Active pectin fragments of high in vitro antiproliferation activities toward human colon adenocarcinoma cells: Rhamnogalacturonan II

Abstract

This study was to identify active pectin fragments of high in vitro anti-proliferation activities against human colon adenocarcinoma Caco-2 cells, using various pectin fragment preparations dominant with rhamnogalacturonan I (RG-I), rhamnogalacturonan II (RG-II), and galacturonic acid oligomers (GAOS). The samples were prepared from citrus high and low methoxy pectins (HPE and LPE) by endo-α-D-(1,4)-polygalacturonase action coupling with a green process as ultrafiltration (membrane molecular weight cut off > 10k, 1k-10k, and < 1k, giving fragment preparations I, II, and III, respectively). It is indicated that, in the fragment preparations HPE-I, II, and III, the molecular fractions HPE-F1 (RG-I), HPE-F2 (RG-II), and HPE-F3 (GAOS) showed an averaged Mw = 26.7k, 3.4k, and 0.3k, respectively, notably higher than their LPE counterparts. All fragment preparations exhibited concentration-dependent, inhibition effects on Caco-2 cells, where HPE-II (RG-II-domain) revealed an interesting inhibition effect, significantly higher than those did HPE-I (RG-I domain) and HPE-III (GAOS). The HPE-F2 (RG-II) was elucidated and found of IR = 88% at 1.0 mg/mL and half-inhibition concentration (IC50) = 0.12 mg/mL, doubling the effect of HPE-F1 (RG-I) (IR = 45% at 1.0 mg/mL). Conclusively, citrus RG-II fragment showed a promisingly high anti-Caco-2 activity, significantly higher than did RG-I and GAOS, possibly attributed to its special branched structure and low molecular size.