In this study, we compared the differences between TDH parameters, which are the main components of antioxidant protection, in HPV infected women without cervical lesions and those who developed cervical dysplasia.
Our results demonstrated that TDH parameters affected in HPV positive- women with cervical intraepithelial lesions. Evaluations from peripheral blood samples of HPV positive-women represented that total and native thiol levels decreased at cervical intraepithelial lesions. Our findings supported that HPV infection related cellular changes activates detoxification systems and causes consumption of cellular antioxidant. However, our results were not statistically significant, differences between study groups were thought that cervical neoplastic progression effects oxidant/antioxidant status and that could be shown in systemic circulation. These findings demonstrated that HPV infection caused cervical neoplastic process is closely related with oxidant and antioxidant regulation. According to this data we concluded that replacement of antioxidants in HPV infection could be a strategy for treatment of infection and prevention from cellular changes.
Experimental and observational studies show that a large portion of HPV infection are spontaneously regressed however a small part of them progress and generate cervical cancer. Being HPV infected is not just enough for cancer development, there is still lack of information about other individual and environmental factors and their mechanisms on pathogenesis. Free oxygen radicals are important factors those effective in carcinogenesis by signaling pathway up regulation, cell differentiation, proliferation and change of cellular survival. HPV reproduces in infected and transformed cells and disrupts the redox balance (12–15). Past studies showed that immune response of the host to HPV infection influence oxidative stress and could be demonstrated with alteration of stress markers. Siegel et al. (16) evaluated the relation between oxidant load and HPV clearance, and they determined a high oxidant status. On the contrary, an increase in oxidant levels, antioxidant enzymes have been shown to be lowered in patients with CIN and cervical carcinoma due to excessive consumption (17–19). According to an in-vivo study evaluating the effect of the Redox system on carcinogenesis, an increased oxidant environment has been shown to be effective in HPV 16 neoplastic progression, and oxidative modification of DNA and proteins in dysplastic tissues have influenced cellular differentiation, leading to neoplastic progression. In cancerous tissue, controlling oxidative damage could be provided by selective reduction of key detoxification proteins. (13).
Histopathological evaluations show an increased inflammatory infiltration in severe HPV-induced lesions. In the early stages, the virus causes infection at basal cells not associated with circulating immune cells therefore inflammation does not play a central role in the pathogenesis of HPV infection. Persistent infection causes chronic inflammation and triggers an imbalance between pro-oxidant and antioxidants (14).
During intracellular reactive oxygen species increase, local antioxidant capacity and numerous intracellular adaptive mechanisms upregulate to prevent the development of apoptosis and to protect the tissue. Throughout free radicals rise above physiological levels, the regulation of redox homeostasis, which was the cellular protection system of the organism, is disrupted and initiates the process of uncontrolled cell growth and carcinogenesis. (20, 21). Redox homeostasis is controlled by oxidizing and reducing of free radicals and thiol-containing proteins in the cell.
Thiols are the parts of the natural antioxidant enzyme system in the organism that contain Sulfhydryl and form disulfide in antioxidant activation (22). Attachment of sulfur and hydrogen atoms to a carbon atom forms sulfhydryl and oxidation reactions form disulfide bonds between two sulfhydryl groups (23). This binding is reversible and disulfides can reduce to thiol groups to sustain homeostasis (24). This homeostasis plays a crucial role in antioxidant protection, detoxification, signal transmission, programmed cell death, organizing enzymatic reaction, transcription factors and intra and inter-cellular signaling mechanisms (25).
Many compounds like cysteine, methionine, glutathione, homocysteine, cysteinyl-glycine and glutamylcysteine are containing thiol groups and have structural alterations under oxidative stress. These proteins oxidize to form reversible disulfide bonds. Structural and functional changes occur in these proteins during losing thiol groups. (6, 7). Plasma and tissue levels of thiol groups decrease in the course of prevention from the destructive effects of free oxygen radicals (8). The transformation of thiols into disulfides is an early indicator of protein oxidation from reactive oxygen radicals. Measurement of total thiol level and determination of TDH is a mirror of excessive free oxygen radical formation in many illnesses (26).
Disruption of this ratio acts a part in the pathogenesis of many inflammatory diseases such as diabetes mellitus, inflammatory arthritis, renal failure, cancer, Parkinson, Alzheimer, multiple sclerosis. Shifting thiol/disulfide balance to disulfide direction was seen in degenerative diseases such as diabetes, obesity, and pneumonia, to thiol direction poses risk factor neoplastic processes such as multiple myeloma, bladder, colon and kidney cancer (27).
The colorimetric method improved by Erel and Neşelioğlu (11) renders possible to provide information about oxidative stress by identifying the total plasma thiol/disulfide ratio. The easy, inexpensive and practical method is carried out with a fully automatic analyzer that does not require separation. It can be used to evaluate free radicals synthesized by many different metabolic pathways, including aerobic respiration in mitochondria. (12). Before this measurement technique was developed, only low molecular weight thiol components which were cysteine, glutathione, and homocysteine could be measured. This method allows measuring the majority part of thiol and disulfides in albumin and proteins. According to the old method, thiol / disulfide measurement did not reflect true homeostasis.
In enzymes containing thiol, free radicals formed after normal metabolites or pathological processes cause structural and functional disturbance and alterations in thiol/disulfide balance. A decrease in plasma thiol concentration indicates an increase in free radical formation. A small proportion of HPV-infected cells progress to cancer, the expression of E6 and E7 oncogenes play role in this process. Camporeale et al. (28) studied the molecular mechanism of potential damages of the oxidative environment in HPV infected cells. They reported that carboxy-terminal of E7 oncoprotein is rich in the domain of cysteine and sensitive to ROS. Exposure to free radicals regulates the transition from the cytoplasm to the nucleus by creating disulfide bonds.
HPV infection has a local effect at cervical epithelium and evaluation of TDH parameters at cervical secretions could be most informative for detection of oxidant/ antioxidant status. This was one of the limitations of our study. The other limitation was cross-sectional design of the study, the levels of TDH parameters previous the infection and cervical lesion were not included in the study.
In conclusion, HPV infection related oxidative stress has systemic effects and could be demonstrated in the systemic circulation by TDH parameters. Consumption of thiol substances play role in cervical neoplastic process, replacement with antioxidants would be a treatment option for HPV infections.