Assessment of silicone gel breast implant biodurability by NMR and EDS techniques.

In a study using explanted gel breast implants and appropriate nonimplanted controls, we examined silicone biodurability after long-term implantation. Using NMR spectroscopy, as well as NMR relaxometry measurements (T(2)), no evidence of hydrolysis or other chemical degradation of the cross-linked silicone matrix was observed in specimens from an early breast implant model (Cronin) explanted after 32 years in vivo or a more recent Silastic II model after 13 years in vivo. In addition, no appreciable differences were seen in T(2) relaxation times comparing explanted breast implants to suitably-matched nonimplanted controls, further underscoring the biostability of the cross-linked silicone shell and gel. Our T(2) data and resultant interpretations differ from a 2004 report by the NMR lab at the University of Münster, highlighting the importance of suitable nonimplanted controls and sample preparation. Energy dispersive spectroscopy (EDS) was also performed, confirming the persistence of a fluorosilicone layer inside the elastomer shells of Silastic II implants.

Assessment of autoimmunity-inducing potential using the brown Norway rat challenge model.

The development of autoimmune disease in humans is thought to occur as a result of the interactions of a genetic predisposition of the host and environmental factors. There is evidence that treatment with certain drugs and exposure to environmental toxicants increase the risk associated with the development and severity of autoimmune disease. When exposed to certain chemicals, Brown Norway (BN) rats develop autoimmune disease similar to human systemic lupus erythematosus (SLE) characterized by elevation of antibody levels to self and non-self antigens which can result in the formation of immune complexes and lead to a fatal glomerulonephritis. A unique characteristic of the BN rat model is that the increase in IgE is self-limiting with levels eventually returning to normal. The objective of these studies was to determine if the BN rat and the self-limiting nature of the IgE response could be used in identifying compounds capable of initiating autoimmune responses. Two compounds known to produce autoimmunity, mercuric chloride and D-penicillamine, were studied as were, trichloroethylene and silicone gel, two agents suspected of inducing autoimmune disease. The results indicated that the BN rat model may prove useful for detecting compounds with the potential to produce autoimmunity, particularly if a HgCl(2) challenge is incorporated into the evaluation.

Toxicology and humoral immunity assessment of octamethylcyclotetrasiloxane (D4) following a 28-day whole body vapor inhalation exposure in Fischer 344 rats.

Octamethylcyclotetrasiloxane, D4, is a low viscosity, silicone fluid consisting of four dimethyl-siloxy units ((CH3)2SiO)4 in a cyclic structure. It is primarily used as a building block in the industrial synthesis of long chain silicone polymers. The combination of D4 with decamethylcyclopentasiloxane (D5) is commonly referred to as cyclomethicone which has a wide range of applications as a formulation aid in personal care products. To extend the existing database regarding the biological activities of D4, a 28 day whole body vapor inhalation study was conducted using Fischer 344 rats at 0 (room air), 7, 20, 60, 180 and 540 ppm for 6 hours/day, 5 days/week. Parameters measured included body weights, organ weights, gross pathology, histopathology, serum chemistries, and urinalysis. In addition to these standard toxicological endpoints, the ability of D4 exposed animals to mount an IgM antibody response was evaluated by a splenic antibody forming cell (AFC) assay and a serum enzyme-linked immunosorbant assay (ELISA). The results of this 28-day inhalation study indicate that D4 exposure caused no adverse effects on body weight, food consumption, or urinalysis parameters. In addition, there were no exposure related histopathological alterations at any site for any exposure group. A statistically significant increase in liver weight and the liver to body weight ratio was observed in both male (180-540 ppm) and female (20-540 ppm) rats, which was not observed in the 14-day recovery group animals. There were no other significant organ weight changes. Although statistically significant changes were observed in several hematological and serum chemistry parameters in both the terminal and 14-day recovery animals, the changes were marginal and within the normal range of values for the rat. Under these experimental conditions, there were no alterations noted in immune system function at any of the D4 exposure levels.

Acute respiratory exposure of human volunteers to octamethylcyclotetrasiloxane (D4): absence of immunological effects.

Humans are exposed to silicones in a number of commercial and consumer products. Some of these silicones, including octamethylcyclotetrasiloxane (D4), are volatile. Therefore, there is a potential for respiratory exposure. A pharmacokinetic analysis of respiratory exposure to D4 is presented in the accompanying paper (M. J. Utell et al., 1998, Toxicol. Sci. 44, 206-213). Possible immune effects of respiratory exposure to D4 are investigated in this paper. Normal volunteers were exposed to 10 ppm D4 or air for 1 h via a mouthpiece using a double-blind, crossover study design. Assays were chosen to screen for immunotoxicity or a systemic inflammatory response. Assessment of immunotoxicity included enumeration of peripheral lymphocyte subsets and functional assays using peripheral blood mononuclear cells. Because in humans there is no direct test for adjuvant effect of respiratory exposure, we analyzed proinflammatory cytokines and acute-phase reactants in peripheral blood, markers for a systemic inflammatory response, as surrogate markers for adjuvancy. These tests were repeated when the volunteers were reexposed to D4 approximately 3 months after this initial exposure. Blood was obtained prior to exposure, immediately postexposure, and 6 and 24 h postexposure. In these short-term, controlled human exposures, no immunotoxic or proinflammatory effects of respiratory exposure to D4 were found.

The non-specific binding of immunoglobulins to silicone implant materials: the lack of a detectable silicone specific antibody.

Recent studies have suggested that anti-silicone antibodies develop in patients implanted with silicone materials. The majority of these studies have utilized enzyme-linked immunosorbent assay (ELISA) methodology with a silicone material substrate as a means to detect the presence of the anti-silicone antibody. The current studies were undertaken to determine whether the binding of IgG to a silicone substrate was consistent with an antigen-specific antibody interaction or the result of non-specific hydrophobic interactions. While significant differences were detected in serum from silicone antibody "positive" and "negative" patients when the ELISA was conducted using a phosphate buffered saline (PBS)-0.05% Tween 20 (Tween) blocking system, the difference in the responses was attenuated when protein blocking systems were used or when incubation times were decreased. Furthermore, ELISA studies, using purified mouse and human IgG, demonstrated a concentration-dependent binding of IgG to silicone elastomer substrate which was also attenuated when a protein blocking system was used in lieu of Tween. In controlled animals studies in which female B6C3F1 mice were implanted with silicone gel or silicone elastomer for 180 days, no difference was observed between the implanted animals and the PBS control animals with respect to binding of IgG to the silicone substrate. Similar studies in female Fischer 344 rats implanted with silicone gel for 84 days also failed to demonstrate the presence of anti-silicone antibody. Collectively, the results suggest that the binding of IgG to silicone implant materials is non-specific in nature, consistent with the well-recognized interactions between hydrophobic molecules (IgGs) and hydrophobic surfaces (silicones) in an aqueous-based system.

Toxicology and humoral immunity assessment of decamethylcyclopentasiloxane (D5) following a 1-month whole body inhalation exposure in Fischer 344 rats.

D5 is a low-molecular-weight cyclic siloxane used for industrial and consumer product applications. The objective of the present study was to assess potential toxic and immunomodulatory consequences of inhalation exposure to D5. Male and female Fischer 344 rats (25/group) were exposed by whole body inhalation to 0, 10, 25, 75, or 160 ppm D5 6 h/day, 7 days/week for 28 days. Clinical signs, body weights, and food consumption were recorded. On the day following the final exposure, 10 rats/group/sex were euthanized and a complete necropsy performed. Following a 14-day nonexposure recovery period, the remaining 5 rats/sex/group were necropsied. Body and organ weights were obtained and a complete set of tissues was taken for histopathology. Samples were also collected for serum chemistry, hematology, and urinalysis. Immunotoxicology-designated rats (10/sex/group) were immunized with sheep erythrocytes (sRBC) 4 days prior to euthanasia and cyclophosphamide (CYP) was administered i.p. to positive controls on days 24 through 28. The anti-sRBC antibody-forming cell (AFC) response was evaluated in a standard plaque assay. Blood was also collected for examination in the anti-sRBC enzyme-linked immunosorbant assay (ELISA). D5 exposure did not modulate humoral immunity, while the internal control, CYP, produced the expected suppression of the AFC response. D5 exposure caused no adverse effects on body weight, food consumption, or urinalysis parameters. Serum alkaline phosphatase (SAP) was significantly decreased in females at terminal (12%, 160 ppm) and recovery sacrifice. A significant increase in the liver-to-body weight ratio was observed in female animals at the end of exposures (13%, 160 ppm), but was not noted in recovery animals from the same exposure group. In males, significant increases in liver-to-body weight (5%) and thymus-to-body weight (14%) ratios were also noted at the high dose at terminal sacrifice and were not present at recovery. At recovery only, a significant increase in spleen-to-body weight ratios (14 and 17%; 25 and 160 ppm, respectively) was noted. At the end of exposure, histopathological analysis indicated an increased incidence and severity of nasal (Level 1) goblet cell proliferation. Focal macrophage accumulation in the lung was also observed to be increased in incidence in both sexes at 160 ppm. At the end of the recovery period, the effects in both of these organs appeared to be reversible. In summary, D5 inhalation exposure did not alter humoral immunity and caused only minor, transient changes in hematological, serum chemistry, and organ weight values. Histopathological changes were confined to the respiratory tract and appeared to be reversible. The no observed effect level for systemic toxicity, based primarily on the liver weight changes, was 75 ppm.

The adjuvancy of silicones: dependency on compartmentalization.

Studies have been conducted in mice (B6C3F1) and rats (Sprague Dawley, Fischer 344) to investigate the adjuvancy potential of silicone mammary gel and the low molecular weight silicone fluid, octamethylcyclotetrasiloxane (D4). Dependent on the experimental conditions employed, a divergent data profile emerges. If the antigen (bovine serum albumin, BSA) is emulsified with either the gel or the D4 prior to intramuscular immunization, an amplified anti-BSA IgG antibody response, as measured by multipoint ELISA methodology, is noted over the 8 week measurement period. In parallel studies, a variety of non-silicone personal care ingredients (lanolin, white mineral oil, isopropyl palmitate) were also capable of amplifying this humoral response relative to the non-adjuvant phosphate buffered saline control. These observations are consistent with the empirical knowledge that hydrophobic substances tend to augment immune responses. However, under conditions in which the antigen is not blended with the silicone prior to immunization, normal immune responses are noted. In short (10 day) and long (180 day) term gel implant studies, the optimal IgM and IgG antibody responses, as determined in the antibody forming cell assay, were equivalent between the gel implanted and control animals. Moreover, under similar exposure conditions, no adjuvancy was noted in the three Host Resistance models (B16F10 Melanoma, Listeria monocytogenes, and Streptococcus pneumoniae) tested. Antibody forming cell studies conducted after 28 days of oral or inhalation exposure to D4 have also yielded responses similar to the non-silicone exposed vehicle controls. Collectively, these data suggest that in the absence of premixing the antigen with the silicone test material, there does not appear to be any silicone induced adjuvant response.

Characterization of a secreted cytoactive factor from Trichomonas vaginalis.

Trichomonas vaginalis, grown in Dulbecco's modified Eagle's medium with or without serum, produced a factor (TVF) which altered the morphology of certain mammalian cells in vitro. TVF had a Mr of approximately 250 kDa by gel filtration, approximately 50 kDa by SDS-PAGE, and was heat (56 degrees C, 30 min) and pH (greater than 6 or less than 8) labile. Co-incubation of TVF with adherent target cells caused a marked rounding and clumping of BHK-21 or CHO-K1 cells, but had no effect on RK-13 or WEHI-3 cells. These morphologic changes were concentration, time, and energy dependent. Reversibility was attained by exogenous serum addition (greater than 10%) or TVF washout. Target cell perturbations were not accompanied by significant changes in growth (as measured by nuclei counts, DNA content, or 3H-thymidine incorporation), in cell leakage (as assessed by lactate dehydrogenase release), or in cell viability (by trypan blue dye exclusion). TVF-induced effects were independent of cyclic AMP and cyclic GMP levels in BHK cells exposed for 5 min-24 hr.

Responsiveness of the Madison 109 lung carcinoma to maleic vinyl ether copolymer.

This study establishes the responsiveness of mice bearing the Madison 109 lung carcinoma (M109), a tumor relatively resistant to chemotherapy, to the immunomodulator maleic vinyl ether (MVE-2; molecular weight 15,500). BALB/c mice inoculated with 5 X 10(5) M109 cells into the hind footpad developed a primary tumor which metastasized to the lung within 7 days and resulted in death of the host between 36 and 42 days. Early in the disease, weekly intratumor (i.t.) or intravenous administration of MVE-2 (25 mg/kg) inhibited the growth of the primary tumor and significantly prolonged the life span of the host. During the pulmonary metastatic process, systemic administration of MVE-2 alone or MVE-2 coupled with surgical excision or radiotherapy of the primary tumor became decreasingly efficacious. Late in the disease only MVE-2 introduced directly into the metastatic tumor bed by intrapleural injection proved to be effective in prolonging life span. These studies indicate that both the primary and metastatic M109 tumors are sensitive to MVE-2 and suggest that the efficacy of MVE-2 treatment is largely dependent upon its distribution in the tumor-bearing mice.

Effects of cannabinoids on host resistance to Listeria monocytogenes and herpes simplex virus.

Previous investigations from our laboratories have demonstrated that cannabinoids possess immunosuppressive properties. The present studies were designed to determine whether these agents decrease host resistance to infections with Listeria monocytogenes and herpes simplex virus type 2. Host resistance was measured by changes in the 50% lethal dose of the pathogen in cannabinoid-treated and control mice. The effect of cannabinoids on resistance to L. monocytogens was dose dependent. Delta-9-tetrhydrocannabinol at doses of 38, 75, and 150 mg/kg suppressed resistance to infection by 10-, 17-, and 657-fold, respectively. Marijuana extract was less active but significantly reduced resistance to L. moncytogenes at all tested doses. Resistance to systemic herpes simplex virus type 2 infection was decreased 96-fold by delta-9-tetrahydrocannabinol, although marijuana extract was inactive. The doses and regimen of treatment with cannabinoids that produced significant decreases in host resistance were similar to those which caused suppression of delayed-type hypersensitivity to sheep erythrocytes. The possible mechanisms and public health aspects of the decreased host resistance produced by marijuana extract and its cannabinoids are discussed.

Immunosuppressive effects of 8,9-epoxyhexahydrocannabinol (EHHC).

8,9-Epoxyhexahydrocannabinol (EHHC)-treated mice showed an inhibition of both humoral and cell-mediated immunity. The hemolytic plaque forming assay was employed to determine both the IgM and IgG antibody response. The effect of EHHC on IgM antibody production was measured in BDG1 male mice given X 10(8) sheep erythrocytes i.p. followed 24 and 48 hours later by i.p. injections of EHHC. EHHC produced a dose-dependent inhibition of plaque forming cells (PFC)/10(6) spleen cells and PFC/spleen on days 3, 4 and 5 after antigen administration. On day 4 the ED50 for PFC/10(6) spleen cells and PFC/spleen was 28 and 18 mg/kg, respectively. Peak response to IgG antibody production was observed on day 9. EHHC (100 mg/kg) administered i.p. 48 hours after antigen produced a 58 and 46% suppression of PFC/10(6) leucocyte on days 7 and 9, respectively. CDF1 male mice received 100 microng of Cornybacterium parvum in the left footpad. Two days after sensitization, EHHC was administered in doses of 0.75 to 50 mg/kg i.p. A challenge dose of 100 microng of Cornybacterium parvum was injected into the right footpad on day 6 and footpad swelling was measured 24 hours later by mercury displacement. EHHC at a dose of 0.78 mg/kg produced a 95% inhibition of the delayed-type hypersensitivity response. These studies showed that EHHC inhibits both the humoral and cellular arm of the immune response.