Dietary nitrite inhibits early glomerular injury in streptozotocin-induced diabetic nephropathy in rats

Protective effects of long-term nitrate administration against ovariectomy-induced kidney dysfunction in rats

BACKGROUND

Menopause is associated with higher risks of chronic kidney disease. We determined the effect of nitrate on ovariectomy-induced kidney dysfunction METHODS: Control, ovariectomized (OVX), control + nitrate, and OVX + nitrate female Wistar rats (n = 10/group); sodium nitrate (100 mg/L) administered in drinking water for 9 months. Glomerular filtration rate (GFR) and albumin excretion rate (AER) were calculated from serum and urine parameters. At month 9, serum and kidney levels of nitric oxide (NO) metabolites (NOx), oxidative stress indices, and mRNA expression of endothelial NO synthase (eNOS) were measured; with histological analyses of the kidney.

RESULTS

Compared to controls, OVX rats had lower GFR (31%, p = 0.0079), higher glomerular tuft volume (30%, p = 0.0402), and Bowman's capsule space (39%, p = 0.0224). OVX rats had lower serum NOx (33%, p = 0.0061) and kidney eNOS mRNA expression (34%, p = 0.0368). Nitrate administration to: (i) control rats increased serum NOx (59%, p < 0.0001), with no effect on other parameters; (ii) OVX rats increased serum (85%, p < 0.0001) and kidney (106%, p = 0.0008) NOx values, and restored kidney eNOS expression to normal value. Nitrate administration to OVX rats increased GFR (36%, p = 0.0361) and restored glomerular tuft volume and Bowman's capsule space to normal values. In OVX rats, it also increased serum catalase (CAT) activity, serum and kidney total antioxidant capacity (TAC), and decreased serum malondialdehyde (MDA).

CONCLUSIONS

Low-dose long-term nitrate administration protects against ovariectomy-induced kidney dysfunction in rats. This effect is associated with reducing ovariectomy-induced oxidative stress and restoring eNOS-derived NO deficiency in systemic circulation and the kidney.

Beneficial Effects of Dietary Nitrite on a Model of Nonalcoholic Steatohepatitis Induced by High-Fat/High-Cholesterol Diets in SHRSP5/Dmcr Rats: A Preliminary Study

Nonalcoholic steatohepatitis (NASH) is a chronic liver disease that leads to liver cirrhosis and hepatocellular carcinoma. Endothelial dysfunction caused by hepatic lipotoxicity is an underlying NASH pathology observed in the liver and the cardiovascular system. Here, we evaluated the effect of dietary nitrite on a rat NASH model. Stroke-prone, spontaneously hypertensive 5/Dmcr rats were fed a high-fat/high-cholesterol diet to develop the NASH model, with nitrite or captopril (100 mg/L, each) supplementation in drinking water for 8 weeks. The effects of nitrite and captopril were evaluated using immunohistochemical analyses of the liver and heart tissues. Dietary nitrite suppressed liver fibrosis in the rats by reducing oxidative stress, as measured using the protein levels of nicotinamide adenine dinucleotide phosphate oxidase components and inflammatory cell accumulation in the liver. Nitrite lowered the blood pressure in hypertensive NASH rats and suppressed left ventricular chamber enlargement. Similar therapeutic effects were observed in a captopril-treated rat NASH model, suggesting the possibility of a common signaling pathway through which nitrite and captopril improve NASH pathology. In conclusion, dietary nitrite attenuates the development of NASH with cardiovascular involvement in rats and provides an alternative NASH therapeutic strategy.

Gut Microbiome Alteration after Reboxetine Administration in Type-1 Diabetic Rats

Antidepressants are drugs commonly used in clinical settings. However, there are very limited studies on the effects of these drugs on the gut microbiota. Herein, we evaluated the effect of reboxetine (RBX), a selective norepinephrine (noradrenaline) reuptake inhibitor (NRI), on gut microbiota in both diabetic and non-diabetic rats. This is the first report of relation between reboxetine use and the gut microbiota to our knowledge. In this study, type-1 diabetes induced by using streptozotocin (STZ) and RBX was administered to diabetic rats and healthy controls for 14 days. At the end of the treatment, stool samples were collected. Following DNA extraction, amplicon libraries for the V3-V4 region were prepared and sequenced with the Illumina Miseq platform. QIIME was used for preprocessing and analysis of the data. As a result, RBX had a significant effect on gut microbiota structure and composition in diabetic and healthy rats. For example, RBX exposure had a pronounced microbial signature in both groups, with a low Firmicutes/Bacteroidetes ratio and low Lactobacillus levels. While another abundance phylum after exposure to RBX was Proteabacteria, other notable taxa in the diabetic group included Flavobacterium, Desulfovibrionaceae, Helicobacteriaceae, Campylobacterales, and Pasteurellacae when compared to the untreated group.

Sodium hydrosulfide has no additive effects on nitrite-inhibited renal gluconeogenesis in type 2 diabetic rats

OBJECTIVE

Increased renal and hepatic gluconeogenesis are important sources of fasting hyperglycemia in type 2 diabetes (T2D). The inhibitory effect of co-administration of sodium nitrite and sodium hydrosulfide (NaSH) on hepatic but not renal gluconeogenesis has been reported in rats with T2D. The present study aimed to determine the effects of co-administration of sodium nitrite and NaSH on the expression of genes involved in renal gluconeogenesis in rats with T2D.

METHODS

T2D was induced by a combination of a high-fat diet and low-dose streptozotocin (30 mg/kg). Male Wistar rats were divided into 5 groups (n = 6/group): Control, T2D, T2D + nitrite, T2D + NaSH, and T2D + nitrite+NaSH. Nitrite and NaSH were administered for nine weeks at a dose of 50 mg/L (in drinking water) and 0.28 mg/kg (daily intraperitoneal injection), respectively. Serum levels of urea and creatinine, and mRNA expressions of PEPCK, G6Pase, FBPase, PC, PI3K, AKT, PGC-1α, and FoxO1 in the renal tissue, were measured at the end of the study.

RESULTS

Nitrite decreased mRNA expression of PEPCK by 39%, G6Pase by 43%, FBPase by 41%, PC by 63%, PGC-1α by 45%, and FoxO1 by 27% in the renal tissue of rats with T2D; co-administration of nitrite and NaSH further decreases FoxO1, while had no additive effects on the tissue expression of the other genes. In addition, nitrite+NaSH decreased elevated serum urea levels by 58% and creatinine by 37% in rats with T2D.

CONCLUSION

The inhibitory effect of nitrite on gluconeogenesis in T2D rats is at least in part due to decreased mRNA expressions of renal gluconeogenic genes. Unlike effects on hepatic gluconeogenesis, co-administration of nitrite and NaSH has no additive effects on genes involved in renal gluconeogenesis in rats with T2D.

The effect of prolonged dietary sodium nitrate treatment on the hypothalamus-pituitary-gonadal axis and testicular structure and function in streptozotocin-induced diabetic male rats

The aim of this study was to evaluate the effect of prolonged dietary nitrate supplementation on the gonadotropin level, testicular histology and morphometry, expression of miR-34b and p53 mRNA, and spermatogenesis in streptozotocin-induced diabetic male rats.

METHODS

Fifty male Wistar rats were divided into 5 groups: Control (C), control + nitrate (CN), diabetes (D), diabetes + insulin (DI), and diabetes + nitrate (DN). Diabetes was induced using 45 mg kg^-1 of streptozotocin intraperitoneally. Rats in the CN and DN groups were administered sodium nitrate in drinking water (100 mg L^-1). NPH insulin (2-4 U d^-1) was injected subcutaneously in the DI group for 2 months. Nitrate and insulin supplementation was started one month after confirmation of diabetes.

RESULTS

Nitrate supplementation in the DN group significantly increased the body weight (p < 0.05), sperm parameters (p < 0.001), indices of spermatogenesis (p < 0.001), and testis histopathology as well as decreased the blood glucose level (p < 0.001) compared to the untreated diabetic group, although it had no significant effect on testicular parameters, LH and FSH levels. Nitrate administration in the DN group also decreased miR-34b (p < 0.001) and p53 mRNA (p < 0.001) expression, and increased serum insulin and NOx levels compared to the untreated diabetic rats.

CONCLUSIONS

Chronic nitrate supplementation in streptozotocin-induced diabetic rats improved fertility parameters, which may be associated with increased miR-34b and decreased p53 mRNA.

Evaluation of ameliorative effect of sodium nitrate in experimental model of streptozotocin-induced diabetic neuropathy in male rats

OBJECTIVE

Diabetes induces sensory symptoms of neuropathy as positive (hyperalgesia), negative (hypoalgesia), or both.

METHODS

In the present study, fifty male Wistar rats were allocated to five groups: control, control+nitrate, diabetes, diabetes+insulin, and diabetes+nitrate. Thirty days after diabetes confirmation, insulin (2-4 U/day) was injected subcutaneously in diabetes+insulin group and nitrate (100 mg/l) was added into drinking water of the control+nitrate and diabetes+nitrate groups for a period of 2 months. In order to assess the mechanical and thermal algesia, tail immersion, hot plate, and von Frey tests were performed. The serum insulin levels were determined with insulin ELISA Kit. Serum level of NOx was determined by the Griess method.

RESULTS

Both thermal and mechanical nociceptive thresholds showed a significant decrease (p<0.05) which was followed by a significant increase (p<0.01) in the thermal nociceptive threshold in the diabetes group. Chronic nitrate or insulin treatment led to a significant decrease (p<0.01) in blood glucose levels, as well as a significant (p<0.05) increase in the body weight and serum NOx. Moreover, nitrate treatment significantly increased serum insulin levels (p<0.001) compared to the other groups.

CONCLUSION

Chronic nitrate treatment modified the thermal and mechanical sensitivities in diabetic animals.

Regulation of carbohydrate metabolism by nitric oxide and hydrogen sulfide: Implications in diabetes

Nitric oxide (NO) and hydrogen sulfide (H₂S) are two gasotransmitters that are produced in the human body and have a key role in many of the physiological activities of the various organ systems. Decreased NO bioavailability and deficiency of H₂S are involved in the pathophysiology of type 2 diabetes and its complications. Restoration of NO levels have favorable metabolic effects in diabetes. The role of H₂S in pathophysiology of diabetes is however controversial; H₂S production is decreased during development of obesity, diabetes, and its complications, suggesting the potential therapeutic effects of H₂S. On the other hand, increased H₂S levels disturb the pancreatic β-cell function and decrease insulin secretion. In addition, there appear to be important interactions between NO and H₂S at the levels of both biosynthesis and signaling pathways, yet clear an insight into this relationship is lacking. H₂S potentiates the effects of NO in the cardiovascular system as well as NO release from its storage pools. Likewise, NO increases the activity and the expression of H₂S-generating enzymes. Inhibition of NO production leads to elimination/attenuation of the cardioprotective effects of H₂S. Regarding the increasing interest in the therapeutic applications of NO or H₂S-releasing molecules in a variety of diseases, particularly in the cardiovascular disorders, much is to be learned about their function in glucose/insulin metabolism, especially in diabetes. The aim of this review is to provide a better understanding of the individual and the interactive roles of NO and H₂S in carbohydrate metabolism.

Hydrogen sulfide potentiates the favorable metabolic effects of inorganic nitrite in type 2 diabetic rats

OBJECTIVE

Decreased nitric oxide (NO) bioavailability and hydrogen sulfide (H₂S) deficiency have been linked with the pathophysiology of type 2 diabetes (T2D). Restoration of NO levels by nitrite have been associated with favorable metabolic effects in T2D. Moreover, H₂S can potentiate the effects of NO in the cardiovascular system. The aim of this study was to determine the effects of long-term co-administration of sodium nitrite and sodium hydrosulfide (NaSH) on carbohydrate metabolism in type 2 diabetic rats.

METHODS

T2D was induced using chronic high fat diet (HFD) feeding combined with low dose streptozotocin (STZ) regimen. Rats were divided into 5 groups (N = 10/group): Control, T2D, T2D + nitrite, T2D + NaSH, and T2D + nitrite + NaSH. Nitrite (50 mg/L in drinking water) and NaSH (0.28 mg/kg, daily i. p. injection) were administered for 9 weeks. Fasting serum glucose, insulin, lipid profile, liver function tests, and oxidative stress indices were measured. Intraperitoneal glucose tolerance test (GTT) was performed at the end of the eighth week, and three days later, intraperitoneal pyruvate tolerance test (PTT) was done. Protein levels and mRNA expression of glucose transporter type 4 (GLUT4) in soleus muscle and epididymal adipose tissue as well as mRNA expression of H₂S-producing enzymes in the liver, soleus muscle, and epididymal adipose tissue were measured at the end of the study.

RESULTS

Compared to the controls, HFD and STZ treated rats developed metabolic dysfunction. Nitrite treatment improved carbohydrate metabolism, liver function, and oxidative stress indices whereas NaSH treatment per se had no significant effects. However, co-administration of NaSH and nitrite resulted in further improvement in serum insulin level, GTT, PTT, liver function, oxidative stress, protein level and mRNA expression of GLUT4, as well as mRNA expression of H₂S-producing enzymes in diabetic rats.

CONCLUSION

Low dose of NaSH per se had no effect on carbohydrate metabolism while it potentiated the favorable metabolic effects of inorganic nitrite in type 2 diabetic rats. These favorable effects were associated with decreased oxidative stress and increased GLUT4 expression in insulin-sensitive tissues as well as improvement of liver function.

Metabolic Effects of Dietary Nitrate in Health and Disease

Nitric oxide (NO), generated from L-arginine and oxygen by NO synthases, is a pleiotropic signaling molecule involved in cardiovascular and metabolic regulation. More recently, an alternative pathway for the formation of this free radical has been explored. The inorganic anions nitrate (NO₃^-) and nitrite (NO₂^-), originating from dietary and endogenous sources, generate NO bioactivity in a process involving seemingly symbiotic oral bacteria and host enzymes in blood and tissues. The described cardio-metabolic effects of dietary nitrate from experimental and clinical studies include lowering of blood pressure, improved endothelial function, increased exercise performance, and reversal of metabolic syndrome, as well as antidiabetic effects. The mechanisms underlying the salutary metabolic effects of nitrate are being revealed and include interaction with mitochondrial respiration, activation of key metabolic regulatory pathways, and reduction of oxidative stress. Here we review the recent advances in the nitrate-nitrite-NO pathway, focusing on metabolic effects in health and disease.

N-acetylcysteine protects against diabetic nephropathy through control of oxidative and nitrosative stress by recovery of nitric oxide in rats

The diabetes mellitus (DM) induces several changes, with substantial increase of reactive oxygen species (ROS). The ROS cause damage to systemic and renal microvasculature, which could be one of the mechanisms involved in the development of diabetic nephropathy (DN). The ROS modulate other substances like the nitric oxide (NO), a vasodilator with important role in the renal function. N-acetylcysteine (NAC) is an antioxidant that acts replenishing intracellular cysteine levels, which is essential for glutathione formation. The aim of this study was to evaluate the effect of early or late NAC treatment on oxidative/nitrosative stress in DN progression. All rats were submitted to unilateral nephrectomy and diabetes was induced with streptozotocin. The animals were allocated into six groups: controls that received water (CTL) or NAC (CTL + NAC); diabetic groups that received early or late, water (DM-E; DM-L) or NAC (DM + NAC-E; DM + NAC-L), started on 5th day (early) or 4th week (late) after diabetes induction, during 8 weeks. After NAC treatment, the rats were placed in individual metabolic cages to obtain urine and blood samples for analysis of metabolic profile, renal function, thiobarbituric acid reactive substances (TBARS) and NO. At the end of the protocol, the renal cortex was removed for TBARS, NOS evaluation, antioxidants markers and histology. The DM-E group compared to CTL showed a significant increase in glycemia and proteinuria and impaired renal function; there was a significant increase of TBARS in plasma, urine and renal tissue, and also a significant decrease in plasma NO, which were reverted after early NAC treatment. The eNOS was decreased and iNOS was increased in DM-E vs. CTL, p < 0.05. The early NAC treatment in DM rats reduced proteinuria, creatinine, urea, TBARS and iNOS and, increased creatinine clearance, NO and eNOS, increasing significantly the antioxidant defenses, promoting elevated catalase and glutathione compared to DM-E group, all p < 0.05. The late NAC treatment in diabetic rats vs.DM-E showed reduced proteinuria and TBARS excretion and higher values of creatinine clearance and NO, all statistically significant. Histological analysis of the animals in DM-E or DM-L showed significant tubular changes with degeneration and vacuolization in tubular cells, dilated tubular lumen, intense glycosidic degeneration, and discreet mesangial expansion with interstitial fibrosis area. The DM + NAC-E group showed moderate glycosidic degeneration, however, did not present tubular degeneration or fibrosis. The DM + NAC-L group showed severe glycosidic degeneration, moderate tubular cell degeneration, light and focal dilatation of the tubules, with no fibrosis. Our study showed that NAC protected the diabetic rats against renal injury, probably due to the control of oxidative stress via recovery of the NO bioavailability, showing that early NAC was more effective than late treatment. All these data suggest that NAC may be useful in the adjuvant treatment in a safe way, in the early phase of the disease. Eventually, prolonged treatment, even if it is started later, could change the natural history of the disease, delaying the complications of diabetes in renal tissue.

Effects of long-term nitrate supplementation on carbohydrate metabolism, lipid profiles, oxidative stress, and inflammation in male obese type 2 diabetic rats

PURPOSE

Supplementation with inorganic nitrate to boost the nitrate-nitrite-nitric oxide (NO) pathway, may act as a potential therapeutic agent in diabetes. The aim of this study was to determine the effects of nitrate on carbohydrate metabolism, lipid profiles, oxidative stress, and inflammation in obese type 2 diabetic rats.

METHODS

Male Wistar rats were divided into 4 groups: Control, control + nitrate, diabetes, and diabetes + nitrate. Diabetes was induced using a high-fat diet and low-dose of streptozotocin. Sodium nitrate (100 mg/L in drinking water) was administered simultaneously for two months. Serum levels of fasting glucose, insulin, and lipid profiles were measured every 2-weeks. Glycated hemoglobin (HbA1c) was measured monthly. Serum thiobarbituric reactive substances (TBARS) level and catalase activity were measured before and after treatment. At the end of the study, glucose, pyruvate, and insulin tolerance tests were done. Glucose-stimulated insulin secretion (GSIS) and insulin content from isolated pancreatic islets were also assessed; mRNA expression of iNOS as well as mRNA expression and protein levels of GLUT4 in insulin-sensitive tissues, and serum IL-1β were determined.

RESULTS

Nitrate supplementation in diabetic rats significantly improved glucose tolerance, lipid profiles, and catalase activity as well as decreased gluconeogenesis, fasting glucose, insulin, and IL-1β; although it had no significant effect on GSIS, islet insulin content, HbA1c, and serum TBARS. Compared to the controls, in diabetic rats, mRNA expression and protein levels of GLUT4 were significantly lower in the soleus muscle (54% and 34%, respectively) and epididymal adipose tissue (67% and 41%, respectively). In diabetic rats, nitrate administration increased GLUT4 mRNA expression and protein levels in both soleus muscle (215% and 17%, respectively) and epididymal adipose tissue (344% and 22%, respectively). In diabetic rats, nitrate significantly decreased elevated iNOS mRNA expression in both the soleus muscle and epididymal adipose tissue.

CONCLUSION

Chronic nitrate supplementation in obese type 2 diabetic rats improved glucose tolerance, insulin resistance, and dyslipidemia; these favorable effects were associated with increased mRNA and protein expression of GLUT4 and decreased mRNA expression of iNOS in insulin-sensitive tissues, and with decreased gluconeogenesis, inflammation, and oxidative stress.

Protective effects of oral glutathione on fasting-induced intestinal atrophy through oxidative stress

AIM

To determine whether oral glutathione (GSH) administration can alleviate the effects of fasting-induced intestinal atrophy in the small intestinal mucosa.

METHODS

Rats were divided into eight groups. One group was fed ad libitum, another was fed ad libitum and received oral GSH, and six groups were administrated saline (SA) or GSH orally during fasting. Mucosal height, apoptosis, and cell proliferation in the jejunum were histologically evaluated. iNOS protein expression (by immunohistochemistry), nitrite levels (by high performance liquid chromatography, as a measure of NO production), 8-hydroxydeoxyguanosine formation (by ELISA, indicating ROS levels), glutathione/oxidized glutathione (GSH/GSSG) ratio (by enzymatic colorimetric detection), and γ-glutamyl transpeptidase (Ggt1) mRNA levels in the jejunum (by semi-quantitative RT-PCR) were also estimated.

RESULTS

Oral GSH administration was demonstrated to drastically reduce fasting-induced intestinal atrophy in the jejunum. In particular, jejunal mucosal height was enhanced in GSH-treated animals compared to SA-treated animals [527.2 ± 6.9 for 50 mg/kg GSH, 567.6 ± 5.4 for 500 mg/kg GSH vs 483.1 ± 4.9 (μm), P < 0.01 at 72 h]. This effect was consistent with decreasing changes in GSH-treated animals compared to SA-treated animals for iNOS protein staining [0.337 ± 0.016 for 50 mg/kg GSH, 0.317 ± 0.017 for 500 mg/kg GSH vs 0.430 ± 0.023 (area of staining part/area of tissue), P < 0.01 at 72 h] and NO [2.99 ± 0.29 for 50 mg/kg GSH, 2.88 ± 0.19 for 500 mg/kg GSH vs 5.34 ± 0.35 (nmol/g tissue), P < 0.01 at 72 h] and ROS [3.92 ± 0.46 for 50 mg/kg GSH, 4.58 ± 0.29 for 500 mg/kg GSH vs 6.42 ± 0.52 (8-OHdG pg/μg DNA), P < 0.01, P < 0.05 at 72 h, respectively] levels as apoptosis mediators in the jejunum. Furthermore, oral GSH administration attenuated cell proliferation decreases in the fasting jejunum [182.5 ± 1.9 for 500 mg/kg GSH vs 155.8 ± 3.4 (5-BrdU positive cells/10 crypts), P < 0.01 at 72 h]. Notably, both GSH concentration and Ggt1 mRNA expression in the jejunum were also attenuated in rats following oral administration of GSH during fasting as compared with fasting alone [0.45 ± 0.12 vs 0.97 ± 0.06 (nmol/mg tissue), P < 0.01; 1.01 ± 0.11 vs 2.79 ± 0.39 (Ggt1 mRNA/Gapdh mRNA), P < 0.01 for 500 mg/kg GSH at 48 h, respectively].

CONCLUSION

Oral GSH administration during fasting enhances jejunal regenerative potential to minimize intestinal mucosal atrophy by diminishing fasting-mediated ROS generation and enterocyte apoptosis and enhancing cell proliferation.

Dietary nitrite reverses features of postmenopausal metabolic syndrome induced by high-fat diet and ovariectomy in mice

Menopausal women are at greater risk of developing metabolic syndrome with reduced endothelial nitric oxide synthase (eNOS) activity. Hormone replacement therapy increases eNOS activity and normalizes some characteristics of metabolic syndrome. We hypothesized that nitric oxide (NO) supplementation should have a therapeutic effect on this syndrome. We examined the effect of dietary nitrite in a mouse model with postmenopausal metabolic syndrome induced by ovariectomy (OVX) and a high fat diet (HF). C57BL/6 female mice were divided into five groups, sham+normal fat diet (NF), sham+ HF, OVX+HF with or without sodium nitrite (50 mg and 150 mg/l) in the drinking water. Daily food intake and weekly body weight were monitored for 18 wk. OVX and HF significantly reduced plasma levels of nitrate/nitrite (NOx), and mice developed obesity with visceral hypertrophic adipocytes and increased transcriptional levels of monocyte chemoattractant protein-1, TNF-α, and IL-6 in visceral fat tissues. The proinflammatory state in the adipocytes provoked severe hepatosteatosis and insulin resistance in OVX+HF group compared with sham+NF group. However, dietary nitrite significantly suppressed adipocyte hypertrophy and transcriptions of proinflammatory cytokines in visceral fat in a dose-dependent manner. The improvement of visceral inflammatory state consequently reversed the hepatosteatosis and insulin resistance observed in OVX+HF mice. These results suggest that an endogenous NO defect might underlie postmenopausal metabolic syndrome and that dietary nitrite provides an alternative source of NO, subsequently compensating for metabolic impairments of this syndrome.

Inducible and neuronal nitric oxide synthases exert contrasting effects during rat intestinal recovery following fasting

We investigated the effects of endogenous inducible (iNOS) and neuronal nitric oxide synthase on recovery from intestinal mucosal atrophy caused by fasting-induced apoptosis and decreased cell proliferation during refeeding in rats. Rats were divided into five groups, one of which was fed ad libitum, and four of which underwent 72 h of fasting, followed by refeeding for 0, 6, 24, and 48 h, respectively. iNOS and neuronal nitric oxide synthase mRNA and protein levels in jejunal tissues were measured, and mucosal height was histologically evaluated. Apoptotic indices, interferon-γ (IFN-γ) transcription levels, nitrite levels (as a measure of nitric oxide [NO] production),8-hydroxydeoxyguanosine formation (indicating reactive oxygen species [ROS] levels), crypt cell proliferation, and the motility indices (MI) were also estimated. Associations between mucosal height and NOS protein levels were determined using Spearman's rank correlation test. Notably, we observed significant increases in mucosal height and in neuronal nitric oxide synthase mRNA and protein expression as refeeding time increased. Indeed, there was a significant positive correlation between neuronal nitric oxide synthase protein level and mucosal height during the 48-h refeeding period ( r = 0.725, P < 0.01). Conversely, iNOS mRNA and protein expression decreased according to refeeding time, with a significant negative correlation between iNOS protein level and mucosal height being recorded during the 48-h refeeding period ( r = -0.898, P < 0.01). We also noted a significant negative correlation between jejunal neuronal nitric oxide synthase and iNOS protein concentrations over this same period ( r = -0.734, P < 0.01). Refeeding also restored the decreased jejunal MI caused by fasting. Our finding suggests that refeeding likely repairs fasting-induced jejunal atrophy by suppressing iNOS expression and subsequently inhibiting NO, ROS, and IFN-γ as apoptosis mediators, and by promoting neuronal nitric oxide synthase production and inducing crypt cell proliferation via mechanical stimulation. Impact statement Besides providing new data confirming the involvement of iNOS and nNOS in intestinal mucosal atrophy caused by fasting, this study details their expression and function during recovery from this condition following refeeding. We demonstrate a significant negative correlation between iNOS and nNOS levels during refeeding, and associate this with cell proliferation and apoptosis in crypts and villi. These novel findings elucidate the relationship between these NOS isoforms and its impact on recovery from intestinal injury. A mechanism is proposed comprising the up-regulation of nNOS activity by mechanical stimulation due to the presence of food in the intestine, restricting iNOS-associated apoptosis and promoting cell proliferation and gut motility. Our investigation sheds light on the molecular basis behind the repercussions of total parenteral nutrition on intestinal mucosal integrity, and more importantly, the beneficial effects of early enteral feeding.

The Consumption of Synbiotic Bread Containing Lactobacillus sporogenes and Inulin Affects Nitric Oxide and Malondialdehyde in Patients with Type 2 Diabetes Mellitus: Randomized, Double-Blind, Placebo-Controlled Trial

OBJECTIVES

To our knowledge, no reports are available indicating the effects of synbiotic bread consumption on nitric oxide (NO), biomarkers of oxidative stress, and liver enzymes among patients with type 2 diabetes mellitus (T2DM). This study was performed to determine the effects of the daily consumption of synbiotic bread on NO, biomarkers of oxidative stress, and liver enzymes in patients with T2DM.

METHODS

This randomized, double-blind, placebo-controlled trial was performed among 81 patients with diabetes, aged 35-70 years old. After a 2-week run-in period, patients were randomly divided into 3 groups: group A (n = 27) received synbiotic bread containing viable and the heat-resistant probiotic Lactobacillus sporogenes (1 × 108 CFU) and 0.07 g inulin per 1 g, group B (n = 27) received probiotic bread containing Lactobacillus sporogenes (1 × 108 CFU), and group C (n = 27) received control bread for 8 weeks. Patients were asked to consume the synbiotic, probiotic, or control breads 3 times a day in 40 g packages for a total of 120 g/day. Fasting blood samples were taken at baseline and after an 8-week intervention for quantificationof related markers.

RESULTS

After 8 weeks, the consumption of synbiotic bread compared to the probiotic and control breads resulted in a significant rise in plasma NO (40.6 ± 34.4 vs 18.5 ± 36.2 and -0.8 ± 24.5 µmol/L, respectively, p < 0.001) and a significant reduction in malondialdehyde (MDA) levels (-0.7 ± 0.7 vs 0.6 ± 1.7 and 0.5 ± 1.5 µmol/L, respectively, p = 0.001). We did not find any significant effect of the synbiotic bread consumption on plasma total antioxidant capacity (TAC), plasma glutathione (GSH), catalase, serum liver enzymes, calcium, iron, magnesium levels, and blood pressure compared to the probiotic and control breads.

CONCLUSION

In conclusion, consumption of the synbiotic bread for 8 weeks among patients with T2DM had beneficial effects on plasma NO and MDA levels; however, it did not affect plasma TAC, GSH, catalase levels, serum liver enzymes, calcium, iron, magnesium levels, and blood pressure.

Beneficial effects of inorganic nitrate/nitrite in type 2 diabetes and its complications

Background and aim

The ability of inorganic nitrate and nitrite to convert to nitric oxide (NO), and some of its properties e.g. regulation of glucose metabolism, vascular homeostasis, and insulin signaling pathway, have recently raised the hypothesis that inorganic nitrate and nitrite could be potential therapeutic agents in type 2 diabetes. In this review, we reviewed experimental and clinical studies investigating the effect of nitrate/nitrite administration on various aspects of type 2 diabetes.

Findings

Studies showed that an altered metabolism of nitrate/nitrite and impaired NO pathway occurs in diabetes which could contribute to its complications. Some important beneficial properties, including regulation of glucose homeostasis and insulin signaling pathway, improvement of insulin resistance and vascular function, hypotensive, hypolipidemic as well as anti-inflammatory and anti-oxidative effects have been observed following administration of inorganic nitrate/nitrite.

Conclusion

It seems that dietary nitrate/nitrite could be a compensatory fuel for a disrupted nitrate/nitrite/NO pathway and related disorders in diabetes. Although some beneficial properties of nitrate/nitrite have been reported by experimental investigations, long-term clinical studies with various doses of inorganic nitrate/nitrite supplementation, are recommended to confirm these effects.

Dietary nitrite supplementation improves insulin resistance in type 2 diabetic KKA(y) mice

BACKGROUND

Because insulin signaling is essential for endothelial nitric oxide synthase (eNOS)-derived nitric oxide (NO) production, the loss of bioavailable NO might be a common molecular mechanism underlying the development of insulin resistance and endothelial dysfunction. Although dietary nitrite acts as a substrate for systemic NO generation, thereby serving as a physiological alternative source of NO for signaling, it is not precisely known how dietary nitrite affects type 2 diabetes mellitus. Here we report the therapeutic effects of dietary nitrite on the metabolic and histological features of KKA(y) diabetic mice.

METHODS

KKA(y) mice were divided into three groups (without nitrite, and with 50 mg/L and 150 mg/L nitrite in drinking water), and two groups of C57BL/6J mice served as controls (without nitrite and with 150 mg/L nitrite in drinking water). After 10 weeks, blood samples, visceral adipose tissues, and gastrocnemius muscles were collected after a 16-hour fast to assess the homeostasis model assessment of insulin resistance (HOMA-IR) levels, the histology of the adipose tissue, insulin-stimulated sequential signaling to glucose transporter 4 (GLUT4), and nitrite and nitrate contents in the muscle using an HPLC system.

RESULTS

KKA(y) mice developed obesity with enhanced fasting plasma levels of glucose and insulin and exhibited increased HOMA-IR scores compared with the C57BL/6J control mice. Dietary nitrite dose-dependently reduced the size of the hypertrophic adipocytes and TNF-α transcription in the adipose tissue of KKA(y) diabetic mice, which also restored the insulin-mediated signal transduction, including p85 and Akt phosphorylation, and subsequently restored the GLUT4 expression in the skeletal muscles.

CONCLUSIONS

These results suggest that dietary nitrite provides an alternative source of NO, and subsequently improves the insulin-mediated signaling and the metabolic and histological features in KKA(y) diabetic mice.

NAD blocks high glucose induced mesangial hypertrophy via activation of the sirtuins-AMPK-mTOR pathway

BACKGROUND/AIMS

Since the discovery of NAD-dependent deacetylases, Sirtuins, it has been recognized that maintaining intracellular levels of NAD is crucial for the management of stress-response of cells. Here we show that high glucose(HG)-induced mesangial hypertrophy is associated with loss of intracellular levels of NAD. This study was designed to investigate the effect of NAD on HG-induced mesangial hypertrophy.

METHODS

The rat glomerular mesangial cells (MCs) were incubated in HG medium with or without NAD. Afterwards, NAD(+)/NADH ratio and enzyme activity of Sirtuins was determined. In addition, the expression analyses of AMPK-mTOR signaling were evaluated by Western blot analysis.

RESULTS

We showed that HG induced the NAD(+)/NADH ratio and the levels of SIRT1 and SIRT3 activity decreased as well as mesangial hypertrophy, but NAD was capable of maintaining intracellular NAD(+)/NADH ratio and levels of SIRT1 and SIRT3 activity as well as of blocking the HG-induced mesangial hypertrophy in vitro. Activating Sirtuins by NAD blocked the activation of pro-hypertrophic Akt signaling, and augmented the activity of the antihypertrophic AMPK signaling in MCs, which prevented the subsequent induction of mTOR-mediated protein synthesis. By AMPK knockdown, we showed it upregulated phosphorylation of mTOR. In such, the NAD inhibited HG-induced mesangial hypertrophy whereas NAD lost its inhibitory effect in the presence of AMPK siRNA.

CONCLUSION

These results reveal a novel role of NAD as an inhibitor of mesangial hypertrophic signaling, and suggest that prevention of NAD depletion may be critical in the treatment of mesangial hypertrophy.

Renoprotective and blood pressure-lowering effect of dietary soy protein via protein kinase C beta II inhibition in a rat model of metabolic syndrome

We studied whether substitution of soy protein for casein can improve insulin sensitivity, lower blood pressure (BP), and inhibit protein kinase C betaII (PKCbetaII) activation in kidney in an acquired model of metabolic syndrome. Adult male rats were fed 4 different diets: (i) starch (60%) and casein (20%) (CCD), (ii) fructose (60%) and casein (20%) (FCD), (iii) fructose (60%) and soy protein (20%) (FSD), and (iv) starch (60%) and soy protein (20%) (CSD). Renal function parameters, BP, pressor mechanisms, PKCbetaII expression, oxidative stress, and renal histology were evaluated after 60 days. FCD rats displayed insulin resistance and significant changes in body weight, kidney weight, urine volume, plasma and urine electrolytes accompanied by significant changes in renal function parameters compared with CCD rats. Elevated BP, plasma angiotensin-converting enzyme (ACE) activity, renal oxidative stress, and reduced nitrite (NO) and kallikrein activity were observed. Western blot analysis revealed enhanced renal expression of membrane-associated PKCbetaII in the FCD group. Histology showed fatty infiltration and thickening of glomeruli while urinary protein profile revealed a 5-fold increase in albumin. Substitution of soy protein for casein improved insulin sensitivity, lowered BP and PKCbetaII activation and restored renal function. Antioxidant action, inhibitory effect on ACE and PKCbetaII activation, and increased availability of kinins and NO could be contributing mechanisms for the benefits of dietary soy protein.

Oral nitrite ameliorates dextran sulfate sodium-induced acute experimental colitis in mice

Inflammatory bowel diseases (IBDs) such as Crohn's disease and ulcerative colitis are chronic inflammatory disorders of the intestinal tract with excessive production of cytokines, adhesion molecules, and reactive oxygen species. Although nitric oxide (NO) is reported to be involved in the onset and progression of IBDs, it remains controversial as to whether NO is toxic or protective in experimental colitis. We investigated the effects of oral nitrite as a NO donor on dextran sulfate sodium (DSS)-induced acute colitis in mice. Mice were fed DSS in their drinking water with or without nitrite for up to 7days. The severity of colitis was assessed by disease activity index (DAI) observed over the experimental period, as well as by the other parameters, including colon lengths, hematocrit levels, and histological scores at day 7. DSS treatment induced severe colitis by day 7 with exacerbation in DAI and histological scores. We first observed a significant decrease in colonic nitrite levels and increase in colonic TNF-alpha expression at day 3 after DSS treatment, followed by increased colonic myeloperoxidase (MPO) activity and increased colonic expressions of both inducible NO synthase (iNOS) and heme oxygenase-1 (HO-1) at day 7. Oral nitrite supplementation to colitis mice reversed colonic nitrite levels and TNF-alpha expression to that of normal control mice at day 3, resulting in the reduction of MPO activity as well as iNOS and HO-1 expressions in colonic tissues with clinical and histological improvements at day 7. These results suggest that oral nitrite inhibits inflammatory process of DSS-induced experimental colitis by supplying nitrite-derived NO instead of impaired colonic NOS activity.

Depressive status does not alter renal oxidative and immunological parameters during early diabetic nephropathy in rats

Depression is frequently observed among patients with diabetes and depressive status has been associated to activation of inflammatory processes, suggesting a role of depression in the inflammatory events observed in diabetes. To test that proposal, it was studied the effect of depression induced by forced swimming test (FST) on the evolution of early diabetic nephropathy. Diabetes was induced by streptozotocin injection. Rats were submitted to FST for 15 days. Struggle time was determined during FST and motor activity previously to FST. Nitric oxide, malondialdehyde, reduced glutathione and catalase activity were measured in kidney homogenates by enzymatic and biochemical methods. Superoxide anion, monocyte/macrophage (ED-1 positive cells) and RAGE were determined by histochemical and immunohistochemical methods. Diabetic rats had decreased struggle time and locomotor activity at day 1 of FST. Both control and diabetic rats had those parameters decreased at day 15. Renal oxidative stress, RAGE expression and ED-1 cells were observed increased in diabetic animals. Those parameters were not significantly altered by FST. The depressive status does not alter oxidative and immune parameters during the early renal changes of diabetic nephropathy.

Nitric oxide and kidney oxygenation

PURPOSE OF REVIEW

The regulatory role of nitric oxide for tissue oxygen availability involves both oxygen delivery, through regulation of vascular tone, and oxygen consumption, through interference with mitochondrial respiration and tubular transport capacity. This review highlights recent findings regarding mechanisms of dysfunctional nitric oxide bioavailability in the kidney and the implications for oxygen availability and mitochondrial respiration.

RECENT FINDINGS

It has been revealed that nitric oxide has several ways to influence and regulate kidney function during normal physiological conditions and that it is also involved in many of the mechanisms resulting in altered kidney function during disease. Recent reports show that nitric oxide regulates kidney oxygenation by influencing both oxygen utilization and supply.

SUMMARY

Increasing evidence has accumulated during recent years for a dysfunctional nitric oxide system resulting in altered kidney oxygenation in several pathological conditions, which contributes to the development of kidney failure. We presently have extensive knowledge regarding the interplay between nitric oxide, oxygenation and kidney function; however, more effort is needed to clarify how dysfunctional nitric oxide regulation progresses to tissue hypoxia and kidney failure in various conditions, in order to identify potential therapeutic targets and develop strategies to prevent or alleviate these adverse effects and maintain adequate kidney function.