Vascular smooth muscle dysfunction induced by monomethylarsonous acid (MMA III ): A contributing factor to arsenic-associated cardiovascular diseases Ok-Nam Bae a,1 , Eun-Kyung Lim a,1 , Kyung-Min Lim a,b , Ji-Yoon Noh a , Seung-Min Chung a , Moo-Yeol Lee c , Yeo-Pyo Yun d , Seong-Chun Kwon e , Jun-Ho Lee f , Seung-Yeol Nah f , Jin-Ho Chung a,à a College of Pharmacy, Seoul National University, Shinrim-dong San 56-1, Seoul 151-742, Republic of Korea b AMOREPACIFIC CO/R&D Center, Gyeonggi-do 446-729, Republic of Korea c College of Pharmacy, Chonnam National University, Gwangju 500-757, Republic of Korea d College of Pharmacy, Chungbuk National University, Cheongju 361-763, Republic of Korea e College of Medicine, Kwandong University, Kangwondo 120-751, Republic of Korea f College of Veterinary Medicine, Konkuk University, Seoul 143-701, Republic of Korea article info Article history: Received 16 January 2008 Received in revised form 3 June 2008 Accepted 26 June 2008 Available online 12 August 2008 Keywords: Smooth muscle dysfunction Arsenic Monomethylarsonous acid (MMA III ) Vasoconstriction Cardiovascular diseases abstract While arsenic in drinking water is known to cause various cardiovascular diseases in human, exact mechanism still remains elusive. Recently, trivalent-methylated arsenicals, the metabolites of inorganic arsenic, were shown to have higher cytotoxic potential than inorganic arsenic. To study the role of these metabolites in arsenic-induced cardiovascular diseases, we investigated the effect of monomethylarso- nous acid (MMA III ), a major trivalent-methylated arsenical, on vasomotor tone of blood vessels. In isolated rat thoracic aorta and small mesenteric arteries, MMA III irreversibly suppressed normal vasoconstriction induced by three distinct agonists of phenylephrine (PE), serotonin and endothelin-1. Inhibition of vasoconstriction was retained in aortic rings without endothelium, suggesting that MMA III directly impaired the contractile function of vascular smooth muscle. The effect of MMA III was mediated by inhibition of PE-induced Ca 2+ increase as found in confocal microscopy and fluorimeter in-lined organ chamber technique. The attenuation of Ca 2+ increase was from concomitant inhibition of release from intracellular store and extracellular Ca 2+ influx via L-type Ca 2+ channel, which was blocked by MMA III as shown in voltage-clamp assay in Xenopus oocytes. MMA III did not affect downstream process of Ca 2+ , as shown in permeabilized arterial strips. In in vivo rat model, MMA III attenuated PE-induced blood pressure increase indeed, supporting the clinical relevance of these in vitro findings. In conclusion, MMA III -induced smooth muscle dysfunction through disturbance of Ca 2+ regulation, which results in impaired vasoconstriction and aberrant blood pressure change. This study will provide a new insight into the role of trivalent-methylated arsenicals in arsenic-associated cardiovascular diseases. & 2008 Elsevier Inc. All rights reserved. 1. Introduction Arsenic is a ubiquitous element found in the natural environ- ment. Introduced into body mainly through arsenic-contaminated drinking water (Abernathy et al., 2003; Mead, 2005), arsenic can cause diverse disorders including cardiovascular diseases like atherosclerosis, blackfoot disease, peripheral artery disease, and aneurysm (Engel and Smith, 1994; Navas-Acien et al., 2005; Tseng, 2005; Yoshida et al., 2004). Although there have been many attempts to elucidate the mechanism of these arsenic-associated disorders, the precise mode of action remains unclear. Predominant form of arsenic in drinking water is inorganic arsenic. After ingestion, it is readily converted to trivalent-, or pentavalent-methylated metabolites by oxidative methylation and reduction in humans (Hughes, 2006; Vahter, 2002). Recent studies on arsenic metabolites discovered that trivalent- methylated arsenicals, monomethylarsonous acid (MMA III ) and dimethylarsinous acid (DMA III ), are more cytotoxic and genotoxic than inorganic arsenic arguing that these metabolites could play a key role in arsenic-associated disorders (Gregus et al., 2000; Styblo et al., 2002). Since the report of Petrick et al. (2000), there have been abundance of studies on the greater carcinogenic, genotoxic, and cytotoxic potentials of trivalent-methylated arsenicals over the inorganic arsenite in various culture cells (Lin et al., 2001; Nesnow et al., 2002). However, few studies have been directed on the roles of trivalent-methylated arsenicals in ARTICLE IN PRESS Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/envres Environmental Research 0013-9351/$ - see front matter & 2008 Elsevier Inc. All rights reserved. doi:10.1016/j.envres.2008.06.012 Abbreviations: ET-1, Endothelin-1; KR, Krebs–Ringer; LDH, Lactate dehydrogen- ase; MLC, Myosin light chain; MMA III , Monomethylarsonous acid; SMC, Smooth muscle cells; PE, Phenylephrine à Corresponding author. Fax: +82 2 885 4157. E-mail address: jhc302@snu.ac.kr (J.-H. Chung). 1 These authors contributed equally to this work. Environmental Research 108 (2008) 300–308