Effects of cAMP modulators on flavonoid accumulation in cell cultures of Hypericum androsaemum L.

Hypericum androsaemum L. has been used in traditional medicine for its diuretic and hepatoprotective properties [1], which are attributed to the diverse flavonoids and phenolic acids found in this species.

Cell suspension cultures established from hypocotyl-derived callus of H. androsaemum were reported [2] to accumulate low amounts of flavonoids, with maximum levels occurring on the 14th day of the growth cycle.

More recently [3], it was shown that treatment of 11-day-old cultures for 72h with 15 mM CaCl₂ or 5µM calcium ionophore A23187 increased considerably the accumulation of flavonoids and the activity of phenylalanine ammonia-lyase (PAL, a key regulatory enzyme of phenylpropanoid metabolism).

Since adenylyl cyclases can be regulated by Ca²⁺, similar experiments were carried out in this study using three different modulators of intracellular cAMP: dibutyryl-cAMP (100µM, a membrane permeable cAMP analogue), IBMX (100µM, a cNMP phosphodiesterase inhibitor) and forskolin (20µM, an adenylyl cyclase activator). The first two treatments induced a marked increase in both PAL activity and flavonoid content of cells, as compared to control cultures. Increased levels of flavonoids were also found in forskolin-treated cells, but in this case accompanied by an insignificant rise in PAL activity.

Considered together, these findings are in agreement with the involvement of cAMP signaling in flavonoid metabolism of H. androsaemum cell cultures.

Acknowledgement: FCT and POCTI/FEDER for financial support.

References: 1. Novais M et al. (2004)J Ethnopharmacol 93: 183–195.

2. Paranhos A (2006) Planta Med 72: 1060–1061.

3. Paranhos A (2007) Planta Med 73: 1017.