Paraoxonase 1 ( PON 1 ) Q 192 R Gene Polymorphism and Cancer Risk : A Meta-Analysis Based on 30 Publications

About 14.1 million cancer cases and 8.2 million cancer deaths were reported in the GLOBOCAN 2012, indicating that cancer has already been a critical public health problem around the world (Torre et al., 2015). It is known to us that cancer is a disorder arising from complex interactions between genetic predispositions and environmental factors (Pharoah et al., 2004; Bredberg, 2011). And gene PON1 is located on the long arm of the chromosome 7q21.3 (Humbert et al., 1993), and the protein encoded by this gene is responsible for the


Introduction
hydrolysing organophosphate pesticides and nerve gasses process. Studies indicated that the activity of PON1 can be influenced by the polymorphisms of the PON1. Besides, several variants in PON1, such as Q192R, L55M etc., have been uncovered as biologically plausible candidates for effects on cancer. The first polymorphism (rs662A>G) was arising from the substitution of glutamine (Q genotype) by arginine (R genotype) at position 192 in exon 6 of the PON1 genes. Previous studies suggested that the PON1 activity of the PON1 192R allele carriers was identified to be higher than that of the Q carriers (Davies et al., 1996;Mackness et al., 1997;Li et al., 2000). Recently, several studies have uncovered the association between Q192R polymorphism and malignant tumor susceptibility, including bladder cancer (Ozturk et al., 2009), renal cancer (Uyar et al., 2011) and glioma (Zhao et al., 2012). In the study conducted by Aygac et al. (2009), they investigated the association between PON1 Q192R polymorphism and ovarian cancer risk in a small sized case-control study of 51 cases and 54 controls in a Turkish Population, and revealed that this polymorphism increased the risk of ovarian cancer. Nevertheless, a lack of association between this polymorphism and brain astrocytoma or meningioma risk was also obtained by Martinez et al. (2010).
Based on the significant role of PON1 in cancer carcinogenesis and the genotype-phenotype correlation, we hypothesized that genetic variant Q192R in PON1 might be associated with cancer susceptibility. Awkward, the data reported are conflicting and inconclusive. Thus, we conducted a meta-analysis aiming to define the association between the Q192R polymorphism and cancer risk.

Search strategy
We searched the PubMed, Web of Science, Google Scholar and Embase for all relevant articles before March 22, 2015, by using the keywords "paraoxonase 1" or "PON1," "polymorphism," "tumor," or "malignancy," or "cancer," or "carcinoma". Additional reports on this issue were uncovered by conducting a hand search of the references extracting from the reviews or original research articles. All the retrieved results were confined to human populations and the genotype frequency can be obtained from these reports. When different authors published more than one of the same population or the same authors reported the overlapping data, we will select the most recent or comprehensive study into our metaanalysis. Besides, when one publication reported more than one cancer types or populations, we will extract the data separately.

Inclusion criteria and exclusion criteria
Reports were enrolled in our study keeping to the following criteria: i) Reports that assessed the association between the Q192R polymorphisms in PON1 and cancer risk; ii) Reports that designed in case-control study; iii) The genotype frequency was available for the cases and controls, or we can get it through calculating. Reports were removed from our report when they were: i) Case-only study, review or case report; ii) Reports without efficient genotype frequency data; iii) Overlapping reports; iv) Reports related to Animals.

Data extraction
Three of the authors (Meng Zhang, Hu Xiong and Lu Fang) extracted the detailed data from these eligible reports independently. Consensus for any controversy was reached and all the case-control studies followed the inclusion criteria. For each report, the following data will be gathered: the last name of the first author, the publication year, the ethnicity of each population, the genotype frequency for the cases and controls, the control source, the genotyping methods and cancer types. The ethnic descents can be divided into Caucasian, Asian, African or Mixed ethnicity group (more than one ethnic descent).

Statistical analysis
We used the OR and 95% CI to estimate the strength of the associations between Q192R polymorphism in PON1 and the cancer risk under five genetic models: allele contrast (R vs Q), homozygote (RR vs QQ), heterozygote comparison (RQ vs QQ), recessive (RR vs RQ/QQ), and dominant (RR/RQ vs QQ) models. We also performed stratified analysis by ethnicity and the type of cancers. Nevertheless, when only one cancer type encompassed less than two case-control studies, we will subdivide it into the group of ''Other Cancers''. Besides, we calculated the heterogeneity via a chi-square based Q statistic test. By calculating I 2 and P values, the effect of heterogeneity can be quantified. Once the I 2 value <50 % and P>0.10, suggesting that no significant heterogeneity was uncovered, and ORs can be pooled by a fixed-effects model. If not, we will select a random-effects model (DerSimonian and Laird, 1986). In addition, a professional web-based program can be used to tested the Hardy-Weinberg equilibrium (HWE) (http://ihg2.helmholtzmuenchen.de/cgibin/hw/hwa1.pl) for the control group (Zamora-Ros et al., 2013); if P>0.05, suggesting that the control group accords with the HWE balance. We further performed sensitivity analysis to evaluate the stability of these data.
When HWE disequilibrium existed, we will apply sensitivity analysis to evaluate the stability of these data by removing a single study from the enrolled publications to uncover the impression of the separate data set on the pooled ORs (P<0.05 was considered statistically significant) (Tobias and Campbell, 1999).Finally, possibility of the publication bias was investigated by using Begg's test and Egger's test (Begg and Mazumdar, 1994;Egger et al., 1997), and P<0.05 was considered as statistically significant. All the statistical tests can be conducted by STATA Software (version 12.0, stata Corp), and P<0.05 for any tests or genetic models were regarded as statistically significant.

Meta-analysis
To sum up, our results have revealed that the PON1-192R allele was associated with a reduced risk of the overall cancers in allele contrast model (R vs Q: OR= 0.843, 95% CI=0.725-0.979, P heterogeneity =0.000) (Table 2, Figure 2a). In the cancer type subgroup analysis, we identified an increased risk in lymphoma (R vs Q: OR=1.537, 95% CI=1.246-1.896, P heterogeneity =0.944; RR    Figure 2b) was uncovered.

Publication bias and sensitivity analysis
Here, we conducted a sensitivity analysis to investigate the impression of individual publications on the integrated data by removing a single report from the pooled analysis each time. And no individual study was revealed influenced the pooled OR (Figure 3) DOI:http://dx.doi.org/10.7314/APJCP.2015.16.10.4457 Paraoxonase 1 (PON1)

Discussion
Previous studies suggested that an increased risk of a variety of cancers may relate to oxidative stress and free radicals (Ames, 1983;Sun, 1990). Plenty of endogenous free-radical scavenging systems were existed in our body. PON1, an antioxidant enzyme, may lead to the imbalance of the antioxidant/oxidant system (Karaman et al., 2010), and induce oxidative stress and the ROS formation. Previous studies have revealed a depressed expression of PON1 in lung cancer (Elkiran et al., 2007), pancreatic (Akcay et al., 2003a), and gastric cancer (Akcay et al., 2003b). Furthermore, publications also showed that Q192R polymorphism increased the risk of bladder cancer (Ozturk et al., 2009) and renal cancer (Uyar et al., 2011), while a lack of association between this polymorphism and brain tumor, colorectal cancer risk was also uncovered (Van Der Logt et al., 2005;Rajaraman et al., 2008). R allele may contribute to the improvement of the detoxification activity of PON1 enzyme confront with latently carcinogenic products of oxidative stress and lipid peroxidation (Cejas et al., 2004).
In our work, we aim to investigate the association between PON1-Q192R polymorphism and cancer risk. We identified that Q192R polymorphism was associated with a decreased risk for cancer development, particularly for breast cancer. In the study conducted by Delimaris et al. (Delimaris et al., 2007), they reported that, during the pathogenesis of breast cancer, oxidative stress may contribute to the cell proliferation and malignant conversion process. Thus, it is fair to predict that PON1, which is a part of the lipid peroxidation scavenging systems, may affect the pathogenesis of breast cancer. In the subgroup analysis by cancer type, the results showed that PON1-192R allele was associated with a decreased risk in breast cancer and prostate cancer (in homozygote and recessive models), indicating that PON1-Q192R polymorphism may work as a protective factor for these two cancer types. Nevertheless, an increased risk was uncovered in lymphoma and prostate cancer (in heterozygote comparison and dominant models), a result consistent with previous studies (Kerridge et al., 2002;Antognelli et al., 2005). Stratifying by control source (hospital based or population based), a decreased risk of the overall cancers was revealed by homozygote and dominant models in hospital based group.
Notably, in the stratified analysis by ethnicity, a significantly reduced risk of the overall cancers under allele contrast model was uncovered in Caucasian. Previous studies indicated that PON1 192 Q allele carriers were reported to be lower than that of the R carriers (Davies et al., 1996;Mackness et al., 1997;Li et al., 2000), and a lower PON1 level was regarded as a risk for cancer (Ellidag et al., 2014); notably, allele distributions varied obviously in control groups when stratified by the ethnic group, a result consistent with those reported by the National Center of Biotechnology Information (NCBI) for Caucasian (Q: 0.668) and Asian population (Q: 0.430).
Although we have conducted a comprehensive retrieve for all attainable eligible publications and presented with a landscape of the association between PON1 Q192R polymorphism and cancer risk, there are still existed several limitations that should be interpreted. Firstly, the number of the publications and the sample size of     each reports were relatively small, when a stratification analysis was performed for the cancer type, ethnicity, or the control source, resulting in insufficient capacity which cannot identify slight influence on cancers. Secondly, most of the enrolled publications were Caucasian that might result in the inconspicuousness. Thirdly, there was no data available for Africans. Fourthly, since the lack of raw data from these publications, no further assessment was performed for the potential gene-gene interactions or gene-environment interactions. In conclusion, our study has successfully elaborated that PON1-192R allele was associated with a significantly decreased risk of the overall cancers. More research will be continued in order to refine the investigation on this issue of interest, with larger sample size, detailed original data, especially investigations for African.