Spontaneous recovery from non-insulin-dependent diabetes mellitus induced by neonatal streptozotocin treatment in spontaneously hypertensive rats

Rodent models for diabetes

Diabetes mellitus (DM) is associated with many health complications and is potentially a morbid condition. As prevalence increases at an alarming rate around the world, research into new antidiabetic compounds with different mechanisms is the top priority. Therefore, the preclinical experimental induction of DM is imperative for advancing knowledge, understanding pathogenesis, and developing new drugs. Efforts have been made to examine recent literature on the various induction methods of Type I and Type II DM. The review summarizes the different in vivo models of DM induced by chemical, surgical, and genetic (immunological) manipulations and the use of pathogens such as viruses. For good preclinical assessment, the animal model must exhibit face, predictive, and construct validity. Among all reported models, chemically induced DM with streptozotocin was found to be the most preferred model. However, the purpose of the research and the outcomes to be achieved should be taken into account. This review was aimed at bringing together models, benefits, limitations, species, and strains. It will help the researcher to understand the pathophysiology of DM and to choose appropriate animal models.

Current status and patent prospective of animal models in diabetic research

Diabetes mellitus is a heterogeneous complex metabolic disorder with multiple etiology which characterized by chronic hyperglycemia resulting from defects in insulin secretion, insulin action or both. The widespread occurrence of diabetes throughout the world has increased dramatically over the past few years. For better understanding, appropriate animal models that closely mimic the changes in humans needed, as vital tool for understanding the etiology and pathogenesis of the disease at the cellular/molecular level and for preclinical testing of drugs. This review aims to describe the animal models of type-1 diabetes (T1Ds) and T2Ds to mimic the causes and progression of the disease in humans. And also we highlight patent applications published in the last few years related to animal models in diabetes as an important milestone for future therapies that are aim to treating diabetes with specific symptoms and complications.

Effect of insufficient insulin treatment in streptozotocin-induced diabetes mellitus

OBJECTIVES

In this study, we investigated clinically, pathologically, and immunohistochemically the effect of insufficient short-acting insulin treatment on streptozotocin (STZ)-induced diabetes mellitus in rats.

METHODS

Three groups composed of 10 rats each were studied as follows: (1) a group that received only STZ (50 mg/kg) (STZ group); (2) a group that received 50 mg/kg STZ and, after 12 hours, 8 IU of short-acting insulin treatment (STZ + INS group), repeated every night for 5 days; and (3) a control group. Ketonuria and blood glucose levels were examined every day. Blood was obtained from 2 rats from each group, and necropsy was performed every day during the 5-day period.

RESULTS

Hyperglycemia was observed in the STZ and STZ + INS groups 24 hours after, but levels were higher in the STS + INS group than those in the STZ-only group. Histopathology was similar in the STZ and STZ + INS groups, and degeneration was observed in both groups, but immunohistochemistry revealed a more severe reduction in insulin-secreting cells in the STZ + INS group than that in the STZ group. There were no hyperglycemia and histopathological or immunochemical alteration in the control group.

CONCLUSIONS

This study showed that insufficient short-acting insulin treatment can increase the diabetogenic effect of STZ in rats.

The effects of acarbose and Rumex patientia L. on ultrastructural and biochemical changes of pancreatic B cells in streptozotocin-induced diabetic rats

This study was performed to observe the effects of acarbose and Rumex patientia on morphological change of pancreatic B cells in streptozotocin (STZ)-induced diabetic (type 2) rats. Two-day-old Wistar albino rats were intraperitoneally injected with 100mg/kg of STZ or vehicle alone for control. Vehicle and STZ given rats were divided into six groups (1st, 2nd and the 3rd groups are control; the 4th, 5th and 6th groups are STZ groups). The 1st and the 4th groups received water, the 2nd and the 5th groups received 40 mg acarbose/100 g feed, the 3rd and the 6th groups received 2% decoction of Rumex patientia grain. During experimentation period, blood glucose levels were checked periodically, and HbA1c level was measured from cardiac blood at the end of the experiment. Pancreas tissues were examined by electron microscope. Glucose and HbA1c levels increased by STZ were decreased by acarbose and Rumex patientia. Morphologically, we found a mitochondrial vacuolization and swelling as well as dilatation of the endoplasmic reticulum in the B cells of STZ-induced diabetic rats. Also, a decrease in the secretory granules of B cells was observed in the STZ-induced diabetic group. No pathological changes were observed in the STZ+acarbose group. In the STZ+Rumex patientia group, a weak swelling in the B cells was observed in the some of the mitochondria.

The role of exercise on long-term effects of alloxan administered in neonatal rats

The present study was designed to analyse the effects of aerobic exercise on the metabolic effects of alloxan. Male Wistar newborn rats (2 days old) received alloxan (200 mg (kg body weight)(-1)) intraperitoneally (A rats). Vehicle-injected rats were used as controls (C rats). At 28 days old, some of the A rats were subjected to swimming for 1 h day(-1), 5 day week(-1) (AT rats). At 28, 60 and 90 days old the animals were subjected to glucose (GTTo) and insulin (ITTsc) tolerance tests. All the animals were then killed by decapitation for blood and tissue evaluations. On the 60th day, there was a reduction in blood glucose level during the GTTo (mmol l(-1) (90 min)(-1)) in the AT rats (7640.7 +/- 694.0) with respect to C (7057.5 +/- 776.9) and A (8555.6 +/- 1096.7) rats. However on the 90th day, AT rats showed higher glucose levels (8004.6 +/- 267.9) when compared to the other groups (C, 7305.5 +/- 871.2; A, 7088.8 +/- 536.9). The serum free fatty acid (FFA) concentration (microEq l(-1)) was higher in the alloxan-treated animals (A, 231.1 +/- 58.5; AT, 169.8 +/- 20.1) than in controls (C, 101.4 +/- 22.4). In conclusion, although the high blood glucose level is transitory in the A animals, some blood and tissue alterations remain and can be harmful to the maintenance of homeostasis. Physical exercise counteracted only partially these alterations. Furthermore, training worsened glucose tolerance at the 90th day, suggesting that exercise intensity should be adjusted to the diabetic condition.

Overview of studies on metabolic and vascular regulatory changes in early diabetic retinopathy

The present review provides an overview of recent research describing functional changes to the retinal vasculature in very early diabetes. The research focuses on the streptozotocin rat model after 4-6 weeks of induced diabetes and describes functional changes to retinal blood flow, vascular control and retinal oxygenation, as well as a strong vasodilatory response to insulin in the retinal vasculature. The review raises the question of whether choroid dysfunction is also a feature of diabetic retinopathy.

Diabetic retinopathy: early functional changes

1. The present review reports some of the earliest physiological changes that occur in the diabetic retina prior to any clinical or anatomical changes in an animal model of diabetes. 2. Using chemically induced diabetes (by streptozotocin) in rats, retinal blood flow and vitreal and retinal oxygen tension were determined after 5 weeks of sustained hyperglycaemia. Blood flow was greater and was also redistributed in the diabetic group compared with values for the control group. At the same time, oxygen tension distribution was altered around retinal arterioles, implying an increase in retinal oxygen consumption in these early diabetic retinas. 3. The possibility that the blood flow changes could be due to altered control mechanisms in the retinal vasculature was confirmed using an isolated, perfused eye preparation. In diabetic eyes an altered reactivity to test pharmacological agents was demonstrated after 4 weeks of diabetes. 4. To further explore these vascular response changes we developed an isolated, perfused retinal arteriolar preparation in which individual segments of the vasculature can be tested. The possibility that insulin has a direct vasodilator effect on retinal arterioles was confirmed and was demonstrated to act via nitric oxide released from the vascular endothelial cells. These data may implicate the diabetic-induced insulin changes in early retinal changes. 5. Evidence is presented that although early glucose control may be vital in stopping the onset of diabetic retinopathy, there comes a stage in the induced diabetic cascade where if the retinopathy has commenced, good glucose control cannot stop the further progression of the retinopathy.

Renoprotective effect of enalapril in uninephrectomized spontaneously hypertensive rats with neonatal streptozotocin-induced diabetes

We compared the renoprotective effect between angiotensin-converting enzyme inhibitor, enalapril, and a dihydropyridine-type calcium channel blocker, nicardipine, in a severe form of renal injury in rats. Two-day-old spontaneously hypertensive rats (SHR) were injected with streptozotocin or vehicle as control. UNX was performed at 3 weeks of age, and enalapril or nicardipine was administered in drinking water from 7 weeks of age. Uninephrectomy (UNX) markedly exacerbated hypertension and renal injury in the nondiabetic and diabetic SHR. Enalapril and nicardipine comparably reduced blood pressure in UNX diabetic SHR. However, serum creatinine was significantly elevated in the nicardipine-treated group as compared with the enalapril-treated group at 24 weeks of age (nicardipine-treated group, 67 +/- 4 microM; enalapril-treated group, 49 +/- 3 microM; P < 0.01; untreated group 57 +/- 4 microM). Furthermore, the incidence of glomerular sclerosis was similar between untreated and nicardipine-treated groups, whereas it tended to be reduced in the enalapril-treated group. In a separate experiment of diabetic SHR without UNX, enalapril therapy significantly ameliorated hyperglycemia and albuminuria (P < 0.01). This study showed that a renoprotective effect was seen in enalapril but not in nicardipine in UNX diabetic SHR despite the comparable reduction of blood pressure. This suggests that enalapril may be more effective than nicardipine in delaying the progression of a severe form of diabetic nephropathy.

Spontaneous remission of diabetes arrests progression of nephropathy in streptozotocin-treated spontaneously hypertensive rats

Although antihypertensive therapy retards the progression of diabetic nephropathy associated with hypertension, it is not known whether glycemic control reverses or arrests diabetic nephropathy under untreated hypertension. We previously reported that spontaneous remission of diabetes occurred in the neonatal streptozotocin (STZ) model of spontaneously hypertensive rats (SHR) after 28 weeks of age, whereas hypertension persisted. Thus, we studied diabetic nephropathy before and after the recovery from hyperglycemia in this model. Two-day-old male SHR were injected intraperitoneally with STZ or vehicle for control. Hypertension was developed and maintained in both STZ and control groups in a similar degree. Before the amelioration of hyperglycemia, urinary albumin excretion increased progressively in STZ-treated SHR as compared with control (24 weeks; 1.6 +/- 0.5 mg/day, 17.5 +/- 2.3 mg/day, P < 0.001), and renal and glomerular hypertrophies were seen with mesangial expansion in STZ-treated SHR. However, along the recovery from hyperglycemia, urinary albumin excretion did not increase in the STZ-treated group, while it consistently increased in the control group (52 weeks; 25.4 +/- 10.0 mg/day, 29.7 +/- 11.4 mg/day, not significant). Furthermore, there were no significant differences in renal weight, glomerular tuft area, and the incidence of glomerular sclerosis between the two groups at 52 weeks of age. This study suggests that glycemic control may be effective for diabetic nephropathy even in the coexistence of untreated hypertension.

A new diabetes model induced by neonatal alloxan treatment in rats

Rats treated with streptozotocin (STZ) during the neonatal period have been used as a model of non-insulin-dependent diabetes mellitus. The present study was designed to produce another diabetes model by substituting alloxan for STZ. Male Sprague-Dawley rats of 2, 4 or 6 days of age were injected intraperitoneally with 200 mg/kg of alloxan monohydrate after 16 h fast. Control rats received vehicle alone at 6 days of age. Non-fasting plasma glucose levels in alloxan-treated rats significantly increased after 8 weeks as compared with control, as the age of alloxan treatment advanced (6.6 +/- 0.2 (S.E.M.) mM in control, 8.3 +/- 0.3 mM in 2 days, P < 0.05, 9.8 +/- 0.9 mM in 4 days, P < 0.05, 17.1 +/- 3.5 mM in 6 days, P < 0.05). For the long-term observation, alloxan-treated rats were divided into mild and severe diabetes groups. Hyperglycemia persisted in both groups until 52 weeks (6.5 +/- 0.1 mM in control, 10.3 +/- 0.7 mM in mild diabetes group, 25.3 +/- 3.6 mM in severe group), but significant albuminuria developed only in severe diabetes group. The diabetogenicity of alloxan rapidly increased during the neonatal period, and the neonatal alloxan diabetes model may be useful for studying chronic diabetic complications.