The Impact of Local Estrogen on the Urogenital Microbiome in Genitourinary Syndrome of Menopause (GSM)

Women who have undergone menopause almost ubiquitously experience pelvic complaints at some point in the postmenopausal period. This is most commonly vaginal dryness and discomfort during sexual intercourse. From previous studies, we know that as estrogen levels decrease in menopause, changes occur in the local urogenital tract that include thinning of the vaginal epithelium, an increase in pH and an alteration of the composition of the local bacterial community, including a decrease in the typically predominant species of bacteria lactobacilli. In conjunction with declining estrogen levels, a subset of postmenopausal women experience bothersome lower urinary tract symptoms such as burning with urination, urinary urgency, incontinence and recurrent urinary tract infections. These symptoms are commonly underreported, under-treated, and have been associated with reduced quality of life and decreased productivity in menopause. "Genitourinary Syndrome of Menopause" (GSM) is a term adapted to be more inclusive of these lower urinary tract symptoms in an effort to reduce delays in evaluation and treatment. It remains controversial whether these symptoms relate directly to estrogen deprivation or are part of the "natural" aging process. Mainstay therapy includes vaginal lubricants and local estrogen therapy. Though treatment with local estrogen improves both vaginal dryness as well as urinary symptoms, the mechanism is not well understood.

Additionally, there is a subset of women who do not respond to estrogen treatment or have contraindications to estrogen use. Recent research efforts have been exploring the potential role that the microbiome may play in female pelvic discomfort and dysfunction. Unlike the vagina, the bladder has historically been considered to be a sterile environment, with the presence of bacteria implying infection. However, recent research has helped to elucidate that, similar to the skin, vagina and gastrointestinal tract, a resident microbial community or "microbiome" exists within the female bladder. Disturbances in the urinary microbial community have been correlated with conditions such as painful bladder syndrome, overactive bladder and urge urinary incontinence. These conditions have considerable symptom overlap with those seen in postmenopausal women who are experiencing GSM and may be considered to be on the same continuum.

Though microbiome research over the last decade has accelerated our understanding of the role that organisms play in health and disease, the urinary microbiome remains poorly defined. Data from ongoing research suggests that the urinary microbiome of pre- and postmenopausal women differ, which would suggest that hormone status may play a role in maintaining the microbial milieu. This research has helped us to better understand how the urinary microbiome varies under normal conditions. In order to better understand the role that estrogen plays in maintaining the bladder and vaginal flora, this study aims to characterize the effect of local estrogen on the urinary and vaginal microbiomes (together termed the "urogenital microbiome") in postmenopausal women.