Evaluation of oxysterol levels in silicosis patients

Silicosis is a chronic inflammatory occupational disease that causes permanent and progressive damage to the lungs resulting from prolonged inhalation of silica (SiO2) particles. A significant number of silicosis cases are diagnosed each year in Turkey. Oxysterols consist of the oxidation of cholesterol. Oxysterols take place two different routes, enzymatic and non-enzymatic. Oxysterol derivatives that form with non-enzymatic (auto-oxidation) pathway have been shown to be associated with many pathological conditions and for this reason it can be used as a biomarker. The aim of this thesis is to evaluate oxysterol levels which are formed by auto-oxidation pathway in silicosis patients; determination of sphingosine-1-phosphate (S1P) levels which is a sphingolipid metabolite. In addition to these parameters, it is aimed to determine the possible lipid peroxidation by different parameters. For this purpose, oxysterol derivatives (7-ketocolesterol (7-KC), 3β, 5α, 6β trihydroxycholesterol (triol), lipid peroxidation parametrs (malondialdehyde (MDA), F2-isoprostan (F2-iP) and hydroxynonenal (HNE) and S1P levels were measured. In the control group, 7-KC and triol levels were measured as 20,26±1,38 ng/ml and 13,83±1,75 ng/ml, respectively, while in the patient group, 40,61±2,07 ng/ml and 16,15±2.22 ng/ml (p<0,001). The patient group was found to have significantly higher plasma 4-HNE, F2-iP and MDA levels in both urine and plasma compared to the control group (p<0,05). S1P levels were 67,57±16,25 ng/ml in the control group and 49,05±10,87 ng/ml in the patient group. The results showed that cholesterol oxidation and lipid peroxidation parameters increased significantly in silicosis patients while a decrease in the S1P levels were observed. The study demonstrated that lipid metabolism is affected and oxidative lipid damage is triggered in silicosis. Therefore, cholesterol oxidation can also be used as an important marker in this exposure group, and pathological changes in lipids may be effective in the disease progression.