Proinsulin-to-C-peptide ratio may help identify individuals at highest risk of type 2 diabetes: Study

African-American adults tend to have higher acute insulin response to glucose, lower insulin sensitivity, and lower hepatic insulin clearance. Catharine A. Couch, Department of Nutrition Sciences, University of Alabama at Birmingham, Birmingham, AL, and colleagues conducted the study to test the hypothesis that the proinsulin–to–C-peptide ratio, as an index of proinsulin secretion, would be higher and associated with indices of β-cell function in African American people relative to European-American adults without type 2 diabetes.

For this purpose, 114 African-American and European-American adult women and men were included. A 2-h oral glucose tolerance test was conducted to measure insulin, glucose, proinsulin, and C-peptide and derive indices of β-ce9ll response to glucose.

The Matsuda index was calculated as an insulin sensitivity measure. The disposition index (DI) was calculated for each phase of β-cell responsivity. DI is the product of insulin sensitivity and β-cell response. Pearson correlations were used to determine the relationship of the PI-to-CP ratio with each β-cell response phase (basal, Φb; dynamic, Φd; static, Φs; total, Φtot), insulin sensitivity, and disposition indices (DId, DIs, DItot). Multiple linear regression analysis was used to evaluate independent contributions of BMI, race, and glucose tolerance status on PI-to-CP levels before and after adjustment for insulin sensitivity.

The study led to the following findings:

• African American participants had higher fasting and 2-h PI-to-CP ratios.
• The fasting PI-to-CP ratio was positively associated with Φb, and the fasting PI-to-CP ratio and 2-h PI-to-CP ratio were inversely associated with DId and insulin sensitivity only in African-American participants.

"The findings reveal that the proinsulin-to–C-peptide ratio could be helpful in the early identification of β-cell dysfunction in African American individuals," the researchers concluded.

Reference:

Catharine A. Couch, Francesca Piccinini, Lauren A. Fowler, W. Timothy Garvey, Barbara A. Gower; Proinsulin–to–C-Peptide Ratio as a Marker of β-Cell Function in African American and European American Adults. Diabetes Care 1 December 2023; 46 (12): 2129–2136. https://doi.org/10.2337/dc22-1763