Cl−-dependent upregulation of human organic anion transporters: different effects on transport kinetics between hOAT1 and hOAT3

Chloride ion has a stimulatory effect on the transport of organic anions across renal basolateral membranes. However, the exact mechanisms at molecular levels have been unclear as of yet. Human organic anion transporters hOAT1 and hOAT3 play important roles in renal basolateral membranes. In this study, the effects of Cl− on the activities of these transporters were evaluated by using HEK293 cells stably expressing hOAT1 or hOAT3 (HEK-hOAT1 or HEK-hOAT3). The uptake of p-[14C]aminohippurate by HEK-hOAT1 and [3H]estrone sulfate by HEK-hOAT3 was greater in the presence of Cl− than in the presence of SO42− or gluconate. Additionally, the uptake of various compounds by HEK-hOAT1 and HEK-hOAT3 was significantly higher in the Cl−-containing medium than the gluconate-containing medium, suggesting that the influences of Cl− are not dependent on substrate and that Cl− directly stimulates the functions of hOAT1 and hOAT3. The substitution of gluconate with Cl− did not change the Km value for the uptake of p-[14C]aminohippurate by HEK-hOAT1 but caused an approximately threefold increase in the maximal uptake rate (Vmax) value. On the other hand, replacement of gluconate with Cl− decreased the Km value for the uptake of [3H]estrone sulfate and cefotiam by HEK-hOAT3 to about one-third, while it did not change the Vmax value. In summary, Cl− upregulates the activities of both hOAT1 and hOAT3, but its effects on transport kinetics differ between these transporters. It was suggested that Cl− participates in the trans-location process for hOAT1, and the substrate recognition process for hOAT3.

Pharmacokinetics of antibiotic prophylaxis in major orthopedic surgery and blood-saving techniques

The pharmacokinetics of cefuroxime, cefotiam, cefamandole, and ampicillin/sulbactam were randomly measured in 40 patients undergoing major orthopedic surgery associated with high blood and volume turnover and intraoperative blood salvage. Serum and bone concentrations and the pharmacokinetics occurring in the context of these procedures were measured. No changes in elimination half-life relative to a normal population occurred with cefuroxime, cefotiam, and ampicillin. Serum and tissue concentrations were slightly lower with cefamandole and sulbactam, but reapplication of the initial dose was required with all antibiotics 4 hours after the first application.

Autolysis of methicillin-resistant Staphylococcus aureus is involved in synergism between imipenem and cefotiam

Imipenem-induced autolysis and the activity of imipenem plus cefotiam were studied in 16 strains of methicillin-resistant Staphylococcus aureus (MRSA). The degree of imipenem-induced autolysis and the rate of synergistic action of imipenem plus cefotiam varied among strains and did not correlate with susceptibility to either imipenem or cefotiam. However, the degree of autolysis correlated well with susceptibility to the synergistic action of imipenem plus cefotiam. In methicillin-susceptible S. aureus strains, both imipenem-induced autolysis and the synergistic activity of the combined drugs were less than those observed in MRSA strains. Differences in the degree of autolysis were not due to differences in autolytic enzyme production. The autolysis of imipenem-pretreated MRSA was enhanced further by cefotiam, while treatment of cells in the reverse order did not enhance autolysis. These findings indicate that cell wall impairment in MRSA is caused by exposure to imipenem but not to cefotiam and that this difference in drug actions results in synergism between imipenem and cefotiam. The possible participation of penicillin-binding proteins PBP 2' and PBP4 in the observed effect is discussed.

Specificity of p-aminohippurate transport system in the OK kidney epithelial cell line

Substrate specificity of the p-aminohippurate (PAH) transport system was investigated in the OK kidney epithelial cells. PAH uptake by OK cells from the basal side was inhibited by beta-lactam antibiotics such as benzylpenicillin (PCG) and cefazolin. The inhibition of PAH uptake by PCG was competitive and the Ki value was calculated as 108.8 microM. Transcellular transport of PCG across OK cell monolayers occurred unidirectionally from the basal to apical side, and transcellular transport and basolateral uptake were inhibited by PAH, probenecid and beta-lactam antibiotics. The basolateral uptake of cefazolin and cefotiam was also inhibited by PAH and probenecid. The basolateral uptake of PAH and PCG were not affected by aliphatic dicarboxylates with 3 or 4 carbon atoms, but were strongly inhibited by those with 5 or 6 carbon atoms. The inhibitory effect became weaker for a longer dicarboxylate with 7 carbon atoms, then increased again with increasing number of carbon atoms. Such a pattern of inhibition by dicarboxylates is essentially the same with that observed in rat renal proximal tubules in situ. These findings suggest that the PAH transport system in OK cells has a substrate specificity similar to that in rat renal proximal tubules, which is involved in the active secretion of various organic anions including drugs.

Interaction of cefpirome and a cephalosporinase from Citrobacter freundii GN7391

The interaction of cefpirome and a cephalosporinase from Citrobacter freundii, including hydrolysis and inhibition, was studied in comparison with those of cefotiam, cefotaxime, and ceftazidime. Cefpirome was hydrolyzed by the enzyme more rapidly at Vmax than were cefotaxime and ceftazidime. However, the low affinity of the enzyme for cefpirome caused a reduction in the hydrolytic rate of cefpirome at a low drug concentration (0.1 microM). The high stability of cefpirome at a low concentration explains the high antimicrobial activity of the agent against cephalosporinase-producing bacteria.