Impact of gavage dosing procedure and gastric content on adverse respiratory effects and mortality in rat toxicity studies

Safety assessment of a proprietary fermented soybean solution, Symbiota®, as an ingredient for use in foods and dietary supplements: Non-clinical studies and a randomized trial

A safety evaluation was performed of Symbiota®, which is made by a proprietary anaerobic fermentation process of soybean with multistrains of probiotics and a yeast. The battery of genotoxicity studies showed that Symbiota® has no genotoxic effects. Safety and tolerability were further assessed by acute or repeated dose 28- and 90-day rodent studies, and no alterations in clinical observations, ophthalmological examination, blood chemistry, urinalysis, or hematology were observed between the control group and the different dosing groups (1.5, 5, and 15 mL/kg/day). There were no adverse effects on specific tissues or organs in terms of weight and histopathology. Importantly, the Symbiota® treatment did not perturb hormones and other endocrine-related endpoints. Of note, the No-Observed-Adverse-Effect-Level was determined to be 15 mL/kg/day in rats. Moreover, a randomized, double-blind, placebo-controlled clinical trial was recently conducted with healthy volunteers who consumed 8 mL/day of placebo or Symbiota® for 8 weeks. Only mild adverse events were reported in both groups, and the blood chemistry and blood cell profiles were also similar between the two groups. In summary, this study concluded that the oral consumption of Symbiota® at 8 mL/day by the general population does not pose any human health concerns.

Evaluation of Parameters Which Influence Voluntary Ingestion of Supplements in Rats

Drug safety and efficacy studies frequently use oral gavage, but repetitive usage may cause problems. Administration through voluntary ingestion represents an opportunity for refinement. We aimed to develop a protocol for voluntary ingestion of gelatin-based supplements in rats, assessing the influence of age, sex, fasting (4 h), and additives (vanilla, VF; sucralose, S), and to test it in lactating dams. Three-week-old and 5-month-old Sprague-Dawley rats were placed individually in an empty cage containing a gelatin cube and trained daily (5 days/week), recording the day the whole cube was consumed (latency). Rats trained prior to gestation were offered a gelatin containing 250 mg/kg cocoa shell extract (CSE) during lactation. Rats that did not eat the cube after 8 training days were considered non-habituated, with a proportion similar in young males (7.1%), young females (11.1%), and adult females (10.3%), but significantly higher in adult males (39.3%). Excluding non-habituated rats, latency was 2-3 days, without differences between young and adult rats (p = 0.657) or between males and females (p = 0.189). VF or VF + S in the gelatin did not modify latency, while fasting significantly reduced it in females (p = 0.007) but not in males (p = 0.501). During lactation, trained females ate the CSE-gelatin within 1-5 min without litter problems. Conclusions: Acceptance of a gelatin-based supplement is negatively influenced by male sex, facilitated by fasting, and not modified by additives. Training is remembered after 2 months and does not interfere with lactation. Gelatin-based voluntary ingestion is suitable to administer drugs that need to pass through the digestive system, ensuring adequate dosage, and is important to detect non-habituated rats prior to the study. The current protocol may be implemented by training the rats in their own cage.

Impact of oral gavage technique of drug-containing microcontainers on the gastrointestinal transit and absorption in rats

Oral gavage is the most common way to administer drug formulations orally to rats. Yet, the technique applied and its influence on gastrointestinal (GI) transit receive little attention. This study aims to investigate the impact of three oral gavage techniques on GI transit and drug absorption utilizing microcontainers (MCs). The MCs were filled with paracetamol and BaSO₄ (1:1 w/w ratio), coated with Eudragit S100, and filled into size-9 gelatin capsules. An in vitro study confirmed the intactness of the coating, and the capsules were administered to rats with air, water, or a piston. X-ray imaging determined the locations of the MCs, and the corresponding plasma concentration of paracetamol established a correlation with the location. The fastest GI transit occurred with air-dosing, while water-dosing caused delayed gastric emptying for 3h with non-quantifiable paracetamol absorption. Piston-dosed MCs were retained in the stomach for up to 1h, though for 3h in one rat. Air-dosing caused discomfort and stress in rats, thus limiting its ethical and physiological relevance. Water-dosing confined its use due to delayed gastric emptying. In conclusion, the oral gavage technique affected the GI transit of MCs and, consequently, drug absorption. Piston-dosing appeared to be the superior dosing technique.

A quick and low-intensity method for oral administration to large numbers of mice: A possible alternative to oral gavage

Oral administration of medication to experimental animals is a cause of significant stress. When coupled to animals who are already under strenuous circumstances due to the disease being modelled, there is a significant risk for increased morbidity and mortality, thus influencing the results. Faced with these constraints, a low-intensity method for oral administration was developed, based solely on the natural behaviour of the animals and minimal conditioning, in which precise doses of medication were administered in a locally available, standard wheat cookie fragment, providing both a palatable vehicle and an absorbent matrix for the medication. Fast administration to large numbers of animals was thus achieved, safeguarding the animals' welfare and ensuring ease of handling. This method is a promising alternative to oral gavage in pre-clinical drug studies with laboratory mice.

Effects of 0.5% and 2.0% Sodium Lauryl Sulfate in Male CD-1 Mice From a 3-Month Oral Gavage Toxicity Study

The tolerability of single daily gavage doses of 0.5% or 2.0% (wt/vol) sodium lauryl sulfate (SLS) in 11- to 12-week-old male CD-1 mice was evaluated in a study of 3 months in duration. Live-phase, gross necropsy, and histopathologic parameters were evaluated. Mortality of 14% occurred in mice administered formulations containing SLS. Clinical observations in mice administered SLS included abnormal respiration (audible, irregular, and/or labored), swollen abdomen, rough haircoat, hunched appearance, and hypoactivity. Necropsy findings in mice administered SLS consisted of enlarged intestines containing abnormal contents with gas. There were no instances of mechanical gavage-related injury. Histologic evaluation of the respiratory tract revealed injury to the nasal passages and nasopharynx, including, but not limited to, inflammation, exudate, apoptosis/necrosis of epithelium, and atrophy of epithelium or olfactory nerves. Collectively, the data indicated that under the experimental conditions of our 3-month study in male CD-1 mice, once-daily gavage administration of vehicle formulations containing SLS at 0.5% or 2.0% resulted in nasal injury and 14% mortality supportive of gastroesophageal reflux. Sponsors utilizing formulations containing SLS in toxicity studies in CD-1 mice should exclude gastroesophageal reflux as a confounding factor in studies with morbidity or mortality associated with respiratory distress or evidence of aerophagia.

Toxicity of a methotrexate metronomic schedule in Wistar rats

Metronomic chemotherapy is a relevant strategy that uses low doses of antineoplastic drugs for sustained periods to control tumor growth, an alternative frequently utilized in veterinary patients. This work aimed to evaluate the toxic effects of a metronomic oral dose of methotrexate (MTX) for 45 days in tumor-free Wistar rats when compared with control animals. Clinical alterations, body weight, food, and water intake were monitored daily, and bone marrow suppression, hematological, biochemical, and histopathological analyses were performed at three points (days 30, 45, and 60). MTX-treated animals did not demonstrate severe systemic involvement. At 30 days, compared with control animals, MTX-treated animals showed significant leukocytosis (11.9 ± 2.3 vs. 7.8 ± 0.2 10⁶/μL; P < .05) and augmentation of immature myeloid populations from bone marrow (9.0 ± 0.8 vs. 6.5 ± 1.5%; P < .05), and at 60 days, treated animals showed significant neutrophilia (35.0 ± 11.0 vs. 23.00 ± 3.0%; P < .05), depletion of bone marrow lymphocytes (8.2 ± 0.7 vs. 11.5 ± 1.9%; P < .05), and immature myeloid populations (7.2 ± 0.7 vs. 8.3 ± 0.6%; P < .05). At a histopathological level, splenic hypoplasia and respiratory inflammatory lesions were significant when compared with control animals, presenting mild to moderate myelotoxicity, immune suppression, and associated clinical compromise that persisted beyond treatment withdrawal. This suggested that MTX metronomic toxicity should not be neglected owing to the observed residual side-effects and special care should be taken regarding myelosuppression.

Effects of Trio and Pair Breeding of Mice on Environmental Parameters and Nasal Pathology and Their Implications for Cage Change Frequency

According to the Guide, cage change frequencies must be considered when cage density requirements are exceeded. We monitored ammonia, carbon dioxide, cage wetness, health status, and breeding parameters of trio and pair breeding cages containing CD1 mice in ventilated and static microisolation caging (4 cages per condition) daily for approximately 6 wk. Minimum cage change frequencies for each condition were determined on the basis of performance data. At 3 d after cage change, static trio and pair cages had average ammonia levels of 74 and 38 ppm. Ventilated cages remained below the 25ppm threshold reported to be potentially deleterious for mice until at least day 7 after cage change. By 7 d after cage change, ammonia levels had risen to an average of 100 ppm and 64 ppm in static trio and pair cages and to 34 ppm and 20 ppm in ventilated trio and pair cages, respectively. Ammonia levels in ventilated cages continued to rise slowly through day 14 after cage change. CO₂ levels exceeded 5000 ppm in all groups at 2 d after cage change. Pair breeders in ventilated cages took the longest-10 to 14 d-to reach cage wetness threshold scores. On day 7, pups in trio static cages were noted to have decreased and squinted eyes, whereas in ventilated cages containing trios and pairs, these clinical signs were rare to absent. Histologically, there was an increasing incidence and severity of nasal lesions in weanlings with increasing housing density and decreasing ventilation, consistent with nasal epithelial toxicity. Given these parameters, we concluded that under the current husbandry conditions, it may be necessary to change breeders in static cages more frequently than every 7 d. Additional studies are necessary to evaluate the effects of more frequent cage changes on reproductive parameters, given that cage changing is stressful for mice and affects breeding results.

Preclinical toxicity evaluation of JD5037, a peripherally restricted CB1 receptor inverse agonist, in rats and dogs for treatment of nonalcoholic steatohepatitis

JD5037 is a novel peripherally restricted CB₁ receptor (CB₁R) inverse agonist being developed for the treatment of visceral obesity and its metabolic complications, including nonalcoholic fatty liver disease and dyslipidemia. JD5037 was administered by oral gavage at 10, 40, and 150 mg/kg/day dose levels for up to 34 days to Sprague Dawley rats, and at 5, 20, and 75 mg/kg/day dose levels for 28 consecutive days to Beagle dogs. In rats, higher incidences of stereotypic behaviors were observed in 10 mg/kg females and 40 mg/kg males, and slower responses for reflex and sensory tests were observed only in males at 10 and 40 mg/kg during neurobehavioral testing. Sporadic minimal incidences of decreased activity (males) and seizures (both sexes) were observed in rats during daily clinical observations, without any clear dose-relationship. Male dogs at 75 mg/kg during treatment period, but not recovery period, had an increased incidence of gut associated lymphoid tissue hyperplasia and inflammation in the intestine. In both species, highest dose resulted in lower AUCs indicative of non-linear kinetics. Free access to food increased the plasma AUC_∞ by ~4.5-fold at 20 mg/kg in dogs, suggesting presence of food may help in systemic absorption of JD5037 in dogs. Based on the study results, 150 mg/kg/day in rats, and 20 and 75 mg/kg/day doses in male and female dogs, respectively, were determined to be the no-observed-adverse-effect-levels (NOAELs).

Reproductive and developmental toxicity screening of polyhexamethylene guanidine phosphate by oral gavage in rats

Polyhexamethylene guanidine phosphate (PHMG-P) has effective antimicrobial activity against various microorganisms and has been widely used as a biocide in commercial products. However, its use as a humidifier disinfectant has provoked fatal idiopathic lung disease in South Korea, especially in pregnant or postpartum women and their young children. PHMG-P-related toxicological studies of reproduction and development in experimental animals have not been identified, and thus, we investigated the potential effects of early-stage oral exposure to PHMG-P by assessing its toxicological properties. PHMG-P was repeatedly administered by oral gavage at dose levels of 0, 13, 40 and 120 mg/kg to Sprague-Dawley rats during the pre-mating, mating, gestation and early lactation periods, and then general systemic and reproductive/developmental toxicities were investigated. At 120 mg/kg, PHMG-P-related toxicities including subdued behavior, thin appearance, decreased body weight, decreased food consumption and decreased F1 pup body weight were observed. Based on the results of this study, the no-observed-adverse-effect levels (NOAELs) of PHMG-P for both general systemic effects and development are considered to be 40 mg/kg/day.

The Endothelin-A Receptor Antagonist Zibotentan Induces Damage to the Nasal Olfactory Epithelium Possibly Mediated in Part through Type 2 Innate Lymphoid Cells

Zibotentan, an endothelin-A receptor antagonist, has been used in the treatment of various cardiovascular disorders and neoplasia. Castrated athymic nude mice receiving zibotentan for a preclinical xenograft efficacy study experienced weight loss, gastrointestinal bloat, and the presence of an audible respiratory click. Human side effects have been reported in the nasal cavity, so we hypothesized that the nasal cavity is a target for toxicity in mice receiving zibotentan. Lesions in the nasal cavity predominantly targeted olfactory epithelium in treated mice and were more pronounced in castrated animals. Minimal lesions were present in vehicle control animals, which suggested possible gavage-related reflux injury. The incidence, distribution, and morphology of lesions suggested direct exposure to the nasal mucosa and a possible systemic effect targeting the olfactory epithelium, driven by a type 2 immune response, with group 2 innate lymphoid cell involvement. Severe nasal lesions may have resulted in recurrent upper airway obstruction, leading to aerophagia and associated clinical morbidity. These data show the nasal cavity is a target of zibotentan when given by gavage in athymic nude mice, and such unanticipated and off-target effects could impact interpretation of research results and animal health in preclinical studies.

Thymine DNA glycosylase as a novel target for melanoma

Melanoma is an aggressive neoplasm with increasing incidence that is classified by the NCI as a recalcitrant cancer, i.e., a cancer with poor prognosis, lacking progress in diagnosis and treatment. In addition to conventional therapy, melanoma treatment is currently based on targeting the BRAF/MEK/ERK signaling pathway and immune checkpoints. As drug resistance remains a major obstacle to treatment success, advanced therapeutic approaches based on novel targets are still urgently needed. We reasoned that the base excision repair enzyme thymine DNA glycosylase (TDG) could be such a target for its dual role in safeguarding the genome and the epigenome, by performing the last of the multiple steps in DNA demethylation. Here we show that TDG knockdown in melanoma cell lines causes cell cycle arrest, senescence, and death by mitotic alterations; alters the transcriptome and methylome; and impairs xenograft tumor formation. Importantly, untransformed melanocytes are minimally affected by TDG knockdown, and adult mice with conditional knockout of Tdg are viable. Candidate TDG inhibitors, identified through a high-throughput fluorescence-based screen, reduced viability and clonogenic capacity of melanoma cell lines and increased cellular levels of 5-carboxylcytosine, the last intermediate in DNA demethylation, indicating successful on-target activity. These findings suggest that TDG may provide critical functions specific to cancer cells that make it a highly suitable anti-melanoma drug target. By potentially disrupting both DNA repair and the epigenetic state, targeting TDG may represent a completely new approach to melanoma therapy.

Exudative Inflammatory Lesions in the Nasal Cavities of the 26-Week Tg.rasH2 Mice Oral Gavage Carcinogenicity Studies

Three levels of nasal cavity sections (anterior, middle, and most posterior) are routinely examined as protocol required tissues in our 26-week carcinogenicity studies involving Tg.rasH2 mice. Exudative inflammation of the nasal cavity was noted in the most posterior section of both males and females that were administered vehicle and/or test article via oral gavage, particularly when the vehicle and/or test article had irritant properties, was in the form of a salt, had a low pH, and/or was viscous. The exudative inflammatory lesion was characterized by the presence of eosinophilic proteinaceous fluid, fibrin, mucin, sloughed cells, and degenerate neutrophils within the nasal cavities. In lesions of increased severity, there was often degeneration, necrosis, and erosion of the underlying mucosa. Often, there was hyperplasia as well as squamous metaplasia of the mucosa. Retrospective analysis of our data, involving thirty-two 26-week Tg.rasH2 carcinogenicity studies, revealed that despite the presence of these exudative inflammatory changes with degeneration, necrosis, and mucosal hyperplasia, progression to tumor formation in the nasal cavities was rare and the incidence of nasal tumors was comparable in animals with or without exudative inflammatory lesions.

Acute and subchronic oral toxicity studies of hydrogenated curcuminoid formulation 'CuroWhite' in rats

Hydrogenated curcuminoids are the major metabolites of the curcumin and ‘CuroWhite’ is a unique blend of hydrogenated curcuminoids encapsulated with β-cyclodextrin. There is no particular scientific evidence for the toxicology regarding the hydrogenated curcuminoids, so the present work reports the results of the studies investigating the acute (single dose) and subchronic (repeatedly 90 days) oral toxicity of the CuroWhite in Sprague Dawley rats. For acute oral toxicity testing a sighting study was conducted on female rats in a sequential manner to allow selection of the appropriate starting dose for the main study. In acute toxicity, the dosage was 2000 mg/kg body weight for four female rats. In the sub-chronic study, rats of both sexes divided into three groups and each group were orally treated with CuroWhite daily at 200, 400 and 800 mg/kg for 90 days consecutively. No evidence of treatment related toxicity was detected during the study. Thus, data analysis of mortality, body weight gain, feed consumption, clinical observations, hematology, organ weights and histopathological findings did not show significant differences between control and treated groups. It is concluded that CuroWhite orally administered to rats was safe and no drug-related toxicity was detected even at the highest doses investigated in both acute (2000 mg/kg) and subchronic toxicity (200, 400 and 800 mg/kg) studies. Based on the study, the no-observed-adverse-effect level (NOAEL) value could be considered as 800 mg/kg per day in both the sexes. These results indicate that CuroWhite can be generally regarded as safe for use as a food additive.

The sub-chronic oral toxicity of dearomatized hydrocarbon solvents in Sprague-Dawley rats

Dearomatized hydrocarbon solvents in the C9-C14 aliphatic carbon number range were developed as alternatives to traditional solvents such as mineral spirits, but with lower aromatic content. Previous subchronic toxicity studies (both published and unpublished) have shown minimal to no systemic effects with exposure to dearomatized solvents, with the exception of rat-specific renal effects that have no relevance to humans. In this study, Sprague-Dawley rats were exposed to 0, 500, 2500 and 5000mg/kg/day of a C10-C13 dearomatized solvent for 90days by oral gavage. Liver enlargement and centrilobular hypertrophy were observed in all treated groups but were considered adaptive consequences of hydrocarbon-induced microsomal enzyme induction. Clinical chemistry data showed elevations of alanine aminotransferase (ALT), gamma glutamyltransferase (GGT) and total bilirubin in mid (ALT alone) and high dose groups, suggesting potential hepatobiliary effects with high dose exposure. Increased absolute kidney weight changes were restricted to male rats and associated with renal lesions indicative of alpha-2u globulin-mediated nephropathy. One limitation of the NOAEL/LOAEL approach in selecting points of departure for exposure limits is its dependence on dose selection/study design. Hence, a more robust approach that incorporates all data points on the dose-response curve, such as bench mark modeling, is preferred. Overall, benchmark dose analysis estimated a BMDL of 1857mg/kg/day based on increased serum ALT. This value is consistent with studies of similar hydrocarbon substances showing a lack of systemic effects at doses up to 1000mg/kg/day in the same rat strain.

Pulmonary edema due to oral gavage in a toxicological study related to aquaporin-1, -4 and -5 expression

A one-time oral gavage can be enough to cause of alveologenic edema with higher expression of AQP-1 and -4 than that with repeated-dose oral gavage, which caused both profound perivascular edema and hydrostatic pressure edema, while AQP-5 was similarly expressed. The alteration of AQPs expression was probably related to alveolar fluid clearance across the alveolar and bronchiolar epithelium in different stages of lung injury. The results clarified the type of lung edema in acute and sub-chronic toxicity studies without treatment related effect of tested material. The pathogenesis of pulmonary edema due to oral gavage toxicological study is associated with the cellular immune response to the reflux materials. Mast cell and leukocyte accumulation may contribute to increase vascular permeability leading to permeability edema. The increase in alveolar septum epithelium, perivascular and peribronchial cuffing, accumulation alveolar lipid containing macrophage and medial hyperplasia of the pulmonary artery might have been caused to increase airway resistance, which resulted in hydrostatic pressure edema.

The effects of repeated oral gavage on the health of male CD-1 mice

Oral gavage is a widely used method for administering substances to animals in pharmacological and toxicological studies. The authors evaluated whether oral gavage causes behavioral indicators of stress, increased mortality rate, alterations in food and water consumption and body weight or histological lesions in CD-1 mice. Gavage was carried out once per d for 5 d per week over 6 consecutive weeks. The mortality rate of mice in this study was 15%. Mice subjected to gavage did not undergo changes in food or water consumption during the study, and their mean body weights and relative organ weights were similar to those of mice in the control group. Serum cortisol levels at the time of euthanasia in mice in both groups were within the normal range. Histopathology showed acute esophagitis and pleurisy, indicative of perforation of the esophagus, in the two mice that died but no abnormalities in the other mice. The results suggest that animal stress and mortality related to oral gavage can be minimized when the procedure is carried out by an experienced technician.