After Intestinal Transplantation Kidney Function Is Impaired by Downregulation of Epithelial Ion Transporters in the Ileum.

BACKGROUND: Intestinal transplantation is a treatment option for intestinal failure. Although nephrotoxic medication after transplantation is a major cause for posttransplant renal insufficiency, it remains unclear why kidney dysfunction is particularly frequent after intestinal transplantation. METHODS: This study analyzed messenger RNA expression of NHE3, DRA, and CFTR in 404 biopsies obtained between day 2 and 1508 from the terminal ileum of 10 adult intestinal transplant recipients. RESULTS: The time courses of immunosuppression and glomerular filtration rate were correlated. In the first posttransplant year, expression of NHE3 and DRA, which mediate NaCl absorption, was diminished to a greater degree than that of CFTR, which mediates chloride secretion. Reduced NHE3 and DRA expression was associated with high tacrolimus trough levels. Titration of tacrolimus to low levels by year 2 was paralleled by partially restored NHE3 and DRA expression. In cell culture experiments, similar effects of tacrolimus on transporter expression were detected. In patients, both reduced tacrolimus levels and recovery of NHE3 and DRA expression were associated with stabilization of renal function. CONCLUSIONS: Our data strongly suggest that tacrolimus impairs absorption of NaCl and water from the transplanted ileum, leading to volume depletion and impaired renal function. This may be reversible by reduction of tacrolimus to lower levels without increased rates of rejection or chronic graft failure.

The PDZ-interaction of the intestinal anion exchanger downregulated in adenoma (DRA; SLC26A3) facilitates its movement into Rab11a-positive recycling endosomes.

Electroneutral NaCl absorption in the ileum and colon is mediated by downregulated in adenoma (DRA) (Cl⁻/HCO3⁻ exchanger; SLC26A3) and Na⁺/H⁺ exchanger 3 (NHE3, SLC9A3). Surface expression of transport proteins undergoes basal and regulated recycling by endo- and exocytosis. Expression and activity of DRA in the plasma membrane depend on intact lipid rafts, phosphatidylinositol 3-kinase (PI3-kinase), and the PDZ interaction of DRA. However, it is unknown how the PDZ interaction of DRA affects its trafficking to the cell surface. Therefore, the (re)cycling pathway of DRA was investigated in HEK cells stably expressing enhanced green fluorescent protein (EGFP)-DRA or EGFP-DRA-ETKFminus (a mutant lacking the PDZ interaction motif). Early, late, and recycling endosomes were immunoisolated by precipitating stably transfected mCherry-hemagglutinin (HA)-Rab5a, -7a, or -11a. EGFP-DRA and EGFP-DRA-ETKFminus were equally present in early endosomes. In recycling endosomes, wild-type DRA was preferentially present, whereas, in late endosomes, DRA-ETKF-minus dominated. Correspondingly, EGFP-DRA colocalized with mCherry-HA-Rab11a in recycling endosomes, whereas EGFP-DRA-ETKFminus colocalized with mCherry-HA-Rab7a in late endosomes. Functionally, this different distribution was reflected by a shorter half-life of the mutant DRA. Transient expression of dominant-negative Rab11a(S25N) inhibited the activity (-17%, P < 0.05) and the cell surface expression of DRA (-30%, P < 0.05). Transient transfection of Rab4a or its dominant-negative mutant Rab4a(S22N) was without effect and thus excluded participation of the rapid recycling pathway. Taken together, the PDZ interaction of DRA facilitates its movement into Rab11a-positive recycling endosomes, from where it is inserted in the plasma membrane. A scenario emerges where specific PDZ adaptor proteins are present along several compartments of the endocytosis-recycling pathway.

Schistosoma mansoni: schistosomicidal effect of mefloquine and primaquine in vitro.

We investigated the effects of the anti-malarials mefloquine and primaquine against the juvenile and adult life stages of Schistosoma mansoniin vitro. Cercariae were incubated with 0.5 µg/ml, 1 µg/ml and 2 µg/ml mefloquine or primaquine and with 1 µg/ml praziquantel for 12h. Schistosomula, pre-adults and adults were incubated with 0.5 µg/ml, 1 µg/ml and 2 µg/ml mefloquine or primaquine and with 1 µg/ml praziquantel for 7 days. The viability status was classified as viable, damaged or dead and was checked every 3h for cercariae and every 12h for schistosomula, pre-adults and adults. Both, mefloquine and primaquine show time and dose-dependent schistosomicidal effects on the four life stages of S. mansoni. The promising in vitro effects on all stages of the blood fluke S. mansoni warrants further evaluation of both anti-malarials and their derivatives for their prophylactic and therapeutic values in early and late schistosomiasis in field trials.