Light Control of Insulin Release and Blood Glucose Using an Injectable Photoactivated Depot

In this work we demonstrate that blood glucose can be controlled remotely through light stimulated release of insulin from an injected cutaneous depot. Human insulin was tethered to an insoluble but injectable polymer via a linker, which was based on the light cleavable di-methoxy nitrophenyl ethyl (DMNPE) group. This material was injected into the skin of streptozotocin-treated diabetic rats. We observed insulin being released into the bloodstream after a 2 min trans-cutaneous irradiation of this site by a compact LED light source. Control animals treated with the same material, but in which light was blocked from the site, showed no release of insulin into the bloodstream. We also demonstrate that additional pulses of light from the light source result in additional pulses of insulin being absorbed into circulation. A significant reduction in blood glucose was then observed. Together, these results demonstrate the feasibility of using light to allow for the continuously variable control of insulin release. This in turn has the potential to allow for the tight control of blood glucose without the invasiveness of insulin pumps and cannulas

Protein levels of Nampt in human islets are greater with age.

<p>Examples of Nampt (blue) and insulin (green) immunofluorescence co-staining in islets from donors varying from 19 weeks gestation to 72 years old. <b>A–D:</b> In fetus and young children Nampt staining was weak with little co-localization with insulin in beta cells. <b>E–H:</b> In adults, Nampt staining was stronger and more localized to beta cells. <b>I:</b> Analysis of the Nampt pixel intensity illustrates the change with age.</p

Donor Demographics.

<p>KU Path, University of Kansas Pathology; BTB, National Institute of Childhood Diseases Brain and Tissue bank for Developmental Disorders at the University of Maryland, Baltimore MD; n/a, not available.</p

Co-localization of insulin, glucagon, and Nampt.

<p>Immunofluorescence image of an islet from an adult male stained for insulin, glucagon and Nampt. <b>A:</b> insulin staining (beta cells) using anti-insulin antibody (green). <b>B:</b> Glucagon was identified in the same islet (alpha cells) using anti-glucagon antibody (blue). <b>C:</b> Nampt was identified in the same islet using anti-Nampt antibody (red) and is found in both the islet and surrounding exocrine tissue. <b>D:</b> Overlap of all 3 images shows that the majority of Nampt co-localizes with insulin in beta cells.</p

Nampt in situ binding assay – summary of conditions tested.

<p>PFA, paraformaldehye; HCL, hydrochloric acid; RT, room temperature.</p

Protein pattern of Nampt in human islets changes with age.

<p>The difference in Nampt staining in endocrine and exocrine cells is clear. A: Fetal pancreatic tissues showed nearly equal Nampt staining levels in endocrine (within white circled regions) and exocrine tissue. B: In contrast, tissue from a 39 year old shows bright Nampt staining within the islet. C: The ratio of endocrine to exocrine pixel intensity illustrates the change with age. Of note, total image brightness was increased by 20% for every pancreatic image analyzed for figure C in order to visualize the low levels of Nampt staining in the fetal tissues.</p

The effects of glucose on Nampt gene and protein expression levels in human islets.

<p>Total RNA or protein was isolated from islets treated for 1 hour in 20 mM glucose. <b>A:</b> Nampt gene expression was upregulated in the presence of 20 mM glucose compared to control (2.2 mM glucose) by qRT-PCR. Each bar represents the mean fold change normalized to β-actin from five separate experiments.*P<0.05; student T test <b>B:</b> Nampt protein content did not increase in the presence of 20 mM compared to 2.2 mM glucose by western blot analysis. Shown is a representative blot from 6 separate experiments.</p

Quantification of Nampt mRNA

<p>. Total RNA was isolated from <b>A.</b> human pancreatic tissue or <b>B.</b> isolated human islets. NAMPT mRNA was quantified using a Nampt specific Taqman assay (Applied Biosystems/Life Technologies, Carlsbad, CA.) according to the manufacturer's instructions and normalized with GUSB. *Note: The Y axis uses C_T values (C_T is the threshold cycle of detection), thus increased target mRNA results in earlier detection by qRT-PCR (i.e., a smaller C_T).</p