Background: Diseases related to oxidative stress are increasingly linked to proteotoxicity as a causative mechanism, particularly in the heart and brain. In amyloid, misfolded protein monomers coassemble initially to form preamyloid oligomers (PAOs) now recognized to be the primary cytotoxic species in this process. With aging, amyloidosis universally develops in the human atrium, composed of atrial and B-type natriuretic peptides (ANP, BNP). We have previously shown that oxidative stress accelerates formation of PAOs that alter ATP production and action potentials in atrial cells.
Objective: To characterize the metabolic effects of ANP and BNP oligomers in atrial cells and to investigate whether atrial PAOs are associated with human AF.
Methods: Bioenergetic profiling of atrial HL-1 cells was performed using extracellular flux analysis (Seahorse Bioscience XFe96) to quantitate oxygen consumption rate (OCR; normalized to total cell number), an indicator of mitochondrial respiration, in the absence and presence of natriuretic peptide (NP) oligomers (0.45-4.5 uM, 1 and 3 d exposure; n=5 each). Atrial tissue was obtained during elective cardiac surgery from patients with a history of AF, and control patients matched for demographics, surgery, and AF risk factors. Oligomer burden was assayed using a previously-published method that quantifies the fraction of atrial tissue containing PAOs.
Results: Both NP oligomers significantly reduced parameters of mitochondrial respiration. For BNP, this occurred at the lowest concentration (0.45 uM) after 1 d (ATP -41%; basal and maximal respiration -37 and -42%; spare respiratory capacity -44%). For ANP, only basal respiration was affected (-26% at 4.5 uM after 1 d). Atrial tissue was analyzed from 32 patients with a median age of 69.5 yrs who were mostly male (69%), hypertensive (84%), and overweight (median BMI 27.7). In patients with AF, PAO burden was significantly increased compared to controls without AF (0.61+0.04 vs 0.38+0.04; n=13, 19; P=0.0005).
Conclusion: Preamyloid oligomers derived from NPs cause arrhythmogenic changes in atrial metabolic properties, and they are increased in the atria of patients with AF. These findings suggest that cytotoxic atrial PAOs promote AF susceptibility in humans.