A critical appraisal of the process of regulatory implementation of novelin vivoandin vitromethods for chemical hazard and risk assessment

Abstract

Regulatory toxicology urgently needs applicable alternative test systems that reduce animal use, testing time, and cost. European regulation on cosmetic ingredients has already banned animal experimentation for hazard identification, and public awareness drives toward additional restrictions in other regulatory frameworks as well. In addition, scientific progress stimulates a more mechanistic approach of hazard identification. Nevertheless, the implementation of alternative methods is lagging far behind their development. In search for general bottlenecks for the implementation of alternative methods, this manuscript reviews the state of the art as to the development and implementation of 10 diverse test systems in various areas of toxicological hazard assessment. They vary widely in complexity and regulatory acceptance status. The assays are reviewed as to parameters assessed, biological system involved, standardization, interpretation of results, extrapolation to human hazard, position in testing strategies, and current regulatory acceptance status. Given the diversity of alternative methods in many aspects, no common bottlenecks could be identified that hamper implementation of individual alternative assays in general. However, specific issues for the regulatory acceptance and application were identified for each assay. Acceptance of one-in-one replacement of complex in vivo tests by relatively simple in vitro assays is not feasible. Rather, innovative approaches using test batteries are required together with metabolic information and in vitro to in vivo dose extrapolation to convincingly provide the same level of information of current in vivo tests. A mechanistically based alternative approach using the Adverse Outcome Pathway concept could stimulate further (regulatory) acceptance of non-animal tests.

Using zebrafish in systems toxicology for developmental toxicity testing

“…Developmental toxicity can be caused by multiple mechanisms. However, certain key genes, either marker or causative genes, are known to be involved in the developmental toxicity of various chemicals (reviewed in Piersma et al 2014). Therefore, transgenic zebrafish, in which fluorescent proteins are expressed under the control of these key genes, can be a powerful tool in ZEBDET to detect developmental toxicities of chemicals with a high degree of sensitivity (reviewed in Dai et al 2014).…”

Innovative testing in reproductive toxicology—The ChemScreen experience

“…The implementation of these in silico and in vitro models in regulatory toxicology lags behind. The causes for the slow implementation of alternative methods in regulatory toxicology are multiple and complex [1,2]. This situation is partly due to the relative simplicity of alternative assays as opposed to the complexity of the biological system.…”

Intersection of toxicogenomics and high throughput screening in the Tox21 program: an NIEHS perspective

“…However, there are accompanying challenges in interpreting in vitro results for their usefulness in predictive toxicology and their adoption by regulatory communities as detailed in recent reviews (Elmore et al, 2014; Persson et al, 2014; Piersma et al, 2014; Zhang et al, 2014). In applying in vitro screening data to in vivo toxicity, some approaches carefully target the use of specific in vitro assays toward predicting adverse effects such as liver injury or bile salt transporter inhibition-mediated cholestasis (Persson et al, 2014) or genotoxicity (Zhang et al, 2014).…”