Women's Implant Support Newsletter 12/07/99

Date: Tue, 7 Dec 1999 07:48:43 -0800

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FROM THE FDA EVIDENTIARY FILES

Undated - estimate 1990

Silicone Carcinogenesis in Perspective

Nirmal K. Mishra D.V.M., Ph.D.

Office of Device Evaluation/CDRH/FDA

Polydimethylsialoxanes (Silicone) are used extensively as medical implants in all three physical forms, solid, gel and fluid. The carcinogenic potential of all forms of silicones have been evaluated in animal models since the sixties.

Animal Bioassays of Silicones:

Ben-Hur (1) first reported the carcinogenic effect of silicone fluid in Albino mice administered through subcutaneous route. Subsequent investigations in this area were performed by Hueper at the National Cancer Institute (2,3) using both vulcanized and non-vulcanized silicone. Bethesda Black rats were implanted with silastic rubber at the neck. To rule out the possibility that free catalyst are not producing the carcinogenic effects, Hueper also tested Benzoyl peroxide (catalyst) in the second set of experiments. The results clearly established that a significant number of tumors over control were produced by Silicones and indicated that the process of cross-linking (vulcanization) had no effect on the rate of tumor yield. Ten out of thirty and ten out of thirty-five animals produced tumors of sarcomatous variety with extensive lymph node involvement. Furthermore, it was significant that two distant site tumors-epicardial mesotheliomas, were also recorded in the test animals in addition to injection site sarcomas. The results of his studies are in agreement with previous reports on carcinogenicity of Silicones (4).

a. The term "carcinogenesis" is used in this review to denote all types of neoplastic events in keeping with the common toxicological practice and is not restricted to carcinoma formation only, as preferred by a number of Pathologists.

b. This review was performed as a scientific exercise and does not imply endorsement by FDA or DHHS. Opinion and views expressed in the article are solely of the author and shall not be construed as regulatory position of the agency or the author.

Other significant studies were conducted by Bischoff and Bryson (5,6,7). In a series of investigation they injected Dow-Corning medical grade 360 fluid, in Long-Evans rats and Marsh mice through subcutaneous and intraperitonial route. The 8/34 female rats in the test group developed reticulum cell sarcomas in the lung or peritonial cavity in addition to one recorded intraperitonial adenocarcinoma. This trend was not present in male rats. The mammary tract injection group (in female mice) developed one each of fibrosarcoma, spindle cell sarcoma, malignant fibrohistiocytic neoplasm, adenocarcinoma and hemartomatous epidermal cystic inclusion.

Various other malignancies were also noted in other test subgroups over control. While noting the carcinogenic potential of silicone, the authors noted the site and species variation of the end tumor types, tumor yield and commented on the similarity of results with silicates (asbestos). An elaborate mechanistic discussion was provided comparing the fibrosis which resulted from the lysis of engulfed phagocytes for silica and asbestos. It was noted that subcutaneous implantation of Asbestos also produces sarcomas in rodents.

The existence of four separate studies were known to be performed by silicone manufacturers (Table-I). Two of the recent studies performed in Fischer rats are noteworthy. In one study, two formulations of the Silicone Gel produced various histopathologically distinct types of sarcomatous tumors at the injection site (24-28%) in excess of control. In some responding animals, the tumors metastasized aggressively. In addition, other distant site tumors such as lung carcinoma, hepatocellular carcinoma, squamous cell carcinoma, thyroid and parathyroid carcinoma in slight excess over control, were seen. Another noteworthy event which were also seen in other studies was, extramedulary hematopoesis. Under identical experimental condition, Silicone elastomer (Shell) did not produce implant site sarcomas which raised serious doubt regarding the purely physical mechanism of silicone carcinogenesis. Two other studies are relatively old and at present difficult to comment.

Mechanistic Considerations:

The results of the above mentioned studies clearly indicate that all forms of Silicone (solid, liquid, and gel) are clearly sarcomogenic and meets all the definitions (sufficient evidence criteria) of an animal carcinogen (8). The mechanism by which silicones produce tuners are not clear at this time.

Bischoff (7) noted that Silicone is highly lipophilic. At room temperature, Progesterone will have fifty-fold more solublity in liquid Silicone than either estradiol or estrone (Table-2). He validated his in vitro solubility results by experimentally measuring the level of these steroids in the Silicone cyst in a patient and in a number of experimental animals. This differential solublity will provide a 400-500 milliliter of endogenous "Progesterone sink" in woman implanted with Silicone devices such as breast implants. Because, free Silicones are engulfed and transported to distant site by macrophages, local hormonal effects at distant sites may also be important.

The role of endogenous estrogen in the pathogenesis of endometrial cancer has been clearly established by the clinical success of therapy for both adenomatous hyperplasia and carcinoma of the endometrium with progesterone which antagonizes mitogenic activity of estrogen. Normally, during the ovulatory cycle increased estrogen values without protective action by progestrone occurs for only 20% time of the cycle. The abnormal shift in local and systemic hormonal concentration gradient may be a crucial factor in Silicone carcinogenesis due to the postulated mechanism of human endometrial carcinoma by continuous stimulation with estrogens periodically unchecked by progesterone. It should be remembered that cells which respond to estrogen stimulation (at least have estrogen receptors) are located not only in the female reproductive tract but also in other organs. Therefore, local effect by silicone can also be envisioned at many sites including reproductive organs and the breast parenchyma even if Silicone is not present at the site in significant quantities.

A number of other mechanism has also been proposed by other authors which primarily assume sarcomas induced by silicone are due to physical (also described as foreign body, solid-state or Openheimer effect) carcinogenesis. Although most primary researchers (2,6,10) in the area of Physical Carcinogenesis do not accept that Silicone fits the general characteristics of a so called "Physical Carcinogen", most of the present complacency on the hazards or silicone are derived from this notion. In general, a solid-state material is a rigid, smooth surfaced, non-porous object which irrespective of its chemical composition produces tumors (primarily sarcomas) when implanted subcutaneously in rodents. (See reference 9, 10 for reviews). The yield of sarcomas greatly disappears or vanishes below the size of 0.5 cm. The tumor types and yields are uncertain when implantation were made at sites other than subcutaneous injection. These types of materials are generally non-genotoxic and are not metabolized by the body. In a large series of studies (11), Shubik et al has shown rigidity is one of the key characteristic required for sarcomogenesis. Similarly, Bates (12) demonstrated that continuity or smoothness of the surface to be an essential requirement. One of the key parameters is the diameter or the total surface area of the implant as powdered form (at least noble metals) are not sarcomogenic. Nickel and other carcinogenic metals are exceptions to this rule. There are numerous examples available from Polymer testing which indicate that the exceptions are more abundant then the rule itself. The hypothesis is relatively old, nonetheless, many toxicologist without a critical review of the actual experimental data rely on this hypothesis to explain discomforting observations such as DEAE-Dextran and PVP carcinogenesis in both man and in animal. The hypothesis itself needs to be reexamined in light of various observations made to date (see Table-3 and 4).

Whatever may be the merit of this hypothesis, it is to be recognized that both crystalline Silica and asbestos (and other mineral fibers) are also recognized as epigenetic physical carcinogen. The striking resemblance between silicone, silica, and silicates on chemical structure (si-o--si backbone), lack of catabolism by known enzymes, lack of genotoxicity and their biologic responses such as engulfment by macrophages, induction of intense fibrosis, physical form dependence, are quite interesting. Both silica and asbestos produce a variety of implant site dependent tumors and a number of experimental animal are resistant to their carcinogenic effects. Both agents are known to require 20-25 years of expression time in man for tumorogenicity. Interestingly, even though asbestos inhalation are usually detected by the marker tumor (mesotheliomas), subcutaneous asbestos implant in rodents produce sarcomas (see table 5,6,7) and references (13,14).

In agreement with the observations made by Bischoff (6) and Autian (10), this reviewer does not subscribe to the hypothesis, that tumors produced by Silicone in animal models can reasonably be explained by physical mechanism alone. It is quite plausible that both physical and chemical (hormonal) mechanisms are involved. The relative contribution of each mechanism is dependent on the particulate or droplet sizes which will determine the ability of the macrophages to phagocytize (roughly 5 micron) and the total mass of non-migrating Silicone at or around the implant site. Histopathological evaluation of animals injected with liquid silicone are quite instructive. After subcutaneous or intraperitonial injection in mice (7), silicone granulomas appeared in the Corticomedulary junction of the adrenal gland and lung, liver, kidney, spleen, pancreas, ovaries and lymph nodes showed focal infiltration of macrophages with large clear cytoplasmic areas (silicone). This form of slow, low volume cellular transport are not very amenable to classical pharmacokinetic studies which rely on the measurement of mass transfer between defined organ compartments for short durations. It must be remembered that even for Silicone gel, the primary component of Silicone which moves out the shell (gel bleed) is akin to low molecular weight Silicone fluid (15). One of the proposed mechanism of carcinogenesis by Silica involve macrophage lysis (21). The dead or moribund macrophages release highly reactive superoxide anions and hydrogen peroxides, Which are known to be radiominiatic. Such lytic release of reactive oxygen species may also be qualitatively applicable for Silicone-engulfed macrophages as well. These observations, clearly implicate that both local and distant site tumerogenesis are of toxicological concern and should be carefully and perhaps thoughtfully monitored.

Human Risk Considerations:

Irrespective of the biologic mechanism involved, results of positive and reproducible animal bioassays generally raise great public health concern for chemical entities used in foods, drugs, and as environmental and occupational agents. It is therefore puzzling to note a sense of complacency regarding polydimethylsialoxanes, when Hueper in 1964 noted that "indiscriminate use of silastic for paranteral implantation is potentially dangerous and thus inadvisable on the grounds of medical ethics and exercise of good judgement" (3). His views were later supported by other researchers in the field (7,10) and were summarized a decade later Brand, who recommended a more cautious and restrictive approach "especially at the exclusion of medically unnecessary cosmetic procedure" and for establishment of a "centralized registry for gathering information on general complications as well as instances of neoplasm".(9).

In view of the fact that Huper, Brand and other who commented on the safety of silicones are well-regarded researchers in area of physical carcinogenesis research and no new and significant research in the public domain has been conducted since their appraisal of Silicones, it is puzzling that little attention has been paid on the carcinogenic safety of this ubiquitous biomaterial. The genesis of this paradox can only be understood in the framework of often cited paradigm which has been cleverly perpituated for last few years.

This paradigm stipulates that the Silicones are physical carcinogens because they produce on site sarcomas in rodents like many other solid materials. The reported incidence of human sarcomas are low or rare. In view of large numbers of implants performed annually, the carcinogenic risk from implants are therefore very small. This logic is specifically applicable to Silicone because general population are exposed to Silicone through injections and ingestion of various food and drugs (such as antiflatulants). Therefore, any concern regarding the carcinogenic Safety of Silicone is misplaced and at best valid for rodents only. careful review of facts however fail to justify such assertions. On site sarcomas do not necessarily imply physical mechanism. As discussed above, a chemical mechanism may also be envisioned. It should also be recalled that tumor formation by powdered or Porous forms are taken as typical chemical carcinogen and silicone meets such criteria (10,3). It is also hard to see how a liquid, gel and solid forms of a substance can all meet the characteristics of a physical carcinogen only. Engulfment and transport of Silicone by macrophages are certainly ominous and may place this material at least in the category of silica and asbestos fiber both of which are known to pose human carcinogenic risk. It is hard to imagine that man is refractory to only one type of a physical carcinogenesis, which has been demonstrated in mice, rat, rabbits, chickens, dogs, and in man (Asbestos). Even the implant associated Sarcomas have been reported in humans within expected time - frames, although a low level of risk was projected due to a law frequency of such events (16). Such low level unit risk computed for the human sarcomas, however, may be totally inappropriate. Most permanent implants such as hips and knees are made in older patients and will, not be reflected in cancer death cohort due to 20-25 year expression time. Medico-legal questions, unawareness of the oncologists to past implants and lack of interest in publication of isolated cases by pathologist, all can further skew-up the statistics as computed from literature. The diverse accidental implants like Shrapnel, bullet and glass are rarely permanent in patients and do not constitute a reliable or homogeneous population base for even a crude estimation of the level of risk for physical carcinogenesis. The mere fact that such associative cases of sarcomas has been reported attest to the vulnerability of humans to physical carcinogenesis.

The implant site sarcomas are also not necessarily the final tumor end-point to be investigated. Two analogies may be pertinent in this respect. Aflatoxin B, a potent genotoxic chemical carcinogen produces sarcomas when administered by subcutaneous injection. When different routes are used, it produces malignant carcinoma of the liver and other soft organs. Similarly, chrysotile asbestos and other similar non-genotoxic non biodegradable fiber carcinogens when implanted subcutaneously in rodents yield injection site sarcomas, while change in administration route results in mesotheliomas and carcinomas at the target organs. Both agents are recognized as a significant risk to humans. Sarcomogenic effects of other recognized chemical and hormonal carcinogens by subcutaneous injection are well known and are suggestive of the fact that the intrinsic carcinogenic property of an agent are more prone to be expressed as sarcomas at this site irrespective of the modalities involved. The same agent then may express the carcinogenic property as different histologic form of tumors at other sites. Solid plastics such as Polyethylene implants in the uterus produce epidermoid carcinomas in rats (20) but only sarcomas are detected by subcutaneous implantation. Thus it appears that a stipulation of low risk from silicone implant because of low rate of observed human sarcomas in implanted patients, may not be entirely axiomatic.

The other argument on the Safety of Silicone may also be equally superfluous. No population database exist on the body burden of Silicone in human. Certainly some Silicones are extruded from most commonly used syringes (17). But most, if not all ingestible silicones transites through the G.I. tract unabsorbed and are totally excreted. Interestingly, during a study of tissue load of Silicone in patients implanted with Silicone devices, Thompsen, et al, (18) detected no silicone in the tissues of matched nonimplant controls. Limits of detection for Silicone in this study was 0.5 micrograms per gram of the tissue. Until the experimental data is available on general Population, Safety of Silicone should not be based on assumption of its supposed presence in the body.

Thus, each part of the paradigm which has been constructed to attest the lack of concern over animal data can be debated. It must be recognized that the major implanted form of Silicone device, i.e, breast implant has been implanted in two million women in the United States of 1~merica. Most of these implants were used in relatively young patients (median age of 35) only in the last decade. No other mass volume implants at this age group are known to be used in this scale. Cancer epidemiology thus will only be meaningful during the end of this decade. In the meantime, the devices have changed. More toxic components such as flurosilicone has been incorporated in the shell as a barrier to gel migration. Nothing is known about the extent of solubility of flurosilicones in migrating Silicone fluid or its effects in the body.

It is interesting to note that both animal and epidemiologic studies shows some slight increase in tumor incidences at distant sites. These numbers may assume future significance when we consider that Silicone containing macrophages migrate throughout the body. The cost of bioassay usually restrict the size of the study to one hundred animals. Under such design, only relatively potent carcinogens with a specific target organ or a marker tumor can be determined with any degree of certainty. Even if it is reasonably potent, the cancer causing effect of Silicone migrating randomly to various tissues are not likely to achieve statistical significance due to the size of test population and the standard procedure used for stratification of tumors for various organs. It is sobering to know that an excess of single tumor bearing rat is surrogating for approximately twenty thousand patients. Similarly, excess tumors of the reproductive organs reported in epidemiologic study (19) may someday add a new dimension in our thought process if one ponders over hormonal mechanism of Silicone carcinogenesis at large.

References:

1. Ben - Hur, N., Neumann, z. - Isreal Ned. J. 22: 15 - 20 (1963)

2. Rueper, W.C. - Path. Microbial. 24: 77 - 106 (1961)

3. Hueper, W.C. - J. Nat. Cancer Inst. 33: 1005 - 1027 (1964)

4. Russell, F.E., Snooker, M.H, and Hirst. A.E - J. Nat. Cancer Inst. 23:305 - 315. (1959)

5. Bryson, G., F. - Progr. Exp. Thinor Res. 9: 77 - , (1967)

6. Bischoff, F Advances in lipid Res. 7: 165 124 (1969)

7. Bischoff, F - Clinical Chemistry 18: 869 - 894 (1972)

8. Preamble. IARC Monographs on the evaluation of the Carcinogenic Risk of chemicals to Humans 17: 11 - 34. (1978)

9. Brand, K.G., Johnson, K.R., Buoen. L.C.,- CRC Critical Rev. Toxicol 4: 353 - 394 (1976)

10. Autian, J., - Essays in Toxicology 6: 1 - 33 (1975)

11. Shubik P., Saffotti W., Lijinsky, W., Pietra, G.W., Rappaport, H., Toth B., Raha C., Tomatis L., Feldman R. and Ramahi H., Toxicol 1~ppl. Pharmacol: 4 (suppl.): 1 - 62. (1962)

12. Bates, R.R., Klein, M., - J. Nat. Cancer Inst. 37: 145 - 151 (1966)

13. Pott F., Friedrick K.H., and Huth. F.,- zbl. Bakt. Hyg. 162: 467 - 505 (1976)

14. Roe. F.J., Carter R.L., Walters M.A., Harington J.S.,- mt. 3. Cancer 2: 628 - 638 (1967)

15. Bergman R.B., Van der Ende A.E.,- Brit 3. Plast. Surg. 32: 31 - (1979)

16. Brand G.K., and Brand I.,- Plastic Reconstr. Surg. 66: 591 – 595 (1980)

17. Miller R.J., Heiprin 3.3., and Finilayson J.,- Pharma Sci. 58: 55 - 56 (1969)

18. Thomsen J.L., Christensen L., Nielsen N., Brand B., Breiting V.B., Felby S., and Nielsen E.,- Plast. Reconstr. Surg. 85: 38 - 41 (1990)

19.Deapen DJ'l. and Brody G.S. - Presentation at the FDh Conference on Silicone in Medical devices. 1991 (also refer to: Plast. Reconstr. Surg. 77: 361-367 1986)

20. Corfman P.A., Ralph N., and Richart ?4.,-Am. .3. Obstet. Gynecol 98: 987- (1967)

21. Saffiotti U.,- in "Silica, silicosis, and cancer": 287-307(Goldsmith D.F., Winn D.M., and Shy C.M., - eds.) Preger New York (1986).

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ABSTRACT

MEDICAL DEVICE MATERIALS TOXICOLOGY

Genetic Effects of Endogenous Bioregulator Nitric Oxide Nitric oxide (NO) is a bioregulator and toxin induced in the immune, cardiovascular, neuronal and other systems. It is the endogenous mediator of toxic shock resulting from certain bacterial infections. However, it has increasing therapeutic uses related to the control of blood pressure (drugs such as nitroglycerine) and alleviation of respiratory insufficiency in newborns (devices instilling NO gas directly into the lungs). Studies in OST, in collaboration with scientists at NCI, have established that NO gas and drugs that generate it, including nitroglycerine, are mutagenic. Therefore, it is necessary to understand the genetic toxicology of NO in order to assess the benefits and risks of NO-based therapies. OST is working to understand the types of damage and the types of mutations generated by NO in vitro, as a fingerprint that can be identified in vivo. Recently we found that E. coli, a likely target of NO in vivo, is immune to mutagenesis by NO, even when a major repair system is inactivated. A close relative, Salmonella typhimurium, is susceptible to mutagenesis. Understanding the reason for this surprising result in these closely related organisms should help to understand how NO functions as a genotoxin in cells. [ProA]

Development of Biomarkers of Exposure to Polyurethane

Poly(ester)urethanes are or have been used in a number of medical devices, for example breast implants, gastric bubbles, endotracheal tubes, catheters, blood and plasma bags, etc. In order to understand the impact of this material in human beings, some means to identify and track the degradation of the polyurethane in vivo needs to be developed. OST has identified a possible in vivo biomarker of exposure to polyurethane exposure in humans: 2, 4-TDA- Human Serum Albumin. We are currently examining this as a potential biomarker for women with breast implants. Preliminary results indicate that this may not be a conjugate which would exclusively indicate polyurethane exposure, as with a breast implant. This may be due to a number of factors, not least of which is "environmental" exposure to products which contain TDI (toluene diisocyanate) and TDA, such as furniture refinishing products, paints, etc. Other possible biomarkers selective for polyurethane are currently being explored.

In addition, studies indicate the particles and monomers released from the metabolism of polyurethane can create adverse effects. To assess the cytotoxic potential of a material, simple means to screen for the cytotoxic potential of polyurethane in vivo must be developed. We have used a number of different extraction conditions and solvents to provide a more complete evaluation of the cytotoxic potential of polyurethane to a number of different cell lines in vitro. Some conditions indicate that there is a strong cytotoxic effect of polyurethane extracts over time. OST has just completed a full scale study to characterize this cytotoxic effect and then will apply these new techniques to assess the cytotoxicity of other biomaterial extracts.

The impact of this work would be to provide better methods and strategies to test biomaterials in general. By designing methods to easily screen for cytotoxic effects and strategies for developing and validating biomarkers, the benefit to the regulatory aspect of this work is to provide specific information on polyurethanes. The general benefit to the FDA would be to provide information on strategies to better evaluate and regulate materials for toxic potential. [ProA]

Immunotoxicity Testing

OST, with ODE, prepared an overview of the current role of immunotoxicity testing in regulatory review of medical device applications. Based on this survey, a joint OST/ODE committee to develop an "Immunotoxicity Testing Framework" that will provide reviewers and manufacturers with a coherent process for optimizing immunotoxicity testing was established. A revised draft framework is being prepared. [ProA]

Latex Allergy Research

Natural latex in medical devices can cause life-threatening Type 1 allergic reactions in individuals sensitized to latex proteins. HSB latex research project was initiated to solve the problem of severe allergic reactions. It included efforts to provide basic data on the nature of allergens and to develop methodology for evaluating the allergenic potential of latex products. The studies are focused on the identification of allergenic proteins in latex in order to reduce or eliminate them from finished latex products.

Furthermore, OST is studying the correlation of the extractable protein level and several in vitro tests for latex allergenicity with skin testing in vivo. This initiative resulted in the collaborative project with the Johns Hopkins University and will ultimately define, clinically, the most relevant in vitro test as an alternative to skin testing in humans for the evaluation of the safety of latex products and assessment of latex sensitivity.

Significant effort is focused on the development of methodology for a total protein measurement. In collaboration with ASTM, OST's modification of the Lowry method was developed into a standard protocol. OST scientists are continuing joint efforts with ASTM to further develop a more sensitive method for detecting very small amounts of protein and insure the safety of latex products. A standardized, relevant methodology for the assessment of allergenic potential of finished latex products is critical to manufacturers in their efforts to develop safe, nonallergenic products and help prevent life- threatening reactions. [ProA]

Latex Gloves Residual Powder Test Method

Sensitivity to natural rubber latex and the fact that powder used on latex gloves can carry latex allergens are both well established. Minimizing or eliminating powder on gloves helps address the sensitivity problem. Hence, a need for determining powder residues on "powderless" gloves arose in order to establish operational qualifications for these products as needed by FDA for product review and compliance assessments. ASTM D11.40 task group proposed a draft method for determining powder residues. In-house laboratory efforts showed that the original method for determining powder residues. These included minimization of the number of transfer steps and, most importantly, the inclusion of a glove rinse step. The laboratory efforts also established the validity of the modified method and established that its capabilities are sufficient for regulatory purposes. The results have been communicated to DGRDG and ASTM D11.40. This work has been submitted to the ASTM Journal of Research and Testing for publication. [Stds]

Mercury-Induced Changes in Brain Gene Expression

Studies are being conducted in order to evaluate the effects of mercury vapor on gene expression in rat brain. Mercury constitutes 50% of dental amalgam, and amalgam restorations release small amounts of mercury vapor (elemental mercury).

This vapor is absorbed and distributed throughout the body, localizing in the kidney and brain. Dental practitioners who use mercury have elevated urinary mercury levels, and in persons who have amalgam restorations, the number of amalgams is directly proportional to the urinary mercury concentration. Since mercury is a known neurotoxicant, exposure to mercury vapor during pregnancy may interfere with brain development. In contrast to animal studies, reports of human reproductive and developmental effects due to occupational vapor exposure have been inconclusive.

Since controlled mercury vapor (the form of mercury that is of concern) exposures require an inhalation facility with analytical capability and safety controls, initial series of experiments will be conducted using methyl mercury (MeHg). Like mercury vapor MeHg is lipophilic, and mercury levels can be easily elevated in brains of rats injected with MeHg. Progress to date has focused on dissecting rat brain into six regions, including targets for mercury (cerebellum, cortex, and hippocampus).

Immunoblotting experiments with heat shock protein (hsp) antibodies are planned in order to identify region-specific induction of hsps, as well as radiolabeling studies to asses de novo synthesis and immunohistochemistry to identify cell-specific induction.

Future mercury vapor inhalation studies in rats are being coordinated through the NIEHS Inhalation Toxicology Group, RTP, NC.

These studies will help in identifying the responses of target tissues to low-level mercury exposures. This will equip the PHS to better assess the risks associated with exposures to mercury from amalgam restorations. [PreME, PostMS]

Immunochemical Localization of Molecular Markers of Mercury-induced Renal Injury

Current methods to identify potential hazards of medical device materials are based on limited toxicity information, resemblance to known chemical toxicants, and extensive extrapolation. Perturbation of stress gene expression is being evaluated as a marker of chemical exposure and toxicity. Previous studies in OST labs demonstrated that the expression of inducible gene products, i.e., stress proteins, after exposure to mercury is target tissue-specific. Studies are now being undertaken in order to assess the cell-type specificity of the stress response within a target tissue.

Immunohistochemical localization of stress proteins using monoclonal antibodies specific for various stress proteins was undertaken in kidney. Immunohistochemical staining for stress proteins revealed intense staining primarily in renal tubule cells undamaged by mercury. Induction of stress proteins in kidney may play a role in mediating the nephrotoxicity of mercuty.

Improvements in molecular toxicology methods and their integration into routine testing regimes will enable FDA to enhance identification of toxic materials, respond to materials safety issues, and improve assessments of risk regarding materials used in medical devices. [PreME, PostMS]

Molecular Biomarker for Screening of Developmental Toxicants

In order to assess the pertubations of gene expression in embryos as a biomarker of developmental toxicity, we are evaluating interspecies comparisons of the effects of metals, known to be developmental toxicants, on stress protein synthesis in developing rat and avian embryos.

Cadmiun, a strong stress protein inducer in many biological systems, does not induce stress protein synthesis in cultured rat embryos, even though stress proteins are easily induced in this organism following heat shock. OST has conducted experiments to see if this teratogen, along with arsenite and mercury, are inducers of stress proteins in avian embryos. The metals induced the synthesis of major proteins (hsp70, hsp90, hsp28) in a dose- and time-dependent manner. All three metals induced the synthesis of hsp70 and hsp90, with arsenite being the most efficacious, and arsenite induced a unique protein: hsp27. Thus, several changes in gene expression appear to be related to specific metals. Morphologic evaluation of the embryos indicated that the expression of these gene products occurs prior to gross morphologic changes.

A major uncertainty inherent in toxicology testing is the extrapolation of data across species, e.g., are results from 2-year rodent studies predictive of human health effect? If endogenous molecular mechanisms common to all species appear to be involved with the toxic response, the application of a toxicity screening method for human risk assessments related to medical device materials becomes more plausible. [PreME, PostMS]

Hormonal Effects of Medical Device Materials

Some chemicals associated with medical devices (as plastics, plasticizers, binders, solvents, monomers, or other components) have been shown to act as hormones. Because of increasing interest in women's health issues, OST has started examining the estrogenic effects of some chemicals associated with medical devices. The first group of chemicals to be examined are the phthalates, used as plasticizers.

A portion of the work this year consisted of developing the mouse uterotrophic assay in the laboratory by working out the details of dose, strain, time, and age. In addition, OST scientists have conducted a survey of nine phthalates. While variability was a problem, OST obtained evidence of oestrogenic activity (either estrogenic or antiestrogenic) for several of these chemicals. Four gave responses that were more equivocal and need further definition. OST scientists are undertaking more definitive assays for each of these responses in ovariectomized mice.

They also sought to make the assay more sophisticated by examining the use of heat shock proteins (which are known to be involved in estrogen receptor binding) as markers for estrogenic effect. This work is in the preliminary stages of methods development and is the subject of a pending proposal for next year.

The results already obtained suggest that the initial premise of this research-that materials found as components of medical devices may have hormonal effects- is correct, although these effects are, as yet, poorly defined or quantified. While the levels of these materials released from devices is probably small, hormones are highly potent. In the healthy woman, the amount of estrogenic activity contributed by device materials may be of no significance, but in the compromised patient, or the patient receiving hormonal/antihormonal therapies, the contribution from devices might have medical significance. Knowledge of the hormonal activity from medical device materials might lead to alterations of the therapeutic regime and may significantly affect device evaluation. [PreME, PostMS]

Biological Response to Medical Device Materials

Any material implanted into the body evokes a biological response. Some responses are simply fibrous capsule formation protecting both the implant and the host. However some responses develop into chronic inflammatory responses with macrophage accumulation and development of giant cells. It is the purpose of these studies to document the in vitro responses of mouse macrophages to particles from biomaterials and to document the in vivo response to these same materials in particle form or as solid materials.

The in vitro studies are being developed, and so far there is much data accumulated on PMMA (polymethyl-methacrylate: bone cement), HA (hydroxyapatite, a calcium phosphate ceramic used to coat dental and orthopedic implants), and the oxides of titanium and cadmium which would be the surface of implants made of these metals. The production of biologically active substances such as nitric oxide and tumor necrosis factor alpha (which are important substances in inflammatory responses and the production of cytokines such as Il-6, Il-4, and Il-10) involved in the immune responses are being assessed. Lipopolysaccharide (LPS), which is a component of the cell wall of Gram negative bacteria and a known stimulant of cells, is added to macrophage cultures in the presence and absence of the particles. It is evident to date that there is strong production of the biologically active substances by the LPS alone. The addition of HA or PMMA, with the LPS to the macrophage cultures, markedly potentiates the production of these substances.

Whether it is additive or synergistic is still being assessed. On the other hand, the presence of the metallic oxides depresses the response to LPS.

The in vivo data have indicated the formation of a capsule composed of fibroblasts and macrophages when the material is placed into the peritoneal cavity for several days. These cells can then be grown in culture and their activity assessed. The production of the biologically active substances by these peritoneal cells in the absence of LPS is very low. The addition of LPS stimulates the active response. The in vitro data and the in vivo data seem to be in agreement and giving correlative studies.

These findings on the different responses to the different particles and materials will help delineate the differences in biological responses and nature of the inflammatory responses to devices. It will assist in understanding and predicting tissue responses.

The observations on the interaction between LPS and the materials is important in assessing the impact of infection on the tissue response to materials and loss of tissue such as bone resorption. There will be a much better understanding of the role of materials and particles in adverse biological responses to devices and in the development of, or consequences of, infection. [PreME, PostMS]

Molecular Interactions and Medical Device Materials: Risks Associated with Metals in Medical Prostheses

Development of tumors near medical implants raises concerns regarding the safety of certain implant materials. Metal prostheses consist mainly of iron in titanium and cobalt alloys. Copper is the main component of one of the intrauterine contraceptive devices and a component of dental casting alloys and amalgams. All implanted metallic materials corrode and release ions or particulate matter into the surrounding tissue. It has been suggested that long-term use of medical implants, made from either metallic or synthetic materials, may cause mutations or be carcinogenic. Better understanding of the processes and interactions between materials and the biological environment is needed for assessing the risk of a variety of metal-containing medical implants.

In this study, a method was developed for the early detection of DNA base modifications that are associated with mutagenesis. The mutagenicity of iron ions alone or combined with a chelator was studied. Genetic modifications were detected in experimental animals surrounding copper leaching implants. The data gathered in this project may assist in assessing the potential health (e.g. carcinogenic) risk of copper-releasing devices. [PreME, PostMS]

Axial Skeletal Development and Stress Protein Induction

This project is designed to examine the association between insults during prenatal organogenesis and the alteration of embryonic and perinatal morphology and the expression of heat shock proteins (HSPs) and other molecular events. The ultimate focus of the project is to determine if HSPs and other molecular endpoints can be used as biological markers of exposure and/or effect of developmental toxicants. Previous work demonstrated that heat exposure at different temperatures and durations of time and, at different critical periods, will alter endpoints of embryo/fetal development.

Our studies have indicated that, both in vivo and in vitro, the temperature and duration of exposure at the target site (i.e., the embryo) is critical. The extent of effect is dependent on the time of insult and may be related to the genetic expression that is occurring at that time. OST studies on HSP expression indicate a strong association with levels of hyperthermia that produce morphological alterations. Future studies in this area are focusing on 1) further definition of the association of morphological development with HSP expression; 2) investigation of the cellular events that are altered by insult; 3) modeling of the relationship of exposure level, duration, and effect for use in biologically-based, dose-response models and risk assessment; and 4) extension of the model to other potential developmental toxicants.

The Center for Devices and Radiological Health, FDA, and the Office of Research and Development, EPA, are responsible for developing experimental methods that can assist in the testing and assessment of chemical and physical agents. Within the field of developmental toxicology, there is an increasing emphasis on developing biologically-based, dose-response models that will assist in the incorporation of experimental and test data into the risk assessment process. Currently, the use of pharmocokinetic and mechanistic data is limited. The on-going studies noted above are part of a major research effort in expanding understanding of biologicallybased, dose-response models and developing more biologically appropriate methods for assessing the human health risk of real or potential exposures. [ProA]

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A note from one that is receiving notice of filings in the Dow Corning bankruptcy

Very enlightening as to who is benefiting from the bankruptcy.

From" Notice for Allowance of Compensation"

Blizzard & McCarthy (filed 11-30-99) for period 5-1-99 to 10-31-99 fees=$451,842.50, expenses= $59,243.96 Total= $511,086.46 Verner, Liipfert, etc. (filled 11-29-99) for period 5-1-99 to 10-31-99 fees=$720,439.66, expenses=$106,614.41 Total=$827,054.07 Shermets, Chimko, Kilpatrick (filled 11-29-99) for period5-1-99 to 10-3`1-99 fees= $50,004.00 expenses=$7,712.59 Total= $57,716.59

This represents a total of $1,395,857.12 billed to the bankruptcy for co-counsels to the TCC. Who is making the "Big Bucks" here? Who are these firms really representing? The women or the attorneys?

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Kava is a leafy tropical plant (Piper methysticum) in the pepper family, and kava is also the name given a pungent sedative beverage prepared from its roots.

Traditional Use: Kava has occupied a central place in the cultures of the South Pacific since at least the 1770's, when English explorer Captain Cook described its use as a calming, ceremonial, psychoactive drug. Native people drink kava as a social drug and ceremonial sacrament, and to treat a wide range of ailments-primarily urogenital inflammation, cystitis gonorrhea, headaches fatigue, gastric upsets, asthma tuberculosis, and pediatric whooping cough. Applied topically, kava is used to treat fungal infections, insect stings and skin inflammations.

Modern perspective: Kava appears to offer a safe, effective alternative to prescription drugs for anxiety and insomnia and may in some cases provide relief for depression In word recognition tests, kava extract increases reaction time and recognition slightly and does not adversely affect mental function. Doses of kava sufficient to cause sedation do not appear to impair coordination, visual perception, memory, mental clarity or judgement. And, kava's effectiveness does not fade with repeated use.

Since 1920, kava has been listed in European and U.S dispensaries as an effective therapeutic agent for anxiety and other nervous disorders, hypertension, chronic irritations of the urogenital tract, and gonorrhea. Do scientists know how it works? The medicinally active constituents are a group of resinous compounds known as kavalactones or kavapyrones. While as many as fifteen kavalactones are known, only six appear in kava to any significant extent (demethoxy-yangonin, dihydrokavain, yangonin, kavain, dihydromethysticin and methysticin). Kava cultivars favored by native peoples contain kavalactones in particular, specific ratios, while others produce headaches with little relaxant effect.

Kavalactones produce sedative, soporific, and muscle relaxant effects, but the mode of action remains uncertain. In 1991, researchers reported that the preferential site of action for both whole kava resin and synthetic kawain is the amygdala, in the limbic system. Unlike the benzodiazepines (Valium®, etc.), kavalactones do not appear to interact with gamma-aminobutyric acid or its receptor sites.

The most significant anti-anxiety studies of kava show that an effective daily dose consists of 70 to 210 mg of kavalactones. To promote sleep, a dose of approximately 200 mg of kavalactones taken thirty to sixty minutes prior to retiring has been recommended.

Recent findings: In a randomized, placebo-controlled clinical trial lasting 25 weeks, German researchers reported that a standardized kava extract produced anti-anxiety effects in 101 outpatients suffering from anxiety of non-psychotic origin. As their report concluded: "These results support WS 1490 [kava extract] as a treatment alternative to tricyclic antidepressants and benzodiazepines in anxiety disorders, with proven long-term efficacy and none of the tolerance problems associated with tricyclics and benzodiazepines." Other German researchers reported that selected kavapyrones inhibited the reuptake of [3H]- noradrenaline, and speculated that this action might be responsible for or, at least, contribute to the psychotropic properties of kava pyrones.

Selected References

* Kava, The Pacific Drug, by Lebot, Merlin and Lindstrom, Yale University Press 1992.

* Lindenberg, D. and Pitule-Schodel, H. 1990. D,L - Kavain in comparison with oxazepam in anxiety disorders. A double-blind study of clinical effectiveness. Forschr Med 108, 49 - 50, 53- 54. [Article in German]

* Lehmann E, Klieser E, Klimke A, Krach H, Spatz R. The efficacy of Cavain in patients suffering from anxiety. Pharmacopsychiatry 1989 ov;22(6):258-62. [Article in German]

* Volz HP, Kieser M . Kava-kava extract WS 1490 versus placebo in anxiety disorders--a randomized placebo-controlled 25-week outpatient trial. Pharmacopsychiatry 1997 Jan;30(1):1-5.

* Heinze HJ, Munthe TF, Steitz J, Matzke M. Pharmacopsychological effects of oxazepam and kava-extract in a visual search paradigm assessed with event-related potentials. Pharmacopsychiatry 1994 Nov;27(6):224-30

* Herberg KW. [Effect of Kava-Special Extract WS 1490 combined with ethyl alcohol on safety-relevant performance parameters]. Blutalkohol 1993 Mar;30(2):96-105. [Article in German]

* Munte TF, Heinze HJ, Matzke M, Steitz J. Effects of oxazepam and an extract of kava roots (Piper methysticum) on event-related potentials in a word recognition task. Neuropsychobiology 1993;27(1):46-53.

* Kinzler E, Kromer J, Lehmann E. [Effect of a special kava extract in patients with anxiety-, tension-, and excitation states of non- psychotic genesis. Double blind study with placebos over 4 weeks]. Arzneimittelforschung 1991 Jun;41(6):584-8. [Article in German].

* Warnecke G. [Psychosomatic dysfunctions in the female climacteric. Clinical effectiveness and tolerance of Kava Extract WS 1490]. Fortschr Med 1991 Feb 10;109(4):119-22. [Article in German]

* Davies LP, Drew CA, Duffield P, Johnston GA, Jamieson DD. Kava pyrones and resin: studies on GABAA, GABAB and benzodiazepine binding sites in rodent brain. Pharmacol Toxicol 1992 Aug;71(2):120-6.

* Nowakowska E, Ostrowicz A, Chodera A [Kava-kava preparations--alternative anxiolytics]. Pol Merkuriusz Lek 1998 Mar;4(21):179-180a [Article in Polish].

* Seitz U, Schule A, Gleitz J . [3H]-monoamine uptake inhibition properties of kava pyrones. Planta Med 1997 Dec;63(6):548-9.

* Seitz U, Ameri A, Pelzer H, Gleitz J, Peters T. Relaxation of evoked contractile activity of isolated guinea-pig ileum by (+/-)- kavain. Planta Med 1997 Aug;63(4):303-6.

* Walden J, von Wegerer J, Winter U, Berger M, Grunze H . Effects of kawain and dihydromethysticin on field potential changes in the hippocampus. Prog Neuropsychopharmacol Biol Psychiatry 1997 May;21(4):697-706.

* Suss R, Lehmann P. [Hematogenous contact eczema cause by phytogenic drugs exemplified by kava root extract]. Hautarzt 1996 Jun;47(6):459-61. [Article in German].

* Jussofie A, Schmiz A, Hiemke C. Kavapyrone enriched extract from Piper methysticum as modulator of the GABA binding site in different regions of rat brain. Psychopharmacology (Berl) 1994 Dec;116(4):469-74.

* Mathews JD, Riley MD, Fejo L, Munoz E, Milns NR, Gardner ID, Powers JR, Ganygulpa E, Gununuwawuy BJ. Effects of the heavy usage of kava on physical health: summary of a pilot survey in an aboriginal community. Med J Aust 1988 Jun 6;148(11):548-55.

* Jamieson DD, Duffield PH. The antinociceptive actions of kava components in mice. Clin Exp Pharmacol Physiol 1990 Jul;17(7):495- 507.

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OTHER SILICONE RELATED RESOURCES ARE AVAILABLE THROUGH THE SILICONE WEBRING

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WHERE THERE'S SMOKE THERE'S FIRE ~ On The Net

The following websites have the "Where There's Smoke There's Fire" documents:

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FOR AOL MEMBERS OR OTHERS, WORKING WITH ON-LINE SERVICES NOT EASILY ACCOMMODATING THE FORMAT OF THESE NEWSLETTERS, YOU MAY ACCESS THEM FROM THE CANADIAN CONNECTION WEBSITE AT THE HYPERLINK BELOW. TONY & MICHELINE LAMBERT HAVE GRACIOUSLY ARCHIVED THEM FOR US.

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Sarcastic things to say

Thank you, we're all refreshed and challenged by your unique point of view

The fact that no one understands you doesn't mean you're an artist

Any connection between your reality and mine is purely coincidental

No, my powers can only be used for good

I have plenty of talent and vision. I just don't care

You sound reasonable...Time to up my medication

I like you. You remind me of when I was young and stupid

What am I? Flypaper for freaks!

I'm already visualizing the duct tape over your mouth

Ahh... I see the screw-up fairy has visited us again

I will always cherish the initial misconceptions I had about you

It's a thankless job, but I've got a lot of Karma to burn off

Yes, I am an agent of Satan, but my duties are largely ceremonial

How about never? Is never good for you

I'm really easy to get along with once you people learn to worship me

I'll try being nicer if you'll try being smarter

I'm out of my mind, but feel free to leave a message

I don't work here. I'm a consultant

At least I have a positive attitude about my destructive habits

You are validating my inherent mistrust of strangers

I see you've set aside this special time to humiliate yourself in public