Effects of levothyroxine replacement therapy on parameters of metabolic syndrome and atherosclerosis in hypothyroid patients: a prospective pilot study

Hypothyroidism in Metabolic Syndrome

INTRODUCTION

Metabolic syndrome (MetS) and hypothyroidism are well-established forerunners of atherogenic cardiovascular disease (CVD). It is possible that patients suffering from both these disease entities may have a compounded risk. This study aimed at determining the prevalence of hypothyroidism in MetS.

MATERIALS AND METHODS

This cross-sectional study was conducted from September 2017 to August 2018 in the department of medicine at a tertiary care hospital in Northern India. Ethical approval was obtained from the institutional ethical committee. The study subjects consisted of 157 patients with MetS, the diagnosis of which was based on the International Diabetes Federation criteria. After a detailed history and physical examination, relevant investigations including complete thyroid profile were done. The data were analyzed using appropriate statistical tests (P < 0.05).

RESULTS

In our study, the age of subjects ranged between 14 and 92 years, with a mean ± standard deviation of 48.1 ± 17.01 years. There were more females than males with a male-to-female ratio of 1:1.3. The prevalence of hypothyroidism was 46.5%. Hypothyroidism was more common in females (58.9%) as compared to males (41.1%). Patients with hypothyroidism had significantly higher body weight and body mass index (BMI) in comparison to euthyroid patients. The rest of the anthropometric parameters were comparable. Waist circumference and BMI of overt hypothyroid patients were found to be higher as compared to subclinical hypothyroid patients. Total cholesterol and triglyceride were significantly higher (P = 0.001 and P < 0.001, respectively), while high-density lipoprotein levels were significantly lower in patients with hypothyroidism than the euthyroid group (P < 0.001).

CONCLUSION

Hypothyroidism, especially subclinical hypothyroidism, is a common endocrine disorder in patients with MetS. As MetS and hypothyroidism are independent risk factors for CVD, hence there is a need for screening for hypothyroidism and the treatment of the same can be beneficial in reducing the cardiovascular morbidity and mortality in patients with MetS.

Increased thyroid stimulating hormone (TSH) as a possible risk factor for atherosclerosis in subclinical hypothyroidism

Primary hypothyroidism (PHT) is associated with an increased risk for the development of atherosclerosis (AS) and other cardiovascular disorders. PHT induces atherosclerosis (AS) through the induction of endothelial dysfunction, and insulin resistance (IR). PHT promotes vasoconstriction and the development of hypertension. However, patients with subclinical PHT with normal thyroid hormones (THs) are also at risk for cardiovascular complications. In subclinical PHT, increasing thyroid stimulating hormone (TSH) levels could be one of the causative factors intricate in the progression of cardiovascular complications including AS. Nevertheless, the mechanistic role of PHT in AS has not been fully clarified in relation to increased TSH. Therefore, in this review, we discuss the association between increased TSH and AS, and how increased TSH may be involved in the pathogenesis of AS. In addition, we also discuss how L-thyroxine treatment affects the development of AS.

The protective role of nutritional antioxidants against oxidative stress in thyroid disorders

An imbalance between pro-oxidative and antioxidative cellular mechanisms is oxidative stress (OxS) which may be systemic or organ-specific. Although OxS is a consequence of normal body and organ physiology, severely impaired oxidative homeostasis results in DNA hydroxylation, protein denaturation, lipid peroxidation, and apoptosis, ultimately compromising cells' function and viability. The thyroid gland is an organ that exhibits both oxidative and antioxidative processes. In terms of OxS severity, the thyroid gland's response could be physiological (i.e. hormone production and secretion) or pathological (i.e. development of diseases, such as goitre, thyroid cancer, or thyroiditis). Protective nutritional antioxidants may benefit defensive antioxidative systems in resolving pro-oxidative dominance and redox imbalance, preventing or delaying chronic thyroid diseases. This review provides information on nutritional antioxidants and their protective roles against impaired redox homeostasis in various thyroid pathologies. We also review novel findings related to the connection between the thyroid gland and gut microbiome and analyze the effects of probiotics with antioxidant properties on thyroid diseases.

Hypothyroidism and Risk of Cardiovascular Disease

Thyroid hormones (TH) have a significant impact on cellular oxidative metabolism. Besides that, they maintain vascular homeostasis by positive effects on endothelial and vascular smooth muscle cells. Subclinical (SCH) and clinical (CH) hypothyroidism influences target organs by changing their morphology and function and impaired blood and oxygen supply induced by accelerated atherosclerosis. The increased risk of acceleration and extension of atherosclerosis in patients with SCH and CH could be explained by dyslipidemia, diastolic hypertension, increased arterial stiffness, endothelial dysfunction, and altered blood coagulation. Instability of atherosclerotic plaque in hypothyroidism could cause excessive activity of the elements of innate immunity, which are characterized by: the significant presence of macrophages in atherosclerotic plaques, increased nuclear factor kappa B (NFkB) expression, and elevated levels of tumor necrosis factor α (TNF-α) and matrix metalloproteinase (MMP) 9, with reduced interstitial collagen, which all together creates inflammation milieu resulted in plaque rupture. Optimal substitution by levothyroxine (LT4) restores biochemical euthyroidism. In postmenopausal women and elderly patients with hypothyroidism and associated vascular comorbidity, excessive LT4 substitution could lead to atrial rhythm disorders and osteoporosis. Therefore, it is of interest to maintain thyroid-stimulating hormone (TSH) levels in the reference range, thus eliminating the deleterious effects of lower or higher TSH levels on the cardiovascular system. This review summarizes the recent literature on subclinical and clinical hypothyroidism and atherosclerotic cardiovascular disease and discusses the effects of LT4 replacement therapy on restoring biochemical euthyroidism and atherosclerosis processes.

Predictability Of Metabolic Syndrome Diagnosed By Body Mass Index For Cardiovascular Risk In Older Patients Treated With Levothyroxine

Background

We investigated the prevalence and metabolic features of two definitions of metabolic syndrome (MS) between older patients with chronic thyroiditis treated with levothyroxine (LT4) and controls. We also assessed the ability of both criteria to predict cardiovascular (CV) risk.

Methods

This cross-sectional, retrospective study included individuals aged ≥60 years who attended a geriatric outpatient clinic between January 2015 and December 2018. The LT4 treatment group was classified as having high or low CV risk based on the Framingham score.

Results

This study enrolled 111 patients with chronic thyroiditis treated with LT4 and 131 patients without thyroid disease as the control group. The prevalence of MS according to the World Health Organization (WHO) criteria and American Association of Clinical (AACE) criteria was similar in the LT4 treatment (21.6% and 26.1%, respectively) and the control (30.5% and 34.4%, respectively) groups (p>0.05). While the prevalence of MS and CV risk did not differ significantly between the control and LT4 treatment groups, the prevalence of MS with both definitions was higher among individuals with high CV risk in the LT4 treatment group (p<0.05). For the prediction of CV risk, the sensitivity and specificity of the AACE criteria were higher than those of the WHO criteria in the LT4 treatment group.

Conclusions

The prevalence of MS in euthyroid patients treated with LT4 was similar to that of patients without thyroid disease. When the LT4 treatment group was classified based on CV risk, MS was more common in those with a high CV risk.

Regulation of nitric oxide production in hypothyroidism

Hypothyroidism is a common endocrine disorder that predominantly occurs in females. It is associated with an increased risk of cardiovascular diseases (CVD), but the molecular mechanism is not known. Disturbance in lipid metabolism, the regulation of oxidative stress, and inflammation characterize the progression of subclinical hypothyroidism. The initiation and progression of endothelial dysfunction also exhibit these changes, which is the initial step in developing CVD. Animal and human studies highlight the critical role of nitric oxide (NO) as a reliable biomarker for cardiovascular risk in subclinical and clinical hypothyroidism. In this review, we summarize the recent literature findings associated with NO production by the thyroid hormones in both physiological and pathophysiological conditions. We also discuss the levothyroxine treatment effect on serum NO levels in hypothyroid patients.

Effect of Hyperbaric Oxygen Therapy on Fatty Acid Composition and Insulin-like Growth Factor Binding Protein 1 in Adult Type 1 Diabetes Mellitus Patients: A Pilot Study

OBJECTIVE

Metabolic changes in type 1 diabetes mellitus (T1DM) impair vasodilation, and this leads to tissue hypoxia and microvascular pathology. Hyperbaric oxygen therapy (HBOT) can significantly improve the outcome of ischemic conditions in T1DM patients and reduce vascular complications. The aim of our study was to assess the effects of HBOT on plasma fatty acid (FA) composition, and expression of insulin-like growth factor binding protein 1 (IGFBP-1) in T1DM patients.

METHODS

Our study included 24 adult T1DM patients diagnosed with peripheral vascular complications. The patients were exposed to 10 sessions of 100% oxygen inhalation at 2.4 atmosphere absolute for 1 hour. Blood samples were collected at admission and after HBOT for measurement of metabolic parameters, FA composition and IGFBP-1. Measurement of plasma FA composition was determined by gas chromatography. Expression of IGFBP-1 in the serum was estimated by Western blot analysis.

RESULTS

HBOT decreased blood levels of total cholesterol (p<0.05), triglycerides (p<0.05) and low-density lipoprotein (p<0.05). HBOT increased plasma levels of individual FAs: palmitic acid (p<0.05), palmitoleic acid (p<0.05), docosapentaenoic acid (p<0.05) and docosahexaenoic acid (p<0.01), and decreased levels of stearic acid (p<0.05), alpha linolenic acid (p<0.05) and linoleic acid (p<0.01). Expression of IGFBP-1 (p<0.01) was increased, whereas the level of insulin (p<0.001) was decreased in the serum after HBOT.

CONCLUSIONS

Our results indicate that HBOT exerts beneficial effects in T1DM patients by improving the lipid profile and altering FA composition.

Serum nitric oxide levels correlate with quality of life questionnaires scores of hypothyroid females

Primary hypothyroidism can affect lipid metabolism, cardiovascular (CV) function, and overall patients' quality of life (QoL). Decrease in serum nitric oxide (NO) levels could promote the atherosclerosis acceleration in hypothyroid patients. Our hypothesis is that serum NO level is altered in hypothyroidism; more specifically, we hypothesize that the early vascular changes that can be observed in hypothyroidism could be due to these alterations and that serum NO levels are associated with lipid levels in female patients diagnosed with subclinical hypothyroidism (SCH) or clinical hypothyroidism (CH). Furthermore, since serum NO level is an early marker of atherosclerosis and related CV disorders, which are commonly present and follow hypothyreosis and greatly contribute to overall QoL, we further hypothesized that NO level would correlate with Thyroid Symptom Questionnaire (TSQ) and General Health Questionnaire 12 (GHQ12) scores in hypothyroid patients. A collaterally of our hypothesis was that levothyroxine (LT4) treatment would affect serum NO levels as well as TSQ and GHQ12 scores. Therefore, we have analyzed lipid profile, the level of NO and QoL scores in female patients diagnosed with SCH and CH in order to determine the correlation between NO and generic and thyroid disease symptoms in treatment naïve SCH and CH patients and after LT4 treatment and laboratory euthyroidism achievement. As a consequence of our hypothesis is that measurement of serum NO level in SCH and CH patients may be an innovative way to improve LT4 treatment efficacy. This assumption could have a practical significance for future investigations regarding the management of hypothyroidism treatment protocols in current guidelines.

Aliskiren, Fosinopril, and Their Outcome on Renin-Angiotensin-Aldosterone System (RAAS) in Rats with Thyroid Dysfunction

BACKGROUND AND OBJECTIVES

Thyroid hormones have an important role in the growth and development of various tissues including the kidney, which is the major site of renin release and the consequent angiotensin and aldosterone formation. Therefore any derangement in thyroid function can result in abnormal functioning in the renin-angiotensin-aldosterone system. The current study was undertaken to find the impact of using a direct renin inhibitor (Aliskiren) and an angiotensin-converting enzyme inhibitor (Fosinopril) on the components of the renin-angiotensin-aldosterone system (RAAS) in rats with thyroid dysfunctions.

METHOD

Forty-two male albino rats were divided into three subgroups. First group (6 rats) served as control. Second group (18 rats) served as hyperthyroid group (6 rats positive control, 6 rats given Aliskiren, and 6 rats given Fosinopril). Third group (18 rats) served as hypothyroid group (6 rats positive control, 6 rats given Aliskiren, and 6 rats given Fosinopril). Induction of hyperthyroidism and hypothyroidism was done through daily oral administration of L-Thyroxine and Propylthiouracil, respectively. On day 40 of the study, the rats were sacrificed and blood was collected for estimation of renin, angiotensin I, angiotensin II, aldosterone, TSH, T₃, and T₄. The collected blood samples were also used for estimation of levels blood urea, serum creatinine, liver enzymes, and serum electrolytes. Blood pressure and urine collection were done on days 1 and 40. The collected urine was used for estimation of urine flow, sodium excretion, and potassium excretion rates.

RESULTS

In hypothyroid induced rats, serum renin level dropped as expected, while the use of Aliskiren and Fosinopril on these hypothyroid rats raised renin level due to the feedback mechanism. Both angiotensin I and II were significantly (P <0.05) lower than normal levels in the hypothyroid rats, unlike the level of aldosterone, which was higher than normal level. There was nonsignificant lowering in BP (systolic, diastolic, and mean BP) in the hypothyroid rats. Treatment of these rats with Aliskiren and Fosinopril did not lower the blood pressure more than normal when compared to the hypothyroid group. The hypothyroid rats also showed a decrease in level of serum creatinine. In hyperthyroid rats, there was a rise in levels of serum renin, angiotensin II, and aldosterone; nevertheless, the increase in angiotensin I level was significant. The use of Aliskiren and Fosinopril increased the level of renin nonsignificantly (decreased angiotensin I significantly). Hyperthyroid rats showed a significant increase in systolic, diastolic, and mean blood pressure. Both Aliskiren and Fosinopril increased urine flow, Na⁺ excretion, and K⁺ excretion rates. Aliskiren was better at reducing the high blood pressure.

CONCLUSION

Aliskiren and Fosinopril in hyperthyroid rats decreased serum angiotensin I, angiotensin II, and aldosterone. Blockade of renin and inhibition of angiotensin-converting enzyme both resulted in a rebound increase in level of renin in hypothyroid rats. Aliskiren is better at controlling blood pressure in hyperthyroid rats. Urine flow, sodium excretion, and potassium excretion rates were improved by the use of Aliskiren and Fosinopril in hyperthyroid rats.

The association between adherence to levothyroxine and economic and clinical outcomes in patients with hypothyroidism in the US

OBJECTIVE

To evaluate outcomes associated with adherence to levothyroxine (LT4) in the US adult hypothyroidism population.

METHODS

We used data from Truven's MarketScan databases from 1 July 2011 through 31 December 2015. Patients aged 18 or older were diagnosed with hypothyroidism (confirmed at least twice) and prescribed LT4. Patients were excluded if they did not have continuous insurance coverage or if they received a diagnosis of thyroid cancer or pregnancy during the study period. Multivariable analyses on a matched cohort of adherent and nonadherent patients examined the relationships among patient outcomes and adherence, defined as the proportion of days covered ≥80%. Outcomes included all-cause and hypothyroidism-related medical costs and resource utilization and comorbid diagnoses measured over the 1 year post-period following the first prescription for LT4. The analyses controlled for patient age, sex, region of residence, type of insurance coverage, diagnosing physician and pre-period general health status as proxied by the Charlson Comorbidity Index.

RESULTS

Prior to matching, there were 168,457 patients identified as adherent and 198,443 patients identified as nonadherent. The matched cohort consisted of 318,628 individuals, with equal numbers of adherent and nonadherent patients (n = 159,314). Patients who were adherent used significantly fewer resources and had significantly lower all-cause ($14,136 vs. $14,926; p < .0001) and hypothyroidism-related ($1672 vs. $1709; p < .0001) total costs, although the costs of drugs were higher in the adherent group. Furthermore, adherent patients, compared to nonadherent patients, were significantly less likely to be diagnosed with comorbid Addison's disease, bipolar disorder, chronic kidney disease, depression, migraine, obesity, type 1 diabetes or type 2 diabetes during the follow-up period.

CONCLUSIONS

Compared to nonadherence, adherence to LT4 among patients with hypothyroidism was associated with a significant reduction in all-cause and hypothyroidism-related costs and resource utilization as well as significantly lower rates of many comorbid diagnoses.

Thyroid dysfunction in metabolic syndrome patients and its relationship with components of metabolic syndrome

Background

A growing body of evidence suggests that metabolic syndrome is associated with endocrine disorders including thyroid dysfunction. Thyroid dysfunction in metabolic syndrome patients may further add to cardiovascular disease risk thereby increasing mortality. This study was done to assess thyroid function in metabolic syndrome patients and evaluate its relationship with the components of metabolic syndrome.

Methods

A cross sectional study was carried out among 169 metabolic syndrome patients at B P Koirala Institute of Health Sciences, Dharan, Nepal. Anthropometric measurements (height, weight, waist circumference) and blood pressure were taken. Fasting blood samples were analysed to measure glucose, triglyceride, high density lipoprotein (HDL) cholesterol and thyroid hormones (triiodothyronine, thyroxine and thyroid stimulating hormone).

Results

Thyroid dysfunction was seen in 31.9 % (n = 54) metabolic syndrome patients. Subclinical hypothyroidism (26.6 %) was the major thyroid dysfunction followed by overt hypothyroidism (3.5 %) and subclinical hyperthyroidism (1.7 %). Thyroid dysfunction was much common in females (39.7 %, n = 29) than males (26 %, n = 25) but not statistically significant (p = 0.068). The relative risk of having thyroid dysfunction in females was 1.525 (CI: 0.983–2.368) as compared to males. Significant differences (p = 0.001) were observed in waist circumference between patients with and without thyroid dysfunction and HDL cholesterol which had significant negative correlation with thyroid stimulating hormone.

Conclusions

Thyroid dysfunction, particularly subclinical hypothyroidism is common among metabolic syndrome patients, and is associated with some components of metabolic syndrome (waist circumference and HDL cholesterol).