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Biomedical subjects

I Holmberg

Publications and source records attributed to I Holmberg.

At least 19 recordsLinked to original sources
PubMed2000

Visual speechreading and cognitive performance in hearing-impaired and normal hearing children (11-14 years).

BACKGROUND: Previous research has demonstrated that parts of the variation in adults' speechreading performance can be explained by the characteristics of some cognitive components. However, these results apply to populations of adults and less is known as to how results for populations of adults can be generalised to populations of children. AIM: This study aimed to examine cognitive and visual skills in a group of bilaterally, moderately hearing-impaired children and a group of normal hearing children and how these two skills relate to variability in speechreading of context-embedded sentences. SAMPLE: Twenty-three hearing-impaired children (mean age: 12.7) and 23 normal hearing children (mean age: 12.5) matched for age, sex, verbal ability and school grades. The mean 'better ear' auditory threshold for the hearing-impaired was 44.8 dB. RESULTS: The hearing-impaired children outperformed the normal hearing children on a sentence-based speechreading task and on a visual-visual word-decoding task, but not on a word-discrimination task. Differing from the case of adults, most cognitive tasks proved to be significantly related to sentence-based speechreading performance, where working memory capacity and visual word-decoding skill proved to be the strongest predictors. CONCLUSIONS: Speechreading is more cognitively demanding for children than for adults as they have not developed their cognitive abilities to the same extent as adults. Thus, they have to devote more processing capacity, relative to their total cognitive processing capacity, to the speechreading task. Skilled visual word-decoding and cognitive skills, together with everyday exposure to situations where speechreading is required, are some of the candidates for explanation of the hearing-impaired children's superior speechreading skill.

Adolescent↗
PubMed1999

Quantitative determination of 8-hydroxy-2'-deoxyguanosine in human urine by isotope dilution mass spectrometry: normal levels in hemochromatosis.

A previously developed method for quantitative determination of 8-hydroxyguanine by gas chromatography-mass spectrometry was modified to allow measurement of 8-hydroxy-2'-deoxyguanosine in human urine. [4,5,6,8-(13)C4]8-Hydroxy-2'-deoxyguanosine was prepared by enzymatic coupling of [4,5,6,8-(13)C4]8-hydroxyguanine to deoxyribose-1-phosphate. Samples of human urine (2 ml) were spiked with the labeled nucleoside (13 nmol) and subjected to solid phase extraction and reversed phase high performance liquid chromatography. The 8-hydroxy-2'-deoxyguanosine thus isolated was hydrolyzed by treatment with aqueous formic acid, and the resulting 8-hydroxyguanine was converted into its tetrakis-trimethylsilyl derivative and subjected to gas-liquid chromatographic-mass spectrometric analysis. Repeated determinations of 8-hydroxy-2'-deoxyguanosine in pools of urine showed coefficients of variation of 5 and 8% at concentrations of 8-hydroxy-2'-deoxyguanosine equal to 18 and 2 nM, respectively. Determination of 8-hydroxy-2'-deoxyguanosine in samples of urine spiked with different amounts of the unlabeled nucleoside showed a mean recovery of 102%. Application of the analytical method to a group of 11 apparently healthy subjects (mean age, 47 years) showed a mean level of endogenously produced 8-hydroxy-2'-deoxyguanosine equal to 1.33 +/- 0.29 micromol/mol creatinine. The level recorded for another group of 15 younger subjects (mean age, 28 years) was somewhat higher, that is, 1.58 +/- 0.84 micromol/mol creatinine, corresponding to a 24-h production rate of 8-hydroxy-2'-deoxyguanosine equal to 20.6 +/- 11.6 nmol (288 +/- 140 pmol/24 h x kg body weight). Hemochromatosis is a hereditary disease characterized by increased absorption of iron from the gastrointestinal tract and deposition of iron in organs. Application of the analytical method to a group of 12 patients with hereditary hemochromatosis who were under treatment with venesections showed a mean level of urinary 8-hydroxy-2'-deoxyguanosine equal to 1.39 +/- 0.40 micromol/mol creatinine. This value was not significantly different from those of healthy subjects. The fact that these patients had only slight or moderate iron overload at the time of urinary sample collection may have influenced the urinary levels of 8-hydroxy-2'-deoxyguanosine in the present study.

8-Hydroxy-2'-Deoxyguanosine↗
PubMed1998

A study of plasmalogen as an index of oxidative stress in patients with chronic renal failure. Evidence of increased oxidative stress in malnourished patients.

BACKGROUND: The incidence of premature cardiovascular disease is high in patients with chronic renal failure (CRF). Free-radical-induced tissue damage is thought to play a major role in the pathogenesis of atherosclerosis and several reports indicate increased oxidative stress in patients with CRF. However, the cause of such stress in CRF is not exactly known. Plasmalogens, a group of phospholipids with a vinyl ether bond in the sn-1 position, are supposed to be sensitive markers of oxidative stress. METHODS: The fasting relative plasmalogen levels of erythrocyte membranes (DMA 16/C16:0 and DMA 18/C18:0), as well as of vitamin E and serum lipids, were determined in a cohort of 105 patients (mean age 51+/-2 years) with advanced CRF (creatinine clearance 9+/-1 ml/min) before starting dialysis treatment. Twenty-nine healthy controls (47+/-2 years) were also investigated. RESULTS: Significantly lower relative plasmalogen levels (DMA 16/C16:0 and DMA 18/C18:0) were found in erythrocytes of predialysis patients than in controls. When the patients were divided on the basis of subjective global assessment of nutritional status (SGA), the malnourished patients (SGA 2-4) had significantly (P<0.05) lower relative plasmalogen levels than the well-nourished predialysis patients (SGA 1). In the prospective part of the study, we found that a 12-month dialysis treatment in 38 patients was associated with significant increases in both erythrocyte DMA 16/C16:0 (P<0.001) and DMA18/C18:0 (P<0.05) ratios. CONCLUSION: The present results suggest that predialysis patients are exposed to an augmented oxidative stress which is partially reversed by 12 months of dialysis treatment. The present study also demonstrates lower relative plasmalogen levels in erythrocyte membranes in malnourished than in well-nourished predialysis patients. One could speculate that an increased oxidative stress may be a factor contributing to the high prevalence of cardiovascular disease documented in malnourished CRF patients.

Adult↗
PubMed1990

Oxidation of 5 beta-cholestane-3 alpha,7 alpha, 12 alpha-triol into 3 alpha,7 alpha,12 alpha-trihydroxy-5 beta-cholestanoic acid by cytochrome P-450(26) from rabbit liver mitochondria.

The mitochondrial cytochrome P-450(26), previously shown to catalyze 26-hydroxylation of 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha-triol, was found to convert this substrate also into 3 alpha,7 alpha,12 alpha-trihydroxy-5 beta-cholestanoic acid. The formation of 3 alpha,7 alpha,12 alpha-trihydroxy-5 beta-cholestanoic acid increased with increasing incubation time and enzyme concentration. Addition of NAD+ to the incubation mixture did not increase the formation of the acid. Incubation with 5 beta-cholestane-3 alpha,7 alpha,12 alpha,26-tetrol, cytochrome P-450(26), ferredoxin, ferredoxin reductase and NADPH resulted in one major product, 3 alpha,7 alpha, 12 alpha-trihydroxy-5 beta-cholestanoic acid. The cytochrome P-450 required both ferredoxin, ferredoxin reductase and NADPH for activity. NADPH could not be replaced by NAD+ or NADP+.

Animals↗
PubMed1990

Absorption of a pharmacological dose of vitamin D3 from two different lipid vehicles in man: comparison of peanut oil and a medium chain triglyceride.

The absorption of a pharmacological dose of vitamin D3 from two different lipid vehicles, peanut oil, containing long chain fatty acids, and a medium chain triglyceride was compared. Serial measurements of the serum concentration of vitamin D3 after dosage were made. The serum levels of 25-hydroxyvitamin D3, the major circulating vitamin D3 metabolite, were also determined. The analytical methods used were based on HPLC. In the fasting state, the serum levels of vitamin D3 were significantly higher after administration in peanut oil than after administration in the medium chain triglyceride. When the vitamin D3 dose was ingested together with food no difference between the two formulations was observed. Only small inter-formulation differences in serum 25-hydroxyvitamin D3 levels were detected. The results indicate that the presence of long chain fatty acids facilitates the absorption of vitamin D3.

Adult↗
PubMed1990

Effect of retinoids and 1,25(OH)2 vitamin D3 bound to their plasma transport proteins on growth and differentiation of HL-60 cells.

We have compared the effect of physiological and pharmacological concentrations of retinoids and 1,25(OH)2 vitamin D3 bound to their plasma transport proteins upon the proliferation and differentiation of HL-60 cells. Concentrations of chylomicron remnant retinyl ester similar to that obtained in plasma after a vitamin A-rich meal reduced the proliferation in more than 50% of HL-60 cells. Pharmacological concentrations of chylomicron remnant retinyl ester completely blocked the proliferation of the cells, and induced differentiation in 60% of the cells after 5 days. Physiological and pharmacological concentrations of retinoic acid bound to albumin had comparable effects. In contrast to earlier published data, which have been obtained with retinoids dissolved in ethanol, our results suggest that physiological and pharmacological concentrations of retinol (i.e. retinyl esters in chylomicron remnants) are as active as retinoic acid in reduction of proliferation and induction of differentiation of HL-60 cells. Physiological concentrations of 1,25(OH)2 vitamin D3 bound to vitamin D-binding protein (DBP) and retinol bound to retinol-binding protein had only a small effect on differentiation and proliferation of HL-60 cells.

Calcitriol↗
PubMed1988

Validation of a radioreceptor assay for 1,25-dihydroxyvitamin D using selected ion monitoring GC-MS.

This report describes two methods for the measurement of 1,25-dihydroxyvitamin D [1,25(OH)2D] in serum: A modified radio receptor assay (RRA), employing a 1,25(OH)2D receptor from calf thymus, and selected ion monitoring (SIM) with combined capillary gas chromatography (GC)-mass spectrometry (MS). The intra-assay coefficient of variation was close to 13% for both methods, and the inter-assay coefficients of variation were 14.0 and 6.5% for RRA and SIM (GC-MS), respectively. Aliquots of 2 ml (RRA) and 20 ml (SIM) serum were used, and the limits of detection were 10 and 6 pmol/l, respectively. The analytical recovery of each method was assessed, and a maximum deviation from the expected value of 10 and 2% was found for RRA and SIM, respectively. A correlation coefficient of 0.93 (slope 0.97) was obtained when 27 different serum samples were analyzed by both methods. Included in this study were serum samples from healthy subjects and patients with subnormal as well as supranormal 1,25(OH)2D levels. This result showed that the RRA accurately measured the serum levels of 1,25(OH)2D and therefore should be useful in the diagnosis and control of vitamin D dependent diseases.

Adult↗
PubMed1986

Assay of 25-hydroxy vitamin D3-1 alpha-hydroxylase in pig kidney mitochondria using isotope dilution-mass spectrometry.

An assay of 1 alpha-hydroxylation of 25-hydroxy vitamin D3 in pig kidney mitochondria, based on selected ion monitoring, has been developed. Trideuterium-labeled 1,25-dihydroxy vitamin D3 was synthesized and used as internal standard. This standard was added immediately after incubation of 25-hydroxy vitamin D3 with the mitochondrial fraction. The incubation extracts were purified by high-performance liquid chromatography. After formation of the trimethylsilyl derivative, the product was quantitated by mass fragmentography using the ion at m/z 452 and m/z 455. With the use of this assay it was found that formation of 1,25-dihydroxy vitamin D3 was linear with the amount of mitochondrial protein and time of incubation. Substrate saturation was obtained at about 20 microM of 25-hydroxy vitamin D3. The maximal rate of conversion obtained under the conditions employed was about 0.1 pmol/mg protein X minute.

25-Hydroxyvitamin D3 1-alpha-Hydroxylase↗
PubMed1986

Mental disorder at seventy in relation to social factors and attitudes during life.

Associations between social factors or attitudes during their life-span and mental disorders at 70 were studied in 166 men and 226 women belonging to the population study "70-year-olds in Gothenburg". Poverty during childhood, arduous job during mature age, and low frequency of social visiting were associated with mental disorder in men, and poverty during childhood and indications of current isolation, with mental disorder in women. Living alone was associated with mental disorder only if combined with factors, such as lack of daily contact with others, or low frequency of social visiting. Combinations of stress and strain during the life-span were associated with feelings of fatigue, while there was no association between losses and mental disorder. Dissatisfaction during the life-span, in women especially with regard to their childhood, was associated with mental disorder.

Aged↗
PubMed1986

High circulating levels of 25-hydroxyvitamin D3 in renal stone formers with hyperabsorptive hypercalciuria.

Normocalcaemic male stone formers, 31-51 years old (n = 108) on a free diet, were divided into a hypercalciuric group (n = 47) with calcium excretion rates higher than 8.0 mmol/24 h, a normocalciuric group (n = 32) with calcium excretion rates below 6.1 mmol/24 h and an intermediate group (n = 29). There were no statistically significant differences between the hypercalciuric and the normocalciuric groups with respect to serum levels of calcium, phosphate, creatinine, urate, ALAT, albumin, PTH, 1,25-dihydroxyvitamin D or urinary excretion of cAMP. The group of patients with high calcium excretion had significantly higher serum levels of 25-hydroxyvitamin D3 (75 +/- 4 nmol/l) than the group with low calcium excretion (57 +/- 4 nmol/l) (p less than 0.002), while the group of patients with intermediate calcium excretion had 25-hydroxyvitamin D3 levels between the other two groups (69 +/- 4 nmol/l). A highly accurate method based on isotope dilution-mass spectrometry was used to assay 25-hydroxyvitamin D3. Of the patients with hypercalciuria (n = 47), seven were classified as hyperabsorbers on the basis of calcium load tests. These patients were found to have even higher serum levels of 25-hydroxyvitamin D3 (108 +/- 10 nmol/l)--significantly higher than that of the hypercalciuric patients as a whole. The above study was carried out in March 1983. In September, the group of patients with high urinary calcium excretion also had significantly higher levels of 25-hydroxyvitamin D3 than the group of patients with low calcium excretion.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1986

25-Hydroxylase activity in subcellular fractions from human liver. Evidence for different rates of mitochondrial hydroxylation of vitamin D2 and D3.

25-Hydroxylation of vitamin D2 and D3 was studied in subcellular fractions from human liver, using a technique based on isotope dilution-mass spectrometry. The mitochondrial fraction fortified with isocitrate catalysed 25-hydroxylation of vitamin D3 at a rate of about 10 pmol/mg protein X min. Under the same conditions, the rate of 25-hydroxylation of vitamin D2 was less than 2 pmol/mg protein X min. Crude microsomes fortified with NADPH catalysed 25-hydroxylation of vitamin D3 to a very low extent, and this activity was not linear with the amount of microsomal protein. A higher rate of conversion was obtained with a partially purified cytochrome P-450 fraction in the presence of NADPH-cytochrome P-450 reductase and NADPH. This fraction also catalysed 25-hydroxylation of 1 alpha-hydroxyvitamin D3 and 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha-triol. 25-Hydroxylation of vitamin D2 could not be detected, neither with crude microsomes, nor with the microsomal cytochrome P-450 fraction. Since the assay for 25-hydroxyvitamin D2 was less sensitive than that for 25-hydroxyvitamin D3, these experiments do not rule out the presence of some 25-hydroxylase activity towards vitamin D2 in the microsomes. The results are discussed in relation to previous work in which a lower toxicity has been reported for vitamin D2 than for vitamin D3 in some mammalian species.

Cholecalciferol↗
PubMed1984

Inhibition of reconstituted vitamin D3 25-hydroxylase by a protein fraction from rat liver microsomes.

A cytochrome P-450 fraction, containing vitamin D3 25-hydroxylase activity after reconstitution, was prepared from rat liver microsomes. The 25-hydroxylase activity increased considerably upon purification. A protein fraction isolated from the microsomes during the preparation markedly inhibited the reconstituted vitamin D3 25-hydroxylase activity. The inhibition was dependent on the amount of protein and completely reversed by heat treatment.

Animals↗
PubMed1984

Differences in the metabolism of vitamin D2 and vitamin D3 by subcellular fractions from rat liver.

The 25-hydroxylation of vitamin D2 and vitamin D3 was studied in the mitochondrial fraction from rat liver and in a reconstituted system containing cytochrome P-450 from rat liver microsomes. The mitochondrial fraction catalyzed the 25-hydroxylation of vitamin D3 at least two times more effectively than the 25-hydroxylation of vitamin D2. Microsomal cytochrome P-450 catalyzed an efficient 25-hydroxylation of vitamin D3, but no 25-hydroxylation of vitamin D2 could be detected. The present results show a difference in the 25-hydroxylation of vitamin D2 and vitamin D3 in rat liver in vitro.

Animals↗
PubMed1984

Hypoparathyroidism and liver disease--evidence for a vitamin D hydroxylation defect. A case report.

The case history of a 4 year old girl with primary hypoparathyroidism is reported. Treatment with oral 1 alpha-hydroxyvitamin D3 did not result in normal calcium and phosphate levels, whereas treatment with oral 1 alpha,25-dihydroxyvitamin D3 did. During the treatment period, the patient developed signs of severe liver disease and died in a picture of increased intracranial pressure. Post-mortem examination revealed a giant cell hepatitis and severe cirrhosis. The clinical course is consistent with a liver vitamin D3 hydroxylation defect.

Calcitriol↗
PubMed1984

Determination of 25-hydroxyvitamin D3 in serum by high performance liquid chromatography and isotope dilution-mass spectrometry.

Four different HPLC methods for analysis of 25-hydroxyvitamin D3 in serum were evaluated with a method based on isotope dilution-mass spectrometry (ID-MS). Method I utilized Sephadex LH-20 chromatography as the only prepurification step. No correlation with the ID-MS method was obtained. Method II utilized Sephadex LH-20 chromatography and a subsequent reversed phase HPLC step as prepurification. The correlation coefficient was 0.99 (regression coefficient 1.2 and intercept - 3.9 micrograms/l). Method III included open silicic acid chromatography and straight phase HPLC as prepurification. The correlation when compared with the ID-MS method was 0.94 (regression coefficient 1.2 and intercept - 0.4 micrograms/l). In method IV Sep-pak C18 chromatography and open silicic acid chromatography were used as prepurification. The correlation coefficient when compared with the ID-MS method was 0.97 (regression coefficient 0.8 and intercept 0.1 microgram/l). It is concluded that a single Sephadex LH-20 step is not sufficient as prepurification and that method IV had an accuracy sufficient for its intended use to analyse 25-hydroxyvitamin D3 in serum from cattle.

Calcifediol↗
PubMed1983

25-hydroxylation of C27-steroids and vitamin D3 by a constitutive cytochrome P-450 from rat liver microsomes.

A constitutive cytochrome P-450 catalyzing 25-hydroxylation of C27-steroids and vitamin D3 was purified from rat liver microsomes. The enzyme fraction contained 16 nmol of cytochrome P-450/mg of protein and showed only one protein band with a minimum molecular weight of 51,000 upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The purified cytochrome P-450 catalyzed 25-hydroxylation of 5 beta-cholestane-3 alpha, 7 alpha-diol, 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha-triol, and 1 alpha-hydroxyvitamin D3 up to 50 times more efficiently, and 25-hydroxylation of vitamin D3 about 150 times more efficiently than the microsomes. The cytochrome P-450 showed no detectable 25-hydroxylase activity towards vitamin D2 and was inactive in cholesterol 7 alpha-hydroxylation as well as in 12 alpha- and 26-hydroxylations of C27-steroids. It catalyzed hydroxylations of testosterone and demethylation of ethylmorphine at the same rates as, or lower rates than, microsomes. The 25-hydroxylation of 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha-triol and vitamin D3 with the purified cytochrome P-450 was not stimulated by addition of phospholipid or cytochrome b5 to the reconstituted system. Emulgen inhibited 25-hydroxylase activity towards both substrates. The possibility that 25-hydroxylation of C27-steroids and vitamin D3 is catalyzed by the same species of cytochrome P-450 is discussed.

Animals↗
PubMed1983

25-Hydroxyvitamin D3-24-hydroxylase in rat kidney mitochondria.

Assay conditions for the measurement of 25-hydroxyvitamin D3-24-hydroxylase activity in rat kidney mitochondria have been worked out. The product, 24,25-dihydroxyvitamin D3 was quantitated either by high pressure liquid chromatography or by isotope dilution-mass spectrometry. By these procedures, the enzyme activity could be measured with saturating concentration (greater than 2.5 X 10(-6) M) of substrate. Pretreatment of the animals by aminophylline (Kulkowski, J. A., Chow, T., Martinez, J., and Ghazarian, J. G. (1979) Biochem. Biophys. Res. Commun. 90, 50-57) stimulated the 24-hydroxylase activity in vitro at least 2 to 3-fold. The identity of the product was verified by gas chromatography-mass spectrometry. The rates of the reaction varied between 1.5 and 5 pmol/mg of mitochondrial protein.min (at 25 degrees C), and the K'm was determined to be 4.2 X 10(-7) M. Malate, succinate, and isocitrate were all able to support the reaction. Low O2 tension, CO, KCN, and the uncoupler carbonyl cyanide m-chlorophenylhydrazone inhibited the reaction, while the respiratory inhibitor rotenone had no effect. Metyrapone inhibited the reaction with 50% inhibition at a concentration of 2.5 mumol/ml. The enzyme was found to be localized inside the inner mitochondrial membrane. The results indicate that in the rat the renal mitochondrial 25-hydroxyvitamin D3-24-hydroxylase is a cytochrome P-450 and that the reducing equivalents are primarily supplied by NADPH via the energy-dependent transhydrogenase.

24,25-Dihydroxyvitamin D 3↗