Question: 

Beta-cell dysfunction during the pathogenesis of type 2 diabetes mellitus is mainly caused by a dramatic increase of reactive oxygen and nitrogen species (ROS, RNS). Based on our findings that K_ATP channel inhibitiors induce upregulation of antioxidant enzymes we investigated whether the sulfonylurea gliclazide protects against glucolipotoxicity and oxidative stress caused by mitochondrial dysfunction.

Methods: 

Glucose-stimulated insulin secretion (GSIS) was measured by radioimmunoassay, cytosolic Ca²⁺ concentration [Ca²⁺]_c by fura-2 and ROS by 2',7'-dichlorofluorescein diacetate.

Results: 

3-nitropropionic acid (3-NPA), an inductor of mitochondrial oxidative stress, inhibited GSIS concentration-dependently (15mM glucose: 1.3±0.2ng/islet*h, + 1mM 3-NPA: 0.4±0.06ng/islet*h, n=7, p<=0.05). By contrast, the effect of 3-NPA was drastically reduced in beta-cells pretreated with gliclazide (1.1±0.1ng/islet*h, n=4, n.s.). Protection against mitochondrial ROS was also achieved by mitoTEMPO (100mM), a mimetic of mitochondrial superoxide dismutase (n=3). In addition gliclazide pretreatment attenuated the inhibition of GSIS caused by the NO donor S-nitrosocysteine (250mM SNOC: 0.2±0.07ng/islet*h, + 10mM gliclazide: 0.5±0.1ng/islet*h, n=10, p<=0.05).

To investigate the effect of gliclazide on glucolipotoxicity beta-cells were cultured for 2 days with 25mM glucose and 100mM palmitate (0.5% BSA). 53.7±8.4% of beta-cells were functionally damaged with respect to glucose-induced oscillations in [Ca²⁺]_c or the ability to lower [Ca²⁺]_c to basal levels in 0.5mM glucose (n=48–63 of 3–5 independent preparations). In the presence of gliclazide glucolipotoxicity was clearly reduced (30.3±2.6%, p<=0.05). This protection was due to a significant decrease in intracellular ROS levels (n=4).

Conclusions: 

Our data show that suppression of K_ATP channel activity protects against oxidative damage induced by different stress conditions and represents a potent strategy to preserve beta-cell functionality during development of diabetes.