monascus species on steamed rice, has been reported to lower blood glucose levels in diabetic animal models. However, the action mechanism is not yet completely understood.

Objective

The objective of this study was to examine the mechanism underlying the hypoglycemic action of RRK extract in two diabetic animal models: the insulin-deficiency mice, where the insulin deficiency was induced by streptozotocin (STZ), and insulin-resistance mice, where the insulin resistance was induced by a high-fat diet (HFD).

Design

Low (12.5 mg/kg body weight [BW]) and high (50.0 mg/kg BW) doses of RRK extract were orally administered to the mice for 10 successive days (0.25 mL/day/mouse). The protein expression levels of glucose transporter type 4 (GLUT4) in the skeletal muscle and glucose transporter type 2 (GLUT2) in the liver were measured. Blood glucose (BG) levels of STZ-treated mice in insulin tolerance test (ITT) and BG and insulin levels of HFD-fed mice in intraperitoneal glucose tolerance test (IPGTT) were investigated.

Results

In the STZ-treated mice, oral administration of RRK extract lowered BG levels and food intake but increased plasma 1,5-anhydroglucitol level. Moreover, the RRK extract lowered the BG levels of STZ-treated mice as measured by ITT. In the HFD-fed mice, we confirmed that the orally administered RRK extract lowered the BG and the homeostasis model assessment index for insulin resistance. Furthermore, the RRK extract lowered the BG and insulin levels of HFD-fed mice in IPGTT. Regarding the protein levels of GLUT, the orally administered RRK extract increased the GLUT4 level in the skeletal muscle; however, the RRK extract did not alter the GLUT2 level in the liver of either the STZ-treated or the HFD-fed mice.

Discussion

Our study demonstrates that RRK extract can improve impaired glucose tolerance in mouse models of diabetes by enhancing GLUT4 expression in skeletal muscle.

Conclusion

These results suggest that RRK extract could potentially be a functional food for the treatment of diabetes mellitus.

Drosophila glucome screening identifies Ck1alpha as a regulator of mammalian glucose metabolism

Circulating carbohydrates are an essential energy source, perturbations in which are pathognomonic of various diseases, diabetes being the most prevalent. Yet many of the genes underlying diabetes and its characteristic hyperglycaemia remain elusive. Here we use physiological and genetic interrogations in D. melanogaster to uncover the ‘glucome', the complete set of genes involved in glucose regulation in flies. Partial genomic screens of ∼1,000 genes yield ∼160 hyperglycaemia ‘flyabetes' candidates that we classify using fat body- and muscle-specific knockdown and biochemical assays. The results highlight the minor glucose fraction as a physiological indicator of metabolism in Drosophila. The hits uncovered in our screen may have conserved functions in mammalian glucose homeostasis, as heterozygous and homozygous mutants of Ck1alpha in the murine adipose lineage, develop diabetes. Our findings demonstrate that glucose has a role in fly biology and that genetic screenings carried out in flies may increase our understanding of mammalian pathophysiology.

Diabetes is associated with aberrations in glucose metabolism. Here the authors perform a genomic screen in fruit flies to identify new regulators of fly glucose metabolism, and show that mice lacking the murine homologue of one of their hits, the protein kinase CK1alpha, in the adipose lineage develop diabetes.

Characterization of Streptozotocin-induced Diabetic Rats and Pharmacodynamics of Insulin Formulations

Morphological and functional changes of rat pancreatic islets caused by administration of streptozotocin (STZ) and the bioavailability of insulin formulations administered to STZ-induced diabetic rats with fasting (12 h) or non-fasting were investigated. Islets isolated from normal rats maintained a good three-dimensional structure and the islet yield was 962.5+/-86.5 islet equivalent number (IEQ, islets converted to an average diameter of 150 microm). In the diabetic group (>500 mg/ml blood glucose), the islet yield was only 44.4+/-8.3 IEQ and the islet was severely damaged. The minimum reduction of blood glucose of each formulation, such as insulin solution, microcrystal, and insulin microcrystal capsule, was shown to be 11.3, 11.0, and 16.3 mg/dl, respectively, at 6 h in fasting with diabetic rats. These results indicated that the administration of insulin formulations to the fasting groups increased the severe hypoglycemic effect of insulin action more than in non-fasting diabetic rats. The diabetic rat with fasting has a regulatory disorder in maintaining the blood glucose level. Accordingly, the validity of pharmacological availability as an optimal modeling of insulin formulations is best in non-fasting STZ-induced diabetic rats.

Pachymic acid stimulates glucose uptake through enhanced GLUT4 expression and translocation

In an effort to investigate the effect and mechanism of Poria cocos on glucose uptake, six lanostane-type triterpenoids were isolated and analyzed. Among them, pachymic acid displayed the most significant stimulating activity on glucose uptake in 3T3-L1 adipocytes. The effect of pachymic acid on the expression profile of glucose transporters in differentiated 3T3-L1 adipocytes was also analyzed. Our results demonstrated that pachymic acid induced an increase in GLUT4, but not GLUT1, expression at both the mRNA and protein levels. The role of GLUT4 was further confirmed using the lentiviral vector-derived GLUT4 short hairpin RNA (shRNA). The stimulating activity of pachymic acid on glucose uptake was abolished when the endogenous GLUT4 expression was suppressed in 3T3-L1 adipocytes. In addition to increased GLUT4 expression, pachymic acid stimulated GLUT4 redistribution from intracellular vesicles to the plasma membrane in adipocytes. Exposure of the differentiated adipocytes to pachymic acid increased the phosphorylation of insulin receptor substrate (IRS)-1, AKT and AMP-activated kinase (AMPK). The involvement of PI3K and AMPK in the action of pachymic acid was further confirmed as PI3K and AMPK inhibitors completely blocked the pachymic acid-mediated activities in adipocytes. In addition, pachymic acid was shown to induce triglyceride accumulation and inhibit lipolysis in differentiated adipocytes. Taken together, we demonstrated the insulin-like activities of this compound in stimulating glucose uptake, GLUT4 gene expression and translocation, and promoting triglyceride accumulation in adipocytes. Our study provides important insights into the underlying mechanism of hypoglycemic activity of P. cocos.

Effect of 2-month detraining on body composition and insulin sensitivity in young female dancers

OBJECTIVE

To investigate the effect of 2-month detraining on body composition and glucose tolerance for female collegiate dancers.

DESIGN

Longitudinal study of dancers who stopped their regular training for 2 months.

SUBJECTS

16 female collegiate dancers (age: 19.7 +/-0.11 year, body mass index (BMI): 20.7 +/- 0.56 kg/m(2)).

MEASUREMENTS

BMI, waist-to-hip ratio (WHR), oral glucose tolerance test (OGTT), insulin response during OGTT, and blood lipids at baseline and after a 2-month detraining.

RESULTS

Glucose tolerance was not significantly affected by the detraining, but the fasted insulin and insulin levels during OGTT were significantly elevated. Fasted free fatty acid (FFA) and triglyceride levels were significantly elevated without change in cholesterol level. BMI was not significantly altered during this detraining period, but the waist circumference and WHR ratio were significantly elevated.

CONCLUSION

Only a 2-month cessation of regular training in female dancers significantly elevated basal and postprandial insulin levels and triglycerides, and were associated with increased basal FFA. This result appears to be partly related to the increased central fatness but not body mass, indicating that the early development of obesity due to reduced physical activity may not necessarily reflect on weight status. A warning is thus warranted for those young women who depend on weight measurement for body fat status monitoring.

Obesity and extreme obesity, manifest by ages 20-24 years, continuing through 32-41 years in women, should alert physicians to the diagnostic likelihood of polycystic ovary syndrome as a reversible underlying endocrinopathy

OBJECTIVES

Document obesity-extreme obesity in most 20-24, 25-29, and 32-41 years old women with PCOS as a stimulus for physicians to consider the diagnosis of PCOS, an underlying reversible endocrinopathy.

STUDY DESIGN

In matched age groups 20-24, 25-29, and 32-41 years, we compared BMI in 84, 129, and 188 Caucasian women with PCOS versus 956, 815, and 815 women in NHANES I (general population), and 25, 36, and 45 non-pregnant women (community obstetrics practice).

RESULTS

At ages 20-24, 25-29, and 32-41 years, mean+/-S.D. BMIs in women with PCOS (35.3+/-7.7, 36.0+/-9.4, 36.7+/-8.2) were much greater than NHANES I (22.8+/-4.6, 23.3+/-5.0, 24.5+/-5.6; p < .0001), and community (26.1+/-6.8, 26.9+/-6.6, 25.2+/-5.2; p < .0001). Classifying BMI <25 (normal), > or =25-30 (overweight), > or =30-40 (obese), > or =40 (extremely obese), at ages 20-24, 25-29, and 32-41 years: 76, 73, and 78% of PCOS women were obese-extremely obese, versus 7, 11, and 14% of NHANES I, and 20, 28, and 15% of community women. At ages 20-24, 25-29, and 32-41 years, only 10, 12, and 7% PCOS women had BMIs <25, versus 78, 74, and 66% NHANES I, and 48, 47, and 58% of community women.

CONCLUSIONS

Obesity-extreme obesity in women, manifest by ages 20-24 years, continuing through 32-41 years, should alert physicians to the likelihood of PCOS, an underlying, heritable, potentially reversible, insulin resistant endocrinopathy that promotes obesity.

Effect of prolonged intermittent hypoxia and exercise training on glucose tolerance and muscle GLUT4 protein expression in rats

We compared the chronic effect of intermittent hypoxia and endurance training on the glucose tolerance and GLUT4 protein expression in rat skeletal muscle. Thirty-two Sprague-Dawley rats were matched for weight and assigned to one of the following four groups: control, endurance training, hypoxia, or hypoxia followed by endurance training. Hypoxic treatment consisted of breathing 14% O2 for 12 h/day under normobaric conditions, and the training protocol consisted of making animals swim 2 times for 3 h/day. At the end of the 3rd week, an oral glucose tolerance test (OGTT) was performed 16 h after treatments. At the end of the 4th week, GLUT4 protein, mRNA, and glycogen storage in skeletal muscle were determined. Endurance training significantly improved OGTT results. Glycogen content and GLUT4 protein expression in the plantaris and red gastrocnemius, but not in the soleus or white gastrocnemius muscles, were also elevated. Chronic intermittent hypoxia also improved OGTT results, but did not alter GLUT4 protein expression. Additionally, hypoxia followed by exercise training produced significant increases in GLUT4 protein and mRNA in a greater number of muscles compared to endurance training alone. Both exercise training and hypoxia significantly reduced body mass, and an additive effect of both treatments was found. In conclusion, chronic intermittent hypoxia improved glucose tolerance in the absence of increased GLUT4 protein expression. This treatment facilitated the exercise training effect on muscle GLUT4 expression and glycogen storage. These new findings open the possibility of utilizing intermittent hypoxia, with or without exercise training, for the prevention and clinical treatment of type 2 diabetes or insulin resistance.

Deletion of PPARgamma in adipose tissues of mice protects against high fat diet-induced obesity and insulin resistance

Peroxisome proliferator-activated receptor gamma (PPARgamma) plays a crucial role in adipocyte differentiation, glucose metabolism, and other physiological processes. To further explore the role of PPARgamma in adipose tissues, we used a Cre/loxP strategy to generate adipose-specific PPARgamma knockout mice. These animals exhibited marked abnormalities in the formation and function of both brown and white adipose tissues. When fed a high-fat diet, adipose-specific PPARgamma knockout mice displayed diminished weight gain despite hyperphagia, had diminished serum concentrations of both leptin and adiponectin, and did not develop glucose intolerance or insulin resistance. Characterization of in vivo glucose dynamics pointed to improved hepatic glucose metabolism as the basis for preventing high-fat diet-induced insulin resistance. Our findings further illustrate the essential role for PPARgamma in the development of adipose tissues and suggest that a compensatory induction of hepatic PPARgamma may stimulate an increase in glucose disposal by the liver.

Controlled Unfolding and Refolding of a Single Sodium-proton Antiporter using Atomic Force Microscopy

Single-molecule force-spectroscopy was employed to unfold and refold single sodium-proton antiporters (NhaA) of Escherichia coli from membrane patches. Although transmembrane alpha-helices and extracellular polypeptide loops exhibited sufficient stability to individually establish potential barriers against unfolding, two helices predominantly unfolded pairwise, thereby acting as one structural unit. Many of the potential barriers were detected unfolding NhaA either from the C-terminal or the N-terminal end. It was found that some molecular interactions stabilizing secondary structural elements were directional, while others were not. Additionally, some interactions appeared to occur between the secondary structural elements. After unfolding ten of the 12 helices, the extracted polypeptide was allowed to refold back into the membrane. After five seconds, the refolded polypeptide established all secondary structure elements of the native protein. One helical pair showed a characteristic spring like "snap in" into its folded conformation, while the refolding process of other helices was not detected in particular. Additionally, individual helices required characteristic periods of time to fold. Correlating these results with the primary structure of NhaA allowed us to obtain the first insights into how potential barriers establish and determine the folding kinetics of the secondary structure elements.

Short-term altitude mountain living improves glycemic control

The aim of this study was to investigate the effect of mountain living conditions and high altitude hiking activities on glucose tolerance. In study I, we performed an oral glucose tolerance test on nine untrained subjects before and after 3 days of mountain living. In study II, the same measurement was used to determine the effect of high altitude hiking in two distinct geographic environments; participants included 19 professionally trained mountaineers. We found that trained mountaineers displayed significantly better sea-level glucose tolerance than sedentary subjects of a similar age (p < 0.05). This result suggests that mountaineering training could produce a beneficial effect on glucose tolerance. More importantly, in study I we demonstrated that 3 days of high altitude living (altitude approximately 2400 m) was sufficient to improve glucose tolerance. Furthermore, hiking in a relatively flat plateau area (Pamirs highland area, China, altitude approximately 4000 m) generated significantly better improvement in glucose tolerance than hiking in a mountain that contained many rough hills at a similar altitude (Mountain Snow, Taiwan, altitude approximately 3800 m). In conclusion, we found that living at a high altitude for the short term can significantly improve glucose tolerance. Additionally, the improving effect of hiking at high altitudes on glucose tolerance appears to be influenced by the geographic environment. These preliminary results suggest that high altitude living conditions and activities may possibly be developed as potential natural medicines for the prevention and treatment of type II diabetes in the future.

Role of Akt/protein kinase B in metabolism

Since its discovery more than a decade ago, the Ser/Thr kinase Akt/PKB (protein kinase B) has been recognized as being remarkably well conserved across a broad range of species and involved in a diverse array of cellular processes. Among its many roles, Akt appears to be common to signaling pathways that mediate the metabolic effects of insulin in several physiologically important target tissues. Refining our understanding of those pivotal molecular components that normally coordinate insulin action throughout the body is essential for a full understanding of insulin resistance in diabetes mellitus and ultimately the successful treatment of this disease.

Treatment of polycystic ovary syndrome with insulin-lowering agents

Early diagnosis and therapy of the underlying insulin resistance of heritable polycystic ovary syndrome (PCOS), often manifested at menarche, facilitate the reduction and/or reversal of the reproductive and metabolic morbidity of PCOS, as well as reduce the risk factors for cardiovascular disease. PCOS is characterised by oligoamenorrhoea, clinical and biochemical hyperandrogenism, infertility, recurrent miscarriage, insulin resistance, hyperinsulinaemia, gestational diabetes, impaired glucose tolerance, Type 2 diabetes, morbid obesity, hypertension, hypofibrinolysis, hypertriglyceridaemia, low levels of high density lipoprotein-cholesterol and a sevenfold risk increase in cardiovascular disease. Insulin sensitising-lowering agents reduce insulin resistance and hyperinsulinaemia, reverse PCOS endocrinopathy and ameliorate the reproductive, metabolic and cardiovascular morbidity of the disorder. The largest literature on the subject discusses metformin. Improved pregnancy outcomes in women with PCOS receiving metformin may be attributed to its ability to reduce insulin resistance, hyperinsulinaemia and hypofibrinolytic plasminogen activator inhibitor activity by the enhancement of folliculogenesis and improvement of oocyte quality.

Digenic inheritance of severe insulin resistance in a human pedigree

Impaired insulin action is a key feature of type 2 diabetes and is also found, to a more extreme degree, in familial syndromes of insulin resistance. Although inherited susceptibility to insulin resistance may involve the interplay of several genetic loci, no clear examples of interactions among genes have yet been reported. Here we describe a family in which five individuals with severe insulin resistance, but no unaffected family members, were doubly [corrected] heterozygous with respect to frameshift/premature stop mutations in two unlinked genes, PPARG and PPP1R3A these encode peroxisome proliferator activated receptor gamma, which is highly expressed in adipocytes, and protein phosphatase 1, regulatory subunit 3, the muscle-specific regulatory subunit of protein phosphatase 1, which are centrally involved in the regulation of carbohydrate and lipid metabolism, respectively. That mutant molecules primarily involved in either carbohydrate or lipid metabolism can combine to produce a phenotype of extreme insulin resistance provides a model of interactions among genes that may underlie common human metabolic disorders such as type 2 diabetes.

HIV-associated lipodystrophy: description, pathogenesis, and molecular pathways

HIV-infected individuals taking antiretroviral medications may experience changes in body shape and metabolism, commonly known as HIV-associated lipodystrophy (HIVLD). In vitro and in vivo research have revealed numerous effects of both protease inhibitors and nucleoside reverse transcriptase inhibitors on the function of various organs--most importantly adipose tissue, liver, and muscle. The metabolic abnormalities could result in an increased risk of cardiovascular disease in this vulnerable and relatively young population. Treatment strategies, normally successful in the general population, have generally been less effective in this group of people, in which the detrimental effects of the antiretroviral medications are ongoing.

Insulin resistance and periodontal disease: an epidemiologic overview of research needs and future directions

Poor periodontal health is known to be associated with Type 2 diabetes mellitus (DM). This relationship and underlying mechanisms are discussed elsewhere in this issue. Less is known concerning the link between the metabolic precursors to DM, including insulin resistance (IR), and its possible association with periodontitis. Indeed, there has been relatively little research to date in human populations concerning periodontal disease, IR, and the subsequent risk of chronic diseases, including DM. This paper will present an epidemiologist's view of how IR may link periodontal disease with DM and suggest several avenues of investigation to help clarify some of the outstanding issues.

Antiretoviral Therapy and the Lipodystrophy Syndrome, Part 2: Concepts in Aetiopathogenesis

Clinical research has indicated that the use of nucleoside reverse transcriptase inhibitor (NRTI) and HIV protease inhibitor (PI) therapy is associated with a risk of long-term toxicity syndromes, and that the aetiopathogenesis of these adverse effects is independent of the antiretroviral effects of these drugs. In relation to the lipodystrophy syndrome, it appears that the most powerful determinant of subcutaneous fat wasting is an interaction between these two drug classes. In this review, possible mechanisms underlying the contributions of both PI and NRTI drugs are reviewed, with an emphasis on their effects on adipose tissue. On this basis, an ‘adipocentric’, or minimal model of the syndrome is developed, in which divergent effects at the adipocyte of NRTIs (mitochondrial toxicity) and PIs (insulin resistance and impaired adipocyte maturation) interact to produce a phenotype that is consistent with clinical observations.