Molecular and Cellul ar PharmacologyStructure –function relationships of citrus limonoids on p38 MAP kinase activity inhuman aortic smooth muscle cellsJinhee Kim a , Guddadarangavvanahally K. Jayaprakasha a,Mariappan Muthuchamy b , ⁎, Bhimanagouda S. Patil a, ⁎⁎a Vegetable and Fruit Improvement Center, Department of Horticultural Sciences, Texas A&M University, College Station, TX 77845-2119, USAb Department of Systems Biology and Translational Medicine, Texas A&M Health Science Center, College of Medicine, College Station, TX 77843-1114, USAabstractarticle i nfoArticle histo ry:Received 18 February 2011Received in revised form 4 August 2011Accepted 27 August 2011Available online 10 September 2011Keywords:Citrus limonoidsHASMCp38 MAPKStructure – function relationshipTNF- αLimonoids , abundantly present in citrus fruits, have potential role in reducing risk of different type of cancer.In the present study, we hypothesi zed that seven structurally different limonoids would involve in in flamma-tory pathway via modulating p38 MAP kinase activity at various extent in vascular smooth muscle cells.Results demonstrated that the different functional groups contain ing limonoids had differential effect s onthe p38 MAP kinase activity in human aortic smooth muscle cells. Among seven limonoids, nomilin exhibitedthe highest (38%) inhibition of p38 MAP kinase activity, followed by limonin (19%), deacetyl nomilin (19%),and defuran nomilin (17%). While defuran limonin and methyl nomilinate showed no signi fi cant decrease inp38 MAP kinase activity, obacunone signi fi cantly increased the p38 MAP kinase activity by 38%. Furthermore,TNF- α induced p38 MAP kinase activity in the smooth m uscle cells was completely inhibited by nomilin.Thus our data provide the first evidence that nomilin is the potent natural inhibitor for p38 MAP kinaseactivity in human aortic smooth muscle cells. These data also suggest that a seven-membered A ring withacetoxy group, present in nomilin, seems to be essential for its inhibitory activity on p38 MAP kinase.© 2011 Elsevier B.V. All rights reserved.1. IntroductionCitrus fruits contain different category of health promoting com-pounds such as flavonoids, ascorbic acid, vitamins, carotenoids, limo-noids, and pectin (Patil et al., 2006). Among these health promotingcompounds, tetranorterpenoid derivatives called limonoids are uniquebitter compounds mostly present in citrus and neem (Dai et al., 1999).Accumulating evidences suggest that limonoids reduce the risk ofdiverse spectrum of diseases including cancer (Jayaprakasha et al.,2008a, 2010; Miller et al., 2004; Tanaka et al., 2001), cardiovascular(Kurowska et al., 2000a, 2000b), and neurodegenerative disease(Poulose et al., 2006). Previous studies suggest that the presence offuran and an intact A-ring of limonoids is associated with increasingchemopreventive activity in cancer cells (Lam et al., 1994; Perez et al.,2009). While current evidences seem to suggest that chemical structureof citrus limonoids play a critical role in reducing risk of certain cancers,ve ry li tt le in fo rm ati on i s a va il a ble a bou t t he ef fe ct s of lim on oi d s oncardiovascular cells.Pro-inflammatory cytokines, such as interleukin (IL)-1β, IL-6, andIL-12, and tumor necrosis factor-α (TNF-α) play an important role inthe regulation of in flammatory mechanisms in mammalian cells( Kyriakis and Avruch, 2001; Mehra et al., 2005 ). However, overpro-duction of these cytokines has been implicated in inducing a varietyof chronic cardiovascular diseases such as atherosclerosis, coronaryartery disease, arrhythmia, heart failure, hypertension, and ischemia( Anderson et al., 2006; Mehra et al., 2005). Since the TNF-α is regulat-ed by the p38 mitogen-activated protein (MAP) kinase signaling cas-cade (Kotlyarov et al., 1999), the regulation of the p38 MAP kinasesign al transduction pathwa y i s a significant t a rge t for a nti -i nflammatoryth er apy. Indeed, accumulati ng evidences sug ge st that up-regulation o fp38 is a ssoci ate d wit h the d ev el opment o f human c a rdiov ascular di s ease(Han e t al., 1997; Yang e t al., 2000). Ther ef or e, p 3 8 M AP kin a se is o n e ofth e i mport a nt ce ntr a l tar ge ts for t her a peuti c approa ches in c ont rol li nghuman c ardio vascular di se a se. Alt ho ug h sy nt het ic p38 i nhibit or s a r ecomme rci a ll y use d in c ar di ovascula r d i se a se tr eat m en ts, c l ini cal tr ialsare s ti ll ong oin g d ue t o si de e ffe ct ( m ainl y he p ato to xi c it y) an d the in te r-rupti on o f o the r si gnal ing pat hway s (Behr et al., 2003). T he ref o re, t her e i sa cri ti cal need f or po te ntial natural bioactive c ompound, such asli monoi d s, whi c h d isti nct ly s uppr ess p38 MAP kin a se s wit hout an y s ideeffects.We have previously shown that limonoids decrease proliferation ofcancer cells (Jayaprakasha et al., 2010; Patil et al., 2009; Poulo
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