Description

Infections by helminths are one of the major health problems in developing countries. Fast adaptation of parasitic organisms has conferred resistance to drug therapies used for decades (Burns et al., 2015), causing a threat to control worm parasites and generating an urgent need for new emergent molecules with therapeutic potential, in particular for nematodes. The nematode Caenorhabditis elegans is phylogenetically-related to parasitic species of helminths in which high throughput assays are challenging; thus, this species is an excellent model to study and evaluate novel anthelmintic drugs (Gilleard, 2004; Yoon et al., 2006). One interesting molecular target for drug development are the GABA receptors of parasitic helminths which are evolutionarily preserved in invertebrates and vertebrates and are present in C. elegans (Castillo et al., 1967; del Castillo et al., 1964; Jorgensen, 2005). GABA receptors from C. elegans are ionotropic channels that belong to the Cys-loop superfamily of ligand gated ion channels widely spread in multiple species, including humans (Olsen and Sieghart, 2008).

Flavonoids are natural products of fruits and vegetables commonly present in the human diet. They exhibit a wide range of biological activities such as antibacterial, anti-inflammatory, antiallergic, antithrombotic, vasodilatory and anticarcinogenic. Furthermore, flavonoids are modulators of human ionotropic GABA receptors (Goutman et al., 2003). In recent years, chrysin, a 5,7-dihydroxyflavone produced in plants that elicits hyperalgesia via GABA-A receptors (Kui Zhai et al., 2008), has been chemically modified to test its anthelmintic activity (Rendon-Nava et al., 2017). Here we modified chrysin at the 7-OH by introducing alkyl bromide groups to generate its derivative: 7-O-(3-bromopropyl)-chrysin. To evaluate its activity, we employed two strategies:

1.We injected the mRNA of human GABA-A rho1 receptor in Xenopus laevis oocytes (Martinez-Torres et al., 1998) and after 2-4 days its effect was tested on GABA-currents generated by perfusing GABA (3 µM), these basal currents were used as control. GABA-currents were not significantly modified in presence of chrysin. In contrast, 50 µM of 7-O-(3-bromopropyl)-chrysin reduced the amplitude of GABA-currents when perfused onto the bath (reduction to 67.5 ± 6.8 % from control) and 100 µM (reduction to 68.4 ± 8.7 % from control): neither chrysin or 7-O-(3-bromopropyl)-chrysin induced any evident current on the oocytes, not induced evident changes in these cells.

2. We tested whether chrysin and 7-O-(3-bromopropyl)-chrysin elicits changes on locomotion on C. elegans. The speed of displacement of the worm and the wave amplitude of its shape in free-movement were evaluated after 3 h of drug exposure. Results showed that chrysin at 100 uM reduced the speed movement without changes on the wave amplitude of the nematode. 7-O-(3-bromopropyl)-chrysin did not elicit significant difference compared to the control. Exposure to the compounds for more than 24 h did not show further effects.

The insertion of an aliphatic bromide chain in the OH of chrysin’s position 7 (Figure 1A) potentially enhance the lipophilic capacity of the compound due to the presence of the methylene group. We expected these modifications to enhance cell permeability and that the presence of a halide to promote ionic interactions. However, the results showed that 7-O-(3-bromopropyl)-chrysin partially blocks GABA-A rho1 receptors expressed in frog oocytes (Figure 1B). In C. elegans, reduction of speed movement could be due to the inhibition of native GABA-receptors normally expressed in muscle and neurons, thus affecting locomotion. We expected that the amplitude of the shape was modified as a result of the effects on muscle contraction, but we did not find evidence of such effect.

In conclusion, we report that the chrysin derivative 7-O-(3-bromopropyl)-chrysin negatively modulates human ionotropic GABA-A rho1 receptors expressed in frog oocytes. Chrysin reduces significantly the speed movement of C. elegans, however the 7-O-(3-bromopropyl)-chrysin does not have effect, in summary chrysin could be potentially used as template to generate new drugs for anthelmintic properties or synaptic modulators.