The Toxicologist - Society of Toxicology

1312 EVALUATION OF THE SENSITIVITY OF ENDPOINTS
IN THE ISO 10993-11 SYSTEMIC TOXICITY STANDARD
USING POSITIVE CONTROL COMPOUNDS.
A. Freeman 1, 2 , A. Komiyama 1 , J. Fazio 1, 3 , S. Hamilla 1, 4 , H. Dinesdurage 1 and
R. P. Brown 1 . 1 U.S. FDA, Silver Spring, MD, 2 University of Maryland, College
Park, MD, 3 Western New England College, Springfield, MA and 4 University of
Connecticut, Storrs, CT.
The preclinical biological safety evaluation of medical devices often includes an assessment
of acute systemic toxicity. This assay is typically conducted using the test
method outlined in the ISO 10993-11 (2008) standard. Criteria are included in the
standard to determine if an extract of a device is toxic or not. These criteria include
death of one or more animals, behavioral changes, or greater than 10% change in
body weight (BW). Since the test methods outlined in this standard have been criticized
as being too insensitive to detect toxic effects, a proof-of-principle study was
conducted to compare the sensitivity of these endpoints to clinical chemistry results
for two positive control compounds, cadmium chloride (Cd) and mercuric chloride
(Hg). Intraperitoneal injection of the compounds (0.5 or 1 mg/kg) to male CD-1
and Balb/c mice resulted in slight change in body weight after 24 hours, compared
to saline injected controls; however the changes were less than 10% of the total BW.
There was no statistically significant difference in BW between treated and control
animals at the 72-hour time point. Behavioral changes were observed in high-dose
Cd animals shortly after injection, but not those treated with 0.5 mg/kg; however,
ALT levels were elevated, relative to controls, at both doses, but only at the 24-hr
time point. These results suggest that the endpoints in the standard are sufficiently
sensitive to detect overt but not subtle signs of toxicity. The incorporation of endpoints
such as clinical chemistry may improve the sensitivity of the acute systemic
toxicity assay for some compounds.
1313 RAPID TOXICITY SCREENING OF POLYMERIC
MATERIALS USING THE MICROTOX ASSAY.
P. Kulkarni, H. Dinesdurage and R. P. Brown. CDRH, U.S. FDA, Silver Spring, MD.
Cytotoxicity is assessed as part of the biological safety evaluation of essentially every
new medical device. The in vitro cytotoxic effects of device extracts are typically assessed
using cells in suspension (e.g., direct hemolysis) or in culture. The Microtox
assay, based on light emission from photoluminescent bacteria (Vibrio fischeri), is
widely used in aquatic toxicology to screen water samples for cytotoxic effects. The
potential for these bacteria to be used as an adjunct to the use of mammalian cellbased
cytotoxicity assays for rapid toxicity screening of extracts of device materials
was evaluated. In this study, the direct hemolysis assay was conducted using a modification
of the method in the ASTM F756 standard to classify polymeric materials
(BUNA, nitrile, latex (2 types), neoprene, silicone, polyurethane, high density
polyethylene, butyl rubber, norprene, polypropylene, F-4040-A tubing) as being
toxic (≥5% hemolysis) or nontoxic. The materials were then extracted in 50%
ethanol (24 hrs at 37 o C) and the extracts were used in the Microtox and indirect
hemolysis assays. Microtox was able to differentiate toxic from nontoxic materials
with a sensitivity of 100% and a specificity of 57%, assuming cell death ≥ 10% represents
a toxic response in this assay. There were no false negatives and three false
positives, suggesting that the Microtox assay is more sensitive than the direct hemolysis
assay. There was complete agreement between the results of the Microtox
assay and the indirect hemolysis assay. Since the Microtox assay is sensitive, does
not require sterile technique and results can be obtained in 15 minutes, it represents
a promising adjunct to the direct and indirect hemolysis assays for the rapid toxicity
screening of polymeric materials used to manufacture medical devices.
1314 USE OF AN IN VITRO SCREEN FOR ASSESSING THE
VAGINAL IRRITATION POTENTIAL OF INTIMATE
CARE PRODUCTS.
P. Clay 1 and N. Belot 2 . 1 SSL International, Manchester, United Kingdom and
2 Straticell, Gembloux, Belgium. Sponsor: D. Kent.
Intimate care products such as personal lubricants and vaginal moisturisers are classified
as medical devices in certain regulatory regions. When developing new products,
assessment of the irritancy of the product forms part of the assessment of the
overall biological safety prior to performance evaluation in volunteers. If considered
necessary, the pre-clinical assessment of irritation potential can include a vaginal
irritation study in the rabbit (ISO 10993/10). A recent product development
called into question the sensitivity and relevance of this test to the effects seen in
humans for this type of product and therefore an alternative/additional test was
sought. For ethical reasons, an in vitro test method has been developed; this also offers
potential cost and time benefits which may make the method suitable as an
early candidate screen. The test methods used were those given by SkinEthic
Laboratories for use with their Skin Ethic HVE reconstituted human vaginal epithelium
model. Briefly, day 6 cultures of tissue were treated in duplicate with
70μL of the test sample for 20mins, 1, 2 and 4 hours after which the viability of
the tissue was assessed by MTT assay. From these data, an ET50 (time taken to reduce
viability to 50% of the control) value was calculated and used as an indictor
of the irritant potential of the formulation. Initial experiments with a range of
commercially available vaginal moisturisers (Replens MD, Saugella Intilac,
Monasens Intimate Care, Durex Sensilube) suggested that these methods could
provide an appropriate level of sensitivity and also showed a good correlation with
irritancy reported in volunteer trials. Further validation of the methods to establish
inter-experimental variability has shown the methods to be highly reproducible and
confirmed the sensitivity of the methods. These experiments demonstrate that the
methods used are suitable as a screen for candidate formulations and have the potential
to offer more relevant sensitivity than the current animal tests used for regulatory
biocompatibility assessment.
1315 DETERMINATION OF BISPHENOL-A COMPOUNDS
LEACHABLE FROM POLYCARBONATE- AND
POLYSULFONE-BASED HEMODIALYZERS.
J. Guo, S. Cho and H. D. Luu. Division of Chemistry and Materials Sciences, U.S.
FDA, Center for Devices and Radiological Health, Office of Science and Engineering
Laboratories, Silver Spring, MD.
Bisphenol A (BPA) is an organic compound used to produce polycarbonate (PC)
and polysulfone (PS) plastics. Both polymers have been widely used, not only for
consumer products such as baby and water bottles and electronics, but also for
medical devices. However, many studies have reported that BPA acts as an endocrine
disruptor, which is a possible health hazard to humans, especially to the pediatric
population. Recent concerns over the release of BPA from PC- and PS-based
products in daily use have prompted us to measure the amount of BPA compounds
leachable from PC- and PS-based medical devices. In particular, hemodialyzers
have a high possibility of exposing residual or hydrolytically generated BPA to patients,
because these devices have direct contact with the blood stream during extracorporeal
circulation. In this study, we focused on identifying and quantifying
BPA compounds leachable from PS/PC-based hemodialyzers. We used exhaustive
extraction methods to determine the maximum BPA present as a worst case scenario
and dynamic extraction methods to determine the amount of BPA leachable
under simulated physiological conditions. Finally, we used gas
chromatography/mass spectrometry (GC/MS) to analyze the BPA compounds.
1316 HUMAN BIOKINETIC MODEL OF NICKEL RELEASE
FROM MEDICAL DEVICES.
J. S. Tsuji 1 and K. T. Bogen 2 . 1 Exponent, Bellevue, WA and 2 Exponent, Oakland, CA.
Quantifying the magnitude of nickel (Ni) release over time is important for understanding
the potential for health impacts of medical devices containing Ni.
Transient increases in Ni serum levels have been reported for patients with implanted
medical devices made of Ni-containing alloys (e.g., stainless steel, nitinol).
Nitinol (55% titanium/45% Ni) has been used in metal wire structures of various
cardiovascular occlusion devices, such as for closure of atrial septal defects or as a
vascular plug. Ni release rates and their timing in vivo, however, cannot be directly
inferred from discrete measurements of Ni serum concentrations because of the
complex biokinetics of Ni in the body, affecting both the magnitude of serum levels
and their time course. A biokinetic model for internal Ni release was developed
using a published short-term model based on oral dosing of Ni in humans, as modified
to include more complicated and longer-term kinetics noted in other studies.
The model was fit to Ni serum data at discrete time points reported in clinical studies
of patients with implanted nitinol devices (septal occluders), with adjustment of
parameters as necessarily and derivation of corresponding Ni release rate curves.
The overall pattern of Ni release predicted by the model showed increases in the Ni
release rate after implantation that peaked within the first week. The predicted in
vivo release rates declined to zero by 145 days after implantation. Estimated total
Ni released per patient was less than 1/10th of the normal human Ni body burden,
and represents a relatively small amount of Ni dosing to the body at any one time.
By comparison, internal Ni releases occur over much longer time periods for other
medical devices such as stainless steel spinal implants based on elevated serum Ni
levels up to 4 years post-implantation. Ni-containing medical devices in humans or
dogs, however, have not been associated with long-term health effects due to high
Ni release, as observed in rodents injected or implanted with pure Ni powders or
pellets.
SOT 2011 ANNUAL MEETING 281