Decline in serum cholinesterase activities predicts 2-year major adverse cardiac events

Abstract

Parasympathetic activity influences long-term outcome in patients with cardiovascular disease, but the underlying mechanism(s) linking parasympathetic activity and the occurrence of major adverse cardiovascular events (MACEs) are incompletely understood. The aim of this pilot study was to evaluate the association between serum cholinesterase activities as parasympathetic biomarkers and the risk for the occurrence of MACEs. Cholinergic status was determined by measuring the cumulative capacity of serum acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) to hydrolyze the AChE substrate acetylthiocholine. Cholinergic status was evaluated in randomly selected patients undergoing cardiac catheterization. The patients were divided into two groups of 100 patients in each group, with or without occurrence of MACEs during a follow-up period of 40 months. Cox regression models adjusted for potential clinical, metabolic and inflammatory confounders served to evaluate association with clinical outcome. We found that patients with MACE presented lower cholinergic status and AChE values at catheterization (1,127 ± 422 and 359 ± 153 nmol substrate hydrolyzed per minute per milliliter, respectively) than no-MACE patients (1,760 ± 546 and 508 ± 183 nmol substrate hydrolyzed per minute per milliliter, p < 0.001 and p < 0.001, respectively), whose levels were comparable to those of matched healthy controls (1,622 ± 303 and 504 ± 126 nmol substrate hydrolyzed per minute per milliliter, respectively). In a multivariate analysis, patients with AChE or total cholinergic status values below median showed conspicuously elevated risk for MACE (hazard ratio 1.85 [95% confidence interval [CI] 1.09-3.15, p = 0.02] and 2.21 [95% CI 1.22-4.00, p = 0.009]) compared with those above median, even after adjusting for potential confounders. We conclude that parasympathetic dysfunction expressed as reduced serum AChE and AChE activities in patients compared to healthy controls can together reflect impaired parasympathetic activity. This impairment predicts the risk of MACE up to 40 months in such patients. Monitoring these parasympathetic parameters might help in the risk stratification of patients with cardiovascular disease.

Figure 1

Decreased serum levels of AChE, BChE and cholinergic status in MACE patients. Histograms of enzymatic levels of AChE (red), BChE (yellow) and cholinergic status (green) are presented for MACE, no-MACE and age-, sex- and body mass index–matched controls. The MACE histograms are left-shifted, reflecting reduced enzymatic activities in all three measurements, whereas no-MACE patients present similar distribution to that of matched controls. Hydrolyzed/min × mL, hydrolyzed per minute per milliliter.

Figure 2

HR for MACE. Means and CIs for MACE of the cardiac catheterization group are presented by using univariate and multivariate Cox proportional hazard regression for lower medians of AChE or total cholinergic status. Adj, adjusted model for conventional risk factors (see Materials and Methods).

Figure 3

Lower AChE and total cholinergic status medians predict worse outcome. Cumulative (Cum) survival curves for cardiac catheterization patients in the higher and lower median groups of AChE or total cholinergic status activity values are shown.

Figure 4

Cholinergic status values are positively correlated with inflammation and anemia. Tertiles of C-reactive protein and hemoglobin are shown, with total cholinergic status for the cardiac catheterization group of patients. Note the inverse correlations; higher cholinergic status and AChE values were associated with higher hemoglobin levels and lower hs-CRP values.

Figure 5

Measurement characteristics. Kinetic curves of thiocholine release from ATCh are shown, as measured by quantifying absorbance at 405 nm for a consecutive 1,200 s in the absence of iso-OMPA (cholinergic status) or in its presence (AChE) compared with spontaneous thiocholine release in phosphate-buffered saline (PBS) (A). Note the linearity of curves and minimal SD values. The crystallographic structures of BChE (B) and AChE (C) illustrate the general resemblance between the two enzymes. Zoom-in to the active site of BChE (D) and AChE (E); the narrower gouge in the active site of AChE can explain its capacity to hydrolyze ACh more efficiently than BChE.

Figure 6

Scheme: Two cholinesterases contribute to the cholinergic status. Schemes of the brain are shown, from which ACh is sent to the periphery and affects stress responses, cardiac functioning and cytokines release from macrophages through activation of AChR, among other functions. Also shown are AChE and BChE in the circulation, both of which hydrolyze ACh, albeit at different rates.