Oleanolic acid-3-glucoside, a synthetic oleanane-type saponin, ameliorates methylmercury-induced dysfunction of synaptic transmission in mice

Methylmercury (MeHg) is widely distributed in nature and is known to cause neurotoxic effects. This study aimed to examine the anti-MeHg activity of oleanolic acid-3-glucoside (OA3Glu), a synthetic oleanane-type saponin derivative, by evaluating its effects on motor function, pathology, and electrophysiological properties in a mouse model of MeHg poisoning. Mice were orally administered 2 or 4 mg·kg-1·d-1 MeHg with or without 100 µg·kg-1·d-1 OA3Glu 5x/week for four weeks. Motor function was evaluated using beam-walking and dynamic weight-bearing (DWB) tests. High-dose MeHg exposure significantly increased the frequency of stepping off the hind leg while crossing the beam in the beam-walking test, and increased weight on forelegs when moving freely in the DWB test. OA3Glu treatment alleviated motor abnormality caused by high-dose MeHg exposure in both motor function tests. Additionally, OA3Glu treatment reduced the number of contracted Purkinje cells frequently observed in the cerebellum of MeHg-treated groups, although cerebrum histology was similar in all experimental groups. The synaptic potential amplitude in the cerebellum decreased as MeHg exposure increased, which was restored by OA3Glu treatment. Even in the cerebrum, where the effects of MeHg were not observed, the amplitude of the field potential was suppressed with increasing MeHg exposure but was restored with OA3Glu treatment. Taken together, the study findings suggest that OA3Glu improves neurotransmission and movement disorders associated with MeHg exposure via protection of Purkinje cells in the cerebellum while ameliorating pre/post-synaptic deficits in the cerebral cortex in which no changes were observed at the tissue level, potentially providing a treatment to mitigate MeHg toxicity.

Suppression of Airway Allergic Reactions by a Photocatalytic Filter Using Mouse Model

Photocatalytic filters installed in air purifiers have been used to purify spaces by decomposing allergenic substances. However, we have not found any reports that evaluate the effectiveness of photocatalytic filters in suppressing allergic reactions in living organisms. In this study, we intratracheally instilled ovalbumin (OVA) into OVA-sensitized mice after the OVA was photocatalyzed by a titanium dioxide (TiO₂) filter, and verified the experimental model for evaluating the allergy-suppressing effect of photocatalysts. Mice were sensitized to OVA (10 µg/mouse) four times, and were intratracheally instilled with OVA (10 µg/mouse) after photocatalysis three times. Non-sensitized animals were instilled with normal saline following the same exposure schedule. The mice were dissected 24 h after final exposure. The OVA after photocatalysis significantly decreased the number of eosinophils in bronchoalveolar lavage fluid, and the concentration of OVA-specific IgE and IgG1 in serum, which were elevated in untreated OVA. Moreover, our experimental model showed the suppression of allergic reactions in mice, along with the decomposition of OVA after photocatalysis using the photocatalytic filter. Taken together, our experimental model for evaluating allergic reactions in the respiratory tract suggested that the allergy-suppressing effect of the photocatalytic filter can be evaluated.

Oleanolic acid 3-glucoside, a synthetic oleanane-type saponin, alleviates methylmercury toxicity in vitro and in vivo

Methylmercury (MeHg) is one of the most toxic environmental pollutants, presenting a serious health hazard worldwide. In this study, we examined the potential of derivatives of oleanolic acid (OA), such as OA 3-glucoside, OA 28-glucoside, and OA 3,28-diglucoside, to mitigate MeHg toxicity in vitro and in vivo. We found that OA 3-glucoside suppressed the cellular MeHg uptake by 63.4% compared with that of the control and improved the cell viability from 75.4% to 107.9% upon exposure to cytotoxic MeHg in Caco-2 cells. To verify the anti-MeHg activity of OA 3-glucoside, mice were orally administered MeHg (0, 1.0, or 5.0 mg kg^-1·d^-1), with or without OA 3-glucoside, and then mercury accumulation was measured in various organs of the mice. The mice co-treated with MeHg and OA 3-glucoside showed significantly lower mercury content in organs such as the cerebrum, cerebellum, liver, kidney, and spleen, with 83.1%, 68.7%, 71.7%, 82.1%, and 18.2% of those in the OA 3-glucoside-untreated group, respectively. This suggested OA 3-glucoside had the potential as an anti-MeHg compound, owing to its ability to suppress the distribution of MeHg into organs. Supporting this hypothesis, the mice treated with MeHg and OA 3-glucoside showed a tendency to survive one day longer than the control mice. Our findings suggest OA 3-glucoside administration alleviates the toxicity of MeHg by suppressing MeHg accumulation in organs.

Sequestosome1/p62 protects mouse embryonic fibroblasts against low-dose methylercury-induced cytotoxicity and is involved in clearance of ubiquitinated proteins

Methylmercury (MeHg) is a widely distributed environmental pollutant that causes a series of cytotoxic effects. However, molecular mechanisms underlying MeHg toxicity are not fully understood. Here, we report that sequestosome1/p62 protects mouse embryonic fibroblasts (MEFs) against low-dose MeHg cytotoxicity via clearance of MeHg-induced ubiquitinated proteins. p62 mRNA and protein expression in MEFs were temporally induced by MeHg exposure p62-deficient MEFs exhibited higher sensitivity to MeHg exposure compared to their wild-type (WT) counterparts. An earlier and higher level of accumulation of ubiquitinated proteins was detected in p62-deficient cells compared with WT MEFs. Confocal microscopy revealed that p62 and ubiquitinated proteins co-localized in the perinuclear region of MEFs following MeHg treatment. Further analysis of MEFs revealed that ubiquitinated proteins co-localized with LC3-positive puncta upon co-treatment with MeHg and chloroquine, an autophagy inhibitor. In contrast, there was minimal co-localization in p62-deficient MEFs. The present study, for the first time, examined the expression and distribution of p62 and ubiquitinated proteins in cells exposed to low-dose MeHg. Our findings suggest that p62 is crucial for cytoprotection against MeHg-induced toxicity and is required for MeHg-induced ubiquitinated protein clearance.