Toxicogenetic relevance of MMP-9 polymorphisms in mercury exposed subjects

Author(s)

Anna Laura Bechara Jacob Ferreira

• Document type: Doctoral Thesis
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Faculdade de Ciências Médicas
• Defense date: 2010-01-07

Examining board members

Jose Eduardo Tanus Santos; Eduardo Mello De Capitani; Wilson Araújo da Silva Junior; Márcia Andréia Mesquita da Silva Veiga; Edson Antunes

• Advisor: Jose Eduardo Tanus Santos

Abstract

Mercury (Hg) exposure causes health problems, including cardiovascular diseases. Although the mechanisms are not precisely defined, metalloproteinases (MMP) -2 and -9 may be involved. Increased expression and activities of these MMPs are demonstrated in several pathological conditions, and recent studies have demonstrated that circulating levels of MMPs could be used as a blood-borne biomarker for cardiovascular risk, even in healthy individuals. The gene encoding MMP-9 presents genetic polymorphisms which affects the expression and activity level of this enzyme, two of them, present in the promoter region [C- 1562T and (CA)n] are functionally relevant, having been involved in several diseases. We investigated if the association between circulating levels of MMP-2, MMP- 9 and their endogenous inhibitors (TIMPs) -2 and -1 with circulating levels of Hg in individuals exposed to metal through consumption of fish in the Brazilian Amazon. Then, we examined whether these MMP-9 polymorphisms affect circulating MMP-9 net levels in persons exposed to mercury. For this purpose, we analyzed the concentrations of blood and plasma Hg by inductively coupled plasma-mass spectrometry (ICP-MS). MMPs and TIMPs concentrations were measured in plasma samples by zymography and ELISA, respectively. Thiobarbituric acid-reactive species (TBARS) were measured in plasma to assess oxidative stress. Selenium (Se) levels were determined by ICPMS, because it is an antioxidant. Genomic DNA was extracted from whole blood, and genotypes for the C- 1562T and the microsatellite (CA)n polymorphisms were determined. The relationships between biomarkers of Hg and MMPs levels, as well as the relationship between MMP-9 genotypes and MMP-9 levels, were examined using multivariate regression models. No relationship was found between Hg in blood or plasma and MMPs. However, plasma Hg levels were negatively associated with TIMPs levels, and thereby with increasing MMP-9/ TIMP-1 and MMP-2/TIMP-2 ratios, thus indicating a positive association between plasma Hg and circulating net MMP-9 and MMP-2 activities. The polymorphisms of MMP-9 were not related to MMP-9 net levels when all subjects were analyzed together. However, when we divided the population into tertiles of plasma Hg concentrations, the polymorphism (CA)n affected MMP-9 concentrations and MMP-9/TIMP-1 ratios in people with lower levels of Hg. MMP-9 levels were higher in persons with genotypes including alleles with more than 21 CA repeats (H alleles) and lower in those whose genotype including alleles with less than 21 CA repeats (L alleles). Conversely, this polymorphism had no effects in persons with intermediate or high plasma Hg level. No association was found between the C-1562T polymorphism and MMP-9 levels in the three groups. These findings show the effect of Hg on MMP-9 net, and that this effect is modulated by the (CA)n polymorphism of MMP-9. The increase in MMPs levels could increase the risk of developing cardiovascular diseases in persons exposed to Hg, especially those with HH genotype. (AU)