Vivekanandarajah, Saravanan; (2018) Plants used to treat diabetes in Sri Lankan Siddha Medicine. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

In recent decades diabetes, most notably type 2, has become a considerable health problem in countries like Sri Lanka. Siddha Medicine is one of the four traditional medicines practised in Sri Lanka. α-Glucosidase inhibitors are one of the drugs types currently used to treat type 2 diabetes. However, they cause adverse side effects. The aims of this project are to identify, document, and make publicly available the plants historically and currently utilised to treat diabetes in Sri Lankan Siddha Medicine and identify one or more compounds capable of inhibiting α-glucosidase from the various plants studied. Historical documents used as Siddha Medicine degree textbooks in Sri Lankan universities were employed to obtain details on the plant species historically utilised. Apart from this, an ethnobotanical survey was carried out in the Eastern Province of Sri Lanka to identify the plant species currently used by Siddha empirical healers. Based on both the information from the historical documents and survey as well as the elimination of globally distributed and very well studied plant species, Achyranthes aspera, Coccinia grandis, Ipomoea aquatica, Mukia maderaspatana, and Artocarpus heterophyllus were selected for further study. The α-glucosidase inhibition assay was used to test inhibitory activity and Nuclear Magnetic Resonance spectroscopy was employed for metabolite profiling. In addition, Orthogonal Partial Least Square - Discriminant Analysis was employed to identify the compounds that showed α-glucosidase inhibition. Overall 171 species in 73 families were identified from the historical documents. Among them, Senna auriculata had been the most frequently cited species and the largest number of taxa was from the Fabaceae. Consultations with 27 Siddha empirical healers revealed 88 species from 46 families are currently used, while Syzygium cumini was the most frequently reported species. Remarkably, one-third of the currently used species was not listed in the historical documents. Again, Fabaceae yielded the largest number of species applied. The literature review of the documented plant species revealed that the majority of the species had in vivo antidiabetic evidence and the most number of studies were conducted in Type 1 diabetes models. The methanol extract of mature A. heterophyllus leaf exhibited the highest α-glucosidase inhibitory activity among the various extracts tested. Additionally, 38 samples of mature A. heterophyllus leaves had a range of IC50 values from 7.56 to 185.03 µg/ml. There was a correlation observed between the α-glucosidase inhibitory activity and the climatic conditions of the region from which the plant specimens used to prepare the extract was collected and the phytochemical composition. Metabolite profiling identified that Artoheterophyllin B might be the α-glucosidase inhibitory compound found in the mature A. heterophyllus leaves. Hence, further phytochemical and pharmacological studies should be carried out to confirm this. This work created the foundation for more efficient studies of antidiabetic Sri Lankan SM preparations and the plants utilised in the future.

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