Serum proinsulin levels in LADA patients / 中华内分泌代谢杂志

ABSTRACT

Objective To explore the characteristics of proinsulin secretion in latent autoimmune diabetes in adults (LADA). Methods Fasting and 2 h sera in oral glucose tolerance test from 36 LADA patients, 37 type 2 diabetic patients and 43 healthy controls were collected to test glucose, proinsulin (PI) and C-peptide (CP) by radioimmune assay. Glutamie acid decarboxylase antibodies (GAD-Ab) were determined by radioligand assay.Results (1) Fasting proinsulin (FPI) and 2 h proinsulin (PPI) level in LADA patients were lower than those in type 2 diabetic patients (P<0.05), being both significantly inereasad compared with healthy controls (P<0.05 or P<0.01); The ratios of FPI/FCP and PPI/PCP (%) in LADA were beth significantly higer than those of type 2 diabetes mellitus and controls (P<0.05 or P<0.01); (2) LADA type-1 (GAD-Abe>0.3) patients showed lower PI levels(P<0.05 or P<0.01) and higher PI/CP ratio (all P<0.05) than LADA type-2 (0.05≤GAD-Ab<0.3); Meanwhile, there were no significant differences in above parameters between LADA type-2 and type 2 diabetes meUitus (P>0.05). (3) GAD-Ab index was negatively correlated with FPI and PPI in LADA group (r=-0.236 and-0.268, both P<0.05), and positively correlated with PPI/PCP (r=0.254, P=0.030).Meanwhile BMI was positively correlated with FPI, PPI and PI/CP in type 2 diabetes mellitus (all P<0.01). No factor entered the multiple regression analysis for predieting the hyperproinsulinemia and dispropriately elevated proinsulin levels in LADA patients. (4) According to the 99.5 th percentile of proinsulinemia in the healthy controls, which is defined as the cutoff point dispropriately elevated proinsulin levels, the proportion of subjects with fasting dispropriately elevated proinsulin levels (FPI/FCP) were 77.8%, 62.2% and 2.3% in LADA, type 2 diabetes meUitus and controls respectively, and PPI/PCP 83.3%, 51.4% and 2.3% respectively. Conclusion LADA patients, as well as type 2 diabetic patients, all showed hyperproinsulinemia and disproportionately elevated proiasulin levels that were one of characteristics of defective β-cell function. Moreover, disproportionately elevated nproinsulin level is more evident in LADA patients than that in type 2 diabetics and this may be related to humoral immunity.