Wavelength Dependence of the Efficiency of in vivo Photolysis of Carboxyhemoglobin

Introduction. Carbon monoxide (CO) poisoning occurs on a massive scale, starting from exposure to low concentrations in the air over large cities and chronic poisoning experienced by smokers and ending with severe clinical cases, often resulting in death, occurring in household accidents and fi res [1, 2]. The mechanism for the toxic effect of carbon monoxide is based on formation of a stable complex of carboxyhemoglobin (COHb): a hemoglobin compound in which the iron atoms bind to carbon monoxide instead of to molecular oxygen, where carbon monoxide has a chemical affi nity for hemoglobin that is 200–300 times greater than for oxygen as well as a clearance time from the body that is 3–4 orders of magnitude longer. Formation of COHb reduces the ability of blood to transport oxygen and then to release the oxygen in the tissues, causing tissue hypoxia, which especially affects organs having a high oxygen demand, especially in the heart and brain [2]. When carbon monoxide binds to hemoglobin, it makes the hemoglobin incapable of binding to oxygen. Furthermore, binding between one or more iron atoms and CO causes conformational changes in the hemoglobin molecule, having an effect on detachment of oxygen from other parts of the hemoglobin and disrupting supply of oxygen to the tissues even more [2]. At the cellular level, carbon monoxide binds to such proteins and enzymes as myoglobin, cytochrome oxidase, cytoglobin, neuroglobin, mixed-function oxidases (cytochromes a3, P-450), tryptophan oxygenase, etc. [2–5]. After supply of outside CO stops, the COHb molecules dissociate to form oxyhemoglobin, and the carbon monoxide is gradually excreted through the lungs. The mechanism primarily involved in excretion of CO from the body includes CO binding by heme-containing protein structures (hemoglobin, myoglobin, cytoglobin, neuroglobin, cytochrome), brief storage of the CO on the proteins and then its transport along an O2 concentration gradient from the cells and tissues to the lungs [3–5]. Most of the population is exposed to a relatively low CO concentration in the environment, which leads to an average COHb level in blood < 2% [6]. Endogenous carboxyhemoglobin, due to internal production of CO as a result of enzymatically controlled catabolism of heme-containing compounds, yields levels ranging from 0.4 to 1%. The average COHb level in moderate smokers is 5%, and in heavy smokers the level may exceed 10% and sometimes can be as high as 15% [6]. The signs and symptoms of CO poisoning appear when the blood COHb concentration exceeds 10% [3], but even lower concentrations cause adverse effects on health, especially in high-risk groups such as individuals with cardiovascular and pulmonary diseases, smokers, pregnant women, and individuals in certain professions (drivers, roadworkers, steelworkers, oilfi eld workers, etc.).