Acute Kidney Injury Induces Oxidative Stress and Hepatic Lipid Accumulation through AMPK Signaling Pathway

Acute kidney injury (AKI) often impairs the function of other organs leading to distant organ injury. The liver is the major organ that regulates metabolism and lipid homeostasis in the body. It has been reported that AKI causes liver injury with increased oxidative stress, inflammatory response and steatosis. In the present study, we investigated the mechanisms by which ischemia-reperfusion-induced AKI caused hepatic lipid accumulation. Kidney ischemia (45 min)-reperfusion (24 h) led to a significant increase in plasma creatinine and transaminase in Sprague Dawley rats, indicating kidney and liver injury. Histological and biochemical analyses revealed hepatic lipid accumulation with a significant elevation of triglyceride and cholesterol levels in the liver. This was accompanied by a decreased AMP-activated protein kinase (AMPK) phosphorylation, indicating the reduced activation of AMPK, which is an energy sensor that regulates lipid metabolism. The expression of AMPK-regulated genes that were responsible for fatty acid oxidation (CPTIα, ACOX) was significantly decreased, while the expression of lipogenesis genes (SREPB-1c, ACC1) was significantly elevated. The oxidative stress biomarker malondialdehyde was elevated in the plasma and liver. Incubation of HepG2 cells with an oxidative stress inducer hydrogen peroxide inhibited AMPK phosphorylation and caused cellular lipid accumulation. This was accompanied by decreased expression of genes responsible for fatty acid oxidation and increased expression of genes responsible for lipogenesis. These results suggest that AKI elicits hepatic lipid accumulation through decreased fatty acid metabolism and increased lipogenesis. Oxidative stress may contribute, in part, to the downregulation of the AMPK signaling pathway leading to hepatic lipid accumulation and injury.

Lingonberry Improves Hepatic Lipid Metabolism by Targeting Notch1 Signaling

Impaired hepatic lipid metabolism is a hallmark of non-alcoholic fatty liver disease (NAFLD), which has no effective treatment option. Recently, Notch signaling has been identified as an important mediator of hepatic lipid metabolism. Lingonberry (Vaccinium vitis-idaea L.) is an anthocyanin-rich fruit with significant lipid-lowering properties. In this study, we examined how lingonberry influenced Notch signaling and fatty acid metabolism in a mouse model of NAFLD. Mice (C57BL/6J) fed a high-fat diet (HFD) for 12 weeks developed fatty liver and activated hepatic Notch1 signaling. Lingonberry supplementation inhibited hepatic Notch1 signaling and improved lipid profile by improving the expression of the genes involved in hepatic lipid metabolism. The results were verified using a palmitic-acid-challenged cell model. Similar to the animal data, palmitic acid impaired cellular lipid metabolism and induced Notch1 in HepG2 cells. Lingonberry extract or cyanidin-3-glucoside attenuated Notch1 signaling and decreased intracellular triglyceride accumulation. The inhibition of Notch in the hepatocytes attenuated sterol-regulatory-element-binding-transcription-factor-1 (SREBP-1c)-mediated lipogenesis and increased the expression of carnitine palmitoyltransferase-I-alpha (CPTIα) and acyl-CoA oxidase1 (ACOX1). Taken together, lingonberry’s hepatoprotective effect is mediated by, in part, improving hepatic lipid metabolism via inhibiting Notch1 signaling in HFD-induced fatty liver.

Saskatoon berry supplementation prevents cardiac remodeling without improving renal disease in an animal model of reno-cardiac syndrome

Saskatoon berry (SKB) may have the potential to counter reno-cardiac syndrome owing to its antioxidant capacity. Here, we investigated the renal and cardiovascular effects of SKB-enriched diet in a rat model of reno-cardiac disease. Two groups of wild-type rats (+/+) and two groups of Hannover Sprague-Dawley (Han:SPRD-Cy/+) rats were given either regular diet or SKB diet (10% w/w total diet) for 8 weeks. Body weight, kidney weight, kidney water content, and left ventricle (LV) weight were measured. Blood pressure (BP) was measured by the tail-cuff method. Echocardiography was performed to assess cardiac structure and function. Serum creatinine and malondialdehyde (MDA) were also measured. Han:SPRD-Cy/+ rats had significantly higher kidney weight, kidney water content, LV weight, BP, and creatinine compared with wild-type rats (+/+). The SKB diet supplementation did not reduce kidney weight, kidney water content, BP, and LV weight in Han:SPRD-Cy/+ rats. The SKB diet also resulted in higher systolic BP in Han:SPRD-Cy/+rats. Han:SPRD-Cy/+rats showed cardiac structural remodeling (higher LV wall thickness) without any cardiac functional abnormalities. Han:SPRD-Cy/+ rats also had significantly higher creatinine whereas the concentration of MDA was not different. The SKB diet supplementation reduced cardiac remodeling and the concentration of MDA without altering the concentration of creatinine in Han:SPRD-Cy/+ rats. In conclusion, Han:SPRD-Cy/+ rats developed significant renal disease, high BP, and cardiac remodeling by 8 weeks without cardiac functional impairment. The SKB diet may be useful in preventing cardiac remodeling and oxidative stress in Han:SPRD-Cy/+rats. PRACTICAL APPLICATIONS: Saskatoon berry (SKB) is widely consumed as fresh fruit or processed fruit items and has significant commercial value. It may offer health benefits due to the presence of bioactives such as anthocyanins. SKB has very good culinary flavors, and it is an economically viable fruit crop in many parts of the world. The disease-modifying benefits of SKB are mainly ascribed to the antioxidant nature of its bioactive content. Polycystic kidney disease is a serious condition that can lead to renal and cardiac abnormalities. Here, we showed that SKB supplementation was able to mitigate cardiac remodeling and lower the level of a marker of oxidative stress in an animal model of reno-cardiac syndrome. Our study suggests that SKB possesses beneficial cardioprotective properties. Further evidence from human studies may help in increasing the consumption of SKB as a functional food.

Effects of dietary red-osier dogwood (Cornus stolonifera) on growth performance, blood profile, ileal morphology, and oxidative status in weaned pigs challenged with Escherichia coli K88+

A total of 28 piglets weaned at 21 d of age (6.94 ± 0.28 kg of body weight) were assigned to one of four dietary treatments for 14 d: (1) negative control (NC; a corn–wheat–soybean meal diet), (2) positive control [PC; NC + 0.025% antimicrobial growth promoter (AGP)], (3) ROD2 [2% red-osier dogwood (ROD)], and (4) ROD4 (4% ROD). All pigs were orally inoculated with Escherichia coli K88+ on day 8. The pre-planned orthogonal test was performed to compare (1) NC vs. PC and (2) NC vs. ROD. The inclusion of ROD in a nursery diet increased (P < 0.05) superoxide dismutase (SOD) activities and decreased (P < 0.05) malondialdehyde (MDA) concentrations in the serum. Moreover, pigs fed with ROD diets had shallower (P < 0.05) crypt depth and higher (P < 0.05) villus height to crypt depth ratio than those fed the NC diet. Dietary AGP supplementation reduced (P < 0.05) the MDA concentration in the ileum and serum at 24 h after challenge, and improved (P < 0.01) the SOD activities in the serum. In conclusion, the inclusion of ROD in a nursery diet enhanced the antioxidative defense system and intestinal morphology, showing comparable effects with AGP supplementation.

Ischemia-Reperfusion Injury Reduces Kidney Folate Transporter Expression and Plasma Folate Levels

Acute or chronic kidney disease can cause micronutrient deficiency. Patients with end-stage renal disease, kidney transplantation or on dialysis have reduced circulating levels of folate, an essential B vitamin. However, the molecular mechanism is not well understood. Reabsorption of folate in renal proximal tubules through folate transporters is an important process to prevent urinary loss of folate. The present study investigated the impact of acute kidney injury (AKI) on folate transporter expression and the underlying mechanism. AKI was induced in Sprague-Dawley rats that were subjected to kidney ischemia (45 min)-reperfusion (24 h). Both male and female rats displayed kidney injury and low plasma folate levels compared with sham-operated rats. The plasma folate levels were inversely correlated to plasma creatinine levels. There was a significant increase in neutrophil gelatinase-associated lipocalin (NGAL) and IL-6 mRNA expression in the kidneys of rats with ischemia-reperfusion, indicating kidney injury and increased inflammatory cytokine expression. Ischemia-reperfusion decreased mRNA and protein expression of folate transporters including folate receptor 1 (FOLR1) and reduced folate carrier (RFC); and inhibited transcription factor Sp1/DNA binding activity in the kidneys. Simulated ischemia-reperfusion through hypoxia-reoxygenation or Sp1 siRNA transfection in human proximal tubular cells inhibited folate transporter expression and reduced intracellular folate levels. These results suggest that ischemia-reperfusion injury downregulates renal folate transporter expression and decreases folate uptake by tubular cells, which may contribute to low folate status in AKI. In conclusion, ischemia-reperfusion injury can downregulate Sp1 mediated-folate transporter expression in tubular cells, which may reduce folate reabsorption and lead to low folate status.

Kidney Ischemia-Reperfusion Elicits Acute Liver Injury and Inflammatory Response

Ischemia-reperfusion (IR) is a common risk factor that causes acute kidney injury (AKI). AKI is associated with dysfunction of other organs also known as distant organ injury. The liver function is often compromised in patients with AKI and in animal models. However, the underlying mechanisms are not fully understood. Inflammatory response plays an important role in IR-induced tissue injury. Although increased proinflammatory cytokines have been detected in the kidney and the distant organs after renal IR, their original sources remain uncertain. In the present study, we investigated the acute effect of renal IR on hepatic inflammatory cytokine expression and the mechanism involved. Sprague-Dawley rats that were subjected to renal IR (ischemia for 45 min followed by reperfusion for 1 h or 6 h) had increased plasma levels of creatinine, urea, and transaminases, indicating kidney and liver injuries. There was a significant increase in the expression of proinflammatory cytokine mRNA (MCP-1, TNF-α, IL-6) in the kidney and liver in rats with renal IR. This was accompanied by a significant increase in proinflammatory cytokine protein levels in the plasma, kidney, and liver. Activation of a nuclear transcription factor kappa B (NF-κB) was detected in the liver after renal IR. The inflammatory foci and an increased myeloperoxidase (MPO) activity were detected in the liver after renal IR, indicating hepatic inflammatory response and leukocyte infiltration. These results suggest that renal IR can directly activate NF-κB and induce acute production of proinflammatory cytokines in the liver. Renal IR-induced hepatic inflammatory response may contribute to impaired liver function and systemic inflammation.

Inhibition of Inflammatory Cytokine Expression Prevents High-Fat Diet-Induced Kidney Injury: Role of Lingonberry Supplementation

Chronic low-grade inflammation is a major stimulus for progression of chronic kidney disease (CKD) in individuals consuming high-fat diet. Currently, there are limited treatment options for CKD other than controlling the progression rate and its associated complications. Lingonberry (Vaccinium vitis-idaea L.) is rich in anthocyanins with demonstrated anti-inflammatory effect. In the current study, we investigated the potential renal protective effect of lingonberry and its anthocyanin (cyanidin-3-glucoside) in high-fat diet fed obese mice and in human proximal tubular cells. Prolonged consumption of high-fat diets is strongly associated with obesity, abnormal lipid and glucose metabolism. Mice (C57BL/6J) fed a high-fat diet (62% kcal fat) for 12 weeks developed renal injury as indicated by an elevation of blood urea nitrogen (BUN) level as well as an increase in renal kidney injury molecule-1 (KIM-1), neutrophil gelatinase-associated lipocalin (NGAL) and renin expression. Those mice displayed an activation of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) and increased expression of inflammatory cytokines-monocyte chemoattractant-1 (MCP-1), tumor necrosis factor alpha (TNF-α), interleukin-6 (IL-6) in the kidneys. Mice fed a high-fat diet also had a significant elevation of inflammatory cytokine levels in the plasma. Dietary supplementation of lingonberry for 12 weeks not only attenuated high-fat diet-induced renal inflammatory response but also reduced kidney injury. Such a treatment improved plasma lipid and glucose profiles, reduced plasma inflammatory cytokine levels but did not affect body weight gain induced by high-fat diet feeding. Lingonberry extract or its active component cyanidin-3-glucoside effectively inhibited palmitic acid-induced NF-κB activation and inflammatory cytokine expression in proximal tubular cells. These results suggest that lingonberry supplementation can reduce inflammatory response and prevent chronic kidney injury. Such a renal protective effect by lingonberry and its active component may be mediated, in part, through NF-κB signaling pathway.

Folic Acid Supplementation Attenuates Chronic Hepatic Inflammation in High-Fat Diet Fed Mice

Nonalcoholic fatty liver disease (NAFLD) is the most common form of chronic liver disease worldwide. Hepatic inflammation is an important pathogenic mediator of NAFLD. There is currently no pharmacological agent approved for the treatment of NAFLD. Folic acid is a water-soluble B vitamin that has been shown to have lipid-lowering and antioxidant effects. The objective of this study was to investigate the effect of folic acid supplementation on hepatic inflammation and to identify the underlying mechanisms. Male C57BL/6 J mice were fed a control diet (10% kcal fat), a high-fat diet (HFD) (60% kcal fat), or a HFD supplemented with folic acid (26 mg/kg diet) for 8 weeks. HFD feeding led to increased body mass gain, lipid accumulation, activation of transcription factor nuclear factor-κB (NF-κB), and elevation of inflammatory cytokine gene expression in the liver. Folic acid supplementation attenuated hepatic lipid accumulation and aggregation of inflammatory foci induced by HFD feeding. This was associated with a significant reduction of NF-κB activation and inflammatory cytokine expression. These results suggest that the hepatoprotective effect of folic acid in NAFLD may be attributed, in part, to its anti-inflammatory action.

High-fat diet consumption reduces hepatic folate transporter expression via nuclear respiratory factor-1

Folate is an essential micronutrient for biological function. The liver, a primary organ for folate metabolism and storage, plays an important role in folate homeostasis. Proton-coupled folate transporter (PCFT) and reduced folate carrier (RFC) are the major folate transporters responsible for folate uptake at basolateral membrane of hepatocytes. Low serum folate levels are frequently associated with obesity. We investigated the mechanism that regulated folate status in a mouse model with diet-induced obesity. Mice (C57BL/6J) were fed a high-fat diet (60% kcal fat) for 8 weeks. Mice displayed increased hepatic lipid accumulation and decreased folate levels in the liver and serum compared to mice fed a normal chow diet (10% kcal fat). High-fat diet-fed mice had low expression of PCFT and RFC and decreased nuclear respiratory factor-1 (NRF-1)/DNA-binding activity. Treatment with NRF-1 siRNA or palmitic acid reduced folate transporter expression in hepatocytes. Inhibition of NRF-1 mediated folate transporter expression significantly reduced intracellular folate levels. These results suggest that chronic consumption of high-fat diets impairs folate transporter expression via NRF-1-dependent mechanism, leading to reduced hepatic folate storage. Understanding the regulation of folate homeostasis in obesity may have an important implication in current guideline of folate intake. KEY MESSAGES: Serum and liver folate levels are decreased in diet-induced obese mice. Chronic high-fat diet consumption impairs expression of hepatic PCFT and RFC. NRF-1 regulates hepatic folate transporters expression and folate levels.

Germinated Brown Rice Attenuates Atherosclerosis and Vascular Inflammation in Low-Density Lipoprotein Receptor-Knockout Mice

The present study investigates the impact of germinated brown rice (GBR) on atherosclerosis and the underlying mechanism in low-density lipoprotein receptor-knockout (LDLr-KO) mice. The intensity of atherosclerosis in aortas of LDLr-KO mice receiving diet supplemented with 60% GBR (weight/weight) was significantly less than that in mice fed with 60% white rice (WR) or control diet ( p < 0.05); all diets contained 0.06% cholesterol. WR or GBR diet did not significantly alter plasma total or LDL-cholesterol, fecal sterols, or glucose, or the activities of antioxidant enzymes, compared to the control diet. The adhesion of monocytes to aortas from LDLr-KO mice fed with WR diet was significantly more than that from mice receiving the control diet ( p < 0.01). GBR diet decreased monocyte adhesion to aortas compared to WR diet ( p < 0.01). GBR diet also reduced the levels of plasminogen activator inhibitor-1 (PAI-1), monocyte chemotactic protein-1 (MCP-1), and tumor necrosis factor-α (TNF-α) in plasma, and the abundances of MCP-1, PAI-1, TNF-α, intracellular cell adhesion molecule-1, toll-like receptor-4, PAI-1, LDLr-like protein, and urokinase plasminogen activator and its receptor in aortas or hearts from LDLr-KO mice in comparison to the WR diet ( p < 0.05, 0.01, respectively). The findings suggest that GBR administration attenuated atherosclerosis and vascular inflammation in LDLr-KO mice compared to WR. The anti-atherosclerotic effect of GBR in LDLr-KO mice at least in part results from its anti-inflammatory activity.

Metabolic Imbalance of Homocysteine and Hydrogen Sulfide in Kidney Disease

Homocysteine (Hcy) and hydrogen sulfide (H2S) are important molecules produced during the metabolism of sulfur-containing amino acids. Hcy metabolism is central to the supply of methyl groups that are essential for biological function. Hcy can be either regenerated to methionine or metabolized to cysteine, a precursor for glutathione synthesis. Cystathionine-β-synthase (CBS) and cystathionine-γ-lyase (CSE) play a crucial role in metabolizing Hcy to cysteine through the transsulfuration pathway. These two enzymes are also responsible for H2S generation through desulfuration reactions. H2S, at physiological levels serves as a gaseous mediator and has multifaceted effects. Metabolic imbalance of Hcy and H2S has been implicated in pathological conditions including oxidative stress, inflammation, cardiovascular and cerebral dysfunction, fatty liver disease and ischemiareperfusion injury. Organs such as liver, kidney, gut and pancreas contain all the enzymes that are required for Hcy metabolism. The kidney plays an important role in removing Hcy from the circulation. Hyperhomocysteinemia, a condition of elevated blood Hcy level, is a common clinical finding in patients with chronic kidney disease (CKD) or acute kidney injury (AKI), the latter is often caused by ischemia-reperfusion. This paper reviews exiting literatures regarding (1) the role of kidney in regulating Hcy and H2S metabolism; (2) disruption of sulfur-containing amino acid metabolism during ischemiareperfusion; (3) impact of metabolic imbalance of Hcy and H2S on kidney function. Better understanding of molecular mechanisms that regulate Hcy and H2S metabolism under physiological and pathophysiological conditions will help improve therapeutic strategies for patients with kidney disease or other organ injuries.

Supplementing diet with Manitoba lingonberry juice reduces kidney ischemia-reperfusion injury

BACKGROUND

Lingonberry (Vaccinium vitis-idaea L.) contains high levels of anthocyanins which are bioavailable in the kidney and may be protective against ischemia-reperfusion (IR)-induced acute kidney injury. This study investigated the effect of lingonberry juice on the IR-induced stress-activated signalling pathway and inflammatory response in the kidney.

RESULTS

Sprague-Dawley rats subjected to kidney IR had significantly impaired kidney function, with increased activation of the JNK signalling pathway and increased inflammatory response, measured using a multiplex panel containing an extensive array of inflammatory biomarkers. In rats fed 1 mL lingonberry juice daily for 3 weeks prior to IR, kidney function was protected and attenuation of inflammatory response and JNK signalling was reflected in the reduction of the measured biomarkers. In vitro results in cultured HK-2 cells confirmed that lingonberry anthocyanins reduced JNK signalling and inflammatory gene expression after IR.

CONCLUSION

This study shows, for the first time, that daily supplementation with lingonberry juice may protect against loss of kidney function induced by IR injury by modulating JNK signalling and inhibiting the subsequent inflammatory response. © 2017 Her Majesty the Queen in Right of Canada. Journal of the Science of Food and Agriculture © 2017 Society of Chemical Industry.

Role of folate in nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is a spectrum of chronic liver conditions that are characterized by steatosis, inflammation, fibrosis, and liver injury. The global prevalence of NAFLD is rapidly increasing in proportion to the rising incidence of obesity and type 2 diabetes. Because NAFLD is a multifaceted disorder with many underlying metabolic abnormalities, currently, there is no pharmacological agent that is therapeutically approved for the treatment of this disease. Folate is a water-soluble B vitamin that plays an essential role in one-carbon transfer reactions involved in nucleic acid biosynthesis, methylation reactions, and sulfur-containing amino acid metabolism. The liver is the primary organ responsible for storage and metabolism of folates. Low serum folate levels have been observed in patients with obesity and diabetes. It has been reported that a low level of endogenous folates in rodents perturbs folate-dependent one-carbon metabolism, and may be associated with development of metabolic diseases such as NAFLD. This review highlights the biological role of folate in the progression of NAFLD and its associated metabolic complications including obesity and type 2 diabetes. Understanding the role of folate in metabolic disease may position this vitamin as a potential therapeutic for NAFLD.

Lingonberry anthocyanins protect cardiac cells from oxidative-stress-induced apoptosis

Lingonberry grown in northern Manitoba, Canada, contains exceptionally high levels of anthocyanins and other polyphenols. Previous studies from our lab have shown that lingonberry anthocyanins can protect H9c2 cells from ischemia-reperfusion injury and anthocyanin-rich diets have been shown to be associated with decreased cardiovascular disease and mortality. Oxidative stress can impair function and trigger apoptosis in cardiomyocytes. This study investigated the protective effects of physiologically relevant doses of lingonberry extracts and pure anthocyanins against hydrogen-peroxide-induced cell death. Apoptosis and necrosis were detected in H9c2 cells after hydrogen peroxide treatment via flow cytometry using FLICA 660 caspase 3/7 combined with YO-PRO-1 and then confirmed with Hoechst staining and fluorescence microscopy. Each of the 3 major anthocyanins found in lingonberry (cyanidin-3-galactoside, cyanidin-3-glucoside, and cyanidin-3-arabinoside) was protective against hydrogen-peroxide-induced apoptosis in H9c2 cells at 10 ng·mL^-1 (20 nmol·L^-1) and restored the number of viable cells to match the control group. A combination of the 3 anthocyanins was also protective and a lingonberry extract tested at 3 concentrations produced a dose-dependent protective effect. Lingonberry anthocyanins protected cardiac cells from oxidative-stress-induced apoptosis and may have cardioprotective effects as a dietary modification.

Effect of Vitamin D3 Fortification and Saskatoon Berry Syrup Addition on the Flavor Profile, Acceptability, and Antioxidant Properties of Rooibos Tea (Aspalathus linearis)

The unique characteristics and healthful reputation of caffeine-free rooibos tea (RT) make it an ideal carrier for vitamin D₃ supplementation, and a potential base for the addition of Saskatoon berry syrup (SBS), a natural flavor additive. The objective of this study was to determine the effect of vitamin D₃ fortification and SBS addition on the flavor profile, consumer acceptability, and antioxidant properties of RT. Six formulations (RT, RT with SBS, RT with SBS and vitamin D₃ , RT with vitamin D₃ , green tea [GT], and GT with SBS) were evaluated by 12 trained panelists and 114 consumers. The formulations were also assessed for antioxidant capacity, physical characteristics, and untargeted phytochemical content. Sensory results revealed that the mean intensity values for berry and sweet attributes were significantly higher (P < 0.05) while bitter and astringent attributes were significantly lower when SBS was added to RT samples compared to those without syrup. Acceptability of flavor, aftertaste, and overall acceptability were also significantly higher for the RT with SBS. The addition of SBS to RT significantly increased the antioxidant capacities which may increase the related health benefits of RT. SBS contributed several polyphenols, particularly flavonoids, to the tea. Vitamin D₃ added to RT formulations did not significantly affect the sensory attributes, acceptability, or antioxidant content. For the development of a functional vitamin D₃ fortified iced-tea beverage that can be consumed as part of the daily diet, SBS could be a favorable flavoring additive that may provide additional health benefits.

The CBS/CSE system: a potential therapeutic target in NAFLD?

Non-alcoholic fatty liver disease (NAFLD) is a broad spectrum liver disorder diagnosed in patients without a history of alcohol abuse. NAFLD is growing at alarming rates worldwide. Its pathogenesis is complex and incompletely understood. The cystathionine-β-synthase (CBS) and cystathionine-γ-lyase (CSE) system regulates homocysteine and cysteine metabolism and contributes to endogenous hydrogen sulfide (H2S) biosynthesis. This review summarizes our current understanding of the hepatic CBS/CSE system, and for the first time, positions this system as a potential therapeutic target in NAFLD. As will be discussed, the CBS/CSE system is highly expressed and active in the liver. Its dysregulation, presenting as alterations in circulating homocysteine and (or) H2S levels, has been reported in NAFLD patients and in NAFLD-associated co-morbidities such as obesity and type 2 diabetes. Intricate links between the CBS/CSE system and a number of metabolic and stress related molecular mediators have also emerged. Various dysfunctions in the hepatic CBS/CSE system have been reported in animal models representative of each NAFLD spectrum. It is anticipated that a newfound appreciation for the hepatic CBS/CSE system will emerge that will improve our understanding of NAFLD pathogenesis, and give rise to new prospective targets for management of this disorder.

Tyrosol Attenuates High Fat Diet-Induced Hepatic Oxidative Stress: Potential Involvement of Cystathionine β-Synthase and Cystathionine γ-Lyase

The Mediterranean diet is known for its cardioprotective effects. Recently, its protective qualities have also been reported in patients with non-alcoholic fatty liver disease (NAFLD). Oxidative stress is one of the important factors responsible for the development and progression of NAFLD. Hydrogen sulfide (H2S), a multifaceted gasotransmitter, has emerged as a potential therapeutic target in NAFLD. Cystathionine β-synthase (CBS) and cystathionine γ-lyase (CSE) are major enzymes responsible for endogenous H2S synthesis. Since oxidative stress contributes to NAFLD pathogenesis, the objective of this study was to investigate the effect of tyrosol, a major compound in olive oil and white wine, on high fat diet-induced hepatic oxidative stress and the mechanisms involved. Mice (C57BL/6) were fed for 5 weeks with a control diet (10 % kcal fat), a high fat diet (60 % kcal fat, HFD) or a HFD supplemented with tyrosol. High fat diet feeding induced hepatic oxidative stress, as indicated by the significant increase in lipid peroxidation and NADPH oxidase activity. Tyrosol supplementation significantly increased hepatic CBS and CSE expression and H2S synthesis in high fat diet-fed mice. Such effects were associated with the attenuation of high fat diet-induced hepatic lipid peroxidation and the restoration of the redox equilibrium of the antioxidant glutathione. Tyrosol also inhibited palmitic acid-induced oxidative stress in hepatocytes (HepG2 cells). These results suggest that the antioxidant properties of tyrosol may be mediated through functional changes in CBS and CSE activity, which might contribute to the hepatoprotective effect of the Mediterranean diet.

Folic acid supplementation during high-fat diet feeding restores AMPK activation via an AMP-LKB1-dependent mechanism

AMPK is an endogenous energy sensor that regulates lipid and carbohydrate metabolism. Nonalcoholic fatty liver disease (NAFLD) is regarded as a hepatic manifestation of metabolic syndrome with impaired lipid and glucose metabolism and increased oxidative stress. Our recent study showed that folic acid supplementation attenuated hepatic oxidative stress and lipid accumulation in high-fat diet-fed mice. The aim of the present study was to investigate the effect of folic acid on hepatic AMPK during high-fat diet feeding and the mechanisms involved. Male C57BL/6J mice were fed a control diet (10% kcal fat), a high-fat diet (60% kcal fat), or a high-fat diet supplemented with folic acid (26 mg/kg diet) for 5 wk. Mice fed a high-fat diet exhibited hyperglycemia, hepatic cholesterol accumulation, and reduced hepatic AMPK phosphorylation. Folic acid supplementation restored AMPK phosphorylation (activation) and reduced blood glucose and hepatic cholesterol levels. Activation of AMPK by folic acid was mediated through an elevation of its allosteric activator AMP and activation of its upstream kinase, namely, liver kinase B1 (LKB1) in the liver. Consistent with in vivo findings, 5-methyltetrahydrofolate (bioactive form of folate) restored phosphorylation (activation) of both AMPK and LKB1 in palmitic acid-treated HepG2 cells. Activation of AMPK by folic acid might be responsible for AMPK-dependent phosphorylation of HMG-CoA reductase, leading to reduced hepatic cholesterol synthesis during high-fat diet feeding. These results suggest that folic acid supplementation may improve cholesterol and glucose metabolism by restoration of AMPK activation in the liver.

Manitoba Lingonberry (Vaccinium vitis-idaea) Bioactivities in Ischemia-Reperfusion Injury

Evidence for the efficacy of dietary interventions in protecting against cardiovascular disease has grown significantly, with flavonoids and anthocyanins receiving special attention. Lingonberry (Vaccinium vitis-idaea L.) is a good source of these compounds, and this study examined the protective effects of wild lingonberry found in Manitoba, Canada, against ischemia-reperfusion (IR) injury. Manitoba lingonberry contained 3793 ± 27 mg gallic acid equiv, 120,501 ± 7651 μmol trolox equiv, and 575 ± 20 mg cyanidin-3-glucoside equiv per 100 g dry weight, which correspond with high total phenolic content, antioxidant activity, and anthocyanin content, respectively. A complete methanolic extract and both anthocyanin-rich and phenolic-rich fractions inhibited apoptosis in H9c2 cells during simulated IR. Lingonberry extract and fractions significantly inhibited several markers of apoptosis induced by IR, including nuclei condensation, caspase-3 activation, and MAP kinase signaling. These results provide the first analysis of Manitoba lingonberry and highlight the mechanistic importance of dietary berry compounds for cardiovascular health.

Downregulation of cystathionine β-synthase and cystathionine γ-lyase expression stimulates inflammation in kidney ischemia-reperfusion injury

Inflammation plays a critical role in kidney ischemia-reperfusion injury but mechanisms of increased proinflammatory cytokine expression are not completely understood. Kidney has a high expression of cystathionine-β-synthase (CBS) and cystathionine-γ-lyase (CSE) that can synthesize hydrogen sulfide. CBE and CSE are also responsible for the synthesis of cysteine, an essential precursor for glutathione, an antioxidant. Reduced hydrogen sulfide and glutathione production is associated with multiple organ injury. Although pro- and anti-inflammatory effects of hydrogen sulfide have been reported, its role in ischemia-reperfusion-induced inflammation in the kidney has not been well addressed. The aim of this study was to investigate the effect of CBS and CSE-mediated hydrogen sulfide and glutathione production on kidney inflammatory response and the mechanism involved. The left kidney of Sprague-Dawley rat was subjected to 45-min ischemia followed by reperfusion for 24 h. Ischemia-reperfusion caused a significant decrease in CBS and CSE mRNA and protein levels with a concomitant reduction of glutathione and hydrogen sulfide production in the kidney while the expression of proinflammatory cytokine expression (MCP-1, IL-6) was elevated. Hypoxia-reoxygenation of proximal tubular cells led to a decrease in CBS and CSE expression and an increase in proinflammatory cytokine expression. Supplementation of glutathione or hydrogen sulfide donor (NaHS) effectively attenuated cytokine expression in tubular cells. These results suggested that ischemia-reperfusion impaired CBS and CSE-mediated glutathione and hydrogen sulfide production in the kidney, which augmented the expression of proinflammatory cytokines. Regulation of CBS and CSE expression may be therapeutically relevant in alleviating ischemia-reperfusion-induced inflammation and improving kidney function.

High-fat diet stimulates hepatic cystathionine β-synthase and cystathionine γ-lyase expression

Cystathionine-β-synthase (CBS) and cystathionine-γ-lyase (CSE) catalyze homocysteine (Hcy) metabolism via the trans-sulfuration pathway. They are also responsible for hydrogen sulfide (H2S) production via desulfuration reactions. The liver contributes significantly to the regulation of Hcy and H2S homeostasis, which might participate in many physiological and pathological processes. The aim of this study was to investigate the effect of a high-fat diet (HFD) on hepatic CBS and CSE expression and its impact on Hcy and H2S metabolism. Mice (C57BL/6) fed a HFD (60% kcal fat) for 5 weeks developed fatty liver. The mRNA and protein levels of CBS and CSE in the liver were significantly elevated in mice fed a HFD. Subsequently the metabolism of Hcy by CBS and CSE was increased in the liver, and its level decreased in the circulation. Increased CBS and CSE expression also caused a significant elevation in H2S production in the liver. The level of lipid peroxides was elevated, indicating oxidative stress, while the level of total glutathione remained unchanged in the liver of HFD-fed mice. Upregulation of the trans-sulfuration pathway might play an adaptive role against oxidative stress by maintaining total glutathione levels in the liver.

Tyrosol attenuates ischemia-reperfusion-induced kidney injury via inhibition of inducible nitric oxide synthase

Tyrosol is a natural phenolic antioxidant compound. Oxidative stress represents one of the important mechanisms underlying ischemia-reperfusion-induced kidney injury. The aim of this study was to investigate the effect of tyrosol against ischemia-reperfusion-induced acute kidney injury. The left kidney of Sprague-Dawley rats was subjected to 45 min of ischemia followed by reperfusion for 6 h. Ischemia-reperfusion caused an increase in peroxynitrite formation and lipid peroxidation. The level of nitric oxide (NO) metabolites and the mRNA of inducible nitric oxide synthase (iNOS) were elevated in ischemia-reperfused kidneys. Administration of tyrosol (100 mg/kg body weight) to rats prior to the induction of ischemia significantly reduced peroxynitrite formation, lipid peroxidation, and the level of NO metabolites. Tyrosol administration also attenuated ischemia-reperfusion-induced NF-κB activation and iNOS expression. Such a treatment improved kidney function. Results suggest that tyrosol may have a protective effect against acute kidney injury through inhibition of iNOS-mediated oxidative stress.

The evolution of nutrition research

"The doctor of the future will no longer treat the human frame with drugs, but will rather cure and prevent disease with nutrition". Thomas Edison's contemplation may come to fruition if the nutritional revolution continues in its current course. Two realizations have propelled the world into a new age of personalized nutrition: (i) food can provide benefits beyond its intrinsic nutrient content, and (ii) we are not all created equal in our ability to realize to these benefits. Nutrigenomics is concerned with delineating genomic propensities to respond to various nutritional stimuli and the resulting impact on individual health. This review will examine the current technologies utilized by nutrigeneticists, the available literature regarding nutrient-gene interactions, and the translation of this new awareness into public health.

Oxidative stress is associated with visceral adipose tissue and subclinical atherosclerosis in a healthy multi-ethnic population

Oxidative stress plays an important role in the development of atherosclerosis. Excess visceral adipose tissue (VAT) and increased carotid intima-media thickness (IMT) are risk factors for coronary artery disease. We tested the hypothesis that VAT and IMT were associated with systemic oxidative stress. Healthy men and women (n = 565) matched for ethnicity (Aboriginal, Chinese, European, and South Asian) were recruited. Plasma malondialdehyde, a biomarker of oxidative stress, was measured as thiobarbituric acid reactive substances (TBARS). VAT and IMT were determined by computerized tomography and ultrasound scans, respectively. Plasma TBARS levels correlated with VAT and total atheroma burden (sum of IMT area and plaque area) in the entire cohort. When stratified by ethnicity, plasma TBARS levels correlated with distinct body composition and arterial measures in different ethnic populations with more associations present amongst Chinese and Europeans relative to Aboriginals and South Asians. VAT was associated with plasma TBARS levels independent of age, sex, ethnicity, smoking, and body mass index. Plasma TBARS levels were associated with IMT, the presence of plaques, and total atheroma burden, independent of age, sex, ethnicity, smoking, body mass index, and VAT. The association with total atheroma burden remained significant even when adjusted for apolipoprotein B. Results from the present study indicate that oxidative stress is positively associated with VAT as well as diffuse and focal carotid atherosclerosis in apparently healthy men and women.

Salidroside and tyrosol from Rhodiola protect H9c2 cells from ischemia/reperfusion-induced apoptosis

AIMS

Heart disease is the leading cause of death worldwide. Ischemia-reperfusion injury can lead to apoptotic death of heart cells and subsequently heart failure. Rhodiola is an herbal medicine with two main bioactive compounds--salidroside (SAL) and tyrosol (TYR). This study aimed to investigate whether these two compounds can prevent ischemia/reperfusion-induced apoptosis in H9c2 cells.

MAIN METHODS

Assays for total phenolics assay and Oxygen Radical Absorbance Capacity showed high antioxidant capacity of SAL and TYR. H9c2 cells were subjected to simulated ischemia/reperfusion (IR) in the presence and absence of SAL and/or TYR, and nuclei condensation, caspase-3 activity, cytochrome c release and JNK phosphorylation were determined.

KEY FINDINGS

In H9c2 cells, IR can lead to a 5-fold increase in p-JNK level. Apoptotic nuclei condensation, caspase-3 activity and cytochrome c release were markedly elevated, indicating the occurrence of apoptosis. SAL and TYR caused a dose-dependent inhibition of nuclear condensation. Furthermore, SAL and TYR, separately and in combination, significantly reduced caspase-3 activity, cytochrome c release and JNK activation. The anti-apoptotic effect of the combination was markedly higher than that of SAL or TYR alone.

SIGNIFICANCE

The inhibition of the JNK signaling pathway is the key mechanism for the cytoprotective effect of SAL and TYR in IR-induced apoptosis.

Folic acid supplementation attenuates high fat diet induced hepatic oxidative stress via regulation of NADPH oxidase

Diets high in saturated fat and cholesterol facilitate weight gain, a predisposing factor that contributes to the onset of obesity and metabolic disorders. Hepatic oxidative stress is commonly reported in various animal models of obesity and has been associated with enhanced expression of NADPH oxidase. We have previously reported several antioxidant mechanisms through which folic acid confers protection during hyperhomocysteinemia-induced oxidative stress. The objective of the present study was to investigate whether folic acid supplementation ameliorates high-fat diet induced oxidative stress in the liver, and to identify the underlying mechanisms. Male C57BL/6J mice were fed a control diet, a high-fat diet, or a high-fat diet supplemented with folic acid for 12 weeks. A high-fat diet led to increased body mass, hepatic lipid peroxidation, and liver injury. There was a significant increase in hepatic NADPH oxidase activity, which was associated with enhanced expression of several NADPH-oxidase subunits. Folic acid supplementation had a protective effect against high-fat diet induced hepatic oxidative stress and liver injury. Further analysis revealed that the antioxidant effect of folic acid was attributed, in part, to transcriptional regulation of NADPH oxidase. These results suggested that folic acid supplementation may be hepatoprotective from liver injury associated with a high-fat diet.

Regulation of stress-associated scaffold proteins JIP1 and JIP3 on the c-Jun NH2-terminal kinase in ischemia-reperfusion

Ischemia-reperfusion (IR)-induced cell apoptosis involves the activation of c-Jun NH2-terminal kinase (JNK). The activation of JNK requires the presence of scaffold proteins called JNK-interacting proteins (JIP), which bind several members of a signaling cascade for proper signaling specificity. In this study, the expression of scaffold proteins JIP1 and JIP3 and their roles in the regulation of JNK activity were investigated in simulated IR in a cell model (H9c2). JIP1 protein expression was significantly decreased, whereas JIP3 protein expression was increased in IR H9c2 cells. Adenovirus-induced overexpression of JIP1 reduced IR-induced JNK activity and apoptosis. Conversely, overexpression of JIP3 increased JNK activity and apoptosis following IR. Depletion of endogenous JIP1 by siRNA treatment increased the IR-induced JNK activity, whereas siRNA-mediated depletion of endogenous JIP3 inhibited JNK activity. These results suggest that JIP1 and JIP3 play important roles in the activation of JNK during simulated IR challenge in H9c2 cells.

Regulation of hepatic cholesterol biosynthesis by berberine during hyperhomocysteinemia

Hyperhomocysteinemia, an elevation of blood homocysteine levels, is a metabolic disorder associated with dysfunction of multiple organs. We previously demonstrated that hyperhomocysteinemia stimulated hepatic 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase leading to hepatic lipid accumulation and liver injury. The liver plays an important role in cholesterol biosynthesis and overall homeostasis. HMG-CoA reductase catalyzes the rate-limiting step in cholesterol biosynthesis. Hepatic HMG-CoA reductase is a major target for lowering cholesterol levels in patients with hypercholesterolemia. The aim of the present study was to examine the effect of berberine, a plant-derived alkaloid, on hepatic cholesterol biosynthesis in hyperhomocysteinemic rats and to identify the underlying mechanism. Hyperhomocysteinemia was induced in Sprague-Dawley rats by feeding a high-methionine diet for 4 wk. HMG-CoA reductase activity was markedly elevated in the liver of hyperhomocysteinemic rats, which was accompanied by hepatic lipid accumulation. Activation of HMG-CoA reductase was caused by an increase in its gene expression and a reduction in its phosphorylation (an inactive form of the enzyme). Treatment of hyperhomocysteinemic rats with berberine for 5 days inhibited HMG-CoA reductase activity and reduced hepatic cholesterol content. Such an inhibitory effect was mediated by increased phosphorylation of HMG-CoA reductase. Berberine treatment also improved liver function. These results suggest that berberine regulates hepatic cholesterol biosynthesis via increased phosphorylation of HMG-CoA reductase. Berberine may be therapeutically useful for the management of cholesterol homeostasis.

Folic acid supplementation inhibits NADPH oxidase-mediated superoxide anion production in the kidney

Hyperhomocysteinemia, a condition of elevated blood homocysteine (Hcy) levels, is a metabolic disease. It is a common clinical finding in patients with chronic kidney diseases and occurs almost uniformly in patients with end-stage renal disease. Hyperhomocysteinemia is also a risk factor for cardiovascular disease. Our recent studies indicate that hyperhomocysteinemia can lead to renal injury by inducing oxidative stress. Oxidative stress is one of the important mechanisms contributing to Hcy-induced tissue injury. Folic acid supplementation is regarded as a promising approach for prevention and treatment of cardiovascular disease associated with hyperhomocysteinemia due to its Hcy-lowering effect. However, its effect on the kidney is not clear. The aim of this study was to examine the effect of folic acid supplementation on Hcy-induced superoxide anion production via nicotinamide adenine dinucleotide phosphate (NADPH) oxidase in the kidney during hyperhomocysteinemia. Hyperhomocysteinemia was induced in male Sprague-Dawley rats fed a high-methionine diet for 12 wk with or without folic acid supplementation. A group of rats fed a regular diet was used as control. There was a significant increase in levels of superoxide anions and lipid peroxides in kidneys isolated from hyperhomocysteinemic rats. Activation of NADPH oxidase was responsible for hyperhomocysteinemia-induced oxidative stress in the kidney. Folic acid supplementation effectively antagonized hyperhomocysteinemia-induced oxidative stress via its Hcy-lowering and Hcy-independent effect. In vitro study also showed that 5-methyltetrahydrofolate, an active form of folate, effectively reduced Hcy-induced superoxide anion production via NADPH oxidase. Xanthine oxidase activity was increased and superoxide dismutase (SOD) activity was decreased in the kidney of hyperhomocysteinemic rats, which might also contribute to an elevation of superoxide anion level in the kidney. Folic acid supplementation attenuated xanthine oxidase activity and restored SOD activity in the kidney of hyperhomocysteinemic rats. These results suggest that folic acid supplementation may offer renal protective effect against oxidative stress.

Ischemia/reperfusion reduces transcription factor Sp1-mediated cystathionine beta-synthase expression in the kidney

Cystathionine beta-synthase (CBS) is a key enzyme that catalyzes the rate-limiting step for homocysteine (Hcy) metabolism via the trans-sulfuration pathway and is also responsible for the production of H(2)S through the desulfhydration reaction. Our recent studies demonstrate that renal ischemia/reperfusion decreased the CBS activity leading to Hcy accumulation and H(2)S reduction in the kidney, which in turn contributed to kidney injury. Both Hcy and H(2)S play important roles in physiological and pathological processes. In this study we investigated the molecular mechanism by which CBS activity was regulated in the kidney. The left kidney of Sprague-Dawley rat was subjected to 45 min of ischemia followed by 6 h of reperfusion. Ischemia/reperfusion caused a significant decrease in CBS mRNA and protein levels in the kidney. As a consequence, there was a marked reduction in the CBS enzyme activity. Transfection of kidney proximal tubular cells with transcription factor (Sp1) small interfering RNA caused a marked reduction in CBS mRNA, indicating a pivotal role for Sp1 in regulating CBS expression in kidney cells. Electrophoretic mobility shift assay and chromatin immunoprecipitation assay detected a lower Sp1 activity in kidneys subjected to ischemia/reperfusion as compared with that in a sham-operated group. ERK-mediated phosphorylation of Sp1 was responsible for a decreased transcriptional activity of Sp1 in the kidney upon ischemia/reperfusion. These results suggest that reduced kidney CBS gene expression during ischemia/reperfusion is mediated via a decrease in Sp1 transcriptional activity. Regulation of CBS-mediated Hcy and H(2)S homeostasis may offer a renal protective effect against ischemia/reperfusion injury.

Berberine inhibits NADPH oxidase mediated superoxide anion production in macrophagesThis article is one of a selection of papers published in a Special Issue on Oxidative Stress in Health and Disease

Oxidative stress and amplified redox signaling contribute to the pathogenesis of many human diseases including atherosclerosis. The superoxide-generating phagocytic NADPH oxidase is a key source of oxidative stress in the developing atheroma. The aim of the present study was to examine the effect of berberine, a plant-derived alkaloid, on NADPH oxidase-mediated superoxide anion production in macrophages. Lipopolysaccharide (LPS) treatment activated NADPH oxidase in THP-1 monocyte-derived macrophages and increased the intracellular level of superoxide anions. Preincubation of cells with berberine demonstrated a concentration-dependent (10–50 µmol/L) and time-dependent (6–24 h) inhibition of superoxide anion generation in LPS-stimulated macrophages. Cell viability tests confirmed that berberine, at concentrations sufficient for inhibiting NADPH oxidase-mediated superoxide anion generation in macrophages, did not affect cell viability. Real-time PCR analysis revealed that addition of berberine to the culture medium was able to reduce gp91phox mRNA expression in LPS-treated cells. Berberine also restored superoxide dismutase (SOD) activity, which was found to be inhibited by LPS treatment. In conclusion, results from the present study demonstrate that berberine can effectively reduce intracellular superoxide levels in LPS- stimulated macrophages. Such a restoration of cellular redox by berberine is mediated by its selective inhibition of gp91phox expression and enhancement of SOD activity. The therapeutic relevance of berberine in the prevention and management of atherosclerosis remains to be further investigated.

Induction of hepatic cyclooxygenase-2 by hyperhomocysteinemia via nuclear factor-κB activation

Hyperhomocysteinemia, an elevation of blood homocysteine (Hcy), is a metabolic disorder associated with dysfunction of multiple organs. Apart from endothelial dysfunction, Hcy can cause hepatic lipid accumulation and liver injury. However, the mechanism responsible for Hcy-induced liver injury is poorly understood. The aim of this study was to investigate the regulation of cyclooxygenase-2 (COX-2), a proinflammatory factor, expression in the liver during the initial phase of hyperhomocysteinemia. Sprague-Dawley rats were fed a high-methionine diet for 1 or 4 wk. Serum and liver concentrations of Hcy were significantly elevated after 1 or 4 wk of dietary treatment. COX-2 mRNA and protein levels were significantly elevated in the liver of hyperhomocysteinemic rats. The induction of COX-2 expression was more prominent in 1-wk hyperhomocysteinemic rats than that in the 4-wk group. EMSA revealed an activation of NF-κB in the same liver tissue in which COX-2 was induced. Administration of a NF-κB inhibitor to hyperhomocysteinemic rats effectively abolished hepatic COX-2 expression, inhibited the formation of inflammatory foci, and improved liver function. Further investigation revealed that oxidative stress due to increased superoxide generation was responsible for increased phosphorylation and degradation of IκBα leading to NF-κB activation in the liver. Administration of 4-hydroxy-tetramethyl-piperidine-1-oxyl, an SOD mimetic, to hyperhomocysteinemic rats not only inhibited NF-κB activation but also prevented hepatic COX-2 induction and improved liver function. These results suggest that hyperhomocysteinemia-induced COX-2 expression is mediated via NF-κB activation. Increased oxidative stress and inflammatory response may contribute to liver injury associated with hyperhomocysteinemia.

Ischemia-reperfusion reduces cystathionine-beta-synthase-mediated hydrogen sulfide generation in the kidney

Cystathionine-beta-synthase (CBS) catalyzes the rate-limiting step in the transsulfuration pathway for the metabolism of homocysteine (Hcy) in the kidney. Our recent study demonstrates that ischemia-reperfusion reduces the activity of CBS leading to Hcy accumulation in the kidney, which in turn contributes to renal injury. CBS is also capable of catalyzing the reaction of cysteine with Hcy to produce hydrogen sulfide (H(2)S), a gaseous molecule that plays an important role in many physiological and pathological processes. The aim of the present study was to examine the effect of ischemia-reperfusion on CBS-mediated H(2)S production in the kidney and to determine whether changes in the endogenous H(2)S generation had any impact on renal ischemia-reperfusion injury. The left kidney of Sprague-Dawley rat was subjected to 45-min ischemia followed by 6-h reperfusion. The ischemia-reperfusion caused lipid peroxidation and cell death in the kidney. The CBS-mediated H(2)S production was decreased, leading to a significant reduction in the renal H(2)S level. The activity of cystathionine-gamma-lyase, another enzyme responsible for endogenous H(2)S generation, was not significantly altered in the kidney upon ischemia-reperfusion. Partial restoration of CBS activity by intraperitoneal injection of the nitric oxide scavenger, 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide not only increased renal H(2)S levels but also alleviated ischemia-reperfusion-induced lipid peroxidation and reduced cell damage in the kidney tissue. Furthermore, administration of an exogenous H(2)S donor, NaHS (100 microg/kg), improved renal function. Taken together, these results suggest that maintenance of tissue H(2)S level may offer a renal protective effect against ischemia-reperfusion injury.

Inhibition of cystathionine-beta-synthase activity during renal ischemia-reperfusion: role of pH and nitric oxide

Our recent study (Prathapasinghe GA, Siow YL, O K. Am J Physiol Renal Physiol 292: F1354-F1363, 2007) indicates that homocysteine (Hcy) plays a detrimental role in ischemia-reperfusion-induced renal injury. Elevation of renal Hcy concentration during ischemia-reperfusion is attributed to reduced activity of cystathionine-beta-synthase (CBS) that catalyzes the rate-limiting step in the transsulfuration pathway for the metabolism of the majority of Hcy in the kidney. However, the mechanisms of impaired CBS activity in the kidney are unknown. The aim of this study was to investigate the effects of pH and nitric oxide (NO) on the CBS activity in the kidney during ischemia-reperfusion. The left kidney of a Sprague-Dawley rat was subjected to ischemia-reperfusion. The CBS activity was significantly reduced in kidneys subjected to ischemia alone (15-60 min) or subjected to ischemia followed by reperfusion for 1-24 h. The pH was markedly reduced in kidneys upon ischemia. Injection of alkaline solution into the kidney partially restored the CBS activity during ischemia. Further analysis revealed that reduction of CBS activity during reperfusion was accompanied by an elevation of NO metabolites (nitrate and nitrite) in the kidney tissue. Injection of a NO scavenger, 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO), restored the CBS activity in the kidneys subjected to ischemia-reperfusion. Treatment with PTIO could abolish ischemia-reperfusion-induced lipid peroxidation and prevent cell death in the kidney. These results suggested that metabolic acidosis during ischemia and accumulation of NO metabolites during reperfusion contributed, in part, to reduced CBS activity leading to an elevation of renal Hcy levels, which in turn, played a detrimental role in the kidney.

Homocysteine stimulates monocyte chemoattractant protein-1 expression in mesangial cells via NF-kappaB activation

Hyperhomocysteinemia is regarded as an independent risk factor for cardiovascular disorders. Although renal dysfunction or failure is one of the important factors causing hyperhomocysteinemia, the role of homocysteine (Hcy) in the development of glomerulosclerosis is largely unknown. One of the key events in the pathogenesis of glomerulosclerosis is the infiltration of circulating monocytes into affected glomeruli. The objective of the present study was to investigate the effect of Hcy on the expression of monocyte chemoattractant protein-1 (MCP-1) in kidney mesangial cells and the mechanisms involved. Levels of MCP-1 and mRNA were significantly elevated in Hcy-treated rat mesangial cells. This increase was associated with activation of NF-kappaB as a result of increased phosphorylation of the inhibitor protein IkappaBalpha. Monocyte chemotactic activity in these cells was also enhanced. In addition, there was a significant elevation of superoxide anion produced by Hcy-treated cells, which preceded the increased phosphorylation of IkappaBalpha. Addition of superoxide dismutase or NF-kappaB inhibitors to the culture medium abolished Hcy-induced NF-kappaB activation and MCP-1 expression. Taken together, these results indicate that Hcy induced MCP-1 expression in mesangial cells. Such a process was mediated by oxidative stress and NF-kappaB activation. This may further aggravate renal function in patients with hyperhomocysteinemia.

Homocysteine stimulates monocyte chemoattractant protein-1 expression in the kidney via nuclear factor-κB activation

Hyperhomocysteinemia, or an elevation of blood homocysteine (Hcy) levels, is associated with cardiovascular disorders. Although kidney dysfunction is an important risk factor causing hyperhomocysteinemia, the direct effect of Hcy on the kidney is not well documented. There is a positive association between an elevation of blood Hcy levels and the development of chronic kidney disease. Inflammatory response such as increased chemokine expression has been implicated as one of the mechanisms for renal disease. Monocyte chemoattractant protein-1 (MCP-1) is a potent chemokine that is involved in the inflammatory response in renal disease. Nuclear factor-κB (NF-κB) plays an important role in upregulation of MCP-1 expression. We investigated the effect of hyperhomocysteinemia on MCP-1 expression and the molecular mechanism underling such an effect in rat kidneys as well as in proximal tubular cells. Hyperhomocysteinemia was induced in rats fed a high-methionine diet for 12 wk. The MCP-1 mRNA expression and MCP-1 protein levels were significantly increased in kidneys isolated from hyperhomocysteinemic rats. The NF-κB activity was significantly increased in the same kidneys. Pretreatment of hyperhomocysteinemic rats with a NF-κB inhibitor abolished hyperhomocysteinemia-induced MCP-1 expression in the kidney. To confirm the causative role of NF-κB activation in MCP-1 expression, human kidney proximal tubular cells were transfected with decoy NF-κB oligodeoxynucleotide to inhibit NF-κB activation. Such a treatment prevented Hcy-induced MCP-1 mRNA expression in tubular cells. Our results suggest that hyperhomocysteinemia stimulates MCP-1 expression in the kidney via NF-κB activation. Such an inflammatory response may contribute to renal injury associated with hyperhomocysteinemia.