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Title: A phytochemical and pharmacological investigation of Momordica charantia Linn. fruit with respect to its reputed anti-diabetic properties
Author: Lau, Clara Bik-San
ISNI:       0000 0001 3605 4957
Awarding Body: University of London
Current Institution: King's College London (University of London)
Date of Award: 1998
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Plants have been used traditionally for the treatment of diabetes mellitus all over the world. One such example is the bitter-tasting unripe fruit of Momordica charantia Linn. (Cucurbitaceae), commonly known as karela. Numerous studies in humans, animals and in vitro models have demonstrated a potential beneficial effect of karela juice or extracts in diabetes. However, the mode of action and active components of karela have not been satisfactorily explained. The present study aimed to use a systematic, relevant approach (bioassay-guided fractionation) to isolate and identify orally active anti-diabetic phytochemicals in karela, and to elucidate its mode of action. Our results showed that karela from different geographical origins varied in both their physical appearance and chemical constituents. Two varieties (Thai and Kenyan) of karela juice exhibited anti-hyperglycaemic (significant improvement in oral glucose tolerance) but not hypoglycaemic (no effect on basal glycaemia) activities in streptozotocin-induced non-insulin-dependent diabetic (NIDD) rats. Thai karela, being more potent, was studied further. We observed for the first time in vivo insulin secretagogue activity by karela juice. The water extract of karela juice significantly improved oral glucose tolerance but not intraperitoneal or intravenous glucose tolerance, implying that it inhibits glucose absorption from the gut or influences glucose sensitive gut hormones. The hexane extract improved oral and intraperitgneal but not intravenous glucose tolerance suggesting that it may possess a hepatic insulin sensitising effect, possibly in addition to an effect on the gut. This extract also inhibited in vitro intestinal glucose absorption in a brush border membrane vesicle model. Bioassay-guided fractionation of the hexane extract led to the isolation and identification of 3 compounds: 5,25-stigmastadien-3-ol (approx. 0.15%w/w yield), momordicine I (0.05%w/w) and ß-sitosterol. Both 5,25-stigmastadienol and ßsitosterol were shown to improve oral glucose tolerance at doses of 4.6mg/kg and 3.1mg/kg respectively in NIDD rats. Momordicine I was not tested. We concluded that karela is most likely to contain more than a single anti-diabetic component and it exhibits its anti-hyperglycaemic activity via a combination of modes of action
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available