Do insulinotropic glucose-lowering drugs do more harm than good? The hypersecretion hypothesis revisited

Telmisartan Potentiates Insulin Secretion via Ion Channels, Independent of the AT1 Receptor and PPARγ

Angiotensin II type 1 (AT1) receptor blockers (ARBs), as antihypertensive drugs, have drawn attention for their benefits to individuals with diabetes and prediabetes. However, the direct effects of ARBs on insulin secretion remain unclear. In this study, we aimed to investigate the insulinotropic effect of ARBs and the underlying electrophysiological mechanism. We found that only telmisartan among the three ARBs (telmisartan, valsartan, and irbesartan) exhibited an insulin secretagogue role in rat islets. Independent of AT1 receptor and peroxisome proliferator-activated receptor γ (PPARγ), telmisartan exerted effects on ion channels including voltage-dependent potassium (Kv) channels and L-type voltage-gated calcium channels (VGCCs) to promote extracellular Ca²⁺ influx, thereby potentiating insulin secretion in a glucose-dependent manner. Furthermore, we identified that telmisartan directly inhibited Kv2.1 channel on a Chinese hamster ovary cell line with Kv2.1 channel overexpression. Acute exposure of db/db mice to a telmisartan dose equivalent to therapeutic doses in humans resulted in lower blood glucose and increased plasma insulin concentration in OGTT. We further observed the telmisartan-induced insulinotropic and electrophysiological effects on pathological pancreatic islets or β-cells isolated from db/db mice. Collectively, our results establish an important insulinotropic function of telmisartan distinct from other ARBs in the treatment of diabetes.

Improving glycaemic control in type 2 diabetes: Stimulate insulin secretion or provide beta-cell rest?

Type 2 diabetes (T2D) is characterized by a gradual decline in pancreatic beta cell function that determines the progressive course of the disease. While beta-cell failure is an important contributor to hyperglycaemia, chronic hyperglycaemia itself is also detrimental for beta-cell function, probably by inducing prolonged secretory stress on the beta cell as well as through direct glucotoxic mechanisms that have not been fully defined. For years, research has been carried out in search of therapies targeting hyperglycaemia that preserve long-term beta-cell function in T2D, a quest that is still ongoing. Current strategies aim to improve glycaemic control, either by promoting endogenous insulin secretion, such as sulfonylureas, or by mechanisms that may impact the beta cell indirectly, for example, providing beta-cell rest through insulin treatment. Although overall long-term success is limited with currently available interventions, in this review we argue that strategies that induce beta-cell rest have considerable potential to preserve long-term beta-cell function. This is based on laboratory-based studies involving human islets as well as clinical studies employing intensive insulin therapy, thiazolidinediones, bariatric surgery, short-acting glucagon-like peptide (GLP)-1 receptor agonists and a promising new class of diabetes drugs, sodium-glucose-linked transporter (SGLT)-2 inhibitors. Nevertheless, a lack of long-term clinical studies that focus on beta-cell function for the newer glucose-lowering agents, as well as commonly used combination therapies, preclude a straightforward conclusion; this gap in our knowledge should be a focus of future studies.

Gliclazide may have an antiapoptotic effect related to its antioxidant properties in human normal and cancer cells

Experimental and clinical studies suggest that gliclazide may protect pancreatic β-cells from apoptosis induced by an oxidative stress. However, the precise mechanism(s) of this action are not fully understood and requires further clarification. Therefore, using human normal and cancer cells we examined whether the anti-apoptotic effects of this sulfonylurea is due to its free radical scavenger properties. Hydrogen peroxide (H₂O₂) as a model trigger of oxidative stress was used to induce cell death. Our experiments were performed on human normal cell line (human umbilical vein endothelial cell line, HUVEC-c) and human cancer cell lines (human mammary gland cell line, Hs578T; human pancreatic duct epithelioid carcinoma cell line, PANC-1). To assess the effect of gliclazide the cells were pre-treated with the drug. The 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide assay was employed to measure the impact of gliclazide on cell viability. Generation of reactive oxygen species, mitochondrial membrane potential (∆Ψ_m), and intracellular Ca²⁺ concentration [Ca²⁺] were monitored. Furthermore, the morphological changes associated with apoptosis were determined using double staining with Hoechst 33258-propidium iodide (PI). Gliclazide protects the tested cells from H₂O₂-induced cell death most likely throughout the inhibition of ROS production. Moreover, the drug restored loss of ΔΨ_m and diminished intracellular [Ca²⁺] evoked by H₂O₂. Double staining with Hoechst 33258-PI revealed that pre-treatment with gliclazide diminished the number of apoptotic cells. Our findings indicate that gliclazide may protect both normal and cancer human cells against apoptosis induced by H₂O₂. It appears that the anti-apoptotic effect of the drug is most likely associated with reduction of oxidative stress.

[Cardial target-organ damage in diabetes]

Coronary heart disease and type 2 diabetes mellitus can be considered as a syntropy. Accordingly, cardiologists and diabetologists should organize an interdisciplinary car of the patient with both cardiac disease and diabetes mellitus. Arterial hypertension is frequently present in the diabetic condition and increases further morbidity and mortality rates due to the involvement of the coronary microcirculation. Coronary artery disease is characterized by a rapid progression and a diffuse distribution particularly in the periphery. Consequently in severe diabetic coronary artery disease coronary bypass surgery should be preferred rather than percutaneous coronary stenting, which should be favored in less severe cases. In the antihyperglycemic treatment a reduction in cardiovascular endpoints has only be documented after metformin. Therapy with thiazolidinediones has been terminated due to an increase in coronary morbidity and mortality under rosiglitazone. In as much glucagon-like peptide-I analogues and dipeptidylpeptidase 4 inhibitors will reduce cardiovascular endpoints has to be waited for. Thus an endpoint orientated antihyperglycemic treatment is limited to insulin, metformin and sulfonylureas.