Abstract
Seven triterpenoid saponins were identified in methanolic extracts of seeds of the Zolfino bean landrace (Phaseolus vulgaris L.) by HPLC fractionation, revealing their ability to inhibit highly purified human recombinant aldose reductase (hAKR1B1). Six of these compounds were associated by MS analysis with the following saponins already reported in different Phaseolus vulgaris varieties: soyasaponin Ba (V), soyasaponin Bb, soyasaponin Bd (sandosaponin A), soyasaponin αg, 3-O-[R-l-rhamnopyranosyl(1 → 2)-α-d-glucopyranosyl(1 → 2)-α-d-glucuronopyranosyl]olean-12-en-22-oxo-3α,-24-diol, and soyasaponin βg. The inhibitory activity of the collected fractions containing the above compounds was tested for hAKR1B1-dependent reduction of both l-idose and 4-hydroxynonenal, revealing that some are able to differentially inhibit the enzyme. The present work also highlights the difficulties in the search for aldose reductase differential inhibitors (ARDIs) in mixtures due to the masking effect on ARDIs exerted by the presence of conventional aldose reductase inhibitors. The possibility of differential inhibition generated by a different inhibitory model of action of molecules on different substrates undergoing transformation is also discussed.
Highlights
Saponins represent a wide family of compounds characterised by the presence of either a triterpenoid or a steroidal aglycone moiety and of one or more linked straight or branched sugar chains[1]
NADPH, L-idose, soyasaponin Ba (SSBa) and soyasaponin Bb (SSBb) were supplied by Carbosynth (Compton, England); YM10 ultrafiltration membranes were obtained from Merck-Millipore (Darmstad, Germany); soyasaponin Bd (SSBd) was obtained from ALB Technology Limited (Mongkok Kowloon, Hong Kong); PTFE filtration membranes 0.45 mm pore size were from Phenomenex Italy (Bologna, Italy); HPLC grade methanol, formic acid, and acetic acid were purchased from VWR (Milano, Italy)
We recently reported that components of a methanolic extract of Zolfino bean, eluting as the most hydrophobic fractions from an HPLC reverse phase column, act as a promising source of ARDIs16
Summary
Saponins represent a wide family of compounds characterised by the presence of either a triterpenoid or a steroidal aglycone moiety and of one or more linked straight or branched sugar chains[1]. The amphiphilic nature of saponins provides these compounds with a significant biological action by enabling them to interact at the membrane level of the cell systems. They have been reported to act as anti-inflammatory, hypocholesterolemic, expectorant, vasoprotective, and immunomodulating agents[4,5]. Attention must be paid to the adverse cytotoxic action of saponins[6,7]. This feature of saponins has been widely investigated as a potential tool to act against cell proliferation in cancer[8]
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