Antibacterial and Anti-Inflammatory Activity of an Antimicrobial Peptide Synthesized with D Amino Acids

Abstract

The peptide SET-M33 is a molecule synthesized in tetra-branched form which is being developed as a new antibiotic against Gram-negative bacteria. Its isomeric form with D amino acids instead of the L version (SET-M33D) is also able to kill Gram-positive bacteria because of its higher resistance to bacterial proteases (Falciani et al., PLoS ONE, 2012, 7, e46259). Here we report the strong in vitro activity of SET-M33D (MIC range 0.7–6.0 µM) against multiresistant pathogens of clinical interest, including Gram-positives Staphylococcus aureus, Staphylococcus saprophyticus, and Enterococcus faecalis, and various Gram-negative enterobacteriaceae. SET-M33D antibacterial activity is also confirmed in vivo against a MRSA strain of S. aureus with doses perfectly compatible with clinical use (5 and 2.5 mg/Kg). Moreover, SET-M33D strongly neutralized lipopolysaccharide (LPS) and lipoteichoic acid (LTA), thus exerting a strong anti-inflammatory effect, reducing expression of cytokines, enzymes, and transcription factors (TNF-α, IL6, COX-2, KC, MIP-1, IP10, iNOS, NF-κB) involved in the onset and evolution of the inflammatory process. These results, along with in vitro and in vivo toxicity data and the low frequency of resistance selection reported here, make SET-M33D a strong candidate for the development of a new broad spectrum antibiotic.

Antimicrobial Peptides Active in In Vitro Models of Endodontic Bacterial Infections Modulate Inflammation in Human Cardiac Fibroblasts

“…In dentistry, antimicrobial peptides have been suggested to fight pathogens in implants and dental adhesives [ 15 ]. The peptide M33D is a tetrabranched peptide active against Gram-negative and Gram-positive bacteria [ 16 , 17 ]. It has a long life, unusual for peptides, since the branched form imparts resistance to plasma, serum, and bacteria proteases [ 18 ].…”

“…M33D shows MICs of 0.7–6.0 μM (4–32 µg/mL) against multiresistant pathogens of clinical interest, such as Gram-positive Staphylococcus aureus , Staphylococcus saprophyticus , and Enterococcus faecalis , including a vancomycin-resistant strain, and various Gram-negative enterobacteriaceae [ 17 ]. The activity is accompanied by a low frequency of resistance selection [ 17 ].…”

“…M33D has been successfully tested against multidrug-resistant strains of seriously dangerous Gram-negative species, such as Escherichia coli, Klebsiella pneumonia, Acinetobacter baumannii , and Pseudomonas aeruginosa , resistant to carbapenem, extended-spectrum cephalosporin, fluoroquinolone, aminoglycoside, and, importantly, colistin [ 17 ].…”

“…M33D also neutralizes lipopolysaccharide and lipoteichoic acid, thus exerting anti-inflammatory activity by reducing expression of cytokines, enzymes, and transcription factors (TNF-α, IL6, COX-2, KC, MIP-1, IP10, iNOS, NF-kB) involved in the onset and evolution of inflammatory processes [ 17 ].…”

“…By virtue of all these characteristics and its low toxicity [ 17 ], M33D and its analog M33i/l are considered good candidates to fight endodontic and periodontal disease.…”