Aim Individuals with olfactory or gustatory impairment often have associated difficulties with food‐related activities. As both functions decline in older adults, we investigated the association of these impairments with sarcopenia/frailty indexes in community‐dwelling older adults. Methods A total of 141 participants (69 men and 72 women, mean age 73.0 years) were enrolled. Odor identification was examined using the Open Essence test. Salty and sweet tastes were assessed using a whole‐mouth gustatory test. Participants underwent evaluation of the appendicular skeletal muscle mass index (ASMI) by InBody720 and grip strength, and determination of the Study of Osteoporotic Fractures frailty index. Results Participants with olfactory impairment (Open Essence ≤7), but not with gustatory impairment, showed a significantly higher prevalence of ASMI and grip strength less than the cut‐off values recommended by the Asian Working Group for Sarcopenia, and Study of Osteoporotic Fractures frailty and/or pre‐frailty status, compared with those without impairment. Multivariate logistic regression analysis showed a significant association of olfactory impairment with ASMI less than the cut‐off value, grip strength less than the cut‐off value, Asian Working Group for Sarcopenia sarcopenia and pre‐frailty/frailty in the Study of Osteoporotic Fractures index in the whole population, and with ASMI less than the cut‐off value and Asian Working Group for Sarcopenia sarcopenia in women, after adjustment. Three (Japanese cypress, wood and roasted garlic) and four (Japanese orange, India ink, menthol and curry) Open Essence odorants were elucidated as the “sarcopenia subset” and “frailty subset,” respectively, and showed higher ability to identify sarcopenia and frailty status, compared with the remaining five odorants. Conclusions These findings suggest that olfactory impairment is closely associated with sarcopenia and/or frailty in community‐dwelling older adults. Geriatr Gerontol Int 2019; 19: 384–391.

Post-upper respiratory tract infection related olfactory dysfunction typically occurs due to neural damage after an upper respiratory tract infection associated with a common cold or influenza. At present, Tokishakuyakusan, a Japanese traditional Kampo medicine, has been found to be effective for post-viral olfactory dysfunction. However, the pharmacodynamics of Tokishakuyakusan in the treatment of post-viral olfactory dysfunction remains unresolved. We investigated the effects of Tokishakuyakusan on the regeneration of olfactory neurons and expression of nerve growth factor (NGF) in neural systems, using in vivo murine studies and in vitro cell culture studies. Eight-week-old BALB/C female mice were fed a pellet diet with or without Tokishakuyakusan. Degeneration of cells in olfactory epithelium was induced by intraperitoneal methimazole injection. Regeneration of olfactory neurons was observed by histological and immunohistochemical procedures. NGF expression in the olfactory bulb was measured by enzyme-linked immunosorbent assay. NGF gene and protein expression were measured using rat primary cultured astrocytes by real-time polymerase chain reaction and enzyme-linked immunosorbent assay. We found that olfactory marker protein, Ki-67, and NGF were more highly expressed in the olfactory epithelium during the regeneration period in mice receiving Tokishakuyakusan. In cultured astrocytes, Tokishakuyakusan as well as its individual components, Atractylodes lancea rhizome and Japanese angelica root, increased NGF expression. Screening assays revealed that NGF production was increased by atractylodin and levistolide A, which are ingredients in Atractylodes lancea rhizome and Japanese angelica root, respectively. These results suggest that Tokishakuyakusan promotes regeneration of olfactory neurons by increasing NGF expression in the olfactory bulb.

Although the olfactory nerve is involved in nasal transport of insulin-like growth factor-1 (IGF-1) to the brain, to our knowledge there have been no direct assessments of the effects of olfactory nerve damage on this transport. To determine whether olfactory bulb resection resulted in reduced transport of nasally administered human recombinant IGF-1 (hIGF-1) to the cerebrum, we measured the uptake of nasally administered iodine-125 hIGF-1 ((125)I-hIGF-1) in the cerebrum as a percentage of that in the blood in male ICR mice subjected to left olfactory bulb resection (model mice) and in sham-operated male ICR mice (control mice). Phosphorylated extracellular signal-regulated kinase (ERK) 1/2 (Thr202/Tyr204)/(Thr185/Tyr187) as a percentage of total ERK 1/2 in the left cerebrum was also assessed by using enzyme-linked immunosorbent assay after nasal administration of hIGF-1. Uptake of nasally administered (125)I-hIGF-1 in the cerebrum as a percentage of that in the blood was significantly lower in the model group than in the control group 30min after nasal administration of hIGF-1. Unilateral olfactory bulb resection prevented nasally administered hIGF-1 from increasing the phosphorylation of ERK 1/2 in the mouse cerebrum in vivo. These findings suggest that olfactory bulb damage reduces nasal transport of hIGF-1 to the brain in vivo.

Estrogen has been shown to affect differentiation and proliferation as a mitogen in various neural systems. Olfactory receptor cells are unique within the nervous system, and have the ability to regenerate even after an individual has reached maturity. Olfactory receptor cells also regenerate after experimentally induced degeneration. The purpose of this study is to observe the influence of estrogen depletion induced by ovariectomy on olfactory nerve regeneration. Female mice underwent bilateral ovariectomy at 8 weeks of age and received intraperitoneal administration of methimazole 1 week later. At 2, 4, and 6 weeks after methimazole administration, the olfactory mucosa was analyzed histochemically to determine olfactory epithelium (OE) thickness, olfactory marker protein distribution, and Ki-67 immunoreactivity. Furthermore, 2 weeks after ovariectomy, trkA protein distribution in the OE and nerve growth factor (NGF) levels in the olfactory bulb were determined by immunohistochemistry and enzyme-linked immunosorbent assay, respectively. Our results showed that in ovariectomized mice OMP, Ki-67, and trkA-immunopositive cells expression decreased at 2 weeks after methimazole injection, a time point at which regeneration is underway. At this same time point, although NGF production in the olfactory bulb had increased before methimazole administration, no differences were observed between the ovx and control groups. These results suggest that estrogen depletion induces a suppressive effect on regeneration of olfactory neurons, and that estrogen may have a potential use in the treatment of sensorineural olfactory dysfunction.