Influence of Hypericum perforatum L. extract STW 3-VI, hyperoside, and hyperforin on the binding behavior and lateral mobility of 5-HT2A-receptors

Objectives:

Depressive disorders belong to the most frequent diseases. Antidepressant treatment approaches try to normalize disturbed noradrenergic and/or serotonergic neurotransmitter systems. Strong interest exists for the understanding of the antidepressant mode of action.

Methods:

Influence of STW 3-VI, hyperoside, and hyperforin on the binding behavior and lateral mobility of 5-HT_2A-receptors was investigated on SH-SY5Y cells using fluorescence correlation spectroscopy.

Results:

A 6-day pretreatment of SH-SY5Y cells with 0.02 mg/ml STW 3-VI resulted in a 27% increase in 5-HT_2A-receptor binding compared to control. Lower concentrations of 0.002 mg/ml and 0.0002 mg/ml STW 3-VI showed no effect. Without influence on the 5-HT_2A-receptor binding were concentrations up to 1µM hyperoside or hyperforin.

Considering the distribution of 5-HT_2A-receptor binding to receptor-ligand complexes with free (diffusion time constant Tdiff2) and hindered (diffusion time constant Tdiff3) lateral mobility, a significant increase of receptor-ligand complexes with Tdiff2 by +187% and +42% was found for 0.02 mg/ml and 0.002 mg/ml STW3-VI, respectively. In contrast, receptor-ligand complexes with Tdiff3 decreased by -46% and -25%, respectively. For 1µM and 0.1µM hyperoside, comparable effects were found with +62% and +85% for Tdiff2 and -21% and -30% for Tdiff3, respectively. One µM hyperforin increased Tdiff2 by +87% and decreased Tdiff3 by -28%.

Compared to control, diffusion time constants for fast diffusing receptor-ligand complexes (Tdiff2) was not influenced by STW 3-VI, hyperforin, and hyperoside, respectively. In contrast, diffusion time constants for slow diffusing receptor-ligand complexes (Tdiff3) significantly increased, which can be explained by redistribution of slower diffusing receptor-ligand complexes into coated pits for subsequent receptor internalization. Hyperoside had no effect on Tdiff3.

Remarkably, hyperoside and hyperforin affect the lateral mobility of receptor-ligand complexes and their occurrence, although both compounds had no effect on total 5-HT_2A-receptor binding.

Conclusion:

Our data on the influence of STW 3-VI, hyperoside and hyperforin on the 5-HT_2A receptor represent another building block for the understanding of the multimodal mode of action of Hypericum perforatum L.