Development and validation of HPLC-MS2 methodology for the accurate determination of C4-C8 B-type flavanols and procyanidins

Fingerprinting and Quantification of Procyanidins via LC-MS/MS and ESI In-Source Fragmentation

Procyanidins (PCs), or condensed tannins (CTs), are critical for the quality of red wine and other polyphenol-rich foods because of their contribution to the mouthfeel. However, current analytical methods often show a lack of correlation with perceived astringency, biological activities (such as antioxidant activity), and health-related benefits. This is partly because methods such as the Folin-Ciocalteu and tannin affinity precipitation assays report a simplified total phenolic or tannin value that does not consider the diverse structures of CTs. Using procyanidin in-source fragmentation (PC-ISF) allows visualization of diverse CTs, from smaller oligomers to larger polymers, after chromatographic separation and compound depolymerization in the ion source. However, previous PC-ISF has not been optimized, particularly for predicting the structure of CTs with a degree of polymerization (DP) greater than 3. This study introduces a rapid ISF-based PC fingerprinting method, condensed tannin fragmentation fingerprinting (C-TFF), that uses three in-source energies per instrument, cone voltages of 30, 110, and 140 V on the Waters system and fragmentor voltages of 135, 330, and 380 V on the Agilent system, to depolymerize PCs and generate their in-source ions and fragments. The depolymerized spectra that contribute the most to PC differentiation are further fragmented in the collision cell, using multiple reaction monitoring (MRM). The collected MRM transitions of analytical PC standards are correlated to target samples with unidentified PCs via multiple linear regression (MLR), allowing for comprehensive fingerprinting by identifying and quantifying each PC. Nineteen mixtures of five B-type PCs (DPs 1-5) with a known mean degree of polymerization (mDP) and commercial cider samples were characterized via C-TFF, demonstrating high accuracy and precision. This study contributes to the analysis of CTs in complex samples. Future efforts will focus on characterizing structures with mDPs > 5, such as those found in wines with diverse CT profiles.

Structural characterization of a proanthocyanidin-rich fraction from Hancornia speciosa leaves and its effect on the release of pro-inflammatory cytokines and oxidative stress in THP-1 cells

ETHNOPHARMACOLOGICAL RELEVANCE

In Brazil, the leaves of Hancornia speciosa Gomes have a traditional use for treating hypertension and diabetes. Experimental investigations have confirmed the anti-hypertensive and hypoglycemic properties of extracts derived from H. speciosa leaves across various experimental models. These biological activities have been mostly ascribed to its major constituent, bornesitol, along with other cyclitols, flavonoids, and cinnamic acid derivatives.

AIM OF STUDY

The objective of this study was to characterize the chemical structure of proanthocyanidins from H. speciosa leaves and explore their in vitro activity on the release of pro-inflammatory cytokines and oxidative stress.

MATERIAL AND METHODS

The acetone/water (7:3) extract of H. speciosa leaves (HsE) was prepared by percolation and fractionated by column chromatography over Sephadex LH20 to afford the proanthocyanidin-rich fraction HsFr3. Structure characterization of the proanthocyanidins constituents of HsFr3 was accomplished by extensive UPLC-DAD-ESI-MS/MS analysis coupled to degradation reaction through thiolysis. The effect of HsE, HsFr3, and bornesitol on the release of TNF, IL-1β and IL-6 in LPS-stimulated THP-1 cells was assayed by ELISA. The effect of the samples on oxidative stress induced by LPS in THP-1 cell was investigated using a DCFH-DA fluorescent assay.

RESULTS

Fractionation of HsE afforded HsFr3, primarily composed of six proanthocyanidins. Their chemical structures were characterized as dimeric (4 isomers) and trimeric (2 isomers) procyanidins C-glycosides of the B-type. HsE, HsFr3, and bornesitol reduced the release of pro-inflammatory cytokines TNF and IL-1β in LPS-stimulated THP-1 cells, while no significant effect was observed on IL-6. All samples reduced the oxidative stress induced by LPS in THP-1 cells, whereas bornesitol, tested at lower concentrations, induced an equivalent response to HsE and HsFr3.

CONCLUSIONS

Our findings provide additional evidence to support the ethnomedical use of H. speciosa in managing hypertension and hyperglycemia, due to the direct association of oxidative stress, TNF, and IL-1β with the maintenance and aggravation of these deleterious conditions. The dimeric and trimeric procyanidin C-glycosides, characterized in the species, contribute to diminish oxidative stress and the release or pro-inflammatory cytokines, whereas bornesitol was shown to induce similar effect at lower concentrations.

Determination of total phenol and six polyphenolic components in the polyphenol extract of Cinnamomi cortex by quantitative nuclear magnetic resonance spectroscopy

A quantitative nuclear magnetic resonance spectroscopy (qNMR) method was established for determining the total phenol and six polyphenolic components in the polyphenol extract of Cinnamomi cortex. The qNMR approach utilized DMSO-d6 as the deuterated solvent and potassium hydrogen phthalate as the internal standard for quantifying the total phenolic content, expressed as epicatechin equivalence in the sample. Two complementary qNMR methods with DMSO-d6 or D2O as solvent were established to simultaneously determine 6 polyphenol components in the cinnamon polyphenol extract, including epigallocatechin gallate (EGCG), epicatechingallate (ECG), epicatechin (EC), epigallocatechin (EGC), gallocatechin gallate (GCG) and gallic acid (GA). Method validation demonstrated excellent precision with intraday relative standard deviation (RSD) below 1.08% and interday RSD below 1.48%. The linear correlation coefficient (r) exceeded 0.999, and the limits of detection (LOD) were from 0.01 to 0.14 mg mL-1, while the limits of quantification (LOQ) were from 0.07 to 0.69 mg mL-1. Recovery rates for this method fell within the range of 98.2% to 101.7%. Furthermore, the method has been successfully applied for determining the polyphenolic content in authentic cinnamon polyphenol extracts obtained from different sources.

Human colonic catabolism of dietary flavan-3-ol bioactives

Understanding the fate of ingested polyphenols is crucial in elucidating the molecular mechanisms underlying the beneficial effects of a fruit and vegetable-based diet. This review focuses on the colon microbiota-mediated transformation of the flavan-3-ols and the structurally related procyanidins found in dietary plant foods and beverages, plus the flavan-3-ol-derived theaflavins of black tea, and the post-absorption phase II metabolism of the gut microbiota catabolites. Despite significant advances in the last decade major analytical challenges remain. Strategies to address them are presented.

OUP accepted manuscript

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