Sampling the Rat Mesenteric Artery

Vascular injury can be induced by different classes of drug candidates, and it can affect the mesenteric vasculature. Sampling of the mesenteric vessels in the rat is crucial for proper assessment of potential adverse or pharmacologic effects of drugs in nonclinical rodent studies. To date, several sampling and processing techniques for the histopathologic evaluation of the mesenteric artery in rodents have been described and used in studies with candidate drugs that may affect the vascular system. However, most of those techniques require a significant amount of time and effort. A less labor-intensive, time-consuming, and expensive technique that allows examination of the mesentery vasculature with abundant longitudinal and cross sections of the vessels when examined microscopically was developed and presented here.

Proceedings of the 2014 National Toxicology Program Satellite Symposium

The 2014 annual National Toxicology Program (NTP) Satellite Symposium, entitled "Pathology Potpourri" was held in Washington, D.C., in advance of the Society of Toxicologic Pathology's 33rd annual meeting. The goal of this annual NTP Symposium is to present current diagnostic pathology or nomenclature issues to the toxicologic pathology community. This article presents summaries of the speakers' presentations, including diagnostic or nomenclature issues that were presented, along with select images that were used for audience voting and discussion. Some lesions and topics covered during the symposium included a pulmonary mucinous adenocarcinoma in a male B6C3F1 mouse; plexiform vasculopathy in Wistar Han (Crl:WI[Han]) rats; staging of the estrous cycle in rats and mice; peri-islet fibrosis, hemorrhage, lobular atrophy and inflammation in male Sprague-Dawley (SD) rats; retinal dysplasia in Crl:WI[Han] rats and B6C3F1 mice; multicentric lymphoma with intravascular microemboli and tumor lysis syndrome, and 2 cases of myopathy and vascular anomaly in Tg.rasH2 mice; benign thymomas in Crl:WI[Han] rats; angiomatous lesions in the mesenteric lymph nodes of Crl:WI[Han] rats; an unusual foveal lesion in a cynomolgous monkey; and finally a series of nomenclatures challenges from the endocrine International Harmonization of Nomenclature and Diagnostic Criteria (INHAND) Organ Working Group (OWG).

Nonclinical Safety Biomarkers of Drug-induced Vascular Injury

Better biomarkers are needed to identify, characterize, and/or monitor drug-induced vascular injury (DIVI) in nonclinical species and patients. The Predictive Safety Testing Consortium (PSTC), a precompetitive collaboration of pharmaceutical companies and the U.S. Food and Drug Administration (FDA), formed the Vascular Injury Working Group (VIWG) to develop and qualify translatable biomarkers of DIVI. The VIWG focused its research on acute DIVI because early detection for clinical and nonclinical safety monitoring is desirable. The VIWG developed a strategy based on the premise that biomarkers of DIVI in rat would be translatable to humans due to the morphologic similarity of vascular injury between species regardless of mechanism. The histomorphologic lexicon for DIVI in rat defines degenerative and adaptive findings of the vascular endothelium and smooth muscles, and characterizes inflammatory components. We describe the mechanisms of these changes and their associations with candidate biomarkers for which advanced analytical method validation was completed. Further development is recommended for circulating microRNAs, endothelial microparticles, and imaging techniques. Recommendations for sample collection and processing, analytical methods, and confirmation of target localization using immunohistochemistry and in situ hybridization are described. The methods described are anticipated to aid in the identification and qualification of translational biomarkers for DIVI.

The Relationship of Glucokinase Activator–induced Hypoglycemia with Arteriopathy, Neuronal Necrosis, and Peripheral Neuropathy in Nonclinical Studies

Glucokinase activators (GKAs) are being developed for the treatment of type 2 diabetes. The toxicity of 4 GKAs (PF-04279405, PF-04651887, piragliatin, and PF-04937319) was assessed in mice, rats, dogs, and/or monkeys. GKAs were administered for 2 to 8 weeks. Standard endpoints, glucose, and insulin were assessed. All compounds produced varying degrees of hypoglycemia in all species. Brain neuronal necrosis and/or peripheral neuropathy were observed with most compounds. These findings are consistent with literature reports linking hypoglycemia with nervous system effects. Arteriopathy, mainly of cardiac vessels, was observed at a low frequency in monkey and/or dog. Arteriopathy occurred only at doses that produced severe and prolonged periods of repeated hypoglycemia. Since this lesion occurred in multiple studies with structurally distinct GKAs, these results suggested arteriopathy was related to GKA pharmacology. The morphological characteristics of the arteriopathy were consistent with that produced by experimental catecholamine administration. We hypothesize that the prolonged periods of hypoglycemia resulted in increased local and/or systemic concentrations of catecholamines via a counterregulatory and/or stress-related mechanism. Alternatively, prolonged hypoglycemia may have resulted in endothelial dysfunction leading to arteriopathy. This risk can be managed in human patients in clinical studies by careful glucose monitoring and intervention to avoid prolonged episodes of hypoglycemia.

The role of eNOS phosphorylation in causing drug-induced vascular injury

Previously we found that regulation of eNOS is an important part of the pathogenic process of Drug-induced vascular injury (DIVI) for PDE4i. The aims of the current study were to examine the phosphorylation of eNOS in mesentery versus aorta at known regulatory sites across DIVI-inducing drug classes and to compare changes across species. We found that phosphorylation at S615 in rats was elevated 35-fold 2 hr after the last dose of CI-1044 in mesentery versus 3-fold in aorta. Immunoprecipitation studies revealed that many of the upstream regulators of eNOS activation were associated with eNOS in 1 or more signalosome complexes. Next rats were treated with drugs from 4 other classes known to cause DIVI. Each drug was given alone and in combination with SIN-1 (NO donor) or L-NAME (eNOS inhibitor), and the level of eNOS phosphorylation in mesentery and aorta tissue was correlated with the extent of vascular injury and measured serum nitrite. Drugs or combinations produced altered serum nitrite levels as well as vascular injury score in the mesentery. The results suggested that phosphorylation of S615 may be associated with DIVI activity. Studies with the species-specific A2A adenosine agonist CI-947 in rats versus primates showed a similar pattern.

Hemodynamic Correlates of Drug-induced Vascular Injury in the Rat Using High-frequency Ultrasound Imaging

Several classes of drugs have been shown to cause drug-induced vascular injury (DIVI) in preclinical toxicity studies. Measurement of blood flow and vessel diameter in numerous vessels and across various tissues by ultrasound imaging has the potential to be a noninvasive translatable biomarker of DIVI. Our objective was to demonstrate the utility of high-frequency ultrasound imaging for measuring changes in vascular function by evaluating blood flow and vessel diameter in the superior mesenteric arteries (SMA) of rats treated with compounds that are known to cause DIVI and are known vasodilators in rat: fenoldopam, CI-1044, and SK&F 95654. Blood flow, vessel diameter, and other parameters were measured in the SMA at 4, 8, and 24 hr after dosing. Mild to moderate perivascular accumulations of mononuclear cells, neutrophils in tunica adventitia, and superficial tunica media as well as multifocal hemorrhage and necrosis in the tunica media were found in animals 24 hr after treatment with fenoldopam and SK&F 95654. Each compound caused marked increases in blood flow and shear stress as early as 4 hr after dosing. These results suggest that ultrasound imaging may constitute a functional correlate for the microscopic finding of DIVI in the rat.

Selective inhibition of PDE4 in Wistar rats can lead to dilatation in testis, efferent ducts, and epididymis and subsequent formation of sperm granulomas

Testicular tubular dilatation and degeneration and epididymal sperm granulomas were frequently seen in 4-week toxicity studies using different phosphodiesterase-4 (PDE4) inhibitors in Wistar rats, including the prototypic PDE4 inhibitor BYK169171. To investigate the pathogenesis of testicular and epididymal lesions, a time course study with BYK169171 was conducted with sequential necropsies after 7, 14, 21, and 28 days of treatment. After 7 days, a dilatation of efferent ducts and of the initial segment of the epididymis and a subacute interstitial inflammation were seen followed by a diffuse dilatation of seminiferous tubules in the testis. Dilatation and inflammation were most pronounced after 14 days. Single animals also exhibited vascular necrosis in the inflamed interstitium. Although dilatation decreased later in the study, the incidence and severity of tubular degeneration increased from 14 days onward. Sperm granulomas developed in efferent ducts and in the caput and cauda of the epididymis after 14 days. Our results demonstrate a clear time course of PDE4 inhibition-induced lesions, with dilatation preceding sperm granuloma formation. We conclude that the most likely mechanism of toxicity is a disturbance of fluid homeostasis in efferent and epididymal ducts resulting in abnormal luminal fluid and sperm contents, epithelial damage at specific sites of the excurrent duct system, sperm leakage, and granuloma formation.