Neonatal STZ model of type II diabetes mellitus in the Fischer 344 rat: characteristics and assessment of the status of the hepatic adrenergic receptors

Olfactory Dysfunction in Diabetic Rats is Associated with miR-146a Overexpression and Inflammation

Type 2 diabetes (T2D) is associated with cognitive decline and dementia. Both neurodegenerative conditions are characterized by olfactory dysfunction (OD) which is also observed in diabetic patients. Diabetes and neurodegeneration display altered miRNAs expression; therefore, the study of miRNAs in the diabetic olfactory system is important in order to know the mechanisms involved in neurodegeneration induced by T2D. In this work we evaluated the expression of miRs206, 451, 146a and 34a in the olfactory bulb (OB) of T2D rats and its association with OD. T2D induction was performed by administering streptozotocin to neonatal rats. The olfactory function was evaluated after reaching the adulthood by employing the buried pellet and social recognition tests. After 18 weeks, animals were sacrificed to determinate miRNAs and protein expression in the OB. T2D animals showed a significant increase in the latency to find the odor stimulus in the buried pellet test and a significant reduction in the interest to investigate the novel juvenile subjects in the social recognition test, indicating OD. In miRNAs analysis we observed a significant increase of miR-146a expression in the OB of T2D rats when compared to controls. This increase in miR-146a correlated with the overexpression of IL-1β in the OB of T2D rats. The present results showed that OD in T2D rats is associated with IL-1β mediated-inflammation and miR-146a overexpression, suggesting that high levels of IL-1β could trigger miR-146a upregulation as a negative feedback of the inflammatory response in the OB of T2D rats.

A Comprehensive Review on Preclinical Diabetic Models

BACKGROUND

Preclinical experimental models historically play a critical role in the exploration and characterization of disease pathophysiology. Further, these in-vivo and in-vitro preclinical experiments help in target identification, evaluation of novel therapeutic agents and validation of treatments.

INTRODUCTION

Diabetes mellitus (DM) is a multifaceted metabolic disorder of multidimensional aetiologies with the cardinal feature of chronic hyperglycemia. To avoid or minimize late complications of diabetes and related costs, primary prevention and early treatment are therefore necessary. Due to its chronic manifestations, new treatment strategies need to be developed, because of the limited effectiveness of the current therapies.

METHODS

The study included electronic databases such as Pubmed, Web of Science and Scopus. The datasets were searched for entries of studies up to June, 2018.

RESULTS

A large number of in-vivo and in-vitro models have been presented for evaluating the mechanism of anti-hyperglycaemic effect of drugs in hormone-, chemically-, pathogen-induced animal models of diabetes mellitus. The advantages and limitations of each model have also been addressed in this review.

CONCLUSION

This review encompasses the wide pathophysiological and molecular mechanisms associated with diabetes, particularly focusing on the challenges associated with the evaluation and predictive validation of these models as ideal animal models for preclinical assessments and discovering new drugs and therapeutic agents for translational application in humans. This review may further contribute to discover a novel drug to treat diabetes more efficaciously with minimum or no side effects. Furthermore, it also highlights ongoing research and considers the future perspectives in the field of diabetes.

Neonatal hyperglycemia induces CXCL10/CXCR3 signaling and microglial activation and impairs long-term synaptogenesis in the hippocampus and alters behavior in rats

BACKGROUND

Hyperglycemia is common in extremely low gestational age newborns (ELGAN) and is associated with increased mortality and morbidity, including abnormal neurodevelopment. Hippocampus-mediated cognitive deficits are common in this population, but the specific effects of hyperglycemia on the developing hippocampus are not known.

METHODS

The objective of this study was to determine the acute and long-term effects of hyperglycemia on the developing hippocampus in neonatal rats using a streptozotocin (STZ)-induced model of hyperglycemia. STZ was injected on postnatal day (P) 2, and littermates in the control group were injected with an equivalent volume of citrate buffer. The acute effects of hyperglycemia on markers of oxidative stress, inflammatory cytokines, microglial activation, and reactive astrocytosis in the hippocampus were determined in the brain tissue collected on P6. The long-term effects on hippocampus-mediated behavior and hippocampal dendrite structure were determined on P90.

RESULTS

On P6, the transcript and protein expression of markers of oxidative stress and inflammatory cytokines, including the CXCL10/CXCR3 pathway, were upregulated in the hyperglycemia group. Histological evaluation revealed microglial activation and astrocytosis. The long-term assessment on P90 demonstrated abnormal performance in Barnes maze neurobehavioral testing and altered dendrite structure in the hippocampus of formerly hyperglycemic rats.

CONCLUSIONS

Neonatal hyperglycemia induces CXCL10/CXCR3 signaling, microglial activation, and astrocytosis in the rat hippocampus and alters long-term synaptogenesis and behavior. These results may explain the hippocampus-specific cognitive deficits common in ELGAN who experience neonatal hyperglycemia.

Evaluation of neonatal streptozotocin induced diabetic rat model for the development of cataract

Type 2 diabetes (T2D) generally follows prediabetes (PD) conditions such as impaired fasting glucose (IFG) and/or impaired glucose tolerance (IGT). Although studies reported an association of IGT or IFG with cataract, the experimental basis for PD associated cataract is not known. Hence, we evaluated neonatal streptozotocin (nSTZ) induced rat model to study PD associated cataractogenesis by injecting STZ to two-day old rats. While majority (70%) of nSTZ injected pups developed IGT (nSTZ-PD) by two months but not cataract even after seven months, remaining (30%) nSTZ rats developed hyperglycemia (nSTZ-D) by two months and mature cataract by seven months. Lens biochemical analysis indicated increased oxidative stress as indicated by increased SOD activity, lipid peroxidation, and protein carbonyl levels in nSTZ-D cataractous lens. There was also increased polyol pathway as assessed by aldose reductase activity and sorbitol levels. Though nSTZ-PD animals have not shown any signs of lenticular opacity, insolubilization of proteins along with enhanced polyol pathway was observed in the lens. Further there was increased oxidative stress in lens of IGT animals. These results suggest that oxidative stress along with increased polyol pathway might play a role in IGT-associated lens abnormalities. In conclusion, nSTZ-PD rat model could aid to investigate IGT-associated lens abnormalities.

Intranasal insulin affects adenyl cyclase system in rat tissues in neonatal diabetes

The changes in hormone-regulated adenylyl cyclase (AC) signaling system implicated in control of the nervous, cardiovascular and reproductive systems may contribute to complications of diabetes mellitus (DM). We investigated the functional state of AC system in the brain, myocardium, ovary and uterus of rats with neonatal DM and examined the influence of intranasally administered insulin on the sensitivity of this system to biogenic amines and polypeptide hormones. The regulatory effects of somatostatin and 5-HT1BR-agonist 5-nonyloxytryptamine acting via Gi protein-coupled receptors were significantly decreased in DM and partially restored in insulin-treated rats. The effects of hormones, activators of AC, are changed in tissue- and receptorspecific manner, and intranasal insulin restored the effects rather close to the level in control. In insulin-treated non-diabetic rats, AC stimulating effects of isoproterenol and relaxin in the myocardium and of human chorionic gonadotropin in the ovaries were decreased, while the effects of hormones, inhibitors of AC, were increased. These data indicate that with intranasal insulin, Gi protein-mediated signaling pathways continue to gain strength. The obtained data on the influence of hormones on AC system in the brain, myocardium, ovary and uterus allow looking anew into the mechanisms of therapeutic effects of intranasal insulin.

[A decrease of sensitivity of adenylyl cyclase and heterotrimeric G-proteins to chorionic gonadotropin and peptide hormones action in the tissues of reproductive system of the rats in the condition of experimental type 2 diabetes]

Patients with different forms of the diabetes, particularly with insulin-independent type 2 diabetes have a wide spectrum of the disturbances of the functions of reproductive system. It is supposed that the main reason of these disturbances is altered sensitivity of reproductive system tissues to regulatory action of hormones. The aim of the work was the identification of the changes in functioning of human chorionic gonadotropin (hCG)--and peptide hormones-sensitive adenylyl cyclase system (ACS) in the ovary, testes and uterus of rats with neonatal streptozotocin (STZ) diabetes that is similar to the type 2 diabetes in humans. The effects of hCG, PACAP-38 and relaxin, realizing their effects via G-protein of the stimulatory type (Gs), and somatostatin, acting via G-protein of the inhibitory type (Gi), on adenylyl cyclase (AC) activity and the GTP binding of the G-proteins were studied. Regulatory effects of hCG and PACAP-38 decreased in the ovary and testes of rats with STZ type 2 diabetes, while the effects of somatostatin decreased in all investigated tissues (in a considerable extent in the uterus). This expressed in the weakening of hormonal effects on AC activity, stimulating in the case of hCG and PACAP-38 and inhibiting in the case of somatostatin, and in the decrease of stimulation of the GTP binding by the hormones. At the same time a significant decrease of ACS sensitivity to relaxin in the tissues of diabetic rats was not found. Data obtained suggest that the key reason of the disturbances of reproductive functions in experimental type 2 diabetes is the decrease of ACS sensitivity to the hormones, such as hCG, PACAP-38 and somatostatin, that play a important role in functioning of reproductive system.

Method for liver tissue metabolic profiling study and its application in type 2 diabetic rats based on ultra performance liquid chromatography-mass spectrometry

A protocol for the metabolic profiling of rat liver was developed based on ultra-performance liquid chromatography coupled to quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF/MS) to explore metabolic state directly. Methanol/water (4:1, v:v) was selected as the optimal extraction solvent. The established method was validated with a linearity over the 10-5000 ng/mL for internal standards (IS) and got an average correlation coefficient of 0.9986. The intra-day and inter-day RSD for most endogenous compounds were below 15%. And the absolute recovery of IS was from 84.8% to 109.1%. Liver tissues from diabetic and control rats were enrolled in the subsequent study to show the usefulness of the method. A clear classification between the control and model animals was achieved, some significant metabolites were successfully filtered. These metabolites reflected the abnormal metabolism of diabetic rats. This initial application indicated that the method is suitable and reliable for liver tissue metabolic profiling. It is expected this protocol could also be extended to metabonomic studies of other tissues.

Effects of sleeve gastrectomy in neonatally streptozotocin-induced diabetic rats

Background

Sleeve gastrectomy (SG) has emerged recently as a stand-alone bariatric procedure to treat morbid obesity and enhance glucose homeostasis. The aim of the study was to evaluate its effects in neonatally streptozotocin (STZ)-induced diabetic rats (n-STZ diabetic rats).

Methodology and Principal Findings

To induce diabetes, STZ (90 mg/kg) was administered intraperitoneally to 2-day-old male pups. When 12 weeks old, diabetic rats were randomized into sleeve operation group (SLG, n = 6) and sham operation group (SOG, n = 6). Body weights were monitored weekly, and daily consumption of water and food were followed for eight consecutive weeks postoperatively. Serum glucose levels were measured periodically at the 4th and 8th week after surgery. Insulin, ghrelin, glucose-dependent insulinotropic polypeptide (GIP) and Glucagon-like peptide-1 (GLP-1) levels were assayed at the end of the study. Our data showed that SLG rats exhibited significantly lower body weight gain in addition to reduced food and water intakes postoperatively compared to their sham-operation counterparts. However, resolution of diabetes was not observed in our study. Correspondingly, there were no significant differences between SOG rats and SLG rats in glucose metabolism-associated hormones, including insulin, GIP and GLP-1. In contrast, ghrelin level significantly decreased (P<0.01) in SLG group (58.01±3.75 pg/ml) after SG surgery compared to SOG group (76.36±3.51 pg/ml).

Conclusions

These observations strongly suggest that SG is effective in controlling body weight. However, SG did not achieve resolution or improvement of diabetes in n-STZ diabetic rats.

The influence of improved glycaemic control with chlorpropamide on microvascular reactivity and nitric oxide synthase activity in diabetic rats

Hyperglycaemia is a primary cause of vascular complications in diabetes. A hallmark of these vascular complications is endothelial cell dysfunction, which is partly due to reduced production of nitric oxide. The aim of this study was to verify the influence of improved glycaemic control with chlorpropamide on microvascular reactivity, endothelial nitric oxide synthase (e-NOS) expression, and NOS activity in neonatal streptozotocin-induced diabetic rats (n-STZ). Diabetes was induced by STZ injection into neonates Wistar rats. n-STZ diabetic rats were treated with chlorpropamide (200 mg kg−1, 15 days, by gavage). The changes in mesenteric arteriolar and venular diameters were determined in anaesthetized control and n-STZ diabetic rats, before and after topical application of acetylcholine, bradykinin and sodium nitroprusside (SNP). We also assessed e-NOS expression (using polymerase chain reaction after reverse transcription of mRNAs into cDNAs) and NOS activity (conversion of L-arginine to citrulline) in the mesenteric vascular bed of chlorpropamide-treated n-STZ, vehicle-treated n-STZ, and control rats. In n-STZ, chlorpropamide treatment reduced high glycaemic levels, improved glucose tolerance and homoeostatic model assessment (HOMA-beta), and restored NOS activity. Impaired vasodilator responses of arterioles and venules to acetylcholine, bradykinin and SNP were partially corrected by chlorpropamide treatment in n-STZ. We concluded that improved metabolic control and restored NOS activity might be collaborating with improved microvascular reactivity found in chlorpropamide-treated n-STZ.

Enalapril treatment corrects the reduced response to bradykinin in diabetes increasing the B2 protein expression

Considering the growing importance of the interaction between components of kallikrein-kinin and renin-angiotensin systems in physiological and pathological processes, particularly in diabetes mellitus, the aim of the present study was to investigate the effect of enalapril on the reduced response of bradykinin and on the interaction between angiotensin-(1-7) (Ang-(1-7)) and bradykinin (BK), important components of these systems, in an insulin-resistance model of diabetes. For the above purpose, the response of mesenteric arterioles of anesthetized neonatal streptozotocin-induced (n-STZ) diabetic and control rats was evaluated using intravital microscopy. In n-STZ diabetic rats, enalapril treatment restored the reduced response to BK but not the potentiation of BK by Ang-(1-7) present in non-diabetic rats. The restorative effect of enalapril was observed at a dose that did not correct the altered parameters induced by diabetes such as hyperglycemia, glicosuria, insulin resistance but did reduce the high blood pressure levels of n-SZT diabetic rats. There was no difference in mRNA and protein expressions of B1 and B2 kinin receptor subtypes between n-STZ diabetic and control rats. Enalapril treatment increased the B2 kinin receptor expression. From our data, we conclude that in diabetes enalapril corrects the impaired BK response probably by increasing the expression of B2 receptors. The lack of potentiation of BK by Ang-(1-7) is not corrected by this agent.

Decrease in functional activity of G-proteins hormone-sensitive adenylate cyclase signaling system, during experimental type II diabetes mellitus

The development of experimental type II diabetes mellitus in rats was accompanied by dysfunction of inhibitory and stimulatory heterotrimeric G-proteins, components of hormone-sensitive adenylate cyclase signal system. The function of inhibitory G-proteins decreased most significantly under these conditions, which is seen from weakened regulatory effects of somatostatin (in the myocardium) and bromocriptine (in the brain striatum) realized via inhibitory G-proteins in diabetic rats compared to controls. These hormones produce less pronounced inhibitory effect on forskolin-induced activation of adenylate cyclase. In the myocardium of diabetic rats, the stimulatory effects of isoproterenol and relaxin on adenylate cyclase realized via stimulatory G-proteins were decreased to a lesser extent. In the striatum of diabetic rats the stimulatory effect of serotonin and relaxin did not differ from the control. Therefore, dysfunction of stimulatory G-proteins during type II diabetes mellitus is characterized by tissue specificity. Synthetic peptides corresponding to functionally important regions in a-subunits of G-proteins and relaxin receptor LGR7 less effectively inhibited hormone signal transduction via the adenylate cyclase system in rats with type II diabetes. These changes reflect abnormal coupling between receptors and G-proteins in tissues of diabetic rats.

Lack of potentiation of bradykinin by angiotensin-(1-7) in a type 2 diabetes model: role of insulin

Considering the growing importance of the interaction between components of kallikrein-kinin and renin-angiotensin systems in physiological and pathological processes, particularly in diabetes mellitus, the aim of the present study was to investigate the interaction between angiotensin-(1-7) (Ang-(1-7)) and bradykinin (BK), important components of these systems in an insulin resistance model of diabetes, and the effect of insulin on it. For this the response of mesenteric arterioles of anesthetized neonatal streptozotocin-induced (n-STZ) diabetic and control rats was evaluated using intravital microscopy. Though capable of potentiating BK in non-diabetic rats, Ang-(1-7) did not potentiate BK in n-STZ rats. Chronic but not acute insulin treatment restored the potentiation. This restorative effect of insulin was abolished by a K+ channel blocker (tetraethylammonium), by nitric oxide synthase inhibitor (N-nitro-L-arginine methyl ester) and by a cyclooxygenase inhibitor (indomethacin). On the other hand, Na(+)-,K(+)-ATPase inhibition (by ouabain) did not abolish the effect of insulin. There was no difference in mRNA and protein expression of B1 and B2 kinin receptor subtypes between n-STZ diabetic and control rats. Insulin treatment did not alter the kinin receptor expression. Our data allow us to conclude that diabetes impaired the interaction between BK and Ang-(1-7) and that insulin restores it. The restoring effect of insulin depends on membrane hyperpolarization, nitric oxide release and cyclooxygenease metabolites but not Na+K+-ATPase. Alteration of kinin receptor expression might not be involved in the restoring effect of insulin on the potentiation of BK by Ang-(1-7).

Metformin treatment restores the altered microvascular reactivity in neonatal streptozotocin-induced diabetic rats increasing NOS activity, but not NOS expression

Abnormalities in vascular function are well recognized in diabetes. Hyperglycemia may be central to the pathogenesis of vascular dysfunction but is not certain whether improvements in glycaemic control will improve vascular function. The effects of metformin, an antidiabetic agent that improves insulin sensitivity and glycaemic control, on the microvascular reactivity have not been reported in neonatal streptozotocin-induced (n-STZ) diabetes. Diabetes was induced by STZ injection (160 mg/kg, ip) in neonates (2-day-old) Wistar rats. n-STZ diabetic rats were treated with metformin (300 mg/kg, 15 d, by gavage). Using intravital microscopy the changes in mesenteric arteriolar and venular diameters were determined in anesthetized control and n-STZ diabetic rats, before and after topical application of endothelium-dependent vasodilator agents, mediators or not of the inflammatory response, and endothelium-independent vasodilator agent. We also determined the total nitric oxide synthase (NOS) activity (conversion of L-arginine to citrulline) and endothelial(e), inducible(i), and neuronal(n) NOS expression (using polymerase chain reaction after reverse transcription of the mRNAs into cDNAs) in the mesentery of metformin-treated n-STZ diabetic and vehicle-treated n-STZ diabetic and control rats. Although metformin treatment did not correct the high glycaemic levels and the impaired glucose tolerance, the reduced vasodilator responses and total NOS activity in n-STZ diabetic rats were corrected by the treatment. Neither diabetes nor metformin treatment altered the expression of the three NOS isoforms. We concluded that metformin restores the reduced response to vasodilator agents, independently of the correction of the metabolic alterations. Improvement of total NOS activity might be in part responsible for the correction.

The effects of elk velvet antler consumption on the rat: development, behavior, toxicity and the activity of liver gamma-glutamyltranspeptidase

The effect of exposure to, followed by consumption of, a diet containing 10% powdered elk velvet antler (EVA) from the 18th day of gestation to the 88th day after birth was examined in male and female Fischer 344 rats. There were no teratogenic effects of EVA exposure in utero or differences in birth outcomes between pups born to regular chow fed and EVA chow fed dams. Growth curves of the EVA fed rats were identical to those of regular chow fed rats, as were developmental milestones of pinna development and eye-opening. Acoustical startle and righting reflexes, developmental and behavioral indices, were identical. Blood glucose levels were comparable in EVA chow fed and regular chow fed rats, indicating that EVA is without effect on glucose balance. There were no signs of toxicity in the EVA chow fed compared to regular chow fed rats as judged from plasma enzyme markers of liver damage: plasma levels of alanine aminotransferase were 50% lower in EVA chow fed rats compared to regular chow fed rats; and plasma levels of gamma-glutamyltranspeptidase (gammaGT) were the same. The activity of gammaGT displayed a decrease in the livers of EVA chow fed rats, more so in the male (22%) than in the female (14%), suggestive of an androgenic effect. A possible hepatobeneficial effect of the EVA induced decrease in liver gammaGT is discussed. In summary, dietary10% EVA chow is without long term effect on growth, development and behavior is non-toxic and may be hepatobeneficial.

Lymphosarcoma-induced alterations in hepatic adrenergic receptors: implications to the hypoglycemia of cancer cachexia

A highly malignant transplantable rat lymphosarcoma was studied to determine the involvement of hepatic adrenergic receptors in the development of the hypoglycemia of cancer cachexia. Following inoculation of Fischer 344 rats with lymphosarcoma cells, rats were examined at 2 and 4 weeks, at the pre-cachexic stage; 6 weeks, at the transitional stage; and 7 weeks, at the cachexic hypoglycemic stage of lymphosarcoma progression. Death occurred by the 8th week. Blood glucose levels in lymphosarcoma-bearing rats relative to control rats were: unaffected at week 2; significantly reduced 8% at weeks 4 and 6; and reduced 24% at week 7. Alpha1 adrenergic receptor binding to plasma membranes isolated from the livers of lymphosarcoma-bearing rats was: 114, 89, 67 and 30% of control at weeks 2, 4, 6, and 7, respectively. Kinetic analysis indicated that the lymphosarcoma-induced decrease at week 7 was due to a decrease in numbers of receptors with no change in affinity: B(max)(control): 1411.1 fmol/mg: Kd(control): 0.44 nm; B(max)(lympho): 345.5 fmol/mg; Kd(lympho): 0.50 nm. Alpha2 adrenergic receptor binding to plasma membranes isolated from the livers of lymphosarcoma-bearing rats was: 130, 137, 243 and 212% of control at weeks 2,4, 6, and 7, respectively. The pattern of changes in hepatic alpha1, alpha2 and beta adrenergic receptors at week 6 was comparable to that of 17 day fetal liver: a decrease in alpha1 and beta and an increase in alpha2. Hepatic adrenergic receptor changes occurred in the absence of liver damage and were not due to contamination of the liver plasma membrane fractions with lymphosarcoma cells. Plasma insulin levels displayed modest (10-15%), but not statistically significant, increases post-inoculation after week 4. Plasma glucagon levels fluctuated post-inoculation until week 7 where they were significantly increased: 202% of control. Plasma T3 and T4 levels displayed an early and steady decline after lymphosarcoma inoculation: T3: unchanged at week 2 and significantly decreased 14, 44 and 50% at weeks 4, 6 and 7, respectively. T4 increased 20% at week 1; decreased 9% at week 4 and significantly decreased thereafter: 55 and 49% at weeks 6 and 7, respectively. We propose that the development of the hypoglycemia of cancer cachexia in this lymphosarcoma model is due primarily to an early and progressive thyroid hormone dependent decrease in the number of hepatic alpha1 adrenergic receptors, compounded by an increase and decrease, respectively, in the hepatic beta and alpha2 adrenergic receptors.

Prostanoid release and constrictor responses to noradrenaline in the rat mesenteric vascular bed in non-insulin-dependent diabetes mellitus

1. The administration of streptozotocin (STZ) to 2-day old rats induced a non-insulin-dependent diabetes mellitus (NIDDM)-like state, with mild hyperglycaemia and no alterations in body weight at the adult age. 2. In the isolated and perfused mesenteric vascular bed of NIDDM animals, the constrictor responses to either noradrenaline (NA) or potassium chloride (KCl) were not modified as compared with age-matched non-diabetic controls. 3. The reduction in NA contractions induced by the cyclooxygenase inhibitor, 10 microM indomethacin in the control group was absent in the NIDDM rats. 4. The increase in the NA-induced contractions caused by endothelium removal was suppressed by indomethacin in the controls but not in the NIDDM group. 5. The prostanoid release from the mesenteric vascular beds of NIDDM rats was markedly reduced as compared with non-diabetic controls. Noradrenaline increased production of the constrictor prostaglandin (PG) F2alpha in control but not in NIDDM rats. 6. In summary, these results show that in STZ-induced NIDDM rats, there is an impairment of the prostanoid production, as well as a suppression of the role of prostanoids in the contractile effects of NA in the mesenteric vascular bed. These alterations are more severe than those previously observed in a model of insulin-dependent diabetes mellitus (IDDM), in which hyperglycaemia and reduction of body weight were more marked. The conclusion is that, in these models of diabetes and in the preparation studied, vascular alterations and modifications of glycaemia and body weight are not closely related.