Streptozotocin-treated Rats Research Articles

Reduced expression and secretion of apolipoprotein M in fat-fed, streptozotocin-diabetic rats is partially reversed by an artificial ligand of PPARγ

To investigate the effect of administration of rosiglitazone, an artificial ligand of PPARγ, on the expression and secretion of apolipoprotein (apoM) in fat-fed, streptozotocin-treated rats, an animal model for type 2-like diabetes. Healthy male SD rats were divided into 4 groups: a control group (n=7), a high-fat chow group (HF group, n=8), a diabetes mellitus group (DM group, n=7), and a diabetes mellitus group with rosiglitazone intervention group (RSG group, n=7). Fasting blood glucose (FBG), fasting insulin (FINS), triglyceride (TG) and total cholesterol (TC) were measured at the beginning of the study. The diabetic rats model was established by feeding high fat chow and intraperitoneal injection of streprozotocin. Then the randomly selected treatment group was given rosiglitazone by daily gavage for 8 weeks. All the rats were killed at the fifteenth week, at which time blood and tissues (liver, kidney, adipose) were collected and prepared. The levels of FBG, FINS, TG and TC were assayed. The level of apoM in serum was measured by enzyme-linked immunosorbent assay (ELISA). Reverse transcription polymerase chain reaction (RT-PCR) was used to determine apoM mRNA expression in liver, kidney, and adipose tissues. Compared with either control group or HF group, serum apoM concentration in the DM group was reduced significantly (P<0.05); compared with the DM group, however, serum apoM concentrations in RSG group were increased (P<0.05). The expression of apoM mRNA in liver was highest, in kidney medium, and in adipose tissue extremely low (P<0.05). ApoM mRNA expression in liver and kidney was decreased in both DM and HF groups compared to control group (P<0.05). But, as with serum apoM concentration, apoM mRNA in the liver, kidney and adipose tissues of the RSG group were all increased markedly (P<0.05). The level of serum apoM in SD rats correlated negatively with TG (r=-0.466, P=0.011), TC (r=-0.568, P= 0.001), FBS (r =-0.371, P<0.001), and FINS(r=-0.768, P= 0.048 ). These results suggest that apoM may participate in the glucose and lipid metabolism by the regulation of PPARγ.

FK1706, a novel non-immunosuppressive immunophilin ligand, modifies gene expression in the dorsal root ganglia during painful diabetic neuropathy

Objectives: FK1706, a non-immunosuppressive immunophilin ligand, potentiated nerve growth factor-induced neurite outgrowth, putatively mediated via FKBP-52 and the Ras/Raf/MAPK signaling pathway. It also improved mechanical allodynia accompanied by the recovery of intraepidermal nerve fiber density in a painful diabetic neuropathy in rats. The aim of this study was to demonstrate the gene expression profiling in dorsal root ganglion in streptozotocin-induced diabetic rats related to pain and anti-allodynia effects of FK1706 administration to elucidate the putative mechanisms of its neurotrophic activity in vivo. Here, we analyzed gene expression of the dorsal root ganglia using microarray together with behavioral measurement of mechanical allodynia in diabetic rats to try to capture the global fingerprint of changes in gene expression associated with FK1706 administration.Methods: The withdrawal threshold of streptozotocin-induced diabetic rats was measured by an electronic von Frey system. The gene expression of the ganglia from L4 to L6 obtained from streptozotocin-treated rats with or without chronic administration of FK1706 was analyzed using an Affymetrix GeneChip to extract interesting genes in the development of mechanical allodynia in diabetes and anti-allodynia effect of FK1706.Results: Daily oral administration of FK1706 improved mechanical allodynia without decreasing plasma glucose levels. From gene expression analysis, the expression of thioredoxin interacting protein gene was sustained to increased change, whereas those of collagen I alpha1, II alpha1 and IX alpha1 genes were decreased from 2 to 4 weeks after streptozotocin injection. While no changes occurred after 1 week of commencing of FK1706 administration (2 weeks after streptozotocin injection), changes in expression more than 1·5-fold were observed for genes such as Ckm, Actn3, Atp2a1, Bglap, Acta1, Myl1, Tnnc2, and Mylpf at 2 weeks of FK1706 administration (3 weeks after streptozotocin injection). The genes RGD1564519, Hbb, LOC689064, Arpc4 and S100a9 were upregulated in comparison with streptozotocin-injected control group at 3 weeks of FK1706 administration; on the other hand, those of Actn3, Atp2a1 were downregulated by FK1706.Discussion: FK1706 ameliorates mechanical allodynia with accompanying increases in gene expressions possibly related to neurite outgrowth, development, differentiation, and nociceptive sensitivity.

Compound 49b Prevents Diabetes-Induced Apoptosis through Increased IGFBP-3 Levels

To determine whether Compound 49b, a novel PKA-activating drug, can prevent diabetic-like changes in the rat retina through increased insulin-like growth factor binding protein-3 (IGFBP-3) levels. For the cell culture studies, we used both human retinal endothelial cells (REC) and retinal Müller cells in either 5 mM (normal) or 25 mM (high) glucose. Cells were treated with 50 nM Compound 49b alone of following treatment with protein kinase A (PKA) siRNA or IGFBP-3 siRNA. Western blotting and ELISA analyses were done to verify PKA and IGFBP-3 knockdown, as well as to measure apoptotic markers. For animal studies, we used streptozotocin-treated rats after 2 and 8 months of diabetes. Some rats were treated topically with 1 mM Compound 49b. Analyses were done for retinal thickness, cell numbers in the ganglion cell layer, pericyte ghosts, and numbers of degenerate capillaries, as well as electroretinogram and heart morphology. Compound 49b requires active PKA and IGFBP-3 to prevent apoptosis of REC. Compound 49b significantly reduced the numbers of degenerate capillaries and pericyte ghosts, while preventing the decreased retinal thickness and loss of cells in the ganglion cell layer. Compound 49b maintained a normal electroretinogram, with no changes in blood pressure, intraocular pressure, or heart morphological changes. Topical Compound 49b is able to prevent diabetic-like changes in the rat retina, without producing systemic changes. Compound 49b is able to prevent REC apoptosis through increasing IGFBP-3 levels, which are reduced in response to hyperglycemia.

Characterization of Angiotensin-(1–7) effects on the cardiovascular system in an experimental model of Type-1 diabetes

Although exogenous administration of Angiotensin-(1–7) [Ang-(1–7)] can prevent development of diabetes induced end-organ damage, little is known about the role of endogenous Ang-(1–7) in diabetes and requires further characterization. Here, we studied the effects of chronically inhibiting endogenous Ang-(1–7) formation with DX600, a selective angiotensin converting enzyme-2 (ACE2) inhibitor, on renal and cardiac NADPH oxidase (NOX) activity, vascular reactivity and cardiac function in a model of Type-1 diabetes. The contribution of endogenous Ang-(1–7) to the protective effects of Losartan and Captopril and that of prostaglandins to the cardiovascular effects of exogenous Ang-(1–7) were also examined. Cardiac and renal NOX activity, vascular reactivity to endothelin-1 (ET-1) and cardiac recovery from ischemia/reperfusion (I/R) injury were evaluated in streptozotocin-treated rats. Chronic treatment with DX600 exacerbated diabetes-induced increase in cardiac and renal NOX activity. Diabetes-induced abnormal vascular reactivity to ET-1 and cardiac dysfunction were improved by treatment with Ang-(1–7) and worsened by treatment with DX600 or A779, a Mas receptor antagonist. Ang-(1–7)-mediated improvement in cardiac recovery or vascular reactivity was attenuated by Indomethacin. Captopril and Losartan-induced improvement in cardiovascular function was attenuated when these drugs were co-administered with A779. Ang-(1–7)-mediated decrease in renal NOX activity was prevented by indomethacin. Losartan also decreased renal NOX activity that could be attenuated with A779 co-treatment. In conclusion, endogenous Ang-(1–7) inhibits diabetes-induced cardiac/renal NOX activity and end-organ damage, and mediates the actions of Captopril and Losartan. Further, prostaglandins are important intermediaries in the beneficial effects of Ang-(1–7) in diabetes. Combining either Losartan or Captopril with Ang-(1–7) had additional beneficial effects in preventing diabetes-induced cardiac dysfunction and this may represent a novel therapeutic strategy. Collectively, these data shed new insights into the likely mechanism of action through which the ACE2/Ang-(1–7)/Mas receptor axis prevents Type 1 diabetes-induced cardiovascular dysfunction.

Increased susceptibility to hypertensive renal disease in streptozotocin-treated diabetic rats is not modulated by salt intake

In early type 1 diabetes mellitus, renal salt handling is dysregulated, so that the glomerular filtration rate becomes inversely proportional to salt intake. The salt paradox occurs in both humans and rats and, with low salt intake, results in diabetic hyperfiltration. We tested whether increased salt intake could reduce the susceptibility to injury of non-clipped kidneys in diabetic rats with pre-existing Goldblatt hypertension. Male Long-Evans rats were made hypertensive and half were then made diabetic. Blood glucose was maintained at ~20-25 mmol/l by insulin implants. One half of each received only the salt in normal chow (1% by weight) and the other half received added salt in drinking water to equal 2.7% by weight of food intake. Weekly 24 h blood pressure records were acquired by telemetry during the 4-month experiment. Systolic blood pressure was not affected by diabetes or increased salt intake, alone or together. Autoregulation was highly efficient in the non-clipped kidney of both intact and diabetic rats. Histological examination showed minor injury in the clipped kidney, which did not differ among groups. The non-clipped kidney showed extensive pressure-dependent glomerular and vascular injury in both intact and diabetic rats. The relationship between pressure and injury was shifted toward lower blood pressure in diabetic rats, indicating that diabetes increased the susceptibility of the kidney to injury despite preservation of autoregulation. The increased susceptibility was not affected by high salt intake in the diabetic rats, thus disproving the hypothesis.

Non-insulin dependent anti-diabetic activity of (2S, 3R, 4S) 4-hydroxyisoleucine of fenugreek (Trigonella foenum graecum) in streptozotocin-induced type I diabetic rats

The seeds of fenugreek, Trigonella foenum graecum, commonly used as a spice in Middle Eastern countries and widely used in south Asia and Europe, are known to have anti-diabetic properties. They contain an unusual amino acid (2S, 3R, 4S) 4-hydroxyisoleucine (4HO-Ile), so far found only in fenugreek, which has anti-diabetic properties of enhancing insulin secretion under hyperglycaemic conditions, and increasing insulin sensitivity. Here we describe for the first time the anti-diabetic activity of 4HO-Ile in a model of type I diabetes, streptozotocin-treated rats, where levels of insulin are much reduced, by 65%, compared to normal animals. Treatment of diabetic rats with daily doses of 4HO-Ile at 50mg/kg/day for four weeks could reduce plasma glucose in the diabetic group. Moreover the high levels of lipids (cholesterol, HDL, LDL and triglycerides) and uric acid in the diabetic rats, could be restored to levels found in non-diabetic controls by the treatment with 4HO-Ile. These results demonstrate that 4HO-Ile has significant anti-diabetic activities that are independent of insulin and suggest the potential of 4HO-Ile as an adjunct to diabetes treatment and for type 1 as well as type 2 diabetes.

Des-Acyl Ghrelin Fragments and Analogues Promote Survival of Pancreatic β-Cells and Human Pancreatic Islets and Prevent Diabetes in Streptozotocin-Treated Rats

Des-acyl ghrelin, although devoid of binding to ghrelin receptor (GRLN), exerts many biological effects, including regulation of glucose and lipid metabolism. Indeed, des-acyl ghrelin promotes pancreatic β-cell and human islet cell survival and prevents diabetes in streptozotocin (STZ) treated rats. We investigated whether des-acyl ghrelin fragments excluding serine(3), which is essential for binding to GRLN, would display similar actions. Among the different compounds tested, des-acyl ghrelin((6-13)) and des-acyl ghrelin((6-13)) with alanine substitutions or cyclization, but not with d-amino acid substitutions, showed the best survival effect, similar to des-acyl ghrelin. Des-acyl ghrelin((6-13)) even prevented diabetes in STZ-treated rats and protected human circulating angiogenic cells from oxidative stress and senescence, similar to des-acyl ghrelin. These results suggest that not only full-length des-acyl ghrelin but also short des-acyl ghrelin fragments have clear beneficial effects on several tissues in vitro and in vivo.

Possible mechanism of the cardio-renal protective effects of AVE-0991, a non-peptide Mas-receptor agonist, in diabetic rats

This study was designed to investigate the cardio-renal protective effect of AVE-0991, a non-peptide Mas-receptor agonist, and A-779, a Mas-receptor antagonist, in diabetic rats. Wistar rats treated with streptozotocin (50 mg/kg, i.p., once), developed diabetes mellitus after 1 week. After 8 weeks, myocardial functions were assessed by measuring left ventricular developed pressure (LVDP), rate of left ventricular pressure development (dp/dt (max)), rate of left ventricular pressure decay (dp/dt (min)) and left ventricular end diastolic pressure (LVEDP) on an isolated Langendorff's heart preparation. Further, mean arterial blood pressure (MABP) was measured by using the tail-cuff method. Assessment of renal functions and lipid profile was carried out using a spectrophotometer. The administration of streptozotocin to rats produced persistent hyperglycaemia, dyslipidaemia and hypertension which consequently produced cardiac and renal dysfunction in 8 weeks. AVE0991 treatment produced cardio-renal protective effects, as evidenced by a significant increase in LVDP, dp/dt (max), dp/dt (min) and a significant decrease in LVEDP, BUN, and protein urea. Further, AVE-0991 treatment for the first time has been shown to reduce dyslipidaemia and produced antihyperglycaemic activity in streptozotocin-treated rats. However, MABP and creatinine clearance remained unaffected with AVE-0991 treatment. AVE-0991 produced cardio-renal protection possibly by improving glucose and lipid metabolism in diabetic rats, independent of its blood pressure lowering action.

Control of Glycogen Content in Retina: Allosteric Regulation of Glycogen Synthase

Retinal tissue is exceptional because it shows a high level of energy metabolism. Glycogen content represents the only energy reserve in retina, but its levels are limited. Therefore, elucidation of the mechanisms controlling glycogen content in retina will allow us to understand retina response under local energy demands that can occur under normal and pathological conditions. Thus, we studied retina glycogen levels under different experimental conditions and correlated them with glucose-6-phosphate (G-6-P) content and glycogen synthase (GS) activity.Glycogen and G-6-P content were studied in ex vivo retinas from normal, fasted, streptozotocin-treated, and insulin-induced hypoglycemic rats. Expression levels of GS and its phosphorylated form were also analyzed. Ex vivo retina from normal rats showed low G-6-P (14±2 pmol/mg protein) and glycogen levels (43±3 nmol glycosyl residues/mg protein), which were increased 6 and 3 times, respectively, in streptozotocin diabetic rats. While no changes in phosphorylated GS levels were observed in any condition tested, a positive correlation was found between G-6-P levels with GS activity and glycogen content. The results indicated that in vivo, retina glycogen may act as an immediately accessible energy reserve and that its content was controlled primarily by G-6-P allosteric activation of GS. Therefore, under hypoglycemic situations retina energy supply is strongly compromised and could lead to the alterations observed in type 1 diabetes.

Impaired synthesis contributes to diabetes-induced decrease in liver glutathione

Diabetes-induced glutathione (GSH) decrease is usually ascribed to GSH oxidation. Here we investigate, in streptozotocin-treated rats, if impairment of GSH synthesis contributes to GSH decrease in diabetic liver, and if antioxidant treatments can provide protection. Diabetic rats were divided into 3 groups: untreated diabetic rats (UD); N-acetyl-cysteine (NAC)-treated diabetic rats; taurine (TAU)-treated diabetic rats; a group of non-streptozotocin-treated rats was used as control (CTR). All rats were sacrificed at 40 weeks of age. Diabetes induced hepatic glutathione decrease, but oxidized glutathione (GSSG) did not increase significantly. Accumulations of cysteine and cysteinyl-glycine in UD suggest respectively decreased glutathione synthesis and increased loss through the plasma membrane with subsequent degradation. Decreased expression of γ-glutamyl-cysteine synthetase in UD is consistent with repressed GSH synthesis. Moreover, diabetes caused increase of GSSG/GSH ratio and induction of heme oxygenase-1, both signs of oxidative stress. Supplementation with NAC or TAU resulted in amelioration of glutathione levels, probably depending on antioxidant activity, more efficient glutathione synthesis and decreased GSH loss and degradation. In conclusion, impaired synthesis and increased loss and degradation of GSH appear to contribute to a decrease in GSH levels in diabetic liver. NAC and TAU are able to partially protect from oxidative stress and GSH decrease, while enhancing GSH synthesis and restricting GSH loss.

Diabetes-induced myelin abnormalities are associated with an altered lipid pattern: protective effects of LXR activation

Diabetic peripheral neuropathy (DPN) is characterized by myelin abnormalities; however, the molecular mechanisms underlying such deficits remain obscure. To uncover the effects of diabetes on myelin alterations, we have analyzed myelin composition. In a streptozotocin-treated rat model of diabetic neuropathy, analysis of sciatic nerve myelin lipids revealed that diabetes alters myelin's phospholipid, FA, and cholesterol content in a pattern that can modify membrane fluidity. Reduced expression of relevant genes in the FA biosynthetic pathway and decreased levels of the transcriptionally active form of the lipogenic factor sterol-regulatory element binding factor-1c (SREBF-1c) were found in diabetic sciatic nerve. Expression of myelin's major protein, myelin protein zero (P0), was also suppressed by diabetes. In addition, we confirmed that diabetes induces sciatic nerve myelin abnormalities, primarily infoldings that have previously been associated with altered membrane fluidity. In a diabetic setting, synthetic activator of the nuclear receptor liver X receptor (LXR) increased SREBF-1c function and restored myelin lipid species and P0 expression levels to normal. These LXR-modulated improvements were associated with restored myelin structure in sciatic nerve and enhanced performance in functional tests such as thermal nociceptive threshold and nerve conduction velocity. These findings demonstrate an important role for the LXR-SREBF-1c axis in protection from diabetes-induced myelin abnormalities.

Changes in hippocampal synapses and learning-memory abilities in a streptozotocin-treated rat model and intervention by using fasudil hydrochloride

Fasudil hydrochloride (FH), a Rho kinase inhibitor, is used to treat neurological diseases. This study aims to elucidate the anti-dementia role of FH in Alzheimer's disease. Twenty-four Sprague-Dawley rats were randomly divided into four groups: (1) sham-operated group (control), (2) sham-operated followed by FH administration group (sham+FH), (3) streptozotocin (STZ)-treated group (STZ), and (4) STZ treatment followed by FH administration group (STZ+FH). Rats in the STZ and STZ+FH groups received two divided doses of STZ (1.5 mg/kg) intracerebroventricularly on days 1 and 3, whereas control and sham+FH group rats were given citric acid/sodium citrate buffer. Rats in the sham+FH and STZ+FH groups were then treated intraperitoneally with FH (10 mg/kg) for 4 weeks, and rats in the STZ and control groups were treated with saline. Learning and memory were measured using the Morris water maze test. The synaptic ultrastructure in the CA1 region of the hippocampus was observed using electronic microscopy. The expression of synaptophysin (SYP) was measured using real-time polymerase chain reaction and western blot analyses; the expression of p-LIMK2 and p-cofilin were also detected using western blot analysis. The results indicate that STZ induced deficit in learning/memory, decrease in SYP expression, degeneration in synaptic structures, and increase in the expressions of p-LIMK2 and p-cofilin. These changes were reversed by the administration of FH, suggesting that FH has anti-dementia properties that protect synaptic structure and function. FH induced dephosphorylation (inactivation) of LIMK2 and subsequent dephosphorylation (activation) of cofilin, which may be responsible for the amelioration of neuronal synaptic structure and function.

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.

Streptozotocin糖尿病ラットの糖尿病性神経障害の発症・進展に及ぼす高果糖食の影響とAldose Reductase阻害剤の効果

Streptozotocin糖尿病ラットの糖尿病性神経障害の発症・進展に及ぼす高果糖食の影響とAldose Reductase阻害剤の効果

Neuroprotective Effect of Cyclooxygenase Inhibitors in ICV-STZ Induced Sporadic Alzheimer’s Disease in Rats

Sporadic Alzheimer's disease is an age-related neurological and psychiatric disorder characterized by impaired energy metabolism. Oxidative stress and neuroinflammation have been implicated in pathophysiology of sporadic type of dementia. The central streptozotocin administration induces behavioral and biochemical alterations resembling those in sporadic type of Alzheimer's patients. The present study was designed to investigate the effects of chronic pretreatment with cyclooxygenase-1 or cyclooxygenase-2 or cyclooxygenase-3 selective inhibitors on cognitive dysfunction and oxidative stress markers in intracerebroventricular streptozotocin-treated rats. Chronic treatment with valeryl salicylate (5 and 10 mg/kg, i.p.) and etoricoxib (5 and 10 mg/kg, i.p.) on a daily basis for a period of 21 days, beginning 1 h prior to first intracerebroventricular streptozotocin injection, significantly improved streptozotocin-induced cognitive impairment. However, phenacetin (20 and 40 mg/kg, i.p.) failed to restore the cognitive performances of streptozotocin-treated rats. Besides, improving cognitive dysfunction, chronic administration of highly selective cyclooxygenase-1 and/or cyclooxygenase-2 inhibitors (valeryl salicylate and etoricoxib, respectively), but not cyclooxygenase-3 inhibitor (phenacetin), significantly reduced elevated malondialdehyde, nitrite levels, and restored reduced glutathione and superoxide dismutase levels. Furthermore, cyclooxygenase-1 and/or cyclooxygenase-2 inhibitors significantly increased the survival of pyramidal neurons. In summary, we demonstrate for the first time that both cyclooxygenase-1 and cyclooxygenase-2 isoforms, but not cyclooxygenase-3, are involved in the progression of neuronal damage in intracerebroventricular streptozotocin-treated rats.

18F-Fallypride PET of Pancreatic Islets: In Vitro and In Vivo Rodent Studies

Islet cell loss in the pancreas results in diabetes. A noninvasive method that measures islet cell loss and also tracks the fate of transplanted islets would facilitate the development of novel therapeutics and improve the management of diabetes. We describe a novel dopamine D(2)/D(3) receptor (D(2)/D(3)R)-based PET method to study islet cells in the rat pancreas and in islet cell transplantation. (18)F-fallypride binding to isolated rat islets and pancreas was evaluated in the absence and presence of the D(2)/D(3)R inhibitor haloperidol. After intravenous (18)F-fallypride (28-37 MBq) administration, normal rats and rats pretreated with haloperidol were imaged in a PET/CT scanner and subsequently studied ex vivo for (18)F-fallypride localization in the pancreas. A streptozotocin-treated diabetic rat model was used to study localization of (18)F-fallypride in the pancreas, in vitro and ex vivo. Rat islet cells were transplanted into the spleen and visualized using (18)F-fallypride PET. (18)F-fallypride bound to isolated islet cells and pancreatic sections with an endocrine or exocrine selectivity of approximately 4; selectivity was reduced by haloperidol, suggesting that binding was D(2)/D(3)R-specific. Chemical destruction of islets by streptozotocin decreased (18)F-fallypride binding in pancreas by greater than 50%, paralleling the decrease in insulin immunostaining. Uptake of (18)F-fallypride in the pancreas was confirmed by radiochromatography and was 0.05% injected dose/cm(3) as measured by PET/CT. The ratio of (18)F-fallypride uptake in the pancreas to reference tissue (erector spinae muscle) was 5.5. Rat islets transplanted into the spleen were visualized in vivo by (18)F-fallypride and confirmed by immunostaining. The ratio of spleen-transplanted islets to erector spinae muscle was greater than 5, compared with a ratio of 2.8 in untransplanted rats. These studies demonstrate the potential utility of (18)F-fallypride as a PET agent for islet cells.

Increased expression of the multidrug resistance-associated protein 1 (MRP1) in kidney glomeruli of streptozotocin-induced diabetic rats

Oxidative stress has been linked to the podocytopathy, mesangial expansion and progression of diabetic nephropathy. The major cell defence mechanism against oxidative stress is reduced glutathione (GSH). Some ABC transporters have been shown to extrude GSH, oxidised glutathione or their conjugates out of the cell, thus implying a role for these transporters in GSH homeostasis. We found a remarkable expression of mRNA for multidrug resistance-associated proteins (MRP/ABCC) 1, 3, 4 and 5 in rat glomeruli. Three weeks after induction of diabetes in glomeruli of streptozotocin-treated rats, we observed a decline in reduced GSH levels and an increase in the expression and activity of MRP1 (ABCC1). These lower GSH levels were improved by ex vivo treatment with pharmacological inhibitors of MRP1 activity (MK571). We conclude that increased activity of MRP1 in diabetic glomeruli is correlated with an inadequate adaptive response to oxidative stress.

Mitochondrial GSH status in compensatory renal hypertrophy due to uninephrectomy and diabetic nephropathy

Renal proximal tubular (PT) cells exhibit compensatory cellular hypertrophy after either uninephrectomy (NPX rats) or in diabetic nephropathy (streptozotocin-treated rat). In both models, PT cells exhibit increased rates of mitochondrial respiration and activities of several enzymes (‘hypermetabolic state’), which are associated with enhanced oxidative stress and susceptibility to many toxicants. GSH concentrations are elevated in both cytoplasm and mitochondria. Transport of GSH into mitochondria by both the dicarboxylate (DIC) and 2-oxoglutarate (OGC) carriers was markedly increased, although no differences were observed in mRNA expression. In NPX rats, no differences were observed in renal protein expression of either carrier. In contrast, protein levels of the DIC, but not the OGC, were substantially increased in renal mitochondria from diabetic rats. Hence, although levels of GSH in kidneys are elevated in renal mitochondria from both NPX and diabetic rats, mechanisms underlying the increases differ. In NPX rats, the increases are due to the hypermetabolic state whereas in diabetes, there is also an increase in DIC protein levels due to increased protein stability.

Diabetic rats show reduced cardiac–somatic reflex evoked by intrapericardial capsaicin

Painless myocardial infarction is a serious complication of diabetes. The present study examined whether cardiac nociception was altered in the streptozotocin-induced diabetic rat model by assessing intrapericardial capsaicin-evoked electromyography (EMG) responses in the spinotrapezius muscle. Somatic sensitivities to mechanical and thermal stimulation of the skin were also determined. Intrapericardial administration of capsaicin evoked a concentration-dependent EMG response, which was reproducible with repeated administration. However, the capsaicin-induced EMG responses were different in streptozotocin-induced diabetic rats and controls. Intrapericardial capsaicin produced fewer EMG responses, which were delayed and reduced in streptozotocin-treated rats compared to controls. Pretreatment with capsazepine, a TRPV1 antagonist, significantly decreased capsaicin-evoked EMG activity in both streptozotocin-treated and control rats. In addition, streptozotocin-treated rats showed a decreased paw withdrawal threshold in response to mechanical stimulation but no change in response to radiant heat stimulation. These results suggest that streptozotocin-induced diabetic rats develop somatic mechanical hypersensitivity (allodynia), but reduced cardiac nociception. Decreased TRPV1 function may contribute to the reduction of cardiac nociception in the diabetic rat.

Protective effect of N-acetylcysteine supplementation on mitochondrial oxidative stress and mitochondrial enzymes in cerebral cortex of streptozotocin-treated diabetic rats

Diabetic encephalopathy, characterized by cognitive deficits involves hyperglycemia-induced oxidative stress. Impaired mitochondrial functions might play an important role in accelerated oxidative damage observed in diabetic brain. The aim of the present study was to examine the role of mitochondrial oxidative stress and dysfunctions in the development of diabetic encephalopathy along with the neuroprotective potential of N-acetylcysteine (NAC). Chronic hyperglycemia accentuated mitochondrial oxidative stress in terms of increased ROS production and lipid peroxidation. Significant decrease in Mn-SOD activity along with protein and non-protein thiols was observed in the mitochondria from diabetic brain. The activities of mitochondrial enzymes; NADH dehydrogenase, succinate dehydrogenase and cytochrome oxidase were decreased in the diabetic brain. Increased mitochondrial oxidative stress and dysfunctions were associated with increased cytochrome c and active caspase-3 levels in cytosol. Electron microscopy revealed mitochondrial swelling and chromatin condensation in neurons of diabetic animals. NAC administration, on the other hand was found to significantly improve diabetes-induced biochemical and morphological changes, bringing them closer to the controls. The results from the study provide evidence for the role of mitochondrial oxidative stress and dysfunctions in the development of diabetic encephalopathy and point towards the clinical potential of NAC as an adjuvant therapy to conventional anti-hyperglycemic regimens for the prevention and/or delaying the progression of CNS complications.