The effect of low doses of echinochrome A (EchA), a natural polyhydroxy-1,4-naphthoquinone pigment from the sea urchin Scaphechinus mirabilis, has been studied in clinical trials, when it was used as an active substance of the drug Histochrome® and biologically active supplement Thymarin. Several parameters of lipid metabolism, antioxidant status, and the state of the immune system were analyzed in patients with cardiovascular diseases (CVD), including contaminating atherosclerosis. It has been shown that EchA effectively normalizes lipid metabolism, recovers antioxidant status and reduces atherosclerotic inflammation, regardless of the method of these preparations’ administrations. Treatment of EchA has led to the stabilization of patients, improved function of the intracellular matrix and decreased epithelial dysfunction. The increased expression of surface human leukocyte antigen DR isotype (HLA-DR) receptors reflects the intensification of intercellular cooperation of immune cells, as well as an increase in the efficiency of processing and presentation of antigens, while the regulation of CD95 + expression levels suggests the stimulation of cell renewal processes. The immune system goes to a different level of functioning. Computer simulations suggest that EchA, with its aromatic structure of the naphthoquinone nucleus, may be a suitable ligand of the cytosolic aryl cell receptor, which affects the response of the immune system and causes the rapid expression of detoxification enzymes such as CYP and DT diaphorase, which play a protective role with CVD. Therefore, EchA possesses not only an antiradical effect and antioxidant activity, but is also a SOD3 mimetic, producing hydrogen peroxide and controlling the expression of cell enzymes through hypoxia-inducible factors (HIF), peroxisome proliferator-activated receptors (PPARs) and aryl hydrocarbon receptor (AhR).

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The molecular geometry and electronic structure of hydroxy substituted naphthazarin (NZ) 7 ethyl 2,3,5,6,8 pentahydroxy 1,4 naphthoquinone (echinochrome A, (Et)NZ(β OH) 3 , 1) were calculated by the B3LYP/6 311G(d) method. The influence of the (i) character of the β OH groups dissociation and (ii) conformational mobility of molecule 1 and the anions, radicals, and radical anions derived from 1 on the energy of their reactions with hydroperoxyl radical was studied by the (U)B3LYP/6 31G and (U)B3LYP/6 311G(d) methods. The enol enolic tautomerism due to the transfer of hydrogen atoms of α OH groups and rotational isomerism of the β OH groups at the C(2) and C(3) atoms and of the α OH groups at the C(5) and C(8) atoms were studied. The equilibrium in the gas phase reaction 1 + • OOH (Et)(HO β) 2 NZ(β О • ) + НOOH (1) (quenching of hydroperoxyl radical) is shifted to the separated reagents. Heterolysis of the O-H bond in one of the three β hydroxy groups considerably reduces the energy of subsequent O-H bond homolysis in either of the two remaining β hydroxy groups. As a consequence, the reaction (Et)(HO β) 2 NZ(β O -) + • OOH (Et)(HO β, -О β)NZ(β О • ) + НOOH (2) (quenching of hydroperoxyl radical) becomes exothermic and the equilibrium is shifted to the formation of hydrogen peroxide. The Gibbs energy gain in reaction (2) varies from -6.4 to -10.9 kcal mol -1 depending on which β hydroxy group is involved in the O-H bond homolysis.

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