Biomarkers and Risk Assessment for Chromium(VI)

							    Biomarkers and Risk
Assessment for Chromium(VI)

        Qingshan Qu, MD (PI)
       Roy Shore, PhD (Co-I)
     Dept. of Environmental Med.
       NYU School of Medicine
             Background

Toxicity of oxidation states of
Chromium (Cr)
– Cr(III) is relatively nontoxic, poorly
  absorbed, little crosses cell membranes,
  & may be an essential element
– Cr(VI) is strong oxidizing agent: toxic
  and carcinogenic; crosses cell
  membranes
       Public Health Risks
Cr(VI) is public health concern:
Superfund site contaminant

Current Risk Assessments based on
extrapolations: high-to-low
concentrations and/or animal-to-
human
         Study Approach
Measure exposure levels, internal dose,
markers for biologically effective dose &
genotoxicity.
Ultimate goal: determine which
biomarkers are useful quantitative
indicators of Cr(VI) exposure at low levels
for future epidemiology or surveillance
   Intermediate Objectives for
  Biomarker Validation & Utility
Examine the reproducibility of each
biomarker (intraindividual vs.
interindividual variability)
Measure sensitivity of biomarker at
progressively lower levels
Examine the specificity of the biomarker
(? affected by smoking, diet, age, other
metal exposures?)
      Exposure Biomarkers
Plasma Cr – Cr(III), some Cr(VI)

Erythrocyte or Lymphocyte Cr – source
mainly Cr(VI) [but is reduced to Cr(III)
within the cell]

Dose-response may be affected by plasma
reduction capacity
Markers of Biological Effects or Susceptibility

 DNA-protein cross-links (DPC) in leukocytes
 (assess biologically effective dose?)
 Comet assay – detects DNA single-strand breaks
 or incomplete repair, alkali-labile sites, DNA-DNA
 or DNA-protein cross-linking
 Susceptibility markers of extracellular reduction
 capacity
  – Ratio of Cr in erythrocytes to that in plasma
  – Plasma ascorbate levels
  – Plasma oxidative status
  Methods & Procedures – I.
Identified factories with Cr exposure
Conducted walk-throughs to select
factories
Talked with management & then
employees about the study
Administered questionnaire re: smoking,
health status, etc. so as to select subjects
 Methods & Procedures – II.
Physical exam
Personal exposure monitoring – one 8 hr shift
– Used personal monitor with pump
Urine sample at end of workday – for cotinine &
creatinine
10 ml blood sample – separated into plasma,
lymphocytes & erythrocytes
For 8 subjects monitored & blood on 3
successive Mondays
 Methods & Procedures – III.
In year 1, obtained 25 exposed & 25 unexposed
(farmers >50 miles away)
In year 2, just completed obtaining exposure &
bloods on another 125 exposed & 30 unexposed
Subjects in year 1 were mostly highly exposed,
those in year 2 have a broad range of lower
exposures
Each year spent >1 mo. in China collecting data
 Principal Statistical Analyses
Examine reproducibility of biomarker
Determine initial sensitivity of biomarker
assay to detect high-exposure effects
Examine slope & shape of exposure-
response curve
Evaluate sensitivity of biomarker at lower
exposure levels
   Statistical Analyses – Other
          Considerations
Control for possible confounding variables:
age, sex, smoking
For Cr(VI), evaluate & adjust for
exposures to Cr(III) & to nickel
Is Cr(VI) exposure-response relation
modified by plasma reduction capacity,
serum vitamin C or oxidative status?
                                 2.0
 Cr in RBC [Log(xug/1012 RBC)]

                                 1.5


                                 1.0


                                 0.5
                                                                             y = 2.1621x + 0.3563
                                                                                  R = 0.6541
                                 0.0                                               P<0.0001
                                        0.0   0.1     0.2      0.3     0.4      0.5      0.6        0.7

                                 -0.5
                                                    Cr(VI) Exposure [Ln(1 + xm g/m 3)



Fig. 1 Correlation between personal exposure and Cr
levels in RBC
                        120
Scores of Comet Assay
                        100

                        80

                        60

                        40                       y = 105.81x + 27.955
                                                      R = 0.5615
                        20                             P<0.0001
                         0
                              0.0     0.2          0.4          0.6     0.8
                                    Cr(VI) Exposure [Ln(1+x m g/m 3)]



Fig. 3 Correlation between comet scores and
personal exposure to Cr(VI)
Scores of Comet Assay   100

                        80


                        60

                        40                           y = 39.615x + 15.69
                                                          R = 0.6951
                        20                                 P<0.0001

                         0
                         -0.5   0.0       0.5        1.0           1.5     2.0
                                  Cr in RBC [log(x ug/1012 RBC)]



            Fig. 4 Correlation between comet scores and Cr
            levels in RBC
                                  4
8-OHdG [log(x ug/g creatinine)]

                                  3



                                  2
                                                                   y = 1.5366x + 1.4265
                                                                        R = 0.8085
                                                                         P<0.0001
                                  1


                                  0
                                  -0.5   0.0          0.5          1.0           1.5      2.0
                                               Cr in RBC [log(x ug/10 12 RBC)]


                    Fig. 6 Correlation between urinary 8-OHdG and Cr
                    levels in RBC
    Biomarkers and Risk
Assessment for Chromium(VI)

        Qingshan Qu, MD (PI)
     qingshan@env.med.nyu.edu
     Dept. of Environmental Med.
       NYU School of Medicine