Oral Antidiabetic Therapy in Patients with Heart Disease

Synthesis of 2-(4-hydroxyphenyl)ethyl 3,4,5-Trihydroxybenzoate and Its Inhibitory Effect on Sucrase and Maltase

We report on the synthesis of an active component, 2-(4-hydroxyphenyl)ethyl 3,4,5-trihydroxybenzoate (HETB), from Rhodiola crenulata. Subsequent analysis revealed that HETB exhibits α-glucosidase inhibitory activities on maltase and sucrase, with potency exceeding that of the known α-glucosidase inhibitors (voglibose and acarbose). An inhibition kinetics study revealed that HETB, acarbose, and voglibose bind to maltase and sucrase, and HETB was shown to be a strong competitive inhibitor of maltase and sucrase. In a molecular docking study based on the crystal structure of α-glucosidase from Saccharomyces cerevisiae, we revealed the HETB binding in the active site of maltase via hydrogen-bond interactions with five amino acid residues: Ser 240, Asp 242, Glu 277, Arg 315, and Asn 350. For HETB docked to the sucrase active site, seven hydrogen bonds (with Asn 114, Glu 148, Gln 201, Asn 228, Gln 381, Ile 383, and Ser 412) were shown.

Antidiabetic and antihyperlipidemic activity of hydroalcoholic extract of Withania coagulans Dunal dried fruit in experimental rat models

Objective:

Evaluation of antidiabetic potential of the hydroalcoholic extract of Withania coagulans Dunal dried fruit (WCDF) alone and in combination with glipizide, in streptozotocin-induced diabetes, and evaluation of possible antihyperlipidemic activity of the same extract in high-cholesterol diet-induced hyperlipidemia, in albino rats.

Materials and Methods:

Experimental diabetes was induced in 30 albino rats with intraperitoneal injection of streptozotocin (55 mg/kg). The rats were divided into five groups receiving the following treatments orally for 4 weeks: Vehicle, glipizide (2.5 mg/kg), WCDF extract (1000 mg/kg), WCDF extract (1000 mg/kg) plus glipizide (1 mg/kg) and WCDF extract (1000 mg/kg) plus glipizide (2.5 mg/kg). Fasting and postprandial blood glucose levels were measured every week for 4 weeks. Endocrine pancreas histopathology was done at the end. In a separate set of experiment, five groups of six albino rats each, received orally for 4 weeks, vehicle, cholesterol (25 mg/kg/day), cholesterol (25 mg/kg/day) plus atorvastatin (7.2 mg/kg/day), cholesterol (25 mg/kg/day) plus WCDF extract (1000 mg/kg/day) and no treatment, respectively. Estimation of serum lipid profile and liver histopathology was done at the end of 4 weeks.

Statistical Analysis:

Between-group and within-group comparisons were respectively done by analysis of variance (ANOVA) and repeated measures ANOVA, followed by post hoc Tukey's test, with a significance level of P < 0.05.

Results and Conclusions:

The 4-week treatment with WCDF extract significantly reversed hyperglycemia in streptozotocin-induced diabetes that was comparable to glipizide. When combined with glipizide (2.5 mg/kg), WCDF extract produced a synergistic antihyperglycemic effect as well as improvement in pancreatic histopathology. Moreover, hydroalcoholic extract of WCDF was effective and comparable to atorvastatin in controlling the high-cholesterol diet-induced hyperlipidemia in rats.

Metformin and heart failure: never say never again

Metformin represents the cornerstone of treatment for type 2 diabetes mellitus. Traditionally, heart failure (HF) was considered a contraindication to its use. However, more recent evidence has shown that this should no longer be the case. Indeed, studies have demonstrated that metformin may even reduce the risk of incident HF and mortality in diabetic patients, while improving up to 2-year survival rates in those with HF. In addition, it appears to exert cardioprotective actions. Although longer follow-up data and more explicit information about the situation in patients with very advanced HF are needed, the cardiac safety of metformin has profound clinical implications and may be anticipated to further encourage its widespread use.

Understanding the cardiovascular effects of incretin

Cardiovascular disease (CVD), a leading cause of death in patients with diabetes mellitus, has several pathogenic mechanisms that are well established. However, the traditional hypoglycemic agents do not have proven positive effects on macrovascular disease. Novel therapeutic agents target the incretin pathway including the glucagon-like peptide 1 (GLP-1) receptor (GLP-1R) agonists and the dipeptidyl peptidase-4 inhibitors. The glucose-regulatory actions of these agents function by increasing insulin secretion and suppressing glucagon. They also act to increase weight loss not only by inhibiting gastric emptying, but also by reducing appetite. Although GLP-1 and GLP-1R agonists have demonstrated beneficial effects on myocardium and vascular endothelium including coronary and peripheral mouse vessels, they also have anti-inflammatory and anti-atherogenic actions. These agents also have positive effects on the lipid profile and blood pressure. Although these cardioprotective actions seem to be beyond the effects of glucose control and weight loss, they are mediated through GLP-1R- or GLP-1R-independent actions of cleaved GLP-1 (9-36). Larger randomized controlled trials are necessary to elucidate the clinical promise of these beneficial CVD effects.

Cardiovascular prevention in type 2 diabetes mellitus patients: the role of oral glucose-lowering agents

Diabetes mellitus (DM) is a metabolic disorder that requires medical diagnosis and treatment. Type 2 DM is due to a combination of defective secretion of and responsiveness to insulin. In early stages, the predominant abnormality is reduced insulin sensitivity, and hyperglycemia can be reversed by a variety of measures and medications. In this stage, the cornerstone of glucose-lowering therapy is lifestyle modification, but when counseling does not adequately achieve the recommended glycemic targets, at least five classes of oral drugs are available. In general, alpha-glucosidase inhibitors delay carbohydrate absorption, metiglinides and sulfonylureas increase insulin supply, and biguanides and thiazolidinediones enhance insulin action. Given the high cardiovascular morbidity and mortality in type 2 DM patients, the attempt to reduce cardiovascular complications, beyond the glucose lowering itself, is an extremely relevant task. Indeed, the role of oral glucose-lowering agents concerning hyperglycemia reduction is defined; however, they have not clearly demonstrated to reduce micro- and macrovascular disease, and hitherto, no firm evidence favors one pharmacological treatment over another. The aim of this update is to describe the existing experiences with oral glucose-lowering agents for type 2 DM treatment with respect to cardiovascular prevention.

A cardiologic approach to non-insulin antidiabetic pharmacotherapy in patients with heart disease

Classical non-insulin antihyperglycemic drugs currently approved for the treatment of type 2 diabetes mellitus (T2DM) comprise five groups: biguanides, sulfonylureas, meglitinides, glitazones and alpha-glucosidase inhibitors. Novel compounds are represented by the incretin mimetic drugs like glucagon like peptide-1 (GLP-1), the dipeptidyl peptidase 4 (DPP-4) inhibitors, dual peroxisome proliferator-activated receptors (PPAR) agonists (glitazars) and amylin mimetic drugs. We review the cardiovascular effects of these drugs in an attempt to improve knowledge regarding their potential risks when treating T2DM in cardiac patients. Metformin may lead to lethal lactic acidosis, especially in patients with clinical conditions that predispose to this complication, such as recent myocardial infarction, heart or renal failure. Sulfonylureas exert their effect by closing the ATP-dependent potassium channels. This prevents the opening of these channels during myocardial ischemia, impeding the necessary hyperpolarization that protects the cell. The combined sulfonylurea/metformin therapy reveals additive effects on mortality in patients with coronary artery disease (CAD). Meglitinides effects are similar to those of sulfonylureas, due to their almost analogous mechanism of action. Glitazones lower leptin levels, leading to weight gain and are unsafe in NYHA class III or IV. The long-term effects of alpha-glucosidase inhibitors on morbidity and mortality rates is yet unknown. The incretin GLP-1 is associated with reductions in body weight and appears to present positive inotropic effects. DPP-4 inhibitors influences on the cardiovascular system seem to be neutral and patients do not gain weight. The future of glitazars is presently uncertain following concerns about their safety. The amylin mimetic drug paramlintide, while a satisfactory adjuvant medication in insulin-dependent diabetes, is unlikely to play a major role in the management of T2DM. Summarizing the present information it can be stated that 1. Four out the five classical oral antidiabetic drug groups present proven or potential cardiac hazards; 2. These hazards are not mere 'side effects', but biochemical phenomena which are deeply rooted in the drugs' mechanism of action; 3. Current data indicate that the combined glibenclamide/metformin therapy seems to present special risk and should be avoided in the long-term management of T2DM with proven CAD; 4. Glitazones should be avoided in patients with overt heart failure; 5, The novel incretin mimetic drugs and DPP-4 inhibitors--while usually inadequate as monotherapy--appear to be satisfactory adjuvant drugs due to the lack of known undesirable cardiovascular effects; 6. Customized antihyperglycemic pharmacological approaches should be implemented for the achievement of optimal treatment of T2DM patients with heart disease. In this context, it should be carefully taken into consideration whether the leading clinical status is CAD or heart failure.

Heart failure in sub-Saharan Africa: a literature review with emphasis on individuals with diabetes

PURPOSE

Heart failure is the ultimate complication of cardiac involvements in diabetes. The purpose of this review was to summarize current literature on heart failure among people with diabetes mellitus in sub-Saharan Africa (SSA).

METHOD

Bibliographic search of published data on heart failure and diabetes in sub-Saharan Africa over the past 26 years.

RESULTS

Heart failure remains largely unexplored in general population and among people with diabetes in Africa. Heart failure accounts for over 30% of hospital admission in specialized cardiovascular units and 3%-7% in general internal medicine. Over 11% of adults with heart failure have diabetes. Risk factors for heart failure among those with diabetes include classical cardiovascular risk factors, without evidence of diabetes distinctiveness for other predictors common in Africa. Prevention, management, and outcomes of heart failure are less well known; recent data suggest improvement in the management of risk factors in clinical settings.

CONCLUSIONS

Diabetes mellitus is growing in SSA. Related cardiovascular diseases are emerging as potential health problem. Heart failure as cardiovascular complication remains largely unexplored. Efforts are needed through research to improve our knowledge of heart failure at large in Africa. Multilevel preventive measures, building on evidences from other parts of the world must go along side.

'Warm-up' phenomenon in diabetic patients with stable angina treated with diet or sulfonylureas

BACKGROUND

Classic sulfonyloureas (SUs) are known to attenuate ischaemic preconditioning. Gliclazide is an SU agent believed to be more protective. We assessed the effects of diet, glibenclamide, or gliclazide on the warm-up effect in type 2 diabetic patients with stable angina.

METHODS

The study group consisted of 64 men, aged 54+/-5 years: 17 patients without diabetes (G I) and 47 diabetic patients: 16 patients treated with glibenclamide (G II), 16 with gliclazide (G III) and 15 patients treated with diet (G IV). After the baseline positive exercise test (ET1), all patients reexercised after 30-min rest (ET2). We analysed exercise duration (ED, s), time to 1 mm ST depression (T-STD, s), max STD (mm), heart rate-systolic blood pressure product at 1 mm STD, or ischaemic threshold (mmHg/min x 100) and the total ischaemic time (s).

RESULTS

In G I, all analysed variables improved significantly during ET2 relative to ET1. Glibenclamide (G II) completely abolished the protective effect of exercise-induced ischaemia because only ED increased during ET2 (431 vs. 451, P<0.05). In G III, however, ED (486 vs. 537, P<0.001), T-STD (364 vs. 388, P<0.05) and max STD (2.5 vs. 2.0, P<0.05) improved significantly during ET2, whereas ischaemic threshold and total ischaemic time did not (PNS). In G IV, similar to G I, all variables improved significantly during ET2 relative to ET1.

CONCLUSION

Warm-up effect is preserved in diabetic patients with stable angina treated with diet, partially preserved in gliclazide-treated and abolished in glibenclamide-treated patients.

Review of the pleiotropic effects of peroxisome proliferator-activated receptor gamma agonists on platelet function

The primary target receptor for thiazolidinediones (TZDs) or peroxisome proliferator-activated receptor gamma (PPARgamma) agonists is a transcription factor in the nucleus of adipocytes and other metabolically active cells, where they improve insulin sensitivity and glucose utilization. TZDs are also able to modify gene expression in macrophages, smooth muscle cells, and endothelial cells. Although PPARgamma is considered to be a nuclear receptor, enucleate platelets also highly express this receptor. The aim of this review is to present the current understanding of a direct or indirect effect of TZDs on platelet function. By means of a comprehensive literature search (January 1990-June 2006), publications were obtained that contained specific information about in vitro and in vivo effects of TZDs on platelet function. The effects were studied for different risk biochemical markers, i.e., proteins found to be elevated in the state of procoagulant inflammation and endothelial dysfunction. Improvement of platelet function was reported for all TZDs-troglitazone, pioglitazone, and rosiglitazone. The described effects included reduction of platelet aggregation, suppression of thrombin-induced protein kinase C-alpha and -beta activation, decrease in plasma P-selectin and platelet P-selectin expression, increase in nitric oxide production, inhibition of the Rho/Rho kinase pathway, and inhibition of tissue factor- and platelet-activating factor-induced morphological changes in macrophages. These findings appeared in parallel with reduction of the plasma concentrations of pro-inflammatory risk markers. TZDs seem to have a direct pleiotropic positive influence on platelet function and coagulation and may be helpful in treating the prothrombotic state observed in patients with type 2 diabetes and metabolic syndrome.

Hypolipidemic effects of acute and sub-chronic administration of an aqueous extract of Ajuga iva L. whole plant in normal and diabetic rats

Diabetes is often accompanied by lipid abnormalities, which contribute significantly to cardiovascular (CV) morbidity and mortality in diabetic patients. The plant Ajuga iva (L.) Schreiber (Labiatea) is used in the treatment of diabetes in Moroccan folk medicine. Previously, we have demonstrated potent hypoglycemic activity and relatively non-toxic nature of a lyophilized aqueous extract of the whole plant (AI-extract) in normal (normoglycemic) and streptozotocin (STZ)-diabetic rats. In this study, we examined the AI-extract for its possible lipid-lowering activity in normal and STZ-diabetic rats. Taurine (TR) and glibenclamide (GLB) were used as reference substances. As shown previously, the AI-extract (10 mg/kg; oral) reduced plasma glucose levels after acute (single) and sub-chronic (3 weeks) dosing both in normal and diabetic rats. In normal rats, single and repeated oral administration of the AI-extract, at a dose of 10 mg/kg produced a small but significant decrease in plasma CHL levels (P<0.05). A single dose of the AI-extract did not produce a significant change in plasma TG, but sub-chronic dosing (for up to 21 days) caused a significant decrease in plasma TG (P<0.05). In STZ-diabetic rats, a single dose as well as repeated (3 weeks) treatment with the AI-extract produced a significant decrease in plasma CHL (P<0.01), and triglyceride (P<0.01) levels. The AI-extract also prevented weight loss in the diabetic animals. In summary, an aqueous extract of the Ajuga iva whole plant showed hypolipidemic activity, in addition to its hypoglycemic effect in normoglycemic and diabetic rats. In view of the hypoglycemic and hypolipidemic activity, and its relatively non-toxic nature (shown previously), Ajuga iva may be a candidate for development as an anti-diabetic agent in humans. Further studies are warranted to confirm our results and fractionate the AI-extract to isolate and identify the active principle(s), and to determine the exact mechanism(s) of action.