Proinsulin–to–C-Peptide Ratio as a Marker of β-Cell Function in African American and European American Adults

• Published in: Diabetes care Vol. 46; no. 12; pp. 2129 - 2136
• Main Authors: Couch, Catharine A., Piccinini, Francesca, Fowler, Lauren A., Garvey, W. Timothy, Gower, Barbara A.
• Format: Journal Article
• Language: English
• Published: United States American Diabetes Association 01.12.2023
• Subjects: Adult; Adults; African Americans; Beta cells; Black or African American; Blood Glucose; C-Peptide; Diabetes; Diabetes mellitus; Diabetes mellitus (non-insulin dependent); Diabetes Mellitus, Type 2; Fasting; Female; Glucose; Glucose tolerance; Humans; Insulin; Insulin Resistance; Insulin-Secreting Cells - metabolism; Insulin-Secreting Cells - physiology; Laboratory testing; Male; Mathematical analysis; Original; Peptides; Proinsulin; Regression analysis; Research design; Sensitivity analysis; White
• ISSN: 0149-5992; 1935-5548; 1935-5548
• DOI: 10.2337/dc22-1763

The primary purpose of the current study was to test the hypothesis that the proinsulin-to-C-peptide (PI-to-CP) ratio, as an index of proinsulin secretion, would be higher and associated with indices of β-cell function in African American adults relative to European American adults without type 2 diabetes. Participants were 114 African American and European American adult men and women. A 2-h oral glucose tolerance test was conducted to measure glucose, insulin, C-peptide, and proinsulin and derive indices of β-cell response to glucose. The Matsuda index was calculated as a measure of insulin sensitivity. The disposition index (DI), the product of insulin sensitivity and β-cell response, was calculated for each phase of β-cell responsivity. Pearson correlations were used to investigate the relationship of the PI-to-CP ratio with each phase of β-cell response (basal, Φb; dynamic, Φd; static, Φs; total, Φtot), disposition indices (DId, DIs, DItot), and insulin sensitivity. Multiple linear regression analysis was used to evaluate independent contributions of race, BMI, and glucose tolerance status on PI-to-CP levels before and after adjustment for insulin sensitivity. 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 PI-to-CP ratio could be useful in identifying African American individuals at highest risk for β-cell dysfunction and ultimately type 2 diabetes.