Keith A. Yagaloff

Melanocortin receptors in leptin effects

Leptin acts on the central nervous system to cause a reduction in food intake and body weight,. The melanocortin system in the brain is also implicated in energy homeostasis, with agonists of the melanocortin-4 (MC4) receptor reducing food intake and targeted mutation of the MC4 receptor causing obesity. We now show that MC4 receptor signalling is an important mediator of leptins effects on food intake and body weight, demonstrating a link between the two systems.

Central infusion of melanocortin agonist MTII in rats: assessment of c-Fos expression and taste aversion

Like leptin (OB protein), central infusion of the nonspecific melanocortin agonist MTII reduces food intake for relatively long periods of time (i.e., 12 h; W. Fan, B. A. Boston, R. A. Kesterson, V. J. Hruby, and R. D. Cone, Nature: 385: 165-168, 1997). To test the hypothesis that MTII may influence ingestive behavior via mechanisms similar to those that mediate the effects of leptin, we infused a single dose of MTII into the third ventricle (i3vt) of Long-Evans rats and examined three dependent measures that have been studied following i3vt infusion of leptin: 1) effects on long-term food intake and body weight (48 h), 2) patterns of c-Fos expression in the brain, and 3) conditioned taste aversion learning. Similar to leptin, MTII reduced 48-h food intake (1.0 nmol dose), reduced body weight at 24 and 48 h (0.1 and 1.0 nmol doses, respectively), and induced c-Fos expression in the paraventricular nucleus of the hypothalamus and the central nucleus of the amygdala. In contrast to leptin, MTII was found to produce conditioned taste aversions. These results are consistent with the hypothesis that MTII may influence regulatory behavior via mechanisms similar to those that mediate the effects of leptin.Like leptin (OB protein), central infusion of the nonspecific melanocortin agonist MTII reduces food intake for relatively long periods of time (i.e., 12 h; W. Fan, B. A. Boston, R. A. Kesterson, V. J. Hruby, and R. D. Cone, Nature; 385: 165-168, 1997). To test the hypothesis that MTII may influence ingestive behavior via mechanisms similar to those that mediate the effects of leptin, we infused a single dose of MTII into the third ventricle (i3vt) of Long-Evans rats and examined three dependent measures that have been studied following i3vt infusion of leptin: 1) effects on long-term food intake and body weight (48 h), 2) patterns of c-Fos expression in the brain, and 3) conditioned taste aversion learning. Similar to leptin, MTII reduced 48-h food intake (1.0 nmol dose), reduced body weight at 24 and 48 h (0.1 and 1.0 nmol doses, respectively), and induced c-Fos expression in the paraventricular nucleus of the hypothalamus and the central nucleus of the amygdala. In contrast to leptin, MTII was found to produce conditioned taste aversions. These results are consistent with the hypothesis that MTII may influence regulatory behavior via mechanisms similar to those that mediate the effects of leptin.

Structure–Activity relationship of linear peptide Bu-His-DPhe-Arg-Trp-Gly-NH2 at the human melanocortin-1 and -4 receptors: histidine substitution

Systematic substitution of His(6) residue using non-selective hMC4R pentapeptide agonist (Bu-His(6)-DPhe(7)-Arg(8)-Trp(9)-Gly(10)-NH(2)) as the template led to the identification of Bu-Atc(6)(2-aminotetraline-2-carboxylic acid)-DPhe(7)-Arg(8)-Trp(9)-Gly(10)-NH(2) which showed moderate selectivity towards hMC4R over hMC1R. Further SAR studies resulted in the discovery of Penta-5-BrAtc(6)-DPhe(7)-Arg(8)-Trp(9)-Gly(10)-NH(2) and Penta-5-Me(2)NAtc(6)-DPhe(7)-Arg(8)-Trp(9)-Gly(10)-NH(2) which are potent hMC4R agonists and are inactive in hMC1R, hMC3R and hMC5R agonist assays.

Essential fatty acids are antagonists of the leukotriene B4 receptor

A series of essential fatty acids and fatty acid derivatives were evaluated for their ability to inhibit [3H] leukotriene B4 (LTB4) binding to pig neutrophil membranes. The fatty acids varied in chain length, extent of unsaturation, position of unsaturation, and isomerization. Generally, fatty acids with two or more unsaturated sites and chain lengths of 18-22 were potent inhibitors of [3H]LTB4 binding; both n-3 and n-6 fatty acids were inhibitory. The most potent compounds tested were homogammalinolenic acid and ricinelaidic acid which gave Ki values of 1 microM and 2 microM in the binding assay. Ricinelaidic acid was also tested for its ability to inhibit LTB4-mediated chemotaxis (IC50 = 10 microM) and LTB4-induced calcium fluxes (IC50 = 7 microM) in isolated human neutrophils. Ricinelaidic acid did not show agonist activity in these assays. In an in vivo model of LTB4-induced bronchoconstriction, ricinelaidic acid and homogammalinolenic acid gave 46% and 53% inhibition, respectively, at a 1 mg/kg i.v. dose. These results indicate that essential fatty acids are LTB4 receptor antagonists, which may account in part for their reported anti-inflammatory activities.

Structure-activity relationship of linear peptide Bu-His6-DPhe7-Arg8-Trp9-Gly10-NH2 at the human melanocortin-1 and -4 receptors: DPhe7 and Trp9 substitution.

A series of pentapeptides, based on hMC4R pentapeptide agonist (Bu-His(6)-DPhe(7)-Arg(8)-Trp(9)-Gly(10)-NH(2)), was prepared in which either DPhe(7) or Trp(9) residue was systematically substituted. A number of interesting DPhe surrogates (D-Thi, D-3-CF(3)Phe, D-2-Nal and D-3,4-diClPhe) as well as Trp surrogates (2-Nal and Bta) were identified in this study.

Structure–activity relationship of cyclic peptide penta-c[Asp-His6-DPhe7-Arg8-Trp9-Lys]-NH2 at the human melanocortin-1 and -4 receptors: His6 substitution

A series of MT-II related cyclic peptides, based on potent but non-selective hMC4R agonist (Penta-c[Asp-His(6)-DPhe(7)-Arg(8)-Trp(9)-Lys]-NH(2)) was prepared in which His(6) residue was systematically substituted. Two of the most interesting peptides identified in this study are Penta-c[Asp-5-ClAtc-DPhe-Arg-Trp-Lys]-NH(2) and Penta-c[Asp-5-ClAtc-DPhe-Cit-Trp-Lys]-NH(2) which are potent hMC4R agonists and are either inactive or weak partial agonists (not tested for their antagonist activities) in hMC1R, hMC3R and hMC5R agonist assays.

Section Review: Recent progress in the development of leukotriene B4 antagonists

Leukotriene B4 (LTB4) is a potent proinflammatory lipid mediator derived from arachidonic acid via the 5-lipoxygenase pathway. It is a powerful chemoattractant and activator of neutrophils and exhibits effects on other cell types as well. This eicosanoid has been implicated in a variety of inflammatory diseases including asthma, acute respiratory distress syndrome, chronic obstructive pulmonary disease, contact dermatitis, cystic fibrosis, inflammatory bowel disease, gout, myocardial ischaemia, NSAID-induced gastropathy, psoriasis and rheumatoid arthritis. Thus orally active and non-toxic antagonists of LTB4 could prove to be novel anti-inflammatory drugs with potential advantages over existing therapies. This article reviews recent developments regarding the discovery of second generation LTB4 antagonists with sufficient potency and oral activity in animal models to justify clinical examination in humans. It is hoped that such trials will lead to new treatment modalities for inflammatory disorders.

Benzenepropanoic acids containing chromanone or naphthalenone moieties are potent and orally active leukotriene B4 antagonists

Abstract Systematic structural modification of peptidoleukotriene antagonists of the o-hydroxyacetophenone class has led to the discovery of certain [[(3,4-dihydro-4-oxo-8-propyl-2H-1-benzopyran-7-yl)oxy]alkyl]benzenepropanoic acids and related compounds ( 7 ), which appear to be potent and selective antagonists of the proinflammatory mediator leukotriene B 4 .

Highly Selective Cyclic Peptides for Human Melanocortin-4 Receptor (MC-4 R): Design, Synthesis, Bioactive Conformation, and Pharmacological Evaluation as an Anti-Obesity Agent

Melanocortin (MC) peptides α-, β-, and γ-MSH and adreno-corticotropic hormone (ACTH) are a group of neuropeptides derived from pro-opiomelanocortin hormone (POMC). The physiological actions of these peptides are mediated through five (MCR-1–5) seven-transmembrane G-protein-coupled receptor subtypes. The MSH peptides have been implicated in numerous biological functions [1] including regulation of skin pigmentation, regulation of steroid production, modulation of the immune response, thermo-regulation and obesity [2]. Clarification of the role of melanocortin receptor subtypes, in particular the recently discovered MC-3, MC-4 and MC-5 receptors, has been hampered by the lack of selective peptide ligands. However, recent studies on MCR knockout animals demonstrated that the MC-4 receptor is involved in regulation of feeding. MCR-4 knockout mice display an obesity phenotype that includes maturity onset obesity, hyperglycemia, and hyperinsulinemia. Moreover, it has been reported that a non-selective cyclic MCR-4 peptide agonist (MT II) inhibits food intake when given icv to mice [3]. Consequently, a potent and selective MC-4R agonist is regarded as potentially useful in therapeutic approaches to obesity management. The goal of this work was to identify a selective MCR-4 cyclic peptide agonist for use as a pharmacological tool in obesity and feeding studies and to develop a pharmacophore model applicable to structure-based drug design.