The anti-inflammatory effects of Indonesian and Japanese bitter melon (Momordica charantia L.) fruit extracts on interleukin-1β-treated hepatocytes

Abstract

Background: Bitter melon, Momordica charantia L. (Cucurbitaceae), grows in tropical to temperate regions in Asia, including Indonesia and Japan. Bitter melon contains triterpenoids, steroidal glycosides, flavonoids, and alkaloids. The green immature fruit of bitter melon is a popular vegetable in Indonesia and Japan and has been used as a traditional Indonesian medicine (Jamu) to treat microbial infections and diabetes mellitus. However, there are currently few reports about the pharmacological effects of the constituents of bitter melon.

Objective: To compare the effects of Indonesian and Japanese bitter melon, the production of pro-inflammatory mediators, such as nitric oxide (NO) and pro-inflammatory cytokines, was monitored.

Methods: Immature fruits of bitter melons collected from Indonesia and Japan were lyophilized and extracted with methanol. The resultant extracts were fractionated by hydrophobicity into ethyl acetate-soluble (A), n-butanol-soluble (B), and water-soluble (C) fractions. Primary cultured hepatocytes prepared from rat liver were treated with interleukin-1β (IL-1β) and each extract or fraction. Nitrite in the medium was measured, and the half-maximal inhibitory concentration (IC₅₀) value was determined. Lactate dehydrogenase activity in the medium was measured to monitor cytotoxicity. The expression of inducible nitric oxide synthase (iNOS) was detected by western blot analysis. The mRNA levels were measured by reverse transcription-polymerase chain reaction. 

Results: Indonesian and Japanese bitter melon extracts (BMEs) suppressed NO production by IL-1β-treated hepatocytes without showing cytotoxicity. The IC₅₀ values of the BMEs were 86 μg/mL (Indonesian) and 171 μg/mL (Japanese). Both BMEs suppressed iNOS protein expression. Fractions A and B of both BMEs suppressed NO production. The IC₅₀ values of the Indonesian BME fractions A and B were comparable to those of Japanese BME. Fraction A of both BMEs decreased the levels of iNOS protein and mRNA, as well as those of pro-inflammatory cytokine mRNAs. Fraction C of both BMEs did not affect NO production.

Conclusion: The ethyl acetate-soluble fraction (A) of Indonesian and Japanese BMEs exhibited a comparable ability to suppress the induction of the iNOS and pro-inflammatory cytokine genes. These data suggest that hydrophobic constituents in fraction A, such as cucurbitane-type triterpenoids, may be responsible for the observed anti-inflammatory effects of bitter melon from Indonesia and Japan.

Keywords: Momordica charantia, nitric oxide, inflammation, Jamu, Goya.