Effects of Short-Term Hypothyroidism on the Lipid Transfer to High-Density Lipoprotein and Other Parameters Related to Lipoprotein Metabolism in Patients Submitted to Thyroidectomy for Thyroid Cancer

Abstract

Background:

Elevation of low-density lipoprotein (LDL) cholesterol is the hallmark of the dyslipidemia observed in hypothyroidism, but alterations on high-density lipoprotein (HDL) plasma levels and metabolism are less understood. The aim of this study was to explore aspects of HDL metabolism and enzymes that act on HDL after a short period of overt hypothyroidism.

Methods:

Eighteen women (age 44 ± 11 years; body mass index 27.9 ± 5.2 kg/m²) were studied before total thyroidectomy for thyroid cancer, when they were euthyroid, and after thyroidectomy, in overt hypothyroidism for three weeks, following levothyroxine withdrawal for performance of a whole-body scan.

Results:

Thyrotropin and free thyroxine confirmed hypothyroidism; low thyroglobulin and radioiodine uptake indicated near absence of thyroid tissue. LDL cholesterol (125 ± 35 vs. 167 ± 40 mg/dL; p = 0.0002), HDL cholesterol (HDL-C; 39 ± 8 vs. 46 ± 10 mg/dL; p = 0.0025), non-HDL-C (149 ± 38 vs. 201 ± 46 mg/dL; p < 0.0001), unesterified cholesterol (53 ± 10 vs. 70 ± 16 mg/dL; p = 0.0003), apolipoprotein (apo) A-I (1.32 ± 0.19 vs. 1.44 ± 0.22 g/L; p < 0.04), and apo B (0.97 ± 0.25 vs. 1.31 ± 0.28 g/L; p < 0.0001) plasma concentrations were all higher in hypothyroidism compared to values in the euthyroid state, but triglycerides and Lp(a) were unchanged. There were no changes in HDL particle size and lipid composition, cholesteryl ester transfer protein and lecithin cholesterol acyltransferase concentrations and in paraoxonase-1 activity. Regarding the in vitro assay to estimate lipid transfer to HDL, there were no changes when comparing the euthyroid to the hypothyroid state, but when adjusted for HDL-C, the unesterified cholesterol (0.14 ± 0.03 vs. 0.11 ± 0.02; p < 0.0001), triglycerides (0.11 ± 0.02 vs. 0.09 ± 0.02; p < 0.0001), phospholipids (0.44 ± 0.09 vs. 0.40 ± 0.07; p = 0.0205), and esterified cholesterol (0.14 ± 0.03 vs. 0.13 ± 0.03; p = 0.0043) transfer to HDL were all diminished in hypothyroidism.

Conclusions:

In short-term hypothyroidism, HDL-C increased, but this did not increase the capacity of the HDL fraction to receive lipids or the activity of paraoxonase-1, the anti-oxidation enzyme associated to HDL.

Introduction

Hypothyroidism predisposes patients to atherosclerosis (1), and this relation is, among other factors, linked to the lipoprotein disturbances consequent to thyroid hormone deficiency. Low-density lipoprotein cholesterol (LDL-C), an important risk factor for atherosclerotic cardiovascular disease, is increased in overt hypothyroidism, but high-density lipoprotein cholesterol (HDL-C) levels, which are protective against the complications of atherosclerosis, have been reported as either normal or increased (2). HDL metabolism is complex, and it has been recognized that HDL-C alone is not sufficient to characterize all aspects of HDL-associated atheroprotection, such as cholesterol esterification and reverse cholesterol transport, anti-oxidative actions, nitric oxide release, and vasodilation, as well as anti-inflammatory effects (3).

Plasma lipoproteins continuously exchange lipids, such as unesterified and esterified cholesterol, triglycerides, and phospholipids, a process mediated by the lipid transfer proteins cholesteryl ester transfer protein (CETP) and phospholipid transfer protein (PLTP) (4). CETP activity has been described as either decreased (5 –7) or normal (8) in hypothyroidism, but the action of the transfer proteins, which predominantly affect HDL metabolism, is only part of this process. Lipid transfer also depends on the composition and concentration of the lipoprotein classes and the activity of enzymes that regulate plasma lipid metabolism, such as lecithin cholesterol acyltransferase (LCAT). LCAT catalyzes the esterification of cholesterol using apolipoprotein (apo) A-I, the main HDL apolipoprotein, as a cofactor (3).

The first practical in vitro assay to evaluate lipid transfer simultaneously in whole plasma was developed and validated in the authors' laboratory using an artificially made nanoparticle as the lipid donor (3). It was found that the transfer of unesterified and esterified cholesterol to HDL are diminished in patients with coronary artery disease (9,10). It was also shown that in women with subclinical hypothyroidism, the transfer of triglycerides and of phospholipids to HDL is decreased. Defective transfer was found to be reversed by levothyroxine (LT4) treatment and achievement of euthyroidism (11).

HDL status in thyroid dysfunction is of chief importance for the understanding of the thyroid-related dyslipidemia and the mechanisms through which thyroid dysfunction predisposes to atherosclerosis. Thus, the aim of this study was to examine the effects of the near absence of thyroid hormones on the lipid transfer to HDL. The plasma lipid and apolipoprotein profile and other important parameters of plasma lipid metabolism, such as CETP and LCAT concentration and the activity of PON-1, an antioxidant enzyme associated with the HDL plasma fraction, were also determined. To circumvent the interference of factors not related with thyroid hormone action, such as the existence of thyroid inflammation, this study was performed in women with non-metastatic thyroid cancer submitted to total thyroidectomy, when thyroid tissue is absent or nearly absent and autoimmune processes such as that of Hashimoto's thyroiditis are not at play. The results obtained after three weeks of hypothyroidism were compared to those prior to thyroidectomy when the subjects were euthyroid.

Methods

Patients

Eighteen women diagnosed with differentiated thyroid cancer (aged 19–63 years; 44 ± 11 years) who were admitted to the nursery of the Cancer Institute of São Paulo State Hospital for thyroidectomy were enrolled. Three patients were smokers. All the procedures in this study were in accordance with the guidelines of the Declaration of Helsinki on human experimentation. The study protocol was approved by the Ethical Committee of the Medical Hospital of the University of São Paulo, and written informed consent was obtained from all participants.

Exclusion criteria included pregnancy, thyroid dysfunction, dyslipidemia, anemia, renal failure, alcoholism, and use of lipid-lowering medications, thyroid hormone, or antithyroid drugs. Patients denied a history of liver disease, chronic pancreatitis, systemic lupus erythematosus, or other systemic disease. Patients with possible metastasis detected on the whole-body scan routinely performed after thyroidectomy were excluded.

Blood was collected twice for biochemical analysis from all participants. The first blood sample was drawn when they were euthyroid, just before they entered the surgery room to undergo thyroidectomy. After thyroidectomy, patients were submitted to hormone replacement therapy with LT4 that was interrupted for the routine performance of whole-body scanning. The second blood sample was taken when they were in the hypothyroid state three weeks after LT4 therapy cessation.

Blood was collected when patients had been fasting for at least 12 hours. In both the euthyroid and hypothyroid states, thyrotropin (TSH), free thyroxine (fT4), paraoxonase-1 (PON-1) activity, HDL size, CETP, LCAT, total cholesterol, LDL-C, non-HDL-C, HDL-C, triglycerides, apo A-I, apoB, Lp(a), and unesterified cholesterol were measured. The in vitro lipid transfer to HDL and the percentage lipid composition of the HDL fraction were also characterized. Determination of thyroglobulin and antithyroglobulin antibodies was performed in samples of the patients in the hypothyroid state only.

Serum biochemical determinations

Blood samples were collected after a 12-hour fast. Commercial enzymatic methods were used to determine total cholesterol (Boehringer-Mannheim, Penzberg, Germany), free cholesterol (Wako, Osaka, Japan), and triglycerides (Abbott, North Chicago, IL). HDL-C was measured by the same method used for total cholesterol after lipoprotein precipitation with magnesium phosphotungstate. LDL-C was calculated by the Friedewald equation (12), and non-HDL-C was determined by the equation: total cholesterol – HDL-C. Apolipoprotein (apo) A-I and apo B were measured by rate nephelometry on an Image Immunochemistry System (Beckman Coulter, Brea, CA). Serum TSH and fT4 were assayed by fluoroimmunoassay (AutoDELFIA equipment, AutoDELFIA Ultrakit, Wallac Oy) 4.4% and 3.4% for fT4, respectively.

Determination of CETP and LCAT concentration

The quantitative determination of CETP and LCAT in serum was determined by the enzyme-linked immunosorbent assay (ALPCO Diagnostics, Salem, MA).

Determination of PON-1 activity

PON-1 activity was measured by adding serum to 1 M Tris-HCl buffer (100 mmol/L, pH 8.0) containing 2 mmol/L CaCl₂ and 5.5 mmol/L paraoxon (Sigma Chemical Company, Seelze, Germany). The generation of p-nitrophenol was measured at 405 nm at 37°C in a plate reader (Victor™ X3; PerkinElmer, Singapore) (13).

HDL particle size and assay of lipid transfer to HDL

The diameters of HDL particles were determined by Zetasizer nano ZS90 (Malvern Panalytical, Malvern, United Kingdom) as described elsewhere (14). The in vitro assay of the simultaneous transfer of radioactively labeled phospholipids, triglycerides, and unesterified and esterified cholesterol from an artificial nanoparticle to the HDL plasma fraction was performed, as described by Lo Prete et al. (15). In brief, the donor lipidic nanoparticle containing the labeled lipids was incubated for one hour with whole plasma. After chemical precipitation of the nanoparticle and the apo B-containing lipoprotein fractions, the supernatant containing the HDL fraction was counted for radioactivity in a scintillation solution, and the percentage radioactivity of each lipid that transferred from the nanoparticle to HDL was then estimated.

Lipid composition of the HDL fraction

The HDL fraction was obtained from the whole plasma after precipitation of the apo B-containing lipoproteins with magnesium phosphotungstate. Triglyceride (Labtest, Minas Gerais, Brazil), unesterified cholesterol, and phospholipid (Wako, Richmond, VA) were determined by using commercial kits. Esterified cholesterol was calculated as the difference between total and unesterified cholesterol of the HDL multiplied by 1.67 to adjust for the molecular weight of esterified cholesterol (16).

Statistical analysis

Results are presented as means ± standard deviation. Data of euthyroid and hypothyroid states were compared using Student's paired t-test. GraphPad InStat Biostatistics v3.05 (GraphPad Software, Inc., San Diego, CA) was used for the analyses. In all analyses, parameters were considered significantly different when p < 0.05.

Results

As shown in Table 1, euthyroid and hypothyroid states were confirmed in all patients with TSH values (1.9 ± 1.3 vs. 72.1 ± 41.7 μIU/mL) and fT4 values (1.06 ± 0.18 vs. 0.06 ± 0.13 ng/dL). One of the patients had normal TSH levels in the hypothyroid state but undetectable levels of fT4, thus confirming hypothyroidism. This patient probably had a concomitant hypothalamic or pituitary disease.

Table 1.

Thyroid Parameters in Euthyroidism and Hypothyroidism in Women Submitted to Thyroidectomy (n = 18)

	Euthyroidism	Hypothyroidism	p-Value
TSH (μIU/mL)	1.9 ± 1.3	72.1 ± 41.7	<0.0001
fT4 (ng/dL)	1.06 ± 0.18	0.06 ± 0.13	<0.0001
Tg (ng/mL)		3.1 ± 5.02
Anti-Tg (IU/mL)		<4 (14 subjects)
		>4 (4 subjects)
Uptake (%)^a		1.68 ± 2.24
WBS		NM

Data are expressed as means ± standard deviation.

Performed in 16 subjects.

TSH, thyrotropin; fT4, free thyroxine; Tg, thyroglobulin; WBS, whole-body scan; NM, no metastases.

The radioiodine uptake in the hypothyroid state was very low, which suggests little remaining thyroid tissue (Table 1), and in all patients, the whole-body scan detected no metastatic sites. A lack of appreciable amounts of remaining thyroid tissue or metastatic sites was confirmed by the very low serum thyroglobulin levels. Antithyroglobulin antibodies were present in only four subjects, which may have made thyroglobulin determinations inaccurate.

As shown in Table 2, in overt hypothyroidism, baseline serum levels of total cholesterol, LDL-C, non-HDL-C, HDL-C, unesterified cholesterol, apo A1, and apo B were elevated. Plasma levels of Lp(a) and triglycerides tended to rise in overt hypothyroidism, but the differences did not achieve statistical significance (p = 0.055 and p = 0.061, respectively). Table 2 also shows that the serum concentration of CETP and LCAT and the activity of PON-1 were equal in euthyroidism and overt hypothyroidism. The size of the HDL particles was also similar in the two conditions.

Table 2.

Lipid Metabolism Parameters in Euthyroidism and Hypothyroidism in Women Submitted to Thyroidectomy (n = 18)

	Euthyroidism	Hypothyroidism	p-Value
Cholesterol (mg/dL)
Total	187 ± 39	247 ± 45	<0.0001
LDL-C	125 ± 35	167 ± 40	0.0002
HDL-C	39 ± 8	46 ± 10	0.003
Non-HDL-C	149 ± 38	201 ± 46	<0.0001
Unesterified cholesterol	53 ± 10	70 ± 16	0.0003
Lp(a) (mg/dL)	46 ± 41	53 ± 48	0.055
Triglycerides (mg/dL)	120 ± 46	180 ± 140	0.061
Apolipoprotein (g/L)
ApoA-I	1.32 ± 0.19	1.44 ± 0.22	0.045
ApoB	0.97 ± 0.25	1.31 ± 0.28	<0.0001
CETP (ug/mL)	2.7 ± 1.2	2.6 ± 1.1	0.696
LCAT(ug/mL)	8.3 ± 1.9	8.8 ± 1.9	0.188
PON-1 (nmol/(min/mL)	113 ± 62	134 ± 78	0.171
HDL diameter (nm)	8.6 ± 0.6	8.5 ± 0.6	0.516

Data are expressed as means ± SD.

LDL-C, low-density lipoprotein cholesterol; HDL-C, high-density lipoprotein cholesterol; CETP, cholesterol ester transfer protein; LCAT, lecithin-cholesterol acyltransferase; PON-1, paraoxonase-1.

Table 3 shows the percentage of transfer of the four radioactively labeled lipids from the artificial donor nanoparticle to the HDL fraction after one hour of incubation of the nanoemulsion with whole plasma. The transfer of unesterified cholesterol and phospholipids tended to be lower in overt hypothyroidism than in euthyroidism, but this did not achieve statistical significance (p = 0.095 and p = 0.057, respectively). Transfer of esterified cholesterol and triglycerides did not change from the euthyroid to the hypothyroid state. However, when lipid transfer data were adjusted for HDL-C values (Table 4), the transfer of all four lipids was significantly lower in overt hypothyroidism compared to the euthyroid state.

Table 3.

Lipid Transfers (%) in Euthyroidism and Hypothyroidism in Women Submitted to Thyroidectomy (n = 18)

Lipid transfer (%)	Euthyroidism	Hypothyroidism	p-Value
Esterified cholesterol	5.5 ± 1.0	5.7 ± 0.7	0.365
Unesterified cholesterol	5.4 ± 1.6	4.9 ± 1.0	0.095
Phospholipids	16.6 ± 1.5	17.4 ± 1.0	0.057
Triglycerides	4.2 ± 1.0	3.9 ± 0.6	0.125

Data are expressed as means ± standard deviation.

Table 4.

Lipid Transfers Adjusted by HDL-C (%/mg/dL) in Euthyroidism and Hypothyroidism in Women Submitted to Thyroidectomy (n = 18)

	Euthyroidism	Hypothyroidism	p-Value
Esterified cholesterol	0.14 ± 0.03	0.13 ± 0.03	0.0043
Unesterified cholesterol	0.14 ± 0.03	0.11 ± 0.02	<0.0001
Phospholípids	0.44 ± 0.09	0.40 ± 0.07	0.0205
Triglycerides	0.11 ± 0.02	0.09 ± 0.02	<0.0001

Data are expressed as means ± standard deviation.

As shown in Table 5, the lipid composition of the HDL plasma fraction was equal in the euthyroid and in the hypothyroid state.

Table 5.

Lipid Composition of HDL (%) in Euthyroidism and Hypothyroidism in Women Submitted to Thyroidectomy (n = 18)

	Euthyroidism	Hypothyroidism	p-Value
Esterified cholesterol	33 ± 3	32 ± 4	0.321
Unesterified cholesterol	5 ± 1	5 ± 1	0.789
Phospholipids	51 ± 2	51 ± 2	0.835
Triglycerides	11 ± 3	12 ± 3	0.312

Data are expressed as mean ± standard deviation.

Discussion

In this study, overt hypothyroidism three weeks after the withdrawal of LT4 was confirmed by documenting an elevated TSH and very low fT4 concentrations. This short-term LT4 withdrawal was sufficient to result in the classical increase in LDL-C and apo B associated with hypothyroidism, as well as in an increase in non-HDL-C. There was a nonsignificant increasing trend (p = 0.061) for plasma triglycerides. In this respect, previous studies on hypothyroid patients have documented normal to elevated triglyceride levels, as reviewed by Duntas (17) and Pearce (18). The concentration of the pro-atherogenic Lp(a) has been reported as normal (19) or elevated in hypothyroid patients (20). In this study, the patients showed a trend toward an increase in Lp(a) in the hypothyroid state that was, however, not statistically significant (p = 0.055). With regard to HDL, there was an 18% increase in HDL-C and a 9% increase in apo A-I, the main apolipoprotein of the HDL fraction, from the euthyroid to the hypothyroid state. In previous studies, HDL-C was reported to be normal, increased, or decreased in overt hypothyroidism (21 –24).

As TSH was elevated in hypothyroid patients, a possible direct effect of a high TSH on plasma lipids might be a possible explanation. However, this does not seem to be the case, as illustrated in the study by Beukhof et al. (25) who administered recombinant human TSH (rhTSH) to 82 patients on LT4 after thyroidectomy and radioiodine remnant ablation for thyroid cancer treatment. After rhTSH administration, there was an increase in apo B, Lp(a), and triglycerides and a decrease in HDL-C that the authors attributed to a decrease in T3 plasma levels and not directly to the use of rhTSH.

The HDL-C increase that was observed in the study presented here can be ascribed to the reduction in hypothyroidism of the hepatic lipase activity, a phospholipase that accelerates HDL catabolism (26,27). Therefore, the overall changes in the plasma lipoproteins from the euthyroid to the hypothyroid state observed here are in accordance with previous reports of the literature on overt hypothyroidism (17).

HDL metabolism is prone to profound changes in the presence of chronic inflammatory processes. Apo A-I synthesis is decreased, and among other metabolic events, the high levels in the plasma of acute-phase reactant serum amyloid A (SAA) results in the substitution of SAA for apo A-I in the HDL composition. This results in generation of dysfunctional HDL and loss of the athero-protective functions (28). Thus, due to autoimmunity and chronic inflammation existing in many hypothyroid states, changes in HDL composition and metabolism could not be exclusively ascribed solely to the hormonal deficiency but also to the concomitant inflammation. In the present study, because of the near-total removal of the thyroid tissue, the inflammatory component was not at play in the hypothyroid state. The presence of postsurgical thyroid cancer metastasis, with intrinsic effects on the plasma lipid metabolism, was also excluded by whole-body scan imaging and by the very low serum thyroglobulin levels.

Another factor potentially influencing the results could be the surgical procedure itself. However, as the blood determinations were performed around four months after thyroidectomy, it is unlikely that the metabolic effects of the surgery and the anesthesia could persist for such a long time. Therefore, it is reasonable to assume that the current results are predominantly explained by thyroid hormone deficiency.

In this study, the hypothyroid state had no impact on the LCAT serum concentration, the activity of PON-1, or the concentration of CETP. Regarding LCAT, to the authors' knowledge, there are no previous reports in the literature on the status of this enzyme in human overt hypothyroidism to compare to the present results. In subclinical hypothyroidism, McGowan et al. (29) did not find changes in the activity of this enzyme in either the fasting or the post-prandial state. In experimental hypothyroidism induced in rats, Ridgway et al. (30) found low LCAT activity, which was confirmed by Franco et al. (24). Lowering of LCAT was ascribed to decreased hepatic secretion of the enzyme (31).

Consistent with the present results, Coria et al. (32) did not observe an effect of overt hypothyroidism on PON-1 activity, but in two other studies, decreased PON-1 was found in this condition (33,34). Blatter et al. (35) postulated that PON-1 activity increases when apoA-I concentration increases, thus linking the enzyme activity to the HDL particle number. Clearly, this was not confirmed by the present results, since apo A-I and HDL-C increased in hypothyroidism without an increase in PON-1 activity. It has been reported that PON-1 activity may vary due to differences in HDL-C composition (35), a finding that could not be confirmed in hypothyroid subjects in the current study.

It was found that the CETP concentration in the plasma was unchanged in the hypothyroid compared to the euthyroid state, confirming the findings by Ritter et al. (6). Dedecjus et al. (8) found a decreased CETP concentration in their hypothyroid patients. Skoczyńska et al. (36) reported a decreased activity of CETP and PLTP in their hypothyroid patients. In contrast to these studies, the current study did not determine CETP concentration but its activity.

The lipid composition of the HDL plasma fraction did not change from the euthyroid to the hypothyroid state. The composition is determined by the particle diameter, which is in agreement with the present finding that the diameter of the HDL particles did not change from the euthyroid to the hypothyroid state.

When the whole HDL fraction is considered, the shift from euthyroidism to hypothyroidism did not affect the transfer of esterified and unesterified cholesterol, phospholipids, and triglycerides from the donor nanoparticle to HDL. However, when the lipid transfer values are normalized for HDL-C, it transpires that the transfer of all lipids to HDL was diminished. Thus, it can be postulated that each HDL particle received fewer lipids from the donor nanoparticle, but the rise of HDL-C, that is, the increased number of HDL particles elicited by the hypothyroid state, compensated for this defect so that the lipid transfer to the whole HDL fraction became equal in the euthyroid and the hypothyroid periods. At any rate, in the in vitro assay for quantification of lipid transfer to HDL, a decrease in both unesterified and esterified cholesterol transfer was associated with the presence of coronary artery disease (9,10,37). It is worth pointing out that in patients with subclinical hypothyroidism, alterations in those lipid transfers that were corrected by treatment with LT4 have been previously documented (11).

An important aspect of the current results refers to the increase in the concentration of unesterified cholesterol in the plasma in the hypothyroid state. Esterification of cholesterol occurs mainly in the HDL fraction that contains most of the apo A-I and to which LCAT is mostly associated (38). Unesterified cholesterol from the other plasma lipoprotein fractions and from the peripheral cells is continuously being transferred to HDL where it is esterified, thereby being transferred back to the other lipoprotein classes. Alternatively, this newly esterified cholesterol remains in the HDL particles and is taken up by the liver and excreted in the bile (3). Thus, the increase in the unesterified cholesterol in the plasma might be partially accounted for in the defect in the transfer of this lipid to HDL particles, observed here when the transfer values were normalized by HDL-C. However, the bulk of this increase should be ascribed to the rise in LDL-C elicited by hypothyroidism. Most of the unesterified cholesterol is contained in the LDL fraction. Thus, the increase in LDL leads to an increase in plasma unesterified cholesterol.

In conclusion, the rise in the hypothyroid state of the HDL fraction, as indicated by the increase of both HDL-C and apo A-I, was not accompanied by an increase in the lipid transfer. There was excess unesterified cholesterol resulting from the LDL-C accumulation, but either LCAT concentration or the unesterified cholesterol transfer to HDL increased to match the greater amounts of this compound in the plasma. Thus, as far as could be observed, the raise in LDL-C in hypothyroidism was not attenuated by the HDL protective function, despite the increase in HDL-C. In patients submitted to short-term hypothyroidism, the elevated HDL-C levels may not be protective against the complications of atherosclerosis. This might be important in those with a previous history of cardiovascular disease.

Footnotes

Acknowledgments

The authors thank Dr. Marco Aurélio V. Kulcsar for his support in patient enrollment and Mrs. Josefa Maria da Hora Silva Lima for technical support. This study was supported by the Foundation for Research Support of the State of São Paulo (FAPESP, São Paulo, Brazil; grant number 2013/24197-8). R.C.M. is a Research Career Awardee from the National Council for Scientific and Technological Development (CNPq, Brasilia, Brazil).

Author Disclosure Statement

The authors declare that no competing financial interests exist.

References

Mason

, Hunt

, Hurxthal

. 1930. Blood cholesterol values in hyperthyroidism and hypothyroidism—their significance. N Engl J Med, 203:1273–1278.

Duntas

, Brenta

. 2012. The effect of thyroid disorders on lipid levels and metabolism. Med Clin North Am, 96:269–281.

Maranhão

, Freitas

. 2014. HDL metabolism and atheroprotection: predictive value of lipid transfers. Adv Clin Chem, 65:1–41.

Ginsberg

. 1998. Lipoprotein physiology. Endocrinol Metab Clin North Am, 27:503–519.

Tan

, Shiu

, Kung

. 1998. Plasma cholesteryl ester transfer protein activity in hyper- and hypothyroidism. J Clin Endocrinol Metab, 83:140–143.

Ritter

, Kannan

, Bagdade

. 1996. The effects of hypothyroidism and replacement therapy on cholesteryl ester transfer. J Clin Endocrinol Metab, 81:797–800.

Tan

, Shiu

, Kung

. 1998. Effect of thyroid dysfunction on high density lipoprotein subfraction metabolism: roles of hepatic lipase and cholesteryl ester transfer protein. J Clin Endocrinol Metab, 83:2921–2924.

Dedecjus

, Masson

, Gautier

, de Barros

, Gambert

, Lewinski

, Adamczewski

, Moulin

, Lagrost

. 2003. Low cholesteryl ester transfer protein (CETP) concentration but normal CETP activity in serum from patients with short-term hypothyroidism: lack of relationship to lipoprotein abnormalities. Clin Endocrinol (Oxf), 58:581–588.

Maranhão

, Freitas

, Strunz

, Santos

, Mansur

. 2012. Lipid transfers to HDL are predictors of precocious clinical coronary heart disease. Clin Chim Acta, 413:502–505.

10.

Sprandel

, Hueb

, Segre

, Ramires

, Kalil-Filho

, Maranhão

. 2015. Alterations in lipid transfers to HDL associated with the presence of coronary artery disease in patients with type 2 diabetes mellitus. Cardiovasc Diabetol, 14:107.

11.

Sigal

, Medeiros-Neto

, Vinagre

, Diament

, Maranhão

. 2011. Lipid metabolism in subclinical hypothyroidism: plasma kinetics of triglyceride-rich lipoproteins and lipid transfers to high-density lipoprotein before and after levothyroxine treatment. Thyroid, 21:347–353.

12.

Friedewald

, Levy

, Fredrickson

. 1972. Estimation of the concentration of low-density lipoprotein cholesterol in plasma, without use of the preparative ultracentrifuge. Clin Chem, 18:499–502.

13.

Mackness

, Harty

, Bhatnagar

, Winocour

, Arrol

, Ishola

, Durrington

. 1991. Serum paraoxonase activity in familial hypercholesterolaemia and insulin-dependent diabetes mellitus. Atherosclerosis, 86:193–199.

14.

Lima

, Maranhão

. 2004. Rapid, simple laser-light scattering method for HDL particle sizing in whole plasma. Clin Chem, 50:1086–1088.

15.

Lo Prete

, Dina

, Azevedo

, Puk

, Lopes

, Hueb

, Maranhão

. 2009. In vitro simultaneous transfer of lipids to HDL in coronary artery disease and in statin treatment. Lipids, 44:917–924.

16.

Bragdon

, Eder

, Gould

, Havel

. 1956. Lipid nomenclature; recommendations regarding the reporting of serum lipids and lipoproteins made by the Committee on Lipid and Lipoprotein Nomenclature of the American Society for the Study of Arteriosclerosis. Circ Res, 4:129.

17.

Duntas

. 2002. Thyroid disease and lipids. Thyroid, 12:287–293.

18.

Pearce

. 2012. Update in lipid alterations in subclinical hypothyroidism. J Clin Endocrinol Metab, 97:326–333.

19.

Klausen

, Nielsen F

, Hegedus

, Gerdes

, Charles

, Faergeman

. 1992. Treatment of hypothyroidism reduces low-density lipoproteins but not lipoprotein(a). Metabolism, 41:911–914.

20.

Tzotzas

, Krassas

G E

, Konstantinidis

, Bougoulia

. 2000. Changes in lipoprotein(a) levels in overt and subclinical hypothyroidism before and during treatment. Thyroid, 10:803–808.

21.

Lithell

, Boberg

, Hellsing

, Ljunghall

, Lundqvist

, Vessby

, Wide

. 1981. Serum lipoprotein and apolipoprotein concentrations and tissue lipoprotein-lipase activity in overt and subclinical hypothyroidism: the effect of substitution therapy. Eur J Clin Invest, 11:3–10.

22.

Aviram

, Luboshitzky

, Brook

. 1982. Lipid and lipoprotein pattern in thyroid dysfunction and the effect of therapy. Clin Biochem, 15:62–66.

23.

Agdeppa

, Macaron

, Mallik

, Schnuda

. 1979. Plasma high density lipoprotein cholesterol in thyroid disease. J Clin Endocrinol Metab, 49:726–729.

24.

Franco

, Chávez

, Pérez-Méndez

. 2011. Pleiotropic effects of thyroid hormones: learning from hypothyroidism. J Thyroid Res, 2011:1–17.

25.

Beukhof

, Massolt

, Visser

, Korevaar

TIM

, Medici

, de Herder

, Roeters van Lennep

, Mulder

, de Rijke

, Reiners

, Verburg

, Peeters

. 2018. Effects of thyrotropin on peripheral thyroid hormone metabolism and serum lipids. Thyroid, 28:168–174.

26.

Brenta

, Berg

, Miksztowicz

, Lopez

, Lucero

, Faingold

, Murakami

, Machima

, Nakajima

, Schreier

. 2016. Atherogenic lipoproteins in subclinical hypothyroidism and their relationship with hepaticlipase activity: response to replacement treatment with levothyroxine. Thyroid, 26:365–372.

27.

Kobayashi

, Miyashita

, Nakajima

, Mabuchi

. 2015. Hepatic lipase: a comprehensive view of its role on plasma lipid and lipoprotein metabolism. J Atheroscler Thromb, 22:1001–1011.

28.

Rosenson

, Brewer

Jr , Ansell

, Barter

, Chapman

, Heinecke

, Kontush

, Tall

, Webb

. 2016. Dysfunctional HDL and atherosclerotic cardiovascular disease. Nat Rev Cardiol, 13:48–60.

29.

McGowan

, Widdowson

, O'Regan

, Young

, Boran

, McEneny

, Gibney

. 2016. Postprandial studies uncover differing effects on HDL particles of overt and subclinical hypothyroidism. Thyroid, 26:356–364.

30.

Franco

, Castro

, Romero

, Regalado

, Medina

, Huesca-Gómez

, Ramírez

, Montaño

, Posadas-Romero

, Pérez-Méndez

. 2003. Decreased activity of lecithin:cholesterol acyltransferase and hepatic lipase in chronic hypothyroid rats: implications for reverse cholesterol transport. Mol Cell Biochem, 246:51–56.

31.

Ridgway

, Dolphin

. 1985. Serum activity and hepatic secretion of lecithin:cholesterol acyltransferase in experimental hypothyroidism and hypercholesterolemia. J Lipid Res, 26:1300–1313.

32.

Coria

, Pastrán

, Gimenez

. 2009. Serum oxidative stress parameters of women with hypothyroidism. Acta Biomed, 80:135–139.

33.

Singh

, Dey Sarkar

. 2014. Serum lipids, tHcy, hs-CRP, MDA and PON-1 levels in SCH and overt hypothyroidism: effect of treatment. Acta Biomed, 85:127–134.

34.

Jung

, Ahn

, Han

, Park

, Cho

, Moon

. 2017. Association between thyroid function and lipid profiles, apolipoproteins, and high-density lipoprotein function. J Clin Lipidol, 11:1347–1353.

35.

Blatter Garin

, Abbott

, Messmer

, Mackness

, Durrington

, Pometta

, James

. 1994. Quantification of human serum paraoxonase by enzyme-linked immunoassay: population differences in protein concentrations. Biochem J, 304:549–554.

36.

Skoczyńska

, Wojakowska

, Turczyn

, Zatońska

, Wołyniec

, Rogala

, Szuba

, Bednarek-Tupikowska

. 2016. Serum lipid transfer proteins in hypothyreotic patients are inversely correlated with thyroid-stimulating hormone (TSH) levels. Med Sci Monit, 22:4661–4669.

37.

Marmillot

, Patel

, Lakshman

. 2007. Reverse cholesterol transport is regulated by varying fatty acyl chain saturation and sphingomyelin content in reconstituted high-density lipoproteins. Metabolism, 56:251–259.

38.

Kontush

, Chapman

. 2006. Functionally defective high-density lipoprotein: a newtherapeutic target at the crossroads of dyslipidemia, inflammation, and atherosclerosis. Pharmacol Rev, 58:342–374.