Acid glycosaminoglycans in myxoedema

Spontaneous Coronary Artery Dissection and Hypothyroidism

INTRODUCTION AND OBJECTIVES

Thyroid hormone affects the metabolism of all tissues in the body. The aim of this study was to analyze the prevalence and implications of thyroid disorders in a cohort of consecutive patients with spontaneous coronary artery dissection (SCAD).

METHODS

A total of 73 patients with SCAD were analyzed. Baseline characteristics and clinical outcomes were compared between euthyroid and hypothyroid patients. Subsequently, the prevalence of thyroid function abnormalities and the clinical characteristics of SCAD patients were compared with those in 73 patients with acute coronary syndrome but without SCAD, matched by age, sex, and presentation.

RESULTS

Mean age was 55 ± 12 years and 26% had hypothyroidism. Compared with patients with normal thyroid function, patients with SCAD and hypothyroidism were all women (100% vs 69%, P = .01), more frequently had dissection in distal (74% vs 41%, P = .03) and tortuous coronary segments (68% vs 41%, p = .03), and more frequently received conservative medical management (79% vs 41%, P = .007). During a mean clinical follow-up of 4.1 ± 3.8 years, 23% of the patients had adverse cardiac events irrespective of thyroid function status. The prevalence of hypothyroidism was higher in patients with SCAD than in matched patients with acute coronary syndrome without SCAD (26% vs 8%, P = .004).

CONCLUSIONS

There is a high prevalence of hypothyroidism in patients with SCAD. Patients with SCAD and hypothyroidism are more frequently women, more frequently have distal dissections in tortuous vessels, and are more frequently managed with a conservative medical strategy.

Reversibility of fibrotic appearance of lungs with thyroxine replacement therapy in patients with severe hypothyroidism

OBJECTIVE

To present 2 cases of hypothyroidism with hypoxia associated with computed tomographic (CT) features suggestive of pulmonary fibrosis that resolved with correction of the hypothyroidism.

METHODS

Clinical case histories are described, comparative radiologic pulmonary images before and after treatment are provided, and the pertinent literature regarding possible pathologic mechanisms is reviewed.

RESULTS

Our first patient, a 68-year-old woman, presented with symptomatic severe hypothyroidism associated with respiratory failure. A CT scan of her lungs showed appearances suggestive of pulmonary fibrosis. Replacement therapy with levothyroxine led to correction of hypoxia and radiologic abnormalities. Our second patient, a 26-year-old man, presented with symptoms suggestive of obstructive sleep apnea that persisted despite use of positive pressure ventilation. Biochemical evaluation revealed severe hypothyroidism, and a CT scan disclosed pulmonary appearances consistent with fibrosis. His symptoms and radiologic abnormalities also improved after correction of hypothyroidism with levothyroxine therapy.

CONCLUSION

Radiologic pulmonary abnormalities suggestive of fibrotic disease are associated with severe hypothyroidism. Invasive investigations such as lung biopsy should be deferred until the clinical and radiologic responses to thyroxine replacement therapy have been assessed.

Thyroid hormone regulates heparan sulfate proteoglycan expression in the growth plate

Thyroid hormone is essential for normal skeletal development. Hypothyroidism is associated with growth arrest, failure of chondrocyte differentiation, and abnormal matrix synthesis. Thyroid hormone modulates the Indian hedgehog/PTHrP feedback loop and regulates fibroblast growth factor (FGF)/FGF receptor signaling. Because heparan sulfate (HS) proteoglycans (Prgs) (HSPGs) are absolutely required by these signaling pathways, we have investigated whether thyroid status affects HSPG expression within the growth plate. Tibial growth plate sections were obtained from 12-wk-old rats rendered euthyroid, thyrotoxic, or hypothyroid at 6 wk of age, 14-d-old congenitally hypothyroid Pax8-null mice, and TRalpha/TRbeta double-null mice lacking all thyroid hormone receptors. HS and chondroitin sulfate Prg expression was determined by immunohistochemistry using three monoclonal antibodies. There was increased HS staining in growth plates from hypothyroid animals predominantly within the extracellular matrix of reserve and proliferative zones. Cellular HS staining was also increased particularly in prehypertrophic chondrocytes. T3 regulation of HSPG core protein and HS synthetic and modification enzyme expression was studied in ATDC5 cells using semiquantitative RT-PCR. Thyroid hormone negatively regulated expression of the core protein Gpc6, the polymerase Ext1, and the modification enzyme Hs6st2. These studies demonstrate that the expression and distribution of growth plate Prgs are regulated by thyroid hormone, and the regulation of HSPG expression provides an important additional link between FGF and Indian hedgehog signaling and T3. These novel observations suggest that the cartilage matrix and especially HSPGs are critical mediators of the skeletal response to thyroid hormone.

Histochemical study of cutaneous mucins in hypothyroid dogs

A dermal mucinosis, visualized as dermal alcianophilic material, is occasionally present in canine hypothyroidism (myxedema). Various histochemical reactions (alcian blue/periodic acid-Schiff [PAS], alcian blue at pH 2.6, alcian blue at pH 1.0, critical electrolytical concentrations with and without dimethylsulfoxide, differential hydrolysis by hyaluronidases) were performed on skin biopsies from six dogs (four females and two males ranging from 8 to 13 years) affected by hypothyroidism, all of them presenting dermal mucinosis in hematoxylin and eosin-stained sections. In these dogs, the only polysaccharidic compound involved in the dermal mucinosis was hyaluronic acid. In this study, hyaluronic acid dermal deposits of hypothyroid dogs were significantly different from those of controls in subepidermal connective tissue and loose reticular connective tissue but not in periadnexal zones. We recommend the combined alcian blue/PAS reaction as a routine technique to assess dermal mucinosis in hypothyroid dogs.

Hyaluronan turnover in the rat small intestine

The main metabolic pathway for the interstitial matrix component hyaluronan seems to be via lymph. Present estimates of turnover of intestinal hyaluronan are based on isolated organs and/or experiments in anaesthesia over a few hours. In this study lymph was sampled from the main mesenteric lymphatic for 24 h in awake, restrained rats. The tissue content of hyaluronan averaged 28 micrograms g-1 in the duodenum/jejunum and 124 micrograms g-1 in the colon. Based on tissue content and lymphatic output, the turnover rate of hyaluronan in the small intestine was estimated at approximately 50%. In another experimental group anaesthetized rats were fed either phosphate buffer or triolein in buffer via a gastric tube. Lymph flow increased with fluid absorption from the gut and hyaluronan output in lymph was elevated correspondingly. However, no effect of acute fat administration on hyaluronan concentration or lymph flow could be demonstrated.

Incorporation of D3H glucosamine to the adult and developing cochlear tectorial membrane of normal and hypothyroid rats

The uptake of D-3H-glucosamine by the developing cochlea of normal and hypothyroid rats was examined using light microscopic radioautography. During postnatal development, normal and hypothyroid rat cochleas exhibited a layer of radiolabelling in the tectorial membrane (TM). This layer first appeared in the TM region which covers the spiral limbus and the Kölliker's organ (KO), then progressively reached the apical part of the TM covering the organ of Corti. Radiolabelling was significantly greater in hypothyroid than in normal cochleas. These findings suggests that the enormous size reached by the TM in the congenital hypothyroidism could be related to an increase of epithelial secretion, at least for carbohydrates. It also suggests that TM, in normal and hypothyroid cochleas, could be formed during development by the addition of successive layers. Older layers could be displaced upwards by the new ones. Cochleas of normal young adult rats, treated with D-3H-glucosamine, showed a very scarce and diffuse radiolabelling. Cochleas of hypothyroid young adult rats exhibited a thickened and distorted TM, which incorporated a significant amount of carbohydrates. These results suggest that TM secretion is highly reduced in young adult normal animals, while in young adult hypothyroid ones it is still active. During cochlear maturation, thyroxine seems to be necessary, not only for the synthesis of normal glycoproteins (as suggested by previous reports), but also for the control of glycoprotein secretion.

Human temporal bone findings in acquired hypothyroidism

Histological studies of the auditory organ in patients with acquired hypothyroidism are scarce. Thus the aim of the present study was to examine the temporal bones and the brain in subjects with hypothyroidism. Four temporal bones and two brains from clinically and biochemically hypothyroid subjects were removed and evaluated by light microscopy determine to the morphological changes and deposition of neutral and acid glycosaminoglycans. An audiogram from one of the patients showed a sensorineural hearing loss, which could be ascribed to occupational noise exposure. The study revealed histological changes compatible with age and infectious disease. No accumulation of neutral or acid glycosaminoglycans could be demonstrated in the temporal bones, or in the brains.

Effects of perinatal hypothyroidism in the carbohydrate composition of cochlear tectorial membrane

The presence of carbohydrates in the cochlear tectorial membrane (TM) of normal and hypothyroid rats was analyzed using fluorescent lectin probes. SBA and WGA lectins exhibited a similar reactivity in both normal and hypothyroid TMs. DBA, RCA1, UEA1 and Con A lectins were also reactive, although they showed a different distribution pattern between normal and hypothyroid TMs. Lastly, one of the lectins, PNA, was only labeled in hypothyroid TMs. These findings suggest that carbohydrate chains containing residues of N-acetyl-D-galactosamine (GalNAc) and N-acetyl-D-glucosamine, are similarly distributed in normal and hypothyroid TMs. Other carbohydrate residues as GalNAc alpha 1,3 GalNAc, D-galactose (Gal), L-fucose and D-mannose, are present, but are abnormally distributed in hypothyroid TMs. The Gal beta 1,3GalNAc residues, recognized by PNA, could be present only in the hypothyroid TMs. Alterations in glycosylation of the glycoproteins in the hypothyroid TM could be responsible for the abnormal distribution pattern of carbohydrate residues here described, and for the distorted shape of the hypothyroid TM.

Urinary glycosaminoglycans in patients with hypothyroidism and in healthy subjects

Although the changes in urinary glycosaminoglycans have been investigated in several endocrinopathies, no information was hitherto available on the content and composition of urinary glycosaminoglycans in hypothyroidism. Urinary glycosaminoglycans were therefore investigated in patients with hypothyroidism and in healthy subjects. The total daily excretion of urinary glycosaminoglycans was found to be significantly increased (by 41%) in hypothyroidism. Two electrophoretic bands were always detected in both examined groups: a major band of chondroitin sulphate and a minor band of heparan sulphate. Heparan sulphate and chondroitin sulphate levels were respectively 114% and 42% higher in patients with hypothyroidism than in controls. The respective increases in chondroitin-4-sulphate and chondroitin-6-sulphate were 31% and 41%. The relative quantities of chondroitin-4-sulphate, dermatan sulphate, chondroitin-6-sulphate and non-sulphated chondroitin sulphate were unchanged in the two examined groups. The changes observed in the levels of the excreted glycosaminoglycans may reflect the altered metabolism of connective tissue in hypothyroidism.

Audiological and temporal bone findings in myxedema

Fifteen patients with confirmed myxedema at a median age of 48 years (range 32 to 60 years) were referred for audiological evaluation before and after treatment with levothyroxine. The median interval between the pretreatment and posttreatment investigations was 18 months (range 9 to 27 months). In addition, 13 patients at a median age of 78 years (range 64 to 95 years) were audiologically reexamined after long-standing levothyroxine treatment. The observation period upon treatment with levothyroxine was 40 months (range 32 to 46 months). No improvement in hearing sensitivity could be demonstrated either in the younger patients or in the elderly. When compared to an age- and sex-matched unscreened population, the myxedematous patients did not demonstrate any different degree of hearing loss. Histological investigation of the temporal bones from an 83-year-old woman with myxedema, however, showed no morphological changes or deposition of glycosaminoglycans, changes which are compatible with true age-related hearing loss. It is concluded that no association exists between myxedema and hearing impairment and that no morphological or structural changes due to myxedema can be demonstrated in the temporal bones.

Increased urinary excretion of acid mucopolysaccharides and glycopeptides in hypothyroidism following thyroid hormone therapy

Urinary excretion of acid mucopolysaccharides and glycopeptides in the urine of an untreated patient with cretinism were measured before and after thyroid hormone replacement. Urinary uronic acid and hexose excretion in the CPC-precipitated fraction increased four to ten times after thyroid hormone administration. The maximum excretion was observed after 2 months of thyroid replacement. The excreted acid mucopolysaccharides consisted of chondroitin sulphate A/C and minor quantities of heparan sulphate. Urinary excretion of glycopeptides, particularly small molecular glycopeptides rose also four to five-fold with thyroid hormone administration. These data suggest that thyroid hormone markedly influences the metabolism of acid mucopolysaccharides and glycoproteins. Possibly, the lack of thyroid hormone caused a decreased activity of various lysosomal glycosidases and sulphatases.