Cervical Microbiota Associated with Higher Grade Cervical Intraepithelial Neoplasia in Women Infected with High-Risk Human Papillomaviruses

Abstract

It is increasingly recognized that microbes that reside in and on human body sites play major roles in modifying the pathogenesis of several diseases including cancer. However, specific microbes or microbial communities that can be mechanistically linked to cervical carcinogenesis remain largely unexplored. The purpose of the study was to examine the association between cervical microbiota and high-grade cervical intraepithelial neoplasia (CIN 2+) in women infected with high-risk (HR) human papillomaviruses (HPVs) and to assess whether the cervical microbiota are associated with oxidative DNA damage as indicated by the presence of cervical cells positive for 8-hydroxy-2′-deoxyguanosine. Study included 340 women diagnosed with CIN 2+ (cases) and 90 diagnosed with CIN 1 (non-cases). Microbiota composition was determined by Illumina sequencing of the 16S rRNA gene amplified from DNA extracted from cervical mucus samples. Measures of alpha/beta-diversity were not associated with either CIN severity or oxidative DNA damage. However, a cervical mucosal community type (CT) dominated by L. iners and unclassified Lactobacillus spp. was associated with CIN 2+ (OR=3.48, 95% CI: 1.27–9.55). Sequence reads mapping to Lactobacillaceae, Lactobacillus, L. reuteri and several sub-genus level Lactobacillus OTUs were also associated with CIN 2+ when examined independently (effect size >2.0; p < 0.05). Our 16S rRNA sequencing results need confirmation in independent studies using whole-genome shotgun sequencing and that would allow sharpening the suggested associations at finer taxonomic levels. Our results provide little evidence that DNA oxidative damage mediates the effect of the microbiome on the natural history of HPV infection and CIN severity.

The vaginal microbiota, human papillomavirus infection and cervical intraepithelial neoplasia: what do we know and where are we going next?

“…However, further studies have shown that under the hypoxic conditions of the vagina, bacteria are unable to make significant levels of H 2 O 2 , which is subsequently present at low levels in the human vagina, and these physiological levels are unable to inhibit growth of BV-associated species in vitro [83, 84]. The observation that L. iners often predominates in the presence of HPV infection [53] and CIN [56, 57] may also be linked to the relative instability of this CST in comparison to other Lactobacillus spp.-dominant CSTs [21], allowing growth of strict anaerobes resulting in transition to CST IV, which as previously discussed is commonly found in association with dysplasia [54–56]. However, vaginal lactobacilli can exhibit cytotoxic effects on cervical tumour cells in vitro, independent of pH and lactic acid, without the same effects on normal cervical cells [85].…”

“…The HPV E6 oncoprotein [98] is also known to use this mechanism which results in the loss of E1 and E2 genes, and subsequently uncontrolled transcription of E6 and E7 enabling increased cellular proliferation, and decrease apoptosis [99]. Despite this evidence, a recent study by Piyathilake and co-workers [57] did not report any significance associated between VMB composition and oxidative stress-induced DNA damage.…”

“…Piyathilake and colleagues [57] have also studied women with CIN (cytologically defined HSIL ( n  = 340) vs LSIL ( n  = 90); all women were hrHPV positive) and used the Dirichlet multinomial mixture model to partition samples into four different metacommunities (partitions 1–4), rather than the previously defined CSTs. Unlike the three previously described studies, this group did not find a high vaginal microbial diversity (CST IV/BV-like VMB) to be associated with HSIL.…”

“…All four studies in patients with CIN [54–57] are observational studies, and with lack of longitudinal data, it is only possible to demonstrate association with disease states rather than causality. This has been acknowledged as one of the current limitations of ongoing research into the ‘oncobiome’; that is the microbiota associated with cancer development [59].…”

Dimensions of Cooperative Cervical Oncogenesis in Abortive Infection by Human Papillomavirus

“…It is increasingly recognized that microbes resident in the human body play major roles in modifying carcinogenesis [7,8]. The effects of inhibition and degradation via the ubiquitin pathway of p53 by E6 and the inhibition of the retinoblastoma gene and subsequent released actions of E2F transcription factors are centered on essential loss of control of check-points in epithelial cell proliferation.…”