Original article Localization and interaction of hydroxyflavones with lipid bilayer model membranes: A study using DSC and multinuclear NMR Ragini Sinha a , Akshada Joshi b , Urmila J. Joshi b, * , Sudha Srivastava a , Girjesh Govil a a National Facility for High Field NMR, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400 005, India b Principal K.M. Kundnani College of Pharmacy, Cuffe Parade, Mumbai 400 005, India article info Article history: Received 23 July 2013 Received in revised form 17 April 2014 Accepted 19 April 2014 Available online 22 April 2014 Keywords: Flavones DPPC DSC NMR Chemical shifts CSA abstract The localization and interaction of six naturally occurring flavones (FLV, 5HF, 6HF, 7HF, CHYand BLN) in DPPC bilayers were studied using DSC and multi-nuclear NMR. DSC results indicate that FLV and 6HF interact with alkyl chains. The 1 H NMR shows interaction of flavones with the sn-glycero region. Ring current induced chemical shifts indicate that 6HF and BLN acquire parallel orientation in bilayers. 2D NOESY spectra indicate partitioning of the B-ring into the alkyl chain region. The DSC, NMR and binding studies indicate that 5HF and 7HF are located near head group region, while 6HF, CHY and BLN are located in the vicinity of sn-glycero region, and FLV is inserted deepest in the membrane. Ó 2014 Elsevier Masson SAS. All rights reserved. 1. Introduction Flavonoids have emerged as potential therapeutic drugs and are effective against several diseases. Prominent among them, are free radical mediated [1,2] and cell proliferative diseases [3,4]. Flavones and flavonols are found in nature and have shown promising antioxidant and anticancer activity [5,6]. The antioxidant activity of 7-hydroxyflavone in egg yolk phosphatidylcholine liposomes has been reported [7]. Tsuchiya has reported that chrysin and baicalein show significant inhibition of lipid peroxidation in 1, 2-dio- lieolylphosphatidylcholine liposomal membranes [8]. Greeff et al. have shown potent peroxyl radical scavenging activity of 6- hydroxyflavone against fluoroscence decay of fluorescein [9]. Antioxidant activity of 5-hydroxyflavone, chrysin and baicalein has also been reported [10]. Chrysin (5, 7-dihydroxyflavone) possesses several biological properties [11,12], including antioxidant [13] and anticancer activity [14]. Arora et al. [6] have compared membrane interaction of nine flavonoids, and related them to their antioxidant effects. Flavones were not included in their studies, though they have important bioactivity [15]. Membrane interaction of flavo- noids has been compared and their effects on membrane leakage and lipid peroxidation have been evaluated [16,17]. There are very few studies on the interaction of structurally different flavones with membranes and their relation to bioactivity. The number, position and phenolic hydroxyl groups influence physiochemical properties such as dipole moment and hydropho- bicity. In turn, these determine their partitioning into lipid mem- branes. Interaction of flavones with membranes plays a crucial role in their biological activity [18]. Understanding interaction of fla- vones with biological membranes may help to elucidate mecha- nisms of action of flavones as antioxidant and anti-proliferative agents. Model membranes mimic the behavior of biological membranes [19]. The phase transition temperature (T m ) of model membranes plays an important role in binding studies, which in turn depends on the lipid composition. DPPC lipid bilayers are ideally suited for drugemembrane interaction for physical studies due to its above room temperature T m value 314 K [20,21]. In this paper we report membrane partitioning of six flavone molecules with varying number and position of hydroxyl groups (Fig. 1). DSC and multinuclear NMR techniques have been used to determine localization and interaction of the hydroxyflavones with model bilayer membranes formed by DPPC. Antioxidant and anti- proliferative activities have also been studied. * Corresponding author. Department of Pharmaceutical Chemistry, Prin. K.M. Kundnani College of Pharmacy, 23-Jote Joy Building, R.S. Marg, Cuffe Parade, Colaba, Mumbai, Maharashtra 05, India. E-mail addresses: urmilajjoshi@hotmail.com, urmila.joshi1365@gmail.com (U.J. Joshi). Contents lists available at ScienceDirect European Journal of Medicinal Chemistry journal homepage: http://www.elsevier.com/locate/ejmech http://dx.doi.org/10.1016/j.ejmech.2014.04.054 0223-5234/Ó 2014 Elsevier Masson SAS. All rights reserved. European Journal of Medicinal Chemistry 80 (2014) 285e294