Exploring biomarkers of neurodegenerative risk: associations of oxysterols, sex hormones, and reproductive characteristics in older women

Women face a higher lifetime risk of developing neurodegenerative diseases such as Alzheimer's disease and related dementias. The menopausal transition, characterized by a decline in estrogen levels, may affect cholesterol metabolism and neurodegenerative processes. Oxysterols, oxidized cholesterol derivatives, play a role in these pathways, with 24(S)-hydroxycholesterol (24HC) reflecting brain cholesterol turnover and 27-hydroxycholesterol (27HC) linked to systemic cholesterol metabolism. We investigated associations of plasma oxysterols with circulating sex hormones and characteristics of reproductive history in 1,974 postmenopausal women with no history of dementia from the Women's Health Initiative, taking into account APOE4 status and cholesterol-lowering medication. We found that higher levels of bioavailable estradiol were associated with higher 24HC and 27HC levels, and higher estrone was associated with higher 24HC (all P values <0.05). Associations of estradiol with 24HC and 27HC were stronger among APOE4 carriers and those not using cholesterol-lowering medication, with a significant interaction between bioavailable estradiol and APOE4 in relation to 27HC (p for interaction = 0.04). Having an older age at menopause was associated with lower 24HC among those taking cholesterol medication (p for interaction = 0.03). Our findings suggest that 24HC and 27HC may be proxy biomarkers of neuronal health and estrogen status in postmenopausal women. The stronger associations between estradiol and oxysterols among APOE4 carriers and those not using cholesterol medication suggest the need to account for hormonal, genetic, and pharmacological factors when evaluating neurodegenerative risk. Longitudinal studies are warranted to further investigate oxysterols as potential early biomarkers of risk for Alzheimer's disease and related dementias.