Characterizing Uncertainty: Insights from naturally occurring nanoscale structures in food and other lines of evidence Linda Abbott United States Department.

Characterizing Uncertainty: Insights from naturally occurring nanoscale structures in food and

other lines of evidence

Linda AbbottUnited States Department of Agriculture

Office of Risk Assessment and Cost-Benefit Analysis

Uncertainty is associated with risk assessments of nanomaterials

• This is not unique to nanomaterials – uncertainty is expected in a risk assessment

• Sometimes uncertainty can be reduced• Uncertainty should be characterized and

communicated to the decision maker and the public

Uncertainty may be reduced

• Gathering more data about the nanomaterial• Using different lines of evidence to fill data

gaps• Gathering more information about the issue

to be addressed• Using problem formulation to narrow the

scope of the risk assessment

Using a tiered approach limits the need to reduce uncertainty

• Lower tiers use conservative assumptions as defaults when data are not available

• No need to reduce uncertainty further if the lower tier (screening) risk estimate is below the threshold of concern

• Reserves the use of sophisticated, more refined risk assessment techniques for situations where reducing uncertainty will have the greatest impact

Sources of Uncertainty in risk assessment of hypothetical nanomaterial in food

• Toxicity – Fewer oral toxicity tests for engineered nanomaterial (ENM )than for inhalation or dermal pathway

• Uptake and distribution of ENM in the human body may be a data gap

• Effect of the mixture of food and other substances in the digestive system may affect uptake

• Behavior of ENM in living organisms not well studied – under what circumstances will the ENM agglomerate or aggregate in fluid environments in the body

Data gaps may be filled by examining research in other disciplines

• Microbiology and virology• Oral drug delivery • Dietary supplements and vitamins• Food science and technology• Molecular gastronomy

Characteristics of successful orally delivered drugs

• Must cross biological membranes and enter systemic circulation to their site of action

• Lipanski’s Rule of 5 governs 90% of orally active drugs in commerce or phase II testing

• ≤ 5 H donors (∑OH & NH); ≤ 10 H acceptors (∑O & N); Molecular weight ≤ 500; ≤ 5 Log P octanol water

• Oral antibiotics, antifungals, vitamins and cardiac glycosides violate the Rule of 5

• Computational approaches to evaluate oral absorption and permeability of potential drugs resulted in database

Characteristics of orally delivered drugs crossing mucosal barriers

• Surface densely coated with positive and negative charges resulting in a neutral surface (like IgG)

• Strong hydrophilic surface• Lai et al., 2009 demonstrated that

mucopenetrating particles as large as 200 nm are capable of traversing mucosal barriers

Drug delivery across tight junctions

• Reversibly open tight junction to allow passage of material

• Mucoadhesive – ionic interaction between positively charged carrier and negatively charged intestinal surface

• Chitosan - colloidal NP carrier

Factors Enhancing Uptake of NP in the Gut Associated Lymphoid Tissue (GALT)

• Florence (1997, 2005) suggested several factors• Stability of NP in the gut lumen• Submicron particle size < 5 μm• Lack of surface charge• Shape effects not clear – elasticity important for

transport in blood vessels• Surface hydrophobocity• Presence of specific ligands – lectins and invasins – for

uptake by epithelial cells, but not transport

Dietary supplements used in the oral exposure pathway

• Nutritional research in uptake of nanoscale nutrients provides additional lines of evidence for risk assessment

• Data on oral toxicity testing of NP of nutritional interest exists (red elemental selenium and curcumin)

• Uptake of colloidal forms of nutrients may provide data

Food Processing

• Naturally-occurring nanoscale structures in food influence processing techniques

• Nanoscale foams, emulsions, micelles and surfactants have been used throughout historical time

• Examining how these natural nanoscale structures facilitate or inhibit uptake, transport or distribution could inform risk assessments for ENM

Molecular Gastronomy Science of Culinary Processes

• Increased interest in the chemistry and physics behind recipes – why mayonnaise becomes firm or soufflés rise

• Molecular gastronomy scientists studying the evolution of sauces have identified 23 different complex disperse systems in French cuisine

• Categorizing consistency of foods and relating that to how water is organized in those foods at the molecular level

Problem Formulation

• Uncertainty can be reduced by framing the problem to be assessed

• The range of expected use (and misuse) provides a boundary about the system of interest and will eliminate encyclopedic analysis of all uncertainty

• Limits analysis to only uncertainty that is relevant to the issue addressed by the assessment

Characterizing Uncertainty

• Quantitative techniques to address uncertainty - parameter uncertainty or model uncertainty (sensitivity analysis, uncertainty analysis)

• Qualitative techniques also available for non-quantitative models - expert elicitation

• Uncertainty should be discussed in the risk assessment

Communicating Uncertainty to Decision Makers and the Public

• Uncertainty - and its impact on the risk estimate - should be disclosed to the decision maker and the public