Triglyceride metabolism in thyroid disease

Association between thyroid hormone and components of metabolic syndrome in euthyroid Korean adults: A population-based study

Thyroid dysfunction increases the prevalence of metabolic syndrome. However, the link between thyroid hormones and metabolic syndrome remains debatable, and the effect of sex on their relationship is not completely understood. To elucidate the relationship of thyroid hormones with metabolic syndrome and its components according to sex in euthyroid individuals in South Korea. Adult participants who underwent thyroid tests at our institution between January 2015 and December 2018 and had thyroid-stimulating hormone (TSH; 0.270-4.200 μIU/mL) and free thyroxine (FT4; 0.93-1.70 ng/dL) levels in the normal range were included. After correcting for age and body mass index, multiple linear regression was performed to assess the association of TSH and FT4 with metabolic syndrome and its components, and logistic regression was performed to estimate the risk of developing metabolic syndrome and its components according to different thyroid hormone quartiles. We included 12,478 men and 7,575 women in this study. The prevalence of metabolic syndrome was 9.68%. In men, TSH was positively associated with blood pressure and triglycerides, and the odds ratio for high blood pressure and hypertriglyceridemia was approximately 1.3 times higher in the fourth quartile than in the first quartile. FT4 associated positively with waist circumference, and a high odds ratio for abdominal obesity in the fourth quartile was observed in both men (odds ratio [OR], 1.239; 95% confidence interval [CI], 1.045-1.470) and women (OR, 1.302; 95% CI, 1.029-1.649). A negative association was found between FT4 and triglycerides, and concurrently, the odds ratios for hypertriglyceridemia were lower in the fourth quartile in both men (OR, 0.692; 95% CI, 0.619-0.774) and women (OR: 0.641; 95% CI: 0.512-0.803). In addition, a higher odds ratio for high blood pressure was observed in the fourth quartiles of FT4 and TSH in women. However, there was no association between TSH and FT4 levels and the onset of metabolic syndrome in either of the sexes. Serum TSH and FT4 levels were associated with different metabolic syndrome components in men and women, but there was no association with the onset of metabolic syndrome.

Association between thyroid hormones and the components of metabolic syndrome

BACKGROUND

Thyroid hormones are known to have direct and indirect effects on metabolism. Individuals with metabolic syndrome, a disease that is growing in incidence at a rapid rate, are at higher risk for cardiovascular disease, diabetes, and cancer. The aim of this study was to identify whether significant correlations exist between thyroid hormone levels and components of the metabolic syndrome in the general population of Korea.

METHODS

The data were collected from the sixth Korea National Health and Nutrition Examination Surveys from 2013 to 2015. A total of 1423 participants were tested for thyroid function. The analysis of variance and multiple linear regression were performed to analyze the relationship between thyroid hormone level and components of the metabolic syndrome.

RESULTS

A positive association between free thyroxine and fasting glucose level was observed in patients with high free thyroxine levels (≥1.70 ng/dL, β = 15.992, p = < 0.0001), when compared with patients with normal-middle free thyroxine levels. Moreover, a negative association was observed between free thyroxine and triglyceride levels in patients with normal-high free thyroxine levels (β = - 21.145, p = 0.0054) and those with high free thyroxine levels (β = - 49.713, p = 0.0404).

CONCLUSION

Free thyroxine shows a partially positive association with fasting glucose and a partially negative association with triglycerides in the Korean population. In patients with abnormal thyroid function, follow up tests for glucose levels and lipid profiling during treatment for thyroid dysfunction would be beneficial in terms of overlooking metabolic syndrome and to prevent related diseases.

Influence of high-normal serum TSH levels on major cardiovascular risk factors and Visceral Adiposity Index in euthyroid type 2 diabetic subjects

Although several observations indicate that serum TSH levels in the high normal range are related to cardiovascular (CVD) risk factors in the general population, similar data are limited in diabetic subjects. The aim of this study was to investigate the potential associations between TSH serum levels within the normal range and major metabolic and non-metabolic CVD risk factors in a cohort of euthyroid type 2 diabetic subjects. Thyroid hormones, TSH levels, anthropometric parameters, lipid profile, glucose control, and blood pressure were measured in 490 euthyroid type 2 diabetic subjects, consecutively attending two outpatient diabetic units in Southern Italy. In all subjects, we also calculated the Visceral Adiposity Index (VAI), an obesity-related index associated with CVD risk. Diabetic women showed higher mean serum TSH levels and lower FT4 concentration than diabetic men, while FT3 levels were comparable in the two genders. Stratifying the study population according to quartiles of TSH levels, subjects in the highest TSH quartile were more likely to be female and younger, with higher values of BMI and waist circumference (P = 0.05 both), higher triglycerides (P = 0.002) and non-HDL cholesterol concentrations (P = 0.01), higher VAI values (P = 0.02), and lower FT4 levels (P = 0.05), when compared to those in the lowest quartile. At multivariate analysis, a younger age, female gender, triglycerides levels, and waist circumference were independently associated with higher TSH levels. In conclusion, in type 2 diabetic subjects with no evidence of thyroid disease, higher TSH concentrations within the normal range were more frequent in women and in younger subjects, and they were associated with visceral obesity and higher triglycerides concentrations, two well-known CVD risk factors.

Nuclear receptors and their selective pharmacologic modulators

Nuclear receptors are ligand-activated transcription factors and include the receptors for steroid hormones, lipophilic vitamins, sterols, and bile acids. These receptors serve as targets for development of myriad drugs that target a range of disorders. Classically defined ligands that bind to the ligand-binding domain of nuclear receptors, whether they are endogenous or synthetic, either activate receptor activity (agonists) or block activation (antagonists) and due to the ability to alter activity of the receptors are often termed receptor "modulators." The complex pharmacology of nuclear receptors has provided a class of ligands distinct from these simple modulators where ligands display agonist/partial agonist/antagonist function in a tissue or gene selective manner. This class of ligands is defined as selective modulators. Here, we review the development and pharmacology of a range of selective nuclear receptor modulators.

Thyroid function in childhood obesity and metabolic comorbidity

Childhood obesity is a worldwide health problem and its prevalence is increasing steadily and dramatically all over the world. Obese subjects have a much greater likelihood than normal-weight children of acquiring dyslipidemia, elevated blood pressure, and impaired glucose metabolism, which significantly increase their risk of cardiovascular and metabolic diseases. Elevated TSH concentrations in association with normal or slightly elevated free T4 and/or free T3 levels have been consistently found in obese subjects, but the mechanisms underlying these thyroid hormonal changes are still unclear. Whether higher TSH in childhood obesity is adaptive, increasing metabolic rate in an attempt to reduce further weight gain, or indicates subclinical hypothyroidism or resistance and thereby contributes to lipid and/or glucose dysmetabolism, remains controversial. This review highlights current evidence on thyroid involvement in obese children and discusses the current controversy regarding the relationship between thyroid hormonal derangements and obesity-related metabolic changes (hypertension, dyslipidemia, hyperglycemia and insulin resistance, nonalcoholic fatty liver disease) in such population. Moreover, the possible mechanisms linking thyroid dysfunction and pediatric obesity are reviewed. Finally, the potential role of lifestyle intervention as well as of therapy with thyroid hormone in the treatment of thyroid abnormalities in childhood obesity is discussed.

The relation of thyroid function to components of the metabolic syndrome in Korean men and women

This study was to assess the relation of thyroid dysfunction to metabolic syndrome (MetS) at an earlier stage in Korean population. Metabolic parameters such as body composition, blood pressure (BP), fasting glucose, total cholesterol, triglyceride (TG), HDL-cholesterol (HDL-C), LDL-cholesterol (LDL-C), thyroid-stimulating hormone (TSH) and free thyroxine 4 (fT(4)) were measured. During a mean follow-up of 3 yr, 5,998 Koreans ages over 18 yr were assessed. There were 694 cases of MetS at follow-up. The mean age of the subjects was 45.6 ± 9.5 yr. Mean level of TSH was 2.02 ± 1.50 mIU/L, mean level of fT(4) was 1.23 ± 0.20 ρM/L. At baseline, TSH levels and fT(4) levels were associated to waist circumference, BP, glucose and lipids in the subjects. Increase in systolic blood pressure, diastolic blood pressure (DBP), total cholesterol and TG were significantly associated with changes in TSH levels after adjustment. Changes in DBP, TG, HDL-C and fasting glucose were significantly associated with changes in fT(4) levels after adjustment. Increase in TSH levels even after further controlling for baseline TSH level predicted the MetS over the study period. In conclusion, there is a relationship between thyroid function and cardiovascular risk factors, such as BP, total cholesterol, TG, HDL-C and fasting glucose. Also, higher levels of TSH may predict the MetS in Korean.

Role of thyroid receptor β in lipid metabolism

Thyroid hormones (THs) exert their actions by binding to thyroid hormone receptors (TRs) and thereby affect tissue differentiation, development, and metabolism in most tissues. TH-deficiency creates a less favorable lipid profile (e.g. increased plasma cholesterol levels), whereas TH-excess is associated with both positive (e.g. reduced plasma cholesterol levels) and negative (e.g. increased heart rate) effects. TRs are encoded by two genes, THRA and THRB, which, by alternative splicing, generate several isoforms (e.g. TRα1, TRα2, TRβ1, and TRβ2). TRα, the major TR in the heart, is crucial for heart rate and for cardiac contractility and relaxation, whereas TRβ1, the major TR in the liver, is important for lipid metabolism. Selective modulation of TRβ1 is thus considered as a potential therapeutic target to treat dyslipidemia without cardiac side effects. Several selective TH analogs have been tested in preclinical studies with promising results, but only a few of these compounds have so far been tested in clinical studies. This review focuses on the role of THs, TRs, and selective and non-selective TH analogs in lipid metabolism. This article is part of a Special Issue entitled: Translating nuclear receptors from health to disease.

Insulin action in hyperthyroidism: a focus on muscle and adipose tissue

Hyperthyroidism leads to an enhanced demand for glucose, which is primarily provided by increased rates of hepatic glucose production due to increased gluconeogenesis (in the fasting state) and increased Cori cycle activity (in the late postprandial and fasting state). Adipose tissue lipolysis is increased in the fasting state, resulting in increased production of glycerol and nonesterified fatty acids. Under these conditions, increased glycerol generated by lipolysis and increased amino acids generated by proteolysis are used as substrates for gluconeogenesis. Increased nonesterified fatty acid levels are necessary to stimulate gluconeogenesis and provide substrate for oxidation in other tissues (such as muscle). In the postprandial period, insulin-stimulated glucose uptake by the skeletal muscle has been found to be normal or increased, mainly due to increased blood flow. Under hyperthyroid conditions, insulin-stimulated rates of glycogen synthesis in skeletal muscle are decreased, whereas there is a preferential increase in the rates of lactate formation vs. glucose oxidation leading to increased Cori cycle activity. In hyperthyroidism, the Cori cycle could be considered as a large substrate cycle; by maintaining a high flux through it, a dynamic buffer of glucose and lactate is provided, which can be used by other tissues as required. Moreover, lipolysis is rapidly suppressed to normal after the meal to facilitate the disposal of glucose by the insulin-resistant muscle. This ensures the preferential use of glucose when available and helps to preserve fat stores.

Decreased lipid intermediate levels and lipid oxidation rates despite normal lipolysis in patients with hypothyroidism

BACKGROUND

Hypothyroidism decreases energy expenditure and combustion of fuels, but the reported effects on lipid metabolism and insulin sensitivity are divergent and there is a lack of studies assessing rates of lipolysis and lipid oxidation. The present study was conducted to test the hypotheses that hypothyroidism decreases lipolysis, blood concentrations of free fatty acid, lipid oxidation, and insulin sensitivity.

METHODS

We studied 11 hypothyroid patients (thyroid-stimulating hormone: 150 mU/L) with autoimmune thyroiditis (i) before and (ii) after 2 months of triiodothyronine-euthyroidism upon levothyroxine treatment and (iii) compared the patients to 10 healthy volunteers. Subjects underwent a 3-hour study in the basal state followed by a 3-hour euglycemic clamp study, and we used a combination of lipid blood concentrations, palmitate tracer dilution, and indirect calorimetry to assess lipid metabolism.

RESULTS

Compared to euthyroid control subjects and/or euthyroid posttreatment values hypothyroid patients were characterized by (i) 40%-50% decreased concentrations of plasma free fatty acids, palmitate, and 3-OH-butyrate (p < 0.05); (ii) >50% decreased lipid oxidation by indirect calorimetry (p < 0.001); (iii) unchanged whole-body lipolysis by palmitate dilution (all p's > 0.45); (iv) 50% increased triglyceride levels (p < 0.05); and (v) approximately 30% decreased insulin sensitivity judged by glucose infusion rate values (p = 0.05).

CONCLUSIONS

Our data show that hypothyroidism leads to decreased concentrations and oxidation rates of lipid intermediates and increased triglyceride concentrations in the presence of unaltered rates of lipolysis. The combination of normal lipolysis, low lipid oxidation rates, and high triglyceride concentrations is compatible with increased triglyceride synthesis.

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.

Plasma CRP, apolipoprotein A-1, apolipoprotein B and Lp(a) levels according to thyroid function status

BACKGROUND

Altered lipid profile is a well-known manifestation of thyroid dysfunction. Recently, serum Lp(a) and C-reactive protein (CRP) have emerged as new cardiovascular risk factors, but studies on changes of these markers with respect to thyroid function status have produced variable results. To better understand the effects of thyroid dysfunction on the development of atherosclerosis, we investigated plasma CRP and lipid profiles such as apoA1, apoB, and Lp(a) in cases with differing severities of thyroid dysfunction.

METHODS

Fifty four patients with hyperthyroidism, 35 patients with subclinical hyperthyroidism, 33 patients with overt hypothyroidism, 190 patients with subclinical hypothyroidism and 100 age- and sex-matched healthy control subjects were evaluated. Serum high sensitivity (hs)-CRP and Lp(a) were measured by immunonephelometry.

RESULTS

No significant differences were found in serum hs-CRP, Lp(a), HDL-C or ApoA1 in different thyroid function groups. Serum total cholesterol and LDL-C levels were significantly lower in cases of hyperthyroidism than in cases of overt hypothyroidism, subclinical hypothyroidism or subclinical hyperthyroidism, or in healthy control subjects (p <0.01). Serum triglyceride levels were higher in overt hypothyroidism than in hyperthyroidism or healthy controls (p <0.05). Serum apoB levels were significantly lower in hyperthyroidism than in overt hypothyroidism, subclinical hypothyroidism or in healthy control subjects (p <0.01). These differences were consistently significant after adjustment for age and BMI.

CONCLUSIONS

Serum CRP and Lp(a) levels, risk factors for atherosclerosis, were not found to be significantly affected by the degree of thyroid dysfunction. Increased risk of atherosclerosis in hypothyroidism does not appear to be associated with non-traditional cardiovascular risk factors, such as serum CRP, Lp(a) or apoA1 levels.

Diterpene composition of oils from Arabica and Robusta coffee beans and their effects on serum lipids in man

OBJECTIVES

The cholesterol-raising effect of boiled coffee is caused by diterpenes from coffee oil. In order to identify the diterpene responsible, we analysed the diterpene composition of oils from Arabica (Coffea arabica) and Robusta (Coffea canephora robusta) beans and their effects on serum lipids and thyroid function.

DESIGN, SUBJECTS, AND INTERVENTION

During the first 3-week period of a randomized, cross-over trial, 11 healthy, normolipaemic volunteers received per day either 2 g of coffee oil (n = 5) or placebo oil (n = 6). After a 2-week wash-out, the reverse treatments were applied for another 3 weeks. Six subjects received Arabica oil, supplying 72 mg day-1 cafestol and 53 mg day-1 kahweol, and five received Robusta oil, which provided 40 mg of cafestol, 19 mg of 16-O-methyl-cafestol, and 2 mg of kahweol per day. Background diets were constant.

RESULTS

The average serum cholesterol levels rose by 0.65 mmol L-1 (13%) on Arabica oil (P < 0.025; 95% CI, 0.21-1.09 mmol L-1) and by 0.53 mmol L-1 (13%) on Robusta oil (NS; 95% CI -0.36-1.42 mmol L-1). The triglycerides levels rose by 0.54 mmol L-1 (71%) on Arabica (P < 0.005; 95% CI, 0.22-0.76 mmol L-1) and 0.49 mmol L-1 (61%) on Robusta oil (P < 0.005; 95% CI, 0.30-0.68 mmol L-1). None of the effects on serum lipids or lipoprotein cholesterol levels was significantly different between Arabica and Robusta oil. Concentrations of serum total and free thyroxine (T4), triiodothyronine (T3), and thyroid-stimulating hormone (TSH) were largely unaffected.

CONCLUSIONS

Both Arabica and Robusta oil elevated serum lipid levels; therefore, cafestol must be involved and kahweol cannot be the sole cholesterol-raising diterpene. The mode of action of coffee diterpenes does not involve induction of hypothyroidism.

Hypodipsic hypernatremia and hypertriglyceridemia associated with cleft lip and cleft palate: a new hypothalamic dysfunction syndrome?

We report on a 4-month-old girl with congenital hypodipsic hypernatremia resulting from decreased sensitivity of the hypothalamic osmoreceptors with increased tonicity in association with hyperlipemia and cleft lip and cleft palate. We postulate that the link among these various derangements is hypothalamic dysfunction.

Thyroid hormone action on intermediary metabolism. Part II: Lipid metabolism in hypo- and hyperthyroidism

Despite their enhanced endogenous de novo cholesterol synthesis, hyperthyroid patients exhibit decreased total and low-density lipoprotein (LDL) cholesterol levels in the serum because of a concomitant increase in LDL catabolism, cholesterol excretion by bile and a reduced enterohepatic bile acid circulation. Hypothyroidism exhibits a reduction (1) in the synthesis of cholesterol and (2) in LDL catabolism, whereas cholesterol reabsorption is unchanged or even enhanced. In addition, obese hypothyroid patients showed an increased cholesterol synthesis which is independent of thyroid hormones and which contributes to the observed LDL cholesterolaemia. Thyroid hormones per se have only a minor influence on plasma triglyceride (TG) levels, but they induce an acceleration of TG turnover and chylomicron clearance rate. In addition, the hepatic lipogenic capacity is increased in hyperthyroidism and reduced in hypothyroidism. However, hepatic total and very low-density lipoprotein (VLDL) triglyceride output is decreased by thyroid hormones due to a reduced re-esterification and a simultaneously increased oxidation of newly synthesized fatty acids. Hypothyroid livers, by contrast, reveal an increased VLDL secretion. Despite their reduced lipogenesis, obese hypothyroidism is often accompanied by a hypertriglyceridaemia type III. The simultaneous stimulation of the synthesis of fatty acids, which are still in part converted to TG, and the degradation of TG contributes to the enhanced thermogenesis in hyperthyroid patients. The concentration and turnover of free fatty acids (FFA) are increased in hyperthyroidism, resulting from a thyroid hormone-induced increase in: (1) lipolysis, explained by an increased adipose tissue sensitivity for lipolytic hormones; and (2) oxidation of fatty acids to CO2 as well as to ketone bodies (KB).(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of altered thyroid status on lipid metabolism in Nubian goats

The effects of triiodothyronine (T3)-induced hyperthyroidism and of carbimazole (CZ)-produced hypothyroidism on lipid metabolism were studied in Nubian goats (Capra hircus). T3 treatment decreased the serum, liver and heart triglyceride, cholesterol and phospholipid concentrations. These changes were accompanied by an increase in the activity of lipoprotein lipase (LPL) in the heart and skeletal muscles. CZ treatment at a dose of 90 mg/goat significantly increased the serum triglyceride, liver cholesterol and heart phospholipid. CZ treatment significantly increased the liver and heart triglyceride concentration but the activity of LPL was not affected.

Effects of thyroidectomy and starvation on the activity and properties of hepatic carnitine palmitoyltransferase

1. Hepatic carnitine palmitoyltransferase activity was measured over a range of concentrations of palmitoyl-CoA and in the presence of several concentrations of the inhibitor malonyl-CoA. These measurements were made in mitochondria obtained from the livers of fed and starved (24 h) normal rats and of fed and starved thyroidectomized rats. 2. In the fed state thyroidectomy substantially decreased overt carnitine palmitoyltransferase activity and also decreased both the Hill coefficient and the s0.5 when palmitoyl-CoA concentration was varied as substrate. Thyroidectomy did not appreciably alter the inhibitory effect of malonyl-CoA on the enzyme. 3. Starvation increased overt carnitine palmitoyltransferase activity in both the fed and the thyroidectomized state. In percentage terms this response to starvation was substantially greater after thyroidectomy. In both the hypothyroid and normal states starvation decreased sensitivity to inhibition by malonyl-CoA.

Secretion of nascent lipoproteins by isolated hepatocytes from hypothyroid and hypothyroid, hypercholesterolemic rats

The induction of hypothyroidism in the rat is necessary for the development of pronounced dietary-induced hypercholesterolemia. The nature of nascent lipoproteins secreted by isolated hepatocytes from euthyroid, hypothyroid and hypothyroid, cholesterol-fed rats was investigated to distinguish between these hormonal and dietary effects. Serum total lipids, apolipoproteins, B, E and A-I, were greatly elevated in hypercholesterolemia. In hypothyroidism, serum apolipoproteins B and E were elevated, triacylglycerols were reduced by 65% and free cholesterol was increased by 50%. The total lipid, apolipoprotein B and E, secreted by hypercholesterolemic rat hepatocytes was markedly elevated when compared to normal. Triacylglycerol and phospholipid secretion was slightly increased by hypothyroid rat hepatocytes; however, apolipoprotein B, E and A-I secretion rates were unaffected. Gel filtration of the nascent lipoproteins demonstrated that compared to normal, proportionately more apolipoprotein B and E from hypercholesterolemic rat hepatocytes and apolipoprotein E from hypothyroid rat hepatocytes was secreted as larger lipoproteins. Hypercholesterolemic rat hepatocytes secreted abnormal cholesterol-rich particles even after 24 h of incubation in a lipid-deficient medium. Hypothyroidism alone cannot account for this observation, as hypothyroid rat hepatocytes secreted a triacylglycerol-rich, cholesterol-deficient lipoprotein having a normal nascent lipoprotein lipid composition. These observations are consistent with the hypothesis that in hypothyroidism the accumulation of beta-migrating lipoproteins results from impaired removal of lipoprotein catabolites from the serum, a condition which would only promote hypercholesterolemia in cholesterol feeding where direct synthesis of abnormal lipoproteins occurs.

Reversal of decreased hepatic lipase and lipoprotein lipase activities after treatment of hypothyroidism

Plasma lipoprotein concentrations, activities of hepatic lipase and lipoprotein lipase in post-heparin plasma, and the removal rate of exogenous triglyceride were measured in fourteen patients with severe primary hypothyroidism before and after 4 months substitution therapy with 1-thyroxine. Before treatment plasma LDL cholesterol concentrations were markedly increased while HDL cholesterol and plasma triglycerides were in the upper reference range. Thyroxine substitution led to a normalization of LDL cholesterol in all patients. Plasma triglycerides and HDL cholesterol decreased moderately. Hepatic lipase and lipoprotein lipase activities were initially reduced but increased significantly after treatment, by about 170% and 55%, respectively. The increase in hepatic lipase activities was significantly correlated to the increase in serum triiodothyronine levels and also to the reduction in LDL cholesterol concentrations. The decrease in LDL cholesterol was also significantly correlated to the increase in serum triiodothyronine concentration. In two patients initially treated with triiodothyronine, the activity of hepatic lipase, but not that of lipoprotein lipase, increased after 24 and 48 h, while LDL cholesterol levels decreased substantially. We suggest that the reduced activities of hepatic lipase as well as of lipoprotein lipase are important pathogenetic factors for the dyslipoproteinaemia occurring in hypothyroidism and that the low serum triiodothyronine concentration is of major importance for the alterations in lipid transport.

Lipid and lipoprotein pattern in thyroid dysfunction and the effect of therapy

Lipid and lipoprotein concentrations were studied in 12 hypothyroid and 11 hyperthyroid female subjects, both before and after therapy, and in 27 age matched female controls. Recognized clinical and laboratory criteria established the diagnosis. Lipoproteins, including the sub-fractions of the high density lipoproteins (HDL), were isolated by preparative ultracentrifugation, and the cholesterol (c) and protein (p) contents of each were determined. Total cholesterol, and in particular HDL-c, were elevated in the hypothyroid patients. The low density lipoprotein (LDL) -c/HDL-c ratio was 1.9 in this group, compared to 2.2 in the control group and 1.35 in the hyperthyroid patients. The HDL-2/HDL-3 ratio in the hypothyroid group was 3.75, as compared to 1.75 in the controls and 4.2 in the hyperthyroid group. Plasma triglycerides were moderately elevated in the hypothyroid patients and were significantly reduced in the hyperthyroid group. Total cholesterol was significantly lower in the hyperthyroid group as compared to the control group. Very low density (VLDL) cholesterol and protein were significantly increased and LDL and HDL cholesterol were reduced in the hyperthyroid patients. On rendering the patients euthyroid, most of these changes were reversed. Thyroid function profoundly affects lipoprotein concentration and composition. The change in the plasma HDL concentrations of the hypothyroid group questions the relationship of this group to arteriosclerosis. Therapy partially corrects the abnormalities, but complete correction may be related to duration of therapy.

High-density lipoprotein cholesterol: methods and clinical significance

The known limitations and advantages of methods for determining serum high-density lipoprotein (HDL) cholesterol concentration are reviewed with special emphasis on the applicability of each method to clinical medicine. The evidence for and against the relevance of serum HDL cholesterol to the prediction of the likelihood of an individual man or woman developing clinically evident ischemic heart disease is discussed. The possibility that HDL subfractions may be more relevant to this issue is also discussed. Information about serum HDL cholesterol concentration in diseases other than ischemic heart disease is reviewed. The effect of diet, body-weight, exercise, cigarette-smoking, alcohol intake, and hyperlipoproteinemia and the effect of modification of these factors on serum HDL cholesterol levels is discussed. Finally, a practical approach to the patient with a low concentration of serum HDL cholesterol is suggested.

Hydrolase activities in the rat aorta. V. Comparison to activities in liver and kidney after thyroidectomy and relation to dynamic clearance of circulating low density lipoproteins

Thyroid hormones influence circulating low density lipoprotein (LDL) levels in humans; they could have an effect on LDL catabolism. Male rats were thyroidectomized (H); half were treated for 7 days with 2 micrograms triiodothyronine/100 g body weight (T) and both groups were compared to controls (C). Aorta, liver, and kidney were assayed for cellular marker enzymes, including lysosomal acid cholesteryl esterase (ACE). Specific activities of ACE (mU/mg DNA; mean +/- SD) were: Aorta, C, 0.19 +/- 0.01; H, 0.16 +/- 0.01; T, 0.21 +/- 0.01; Liver: C, 15.55 +/- 1.49; H, 9.16 +/- 1.54; T, 15.43 +/- 2.28; Kidney: C, 1.70 +/- 0.23; H, 1.04 +/- 0.13; T, 2.08 +/- 0.35. Half lives for injected unmodified 125I-labeled human LDL were 11.5 +/- 0.7 hour in C, 16.2 +/- 3.1 in H, and 12.9 +/- 0.9 in T groups. Fractional catabolic rates (FCR) of LDL in %/hr were 6.5 +/- 0.6 in C; 4.8 +/- 0.5 in H, and 6.0 +/- 0.3 in T. Reductively methylated 125I-labeled human LDL had half-lives of 14.9 +/0 1.4 hour in C and 15.1 +/- 1.6 hour in H and the FCR of this modified LDL was 5.3 +/- 0.5 %/hr in C and 5.2 +/- 0.7 %/hr in H groups. Thus, thyroidectomy results in marked decreases in ACE specific activity of liver and kidney and a marked decrease in FCR and prolonged half-life of non-modified LDL (all P less than 0.05). On the other hand, methylated LDL showed a similarly reduced FCR and prolonged half-life in control and thyroidectomized rats (P less than 0.05). This suggests a major effect of thyroid deficiency on receptor-mediated uptake of LDL in vivo and demonstrates the influence of hormonal status on dynamic clearance and catabolism of LDL.

Lipid transport in the hypothyroid rat as reflected by the serum concentrations of free fatty acids, lipoproteins, lecithin-cholesterol acyltransferase and lipoprotein lipase activity in adipose tissue

An experimental model was explored for the study of the effect of thyroid hormone on lipid transport and metabolism in the rat. The development of the hypothyroid state was accompanied by an early decrease in free fatty acids (FFA) followed by an increase in the level of cholesterol and a decrease in triglyceride concentration. Simultaneously, the adipose tissue lipoprotein lipase activity increased while the lecithin-cholesterol acyltransferase was unchanged. The hypothyroid state was also accompanied by a decrease in the concentrations of tryglycerides and cholesterol in very low density lipoproteins (VLDL) while the 2 lipids increased in the low density lipoprotein (LDL) fraction. Administration of triiodothyronine markedly reduced the amount of cholesterol in both the LDL and high density lipoprotein (HDL) fractions. The animal model has been shown to have similarities with findings in human subjects.

Serum lipids, "double pre-beta lipoproteinemia," and distribution of the apo-very-low density (VLDL) lipoprotein peptides in hypothyroid patients before and after substitution therapy

Thirty-six hypothyroid patients had total thyroidectomy for cancer. Thirty of them were studied before and during hormone replacement therapy, 1-1 .1 microgram/kg triiodothyronine (T3) per day. Mean treatment period was 90 days. During treatment mean serum total cholesterol (TC), triglycerides (TG), the ratio of TC to TG in very-low-density lipoprotein and the prevalence of the "double pre-beta VLDL lipoproteinemia" (Double-PBL) were significantly reduced as compared to the pretreatment values. The VLDL peptides were separated bysoelectric focusing (IEF) in polyacrylamide gel. The relative content of apolipoprotein E (arginine-rich apoprotein) and the E/C-peptides ratio were significantly reduced after T3 therapy. On the contrary, the content of C11 peptide was significantly increased. Apoprotein E was positively correlated with serum TC. The proportion of the intermediate density lipoprotein fraction, evaluated by agarose gel electrophoresis, consistently decreased after treatment. The results of our study suggest that thyroid hormones affect the metabolism of remnant lipoproteins.

A selective decline of postheparin plasma hepatic triglyceride lipase in hypothyroid rats

The present study aimed to define the effect of thyroid status on two postheparin plasma lipases, i.e., lipoprotein lipase and hepatic triglyceride lipase. Rats with hypo- and hyperthyroidism were used for this purpose. Separate measurement of these two lipases was done by an immunochemical method utilizing antiserum specific to hepatic triglyceride lipase. The 5-wk thyroidectomized, hypothyroid rats had normal plasma concentrations of both triglyceride and cholesterol. These rats showed a selective decline in the activity of postheparin plasma hepatic triglyceride lipase with normal lipoprotein lipase activity. The rats made thyrotoxic by thyroxine treatment had normal plasma levels of both triglyceride and cholesterol. These rats showed normal activities of both hepatic triglyceride lipase and lipoprotein lipase. The observed finding of a selective decline of hepatic triglyceride lipase in hypothyroid rats is discussed in connection with the possible function of this enzyme in lipoprotein metabolism.

Influence of thyroid status on skeletal muscle LPL activity and TG uptake

The influence of thyroid status on the clearance of chylomicron 14C-labeled triglycerides (14C-TG), the fractional uptake of 14C-TG, and activity of lipoprotein lipase (LPL) in the different skeletal muscle fiber types was evaluated in pentobarbital-anesthetized rats. The turnover of plasma TG was approximately fourfold greater in the hyperthyroid (HyperT) compared to either euthyroid (EUT) or hypothyroid (HypoT) animals. The uptake of 14C-TG was increased in slow-twitch red and fast-twitch red muscle sections of the HyperT group and normal in the HypoT group. The changes in LPL activity in these two fiber types were inversely related to thyroid influence, with decreases found in the HyperT group and increases found in the HypoT group. Thus, the uptake of 14C-TG in these high-oxidative fibers, relative to the LPL activity, varied directly with thyroid influence. As a result, the normal linear relationship, apparent for the different types of skeletal muscle, between LPL activity measured in vitro and TG uptake determined in situ was not maintained.

Lipoprotein composition in hypothyroidism

Sixteen patients with hypothyroidism have had their lipid status assessed before and during replacement therapy. More than 60% had hypercholesterolaemia and more than 60% had hypertriglyceridaemia. Significant reductions in plasma cholesterol, but not in plasma triglyceride, were seen during replacement therapy. A high cholesterol: triglyceride ratio was observed in VLDL and this relationship tended back to normal during treatment. This raises the possibility that in hypothyroidism, as in Type III hyperlipoproteinaemia, an abnormality in VLDL conversion to LDL is present.

Hypothyroidism, an important cause of reversible hyperlipidemia

Primary hypothyroidism was found to be the cause of hyperlipidemia in 22 patients. The mean age was 46 years, 59% were males, 27% had vascular disease, 14% had xanthomas and 86% had thyroid antibodies. Familial involvement was shown in 3 propositi. All patients were treated with L-thyroxine, 0.05--0.2 mg/day for a mean of 16 months. Combined hyperlipidemia was common (77%), and lipoprotein phenotyping revealed types IIB hyperlipopro-teinemia in 11, IIA in 5, III in 3 and IV in 3 patients. With treatment, normal plasma cholesterol (less than 265 mg/dl) and triglycerides (less than 200 mg/dl) were obtained in 91% and 86%, respectively. The mean maintenance L-thyroxine dose was 0.15 mg/day, but smaller doses often showed marked hypolipidemic effect. The mean +/- S. D. pretreatment fasting plasma cholesterol and triglycerides were 387 +/- 120 and 328 +/-247 mg/dl and on thyroid treatment the mean minimum levels were 205 +/- 46 and 133 +/- 65 mg/dl, respectively (both p values less than 0.005). Hypothyroidism has proved to be a common reversible form of hyperlipidemia. One cardiac patient died and three others had to have their L-thyroxine titrated to prevent angina. Family screening has been of use in case finding for auto-immune disease in 3 families.

Study of the lipid-lowering action of choloxin and nilevar in patients with chronic renal failure

Lowering of lipids in patients with chronic renal failure is advantageous but cannot be done by calorie restriction. In a controlled study the anabolic steroid norethandrolone (Nilevar) was found to lower triglycerides by 50%, while D-thyroxine (Choloxin) lowered the cholesterol by 25%. Both drugs increased the activity of lipoprotein lipase in spite of uraemic inhibition. Norethandrolone also reduced basal serum insulin levels. Norethandrolone seems appropriate for underweight patients and D-thyroxine for overweight patients, but side effects are more frequent than in non-uraemic patients.