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Biomedical subjects

Mark M Kushnir

Publications and source records attributed to Mark M Kushnir.

13 recordsLinked to original sources
PubMed2007

Asymmetric dimethylarginine, cortisol/cortisone ratio, and C-peptide: markers for diabetes and cardiovascular risk?

BACKGROUND: Diabetes and prediabetic conditions are growing cardiovascular risk factors. Better understanding and earlier recognition and treatment of dysglycemia-related risk are health priorities. We assessed the predictive value of 3 proposed new markers for diabetes and cardiovascular risk. We tested whether the plasma levels of (1) asymmetric dimethylarginine (ADMA), (2) cortisol/cortisone (Cl/Cn) ratio, and (3) C-peptide predicted glycemic status, coronary artery disease, and death or myocardial infarction (MI) in a nested case-control cohort (N = 850) with normal fasting glucose (< 110 mg/dL), impaired fasting glucose (110-125), or diabetic (> or = 126) status. METHODS: High-sensitivity C-reactive protein (hsCRP) served as a control risk marker. Follow-up averaged 2.6 +/- 1.4 years. High-pressure liquid chromatography with pre-column derivitization and fluorescence was used to assay ADMA, liquid chromatography/tandem mass spectrometry for Cl and Cn, and chemiluminescent immunoassay for C-peptide. RESULTS: Asymmetric dimethylarginine levels were positively associated with glycemic category (P < .001). Quartiles 2 to 4 ADMA also conferred increased risk of death/MI independent of hsCRP and other risk factors (adjusted hazard ratio, 2.1; P = .002). Cortisol/Cortisone ratios (P = .013) and C-peptide (P = .047) were associated with glycemic categories but less strongly than ADMA. Quartiles 2 to 4 Cl/Cn were protective against incident death/MI (adjusted hazard ratio, 0.48; P < .001), whereas C-peptide did not predict outcomes. CONCLUSIONS: Among a high coronary risk case-control cohort, ADMA (strongly), Cl/Cn (moderately), and C-peptide (weakly) predicted glycemic categories. Asymmetric dimethylarginine and Cl/Cn also predicted clinical outcome independent of and more strongly than hsCRP. Asymmetric dimethylarginine and Cl/Cn represent promising new candidate markers of dysglycemia and associated cardiovascular risk.

Arginine↗
PubMed2006

Development and performance evaluation of a tandem mass spectrometry assay for 4 adrenal steroids.

BACKGROUND: Congenital adrenal hyperplasia is a group of autosomal recessive disorders caused by a deficiency of 1 of 4 enzymes required for the synthesis of glucocorticoids, mineralocorticoids, and sex hormones. Analysis of 11-deoxycortisol (11DC), 17-hydroxyprogesterone (17OHP), 17-hydroxypregnenolone (17OHPr), and pregnenolone (Pr) in blood allows detection of these enzyme defects. METHODS: The steroids were extracted from 200 microL of serum or plasma by solid-phase extraction, derivatized to form oximes, and extracted again with methyl t-butyl ether. Instrumental analysis was performed on an API 4000 tandem mass spectrometer with electrospray ionization in positive mode and multiple reaction-monitoring acquisition. RESULTS: The limits of detection were 0.025 microg/L for 11DC, 17OHP, and Pr and 0.10 microg/L for 17OHPr. The method was linear to 100 microg/L for 11DC, 17OHP, and Pr, respectively, and to 40 microg/L for 17OHPr. Within- and between-run (total) imprecision (CVs) were <7.1% and 11%, respectively. Reference intervals for children in Tanner stages 1 through 5 and adult males and females for 17OHP, 11DC, Pr, and 17OHPr were established. Prepared samples were stable for >72 h. CONCLUSIONS: The detection limit and selectivity of this method and its small sample volume requirement allow analysis of endogenous concentrations of adrenal steroids in serum or plasma from children and adults. The method thus has an important potential role in the evaluation of the status of 4 of the enzymes involved in adrenal steroid biosynthesis.

17-alpha-Hydroxypregnenolone↗
PubMed2005

Measurement of total vitamin B12 and holotranscobalamin, singly and in combination, in screening for metabolic vitamin B12 deficiency.

BACKGROUND: The standard screening test for vitamin B12 deficiency, measurement of total plasma vitamin B12, has limitations of sensitivity and specificity. Plasma vitamin B12 bound to transcobalamin (holoTC) is the fraction of total vitamin B12 available for tissue uptake and therefore has been proposed as a potentially useful alternative indicator of vitamin B12 status. METHODS: We compared the diagnostic accuracy of total vitamin B12, holoTC, and a combination of both measures to screen for metabolic vitamin B12 deficiency in an elderly cohort (age > or = 60 years). Plasma methylmalonic acid and homocysteine were used as indicators of vitamin B12 deficiency. RESULTS: Low total vitamin B12 (< 148 pmol/L) and low holoTC (< 35 pmol/L) were observed in 6.5% and 8.0%, and increased methylmalonic acid (> 350 nmol/L) and homocysteine (> 13 micromol/L) were observed in 12.1% and 17.0% of the study participants. In multiple regression models, holoTC explained 5%-6% more of the observed variance in methylmalonic acid and homocysteine than did total vitamin B12 (P < or = 0.004). ROC curve analysis indicated that total vitamin B12 and holoTC were essentially equivalent in their ability to discriminate persons with and without vitamin B12 deficiency. Individuals with low concentrations of both total vitamin B12 and holoTC had significantly higher concentrations of methylmalonic acid and homocysteine than did individuals with total vitamin B12 and/or holoTC within the reference intervals (P < 0.001). CONCLUSIONS: HoloTC and total vitamin B12 have equal diagnostic accuracy in screening for metabolic vitamin B12 deficiency. Measurement of both holoTC and total vitamin B12 provides a better screen for vitamin B12 deficiency than either assay alone.

Aged↗
PubMed2005

Performance characteristics of a novel tandem mass spectrometry assay for serum testosterone.

BACKGROUND: Commercial immunoassays for testosterone (Te) may give inaccurate results for samples from women and children, leading to misdiagnosis and inappropriate treatment. We developed a sensitive and specific tandem mass spectrometric assay for measurement of Te at the concentrations encountered in women and children. METHODS: Te was extracted with methyl tert-butyl ether from 100 microL of serum or plasma, derivatized to form an oxime, and reextracted by solid-phase extraction. Instrumental analysis was performed on an API 4000 HPLC tandem mass spectrometer in the multiple-reaction monitoring (MRM) mode. The MRM transitions (m/z) were 304-->124 and 304-->112 for Te and 307-->124 and 307-->112 for d3-Te. RESULTS: Within- and between-run CVs were <12% and 7.9%, respectively. The limit of quantification was 0.0346 nmol/L (1 ng/dL). Reference intervals for sex hormone-binding globulin and total, free, and bioavailable Te were established for children of Tanner stages 1 through 5 and adult males and females. CONCLUSIONS: The sensitivity and specificity of the method are adequate for analysis of Te in samples from women and children. The method requires small sample volumes, has adequate precision, and is not subject to interferences.

Adolescent↗
PubMed2005

Assessing analytical specificity in quantitative analysis using tandem mass spectrometry.

OBJECTIVES: The necessity of confirmation of compound identity in quantitative analysis is well recognized for methods utilizing single mass spectrometry detection but is not commonly addressed for applications utilizing multiple-stage mass spectrometry (MSn). For MSn detection, no commonly accepted rules for assessment of analytical specificity in quantitative analyses have been established to date. METHODS: To assure compound identity, we evaluated approaches based on monitoring multiple mass transitions of a target compound followed by comparison of the branching ratios of the mass transitions. RESULTS: Monitoring multiple mass transitions along with evaluation of the ratio of their relative intensities allows the analyst to distinguish the target analyte from interferences in quantitative analysis. The strategy and the acceptance criteria are compound and method specific and should be established during the method development and validation. CONCLUSIONS: The certainty of analyte identity is very important in quantitative analysis using MSn detection; methods to verify analyte identity should be used in all critical applications.

Cortisone↗
PubMed2004

Solid phase extraction procedure for urinary organic acid analysis by gas chromatography mass spectrometry.

We have developed a solid phase extraction procedure for the detection of organic acids by GC-MS using a strong anion exchange column (Sep-Pak Vac RC, Accell Plus QMA cartridge). Extraction efficiencies of 25 organic acids were established by analyzing standards in water based solutions. High extraction efficiencies (90 to 100%) were found for many of the compounds studied. We estimated the limit of detection for 48 organic acids and glycine conjugates. They were below 5 nmole with the exception of malonic and oxalic acids and mevalonic acid lactone. This method provides the advantage of higher recoveries for a wide range of compounds of interest and therefore can be a potential alternative to liquid-liquid extraction for organic acid screening. It is especially sensitive for the detection of some polar compounds, such as 3-OH-glutaric and N-acetylaspartic acids.

Acids↗
PubMed2004

Simultaneous quantitative analysis of isobars by tandem mass spectrometry from unresolved chromatographic peaks.

A method was developed for the simultaneous quantitation of isobars from unresolved chromatographic peaks. The method is based on differences in branching ratios of ion abundances in their tandem mass spectra and an assumption that the product ion mass spectra of a mixture can be considered as a linear combination of the spectra of individual constituents. We present analytical equations and a matrix-based approach for deconvoluting the concentration of individual components from the total peak intensity for two and three isobars and also a matrix-based generalization to any number of compounds. The feasibility of the simultaneous analysis of mixtures containing two compounds was assessed. The approach was evaluated for the analysis of structural isomers of methylmalonic and succinic acids in human plasma and urine samples for a group of 270 samples. The linear regression equation, standard error and correlation coefficient for the agreement with a traditional method utilizing chromatographic separation of the isomers were y = 0.999x - 0.005, 0.024 micro mol l(-1), and 0.985, respectively. The utility of a spectral contrast angle as a predictor of analysis feasibility was evaluated.

Algorithms↗
PubMed2004

Cortisol and cortisone analysis in serum and plasma by atmospheric pressure photoionization tandem mass spectrometry.

OBJECTIVES: Cortisol metabolism is controlled by 11beta-hydroxysteroid dehydrogenase (11beta-HSD) isoenzymes, which interconvert cortisol and cortisone. Accurate measurement of the cortisol and cortisone concentrations and their ratio provide useful information about 11beta-HSD activity. METHODS: Cortisol and cortisone were extracted with methyl-tert-butyl ether from 100 microl of serum or plasma. The extract was evaporated, reconstituted with mobile phase, and analyzed by tandem mass spectrometry using a photoionization interface. The transitions monitored were: m/z 363 to 121 and 363 to 97 for cortisol, 361 to 163 and 361 to 105 for cortisone. RESULTS: Within-run and between-run coefficients of variation were less than 6% and 12%; 14% and 22%; 11% and 21% for cortisol, cortisone, and their ratio, respectively. The limit of detection was 1 microg/l for cortisol and 5 microg/l for cortisone. Normal ranges for cortisol and cortisone concentration and for their ratio in plasma (n = 120) determined as the central 95% were 33-246 microg/l for cortisol, 8-27 microg/l for cortisone, and 0.081-0.301 for the cortisone/cortisol ratio. CONCLUSIONS: We developed a simple sensitive method for cortisol and cortisone analysis in plasma and serum that uses a small sample volume. The method is very specific, fast, does not have any known interference, and is useful for diagnosis of variety of disease and pathologic conditions.

11-beta-Hydroxysteroid Dehydrogenases↗
PubMed2003

Dissociation of individual isotopic peaks: predicting isotopic distributions of product ions in MSn.

Traditional practice in tandem mass spectrometry is to select the mono-isotopic ion for dissociation. However, high molecular weight compounds often have weak mono-isotopic peaks, which limit that approach. Furthermore, the traditional approach does not take advantage of the very rich store of information available in the isotopic patterns from the dissociation of individual non-mono-isotopic peaks. Interpretation of these isotopic patterns requires a theory capable of predicting the patterns. However, a general theory for the prediction of these patterns has been lacking. This paper shows that the patterns can be obtained from a certain vector product, the outer product, of the full isotopic distribution of the product ion with the full isotopic distribution of the complementary product. Unlike previous approaches, the method is applicable to systems of arbitrary isotopic complexity. The patterns are potentially useful for elucidation of dissociation pathways, elemental composition, and chemical structure. The paper presents several applications of the theory.

Journal Article↗
PubMed2003

Pseudo-Cushing syndrome caused by fenofibrate interference with urinary cortisol assayed by high-performance liquid chromatography.

Urinary free cortisol (UFC) excretion over 24 h reflects the production rate of cortisol and is used commonly in the diagnosis of Cushing syndrome. We report on two patients evaluated for Cushing syndrome who had elevated UFC when analyzed by HPLC but normal values for the analysis performed by RIA and HPLC-mass spectrometry/mass spectrometry (HPLC-MS/MS). Other laboratory testing was inconsistent with the diagnosis of Cushing syndrome and raised doubts about the diagnosis. We identified a probable cause of analytical interference as coming from fenofibrate (Tricor), medication taken by the patients. Fenofibrate peak overlapped with the HPLC peak of cortisol and produced an MS/MS transition overlapping the major transition of cortisol. A second MS/MS transition was free from interference. In summary, fenofibrate administration may cause false elevation of UFC values determined by HPLC or HPLC-MS/MS in patients evaluated for Cushing syndrome. An HPLC-MS/MS method using multiple mass transitions, rather than a single transition, allows accurate quantitation of urinary cortisol in patients taking fenofibrate.

Adult↗
PubMed2002

Analysis of catecholamines in urine by positive-ion electrospray tandem mass spectrometry.

BACKGROUND: Determination of urinary catecholamines (CATs) is considered important for clinical diagnosis of pheochromocytoma, paraganglioma, and neuroblastoma. The major disadvantages of existing tests include relatively long instrumental analysis time and potential interference from drugs and drug metabolites that are structurally similar to CATs. METHODS: CATs were extracted from a 300-microL aliquot of urine by a two-step liquid-liquid extraction method specific for compounds containing a catechol group. Chromatographic separation did not require the use of ion-pairing reagents, which typically hinder MS detection but are frequently used in HPLC analysis of CATs. Instrumental analysis was performed by electrospray ionization tandem mass spectrometry (ESI-MS/MS) in the multiple-reaction monitoring mode. Stable-isotope-labeled CATs were used as internal standards. RESULTS: Epinephrine (E), norepinephrine (NE), and dopamine (D) were measured within 3.5 min instrumental run time. Quantification limits were 2.5 microg/L for E and D and 10 microg/L for NE. The total imprecision (CV) was < or =9.6%; extraction recoveries were 71% +/- 12%. CONCLUSIONS: HPLC with ESI-MS/MS in combination with sample preparation specific to catechol group-containing compounds allows rapid testing for disorders associated with increased CAT concentrations. The method is free of interferences from drugs and drug metabolites, which commonly interfere with HPLC methods.

Catecholamines↗