Twenty-seven chalcogenopyrylium derivatives varying in the heteroatom of the pyrylium core and substituents at the 2-, 4-, and 6-positions were examined for their effect on human MRP1-mediated uptake of tritiated estradiol glucuronide into inside-out membrane vesicles, their affinity for and ability to stimulate the ATPase activity of purified human P-glycoprotein (P-gp)-His(10), and their ability to promote uptake of calcein AM and vinblastine in multidrug-resistant cells. Differences in their effects on MRP1 and P-gp activity were noted, and a second set of thiopyrylium compounds with systematic substituent changes was examined to refine these differences further. Derivatives with tert-butyl substituents in the 2- and 6-positions had the lowest inhibitory activity toward both transporters. Derivatives with thioamide functionality in the 4-position were more active against MRP1 than derivatives with amide functionality. Conversely, derivatives with amide functionality in the 4-position were more active in P-gp than derivatives with thioamide functionality.

Extracellular vesicles (EVs) are important mediators of intercellular communication. Since EVs are also released during pathological conditions, there has been considerable interest in their potential as sensitive biomarkers of cellular stress and/or injury. In the context of kidney disease, urinary EVs are promising indicators of glomerular and tubular damage. In the present review we discuss the role of urinary EVs in kidney health and disease. Our focus is to explore urinary large EVs (lEVs, often referred to as microparticles or microvesicles) as direct and noninvasive early biomarkers of renal injury. In this regard, studies have been demonstrating altered levels of urinary lEVs, especially podocyte-derived lEVs, preceding the decrease of renal function assessed by classical markers. In addition, we discuss the role of small EVs (sEVs, often referred to as exosomes) and their contents in kidney pathophysiology. Even though results concerning the production of sEVs during diseased conditions are varied, there has been a consensus on the importance of urinary sEV content assessment in kidney disease. These mediators, including EV-released miRNAs and mRNAs, are responsible for EV-mediated signaling in the regulation of renal cellular homeostasis, pathogenesis and regeneration. Finally, steps necessary for the validation of EVs as reliable markers will be discussed. Review

Multidrug resistance proteins (MRPs) mediate the ATP-dependent efflux of structurally diverse compounds, including anticancer drugs and physiologic organic anions. Five classes of chalcogenopyrylium dyes (CGPs) were examined for their ability to modulate transport of [ 3 H]estradiol glucuronide (E 2 17bG; a prototypical MRP substrate) into MRP-enriched inside-out membrane vesicles.Additionally, some CGPs were tested in intact transfected cells using a calcein efflux assay. Sixteen of 34 CGPs inhibited MRP1-mediated E 2 17bG uptake by >50% (IC 50 values: 0.7-7.6 mM). Of 9 CGPs with IC 50 values £2 mM, two belonged to class I, two to class III, and five to class V. When tested in the intact cells, only 4 of 16 CGPs (at 10 mM) inhibited MRP1-mediated calcein efflux by >50% (III-1, V-3, V-4, V-6), whereas a fifth (I-5) inhibited efflux by just 23%.These five CGPs also inhibited [ 3 H]E 2 17bG uptake by MRP4. In contrast, their effects on MRP2 varied, with two (V-4, V-6) inhibiting E 2 17bG transport (IC 50 values: 2.0 and 9.2 mM) and two (V-3, III-1) stimulating transport (>2-fold), whereas CGP I-5 had no effect. Strikingly, although V-3 and V-4 had opposite effects on MRP2 activity, they are structurally identical except for their chalcogen atom (Se versus Te). This study is the first to identify class V CGPs, with their distinctive methine or trimethine linkage between two disubstituted pyrylium moieties, as a particularly potent class of MRP modulators, and to show that, within this core structure, differences in the electronegativity associated with a chalcogen atom can be the sole determinant of whether a compound will stimulate or inhibit MRP2.