ABSTRACT
The human telomeric G-quadruplex structural motif of DNA has come to be known as a new and stimulating target for anticancer drug discovery. Small molecules that interact with G-quadruplex structures in a selective way have gained impressive interest in recent years as they may serve as potential therapeutic agents. Here, we show how circular dichroism, UV resonance Raman and small angle X-ray scattering spectroscopies can be effectively combined to provide insights into structural and molecular aspects of the interaction between human telomeric quadruplexes and ligands. This study focuses on the ability of berberine and palmatine to bind with human telomeric quadruplexes and provides analysis of the conformational landscape visited by the relevant complexes upon thermal unfolding. With increasing temperature, both free and bound G-quadruplexes undergo melting through a multi-state process, populating different intermediate states. Despite the structural similarity of the two ligands, valuable distinctive features characterising their interaction with the G-quadruplex emerged from our multi-technique approach.
Subject(s)
Berberine Alkaloids/metabolism , Berberine/metabolism , DNA/metabolism , G-Quadruplexes , Berberine/chemistry , Berberine Alkaloids/chemistry , Circular Dichroism , DNA/chemistry , DNA/genetics , Humans , Ligands , Scattering, Small Angle , Spectrum Analysis, Raman , X-Ray DiffractionABSTRACT
A possible defect of guanosine 3'-5'-cyclic monophosphate (cGMP) content in the renal tissue caused by an increased activity of cGMP phosphodiesterase (PDE) has, so far, not been evaluated in the pathogenesis of renal resistance to endogenous natriuretic peptides (ENP) in cirrhosis with ascites. To test this hypothesis the activity of cGMP-PDE and the concentration of cGMP were evaluated in vitro in the renal tissue of 10 control rats and 10 cirrhotic rats with ascites before and after the intravenous (IV) administration of Zaprinast (Sigma, St. Louis, MO), a specific cGMP-PDE inhibitor (30 microgram/kg/min). Moreover, the effects of the intravenous administration of Zaprinast (15 microgram/kg/min and 30 microgram/kg/min) on renal plasma flow (RPF), glomerular filtration rate (GFR), and urinary sodium excretion (U(Na)V) were evaluated in 10 conscious control rats and 10 conscious cirrhotic rats with ascites. The effects of Zaprinast on plasma renin activity (PRA) was also evaluated in 10 control rats and in 10 cirrhotic rats with ascites. Finally, the effect of Zaprinast on RPF, GFR, and U(Na)V were evaluated in 10 cirrhotic rats after the IV administration of the ENP-receptor antagonist, HS-142-1. The renal content of cGMP was reduced in cirrhotic rats because of increased activity of cGMP-PDE. Zaprinast inhibited cGMP-PDE activity and increased the renal content of cGMP in these animals. The inhibition of cGMP-PDE was associated with an increase in RPF, GFR, and U(Na)V and a reduction in PRA. HS-142-1 prevented any renal effect of Zaprinast in cirrhotic rats. In conclusion, an increased activity of the cGMP-PDE in renal tissue contributes to the renal resistance to ENP in cirrhosis with ascites.
