The aetiology of ischemic heart diseases is mainly based on atherosclerosis of coronary artery. Inflammation and oxidative reactions are initiating and aggravating the illness resulting in pathological remodelling of vasculaturze at site of injury. Endothelium lining of blood vessels participated in the reaction biochemically through releasing some proteins into circulatory system which further complicate the condition. The aim of this study was to determine early diagnosed hyperlipidaemia-associated changes of the plasma level of some of these endothelial biomolecules. Compared to healthy control, hyperlipidaemic patients have significantly increased arginase, metalloendopeptidase, peroxidase, myeloperoxidase, and peroxynitrite with concomitant reduction in arylesterase and nitric oxide. The present study concluded that hyperlipidaemia play a great role in modulation of certain plasma protein markers which might be directly related to patient pathological condition or could be used as a tool for diagnosis or patient follow up indicating the stage of vasculature remodelling, healing, inflammation or resolution.

Arginase, Aryleasterase, Metalloendopeptidase, Myeloperoxidase, Nitric oxide

Coronary artery disease is one of the major cardiovascular illnesses associated with great morbidity and mortality (Song et al. 2015). Atherosclerosis is the hallmark of the underlying etiology of coronary artery diseases leading to stenosis of the vasculature system (Mohammad et al. 2021). At the site of stenosis, different pathophysiological reactions are continuously propagating culminating and coordinating together to tackle the pathological condition associated with stenosis (Joseph et al. 1992). These reactions include, inflammatory process and oxidation reaction resulting in exacerbation of the condition at site of injury or stenosis (Vaisman et al. 2012). Vascular endothelium has been shown to play a great role in the overall scenario of the coronary arterial disease. The contribution of endothelium has been rely on two important parameters (Almulathanon et al. 2021; Joseph et al. 1992); local reaction processing and systemic secretome released in response to the inflammation (Song et al. 2015).

The systemic biomolecules served as potential markers to shape the severity of the atherosclerotic plaques (Joseph et al. 1992). Some of these biomolecules are useful while others are harmful reflecting the situation of atherosclerotic plaque at site of injury or inflammation (Pacher et al. 2007). Moreover, the plasma level of these biomolecules clarifies the prognosis of the atherosclerotic plaque and could be used as a diagnostic tool predicting the future status of the patient (Zouki et al. 2001). However, some of these parameters are intrinsically derived from endothelium itself while other are inducible; in response to stress or injury, by extravascular cells (e.g., immune cells and to certain extents platelets) to secrete their components but still under control of endothelial signaling (Pacher et al. 2007; Song et al. 2015). For example, myeloperoxidase, arginase, nitric oxide, metalloproteinase, and peroxidase.

The endothelium play a great role in cardiovascular homeostasis in health and diseases (Pacher et al. 2007). This role has been dramatically linked to vasoactive biomolecules production (Vaisman et al. 2012). Hyperlipidemia is the initial step in atherosclerotic plaque formation which is primarily started by few successive steps including expression of endothelial adhesion molecules, trapping leucocytes, accumulating LDL together with oxidative stress and endothelial dysfunction (Pacher et al. 2007, Zouki et al. 2001). Some of these steps are partly inhibited by free radical nitric oxide NO˙ formation from arginine aided by nitric oxide synthase enzyme. Upregulation of arginase inhibit this metabolic pathway and encourage arginine conversion to threonine and urea (Hwang et al. 2015). This study has proved that newly diagnosed hyperlipidemia was associated with elevated arginase expression and subsequently reduced NO˙. The results have been confirmed by other studies conducted on experimental animal and hyperlipidemic patients. A study conducted by Hwang et al. (2015), reported that elevated arginase and reduced NO levels has been associated with hyperlipidemia. Moreover, the condition has improved with lipid lowering agents or using plant-derived arginase inhibitor (Akinyemi et al. 2016). Arginase inhibition has been associated with restoration of hyperlipidemia-associated endothelial dysfunction in laboratory animals (Minozzo et al. 2018). Moreover, treatment of hyperlipidemic patients with atorvastatin (hypolipidemic agents) induced significant increase in NO level and reduced arginase activity (Khaleel et al. 2018). However, Ibrahim Suhad et al. (2019), reported that when hyperlipidemia coexist with type 2 diabetes mellitus the arginase overexpression is gender linked with greater expression in female than male patients.

Both NO and superoxide (O₂•−) are considered as an important parameters in vascular endothelial physiology (Libby et al. 2011). In pathological condition, these two important physiologically active biomolecules interact to form tissue destructive biogenic compound; peroxynitrite (ONOO−) (Li et al. 2013, Pacher et al. 2007). The key point in ONOO− pathology is stimulation leukocyte activation and subsequent endothelial adherence and translocation resulting in loss of endothelial integrity (Pacher et al. 2007, Zouki et al. 2001). The present study demonstrated that early stages of hyperlipidemia were associated with elevated plasma ONOO− levels; which could be a marker for early endothelial injury. When hyperlipidemia coincide with peroxynitrite overproduction; due to pathological events, this will ensue LDL oxidation forming ox-LDL; a molecule with high affinity for vascular endothelial deposition (Lai and Yen 2002). In vitro induced hyperlipidemia model using laboratory animals revealed that there are a coexistence of hyperlipidemia with peroxynitrite overproduction, the study has explained that this effect might be primarily linked with elevated plasma lipid levels resulting in cholesterol deposition at subcellular level and increased ox-LDL levels (Kupai et al. 2009, Onody et al. 2003), alongside increasing susceptibility of cardiac defects (Li et al. 2013). Furthermore, subsequent study has demonstrated that inhibition of peroxynitrite formation using plant-derived isoflavones; has been associated with reducing of lipid-derangement associated with peroxynitrite; imparting cardiac protection (Csont et al. 2007, Lai and Yen 2002).

Once endothelial injury initiated; lipid deposition enhanced within vascular layer through LDL oxidation step which eventually lead to increase in intima media thickness (Odawara et al. 1997, Pati and Pati 1998). Oxidation of lipoproteins; especially LDL, has been antagonized by a family of protein called paraoxonase-1 (Antikainen et al. 1996). Arylesterase is a member of paraoxonase-1 family responsible about hydrolysis of lactone ring of these biomolecules and hence modulating the oxidation step (Pati and Pati 1998). The present study confirmed that hyperlipidemia reduced the plasma level of arylesterase encouraging lipid oxidation and subsequently its deposition in vascular spaces. The results are in agreement with studies conducted on hyperlipidemic patients versus control group; the results showed association between different paraoxonase isoforms expression and hyperlipidemia (Odawara et al. 1997, Pati and Pati 1998). However, results from other studies confirmed contradictory outcomes and suggested that genotype polymorphism and advanced cases might be linked to such variation in the results (Antikainen et al. 1996, Aubo et al. 2000, Suehiro et al. 1996).

Leukocyte activation were associated with increased myeloperoxidase activity, especially macrophages and neutrophils (Fathi et al. 2020). Myeloperoxidase associated with beneficial microbial killing, these actions were inevitably associated with tissue damage at the battle zone (Askari et al. 2003, Brennan and Hazen 2003). Correspondingly, the macrophages dealing with lipid digestion converted to foam cells in atherosclerotic plaque, during processing they release myeloperoxidase resulting in further endothelial damage and dysfunction. The vascular dysfunction were the result of increased NO consumption and LDL and HDL oxidation (Brennan and Hazen 2003). HOCl produced by myeloperoxidase associated with tissue destruction and plaque instability and increased vulnerability (Askari et al. 2003, Vasilyev et al. 2005). The present study demonstrated that early stages of hyperlipidemia were associated with increased plasma peroxidase and myeloperoxidase concentration and this might be associated with endothelial dysfunction and damage. A study conducted by Song et al. (2015) demonstrated that peroxidase and myeloperoxidase associated with atherosclerosis and promote cardiovascular disease progression (Brennan and Hazen 2003). Furthermore, knockout of MPO gene from laboratory animal after induction of myocardial infarction revealed reduction in leucocyte recruitment at subendothelial spaces (Askari et al. 2003) and reduced generation of tissue destructive aldehyde species (Vasilyev et al. 2005), confirming the great role of MPO in these inevitable actions.

Atherosclerotic plaque formation is associated with hyperlipidemia. Stable plaque by itself will not lead to acute and urgent effect. Stability is correlated to extracellular matrix intactness. Metalloendopeptidase enzyme degrade the extracellular matrix and increase plaque vulnerability leading to urgent conditions (thrombus or thromboembolic status). The endothelial damage associated with increased vulnerability to leukocyte infiltration and subsequent inflammatory pathway stimulation. The present study confirmed that early stages of hyperlipidemia might be associated with slight increase in plasma concentration of metalloendopeptidase enzyme and this could be a representative of progression of the hyperlipidemia to lipid deposition in sub-vascular spaces and also indicate leukocyte infiltration. Discrepant results have been reported by various studies regarding correlation between hyperlipidemia and increased plasma endopeptidases level; a study conducted by Weiß et al. (2020), confirmed that the metalloendopeptidases elevated in hyperlipidemic patients.

The present study confirmed that newly diagnosed hyperlipidemia is associated with a microscopic vascular lesion which are correlated with an elevation of vascular biomolecules.

The authors are grateful to the University of Mosul for its continuous support and encouragement to all researchers.