rs705379 — PON1 PON1 promoter -108C>T

PON1 Promoter -108C>T — The Gene Expression Switch for Your HDL's Antioxidant Guard

Paraoxonase-1 (PON1) is an enzyme that travels on HDL particles¹¹ HDL particles
High-density lipoprotein — the so-called "good cholesterol" that carries cholesterol from tissues to the liver and provides antioxidant protection in the arterial wall and functions as your bloodstream's primary defense against oxidized LDL — the form of "bad cholesterol" that initiates plaque buildup in artery walls. While most research on PON1 focuses on the coding-region variants Q192R and L55M, the promoter polymorphism at position -108 (rs705379) is arguably the strongest single genetic determinant of how much PON1 your body actually produces. Less enzyme means less protection — and the T allele cuts that protection by roughly half.

The Mechanism

The PON1 gene sits on the minus (reverse) strand of chromosome 7. In the promoter region 108 base pairs upstream of the transcription start site, a C-to-T substitution (reported as G>A in plus-strand genome files) alters the binding affinity of a transcription factor that drives PON1 expression. The -108C/T variant accounts for 22.8% of the observed variability in PON1 expression levels²² The -108C/T variant accounts for 22.8% of the observed variability in PON1 expression levels in the human liver — more than any other single PON1 polymorphism, including the widely studied coding variants. Individuals homozygous for the T allele (TT genotype; AA in plus-strand notation) show arylesterase activity of only 67.5 U/ml on average, compared to 140.9 U/ml in CC carriers — a reduction of more than 50%. Heterozygotes (CT/AG) fall between these extremes.

Beyond its direct effect on expression, a 2021 multi-omics study³³ a 2021 multi-omics study showed that the T allele also triggers DNA hypermethylation at CpG sites near the promoter, further silencing PON1 transcription. This epigenetic layer amplifies the initial transcription-factor effect, making the T allele's impact on expression self-reinforcing.

The Evidence

The expression-lowering effect of the T allele has downstream consequences for cardiovascular health. In type 2 diabetes patients, the TT genotype at the -108 position was significantly associated with elevated oxidized LDL/apoB ratios (P = 0.02)⁴⁴ the TT genotype at the -108 position was significantly associated with elevated oxidized LDL/apoB ratios (P = 0.02), providing a direct biochemical link between reduced PON1 expression and impaired LDL antioxidant protection.

For cardiovascular outcomes, a Polish cohort of 865 hemodialysis patients found the TT genotype associated with cardiovascular mortality (HR 1.27, 95% CI 1.03-1.57, P = 0.025) and cardiac mortality (HR 1.34, 95% CI 1.05-1.71, P = 0.018)⁵⁵ the TT genotype associated with cardiovascular mortality (HR 1.27, 95% CI 1.03-1.57, P = 0.025) and cardiac mortality (HR 1.34, 95% CI 1.05-1.71, P = 0.018). A companion study from the same group confirmed the cardiovascular mortality association was particularly pronounced in cigarette smokers with the TT genotype⁶⁶ cigarette smokers with the TT genotype, with significant associations for cardiac non-CHD-related mortality (P = 0.001) — suggesting that combined low-PON1 and oxidative stress from smoking is especially dangerous.

Beyond the heart, a 2021 meta-analysis of Alzheimer's disease⁷⁷ 2021 meta-analysis of Alzheimer's disease covering 15 studies found the A allele (T in coding notation) significantly associated with AD risk in Caucasians (OR 1.21, 95% CI 1.05-1.39, P = 0.009), while the GG genotype was protective (OR 0.70, 95% CI 0.56-0.88, P = 0.002). PON1's antioxidant and anti-inflammatory actions in the brain may explain this connection.

Practical Implications

Since the T allele reduces PON1 production rather than altering its catalytic efficiency, the relevant interventions focus on compensating for reduced enzyme levels. Several dietary factors have been shown to upregulate PON1 expression or activity, regardless of genotype. Polyphenols — particularly pomegranate juice, olive oil, and red wine components⁸⁸ pomegranate juice, olive oil, and red wine components — increase PON1 activity in human studies. Omega-3 fatty acids (EPA and DHA) enhance HDL functionality and support PON1's lipid-protective environment.

Smoking is the most important lifestyle factor to address: cigarette smoke both reduces PON1 activity and multiplies the cardiovascular mortality risk of the TT genotype, as demonstrated by the hemodialysis cohort data above.

Interactions

This variant interacts with both coding-region PON1 variants in the database. rs662 (Q192R)⁹⁹ rs662 (Q192R) affects the enzymatic efficiency of the PON1 that is produced, while -108C>T controls how much PON1 is made. Carrying both the TT (low expression) and RR (low antioxidant efficiency) genotypes compounds cardiovascular risk beyond either alone. Similarly, rs854560 (L55M) affects PON1 protein stability and circulating concentrations, and unfavorable combinations across all three variants produce the lowest observed PON1 activity phenotypes. Describing the specific combined effects of these three genotypes belongs in compound actions.