(626a) Electrostatic Complexation of Insulin and Polycations As Glucose-Responsive Delivery Systems

115%">Electrostatic
complexation of insulin and polycations as glucose-responsive
delivery systems

115%">Lisa R Volpatti, Delaney M. Burns, Arijit
Basu, Robert Langer, and Daniel G. Anderson

.0001pt;mso-add-space:auto;text-align:center;line-height:115%">Koch Institute & Department of
Chemical Engineering, MIT, Cambridge, MA 02139

Motivation: Diabetes mellitus is a disease characterized by poor glycemic control
which often leads to severe complications including cardiovascular disease and
kidney failure. Many diabetic patients continually monitor their blood sugar
and self-administer multiple daily doses of insulin to combat hyperglycemia. To
reduce this burden and better mimic native insulin activity, extensive progress
has been made on biomaterials-based self-regulated insulin delivery systems.
However, the vast majority of these glucose-responsive systems do not rapidly respond
to small, physiologically relevant changes in blood sugar. Here, we report a
glucose-responsive insulin delivery system based on the electrostatic
complexation of insulin and a model polycation with
enhanced glucose sensitivity and release kinetics.

" arial>Methods: font-family:" arial> Since insulin has an isoelectric point around
neutral pH, it is slightly negatively charged at physiological pH. A model polycation, polyethylenimine (PEI) was used to test the hypothesis that
electrostatic complexes could serve as glucose-responsive insulin delivery
vehicles. Nanoparticles (NPs) were fabricated using a sonication/solvent evaporation
method under basic conditions to form insulin-PEI complexes containing glucose
oxidase (GOx). GOx converts
glucose to gluconic acid and reduces the pH of the
microenvironment when glucose levels are high. The shift in pH causes the
insulin to switch from negatively to positively charged, thus repelling the polycation and being released from the complex (Fig 1a).

" arial>Results: font-family:" arial>Insulin is released from the complexes after ~2
h in response to elevated glucose concentrations (400 mg/dL)
in vitro (Fig  1b).
Under physiological glucose conditions (100 mg/mL), on the other hand, < 30
% of insulin is released after 18 h of incubation in 37 °C and shaking, showing
high sensitivity to physiologically relevant glucose changes. Furthermore, virtually
no insulin is released when no glucose is present. The NPs also show reversible
release in response to alternating concentrations of glucose. In Fig 1c, the
blue circles represent NPs that were incubated in 400 mg/dL
glucose for the first hour and then alternatively incubated in low and high
glucose concentrations for subsequent hours. The orange squares represent NPs first
incubated in 100 mg/dL glucose and similarly incubated
in alternating glucose concentrations for the following 7 h. The amount of
insulin released in each case shows a reversible increase in response to
elevated glucose concentrations, and this trend holds for the duration of the
study. Additionally, preliminary in vivo data using a diabetic mouse model shows
that the insulin remains active after encapsulation and release and can
successfully reduce blood glucose levels.

Conclusions: Nanoparticles formed from the electrostatic complexation of insulin and a
polycation may be an effective self-regulated insulin
delivery system. Here we show proof-of-concept that these NPs provide rapid and
sensitive glucose-responsive insulin release. 11.0pt;font-family:" arial>