V Pitsiavas, P Smerdely and SC Boyages
Amiodarone (AMD) is a powerful anti-arrhythmic drug used for the treatment of a wide variety of cardiac arrhythmias and its most striking feature is its high iodine content. Thyroid dysfunction is a limiting side-effect of the drug and both AMD-induced hypothyroidism (AIH) and AMD-induced thyrotoxicosis (AIT) are reported. To examine the hypothesis that altered bioavailability of iodine is a contributing event in the pathogenesis of AIH, we compared the effects of AMD and inorganic iodine in vitro on events involved in the process of thyroid autoregulation. FRTL-5 cells and JP26 CHO cells (transfected with the human TSH receptor) were exposed to AMD or NaI in the presence of TSH, and cAMP production was measured as an indicator of cellular function. Forskolin and cholera toxin were also used to determine the possible target sites of AMD and iodide. Our results indicated that there was a difference between the effects of AMD versus those of physiological doses of iodide. The inhibitory effects of AMD occurred at lower concentrations of iodide than those seen in the NaI-treated cells. The effects of AMD were irreversible indicating a possible persistence of the Wolff-Chaikoff effect due to a constant high intracellular iodide level. The inhibitory effects of AMD (also seen at supraphysiological doses of iodide) were partially overcome by forskolin but not by cholera toxin indicating an effect on TSH receptor interactions with the other signal transduction elements such as G proteins and adenylate cyclase. The persistence of the Wolff-Chaikoff effect through loss of autoregulation may be a mechanism of the observed hypothyroidism in some patients taking AMD. The combined effects of the constant release of iodide together with the drug toxicity may be the mechanism for the observed effects.
S Brahmbhatt, RM Brahmbhatt and SC Boyages
OBJECTIVES: (i) To assess the severity of iodine deficiency disorders (IDD), (ii) to determine the aetiology of IDD in Gujarat, (iii) to identify the best prevalence indicator of IDD, and (iv) to compare thyroid volume (TV) results with the WHO International reference. METHODS: Five hundred and thirty schoolchildren (6-15 years) were studied from two districts (Baroda and Dang) and data were collected on dietary habits and parameters such as height, weight, thyroid size by palpation and ultrasonography, urinary iodine (UI), and blood thyroid stimulating hormone (TSH). Drinking water was analyzed for iodine content and food articles for goitrogens. RESULTS: In Gujarat children median UI (interquartile range)=56 (30-96)microg/l, mean TSH=1.71 +/- 2.10mU/l, goiter by palpatio n = 30%, and median TV = 27.8 (23-35)ml. Females had lower median UI (48 (27-82) microg/l) and higher mean TSH levels (2.0 +/- 2.5mU/l) than males. Applying the WHO ultrasonography reference to Gujarat children resulted in an enlarged TV-for-body surface area in almost 100% of subjects. Ninety-nine percent of females and 95% of males had enlarged TV-for-age. Three to eight times larger TV were seen in all subjects as compared with European children. Dang children were severely malnourished. Flavonoids like vitexin, glucosyl vitexin and apigenin were detected in pearl millet. Apigenin was never identified in pearl millet. Dang district water was lacking in iodine content. CONCLUSIONS: IDD is a severe public health problem in Gujarat. Baroda district is a new pocket of IDD. High amounts of dietary flavonoids in Baroda and Dang districts, and lack of iodine in Dang water, account for IDD. TV measurement by ultrasound is the best prevalence indicator of IDD.
SR Brahmbhatt, RM Brahmbhatt and SC Boyages
OBJECTIVE: To assess the severity of protein energy malnutrition (PEM) in iodine deficient subjects and to assess the impact of PEM on thyroid size. METHODS: 1002 subjects (530 school-aged children and 472 adults) were assessed for PEM by direct anthropometric measurements of height, weight, triceps skinfold (TSF) thickness, mid upper arm circumference (MUAC) and thigh circumference (TC), and derived indices of body surface area (BSA), body mass index (BMI), and Z-scores for weight-for-age (WAZ), height-for-age (HAZ), and weight-for-height (WHZ). Severity of PEM was based on the World Health Organization (WHO) criteria and the threshold on the Waterlow classification. Thyroid size was measured by ultrasonography to determine the thyroid volume (TV). Linear regression analysis was performed between TV and anthropometric parameters. RESULTS: Children had severe PEM as evident from the WHO percentage prevalence of stunting (HAZ<-2SD)=64% (where <-2SD is the Z-score deficit), wasting (WHZ<-2SD)=43%, underweight (WAZ<-2SD)=82% and BMI<16 kg/m=90%. Waterlow classification showed that children were either stunted or wasted, or stunted and wasted, or stunted and obese. Nearly 100% (529/530) of the children had goiter as evidenced from enlarged TV-for-BSA when compared with the WHO reference. There was a weak but statistically significant (P<0.05) positive correlation between TV and BSA, weight, height, MUAC, TC and HAZ but a negative correlation between TV and WHZ, BMI and TSF (r=-0.1-0.2). Adults had PEM as evident from BMI<18.5 kg/m in 54% subjects. Median MUAC=22.7 cm reveals prolonged severe PEM. Eighty-two percent had enlarged TV (>20 ml). There was a significant (P=0.01) negative correlation between TV and MUAC. CONCLUSIONS: (i) The severity of acute (wasting) and chronic (stunting) PEM is very high in Gujarati children. They are stunted or wasted, or stunted and wasted, or stunted and obese. Gujarati adults are thin with low protein and fat reserves. (ii) Anthropometric parameters showed a significant (P<0.001) correlation (r=0.1-0.2) with thyroid size. (iii) Higher prevalence of goiter may be due to macro-nutrient malnutrition (PEM) in the face of micro-nutrient malnutrition (iodine deficiency disorders, IDD).
V Pitsiavas, P Smerdely, M Li and SC Boyages
Amiodarone (AMD)-induced toxicity can be a life-threatening complication which limits the use of amiodarone as an anti-arrhythmic agent. The aim of the present study was to determine the nature of AMD toxicity by comparing ultrastructural changes induced by AMD and equivalent amounts of iodide in two animal models, the Wistar and the autoimmune BB/W rat. Rats were divided into control (water), AMD- (30 mg AMD/kg) or iodide-treated (10 mg/kg) groups. Thyroids were removed at 15 weeks and processed for electron microscopy. We found that AMD induced specific ultrastructural changes of thyroid cytotoxicity in both rat models, which were distinct compared with changes induced by excess iodide alone. Specific changes included marked distortion of thyroid architecture, evidence of necrosis and apoptosis, inclusion bodies, lipofuscinogenesis and markedly dilated endoplasmic reticulum (ER). Our data indicate that AMD is directly cytotoxic to the thyroid an effect mediated by disruption of subcellular organelle function. ER dilatation is suggestive that AMD cytotoxicity may be mediated through disruption of the protein sorting pathways leading to a drug-induced form of ER storage disease. The predilection of the thyroid to AMD may be explained by the additive effects of excess iodine and AMD drug toxicity on protein sorting pathways.