Safety of an oral combination of moxidectin, afoxolaner, and pyrantel pamoate in dogs.

NexGard®PLUS (moxidectin, afoxolaner, and pyrantel pamoate), is an oral combination product for dogs indicated for the prevention of heartworm disease, the treatment and prevention of flea and tick infestations, and the treatment of gastro-intestinal nematode infections. The safety of this product in dogs was evaluated in three studies. Study #1 was a margin-of-safety study conducted in puppies, dosed six times at 28-day intervals at 1X, 3X, or 5X multiples of the maximum exposure dose (equivalent to 24 µg/kg moxidectin, 5 mg/kg afoxolaner, and 10 mg/kg pyrantel). In Study #2, the product was administered to ABCB1-deficient collie dogs at a 1X dose twice at a 28-day interval, and at a 3X or 5X dose once. Study #3 evaluated the safety of the product at 1X and 3X doses administered three times at 4-week intervals, to dogs harboring adult Dirofilaria immitis. In the three studies, the safety was evaluated on the basis of multiple clinical observations and physical examinations, including a complete assessment of toxicity to macrocyclic lactones, and on comprehensive clinical and anatomical pathology evaluations in Study #1. No clinically significant combination product-related effects were observed in any of the three studies. No signs of macrocyclic lactone toxicity were observed in the ABCB1-deficient collie dogs. Some mild and self-resolving instances of emesis or diarrhea were occasionally observed in the 3X and 5X dosed dogs. NexGard® PLUS was demonstrated to be safe following multiple administrations in puppies, in ABCB1-deficient collie dogs, and in microfilaremic dogs infected with adult D. immitis.

Evaluation of the chronic toxicity and carcinogenicity of perfluorohexanoic acid (PFHxA) in Sprague-Dawley rats.

Perfluorohexanoic acid (PFHxA), a 6-carbon perfluoroalkyl (C6; CAS # 307-24-4), has been proposed as a replacement for the commonly used 8-carbon perfluoroalkyls: perfluorooctanoic acid and perfluorooctane sulfonate. PFHxA is not currently a commercial product but rather the ultimate degradation product of C6 fluorotelomer used to make C6 fluorotelomer acrylate polymers. It can be expected that, to a greater or lesser extent, the environmental loading of PFHxA will increase, as C6 fluorotelomer acrylate treatments are used and waste is generated. This article reports on a chronic study (duration 104 weeks) that was performed to evaluate the possible toxicologic and carcinogenic effects of PFHxA in gavage (daily gavage, 7 days per week) treated male and female Sprague-Dawley (SD) rats. In the current study, dosage levels of 0, 2.5, 15, and 100 mg/kg/day of PFHxA (males) and 5, 30, and 200 mg/kg/day of PFHxA (females) were selected based on a previous subchronic investigation. No effects on body weights, food consumption, a functional observational battery, or motor activity were observed after exposure to PFHxA. While no difference in survival rates in males was seen, a dose-dependent decrease in survival in PFHxA-treated female rats was observed. Hematology and serum chemistry were unaffected by PFHxA. PFHxA-related histologic changes were noted in the kidneys of the 200-mg/kg/day group females. Finally, there was no evidence that PFHxA was tumorigenic in male or female SD rats at any of the dosage levels examined.

Renal histopathology in toxicity and carcinogenicity studies with tert-butyl alcohol administered in drinking water to F344 rats: a pathology working group review and re-evaluation.

An independent Pathology Working Group (PWG) re-evaluated the kidney changes in National Toxicology Program (NTP) toxicology/carcinogenicity studies of tert-butyl alcohol (TBA) in F344/N rats to determine possible mode(s) of action underlying renal tubule tumors in male rats at 2-years. In the 13-week study, the PWG confirmed that the normal pattern of round hyaline droplets in proximal convoluted tubules was replaced by angular droplet accumulation, and identified precursors of granular casts in the outer medulla, changes typical of alpha(2u)-globulin (α(2u)-g) nephropathy. In the 2-year study, the PWG confirmed the NTP observation of increased renal tubule tumors in treated male groups. Linear papillary mineralization, another hallmark of the α(2u)-g pathway was present only in treated male rats. Chronic progressive nephropathy (CPN) was exacerbated in high-dose males and females, with a relationship between advanced grades of CPN and renal tumor occurrence. Hyperplasia of the papilla lining was a component of CPN in both sexes, but there was no pelvic urothelial hyperplasia. High-dose females showed no TBA-related nephrotoxicity. The PWG concluded that both α(2u)-g nephropathy and exacerbated CPN modes of action were operative in TBA renal tumorigenicity in male rats, neither of which has relevance for human cancer risk.

Histopathologic changes in the kidneys of male F344 rats from a 2-year inhalation carcinogenicity study of tetrahydrofuran: a pathology working group review and re-evaluation.

Risk evaluation and hazard classification for tetrahydrofuran (THF) is based partly on the incidences of renal tumors in male F344/N rats reported in a 2-year carcinogenicity study by the National Toxicology Program (NTP). A Pathology Working Group (PWG) was commissioned to conduct an independent review of the kidney slides from this bioassay (along with two subchronic studies) to assess renal changes in light of recent scientific work on pathogenesis of pre-neoplastic and neoplastic lesions in rat kidney. PWG pathologists confirmed the NTP assessment that adenomas were non-statistically increased in animals exposed to the highest level of THF. However, when pre-neoplastic and neoplastic lesions were combined, there was no difference between control and THF-exposed groups. Also, the majority of these proliferative lesions were in rats with severe chronic progressive nephropathy (CPN). Accordingly, the PWG concluded that renal lesions in the control and THF-exposed groups resulted primarily from regenerative processes associated with advanced CPN. Based on an alpha(2u)-globulin/hyaline droplet response observed in a 4-week study with THF, the PWG could not exclude the possibility of both advanced CPN and low-grade alpha2u-g nephropathy contributing to the renal proliferative lesions developing chronically in high-dose males. Neither condition has a pathologic counterpart in humans.

Safety assessment of heat-sterilized green tea catechin preparation: a 6-month repeat-dose study in rats.

Evidence suggests that the purported health benefits associated with green tea consumption are related to tea catechins. In the present study, potential adverse effects of a standardized heat-sterilized green tea catechin (GTC-H) preparation was investigated following gavage administration to rats at doses of 0, 120, 400, 1200 mg/kg/day for 6 months. A decaffeinated high-dose group (1200 mg/kg/day) (GTC-HDC), was included for comparison. A possibly test article-related clinical finding of intermittent increased activity was noted in the 400 and 1200 mg/kg/day GTC-H groups, but was not considered to be adverse. Lower body weight gains without any decrease in food consumption were noted in the high-dose (1200 mg/kg/day)-treated GTC-H and GTC-HDC females. In the high-dose male GTC-H group, a lower total motor activity count for the 60-min session was noted prior to dosing at the study week 25 evaluations compared to the control group. Similar changes were not observed in the GTC-HDC group. Based on the results of this study, the no-observed-adverse-effect level (NOAEL) for GTC-H was 1200 mg/kg/day for males, the highest dose tested, and 400mg/kg/day for females based on reduced body weight gains. The NOAEL for GTC-HDC was 1200 mg/kg/day for males and could not be determined in females.

Spontaneous hibernomas in Sprague-Dawley rats.

Hibernomas are rare neoplasms originating in brown adipose tissue of humans and other animal species, including laboratory animals. Background incidence values for these tumors in all common strains of laboratory rats are generally accepted as being <0.1%. Between April 2000 and April 2007, however, sixty-two hibernomas (an overall prevalence of 3.52%) were observed in a total of 1760 Sprague-Dawley rats assigned to three carcinogenesis bioassays at two separate research laboratories. All rats were obtained from Charles River's breeding facilities in either Portage, Michigan, or Raleigh, North Carolina. Tumors (twenty-nine benign and thirty-three malignant) were randomly distributed among test article-treated and control groups and were considered to be spontaneous. Most tumors originated in the thoracic cavity, and they were usually described as soft, mottled to tan masses with nodular to lobulated profiles. Immunohistochemical procedures for uncoupling protein 1 (UCP1) confirmed brown adipose tissue as the site of origin rather than white fat. The marked increase in hibernomas in our studies suggests that greater numbers of spontaneous hibernomas may be sporadically encountered in future carcinogenesis studies with Sprague-Dawley rats. The increased potential for hibernomas to arise as spontaneous neoplasms has important implications in studies involving peroxisome proliferators-activated receptor (PPAR) drugs, lipophilic environmental chemicals (e.g., polychlorinated biphenyls), and other molecules or physiologic processes (e.g., beta-adrenergic stimulation) that may target brown fat adipocytes.

A 24-month dietary carcinogenicity study of DAG in mice.

This study evaluated the possible carcinogenic effects of DAG (diacylglycerol) oil when given in the diet at levels up to 6.0% for 24 months to mice. Dietary fat was provided by DAG and/or the control article, TG (triacylglycerol oil). Dietary concentrations (% DAG/% TG) were 0%/6.0% (TG control), 1.5%/4.5%, 3.0%/3.0%, and 6.0%/0%. An additional control group received the standard rodent diet (fat content 4.5%). The clinical condition of the animals, ophthalmic findings, palpable mass occurrence, body weights and gross and histopathologic findings were unaffected by DAG in comparison to TG. The findings in DAG-treated groups were no different than those observed in the TG control group. The standard basal diet had 4.5% fat content. Both TG and/or DAG, when presented separately or together in the diet at a total fat level of 6.0%, resulted in some differences relative to the basal diet control (lower survival, higher body weights, lower food consumption, and higher incidences of macroscopic and microscopic findings), presumably related to the higher dietary fat content and/or the semi-purified diet. However, these parameters were similar in groups fed a diet with 6.0% dietary fat that was either DAG or TG. Thus, DAG at dietary concentrations up to 6.0% for 24 months produced no signs of systemic toxicity and had no effect on the incidence of neoplastic findings.

A 24-month dietary carcinogenicity study of DAG (diacylglycerol) in rats.

Toxicologic and carcinogenic effects of DAG (diacylglycerol) oil, administered in diet for 24 months to Crl:CD((R))(SD)-IGS BR rats, were evaluated using diet-restricted and ad libitum-fed groups. All dietary fat (consistently 5.5%) was provided by DAG and/or the control article, TG (triacylglycerol) oil. Dietary concentrations (% DAG/% TG) were 0%/5.5%, 1%/4.5%, 2.75%/2.75% and 5.5%/0%. Separate groups were fed the 0%/5.5% and 5.5%/0% diets ad libitum. Another group received the standard rodent diet (fat content 4.5%) on the restricted feeding regimen. Clinical condition, ophthalmic findings, palpable mass occurrence, body composition, clinical pathology parameters and incidence of neoplastic lesions were unaffected by DAG in comparison to TG. Groups fed the 5.5% (DAG and/or TG) fat diet when compared to the 4.5% fat diet group displayed lower survival, higher body weights, organ weights, percent body fat, higher fat-related serum chemistry parameters, incidence of microscopic changes in the heart, kidneys, liver, bone marrow, spleen, and incidences of pituitary and mammary gland neoplasms. Parameters more affected in all the ad libitum groups than in the restricted diet groups (regardless of test article) fed the same diet included survival, body weights, body fat, fat-related serum chemistry parameters, and incidences of heart, kidney and liver microscopic changes. However, the DAG and TG ad libitum-fed groups were not different from one another. Thus, DAG-treated animals had no higher risk of carcinogenic effects than rats fed on similar feeding regimens with a diet in which all dietary fat came from TG.

The multidrug resistance-associated protein 1 transports methoxychlor and protects the seminiferous epithelium from injury.

We examined the ability of the multidrug resistance-associated protein 1 (MRP1/ABCC1) to transport pesticides, as this transporter mediates the cellular efflux of a variety of xenobiotics, typically as glucuronide, sulfate, or glutathione conjugates. NIH3T3 cells stably expressing MRP1 were 3.37-fold more resistant to the toxicity of fenitrothion, 3.12-fold more resistant to chlorpropham, and 2.5-fold more resistant to methoxychlor, a pesticide with estrogenic and anti-androgenic metabolites. The cells expressing MRP1 also eliminated methoxychlor two times more rapidly than their mock-transfected counterparts. We then examined whether mrp1 expression could alter the toxicity of methoxychlor in vivo using male FVB/mrp1 knockout mice (FVB/mrp1-/-). Both control and knockout mice were fed 25 mg/kg methoxychlor in honey for 39 days, and its effects on testicular morphology were examined. Methoxychlor treatment did not significantly affect testicular morphology in the FVB mice, but markedly reduced the number of developing spermatocytes in the FVB/mrp1-/- mice. These results suggest that MRPI may play a role in protecting the seminiferous tubules from methoxychlor-induced damage.