Effects of a crystalline silica on antibody production to T-dependent and T-independent antigens in Balb/c mice

Impact of environmental factors and Sahara dust intrusions on incidence and severity of COVID-19 disease in Spain. Effect in the first and second pandemic waves

Scientific evidence suggests that Saharan dust intrusions in Southern Europe contribute to the worsening of multiple pathologies and increase the concentrations of particulate matter (PM) and other pollutants. However, few studies have examined whether Saharan dust intrusions influence the incidence and severity of COVID-19 cases. To address this question, in this study we carried out generalized linear models with Poisson link between incidence rates and daily hospital admissions and average daily concentrations of PM10, NO2, and O3 in nine Spanish regions for the period from February 1, 2020 to December 31, 2020. The models were adjusted by maximum daily temperature and average daily absolute humidity. Furthermore, we controlled for trend, seasonality, and the autoregressive nature of the series. The variable relating to Saharan dust intrusions was introduced using a dichotomous variable, NAF, averaged across daily lags in ranges of 0-7 days, 8-14 days, 14-21 days, and 22-28 days. The results obtained in this study suggest that chemical air pollutants, and especially NO2, are related to the incidence and severity of COVID-19 in Spain. Furthermore, Saharan dust intrusions have an additional effect beyond what is attributable to the variation in air pollution; they are related, in different lags, to both the incidence and hospital admissions rates for COVID-19. These results serve to support public health measures that minimize population exposure on days with particulate matter advection from the Sahara.

Preventive Effect of Synthetic Tryptophan Metabolite on Silicone Breast Implant-Induced Capsule Formation

BACKGROUND

In the field of plastic surgery, capsular contracture after silicone breast implant surgery is a major clinical problem. This experimental study confirms that the synthetic tryptophan metabolite N-(3',4'-dimethoxycinnamonyl) anthranilic acid (Tranilast) reduces capsule formation and prevents capsular contracture.

METHODS

Eighteen New Zealand white rabbits were divided into 2 groups. In the experimental group, implants were inserted into each rabbit, and oral synthetic tryptophan metabolite was administered daily at a dose of 5 mg/kg in 10 mL of saline. In the control group, rabbits received implants and the same amount of saline without the metabolite. After 2 months, peri-implant tissues were harvested and analyzed.

RESULTS

The thickness of the capsules and the inflammatory cell counts were decreased in the experimental group (P < 0.001). The collagen fibers in the experimental group were thinner, less dense, and more organized than in control group. The results of reverse transcription quantitative polymerase chain reaction analysis showed that the genes for transforming growth factor β1 (P = 0.002), alpha smooth muscle actin (P < 0.001), and collagen types I (P = 0.002) and III (P = 0.004) were underexpressed in the experimental groups. Furthermore, the counts of T-cell immunity-related cytokine presenting cells were decreased in the experimental groups (CD3, 4, 25, 45RA, 45RO, 69, interleukin-2, 4 [P < 0.001], and interferon γ [P = 0.028]).

CONCLUSIONS

This study confirms that a synthetic derivative of a tryptophan metabolite decreases capsule formation and prevents capsular contracture by inhibiting the differentiation of fibroblasts to myofibroblasts, selectively inhibiting collagen synthesis, and decreasing specific T-cell immune responses by changing anti-inflammatory cytokine expression.

Short-term effects of the particulate pollutants contained in Saharan dust on the visits of children to the emergency department due to asthmatic conditions in Guadeloupe (French Archipelago of the Caribbean)

Background

The prevalence of asthma in children is a significant phenomenon in the Caribbean. Among the etiologic factors aggravating asthma in children, environmental pollution is one of the main causes. In Guadeloupe, pollution is primarily transported by Saharan dust including inhalable particles.

Methods

This study assesses, over one year (2011), the short-term effects of pollutants referred to as PM₁₀ (PM₁₀: particulate matter <10 µm) and PM_2.5–10 (PM_2.5–10: particulate matter >2.5 µm and <10 µm) contained in Saharan dust, on the visits of children aged between 5 and 15 years for asthma in the health emergency department of the main medical facility of the archipelago of Guadeloupe. A time-stratified case-crossover model was applied and the data were analysed by a conditional logistic regression for all of the children but also for sub-groups corresponding to different age classes and genders.

Results

The visits for asthma concerned 836 children including 514 boys and 322 girls. The Saharan dust has affected 15% of the days of the study (337 days) and involved an increase in the average daily concentrations of PM₁₀ (49.7 µg/m³ vs. 19.2 µg/m³) and PM _2.5–10 (36.2 µg/m³ vs. 10.3 µg/m³) compared to days without dust. The excess risk percentages (IR%) for visits related to asthma in children aged between 5 and 15 years on days with dust compared to days without dust were, for PM_{10, (}(IR %: 9.1% (CI95%, 7.1%–11.1%) versus 1.1%(CI95%, −5.9%–4.6%)) and for PM_2.5–10 (IR%: 4.5%(CI95%, 2.5%–6.5%) versus 1.6% (CI95%, −1.1%–3.4%). There was no statistical difference in the IR% for periods with Saharan dust among different age group of children and between boys and girls for PM₁₀ and PM_2.5–10.

Conclusion

The PM₁₀ and PM_2.5–10 pollutants contained in the Saharan dust increased the risk of visiting the health emergency department for children with asthma in Guadeloupe during the study period.

Indoor particle counts during Asian dust events under everyday conditions at an apartment in Japan

OBJECTIVE

Asian dust storms originating from arid regions of Mongolia and China are a well-known springtime phenomenon throughout East Asia. Evidence is increasing for the adverse health effects caused by airborne desert dust inhalation. Given that people spend approximately 90 % of their time indoors, indoor air quality is a significant concern. The present study aimed to examine the influence of outdoor particulate matter (PM) levels on indoor PM levels during Asian dust events under everyday conditions.

METHODS

We simultaneously monitored counts of particles larger than 0.3, 0.5, 1, 2, and 5 μm using two direct-reading instruments (KC-01D1 airborne particle counter; Rion), one placed in an apartment room and another on the veranda, under everyday conditions before and during an Asian dust event. We also examined how indoor particle counts were affected by opening a window, crawling, and air purifier use.

RESULTS

An Asian dust event on 24 April 2012 caused 50- and 20-fold increases in PM counts in outdoor and indoor air, respectively. A window open for 10 min resulted in a rapid increase of indoor PM counts up to 70 % of outside levels that did not return to baseline levels after 3 h. An air purifier rapidly reduced PM counts for all particle sizes measured.

CONCLUSIONS

It is important to account for occupant behavior, such as window-opening and air purifier use, when estimating residential exposure to particulate matter.

Influence of curing agent on fibrosis around silicone implants

Severe capsular contracture around silicone expander breast implants leading to pain and failure is a major clinical problem. Even though earlier studies have implicated the immunogenicity of silicone, the role of physical and chemical properties of the silicone material in excessive collagen deposition and fibrosis has been less addressed. The present study investigates whether there is any correlation between the type of curing systems i.e. addition and free radical curing and the fibrosis around silicone elastomer. The experiment carried out uses commercially available silicone ventriculo-peritoneal shunt material elastomer cured by platinum and the results are compared with results obtained in a similar study carried out by the authors using commercially available silicone tissue expander material cured by peroxide. Ultra-high molecular weight poly-ethylene (UHMWPE), the standard reference for biocompatibility evaluation, was used as the control material. The materials were implanted in rat skeletal muscle for 30 and 90 days. Inflammatory cells, myofibroblasts, cytokines, and collagen deposition at the material-tissue interface were identified by haematoxylin-eosin and Masson's Trichrome stains and semi-quantitated based on immunohistochemical studies. Results indicate that even though the cellular response in the initial phase of wound healing was similar in both platinum and peroxide-cured materials, the collagen deposition in the proliferative phase was more around peroxide-cured material in comparison to the platinum-cured silicone elastomer. There is a need to look into the molecular mechanisms of this interaction and the possibility of using curing systems other than free radical peroxide in the manufacture of silicone elastomer expanders for breast prosthesis.

Dust storms and the risk of asthma admissions to hospitals in Kuwait

OBJECTIVE

Arid areas in the Arabian Peninsula are one of the largest sources of global dust, yet there is no data on the impact of this on human health. This study aimed to investigate the impact of dust storms on hospital admissions due to asthma and all respiratory diseases over a period of 5 years in Kuwait.

METHODS

A population-based retrospective time series study of daily emergency asthma admissions and admissions due to respiratory causes in public hospitals in Kuwait was analyzed in relation to dust storm events. Dust storm days were defined as the mean daily PM(10)>200 μg/m(3) based on measurements obtained from all six monitoring sites in the country.

FINDINGS

During the five-year study period, 569 (33.6%) days had dust storm events and they were significantly associated with an increased risk of same-day asthma and respiratory admission, adjusted relative risk of 1.07 (95% CI: 1.02-1.12) and 1.06 (95% CI: 1.04-1.08), respectively. This was particularly evident among children.

CONCLUSION

Dust storms have a significant impact on respiratory and asthma admissions. Evidence is more convincing and robust compared to that from other geographical settings which highlights the importance of public health measures to protect people's health during dust storms and reduce the burden on health services due to dust events.

Urban particulate matter in Beijing, China, enhances allergen-induced murine lung eosinophilia

It has been reported that ambient particulate matter (PM) in some large cities, such as Beijing, China, causes adverse respiratory health effects. However, there is currently no experimental report on the relationship between bronchial asthma and urban PM (UPM) in northeast Asia. In this study, the microbial and chemical substances adsorbed onto UPM collected in Beijing were excluded by heat-treatment at 360 degrees C for 30 min. The effects of UPM or heated UPM (H-UPM) toward allergic lung inflammation were compared in murine lungs to investigate the role of organic substances. ICR mice were administrated intratracheally with the two kinds of UPM and/or ovalbumin (OVA) 4 times at 2-week intervals. UPM and H-UPM enhanced eosinophil recruitment induced by OVA in the alveoli and in the submucosa of the airway, which has a goblet cell proliferation in the bronchial epithelium. UPM and H-UPM synergistically increased Th-2 cytokines--interleukin (IL)-4 and IL-13, eosinophil-relevant cytokines and chemokines, such as IL-5 and monocyte chemotactic protein-3 (MCP-3), induced by OVA in bronchoalveolar lavage fluid (BALF). The enhancing effects were much greater in UPM than in H-UPM. UPM induced adjuvant effects on specific immunoglobulin E (IgE) and IgG1 production by OVA. In an in vitro study using RAW264.7 cells, UPM increased the expression of Toll-like receptor 2 (TLR2) mRNA, but not TLR4 mRNA. H-UPM caused no expression of both TLR mRNAs. These results suggest that the aggravated lung eosinophilia in UPM was due to activation of a Th2-associated immune response via the activation of TLR2 by microbial materials. Chemical materials of air pollutant origin contained in UPM, and inorganic components (elemental carbon, mineral elements) in H-UPM, could also cause the aggravation.

Desert dust exposure is associated with increased risk of asthma hospitalization in children

RATIONALE

Desert dust particles, including quartz, which causes inflammatory responses in the airway in animal studies, are transported to widespread regions around the globe. Epidemiologically, areas impacted by desert dust storms, such as communities in the Middle East and the Caribbean, seem to have higher incidences of asthma than might be expected.

OBJECTIVES

We investigated the magnitude of association between airborne mineral dust concentration and hospitalization of children for asthma exacerbation by using Light Detection And Ranging (LIDAR) with a polarization analyzer for an exposure measurement, which can distinguish mineral dust particles from other particles.

METHODS

A case-crossover design was used. The exposure measurement was LIDAR's nonspherical extinction coefficient. The outcome measurement was hospitalization of children aged 1 to 15 years for asthma exacerbation in eight principal hospitals in Toyama, a local area in Japan bordering the Japan Sea, during February to April, 2005 to 2009.

MEASUREMENTS AND MAIN RESULTS

During the study period, there were 620 admissions for asthma exacerbation, and 6 days with a heavy dust event (daily mineral dust concentration > 0.1 mg/m(3)). Conditional logistic regression showed a statistically significant association between asthma hospitalization and a heavy dust event. The crude odds ratio (OR) of the heavy dust event for hospitalization on the day was 1.88 (95% confidence interval [CI], 1.04-3.41; P = 0.037), and the OR of heavy dust event during the previous week was 1.83 (95% CI, 1.31-2.56; P = 0.00043). The OR adjusted by other air pollutant levels, pollen, and meteorological factors was 1.71 (95% CI, 1.18-2.48; P = 0.0050).

CONCLUSIONS

Heavy dust events are associated with an increased risk of hospitalizations for asthma.

Role of immune cells and inflammatory cytokines in regulation of fibrosis around silicone expander implants

This study aimed to investigate the progress of wound healing around silicone expander with particular emphasis on fibroblasts, myofibroblasts and collagen in the repair phase. Semi-quantitative evaluation of inflammatory cells and their cytokines, fibroblasts and myofibroblasts at the tissue-material interface was carried out. Commercially available silicone expander was implanted in gluteus muscle of young female Wistar rats for 3, 7, 14, 30, 90 and 180 days. Ultra high molecular weight polyethylene served as control. The cellular response was studied by immunohistochemistry and Transmission Electron Microscopy. A thick collagenous fibrous capsule was observed around the silicone expander at 180 days, with persistent myofibroblasts, lymphocytes and macrophages as compared to the thin fibrous encapsulation around the UHMWPE implants. The regulatory role of cytokines and immune cells in myofibroblast persistence in tissue-implant interface around silicone expander has been extensively studied. Results of this study indicate the need to elucidate the signaling molecules in the transition of fibroblast to myofibroblast around silicone expander implants.

The effects of microbial materials adhered to Asian sand dust on allergic lung inflammation

Asian sand dust (ASD) containing microbiological materials, sulfate (SO(4)(2)), and nitrate (NO(3)(-) ) derived from air pollutants in East China, reportedly cause adverse respiratory health effects. ASD aggravates ovalbumin (OVA)-associated experimental lung eosinophilia. In this study, the toxic materials adsorbed onto ASD were excluded by heat treatment at 360 degrees C for 30 min. The effects of nonheated ASD or heated ASD (H-ASD) toward the allergic lung inflammation were compared in murine lungs. ICR mice were administered intratracheally with normal saline (control), H-ASD, ASD, OVA, OVA + H-ASD, and OVA + ASD, four times at 2-week intervals. ASD only increased neutrophils in bronchoalveolar lavage fluids (BALFs) along with pro-inflammatory mediators, such as keratinocyte chemoattractant (KC). H-ASD and ASD enhanced eosinophil recruitment induced by OVA in the alveoli and in the submucosa of the airway, which has a goblet cell proliferation in the bronchial epithelium. The two ASDs synergistically increased interleukin-5 (IL-5), monocyte chemotactic protein-3 (MCP-3), and eotaxin, which were associated with OVA, in BALF. The enhancing effects were much greater in ASD than in H-ASD. The two ASDs induced the adjuvant effects to specific IgE and IgG1 production by OVA. In the in vitro study using RAW264.7 cells, ASD increased the expression of Toll-like receptor 2 (TLR 2) mRNA but not TLR4 mRNA. H-ASD caused no expression of either TLR mRNA. These results suggest that the aggravated lung eosinophilia by ASD may be due to activation of Th2-associated immune response via the activation of TLR2 by microbial components adhered to ASD.

Efficient in vitro model for immunotoxicologic assessment of mammary silicone implants

In clinical and experimental studies, silicone gel has been assumed to cause immune alterations that may be related to macrophage activation of silicone implants. However, it has not been proven that the immunotoxicities are caused by the direct contact of macrophages and silicone gel because there has not been an adequate experimental model. In the present study, silicone gel was loaded directly onto Petri dishes and was distributed uniformly to the bottom by centrifugation. Peritoneal macrophages and splenic lymphocytes were cultured either on the silicone-coated plates or on the conventional, normal plates, and their functions were compared with each other. The experiments were repeated three times. The cytotoxic activities of peritoneal macrophages on cancer cells were markedly augmented by cultivation on silicone gel, and the primary T-dependent immunoglobulin M response in which macrophages participated as antigen presenting cells was also enhanced by incubation on silicone gel. However, macrophage-unrelated functions mediated by B and T lymphocytes were not affected by the silicone gel treatment. It was proven that the direct contact of macrophages with silicone gel was a primary cause of acute immune activation that was related to foreign body reaction. In addition, the present in vitro model exhibited similar silicone-induced immunotoxicities in previous animal and clinical studies.

Silicone gel and octamethylcyclotetrasiloxane (D4) enhances antibody production to bovine serum albumin in mice

The purpose of the present study was to determine whether components of silicone breast implants [silicon (polydimethylsiloxane) oil, silicone gel, and octamethylcyclotetrasiloxane (D4)] potentiate the antibody response to bovine serum albumin (BSA) in mice. Seventy A/J mice were divided into seven groups which received the following: group I--phosphate buffer solution (PBS); group II--20 centistoke (cs) silicone oil; group III--50% silicone gel homogenized in silicone oil; group IV--incomplete Freunds' adjuvant (IFA); group V--IFA mixed with an equal volume of silicone oil; group VI--D4; and group VII--IFA mixed with an equal volume of DA. Each 0.1 mL of treatment material(s) was mixed or emulsified with an equal 0.1-mL volume of 250 micrograms/mL BSA in PBS solution. Antibodies to BSA were measured using an enzyme-linked immunosorbent assay. Our study demonstrates for the first time that both D4 and the silicone gel potentiate antibody production to BSA in mice. Histopathologic evaluation of the injection sites reveals granulomas for mice injected with IFA and D4 preparations. Whether D4 or silicone gel acts as an adjuvant against self-antigens has yet to be determined.

Silicone breast implants and autoimmunity: causation, association, or myth?

In vivo and in vitro studies, case reports and population studies show that: (1) silicone is immunogenic; (2) silicone is biodegradable and transported via the reticuloendothelial system to distant locations; (3) silicone breast implants "leak" and in turn silicone migrates outside the breast tissue; (4) case reports and population studies document an autoimmune reaction and immunological dysfunction in patients with silicone breast implants; (5) these immunological abnormalities and symptoms are reversible upon removal of the breast implants (in 50-70% of cases). The criteria to establish medical causation are defined, and based on those criteria it is concluded that silicone breast implants cause immunological disease.

Novel functional polymers: poly(dimethylsiloxane)-polyamide multiblock copolymer. V. The interaction between biomolecules and the surface of aramid-silicone resins

Multiblock copolymers consisting of aromatic polyamide(aramid) and poly(dimethylsiloxane) (PDMS) aramid-silicone resins (PASs) were synthesized by low temperature solution polycondensation, and PAS films were prepared by casting from an N,N'-dimethylacetamide solution. In this study, we investigated bovine serum albumin (BSA) adsorption, L929 cell adhesion, and tissue reaction on the surface of PAS in order to clarify the interaction between PAS and biomolecules. It was found that the amount of adsorbed biomolecules on PAS was extremely low in contrast with those on aramid and nylon films, and it was comparable to SILASTIC 500-1 film. This suppression of adsorption of biomolecules onto PAS seemed to be due to the low surface free energy of the outermost surface of PAS, where PDMS block was condensed.

Do silicone breast implants cause autoimmune rheumatic diseases?

Current estimates are that up to a million women in the U.S. have breast implants with the predominant type being the silicone gel implant. Concerns have been raised regarding the safety of silicone gel breast implants with focus upon whether escaped gel might cause inflammatory and immune responses that subsequently lead to autoimmune rheumatic diseases such as progressive systemic sclerosis (scleroderma), systemic lupus erythematosus (SLE), Sjögren's syndrome or rheumatoid arthritis. A spectrum of illnesses ranging from local symptoms to systemic disease is seen in some patients with silicone breast implants, however, it remains to be determined whether such illnesses in these patients are coincidentally associated or are secondary to the implants. Our understanding of the relationship between the presence of autoimmune rheumatic diseases and silicone breast implants is limited. The available data indicate that silicone elicits a minimal immunological response as compared to conventional antigens. The histological, immunological and epidemiological experimental data derived from patients with silicone implants, as well as those from animal studies, are reviewed. These data do not convincingly demonstrate that there is a cause and effect relationship between silicone breast implants and autoimmune diseases. Further investigations are needed to clarify the interaction of silicone with the cellular and humoral immune systems, as well as with host and environmental factors.

Silicone breast implants: immunotoxic and epidemiologic issues

Silicone gel implants for breast augmentation and reconstruction have been in use since 1962. Significant local complications include capsular contracture, rupture, gel "bleed", and spread of the implant material to regional lymph nodes (1-7) as well as histologic findings of foreign body granulomas in the capsular tissue and in lymph nodes (7-9). Through magnetic resonance spectroscopy and atomic emission spectroscopy, silicon compounds were found in the blood of some women with silicone breast implants; silicone and silica have also been found in liver (10). Well-publicized case reports have raised significant concerns regarding an association between implants and systemic disease. However, despite the availability of silicone implants for over 30 years, controlled epidemiological studies were not carried out until 1992. Currently available epidemiologic data are extremely limited. In part, because the majority of implants were used after 1981, the incidence of long-term problems is not yet known. In 1992, due to the unavailability of studies demonstrating the safety of implants, the U.S. Food and Drug Administration advised that silicone breast implants should be used only in reconstructive surgery and as part of clinical trials (11). This decision spurred a wave of research on the bioreactivity of silicone and clinical observations of patients with implants. Herein, we review the adverse immune effects following contact with silicone as well as the epidemiologic data available.

Silicone breast implants: the role of immune system on capsular contracture formation

We evaluated the role of the immune system in the pathogenesis of the periprosthetic capsular contracture, the most frequently occurring complication following the implant of silicone prostheses. Peripheral blood samples from 22 patients with silicone-gel-filled implants were examined. In all cases a capsule was felt by palpation, and it was classified according to the Baker scale. Ten patients (group 1) had a Baker 2 contracture, and 12 (group 2) had severe contracture rated 3 and 4. The cells positive to antigens CD3, CD4, CD8, HLA-DR, CD19, CD25, CD57, CD16, and CD14, and the cytotoxic activity of the lymphocytes on target cells K562 were assessed by cytofluorimetric analysis. At time 0 there were no statistically significant differences between patients and normal subjects, nor between the two groups. At 48 h, the group 2 patients had a number/mm3 of cells CD57 + significantly higher than both group 1 and control group (P < .05). In group 1 patients, the cytotoxic activity was similar to that of normal subjects, whereas in group 2 it was significantly increased, in respect to both the controls (P < .05) and group 1 (P < .001). In all groups, the contact of the lymphocytes with the silicone extract did not modify either the antigen expression or the lymphocyte functional activity. On the basis of these results we hypothesize the involvement of the immune system in the formation of the capsular contracture around the prosthesis.

Migration and accumulation of silicone in the liver of women with silicone gel-filled breast implants

1H NMR localized spectroscopy (STEAM), combined with echocardiography (ECG), respiratory gating, and water and fat suppression, was used to quantify silicone concentrations in the liver of women with silicone gel-filled breast implants. Localized spectroscopy was performed on 15 patients with silicone gel-filled breast prostheses and on eight volunteers with no implants. The 1H spectra in the liver of patients showed silicone resonances from 0.3 to -0.8 ppm, attributable to protons in the methyl groups of silicone. The presence of silicone in the liver could first be detected 3-4 years after breast prostheses implantation. No correlation between silicone concentrations and implantation times was observed. However, our results indicated that silicone concentrations may reflect implant integrity: detectable silicone concentrations in the liver appeared to be higher when the implants were ruptured than when the implants appeared intact. Moreover, new resonances in the range of -2.6 to -4 ppm were observed in most patients after long-term implantation. As these species increase with implantation time, the new resonances may reflect chemically changed silicone (paramagnetically shifted silicon complexes bound to iron) accumulated over time. The sensitivity of 1H NMR localized spectroscopy is sufficient to detect silicon concentrations as low as 0.20 mM. Results from one patient whose implants had been removed 14 months prior to the NMR examination showed no detectable silicone in the liver, indicating that it may have been excreted via bile or degraded to silica and high coordinated silicon complexes. Quantitative 1H localized spectroscopy of the liver in women with silicone gel-filled breast implants may provide valuable information concerning silicone accumulation and degradation in vivo, as well as about the kinetics of its elimination from the body after implant removal.

Immunotoxicity of silicone: implications of oxidant balance towards adjuvant activity

A variety of mechanisms can be proposed to explain the potential effects of silicone and silicone by-products on the immune response. In this paper, we discuss information on the chemistry of silicon and silicone gels/elastomers, and the manufacture of silicone breast implants as they pertain to the bioreactivity of silicone. Moreover, with reference to silicone-mediated human adjuvant disease, an overview of experimental adjuvant-induced arthritis is presented; comparisons with graft-versus-host disease and chemically induced autoimmunity then follow. Particular attention is paid to similarities in the characteristics of silicone and classic lipid adjuvants. For example, macrophage activation is presumed to be a central event in silicone-induced autoimmunity. Since those genes uniquely expressed in macrophages activated by plastic adherence are similar to those induced by lipopolysaccharide, adherence to silicone rubber may initiate an inflammatory response by the same mechanism. Macrophage effects would also include the erosion of implants through the generation of oxidants and localized pH changes. The degradation products of silicone are also implicated in the adjuvant effects of silicone implants. There is evidence to suggest that oxidants produced by inflammatory cells preferentially inactivate CD8+ suppressor T cells. This could then lead to an inflammatory state, perhaps through oxidant-induced transcription factors such as NF-kB, resulting in a long-term pro-oxidant imbalance that manifests itself as a breakdown in immunological self-tolerance. The authors hypothesize that autoreactivity following oxidant stress evolved to enhance inflammatory repair mechanisms after tissue, cell or molecular damage by oxidants.

In vivo degradation of silicones

29Si nuclear magnetic resonance (NMR) spectroscopy is applied to study the degradation of polysiloxanes (silicones) in vivo. Our results with animal models show that silicone migrates from the implant to the liver (29Si resonance at -20 ppm) and new silicon containing compounds form after the silicones are introduced into the rats. The new 29Si resonances in the chemical shift range of -40 to -85 ppm are related to hydrolyzed silicone, those at -90 to -115 ppm are indicative of the presence of silica (SiO2), and the peaks observed at -120 to -150 are related to high coordinated silicon complexes. These resonances are not present in the 29Si spectra of the silicones before implantation. Our findings demonstrate that silicones are not metabolically inert.

In vivo 1H chemical shift imaging of silicone implants

In order to study the aging process (i.e., silicone migration, fat infiltration) of silicone (polydimethylsiloxane, PDMS) based biomaterials in living subjects by NMR imaging, a hybrid 1H selective excitation and saturation chemical shift imaging technique (IR/CHESS-CSSE) has been developed. This sequence allows selective mapping of the distribution of silicone protons in vivo, while suppressing the contributions of fat and water. Our results indicate that a combined inversion recovery and CHESS pulse, followed by a spoiler gradient, must be applied to suppress all contributions of fat protons to the NMR signal. The sensitivity of our experiments allows the detection of a chemically unchanged silicone concentration of 5% in a voxel of 0.9 mm3 at a signal/noise ratio of 2.