Nitrite and nitrate analyses: a clinical biochemistry perspective

OBJECTIVE

To review the assays available for measurement of nitrite and nitrate ions in body fluids and their clinical applications.

DESIGN AND METHODS

Literature searches were done of Medline and Current Contents to November 1997.

RESULTS

The influence of dietary nitrite and nitrate on the concentrations of these ions in various body fluids is reviewed. An overview is presented of the metabolism of nitric oxide (which is converted to nitrite and nitrate). Methods for measurement of the ions are reviewed. Reference values are summarized and the changes reported in various clinical conditions. These include: infection, gastroenterological conditions, hypertension, renal and cardiac disease, inflammatory diseases, transplant rejection, diseases of the central nervous system, and others. Possible effects of environmental nitrite and nitrate on disease incidence are reviewed.

CONCLUSIONS

Most studies of changes in human disease have been descriptive. Diagnostic utility is limited because the concentrations in a significant proportion of affected individuals overlap with those in controls. Changes in concentration may also be caused by diet, outside the clinical investigational setting. The role of nitrite and nitrate assays (alongside direct measurements of nitric oxide in breath) may be restricted to the monitoring of disease progression, or response to therapy in individual patients or subgroups. Associations between disease incidence and drinking water nitrate content are controversial (except for methemoglobinemia in infants).

Determination of aldehydes and other lipid peroxidation products in biological samples by gas chromatography-mass spectrometry

The extremely broad spectrum of the biological effects of aldehydic lipid peroxidation products has necessitated the development of a technique that can quantitate all of the aldehydes formed in biological materials. The proposed method is based on the use of O-(2, 3, 4, 5, 6-pentafluorobenzyl) hydroxylamine hydrochloride (PFBHA.HCl) to form the O-pentafluorobenzyl-oxime (PFB-oxime) derivatives of 22 saturated and unsaturated aldehydes (C2-C12) including hexanal, 4-hydroxy-non-2-enal (HNE), and malondialdehyde (MDA), followed by trimethylsilylation of the hydroxyl group to trimethylsilyl (TMS) ethers. The PFB-oxime-TMS derivatives were analyzed by capillary column gas chromatography-negative-ion chemical ionization mass spectrometry (GC-NICIMS) with ammonia as reagent gas. Quantitation was achieved using benzaldehyde-ring-D5 as an internal standard in selected ion recording (SIR) mode. Standard curves were linear (r > 0.99) for all individual aldehydes. The detection limit was between 50 and 100 fmol per 1 microliter injected aldehyde. Recovery of all aldehydes from urine, plasma, and tissue homogenate was over 85%, except HNE, trans-2-octenal and trans-2,-cis-6-nonadienal from plasma and tissue sample, which were between 60 and 80%, suggesting these aldehydes may bind to protein and lipid components, especially to SH groups of proteins. The high sensitivity of this method allows the measurement of physiological aldehyde levels in biological samples. The products of aldehyde metabolism can also be measured by this assay.

Replication of TPMT and ABCC3 genetic variants highly associated with cisplatin-induced hearing loss in children

Cisplatin is a widely used chemotherapeutic agent for the treatment of solid tumors. A serious complication of cisplatin treatment is permanent hearing loss. The aim of this study was to replicate previous genetic findings in an independent cohort of 155 pediatric patients. Associations were replicated for genetic variants in TPMT (rs12201199, P = 0.0013, odds ratio (OR) 6.1) and ABCC3 (rs1051640, P = 0.036, OR 1.8). A predictive model combining variants in TPMT, ABCC3, and COMT with clinical variables (patient age, vincristine treatment, germ-cell tumor, and cranial irradiation) significantly improved the prediction of hearing-loss development as compared with using clinical risk factors alone (area under the curve (AUC) 0.786 vs. 0.708, P = 0.00048). The novel combination of genetic and clinical factors predicted the risk of hearing loss with a sensitivity of 50.3% and a specificity of 92.7%. These findings provide evidence to support the importance of TPMT, COMT, and ABCC3 in the prediction of cisplatin-induced hearing loss in children.

Sex-specific genetic effects influence variation in body composition

AIMS/HYPOTHESIS

Despite well-known sex differences in body composition it is not known whether sex-specific genetic or environmental effects contribute to these differences.

METHODS

We assessed body composition in 2,506 individuals, from a young Dutch genetic isolate participating in the Erasmus Rucphen Family study, by dual-energy X-ray absorptiometry and anthropometry. We used variance decomposition procedures to partition variation of body composition into genetic and environmental components common to both sexes and to men and women separately and calculated the correlation between genetic components in men and women.

RESULTS

After accounting for age, sex and inbreeding, heritability ranged from 0.39 for fat mass index to 0.84 for height. We found sex-specific genetic effects for fat percentage (fat%), lean mass, lean mass index (LMI) and fat distribution, but not for BMI and height. Genetic correlations between sexes were significantly different from 1 for fat%, lean mass, LMI, android fat, android:gynoid fat ratio and WHR, indicating that there are sex-specific genes contributing to variation of these traits. Genetic variance was significantly higher in women for the waist, hip and thigh circumference and WHR, implying that genes account for more variance of fat distribution in women than in men. Environmental variance was significantly higher in men for the android:gynoid fat ratio.

CONCLUSIONS/INTERPRETATION

Sex-specific genetic effects underlie sexual dimorphism in several body composition traits. The findings are relevant for studies on the relationship of body composition with common diseases like cardiovascular disease and type 2 diabetes and for genetic association studies.

Cytotoxic aldehydes as possible markers for childhood cancer

Concentrations of 22 known aldehydes (byproducts of lipid peroxidation), 5 acyloins, free and total carnitine and acylcarnitines were measured in plasma and urine obtained from pediatric patients with various forms of cancer before any treatment, and following treatment with doxorubicin or daunorubicin. Aldehydes, before the initiation of chemotherapy, were significantly elevated in cancer patients compared to controls. Aldehydes such as hexanal, heptanal, and malondialdehyde were strikingly higher in samples from cancer patients, while trans 4-cis-4-decenal was the prominent aldehyde in the blood of controls. In addition, in each form of cancer the pattern of aldehydes appeared to be unique when compared to controls, or to others forms of cancer. In cancer patients receiving chemotherapy there was a general trend toward a reduction 24 h after both the first and after the fifth doxorubicin dose. These changes however were not significant statistically due to large inter-patient variation. Free and total plasma carnitine levels remained in the normal range, and there were no abnormal acylcarnitines detected in urine. Possible hypotheses to explain the elevations in aldehydes, and the reasons for the changed aldehyde profiles in different forms of cancer are discussed.

Polymorphisms of the renin-angiotensin system are associated with blood pressure, atherosclerosis and cerebral white matter pathology

BACKGROUND

The renin-angiotensin system is involved in the development of hypertension, atherosclerosis and cardiovascular disease. We studied the association between the M235T polymorphism of the angiotensinogen gene (AGT) and the C573T polymorphism of the angiotensin II type 1 receptor (AT1R) and blood pressure, carotid atherosclerosis and cerebrovascular disease.

METHODS

We genotyped over 6000 subjects from the Rotterdam Study and more than 1000 subjects from the Rotterdam Scan Study. We used logistic regression and univariate analyses, adjusting for age and sex with, for AGT, the MM and, for AT1R, the TT genotype as reference.

RESULTS

We found that AGT-235T increased systolic (p for trend = 0.03) and diastolic blood pressure (p for trend = 0.04). The prevalence of carotid plaques was increased 1.25-fold (95% CI 1.02-1.52) in AGT-TT carriers. There was a significant increase in mean volume deep subcortical white matter lesions (WML) for AGT-TT carriers (1.78 ml vs 1.09 ml in the reference group; p = 0.008). A significant interaction was found between AGT and AT1R, further increasing the effect on periventricular and subtotal WML (p for interaction = 0.02). We found a non-significant increased risk of silent brain infarction for AGT-TT carriers and AT1R-CC carriers, but no effect on stroke.

CONCLUSION

We found an association between AGT and blood pressure, atherosclerosis and WML. Also, we found synergistic effects between AGT and AT1R on the development of WML. These findings raise the question of whether the renin-angiotensin system may be a therapeutic target for the prevention of cerebral white matter pathology.

Differential roles of Angiotensinogen and Angiotensin Receptor type 1 polymorphisms in breast cancer risk

While angiotensinogen (AGT) seems to have anti proliferative properties, angiotensin II (ATII) is a potent growth factor and it mediates its actions through the angiotensin type 1 receptor (AGTR1). In the AGT gene, the M235T polymorphism has been associated with the variation in angiotensinogen levels and in the AGTR1 gene; the C573T variant is associated with different pathologies. We aimed to evaluate the relationship of these two variants and the risk of breast cancer. These polymorphisms were genotyped in 3787 women participating the Rotterdam Study. We performed a logistic regression and a disease free survival analysis by genotype. The logistic regression yielded an odds ratio of 1.4 (95% CI: 1.1-1.9) for the MM genotype carriers versus the T allele carriers. The breast cancer free survival by AGT genotype was significantly reduced in MM genotype carriers compared to non-carriers (hazard ratio (HR) = 1.5; 95% CI: 1.1-2.2). We did not find any association of the AGTR1 polymorphism and breast cancer risk or disease free survival. Our results suggest that AGT plays a role in breast cancer risk in postmenopausal women, whereas the role of AGTR1 needs further studying.

The validity and reliability of the functional rating index for evaluating low back pain in athletes

The purpose of the present study was to determine the reliability and validity of the Functional Rating Index (FRI) for athletes with low back pain (LBP). In this cross-sectional and prospective cohort study, the validated Persian FRI (PFRI) was tested in 100 athletes with LBP and 50 healthy athletes. From the athletes with LBP, data were recollected among 50 athletes with a 7-day interval to examine test-retest reliability. The content validity was excellent, and the athletes with LBP responded to all items with no floor or ceiling effects. The discriminative validity was supported by a statistically significant difference in PFRI total scores between the athletes with LBP and healthy athletes. The concurrent criterion validity was good (rho = 0.72). The construct, convergent validity was good (r = 0.83). The internal consistency reliability estimate was high (Cronbach's α = 0.90). Factor analysis demonstrated a single-factor structure with an explained variance of 52.22%. The test-retest reliability was excellent, indicated by an ICC(agreement) of 0.97, and the agreement observed in the Bland and Altman plot demonstrated no systematic bias. It is concluded that the PFRI has excellent psychometric properties for assessing athletes with LBP.

Common variants in PCSK1 influence blood pressure and body mass index

Proprotein convertase subtilisin/kexin-type 1 (PCSK1) activates precursors pro-opiomelanocortin (POMC), proinsulin and prorenin. We investigated if common variants in the PCSK1 gene influence blood pressure and risk of hypertension. Additionally, we investigated the risk of obesity and type 2 diabetes (T2D). In the Rotterdam Study (RS1), a prospective, population-based cohort (n=5974), four single-nucleotide polymorphisms (rs10515237, rs6232, rs436321 and rs3792747) in PCSK1 were studied. Linear and Cox regression models served to analyze associations between variants and end points. Replication was performed in the Rotterdam Study Plus1 (RSPlus1, n=1895). Rs436321 was significantly associated with systolic and diastolic blood pressure and risk of hypertension (odds ratio (OR): 1.1-1.3; P<0.05 in both populations). Rs6232 was associated with body mass index (BMI) (P=0.007 and P=0.04 in RS1 and RSPlus1, respectively). In RSPlus1, heterozygotes for rs6232 had 1.5 times higher risk of obesity (OR: 1.46; 95% confidence interval: 1.04-2.03; P=0.03). We did not find significant associations of PCSK1 with fasting insulin levels and T2D. We found an association of genetic variation in the PCSK1 gene with blood pressure and hypertension. Furthermore, we replicated the association of PCSK1 with BMI and obesity. No relationship was found between PCSK1 variants and fasting insulin levels and T2D. Our findings suggest that genetic variation in PCSK1 may contribute to, at least, some of these interrelated disorders.

Evaluation of Karhunen-Loève expansion for feature selection in computer-assisted classification of bioprosthetic heart-valve status

This paper analyses the performance of four different feature-selection approaches of the Karhunen-Loève expansion (KLE) method to select the most discriminant set of features for computer-assisted classification of bioprosthetic heart-valve status. First, an evaluation test reducing the number of initial features while maintaining the performance of the original classifier is developed. Secondly, the effectiveness of the classification in a simulated practical situation where a new sample has to be classified is estimated with a validation test. Results from both tests applied to a reference database show that the most efficient feature selection and classification (> or = 97% of correct classifications (CCs)) are performed by the Kittler and Young approach. For the clinical databases, this approach provides poor classification results for simulated 'new samples' (between 50 and 69% of CCs). For both the evaluation and the validation tests, only the Heydorn and Tou approach provides classification results comparable with those of the original classifier (a difference always < or = 7%). However, the degree of feature reduction is particularly variable. The study demonstrates that the KLE feature-selection approaches are highly population-dependent. It also shows that the validation method proposed is advantageous in clinical applications where the data collection is difficult to perform.

Plasma Branched-Chain Amino Acid Concentrations and Glucose Homeostasis in Kidney Transplant Recipients and Candidates

Background

Post-transplant diabetes mellitus (PTDM) encompasses new-onset and previously unrecognized type 2 diabetes. Kidney failure masks type 2 diabetes. Branched-chain amino acids (BCAA) are closely associated with glucose metabolism. Therefore, understanding BCAA metabolism both in kidney failure and after kidney transplantation may inform PTDM mechanisms.

Objective

To understand the impact of present or absent kidney function on plasma BCAA concentrations.

Design

Cross-sectional study of kidney transplant recipients and kidney transplant candidates.

Setting

Large kidney transplant center in Toronto, Canada.

Measurements

We measured plasma BCAA and aromatic amino acid (AAA) concentrations in 45 pre-kidney transplant candidates (15 with type 2 diabetes, 30 without type 2 diabetes) and 45 post-kidney transplant recipients (15 PTDM, 30 non-PTDM), along with insulin resistance and sensitivity by 75 g oral glucose loading for those in each group without type 2 diabetes.

Methods

Plasma AA concentrations were analyzed using MassChrom AA Analysis and compared between groups. The insulin sensitivity for oral glucose tolerance tests or Matsuda index (a measure of whole-body insulin resistance), Homeostatic Model Assessment for Insulin Resistance (a measure of hepatic insulin resistance), and Insulin Secretion-Sensitivity Index-2 (ISSI-2, a measure of pancreatic β-cell response) was calculated from fasting insulin and glucose concentrations, and compared with BCAA concentrations.

Results

Each BCAA concentration was higher in post-transplant subjects than pre-transplant subjects (P < .001 for leucine, isoleucine, valine). In post-transplant subjects, each BCAA concentration was higher in PTDM versus non-PTDM (odds ratio for PTDM 3-4 per 1 SD increase in BCAA concentration, P < .001 for each). Tyrosine concentrations were also higher in post-transplant subjects than pre-transplant subjects, but tyrosine did not differ by PTDM status. By contrast, neither BCAA nor AAA concentrations were different in pre-transplant subjects with or without type 2 diabetes. Whole-body insulin resistance, hepatic insulin resistance, and pancreatic β-cell response did not differ between nondiabetic post-transplant and pre-transplant subjects. Branched-chain amino acid concentrations correlated with the Matsuda index and Homeostatic Model Assessment for Insulin Resistance (P < .05 for each) only in nondiabetic post-transplant subjects-not in nondiabetic pre-transplant subjects. Branched-chain amino acid concentrations did not correlate with ISSI-2 in either pre-transplant or post-transplant subjects.

Limitations

The sample size was small, and subjects were not studied prospectively for the development of type 2 diabetes.

Conclusions

Plasma BCAA concentrations are higher post-transplant in type 2 diabetic states, but do not differ by diabetes status in the presence of kidney failure. The association of BCAA with measures of hepatic insulin resistance among nondiabetic post-transplant patients is consistent with impaired BCAA metabolism as a characteristic of kidney transplantation.

Unsaturated aldehydes including 4-OH-nonenal are elevated in patients with congestive heart failure

BACKGROUND

Lipid peroxidation generates several unsaturated aldehydes, such as 4-OH-nonenal (HNE), which may interact with and modify the function of other molecules that are of biological importance. Although congestive heart failure (CHF) is a state of generalized oxidative stress, the resultant spectrum of saturated and unsaturated aldehydes has not been systematically characterized in this condition.

METHODS

We studied 8 CHF patients and 8 age-matched patients with normal left ventricular (LV) function. The concentrations of 22 aldehydes produced by lipid peroxidation, including saturated (n-alkanals) and unsaturated (t-2-alkenals, t-2,t-4-alkadienals, 4-OH-alkenals) aldehydes, were measured in arterial plasma by gas chromatography mass spectrometry (GC/MS). LV contractility (+dP/dt) and relaxation (Tau) were directly measured with a micromanometer-tipped catheter.

RESULTS

Compared with patients who have normal LV function, CHF patients had higher levels of total aldehydes (9,311 +/- 835 v 6,594 +/- 344 nmol/L, P < .01), as well as multiple unsaturated aldehydes (t-2-alkenals and 4-OH-alkenals, including HNE). In the CHF group, a strong relationship was observed between total aldehyde concentration and both +dP/dt (correlation coefficient = -0.76, P < .05) and Tau (correlation coefficient = 0.78, P < .05).

CONCLUSION

Unsaturated aldehyde levels were consistently elevated in the plasma of CHF patients compared with patients who have normal LV function. In CHF patients, elevated aldehyde levels were associated with impairment of LV contractility.