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. 2022 Dec 5;14(23):5168.
doi: 10.3390/nu14235168.

Exploring the Chemical Space of Kawakawa Leaf (Piper excelsum)

Ramya Jayaprakash  1 , Farha Ramzan  1 , Jennifer L Miles-Chan  2 , Meika Foster  1   3   4 , Richard F Mithen  1 , Chris Pook  1
Affiliations

Exploring the Chemical Space of Kawakawa Leaf (Piper excelsum)

Ramya Jayaprakash et al. Nutrients. .

Abstract

The chemical profiles of kawakawa (Piper excelsum) leaves were analysed through targeted and non-targeted LC-MS/MS. The phytochemical profile was obtained for both aqueous extracts representative of kawakawa tea and methanolic extracts. Sixty-four compounds were identified from eight leaf sources including phenylpropanoids, lignans, flavonoids, alkaloids and amides. Eight of these compounds were absolutely quantified. The chemical content varied significantly by leaf source, with two commercially available sources of dried kawakawa leaves being relatively high in phenylpropanoids and flavonoids compared with field-collected fresh samples that were richer in amides, alkaloids and lignans. The concentrations of pharmacologically active metabolites ingested from the traditional consumption of kawakawa leaf as an aqueous infusion, or from novel use as a seasoning, are well below documented toxicity thresholds.

Keywords: LC-MS/MS; ethnobotany; ethnopharmacology; functional food; metabolomics; molecular networking; natural products; phytochemicals; toxicity.

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Conflict of interest statement

M.F. is the Pou Rangahau Huataki—Taketake a Tāne (Research Lead—Indigenous Organisms) for AuOra Ltd., Wakatū Incorporation. The other authors declare that they have no competing interests.

Figures

Figure 1
Figure 1
Molecular networking of LC-MS/MS features in kawakawa extracts. Nodes are unique features resolved by retention time or m/z. Numbers correspond to Table 2. Node borders are coloured by retention time from yellow to purple. Edge width indicates dot product 0.75–1. (A) The main cluster contains features that were either identified as or annotated as amides. (B) Features not connected to the main network of amides. Minor clusters include flavonoids, lignans and several amides. Six nodes were orphans, including several amides not connected to the main network, a lignan, phenylpropanoids and the unique compound trigonelline.
Figure 1
Figure 1
Molecular networking of LC-MS/MS features in kawakawa extracts. Nodes are unique features resolved by retention time or m/z. Numbers correspond to Table 2. Node borders are coloured by retention time from yellow to purple. Edge width indicates dot product 0.75–1. (A) The main cluster contains features that were either identified as or annotated as amides. (B) Features not connected to the main network of amides. Minor clusters include flavonoids, lignans and several amides. Six nodes were orphans, including several amides not connected to the main network, a lignan, phenylpropanoids and the unique compound trigonelline.
Figure 2
Figure 2
Clustergram of normalised and autoscaled peak areas from LC-MS/MS analysis of aqueous extracts. Each row represents a resolved feature (Table 2) and each column represents one triplicate analysis from the eight different leaf sources. Heat scale units are standard deviations from the mean of all peaks for that feature. Hierarchical clustering on each axis demonstrates similarity of features (y axis) and samples (x axis). The first letter of the sample label indicates aqueous extraction (A), the second letter commercial dried leaves (C) or fresh leaves (F) and the third the source as listed in Table 1. Te Tauihu samples were collected on multiple occasions throughout 2021, so a number is added to index this.
Figure 3
Figure 3
Clustergram derived from the area ratio of the phytochemicals estimated from the LC-MS/MS analysis of triplicate methanolic extracts of three types of kawakawa. Each row represents a resolved feature (Table 2) and each column represents one triplicate analysis from the eight different leaf sources. Heat scale units are standard deviations from the mean of all peaks for that feature. Hierarchical clustering on each axis demonstrates similarity of features (y axis) and samples (x axis). The first letter of the sample label indicates methanolic, the second letter commercial dried leaves (C) or fresh leaves (F) and the third the source as listed in Table 1.
Figure 4
Figure 4
Absolute quantification of kawakawa phytochemicals obtained from (A) aqueous extraction of ŌKU leaf powder (ACO) and fresh leaves from the Nelson region (AFT1), and (B) methanol extraction of ŌKU leaf powder (MCO) and fresh leaf powders collected from Arapaoa Island (MFA) and Pōhara (MFP). Values are mean ± SD (n = 3). * indicates p < 0.01, ** indicates p < 0.001.
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