Baclofen-induced neurotoxicity in patients with compromised renal function: Review.

Baclofen is a centrally-acting γ-amino butyric acid agonist used mainly in the symptomatic management of spasticity originating from the spinal cord. It is absorbed completely from the gastrointestinal tract, metabolized by the liver to a minor degree, and excreted unchanged by the kidneys. Baclofen is moderately lipophilic and can cross the blood-brain barrier easily. At the usual dosage, it acts mainly at the spinal level without central nervous system (CNS) side effects. During renal failure, however, the elimination of the drug will decrease with a prolonged half-life, resulting in a larger area-under-the-curve exposure and disproportionate CNS toxicity. Clinically, these patients with renal failure may present with a variety of toxic symptoms manifesting at therapeutic/sub-therapeutic doses of baclofen. In cases of unexplained mental status changes in a patient receiving baclofen therapy, a careful assessment of renal function and a high suspicion of baclofen-induced encephalopathy will be key to the diagnosis.
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ADAM17 promotes proliferation of collecting duct kidney epithelial cells through ERK activation and increased glycolysis in polycystic kidney disease.

Polycystic kidney disease (PKD) is a common genetic disorder leading to cyst formation in the kidneys and other organs that ultimately results in kidney failure and death. Currently, there is no therapy for slowing down or stopping the progression of PKD. In this study, we identified the disintegrin metalloenzyme 17 (ADAM17) as a key regulator of cell proliferation in kidney tissues of conditional knockout Ift88(-/-) mice and collecting duct epithelial cells from Ift88°(rpk) mice, animal models of autosomal recessive polycystic kidney disease (ARPKD). Using Western blotting, an enzyme activity assay, and a growth factor-shedding assay in the presence or absence of the specific ADAM17 inhibitor TMI-005, we show that increased expression and activation of ADAM17 in the cystic kidney and in collecting duct epithelial cells originating from the Ift88°(rpk) mice (designated as PKD cells) lead to constitutive shedding of several growth factors, including heparin-binding EGF-like growth factor (HB-EGF), amphiregulin, and transforming growth factor-α (TGF-α). Increased growth factor shedding induces activation of the EGFR/MAPK/ERK pathway and maintains higher cell proliferation rate in PKD cells compared with control cells. PKD cells also displayed increased lactate formation and extracellular acidification indicative of aerobic glycolysis (Warburg effect), which was blocked by ADAM17 inhibition. We propose that ADAM17 is a key promoter of cellular proliferation in PKD cells by activating the EGFR/ERK axis and a proproliferative glycolytic phenotype.

Nitrite Modification of Extracellular Matrix Alters CD46 Expression and VEGF Release in Human Retinal Pigment Epithelium.

PURPOSE: Loss of CD46 has recently been implicated in choroidal neovascularization in mice. Herein we investigated the effect of nitrite modification of the extracellular matrix (ECM) as an in vitro model of "aging" and its effect on CD46 expression and vascular endothelial growth factor (VEGF) release in cocultured human retinal pigment epithelium (RPE). METHODS: ARPE-19 cells were plated onto RPE-derived ECM conditions (untreated; nitrite modified; nitrite modified followed by washing with Triton X-100; or nitrite modified followed by washing with Triton X-100 and coated with extracellular matrix ligands). Cells were cultured for 7 days and CD46 expression was analyzed by immunohistochemistry and Western blot. Additionally, CD46 short interfering RNA (siRNA) was transfected into ARPE-19 cells, and VEGF levels were determined by ELISA. Finally, in the same ECM conditions, ARPE-19 cells were challenged with normal human serum and VEGF levels determined by ELISA. RESULTS: CD46 is expressed on the basolateral surface of ARPE-19 cells on RPE-derived ECM. Nitrite modification of ECM reduced the expression of CD46 on ARPE-19 cells by 0.5-fold (P = 0.003) and increased VEGF release in ARPE-19 cells by 1.7-fold (P < 0.001). CD46 knockdown also increased release of VEGF on the apical and basal sides of ARPE-19 cells in culture by 1.3- (P = 0.012) and 1.2-fold (P = 0.017), respectively. CONCLUSIONS: Nitrite modification of the ECM decreased CD46 expression and increased the release of VEGF from ARPE-19 cells. Changes in CD46 expression may lead to changes in VEGF and play a pathologic role in the development of age-related macular degeneration.