Evaluation of Rat Acute Phase Proteins as Inflammatory Biomarkers for Vaccine Nonclinical Safety Studies

The objectives were to characterize the kinetics of acute phase proteins (APPs) α-2 macroglobulin (A2M), α-1 acid glycoprotein (A1AGP), and fibrinogen (FIB), and injection site macroscopic and microscopic findings following intramuscular administration of tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis vaccine (TDaP; Adacel); adjuvants (aluminum phosphate [AlPO₄]; aluminum hydroxide, Al[OH]₃; CpG/Al[OH]₃; or Quillaja saponaria 21 [QS-21]); or saline to female Wistar Han rats. Intravascular lipopolysaccharide (LPS) was a positive control. Injection sites and lymph nodes were evaluated microscopically, using hematoxylin and eosin (H&E) stained sections, 48 hours postdose (HPD) and compared with APP concentrations; A2M and A1AGP were measured using Meso Scale Discovery analyzer. Fibrinogen was measured on STA Compact analyzer. In a time-course study, APP peaked at 24 or 48 HPD. In a subsequent study at 48 HPD, injection site microscopic changes included inflammation and muscle degeneration/necrosis, which was different in severity/nature between groups. The APPs were not increased in rats administered saline, Al(OH)₃, or AlPO₄. Fibrinogen and A1AGP increased in rats administered CpG/Al(OH)₃, QS-21, or TDaP; and A2M increased in rats administered QS-21. Fibrinogen, A2M, and A1AGP increased after LPS administration. Acute phase proteins can be used to monitor inflammatory responses to adjuvants; however, some adjuvants may induce inflammation without higher APPs.

Glutamate dehydrogenase as a biomarker for mitotoxicity; insights from furosemide hepatotoxicity in the mouse

Glutamate dehydrogenase (GLDH) is a liver-specific biomarker of hepatocellular damage currently undergoing qualification as a drug development tool. Since GLDH is located within the mitochondrial matrix, it has been hypothesized that it might also be useful in assessing mitotoxicity as an initiating event during drug-induced liver injury. According to this hypothesis, hepatocyte death that does not involve primary mitochondrial injury would result in release of intact mitochondria into circulation that could be removed by high speed centrifugation and result in lower GLDH activity measured in spun serum vs un-spun serum. A single prior study in mice has provided some support for this hypothesis. We sought to repeat and extend the findings of this study. Accordingly, mice were treated with the known mitochondrial toxicant, acetaminophen (APAP), or with furosemide (FS), a toxicant believed to cause hepatocyte death through mechanisms not involving mitotoxicity as initiating event. We measured GLDH levels in fresh plasma before and after high speed centrifugation to remove intact mitochondria. We found that both APAP and FS treatments caused substantial hepatocellular necrosis that correlated with plasma alanine aminotransferase (ALT) and GLDH elevations. The plasma GLDH activity in both the APAP- and FS- treated mice was not affected by high-speed centrifugation. Interestingly, the ratio of GLDH:ALT was 5-fold lower during FS compared to APAP hepatotoxicity. Electron microscopy confirmed that both APAP- and FS-treatments had resulted in mitochondrial injury. Mitochondria within vesicles were only observed in the FS-treated mice raising the possibility that mitophagy might account for reduced release of GLDH in the FS-treated mice. Although our results show that plasma GLDH is not clinically useful for evaluating mitotoxicity, the GLDH:ALT ratio as a measure of mitophagy needs to be further studied.

Candidate biomarkers for the diagnosis and prognosis of drug-induced liver injury: An international collaborative effort

Current blood biomarkers are suboptimal in detecting drug-induced liver injury (DILI) and predicting its outcome. We sought to characterize the natural variabilty and performance characteristics of 14 promising DILI biomarker candidates. Serum or plasma from multiple cohorts of healthy volunteers (n = 192 and n = 81), subjects who safely took potentially hepatotoxic drugs without adverse effects (n = 55 and n = 92) and DILI patients (n = 98, n = 28, and n = 143) were assayed for microRNA-122 (miR-122), glutamate dehydrogenase (GLDH), total cytokeratin 18 (K18), caspase cleaved K18, glutathione S-transferase α, alpha-fetoprotein, arginase-1, osteopontin (OPN), sorbitol dehydrogenase, fatty acid binding protein, cadherin-5, macrophage colony-stimulating factor receptor (MCSFR), paraoxonase 1 (normalized to prothrombin protein), and leukocyte cell-derived chemotaxin-2. Most candidate biomarkers were significantly altered in DILI cases compared with healthy volunteers. GLDH correlated more closely with gold standard alanine aminotransferase than miR-122, and there was a surprisingly wide inter- and intra-individual variability of miR-122 levels among healthy volunteers. Serum K18, OPN, and MCSFR levels were most strongly associated with liver-related death or transplantation within 6 months of DILI onset. Prediction of prognosis among DILI patients using the Model for End-Stage Liver Disease was improved by incorporation of K18 and MCSFR levels. Conclusion: GLDH appears to be more useful than miR-122 in identifying DILI patients, and K18, OPN, and MCSFR are promising candidates for prediction of prognosis during an acute DILI event. Serial assessment of these biomarkers in large prospective studies will help further delineate their role in DILI diagnosis and management.

Serum microRNA signatures as "liquid biopsies" for interrogating hepatotoxic mechanisms and liver pathogenesis in human

MicroRNAs (miRNAs) released into the peripheral circulation upon cellular injury have shown a promise as a new class of tissue-specific biomarkers. We were first to demonstrate that next-generation sequencing analysis of serum from human subjects with acetaminophen-induced liver injury revealed a specific signature of circulating miRNAs. We consequently hypothesized that different types of hepatic liver impairments might feature distinct signatures of circulating miRNAs and that this approach might be useful as minimally invasive diagnostic "liquid biopsies" enabling the interrogation of underlying molecular mechanisms of injury in distant tissues. Therefore we examined serum circulating miRNAs in a total of 72 serum samples from a group of 53 subjects that included patients with accidental acetaminophen overdose, hepatitis B infection, liver cirrhosis and type 2 diabetes as well as gender- and age-matched healthy subjects with no evidence of liver disease. The miRNA signatures were identified using next-generation sequencing that provided analysis for the whole miRNome, including miRNA isoforms. Compared to the healthy subjects, a total of 179 miRNAs showed altered serum levels across the diseased subjects. Although many subjects have elevated alanine aminotransferase suggesting liver impairments, we identified distinct miRNA signatures for different impairments with minimum overlap. Furthermore, the bioinformatics analysis of miRNA signatures revealed relevant molecular pathways associated with the mechanisms of toxicity and or pathogenesis of disease. Interestingly, the high proportion of miRNA isoforms present in the respective signatures indicated a new level of complexity in cellular response to stress or disease. Our study demonstrates for the first time that signatures of circulating miRNAs show specificity for liver injury phenotypes and, once validated, might become useful for diagnosis of organ pathologies as "liquid biopsies".

Application of high-throughput sequencing to circulating microRNAs reveals novel biomarkers for drug-induced liver injury

Drug-induced liver injury (DILI) is a leading cause of acute liver failure and the major reason for withdrawal of drugs from the market. Preclinical evaluation of drug candidates has failed to detect about 40% of potentially hepatotoxic compounds in humans. At the onset of liver injury in humans, currently used biomarkers have difficulty differentiating severe DILI from mild, and/or predict the outcome of injury for individual subjects. Therefore, new biomarker approaches for predicting and diagnosing DILI in humans are urgently needed. Recently, circulating microRNAs (miRNAs) such as miR-122 and miR-192 have emerged as promising biomarkers of liver injury in preclinical species and in DILI patients. In this study, we focused on examining global circulating miRNA profiles in serum samples from subjects with liver injury caused by accidental acetaminophen (APAP) overdose. Upon applying next generation high-throughput sequencing of small RNA libraries, we identified 36 miRNAs, including 3 novel miRNA-like small nuclear RNAs, which were enriched in the serum of APAP overdosed subjects. The set comprised miRNAs that are functionally associated with liver-specific biological processes and relevant to APAP toxic mechanisms. Although more patients need to be investigated, our study suggests that profiles of circulating miRNAs in human serum might provide additional biomarker candidates and possibly mechanistic information relevant to liver injury.

Emerging hepatotoxicity biomarkers and their potential to improve understanding and management of drug-induced liver injury

Biomarkers of drug-induced liver injury (DILI) are essential for the diagnosis of severe cases of DILI in clinical trials and clinical practice, but the currently used biomarker paradigm detects damage after it has occurred and has limited prognostic value. The development of new biomarker strategies that improve the diagnosis of DILI by providing increased specificity and/or by identifying individual patients who are at risk for DILI is therefore crucial.

See related Research, http://genomemedicine.com/content/5/9/86

The early effects of short-term dexamethasone administration on hepatic and serum alanine aminotransferase in the rat

Dexamethasone (DEXA) administration has been associated with serum alanine aminotransferase (ALT) elevations that may result from enhanced ALT expression. The aim of our current study was to compare liver vs. serum ALT activity and to examine the onset of any hepatocellular changes. Groups of 4 male Sprague-Dawley rats were administered a single dose of DEXA or corn oil at 12, 16, and 24 h prior to euthanasia or once-daily for 2, 3, or 4 days. All (nonfasted) rats were necropsied together on Day 5. While DEXA incrementally increased liver ALT activity in the 1-, 2-, 3-, and 4-day treatment groups (maximal, 3.7-fold), liver aspartate aminotransferase (AST) never exceeded 1.4-fold over control. Significant hepatic glycogen elevations were detected after DEXA treatment, which correlated with microscopic observations. Serum ALT, AST, sorbitol dehydrogenase, and glutamate dehydrogenase (GLDH) increased after 2, 3, and 4 days of DEXA dosing (1.3-10.3-fold). DEXA-related necropsy findings included pale livers consistent with glycogen deposition. The relative percent liver to body weight was elevated in all DEXA-treated rats. Hepatocellular necrosis was observed in 1/4 rats at 12 h, 2/4 rats at 2 days, 4/4 rats at 3 days, and 3/4 rats at 4 days. DEXA treatment <2 days failed to produce consistent evidence of hepatic injury, as detected by serum biomarkers and pathology assessment. However, early DEXA treatment did correlate with apparent ALT induction. Ultimately, this may explain some early asymptomatic serum ALT elevations seen clinically.

The relationship among microsomal enzyme induction, liver weight, and histological change in cynomolgus monkey toxicology studies

The purpose of this investigation was to examine the relationship among hepatic microsomal enzyme induction, liver weight, histological evidence of hepatic injury, and serum clinical chemistry markers of hepatic origin in the cynomolgus monkey. We report here the results from independent toxicology studies for 10 investigative drug candidates representing four therapeutic classes. Study conditions were selected to elicit target organ toxicity. We found that six of the 10 compounds altered cytochrome P450-associated activities in both male and female monkeys, two in females only, and one altered similar activities in males only. Frequently, significant treatment-related elevations in NADPH cytochrome c reductase and ethylmorphine N-demethylase were noted. When the results from all 10 studies were pooled, 14 cytochrome P450-associated activities were significantly increased and five were decreased in males compared to 15 significantly increased and three decreased in the females. Treatment-associated liver weight increases were noted in four studies. Except for hepatocellular hypertrophy in one study, no significant treatment-related microscopic changes in liver and no elevations of serum biomarkers commonly associated with liver toxicity were observed in any of the studies that demonstrated significant hepatic enzyme induction. Compared to parallel rat studies, one compound was an inducer only in monkeys and one was an inducer only in rats. Significant elevations of microsomal drug-metabolizing enzymes in the cynomolgus monkey liver are not accompanied by substantial hepatic changes except for hepatomegaly. These alterations in the hepatic drug-metabolizing enzyme system were benign based the absence of histopathological lesions and serum biomarkers of hepatobiliary toxicity.

Analysis of rat bone marrow by flow cytometry following in vivo exposure to cyclohexanone oxime or daunomycin HCl

The purpose of these studies was to evaluate bone marrow from male CD rats following exposure to known hematotoxins using flow cytometry (FC) and a monoclonal antibody to the cell surface antigen CD71. Rats were treated with either CHO (300 mg/kg for 10 days) or DAUN (10 mg/kg for 1 day). Control groups received the appropriate vehicle. Half of the animals from each group were euthanized at the end of the dosing schedule and the remaining animals were euthanized after a recovery period. Hematology analyses were completed prior to the onset of each study and on the day of necropsy. Marrow was isolated from the tibia, stained with R-phycoerythrin-conjugated mouse anti-rat CD71 (transferrin receptor on proliferating cells) monoclonal antibody, and then analyzed by FC for myeloid:erythroid (M:E) ratios. FC determinations of myeloid and erythroid population percentages and M:E ratios from untreated rats were confirmed by microscopic examination of marrow cytospins and selected flow cell sorts. M:E ratios for control animals determined by FC were not significantly different between the two studies (1.83 vs 1.89). CHO treatment caused a significant (p < 0.01) decrease in M:E ratios (0.96 for CHO vs 1.48 for control) at day 11 due to increased erythroid cells. M:E ratios were significantly increased (p < 0.05) with DAUN treatment at day 3 (5.07 for DAUN vs 1.70 for control) and corresponded to generalized depletion of all marrow cell lines, especially erythroid cells. After recovery, M:E ratios of CHO and DAUN rats were similar to controls. Hematological values corroborated changes in marrow myeloid and erythroid populations evaluated by this FC technique. Using FC and a monoclonal antibody to the cell surface antigen CD71, this study confirmed the reversible selective toxicity on myeloid and erythroid marrow populations following in vivo exposure to CHO or DAUN. This FC procedure provides a rapid, sensitive method for bone marrow analysis compared to conventional cytological examination.

The relationship among microsomal enzyme induction, liver weight and histological change in beagle dog toxicology studies

The present study represents a retrospective analysis of hepatic microsomal enzyme induction data collected over a period of years for the beagle dog. Comparisons were completed for up to six enzyme activities and P450 content versus histopathological examination of the liver for hepatic changes and serum chemistry data analysis for markers indicative of hepatic injury. In addition, qualitative comparisons were made for these compounds to data reported in the rat by the same authors. In this analysis of canine study data for nine different compounds comprising five different pharmacological classes, significant elevations in several microsomal enzyme activities were observed under study conditions that did not result in liver weight increases, histological changes or serum chemistry changes that would be indicative of hepatocellular or hepatobiliary damage. Despite some species differences in cytochrome P450 homologues, for this compound set, there was clearly a general association between the response in dog liver and that of the rat liver. Compounds that elicited significant increases in more than one canine P450 endpoints were also likely to produce an inductive response in rat liver; however, the magnitude of the response and the P450 endpoint involved were not always identical. We conclude that hepatic drug-metabolizing enzyme induction in the beagle dog liver is typically a benign adaptive response, which parallels that reported previously in the rat.

A comparison of the direct and reporter antigen popliteal lymph node assay for the detection of immunomodulation by low molecular weight compounds

The direct popliteal lymph node assay (PLNA) is a predictive test used to detect the immune-stimulating potential of pharmaceuticals and other low molecular weight compounds (LMWCs) with known autoimmunogenic or sensitizing properties. Two limitations in the PLNA are the existence of false negatives and the inability of the assay to provide mechanistic information. Recently the direct PLNA was modified by incorporating reporter antigens (RA), either TNP-Ficoll or TNP-OVA. In the RA-PLNA, immune stimulation is detected by measuring IgM or IgG TNP-specific antibody-forming cells (AFC) using an enzyme-linked immunospot (ELISPOT) assay. The RA-PLNA, when using potent, known autoimmunogenic compounds, may provide greater sensitivity compared to the direct PLNA and might distinguish LMWCs that have intrinsic adjuvant activity from those that create neo-antigens, using TNP-OVA and TNP-Ficoll, respectively. The purpose of this study was to rigorously compare the two assays. Our first objective was to investigate the interlaboratory reproducibility of the RA-PLNA using four autoimmunogenic LMWC models, plus one negative control LMWC. Subsequently, we tested seven LMWCs with known sensitizing properties and compared the results from the direct and modified assay. The test group included LMWCs thought to be mechanistically distinct and similar to compounds typically encountered in preclinical safety assessment. All control and treatment AFC plaques were collected (76 total), pooled, coded to conceal their source, and counted. The interlaboratory reproducibility of the RA-PLNA was demonstrated with the model autoimmunogenic compounds HgCl2, diphenylhydantoin, D-penicillamine, and the negative control compound phenobarbital, by detecting TNP-specific IgM and polyclonal IgG production to both reporter antigens. Additionally, the sensitizing effects of streptozotocin were identified using an IgG2a ELISPOT with both TNP-OVA and TNP-Ficoll. With the extended test group, the sensitizing effects of aniline, a false negative LMWC in the direct PLNA, was not detected in this study when using the direct PLNA. However, there was an increase of IgG1 AFCs using TNP-OVA, when compared to control (508 +/- 113 vs. 12 +/- 4 respectively). Glafenine, diclofenac, and ibuprofen, all associated with drug-induced anaphylaxis in humans, produced significant increases in IgG1 production to TNP-OVA. Of these three LMWCs, only diclofenac, which has been documented to induce neo-antigen formation, was detected with TNP-Ficoll. Hydralazine immunomodulation could be detected only with the direct PLNA although significant increases in IgM were identified with the co-injection of either reporter antigen. Isoniazid and methyldopa consistently produced negative responses in both assays. In summary, this study has demonstrated acceptable interlaboratory reproducibility of the RA-PLNA, using model autoimmunogenic LMWCs. Additionally, it demonstrated that an advantage of the RA-PLNA was that it identified all anaphylactic-associated LMWCs tested, detected the false negative compound aniline, and revealed what is thought to be the mechanism(s) associated with diclofenac-induced immunostimulation.

The relationship among microsomal enzyme induction, liver weight and histological change in rat toxicology studies

The purpose of this study was to determine what histological changes, if any, accompany liver enlargement and microsomal enzyme induction in rats administered high doses of therapeutic agents in preclinical toxicology studies. This was accomplished by evaluating a database derived from a series of 11 induction studies in rats with 10 novel compounds comprising five therapeutic classes. Results from serum enzyme chemistry analyses, gross organ weight changes, and histological analyses of the liver sections were evaluated and compared with the magnitude and extent of hepatic cytochrome P450 induction. All compounds were administrated via oral intubation once a day for the duration of the study using multiple doses, each proportionally based on body weight. During the course of these studies, serum clinical chemistry data and clinical observations were recorded. After necropsy, histopathology observations were made, and hepatic microsomes were assayed for cytochrome P450 content and associated drug-metabolizing enzymes. In some cases, cyanide-insensitive beta-oxidation of palmitoyl CoA was also assayed. Liver weight increases of 20% or greater were associated with histological evidence of hypertrophy, but neither the severity of hypertrophy nor the magnitude of liver weight increase correlated with the magnitude of drug-metabolizing enzyme elevations. Hypertrophy alone was not associated with serum enzyme increases. While there was a correlation between the incidence of increased liver weights and microsomal enzyme induction, the magnitudes of these increases were not related. Decreased serum triglycerides were often associated with elevated beta-oxidation attributed to hepatic peroxisome proliferation. It was concluded that, while slight ALT elevations occasionally were observed, hepatic microsomal enzyme induction was generally not accompanied by substantial morphological changes or elevated serum enzyme levels considered indicative of liver injury.

Ethylmorphine N-demethylase activity as a marker for cytochrome P450 CYP3A activity in rat hepatic microsomes

The purpose of this study was to evaluate the selectivity and sensitivity of ethylmorphine N-demethylase (EMD) as an indicator of chemically-induced cytochrome P450 CYP3A activity in liver microsomes of rats following treatment with selective enzyme inducers. Male and female Sprague-Dawley (CD) rats were dosed with either pregnenolone-16alpha-carbonitrile (PCN; 50 mg/kg per day for 5 days), phenobarbital (PB; 100 mg/kg per day for 4 days), beta-naphthoflavone (betaNF; 100 mg/kg per day for 3 days), clofibrate (CF; 300 mg/kg per day for 14 days), isoniazid (ISO; 100 mg/kg per day for 3 days), or dexamethasone (DEX; 50 mg/kg per day for 4 days). Microsomes were isolated, frozen and subsequently assayed for protein, cytochrome P450 content and EMD activity. In males, significant elevations (P < 0.01) in EMD activity were observed in microsomes from PB-, DEX- and PCN-dosed animals compared with untreated controls. Microsomes from ISO- and betaNF-dosed males showed a reduction (P < 0.05) in EMD activity when compared with control microsomes, and CF was without effect. In females, EMD activities were significantly increased in microsomes from PCN, DEX and PB-dosed but not betaNF, ISO, or CF-dosed animals. As expected on the basis of sex-related differences in gene expression, EMD activities in untreated animals were considerably higher in males than females, attributable to constitutive CYP3A and CYP2C11 activities. The selectivity of EMD for induced CYP3A was confirmed on the basis of inhibition studies with selected steroid substrates of CYP3A, polyclonal anti-CYP3A1 antibodies and triacetyloleandomycin (TAO), a selective inhibitor of CYP3A. In conclusion, for both sexes, the greatest elevations (approximately 3-13-fold) in EMD activity were observed in microsomes from rats dosed with DEX, a potent archetypal inducer with lesser but significant increases noted for PCN and PB, indicating that EMD is a reliable indicator of induced rat hepatic cytochrome P450 CYP3A activity.

Hepatic microsomal enzyme induction, beta-oxidation, and cell proliferation following administration of clofibrate, gemfibrozil, or bezafibrate in the CD rat

Male and female CD rats were administered one of two dose levels of clofibrate, gemfibrozil, or bezafibrate daily by oral gavage for a period of 14 days in order to establish an empirical data base using the Charles River CD rat with a single class of drugs against which the potency of novel proprietary compounds could be compared. Subsequent gross examination of the liver indicated significant and dose-related increases in relative and absolute liver weights in males following clofibrate and gemfibrozil. In females, absolute and relative liver weights were significantly elevated to a similar degree with either dose of gemfibrozil, and absolute liver weights were higher in clofibrate-dosed animals. Bezafibrate had no effect on female liver weights. Clofibrate and gemfibrozil increased hepatic palmitoyl CoA beta-oxidation in both sexes; however, clofibrate had the greater effect in males and gemfibrozil had the least effect in females. Bezafibrate treatment resulted in a very pronounced elevation of palmitoyl CoA beta-oxidation in the males but had no similar effect in the females. Concurrent ELISA analysis for cytochrome CYP4A revealed very good correspondence between beta-oxidation and cytochrome induction for each of the three compounds in males, but other cytochromes were not greatly affected, except CYP1A1 which was elevated in bezafibrate-dosed females. For males, further analysis for markers of cellular proliferation, namely cyclin-dependent kinases (CDK) and proliferating cell nuclear antigen (PCNA), indicated dose-related increases for both with clofibrate, increases at the high dose for gemfibrozil, and, for PCNA, a dose-related increase for bezafibrate. In females, both markers for cell proliferation showed either slight or no increases following any of the three drug treatments. These results demonstrate clear sex-dependent differences in terms of relative potency in the hepatic response of the Sprague-Dawley-derived rat to these peroxisome proliferators. Bezafibrate is most potent and gemfibrozil is least potent in stimulating peroxisome-associated beta-oxidation and cytochrome P450 4A induction in the males. Even though gemfibrozil significantly increased liver weights, beta-oxidation and cytochrome P450 4A in the females increased only after clofibrate treatment, although to a lesser degree than in the males administered the same dose. Similar sex-related differences were observed for cell proliferation. In conclusion, sex-related differences were noted in the potency to stimulate acyl Co-A oxidation, its association with hepatomegaly, and the stimulation of cell proliferation, but CYP4A induction always accompanied any substantial drug-dependent increases in beta-oxidation.

The Comparative Testing of Eight Coded Chemicals in the Rat Limb Bud Micromass and Rat Embryo Culture Systems

When cultured at high density, mesenchymal cells from rat limb buds proliferate and differentiate into chondrocytes. Inhibition of this in vitro chondrogenic process has been used for the preliminary evaluation of teratogenic potential. Alternatively, intact post-implantation rat embryos, maintained in short-term culture, provide a system for the in vitro study of abnormal development not limited to the skeletal system. Both systems isolate the test agent from maternal metabolism and pharmacokinetic restraints. In this study, drug-associated selective inhibition of alcian blue uptake by cartilage proteoglycans, in micromass cultures of limb bud cells prepared from 13-day-old rat embryos, was used to assess teratogenic potential in vitro following exposure for 48 hours to eight coded compounds (acetylsalicylic acid, isoniazid. penicillin G, saccharine, vincristine sulphate, 6-aminonicotinamide, retinoic acid, and amaranth). Following drug exposure, cultures were incubated for another 96 hours, and the cells were then fixed and stained with 0.5% alcian blue. Bound dye was then extracted and quantitated. In parallel cultures, cell viability was measured by neutral red uptake, and protein content was assayed by using the bicinchoninic acid method. Except for retinoic acid and vincristine sulphate, the maximum test concentration was 1000μg/ml. Inhibition of alcian blue uptake (> 50%) was noted at 0.001μg/ml vincristine sulphate, 0.5/μg/ml retinoic acid and 5μg/ml 6-aminonicotinamide, demonstrating that strong teratogens inhibit differentiation in micromass cultures at lower concentrations than those which affect limb cell viability. When the same eight compounds were tested in a 24-hour embryo culture model, dysmorphogenesis was evident at 0.005μg/ml vincristine sulphate, 0.1μg/ml retinoic acid and 0.3μg/ml 6-aminonicotinamide. For the other five chemicals, little or no toxicity was noted up to the maximum test concentration in either model. We conclude that the two test systems, both based on the developing rat embryo, are consistent with each other, and that either of them would be useful for the preliminary screening of potential teratogens.

Comparison of the effects of the new azalide antibiotic, azithromycin, and erythromycin estolate on rat liver cytochrome P-450

Erythromycin and some other macrolide antibiotics can first induce a cytochrome P-450 isozyme similar to the one induced in rats by pregnenolone-16 alpha-carbonitrile and then inhibit it by forming a stable cytochrome P-450-metabolite complex. The purpose of this study was to compare azithromycin, a novel 15-membered ring azalide, and erythromycin estolate for the potential to cause hepatic microsomal enzyme induction and inhibition in Sprague-Dawley rats. The daily oral administration of 800 mg of erythromycin estolate per kg for 7 days resulted in statistically significant elevations of NADPH-cytochrome c reductase, erythromycin N-demethylase (3.2-fold), and total cytochrome P-450 content. Approximately 40% of cytochrome P-450 was complexed with erythromycin metabolite. In contrast, the daily administration of 200 mg of azithromycin per kg for 7 days caused significant elevations of N-demethylase (2.5-fold) only and did not produce any increases in total cytochrome P-450 content or NADPH-cytochrome c reductase. No complexed cytochrome P-450 was detected in the azithromycin-dosed rats despite liver concentrations of azithromycin that were 118 times greater than the liver concentrations of erythromycin estolate in erythromycin estolate-dosed rats. Although the short-term oral administration of azithromycin produced hepatic accumulation of the drug and elevated azithromycin demethylase activity, there was no other evidence of hepatic cytochrome P-450 induction or inactivation via cytochrome-metabolite complex formation. In contrast to erythromycin estolate, azithromycin is not expected to inhibit its own metabolism or that of other drugs via this pathway.

Selective membrane toxicity of aminoglycoside antibiotics in membrane vesicles isolated from proximal renal tubules of the rat

A considerable body of evidence suggests that the nephrotoxic potential of aminoglycoside antibiotics may be associated with the degree of membrane binding and subsequent membrane damage in the renal tubules. In this study, we isolated functional basolateral and luminal membrane vesicles from rat renal cortex, incubated each membrane type in the presence of 1 mM concentrations of either neomycin, netilmicin, gentamicin, hydroxygentamicin, or amikacin, and monitored the activities of the marker enzymes alkaline phosphatase (ALP) and lambda-glutamyltransferase (GGT) (luminal) or ouabain-sensitive Na+,K+-ATPase (basolateral) to determine if there were any selective drug-related alterations of enzyme activities. While none of the five aminoglycosides had any substantive effect upon enzyme activities of luminal vesicles, all five drugs inhibited the basolateral marker enzyme. Neomycin produced the greatest inhibition, hydroxygentamicin and amikacin the least, and gentamicin and netilmicin were intermediate in the inhibition of the enzyme. These results are in accordance with the known relative nephrotoxicity of these same drugs and indicate the usefulness of isolated renal membrane vesicles for in vitro toxicological studies of novel aminoglycosides.

Further characterization of serum alkaline phosphatase from male and female beagle dogs

Alkaline phosphatase (AP) from the sera of both male and female beagle dogs was partially purified and then analyzed for the presence of AP isoenzymes having intestinal or osseous characteristics as detected by bromotetramisole inhibition or wheat germ lectin agarose electrophoresis, respectively. The sera from both sexes were similar in regard to the presence of AP isoenzymes with intestinal (16 vs. 20%) or osseous (19 vs. 23%) characteristics, but serum AP from the male had a greater sialic acid content and only the male serum contained a detectable constitutive acidic (pI = 3.4) AP isoenzyme. This was similar to a serum AP isoenzyme previously found elevated in the sera of dogs afflicted with hyperadrenocorticalism or of dogs treated with certain corticosteroids.