Journal of Nutritional of Environmental Medicine (2002) 12, 101– 106

D. RADFORD SHANKLIN MD FRSM, ^1,2 DAVID L. SMALLEY PHD, ^1,3 AND

MARY FRANCES HALL MT ³

Departments of ¹ Pathology and ² Obstetrics and Gynecology, University of

Purpose: To study the effect of injected or implanted silicones other than mammary devices on siloxane T_H cell immune memory by lymphoblast transformation.

Design: Study of 43 individuals with silicone implants compared with controls.

Materials and Methods: Twenty-two men and 21 women, injected or implanted with silicones other than mammary devices, were tested for siloxane T_H cell immune memory by lymphoblast transformation. They received an arm muscle implant, block silicone as bone grafts, penile and testicular devices, silicone-containing temporomandibular joint prostheses,silicone-sheathed cardiac pacemaker wires, chin implants, toe replacements, tissue injections, or heavy industrial exposure. The control subjects were drawn from the medical center staff. Concanavalin A (Con A) was the mitogenic control.

Results: The mean stimulation indexes for the Con A control were 269.78 ± 30.24 (subjects) and 284.17 ± 39.18 (controls), p= .3857, not significant. The mean stimulation index for siloxane was 104.44 ± 13.66 for subjects, against 4.47 ± .75 for controls,

p < 0.0001, highly significant.

Conclusions: Injection of silicones or non-mammary silicone device implantation has the immunogenic potential and consequences seen after exposure to mammary devices.

INTRODUCTION

The diversity of medical [1] and commercial [2] applications of silicones over the past half century has been matched by an increasing awareness of their potential to induce disease largely through inflammatory and immunopathic mechanisms [1, 3].

The silicones used medically are complex mixtures of short- and long-chain polymers based, usually, on polydimethysiloxane (PDMS) as the core molecular construct. Siloxane refers to the alternating oxygen and silicon atoms, with the methyl groups in PDMS attached to silicon sterically opposite the oxygens in the – silicon– oxygen– silicon– oxygen– repeating motif [1, 4, 5]. The basic siloxane construct found in all varieties of silicone is

Twenty-one synonyms are listed, including Silicone DC 200 which is a principal starting point for medical device manufacture, with the descriptive note: an experimental teratogen, known experimental reproductive effects. Entered in the Environmental Protection Agency (EPA) Genetic Toxicology Program and in the EPA TSCA Inventory.

shared with all forms of silica and complex silicates, including numerous well-known minerals [6, 7]. The interrelation of these various moieties to the immune system has been described elsewhere [1]. In this paper, we use the term siloxane as the principal reference phrase as it has been shown that comparable T lymphoblast transformation follows stimulation by colloidal crystalline silica, amorphous silica, fumed amorphous silica, Dow Corning 200 fluid, Dow Corning MDX-4– 4011 fluid, samples from a wide variety of silicone implant materials, common teachers’ chalk (silica and calcium carbonate), and several mixtures of these ingredients [8, 9]. Moreover, so-called medical grade silicone elastomers often contain large amounts of silica [10] which has to be accepted as a confounding variable. We do not dismiss the possible significance of lesser ingredients in silicone devices as implanted, e.g. platinum residues, but the T cell response to metals used as catalysts is independent of the response to silicones, silicas, or silicates [8– 11]. Finally, the relative polarity of the siloxane bond with methyls or other organic groups or side chains on one side of the silicon– oxygen links offers a highly reactive common epitope to antigen-presenting cells and established T cell receptors [4, 8–13]. The term silicone will be reserved in connection with specific devices or classes of implant or material.

Little attention has been paid to the consequences of the surgical use of non-mammary silicone medical devices [14, 15], except for the small Swanson joint prostheses [16– 20].

Even less attention has been paid to the occupational or industrial hazards of silicones generally, and the subject is virtually absent from medical literature. Basic chemical and materials compendia sometimes provide otherwise. For example, the fourth edition of Hazardous Chemicals Desk Reference (1997) has an informative entry (Table 1) [21].

Second-order analyses of T lymphocyte data have revealed time-related patterns [3] for silicone mammary devices. A study of T lymphocyte memory using lymphoblast transformation has not yet been reported for less often implanted silicone materials. The isolation of 43 such cases in the database of the Memphis Pathology Laboratory during a recent review represents a significant sample for analysis. Some interesting information was found in this data subset.

MATERIALS AND METHODS

The special immunology section of the Memphis Pathology Laboratory has carried out more than 7500 lymphoblast transformation tests for T cell memory to siloxane epitopes since a development period in late 1993. The research records for this work have been maintained in accordance with standard Institutional Review Board procedures. The records of non-mammary silicone encounters were sanitized by the removal of specific patient identifiers and then underwent independent classification and analysis by the senior author (DRS). This study was based on 43 individuals with siloxane (silicone) device implantation or exposure (Table 2).

The retained information was the age and sex of the person, the type of siloxane exposure, the duration of siloxane exposure, the timing of tests relative to siloxane exposure, and the T cell indexes for siloxane and Concanavalin A (Con A) [3, 10, 12]. As

TABLE 2. Silicone devices and siloxane exposures in 43 individuals

before, control samples from individuals never exposed to silicones were run with each sample or small batches of samples [3, 10, 12].

Briefly, the test consisted of the isolation of lymphocytes from peripheral blood samples through standard Ficoll-Paque (Pharmacia LKB Biotechnology AB, Uppsala, Sweden) centrifugation, washing, and culture in microtiter plate wells; after 4 days of growth, 50 µl of tritiated thymidine was added to all wells. Pulsed lymphocytes were harvested at 18 hours, dried, and tested in a Beckman beta scintillation counter.Triplicate samples were run and the stimulation index (data point/unstimulated background value) for siloxane and Con A as the mitogenic control for cell viability were averaged and recorded [8, 10, 12].

The original data collection included the reported signs and symptoms for each person; these were inventoried independently and are summarized in Table 3.

RESULTS

There were 22 males and 21 females. The average age was 45.74 ± 1.57 years. Silicone exposure times ran from 1.33 to 30.0 years with a mean of 10.68 ± 1.12 years.

Fifteen individuals had their devices removed prior to testing, ranging from 1 month to 6.33 years earlier. Obviously, subjects afflicted by injection or industrial exposure could not have the primary deposit removed.

TABLE 3. Signs and symptoms reported for non-mammary siloxane exposures (patient questionnaires) *

* All diagnoses were by outside physician s with no association with the laboratory or any author of this report.

TABLE 4. T lymphocyte stimulation indexes after non-mammary siloxane (silicone) exposure

* One-tailed test.

SEM, standard error of the mean.

Stimulation indexes, calculated as before [8, 10, 12], revealed strikingly high T cell indexes for active immune siloxane memory following implantation or other exposure (Table 4). By contrast, no difference was expected in the index for mitogen Con A and none was found.

There were several patterns over time, not shown here, which had remarkable similarities to those seen for silicone mammary devices [3]:

• Duration of exposure and/or retention of material were longer with age progression (expected colinearity).
• Sample Con A stimulation indexes fell slightly with age progression.
• Sample siloxane stimulation indexes fell slightly with age progression.
• Direct plots of both the siloxane index and the ratio of the Con A index to the siloxane index showed peaks over time, followed by declines to 30 years. The peak for the direct plot was at 5– 7 years within a broader cluster of peaks from 7 to 13 years. The peak for the ratio was at 9– 12 years. The earlier direct peak was thought to be due to inclusion of individuals subjected to silicone injections or chronic industrial exposure. Further study, after elimination of the subjects receiving injections or exposed industrially, yielded a similar overall pattern with minor differences in peaks, so this factor did not become a major point in the analysis (data not shown). The silicone mammary device peak is over the interval 9– 12 years [3], matching this subset ratio fairly well.
• There was an increased index following removal of these non-mammary devices which peaked at 2.75 years, very close to the silicone mammary implant peak of 3.00 years [3].

INTERPRETATION AND COMMENTARY

A comparable analysis of experience with Norplant® contraceptive devices showed highly similar responses for T lymphocyte memory over coterminous time courses despite the great difference in the aggregate contact surface of the six implanted tubes of Norplant® relative to mammary devices [22].

This principle pertains here as well because several persons had very small volumes of injected silicone, yet their immune memory was as well stimulated as in the other situations, the various specific device implantations.

This leads to a useful interpretation, drawing all of these observations together: the time interval is a more important factor than the volume of material once the minimal threshold has been reached. Moreover, it now seems that the minimum amount needed for immunostimulation is very small, a few cubic centimeters, for volumes, or several square centimeters, for contact surfaces, planar or curved, at most.

Accordingly, what is observed here, in part, is the amplifying power of cellular immune reactions. Amplification of the immune signal, reinforced by autocrine secretion of interleukin-2 by activated T lymphocytes, can be of the order of more than 500 times, at just one step in the process [23].

These conclusions are well supported and confirmed by the histopathology of periprosthetic capsules engendered by implanted silicone (siloxane) devices [3, 13, 24].

The diversity of siloxane oligomers and polymers represented by these devices, in the four main types of mammary implant from different manufacturers, and by the Norplant® design, argues very strongly for a single common epitope, or some immunologically indistinguishable, highly similar physicochemical molecular attribute, as the essential stimulogen.¹ The working hypothesis is in the negative; it does not matter which siloxanes make up a copolymer, elastomer, or oil in contact with the host (patient or experimental animal). As long as the outer casing (envelope), the contact surface for medical devices, is

made of silicone, this simple fact controls the initiation and the direction of the immunopathic reaction. Time will determine the intensity and the ultimate cellular mix of the late stage response, including periprosthetic capsular scars [3].

This report is not an analysis of the symptomatology or the differential diagnosis of sequelae of silicone device implantation. However, the reported signs and symptoms summarized here resemble comparable lists from women with silicone-based mammary devices [25].

NOTE

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