Thyroid disease and lipids

Change of visfatin, C-reactive protein concentrations, and insulin sensitivity in patients with hyperthyroidism

The present study was undertaken to evaluate the change of circulating visfatin, C-reactive protein (CRP) concentrations, and insulin sensitivity in patients with hyperthyroidism. We studied 19 adult patients (14 women and 5 men aged 32.6 +/- 1.8 years) with hyperthyroidism due to Graves disease and 19 age- and sex-matched euthyroid controls (17 women and 2 men aged 36.7 +/- 2.7 years). All hyperthyroid patients were treated with 1 of 2 antithyroid drugs and were reevaluated after thyroid function normalized. Before antithyroid treatment, the hyperthyroid group had significantly higher visfatin plasma concentration (mean +/- standard error of the mean, 20.7 +/- 1.8 ng/mL) than the control group (16.2 +/- 1.3 ng/mL, P = .044); but the visfatin level dropped significantly after treatment (12.0 +/- 1.4 ng/mL, P < .001). The reciprocal index of homeostasis model assessment of insulin resistance (HOMA-IR) in the hyperthyroid group was higher before treatment (2.06 +/- 0.26 mmol mU/L*L) than after treatment (1.21 +/- 0.16 mmol mU/L*L, P = .027). There was no significant difference in serum glucose, high-sensitivity CRP, and insulin levels between hyperthyroid and control groups and in the hyperthyroid group before and after treatment. Body mass index-adjusted visfatin levels were significantly elevated in the hyperthyroid group. Pearson correlation revealed that visfatin, glucose, insulin, and HOMA-IR values positively correlated with triiodothyronine and free thyroxine levels. However, visfatin did not correlate with insulin and HOMA-IR levels. The results indicated that plasma visfatin concentration was elevated in hyperthyroidism due to Graves disease, but serum CRP levels were not. Plasma visfatin levels were not associated with indicators of insulin resistance in hyperthyroid patients.

Higher serum free thyroxine levels are associated with coronary artery disease

Thyroid hormone has many effects on the heart and cardiovascular system. Thyrotoxicosis is associated with increased cardiovascular morbidity and mortality, primarily due to heart failure and thromboembolism. However, the relationship between thyroid hormone excess and the cardiac complications of angina pectoris and myocardial infarction remains largely speculative. Moreover, few studies have been reported on the effect of thyroid hormone levels within normal range on coronary artery disease (CAD). Therefore we examined the association of thyroid function with coronary artery diseases in euthyroid angina patients. Total 192 subjects (mean age; 60.8 yrs) were enrolled in which coronary angiograms were performed due to chest pain. We measured free thyroxine (FT(4)), thyroid stimulating hormone (TSH), serum lipid levels and high-sensitivity C-reactive protein (hsCRP) levels and analyzed their association with the presence of CAD. Serum FT(4) levels were higher in patients with CAD compared with the patients without CAD (1.31 +/- 0.30 vs 1.20 +/- 0.23, p = 0.006), and high FT(4) level was associated with the presence of multi-vessel disease. Multivariate analysis showed that age (odds ratio (OR) 1.04; 95% confidence interval (CI) 1.01-1.07, p = 0.007), hypertension (OR 2.04; 95% CI 1.06-3.90, p = 0.036) and FT(4) (OR 4.23; 95% CI 1.12-15.99, p = 0.033), were the determinants for CAD. The relative risk (RR) for CAD in highest tertile of FT(4) showed increased risk compared with the lowest tertile (RR 1.98; 95% CI 0.98-3.99, p<0.001). Our study showed that FT(4) levels were associated with the presence and the severity of CAD. Also, this study suggests that elevated serum FT(4) levels even within normal range could be a risk factor for CAD. Further studies will be necessary to confirm the relationship of thyroid function and CAD.

Metabolic and cardiovascular risk in patients with a history of differentiated thyroid carcinoma: A case-controlled cohort study

Hyperthyroidism seems to increase metabolic and cardiovascular risk, while the effects of sub-clinical hyperthyroidism are controversial. We evaluated metabolic and cardiovascular parameters in differentiated thyroid carcinoma (DTC) patients with suppressed thyrotropin (TSH) due to levo-thyroxine (L-T4) therapy. We studied DTC patients and, as a control group, patients with a history of surgery for non-malignant thyroid pathology. Significantly higher insulin and lower HDL-cholesterol levels were recorded in DTC subjects. In both groups, insulin levels were significantly related with body mass index (BMI) but not with age or L-T4 dosage. In DTC patients, a significant negative correlation was seen between HDL-cholesterol and BMI or L-T4 dosage. In both groups, intima-media thickness (IMT) correlated positively with age, BMI, glucose levels and systolic blood pressure. In DTC patients, increased IMT was significantly correlated with glycated hemoglobin (HbA1c), cholesterol and triglycerides. In DTC patients, C-reactive protein correlated positively with insulin, insulin resistance, triglycerides and systolic blood pressure, and negatively with HDL-cholesterol. In both DTC and control subjects, fibrinogen correlated positively with age, BMI, increased IMT, HbA1c and systolic blood pressure. In DTC subjects, plasma fibrinogen concentrations correlated positively with insulin resistance, cholesterol and LDL-cholesterol, and negatively with TSH levels. Our data confirm that the favorable evolution of DTC can be impaired by a high incidence of abnormal metabolic and cardiovascular data that are, at least in part, related to L-T4 therapy. These findings underline the need for adequate L-T4 titration.

Statin myopathy as a metabolic muscle disease

The etiology of statin myopathy remains unclear and concern about this toxicity is a leading reason that statins are underutilized. A number of observations suggest that this toxicity may be due to the metabolic effects of lipid-lowering in patients with minor muscle disorders. These patients have a high frequency of mutations for metabolic muscle diseases and often have depleted mitochondrial enzymes. Their exercise physiology and biopsy findings indicate reduced oxidation of fats and mitochondrial dysfunction. These subjects are often intolerant of other lipid-lowering therapies in addition to statins, which suggests that the myopathy is due to lipid-lowering itself more than a simple pharmacokinetic reaction to high statin levels. Altogether, these findings support the concept that statin myopathy is a metabolic muscle disease.

Serum concentrations of adiponectin in patients with hyperthyroidism before and after control of thyroid function

OBJECTIVE

Thyroid hormone affects adipocyte function, which in turn influences lipid and carbohydrate metabolism. Adiponectin is one of the adipocytokines that regulates lipid and carbohydrate metabolism. The aim of our study was to evaluate circulating levels of adiponectin in patients with thyroid dysfunction before and after normalization of thyroid function with appropriate medication.

DESIGN & METHODS

One hundred and twenty patients with hyperthyroidism were recruited at the time of diagnosis. Measurements of free T4 (FT4), thyroid-stimulating hormone (TSH), thyrotropin binding inhibitor immunoglobulin (TBII), adiponectin, fasting blood glucose, fasting serum insulin, lipid profile, and body mass index (BMI) were taken before and after 6 months of medical treatment, at which point all patients were in a euthyroid state.

RESULTS

Any change in BMI was strongly correlated with changes in serum-adiponectin levels (r = -0.789, p<0.001). Any change in serum FT4 was also correlated with changes in BMI and serum adiponectin levels (r = -0.254, p = 0.05 and r = 0.501, p = 0.029 respectively). After controlling for BMI changes, we found correlation also between serum FT4 and adiponectin (r = 0.29, p = 0.005). Multivariate-regression analysis still revealed BMI to be a statistically strong predictor for serum-adiponectin level (p<0.001). However, that analysis also revealed thyroid function level as another predictor (p = 0.029).

CONCLUSIONS

Although BMI is the best predictor of adiponectin, that thyroid hormone might influence circulating levels of adiponectin.

Reduced plasma high-density lipoprotein cholesterol in hyperthyroid mice coincides with decreased hepatic adenosine 5'-triphosphate-binding cassette transporter 1 expression

The aim of the study was to investigate the influence of severe hyperthyroidism on plasma high-density lipoprotein cholesterol (HDL-C). Recently, it was shown in mice that increasing doses of T(3) up-regulate hepatic expression of scavenger receptor class B, type I, resulting in increased clearance of plasma HDL-C. Here, we show that severe hyperthyroidism in mice did not affect hepatic expression of scavenger receptor class B, type I, but reduced hepatic expression of ATP-binding cassette transporter 1, accompanied by a 40% reduction of HDL-C. The sterol content of bile, liver, and feces was markedly increased, accompanied by up-regulation of hepatic cholesterol 7alpha-hydroxylase, and ATP-binding cassette transporter 5, which is known to promote biliary sterol secretion upon dimerization with ATP-binding cassette transporter 8. Both control and hyperthyroid mice exerted identical plasma clearance of iv injected [(3)H]HDL-C, supporting the view that severe hyperthyroidism does not affect HDL-C clearance but, rather, its formation via hepatic ATP-binding cassette transporter 1.

Selective thyromimetics for atherosclerosis and dyslipidaemia: another old target making progress

BACKGROUND

Whereas many new targets for drug discovery have been identified from new biology, such as that from the Human Genome Project, some targets have been known for decades but have not been exploited.

OBJECTIVE

One such target, selective thyromimetics, is reviewed from a historical perspective and in the light of recent developments.

METHODS

The history of thyromimetics in atherosclerosis and dyslipidaemia is reviewed as the background to the recent publication of the first human data on a new selective thyromimetic, KB-2115 (eprotirome).

CONCLUSION

The published data provide proof of concept/mechanism, opening the way to larger studies in a wider range of subjects and in combination with statins.

Free T4 is negatively correlated with body mass index in euthyroid women

BACKGROUND/AIMS

Overt thyroid dysfunction is well known to affect weight. However, the influence of normal-range changes in thyroid status on body mass index (BMI) is unclear. We sought to evaluate thyroid function (free T4, TSH) and its possible relationship with BMI and lipid profiles in euthyroid subjects.

METHODS

A total of 1572 euthyroid women (mean age 46.2 years) who visited Daegu Catholic University Medical Centre for primary health screening participated in this cross-sectional study. Women who were not euthyroid and women who took thyroid medication were excluded. TSH, free T4, and lipid profile [total-cholesterol, triglyceride (TG), HDL-C, LDL-C] were evaluated.

RESULTS

Obese euthyroid women had lower free T4 levels than did lean euthyroid women. After adjustment for age and smoking, free T4, but not TSH, was significantly negatively correlated with BMI. After adjustment for age, smoking, and BMI, free T4 was negatively correlated with TG to a significant degree.

CONCLUSIONS

We demonstrated a negative correlation between free T4 within the normal range and BMI in euthyroid subjects. These findings suggest that low free T4 is associated with obesity in euthyroid subjects.

Risk factors for cardiovascular disease in patients with subclinical hypothyroidism

INTRODUCTION

The relationship between subclinical hypothyroidism (SCH) and cardiovascular disease is not fully understood. We investigated risk factors for cardiovascular disease (lipid profile, lipoproteins, insulin resistance, C-reactive protein [CRP] homocysteine [Hcy] and fibrinogen levels) and their relationships with thyroid hormones in SCH patients and controls.

METHODS

Thirty-eight SCH patients and 44 controls were enrolled in this study. No patients had any substantial confounding medical conditions (including diabetes mellitus or coronary heart disease) or were taking thyroid-related medication.

RESULTS

Serum total cholesterol (P<0.05), low-density lipoprotein cholesterol (P<0.05) and triglycerides (P<0.001) were higher in patients with SCH than in controls. Serum lipoprotein(a) (Lp[a]) levels were higher in SCH subjects but this difference did not reach statistical significance (P=0.07). No significant differences were noted in CRP, Hcy, fibrinogen, high-density lipoprotein cholesterol, apolipoprotein A-1, apolipoprotein B (Apo B) or insulin resistance between patients with SCH and controls (in all cases, P>0.05). Free triiodothyronine (FT3) negatively correlated with Apo B (r=.0.46, P=0.005) and Lp(a) (r=.0.31, P=0.03) in patients with SCH and negatively correlated with Lp(a) (r=.0.30, P=0.04) in controls. All of these parameters were comparable between patients with thyroid-stimulating hormone (TSH) >10 microIU/ml and TSH <10 microIU/ml (in SCH patients, P>0.05).

CONCLUSION

Our results suggest that SCH is associated with some lipid and lipoprotein abnormalities. Our results also suggest that this association does not depend on the subject's TSH level.

Lipid profile in different degrees of hypothyroidism and effects of levothyroxine replacement in mild thyroid failure

The aim of this study was to evaluate the lipid profile of patients with different degrees of hypothyroidism and the effect of levothyroxine replacement in subclinical hypothyroidism (SH). Initially, a cross-sectional study was performed with 226 participants [SH = 133 participants, manifest hypothyroidism (MH) = 23 participants, and euthyroidism (EU) = 70 participants]. The mean levels of atherogenic lipid variables were greater in MH than in SH and were greater in SH than in EU, although the differences between SH and EU did not reach statistical significance. The SH subgroup with greater serum thyrotropin (TSH) levels and that with positive antithyroperoxidase antibodies (TPO-Ab) had greater levels of triglycerides and of the atherogenic index Apo B/Apo A. A positive correlation exists between serum TSH and total cholesterol (rs = 0.167; P = 0.006), triglycerides (rs = 0.219; P < 0.001), and ApoB levels (rs = 0.205; P < 0.001). Eleven patients who received levothyroxine (L-T4) treatment and 15 patients who received placebo were reevaluated 1 year after TSH adjusted intervention. A fall in atherogenic variables was observed in the L-T4-treated group, with significance for total cholesterol (-20.0 vs +16.1 mg/dL in the placebo group) and LDL-c (-21.7 vs +17.2 mg/dL). We concluded that SH leads to an intermediary lipid profile between euthyroid individuals and that found in manifest hypothyroidism and that a significant lipid profile improvement occurred 1 year after L-T4 replacement therapy.

Thyroid function and lipid subparticle sizes in patients with short-term hypothyroidism and a population-based cohort

CONTEXT

Relations between thyroid function and lipids remain incompletely understood.

OBJECTIVE

Our objective was to determine whether lipoprotein subparticle concentrations are associated with thyroid status.

DESIGN AND SETTING

We conducted a prospective clinical study and cross-sectional cohort analysis at a university endocrine clinic and the Framingham Heart Study.

SUBJECTS

Subjects included 28 thyroidectomized patients with short-term overt hypothyroidism and 2944 Framingham Offspring cohort participants.

MAIN OUTCOME MEASURES

Fasting subclass concentrations of very-low-density lipoprotein (VLDL), intermediate-density lipoprotein, low-density lipoprotein cholesterol (LDL-C), and high-density lipoprotein cholesterol (HDL-C) particles were measured by nuclear magnetic resonance spectroscopy. TSH values were also measured.

RESULTS

Total cholesterol and LDL-C were increased during short-term overt hypothyroidism. Large LDL subparticle concentrations increased during hypothyroidism (917+/-294 vs. 491+/-183 nmol/liter; P<0.001), but more atherogenic small LDL was unchanged. Triglycerides marginally increased during hypothyroidism, small VLDL particles significantly increased (P<0.001), whereas more atherogenic large VLDL was unchanged. Total HDL-C increased during hypothyroidism (76+/-13 mg/dl vs. 58+/-15 mg/dl; P<0.001). There was no change in large HDL-C particle concentrations, whereas small (P<0.001) and medium (P=0.002) HDL-C particle concentrations decreased. Among Framingham women, adjusted total cholesterol and LDL-C were positively related to TSH categories (P<or=0.003). This was due to a positive correlation between adjusted large LDL subparticle concentrations and log-TSH (P<0.0001); log small LDL subparticle concentrations decreased slightly as log-TSH increased (P=0.045). Among Framingham men, the only significant association was a positive association between log-TSH and log large HDL subparticle concentrations (P=0.04).

CONCLUSIONS

There is a shift toward less atherogenic large LDL, small VLDL, and large HDL subparticle sizes in hypothyroid women.

Potential therapeutic applications of thyroid hormone analogs

Thyroid hormone (T3 and T4) has many beneficial effects including enhancing cardiac function, promoting weight loss and reducing serum cholesterol. Excess thyroid hormone is, however, associated with unwanted effects on the heart, bone and skeletal muscle. We therefore need analogs that harness the beneficial effects of thyroid hormone without the untoward effects. Such work is largely based on understanding the cellular mechanisms of thyroid hormone action, specifically the crystal structure of the nuclear receptor proteins. In clinical studies, use of naturally occurring thyroid hormone analogs can suppress TSH levels in patients with thyroid cancer without producing tachycardia. Many thyromimetic compounds have been tested in animal models and shown to increase total body oxygen consumption, and to lower weight and serum cholesterol and triglyceride levels while having minor effects on heart rate. Alternatively, analogs that specifically enhance both systolic and diastolic function are potentially useful in the treatment of chronic congestive heart failure. In addition to analogs that are thyroid hormone receptor agonists, several compounds that are thyroid hormone receptor antagonists have been identified and tested. This Review discusses the potential application of thyroid hormone analogs (both agonists and antagonists) in a variety of human disease states.

The clinical significance of subclinical thyroid dysfunction

Subclinical thyroid disease (SCTD) is defined as serum free T(4) and free T(3) levels within their respective reference ranges in the presence of abnormal serum TSH levels. SCTD is being diagnosed more frequently in clinical practice in young and middle-aged people as well as in the elderly. However, the clinical significance of subclinical thyroid dysfunction is much debated. Subclinical hyper- and hypothyroidism can have repercussions on the cardiovascular system and bone, as well as on other organs and systems. However, the treatment and management of SCTD and population screening are controversial despite the potential risk of progression to overt disease, and there is no consensus on the thyroid hormone and thyrotropin cutoff values at which treatment should be contemplated. Opinions differ regarding tissue effects, symptoms, signs, and cardiovascular risk. Here, we critically review the data on the prevalence and progression of SCTD, its tissue effects, and its prognostic implications. We also examine the mechanisms underlying tissue alterations in SCTD and the effects of replacement therapy on progression and tissue parameters. Lastly, we address the issue of the need to treat slight thyroid hormone deficiency or excess in relation to the patient's age.

Possible amelioration of atherogenic diet induced dyslipidemia, hypothyroidism and hyperglycemia by the peel extracts of Mangifera indica, Cucumis melo and Citrullus vulgaris fruits in rats

Hitherto unknown efficacy of the peel extracts of Mangifera indica (MI), Cucumis melo (CM) and Citrullus vulgaris (CV) fruits in ameliorating the diet-induced alterations in dyslipidemia, thyroid dysfunction and diabetes mellitus have been investigated in rats. In one study, out of 4 different doses (50-300 mg/kg), 200 mg/kg of MI and 100 mg/kg for other two peel extracts could inhibit lipidperoxidation (LPO) maximally in liver. In the second experiment rats were maintained on pre-standardized atherogenic diet CCT (supplemented with 4% cholesterol, 1% cholic acid and 0.5% 2-thiouracil) to induce dyslipidemia, hypothyroidism and diabetes mellitus and the effects of the test peel extracts (200 mg/kg of MI and 100 mg/kg for CM and CV for 10 consecutive days) were studied by examining the changes in tissue LPO (in heart, liver and kidney), concentrations of serum lipids, thyroid hormones, insulin and glucose. Rats, treated simultaneously with either of the peel extracts reversed the CCT-diet induced increase in the levels of tissue LPO, serum lipids, glucose, creatinine kinase-MB and decrease in the levels of thyroid hormones and insulin indicating their potential to ameliorate the diet induced alterations in serum lipids, thyroid dysfunctions and hyperglycemia/diabetes mellitus. A phytochemical analysis indicated the presence of a high amount of polyphenols and ascorbic acid in the test peel extracts suggesting that the beneficial effects could be the result of the rich content of polyphenols and ascorbic acid in the studied peels.

Increased serum chitotriosidase activity following restoration of euthyroidism in patients with subclinical hypothyroidism

OBJECTIVE

Whether to treat subclinical hypothyroidism (SH) remains controversial. Serum chitotriosidase activity, a marker of activated macrophages, predicts new cardiovascular events. Chitotriosidase activity (ChT) is a new cardiovascular risk marker and is independent of C-reactive protein. The purpose of this study was to determine ChT levels in SH and to examine the effect of levothyroxine replacement on ChT.

SUBJECTS AND METHODS

A cohort of 60 patients with subclinical hypothyroidism and 62 healthy controls were enrolled in this study. Serum total and LDL cholesterol, total homocysteine (t-Hyc), highly sensitive C-reactive protein (hsCRP) levels and serum ChT in patients with subclinical hypothyroidism at baseline and after achieving euthyroid state by levothyroxine were assessed.

RESULTS

Pretreatment levels of TSH (10.06+/-5.09 vs. 2.08+/-0.95 mIU/L, p<0.05), and free T4 (0.94+/-0.21 vs. 1.35+/-0.26 ng/dl, p<0.05) were significantly higher than controls while total cholesterol, LDL cholesterol, t-Hyc, ChT and hsCRP levels were not different. ChT levels significantly increased after replacement therapy (137.2+/-14.18 vs. 156.88+/-13.10 nmol/mL/h, p<0.05). T-Hyc and hsCRP levels were not significantly different after treatment with levothyroxine therapy even in this subgroup of patients. None of the other biochemical risk factors improved after euthyroidism in patients with SH with average dose of 85+/-30 mug/day when compared to pretreatment levels.

CONCLUSION

We conclude that clinical management of subclinical hypothyroidism does not decrease the serum hsCRP or t-Hyc levels but does increase the serum ChT levels. The clinical significance of this increment should be studied in further studies.

Lack of significant association between intima-media thickness in the carotid artery and serum TSH level. The Tromsø Study

BACKGROUND

Increased arterial wall intima-media thickness (IMT) is an early feature of atherosclerosis and has been reported to be altered in patients with thyroid dysfunction. The present study was performed to examine the relation between carotid artery intima-media thickness and possible variations in thyroid function in normal subjects using serum TSH as a surrogate index of thyroid function.

DESIGN

A total of 2034 subjects (974 males) were studied, 1856 or whom were non-users of thyroxine. The subjects not taking thyroxine were classified into three groups, those with a low serum TSH (0.48 mIU/L (2.5 percentile, those with serum TSH from 0.48 to 4.16 mIU/L, and those with high serum TSH of >4.16 mIU/L (97.5 percentile). Carotid ultrasound was performed in each all 2034 subjects to determine IMT.

RESULTS

Among those not taking thyroxine, subjects in the low serum TSH group had a higher mean IMT as compared to those in the normal and high serum TSH groups but the differences were not significant when adjusted for gender, age, smoking status, body mass index, systolic blood pressure and serum cholesterol (0.88 +/- 0.15 mm, 0.84 +/- 0.16 mm, and 0.84 +/- 0.24 mm respectively). Subjects taking thyroxine had significantly higher IMT than those not taking thyroxine (0.89 + 0.20 mm versus 0.84 + 0.17 mm, p<0.01).

CONCLUSIONS

No significant relationship between carotid IMT and serum TSH levels was observed in normal, non thyroxine taking, subjects. Carotid IMT was increased in subjects taking thyroxine. Whether the increase in carotid IMT is due to thyroxine ingestion or underlying thyroid disease cannot be answered from the study.

Multiple ovarian cysts in a young girl with severe hypothyroidism

Case study of a young female patient with severe hypothyroidism due to autoimmune thyroiditis and multiple ovarian cysts is reported. A 14-year 7-month-old girl presented with pelvic and abdominal pain and severe asthenia. Her last menstrual period was 10 months before presentation. Physical examination showed obesity; apathetic and flat expression; periorbital puffiness; pale, cold, dry skin and slow sustained reflexes; swelling in the hands and feet; no galactorrhea; a hardly palpable thyroid gland; and ovaries with a palpable irregular surface. Her heart rate was 90 bpm with a blood pressure within the normal range (110/70 mmHg). Laboratory findings showed severe hypothyroidism (thyroid-stimulating hormone [TSH]: 960 mIU/L), gravis macrocytic anemia, hyperfibrinogenemia, and hyperprolactinemia. Imaging examinations revealed a normal-size thyroid with irregular echogenicity, strongly hypoechogenous area at the neck ultrasonography, bilateral multilocular ovarian masses with cystic components at pelvic ultrasound and computed tomography, and both anterior and posterior pericardial effusion at echocardiography. As soon as thyroid replacement therapy was initiated, all symptoms progressively disappeared and biochemical and hormonal values normalized, while the right ovary did not decrease in size during the follow-up period. For this reason, our patient underwent right ovarian wedge resection 14 months after the initiation of medication replacement. Ovarian histological examination showed a benign ovarian cyst with extensive hemorrhage and myxedematous infiltration. It is concluded that it is important to recognize early in young girls the association between large multiple ovarian cysts and high elevated levels of TSH in order to resolve this disorder with substitutive therapy.

Carotid artery intima media thickness is inversely related to serum free thyroxine in euthyroid subjects

OBJECTIVE

The effect of thyroid function on cardiovascular risk may extend to the euthyroid range. In euthyroid subjects, we determined whether carotid artery intima media thickness (IMT), a measure of subclinical atherosclerosis, is related to thyroid function.

DESIGN AND SUBJECTS

Cross-sectional study in a cohort of 78 nonsmoking, predominantly middle-aged, euthyroid subjects (44 men and 34 women, mean age 56 years, TSH between 0.5 mU/l and 4.0 mU/l and FT4 between 11.0 pmol/l and 19.5 pmol/l).

MEASUREMENTS

IMT (mean of three segments in both carotid arteries by ultrasonography), clinical factors, insulin resistance (HOMA(ir)), plasma lipids, C-reactive protein (CRP), serum FT4, TSH and thyroid autoantibodies.

RESULTS

In several multiple linear regression models, age- and sex-adjusted IMT was found to be independently related to either pulse pressure and body mass index (BMI), to high density lipoprotein (HDL) cholesterol or to FT4, but not to TSH, thyroid autoantibodies, HOMA(ir), CRP, non-HDL cholesterol and triglycerides. In a subsequent model which included age, sex, pulse pressure, body mass index (BMI), HDL cholesterol and FT4, IMT was independently and positively related to age (beta = 0.43, P < 0.001), male sex (beta = 0.34, P = 0.014), pulse pressure (beta = 0.29, P = 0.002), BMI (beta = 0.24, P = 0.007) and inversely related to FT4 (beta = -0.19, P = 0.046). IMT was also inversely related to FT4 in a model which included HDL cholesterol, non-HDL cholesterol and triglycerides.

CONCLUSIONS

In euthyroid subjects, IMT is associated with FT(4), after controlling for clinical factors, lipid levels and thyroid autoantibodies. These findings raise the possibility that, even within the euthyroid range, low normal thyroid function may adversely affect cardiovascular risk.

Cardiovascular risk and subclinical hypothyroidism: focus on lipids and new emerging risk factors. What is the evidence?

Controversy remains as to the risk of cardiovascular disease (CVD) associated with subclinical hypothyroidism (SCH), defined as an increased serum thyrotropin (TSH) concentration with normal free thyroxine and triiodothyronine levels. Substantial evidence indicates altered cholesterol and lipoprotein metabolism in SCH when serum TSH is above 10 mU/L. Observed abnormalities include elevated plasma levels of total cholesterol (TC) and low-density lipoprotein-cholesterol (LDL-C); the altered TC/high-density lipoprotein-cholesterol (HDL-C) and LDL-C/HDL-C ratios suggest a potential accelerated risk for CVD. The influence of SCH on lipids is directly proportional to the degree of TSH elevation and becomes more significant with the progression from SCH to overt disease, thereby accelerating any propensity to atherosclerosis. Although many clinicians may tend to ignore SCH with TSH levels <10, it is apparent that an enhanced CV risk could apply to these individuals, perhaps compounded by insulin resistance and amplified by the copresence of other risk factors such as endothelial dysfunction and elevated C-reactive protein.

Hypermetabolism in mice caused by the central action of an unliganded thyroid hormone receptor alpha1

Thyroid hormone, via its nuclear receptors TRalpha and TRbeta, controls metabolism by acting locally in peripheral tissues and centrally by regulating sympathetic signaling. We have defined aporeceptor regulation of metabolism by using mice heterozygous for a mutant TRalpha1 with low affinity to T3. The animals were hypermetabolic, showing strongly reduced fat depots, hyperphagia and resistance to diet-induced obesity accompanied by induction of genes involved in glucose handling and fatty acid metabolism in liver and adipose tissues. Increased lipid mobilization and beta-oxidation occurred in adipose tissues, whereas blockade of sympathetic signaling to brown adipose tissue normalized the metabolic phenotype despite a continued perturbed hormone signaling in this cell type. The results define a novel and important role for the TRalpha1 aporeceptor in governing metabolic homeostasis. Furthermore, the data demonstrate that a nuclear hormone receptor affecting sympathetic signaling can override its autonomous effects in peripheral tissues.

Thyroid disease and the heart

The cardiovascular signs and symptoms of thyroid disease are some of the most profound and clinically relevant findings that accompany both hyperthyroidism and hypothyroidism. On the basis of the understanding of the cellular mechanisms of thyroid hormone action on the heart and cardiovascular system, it is possible to explain the changes in cardiac output, cardiac contractility, blood pressure, vascular resistance, and rhythm disturbances that result from thyroid dysfunction. The importance of the recognition of the effects of thyroid disease on the heart also derives from the observation that restoration of normal thyroid function most often reverses the abnormal cardiovascular hemodynamics. In the present review, we discuss the appropriate thyroid function tests to establish a suspected diagnosis as well as the treatment modalities necessary to restore patients to a euthyroid state. We also review the alterations in thyroid hormone metabolism that accompany chronic congestive heart failure and the approach to the management of patients with amiodarone-induced alterations in thyroid function tests.

Atherogenic diet induced diabetes mellitus: involvement of thyroid hormones

An investigation was made to reveal the possible involvement of thyroid hormones in the progression of diabetes mellitus in response to an atherogenic diet; CCT (4% cholesterol, 1% cholic acid and 0.5% 2-thiouracil). Following the intake of CCT diet for 14 consecutive days a decrease in the serum levels of insulin, both the thyroid hormones, triiodothyronine (T(3)) and thyroxine (T(4)); hepatic glycogen content, hepatic type-1 iodothyronine 5'-mono-deiodinase (5'D) and serum alpha-amylase activities were observed, while there was an increase in the levels of serum glucose and nitrite and in lipid peroxidation of heart, liver and kidney tissues as well as in serum. However, simultaneous administration of L-thyroxine (500 microg/kg/day, s.c.) to CCT-diet fed animals resulted in the amelioration of all the aforesaid adverse changes including that of serum glucose, insulin, alpha-amylase, hepatic glycogen content and nitrite levels, suggesting the involvement of thyroid hormones in the progression of CCT-diet induced diabetes mellitus.

Hiperlipidemias e fatores dietéticos: estudo transversal entre nipo-brasileiros

Este estudo teve como objetivo avaliar a associação entre hiperlipidemia e dieta de nipo-brasileiros de Bauru, município do Estado de São Paulo. Foram obtidos de 1.330 indivíduos dados mediante questionários previamente testados (dados demográficos e dietéticos). Os exames físicos e laboratoriais incluíram a coleta (ou dosagem) antropométrica, de pressão arterial, de glicemia de jejum e de 2 horas, de perfil lipídico e de TSH e T4 livre. Utilizaram-se teste qui-quadrado e medida de odds ratio para avaliar associação entre as variáveis estudadas e presença de hiperlipidemia. Foi encontrado 81,5% de hiperlipidêmicos e acometeu, principalmente, indivíduos tabagistas, com excesso de peso, hipotireoidismo, hipertensão arterial e intolerância a glicose. Observaram-se, mediante análise bruta, relações entre hiperlipidemia e ácido graxo saturado, ácido oléico e fibras de grãos e cereais. Após o ajuste para as variáveis de controle, observaram-se associações entre hiperlipidemia e consumo de lípides (totais, ácido oléico, saturados e trans), fibras e álcool. Conclui-se que mudanças no estilo de vida, particularmente no hábito alimentar, podem levar a uma melhora do quadro hiperlipidêmico e que o consumo de lípides pode ser um dos principais fatores para o aumento da hiperlipidemia. Estudos prospectivos auxiliarão para testar essas hipóteses nos nipo-brasileiros de Bauru.

Subclinical hypothyroidism

PURPOSE OF REVIEW

Mild or subclinical hypothyroidism is characterized by normal serum free thyroxine concentrations with elevated serum thyroid-stimulating hormone concentrations. Subclinical hypothyroidism is relatively prevalent in the general population, especially among women and the elderly. The main cause of subclinical hypothyroidism is autoimmune chronic thyroiditis. The present report reviews the most important and recent studies on subclinical hypothyroidism, and discusses the most controversial aspects of this topic.

RECENT FINDINGS

Several studies have demonstrated that subclinical hypothyroidism may affect both diastolic and systolic cardiac function. It may also worsen many risk factors for cardiovascular disease, including hypertension, abnormal endothelial function, and elevated low-density lipoprotein cholesterol concentrations. Furthermore, a growing body of evidence suggests that subclinical hypothyroidism may cause symptoms or progress to symptomatic overt hypothyroidism.

SUMMARY

Prompt treatment of subclinical hypothyroidism in pregnant women is mandatory to decrease risks for pregnancy complications and impaired cognitive development in offspring. Children with subclinical hypothyroidism should be treated to prevent growth retardation. Whether nonpregnant adult patients with subclinical hypothyroidism should be treated, and at what thyroid-stimulating hormone values, is debatable.

Lipoprotein alterations, hepatic lipase activity, and insulin sensitivity in subclinical hypothyroidism: response to L-T(4) treatment

Subclinical hypothyroidism (sH) has been associated with atherosclerotic cardiovascular disease even in the absence of hypercholesterolemia.

OBJECTIVE

Our study was designed to assess the hypothesis that other pro-atherogenic parameters, such as qualitative lipoprotein changes and insulin resistance, might be present in sH.

DESIGN AND METHODS

Twenty-one sH women were compared to 11 female controls matched for body mass index, menopausal status, and age. Before and after 6 months of levothyroxine (L-T(4)) treatment, we determined total cholesterol, low-density lipoprotein (LDL) cholesterol, high-density lipoprotein (HDL) cholesterol, triglycerides (TG), apoB levels, hepatic lipase (HL) activity in postheparin plasma samples, the chemical composition and copper-induced oxidation in isolated LDL and homeostasis model assessment (HOMA), quantitative insulin sensitivity check index, and insulinogenic index.

MAIN OUTCOME

Lipid profiles were similar between the two groups. No differences in LDL oxidability or the insulin sensitivity assessment parameters were found. HL activity was significantly lower in the sH patients: median (range), 13.1 (2.5-26.7) vs. 18.7 (7.9-28.1) micromol free fatty acids/mL, p < 0.04. The LDL-cholesterol/LDL-TG ratio was decreased in sH: 3.9 (1.8-5.5) vs. 4.7 (3.5-6.8), p < 0.02. HL negatively correlated with thyroid-stimulating hormone (TSH) levels (r = - 0.504, p < 0.01) and positively with LDL-cholesterol/LDL-TG (r = 0.46, p < 0.02). Posttreatment results for all these parameters did not differ significantly compared to baseline.

CONCLUSIONS

Increased levels of TSH are associated to a decrease in HL activity, explaining our findings of an LDL particle rich in TG. This qualitative lipoprotein alteration suggests a pro-atherogenic pattern in sH. Treatment with L-T(4), however, did not correct the basal lipid derangement.

Prevalence of subclinical hypothyroidism in patients with metabolic syndrome

Subclinical hypothyroidism (SCH) is a prevalent condition among adult population, however it is frequently overlooked. Thyroid functions affect metabolic syndrome (MetS) parameters including HDL cholesterol, triglycerides, blood pressure and plasma glucose. On the other hand, the relation between MetS and thyroid dysfunction is not clearly identified yet. The aim of the present study was to investigate the prevalence of SCH among MetS patients and to identify its relation with MetS parameters. Two hundred and twenty MetS patients (MetS group; 167 female, 53 male, mean age: 48.5 +/- 11.3) and 190 patients without MetS (Control group; 142 female, 48 male, mean age: 46.3 +/- 11.9) attending consecutively to Internal Medicine outpatient clinics were included in this study. Groups were compared in terms of SCH prevalence. SCH was defined as a condition with high thyrotrophin and normal free thyroxine levels. SCH was found in 36 (16.4%) cases in the MetS group and in 11 (5.8%) cases in the control group (p = 0.001). Only female gender was associated with the presence of SCH. About one sixth of MetS patients had SCH. This finding indicates a need for investigating the presence of SCH during the management of MetS patients.

Thyroid function is associated with components of the metabolic syndrome in euthyroid subjects

CONTEXT

Thyroid disease and the metabolic syndrome are both associated with cardiovascular disease.

OBJECTIVE

The aim of this study was to explore the hypothesis that thyroid function, in euthyroid subjects, is associated with components of the metabolic syndrome, including serum lipid concentrations and insulin resistance.

METHODS

A total of 2703 adult inhabitants of a middle-sized city in The Netherlands participated in this cross-sectional study. Subjects who were not euthyroid were excluded, as were subjects taking thyroid medication, medication for diabetes, and subjects for whom medication data were not available (n = 1122). Homeostasis model assessment for insulin resistance (HOMA-IR) (mU*mmol/liter2) was calculated as fasting insulin (mU/liter) times fasting glucose (mmol/liter) divided by 22.5. The metabolic syndrome was defined according to National Cholesterol Education Program's Adult Treatment Panel III criteria.

RESULTS

After adjustment for age and sex, free T4 (FT4) was significantly associated with total cholesterol [standardized beta (beta) = -0.059; P = 0.014], low-density lipoprotein cholesterol (beta = -0.068; P = 0.004), high-density lipoprotein cholesterol (beta = 0.100; P < 0.001), and triglycerides (beta = -0.102; P < 0.001). Both FT4 and TSH were significantly associated with HOMA-IR (beta = -0.133; P < 0.001 and beta = 0.055; P = 0.024, respectively). Median HOMA-IR increased from 1.42 in the highest tertile of FT4 to 1.66 in the lowest tertile of FT4. FT4 was significantly related to four of five components of the metabolic syndrome (abdominal obesity, triglycerides, high-density lipoprotein cholesterol, and blood pressure), independent of insulin resistance.

CONCLUSIONS

We have demonstrated an association between FT4 levels within the normal reference range and lipids, in accordance with the earlier observed association between (sub)clinical hypothyroidism and hyperlipidemia. Moreover, low normal FT4 levels were significantly associated with increased insulin resistance. These findings are consistent with an increased cardiovascular risk in subjects with low normal thyroid function.

Cardiovascular risk factors in patients with subclinical hypothyroidism

Background/Aims. Overt hypothyroidism is disease associated with accelerated arteriosclerosis and coronary heart disease. Whether subclinical hypothyroidism (SH) is associated with increased cardiovascular risk is contraversial. As SH is a high prevalence thyroid dysfunction, specially in older women, it is important to evaluate cardiovascular risk factors in these patients and that was the aim of this study. Methods. We examined 30 patients with SH and 20 healthy controls. Subclinical hypothireoidism was defined as an elevated thyrotropin (TSH) (> 4.5 mU/L) and normal free thyroxine (FT4) level. In all the participants we determined body mass index (BMI), blood pressure, TSH, FT4, antibodies to thyroid peroxidase, antibodies to thyroglobulin, total cholesterol, high density lipoprotein (HDL) cholesterol, low density lipoprotein (LDL) cholesterol, triglicerides, total cholesterol/HDL cholesterol ratio and LDL/HDL cholesterol ratio. Results. Mean BMI in patients with SH was significantly higher (p < 0.05), as well as diastolic blood pressure (p < 0.01) compared with the controls. Average levels of total cholesterol (5.40?0.62 vs 5.06?0.19 mmol/l, p < 0.01) and triglycerides (2.16?0.56 vs 1.89?0.24 mmol/l, p < 0.05) were also significantly higher in the group with SH. Individual analysis revealed that the percentage of patients with SH having borderline elevated total cholesterol (63.33%), hypertrigliceridemia (43.33%) and elevated total cholesterol/HDL cholesterol ratio (26.67%) were significantly higher than the percentage in the controls. No significant correlation between TSH and lipid parameters was detected. Conclusion. Subclinical hypothyroidism was associated with higher BMI, diastolic hypertension, higher total cholesterol and triglicerides levels and higher total cholesterol/HDL cholesterols ratio. This might increase the risk of accelerated arteriosclerosis in patients with SH.

Short-term hypothyroidism after Levothyroxine-withdrawal in patients with differentiated thyroid cancer: clinical and quality of life consequences

Acute hypothyroidism induced by thyroid hormone withdrawal in patients with differentiated thyroid cancer during monitoring for remnant or metastatic disease, seriously affects multiple organs and systems, and especially in severe cases can impair quality of life. Indeed, it may induce untoward cardiovascular effects and can be hazardous in patients with underlying cardiovascular disease, particularly in the elderly. Moreover, acute hypothyroidism deranges the lipid profile and exacerbates neuropsychiatric illness. The introduction of recombinant human TSH (rhTSH) as a diagnostic and therapeutic tool in the care of patients with thyroid cancer has widened the scope of disease management. The use of rhTSH prevents derangement of various systems at approximately equivalent societal costs to that of withdrawal and promotes compliance while preserving the patient's normal daily functioning and productivity. Its reliability allied with its safety render this compound a valid alternative in the monitoring of patients with differentiated thyroid carcinoma as well as providing an alternative therapeutic procedure whenever LT4-withdrawal may be hazardous or in cases of patient non-compliance.

Plasma thiobarbituric acid-reactive substance levels in subclinical hypothyroidism

OBJECTIVE

The purpose of this study was to determine thiobarbituric acid-reactive substance (TBARS) levels in subclinical hypothyroidism and to examine the effect of levothyroxine replacement on TBARS levels.

SUBJECTS AND METHODS

A cohort of 28 female patients with subclinical hypothyroidism and 24 healthy controls were enrolled in this study. The levels of plasma TBARS, serum lipids, and high-sensitive C-reactive protein (CRP) in patients with subclinical hypothyroidism at baseline and after achieving euthyroid state by levothyroxine were assessed.

RESULTS

TBARS levels of the patients were similar to those of the control group in the subclinical hypothyroid state and after restoration of euthyroidism by levothyroxine replacement. TBARS levels decreased after levothyroxine treatment, but did not reach statistical significance. There was no significant correlation between TBARS, lipid and CRP levels. Serum CRP levels were higher in subclinical hypothyroidism (4.28 +/- 0.9 mg/l) than in the control group (1.95 +/- 0.34 mg/l) and the difference was statistically significant (p = 0.03). After achieving euthyroid state, CRP levels decreased significantly in patients with subclinical hypothyroidism from 4.28 +/- 0.9 to 2.32 +/- 0.6 mg/l (p = 0.006).

CONCLUSION

Our findings suggest that there is no significant alteration of plasma TBARS levels neither in subclinical hypothyroid state nor after achieving euthyroid state. Serum CRP level is higher in patients with subclinical hypothyroidism than in the control group. Normalization of thyroid state seems to effectively reduce serum CRP levels in subclinical hypothyroidism without any correlation with TBARS activity.

Etiology of hypercholesterolemia in patients with anorexia nervosa

OBJECTIVE

Hypercholesterolemia is common in patients with anorexia nervosa (AN) despite emaciation. The objective of this study was to clarify the mechanism of hypercholesterolemia in AN.

METHOD

We measured serum lipids in 39 patients with AN and analyzed serum lipid profiles in the 24 patients in comparison with five age-matched controls.

RESULTS

Mean serum levels of total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), ketone bodies, apolipoprotein (apo)-A1, B, C2, C3, E, and cholesterol ester transfer protein (CETP) activity were significantly higher in patients with AN than in controls. No significant difference in serum free fatty acid (FFA) levels was observed between patients with AN and controls. CETP was accelerated in patients with AN with hypercholesterolemia. No correlation was apparent between serum levels of cholesterol and thyroid hormones.

CONCLUSION

Serum levels of cholesterol, CETP, and apolipoproteins decreased after weight gain, indicating that cholesterol metabolism is accelerated in patients with AN with normal serum levels of FFA.

Hyperinsulinemia, impaired glucose tolerance, and diabetes mellitus in survivors of childhood cancer: prevalence and risk factors

CONTEXT

Hyperinsulinism and its associated metabolic abnormalities, including diabetes mellitus (DM), have been reported in long-term survivors of childhood cancer, mainly after bone marrow transplant (BMT); however, the predisposing factors are unclear, and early markers have not been identified.

METHODS

The prevalence of overweight/obesity, abdominal adiposity and hyperinsulinemia (HI), impaired glucose tolerance (IGT), or DM was examined prospectively in 248 survivors of childhood cancer (36 prepubertal, 88 pubertal, and 124 adult subjects; 67 BMT) at a median of 12.9 yr (2.3-33.6) after diagnosis and compared with healthy controls. Potential risk factors for the development of HI, IGT, or DM were sought.

RESULTS

Overweight/obesity was not increased when comparing subjects with controls; however, the prevalence of abdominal adiposity in prepubertal and pubertal subjects was roughly doubled (P < or = 0.04). Fasting insulin concentrations were higher in prepubertal and pubertal subjects compared with their controls (P < 0.001) and were similar in adult and pubertal subjects. HI, IGT, or DM was detected in 39 of 212 (18%) pubertal or adult subjects (23 BMT). Ten of 88 (11%) pubertal and 14 of 124 (11%) adult subjects had IGT/DM (vs. 0 and 4.9% controls, respectively; P < 0.001). Total body irradiation, untreated hypogonadism, and abdominal adiposity emerged as independent risk factors for the development of HI, IGT, or DM in multivariate regression analysis.

CONCLUSIONS

The risk factors identified suggest the need for reconsideration of BMT protocols and regular screening of survivors. The increased prevalence of abdominal adiposity among prepubertal subjects, none of whom had developed HI/IGT/DM, suggests that a waist to height ratio greater than 0.5 has potential as a clinical screening tool.

Serum lipids in hypothyroidism: Our experience

In order to determine whether the screening of lipid profile is justified in patients with hypothyroidism we estimated serum lipids in cases having different levels of serum TSH. 60 patients of hypothyroidism in the age group of 20 to 60 yrs were studied for thyroid profile over a period of one year. On the basis of serum TSH level the cases were divided into three groups: In the first group TSH concentration was 8.8±2.99 μlU/ml, 95% confidence interval (Cl) 8.8±1.07, whereas serum total cholesterol and LDL-chol levels were 196±37.22 and 126±29.17 mg/dl respectively. The statistical analysis of these two groups showed a significant correlation between raised TSH levels and serum total cholesterol and LDL-chol (P<0.05 & P<0.01) respectively. We conclude that hypothyrodism is associated with changes in lipid profile.

Serum TSH is positively associated with BMI

OBJECTIVE

To investigate whether there is an association between serum thyroid-stimulating hormone (TSH) within the normal range and body mass index (BMI).

DESIGN AND SUBJECTS

The study was performed in 6164 subjects (2813 males) who attended the fifth Tromsø study in 2001, and in 1867 subjects (873 males) that attended both the fourth Tromsø study in 1994/1995 as well as the fifth Tromsø study.

MEASUREMENTS

Height, weight, and serum TSH were measured in all subjects, and smoking status was recorded.

RESULTS

Smokers and nonsmokers were analyzed separately. In the fifth Tromsø study, serum TSH was positively and significantly associated with BMI in the nonsmokers. Within the normal TSH range (defined as the 2.5-97.5 percentile), nonsmoking males in the highest TSH quartile had a mean BMI 0.4 kg/m(2) higher compared to those in the lower quartile, whereas the difference for nonsmoking women was 1.4 kg/m(2). Similarly, in nonsmokers in the longitudinal study, there was a significant and positive association between delta serum TSH (serum TSH in 2001 minus serum TSH in 1994) and delta BMI in those with serum TSH within the normal range both in 1994 and 2001. In these subjects, the quartile with the highest delta serum TSH had a mean increase in BMI from 1994 to 2001 that was 0.3 kg/m(2) higher compared to those in the quartile with the lowest delta serum TSH. For the smokers, relations between serum TSH and BMI were not statistically significant.

CONCLUSION

In nonsmokers there is a positive association between serum TSH within the normal range and BMI.

Resistin levels are normal in hypothyroidism and remain unchanged after attainment of euthyroidism: relationship with insulin levels and anthropometric parameters

The aim of this controlled prospective study was to investigate resistin levels in hypothyroidism before and after restoration of euthyroidism and correlate the results with body weight (BW), body fat (BF), waist circumference (WC), body mass index (BMI) and serum insulin levels. Fifty-three hypothyroid patients with Hashimoto's disease (6 males, 47 females) and 30 controls matched for age, BMI and BF were investigated. Anthropometric parameters, resistin and insulin levels were measured. All patients were started on levothyroxine treatment and 4 to 5 months after initiation of treatment the investigations were repeated. Hypothyroid patients exhibited normal resistin values, which were no different from controls (mean+/-SD 7.4+/-4.0 vs 5.1+/-3.5 ng/ml, p=0.063). Normalization of circulating thyroid hormone levels produced no significant change in resistin levels (7.4+/-4.0 vs 6.8+/-4.2 ng/ml, p=ns) and post-treatment resistin levels did not differ from euthyroid controls. Furthermore, no gender difference was demonstrated in resistin levels either before (6.4+/-3.7 for males vs 7.6+/-4.1 ng/ml for females, p=ns) or after therapy (7.9+/-4.3 vs 6.7+/-4.3 ng/ml, for males and females respectively, p=ns), nor was there a difference in resistin levels in either sex induced by treatment of hypothyroidism (6.4+/-3.7 vs 7.9+/-4.3 ng/ml for males, p=ns, and 7.6+/-4.1 vs 6.7+/-4.3 ng/ml for females, p=ns). However, a small but significant difference in resistin levels was found between female patients and female controls (7.6+/-4.1 vs 5.0+/-4.0 ng/ml, p=0.047). Insulin levels and homeostasis model assessment insulin resistance (HOMA-IR) index did not differ before and after treatment in hypothyroid patients (13.0+/-10.2 vs 12.6+/-11.8 microU/ml, 22.7+/-1.4 vs 21.8+/-1.3, respectively, p=ns for both) or between patients and controls. In conclusion, our results demonstrate that resistin levels are normal in hypothyroidism and remain within normal range after attainment of euthyroidism. Resistin is not associated with serum insulin and HOMA-IR index, as well as BMI, BF, WC and BW.

Postprandial lipemia as a risk factor for cardiovascular disease in patients with hypothyroidism

Postprandial lipoprotein metabolism is suggested to play a role in the pathogenesis of atherosclerosis. In this study, we investigated postprandial lipemia and its relationship to cardiovascular risk factors in patients with overt and subclinical hypothyroidism. Twenty-nine female patients with TSH levels greater than 5 microIU/mL and 12 euthyroid control female subjects were included in the study. Fifteen patients had subclinical hypothyroidism and 14 had overt hypothyroidism. All subjects underwent an oral lipid tolerance test. If triglyceride levels increased by 80% or more, subjects were considered postprandial lipemia positive. Control, overt hypothyroid, and subclinical hypothyroid groups were not statistically different with respect to anthropometric measurements, fasting blood C-reactive protein, uric acid, homocysteine, glucose, insulin, lipoprotein (a), apolipoprotein B levels, and homeostasis model assessment index. Fasting triglyceride levels correlated positively with TSH levels. Postprandial lipemia frequency was higher in overt hypothyroid subjects than in the control group. The subclinical hypothyroid group did not differ from the hypothyroid group with respect to postprandial lipemia frequency. In subjects with TSH levels higher than 5 microIU/mL, PPL risk was increased sevenfold. The results of this study show that postprandial triglyceride metabolism is affected in hypothyroidism.

The Lipoprotein Lipase Inhibitor ANGPTL3 Is Negatively Regulated by Thyroid Hormone

Whereas the role of thyroid hormone is clearly established in the regulation of cholesterol homeostasis, its involvement in the control of serum triglyceride (TG) levels remains largely debated. Angiopoietin-like proteins 3 and 4 have recently been characterized as potent lipoprotein lipase inhibitors and therefore as important components of plasma triglyceride homeostasis. In the present study, the role of thyroid hormone in the regulation of both ANGPTL4 and ANGPTL3 gene expression was investigated. In vivo studies revealed that thyroid hormone down-regulates ANGPTL3 but not ANGPTL4 gene expression in hypothyroid rats. Using thyroid hormone receptor (TR)-deficient mice, we show that thyroid hormone regulates ANGPTL3 gene expression in a TRbeta-dependent manner. Transfection studies revealed that this inhibition occurs at the transcriptional level in a DNA binding-independent fashion and requires the proximal (-171 to +66) region of the ANGPTL3 gene promoter. Moreover, site-directed mutagenesis experiments indicate that the HNF1 site within this proximal region mediates this TRbeta-dependent repression. Finally, co-transfection studies and electrophoretic mobility shift assays suggest that TRbeta antagonizes the HNF1alpha signaling pathway by inhibiting its transcriptional activity without interfering with its DNA-binding capacity. Taken together, our results lead to the identification of ANGPTL3 as a novel TRbeta target gene and provide a new potential mechanism to explain the hypotriglyceridemic properties of TRbeta agonists in vivo.

Blood coagulation, fibrinolytic activity and lipid profile in subclinical thyroid disease: subclinical hyperthyroidism increases plasma factor X activity

BACKGROUND AND OBJECTIVES

Various abnormalities of coagulation and fibrinolysis occur in patients with thyroid diseases, and may range from subclinical laboratory abnormalities to clinically significant disorders of coagulation and, rarely, major haemorrhage or thromboembolism. The influence of subclinical hypothyroidism (SHypo) on haemostasis is controversial, both hypercoagulable and hypocoagulable states have been reported. A hypercoagulable state might be a risk factor for thromboembolic disease in SHypo. On the other hand, subclinical hyperthyroidism (SCHyper) is associated with enhanced cardiovascular risk. In the English literature, there are no studies on changes in coagulation and fibriolytic status in subjects with SCHyper. Therefore, the aim of the present study was to investigate the markers of endogenous coagulation and fibrinolysis, and to evaluate the relationships between serum lipid profile and thyroid hormones and these haemostatic parameters in subclinical thyroid patients.

DESIGN AND METHODS

Various haemostatic parameters were investigated in 30 patients with SHypo and 20 patients with SCHyper and compared to 20 euthyroid controls. Prothrombin time (PT), activated partial thromboplastin time (aPTT), fibrinogen, factors V, VII, VIII, IX and X activities, vWF, antithrombin III (AT III), protein C, protein S, tissue plasminogen activator (t-PA) and tissue plasminogen activator inhibitor-1 (PAI-1), as well as common lipid variables, were measured. The relationships between serum thyroid hormones and these haemostatic parameters were examined.

RESULTS

Compared with the control subjects, only FX activity was significantly increased in patients with SCHyper (P < 0.01). Total cholesterol (TC) and low-density lipoprotein cholesterol (LDL-C) levels were significantly higher in patients with SHypo compared with the control group (P < 0.001 and P < 0.01, respectively). TC levels were significantly higher in patients with SCHyper than in controls (P < 0.05). No differences could be found in coagulation/fibrinolysis parameters between subclinical hypothyroid patients and control subjects. In patients with SCHyper, serum TSH level was positively correlated with FX activity (r: 0.58, P < 0.01) and inversely correlated with PAI-1 (r: -0.55. P < 0.05). Serum TG levels were inversely correlated with plasma activities of factors V, VII, VIII, IX, X and vWF (r: -0.83, P < 0.001; r: -0.68, P < 0.05; r: -0.61, P < 0.05; r: -0.77, P < 0.01; r: -0.63, P < 0.05; r: -0.60, P < 0.05, respectively). Serum TC levels were positively correlated with plasma fibrinogen levels (r: 0.72, P < 0.05). Serum HDL-C levels were positively correlated with protein S activity (r: 0.68, P < 0.05) and negatively correlated with F VII activity (r: -0.69, P < 0.05). Also, in patients with SHypo, serum TG levels were positively correlated with serum TSH levels (r: 0.42, P < 0.05), plasma activities of factors V, VII and X (r: 0.42, P < 0.05; r: 0.54, P < 0.01; r: 0.57, P < 0.01, respectively) and negatively correlated with plasma fibrinogen levels (r: -0.41, P < 0.05). Serum TC levels were positively correlated with factors V and X (r: 0.42, P < 0.05; r: 0.58, P < 0.01, respectively) and negatively correlated with t-PA Ag levels (r: -0.44, P < 0.05). Serum HDL-C levels were inversely correlated with F VII activity (r: -0.48, P < 0.05).

INTERPRETATION AND CONCLUSIONS

Some differences were found in the haemostatic parameters and lipid profile between the subclinical thyroid patients and healthy controls. Increased factor X activity in patients with subclinical hyperthyroidism represent a potential hypercoagulable state, which might augment the already existing risk for atheroscleroic complications. Also, subclinical hypothyroid patients exhibit a more atherogenic lipid profile compared with healthy individuals. Therefore, subclinical hypothyroidism is also associated with an increased risk of cardiovascular disease. However, thyroid hormones may play a role at different levels of the complex haemostatic system in subclinical thyroid disease.

Acute changes in clinical parameters and thyroid function peripheral markers following L-T4 withdrawal in patients totally thyroidectomized for thyroid cancer

After total thyroidectomy, differentiated thyroid cancer (DTC) patients have to undergo L-T4 withdrawal for measuring serum thyroglobulin and 131I whole-body scan (131I WBS) to evaluate residual/recurrent malignant disease. The aim of the present work was to study in these patients the effects of acute thyroid hormone deficiency on various target organs and tissues. Clinical parameters and thyroid function peripheral markers were evaluated in 20 DTC patients, both before and after L-T4 withdrawal. A 24-h urine collection, a fasting blood sample for laboratory examinations, a clinical score for hypothyroidism and cardiovascular, neurological and neuropsychological evaluations were carried out. After L-T4 withdrawal, the clinical score significantly increased, as well as total cholesterol, triglycerides, creatine kinase, lactate dehydrogenase, aspartate aminotransferase and alanine aminotransferase, whereas SHBG, osteocalcin and urine hydroxyproline levels significantly decreased. The acute thyroid hormone deficiency caused a systolic dysfunction of the left ventricle associated with an increase in systemic vascular resistance without cardiac contractility alterations. A significant increase in the left ventricular mass and thickness was also observed. Carpal tunnel syndrome appeared in 30% of patients and a significant reduction in the immediate auditive memorization and in attentive performance was also detected. These observations indicate that acute hypothyroidism causes significant clinical alterations of peripheral tissue function. In the follow-up of DTC patients, therefore, L-T4 withdrawal procedure should be restricted to cases where the cost/benefit ratio is favorable. Alternative procedures, such as the use of recombinant human TSH, should be used whenever possible.

Human low-density lipoprotein receptor gene and its regulation

The low-density lipoprotein (LDL) receptor is a transmembrane glycoprotein that mediates the binding and endocytosis of lipoproteins containing apolipoprotein B and E, especially the cholesterol-rich LDL. Mutations in the LDL receptor gene can produce dysfunctional LDL receptors and cause familial hypercholesterolemia. The expression of the LDL receptor gene is under an intriguing regulation by sterol and nonsterol mediators either at the transcriptional level or at the posttranscriptional level, both of which are linked to cell signaling pathways. Upregulation of liver LDL receptor expression is effective in treating hypercholesterolemia. In this review, we focus on the latest progress on the mechanisms and regulation of the LDL receptor gene expression.

Osteopontin gene expression in the aorta and the heart of propylthiouracil-induced hypothyroid mice

It is known that there is abnormal osteopontin (OPN) expression at the sites of atherosclerotic lesions. In the Apolipoprotein E gene knockout (ApoE-KO) mouse, a model of the atherosclerotic process, altered cholesterol metabolism with associated increase in OPN expression is evident at 12-22 weeks in the aorta and at 22 weeks in the heart. In this study, we analyzed another animal model of hypothyroid mice created by ingestion of propylthiouracil (PTU). After 2 weeks of PTU ingestion, the animals had significant decreases in thyroid hormones (T3 and T4) and immediate increases in blood lipids/cholesterol. Hypothyroid mice showed 1.3-, 1.5-, 2-fold increases in blood levels of total cholesterol, triglycerides, and low density lipoprotein-cholesterol respectively. Semi-quantitative RT-PCR analysis showed that hypothyroid mice had 1.4- to 2-fold increases of OPN mRNA expression in the aorta and 1.5-fold increases in the heart. Hypothyroid animals treated with T3 (5 microg/day for 6 days) or statin (0.2 mg/30 g for 2 weeks) reduce blood lipids and aortic OPN mRNA expression. Data obtained with ELISA analyses showed 1.5- and 1.7-fold increases in OPN protein in the aorta (10 weeks) and the heart (22 weeks), respectively. This increase is close to the mRNA expression in both tissues of hypothyroid mice. In addition, western blots showed several variants of OPN protein expressed in the aorta and the heart. The decrease in the 70 kDa OPN is accompanied by an increase in 45 kDa OPN in the aorta of hypothyroid mice. In contrast, only 45 kDa OPN is found in the heart of control and hypothyroid mice. These data indicate that the increase of OPN mRNA and protein expression occurs in cardiovascular tissues of hypothyroid mice.

Elevation of serum adiponectin levels in Basedow disease

The present study was undertaken to determine whether thyroid hormone affects serum adiponectin levels in the patients with Basedow disease. Sixty-four patients with Basedow disease were examined; 32 patients had hyperthyroid state and 32 patients had euthyroid state who had been treated with antithyroid drugs. In addition, 30 age- and sex-matched subjects served as a control. Serum adiponectin, free T4, free T3, thyroid-stimulating hormone, and thyroid-stimulating hormone receptor antibody (TRAb) were measured. Serum adiponectin levels were 12.9+/-1.6 microg/mL in the hyperthyroid state, a value significantly greater than that of 8.2 +/- 0.5 microg/mL in the euthyroid state (P<.05) and that of 8.6+/-0.7 microg/mL in the control subjects (P<.05). Serum adiponectin levels had positive correlations with either of serum free T4 (r=0.453, P<.001), free T3 (r=0.47, P< .001), or TRAb (r= 0.491, P<.001), but not with body mass index. Multiple regression analysis showed TRAb had the strongest contribution to serum adiponectin concentration in the patients with Basedow disease. The present findings indicate that hyper-adiponectinemia is closely associated with increases in serum thyroid hormone levels and TRAb in Basedow disease.

Thyroid diseases and cerebrovascular disease

BACKGROUND AND PURPOSE

Acute cerebral ischemia has been described in different diseases of the thyroid gland, and not only as a result of thyrotoxic atrial fibrillation and cardioembolic stroke. The purpose of this review is to summarize the studies on the relationship between thyroid diseases and cerebrovascular diseases, discussing the main findings for overt hyperthyroidism and hypothyroidism, as well as for subclinical thyroid dysfunction.

SUMMARY OF REVIEW

In overt hyperthyroidism, cardioembolic stroke is clearly associated to thyrotoxic atrial fibrillation, and in subclinical hyperthyroidism with serum thyroid-stimulating hormone levels <0.1 mU/L, the incidence of atrial fibrillation is increased. Although in vitro and in vivo studies indicate a hypercoagulability state in hyperthyroidism, there is insufficient evidence to prove that this state leads to an increased risk of cardiac emboli. However, the hypothesis that overt hyperthyroidism may cause acute cerebral venous thrombosis is intriguing. Possible associations between hyperthyroidism and Moyamoya or Giant cell arteritis have only been described in case reports. There is enough evidence that overt hypothyroidism is associated with several traditional and newer atherosclerotic risk factors, especially hypertension, hyperlipidemia, and hyperhomocysteinemia. For subclinical hypothyroidism, these associations are less certain. Hypothyroidism has been associated with signs of aortic or coronary atherosclerosis, but no case-control or cohort studies have ever investigated hypothyroidism as a possible risk factor for atherothrombotic stroke.

CONCLUSIONS

Hyperthyroidism is associated with atrial fibrillation and cardioembolic stroke. Hypothyroidism is associated with a worse cardiovascular risk factor profile and leads to progression of atherosclerosis. Associations between hyperthyroidism and acute cerebral venous thrombosis, Moyamoya, and Giant cell arteritis have been suggested, but sound evidence is lacking. Additional studies are needed to clarify these issues.

Transcriptional regulatory networks in lipid metabolism control ABCA1 expression

The ATP-binding cassette transporters, ABCA1 and ABCG1, are major players in mediating cellular efflux of phospholipids and cholesterol to apoA-I containing lipoproteins including prebeta-HDL and alphaHDL and thereby exert important antiatherogenic properties. Although the exact mechanisms how ABC transporters mediate lipid transport are not completely resolved, recent evidence from several laboratories including ours suggests that vesicular transport processes involving different interactive proteins like beta2-syntrophin, alpha1-syntrophin, Lin7, and cdc42 are critically involved in cellular lipid homeostasis controlled by ABCA1 and ABCG1. Besides sterols and fatty acids as known physiological modulators of the LXR/RXR and SREBP pathways, a growing list of natural and synthetic substances and metabolic regulators such as retinoids, PPAR-ligands, hormones, cytokines, and drugs are particularly effective in modulating ABCA1 and ABCG1 gene expression. Although ABCA1 protein amounts are regulated at the level of stability, the majority of potent activating and repressing mechanisms on ABCA1 function directly act on the ABCA1 gene promoter. Among the inducing factors, liver-X-receptors (LXR), retinoic acid receptors (RAR) and peroxisome proliferator-activated receptors (PPARs) along with their coactivators provide an amplification loop for ABCA1 and ABCG1 expression. The ABCA1 promoter is further stimulated by the ubiquitous factor Sp1 and the hypoxia-induced factor 1 (HIF1), which bind to GC-boxes and the E-box, respectively. Shutdown of ABCA1 expression in the absence of sterols or in certain tissues is mediated by corepressor complexes involving unliganded LXR, sterol-regulatory element binding protein 2 (SREBP2), Sp3, and the SCAN-domain protein ZNF202, which also impacts nuclear receptor signaling. Thus, a highly sophisticated transcriptional network controls the balanced expression of ABCA1.

Thyroid disease and increased cardiovascular risk

The effects of thyroid dysfunction are thought to be reversible on restoration of euthyroidism, but postmortem and epidemiologic data suggest that subclinical or treated thyroid disease is associated with increased vascular risk. In order to determine the extent of this risk, and to explore whether the nature and/or treatment of thyroid disease are critical in this relationship, we used medical record linkage to match patients with treated thyroid disease of various etiologies with routinely collected national inpatient and daycase hospital discharge records and death records, and assessed the number of hospitalizations from cardiovascular or cerebrovascular disease or death in patients with thyroid disease and control patients. Patients treated for Graves' disease had more hospitalizations from cardiovascular disease than controls (relative risk, 1.42; 95% confidence interval, 1.20 to 1.67; p < 0.001). Toxic multinodular goiter was also associated with significantly higher rates of cardiovascular disease (relative risk, 1.50; 95% confidence interval, 1.11 to 2.02; p = 0.008). Patients with Hashimoto's thyroiditis aged over 50 years had a threefold increase in cardiovascular admissions compared to controls (23.5% and 6.5%, respectively; 95% confidence interval for difference, 6.0% to 27.9%; p = 0.003). Thus, different forms of thyroid disease were associated with increased long-term vascular risk despite restoration of euthyroidism. The mechanisms that mediate this risk are unclear but may not involve thyroid hormone abnormality.