Presentation 3 BIOCOMPATIBILITY AND MEDICAL APPLICATIONS OF SILICONE-BASED MATERIALS: REVIEW OF PERTINENT FINDINGS

Noel Rose, M.D., Ph.D.

The Johns Hopkins University

Background

The main issues surrounding silicone concern silicone gel-filled breast implants. Despite earlier contentions that implicated these implants in autoimmune diseases, more recent epidemiological studies refute this association. However, this debate did stimulate research on possible immunological effects deriving from a wider range of silicone implants.

Related research at the Rochester General Hospital produced findings in a rat model that silicone gel can act as an adjuvant, which is most simply described as a substance with the ability to enhance the immune response to a foreign or self-antigen. Despite the fact that millions of individuals have safely received adjuvants over the past 70 years as components of standard childhood vaccines, the Rochester report evoked concern. The concern was based on misunderstanding of what happens when adjuvants couple with self-antigen to produce, in laboratory models, autoimmune disease, in which pathology results from a misguided or misdirected immune response deleterious to the host. In response to that understanding, the Rochester study was reevaluated so as to confirm, or not, the contention that silicone gel can, in fact, serve as an adjuvant and, further, to see whether silicone elastomer of the type used in Norplant might have adjuvant properties.*

Methodology

Both rats and mice were used in these experiments. A standard adjuvant (Freund's) was used as the positive control and the silicone oil/gel mixture used in the Rochester study was the experimental material. All these materials were combined with a foreign substance, bovine serum albumen (BSA), to see whether there was any adjuvant effect. The procedure called for bleeding the rats and mice from the heart at regular intervals, carrying out tests to see how much antibody to BSA was present in the serum, and then sacrificing the animal at the end of the experiment and examining the implant sites.

In a second experiment, rats were injected with BSA mixed with particles of silicone elastomer of the type used in Norplant. Both large and small particles were used to reproduce the possible effects for breaking up over the life span of an

*  

JO Naim, RJ Lanzafame, and CJ Van Oss. The effect of silicone-gl on the immune response. Journal of Biomaterial Science-Polymer Edition 7(2):123-132. 1995.



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