Effects of streptozotocin-induced diabetes on lymphocyte POMC and growth hormone gene expression in the rat

Mediation of Endogenous β-Endorphin in the Plasma Glucose-Lowering Action of Herbal Products Observed in Type 1-Like Diabetic Rats

Recently, there have been advances in the development of new substances effective in managing diabetic disorders. Opioid receptors couple multiple systems to result in various biological effects, although opioids are best known for analgesia. In the present review, we used our recent data to describe the advance in plasma glucose-lowering action of herbal products, especially the mediation of β-endorphin in glucose homeostasis of insulin-deficient diabetes. In type 1-like streptozotocin-induced diabetic rats, we identified many products purified from herbs that show a dose-dependent plasma glucose-lowering action. Increase in β-endorphin secretion from the adrenal gland may activate peripheral opioid μ-receptors (MOR) to enhance the expression of muscle glucose transporters and/or to reduce hepatic gluconeogenesis at the gene level, thereby leading to improved glucose utilization in peripheral tissues for amelioration of severe hyperglycemia. It has also been observed that stimulation of α(1)-adrenoceptors (α(1)-ARs) in the adrenal gland by some herbal products is responsible for the increase in β-endorphin secretion via a phospholipase C-protein kinase dependent pathway. However, an increase in β-endorphin secretion from the adrenal gland by herbal products can function via another receptor. New insights into the mediation of endogenous β-endorphin activation of peripheral MOR by herbal products for regulation of glucose homeostasis without the presence of insulin have been established. Therefore, an increase in β-endorphin secretion and/or direct stimulation of peripheral MOR via an insulin-independent action might serve as the potential target for development of a therapeutic agent or promising adjuvant in intensive plasma glucose control.

A biodegradable copolymer for the slow release of growth hormone expedites scarring in diabetic rats

In many diseases wound healing is impaired. This study was designed to establish whether the healing process in diabetes could be improved using a site-specific polymer delivery system containing hGH. The system was first optimized in in vitro experiments performed on cultured fibroblasts taken from healthy and diabetic rats and then tested in an incisional wound model created in the diabetic Wistar rat. In the in vitro experiments using cultured fibroblasts, cell viability, growth, and proliferation were determined, along with polymer degradation, hormone release rates and the expression of TGFbeta1 in the culture medium. For the in vivo experiments, polymer discs with/without GH were inserted through 3 cm incisions made on the backs of the animals. Wound specimens were obtained 7 and 30 days after surgery to evaluate inflammatory/apoptotic cells, metalloprotease expression and neoangiogenesis using microscopy and immunohistochemical techniques. The local administration of GH using a polymer delivery system did not affect the normal wound healing process. Conversely, when used in diabetic animals, epidermal and dermal repair was expedited. Our findings indicate that GH induces cell proliferation, enhances CD4(+) infiltration; increases extracellular matrix protein deposition; stimulates angiogenesis; and diminishes apoptosis at the diabetic wound site. These effects give rise to a comparable wound healing process to that observed in healthy animals.

Increase of beta-endorphin biosynthesis in the adrenal gland of streptozotocin-induced diabetic rats

Opioid plays an important role in the regulation of glucose homeostasis in diabetic rats lacking insulin. The present study investigated the changes of beta-endorphin biosynthesis in the adrenal medulla of streptozotocin-induced diabetic rats (STZ-diabetic rats) by determination of the gene expression of pro-opiomelanocortin (POMC) and the amount of beta-endorphin. Expression of the distinct mRNA that encodes proteins of POMC was studied using reverse transcription combined with polymerase chain reaction (RT-PCR). Results of RT-PCR demonstrated that the mRNA level of POMC in the adrenal gland markedly increased in STZ-diabetic rats as compared with that in normal rats. The content of beta-endorphin-like immunoreactivity (BER) in the adrenal medulla, determined by enzyme-linked immunosorbent assay, was actually higher in diabetic rats with insulin deficiency. Normalization of the plasma glucose concentration in STZ-diabetic rats with exogenous insulin or phlorizin, an inhibitor of the renal tubular glucose transport, reversed the mRNA level of POMC in the adrenal gland after 4 days of treatment. A similar decrease of BER amount also observed in the adrenal medulla of STZ-diabetic rats received the same treatment with exogenous insulin or phlorizin. Therefore, correction of hyperglycemia in STZ-diabetic rats could reverse the higher gene expression of POMC in the adrenal gland. These results suggest that hyperglycemia is responsible for the increase of POMC gene expression to enhance beta-endorphin biosynthesis in the adrenal gland of STZ-diabetic rats.

Up-regulation of splenic prohormone convertases PC1 and PC2 in diabetic rats

Organisms respond to infection in a complex manner involving bidirectional interactions between the neuroendocrine and immune systems. Many of the bioactive endocrine/immune factors are synthesized in a precursor form and are expected to be activated by prohormone convertases (PCs). Since patients with both type 1 and type 2 diabetes have an increased incidence and severity of infections, we hypothesized that in a condition of hyperglycemia, these processing enzymes would be activated in an immune tissue, the spleen. To test this hypothesis, we treated rats with intraperitoneal streptozotocin (STZ) (50 mg/kg/day) daily for 5 days and measured splenic PC1 and PC2 mRNA by ribonuclease protection assay. We found that PC1 mRNA was increased 6.0+/-0.02-fold (P<0.05) and PC2 mRNA was increased 1.80+/-0.01-fold (P<0.005) in the spleen of rats that received STZ compared to rats that received vehicle. Western blot indicated that the 75-kDa form of PC1 was the only form of PC1 present in the spleen and that this form increased with STZ treatment. Immunohistochemistry revealed that PC1 was found in both the white pulp (T-lymphocytes) and red pulp (monocytes and macrophages) and that its increase in immunoreactivity occurred primarily in the white pulp. PC2 and pro-opiomelanocortin (POMC, a possible splenic substrate for PC1/PC2) immunoreactivity was found predominantly in the red pulp. STZ induced an increase in splenic PC1 and POMC, but not PC2 protein levels. We conclude that in the STZ model of diabetes, splenic PCs are induced, which could lead to an increased activation of many immune-derived hormones. We speculate that this up-regulation of prohormone converting enzymes may be related to the increased infections seen in patients with both type 1 and type 2 diabetes.

Quantification of proopiomelanocortin mRNA in peripheral lymphocytes of alcoholics

Recent studies indicate the production of adrenocorticotropic hormone (ACTH) by human mononuclear leucocytes constitutively or in response to hypothalamic factors and interferon inducers. These results have led to the proposal that the control mechanisms for the proopiomelanocortin (POMC) gene in lymphocytes may be similar to that of pituitary cells. After chronic ethanol treatment, changes in the pituitary POMC mRNA in rats have been reported, but so far nothing is known about changes in the POMC gene expression in lymphocytes under these conditions. Therefore, the expression of the POMC gene was investigated in human peripheral lymphocytes in both volunteers and alcoholics. POMC mRNA levels in these cells were significantly increased in alcoholics, with one alcoholic showing an even more than five times higher POMC mRNA level compared to the other patients. After detoxification, a significant decrease in the POMC mRNA of alcoholic patients was observed, except in the one with the extremely elevated POMC mRNA level, where the opposite occurred. An influence of chronic ethanol ingestion on POMC gene expression in lymphocytes could be assumed. The observed changes seem to be correlated with ethanol intake, because the elevated POMC mRNA amounts found in lymphocytes of alcoholics after admission to the hospital were already declining after the detoxification period.