Drug-induced Obstructive and Retrograde Nephropathy Associated with α2u-globulin in Male Rats.

The chemically induced accumulation of α2u-globulin protein in male rats causes specific renal lesions and subsequent nephropathy. Herein, we report additional parallel findings in the kidney of male rats consistent with obstructive and retrograde nephropathy. Kidney and urinary bladder samples were evaluated from Wistar rats treated with RG7129 for 2 week and 8 week and from an 8-week mechanistic study using females, intact and castrated males. Histopathological findings were present in intact males in all studies, including hyaline droplet accumulation and granular casts consistent with α2u-globulin nephropathy. In addition, tubular degeneration and regeneration, tubular changes extending from papilla to cortex, tubular dilation, and interstitial and luminal inflammation were observed consistent with retrograde and obstructive nephropathy. Renal and urinary lesions and their severity increased in a time- and dose-dependent manner. Urinalysis findings, including increases in leukocytes, protein, and in kidney biomarkers, kidney injury molecule 1 and clusterin, were present only in intact males. No treatment-related changes were observed in female rats or in castrated males. These results indicate that RG7129 induces α2u-globulin nephropathy, associated with retrograde and obstructive nephropathy secondary to precipitation in intact male rats only, constituting a species- and sex-specific syndrome that is not expected to occur in humans or other species.

Temporal Patterns of Novel Circulating Biomarkers in IL-2-mediated Vascular Injury in the Rat.

Recombinant interleukin-2 (rIL-2) administration in oncology indications is hampered by vascular toxicity, which presents as a vascular leak syndrome. We used this aspect of the toxicity of rIL-2 to evaluate candidate biomarkers of drug-induced vascular injury (DIVI) in rats given 0.36 mg/kg rIL-2 daily. Groups of rats were given either 2 or 5 doses of rIL-2 or 5 doses of rIL-2 followed by a 7-day recovery. The histomorphologic lexicon and grading scheme developed by the Vascular Injury Working Group of the Predictive Safety Testing Consortium of the Critical Path Institute were utilized to enable semiquantitative integration with circulating biomarker levels. The administration of rIL-2 was associated with time-dependent endothelial cell hyperplasia and hypertrophy and perivascular inflammation that correlated with increases in circulating angiopoietin-2, lipocalin-2, monocyte chemotactic protein-1, tissue inhibitor of metalloproteinase-1, vascular endothelial growth factor A, E-selectin, and chemokine (C-X-C motif) ligand-1, and the microRNAs miR-21, miR-132, and miR-155. The dose groups were differentially identified by panels comprising novel candidate biomarkers and traditional hematologic parameters. These results identify biomarkers of the early stages of DIVI prior to the onset of vascular smooth muscle necrosis.

Characterization of xenobiotic-induced hepatocellular enzyme induction in rats: anticipated thyroid effects and unique pituitary gland findings.

During routine safety evaluation of RO2910, a non-nucleoside reverse transcriptase inhibitor for HIV infection, histopathology findings concurrent with robust hepatocellular induction occurred in multiple organs, including a unique, albeit related, finding in the pituitary gland. For fourteen days, male and female rats were administered, by oral gavage vehicle, 100, 300, or 1000 mg/kg/day of RO2910. Treated groups had elevated serum thyroid-stimulating hormone and decreased total thyroxine, and hypertrophy in the liver, thyroid gland, and pituitary pars distalis. These were considered consequences of hepatocellular induction and often were dose dependent and more pronounced in males than in females. Hepatocellular centrilobular hypertrophy corresponded with increased expression of cytochrome P450s 2B1/2, 3A1, and 3A2 and UGT 2B1. Bilateral thyroid follicular cell hypertrophy occurred concurrent to increased mitotic activity and sometimes colloid depletion, which were attributed to changes in thyroid hormone levels. Males had hypertrophy of thyroid-stimulating hormone-producing cells (thyrotrophs) in the pituitary pars distalis. All findings were consistent with the well-established adaptive physiologic response of rodents to xenobiotic-induced hepatocellular microsomal enzyme induction. Although the effects on the pituitary gland following hepatic enzyme induction-mediated hypothyroidism have not been reported previously, other models of stress and thyroid depletion leading to pituitary stimulation support such a shared pathogenesis.

Spontaneous cardiomyopathy in cynomolgus monkeys (Macaca fascicularis).

A previously undescribed spontaneous cardiomyopathy was identified by routine light microscopic examination of the heart from four clinically healthy purpose-bred cynomolgus monkeys that ranged from four to nine years of age and included 2 males and 2 females. Special stains of Sirius red, Masson's trichrome, and Mallory's phosphotungstic acid hematoxylin (PTAH); and immunohistochemistry using anti-CD68, troponin-I, and desmin antibodies were used to facilitate lesion characterization and assess cardiomyocyte viability. Microscopically, the apical to mid-ventricular myocardium to subendocardium had foci of cardiomyocyte disarray with cytoplasmic pallor to stippling and karyomegaly, vacuolization of the perimyseal connective tissue, a meshwork of fibrous tissue that concentrated around medium-sized blood vessels and dissected between or less often replaced affected cardiomyocytes; and a minimal, predominantly macrophage infiltrate. The disrupted cardiomyocytes were immunoreactive to desmin and troponin-I antibodies and had a normal cross-striation pattern by PTAH, indicating the chronic cardiomyopathy was not associated with active cardiomyocyte damage. The consistent distribution and morphology of the cardiomyopathy suggested a common etiology and pathogenesis. The features were reminiscent of chronic catecholamine-induced experimental cardiomyopathy and stress cardiomyopathy in monkeys and humans, respectively. This report documents another spontaneous heart lesion in clinically healthy monkeys for consideration during interpretation of toxicology studies.

Application of Imaging Techniques to Cases of Drug-Induced Crystal Nephropathy in Preclinical Studies.

A number of drugs can cause precipitates within renal tubules leading to crystal nephropathy. Crystal nephropathy is usually an exposure-related finding and is not uncommon in preclinical studies, where high doses are tested. An understanding of the nature of precipitates is important for human risk assessment and further development. Our aim was to investigate the ability of various imaging techniques to detect the presence of drugs or metabolites in renal crystals. We applied matrix-assisted laser desorption/ionization-Fourier transform ion cyclotron resonance mass spectrometry (MALDI-FTICR MS) imaging, Raman and infrared microspectroscopy, scanning electron microscopy coupled with energy dispersive X-ray (SEM/EDX) spectroscopy and standard histopathology to cases of drug-induced crystal nephropathy, induced in rodents and primates by 4 compounds. MALDI-FTICR MS imaging enabled the identification of the drug-related crystal content in all 4 cases of nephropathy, without reference material and with high accuracy. Crystals were composed of unchanged parent drug and/or metabolites. Similar results were obtained using Raman and infrared microspectroscopy for 2 compounds. In the absence of reference standards of metabolites, Raman and infrared microspectroscopy showed that the crystals consisted of components similar, but not identical, to the administered drug for the other compounds, a limitation for these techniques. SEM/EDX showed which counter ions were colocalized with the identified drug-related material, complementing the MALDI-FTICR MS findings. Therefore, we recommend MALDI-FTICR MS as a first-line methodology to characterize crystal nephropathies. Raman and infrared microspectroscopy may be useful when MALDI-FTICR MS imaging cannot be applied. SEM/EDX could be considered as a complementary technology.

From the Cover: The Minipig is a Suitable Non-Rodent Model in the Safety Assessment of Single Stranded Oligonucleotides.

Non-human primates (NHPs) are currently considered to be the non-rodent species of choice for the preclinical safety assessment of single-stranded oligonucleotide (SSO) drugs. We evaluated minipigs as a potential alternative to NHPs to test the safety of this class of compounds. Four different phosphorothioated locked nucleic acid-based SSOs (3 antisense and 1 anti-miR), all with known safety profiles, were administered to minipigs using similar study designs and read-outs as in earlier NHP studies with the same compounds. The studies included toxicokinetic investigations, in-life monitoring, clinical and anatomic pathology. In the minipig, we demonstrated target engagement by the SSOs where relevant, and a similar toxicokinetic behavior in plasma, kidney, and liver when compared with NHPs. Clinical tolerability was similar between minipig and NHPs. For the first time, we showed similar and dose-dependent effects on the coagulation and complement cascade after intravenous dosing similar to those observed in NHPs. Similar to NHPs, morphological changes were seen in proximal tubular epithelial cells of the kidney, Kupffer cells, hepatocytes, and lymph nodes. Minipigs appeared more sensitive to the high-dose kidney toxicity of most of the selected SSOs than NHPs. No new target organ or off-target toxicities were identified in the minipig. The minipig did not predict the clinical features of human injection site reactions better than the NHPs, but histopathological similarities were observed between minipigs and NHPs. We conclude that there is no impediment, as default, to the use of minipigs as the non-rodent species in SSO candidate non-clinical safety packages.

Acute coronary artery injury in dogs following administration of CI-1034, an endothelin A receptor antagonist.

The objective of this study was to characterize acute coronary artery injury evoked by the endothelin A receptor (ETAR) antagonist, CI-1034. Male dogs (n = 5) were intravenously administered CI-1034 at 120 mg/kg for 4 d. Control animals (n = 3) received vehicle. Macroscopically, drug-related hemorrhage was observed in the right coronary groove and atrium. Histologically, drugrelated coronary changes were characterized as medial hemorrhage and necrosis, with mixed inflammatory-cell infiltrates in the adventitia and media. Immunohistochemistry staining indicated increased expression of inducible nitric oxide synthase (iNOS), cleaved caspase-3, and S100A8/A9 (within in monocytes and neutrophils) proteins in coronary arteries of CI-1034-treated animals. However, there were similar expression levels of endothelial nitric oxide synthase (eNOS) among control and CI-1034-treated animals. Significant drug-related nitric oxide (NO) accumulation occurred on days 1 through 4 in serum. Increased interleukin (IL)-6 and fibrinogen in plasma and serum amyloid A (SAA) occurred on days 2 through 5 in CI-1034-treated animals. Increased levels of NO accumulation in serum; increased IL-6 and fibrinogen levels in plasma; increased SAA levels; and increased expressions of iNOS, cleaved caspase-3, and S100A8/A9 complex appear to be characteristic of CI-1034-induced acute vascular injury in dogs.

Immunogenicity, Inflammation, and Lipid Accumulation in Cynomolgus Monkeys Infused with a Lipidated Tetranectin-ApoA-I Fusion Protein.

High density lipoprotein (HDL)-targeted therapies, which promote cholesterol efflux from cells, are currently in development for reducing cardiovascular events in acute coronary syndrome. Human apolipoprotein A-I (apoA-I), the major HDL protein, was fused to the trimerization domain of tetranectin (TN) and complexed with phospholipids to generate a HDL mimetic (lipidated TN-ApoA-I) with reduced renal clearance and enhanced efficacy. Cynomolgus monkeys received 24-h intravenous infusions of control, 100 mg/kg or 400 mg/kg lipidated TN-ApoA-I every 4 days for 3 weeks, followed by a 6-week recovery period. After multiple infusions of lipidated TN-ApoA-I, clinical condition deteriorated and was accompanied by changes indicative of a progressive inflammatory response; increased levels of cytokines, C-reactive protein and vascular/perivascular infiltrates in multiple tissues. Rapid formation of antidrug antibodies occurred in all animals receiving lipidated TN-ApoA-I. Enhanced drug clearance corresponding to a relative lack of high molecular weight immune complexes in blood, suggestive of preferred removal/clearance, was observed in some animals. Expected dose-dependent increases in serum lipids were accompanied by vacuolated monocytes/macrophages in multiple organs, which in the glomeruli were shown to be CD68-positive, contain lipid and co-localized with granular IgG deposits. Lipid accumulation may have been a direct result of a high drug load, possibly enhanced by immune complex formation, inflammation, and altered lipid metabolism. Noteworthy was the inter- individual inconsistency in the severity of clinical and histopathologic findings, drug clearance and inflammatory markers. In conclusion, multiple infusions of lipidated TN-ApoA-I resulted in high immunogenicity, lipid accumulation and were not well tolerated in nonhuman primates.

Susceptibility of rats to corneal lesions after injectable anesthesia.

Corneal injury is not a commonly reported side effect after injectable or inhalation anesthesia in rats, but a number of surgery studies at our facility resulted in a high incidence of these injuries. To explore the potential association of various anesthetic protocols with the development of corneal lesions in rats, we retrospectively evaluated clinical records and sections of eyes from 215 male and 187 female Wistar rats used in eight intravenous infusion toxicology studies. None of the studied compounds was associated with eye toxicity. For placement of jugular vein vascular access ports, rats were anesthetized with enflurane, isoflurane, ketamine-xylazine, or Hypnorm-midazolam. Histologically, corneal changes were scored from 0 to 4 in light of degree of mineralization, leukocytic infiltrates, neovascularization, fibrosis, and ulceration. Prestudy (postsurgical) ophthalmic examination findings of corneal opacities were correlated with mineralization of the anterior limiting membrane and corneal ulceration. Corneal lesions were more severe in animals anesthetized with ketamine-xylazine, and minimal changes occurred after anesthesia with either enflurane or isoflurane. The results of further analysis suggest that corneal lesions can be observed within 24 h after injectable anesthetic administration and are not reversible. The severity of corneal changes was reduced when ketamine-xylazine anesthesia was reversed with yohimbine. Compared with Sprague-Dawley and Lewis rats, Wistar, Long-Evans, and Fischer 344 rats had increased incidence and severity of corneal lesions after anesthesia with ketamine-xylazine, suggesting that these three strains are at increased risk for developing postanesthetic corneal lesions with this regimen.

Specific inhibition of cyclin-dependent kinase 4/6 by PD 0332991 and associated antitumor activity in human tumor xenografts.

PD 0332991 is a highly specific inhibitor of cyclin-dependent kinase 4 (Cdk4) (IC50, 0.011 micromol/L) and Cdk6 (IC50, 0.016 micromol/L), having no activity against a panel of 36 additional protein kinases. It is a potent antiproliferative agent against retinoblastoma (Rb)-positive tumor cells in vitro, inducing an exclusive G1 arrest, with a concomitant reduction of phospho-Ser780/Ser795 on the Rb protein. Oral administration of PD 0332991 to mice bearing the Colo-205 human colon carcinoma produces marked tumor regression. Therapeutic doses of PD 0332991 cause elimination of phospho-Rb and the proliferative marker Ki-67 in tumor tissue and down-regulation of genes under the transcriptional control of E2F. The results indicate that inhibition of Cdk4/6 alone is sufficient to cause tumor regression and a net reduction in tumor burden in some tumors.

A stepwise method for the isolation of endothelial cells and smooth muscle cells from individual canine coronary arteries.

Methods for the stepwise isolation of endothelial cells and smooth muscle cells from individual canine coronary arteries are described. Both cell types can be isolated in pure culture with high yields. Dogs are a common species used in the study of atherosclerosis and coronary artery disease. Capacity to isolate endothelial cells and smooth muscle cells from individual canine coronary arteries should prove useful in the study of coronary artery disease.

Quantitative histological assessment of xenobiotic-induced liver enzyme induction and pituitary-thyroid axis stimulation in rats using whole-slide automated image analysis.

Preclinical evaluation of a new compound, RO2910, identified a hypertrophic response in liver, thyroid gland, and pituitary gland (pars distalis). We aimed to develop and validate automated image analysis methods to quantify and refine the interpretation of semi-quantitative histology. Wistar-Han rats were administered RO2910 for 14 days. Liver, thyroid, and pituitary gland tissues were processed for routine histology and immunolabeled with anti-thyroid stimulating hormone (TSH) antibody (pituitary) and anti-topoisomerase II antibody (thyroid). Glass slides were scanned, image analysis methods were developed and applied to whole-slide images, and numerical results were compared with histopathology, circulating hormone levels, and liver enzyme mRNA expression for validation. Quantitative analysis of slides had strong individual correlation with semi-quantitative histological evaluation of all tissues studied. Hepatocellular hypertrophy quantification also correlated strongly with liver enzyme mRNA expression. In the pars distalis, measurement of TSH weak-staining areas correlated with both hypertrophy scores and circulating TSH levels. Whole-slide image analysis enabled automated quantification of semi-quantitative histopathology findings and a more refined interpretation of these data. The analysis also enabled a direct correlation with non-histological parameters using straightforward statistical analysis to provide a more refined dose- and sex-response relationship and integration among affected parameters. These findings demonstrate the utility of our image analysis to support preclinical safety evaluations.

Key components of the mode of action for hemangiosarcoma induction in pregabalin-treated mice: evidence of increased bicarbonate, dysregulated erythropoiesis, macrophage activation, and increased angiogenic growth factors in mice but not in rats.

In carcinogenicity studies, pregabalin increased hemangiosarcoma incidence in mice but not in rats. Investigative studies, ranging in length from 24 h to 12 months, were conducted in mice (1000 or 5000 mg/kg) and rats (900 mg/kg) to evaluate a potential mode-of-action scheme for tumor formation. Three areas were evaluated: (1) hematopoiesis (because endothelial and hematopoietic cells arise from the same precursor and hemangiosarcomas are primarily located in mouse hematopoietic tissues), (2) angiogenic growth factors (because increased angiogenic growth factors may stimulate vascular tumors), and (3) pulmonary/blood gas parameters (because hypoxia is a known driver for endothelial cell proliferation). In mice, pregabalin rapidly increased platelet and megakaryocyte counts, activated platelets and bone marrow erythrophages, decreased the myeloid-to-erythroid (M:E) ratio (49%), and produced bone marrow and splenic congestion and extramedullary hematopoiesis (EMH). Vascular endothelial growth factor (VEGF) and basic fibroblast growth factor immunohistochemical staining were also increased in mouse bone marrow and spleen and vascular endothelial growth factor receptor 2 immunolabeling was increased in liver. Serum bicarbonate was increased within 24 h of pregabalin administration, persisted over time, and was accompanied by decreased respiratory rate (up to 34%) and increased partial pressure of carbon dioxide (pCO(2)), resulting in sustained metabolic alkalosis and elevated blood pH in mice. In contrast, in rats, pregabalin decreased overall bone marrow cellularity, including decreased number of megakaryocytes (24%) with no evidence of erythrophages, no change in M:E ratio, no EMH, and no increase in angiogenic growth factors or blood pH. Persistent alterations in serum bicarbonate, respiratory function, and blood gas parameters in mice, without adequate compensatory mechanisms, has the potential to create chronic tissue hypoxia, an accepted driver of endothelial cell proliferation.

Current challenges and controversies in drug-induced liver injury.

Current key challenges and controversies encountered in the identification of potentially hepatotoxic drugs and the assessment of drug-induced liver injury (DILI) are covered in this article. There is substantial debate over the classification of DILI itself, including the definition and validity of terms such as 'intrinsic' and 'idiosyncratic'. So-called idiosyncratic DILI is typically rare and requires one or more susceptibility factors in individuals. Consequently, it has been difficult to reproduce in animal models, which has limited the understanding of its underlying mechanisms despite numerous hypotheses. Advances in predictive models would also help to enable preclinical elimination of drug candidates and development of novel biomarkers. A small number of liver laboratory tests have been routinely used to help identify DILI, but their interpretation can be limited and confounded by multiple factors. Improved preclinical and clinical biomarkers are therefore needed to accurately detect early signals of liver injury, distinguish drug hepatotoxicity from other forms of liver injury, and differentiate mild from clinically important liver injury. A range of potentially useful biomarkers are emerging, although so far most have only been used preclinically, with only a few validated and used in the clinic for specific circumstances. Advances in the development of genomic biomarkers will improve the prediction and detection of hepatic injury in future. Establishing a definitive clinical diagnosis of DILI can be difficult, since it is based on circumstantial evidence by excluding other aetiologies and, when possible, identifying a drug-specific signature. DILI signals based on standard liver test abnormalities may be affected by underlying diseases such as hepatitis B and C, HIV and cancer, as well as the concomitant use of hepatotoxic drugs to treat some of these conditions. Therefore, a modified approach to DILI assessment is justified in these special populations and a suggested framework is presented that takes into account underlying disease when evaluating DILI signals in individuals. Detection of idiosyncratic DILI should, in some respects, be easier in the postmarketing setting compared with the clinical development programme, since there is a much larger and more varied patient population exposure over longer timeframes. However, postmarketing safety surveillance is currently limited by the quantity and quality of information available to make an accurate diagnosis, the lack of a control group and the rarity of cases. The pooling of multiple healthcare databases, which could potentially contain different types of patient data, is advised to address some of these deficiencies.

Comparative methods for multiplex analysis of cytokine protein expression in plasma of lipopolysaccharide-treated mice.

Changes in circulating cytokines might serve as predictors of compound-evoked inflammatory responses. CD-1 mice were treated with lipopolysaccharide (LPS; 0.2 ml of 0.25 mg/ml, intraperitoneal) for subsequent expression measurement of plasma cytokine protein expression at 24-h post-treatment using multiple antibody Western blot, and at both 2-h and 24-h post-treatment using antibody array and suspension bead array. Antibody array provided a semi-qualitative assessment and suggested significantly increased expression of GCSF at 2-h post-treatment and GCSF, IL-6, IL-12, MCP-1, MCP-5, RANTES and sTNFR1 at 24-h post-treatment. Densitometric analysis of multiple antibody Western blots provided a semi-quantitative assessment and indicated significantly increased expression of IL-6, IL-12, IL-17, GCSF, eotaxin, and MCP-2 at 24-h post-treatment. The suspension bead array yielded statistically significant cytokine protein expression increases for IL-6, IL-10, IFNgamma and TNFalpha at both 2-h and 24-h post-treatments, while significant expression at 24-h post-treatment only was noted for IL-1beta, IL-5, IL-12 and GM-CSF. Suspension bead array provided the greatest range of detection, revealing subtle increased expression of GM-CSF, IL-1beta, IL-5, IL-10, TNFalpha and IFNgamma at 24-h post-treatment, not detected by antibody array or multiple antibody Western blot. Suspension bead array proved to be the best method for detection of LPS-evoked changes in plasma cytokine levels.

Apoptosis and nitrative stress associated with phosphodiesterase inhibitor-induced mesenteric vasculitis in rats.

Nitric oxide may play a role in phosphodiesterase (PDE) inhibitor-induced rat mesenteric vasculitis. The present study was conducted to identify cellular sources of iNOS, determine the distribution of nitrotyrosine (NT) residues as a footprint of peroxynitrite (ONOO-) production, and evaluate their association with vascular apoptosis. To dissociate primary events from secondary changes associated with the inflammatory response, rats were given the PDE IV inhibitor CI-1018 orally at 750 mg/kg alone or concurrently with dexamethasone (DEX) intraperitoneally at 1 mg/kg for 4-5 days. Neutrophil (PMN) involvement in apoptosis was investigated in CI-1018 treated rats dosed with rabbit anti-rat PMN serum (APS). iNOS expression, NT residues, and caspase-3 were detected by immuno-histochemistry. Apoptosis was evaluated by TUNEL assay. CI-1018 induced vascular lesions were associated with iNOS expression in endothelial cells and inflammatory infiltrates; NT was evident only in the latter. Caspase-3 and TUNEL-positive staining were prominent only in medial smooth muscle cells (SMC) from CI-1018-treated rats and only when associated with active inflammation. iNOS- and NT-positive inflammatory cells were present in close proximity to SMC with caspase-3 staining. Inflammatory infiltrates were absent in rats given DEX with minimal SMC necrosis and hemorrhage remained. DEX eliminated apoptosis and immunoreactivity associated with caspase-3, iNOS, and NT. APS depletion of PMNs decreased the incidence and severity of vasculitis but failed to abolish completely caspase-3 immunoreactivity. Expression patterns for caspase-3, iNOS, and NT demonstrated that nitrative stress is a prominent feature of PDE inhibitor-induced vasculitis, with a possible role in medial SMC apoptosis. Further, medial SMC apoptosis may not be a primary event, but instead may be secondary to the inflammatory response.

Differentiating spontaneous from drug-induced vascular injury in the dog.

When vascular injury is observed in dogs used in preclinical toxicology studies, careful evaluation of the lesions is warranted, especially when differentiating drug-induced vascular changes from spontaneous findings, such as idiopathic canine polyarteritis. The clinical signs as well as the nature and distribution of lesions can often be distinguishing, as is the case with vasoactive drugs, including vasodilators and/or positive inotropes (hydralazine, minoxidil, endothelin receptor antagonists, and phosphodiesterase III inhibitors). For most types of vasodilator-induced vascular injury, the lesion is often restricted to coronary arteries, whereas in idiopathic canine polyarteritis, arterial lesions not only involve coronary arteries, but also medium to small arteries of other organs. In addition, the nature of the changes in vessels yields important clues. Medial and adventitial hemorrhage is generally associated with vasodilator-induced arterial lesion, whereas hemorrhage is generally absent in idiopathic polyarteritis. Although idiopathic canine polyarteritis can generally be differentiated from vasoactive-induced vascular injury in dogs, there are increasing incidences of this type of polyarteritis in dogs receiving any 1 of a number of unrelated classes of compounds, suggestive of an exacerbation of the spontaneous disease. Therefore, in order to differentiate drug-induced injury from idiopathic canine polyarteritis, it is critical that examination of the vascular pathology be conducted with good understanding of clinical, pharmacological, and mechanistic data associated with the drug.

Effect of dexamethasone on the metabonomics profile associated with phosphodiesterase inhibitor-induced vascular lesions in rats.

Metabonomics is the evaluation of the multiparametric metabolic response of biological systems to pathophysiological stimuli. High-resolution nuclear magnetic resonance (NMR) spectroscopy of biofluids coupled with pattern recognition-based chemometric analysis is an emerging approach to the study of metabonomics and may be used for the prediction of toxicity in vivo and for identification of surrogate markers of toxicity. Previously, we established that metabonomic analysis of urine samples has significant potential for identification of phosphodiesterase type 4 (PDE-4) inhibitor-induced vascular lesions in rats. It was not clear, however, whether the observed changes in metabonomics profile were related mechanistically to the pathogenesis of these vascular lesions or whether these changes were reflective primarily of the ensuing inflammatory response. In the present study, dexamethasone was used to suppress inflammation associated with vascular lesions induced in rats by the PDE-4 inhibitor CI-1018 and urine samples were evaluated for resultant changes in metabonomic profile. Female Wistar rats were given CI-1018 by gavage at 750 mg/kg with or without concurrent intraperitoneal administration of dexamethasone at 1 mg/kg for 4 days. Dexamethasone induced a characteristic lymphoid depletion and lymphocytolysis but no evidence of vascular lesions. Rats dosed with CI-1018 had mild vascular changes in liver and/or marked vascular lesions in mesentery characterized by medial necrosis, hemorrhage, and/or edema accompanied by perivascular mixed inflammatory cell infiltrates. Inflammatory infiltrates associated with these lesions were eliminated in rats given dexamethasone, yet minimal medial smooth muscle necrosis and degeneration still occurred, suggestive of etiologic changes rather than effects secondary to the inflammatory response. Principle component analysis of urine NMR spectra produced a clear pattern separation within 48 to 72 h between CI-1018-treated rats with vascular lesions and vehicle controls or rats given dexamethasone alone. There was no pattern separation, however, between rats given CI-1018 alone and rats given CI-1018 and dexamethasone concurrently, suggesting that CI-1018-induced urine spectral changes were associated with the vascular lesions, yet were independent of the inflammatory response. These findings provide new insight into the mechanism(s) of PDE inhibitor-induced vasculitis and support the potential use of metabonomics for developing reliable noninvasive methods for detecting vascular changes in rats.