Studies on the antioxidant activity and immunomodulatory properties of black tea

Abstract

The effect of black tea ingestion of serum antioxidant capacity was investigated in Wistar rats. Serum total radical trapping antioxidant parameter (TRAP) values increased two hours after the ingestion of a tea extract and remained elevated after four hours and decreased to baseline level after eight hours, indicating that black tea components are absorbed through the digestive tract and they have antioxidant activity in vivo.

Large amounts of reactive oxygen species and free radicals are produced during the inflammatory response. These oxidant species enhance the production of cytokines, the mediators of the inflammatory response. Synthetic antioxidants are known to alter the inflammatory response by their action on reactive oxygen species and free radicals. Therefore the effect of black tea components on inflammatory response induced by endotoxin (lipopolysaccharide from E. coli strain) was studied in Wistar rats. When the antioxidant defences of animals were compromised by feeding a vitamin E deficient diet plasma concentrations of the cytokine interleukin-6 and caeruloplasmin were decreased and liver glutathione concentration increased indicating the antioxidant activity of black tea components during inflammatory response. Paradoxically black tea solids (5g/kg diet) increased the number of neutrophils and myeloperoxidase activity in lung after endotoxin treatment. This may be due to increased recruitment of neutrophils to the lung by increased secretion of neutrophil chemotactic factor by alveolar macrophages under the influence of components of black tea during inflammatory response. Thus black tea solids may have two important properties which modulate the action of the immune system. Firstly in modifying the extent of the inflammatory response when antioxidant defences are compromised and secondly by enhancing neutrophil recruitment to lung when defences are normal.

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