Masae Furukawa

Objective The oral microbiome is one of the most complex microbial ecosystems in the host. This study aimed to investigate and characterize the oral microbiome composition in Kazakhstani adolescents associated with dental caries. Methodology The study included 312 adolescents, with 241 individuals presenting with caries and 71 caries-free, aged 12-15 years. Dental caries assessment was performed using DMFT (Decayed, missed, filled teeth) index. Oral samples were collected, and 16S rRNA (16S ribosomal ribonucleic acid) gene sequencing targeting the V3-V4 hypervariable regions on an Illumina MiSeq platform was performed to profile the microbial communities. Functional metagenomic predictions were generated using PICRUSt2 v2.5.0, using the KEGG database for bacterial pathway abundance estimation. Data analysis was conducted using Python 3.9.16 and R 4.2.2. Results The alpha diversity was insignificant, while beta diversity analysis demonstrated clear distinctions by Bray-Curtis (F=2.5, p=0.003) and weighted UniFrac distances (F=4.4, p=0.002). The Neisseria and Prevotella genera, and Gammaproteobacteria class showed significant associations with dental caries (MaAsLin2 p≤0.05, LDA≥2), stronger predictive power (AUC=0.65, F1=0.83), and higher predicted functional activity through glutathione metabolism, RNA degradation, and unsaturated fatty acid metabolism pathways. Conclusions This study identified specific oral microbiome patterns associated with dental caries in Kazakhstani adolescents, revealing interactions between key bacterial taxa and metabolic pathways.

Aging is associated with a decline in oral immune function, marked by reduced levels of antimicrobial peptides such as defensins. Capsaicin, a bioactive component found in chili peppers, has been theorized to modulate immune responses through specific receptor pathways. This study examined the effects of aging on oral defensin levels and the potential mitigating role of capsaicin, mediated by the immune response in oral tissues. We conducted a comparative analysis between young and aged mice, with or without capsaicin supplementation, for 3 months. The effect of capsaicin was also studied in vitro in senescence‐induced human oral keratinocytes. We found that aging did not reduce defensin levels uniformly but did so in some instances. Capsaicin treatment increased defensin levels in these cases, potentially through transient receptor potential cation channel subfamily V member 1 (TRPV1)‐mediated pathways in the oral cavity. Capsaicin supplementation may counteract age‐related declines in oral defensin levels, enabling the maintenance of oral immune function during aging.

Upon review, we have identified an error in the human TNF-α primer sequence reported in Table 1 of our paper titled “Erythritol can inhibit the expression of senescence molecules in mouse gingival tissues and human gingival fibroblasts”

The systemic effects of the artificial sweetener sorbitol on older adult individuals have not been elucidated. We assessed the effects of sorbitol consumption on cognitive and gingival health in a mouse model. Aged mice were fed 5% sorbitol for 3 months before their behavior was assessed, and brain and gingival tissues were collected. Long‐term sorbitol consumption inhibited gingival tissue aging in aged mice. However, it caused cognitive decline and decreased brain‐derived neurotrophic factor (BDNF) in the hippocampus. Sorbitol consumption did not affect homeostatic function; however, it may exert effects within the brain, particularly in the hippocampus.

The exact sites of premature hair graying and whether tooth loss causes this condition remain unknown. In this study, we aimed to explore the effect of reduced mastication on premature hair graying. Maxillary first molars were extracted from young mice, and the mice were observed for 3 months, along with non‐extraction control group mice. After 3 months, gray hair emerged in the interbrow region of mice in the tooth extraction group but not in the control group. The expression of tyrosinase‐related protein‐2 (TRP‐2) mRNA was lower in the interbrow tissues of young mice without maxillary molars than in those with maxillary molars. Tooth loss leads to interbrow gray hair growth, possibly because of weakened trigeminal nerve input, suggesting that reduced mastication causes premature graying. Thus, prompt prosthetic treatment after molar loss is highly recommended.

Oral aging causes conditions including periodontal disease. We investigated how the sugar alcohol erythritol, which has anti-caries effects, impacts aging periodontal tissues and gingival fibroblasts in mice and humans in vivo and in vitro. Mice were classified into three groups: control groups of six-week-old (YC) and eighteen-month-old mice (AC) and a group receiving 5% w/w erythritol water for 6 months (AE). After rearing, RNA was extracted from the gingiva, and the levels of aging-related molecules were measured using PCR. Immunostaining was performed for the aging markers p21, γH2AX, and NF-κB p65. p16, p21, γH2AX, IL-1β, and TNFα mRNA expression levels were higher in the gingiva of the AC group than in the YC group, while this enhanced expression was significantly suppressed in AE gingiva. NF-κB p65 expression was high in the AC group but was strongly suppressed in the AE group. We induced senescence in cultured human gingival fibroblasts using H₂O₂ and lipopolysaccharide before erythritol treatment, which reduced elevated senescence-related marker (p16, p21, SA-β-gal, IL-1β, and TNFα) expression levels. Knockdown of PFK or PGAM promoted p16 and p21 mRNA expression, but erythritol subsequently rescued pyruvate production. Overall, intraoral erythritol administration may prevent age-related oral mucosal diseases.

Tooth loss and decreased masticatory function reportedly affect cognitive function; tooth loss allegedly induces astrogliosis and aging of astrocytes in the hippocampus and hypothalamus, which is a response specific to the central nervous system owing to homeostasis in different brain regions. Capsaicin, a component of red peppers, has positive effects on brain disorders in mice. Decreased expression of transient receptor potential vanilloid 1, a receptor of capsaicin, is associated with the development of dementia. In this study, we investigated the effect of capsaicin administration in aged mice (C57BL/6N mice) with reduced masticatory function owing to the extraction of maxillary molars to investigate preventive/therapeutic methods for cognitive decline attributed to age-related masticatory function loss. The results demonstrated that mice with impaired masticatory function showed decreased motor and cognitive function at the behavioral level. At the genetic level, neuroinflammation, microglial activity, and astrogliosis, such as increased glial fibrillary acidic protein levels, were observed in the mouse brain. The mice with extracted molars fed on a diet containing capsaicin for 3 months demonstrated improved behavioral levels and astrogliosis, which suggest that capsaicin is useful in maintaining brain function in cases of poor oral function and prosthetic difficulties.