ChemSkin Reference Chemical Database for the Development of an In Vitro Skin Irritation Test.

Since the animal test ban on cosmetics in the EU in 2013, alternative in vitro safety tests have been actively researched to replace in vivo animal tests. For the development and evaluation of a new test method, reference chemicals with quality in vivo data are essential to assess the predictive capacity and applicability domain. Here, we compiled a reference chemical database (ChemSkin DB) for the development and evaluation of new in vitro skin irritation tests. The first candidates were selected from 317 chemicals (source data n = 1567) searched from the literature from the last 20 years, including previous validation study reports, ECETOC, and published papers. Chemicals showing inconsistent classification or those that were commercially unavailable, difficult or dangerous to handle, prohibitively expensive, or without quality in vivo or in vitro data were removed, leaving a total of 100 chemicals. Supporting references, in vivo Draize scores, UN GHS/EU CLP classifications and commercial sources were compiled. Test results produced by the approved methods of OECD Test No. 439 were included and compared using the classification table, scatter plot, and Pearson correlation analysis to identify the false predictions and differences between in vitro skin irritation tests. These results may provide an insight into the future development of new in vitro skin irritation tests.

Effects of Intestinal Microbiota on Pharmacokinetics of Crocin and Crocetin in Male Sprague-Dawley Rats.

In addition to the hepatic metabolism, the role of intestinal microbiota in drug metabolism has been considered important in the biotransformation of xenobiotics. Crocin and its aglycone, crocetin, isolated from many plants, including the dried stigma of Crocus sativus and the fruit of Gardenia jasminoides, have been used in treatment of inflammation, cancer, and metabolic disorders. In this study, the effect of intestinal microbiota on the pharmacokinetics of crocin was studied following single oral treatment with 600 mg/kg crocin to male rats pre-treated with a mixture of antibiotics, such as cefadroxil, oxytetracycline, and erythromycin, for three consecutive days. Following crocin treatment, blood, urine, and feces were collected at various time points for evaluating pharmacokinetic characteristics of crocin and crocetin by using LC-MS. Results showed that intestinal absorption of crocin was relatively marginal when compared with that of crocetin, and that crocin metabolism to crocetin by intestinal microbiota would be a critical step for absorption. The present results clearly suggested that the in vivo pharmacological effects of crocin might be considered as the effects by its aglycone, crocetin, mainly, and that the metabolism of glycosidic natural products by intestinal microbiota should be considered to understand their pharmacodynamic actions.

Me-too validation study for in vitro skin irritation test with a reconstructed human epidermis model, KeraSkin™ for OECD test guideline 439.

We conducted a me-too validation study to confirm the reproducibility, reliability, and predictive capacity of KeraSkin™ skin irritation test (SIT) as a me-too method of OECD TG 439. With 20 reference chemicals, within-laboratory reproducibility (WLR) of KeraSkin™ SIT in the decision of irritant or non-irritant was 100%, 100%, and 95% while between-laboratory reproducibility (BLR) was 100%, which met the criteria of performance standard (PS, WLR≥90%, BLR≥80%). WLR and BLR were further confirmed with intra-class correlation (ICC, coefficients >0.950). WLR and BLR in raw data (viability) were also shown with a scatter plot and Bland-Altman plot. Comparison with existing VRMs with Bland-Altman plot, ICC and kappa statistics confirmed the compatibility of KeraSkin™ SIT with OECD TG 439. The predictive capacity of KeraSkin™ SIT was estimated with 20 reference chemicals (the sensitivity of 98.9%, the specificity of 70%, and the accuracy of 84.4%) and additional 46 chemicals (for 66 chemicals [20 + 46 chemicals, the sensitivity, specificity and accuracy: 95.2%, 82.2% and 86.4%]). The receiver operating characteristic (ROC) analysis suggested a potential improvement of the predictive capacity, especially sensitivity, when changing cut-off (50% → 60-75%). Collectively, the me-too validation study demonstrated that KeraSkin™ SIT can be a new me-too method for OECD TG 439.

Role of Intestinal Microbiota in Metabolism of Voglibose In Vitro and In Vivo.

BACKGROUND: Voglibose, an α-glucosidase inhibitor, inhibits breakdown of complex carbohydrates into simple sugar units in intestine. Studies showed that voglibose metabolism in the liver might be negligible due to its poor intestinal absorption. Numerous microorganisms live in intestine and have several roles in metabolism and detoxification of various xenobiotics. Due to the limited information, the possible metabolism of voglibose by intestinal microbiota was investigated in vitro and in vivo. METHODS: For the in vitro study, different concentrations of voglibose were incubated with intestinal contents, prepared from both vehicle- and antibiotics-treated mice, to determine the decreased amount of voglibose over time by using liquid chromatography-mass spectrometry. Similarly, in vivo pharmacodynamic effect of voglibose was determined following the administration of voglibose and starch in vehicle- and antibiotic-pretreated non-diabetic and diabetic mice, by measuring the modulatory effects of voglibose on blood glucose levels. RESULTS: The in vitro results indicated that the remaining voglibose could be significantly decreased when incubated with the intestinal contents from normal mice compared to those from antibiotic-treated mice, which had less enzyme activities. The in vivo results showed that the antibiotic pretreatment resulted in reduced metabolism of voglibose. This significantly lowered blood glucose levels in antibiotic-pretreated mice compared to the control animals. CONCLUSION: The present results indicate that voglibose would be metabolized by the intestinal microbiota, and that this metabolism might be pharmacodynamically critical in lowering blood glucose levels in mice.

Role of Intestinal Microbiota in Metabolism of Gastrodin In Vitro and In Vivo.

Alteration in the number and composition of intestinal microbiota affects the metabolism of several xenobiotics. Gastrodin, isolated from Gastrodia elata, is prone to be hydrolyzed by intestinal microbiota. In the present study, the role of intestinal microbiota in gastrodin metabolism was investigated in vitro and in vivo. Gastrodin was incubated in an anaerobic condition with intestinal contents prepared from vehicle- and antibiotics-treated rats and the disappearance of gastrodin and formation of 4-hydroxybenzyl alcohol (4-HBA) was measured by liquid chromatography coupled to mass spectroscopy (LC-MS/MS). The results showed that almost all gastrodin incubated with control intestinal contents was metabolized to its aglycone in time- and concentration-dependent manners. In contrast, much less formation of 4-HBA was detected in intestinal contents from antibiotics-treated rats. Subsequently, in vivo pharmacokinetic study revealed that the antibiotic pretreatment of rats significantly affected the metabolism of gastrodin to 4-HBA. When administered orally, gastrodin was rapidly absorbed rapidly into plasma, metabolized to 4-HBA, and disappeared from the body within six hours. Interestingly, the pharmacokinetic parameters of 4-HBA were changed remarkably in antibiotics-treated rats, compared to control rats. The results clearly indicated that the antibiotics treatment of rats suppressed the ability of intestinal microbiota to metabolize gastrodin to 4-HBA and that, thereby, the pharmacodynamic action was significantly modulated.

Identification of pre- and pro-haptens with a ß-galactosidase-expressing E. coli culture system for skin sensitization.

Although several in vitro approaches were successful in separating chemicals as skin sensitizers and non-sensitizers, none of the available methods completely mimics the absolute in vivo scenario of skin sensitization. One of the major challenges with currently available systems would be the limited or no metabolic capacity to activate pre- or pro-haptens to reactive metabolites in the system. In the present study, E. coli cells with ß-galactosidase-expressing LacZ gene were combined with either induced rat liver S-9 fractions or microsomal fractions to detect pre- or pro-haptens to cause skin sensitization. Following optimization of some experimental conditions, we examined 20 sensitizers classified as pre- or pro-haptens and 11 non-sensitizers in these E. coli cultures by incubating bacterial cells and test chemicals with and without S-9 or microsomal proteins. After a 6-h incubation in the presence of IPTG, cells were lyzed to determine the suppression of ß-galactosidase enzyme. A cut-off of 17.3% was applied to determine the percent suppression of ß-galactosidase activity by test chemicals to classify skin sensitizers and non-sensitizers. Among chemicals tested, 19 pre- or pro-haptens were categorized as true positives and 8 non-sensitizers were categorized as true negatives. Thereby, the overall sensitivity, specificity and accuracy achieved with microsome-incorporated and S-9 fraction-incorporated group were 95.0%, 72.7% and 87.1% and 80.0%, 81.8% and 80.6%, respectively. The results suggested that the present bacterial system incorporated with the microsomal activation system could be considered as a useful alternative method to classify not only direct-acting sensitizers but also pre- or pro-haptens requiring metabolic activation in vitro.

Me-too validation study for in vitro eye irritation test with 3D-reconstructed human cornea epithelium, MCTT HCETM.

The need for in vitro eye irritation test replacing in vivo is steadily increasing. The MCTT HCE™ eye irritation test (EIT) using 3D reconstructed human cornea-like epithelium, was developed to identify ocular irritants from non-irritants those that are not requiring classification and labelling for eye irritation. Here, we report the results of me-too validation study, which was conducted to evaluate the reliability and relevance of the MCTT HCETM EIT, according to performance standards (PS) of OECD TG 492. The optimal cutoff to determine irritation in the prediction model was preliminarily established at 45% with the receiver operation characteristics (ROC) curve for 141 reference substances. To demonstrate the reproducibility of within- and between-laboratory (WLR and BLR), a set of 30 PS reference chemicals were tested in three laboratories three times. The WLR and BLR concordance with the binary decision of whether non-irritant or irritant was estimated to be 90-100% and 90%, respectively, and both met the PS requirements. The predictive capacity of the respective laboratories for the 30 reference chemicals were evaluated based on three different estimation methods, and the results were comparable, with sensitivity ranging from 89.6 to 93.3%, the specificity ranging from 62.2 to 66.7%, and the accuracy ranging from 75.9 to 80.0%. Additional test with the new set of 30 PS substances in the revised OECD GD 216 yielded a performance of sensitivity ranging from 92.6-93.3%, the specificity 62.2-66.7% and the accuracy 77.4-80.0%. 95.0% sensitivity, 67.2% specificity, and 83.0% accuracy were obtained for 141 reference substances in total. Furthermore, separate cutoffs for liquids and solids, 35% and 60%, respectively, produced better predictivity, which was established as a final prediction model. Collectively, our study demonstrated that MCTT HCETM EIT meets the reproducibility and predictivity criteria stated in OECD TG 492 PS.

Exploring the Metabolism of Loxoprofen in Liver Microsomes: The Role of Cytochrome P450 and UDP-Glucuronosyltransferase in Its Biotransformation.

Loxoprofen, a propionic acid derivative, non-steroidal anti-inflammatory drug (NSAID) is a prodrug that is reduced to its active metabolite, trans-alcohol form (Trans-OH) by carbonyl reductase enzyme in the liver. Previous studies demonstrated the hydroxylation and glucuronidation of loxoprofen. However, the specific enzymes catalyzing its metabolism have yet to be identified. In the present study, we investigated metabolic enzymes, such as cytochrome P450 (CYP) and UDP-glucuronosyltransferase (UGT), which are involved in the metabolism of loxoprofen. Eight microsomal metabolites of loxoprofen were identified, including two alcohol metabolites (M1 and M2), two mono-hydroxylated metabolites (M3 and M4), and four glucuronide conjugates (M5, M6, M7, and M8). Based on the results for the formation of metabolites when incubated in dexamethasone-induced microsomes, incubation with ketoconazole, and human recombinant cDNA-expressed cytochrome P450s, we identified CYP3A4 and CYP3A5 as the major CYP isoforms involved in the hydroxylation of loxoprofen (M3 and M4). Moreover, we identified that UGT2B7 is the major UGT isoform catalyzing the glucuronidation of loxoprofen and its alcoholic metabolites. Further experimental studies should be carried out to determine the potency and toxicity of these identified metabolites of loxoprofen, in order to fully understand of mechanism of loxoprofen toxicity.

A simple in chemico method for testing skin sensitizing potential of chemicals using small endogenous molecules.

Among many of the validated methods for testing skin sensitization, direct peptide reactivity assay (DPRA) employs no cells or animals. Although no immune cells are involved in this assay, it reliably predicts the skin sensitization potential of a chemical in chemico. Herein, a new method was developed using endogenous small-molecular-weight compounds, cysteamine and glutathione, rather than synthetic peptides, to differentiate skin sensitizers from non-sensitizers with an accuracy as high as DPRA. The percent depletion of cysteamine and glutathione by test chemicals was measured by an HPLC equipped with a PDA detector. To detect small-size molecules, such as cysteamine and glutathione, a derivatization by 4-(4-dimethylaminophenylazo) benzenesulfonyl chloride (DABS-Cl) was employed prior to the HPLC analysis. Following test method optimization, a cut-off criterion of 7.14% depletion was applied to differentiate skin sensitizers from non-sensitizers in combination of the ratio of 1:25 for cysteamine:test chemical with 1:50 for glutathione:test chemical for the best predictivity among various single or combination conditions. Although overlapping HPLC peaks could not be fully resolved for some test chemicals, high levels of sensitivity (100.0%), specificity (81.8%), and accuracy (93.3%) were obtained for 30 chemicals tested, which were comparable or better than those achieved with DPRA.

A ß-galactosidase-expressing E. coli culture as an alternative test to identify skin sensitizers and non-sensitizers.

Although the Organization for Economic Cooperation and Development (OECD) has adopted several in vitro methods with reasonable predictive capacity, alternative methods for identifying skin sensitizers and non-sensitizers with reliability and simplicity are still required for more efficient and economic prediction. The present study was to design an in vitro system with the use of a ß-galactosidase-expressing E. coli culture for simpler but sufficiently accurate classification of skin sensitizers and non-sensitizers. A LacZ gene-containing E. coli strain that is capable of producing ß-galactosidase enzyme was induced by isopropyl ß-D-1-thiogalactopyranoside with concomitant treatment with test chemicals. After 6-hr incubation, cells were lysed and ß-galactosidase enzyme activity was monitored colorimetrically by using O-nitrophenyl-D-galactopyranoside as a substrate. Following optimization of several experimental conditions, 22 skin sensitizers and 11 non-sensitizers were examined to assess predictive capacity of this method. The results indicated that predictivity was as follows: 90.9% sensitivity, 81.8% specificity, and 87.9% accuracy, when 17.3% of control activity was used as the cut-off value to separate sensitizers from non-sensitizers. Data suggested that the current bacterial system expressing ß-galactosidase may serve as a useful alternative test for classifying skin sensitizers and non-sensitizers, without the utilization of animals or mammalian cell cultures.

Intra- and inter-laboratory reproducibility and predictivity of the HaCaSens assay: A skin sensitization test using human keratinocytes, HaCaT.

Due to considerable constraints in using animals for risk assessment, much effort has been directed at developing non-animal test methods. Developing assays for skin sensitization, the leading cause of contact dermatitis, is particularly important, but there are currently no in vitro skin sensitization tests that completely replace animal tests. HaCaSens, a simple skin sensitization test using non-transformed HaCaT cells, predicts keratinocyte activation by skin sensitizers with 75% sensitivity, 83% specificity and 77% accuracy in a previous study using 22 coded substances. Although the data show promising results, the number of tested substances is insufficient to prove predictive capacity. Moreover, reproducibility among different laboratories has not been studied. Here, three laboratories participated in a validation in order to assess HaCaSens feasibility for official validation. To examine transferability, intra- and inter-lab reproducibility and predictive capacity, HaCaSens was assessed on a set of 30 test substances coordinated by the Validation Management Team (VMT). The results showed satisfactory transferability as well as intra- and inter-laboratory reproducibility. Further assessment of its predictive capacity on 20 test substances demonstrated a sensitivity of 81.8% (18/22), specificity of 87.5% (7/8), and accuracy of 83.3% (25/30) in identifying skin sensitizers, which is comparable with presently validated assays, KeratinoSens™ and LuSens. This validation study shows that the HaCaSens assay is easily transferable, reproducible and highly predictable for identifying skin sensitizers.

Impact of gut microbiota on drug metabolism: an update for safe and effective use of drugs.

The intestinal mucosa and liver have long been considered as the main sites of drug metabolism, and the contribution of gut microbiota to drug metabolism has been under-estimated. However, it is now generally accepted that the gut microbiota plays an important role in drug metabolism prior to drug absorption or during enterohepatic circulation via various microbial enzymatic reactions in the intestine. Moreover, some drugs are metabolized by gut microbiota to specific metabolite(s) that cannot be formed in the liver. More importantly, the metabolism of drugs by gut microbiota prior to absorption can alter the systemic bioavailability of certain drugs. Therefore, understanding drug metabolism by gut microbiota is critical for explaining changes in the pharmacokinetics of drugs, which may cause significant alterations in drug-induced pharmacodynamics and toxicities. In this review, we describe recent progress with regard to the role of metabolism by gut microbiota in some drug-induced alterations of either pharmacological or toxicological effects to emphasize the clinical importance of gut microbiota for safe and effective use of drugs.

Phase I and phase II metabolite identification of rutaecarpine in freshly isolated hepatocytes from male Sprague-Dawley rats.

Rutaecarpine, an alkaloid originally isolated from Evodia rutaecarpa, has been used for the treatment of gastrointestinal disorders in Asia. In the present study, the phase I and phase II metabolites of rutaecarpine were investigated in freshly isolated hepatocytes from male Sprague-Dawley rats. The individual metabolites were characterized via liquid chromatography-tandem mass spectrometry. The incubation of rutaecarpine with freshly isolated hepatocytes for 2 h yielded five major phase I metabolites. In addition, three glucuronide conjugates and four sulfate conjugates were observed. Because the majority of metabolites observed in vivo were identified, freshly isolated hepatocytes might be useful for the identification of certain metabolites formed from drug candidates from a reduced number of experimental animals.

Graphemes Sharing Phonetic Features Tend to Induce Similar Synesthetic Colors.

Individuals with grapheme-color synesthesia experience idiosyncratic colors when viewing achromatic letters or digits. Despite large individual differences in grapheme-color association, synesthetes tend to associate graphemes sharing a perceptual feature with similar synesthetic colors. Sound has been suggested as one such feature. In the present study, we investigated whether graphemes of which representative phonemes have similar phonetic features tend to be associated with analogous synesthetic colors. We tested five Korean multilingual synesthetes on a color-matching task using graphemes from Korean, English, and Japanese orthography. We then compared the similarity of synesthetic colors induced by those characters sharing a phonetic feature. Results showed that graphemes associated with the same phonetic feature tend to induce synesthetic color in both within- and cross-script analyses. Moreover, this tendency was consistent for graphemes that are not transliterable into each other as well as graphemes that are. These results suggest that it is the perceptual-i.e., phonetic-properties associated with graphemes, not just conceptual associations such as transliteration, that determine synesthetic color.

Prevalidation trial for a novel in vitro eye irritation test using the reconstructed human cornea-like epithelial model, MCTT HCE™.

Here, we report the results of a prevalidation trial for an in vitro eye irritation test (EIT) using the reconstructed human cornea-like epithelium, MCTT HCE™. The optimal cutoff to determine irritation in the prediction model was established at 35% with the receiver operation characteristics(ROC) curve for 126 substances. Within-lab(WL) and between-lab(BL) reproducibility was tested for 20 reference substances by 3 participating laboratories. Viability data described by mean±SD or ±1/2 difference between duplicate wells, and scatter plots, demonstrated the WL/BL consistency. WL/BL concordance with the binary decision, whether non-irritant or irritant was estimated to be 85-95% and 95%, respectively. WL/BL reproducibility of viability data was further supported by a strong correlation(ICC, r>0.9). WL/BL agreement of binary decisions was also examined by Fleiss' Kappa statistics, which showed a strong level of agreement (>0.78), nevertheless weaker than the reproducibility of the viability. The EIT with MCTT HCE™ exhibited a sensitivity of 82.2% (60/73), a specificity of 81.1% (43/53), and an accuracy of 81.8% (103/126) for 126 reference substances (for liquids; a sensitivity of 100% (47/47), a specificity of 70.6% (24/34), and an accuracy of 87.7% (71/81), and for solids, a sensitivity of 50% (13/26), a specificity of 100% (19/19), and an accuracy of 71.1% (32/45), suggesting that the accuracy is satisfactory but the sensitivity needs improvement, which shall be addressed through correcting the poor sensitivity for solid substances in future full validation trials.

Pharmacokinetic Interaction of Chrysin with Caffeine in Rats.

Pharmacokinetic interaction of chrysin, a flavone present in honey, propolis and herbs, with caffeine was investigated in male Sprague-Dawley rats. Because chrysin inhibited CYP1A-selective ethoxyresorufin O-deethylase and methoxyresorufin O-demethylase activities in enriched rat liver microsomes, the pharmacokinetics of caffeine, a CYP 1A substrate, was studied following an intragastric administration with 100 mg/kg chrysin. In addition to the oral bioavailability of chrysin, its phase 2 metabolites, chrysin sulfate and chrysin glucuronide, were determined in rat plasma. As results, the pharmacokinetic parameters for caffeine and its three metabolites (i.e., paraxanthine, theobromine and theophylline) were not changed following chrysin treatment in vivo, despite of its inhibitory effect on CYP 1A in vitro. The bioavailability of chrysin was found to be almost zero, because chrysin was rapidly metabolized to its sulfate and glucuronide conjugates in rats. Taken together, it was concluded that the little interaction of chrysin with caffeine might be resulted from the rapid metabolism of chrysin to its phase 2 metabolites which would not have inhibitory effects on CYP enzymes responsible for caffeine metabolism.

Role of Intestinal Microbiota in Baicalin-Induced Drug Interaction and Its Pharmacokinetics.

Since many glycoside compounds in natural products are hydrolyzed by intestinal microbiota when administered orally, it is of interest to know whether their pharmacological effects are derived from the glycoside itself or from the aglycone form in vivo. An interesting example is baicalin versus baicalein, the aglycone of baicalin, which is contained in some herbs from Labiatae including Scutellaria baicalensis Georgi and Scutellaria lateriflora Linne. The herbs have been extensively used for treatment of inflammatory diseases in Asia. Although there have been numerous reports regarding the pharmacological effects of baicalin and baicalein in vivo and in vitro, some reports indicated that the glycoside form would hardly be absorbed in the intestine and that it should be hydrolyzed to baicalein in advance for absorption. Therefore, the role of metabolism by intestinal microbiota should also be considered in the metabolism of baicalin. In addition, baicalin contains a glucuronide moiety in its structure, by which baicalin and baicalein show complex pharmacokinetic behaviors, due to the interconversion between them by phase II enzymes in the body. Recently, concerns about drug interaction with baicalin and/or baicalein have been raised, because of the co-administration of Scutellaria species with certain drugs. Herein, we reviewed the role of intestinal microbiota in pharmacokinetic characteristics of baicalin and baicalein, with regards to their pharmacological and toxicological effects.

Effects of baicalin on oral pharmacokinetics of caffeine in rats.

Scutellaria baicalensis is one of the most widely used herbal medicines in East Asia. Because baicalein and baicalin are major components of this herb, it is important to understand the effects of these compounds on drug metabolizing enzymes, such as cytochrome P450 (CYP), for evaluating herb-drug interaction. The effects of baicalin and baicalein on activities of ethoxyresorufin O-deethylase (EROD), methoxyresorufin O-demethylase (MROD), benzyloxyresorufin O-debenzylase (BROD), p-nitrophenol hydroxylase and erythromycin N-demethylase were assessed in rat liver microsomes in the present study. In addition, the pharmacokinetics of caffeine and its three metabolites (i.e., paraxanthine, theobromine and theophylline) in baicalin-treated rats were compared with untreated control. As results, EROD, MROD and BROD activities were inhibited by both baicalin and baicalein. However, there were no significant differences in the pharmacokinetic parameters of oral caffeine and its three metabolites between control and baicalin-treated rats. When the plasma concentration of baicalin was determined, the maximum concentration of baicalin was below the estimated IC50 values observed in vitro. In conclusion, baicalin had no effects on the pharmacokinetics of caffeine and its metabolites in vivo, following single oral administration in rats.

Nephrotoxic potential and toxicokinetics of melamine combined with cyanuric acid in rats.

To investigate the nephrotoxic potential of melamine (MEL) and cyanuric acid (CA) in male Sprague-Dawley rats, 7-d repeated-dose studies were performed. The experimental groups of MEL100 and CA100 were orally administered with MEL and CA at 100 mg/kg/d for 7 d, respectively. In groups dosed with MEL-CA mixtures, melamine and cyanuric acid (1:1) were simultaneously administered at 4, 20, or 100 mg/kg/d for 7 d (i.e., MEL-CA4, MEL-CA20, or MEL-CA100, respectively). Body weights were not markedly affected in MEL100, CA100, and MEL-CA4 groups, but significantly reduced in MEL-CA 20 and 100 rats. Most parameters determined in sera and tissues were not markedly altered in MEL100, CA100, and MEL-CA4-treated rodents. However, BUN, creatinine, total protein, and kidney weights were significantly increased in MEL-CA20- and MEL-CA100-treated animals. Renal histopathologic findings also revealed signs of toxicity, including tubular dilatation, crystal deposition, granulomatous tubulo-interstitial inflammation, and tubular necrosis with regeneration. Data suggested that the combination of MEL and CA might be responsible for observed nephrotoxicity that was not seen following individual exposure to either MEL or CA alone. Subsequently, the concentrations of MEL and CA were determined in serum, urine, and kidney tissues by using liquid chromatography-mass spectrometry. Toxicokinetic studies indicated that MEL or CA alone might be eliminated almost completely within 24 h after dosing showing no accumulation in kidney. However, the combined MEL-CA dose produced marked accumulation of chemicals in blood and kidneys. These results suggested that combined MEL and CA might produce renal toxicity due to significant chemical accumulation in kidney accompanied by low excretion.

Protective Effects of Diallyl Sulfide against Thioacetamide-Induced Toxicity: A Possible Role of Cytochrome P450 2E1.

Effects of diallyl sulfide (DAS) on thioacetamide-induced hepatotoxicity and immunotoxicity were investigated. When male Sprague-Dawley rats were treated orally with 100, 200 and 400 mg/kg of DAS in corn oil for three consecutive days, the activity of cytochrome P450 (CYP) 2E1-selective p-nitrophenol hydroxylase was dose-dependently suppressed. In addition, the activities of CYP 2B-selective benzyloxyresorufin O-debenzylase and pentoxyresorufin O-depentylase were significantly induced by the treatment with DAS. Western immunoblotting analyses also indicated the suppression of CYP 2E1 protein and/or the induction of CYP 2B protein by DAS. To investigate a possible role of metabolic activation by CYP enzymes in thioacetamide-induced hepatotoxicity, rats were pre-treated with 400 mg/kg of DAS for 3 days, followed by a single intraperitoneal treatment with 100 and 200 mg/kg of thioacetamide in saline for 24 hr. The activities of serum alanine aminotransferase and aspartate aminotransferase significantly elevated by thioacetamide were protected in DAS-pretreated animals. Likewise, the suppressed antibody response to sheep erythrocytes by thioacetamide was protected by DAS pretreatment in female BALB/c mice. Taken together, our present results indicated that thioacetamide might be activated to its toxic metabolite(s) by CYP 2E1, not by CYP 2B, in rats and mice.