Liver-type fatty acid binding protein (L-FABP) binds with high affinity to hydrophobic molecules including free fatty acid, bile acid and bilirubin, which are potentially nephrotoxic, and is involved in their metabolism mainly in hepatocytes. L-FABP is released into the circulation, and patients with liver damage have an elevated plasma L-FABP level. L-FABP is also present in renal tubules; however, the precise localization of L-FABP and its potential role in the renal tubules are not known. In this study, we examined the cellular and subcellular localization of L-FABP in the rat kidney and tried to determine from where the L-FABP in kidney tissues had originated. Immunohistochemical studies of kidney sections localized L-FABP in the lysosomes of proximal tubule cells (PTC). In rats with carbon tetrachloride (CCl 4 )-induced acute liver injury, we detected high levels of L-FABP in the circulation and in the kidney compared with those in the control rat by immunoblotting, while reverse transcription-polymerase chain reaction showed that the level of L-FABP mRNA expression in the kidney of CCl 4 -treated rats was low and did not differ from that in the control rat. When 35 S-L-FABP was intravenously administered to rats, the kidneys took up 35 S-L-FABP more preferentially than the liver and heart, and histoautoradiography of kidney sections revealed that 35 S-L-FABP was internalized via the apical domains of PTC. Quartz-crystal microbalance analysis revealed that L-FABP bound to megalin, a multiligand endocytotic receptor on PTC, in a Ca 2 þ -dependent manner. Degradation assays using megalin-expressing rat yolk sac tumor-derived L2 cells demonstrated that megalin mediated the cellular uptake and catabolism of 125 I-L-FABP. In conclusion, circulatory L-FABP was found to be filtered by glomeruli and internalized by PTC probably via megalin-mediated endocytosis. These results suggest a novel renal uptake pathway for L-FABP, a carrier of hydrophobic molecules, some of which may exert nephrotoxic effects.

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Objective: To evaluate the development of speech perception and auditory skills after cochlear implantation in deaf children with asymptomatic congenital cytomegalovirus (CMV) infection diagnosed based on the presence of CMV DNA in the neonatal urine. Study Design: A prospective study of congenital CMV infection was done between 1996 and 2003. Of 18 children diagnosed with congenital CMV infection, 2 deaf children with asymptomatic CMV infections received cochlear implantation. Results: The 2 deaf children who received cochlear implantation had delayed-onset, progressive sensorineural hearing loss on follow-up audiometric examinations administered at 29 and 39 months of age. After cochlear implantation, their Infant-Toddler Meaningful Auditory Integration Scale scores increased consistently during 36 months of follow-up; these results were similar to those of 5 congenitally deaf children without CMV infection who had cochlear implantation. Conclusions: Cochlear implantation was effective for improving the development of speech perception and auditory skills in deaf children with asymptomatic congenital CMV infection. There was no significant difference in the development of useful auditory integration between our general pediatric cochlear implant population without CMV infection and those with asymptomatic CMV infection.

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