ABSTRACT
OBJECTIVES: Angiotensin II (Ang II)-induced atrial fibrosis plays a vital role in the development of atrial fibrillation (AF). Lysyl oxidase-like 2 (LOXL2) plays an essential role in matrix remodeling and fibrogenesis, indicating it may involve fibrosis-associated diseases. This study aims to elucidate the role of LOXL2 in AF, and its specific inhibitor can suppress Ang II-induced inflammatory atrial fibrosis and attenuate the enhanced vulnerability to AF. METHODS: Male mice C57BL/6 were subcutaneously infused with either saline or Ang II (2 mg/kg/day) for 4 weeks. DMSO or LOXL2 inhibitor LOXL2-IN-1 hydrochloride (LOXL2-IN-1) at a dose of 100 µg/kg/day were intraperitoneally injected once daily for 4 weeks. Morphological, histological, and biochemical analyses were performed. AF was induced by transesophageal burst pacing in vivo. RESULTS: Expression of LOXL2 was increased in serum of AF patients and Ang II-treated mice. LOXL2-IN-1 significantly attenuated Ang II-induced AF vulnerability, cardiac hypertrophy, atrial inflammation, and fibrosis. LOXL2-IN-1 suppressed Ang II-induced expression of transforming growth factor beta-1 (TGF-ß1) and collagen I and phosphorylation of Smad2/3 in atrial tissue. CONCLUSIONS: LOXL2 is a target of AF, and its inhibitor prevents atrial fibrosis and attenuated enhanced vulnerability to AF potentially through the TGF-ß/Smad pathway.
Subject(s)
Angiotensin II , Atrial Fibrillation , Amino Acid Oxidoreductases/adverse effects , Amino Acid Oxidoreductases/genetics , Amino Acid Oxidoreductases/metabolism , Angiotensin II/adverse effects , Angiotensin II/metabolism , Animals , Atrial Fibrillation/chemically induced , Atrial Fibrillation/drug therapy , Atrial Fibrillation/prevention & control , Fibrosis , Humans , Male , Mice , Mice, Inbred C57BL , Smad2 Protein/metabolism , Transforming Growth Factor beta/adverse effects , Transforming Growth Factor beta/metabolism , Transforming Growth Factor beta1/metabolismABSTRACT
Venoms of several snake species contain large amounts of L-amino acid oxidase but its effects on human plasma coagulation and platelet aggregation have not been explored. We have purified L-amino acid oxidase from king cobra venom through CM-Sephadex C-25, Sephadex G-100 and DEAE Sephadex A-50 chromatographies. The purified enzyme has a mol. wt of 135,000 as determined by gel filtration and 65,000 by SDS-PAGE under non-reducing and reducing conditions. Incubation of plasma with L-amino acid oxidase at 200 micrograms/ml did not affect prothrombin time, activated partial thromboplastin time, or thrombin time. Upon addition of L-amino acid oxidase, platelets in platelet-rich plasma were aggregated. The enzyme-induced aggregation was abolished by catalase. The aggregation was also inhibited by indomethacin, aspirin, ethylenediaminetetraacetate, sodium nitroprusside, prostaglandin E1, mepacrine and verapamil, but not by heparin, hirudin, creatine phosphate/creatine phosphokinase or antimycin/2-deoxy-D-glucose. These results suggest that L-amino acid oxidase induces human platelet aggregation through the formation of H2O2, and subsequent thromboxane A2 synthesis requiring Ca2+ but independent of ADP release. The platelet aggregation caused by L-amino acid oxidase is likely to contribute to toxicity inflicted by cobra venom.
