Interaction of beta-lactam antibiotics with the mitochondrial carnitine/acylcarnitine transporter.
The interaction of beta-lactams with the purified mitochondrial carnitine/acylcarnitine transporter reconstituted in liposomes has been studied. Cefonicid, cefazolin, cephalothin, ampicillin, piperacillin externally added to the proteoliposomes, inhibited the carnitine/carnitine antiport catalysed by the reconstituted transporter. The most effective inhibitors were cefonicid and ampicillin with IC50 of 6.8 and 7.6mM, respectively. The other inhibitors exhibited IC50 values above 36 mM. Kinetic analysis performed with cefonicid and ampicillin revealed that the inhibition is completely competitive, i.e., the inhibitors interact with the substrate binding site. The Ki of the transporter is 4.9 mM for cefonicid and 9.9 mM for ampicillin. Cefonicid inhibited the transporter also on its internal side. The IC50 was 12.9 mM indicating that the inhibition was less pronounced than on the external side. Ampicillin and the other inhibitors were much less effective on the internal side. The beta-lactams were not transported by the carnitine/acylcarnitine transporter. Cephalosporins, and at much lower extent penicillins, caused irreversible inhibition of the transporter after prolonged time of incubation. The most effective among the tested antibiotics was cefonicid with IC50 of 0.12 mM after 60 h of incubation. The possible in vivo implications of the interaction of the beta-lactam antibiotics with the transporter are discussed.
Pochini
Lorena
L
Department of Cell Biology, University of Calabria, Via P.Bucci 4c, 87036 Arcavacata di Rende, Italy.
Galluccio
Michele
M
Scumaci
Domenica
D
Giangregorio
Nicola
N
Tonazzi
Annamaria
A
Palmieri
Ferdinando
F
Indiveri
Cesare
C
D000818:Animals; D000900:Anti-Bacterial Agents / Q000378:metabolism* / Q000494:pharmacology; D001667:Binding, Competitive / Q000187:drug effects; D002333:Carnitine Acyltransferases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D008930:Mitochondria, Liver / Q000201:enzymology*; D015394:Molecular Structure; D051381:Rats; D047090:beta-Lactams / Q000378:metabolism* / Q000494:pharmacology
D000900:Anti-Bacterial Agents; D047090:beta-Lactams; D002333:Carnitine Acyltransferases