Possible New Strategies for the Treatment of Congenital Hyperinsulinism

Objective: Congenital hyperinsulinism (CHI) is a rare disease characterized by persistent hypoglycemia as a result of inappropriate insulin secretion, which can lead to irreversible neurological defects in infants. Poor efficacy and strong adverse effects of the current medications impede successful treatment. The aim of the study was to investigate new approaches to silence β-cells and thus attenuate insulin secretion.

Research Design And Methods: In the scope of our research, we tested substances more selective and more potent than the gold standard diazoxide that also interact with neuroendocrine ATP-sensitive K (K) channels. Additionally, K channel-independent targets as Ca-activated K channels of intermediate conductance (K3.1) and L-type Ca channels were investigated. Experiments were performed using human islet cell clusters isolated from tissue of CHI patients (histologically classified as pathological) and islet cell clusters obtained from C57BL/6N (WT) or SUR1 knockout (SUR1) mice. The cytosolic Ca concentration ([Ca]) was used as a parameter for the pathway regulated by electrical activity and was determined by fura-2 fluorescence. The mitochondrial membrane potential (ΔΨ) was determined by rhodamine 123 fluorescence and single channel currents were measured by the patch-clamp technique.

Results: The selective K channel opener NN414 (5 µM) diminished [Ca] in isolated human CHI islet cell clusters and WT mouse islet cell clusters stimulated with 10 mM glucose. In islet cell clusters lacking functional K channels (SUR1) the drug was without effect. VU0071063 (30 µM), another K channel opener considered to be selective, lowered [Ca] in human CHI islet cell clusters. The compound was also effective in islet cell clusters from SUR1 mice, showing that [Ca] is influenced by additional effects besides K channels. Contrasting to NN414, the drug depolarized ΔΨ in murine islet cell clusters pointing to severe interference with mitochondrial metabolism. An opener of K3.1 channels, DCEBIO (100 µM), significantly decreased [Ca] in SUR1 and human CHI islet cell clusters. To target L-type Ca channels we tested two already approved drugs, dextromethorphan (DXM) and simvastatin. DXM (100 µM) efficiently diminished [Ca] in stimulated human CHI islet cell clusters as well as in stimulated SUR1 islet cell clusters. Similar effects on [Ca] were observed in experiments with simvastatin (7.2 µM).

Conclusions: NN414 seems to provide a good alternative to the currently used K channel opener diazoxide. Targeting K3.1 channels by channel openers or L-type Ca channels by DXM or simvastatin might be valuable approaches for treatment of CHI caused by mutations of K channels not sensitive to K channel openers.