Gastrointestinal enhancement of MRI with melanin derived from tea leaves (Thea sinensis Linn.).

Melanin was extracted from tea leaves (Thea sinensis Linn.) for the first time. Characterization of melanin proved similarity of the original compound to standard melanin. The Langmuir adsorption isotherms for gadolinium (Gd) binding were obtained using melanin. Melanin-Gd preparation demonstrated low acute toxicity. LD(50) for this preparation was in a range of 1250-1500 mg/kg in mice. Magnetic Resonance Imaging (MRI) properties of melanin itself and melanin-Gd complexes have been estimated. Gd free melanin fractions possess slighter relaxivity compared with its complexes. The relaxivity of lower molecular weight fraction was two times higher than relaxivity of Gd(DTPA) standard. Postcontrast images demonstrate that oral administration of melanin complexes in concentration 0.1 mM provides essential enhancement to longitudinal relaxation times (T(1))-weighted spin echo image. The required contrast and delineation of the stomach wall demonstrated uniform enhancement of MRI with proposed melanin complex.