Aged garlic extract maintains cardiovascular homeostasis in mice and rats

Deodorized Garlic Decreases Oxidative Stress Caused by Lipopolysaccharide in Rat Heart through Hydrogen Sulfide: Preliminary Findings

Deodorized garlic (DG) may favor the activity of the antioxidant enzymes and promote the synthesis of hydrogen sulfide (H₂S). The objective was to test if DG favors an increase in H₂S and if it decreases the oxidative stress caused by lipopolysaccharide (LPS) in rat hearts. A total of 24 rats were divided into 4 groups: Group 1 control (C), Group 2 LPS, Group 3 DG, and Group 4 LPS plus DG. The cardiac mechanical performance (CMP), coronary vascular resistance (CVR), and oxidative stress markers, such as total antioxidant capacity (TAC), glutathione (GSH), selenium (Se), lipid peroxidation (LPO), thiols, hydrogen sulfide (H₂S), and the activities and expressions of thioredoxin reductase (TrxR), glutathione peroxidase (GPx), and glutathione-S-transferase (GST), cystathionine synthetase (CBS), cystathionine γ-lyase (CTH), iNOS, and eNOS-p, were analyzed in the heart. Infarct zones in the cardiac tissue were present (p = 0.01). The CMP and CVR decreased and increased (p ≤ 0.05), TAC, GSH, H₂S, NO, thiols, and GST activity (p ≤ 0.01) decreased, and LPO and iNOS increased (p ≤ 0.05). The activities and expressions of TrxR, GPx, eNOS-p, CTH, and CBS (p ≤ 0.05) decreased with the LPS treatment; however, DG normalized this effect. DG treatment decreases heart damage caused by LPS through the cross-talk between the H₂S and NO systems.

Effect of resistance training and garlic extract on insulin sensitivity/resistance and biochemical parameters in diabetic rats

Diabetes is one of the most important endocrine diseases in the world and obesity is one of the risk factors for this disease. The aim of this study was to evaluate the effect of a resistance exercise and garlic extract on insulin sensitivity/resistance and signal pathway of white adipose tissue to brown factors in diabetic rats. A total of 48 male Wistar rats weighing 180 to 250 g were divided into six groups (n=8): healthy control (C), diabetic control (D), diabetic with garlic extract at a dose of 50 mg/kg body weight (bw) (D+50), diabetic with garlic extract dose of 200 mg/kg bw (D+200), diabetic resistance training (D+Ex), and diabetic resistance training with garlic extract dose of 200 mg/kg bw (D+Ex+200). Plasma irisin levels in the D+200 and D+Ex groups, as well as the D+Ex+200 group showed a significant increase compared to the D group (P<0.001), while in the D+50 group no significant change was observed. Compared with group D, the expression of peroxisome proliferator-activated receptor-gamma coactivator (PGC)-1α gene was significantly increased in groups D+200 and D+Ex, as well as group D+Ex+200 (P<0.001). It can be said that resistance exercise with garlic extract is effective in controlling diabetes and reducing its complications. It also increases the expression of PGC-1α and uncoupling protein 1 genes in white adipose tissue and therefore has a positive effect on beta cell function by irisin.

Antihypertensive phytocomplexes of proven efficacy and well-established use: Mode of action and individual characterization of the active constituents

Hypertension has become the leading risk factor for worldwide cardiovascular diseases. Conventional pharmacological treatment, after both dietary and lifestyle changes, is generally proposed. In this review, we present the antihypertensive properties of phytocomplexes from thirteen plants, long ago widely employed in ethnomedicines and, in recent years, increasingly evaluated for their activity in vitro and in vivo, also in humans, in comparison with synthetic drugs acting on the same systems. Here, we focus on the demonstrated or proposed mechanisms of action of such phytocomplexes and of their constituents proven to exert cardiovascular effects. Almost seventy phytochemicals are described and scientifically sound pertinent literature, published up to now, is summarized. The review emphasizes the therapeutic potential of these natural substances in the treatment of the 'high normal blood pressure' or 'stage 1 hypertension', so-named according to the most recent European and U.S. guidelines, and as a supplementation in more advanced stages of hypertension, however needing further validation by clinical trial intensification.

Antioxidant and hypolipidemic potential of aged garlic extract and its constituent, s-allyl cysteine, in rats

Aged garlic extract (AGE) is one of the unique preparations standardized with 100% bioavailable active ingredients found in the bloodstream. The current research was aimed at exploring the role of AGE and its chief active constituent, s-allyl cysteine (SAC) as antioxidant and hypolipidemic agent in rats. At the end of treatment of AGE and SAC, separated serum and freshly prepared liver tissue homogenate were analyzed for biochemical enzymes and biomarkers to evaluate and compare potencies of investigational agents. Both AGE and SAC significantly declined elevated levels of triglyceride, total cholesterol, ALP, AST, ALT, malondialdehyde, glutathione peroxidase enzyme activity, total glutathione and oxidised glutathione in serum and inclined superoxide dismutase, catalase, ferric reducing/antioxidant power, and total sulfhydryl values in liver tissue with reduction in thiobarbituric acid reactive species. The protective effects were superior with AGE compared with SAC indicating potential implication of other active constituents apart from SAC in AGE for combating hyperlipidemic stress.

Proteomic analysis of the effects of aged garlic extract and its FruArg component on lipopolysaccharide-induced neuroinflammatory response in microglial cells

Aged garlic extract (AGE) is widely used as a dietary supplement, and is claimed to promote human health through anti-oxidant/anti-inflammatory activities with hypolipidemic, antiplatelet and neuroprotective effects. Prior studies of AGE have mainly focused on its organosulfur compounds, with little attention paid to its carbohydrate derivatives, such as N-α-(1-deoxy-D-fructos-1-yl)-L-arginine (FruArg). The goal of this study is to investigate actions of AGE and FruArg on antioxidative and neuroinflammatory responses in lipopolysaccharide (LPS)-activated murine BV-2 microglial cells using a proteomic approach. Our data show that both AGE and FruArg can significantly inhibit LPS-induced nitric oxide (NO) production in BV-2 cells. Quantitative proteomic analysis by combining two dimensional differential in-gel electrophoresis (2D-DIGE) with mass spectrometry revealed that expressions of 26 proteins were significantly altered upon LPS exposure, while levels of 20 and 21 proteins exhibited significant changes in response to AGE and FruArg treatments, respectively, in LPS-stimulated BV-2 cells. Notably, approximate 78% of the proteins responding to AGE and FruArg treatments are in common, suggesting that FruArg is a major active component of AGE. MULTICOM-PDCN and Ingenuity Pathway Analyses indicate that the proteins differentially affected by treatment with AGE and FruArg are involved in inflammatory responses and the Nrf2-mediated oxidative stress response. Collectively, these results suggest that AGE and FruArg attenuate neuroinflammatory responses and promote resilience in LPS-activated BV-2 cells by suppressing NO production and by regulating expression of multiple protein targets associated with oxidative stress.

Development of an Antioxidant Phytoextract of Lantana grisebachii with Lymphoprotective Activity against In Vitro Arsenic Toxicity

Phytochemicals have been presumed to possess prophylactic and curative properties in several pathologies, such as arsenic- (As-) induced immunosuppression. Our aim was to discover a lymphoprotective extract from Lantana grisebachii Stuck. (Verbenaceae) (LG). We assessed its bioactivity and chemical composition using cell-based assays. Fractions produced from a hexane extract acutely induced nitrite formation in T-activated cell cultures (P < 0.0001). Water extraction released a fraction lacking nitrite inducing activity in both lymphocyte types. Aqueous LG was found to be safe in proliferated and proliferating cells. The infusion-derived extract presented better antioxidant capacity in proportion to phenolic amount in lymphocytes (infusive LG-1i at 100 μg/mL), which protected them against in vitro As-induced lymphotoxicity (P < 0.0001). This infusive LG phytoextract contained 10.23 ± 0.43 mg/g of phenolics, with 58.46% being flavonoids. Among the phenolics, the only predominant compound was 0.723 mg of chlorogenic acid per gram of dry plant, in addition to 10 unknown minor compounds. A fatty acid profile was assessed. It contained one-third of saturated fatty acids, one-third of ω9, followed by ω6 (~24%) and ω3 (~4%), and scarce ω7. Summing up, L. grisebachii was a source of bioactive and lymphoprotective compounds, which could counteract As-toxicity. This supports its phytomedical use and research in order to reduce As-related dysfunctions.

Effects of aged garlic extract on left ventricular diastolic function and fibrosis in a rat hypertension model

Daily consumption of garlic is known to lower the risk of hypertension and ischemic heart disease. In this study, we examined whether aged garlic extract (AGE) prevents hypertension and the progression of compensated left ventricular (LV) hypertrophy in Dahl salt-sensitive (DS) rats. DS rats were randomly divided into three groups: those fed an 8% NaCl diet until 18 weeks of age (8% NaCl group), those additionally treated with AGE (8% NaCl + AGE group), and control rats maintained on a diet containing 0.3% NaCl until 18 weeks of age (0.3% NaCl group). AGE was administered orally by gastric gavage once a day until 18 weeks of age. LV mass was significantly higher in the 8% NaCl + AGE group than in the 0.3% NaCl group at 18 weeks of age, but significantly lower in the 8% NaCl + AGE group than in the 8% NaCl group. No significant differences were observed in systolic blood pressure (SBP) between the 8% NaCl and 8% NaCl + AGE groups at 12 and 18 weeks of age. LV end-diastolic pressure and pressure half-time at 12 and 18 weeks of age were significantly lower in the 8% NaCl + AGE group compared with the 8% NaCl group. AGE significantly reduced LV interstitial fibrosis at 12 and 18 weeks of age. Chronic AGE intake attenuated LV diastolic dysfunction and fibrosis without significantly decreasing SBP in hypertensive DS rats.

Effects of aged garlic extract and endurance exercise on skeletal muscle FNDC-5 and circulating irisin in high-fat-diet rat models

BACKGROUND/OBJECTIVES

Irisin, a newly identified hormone, is associated with energy homeostasis. We investigated whether aged garlic extract (AGE) and exercise training intervention could improve body weight, insulin sensitivity, skeletal muscle fibronectin domain containing protein 5 (FNDC-5) levels, and plasma irisin in high-fat diet (HFD).

MATERIALS/METHODS

Male Sprague Dawley rats were fed a ND (normal diet, n = 5) or HFD (n = 28) for 6 weeks. After 6 weeks, all rats were divided into 5 groups for the next 4 weeks: ND, (normal diet, n = 5), HFD (high-fat diet, n = 7), HFDA (high-fat diet + aged garlic extract, n = 7), HFDE (high-fat diet + exercise, n = 7), and HFDEA (high-fat diet + exercise + aged garlic extract, n = 7). Exercise groups performed treadmill exercises for 15-60 min, 5 days/week, and AGE groups received AGE (2.86 g/kg, orally injected) for 4 weeks.

RESULTS

Significant decreases in body weight were observed in the ND, HFDE, and HFDEA groups, as compared with the HFD group. Neither intervention affected the masses of the gastrocnemius muscle or liver. There were no significant differences in glucose levels across the groups. The homeostatic model assessments of insulin resistance were significantly higher in the HFD group, as compared with the ND, HFDA, HFDE, and HFDEA groups. However, skeletal muscle FNDC-5 levels and plasma irisin concentrations were unaffected by AGE or exercise in obese rats. AGE supplementation and exercise training did not affect skeletal muscle FNDC-5 or plasma irisin, which are associated with insulin sensitivity in obese rats.

CONCLUSION

Our results suggest that the protection against HFD-induced increases in body fat/weight and insulin resistance that are provided by AGE supplementation and exercise training may not be mediated by the regulation of FNDC-5 or irisin.

Mechanisms underlying the antihypertensive effects of garlic bioactives

Cardiovascular disease remains the leading cause of death worldwide with hypertension being a major contributing factor to cardiovascular disease-associated mortality. On a population level, non-pharmacological approaches, such as alternative/complementary medicine, including phytochemicals, have the potential to ameliorate cardiovascular risk factors, including high blood pressure. Several epidemiological studies suggest an antihypertensive effect of garlic (Allium sativum) and of many its bioactive components. The aim of this review is to present an in-depth discussion regarding the molecular, biochemical and cellular rationale underlying the antihypertensive properties of garlic and its bioactive constituents with a primary focus on S-allyl cysteine and allicin. Key studies, largely from PubMed, were selected and screened to develop a comprehensive understanding of the specific role of garlic and its bioactive constituents in the management of hypertension. We also reviewed recent advances focusing on the role of garlic bioactives, S-allyl cysteine and allicin, in modulating various parameters implicated in the pathogenesis of hypertension. These parameters include oxidative stress, nitric oxide bioavailability, hydrogen sulfide production, angiotensin converting enzyme activity, expression of nuclear factor-κB and the proliferation of vascular smooth muscle cells. This review suggests that garlic and garlic derived bioactives have significant medicinal properties with the potential for ameliorating hypertension and associated morbidity; however, further clinical and epidemiological studies are required to determine completely the specific physiological and biochemical mechanisms involved in disease prevention and management.

Histopathological study of the combination of metformin and garlic juice for the attenuation of gentamicin renal toxicity in rats

INTRODUCTION

Tubular toxicity is one of the most important side effects of aminoglycoside antibiotics, especially gentamicin.

OBJECTIVES

We histopathologically studied the effect of garlic extract and metformin co-administration, in attenuation of genetamicin induced tubular toxicity in rats.

MATERIALS AND METHODS

In this study seventy rats were divided into seven equal groups and except group 1 (control) were injected 100 mg/kg/day gentamicin (GM) intraperitoneally (i.p.) for 10 days. Other than GM, group III received 20 mg/kg garlic (i.p.), group IV metformin (MF) (100 mg/kg, orally), group V a combination of MF with garlic juice (100 and 20 mg/kg/day, respectively) and group VI a combination of MF and garlic juice (50 and 10 mg/kg/day, respectively) for following 10 days. Group VII received a combination of MF and garlic juice (100 and 20 mg/kg, respectively) along with GM. Animals were sacrificed on the 20(th) day of the experiment and the kidneys were removed for histological examinations.

RESULTS

GM induced nephrotoxicity and garlic or MF alone and a combination of both with high doses (not low doses) significantly abolished the kidney tubular injury induced by GM. In addition, co-administration of GM, MF and garlic (group 7) prevented the GM- induced tissue damage more than the groups in which MF and garlic were injected 10 days post GM administration.

CONCLUSION

Garlic extract and Metformin, alone or in a combination, might be safely used to ameliorate GM induced tubular toxicity.

Sildenafil restores endothelial function in the apolipoprotein E knockout mouse

Background

Atherosclerosis is an inflammatory process of the arterial walls and is initiated by endothelial dysfunction accompanied by an imbalance in the production of reactive oxygen species (ROS) and nitric oxide (NO). Sildenafil, a selective phosphodiesterase-5 (PDE5) inhibitor used for erectile dysfunction, exerts its cardiovascular effects by enhancing the effects of NO. The aim of this study was to investigate the influence of sildenafil on endothelial function and atherosclerosis progression in apolipoprotein E knockout (apoE^−/−) mice.

Methods

ApoE^−/− mice treated with sildenafil (Viagra®, 40 mg/kg/day, for 3 weeks, by oral gavage) were compared to the untreated apoE^−/− and the wild-type (WT) mice.

Aortic rings were used to evaluate the relaxation responses to acetylcholine (ACh) in all of the groups. In a separate set of experiments, the roles of NO and ROS in the relaxation response to ACh were evaluated by incubating the aortic rings with L-NAME (NO synthase inhibitor) or apocynin (NADPH oxidase inhibitor). In addition, the atherosclerotic lesions were quantified and superoxide production was assessed.

Results

Sildenafil restored the vasodilator response to acetylcholine (ACh) in the aortic rings of the apoE^−/− mice. Treatment with L-NAME abolished the vasodilator responses to ACh in all three groups of mice and revealed an augmented participation of NO in the endothelium-dependent vasodilation in the sildenafil-treated animals. The normalized endothelial function in sildenafil-treated apoE^−/− mice was unaffected by apocynin highlighting the low levels of ROS production in these animals. Moreover, morphological analysis showed that sildenafil treatment caused approximately a 40% decrease in plaque deposition in the aorta.

Conclusion

This is the first study demonstrating the beneficial effects of chronic treatment with sildenafil on endothelial dysfunction and atherosclerosis in a model of spontaneous hypercholesterolemia. These data indicate that the main mechanism of the beneficial effect of sildenafil on the endothelial function appears to involve an enhancement of the NO pathway along with a reduction in oxidative stress.

Garlic extracts prevent oxidative stress, hypertrophy and apoptosis in cardiomyocytes: a role for nitric oxide and hydrogen sulfide

Background

In ancient times, plants were recognized for their medicinal properties. Later, the arrival of synthetic drugs pushed it to the backstage. However, from being merely used for food, plants are now been widely explored for their therapeutic value. The current study explores the potential of skin and flesh extracts from a hard-necked Rocambole variety of purple garlic in preventing cardiomyocyte hypertrophy and cell death.

Methods

Norepinephrine (NE) was used to induce hypertrophy in adult rat cardiomyocytes pretreated with garlic skin and flesh extracts. Cell death was measured as ratio of rod to round shaped cardiomyocytes. Fluorescent probes were used to measure apoptosis and oxidative stress in cardiomyocytes treated with and without extracts and NE. Pharmacological blockade of nitric oxide (NO) and hydrogen sulfide (H₂S) were used to elucidate the mechanism of action of garlic extracts. Garlic extract samples were also tested for alliin and allicin concentrations.

Results

Exposure of cardiomyocytes to NE induced an increase in cell size and cell death; this increase was significantly prevented upon treatment with garlic skin and flesh extracts. Norepinephrine increased apoptosis and oxidative stress in cardiomyocytes which was prevented upon pretreatment with skin and flesh extracts; NO, and H₂S blockers significantly inhibited this beneficial effect. Allicin and alliin concentration were significantly higher in garlic flesh extract when compared to the skin extract.

Conclusion

These results suggest that both skin and flesh garlic extracts are effective in preventing NE induced cardiomyocyte hypertrophy and cell death. Reduction in oxidative stress may also play an important role in the anti-hypertrophic and anti-apoptotic properties of garlic extracts. These beneficial effects may in part be mediated by NO and H₂S.

Independent beneficial effects of aged garlic extract intake with regular exercise on cardiovascular risk in postmenopausal women

The purpose of the study was to assess the effects of a 12 weeks aged garlic extract (AGE) regimen with regular exercise on cardiovascular disease (CVD) risk in postmenopausal women. A total of 30 postmenopausal women (54.4 ± 5.4 years) were randomly divided into the following four groups: Placebo (Placebo; n = 6), AGE intake (AGEI; n = 8), exercise and placebo (Ex + Placebo; n = 8), exercise and AGE (Ex + AGE; n = 8) groups. The AGE group consume 80 mg per day, and exercise groups performed moderate exercise (aerobic and resistance) three times per week. After 12 weeks of treatment, body composition, lipid profile, and CVD risk factors were analyzed. Body weight was significantly decreased in AGEI, Ex + Placebo, and Ex + AGE groups compared to baseline. Body fat % was significantly decreased in the AGEI and Ex + Placebo groups. Body mass index (BMI) was significantly decreased in the AGEI, Ex + Placebo, and Ex + AGE groups. Fat-free mass was significantly decreased in the AGEI group. Total cholesterol (TC) was significantly lower in the Ex + Placebo compared to the Placebo group. AGE supplementation or exercise effectively reduced low-density lipoprotein (LDL-C). Triglyceride (TG) was significantly increased in the AGEI group. Malondialdehyde (MDA) levels were significantly decreased in the AGEI, Ex + Placebo, and Ex + AGE compared to the placebo group. AGE supplementation reduced homocysteine levels regardless of whether the women also exercised. The present results suggest that AGE supplementation reduces cardiovascular risk factors independently of exercise in postmenopausal women.

Biochemical and histological liver changes occurred after iron supplementation and possible remediation by garlic consumption

Iron liver excess is associated to biochemical and histological liver perturbations. Our aim was to know even if fresh garlic consumption can remediate these problems. Three groups of rats were utilized: control group A, iron overload group B and garlic and iron overload group C. Important morphological and biochemical modifications were obtained in group B rats comparatively to control group A. Indeed, body and liver weights and liver iron contents increased, respectively, by 12.5 ± 0.06%; 17 ± 0.25% and 35 ± 0.11% comparatively to controls. Radical cation scavenging ability in liver cytosol of group B rats was significantly low (54 ± 0,1%) in comparison to group A. Garlic consumption allowed the group C to achieve an increase by 46 ± 0,11 and 75 ± 0,14% of total antioxidant capacity comparatively to group A and B rats. For the serum ALAT, ASAT, triglyceride and LDH levels, they increased in iron-treated rats, respectively, by 25 ± 0.21; 15 ± 0.12; 30 ± 0.14 and 22 ± 0.16% comparatively to controls. These perturbations were accompanied by deep histological changes. After food fresh garlic supplementation, we had found a deep regulation of all modified parameters showing a hepatoprotective effect of garlic against iron liver excess. Garlic chemical compounds have curative effects on iron liver excess.

Garlic components inhibit angiotensin II-induced cell-cycle progression and migration: Involvement of cell-cycle inhibitor p27(Kip1) and mitogen-activated protein kinase

Garlic has been used for prevention and treatment of hypertension; however, the molecular mechanisms of garlic's effects remain to be elucidated. In this study, the mechanisms of the in vitro effect of organosulphur compounds derived from garlic on growth and migration of cultured aortic smooth muscle cells isolated from spontaneously hypertensive rats were investigated. We demonstrated that allyl methyl sulphide (AMS) and diallyl sulphide (DAS) inhibited aortic smooth muscle cell angiotensin II-stimulated cell-cycle progression and migration. Neither cell viability nor annexin-V-binding analysis revealed cytotoxic effects of both organosulphur compounds at the used concentrations. Instead, their inhibitory effects were associated to the prevention of the cell-cycle inhibitor p27(Kip1) (p27) downregulation and the reduction of extracellular signal-regulated kinase 1/2 phosphorylation. When we assessed the antioxidant activity of AMS and DAS, we found that both organosulphur compounds inhibited angiotensin II-reactive oxygen species generation. Our findings show that AMS and DAS, compounds derivate from garlic, could be effective antioxidants targeted at the arterial remodelling seen in hypertension.

In vivo evidence of hepato- and reno-protective effect of garlic oil against sodium nitrite-induced oxidative stress

Sodium nitrite (NaNO2), a food color fixative and preservative, contributes to carcinogenesis. We investigated the protective role of garlic oil against NaNO2-induced abnormalities in metabolic biochemical parameters and oxidative status in male albino rats. NaNO2 treatment for a period of three months induced a significant increase in serum levels of glucose, aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP), bilirubin, urea and creatinine as well as hepatic AST and ALT. However, significant decrease was recorded in liver ALP activity, glycogen content, and renal urea and creatinine levels. In parallel, a significant increase in lipid peroxidation, and a decrease in glutathione content and catalase activity were observed in the liver and the kidney. However, garlic oil supplementation showed a remarkable amelioration of these abnormalities. Our data indicate that garlic is a phytoantioxidant with powerful chemopreventive properties against chemically-induced oxidative stress.

Renoprotective and antihypertensive effects of S-allylcysteine in 5/6 nephrectomized rats

Progressive renal damage and hypertension are associated with oxidative and nitrosative stress. On the other hand, S-allylcysteine (SAC), the most abundant organosulfur compound in aged garlic extract (AG), has antioxidant properties. The effects of SAC and AG on blood pressure, renal damage, and oxidative and nitrosative stress were studied in five-sixths nephrectomized rats treated with SAC (200 mg/kg ip) and AG (1.2 ml/kg ip) every other day for 30 days. Proteinuria and serum creatinine and blood urea nitrogen concentrations were measured on days 0, 5, 10, 15, and 30, and systolic blood pressure was recorded on days 0, 15, and 30. The degree of glomerulosclerosis and tubulointerstitial damage, the immunostaining for inducible nitric oxide synthase, 3-nitrotyrosine, poly(ADP-ribose), and the subunits of NADPH oxidase p22phox and gp91phox, and the activity of SOD were determined on day 30. SAC and AG reduced hypertension, renal damage, and the abundance of inducible nitric oxide synthase, 3-nitrotyrosine, poly(ADP-ribose), p22phox, and gp91phox and increased SOD activity. Our data suggest that the antihypertensive and renoprotective effects of SAC and AG are associated with their antioxidant properties and that they may be used to ameliorate hypertension and delay the progression of renal damage.

Recent methodological advances in the analysis of nitrite in the human circulation: nitrite as a biochemical parameter of the L-arginine/NO pathway

Nitric oxide (NO) plays a pivotal role in the modulation of multiple physiological processes. It acts as a messenger molecule within the cardiovascular system. NO is a highly unstable free radical in circulating blood and is oxidized rapidly to nitrite and nitrate. Recent studies suggest that nitrite has the potential to function as a surrogate of NO production under physiological and pathophysiological conditions and could therefore be of high relevance as a biochemical parameter in experimental and clinical studies. Under hypoxic conditions nitrite is reduced to bioactive NO by deoxyhemoglobin. This mechanism may represent a dynamic cycle of NO generation to adapt the demand and supply for the vascular system. Because of these potential biological functions the concentration of nitrite in blood is thought to be of particular importance. The determination of nitrite in biological matrices represents a considerable analytical challenge. Methodological problems often arise from pre-analytical sample preparation, sample contamination due to the ubiquity of nitrite, and from lack of selectivity and sensitivity. These analytical difficulties may be a plausible explanation for reported highly diverging concentrations of nitrite in the human circulation. The aim of this article is to review the methods of quantitative analysis of nitrite in the human circulation, notably in plasma and blood, and to discuss pre-analytical and analytical factors potentially affecting accurate quantification of nitrite in these human fluids.

Chronic preconditioning: a novel approach for cardiac protection

Ischemic preconditioning is the most powerful protective mechanism known against lethal ischemia. Unfortunately, the protection lasts for only a few hours. Here we tested the hypothesis that the heart can be kept in a preconditioned state for constant protection against ischemia. In this study we chose BMS-191095 (BMS), a highly selective opener of mitochondrial ATP-sensitive K(+) (mitoK(ATP)) channels. BMS (1 mg/kg ip) was administered to rats every 24 h until 96 h. In other groups, BMS plus wortmannin (WTN, 15 microg/kg ip), an inhibitor of the phosphatidylinositol 3-kinase (PI3-K), or BMS plus 5-hydroxydecanoic acid (5-HD, 5 mg/kg ip), an inhibitor of mitoK(ATP), or BMS plus N(omega)-nitro-L-arginine methyl ester (L-NAME) (30 microg/kg ip), an inhibitor of nitric oxide (NO) synthase, were administered to rats. Rats were then subjected to 30-min left anterior descending coronary artery occlusion and 120-min reperfusion. Cardiac function, infarct size, pathological changes, and apoptosis were assessed at the end of treatments. Saline-treated hearts displayed marked contractile dysfunction and underwent pathological changes. BMS-treated rats showed significant improvement in cardiac function, and infarct size was significantly reduced in BMS-treated hearts. However, protection by BMS was abolished by 5-HD, WTN, or L-NAME. These data demonstrate that hearts can be chronically preconditioned and retain their ability to remain resistant against lethal ischemia and that this protection is mediated by activation of mitoK(ATP) via NO and PI3-K/Akt signaling pathways.