Research paperThe inhibition of inducible nitric oxide synthase and oxidative stress by agmatine attenuates vascular dysfunction in rat acute endotoxemic model
Introduction
Sepsis is a serious life threatening manifestation of severe systemic infection. It imposes a medico-economic burden on healthcare systems. The mortality rates associated with sepsis exceeds those of HIV/AIDS, breast cancer and prostate cancer combined (Chaudhry and Duggal, 2014).
Sepsis is manifested by multi-organ dysfunction, most commonly affecting respiratory and cardiovascular systems. This multi-organ dysfunction provoked by sepsis can cause hypovolemia, a decrease in vascular tone and myocardial depression (De Backer et al., 2014).
The increased release of nitric oxide (NO) is observable in sepsis-induced cardiovascular dysfunction and it is believed to be due to the increase in inducible nitric oxide synthase (iNOS) mRNA expression as a part of the body’s self defensive mechanism against endotoxemia. The iNOS expression increases throughout the body in tissues such as endothelial cells, platelets, macrophages and cardiac myocytes (Chuaiphichai et al., 2016, Titheradge, 1999).
Lipid peroxidation and the decrease in superoxide dismutase (SOD) caused by oxidative stress can also account for the deleterious cytotoxic effects of sepsis (Li et al., 2016). The role of mitochondrial dysfunction in sepsis relies not only on reactive oxygen species (ROS) but also on reactive nitrogen species (RNS) that are formed due to excessive NO production (Galley, 2011).
The systemic inflammatory response associated with sepsis can be triggered by infection with bacteria such as Escherichia coli (E.Coli) (Opal et al., 2003) or the bacterial prime endotoxin lipopolysaccharide (LPS) (Ramachandran, 2014). LPS is the main constituent of gram-negative bacterial cell wall. Injecting the experimental animals with LPS is widely used as a simple and reproducible model for sepsis (Poli-de-Figueiredo et al., 2008).
Targeting the excessive release of NO and oxidative stress with a natural endogenous compound was the burgeoning goal behind this study.
Agmatine (AGM), a polycationic amine, is the endogenous metabolite of L‐arginine, formed by the action of arginine decarboxylase enzyme (Tabor and Tabor, 1984). The versatile pharmacological targets of AGM (imidazoline receptors, NO release and α2-receptors among many other targets) make it a reliable compound for treating wide spectrum of disorders such as diabetes mellitus, insulin resistance, endothelial dysfunction, neurodegenerative disorders, addiction, neuropathic pain and many inflammatory disorders (Chang et al., 2010, El-Agamy et al., 2014, El-Awady and Suddek, 2014, Gilad et al., 1996, Keynan et al., 2010, Piletz et al., 2013, Sharawy et al., 2016). In addition, AGM has a potent antioxidant effect shown in its ability to decrease lipid peroxidation and increase SOD activity and reduced glutathione (GSH) content (El-Agamy et al., 2014, Freitas et al., 2014). AGM consumption for long term is believed to be safe (Gilad and Gilad, 2013, Gilad and Gilad, 2014, Keynan et al., 2010).
Since AGM has a potential inhibitory effect on iNOS and oxidative stress, therefore this study investigates its protective effect in LPS-induced vascular dysfunction in rats.
Section snippets
Materials
AGM sulphate, pentobarbital sodium and LPS (E. coli O55:B5) were purchased from Sigma Chemical Co. (Saint Louis, Mo, USA). AGM (1-Amino-4-guanidinobutane sulfate salt) was available as white to off-white powder with purity ≥97%, it is soluble in water (50 mg/ml). AGM was dissolved in saline directly before use. LPS was available as white powder, purified by phenol extraction, and is soluble in water (5 mg/ml). All chemicals and reagents used in this study were procured from approved chemical
Effect of AGM on mortality rate
The LPS injection caused high mortality rate of 50% compared to the control group. The mortality rate dropped to only 5% by injecting the rats with AGM 1 h prior to LPS injection, this change was significantly different compared to the LPS group (Fig. 1). The mortality rate in control and AGM groups was 0%.
Effect of AGM on serum CK-MB, LDH and CRP
The injection of LPS significantly increased the activity of CK‐MB and LDH to 247% and 371% respectively compared to the control group. Preinjection with AGM significantly decreased this
Discussion
In the present study, LPS model in rats was used to demonstrate the protective action of AGM against vascular abnormalities induced by endotoxemia. AGM was selected as an endogenous, natural and safe compound beside its effect as a modulator for NO haemostasis and as an antioxidant in the body.
In this study, injecting LPS to rats caused a profound damage to the myocardial muscle as shown by the elevation of CK-MB and CRP levels, and LDH activity. The CK-MB isozyme is distributed primarily in
Conclusion
The endogenous compound AGM has a promising therapeutic potential against LPS induced vascular endothelial dysfunction and can be helpful in case of systemic shock by its inhibitory effects on iNOS expression and oxidative stress.
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