Seminar Information:

Speaker:

Sheldon Lin, MD
Associate Professor
Department of Orthopedic Surgery
University of Medicine and Dentistry of New Jersey
NJ Medical School

Title:

The Effect of Local Ultralente Insulin on Non-Diabetic Fracture Healing

Abstract:

With over six million annual fractures, approximately 600,000 of which result in non-union, clearly a need exists to treat patients suffering from non-healing fractures.  Some risk factors for compromised healing include smoking, excessive drinking, obesity, and several endocrine and metabolic diseases.  Several studies looking at tight systemic glucose control and local insulin depot, despite a poorly controlled DM state, demonstrated normalization of DM fracture healing (Beam et al 2002, Gandhi et al Bone 2005)We hypothesize local insulin may accelerate osseous healing in non DM fracture model.

The purpose of this study was to quantify the effect of local Ultralente insulin (10 units intramedullary(IM)) on bone fracture healing, compared to untreated saline controls in non-DM (diabetes mellitus) BB Wistar rats upon the early and late parameters of fracture healing.  Early parameters included cell proliferation using 5-bromo-2’deoxyuridine (BrDU) and early histology was performed at days 4 and 7 post fracture.  Other parameters included real time PCR analysis for the expression of osteogenic and chondrogenic markers. Late outcome parameters included mechanical testing using torsional testing and histomorphometry at 3 and 4 weeks.

First we analyzed the duration of local insulin implanted IM. Normalized to total protein levels (ng/mg) using BCA, local insulin levels showed no significant increase of local insulin levels between the fractured and contralateral femora at days 2 and 4, demonstrating complete release at 2 days.  Further analysis will examine release at 12 and 24 hours after local delivery. 

Histomorphometric analysis showed no difference in callus area or number of proliferating cells per unit area at 4 days, indicating no enhancement of cell proliferation at this time point.  The osteoid matrix area appeared to be enhanced with insulin, but values only trended towards significance.  At day 7, histomorphometry of local insulin group showed a significant increase in osteoid matrix (P=0.03), with no significant increase in callus area.  Real time PCR analysis revealed local insulin treatment significantly enhances the expression of osteopontin by day 4 post-fracture and  of collagen type  1a2 by day 7 post-fracture when compared to the untreated saline group.  Analysis of collagen type 2a1 and type 10a1 expression showed no difference at days 4 and 7.  By week 3, percent bone was significantly increased in insulin treated animals compared to saline controls (P=0.036).  .  This suggests that local insulin is having its primary osteogenic effect at early time points (1-3 weeks).

Mechanical testing revealed a significantly greater maximum torque to failure (P=0.005) and shear stress (P=0.02) in insulin treated animals, with torsional rigidity and shear modulus trending toward significance at four weeks.  Six week mechanical testing results revealed no difference in mechanical parameters between the saline and insulin treated animals. 

These results suggest the role of Ultralente insulin as an adjunct for normal fracture healing by altering the slope of the normal stress-strain curve in bone and accelerating healing by week 3, with untreated animals catching up at week 6 in their healing.