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)