Post on 27-May-2020
Modern Approaches and Special Cases
Whitney V. Christian, Ph.D.
I am a medical device toxicologist employed by Medtronic. Any views presented herein are those of the author and should not be construed to represent the views of Medtronic.
Formerly I was an external consultant to DePuy Orthopaedics, which funded some of the work presented herein. Neither myself nor any members of my immediate families have any financial interest or affiliation with DePuy Orthopaedics.
“An instrument, apparatus, implement, machine, contrivance, implant, in vitro reagent, or other similar or related article, including a component part, or accessory which is:
◦ recognized in the official National Formulary, or the United States Pharmacopoeia, or any supplement to them,
◦ intended for use in the diagnosis of disease or other conditions, or in the cure, mitigation, treatment, or prevention of disease, in man or other animals, or
◦ intended to affect the structure or any function of the body of man or other animals, and which does not achieve any of its primary intended purposes through chemical action within or on the body of man or other animals and which is not dependent upon being metabolized for the achievement of any of its primary intended purposes.”
FDA, 2015: http://www.fda.gov/AboutFDA/Transparency/Basics/ucm211822.htm
Biocompatibility:
◦ “The ability of a material to perform with an appropriate host response in a specific application.”
ISO 10993 standards are testing recommendations and guidelines for evaluating the biocompatibility of medical devices
Chester Consensus Conference, 1986 FDA, 2015: http://www.fda.gov/AboutFDA/Transparency/Basics/ucm194438.htm
FDA, 2014: http://www.fda.gov/MedicalDevices/ResourcesforYou/Consumers/ucm142523.htm
Class Description Percent Examples
I Non-invasive 47% Band-Aids, examination gloves,
hospital beds
II Invasive 43% Infusion pumps, bone fixation
screws, condoms
III Life supporting/sustaining, implanted, or present
potential unreasonable risk of illness/injury 10%
Pacemakers, total hip arthroplasty (MoMs), breast implants
ANSI/AAMI/ISO 10993-1:2009 Cor 1:2010/(R)2013 FDA GPM #G95-1: Table 1 & Attachment B –Table 2, 1995
ISO Standard Title Immunological Endpoint
10993-6 Tests for local effects after implantation Foreign-body response
10993-10 Tests for irritation and skin sensitization Irritation (erythema/edema),
sensitization
10993-11 Tests for systemic toxicity Material-mediated pyrogenicity
10993-20* Principles and methods for immunotoxicology
testing of medical devices
Inflammation, immunosuppression, immunostimulation, hypersensitivity,
auto-immunity *Standard not recognized by the FDA
Leveraging “big data” for regulatory decision making
Leveraging evidence from clinical experience and employing evidence synthesis across multiple domains in regulatory decision making
Improving the quality and effectiveness of reprocessing reusable medical devices
Developing computational modeling technologies to support regulatory decision making
Enhancing performance of digital health and medical device cybersecurity
Incorporating human factors engineering principles into device design
Modernizing biocompatibility/biological risk evaluation of device materials
Advancing methods to predict clinical performance of medical devices and their materials
Advancing the use of patient-reported outcome measures in regulatory decision making
Collecting and using patient experience/preference in regulatory decision making
AAMI, 2015: http://www.aami.org/productspublications/articledetail.aspx?ItemNumber=2909
Modern Approaches:
In Vitro Assays for Risk Assessment
Toxicology in the 21st Century (Tox21) ◦ Development/validation of in vitro cell-based assays
to quickly and efficiently determine the potential of chemicals to disrupt processes in the human body that may lead to negative health effects.
In vitro toxicity/risk assessment
Adverse outcome pathways (AOP) framework
◦ Perturbations of toxicity pathways apical endpoints
Molecular Initiating Event
(MIE)
Intermediate Key Events
(KEs)
Adverse Outcome
(AO)
ISO Endpoint Current Animal Test Number of Animals In Vitro Alternatives
Irritation Rabbit skin irritation test 3 – 6 EpiSkin®, SkinEthicTM RHE,
EpiDermTM SIT
Sensitization Guinea pig maximization test 15 - 30 DPRA, KeratinoSens, h-CLAT,
mMUSST, SenCeeTox
Pyrogenicity Rabbit pyrogen test 3 - 5 PyroCheck, EndosafeTM-IPT,
PyroDetect
OECD, 2010; Coleman et al., 2015; Hartung, 2015
OECD, 2012; Coleman et al., 2015
Natsch et al., 2013; Urbisch et al., 2015; Coleman et al., 2015
Assay AOP Sensitization Key Event Description
DPRA Haptenation (1) Measure chemical reactivity with Cys and Lys containing
synthetic peptides
KeratinoSens Keratinocyte activation (2) Measure Keap1-Nrf2-ARE pathway activation in HaCaT
cells transfected with ARE-Nrf2 luciferase reporter
h-CLAT Dendritic cell activation (3) Measure cell surface expression of CD86 and CD54 in
THP-1 cells via FLOW cytometry
mMUSST Dendritic cell activation (3) Measure cell surface expression of CD86 in U937 cells
via FLOW cytometry
SenCeeTox Haptenation (1)
Keratinocyte activation (2)
Measure cell viability (LDH release), GSH depletion, and gene expression changes in ARE/Keap1/Nrf2,
AhR/ARNT/XRE, and Nrf1/MTF/MRE pathways (qRT-PCR) in HaCaT cells or RHE (EpiDerm/SkinEthic)
Special Cases:
Sensitization from MoM Wear Debris
Corrosion, fretting wear, articulation, and
dissolucytosis generate:
◦ Metal ions
◦ Metal particulate
Depuy, 2013; Langton et al., 2011; Gill et al., 2012; Cooper et al., 2012; Kop et al., 2009; Dunbar, 2010; Higgs et al., 2013; Gascoyne et al., 2014; Soh et al., 1996; Topolovec et al., 2013
Are well functioning MoMs capable of inducing sensitization?
◦ At what dose does wear debris from a well functioning MoM induce sensitization?
Induction establishment of memory T cells
Elicitation activation of memory T cells
Janeway et al., 2001
Proliferative response
Are well functioning MoMs capable of inducing sensitization?
◦ At what dose does wear debris from a well functioning MoM induce sensitization?
Basketter et al., 2003
Assay Animal Route Type
Guinea Pig Maximization Test (GPMT)
Guinea pig Intradermal
(injection into dermis) Qualitative
Buehler Test (Closed-Patch Test)
Guinea pig Dermal (topical)
Qualitative
Local Lymph Node Assay (LLNA)
Mouse Dermal (topical)
Quantitative
LLNA (Ian Kimber)
PLNA
◦ Positive response: SI >3
Basketter et al., 1996; Chamberlain and Basketter, 1996; Kimber et al., 1998 De Bakker et al., 1990; Bloksma et al., 1995; Schielen et al., 1996; Ravel and Descotes, 2005
X
X
Inject label ([3H]-TdR/ [125I]-IUdR+ FUdR)
Day 6
Ear application (daily, 3x) Day 1-3
Footpad injection (1x) Day 1
Inject label (3H-TdR/BrdU)
Sac, isolate auricular lymph nodes, make single-cell
suspension of LNC
Quantify proliferation (Liquid Scintillation)
Quantify proliferation (Liquid Scintillation/FLOW)
2 Days
4-10 Days
5 hours
5 hours
Sac, isolate popliteal lymph nodes, make single-cell
suspension of LNC
Post in-life phase
Post in-life phase
Year Investigator Study/Finding
1970 Ford et al. Injection of histo-incompatible lymphocytes produced GvH reaction, PLN enlargement.
1981 Gleichmann Footpad injection of anticonvulsant diphenylhydantoin increases PLN weight (PLNA born). PLNA may be useful for studying drug/chemical induced auto-immunity (ISO 10993-20).
FDA (2002) supports PLNA for immunotoxicological evaluation of new drugs.
1989 Kimber et al. LLNA identifies contact allergens. PLNA may be useful for studying sensitizing or
immunostimulatory chemicals.
1989 Kammüller et al. PLNA responses to contact allergens. PLNA is useful for detecting sensitizing chemicals.
1990 Schuhmann et al. PLNA responses to Au3+. Suggests PLNA can be used to assess metal sensitization.
1999 Artik et al. PLNA responses to Ni3+/Ni2+. Suggests PLNA can be used to assess metal sensitization.
Surrogate MoM wear debris: mixture of commercial metal particles and metal ions (from metal salts)
◦ Test article: Cr2O3 particles + Co2+, Cr3+, and Ni2+ ions
Dose Cumulative Wear at 1 mm3/yr
Low 10 days
Medium 20 years
High 40 years
Physiological relevance of doses
Proliferative response
Quantify immune response ◦ Lymph node weight, cellularity, and SI
In situ proliferation vs. lymphocyte influx
◦ Footpad swelling
Characterize immune response ◦ Immunoprofiling (CD3/B220, CD4/CD8, I-AD/CD69)
◦ H&E histology on PLN sections
Distinguish between irritation and sensitization responses
Administered Compound SI WI CI Footpad Swelling
B220+/control
CD4+ CD8+ I-AD+
CD69+ Histology
Negative Control
Weak sensitizer
DCNB <3 C C – <1.25 C C C –
Irritant SDS <3 C C ++ >1.25 C C C –
Positive Control
Strong sensitizer
DNCB >3 >C >C ++ >1.25 >C >C >C +
Metal sensitizer
AuCl3 >3 >C >C ++ >1.25 >C >C >C –
Test Article
NOAEL Low <3 C C - <1.25 C C C –
LOAEL Med >3 >C >C + >1.25 >C >C >C –
SI – stimulation index; WI – weight index; CI – cellularity index
C – equivalent to control; >C – significantly greater than control
Gerberick et al. 2002
The PLNA is a useful model for evaluating the induction threshold for “deep tissue” metal sensitization
A dose of surrogate wear debris representing 20 years of well functioning MoM wear induced immune stimulation
◦ Doses of metal ions alone (i.e., without Cr2O3 particulate) induced similar immune stimulation
Patients with normal wearing MoMs are unlikely to become sensitized to wear debris
Incomplete characterization of dose-response ◦ Assess doses between NOAEL (10 days of wear debris) and
the LOAEL (20 years of wear debris)
Kinetics of immunological response ◦ Assess PLNA response at different times after
administration (4 days vs. 10 days)
Route of exposure ◦ PLNA (footpad) vs. MoM patient (articulating joint)
Duration of exposure ◦ PLNA (acute) vs. MoM patient (chronic)
Extrapolation to humans ◦ Differences in inter-individual immune responses
(weak vs. moderate vs. strong responders)