Effect of Age on Diabetogenicity of Alloxan in Ossabaw Miniature Swine

Abstract

According to a single study in dogs that was conducted in 1949, the diabetic effects of the β-cell toxin alloxan are dependent on age. The current study examined whether this age-dependence of alloxan is present in the clinically relevant Ossabaw miniature swine (Sus scrofa domestica) model of metabolic syndrome. Juvenile swine (n = 8; age, 4.3 ± 0.2 mo) and adult swine (n = 8; age, 7.4 ± 0.2 mo) received alloxan (average dosage, 140 mg/kg IV) and were placed on a hypercaloric, atherogenic diet for 6 mo. The metabolic syndrome profile was confirmed by measuring body weight, cholesterol, and triglycerides. Intravenous glucose tolerance testing was used to assess glucose clearance and peripheral plasma insulin levels. The β-cell mass was calculated by immunohistochemical staining of pancreatic tissue. Although juvenile and adult swine exhibited comparable severity of metabolic syndrome, adult swine developed impaired glucose clearance and elevated fasting blood glucose levels at 6 mo after alloxan administration on the atherogenic diet. Peripheral plasma insulin levels in juvenile and adult swine were comparable at all time points and lower than in nonalloxan-treated age-matched controls, which is reflected in the lower pancreatic β-cell mass of the 2 treated groups. However, compared with adult pigs, juvenile swine exhibited greater insulin response recovery (complete or partial restoration of peripheral insulin levels to reference values) at 6 mo after alloxan administration. Overall, these results indicate that youth can confer some protection against the diabetogenic effects of alloxan in swine, potentially due in part to the greater insulin response recovery of young pigs. This study supports previous research that the effects of alloxan are dependent on the developmental maturity of the animal.

Figure 1.

Adult swine exhibited prolonged impaired glucose clearance after intravenous glucose tolerance testing. Blood glucose levels were tested for 60 min after a bolus of glucose (1 mg/kg body weight). (A) At 1 wk alloxan administration, adult swine (n = 8) showed a significant deficit in glucose clearance at all time points compared with pretreatment controls (n = 16) and juvenile swine (n = 8). (B) The fasting blood glucose level was elevated in juvenile animals at baseline and in the adult group at 1 wk after alloxan administration. (C) AUC analysis at 1 wk after alloxan administration shows impaired glucose clearance in adult alloxanized pigs compared with pretreatment controls and juvenile swine. (D) At 6 mo after alloxan administration, adult swine continued to exhibit impaired glucose clearance compared with nonalloxanized swine and juvenile swine at most time points. (E) The baseline fasting glucose concentration was elevated in adult swine at 6 mo after alloxan administration. (F) At 6 mo after alloxan administration, AUC analysis using the fasting blood glucose concentration as a baseline for each group shows impaired glucose clearance in juvenile alloxanized pigs compared with untreated controls; this impaired glucose clearance is exacerbated in adult alloxanized animals. *, P < 0.05.

Figure 2.

Correlation of fasting blood glucose level with age at alloxan administration. The fasting blood glucose concentration at 1 wk after alloxan administration is significantly positively correlated to the age of swine at time of alloxan administration (black). The dose of alloxan, however, is not correlated to age (red) and is not significantly different between groups. In animals given 2 doses of alloxan, the average of the doses was plotted.

Figure 3.

Hypoinsulinemia in juvenile and adult swine at 6 mo after alloxanization. (A) Peripheral insulin during intravenous glucose tolerance testing was significantly lower in juvenile (n = 7) and adult (n = 8) swine compared with prealloxan controls (n = 16) at 1 wk after alloxan administration. (B) AUC analysis reveals comparable hypoinsulinemia in both the juvenile and adult alloxan-treated swine at 1 wk after alloxan administration. (C) At 6 mo after alloxan administration, juvenile and adult swine still exhibited hypoinsulinemia at several time points compared with nonalloxanized, age-matched controls (n = 8). (D) AUC analysis revealed comparable hypoinsulinemia in both juvenile and adult alloxanized swine 6 mo after alloxan administration. (E) The fold change in peripheral insulin from 1 wk to 6 mo after alloxan was greater in juvenile than adult swine. *, P < 0.05 compared with prealloxan or nonalloxanized controls.

Figure 4.

Change in β-cell mass in young and adult alloxanized swine. Immunohistochemical staining of insulin in pancreas from (A) juvenile and (B) adult swine revealed that, at 6 mo after alloxan administration, both juvenile and adult swine had a lower β-cell mass than nonalloxanized controls (in which the insulin-stained area is approximately 7.5%). However, (C) β-cell mass did not differ significantly between alloxan-treated juvenile and adult swine.