Grant title
Evaluation of the role of cervical cell folate status and gene specific methylation motif as determinants of HPV persistence: a nested case-control study.
Background
Persistent or repeated infection with a high risk HPV (HR-HPV) strain is the major causal factor for intraepithelial neoplasia and cervical cancer. Folate status may influence HPV persistence.
Methods
A nested case-control study was conducted to investigate cervical cell folate concentration and tumour suppressor gene methylation as risk factors for HR-HPV persistence. Cervical cell samples from 955 women with HR-HPV infection and normal or borderline or mild cervical cell abnormalities were retrieved from the ARTISTIC study archive. These samples were designated ‘baseline’ samples.
Women were classified as cases or controls, reflecting the presence or absence of HR-HPV infection at a follow-up clinic at least 6 months from baseline. Cervical cell folate concentration, promoter methylation of five tumour suppressor genes, and cell metabolome, were measured in samples from cases and controls.
Results
A higher cervical cell folate concentration (P= 0.015) was an independent predictor of infection at follow-up. Methylation of the tumour suppressor gene DAPK was associated with a 2.64-fold (95% CI, 1.35-5.17) increased likelihood of HPV infection at follow-up whilst CDH1 methylation was associated with a 0.53-fold (95% CI, 0.331-0.844) likelihood of HPV infection at follow-up.
The predictive effect of higher cervical cell folate (P = 0.02) was also seen when only samples from women with mildly abnormal cytology were examined but not in women with normal cytology; similarly the effect of DAPK methylation (P <0.01) was seen in women with borderline or mild cervical cell abnormality but not in women with normal cytology.
The cellular metabolome from women with mild cytology at baseline was significantly different between cases and controls (P<0.001) and was suggestive of differences in host immune response pathways. Additionally, women carrying infection with high risk HPV strains 16, 18, 52 and 58 were more likely to be HPV positive at the follow-up clinic (P<0.05).
Conclusion
A higher concentration of folate in cervical cells, and promoter methylation of the tumour suppressor gene DAPK, are significant independent predictors of HPV persistence. These effects were not seen in women with normal cervical cytology.
These finding suggest that a higher cervical tissue folate concentration may adversely affect risk of cervical cancer in women with HPV infection and cellular abnormalities. Whether folate status and DAPK methylation are causally related is not known.