Search PubMed⌕ Search

Biomedical subjects

J Aarbakke

Publications and source records attributed to J Aarbakke.

At least 37 records · Page 2Linked to original sources
PubMed1997

Gender difference in the elimination of 2-methoxyethanol, methoxyacetic acid and ethoxyacetic acid in rat.

1. The elimination of 2-methoxyethanol (2-ME) and its toxic metabolite methoxyacetic acid (MAA) was studied in the male and female rat. We also studied the elimination of ethoxyacetic acid (EAA), the toxic metabolite formed by 2-ethoxyethanol (2-EE). 2. The rate of 2-ME elimination after i.p. injection of 2-ME (150 mg/kg) was significantly higher in the female compared with male. The elimination half-life was estimated to 49 +/- 10 min in the male and 28 +/- 5 min in the female. There was, however, no gender difference in the elimination of MAA after i.p. injection of 2-ME (100 mg/kg), and the elimination of MAA was markedly slower compared with 2-ME. The elimination half-life for MAA was estimated to 12.6 +/- 1.3 h in the male and 14.1 +/- 1.4 in the female. 3. The elimination half-life of EAA after i.p. injections of 100 mg/kg 2-EE was estimated to 7.6 +/- 1.1 h and 7.6 +/- 0.75 h in the male and female rat respectively. There was no gender difference in the elimination of EAA, but the rate of elimination of EAA was significantly higher compared with MAA. 4. Accumulation of the toxic metabolites MAA and EAA following frequent exposures to 2-ME and 2-EE respectively can then occur, and it remains to be determined whether there is a sex-difference in the susceptibility to toxic effects following exposure to 2-ME and 2-EE.

Acetates↗
PubMed1997

Possibilities for therapeutic drug monitoring of azathioprine: 6-thioguanine nucleotide concentrations and thiopurine methyltransferase activity in red blood cells.

The objectives of this study were to establish monitoring of azathioprine (AZA) treatment in renal allograft recipients by red blood cell (RBC) 6-thioguanine nucleotide (6-TGN) measurements and to characterize the variability of RBC thiopurine methyltransferase (TPMT) activity and the effects on 6-TGN levels and the incidence of rejection episodes. In 82 renal allograft recipients, the effect of standard AZA dosage (3 mg/kg tapered to 1 mg/kg) was compared with higher dosages (3 mg/kg for several days) under 6-TGN monitoring. The authors measured TPMT in these patients and in a group not receiving AZA. The authors did not find an inverse correlation between RBC TPMT activity and 6-TGN concentrations, and baseline TPMT activity did not predict the incidence of rejection episodes The slight increase in RBC TPMT activity after transplant was associated with the use of furosemide rather than AZA; in the five patients receiving furosemide for less than 10 days, TPMT activity declined. The higher AZA dosage in the 6-TGN monitored group was not sufficient to increase RBC 6-TGN to target levels (100 to 200 pmol/8 x 10(8) RBC); median 6-TGN levels were similar in the two groups, as was the incidence of rejection episodes. Based on these findings, the authors suggest that higher dosages be studied in conjunction with 6-TGN monitoring, to explore the possibilities for therapeutic improvements.

Adolescent↗
PubMed1997

Analysis of methylated 6-mercaptopurine metabolites in human red blood cells: comparison of two methods.

Blood samples from 34 recipients of kidney transplants who were on multidrug therapy including azathioprine were analyzed using two methods in parallel for red blood cell (RBC) concentrations of methylated 6-mercaptopurine (6-MP) metabolites. Chemical hydrolysis with high-performance liquid chromatography (HPLC) showed values ranging from 0 to 20,259 pmol/8 x 10(8) RBCs, compared with enzymatic hydrolysis with HPLC that resulted in values ranging from 16 to 22,252 pmol/100 microl packed RBC. Results of the two methods were highly correlated; the coefficient of correlation (r) was equal to 0.93 (95% confidence interval [CI] = 0.87-0.97 [y = 1.12x + 187]). Within series imprecision was 3.1% compared with 6.3%, and between-run imprecision was 10.3% compared with 20.7%, for the enzymatic and chemical methods, respectively. The enzymatic method was found to be more specific and to save time and labor, but with the chemical method methylated metabolites and 6-thioguanine nucleotides (6-TGN), the main active metabolites of azathioprine and 6-MP, can be measured in the same run. The results indicate that methylated 6-MP metabolites mainly exist as ribonucleotides in RBCs.

Azathioprine↗
PubMed1997

Effects of 3-deazaadenosine on apoptosis-related gene transcripts in HL-60 cells.

The effect of the transmethylation inhibitor 3-deazaadenosine on transcription levels of genes associated with apoptosis was investigated in HL-60 cells. After incubation of HL-60 cells with 100 microM 3-deazaadenosine for 45 min., a schedule known to perturb transmethylation metabolites and initiate apoptosis in these cells, a 50% decrease in c-myc and a 50% increase in bcl-2 RNA steady-state levels compared to control cells were observed. Transcription levels of c-myc continued to decrease after extended exposure to 3-deazaadenosine, while bcl-2 mRNA levels dropped to 25% and 30% below those in control cells after 1.5 hr and 3 hr, respectively. The expression levels of the bcl-2 related bax gene, showed a similar pattern as bcl-2; a 60% increase was initially measured, but after 1.5 and 3 hr, bax transcripts were 80% and 70% respectively, of those found in untreated cells. Another bcl-2 related gene, bcl-x, was previously reported to generate two transcripts in human cells. The long variant bcl-x1 acts as bcl-2, while the short form bcl-xs induces apoptosis. We were unable to detect bcl-xs transcripts in untreated and 3-deazaadenosine treated cells by the highly sensitive reverse transcriptase polymerase chain reaction method. This suggests that this gene product may not be involved in 3-deazaadenosine induced apoptosis in HL-60 cells. Bcl-x1 mRNA levels, however, slowly decreased with about 50% after 1.5 or 3 hr 3-deazaadenosine treatment. It is concluded that 3-deazaadenosine initiated apoptosis affects c-myc, bcl-2, bax and bcl-x1 mRNA levels.

Apoptosis↗
PubMed1996

[Injuries and drug use among soccer players].

Injuries in sports are well-known through retrospective studies of different kinds of sports, especially soccer. In this study on injury and drug use, the adverse effects of drugs and the use of medical services were registered in a group of male elite soccer players and in a referent group. There was a higher percentage of injuries and a higher use of drugs in the soccer group compared with the referent group, the largest difference being in the use of antiflogistics. Both groups reported low adverse effects of drugs, and similar frequency of such effects. Doctors and physiotherapists were usually consulted, but more frequently by the soccer group than by the referent group. The results of this study indicate that playing top division soccer is associated with higher risk of injury with a concomitant higher use of drugs than experienced in the referent group.

Adult↗
PubMed1996

Inhibition of human thiopurine methyltransferase by furosemide, bendroflumethiazide and trichlormethiazide.

RESULTS: Incubation in vitro of human recombinant and erythrocyte (RBC) thiopurine methyl transferase (TPMT) with furosemide, bendroflumethiazide and trichlormethiazide demonstrated inhibition of both enzyme preparations, with IC50 values of 170 microM, 360 microM and 1 mM, respectively. Kinetic studies revealed that the inhibition was mixed or non-competitive with regard both to the thiopurine substrate 6-mercaptopurine (6-MP) and the methyl donor S-adenosyl-L-methionine. CONCLUSION: Since S-methylation is a major pathway in the metabolism of thiopurines, our data point to the possibility of a clinically significant diuretic-thiopurine interaction in patients treated simultaneously with these drugs.

Bendroflumethiazide↗
PubMed1996

Intraindividual variability in red blood cell thiopurine methyltransferase activity.

OBJECTIVE: Long-term (13 weeks) and circadian (24 hours) intraindividual variability in red blood cell (RBC) thiopurine methyltransferase (TPMT) activity in healthy subjects was studied. METHODS: RBC TPMT activity was measured radiochemically. RESULTS: The variability in RBC TPMT activity was low and was only slightly higher than the imprecision of he TPMT assay. Mean long-term intraindividual variability in RBC TPMT activity was 6.5% (CV) (n = 46). Mean intraindividual circadian variability in RBC TPMT activity was 6.4% (CV) (n = 18). CONCLUSIONS: In contrast to what has been observed in children with acute lymphoblastic leukaemia, the intraindividual variability in RBC TPMT activity in healthy subjects was low. The reported changes in baseline RBC TPMT activity in patients are probably therefore due to drugs, disease, assay variation or other, unidentified factors.

Adult↗
PubMed1996

High-dose 7-hydromethotrexate: acute toxicity and lethality in a rat model.

To elucidate mechanisms for methotrexate (MTX)-induced renal and hepatic toxicity, we investigated the acute effects of bolus plus continuous infusion of up to 0.4 g/kg 7-hydroxymethotrexate (7-OH-MTX) in the rat. We demonstrate for the first time in any species the occurrence of acute lethal toxicity within a few hours after 7-OH-MTX administration. Serum concentrations of 7-OH-MTX measured at the time of death were 1.4 mM (mean), about one-half of those achieved in some patients after infusion of high-dose MTX (HD-MTX) in the clinic. The data suggest an approximate LD50 (the dose lethal to 50% of the study population) of 0.3 g/kg and a steep dose/lethality curve for 7-OH-MTX. Moreover, acute renal and hepatic toxicity occurred as evidenced by severe morphological findings and increased serum levels of creatinine and liver transaminases. In all rats subjected to continuous infusion of 7-OH-MTX, yellow microscopic precipitations were apparent in the kidney tubules. Crystallization was also seen in bile ducts of the liver in some of the rats. These results further support that the formation of 7-OH-MTX is disadvantageous and that reported attempts to prevent its formation during MTX treatment are warranted.

Animals↗
PubMed1996

Thiopurine methyltransferase activity in a Korean population sample of children.

Thiopurine methyltransferase (TPMT) is a cytoplasmic enzyme that catalyzes the S-methylation of the cytotoxic drugs 6-mercaptopurine and azathioprine. Red blood cell (RBC) TPMT activity is subject to genetic polymorphism, and we have previously demonstrated an interethnic difference in TPMT activity. To investigate whether there was a race-related difference in RBC TPMT activity, TPMT was measured in a Korean population sample of 309 healthy children. Mean TPMT activity in healthy Korean children was 12.4 +/- 2.4 units/ml RBC, which is similar to the earlier reported TPMT activities in white populations. In contrast to the bimodal or trimodal frequency distributions of RBC TPMT activity in most other population samples, the frequency distribution histogram, the probit plot, and the Shapiro-Wilk test supported a normal distribution of TPMT activity in this Korean population sample of healthy children. Mean RBC TPMT activity showed a tendency to decrease with age, but it was not statistically significant. No gender-related difference in RBC TPMT activity was found.

Age Factors↗
PubMed1996

Apoptosis and transmethylation metabolites in HL-60 cells.

To investigate the role of transmethylation metabolites in initiation of apoptosis in human leukemia HL-60 cells exposed to 3-deazaadenosine (c3 Ado) as single agent and c3Ado plus homocysteine thiolactone (Hcy), S-adenosylmethionine (AdoMet), S-adenosylhomocysteine (AdoHcy) and 3-deazaadenosylhomocysteine (c3AdoHcy), were measured by HPLC in HL-60 cells exposed to 1-100 microM c3Ado as single agent and 1 to 100 microM c3Ado plus 1 mM Hcy. 3-deaza-(+/-)-aristeromycin (c3Ari), a more specific and potent S-adenosylhomocysteine hydrolase inhibitor compared with c3Ado, was used to inhibit synthesis of c3AdoHcy. AdoMet increased to maximum values 1.5- and 2.3-fold control in cultures treated with c3Ado as single agent and c3Ado plus Hcy, respectively. AdoHcy did not change in cultures treated with c3Ado as single agent, but increased to maximum values 2.0-fold control when Hcy was added. The synthesis of c3AdoHcy was favored by Hcy, and 35- to 70-fold higher levels of c3AdoHcy were found in cultures treated with c3Ado plus Hcy vs. c3Ado as single agent. The amounts of c3AdoHcy in cultures treated with c3Ado at concentrations initiating apoptosis did not exceed c3AdoHcy levels in cultures treated with c3Ado plus Hcy at concentrations not initiating apoptosis. Pretreatment of c3Ado plus Hcy cultures with c3Ari diminished c3AdoHcy and almost completely abrogated apoptosis. Exposure of cells to 100 microM c3Ari as single agent resulted in an increase in AdoHcy to 8.4-fold control but no changes in AdoMet and no initiation of apoptosis. Our findings indicate that c3Ado as single agent exerts its apoptosis-initiating effect through a nontransmethylase-related bio-chemical action. c3AdoHcy seems to be related to biochemical events initiating apoptotic cell death of HL-60 cells when c3Ado and Hcy are combined.

Adenosine↗
PubMed1995

A new flow cytometric method for discrimination of apoptotic cells and detection of their cell cycle specificity through staining of F-actin and DNA.

Drug-initiated apoptosis of human leukemia HL-60, THP-1, and U-937 cells was studied via multiparameter flow cytometry and cell sorting. A new flow cytometric method that allows both identification and quantitation of apoptotic cells and estimation of their cell cycle specificity is presented. The method is based on paraformaldehyde fixation followed by staining of F-actin and DNA with fluorescein isothiocyanate (FITC)-phalloidin and propidium iodide (PI), respectively. Bivariate green fluorescence (F-actin) vs. side scatterplots of HL-60 cells treated with 10 microM etoposide for 4 h showed two cell populations, one with high green fluorescence and low side scatter and one with low green fluorescence and high side scatter. Sorting revealed cells with intact nuclei in the high green fluorescence/low side scatter population and cells with fragmented nuclei in the low green fluorescence/high side scatter population, demonstrating that the cells in the latter population were apoptotic. Exposure of HL-60 cells to 10 microM etoposide for 4 h resulted in S-phase selective apoptosis, whereas 5 micrograms/ml cycloheximide initiated apoptosis mainly in G0/G1-phase and S-phase cells. The apoptotic response of HL-60 cells to 20 GY gamma-irradiation was selective for S-phase and G2 + M-phase cells. The present method offers the opportunity to estimate the cell cycle distributions of both the apoptotic and the nonapoptotic cell populations, which is especially valuable when apoptosis occurs in association with cell cycle perturbations. A similar shift from one to two cell populations in green fluorescence vs. side scatter-plots, similar to that observed for HL-60 cells, was observed in the THP-1 and U-937 cell lines secondary to etoposide treatment.

Actins↗
PubMed1995

Is there a gender difference in red blood cell thiopurine methyltransferase activity in healthy children?

We have examined red blood cell (RBC) thiopurine methyltransferase (TPMT) activity in a healthy population sample of Norwegian children, age 1-10 years. Boys had mean RBC TPMT activity of 11.1 +/- 2.0 U (n = 87) vs. 10.6 +/- 2.2 U (n = 71) in girls, the difference was not significant (P = 0.3). Age was negatively correlated to RBC TPMT activity (rs = -0.2, P = 0.01). As boys with acute lymphoblastic leukemia (ALL) tolerate more 6-mercaptopurine (6-MP) than girls and have a higher risk of relapse, we have searched for pharmacokinetic causes of these gender differences. The gender difference in 6-MP tolerance and clinical outcome in children with ALL cannot be explained by the minor and nonsignificant higher RBC TPMT activity in boys compared to girls.

Child↗
PubMed1995

Morphological modifications of apoptosis in HL-60 cells: effects of homocysteine and cytochalasins on apoptosis initiated by 3-deazaadenosine.

Using electron microscopy, confocal laser scanning microscopy and measurements of intact DNA we have studied the morphology and DNA degradation of human leukaemia HL-60 cells undergoing drug initiated apoptosis. Apoptosis was initiated by 100 microM 3-deazaadenosine (c3Ado), 25 microM c3Ado plus 1 mM homocysteine thiolactone (Hcy) and 100 microM c3Ado plus 5 micrograms/ml cytochalasin B (CB). Two different phenotypes of apoptotic cells (APC), blebbed and non-blebbed, were present in the cultures. Blebbed APC dominated in cultures exposed to c3Ado, whereas most APC in cultures treated with c3Ado plus Hcy and all the APC in cultures treated with c3Ado plus CB displayed a non-blebbed phenotype. A more pronounced reduction of the chromatin/cytoplasm ratio, lower volume fractions of uncondensed chromatin and higher volume fractions of highly condensed chromatin (micronuclei) were found in cultures exposed to c3Ado and c3Ado plus Hcy when compared with cultures exposed to c3Ado plus CB. A partial inhibition of c3Ado apoptosis by CB was confirmed by measurements of intact DNA. The inhibitory effect of CB was not reproducible by CE, indicating that CB exerts its effect by an actin independent mechanism. Both blebbed and non-blebbed APC displayed nuclear fragmentation, segregation of organelles and cytoplasmic vesiculation, suggesting that the differences between the phenotypes were restricted to the cytoplasmic membrane. We were not able to demonstrate the presence of F-actin by fluorescein isothiocyanate-phalloidin staining in blebbed APC nor in non-blebbed APC in cultures treated with c3Ado plus Hcy. Non-blebbed APC in cultures treated with c3Ado plus CB displayed foci of F-actin at the internal part of the cytoplasmic membrane. This suggests that F-actin is preserved by the mechanism by which CB inhibits blebbing, and may indicate that blebbing of the cytoplasmic membrane during apoptosis is associated with F-actin deficiency rather than a result of actin-myosin interactions.

Actins↗
PubMed1995

Erythrocyte fraction affects red blood cell thiopurine methyltransferase activity.

Red blood cell (RBC) thiopurine methyltransferase (TPMT) metabolizes the cytotoxic drugs 6-mercaptopurine and azathioprine. RBC TPMT activity has been reported to predict clinical outcome in children with acute lymphoblastic leukaemia and in kidney transplant patients. We first suspected that the erythrocyte fraction affected the calculated TPMT activity when we examined intraindividual TPMT activities in kidney transplant recipients. We demonstrated that the erythrocyte fraction affected the calculated TPMT activity, thus causing a methodological inaccuracy. A low erythrocyte fraction gave an erroneously low TPMT activity. Mean variation of 7.0% was observed within the normal limits of the haematocrit level in healthy subjects. The slopes of the TPMT activity between erythrocyte fraction 0.1 and 0.5 were all significantly different from zero, and the activity displayed good linearity from erythrocyte fraction 0.2. There was a strong association between TPMT activity and erythrocyte fraction in a population sample of children, but not in two other population samples. We propose that the TPMT assay should be performed in lysates at a standardized erythrocyte fraction to avoid variation in activity due to the range of the haematocrit in a population.

Adult↗
PubMed1995

Body fat as a predictor of the antihypertensive effect of nifedipine.

OBJECTIVE: The aim of this study was to investigate the relationship between the blood pressure response and body fat in patients treated with the calcium entry blocker nifedipine. SUBJECTS: Forty untreated subjects with moderate hypertension completed the study. INTERVENTIONS: Height, weight, body mass index (BMI) and body fat (measured by near infrared spectrophotometry using Futrex 5000) were measured before the start of the study. Based on blood pressure measurements before and 30 min after one capsule of 10 mg nifedipine, the patients were allocated to treatment with 10 mg nifedipine daily in the responder group (reduction in diastolic blood pressure > or = 10 mmHg) and with 20 mg nifedipine daily in the non-responder group. Finally, the blood pressure was measured after 1 week. RESULTS: Twelve patients were classified as responders and 28 patients as non-responders. The responder/non-responder groups were comparable with respect to the blood pressure readings initially and to age, whereas the non-responders had higher weight (P < 0.01) and BMI (P < 0.01), more body fat (P < 0.01) and were smaller in height (P < 0.01). After 1 week no additional antihypertensive effect was observed in either group. The blood pressure reduction was negatively correlated to the body fat mass in kilogrammes (P < 0.05 for systolic and P < 0.01 for diastolic blood pressure) in the responder group but not in the non-responder group, whereas no significant correlations were found to BMI in either group. CONCLUSION: Our data indicate that the body fat can be used to predict the antihypertensive effect of nifedipine.

Adipose Tissue↗