RISK ASSESSMENT OF ESSENTIAL ELEMENTS: COPPER: … · OBJECTIVE • Overview and update of the Cu...
Transcript of RISK ASSESSMENT OF ESSENTIAL ELEMENTS: COPPER: … · OBJECTIVE • Overview and update of the Cu...
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RISK ASSESSMENT OF ESSENTIAL ELEMENTS:COPPER: OVERVIEW AND UPDATEUPDATEBonnie Ransom Stern, PhD, MPHBR St d A i t LLCBR Stern and Associates LLCAnnandale, VA 22003, USA
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“Given the importance of copper as an essential mineral for human health, it is conceivable that this and other minerals with health significance should be approached differently from nonessentialapproached differently from nonessential minerals”
M Oli d R U (1996)M. Olivares and R. Uauy (1996)
Cu Overview and Update BR Stern Associates LLC
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OBJECTIVE
• Overview and update of the Cu data base• Health issues surrounding copper-induced toxicity g pp y
and deficiency• Challenges for developing risk assessment
methodologies, strategies and policies that are public health protective
• Health is not only absence of disease but reduction in risk of developing disease
Cu Overview and Update BR Stern Associates LLC
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Conceptual Framework forConceptual Framework for Essential Metals Risk Assessment
• Different from nonessential metal or chemical risk assessment
• Essential: zero intake ≠ optimal• Homeostatically regulated over a range of intakes• Basal vs. normative requirements – sufficient nutrient
to prevent pathology + provide tissue stores (protective buffer)(protective buffer)
• Bioavailability: intake ≠ absorption
Cu Overview and Update BR Stern Associates LLC
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A Theoretical U-Shaped Dose-ResponseA Theoretical U Shaped Dose Response Curve
1.0 1.0
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Cu Overview and Update BR Stern Associates LLC
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What is Copper?What is Copper?• Atomic # 29, mass = 63.546• Member of 3rd transition
series (w Zn, Mn, Fe, Ni)• Isotopes:• Isotopes:
Two stable 63Cu, 65CuTwo radioactive 64Cu,67Cu,
• Three oxidation states: Cu0 (metal), Cu1+ (cuprous), Cu2+ (cupric)Cu2+ (cupric)
• Redox cycling=essentiality • Redox cycling=potential
Cu Overview and Update BR Stern Associates LLC
y g ptoxicity
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Some Key Copper EnzymesFunction
Amine oxidases Oxidation of biogenic amines
Ceruloplasmin (Ferroxidase I) [Cp]
Plasma transporter of Fe and Cu
Cytochrome c oxidase [CCO] Mitochondrial electron transport
Dopamine-β-hydroxylase Catecholamine metabolism
Haphaestin Transmucosal Fe transporter
Lysyl oxidase Collagen/elastin cross-linking
PAM Peptide/neuropeptide amidation
Superoxide dismutase [SOD] Free-radical scavenging
Cu Overview and Update BR Stern Associates LLC
p [ ] g g
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C KineticsCu Kinetics• Fractional g.i. absorption – primary site is g p p y
duodenum• Bioavailability – varies inversely w amt.
i t d ff t d b di t t i ( Zingested, affected by dietary matrix (e.g., Zn, ascorbate, protein, sugars, fat)
• Portal circulation to liver – site of Cu• Portal circulation to liver – site of Cu incorporation into Cp for systemic distribution, excess stored in metallothionen (MT) and lysosomes, excess excreted in bile
• Intake ≠ Bioavailability
Cu Overview and Update BR Stern Associates LLC
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Cu TransportCu Transport
• Tightly regulated and coordinatedg y g• Specific Transporters - DMT, ATP7A, Ctr1,
ATP7B, others• Specific Metallochaperones include:
Atox1 (HAH1) to transporter ATPases (A d B)and B)
COX17 (yeast) to mitochondria for incorporation into CCOincorporation into CCOCCS to cytosol for incorporation into Cu,Zn SOD
Cu Overview and Update BR Stern Associates LLC
SOD
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lResults??
Homeostatic control:Precise orchestration of Cu transportPrecise orchestration of Cu transport to sites of enzyme synthesis/functionProcesses ensure that unbound ionicProcesses ensure that unbound ionic Cu (toxic moiety) does not exist unless homeostatic capacity isunless homeostatic capacity is exceeded
Cu Overview and Update BR Stern Associates LLC
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b f b liInborn Errors of Cu Metabolism
Menkes Disease (MNK): Cu deficiency• X-linked, freq ≈ 1/300,000, ATP7A defect, q , ,
Wilson Disease (WD): Cu overloadWilson Disease (WD): Cu overload• Autosomal recessive, freq ≈ 1/30,000,
ATP7B defect severe liver damageATP7B defect, severe liver damage• Treatable with Cu chelation and diet control
Cu Overview and Update BR Stern Associates LLC
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b f b liInborn Errors of Cu Metabolism• WD diagnosis: low Cp,
high ratio of non-Cp Cu:Cp Cu, elevated liver Cu Kayser-FleischerCu, Kayser-Fleischer rings
• WD HZ: WD HZ, freq ≈ , q1/90 are carriers
• Susceptible to Cu l d???overload???
No evidence
Cu Overview and Update BR Stern Associates LLC
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Copper Circulation in HumansFetus
5 mg Cu/dayIntestine
Bil
Milk
MenkesC +
Cu+
Bile
DMT1?
WilsonCu+
Cu+
Cu+
?Cu+
Wilson Brain
MT
MT Atox1
Wilson
MenkesCu+
?
Liver MT
MT
MT
Menkes
Menkes
C
Ctr1 BBB
Cu-histidineCu+ BloodAlbuminCu- CPCu-
TranscupreinCu-Cu-GSH
©Marc Solioz
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Other Copper-RelatedOther Copper Related Hereditary Syndromes
• Indian childhood cirrhosis (ICC), Non-Indian childhood cirrhosis (NICC), Idiopathic copper ( ), p pptoxicosis (ICT)
• Syndromes similar in etiology and presentationSyndromes similar in etiology and presentation• Have both genetic component (unidentified)
and contribution from elevated intakeand contribution from elevated intake• High frequency of parental consanguinity
Cu Overview and Update BR Stern Associates LLC
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Deficiency: Effects Evaluation
Humans: Case reports, case seriesDepletion-repletion clinical studiesDepletion repletion clinical studies
Dose metric: mg/dayR i C b l l i iResponses: negative Cu balance, alterations in phospholipids, glucose/insulin, immune
l l diparameters, cuproenzyme levels, cardiac
Cu Overview and Update BR Stern Associates LLC
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Deficiency: Effects EvaluationDeficiency: Effects Evaluation
Animals: Anemia, “Swayback disease” (zoonotic ataxia) (1930’s).
h i l d fi i dShort-term experiments: 1 severely deficient dose, developing young (gestation, lactation and/or postweaning). Dose metric = mg Cu/kg feed (e.g.postweaning). Dose metric mg Cu/kg feed (e.g. CuD = 0.6, CuA = 6).
Responses: target-organ specific (blood, heart, brain/behavior, immune), cuproenzyme levels
More recently, studies of marginal Cu def., longer dur.
Cu Overview and Update BR Stern Associates LLC
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Deficiency: Effects EvaluationDeficiency: Effects EvaluationIn both humans and animals, major target organs
bl d d h t i ti t• blood and hematopoietic system• cardiovascular system• connective tissue and bone, • nervous systemnervous system• immune system
t t i it• teratogenicity
Cu Overview and Update BR Stern Associates LLC
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Deficiency: Effects EvaluationDeficiency: Effects EvaluationSummary
• Clinically-evident copper deficiency considered to be very rare except in premature y p plow-birth weight infants, malnourished infants, adults receiving TPN without added Cu. g
• Marginal deficiency thought to occur extensively but no available biomarkers ofextensively but no available biomarkers of marginal Cu status to confirm.
Cu Overview and Update BR Stern Associates LLC
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Deficiency: Effects EvaluationNEW DATANEW DATA
Adult onset Cu-deficiency myeloneuropathy R bl b bi d d i f• Resembles subacute combined degeneration of Vit B12 def.May also present with neuromuscular• May also present with neuromuscular degeneration similar to ALS
• Clear presentation, diagnostics, progressionClear presentation, diagnostics, progression• Cu status not assessed in initial diagnostic
workup. Often misdiagnosis (e.g. ALS) or no p g ( g )diagnosis (idiopathic neuropathy)
• Myeloneuropathy progressive.
Cu Overview and Update BR Stern Associates LLC
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Toxicity: Effects Evaluation
Humans: Case reportsMetabolic unit studiesMetabolic-unit studiesAcute exposure studiesPopulation-based studies (M. Araya)
Dose metric mg C /da mg C /LDose metric = mg Cu/day, mg Cu/L
Cu Overview and Update BR Stern Associates LLC
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Toxicity: Effects EvaluationToxicity: Effects EvaluationAnimals:• Single-dose studies targeting liver and kidney• One guidelines subchronic toxicity studyNEW DATA
• Two-gen reproductive toxicity study• Unpublished rabbit dev. tox study• Infant rhesus monkey study (Araya)Dose metric: mg Cu/kg feed, mg Cu/L water, mg
Cu/day mg Cu/kg bw/day
Cu Overview and Update BR Stern Associates LLC
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Toxicity: Effects EvaluationToxicity: Effects Evaluation
• Acute toxicity: Gastrointestinal in humans (nausea and vomiting), repeated acute dosing(nausea and vomiting), repeated acute dosing right-shift in LOAEL and NOAEL
• Repeated dose toxicity: Primary target organ in• Repeated-dose toxicity: Primary target organ in humans and animals is the liver, other organs include kidney and g i tinclude kidney and g.i.t.
Cu Overview and Update BR Stern Associates LLC
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Toxicity: Effects Evaluation
• Animal studies (Haywood) show almost complete regression & regeneration in liver p g gand kidney histopathology over dosing period Appears to be considerable adaptation to pp pcopper loading over a range of high doses
• Liver Cu content remains elevatedLiver Cu content remains elevated
Cu Overview and Update BR Stern Associates LLC
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/ d liDose-Response Assessment/Modeling
• Conceptual Approach: Homeostatic model providing an acceptable range of oral intake (AROI) to meet nutritional requirements and avoid toxicity (WHOnutritional requirements and avoid toxicity (WHO 2002)
• Common Currency: Risk-risk or risk-benefitCommon Currency: Risk risk or risk benefit comparison – decreasing the risk of one adverse health effect (deficiency) balanced against increasing i k f th d h lth ff t (t i it )risk of another adverse health effect (toxicity)
(Renwick et al. 2004)
Cu Overview and Update BR Stern Associates LLC
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/ d liDose-Response Assessment/Modeling
Key Considerations:• Quality of studies (toxicity deficiency)• Quality of studies (toxicity, deficiency)• Use of biological endpoints of comparable
functional significance to define AROIfunctional significance to define AROI boundaries (or make other adjustments)K l d f h i h i & f• Knowledge of homeostatic mechanisms & of coefficient of variation (CV) of susceptibility
i hi h l iCu Overview and Update BR Stern Associates LLC
within human population
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/ d liDose-Response Assessment/Modeling
• Appropriate dose metric (mg/day, mg/kg/d)• Appropriate response metric (defining pp p p ( g
acceptable level of response)• Incorporation of variabilityp y• Incorporation of uncertainty• CV and/or uncertainty factors (UFs) ?CV and/or uncertainty factors (UFs) ?• Similar modeling approach for both D and T
Cu Overview and Update BR Stern Associates LLC
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Essential Metal Requirements
• “Requirement for what?”• Related to specified criteria of adequacy• Related to specified criteria of adequacy
Prevention of clinical disease? H l h b fi i k RDA?Health benefits at intakes > RDA?Highest intake level without
appreciable risk of adverse effects ? (UL)
Cu Overview and Update BR Stern Associates LLC
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Severity Scores for Cu-Associated OutcomesSeverity Scores for Cu Associated Outcomes
<<<<<Deficiency <Homeostasis> Excess >>>>>
4 3 2 1 1 2 3 4
Gross Deficiency
Metabolic Perturbation
Loss of Cu-dependent Enzyme
Molecular Manifestation
Molecular Manifestation
Loss of Cu-Dependent Enzyme Function
Metabolic Perturbation
Gross Excess
Activity
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Severity Scoring: Deficiency
Severity Score Types of End Points
1D Cu body burden; MT; urine Cu levels1D Cu body burden; MT; urine Cu levels
2D Loss of Cu-dependent enzyme function (SOD), changes in blood cell #s or function,
3D Severe body wt, changes, organ wt. changes, plasma glucose/insulin, minor histopathololgy, white blood cell activities/count
4D Death, gross histopathology,
Cu Overview and Update BR Stern Associates LLC
reproductive/development changes
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i iSeverity Scoring: Excess
Severity Score Types of End Points
1E Cu body burden; MT; urine Cu levels1E Cu body burden; MT; urine Cu levels
2E Changes in cholesterol/triglycerides; lge Cu burdens; nausea, vomiting, g gdiarrhea; enzyme changes without histopathology
3E Lge body weight changes; anemia; 3E g y g g ; ;hemolysis; vitamin/mineral levels; liver enzymes; inflammation; organ weights
4E death; gross histopathology; reproductive function changes
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SummarySummary
Rich Cu data base, excellent case study for RARich Cu data base, excellent case study for RAAreas of research:Bi k iti ifi d iBiomarkers – sensitive, specific, dose-responsive,
predictive of adverse clinical outcome; few d bi k f i l C t tgood biomarkers of marginal Cu status
Exposure – Recent multi-route studies (Sadhra et al. 2006, Georgopoulos et al., 2007) show deficiency more of a concern than toxicity
Cu Overview and Update BR Stern Associates LLC