Design of MC1R Selective γ-MSH Analogues with Canonical Amino Acids Leads to Potency and Pigmentation.

Melanoma is a lethal form of skin cancer. Skin pigmentation, which is regulated by the melanocortin 1 receptor (MC1R), is an effective protection against melanoma. However, the endogenous MC1R agonists lack selectivity for the MC1R and thus can have side effects. The use of noncanonical amino acids in previous MC1R ligand development raises safety concerns. Here we report the development of the first potent and selective hMC1R agonist with only canonical amino acids. Using γ-MSH as a template, we developed a peptide, [Leu3, Leu7, Phe8]-γ-MSH-NH2 (compound 5), which is 16-fold selective for the hMC1R (EC50 = 4.5 nM) versus other melanocortin receptors. Conformational studies revealed a constrained conformation for this linear peptide. Molecular docking demonstrated a hydrophobic binding pocket for the melanocortin 1 receptor. In vivo pigmentation study shows high potency and short duration. [Leu3, Leu7, Phe8]-γ-MSH-NH2 is ideal for inducing short-term skin pigmentation without sun for melanoma prevention.

El concepto darwiniano de la allostasis. Epigénesis / The Darwinian concept of allostasis. Epigenetic programming

El concepto de allostasis fué establecido a finales del siglo pasado como el conjunto de respuestas de los organismos vivos, regidas por el cerebro, para conservar su equilibrio interno y, por tanto, su supervivencia. Pero todo ello tiene resonancias Darwinianas . Cuestiones establecidas en el siglo XX. El axis HPA - hipotálamo -pituitaria-adrenal- es el más importante entre todos los sistemas movilizados por la allostasis. Y este axis se programa en periodo gestacional en los mamíferos. Cuando circunstancias de estrés maternal activan su axis HPA, grandes cantidades de glucocorticoides (GC) pasan al feto, y su axis HPA se programa de forma anómala, e irreversible en periodo adulto, además, se reduce el peso al nacimiento. Y todo ello es factor de riesgo de posibles patologías adultas (diabetes 2, cardiovasculares o hipertensión crónica). La causa es la reducción de receptores de glucocorticoides (GR) en el hipocampo, ya que ellos ejercen una acción tónica en la retroalimentación negativa del axis HPA. Sin embargo, se desconocía, en el siglo XX, por qué mecanismo los GC reducen la expresión de GR en hipocampo. Cuestiones establecidas en siglo XXI. Se eligen y exponen una serie de trabajos publicados en el siglo XXI sobre esta vertiente que nos han llevado al conocimiento de que la reducción en hipocampo de los GR se produce por un mecanismo epigenético. Sucintamente, se enumeran los principales mecanismos epigenéticos conocidos. Finalmente, se enuncian las grandes posibilidades terapéuticas que abren estos mecanismos epigenéticos para el futuro y para la posible explicación de procesos evolutivos

At the end of last Century the concept of allostasis was proposed as the group of responses from live beings, regulated by the brain, leading to maintain the organism balance and, therefore, to survival. But this concept has clear Darwinian significance. Questions established in the XX Century. The HPA (hypothalamus-pituitary-adrenal gland) axis is the most important among all regulatory systems triggered by allostasis, and it is programmed during the gestational period in mammals. Under a stressful situation the mother HPA axis operates secreting high amounts of glucocorticoids (GC) that get into the foetus affecting to the normal HPA programming; this abnormal development is irreversible in adulthood and will also reduce birth weight. Besides, it is a risk factor for possible adult pathologies such as diabetes mellitus type 2, cardiovascular disease or chronic hypertension. The reason is the decrease of glucocorticoid receptors (GR) in hippocampus, since they are crucial for the negative feedback of HPA axis. However, the mechanism by which GC reduce GR expression in hippocampus was unknown in the XX Century. Questions established in the XXI Century. A number of research articles published in the XXI Century reporting information about the epigenetic mechanism involved in the hippocampal reduction of GR are selected and presented. The main epigenetic mechanisms known up to date are also mentioned. Finally, the great therapeutic possibilities of the epigenetic mechanisms in the near future are enunciated as well as the possible explanation of evolutional processes

Characterization of [Phe(13), Tyr(19)]-MCH analog binding activity to the MCH receptor.

Melanin concentrating hormone (MCH), a hypothalamic neuropeptide, is an important regulator of energy homeostasis in mammals. Characterization of an MCH specific receptor has been hampered by the lack of a suitable radioligand. The [Phe(13), Tyr(19)]-MCH analog has been shown by different investigators to bind specifically to cell lines of epithelial or pigment cell origin. Recently, using functional assays, the MCH receptor has been characterized as a seven transmembrane G-coupled protein initially identified as SLC-1. In the present study, we used tyrosine iodinated [Phe(13), Tyr(19)]-MCH analog, which stimulates food intake in a manner similar to that of MCH, as well as native MCH to conduct binding studies. Specific binding could not be demonstrated in intact cells of several cell lines, including A431 and B16. Specific binding associated with membranes localized to the microsomal, not the plasma membrane, fraction. Message for SLC-1 was absent in these cell lines, as assessed by Northern blot analysis. We conclude that cells previously reported to express the MCH receptor do not express SLC-1 and that both iodinated MCH and the [Phe(13), Tyr(19)]-MCH have a large component of non-specific binding. These ligands may be useful for binding studies in transfected cells with high levels of SLC-1 expression. However they do not appear to be suitable for screening for the MCH receptor as most cells demonstrate significant low affinity non-specific binding.

Phe(13),Tyr(19)-melanin-concentration hormone and the blood-brain barrier: role of protein binding.

Melanin-concentrating hormone (MCH), found both peripherally and centrally, is involved in food ingestion. Although its expression in brain is increased by fasting, it is not known whether it crosses the blood-brain barrier (BBB). Use of the sensitive method of multiple-time regression analysis has shown that almost all of the peptides and polypeptides tested cross the BBB at a rate faster than the vascular marker albumin. With this same method, however, we found that the 19-amino acid 125I-Phe13,Tyr19-MCH did not cross faster than 99mTc-albumin. Several mechanisms were excluded as possible explanations for the slow rate of influx. These included degradation, association with capillary endothelial cells, and transport from brain to blood. When Phe13,Tyr19-MCH was perfused in blood-free buffer, however, it entered the brain significantly faster than albumin. This suggested protein binding as an explanation for the slow rate of influx when the MCH was administered in blood. Protein binding was confirmed by capillary zone electrophoresis, which showed that almost all of the Phe13,Tyr19-MCH added to blood migrated with a large-molecular-weight substance. Sodium dodecyl sulfate-capillary gel electrophoresis of Phe13,Tyr19-MCH in buffer additionally showed that the MCH aggregated as a trimer, a factor not preventing its influx by blood-free perfusion. Thus, the results show that blood-borne Phe13,Tyr19-MCH does not significantly cross the BBB, probably because of its binding to serum proteins.