Ligands

Prostaglandins

            1.  15-deoxy-d12,14-prostaglandin J2 (PGJ2)

                        a)  physiological ligand

                                    1)  may be a physiological ligand (Forman, Tontonoz et al. 1995; Kliewer, Lenhard et al. 1995; Yu, Bayona et al. 1995)

                        c)  direct interaction with PPARg (Kliewer, Lenhard et al. 1995; Kliewer, Sundseth et al. 1997)

                        e)  LPS-induced iNOS can be inhibited by high levels of PGJ2 in PPARg knockouts, at doses higher than those required for PPARg-dependent inhibition (Ricote, Li et al. 1998)

                        f)  Kd varies between 325nM and 2.5mM (Forman, Tontonoz et al. 1995; Kliewer, Lenhard et al. 1995)

            2.  PGJ2 is not specific for PPARg

                        a)  competition doesn’t stop pGJ2 effects

                                    1)  cotreatment experiment with a competitive inhibitor (a PPARg ligand that could not produce anti-inflammatory effects) did not prevent the anti-inflammatory effects of PGJ2 in vitro (Thieringer, Fenyk-Melody et al. 2000)

                        b)  effects not mediated through PPARg

                                    1)  can inhibit NFkB through two additional PPARg-independent mechanisms (Straus, Pascual et al. 2000)

                                                a)  15d-PGJ2 reduces the activity of NFkB through covalent modification of cysteine residues in the IkB kinase b subunit and the DNA binding domains of the NFkB subunits (Moore, Fitzgerald et al. 2001)-14,15

                                                b)  alters DNA binding ability

                                                c)  a,b unsaturated carbonyl group in the cyclopentone ring is required for the inhibition of IKK independent of PPARg (Wang, Fu et al. 2001)-52

                                    2)  15d-PGJ2 still functions in the PPARg deficient macrophages (Moore, Fitzgerald et al. 2001)-6,7

                        c)  may function in a negative feedback loop (Straus, Pascual et al. 2000)

                        d)  probably functions as an autocrine factor (Straus, Pascual et al. 2000)

            3.  prostanoids are natural ligands of PPARg (Gaillard, Negrel et al. 1989; Negrel, Gaillard et al. 1989; Forman, Tontonoz et al. 1995; Kliewer, Lenhard et al. 1995)

            4.  9- and 13-hydroxyoctadecadienoic acid (HODE) (Nagy, Tontonoz et al. 1998)

                        a)  9-HODE and 13-HODE as PPARg ligands

                                    1)  more potent than PUFAs

                                    2)  present in oxidized low-density lipoproteins

                                    3)  PPARg ligands (Nagy, Tontonoz et al. 1998)

                        b)  roles of the HODEs

                                    1)  15-lipoxygenase-1 can synthesize 13-HODE

                                                a)  converts linoleic acid to 13-(S)-HODE

                                                b)  converts arachidonic acid to 15-(S)-HETE

                                    2)  15-lipoxygenase-2 (Hsi, Wilson et al. 2001)-4

                                                a)  cannot metabolize linoleic acid

                                                b)  converts arachidonic acid to 15-(S)-HETE

                                    3)  13-(S)-HpODE and 13-(S)-HODE, but not 15-(S)-HETE in combo with EGF to Syrian hamster embryo cells inhibits the dephos of the EGF receptor, upregulating the EGF cascade and potentiating the mitogenic response (Hsi, Wilson et al. 2001)-20

                                                a)  15-LO-1 linoleic acid metabolites, 13-(S)-HpODE and 13-(S)-HODE both up/regulated EGF-dependent cell proliferation and enhanced MAPK activity, but the 15-LO-1 arachidonic acid metabolite, 15-(S)-HETE, was not active (Hsi, Wilson et al. 2001)-20

                        d)  macrophages transfected with 15-LO-1, treated with linoleic acd and arachidonic acid show activation of PPARg (Hsi, Wilson et al. 2001)-18

                        e)  13-HODE represses PPARg indirectly

                                    1)  at 1-10mM causes a down-regulation of PPARg through the MAPK pathway (Hsi, Wilson et al. 2001)

                                                a)  upregulates the EGF and serum-dependent MAPK pathway, causing PPARg phosphorylation

                        f)  15-S-HETE

                                    1)  15-lipoxygenase-1 can synthesize 13-HODE

                                                a)  converts linoleic acid to 13-(S)-HODE

                                                b)  converts arachidonic acid to 15-(S)-HETE

                                    2)  15-lipoxygenase-2 (Hsi, Wilson et al. 2001)-4

                                                a)  cannot metabolize linoleic acid

                                                b)  converts arachidonic acid to 15-(S)-HETE

                                    3)  15S-HETE can transactivate PPARg (Shappell, Gupta et al. 2001)

            5.  oxidized low density lipoproteins (OxLDLs)

                        a)  hexadecyl azeloyl phosphatidyl choline (azPC), similar potency to rosiglitazone (Davies, Pontsler et al. 2001)

                                    1)  Kd=40nM

                                    2)  azPC enhances production of CD36 in primary human monocytes

                        b)  oxidized LDL contains PPARg agonists (Nagy, Tontonoz et al. 1998)

                        c)  oxidized alkylacylphospholipids in oxLDL are the PPARg activators

                                    1)  bioactive lipids not present prior to oxidation of LDL particles

                                    2)  treatment of oxidized LDL particles with phospholipase A2, and not A1, removes PPARg activating activity

                                                a)  sn-2 residue is critical for ability to stimulate COX-2 expression

                                    3)  alkylphosphatidylcholines are only 0.05% of the total phosphatidylhcoline pool, and are required forplatelet-activating factor-like activity (Pontsler, St Hilaire et al. 2002)-2 and for COX-2 expression via PPARg (Pontsler, St Hilaire et al. 2002)

            6.  cyclopentenone prostaglandins 

                        a)  anti-inflammatory (Tontonoz, Nagy et al. 1998)- 7

                        b)  antiviral activity (Tontonoz, Nagy et al. 1998)- 12, 13

                        c)  inhibit NF-kB activation in human cells stimulated with TNFa or TPA (Tontonoz, Nagy et al. 1998)- 14

                                    1)  prevent phosphorylation and degradation of IkBalpha

                                                a)  normally, IkKalpha is phosphorylated which initiates a ubiquitination pathway

 

 

Thiazolidinediones

            1. antidiabetic thiazolidinediones (TZDs)

            e.g.  Rezulin (Spiegelman 1998)

                        a)  bind with high affinity (Kd of 40nM)

                        d)  glitazones, used as insulin sensitizers, are synthetic high affinity ligands for PPARg (Lehmann, Moore et al. 1995)

                        c)  lower circulating levels of FAs

                        d)  enhance insulin sensitivity in humans (Saltiel and Olefsky 1996; Willson, Cobb et al. 1996)

                        e  mediate these effects through PPARg interactions (Lehmann, Moore et al. 1995; Willson, Cobb et al. 1996)

            2.  BRL49653

                        a)  role

                                    1)  antidiabetic drug

                        b)  binds to PPARg

                                    1)  bind to PPARg with high selectivity and affinity (Lehmann, Moore et al. 1995)

                        c)  requires PPARg to function

                                    1)  BRL49653 does not work in PPARg knockouts, unlike PGJ2, as far as inhibiting NFkB activity (Ricote, Li et al. 1998)

            3.  ciglitazone

                        a)  potent activators of PPARg in vitro (Lambe and Tugwood 1996)

            4.  troglitazone

                        a)  potent activators of PPARg in vitro (Lambe and Tugwood 1996)

                        b)  increases susceptibility to ventricular fibrillation during myocardial ischemia and reperfusion (Xu, Lu et al. 2003)

            5.  Rezulin (Spiegelman 1998)

                        a)  role

                                    1)  lower glucose levels in rodent models of insulin resistance

                                    2)  lower circulating levels of FAs

                        b)  operates through PPARg

                                    1)  mediate these effects through PPARg interactions (Lehmann, Moore et al. 1995; Willson, Cobb et al. 1996)

            6.  pioglitazone (PIOG)

            76.  rosiglitazone

                        a)  role

                        b)  PPARg ligand (Gupta, Brockman et al. 2001)-31

                                    1)  1mM is enough to activate trasactivation in M-S colon epithelial carcinoma cells (Gupta, Brockman et al. 2001)

Fatty Acids

            1.  physiological concentrations of various FAs (Gottlicher, Widmark et al. 1992; Krey, Keller et al. 1993; Kliewer, Lenhard et al. 1995; Yu, Bayona et al. 1995; Forman, Chen et al. 1997; Krey, Braissant et al. 1997)

                        a)  PPARg prefers PUFAs over mono- or unsaturated fatty acids

            2.  fatty acid metabolites

                        a)  cyclooxygenase and lipoxygenase metabolites of polyunsaturated FAs (Kliewer, Lenhard et al. 1995; Yu, Bayona et al. 1995; Forman, Chen et al. 1997; Krey, Braissant et al. 1997; Nagy, Tontonoz et al. 1998)

            3.  lysophosphatidic acid (LPA)

                        a)  role

                                    1)  pluripotent lipid mediator controlling growth, mobility, and differentiation (McIntyre, Pontsler et al. 2003)-1,2

                                    2)  linked to ovarian cancer, elevated in serum (McIntyre, Pontsler et al. 2003)-3

                                    3)  controls adipogenesis (McIntyre, Pontsler et al. 2003)-4

                                                a)  stimulates lipid accumulation

                                    4)  generated during platelet activation (McIntyre, Pontsler et al. 2003)-5

                        b)  LPA is a PPARg ligand

                                    1)  competes away binding of rosiglitazone (McIntyre, Pontsler et al. 2003)

                                    2)  drives a PPRE-Acox luciferase reporter (McIntyre, Pontsler et al. 2003)

                        c)  other isoforms (generated by acyltransferase) are not active PPARg ligands

Non-thiazolidinediones

            1.  phenylacetic acid derivatives (Berger, Leibowitz et al. 1999)

                        L-796449 – 2nM

                        L-783483 – 15nM

                        L-165461 – 14nM

            2.  NSAIDs (reference?)

            3.  GW2331 - high affinity ligand for both PPARa and gamma (Kliewer, Sundseth et al. 1997)

            4.  GW0072

                        a)  partial agnoist (Oberfield, Collins et al. 1999)

                                    1)  doesn’t interact with the helix AF-2

                                    2)  doesn’t cause recruitment of SRC-1, but does allow release of NCoR

            5.  GW7845

                        a)  a selective PPARg agonist (Oliver, Shenk et al. 2001)-1,25 (EC50 = 3500, 0.7, and >10,000 nM on human PPARa, g, and b)

                                    1)  tyrosine analoge PPARg agonist (Gupta, Brockman et al. 2001)-32

                        b)  1mM is enough to activate PPARg (natural) in M-S colon carcinoma cells (Gupta, Brockman et al. 2001)

            6. 

            6.  GW9662

                        a)  irreversible antagonist for PPARg (Gupta, Brockman et al. 2001)-9

                                    1)  covalently modifies a cysteine residue (285) in the LBD of PPARg (Leesnitzer, Parks et al. 2002)

                                    2)  inhibits adipogenesis of C3H10T1/2 cells in vitro (Leesnitzer, Parks et al. 2002)

                        b)  specific for PPARg

                                    1)  10-fold more potent binding to PPARa and 600-fold more potent binding than to PPARb (Leesnitzer, Parks et al. 2002)

            7.  LG100754

                        a)  is a RXRa ligand (see above under RXRa)

                                    1)  reduce insulin resistance in vivo (Forman 2002)-18

                        b)  LG100754 does not activate PPARg well (Forman 2002)

                                    1)  LG754 does not recruit coactivators to the PPARg/RXRa complex

                                    2)  activates a reporter only 5 fold (versus 28 fold at the same concentration for rosiglitazone at 1mM) (Forman 2002)

                        c)  LG100754 sensitizes PPARg for its ligands

                                    2)  125I ligand shows that increased PPARg affinity for ligand in the presence of LG754

 

PPARa Ligands

            1.  fibrates

                        a)  fenofibric acid and clofibric acid activate PPARg with 10X less selectivity for PPARa (Brown, Winegar et al. 1999)

                        b)  bezafibrate activates PPARa and PPARg at the same concentration (Brown, Winegar et al. 1999)

            2.  Wy-14,643

                        a)  can activate mPPARg2 1165-17,20

                        b)  can’t activate mPPARg2 1165-6,34

            3.  CLA

                        a)  binds to PPARg with lower affinity than PPARa (IC50 = 5-7mM) (Moya-Camarena, Vanden Heuvel et al. 1999)

                        b)  role

                                    1)  CLA protects against tumor development in the rat mammary gland (Ip, Ip et al. 2000)-1-3

                                                a)  inhibits proliferation of TEB cells, the sites for chemical induction of mammary carcinogenesis in rodents (Ip, Ip et al. 2000)-4

                                                b)  stops the growth of a tumor cell line at 32mM CLA and 64mM (Ip, Ip et al. 2000)

                                                c)   causes increase in the apoptosis of rat mammary tumor cell lines as well (Ip, Ip et al. 2000)

                                    2)  anti-inflammatory in RAW cells (Yu, Correll et al. 2002)

                                                a)  IFNg-dependent expression of iNOS is repressed by CLA treatment of RAW cells (Yu, Correll et al. 2002)

                                                b)  COX2 mRNA, COX2 protein, COX2 promoter activity, PGE2 production are all repressed by CLA treatment (Yu, Correll et al. 2002)

                                                c)  TNFa at the mRNA and protein level, IL1b protein, and IL-6 are all decreased at the protein level (Yu, Correll et al. 2002)

PPARg antagonists

            1.  BADGE – bisphenol A diglycidyl ether

                        a)  selective antagonist for PPARg (Yamauchi, Waki et al. 2001)-16

                                    1)  inhibits PPARg transactivation by 70%, whereas PPARb was 23% and PPARa was unaffected

                                    2)  reduces expression of PPARg targets such as CD36

                        b)  nonselective effects on RXRa

                                    1)  30% inhibition of RXRa (Yamauchi, Waki et al. 2001)-16

                        c)  prevents HF-diet induced obesity, insulin resistance, and diabetes

                                    1)  increases serum leptin and leptin sensitivity (Yamauchi, Waki et al. 2001)

                                    2)  increases expression of PPARa target genes lik eACO and UCP2 in PPARa expressing tissues, allowing fatty acid combustion (Yamauchi, Waki et al. 2001)

                        d)  non-PPARg-dependent effects of BADGE

                                    1)  pretreatment of HCT-116 colon carcinomas and Jurkat cells (PPARg-negative) with BADGE increases sensitivity to indomethacin-induced apoptosis (Fehlberg, Trautwein et al. 2002)

                                    2)  BADGE induces apoptosis

                                                a)  annexin staining increases, TRAIL-induced apoptosis increases (Fehlberg, Trautwein et al. 2002)

                                                b)  Z-VAD-fmk, a caspase 9 inhibitor, inhibits the BADGE-induced apoptosis (Fehlberg, Trautwein et al. 2002)

            2.  diclofenac

                        a)  binding to PPARg

                                    1)  binds at 700nM, but can only induce 2-fold activation at doses of 25uM (Adamson, Frew et al. 2002)

                        b)  antagonism

                                    1)  antagonizes activation of PPARg by rosiglitazone (Adamson, Frew et al. 2002)

                                    2)  lowers PPARg-dependent adipose cell differentiation by 60% and inhibts the action of rosiglitazone on prostate cancer cell line DU-145, allowing increase in proliferation of these cells (Adamson, Frew et al. 2002)

            3.  T0070907

                        a)  binding to PPARg

                                    1)  binds with an IC50 in the nanomolar range (Lee, Elwood et al. 2002)

                        b)  antagonism

                                    1)  antagonizes the activation of PPARg by GW2433 (Lee, Elwood et al. 2002)

                                    2)  stops differentiation of 3T3-L1s in response to dex/insulin mix (Lee, Elwood et al. 2002)

                                    3)  intereferes with PPARg protein interaction

                                                a)  suppresses agonist-induced interactions between the PPARg LBD and coactivator-derived peptides (Lee, Elwood et al. 2002)

                                                b)  promotes recruitment of corepressor-derived peptide in HTRF assays (Lee, Elwood et al. 2002)

Other Ligands

            1.  genistein

                        a)  genistein induces adipogenisis at doses greater than 10uM, even in KS483 mouse bone marrow cells (Dang, Audinot et al. 2003)

                        b)  PPARg inhibits the effects due to estrogen receptor activation at higher doses of genistein (Dang, Audinot et al. 2003)

                        c)  dose curve shows induction at 5uM for a KS483 reporter assay (Dang, Audinot et al. 2003)