Prachi Katre

Vitamin B12: one carbon metabolism, fetal growth and programming for chronic disease

This review brings together human and animal studies and reviews that examine the possible role of maternal vitamin B12 (B12) on fetal growth and its programming for susceptibility to chronic disease. A selective literature review was undertaken to identify studies and reviews that investigate these issues, particularly in the context of a vegetarian diet that may be low in B12 and protein and high in carbohydrate. Evidence is accumulating that maternal B12 status influences fetal growth and development. Low maternal vitamin B12 status and protein intake are associated with increased risk of neural tube defect, low lean mass and excess adiposity, increased insulin resistance, impaired neurodevelopment and altered risk of cancer in the offspring. Vitamin B12 is a key nutrient associated with one carbon metabolic pathways related to substrate metabolism, synthesis and stability of nucleic acids and methylation of DNA which regulates gene expression. Understanding of factors regulating maternal–fetal one carbon metabolism and its role in fetal programming of non communicable diseases could help design effective interventions, starting with maternal nutrition before conception.

Spuriously High Prevalence of Prediabetes Diagnosed by HbA1c in Young Indians Partly Explained by Hematological Factors and Iron Deficiency Anemia

OBJECTIVE To examine the influence of glycemic and nonglycemic parameters on HbA1c concentrations in young adults, the majority of whom had normal glucose tolerance. RESEARCH DESIGN AND METHODS We compared the diagnosis of normal glucose tolerance, prediabetes, and diabetes between a standard oral glucose tolerance test (OGTT; World Health Organization 2006 criteria) and HbA1c concentrations (American Diabetes Association [ADA] 2009 criteria) in 116 young adults (average age 21.6 years) from the Pune Children’s Study. We also studied the contribution of glycemic and nonglycemic determinants to HbA1c concentrations. RESULTS The OGTT showed that 7.8% of participants were prediabetic and 2.6% were diabetic. By ADA HbA1c criteria, 23.3% were prediabetic and 2.6% were diabetic. The negative predictive value of HbA1c was 93% and the positive predictive value was 20% (only 20% had prediabetes or diabetes according to the OGTT; this figure was 7% in anemic participants). Of participants, 34% were anemic, 37% were iron deficient (ferritin <15 ng/mL), 40% were vitamin B12 deficient (<150 pmol/L), and 22% were folate deficient (<7 nmol/L). On multiple linear regression analysis, HbA1c was predicted by higher 2-h glucose (R2 = 25.6%) and lower hemoglobin (R2 = 7.7%). When hematological parameters were replaced by ferritin, vitamin B12, and folate, HbA1c was predicted by higher glycemia (R2 = 25.6%) and lower ferritin (R2 = 4.3%). CONCLUSIONS The use of HbA1c to diagnose prediabetes and diabetes in iron-deficient populations may lead to a spuriously exaggerated prevalence. Further investigation is required before using HbA1c as a screening tool in nutritionally compromised populations.

Maternal homocysteine in pregnancy and offspring birthweight: epidemiological associations and Mendelian randomization analysis

BACKGROUND Disturbed one-carbon (1-C) metabolism in the mother is associated with poor fetal growth but causality of this relationship has not been established. METHODS We studied the association between maternal total homocysteine and offspring birthweight in the Pune Maternal Nutrition Study (PMNS, Pune, India) and Parthenon Cohort Study (Mysore, India). We tested for evidence of causality within a Mendelian randomization framework, using a methylenetetrahydrofolatereductase (MTHFR) gene variant rs1801133 (earlier known as 677C→T) by instrumental variable and triangulation analysis, separately and using meta-analysis. RESULTS Median (IQR) homocysteine concentration and mean (SD) birthweight were 8.6 µmol/l (6.7,10.8) and 2642 g (379) in the PMNS and 6.0 µmol/l (5.1,7.1) and 2871 g (443) in the Parthenon study. Offspring birthweight was inversely related to maternal homocysteine concentration-PMNS: -22 g/SD [95% confidence interval (CI): (-50, 5), adjusted for gestational age and offspring gender]; Parthenon: -57 g (-92, -21); meta-analysis: -40 g (-62, -17)]. Maternal risk genotype at rs1801133 predicted higher homocysteine concentration [PMNS: 0.30 SD/allele (0.14, 0.46); Parthenon: 0.21 SD (0.02, 0.40); meta-analysis: 0.26 SD (0.14, 0.39)]; and lower birthweight [PMNS: -46 g (-102, 11, adjusted for gestational age, offspring gender and rs1801133 genotype); Parthenon: -78 g (-170, 15); meta-analysis: -61 g (-111, -10)]. Instrumental variable and triangulation analysis supported a causal association between maternal homocysteine concentration and offspring birthweight. CONCLUSIONS Our findings suggest a causal role for maternal homocysteine (1-C metabolism) in fetal growth. Reducing maternal homocysteine concentrations may improve fetal growth.

Marked Gender Difference in Plasma Total Homocysteine Concentrations in Indian Adults with low Vitamin B12

CONTEXT Plasma total homocysteine (tHcy) is higher in men than women. OBJECTIVE To explore the gender differences in tHcy in relation to determinants of one-carbon metabolism in Indian people with low B₁₂ and adequate folate. SETTING The study took place in rural and urban areas of Pune, India. DESIGN AND PARTICIPANTS Participants were 441 men from the cross-sectional Coronary Risk of Insulin Sensitivity in Indian Subjects study (CRISIS) and premenopausal wives of 146 men (median ages 38 and 34 years, respectively). MAIN OUTCOME MEASURES Gender difference in fasting tHcy in relation to plasma albumin and creatinine concentrations, lifestyle factors, diet and lean mass, plasma B₁₂ and red cell folate (RCF) was assessed. RESULTS Prevalence of high tHcy (> 15 µmol/L, median 14.4 µM) was 40 %, low B12 (< 150 pmol/L, 114 pmol/L) 66 %, and low RCF (< 283 nmol/L, 525 nmol/L) 8 %. Men had higher (1.8x) plasma tHcy concentrations (16.2 µmol/L) than women (9.5 µmol/L). Only 50 % of the gender difference was explained by age, lean mass, B₁₂, and RCF. The difference remained after controlling for other explanatory variables. Women with a tHcy of 9.3 µM had the same B₁₂ concentration (129 pmol/L) as men with a tHcy of 15 µM; and for a tHcy of 10.0 µmol/L women had the same RCF concentration (533 nmol/L) as men with a tHcy of 15 µmol/L. CONCLUSIONS Adult Indian women have markedly lower tHcy concentrations compared to men. This suggests a lower threshold for supplementation to improve reproductive and cardiovascular outcomes.

Effect of multi-nutrient insufficiency on markers of one carbon metabolism in young women: response to a methionine load.

Background/Objectives:Multi-nutrient insufficiencies as a consequence of nutritional and economic factors are common in India and other developing countries. We have examined the impact of multi-nutrient insufficiency on markers of one carbon (1C) metabolism in the blood, and response to a methionine load in clinically healthy young women.Subjects/Methods:Young women from Pune, India (n=10) and Cleveland, USA (n=13) were studied. Blood samples were obtained in the basal state and following an oral methionine load (50 mg/kg of body weight in orange juice). Plasma concentrations of vitamin B12, folate and B6 were measured in the basal state. The effect of methionine load on the levels of methionine, total homocysteine, cysteine, glutathione and amino acids was examined.Results:Indian women were significantly shorter and lighter compared with the American women and had lower plasma concentration of vitamins B12, folate and B6, essential amino acids and glutathione, but higher concentration of total homocysteine. The homocysteine response to methionine load was higher in Indian women. The plasma concentrations of glycine and serine increased in the Indian women after methionine (in juice) load. A significant negative correlation between plasma B6 and homocysteine (r= −0.70), and plasma folate and glycine and serine levels were observed in the Indian group (P<0.05) but not in the American group.Conclusions:Multi-nutrient insufficiency in the Indian women caused unique changes in markers of whole body protein and 1C metabolism. These data would be useful in developing nutrient intervention strategies.

Response to Comment on: Hardikar et al. Spuriously High Prevalence of Prediabetes Diagnosed by HbA1c in Young Indians Partly Explained by Hematological Factors and Iron Deficiency Anemia. Diabetes Care 2012;35:797–802

We are grateful to Schindhelm et al. (1) for their interest in our article. We measured HbA1c during follow-up of a birth cohort in the hope of substituting it for an oral glucose tolerance test. We found a discrepancy between the results of the oral glucose tolerance test (World Health Organization, 1999) and HbA1c (American Diabetes Association, 2009): A large number of individuals were classified as having “prediabetes” by HbA1c when considered normal glucose tolerant by oral glucose tolerance test (2). This prompted us to investigate possible causes of this discrepancy. We found that a number of hematological parameters (lower hemoglobin …

Evaluation of tracer labelled methionine load test in Vitamin B-12 deficient adolescent women

Background Methionine loading test (MLT) has been used primarily to identify defects in transsulfuration of homocysteine in cystathionine beta synthase deficiency. It may not be as useful to evaluate remethylation pathway, in vitamin B-12 and folate deficiencies. Objective We used tracer isotope labelled MLT to interrogate transsulfuration and remethylation independently in vitamin B-12 deficiency. Design We studied vitamin B-12 deficient women with a tracer labelled MLT before and eleven months after treatment with vitamin B-12. The fractional contribution of [13C]homocysteine to breath CO2 was used as a measure of transsulfuration, and difference in the intracellular enrichment of [13C]methionine and that of [C2H3]methionine as a measure of remethylation of homocysteine. Combined pre- and post-treatment results were analyzed to investigate the association between plasma vitamin B-12 concentrations and measures of homocysteine metabolism. Results The subjects were 17 years old, with a BMI of 19.4 kg/m2. Treatment with vitamin B-12, 2µg/day increased plasma B-12 from 93 (78.7, 106.2) [median (25th, 75th centiles)] to 161.5 (125.5, 226.2) pmol/L; 44% were below <150pmol/L after treatment. Fasting homocysteine concentration was significantly lower and that of cysteine higher in subjects with B-12 levels >150pmol/L. The tracer estimated transsulfuration of homocysteine was lower and remethylation higher with B-12 levels >150pmol/L when compared with those <150pmol/L. Conclusions The tracer labelled MLT in combination with fasting parameters is a robust way to estimate parameters of methionine metabolism and can be used in the field where prime-constant rate infusion studies cannot be done efficiently.