Histopathology of vascular injury in Sprague-Dawley rats treated with phosphodiesterase IV inhibitor SCH 351591 or SCH 534385.

Histopathological and immunohistochemical studies were conducted to characterize vascular injuries in rats treated with phosphodiesterase (PDE) IV inhibitors SCH 351591 or SCH 534385. Sprague-Dawley rats were administered PDE IV inhibitors by gavage at a range of doses and times. The two PDE IV inhibitors induced comparable levels of vascular injury, primarily in the mesentery and to a lesser extent in the pancreas, kidney, liver, small intestine, and stomach. Mesenteric vascular changes occurred as early as one hour, progressively developed over twenty-four to forty-eight hours, peaked at seventy-two hours, and gradually subsided from seven to nine days. The typical morphology of the vascular toxicity consisted of hemorrhage and necrosis of arterioles and arteries, microvascular injury, fibrin deposition, and perivascular inflammation of a variety of blood vessels. The incidence and severity of mesenteric vascular injury increased in a time- and dose-dependent manner in SCH 351591- or SCH 534385-treated rats. Mesenteric vascular injury was frequently associated with activation of mast cells (MC), endothelial cells (EC), and macrophages (MØ). Immunohistochemical studies showed increases in CD63 immunoreactivity of mesenteric MC and in nitrotyrosine immunoreactivity of mesenteric EC and MØ. The present study also provides a morphological and cellular basis for evaluating candidate biomarkers of drug-induced vascular injury.

Biomarkers in peripheral blood associated with vascular injury in Sprague-Dawley rats treated with the phosphodiesterase IV inhibitors SCH 351591 or SCH 534385.

Drug-associated vascular injury can be caused by phosphodiesterase (PDE) IV inhibitors and drugs from several other classes. The pathogenesis is poorly understood, but it appears to include vascular and innate immunological components. This research was undertaken to identify changes in peripheral blood associated with vascular injury caused by PDE IV inhibitors. We evaluated twelve proteins, serum nitrite, and leukocyte populations in peripheral blood of rats treated with experimental PDE IV inhibitors. We found that these compounds produced histological microvascular injury in a dose- and time-dependent manner. Measurement of these serum proteins showed changes in eight of the twelve examined. Changes were seen in the levels of: tissue inhibitor of metalloproteinase-1, alpha1-acid glycoprotein, GRO/CINC-1, vascular endothelial growth factor, C-reactive protein, haptoglobin, thrombomodulin, and interleukin-6. No changes were seen in levels of tumor necrosis factor-alpha, hepatocyte growth factor, nerve growth factor, and granulocyte-monocyte colony stimulating factor. Serum levels of nitrite were also increased. Circulating granulocyte numbers were increased, and lymphocyte numbers were decreased. The changes in these parameters showed both a dose- and time-dependent association with histopathologic changes. These biomarkers could provide an additional tool for the nonclinical and clinical evaluation of investigational compounds.

Early alterations in heart gene expression profiles associated with doxorubicin cardiotoxicity in rats.

PURPOSE: The antineoplastic anthracycline doxorubicin can induce a dose-dependent cardiomyopathy that limits the total cumulative dose prescribed to cancer patients. In both preclinical and clinical studies, pretreatment with dexrazoxane, an intracellular iron chelator, partially protects against anthracycline-induced cardiomyopathy. To identify potential additional cardioprotective treatment strategies, we investigated early doxorubicin-induced changes in cardiac gene expression. METHODS: Spontaneously hypertensive male rats (n = 47) received weekly intravenous injections of doxorubicin (3 mg/kg) or saline 30 min after pretreatment with dexrazoxane (50 mg/kg) or saline by intraperitoneal injection. Cardiac samples were analyzed 24 h after the first (n = 20), second (n = 13), or third (n = 14) intravenous injection on days 1, 8, or 15 of the study, respectively. RESULTS: Rats receiving three doses of doxorubicin had minimal myocardial alterations that were attenuated by dexrazoxane. Cardiac expression levels of genes associated with the Nrf2-mediated stress response were increased after a single dose of doxorubicin, but not affected by cardioprotectant pretreatment. In contrast, an early repressive effect of doxorubicin on transcript levels of genes associated with mitochondrial function was attenuated by dexrazoxane pretreatment. Dexrazoxane had little effect on gene expression by itself. CONCLUSIONS: Genomic analysis provided further evidence that mitochondria are the primary target of doxorubicin-induced oxidative damage that leads to cardiomyopathy and the primary site of cardioprotective action by dexrazoxane. Additional strategies that prevent the formation of oxygen radicals by doxorubicin in mitochondria may provide increased cardioprotection.

Mechanisms and biomarkers of cardiovascular injury induced by phosphodiesterase inhibitor III SK&F 95654 in the spontaneously hypertensive rat.

The cardiovascular injury of the type III selective PDE inhibitor SK&F 95654 was investigated in SHR. Twenty-four hours after a single sc injection of 100 or 200 mg/kg of the drug, rats exhibited cardiomyocyte necrosis and apoptosis, interstitial inflammation, hemorrhage and edema, as well as mesenteric arterial hemorrhage and necrosis, periarteritis, EC and VSMC apoptosis, EC activation, and MC activation and degranulation. Elevated serum levels of cTnT and decreased cTnT immunoperoxidase staining on cardiomyocytes were detected in the drug-treated rats. Serum levels of alpha2-macroglobulin and IL-6 were significantly elevated following drug treatment. NMR spectral patterns of urine samples are significantly different between the drug-treated and control rats. These results indicate that measurement of serum cTnT, acute phase proteins, and cytokines as well as metabonomic urine profiles may serve as potential biomarkers for drug-induced cardiovascular injury in rats. Increased expression of CD63 on MC (tissue biomarker of MC), of nitrotyrosine on MC and EC (an indirect indicator of NO in vivo), and of iNOS on MC and EC (source of NO) suggest that NO produced by activated and degranulated MC as well as activated EC play an important role in SK&F 95654-induced mesenteric vascular injury.

Evaluation of the Tg.AC transgenic mouse assay for testing the human carcinogenic potential of pharmaceuticals--practical pointers, mechanistic clues, and new questions.

Transgenic mouse strains with genetic alterations known to play a role in the multistage process of carcinogenesis are being used increasingly as models for evaluating the human carcinogenic potential of chemicals and pharmaceuticals. The Tg.AC transgenic mouse is one of the strains currently being used in such alternative short-term carcinogenicity testing protocols. This review is focused on recent data from studies designed to evaluate this model's ability to discriminate carcinogens from noncarcinogens. Details relating to protocol design that can significantly impact study outcome are described. Data relating to mechanisms of chemical tumor induction in the Tg.AC model are reviewed, and questions have been formulated to encourage research to further guide appropriate future applications of this model.