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Biomedical subjects

R M Kok

Publications and source records attributed to R M Kok.

At least 19 recordsLinked to original sources
PubMed2006

Cellular folate vitamer distribution during and after correction of vitamin B12 deficiency: a case for the methylfolate trap.

Haematological sequellae of vitamin B12 deficiency are attributed to disturbed DNA synthesis, but vitamin B12 itself plays no role in DNA biosynthesis. A proposed explanation for this is the methylfolate trap hypothesis. This hypothesis states that B12 deficiency impairs overall folate metabolism because 5-methyltetrahydrofolate (5MTHF) becomes metabolically trapped. This trap results from the fact that 5MTHF can neither be metabolised via the methionine synthase pathway, nor can it be reconverted to its precursor, methylenetetrahydrofolate. Other manifestations of the methylfolate trap include cellular folate loss because of shorter 5MTHF polyglutamate chains and global hypomethylation. The methylfolate trap has never been demonstrated in humans. We describe a patient with B12 deficiency who was homozygous for the common methylenetetrahydrofolate reductase (MTHFR) C677T mutation. We analysed red blood cell (RBC) folate vitamers and global DNA methylation by liquid chromatography (LC) in combination with tandem mass spectrometry, and 5MTHF polyglutamate length by LC-electrochemical detection. Compared to post-B12 supplementation values, homocysteine was higher (52.9 micromol/l vs. 16.8 micromol/l), RBC folate was lower (268.92 nmol/l vs. 501.2 nmol/l), the 5MTHF fraction of RBC folate was much higher (94.5% vs. 67.4%), polyglutamate chain length was shorter (more tetra- and pentaglutamates), and global DNA methylation was 22% lower. This is the first time that virtually all features of the methylfolate trap hypothesis have been demonstrated in a human with vitamin B12 deficiency.

Chromatography, Liquid↗
PubMed2005

[Psychic consequences on the elderly of sexual abuse in their youth].

Three women, aged 64, 65 and 60 years, who were admitted for psychopathology revealed for the first time that they had been sexually abused as a child by a relative. The first woman sought help following the death of her husband, the second after her daughter was raped, and the third suffered from increasing cognitive impairment. Through therapy, they learned how to process their history of incest. In psychiatric patients, the prevalence of sexual abuse in their youth varies from 5-45% in different studies, depending on the definition of sexual abuse. Two Dutch studies of elderly psychiatric inpatients found a prevalence of 16% sexual abuse in 32 male and female patients and 8% in 110 female patients, respectively. Sexual abuse may have a great, lifelong impact on the victims. Many psychiatric and psychological consequences are found in adult populations, but no study has yet included the elderly. All clinicians should be aware that signs and symptoms in the elderly might be related to sexual abuse.

Aged↗
PubMed2005

[6S]5-methyltetrahydrofolate or folic acid supplementation and absorption and initial elimination of folate in young and middle-aged adults.

OBJECTIVES: To assess the effects of supplementation with the diastereoisomer of 5-methyltetrahydrofolate ([6S]5-methylTHF), as an alternative supplement for folic acid, on folate absorption and elimination, in two age groups. DESIGN: A randomized, double-blind intervention study. SUBJECTS: A total of 12 young (<30 y) and 12 middle-aged (> or =50 y) healthy volunteers were recruited. METHODS: Volunteers were randomized to receive daily supplementation with 400 mug folic acid or equimolar amounts of [6S]5-methylTHF during 5 weeks. Before and after supplementation, absorption and initial elimination were calculated following oral [(2)H(2)]folic acid test doses using isotope kinetics in plasma. RESULTS: Folic acid absorption was lower in the middle-aged as compared to the young adults, both before (P = 0.03) and after (P = 0.05) supplementation. In the young adults, absorption decreased by 22% after [6S]5-methylTHF and increased by 21% after folic acid (P = 0.02). In the other age group, no such changes were found. The folate rate constant of elimination increased after folic acid supplementation in the young (+50%; P = 0.05) but not in the middle-aged (+18%; P = 0.5) adults. CONCLUSIONS: Young adults show increased folate turnover after folic acid supplementation relative to the effect of [6S]5-methylTHF supplementation. Similar differences are not observed in middle-aged adults, in whom folic acid absorption was found to be lower as compared to the young adults. SPONSORSHIP: Financial support was received from the European Union 5th Framework Programme (Grant QLRT-1999-00576).

Adult↗
PubMed2004

5-Methyltetrahydrofolic acid and folic acid measured in plasma with liquid chromatography tandem mass spectrometry: applications to folate absorption and metabolism.

We describe a liquid chromatography (LC) tandem mass spectrometry (MS-MS) method for the determination of 5-methyltetrahydrofolic acid (5-methylTHF) and folic acid concentrations and enrichments in human plasma. It was used to study absorption and initial metabolism in five volunteers with two simultaneously administered oral test doses ([(13)C(6)]folic acid in capsules and [(2)H(2)]folic acid in a drink). [(13)C(5)]5-methylTHF and [(2)H(4)]folic acid were used as internal standards. Plasma samples (2 ml) were purified using folate binding protein affinity columns, followed by a concentration step. After LC separation, folates were detected using positive electrospray ionization MS-MS under multiple reaction monitoring conditions. Calibrations were linear for 5-methylTHF over the range 1.2 x 10(-11) (=limit of detection) to 3.2 x 10(-7)mol/L and for folic acid over the range 5 x 10(-10) (=limit of detection) to 4.5 x 10(-8)mol/L. For 5-methylTHF concentration in plasma, intraassay coefficient of variation was within 8.6% (and for unlabeled 5-methylTHF it was within 2.8%) and interassay coefficient of variation was within 9.0%. For folic acid concentrations these coefficient of variations were within 7.5% and within 6.5%, respectively. The [(13)C(6)] and [(2)H(2)] isotopomers of folic acid and 5-methylTHF were measured in the plasma of each volunteer for 8h. After accounting for the time delay due to capsule opening, the modeling results showed no significant differences in absorption time, first pass effect, and elimination rate in the folic acid test doses in capsule or drink. We conclude that LC-MS-MS offers increased sensitivity for quantification of plasma concentrations and enrichments of 5-methylTHF and folic acid and is applicable to stable-isotope studies in humans.

Administration, Oral↗
PubMed2003

Determination of 13C and 15N enrichments of urea in plasma by gas chromatography-combustion isotope ratio mass spectrometry and gas chromatography-mass spectrometry using the 2-methoxypyrimidine derivative.

We describe a GC-MS and GC-c-IRMS method for the determination of labeled urea tracer enrichments in plasma as a result of combined 13C- and 15N(2)-urea infusion experiments in piglets. Urea was converted into 2-methoxypyrimidine, a stable derivative, suited for analyses by both GC-MS and GC-c-IRMS. Using calibration curves for the respective working ranges (13C-urea: 0-1% APE; 15N(2)-urea: 0-7% MPE) enrichments were established in single point measurements; for 15N(2)-urea as values+/-0.15% MPE (95% confidence interval); for 13C-urea as values+/-0.02% APE (95% confidence interval). 15N(1)-urea enrichments were determined by measurement of the same sample with GC-c-IRMS and GC-MS. Subtraction of the 13C specific GC-c-IRMS data from the nondiscriminating GC-MS data for the sum of 13C- and 15N(1)-urea resulted in 15N(1)-urea enrichments+/-0.15% MPE (95% confidence interval). Application of the method in a combined 13C-urea bolus and 15N(2)-urea primed constant infusion experiment in piglet was demonstrated.

Animals↗
PubMed2000

Determination of isotopic enrichments of [1-13C]homocysteine, [1-13C]methionine and [2H3-methyl-1-13C]methionine in human plasma by gas chromatography-negative chemical ionization mass spectrometry.

We describe a reliable method for the simultaneous determination of isotopic enrichments of [1-13C]homocysteine, [1-13C]methionine and [2H3-methyl-1-13C]methionine in human plasma. Accurate [1-13C]homocysteine calibration standards were prepared by chemical conversion via thiolactonisation of [1-13C]methionine standards. Based upon anion-exchange chromatography, (di)acetyl-3,5-bis-trifluoromethylbenzyl derivatives, preparation of accurate calibration curves and gas chromatography-negative chemical ionization mass spectrometry, isotopic enrichments in human plasma could be determined with TTR (%) <+/-0.2% (N=3) for [1-13C]homocysteine (enrichment range 0-8%), [1-13C]methionine (enrichment range 0-3%) and [2H3-methyl-1-13C]methionine (enrichment range 0-12%). The method was applied in a [2H3-methyl-1-13C]methionine tracer infusion study in a biological model.

Carbon Isotopes↗
PubMed1998

Methylmalonic semialdehyde dehydrogenase deficiency: psychomotor delay and methylmalonic aciduria without metabolic decompensation.

A patient presenting with developmental delay but no episodes of metabolic acidosis was found to excrete significant amounts of methylmalonate (MMA) without any associated increased excretion of malonate, ethylmalonate, 3-hydroxypropionate, or beta-alanine. In contrast to patients with methylmalonic aciduria due to deficient mutase or impaired cobalamin metabolism, there was no increase of propionylcarnitine in blood or urine. The activity of methylmalonyl-CoA mutase and the pathway for cobalamin metabolism were also intact. The quantitative levels of the various labeled enantiomers of 3-hydroxyisobutyric (3-HIBA), 3-aminoisobutyric (3-AIBA), MMA, and propionylcarnitine were compared following separate intravenous infusions of equimolar doses of [2H8]-valine or [2H4]thymine in this patient and another with methylmalonyl-CoA mutase deficiency. Levels of labeled S- and R-3-HIBA and S- and R-3-AIBA indicated an isolated defect in methylmalonic semialdehyde dehydrogenase in this patient. This condition can be recognized by plasma MMA levels of approximately 8.5 microM (cf. 400 microM in mutase deficiency), urine MMA of 20-55 micromol/kg/24 h (cf. 1150 micromol/kg/24 h), no increase in propionylcarnitine following an oral carnitine load, and increased excretion of S-3-AIBA-nearly 10 times that observed in mutase deficiency. The ratio of R-AIBA to S-AIBA of <1 also reflects this disorder.

Aldehyde Oxidoreductases↗
PubMed1998

Phytanic acid and pristanic acid are oxidized by sequential peroxisomal and mitochondrial reactions in cultured fibroblasts.

The relationship between peroxisomal and mitochondrial oxidation of the methyl branched fatty acids, phytanic acid and pristanic acid, was studied in normal and mutant human skin fibroblasts with established enzyme deficiencies. Tandem mass spectrometry was used for analysis of the acylcarnitine intermediates. In normal cells, 4,8-dimethylnonanoylcarnitine (C11:0) and 2,6-dimethylheptanoylcarnitine (C9:0) accumulated after incubation with either phytanic acid or pristanic acid. These intermediates were not observed when peroxisome-deficient cells from Zellweger patients were incubated with the same compounds, pointing to the involvement of peroxisomes in the formation of these acylcarnitine intermediates. Similar experiments with fibroblasts deficient in carnitine palmitoyltransferase I, carnitine-acylcarnitine translocase or carnitine palmitoyltransferase II revealed that mitochondrial carnitine palmitoyltransferase I is not required for the oxidation of phytanic acid or pristanic acid, whereas both carnitine-acylcarnitine translocase and carnitine palmitoyltransferase II are necessary. These studies demonstrate that both phytanic acid and pristanic acid are initially oxidized in peroxisomes to 4,8-dimethylnonanoyl-CoA, which is converted to the corresponding acylcarnitine (presumably by peroxisomal carnitine octanoyltransferase), and exported to the mitochondrion. After transport across the mitochondrial membrane and transfer of the acylgroup to coenzyme A, further oxidation to 2,6-dimethylheptanoyl-CoA occurs.

Carnitine Acyltransferases↗
PubMed1995

The prevalence of depression in elderly medical inpatients.

To estimate the point-prevalence of major depression in elderly medical inpatients according to a computerized diagnostic system, a two-phase design was carried out. A consecutive series of 198 elderly medical inpatients completed two self-rating scales for depression (Beck Depression Inventory, Geriatric Depression Scale) and the Mini-Mental State Examination. According to these screening instruments, 69 'probable cases' were identified and were referred for psychiatric evaluation using the Geriatric Mental State Schedule. Only 10 patients were identified as diagnostic cases of depression according to the GMS-AGECAT package. The estimated prevalence rate for depression according to AGECAT in this population was 5.9% (95% confidence limits 2.3-9.3%). This is lower than has been found in previous studies in elderly medical inpatients. Possible reasons for this finding are discussed.

Aged↗
PubMed1994

[Self-evaluation scales for depression in the elderly].

The literature on four self-rating scales for depression, the Beck Depression Inventory, the Zung, the Centre for Epidemiologic Studies Depression Scale and the Geriatric Depression Scale is discussed. Evidence from the literature suggests that the reliability and validity of these scales are alike in elderly and (younger) adults. The GDS is advised as the first choice among these self-rating scales. Self-rating scales for depression are not sufficient for diagnosing depression, additional information derived from observation and a psychiatric interview are necessary.

Aged↗
PubMed1993

Prolonged retention of high concentrations of 5-fluorouracil in human and murine tumors as compared with plasma.

Concentrations of 5-fluorouracil (5-FU) and its active metabolite 5-fluoro-2'-deoxy-5'-monophosphate (FdUMP) were measured in biopsy specimens of tumor tissue, normal mucosa, metastatic liver nodules, and normal liver tissue obtained from 39 patients and in two murine colon tumors (colon 26 and colon 38) after a single injection of 5FU at a therapeutic dose (500 mg/m2 and 100 mg/kg, respectively). These data were compared with plasma concentrations. Peak plasma concentrations (300-500 microM) of 5FU were comparable in human and murine plasma. The half-life of plasma elimination (during the period from 15 to 120 min) in both mouse and man ranged from 10 to 20 min, whereas at between 2 and 8 h, plasma concentrations varied from 0.1 to 1 microM, the half-life being about 100 min. In both species, 5FU could be measured in plasma at concentrations ranging from 0.01 to 1 microM for several days after 5FU treatment. 5FU concentrations in tissue samples obtained from 14 patients were measured during the time range of 1-6 h, those in samples taken from 7 patients, during the interval of 19-27 h; and those in samples obtained from 18 patients, within the interval of 40-48 h after injection. 5FU tumor concentrations varied between 0.78-21.6, 0.44-6.1, and 0.17-10.8 mumol/kg wet wt., respectively. Some of the 48-h samples were obtained from patients who had received leucovorin plus 5FU; coadministration of leucovorin did not alter 5FU tissue concentrations. At between 4 and 48 h, the tissue concentration/plasma concentration ratio was at least 10. 5FU concentrations in murine tumors were measured for up to 10 days after 5FU administration, with plateau 5FU tumor concentrations being about 50 mumol/kg wet wt. in colon 38 and about 200 mumol/kg wet wt. in colon 26 at 2 h after treatment; after 4 days, values of 0.5 and 4.8 mumol/kg, respectively, were obtained and after 10 days, respective concentrations of 0.1 and 0.07 mumol/kg were detected. The FdUMP concentrations measured in colon 26 and colon 38 tumors were 214 and 46 pmol/g, respectively, at 2 h after 5FU administration, and these values subsequently decreased to about 15 pmol/g in both tumors. In human tumors the initial FdUMP concentration ranged from 10 to 1000 pmol/g; at later time points the level of FdUMP was just above the detection limit of the assay. In liver metastases, high 5FU concentrations seemed to be related to high levels of FdUMP, which was likely of importance for the antitumor effect.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1993

Stable-isotope dilution analysis of D- and L-2-hydroxyglutaric acid: application to the detection and prenatal diagnosis of D- and L-2-hydroxyglutaric acidemias.

A stable-isotope dilution assay has been developed for quantitation of D- and L-2-hydroxyglutaric acids in physiologic fluids. D- and L-2-hydroxyglutaric acids are separated as the O-acetyl-di-(D)-2-butyl esters. The method uses D,L-[3,3,4,4-2H4]-2-hydroxyglutaric acid as internal standard with ammonia chemical ionization, selected ion monitoring gas chromatography-mass spectrometry. For 13 patients with L-2-hydroxyglutaric aciduria, the concentrations of L-2-hydroxyglutaric acid were urine, 1283 +/- 676 mmol/mol creatinine (range, 332-2742; n = 12 patients); plasma, 47 +/- 13 mumol/L (range, 27-62; n = 8); cerebrospinal fluid, 62 +/- 30 mumol/L (range, 34-100; n = 6). In a child with D-2-hydroxyglutaric aciduria, the levels of D-2-hydroxyglutaric acid were urine, 1565 +/- 847 mmol/mol creatinine (range, 729-2668; n = 4); plasma, 61 +/- 14 mumol/L (range, 46-73; n = 3); cerebrospinal fluid, 15 and 25 mumol/L (n = 2). Control concentrations of D- and L-2-hydroxyglutaric acids were (D:L): urine (n = 18), 6.0 +/- 3.6 mmol/mol creatinine (range, 2.8-17): 6.0 +/- 5.4 (range, 1.3-19); plasma (n = 10), 0.7 +/- 0.2 mumol/L (range, 0.3-0.9): 0.6 +/- 0.2 (range, 0.5-1.0); cerebrospinal fluid (n = 10), 0.1 +/- 0.1 mumol/L (range, 0.07-0.3): 0.7 +/- 0.6 (range, 0.3-2.3). Investigation of control amniotic fluid (n = 10) revealed the following values (D:L): 1.2 +/- 0.4 mumol/L (range, 0.6-1.8): 4.0 +/- 0.7 (range, 3.1-5.2), suggesting the feasibility of prenatal diagnosis in families at risk.

Acyl-CoA Dehydrogenase↗
PubMed1992

[Psychiatric disorders in elderly patients admitted in a general hospital].

STUDY OBJECTIVE: To determine the prevalence of psychiatric disorders, especially depressive illness, in elderly medical inpatients. SETTING: University Hospital Leiden. DESIGN: Two-stage design. PATIENTS AND METHODS: In six somatic wards a series of 250 patients were randomly selected and screened with two self-rating scales for depression (Beck Depression Inventory, Geriatric Depression Scale) and one screening scale for cognitive dysfunctions (Mini-Mental State Examination). The 52 drop-outs differed significantly from the other patients only in a greater general illness severity, and a higher prevalence of a psychiatric history. Eighty-two patients were selected for a diagnostic procedure with a standardised, semi-structured psychiatric interview, and were classified according to the DSM III-R. Fifty-nine of them were probable cases according to the screening instruments, 23 were selected at random from the probable non-cases. RESULTS: A psychiatric disorder was detected in 25 patients, all but one patient with schizophrenia were found in the group of probable cases. Only five patients were classified as major depression, which lead to a prevalence rate of 2.9% (95% CI 0.4-5.4%). We found evidence of many psychiatric disorders in the group of 52 drop-outs, but these were mostly organic psychiatric disorders, and just one mood disorder. CONCLUSION: The prevalence of major depression is lower than found until now among elderly medical inpatients.

Aged↗
PubMed1992

In vivo study of phytanic acid alpha-oxidation in classic Refsum's disease and chondrodysplasia punctata.

A series of in vivo experiments is described in which [1-13C]phytanic acid was given as an oral substrate to a healthy subject and two patients showing an impairment in phytanic acid degradation, one with Refsum's disease and one with chondrodysplasia punctata. After intake of the substrate by the control in a dose of 20 mg/kg body weight, the production of 13CO2 was measured in exhaled breath air and the concomitant formation of labeled 2-hydroxyphytanic acid and of pristanic acid was demonstrated by plasma analysis. After application of a substrate dose of 1 mg/kg body weight to the control, no substantial amounts of 13CO2 were measured, whereas time-dependent analysis of labeled 2-hydroxyphytanic acid in plasma yielded a concentration curve superimposed upon the baseline value (0.2 mumol/L) of the unlabeled substance. Phytanic acid accumulated in plasma from the Refsum's disease patient [649 mumol/L, controls > 1 y (n = 100): < 10 mumol/L], whereas the pristanic acid concentration was within the control range [1.4 mumol/L, controls > 1 y (n = 100): < 3 mumol/L]. Low amounts of 2-hydroxyphytanic acid were found normally present [0.04 mumol/L, controls > 1 y (n = 11): < 0.2 mumol/L], and formation of labeled 2-hydroxyphytanic acid could not be demonstrated after ingestion of [1-13C]phytanic acid in a dose of 1 mg/kg body weight. In addition to phytanic acid accumulation (232 mumol/L), the chondrodysplasia punctata patient showed an elevated 2-hydroxyphytanic acid plasma concentration (0.4 mumol/L), whereas the plasma pristanic acid level was in the control range (0.7 mumol/L).(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Oral↗
PubMed1992

Pristanic acid and phytanic acid in plasma from patients with peroxisomal disorders: stable isotope dilution analysis with electron capture negative ion mass fragmentography.

A sensitive and selective stable isotope dilution method was developed for the accurate quantitation of pristanic acid and phytanic acid using electron capture negative ion mass fragmentography on pentafluorobenzyl derivatives. This technique allows detection of 1 pg of each compound and was applied to plasma from healthy controls and patients suffering from various peroxisomal disorders. The age-dependency of phytanic and pristanic acid levels in plasma from healthy controls was demonstrated. The involvement of peroxisomes in the beta-oxidation of pristanic acid was concluded from its accumulation in plasma from patients with peroxisomal deficiencies. Pristanic acid/phytanic acid ratios were markedly increased in bifunctional protein and/or 3-oxoacyl-CoA thiolase deficiency, indicating their role in the (differential) diagnosis of disorders of peroxisomal beta-oxidation.

Aging↗
PubMed1992

Phytanic acid alpha-oxidation: accumulation of 2-hydroxyphytanic acid and absence of 2-oxophytanic acid in plasma from patients with peroxisomal disorders.

A stable isotope dilution method was developed for the measurement of 2-hydroxyphytanic acid and 2-oxophytanic acid in plasma. In plasma from healthy individuals and from patients with Refsum's disease, 2-hydroxyphytanic acid was found at levels less than 0.2 mumol/l, whereas the acid accumulated in plasma from patients with rhizomelic chondrodysplasia punctata, generalized peroxisomal dysfunction, and a single peroxisomal beta-oxidation enzyme deficiency. In plasma from both healthy controls and patients with peroxisomal disorders, 2-oxophytanic acid was undetectable. Four different groups of diseases were characterized with a defective phytanic acid alpha-oxidation and/or pristanic acid beta-oxidation: 1) Refsum's disease, with a defect at phytanic acid alpha-hydroxylation; 2) rhizomelic chondrodysplasia punctata, with a defect at 2-hydroxyphytanic acid decarboxylation; 3) generalized peroxisomal disorders, with defects at 2-hydroxyphytanic acid decarboxylation and at pristanic acid beta-oxidation; 4) single peroxisomal beta-oxidation enzyme deficiencies, with a defect at pristanic acid beta-oxidation, resulting in an impaired phytanic acid alpha-oxidation by inhibition. The results indicate that 2-hydroxyphytanic acid decarboxylation and pristanic acid beta-oxidation take place in peroxisomes.

Adolescent↗