The use of homocysteine and other metabolites in the specific diagnosis of vitamin B-12 deficiency

Vitamin B12 deficiency: correction of P-methylmalonic acid for estimated glomerular filtration rate to improve diagnostic value - a confirmatory study

Objectives: For diagnosis of vitamin B12 deficiency, plasma methylmalonic acid (P-MMA) is considered superior to plasma vitamin B12 (P-B12). Reduced kidney function elevates P-MMA, hence, hampering P-MMA as a biomarker. We assessed whether correcting P-MMA for estimated glomerular filtration rate (eGFR) can affect the estimated prevalence of B12 deficiency. Methods: We included 115,245 patients with concomitant measurements of P-MMA, P-B12 and P-Creatinine. B12 deficiency was classified using P-MMA decision limits at >0.75 and >0.43 µmol/L. The non-linear relation between eGFR and P-MMA was estimated using spline regression. We calculated the percentage-wise reclassification of B12 deficiency by using an eGFR corrected P-MMA formula with eGFR reference points of 90 and 60 mL/min. Results: 6% with B12 deficiency were reclassified as non-deficient after adjusting for eGFR (reference point eGFR 90 mL/min) with both P-MMA decision limits. Overall B12 deficiency prevalence was reduced from 9.6% to 9.0% (P-MMA decision limit 0.43 µmol/L). With P-MMA decision limits at 0.75 and 0.43 µmol/L, 33.6% and 44.8% of B12 deficient patients with an eGFR <60 mL/min were reclassified as non-deficient. Conclusions: We have demonstrated that correcting P-MMA for eGFR can reclassify P-MMA levels across decision limits for diagnosing B12 deficiency, in particular for patients with reduced kidney function. This may have clinical implications for avoiding overdiagnosis of this chronic disease.

Problem in the Recent American Heart Association Guideline on Secondary Stroke Prevention: B Vitamins to Lower Homocysteine Do Prevent Stroke

In this article, we discuss a problem in the most recent American Heart Association guideline on secondary stroke prevention that apparently arose from the rules of evidence imposed on the guideline panel. We are told by the cochair of the panel that American Heart Association rules about guidelines for secondary prevention prohibited consideration of primary prevention studies and secondary analyses of secondary prevention studies. However, evidence-based medicine should consider all the best external evidence available and also clinical judgement. The most important problem in the guideline was the recommendation that B vitamins to lower homocysteine do not prevent recurrent stroke. When considering all the best external evidence, it is clear that B vitamins do prevent stroke, but in the early secondary stroke prevention studies, the benefit of B vitamins in participants with good renal function was apparently offset by harm from cyanocobalamin among participants with renal failure (level B-R evidence). We review the evidence that B vitamins should be used to prevent stroke, both in primary and secondary stroke prevention (class 2a recommendation). We also review issues in folate metabolism that require further study, with regard to the form of folate to be used for stroke prevention. We recommend that the guideline be revised to say that B vitamins to lower homocysteine prevent stroke and that methylcobalamin or hydroxycobalamin should be used instead of cyanocobalamin.

Perspective: The High-Folate-Low-Vitamin B-12 Interaction Is a Novel Cause of Vitamin B-12 Depletion with a Specific Etiology-A Hypothesis

Vitamin B-12 is a water-soluble vitamin that plays important roles in intermediary metabolism. Vitamin B-12 deficiency has many identifiable causes, including autoimmune and other gastrointestinal malabsorption disorders, dietary deficiency, and congenital defects in genes that are involved in vitamin B-12 trafficking and functions. Another putative cause of vitamin B-12 deficiency is the high-folate-low vitamin B-12 interaction, first suspected as the cause for observed relapse and exacerbation of the neurological symptoms in patients with pernicious anemia who were prescribed high oral doses of folic acid. We propose that this interaction is real and represents a novel cause of vitamin B-12 depletion with specific etiology. We hypothesize that excessive intake of folic acid depletes serum holotranscobalamin (holoTC), thereby decreasing active vitamin B-12 in the circulation and limiting its availability for tissues. This effect is specific for holoTC and does not affect holohaptocorrin, the inert form of serum vitamin B-12. Depletion of holoTC by folic acid in individuals with already low vitamin B-12 status further compromises the availability of vitamin B-12 coenzymes to their respective enzymes, and consequently a more pronounced state of biochemical deficiency. This hypothesis is drawn from evidence of observational and intervention studies of vitamin B-12-deficient patients and epidemiological cohorts. The evidence also suggests that, in a depleted state, vitamin B-12 is diverted to the hematopoietic system or the kidney. This most likely reflects a selective response of tissues expressing folate receptors with high affinity for unmetabolized folic acid (UMFA; e.g., hematopoietic progenitors and renal tubules) compared with those tissues (e.g., liver) that only express the reduced folate carrier, which is universally expressed but has poor affinity for UMFA. The biochemical and physiological mechanisms underlying this interaction require elucidation to clarify its potential public health significance.

Loss of the Vitamin B-12 Transport Protein Tcn2 Results in Maternally Inherited Growth and Developmental Defects in Zebrafish

BACKGROUND

In humans, vitamin B-12 (cobalamin) transport involves 3 paralogous proteins: transcobalamin, haptocorrin, and intrinsic factor. Zebrafish (Danio rerio) express 3 genes that encode proteins homologous to known B-12 carrier proteins: tcn2 (a transcobalamin ortholog) and 2 atypical β-domain-only homologs, tcnba and tcnbb.

OBJECTIVES

Given the orthologous relation between zebrafish Tcn2 and human transcobalamin, we hypothesized that zebrafish carrying null mutations of tcn2 would exhibit phenotypes consistent with vitamin B-12 deficiency.

METHODS

First-generation and second-generation tcn2-/- zebrafish were characterized using phenotypic assessments, metabolic analyses, viability studies, and transcriptomics.

RESULTS

Homozygous tcn2-/- fish produced from a heterozygous cross are viable and fertile but exhibit reduced growth, which persists into adulthood. When first-generation female tcn2-/- fish are bred, their offspring exhibit gross developmental and metabolic defects. These phenotypes are observed in all offspring from a tcn2-/- female regardless of the genotype of the male mating partner, suggesting a maternal effect, and can be rescued with vitamin B-12 supplementation. Transcriptome analyses indicate that offspring from a tcn2-/- female exhibit expression profiles distinct from those of offspring from a tcn2+/+ female, which demonstrate dysregulation of visual perception, fatty acid metabolism, and neurotransmitter signaling pathways.

CONCLUSIONS

Our findings suggest that the deposition of vitamin B-12 in the yolk by tcn2-/- females may be insufficient to support the early development of their offspring. These data present a compelling model to study the effects of vitamin B-12 deficiency on early development, with a particular emphasis on transgenerational effects and gene-environment interactions.

Stroke Prevention

In 44 years of practicing stroke prevention, I have learned many lessons; in this article, I hope to impart some of them. Three areas of my research are discussed. Controlling resistant hypertension is markedly improved by physiologically individualized therapy based on renin/aldosterone phenotyping; this is particularly important in black patients. Measurement of carotid plaque burden strongly predicts cardiovascular risk and is useful for genetic research and for a process called treating arteries instead of risk factors. Doing so in high-risk patients with asymptomatic carotid stenosis was associated with a >80% reduction in the 2-year risk of stroke and myocardial infarction. It also permitted the identification of extremes of atherosclerosis that are useful for studying both the genetics and the biology of atherosclerosis. Patients with very high plaque burden despite low levels of risk factors have an unexplained phenotype; those with little or no plaque despite high levels of risk factors are protected. Patients with unexplained atherosclerosis have higher plasma levels of toxic metabolites produced by the intestinal microbiome largely from egg yolk, red meat, and protein, and those metabolites are renally excreted. This has important dietary implications for stroke prevention. Lowering of plasma total homocysteine with B vitamins significantly reduces the risk of stroke. That was not apparent in early studies because harm from cyanocobalamin among participants with renal failure obscured the benefit among those with good renal function. We should be using B vitamins to prevent stroke but should use methylcobalamin or oxocobalamin instead of cyanocobalamin.

Vitamin B 12 deficiency and hyperhomocysteinaemia in outpatients with stroke or transient ischaemic attack: a cohort study at an academic medical centre

OBJECTIVE

We sought to assess the current magnitude of the opportunity for secondary stroke prevention with B vitamins.

DESIGN

A cohort study.

SETTING

The Urgent TIA (Transient Ischaemic Attack) Clinic at an academic medical centre.

MAIN OUTCOME MEASURES

We assessed the prevalence of biochemical vitamin B12 deficiency (B12Def, serum B12 <156 pmol/L), hyperhomocysteinaemia (HHcy; plasma total homocysteine [tHcy] >14 µmol/L) and metabolic B12 deficiency (MetB12Def, serum B12 <258 pmol/L and HHcy) between 2002 and 2017, by age group and by stroke subtype.

RESULTS

Data were available in 4055 patients. B12Def was present in 8.2% of patients overall; it declined from 10.9% of patients referred before 2009 to 5.4% thereafter (p=0.0001). MetB12Def was present in 10.6% of patients, and HHcy was present in 19.1% of patients. Among the patients aged ≥80 years, MetB12Def was present in 18.1% and HHcy in 35%. Among the 3410 patients whose stroke subtype was determined, HHcy was present in 18.4% of patients: 23.3% of large artery atherosclerosis, 18.1% of cardioembolic, 16.3% of small vessel disease, 10.8% of other unusual aetiologies and 13.6% of undetermined subtypes (p=0.0001).

CONCLUSIONS

Despite a decline in our referral area since 2009, B12Def, MetB12Def and HHcy remain common in patients with stroke/TIA. Because these conditions are easily treated and have serious consequences, all patients with stroke/TIA should have their serum B12 and tHcy measured.

Population Reference Values for Serum Methylmalonic Acid Concentrations and Its Relationship with Age, Sex, Race-Ethnicity, Supplement Use, Kidney Function and Serum Vitamin B12 in the Post-Folic Acid Fortification Period

Serum methylmalonic acid (MMA) is elevated in vitamin B-12 deficiency and in kidney dysfunction. Population reference values for serum MMA concentrations in post-folic acid fortification period are lacking. Aims of this study were to report the population reference values for serum MMA and to evaluate the relation between serum MMA and sex, age, race-ethnicity, kidney dysfunction and vitamin B-12. We used data from three National Health and Nutrition Examination Surveys, 1999–2000, 2001–2002 and 2003–2004 conducted after folic acid fortification commenced (n = 18,569). Geometric mean MMA was ≈22.3% higher in non-Hispanic white compared to non-Hispanic black (141.2 vs. 115.5 nmol/L) and was ≈62.7% higher in >70 years old persons compared to 21–30 years old persons (196.9 vs. 121.0 nmol/L). Median serum MMA was ≈28.5% higher in the 1st the quartile of serum vitamin B-12 than in the 4th quartile of serum vitamin B-12 and was ≈35.8% higher in the 4th quartile of serum creatinine than in the 1st quartile of serum creatinine. Multivariate-adjusted serum MMA concentration was significantly associated with race-ethnicity (p < 0.001) and age (p < 0.001) but not with sex (p = 0.057). In this large US population based study, serum MMA concentrations presented here reflect the post-folic acid fortification scenario. Serum MMA concentrations begin to rise at the age of 18–20 years and continue to rise afterwards. Age-related increase in serum MMA concentration is likely to be due to a concomitant decline in kidney function and vitamin B-12 status.

Vitamin B12 among Vegetarians: Status, Assessment and Supplementation

Cobalamin is an essential molecule for humans. It acts as a cofactor in one-carbon transfers through methylation and molecular rearrangement. These functions take place in fatty acid, amino acid and nucleic acid metabolic pathways. The deficiency of vitamin B12 is clinically manifested in the blood and nervous system where the cobalamin plays a key role in cell replication and in fatty acid metabolism. Hypovitaminosis arises from inadequate absorption, from genetic defects that alter transport through the body, or from inadequate intake as a result of diet. With the growing adoption of vegetarian eating styles in Western countries, there is growing focus on whether diets that exclude animal foods are adequate. Since food availability in these countries is not a problem, and therefore plant foods are sufficiently adequate, the most delicate issue remains the contribution of cobalamin, which is poorly represented in plants. In this review, we will discuss the status of vitamin B12 among vegetarians, the diagnostic markers for the detection of cobalamin deficiency and appropriate sources for sufficient intake, through the description of the features and functions of vitamin B12 and its absorption mechanism.

A Common Polymorphism in HIBCH Influences Methylmalonic Acid Concentrations in Blood Independently of Cobalamin

Methylmalonic acid (MMA) is a by-product of propionic acid metabolism through the vitamin B12 (cobalamin)-dependent enzyme methylmalonyl CoA mutase. Elevated MMA concentrations are a hallmark of several inborn errors of metabolism and indicators of cobalamin deficiency in older persons. In a genome-wide analysis of 2,210 healthy young Irish adults (median age 22 years) we identified a strong association of plasma MMA with SNPs in 3-hydroxyisobutyryl-CoA hydrolase (HIBCH, p = 8.42 × 10(-89)) and acyl-CoA synthetase family member 3 (ACSF3, p = 3.48 × 10(-19)). These loci accounted for 12% of the variance in MMA concentration. The most strongly associated SNP (HIBCH rs291466; c:2T>C) causes a missense change of the initiator methionine codon (minor-allele frequency = 0.43) to threonine. Surprisingly, the resulting variant, p.Met1?, is associated with increased expression of HIBCH mRNA and encoded protein. These homozygotes had, on average, 46% higher MMA concentrations than methionine-encoding homozygotes in young adults with generally low MMA concentrations (0.17 [0.14-0.21] μmol/L; median [25(th)-75(th) quartile]). The association between MMA levels and HIBCH rs291466 was highly significant in a replication cohort of 1,481 older individuals (median age 79 years) with elevated plasma MMA concentrations (0.34 [0.24-0.51] μmol/L; p = 4.0 × 10(-26)). In a longitudinal study of 185 pregnant women and their newborns, the association of this SNP remained significant across the gestational trimesters and in newborns. HIBCH is unique to valine catabolism. Studies evaluating flux through the valine catabolic pathway in humans should account for these variants. Furthermore, this SNP could help resolve equivocal clinical tests where plasma MMA values have been used to diagnose cobalamin deficiency.

Holotranscobalamin Levels in Children with Helicobacter pylori Infection

BACKGROUND

The purpose of this study was to evaluate the association between vitamin B12 levels and Helicobacter Pylori infection and to examine the clinical usefulness of holotranscobalamin (holoTC) measurement in children.

MATERIALS AND METHODS

Thirty patients between 6 and 15 years of age, who were diagnosed as H. pylori infected by C(14) urea breath test, and 26 controls were enrolled in the study. Tests for complete blood count, serum vitamin B12 and folate, plasma total homocysteine, and holoTC levels were performed in each patient in the study and control groups.

RESULTS

Mean plasma holoTC concentrations were significantly lower in children with H. pylori infection before treatment (median 23.7 pmol/L (12.9-37.1 pmol/L)) versus after treatment (median 38.2 pmol/L (21.2-61.4 pmol/L)) and controls (median 36.1 pmol/L (12.6-58.7 pmol/L)).

CONCLUSIONS

The findings of our study suggest that H. pylori infection has a reversible negative effect on vitamin B12 status reflected in a decreased level of plasma holoTC that normalizes upon treatment of the infection, while no change is observed in total plasma vitamin B12 .

Determining Functional Vitamin B12 Deficiency in the Elderly

BACKGROUND

Elevated concentration of serum total homocysteine usually occurs in vitamin B-12 deficiency. This metabolite can be measured and used for screening functional vitamin B-12 deficiency.

OBJECTIVES

We assessed functional vitamin B12 deficiency in Tehranian elderly admitted to elderly research center, University of Social Welfare and Rehabilitation Sciences.

PATIENTS AND MATERIALS

A cross-sectional study was performed on 232 elderly admitted to elderly research center in Tehran, Iran in 2012. According to other studies, individuals were classified into two groups: high risk of vitamin B-12 deficiency (< 220 pmol/L) and borderline vitamin B-12 (220-258 pmol/L) accompanied by elevated homocysteine (> 15 micmol/L).

RESULTS

Cut-off of 15.0 pmol/L for homocysteine was identified for persons with normal or elevated concentrations. Among persons aged 65-74 and ≥ 75 years, respectively, 56% and 93% were at high risk of vitamin B-12 deficiency.

CONCLUSIONS

The prevalence of B12 deficiency was higher in this study compared to other studies, so more attention and massive efficacious policy should be designed to reduce the deficiency of this vitamin.

Association of Transcobalamin II (TCN2) and Transcobalamin II-Receptor (TCblR) Genetic Variations With Cobalamin Deficiency Parameters in Elderly Women

Cobalamin (vitamin B12) deficiency is a subtle progressive clinical disorder, affecting nearly 1 in 5 individuals > 60 years old. This deficiency is produced by age-related decreases in nutrient absorption, medications that interfere with vitamin B12 absorption, and other comorbidities. Clinical heterogeneity confounds symptom detection for elderly adults, as deficiency sequelae range from mild fatigue and weakness to debilitating megaloblastic anemia and permanent neuropathic injury. A better understanding of genetic factors that contribute to cobalamin deficiency in the elderly would allow for targeted nursing care and preventive interventions. We tested for associations of common variants in genes involved in cobalamin transport and homeostasis with metabolic indicators of cobalamin deficiency (homocysteine and methylmalonic acid) as well as hematologic, neurologic, and functional performance features of cobalamin deficiency in 789 participants of the Women’s Health and Aging Studies. Although not significant when corrected for multiple testing, eight single nucleotide polymorphisms (SNPs) in two genes, transcobalamin II ( TCN2) and the transcobalamin II-receptor ( TCblR), were found to influence several clinical traits of cobalamin deficiency. The three most significant findings were the identified associations involving missense coding SNPs, namely, TCblR G220R (rs2336573) with serum cobalamin, TCN2 S348F (rs9621049) with homocysteine, and TCN2 P259R (rs1801198) with red blood cell mean corpuscular volume. These SNPs may modify the phenotype in older adults who are more likely to develop symptoms of vitamin B12 malabsorption.

Treatment of confirmed B12 deficiency in hemodialysis patients improves Epogen® requirements

Background

Vitamin B12 deficiency may have deleterious effects on end stage renal disease (ESRD) patients on maintenance hemodialysis, and may increase erythropoietin stimulating agent (ESA) resistance, yet little is known about its prevalence in this population.

Methods

Serum vitamin B12 and methylmalonic acid (MMA) levels were drawn from ESRD patients prior to hemodialysis. All patients with MMA levels greater than 800 nmol/L had peripheral smears evaluated for B12 deficiency. Those with confirmatory smears were considered to be deficient and received intramuscular vitamin B12 injections for 4 months. Post-treatment MMA levels and smears were obtained. Erythropoietin dosages were monitored throughout the treatment period.

Results

There was a 58% (60/103) prevalence of vitamin B12 deficiency as defined by a positive MMA level and a positive blood smear. Out of 52 patients with positive smears, 36 (69.2%) were negative on repeat analysis after B12 treatment. Mean Epogen® (EPO) dosages significantly decreased by 16,572 ± 41,902 units per month from baseline to the post-B12 t reatment period (P = 0.0082, Wilcoxon signed-rank test). Three months prior to treatment, the mean monthly EPO dose was 82,067 ± 47,906 and post, the mean EPO usage was 65,495 ± 39,691. Post treatment hemoglobin levels were not significantly different from baseline.

Conclusion

Vitamin B12 supplementation was associated with a decrease in the mean dose of ESA administration while maintaining a stable hemoglobin level. Maintaining serum vitamin B12 levels improves functionality, and may allow a decrease in the use of ESA’s, avoiding their toxicities and significant costs.

Cobalamin deficiency

Cobalamin (Cbl, vitamin B12) consists of a corrinoid structure with cobalt in the centre of the molecule. Neither humans nor animals are able to synthesize this vitamin. Foods of animal source are the only natural source of cobalamin in human diet. There are only two enzymatic reactions in mammalian cells that require cobalamin as cofactor. Methylcobolamin is a cofactor for methionine synthase. The enzyme methylmalonyl-CoA-mutase requires adenosylcobalamin as a cofactor. Therefore, serum concentrations of homocysteine (tHcy) and methylmalonic acid (MMA) will increase in cobalamin deficiency. The cobalamin absorption from diet is a complex process that involves different proteins: haptocorrin, intrinsic factor and transcobalamin (TC). Cobalamin that is bound to TC is called holotranscobalamin (holoTC) which is the metabolically active vitamin B12 fraction. HoloTC consists 6 and 20% of total cobalamin whereas 80% of total serum cobalamin is bound to another binding protein, haptocorrin. Cobalamin deficiency is common worldwide. Cobalamin malabsorption is common in elderly subjects which might explain low vitamin status. Subjects who ingest low amount of cobalamin like vegetarians develop vitamin deficiency. No single parameter can be used to diagnose cobalamin deficiency. Total serum cobalamin is neither sensitive nor it is specific for cobalamin deficiency. This might explain why many deficient subjects would be overlooked by utilizing total cobalamin as status marker. Concentration of holotranscobalamin (holoTC) in serum is an earlier marker that becomes decreased before total serum cobalamin. Concentrations of MMA and tHcy increase in blood of cobalamin deficient subjects. Despite limitations of these markers in patients with renal dysfunction, concentrations of MMA and tHcy are useful functional markers of cobalamin status. The combined use of holoTC and MMA assays may better indicate cobalamin status than either of them. Because Cbl deficiency is a risk factor for neurodegenerative diseases an early diagnosis of a low B12 status is required which should be followed by an effective treatment in order to prevent irreversible damages.

Assessment of the vitamin B12 status of pregnant women in Nigeria using plasma holotranscobalamin

Maternal vitamin B12 deficiency during pregnancy is an independent risk factor for neural tube defects and other neurological problems in infants. We determined the vitamin B12 status of 143 pregnant women in Nigeria representing all trimesters who presented to an antenatal clinic in Jos, Nigeria, using holotranscobalamin II levels (holoTCII), which is a measure of the vitamin B12 that is available for uptake into tissues. The holoTCII concentration ranged from 13 to 128 pmol/L. Using a cutoff of 40 pmol/L, 36% of the women were classified as vitamin B12-deficient. HoloTCII concentrations correlated negatively with plasma homocysteine levels (r = −0.24, P = 0.003) and positively with red blood cell folate concentrations (r = 0.28, P < 0.001). These data underscore the importance of supplementing pregnant women in Nigeria with vitamin B12 in order to ensure adequate vitamin B12 status and decrease the risk for neural tube defects.

Cysteine: a potential biomarker for obstructive sleep apnea

OBJECTIVE

Obstructive sleep apnea (OSA) is a risk factor for a number of cardiovascular conditions. Although homocysteine (Hcy) and cysteine (Cys) are regarded as cardiovascular risk factors, few studies have analyzed Hcy and Cys plasma concentrations in patients with OSA. The aim of this study was to evaluate the role of Hcy and Cys in OSA in comparison with subjects without OSA and to determine the possible influence of obesity on these variables.

METHODS

Patients who submitted to polysomnography studies were recruited to engage in an 8-h fasting period for blood sample withdrawal, physical examination, ECG, and echocardiogram. A subgroup of lean patients with OSA (BMI < 25 kg/m(2)) were analyzed to rule out the influence of obesity. Fifteen patients were randomly assigned to participate in a continuous positive airway pressure (CPAP) protocol to assess the influence of OSA treatment on the obtained measurements.

RESULTS

A total of 75 patients and 75 control subjects matched for age and sex were analyzed. The Cys plasma levels were higher in patients with OSA compared with control subjects (490.16 ± 67.00 μmol/L vs 439.81 ± 76.12 μmol/L, respectively, P < .01); however, the Hcy plasma levels did not differ between groups. Cys plasma levels were also higher in the OSA lean subgroup when compared with lean control subjects (484.21 ± 71.99 μmol/L vs 412.01 ± 70.73 μmol/L, respectively, P = .009). There was a significant decrease of Cys plasma levels after 6 months of CPAP effective therapy.

CONCLUSION

Cys is a potential biomarker of OSA in obese and nonobese patients and is reduced after effective OSA treatment.

Determinants of plasma methylmalonic acid in a large population: implications for assessment of vitamin B12 status

BACKGROUND

Methylmalonic acid (MMA) in plasma or serum is widely used for assessment of vitamin B(12) status. However, data are sparse regarding factors, besides renal function, that may influence MMA concentrations. We searched for important determinants of plasma MMA in the general population.

METHODS

In 6946 middle-aged (47-49 years) and elderly (71-74 years) individuals from the Hordaland Homocysteine Study in Norway, we collected anthropometric measurements, lifestyle data, and plasma MMA, vitamin B(12), and creatinine measurements. For 5820 individuals, we also collected dietary data.

RESULTS

Age and plasma creatinine were positively associated with plasma MMA, whereas plasma vitamin B(12) was negatively associated. These variables together with sex were the strongest determinants of plasma MMA, accounting for 16% of the variation (R(2) = 0.16). Addition of anthropometric measures and lifestyle and dietary factors only gave slight improvement (total R(2) = 0.167). Increased plasma MMA was seen when plasma vitamin B(12) was <400 pmol/L. In individuals with vitamin B(12) >or =400 micromol/L (vitamin B(12)-replete), the 2.5th-97.5th percentile reference limits for MMA were 0.10-0.28 micromol/L (middle-aged) and 0.10-0.36 micromol/L (elderly). When plotted against creatinine (nomograms), the 97.5th percentile of MMA was similar in men and women but approximately 0.15 micromol/L higher in elderly than middle-aged individuals. Vitamin B(12)-replete participants had MMA upper limits approximately 0.1 micromol/L (elderly) and 0.04 micromol/L (middle-aged) below those of the unselected population at all creatinine concentrations.

CONCLUSIONS

Identified determinants accounted for <17% of the overall variation in plasma MMA. The difference in MMA between middle-aged and elderly individuals is only partly explained by creatinine and vitamin B(12) concentrations.

Long-term effects of folic acid fortification and B-vitamin supplementation on total folate, homocysteine, methylmalonic acid and cobalamin in older adults

OBJECTIVE

To investigate the long-term effects of the Canadian folic acid fortification program in older adults' whole blood cell folate (folate) and cobalamin (Cbl) status, including homocysteine (tHcy) and methylmalonic acid (MMA), with and without voluntary B-vitamin intake, from 1997 to 2004.

METHODS

Cohort of community-dwelling volunteer older adults. Clinical and biochemical data, including intake of B-vitamin supplements, were obtained at 2- to 2.5-year intervals and divided in 4 periods. Random coefficients (mixed effects) models were used to estimate the linear trend in folate and to compare levels of biochemical parameters between periods. All models were estimated by restricted maximum likelihood as implemented in PROC MIXED of SAS V8.2.

RESULTS

Folate levels increased continuously at a yearly rate of 234 ng/mL (95% CI 213-254; p < 0.001) and had not plateaued by the last period when 84% of subjects without B-vitamins had elevated folate. Homocysteine did not remain suppressed. Elevated tHcy was as prevalent in the last study period as in the first. No significant deficits of Cbl or increases of MMA were observed, but MMA levels tended to increase with time in subjects without B-vitamins. B-vitamin supplements significantly affected all results, reducing tHcy and MMA levels.

CONCLUSION

In this population, fortification with folic acid has resulted in cumulative increases of folate with no long-term reduction in tHcy or changes in Cbl or MMA. Possible deleterious effects of cumulative increases of folate, and beneficial effects of B-vitamin supplements in reducing tHcy and MMA, should be investigated.

Epidemiology of anemia in older adults

Anemia is a common, multifactorial condition among older adults. The World Health Organization (WHO) definition of anemia (hemoglobin concentration <12 g/dL in women and <13 g/dL in men) is most often used in epidemiologic studies of older adults. More than 10% of community-dwelling adults age 65 years and older has WHO-defined anemia. After age 50 years, prevalence of anemia increases with advancing age and exceeds 20% in those 85 years and older. In nursing homes, anemia is present in 48% to 63% of residents. Incidence of anemia in older adults is not well characterized. Among older adults with anemia, approximately one third have evidence of iron, folate, and/or vitamin B(12) deficiency, another third have renal insufficiency and/or chronic inflammation, and the remaining third have anemia that is unexplained. Several studies demonstrate that anemia is associated with poorer survival in older adults. This review details the distribution and consequences of anemia in older adults and identifies future epidemiologic research needs.

Vitamin B12 deficiency in hypersecretors during long-term acid suppression with proton pump inhibitors

BACKGROUND

Proton pump inhibitors (PPIs) may cause cyanocobalamin (vitamin B12) malabsorption, but measuring serum B12 alone may underestimate the prevalence. However, B12 deficiency elevates methylmalonic acid and homocysteine, both additional markers of B12 deficiency.

AIM

To determine the true prevalence of B12 deficiency and whether acid suppression by PPI caused it.

METHODS

Sixty-one acid hypersecretors (basal acid output >15 mmol/h), 46 with gastrinoma [Zollinger-Ellison (ZE) syndrome] and 15 without [acid hypersecretor without gastrinoma (pseudo-ZE)], were treated with lansoprazole to determine its long-term (up to 18 years) pharmacological and clinical efficacy and safety, particularly as regards malabsorption of B12.

RESULTS

Of 61 patients, six (10%) had low serum B12. Additional tests uncovered B12 deficiency in 13 (31%) of 41 still-available patients, despite normal serum B12. B12 replacement reduced elevated homocysteine and methylmalonic acid, supporting the diagnosis. Also, measuring both basal and stimulated gastric secretion, we found that acid suppression was neither prolonged nor profound enough to explain the B12 deficiency.

CONCLUSIONS

In long-term recipients of PPIs, B12 deficiency was more frequent (29%) than detected by measuring only serum B12, and there was not enough acid suppression to explain this deficiency.

Vitamin B12 deficiency results in the abnormal regulation of serine dehydratase and tyrosine aminotransferase activities correlated with impairment of the adenylyl cyclase system in rat liver

The aim of the present study was to elucidate the mechanism of the vitamin B(12) deficiency-induced changes of the serine dehydratase (SDH) and tyrosine aminotransferase (TAT) activities in the rat liver. When rats were maintained on a vitamin B(12)-deficient diet, the activities of these two enzymes in the liver were significantly reduced compared with those in the B12-sufficient control rats (SDH 2.8 (sd 0.56) v. 17.5 (sd 6.22) nmol/mg protein per min (n 5); P < 0.05) (TAT 25.2 (sd 5.22) v. 41.3 (sd 8.11) nmol/mg protein per min (n 5); P < 0.05). In the B(12)-deficient rats, the level of SDH induction in response to the administration of glucagon and dexamethasone was significantly lower than in the B(12)-sufficient controls. Dexamethasone induced a significant increase in TAT activity in the primary culture of the hepatocytes prepared from the deficient rats, as well as in the cells from the control rats. However, a further increase in TAT activity was not observed in the hepatocytes from the deficient rats, in contrast to the cells from the controls, when glucagon was added simultaneously with dexamethasone. The glucagon-stimulated production of cAMP was significantly reduced in the hepatocytes from the deficient rats relative to the cells from the control rats. Furthermore, the glucagon-stimulated adenylyl cyclase activity in the liver was significantly lower in the deficient rats than in the controls. These results suggest that vitamin B(12) deficiency results in decreases in SDH and TAT activities correlated with the impairment of the glucagon signal transduction through the activation of the adenylyl cyclase system in the liver.

Vitamin B12, homocysteine and carotid plaque in the era of folic acid fortification of enriched cereal grain products

BACKGROUND

Carotid plaque area is a strong predictor of cardiovascular events. High homocysteine levels, which are associated with plaque formation, can result from inadequate intake of folate and vitamin B12. Now that folic acid fortification is widespread in North America, vitamin B12 has become an important determinant of homocysteine levels. We sought to determine the prevalence of low serum levels of vitamin B12, and their relation to homocysteine levels and carotid plaque area among patients referred for treatment of vascular disease since folic acid fortification of enriched grain products.

METHODS

We evaluated 421 consecutive new patients with complete data whom we saw in our vascular disease prevention clinics between January 1998 and January 2002. We measured total carotid plaque area by ultrasound and determined homocysteine and serum vitamin B12 levels in all patients.

RESULTS

The patients, 215 men and 206 women, ranged in age from 37 to 90 years (mean 66 years). Most were taking medications for hypertension (67%) and dyslipidemia (62%). Seventy-three patients (17%) had vitamin B12 deficiency (vitamin B12 level < 258 pmol/L with homocysteine level > 14 mumol/L or methylmalonic acid level > 271 nmol/L). The mean area of carotid plaque was significantly larger among the group of patients whose vitamin B12 level was below the median of 253 pmol/L than among those whose vitamin B12 level was above the median: 1.36 (standard deviation [SD] 1.27) cm2 v. 1.09 (SD 1.0) cm2; p = 0.016.

CONCLUSIONS

Vitamin B12 deficiency is surprisingly common among patients with vascular disease, and, in the setting of folic acid fortification, low serum vitamin B12 levels are a major determinant of elevated homocysteine levels and increased carotid plaque area.

Effects of moderate alcohol consumption on folate and vitamin B(12) status in postmenopausal women

BACKGROUND

Although alcohol intake has been positively associated with breast cancer risk in epidemiologic studies, a causal relationship has not been established, and the mechanisms mediating this association are speculative. Alcohol may act through altered status of folate and vitamin B(12), two vitamins required for DNA methylation and nucleotide synthesis, and thus cell integrity. Although the effects of heavy alcohol intake on folate and vitamin B(12) status have been well-documented, few studies have addressed the effects of moderate alcohol intake in a controlled setting.

OBJECTIVE

The objective of this study was to determine the effects of moderate alcohol intake on folate and vitamin B(12) status in healthy, well-nourished, postmenopausal women.

DESIGN

The study design was a randomized, diet-controlled crossover intervention. Postmenopausal women (n=53) received three 8-week alcohol treatments in random order: 0, 15, and 30 g/day. Treatment periods were preceded by 2-5-week washout periods. Blood collected at baseline and week 8 of each treatment period was analyzed for serum folate, vitamin B(12), homocysteine (HCY), and methylmalonic acid (MMA) concentrations.

RESULTS

After adjusting for body mass index (BMI), a significant 5% decrease was observed in mean serum vitamin B(12) concentrations from 0 to 30 g of alcohol/day (461.45+/-30.26 vs 440.25+/-30.24 pg/ml; P=0.03). Mean serum HCY concentrations tended to increase by 3% from 0 to 30 g of alcohol/day (9.44+/-0.37 vs 9.73+/-0.37 micromol/l; P=0.05). Alcohol intake had no significant effects on serum folate or MMA concentrations.

CONCLUSIONS

Among healthy, well-nourished, postmenopausal women, moderate alcohol intake may diminish vitamin B(12) status.

Choline deficiency in mice and humans is associated with increased plasma homocysteine concentration after a methionine load

BACKGROUND

Elevated concentrations of homocysteine in blood may be an independent risk factor for the development of atherosclerosis. Elevated homocysteine concentrations can be caused by decreased methylation of homocysteine to form methionine, as occurs in folate deficiency. A parallel pathway exists for methylation of homocysteine, in which choline, by way of betaine, is the methyl donor.

OBJECTIVE

Our goal was to determine whether choline deficiency results in a decreased capacity to methylate homocysteine.

DESIGN

C57BL/6J mice were fed diets containing 0, 10, or 35 mmol choline/kg diet for 3 wk. We then administered an oral methionine load to the animals and measured plasma homocysteine concentrations. Also, in a pilot study, we examined 8 men who were fed a diet providing 550 mg choline/d per 70 kg body weight for 10 d, followed by a diet providing almost no choline, until the subjects were clinically judged to be choline deficient or for <or=42 d. A methionine load was administered at the end of each dietary phase.

RESULTS

Two hours after the methionine load, choline-deficient mice had plasma homocysteine concentrations twice those of choline-fed mice. Four hours after the methionine load, clinically choline-depleted men had plasma homocysteine concentrations that were 35% greater than those in men not choline depleted.

CONCLUSION

These results suggest that choline, like folate, plays an important role in the metabolism of homocysteine in humans and that response to a methionine load may be useful when assessing choline nutriture.

Cobalamin: a critical vitamin in the elderly

Vitamin B(12) deficiency is a common problem in elderly subjects. If a serum cobalamin level of about 150 pmol/L (200 pg/mL) is considered normal, 10-15% of the elderly are deficient. Today, however, a threshold of 220-258 pmol/L (300-350 pg/mL) is recognized as desirable in the elderly, or else sensitive markers like the blood concentration of homocysteine or methylmalonic acid (MMA) are used. Then the prevalence of cobalamin deficiency rises to up to 43%. In the elderly, this high prevalence of poor cobalamin status is predominantly caused by atrophic gastritis type B. Atrophic gastritis results in declining gastric acid and pepsinogen secretion, and hence decreasing intestinal absorption of the cobalamin protein complexes from food. About 20-50% of the elderly are affected. Furthermore, the reduced acid secretion leads to an alkalinization of the small intestine, which may result in bacterial overgrowth and thus to a further decrease of the bioavailability of the vitamin. In addition, some drugs such as proton pump inhibitors or H2 receptor antagonists inhibit the intestinal absorption of vitamin B(12). An already moderately reduced vitamin B(12) level is associated with vascular disease and neurocognitive disorders such as depression and impaired cognitive performance. Furthermore, a poor vitamin B(12) status is assumed to be involved in the development and progression of dementia (e.g., Alzheimer's dementia). This is especially observable if the folic acid status is reduced as well. Due to the insecure supply, the cobalamin status of elderly persons (>/=60 years) should be regularly controlled and a general supplementation with vitamin B(12) (>50 microg/day) should be considered.

A critical evaluation of the relationship between serum vitamin B12, folate and total homocysteine with cognitive impairment in the elderly

BACKGROUND

Serum homocysteine increases with age and is also considered a marker for low serum vitamin B(12) and folate. Furthermore, raised serum total homocysteine has been associated with atrophic changes in the brain. An association between serum vitamin B(12)/folate and cognitive impairment would be of considerable public health importance in view of the increasing numbers of elderly people.

AIM

To systematically review published studies on the relationship between serum vitamin B(12), folate and total homocysteine and cognitive function in the elderly.

DESIGN AND DATA SOURCES

A systematic review was undertaken of published evidence in English, examining the association between low serum vitamin B(12)/folate and raised total homocysteine with cognitive impairment (as indicated by low scores on neuropsychological testing) in subjects aged over 60 years. Sixteen electronic databases and cited articles were searched. Of 383 potential articles, six fulfilled the eligibility criteria: three case control and three cohort studies were identified. 'The Cochrane Non-Randomized Studies Methods Group' guidelines were used for assessment and extraction of data from these studies.

RESULTS

All three case control studies found that serum total homocysteine was significantly higher in cases when compared with controls, and there was wide variation for both serum vitamin B(12) and folate in both groups of participants. The relationship of serum folate and vitamin B(12) status with cognitive impairment was heterogeneous and one case control study reported decreasing cognitive scores with increasing serum vitamin B(12). In the cohort studies, although serum total homocysteine could predict the rate of decline in neuropsychological testing, the overall odds ratio/relative risk (RR) of developing cognitive impairment in relation to levels of serum B(12) and serum folate were not significant. Although one study reported a significant RR of developing Alzheimer's disease when both serum folate and B(12) levels were low. One cohort study reported an increased prevalence of Alzheimer's type dementia in subjects who had normal serum vitamin B(12) at baseline.

CONCLUSION

Serum total homocysteine is negatively correlated with neuropsychological tests scores. But the evidence does not support a correlation between serum vitamin B(12) or folate and cognitive impairment in people aged over 60 years. Hence, there is little evidence to justify treating cognitive impairment with vitamin B(12) or folate supplementation. This is consistent with the findings from recent systematic reviews of randomized double-blind trials, which have not found any evidence of potential benefit of vitamin supplementation. Further research is required in order to establish whether raised serum total homocysteine is a cause or consequence of disease.

Prevalence of anemia in persons 65 years and older in the United States: evidence for a high rate of unexplained anemia

Clinicians frequently identify anemia in their older patients, but national data on the prevalence and causes of anemia in this population in the United States have been unavailable. Data presented here are from the noninstitutionalized US population assessed in the third National Health and Nutrition Examination Survey (1988-1994). Anemia was defined by World Health Organization criteria; causes of anemia included iron, folate, and B(12) deficiencies, renal insufficiency, anemia of chronic inflammation (ACI), formerly termed anemia of chronic disease, and unexplained anemia (UA). ACI by definition required normal iron stores with low circulating iron (less than 60 microg/dL). After age 50 years, anemia prevalence rates rose rapidly, to a rate greater than 20% at age 85 and older. Overall, 11.0% of men and 10.2% of women 65 years and older were anemic. Of older persons with anemia, evidence of nutrient deficiency was present in one third, ACI or chronic renal disease or both was present in one third, and UA was present in one third. Most occurrences of anemia were mild; 2.8% of women and 1.6% of men had hemoglobin levels lower than 110 g/L (11 g/dL). Therefore, anemia is common, albeit not severe, in the older population, and a substantial proportion of anemia is of indeterminate cause. The impact of anemia on quality of life, recovery from illness, and functional abilities must be further investigated in older persons.

Potential Association of Thyrotoxicosis with Vitamin B and Folate Deficiencies, Resulting in Risk for Hyperhomocysteinemia and Subsequent Thromboembolic Events

OBJECTIVE

To describe a patient with severe thyrotoxicosis attributable to Graves' disease who had a thrombotic cerebrovascular accident and hyperhomocysteinuria, which resolved on correction of the thyrotoxicosis, and to present findings in a pilot study undertaken to investigate the relationship among thyrotoxicosis, homocysteine, folate, and vitamin B(12).

METHODS

We present a case report of the index case, with clinical and laboratory details. For the investigative analysis, 21 patients who were 18 to 50 years old and had newly diagnosed, untreated Graves' disease and 10 age-and sex-matched euthyroid control subjects were studied. Of the patients with Graves' disease, 11 underwent studies both at diagnosis and after treatment. Fasting blood tests were performed for thyrotropin, free thyroxine, homocys-teine, vitamin B(12), folate, and methylmalonic acid, a marker of vitamin B(12) deficiency.

RESULTS

Vitamin B(12), folate, homocysteine, and methylmalonic acid levels were not significantly different between the thyrotoxic and control or posttreatment groups. In patients with thyrotoxicosis, however, free thyroxine was positively correlated with both homocysteine (r = 0.67; P = 0.03) and methylmalonic acid (r = 0.89; P = 0.003).

CONCLUSION

The positive correlation between free thyroxine levels and both homocysteine and methylmalonic acid suggests that thyrotoxicosis may be associated with functional vitamin B(12) deficiency. Such a deficiency may result in clinically important hyperhomocysteine-mia.

Development and evaluation of an isotope dilution LC/MS method for the determination of total homocysteine in human plasma

Elevated plasma homocysteine has been identified as a strong and independent risk factor for cardiovascular diseases, and recently, it has been associated with the development of dementia in older adults. Selected ion-monitoring isotope-dilution LC/MS (electrospray) has been developed and evaluated as a reference method for the accurate determination of total homocysteine in human plasma. Homocysteine is quantitatively isolated from plasma via the use of anion-exchange resins and then detected and quantified in stabilized plasma extracts with selected ion-monitoring LC/MS. This method is shown to be highly comparable to LC/MS/MS determinations in terms of its analytical accuracy and precision, yet this alternative measurement approach does not necessitate the enhanced instrumentation or added expense required of tandem MS/MS determinations. LC/MS detection of homocysteine was linear (standard error of the estimate for the regression line was 0.0323) over 3 orders of magnitude, and the calculated limits of detection and quantification were 0.06 micromol/L (0.12 ng on column) and 0.6 micromol/L (1.2 ng on column), respectively. Independent calibration curves showed excellent linearity (r2 > or = 0.996) between 0 and 25 micromol/L homocysteine over a 3-day period. The accuracy and precision of total homocysteine measurements for patient samples and quality control pools using LC/MS were compared to total homocysteine measurements using LC/MS/MS, GC/MS, FPIA, and LC-FD. LC/MS performed well in relation to the other homocysteine methods in terms of its capability to accurately quantify plasma homocysteine over the normal range (5-15 micromol/L).

Vegetarian lifestyle and monitoring of vitamin B-12 status

Vegetarians are at risk to develop deficiencies of some essential nutrients, especially vitamin B-12 (cobalamin). Cobalamin occurs in substantial amounts only in foods derived from animals and is essential for one-carbon metabolism and cell division. Low nutritional intake of vitamin B-12 may lead to negative balance and, finally, to functional deficiency when tissue stores of vitamin B-12 are depleted. Early diagnosis of vitamin B-12 deficiency seems to be useful because irreversible neurological damages may be prevented by cobalamin substitution. The search for a specific and sensitive test to diagnose vitamin B-12 deficiency is ongoing. Serum vitamin B-12 measurement is a widely applied standard method. However, the test has poor predictive value. Optimal monitoring of cobalamin status in vegetarians should include the measurement of homocysteine (HCY), methylmalonic acid (MMA), and holotranscobalamin II. Vitamin B-12 deficiency can be divided into four stages. In stages I and II, indicated by a low plasma level of holotranscobalamin II, the plasma and cell stores become depleted. Stage III is characterized by increased levels of HCY and MMA in addition to lowered holotranscobalamin II. In stage IV, clinical signs become recognizable like macroovalocytosis, elevated MCV of erythrocytes or lowered haemoglobin. In our investigations, we have found stage III of vitamin B-12 deficiency in over 60% of vegetarians, thus underlining the importance of cobalamin monitoring in this dietary group.

Elevated serum methylmalonic acid concentrations are common among elderly Americans

To describe serum methylmalonic acid (MMA) concentrations of elderly Americans and examine relationships between serum MMA and other factors, we used surplus serum samples collected from elderly (n = 1145) and young-adult (n = 1026) participants in Phase 2 of the third National Health and Nutrition Examination Survey (1991-1994). In approximately 20% of participants >/=65 y old, serum MMA was >370 nmol/L, the 90th percentile of the distribution of participants aged 30-39 y. Consistent with previous reports, we observed strong, independent positive associations between serum MMA concentration and serum concentrations of creatinine and homocysteine. After controlling for demographic factors and creatinine, geometric mean MMA concentration was lower in non-Hispanic blacks [223.6 nmol/L; 95% confidence interval (CI), 198.8-251.5] than non-Hispanic whites (265.1 nmol/L; 95% CI, 240.3-292.4). However, the prevalence of elevated levels did not vary with race/ethnicity. Serum MMA concentration bore a strong inverse relation to serum vitamin B-12 concentration. Nevertheless, elevated serum MMA concentrations affected approximately 15% of those with both normal serum creatinine concentrations and serum B-12 concentrations >148 pmol/L. We conclude that many elderly Americans demonstrate metabolic evidence of low B-12 status, that elevations occur frequently in the absence of traditional deficiency indicators and that levels vary with race/ethnicity and renal function.

Erythrocyte mean cellular volume and its relation to serum homocysteine, vitamin B12 and folate

Cobalamin (B12) and folate deficiency is related to both increased erythrocyte mean cellular volume (MCV) and raised serum total homocysteine (tHcy) values. Furthermore, there are indications that B12 and folate serum values do not represent the tissue status of the two vitamins exactly. Therefore, a direct relationship between MCV and tHcy, if demonstrated, could support the hypothesis that tHcy is a better indicator for the cited vitamin status than the serum levels of B12 and folate. We studied MCV, gamma glutamyl transferase (GGT), serum B12, folate and tHcy values in 200 hospitalized patients. There was a significant correlation of MCV with GGT (r = 0.266, P < 0.001) and with tHcy (r = 0.248, P < 0.001), but not with serum B12 and folate. Stepwise multiple linear regression with MCV as dependent and GGT, B12, folate and tHcy as independent variables, respectively, revealed significant associations of MCV with GGT (B = 2.18, 95% CI 0.95-3.42, P = 0.001) and tHcy (B = 3.33, 95% CI 1.26-5.39, P = 0.002). By removing tHcy from this model, serum B12 became a significant predictor of MCV (B = -1.70, 95% CI -3.25 to -0.15, P = 0.032). Serum folate was not significantly associated with MCV in multivariate analysis. In conclusion, the present study confirms indications that serum B12 and folate values lack clinical sensitivity and specificity in diagnosing vitamin deficiency states by showing MCV was better associated to tHcy, than to B12 or folate serum levels. This observation demonstrates that tHcy may be useful in diagnosing patients with B12 and/or folate deficiency.

Selenium deficiency in Fisher-344 rats decreases plasma and tissue homocysteine concentrations and alters plasma homocysteine and cysteine redox status

The purpose of the present study was to determine the effect of graded amounts of dietary selenium on plasma and tissue parameters of methionine metabolism including homocysteine. Male weanling Fisher-344 rats (n = 7-8/group) were fed a selenium-deficient, torula yeast-based diet, supplemented with 0 (selenium deficient), 0.02, 0.05 or 0.1 microg (adequate) selenium (as selenite)/g diet. After 61 d, plasma total homocysteine and cysteine were decreased (P < 0.0001) and glutathione increased (P < 0.0001) by selenium deficiency. The concentrations of homocysteine in kidney and heart were decreased (P = 0.02) by selenium deficiency. The activities of liver betaine homocysteine methyltransferase, methionine synthase, S-adenosylmethionine synthase, cystathionine synthase and cystathionase were determined; selenium deficiency affected only betaine homocysteine methyltransferase, which was decreased (P < 0.0001). The ratios of plasma free reduced homocysteine (or cysteine) to free oxidized homocysteine (or cysteine) or to total homocysteine (or cysteine) were increased by selenium deficiency, suggesting that selenium status affects the normally tightly controlled redox status of these thiols. Most differences due to dietary selenium were between rats fed 0 or 0.02 microg selenium/g diet and those fed 0.05 or 0.1 microg selenium/g diet. The metabolic consequences of a marked decrease in plasma homocysteine and smaller but significant decreases in tissue homocysteine are not known.

Cobalamin deficiency results in severe metabolic disorder of serine and threonine in rats

Dietary cobalamin (vitamin B12; Cbl) deficiency caused significant increases in plasma serine, threonine, glycine, alanine, tyrosine, lysine and histidine levels in rats. In particular, the serine and threonine levels were over five and eight times, respectively, higher in the Cbl-deficient rats than those in the sufficient controls. In addition, some amino acids, including serine and threonine, were excreted into urine at significantly higher levels in the deficient rats. When Cbl was supplemented into the deficient rats for 2 weeks, in coincidence with the disappearance of the urinary excretion of methylmalonic acid (an index of Cbl deficiency), the plasma serine and threonine levels were normalized. These results indicate that Cbl deficiency results in metabolic disorder of certain amino acids, including serine and threonine. The expression level of hepatic serine dehydratase (SDH), which catalyzes the conversion of serine and threonine to pyruvate and 2-oxobutyrate, respectively, was significantly lowered by Cbl deficiency, even though Cbl does not participate directly in the enzyme reaction. The SDH activity in the deficient rats was less than 20% of that in the sufficient controls, and was normalized 2 weeks after the Cbl supplementation. It is thus suggested that the decrease of the SDH expression relates closely with the abnormalities in the plasma and urinary levels of serine and threonine in the Cbl-deficient rats.

[Population reference ranges and determinants of plasma homocysteine levels]

BACKGROUND

There is a well-known relationship between plasma homocysteine levels and the risk of cardiovascular events. Determination of homocysteine levels may also be of potential diagnostic aid in several clinical situations. The construction of reference ranges should take age and sex variations into account.

SUBJECTS AND METHODS

396 healthy subjects were recruited (172 males and 224 females). Fasting plasma homocysteine levels were measured using the fluorescein polarization immunoassay technique (FPIA). Plasma levels of creatinine, folates, vitamin B12 and TSH were measured. 90% reference ranges were estimated by fractional polynomial regression methods.

RESULTS

Homocysteine plasma levels ranged from 4.35 micromol/l to 17,71 micromol/l (median 8.62 micromol/l). These concentrations increased with age and were higher in males (median 9.53 micromol/l [range: 5.45-17.5]) than in females (median 7.79 micromol/l[range: 4.35-17.71]). Sex differences decreased in the elderly. Creatinine plasma levels (with a positive association) and folate levels (with a negative association) had a statistically significant effect on the specific distribution of homocysteine levels according to age and sex.

CONCLUSIONS

Age-and sex-specific reference ranges of plasma homocysteine have been defined. Renal function along with folate plasma levels have to be accounted for when assessing these distribution ranges.

Association between erythrocyte mean corpuscular volume and peripheral arterial disease in male subjects: a case control study

Elevated serum total homocysteine, an established risk factor for peripheral arterial disease, is influenced by the vitamin B12 and folate status. Since these vitamins are inversely correlated with erythrocyte mean corpuscular volume, an investigation of whether mean corpuscular volume is higher in patients with symptomatic peripheral arterial disease than in healthy subjects was performed. Furthermore, a determination of predictors of increased mean corpuscular volume levels in this population free of symptomatic coronary artery disease, cerebrovascular disease, and diabetes mellitus was carried out. From 469 consecutive patients with symptomatic peripheral arterial disease, 100 fulfilled study inclusion criteria. Peripheral arterial disease was confirmed by angiography. One hundred age-matched subjects without peripheral arterial disease as verified by ankle-brachial index measurements >0.9 served as control subjects. Patients with PAD displayed a significantly higher mean corpuscular volume level (94.5 fl) than control subjects (90.9 fl, p<0.001). Logistic regression analysis showed that current smoking status (p<0.001) and mean corpuscular volume (p=0.009), but not total homocysteine or lipid parameters discriminated case control status. In addition, logistic regression analysis revealed a relationship of mean corpuscular volume with smoking (p=0.001), gamma-glutamyltransferase (p<0.001), and total homocysteine (p=0.012). This model predicted mean corpuscular volume values with an accuracy of 83%. Elevated mean corpuscular volume is a predictor of symptomatic peripheral arterial disease in the sample studied. A deficiency of folate and/or vitamin B12 may be responsible for this observation, as indicated by the correlation of mean corpuscular volume with total homocysteine. Due to the additional association of mean corpuscular volume with smoking and gamma-glutamyltransferase, an unhealthy lifestyle with low vitamin intake may cause elevated mean corpuscular volume values in patients with PAD.

Vitamin B12 Treatment Normalizes Metabolic Markers But Has Limited Clinical Effect: A Randomized Placebo-controlled Study

Background: The clinical significance of increased plasma methylmalonic acid (P-MMA) is unclear. We assessed the efficacy of vitamin B12 treatment in reducing P-MMA and plasma total homocysteine compared with the clinical benefits of treatment.

Methods: We studied 140 individuals with mildly to modestly increased P-MMA (0.40–2.00 μmol/L), not previously treated with vitamin B12, in a randomized, placebo-controlled study. A detailed medical history was obtained, and laboratory tests as well as an objective neurologic disability score were performed at baseline and 3 months after the start of intervention.

Results: P-MMA (P &lt;0.001) or plasma total homocysteine (P &lt;0.001) decreased in the treatment group vs the placebo group, but no significant difference was found in the change of blood hemoglobin (P = 0.18) and mean cell volume (P = 0.71). Changes in symptom scores did not differ between the groups for symptoms of anemia (P = 0.63), neurologic symptoms (P = 0.21), gastroenterologic symptoms (P = 0.32), or the Neurological Disability Score (P = 0.85).

Conclusions: Treatment with vitamin B12 reduces P-MMA and plasma total homocysteine, but individuals with a mild to modest increase in P-MMA may have only limited clinical benefit from vitamin B12 treatment, at least in the short term.

Homocysteine, cystathionine, methylmalonic acid and B-vitamins in patients with renal disease

Moderate hyperhomocysteinemia is very frequent in renal patients. Aside from homocysteine (HCY) itself, the metabolites methylmalonic acid (MMA) and cystathionine (CYS) supply further information about disturbances in HCY metabolism. In two groups of renal patients, transplant and hemodialysis patients, we measured HCY, MMA and CYS and evaluated their diagnostic value for impaired HCY metabolism due to vitamin deficiency and renal insufficiency. We investigated serum samples from 63 transplant patients and 38 patients undergoing hemodialysis. HCY, MMA and CYS were assayed by gas chromatography-mass spectrometry, vitamin B6 by HPLC, B12 and folate by chemiluminescence immunoassay. The determination of HCY, MMA, and CYS in renal patients provides specific information about intracellular disturbances of HCY metabolism. The frequency of increased metabolite levels in renal patients was much higher than the frequency of lowered vitamin concentrations in serum. Furthermore, the metabolite levels in transplant patients were only moderately increased, whereas they were strongly increased in patients on hemodialysis (HCY 19.2 vs. 28.8 micromol/l, MMA 292 vs. 1025 nmol/l, CYS 733 vs. 2711 nmol/l). Our findings may support the use of MMA determination in the diagnosis of vitamin B12 deficiency in renal patients. Compared to vitamin B12 deficiency, renal dysfunction itself appears to cause only a modest elevation in serum MMA. Regression analysis revealed that the moderate elevation of HCY and CYS in transplant patients is mainly a consequence of impaired remethylation of HCY to methionine with activated transsulfuration, whereas the mildly elevated MMA level is attributable to renal dysfunction. In patients on hemodialysis, all three metabolites were markedly elevated, indicating a strongly disturbed HCY metabolism. Based on a backward regression, we discovered that the HCY metabolism was strongly disturbed by renal insufficiency and vitamin deficiency. The markedly elevated HCY level was mainly attributable to functional vitamin B12 deficiency indicated by high MMA, and the strong CYS elevation was due to renal dysfunction and inhibition of this pathway by low levels of vitamin B6. In conclusion, besides HCY, the determination of MMA and CYS levels supports an early diagnosis of B-vitamin deficiency in renal patients. MMA is a more sensitive indicator of intracellular vitamin B12 deficiency than vitamin B12 in serum.

Vitamin B intake and status in healthy Havanan men, 2 years after the Cuban neuropathy epidemic

A prospective epidemiological study was carried out over 1 year to evaluate vitamin B complex dietary intake and status in Cuba, 2 years after the Cuban neuropathy epidemic of 1993. Of the 199 healthy middle-aged men selected, 141 completed the study. Volunteers were followed up every 3 months for 1 year. Dietary intake and status of thiamin, riboflavin, vitamin B6, folate and vitamin B12 were assessed each time. The dietary intake of vitamin B complex was low, particularly in June and July (folate), and October (thiamin). A deficient status was observed for vitamin B complex, except for vitamin B6. Vitamin B complex intake and status varied over the year. However, dietary intake and status were poorly related. The results prove that healthy Cuban men represent a vulnerable population in terms of vitamin B complex status and stress the necessity to both promote preventive multivitamin supplementation and produce local food rich in vitamin B complex.

Homocysteine, its metabolites, and B-group vitamins in renal transplant patients

BACKGROUND

Increased plasma total homocysteine (tHcy) levels are an independent risk factor for cardiovascular morbidity in patients with normal and impaired renal function, including stable renal transplant recipients (RTRs). Plasma concentrations of the metabolites of Hcy, such as cystathionine (Cys), methylmalonic acid (MMA), 2-methylcitric acid (MC), and its diastereomers MCI and MCII have been reported in only a few articles. We therefore looked for the serum concentration of these metabolites and their relationship to renal function, cardiovascular diseases, the immunosuppressive treatment, and serum concentrations of cobalamin and folate.

METHODS

Fifty RTRs (mean age 50.4 +/- 11.8 years, 35.9 +/- 44.4 months after kidney transplantation) and 35 controls (NP; mean age 43.5 +/- 14.4 years) were studied. Total Hcy and its metabolites were measured by gas chromatography-mass spectrometry (GC-MS).

RESULTS

Total Hcy, MMA, Cys, and MC were elevated twofold to sixfold as compared with NP, with a significant interrelationship between these compounds. With the exception of Cys, they were significantly correlated with serum creatinine. Serum folate levels were inversely correlated with tHcy, Cys and cobalamin with MMA and the ratio of MCI/MCII. There was no correlation between tHcy concentration and its metabolites with immunosuppressive treatment (CsA vs. FK506), clinical history, or current findings of cardiovascular complications and blood pressure profile.

CONCLUSION

Prospective studies are needed to find out whether the lowering or normalization of serum concentrations of tHcy and its metabolites due to treatment with B vitamins should be achieved to reduce the cardiovascular risk and improve the long-term outcome of allografts and of patients.

Hyperhomocysteinemia is associated with venous thrombosis in patients with short bowel syndrome

BACKGROUND

Hyperhomocysteinemia is associated with venous thrombosis and vitamin deficiency. Patients with short bowel syndrome have increased risk of venous thrombosis due to central catheters, and of vitamin deficiency due to malabsorption. The current investigation was designed to evaluate the relationship between history of venous thrombosis and current hyperhomocystinemia and vitamin deficiency in patients with short bowel syndrome.

METHODS

Plasma total homocysteine (tHcy), serum vitamin B12, folate, B6, and methylmalonic acid (MMA) were measured. Venous thrombosis was documented by venogram or ultrasound.

RESULTS

Ten of 17 patients had venous thromboses, including 17 of 38 observed superior and 12 of 26 inferior veins. Total homocysteine was correlated with number of thromboses. The relative risk of multiple thromboses in the highest tHcy tertile was 3.6-fold that of the lowest tertile. Vitamin B12 and folate levels were within normal limits, but B12 deficiency by MMA or tHcy level was apparent in 7 patients. Vitamin-deficient patients had higher tHcy and MMA than those without deficiency.

CONCLUSIONS

Venous thrombosis in patients with short bowel syndrome is related to hyperhomocystinemia, which is also related to vitamin B12 deficiency, not detected by serum vitamin B12 concentration. Whether treatment of vitamin deficiencies and associated reduction in tHcy will reduce recurrent venous thrombosis in these patients is not known.