Designing a Multilevel Strategy to Enhance Secondary Prevention of Heart Disease.

Background Coronary artery calcification (CAC), the presence and severity of which strongly predict underlying coronary artery disease (CAD), can be seen on dedicated cardiac imaging studies or incidentally on noncardiac ones; however, the latter findings are commonly managed by primary care clinicians without clear accompanying recommendations and may represent an underrecognized opportunity to optimize secondary prevention of CAD. Methods Standardized practice guidelines and a multilevel implementation strategy for improving secondary prevention of cardiovascular disease through incidentally identified CAC were developed by an interdisciplinary committee. Evidence-based implementation strategies were selected1 and included integrating practice guidelines into radiology reports within the electronic medical records. Outpatient noncardiac computerized tomography scans performed before and after this initiative were retrospectively reviewed to evaluate changes in statin prescribing. Results Authors demonstrated an increase in the percentage of patients with mild CAC prescribed a statin and an increase in the percentage of patients with severe CAC prescribed a high-intensity statin after implementation of standardized practice guidelines and evidence-based implementation strategies. Conclusion Incidental CAC identification is common, particularly in those without known CAD. A multilevel implementation strategy and use of standardized practice guidelines appeared to improve provider prescribing behavior in the primary care setting and may provide an opportunity to enhance secondary CAC prevention.

Fractional Excretion of Urate for Diuresis Management in Heart Failure and Cardiorenal Syndrome.

Most heart failure hospitalizations are due to volume overload; however, it is not easily evaluated by physical examination. Avoidance of diuresis in patients with fluid overload to avoid acute kidney injury increases morbidity in heart failure. We hypothesize that fractional excretion of urate can be used to guide diuresis. (Level of Difficulty: Advanced.).

Negative spot sign in primary intracerebral hemorrhage: potential impact in reducing imaging.

Intracerebral hemorrhage (ICH) is one of the most devastating and costly diagnoses in the USA. ICH is a common diagnosis, accounting for 10-15 % of all strokes and affecting 20 out of 100,000 people. The CT angiography (CTA) spot sign, or contrast extravasation into the hematoma, is a reliable predictor of hematoma expansion, clinical deterioration, and increased mortality. Multiple studies have demonstrated a high negative predictive value (NPV) for ICH expansion in patients without spot sign. Our aim is to determine the absolute NPV of the spot sign and clinical characteristics of patients who had ICH expansion despite the absence of a spot sign. This information may be helpful in the development of a cost effective imaging protocol of patients with ICH. During a 3-year period, 204 patients with a CTA with primary intracerebral hemorrhage were evaluated for subsequent hematoma expansion during their hospitalization. Patients with intraventricular hemorrhage were excluded. Clinical characteristics and antithrombotic treatment on admission were noted. The number of follow-up NCCT was recorded. Of the resulting 123 patients, 108 had a negative spot sign and 7 of those patients subsequently had significant hematoma expansion, 6 of which were on antithrombotic therapy. The NPV of the CTA spot sign was calculated at 0.93. In patients without antithrombotic therapy, the NPV was 0.98. In summary, the negative predictive value of the CTA spot sign for expansion of ICH, in the absence of antithrombotic therapy and intraventricular hemorrhage (IVH) on admission, is very high. These results have the potential to redirect follow-up imaging protocols and reduce cost.

Fuzzy Modeling to Predict Severely Depressed Left Ventricular Ejection Fraction following Admission to the Intensive Care Unit Using Clinical Physiology.

Left ventricular ejection fraction (LVEF) constitutes an important physiological parameter for the assessment of cardiac function, particularly in the settings of coronary artery disease and heart failure. This study explores the use of routinely and easily acquired variables in the intensive care unit (ICU) to predict severely depressed LVEF following ICU admission. A retrospective study was conducted. We extracted clinical physiological variables derived from ICU monitoring and available within the MIMIC II database and developed a fuzzy model using sequential feature selection and compared it with the conventional logistic regression (LR) model. Maximum predictive performance was observed using easily acquired ICU variables within 6 hours after admission and satisfactory predictive performance was achieved using variables acquired as early as one hour after admission. The fuzzy model is able to predict LVEF ≤ 25% with an AUC of 0.71 ± 0.07, outperforming the LR model, with an AUC of 0.67 ± 0.07. To the best of the authors' knowledge, this is the first study predicting severely impaired LVEF using multivariate analysis of routinely collected data in the ICU. We recommend inclusion of these findings into triaged management plans that balance urgency with resources and clinical status, particularly for reducing the time of echocardiographic examination.

PTPMT1 Inhibition Lowers Glucose through Succinate Dehydrogenase Phosphorylation.

Virtually all organisms seek to maximize fitness by matching fuel availability with energy expenditure. In vertebrates, glucose homeostasis is central to this process, with glucose levels finely tuned to match changing energy requirements. To discover new pathways regulating glucose levels in vivo, we performed a large-scale chemical screen in live zebrafish and identified the small molecule alexidine as a potent glucose-lowering agent. We found that alexidine inhibits the PTEN-like mitochondrial phosphatase PTPMT1 and that other pharmacological and genetic means of inactivating PTPMT1 also decrease glucose levels in zebrafish. Mutation of ptpmt1 eliminates the effect of alexidine, further confirming it as the glucose-lowering target of alexidine. We then identified succinate dehydrogenase (SDH) as a substrate of PTPMT1. Inactivation of PTPMT1 causes hyperphosphorylation and activation of SDH, providing a possible mechanism by which PTPMT1 coordinates glucose homeostasis. Therefore, PTPMT1 appears to be an important regulator of SDH phosphorylation status and glucose concentration.

The effect of age and clinical circumstances on the outcome of red blood cell transfusion in critically ill patients.

INTRODUCTION: Whether red blood cell (RBC) transfusion is beneficial remains controversial. In both retrospective and prospective evaluations, transfusion has been associated with adverse, neutral, or protective effects. These varying results likely stem from a complex interplay between transfusion, patient characteristics, and clinical context. The objective was to test whether age, comorbidities, and clinical context modulate the effect of transfusion on survival. METHODS: By using the multiparameter intelligent monitoring in intensive care II database (v. 2.6), a retrospective analysis of 9,809 critically ill patients, we evaluated the effect of RBC transfusion on 30-day and 1-year mortality. Propensity score modeling and logistic regression adjusted for known confounding and assessed the independent effect of transfusion on 30-day and 1-year mortality. Sensitivity analysis was performed by using 3,164 transfused and non-transfused pairs, matched according the previously validated propensity model for RBC transfusion. RESULTS: RBC transfusion did not affect 30-day or 1-year mortality in the overall cohort. Patients younger than 55 years had increased odds of mortality (OR, 1.71; P < 0.01) with transfusion. Patients older than 75 years had lower odds of 30-day and 1-year mortality (OR, 0.70; P < 0.01) with transfusion. Transfusion was associated with worse outcome among patients undergoing cardiac surgery (OR, 2.1; P < 0.01). The propensity-matched population corroborated findings identified by regression adjustment. CONCLUSION: A complex relation exists between RBC transfusion and clinical outcome. Our results show that transfusion is associated with improved outcomes in some cohorts and worse outcome in others, depending on comorbidities and patient characteristics. As such, future investigations and clinical decisions evaluating the value of transfusion should account for variations in baseline characteristics and clinical context.

ß-Aminoisobutyric acid induces browning of white fat and hepatic ß-oxidation and is inversely correlated with cardiometabolic risk factors.

The transcriptional coactivator peroxisome proliferator-activated receptor-gamma coactivator-1α (PGC-1α) regulates metabolic genes in skeletal muscle and contributes to the response of muscle to exercise. Muscle PGC-1α transgenic expression and exercise both increase the expression of thermogenic genes within white adipose. How the PGC-1α-mediated response to exercise in muscle conveys signals to other tissues remains incompletely defined. We employed a metabolomic approach to examine metabolites secreted from myocytes with forced expression of PGC-1α, and identified ß-aminoisobutyric acid (BAIBA) as a small molecule myokine. BAIBA increases the expression of brown adipocyte-specific genes in white adipocytes and ß-oxidation in hepatocytes both in vitro and in vivo through a PPARα-mediated mechanism, induces a brown adipose-like phenotype in human pluripotent stem cells, and improves glucose homeostasis in mice. In humans, plasma BAIBA concentrations are increased with exercise and inversely associated with metabolic risk factors. BAIBA may thus contribute to exercise-induced protection from metabolic diseases.

Role of endothelial progenitor cells and inflammatory cytokines in healing of diabetic foot ulcers.

BACKGROUND: To evaluate changes in endothelial progenitor cells (EPCs) and cytokines in patients with diabetic foot ulceration (DFU) in association with wound healing. METHODS: We studied healthy subjects, diabetic patients not at risk of DFU, at risk of DFU and with active DFU. We prospectively followed the DFU patients over a 12-week period. We also investigated similar changes in diabetic rabbit and mouse models of wound healing. RESULTS: All EPC phenotypes except the kinase insert domain receptor (KDR)(+)CD133(+) were reduced in the at risk and the DFU groups compared to the controls. There were no major EPC differences between the control and not at risk group, and between the at risk and DFU groups. Serum stromal-cell derived factor-1 (SDF-1) and stem cell factor (SCF) were increased in DFU patients. DFU patients who healed their ulcers had lower CD34(+)KDR(+) count at visits 3 and 4, serum c-reactive protein (CRP) and granulocyte-macrophage colony-stimulating factor (GM-CSF) at visit 1, interleukin-1 (IL-1) at visits 1 and 4. EPCs tended to be higher in both diabetic animal models when compared to their non-diabetic counterparts both before and ten days after wounding. CONCLUSIONS: Uncomplicated diabetes does not affect EPCs. EPCs are reduced in patients at risk or with DFU while complete wound healing is associated with CD34(+)KDR(+) reduction, suggesting possible increased homing. Low baseline CRP, IL-1α and GM-CSF serum levels were associated with complete wound healing and may potentially serve as prognostic markers of DFU healing. No animal model alone is representative of the human condition, indicating the need for multiple experimental models.

2-Aminoadipic acid is a biomarker for diabetes risk.

Improvements in metabolite-profiling techniques are providing increased breadth of coverage of the human metabolome and may highlight biomarkers and pathways in common diseases such as diabetes. Using a metabolomics platform that analyzes intermediary organic acids, purines, pyrimidines, and other compounds, we performed a nested case-control study of 188 individuals who developed diabetes and 188 propensity-matched controls from 2,422 normoglycemic participants followed for 12 years in the Framingham Heart Study. The metabolite 2-aminoadipic acid (2-AAA) was most strongly associated with the risk of developing diabetes. Individuals with 2-AAA concentrations in the top quartile had greater than a 4-fold risk of developing diabetes. Levels of 2-AAA were not well correlated with other metabolite biomarkers of diabetes, such as branched chain amino acids and aromatic amino acids, suggesting they report on a distinct pathophysiological pathway. In experimental studies, administration of 2-AAA lowered fasting plasma glucose levels in mice fed both standard chow and high-fat diets. Further, 2-AAA treatment enhanced insulin secretion from a pancreatic ß cell line as well as murine and human islets. These data highlight a metabolite not previously associated with diabetes risk that is increased up to 12 years before the onset of overt disease. Our findings suggest that 2-AAA is a marker of diabetes risk and a potential modulator of glucose homeostasis in humans.

APACHE II scoring to predict outcome in post-cardiac arrest.

INTRODUCTION: Despite advancements in management of cardiac arrest, mortality remains high and few severity of illness scoring systems have been calibrated in this population. The goal of the current investigation was to assess the Acute Physiology and Chronic Health Evaluation II score in post-cardiac arrest. MEASUREMENTS: This is a prospective observational study of adult post-cardiac arrest patients at a tertiary-care center. The primary outcome variable was in-hospital mortality and secondary outcome variable was neurologic outcome. APACHE II scores were used to predict outcomes using logistic modeling. MAIN RESULTS: A total of 228 subjects were included in the analysis. The median age of the cohort was 70 (IQR: 64-71) and 32% (72/228) of the patients were female. The median downtime was 15 min (IQR: 7-27) and initial lactate 5.9 mmol/L (IQR: 3.5-8.4). 71 (57%) of deaths occurred prior to the 72-h follow-up and overall in-hospital mortality was 55% (125/228). Discrimination of APACHE II score in all cardiac arrest patients increased in stepwise fashion from 0-h to 72-h follow-up (AUC: 0-h: 0.62; 24-h: 0.75; 48-h: 0.82; 72-h: 0.86). CONCLUSIONS: APACHE II score is a poor predictor of outcome at time zero for out-of-hospital cardiac arrest (OHCA) post-arrest patients consistent with the original development of the score in the critically ill. For in-hospital cardiac arrest (IHCA) at time zero and for both IHCA and OHCA at 24h and beyond, the APACHE II score was a modest indicator of illness severity and predictor of mortality/neurologic morbidity.

Metabolite profiling identifies pathways associated with metabolic risk in humans.

BACKGROUND: Although metabolic risk factors are known to cluster in individuals who are prone to developing diabetes mellitus and cardiovascular disease, the underlying biological mechanisms remain poorly understood. METHODS AND RESULTS: To identify pathways associated with cardiometabolic risk, we used liquid chromatography/mass spectrometry to determine the plasma concentrations of 45 distinct metabolites and to examine their relation to cardiometabolic risk in the Framingham Heart Study (FHS; n=1015) and the Malmö Diet and Cancer Study (MDC; n=746). We then interrogated significant findings in experimental models of cardiovascular and metabolic disease. We observed that metabolic risk factors (obesity, insulin resistance, high blood pressure, and dyslipidemia) were associated with multiple metabolites, including branched-chain amino acids, other hydrophobic amino acids, tryptophan breakdown products, and nucleotide metabolites. We observed strong associations of insulin resistance traits with glutamine (standardized regression coefficients, -0.04 to -0.22 per 1-SD change in log-glutamine; P<0.001), glutamate (0.05 to 0.14; P<0.001), and the glutamine-to-glutamate ratio (-0.05 to -0.20; P<0.001) in the discovery sample (FHS); similar associations were observed in the replication sample (MDC). High glutamine-to-glutamate ratio was associated with lower risk of incident diabetes mellitus in FHS (odds ratio, 0.79; adjusted P=0.03) but not in MDC. In experimental models, administration of glutamine in mice led to both increased glucose tolerance (P=0.01) and decreased blood pressure (P<0.05). CONCLUSIONS: Biochemical profiling identified circulating metabolites not previously associated with metabolic traits. Experimentally interrogating one of these pathways demonstrated that excess glutamine relative to glutamate, resulting from exogenous administration, is associated with reduced metabolic risk in mice.

Benefit of transferring ST-segment-elevation myocardial infarction patients for percutaneous coronary intervention compared with administration of onsite fibrinolytic declines as delays increase.

BACKGROUND: Although randomized trials suggest that transfer for primary percutaneous coronary intervention (X-PCI) in ST-segment-elevation myocardial infarction is superior to onsite fibrinolytic therapy (O-FT), the generalizability of these findings to routine clinical practice is unclear because door-to-balloon (XDB) times are rapid in randomized trials but are frequently prolonged in practice. We hypothesized that delays resulting from transfer would reduce the survival advantage of X-PCI compared with O-FT. METHODS AND RESULTS: ST-segment-elevation myocardial infarction patients enrolled in the National Registry of Myocardial Infarction (NRMI) within 12 hours of pain onset were identified. Propensity matching of patients treated with X-PCI and O-FT was performed, and the effect of PCI-related delay on in-hospital mortality was assessed. PCI-related delay was calculated by subtracting the XDB from the door-to-needle time in each matched pair. Conditional logistic regression adjusted for patient and hospital variables identified the XDB door-to-needle time at which no mortality advantage for X-PCI over O-FT was present. Eighty-one percent of X-PCI patients were matched (n=9506) to O-FT patients (n=9506). In the matched cohort, X-PCI was performed with delays >90 minutes in 68%. Multivariable analysis found no mortality advantage for X-PCI over O-FT when XDB door-to-needle time exceeded ≈120 minutes. CONCLUSION: PCI-related delays are extensive among patients transferred for X-PCI and are associated with poorer outcomes. No differential excess in mortality was seen with X-PCI compared with O-FT even with long PCI-related delays, but as XDB door-to-needle time times increase, the mortality advantage for X-PCI over O-FT declines.

Repeated successful balloon valvuloplasty of a bioprosthetic aortic valve in a nonagenerian.

Calcific aortic stenosis remains a major cause of mortality and morbidity in the aging population. Surgical replacement remains the treatment of choice for this disease. Balloon aortic valvuloplasty was introduced as a palliative procedure for these patients, but was tempered by a high rate of recurrence, which has limited its usefulness. However, the introduction of smaller-profile balloons, rapid pacing, and closure devices have brought it back as an alternative treatment strategy in selected patients who are at too high risk for surgery with repeat valvuloplasty as needed for recurrences. We report a case of prosthetic aortic valve stenosis treated with valvuloplasty with intracardiac and fluoroscopic guidance with recurrence treated with repeat valvuloplasty with promising intermediate-term outcome and describe the growing valve in valve procedures.

Characterization of erythrocytic uptake and release and disposition pathways of nitrite, nitrate, methemoglobin, and iron-nitrosyl hemoglobin in the human circulation.

Nitrite-hemoglobin reactions have been studied extensively in vitro, but there is a lack of information on the kinetics of nitrite and its metabolites in humans. In this study, we developed a nine-compartment physiological pharmacokinetic model to describe the in vivo erythrocytic uptake and release and disposition pathways of nitrite, nitrate, methemoglobin, and iron-nitrosyl hemoglobin in the human circulation. Our model revealed that nitrite entered erythrocytes rapidly with a rate constant of 0.256 min(-1) (i.e., half-life = 2.71 min). The formation of iron-nitrosyl hemoglobin from nitrite, which involves the reduction of nitrite by deoxyhemoglobin to generate nitric oxide (NO) and reaction of NO with deoxyhemoglobin to form iron-nitrosyl hemoglobin, occurred rapidly as well (k = 2.02 min(-1); half-life = 0.343 min = 21 s). The disposition kinetics of methemoglobin was complex. Nitrate formation occurred primarily in erythrocytes through the nitrite-oxyhemoglobin reaction and was higher when nitrite was administered intra-arterially than intravenously. Nitrate reduction was an insignificant metabolic pathway. This study is the first to comprehensively evaluate the kinetics of nitrite and its metabolites in humans and provides unique insights into the rapid equilibrium of nitrite into erythrocytes and conversion to NO in the red cell, which is kinetically associated with vasodilation.

Nitrite infusion in humans and nonhuman primates: endocrine effects, pharmacokinetics, and tolerance formation.

BACKGROUND: The recent discovery that nitrite is an intrinsic vasodilator and signaling molecule at near-physiological concentrations has raised the possibility that nitrite contributes to hypoxic vasodilation and to the bioactivity of nitroglycerin and mediates the cardiovascular protective effects of nitrate in the Mediterranean diet. However, important questions of potency, kinetics, mechanism of action, and possible induction of tolerance remain unanswered. METHODS AND RESULTS: In the present study, we performed biochemical, physiological, and pharmacological studies using nitrite infusion protocols in 20 normal human volunteers and in nonhuman primates to answer these questions, and we specifically tested 3 proposed mechanisms of bioactivation: reduction to nitric oxide by xanthine oxidoreductase, nonenzymatic disproportionation, and reduction by deoxyhemoglobin. We found that (1) nitrite is a relatively potent and fast vasodilator at near-physiological concentrations; (2) nitrite functions as an endocrine reservoir of nitric oxide, producing remote vasodilation during first-pass perfusion of the opposite limb; (3) nitrite is reduced to nitric oxide by intravascular reactions with hemoglobin and with intravascular reductants (ie, ascorbate); (4) inhibition of xanthine oxidoreductase with oxypurinol does not inhibit nitrite-dependent vasodilation but potentiates it; and (5) nitrite does not induce tolerance as observed with the organic nitrates. CONCLUSIONS: We propose that nitrite functions as a physiological regulator of vascular function and endocrine nitric oxide homeostasis and suggest that it is an active metabolite of the organic nitrates that can be used therapeutically to bypass enzymatic tolerance.

A novel method of measuring reduction of nitrite-induced methemoglobin applied to fetal and adult blood of humans and sheep.

The reaction of nitrite with deoxyhemoglobin results in the production of nitric oxide and methemoglobin, a reaction recently proposed as an important oxygen-sensitive source of vasoactive nitric oxide during hypoxic and anoxic stress, with several animal studies suggesting that nitrite may have therapeutic potential. Accumulation of toxic levels of methemoglobin is suppressed by reductase enzymes present within the erythrocyte. Using a novel method of measuring methemoglobin reductase activity in intact erythrocytes, we compared fetal and adult sheep and human blood. After nitrite-induced production of 20% methemoglobin, the blood was equilibrated with carbon monoxide, which effectively stopped further production. Methemoglobin disappearance was first order in nature with specific rate constants (k x 1,000) of 12.9 +/- 1.3 min(-1) for fetal sheep, 5.88 +/- 0.26 min(-1) for adult sheep, 4.27 +/- 0.34 for adult humans, and 3.30 +/- 0.15 for newborn cord blood, all statistically different from one another. The effects of oxygen tensions, pH, hemolysis, and methylene blue are reported. Studies of temperature dependence indicated an activation energy of 8,620 +/- 1,060 calories/mol (2.06 kJ/mol), appreciably higher than would be characteristic of processes limited by passive membrane diffusion. In conclusion, the novel methodology permits absolute quantification of the reduction of nitrite-induced methemoglobin in whole blood.

Endothelial progenitor cell mobilization and increased intravascular nitric oxide in patients undergoing cardiac rehabilitation.

PURPOSE: We investigated whether cardiac rehabilitation participation increases circulating endothelial progenitor cells (EPCs) and benefits vasculature in patients already on stable therapy previously shown to augment EPCs and improve endothelial function. METHODS: Forty-six of 50 patients with coronary artery disease completed a 36-session cardiac rehabilitation program: 45 were treated with HMG-CoA reductase inhibitor (statin) therapy > or = 1 month (average baseline low-density lipoprotein cholesterol = 81 mg/dL). Mononuclear cells isolated from blood were quantified for EPCs by flow cytometry (CD133/VEGFR-2 cells) and assayed in culture for EPC colony-forming units (CFUs). In 23 patients, EPCs were stained for annexin-V as a marker of apoptosis, and nitrite was measured in blood as an indicator of intravascular nitric oxide. RESULTS: Endothelial progenitor cells increased from 35 +/- 5 to 63 +/- 10 cells/mL, and EPC-CFUs increased from 0.9 +/- 0.2 to 3.1 +/- 0.6 per well (both P < .01), but 11 patients had no increase in either measure. Those patients whose EPCs increased from baseline showed significant increases in nitrite and reduction in annexin-V staining (both P < .01) versus no change in patients without increase in EPCs. Over the course of the program, EPCs increased prior to increase in nitrite in the blood. CONCLUSIONS: Cardiac rehabilitation in patients receiving stable statin therapy and with low-density lipoprotein cholesterol at goal increases EPC number, EPC survival, and endothelial differentiation potential, associated with increased nitric oxide in the blood. Although this response was observed in most patients, a significant minority showed neither EPC mobilization nor increased nitric oxide in the blood.

The reductase NCB5OR is responsive to the redox status in beta-cells and is not involved in the ER stress response.

The novel reductase NCB5OR (NADPH cytochrome b5 oxidoreductase) resides in the ER (endoplasmic reticulum) and may protect cells against ER stress. Levels of BiP (immunoglobulin heavy-chain-binding protein), CHOP (CCAAT/enhancer-binding protein homologous protein) and XBP-1 (X-box-binding protein-1) did not differ in WT (wild-type) and KO (Ncb5or-null) tissues or MEFs (mouse embryonic fibroblasts), and XBP-1 remained unspliced. MEFs treated with inducers of ER stress demonstrated no change in Ncb5or expression and expression of ER-stress-induced genes was not enhanced. Induction of ER stress in beta-cell lines did not change Ncb5or expression or promoter activity. Transfection with Ncb5or-specific siRNA (small interfering RNA) yielded similar results. Microarray analysis of mRNA from islets and liver of WT and KO animals revealed no significant changes in ER-stress-response genes. Induction of oxidative stress in betaTC3 cells did not alter Ncb5or mRNA levels or promoter activity. However, KO islets were more sensitive to streptozotocin when compared with WT islets. MEFs incubated with nitric oxide donors showed no difference in cell viability or levels of nitrite produced. No significant differences in mRNA expression of antioxidant enzymes were observed when comparing WT and KO tissues; however, microarray analysis of islets indicated slightly enhanced expression of some antioxidant enzymes in the KO islets. Short-term tBHQ (t-butylhydroquinone) treatment increased Ncb5or promoter activity, although longer incubation times yielded a dose-dependent decrease in activity. This response appears to be due to a consensus ARE (antioxidant-response element) present in the Ncb5or promoter. In summary, NCB5OR does not appear to be involved in ER stress, although it may be involved in maintaining or regulating the redox status in beta-cells.

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.