C: A closer look at the homocysteine paradox

Blom, H.J. [Promotor]Smulders, Y.M. [Promotor

Changes in intracellular folate metabolism during high-dose methotrexate and Leucovorin rescue therapy in children with acute lymphoblastic leukemia

Background Methotrexate (MTX) is an important anti-folate agent in pediatric acute lymphoblastic leukemia (ALL) treatment. Folinic acid rescue therapy (Leucovorin) is administered after MTX to reduce toxicity. Previous studies hypothesized that Leucovorin could ‘rescue’ both normal healthy cells and leukemic blasts from cell death. We assessed whether Leucovorin is able to restore red blood cell folate levels after MTX. Methods We prospectively determined erythrocyte folate levels (5-methyltetrahydrofolate (THF) and non-methyl THF) and serum folate levels in 67 children with ALL before start (T0) and after stop (T1) of HD-MTX and Leucovorin courses. Results Erythrocyte folate levels increased between T0 and T1 (mean ± SD: 416.7 ± 145.5 nmol/L and 641.2 ± 196.3 nmol/L respectively, pT genotype. Conclusion Intracellular folate levels accumulate after HD-MTX and Leucovorin therapy in children with ALL, suggesting that Leucovorin restores the intracellular folate pool. Future studies are necessary to assess concomitant lower uptake of MTX

The evaluation of red blood cell folate and methotrexate levels during protocol M in childhood acute lymphoblastic leukemia

Background: After High-Dose Methotrexate (HD-MTX), folinic acid rescue therapy (Leucovorin) is administered to reduce side effects in pediatric acute lymphoblastic leukemia (ALL) patients. Leucovorin and MTX are structural analogues, possibly competing for cellular transport and intracellular metabolism. We hypothesize that Leucovorin accumulates during consecutive courses, which might result in a lower MTX uptake. Methods: We prospectively measured red blood cell (RBC) folate and MTX levels during four HD-MTX and Leucovorin courses in 43 patients treated according the DCOG ALL-11 protocol with 2-weekly HD-MTX (5 g/m2 /dose) and Leucovorin (15 mg/m2 /dose) using LC-MS/MS. We estimated a linear mixed model to assess the relationship between these variables over time. Results: Both RBC MTX-PG and folate levels increased significantly during protocol M. MTX-PG2–5 levels increased most substantially after the first two HD-MTX courses (until median 113.0 nmol/L, IQR 76.8–165.2) after which levels plateaued during the 3d and 4th course (until median 141.3 nmol/L, IQR 100.2–190.2). In parallel, folate levels increased most substantially after the first two HD-MTX courses (until median 401.6 nmol/L, IQR 163.3–594.2) after which levels plateaued during the 3d and 4th course (until median 411.5 nmol/L, IQR 240.3–665.6). The ratio folate/MTX-PG decreased significantly over time, which was mostly due to the relatively higher increase (delta) of MTX-PG. Conclusion: These results suggest that the increase in RBC folate levels does not seem to have a large effect on RBC MTX levels. Future studies, assessing competition of Leucovorin and MTX on other cellular mechanisms which might negatively affect treatment efficacy, are necessary

Red blood cell folate vitamer distribution in healthy subjects is determined by the methylenetetrahydrofolate reductase C677T polymorphism and by the total folate status

Background: Red blood cells (RBCs) represent a storage pool for folate. In contrast to plasma, RBC folate can appear in different biochemical isoforms. So far, only the methylenetetrahydrofolate reductase (MTHFR) 677 TT genotype has been identified as a determinant of RBC folate vitamer distribution. Objective: The purpose of this study is to identify clinical and biochemical determinants of RBC folate vitamer distribution in healthy subjects. Design: In an observational study, 109 subjects, aged 18 to 65 years, were studied. Red blood cell folate vitamers were analyzed using a liquid chromatography-tandem mass spectrometry method. Other variables recorded included vitamin B2, B6 and B12 status, homocysteine, plasma and RBC S-adenosylhomocysteine and S-adenosylmethionine, renal function and the MTHFR C677T polymorphism. Results: The MTHFR C677T genotype was the dominant determinant of nonmethylfolate accumulation. The median (range) nonmethylfolate/total folate ratio was 0.58% (0-12.2%) in the MTHFR CC group (n=55), 0.99% (0-14.3%) in the CT group (n=39) and 30.3% (5.7-73.3%) in the TT genotype group (n=15), P<.001. The 95th percentile for the nonmethylfolate/total folate ratio was 2.8% for the CC group, 9.1% for the CT group and 73.3% for the TT group. In the CC and CT genotype subjects, the T-allele and total folate status were positively and independently correlated with nonmethylfolate accumulation, but the degree of nonmethylfolate accumulation in these subjects was usually minor compared with those with the TT genotype. None of the other studied variables was associated with nonmethylfolate accumulation. Conclusions: The MTHFR C677T genotype is the dominant determinant of nonmethylfolate accumulation in RBCs. In addition, high total folate status may contribute to minor to moderate nonmethylfolate accumulation in MTHFR CC and CT subjects. © 2007 Elsevier Inc. All rights reserved

Post-transcriptional regulation of the creatine transporter gene: Functional relevance of alternative splicing

Background Aberrations in about 10-15% of X-chromosome genes account for intellectual disability (ID); with a prevalence of 1-3% (Gécz et al., 2009 [1]). The SLC6A8 gene, mapped to Xq28, encodes the creatine transporter (CTR1). Mutations in SLC6A8, and the ensuing decrease in brain creatine, lead to co-occurrence of speech/language delay, autism-like behaviors and epilepsy with ID. A splice variant of SLC6A8-SLC6A8C, containing intron 4 and exons 5-13, was identified. Herein, we report the identification of a novel variant - SLC6A8D, and functional relevance of these isoforms. Methods Via (quantitative) RT-PCR, uptake assays, and confocal microscopy, we investigated their expression and function vis-à-vis creatine transport. Results SLC6A8D is homologous to SLC6A8C except for a deletion of exon 9 (without occurrence of a frame shift). Both contain an open reading frame encoding a truncated protein but otherwise identical to CTR1. Like SLC6A8, both variants are predominantly expressed in tissues with high energy requirement. Our experiments reveal that these truncated isoforms do not transport creatine. However, in SLC6A8 (CTR1)-overexpressing cells, a subsequent infection (transduction) with viral constructs encoding either the SLC6A8C (CTR4) or SLC6A8D (CTR5) isoform resulted in a significant increase in creatine accumulation compared to CTR1 cells re-infected with viral constructs containing the empty vector. Moreover, transient transfection of CTR4 or CTR5 into HEK293 cells resulted in significantly higher creatine uptake. Conclusions CTR4 and CTR5 are possible regulators of the creatine transporter since their overexpression results in upregulated CTR1 protein and creatine uptake. General significance Provides added insight into the mechanism(s) of creatine transport regulation. © 2014 Elsevier B.V

Homocysteine clearance and methylation flux rates in health and end-stage renal disease: association with S-adenosylhomocysteine

Homocysteine clearance and methylation flux rates in health and end-stage renal disease: association with S-adenosylhomocysteine. Stam F, van Guldener C, ter Wee PM, Kulik W, Smith DE, Jakobs C, Stehouwer CD, de Meer K. Department of Internal Medicine, and Institute for Cardiovascular Research, Vrije Universiteit Medical Center, 1081 HV Amsterdam, The Netherlands . [email protected] Hyperhomocysteinemia is a risk factor for cardiovascular disease and occurs frequently in end-stage renal disease (ESRD), but its pathogenesis is poorly understood. We aimed to evaluate one-carbon flux rates of methionine and homocysteine (Hcy) in ESRD patients and healthy controls. Transmethylation (TM), remethylation (RM), and transsulfuration (TS), as well as Hcy clearance by TS (i.e., TS/plasma total Hcy concentration) and by RM (i.e., RM/plasma total Hcy concentration) were evaluated in relation to body composition, vitamins, and S-adenosylhomocysteine (AdoHcy) and S-adenosylmethionine (AdoMet) levels. After a fixed protein diet for 3 days, primed-continuous infusion of [(2)H(3)-methyl-1-(13)C]methionine was performed in the postabsorptive state in 12 hemodialysis patients and 16 healthy volunteers. Hcy clearance by TS (-80%, P < 0.001) and by RM (-77%, P < 0.001) in ESRD patients was decreased compared with healthy controls. The absolute flux rates of TM (-27%, P < 0.01) and RM (-28%, P = 0.02) were lower in the ESRD patients. After adjustment for age, TS was not significantly reduced. Whole blood AdoHcy was significantly elevated in ESRD and was a significant determinant of TM (standardized beta = -1.24, P = 0.01) and RM (standardized beta = -1.43, P = 0.03). In conclusion, patients with ESRD have impaired Hcy clearance by TS and RM. Elevated whole blood AdoHcy levels are associated with impaired RM and TM flux rates in these patients, and AdoHcy may be a key regulatory compound in one-carbon flu