Evidence that epithelial glycoprotein 330/megalin mediates uptake of polybasic drugs.

Abstract

Glycoprotein 330 (gp330) is an endocytic receptor expressed in the renal proximal tubules and some other absorptive epithelia, e.g., in the inner ear. The present study shows that the antifibrinolytic polypeptide, aprotinin, and the nephroand ototoxic antibiotics, aminoglycosides, and polymyxin B compete for binding of '"I-urokinase-plasminogen activator inhibitor type-i complexes to purified rabbit gp330. Half maximal inhibition was measured at 4 ,uM for aprotinin, 50 tiM for gentamicin, and 0.5 tiM for polymyxin B. Drug binding to gp330 was validated by equilibrium dialysis of [3H]gentamicin-gp330 incubations and binding/uptake studies in rat proximal tubules and gp330-expressing L2 carcinoma cells. Analyses of mutant aprotinins expressed in Saccharomyces cerevisiae revealed that basic residues are essential for the binding to gp330 and renal uptake. The polybasic drugs also antagonized ligand binding to the human a2-macroglobulin receptor. However, the rapid glomerular filtration of the drugs suggests kidney gp330 to be the quantitatively most important target.In conclusion, a novel role of gp330 as a drug receptor is demonstrated. The new insight into the mechanism of epithelial uptake of polybasic drugs might provide a basis for future design of drugs with reduced toxicity. (J. Clin.

Influence on Mitochondria and Cytotoxicity of Different Antibiotics Administered in High Concentrations on Primary Human Osteoblasts and Cell Lines

“…Some of our observed cytotoxic and cytostatic effects of clindamycin, macrolides, fluoroquinolones, linezolid, chloramphenicol, rifampin, and tetracycline on PHO can be explained by an impairment of mitochondrial energetics, whereas the inhibitors of the bacterial cell wall syntheses (with the exception of cefazolin with an unknown eukaryotic target [16]) and aminoglycosides displayed no effect on PHO because of ab- sence of a specific target or because they could not enter the cells in the absence of a specific receptor (34,43). In contrast, chloramphenicol and linezolid increased the lactate production comparable to the specific inhibitors of the respiratory chain presumably by inhibition of mitochondrial protein synthesis, which was actually shown in vitro for chloramphenicol (30,39).…”

Identification of genes involved in gentamicin-induced nephrotoxicity in rats – A toxicogenomic investigation

“…This is of interest as gentamicin is transported retrograde through the secretory pathway to the Golgi complex and to the endoplasmatic reticulum (Sandoval and Molitoris, 2003). Deregulation of the megalin receptor which is described to play an important role in receptor mediated endocytosis of gentamicin (Sandoval et al, 2004;Moestrup et al, 1995) were not represented on the RG_U34A Gene Chip and could not be analyzed.…”

“…Its tissue specific toxicity is considered to be caused by a selective accumulation of this drug in the tubular epithelial cells in renal cortex, where its concentration is several times higher than in the plasma (Nagai et al, 2004;Goodman et al, 2001;Mingeot-Leclerq and Tulkens, 1999). On the cellular level an intense binding of the drug to the brush border of the proximal tubule could be demonstrated (Moestrup et al, 1995). After binding, gentamicin is taken into the cell by endocytosis where it inhibits the activities of lysosomal phospholipases and sphingomyelinase (Laurent et al, 1982).…”

Intracellular pharmacodynamics of antibiotics

“…Cells displaying surface binding sites, such as kidney proximal tubular cells in vivo, however, accumulate aminoglycosides quite fast and extensively [50,51]. These sites have been identified as megalin (a protein binding polybasic compounds; [52][53][54]) on the one hand, and acidic phospholipids on the other hand [55].…”