Mibefradil reduces blood glucose concentration in db/db mice

OBJECTIVE:

Numerous recent studies suggest that abnormal intracellular calcium concentration (Ca²⁺]_i) is a common defect in diabetic animal models and patients. Abnormal calcium handling is an important mechanism in the defective pancreatic β-cell function in type 2 diabetes. T-type Ca²⁺ channel antagonists lower blood glucose in type 2 diabetes, but the mechanism remains unknown.

METHODS:

We examined the effect of the Ca²⁺ channel antagonist mibefradil on blood glucose in male db/db mice and phenotypically normal heterozygous mice by intraperitoneal injection.

RESULTS:

Mibefradil (15 mg/kg, i.p., b.i.d.) caused a profound reduction of fasting blood glucose from 430.92±20.46 mg/dl to 285.20±5.74 mg/dl in three days. The hypoglycemic effect of mibefradil was reproduced by NNC 55-0396, a compound structurally similar to mibefradil but more selective for T-type Ca²⁺ channels, but not by the specific L-type Ca²⁺ channel blocker nicardipine. Mibefradil did not show such hypoglycemic effects in heterozygous animals. In addition, triglycerides, basal insulin and food intake were significantly decreased by mibefradil treatment in the db/db mice but not in the controls. Western blot analysis, immunohistochemistry and immunofluorescence staining showed a significantly increased expression of T-type Ca²⁺ channel α-subunits Cav3.1 and Cav3.2 in liver and brain tissues from db/db mice compared to those from heterozygous animals.

CONCLUSIONS:

Collectively, these results suggest that T-type Ca²⁺ channels are potential therapeutic targets for antidiabetic drugs.