Nonhuman Primate Models for Islet Transplantation in Type 1 Diabetes Research

Characterization and validation of a streptozotocin-induced diabetes model in the vervet monkey

INTRODUCTION

Streptozotocin (STZ), preferentially toxic to pancreatic beta cells, is commonly used to model Type 1 diabetes mellitus (DM) in numerous species, including nonhuman primates.

METHODS

We induced DM in twenty vervet monkeys (Chlorocebus aethiops) by intravenous administration of either 45 (n=8, STZ-45) or 55 mg/kg STZ (n=12, STZ-55); ten control (CTL) monkeys received saline.

RESULTS

Overall there was 15% mortality, likely secondary to renal toxicity. Twice-daily insulin therapy was initiated to maintain comparable glycemic control, confirmed by comparable glycated hemoglobin levels. Exogenous insulin requirements increased rapidly for 4weeks; STZ-45 insulin doses stabilized thereafter while STZ-55 doses continued to increase through 16weeks. Glucose tolerance testing and arginine-stimulated insulin secretion confirmed 80-90% reduction in pancreatic beta cell function in both groups. Body weight was reduced in all STZ monkeys, with return to baseline only in STZ-45 at 16 wks. Elevated blood urea nitrogen (BUN) and creatinine were noted in the STZ-55 group. Alkaline phosphatase (ALKP) was also increased with STZ-55 (p < 0.05 vs. CTL) whereas STZ-45 ALKP elevation resolved by study end. Red cell parameters were reduced in all STZ monkeys, but more severely in the STZ-55 group.

DISCUSSION

We have demonstrated that a model of DM can be induced and maintained in vervets with a single dose of STZ. The lower dose of STZ (45 mg/kg) significantly improved the toxicity profile without altering efficacy in inducing DM. Finally, sufficient time following induction is recommended to allow transient renal, hepatic and hematologic parameters to resolve.

Clinicopathologic characterization of naturally occurring diabetes mellitus in vervet monkeys

Diabetes mellitus (DM) is a group of chronic metabolic diseases characterized by persistent fasting hyperglycemia, and it can be of either polygenic or monogenic origin. Animal models have played an important role in elucidating the pathophysiology of the polygenic Type 1 and type 2 DM forms; however, useful animal models of the monogenic forms do not exist. The authors describe 4 cases of naturally occurring DM in vervet monkeys (Chlorocebus aethiops sabaeus), 1 of which has clinicopathologic findings consistent with type 2 DM, including persistent hyperglycemia, hypertriglyceridemia, islet amyloidosis, and reduced islet insulin immunostaining. In contrast, the 3 remaining animals have clinicopathologic similarities to a monogenic form of the disease, including a lack of islet amyloidosis and hypertriglyceridemia, as well as normal islet insulin immunostaining. In addition, pedigree analysis conducted on one of these animals is consistent with either an autosomal dominant or mitochondrial inheritance pattern, which supports a monogenic form of DM. The authors thus hypothesize that a naturally occurring monogenic form of diabetes may occur in vervet monkeys, making them a potential animal model for future studies.

Effect of various immunosuppressive monotherapies on survival and histopathology of monkey islet xenografts in rats

BACKGROUND

The isolation and testing of monkey islets after transplantation in small animal models provides basic information about their functional capacity. We describe the effect of cyclosporine A (CsA), tacrolimus (FK506) or prednisolone monotherapy on preventing monkey islet graft rejection after xenoTx in a rat model. Histopathological aspects are reported.

METHODS

Indian bonnet monkey (Macaca radiata radiata) islets were isolated by a simple stationary digestion technique using collagenase. The islets were purified with dextran density gradients and were transplanted under the renal capsule of normal or diabetic rats. The rats received a daily dose of CsA, or FK506, or prednisolone, and the grafts were removed at different intervals to determine islet survival. The effect of discontinuation of CsA on islet graft survival was also monitored. Histological examination of islets transplanted into normal or streptozotocin-induced diabetic rats was carried out. In diabetic rats, islet survival was determined by the graft's ability to achieve euglycemia.

RESULTS

Reversal of diabetes was achieved in all transplanted diabetic rats, demonstrating the efficacy of the isolated monkey islets. Histological examination indicated that monkey islets survived in the presence of continuous high-dose immunosuppressive monotherapy in rats. Various types of infiltrating cells were observed in the grafted area at varying times after transplantation, depending on the immunosuppressive treatment. After discontinuation of CsA, the grafts were protected for a short period.

CONCLUSIONS

This study provided evidence for monkey islet survival after transplantation into rats receiving immunosuppressive monotherapy. Basic information on infiltrating cell types may be important in the study of xenograft rejection.