A baboon (Papio hamadryas) model of insulin-dependent diabetes

Age-associated alterations in immune and inflammatory responses in captive olive baboons (Papio anubis)

Introduction

Advanced age is a primary risk factor for many chronic diseases and conditions; however, age-related immune dysregulation is not well understood. Animal models, particularly those that resemble human age-related physiological changes, are needed to better understand immunosenescence and to improve health outcomes. Here, we explore the utility of the olive baboon (Papio anubis) in studying age-related changes to the immune system and understanding mechanisms of immunosenescence.

Methods

We examined immune cell, inflammatory responses, cytokines, and cortisol levels using hematology and flow cytometry, mitogen stimulation, multiplex cytokine assay, and cortisol immunoassay.

Results and Discussion

Our results reveal significant age effects on numerous immune and inflammatory responses. For instance, adult and aged monkeys exhibited significantly fewer monocytes than young monkeys. After stimulation with Con A and PWM (separately), we found that old baboons had higher INFγ expression compared to young baboons. Similarly, after stimulation with LPS and PWM (separately), we found that old baboons had higher TNFα expression compared to young baboons. These findings suggest that the olive baboon is a suitable model for biogerontology research, immune senescence, and development of vaccines. Though there are phenotypic and functional similarities between baboons and humans, specific differences exist in immune cell expression and immune function of lymphocytes that should be considered for better experimental outcomes in the development of therapeutics and restoring innate and adaptive immune function in aged individuals.

A survey of diabetes prevalence in zoo-housed primates

In humans, type II diabetes mellitus is a condition in which the pancreas is capable of producing insulin but cells do not appropriately respond to insulin with an uptake of glucose. While multiple factors are associated with type II diabetes in humans, a high calorie diet and limited exercise are significant risk factors for the development of this disease. Zoo primates, with relatively high caloric density diets and sedentary lifestyles, may experience similar conditions that could predispose them to the development of diabetes. We surveyed all Association of Zoos and Aquariums (AZA) facilities with primates in their collections to determine the prevalence of diabetes, diagnosis and treatment methods, and treatment outcomes. Nearly 30% of responding institutions reported at least one diabetic primate in their current collection. Although the majority of reported cases were in Old World Monkeys (51%), all major taxonomic groups were represented. Females represented nearly 80% of the diagnosed cases. A wide variety of diagnosing, monitoring, and treatment techniques were reported. It is clear from these results diabetes should be considered prominently in decisions relating to diet, weight and activity levels in zoo-housed primates, as well as discussions surrounding animal health and welfare.

Renal histopathology of a baboon model with type 2 diabetes

Naturally occurring type 2 diabetes has been found in a colony of baboons. Ongoing characterization of the baboon colony maintained at the Southwest National Primate Research Center has revealed a significant range of glucose sensitivity with some animals clearly diabetic.   Seven baboons, four with diabetes and three without diabetes, underwent histopathological investigation. Three diabetic animals were diagnosed using fasting blood glucose, hemoglobin A1C, and intravenous glucose tolerance test, and a fourth one was known to have hyperglycemia. One control baboon and three baboons with diabetes had microalbuminuria. On kidney biopsy, diabetic baboons had thickening of the glomerular basement membrane and mesangial matrix expansion compared to controls. Immunohistochemistry showed the diabetic animals had increased mesangial expression of cellular fibronectin ED-A. Two diabetic animals with microalbuminuria had evidence of mesangiolysis with the formation of an early nodule. One diabetic animal had a Kimmestiel-Wilson nodule. We conclude that the baboon represents a useful primate model of diabetes and nephropathy that resembles the nephropathy associated with type 2 diabetes in humans.

A novel primate model of delayed wound healing in diabetes: dysregulation of connective tissue growth factor

AIMS/HYPOTHESIS

Chronic non-healing wounds are a common complication of diabetes. Prolonged inflammation and decreased matrix accumulation may contribute. Connective tissue growth factor (CTGF) is induced during normal wound healing, but its regulation in diabetic wounds is unknown. We developed a primate model for the study of in vivo wound healing in baboons with long diabetes duration.

METHODS

Drum implants were placed subcutaneously into thighs of diabetic and non-diabetic control baboons. After 2 and 4 weeks the skin incision sites were removed for measurement of breaking strength and epithelial thickness. Drum implants were removed for analysis of granulation tissue and inflammatory cells, CTGF and tissue inhibitor of matrix metalloproteinase (TIMP-1). Degradation of added CTGF by wound fluid was also examined.

RESULTS

Healed incision site skin was stiffer (less elastic) in diabetic baboons and epithelial remodelling was slower compared with controls. Granulation tissue from diabetic baboons was reduced at 2 and 4 weeks, with increased vessel lumen areas at 4 weeks. Macrophages were reduced while neutrophils persisted in diabetic tissue. In diabetic wound tissue at 4 weeks there was less CTGF induced, as shown by immunohistochemistry, compared with controls. In contrast, immunoreactive fragments of CTGF were significantly increased in whole tissue lysate in diabetic baboons, suggesting that CTGF is redistributed in diabetes from granulation tissue into wound fluid. When recombinant human CTGF was co-incubated with wound fluid, increased CTGF degradation products were observed in both control and diabetic samples.

CONCLUSIONS/INTERPRETATION

This baboon model of wound healing reflects the abnormal microenvironment seen in human diabetic wounds and provides insights into the dysregulation of CTGF in diabetic wounds.

Renal connective tissue growth factor correlates with glomerular basement membrane thickness and prospective albuminuria in a non-human primate model of diabetes: possible predictive marker for incipient diabetic nephropathy

Diabetic renal disease is characterized by accumulation of extracellular matrix, glomerulosclerosis, and tubulointerstitial fibrosis. Connective tissue growth factor (CTGF) is implicated in these changes, as it contributes to new matrix synthesis and is increased in the diabetic kidney. CTGF also inhibits mesangial matrix degradation through up-regulation of the tissue inhibitor of matrix metalloproteinase 1 (TIMP-1). In a non-human primate model of diabetes, we determined whether the level of renal CTGF protein before development of albuminuria correlated with renal matrix and TIMP-1 changes and whether renal CTGF predicts progression to albuminuria.

METHODS

In a group of diabetic (n=9) and control (n=6) baboons after a 5-year duration of diabetes, renal tissue CTGF and TIMP-1 were detected by immunohistochemistry and compared with glomerular basement membrane (GBM) thickness and mesangial volume measurements from electron photomicrographs of renal biopsies. Urinary albumin levels were measured at 5 and 10 years of diabetes.

RESULTS

GBM thickness, CTGF protein, and TIMP-1 protein were increased after 5 years of diabetes (each P<.05). Tubular fibronectin scores correlated with tubular CTGF scores (r=0.72, P=.002). In diabetic animals, GBM thickness correlated with tubular and total CTGF levels (P=.002 and P=.04, respectively), whereas mesangial cell and total matrix volume correlated with glomerular TIMP-1 (P=.02 and P=.01, respectively). Tubular CTGF scores (P=.008) and GBM thickness (P=.03) at 5 years in diabetes each predicted the degree of albuminuria at 10 years.

CONCLUSIONS

These results suggest that early increases in renal CTGF protein contribute to incipient diabetic nephropathy and that renal CTGF may have utility as an early marker for progression to dysfunction in the diabetic kidney.

Alterations in liver sinusoidal endothelium in a baboon model of type 1 diabetes

AIMS/HYPOTHESIS

Diabetes mellitus is associated with extensive vascular pathology, yet little is known about its long-term effects on liver sinusoidal endothelial cells (LSECs). Potential diabetic changes in LSECs are important because of the role played by fenestrations in the LSECs in hepatic disposition of lipoproteins.

MATERIALS AND METHODS

Surgical liver biopsies for electron microscopy and immunohistochemistry were obtained from baboons with long-standing streptozotocin-induced, insulin-treated diabetes mellitus and compared with those from age-matched control animals.

RESULTS

There was an increase in the thickness of LSECs (170 +/- 17 vs 123 +/- 10 nm, p < 0.01). Fenestrations in LSECs, as determined by overall porosity, were markedly reduced (1.4 +/- 0.1% vs 2.6 +/- 0.2%, p < 0.01). Increased numbers of stellate cells were seen on electron microscopy, and this finding was corroborated by increased smooth muscle actin expression. Diabetes mellitus was also associated with increased endothelial production of von Willebrand factor and caveolin-1.

CONCLUSIONS/INTERPRETATION

Diabetes mellitus in the non-human primate is associated with marked changes in LSECs, including a reduction in fenestrations. Such changes provide an additional and novel mechanism for impaired hepatic lipoprotein clearance and post-prandial hyperlipidaemia in diabetes mellitus.

Hepatic sinusoidal pseudocapillarization with aging in the non-human primate

BACKGROUND/AIMS

Age-related changes in the hepatic sinusoid termed pseudocapillarization have been reported in the rat and human and have implications for disease susceptibility in old age. In this study, we investigated whether similar changes occur in the livers of old baboons and thus represent a widespread aging change.

METHODS

Liver tissue from five young baboons (5.4+/-0.5yrs) and five old baboons (21.8+/-0.7yrs) was compared by transmission electron microscopy, scanning electron microscopy and immunohistochemistry.

RESULTS

The thickness of the sinusoidal endothelium was increased in old baboons (130+/-8 nm versus 186+/-9 nm, P<0.001) and the frequency of endothelial fenestrae decreased, with the porosity declining from 4.2+/-0.5% to 2.4+/-0.4% (P=0.006). The expression of laminin and von Willebrands factor was more extensive in old baboons. Novel perisinusoidal ring-shaped cells, probably fat-engorged stellate cells, were prominent in the old baboons.

CONCLUSIONS

Pseudocapillarization is a significant age-related change in the baboon liver. Aging in baboons is associated with a novel aging change in the stellate cell not reported in other species. Hepatic pseudocapillarization is a widespread aging liver change found in several species including humans and other non-human primates.

Human beta cells are exceedingly resistant to streptozotocin in vivo

Streptozotocin (STZ) causes beta cell death in rodents via the mechanism of DNA damage precipitating poly(ADP-ribose) synthetase activation followed by lethal nicotinamide adenine dinucleotide depletion. It is unclear whether humans are susceptible to this mechanism. Islets were isolated from STZ-sensitive (CD1 mice and Lewis rats) and resistant [fish (tilapia)] species and from man and then were transplanted into diabetic nude mice under the kidney capsule. Normoglycemic recipients with normal glucose tolerance tests on d 30 were injected with increasing iv doses of STZ and their plasma glucose levels followed for 5 d; glucose tolerance tests were repeated on nondiabetic mice. Mice were then killed; grafts and native pancreata were examined. Based upon three criteria (i.e. nonfasting plasma glucose levels, glucose tolerance tests, and islet histology), the following observations were made: 1) Recipients of rat islets were resistant to 25 mg/kg but were uniformly diabetic at doses of 50 or 75 mg/kg. 2) Recipients of mouse islets were resistant to 75 mg/kg but were uniformly diabetic at 150 or 200 mg/kg. 3) Recipients of the fish islets were resistant to 300, 400, and 450 mg/kg. 4) Recipients of human islets were resistant to 100, 200, 300, 400, and 450 mg/kg. The results in recipient mice bearing long-term rat, mouse, or fish islet grafts were the same as previously published dose-response data for each donor species. We extrapolate from our results based on human islet grafts in mice that human beta cells are exceedingly resistant to STZ.

The effects of aminoguanidine on renal changes in a baboon model of Type 1 diabetes

BACKGROUND

The efficacy of aminoguanidine (AG) on primary prevention of diabetic nephropathy was investigated in a nonhuman primate model of Type 1 diabetes over a period of 4 years.

METHODS

Adolescent male baboons (Papio hamadryas) were assigned to four groups: control, diabetic, and control and diabetic treated with AG. Diabetes was induced with streptozocin (60 mg/kg) and treated with insulin to maintain a mean HbA1c level of about 9%. AG was given subcutaneously (10 mg/kg) each day. All animals had annual renal biopsies and 24-h urine collections for measurements of glomerular basement membrane (GBM) thickness, fractional mesangium volume (FMV), albumin excretion rate (AER), and creatinine clearance. Glomerular filtration rate (GFR) and renal plasma flow (RPF) were also determined.

RESULT

The diabetic animals had increased GBM after 2 years of diabetes, but there was no increase in FMV over the study period. AG prevented the thickening of GBM at the 3- and 4-year time points. AG and diabetes synergistically increased the GFR. All diabetic animals developed increased albuminuria during the study although lower than the conventionally accepted microalbuminuria range. AG was not able to prevent this and, in fact, led to the nondiabetic animals also developing albuminuria.

CONCLUSION

This is the first study to investigate the early use of AG in ameliorating renal damage in a primate model of Type 1 diabetes. The structural and functional changes in the kidney of these animals resemble those seen in the early stages of the human disease. AG was able to significantly reduce the thickening of GBM due to diabetes. This may suggest a potential role for this in primary prevention of diabetic nephropathy in the future.

Cardiovascular structure and function in baboons with Type 1 diabetes -- a transvenous ultrasound study

Diabetes mellitus is an important risk factor for both macrovascular and cardiac disease in humans. The availability of a novel intravenous ultrasound probe allows detailed interrogation of a large proportion of the vasculature, as well as the heart, during the same examination. Six male baboons (Papio hamadryas) with Type 1 diabetes and known microangiopathy, and six control animals were studied. Vascular structure in the major large arteries and cardiac function were studied using transvenous ultrasound introduced via the right femoral vein and positioned under fluoroscopy. All arteries were examined for atherosclerotic plaque and for presence of increased intima-media thickness (IMT). Left ventricular function was assessed at rest and following infusions of dobutamine (positive inotrope) and esmolol (negative inotrope). The procedure was performed safely and successfully in all cases. No atherosclerotic plaque was seen in either diabetic or normal baboons. There was no difference in the aortic IMT (0.38+/-0.04 vs. 0.37+/-0.05 mm, normal vs. diabetic, P=NS) or in doppler flow in the renal or iliac arteries between diabetic and normal baboons. Left ventricular wall thickness and systolic tissue velocity were similar in the two groups at rest (6.9+/-2.5 vs. 6.2+/-1.4 cm/s, normal vs. diabetic, P=NS), after dobutamine (15.5+/-2.2 vs. 12.7+/-3.9 cm/s, normal vs. diabetic, P=NS), and after esmolol (4.3+/-1.0 vs. 5.6+/-1.0 cm/s, normal vs. diabetic, P=NS). In a high primate model of diabetes with microangiopathy, the presence of hyperglycemia for 7 years per se does not produce abnormalities of macrovascular or cardiac structure.

Effects of ketamine sedation on glucose clearance, insulin secretion and counterregulatory hormone production in baboons (Papio hamadryas)

Since the effects of ketamine sedation seem to differ between subspecies of baboons, we assessed the endocrine response to an intravenous glucose tolerance test (IVGTT) in 12 hamadryas baboons. The first phase insulin secretion, basal insulin, and glucose levels, as well as the glucose clearance, were significantly lower in sedated baboons as compared to fully awake animals. Glucagon and cortisol were significantly higher, while growth hormone was lower during ketamine sedation. Papio hamadryas appears to be a promising pre-clinical model for the study of endocrine replacement therapy in insulin-dependent diabetes. However, the data obtained must be interpreted with the knowledge that the anesthetic employed to allow for testing of the animals does have an effect on the parameters described in this report.

Changes in the molecular structure of hair in insulin-dependent diabetes

Low-angle synchrotron X-ray diffraction has revealed clear and consistent changes in the molecular structure of alpha-keratin of hair in insulin-dependent diabetes (IDDM) both for human IDDM subjects and for baboons with streptozocin induced diabetes. These changes in both meridional and equatorial intensity distributions are fully explained by a newly developed hexagonally packed model for keratin which locates the modification produced in hair in IDDM in the labile structure of the matrix at established intermediate filament linkage sites. The nature of the extracellular bonding suggests that the change is endogenous, occurring via the blood during the aggregation of the IFs in the follicle. The reproducibility of these changes indicate that hair may represent an easily accessible tissue for the study of how hyperglycaemia can modify extracellular matrix materials which lead to diabetic complications.

Changes of extracellular matrix in a baboon (Papio hamadryas) model of insulin dependent diabetes: studies using electron microscopy and X-ray diffraction techniques

Extracellular matrix plays an important role in many physiological functions and its abnormalities are thought to play a key role in the pathogenesis of diabetic complications. In this paper we used the techniques of electron microscopy, immunostaining and X-ray diffraction to document some of the early events in the changes of extracellular matrix in a model of insulin dependent diabetes in baboons. Our results show that thickening of basement membrane and enlargement of mesangium are demonstrable in the glomeruli of prepubertal diabetic baboons within 2 years from the onset of diabetes. Concomitant with this was the accumulation of type IV collagen and laminin in the mesangium. By contrast, even the very sensitive technique of X-ray diffraction failed to demonstrate changes in the equatorial direction of collagen molecules of the skin and tendon. We conclude that changes of glomerular extracellular matrix are demonstrable early in insulin dependent diabetes even in prepubertal baboons. These can be used as endpoints in evaluating the efficacy of pharmacological agents such as aminoguanidine in preventing diabetic complications.