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.

Oxidative and mitochondrial toxic effects of cephalosporin antibiotics in the kidney. A comparative study of cephaloridine and cephaloglycin.

Cephaloridine and cephaloglycin are the two most nephrotoxic cephalosporins released for human use. Cephaloridine has been shown to produce both oxidative and mitochondrial respiratory injury in renal cortex in patterns of dose (or concentration) and time that are consistent with pathogenicity. Cephaloglycin also produces respiratory toxicity, and recent studies have provided evidence that this injury results from an inactivation of mitochondrial anionic substrate transporters. The abilities of cephaloglycin to produce oxidative changes and cephaloridine to block mitochondrial substrate uptake have not been examined yet. We therefore compared these two cephalosporins with one another and with cephalexin, which is not nephrotoxic, in the production of the following: (1) several components of oxidative stress or damage [depletion of reduced glutathione (GSH) and production of oxidized glutathione (GSSG) in renal cortex, inhibition of glutathione reductase in vitro, and production of the lipid peroxidation products malondialdehyde (MDA) and conjugated dienes (CDs) in renal cortex]; and (2) renal cortical mitochondrial toxicity [to both respiration with, and the transport of, succinate]. Cephaloridine depleted GSH and elevated GSSG in renal cortex, inhibited glutathione reductase, and increased both MDA in whole cortex and CDs in cortical microsomes and mitochondria. While cephaloglycin depleted GSH at least as much as did cephaloridine, it produced one-fifth as much GSSG and had little or no effect on glutathione reductase activity or on cortical MDA or microsomal CDs; cephaloglycin caused a transient small increase of mitochondrial CDs. Cephalexin produced no oxidative changes except for a slight increase of mitochondrial CDs comparable to that produced by cephaloglycin. Both cephaloridine and cephaloglycin, but not cephalexin, decreased the unidirectional uptake of, and respiration with, succinate in cortical mitochondria. We conclude that cephaloridine and cephaloglycin are both toxic to mitochondrial substrate uptake and respiration, but differ significantly in their generation of products of oxidation.

Synthesis and antibacterial activities of new (alpha-hydrazinobenzyl)cephalosporins.

Some (alpha-hydrazinobenzyl)cephalosporins, I (R = Me, CH2OAc, Cl) and II (R = Me, CH2OAc), structurally related (formula; see text) to cephalexin, cephaloglycin, and cefaclor have been prepared and evaluated in vitro for their antimicrobial activity. The synthesis involves the condensation of the chloride hydrochloride III (R = H or Me) with the 7-aminocephem derivatives IV. The hydrazino compound I (R = Cl), an analogue of cefaclor, resulted in being the most active compound of the series.

Reactivity and binding of beta-lactam antibiotics in rabbit renal cortex.

In studies designed to evaluate the reactivity of the beta-lactam antibiotics in the rabbit kidney, the binding to cortical macromolecules of isotopically labeled cephaloglycin (highly toxic) was compared in vivo and in vitro with that of cephalothin (minimally toxic) and benzylpenicillin (nontoxic). Three hours after administration of equal doses, the amounts of firmly bound antibiotic in whole cortex and in nuclear, mitochondrial, microsomal and cytosolic fractions of cortex were greatest for cephaloglycin (cortical concentration 7% of that measured at 0.5 hr), intermediate for cephalothin (2%) and least for benzylpenicillin (1%); the amounts of firmly bound antibiotic were unrelated to the earlier, peak cortical concentrations. Binding to cortical microsomes in vitro showed a similar pattern (greatest for cephaloglycin, least for benzylpenicillin); in addition, the binding in vitro of cephaloglycin was decreased by the addition of an NADPH-generating system and was not decreased by piperonyl butoxide. These studies provide evidence that the spontaneous reactivity of the beta-lactam ring may be an important determinant of the nephrotoxicity of the cephalosporins and fail to support the existence of a role of the cytochrome P-450 mixed-function oxidases in this reactivity.

Pathogenesis of nephrotoxicity of cephalosporins and aminoglycosides: a review of current concepts.

Third-generation cephalosporins promise to replace combinations containing aminoglycosides as safer, broad-spectrum antibiotic therapy. First, however, the possibility of nephrotoxicity as demonstrated with cephaloridine, must be excluded. For this reason, we must understand more about how cephalosporins and aminoglycosides damage the kidneys. Aminoglycosides accumulate in the renal lysosomes and may interfere with Na+-, K+-dependent adenosine triphosphatase activity. Experiments with cephaloridine and cephaloglycin, two nephrotoxic cephalosporins, indicate that they cause mitochondrial injury that leads to impaired cellular respiration. Results of experiments on the effects of treatments that combine cephalosporin with aminoglycosides or other drugs are confusing because inappropriate experimental models were used. Use of insensitive animals, administration of diuretics without prior induction of tubule damage, and insufficient dosages of drugs all cloud the interpretation of results. The standards for animal studies of cephalosporin nephrotoxicity should be revised to make them more relevant to humans.

Effects of ureteral obstruction on the toxicity of cephalosporins in the rabbit kidney.

The nephrotoxicity of the cephalosporin antibiotics is closely related to their secretory transport into the proximal tubular cell at the antiluminal (blood) site. The present report describes the effects of transient ureteral obstruction, which increases intracellular concentrations of secreted organic anions, on the cortical uptake and the proximal tubular toxicity of several cephalosporins given in mildly toxic doses. Unilateral obstruction for 1-2 hr increased the cytotoxicity of cephaloglycin and cefaclor, both of which are rapidly secreted across the tubular cell, but not of cephaloridine, which undergoes minimal secretion. Bilateral obstruction significantly increased the toxicity of cefaclor, which is rapidly secreted, but not of cefazolin, which is slowly secreted. Finally, there was a further augmentation of the effects of obstruction on the toxicity of cefaclor by a minimally toxic pretreatment regimen of neomycin. Studies of cortical antibiotic concentrations support the conclusion that the effects on toxicity are largely the result of the increased intracellular accumulation that results from obstruction.

Prevention of cephalosporin nephrotoxicity by other cephalosporins and by penicillins without significant inhibition of renal cortical uptake.

Prevention of cephalosporin nephrotoxicity in animal models by probenecid or p-aminohippurate requires treatment regimen that produce sustained inhibition of cortical accumulation of the toxic antibiotic. In contrast, cephaloridine nephrotoxicity in the rabbit can be prevented by a limited single dose of cephalothin. In the present report further studies were done in which it was demonstrated that cephaloridine nephrotoxicity can be prevented by doses of other cephalosporins or penicillins that produce little or no reduction of the cortical concentrations of toxic cephalosporin. More limited studies revealed similar protection by benzylpenicillin against cephaloglycin, also without reduction of cortical concentration. Finally, similar limited-dose administration of penicillin eliminated tha additive toxicity of cefazolin and neomycin. This selective protection against the toxic cephalosporins by the less toxic or nontoxic cephalosporins and by the penicillins, without inhibition of overall cortical accumulation of the toxic antibiotic, may provide a subcellular probe for the study of the molecular basis of cephalosporin nephrotoxicity.

Cephalosporin nephrotoxicity. Transport, cytotoxicity and mitochondrial toxicity of cephaloglycin.

The cephalosporin antibiotics are secreted by the renal organic anion transport system. Several of them, including cephaloridine and caphaloglycin, produce a proximal renal tubular necrosis which can be prevented by inhibitors of organic anion transport. Although cephaloridine is actively transported into the tubular cell at the antiluminal side like other cephalosporins, it undergoes a limited rate of subsequent movement across the luminal membrane into the tubular fluid. The very high intracellular concentrations that result from this unusual process are believed to contribute to the significant toxicity of cephaloridine. Cephaloglycin is at least as toxic, but is secreted more normally across the proximal tubular cell. For this reason, studies were undertaken to evaluate the cytotoxicity, cortical concentrations and mitochondrial respiratory toxicity of this cephalosporin in the rabbit kidney. A dose of 100 mg/kg of caphaloglycin produces as much damage as does 150 mg/kg of cephaloridine. The steady-state cortex-to-serum concentration ratio of cephaloglycin, 5.6 +/- 0.8 S.E. (n = 5), is significantly lower (P < .001) than the corresponding measurement for cephaloridine, 121.9 +/- 1.2 (n = 7), and is not significantly different from that of p-aminohippurate. In further contrast to cephaloridine, the cortical concentration of cephaloglycin declines substantially, from 930 +/- 112 (n = 5) to 297 +/- 46 (n = 5) micrograms/g of wet tissue, over the first hour after cessation of infusion (P < .001) and is essentially unmeasurable by 2 hr. The fact that there is not the prolonged intracellular trapping of cephaloglycin that is seen with cephaloridine leads to the conclusion that the former must either bind more strongly to its target receptor or produce a more irreversible insult than does the latter cephalosporin. Several lines of evidence are presented which support this hypothesis. The most important of these are that cephaloglycin is cumulatively nephrotoxic, whereas cephaloridine is not, and that the in vivo toxicity of cephaloglycin to cortical mitochondria, unlike that of cephaloridine, is not significantly diminished by the mitochondrial isolation process. This very early in vivo respiratory toxicity of cephaloglycin and the lack of significant similar toxicity of cephalexin provide new evidence that the effect on mitochondria may have a pathogenic role in cephalosporin nephrotoxicity.