A tale of two homocysteines--and two hemodialysis units.

Pharmacologic doses of folic acid are commonly used to reduce the hyperhomocysteinemia of end-stage renal disease (ESRD). Vitamin B12 acts at the same metabolic locus as folic acid, but information is lacking about the specific effects of high doses of this vitamin on homocysteine levels in renal failure. We therefore compared the plasma homocysteine concentrations of maintenance hemodialysis patients in two McGill University-affiliated urban tertiary-care medical centers that differed in the use of vitamin B12 and folic acid therapy. Patients in the first hemodialysis unit are routinely prescribed high-dose folic acid (HI-F, 6 mg/d), whereas those in the second unit receive high-dose vitamin B12 in the form of a monthly 1-mg intravenous injection, along with conventional oral folic acid (HI-B12, 1 mg/d). Predialysis homocysteine was 23.4 +/- 6.8 micromol/L (mean +/- SD) in the HI-F unit and 18.2 +/- 6.1 micromol/L in the HI-B12 unit (P < .002). Postdialysis homocysteine was 14.5 +/- 4.1 in the HI-F unit and 10.6 +/- 3.4 micromol/L in the HI-B12 unit (P = .0001). Multiple regression analysis indicated that high-dose parenteral vitamin B12 was associated with a lower homocysteine concentration even after controlling for the potential confounders of sex, serum urea, serum creatinine, urea reduction ratio, and plasma cysteine. Because this was a cross-sectional observational study, we cannot exclude the possibility that unidentified factors, rather than the different vitamin therapies, account for the different homocysteine levels in the two units. Careful prospective studies of the homocysteine-lowering effect of high-dose parenteral vitamin B12 in ESRD should be undertaken.

Use of cold-set whey protein gelation to improve poultry meat batters.

The effect of using preheated whey protein isolate (WPI) to replace part of the poultry meat proteins in batters formulated with different salt levels was studied. Substitution with 2% preheated whey proteins followed by cold set gelation (16 h at 1 C) significantly (P < 0.05) improved binding and water holding capacity of the raw batters. In the cooked state, WPI substitution reduced cook loss and improved textural parameters, especially at < or = 1.5% salt. Unheated whey proteins (i.e., lacking the ability to gel at low temperature) did not exhibit a negative effect on the texture of the cooked batters, but reduced water holding capacity of the raw batters. Overall, cold setting of WPI improved the binding of raw and cooked meat batters, particularly at low salt level.

Plasma reduced homocysteine concentrations are increased in end-stage renal disease.

BACKGROUND: Plasma total homocysteine (tHcy) concentrations> 15 micromol/L are associated with an increased risk of cardiovascular disease. This is especially the case in end-stage renal disease (ESRD), in which tHcy concentrations commonly range between 20 and 30 micromol/L. Adverse vascular or prothrombotic effects associated with hyperhomocysteinemia are assumed to be mediated by the free sulfhydryl (reduced) form of the molecule (rHcy), but data based on fluorescence high-pressure liquid chromatography (HPLC) indicate that rHcy concentrations are not increased in ESRD despite two- to threefold elevations in tHcy. METHODS: We developed a sensitive method for measuring plasma rHcy concentrations in which freshly drawn blood is incubated with sodium iodoacetate, and the resulting S-carboxymethylhomocysteine is analyzed by gas chromatography mass spectrometry. RESULTS: Unlike with the earlier methodology, we found plasma rHcy concentrations two to four times higher than normal in ESRD. These concentrations were lowered by hemodialysis and were proportional to plasma tHcy over the range of tHcy concentrations that has been associated with increased cardiovascular risk (r2 = 0.39, P < 0.0001). CONCLUSIONS: These results support the hypothesis that homocysteine could directly mediate vascular disease through mechanisms related to the reactivity of its free sulfhydryl group. It remains to be determined how much of the variability between plasma tHcy and rHcy is due to analytical variation and how much is due to biologic factors that separately influence concentrations of the disease marker, tHcy, and its presumed mediator, rHcy.

Human extracellular water volume can be measured using the stable isotope Na234SO4.

The volume of human extracellular water (ECW) may be estimated from the sulfate space (SS). Although it may better approximate ECW volume than the bromide space, a common alternative, SS measurement is limited by the need to administer a radioactive substance, sodium [35S]sulfate. In this paper, we demonstrate the measurement of the SS using the stable isotope, sodium [34S]sulfate. Eight healthy nonobese men ingested 0.50-0.78 mg (3.47-5.42 micromol) Na234SO4/kg body weight and 30 mg NaBr/kg body weight. Sulfate concentrations and 34SO4 enrichments were measured by electrospray tandem mass spectrometry before and during the 5 h after tracer administration. SS was calculated by linear extrapolation of the natural logarithm of serum 34SO4 concentrations obtained at h 2, 3 and 4 compared with h 3, 4 and 5. The SS obtained using values between h 3 and 5 (187 +/- 17 mL/kg) was similar to published determinations using intravenous or oral radiosulfate, and was 80% of the simultaneously measured corrected bromide space (234 +/- 10 mL/kg, P = 0.01). Oral sodium [34S]sulfate administration is a suitable technique for measuring ECW and avoids radiation exposure.

Measurement of sulfate concentrations and tracer/tracee ratios in biological fluids by electrospray tandem mass spectrometry.

A reproducible and very sensitive method is described for the quantitation of inorganic sulfate in biological fluids by negative electrospray ionization tandem mass spectrometry. After addition to the sample of (34)S-labeled sodium sulfate internal standard and deproteinization with methanol, interfering bicarbonate anions are removed by acidification and chloride and phosphate by means of a single filtration step. The tandem mass spectrometer is used in neutral loss mode to detect HSO(4)(-) ions free of interference from residual isobaric H(2)PO(4)(-) ions. Organic sulfates do not interfere with the measurement. Serum and urinary inorganic sulfate concentrations measured with this technique agree closely with determinations by ion-exchange chromatography with conductivity detection. Unlike the latter method, this technique does not require dedicated equipment. The method is also suitable for measuring the ratio of (34)S-labeled sulfate to unlabeled sulfate in serum and hence represents an attractive alternative for the use of the radioactive (35)S isotope in human studies of body composition and oxidation of sulfur-containing substrates to sulfate.

Plasma homocysteine concentrations of preterm infants.

Mild hyperhomocysteinemia in adults is associated with an increased risk of vascular disease. Although information is available about plasma homocysteine concentrations in childhood, data are entirely lacking for preterm infants despite their known abnormalities of sulfur amino acid metabolism. We measured plasma total homocysteine concentrations of 9 preterm infants (gestational age 23-31 weeks) within 48 h of birth and over the subsequent 14 days of life, and 4 term infants (gestational age 36-39 weeks) on a single occasion within 72 h of birth. As measured within 48 h of birth, average plasma homocysteine and cysteine concentrations of the preterm infants were 3.8 +/- 0.3 and 122 +/- 8 microM, both significantly less than those of the term infants (6.1 +/- 1.3 and 187 +/- 39) and of normal adults (8.2 +/- 0.5 and 232 +/- 6). Plasma homocysteine (but not cysteine) appeared to gradually increase during the first 2 weeks of life (p = 0.053). Our results indicate that hyperhomocysteinemia does not normally occur in preterm infants.