(396g) Targeting and Altering In Vivo macrophage Responses with Modified Polymer Properties

Targeting and altering in vivo macrophage responses with
modified polymer properties

Kaitlin
Bratlie

Departments
of Materials Science & Engineering and Chemical
& Biological Engineering, Iowa State University

Introduction:
Two
pathways for activating macrophages (MΦs) exist. One of these routes is
termed the classically activated M1 pathway and is achieved through exposure to
lipopolysaccharide (LPS). M1 MΦs are known as pro-inflammatory cells. The
other pathway is reached through interleukin-4 (IL-4) and is known as the
alternatively activated M2 pathway. M2 MΦ produce pro-angiogenic factors.
Here, we successfully use in vivo
imaging and histological analysis to identify the MΦ response and
activation. We demonstrate the ability to induce various MΦ phenotypes
with a change in material functionality as well as identify certain materials
parameters that seem to correlate with each phenotype. This suggests the
potential to develop materials for specific applications and predict the
outcome of MΦ activation in response to new surface chemistries.

Materials
and Methods: The poly(N-isopropylacrylamide) (pNIPAm)
(~600nm) particles were synthesized using established methods and modified
through conjugation with surface modifiers through carbodiimide chemistry.
MΦs were polarized to the M1 and M2 phenotypes and internalization of
functionalized pNIPAm particles were measured. These
materials were also subcutaneously injected in SKH1-E mice. Arginase:iNOS profiles have been consistently used as a
measure of MΦ phenotype. Arginine
activity was measured indirectly through a urea assay in which the lysate was
activated, exposed to arginine, and conversion to urea was quantified. Nitrites
were measured through a Griess reagent assay to
indirectly determine the levels of inducible nitric oxide synthase (iNOS). Material properties of the modified particles
including water contact angle, melting temperature, and zeta-potential were
also measured.

Results
and Discussion: SKH1-E mice were injected with the polymer
particles and imaged for cathepsin activity (Figure 1). A range
in cathepsin activity was observed for the different surface modifiers. The
tissue sections from the mice in Figure 1 were excised and homogenized.
The arginase:iNOS displayed
a spectrum between the M1 and M2 phenotypes for different surface modifiers as
shown in Figure 2.

Distinct material parameters influence MΦ phenotypes.
For example, increasing the hydrogen bonding of polymeric particles can
polarize MΦs towards the M1
phenotype. The induction of multiple MΦ phenotypes confirms the
ability to control MΦ activation in
vivo and suggests the importance of chemical properties in the
biocompatibility of materials. The results obtained suggest that changing
properties can result in opposite MΦ phenotypes.

Conclusions:  With
this work, useful insight was gained about in
vivo MΦ response to various material functionalities. Overall, this in vivo study was successful at drawing
conclusions about the biomaterial parameters that will allow for tuning MΦ
polarization responses to biomaterials and targeting MΦs.