Streptozotocin dose-response curve in tilapia, a glucose-responsive teleost fish

Animal Models in Diabetic Research-History, Presence, and Future Perspectives

Diabetes mellitus (DM) is a very serious disease, the incidence of which has been increasing worldwide. The beginning of diabetic research can be traced back to the 17th century. Since then, animals have been experimented on for diabetic research. However, the greatest development of diabetes research occurred in the second half of the last century, along with the development of laboratory techniques. Information obtained by monitoring patients and animal models led to the finding that there are several types of DM that differ significantly from each other in the causes of the onset and course of the disease. Through different types of animal models, researchers have studied the pathophysiology of all types of diabetic conditions and discovered suitable methods for therapy. Interestingly, despite the unquestionable success in understanding DM through animal models, we did not fully succeed in transferring the data obtained from animal models to human clinical research. On the contrary, we have observed that the chances of drug failure in human clinical trials are very high. In this review, we will summarize the history and presence of animal models in the research of DM over the last hundred years. Furthermore, we have summarized the new methodological approaches, such as "organ-on-chip," that have the potential to screen the newly discovered drugs for human clinical trials and advance the level of knowledge about diabetes, as well as its therapy, towards a personalized approach.

Goldfish adipocytes are pancreatic beta cell-like, glucose-responsive insulin-producing cells

Glucose homeostasis plays a key role in maintaining stable physiological conditions, and its dysfunction causes severe chronic health issues including diabetes. In this study, we have characterized goldfish adipocytes as cells with properties similar to that of pancreatic β-cells: they express considerable high levels of preproinsulin mRNAs, possess the necessary machinery for processing preproinsulin (prohormone convertases 1 and 2, carboxypeptidase E and trypsin) and responding to extracellular glucose (glucokinase and the glucose transporters 1, 2, and 4), produce insulin in a glucose-responsive manner and express key transcription factors typically involved in pancreas development (Pdx1, Neurogenin3, Nkx2.2, Pax6, and FOXO1A). These findings reinforce the feature of fish adipocytes as alternate sources of active insulin, holding the promise that they could eventually be developed as transplantable sources of this vital hormone.

Changes of DNA Methylation Pattern in Metabolic Pathways Induced by High-Carbohydrate Diet Contribute to Hyperglycemia and Fat Deposition in Grass Carp (Ctenopharyngodon idellus)

Although studies have determined that epigenetics plays an essential role in regulating metabolism in mammals, research on nutrition-related DNA methylation remains to be lacking in teleosts. In the present study, we provided a hepatic whole-genome DNA methylation analysis in grass carp fed with moderate- or excessive-carbohydrate-level diet. Although a high-carbohydrate (HC) diet significantly changed the mRNA expression levels of metabolic genes, it did not affect the global genomic DNA methylation levels in grass carp liver. However, compared with the control group, 3,972 genes were hyper-methylated and 2,904 genes were hypo-methylated in the promoter region. Meanwhile, 10,711 genes were hyper-methylated and 6,764 genes were hypo-methylated in the gene body region in the HC group. These differentially methylated genes (DMGs) were enriched in multiple pathways, including carbohydrate metabolism, insulin pathway, lipid metabolism, and adipocytokine signaling pathway. In addition, the variations in DNA methylation significantly regulated the transcription levels of key genes of metabolism, which could affect the glucose concentrations and the lipid deposition of grass carp. Furthermore, we compared the DNA methylation alterations of genes in glucose metabolism and obesity pathways of grass carp with those of mammalian models in different nutritional states. The results showed that most of the DMGs in grass carp were also regulated by DNA methylation in mammals when the nutritional state changed. The findings revealed more differentially methylated regions and candidate genes for glucose metabolism and broken species boundaries.

Phytotherapeutic efficacy of the medicinal plant Terminalia catappa L

Diabetes is a chronic, lifelong condition due to inadequate production of insulin or the cells does not properly respond it. Recently, the significance and effectiveness of herbal drugs associated with diabetes has emerged. The aim of the present study was to determine the anti-diabetic effects of Terminalia catappa L. leaves on streptozotocin (STZ)-treated rats. Two different concentrations of ethanolic leaf extract (300 and 500 mg/kg) of T. catappa were used to treat diabetic rats, and biochemical parameters were analyzed in blood samples. The results of herbal treatments were compared with the standard drug, glibenclamide. The ethanol extract (500 mg/kg) had significant anti-diabetic activity by altering blood glucose, glycosylated hemoglobin, liver glycogen, glucose 6-phosphatase, fructose 1,6-bisphosphatase, glucokinase, aspartate transaminase, alanine transaminase, alkaline phosphatase, urea, uric acid and creatinine levels while increasing insulin levels. Thus, the present study suggests that the supplementation of the diabetic patients with T. catappa leaves can lead to recovery from diabetic effects.

Sweet fish: Fish models for the study of hyperglycemia and diabetes

Fish are good for your health in more ways than you may expect. For one, eating fish is a common dietary recommendation for a healthy diet. However, fish have much more to provide than omega-3 fatty acids to your circulatory system. Some fish species now serve as important and innovative model systems for diabetes research, providing novel and unique advantages compared with classical research models. Not surprisingly, the largest share of diabetes research in fish occurs in the laboratory workhorse among fish, the zebrafish (Danio rerio). Established as a genetic model system to study development, these small cyprinid fish have eventually conquered almost every scientific discipline and, over the past decade, have emerged as an important model system for metabolic diseases, including diabetes mellitus. In this review we highlight the practicability of using zebrafish to study diabetes and hyperglycemia, and summarize some of the recent research and breakthroughs made using this model. Equally exciting is the appearance of another emerging discipline, one that is taking advantage of evolution by studying cases of naturally occurring insulin resistance in fish species. We briefly discuss two such models in this review, namely the rainbow trout (Oncorhynchus mykiss) and the cavefish (Astyanax mexicanus).

Zebrafish Pancreas Development and Regeneration: Fishing for Diabetes Therapies

The zebrafish pancreas shares its basic organization and cell types with the mammalian pancreas. In addition, the developmental pathways that lead to the establishment of the pancreatic islets of Langherhans are generally conserved from fish to mammals. Zebrafish provides a powerful tool to probe the mechanisms controlling establishment of the pancreatic endocrine cell types from early embryonic progenitor cells, as well as the regeneration of endocrine cells after damage. This knowledge is, in turn, applicable to refining protocols to generate renewable sources of human pancreatic islet cells that are critical for regulation of blood sugar levels. Here, we review how previous and ongoing studies in zebrafish and beyond are influencing the understanding of molecular mechanisms underlying various forms of diabetes and efforts to develop cell-based approaches to cure this increasingly widespread disease.

The Ultrastructure of Secretory Cells of the Islets of Langerhans in South American Catfish Rhamdia quelen

The present work shows that a detailed description of the ultrastructure of the secretory cells of the South American catfish Rhamdia quelen pancreatic islets is presented. Evidence is offered to support the contention that the α-granules consist of a central and an outer portion of different electron densities and solubilities, that the δ-cells are most probably morphologically altered but viable α-cells, and that the β-granules possibly possess a repeating substructure and may therefore represent an intracellular crystalline storage form of insulin.

A review of piscine islet xenotransplantation using wild-type tilapia donors and the production of transgenic tilapia expressing a "humanized" tilapia insulin

Most islet xenotransplantation laboratories have focused on porcine islets, which are both costly and difficult to isolate. Teleost (bony) fish, such as tilapia, possess macroscopically visible distinct islet organs called Brockmann bodies which can be inexpensively harvested. When transplanted into diabetic nude mice, tilapia islets maintain long-term normoglycemia and provide human-like glucose tolerance profiles. Like porcine islets, when transplanted into euthymic mice, they are rejected in a CD4 T-cell-dependent manner. However, unlike pigs, tilapia are so phylogenetically primitive that their cells do not express α(1,3)Gal and, because tilapia are highly evolved to live in warm stagnant waters nearly devoid of dissolved oxygen, their islet cells are exceedingly resistant to hypoxia, making them ideal for transplantation within encapsulation devices. Encapsulation, especially when combined with co-stimulatory blockade, markedly prolongs tilapia islet xenograft survival in small animal recipients, and a collaborator has shown function in diabetic cynomolgus monkeys. In anticipation of preclinical xenotransplantation studies, we have extensively characterized tilapia islets (morphology, embryologic development, cell biology, peptides, etc.) and their regulation of glucose homeostasis. Because tilapia insulin differs structurally from human insulin by 17 amino acids, we have produced transgenic tilapia whose islets stably express physiological levels of humanized insulin and have now bred these to homozygosity. These transgenic fish can serve as a platform for further development into a cell therapy product for diabetes.

That which does not kill us makes us stronger--does Nietzsche's quote apply to islets? A re-evaluation of the passenger leukocyte theory, free radicals, and glucose toxicity in islet cell transplantation

In clinical islet transplantation, isolated islets are embolized into the liver via the portal vein (PV); however, up to 70% of the islets are lost in the first few days after transplantation (i.e., too quickly to be mediated by the adaptive immune system). Part of early loss is due to instant blood-mediated inflammatory reaction, an immune/thrombotic process caused by islets interacting with complement. We have shown that glucose toxicity (GT) also plays a critical role based upon the observation that islets embolized into the PVs of diabetic athymic mice are rapidly lost but, if recipients are not diabetic, the islet grafts persist. Using donor islets resistant to the β-cell toxin streptozotocin, we have shown that intraportal islets engrafted in non-diabetic athymic mice for as little as 3 days will maintain normoglycemia when streptozotocin is administered destroying the recipient's native pancreas β-cells. What is the mechanism of GT in β-cells? Chronic exposure to hyperglycemia over-exerts β-cells and their electron transport chains leak superoxide radicals during aerobic metabolism. Here we reinterpret old data and present some compelling new data supporting a new model of early intraportal islet graft loss. We hypothesize that diabetes stimulates overproduction of superoxide in both the β-cells of the islet grafts and the endothelial cells lining the intraportal microvasculature adjacent to where the embolized islets become lodged. This double dose of oxidant damage stresses both the islets, which are highly susceptible to free radicals because of inherent low levels of scavenging enzymes, and the adjacent hepatic endothelial cells. This, superimposed upon localized endothelial damage caused by embolization, precipitates inflammation and coagulation which further damages islet grafts. Based upon this model, we predict that pre-exposing islets to sub-lethal hyperoxia should up-regulate islet free radical scavenging enzyme levels and promote initial engraftment; reinterpretation of 30 years old "passenger leukocyte" data and preliminary new data support this. Other data suggests that pre-exposure of recipients to hyperoxia could up-regulate antioxidant enzymes in the hepatic endothelium. The combination of both effects could markedly enhance early intraportal islet graft survival and engraftment. Finally, if our model is correct, current in vitro and in vivo tests used to test batches of harvested islets for viability and function prior to transplantation are poorly conceived (n.b., it is already well-known that results using these tests often do not predict clinical islet transplantation success) and a different testing paradigm is suggested.

Antidiabetic and antihyperlipidemic effects of Dillenia indica (L.) leaves extract

The present study was carried out to evaluate antidiabetic and antihyperlipidemic effects of Dillenia indica methanolic leaves extracts in streptozotocin induced diabetic Wistar rats by administering graded oral doses (250 and 500 mg/kg body weight) for 21 days. The extract showed significant antidiabetic activity (p<0.001). Furthermore, the decreased body weight of rats was significantly improved after extract treatments. Daily oral treatment with the extract for 21 days to diabetic rats, also resulted in significant reduction in serum cholesterol, triglycerides and serum transaminase levels but HDL-cholesterol level was found to be improved (p<0.001) as compared to the diabetic control group. The extract treatment also showed to enhance serum insulin level in diabetic rats as compared to the diabetic control group. In conclusion, D. indica leaf extract might be useful for diabetes mellitus management and other abnormalities associated with this metabolic disorder.

Preclinical evaluation of antihyperglycemic activity of Clerodendron infortunatum leaf against streptozotocin-induced diabetic rats

INTRODUCTION

Clerodendron infortunatum Linn. (Verbenaceae), commonly known as Bhant in Hindi, is a small shrub occurring throughout the plains of India, which is traditionally used for several medicinal purposes. The aim of the present study was to evaluate the preclinical antihyperglycemic activity of the methanol extract of the leaves of C. infortunatum (MECI) in Wistar rats.

METHODS

Hyperglycemia was induced in rats by a single intraperitoneal injection of streptozotocin (STZ, 65 mg/kg body weight). Three days after STZ induction, the hyperglycemic rats were treated with MECI intraperitoneally at the doses of 250 and 500 mg/kg body weight daily for 15 days. Glibenclamide (0.5 mg/kg, orally) was used as a reference drug. The fasting blood glucose levels were measured on every fifth day during the 15 days of treatment. Serum biochemical parameters such as glutamate pyruvate transaminase, glutamate oxaloacetate transaminase, alkaline phosphatase, cholesterol, and total protein were estimated. Antioxidant properties were assessed by estimating hepatic lipid peroxidation, reduced glutathione (GSH), and catalase (CAT).

RESULTS

MECI at the doses of 250 and 500 mg/kg intraperitoneally significantly (P<0.001) and dose-dependently reduced and normalized blood glucose levels as compared to that of the STZ control group. Serum biochemical parameters were significantly (P<0.001) restored towards normal levels in MECI-treated rats as compared to the STZ control. MECI treatment also significantly (P<0.001) decreased lipid peroxidation and recovered GSH levels and CAT activity towards normal values, as compared to the STZ control.

CONCLUSION

The present study demonstrated that the leaves of C. infortunatum had remarkable preclinical antihyperglycemic activity in STZ-induced diabetic rats.

Antihyperglycemic activity and antioxidant role of Terminalia arjuna leaf in streptozotocin-induced diabetic rats

CONTEXT

Terminalia arjuna Roxb. (Combretaceae), commonly known as Arjuna, is a large tree grown throughout the Indian peninsula and used traditionally for several medicinal purposes.

OBJECTIVE

To evaluate antihyperglycemic and antioxidant role of methanol extract of T. arjuna leaf (META) in Wistar rats.

MATERIALS AND METHODS

Hyperglycemia was induced in rats by single intraperitoneal injection of streptozotocin (STZ, 65 mg/kg body weight). Three days after STZ induction, the hyperglycemic rats were treated with META orally at the dose of 100 and 200 mg/kg body weight daily for 15 days. Glibenclamide (0.5 mg/kg, orally) was used as reference drug. The fasting blood glucose levels were measured on every fifth day during the 15-day treatment. Serum biochemical parameters such as serum glutamate pyruvate transaminase (SGPT), serum glutamate oxaloacetate transaminase (SGOT), alkaline phosphatase (ALP), cholesterol, and total protein were estimated. Antioxidant properties were assessed by estimating hepatic lipid peroxidation, reduced glutathione (GSH), and catalase (CAT).

RESULTS AND DISCUSSION

META at the dose of 100 and 200 mg/kg orally significantly (P < 0.001) and dose-dependently reduced and normalized blood glucose levels as compared with that of STZ control group. Serum biochemical parameters were significantly (P < 0.001) restored toward normal levels in META-treated rats as compared with STZ control. META treatment also significantly (P < 0.001) decreased lipid peroxidation and recovered GSH level and CAT activity toward normal as compared with STZ control.

CONCLUSION

The present study infers that T. arjuna leaf demonstrated remarkable antihyperglycemic activity in STZ-induced diabetic rats. The potential antihyperglycemic action is plausibly due to its underlying antioxidant role.

Limb regeneration is impaired in an adult zebrafish model of diabetes mellitus

The zebrafish (Danio rerio) is an established model organism for the study of developmental processes, human disease, and tissue regeneration. We report that limb regeneration is severely impaired in our newly developed adult zebrafish model of type I diabetes mellitus. Intraperitoneal streptozocin injection of adult, wild-type zebrafish results in a sustained hyperglycemic state as determined by elevated fasting blood glucose values and increased glycation of serum protein. Serum insulin levels are also decreased and pancreas immunohistochemisty revealed a decreased amount of insulin signal in hyperglycemic fish. Additionally, the diabetic complications of retinal thinning and glomerular basement membrane thickening (early signs of retinopathy and nephropathy) resulting from the hyperglycemic state were evident in streptozocin-injected fish at 3 weeks. Most significantly, limb regeneration, following caudal fin amputation, is severely impaired in diabetic zebrafish and nonspecific toxic effects outside the pancreas were not found to contribute to impaired limb regeneration. This experimental system using adult zebrafish facilitates a broad spectrum of genetic and molecular approaches to study regeneration in the diabetic background.

Regeneration of the pancreas in adult zebrafish

OBJECTIVE

Regenerating organs in diverse biological systems have provided clues to processes that can be harnessed to repair damaged tissue. Adult mammalian beta-cells have a limited capacity to regenerate, resulting in diabetes and lifelong reliance on insulin. Zebrafish have been used as a model for the regeneration of many organs. We demonstrate the regeneration of adult zebrafish pancreatic beta-cells. This nonmammalian model can be used to define pathways for islet-cell regeneration in humans.

RESEARCH DESIGN AND METHODS

Adult transgenic zebrafish were injected with a single high dose of streptozotocin or metronidazole and anesthetized at 3, 7, or 14 days or pancreatectomized. Blood glucose measurements were determined and gut sections were analyzed using specific endocrine, exocrine, and duct cell markers as well as markers for dividing cells.

RESULTS

Zebrafish recovered rapidly without the need for insulin injections, and normoglycemia was attained within 2 weeks. Although few proliferating cells were present in vehicles, ablation caused islet destruction and a striking increase of proliferating cells, some of which were Pdx1 positive. Dividing cells were primarily associated with affected islets and ducts but, with the exception of surgical partial pancreatectomy, were not extensively beta-cells.

CONCLUSIONS

The ability of the zebrafish to regenerate a functional pancreas using chemical, genetic, and surgical approaches enabled us to identify patterns of cell proliferation in islets and ducts. Further study of the origin and contribution of proliferating cells in reestablishing islet function could provide strategies for treating human diseases.

Evidence for the presence of a glucosensor in hypothalamus, hindbrain, and Brockmann bodies of rainbow trout

The aim of this study was to evaluate the existence of a glucosensor in different regions of the brain and in the Brockmann bodies (BB) of the rainbow trout, Oncorhynchus mykiss. Five groups ( n = 12) of trout were injected intraperitoneally with saline alone (control) or saline-containing bovine glucagon (100 μg/kg), bovine insulin (4 mg/kg), 2-deoxy-d-glucose (100 mg/kg), or d-glucose (500 mg/kg) to promote hyperglycemia (glucagon, d-glucose, 2-deoxy-d-glucose) or hypoglycemia (insulin). Six hours after injection, samples from four brain regions (hypothalamus, telencephalon, hindbrain, and midbrain) and the entire BB were taken. Our results demonstrate within the BB and both the hypothalamus and hindbrain a metabolic response different to that observed in other tissues (midbrain, telencephalon) but similar to that described in tissues known to be glucosensors in mammals. The metabolic responses of these areas to changes in plasma glycemia were characterized by parallel changes in GLUT-2 expression, hexokinase-IV, or glucokinase activity and expression, glycolytic potential, and levels of glycogen and glucose. These changes are similar to those reported in mammalian pancreatic β-cells and glucose-excited (GE) neurons, two cell types containing glucosensors. This study provides evidence for the presence of glucosensors responsive to hyper- and hypoglycemia in rainbow trout BB, hypothalamus, and hindbrain.

Things we have learned from tilapia islet xenotransplantation

An islet xenotransplantation model has been developed using tilapia (Oreochromis niloticus) as the donors. Studies using this model for the treatment of experimental type 1 diabetes in mice have produced promising results including the maintenance of long-term normoglycemia and mammalian-like glucose tolerance profiles in islet graft recipients. Islet encapsulation has also provided a promising method for the prevention of graft rejection, and strains of transgenic tilapia expressing a [desThrB30] human insulin molecule have been produced. In addition to studying islet transplantation for the treatment of type 1 diabetes, these studies have also produced insights into piscine glucose homeostasis. Studies demonstrating the glucose responsiveness of tilapia islets are described. In addition, work performed by our group and by others pertaining to presence and nature of piscine glucose transporters is reviewed. Finally, studies addressing some of the broader challenges of islet xenotransplantation are discussed with particular attention paid to the post-transplantation fate of the various islet cell populations and the proteins they produce.

Effect of glucose toxicity on intraportal tilapia islet xenotransplantation in nude mice

BACKGROUND

Discordant xenogeneic islets transplanted intraportally into athymic nude rats experience primary non-function and are rapidly destroyed. Recently, it has been reported that adult porcine islets transplanted intraportally into nude mice are also rapidly destroyed and that this constitutes a new model for instant blood-mediated inflammatory reaction (IBMIR).

METHODS

Tilapia (fish) islets were harvested, mechanically broken into mammalian islet-sized fragments, cultured for 48 h, and transplanted via the portal vein into athymic or euthymic mice.

RESULTS

There were several groups of recipient mice. Streptozotocin-diabetic nude mice received 400 islets via the portal vein (n = 12). Recipients were killed when hyperglycemic (>200 mg/dl); livers and native pancreases were examined histologically. Mean graft survival time, based on function, was 5.4 +/- 1.2 days; at autopsy, histology showed occasional viable islets. We also performed a group of transplants in non-diabetic nude mice (n = 6) and then killed the recipients 2 or 4 weeks later; all had abundant viable, well-granulated islet grafts based on histology. Therefore, the intraportal environs in nude mice are not incompatible with discordant fish islets; rather, it appears as if hyperglycemia adversely affects the intraportal islet grafts (i.e. ''glucose toxicity''). To test this hypothesis, transplants were performed into non-diabetic nude mice and allowed to engraft for either 3 days (n = 6) or 10 days (n = 8) prior to injection of streptozotocin (200 to 220 mg/kg i.v.) to destroy the beta-cells in the recipients' native islets (n.b. tilapia islets are exceedingly resistant to streptozotocin); these recipients were followed for 28 days post-transplantation (or until hyperglycemic) and then killed for histology. Mean graft function exceeded 25 days for both groups and viable well-granulated, tilapia islets grafts were readily identified in all recipients; in all but one, the native pancreases were markedly beta-cell depleted -- confirming that normoglycemia was due to functional fish islet xenografts.

CONCLUSIONS

Our results suggest that ''glucose toxicity'' plays a role in the immediate demise of intraportal tilapia islet xenografts.

Tilapia islet grafts are highly alloxan-resistant

We have previously shown that dose-response studies performed in streptozotocin (STZ)-diabetic nude mouse recipients bearing established, functioning islet xenografts can be used to directly compare in vivo STZ-sensitivity between donor species and that tilapia (fish) islet grafts are exceedingly STZ-resistant. Using this method, we tested whether tilapia islets are sensitive to alloxan. Tilapia or rat islets were transplanted under the renal capsules of STZ-diabetic nude mice. Recipients with normal glucose tolerance tests (GTTs) on day 30-35 were injected with increasing i.v. doses of alloxan and blood glucose levels were followed for 5-7 days and then GTTs were repeated. Next, mice were killed and their grafts/native pancreata examined histologically (including insulin stains). Control nude mice were also injected with increasing i.v. doses of alloxan. Based upon non-fasting blood glucose levels, GTT, and graft histology, the following observations were made: (1) Tilapia islet xenografts were uniformly resistant to i.v. doses of 75 mg/kg (n=3), 150 mg/kg (n=4), and 300 mg/kg (n=3). (2) Rat islet recipients became uniformly severely diabetic after alloxan i.v. doses of 50-70 mg/kg (n=6) (i.e., equivalent to the dosage needed to induce diabetes in rats). (3) Control nude mice were severely diabetic at doses of 75 mg/kg (4/5) and 150 mg/kg (n=3/3). Alloxan dose-response studies were also performed in tilapia. Interestingly, tilapia appeared more sensitive than tilapia islet grafts. Although 75 mg/kg i.v. had little effect in tilapia, higher doses caused severe beta cell necrosis, diabetes, and systemic damage; however, this seeming discrepancy can be explained as tilapia have about one-quarter of the blood volume of mice (i.e., as a percentage of body weight) and so the actual concentration in the blood was about 4-fold higher at each dose. We conclude that tilapia beta cells are highly resistant to the beta cell toxin alloxan.

Antidiabetic effects of quercetin in streptozocin-induced diabetic rats

Effects of the intraperitoneal injection of quercetin in streptozocin-induced diabetic and normal rats were investigated and compared. Although quercetin had no effect on plasma glucose level of normal animals, it significantly and dose-dependently decreased the plasma glucose level of streptozocin-induced diabetic rats. Glucose tolerance tests of the diabetic animals approached those of normal rats, their plasma cholesterol and triglycerides were reduced significantly, while their hepatic glucokinase activity was significantly increased upon quercetin treatment. In normal rats, quercetin did not affect the glucose tolerance test, but resulted in an increase of plasma cholesterol and triglycerides and a decrease in hepatic glucokinase activity. No significant pathologic changes were noted in hepatocytes or kidney tubules and glomeruli, while the number of pancreatic islets significantly increased in both treated normal and diabetic groups. It is concluded that quercetin, a flavonoid with antioxidant properties brings about the regeneration of the pancreatic islets and probably increases insulin release in streptozocin-induced diabetic rats; thus exerting its beneficial antidiabetic effects. However, it may be of little value in normoglycemic animals.

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.