:: Volume 2, Issue 3 (9-2000) ::
2000, 2(3): 151-158 Back to browse issues page
Association of serum lipoproteins, apolipoproteins, and HDL-associated paraoxonase enzyme activity with thyroid function
F Azizi , F Raiszadeh , M Rahmani , SM Solati , M Arabi , M Hedayati
Abstract:   (33437 Views)
Abstract: Thyroid dysfunction, specially hypothyroidism is associated with an increased risk of atherosclerosis, which is attributed to impaired metabolism of atherogenic lipids and lipoproteins. Human paraoxonase (PON) is an HDL-associated enzyme which is believed to protect lipoproteins against oxidative modification. We have studied the status of lipids, apolipoproteins, and activity of paraoxonase enzyme in 14 hypothyroid (7 females and 7 males), 8 hyperthyroid (4 females and 4 males), and 32 euthyroid subjects (18 females and 14 males). Apolipoprotein (apo) concentrations were measured in a fasting serum sample by immunoturbidometric assay and paraoxonase/arylesterase activities by spectrophotometric assay of p-nitrophenol/phenol production following addition of paraoxon/phenylacetate. Hypothyroid subjects had significantly higher levels of total cholesterol (204±69 vs 171±37, p<0.05) and low-density lipoprotein cholesterol (LDL-c) (115±49 vs 82±34, P<0.05) and lower levels of high-density lipoprotein cholesterol (HDL-c) (52±15 vs 63±17, P<0.05) than euthyroid controls. The ratios of TC/HDL-c (4.0 ± 1.3 vs 2.9 ± 1, P<0.01) and LDL-c/HDL-c (2.3 ± 0.8 vs 1.5 ± 0.8, P<0.01) were significantly higher in hypothyroid subjects than in controls. As compared to healthy controls, hyperthyroid subjects had lower levels of HDL-c (50±10 vs 63±17, P<0.05) and lower activity of paraoxonase enzyme (27±14 vs 66±41, P<0.01). No significant difference was observed between the hypo- and hyperthyroid subjects with euthyroid controls in serum levels of total cholesterol(TC), triglycerides(TGs), apo A-I, apo B, and arylesterase activity. Serum concentration of TSH had a significant positive correlation with TC and LDL-c, serum T3 was negatively correlated with TC and apo B and serum T4 level was negatively correlated with TC and LDL-c Significant negative correlation was observed between serum T4 and paraoxonase activity (r=-0.3, P<0.05). The results demonstrate that both hypothyroidism and hyperthyroidism are associated with atherogenic lipid profiles. Correlation between thyroid hormones, paraoxonase enzyme activity, and lipid levels confirms the role of thyroid hormones in the metabolism of lipids and their associated enzymes. The higher LDL oxidation previously observed in hyperthyroid subjects can be attributed to decreased HDL paraoxonase activity.
Keywords: Paraoxonase, Lipoprotein, Apolipoprotein, Hyperthyroidism, Hypothyroidism
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Type of Study: Original | Subject: Endocrinology
Received: 2006/11/15 | Published: 2000/09/15

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Volume 2, Issue 3 (9-2000) Back to browse issues page