BIOLOGICAL ACTIVITY OF NORBELADINE ANALOGS AGAINST METHICILLIN-RESISTANT Staphylococcus aureus

DANIELA ECHENIQUE; CLAUDIA MATTANA; MARIEL MOHAMED; FLORENCIA CARMONA VIGLIANCO; ALEJANDRO A. ORDEN; SARA SATORRES

Congreso; Cuarta Reunión Conjunta de Sociedades de Biología de la República Argentina; 2020

Staphylococcus aureus is a pathogenic microorganism and a frequent colonizer of human mucosa and skin. Nasal carriers are important reservoirs at risk of transmitting or spreading this bacterium to susceptible people or developing endogenous infections. Mice are a good model for the study of bacterial and host factors that influence nasal colonization by S. aureus. Medicinal plants that present active metabolites with antistaphylococcal activity offer an important alternative for the treatment of infections caused by methicillin-resistant S. aureus (MRSA). 4´-O-methylnorbelladin is a protoalkaloid which can undergo three different types of phenol oxidative coupling reactions to give Amaryllidaceae alkaloids such as hemanthamine, licorin, and galantamine. The latter is primarily isolated from daffodil (Narcissus spp.), snowdrop (Galanthus spp.), and summer snowflake (Leucojum aestivum) and is currently used in the palliative treatment of Alzheimer?s disease in the early stage. In this study, the in vitro and in vivo activity of two halogenated analogs of 4´-O-methylnorbelladin were evaluated: 2´-chloro-MN (1) and 2´-bromo-MN (2) against S. aureus ATCC 43300, a methicillin-resistant strain (MRSA). Compounds 1 and 2 as  hydrochlorides, were synthesized by condensation of the corresponding substituted aromatic aldehydes and tyramine and further reduction with sodium borohydride. For both  compounds, the minimum inhibitory concentration (MIC) was determined by the  microdilution method in broth and the minimum bactericidal concentration (MBC) by subcultures in tryptic soy agar. The in vivo study was implemented during three consecutive days. The first day, eight BALB/c mice were infected by instilling 10 μL of a bacterial suspension with 1×10 (8) CFU/mL in each nostril; on the second day, the compound 1 suspension was administered intranasally at a concentration of 250 μg/ml in half of these mice, using the other half of mice as control (without compounds). The third day, all mice were sacrificed. The nostrils and internal organs (spleen and lung) were extracted and homogenized for bacterial quantification. The same experience was carried out with compound 2. MIC and MBC values against MRSA for both compounds were 250 µg/mL each. Compounds 1 and 2 showed significant in vivo antistaphylococcal activity reflected in a significant decrease in the bacterial count of MRSA in nasal homogenates compared to the control group (P = 0.0001, P = 0.0017, respectively). Bacteria were not isolated from internal organ homogenates. There are a limited number of studies on the  bioactivities of precursors or analogues of Amaryllidaceae alkaloids. This study contributes to the discovery of new compounds with antibacterial properties, demonstrating an antistaphylococcal effect in an in vivo mouse model.