Functions of Macrolide Antibiotics
An antibiotic is defined as a substance produced by a microorganism that selectively inhibits the growth of another. However, some antibiotics show anticancer mechanisms to disrupt cancer cell membrane or to inhibit replication and synthesis of DNA or RNA. Moreover, antibiotics are known to have various activities besides antimicrobial effect.
The macrolides consist of a lactone ring to which amine or neutral sugars are bonded. They are subdivided into 14-, 15-, and 16-membered macrolides depending on the structure of the lactone ring. Erythromycin as a 14-membered macrolide, tulathromycin and gamithromycin as 15-membered macrolides, and spiramycin, tylosin, tilmicosin, and mirosomycin as 16-membered macrolides are approved in veterinary medicine, and they are mainly used for respiratory infections due to their greater migration to the lung. Macrolides exhibit antibacterial activity for gram-positive bacteria, Mycoplasma, Chlamydia, and some gram-negative bacteria such as Haemophilus and Campylobacter. They selectively combine with 50S subunit of ribosome, and inhibit the synthesis of proteins by inhibiting transpeptidation.
By the way, erythromycin is also known to have enterokinesis aggravating action as a motilin agonist. Additionally, it is effective for chronic diffuse panbronchiolitis, and induces anti-inflammatory action through immune cells surrounding chronic bronchitis, considered the inhibition of neutrophils bonding to endothelial cells or inhibition of releasing IL-8. Moreover, erythromycin is known to inhibit the production of bacterial toxin and biofilms, and adhesion to bacterial cells.
Ivermectin, one of macrolides, discovered by Satoshi Omura, the Novel Prize winner 2015, has no antibacterial effect but annihilation effect for nematodes and arthropods. Tacrolimus (FK506), which was discovered from actinomyces isolated from Japanese soil, is a 23-membered macrolide and shows strong immunosuppression. It is used for inhibition of graft rejection, application for atopic dermatitis, and articular rheumatism. Therefore, macrolides have various functions other than antibiotic effect, and show distinctive presence compared with the other antibiotics.
It is considered that antibiotics are produced by bacteria to sustain their lives by killing another microorganisms and advantageously taking nutritional composition. Mentioned above, they also show various functions such as immune inhibition besides antimicrobial effect. Therefore, they might become indispensable seeds for new drug development.