Squalene: strong points and weaknesses[Squalene pregi e difetti]

Squalene typically represents isoprene derived structures. In nature, squalene can be found in the plant kingdom, as well as in the animal kingdom, and even in archibacteria. In fact, squalene is an important structure which in the course of time has specialized, focusing on mostly structural and metabolic specific functions. In plant cell membranes, squalene probably modulates cation backscattering but its main characteristic is the fact that it cannot be employed as an energy source and that it can metabolically transform into cyclized structures such as hopanoids and steroids. In animal cells, squalene mostly acts as a substrate for the synthesis of cholesterol. Squalene is present in many kinds of food and it is likely to give a variable exogenous contribution. Therefore, its administration can increase the levels of all the intermediates and of the esterificated forms of sterols before cholesterol. Not only squalene does act as an intermediate of the cholesterol synthesis but it also stimulates the acyl-coenzyme A (cholesterol acyltransferase), which governs the esterification of cholesterol and which is also related to the levels of triglycerides. There is a sort of barrier between food squalene and cholesterol; such barrier makes their relationship finely articulated and involves the absorption and elimination of cholesterol itself. Therefore, a powerful administration or a supply of squalene do not produce an immediate cholesterol levels increase: there is no direct connection. Thus squalene's second major role is to regulate the processes of cholesterol absorption, synthesis, esterification and elimination. As far as lipoproteins are concerned, squalene's action can be considered similar to that of triglycerides. In fact, a close connection between squalene and triglycerides must be supposed, as far as the esterification processes related to the latter are concerned. The concentration of squalene in the deposits rich in triglycerides is such that it is unlikely to perform truly stoichiometric functions, such as the spacing between different lipidic chains, while squalene may act as a coenzyme. The fact that high levels of squalene can be observed in coronary heart diseases, particularly in menopausal women, must be evaluated with extreme care because that is probably a reactive growth which tends to increase the option of sterol esterification to counterbalance hyperlipoproteinemia. Therefore, the Mediterranean diet, provided it is not too rich in calories and it makes a balanced use of olive oil, rises in value since it seems to allow that kind of regulation. Squalene's antioxidant action is important too, especially on the skin, where its concentrations are extremely high thanks to its plentiful secretion through sebum. According to some in vitro tests on cellular cultures, squalene's antioxidant action is similar to that of the all-trans retinol. It is a summation of the quencher action of each isoprene unity. These last characteristics of squalene make it possible for us to use it as a human antioxidant, both for topic and systemic applications.