Anti-Thyroid Activity of Myrica Salicifolia (Bayberry) Methanol Root Extract in Levothyroxine-Induced Hyperthyroidism in Male Wistar Albino Rats

Abstract

Hyperthyroidism is defined as the excess production and release of thyroid hormones by the thyroid gland resulting in inappropriately high serum levels. The most common causes include diffuse toxic goiter, toxic multinodular goiter and toxic adenoma. Integration of traditional medicine in the management and treatment of hyperthyroidism has been recommended by the World Health Organization since 1978. Traditional medicine strategy by WHO aims to support member states in developing proactive policies and implementing action plans that will strengthen the role traditional medicine plays in keeping populations healthy. Myrica salicifolia is a shrub of 1 m in height but can grow into a tree of up to 20 m, is usually aromatic and resinous. It belongs to the family Myricaceae found mostly in temperate to subtropical regions of the world. The aim of this study was to determine Antithyroid activity of Myrica salicifolia (bayberry) methanol root extract (MSRE) in levothyroxine-induced hyperthyroidism in male wistar albino rats. The study adopted an experimental study design and the study site was the SAFARI animal House of JKUAT. Forty-five male wistar albino rats, acquired from the SAFARI animal house were randomly divided into five groups. The first group served as the normal control and received distilled water only. At the onset of the experiment, rats in 2nd, 3rd, 4th and 5th groups were treated with levothyroxine in order to induce hyperthyroidism. Three rats from Group 2 were sacrificed on day 14 and blood serum processed for immediate confirmation of induction of hyperthyroidism through chemiluminescence assay test for TSH and T3. Subsequently, from day 15 of experiment GP3 rats were treated with propylthiouracil, GP4 treated with low dose of MSRE (200mg/kg) and GP5 treated with high dose MSRE (400mg/kg) for a period of 21 days post-induction. During the course of the experiment the rats were closely observed daily for any behavioral and clinical changes and body weights recorded weekly. Serial sacrifice of three animals per group was done on days 21 and 28 and experiment terminated on day 35. Prior to euthanization, using CO2 gas, the rats were fasted for 12 hours. Fresh blood samples were obtained through intracardiac puncture for determining TSH and T3 levels and the thyroid gland harvested for microscopic examination. Prior to the animal experiment, phytochemical screening of the Myrica salicifolia root extract was done and it was found to contain alkaloids, flavonoids sterols, phenolics and tannins. Acute oral toxicity tests of the extract on LT4 induced hyperthyroid rats were also carried out at different doses of extract, from 10mg/kg to 5000mg/kg body weight. No mortality nor significant behavioral changes were recorded except for some overcrowding and reduced activity for rats administered with 5000mg/kg body weight of the root extract. From the current study the LD50 of M. salicifolia root extract was found to be > 5000 mg/kg body weight. Data analysis for hormone levels was undertaken using Statistical Package for Social Sciences (SPSS) -Version 21.0). Median (Interquartile range-IQR) and Kruskal Wallis test were employed in the analysis and p-value < 0.05 was considered statistically significant. Levothyroxine administration altered thyroid function by significantly decreasing serum levels of TSH (p=0.0162) and significantly increasing T3 (p= 0.0081) serum levels in group 2 rats sacrificed on day 14, confirming successful induction of hyperthyroidism. Treatment with the standard drug, PTU, reversed the trend by significantly increasing serum TSH levels on days 21 (p=0.0022), day 28 (p=0.0055) and day 35 (p=0.0175) and decreasing T3 serum levels significantly on days 28 (p=0.0066) and 35 (p=0.0016) post-treatment. Following treatment with low dose (200mg/kg body weight) MSRE (GP4), there was no significant change in hormone levels (p>0.05). Treatment with high dose MSRE (GP5) led to significant decrease of T3 serum levels on day 28 (p=0.0235) and day 35 (p=0.0398) accompanied by non-significant increase of TSH. Comparing serum levels of TSH and T3 between groups treated with PTU and high dose MSRE did not show any significant difference over the treatment period. Histological analysis of thyroid gland in normal control rats (GP1) showed normal cuboidal epithelial cells and follicles full of colloidal material. Histopathology of thyroid gland showed marked changes in the follicular cells of the treated male wistar albino rats, as compared to the positive control and normal control groups. Thyroid follicles in hyperthyroid but untreated rats (GP2) were atrophied and contained scanty colloid material. Histological examination of thyroid glands from formerly hyperthyroid rats treated with PTU (GP3) and MSRE showed normal cuboidal epithelium and follicles containing colloid. This study concludes that MSRE has shown anti-thyroid activity especially at high doses of 400mg/kg. The MSRE at high doses has comparable activity to the standard drug (PTU) in the treatment of hyperthyroidism.