Protective effects of melatonin and structurally-related molecules in reducing membrane rigidity due to lipid peroxidation

Lipid peroxidation is the expression of free radicals damage in biological membranes. The biochemical reaction is an autooxidative and degenerative process in which the acyl chains of the phospholipids are especially vulnerable to free radical attack. Structural changes in biomembranes produced during lipid peroxidation disrupt molecular motion in the membrane and tends to increase phospholipid bilayer rigidity. Changes in membrane fluidity are critically important for the homeostasis of numerous cell functions. Even slight changes in membrane fluidity may cause aberrant cellular function and induce pathological processes. Thus, there is considerable interest in molecules which are able to preserve fluidity levels in the membranes because of their protective effects against lipid peroxidation. The discovery of melatonin as a highly efficient free radical scavenger and general antioxidant in a wide variety of tissue homogenates and organisms as well, has stimulated a large number of studies related to the ability of this molecule to stabilize membranes from oxidative damage. While numerous reports have shown the ability of this indoleamine to preserve optimal levels of fluidity in biological membranes and to resist the rigidity induced by free radical attack, there is little information regarding the antioxidant ability of other indoleamines and β-carbolines synthesized in the pineal gland. In the present work, we review the current findings related to the beneficial effects of melatonin and structurally-related compounds in maintaining the fluidity of biological membranes against lipid peroxidation, and further, we discuss its implications in ageing and disease.