Chemical and biological studies of Siddha medicinal plants

Siddha is a traditional system of medicine being practiced in the southern part of India. Siddha medicines are predominantly plant based, usually containing polyherbal combinations. Following the establishment of a collaborative research partnership with a Siddha practitioner, Dr R. Velmurugan, information on some medicinal plants that he identified to be effective in treating cancer, pain and swelling were provided. The overall aim of this study was to isolate and identify biologically active molecules from some of these plants. This study consisted of reviewing the literature on the Siddha medicinal plants identified by Dr Velmurugan, biological studies and isolation and characterisation of bioactive constituents from a selection of these plants.A broad literature search was undertaken on these plants to identify those plants that have not been well studied phytochemically and/or biologically, thus having the potential for further investigations. This led to the selection of nine plants for biological screening studies.Antiproliferative and antiinflammatory studies were employed for the evaluation of the biological activities. The antiproliferative screenings were performed against SKNMC (neuroepithelioma), MCF 7 (Breast Cancer) and MRC 5 (normal) cell lines using the MTT assay. Antiinflammatory studies were carried out by using cyclooxygenase inhibitory assays. Significant antiproliferative activity of Cardiospermum halicacabum and Caralluma fimbriata was identified in the MTT assay. Both these plants also exhibited potent COX 1 and COX 2 inhibitory activity.Inhibition studies with the enzyme indoleamine 2,3-dioxygenase (IDO), which is involved in cancers and inflammatory diseases, were also conducted on all plants. IDO inhibitory studies revealed the IDO inhibitory activity of Marsdenia tinctoria, Evolvulus alsinoides and C. halicacabum.Based on the initial antiproliferative screening results, C. halicacabum and C. fimbriata were selected for further biological and chemical investigations. The bioassay guided isolation of the water partition of the ethanolic extract of the leaves of C. halicacabum led to the isolation of five compounds: quercetin 3-O-β-D-rutinoside, apigenin 7-O-β-Dvii glucoside, chrysoeriol, luteolin and scutellarein. The antiproliferative activities of the isolated compounds were evaluated against the SKNMC, MCF 7 and MRC 5 cell lines. Chrysoeriol and scutellarein exhibited the highest antiproliferative activity. The other three molecules also demonstrated antiproliferative activity. A comparison of the activity exhibited by the compounds against the MCF 7 and SKNMC cell lines indicated some selectivity of these molecules for the breast cancer cell line. This is the first report of apigenin 7-O-β-D-glucoside and scutellarein from C. halicacabum.Bioassay guided studies on the ethyl acetate fraction of C. fimbriata led to the isolation of cleomiscosin A, N-(p-trans-coumaroyl)tyramine, aristolochic acid 1 and aristolactam1a-N-β-D-glucoside . This is the first report of all these molecules from this plant and the first report of aristolochic acid 1 and aristolactam1a-N-β-D-glucoside from the Ascelpedeaceae family. The compounds were tested for antiproliferative activities. Aristolochic acid 1 demonstrated the most potent activity. Cleomiscosin A and N-(ptrans-coumaroyl)tyramine also demonstrated antiproliferative activity and aristolactam1a-N-β-D-glucoside was found to be less active. No remarkable selectivity in activity was observed with these compounds.This study also identified the IDO inhibitory activity of N-(p-trans-coumaroyl)tyramine for the first time.The biological activities of the plant extracts and the isolated molecules were consistent with the use of these plants by Dr Velmurugan, thus providing strong support for their use in the Siddha system of medicine for treatment of cancers.