Abnormalities In Diabetic Rats Research Articles

Low-dose dipyridamole treatment partially prevents diabetes mellitus-induced vascular endothelial and renal abnormalities in rats

Dipyridamole is a conventionally used platelet inhibitor employed for the secondary prevention of transient ischemic attack. Dipyridamole could potentiate some of the vascular protective effects of nitric oxide (NO) [1]. Intriguingly, the vascular protective action of dipyridamole was reported to be mediated by its stimulatory action on endothelial nitric oxide synthase (eNOS) activity [2]. However, the effect of dipyridamole in diabetes mellitus-induced vascular endothelial dysfunction (VED) is not yet known. There are strong associations between diabetic VED and nephropathy [3,4]. Administration of dipyridamole either alone or in combination with aspirin reduced the incidence of proteinuria in patients with diabetic nephropathy [5]. Dipyridamole at high-dose is considered proischemic, and it could cause a marked coronary steal effect. Dipyridamole, however, at lowdose orallymight have aminimal hemodynamic effect [6]. The present study investigated the effect of low-dose dipyridamole in diabetes mellitus-induced VED and nephropathy in rats. The experimental protocol of this study was approved by the ‘Institutional Animal Ethics Committee’. Wistar albino rats of either sex (n = 6) weighing about 250 to 350 g were used. Group I (Normal Control), rats were maintained on standard food and water, and no treatment was given. Group II (Diabetic Control), rats were administered streptozotocin (STZ) (50 mg/kg, i.p., once), andwere allowed for 8 weeks to develop experimental VED and nephropathy (rats showing blood glucose level of greater than 200 mg/dl after 72 h of STZ administration were selected and named as diabetics). Group III (Dipyridamole per se), normal rats were administered low-dose dipyridamole (30 mg/kg/day, p.o.) for 4 weeks. Group IV (Dipyrida), the diabetic rats after 4 weeks of STZ-administration were treated with low-dose dipyridamole (30 mg/kg/day, p.o.) for 4 weeks. Groups V and VI (Wortmannin or L-NAME Incubated Aortic Ring of Dipyridamole Treated), the diabetic rats were treated with low-dose dipyridamole (30 mg/kg/day, p.o., 4 weeks) as mentioned in group IV. The in vitro effects of wortmannin (100 nM) or L-NAME (100 μM) (the aortic ring was incubated with either wortmannin or L-NAME for 30-min) on endothelium-dependent and -independent relaxation in the phenylephrine (3 × 10−6 M)-precontracted isolated aortic ring preparation were evaluated. One way ANOVA, followed by Tukey's multiple comparison test was employed to analyse the data. STZ-induced diabetic rats developed VED and nephropathy in 8 weeks. Diabetes mellitus-induced VED was associated with marked reduction in acetylcholine-induced endothelium-dependent relaxation, decrease in aortic and serum nitrite/nitrate concentration, and induction of oxidative stress and lipid alteration. Scanning electron microscopic and histological studies on thoracic aorta revealed a marked impairment in vascular endothelial integrity. Moreover, elevation of serum creatinine and blood urea nitrogen, and induction of proteinuria accompanying with renal oxidative stress were noted in diabetic rats. However, treatment with low-dose dipyridamole partially, but substantially prevented aforementioned vascular endothelial and renal abnormalities in diabetic rats without affecting the elevated glucose concentration. Interestingly, incubation of aortic rings, isolated from dipyridamole-treated diabetic rats, with either wortmannin (inhibitor of phosphatidylinositide 3-kinase, PI3-K) or LNAME (inhibitor of nitric oxide synthase, NOS) markedly abolished dipyridamole-associated improvement in acetylcholine-induced endothelium-dependent relaxation (Table 1, Figs. 1 and 2). To summarize, dipyridamole in low-dose partially, but significantly prevents diabetes mellitus-induced VED by activating endothelial PI3K-eNOS-NO signalling pathways. The renovascular reduction of oxidative stress might explain the mechanism pertaining to the partial renoprotective action of low-dose dipyridamole in diabetes mellitus. We express our gratitude to the management of RITS, Sirsa, Haryana, India for the support. The authors of this manuscript have certified that

Catechin Averts Experimental Diabetes Mellitus-Induced Vascular Endothelial Structural and Functional Abnormalities

Diabetes mellitus is associated with an induction of vascular endothelial dysfunction (VED), an initial event that could lead to the pathogenesis of atherosclerosis and hypertension. Previous studies showed that catechin, a key component of green tea, possesses vascular beneficial effects. We investigated the effect of catechin hydrate in diabetes mellitus-induced experimental vascular endothelial abnormalities (VEA). Streptozotocin (50mg/kg, i.p., once) administration to rats produced diabetes mellitus, which subsequently induced VEA in 8weeks by markedly attenuating acetylcholine-induced endothelium-dependent relaxation in the isolated aortic ring preparation, decreasing aortic and serum nitrite/nitrate concentrations and impairing aortic endothelial integrity. These abnormalities in diabetic rats were accompanied with elevated aortic superoxide anion generation and serum lipid peroxidation in addition to hyperglycemia. Catechin hydrate treatment (50mg/kg/day p.o., 3weeks) markedly prevented diabetes mellitus-induced VEA and vascular oxidative stress. Intriguingly, in vitro incubation of L-NAME (100μM), an inhibitor of nitric oxide synthase, or Wortmannin (100nM), a selective inhibitor of phosphatidylinositol 3-kinase (PI3K), markedly prevented catechin hydrate-induced improvement in acetylcholine-provoked endothelium-dependent relaxation in the diabetic rat aorta. Moreover, catechin hydrate treatment considerably reduced the elevated level of serum glucose in diabetic rats. In conclusion, catechin hydrate treatment prevents diabetes mellitus-induced VED through the activation of endothelial PI3K signal and subsequent activation of eNOS and generation of nitric oxide. In addition, reduction in high glucose, vascular oxidative stress, and lipid peroxidation might additionally contribute to catechin hydrate-associated prevention of diabetic VEA.

Effects of Crataegus microphylla on Vascular Dysfunction in Streptozotocin‐induced Diabetic Rats

Vascular dysfunction plays a key role in the pathogenesis of diabetic vascular disease. In this study, we aimed to investigate whether chronic in vivo treatment of Crataegus microphylla (CM) extract in diabetic rats induced with streptozotocin (STZ, intraperitoneal, 65 mg/kg) preserves vascular function and to evaluate whether the reduction of inducible nitric oxide synthase (iNOS), proinflammatory cytokines, and lipid peroxidation mediates its mechanisms of action. Starting at 4 weeks of diabetes, CM extract (100 mg/kg) was administrated to diabetic rats for 4 weeks. In aortic rings, relaxation to acetylcholine and vasoreactivity to noradrenaline were impaired, whereas aortic iNOS expression and plasma tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6), total nitrite-nitrate, and malondialdehite levels were increased in diabetic rats compared with controls. Chronic CM treatment significantly corrected all the above abnormalities in diabetic rats. In comparison, pretreatment of the aorta of diabetic rats with N-[3(aminomethyl) benzyl]-acetamidine, dihydrochloride (10(-5) M), a selective inhibitor of iNOS, produced a similar recovery in vascular reactivity. These results suggest that chronic in vivo treatment of CM preserves endothelium-dependent relaxation and vascular contraction in STZ-induced diabetes, possibly by reducing iNOS expression in the aorta and by decreasing plasma levels of TNF-α and IL-6 and by preventing lipid peroxidation.

The Important Roles of Interstitial Cells of Cajal and Cholinergic Receptors on Diabetes Related Dysfunction of Colon

Diabetes mellitus (DM) is a chronic disease that develops at the time of inappropriate insulin production and utilization. Lifelong medical attention is required for inhibiting the development of potentially devastating late complications of DM. Diabetic patients are generally affected with gastrointestinal (GI) disorders.1,2 The common symptoms are dysphagia, satiety, reflux, constipation, abdominal pain, nausea, vomiting and diarrhea.3-5 These symptoms are eventually caused by the neuropathy involving the entire GI tract. In particular, it has been well known that abnormal motility of the GI tract occurs in the development of diabetes.6 So far many studies have demonstrated that DM patients have slow transit and abnormal motility. GI abnormalities such as motor dysfunction, autonomic neuropathy, inadequate glucose control, psychological factors, or morphological changing in the GI tract have been reported.7-9 However, the underlying mechanism is not clearly understood. Interstitial cells of Cajal (ICCs) are known as pacemaking cells, mediators of neurotransmission in GI tract and play a crucial roles in GI motility.10-12 They are network-forming cells connected electrically with each other and with smooth muscle cells via gap junctions.13 Recently, it has been shown that some populations of ICCs express the proto-oncogene c-Kit, and the antibodies to its gene product, the Kit (or c-Kit) receptor which a membrane receptor tyrosine kinase, are now available for use as an immunohistochemical label for ICCs in some species.14 Many regions of the GI tract display spontaneous electrical rhythmicity.15 Auto-rhythmicity in GI muscles is an exclusive property of ICCs and the spread of slow waves through GI muscles occurs electronically, not by active regeneration. Slow waves, pacemaking by ICCs, are organized into electrically coupled networks within discrete areas of the stomach, small bowel and colon. Interestingly, some reports have recently suggested the loss of ICC networks in diabetic patients and animal models.16,17 These showed the involvement of ICCs on DM-related GI motor abnormalities. Kim et al18 examined the nature of colonic dysfunction in a long-term diabetic rat model. They found that the spontaneous contractility of proximal colon and the ICC networks were decreased in the diabetes rats. This result supports the previous findings that the involvement of ICCs has showed in diabetic patients and animal models.16,17 Kim et al18 indicated that the response of carbachol or nitric oxide in proximal colon of the diabetic rats was significantly decreased. It is well known that acetylcholine plays important roles for modulation of GI motility and the existence of receptors for acetylcholine in ICCs and smooth muscle of the GI tract was mentioned in many reports.19-21 Nitric oxide (NO) is also a major nonadrenergic, noncholinergic inhibitory neurotransmitter in GI tract and the release of NO causes relaxation of the smooth muscle.22,23 It has been reported that NO has an effect on the electrical activity of ICCs as well.24 However, Kim et al18 did not show the exact mechanism what kind of cells is involved in the diabetic rats. Nevertheless, they proposes strong evidence regarding the role of ICCs on GI motor abnormalities in diabetic rats. The number of acetylcholine receptor and the production of nitric oxide can affect the DM-related motor symptoms.

Plasma Kallikrein Mediates Retinal Vascular Dysfunction and Induces Retinal Thickening in Diabetic Rats

OBJECTIVEPlasma kallikrein (PK) has been identified in vitreous fluid obtained from individuals with diabetic retinopathy and has been implicated in contributing to retinal vascular dysfunction. In this report, we examined the effects of PK on retinal vascular functions and thickness in diabetic rats.RESEARCH DESIGN AND METHODSWe investigated the effects of a selective PK inhibitor, ASP-440, and C1 inhibitor (C1-INH), the primary physiological inhibitor of PK, on retinal vascular permeability (RVP) and hemodynamics in rats with streptozotocin-induced diabetes. The effect of intravitreal PK injection on retinal thickness was examined by spectral domain optical coherence tomography.RESULTSSystemic continuous administration of ASP-440 for 4 weeks initiated at the time of diabetes onset inhibited RVP by 42% (P = 0.013) and 83% (P < 0.001) at doses of 0.25 and 0.6 mg/kg per day, respectively. Administration of ASP-440 initiated 2 weeks after the onset of diabetes ameliorated both RVP and retinal blood flow abnormalities in diabetic rats measured at 4 weeks’ diabetes duration. Intravitreal injection of C1-INH similarly decreased impaired RVP in rats with 2 weeks’ diabetes duration. Intravitreal injection of PK increased both acute RVP and sustained focal RVP (24 h postinjection) to a greater extent in diabetic rats compared with nondiabetic control rats. Intravitreal injection of PK increased retinal thickness compared with baseline to a greater extent (P = 0.017) in diabetic rats (from 193 ± 10 μm to 223 ± 13 μm) compared with nondiabetic rats (from 182 ± 8 μm to 193 ± 9 μm).CONCLUSIONSThese results show that PK contributes to retinal vascular dysfunctions in diabetic rats and that the combination of diabetes and intravitreal injection of PK in rats induces retinal thickening.

Early exercise training attenuates left ventricular dysfunction, myocardial infarction area and molecular abnormalities in diabetic rats

In this study we evaluated the effects of early exercise training (ET) on mortality rate, myocardial infarction (MI) area and VEGF gene levels, as well as on left ventricular (LV) function and calcium handling abnormalities in diabetic rats after MI. Male Wistar rats were divided in sedentary (S) and exercise training (ET) groups: control (C), MI+S (SI), MI+ET (TI), diabetes+MI+S (SDI) and diabetes+MI+ET (TDI). After 20 weeks of ET, MI size although similar at the beginning (~40±3%), was reduced at the end of the protocol in trained groups. MI size reduction was associated with increased mRNA VEGF levels in trained animals. Trained rats displayed higher cardiac output and ejection fraction (TI: 59±4 and TDI: 58±4% vs SI: 40±1 and SDI: 54±1%) when compared to sedentary ones. This improvement on LV function in trained animals was associated with increased expressions of SERCA2 (25%) and phospholamban phosphorilated at serine 16 (34%). In addition, survival rate was improved after ET period (TI: 87 vs SI: 41% and TDI: 75 vs SDI: 30%). These results showed that early ET intervention induced MI area reduction, LV function and survival improvement in trained animals. Moreover, the improvement of mRNA VEGF levels and Ca2+ handling proteins gives support to consider ET as a coadjuvant therapy able to induce additional changes at myocardium molecular levels in diabetic subjects after an ischemic event.CNPq

Scientific Opinion on the substantiation of health claims related to gamma linolenic acid and maintenance of joints (ID 494, 637, 1774, 2098), weight maintenance following weight loss (ID 496), maintenance of peripheral blood flow (ID 638), maintenance of normal blood pressure (ID 1771), maintenance of normal blood cholesterol concentrations (ID 1771) and maintenance of bone (ID 1774) pursuant to Article

Scientific Opinion on the substantiation of health claims related to gamma linolenic acid and maintenance of joints (ID 494, 637, 1774, 2098), weight maintenance following weight loss (ID 496), maintenance of peripheral blood flow (ID 638), maintenance of normal blood pressure (ID 1771), maintenance of normal blood cholesterol concentrations (ID 1771) and maintenance of bone (ID 1774) pursuant to Article

El pentosán polisulfato de sodio previene las alteraciones morfológicas renales y la albuminuria en ratas con diabetes tipo 1

Decreased levels of glycosaminoglycans (GAGs) have been observed in the kidney and other organs, in human and animal models of diabetes. Long-term administration of heparins and other glycosaminoglycans has demonstrated a beneficial effect on morphological and functional kidney abnormalities in diabetic rats. We assessed the effect of pentosan polysulfate sodium (PPS), a semi-synthetic glycosaminoglycan with low anticoagulant activity, on kidney involvement in streptozotocin diabetic rats. Diabetes was induced in male Sprague-Dawley rats by i.v. administration of streptozotocin (STZ). Animals were randomly allocated to three groups: C = control, STZ and STZ + PPS = pretreated with PPS (15 mg/kg, s.c.). After three months of follow-up, blood and 24 h-urine samples were obtained, the animals were sacrificed and the kidney microdissected for morphometric analysis. Urinary albumin excretion was markedly increased in untreated diabetic rats (C = 0.26 ± 0.03 vs STZ = 7.75 ± 1.8 mg/24 h) and PPS treatment partially prevented the albumin rise (3.7 ± 0.7 mg/24 h), without affecting the metabolic control HbA1c (C = 3.6 ± 1.7; STZ = 8.82 ± 0.47; STZ + PPS = 8.63 ± 0.54). Electron microscope observation revealed typical renal lesions described in experimental diabetes (STZ group). PPS administration prevents the tubular basement membrane thickening and the loss of cytoarchitecture induced by experimental diabetes. Our data demonstrate that long-term administration of PPS has a favourable effect on morphological and functional abnormalities in kidneys of diabetic rats and suggests a potential therapeutic use for this compound.

Beneficial Effect of Docosahexanoic Acid and Lutein on Retinal Structural, Metabolic, and Functional Abnormalities in Diabetic Rats

Purpose: To assess the effect of docosahexanoic acid (DHA) and lutein (both compounds with anti-inflammatory and antioxidant properties) on experimental diabetic retinopathy.Methods: Male Wistar rats were studied: non-diabetic controls, untreated diabetic controls, and diabetic rats were treated with DHA and lutein or the combination of DHA + insulin and lutein + insulin for 12 weeks. Oxidative stress and inflammatory markers, apoptosis, and functional tests were studied to confirm biochemical and functional changes in the retina of diabetic rats. Malondialdehyde (MDA), glutathione concentrations (GSH), and glutathione peroxidase activity (GPx) were measured as oxidative stress markers. TUNEL assay and caspase-3 immunohistochemistry and electroretinogram were performed.Results: Diabetes increases oxidative stress, nitrotyrosine concentrations, and apoptosis in the retina. At 12 weeks after onset of diabetes, total thickness of retinas of diabetic rats was significantly less than that in control rats. Specifically, the thickness of the outer and inner nuclear layers was reduced significantly in diabetic rats and demonstrated a loss of cells in the GCL. These retinal changes were avoided by the administration of insulin and DHA and lutein alone or in combination with insulin. Impairment of the electroretinogram (b-wave amplitude and latency time) was observed in diabetic rats. DHA and lutein prevented all these changes even under hyperglycemic conditions.Conclusions: Lutein and DHA are capable of normalizing all the diabetes-induced biochemical, histological, and functional modifications. Specifically, the cell death mechanisms involved deserve further studies to allow the proposal as potential adjuvant therapies to help prevent vision loss in diabetic patients.

Inhibition of retinopathy and retinal metabolic abnormalities in diabetic rats with AREDS-based micronutrients.

To investigate whether the micronutrients that were shown to reduce the risk of development of age-related macular degeneration in the Age-Related Eye Disease Study (AREDS) can have the same effect on the development of diabetic retinopathy in rats, and to understand the possible mechanisms. Streptozotocin-induced diabetic rats received a powdered diet with or without supplemental micronutrients (ascorbic acid, vitamin E, beta-carotene, zinc, and copper). The retina was used after the rats had diabetes for 12 months to detect vascular histopathology and to measure the biochemical parameters and messenger RNA levels of the genes involved in oxidative and nitrative stress. The AREDS-based micronutrients prevented a diabetes-induced increase in the number of retinal acellular capillaries. In the same rats, micronutrients inhibited increases in retinal oxidatively modified DNA and nitrotyrosine and decreases in manganese superoxide dismutase. Diabetes-induced alterations in the messenger RNA expression of mitochondrial electron transport complex III (coenzyme Q cytochrome-c reductase) and inducible nitric oxide synthase were also prevented. Age-Related Eye Disease Study-based micronutrients inhibit the development of diabetic retinopathy in rodents by inhibiting oxidative and nitrative stress. Micronutrients that slow down the onset and progression of age-related macular degeneration have the potential to inhibit the development of diabetic retinopathy.

Beneficial Effect of Zeaxanthin on Retinal Metabolic Abnormalities in Diabetic Rats

Oxidative damage and growth factors are implicated in the pathogenesis of retinopathy in diabetes. Recent studies have shown that two dietary carotenoids, lutein and zeaxanthin (Zx), that are specifically concentrated within ocular tissues, may play important roles in maintaining their integrity. This study is to evaluate the potential protective effects of Zx against retinal oxidative damage and growth factors in diabetes. A group of rats received normal powdered diet or powdered diet supplemented with 0.02% or 0.1% Zx soon after induction of diabetes. Age-matched normal rats served as control subjects. At 2 months of diabetes, oxidative stress, vascular endothelial cell growth factor (VEGF), and intercellular adhesion molecule (ICAM)-1 were quantified in the retina. Zx supplementation prevented diabetes-induced increase in retinal damage, and increases in VEGF and ICAM-1. The levels of lipid peroxide, oxidatively modified DNA, electron transport complex III, nitrotyrosine, and mitochondrial superoxide dismutase were similar in the retinas of Zx-treated diabetic rats and normal control rats, and these values were significantly different from those obtained from diabetic rats without any supplementation. In the same rats, Zx also prevented diabetes-induced increases in retinal VEGF and ICAM-1. Both 0.02% and 0.1% Zx had similar effects on diabetes-induced retinal abnormalities, and these effects were achieved without ameliorating the severity of hyperglycemia. However, Zx administration failed to prevent a diabetes-induced decrease in retinal GSH levels. Zx significantly inhibits diabetes-induced retinal oxidative damage and elevation in VEGF and adhesion molecule, all abnormalities that are associated with the pathogenesis of diabetic retinopathy. The results suggest that Zx supplementation has the potential to inhibit the development of retinopathy in diabetic patients.

Transition metals and polyol pathway in the development of diabetic neuropathy in rats

The transition metal-catalyzed reaction is a major source of oxygen free radicals, which play an important role in vascular dysfunction leading to ischemia in diabetic tissues. The inhibition of polyol pathway hyperactivity has been reported to ameliorate neurovascular abnormalities in diabetic rats and has been proposed to improve the oxygen free radical scavenging capacity. The present study was conducted to compare the effect of a transition metal chelating agent, trientine (TRI), on diabetic neuropathy with that of an aldose reductase inhibitor, NZ-314 (NZ). Diabetic rats were divided into three groups: (1). untreated, (2). TRI-treated, and (3). NZ-treated. TRI (20 mg/kg) or NZ (100 mg/kg) was administered by gavage or chow containing NZ, respectively, for 8 weeks. Motor nerve conduction velocity (MNCV), coefficient of variation of the R - R interval on electrocardiogram (CVr-r), sciatic nerve blood flow (SNBF), platelet aggregation activities, and serum concentrations of malondialdehyde were measured. Untreated diabetic rats showed delayed MNCV, decreased CV(R-R), and reduced SNBF compared to normal rats. TRI or NZ completely prevented these deficits. Platelet hyperaggregation activities in diabetic rats were prevented by NZ, but not by TRI. Increased concentrations of malondialdehyde in diabetic rats were partially but significantly ameliorated by either TRI or NZ. These observations suggest that increased free radical formation through the transition metal-catalyzed reaction plays an important role in the development of diabetic neuropathy and that the preventive effect of an aldose reductase inhibitor on diabetic neuropathy may also be mediated by decreasing oxygen free radicals.

Reduced activity of mtTFA decreases the transcription in mitochondria isolated from diabetic rat heart.

To evaluate abnormalities in the mitochondrial transcription factor A (mtTFA) function as a cause of mitochondrial dysfunction in diabetes, we measured the mRNA contents of the proteins consisting of the mitochondrial respiratory chain as well as transcriptional and translational activities in the mitochondria isolated from controls and streptozotocin-induced diabetic rat hearts. Using Northern blot analysis, we found 40% reduced mRNA contents of mitochondrial-encoded cytochrome b and ATP synthase subunit 6 in diabetic rat hearts compared with control rats (P < 0.05). These abnormalities were completely recovered by insulin treatment. Furthermore, the mitochondrial activities of transcription and translation were decreased significantly in mitochondria isolated from diabetic rats by 60% (P < 0.01) and 71% (P < 0.01), respectively, compared with control rats. The insulin treatment also completely normalized these abnormalities in diabetic rats. Consistently, gel retardation assay showed a reduced binding of mtTFA to the D-loop of mitochondrial DNA in diabetic rats, although there was no difference in the mtTFA mRNA and protein content between the two groups. On the basis of these findings, a reduced binding activity of mtTFA to the D-loop region in the hearts of diabetic rats may contribute to the decreased mitochondrial protein synthesis.

Combined antioxidant and COMT inhibitor treatment reverses renal abnormalities in diabetic rats.

The development and progression of diabetic nephropathy is dependent on glucose homeostasis and many other contributing factors. In the present study, we examined the effect of nitecapone, an inhibitor of the dopamine-metabolizing enzyme catechol-O-methyl transferase (COMT) and a potent antioxidant, on functional and cellular determinants of renal function in rats with streptozotocin-induced diabetes. Administration of nitecapone to diabetic rats normalized urinary sodium excretion in a manner consistent with the dopamine-dependent inhibition of proximal tubule Na,K-ATPase activity. Hyperfiltration, focal glomerulosclerosis, and albuminuria were also reversed by nitecapone, but in a manner that is more readily attributed to the antioxidant potential of the agent. A pattern of elevated oxidative stress, measured as CuZn superoxide dismutase gene expression and thiobarbituric acid-reactive substance content, was noted in diabetic rats, and both parameters were normalized by nitecapone treatment. In diabetic rats, activation of glomerular protein kinase C (PKC) was confirmed by isoform-specific translocation and Ser23 phosphorylation of the PKC substrate Na,K-ATPase. PKC-dependent changes in Na,K-ATPase phosphorylation were associated with decreased glomerular Na,K-ATPase activity. Nitecapone-treated diabetic rats were protected from these intracellular modifications. The combined results suggest that the COMT-inhibitory and antioxidant properties of nitecapone provide a protective therapy against the development of diabetic nephropathy.

Effects of inhibition of glycation and oxidative stress on the development of cataract and retinal vessel abnormalities in diabetic rats

To study effects of inhibition of glycation, and oxidative stress on the development of cataract and retinal vessel abnormalities in diabetic rats. Diabetes was induced in male Wistar rats with streptozocin (STZ; 60 mg/kg BW, i.p.). Diabetic as well as strain matched control rats were fed 1) a normal diet, 2) addition of aminoguanidine in the drinking water (0.5 g/l for diabetic rats and 1.0 g/l for control rats) or 3) probucol in the pellets (1% w/w). After 6 months, the number of acellular vessels, endothelial cells and pericytes were counted in trypsin digested retinal vessel preparations, and the total retinal tissue amount of glutathione (GSH) and cysteine was measured with HPLC. Cataract formation occurred after 13 weeks in diabetic animals compared with 17 weeks for those treated with aminoguanidine, and 16 weeks for those treated with probucol (p < 0.001 in both cases). Aminoguanidine inhibited the formation of acellular collapsed capillary strands, 9 (3-14) vs. 18 (12-262) (median, range) per quadrant in untreated diabetic rats (p = 0.004), while probucol did not have any effect. Neither aminoguanidine, nor probucol influenced the endothelial/pericyte ratio. Diabetes caused a reduction in the GSH/cysteine ratio (10.7 +/- 0.6 vs. 15.3 +/- 1. 5) (mean +/- SD; p < 0.001). Probucol partly restored this imbalance (p < 0.05) whereas aminoguanidine did not. The results indicate that cataract formation in diabetes involves both glycation and oxidative stress processes. The reduced formation of acellular collapsed capillary strands by aminoguanidine suggests a potential role for glycation in vascular damage. The positive effect of probucol on cysteine/GSH metabolism imbalance indicates that derangements of one of the retinal defense systems against oxidative stress can be normalized by antioxidants.

Effects of inhibition of glycation and oxidative stress on the development of cataract and retinal vessel abnormalities in diabetic rats

Purpose. To study effects of inhibition of glycation, and oxidative stress on the development of cataract and retinal vessel abnormalities in diabetic rats. Methods. Diabetes was induced in male Wistar rats with streptozocin (STZ; 60 mg/kg BW, i.p.). Diabetic as well as strain matched control rats were fed 1) a normal diet, 2) addition of aminoguanidine in the drinking water (0.5 g/l for diabetic rats and 1.0 g/l for control rats) or 3) probucol in the pellets (1% w/w). After 6 months, the number of acellular vessels, endothelial cells and pericytes were counted in trypsin digested retinal vessel preparations, and the total retinal tissue amount of glutathione (GSH) and cysteine was measured with HPLC. Results. Cataract formation occurred after 13 weeks in diabetic animals compared with 17 weeks for those treated with aminoguanidine, and 16 weeks for those treated with probucol (p < 0.001 in both cases). Aminoguanidine inhibited the formation of acellular collapsed capillary strands, 9 (3–14) vs. 18 (12–262) (median, range) per quadrant in untreated diabetic rats (p = 0.004), while probucol did not have any effect. Neither aminoguanidine, nor probucol influenced the endothelial/pericyte ratio. Diabetes caused a reduction in the GSH/cysteine ratio (10.7 ± 0.6 vs. 15.3 ± 1.5) (mean ± SD; p < 0.001). Probucol partly restored this imbalance (p < 0.05) whereas aminoguanidine did not. Conclusions. The results indicate that cataract formation in diabetes involves both glycation and oxidative stress processes. The reduced formation of acellular collapsed capillary strands by aminoguanidine suggests a potential role for glycation in vascular damage. The positive effect of probucol on cysteine/GSH metabolism imbalance indicates that derangements of one of the retinal defense systems against oxidative stress can be normalized by antioxidants.

Prevention of glomerular dysfunction in diabetic rats by treatment with d-alpha-tocopherol.

Because d-alpha-tocopherol (vitamin E) has been shown to decrease diacylglycerol (DAG) levels and prevent the activation of protein kinase C (PKC), which is associated with retinal and renal dysfunctions in diabetes, the study presented here characterized the effect of d-alpha-tocopherol treatment to prevent glomerular hyperfiltration and increased albuminuria as well as PKC activities in streptozotocin (STZ)-induced diabetic rats. Two weeks after the induction of diabetes, total DAG content and PKC activity in glomeruli were significantly increased in diabetic rats by 106.4 +/- 16.8% and 66.4 +/- 8.4%, respectively, compared with control rats. Intraperitoneal injection of d-alpha-tocopherol (40 mg/kg of body weight) every other day prevented the increases in total DAG content and PKC activity in glomeruli of diabetic rats. Glomerular filtration rate (GFR) and filtration fraction (FF) were significantly elevated to 4.98 +/- 0.34 mL/min and 0.36 +/- 0.05, respectively, in diabetic rats, compared with 2.90 +/- 0.14 mL/min and 0.25 +/- 0.02, respectively, in control rats. These hemodynamic abnormalities in diabetic rats were normalized to 2.98 +/- 0.09 mL/min and 0.24 +/- 0.01, respectively, by d-alpha-tocopherol. Albuminuria in 10-wk diabetic rats was significantly increased to 9.1 +/- 2.2 mg/day compared with 1.2 +/- 0.3 mg/day in control rats, whereas d-alpha-tocopherol treatment improved albumin excretion rate to 2.4 +/- 0.6 mg/day in diabetic rats. To clarify the mechanism of d-alpha-tocopherol's effect on DAG-PKC pathway, the activity and protein levels of DAG kinase alpha and gamma, which metabolize DAG to phosphatidic acid, were examined. Treatment with d-alpha-tocopherol increased DAG kinase activity in the glomeruli of both control and diabetic rats, by 22.6 +/- 3.6% and 28.5 +/- 2.3% respectively, although no differences were observed in the basal DAG kinase activity between control and diabetic rats. Because immunoblotting studies did not exhibit any difference in the protein levels of DAG kinase alpha and gamma, the effect of d-alpha-tocopherol is probably modulating the enzyme kinetics of DAG kinase. These findings suggest that the increases in DAG-PKC pathway play an important role for the development of glomerular hyperfiltration and increased albuminuria in diabetes and that d-alpha-tocopherol treatment could be preventing early changes of diabetic renal dysfunctions by normalizing the increases in DAG and PKC levels in glomerular cells.

Effectiveness of natural oils as sources of γ-linolenic acid to correct peripheral nerve conduction velocity abnormalities in diabetic rats: modulation by thromboxane A 2 inhibition

Reduced nerve conduction velocity (NCV) in experimental diabetes can be prevented by evening primrose oil (EP), which is rich in γ-linolenic acid (GLA). This study examined the efficacy of natural GLA sources, blackcurrant (BC), borage (BO) and fungal (FU) oils, compared with EP, in correcting motor and sensory NCV deficits in streptozotocin-diabetic rats, and any potential contribution of thromboxane (TX) A 2 synthesis using the TX antagonist, ZD1542, alone and jointly with GLA-rich oils. Sciatic motor NCV, 20% reduced by 8 weeks of diabetes, was partially (16%) corrected by 2 weeks ZD1542 treatment. 1% BC, BO, FU and EP dietary supplementation caused 11%, 32%, 41% and 53% NCV ameliorations, respectively. A 2% EP diet, more closely matching the GLA intake from the other oils, caused 67% correction. Joint oil/ZD1542 treatment produced further motor NCV improvements for BC and, particularly, BO. A 13% sensory saphenous NCV deficit in diabetic rats was ameliorated by 31%, 24%, 49%, 81%, 70% and 94% for ZD1542, BC, BO, FU, EP and 2% EP, respectively. Joint ZD1542-oil treatment further improved NCV, particularly for BO. Therefore, efficacy against experimental diabetic neuropathy is not predictable from the GLA content of natural oils, EP consistently outperforming BC, BO and FU. Increased TXA 2 with diabetes made a minor contribution to NCV deficits, but blockade improved the response to BO.

Doxazosin Prevents Proteinuria and Glomerular Loss of Heparan Sulfate in Diabetic Rats

We examined whether blood pressure reduction or good glycemic control equally lower albuminuria by preventing glomerular loss of heparan sulfate and progression of glomerulosclerosis in streptozotocin-induced diabetic rats. We used doxazosin, and alpha 1-adrenergic blocker, to lower systemic blood pressure, and good glycemic control was achieved by insulin treatment. Rats were killed after 20 weeks of treatment. Doxazosin significantly lowered systolic pressure in diabetic rats; however, it had no effect in normal rats. Good glycemic control also lowered systolic pressure. In diabetic rats with good glycemic control, doxazosin had an additive effect on blood pressure. Glomerular heparan sulfate synthesis was significantly lower and urinary albumin excretion higher in diabetic than in normal rats. Both doxazosin treatment and good glycemic control normalized these abnormalities in diabetic rats. Insulin normalized plasma glucose and glycosylated HbA1 concentrations in diabetic rats, as did doxazosin. Significant increases in mesangial area and glomeruloscelerosis were observed in diabetic rats. Only good glycemic control normalized these pathological changes in all diabetic rats. Two-way factorial ANOVA showed an interaction between the effects of doxazosin and insulin on systolic pressure and plasma glucose. The data show that after 20 weeks of doxazosin treatment, albuminuria was reduced by 80%; however, this treatment had no significant effect on mesangial expansion or progression to glomerulosclerosis. Conversely, good glycemic control prevented all three of the preceding sequelae.

An aldose reductase inhibitor, TAT, prevents electroretinographic abnormalities and ADP-induced hyperaggregability in streptozotocin-induced diabetic rats.

Rats with streptozotocin-induced diabetes were oral given TAT, a potent aldose reductase inhibitor, at a dose of 10 mg kg-1 day-1 or 40 mg kg-1 day-1 for 30 days. Prolongation of the peak latency of oscillatory potentials in the b-wave of the electroretinogram (ERG), which is associated with retinal Müller cell dysfunction, was significantly improved by treatment with TAT as compared with untreated diabetic rats [sigma(O1 + O2 + O3) was 106.8 +/- 1.8 ms in normal controls (NC), 118.2 +/- 1.1 ms in diabetic controls (DC) (P < 0.001 vs. NC), 110.8 +/- 1.5 ms with 10 mg kg-1 TAT (P < 0.001 vs. DC) and 111.4 +/- 1.6 ms with 40 mg kg-1 TAT (P < 0.01 vs. DC)]. The improvement in ERG abnormalities in diabetic rats was accompanied by partial reduction of elevated sorbitol levels in the retina and erythrocytes, and by correction of platelet hyperaggregability. The authors' findings suggest that a better understanding of the mechanism by which TAT acts may provide new insights into the pathogenesis of hyperglycaemic retinal dysfunction and contribute to establishing effective therapy for diabetic retinopathy.