Sulfated rhamnoglucan heteropolysaccharide of Spirulina platensis attenuates methimazole-induced hypothyroidism in rats

Ingestion of polysaccharide from microalga-derived 'super food' Spirulina as a dietary supplement can benefit human health against several chronic disorders. A sulfated heteropolysaccharide with [-> 4)-alpha-GlcAp-(1 -> 2)-alpha-Rhap-(1 ->] as key structural moiety and [(3 -> 1)-6-O-SO3-beta-Glcp] (SPP-3) as lateral branch, was obtained from microalga Spirulina platensis. SPP-3 exhibited potential anti-thyroid activities by reducing serum cardiovascular risk indices and protein oxidation and nitration in vital tissues of methimazole (MTZ)-induced hypothyroid rats. Upon treatment with SPP-3 (50 mg/kg BW), hypothyroid biomarkers, such as thyroid stimulating hormone (TSH, 5 mu IU mL(-1)), triiodothyronine (T3, 4.55 ng dL(-1)) and thyroxine (T4, 4.18 mu U dL(-1)) were significantly recovered in comparison with MTZ-induced hypothyroid rats (7.74 mu IU mL(-1), 2 ng dL(-1), 2.49 mu IU mL(-1), respectively). The level of serum cardiovascular risk indices (CV-I and II) of diseased rats was significantly reduced following the administration of SPP-3 (lesser than 12 %, p < 0.05) compared to the hypothyroid-induced group of animals (18-21 %). SPP-3 substantially downregulated protein nitration (46-49 %) and oxidation (37-39 %) levels in vital tissues than those exhibited by diseased control (90 and 65 % for protein nitration; 81 and 52 % of protein oxidation). Therefore, the microalgal rhamnoglucan (SPP-3) might be utilized as a promising naturally derived food-based carbohydrate biopolymer for health benefits against hypothyroid disorders.