Characterization of Phenolic Compounds from Pecan Kernels and their Biological Activities on Adipogenesis and Inflammation

Abstract

Pecan [Carya illinoinensis (Wangenh.) K. Koch] kernels from four cultivars were screened for their phenolic content and antioxidant capacity. Ellagitannin content was quantified by HPLC after hydrolysis as free ellagic acid. Characterization of phenolic compounds present in defatted pecan was conducted by liquid chromatography-mass spectrometry. In addition, ellagic acid metabolites, urolithin A and urolithin B, were evaluated for their anti-adipogenic and anti-inflammatory effects in 3T3-L1 preadiadipocyte cells by protein and gene expression. Variations among cultivars were observed. „GraCross‟ and „Desirable‟ showed the highest total phenolic content; in the same way, „GraCross‟ had the highest values for condensed tannin content, antioxidant capacity using the 2, 2-diphenyl-1-picryl-hydrazyl (DPPH) assay and the oxygen radical absorbance capacity (ORAC). According to these results, the cultivar with the highest condensed tannin content had the highest antioxidant capacity using the DPPH and ORAC assays. „Desirable‟ and „Kiowa‟ had the highest ellagitannin content. Even though ellagitannins comprise a small percentage compared to condensed tannins, the latter have restricted bioavailability and up to trimers can be absorbed. Eleven ellagitannins were identified for the first time in pecans. Their masses ranged from 433 to 1207 m/z. Condensed tannins up to pentamers were detected. Other compounds included gallic acid, ellagic acid, and isorhamnetin in the glucoside, pentosyl and galloyl pentosyl forms. Ellagitannins are metabolized in vivo yielding urolithins which are absorbed by the gut. Urolithins are derivatives from ellagic acid. These compounds, urolithin A and urolithin B, were used to treat 3T3-L1 preadypocytes as an obesity model. Results of the adipocytes' protein expression immediately after differentiation indicated no inhibition of differentiation of the preadipocytes after treating cells with urolithins and ellagic acid. Results on the mature adipocytes indicated that treatments with 25 mM of urolithin A, urolithin B, and ellagic acid during differentiation did not significantly reduce their lipid content. Inflammatory effects in 3T3-L1 adipocytes were evaluated by the LPS model through protein and gene expression. Urolithin A and ellagic acid reduced p-NF-kB protein expression. Urolithin A and urolithin B reduced TNF-a mRNA basal expression, a protective effect in a non-inflammatory state. Interleukin-6 (IL-6) expression was increased by urolithins and lipopolysaccharide (LPS), probablly due to a synergistic inflammatory effect coming from different pathways.