Time-Course of Transcriptomic Change in the Lungs of F344 Rats Repeatedly Exposed to a Multiwalled Carbon Nanotube in a 2-Year Test

Despite intensive toxicological studies of carbon nanotubes (CNTs) over the last two decades, only a few studies have demonstrated their pulmonary carcinogenicities in chronic animal experiments, and the underlying molecular mechanisms are still unclear. To obtain molecular insights into CNT-induced lung carcinogenicity, we performed a transcriptomic analysis using a set of lung tissues collected from rats in a 2-year study, in which lung tumors were induced by repeated intratracheal instillations of a multiwalled carbon nanotube, MWNT-7. The RNA-seq-based transcriptome identified a large number of significantly differentially expressed genes at Year 0.5, Year 1, and Year 2. Ingenuity Pathway Analysis revealed that macrophage-elicited signaling pathways such as phagocytosis, acute phase response, and Toll-like receptor signaling were activated throughout the experimental period. At Year 2, cancer-related pathways including ERBB signaling and some axonal guidance signaling pathways such as EphB4 signaling were perturbed. qRT-PCR and immunohistochemistry indicated that several key molecules such as Osteopontin/Spp1, Hmox1, Mmp12, and ERBB2 were markedly altered and/or localized in the preneoplastic lesions, suggesting their participation in the induction of lung cancer. Our findings support a scenario of inflammation-induced carcinogenesis and contribute to a better understanding of the molecular mechanism of MWCNT carcinogenicity.

N-methylformamide induces multiple organ toxicity in Fischer 344 rats

N-Methylformamide (NMF) is a widely used chemical (CAS No.: 123-39-7) in several industries and its usage is continuously increasing. However, studies for NMF have been focused on hepatotoxicity from now. Its toxicity profile has not yet been established owing to limited toxicity data. Therefore, we evaluated systemic toxicity via NMF inhalation. We exposed 0, 30, 100, and 300 ppm NMF to Fischer 344 rats for 6 h/day, 5 days a week for 2 weeks. Clinical signs, body weights, food consumption, hematologic parameters, serum chemistry measurements, organ weights, necropsy, and histopathology were performed. Two females exposed to 300 ppm NMF died during exposure period. Decrease of food consumption and body weight in both sexes exposed to 300 ppm in females exposed to 100 ppm were noted during exposure period. Increased RBC and HGB were noted in females exposed to 300 ppm. A decrease in the levels of ALP and K and increase in the levels of TCHO and Na were observed in both sexes exposed to 300 and 100 ppm. Increased levels of ALT, AST, BUN and decreased levels of TP, ALB, Ca were observed in females exposed to 300 and 100 ppm. The relative liver weight was elevated in both sexes exposed to 300 and 100 ppm NMF. Hypertrophy in the liver and submandibular glands and nasal cavity injuries were noted in both sexes exposed to 300 and 100 ppm NMF. Tubular basophilia of the kidneys were noted in females exposed to 300 ppm NMF. We revealed that NMF affect several organs including the kidneys not only the liver and NMF-related toxicity is predominant in female rats. These results could contribute to the development of NMF toxicity profile and may help in developing strategies for the control of occupational environmental hazards related to NMF.

Characterizing the gut microbiome changes with aging in a novel Alzheimer's disease rat model

Alzheimer's disease (AD) is one of the most devastating diseases currently in the world with no effective treatments. There is increasing evidence that the gut microbiome plays a role in AD. Here we set out to study the age-related changes in the microbiome of the Tgf344-AD rats. We performed 16S ribosomal RNA sequencing on the fecal samples of male rats at 14 and 20 months of age. We found the Tgf344-AD rats to have decreased microbial diversity compared to controls at 14 months of age and this was found to be opposite at 20 months of age. Interestingly, we found a distinctive shift in the microbial community structure of the rats with aging along with changes in the microbiota composition. Some of the observed changes in the Tgf344AD rats were in the genera Bifidobacterium, Ruminococcus, Parasutterella, Lachnoclostridium and Butyricicoccus. Other age-related changes occuring in both the Tgf344-AD and WT control rats were decreases in Enterohaldus, Escherichia Shigella, Rothia and increase in Turicibacter and Clostrium_senso_stricto. Our study has shown that gut microbiota changes occurs in this Alzheimer's disease rat model.

Genetic Predisposition to Hepatocellular Carcinoma

Liver preneoplastic and neoplastic lesions of the genetically susceptible F344 and resistant BN rats cluster, respectively, with human HCC with better (HCCB) and poorer prognosis (HCCP); therefore, they represent a valid model to study the molecular alterations determining the genetic predisposition to HCC and the response to therapy. The ubiquitin-mediated proteolysis of ERK-inhibitor DUSP1, which characterizes HCC progression, favors the unrestrained ERK activity. DUSP1 represents a valuable prognostic marker, and ERK, CKS1, or SKP2 are potential therapeutic targets for human HCC. In DN (dysplastic nodule) and HCC of F344 rats and human HCCP, DUSP1 downregulation and ERK1/2 overexpression sustain SKP2-CKS1 activity through FOXM1, the expression of which is associated with a susceptible phenotype. SAM-methyl-transferase reactions and SAM/SAH ratio are regulated by GNMT. In addition, GNMT binds to CYP1A, PARP1, and NFKB and PREX2 gene promoters. MYBL2 upregulation deregulates cell cycle and induces the progression of premalignant and malignant liver. During HCC progression, the MYBL2 transcription factor positively correlates with cells proliferation and microvessel density, while it is negatively correlated to apoptosis. Hierarchical supervised analysis, regarding 6132 genes common to human and rat liver, showed a gene expression pattern common to normal liver of both strains and BN nodules, and a second pattern is observed in F344 nodules and HCC of both strains. Comparative genetics studies showed that DNs of BN rats cluster with human HCCB, while F344 DNs and HCCs cluster with HCCP.

A 90-day subchronic toxicity study of Myrrh in F344 rats

Myrrh is a flavoring agent and food additive. Here, we performed a subchronic toxicity study of Myrrh in male and female F344 rats by feeding at 5,000, 15,000 and 50,000 ppm for 90 days. No deaths or clinical signs were observed. Suppression of body weight gain was observed from the early phase of administration in both males and females in the 50,000 ppm group. Because there were no obvious changes in food intake in any of the Myrrh groups compared with the control group, suppression of body weight gain was considered an adverse effect of Myrrh. Hematology and serum biochemistry parameters with significant changes observed in the Myrrh groups were considered to have no toxicological significance. We observed a significant increase in relative kidney weight in male rats treated with 50,000 ppm Myrrh; this effect was considered to be related to the appearance of hyaline droplets in the epithelium of the proximal tubules histopathologically observed in this group. Immunohistochemical staining with anti-α_2u-globulin antibodies suggested that these hyaline droplets were caused by factors other than α_2u-globulin deposition. Thus, the no-observed-adverse-effect level of Myrrh was determined to be 15,000 ppm (males: 0.85 g/kg/day, females: 0.95 g/kg/day).

A 90-day subchronic toxicity study of 5-methyl-2-phenyl-2-hexenal in F344 rats

5-Methyl-2-phenyl-2-hexenal (MPH) has been used as a flavoring agent. In the present study, we performed a subchronic toxicity study in male and female F344 rats with oral administration of MPH by gavage at 0, 8, 24 and 70 mg/kg body weight (BW)/day for 90 days. No mortality or clinical signs were observed during the experimental period. Body weight and food consumption for all treated groups of both sexes were essentially the same as for the respective control groups. Hematologic examination demonstrated significant decreases in monocyte counts for females given 24 and 70 mg/kg BW/day. However, these changes were not substantial and no related histopathological changes were observed, suggesting that these changes were not toxicologically significant. Among organ weights, the absolute and/or relative weights of testes and liver were significantly increased in the 70 mg/kg BW/day groups of males and females, respectively, but no related histopathological changes were observed, suggesting that these changes did not reflect adverse effects. In addition, no treatment-related histopathological changes were observed for any of the tissues examined. Based on the overall data, the no-observed-adverse-effect level (NOAEL) for MPH was determined to be 70 mg/kg BW/day, the highest dose tested, in both male and female rats.

Role of γ-H2AX as a biomarker for detection of bladder carcinogens in F344 rats

Phosphorylation of histone H2AX at serine 139 (γ-H2AX) is known to be induced by direct DNA damage or cellular metabolic imbalances and malfunctions. Previous studies have reported that γ-H2AX is a useful biomarker for early detection of genotoxic bladder carcinogens in rats. The purpose of the present study was to determine the role of γ-H2AX as a biomarker for detection of non-genotoxic bladder carcinogens in rats. Six-week-old male F344 rats were treated with 15 different chemicals for 4 weeks. Immunohistochemical analyses revealed that all three genotoxic bladder carcinogens and six out of seven non-genotoxic bladder carcinogens significantly increased γ-H2AX formation in the bladder urothelium of rats. In addition, four out of five rat bladder noncarcinogens did not increase γ-H2AX formation in the bladder urothelium regardless of genotoxicity. These results suggest that γ-H2AX is a useful biomarker for detection of both genotoxic and non-genotoxic bladder carcinogens in rats.

A 90-day repeated oral dose toxicity study of four stereoisomers of 2,4-dimethyl-4-phenyltetrahydrofuran, a synthetic flavoring substance, in F344 rats

2,4-Dimethyl-4-phenyltetrahydrofuran (CAS no. 82461-14-1) is a food additive used as a synthetic flavoring substance. To investigate the toxicological properties and determine the no-observed-adverse-effect level (NOAEL), a 90-day repeated oral dose toxicity study of 2,4-dimethyl-4-phenyltetrahydrofuran containing four stereoisomers was conducted in F344 rats at doses of 0, 6, 24, and 96 mg/kg body weight (BW)/day. No mortality or abnormal clinical signs related to treatment in any group was observed. At a dose of 96 mg/kg BW, fluctuated serum total protein and total cholesterol and increased absolute and relative liver weights and relative kidney weights were observed in both sexes. Increased serum albumin in males and decreased Na and Cl in females were also observed. On histopathological assessment, at a dose of 96 mg/kg BW, diffuse hepatocellular hypertrophy in the liver in both sexes and tubular regeneration with scattered proximal tubular degeneration and/or necrosis throughout the cortex in the kidney in males were detected. Based on these findings, the NOAEL for 2,4-dimethyl-4-phenyltetrahydrofuran used in the current study was found to be 24 mg/kg BW/day for both sexes.

Target-specific micronucleus induction by colon carcinogens: 2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine and 1,2-dimethylhydrazine

Genotoxicity occurring at the target organs of carcinogenesis is important for understanding the mechanisms of chemical carcinogenicity and also for setting of threshold estimation. In vivo gene mutations have been evaluated by transgenic animal models in which any organ can be targeted; however, the methodologies that have been applied to assess chromosomal aberrations including micronucleus induction, are organ restricted, (often to bone marrow hematopoietic cells, as a common example). For food and food-related chemicals, the digestive tract is the important target organ as it is the organ of first contact. In the present study, we used 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) and 1,2-dimethylhydrazine (DMH) as model chemicals of carcinogens primarily targeting the colon. We evaluated the applicability of colon cells and hepatocytes, together with bone marrow cells, in the micronucleus assay. Both model chemicals induced micronuclei in the colon, which is the target organ of these carcinogens, after short- and long-term treatment(s). The results demonstrate the target specificity of micronucleus induction and the assay using organs other than bone marrow will play an important role in understanding the mechanism of carcinogenicity and predicting new carcinogenic agents.

Dietary acrylamide exposure in F344 rats and colon tumor-bearing nude nu/nu mice: Dataset of gene expression of cancer pathway targets and methylation status of tumor suppressor genes in colon mucosae and tumors

Dietary acrylamide, a thermally induced food contaminant, at a level (2 mg/kg diet) typifying higher occurrence in certain food products - is neither an independent carcinogen nor a tumor promoter in the colon. This is evidenced by our previous studies using the medium-term azoxymethane (AOM)-induced colon tumorigenesis assay in F344 rats and the human colon tumor xenograft model in athymic nude (nu/nu) mice (https://doi.org/10.1371/journal.pone.0073916) [1]. In addition, we found that acrylamide may act as a colon co-carcinogen in association with a known carcinogen (AOM) in F344 rats. Furthermore, exposure to acrylamide at 2 mg/kg in the diet was not associated with any toxicologically relevant changes in clinical biochemistry, hematology, and apical endpoints in healthy rats (exposed only to saline injections) (https://doi.org/10.1016/j.toxrep.2016.08.010) [2]. Here we report data from our previous investigation [1] on gene expression of cancer pathway targets as well as the methylation status of select tumor suppressor genes. Briefly, mRNA and DNA were extracted from (a) colon mucosae and tumors from F344 rats exposed to AOM or saline and (b) athymic nude (nu/nu) mice bearing human colon tumor xenografts, both exposed to dietary acrylamide at concentrations of 0 or 2 mg/kg diet for 20 and 4 weeks, respectively. RT² Profiler PCR Cancer PathwayFinder Arrays (Qiagen) and EpiTect Methyl II DNA Restriction kits and PCR Assays (Qiagen) were used to detect cancer-relevant gene expression (84 genes representing 9 pathways) and the methylation status of the CpG islands associated with 22 tumor suppressor genes in colon mucosae, tumors and xenografts. Additionally, RT² Profiler PCR Arrays (Qiagen) for cell cycle regulation, growth factors, inflammatory cytokines and receptors, and inflammatory response and autoimmunity were used to investigate the gene expression (84 genes in each array) of targets involved in these select cellular pathways in the colon mucosae from AOM-treated F344 rats.

Assessing the safety of an Ephedrae Herba aqueous extract in rats: A repeat dose toxicity study

Ephedrae Herba (EH) has been used in Asian traditional herbal medicine to cure bronchial asthma, cold, flu, chills, fever, headache, nasal congestion, and cough. In this study, we evaluated the subchronic toxicity of an Ephedrae Herba aqueous extract (EHAE) in male and female F344 rats. The EHAE was administered orally daily at doses of 0, 125, 250, 500, and 1000 mg/kg bw/day for 13 weeks. Toxicological assessment was performed to determine mortality, clinical signs, and changes in body weight, food consumption, ophthalmological, urinary, hematological, and serum biochemical parameters, macroscopic and microscopic evaluations, and organ weights. We found that oral administration of EHAE to F344 rats for 13 weeks resulted in histopathological changes in the kidneys and salivary glands. In the kidneys, increased incidence and severity of tubular basophilia were observed in females administered 1000 mg/kg bw/day of the extract. In the salivary glands, acinar cell hypertrophy was observed in males administered 500 mg/kg bw/day and in both sexes administered 1000 mg/kg bw/day of the extract. All test article-treated groups of males and females administered ≥250 mg/kg bw/day showed increased absolute and relative salivary gland weights. Therefore, the NOAEL (No Observed Adverse Effect Level) was determined as 125 mg/kg bw/day for both sexes of rats under the present experimental conditions.

A carcinogenicity study of diphenylarsinic acid in F344 rats in drinking water for 104 weeks

Diphenylarsinic acid (DPAA), a neurotoxic organic arsenical used as a chemical warfare agent, is present in the groundwater and soil in some regions of Japan due to illegal dumping after World War II. We previously demonstrated that DPAA promotes diethylnitrosamine-induced liver carcinogenesis in a medium-term rat liver bioassay. The purpose of the present study was to evaluate the potential carcinogenicity of DPAA, including investigation of whether the bile duct hyperplasia in the liver that was observed in a previous 52 week rat chronic study develops into a tumor, when administered to rats in their drinking water for 104 weeks. DPAA was administered to groups 1-4 at concentrations of 0, 5, 10, and 20 ppm in their drinking water for 104 weeks. A significant decrease in survival rate was found for females in the 20 ppm DPAA group. Body weights of males in the 20 ppm and females in the 10 and 20 ppm DPAA groups were significantly decreased compared to the controls. Overall histopathological evaluation of neoplasms in all tissues showed no significant increase of tumor incidence in any organ or tissue of the 5, 10, or 20 ppm DPAA-treated male or female F344 rats. In conclusion, the present study demonstrated that DPAA is not a complete carcinogen in male or female F344 rats.

Biological relevance of effects following chronic administration of octamethylcyclotetrasiloxane (D4) in Fischer 344 rats

Octamethylcyclotetrasiloxane (D4) is a cyclic siloxane primarily used as a monomer or intermediate in the production of silicone polymers resulting in potential exposure of workers, and potential low level inhalation or dermal exposure for consumers and the general public. Following a two-year inhalation toxicity study with D4 in rats, increases in uterine endometrial cystic hyperplasia and adenomas were observed at the highest concentration of D4 administered (700ppm). No other neoplasms were increased with D4 treatment. In addition, chronic inhalation exposure of rats to D4 induced changes in relative liver and kidney weights, and produced a chronic nephropathy. This manuscript examines the biological relevance and possible modes of action for the effects observed in the F344 rat following chronic inhalation exposure to D4. D4 is not genotoxic and appears to exert its effects through a nongenotoxic mode of action. An alteration in the estrous cycle in the aging F344 rat was the most likely mode of action for the observed uterine effects following chronic inhalation exposure. Data support the conclusion that D4 acts indirectly via a dopamine-like mechanism leading to alteration of the pituitary control of the estrous cycle in aging F344 rats with a decrease in progesterone and an increase in the estrogen/progesterone ratio most likely induced by a decrease in prolactin concentration. D4 also inhibited the pre-ovulatory LH surge causing a delay in ovulation, persistent follicles and thus a prolonged exposure to elevated estrogen in the adult Sprague Dawely rat. A lengthening of the estrous cycle in the F344 rat with an increase in endogenous estrogen was also induced by D4 inhalation. Although the mode of action responsible for induction of uterine adenomas in the female F344 rat has not been clearly confirmed, the subtlety of effects on the effects of D4 on cyclicity may prevent further assessment and definition of the mode of action. The occurrence of uterine endometrial adenoma in the rat is not relevant for human risk characterization because (1) there are differences in ovulatory cycle regulation in rats compared to humans, (2) cystic hyperplasia without atypia in women is not a cancer precursor, and (3) there is no endometrial lesion in women that is directly analogous to endometrial adenoma in the rat. The effects of D4 on liver are due to a phenobarbital-like mechanism that results in induction of cytochrome P450 and other enzymes of xenobiotic biotransformation. The liver effects are adaptive and not adverse. Kidney findings included chonic progressive nephropathy, a rat lesion that has no counterpart in the human and that should not be used in human risk assessment.

A chronic toxicity study of diphenylarsinic acid in F344 rats in drinking water for 52 weeks

Diphenylarsinic acid (DPAA), a chemical warfare-related neurotoxic organic arsenical, is present in the groundwater and soil in some regions of Japan due to illegal dumping after World War II. The purpose of the present study was to evaluate the potential toxicity of DPAA when administered to rats in their drinking water for 52 weeks. DPAA was administered to groups 1-4 at concentrations of 0, 5, 10, and 20ppm in their drinking water for 52 weeks. There were no significant differences in the final body weights between the control groups and the treatment groups in male or female rats. In serum biochemistry, in females 20ppm DPAA significantly increased alkaline phosphatase and γ-glitamyl transferase compared to controls, and 10 and 20ppm DPAA significantly increased total cholesterol compared to controls. Absolute and relative liver weights were significantly increased in females treated with 20ppm DPAA compared to the control group. Dilation of the common bile duct outside the papilla of Vater and stenosis of the papilla of Vater was observed in all male and female rats administered 20ppm DPAA. The incidence of intrahepatic bile duct hyperplasia was significantly increased in male and female rats treated with 20ppm DPAA compared to the control groups. These results suggest that DPAA is toxic to the bile duct epithelium in rats. The no-observed adverse effect levels of DPAA were estimated to be 10ppm (0.48mg/kg b.w./day) for males and 5ppm (0.35mg/kg b.w./day) for females under the conditions of this study.

Early life diets with prebiotics and bioactive milk fractions attenuate the impact of stress on learned helplessness behaviours and alter gene expression within neural circuits important for stress resistance

Manipulating gut microbes may improve mental health. Prebiotics are indigestible compounds that increase the growth and activity of health-promoting microorganisms, yet few studies have examined how prebiotics affect CNS function. Using an acute inescapable stressor known to produce learned helplessness behaviours such as failure to escape and exaggerated fear, we tested whether early life supplementation of a blend of two prebiotics, galactooligosaccharide (GOS) and polydextrose (PDX), and the glycoprotein lactoferrin (LAC) would attenuate behavioural and biological responses to stress later in life. Juvenile, male F344 rats were fed diets containing either GOS and PDX alone, LAC alone, or GOS, PDX and LAC. All diets altered gut bacteria, while diets containing GOS and PDX increased Lactobacillus spp. After 4 weeks, rats were exposed to inescapable stress, and either immediately killed for blood and tissues, or assessed for learned helplessness 24 h later. Diets did not attenuate stress effects on spleen weight, corticosterone and blood glucose; however, all diets differentially attenuated stress-induced learned helplessness. Notably, in situ hybridization revealed that all diets reduced stress-evoked cfos mRNA in the dorsal raphe nucleus (DRN), a structure important for learned helplessness behaviours. In addition, GOS, PDX and LAC diet attenuated stress-evoked decreases in mRNA for the 5-HT_1A autoreceptor in the DRN and increased basal BDNF mRNA within the prefrontal cortex. These data suggest early life diets containing prebiotics and/or LAC promote behavioural stress resistance and uniquely modulate gene expression in corresponding circuits.

Lack of adverse health effects following 30-weeks of dietary exposure to acrylamide at low doses in male F344 rats

Understanding the health hazards following exposure to food-borne acrylamide, especially at low levels typified by human diets, is an ongoing food safety issue. We recently published results from a study that aimed to understand the effects of acrylamide short-term exposure at doses known to cause tumors in rodents, demonstrating that a number of key toxicological end points were altered by acrylamide exposure. Additionally, we reported that at much lower doses for 30 weeks of exposure, dietary acrylamide was 'not a complete carcinogen' to the colon in an organ-specific rodent carcinogenesis study but acted as a co-carcinogen along with azoxymethane (AOM, a colon-specific carcinogen). Here, we present toxicological data from a sub-set of this long-term exposure study from animals that received saline (instead of AOM). Briefly, male F344 rats were randomized to receive acrylamide at 0.5, 1.0 and 2.0 mg/kg diet (∼0.02, 0.04, and 0.09 mg/kg BW/day, respectively) or no acrylamide (control), for 30 weeks; all rats were then euthanized and their tissues harvested and processed for toxicological evaluation. We report that at the doses tested, acrylamide did not cause any changes in general well-being, body weight or food intake. Similarly, acrylamide did not cause any biologically relevant change in parameters associated with immunophenotyping, serum biochemistry or hematology. Histopathology assessment of tissues showed no changes except in the testis, where non-specific mild lesions were observed in all the groups, inclusive of the controls. No neuropathological effects of acrylamide were observed in the brain and nerve tissues. Together, these results suggest that acrylamide administered to rats through the diet at low doses for 30 weeks did not cause any toxicologically relevant changes. Given that the doses of acrylamide in the current study are low and are comparable to human dietary exposure, this null-effect study provides data that contribute to the body of scientific evidence relevant to understanding the health effects of acrylamide.

M1-/M2-macrophage polarization in pseudolobules consisting of adipohilin-rich hepatocytes in thioacetamide (TAA)-induced rat hepatic cirrhosis

INTRODUCTION

Liver steatosis is the most frequent liver disease and may further develop into non-alcoholic steatohepatitis (NASH), liver cirrhosis, and finally hepatocellular carcinoma. Adipophilin (Adp) is localized on lipid droplet membrane in cytoplasm, and its increased expression is related to development of steatosis and NASH. The relationship between M1-/M2-macrophage polarization and Adp-rich hepatocyte-consisting pseudolobules (PLs) was investigated in thioacetamide (TAA)-induced rat cirrhosis.

MATERIALS AND METHOD

F344 rats were injected twice weekly with TAA (100mg/kg bodyweight) and sacrificed at post-first injection (PFI) weeks 5, 10, 15, 20, 25 and 32. Macrophage immunophenotypes and Adp-containing hepatocytes were analyzed by single immunolabeling. Adp and M1-/M2-related factors were analyzed by real -time RT-PCR.

RESULTS

PLs consisting exclusively of Adp-containing hepatocytes (Adp-positive) and PLs consisting of few Adp-containing hepatocytes (Adp-negative) were clearly distinguishable at PFI week 20 onwards. The numbers of M1-macrophages (reacting to CD68 and Iba1) and M2- macrophages (reacting to CD163, CD204 and Gal-3) were considerably greater in Adp-positive PLs. Expressions for both M1 (TNF-α, MCP-1, and Iba1)- and M2 (IL-4, TGF-β1, Gal-3, and Hsp25)-related factors were markedly higher in Adp-positive PLs at PFI week 25. Interestingly, MHC class II-positive macrophages/dendritic cells were increased in Adp-positive clusters/foci at the early stages at PFI weeks 5 and 10, and the level was gradually decreased thereafter.

CONCLUSIONS

M1-/M2-macrophages may simultaneously participate in the pathogenesis of steatosis in TAA-induced cirrhosis through M1- and M2-related factors. MHC class II cells may be responsible for steatosis at early stages, suggesting different functions from the above M1-/M2-macropahges.

Aging Reduces L-Type Calcium Channel Current and the Vasodilatory Response of Small Mesenteric Arteries to Calcium Channel Blockers

Calcium channel blockers (CCBs) are widely used to treat cardiovascular disease (CVD) including hypertension. As aging is an independent risk factor for CVD, the use of CCBs increases with increasing age. Hence, this study was designed to evaluate the effect of aging on the sensitivity of small mesenteric arteries to L-type voltage-gated calcium channel (LTCC) blockers and also to investigate whether there was a concomitant change in calcium current density. Third order mesenteric arteries from male F344 rats, aged 2.5-3 months (young) and 22-26 months (old) were mounted on wire myograph to measure the tension during isometric contraction. Arteries were contracted with 100 mM KCl and were then relaxed in a cumulative concentration-response dependent manner with nifedipine (0.1 nM-1 μM), verapamil (0.1 nM-10 μM), or diltiazem (0.1 nM-10 μM). Relaxation-concentration response curves produced by cumulative concentrations of three different CCBs in arteries of old rats were shifted to the right with statistically significant IC50s. pIC50 ± s.e.m: (8.37 ± 0.06 vs. 8.04 ± 0.05, 7.40 ± 0.07 vs. 6.81 ± 0.04, and 6.58 ± 0.07 vs. 6.34 ± 0.06) in young vs. old. It was observed that the maximal contractions induced by phenylephrine and reversed by sodium nitroprusside were not different between young and old groups. However, Bay K 8644 (1 μM) increased resting tension by 23 ± 4.8% in young arteries and 4.7 ± 1.6% in old arteries. LTCC current density were also significantly lower in old arteries (-2.77 ± 0.45 pA/pF) compared to young arteries (-4.5 ± 0.40 pA/pF); with similar steady-state activation and inactivation curves. Parallel to this reduction, the expression of Cav1.2 protein was reduced by 57 ± 5% in arteries from old rats compared to those from young rats. In conclusion, our results suggest that aging reduces the response of small mesenteric arteries to the vasodilatory effect of the CCBs and this may be due to, at least in part, reduced current density of LTCC.

Hormone Receptor Expression in Spontaneous Uterine Adenocarcinoma in Fischer 344 Rats

Most uterine cancers, the most common gynecological malignancies in women in developed countries, are hormone-dependent endometrial adenocarcinomas (EACs) that express estrogen and progesterone receptors. Although rat strains exist with a high spontaneous incidence of EAC, the Fischer 344 (F344) strain, previously one of the most commonly used strains in carcinogenicity testing, is not a high-incidence strain. To better understand the biology of this neoplasm, we assessed estrogen receptor α (ER), progesterone receptor (PR), and Ki-67 expression using immunohistochemistry in spontaneous EAC in 18 F344 rats used as control animals in 2-year National Toxicology Program bioassays. Of the 18 tumors, 9 were well-differentiated and 9 were poorly differentiated. Most tumors, 7/18, were ER+PR+, as observed in women. Of the remainder, 6/18 were ER+PR-, 2/18 were ER-PR+, and 3/18 were ER-PR-. Well-differentiated tumors were ER+ (8/9) more often than poorly differentiated tumors (5/9). The percentage of ER+ tumors (72%) in rats was similar to that seen in women, but rats less frequently had PR+ (50%) tumors than women. The heterogeneous estrogen and progesterone receptor immunophenotypes observed in F344 rats in this study highlight the importance of evaluating hormone receptor expression in animal models used for chemical evaluations.

Effects of high-fat diet on 1,2-dimethylhydrazine-induced aberrant crypt foci and colorectal tumours in rats

Obesity is one of the leading causes of numerous types of cancer. The present study investigated the impact of a high-fat diet on 1,2-dimethylhydrazine (DMH)-induced colorectal cancer (CRC) in F344 rats. A total of 16 male F344 rats aged 4 weeks were randomly divided into two groups (8 rats/group). Rats in group A were fed a basal diet with a moderate fat (MF) content, while rats in group B were fed a high-fat diet. Upon reaching 5 weeks of age, the rats were injected subcutaneously with DMH (20 mg/kg body weight). DMH was administered once a week for 8 consecutive weeks. All the rats were sacrificed 34 weeks after the first DMH injection and dissected to obtain samples of colorectal tissues. The tissues were examined under a microscope for the presence of aberrant crypt foci (ACFs) and subjected to histopathological analysis. The results showed that at the end of the 34-week experiment, body weights and visceral fat levels were significantly higher in the high-fat diet group compared to the basal diet group. In addition, the incidences of colorectal ACF, adenoma and adenocarcinoma were markedly elevated in the high-fat diet group compared to the basal diet group. These results indicate that the consumption of a high-fat diet promotes the development and progression of CRC and the control of fat intake may prevent CRC.

Dexmedetomidine and regulation of splenic sympathetic nerve discharge in aged F344 rats

Sedatives influence the immune system and centrally-acting alpha2-adrenergic receptor agonists, including Dexmedetomidine (Dex), modulate sympathetic nerve discharge (SND). Because sedatives are used under medical conditions that include elderly patients, and because advancing age attenuates SND responsivity to various interventions, we tested the hypothesis that splenic sympathoinhibitory responses to Dex would be attenuated in aged compared with young Fischer 344 rats. Dex-mediated reductions in splenic SND were similar in aged and young baroreceptor-intact and -denervated rats, indicating that SND changes to Dex administration occur in an age-independent manner. These findings provide new information regarding interactions between alpha2-adrenergic agonists, advanced age, and SND regulation.

The 9L(LUC)/Wistar rat glioma model is not suitable for immunotherapy

The availability of a well-characterized animal brain tumor model will play an important role in identifying treatments for human brain tumors. Wistar rats bearing 9L glioma cells can develop solid, well-circumcised tumors, and may be a useful animal model for the evaluation of various therapeutic approaches for gliosarcomas. In this study, the 9L/Wistar rat glioma model was produced by intracerebral implantation of 9L^LUC glioma cells syngenic to Fischer 344 (F344) rats. Bioluminescence imaging showed that tumors progressively grew from day 7 to day 21 in 9L^LUC/F344 rats, and tumor regression was found in some 9L^LUC/Wistar rats. Hematoxylin-eosin staining verified that intracranial tumors were gliomas. Immunohistochemistry results demonstrated that no CD₄- and CD₈-positive cells were found in the syngeneic 9L^LUC/F344 model. However, many infiltrating CD₄- and CD₈-positive cells were observed within the tumors of the 9L^LUC/Wistar model. Our data suggests that compared with 9L/F344 rats, 9L glioma Wistar rats may not be suitable for evaluating brain glioma immunotherapies, even though the model induced an immune response and exhibited tumor regression.

Physiologically based pharmacokinetic modeling for 1-bromopropane in F344 rats using gas uptake inhalation experiments

1-Bromopropane (1-BP) was introduced into the workplace as an alternative to ozone-depleting solvents and increasingly used in manufacturing industry. The potential exposure to 1-BP and the current reports of adverse effects associated with occupational exposure to high levels of 1-BP have increased the need to understand the mechanism of 1-BP toxicity in animal models as a mean of understanding risk in workers. Physiologically based pharmacokinetic (PBPK) model for 1-BP has been developed to examine 2 metabolic pathway assumptions for gas-uptake inhalation study. Based on previous gas-uptake experiments in the Fischer 344 rat, the PBPK model was developed by simulating the 1-BP concentration in a closed chamber. In the model, we tested the hypothesis that metabolism responsibilities were shared by the p450 CYP2E1 and glutathione (GSH) conjugation. The results showed that 2 metabolic pathways adequately simulated 1-BP closed chamber concentration. Furthermore, the above model was tested by simulating the gas-uptake data of the female rats pretreated with 1-aminobenzotrizole, a general P450 suicide inhibitor, or d,l-buthionine (S,R)-sulfoximine, an inhibitor of GSH synthesis, prior to exposure to 800 ppm 1-BP. The comparative investigation on the metabolic pathway of 1-BP through the PBPK modeling in both sexes provides critical information for understanding the role of p450 and GSH in the metabolism of 1-BP and eventually helps to quantitatively extrapolate current animal studies to human.

Toxicological effects of short-term dietary acrylamide exposure in male F344 rats

We recently reported that acrylamide, a known rodent and probable human carcinogen, does not increase the risk of azoxymethane (AOM)-induced rat colon precancerous lesions when administered through the diet. Here, we present toxicological data from non-AOM-injected rats. Briefly, male F344 rats were randomized into four dietary groups and received experimental diets based on AIN-93G formulation and containing acrylamide at 0 (control), 5, 10 or 50mg/kg diet (wt/wt) ad libitum for 10 weeks, after which they were killed and their blood collected for hematological and biochemical markers. Acrylamide at the higher doses (10 and 50mg/kg diet) significantly lowered (p<0.05) serum total high density lipoprotein and total testosterone and increased serum lipase in comparison to the control. Blood hematocrit values and lymphocyte counts were significantly lower (p<0.05) in the high dose acrylamide (50mg/kg diet) group compared to control, with a concomitant decrease in hemoglobin level, mean corpuscular volume and mean corpuscular hemoglobin. These results provide additional hazard characterization data and strengthen the notion that at high doses, acrylamide may involve systemic toxicity potentiating tumorigenesis in experimental animals. Further studies are required to understand the health effects of food-borne acrylamide, especially at the lower exposures typified by human diets.

No Promoting Effect of Ethyl Tertiary-butyl Ether (ETBE) on Rat Urinary Bladder Carcinogenesis Initiated with N-Butyl-N-(4-hydroxybutyl)nitrosamine

The effects of ethyl tertiary-butyl ether (ETBE) on two-stage urinary bladder carcinogenesis in male F344 rats initiated with N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN) were investigated at various dose levels with regard to possible promoting activity. Groups of 30 rats were given drinking water containing 500 ppm BBN, as an initiator, for 4 weeks and starting one week thereafter received ETBE by gavage (daily, 7 days/week) at dose levels of 0 (control), 100, 300, 500 or 1000 mg/kg/day until experimental week 36. No statistically significant differences in incidences of preneoplastic lesions, papillomas, and carcinomas of the urinary bladder were evident in rats treated with 100–1000 mg/kg/day ETBE as compared with control values. Furthermore, the average numbers of preneoplastic or neoplastic lesions per unit length of basement membrane in rats given 100–1000 mg/kg/day ETBE were also comparable to control values. However, papillomatosis of the urinary bladder was found in 4 out of 30 rats (13%) in the group given 1000 mg/kg/day ETBE, and soft stones in the urinary bladder were found in 3 out of these 4 rats. The results thus demonstrated that ETBE did not exert promotional activity on urinary bladder carcinogenesis. However, papillomatosis of the urinary bladder developed in small numbers of the rats given ETBE at 1000 mg/kg/day but not in rats given 500 mg/kg/day or lower doses.

Assessing the emergence and reliability of cognitive decline over the life span in Fisher 344 rats using the spatial water maze

The spatial water maze is routinely used to investigate hippocampal-dependent spatial memory and the biological mechanisms that underlie variability in cognitive decline during aging. The utility of the task for repeated testing in order to examine the trajectory of cognitive decline and to prescreen animals prior to therapeutic interventions maybe limited due to carryover effects of repeated training. The current study examines the role of carryover effects, as well as the reliability of individual differences, in determining age-related impairment on episodic and reference memory versions of the water maze task. Results indicate that impaired acquisition of episodic spatial information emerges in middle-age and the propensity for impairment increases with advancing age. While learning was variable across animals, acquisition deficits for episodic information were reliable across training sessions in middle-age and aged rats. A significant impairment in the 24~h retention of episodic spatial information was observed in aged animals. When animals were trained to the same location (i.e., reference memory), an impairment was limited to the rate of acquisition in aged animals. However, with continued training, all aged animals were able to acquire a reference memory and no age differences were observed in the 24~h retention of a spatial reference memory. Together, the results point to a progressive impairment in episodic spatial memory with advancing age and suggest that tests of episodic spatial memory are reliable and more sensitive than reference memory for detecting cognitive decline.

Subchronic toxicity evaluation of potassium bromate in Fischer 344 rats

Male F344 rats were exposed to potassium bromate (KBrO₃) in drinking water at concentrations of 0, 5, 20, 100, 200, or 400 mg/L for 2 or 13 weeks. Endpoints evaluated included clinical observations, body weights, serum chemistry, gross pathology, organ weights, and select tissue histopathology (kidney, lung, liver, thyroid, and tunica vaginalis). Weekly body weight and water consumption means were similar between KBrO₃ and control groups throughout the study. Increases in kidney weights were observed in rats of the 400 mg/L group following 2- or 13-weeks exposure. Hyaline droplets were observed in renal tubules of rats of the 200 and 400 mg/L groups following 2 weeks exposure and in rats of the 400 mg/L group at 13 weeks. There were no KBrO₃-related microscopic findings in the lung, liver, thyroid, and tunica vaginalis at the 2- and 13-week time points. A no observed effect level of 100 mg/L KBrO₃ (8.1 mg/kg/day) was selected based on the absence of microscopic alterations in the kidney.

Subchronic toxicity evaluation of anthraquinone in Fischer 344 rats

Female F344 rats were exposed to anthraquinone (AQ) by dietary feed at concentrations of 0, 50, 150, 469, 938, 1875, or 3750 ppm for 2 or 13 weeks. End points evaluated included clinical observations, body weights, serum chemistry, blood AQ, gross pathology, organ weights, and select tissue histopathology. Mean body weight and food consumption were 5% to 10% lower than control values in rats of the ≥938 ppm group during study weeks 2 through 13. Occasional decreases in body weight means were also observed in rats of the 150 and 469 ppm groups. Increases in liver, kidney, and spleen weights were observed in rats exposed to AQ diet concentrations ≥150 ppm for 13 weeks. Urinary bladder weights were increased at ≥469 ppm. Liver and spleen weights were also increased following 2 weeks of exposure. Liver weight increases were clearly dependent on AQ concentration. At 2 weeks, decreases in serum aspartate aminotransferase (AST), blood urea nitrogen, and creatinine concentrations were observed in higher AQ exposure groups, and AST was decreased at 13 weeks (≥1875 ppm). Microscopic alterations were observed in the liver (mild centrilobular hypertrophy), spleen (mild hematopoietic cell proliferation and pigmentation), and kidneys (minimal hyaline droplets) of rats exposed to AQ for 13 weeks. Blood AQ concentrations ranged from 0.75 to 14.8 µg/mL in rats of the 150 to 3750 ppm groups, respectively, and were similar in value following either 2 weeks or 13 weeks of exposure. A no observed adverse effect level of 469 ppm AQ (31.3 mg/kg/d) was selected based on the absence of liver histopathology.