OECD 432

Question 1

What is phototoxicity?

Answer 1

Phototoxicity is a toxic response caused by photoreactive chemicals after exposure to environmental light.

Question 2

What is the purpose of the In Vitro 3T3 NRU Phototoxicity Test?

Answer 2

Used to identify the phototoxic potential of a chemical activated by light exposure.

Question 3

How does the In Vitro 3T3 NRU Phototoxicity Test assess photocytotoxicity?

Answer 3

Assesses photocytotoxicity based on the reduction in cell viability when exposed to the test chemical in light vs. in darkness.

Question 4

What does a positive result in the In Vitro 3T3 NRU Phototoxicity Test indicate?

Answer 4

Chemicals identified as positive could be phototoxic in vivo, particularly affecting the skin or eyes.

Question 5

What is the Molar Extinction Coefficient (MEC) threshold for a chemical to be considered unlikely to be photoreactive?

Answer 5

If the MEC is below 1000 L mol⁻¹ cm⁻¹.

Question 6

What should be determined before testing a chemical for phototoxicity?

Answer 6

A UV/vis absorption spectrum of the chemical may be determined as per OECD Test Guideline 101.

Question 7

What are the limitations of the In Vitro 3T3 NRU Phototoxicity Test?

Answer 7

The test does not predict other adverse effects such as photogenotoxicity, photoallergy, and photocarcinogenicity.

Question 8

True or False: The In Vitro 3T3 NRU Phototoxicity Test requires a metabolic activation system.

Answer 8

False.

Question 9

What is measured to assess cytotoxicity in the In Vitro 3T3 NRU Phototoxicity Test?

Answer 9

Cytotoxicity is measured by the reduction in the uptake of Neutral Red (NR) dye.

Question 10

What is the role of Neutral Red (NR) dye in the test?

Answer 10

NR is a weak cationic dye that penetrates cell membranes and accumulates in lysosomes.

Question 11

What causes cell damage in the presence of phototoxins?

Answer 11

The formation of Reactive Oxygen Species (ROS) and other mechanisms.

Question 12

What cell line is used in the In Vitro 3T3 NRU Phototoxicity Test?

Answer 12

Immortalized mouse fibroblast cell line BALB/c 3T3, clone A31.

Question 13

What is the incubation temperature for cell culture in the test?

Answer 13

37°C with 5-7.5% CO2.

Question 14

What is the maximum concentration of test chemicals used in the In Vitro 3T3 NRU Phototoxicity Test?

Answer 14

The highest concentration should not exceed 1000 μg/mL.

Question 15

What is the purpose of using a positive control like Chlorpromazine (CPZ) in the test?

Answer 15

To establish a baseline for phototoxicity testing.

Question 16

What is the acceptance criterion for irradiated Chlorpromazine (CPZ) IC50?

Answer 16

0.1 to 2.0 μg/mL.

Question 17

Fill in the blank: A chemical is classified as phototoxic if the MPE value exceeds _______.

Answer 17

0.15.

Question 18

What does a Photo Irritation Factor (PIF) value of < 2 predict?

Answer 18

No phototoxicity.

Question 19

What is the purpose of the bootstrap procedure in evaluating photocytotoxicity?

Answer 19

To assess the influence of data variability on the fitted curve.

Question 20

What is the pH range that should be maintained in cell culture to avoid toxicity?

Answer 20

Between 6.5 and 7.8.

Question 21

What is the effect of phototoxins on lysosomal membranes?

Answer 21

Increased permeability, leading to reduced pH gradient and decreased NR uptake.

Question 22

What is the expected outcome of a negative result in the In Vitro 3T3 NRU phototoxicity test?

Answer 22

It may eliminate the need for additional tests, such as photogenotoxicity.

Question 23

What is the significance of the concentration-response curves in the test?

Answer 23

They are compared to predict the phototoxic potential of the chemical.

Question 24

What is the significance of maintaining the lysosomal pH?

Answer 24

It is required for proper Neutral Red uptake by cells.

Question 25

What type of light source is used for irradiation in the test?

Answer 25

A solar simulator with UVA and visible light.

Question 26

What does the Mean Photo Effect (MPE) represent?

Answer 26

A weighted average across a representative set of photo effect values.

Question 27

Describe the Neutral Red Uptake Test procedure briefly.

Answer 27

Cells are incubated with Neutral Red, washed, and then optical density is measured.

Question 28

What is the role of weighting factors (wi) in MPE calculations?

Answer 28

They are determined by the highest response value.

Question 29

What does a PIF of < 5 or an MPE of > 0.1 and < 0.15 predict?

Answer 29

“equivocal” phototoxicity ## Footnote PIF stands for Phototoxicity Index and MPE stands for Maximum Phototoxicity Effect.

Question 30

What does a PIF of > 5 or an MPE of > 0.15 predict?

Answer 30

“phototoxicity” ## Footnote These thresholds are used to classify the severity of phototoxic effects.

Question 31

What should be tested to establish proficiency prior to routine testing for phototoxicity?

Answer 31

Chemicals listed in Table 1 ## Footnote Table 1 contains specific chemicals that serve as standards for proficiency testing.

Question 32

What should PIF or MPE values be close to?

Answer 32

The values mentioned in Table 1 ## Footnote This ensures consistency and reliability in the testing process.

Question 33

What additional considerations may be necessary if phototoxic effects are observed only at the highest test concentration?

Answer 33

Data on skin absorption and accumulation of the chemical in the skin ## Footnote Other tests may include ROS assay, in vitro animal or human skin assays, or skin models.

Question 34

True or False: If phototoxic effects are only observed at the highest concentration, further assessment is unnecessary.

Answer 34

False ## Footnote Further assessment is crucial for accurate hazard evaluation.