Beta-cell insulin secretory response to oral hypoglycemic agents is blunted in humans in vivo during moderate hypoglycemia

Mechanisms and Characteristics of Sulfonylureas and Glinides

BACKGROUND

Type 2 diabetes mellitus is a complex progressive endocrine disease characterized by hyperglycemia and life-threatening complications. It is the most common disorder of pancreatic cell function that causes insulin deficiency. Sulfonylurea is a class of oral hypoglycemic drugs. Over the past half century, these drugs, together with the subsequent non-sulfonylureas (glinides), have been the main oral drugs for insulin secretion.

OBJECTIVE

Through in-depth study, the medical profession considers it as an important drug for improving blood sugar control.

METHODS

The mechanism, characteristics, efficacy and side effects of sulfonylureas and glinides were reviewed in detail.

RESULTS

Sulfonylureas and glinides not only stimulated the release of insulin from pancreatic cells, but also had many extrapanular hypoglycemic effect, such as reducing the clearance rate of insulin in liver, reducing the secretion of glucagon, and enhancing the sensitivity of peripheral tissues to insulin in type 2 diabetes mellitus.

CONCLUSION

Sulfonylureas and glinides are effective first-line drugs for the treatment of diabetes mellitus. Although they have the risk of hypoglycemia, weight gain and cardiovascular disease, their clinical practicability and safety can be guaranteed as long as they are reasonably used.

The anti-diabetic drug repaglinide induces vasorelaxation via activation of PKA and PKG in aortic smooth muscle

We investigated the vasorelaxant effect of repaglinide and its related signaling pathways using phenylephrine (Phe)-induced pre-contracted aortic rings. Repaglinide induced vasorelaxation in a concentration-dependent manner. The repaglinide-induced vasorelaxation was not affected by removal of the endothelium. In addition, application of a nitric oxide synthase inhibitor (L-NAME) and a small-conductance Ca(2+)-activated K(+) (SKCa) channel inhibitor (apamin) did not alter the vasorelaxant effect of repaglinide on endothelium-intact arteries. Pretreatment with an adenylyl cyclase inhibitor (SQ 22536) or a PKA inhibitor (KT 5720) effectively reduced repaglinide-induced vasorelaxation. Also, pretreatment with a guanylyl cyclase inhibitor (ODQ) or a PKG inhibitor (KT 5823) inhibited repaglinide-induced vasorelaxation. However, pretreatment with a voltage-dependent K(+) (Kv) channel inhibitor (4-AP), ATP-sensitive K(+) (KATP) channel inhibitor (glibenclamide), large-conductance Ca(2+)-activated K(+) (BKCa) channel inhibitor (paxilline), or the inwardly rectifying K(+) (Kir) channel inhibitor (Ba(2+)) did not affect the vasorelaxant effect of repaglinide. Furthermore, pretreatment with a Ca(2+) inhibitor (nifedipine) and a sarco-endoplasmic reticulum Ca(2+)-ATPase (SERCA) inhibitor (thapsigargin) did not affect the vasorelaxant effect of repaglinide. The vasorelaxant effect of repaglinide was not affected by elevated glucose (50mM). Based on these results, we conclude that repaglinide induces vasorelaxation via activation of adenylyl cyclase/PKA and guanylyl cyclase/PKG signaling pathways independently of the endothelium, K(+) channels, Ca(2+) channels, and intracellular Ca(2+) ([Ca(2+)]i).

The effect of glibenclamide on insulin secretion at normal glucose concentrations

AIMS/HYPOTHESIS

The aim of this study was to investigate the incremental and proportional effect of a sulfonylurea on insulin secretion rates at low, elevated and high blood glucose, using parallel groups with ascending or descending glucose steps to minimise potential biases of a single stepped clamp order.

METHODS

Following 14 days on placebo or glibenclamide (2.5 mg) tablets twice daily, separated by 14 days washout, 19 type 2 diabetic patients had ascending or descending three-step hyperinsulinaemic glucose clamps at 4, 8 and 12 mmol/l. C-peptide secretion was estimated by two-compartment C-peptide deconvolution.

RESULTS

Patients in the ascending glucose steps group (n = 10) had mean (SD) age of 60.3 (6.5) years, BMI of 29.8 (4.9) kg/m(2) and fasting glucose on diet alone of 10.6 (2.9) mmol/l; while those in the descending glucose steps group (n = 9) had mean age of 58.2 (8.0) years, BMI of 30.5 (5.4) kg/m(2) and fasting glucose on diet alone of 9.8 (2.2) mmol/l. The geometric means (95% CI) of C-peptide secretion rates on placebo for glucose at 4.0, 8.0 and 12.0 mmol/l were 63 (46, 86), 143 (105, 195) and 205 (149, 281) pmol/min, respectively. On glibenclamide, this increased by 140 (99, 181), 126 (85, 167) and 158 (117, 199) pmol/min, respectively (p < 0.001 vs placebo). The absolute increment was significant (p < 0.001) and independent of clamp glucose concentration (p = 0.54). The proportional increase was greater at 4 mmol/l: 2.8-fold (2.4, 3.2), compared with 1.8-fold (1.5, 2.0) and 1.7-fold (1.4, 1.9) at 8 and 12 mmol/l, respectively (p < 0.001).

CONCLUSIONS/INTERPRETATION

At low-normal glucose, glibenclamide exerted a disproportionate effect on insulin secretion. This study highlights the risks of hypoglycaemia when aiming for tight glucose control on this agent.

Comparison of continual insulin or secretagogue treatment in type 2 diabetic patients with alternate insulin-secretagogue administration

BACKGROUND

To compare the compliance and efficacy among three treatment modalities in patients of type 2 diabetes with fairly good islet function.

METHODS

This 38-month open, randomized, prospective study enrolled 536 subjects (HbA1c 9.4+/-0.8%). Patients were divided into three groups including continual insulin injection (I), continual secretagogue administration (S) and alternation of two-month insulin injection and four-month secretagogue treatment (A). At baseline and every three months, HbA1c was measured and a standard bread meal test (100g) was performed.

RESULTS

HbA1c were better controlled in both groups I and A than in S (6.9+/-0.3%, 6.8+/-0.3% vs. 7.6+/-0.5%). Hypoglycemia incidence was much lower in group A than that in I (0.8 times/patient/month vs. 2.4 times/patient/month) also with less weight gain (1.6 kg vs. 2.8 kg/patient/year). From the standard bread meal test, patients in group A got the greatest increment of 2-h C-peptide. Inquiry from all subjects showed that alternate strategy was welcomed by most of them considering for convenience and efficacy.

CONCLUSIONS

Alternate insulin-secretagogue treatment can effectively reduce HbA1c and help to improve islet function with reduced risk of hypoglycemia and weight gain under good compliance.

Meglitinide analogues: a review of clinical data focused on recent trials

Glinides represent a chemically heterogeneous new class of insulin-secreting agents characterized by a rapid onset and short duration of action. They act by closure of the ATP-dependant K channel. Repaglinide, the only glinide available in France, has an equivalent HbA1c lowering effect to conventional sulfonylureas but reduces predominantly postprandial glucose levels. Several studies indicate a decreased risk of hypoglycaemias, particularly nocturnal or in case of a shift or omission of a meal. This drug appears particularly useful in early stage type 2 diabetes or in combination with metformin. The only significant drug-drug interaction concerns gemfibrozil. Due to its hepatic metabolism and biliary elimination, repaglinide can be used in patients with renal insufficiency. Nateglinide has a even shorter duration of action and has almost no effect on fasting plasma glucose levels. For this reason, this drug is only indicated in combination with metformin in the countries where it is licensed. Several experimental data suggest that glinides could preserve B cell function over time better than hypoglycaemic sulfonylureas, and that the improvement of post-prandial glucose levels could exert a long term protective cardiovascular effect.

Dual mechanism of the potentiation by glucose of insulin secretion induced by arginine and tolbutamide in mouse islets

Glucose induces insulin secretion (IS) and also potentiates the insulin-releasing action of secretagogues such as arginine and sulfonylureas. This potentiating effect is known to be impaired in type 2 diabetic patients, but its cellular mechanisms are unclear. IS and cytosolic Ca(2+) concentration ([Ca(2+)](i)) were measured in mouse islets during perifusion with 3-15 mmol/l glucose (G3-G15, respectively) and pulse or stepwise stimulation with 1-10 mmol/l arginine or 5-250 micromol/l tolbutamide. In G3, arginine induced small increases in [Ca(2+)](i) but no IS. G7 alone only slightly increased [Ca(2+)](i) and IS but markedly potentiated arginine effects on [Ca(2+)](i), which resulted in significant IS (already at 1 mmol/l). For each arginine concentration, both responses further increased at G10 and G15, but the relative change was distinctly larger for IS than [Ca(2+)](i). At all glucose concentrations, tolbutamide dose dependently increased [Ca(2+)](i) and IS with thresholds of 25 micromol/l for [Ca(2+)](i) and 100 micromol/l for IS at G3 and of 5 micromol/l for both at G7 and above. Between G7 and G15, the effect of tolbutamide on [Ca(2+)](i) increased only slightly, whereas that on IS was strongly potentiated. The linear relationship between IS and [Ca(2+)](i) at increasing arginine or tolbutamide concentrations became steeper as the glucose concentration was raised. Thus glucose augmented more the effect of each agent on IS than that on [Ca(2+)](i). In conclusion, glucose potentiation of arginine- or tolbutamide-induced IS involves increases in both the rise of [Ca(2+)](i) and the action of Ca(2+) on exocytosis. This dual mechanism must be borne in mind to interpret the alterations of the potentiating action of glucose in type 2 diabetic patients.