Insulin therapy prevents spontaneous recovery from streptozotocin-induced diabetes in Syrian hamsters. An autoradiographic and immunohistochemical study

A novel tissue for islet transplantation in diabetics

BACKGROUND

Islet transplantation for diabetes therapy has remained a challenge. None of the currently used transplantation sites have provided satisfactory results as islets seem to require a specific tissue for survival and growth. Since the submandibular gland (SMG) shares physiological and anatomical similarities with the pancreas, we attempted to use this tissue as the transplantation site.

METHODS

In Experiment 1, a group of 10 female Syrian Golden hamsters' (SGH) received isolated and purified homologous islets transplanted into their right SMG. In Experiment 2, 15 female SGH received islet transplant into their left SMG as above, except that the recipient hamsters were made diabetic by streptozotocin (STZ) before islet transplantation. In Experiment 3, isolated and purified human islets were transplanted into the SMG of 10 female hamsters.

RESULTS

In 8 out of 10 hamsters in Experiment 1 the islets survived and showed the same morphological structure and endocrine cell content, as intrapancreatic islets and presented signs of rapid growth and distribution. Also, as in Experiment 1, well-established islets were present in Experiment 2. Ten of the 15 hamsters pretreated with STZ had blood glucose values between 96 and 125 mg/dl, whereas three hamsters remained hyperglycemic (glucose levels between 194 and 417 mg/dl). Remarkably, the islets in the pancreas of 10 STZ-treated hamsters with functioning SMG islets remained atrophic even after 12 weeks. In two hamsters transplanted islets showed degeneration and remained diabetic until their pancreatic islets regenerated. In Experiment 3, transplanted human islets were completely destroyed.

CONCLUSIONS

SMG appears to be the most suitable site for islet transplantation for the treatment of diabetes.

Potential involvement of the cyclooxygenase-2 pathway in the regulation of tumor-associated angiogenesis and growth in pancreatic cancer

Background

Gleevec (aka STI571, Imatinib) is a recently FDA approved anti-tumor drug for chronic myelogenous leukemia. Gleevec binds specifically to BCR-ABL tyrosine kinase and inhibit the tyrosine kinase activity. It cross-reacts with another two important membrane tyrosine kinase receptors, c-kit and PDGF receptors. We sought to investigate if Gleevec has a potential role in treatment of non-small cell lung cancer.

Results

We have shown that Gleevec alone can inhibit the A549 lung cancer cell growth in dose-dependent manner, and the optimal concentration of Gleevec inhibition of A549 cell growth is at the range of 2–3 μM (IC50). We have also shown that A549 cells are resistant to cisplatin treatment (IC50 64 μM). Addition of Gleevec to the A549 cells treated with cisplatin resulted in a synergistic cell killing effect, suggesting that Gleevec can potentiate the effect of cisplatin on A549 cells. We also showed that the A549 lung cancer cells expresses the platelet derived growth factor receptor α, and the inhibitory effects of Gleevec on A549 cells is likely mediated through inhibition of PDGFR α phosphorylation. We further tested 33 lung cancer patients' tumor specimens to see the frequency of PDGFR-α expression by tissue micro-arrays and immunohistochemistry. We found that 16 of the 18 squamous carcinomas (89%), 11 of the 11 adenocarcinomas (100%), and 4 of the 4 small cell lung cancers (100%) expressed PDGFR-α.

Conclusion

These results suggest a potential role of Gleevec as adjuvant therapeutic agent for treatment of non-small cell lung cancer.

The relationship between diabetes and pancreatic cancer

About 80% of pancreatic cancer patients have glucose intolerance or frank diabetes. This observation has led to the following two hypotheses: i. pancreatic cancer causes the associated diabetes and ii. the conditions associated with diabetes promote the development of pancreatic cancer. Evidence supporting both hypotheses has been accumulated in previous studies. This article reviews these studies, especially those that have been conducted recently.

Functional and histochemical analysis on pancreatic islets of APA hamsters with SZ-induced hyperglycemia and hyperlipidemia

To clarify how Syrian hamsters of the APA strain (APA hamsters) keep a diabetic condition for a long period, the functional and histochemical changes in the pancreatic islets of diabetic APA hamsters were examined. By glucose tolerance test, no glucose-induced insulin secretion was seen in the diabetic APA hamsters. By immunohistochemistry, it was revealed that at 24 hr after SZ-injection, the number of islets had decreased and that remnant islets had become markedly smaller. The islets had hardly any insulin-immunoreactive cells and consisted of cells stained by anti-glucagon and somatostatin antibodies. One, three and six months after SZ-injection, a small number of cells with vacuolative changes, which were positive for PAS staining, were observed in most islets and the vacuolated cells were stained mainly by anti-insulin antibody. In addition, a number of PCNA-positive cells were observed, especially in the periphery of the vacuolated cells, while TUNEL-positive cells were not detected. This data suggests that beta-cells proliferating as a result of the replication of the resident beta-cells in islets had fallen into degeneration and necrosis by a stress, such as the glycogen deposition in hyperglycemia and hyperlipidemia. Consequently, secretion of insulin was maintained at low levels, which allowed the hamsters to live without insulin therapy in the diabetic condition for over 6 months.

Prevention of pancreatic cancer induction in hamsters by metformin

BACKGROUND AND AIMS

Our previous study suggested that the known promotional effect of a high fat diet, which in hamsters induces peripheral insulin resistance, is related to a compensatory proliferation of islet cells. The present study was to examine whether the prevention of islet cell proliferation can inhibit the promotional effect of a high-fat diet in pancreatic carcinogenesis.

METHODS

Two groups of high fat-fed hamsters were used. One group received Metformin in drinking water for life (HF+Met group), and the other group served as a control (HF group). At the time when the normalization of the plasma insulin level was expected, all hamsters were treated with the pancreatic carcinogen, N-nitrosobis-(2-oxopropyl)amine, and the experiment was terminated 42 weeks later.

RESULTS

Although 50% of the hamsters in the high-fat group developed malignant lesions, none was found in the HF+Met group (P < 0.05). Also, significantly more hyperplastic and premalignant lesions, most of which were found within the islets, were detected in the high-fat group (8.6 lesions/hamster) than in the HF+Met group (1.8 lesions/hamster).

CONCLUSIONS

The results lend further support on the significant role of islet cells in pancreatic carcinogenesis and may explain the association between pancreatic cancer and obesity, which is usually associated with peripheral insulin resistance.

Islet neuronal abnormalities associated with impaired insulin secretion in type 2 diabetes in the Chinese hamster

This study examined the relationship between islet neurohormonal characteristics and the defective glucose-stimulated insulin secretion in genetic type 2 diabetic Chinese hamsters. Two different sublines were studied: diabetes-prone CHIG hamsters and control CHIA hamsters. The CHIG hamsters were divided into three subgroups, depending on severity of hyperglycemia. Compared to normoglycemic CHIG hamsters and control CHIA hamsters, severely hyperglycemic CHIG hamsters (glucose > 15 mmol/l) showed marked glucose intolerance during i.p. glucose tolerance test and 75% impairment of glucose-stimulated insulin secretion from isolated islets. Mildly hyperglycemic CHIG animals (glucose 7.2-15 mmol/l) showed only moderate glucose intolerance and a 60% impairment of glucose-stimulated insulin secretion from the islets. Immunostaining for neuropeptide Y and tyrosine hydroxylase (markers for adrenergic nerves) and for vasoactive intestinal peptide (marker for cholinergic nerves) revealed significant reduction in immunostaining of islets in the severely but not in the mildly hyperglycemic animals, compared to control CHIA hamsters. The study therefore provides evidence that in this model of type 2 diabetes in Chinese hamsters, severe hyperglycemia is accompanied not only by marked glucose intolerance and islet dysfunction but also by reduced islet innervation. This suggests that islet neuronal alterations may contribute to islet dysfunction in severe but not in mild diabetes.

The effect of streptozotocin and a high-fat diet on BOP-induced tumors in the pancreas and in the submandibular gland of hamsters bearing transplants of homologous islets

The effect of a high-fat diet (HF) and streptozotocin (STZ) was investigated in the rapid cancer induction model developed in our laboratories. Syrian golden hamsters bearing homologous islets transplanted in their right submandibular gland (SMG) received a HF or a low-fat diet (LF). Half of the animals from each dietary group received STZ (HF-STZ and LF-STZ groups) and the other half did not (HF and LF groups). One week later, all hamsters were treated with N-nitrosobis(2-oxopropyl)amine (BOP) weekly for 3 weeks and the experiment was terminated 12 weeks after the last BOP injection. Pancreatic lesions were found in many hamsters, with a lower incidence in the LF-STZ group (13%) than in other groups (35-45%). A HF diet counteracted the inhibitory effect of STZ on pancreatic tumor induction by yet unknown mechanisms. SMG tumors, all ductal-type adenocarcinomas, developed in all groups and the incidence was lowest in the HF group (6%) compared to the LF group (15%), LF-STZ group (17%) and HF-STZ group (18%). However, the difference was not statistically significant. It was concluded that a HF diet counteracts the inhibitory effect of STZ on BOP-induced pancreatic lesions but has no effect on the induction of tumors in the SMG. STZ pretreatment does not influence tumor induction of the SMG of these hamster.

The patterns of beta-cell regeneration in untreated diabetic and insulin-treated diabetic Syrian hamsters after streptozotocin treatment

Our previous study showed that Syrian hamsters recover from streptozotocin (SZ)-induced diabetes spontaneously and that insulin therapy adversely affects diabetes. The recovery and lack of recovery was associated with beta-cell regeneration and lack of regeneration. In this study, we examined the patterns of beta-cell regeneration in hamsters by using an immunohistochemical-autoradiographical method. We used tritiated thymidine to examine the DNA synthesis in islet cells and evaluated the number of labeled cells that were or were not immunoreactive with antiinsulin, antiglucagon, and anatisomatostatin. The results showed that, in untreated control hamsters, beta-cell regeneration took place both from preexisting beta cells and from undifferentiated cells (labeled cells unstained with any of the three antibodies) in equal proportions. In the SZ-treated hamsters, however, most regenerating cells seemed to derive from undifferentiated cells within the islets. Insulin therapy inhibited beta-cell regeneration from both the preexisting cells, but more so from the undifferentiated cells. The number of extrainsular islet cell foci was the same in all treatment groups and paralleled the number of islets in each animal during the entire experiment. We concluded the following about diabetic hamsters: 1. beta-Cell regeneration occurs primarily from undifferentiated cells within the islet; 2. Exogenous insulin inhibits beta-cell differentiation from the precursor cells; and 3. The response of intrainsular and extrainsular islet cells to SZ and insulin therapy is similar and the number of extrainsular islet cell foci per pancreas parallel the changes in the number of islets.