Download Modulating tetracaine aggregation using nanoparticles to enhance topical administration Results and Discussion

Modulating tetracaine aggregation using
nanoparticles to enhance topical administration
XJ Cai, P Mesquida, SA Jones
Institute of Pharmaceutical Science, King’s College London, 150 Stamford Street, London, SE1 9NH, UK
Introduction and Aims
!  Nanomaterials can enhance drug permeation across a
barrier [1]. One possible mechanism is by adapting the
physical properties of the drug.
!  Amphiphilic drugs tend to aggregate and this can alter
drug-formulation vehicle and drug membrane interactions,
which in turn influence drug permeation rate [2].
!  Nanomaterials can act as surfactants which are known to
affect drug aggregation [3]. Thus, it seems conceivable
that nanomaterials can be used as agents to modulate
drug aggregation in a manner that would improve skin
drug delivery.
!  In this project, tetracaine, an amphiphilic basic local
anaesthetic known to aggregate, was used as a model
drug. Negatively charged nanoparticles (i.e. carboxylmodified polystyrene nanoparticles and silica
nanoparticles) were added to the drug solutions and
changes to the transport across barriers were tracked.
The hypothesis
Drug
aggregatesnanoparticles
mix
Drug
aggregates
Addition of
nanoparticles
Results and Discussion
Effects of nanomaterials on TET transport
!  Tetracaine transport across the
membrane was significantly
enhanced when carboxyl-modified
polystyrene nanoparticles,
(NanoPSCOO-) and silica nanoparticles
(NanoSiO2) were added (p<0.05).
!  Tetracaine transport rates were the
highest when NanoSiO2 were added.
!  The steady state flux of the
tetracaine from the phosphatetetracaine mixture and the 10 µM
tetracaine solutions were not
significantly different (p>0.05).
!  Providing a solid surface resulted in
the greatest enhancement of
tetracaine transport.
Figure 2: Steady-state flux of 10 µM of tetracaine (black)
with the addition of phosphate ions (white), carboxylmodified polystyrene nanoparticles, NanoPSCOO-(grey) and
unmodified silica nanoparticles, NanoSiO2(light grey) across
silicone membrane. Inset shows the permeation profiles.
Each point represents the mean ± standard deviation,
n=5.
Effects of TET-TET aggregation on TET transport
!  Tetracaine displayed fluorescence quenching in the recorded spectra, which
was assigned to molecular aggregation as temperature, pH and chemical
stability were constant (Fig 3).
Drug adsorbed
onto the
nanoparticles
Equilibration
!  The results suggest 0.15 M, the therapeutic dosage, tetracaine exists as
aggregates.
!  Different aggregated sites were detected in a continuous manner over the 2
to 200 μM range.
Non-equilibration
Greater free
molecules
Application on
skin
!  When a different state of aggregation was presented, in 40μM of TET, there
was less enhancement of TET permeation across the barrier.
Figure 1: A schematic representation of the study hypothesis. Drug aggregates formed at
higher concentrations are broken when a solid interface is introduced in a nonequilibrated system. This has the potential to increases drug permeation through the skin.
Methodology
!  Different concentrations of tetracaine were prepared in
ultra pure water from a stock solution of 1 mM. The solutions
were maintained at 32 oC and pH 4. The suspension
medium of additives (i.e. electrolytes and nanoparticles)
were corrected to pH 4 prior to the addition to tetracaine.
!  Transport studies were conducted using vertically upright
Franz diffusion cells fitted with silicone membrane (0.12
mm). At different time points, 1 mL of the receiver fluid was
removed and analyzed using high-performance liquid
chromatrography (HPLC) fitted with a fluorescence
detector.
!  F luorescence spectroscopy (Varian Cary Eclipse
Fluorescence Spectrometer, Agilent Technologies, UK) was
used to characterise the solution state properties of
tetracaine in water at pH 4.
Conclusions
!  The addition of nanoparticles enhanced tetracaine
permeation.
!  N anoparticles were shown to modify tetracaine
aggregation.
!  The provision of a surface in a non-equilibrated system
provided the greatest enhancement of tetracaine.
References
[1] T. Prow et al. , Advanced Drug Delivery Reviews, 63 (2011) 470-491.
[2] S. Schreier et al. , Biochimica Physica Acta, 1508 (2000) 210-234.
[3] B. Feng et al. , Journal of Medicinal Chemistry, 50 (2007) 2385-2390.
Figure 3: Graph depicting the changes in fluorescence
intensity at λemission = 372 nm. The insert is an expansion of
the data when a 2nd derivative function is applied.
Figure 4: Steady-state flux of 40 µM of tetracaine (black)
with the addition of phosphate ions (white), carboxylmodified polystyrene nanoparticles, NanoPSCOO-(grey)
and unmodified silica nanoparticles, NanoSiO2(light grey)
across silicone membrane. Inset shows the permeation
profiles. Each point represents the mean ± standard
deviation, n=5.
Providing a solid surface in a non-equilibrated system
!  NanoPSCOO- generated a significant
blue shift of 21 nm and a 20-fold
increase in fluorescence emission
(p<0.05). However, there was no
significant changes observed when
NanoSiO2 was added (p>0.05)(Fig 5).
!  The data suggested that tetracaine
adsorption to NanoPSCOO- was stronger
than to NanoSiO2.
!  A balance of interactions between
the surface and tetracaine is required
– Strong hydrogen bonds does not
enhance drug permeation
(NanoPSCOO-) but weak interactions
enhance permeation (NanoSiO2).
Figure 5: Fluorescence spectrum of 10 µM of tetracaine
before (black) and after the addition of phosphate ions
(red), carboxyl-modified polystyrene nanoparticles,
NanoPSCOO-(blue) and unmodified silica nanoparticles,
NanoSiO2(pink).