Sex Differences in Insulin Sensitivity and Glomerular Function in African Green Monkeys

Abstract

In the United States, it is estimated that approximately 10.5% of the population has diabetes of which 90% are classified as insulin resistant expressing Type 2 Diabetes Mellitus (T2DM). T2DM is one of the leading causes of end stage renal disease (ESRD) accounting for approximately 40% of new ESRD cases. Previous studies have reported a more prevalent decrease in renal function in glucose intolerant males when compared to pre‐menopausal females. Males also have been reported to have earlier onset and higher prevalence of T2DM compared to pre‐menopausal females. Renal injury can be present before the onset of T2DM however, sex differences in renal injury have yet to be assessed in humans. A subpopulation of African Green Monkeys (AGM; Chlorocebus aethiops sabaeus) in the Caribbean exhibit spontaneous glucose intolerance and co‐morbidities such as insulin insensitivity, and hypertension. The AGM also shares similar genomic expression and metabolic phenotypes to humans making them optimal for translatable diabetes research. We hypothesize that female AGM are protected against renal injury and early onset T2DM. Systolic blood pressure (SBP) was measured by forearm plethysmography. Glucose tolerance was assessed via conscious and anesthetized oral glucose tolerance tests (OGTT). All AGM were fasted 12‐18 hours prior to study with water provided ad libitum. Blood glucose was measured at 0, 15, 30, 60, 90, and 120 min after an oral glucose load. Conscious AGM OGTT were delivered as 0.75g glucose/kg body weight. Sedated AGM (ketamine, 15mg/kg, i.m.), received 5g/dl glucose and 15 ml/kg in water by oral gavage. Venous blood samples were collected at timepoints 0, 30, 60, and 120 minutes post glucose administration. Urine samples were collected for 3 days post OGTT. Kidney histology was performed by staining 10µm sections with Periodic‐Acid Schiff stain (PAS). A minimum of 10 glomeruli were identified at 400x magnification per animal then analyzed with ImageJ. There were no differences between lightly sedated or conscious OGTT. All AGM in this study were normotensive and there were no sex differences in blood pressure between male and female AGM (F=11; 113.9±3.73 mmHg, M=6; 117.6 ± 6.3mmHg). Female AGM OGTT area under the curve (AUC) over 120 minutes post glucose load were lower compared to male AGM (F; 11,961.5± 710.6 min x mg/dl, M; 14,076.3±710.6 min x mg/dl, p<0.05). There were no significant differences in plasma insulin at all time points between male and female AGM (F; 2,013± 1,007 min x mIU/L, M; 5,940± 1,424.6 min x mIU/L) despite the lower glucose AUC in females. Renal glomerular function was assessed by measuring plasma creatinine, urinary albumin, and urinary albumin to creatinine ratio (UACR). Plasma creatinine was not different between male and females (F; 1.35±0.2 mg/dl, M; 1.77±0.25 mg/dl). Microalbuminuria was present in both male and female AGMs, in the absence of sex differences (F; 98.43±23.1 ng/ml, M; 81.15±29.2 ng/ml). UACRs were not different between male and female AGM. Glomerular injury was assessed by determining the intensity of glomerular PAS stain. PAS stain intensity was not different in male and female AGM (F=3; 178.3 ± 8.6, M=3; 181.6± 8.6) regardless of OGTT sensitivity. Together these data suggest that female AGM are more insulin sensitive than male AGM and may be protected against early onset T2DM. Despite differences in OGTT in male and female AGM, microalbuminuria suggested onset of renal dysfunction. We conclude that the AGM provides a strong nonhuman primate model of T2DM for the long‐term study of sex differences in the mechanisms of ESRD.