ISO TR 22019:2019 download

06-23-2021 comment

ISO TR 22019:2019 download.Nanotechnologies-Considerations for performing toxicokinetic studies with nanomaterials.
Nanomaterials (NMs) are a family of chemicals that, like any other chemicals, can exert a range of toxicities. Toxicokinetics can support the safety evaluation oI’compounds including NMs by identifying potential target organs, and especially for NMs. the potential for persistence in organs (including cellular uptake and compartmentaltzation). Also, toxicokinetic Information can be used to evaluate if a NM behaves differently from a similar NM or bulk material with the same chemical composition, e.g. with regard to harrier penetration. As for all studies with NMs, a proper characterization of the NM dispersions or aerosols used in the toxicokinetic studies is essential.
Importance ojtoxicok.netac mformauonfo, risk assessment (of nanomatertals)
Toxlcokinetics describes the absorption, distribution, metabolism and excretion (ADME) of foreign compounds in the body with time. It links the external exposure with the Internal dose and is thus a key aspect for toxicity. If a NM is absorbed by the body through any of the potential exposure routes (oral. respiratory dermal) it can enter into the blood or lymph circulation. Subsequent distribution to internal organs determines potential target tissues and potential toxicity. Alternatively. NMs can be intravenously administered (e,g. as nanomedicine) thus directly entering the blood circulation, potentially resulting In wide spread tissue distribution. Toxicoklnetics therefore aids In the design of targeted toxicity studies and In identifying potential target organs and can thus also provide relevant information for justification or waiving of toxicity studies, In addition, toxicokinetic information can be useful as basis for grouping and read-across ofNMs. Risk assessments based on Internal concentrations, determined using toxicokinetic Information, can be more realistic than risk assessments based on external doses, as nanoparticles (NPs) can show specific tissue distribution and accumulation. Toxicokinetic studies can be used to build toxicokinetic models, especially physiologically based pharmacokinetic (PBPIC) models, which then can be used to extrapolate experimental toxicity data to other species, tissues, exposure routes, exposure durations and doses. Due to the accumulation of some NPs, the ability to extrapolate to longer exposure durations is of special importance for NMs.
Why a technical report specifically for nanornateriols?
A considerable body of published literature, including many national and international guidelines, exists on the use of toxicokinetic methods to study the fate of chemicals in the body. In addition, OECD Test Guideline (TG) 417 on Toxlcoklnetlcs (latest update dated 2010) gives an extensive description for evaluation of the toxAcolclnetic profile of chemicals but excludes NMs specifically. ISO 10993-16:2017 Biological evaluation of medical devices — Plsrt 1& Toxkoklnetic study design for degradation products and kachabks, provides an overview for toxlcoklnetic studies for leachables of medical devices. Furthermore, the European Medicines Agency’s ICH S3A (Toxicokinetics. A Guidance far Assessing Systemic Exposure in Toxicology Studies) and ICH S38 (Pharmacokinetics: Repeated Dose Tissue Distribution Studies) give guidance on the design and conduct of toxicokinetic studies to assist in the development of new drugs.
Guidelines also exist on toxlcokinetk modelling, especially the development and application of physIologIcally-based pharmacokinetic (PBPK) models. For example, the United States Food and Drug AdminIstratIon’s Draft Physiologically Based Pharmacoklnetlc Analyses — Formal and Content Guidance for Industry, provides the standard content and format of PHPK study reports while the United States Environmental Protection Agency’s Approaches for the Application of Physiologically Based Pharmacokinetic (PBPK) Models and Supporting Data In Risk Assessment, addresses the application and evaluation of PBPK models for risk assessment purposes. The European Medicines Agency (EMA) has published a “Guideline on the qualification and reporting of physiologically based pharmacokinetic (PIIPK) modelling and samubtion In 2016W. WHO has published the Characterization and application of physiologically based pharmacoklnetic models In risk assessmenr’iZl.
As stated, the current OECD toxbcokinrtics TG 417 explIcitly states that the guideline is not intended [or the testing ol NMsL3I, as the toxlcokinetlcs of NMs are different from dissolved ions/molecules and large particles. This was confirmed in a report on preliminary review of OECD Test Guidelines for their applicability to NMsISI. Additionally, the PBPK models described in the current and mentioned guidance documents are not suitable for NMs. as the processes governing the distribution of NPs is different from
length range approximately from I nm to 100 nm
Note I to entry: Properties that are not extrapolations from larger sizes are predominantly exhibited in this length range.
ISOLJRCE: ISO/TS 80004-1: 2015, 2.11
application of scientific knowledge to manipulate and control matter predominantly in the ncrnoscule (13) to make use of size- and structure-dependent properties and phenomena distinct From those associated with individual atoms or molecules, or extrapolation from larger sizes of the same material
Note Ito entry: Manipulation and control includes matenal synthesis.
ISOURCE: ISO/TS 80004-1: 2015,2.31
material with any external dimension in the nanoscuk (13) or having Internal structure or surface structure in the nanoscale
Note Ito entry: This generic term is inclusive of nono-object (16) and nanostructured materiel (16). Note 2 to entry: See also 16 to 3.11.
ISOURCE: lSO/T5 80004-1:2015, 2.4j
discrete piece of material with one, two or three external dimensions in the .wnoscak (33)
Note Ito enrry The second and third external dimensions are orthogonal to the first dimension and to each other.
ISOURCE: ISO/TS 80004-1: 2015, 2.51
composition of inter-related constituent parts in which one or more of those parts Is a nunoscale (3.3) regIon
Note Ito entry: A region is defined by a boundary representing a discontinuity in properties.
(SOURCE: ISO/TS 80004-1: 2015,2.61
nanostruclured material
material having Internal nanostructure (31) or surface nanostructure
Note I to entry: This definition does nnt exclude the possibility For a nano-objec: (16) to have Internal structure or surface structure. liexternal dimension(s) are In the ,,anoscak (3.3), the term nano-ohiect is recommended.
(SOURCE: ISO/TS 80004-1: 2015, 2.7)
none-object (3.6) with all external dimensions In the nanoscak (13) where the lengths of the longest and the shortest axes o(the nano-object do not differ significantly
Note I to entry: lithe dimensions differ slgnlllcantly (typically by more than 3 tImes), terms such as nanofibre (ISO/’FS 80004-2:2D17, 4.5) or nanoplot. (ISO/TS 80004-2:2017 4.6) may be preferred to the term nanopartlcie.
size. but when taking into account the blood concentration. larger Ag were more readily distributed to breast milk than smaller Ni’s and Ag.lI. Probably, both the blood concentrations and transfer to breast milk were actually caused by silver ions, and not by silver NPs. as the trends in these tissues match those of the % ions released. Ag Ni’s were distributed to breast milk to a greater extent early In the lactation period than later in the lactation period.
Morishita et al.liSl also found that the administered doses of Ag (Ni’s or ions) did not induce any apparent acute damage to the blood.milk barrier, thus their observed translocatlon seemed not to be caused by Increased leakiness of this barrier. Substances in blood are thought to transfer to breast milk by means of transcytotlc. membrane transport, and paracellular transport pathways. As the Ag Ni’s used by Morishita et aLlSI were not small enough to use the membrane transport or paracellular transport pathways, the Ag NPs might have transferred to breast milk by means ol a transcytotc pathway. They found some experimental evidence that this transport was indeed through a nonparacellular and energy-dependent pathway. BuL as indicated previously for Ag Ni’s. this might have been the ions instead of the Ni’s.
Alter inhalation of Au NPs by volunteers Au was demonstrated In blood and urine at 15 mm after inhalation, although the calculated uptake from the Jung was very low (0.02 % of the administered dose)12&111Z421.
Due to the low level of elimination, accumulation is possible and is indeed reported for various types of manufactured NMs and for vanous routes of exposure (e.g. for T202 in ratsllZ.l, for T102 in the environmentlliil. for Ag in rats1Zl, and for Si02 in ratslZ&41).
13 Conclusions
Based on the observations described above several summaries and conclusions can be made, The most Important conclusion to be made Is that the toxicokinetics and tissue distribution or NMs differs considerably from molecular/ionic substances. Table .1 gives an overview of important differences between toxicokinetic processes and aspects of dissolved (molecubrfionic) substances and NMs. These differences are due to the particulate nature of the NMs. which contrasts with the soluble nature of dissolved substances. There are Indications for oxidation of organic NPs. It Is unclear If metal oxides are metabolized but dissolution of some metals and metal oxides can occur. For those NMs that do show some dissolution, like for example nanosllvet zinc oxide and copper oxide NMs. the toxicokinetics and tissue distribution need also to consider their soluble fractions. For the dissolved molecules originating from the NMs the toxicokinetics will be similar to that of dissolved (molecular or ionic) substances.
Due to this aberrant toxicokinctic behaviour of Ni’s. the classical toxicokinetic parameters have typical values for NMs. or may not even be applicable. Iabl2 summarises the limitations of applying some of the classical toxicokinetic parameters to NPs.

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