How confident are you in the data showing non-linearities (Figures 3-5 in white paper) in blood concentration of 1,3-D versus inhaled exposure being an indication of metabolic saturation above 20 ppm? (scale of 1 - very low confidence, 5 - very high confidence) (please explain)

Answer Explanations

• 4 - high confidence

  Expert 13

  With the lower dose range expanded, it is clear to see that supra-linear increases in 1,3-D concentrations
  are evident even at exposures of 20 ppm but certainly above 20 ppm inhaled exposure. This nonlinearity is quite consistent with the depletion of glutathione between 10-30 ppm reported (Lung GSH levels following repeated 6hr exposures to B6C3F1 mice). In addition to 1,3-D AUC and blood level data, additional 2 pieces of evidence support metabolic clearance changes of 1,3-D beyond 30 ppm.

• 4 - high confidence

  Expert 5

  same as above

• 3 - equivocal

  Expert 10

  Metabolic saturation (chemcial free concentrations well above the Km) and Gluthatione depletion (cofactor depletion) are two different mechanisms leading to the same results (lower metabolic rates). With the given information, I cannot exclude one or the other, but pre treatment to DEM highly impacts kinetics at 300 ppm exposure (Yang 1989). Hence, I would tend to think that a cofactor depletion explanation does not fully explain the non-linearity.

• 4 - high confidence

  Expert 12

  It is clear that there is a dose-non linearity after about 20 ppm. However, studying also a lower specific dose of 15 ppm and higher dose of 30 ppm would help to define the curve better, i.e., the real starting dose where the non-linearity really becomes relevant. This is because in the Figure 5, we may observe that the non-linearity may be observed relatively below 20 ppm (i.e., between 10 and 20 ppm instead). Based on this Figure 5 we may get the impression that at about 15 ppm the non-linearity appeared by contrast to about 20 ppm, which is a dose 1.3-fold lower. This could become statistically relevant. Overall, it is clear that there is a dose non-linearity in the blood kinetics whether this appeared at 10, 15 or 20 ppm.