The Journal of Clinical Endocrinology & Metabolism Vol. 83, No. 8 2921-2924
Copyright © 1998 by The Endocrine Society
Effect of Thyroid Dysfunction on High-Density Lipoprotein Subfraction Metabolism: Roles of Hepatic Lipase and Cholesteryl Ester Transfer Protein1
K. C. B. Tan,
S. W. M. Shiu and
A. W. C. Kung.
Department of Medicine, University of Hong Kong, Hong Kong
Address all correspondence and requests for reprints to: Kathryn C.B. Tan, Department of Medicine, Queen Mary Hospital, Pokfulam Road, Hong Kong.
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Abstract
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To investigate the effect of thyroid dysfunction on high-density
lipoprotein (HDL) metabolism, we measured HDL subfractions,
apolipoprotein A-I containing particles (LpA-I and LpA-I:A-II), and the
activities of enzymes involved in the remodeling and metabolism of HDL
[namely hepatic lipase (HL), lipoprotein lipase, and cholesteryl ester
transfer protein (CETP)] in 18 hyperthyroid and 17 hypothyroid
patients before and after treatment. HDL was subfractionated by density
gradient ultracentrifugation, and LpA-I was analyzed by
electroimmunodiffusion. The major changes were found in the
HDL2 subfraction and in LpA-I particles.
HDL2-C and LpA-I were reduced in hyperthyroidism
(P < 0.01, P < 0.05,
respectively) and increased in hypothyroidism (both
P < 0.05) compared with their respective euthyroid
matched controls. Changes in HDL2-cholesterol were reversed
after treatment in both hyper- and hypothyroid patients, and LpA-I also
decreased in the hypothyroid patients after treatment. HL
(P < 0.05) and CETP activities
(P < 0.05) were elevated in hyperthyroidism and
reduced in hypothyroidism (P < 0.05,
P < 0.01 respectively) and both were related to
free T4 levels. The changes in HDL2-C and LpA-I
correlated significantly with changes in HL after treatment but not
with CETP or lipoprotein lipase. In summary, HDL metabolism was altered
in thyroid dysfunction, and the effect of thyroid hormone on HDL was
mediated mainly via its effect on HL activity.
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Introduction
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THE EFFECT of thyroid dysfunction on
low-density lipoprotein (LDL) metabolism is well described in the
literature. Thyroid hormone has been shown to modulate LDL receptor
activity, thus leading to changes in plasma LDL levels, which are
reversible on treatment of the underlying thyroid disorder. However,
the effect of thyroid dysfunction on high-density lipoprotein (HDL)
metabolism is less well understood. HDL cholesterol has been reported
to be normal (1) or decreased (2, 3) in hyperthyroidism, whereas in
hypothyroidism, HDL has been reported to be increased (3, 4, 5), normal
(6), or even decreased (7). Apolipoprotein (apo) A-I level tends to
mirror the changes in HDL cholesterol. Limited information is available
on the effects of thyroid dysfunction on the distribution of HDL
subfractions and their metabolism. There is only one published study
that examined HDL subfractions in hyperthyroidism. Muls et
al. (2) reported that the concentration of HDL2b is
decreased in hyperthyroid patients. In hypothyroidism, several studies
have examined the effect of T4 replacement therapy on HDL
subfractions (4, 6, 8, 9). HDL2 decreased after treatment,
and the changes in HDL subfractions are thought to be mediated by the
effect of thyroid hormone on hepatic lipase (HL) (8).
We have recently shown that plasma cholesteryl ester transfer protein
(CETP) is increased in patients with hyperthyroidism and reduced in
those with hypothyroidism compared with their respective matched
euthyroid controls (10). CETP is a hydrophobic glycoprotein that
mediates the transfer of neutral lipids between lipoproteins and plays
an important role in the metabolism of HDL and apo A-I and in the
reverse cholesterol transport pathway (11). The aim of the present
study was to investigate the relative roles of CETP and HL in the
metabolism of HDL subfractions in patients with thyroid dysfunction. We
had documented HDL subfractions and apo A-I-containing particles (LpA-I
and LpA-I:A-II) in the cohort of patients described in our previous
study (10), and determined whether the changes in HDL subfractions were
related to changes in the activities of plasma lipolytic enzymes and/or
CETP.
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Patients and Methods
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Patients with thyroid dysfunction were recruited from the
Thyroid Clinic of the University of Hong Kong. Eighteen female patients
with active Graves’ disease and 17 patients (3 males and 14 females)
with newly diagnosed hypothyroidism were recruited. The patients’
clinical characteristics were described previously (10). Each patient
was matched with a euthyroid control of similar age, sex, and body mass
index (BMI). All subjects had fasting blood samples taken for the
measurement of lipids, HDL subfractions, apolipoproteins, CETP, free
T4 (FT4), and TSH. A second fasting blood
sample was taken 15 min after 100 U/kg heparin was administered iv for
the measurement of HL and lipoprotein lipase (LPL) activities. The
hyperthyroid patients were started on antithyroid drug, and
T4 replacement was started in the hypothyroid patients. All
parameters were measured again in the both groups of patients after
3–4 months of treatment when they had been rendered euthyroid. All
subjects gave their informed consent, and the protocol was approved by
the Ethics Committee of the University of Hong Kong.
Methods for measuring plasma lipids and thyroid function were described
previously (10). The normal range of FT4 was 10–19 pmol/L,
and of TSH was 0.35–5.5 mIU/L. Serum apo A-I and apo B were measured
by rate nephelometry using the Beckman Array System (Beckman
Instruments, Palo Alto, CA). LpA-I was analyzed by
electroimmunodiffusion using commercially available kits (Sebia,
Issy les Moulineaus, France). The concentration of LpA-I:A-II was
determined by the difference between total serum apo A-I and LpA-I
concentrations.
HDL subfractions were isolated by density gradient ultracentrifugation
as described by Kelley and Kruski (12) with minor modifications to the
density gradient to improve the separation of HDL subfractions.
Ultracentrifugation was carried out at 14 C, 38,000 rpm for 24 h
in a Beckman SW-40 rotor. The gradient containing the separated HDL
fractions was displaced upwards from the tube by infusing a dense,
hydrophobic material (Maxidens, 1.9 g/mL, Sigma, CA) under the
plasma layer by a constant infusion pump. The elute was passed through
a ultraviolet detector and continuously monitored at 280 nm, and
fractions were collected for analysis of cholesterol and protein.
Total lipolytic activity in postheparin plasma was measured using an
emulsion of triolein and gum arabic as substrate (13). HL activity was
determined as the activity of the salt-resistant lipase in the presence
of 1 M NaCl. LPL activity was obtained as the difference
between total postheparin plasma lipase activity and HL activity (14).
Plasma CETP activity was measured as previously described (10).
Data were tested for normality using the Wilk-Shapiro test.
FT4 level was logarithmically transformed before analyses
were made because of its skewed distribution. The longitudinal analysis
of each variable pre- and posttreatment in the patient groups was
evaluated by paired t test. Associations between different
parameters were determined by Pearson correlation coefficients. The
statistical package RS/1 (Bolt Beranek and Newman, Cambridge, MA) was
used for data analysis.
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Results
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The hyperthyroid patients and their controls were well matched for
age (27.9 ± 6.4 yr vs. 28.9 ± 4.8 yr,
respectively) and BMI (20.8 ± 3.1 kg/m2vs. 20.9 ± 2.1 kg/m2,
respectively). TSH was suppressed in all patients. The pretreatment
median FT4 level was 111.0 pmol/L (range 25.0–170.0) and
decreased to 12.0 pmol/L (range 9.0–18.0) after treatment. There was a
significant rise in BMI after treatment (pretreatment 20.8 ± 3.1
kg/m2 vs. after treatment 22.1 ± 3.5
kg/m2, P < 0.01). The fasting lipid
profiles and HDL subfractions of the hyperthyroid patients and their
matched controls are shown in Table 1
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HDL-cholesterol was lower in the hyperthyroid patients
(P < 0.01), and this was caused by a reduction in
HDL2-C (P < 0.01), because
HDL3-C was similar to the controls. LpA-I concentration was
also lower in the hyperthyroid patients (P < 0.05)
(Table 1). After treatment of hyperthyroidism, HDL2
increased (P < 0.001), whereas HDL3
decreased (P < 0.001). No marked changes were seen in
LpA-I or LpA-I:A-II levels. LPL activity was similar to the controls
but HL and CETP activities were both increased (P <
0.05). HL activity returned to normal (P < 0.001), but
no significant change was observed in CETP activity after 4 months of
treatment (Table 1).
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Table 1. Fasting lipid profiles, apolipoproteins, lipolytic
enzymes, and CETP in hyperthyroid patients and controls
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The age and BMI of the hypothyroid patients (39.9 ± 14.6 yr,
24.7 ± 4.9 kg/m2) were also similar to their controls
(40.4 ± 15.6 yr, 24.8 ± 4.5 kg/m2). The median
pretreatment TSH was 56.0 mIU/L (range 9.3–826.0), and FT4
was 7.0 pmol/L (range 1.3–9.0). After T4 replacement, TSH
was 1.9 mIU/L (0.5–16.0), FT4 was 14.0 pmol/L
(10.0–19.0), and BMI decreased (24.7 ± 4.9 kg/m2vs. 23.8 ± 4.9 kg/m2,
P < 0.05). Before treatment, there was a trend that
both HDL-C and apo A-I concentrations were higher in the hypothyroid
patients than the controls, but this did not reach statistical
significance. However, significant changes were seen in HDL
subfractions (Table 2). Hypothyroid
patients had higher HDL2-C (P < 0.05) and
lower HDL3-C than the controls (P < 0.05).
After T4 replacement, there was a reduction mainly in
HDL2-C (P < 0.01). Apo A-I also decreased
(P < 0.05), and the changes were seen in the LpA-I
particles, because the concentration of LpA-I:A-II particles remained
unchanged (Table 2). Plasma HL and CETP were lower than the controls
(P < 0.05 and P < 0.01, respectively)
and increased after treatment (P < 0.001 and
P < 0.01, respectively). No change was seen in LPL
activity.
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Table 2. Fasting lipid profiles, apolipoproteins, lipolytic
enzymes, and CETP in hypothyroid patients and controls
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Hyper- and hypothyroidism appeared to cause reciprocal changes in HL
and CETP activities, and baseline HL and CETP activities were both
related to log(FT4) when data from the hyper- and
hypothyroid patients were combined (HL: r = 0.55,
P < 0.001; CETP: r = 0.63, P <
0.001). To determine whether the changes in HDL subfractions and apo
A-I-containing particles were related to changes in lipase and CETP
activities, correlation analyses were performed. The changes in
HDL2-C (
HDL2-C) after treatment were related
to changes in HL (HL) (Fig. 1) and the
changes in BMI (r = 0.45, P < 0.01) but not with
CETP or LPL. The relationship between HDL2-C and HL
remained significant after controlling for changes in BMI (partial
correlation coefficient 0.48, P < 0.01). The changes
in HDL3-C after treatment correlated only with HL
(r = 0.51, P < 0.01) and not with any of the
other parameters including CETP, LPL, and BMI. Changes in LpA-I
(LpA-I) also correlated only with HL (Fig. 2).
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Discussion
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Thyroid dysfunction has a marked effect on the distribution and
composition of HDL particles, and the major HDL subfraction affected
appears to be HDL2. The present study showed that
HDL2 is reduced in hyperthyroidism and elevated in patients
with hypothyroidism, and this is in keeping with the findings of
previous studies (2, 8). In addition to classifying HDL particles
according to their size and density, HDL particles can also be
characterised according to the apolipoprotein composition. Apo A-I and
A-II are the major proteins found in HDL and form the two major HDL
subclasses: those that contain only apo A-I (LpA-I) and those that
contain both apo A-I and apo A-II (LpA-I:A-II). In normal subjects, the
relative proportion of LpA-I is greater in HDL2 than in
HDL3. There is recent evidence to suggest that the protein
composition of HDL significantly affects its antiatherogenic potential,
and data from clinical and experimental studies suggest that LpA-I is
more antiatherogenic (15). The changes in LpA-I and LpA-I:A-II
particles in thyroid disorders have not been studied previously. We
showed that LpA-I concentration was lowered in hyperthyroidism and
increased in hypothyroidism, whereas LpA-I:A-II concentration was
unaffected. The previously well-described changes in plasma apo A-I in
hyper- and hypothyroidism are mainly caused by changes in the
concentration of LpA-I rather than in LpA-I:A-II particles. This is
supported by the findings of O’Brien et al. (5) who
reported significant changes in apo A-I concentrations after treatment
of hyper- and hypothyroid patients but levels of apo A-II that remained
unchanged (5). Whether the increase in LpA-I level in hypothyroidism
may partially counteract the harmful effect of raised LDL in
hypothyroidism remains to be proven.
Factors that influence HDL lipid composition and therefore size are
known to have an important effect in modulating HDL and apo A-I
metabolism. HDL particle size appears to be inversely correlated with
the rate of apo A-I catabolism, with smaller HDL particles and
lipid-poor apo A-I being catabolized more rapidly (16). Because
plasma lipoproteins are continuously remodeled during their transit
through the plasma compartment by the actions of lipolytic enzymes and
lipid transfer proteins, the activities of these proteins are important
determinants of the lipid composition and size of HDL and hence its
metabolism (17). Changes in postheparin lipase and CETP activities have
been described in hyper- and hypothyroidism, and this is the first
study to evaluate the relative roles of these enzymes in thyroid
hormone-induced changes in HDL subfractions. Because the changes in
HDL subfractions after correction of the underlying thyroid disorder
correlated mainly with the changes in HL activity, HL appears to be the
major factor in determining HDL levels. CETP and LPL appear not to play
a significant role. HL is involved in the conversion of
HDL2 to HDL3, and transgenic mice and rabbits
that overexpress HL have markedly reduced HDL-C and apo A-I (18, 19).
Whether the changes in apo A-I observed in our study is because of
changes in synthesis and/or because of changes in metabolism remains to
be determined. Experimental studies have shown that apo A-I messenger
RNA (mRNA) synthesis is reduced in the liver and in the intestine in
hypothyroidism, and that thyroid hormone stimulates apo A-I
transcription (20, 21). However, plasma apo A-I concentration actually
decreased after T4 replacement in our hypothyroid patients.
We postulate that because smaller HDL particles and lipid-poor apo-AI
are known to be catabolized more rapidly (16, 19), the changes in HL
activity might indirectly affect the catabolism of apo A-I through its
lipolytic effect on the lipid portion of HDL particles and hence
override the effect of thyroid hormone on apo A-I mRNA synthesis.
In the present study, both HL and CETP activities correlated strongly
with thyroid hormone levels, suggesting that thyroid hormone has a
significant effect on the activities of these proteins, although the
underlying mechanisms are not clear. Thyroid hormone regulates the
transcription of certain genes. For instance thyroid hormone regulates
the expression of LDL receptor at the mRNA level. Staels et
al. (20) reported that HL gene expression is relatively resistant
to alterations in thyroid status, but whether thyroid hormone affects
posttranscriptional regulation of HL activity is not known (20). The
effect of thyroid hormone on CETP gene expression has not been
studied.
In conclusion, thyroid hormone has multiple effects on lipid
metabolism. In addition to its well-known effect on LDL metabolism, the
present study has demonstrated that HDL metabolism is also altered in
thyroid dysfunction. The effect of thyroid hormone on HDL is mediated
mainly via its effect on HL activity.
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Acknowledgments
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We are grateful to Ms. Betty Chu for her technical
assistance.
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Footnotes
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1 This work was supported by a grant from the Committee on Research
and Conference Grants of the University of Hong Kong (CRCG
337/041/0052). 
Received March 27, 1998.
Revised May 1, 1998.
Accepted May 15, 1998.
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References
|
|---|
-
Nishitani H, Okamura K, Noguchi S, Inoue K,
Morotomi Y, Fujishima M. 1990 Serum lipid levels in thyroid
dysfunction with special reference to transient elevation during
treatment in hyperthyroid Graves’ disease. Horm Metab Res. 22:490–493.[Medline]
-
Muls E, Blaton V, Rosseneu M, Lesaffre E, Lamberigts G,
de Moor P. 1982 Serum lipids and apolipoproteins A-I, A-II, and B
in hyperthyroidism before and after treatment. J Clin Endocrinol
Metab. 55:459–464.[Abstract/Free Full Text]
-
Friis T, Pedersen LR. 1987 Serum lipids in hyper-
and hypothyroidism before and after treatment. Clinica Chimica Acta. 162:155–163.[CrossRef][Medline]
-
Muls E, Rosseneu M, Blaton V, Lesaffre E, Lamberigts G,
de Moor P. 1984 Serum lipids and apolipoproteins A-I, A-II, and B
in primary hypothyroidism before and during treatment. Eur J Clin
Invest. 14:12–15.[Medline]
-
O’Brien T, Katz K, Hodge D, Nguyen TT, Kottke BA, Hay
ID. 1997 The effect of treatment of hypothyroidism and
hyperthyroidism on plasma lipids and apolipoproteins AI, AII and E. Clin Endocrinol (Oxf). 46:17–20.[CrossRef][Medline]
-
Verdugo C, Perrot L, Ponsin G, Valentin C, Berthezene
F. 1987 Time-course of alterations of high density lipoproteins
during thyroxine administration to hypothyroid women. Eur J Clin
Invest. 17:313–316.[Medline]
-
Agdeppa D, Macaron C, Mallik T, Schnuda ND. 1979 Plasma high density lipoprotein cholesterol concentration in thyroid
disease. J Clin Endocrinol Metab. 49:726–729.[Abstract/Free Full Text]
-
Kussi T, Taskinen MR, Nikkila EA. 1988 Lipoproteins, lipolytic enzymes, and hormonal status in hypothyroid
women at different levels of substitution. J Clin Endocrinol
Metab. 66:61–66.
-
Pazos F, Alvarez JJ, Rubies-Prat J, Varela C, Lasuncion
MA. 1995 Long term thyroid replacement therapy and levels of
lipoprotein (a) and other lipoproteins. J Clin Endocrinol Metab. 80:562–566.[Abstract]
-
Tan KCB, Shiu SWM, Kung AWC. 1998 Plasma
cholesteryl ester transfer protein activity in hyper- and
hypothyroidism. J Clin Endocrinol Metab. 83:140–143.[Abstract/Free Full Text]
-
Tall AR. 1993 Plasma cholesteryl ester transfer
protein. J Lipid Res. 34:1255–1274.[Medline]
-
Kelley JL, Kruski AW. 1986 Density gradient
ultracentrifugation of serum lipoproteins in a swinging bucket rotor. Methods Enzymol. 128:170–181.[Medline]
-
Ehnholm C, Kuusi T. 1986 Preparation,
characterisation, and measurement of hepatic lipase. Methods Enzymol. 129:716–738.[Medline]
-
Eckel RH, Goldberg IJ, Steiner L, Yost TJ, Paterniti
JR. 1988 Plasma lipolytic activity. Relationship to postheparin
lipolytic activity and evidence for metabolic regulation. Diabetes. 37:610–615.[Abstract]
-
Fruchart JC, Ailhaud G. 1992 Apolipoprotein
A-containing lipoprotein particles: physiological role, quantification,
and clinical significance. Clin Chem. 38:793–797.[Abstract/Free Full Text]
-
Brinton EA, Eisenberg S, Breslow JL. 1994 Human HDL
cholesterol levels are determined by apo A-I fractional catabolic rate,
which correlates inversely with estimates of HDL particle size. Arterioscler Thromb. 14:707–720.[Abstract/Free Full Text]
-
Clay MA, Newham HH, Forte TM, Barter PJ. 1992 Cholesteryl ester transfer protein and hepatic lipase activity promote
shedding of apo A-I from HDL and subsequent formation of discoidal HDL. Biochim Biophys Acta. 1124:52–58.[Medline]
-
Busch SJ, Barnhart RL, Martin GA, et al. 1994 Human
hepatic triglyceride expression reduces high density lipoprotein and
aortic cholesterol in cholesterol-fed transgenic mice. J Biol
Chem. 269:16376–16382.[Abstract/Free Full Text]
-
Fan J, Wang J, Bensadoun A, et al. 1994 Overexpression of hepatic lipase in transgenic rabbits leads to a
marked reduction of plasma high density lipoproteins and intermediate
density lipoproteins. Proc Natl Acad Sci USA. 91:8724–8728.[Abstract/Free Full Text]
-
Staels B, Van Tol A, Chan L, Will H, Verhoeven G, Auwerx
J. 1990 Alterations in thyroid status modulates apolipoprotein,
hepatic triglyceride lipase, and low density lipoprotein receptor in
rats. Endocrinology. 127:1144–1152.[Abstract/Free Full Text]
-
Strobl W, Gorder NL, Lee YCL, Gotto AM, Patsch W. 1990 Role of thyroid hormone in apolipoprotein A-I gene expression in
rat liver. J Clin Invest. 85:659–667.
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Abstract
Introduction
