Preventive effect of betamipron on nephrotoxicity and uptake of carbapenems in rabbit renal cortex

A Multiwell-Based Assay for Screening Thyroid Hormone Signaling Disruptors Using thibz Expression as a Sensitive Endpoint in Xenopus laevis

There is a need for rapidly screening thyroid hormone (TH) signaling disruptors in vivo considering the essential role of TH signaling in vertebrates. We aimed to establish a rapid in vivo screening assay using Xenopus laevis based on the T3-induced Xenopus metamorphosis assay we established previously, as well as the Xenopus Eleutheroembryonic Thyroid Assay (XETA). Stage 48 tadpoles were treated with a series of concentrations of T3 in 6-well plates for 24 h and the expression of six TH-response genes was analyzed for choosing a proper T3 concentration. Next, bisphenol A (BPA) and tetrabromobisphenol A (TBBPA), two known TH signaling disruptors, were tested for determining the most sensitive TH-response gene, followed by the detection of several suspected TH signaling disruptors. We determined 1 nM as the induction concentration of T3 and thibz expression as the sensitive endpoint for detecting TH signaling disruptors given its highest response to T3, BPA, and TBBPA. And we identified betamipron as a TH signaling agonist, and 2,2′,4,4′-tetrabromodiphenyl ether (BDE-47) as a TH signaling antagonist. Overall, we developed a multiwell-based assay for rapidly screening TH signaling disruptors using thibz expression as a sensitive endpoint in X. laevis.

Cilastatin protects against imipenem-induced nephrotoxicity via inhibition of renal organic anion transporters (OATs)

Imipenem is a carbapenem antibiotic. However, Imipenem could not be marketed owing to its instability and nephrotoxicity until cilastatin, an inhibitor of renal dehydropeptidase-I (DHP-I), was developed. In present study, the potential roles of renal organic anion transporters (OATs) in alleviating the nephrotoxicity of imipenem by cilastatin were investigated in vitro and in rabbits. Our results indicated that imipenem and cilastatin were substrates of hOAT1 and hOAT3. Cilastatin inhibited hOAT1/3-mediated transport of imipenem with IC₅₀ values comparable to the clinical concentration, suggesting the potential to cause a clinical drug–drug interaction (DDI). Moreover, imipenem exhibited hOAT1/3-dependent cytotoxicity, which was alleviated by cilastatin and probenecid. Furthermore, cilastatin and probenecid ameliorated imipenem-induced rabbit acute kidney injury, and reduced the renal secretion of imipenem. Cilastatin and probenecid inhibited intracellular accumulation of imipenem and sequentially decreased the nephrocyte toxicity in rabbit primary proximal tubule cells. Renal OATs, besides DHP-I, was also the target of interaction between imipenem and cilastatin, and contributed to the nephrotoxicity of imipenem. This therefore gives in part the explanation about the mechanism by which cilastatin protected against imipenem-induced nephrotoxicity. Thus, OATs can potentially be used as a therapeutic target to avoid the renal adverse reaction of imipenem in clinic.

Limited Chemical Structural Diversity Found to Modulate Thyroid Hormone Receptor in the Tox21 Chemical Library

BACKGROUND

Thyroid hormone receptors (TRs) are critical endocrine receptors that regulate a multitude of processes in adult and developing organisms, and thyroid hormone disruption is of high concern for neurodevelopmental and reproductive toxicities in particular. To date, only a small number of chemical classes have been identified as possible TR modulators, and the receptors appear highly selective with respect to the ligand structural diversity. Thus, the question of whether TRs are an important screening target for protection of human and wildlife health remains.

OBJECTIVE

Our goal was to evaluate the hypothesis that there is limited structural diversity among environmentally relevant chemicals capable of modulating TR activity via the collaborative interagency Tox21 project.

METHODS

We screened the Tox21 chemical library (8,305 unique structures) in a quantitative high-throughput, cell-based reporter gene assay for TR agonist or antagonist activity. Active compounds were further characterized using additional orthogonal assays, including mammalian one-hybrid assays, coactivator recruitment assays, and a high-throughput, fluorescent imaging, nuclear receptor translocation assay.

RESULTS

Known agonist reference chemicals were readily identified in the TR transactivation assay, but only a single novel, direct agonist was found, the pharmaceutical betamipron. Indirect activation of TR through activation of its heterodimer partner, the retinoid-X-receptor (RXR), was also readily detected by confirmation in an RXR agonist assay. Identifying antagonists with high confidence was a challenge with the presence of significant confounding cytotoxicity and other, non-TR-specific mechanisms common to the transactivation assays. Only three pharmaceuticals-mefenamic acid, diclazuril, and risarestat-were confirmed as antagonists.

DISCUSSION

The results support limited structural diversity for direct ligand effects on TR and imply that other potential target sites in the thyroid hormone axis should be a greater priority for bioactivity screening for thyroid axis disruptors. https://doi.org/10.1289/EHP5314.

Flavonoids are inhibitors of human organic anion transporter 1 (OAT1)-mediated transport

Organic anion transporter 1 (OAT1) has been reported to be involved in the nephrotoxicity of many anionic xenobiotics. As current clinically used OAT1 inhibitors are often associated with safety issues, identifying potent OAT1 inhibitors with little toxicity is of great value in reducing OAT1-mediated drug nephrotoxicity. Flavonoids are a class of polyphenolic compounds with exceptional safety records. Our objective was to evaluate the effects of 18 naturally occurring flavonoids, and some of their glycosides, on the uptake of para-aminohippuric acid (PAH) in both OAT1-expressing and OAT1-negative LLC-PK1 cells. Most flavonoid aglycones produced substantial decreases in PAH uptake in OAT1-expressing cells. Among the flavonoids screened, fisetin, luteolin, morin, and quercetin exhibited the strongest effect and produced complete inhibition of OAT1-mediated PAH uptake at a concentration of 50 μM. Further concentration-dependent studies revealed that both morin and luteolin are potent OAT1 inhibitors, with IC50 values of <0.3 and 0.47 μM, respectively. In contrast to the tested flavonoid aglycones, all flavonoid glycosides had negligible or small effects on OAT1. In addition, the role of OAT1 in the uptake of fisetin, luteolin, morin, and quercetin was investigated and fisetin was found to be a substrate of OAT1. Taken together, our results indicate that flavonoids are a novel class of OAT1 modulators. Considering the high consumption of flavonoids in the diet and in herbal products, OAT1-mediated flavonoid-drug interactions may be clinically relevant. Further investigation is warranted to evaluate the nephroprotective role of flavonoids in relation to drug-induced nephrotoxicity mediated by the OAT1 pathway.

Novel carbapenem antibiotics for parenteral and oral applications: in vitro and in vivo activities of 2-aryl carbapenems and their pharmacokinetics in laboratory animals

SM-295291 and SM-369926 are new parenteral 2-aryl carbapenems with strong activity against major causative pathogens of community-acquired infections such as methicillin-susceptible Staphylococcus aureus, Streptococcus pneumoniae (including penicillin-resistant strains), Streptococcus pyogenes, Enterococcus faecalis, Klebsiella pneumoniae, Moraxella catarrhalis, Haemophilus influenzae (including β-lactamase-negative ampicillin-resistant strains), and Neisseria gonorrhoeae (including ciprofloxacin-resistant strains), with MIC(90)s of ≤ 1 μg/ml. Unlike tebipenem (MIC(50), 8 μg/ml), SM-295291 and SM-369926 had no activity against hospital pathogens such as Pseudomonas aeruginosa (MIC(50), ≥ 128 μg/ml). The bactericidal activities of SM-295291 and SM-369926 against penicillin-resistant S. pneumoniae and β-lactamase-negative ampicillin-resistant H. influenzae were equal or superior to that of tebipenem and greater than that of cefditoren. The therapeutic efficacies of intravenous administrations of SM-295291 and SM-369926 against experimentally induced infections in mice caused by penicillin-resistant S. pneumoniae and β-lactamase-negative ampicillin-resistant H. influenzae were equal or superior to that of tebipenem and greater than that of cefditoren, respectively, reflecting their in vitro activities. SM-295291 and SM-369926 showed intravenous pharmacokinetics similar to those of meropenem in terms of half-life in monkeys (0.4 h) and were stable against human dehydropeptidase I. SM-368589 and SM-375769, which are medoxomil esters of SM-295291 and SM-369926, respectively, showed good oral bioavailability in rats, dogs, and monkeys (4.2 to 62.3%). Thus, 2-aryl carbapenems are promising candidates that show an ideal broad spectrum for the treatment of community-acquired infections, including infections caused by penicillin-resistant S. pneumoniae and β-lactamase-negative ampicillin-resistant H. influenzae, have low selective pressure on antipseudomonal carbapenem-resistant nosocomial pathogens, and allow parenteral, oral, and switch therapies.

Assessment of the role of renal organic anion transporters in drug-induced nephrotoxicity

In the present review we have attempted to assess the involvement of the organic anion transporters OAT1, OAT2, OAT3, and OAT4, belonging to the SLC22 family of polyspecific carriers, in drug-induced renal damage in humans. We have focused on drugs with widely recognized nephrotoxic potential, which have previously been reported to interact with OAT family members, and whose underlying pathogenic mechanism suggests the participation of tubular transport. Thus, only compounds generally believed to cause kidney injury either by means of direct tubular toxicity or crystal nephropathy have been considered. For each drug, or class of agents, the evidence for actual transport mediated by individual OATs under in vivo conditions is discussed. We have then examined their role in the context of other carriers present in the renal proximal tubule sharing certain substrates with OATs, as these are critical determinants of the overall contribution of OAT-dependent transport to intracellular accumulation and transepithelial drug secretion, and thus the impact it may have in drug-induced nephrotoxicity.

Protective effect of morin on the imipenem-induced nephrotoxicity in rabbits

The present study investigated the protective effect of morin, a natural flavonoid, on the imipenem-induced nephrotoxicity in rabbits. Nephrotoxicity of imipenem was examined after the intravenous administrations of imipenem (200 mg/kg) to rabbits in the presence and the absence of morin (12, 25, 50 mg/kg, p.o.). Cytotoxicity of imipenem was also examined in the presence and the absence of morin (100 microM) by using MDCK cells overexpressing human organic anion transporter 1 and 3 (MDCK/hOAT1 or MDCK/hOAT3). Intravenous dosing of imipenem alone induced severe proximal tubular necrosis in rabbits, however, the concurrent use of morin (25 or 50 mg/kg, p.o.) significantly suppressed the histopathological damage in the kidney induced by imipenem. While imipenem was not cytotoxic in MDCK/hOAT1 cells over the tested concentrations up to 10 mM, it showed significant cellular toxicity with CC(50) of 0.77 mM in MDCK/hOAT3 cells, implying that OAT3 may involve more actively in the imipenem-induced nephrotoxicity. In addition, the cellular toxicity of imipenem decreased by approximately 20 folds in the presence of morin in MDCK/hOAT3 cells. In conclusion, the present study suggests that morin might be beneficial to reduce the nephrotoxicity of imipenem, at least in part, via the inhibition of OAT3-mediated renal excretion of imipenem.

Population Pharmacokinetic Analysis of Panipenem/Betamipron in Patients with Various Degrees of Renal Function

BACKGROUND

Although plasma concentrations of panipenem were elevated and the risk of adverse events would increase in patients with renal impairment, a precise dosage regimen for patients with renal impairment has not been established.

METHODS

Population pharmacokinetic analyses were performed with plasma concentrations from 26 healthy volunteers and 41 patients. Optimal dosage regimens for patients with renal impairment were determined based on the bacteriostatic index of C(20%T)>(MIC), the concentration corresponding to the time above MIC of 20% of the dosing interval.

RESULTS

The clearance of panipenem and betamipron was correlated with creatinine clearance and the volume of the distribution of panipenem was correlated with body weight. C(20%T)>(MIC) for a standard dosage regimen of panipenem was 4.3 microg/ml, and the optimal dosage regimen for the patients was established based on this value.

CONCLUSION

The dosage regimen of panipenem for patients with renal impairment should be reduced when creatinine clearance is lower than 60 ml/min.

Pharmacokinetic study of pleural fluid penetration of carbapenem antibiotic agents in chemical pleurisy

STUDY OBJECTIVES

We investigated pleural fluid penetration of carbapenem antibiotic agents [imipenem (IPM), panipenem (PAPM), meropenem (MEPM), and biapenem (BIPM)] using an experimental rabbit pleuritis model to clarify the usefulness of the carbapenem agents for the treatment of bacterial pleurisy or pyothorax.

MEASUREMENTS AND RESULTS

Serum and pleural fluid specimens were serially collected at 5, 10, 15, 30, 60, 90, 120, 180, 240, 300, and 360 min after antibiotic administration for measurement of antibiotic levels. We investigated each agent alone as well as drug solutions containing each agent and a dehydropeptidase-I-specific inhibitor, cilastatin (CS), to remove the influence of dehydropeptidase-I-related hydrolysis. Groups of animals (n=3) received each carbapenem agent with or without CS. Serum and pleural fluid antibiotic levels were measured by high-performance liquid chromatography (HPLC). Because Cmax is not useful for evaluating the antimicrobial effects of carbapenem antibiotic agents due to their dose-dependent antimicrobial activity, we also investigated the AUC, which is correlated with the total drug levels in vivo. Among the drug solutions containing CS, MEPM/CS had the highest pleural fluid AUC0-360 (1594.8+/-510.3 microg min/ml), and the highest pleural fluid AUC0-360/plasma AUC0-360 ratio (0.79+/-0.04). BIPM/CS had the highest plasma AUC0-360 (3040.1+/-1525.9 microg min/ml). In pleural fluid AUC0-360/plasma AUC0-360 ratio MEPM/CS was significantly higher than those for the remaining agents. In pleural fluid AUC0-360 and plasma AUC0-360 there were no significant differences among these mixed solutions.

CONCLUSIONS

MEPM had the most favorable pleural fluid penetration. Pleural fluid penetration should be examined in infection models and in clinical trials.

Antibacterial Dosing in Intensive Care

Treatment of sepsis remains a significant challenge with persisting high mortality and morbidity. Early and appropriate antibacterial therapy remains an important intervention for such patients. To optimise antibacterial therapy, the clinician must possess knowledge of the pharmacokinetic and pharmacodynamic properties of commonly used antibacterials and how these parameters may be affected by the constellation of pathophysiological changes occurring during sepsis. Sepsis, and the treatment thereof, increases renal preload and, via capillary permeability, leads to 'third-spacing', both resulting in higher antibacterial clearances. Alternatively, sepsis can induce multiple organ dysfunction, including renal and/or hepatic dysfunction, causing a decrease in antibacterial clearance. Aminoglycosides are concentration-dependent antibacterials and they display an increased volume of distribution (V(d)) in sepsis, resulting in decreased peak serum concentrations. Reduced clearance from renal dysfunction would increase the likelihood of toxicity. Individualised dosing using extended interval dosing, which maximises the peak serum drug concentration (C(max))/minimum inhibitory concentration ratio is recommended. Beta-lactams and carbapenems are time-dependent antibacterials. An increase in V(d) and renal clearance will require increased dosing or administration by continuous infusion. If renal impairment occurs a corresponding dose reduction may be required. Vancomycin displays predominantly time-dependent pharmacodynamic properties and probably requires higher than conventionally recommended doses because of an increased V(d) and clearance during sepsis without organ dysfunction. However, optimal dosing regimens remain unresolved. The poor penetration of vancomycin into solid organs may require alternative therapies when sepsis involves solid organs (e.g. lung). Ciprofloxacin displays largely concentration-dependent kill characteristics, but also exerts some time-dependent effects. The V(d) of ciprofloxacin is not altered with fluid shifts or over time, and thus no alterations of standard doses are required unless renal dysfunction occurs. In order to optimise antibacterial regimens in patients with sepsis, the pathophysiological effects of systemic inflammatory response syndrome need consideration, in conjunction with knowledge of the different kill characteristics of the various antibacterial classes. In conclusion, certain antibacterials can have a very high V(d), therefore leading to a low C(max) and if a high peak is needed, then this would lead to underdosing. The V(d) of certain antibacterials, namely aminoglycosides and vancomycin, changes over time, which means dosing may need to be altered over time. Some patients with serum creatinine values within the normal range can have very high drug clearances, thereby producing low serum drug levels and again leading to underdosing.

A Beneficial Interaction between Imipenem and Piperacillin Possibly through Their Renal Excretory Process

In order to assess the beneficial mechanism of the concomitant use of imipenem (IPM) with piperacillin (PIPC) for the treatment of serious infectious diseases such as sepsis, the effects of PIPC on the uptake of IPM by rat renal cortical slices and on the plasma concentrations of IPM after intravenous infusion to rabbits were studied. The uptake of IPM by the rat renal cortical slices was significantly inhibited by p-aminohippurate, probenecid and PIPC whereas the uptake of PIPC by the slices was slightly decreased in the presence of IPM. When IPM was administered together with PIPC by 1-h infusion, the plasma concentrations of IPM were significantly increased during the infusion. These results imply that PIPC possibly interferes with the renal transport of IPM mediated by an organic anion transporter across the renal basolateral membranes, which leads to a longer period above the minimum inhibitory concentrations of IPM.

Organic anion transporter (Slc22a) family members as mediators of toxicity

Exposure of the body to toxic organic anions is unavoidable and occurs from both intentional and unintentional sources. Many hormones, neurotransmitters, and waste products of cellular metabolism, or their metabolites, are organic anions. The same is true for a wide variety of medications, herbicides, pesticides, plant and animal toxins, and industrial chemicals and solvents. Rapid and efficient elimination of these substances is often the body's best defense for limiting both systemic exposure and the duration of their pharmacological or toxicological effects. For organic anions, active transepithelial transport across the renal proximal tubule followed by elimination via the urine is a major pathway in this detoxification process. Accordingly, a large number of organic anion transport proteins belonging to several different gene families have been identified and found to be expressed in the proximal nephron. The function of these transporters, in combination with the high volume of renal blood flow, predisposes the kidney to increased toxic susceptibility. Understanding how the kidney mediates the transport of organic anions is integral to achieving desired therapeutic outcomes in response to drug interactions and chemical exposures, to understanding the progression of some disease states, and to predicting the influence of genetic variation upon these processes. This review will focus on the organic anion transporter (OAT) family and discuss the known members, their mechanisms of action, subcellular localization, and current evidence implicating their function as a determinant of the toxicity of certain endogenous and xenobiotic agents.

Pharmacokinetics of panipenem/betamipron in patients with end-stage renal disease

Panipenem/betamipron (Carbenin), a parenteral carbapenem antibiotic, is used for the treatment of severe and intractable bacterial infections caused by gram-positive and gram-negative bacteria. Because 30% of panipenem and most of the betamipron are excreted in the urine in an unchanged form, renal function is the important determinant of the dosage regimen of panipenem/betamipron. In this study, the pharmacokinetics of panipenem/betamipron were investigated in patients with end-stage renal disease (ESRD) undergoing hemodialysis treatment to establish an appropriate dose regimen. We further attempted to predict the in vivo clearance in patients undergoing hemodialysis based on the in vitro dializability. The pharmacokinetics of panipenem/betamipron were investigated in eight patients after a 1-h intravenous infusion of panipenem/betamipron (500 mg/500 mg). The in vitro extraction ratios of panipenem/betamipron through a high-flux dialyzer were obtained, and compared with those obtained in vivo. The clearances of panipenem in patients were 9.53 +/- 1.26 l/h with hemodialysis, and 2.92 +/- 0.238 l/h without hemodialysis. In contrast, those of betamipron were 4.18 +/- 0.643 l/h and 0.615 +/- 0.511 l/h, respectively. The clearance of panipenem with hemodialysis were predicted well from in vitro extraction ratios, while that of betamipron was overestimated about 1.4-fold, probably due to high plasma protein binding and the binding difference between patients and healthy subjects. After comparing the pharmacokinetic behavior of panipenem in patients with ESRD and that of a surrogate marker of efficacy, we recommend that these patients be treated with 500 mg/500 mg of panipenem/betamipron once daily, which gives a similar clinical result in a patient with normal renal function.

Quantitative Evaluation of Effect of Renal Failure on the Pharmacokinetics of Panipenem in Rats

The pharmacokinetics of panipenem in experimental renal failure animal models was investigated in order to identify the appropriate covariates affecting the pharmacokinetic behavior. Panipenem and betamipron were administered intravenously to rats with a variety of renal failures, such as nephritis induced by glycerol, gentamicin, uranium and antiserum against glomerular basement membrane as well as 5/6 subtotal nephrectomy. Panipenem in plasma and urine was determined and pharmacokinetic analysis was performed using a one-compartment open model. The elimination half-life prolonged and total body clearance, renal clearance (CL(R)) and renal excretion ratio were decreased according to the renal function, i.e. control>glycerol>anti-GBM=gentamicin>nephrectomy=uranium in order. However, distribution volume was consistent in all models. CL(R) showed strong positive correlation with the glomerular filtration rate in spite of a weak correlation with the reciprocal of blood urea nitrogen. However, no obvious correlation was observed with secretory clearance of N-1-methylnicotinamide. This preliminary information based on animal model might be useful for designing pharmacokinetic studies in special population at early stage of new drug development.

Interactions of Human- and Rat-Organic Anion Transporters With Pravastatin and Cimetidine

We have elucidated the interactions of human and rat organic anion transporters (hOATs and rOATs) with pravastatin and cimetidine. Pravastatin inhibited hOAT1/rOAT1, hOAT2/rOAT2, hOAT3/rOAT3, and hOAT4. The mode of inhibition was noncompetitive for hOAT1 and hOAT2, whereas it was competitive for hOAT3 and hOAT4. Cimetidine also inhibited hOAT1/rOAT1, hOAT3/rOAT3, and hOAT4. The mode of inhibition was a combination of competitive and noncompetitive manners for hOAT1, whereas it was competitive for hOAT3. The effects of OAT inhibitors on OAT1, OAT2, and OAT3 exhibited some but not so remarkable interspecies differences between humans and rats. In conclusion, we have characterized pravastatin and cimetidine as OAT inhibitors.

Panipenem/betamipron

Panipenem is a parenteral carbapenem antibacterial agent with a broad spectrum of in vitro activity covering a wide range of Gram-negative and Gram-positive aerobic and anaerobic bacteria, including Streptococcus pneumoniae and species producing beta-lactamases. Panipenem is coadministered with betamipron to inhibit panipenem uptake into the renal tubule and prevent nephrotoxicity. In large, randomised clinical trials, panipenem/betamipron demonstrated good clinical and bacteriological efficacy (similar to that of imipenem/cilastatin) in adults with respiratory tract or urinary tract infections. Panipenem/betamipron was also effective in adults with surgical or gynaecological infections, and in paediatric patients with respiratory tract and urinary tract infections in noncomparative trials. In small trials in elderly patients reported as abstracts, panipenem/betamipron demonstrated clinical efficacy similar to intravenous piperacillin and greater than oral ofloxacin in urinary tract infections. Elderly patients with respiratory tract infections also responded to therapy. Panipenem/betamipron is well tolerated with few adverse events reported in clinical trials, most commonly elevated serum levels of hepatic transaminases and eosinophils, rash and diarrhoea.

Interaction of human organic anion transporters 2 and 4 with organic anion transport inhibitors

The organic anion transport system is involved in the tubular excretion and reabsorption of various drugs and substances. The purpose of this study was to characterize the effects of various organic anion transport inhibitors on renal organic anion transport using proximal tubule cells stably expressing human organic anion transporter 2 (hOAT2) and hOAT4. Immunohistochemical analysis revealed that hOAT2 is localized to the basolateral side of the proximal tubule in the kidney. hOAT2 mediated a time- and concentration-dependent increase in prostaglandin F(2alpha) (PGF(2alpha)) uptake. The organic anion transport inhibitors used for this study were probenecid, 8-(noradamantan-3-yl)-1,3-dipropylxanthine (KW-3902), betamipron, and cilastatin. Probenecid, but not KW-3902, betamipron, and cilastatin, significantly inhibited hOAT2-mediated PGF(2alpha) uptake. In contrast, probenecid, KW-3902, and betamipron, but not cilastatin, inhibited hOAT4-mediated estrone sulfate (ES) uptake. Kinetic analyses revealed that these inhibitions were competitive. The K(i) value of probenecid for hOAT2 was 766 microM, whereas those of probenecid, KW-3902, and betamipron for hOAT4 were 54.9, 20.7, and 502 microM, respectively. These results suggest that probenecid, KW-3902, and betamipron could inhibit hOAT4-mediated ES uptake in vitro, whereas probenecid alone could inhibit the hOAT2-mediated PGF(2alpha) uptake. Comparing the K(i) values with the therapeutically relevant concentrations of unbound inhibitors in the plasma, probenecid alone was predicted to inhibit hOAT4-mediated organic anion transport in vivo.

Characterization of organic anion transport inhibitors using cells stably expressing human organic anion transporters

The organic anion transport system is involved in the tubular excretion of various clinically important drugs. The purpose of this study was to characterize the effects of various organic anion transport inhibitors on organic anion transport using proximal tubule cells stably expressing human organic anion transporter 1 (human-OAT1) and human-OAT3, which are localized to the basolateral membrane of the proximal tubule. Organic anion transport inhibitors including betamipron, cilastatin, KW-3902 (8-(noradamantan-3-yl)-1,3-dipropylxanthine) and probenecid significantly inhibited human-OAT1- and human-OAT3-mediated organic anion uptake in a dose-dependent manner. Kinetic analyses revealed that these inhibitions were competitive. The Ki values of betamipron, cilastatin, KW-3902 and probencid for human-OAT1 were 23.6, 1470, 7.82 and 12.1 microM, whereas those for human-OAT3 were 48.3, 231, 3.70 and 9.0 microM. These results suggest that betamipron and probenecid could inhibit both human-OAT1- and human-OAT3-mediated organic anion transport in vivo, whereas cilastatin could inhibit only human-OAT3-mediated one. In contrast, KW-3902 did not exert the effects of significance, whereas KW-3902 was the most potent.

Cytotoxicity of antiviral nucleotides adefovir and cidofovir is induced by the expression of human renal organic anion transporter 1

The transport of organic anions in proximal convoluted tubules plays an essential role in the active secretion of a variety of small molecules by the kidney. In addition to other anionic substrates, the human renal organic anion transporter 1 (hOATI) is capable of transporting the nucleotide analogs adefovir and cidofovir. To investigate the involvement of hOATI in the mechanism of nephrotoxicity associated with these two clinically important antiviral agents, Chinese hamster ovary (CHO) cells were stably transfected with hOATI cDNA. The resulting CHOhOAT cells showed probenecid-sensitive and pH-dependent uptake of p-aminohippurate (Km = 15.4 FtM, V,,, ..ax = 20.6 pmol/106 cells min), a prototypical organic anion substrate. In addition, the stably expressed hOATI mediated efficient transport of adefovir (Km, = 23.8 tLM, V, a,, = 46.0 pmol/106 cells min) and cidofovir (K, = 58.0 /iM, Vt,ax = 103 pmol/106 cells * min) such that the levels of intracellular metabolites of both nucleotides were > 1 00-fold higher in CHOh OAT cells than in parental CHO. Consequently, adefovir and cidofovir were approximately 500-fold and 400-fold more cytotoxic, respectively, in CHOh OAT cells compared to CHO. The cytotoxicity of both drugs in CHOh OAT cells was markedly reduced in the presence of hOATI inhibitors. The cyclic prodrug of cidofovir, which exhibits reduced in vivo nephrotoxicity, was a poor substrate for hOATI and showed only marginally increased cytotoxicity in CHOh OAT cells. In conclusion, these studies demonstrate that hOATI plays a critical role in the organ-specific toxicity of adefovir and cidofovir, and indicates that CHOh OAT cells may represent a useful in vitro model to investigate the potential nephrotoxicity of clinically relevant organic anion agents.

Nephroprotective effect of betamipron on a new carbapenem, DA-1131, in rabbits

The nephroprotective effect of betamipron (200 mg/kg) was evaluated after intravenous administration of a high dose of DA-1131 (200 mg/kg) to rabbits. Extensive tubular necrosis was observed without betamipron but the necrosis was not observed with betamipron at 8 h after intravenous administration of DA-1131 based on kidney microscopy. By treatment with betamipron, the amounts and tissue to plasma (T/P) ratios of DA-1131 in renal cortex and whole kidney decreased significantly (65-91% decrease) at both 30 min and 2 h after intravenous administration of the drug to rabbits. This indicated that the accumulation of DA-1131 in rabbit renal cortex and whole kidney was inhibited by betamipron. This resulted in significantly greater percentages of intravenous DA-1131 excreted in urine as unchanged drug, 60.9 versus 40.1%, and significantly faster renal clearance (Cl(r)) of DA-1131 (6.10 versus 3.22 mL/min/kg) by treatment with betamipron. By treatment with betamipron, the amounts and T/P ratios of DA-1131 in renal cortex and whole kidney decreased significantly from 30 min and the renal function remained intact at 8 h after intravenous administration of DA-1131. The above data suggested that the nephroprotective effect of betamipron was fast and persisted for a long period of time in rabbits.

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.