Immunochemical Identification of Immunoreactive Ghrelin in Tea Plant, Camellia sinensis (L) O. Kuntze

Ghrelin was originally described as a growth hormone (GH)-releasing and appetite stimulating hormone in mammals, which is highly conserved and extensively expressed in all eukaryotic organisms investigated. Ghrelin is a natural ligand of the growth hormone secretagogue-receptor, and functions primarily as a GH-releasing hormone and an orexigen, as well as having several other biological actions. Although ghrelin has been well characterized in mammalian systems, the most recent investigations demonstrated that plants have ghrelin immunoreactivity. The aim in this study is to determine ghrelin-like immunoreactive substances in fresh vegetative tissue of tea plant [Camellia sinensis (L.) O. Kuntze (Theaceae)]. Total protein was extracted from the plant samples by using trichloroacetic acid/acetone precipitation. Ghrelin-like immunoreactive substances in the tea plant extracts were investigated with indirect enzyme-linked immunosorbent assay method. From the tea plant samples human-ghrelin-like immunoreactive substances were isolated and characterized using tricine-sodium dodecyl sulfate–polyacrylamide gel electrophoresis and immunoblotting techniques. The ghrelin immunoreactivity of tea extract and human serum were found to be 1.94 ± 0.27 and 0.31 ± 0.012 ng/mg protein, respectively. As a result, in fresh vegetative tissues of tea a single ghrelin-like protein band with a molecular mass of ~13 kDa was observed using tricine-SDS-PAGE and western blotting. This study reflects the importance of ghrelin in living organisms, and speculates the ghrelin-like bioactive peptides derived from plants may play a role in the regulation of appetite and body weight control.