The effects of propranolol on skeletal muscle contraction, lipid peroxidation products and antioxidant activity in experimental hyperthyroidism

Differential involvement of various sources of reactive oxygen species in thyroxin-induced hemodynamic changes and contractile dysfunction of the heart and diaphragm muscles

Thyroid hormones are key regulators of basal metabolic state and oxidative metabolism. Hyperthyroidism has been reported to cause significant alterations in hemodynamics, and in cardiac and diaphragm muscle functions, all of which have been linked to increased oxidative stress. However, the definite source of increased reactive oxygen species (ROS) in each of these phenotypes is still unknown. The goal of the current study was to test the hypothesis that thyroxin (T4) may produce distinct hemodynamic, cardiac, and diaphragm muscle abnormalities by differentially affecting various sources of ROS. Wild-type and T4 mice with and without 2-week treatments with allopurinol (xanthine oxidase inhibitor), apocynin (NADPH oxidase inhibitor), L-NIO (nitric oxide synthase inhibitor), or MitoTEMPO (mitochondria-targeted antioxidant) were studied. Blood pressure and echocardiography were noninvasively evaluated, followed by ex vivo assessments of isolated heart and diaphragm muscle functions. Treatment with L-NIO attenuated the T4-induced hypertension in mice. However, apocynin improved the left-ventricular (LV) dysfunction without preventing the cardiac hypertrophy in these mice. Both allopurinol and MitoTEMPO reduced the T4-induced fatigability of the diaphragm muscles. In conclusion, we show here for the first time that T4 exerts differential effects on various sources of ROS to induce distinct cardiovascular and skeletal muscle phenotypes. Additionally, we find that T4-induced LV dysfunction is independent of cardiac hypertrophy and NADPH oxidase is a key player in this process. Furthermore, we prove the significance of both xanthine oxidase and mitochondrial ROS pathways in T4-induced fatigability of diaphragm muscles. Finally, we confirm the importance of the nitric oxide pathway in T4-induced hypertension.

Thyroid status affects membranes susceptibility to free radicals and oxidative balance in skeletal muscle of Muscovy ducklings (Cairina moschata)

Thyroid hormones (TH) are major contributor to oxidative stress in mammals because they (1) stimulate reactive oxygen species generation (ROS), (2) impair antioxidant defenses, and (3) increase the susceptibility to free radicals of most tissues. Unlike mammals, THs seem to diminish mitochondrial ROS while they have limited effect on the antioxidant machinery in birds. However, how THs modify the susceptibility to ROS has never been explored in an avian model, and very little is known about their effect on oxidative balance in birds. Therefore, the objective of our study was to examine the effect of chronic pharmacological hypo- and hyperthyroidism on (i) the susceptibility of mitochondrial membranes to ROS; and (ii) the level of oxidative stress assessed by measuring oxidative damage to lipids, nucleic acids and proteins in the gastrocnemius muscle of ducklings. We show that hypothyroidism had no effect on the susceptibility of mitochondrial membranes to free radicals. Hypothyroid ducklings had lower oxidized lipids (-31%) and DNA (-25%) but a similar level of protein carbonylation relative to controls. Conversely, mitochondrial membranes of hyperthyroid ducklings exhibited higher unsaturation (+12%) and peroxidation (+31%) indexes than in controls indicating a greater susceptibility to free radicals. However, hyperthyroid ducklings exhibited more oxidative damages on proteins (+67%) only, whereas lipid damages remained unchanged, and there was a slight reduction (-15%) in damages to DNA compared to euthyroid controls. Our results indicate that birds and mammals present fundamental differences in their oxidative stress response to thyroid status.

Vitamin E management of oxidative damage-linked dysfunctions of hyperthyroid tissues

INTRODUCTION

Thyroid hormones affect growth, development, and metabolism of vertebrates, and are considered the major regulators of their homeostasis. On the other hand, elevated circulating levels of thyroid hormones are associated with modifications in the whole organism (weight loss and increased metabolism and temperature) and in several body regions. Indeed, tachycardia, atrial arrhythmias, heart failure, muscle weakness and wasting, bone mass loss, and hepatobiliary complications are commonly found in hyperthyroid animals and humans.

RESULTS

Most thyroid hormone actions result from influences on transcription of T3-responsive genes, which are mediated through nuclear receptors. However, there is significant evidence that tissue oxidative stress underlies some dysfunctions produced by hyperthyroidism.

DISCUSSION

During the last decades, increasing interest has been turned to the use of antioxidants as therapeutic agents in various diseases and pathophysiological disorders believed to be mediated by oxidative stress. In particular, because elevated circulating levels of thyroid hormones are associated with tissue oxidative injury, more attention has been paid to explore the application of antioxidants as therapeutic agents in thyroid related disorders.

CONCLUSIONS

At present, vitamin E is among the most commonly consumed dietary supplements due to the belief that it, as an antioxidant, may attenuate morbidity and mortality. This is due to the results of numerous scientific studies, which demonstrate that vitamin E has a primary function to destroy peroxyl radicals, thus protecting polyunsaturated fatty acids biological membranes from oxidative damage. However, results are also available indicating that protective vitamin E effects against oxidative damage can be obtained even through different mechanisms.

Effect of T3 on metabolic response and oxidative stress in skeletal muscle from sedentary and trained rats

We investigated whether swim training modifies the effect of T3-induced hyperthyroidism on metabolism and oxidative damage in rat muscle. Respiratory capacities, oxidative damage, levels of antioxidants, and susceptibility to oxidative challenge of homogenates were determined. Mitochondrial respiratory capacities, H2O2 release rates, and oxidative damage were also evaluated. T3-treated rats exhibited increases in muscle respiratory capacity, which were associated with enhancements in mitochondrial respiratory capacity and tissue mitochondrial protein content in sedentary and trained animals, respectively. Hormonal treatment induced muscle oxidative damage and GSH depletion. Both effects were reduced by training, which also attenuated tissue susceptibility to oxidative challenge. The changes in single antioxidant levels were slightly related to oxidative damage extent, but the examination of parameters affecting the susceptibility to oxidants indicated that training was associated with greater effectiveness of the muscle antioxidant system. Training also attenuated T3-induced increases in H2O2 production and, therefore, oxidative damage of mitochondria by lowering their content of autoxidizable electron carriers. The above results suggest that moderate training is able to reduce hyperthyroid state-linked tissue oxidative damage, increasing antioxidant protection and decreasing the ROS flow from the mitochondria to the cytoplasmic compartment.

The role of thyroid hormone in testicular development and function

Thyroid hormone is a critical regulator of growth, development, and metabolism in virtually all tissues, and altered thyroid status affects many organs and systems. Although for many years testis has been regarded as a thyroid hormone unresponsive organ, it is now evident that thyroid hormone plays an important role in testicular development and function. A considerable amount of data show that thyroid hormone influences steroidogenesis as well as spermatogenesis. The involvement of tri-iodothyronine (T(3)) in the control of Sertoli cell proliferation and functional maturation is widely accepted, as well as its role in postnatal Leydig cell differentiation and steroidogenesis. The presence of thyroid hormone receptors in testicular cells throughout development and in adulthood implies that T(3) may act directly on these cells to bring about its effects. Several recent studies have employed different methodologies and techniques in an attempt to understand the mechanisms underlying thyroid hormone effects on testicular cells. The current review aims at presenting an updated picture of the recent advances made regarding the role of thyroid hormones in male gonadal function.

Dynamic changes in parameters of redox balance after mild heat stress in aged laying hens (Gallus gallus domesticus)

In order to evaluate the metabolic responses of laying hens induced by high temperature at later laying stage, nine 60-wk-old laying hens (Gallus gallus domesticus) were employed in the present study. The hens were exposed to 32 degrees C for 21 d and blood samples were obtained before and at 1, 7, 14 and 21 d of heat exposure. The reactive oxygen species (ROS) formed in blood during heat exposure were estimated by the ex vivo spin-trapping method. Body temperature and plasma concentrations of glucose, urate, creatine kinase (CK), triiodothyronine (T(3)), thyroxine (T(4)), corticosterone (CORT), thiobarbituric acid reacting substances (TBARS), ferric/reducing antioxidant power (FRAP) and superoxide dismutase (SOD) activity were measured. Plasma levels of glucose, CK and CORT were not significantly influenced by heat exposure at any time point. The circulating concentrations of T(3) were decreased while plasma T(4) levels changed in the opposite way. The formation of ROS was significantly augmented by heat exposure in laying hens though the body temperature was not significantly altered. The enhanced enzymatic and non-enzymatic antioxidant systems acted in concert to alleviate the heat stress evoked oxidative damage.

Hyperthyroidism in the developing rat testis is associated with oxidative stress and hyperphosphorylated vimentin accumulation

Hyperthyroidism was induced in rats and somatic indices and metabolic parameters were analyzed in testis. In addition, the morphological analysis evidenced testes maturation and intense protein synthesis and processing, supporting the enhancement in vimentin synthesis in hyperthyroid testis. Furthermore, vimentin phosphorylation was increased, indicating an accumulation of phosphorylated vimentin associated to the cytoskeleton, which could be a consequence of the extracellular-regulated kinase (ERK) activation regulating the cytoskeleton. Biomarkers of oxidative stress demonstrated an increased basal metabolic rate measured by tissue oxygen consumption, as well as, increased TBARS levels. In addition, the enzymatic and non-enzymatic antioxidant defences appeared to respond according to the augmented oxygen consumption. We observed decreased total glutathione levels, with enhancement of reduced glutathione, whereas most of the antioxidant enzyme activities were induced. Otherwise, superoxide dismutase activity was inhibited. These results support the idea that an increase in mitochondrial ROS generation, underlying cellular oxidative damage, is a side effect of hyperthyroid-induced biochemical changes by which rat testis increase their metabolic capacity.

Myofibrillar protein oxidation and contractile dysfunction in hyperthyroid rat diaphragm

The purpose of the present study was to test the hypothesis that administration of thyroid hormone [3,5,3'-triiodo-L-thyronine (T(3))] could result in oxidation of myofibrillar proteins and, in turn, induce alterations in respiratory muscle function. Daily injection of T(3) for 21 days depressed isometric forces of diaphragm fiber bundles across a range of stimulus frequencies (1, 10, 20, 40, 75, and 100 Hz) (P < 0.05). These reductions in force production were accompanied by a remarkable increment (104%; P < 0.05) in carbonyl groups of myofibrillar proteins. In contrast, T(3) treatment has no effects on the carbonyl content in myosin heavy chain. In additional experiments, we have also tested the efficacy of carvedilol, a nonselective beta(1)- beta(2)-blocker that possesses antioxidative properties. Treatment with carvedilol dramatically improved isometric tetanic force production at stimulus frequencies from 40 to 100 Hz (P < 0.05). Carvedilol also prevented T(3)-induced contractile protein oxidation (P < 0.05). These data suggest that the oxidative modification of myofibrillar proteins may account, at least in part, for an impairment of diaphragm in hyperthyroidism.

Mitochondrial Disorder Aggravated by Propranolol

Although there are indications that beta-blockers affect the skeletal muscle in therapeutic dosages, their influence on mitochondrial disorders is unknown. A 52-year-old woman developed double vision, myalgias, muscle cramps, and hip and thigh muscle stiffness. Clinical neurologic examination revealed ptosis, dysarthria, sore neck muscles, weakness and wasting of the thighs, and generally brisk tendon reflexes. Lactate stress testing was significantly abnormal. Needle electromyography was nonspecifically abnormal and myopathic. Muscle biopsy showed mild myopathic changes, target fibers, and a single COX-negative fiber. Probable mitochondrial disorder was diagnosed. The patient had been on 30 mg of propranolol during 7 years for arterial hypertension. Shortly after discontinuation of the drug, her double vision gradually disappeared, myalgias and muscle cramps gradually resolved, and the patient reported an increase in muscle mass on repeated follow-ups. Long-term administration of propranolol may aggravate a mitochondrial disorder. Discontinuation of propranolol may result in a gradual resolution of these adverse reactions.

Acute heat stress induces oxidative stress in broiler chickens

The stress responses and possible oxidative damage in plasma, liver and heart were investigated in broiler chickens acutely exposed to high temperature. Eighty 5-week old broiler chickens were exposed to 32 degrees C for 6h. The extent of lipid peroxidation, activities of superoxide dismutase and total antioxidant power in plasma, liver and heart tissues were investigated. Meanwhile, the blood metabolites such as glucose, urate, triiodothyronine, thyroxine, corticosterone, ceruloplasmin and creatine kinase were measured before and after 3 and 6h of heat exposure. The results showed that oxidative stress could be induced in 5-week old broiler chickens by acute heat exposure (32 degrees C, 6h). The results suggest that the elevated body temperature can induce the metabolic changes that are involved in the induction of oxidative stress. The liver is more susceptible to oxidative stress than heart during acute heat exposure in broiler chickens. The oxidative stress should be considered as part of the stress response of broiler chickens to heat exposure.

Oxidation of myosin heavy chain and reduction in force production in hyperthyroid rat soleus

We tested the hypothesis that a force reduction in hyperthyroid rat soleus muscle would be associated with oxidative modification in myosin heavy chain (MHC). Daily injection of thyroid hormone [3,5,3'-triiodo-L-thyronine (T3)] for 21 days depressed isometric forces of whole soleus muscle across a range of stimulus frequencies (P < 0.01). In fiber bundles, hyperthyroidism also led to pronounced reductions (P < 0.01) in both K+ - and 4-chloro-m-cresol-induced contracture forces. The degrees of the reductions were similar between these two contractures that were induced by distinct reagents. Treatment with T3 elicited a significant decrease ( approximately 14%; P < 0.05) in the relative content of MHC contained in myofibrillar proteins. The content of carbonyl groups in myofibrillar protein extracts was elevated (P < 0.05) by approximately 50% in T3-treated muscles. Immunoblot analyses on T3-treated muscles showed a greater increase (106%; P < 0.05) of the carbonyl content in MHC than in myofibrillar protein extracts. These data suggest that in hyperthyroidism the decrease in force production of skeletal muscles may stem primarily from failure in myofibrillar protein function resulting from oxidative modification of MHC.

Effects of melatonin on skeletal muscle of rats with experimental hyperthyroidism

The aim of this study was to investigate structural changes that occurred in the skeletal muscle of rats with experimental hyperthyroidism and the effect of melatonin on these changes. Groups of animals were designated as controls, 3,3',5-triiodothyronine (T3) injected and T3 + melatonin injected group. At the end of the study the tissue specimens were harvested and their structure examined. In the skeletal muscle of T3 injected rats a decrease was observed in muscle fiber diameter, splitting of fiber, collections of adipose tissue in perimysium, and gathering of nuclei in central compared to the control. Electron microscopic examination showed that mitochondria were dilated and the I band was less clear. In the T3 + melatonin injected group, the structure of fibers was similar to control. In conclusion, this study showed that T3 injection caused structural changes in the skeletal muscle and that melatonin had a positive effect on these changes.

Effect of altered thyroid state on the in situ mechanical properties of adult cat soleus

To determine the responsiveness of cat hindlimb muscles to thyroid manipulation, adult female cats were made hypothyroid (thyroidectomy plus tapazole treatment), hyperthyroid (synthroid pellets), or maintained euthyroid. After 4 months, the hypothyroid soleus had slower time-to-peak (TPT, 80%) and half-relaxation (HRT) times, whereas the hyperthyroid soleus had faster TPT (20%) and HRT than euthyroid cats. The tension at low stimulation frequencies (5-15 Hz) was higher in hypothyroid and lower in hyperthyroid cats compared to euthyroid cats. Muscle weight, maximum twitch and tetanic (Po) tensions, and maximum rates of shortening (Vmax) were similar across groups. The soleus of hypothyroid cats was more fatigable than normal. The myosin heavy chain (MHC) composition, based on gel electrophoresis, was unaffected by thyroid hormone manipulation. Based on the reaction of monoclonal antibodies for specific MHCs, some fast fibers in the hypothyroid cats coexpressed developmental MHC. These data indicate that 4 months of an altered thyroid state result in changes in the isometric twitch speed properties of the cat soleus, but not the tension-related or isotonic properties. Further, a chronic decrease in thyroid hormone had a greater impact than a chronic increase in thyroid hormone on the mechanical properties of the adult cat soleus.

Generation of protein adducts with malondialdehyde and acetaldehyde in muscles with predominantly type I or type II fibers in rats exposed to ethanol and the acetaldehyde dehydrogenase inhibitor cyanamide

BACKGROUND

Alcoholic myopathy is known to primarily affect type II muscle fibers (glycolytic, fast-twitch, anaerobic), whereas type I fibers (oxidative, slow-twitch, aerobic) are relatively protected.

OBJECTIVE

We investigated whether aldehyde-derived adducts of proteins with malondialdehyde and acetaldehyde are formed in muscle of rats as a result of acute exposure to ethanol and acetaldehyde. The differences between type I muscle, type II muscle, and liver tissue were also assessed.

DESIGN

The formation and distribution of malondialdehyde- and acetaldehyde-protein adducts were studied with immunohistochemistry in soleus (type I) muscle, plantaris (type II) muscle, and liver in 4 groups of rats. The different groups were administered saline (control), cyanamide (an acetaldehyde dehydrogenase inhibitor), ethanol, and cyanamide + ethanol.

RESULTS

Treatment of rats with ethanol and cyanamide + ethanol increased the amount of aldehyde-derived protein adducts in both soleus and plantaris muscle. The greatest responses in malondialdehyde-protein and acetaldehyde-protein adducts were observed in plantaris muscle, in which the effect of alcohol was further potentiated by cyanamide pretreatment. Malondialdehyde- and acetaldehyde-protein adducts were also found in liver specimens from rats treated with ethanol and ethanol + cyanamide; the most abundant amounts were found in rats given cyanamide pretreatment.

CONCLUSIONS

Acute ethanol administration increases protein adducts with malondialdehyde and acetaldehyde, primarily in type II muscle. This may be associated with the increased susceptibility of anaerobic muscle to alcohol toxicity. Higher acetaldehyde concentrations exacerbate adduct formation, especially in type II-predominant muscles. The present findings are relevant to studies on the pathogenesis of alcohol-induced myopathy.

Effects of propylthiouracil, propranolol, and vitamin E on lipid peroxidation and antioxidant status in hyperthyroid patients

OBJECTIVE

The purpose of this study was to examine lipid peroxidation and antioxidant states during hyperthyroidism states and after given different treatments.

DESIGN AND METHODS

We examined 44 hyperthyroid patients and 19 euthyroid healthy controls. Patients were divided into three groups according to the treatment: Propylthiouracil (PTU) group, PTU + propranolol (PRP) group, PTU + PRP + vitamin E (vitE) group.

RESULTS

In the hyperthyroid patients plasma malondialdehyde (MDA) levels were significantly high as compared to the control group (p < 0,001). There was a significant decrease in the MDA levels post-treatment (p < 0.001 in the PTU + PRP group and PTU + PRP + vitE group, p < 0.01 in the PTU group). In the hyperthyroidism, blood reduced glutathione (GSH) levels were lower, erythrocyte superoxide dismutase (SOD) and catalase (CAT) activities were higher than in the control group, but these changes were not significant. Post-treatment in each of the three groups the GSH levels were increased significantly as compared to the pretreatment levels (p < 0.001). There was significant decrease in the SOD activity post treatment (p < 0.01 in all three groups). Post-treatment CAT activity was decreased (p < 0.05 in the PTU group, p < 0.001 in the other two groups). The erythrocyte glutathione peroxidase (Gpx) activity was lower significantly in the hyperthyroidism as compared to the control group (p < 0.001). Post-treatment, in the three groups Gpx activity increased significantly as compared to the pretreatment levels (p < 0.05 in the PTU group, p < 0.001 in the PTU + PRP group and PTU + PRP + vitE group).

CONCLUSION

We considered that giving all three treatments would be useful to the prevention of oxidative stress in the hyperthyroidism states.

Palm vitamin E improves bone metabolism and survival rate in thyrotoxic rats

The effects of vitamin E derived from palm oil on bone turnover in thyrotoxic rats were studied. Palm vitamin E reduced bone resorption to a greater extent than bone formation in thyrotoxic rats, suggesting a net reduction in bone loss. The action of palm vitamin E is probably due to its antioxidant properties. Survival rates were also significantly increased in thyrotoxic rats given palm vitamin E, suggesting the role of free radicals in the overall morbidity and mortality in thyrotoxicosis.

Skeletal muscle function and body composition of patients with hyperthyroidism

The purpose of this study was to determine whether the improvement in muscle performance after treatment of hyperthyroidism is only a result of an increased muscle mass or if it also depends on the improvement of intrinsic contractile function. Nine patients with Graves' disease were evaluated 1) at the time of diagnosis, 2) after 1 wk of monotherapy with propranolol, and 3) after the euthyroid state had been achieved with antithyroid drugs. At each evaluation the patients were submitted, on the dominant side, to anthropometric measurements and to skeletal muscle function tests to determine the maximal static voluntary contraction (MAX) and endurance (END); "endurance" is defined as the time limit at maintaining 30% of MAX. Three movements were tested: hip flexion, ankle dorsiflexion, and handgrip. Body weight changed from 53.4 +/- 3.2 to 58.2 +/- 2.9 kg (P = 0.004) and the sum of skinfold-corrected limb circumferences changed from 90.7 +/- 3.1 to 94.4 +/- 3.1 cm (P = 0.017). MAX and END of all movements increased at the end of the study even if adjusted for the sum of skinfold-corrected limb circumferences: Hip flexion: MAX 20.60 +/- 3.32 to 31.26 +/- 5.07 g.cm-1, END 0.43 +/- 0.18 to 1.18 +/- 0.42 kg.s-1.cm-1. Ankle dorsiflexion: MAX 12.34 +/- 1.97 to 26.88 +/- 2.46 g.cm-1, END 0.97 +/- 0.28 to 2.50 +/- 0.58 kg.s-1.cm-1; Handgrip: MAX: 2.20 +/- 0.23 to 2.9 +/- 0.2 g.cm-1, END 0.13 +/- 0.01 to 0.20 +/- 0.02 kg.s-1.cm-1. In conclusion, improved muscle performance resulting from the treatment of hyperthyroidism is a consequence of an enhanced intrinsic muscle function as well as a greater muscle mass.