Streptozotocin-Induced Diabetic Models in Mice and Rats.

Streptozotocin (STZ) is an antibiotic that causes pancreatic islet ß-cell destruction and is widely used experimentally to produce a model of type 1 diabetes mellitus (T1DM). Detailed in this article are protocols for producing STZ-induced insulin deficiency and hyperglycemia in mice and rats. Also described are protocols for creating animal models for type 2 diabetes using STZ. These animals are employed for assessing the pathological consequences of diabetes and for screening potential therapies for the treatment of this condition. © 2021 The Authors.

Reduction of blood glucose by plant extracts and their use in the treatment of diabetes mellitus; discrepancies in effectiveness between animal and human studies.

ETHNOPHARMACOLOGICAL RELEVANCE: The global problem of diabetes, together with the limited access of large numbers of patients to conventional antidiabetic medicines, continues to drive the search for new agents. Ancient Asian systems such as traditional Chinese medicine, Japanese Kampo medicine, and Indian Ayurvedic medicine, as well as African traditional medicine and many others have identified numerous plants reported anecdotally to treat diabetes; there are probably more than 800 such plants for which there is scientific evidence for their activity, mostly from studies using various models of diabetes in experimental animals. AIM OF THE REVIEW: Rather than a comprehensive coverage of the literature, this article aims to identify discrepancies between findings in animal and human studies, and to highlight some of the problems in developing plant extract-based medicines that lower blood glucose in patients with diabetes, as well as to suggest potential ways forward. METHODS: In addition to searching the 2018 PubMed literature using the terms 'extract AND blood glucose, a search of the whole literature was conducted using the terms 'plant extracts' AND 'blood glucose' AND 'diabetes' AND 'double blind' with 'clinical trials' as a filter. A third search using PubMed and Medline was undertaken for systematic reviews and meta-analyses investigating the effects of plant extracts on blood glucose/glycosylated haemoglobin in patients with relevant metabolic pathologies. FINDINGS: Despite numerous animal studies demonstrating the effects of plant extracts on blood glucose, few randomised, double-blind, placebo-controlled trials have been conducted to confirm efficacy in treating humans with diabetes; there have been only a small number of systematic reviews with meta-analyses of clinical studies. Qualitative and quantitative discrepancies between animal and human clinical studies in some cases were marked; the factors contributing to this included variations in the products among different studies, the doses used, differences between animal models and the human disease, and the impact of concomitant therapy in patients, as well as differences in the duration of treatment, and the fact that treatment in animals may begin before or very soon after the induction of diabetes. CONCLUSION: The potential afforded by natural products has not yet been realised in the context of treating diabetes mellitus. A systematic, coordinated, international effort is required to achieve the goal of providing anti-diabetic treatments derived from medicinal plants.

Streptozotocin-Induced Diabetic Models in Mice and Rats.

Streptozotocin (STZ) is an antibiotic that produces pancreatic islet ß-cell destruction and is widely used experimentally to produce a model of type 1 diabetes mellitus (T1DM). Detailed in this unit are protocols for producing STZ-induced insulin deficiency and hyperglycemia in mice and rats. Also described are protocols for creating animal models for type 2 diabetes using STZ. These animals are employed for assessing the pathological consequences of diabetes and for screening potential therapies for the treatment of this condition.

The development of Byetta (exenatide) from the venom of the Gila monster as an anti-diabetic agent.

The development of Byetta (synthetic exendin-4; exenatide) as a treatment of diabetes arose from two, parallel lines of investigation. The development of the 'incretin concept' which hypothesised that hormones from the gut contributed to the insulin secretion in response to meals, led to the identification of glucagon-like peptide 1 (GLP-1) as an important 'incretin' hormone. GLP-1 not only increases insulin secretion but increases ß-cell proliferation and survival, suppresses glucagon secretion, delays gastric emptying and suppresses appetite, all of these actions contributing to a potential anti-diabetic effect. However, GLP-1 has a very short half due to its rapid breakdown by dipeptidyl peptidase IV and ectopeptidases. A systematic investigation of the composition and activity of venom from the Gila monster, Heloderma suspectum, led to the isolation of a 39-amino acid peptide, designated exendin-4, showing 53% structural homology with GLP-1(7-36). Exendin-4 mimicked GLP-1 through stimulating the GLP-1 receptor. The much greater stability of exendin-4 led to its experimental and clinical evaluation as an anti-diabetic agent and its introduction to the market in 2005.

Reactive oxygen species and endothelial function in diabetes.

An increasing body of evidence suggests that oxidant stress is involved in the pathogenesis of many cardiovascular diseases, including hypercholesterolemia, atherosclerosis, hypertension, heart failure and diabetes. Recent studies have also provided important new insights into potential mechanisms underlying the pathogenesis of vascular disease induced by diabetes. Glycosylation of proteins and lipids, which can interfere with their normal function, activation of protein kinase C with subsequent alteration in growth factor expression, promotion of inflammation through the induction of cytokine secretion and hyperglycemia-induced oxidative stress are some of these mechanisms. It is widely accepted that hyperglycemia-induced reactive oxygen species contribute to cell and tissue dysfunction in diabetes. A variety of enzymatic and non-enzymatic sources of reactive oxygen species exist in the blood vessels. These include NADPH oxidase, mitochondrial electron transport chain, xanthine oxidase and nitric oxide synthase. The present article reviews the effects of reactive oxygen species on endothelial function in diabetes and addresses possible therapeutic interventions.

Benzylguanidines and other galegine analogues inducing weight loss in mice.

Dimethylallylguanidine, also known as galegine, isolated from Galega officinalis, has been shown to have weight reducing properties in vivo. Substitution of the guanidine group with an N-cyano group and replacement of guanidine with amidine, pyrimidine, pyridine, or the imidazole moieties removed the weight reducing properties when evaluated in BALB/c mice. However, retention of the guanidine and replacement of the dimethylallyl group by a series of functionalized benzyl substituents was shown to exhibit, and in some cases significantly improve, the weight reducing properties of these molecules in BALB/c, ob/ob, and diet induced obesity (DIO) mice models. The lead compound identified, across all models, was 1-(4-chlorobenzyl)guanidine hemisulfate, which gave an average daily weight difference (% from time-matched controls; +/- SEM) of -19.7 +/- 1.0, -11.0 +/- 0.7, and -7.3 +/- 0.8 in BALB/c, ob/ob, and DIO models, respectively.

Comparison of urethane/chloralose and pentobarbitone anaesthesia for examining effects of bacterial lipopolysaccharide in mice.

Although anaesthetics are widely used to alleviate stress in endotoxaemic animals, these drugs themselves may interfere with the effects of lipopolysaccharide (LPS). The effects of LPS on serum glucose, biochemical markers of hepatic, renal and pancreatic exocrine function, and lung myeloperoxidase (MPO) activity were compared using anaesthesia with either urethane/chloralose or pentobarbitone. Groups of 10-13 of C57B1/6 mice (22.3 +/- 0.18 g) were treated with 40 mg/kg LPS or the same volume of saline (10 mL/kg, i.p.) at time 0, Animals were anaesthetized either with urethane (1000 mg/kg) and chloralose (50 mg/kg) or with pentobarbitone (90 mg/kg, i.p.) after 2 h and blood and lung samples obtained after 6 h. In pentobarbitone-anaesthetized mice, LPS caused hypoglycaemia and increased serum levels of alanine aminotransferase (ALT), lipase and creatinine suggesting damage/dysfunction of liver, exocrine pancreas and kidney respectively. Lung tissue MPO activity, an indicator of neutrophil infiltration, was also increased. Urethane/chloralose-treated mice demonstrated hypoglycaemia and enhanced serum levels of ALT and creatinine in response to LPS, but failed to show LPS-induced increases in serum lipase and lung MPO activity. It is concluded that while pentobarbitone may be successfully used in experimental models of endotoxaemia in mice, anaesthesia with urethane and chloralose may protect mice against LPS-mediated damage/dysfunction in the exocrine pancreas and in the lung, and therefore, is not recommended in studies on endotoxaemic mice.

Lack of effect of proteinase-activated receptor-2 (PAR-2) deletion on the pathophysiological changes produced by lipopolysaccharide in the mouse: comparison with dexamethasone.

This study tested the hypothesis that activation of proteinase-activated receptor-2 (PAR-2) contributes towards the pathophysiology of lipopolysaccharide (LPS)-induced shock in the mouse. The effects of LPS on plasma glucose, biochemical markers of hepatic, renal and pancreatic exocrine function and lung content of myeloperoxidase (MPO) were examined in homozygous PAR-2 knockout mice (PAR-2 -/-) and genetically equivalent, homozygous PAR-2 +/+ mice. The effect of LPS was also examined in normal mice receiving dexamethasone (10 mg kg(-1), i. p.) or saline as a positive control. At six hours after intraperitoneal injection, LPS (40 mg kg(-1)) produced an increase in rectal temperature, hypoglycaemia and elevations in serum concentrations of alanine aminotransferase (ALT), creatinine and lipase, as well as an increase in lung MPO content. Dexamethasone treatment reduced LPS-induced hypoglycaemia and elevation of serum ALT concentrations but did not modify elevations in serum creatinine and lipase concentrations or the increase in lung MPO content. The changes in serum concentrations of glucose, ALT, creatinine and lipase produced by LPS in PAR-2 -/- mice were not different from those seen in wild-type or PAR-2 +/+ mice. These data suggest that activation of PAR-2 may not play a pivotal role in LPS-induced multi-organ dysfunction.

Ryanodine receptors of pancreatic beta-cells mediate a distinct context-dependent signal for insulin secretion.

The ryanodine (RY) receptors in beta-cells amplify signals by Ca2+-induced Ca2+ release (CICR). The role of CICR in insulin secretion remains unclear in spite of the fact that caffeine is known to stimulate secretion. This effect of caffeine is attributed solely to the inhibition of cAMP-phosphodiesterases (cAMP-PDEs). We demonstrate that stimulation of insulin secretion by caffeine is due to a sensitization of the RY receptors. The dose-response relationship of caffeine-induced inhibition of cAMP-PDEs was not correlated with the stimulation of insulin secretion. Sensitization of the RY receptors stimulated insulin secretion in a context-dependent manner, that is, only in the presence of a high concentration of glucose. This effect of caffeine depended on an increase in [Ca2+]i. Confocal images of beta-cells demonstrated an increase in [Ca2+]i induced by caffeine but not by forskolin. 9-Methyl-7-bromoeudistomin D (MBED), which sensitizes RY receptors, did not inhibit cAMP-PDEs, but it stimulated secretion in a glucose-dependent manner. The stimulation of secretion by caffeine and MBED involved both the first and the second phases of secretion. We conclude that the RY receptors of beta-cells mediate a distinct glucose-dependent signal for insulin secretion and may be a target for developing drugs that will stimulate insulin secretion only in a glucose-dependent manner.

Streptozotocin diabetes protects against arrhythmias in rat isolated hearts: role of hypothyroidism.

We examined the contribution of hypothyroidism to streptozotocin diabetes-induced alterations in the arrhythmia susceptibility of ex vivo hearts to regional zero-flow ischaemia. Diabetic rats received either protamine zinc insulin (10 IU/kg/day, s.c.) or triiodothyronine (10 microg/kg/day, s.c.) for 8 weeks commencing 72 h after injection of streptozotocin (60 mg/kg, i.p.). Arrhythmias were determined in ex vivo Langendorff-perfused hearts, subjected to a 30-min main left coronary artery occlusion, followed by 30-min reperfusion. Serum free thyroxine concentrations, rectal temperature and ex vivo heart rate were significantly decreased in the 8-week diabetic group (P<0.001). These changes were prevented by administration of triiodothyronine or insulin. Ventricular fibrillation during reperfusion was abolished in hearts from diabetic rats. This protection was prevented by treatment with either triiodothyronine or insulin. Hearts from methimazole-hypothyroid rats also showed no ventricular fibrillation during reperfusion. The protection against ischaemia-reperfusion-arrhythmias observed in hearts from streptozotocin-diabetic rats may be due to diabetes-induced hypothyroidism.