*3.1. Chemical Structure and Mechanism of Action*

Astaxanthin is a xanthophyll carotenoid which contains two additional oxygenated groups on each ring structure compared with other carotenoids, resulting in enhanced antioxidant properties, approved in the 1999 as a dietary supplement by Food and Drug Amninistration. This compound occurs naturally in a wide variety of living organisms including microalgae (*Haematococcus pluvialis*, *Chlorella zofingiensis*, and *Chlorococcum* sp.), fungi (red yeast *Phaffia rhodozyma*), complex plants, seafood, and some birds such as flamingos and quail; it is reddishcoloured, and gives salmon, shrimp and lobster their distinctive colouration [17]. The microalga *H. pluvialis* has the highest capacity to accumulate astaxanthin up to 4–5% of cell dry weight. Astaxanthin has been attributed with extraordinary potential for protecting the organism against a wide range of diseases, and has considerable potential and promising applications in the prevention and treatment of various diseases, such as cancers, chronic inflammatory diseases, metabolic syndrome, diabetes, diabetic nephropathy, CVD, gastrointestinal and liver diseases, and neurodegenerative diseases [18]. 

Astaxanthin cannot be manufactured in animals or converted to vitamin A and therefore must be consumed in the diet. Xanthophyll carotenoids such as astaxanthin and canthaxanthin have antioxidant activity, are free radical scavengers, potent quenchers of ROS and nitrogen oxygen species (NOS), and chain-breaking  antioxidants. They are superior antioxidants and scavengers of free radicals (FRs) compared to the carotenoids such as β-carotene [19]. 

Available forms of astaxanthin are represented by natural forms on an industrial scale of 

production [20,21]. The disodium disuccinate astaxanthin (DDA), a synthetic form of astaxanthin, overcame the limitations of caroteniods related to their poor aqueous solubility and enabled investigation of this agent in the animal models of myocardial ischaemia and reperfusion using both intravenous and oral routes of administration [22]. DDA has been shown to be very effective in animal cardiovascular studies administered both intravenously and orally [23–25]. 
