Hydrodynamic stress induces monoterpenoid oxindole alkaloid accumulation by Uncaria tomentosa (Willd) D. C. cell suspension cultures via oxidative burst

Uncaria tomentosa cell suspension cultures were grown in a 2-L stirred tank bioreactor operating at a shear rate γ̇_avg =86 s ^_1. The cultures showed an early monophasic oxidative burst measured as H₂O₂ production (2.15 μmol H₂O ₂ g^-1 dw). This response was followed by a transient production of monoterpenoid oxindole alkaloids (178 ± 40 μg L ^-1 at 24 h). At the stationary phase (144 h), the increase of the shear rate γ̇_avg up to 150 s^-1 and/or oxygen tension up to 85% generated H₂O₂, restoring oxindole alkaloid production. U. tomentosa cells cultured in Erlenmeyer flasks also exhibited the monophasic oxidative burst but the H₂O₂ production was 16-fold lower and the alkaloids were not detected. These cells exposed to H₂O₂ generated in situ produced oxindole alkaloids reaching a maximum of 234 ± 40 μg L^-1. A positive correlation was observed between the oxindole alkaloid production and the endogenous H₂O₂ level. On the other hand, addition of 1 μM diphenyleneiodonium (NAD(P)H oxidase inhibitor) or 10 μM sodium azide (peroxidases inhibitor) reduced both H₂O₂ production and oxindole alkaloids build up, suggesting that these enzymes might play a role in the oxidative burst induced by the hydrodynamic stress.