Phytochemistry

Volume 106, October 2014, Pages 104–115

What the devil is in your phytomedicine? Exploring species substitution in Harpagophytum through chemometric modeling of ¹H-NMR and UHPLC-MS datasets

• Nontobeko P. Mncwangi^a,
• Alvaro M. Viljoen^{a, b, ,} ,
• Jianping Zhao^c,
• Ilze Vermaak^a,
• Wei Chen^a,
• Ikhlas Khan^{c, d}

doi:10.1016/j.phytochem.2014.06.012

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Highlights

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Harpagophytum procumbens and H. zeyheri are currently used interchangeably.

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UHPLC-MS analysis shows that harpagoside content is higher in H. procumbens (0.17–4.37%) than in H. zeyheri (0.00–3.07%).

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PCA and OPLS-DA analysis revealed cluster formation based on species.

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Biomarkers (retention time-mass/charge ratio pairs) were identified using OPLS-DA.

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Harpagophytum procumbens and H. zeyheri are not chemically equivalent.

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Abstract

Harpagophytum procumbens (Pedaliaceae) and its close taxonomical ally Harpagophytum zeyheri, indigenous to southern Africa, are being harvested for exportation to Europe where phytomedicines are developed to treat inflammation-related disorders. The phytochemical variation within and between natural populations of H. procumbens (n = 241) and H. zeyheri (n = 107) was explored using proton nuclear magnetic resonance (¹H-NMR) and ultra-high performance liquid chromatography coupled to mass spectrometry (UHPLC-MS) in combination with multivariate data analysis methods. The UHPLC-MS results revealed significant variation in the harpagoside content: H. procumbens (0.17–4.37%); H. zeyheri (0.00–3.07%). Only 41% of the H. procumbens samples and 17% of the H. zeyheri samples met the pharmacopoeial specification of ⩾1.2%. Both principal component analysis (PCA) and orthogonal projections to latent structures discriminant analysis (OPLS-DA) indicated separation based on species (UHPLC-MS data OPLS-DA model statistics: R²X = 0.258, R²Y (cum) = 0.957 and Q²(cum) = 0.934; ¹H-NMR data OPLS-DA model statistics: R²X = 0.830, R²Y = 0.865 (cum) and Q²(cum) = 0.829). It was concluded that two species are not chemically equivalent and should not be used interchangeably.

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Graphical abstract

The results showed that Harpagophytum procumbens and H. zeyheri are not chemically equivalent and therefore should not be used interchangeably as a source of Devil’s Claw as proposed in the pharmacopoeias.

Keywords

• Harpagophytum procumbens;
• Harpagophytum zeyheri;
• Pedaliaceae;
• Devil’s Claw;
• Chemometrics;
• Nuclear magnetic resonance;
• Ultra-high performance liquid chromatography-mass spectrometry;
• Iridoid glycosides;
• Harpagoside

Corresponding author at: Department of Pharmaceutical Sciences, Tshwane University of Technology, Private Bag X680, Pretoria 0001, South Africa. Tel.: +27 12 382 6373; fax: +27 12 382 6243.

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