Antimicrobial Essential Oil Formulation: Chitosan Coated Nanoemulsions for Nose to Brain Delivery

Abstract

Brain infections as meningitis and encephalitis are attracting a great interest. Challenges in the treatment of these diseases are mainly represented by the blood brain barrier (BBB) that impairs the efficient delivery of even very potent drugs to reach the brain. The nose to the brain administration route, is a non-invasive alternative for a quick onset of action, and enables the transport of numerous medicinal agents straight to the brain thus workarounding the BBB through the highly vascularized olfactory region. In this report, Thymus vulgaris and Syzygium aromaticum essential oils (EOs) were selected to be included in chitosan coated nanoemulsions (NEs). The EOs were firstly analyzed to determine their chemical composition, then used to prepare NEs, that were deeply characterized in order to evaluate their use in intranasal administration. An in vitro evaluation against a collection of clinical isolated bacterial strains was carried out for both free and nanoemulsioned EOs. Chitosan coated NEs showed to be a potential and effective intranasal formulation against multi-drug resistant Gram-negative bacteria such as methicillin-susceptible Staphylococcus aureus and multi-drug resistant Gram-negative microorganisms including carbapenem-resistant Acinetobacter baumannii and Klebsiella pneumoniae.

Keywords: Syzygium aromaticum; Thymus vulgaris; antibacterial activity; chitosan coating; essential oils; nanoemulsions; nose to brain delivery.

Figure 1

Physical stability studies in terms of hydrodynamic diameter and ζ-potential variations of uncoated (SA- and TV-NEs) (A,B) and of chitosan coated nanoemulsions (C-SA- and C-TV-NEs (C,D) up to 90 days at two different storage temperatures (* = p < 0.05 when compared with day 1).

Figure 2

Variations of hydrodynamic diameter (A) and ζ-potential (B) of SA- and TV-NEs in the presence of aCSF up to 3 h (* = p < 0.05 when compared with t = 0).

Figure 3

Kinetic interaction between coated and uncoated NEs and mucin, evaluated by hydrodynamic diameter (A) and ζ-potential (B) variations by DLS measurements. Panel A: Error bars are smaller than the symbol size.

Figure 4

Mucoadhesive efficiency of nanoemulsions: Mucin interaction evaluating the percent of precipitated mucin (* = p < 0.05 SA samples when compared with mucin).

Figure 5

Profile of Nile Red released by NEs expressed as a concentration of Nile Red in the external medium and as a % of Nile Red released.

Figure 6

Activity SA-NEs and TV-NEs against CR-Ab (A,B) and CR-Kp (C,D) at different concentrations throughout the killing study. GC: Growth Control. The horizontal dashed line represents bactericidal activity. CR-Ab: Carbapenem-resistant Acinetobacter baumannii; CR-Kp: Carbapenem-resistant Klebsiella pneumoniae. The MIC values of CR-Ab and CR-Kp for SA-NEs and TV-NEs were 0.03% v/v and 0.03% v/v.