The role of oral antidiabetic agents: why and when to use an early-phase insulin secretion agent in Type II diabetes mellitus

Synthesis and biological evaluation of 4-hydroxy-5-oxo-2,5-dihydro-1H-pyrrole-3-carboxamides and their zinc(ii) complexes as candidate antidiabetic agents

Five new zinc(ii) complexes with 4-hydroxy-5-oxo-2,5-dihydro-1H-pyrrole-3-carboxamides were synthesized, and four of them exhibited insulin-mimetic activity in vitro.

Recovery of oral glucose tolerance by Wistar rats after treatment with Coreopsis tinctoria infusion

Infusions of Coreopsis tinctoria flowering tops have traditionally been used in Portugal to control hyperglycaemia but no pharmacological or toxicological studies have been reported until now. The chalcones marein and okanin were isolated from the aqueous extract, together with the 2S-3',4',7,8-tetrahydroxyflavanone. The content of marein in extracts was determined by HPLC-UV and the radical scavenging capacity evaluated by the DPPH method (EC(50) = 21 microg/mL). Glucose intolerance was induced by a single intraperitoneal injection of streptozotocin in saline (40 mg/Kg). After three weeks of oral treatment with C. tinctoria extract (500 mg/Kg/day) the animals were no longer glucose-intolerant (p > 0.05). Additionally, this oral treatment caused no hepatotoxicity in the rats, as determined by blood alanine and aspartate transaminases. A single administration of extract had no effect on oral glucose tolerance in normal Wistar rats. The extract also had no effect on insulin secretion by MIN6 cells. In conclusion, C. tinctoria infusion is able to abolish the streptozotocin-induced glucose-intolerance in rats after three weeks of oral treatment by a mechanism other than induction of insulin secretion. The recovery of beta-pancreatic function mediated by an antioxidant mechanism is a possibility that deserves further investigation.

Is the current therapeutic armamentarium in diabetes enough to control the epidemic and its consequences? What are the current shortcomings?

The prevalence of diabetes is expected to rise together with an increase in morbidity and a reduction in life expectancy. A leading cause of death is cardiovascular disease, and hypertension and diabetes are additive risk factors for this complication. Selected treatment options should neither increase cardiovascular risk in patients with diabetes, nor increase risk of hyperglycaemia in patients with hypertension. The efficacy of present antihyperglycaemic agents is limited and new therapies, such as incretin-targeted agents, are under development. Even though most patients do not achieve glycated haemoglobin targets, trial data show that such interventions reduce the incidence of macrovascular events; however, intensive lowering may be detrimental in patients with existing cardiovascular disease. Currently available oral drugs do not address the key driver of type 2 diabetes--loss of functional beta-cell mass. In the future, new oral treatments must improve this, whilst providing durable blood glucose control and long-term tolerability.

Targeting postprandial hyperglycemia

In healthy individuals, blood glucose levels in the fasting state are maintained by the continuous basal-level insulin secretion. After a meal, the rise in postprandial glucose (PPG) is controlled by the rapid pancreatic release of insulin, stimulated by both glucose and the intestinal production of the incretins glucose-dependent insulinotropic polypeptide and glucagon-like peptide 1. In diabetic individuals, postprandial insulin secretion is insufficient to suppress an excessive rise in PPG. There is increasing evidence that elevated PPG exerts a more deleterious effect on the vascular system than elevation of fasting plasma glucose. In particular, individuals with normal fasting plasma glucose but impaired glucose tolerance have significantly increased risk of cardiovascular events. With the recognition of the importance of PPG and the availability of new pharmacologic options, management of diabetes will shift to greater attention to PPG levels. The prototype for such an approach is in the treatment of gestational diabetes and diabetic pregnancies where PPG is the primary target of efforts at glycemic control. These efforts have been extremely successful in improving the outlook for diabetic pregnant women. There are many approaches to reduction of PPG; dietary management and promotion of exercise are very effective. Sulfonylureas, meglitinides, metformin, thiazolidinediones, and disaccharidase inhibitors all counteract PPG elevation. The development of glucagon-like peptide 1 agonists such as exendin and dipeptidyl peptidase IV inhibitors such as vildagliptin offers a new approach to suppression of PPG elevation. New semisynthetic insulin analogues permit a more aggressive response to postprandial glucose elevation, with lower risk of hypoglycemia, than with regular insulin. Inhaled insulin also has a rapid onset of action and offers benefits in PPG control. It is proposed that an aggressive treatment approach focusing on PPG, similar to the current standards for diabetic pregancies, be directed at individuals with diabetes and impaired glucose tolerance.

Repaglinide in the management of new-onset diabetes mellitus after renal transplantation

The purpose of this study was to investigate the use of the short-acting insulin secretion drug repaglinide in new-onset diabetes mellitus (NODM) after renal transplantation. Twenty-three Caucasian patients with NODM after renal transplantation were selected to receive repaglinide therapy and were followed for at least 6 months. A control group treated with rosiglitazone was chosen for comparison. Successful repaglinide treatment was defined as a significant improvement of blood glucose concentrations and HbA1c <7% in the absence of glucosuria and without the need for the addition of further anti-diabetic agents. After 6 months of treatment with repaglinide, 14 of the 23 patients were successfully treated. Mean HbA1c decreased from 7.6 +/- 0.6% to 5.8 +/- 0.6% in 14 patients treated successfully. In nine patients, hyperglycemia persisted, and they were switched to insulin treatment (HbA1c 8.5 +/- 2.9% at the beginning to 7.4 +/- 2.2%). Mean serum creatinine levels, cyclosporine A and tacrolimus blood levels did not change significantly following institution of repaglinide therapy. The rate of successful treatment and the degree of HbA1c decrease were similar compared to rosiglitazone-treated control patients. The data from our observational study indicate that repaglinide can be an effective treatment option in Caucasian patients with NODM after renal transplantation.

Characterization of the action of S 21403 (mitiglinide) on insulin secretion and biosynthesis in normal and diabetic beta-cells

S 21403 (mitiglinide) is a new drug for type 2 diabetes mellitus (T2DM). Its action on insulin release and biosynthesis was investigated in several experimental systems utilizing pancreas from normal and T2DM animals. At high concentrations (10 microM), S 21403, like classical sulphonylurea, induced insulin release in the absence of glucose. In contrast, at therapeutic (0.1-1.0 microM) concentrations, S 21403 amplified insulin secretion glucose dose-dependently and with similar magnitude in normal and diabetic GK rat islets. In perfused GK rat pancreas, S 21403 induced normal kinetics of insulin secretion including first-phase response. The effect of S 21403 was strongly modulated by physiological factors. Thus, 0.1 microM adrenaline inhibited S 21403-induced insulin release. There was marked synergism between S 21403 and arginine in GK rat islets, combination of the two normalizing insulin secretion. In primary islet cultures from normal rats or prediabetic Psammomys obesus, prolonged exposure to S 21403 did not induce further depletion of insulin stores under normal or 'glucotoxic' conditions. Proinsulin biosynthesis was not affected by 2-h exposure of rat or prediabetic P. obesus islets to 1 microM S 21403. Yet, 24-h exposure of rat islets to S 21403 resulted in 30% increase in proinsulin biosynthesis at 8.3 mM glucose. Amplification by S 21403 of glucose-induced insulin secretion in diabetic GK beta-cells with restoration of first-phase response, a strong synergistic interaction with arginine and marked inhibition by adrenaline, make it a prime candidate for successful oral antidiabetic agent.

An overview of the rationale for pharmacological strategies in type 2 diabetes: from the evidence to new perspectives

Therapeutic strategies in type 2 diabetic patients should not only integrate both the targets and indications of the different therapies but should be also a compromise between the patient's and physician's goals and willingnesses. The rationale for therapeutic targets is based on recommendations that differ from one country to another. Even though HbA1c remains the "gold standard", monitoring of blood glucose at fasting and postprandial time-points is a complementary tool for estimating both the quality and safety of diabetic control. Despite the lack of available strong evidence-based data it seems that achieving glucose levels < 130 mg/dl at fasting and < 180 mg/dl or < 140 mg/dl over postbreakfast or postlunch periods, respectively, might be a reasonable goal in most countries. The choice of appropriate strategies for treating type 2 diabetic patients should ideally be based on pathophysiological considerations. However for practical reasons, decisions for initiating or completing antidiabetic treatments are usually made by using such simple parameters as HbA1c and plasma glucose levels. The bridge between pathophysiological and clinical rationales can be obtained from the analysis of the relative contributions of fasting and postprandial glucose to the overall hyperglycaemia. In patients with HbA1c < 7.3%, postprandial glucose makes the major contribution to the overall hyperglycaemia, whereas the contribution of fasting glucose becomes progressively predominant in patients with HbA1c > 7.3%. As a consequence of these observations, initiation of antidiabetic treatments or implementation of second-line therapies should be aimed at reducing either postprandial excursions or fasting hyperglycaemia according to whether HbA1c levels are found respectively below or above a cut-off value of 7.3%.