Intervariability and Intravariability of Bone Morphogenetic Proteins in Commercially Available Demineralized Bone Matrix Products

Abstract

Study Design. 

Enzyme-linked immunosorbent assay was used to detect bone morphogenetic proteins (BMPs) 2, 4, and 7 in 9 commercially available (“off the shelf”) demineralized bone matrix (DBM) product formulations using 3 different manufacturer’s production lots of each DBM formulation.

Objectives. 

To evaluate and compare the quantity of BMPs among several different DBM formulations (inter-product variability), as well as examine the variability of these proteins in different production lots within the same DBM formulation (intra-product variability).

Summary of Background Data. 

DBMs are commonly used to augment available bone graft in spinal fusion procedures. Surgeons are presented with an ever-increasing variety of commercially available human DBMs from which to choose. Yet, there is limited information on a specific DBM product’s osteoinductive efficacy, potency, and constancy.

Methods. 

There were protein extracts from each DBM sample separately dialyzed 4 times against distilled water at 4°C for 48 hours. The amount of BMP-2, BMP-4, and BMP-7 was determined using enzyme-linked immunosorbent assay.

Results. 

The concentrations of detected BMP-2 and BMP-7 were low for all DBM formulations, only nanograms of BMP were extracted from each gram of DBM (20.2–120.6 ng BMP-2/ g DBM product; 54.2–226.8 ng BMP-7/ g DBM). The variability of BMP concentrations among different lots of the same DBM formulation, intra-product variability, was higher than the variability of concentrations among different DBM formulations, inter-product variability (coefficient of variation range BMP-2 [16.34% to 76.01%], P < 0.01; BMP-7 [3.71% to 82.08%], P < 0.001). BMP-4 was undetectable.

Conclusions. 

The relative quantities of BMPs in DBMs are low, in the order of 1 × 10⁻⁹ g of BMP/g of DBM. There is higher variability in concentration of BMPs among 3 different lots of the same DBM formulation than among different DBM formulations. This variability questions DBM products’ reliability and, possibly, efficacy in providing consistent osteoinduction.

In Brief

The concentrations of bone morphogenetic proteins (BMPs) 2, 4, and 7 were assayed in commercially available demineralized bone matrix (DBM) products. BMP-2 and BMP-7 were detected, while BMP-4 was not detected using enzyme-linked immunosorbent assay. There was higher variability in the concentration of BMPs between different production lots of the same formulation (intra-product variability) than among different DBM products (inter-product variability). In previous animal and human clinical studies, this lot-to-lot variability was not recognized. Each tested DBM product was assumed to be identical in quality to the next, as long as its product name was identical. This intra-product variability may explain the inconsistent results in previous animal studies and should be considered in future studies evaluating DBM products.