Phenolic Compounds and Capsaicinoids in Three Capsicum annuum Varieties: From Analytical Characterization to In Silico Hypotheses on Biological Activity

Abstract

The affinity of specific phenolic compounds (PCs) and capsaicinoids (CAPs) present in three Capsicum annuum varieties (Friariello, Cayenne and Dzuljunska Sipka) to the transient receptor potential vanilloid member 1 (TRPV1) was investigated by integrating an analytic approach for the simultaneous extraction and analysis through high-performance liquid chromatography coupled with ion trap mass spectrometry (HPLC/ITMS) and UV detection (HPLC-UV) of PCs and CAPs and structural bioinformatics based on the protein modelling and molecular simulations of protein-ligand docking. Overall, a total of 35 compounds were identified in the different samples and CAPs were quantified. The highest content of total polyphenols was recorded in the pungent Dzuljunska Sipka variety (8.91 ± 0.05 gGAE/Kg DW) while the lowest was found in the non-pungent variety Friariello (3.58 ± 0.02 gGAE/Kg DW). Protein modelling generated for the first time a complete model of the homotetrameric human TRPV1, and it was used for docking simulations with the compounds detected via the analytic approach, as well as with other compounds, as an inhibitor reference. The simulations indicate that different capsaicinoids can interact with the receptor, providing details on the molecular interaction, with similar predicted binding energy values. These results offer new insights into the interaction of capsaicinoids with TRPV1 and their possible actions.

Keywords: Capsicum annuum; HPLC-MS; TRPV1–capsaicin interaction; capsaicinoids; docking simulations; phenolic compounds; protein modelling; transient receptor potential vanilloid member 1 (TRPV1).

Figure 1

HPLC-UV chromatograms of extracts from green pepper (GP) (A) and red pepper 3 (RP3) (B) recorded at 280 nm. For peak assignments, see Table 2.

Figure 2

Model of the human TRPV1. (A) The ‘cartoon’ representation of the homotetrameric model of TPRV1, coloured by chain. (B) Overlap between the model of TRPV1 (green) and the template (PDB code: 7LPB) (cartoon). (C) Overlap between the chain A of the TRPV1 model (green) and the single chain of the Alpha Fold model (pink).

Figure 3

Docking results for capsaicin and inhibitor. (A) Overlay of the docking pose of the capsaicin with the best energy cluster (orange stick) with the capsaicin with the best numerousness in cluster (cyan stick) and the inhibitor (pink stick). (B) Overlay of the docking pose of the capsaicin with the best energy cluster (orange stick) with the capsaicin with the best numerousness in the cluster (cyan stick) and the capsaicin bound to the TRPV1 agonist-bound conformation (pink stick); in cyan/beige and pink cartoon TRPV1 in antagonist- and agonist-bound conformation, respectively. Pointed by the red arrows the different orientations of the Arg 557 before and after the conformational change.

Figure 4

Docking results for capsaicinoids. Overlay of the docking pose of the capsaicin (green stick), dihydrocapsaicin (yellow stick), homocapsaicin (pink stick) and nordihydrocapsaicin (cyan stick). TRPV1, in agonist-bound conformation, is represented in cartoon, with cyan and beige colours for two different chains.

Figure 5

Docking results for TRPV1 agonist, antagonist, and caffeic acid hexoside. Docking interactions between TRPV1 in antagonist-bound conformation (cyan and beige depict chain A and B, respectively) and capsaicin (pink sticks in panel (A)), SB-366791 (yellow sticks in panel (B)), caffeic acid (orange sticks in panel (C)) and caffeic acid hexoside (green sticks in panel (D)). In beige and cyan, stick residues depict the interaction between the ligand s and the chain A and B, respectively. Caffeic acid hexoside, as well the caffeic acid, and the inhibitor SB-366791 do not interact with S6 helix.