1H-n.m.r. studies on the specificity of the interaction between bovine pancreatic ribonuclease A and dideoxynucleoside monophosphates

The titration curves of the C-2 histidine protons of bovine pancreatic ribonuclease A in the presence of several dideoxynucleoside monophosphates (dNpdN) were studied by means of proton nuclear magnetic resonance at 270 MHz in order to obtain information on the ligand — RNase A interaction. The changes in the chemical shift and pKs of the C-2 proton resonances of His-12, -48, -119 in the complexes RNase A — dNpdN were smaller than those previously found when the enzyme interacted with mononucleotides. The pK₂ of His-12 was not affected by the interaction of the enzyme with these ligands, whereas, the perturbation of the pK₂ of His-119 was clearly dependent on the nature of the ligand. If there is a pyrimidine nucleoside at the 3′ side of the dideoxynucleoside monophosphates, as in TpdA and TpT, an enhancement due to the well known interaction of the phosphate in p₁, the catalytic site, was found. However, when there is a purine nucleoside, as in dApT and dApdA, a decrease in the pK₂ value was observed and we propose that in such cases the phosphate group interacts in a secondary phosphate binding site, p₂. The results obtained suggest the existence of different specific interactions depending on the structure of the dideoxynucleoside monophosphate studied.     

Impact of long-term treatment with neurotoxic dideoxynucleoside antiretrovirals: implications for clinical care in resource-limited settings

Objectives

A minority of HIV‐infected patients taking an antiretroviral (ARV) regimen containing dideoxynucleosides (d‐drugs) such as stavudine (d4T) and didanosine (DDI) experiences dose‐limiting neuropathic pain and paraesthesias, usually within weeks of starting these drugs. Because d‐drugs are among the few affordable options available in developing countries, continuing d‐drug therapy would be a desirable strategy for many HIV‐infected individuals. Therefore, we evaluated the safety of continuing d‐drug therapy.

Methods

In a US cohort, we compared the rates of worsening neuropathic symptoms and signs in HIV‐infected individuals on stable ARV regimens that did (n=252) or did not (n=250) include d‐drugs. Rates of worsening were compared using proportional hazards model and the log‐rank test.

Results

The risk ratios (RR) were not significantly larger for worsening neuropathy signs [0.94; 95% confidence interval (CI) 0.84–1.07] or symptoms (0.99; 95% CI 0.88–1.14) in patients taking d‐drugs continuously compared to those not taking d‐drugs.

Conclusions

Continued d‐drug exposure among patients tolerating an initial trial did not increase the risk of worsening neuropathy compared to non‐d‐drug‐containing regimens. If applicable in developing countries, these findings suggest that in most patients d‐drugs can be continued safely in the long term without increasing the risk of worsening neuropathy.     

Prevalence of multiple dideoxynucleoside analogue resistance (MddNR) in a cohort of Italian HIV-1 seropositive patients extensively treated with antiretroviral drugs

As the emergence of highly resistant virus might compromise antiretroviral regimens in HIV-1 infected patients, a constant analysis of genotypic mutations should be performed to establish the magnitude of mutation prevalence and gauge their impact in patients treated extensively with combination therapy. The frequency of multiple dideoxynucleoside analogue resistance (MddNR) was evaluated in a group of Italian HIV-1 seropositive patients who failed to respond to therapy despite a long-lasting drug treatment. Results showed the presence of one or more mutations (A62V, V75I, F77L, F116Y and Q151M) able to confer resistance to all NRTIs in a relatively high percentage (7.9%) of patients enrolled in the study. Moreover, a significantly lower HIV-1 viral replication in patients with MddNR, suggested the importance of monitoring HIV-1 subjects not only by viral load, but also by drug resistance testing, so that a correct drug regimen may be chosen.