guanosine-monophosphate and Leishmaniasis

It has been shown previously that Sb(V) forms mono- and bis-adducts with adenine and guanine ribonucleosides, suggesting that ribonucleosides may be a target for pentavalent antimonial drugs in the treatment of leishmaniasis. In the present work, the reactions of antimoniate (KSb(OH)(6)) and meglumine antimoniate (MA) with guanosine 5'-monophosphate (GMP) have been characterized at 37 degrees C in aqueous solution and two different pH (5 and 6.5), using ESI(-)-MS and (1)H NMR. Acid and base species for both 1:1 and 1:2 Sb(V)-GMP complexes were identified by ESI(-)-MS. The (1)H NMR anomeric region was explored for determining the concentrations of mono- and bis-adducts. This allows for the determination of stability constants for these complexes (5,900 L mol(-1) for 1:1 complex and 370 L mol(-1) for 1:2 complex, at pD 5 and 37 degrees C). Kinetic studies at different pH indicated that formation and dissociation of both 1:1 and 1:2 Sb-GMP complexes are slow processes and favored at acidic pH (2,150 L mol(-1) h(-1) for the rate constant of 1:1 complex formation and 0.25 h(-1) for the rate constant of 1:1 complex dissociation, at pD 5 and 37 degrees C). When MA was used, instead of antimoniate, formation of 1:1 Sb-GMP complex occurred, but with a slower rate constant. Assuming that MA consists essentially of a 1:1 Sb-meglumine complex, a stability constant for MA could also be estimated (8,600 L mol(-1) at pD 5 and 37 degrees C). Thermodynamic and kinetic data are consistent with the formation of 1:1 Sb-ribonucleoside complexes in vertebrate hosts, following treatment with pentavalent antimonial drugs.

Topics: Animals; Antimony; Antiprotozoal Agents; Guanosine Monophosphate; Hydrogen-Ion Concentration; Leishmaniasis; Meglumine; Meglumine Antimoniate; Nuclear Magnetic Resonance, Biomolecular; Organometallic Compounds; Spectrometry, Mass, Electrospray Ionization; Thermodynamics

In spite of the extensive use of pentavalent antimony chemotherapy, the mechanism of its anti-leishmania action is still not clear. Here, we report the interactions of Sb(V), including the clinically used drug stibogluconate, with guanosine 5'-monophosphate (5'-GMP) and guanosine 5'-diphospho-d-mannose (5'-GDP-mannose) in aqueous solution. The deprotonated hydroxyl groups (-OH) of the ribose ring are shown to be the binding site for Sb(V), probably via chelation. Both mono- and bis-adducts were formed as determined by NMR, high performance liquid chromatography (HPLC) and electrospray ionization mass spectrometry (ESI-MS), and both of them are stable in the pH range of 4 to around 9.5. The formation of the mono-adduct (k(1)=1.67x10(-3) and 3.43x10(-3) mM(-1) min(-1) for Sb(5'-GMP) and Sb(5'-GDP-mannose), respectively, at 298 K) was 10-fold faster than that of the bis-adduct (k(2)=0.16x10(-3) and 0.21x10(-3) mM(-1) min(-1), for Sb(5'-GMP)(2) and Sb(5'-GDP-mannose)(2), respectively), and the mono-adduct was the major species in solution with the [bis-adduct]/[mono-adduct]<0.5. The reactions of stibogluconate with 5'-GMP and 5'-GDP-mannose were slower than that of antimonate under similar conditions.

Topics: Animals; Antimony; Antimony Sodium Gluconate; Antiprotozoal Agents; Chromatography, High Pressure Liquid; Guanosine Diphosphate Mannose; Guanosine Monophosphate; Humans; In Vitro Techniques; Kinetics; Leishmania; Leishmaniasis; Magnetic Resonance Spectroscopy; Spectrometry, Mass, Electrospray Ionization