Relationship between serum copper and protein thi

　　 作者：Jeevan K Shetty1*， Suresh Babu2， Sudeshna Tripathy3， Mungli Prakash4

【摘要】 Objective:To measure serum copper and protein thiols along with lipid profile in hyperlipidemic patients and to establish the relationship between serum copper， protein thiols and lipid profile parameters. Methods: The study group consisted of 26 newly diagnosed hyperlipidemic patients not associated with any other systemic diseases and 26 age and sex matched healthy controls. Fasting lipid profile was done by enzymatic method using automated analyzer. Serum copper and protein thiols were measured spectrophotometrically. Results: Serum copper and protein–SH levels were significantly decreased in cases (P&<0.01， P&<0.01) compared to controls. Serum copper correlated positively with protein thiols (r=0.800， P&<0.01) and negatively with LDL cholesterol (r=-0.351 P&<0.05). Conclusion: Serum copper and protein thiols were decreased in hyperlipidemia and they correlated positively indicating protective role of copper in preventing homocysteinylation of protein and hence in preventing atherosclerosis.

【关键词】 Hyperlipidemia; Serum Copper; Protein thiols; Low density lipoprotein

　Introduction

　　Hyperlipidemia is characterized by elevated levels of total cholesterol (TC)， triglycerides (TG)， LDLcholesterol or decreased HDL[1]. It has long been known that copper is an essential nutrient in man and animals[2]. Previous studies had shown that， copper has an important role on biochemical functions related to enzymatic components of antioxidant defense system[3]. Therefore， copper deficiency has increased susceptibility to oxidative damage which may have one of the biological consequences， which include hyperlipidemia and atherosclerosis， both in human and experimental animals[4，5]. A previous study indicates dietary copper supplementation had beneficial effect on lipid profile by improving endogenous antioxidant defense and decreasing oxidative stress in animals[3]. Protein thiols acts as major extracellular antioxidant， they react with reactive oxygen species (ROS) and prevents LDL oxidation . In the current work we have measured the level of serum copper and protein thiols along with lipid profile in newly diagnosed hyperlipidemic patients and we tried to establish the relationship between serum copper and protein thiols and lipid profile parameters.

　　Materials and Methods

　　Subjects

　　The study group consisted of twenty six newly diagnosed hyperlipidemic patients not associated with any other systemic diseases and twenty six age and sex matched healthy controls. Mean age and sex of patients was 45±9 years and 15 males/11 females， and that of controls 41±13 years and 16 males/10 females respectively. Patients with fasting total cholesterol &>200mg/dL and triglycerides &>200mg/dL were considered having hyperlipidemia.

　　Jeevan K Shetty et al. Relationship between serum copper and protein thiols in hyperlipidemic patients

　　Newly diagnosed hyperlipidemic subjects were recruited from Kasturba Medical college hospital; who came for routine check up. Hyperlipidemics having associated diabetes mellitus， hypothyroidism， and coronary artery disease were excluded from study. Informed consent was obtained from all the subjects involved and ethical clearance was obtained from institutional ethical clearance committee. Serum copper， protein thiols and lipid profile levels were estimated at the time of diagnosis.

　　Reagents and methods

　　Special chemicals like Bathocuproine disulphonate (BCDS) and 5， 5′ dithiobis (2nitrobenzoic acid) (DTNB) were obtained from Sigma chemicals co， St Louis， MO， USA. All other reagents used were of analytical grade.

　　Serum protein thiols were measured by spectrophotometric method using 5， 5′ dithiobis (2nitrobenzoic acid) (DTNB) . Serum copper was estimated by spectrophotometrically using BCDS reagent[6]. Fasting lipid profile was analyzed by enzymatic kinetic assay method using automated analyzer， Hitachi model 912. Total cholesterol estimation was done by cholesterol oxidase method; HDL cholesterol was estimated by same method after precipitating the LDL， VLDL， and Chylomicrons. Triglycerides were estimated by enzymatic mixture containing lipoprotein lipase， glycerol kinase and glycerol 3 phosphate oxidase and peroxidase. Low density lipoprotein levels were calculated by using Friedewald′s formula.

　　Statistical Analysis

　　Statistical analysis was performed using the Statistical Package for Social Sciences ( SPSS10， Chicago， USA) .Values were expressed as mean ± SD， and P value&<0.05 considered significant. Independent sample student‘t′ test was used to compare mean values. Pearson correlation test was applied to correlate between the parameters.

　　Results

　　As shown in Table 1， serum copper， protein thiol levels were significantly decreased， and total cholesterol， triglycerides and LDLcholesterol were increased in cases compared to healthy controls (P&<0.01). On applying Pearson Correlation， Serum copper correlated positively with protein thiols ( r=0.800， P&<0.01) and negatively with LDL cholesterol (r=-0.351 P&< 0.05).

　　Table1 Serum Copper， protein thiols and lipid profile parameters in healthy controls and hyperlipidemia cases， values expressed in mean ± SD

　　Discussion

　　In agreement with previous studies[7]， we have found decrease in serum copper in hyperlipidemics. A number of previous studies suggest that hypercholesterolemia associated with copper deficiency was due mainly to and impairment in the cholesterol degradation process. Copper being an essential component of ceruloplasmin and copper zinc superoxide dismutase it has an important role on biochemical functions related to enzymatic components of antioxidant defense system. Deficiency of copper will increase the risk of oxidative damage and susceptibility of LDL for oxidation leading to atherosclerosis. However， the mechanisms for Copper actions on oxidative stress and antioxidants defenses are not completely understood. In our study， we have found decrease in protein thiols， which is contributed by increased consumption thiol groups on protein by ROS[3].

　　Negative correlation of serum copper with LDL indicates progressive decrease in copper levels with increase in cholesterol levels. These decreased copper in turn weaken the antioxidant enzymatic systems， leads to increased generation of ROS. ROS may react with protein thiols moieties and they decrease the levels of protein thiols as well as generate variety of sulphur oxidation products[8]. This alters the lipoprotein receptors and inhibiting cellular uptake of TG from blood and makes the LDL less dense which is more susceptible for oxidation[9].

　　Decrease in serum copper correlated positively with protein thiols indicating increased consumption thiol groups on protein. Earlier studies indicated copper can bind to homocysteine and thereby reduce homocysteine mediated LDL oxidation[10]. The positive correlation between copper and protein thiols indicates decrease in copper may increase homocysteine levels in body， hence homocysteinylation of proteins at cysteinSH groups there by decrease in available thiol groups over proteins.

　　Conclusion

　　Serum copper and protein thiols were decreased in hyperlipidemia and they correlated positively indicating protective role of copper in preventing protein homocysteinylation and hence in preventing atherosclerosis.

参考文献

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