Dermal toxicity studies: factors impacting study interpretation and outcome.

The field of dermal toxicity continues to evolve in order to accurately predict dermal (and systemic) responses in humans to topically applied chemicals. Although the testing methods have undergone extensive refinements, idiosyncrasies and unexpected issues during the conduct of these studies are not unusual due to the plethora of new vehicles available for formulating test substances, changing regulatory requirements, and introducting new strain and/or species of laboratory animals as no single species or method seems to suffice for evaluating skin toxicity. The objective of this article is to illustrate some pragmatic issues that should be considered during the conduct as well as interpretation of dermal toxicity studies. Routine procedure-related issues such as hair clipping, tape stripping, and wrapping the animal's torso to prevent oral ingestion can influence the interpretation. Excipients used in dermal toxicity studies may be nontoxic when used alone but complex dermal formulations can result in unexpected irritation and toxicity. In conclusion, interpretation and risk assessment of dermal toxicity studies should be done in a comprehensive manner, taking into account procedure-related impact on study results, unique species susceptibility, limitation of gross visual (naked eye) observation for evidence of toxicity, and normal anatomical variation.

Effect of estrous cycle phase on clinical pathology values in beagle dogs.

BACKGROUND: In dogs, the diestrus phase is considerably longer than in most domestic animals, and is characterized by high circulating progesterone concentrations that may influence clinical pathology values. OBJECTIVE: The objective of this retrospective study was to investigate differences in clinical pathology data in dogs in diestrus compared with data from dogs in all other phases of the estrous cycle. METHODS: Phase of the estrous cycle was determined by histologic evaluation of reproductive tissues from 86 control female Beagles that had participated in 23 toxicity studies. Serum biochemical, hematologic, and urinalysis values from dogs in diestrus were compared with data from dogs in all other estrous cycle phases using a 2-tailed t-test. RESULTS: In Beagles in diestrus (n = 38), serum cholesterol concentrations and eosinophil counts were 35% (P < .0001) and 45.8% (P = .0035) higher, respectively, than for Beagles in all other phases of the estrous cycle (n = 48). Furthermore, Beagles in diestrus had 14% lower AST activity (P = .0011), 1% lower chloride concentration (P = .0224), 7.8% lower hemoglobin concentration (P < .0001), 7.8% lower RBC count (P < .0001), and 7.6% lower hematocrit (P < .0001) compared with female dogs in all other phases of the estrous cycle. Urine values did not differ significantly between groups. CONCLUSIONS: Differences in clinical pathology values between dogs in different phases of the estrous cycle could potentially confound interpretation of data in toxicity studies, which often have small group sizes. Interpretation of clinical pathology data in female dogs should be performed with due consideration given to the phase of the estrous cycle.

Cyclic morphological changes in the beagle mammary gland.

Interpretation of chemical-induced effects on the female beagle mammary gland can be difficult owing to the wide variation of normal glandular morphology. In this retrospective study, morphological features of the gland in four (proestrus, estrus, diestrus, and anestrus) phases of the cycle are described. The gland was quiescent (inactive) in proestrus and estrus. In diestrus, with the rise of progesterone, four (I-IV) distinct morphological changes were evident. In phase I, there was exuberant stromal and ductal proliferation. In phase II, there was early lobular development with branching ducts and alveolar proliferation. In phase III, there was an abundance of glandular tissue with large lobules containing secretory material, whereas phase IV had features of early regression, increased interlobular connective tissue, and eosinophilic secretions in distended ducts and acini. In early anestrus, ducts were distended, with eosinophilic secretions with alveolar regression, whereas regression was complete in late anestrus. Glandular morphology was slightly variable in the mammary chain within the same dog. Progesterone receptor expression was prominent in estrus and early diestrus, and peak estrogen receptor expression was noted in diestrus II. Expression of proliferation marker ki-67 was highest in diestrus I, followed by diestrus II. There was excellent concordance between the estrous stage and the glandular morphology.

Chemical carcinogenesis of the gastrointestinal tract in rodents: an overview with emphasis on NTP carcinogenesis bioassays.

Cancers of the stomach and large intestine (LI) are the second and fourth leading causes of human cancer mortality. A review of the National Toxicology Program (NTP) database and the Carcinogenic Potency Database (CPDB) reveals that chemically induced neoplasms of the gastrointestinal tract (GIT) are relatively common. Within the GIT, epithelial tumors of the forestomach in mice and rats and LI of the rat are most common. Generally, there is a high species concordance for forestomach with at least 26 chemicals inducing tumors in both species. Glandular stomach tumors are rare, and the few reported are usually neuroendocrine tumors (carcinoids) originating from the enterochromaffin-like (ECL) cells. Of 290 carcinogenic agents identified by the NTP, 19 (7%) caused intestinal neoplasia, 14 in the rat and 5 in the mouse. Neoplasms occurred in both males and females, exclusively in the small intestine (SI) of the mouse and in the LI or both SI and LI in the rat. Enteric carcinogens (NTP) frequently induced neoplasms at other alimentary sites (oral cavity, esophagus, and stomach). In conclusion, the most common induced GIT tumors are squamous neoplasms of the forestomach, glandular neoplasms of the stomach are rare, and rats appear more prone to developing LI (colorectal) cancer compared to mice.

Frequency of different estrous stages in purpose-bred beagles: a retrospective study.

The beagle is a monoestric, nonseasonal breeder with a long estrous cycle. Owing to lengthy stages in individual phases of the estrous cycle, limited group size, and typical group assignment focused on homogenized body weight, dogs in the same stage of the cycle can be inadvertently assigned to one treatment group in toxicity studies potentially leading to erroneous interpretation. This study was conducted to better understand the frequency of the different stages of the cycle and review the associated histological features. Histologic sections of reproductive tissues were reviewed from 102 control dogs from thirty-two GLP studies. The average age of dogs at necropsy was 14.38 months, and the mean terminal body weight was 6.87 kg. Based on histological classification, fifty-five dogs were in anestrus, twenty-eight in diestrus, nine in estrus, five in proestrus, and five were classified as immature. Mean ovarian weights were higher in the estrus stage. This review indicates that more than 80% of the dogs in this study were in the anestrus-diestrus stage, and a small percentage of dogs were immature. Interpretation of drug-induced effects on the morphologic changes in the reproductive tract should be performed with due consideration given to the stage of the cycle and the potential for nonuniform assignment to drug treatment groups.