Lipidation of Naturally Occurring α-Helical Antimicrobial Peptides as a Promising Strategy for Drug Design

In this paper, we describe the chemical synthesis, preliminary evaluation of antimicrobial properties and mechanisms of action of a novel group of lipidated derivatives of three naturally occurring α-helical antimicrobial peptides, LL-I (VNWKKVLGKIIKVAK-NH₂), LK6 (IKKILSKILLKKL-NH₂), ATRA-1 (KRFKKFFKKLK-NH₂). The obtained results showed that biological properties of the final compounds were defined both by the length of the fatty acid and by the structural and physico-chemical properties of the initial peptide. We consider C₈-C₁₂ length of the hydrocarbon chain as the optimal for antimicrobial activity improvement. However, the most active analogues exerted relatively high cytotoxicity toward keratinocytes, with the exception of the ATRA-1 derivatives, which had a higher selectivity for microbial cells. The ATRA-1 derivatives had relatively low cytotoxicity against healthy human keratinocytes but high cytotoxicity against human breast cancer cells. Taking into account that ATRA-1 analogues carry the highest positive net charge, it can be assumed that this feature contributes to cell selectivity. As expected, the studied lipopeptides showed a strong tendency to self-assembly into fibrils and/or elongated and spherical micelles, with the least cytotoxic ATRA-1 derivatives forming apparently smaller assemblies. The results of the study also confirmed that the bacterial cell membrane is the target for the studied compounds.

Assessment of salivary opiorphin in oral lichen planus

Opiorphin is a pentapeptide, which could be isolated from human fluids and has a decreasing effect on pain. Aim: Since lichen planus is a chronic mucocutaneous disease, which causes pain or burning feeling in the oral mucosa, this study aimed to compare salivary opiorphin levels of oral lichen planus (OLP) patients with healthy subjects. Methods: This case-control study, was performed on 24 patients with OLP lesions and 21 healthy subjects. After collecting unstimulated saliva, opiorphin levels were compared between two groups through statistical analyses. Results: There was not any significant difference between OLP patients and healthy subjects according to salivary opiorphin concentration (p=0.378). Also, in the OLP group, opiorphin concentration was not significantly different between males and females (p=0.601). Analytical analysis could not show any remarkable difference between various severity of OLP lesions regarding to salivary opiorphin levels (p=0.653). Conclusion: In this study, salivary opiorphin levels was not significantly different between patients with OLP and healthy subjects; however, more studies are suggested for better assessment of salivary opiorphin levels in various types of OLP lesions and its correlation with pain severity.

Effect of glutamic acid elimination/substitution on the biological activities of S3 cationic amphiphilic peptides

Cationic amphiphilic peptides (CAPs) are usually classified as bacterial membrane targeting molecules. Rational design and modification of cationic and amphiphilic properties of CAPs have made them to be used in new medical and biotechnological applications. However, CAPs modification and development strategies are challenging issues due to the risk of cytotoxicity or hemolytic activity. In this research, modified variants of S3 peptide were introduced. S3 is a linear 34 amino acid peptide derived from the lipopolysaccharide (LPS) binding site of factor C in horseshoe crab's hemolymph. Net positive charges of variants (S3E3 and S3E3A) increased by either eliminating negatively charged residues of the peptides or substituting them with alanine. Different biological activities of new variants including LPS binding affinity, antimicrobial activity, cytotoxicity against human breast tumor cell line, and hemolytic property were studied and compared to those of S3 peptide. S3E3 variant showed 68.5% higher LPS binding affinity, 40.4% stronger anti-microbial activity, conserved hemolytic property with the same anti-cancer activity compared to S3peptide. These results revealed that elimination/substitution of negatively charged residues will be a proper strategy for modification of S3 peptide.

Neutral endopeptidase (NEP) inhibitors - thiorphan, sialorphin, and its derivatives exert anti-proliferative activity towards colorectal cancer cells in vitro

Neutral endopeptidase (NEP) is an enzyme implicated in development of different tumors, e.g. colorectal cancer (CRC). In this study, the anti-cancer effects of NEP inhibitors, thiorphan (synthetic compound) and sialorphin (naturally occurring pentapeptide) on CRC cells were investigated. Moreover, we synthesized some derivatives of sialorphin (alanine scan analogues: AHNPR, QANPR, QHAPR, QHNAR; N-acetylated sialorphin; C-amidated sialorphin, and C-amidated alanine scan analogues) to examine the biological activity of these inhibitors on CRC cells. The cytotoxic activity of the NEP inhibitors against CRC cell lines (SW620 and LS180) and normal human fibroblasts (HSF) was evaluated. Additionally, the influence of NEP inhibitors on proliferation, cell cycle progression, induction of apoptosis, and the level of phosphorylation of MAP kinases and mTORC1 signaling pathway proteins in CRC cells were examined. The NEP inhibitors were non-cytotoxic to HSF cells; however, most of them slightly decreased the viability and inhibited proliferation of CRC cells. The N-acetylation or C-amidation of sialorphin or its alanine scan analogues resulted in decreased or abolished anti-proliferative activity of the NEP inhibitors towards the CRC cells. Additionally, thiorphan and sialorphin enhanced the anti-proliferative activity of other CRC-cell growth inhibitors (atrial natriuretic peptide-ANP and melphalan-MEL). The mechanisms involved in the anti-proliferative effects of the tested inhibitors were mediated via NEP and associated with induction of cell cycle arrest in the G0/G1 phase, increased activity of ERK1/2, and a reduced level of phosphorylation of mTOR (Ser2448), 4E-BP1, and p70S6K. However, the NEP inhibitors did not induce apoptosis in the CRC cells. These results have indicated that thiorphan and sialorphin or its derivatives AHNPR, QANPR, QHAPR, and QHNAR have the potential to be used as agents in treatment of patients with CRC.