Explore the vast range of titles available.

Research into the biological role of the Ca 2+ -releasing second messenger NAADP (nicotinic acid adenine dinucleotide phosphate) has been hampered by a lack of chemical probes. To find new chemical probes for exploring NAADP signaling, we turned to virtual screening, which can evaluate millions of molecules rapidly and inexpensively. We used NAADP as the query ligand to screen the chemical library ZINC for compounds with similar three-dimensional shape and electrostatic properties. We tested the top-ranking hits in a sea urchin egg bioassay and found that one hit, Ned-19, blocks NAADP signaling at nanomolar concentrations. In intact cells, Ned-19 blocked NAADP signaling and fluorescently labeled NAADP receptors. Moreover, we show the utility of Ned-19 as a chemical probe by using it to demonstrate that NAADP is a key causal link between glucose sensing and Ca 2+ increases in mouse pancreatic beta cells.

Ca2+ signaling plays a fundamental role in cardiac hypertrophic remodeling, but the underlying mechanisms remain poorly understood. We investigated the role of Ca2+-mobilizing second messengers, NAADP and cADPR, in the cardiac hypertrophy induced by β-adrenergic stimulation by isoproterenol. Isoproterenol induced an initial Ca2+ transients followed by sustained Ca2+ rises. Inhibition of the cADPR pathway with 8-Br-cADPR abolished only the sustained Ca2+ increase, whereas inhibition of the NAADP pathway with bafilomycin-A1 abolished both rapid and sustained phases of the isoproterenol-mediated signal, indicating that the Ca2+ signal is mediated by a sequential action of NAADP and cADPR. The sequential production of NAADP and cADPR was confirmed biochemically. The isoproterenol-mediated Ca2+ increase and cADPR production, but not NAADP production, were markedly reduced in cardiomyocytes obtained from CD38 knockout mice. CD38 knockout mice were rescued from chronic isoproterenol infusion-induced myocardial hypertrophy, interstitial fibrosis, and decrease in fractional shortening and ejection fraction. Thus, our findings indicate that β-adrenergic stimulation contributes to the development of maladaptive cardiac hypertrophy via Ca2+ signaling mediated by NAADP-synthesizing enzyme and CD38 that produce NAADP and cADPR, respectively.

CD38/cyclic adenosine diphosphate ribose (cADPR) signaling plays an important role in the regulation of intracellular calcium responses to agonists in a variety of cells, including airway smooth muscle (ASM) cells. The present study was aimed at determining the effect of interleukin (IL)-13, a cytokine implicated in the pathogenesis of asthma, on CD38/cADPR signaling and to ascertain the contribution of CD38/cADPR signaling to IL-13-induced airway hyperresponsiveness. Human ASM cells maintained in culture were exposed to 50 ng/ml IL-13 for 22 h and levels of CD38 expression and intracellular calcium responses to agonists were measured. Treatment of human ASM cells with IL-13 resulted in increased CD38 expression as determined by real-time polymerase chain reaction, Western blot analysis, and indirect immunofluorescence. Increased CD38 expression was reflected as increased ADP-ribosyl cyclase activity in the ASM cell membranes. The net intracellular calcium responses to bradykinin, thrombin, and histamine were significantly (P < or = 0.05) higher in cells treated with IL-13 compared with controls. Furthermore, 8-bromo-cADPR, a cADPR antagonist, attenuated IL-13-induced augmented intracellular calcium responses to agonists in human ASM cells. These findings indicate that the CD38/cADPR-dependent pathway has a major role in IL-13-induced modulation of calcium signaling in human ASM.

Novel cADPR mimics, which integrate nucleobase, northern and southern ribose modifications were synthesized. The key steps of the synthesis were a Cu(I)-catalyzed Hüisgen [3+2] cycloaddition and a microwave-assisted intramolecular pyrophosphorylation. Preliminary biological investigations showed that these cADPR mimics are membrane-permeating agonists of the calcium signaling pathway. The introduction of chlorine or fluorine at the 2'-position of the southern riboses led to a decrease of activity. The existence of a hydrophobic group on the 3'-OH of the southern riboses does not obviously alter the agonistic activity.

Bone marrow mesenchymal stem cells (MSCs) are a promising cell source for regenerative medicine. However, the cellular biology of these cells is not fully understood. The present study characterizes the cyclic ADP‐ribose (cADPR)‐mediated Ca2+ signals in human MSCs and finds that externally applied cADPR can increase the frequency of spontaneous intracellular Ca2+ (Ca2+i) oscillations. The increase was abrogated by a specific cADPR antagonist or an inositol trisphosphate receptor (IP3R) inhibitor, but not by ryanodine. In addition, the cADPR‐induced increase of Ca2+i oscillation frequency was prevented by inhibitors of nucleoside transporter or by inhibitors of the transient receptor potential cation melastatin‐2 (TRPM2) channel. RT‐PCR revealed mRNAs for the nucleoside transporters, concentrative nucleoside transporters 1/2 and equilibrative nucleoside transporters 1/3, IP3R1/2/3 and the TRPM2 channel, but not those for ryanodine receptors and CD38 in human MSCs. Knockdown of the TRPM2 channel by specific short interference RNA abolished the effect of cADPR on the Ca2+i oscillation frequency, and prevented the stimulation of proliferation by cADPR. Moreover, cADPR remarkably increased phosphorylated extracellular‐signal‐regulated kinases 1/2 (ERK1/2), but not Akt or p38 mitogen‐activated protein kinase (MAPK). However, cADPR had no effect on adipogenesis or osteogenesis in human MSCs. Our results indicate that cADPR is a novel regulator of Ca2+i oscillations in human MSCs. It permeates the cell membrane through the nucleoside transporters and increases Ca2+ oscillation via activation of the TRPM2 channel, resulting in enhanced phosphorylation of ERK1/2 and, thereby, stimulation of human MSC proliferation. This study delineates an alternate signalling pathway of cADPR that is distinct from its well‐established role of serving as a Ca2+ messenger for mobilizing the internal Ca2+ stores. Whether cADPR can be used clinically for stimulating marrow function in patients with marrow disorders remains to be further studied.

Cyclic adenosine diphosphoribose (cADPR) is an endogenous Ca2+ mobilizing nucleotide in many cell types and different species covering protozoa, plants and animals, including humans. cADPR is formed by ADP-ribosyl cyclases from nicotinamide adenine dinucleotide (NAD). Since at least some of the ADP-ribosyl cyclases are under the control of receptors for exogenous ligands, cADPR is regarded as a second messenger for Ca2+ signaling. The main intracellular target for cADPR is the ryanodine receptor, but it is unclear whether cADPR elicits Ca2+ release by direct binding or via a binding protein. Derivatives of NAD and cADPR are potent ADP-ribosyl cyclase inhibitors and cADPR antagonists. Since Ca2+ ions are regulators of many diverse cell functions, e.g. muscle contraction, secretion of neurotransmitters, hormones and enzymes, fertilization of oocytes, and lymphocyte activation and proliferation, the cADPR signaling pathway may become a valuable target for pharmaceutical intervention.

We and others have demonstrated a protective effect of pacing postconditioning (PPC) against ischemia/reperfusion (I/R) injury. However, the mechanisms underlying this protection are not completely clear. In the present study, we evaluated the effects of calcium release from the sarcoplasmic reticulum (SR) and the novel intracellular acidic stores (AS). Isolated rat hearts ( n  = 6 per group) were subjected to coronary occlusion followed by reperfusion using a modified Langendorff system. Cardiac hemodynamics and contractility were assessed using a data acquisition program, and cardiac injury was evaluated by creatine kinase (CK) and lactate dehydrogenase (LDH) levels. Hearts were subjected to 30 min of regional ischemia, produced by ligation of the left anterior descending (LAD) coronary artery, followed by 30 min of reperfusion. The hearts were also subjected to PPC (3 cycles of 30 s of left ventricle (LV) pacing alternated with 30 s of right atrium (RA) pacing) and/or were treated during reperfusion with agonists or antagonists of release of calcium from SR or AS. PPC significantly ( P  < 0.05) normalized LV, contractility, and coronary vascular dynamics and significantly ( P  < 0.001) decreased heart enzyme levels compared to the control treatments. The blockade of SR calcium release resulted in a significant ( P  < 0.01) recovery in LV function and contractility and a significant reduction in CK and LDH levels ( P  < 0.01) when applied alone or in combination with PPC. Interestingly, the release of calcium from AS alone or in combination with PPC significantly improved LV function and contractility ( P  < 0.05) and significantly decreased the CK and LDH levels ( P  < 0.01) compared to the control treatments. An additive effect was produced when agonism of calcium release from AS or blockade of calcium release from the SR was combined with PPC. Calcium release from AS and blockade of calcium release from the SR protect the heart against I/R. Combining calcium release from acidic stores or blockade of calcium release from the SR with PPC produced a synergistic protective effect.

Cyclic ADP‐ribose (cADPR) is a novel Ca2+ mobilizing second messenger, which is capable of inducing Ca2+ release from the sarcoplasmic reticulum (SR) via activation of ryanodine receptors (RyR) in vascular cells. This signaling nucleotide has also been reported to participate in generation or modulation of intracellular Ca2+ sparks 2+waves or oscillations, Ca2+‐induced Ca2+ release (CICR) and spontaneous transient outward currents (STOCs) in vascular smooth muscle cells (VSMCs). With respect to the role of cADPR‐mediated signaling in mediation of vascular responses to different stimuli, there is accumulating evidence showing that cADPR is importantly involved in the Ca2+ response of vascular endothelial cells (ECs) and VSMCs to various chemical factors such as vasoactive agonists acetylcholine, oxotemorine, endothelin, and physical stimuli such as stretch, electrical depolarization and sheer stress. This cADPR‐RyR‐mediated Ca2+ signaling is now recognized as a fundamental mechanism regulating vascular function. Here we reviewed the literature regarding this cADPR signaling pathway in vascular cells with a major focus on the production of cADPR and its physiological roles in the control of vascular tone and vasomotor response. We also summarized some publish results that unveil the underlying mechanisms mediating the actions of cADPR in vascular cells. Given the importance of Ca2+ in the regulation of vascular function, the results summarized in this brief review will provide new insights into vascular physiology and circulatory regulation.

Background and purpose: Recently, a number of mimics of the second messenger cyclic ADP‐ribose (cADPR) with replacement of adenosine by inosine were introduced. In addition, various alterations in the molecule ranging from substitutions at C8 of the base up to full replacement of the ribose moieties still retained biological activity. However, nothing is known about the metabolic stability and cellular effects of these novel analogues. Experimental approach: cADPR and the inosine‐based analogues were incubated with CD38, ADP‐ribosyl cyclase and NAD‐glycohydrolase and metabolism was analysed by RP‐HPLC. Furthermore, the effect of the analogues on cytokine expression and proliferation was investigated in primary T‐lymphocytes and T‐lymphoma cells. Key results: Incubation of cADPR with CD38 resulted in degradation to adenosine diphosphoribose. ADP‐ribosyl cyclase weakly catabolised cADPR whereas NAD‐glycohydrolase showed no such activity. In contrast, N1‐cyclic inosine 5′‐diphosphoribose (N1‐cIDPR) was not hydrolyzed by CD38. Three additional N1‐cIDPR analogues showed a similar stability. Proliferation of Jurkat T‐lymphoma cells was inhibited by N1‐cIDPR, N1‐[(phosphoryl‐O‐ethoxy)‐methyl]‐N9‐[(phosphoryl‐O‐ethoxy)‐methyl]‐hypoxanthine‐cyclic pyrophosphate (N1‐cIDP‐DE) and N1‐ethoxymethyl‐cIDPR (N1‐cIDPRE). In contrast, in primary T cells neither proliferation nor cytokine expression was affected by these compounds. Conclusions and Implications: The metabolic stability of N1‐cIDPR and its analogues provides an advantage for the development of novel pharmaceutical compounds interfering with cADPR mediated Ca2+ signalling pathways. The differential effects of N1‐cIDPR and N1‐cIDPRE on proliferation and cytokine expression in primary T cells versus T‐lymphoma cells may constitute a starting point for novel anti‐tumor drugs. British Journal of Pharmacology (2006) 149, 337–344. doi:10.1038/sj.bjp.0706869

Cyclic ADP-ribose (cADPr) is a second messenger that regulates intracellular free [Ca2+] ([Ca2+](i)) in a variety of cell types, including immature oocytes from the starfish Astropecten auranciacus. In this study, we employed confocal laser scanning microscopy and voltage clamp techniques to investigate the source of the cADPr-elicited Ca2+ wave originating from the cortical Ca2+ patches we have described previously. The Ca2+ swing was accompanied by a membrane current with a reversal potential of approximately +20 mV. Decreasing external Na+ almost abolished the current without affecting the Ca2+ response. Removal of extracellular Ca2+ altered neither the Ca2+ transient nor the ionic current, nor did the holding potential exert any effect on the Ca2+ wave. Both the Ca2+ response and the membrane current were abolished when BAPTA, ruthenium red or 8-NH(2)-cADPr were preinjected into the oocytes, while perfusion with ADPr did not elicit any [Ca2+](i) increase or ionic current. However, elevating [Ca2+](i) by uncaging Ca2+ from nitrophenyl- (NP-EGTA) or by photoliberating inositol 1,4,5-trisphosphate (InsP(3)) induced an ionic current with biophysical properties similar to that elicited by cADPr. These results suggest that cADPr activates a Ca2+ wave by releasing Ca2+ from intracellular ryanodine receptors and that the rise in [Ca2+](i) triggers a non-selective monovalent cation current that does not seem to contribute to the global Ca2+ elevation.