Aluminum salt adjuvants (Als) have been the most widely used adjuvants in vaccines and known to be effective in intramuscular inoculation. However, in rare cases, some Al containing vaccines caused serious adverse events such as chronic pain at the site of the injection. The Als cause mild tissue damage at the inoculation site, allowing the antigen to be locally retained at the inoculation site and thus potentiate innate immunity. This is required to elicit effectiveness of vaccination. However, there is concern that chronic muscle damage might potentially lead to serious adverse events, such as autoimmune disease and movement disorders. In this study, muscle damage caused by several Al containing vaccines were examined in guinea pigs. Mild and moderate inflammation were observed following Al containing split influenza virus vaccine, formalin-inactivated diphtheria-pertussis-tetanus and Salk polio vaccine. While massive inflammation and muscle damage were observed in Al-containing human papillomavirus vaccine-inoculated animals. However, the severities of damage were not associated with their Al contents. Masson’s trichrome staining and immunostaining revealed that injured muscle at the inoculated site recovered within one month of vaccination, whereas inflammatory nodules remained. Flow cytometric analyses of the infiltrating cells revealed that the number of CD45⁺ lymphocytes and potential granulocytes were increased following vaccination. The number of infiltrated cells seemed to be associated with severity of muscle damages. These observations revealed that Al containing vaccine-induced muscle damage is reparable, and severity of transient muscle damages seemed to be determined by type of antigen or types of Al salts rather than Al content.

Physiologically based pharmacokinetic (PBPK) modeling has the potential to estimate internal chemical exposures. Algorithms for predicting the input parameters for PBPK modeling, such as absorption rate constants (k_a), were previously reported for 323 chemicals in rats. In this study, a currently updated system for estimating the fraction absorbed × intestinal availability of compounds, along with a modified estimation system that generates k_a values, is reported, based on the previously analyzed 323 primary compounds, 10 secondary compounds, and 39 additional substances. The in silico estimation of input parameters for PBPK models (i.e., fraction absorbed × intestinal availability and k_a) was adapted for an updated panel of 372 chemicals using machine learning algorithms based on between 16 and 18 in silico-calculated chemical properties. Simplified human PBPK models were then used to calculate virtual areas under the plasma concentration–time curve (AUC) based on two sets of input parameters, i.e., traditionally derived values from in vivo data and those calculated in silico using the current updated machine learning systems. The AUC data sets were well correlated; the current correlation coefficient increased from 0.61 to 0.82 (p < 0.01, n = 372). Therefore, the above-described computational methods constitute a new alternative approach that could contribute to chemical safety evaluations.

Although both o-toluidine and o-anisidine are known as aromatic amines with bladder carcinogenicity, the specific metabolites involved in carcinogenesis are still unclear. Here, we examined the toxicological effects of head-to-tail dimers of o-toluidine and o-anisidine, 2-methyl-N⁴-(2-methylphenyl) benzene-1,4-diamine (MMBD) and 2-methoxy-N⁴-(2-methoxyphenyl) benzene-1,4-diamine (MxMxBD), respectively, in rats. Six-week-old male F344 rats were orally administered MMBD, MxMxBD, o-toluidine, and o-anisidine at a dose of 100 mg/kg/day for 28 days. Rats administered 400 mg/kg o-toluidine and 600 mg/kg/day o-anisidine were set as high-dose groups for comparison. Histopathology and immunohistochemistry for γ-H2AX, a DNA damage biomarker, and bladder stem cell markers, including aldehyde dehydrogenase 1A1 (ALDH1A1), were performed. MMBD and MxMxBD caused different toxicities than their monomers, inducing hepatotoxicity such as vacuolar degeneration but not splenic lesions due to methemoglobinemia. Bladder lesions, including urothelial hyperplasia, were observed in the high-dose o-toluidine and o-anisidine groups, whereas no obvious changes were induced in the low-dose groups or their dimers. Although γ-H2AX formation was significantly increased by o-toluidine and o-anisidine treatment, γ-H2AX formation did not differ among the MMBD, MxMxBD, and control groups. Notably, immunohistochemistry revealed marked increases in ALDH1A1 expression in the bladder urothelium of the MMBD and MxMxBD groups and in the o-toluidine and o-anisidine groups, suggesting that the two dimers may contribute to the bladder carcinogenic effects of o-toluidine and o-anisidine to some extent. The degrees of bladder lesions and γ-H2AX formation did not correlate with the amount of unchanged o-toluidine and o-anisidine in urine, indicating the presence of other metabolites responsible for these findings.

Acrylamide (AA) is a neurotoxicant that causes synaptic impairment in distal axons. We previously found that developmental exposure to AA decreased proliferation of late-stage neural progenitor cells (NPCs) in the hippocampal neurogenesis of the dentate gyrus (DG) in rats. To investigate whether hippocampal neurogenesis is similarly affected by AA exposure in a general toxicity study, AA was administered to 7-week-old male rats via oral gavage at dosages of 0, 5, 10, and 20 mg/kg for 28 days. In the subgranular zone (SGZ) and granule cell layer, AA decreased the densities of doublecortin-positive ⁽⁺⁾ cells and TOAD-64/Ulip/CRMP protein 4b⁺ cells per SGZ length. In addition, AA decreased the neurite length of doublecortin⁺ cells and downregulated genes related to neurite outgrowth (Ncam2 and Nrep) and neurotrophic factor (Bdnf and Ntrk2) in the DG. These results suggest that AA exposure for 28 days decreases type-3 NPCs and immature granule cells in neurogenesis of granule cell lineages involving the impairment of neurite outgrowth in young-adult rats. In the DG hilus, AA increased the density of cholinergic receptor nicotinic beta 2 subunit⁺ cells. AA also downregulated Reln related to the control of neuronal migration by interneurons in the DG. Furthermore, AA decreased the density of glial fibrillary acidic protein (GFAP)⁺ astrocytes in the DG hilus and downregulated Gfap and the genes of oligodendrocyte progenitor cells (Cspg4 and Pdgfra). Thus, AA decreased granule cell lineage subpopulations in the late-stage differentiation of hippocampal neurogenesis after young-adult stage exposure, exhibiting a pattern similar to the developmental exposure.

A reactive oxygen species (ROS) assay has been widely used for photosafety assessment; however, the phototoxic potential of complex materials, including plant extracts, essential oils, and functional polymers, is unevaluable because of their undefined molecular weights. The present study was undertaken to modify the ROS assay protocol for evaluating phototoxic potentials of those materials with use of their apparent molecular weight (aMw). On preparing sample solutions for the ROS assay, aMw ranging from 150 to 350 was tentatively employed for test substances. The modified ROS assays were applied to 45 phototoxic and 19 non-phototoxic substances, including 44 chemicals and 20 complex materials (plant extracts) for clarification of the predictive performance. Generation of ROS from photo-irradiated samples tended to increase as aMW grew, resulting in the largest number of false-positive predictions at aMW of 350. Some false-negative predictions were also observed when aMW was set at 200 or less. At aMw of 250, all tested phototoxic substances could be correctly identified as photoreactive with no false-negative predictions. Based on these observations, aMw of 250 was found to be suitable for the ROS assay on complex materials, and the sensitivity, specificity, and positive and negative predictivity for the proposed ROS assay were calculated to be 100, 52.6, 83.3, and 100%, respectively. Thus, the proposed approach may be efficacious for predicting phototoxic potentials of complex materials and contribute to the development of new products with a wide photosafety margin.

Lead (Pb) is an environmental pollutant that adversely affects various organs in the human body and is a well-known risk factor for cardiovascular diseases, caused by the dysfunction of vascular endothelial cells that cover the luminal surface of the blood vessels. The Zrt- and Irt-like related protein (ZIP) transporter ZIP8 is one of the primary importers of zinc, iron, manganese, and cadmium, and its expression appears to be important for the metabolism of these metals. In the present study, we investigated the influence of ZIP8 on Pb-induced cytotoxicity in vascular endothelial cells, induction of ZIP8 expression by Pb, and its mechanism of action in vascular endothelial cells. The study revealed the following: (1) Pb cytotoxicity in vascular endothelial cells was potentiated by the knockdown of ZIP8, but the intracellular accumulation of Pb in the cells remain unaffected; (2) Pb induced the expression of ZIP8; (3) the induction of ZIP8 expression by Pb was mediated by nuclear factor (NF)-κB signaling pathway; and (4) Pb activated p38, mitogen-activated protein kinase (MAPK), and c-jun N-terminal kinase (JNK), but the activation of these MAPKs was not involved in the induction of ZIP8 by Pb. Therefore, the study shows that Pb induces the expression of endothelial ZIP8 and this induction appears to be involved in the protection against Pb cytotoxicity by intracellular Pb accumulation independent mechanisms.