The contamination with fluorouracil, cyclophosphamide and methotrexate was studied in a hospital pharmacy department where these drugs were prepared. In the preparation room, air samples were taken before and during preparation of the drugs. Methotrexate was detected in one sample which was collected during preparation (0.3 micrograms/m3). Spot samples were taken in the vertical laminar airflow safety hood before and after preparation of the drugs and after cleaning of the hood. Contamination of the laminar airflow hood was: cyclophosphamide: 1-160 ng/cm2; fluorouracil: 10-62 ng/cm2 and methotrexate: 2-633 ng/cm2. Spot samples from the floor in front of and beneath the laminar airflow hood showed contamination with especially fluorouracil (48-236 micrograms/m2). The gloves used during preparation of the drugs were contaminated mainly with fluorouracil (5-980 ng/cm2). Urine samples from two workers involved in the preparation of the drugs were analysed for unmetabolized cyclophosphamide; it was not detected. Although no uptake of cyclophosphamide was established, it is shown that the methods for measurement of cyclophosphamide, fluorouracil and methotrexate in the preparation room are applicable for the control of occupational exposure to these drugs.

During chronic kidney disease (CKD), drug metabolism is affected leading to changes in drug disposition. Furthermore, there is a progressive accumulation of uremic retention solutes due to impaired renal clearance. Here, we investigated whether uremic toxins can influence the metabolic functionality of human conditionally immortalized renal proximal tubule epithelial cells (ciPTEC) with the focus on UDP-glucuronosyltransferases (UGTs) and mitochondrial activity. Our results showed that ciPTEC express a wide variety of metabolic enzymes, including UGTs. These enzymes were functionally active as demonstrated by the glucuronidation of 7-hydroxycoumarin (7-OHC; K(m) of 12±2μM and a V(max) of 76±3pmol/min/mg) and p-cresol (K(m) of 33±13μM and a V(max) of 266±25pmol/min/mg). Furthermore, a wide variety of uremic toxins, including indole-3-acetic acid, indoxyl sulfate, phenylacetic acid and kynurenic acid, reduced 7-OHC glucuronidation with more than 30% as compared with controls (p<0.05), whereas UGT1A and UGT2B protein expressions remained unaltered. In addition, our results showed that several uremic toxins inhibited mitochondrial succinate dehydrogenase (i.e. complex II) activity with more than 20% as compared with controls (p<0.05). Moreover, indole-3-acetic acid decreased the reserve capacity of the electron transport system with 18% (p<0.03). In conclusion, this study shows that multiple uremic toxins inhibit UGT activity and mitochondrial activity in ciPTEC, thereby affecting the metabolic capacity of the kidney during CKD. This may have a significant impact on drug and uremic retention solute disposition in CKD patients.

Background: Animal studies suggest that the anti-inflammatory effect of methotrexate (MTX) is mediated by increased adenosine concentrations. Objective: To assess the effect of MTX on the vasodilator effects of adenosine and the nucleoside uptake inhibitor, dipyridamole, in humans in vivo as a marker for changes in adenosine kinetics. Methods: Ten patients with active arthritis were treated with MTX (15 mg/week). Measurements were performed before and after 12 weeks of treatment. At these time points, the activity of adenosine deaminase was measured in isolated lymphocytes, and forearm blood flow (FBF) was determined by venous occlusion plethysmography during administration of adenosine and dipyridamole into the brachial artery. Results: The V max of adenosine deaminase in lymphocytes was reduced by MTX treatment (p,0.05). MTX significantly enhanced vasodilator response to adenosine (0.5 and 1.5 mg/min/dl of forearm tissue; mean (SE) FBF ratio increased from 1.2 (0.2) to 1.4 (0.2) and 2.2 (0.2) ml/dl/min, respectively, before and from 1.3 (0.1) to 1.8 (0.2) and 3.2 (0.5) ml/dl/min during MTX treatment; p,0.05). Also, dipyridamoleinduced vasodilatation (30 and 100 mg/min/dl) was enhanced by MTX (FBF ratio increased from 1.2 (0.2) to 1.5 (0.3) and 1.8 (0.2), respectively, before and from 1.3 (0.1) to 1.8 (0.2) and 2.4 (0.4) during MTX treatment; p,0.05). Conclusions: MTX treatment inhibits deamination of adenosine and potentiates adenosine-induced vasodilatation. Also dipyridamole-induced vasodilatation is enhanced by MTX treatment, suggesting an increased extracellular formation of adenosine. These effects on the adenosine kinetics in humans may contribute to the therapeutic efficacy of MTX.

A method for biological monitoring of exposure to the plasticizer di(2-ethylhexyl)phthalate (DEHP) is described. In this method the four main metabolites of DEHP [i.e., mono(2-ethylhexyl)phthalate (MEHP), mono(5-carboxy-2-ethylpentyl)phthalate, mono(2-ethyl-5-oxohexyl)phthalate, and mono(2-ethyl-5-hydroxyhexyl)-phthalate] are determined in urine samples. The procedure includes enzymatic hydrolysis, ether extraction, and derivatization with triethyloxonium tetrafluoroborate. Analysis is performed by gas chromatography-electron impact mass spectrometry. The detection limit for all four metabolites is less than 25 micrograms/l urine. The coefficient of variation based on duplicate determinations of urine samples of workers occupationally exposed to DEHP was 16% for MEHP (mean concentration 0.157 mg/l) and 6%-9% for the other three metabolites (mean concentrations 0.130-0.175 mg/l). The method described here was used to study DEHP metabolism in man. Most persons excrete mono(2-ethyl-5-oxohexyl)-phthalate and mono(2-ethyl-5-hydroxyhexyl)phthalate as a (glucuronide) conjugate. Mono(5-carboxy-2-ethylpentyl)phthalate is mainly excreted in free form, while for MEHP a large interindividual variation in conjugation status was observed. Of the four metabolites quantified, 52% are products of a (omega-1)-hydroxylation reaction of MEHP [i.e., mono(2-ethyl-5-oxohexyl)phthalate and mono(2-ethyl-5-hydroxylation reaction of MEHP [i.e., mono(5-carboxy-2-ethylpentyl)phthalate], and 26% is not oxidized further (i.e., MEHP). A good correlation is obtained when the amount of MEHP omega-hydroxylation products is compared with the amount of MEHP (omega-1)-hydroxylation products in urine samples. When the internal dose of DEHP has to be established we recommend that the levels of all four metabolites of DEHP be studied in urine samples.

No abstract

One week of oral treatment with the nucleoside uptake inhibitor dipyridamole (200 mg, slow release, twice daily) significantly limits ischemia-reperfusion injury in humans in vivo, as assessed by technetium Tc 99m-labeled annexin A5 scintigraphy of forearm skeletal muscle.

Objective-Endogenous adenosine has several cardioprotective effects. We postulate that in patients with hyperhomocysteinemia increased intracellular formation of S-adenosylhomocysteine decreases free intracellular adenosine. Subsequently, facilitated diffusion of extracellular adenosine into cells through dipyridamole-sensitive transporters is enhanced, limiting adenosine receptor stimulation. We tested this hypothesis in patients with classical homocystinuria (nϭ9, plasma homocysteine 93.1Ϯ24.7 mol/L) and matched controls (nϭ8, homocysteine 9.1Ϯ1.0). Methods and Results-Infusion of adenosine (0.5, 1.5, 5.0, and 15.0 g/min/dL forearm) into the brachial artery increased forearm blood flow, as measured with venous occlusion plethysmography, to 2.9Ϯ0.4, 4.3Ϯ0.5, 5.6Ϯ1.1, and 9.6Ϯ2.1 in the patients and to 2.8Ϯ0.6, 4.4Ϯ1.0, 9.0Ϯ1.7, and 17.0Ϯ3.1 mL/min/dL in controls (PϽ0.05). However, adenosine-induced vasodilation in the presence of dipyridamole (100 g/min/dL) was similar in both groups (Pϭ0.9). Additionally, in isolated erythrocytes, adenosine uptake was accelerated by incubation with homocysteine (half-time 6.4Ϯ0.3 versus 8.1Ϯ0.5 minutes, PϽ0.001) associated with increased intracellular formation of S-adenosylhomocysteine (PϽ0.0001). Conclusions-In hyperhomocysteinemia, adenosine-induced vasodilation is impaired but is restored by dipyridamole.Accelerated cellular adenosine uptake probably accounts for these observations. These impaired actions of adenosine could well contribute to the cardiovascular complications of hyperhomocysteinemia. Key Words: adenosine Ⅲ hyperhomocysteinemia Ⅲ dipyridamole Ⅲ forearm Ⅲ nucleoside transport H yperhomocysteinemia is an independent risk factor for atherosclerosis and thromboembolism. It is poorly understood which mechanism is responsible for these cardiovascular complications.Recently, we and others have drawn attention to a new hypothesis, focusing on the influence of homocysteine on the metabolism of the endogenous nucleoside adenosine. 1,2 According to this hypothesis, a homocysteine-induced fall in extracellular adenosine contributes to the cardiovascular sequelae of hyperhomocysteinemia. Fundamental to this is the reversibility of the reaction in which S-adenosylhomocysteine (AdoHcy) is hydrolyzed to form homocysteine and adenosine. 3 Although the equilibrium constant of this reaction favors AdoHcy synthesis, under physiological conditions AdoHcy is hydrolyzed to homocysteine and adenosine, because both reaction products are rapidly metabolized. In hyperhomocysteinemia, the reaction shifts toward AdoHcy synthesis at the expense of free intracellular adenosine. Subsequently, facilitated diffusion of extracellular adenosine into the cells through the dipyridamole-sensitive equilibrative nucleoside transporter is enhanced, limiting stimulation of membrane-bound adenosine receptors (Figure 1).By stimulation of these receptors, extracellular adenosine induces several effects, which could protect against the development of atherosclerosis and thrombosis and against ischemia-re...

ABSTRACT:Cannabinoid type 1 (CB1) receptor antagonists have been developed for the treatment of obesity, but a major disadvantage is that they cause unwanted psychiatric effects. Selective targeting of peripheral CB1 receptors might be an option to circumvent these side effects. Multidrug resistance-associated proteins (MRPs) can influence the pharmacokinetics of drugs and thereby affect their disposition in the body. In this study, we investigated the interaction of the prototypic CB1 receptor antagonist rimonabant and a series of 3,4-diarylpyrazoline CB1 receptor antagonists with MRP1, MRP2, MRP3, and MRP4 in vitro. Their effect on ATP-dependent transport of estradiol 17-␤-D-glucuronide (E 2 17␤G) was measured in inside-out membrane vesicles isolated from transporter-overexpressing human embryonic kidney 293 cells. Rimonabant inhibited MRP1 transport activity more potently than MRP4 (K i of 1.4 and 4 M, respectively), whereas the 3,4-diarylpyrazolines were stronger inhibitors of MRP4-than MRP1-mediated transport. A number of CB1 receptor antagonists, including rimonabant, stimulated MRP2 and MRP3 transport activity at low substrate concentrations but inhibited E 2 17␤G transport at high substrate concentrations. The interaction of 3,4-diarylpyrazolines and rimonabant with MRP1-4 indicates their potential for drug-drug interactions. Preliminary in vivo data suggested that for some 3,4-diarylpyrazolines the relatively lower brain efficacy may be related to their inhibitory potency against MRP4 activity. Furthermore, this study shows that the modulatory effects of the 3,4-diarylpyrazolines were influenced by their chemical properties and that small variations in structure can determine the affinity of these compounds for efflux transporters and thereby affect their pharmacokinetic behavior.