Atrial cardiomyopathy is caused by folate-resistence via endothelial and endothelial progenitor cell dysfunction

Recent insights support the commonly accepted idea that Atrial Fibrillation (AF) per se does not explain the wholeness of embolic strokes 1, thus forcing postulation of a broader Atrial Cardiomyopathy (AC) entity 2. Left atrial fibrosis amount (Fib) is thought to be the fundamental marker of AC. Aging apart, actually, Fib pathogenesis is not elucidated. Folate cycle disorders (FCD) are a yet underrated dysmetabolism partly explained by methylene tetrahydrofolate reductase (MTHFR)-inherited defects, ultimately leading to stroke. FCD can hinder both cellular methyl handling, thus causing endothelial dysfunction (ED) via Arg/ADMA decrease, and circulating endothelial progenitor cell (EPCs) functioning 3. Focusing reciprocal relationship between Fib and FCD might be the key to unravel AC pathogenesis.

This study aims to enquire for the hypothesis that atrial fibrosis (Fib) would relate to: 1) FCD surrogates herein explored through a)Sieric folates, b)MTHFR C677T inherited mutations and c)Arg/ADMA ratio. 2) Dysfunctional endothelial progenitor cell herein assessed through wound healing assay (WHA).

We studied 86 consecutive patients admitted to the Cardiology Unit of one General Hospital, with preserved EF, subjected to paroxysmal AF ablation. Fib was quantified by relative % of low-voltage (<0,5 mV) bipolar peak-to-peak points, with respect to the wholeness of the endocavitary mapping. Blood count cell was evaluated. MTHFR C677T genotypes were elucidated by RT-PCR. Folate were measured by a commercial laboratory test. EPCs were isolated (CD45-, CD34+, CD133+, VEGFR2+) and cultured to be subjected to WHA.

Univariate analysis was carried on through potentially predictive variables (Fig 1. bottom graphs). p-value of MTHFR ANOVA analysis across Fib was statistically significant (Fig. 1 – right graph. p < 0.01), nonetheless, MTHFR logistic regression did not pass multivariate analysis. A stepwise forward analysis was performed. Since aging is a non modifiable risk factor, a multivariate age-weighted least square regression analysis was computed.

The model shows a multiple R of 0.645, indicating a moderately strong correlation between the independent variables (RBC, Folates, Arg/ADMA) and the dependent variable (Fib). R-squared was 0.417 (Fig.2 – superior graph. – p < 0,0001). Every 1-unit increase in RBC, Arg/ADMA and folates, Fib respectively decreases by 18.5% for RBC, 0,1% for Arg/ADMA and increases by 0,9% for folates. Functional wound assay on cultured EPCs show a significantly reduced reparative potential of high-Fib derived EPCs with respect to low-Fib.

Our findings support the hypothesis that, apart from aging, FCD causing folate-resistence (intended as an higher folic sieric status) relies to a greater extent of Fib in the context of AC and such pathogenic mechanism arise from bone-marrow since both anemia (RBC reduction) and EPCs dysfunction are over-expressed.