A novel approach for studying receptor-ligand interactions on living cells surface by using NUS/T1ρ-NMR methodologies combined with computational techniques: The RGDechi15D-αvβ5 integrin complex

Structural investigations of receptor-ligand interactions on living cells surface by high-resolution Nuclear Magnetic Resonance (NMR) are problematic due to their short lifetime, which often prevents the acquisition of experiments longer than few hours. To overcome these limitations, we developed an on-cell NMR-based approach for exploring the molecular determinants driving the receptor-ligand recognition mechanism under native conditions. Our method relies on the combination of high-resolution structural and dynamics NMR data with Molecular Dynamics simulations and Molecular Docking studies. The key point of our strategy is the use of Non Uniform Sampling (NUS) and T1ρ-NMR techniques to collect atomic-resolution structural and dynamics information on the receptor-ligand interactions with living cells, that can be used as conformational constraints in computational studies. In fact, the application of these two NMR methodologies allows to record spectra with high S/N ratio and resolution within the lifetime of cells. In particular, 2D NUS [¹H–¹H] trNOESY spectra are used to explore the ligand conformational changes induced by receptor binding; whereas T1ρ-based experiments are applied to characterize the ligand binding epitope by defining two parameters: T1ρ Attenuation factor and T1ρ Binding Effect. This approach has been tested to characterize the molecular determinants regulating the recognition mechanism of α_vβ₅-integrin by a selective cyclic binder peptide named RGDechi15D. Our data demonstrate that the developed strategy represents an alternative in-cell NMR tool for studying, at atomic resolution, receptor-ligand recognition mechanism on living cells surface. Additionally, our application may be extremely useful for screening of the interaction profiling of drugs with their therapeutic targets in their native cellular environment.

Antiplatelet therapy alters iron requirements in hemodialysis patients

Hemodialysis (HD) patients are prone to develop iron deficiency because of consumption of iron stores during erythropoietin (EPO) therapy. Data are needed to establish the factors involved in the different iron needs among these patients. Sixty-five HD patients were prospectively studied during a year. The subjects were dialyzed through polytetrafluoroethylene (PTFE) grafts (n = 23), arteriovenous native fistulae (n = 41), and a Permcath (n = 1). Twenty-four patients were administered aspirin; 23 patients, ticlopidine; 1 patient, dipyridamole; and 4 patients, anticoagulation with acenocoumarol. Iron supplementation (oral or parenteral) and laboratory parameters were recorded monthly. Significant differences in iron requirements, depending on the use of antiplatelet and/or anticoagulation agents, were found. Total parenteral iron supplements were greater in patients on antiplatelet therapy with either native or graft vascular accesses compared with the rest (2,406 +/- 1,445 versus 1,562 +/- 858 mg; P = 0.0081). Twelve of 52 patients on antiplatelet therapy required oral iron and only 1 of 13 patients not on antiplatelet therapy was administered oral iron supplements (P < 0.05). Patients on antiplatelet therapy were administered more transfusions (1.9 +/- 3.8 transfusions/y) than individuals not on antiplatelet therapy (0.15 +/- 0.3 transfusions/y; P = 0.0015). However, only patients with PTFE grafts on antiplatelet therapy had a post-HD bleeding time longer than patients not on antiplatelet therapy (9.1 +/- 3.6 versus 5.7 +/- 3.9 minutes; P < 0.0001). Multiple logistic regression analysis showed that the use of antiplatelet agents (P < 0.05) is an independent factor that increased the probability of requiring greater parenteral iron supplements (>2.5 g/y). Patients with PTFE grafts required more EPO than those with autologous fistulae (160 +/- 93 versus 100 +/- 63 U/kg/wk; P = 0.012). No differences between groups were found that could explain this finding. Antiplatelet and/or anticoagulation therapy implied the use of greater amounts of iron supplements in HD patients. Although these greater requirements of iron occurred in parallel with bleeding from the vascular access, additional data favor the existence of other factors, eg, interdialytic blood losses. The present study suggests that antiplatelet therapy may be an important factor in determining iron requirements in HD patients. Moreover, our data relate for the first time the use of prosthetic grafts with increased EPO requirements, an issue of great potential importance in the debate about vascular access policy in dialysis units.

Incidence of hypercalcaemia in haemodialysis patients

Secondary hyperparathyroidism is still one of the main problems affecting the dialysis population. The use of aluminium hydroxide as a phosphate binder is limited by significant long-term toxicity. Therefore, actually, most patients on haemodialysis receive treatment with calcium containing phosphate binders to avoid hyperphosphataemia.

Mechanisms of aluminum-induced microcytosis: lessons from accidental aluminum intoxication

Twenty-three hemodialysis patients exposed to an accidental aluminum overload, showed increased erythropoietin requirements and decreased erythrocyte mean corpuscular volume (MCV). At the peak of the intoxication, MCV and plasma aluminum levels changed from unrelated (r = 0.02) to strongly related (r = 0.425) variables. The molar proportion of plasma aluminum to plasma iron increased dramatically (from 1:13.8 to 1:2.4). This significant increment in the aluminum/iron ratio made higher the relative offer of aluminum with respect to iron to the erythroid precursor cells. Accordingly, in a subset of 13 randomly selected aluminum-intoxicated patients we found increased intraerythrocytic aluminum, which paralleled the increase in plasma aluminum. Furthermore, in the aluminum-intoxicated group, intraerythrocytic ferritin, a marker of iron content, and the ratio between erythrocyte and plasma ferritin were lower (P < 0.01 and < 0.001, respectively), than in the control group. These findings support the hypothesis that in some cases of aluminum-related microcytosis, a ferropenic mycrocitosis, as expression of erythroid ferropenia, may exist in spite of the presence of normal body iron stores.