Plasma citrulline measurement using UPLC tandem mass-spectrometry to determine small intestinal enterocyte pathology.

Citrulline is a nonessential free amino acid, detectable in various biological fluids such as plasma, urine and cerebrospinal fluid. The plasma citrulline concentration is increasingly considered to be a reliable biomarker of enterocyte function. Current analysis usually involves lengthy HPLC separations as a part of classical amino acid profiling, or mass spectrometry usually in combination with derivatization. We employed UPLC-HILIC-tandem mass-spectrometry (MS/MS) of acetonitrile-derived supernatants from plasma samples of control subjects and of patients who had received myeloablative chemotherapy. Detection was achieved by the selected reaction monitoring of transitions: m/z 176-->70 and 180-->74 (for the deuterated standard), respectively. The method was precise and accurate with inter-day CV<3.9% (n=30), recoveries ranging from 98.0 to 100.3% and high linearity from 0.3 to at least 2,000 micromol/L. The results for 202 plasma samples agreed well with those obtained by the classical HPLC-fluorescence method. By a simple protein precipitation/extraction step and the UPLC separation the result can be available within 30 min of receipt with a capacity of at least 12 assays per hour. Citrulline in blood and plasma or serum was stable for at least 2 days at room temperature which would permit postal transport to the laboratory. The UPLC-MS/MS method for measuring plasma citrulline concentrations is fast and robust and is therefore an ideal tool for monitoring the intestinal enterocyte capacity of patients with various pathological conditions.

LPS-induced release of IL-1 beta, IL-1Ra, IL-6, and TNF-alpha in whole blood from patients with familial hypercholesterolemia: no effect of cholesterol-lowering treatment.

Proinflammatory cytokines, such as interleukin-1beta (IL-1beta), IL-6, and tumor necrosis factor-alpha (TNF-alpha), are suggested to have an important role in the process of atherosclerosis. Patients with heterozygous familial hypercholesterolemia (FH) have a marked elevation in the plasma level of low-density lipoproteins (LDL), and they show early development of atherosclerosis. The aim of the present study was to test with a whole blood culture system if hyperlipoproteinemia is associated with increased cytokine production capacity in these patients and if treatment with 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors influences this production capacity of blood cells, at both the protein and mRNA levels. The capacity of blood cells in a whole blood culture to produce IL-1beta, IL-6, TNF-alpha, IL-12, IL-18, and IL-1 receptor antagonist (IL-1Ra) in response to lipopolysaccharide (LPS) appeared to be similar for heterozygous FH patients and healthy volunteers. Furthermore, the capacity to produce IL-1beta, IL-6, and TNF-alpha in response to LPS was not modified by cholesterol synthesis inhibitors at the level of mRNA expression or at the level of release. On the other hand, the release of IL-1Ra was significantly increased after treatment with HMG-CoA reductase inhibitors, although only at the protein level. This suggests a possible beneficial anti-inflammatory role for this therapy.

Nomogram to diagnose familial combined hyperlipidemia on the basis of results of a 5-year follow-up study.

BACKGROUND: Familial combined hyperlipidemia (FCH) is traditionally diagnosed by total plasma cholesterol and/or triglyceride levels above the 90th percentile adjusted for age and gender. In a recent study, we showed that the diagnosis of FCH on the basis of these diagnostic criteria was inconsistent in 26% of the subjects over a 5-year period. This result emphasizes the need for reevaluation of the diagnostic criteria for FCH. METHODS AND RESULTS: A total of 32 families (299 subjects) were studied in 1994 and 1999. A subject was defined "truly" FCH when diagnosed FCH in 1994 and/or 1999 on the basis of traditional plasma lipid criteria. Additional lipid and lipoprotein parameters, including apolipoprotein B (apoB) and small, dense LDL, were measured at both time points. In total, 121 subjects (40%) were defined as truly FCH. Multivariate analysis revealed that absolute apoB values combined with triglyceride and total cholesterol levels adjusted for age and gender best predicted truly FCH. A nomogram including these parameters is provided to simply and accurately calculate the probability to be affected by FCH. Furthermore, it is shown that when percentiles of triglyceride and total cholesterol adjusted for age and gender are not available in a population, the definition of FCH can be established on the basis of hypertriglyceridemia (>1.5 mmol/L) and hyper-apoB (>1200 mg/L). CONCLUSIONS: The diagnosis of FCH is best predicted by absolute apoB levels combined with triglyceride and total cholesterol levels adjusted for age and gender and can accurately be calculated by a nomogram. This definition is also a good predictor of cardiovascular risk in FCH.

Diagnosis of familial combined hyperlipidemia based on lipid phenotype expression in 32 families: results of a 5-year follow-up study.

Familial combined hyperlipidemia (FCH) is characterized by a variable expression of hypercholesterolemia and/or hypertriglyceridemia. We evaluated the variability in lipid phenotype expression over a 5-year period and studied factors affecting the lipid phenotype expression. A total of 32 families (299 subjects) were studied in 1994 and in 1999. Subjects were classified as having FCH when total cholesterol and/or triglyceride levels exceeded the 90th percentile adjusted for age and sex. In 1994, 93 (31%) of the 299 subjects were affected, whereas 206 (69%) of the subjects were unaffected relatives. In 1999, a diagnosis of FCH was consistent in 69 (74%) of the 93 subjects. So, 26% of the FCH subjects in 1994 showed a sporadic normolipidemic pattern (ie, total cholesterol and/or triglycerides <90th percentile) in 1999. Among the 206 unaffected relatives in 1994, 178 (86%) remained unaffected in 1999, and 28 (14%) developed an FCH lipid phenotype. Multiple regression analysis showed that sex (odds ratio 2.03, 95% CI 1.09 to 3.87; P=0.03) and body mass index (odds ratio 1.14, 95% CI 1.05 to 1.24; P<0.01) significantly contributed to the variability in lipid phenotype expression. Thus, a diagnosis of FCH, based on plasma total cholesterol and/or triglyceride levels, is consistent in only 74% of the subjects over a 5-year period. Two other major characteristics of our FCH group, compared with the unaffected relatives, included elevated apolipoprotein B (apoB) levels and the presence of small dense low density lipoprotein (LDL), as reflected by a low value of the parameter K (apoB 1461 +/- 305 versus 997 +/- 249 mg/L, respectively [P < 0.001]; K value -0.22 +/- 0.19 versus -0.02 +/- 0.19, respectively [P < 0.001]). We now report that the apoB concentration and the K value show less variability in time and are more consistently associated with FCH, inasmuch as affected FCH subjects, compared with the unaffected relatives, persistently show a higher apoB level and a lower value of parameter K, reflecting small dense LDL, even when they present a sporadic normolipidemic pattern. In conclusion, our results emphasize the need for reevaluation of the diagnostic criteria for FCH. We demonstrate that apoB and small dense LDL are attractive new candidates for defining FCH. Further studies are indicated to evaluate the role of apoB and small dense LDL as diagnostic criteria for FCH.

Changes in the plasma lipid profile as a potential predictor of clinical outcome in dengue hemorrhagic fever.

In 50 consecutive children admitted to the intensive care unit with the clinical diagnosis of dengue hemorrhagic fever (DHF)/dengue shock syndrome (grade III or IV), 20 patients with mild DHF (grade I or II), and 20 healthy control patients, the plasma lipid profile was measured. Levels of total plasma cholesterol, high-density lipoprotein, and low-density lipoprotein were significantly decreased in patients with the severest cases, compared with patients with mild DHF and healthy controls. Changes in the plasma lipid profile differentiate between patients with different stages of DHF disease severity and could be used as a potential predictor for clinical outcome.

Neutrophil superoxide-anion generating capacity in chronic smoking: effect of long-term alpha-tocopherol therapy.

We investigated whether long-term alpha-tocopherol therapy in chronic smoking affects superoxide generating capacity of neutrophils ex vivo. To this purpose, we randomly assigned 128 male chronic smokers (37 +/- 21 pack years of smoking) to treatment with placebo (n = 64) or alpha-tocopherol (400 IU dL-a-tocopherol daily, n = 64). After two years of therapy, we measured phorbol 12-myristate 13-acetate-induced superoxide production of isolated neutrophils and of diluted whole blood by monitoring reduction of ferricytochrome c and luminol-enhanced peroxidase-catalyzed chemiluminescence. Plasma lipids and lipoproteins were not different between the two treatment groups. As expected, concentrations of alpha-tocopherol in plasma and in low-density lipoproteins were markedly elevated in the supplemented group compared to the placebo group (+ 120%, P < 0.0001 and + 83%, P < 0.0001, respectively). Consequently, resistance to in vitro oxidation of low-density lipoproteins (reflected by lag time of conjugated diene formation) was higher in the supplemented group than in the placebo group (+ 22%, P < 0.0001). Superoxide generating capacity of neutrophils and superoxide production in diluted whole blood did not differ between alpha-tocopherol and placebo group. It is concluded that in chronic smoking long-term supranormal alpha-tocopherol intake does not reduce neutrophil superoxide-anion generating capacity, despite large increases in the concentrations of alpha-tocopherol in plasma and in low-density lipoproteins.

Measurement of 25-OH-vitamin D in human serum using liquid chromatography tandem-mass spectrometry with comparison to radioimmunoassay and automated immunoassay.

The plasma 25-OH vitamin D concentration is a reliable biomarker for vitamin D status but assay's variability makes adequate monitoring of vitamin D status difficult. We employed isotope-dilution liquid chromatography (LC) tandem-mass spectrometry (MS/MS) for the measurement of both 25-OH vitamin D3 and 25-OH vitamin D2 in human serum. Hexadeuterium labelled 25-OH vitamin D3 internal standard (IS) was added to calibrators (prepared in phosphate-buffered saline with 60 g/L albumin), controls or patient sera and 25-OH vitamin D metabolites were released from vitamin D binding protein by adding sodium hydroxide prior to protein precipitation by acetonitrile/methanol (9:1, v/v). Subsequent off-line solid-phase extraction was followed by chromatographic separation on a C-18 column using a water/methanol/ammonium acetate gradient. Detection was by Atmospheric Pressure Electrospray Ionisation (AP-EI) followed by selected reaction monitoring. We compared the LC-MS/MS assay to the DiaSorin radioimmunoassay (RIA) and a recently re-standardised version of an automated electrochemiluminescent immunoassay (ECLIA) from Roche Diagnostics. We also analysed external quality control samples from the International Vitamin D External Quality Assessment Scheme (DEQAS) for comparison with other participating laboratories using LC-MS. The method was linear from 5 to at least 550 nmol/L with intra- and interday CV's < or = 6% for both 25-OH vitamin D3 and 25-OH vitamin D2. Recoveries ranged between 94.9 and 106.9% for 25-OH vitamin D3 and 82.7 and 100.3% for 25-OH vitamin D2. Our results for the DEQAS serum pools averaged -7.2% from the overall LC-MS method mean. The DiaSorin RIA agreed well with the LC-MS/MS method (r(2)=0.90; average bias 1.61 nmol/L), the Roche ECLIA considerably disagreed (r(2)=0.58; bias 10.13 nmol/L). This LC-MS/MS method is reliable and robust for the measurement of both 25-OH vitamin D3 and 25-OH vitamin D2 in human serum.

Freeze-thaw and matrix effects in direct high-density lipoprotein cholesterol methods.

BACKGROUND: There is frequent discussion on the susceptibility of direct high-density lipoprotein cholesterol (HDL-C) methods to matrix effects. In Vitro Diagnostics manufacturers recognize this issue and regularly improve their HDL-C reagent formulations in subsequent generations. METHODS: The 3rd generation direct HDL-C assay from Roche was investigated for matrix effects in comparison to the former generation, a Beckman direct HDL-C method and a conventional phosphotungstate (PTA)/Mg(2+) precipitation method. In addition, 235 heparin plasma samples were measured freshly and after a freeze-thaw cycle with the Roche 2nd and 3rd generation direct HDL-C. Biases, outliers, and intraclass correlation coefficients (ICCs) were calculated for both experiments. Multivariate analysis was used to investigate interference by matrix components. RESULTS: In fresh samples, Roche 2nd and 3rd generation HDL-C methods averaged +0.15 mmol/L (95% CI: 0.13-0.16) and +0.08 mmol/L (95% CI: 0.07-0.09) higher compared to frozen samples. In frozen aliquots, ICCs for Roche 2nd and 3rd generation and Beckman direct HDL-C as compared to PTA/MgCl(2) were 0.963, 0.966, and 0.924, respectively. Predictors of outliers (defined as having an absolute difference >0.21 mmol/L) in comparisons of direct methods to the PTA/MgCl(2) precipitation method were high triglyceride and low albumin levels. CONCLUSIONS: The 3rd generation direct HDL-C from Roche has become insensitive to most matrix effects, bringing along more accurate results in hypoalbuminemic and hypertriglyceridemic samples. Surprisingly, Roche direct assays produced significantly higher HDL-C levels in fresh samples compared to frozen plasma samples. If confirmed by others, the latter finding has implications for patient management and necessitates further reagent optimization.

Laboratory-based assessment of plasma lipids and lipoproteins for the classification of familial hypercholesterolemic and hypertriglyceridemic states.

Laboratory-based coronary heart disease risk assessment classically involves measurement of lipids and lipoproteins. In this review, information is provided on the methods commonly used in laboratories for the diagnosis of hyperlipidemia, including aspects of precision and accuracy. The latter, when fulfilled, allows the use of uniform reference values. Special attention is paid to the risk estimation using apolipoprotein B and lipoprotein(a) measurement. The overall aim of this review is to simplify the laboratory-based risk estimation for coronary heart disease and to provide help in interpreting the results for effective prevention and treatment of this complex disease.

Assessment of risk factors for coronary heart disease in vascular medicine: long-term experience and a personal view from the laboratory.

Physicians should be properly informed of the clinical chemistry diagnostic potential for the diagnosis and classification of hyper- and dyslipidemias by laboratory determinations of lipids, lipoproteins, and apolipoproteins. New analytes are regularly found to be relevant for screening and risk estimation for coronary artery disease in vascular medicine. These analytes can be distinguished between parameters working on the long-term or working acutely. However, in times of restricted laboratory budgets, it is not always possible to add the new analyte to the routine diagnostic supply without having answered the question of whether the new analyte indeed adds to the chronic or acute risk estimation power presently available. This is relevant for homocysteine and for C-reactive protein (CRP). Both parameters appear to be interrelated to most common cardiovascular risk factors supposed to promote atherosclerosis and to ultimately provoke cardiovascular disease, and in fact are not independent. The latter certainly has added value in acute situations. With regard to the chronic risk estimators, it must be concluded that there is a multifactorial influence, with an important contribution made by social and lifestyle factors. This review draws attention to the multifactorial aspects of coronary heart disease, risk profiling using computer programs, socioeconomic factors, and implementation problems of interventions.

Improved cardiovascular risk profile and renal function in renal transplant patients after randomized conversion from cyclosporine to tacrolimus.

Cyclosporine is considered to contribute to the high cardiovascular morbidity and mortality in patients after renal transplantation. Tacrolimus may be more favorable in this respect, but controlled data are scarce. In this prospective randomized study in 124 stable renal transplant patients, the effects of conversion from cyclosporine to tacrolimus on cardiovascular risk factors and renal function were investigated. Follow-up was 6 mo. Statistical analysis was performed by ANOVA for repeated measurements. The serum creatinine level decreased from 137 +/- 30 micromol/L to 131 +/- 29 micromol/L (P < 0.01). Three months after conversion from cyclosporine to tacrolimus, mean BP significantly decreased from 104 +/- 13 to 99 +/- 12 mmHg (P < 0.001). Serum LDL cholesterol decreased from 3.48 +/- 0.80 to 3.11 +/- 0.74 mmol/L (P < 0.001,) and serum apolipoprotein B decreased from 1018 +/- 189 to 935 +/- 174 mg/L (P < 0.001). Serum triglycerides decreased from 2.11 +/- 1.12 to 1.72 +/- 0.94 mmol/L (P < 0.001). In addition, both rate and extent of LDL oxidation were reduced. The fibrinogen level decreased from 3638 +/- 857 to 3417 +/- 751 mg/L (P < 0.05). Plasma homocysteine concentration did not change. Three months after conversion, plasma fasting glucose level temporarily increased from 5.4 +/- 1.3 mmol/L to 5.8 +/- 1.9 mmol/L (P < 0.05). Conversion to tacrolimus resulted in a significant reduction of the Framingham risk score. In conclusion, conversion from cyclosporine to tacrolimus in stable renal transplant patients has a beneficial effect on renal function, BP, serum concentration and atherogenic properties of serum lipids, and fibrinogen.

Apolipoprotein C-III isofocusing in the diagnosis of genetic defects in O-glycan biosynthesis.

BACKGROUND: Defects in the biosynthesis of N-glycans may be found by isoelectric focusing (IEF) of plasma transferrin. No test is available to demonstrate O-glycan biosynthesis defects. METHODS: We used isoforms of apolipoprotein C-III (apoC-III) as a marker for the biosynthesis of core 1 mucin type O-glycans. Plasma samples from patients with primary defects and secondary alterations in N-glycan biosynthesis were studied by apoC-III isofocusing. RESULTS: Age-related reference values for apoC-III were determined. Plasma samples from patients with the primary congenital disorders of glycosylation (CDG) types Ia-Ic, Ie, If, IIa, and IId all showed a normal apoC-III isofocusing profile. Plasma from two patients with CDG type IIx were tested: one showed a normal apoC-III distribution, whereas the other showed a hypoglycosylation profile. In plasma from patients with hemolytic uremic syndrome (HUS), a hypoglycosylation profile was obtained. CONCLUSIONS: IEF of apoC-III is a rapid and simple technique that may be used as a screening assay for abnormalities in core 1 mucin type O-glycans. Evidence that a patient in this study has a primary genetic defect affecting both N- and O-glycosylation provides the first example of an inborn error of metabolism affecting the biosynthesis of core 1 mucin type O-glycans. Our data narrow the options for the position of the primary defect in this patient down to a step in the biosynthesis, activation, or transfer of galactose or N-acetylneuraminic acid to both N- and O-glycans. Circulating neuraminidase excreted by Streptococcus pneumoniae caused the high percentage of asialo apoC-III in two HUS patients.

Apolipoprotein-E-deficient mice exhibit an increased susceptibility to disseminated candidiasis.

The effect of hyperlipoproteinemia on systemic candidiasis was investigated by assessing the susceptibility of hyperlipoproteinemic, apolipoprotein E (ApoE)-deficient (ApoE -/-) mice to a systemic Candida albicans infection. The absence of ApoE in these mice resulted in an eightfold increase in plasma lipoprotein concentrations in the very low-density lipoprotein (VLDL) fraction, as compared with levels seen in ApoE +/+ mice. Mortality due to candidemia was significantly higher (86%) in ApoE -/- mice than in ApoE+/+ mice (52%), and in platings of homogenized kidney material on fungal culture medium, ApoE -/- mice yielded significantly higher levels of C. albicans outgrowth than did ApoE+/+ mice. C albicans grew twofold better in ApoE -/- plasma in 4 h than in ApoE+/+ plasma, and depletion of lipoproteins from plasma resulted in a significant seven- to tenfold increase in C. albicans growth. Recombinant ApoE did not directly inhibit C. albicans growth. Our data indicate that the increased susceptibility of ApoE -/- mice to C albicans is due both to increased growth of blastoconidia in ApoE -/- mice in response to the availability of lipids as nutrients, and to the neutralization of candidacidal factors by lipoproteins. This study suggests that lipoproteins play a significant role in host defense against candidiasis.

Native LDL potentiate TNF alpha and IL-8 production by human mononuclear cells.

Native LDL (nLDL) increases expression of adhesion molecules on endothelial cells through induction of Ca(2+) mobilization. Ca(2+) mobilization is also involved in the induction of proinflammatory cytokines, important mediators involved in atherogenesis. The aim of the study was to evaluate the capacity of nLDL to affect spontaneous and lipopolysaccharide (LPS)-stimulated cytokine production. Preincubation of human peripheral blood mononuclear cells (PBMC) with nLDL for 24 h did not influence spontaneous production of tumor necrosis factor alpha (TNF alpha) or interleukin-8 (IL-8), but significantly potentiated LPS-induced production of these cytokines. nLDL preincubation of PBMC did not increase the expression of the LPS receptors Toll-like receptor-4, CD14, or CD11c/CD18. Potentiation of cytokine production by nLDL was mediated through induction of Ca(2+) mobilization, because: a) nLDL induced a sustained pattern of repetitive Ca(2+) transients in human PBMC; b) the Ca(2+) chelator fura 2-acetoxymethyl ester, 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid, an intracellular Ca(2+) chelator, inhibited the potentiating effect of nLDL on LPS-induced cytokine synthesis; c) induction of Ca(2+) mobilization by thapsigargin potentiated LPS-induced cytokine production. nLDL are able to potentiate LPS-induced production of cytokines by human PBMC, and this effect is probably mediated through induction of Ca(2+) mobilization. This may represent an important pathogenetic mechanism in atherogenesis induced by hyperlipoproteinemia.