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 Table of Contents  
ORIGINAL ARTICLE
Year : 2018  |  Volume : 31  |  Issue : 2  |  Page : 481-486

Study of paraoxonase 1 as a marker of atherosclerosis in young patients with subclinical hypothyroidism


1 Department of Internal Medicine, Faculty of Medicine, Menoufia University, Menoufia, Egypt
2 Department of Cardiovascular, Faculty of Medicine, Menoufia University, Menoufia, Egypt
3 Department of Clinical Pathology, Faculty of Medicine, Menoufia University, Menoufia, Egypt, Egypts

Date of Submission31-Dec-2016
Date of Acceptance11-Mar-2017
Date of Web Publication27-Aug-2018

Correspondence Address:
Mai A Ibrahim
Department of Internal Medicine, Faculty of Medicine, Menoufia University, Shebin Al-Kom, Menoufia Governorate
Egypt
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/mmj.mmj_731_16

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  Abstract 


Objective
The aim of this study was to investigate the paraoxonase 1 (PON-1) activity, which is accepted as a marker of atherosclerosis, in serum of patients with subclinical hypothyroidism (SCH).
Background
There is now strong evidence that PON-1 plays an important role in lipoprotein metabolism and thus may affect the risk of atherosclerosis in the general population. SCH and its correlation with the atherosclerosis and atherosclerotic cardiovascular diseases is a subject of debate.
Patient and methods
This study included 40 young patients (<43 years old) from Menoufia University hospitals after exclusion of all known cardiovascular risk factors. They were classified into two groups: group I, healthy controls group (20 patients) and group II, patients with SCH (20 patients). All patients were subjected to thorough history taking, complete physical examination, thyroid function tests, lipid profile, and PON-1 activity.
Results
The mean of PON-1 activity was highly significant higher in group II than control, and there are a significant negative correlation between PON-1 activity and thyroid-stimulating hormone. SCH group was more dyslipidemic as evidenced by decreased high-density lipoprotein and increased total cholesterol, triglycerides, and low-density lipoprotein.
Conclusion
This study suggests that SCH is an independent risk factor for atherosclerosis, and the higher the thyroid-stimulating hormone level and the lower the PON-1 activity, hence the higher the atherosclerotic cardiovascular risk.

Keywords: atherosclerosis, paraoxonase 1, subclinical hypothyroidism


How to cite this article:
El-Kafrawy NA, El-Najjar MM, El-Barbary HS, El-Kersh AM, Helwa MA, Ibrahim MA. Study of paraoxonase 1 as a marker of atherosclerosis in young patients with subclinical hypothyroidism. Menoufia Med J 2018;31:481-6

How to cite this URL:
El-Kafrawy NA, El-Najjar MM, El-Barbary HS, El-Kersh AM, Helwa MA, Ibrahim MA. Study of paraoxonase 1 as a marker of atherosclerosis in young patients with subclinical hypothyroidism. Menoufia Med J [serial online] 2018 [cited 2018 Sep 24];31:481-6. Available from: http://www.mmj.eg.net/text.asp?2018/31/2/481/239770




  Introduction Top


Subclinical hypothyroidism (SCH) is a common biochemical finding in the general population [1]. SCH is typically an asymptomatic condition, biochemically defined by a raised serum thyroid-stimulating hormone (TSH) concentration combined with a normal level of free thyroxine 4 (FT4) [2].

The prevalence ranges from 4 to 15%, and it is present more often in females than males, lower in blacks than in whites, and more in elderly [3].

Dependent on the level of serum TSH, SCH can be mild (TSH = 4.5–9 mU/l) or severe (TSH ≥10 mU/l) [4].

SCH may act directly on the heart, impairing both systolic and diastolic functions or indirectly by altering peripheral vascular resistance and serum lipid and coagulation profiles [5].

Atherosclerosis is an inflammatory disease, regarding its pathogenesis, and according to 'response to retention hypothesis,' the whole sequence of events is found to be initiated by the retention of modified low-density lipoprotein (LDL) [6].

High-density lipoprotein (HDL) definitely has a protective role against atherosclerosis by its involvement in reverse cholesterol transport. Recent evidence, however, suggests HDL also prevents atherosclerosis by inhibiting the oxidative modification of LDL particle, which is done by some of the enzymes of HDL like paraoxonase 1 (PON-1) [6].

Recently, dysfunctional or proinflammatory HDL was indicated as a proatherogenic factor. The protective function of HDL against atherogenesis could be partly explained by its main constituent, PON-1 [7].

PON-1 is a HDL associated-enzyme capable of hydrolyzing lipid peroxides; thus, PON-1 plays a preventing role in atherosclerosis by protecting against lipid peroxidation, modulates the susceptibility of LDL to atherogenic modifications, and even plays an anti-inflammatory role [8].

As reduced PON-1 concentration and/or activity might have a deleterious effect on the protective function of HDL [7], PON-1 has been the focus of intensive research and has been reported as an independent risk factor for cardiovascular disease [9].

PON-1 activity has been suggested to be inversely related to oxidative stress [10]. Thyroid hormones have a strong effect on oxidative stress and the antioxidant system [11]. In SCH, lower PON-1 activity indicated increased oxidative damage [12].

In some studies, it was shown that elevated serum level of TSH has an inverse effect on the levels of serum lipoproteins; owing to these lipid abnormalities, SCH may be considered as a risk factor for atherosclerosis [12].


  Patients and Methods Top


The study was approved by the ethical committees of the hospital and the patients gave an informed consent This study included 40 patients aged from 25 to 43 years from inpatient wards and outpatient clinics at Internal Medicine Department of Menoufia University hospitals from December 2014 to December 2016 after approval of ethical committee of Faculty of Medicine, Menoufia University. They were classified into two groups: group I, healthy controls group (20 patients) and group II, patients with SCH (20 patients).

All patients aged 45 years or older with SCH diagnosed by thyroid function tests were included in this study after exclusion of the following: obesity [BMI ≥25, waist circumference (WC) ≥102 in male or ≥88 in females], patients with diabetes mellitus or prediabetes, cigarette smoker, and patients with chronic renal failure.

All patients underwent full history taking and clinical examination with emphasis on thyroid gland examination and anthropometric measurements.

Both groups were subjected to thyroid function tests, done by Diagnostic system- Enzyme Immuno Assay -thyroid stimulating hormones (DS-EIA-TSH), a one-step immunoassay, based on the principle of the sandwich method; lipid profile [total cholesterol (TC), triglycerides (TG), HDL, and LDL]; and PON-1 activity (by enzyme-linked immunosorbent assay technique).

Blood collected by venipuncture was allowed to coagulate at room temperature for 10–20 min, and then was centrifuge at the speed of 2000–3000 rpm for 20 min to collect supernatant. Specimens were held for a longer frozen time only once at −40°C before assay.

A commercially available kit (PON-1 enzyme-linked immunosorbent assay kit, BYEK2123; Chongqing Biospes Co. Ltd, Paradise Walk, Jiangbei District, Chongqing, 400020, China) was used for two groups according to the method described by Cebeci E et al. [13].

Statistical analysis

The statistical package for the social sciences (SPSS, version 20; SPSS Inc., Chicago, Illinois, USA) software computer program was used for analysis of our data. Data were expressed into two phases:

Descriptive

Mean value and SD for quantitative data, and frequency and percentage for qualitative data.

Analytic

Analytical statistics was done as follows: t test for comparison of two independent quantitative variables normally distributed, U test (Mann–Whitney test) for comparison of more than two independent quantitative variables not normally distributed, K test (Kruskal–Wallis) for comparison of two independent quantitative variables not normally distributed, χ2 for comparison between two or more independent qualitative variables normally distributed, Fisher exact test for comparison between two independent qualitative variables with one cell less than 5, and Pearson's correlation coefficient (r) for comparison between two dependent quantitative normally distributed variables.

The significance level (P) was expressed as follows: P valuegreater than or equal to 0.05 is insignificant, P value less than 0.05 is significant, and P value less than 0.001 is highly significant.


  Results Top


This study included 40 patients from inpatient wards and outpatient clinics at Internal Medicine Department of Menoufia University hospitals from December 2014 to December 2016.

The mean ages of the studied groups [Table 1] were 34.7 ± 9.7 years in control group and 34.3 ± 9.2 years in SCH group; these results showed that there was no significant difference between studied groups regarding age. [Table 1] showed that the control group included 12 (60%) males and eight (40%) females, and SCH group included seven (35%) males and 13 (65%) females; these results showed that SCH is highly prevalent in females.
Table 1: Distribution of the studied patients regarding their demographic data

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All patients with BMI greater than or equal to 25 were excluded from the present study; the mean of BMI was 20.8 ± 1.4 kg/m 2 in group I and 21 ± 2.4 kg/m 2 in group II [Table 2]. These results showed that there was no significant difference between group I and group II regarding BMI.
Table 2: Comparison between studied groups regarding anthropometric measurement

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All patients with WC greater than or equal to 102 or 88 cm in male or female, respectively, were excluded from the study; the mean of WC was 89.7 ± 8.2 cm in group I and 84.7 ± 7.5 cm in group II [Table 2]. These results showed that there was no significant difference between group I and group II regarding WC.

All patients with diabetes mellitus or impaired fasting glucose were excluded from the study; the mean of FBG was 80.9 ± 6.8 mg/dl in group I and 81.8 ± 7.1 mg/dl in group II [Table 3]. These results showed that there was no significant difference between studied groups regarding fasting blood sugar. The mean of 2-h postprandial (PP) blood glucose level was 95.5 ± 3.5 mg/dl in group I and 96.2 ± 6.7 mg/dl in group II [Table 3]. These results showed that there was no significant difference between studied groups regarding 2-h PP blood glucose level.
Table 3: Comparison between studied groups regarding blood glucose level

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The mean of TC value was 165.4 ± 25.9 mg/dl in group I and 232.1 ± 38.5 mg/dl in group II [Table 4]. These results showed that the mean of TC was highly significant higher in group II than group I. The mean of TG was 129.9 ± 10.1 mg/dl in group I and 169.1 ± 19.8 mg/dl in group II [Table 4]. These results showed that the mean TG was highly significant higher in group II than group I. The mean of HDL was 55.6 ± 3.3 mg/dl in group I and 43.4 ± 5.7 mg/dl in group II [Table 4]. These results showed that the mean of HDL was highly significant lower in group II than group I. The mean of LDL was 86.1 ± 12.4 mg/dl in group I and 132.2 ± 17.5 mg/dl in group II [Table 4]. These results showed that the mean of LDL was highly significant higher in group II than group I.
Table 4: Comparison between studied groups regarding lipid profile

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The mean of TSH was 1.9 ± 0.5 μIU/ml in group I and 7.7 ± 1.6 μIU/ml in group II [Table 5]. These results showed that the mean of TSH was significantly higher in group II than in group I. The mean of free thyroxine 3 (FT3) was 1.3 ± 0.4 ng/ml in group I and 1.4 ± 0.3 ng/ml in group II [Table 5]. These results showed that there was no significant difference between studied groups regarding FT3. The mean of FT4 was 9.8 ± 2 μg/dl in group I and 9.7 ± 2.3 μg/dl in group II [Table 5]. These results showed that there was no significant difference between group I and group II regarding FT4.
Table 5: Comparison between studied groups regarding thyroid profile

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The mean of PON-1 was 65.1 ± 7.6 U/l in group I and 18.7 ± 5.2 U/l in group II [Table 6]. These results showed that the mean of PON-1was highly significant lower in group II than group I.
Table 6: Comparison between studied groups regarding paraoxonase 1 activity

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There was significant negative correlation between PON-1 and age. There was a negative but nonsignificant correlation between PON-1 and BMI and WC. There was a negative but nonsignificant correlation between PON-1 and fasting blood sugar and 2-h PP blood glucose level. There was a negative and highly significant correlation between PON-1 and TC, TG, and LDL, whereas there was a positive and highly significant correlation between PON-1 and HDL. There was a negative and significant correlation between PON-1 and TSH. There was a positive and highly significant correlation between PON-1 and FT4, whereas there was a negative but nonsignificant correlation between PON-1 and FT3 [Table 7].
Table 7: Pearson correlation coefficient between paraoxonase 1 and age, anthropometric measurements, and laboratory data

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  Discussion Top


Human and animal studies support the hypothesis that oxidative modification of LDL plays a crucial role in the pathogenesis of atherosclerosis. PON-1 may protect against cardiovascular disease because it is capable of hydrolyzing oxidized LDL cholesterol. It has been found that decreased serum PON-1 activity is associated with more severe atherosclerosis [14].

The influence of SCH on atherosclerosis is still not very well understood. There is substantial evidence that SCH alters several traditional risk factors such as increased circulating levels of LDL cholesterol, direct effects on vascular endothelium, and altered coagulability. However, we do not yet have a good understanding of the mechanism of risk factors for cardiovascular diseases [15].

In this study, the mean age was 36.7 ± 9.7 years in group I and 34.3 ± 9.2 years in SCH group; these results showed that there was no significant difference between studied groups regarding age. [Table 1] showed that control group included 12 (60%) males and eight (40%) females and SCH group included seven (35%) males and 13 (65%) females; these results showed that SCH is highly prevalent in females.

Our results agree with that of Prasad et al. [16] regarding sex, as in their study, patients with SCH comprised 55% women and 36.7% men, which shows that SCH is more common in women than in men [16]. This result agree with that of Singh and Prasad I et al. [17], who found that within subclinical hypothyroid group (n = 56), 30% were males whereas 70% were females; they concluded that the prevalence of thyroid disease is higher in women. This finding was consistent with that of Singh S and Sarkar et al. [18] who noted the predominance of females in cases of hypothyroidism, with M: F ratio 1: 6.5. Our results were consistent with results of National Health and Nutrition Examination Survey III cohort study in which the prevalence is higher in the female population [19] and Colorado study which showed that the percentage of women with elevated serum TSH concentration was higher than that of men in each decade of life, ranging from 4 to 21% in women and 3 to 16% in men [20]. The higher prevalence of thyroid disease in women suggests that estrogen might be involved in the pathophysiology of thyroid dysfunction. Estradiol has an antagonistic effect on the hormones T3 and T4. The reason being, estradiol competes with T3 and T4 for binding sites on the receptor proteins [17].

Regarding lipid profile, we found that TC, TG, and LDL were significantly higher in patients with SCH (group II) than control (group I). Regarding HDL, it was decreased in group II than group I. Our results agree with that of Canaris GJ et al. [21] who found that in SCH, TC, and LDL levels were increased whereas HDL level was decreased when compared with control. Moreover, our results are consistent with that of Canturk Z et al. [16] study that showed increased values of all lipid parameters except HDL in patients with SCH as compared with that of those with euthyroids. Moreover, Patel et al. [22] found that levels of all lipid parameters were significantly increased in patients with SCH except decrease in HDL, which was not statistically significant. Contrary to our observations, National Health and Nutrition Examination Survey III (n = 8586) reported no significant differences in lipid parameters in SCH patients as compared with euthyroid individuals when adjusted for confounding variables [23].

In this study, the mean of PON-1 was 65.1 ± 7.6 U/l in group I and 18.7 ± 5.2 U/l in group II, and these results showed that the mean of PON-1was highly significant lower in group II than group I. Our results agree with that of Singh and Sarkar [17] who found a significant decrease in PON-1 levels in SCH and in overt hypothyroidism cases than control. Moreover, the results of this study are in agreement with the study of El-Laithy NA et al. [12] which enrolled 25 cases with SCH and 20 healthy controls. The patient group and the control group were compared in terms of the activity of PON-1 and the oxidative stress index, and they concluded that the activity of PON-1 was significantly low and oxidative stress was significantly high. Our results are inconsistent with the study of Hueston WJ et al. [24] in which PON-1 activity did not show differences between SCH, overt hypothyroidism, and euthyroid women. Moreover, our results disagree with that of Coria MJ et al. [25] where PON-1 activity was found to be similar among the patients with SCH and control group.

Evidence regarding the association of SCH and the risk of cardiovascular disease appears conflicting in epidemiological studies [26]. The Cardiovascular Health Study, a community-based study (n = 3233), showed no increased incidence of fatal or nonfatal cardiovascular events in individuals with SCH (n = 496) [27]. Another population study (n = 2730) showed an increased risk for heart failure but not for any atherosclerotic events and mortality associated with SCH (n = 338) [28]. In contrast, a meta-analysis of 15 studies showed an increased prevalence and incidence of coronary heart disease in patients with SCH compared with euthyroid individuals; nevertheless, this was true only among patients younger than 65 years [29]. In another community-based study, coronary heart disease was significantly more prevalent among patients with SCH (n = 119) than euthyroid individuals (n = 1906) even after adjustment for conventional cardiovascular risk factors [30].


  Conclusion Top


The level of PON-1 concentration in patients with SCH was highly significant lower than in control. Subclinical hypothyroid group was more dyslipidemic than control.

So it was concluded that SCH could be considered as a possible independent risk factor for atherosclerosis.

Acknowledgements

Funds were provided by the Faculty of Medicine, Menoufia University.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7]



 

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