Antioxidant (NAC) or low oxygen overcome CYP1B1 deficiency and restore capillary morphogenesis of CYP1B1^−/− ECs. NAC can overcome TMS inhibition of CYP1B1^+/+ EC capillary morphogenesis (A). CYP1B1^+/+ ECs, control (A1), with 5 μM TMS (A2), with 1 mM NAC (A3), or with both TMS and NAC (A4) were plated in Matrigel as described in “Methods” (×40). Please note a significant increase in the mean number of branches in cells incubated with both NAC and TMS, compared with cells incubated with TMS alone. CYP1B1^−/− ECs, with (B2) or without (B1) NAC were plated in Matrigel as described in “Methods.” Please note a significant increase in the mean number of branches in CYP1B1^−/− ECs incubated with NAC. CYP1B1^−/− ECs were plated in Matrigel and cultured under low oxygen (2%, C2), compared with room air (20% oxygen, C1). Please note CYP1B1^−/− ECs undergo extensive capillary morphogenesis when cultured in 2% oxygen. All cultures were photographed after 17 hours in digital format. Quantitative assessment of the data is shown in panel D. Data in each bar are the mean number of branches per 5 high-power fields (×100; error bars indicate the standard deviation; n = 3, *P < .05). These experiments were repeated with 2 different preparations of ECs with similar results.