Variations of susceptibility to alloxan induced diabetes in the rabbit

Practical considerations for reducing mortality rates in alloxan-induced diabetic rabbits

Chemically-induced diabetic animal models have been employed in many areas of diabetes mellitus (DM) research, but managing post-induction animal survival rates remains one of the main downsides.

The aim of the present study was to propose a reliable approach to animal management and monitoring after DM induction in a rabbit model in order to reduce animal mortality rates.

DM was induced by injecting alloxan in 12 New Zealand White rabbits. A preventive subcutaneous glucose administration to counteract a potentially lethal hypoglycemic phase following alloxan injection was performed on individual bases. Blood glucose level (BGL) was checked hourly for the first 36 h, then every 2 h until the hyperglycemic state was confirmed.

All 12 rabbits survived a 48-hour post-induction phase. The critical hypoglycemic phase's start points and duration differed significantly among the rabbits, lasting from 6.7 to 37 h (19.75 ± 8.44). The rabbits entered the final hyperglycemic phase 18 h at the earliest and 42 h at the latest after induction (26.63 ± 7.07). The average daily BGLs throughout the study period ranged from 268 to 512 mg/dL (413.73 ± 76.69). Eleven rabbits survived until the end of the experiment.

The variability of rabbits' responses to alloxan injection emphasizes the importance of monitoring rabbit behavior and thoroughly checking BGLs, followed by a preventive glucose administration based on rabbits' individual needs for up to 36 h after alloxan injection. The proposed approach seems to reduce animal mortality.

Determination of the optimal diabetes duration for bone regeneration experiments in an alloxan-induced diabetic rabbit calvarial defect model

Purpose

The purpose of this study was to evaluate the optimal diabetes duration for bone regeneration experiments in an alloxan monohydrate (ALX)–induced diabetic rabbit calvarial defect model by evaluating the association between diabetes duration and bone healing capacity.

Methods

Twenty-four New Zealand white rabbits were used. Twenty-two rabbits were injected with 100 mg/kg of ALX to induce experimental diabetes. These rabbits were divided into 4 groups, including a control group and groups with diabetes durations of 1 week (group 1), 2 weeks (group 2), and 4 weeks (group 3). Calvarial defects were created at 1, 2, and 4 weeks after ALX injection and in the control rabbits. Cone-beam computed tomography (CBCT) scanning was performed on the day of surgery and at 2 and 4 weeks after surgery. The rabbits were sacrificed 4 weeks after surgery, followed by histological and immunofluorescence analysis.

Results

The diabetic state of all diabetic rabbits was well-maintained throughout the experiment. Reconstructed 3-dimensional CBCT imaging showed more rapid and prominent bone regeneration in the control group than in the experimental groups. Histological staining showed notable bone regeneration in the control group, in contrast to scarce bone formation in the experimental groups. The appearance and immunoreactivity of receptor activator of nuclear factor-kappa B and osteoprotegerin did not show notable differences among the groups.

Conclusion

ALX administration at 100 mg/kg successfully induced experimental diabetes in rabbits. The effect of diabetes on bone healing was evident when the interval between diabetes induction and the intervention was ≥1 week.

Evaluating the effect of Sarconesiopsis magellanica (Diptera: Calliphoridae) larvae-derived haemolymph and fat body extracts on chronic wounds in diabetic rabbits

We evaluated extracts taken from S. magellanica third instar larvae fat body and haemolymph using a diabetic rabbit model and compared this to the effect obtained with the same substances taken from Lucilia sericata larvae. Alloxan (a toxic glucose analogue) was used to induce experimental diabetes in twelve rabbits. Dorsal wounds were made in each animal and they were infected with Staphylococcus aureus and Pseudomonas aeruginosa. They were then treated with haemolymph and lyophilized extracts taken from the selected blowflies' larvae fat bodies. Each wound was then evaluated by using rating scales and histological analysis. More favourable scores were recorded on the PUSH and WBS scales for the wounds treated with fat body derived from the larvae of both species compared to that obtained with haemolymph; however, wounds treated with the substances taken from S. magellanica had better evolution. Histological analysis revealed that treatment led to tissue proliferation and more effective neovascularisation in less time with both species' fat body extracts compared to treatment with just haemolymph. The results suggest the effectiveness of the substances evaluated and validate them in the animal model being used here as topical agents in treating chronic wounds.

Creating a long-term diabetic rabbit model

This study was to create a long-term rabbit model of diabetes mellitus for medical studies of up to one year or longer and to evaluate the effects of chronic hyperglycemia on damage of major organs. A single dose of alloxan monohydrate (100 mg/kg) was given intravenously to 20 young New Zealand White rabbits. Another 12 age-matched normal rabbits were used as controls. Hyperglycemia developed within 48 hours after treatment with alloxan. Insulin was given daily after diabetes developed. All animals gained some body weight, but the gain was much less than the age-matched nondiabetic rabbits. Hyperlipidemia, higher blood urea nitrogen and creatinine were found in the diabetic animals. Histologically, the pancreas showed marked beta cell damage. The kidneys showed significantly thickened afferent glomerular arterioles with narrowed lumens along with glomerular atrophy. Lipid accumulation in the cytoplasm of hepatocytes appeared as vacuoles. Full-thickness skin wound healing was delayed. In summary, with careful management, alloxan-induced diabetic rabbits can be maintained for one year or longer in reasonably good health for diabetic studies.

Effect of endogenous beta-hydroxybutyrate on brain glucose metabolism in fetuses of diabetic rabbits, studied by (13)C magnetic resonance spectroscopy

The aim of our research was to uncover perturbations in in-utero fetal cerebral metabolism resulting from hyperglycemia and hyperketonemia, which occur during maternal diabetes. Therefore, we examined the effects of glucose overload and hyperketonemia on glucose metabolism in the diabetic fetal brain; more specifically, the effect of diabetes on the glucose flux via pyruvate dehydrogenase (PDH) and pyruvate carboxylase (PC) and subsequent metabolism in the fetal cerebral tricarboxylic acid (TCA) cycle were examined, as well as the effect of diabetes on energy fuel utilization in the neurons and glia. Diabetes was induced in pregnant rabbits, and towards term, [U-(13)C(6)]glucose was infused into maternal circulation, and [(13)C]glucose metabolites were subsequently studied in fetal brain extracts by (13)C MRS isotopomer analysis. Significantly elevated maternal and fetal plasma glucose levels (three- and up to fivefold, respectively) and fetal brain glucose levels (up to eightfold) accompanied by an increase of beta-hydroxybutyrate (beta-HBA) levels (approximately 20-fold) were found in the hyperketonemic diabetic animals, whereas fetal cerebral lactate levels were decreased. Alterations in the (13)C labeling patterns, mainly of glutamine, led us to suggest that the entry of beta-HBA-derived acetyl-CoA inhibits formation and entry of labeled glucose-derived acetyl-CoA into the TCA cycle, mainly in glia. Accumulation of glucose and the decrease in lactate levels in the fetal brain are most likely the result of an inhibitory effect of beta-HBA on glycolysis. In addition, loss of (13)C enrichment of TCA cycle intermediates and products, glutamate and glutamine, in the hyperketonemic diabetic fetal brain may be attributed to the effect of beta-HBA fuel utilization by the fetal brain.

Effect of endogenous beta-hydroxybutyrate on glucose metabolism in the diabetic rabbit brain: a (13)C-magnetic resonance spectroscopy study of [U-(13)C]glucose metabolites

The neurological consequences of diabetes mellitus have recently been receiving greater attention in both clinical and experimental settings. The deleterious effect of hyperglycemia and altered oxidative substrate availability on the diabetic brain is the subject of many studies. The aim of the present study was to examine the effect of the altered metabolic environment, namely, hyperglycemia and hyperketonemia, on glucose metabolism in the diabetic brain. More specifically, we examined the effect of diabetes on the glucose flux via the pyruvate dehydrogenase (PDH) and pyruvate carboxylase (PC) pathways and subsequent metabolism in the tricarboxylic acid cycles in neurons and glia. To this end, [U-(13)C]glucose was infused into the circulation of alloxan-induced diabetic young adult rabbits, and the [(13)C]glucose metabolites were subsequently studied in brain extracts by (13)C-NMR. Significantly elevated brain glucose levels were found. In the hyperketonemic rabbits, elevated cerebral levels of beta-hydroxybutyrate (beta-HBA) were found. Alterations in the labeling patterns of glutamine in the hyperketonemic group lead to the conclusion that the elevated beta-HBA levels inhibit glucose metabolism, mostly in glia. This results in accumulation of glucose in the diabetic brain. In addition, altered levels of glutamine, glutamate, and GABA were also attributed to the effect of beta-HBA on brain metabolism. The possible role of these metabolic perturbations in causing neurological damage remains to be investigated.

Diabetes attenuates the alterations in both venous endothelial and smooth muscle cell function induced by prolonged hypercholesterolemia in an experimental model

The systemic effects of the combination of diabetes and hypercholesterolemia on venous vasomotor function are poorly understood. This study examines in vitro vasomotor responses of New Zealand White rabbit jugular veins from control, diabetic, hypercholesterolemic, and hypercholesterolemic with diabetes groups. Hypercholesterolemia was induced with a diet supplemented with 1% cholesterol, while diabetes was induced by alloxan. Cumulative dose response curves to norepinephrine, bradykinin, and histamine were performed. After precontraction with norepinephrine to give 80% maximal contraction, relaxation in response to acetylcholine and sodium nitroprusside was determined. Potency of the agonist responses were compared. The contractile responses to all agonists were significantly increased in hypercholesterolemia. Only the response to norepinephrine was increased in diabetes. However, when diabetes and hypercholesterolemia were combined the contractile response to bradykinin was increased, the response to histamine was significantly decreased, but the norepinephrine response was unchanged. There was dose-dependent, endothelium-mediated relaxation in precontracted control and diabetic veins. Hypercholesterolemia and hypercholesterolemia with diabetes interfered with endothelium-mediated relaxation, producing a multiphasic response: relaxation at low concentrations followed by contraction at higher concentrations. Non-endothelium-dependent relaxation to sodium nitroprusside of precontracted veins was unaffected by the presence of diabetes or hypercholesterolemia. This study suggests that the combined presence of diabetes and hypercholesterolemia attenuated the altered contractile responses induced by hypercholesterolemia alone without further alterations in endothelial-mediated responses. The mechanism for these alterations remains to be determined.

Accelerated intimal hyperplasia and increased endogenous inhibitors for NO synthesis in rabbits with alloxan-induced hyperglycaemia

1. We examined whether endogenous inhibitors of NO synthesis are involved in the augmentation of intimal hyperplasia in rabbits with hyperglycaemia induced by alloxan. 2. Four weeks after the endothelial denudation of carotid artery which had been performed 12 weeks after alloxan, the intimal hyperplasia was greatly augmented with hyperglycaemia. The degree of hyperplasia was assessed using three different parameters of histopathological findings as well as changes in luminal area and intima: media ratio. 3. There were positive and significant correlations between intima:media ratio, plasma glucose, and concentrations of N(G)-monomethyl-L-arginine (L-NMMA) and N(G), N(G)-dimethyl-L-arginine (ADMA) in endothelial cells, that is, the intima:media ratio became greater as plasma glucose and endothelial L-NMMA and ADMA were increased. Furthermore, endothelial L-NMMA and ADMA were increased in proportion to the increase in plasma glucose. 4. In contrast, there were inverse and significant correlations between cyclic GMP production by carotid artery strips with endothelium and plasma glucose, between cyclic GMP production and endothelial L-NMMA and ADMA, and between the intima:media ratio and cyclic GMP production. 5. Exogenously applied L-NMMA and ADMA inhibited cyclic GMP production in a concentration-dependent manner. IC50 values were determined to be 12.1 microM for the former and 26.2 microM for the latter. The cyclic GMP production was abolished after the deliberate removal of endothelium from the artery strips. 6. These results suggest that the augmentation of intimal hyperplasia with hyperglycaemia is closely related to increased accumulation of L-NMMA and ADMA with hyperglycaemia, which would result in an accelerated reduction in NO production/release by endothelial cells.

Diabetes mellitus and experimental vein graft structure and function

PURPOSE

Diabetes mellitus is a known risk factor for accelerated atherosclerosis and for postangioplasty restenosis.

METHODS

This study examines the effect of chronic, uncontrolled, alloxan-induced diabetes on the structure and vasomotor function of vein bypass grafts in 20 male New Zealand white rabbits with diabetes and in 10 controls. After 8 weeks of diabetes, a common carotid vein bypass graft was performed. Four weeks after operation, vein grafts and contralateral jugular veins were harvested.

RESULTS

Diabetes induced a twofold increase in the vein graft intimal thickness compared with control. There was no change in medial thickness. Electron microscopy of the vein grafts in diabetes revealed intercellular gaps in the endothelium lining and abnormal endothelial cell junctions compared with controls. Diabetes significantly increased the maximal contractions generated in vein grafts to all contractile agonists tested without any change in sensitivity.

CONCLUSIONS

This study demonstrates that diabetes alters endothelial cell structure and increases the development of intimal hyperplasia with increased maximal contractility in vein grafts and therefore suggests that the vein grafts in diabetes are more susceptible to early stenosis.

Circadian variation in alloxan sensitivity of mice as indicated by mortality and blood glucose alteration

The objective of this study was to determine in mice if a time-dependent pancreatic beta-cell susceptibility to alloxan could be correlated to daily changes in blood glucose levels and to monitor the pattern of blood glucose at various times of day as mice became diabetic. Food was removed from mice standardized to a 12-h light:dark cycle (lights on at 0600 h CST, during the month of June) at 12 h before subcutaneous injection with 0.27 mg/g of alloxan. Six groups of 30 fasted mice were injected at 4-h intervals. Blood glucose levels were measured from each group immediately prior to injection, and at 2, 4, 8, 12, 24, 48, and 216 h after treatment. Animals receiving alloxan during the early- to middark period had an increase in blood glucose after 2 h, followed by a decline to hypoglycemic levels between 4 and 8 h, and recovery to hyperglycemic levels 48 h after alloxan exposure. Three and 30% of these animals were dead at 8 and 48 h, respectively. Mice treated during the midlight span had decreased blood glucose levels 2 h after alloxan treatment followed by an increase to diabetic hyperglycemia within 48 h. Twenty-three and 70% of the animals treated at 1430 h were dead at 8 and 48 h, respectively. At 216 h, total mortality was 45.6% and 81 of the 98 surviving mice were hyperglycemic. These data suggest a greater sensitivity to alloxan during the midlight resting period of the mice. This may be the result of increased sensitivity to the insulin released from the beta cells when alloxan was given during the light span.