Zvi Ben-Zvi

Drug transport across the placenta.

It has become clear that almost any drug or chemical substance administered to the mother is able to cross the placenta to some extent, unless it is metabolized or altered during passage, or else its molecular size and low lipid solubility do not allow transplacental transfer. A number of transport systems have been identified in the placenta, which recognizes a wide variety of pharmacological active drugs as substrates. In recent years, research on human placental transporters has been developing due to the increase of knowledge technology in pharmacology. In this review we will focus on the main placental transporters which are known today. The P-glycoprotein (P-gp), Breast cancer resistance protein (BCRP/ABCG2) and Multidrug resistance associated protein 2 (MDR2) transporters are expressed at the apical surface of the syncytiotrophoblast, and have a protective effect. Transporters for 5-HT (SERT) and NE (NET) are also expressed at the apical surface and regulate extracellular concentrations of monoamines. The physiologic function of Multidrug resistance associated protein (MRP) transporters (which is expressed at the basal surface of the syncytiotrophoblast) may be the removal of metabolic end products from the fetus. Some of the members of the organic anion transporters are also expressed at the basolateral surface of the syncytiotrophoblast.

Lack of interaction of digoxin and P-glycoprotein inhibitors, quinidine and verapamil in human placenta in vitro

OBJECTIVE To determine the effect of quinidine and verapamil, known antiarrhythmic agents and P-glycoprotein (Pgp) inhibitors, on digoxin transport from the maternal to the fetal compartment in the isolated perfused human placenta. STUDY DESIGN Isolated placental cotyledons from normal human placentae (n=20) were dually perfused with M199 medium enriched with albumin (0.3%) and glucose (0.1%). The maternal and the fetal circulation flow rates were 12 and 6 ml/min, respectively. Closed circulations were used to evaluate steady state transplacental gradient formation. In six placentae quinindine was added to the maternal circuit; after 45 min of perfusion, digoxin was added to the maternal circulation. The effect of verapamil on digoxin transfer from the maternal to the fetal compartments was explored in five placentae. In six additional placentae the transfer of digoxin was studied in the absence of quinidine. Transplacental passage of digoxin was calculated from repeated fetal and maternal perfusate samples. Digoxin levels were determined in perfusate samples by fluorescence polarization immunoassay. Antipyrine was added to the maternal reservoir of all placentae as reference substance. RESULTS The transfer of digoxin (alone) and in the presence of quinidine or verapamil was 10.93+/-3.71, 9.00+/-5.2 and 12.94+/-4.86%, respectively. The levels of digoxin in the fetal compartment, 0.62+/-0.20, 0.48+/-0.29 and 0.60+/-0.26 ng/ml, respectively, were not significantly affected by quinidine and verapamil. These Pgp modulators, also did not influence significantly the steady state levels of digoxin in the maternal compartment. CONCLUSION Neither quinidine nor verapamil affected the transplacental transfer of digoxin in vitro in normal human placentae. In contrast to the other tissues, they do not inhibit Pgp activity in term human placentae.

Caffeine metabolism in liver slices during postnatal development in the rat.

Abstract The metabolism of caffeine was investigated in liver slices of young and adult rats. Liver slices from adult male rats metabolized caffeine at an initial rate of 48.31 ± 3.71 nmoles · (g liver)−1 · hr−1 to four main metabolite fractions. By a combination of thin-layer radiochromatography and high performance liquid chromatography, theophylline, paraxanthine and 1, 3, 7-trimethyldihydrouric acid were identified as caffeine metabolites. Apparent Vmax of the overall reaction was 83.30 nmoles caffeine metabolites formed · (g liver)−1 · hr−1. Theophylline competitively inhibited caffeine metabolism [the apparent Km was 19.20, μM in the absence of theophylline, the apparent ki was 36.50 μM in the presence of theophylline (100 μM)]. SKF 525-A inhibited caffeine metabolism; the formation of all of the metabolite fractions was inhibited to a similar extent. Allopurinol (100 μM) had no effect. The specific activity of the enzyme system was extremely low when liver slices of 2-day-old-rats were used [1.46 ± 0.08 nmoles caffeine metabolites formed · (g liver)−1 · hr−1]; the reaction velocity increased gradually with increasing age and reached a peak [52.26 ± 1.41 nmoles caffeine metabolites formed · (g liver)−1 · hr−1]at 30 days of age. Changes in the formation of the four metabolite fractions with age followed the pattern of the overall caffeine metabolism. These results demonstrate that the liver of the newborn rat has an extremely limited capacity to metabolize caffeine in vitro and are consistent with the proposed involvement of the liver microsomal cytochromes P-450 monooxygenase system in the metabolism of caffeine. N-Demethylation is the main pathway of in vitro caffeine metabolism in the rat liver at all ages.

An outbreak of digoxin intoxication

An outbreak of digoxin intoxication brought about by an unannounced change affecting bioavailability by a manufacturer is reported. Public health implications are discussed.

Changes in theophylline metabolism during postnatal development in rat liver slices

The metabolism of theophylline was studied in liver slices of young and adult rats. Theophylline and six metabolite fractions were recognized in adult liver by thin-layer radiochromatography and high performance liquid chromatography: 1-methyluric acid; 1-methylxanthine; 1,3-dimethyluric acid and/or 3-methylxanthine; caffeine; a uracil derivative and two unknown polar compounds. Preincubation with caffeine or theobromine inhibited theophylline metabolism. Allopurinol decreased the formation of three metabolite fractions but markedly increased the production of 1-methylxanthine. SKF 525-A inhibited the overall metabolism of theophylline. The specific activity of the enzyme system was 3.2 +/- 0.4 nmoles X (g liver)-1 X hr-1 in the 4- to 5-day-old rat and increased to a peak of 25.7 +/- 1.7 in the 28-day-old; values for Km and Vmax in the 7- and 28-day-olds were 132.1 and 67.5 microM, and 23.9 and 52.1 nmoles X (g liver)-1 X hr-1 respectively. Theophylline and the same six metabolites were identified in young and adult rats, but the development pattern was not uniform. Peak age-related activity and involvement of mixed-function oxidase system are features which are common to theophylline and caffeine metabolism. Xanthine oxidase played a role in theophylline metabolism. Formation of caffeine from theophylline was not dependent on a lack of activity of other pathways.

Loperamide effects on hepatobiliary function, intestinal transit and analgesia in mice

Loperamide effects on hepatobiliary function, analgesia and gut transit were studied in mice. Varying doses of the antidiarrheal drug, loperamide, were administered to mice by intracerebroventricular, intravenous, subcutaneous and intragastric routes. Gut motility was determined by intestinal transit of India ink, analgesia by warm water tail flick latency, and hepatobiliary function by retention of the anionic dye, sulfobromophthalein in plasma and liver. When given by all routes at modest doses, loperamide slowed intestinal transit. Analgesia, a centrally mediated opiate effect, was only detected after intracerebroventricular or subcutaneous loperamide at high, near-toxic doses. Elevations of plasma and liver sulfobromophthalein were noted at routes and doses which slowed gut transit, well below those needed for analgesia. Intragastric loperamide at one fortieth its LD50 caused marked elevation of sulfobromophthalein levels and gut slowing, but no analgesia. Sulfobromophthalein elevation and gut slowing by intragastric loperamide were not affected by spinal cord transection but were reversed by naltrexone, an opiate antagonist. Non-toxic doses of loperamide slow gut transit and modify hepatobiliary function in mice by opiate actions at peripheral sites.

Monitoring phenytoin therapy using citric acid-stimulated saliva in infants and children.

Two factors have limited the use of saliva in monitoring phenytoin therapy: availability of adequate volume of clear saliva and lack of a sensitive phenytoin assay. The applicability of citric acid-stimulated saliva and of a sensitive analytical assay (fluorescence polarization immunoassay, “TDx” Abbott) was evaluated in this study. Phenytoin was measured in paired plasma-saliva specimens from epileptic children during the long-term or the initial phase of phenytoin therapy. Analysis was carried out in plasma and in the clear supernatant of saliva (following centrifugation). Pooled-estimate SD of the analytical assay variability was 0.175 μg/ml for plasma total phenytoin, 0.063 for plasma free phenytoin, and 0.009 for saliva phenytoin. Recovery measurements of phenytoin spiked into saliva samples gave a coefficient of variation of less than 5%. Correlations between saliva and total plasma phenytoin levels and between saliva and free plasma phenytoin levels were strong and highly significant (r = 0.99, p < 0.01). The percentage of temporal fluctuation (as determined by saliva phenytoin profiles) during 10–24 h ranged between 25.5–177 (mean, 58.3; SD, 47.3). Ratios of plasma total phenytoin/saliva phenytoin and of plasma free phenytoin/saliva phenytoin levels were 9.54 ± 1.05 and 0.71 ± 0.09, respectively. Dialysis experiments showed no binding of phenytoin to saliva supernatant. The greater saliva phenytoin concentrations as compared to plasma free phenytoin concentrations could be due to active transport of phenytoin from plasma to saliva. Measurement of phenytoin in citric acid-stimulated saliva by fluorescent polarization immunoassay is a reliable, noninvasive, and convenient method for monitoring phenytoin therapy in children.

Effect of chronic heat exposure on in-vitro drug metabolism in the rat

Abstract The in-vitro rate of drug metabolizing enzymes was investigated in chronically heat exposed male rats. Exposure to 35±2°C for 30 days resulted in significant reduction in the rates of both hepatic N-demethylation of parachloro-N-methylaniline and aniline hydroxylation. Substantial elevation of rectal temperature and marked reduction in body and liver weights was observed in the same rats. The significance of these results is discussed.

Acetaminophen hepatotoxicity: Is there a role for prostaglandin synthesis?

The hepatotoxicity of acetaminophen (APAP) overdose depends on metabolic activation to a toxic reactive metabolite via hepatic mixed function oxidase. In vitro studies have indicated that APAP may also be cooxidized by prostaglandin H synthetase. The present experiments were designed to assess the possible contribution of hepatic prostaglandin synthesis to APAP toxicity. Adult fed male mice were overdosed with 400 mg APAP/kg. Liver toxicity was estimated by measurement of serum transaminases. Hypertonic xylitol or sodium chloride (2250 mOsm/l), administered intragastrically to stimulate prostaglandin synthesis, increased APAP toxicity. By contrast, the cyclooxygenase inhibiting drugs aspirin (at 25 mg/kg) and indomethacin (at 10 mg/kg) protected against APAP-induced toxicity. APAP kinetics were not affected by hypertonic xylitol or indomethacin, nor were hepatic glutathione levels in overdosed mice. Imidazole, a nonspecific thromboxane synthetase inhibitor, also protected overdosed mice. This drug prolonged hexobarbital sleeping time and prevented the depletion of hepatic glutathione that followed APAP intoxication. Thus, the data support the conclusion that APAP-induced hepatotoxicity may be modulated not only by inhibition of cytochrome P450 mediated oxidation, but also by controlling hepatic cyclooxygenase activity.

Cannabidiol changes P-gp and BCRP expression in trophoblast cell lines

Objectives. Marijuana is the most commonly used illicit drug during pregnancy. Due to high lipophilicity, cannabinoids can easily penetrate physiological barriers like the human placenta and jeopardize the developing fetus. We evaluated the impact of cannabidiol (CBD), a major non-psychoactive cannabinoid, on P-glycoprotein (P-gp) and Breast Cancer Resistance Protein (BCRP) expression, and P-gp function in a placental model, BeWo and Jar choriocarcinoma cell lines (using P-gp induced MCF7 cells (MCF7/P-gp) for comparison). Study design. Following the establishment of the basal expression of these transporters in the membrane fraction of all three cell lines, P-gp and BCRP protein and mRNA levels were determined following chronic (24–72 h) exposure to CBD, by Western Blot and qPCR. CBD impact on P-gp efflux function was examined by uptake of specific P-gp fluorescent substrates (calcein-AM, DiOC2(3) and rhodamine123(rh123)). Cyclosporine A (CsA) served as a positive control. Results. Chronic exposure to CBD resulted in significant changes in the protein and mRNA levels of both transporters. While P-gp was down-regulated, BCRP levels were up-regulated in the choriocarcinoma cell lines. CBD had a remarkably different influence on P-gp and BCRP expression in MCF7/P-gp cells, demonstrating that these are cell type specific effects. P-gp dependent efflux (of calcein, DiOC2(3) and rh123) was inhibited upon short-term exposure to CBD. Conclusions. Our study shows that CBD might alter P-gp and BCRP expression in the human placenta, and inhibit P-gp efflux function. We conclude that marijuana use during pregnancy may reduce placental protective functions and change its morphological and physiological characteristics.