Chieh-Yin Hsu

Thienamycin nephrotoxicity: Mitochondrial injury and oxidative effects of imipenem in the rabbit kidney

The nephrotoxic cephalosoprins cephaloridine and cephaloglycin both produce mitochondrial respiratory toxicity in renal cortex. Recent work has provided evidence that this respiratory toxicity is caused by acylation and inactivation of mitochondrial anionic substrate transporters. While cephaloridine also causes significant lipid peroxidative injury in cortical mitochondria and microsomes, cephaloglycin causes little or no oxidative damage under identical conditions. The recently released thienamycin antibiotic, imipenem, like the toxic cephalosporins, produces acute proximal tubular necrosis which can be prevented completely by prior administration of probenecid. The ability of imipenem to block mitochondrial substrate uptake and respiration and produce oxidative changes has not been examined. We therefore evaluated the effects of imipenem in rabbit renal cortex on the following: (1) mitochondrial function [respiration with and uptake of succinate, and uptake of ADP]; and (2) evidence of oxidative change [depletion of reduced glutathione (GSH), production of oxidized glutathione (GSSG), and production of lipid peroxidative injury, as reflected in microsomal conjugated dienes (CDs)]. The mitochondrial effects of 300 mg/kg body wt of imipenem, given i.v. 1 and 2 hr before killing the animals, were comparable to those of the nephrotoxic cephalosporins. There was significant reduction of respiration with, and unidirectional uptake of, succinate at both times, while mitochondrial ADP transport was comparatively unaffected. Imipenem also depleted GSH and increased GSSG and CDs at 1 hr. These effects, however, were considerably smaller than those of a comparably nephrotoxic dose of cephaloridine, and this evidence of oxidative stress had resolved by 2 hr. We conclude that imipenem and the nephrotoxic cephalosporins have similar effects on mitochondrial substrate uptake and respiration, but differ significantly in their production of oxidative injury.

Cephalosporin and carbacephem nephrotoxicity: Roles of tubular cell uptake and acylating potential

Three beta-lactams, desacetylcephaloglycin, ampicillin, and loracarbef, were studied to test a hypothesis derived from retrospective analysis of previously studied cephalosporins: that beta-lactam nephrotoxicity develops in approximate proportion to tubular cell antibiotic concentrations and lactam ring reactivities. Concentrations of each beta-lactam (and insulin) in rabbit renal cortex and serum were measured at the end of 0.5-hr infusions of 100 mg antibiotic/kg body weight and 0.5 to 0.67 hr later. Total cortical AUCs (total areas under the curve of concentration and time in renal cortex) and transported cortical AUCs (total minus insulin-space beta lactam) were calculated from these measurements. Reactivities, determined by the rate constants of lactam-ring opening at pH 10, were taken from the literature. Nephrotoxicity was quantified by grades of proximal tubular cell necrosis and by serum creatinine concentrations 2 days after infusion of 100-1500 mg/kg of the antibiotics. Desacetylcephaloglycin was slightly less nephrotoxic than cephaloglycin; the AUCs reactivities, and toxicities of these two cephalosporins fit the proposed model, particularly when allowance is made for hepatic and renal deacetylation of cephaloglycin. The very low AUCs, limited reactivity, and absence of nephrotoxicity of ampicillin also fit the model. Loracarbef had a transported AUC less than three times, and reactivity one-thirtieth, those of cefaclor, respectively. Although only at 1500 mg/kg, loracarbef was significantly more nephrotic than cefaclor. If the relativity of loracarbef with its targeted bacterial proteins, which is essentially the same as that of cefaclor, is considered instead of the base hydrolysis rate constant, than loracarbef also fits the model. By the same analysis, the comparatively high in vitro stability of other carbacephems, although pharmaceutically convenient, may not limit their nephrotoxicity.

Toxicity of cephalosporins to fatty acid metabolism in rabbit renal cortical mitochondria

UNLABELLED Cephaloglycin (Cgl) and cephaloridine (Cld) are acutely toxic to the proximal renal tubule, in part because of their cellular uptake by a contraluminal anionic secretory carrier and in part through their intracellular attack on the mitochondrial transport and oxidation of tricarboxylic acid (TCA) cycle anionic substrates. Preliminary studies with Cgl have provided evidence of a role of fatty acid (FA) metabolism in its nephrotoxicity, and work with Cld has shown it to be a potent inhibitor of renal tubular cell and mitochondrial carnitine (Carn) transport. Studies were therefore done to examine the effects of Cgl and Cld on the mitochondrial metabolism of butyrate, the anion of a short-chain FA that does not require the Carn shuttle to enter the inner matrix, and the effects of Cgl on the metabolism of palmitoylcarnitine (PCarn), the Carn conjugate of a long-chain FA that does enter the mitochondrion by the Carn shuttle. The following was found: (1) Cgl reduced the oxidation and uptake of butyrate after in vitro (2000 micrograms/mL, immediate effect) and after in vivo (300 mg/kg body weight, 1 hr before killing) exposure; (2) Cld caused milder in vitro toxicity, and no significant in vivo toxicity, to mitochondrial butyrate metabolism; (3) like Cld, Cgl reduced PCarn-mediated respiration after in vivo exposure, but, unlike Cld, it did not inhibit respiration with PCarn in vitro; (4) the Carn carrier was stimulated slightly by in vitro Cgl but was unaffected by in vivo Cgl; (5) in vivo Cgl had no effect on mitochondrial free Carn or long-chain acylCarn concentrations in the in situ kidney; (6) Cgl increased the excretion of Carn minimally compared with the effect of Cld; and (7) cephalexin, a nontoxic cephalosporin, caused mild reductions of respiration with butyrate and PCarn during in vitro exposure, but stimulated respiration with both substrates after in vivo exposure. CONCLUSIONS Cgl has essentially the same patterns of in vitro and in vivo toxicity against mitochondrial butyrate uptake and oxidation that both Cgl and Cld have against TCA-cycle substrates. Cld has little or no in vivo toxicity to mitochondrial butyrate metabolism, whereas in vivo Cgl is as toxic as Cld to respiration with PCarn. The greater overall in vivo toxicity of Cgl to mitochondrial FA metabolism, with lower cortical concentrations and AUCs than those of Cld, supports earlier evidence that Cld is less toxic than Cgl at the molecular level.

Effects of anti-lipid A human monoclonal antibody on lipopolysaccharide-induced toxicity to the kidney.

Studies were done to evaluate the effects of the human monoclonal anti-lipid A IgM antibody A6(H4C5) on several components of the hemodynamic and renal toxicity of the cell wall lipopolysaccharide of E. coli 0111:B4. Antibody (0.25 to four mg./kg. BW) was administered 0.5 hour before, or premixed for one hour with, lipopolysaccharide (0.05 mg./kg., a 14 to 18% lethal dose), and the following measurements made over 0.5 to 3.5 hours of study: systemic arterial blood pressure, renal plasma flow, and glomerular filtration. The proximal tubular cell cytotoxicity of 90 mg./kg. of the cephalosporin cephaloridine was also quantified in similarly treated animals sacrificed 48 hours later. While one mg./kg. of antibody prevented the reduction by the lipopolysaccharide of renal plasma flow, it did not prevent the nephrotoxic synergy with cephaloridine, and four times the antibody dose did not prevent lipopolysaccharide-induced hypotension or reduced glomerular filtration. These amounts of this antibody protect leukopenic rabbits against the lethality of the slow onset bacteremic model of Pseudomonas conjunctivitis. It is suggested that the incompleteness of protection in this study may be the result of the sensitivity of the assay methods used and/or the acute endotoxemia produced in these animals.

Prevention of nephrotoxicity of beta-lactam antibiotics

The beta-lactam antibiotics in current use include the penicillins, the cephalosporins, and the penems. With one exception, the penicillins have no direct renal toxicity. Although the same was expected from other betalactams, at least two cephalosporins and the first penem, N-formimidoylthienamycin (or imipenem), are highly nephrotoxic, and several other cephalosporins are mildly-to-moderately toxic to the kidney.