The Presence of Two Reduced Function Variants in CYP2C9 Influences the Acute Response to Glipizide

Aims: To examine whether the presence of two common missense variants in the CYP2C9 gene (rs1799853, encoding Arg144Cys and denoted as *2, and rs1057910, encoding Ile359Leu and denoted as *3) influences the acute physiological response to a single glipizide dose in individuals naïve to diabetes medications.

Methods: In the Study to Understand the Genetics of the Acute Response to Metformin and Glipizide in Humans (SUGAR-MGH), 786 individuals genotyped for rs1799853/rs41291560 (*2) and rs1057910/rs9332214 (*3) were treated with 5 mg glipizide in the fasting state. Glucose and insulin levels were measured at baseline, 30, 60, 90, 120, 180 and 240 min for calculation of phenotypic endpoints of glipizide response. The challenge was aborted as a result of hypoglycaemia, defined as glucose <2.8 mmol/l or hypoglycaemia-related symptoms.

Results: Carriers with two reduced function alleles had a 50% larger insulin area under the curve than carriers with zero or one copy (P=0.037), although this finding was primarily driven by an individual with a robust insulin response. In adjusted analyses, the risk of aborting the glipizide challenge was doubled in two-copy carriers (P=0.034). No significant findings were observed in glucose-based endpoints.

Conclusions: Carriers of two reduced function alleles in CYP2C9 may experience an increased insulin response to glipizide and be predisposed to a higher risk of hypoglycaemia, although no effect of genotype was seen in glucose-based measurements. Further studies are needed to clarify the utility of CYP2C9 genotyping to guide sulfonylurea treatment.