Predicitive Biomarkers of Cardiovascular Risks in Hyperthyroid Patients from Lahore, Pakistan

Abstract

Thyroid gland produces amine hormones T3 and T4 which play cardinal roles in maintaining growth and development during embryonic as well as adult life. As major vital organs like liver, kidney and most prominently cardiovascular system are affected by abnormal secretions of thyroid hormones, great significance lies both in hyper and hypo secretions of these hormones. Though, thyroidal abnormalities are evident all over the world, these are found to be most prevalent in Asian societies. Clinical hyperthyroidism is an ailment with prominent cardiovascular effects including sinus tachycardia, changes in ventricular systolic and diastolic function, dysrhythmias, myocardial infarction and congestive heart failure. Despite modern therapeutic measures, outcome has been notoriously bad. There is a dire need, therefore, to work out certain predictive biomarkers of cardiovascular health in hyperthyroid condition that made the basis of the present investigation. For that purpose we approached clinically overt and subclinical (asymptomatic) subjects as well as a significant number of follow-up subjects to check the effectiveness of the anti-thyroid treatment. Additionally, a group of age matched healthy subjects from local population was also approached as controls. This investigation comprises two major parts; biochemical analysis and proteomics. In biochemical analysis, lipids (Cholesterol, Triglycerides, LDL-C, HDL-C), apolipoproteins (Apo-A and Apo-B), inflammatory markers (IL-6 and CRP) homocysteine, fibrinogen, hepatic enzymes (ALT and AST) and renal function (Creatinine) were accessed. Statistical analysis was carried out by one-way ANOVA, whereas, significance of means was compared by ―Student Newman Keuls‖ test. ii As far as lipid profile is concerned, in both clinical and subclinical hyperthyroidism, non atherogenic condition was witnessed. Mildly elevated level of TG and reduced HDL-C was observed in both clinical as well as subclinical phase. Moreover, anti-thyroid treatment with Neomarcazole considerably restored these parameters. Creatinine showed a prominent elevation upon anti-thyroid treatment as overt hyperthyroid condition was accompanied by reduced creatinine level due to its increased clearance rate. Moreover, transaminases, both ALT and AST depicted elevated levels in clinical hyperthyroid state, which can be due to enhanced metabolic activity and apoptosis of the hepatocytes. Upon anti-thyroid treatment of three months both of these parameters showed improvement. A strong link between elevated TH, reduced TSH and increased fibrinogen was observed which forecast the hypercoagulation in both clinical and subclinical hyperthyroid states and pronogsticate future cardiovascular events in these subjects. Inflammatory markers like IL-6 and CRP showed prominent elevation in hyperthyroid subjects. As, CRP and IL-6 are prominent biomarkers of cardiovascular risks, direct association between TH and these inflammatory markers suggested the increased risk of CVD in these subjects. Moreover, homocysteine showed marked improvement upon antithyroid treatment as reduced plasma homocysteine level was observed in both clinical and subclincal hyperthyroid subjects. Additionally, reduced homocysteine level also predispose these subjects to different pathological conditions due to reduced supply of sulpher compounds in the body. Proteomics constitute the second part of this research. Two dimensional gel electrophoresis was performed for control, subclinical, clinical hyperthyroid and follow-up groups. Melanie 9 software was used to analyze 2D gels. iii Some of the selected spots were also confirmed by Mass Spectrometry. Both MALDI-TOF/TOF and LC MS/MS spectrometric analyses were used to confirm the protein spots. Omical investigations are one of the modern fields of human biology. Specially, proteomics which involves the study of total plasma proteins, is reliable in studying deviated protein expressions in pathophysiological states. In our investigation, reduced albumin expression was observed in overt as well as subclinical hyperthyroid conditions. As reduced serum albumin is considered to be a prominent marker of cardiac failure, this reduced serum albumin forecast future predisposition to various ailments including heart disease. Moreover, enhanced expression of haptoglobin is also observed in clinical as well as subclinical state of hyperthyroidism. Enhanced haptoglobin expression signifies inflammation as well as future coronary artery disease. Further, expression of complement C3, a significant marker of metabolic syndrome and myocardial infarction, is also enhanced in subclinical, overt and follow-up groups, suggesting the future cardiovascular risks to these subjects. Retinol binding protein-4 and transthyretin demonstrated an up-regulation after anti-thyroid treatment. Reduced transthyretin in overt and subclinical groups signifies the inflammation in these subjects. Conclusively, increased level of CRP and IL-6, reduced albumin, increased haptoglobin and complement C3 can be considered as prominent contributors of cardiovascular events in overt as well as subclinical hyperthyroid subjects.