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. 2019 Jan 7;19(1):7.
doi: 10.1186/s12906-018-2413-4.

Antioxidants and α-glucosidase inhibitors from Neptunia oleracea fractions using 1H NMR-based metabolomics approach and UHPLC-MS/MS analysis

Soo Yee Lee  1 , Ahmed Mediani  2 , Intan Safinar Ismail  1   3 , Maulidiani  1 , Faridah Abas  4   5
Affiliations

Antioxidants and α-glucosidase inhibitors from Neptunia oleracea fractions using 1H NMR-based metabolomics approach and UHPLC-MS/MS analysis

Soo Yee Lee et al. BMC Complement Altern Med. .

Abstract

Background: Neptunia oleracea is a plant cultivated as vegetable in Southeast Asia. Previous works have revealed the potential of this plant as a source of natural antioxidants and α-glucosidase inhibitors. Continuing our interest on this plant, the present work is focused in identification of the bioactive compounds from different polarity fractions of N. oleracea, namely hexane (HF), chloroform (CF), ethyl acetate (EF) and methanol (MF).

Methods: The N. oleracea fractions were obtained using solid phase extraction (SPE). A metabolomics approach that coupled the use of proton nuclear magnetic resonance (1H NMR) with multivariate data analysis (MVDA) was applied to distinguish the metabolite variations among the N. oleracea fractions, as well as to assess the correlation between metabolite variation and the studied bioactivities (DPPH free radical scavenging and α-glucosidase inhibitory activities). The bioactive fractions were then subjected to ultra-high performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) analysis to profile and identify the potential bioactive constituents.

Results: The principal component analysis (PCA) discriminated EF and MF from the other fractions with the higher distributions of phenolics. Partial least squares (PLS) analysis revealed a strong correlation between the phenolics and the studied bioactivities in the EF and the MF. The UHPLC-MS/MS profiling of EF and MF had tentatively identified the phenolics present. Together with some non-phenolic metabolites, a total of 37 metabolites were tentatively assigned.

Conclusions: The findings of this work supported that N. oleracea is a rich source of phenolics that can be potential antioxidants and α-glucosidase inhibitors for the management of diabetes. To our knowledge, this study is the first report on the metabolite-bioactivity correlation and UHPLC-MS/MS analysis of N. oleracea fractions.

Keywords: 1H NMR-based metabolomics; Diabetes; Neptunia oleracea fractions; Phenolics; UHPLC-MS/MS.

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The authors declare that they have no competing interests.

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Figures

Fig. 1
Fig. 1
The representative 1H NMR spectra of HF (a), CF (b), EF (c) and MF (d) of N. oleracea. 1, fatty acids; 2, alanine; 3, leucine; 4, valine; 5, oleanolic acid; 6, phytosterol; 7, α-glucose; 8, β-glucose; 9, fructose; 10, quercetin derivatives; 11, kaempferol derivatives; 12, myricetin derivatives; 13, apigenin derivatives; 14, catechin; 15, gallic acid; 16, 3,4-O-dimethylgallic acid; 17, caffeic acid
Fig. 2
Fig. 2
The PCA score (a) and loading (b) plots of different fractions of N. oleracea. HF, hexane fraction; CF, chloroform fraction; EF, ethyl acetate fraction; MF, methanol fraction; Der, derivatives; DMGA, 3,4-O-dimethylgallic acid
Fig. 3
Fig. 3
Total phenolic content (a), DPPH free radical scavenging (b) and α-glucosidase inhibition (c) of different fractions of N. oleracea. The values are the means ± standard deviations. Means with different letters are significantly different (P < 0.05). HF, hexane fraction; CF, chloroform fraction; EF, ethyl acetate fraction; MF, methanol fraction
Fig. 4
Fig. 4
Permutation plots of PLS model describing the R2 and Q2 Y-intercepts for DPPH free radical scavenging (a) and α-glucosidase inhibitory (b) activities of N. oleracea fractions
Fig. 5
Fig. 5
The PLS biplot of different fractions of N. oleracea. HF, hexane fraction; CF, chloroform fraction; EF, ethyl acetate fraction; MF, methanol fraction; 1, phytosterol; 2, fatty acids; 3, alanine; 4, leucine; 5, valine; 6, α-glucose; 7, β-glucose; 8, fructose; 9, oleanolic acid; 10, quercetin derivatives; 11, kaempferol derivatives; 12, apigenin derivatives; 13, myricetin derivatives; 14, gallic acid; 15, 3,4-O-dimethylgallic acid; 16, caffeic acid; 17, catechin
Fig. 6
Fig. 6
The overall Pearson’s correlation between the metabolites and bioactivities of different fractions of N. oleracea. The value of the correlation coefficients is represented by the blue and red colour intensities. 1, phytosterol; 2, fatty acids; 3, alanine; 4, leucine; 5, valine; 6, α-glucose; 7, β-glucose; 8, fructose; 9, oleanolic acid; 10, quercetin derivatives; 11, kaempferol derivatives; 12,apigenin derivatives; 13, myricetin derivatives; 14, gallic acid; 15, 3,4-O-dimethylgallic acid; 16, caffeic acid; 17, catechin
Fig. 7
Fig. 7
The total ion chromatogram of EF (a) and MF (b)
See this image and copyright information in PMC

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