Occupational exposure to aromatic amines is a major risk factor for urinary bladder cancer. Our previous studies showed that acetoaceto-o-toluidine, which is produced using o-toluidine as a raw material, promotes urinary bladder carcinogenesis in rats. We also found high concentrations of o-toluidine, a human bladder carcinogen, in the urine of acetoaceto-o-toluidine-treated rats, indicating that urinary o-toluidine derived from acetoaceto-o-toluidine may play an important role in bladder carcinogenesis. However, this has not been investigated in humans. In the present study, we used non-humanized (F1-TKm30 mice) and humanized-liver mice established by human hepatocyte transplantation to compare differences in urinary acetoaceto-o-toluidine metabolites produced by human and mouse liver cells. We also examined the changes in acetoaceto-o-toluidine-induced mRNA expression in the liver and the proliferative effects on the bladder epithelium. Urinary o-toluidine was detected in both non-humanized and humanized mice. Acetoaceto-o-toluidine metabolites in the urine, cell proliferation activities, and DNA damage in the bladder urothelium were similar in non-humanized and humanized-liver mice. RNA expression analysis revealed that CYP1A2 expression increased in the livers of humanized-liver mice, and Cyp2c29 expression (equivalent to human CYP2C9/19) increased in the livers of non-humanized mice. These data suggest that acetoaceto-o-toluidine may be a human carcinogen, as evidenced by the detection of urinary o-toluidine in acetoaceto-o-toluidine-treated humanized-liver mice. This animal model is important for extrapolating toxicity data from animals to humans.

The liver, a major organ involved in substance metabolism, is highly susceptible to toxicity induced by chemicals and their metabolites. Although damage-associated molecular patterns (DAMPs) have been implicated in the development of sterile inflammation following cell injury, their involvement in chemically induced hepatocellular injury remains underexplored. This study aimed to determine the role of high-mobility group box 1 (HMGB1), a DAMP, in a rat model of liver injury treated with thioacetamide, a hepatotoxicant. The rats were administered thioacetamide and treated with HMGB1 neutralizing antibody. Histopathological analysis revealed the absence of significant differences between control rats and HMGB1 neutralizing antibody-treated rats. However, HMGB1 neutralizing antibody-treated rats showed a reduction in the hepatic devitalization enzymes, a decrease in the number of anti-inflammatory cluster of differentiation 163⁺ M2 macrophages and neutrophils in the injured area, and a decrease in cytokine expression. These results suggest that HMGB1 leads to the progression of inflammation after chemically induced hepatocyte injury and may represent a therapeutic target for mitigating such injury.

We performed morphological and immunohistochemical analyses of erythrocyte-rich vascular proliferative lesions of mesenteric lymph nodes in six male and one female Wistar Hannover rats. These lesions are conventionally diagnosed as hemangiomas due to abundant erythrocytes. Immunostaining was positive for prospero-related homeobox 1 (Prox-1) and/or vascular endothelial growth factor receptor 3 (VEGFR3) in all lesions, suggesting a lymphangitic origin. In 6 of 7 lesions, von Willebrand factor (vWF) immunostaining was negative, suggesting a non-blood vascular origin. These results demonstrated that almost all hemangiomas in rat mesenteric lymph nodes were lymphangiomas. To the best of our knowledge, this is the first report highlighting the lymphatic origin of vascular proliferative lesions in the mesenteric lymph nodes of rats.

The FVB/N mouse strain is widely used in transgenic studies and as a model for autoimmune diseases. Although spontaneous lesions have been reported in aged FVB/N mice, information regarding younger FVB/N mice is lacking. This study aimed to investigate the spontaneous lesions in young FVB/N mice. Ten males and 10 females were necropsied at 10 and 26 weeks of age. All tissues were fixed in 10% neutral-buffered formalin, embedded in paraffin, and stained with hematoxylin and eosin. Histopathological examination revealed atrophy of the outer retina in all mice of both ages, with atrophy of the inner nuclear layer at 26 weeks. This ocular lesion is consistent with an autosomal recessive disorder in FVB/N mice. Decreased cellularity in the epiphyseal cartilage plate, reduced bone in the primary spongiosa of the femur, increased cellularity of lymphocytes in the thymus, dilatation of ducts in the mammary glands, and foveolar hyperplasia in the stomach were observed, all of which were indicative of age-related changes. These findings provide valuable background data for future studies using FVB/N mice.

Acute kidney injury induced by stings from multiple wasps is a medical emergency and is a driving factor of acute renal dysfunction. Numerous studies have shown that mitochondrial reactive oxygen species (mtROS) play a key role in ischemia-reperfusion injury-, cisplatin-, and sepsis-induced acute kidney injury. However, the role of mtROS and its underlying mechanisms in wasp-venom-induced acute kidney injury remain inconclusive. In this study, we investigated the role and mechanisms of mtROS in mitochondrial damage and inflammation in a mouse model of acute kidney injury induced using wasp venom. Changes in mitochondrial function, transcription factor A (TFAM) expression, and DNA maintenance levels, renal function, stimulator of interferon gene (STING) expression, and inflammatory mediator levels in model mice with or without the mtROS scavenger Mito-Tempo were analyzed in vivo. Downregulation of mtROS levels reversed renal damage and mitochondrial dysfunction, and reduced STING expression and inflammation in the kidneys of model mice. The suppression of mtROS levels also improved the decrease in TFAM levels and mitochondrial DNA copy numbers in the kidneys of the model mice. In summary, the existing evidence in this study shows that mtROS contribute significantly to mitochondrial damage and inflammation in acute kidney injury induced by wasp venom.

Cystic degeneration (CD) in the liver is a cyst-like lesion composed of one or more pseudocysts lacking lining cells, occurring spontaneously in rats older than 12 months, with a male predilection. In this study, 32 CDs were identified in 23 out of 104 non-treated, control male Sprague-Dawley rats from two combined chronic toxicity and carcinogenicity studies with agrochemicals. They were examined histologically, histochemically, and immunohistochemically to assess the pathogenesis and pathological significance of CD, focusing on pseudocapillarization in aged rat liver. Pseudocapillarization refers to age-related capillarization of hepatic sinusoids and is distinct from sinusoidal capillarization observed in hepatic cirrhosis. Both CD and pseudocapillarization, characterized by factor VIII-related antigen expression, were primarily noted in the periportal regions of the rat liver. CD areas exhibited enhanced vimentin expression in a diffuse linear pattern in their septa with occasional focal linear α-smooth muscle actin expression and the fluid containing hyaluronic acid accumulated in their lumen that are thought to be formed by hepatocellular apoptosis. These findings suggest a series of reactive changes associated with hepatocellular apoptosis due to pseudocapillarization in the sinusoids. In conclusion, spontaneous CD in rat liver is not a degenerative lesion or cystic enlargement of stellate cells, but a structural abnormality in pre-existing liver tissue resulting from aging-related changes in sinusoidal endothelial cells and hepatocytes. Pseudocapillarization of sinusoids is considered a precursor lesion of CD in the rat liver.