Streptozotocin-induced Hyperglycemic Rats Research Articles

The relation among NGF, EGF and insulin is important for triggering pancreatic β cell apoptosis

Nerve growth factor (NGF) is a well-known mediator for maintaining the survival of neurons, while recent studies report that its absence induces apoptosis in cultured β cells of humans and rats. However, its relationship with other growth factors that have important roles in the survival and function of β cells such as epidermal growth factor (EGF) has not yet been elucidated. The aim of this study was to investigate the effects of NGF withdrawal on the synthesis and secretion of EGF, insulin with respect to β cell apoptosis in hyperglycemic rats. β cells were isolated from euglycemic and streptozotocin-induced hyperglycemic rats and treated with NGF neutralizing antibody for withdrawal of NGF in culture medium. NGF, EGF and insulin levels in cell lysates and secretion samples were measured by enzyme-linked immunosorbent assay, and their gene expressions were determined by real-time reverse transcription polymerase chain reaction assay. Apoptosis was quantitatively determined by cytoplasmic histone-associated DNA fragments. Nerve growth factor neutralization triggered β cell apoptosis. In addition decreased insulin, increased NGF and EGF were observed at gene expression and protein levels by NGF neutralization. Moreover, NGF withdrawal decreased secretion of these peptides from β cells. Although the alterations seemed to be similar under euglycemic and hyperglycemic conditions, NGF withdrawal more strongly affected β cells of hyperglycemic rats. These important findings indicate that NGF is an important regulator for the synthesis and secretion of EGF and insulin from the β cells. Moreover, results suggested that NGF withdrawal causes apoptosis by decreasing EGF, NGF and insulin secretion from β cells of hyperglycemic rats.

Loss of calpain 10 causes mitochondrial dysfunction during chronic hyperglycemia

We showed that renal calpain 10, a mitochondrial and cytosolic Ca2+-regulated cysteine protease, is specifically decreased in kidneys of diabetic rats and mice, and is associated with diabetic nephropathy. The goals of this study were to examine renal calpain 10 and mitochondrial dysfunction in streptozotocin-induced hyperglycemic rats and determine the effects of siRNA-mediated knock down of renal calpain 10 on mitochondrial function. Four weeks after streptozotocin injection, calpain 10 protein and mRNA were decreased and calpain 10 substrates accumulated. We detected increased state 2 respiration in isolated renal mitochondria and increased markers of mitochondrial fission and mitophagy. All changes were prevented by daily insulin injection. Compared to scrambled siRNA, calpain 10 siRNA resulted in a marked decrease in renal calpain 10 at 2, 5 and 7days. In concert with the loss of renal calpain 10, calpain 10 substrates accumulated, mitochondrial fusion decreased, mitochondrial fission and mitophagy increased. In summary, insulin-sensitive hyperglycemia induced loss of renal calpain 10 is correlated with renal mitochondrial dysfunction, fission and mitophagy, and specific depletion of renal calpain 10 produces similar mitochondrial defects. These results provide evidence that diabetes-induced renal mitochondrial dysfunction and renal injury may directly result from the loss of renal calpain 10.

Beneficial Impact ofZingiber zerumbeton Insulin Sensitivity in Fructose-Fed Rats

Zingiber zerumbet (L) Smith (Zingiberaceae), commonly known as the pinecone or shampoo ginger, is distributed in many parts of Asia. It has been demonstrated that the aqueous extract of Z. zerumbet exerted a potential blood glucose lowering effect in normoglycemic and streptozotocin-induced hyperglycemic rats. The present study was undertaken to clarify whether the ethanol extract of Zingiber zerumbet (EEZZ) is effective in improving insulin resistance. Insulin resistance was induced in rats by feeding a high-fructose diet for six weeks. Thereafter, rats were maintained on the same diet and treated with oral EEZZ or pioglitazone once daily for eight weeks. At the end of treatment, the degree of basal insulin resistance was measured by homeostasis model assessment (HOMA-IR). Insulin sensitivity was calculated using the composite whole body insulin sensitivity index (ISIcomp). Protein expression was evaluated by immunoblotting. Phytochemicals in EEZZ were determined through liquid chromatography-tandem mass. Not only curcumin but also quercetin and kaempferol were abundant in EEZZ. EEZZ (300 mg/kg/day) displayed similar characteristics to pioglitazone (20 mg/kg/day) in reducing HOMA-IR and elevating ISIcomp as well as enhancing hepatic glycogen accumulation. Elevated glycosylated hemoglobin levels and hyperinsulinemia were ameliorated by EEZZ. Further, EEZZ enhanced the action of insulin on muscle glucose transporter subtype 4 translocation and attenuated hepatic phosphoenolpyruvate carboxykinase expression. This study suggests that EEZZ may be an ethnomedicine for improving insulin sensitivity.

Acute myocardial infarction in streptozotocin-induced hyperglycaemic rats: protection by a carbon monoxide-releasing molecule (CORM-3)

Here, we have studied the effects of a carbon monoxide-releasing molecule (CORM-3, tricarbonylchloro(glycinato)ruthenium(II)) on acute myocardial ischemia/reperfusion (I/R) injury in hyperglycaemic streptozotocin-treated rats (STZ rats). Occlusion of the left descending coronary artery for 25 min followed by a 2-h reperfusion in STZ-induced hyperglycaemic rats was used as the model. CORM-3 and its inactive counterpart (iCORM-3) were administered 1 h prior to ischemia. The parameters measured included myocardial infarct size (IS) and a selection of inflammatory, oxidative markers and endothelial progenitor cells (CD34⁺ and CD117/c-kit⁺. In STZ-induced hyperglycaemic rats, occlusion of the left descending coronary artery caused injury of the myocardial tissue with an IS of ~70%, expressed as fraction of the area at risk. Given intraperitoneally 1 h prior to ischemia, CORM-3 (2-8 mg/kg) afforded significant dose-dependent cardio-protection. Specifically, pre-treatment with CORM-3 reduced infarct size by 14 ± 0.6%, 34 ± 1% and 53 ± 1.6% for doses of 2, 4 and 8 mg/kg, respectively. A negative control (iCORM-3) failed to prevent the cardiac damage induced by I/R. CORM-3 pre-treatment augmented cardiac heme oxygenase-1 (HO-1) protein levels and was associated with an increased number of CD34⁺- and CD117/c-kit⁺-positive immunostaining. Modulation of these markers was associated with augmented cardiac eNOS expression and levels of the cytokines TNF-α and IL-1 beta. CORM-3 afforded significant cardio-protection against acute myocardial infarction in STZ-induced hyperglycaemic rats through liberation of small amounts of CO. Of interest, CORM-3 promoted recruitment of the endogenous endothelial progenitor cells within the myocardium, possibly through modulation of cardiac HO-1 and eNOS expression and/or function.

Absorption, transport and insulin-mimetic properties of bis(maltolato)oxovanadium (IV) in streptozotocin-induced hyperglycemic rats by integrated mass spectrometric techniques

The use of V(IV) complexes as insulin-enhancing agents has been increasing during the last decade. Among them, 3-hydroxy-2-methyl-4-pyrone and 2-ethyl-3-hydroxy-4-pyrone (maltol and ethyl maltol, respectively) have proven to be especially suitable as ligands for vanadyl ions. In fact, they have passed phase I and phase II clinical trials, respectively. However, the mechanism through which those drugs exert their insulin-mimetic properties is still not fully understood. Thus, the aim of this study is to obtain an integrated picture of the absorption, biodistribution and insulin-mimetic properties of the bis(maltolato)oxovanadium (IV) (BMOV) in streptozotocin-induced hyperglycaemic rats. For this purpose, BMOV hypoglycaemic properties were evaluated by monitoring both the circulating glucose and the glycohemoglobin, biomarkers of diabetes mellitus. In both cases, the results were drug concentration dependent. Using doses of vanadium at 3 mg/day, it was possible to reduce the glycaemia of the diabetic rats to almost control levels. BMOV absorption experiments have been conducted by intestinal perfusion revealing that approximately 35% of V is absorbed by the intestinal cells. Additionally, the transport of the absorbed vanadium (IV) by serum proteins was studied. For this purpose, a speciation strategy using high-performance liquid chromatography (HPLC) for separation and inductively coupled serum mass spectrometry, ICP-MS, for detection has been employed. The obtained HPLC-ICP-MS results, confirmed by MALDI-MS data, showed evidence that V, administered orally, is uniquely bound to transferrin in rat serum.

Hypoglycaemic effect of Ipomoea batatas aqueous leaf and stem extract in normal and streptozotocin-induced hyperglycaemic rats

Background: Among the Yoruba herbalists (South-west Nigeria), hot water infusion of the whole plant of Ipomoea batatas continues to be highly valued in the local management of diabetes because of its effectiveness in the control of blood glucose. Therefore, the present study investigates the blood glucose lowering effect of graded oral doses of the extract in normal and streptozotocin (STZ)-induced diabetic rats as a way of validating its folkloric use in the local management of diabetes mellitus. Materials and Methods: 100, 200 and 400 mg/kg/day of the aqueous whole plant extract of Ipomoea batatas (IB) were administered to normal and STZ-induced hyperglycemic rats as single, daily oral treatment for 14 days and their effects on the fasting blood glucose (FBG) was evaluated. In addition, the acute oral toxicity and preliminary phytochemical studies of IB were also conducted. Results: These showed that oral administration of IB for 14 days caused signifi cant dose related reductions (P<0.05, P<0.001) in FBG of both normal and STZinduced hyperglycemic rats. Oral treatment with 400 mg/kg/day IB also signifi cantly attenuated (P<0.05) body weight gain in the treated rats. The oral LD 50 for IB was estimated to be 12 g/kg while the phytochemical analysis of the extract showed the presence of alkaloids, fl avonoids, tannins, saponin, anthraquinones and reducing sugars in the extract. Conclusions: The data generated in this study validate the folkloric use of the hot infusion of the whole plant of IB in the local management of diabetes.

Vanadium‐Enriched Cordyceps sinensis, a Contemporary Treatment Approach to Both Diabetes and Depression in Rats

This article studies a contemporary treatment approach toward both diabetes and depression management by vanadium-enriched Cordyceps sinensis (VECS). Streptozotocin-induced hyperglycemic rats were used in the study. After the rats were administered with VECS, a significant reduction in blood glucose levels was seen (P < .05) and the levels of serum insulin increased significantly (P < .05). At the same time, the study revealed a significant decrease in immobility with a corresponding increase in the swimming and climbing behavior in hyperglycemic rats following VECS treatment. The results described herein demonstrate that VECS is a contemporary treatment approach that advocates an aggressive stance toward both diabetes and depression management.

Effect of Coriandrum sativum L. seeds on blood glucose in streptozotocin-induced diabetic rats

Diabetes mellitus is considered a serious endocrine syndrome. The prevalence of diabetes mellitus in the general population is greater than 6%. Many herbal medicines have been recommended for the treatment of diabetic. The present study was carried out to investigate the effect of the alcoholic extract seeds of Coriandrum sativum L. on blood glucose in streptozotocin-induced diabetic rats. The alcoholic extract was intraperitoneally administrated animals and the levels of blood glucose were measured before and 1.5, 3 and 5 h after extract administration. The extract produced hypoglycemic effect in diabetic animals. In conclusion, our results have shown that alcoholic extract of Coriandrum sativum seeds possess a hypoglycaemic effect on streptozotocin-induced hyperglycaemic rats intraperitoneally. Thus, the folk use of this plant may be validated by this study. However, controlled clinical trials will be required to confirm its hypoglycaemic action and general safety.

SDF‐1α/CXCR4 axis is involved in glucose‐potentiated proliferation and chemotaxis in rat vascular smooth muscle cells

Excessive proliferation of vascular smooth muscle cells (VSMCs), which migrate from the tunica media to the subendothelial region, is one of the primary lesions involved in atherogenesis in diabetes. Here, we investigated whether high glucose potentiated the proliferation and chemotaxis of VSMCs by activating SDF-1α/CXCR4/PI-3K/Akt signalling. The expression of SDF-1α, CXCR4 and PCNA was up-regulated in tunica media of thoracic aortas by streptozotocin-induced hyperglycaemic Sprague-Dawley rats. Exposure of primary VSMCs to high glucose (25 mM) led to the up-regulated expression of SDF-1α and CXCR4, activated PI-3K/Akt signalling, and consequently promoted the proliferation and chemotaxis of VSMCs. Interestingly, the administration of SDF-1 siRNA or neutralizing antibody against SDF-1α abolished high glucose-induced up-regulation of CXCR4. Moreover, pretreatment with SDF-1α neutralizing antibody, CXCR4 specific inhibitor (AMD3100) or PI-3K inhibitor (LY294002) attenuated the high glucose-potentiated proliferation and chemotaxis in VSMCs. These results suggested that high glucose activated the SDF-1α/CXCR4/PI-3K/Akt signalling pathway in VSMCs in an autocrine manner, which enhanced the proliferation and chemotaxis of VSMCs.

A novel insulin formulation can keep providing steady levels of insulin for much longer periods in-vivo.

We have recently succeeded in preparing insulin-loaded microcapsules that release the insulin in a strictly controlled manner with little initial rapid release in-vitro or in-vivo. We show here the superiority of the best formulation prepared with co-poly(D,L-lactic/glycolic) acids (PLGA) (mean MW 5800, L/G ratio 50:50) with a main diameter of 15 approximately 30 microm in-vivo. When 3.2 % insulin-loaded PLGA microcapsules were subcutaneously given as a single dose to streptozotocin-induced hyperglycaemic rats (250 U kg(-1)), plasma insulin levels gradually increased and constant levels (30.3-94.1 microU mL(-1)) were sustained. Rats receiving the formulation once a week showed not only steady plasma insulin levels, but also gained weight at a similar speed to normal rats. Meanwhile, daily treatment with Humulin U (25 U kg(-1)) caused a transient high insulin level (2723.9 microU mL(-1) at 1 h) in plasma, but the body weight of the rats was little changed. A pharmacological study in female Cynomolgus monkeys also revealed that the microcapsular formulation provided a flat release of insulin for longer periods and showed no immunogenic activity. In the near future, therefore, this insulin formulation could become very beneficial as a provider of basal insulin levels for insulin-dependent diabetic patients.

Antihyperglycaemic Properties of the Ethyl acetate Extract of Dennettia tripetala in Diabetic Rats

Antihyperglycemic properties of chloroform (CDT), ethyl acetate (EDT) and methanolic (MDT) extracts of D. tripetala were investigated using alloxan- and streptozotocin-induced hyperglycemic rats. An oral glucose tolerance test (OGTT) was performed in EDT-pretreated in both normal and alloxan-induced hyperglycemic rats. Tolbutamide (TLB) was used as the reference drug. TLB (100 mg/g), EDT (100 mg/kg), MDT (100 mg/kg) significantly (p&lt;0.05) decreased the plasma glucose level at different time intervals after the administration of the extracts/drug. The antihyperglycemic activity of TLB and EDT started at 2 and 3h, respectively, and lasted till 10h. EDT caused the highest reduction (46%) in plasma glucose level in 10h after treatment. In OGTT, EDT (50 mg/kg) significantly (p&lt;0.05) increased glucose tolerance in both normal and hyperglycemic rats. This activity was more prominent in the alloxan-induced hyperglycemic rats. TLB (100 mg/kg) initially caused a slight reduction in plasma glucose level followed by steady level throughout the period of the study. Furthermore, EDT (30 mg/kg) significantly (P&lt;0.05) decreased the plasma glucose level at 6, 8 and 10 h post treatment, when compared with TLB (100 mg/kg). In conclusion, EDT showed promising antihyperglycemic activity, which justified the use of the plant extract by the natives in managing diabetes mellitus.

ECAM: Attacking an Epidemic?

<i>eCAM</i>: Attacking an Epidemic?

A Contemporary Treatment Approach to Both Diabetes and Depression by Cordyceps sinensis, Rich in Vanadium.

Diabetes mellitus is accompanied by hormonal and neurochemical changes that can be associated with anxiety and depression. Both diabetes and depression negatively interact, in that depression leads to poor metabolic control and hyperglycemia exacerbates depression. We hypothesize one novel vanadium complex of vanadium-enriched Cordyceps sinensis (VECS), which is beneficial in preventing depression in diabetes, and influences the long-term course of glycemic control. Vanadium compounds have the ability to imitate the action of insulin, and this mimicry may have further favorable effects on the level of treatment satisfaction and mood. C. sinensis has an antidepressant-like activity, and attenuates the diabetes-induced increase in blood glucose concentrations. We suggest that the VECS may be a potential strategy for contemporary treatment of depression and diabetes through the co-effect of C. sinensis and vanadium. The validity of the hypothesis can most simply be tested by examining blood glucose levels, and swimming and climbing behavior in streptozotocin-induced hyperglycemic rats.

The α-glucosidase inhibitor miglitol decreases glucose fluctuations and gene expression of inflammatory cytokines induced by hyperglycemia in peripheral leukocytes

Objective Postprandial hyperglycemia is thought to cause inflammation in many tissues. In this study, we examined whether the gene expression of inflammatory cytokines/cytokine-like factors in peripheral leukocytes are altered by feeding streptozotocin-treated rats a diet containing an α-glucosidase inhibitor, miglitol. Methods Upregulated gene expression in peripheral leukocytes of streptozotocin-induced hyperglycemic rats was determined by microarray analysis. We examined whether gene expression was altered by supplementing the diet with miglitol. Results Microarray analysis revealed that gene expression of interleukin-1β and putative inflammatory cytokines, S100a4/6/8/9, was induced by streptozotocin treatment. Dietary supplementation with miglitol to the streptozotocin-induced hyperglycemic rats for 20 d not only increased plasma concentrations of a marker for glucose fluctuations, 1,5-anhydroglucitol, the concentration of which is decreased by sustained or postprandial elevated blood glucose levels, but also suppressed the induction of interleukin-1β and S100a4/6/8/9 genes by hyperglycemia. Conclusion These results suggest that miglitol inhibits the gene expression of inflammatory cytokines/cytokine-like factors in peripheral leukocytes by suppressing glucose fluctuations.

Effects of Strobilanthes crispus Tea Aqueous Extracts on Glucose and Lipid Profile in Normal and Streptozotocin-Induced Hyperglycemic Rats

Strobilanthes crispus (Acanthaceae) has been used traditionally as antidiabetic, diuretic, antilytic, and laxative and has been proven scientifically to possess high antioxidant activity, anti-AIDS, and anticancer properties. It is commonly consumed in the form of herbal tea. The ethnopharmacological value of this plant, such as the development of nutraceutical S. crispus herbal tea (fermented and unfermented) and assessment of their antihyperglycemic properties were investigated. The antidiabetic properties of S. crispus fermented and unfermented tea was carried out in normal and streptozotocin-induced hyperglycaemic rats for 21 days. Glucose and lipid profile (total cholesterol, triglyceride, HDL-cholesterol, LDL-cholesterol) were determined at day 0 (baseline), day 7, and day 21. The results showed that the hot water extract of both fermented and unfermented S. crispus tea reduced blood glucose in hyperglycaemic rats. S. crispus unfermented tea also reduced glucose level in normal rat. Both fermented and unfermented S. crispus tea also showed to improve lipid profile. Antioxidant and polyphenol content that present in the extracts might contribute to the antihyperglycemic and antilipidemic properties. Further study is needed to be carried out in pre-clinical and clinical environment to prove its efficacy in human.

Early treadmill exercise decreases intrastriatal hemorrhage-induced neuronal cell death and increases cell proliferation in the dentate gyrus of streptozotocin-induced hyperglycemic rats

Intracerebral hemorrhage (ICH) is a severe complication in diabetic patients. Currently, physical exercise is recommended as a behavioral intervention to promote functional recovery in brain diseases, including ICH. Recently, hyperglycemia is known to aggravate brain injury in experimental ICH. Here, we examined the effect of treadmill exercise on the intrastriatal hemorrhage-induced neuronal cell death and cell proliferation in the dentate gyrus of hyperglycemic rats. Hyperglycemia was induced by the intraperitoneal injection of 50 mg/kg streptozotocin (STZ). Intrastriatal hemorrhage was induced by the infusion of 0.2 U collagenase into the striatum using stereotaxic instrument. Rats in the exercise groups were forced to run on a treadmill for 30 min daily for 10 days. Apoptosis was assessed by the terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assay. Cell proliferation was assessed by the 5-bromo-2′-deoxyuridine (BrdU) immunohistochemistry. Our data showed that in rats started treadmill exercise 24 h after ICH induction, the size of lesion induced by hemorrhage and the number of apoptotic cells were decreased significantly. The number of proliferating cells in the dentate gyrus was significantly decreased in hyperglycemic rats. Treadmill exercise markedly enhanced cell proliferation in the dentate gyrus of hyperglycemic rats. The data suggest that treadmill exercise may provide therapeutic value to ICH patients with hyperglycemia by suppressing neuronal apoptosis and increasing cell proliferation.

Screening for antihyperglycaemic activity in several local herbs of Malaysia

Screening of aqueous extract of Phyllantus niruri (PL), Zingiber zerumbet (ZG), Eurycoma longifolia (TA-a and TA-b) and Andrographis paniculata (AP) to determine their blood glucose lowering effect were conducted in normoglycaemic and Streptozotocin-induced hyperglycaemic rats. Significant reduction in blood glucose level at 52.90% was shown when hyperglycaemic rats were treated with 50 mg/kg body weight (BW) aqueous extract of AP. This effect is enhanced when freeze–dried material was used, where 6.25 mg/kg BW gave 61.81% reduction in blood glucose level. In the administration of TA-a and TA-b, positive results in hyperglyacaemic rats were only obtained when 150 mg/kg BW of the aqueous extract was used. No significant reduction in blood glucose level were shown in hyperglycaemic rats treated with PL and ZG at all concentrations used (50, 100 and 150 mg/kg BW). In normoglycaemic rats, no significant reduction was noted when all the same extracts were used.

Redistribution of Integrins in Tubular Epithelial Cells during Diabetic Glycogen Nephrosis

Background/Aims: Even though many aspects of glycogen nephrosis in diabetes have already been studied, adhesion interactions between the glycogen-accumulating clear cells and the tubular basement membranes have not been addressed. As integrins play key roles in cell-to-matrix interactions, we investigated the expression and distribution of α₃-, α_V-, β₁- and β₃-integrin subunits in renal tissues from streptozotocin-induced hyperglycemic rats (3 months old) and their age-matched controls as well as from streptozotocin-injected normoglycemic animals. Methods: The levels and distribution of integrins were studied by immunocytochemistry and Western blot analysis. Results: Immunoblotting analysis of fractions enriched in glycogen-accumulating clear cells demonstrated enhanced expression of α₃, α_V and β₁ subunits while expression of β₃ did not differ from controls. The most striking cytochemical result was the redistribution of the α₃-, α_V-, and the β₁-integrin subunits to the apical plasma membrane of these cells. This was found by light and electron microscopy. Conclusion: Our results suggest that the altered expression and distribution of integrins in clear cells of diabetic animals must have defined roles in the development of the renal tubulopathy.

Decreased Modulation by Lipopolysaccharide of Aortic Smooth Muscle Contractility in Streptozotocin-Induced Hyperglycemic Rats

Infection is a major complication of patients with diabetes, and endotoxemic shock is a serious complication during sepsis. The purpose of this study was to determine whether the action of bacterial lipopolysaccharide (LPS) on vasocontractility is altered in diabetic vessels. Diabetes was induced in 10-week-old Wistar rats by an intraperitoneal injection of streptozotocin. LPS-induced increase in cGMP (cyclic guanosine 3',5'-monophosphate) level was lower in aortae from streptozotocin-induced hyperglycemic (diabetic) rats than in those from vehicle-injected control rats, while LPS-induced nitric oxide production was not different in the diabetic and control aortae. Phenylephrine-induced contraction of diabetic aortae was lower than that of the control aortae. LPS treatment resulted in depression of contractile response to phenylephrine in both diabetic and control aortae, and the degree of depression was much lower in diabetic aortae. Treatment with N monomethyl l-arginine (l-NMMA) prevented diminution of phenylephrine-induced contraction of the aortae after LPS stimulation, and the degree of the preventive effect by l-NMMA was significantly lower in diabetic aortae than in the control aortae. Protein expression of inducible nitric oxide synthase detected by Western blot analysis was not different in the diabetic and control aortae. The decrease in cGMP production after LPS stimulation in diabetic aortae was not prevented by treatment of the aortae with superoxide dismutase but was partially prevented by that with Tiron (4,5-dihydroxy-1,3-benzene disulfonic acid), a cell-permeable scavenger of reactive oxygen species. These results suggest that LPS-induced depression of vasocontractility is attenuated in diabetic aortae due to a decrease in nitric oxide-stimulated cGMP production, probably resulting from increased inactivation of inducible nitric oxide by excessive intracellular oxidative stress. It is concluded that contractility of aortae from streptozotocin-induced hyperglycemic rats may be less affected by LPS during endotoxemia.

A novel sustained-release formulation of insulin with dramatic reduction in initial rapid release

To ensure a strictly controlled release of insulin, a preparation method for insulin-loaded microcapsules was designed. Microcapsules were prepared with an injectable, biodegradable polymer composed of co-poly( d, l-lactic/glycolic) acids (PLGA) (mean molecular weight 6600, LA/GA ratio 50:50). Morphological examination using scanning electron microphotography demonstrated spherical particles with a main diameter of 15–30 μm. When 3% insulin-loaded PLGA microcapsules were administered subcutaneously as a single dose (250 U/kg) to streptozotocin-induced hyperglycemic rats, plasma insulin levels increased and were sustained at levels showing hypoglycemic effects. When glycerin, ethanol, or distilled water was used throughout the preparation procedure, the resultant microcapsules dramatically reduced the initial burst. The formulation in which glycerin was added to an oil phase containing PLGA, insulin, and ZnO increased plasma insulin levels to 86.7, 108.4, and 84.9 μU/ml at 1, 2, and 6 h, respectively. The levels remained at 36.2–140.7 μU/ml from day 1 to day 9. The AUC 0–24 h/AUC 0–336 h ratio was calculated to be 9.7%. The formulation prepared without additives gave such a rapid insulin release that animals receiving it became transiently hypoglycemic.