Abstract 12332: Sonoporation With Nano-Sized Bubble Liposomes may be a Useful Method of Drug Delivery to Vegetations: An Experimental Study Using Rats With Infective Endocarditis

Abstract

Background: Intractable nature of infective endocarditis (IE) is partly because of the biofilm around microorganisms. An effective method of dissolving biofilm would be helpful to treat IE thereby reducing the dose of antimicrobial agents and hospital stay. Ultrasound modifies the permeability of cellular membranes (sonoporation) and is used for drug and gene delivery. Under the presence of microbubbles, sonoporation has been shown to enhance its effect, but may cause tissue damage. Recently nano-sized bubble liposomes (BLs) (average diameters less than 2 μ m) have been developed. Combination of ultrasound and BLs is expected to deliver various molecules effectively with less tissue damage. We investigated the effect of sonoporation with BLs on vegetations using rats with infective endocarditis.

Methods: Aortic regurgitation (AR) was created in 43 male Sprague-Dawley rats by mechanical injury of the aortic valve with a catheter inserted into the left ventricle from the carotid artery. Three days after catheterization, Enterococcus faecalis (6.8×10⁸ CFU/ml) was intravenously injected. Two days after, the aortic valve was excised to obtain vegetations. Excised vegetations were fixed in saline (400 ml) containing India ink (4 ml). and were assigned to 3 groups: control, (B(-)US(-); sonoporation without BLs, (B(-)US(+) and sonoporaion with BLs, (B(+)US(+). Sonoporation was performed with ultrasound exposure (frequency: 1.0 MHz, intensity: 1.0 W/cm²) for 10 minutes (1s insonification, 4s stop) using a Sonitron 2000.

Results: AR was successfully created in 30 rats (83%) and vegetations were found in 15 rats. Four vegetations were used for B(-)US(-), 4 for B(-)US(+) and 5 for B(+)US(+). Two vegetations were used for gram staining and Enterococci faecalis infection was microscopically confirmed. The penetration score was 0 ± 0 for B(-)US(-), 0.56 ± 1.03 for B(-)US(+), and 1.65 ± 1.09 for B(+)US(+) (p < 0.001 vs. B(-)US(-), and p < 0.05 vs. B(-)US(+)).

Conclusions: We could make infective endocarditis model in rats. India ink particles penetrated into the vegetation effectively with ultrasound exposure under the presence of BLs. Sonoporation with BLs may be a useful method of drug delivery to vegetations.