New natural product carbonic anhydrase inhibitors incorporating phenol moieties

 

Carbonic anhydrases (CAs, EC 4.2.1.1) catalyze the fundamental reaction of CO₂ hydration in all living organisms (eq. 1), being actively involved in the regulation of a plethora of patho/physiological conditions. They represent a typical example of enzyme convergent evolution, as six genetically unrelated families of such enzymes were described so far [1]. Herein we report an in vitro inhibition study of human (h) CA isoforms hCAs I, II, IV, VII and XII with a panel of natural polyphenols including flavones, flavonols, flavanones, flavanols, isoflavones and depsides, some of which extracted from Quercus ilex and Salvia miltiorrhiza.

All compounds were tested by a stopped flow carbon dioxide hydration assay for their in vitro inhibitory activities against five hCA isoforms such as the cytosolic I, II, VII and the membrane bound CA IV and XII.

Several of the investigated derivatives showed interesting inhibition activity and selectivities for inhibiting some important isoforms over the off-target ones hCA I and II. The membrane bound hCA IV was effectively inhibited from Naringenin (6), Eriodictyol (7), Hesperitin (8), Quercetin-3-O-glucoside (13), Quercetin-3-O-rhamnoside (14), Kaempferol-3-O-(3",4"-diacetyl-2",6"-di-E-p-coumaroyl)-β-glucopyranoside (18), the depsides from Salvia milthiorrhizza (19-21), with K_I values in the range of 62.2 – 102.1 nM (comparable to the standard AAZ (acetazolamide), K_I of 74.0 nM). Compounds 5 – 8, 10, 13, 14, 16 and 17 were nanomolar inhibitors of hCA VII, with KIs comparable to the standard AAZ (3.3 – 4.7 vs. 2.5 nM for AAZ). Since hCA VII is preferentially expressed in the CNS, such compounds can be considered useful for the possible treatment of neurodegenerative diseases. Finally, hCA XII was efficiently inhibited by Kaempferol-3-O-glucoside (15) and Lithospermic acid (19) with K_Is of 4.9 and 4.8 nM. Further investigations are needed in order to elucidate the binding modes of the selected compounds on the appropriate hCA isoforms.

Acknowledgements: Research was financed by grants of the 6^th Framework Programme (FP) of the European Union (DeZnIT and Euroxy projects), by a grant of the 7^th FP of EU (Metoxia project).

Keywords: Carbonic anhydrase inhibitors (CAIs); metalloenzymes; phenol, polyphenols, natural products.

References:

[1] Supuran CT. Nature Rev Drug Discov 2008; 7: 168