Platelet P2Y₁₂ is an important ADP receptor that is involved in agonist-induced platelet aggregation and is a valuable target for the development of anti-platelet drugs. Here we characterise the effects of thio-analogues of uridine triphosphate (UTP) on ADP-induced platelet aggregation. Using human platelet-rich plasma we demonstrate that UTP inhibits P2Y₁₂ but not P2Y₁ receptors and antagonises 10 μM ADP-induced platelet aggregation in a concentration-dependent manner with an IC₅₀ value of ~250 μM. An 8-fold higher platelet inhibitory activity was observed with a 2-thio analogue of UTP (2S-UTP), with an IC₅₀ of 30 μM. The 4-thio analogue (4S-UTP) with an IC₅₀ of 7.5 μM was 33-fold more effective. A 3-fold decrease in inhibitory activity, however, was observed by introducing an isobutyl group at the 4S- position. A complete loss of inhibition was observed with thio-modification of the γ phosphate of the sugar moiety, which yields an enzymatically stable analogue. The interaction of UTP analogues with P2Y₁₂ receptors was verified by P2Y₁₂ receptor binding and cAMP assays. These novel data demonstrate for the first time that 2- and 4-thio analogues of UTP are potent P2Y₁₂ receptor antagonists that may be useful for therapeutic intervention.

P2Y2 and P2Y4 receptors are physiologically activated by UTP and are widely expressed in many cell types in humans. They promote an increase in intracellular calcium via PLCβ/ IP3 and act on ion flux and water secretion. P2Y2 plays an important role in inflammation and proliferation of tumor cells, which could be attenuated with the use of antagonists. However, little is known about the physiological functions related to P2Y4 due to the lack of selective ligands for these receptors, which can be solved through the search of novel compounds with antagonistic activity. In the present study, we have applied a methodology of calcium measurement to identify new antagonist candidates for these receptors. Firstly, we established optimal conditions for calcium assay using J774.G8, a murine macrophage cell line, which expresses functional P2Y2 and P2Y4 receptors. J774.G8 cells were loaded with 2 μM of Fluo-4 to test its sensitivity in responding calcium stimuli. ATP and ionomycin, known as inductors of intracellular calcium rise, were used to stimulate cells. The EC50 obtained were 11 μM and 103 nM, respectively. Subsequently, investigation of P2Y2 and P2Y4 expression was performed. These cells responded with EC50 of 1.021 μM to the UTP stimulation. Screening assays were performed and a total of 100 extracts from Brazilian natural products were tested. JA2, RA3, and RB3 extracts stood out for their ability to inhibit UTP-induced responses without causing cytotoxicity and presented IC50 of 32.32 μg/mL, 14.99 μg/mL, and 12.98 μg/mL, respectively. Collectively, our results point to the discovery of potential antagonists candidates from natural products for UTP-activated receptors.

Background: Active case finding for TB was implemented in selected sixty high TB burden wards of Kolkata, India. Community volunteers called TOUCH agents (TAs) identified and referred presumptive TB patients (PTBPs) to health facilities for TB diagnosis and treatment. We aimed to describe the ‘care cascade’ of PTBPs identified during July to December, 2018 and to explore the reasons for attrition as perceived by TAs and PTBPs. Methods: An explanatory mixed methods study with quantitative phase of cohort study using routinely collected data followed by descriptive qualitative study with in-depth interviews was conducted. Results: Of the 3, 86,242 individuals enumerated, 1132 (0.3%) PTBPs were identified. Only 713 (63.0%) PTBPs visited referred facility for TB diagnosis. TB was diagnosed in 177 (24.8%) and the number needed to screen for one TB was 2,183 individuals. The potential reasons for low yield were stigma and apprehension about TB, distrust about TA, wage loss for attending health facilities and substance abuse among PTBPs. Conclusion: The yield of ACF was suboptimal with low PTBP identification rate and high attrition rate. Interviewing each individual for symptoms of TB and supporting PTBPs for diagnosis through sputum collection and transport can be adopted to improve the yield.