Antimicrobial properties of porphyrins

A large number of natural and synthetic porphyrins of diverse chemical comp ositions and characteristics can be isolated from nature or synthesised in the laboratory. Antimicrobial and antiviral activities of porphyrins are ba sed on their ability to catalyse peroxidase and oxidase reactions, absorb p hotons and generate reactive oxygen species (ROS) and partition into lipids of bacterial membranes. Light-dependent, photodynamic activity of natural and synthetic porphyrins and pthalocyanines against Gram-positive and Gram- negative bacteria has been well demonstrated. Some non-iron metalloporphyri ns (MPs) possess a powerful light-independent antimicrobial activity that i s based on the ability of these compounds to increase the sensitivity of ba cteria to ROS or directly produce ROS. MPs mimic haem in their molecular st ructure and are actively accumulated by bacteria via high affinity haem-upt ake systems. The same uptake systems can be used to deliver antibiotic-porp hyrin and antibacterial peptide-porphyrin conjugates. Haemin, the most well known natural porphyrin, possesses a significant antibacterial activity th at is augmented by the presence of physiological concentrations of hydrogen peroxide or a reducing agent. Natural and synthetic porphyrins have relati vely low toxicity in vitro and in vivo. The ability for numerous chemical m odifications and the large number of different mechanisms by which porphyri ns affect microbial and viral pathogens place porphyrins into a group of co mpounds with an outstanding potential for discovery of novel agents, proced ures and materials active against pathogenic microorganisms.