Metformin normalizes nonoxidative glucose metabolism in insulin-resistant normoglycemic first-degree relatives of patients with NIDDM

The relationship between the use of metformin and the risk of pancreatic cancer in patients with diabetes: a systematic review and meta-analysis

OBJECTIVE

We aim to evaluate the relationship between the use of metformin and the risk of pancreatic cancer in type 2 diabetes patients.

METHOD

We systematically searched the observational studies on PubMed, Embase, Web of Science, Cochrane Library, clinicalrials.gov, and CNKI databases, extracted relevant data, combined the OR value and 95% CI using the random effect model, and conducted a sensitivity analysis, subgroup analysis, and meta-regression to evaluate the size and stability of this relationship.

RESULT

Twenty-nine studies from twenty-four articles met our inclusion criteria, including more than 2 million subjects. Overall analysis showed that compared with no use of metformin, the use of metformin could reduce the risk of pancreatic cancer in patients with type 2 diabetes (OR = 0.82, 95% CI (0.69, 0.98)). Subgroup analysis showed that compared with the use of hypoglycemic drugs, the use of metformin could reduce the risk of pancreatic cancer in patients with type 2 diabetes (OR = 0.79, 95% CI (0.66, 0.94)). However, compared with no drugs or only diet therapy, metformin users might increase the risk of pancreatic cancer (OR = 2.19, 95% CI (1.08, 4.44)). Sensitivity analysis confirmed the stability of the study, and there was no significant publication bias.

CONCLUSION

Compared with the no-use of metformin, metformin users with diabetes can reduce the risk of pancreatic cancer. More research is needed to prove it works.

A positive feedback loop between AMPK and GDF15 promotes metformin antidiabetic effects

BACKGROUND AND AIMS

Metformin, the most prescribed drug for the treatment of type 2 diabetes mellitus, has been recently reported to promote weight loss by upregulating the anorectic cytokine growth differentiation factor 15 (GDF15). Since the antidiabetic effects of metformin are mostly mediated by the activation of AMPK, a key metabolic sensor in energy homeostasis, we examined whether the activation of this kinase by metformin was dependent on GDF15.

METHODS

Cultured hepatocytes and myotubes, and wild-type and Gdf15^-/- mice were utilized in a series of studies to investigate the involvement of GDF15 in the activation of AMPK by metformin.

RESULTS

A low dose of metformin increased GDF15 levels without significantly reducing body weight or food intake, but it ameliorated glucose intolerance and activated AMPK in the liver and skeletal muscle of wild-type mice but not Gdf15^-/- mice fed a high-fat diet. Cultured hepatocytes and myotubes treated with metformin showed AMPK-mediated increases in GDF15 levels independently of its central receptor GFRAL, while Gdf15 knockdown blunted the effect of metformin on AMPK activation, suggesting that AMPK is required for the metformin-mediated increase in GDF15, which in turn is needed to sustain the full activation of this kinase independently of the CNS.

CONCLUSION

Overall, these findings uncover a novel mechanism through which GDF15 upregulation by metformin is involved in achieving and sustaining full AMPK activation by this drug independently of the CNS.

Metformin, phenformin, and galegine inhibit complex IV activity and reduce glycerol-derived gluconeogenesis

Metformin is the most commonly prescribed drug for the treatment of type 2 diabetes mellitus, yet the mechanism by which it lowers plasma glucose concentrations has remained elusive. Most studies to date have attributed metformin’s glucose-lowering effects to inhibition of complex I activity. Contrary to this hypothesis, we show that inhibition of complex I activity in vitro and in vivo does not reduce plasma glucose concentrations or inhibit hepatic gluconeogenesis. We go on to show that metformin, and the related guanides/biguanides, phenformin and galegine, inhibit complex IV activity at clinically relevant concentrations, which, in turn, results in inhibition of glycerol-3-phosphate dehydrogenase activity, increased cytosolic redox, and selective inhibition of glycerol-derived hepatic gluconeogenesis both in vitro and in vivo.

Metformin exerts its plasma glucose-lowering therapeutic effect primarily through inhibition of hepatic gluconeogenesis. However, the precise molecular mechanism by which metformin inhibits hepatic gluconeogenesis is still unclear. Although inhibition of mitochondrial complex I is frequently invoked as metformin’s primary mechanism of action, the metabolic effects of complex I inhibition have not been thoroughly evaluated in vivo. Here, we show that acute portal infusion of piericidin A, a potent and specific complex I inhibitor, does not reduce hepatic gluconeogenesis in vivo. In contrast, we show that metformin, phenformin, and galegine selectively inhibit hepatic gluconeogenesis from glycerol. Specifically, we show that guanides/biguanides interact with complex IV to reduce its enzymatic activity, leading to indirect inhibition of glycerol-3-phosphate (G3P) dehydrogenase (GPD2), increased cytosolic redox, and reduced glycerol-derived gluconeogenesis. We report that inhibition of complex IV with potassium cyanide replicates the effects of the guanides/biguanides in vitro by selectively reducing glycerol-derived gluconeogenesis via increased cytosolic redox. Finally, we show that complex IV inhibition is sufficient to inhibit G3P-mediated respiration and gluconeogenesis from glycerol. Taken together, we propose a mechanism of metformin action in which complex IV–mediated inhibition of GPD2 reduces glycerol-derived hepatic gluconeogenesis.

GSK2256294 Decreases sEH (Soluble Epoxide Hydrolase) Activity in Plasma, Muscle, and Adipose and Reduces F2-Isoprostanes but Does Not Alter Insulin Sensitivity in Humans

[Figure: see text].

Cellular and Molecular Mechanisms of Metformin Action

Metformin is a first-line therapy for the treatment of type 2 diabetes, due to its robust glucose-lowering effects, well-established safety profile, and relatively low cost. While metformin has been shown to have pleotropic effects on glucose metabolism, there is a general consensus that the major glucose-lowering effect in patients with type 2 diabetes is mostly mediated through inhibition of hepatic gluconeogenesis. However, despite decades of research, the mechanism by which metformin inhibits this process is still highly debated. A key reason for these discrepant effects is likely due to the inconsistency in dosage of metformin across studies. Widely studied mechanisms of action, such as complex I inhibition leading to AMPK activation, have only been observed in the context of supra-pharmacological (>1 mM) metformin concentrations, which do not occur in the clinical setting. Thus, these mechanisms have been challenged in recent years and new mechanisms have been proposed. Based on the observation that metformin alters cellular redox balance, a redox-dependent mechanism of action has been described by several groups. Recent studies have shown that clinically relevant (50-100 μM) concentrations of metformin inhibit hepatic gluconeogenesis in a substrate-selective manner both in vitro and in vivo, supporting a redox-dependent mechanism of metformin action. Here, we review the current literature regarding metformin's cellular and molecular mechanisms of action.

Immune-mediated anti-tumor effects of metformin; targeting metabolic reprogramming of T cells as a new possible mechanism for anti-cancer effects of metformin

Immunotherapy-based cancer treatment has revolutionized the era of cancer patients recuperation and it has brought a strong hope to treatment of some types of cancers. Metformin, a widely used antidiabetic drug, which has intensely been studied for its anticancer effects, is believed to have positive influences on immune responses against tumor cells. Metformin can affect metabolic pathways within cells mainly through activation of AMPK. Metabolic restriction of tumor microenvironment on effector immune cells is one of the important strategies favoring tumor cells to escape from immunogenic cell death. The metabolism of T cells has an axial role in shaping and supporting immune responses and may have an important role in anticancer immunity, suggesting that the functionality and durability of tumor-specific T cells need sufficient energy and nutrients. Energy biogenesis of tumor-specific cytotoxic T cells has become an interesting field of study and it is suggested that activation and maintenance of effector T cell responses in tumor microenvironment may occur by metabolic reprogramming of T cells. AMPK has been noticed as the main intracellular energy sensor and mitochondrial biogenesis key regulator which can control and regulate metabolic reprogramming in immune cells and increase antitumor immunity. Metabolic reprogramming of T cells to overcome metabolic restriction in tumor microenvironment, maiming effector T cell responses against tumor cells, has been noticed by several studies. Here we represent metformin, an AMPK activator, as a new candidate drug for metabolic reprogramming of tumor-specific T cells to increase the efficacy and accountability of cancer immunotherapy.

Metabolic Effects of Metformin in Humans

BACKGROUND

Both insulin deficiency and insulin resistance due to glucagon secretion cause fasting and postprandial hyperglycemia in patients with diabetes.

INTRODUCTION

Metformin enhances insulin sensitivity, being used to prevent and treat diabetes, although its mechanism of action remains elusive.

RESULTS

Patients with diabetes fail to store glucose as hepatic glycogen via the direct pathway (glycogen synthesis from dietary glucose during the post-prandial period) and via the indirect pathway (glycogen synthesis from "de novo" synthesized glucose) owing to insulin deficiency and glucagoninduced insulin resistance. Depletion of the hepatic glycogen deposit activates gluconeogenesis to replenish the storage via the indirect pathway. Unlike healthy subjects, patients with diabetes experience glycogen cycling due to enhanced gluconeogenesis and failure to store glucose as glycogen. These defects raise hepatic glucose output causing both fasting and post-prandial hyperglycemia. Metformin reduces post-prandial plasma glucose, suggesting that the drug facilitates glucose storage as hepatic glycogen after meals. Replenishment of glycogen store attenuates the accelerated rate of gluconeogenesis and reduces both glycogen cycling and hepatic glucose output. Metformin also reduces fasting hyperglycemia due to declining hepatic glucose production. In addition, metformin reduces plasma insulin concentration in subjects with impaired glucose tolerance and diabetes and decreases the amount of insulin required for metabolic control in patients with diabetes, reflecting improvement of insulin activity. Accordingly, metformin preserves β-cell function in patients with type 2 diabetes.

CONCLUSION

Several mechanisms have been proposed to explain the metabolic effects of metformin, but evidence is not conclusive and the molecular basis of metformin action remains unknown.

Metformin; an old antidiabetic drug with new potentials in bone disorders

The prevalence of diabetes mellitus especially type 2 diabetes mellitus is increasing all over the world. In addition to cardiomyopathy and nephropathy, diabetics are at higher risk of mortality and morbidity due to greater risk of bone fractures and skeletal abnormalities. Patients with diabetes mellitus have lower bone quality in comparison to their non-diabetic counterparts mainly because of hyperglycemia, toxic effects of advanced glycosylation end-products (AGEs) on bone tissue, and impaired bone microvascular system. AGEs may also contribute to the development of osteoarthritis further to osteoporosis. Therefore, glycemic control in diabetic patients is vital for bone health. Metformin, a widely used antidiabetic drug, has been shown to improve bone quality and decrease the risk of fractures in patients with diabetes in addition to glycemic control and improving insulin sensitivity. AMP activated protein kinase (AMPK), the key molecule in metformin antidiabetic mechanism of action, is also effective in signaling pathways involved in bone physiology. This review, discusses the molecules linking diabetes and bone turnover, role of AMPK in bone metabolism, and the effect of metformin as an activator of AMPK on bone disorders and malignancies.

Lactate-Induced Glucose Output Is Unchanged by Metformin at a Therapeutic Concentration - A Mass Spectrometry Imaging Study of the Perfused Rat Liver

Metformin is the first line drug for type 2 diabetes but its molecular mechanisms remain unclear. Here, we have studied the acute effect of a therapeutically relevant intrahepatic concentration of metformin on glucose production from lactate. We selected the perfused rat liver as experimental system since it enables the complete control of drug dosage. We used MALDI (matrix-assisted laser desorption/ionization) mass spectrometry imaging to estimate the concentration of metformin in the livers and we measured the concentration of glucose in the effluent medium under basal conditions and following lactate addition. MALDI mass spectra of thin-sections of freeze-clamped rat liver perfused with metformin showed a peak at 130.16 m/z which was unambiguously assigned to metformin. The mass spectrometric detection limit was at a tissue concentration of about 250 nM, and uptake of metformin from the perfusion medium to the liver occurred with a K_m of 0.44 mM. Metformin was evenly distributed in the liver irrespective of its concentration in the perfusion medium and the duration of a perfusion. At a parenchymal concentration of 30 μM, metformin did not induce any significant suppression of the basal or lactate-induced glucose release from the liver. These results show that matrix-assisted laser desorption/ionization mass spectrometry imaging can be applied to estimate the tissue concentration and distribution of metformin in a therapeutically relevant micromolar concentration range. Our findings challenge the view that metformin causes an inhibition of glucose release from the liver by an acute inhibition of mitochondrial glycerol 3-phosphate dehydrogenase (EC 1.1.5.3).

Guideline-Recommended Medications and Physical Function in Older Adults with Multiple Chronic Conditions

BACKGROUND/OBJECTIVES

The benefit or harm of a single medication recommended for one specific condition can be difficult to determine in individuals with multiple chronic conditions and polypharmacy. There is limited information on the associations between guideline-recommended medications and physical function in older adults with multiple chronic conditions. The objective of this study was to estimate the beneficial or harmful associations between guideline-recommended medications and decline in physical function in older adults with multiple chronic conditions.

DESIGN

Prospective observational cohort.

SETTING

National.

PARTICIPANTS

Community-dwelling adults aged 65 and older from the Medicare Current Beneficiary Survey study (N = 3,273). Participants with atrial fibrillation, coronary artery disease, depression, diabetes mellitus, or heart failure were included.

MEASUREMENTS

Self-reported decline in physical function; guideline-recommended medications; polypharmacy (taking <7 vs ≥7 concomitant medications); chronic conditions; and sociodemographic, behavioral, and health risk factors.

RESULTS

The risk of decline in function in the overall sample was highest in participants with heart failure (35.4%, 95% confidence interval (CI) = 26.3-44.5) and lowest for those with atrial fibrillation (20.6%, 95% CI = 14.9-26.2). In the overall sample, none of the six guideline-recommended medications was associated with decline in physical function across the five study conditions, although in the group with low polypharmacy exposure, there was lower risk of decline in those with heart failure taking renin angiotensin system blockers (hazard ratio (HR) = 0.40, 95% CI = 0.16-0.99) and greater risk of decline in physical function for participants with diabetes mellitus taking statins (HR = 2.27, 95% CI = 1.39-3.69).

CONCLUSIONS

In older adults with multiple chronic conditions, guideline-recommended medications for atrial fibrillation, coronary artery disease, depression, diabetes mellitus, and heart failure were largely not associated with self-reported decline in physical function, although there were associations for some medications in those with less polypharmacy.

Major Pathophysiology in Prediabetes and Type 2 Diabetes: Decreased Insulin in Lean and Insulin Resistance in Obese

CONTEXT

Lowering of body mass index (BMI) to ≥25 kg/m2 as obesity by ADA suggests insulin resistance as a major mechanism of impaired glucose metabolism (IGM) in Asians. However, glimepiride, an insulin secretagogue, delayed onset of type 2 diabetes (DM2) from prediabetes (PreDM), indicating decreased insulin secretion (IS) as a major factor in lean (L; BMI < 27 kg/m2) subjects with IGM.

OBJECTIVE

Assessment of IS and insulin resistance (IR) in L and obese (Ob; BMI ≥ 27 kg/m2) subjects with euglycemia (N), PreDM, and new onset DM2.

SUBJECTS

Seventy-five men and 45 women ages 36 to 75 years were divided into six groups: LN, LPreDM, LDM2, ObN, ObPreDM, and ObDM2.

METHODS

Determination of IS by insulinogenic indices (I/G) at fasting (FI/FG), first phase (∆I/∆G), and cumulative responses over 2 hours of OGTT (CRI/CRG), and IR by FIXFG, ∆IX∆G, and CRIXCRG. Changes in IS and IR for PreDM and DM2 were calculated as % fall and % rise, respectively, from levels in N.

RESULTS

All indices of IS and IR were lower (P < 0.05) in L than corresponding Ob groups (P < 0.05). Moreover, decline in IS and rise in IR were progressive from N to PreDM (P < 0.05) and DM2 (P < 0.05) in both groups. However, the declines in IS were greater (P < 0.05) than rises in IR in LPreDM and LDM2. Whereas, the rises in IR were higher (P < 0.05) than declines in IS in ObPreDM and ObDM2.

CONCLUSION

In L, major mechanism of IGM is declining IS and not rising IR documented among Ob.

Impaired glucose tolerance: do pharmacological therapies correct the underlying metabolic disturbance?

Lifestyle intervention prevents or delays the conversion from impaired glucose tolerance (IGT) to type 2 diabetes. However, many subjects fail to achieve and/or maintain long-term weight loss and to follow a regular exercise regimen may require pharmacologic therapy. Insulin resistance in liver, muscle and fat, along with impaired beta-cell function, plays a central role in the pathogenesis of type 2 diabetes. Insulin sensitising drugs, including metformin and the thiazolidinediones, have significantly reduced the conversion rate of IGT to type 2 diabetes in subjects in several large, well designed clinical trials. Insulin-sensitising drugs are likely to play an important role in future strategies for diabetes prevention.

Management of Polycystic Ovary Syndrome

Polycystic ovary syndrome is a common endocrinological problem in women of reproductive age. Polycystic ovary syndrome is a heterogenous disorder and patients may attend different clinics depending on the main complaint. The exact pathophysiology of polycystic ovary syndrome remains obscure, although there have been insights that have thrown light on this condition. Consensus on the definition of the syndrome has only been recently achieved. The management of polycystic ovary syndrome poses a challenge to the physician as responses to the different treatment regimes have proved to be inconsistent. Diet and lifestyle advice, restoration of menstrual cycle regularity, treatment of hyperandrogenism, treatment of infertility and prevention of long-term consequences form the basis of polycystic ovary syndrome management. This review aims to provide the reader with the latest evidence in the treatment of polycystic ovary syndrome, as well as focus on some of the controversies surrounding its management.

Changes in physical performance in older women according to presence and treatment of diabetes mellitus

OBJECTIVES

To determine whether older women with diabetes mellitus have a greater longitudinal decline in physical performance than those without and whether any decline differs according to insulin sensitizer use.

DESIGN

Prospective cohort study.

SETTING

Baltimore, Maryland; Minneapolis, Minnesota; Portland, Oregon; and the Monongahela, Pennsylvania.

PARTICIPANTS

Community-dwelling women (mean age 78.5 ± 3.6) enrolled in the Study of Osteoporotic Fractures in 1997-98 and restudied 4.9 ± 0.6 years later (N = 2,864).

MEASUREMENTS

Women were categorized as having no diabetes mellitus (n = 2,680) or having diabetes mellitus (n = 184). A prescription medication inventory was used to determine use of insulin sensitizers (metformin and thiazolidinedione). The outcomes were longitudinal changes in physical performance measures, including grip strength, usual walk speed, and rapid walk speed.

RESULTS

Estimates from fully adjusted models showed that women with diabetes mellitus had greater declines in usual walk speed (-0.16 m/s, 95% confidence interval (CI) = -0.19 to -0.14) and rapid walk speed (-0.21 m/s, 95% CI = -0.24 to -0.17) than those without (usual walk speed -0.11 m/s, 95% CI = -0.12 to -0.11, P < .001; rapid walk speed -0.15 m/s, 95% CI = -0.16 to -0.14; P = .005). Women with diabetes mellitus taking insulin sensitizers had less decline in usual walk speed than those not taking insulin sensitizers (P < .001). Declines in grip strength did not differ significantly by diabetes mellitus status or insulin sensitizer use.

CONCLUSION

Older women with diabetes mellitus have a greater decline in walk speed, but not grip strength, than older women without diabetes mellitus. Clinical studies in older adults to determine whether diabetes mellitus treatments such as insulin sensitizers can prevent loss in walk speed and mobility are needed.

Metformin and improvement of the hepatic insulin resistance index independent of anthropometric changes

OBJECTIVE

To determine the change in the hepatic insulin resistance index (HIRI) after metformin treatment.

METHODS

In this retrospective cohort study, Mexican mestizo patients with a body mass index (BMI) of 25 kg/m(2) or greater were evaluated. Participants were classified into 2 groups: patients who received metformin and patients who did not. Both groups were followed up for a median of 6 months (range, 4-10 months). The HIRI was calculated at baseline and at follow-up in both groups. We evaluated the independent effect of metformin on HIRI after adjustment for the difference in basal and final values (DELTA) of BMI, waist circumference, glucose, and insulin.

RESULTS

A total of 71 patients were enrolled (51 [72%] female). Forty-one patients received metformin and 30 patients did not. Mean age was 36.3 ± 12.2 years and mean BMI was 42.2 ± 10.7 kg/m(2). After metformin treatment, HIRI significantly decreased from 38 ± 10.7 to 34.7 ± 9.5 (P = .03). In contrast, the control group had a nonsignificant increase in HIRI (37.6 ± 11.7 to 40.0 ± 14.0, P = .22). Weight significantly decreased in both groups (group 1: 114.6 ± 33.8 kg to 107.6 ± 28.9 kg, P<.01; group 2: 104.8 ± 28.5 kg to 98.9 ± 26.0 kg, P<.01). After BMI adjustment, the total metformin dosage correlated negatively with HIRI (r = -0.36, P = .03). Using a linear regression model (F = 6.0, r2 = 0.37, P = .002) adjusted for DELTA BMI and DELTA waist circumference, the administration of metformin resulted in independent improvement in the HIRI level (standardized β = -0.29, t = -2.0, P = .04).

CONCLUSIONS

Metformin improves HIRI independently of anthropometric changes. In persons with elevated HIRI levels, metformin may be considered among the treatment options.

Insulin sensitizers may attenuate lean mass loss in older men with diabetes

OBJECTIVE

To examine longitudinal changes in total and appendicular lean body mass in older men with impaired fasting glucose (IFG) or diabetes and to determine whether these changes differ by diabetes treatment.

RESEARCH DESIGN AND METHODS

A total of 3,752 ambulatory men aged ≥ 65 years at baseline participated in a multicenter longitudinal cohort study. Baseline glycemic status was categorized as normoglycemia, IFG, undiagnosed/untreated diabetes, or treated diabetes. Insulin sensitizer medication use (metformin and/or thiazolidinediones) was assessed by prescription medication inventory. The change in total lean and appendicular lean mass was derived from dual X-ray absorptiometry scans taken at baseline and 3.5 ± 0.7 years later.

RESULTS

This male cohort included 1,853 individuals with normoglycemia, 1,403 with IFG, 234 with untreated diabetes, 151 with diabetes treated with insulin sensitizers, and 111 with diabetes treated without insulin sensitizers. Men with untreated diabetes, diabetes treated without insulin sensitizers, or IFG had greater percentage loss in total or appendicular lean mass (P ≤ 0.05 in comparison to normoglycemic men). There remained a significantly greater percentage loss in appendicular lean mass for these groups even after adjustment for medical comorbidities or lifestyle factors. In contrast, the percentage loss in total or appendicular lean mass in men with diabetes treated with insulin sensitizers was significantly less than that in normoglycemic men in minimally and fully adjusted models.

CONCLUSIONS

Skeletal muscle loss was accelerated in men with IFG and diabetes, except when the latter was treated with insulin sensitizers. These findings suggest that insulin sensitizers may attenuate muscle loss.

Peroxisome Proliferator-Activated Receptor-gamma in Amyotrophic Lateral Sclerosis and Huntington's Disease

Amyotrophic lateral sclerosis (ALS) is a debilitating and one of the most common adult-onset neurodegenerative diseases with the prevalence of about 5 per 100 000 individuals. It results in the progressive loss of upper and lower motor neurons and leads to gradual muscle weakening ultimately causing paralysis and death. ALS has an obscure cause and currently no effective treatment exists. In this review, a potentially important pathway is described that can be activated by peroxisome proliferator-activated receptor-gamma (PPAR-gamma) agonists and has the ability to block the neuropathological damage caused by inflammation in ALS and possibly in other neudegenerative diseases like Huntington's disease (HD). Neuroinflammation is a common pathological feature in neurodegenerative diseases. Therefore, PPAR-gamma agonists are thought to be neuroprotective in ALS and HD. We and others have tested the neuroprotective effect of pioglitazone (Actos), a PPAR-gamma agonist, in G93A SOD1 transgenic mouse model of ALS and found significant increase in survival of G93A SOD1 mice. These findings suggest that PPAR-gamma may be an important regulator of neuroinflammation and possibly a new target for the development of therapeutic strategies for ALS. The involvement of PPAR-gamma in HD is currently under investigation, one study finds that the treatment with rosiglitazone had no protection in R6/2 transgenic mouse model of HD. PPAR-gamma coactivator-1alpha (PGC-1alpha) is a transcriptional coactivator that works together with combination of other transcription factors like PPAR-gamma in the regulation of mitochondrial biogenesis. Therefore, PPAR-gamma is a possible target for ALS and HD as it functions as transcription factor that interacts with PGC-1alpha. In this review, the role of PPAR-gamma in ALS and HD is discussed based on the current literature and hypotheses.

Recombinant human leptin treatment does not improve insulin action in obese subjects with type 2 diabetes

OBJECTIVE

Leptin therapy improves insulin sensitivity in people with leptin deficiency, but it is not known whether it improves insulin action in people who are not leptin deficient. The purpose of the current study was to determine whether leptin treatment has weight loss-independent effects on insulin action in obese subjects with type 2 diabetes.

RESEARCH DESIGN AND METHODS

We conducted a randomized, placebo-controlled trial in obese subjects (BMI: 35.4 ± 0.6 kg/m(2); mean ± SE) with newly diagnosed type 2 diabetes. Subjects were randomized to treatment with placebo (saline), low-dose (30 mg/day), or high-dose (80 mg/day) recombinant methionyl human (r-Met hu) leptin for 14 days. Multiorgan insulin sensitivity before and after treatment was evaluated by using the hyperinsulinemic-euglycemic clamp procedure in conjunction with stable isotopically labeled tracer infusions to measure glucose, glycerol, and fatty acid kinetics.

RESULTS

Low-dose and high-dose leptin treatment resulted in a threefold (P < 0.01) and 150-fold (P < 0.001) increase in basal plasma leptin concentrations, respectively. However, neither low-dose nor high-dose therapy had an effect on insulin-mediated suppression of glucose, glycerol, or palmitate rates of appearance into plasma compared with placebo. In addition, leptin treatment did not increase insulin-mediated stimulation of glucose disposal compared with placebo (14.3 ± 3.1, 18.4 ± 3.6, 16.7 ± 2.4 vs. 17.5 ± 2.5, 20.7 ± 3.0, 19.1 ± 3.3 μmol/kg body wt/min before vs. after treatment in the placebo, low-dose, and high-dose leptin groups, respectively).

CONCLUSIONS

r-Met hu leptin does not have weight loss-independent, clinically important effects on insulin sensitivity in obese people with type 2 diabetes.

Restoration of muscle mitochondrial function and metabolic flexibility in type 2 diabetes by exercise training is paralleled by increased myocellular fat storage and improved insulin sensitivity

OBJECTIVE

Mitochondrial dysfunction and fat accumulation in skeletal muscle (increased intramyocellular lipid [IMCL]) have been linked to development of type 2 diabetes. We examined whether exercise training could restore mitochondrial function and insulin sensitivity in patients with type 2 diabetes.

RESEARCH DESIGN AND METHODS

Eighteen male type 2 diabetic and 20 healthy male control subjects of comparable body weight, BMI, age, and VO2max participated in a 12-week combined progressive training program (three times per week and 45 min per session). In vivo mitochondrial function (assessed via magnetic resonance spectroscopy), insulin sensitivity (clamp), metabolic flexibility (indirect calorimetry), and IMCL content (histochemically) were measured before and after training.

RESULTS

Mitochondrial function was lower in type 2 diabetic compared with control subjects (P = 0.03), improved by training in control subjects (28% increase; P = 0.02), and restored to control values in type 2 diabetic subjects (48% increase; P < 0.01). Insulin sensitivity tended to improve in control subjects (delta Rd 8% increase; P = 0.08) and improved significantly in type 2 diabetic subjects (delta Rd 63% increase; P < 0.01). Suppression of insulin-stimulated endogenous glucose production improved in both groups (-64%; P < 0.01 in control subjects and -52% in diabetic subjects; P < 0.01). After training, metabolic flexibility in type 2 diabetic subjects was restored (delta respiratory exchange ratio 63% increase; P = 0.01) but was unchanged in control subjects (delta respiratory exchange ratio 7% increase; P = 0.22). Starting with comparable pretraining IMCL levels, training tended to increase IMCL content in type 2 diabetic subjects (27% increase; P = 0.10), especially in type 2 muscle fibers.

CONCLUSIONS

Exercise training restored in vivo mitochondrial function in type 2 diabetic subjects. Insulin-mediated glucose disposal and metabolic flexibility improved in type 2 diabetic subjects in the face of near-significantly increased IMCL content. This indicates that increased capacity to store IMCL and restoration of improved mitochondrial function contribute to improved muscle insulin sensitivity.

The utility of physical activity in the management of global cardiometabolic risk

Major health organizations promote the adoption of a healthy lifestyle, composed of sufficient daily physical activity and a balanced diet for the prevention and management of type 2 diabetes (T2D) and cardiovascular disease risk. In particular, it is recommended that adults accumulate 30 min of moderate-intensity aerobic physical activity on most days of the week. Despite these recommendations, a physically active lifestyle is seldom adopted, and the majority of the North American population remains sedentary. Although the optimal strategy for promoting physical activity in today's environment remains elusive, the evidence for the utility of physical activity in the management of risk factors for T2D and cardiovascular disease is overwhelming. This review examines the influence of aerobic-type physical activity on components of global cardiometabolic risk, that is, the traditional and emerging risk factors for cardiovascular disease and T2D, including visceral obesity, insulin resistance, hypertension, atherogenic dyslipidemia, thrombosis, inflammation, and cardiorespiratory fitness. Where possible, specific consideration is given to the independent effects of an acute bout of physical activity vs. chronic physical activity with weight loss vs. chronic physical activity without weight loss.

The future of obesity reduction: beyond weight loss

Obesity increases the risk of morbidity and mortality and reduces quality of life independent of age, sex or ethnicity. Leading health authorities recommend weight loss as a primary treatment strategy for obesity reduction--weight loss goals range from 5% to 10% of initial body weight. Intentional weight loss in most adults is associated with a reduction in many of the health complications of obesity. Nonetheless, emerging evidence supports the notion that a lifestyle-modification program characterized by an increase in physical activity and a balanced diet can reduce obesity and the risk of obesity-related comorbid conditions despite minimal or no weight loss. The benefits of such an approach include appreciable reductions in abdominal obesity, visceral fat and cardiometabolic risk factors, and increases in both skeletal muscle mass and cardiorespiratory fitness. Individuals with obesity face a serious challenge if they are to attain even modest weight loss in today's obesogenic environment. Clinicians could encourage positive lifestyle changes in their patients by counseling them that obesity and its associated health risks can be reduced in response to an increase in physical activity with or without weight loss.

Evidence-based and potential benefits of metformin in the polycystic ovary syndrome: a comprehensive review

Metformin is an insulin sensitizer widely used for the treatment of patients affected by type 2 diabetes mellitus. Because many women with polycystic ovary syndrome (PCOS) are insulin resistant, metformin was introduced in clinical practice to treat these patients also. Moreover, metformin's effect has other targets beside its insulin-sensitizing action. The present review was aimed at describing all evidence-based and potential uses of metformin in PCOS patients. In particular, we will analyze the uses of metformin not only for the treatment of all PCOS-related disturbances such as menstrual disorders, anovulatory infertility, increased abortion, or complicated pregnancy risk, hyperandrogenism, endometrial, metabolic and cardiovascular abnormalities, but also for the prevention of the syndrome.

Is weight loss the optimal target for obesity-related cardiovascular disease risk reduction?

In the present review, it is argued that while weight loss is associated with substantial reduction in obesity-related cardiovascular disease risk and remains a desired outcome of relevant treatment strategies, increasing physical activity is associated with marked reduction in waist circumference, visceral fat and cardiometabolic risk factors, concurrent with an increase in cardiorespiratory fitness despite minimal or no change in body weight. Failure to recognize the benefits of exercise independent of weight loss masks opportunities to counsel and educate patients whose sole criteria for gauging obesity reduction success is the bathroom scale.

Themed Review: Lifestyle Treatment of the Metabolic Syndrome

The metabolic syndrome is a clustering of metabolic risk factors including abdominal obesity, dysfunctional glucose metabolism, dyslipidemia, and elevated blood pressure. Approximately 1 in 4 Americans currently has the metabolic syndrome and are thus at an elevated risk of cardiovascular disease, type 2 diabetes, and mortality. Leading health authorities recommend lifestyle modification consisting of exercise and caloric restriction for treatment and prevention of the metabolic syndrome. The purpose of this report is to review the evidence that considers lifestyle modification as a treatment strategy for the metabolic syndrome. The influence of lifestyle modification on abdominal obesity, dysfunctional glucose metabolism, dyslipidemia, and elevated blood pressure is considered. Findings suggest that interventions consisting of exercise and/or caloric restriction are associated with improvement in all components of the metabolic syndrome, although the magnitude of this effect varies according to the specific component studied and additional factors such as baseline values. The evidence presented supports the promotion of lifestyle modification as an efficacious strategy for the treatment of the metabolic syndrome.

Long-term beneficial effects of glipizide treatment on glucose tolerance in subjects with impaired glucose tolerance

AIMS

To assess the efficacy and long-term effects of glipizide treatment on glucose and insulin metabolism in individuals with impaired glucose tolerance (IGT).

METHODS

Thirty-seven first-degree relatives of patients with type 2 diabetes fulfilling WHO criteria for IGT were randomized to treatment with either glipizide 2.5 mg once daily or matching placebo for 6 months. A 75 g, 2-h oral (OGTT) and 60 min intravenous glucose tolerance test (IVGTT) were performed at baseline and after 6 months. The subjects were followed up for another 12 months after discontinuation of treatment and a repeat OGTT was performed at 18 months.

RESULTS

Thirty-three subjects fulfilled the study. Markers of insulin sensitivity - i.e. fasting insulin and HOMA(IR)-index - improved in the glipizide group (P = 0.04 and 0.02 respectively) as well as HDL cholesterol (P = 0.05) compared with placebo group after 6 months. At 18 months, both fasting and 2 h glucose concentrations were significantly lower in the glipizide group compared with the placebo group (P = 0.04 and 0.03 respectively). The prevalence of type 2 diabetes was 29.4% in the placebo group and 5.9% in the glipizide group at 18 months. This equals an 80% relative risk reduction in the active treatment group.

CONCLUSIONS

Short-term treatment with glipizide improves glucose and insulin metabolism in subjects with IGT primarily by improving insulin sensitivity mediated by lowering glucose toxicity, thereby providing the beta cells rest. Larger studies are needed to establish whether these effects are sufficient to prevent progression to manifest type 2 diabetes and associated cardiovascular morbidity in subjects at increased risk of developing type 2 diabetes.

Does metabolic syndrome mitigate weight loss in overweight Mexican American women treated for 1-year with orlistat and lifestyle modification?

AIMS

To investigate the effects of a pharmacotherapy (orlistat) plus lifestyle management (OLM) intervention on weight loss in Mexican American women with and without metabolic syndrome (MS).

METHODS

One hundred and seven female participants aged 21-65 years and of Mexican origin were randomized to either OLM or a wait-list control group (WLC) for one year. The lifestyle interventions were tailored to exhibit features of the Mexican culture. Within each group, subjects with MS were compared to those without MS to assess whether its presence mitigates weight loss. Risk factors for MS also were assessed.

RESULTS

Participants with MS in the OLM group experienced significant decreases in weight and body mass index (BMI) as compared to participants without MS. Participants with MS in the OLM group and who completed the study lost 9.3+/-7.5 kg (20.5+/-16.5 lb) as compared to participants with MS in the WLC group, who only lost 0.2+/-3.1 kg (0.4+/-6.8 lb). Further, participants with MS in the OLM group who completed the study experienced a 3.1+/-3.9 kg/m2 decrease in BMI whereas participants with MS in the WLC group only experienced a 0.1+/-1.2 kg/m2 decrease in BMI. No changes in other MS risk factors were significant.

CONCLUSIONS

Patients with MS experienced significant weight loss and decreases in BMI as a result of a lifestyle and pharmacotherapy intervention.

Metformin: mechanisms of antihyperglycemic action, other pharmacodynamic properties, and safety perspectives

OBJECTIVE

To characterize the mechanisms of action of metformin and describe its effects and safety profile.

METHODS

Results of more than 30 years of clinical use in countries other than the United States are summarized. In addition, the pharmacologic properties of metformin are compared with those of other antihyperglycemic agents.

RESULTS

Approximately 90% of all cases of diabetes are non-insulin-dependent diabetes mellitus (NIDDM)--a heterogeneous disease that involves several pathogenic factors and is associated with other coexisting conditions, such as cardiovascular disease, hypertension, and obesity. Thus, an agent that controls blood glucose levels and has favorable effects on the concomitant conditions should be considered when pharmacologic intervention is needed for the treatment of NIDDM. Metformin possesses the pharmacodynamic properties to do both. Its mechanisms of action include the reduction of hepatic glucose production and enhancement of peripheral glucose disposal, making metformin an effective antihyperglycemic agent. It also has other pharmacologic properties, independent of its glycemic effects, that offer additional clinical benefits in comparison with other pharmacologic NIDDM treatments. These benefits include stabilization or even loss of weight in patients for whom weight gain is a concern and reduction of plasma lipid levels in patients with hyperlipidemia.

CONCLUSION

On the basis of 3 decades of clinical experience, metformin has been shown to be not only a well tolerated but also a highly effective antihyperglycemic agent.

Independent and additive effects of energy restriction and exercise on glucose and insulin concentrations in sedentary overweight men

BACKGROUND

Overweight and inactivity are associated with impaired glucose tolerance, reduced insulin sensitivity, and diabetes. Few controlled trials have assessed the independent and combined effects of energy restriction and exercise on the prevention of these conditions.

OBJECTIVE

The objective was to evaluate the independent and additive effects of 16 wk of energy restriction and exercise on glucose and insulin concentrations.

DESIGN

Sixty nonsmoking, overweight, sedentary men aged 20-50 y were randomly assigned to either maintain or restrict their energy intake (4186-6279 kJ/d). Within each of these arms, the subjects were further randomly assigned to either a light-intensity (control) or a vigorous-intensity exercise program for 30 min 3 times/wk.

RESULTS

Fifty-one subjects completed the study. Maximal oxygen uptake increased ( approximately 24%; P < 0.001) with vigorous but not with light exercise. Significant weight loss was observed with energy restriction (x: 10.12 kg; 95% CI: 8.02, 12.22 kg; P < 0.001) but not with exercise. Vigorous exercise reduced fasting glucose and glucose and insulin areas under the curve (AUCs) by 13% (P = 0.01) and 20% (P = 0.02), respectively. Exercise effects were independent of weight change. Energy restriction resulted in a 40% reduction in the insulin AUC (P = 0.01). Vigorous exercise and energy restriction were additive in reducing the insulin AUC.

CONCLUSIONS

Energy restriction and vigorous exercise independently and additively reduce glucose and insulin concentrations in response to an oral-glucose-tolerance test. Both of these lifestyle interventions provide a potent strategy that should be an integral part of any program to reduce the risk of impaired glucose tolerance, insulin resistance, and diabetes in overweight and sedentary persons.

Effect of taurine treatment on insulin secretion and action, and on serum lipid levels in overweight men with a genetic predisposition for type II diabetes mellitus

BACKGROUND

The prevalence of type 2 diabetes mellitus (T2DM) is increasing with an epidemic growth rate. Animal studies with taurine supplementation have shown increased insulin secretion and action, suggesting that taurine supplementation may have a potential to prevent T2DM.

OBJECTIVE

To assess the effect of taurine treatment on insulin secretion and action, and on plasma lipid levels in overweight men with a positive history of T2DM.

DESIGN

20 nondiabetic subjects were included in a double-blinded, randomized, crossover study, receiving a daily supplementation of 1.5 g taurine or placebo for two periods of 8 weeks. The subjects were overweight first-degree relatives of T2DM patients. An intravenous glucose tolerance test (IVGTT) was used to measure first-phase insulin secretory response, and a euglycemic hyperinsulinemic clamp was used to determine peripheral insulin action.

RESULTS

Mean plasma taurine concentration was 39 +/- 7 (s.d.) micromol/l after placebo and 131 +/- 62 micromol/l after taurine intervention (P < 0.0001). There was no significant difference after taurine intervention compared to placebo in incremental insulin response (Insincr.) neither during the IVGTT, nor in insulin-stimulated glucose disposal during the clamp. Insulin secretion, adjusted for insulin sensitivity, was also unchanged. There was no significant effect of taurine supplementation on blood lipid levels as well.

CONCLUSION

Daily supplementation with 1.5 g taurine for 8 weeks had no effect on insulin secretion or sensitivity, or on blood lipid levels. These findings in persons with an increased risk of T2DM are in contrast to those from animal studies, and do not support the assumption that dietary supplementation with taurine can be used to prevent the development of T2DM.

Effects of short-term metformin treatment on insulin sensitivity of blood glucose and free fatty acids

AIM

Based on the known effect of metformin (MET) in improving insulin sensitivity in type 2 diabetes, with the scope to focus the effects on glycaemic and free fatty acids (FFA) levels, we studied the effects of a short-term treatment with this drug in obese subjects and obese patients with diabetes or family history of diabetes (FHD). We used a method to allow us to evaluate the possible difference of insulin sensibility with regard to the insulin action on glycaemia and blood FFA, both in the basal state and during oral glucose tolerance test (OGTT).

METHODS

Insulin sensitivity was investigated before and after MET treatment (850 mg bid for 10 days) in seven obese subjects with normal glucose tolerance and without FHD and 13 obese patients with diabetes (n=7) or FHD (n=6). By using specifically designed formulae, we calculated four insulin-sensitivity indices (ISI) from basal level (b) and area values (a) (during OGTT) of insulinaemia, glycaemia (gly) or FFA (ffa), namely: ISI (gly)-b, ISI (gly)-a, ISI (ffa)-b and ISI (ffa)-a.

RESULTS

In patients with diabetes or FHD, MET improved ISI (gly)-b (0.79 +/- 0.06 vs. 0.59 +/- 0.07, p<0.001) and ISI (gly)-a (0.69 +/- 0.09 vs. 0.51 +/- 0.07, p<0.05), whereas only minor changes occurred for ISI (ffa)-b and ISI (ffa)-a. In contrast, in simple obese subjects, MET induced further deterioration of both ISI (gly)-a (0.47 +/- 0.07 vs. 0.64 +/- 0.10, p<0.01) and ISI (ffa)-a (0.43 +/- 0.07 vs. 0.55 +/- 0.08, p<0.05). Fasting level and total area of lactate were high in the obese patients and were not affected by MET. A statistically significant increase (p<0.01), however, was observed for the 'decremental' area of lactate in obese subjects with diabetes or FHD, which might probably contribute to the reduction of insulin resistance induced by the drug in these patients.

CONCLUSIONS

Although the low number of subjects studied precludes absolute conclusions, data would suggest that MET improved ISI towards glucose but not towards FFA, in the diabetic and 'prediabetic' obese patients, whereas worsened it in the obese subjects without FHD. Therefore, the effects of MET would not be secondary to changes of FFA but rather to a primary action of MET on glucose metabolism. Thus, utilization of MET to treat the insulin resistance in obesity is indicated only in the presence of alterations of glucose metabolism or FHD.

Insulin-lowering agents in the management of polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is a medical condition that has brought multiple specialists together. Gynecologists, endocrinologists, cardiologists, pediatricians, and dermatologists are all concerned with PCOS patients and share research data and design clinical trials to learn more about the syndrome. Insulin resistance is a common feature of PCOS and is more marked in obese women, suggesting that PCOS and obesity have a synergistic effect on the magnitude of the insulin disorder. Hyperinsulinemia associated with insulin resistance has been causally linked to all features of the syndrome, such as hyperandrogenism, reproductive disorders, acne, hirsutism, and metabolic disturbances. Women with PCOS should be evaluated for cardiovascular risk factors, such as lipid profile and blood pressure. Modification of diet and lifestyle should be suggested to those who are obese. Several insulin-lowering agents have been tested in the management of PCOS. In particular, metformin is the only drug currently in widespread clinical use for treatment of PCOS. In a high percentage of patients, treatment with metformin is followed by regularization of menstrual cycle, reduction in hyperandrogenism and in cardiovascular risk factors, and improvement in response to therapies for induction of ovulation.

Medical care from childhood to adulthood in type 1 and type 2 diabetes

Diabetes mellitus comprises a heterogeneous group of diseases that have in common the development of macro- and microvascular complications. It is now possible to identify subjects at high risk of Type 1 or Type 2 diabetes, especially in the patient's family members. Preventive interventions are quickly becoming available, and can help delay the onset of the disease and thereby reduce complications in these subjects. Furthermore the correct etiological diagnosis of diabetes is fundamental in providing the best treatment for the patient. Maturity-onset diabetes of the young (MODY) syndrome should be suspected in cases of a subtle onset of diabetes and autosomal dominant inheritance. Mitochondrial DNA mutations should be considered when a diabetic patient also suffers from deafness or if there is a family history of this combination in the mother side of the family. Atypical diabetes has to be identified by the physician to avoid mistakes when the patient enters the non-insulin-dependent phase. In the case of Wolfram's syndrome a gene analysis for each family member should be performed to identify heterozygote subjects. Recently, many discoveries in genetics help us better understand the pathogenesis of the diseases and diagnose the monogenic form of diabetes more easily. If all family members are followed in the same center, clues from the family history are readily available for differential diagnosis and preventive interventions can be established more effectively.

Metabolic effects of metformin in patients with impaired glucose tolerance

AIMS

To assess the effect of metformin on insulin sensitivity, glucose tolerance and components of the metabolic syndrome in patients with impaired glucose tolerance (IGT).

METHODS

Forty first-degree relatives of patients with Type 2 diabetes fulfilling WHO criteria for IGT and participating in the Botnia study in Finland were randomized to treatment with either metformin 500 mg b.i.d. or placebo for 6 months. An oral glucose tolerance test (OGTT) and a euglycaemic hyperinsulinaemic clamp in combination with indirect calorimetry was performed at 0 and 6 months. The patients were followed after stopping treatment for another 6 months in an open trial and a repeat OGTT was performed at 12 months.

RESULTS

Metformin treatment resulted in a 20% improvement in insulin-stimulated glucose metabolism (from 28.7 +/- 13 to 34.4 +/- 10.7 micromol/kg fat-free mass (FFM)/min) compared with placebo (P = 0.01), which was primarily due to an increase in glucose oxidation (from 16.6 +/- 3.6 to 19.1 +/- 4.4 micromol/kg FFM; P = 0.03) These changes were associated with a minimal improvement in glucose tolerance, which was maintained after 12 months.

CONCLUSIONS

Metformin improves insulin sensitivity in subjects with IGT primarily by reversal of the glucose fatty acid cycle. Obviously large multicentre studies are needed to establish whether these effects are sufficient to prevent progression to manifest Type 2 diabetes and associated cardiovascular morbidity and mortality. Diabet. Med. 18, 578-583 (2001)

Pathophysiology and pharmacological treatment of insulin resistance

Diabetes mellitus type 2 is a world-wide growing health problem affecting more than 150 million people at the beginning of the new millennium. It is believed that this number will double in the next 25 yr. The pathophysiological hallmarks of type 2 diabetes mellitus consist of insulin resistance, pancreatic beta-cell dysfunction, and increased endogenous glucose production. To reduce the marked increase of cardiovascular mortality of type 2 diabetic subjects, optimal treatment aims at normalization of body weight, glycemia, blood pressure, and lipidemia. This review focuses on the pathophysiology and molecular pathogenesis of insulin resistance and on the capability of antihyperglycemic pharmacological agents to treat insulin resistance, i.e., a-glucosidase inhibitors, biguanides, thiazolidinediones, sulfonylureas, and insulin. Finally, a rational treatment approach is proposed based on the dynamic pathophysiological abnormalities of this highly heterogeneous and progressive disease.

Inhibitory effect of metformin on intestinal glucose absorption in the perfused rat intestine

To investigate the effect of metformin on intestinal glucose absorption, a perfusion study of the intestine was performed in the rat. Male Wistar albino rats (8 weeks old) were used in the present study. The glucose absorption by the perfused intestine (788.1+/-81.9 micromol/30 min) was not changed significantly by the direct addition of metformin (90 microg/mL) to the perfusing medium (737.0+/-118.2 micromol/30 min) or by intraduodenal metformin (250 mg/kg in saline solution) infusion (772.8+/-106.3 micromol/30 min). In rats orally administered metformin (250 mg/kg) for 5 days, glucose absorption by the perfused intestine (375.0+/-164.3 micromol/30 min) was significantly (P<0.001) lower than that in control rats (811.0+/-83.1 micromol/30 min). These results indicate that metformin had a significant effect on the digestive tract, and that metformin treatment exerted an inhibitory effect on intestinal glucose absorption in the rat.

Pharmacologic therapy for type 2 diabetes mellitus

Type 2 diabetes mellitus is a chronic metabolic disorder that results from defects in both insulin secretion and insulin action. An elevated rate of basal hepatic glucose production in the presence of hyperinsulinemia is the primary cause of fasting hyperglycemia; after a meal, impaired suppression of hepatic glucose production by insulin and decreased insulin-mediated glucose uptake by muscle contribute almost equally to postprandial hyperglycemia. In the United States, five classes of oral agents, each of which works through a different mechanism of action, are currently available to improve glycemic control in patients with type 2 diabetes. The recently completed United Kingdom Prospective Diabetes Study (UKPDS) has shown that type 2 diabetes mellitus is a progressive disorder that can be treated initially with oral agent monotherapy but will eventually require the addition of other oral agents, and that in many patients, insulin therapy will be needed to achieve targeted glycemic levels. In the UKPDS, improved glycemic control, irrespective of the agent used (sulfonylureas, metformin, or insulin), decreased the incidence of microvascular complications (retinopathy, neuropathy, and nephropathy). This review examines the goals of antihyperglycemic therapy and reviews the mechanism of action, efficacy, nonglycemic benefits, cost, and safety profile of each of the five approved classes of oral agents. A rationale for the use of these oral agents as monotherapy, in combination with each other, and in combination with insulin is provided.

Metformin treatment leads to an increase in basal, but not insulin-stimulated, glucose disposal in obese patients with impaired glucose tolerance

AIMS

This study was initiated to test the hypothesis that metformin treatment leads to enhanced glucose disposal at ambient insulin concentrations.

METHODS

Nineteen obese patients with impaired glucose tolerance (IGT) were treated with either metformin or placebo in a randomized, double-blind, placebo-controlled, cross-over study. Insulin secretion and insulin resistance were quantified using the homeostasis model assessment (HOMA) and insulin-stimulated glucose disposal were measured by determining the steady-state plasma glucose (SSPG).

RESULTS

The average benefit of metformin was 0.6 mmol/l for glucose (95% confidence interval (CI) 0.2-0.9 P = 0.002), 2.8 pmol/l for insulin (95% CI 0.2-5.4, P = 0.019). Insulin resistance, as quantified by HOMA, was improved by 1.1 (95% CI 0.2-2.0, P = 0.004), without any change in insulin secretion. Basal and insulin-stimulated glucose oxidation were comparable in the placebo and metformin-treated groups at the end of each treatment period, as was the SSPG concentration. However, both systolic and diastolic blood pressures fell significantly following metformin administration as compared to treatment with placebo.

CONCLUSIONS

These results indicate that metformin administration to patients with IGT is associated with enhanced glucose disposal at baseline insulin concentrations and a fall in blood pressure. In contrast, neither glucose oxidation nor glucose disposal were increased in association with metformin treatment under conditions of physiological hyperinsulinaemia.

Troglitazone and metformin, but not glibenclamide, decrease blood pressure in Otsuka Long Evans Tokushima Fatty rats

To determine whether hypoglycemic agents such as sulfonylureas, biguanides and the newly developed insulin sensitizers such as troglitazone, have hypotensive effects in an animal model of non-insulin-dependent diabetes mellitus associated with insulin resistance, male Otsuka Long Evans Tokushima Fatty (OLETF) rats aged 12 weeks were administered following hypoglycemic agents or vehicle by gavage for 26 weeks; glibenclamide (5 mg/kg/day), metformin (100 mg/kg/day) and troglitazone (70 mg/kg/day). The gain in body weight was similar in the different groups. At 36 weeks of age, troglitazone significantly decreased fasting plasma glucose levels when compared to controls. The area under the curve (AUC) for insulin during glucose loading (2 g/kg, i.p.) was 50% lower in the group treated with troglitazone. Serum triglyceride levels in troglitazone-treated rats were also significantly lower than in the glibenclamide-treated group. Plasma membrane GLUT4 protein content was significantly augmented by a factor of 1.48-fold (p<0.02) in the glibenclamide-treated group and tended to be increased 1.32 times by administration of metformin (p=0.06). The systolic blood pressure increased with age in controls and the glibenclamide-treated group. In contrast, treatment with either metformin or troglitazone significantly decreased systolic blood pressure after the age of 29 weeks. Plasma norepinephrine and epinephrine concentrations did not show a significant decrease in the treated group when compared with the control group. These results suggest that metformin and troglitazone, but not glibenclamide, lower blood pressure in an animal model of insulin resistance, providing further evidence of the beneficial effect of insulin sensitizing hypoglycemic agents on blood pressure.

The Diabetes Prevention Program. Design and methods for a clinical trial in the prevention of type 2 diabetes

The Diabetes Prevention Program is a randomized clinical trial testing strategies to prevent or delay the development of type 2 diabetes in high-risk individuals with elevated fasting plasma glucose concentrations and impaired glucose tolerance. The 27 clinical centers in the U.S. are recruiting at least 3,000 participants of both sexes, approximately 50% of whom are minority patients and 20% of whom are > or = 65 years old, to be assigned at random to one of three intervention groups: an intensive lifestyle intervention focusing on a healthy diet and exercise and two masked medication treatment groups--metformin or placebo--combined with standard diet and exercise recommendations. Participants are being recruited during a 2 2/3-year period, and all will be followed for an additional 3 1/3 to 5 years after the close of recruitment to a common closing date in 2002. The primary outcome is the development of diabetes, diagnosed by fasting or post-challenge plasma glucose concentrations meeting the 1997 American Diabetes Association criteria. The 3,000 participants will provide 90% power to detect a 33% reduction in an expected diabetes incidence rate of at least 6.5% per year in the placebo group. Secondary outcomes include cardiovascular disease and its risk factors; changes in glycemia, beta-cell function, insulin sensitivity, obesity, diet, physical activity, and health-related quality of life; and occurrence of adverse events. A fourth treatment group--troglitazone combined with standard diet and exercise recommendations--was included initially but discontinued because of the liver toxicity of the drug. This randomized clinical trial will test the possibility of preventing or delaying the onset of type 2 diabetes in individuals at high risk.

Insulin and polycystic ovary syndrome: a new look at an old subject

In recent years the metabolic implications of polycystic ovary syndrome (PCOS) have received a great deal of attention; in fact 50% of women with PCOS are obese and a similar percentage of subjects was found to show exaggerated insulin secretion and reduced insulin-stimulated glucose uptake. The presence of these features in women with PCOS has profound clinical implications in terms of morbidity due to diabetes mellitus, dyslipidemia, hypertension and cardiovascular disease. Moreover, hyperinsulinemia has recently been proposed as a possible independent risk factor for endometrial and breast cancer. In the light of these considerations, the importance of metabolic screening in patients with PCOS in order to improve their quality of life cannot be underestimated. In this review we analyze all the clinical pathologies in which hyperinsulinemia of PCOS could be involved. Furthermore, in order to clarify the possible mechanisms leading to the insulin disorders of the syndrome, we review the available data about the insulin receptor abnormalities, as well as those concerning the insulin resistance and the exaggerated insulin secretion. Finally, we examine the main therapeutic strategies to ameliorate the insulinemic status of PCOS patients in order to potentially be able to prevent the long-term consequences of this syndrome.

Type 2 diabetes care: the role of insulin-sensitizing agents and practical implications for cardiovascular disease prevention

Millions of Americans are at risk for cardiovascular morbidity and mortality related to disorders of glucose intolerance--particularly type 2 diabetes and prediabetic conditions, including the insulin resistance, or "cardiovascular dysmetabolic," syndrome. The latter is apparently more intricately associated with macrovascular disease--myocardial infarction, stroke, and peripheral vascular disease. In some situations the risk of cardiovascular disease might be reduced by the prevention of diabetes and also by prevention or treatment of the cardiovascular dysmetabolic syndrome. Studies have shown that intensive glycemic control can delay the development of microvascular complications in type 1, and possibly type 2, diabetes. Several longitudinal observational studies have demonstrated a relationship between glycemic control and the development of cardiovascular disease. Prospective clinical intervention trials to address this issue are underway. Insulin may have a role in atherogenesis, both directly and by promoting development of such risk factors as hypertension and dyslipidemia. Genetic factors and mechanisms promoting or discouraging development of glucose intolerance are also under investigation. Lifestyle changes--dietary and exercise modification, weight loss, and smoking cessation--have been shown to have a positive effect on cardiovascular disease risk. Clinical trials suggest that oral antidiabetic agents--particularly the new noninsulin secretagogues (including troglitazone and metformin, which act on the liver and on skeletal muscle)--may be useful in delaying or preventing development of type 2 diabetes and the cardiovascular dysmetabolic syndrome, as well as in their treatment, when present. Both agents, acting primarily by different mechanisms of action, have also demonstrated potential beneficial effects on serum lipid profiles and other cardiovascular risk factors and may be useful in patients with cardiovascular dysmetabolic syndrome who do not yet meet the criteria for diabetes.

Prevention of type 2 diabetes

Type 2 diabetes is a major cause of morbidity and mortality resulting from its microangiopathic and macroangiopathic complications. Current approaches to its management and to the prevention of diabetic complications are difficult to implement effectively, and there is little evidence to date that these approaches are reducing the impact of this disease. The recognition that type 2 diabetes usually has a prolonged prediabetic phase raises the possibility that the emergence of hyperglycemia and the atherosclerotic complications associated with diabetes may be preventable by the institution of early treatment modalities. Sufficient data suggest that life-style modification or pharmacotherapy directed at improving insulin sensitivity or insulin secretion in subjects with impaired glucose tolerance may reduce progression to diabetes. Two long-term prospective, controlled trials have been initiated to test this hypothesis.

Efficacy of metformin in type II diabetes: results of a double-blind, placebo-controlled, dose-response trial

PURPOSE

To study the efficacy and safety of various dosages of metformin as compared with placebo in patients with type II diabetes mellitus.

PATIENTS AND METHODS

A 14-week, multicenter, double-blind, dose-response study was conducted. After a 3-week, single-blind, placebo-controlled washout, 451 patients with fasting plasma glucose levels of at least 180 mg/dL were randomized to receive an 11-week course of placebo or metformin given at 500, 1000, 1500, 2000, or 2500 mg daily.

RESULTS

Metformin improved glucose variables as compared with placebo. The adjusted mean changes in fasting plasma glucose from baseline associated with each metformin group at week 7, 11, or at endpoint exceeded those associated with placebo by 19 to 84 mg/dL at dosages of 500 to 2000 mg daily, respectively. The corresponding between-group differences in glycated hemoglobin (HbA1c) ranged from 0.6% to 2.0% at dosages of 500 to 2000 mg daily, respectively. All between-group differences were significant (P < 0.05) for both fasting plasma glucose and HbA1c at week 7, week 11, and endpoint, except for the difference between placebo and metformin 500 mg in fasting plasma glucose at endpoint (P = 0.054). Treatment-related adverse events occurred in 15% of patients in the placebo group and in 28% in the metformin group (P = 0.02); these were primarily manifested as digestive disturbances, such as diarrhea.

CONCLUSIONS

Metformin lowered fasting plasma glucose and HbA1c generally in a dose-related manner. Benefits were observed with as little as 500 mg of metformin; maximal benefits were observed at the upper limits of the recommended daily dosage. All dosages were well tolerated. Metformin appears to be a useful therapeutic option for physicians who wish to titrate drug therapy to achieve target glucose concentrations.

An overview of metformin in the treatment of type 2 diabetes mellitus

Type 2 diabetes mellitus results from impaired insulin secretion and reduced peripheral insulin sensitivity. Treatment options include diet, oral antihyperglycemic agents, and insulin. Metformin, an oral biguanide, ameliorates hyperglycemia by improving peripheral sensitivity to insulin, and reducing gastrointestinal glucose absorption and hepatic glucose production. Unlike sulfonylureas, it does not stimulate insulin secretion, aggravate hyperinsulinemia, or cause hypoglycemia or weight gain (weight stabilizes or decreases). It also has beneficial effects on serum lipid profiles. In lean or overweight type 2 diabetic patients uncontrolled by diet, metformin monotherapy significantly improves glycemic control, compared with placebo, and to similar extents as sulfonylurea monotherapy. In secondary sulfonylurea failure, combination metformin-sulfonylurea treatment significantly improves glycemic control beyond that achieved with either agent along. Metformin-sulfonylurea also appears to be as effective as insulin or insulin plus sulfonylurea, suggesting that such combination therapy may obviate or substantially delay insulin therapy. Limited data suggest that metformin-insulin therapy may improve glycemic control, possibly reducing insulin requirements, in type 2 diabetic patients uncontrolled by insulin alone following secondary sulfonylurea failure. Gastrointestinal side effects are common, but usually tolerated. Lactic acidosis risk is minimal, provided that contraindications, particularly renal impairment, and prescribing guidelines are respected. Aside from elevated plasma metformin levels with cimetidine and synergistic hypoglycemia with sulfonylureas, few interactions occur. Thus, metformin is safe and effective both as monotherapy or in combination with other antihyperglycemic agents in type 2 diabetic patients requiring additional glycemic control and may be advantageous when weight control is desirable and/or hyperlipidemia exists.

Prevention of hyperglycemia in the Zucker diabetic fatty rat by treatment with metformin or troglitazone

To determine whether metformin or troglitazone can delay the onset of diabetes in the Zucker diabetic fatty (ZDF) rat, lean control, fatty, and ZDF rats received metformin, troglitazone, or no treatment from 6 to 12 wk of age. Glucose, insulin, triglyceride (TG), and free fatty acid (FFA) levels and glucose stimulated insulin secretion by the perfused pancreas were measured. Metformin-treated rats gained significantly less weight. Both drugs prevented hyperglycemia by 12 wk in diabetic rats and significantly reduced TG and FFA levels. Insulin secretion at low glucose was elevated in untreated fatty and diabetic animals, and the increment in diabetic animals produced by glucose perfusion was attenuated compared with lean and fatty rats. Both drugs reduced basal insulin secretion in fatty and diabetic rats and improved glucose responsiveness in diabetic rats. Metformin and troglitazone delay the onset of diabetes in the ZDF rat. The significantly improved insulin secretory response of the pancreas undoubtedly contributes to the improved glucose tolerance.