The male foreskin is the main site of HIV entry in heterosexual men as evidenced by the effective protection incurred upon its removal following voluntary medical male circumcision (VMMC). However, the biological mechanism by which circumcision confers this protection remains poorly understood. To understand changes to skin barrier function after VMMC, we measured transepithelial water loss (TEWL) and hydration status in the glans, foreskin and shaft before and after (glans & shaft only) VMMC as in vivo measures for skin barrier integrity. The lower TEWL and higher hydration status equates with more intact skin barrier integrity.
Hand-held vapometers and moisture meters SC & D, designed to measure water loss and content in the skin (and used extensively in dermatology and the cosmetic industry), were used to quantify TEWL (n=45 adult males), surface hydration in the stratum corneum and water content in the skin (n=31 adults) of the glans, inner foreskin and penile shaft before VMMC. These in vivo proxy measurements for skin integrity were then made two weeks after circumcision. First-pass urine samples were tested for common curable sexually transmitted infections (STIs): Chlamydia trachomatis, Neisseria gonorrhoea, Trichomonas vaginalis & Mycoplasma genitalium.
To date, we show that 20-25% men have an asymptomatic STI. In males who were STI negative prior to circumcision, the inner foreskin and glans had higher TEWL readings compared to the shaft, whereas the surface hydration and water content were the same across all anatomical sites. Two weeks after circumcision, the TEWL readings in the glans significantly decreased (from a median of 27.6 to 17 g/hr/m2) to match the shaft readings and the hydration content also decreased in all three sites but especially surface hydration in the shaft (from a median of 48 to 28 au, p=0,0061). Comparing men who were STI positive (n=9) versus STI negative at the time of VMMC, there was lower TEWL in the glans in the presence of an STI (median of 26 vs 9 g/hr/m2, p=0,033), but no differences in the hydration status.
Our data show that prior to VMMC, the inner foreskin and glans had lower skin barrier integrity which increased soon after circumcision in STI negative males, but not in those with an asymptomatic STI. This finding has implications for understanding how MMC disciplines penile tissue and gives insight into how HIV acquisition may be prevented after circumcision.