The role of tegumental aquaporin from the human parasitic worm, Schistosoma mansoni, in osmoregulation and drug uptake.

Schistosomes are parasitic platyhelminths that constitute an important public health problem globally. Infection is characterized by the presence of adult worms within the vasculature of their hosts, where they can reside for many years. The worms are covered by an unusual dual lipid bilayer through which they import nutrients. How the parasites import other vital molecules, such as water, is not known. Recent proteomic analysis of the schistosome tegumental membranes revealed the presence of an aquaporin homologue at the host-interactive surface whose cDNA we have cloned and characterized. The cDNA encodes a predicted 304-aa protein (SmAQP) that is found largely in the parasite tegument by immunolocalization and is most highly expressed in the intravascular life stages. Treatment of parasites with short interfering RNAs targeting the SmAQP gene results in potent (>90%) suppression. These suppressed parasites resist swelling when placed in hypotonic medium, unlike their control counterparts, which rapidly double in volume. In addition, SmAQP-suppressed parasites, unlike controls, resist shrinkage when incubated in hyperosmotic solution. While suppressed parasites exhibit lower viability in culture relative to controls and exhibit a stunted appearance following prolonged suppression, they are nonetheless more resistant to killing by the drug potassium antimonyl tartrate (PAT). This is likely because SmAQP acts as a conduit for this drug, as is the case for aquaporins in other systems. These experiments reveal a heretofore unrecognized role of the schistosome tegument in controlling water and drug movement into the parasites and highlight the importance of the tegument in parasite osmoregulation and drug uptake.

The MRP1-mediated effluxes of arsenic and antimony do not require arsenic-glutathione and antimony-glutathione complex formation.

Arsenic trioxide is an effective treatment for acute promyelocytic leukemia, but resistance to metalloid salts is found in humans. Using atomic absorption spectroscopy, we have measured the rate of uptake of arsenic trioxide and of antimony tartrate in GLC4 and GLC4/ADR cells overexpressing MRP1 and the rate of their MRP1-mediated effluxes as a function of the intracellular GSH concentration. In sensitive cells, after 1 h, a pseudosteady state is reached where intra- and extracellular concentrations of metalloid are the same. This precludes the formation, at short term, of complexes between arsenic or antimony with GSH. In resistant cells reduced intracellular accumulation of arsenic (or antimony), reflecting an increased rate of arsenic (or antimony) efflux from the cells, is observed. No efflux of the metalloid is observed in GSH depleted cells. The two metalloids and GSH are pumped out by MRP1 with the same efficiency. Moreover for the three compounds 50% of the efflux is inhibited by 2 microM MK571. This led us to suggest that As- and Sb-containing species could be cotransported with GSH.

Comparative toxicity and tissue distribution of antimony potassium tartrate in rats and mice dosed by drinking water or intraperitoneal injection.

Antimony potassium tartrate (APT) is a complex salt that until recently was used worldwide as an antischistosomal drug. Treatment was efficacious only if APT was administered intravenously to humans at a near lethal total dose of 36 mg/kg. Because unconfirmed epidemiologic studies suggested there might be an association between APT treatment and bladder cancer, we initiated prechronic toxicity studies with the drug to select a route of administration and doses in the event that chronic studies of APT were needed. The toxicity and concentration of tissue antimony levels were compared in 14-d studies with F344 rats and B6C3F1 mice administered APT in the drinking water or by ip injection to determine the most appropriate route for longer term studies. Drinking water doses estimated by water consumption were 0, 16, 28, 59, 94 and 168 mg/kg in rats and 0, 59, 98, 174, 273, and 407 mg/kg in mice. APT was poorly absorbed and relatively nontoxic orally, whereas ip administration of the drug caused mortality, body weight decrements, and lesions in the liver and kidney at doses about one order of magnitude below those in drinking water. Because of these data and the dose-related accumulation of antimony in the target organs, an ip dose regimen was selected for subsequent studies. Both sexes of F344 rats and B6C3F1 mice were given 0, 1.5, 3, 6, 12, and 24 mg/kg doses of APT every other day for 90 d by ip injection. There were no clinical signs of toxicity nor gross or microscopic lesions in mice that could be attributed to toxicity of APT, although elevated concentrations of antimony were detected in the liver and spleen of mice. Rats were more sensitive than mice to the toxic effects of APT, exhibiting dose-related mortality, body weight decrements, and hepatotoxicity. The concentrations of antimony measured in liver, blood, kidney, spleen, and heart of rats were proportional to dose, but there were no biochemical changes indicative of toxicity except in the liver. Hepatocellular degeneration and necrosis occurred in association with dose-related elevations in activities of the liver-specific serum enzymes sorbitol dehydrogenase and alanine aminotransferase. By alternating the site of abdominal injection and the days of treatment, mesenteric inflammation at the site of administration was minimized in the rats and mice, indicating that the ip route would be suitable for chronic studies.(ABSTRACT TRUNCATED AT 400 WORDS)