Azasulfurylpeptide Modulation of CD36-Mediated Inflammation Without Effect on Neovascularization

Diversity-Oriented A3-Macrocyclization for Studying Influences of Ring-Size and Shape of Cyclic Peptides: CD36 Receptor Modulators

Cyclic peptide diversity has been broadened by elaborating the A³-macrocyclization to include various di-amino carboxylate components with different N^ε-amine substituents. Triple-bond reduction provided new cyclic peptide macrocycles with Z-olefin and completely saturated structures. Moreover, cyclic azasulfurylpeptides were prepared by exchanging the propargylglycine (Pra) component for an amino sulfamide surrogate. Examination of such diversity-oriented methods on potent cyclic azapeptide modulators of the cluster of differentiation 36 receptor (CD36) identified the importance of the triple bond as well as the N^ε-allyl lysine and azaPra residues for high CD36 binding affinity. Cyclic azapeptides which engaged CD36 effectively reduced pro-inflammatory nitric oxide and downstream cytokine and chemokine production in macrophages stimulated with a Toll-like receptor-2 agonist. Studying the triple bond and amine components in the multiple-component A³-macrocyclization has given a diverse array of macrocycles and pertinent information to guide the development of ideal CD36 modulators with biomedical potential for curbing macrophage-driven inflammation.

Hydrazine derivative synthesis by trifluoroacetyl hydrazide alkylation

N′-Alkyl hydrazides were effectively synthesized by routes featuring installation, alkylation, and removal of a trifluoroacetyl group. A set of amino acid derived hydrazides were acylated using trifluoroacetic anhydride, and the resulting trifluoroacetyl hydrazides were alkylated with alcohols in Mitsunobu reactions and with alkyl halides under alkaline conditions. Removal of the trifluoroacetyl group was affected under reductive and hydrolytic conditions to provide the respective N′-alkyl hydrazides. This three-step process may be performed without isolation of intermediates to yield N′-alkyl hydrazide after a single chromatographic purification.

Synthesis and Biomedical Potential of Azapeptide Modulators of the Cluster of Differentiation 36 Receptor (CD36)

The innovative development of azapeptide analogues of growth hormone releasing peptide-6 (GHRP-6) has produced selective modulators of the cluster of differentiation 36 receptor (CD36). The azapeptide CD36 modulators curb macrophage-driven inflammation and mitigate atherosclerotic and angiogenic pathology. In macrophages activated with Toll-like receptor-2 heterodimer agonist, they reduced nitric oxide production and proinflammatory cytokine release. In a mouse choroidal explant microvascular sprouting model, they inhibited neovascularization. In murine models of cardiovascular injury, CD36-selective azapeptide modulators exhibited cardioprotective and anti-atherosclerotic effects. In subretinal inflammation models, they altered activated mononuclear phagocyte metabolism and decreased immune responses to alleviate subsequent inflammation-dependent neuronal injury associated with retinitis pigmentosa, diabetic retinopathy and age-related macular degeneration. The translation of GHRP-6 to potent and selective linear and cyclic azapeptide modulators of CD36 is outlined in this review which highlights the relevance of turn geometry for activity and the biomedical potential of prototypes for the beneficial treatment of a wide range of cardiovascular, metabolic and immunological disorders.

Atheroprotective and atheroregressive potential of azapeptide derivatives of GHRP-6 as selective CD36 ligands in apolipoprotein E-deficient mice

BACKGROUND AND AIMS

Scavenger receptor class B member 3, also known as cluster of differentiation-36 (CD36) receptor, is involved in the uptake and accumulation of modified lipoprotein in macrophages, driving atherosclerosis progression. Azapeptide analogs of growth hormone-releasing peptide-6 (GHRP-6) have been developed as selective CD36 ligands and evaluated for their anti-atherosclerotic properties in apoe^-/- mice.

METHODS

From 4 to 19 weeks of age, male apoe^-/- mice were fed a high fat high cholesterol (HFHC) diet, then switched to normal chow and treated daily with 300 nmol/kg of MPE-001 ([aza-Tyr⁴]-GHRP-6) or MPE-003 ([aza-(N,N-diallylaminobut-2-ynyl)Gly⁴]-GHRP-6) for 9 weeks. In another protocol, mice were fed a HFHC diet throughout the study.

RESULTS

Azapeptides decreased lesion progression in the aortic arch and reduced aortic sinus lesion areas below pre-existing lesions levels in apoe^-/- mice which were switched to chow diet. In mice fed a HFHC throughout the study, azapeptides reduced lesion progression in the aortic vessel and sinus. The anti-atherosclerotic effect of azapeptides was associated with a reduced ratio of iNOS⁺/CD206⁺ macrophages within lesions, and lowered plasma inflammatory cytokine levels. Monocytes from azapeptide-treated mice showed altered mitochondrial oxygen consumption rates, consistent with an M2-like phenotype. These effects were dependent on CD36, and not observed in apoe^-/-cd36^-/- mice.

CONCLUSIONS

Azapeptides MPE-001 and MPE-003 diminished aortic lesion progression and reduced, below pre-existing levels, lesions in the aortic sinus of atherosclerotic mice. A relative increase of M2-like macrophages was observed in lesions, associated with reduced systemic inflammation. Development of CD36-selective azapeptide ligands merits consideration for treating atherosclerotic disease.

Side-Chain Modification of Peptides Using a Phosphoranylidene Amino Acid

The flexible variation of peptidomimetics is of great interest for the identification of optimized protein ligands. Here we present a general concept for introducing side-chain modifications into peptides using triarylphosphonium amino acids. Building blocks 4a and 4b are activated for amidation and incorporated into stable peptides. The obtained phosphoranylidene peptides undergo Wittig olefinations and 1,3-dipolar cycloaddition reactions, yielding peptidomimetics with vinyl ketones and 5-substituted 1,2,3-triazoles as non-native peptide side chains.