Intracellular Bacteria and Protozoa - Intracellular Delivery: Fundamentals and Applications - page 772

3.2.2 Biodistribution and Therapeutic Efficacy of Nanoparticles

Early work employed ampicillin, that was loaded to ~190 nm polyisohexylcyano-
acrylate (PIHCA) nanoparticles and administered to C57BL/6 mice experimentally
infected with S. typhimurium C5 (Fattal et al. 1989 ). All control mice and all those
treated with nonloaded nanoparticles died within 10 days of infection. By contrast,
all mice treated with a single injection of 0.8 mg of nanoparticle-bound ampicillin
survived. With free ampicillin, a similar curative effect required three doses of
32 mg each. Lower doses delayed but did not reduce mortality. The therapeutic
index of ampicillin, calculated on the basis of mouse mortality, was therefore
increased by 120-fold when it was bound to nanoparticles, probably due to its
delivery to liver and spleen, the primary foci of infection in the experimental model
that was used. However, neither the liver nor the spleen was sterilized in any of the
surviving mice, even 60 days after injection.
More recently, azithromycin was loaded into PLGA nanoparticles and its anti-
bacterial activity in vitro was examined against S. typhi . The results showed that
physicochemical properties were affected by drug to polymer ratio. Zeta potential
of the nanoparticles was fairly negative. In vitro release study showed two phases:
an initial burst for 4 h followed by a very slow release pattern during a period of
24 h. The results of antimicrobial activity test showed that the nanoparticles were
more effective than pure azithromycin against S. typhi with the nanoparticles show-
ing equal antibacterial effect at 1/8 concentration of the free drug. In conclusion,
the azithromycin-loaded PLGA nanoparticles showed appropriate physicochemical
and improved antimicrobial properties which can be useful for oral administration
(Mohammadi et al. 2010 ).
Lately, a series of non convencional micro and nanoparticles were employed as
carriers for aminoglycosides. Most of the assays were proofs of principle and their
performance against typhoid fever was not determined.
For instance, the encapsulation of antibiotics in carrier erythrocytes is able to
give rise to a sustained release of the antibiotic, since the plasma half-life and the
area under the curve of the antibiotic are increased, together with possible RES
targeting when the loaded erythrocytes are phagocytosed (Gening and Manuilov
1991 ; Gutiérrez Millán et al. 2005 ). AMK was loaded into glutaraldehyde-treated
erythrocytes as a delivery system and i.v. administered to rats at 2.7 +/− 1 mg/kg to
determine pharmacokinetics and tissue distribution (Gutiérrez Millán et al. 2008 ).
AMK is a polar drug and, once entrapped inside the erythrocyte, it does not undergo
processes of diffusion across the cell membrane owing to its polar nature.
Thus, release must occur through a process of cell lysis, as happens with other
aminoglycosides.
In another approach, GEN cores were prepared by complexing the antibiotic
with polyacrylate anions that were further incorporated into nanostructures made of
having either amphiphilic N1 (containing poly(ethylene oxide), poly(propylene
oxide) and polyacrylate) or hydrophilic N2 (containing polyacrylate) surfaces and
incubated with cells (Ranjan et al. 2009 ; Tian et al. 2007 ). Flow cytometry and
confocal microscopy studies demonstrated higher rate of uptake for amphiphilic