Post on 18-Dec-2015
Hormesis: What it Means for Toxicology, the Environment and
Public Health
Edward J. Calabrese, Ph.D
Environmental Health Sciences
School of Public Health
University of Massachusetts
Overview
• How I Became Involved with Hormesis
• Hormesis:Toxicological Foundations
• Examples of Hormetic Responses
• Comparison with Threshold Model
• Hormesis and Risk Assessment
Hormesis
Definition:• Dose response phenomenon characterized by a
low dose stimulation and a high dose inhibition.• Generally similar quantitative features with
respect to amplitude and range of the stimulatory response.
• May be directly induced or the result of compensatory biological processes following an initial disruption in homeostasis.
HORMESIS
Interpretation:• Issue of beneficial/harmful effects should
not be part of the definition of hormesis.
• This assessment should be reserved for a subsequent evaluation of the biological and ecological context of the response.
Response
Response
Dose
A
B
(A) The most common form of the hormetic dose-response curve depicting low-dose stimulatory and high-dose inhibitory responses, the - or inverted U-shaped curve.
(B) The hormetic dose-response curve depicting low-dose reduction and high-dose enhancement of adverse effects, the J- or U-shaped curve.
Hormesis and Evaluative Criteria
Assessing the Dose-Response Continuum:
• LOAEL-defining the toxic phase of the dose response
• NOAEL (or BMD)-defining the approximate threshold
• Below NOAEL (or BMD) doses-number and range
• Concurrent Control
Hormesis and Assessment Criteria
Dose Response Patterns
Statistical Significance
Replication of Findings
Evidence of Hormesis
General Summary:• Hormesis databases: thousands of dose
responses indicative of hormesis
• Hormesis is a very general phenomenon: independent of model, endpoint and agent
• Frequency of hormesis: far more frequent than threshold model in fair head-to-head comparisons
Dose Response FeaturesStimulation Amplitude:
• Modest
• 30-60% Greater Than Control
• Usually Not More Than 100% Greater Than The Control
Stimulatory Range~75 % - Within 20-Fold of NOAEL
~20% - >20<1000-Fold of NOAEL
~<2% - > 1000-Fold of NOAEL
Maximum response(averages 130-160% of control)
Distance to NOAEL(averages 5-fold)
Hormetic Zone(averages 10- to 20-fold)
NOAEL
Control
Dose-response curve depicting the quantitative features of hormesis
Increasing Dose
Hormetic MechanismsMany studies have provided mechanistic
explanations to account for observed hormesis responses;
Each mechanism is unique to the model, tissue, endpoint and agent
Some general examples: Often existence of opposing receptors
0
20
40
60
80
100
120
140
0.00 0.25 0.50 1.00 2.00 4.00 8.00
Methanol (%)
Long
evity
(%
con
trol
)FemalesMales
Methanol and Fruit Fly Longevity
0
20
40
60
80
100
120
140
0 10 25 50 100 150 200 300
Gamma ray dose (rad)
Inci
denc
e (%
con
trol
)FemalesMales
Gamma Rays and Mouse Lung Adenomas
0
20
40
60
80
100
120
140
0.0 2.5 5.0 10.0 20.0 40.0 80.0 160.0
Transformng Growth Factor Beta (pg/ml)
Cel
l pro
lifer
atio
n (%
con
trol
)
Transforming Growth Factor-Beta and Human Lung Fibroblasts
0
20
40
60
80
100
120
140
160
180
0.00 0.25 0.50 0.75 1.00 2.00 3.00 4.00
Ethanol (g/kg)
(%
con
trol
)
Effects of Acute Ethanol on Overall Social Activity of Adolescent Rats Tested on Postnatal Day 30
0
20
40
60
80
100
120
140
160
0 10 20 40 80 150 300 600 1200 2500 5000
X-rays (R)
Roo
t L
engt
h(%
of
Con
trol
)
Effect of X-rays on the Root Length of Carnation Cuttings
* **
*
*
*
*
*
0
20
40
60
80
100
120
140
160
0 10 25 50 100 500 1000 2500 3500 4000 5000
Aluminum (uM)
Spe
cific
act
ivity
(%
con
trol
)
Aluminum andMouse Blood Gamma-AminolevulinicAcid Activity
0
20
40
60
80
100
120
140
160
0 7 14 29 57 114 171 228 342 456
Mercury Chloride (ug/L)
(%
Con
trol
)Above ground (G)
Below G
Total Biomass
Stem Density
Max Shoot Height
Evap/transpir
Effect on Growth of Salt Marsh Grass
*
*
0
20
40
60
80
100
120
140
160
180
0.00
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0.05
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075
0.10
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0.25
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0.40
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0.80
01.
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1.25
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1.60
02.
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03.
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05.
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8.00
010
.000
16.0
0020
.000
25.0
0040
.000
Drug Concentration (mg/kg)
% C
ontr
ol
YohimbineApomorphinePromethazine
Comparative Dose Response Relationships for the Pain Threshold for Vocalization
0
25
50
75
100
125
150
0.00
0000
0.00
0001
0.00
0010
0.00
1000
0.10
0000
0.50
0000
1.00
0000
3.00
0000
7.50
0000
15.0
0000
0
20.0
0000
0
30.0
0000
0
60.0
0000
0
100.
0000
00
Morphine (mg/kg)
% C
ontr
ol
Effect of Different Doses of Morphine on PTZ-induced Seizure Threshold
*
* *
*
**
*
020406080
100120140160180200220240260
0.00 0.50 0.75 1.00 1.25 1.50 2.00 2.50 3.00
Alcohol (g/kg)
Ser
um le
vel (
% c
ontr
ol)
TestosteroneLuteinizing hormone
*
Alcohol andRat Serum Levels
*
*
0
50
100
150
0.00 0.00 0.01 0.05 0.10 0.50 1.00 2.00 5.00 10.00
4-Chloro-2-methylphenoxyacetic acid (MCPA) (mg/pot)
Dry
wei
ght
(% c
ontr
ol)
*
MCPA +OAT SHOOT GROWTH
**
0
20
40
60
80
100
120
140
160
180
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220
240
260
0.00E+00 1.00E-09 1.00E-08 1.00E-07 1.00E-06 1.00E-05 1.00E-04 1.00E-03
Metal Concentration (M)
Ph
ag
ocy
tosi
s A
ctiv
ity (
% c
on
tro
l)
HgCl2
MethHgClCdCl2
ZnCl2
Effects of Metals on Phagocytosis in the Clam, Mya arenaria, hemocytes
0
20
40
60
80
100
120
140
160
0.00 0.01 0.10 1.00 10.00 40.00 80.00
Cadmium (uM)
Nitr
ate
redu
ctas
e (%
con
trol
) In VitroIn Vivo*
Cadmium andAquatic Plant (H. verticillata)Nitrate Reductase Activity
**
* *
***
*
**
0
20
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0.00E+00
1.00E-05
2.00E-05
3.00E-05
4.00E-05
5.50E-05
6.00E-05
6.50E-05
7.00E-05
8.00E-05
9.00E-05
1.00E-04
2.50E-04
3.00E-04
Sodium Arsenate (M)
Lym
ph
ocy
te S
timu
latio
n (
% c
on
tro
l)
Effect of Sodium Arsenate on PHA-treated Bovine Lymphocytes
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20
40
60
80
100
120
140
160
180
Mercury (ug/L)
Cat
alas
e ac
tivity
(%
con
trol
) **
*
* * *
Methyl mercuric chloride
Mercuric chloride
Mercury and Duckweed
Catalase Activity
0
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175
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0 500 1000 2000 4000 6000 8000 10000
Gamma Rays (R)
Day
s(%
of
con
trol
)
Effect of Gamma Rays on the Life Span of Female House Crickets
*
*
*
* ** *
0
25
50
75
100
125
150
0.0 0.1 0.2 0.4 0.8 1.6 3.2
Acridine (mg/L)
bro
ods/
dap
hn
id(%
of
con
trol
)
Effect of Acridine on the Number of Broods per Daphnid
* **
*
*
*
0
40
80
120
160
200
240
280
0 1 10 50
Lectin Concentration (ng/ml)
Th
ymid
ine
Up
take
(%
co
ntr
ol)
ProstateProstateProstateRenalRenalColorectalColorectalColorectalGastricLiposarcoma
Effect of Mistletoe Lectin on Human Tumors in Culture
0
20
40
60
80
100
120
140
0.00E+00 1.00E-08 1.00E-07 1.00E-06 1.00E-05
Ten Estradiol A-Ring Metabolites (M)
Ch
an
ge
in C
ell
Nu
mb
er
(% c
on
tro
l)
2-HE
2-ME
2-HEOL
2-MEOL
2-H
2-M
4-HE
4-ME
4-HEOL
4-MEOL
Effects of Ten Estradiol A-ring Metabolites on Endothelial Cells from Human Umbilical Veins
0
20
40
60
80
100
120
140
160
0.00E+00
2.50E-09
2.50E-08
2.50E-07
2.50E-06
2.50E-05
2.50E-04
2.50E-03
2.50E-02
2.50E-01
2.50E+00
Plumbagin (ug/ml culture)
Gra
nulo
cyte
Pha
gocy
tosi
s (%
con
trol
)
Effect of Plumbagin on Human Granulocyte Phagocytosis
0
20
40
60
80
100
120
140
160
0.000 0.001 0.010 0.100 1.000 10.000 100.000
Tin (II) (ug/ml)
% C
ontr
ol
Effect of Tin (II) on MTT Conversion in C6 Glioma Cells
0
25
50
75
100
125
150
175
200
0.0000.001
0.0060.060
0.6001.000
6.00030.000
DHEA (mg/kg)
% C
ontr
ol
Number of Open Arm Entries in the Elevated Plus Maze in Male C57BL/6 Mice Treated with DHEA
*
* *
*
*
*
0
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125
150
175
0 1 10 100 1000 10000
Allixin (ng/ml)
Neu
rona
l Sur
viva
l (%
con
trol
)
The Effects of Allixin on the Survival of Primary Cultured Hippocampal Neurons from Embryonic (E18) Wistar Rats
*
*
*
*
0
25
50
75
100
125
150
0.0 0.1 0.5 1.0 5.0 10.0 25.0 500.0
Methyl Mercury (µM)
Via
bilit
y (%
con
trol
)
The Effects of Methyl Mercury on Viability as Measured by Mitochondrial Dehydrogenase Activity in the D407 Cell Line
*
*
*
*
**
0
25
50
75
100
125
150
175
200
0 15 30 60 120 180 240
3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX) (mM)
% C
ontr
ol
Effects of the Disinfectant Byproduct MX on the Occurrence of DNA Damage in the Comet Assay Using Rat Liver Epithelial Cell Line WB-F344
0255075
100125150175200225250275300
0.000
0
0.007
5
0.075
0
0.750
0
7.500
0
15.00
00
75.00
00
150.0
000
300.0
000
n -Hexane (mg/L)
% C
ontr
ol
Effects of n-Hexane on DNA Damage in Human Lymphocytes in the Comet Assay
0
25
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75
100
125
150
175
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225
250
275
300
0.00E+00 3.00E-07 1.20E-06 3.60E-06
As2O5 (M)
% C
ontr
ol
Effects of As2O5 on Total Chromosomal Aberrations in Human Leukocytes
0
25
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275
300
0.00 3.13 5.80 9.65 19.30 28.80 47.70 290.00
X-Rays (mGy)
% C
ontr
ol
Effects of X-rays on Chromosomal Aberrations (i.e., Dicentrics) in Human Lymphocytes (pooled results of four donors and six laboratories)
0
50
100
150
200
250
0.00
00.
005
0.01
00.
100
0.20
00.
500
1.00
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0
20.0
00
100.
000
500.
000
DDT(ppm)
GS
T-P
Po
sitiv
e F
oci
(%
co
ntr
ol)
Effect of DDT on Liver Foci Formation in Male F344 Rats
0
2040
6080
100
120140
160180
200
220240
0 30 35 45 60 75 100 150
AAF (ppm))
(%
co
ntr
ol)
Bladder Tumor Incidence Adjusted for Time in ED01 Megamouse Study
Hormetic or Threshold
Which Dose Response Is More Common?
The Threshold ModelPrediction: Random Bounce Below the
Threshold as Practically Defined by the NOA(E)L or BMD
The Hormesis Model
• Predicts that responses to doses in the below toxic threshold zone should be non-randomly distributed
• The non-randomness should be reflected in the frequency of responses above and below the control value and in the magnitude of the deviation from the control
Hypothesis Evaluation
Dose-Response Evaluation CriteriaEntry Criteria:
Estimate a LO(A)EL
Estimate a NO(A)EL or BMD
One or more doses below NO(A)EL or BMD
Testing Threshold Model Predictions
Three Separate Database Evaluations:• Toxicological Literature - multiple
models/endpoints - reviewed 21,000 articles with entry criteria to yield 800 dose responses
• Yeast Cell Strains - 13 strains/2,200-57,000 dose responses-cell proliferation
• E. coli – approximately 2,000 chemicals tested over 11 concentrations - cell proliferation
Percent Difference From Control Growth
Cum
ulat
ive
Per
cent
of
Che
mic
als
Mean
Prediction Interval 95%
Threshold Model Predicted Mean
10
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80
90
0 10 20
30 40 50 60 70 -10
-20
100
-20 -10 0 10 20 30 40 50 60 70 800
10
20
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40
50
60
70
80
90
100C
umul
ativ
e Pe
rcen
t of
Che
mic
als
BMD 10.0
BMD 7.5
BMD 5.0
BMD 2.5
Percent Difference From Control Growth
Threshold Model Inconsistencies
• Below threshold responses do not provide evidence of random bounce
• Non-random responses clearly predominate
• The non-random responses discredit the Threshold Dose Response Model
• Findings are consistent with the Hormetic Dose Response Model
Why Has Toxicology Missed Hormesis?
• Modest Response - could be normal variation
• Emphasis on High Doses - need to define the NOAEL and LOAEL
• Use of only few doses
Why is Hormesis Important?
• It will change how toxicologists, pharmacologists, risk assessors, and physicians do their jobs
• It will change the risk communication message
Hypothesis Testing
• Expands Dose Response Spectrum
• Creates New Categories of Questions
Study Design• Number of Doses/Concentrations
• Spacing of Doses/Concentrations
• Temporal Features
– Key feature in recognizing the compensatory nature of the hormetic dose response
Implications of New Design Considerations
Additional Costs For:
• Extra Doses
• Multiple Temporal Evaluations
• Enhanced Need for Replication
Possible Adjustments
• Less than lifetime studies/different endpoints
• Less expensive models: cell culture, invertebrates, fish, etc.– increases sample size for statistical
power
Endpoint Selection
Background Incidence:• Low Background Disease Incidence
Precludes Ability to Detect Possible Hormetic Response
Biomathematical ModelingImplications for Cancer Risk Assessment:
• Models: flexibility to fit observed data;• Models: not constrained to always be
linearly decreasing at low doses;• Low Dose Risk Characterization: include
likelihood of below background risks;• Uncertainty Characterization: include both
upper and lower bounds.
Environmental• Re-Defining Hazard Assessment• Re-Defining Dose Response Default• Re-Evaluation of Risk Assessment
Practices• Harmonization: Cancer and Non-
Cancer• Cost-Benefit Re-Assessment
Therapeutics• Cognitive
Dysfunction
• Immune Stimulation
• Anti-Tumor
• Anti-Viral
• Anti-Bacterial
• Angiogenesis
• Cytokine/Hospital Infections
• Hair Growth
• Molecular Designs
Life Style
• Exercise
• Alcohol Consumption
• Stress
Perspective #1
The Threshold Dose Response Model fails to make accurate predictions in the below threshold zone
Perspective #2
The Threshold Dose Response Model has been significantly out-competed by the Hormetic Dose Response Model in multiple, independent comparisons
Perspective #3
There is little toxicological justification for the continued use of the threshold dose response to estimate below threshold responses
Perspective #4
Given Perspectives 1-3, there is no basis to use the threshold dose response model in risk assessment practices. This has significant implications for current standards based on the threshold model and future risk assessment practices
Perspective #5
HORMESIS: a concept with much supportive experimental evidence that is reproducible
Perspective #6
HORMESIS: Based on Perspective # 5 it should be considered as a real concept in the biological sciences
Perspective #7
HORMESIS is Generalizable
• Across Biological Models
• Across Endpoints Measured
• Across Chemical Class/Physical Agents
Perspective #8
Based on Perspective # 7, HORMESIS is evolutionarily based, with broad potential implications
Perspective #9
HORMESIS: very common in toxicological/pharmacological literature, making it a central concept
Perspective #10
HORMESIS: a normal component of the traditional dose response, being graphically contiguous with the NO(A)EL
Perspective #11
HORMESIS: readily definable quantitative features, that are broadly generalizable, making it reasonably predictable
Perspective #12
HORMESIS: far more common than the threshold dose response in fair, head-to-head comparisons; this would make the hormetic model the most dominant in toxicology
Perspective #13
The low dose hormetic stimulatory response is a manifestation of biological performance and estimates biological plasticity in the effected systems
Perspective #14
HORMESIS: no single specific hormetic mechanism; there appears to be a common biological strategy underlying such phenomena
Perspective #15
HORMESIS: important implications for toxicology, risk assessment, risk communication, cost-benefit assessments, clinical medicine, drug development and numerous other areas
Perspective #16
HORMESIS: Should Become the Default Model in Risk Assessment – Why?
• More Common By Far Than Other Models
• Can Be Validated or Discredited with Testing
• Generalizable by Biological Model, Endpoint and Chemical Class
Perspective #17
HORMESIS: should become the object of formal evaluation by leading advisory bodies such as the National Academy of Sciences