Clopidogrel; a prescription drug to reduce ischemic events in cardiovascular patients; has been extensively studied in mostly European individuals but not among Caribbean Hispanics. This study evaluated the low abundance and reduced activity of paraoxonase-1 (PON1) in clopidogrel-resistant patients as a predictive risk biomarker of poor responders and disease severity in this population. Thirty-six patients on clopidogrel (cases; divided into poor and normal responders) were enrolled along with 11 cardiovascular patients with no clopidogrel indications (positive control) and 13 healthy volunteers (negative control). Residual on-treatment platelet function (PRU); PON1 abundance by western blotting and PON1 activity by enzymatic assays were measured. PON1 genotyping and computational haplotype phasing were performed on 512 DNA specimens for two genetic loci (rs662 and rs854560). No statistical differences in mean relative PON1 abundance were found among the groups (p> 0.05). However; a significantly lower enzymatic activity was found in poor responders (10.57 ± 6.79 µU/mL) when compared to controls (22.66 ± 8.30 µU/mL and 22.21 ± 9.66 µU/mL; p= 0.004). PON1 activity among carriers of the most prevalent PON1 haplotype (AA|AA) was significantly lower than in wild-types (7.90 µU/mL vs 22.03 µU/mL; p= 0.005). Our findings suggested that PON1 is a potential biomarker of cardiovascular disease severity in Caribbean Hispanics.

Anti-oxidative and anti-inflammatory properties of high-density lipoprotein (HDL) are thought to be mediated by paraoxonase 1 (PON1), a calcium-dependent hydrolytic enzyme carried on a subfraction of HDL that also carries other anti-oxidative and anti-inflammatory proteins. In humans and mice, low PON1 activity is associated with elevated oxidized lipids, homocysteine (Hcy)-thiolactone, and proteins modified by these metabolites, which can cause oxidative stress and inflammation. PON1-dependent metabolic changes can lead to atherothrombotic cardiovascular disease, Alzheimer’s disease, and cancer. The molecular bases underlying these associations are not fully understood. Biochemical, proteomic, and metabolic studies have significantly expanded our understanding of mechanisms by which low PON1 leads to disease and high PON1 is protective. Studies discussed in this review highlight the changes in gene expression affecting proteostasis as a cause of the pro-oxidative and pro-inflammatory phenotypes associated with attenuated PON1 activity. Accumulating evidence supports the conclusion that PON1 regulates the expression of anti-oxidative and anti-inflammatory proteins, and that disruption of these processes leads to disease.

Elevated levels of homocysteine (Hcy) and related metabolites are associated with Alzheimer’s disease (AD). Severe hyperhomocysteinemia causes neurological deficits and worsens behavioral and biochemical traits associated with AD. Although Hcy is precluded from entering the Genetic Code by proofreading mechanisms of aminoacyl-tRNA synthetases, and thus is a non-protein amino acid, it can be attached to proteins via an N-homocysteinylation reaction mediated by Hcy-thiolactone. Because N-homocysteinylation is detrimental to protein’s function and biological integrity, Hcy-thiolactone detoxifying enzymes – PON1, BLMH, BPHL – have evolved. This review provides an account of the biological function of these enzymes and of consequences of their impairments leading to phenotypes characteristic of AD.