Nicotinamide Adenine Dinucleotide Metabolites Research Articles

Effect of circadian rhythm on NAD and other metabolites in human brain.

Nicotinamide Adenine Dinucleotide (NAD) plays a central role in the master circadian clock of the brain (the suprachiasmatic nuclei, SCN) as demonstrated in many model organisms. NAD acts as an enzyme co-factor and substrate and its modulation was found to be tightly regulated to the periodicity of the cycles. However, in human brain, the effect of the circadian rhythm (CR) on the metabolism of the SCN and other brain regions is poorly understood. We conducted a magnetic resonance spectroscopy (MRS) study at a high magnetic field, measuring the occipital brain NAD levels and other metabolites in two different morning and afternoon diurnal states in 25 healthy participants. Salivary cortisol levels were determined to confirm that the experiment was done in two chronologically different physiological conditions, and a behavioral test of risk-taking propensity was administered. Overall, we found that the CR did not significantly affect NAD levels in the occipital brain region. The other brain metabolites measured, including lactate, were not significantly affected by the CR either, except for taurine. The CR did impact risk-taking behavior and salivary cortisol level, confirming that the participants were in two circadian different behavioral and physiological states in the morning and in the afternoon. Measurement of the CR effect on NAD and taurine levels in other brain regions might provide stronger effects.

Reduced Levels of NAD in Skeletal Muscle and Increased Physiologic Frailty Are Associated With Viral Coinfection in Asymptomatic Middle-Aged Adults.

Background:People living with HIV (PLWH) are disproportionately burdened with multimorbidity and decline in physiologic function compared with their uninfected counterparts, but biological mechanisms that differentially contribute to the decline in muscle function in PLWH compared with uninfected people remain understudied.Setting:The study site was Brigham and Women's Hospital, Harvard Medical School, Boston, MA.Methods:We evaluated skeletal muscle tissue for levels of total nicotinamide adenine dinucleotide (NAD), NAD+, and nicotinamide adenine dinucleotide (NADH) in middle-aged asymptomatic PLWH, coinfected with hepatitis C virus and/or cytomegalovirus and compared them with uninfected control participants.Results:Of the 54 persons with muscle biopsy data, the mean age was 57 years with 33% women. Total NAD levels declined in skeletal muscle in association with HIV infection and was exacerbated by hepatitis C virus and cytomegalovirus coinfection, with lowest levels of total NAD, NAD+, and NADH among persons who were coinfected with all 3 viruses (P = 0.015, P = 0.014, and P = 0.076, respectively). Levels of total NAD, NAD+, and NADH in skeletal muscle were inversely associated with inflammation (P = 0.014, P = 0.013, and P = 0.055, respectively). Coinfections were also associated with measures of inflammation (CD4/CD8 ratio: P < 0.001 and sCD163: P < 0.001) and immune activation (CD38 and human leukocyte antigen-DR expression on CD8 T cells: P < 0.001). In addition, coinfection was associated with increased physiologic frailty based on the Veteran Aging Cohort Study 1.0 index assessment (P = 0.001).Conclusions:Further research is warranted to determine the clinical relevance of preclinical deficits in NAD metabolites in skeletal muscle in association with viral coinfection and inflammation, as well as the observed association between viral coinfection and physiologic frailty.

Adenine Nucleotide Metabolites in Uremic Erythrocytes as Metabolic Markers of Chronic Kidney Disease in Children.

Chronic kidney disease (CKD) is associated with multifaceted pathophysiological lesions including metabolic pathways in red blood cells (RBC). The aim of the study was to determine the concentration of adenine nucleotide metabolites, i.e., nicotinamide adenine dinucleotide (NAD)-oxidized form, nicotinamide adenine dinucleotide hydrate (NADH)-reduced form, nicotinic acid mononucleotide (NAMN), β-nicotinamide mononucleotide (NMN), nicotinic acid adenine dinucleotide (NAAD), nicotinic acid (NA) and nicotinamide (NAM) in RBC and to determine a relationship between NAD metabolites and CKD progression. Forty-eight CKD children and 33 age-matched controls were examined. Patients were divided into groups depending on the CKD stages (Group II-stage II, Group III- stage III, Group IV- stage IV and Group RRT children on dialysis). To determine the above-mentioned metabolites concentrations in RBC liquid chromatography-mass spectrometry was used. Results: the only difference between the groups was shown concerning NAD in RBC, although the values did not differ significantly from controls. The lowest NAD values were found in Group II (188.6 ± 124.49 nmol/mL, the highest in group IV (324.94 ± 63.06 nmol/mL. Between Groups II and IV, as well as III and IV, the differences were statistically significant (p < 0.032, p < 0.046 respectively). Conclusions. CKD children do not have evident abnormalities of RBC metabolism with respect to adenine nucleotide metabolites. The significant differences in erythrocyte NAD concentrations between CKD stages may suggest the activation of adaptive defense mechanisms aimed at erythrocyte metabolic stabilization. It seems that the implementation of RRT has a positive impact on RBC NAD metabolism, but further research performed on a larger population is needed to confirm it.

Elucidating the tunability of binding behavior for the MERS-CoV macro domain with NAD metabolites

The macro domain is an ADP-ribose (ADPR) binding module, which is considered to act as a sensor to recognize nicotinamide adenine dinucleotide (NAD) metabolites, including poly ADPR (PAR) and other small molecules. The recognition of macro domains with various ligands is important for a variety of biological functions involved in NAD metabolism, including DNA repair, chromatin remodeling, maintenance of genomic stability, and response to viral infection. Nevertheless, how the macro domain binds to moieties with such structural obstacles using a simple cleft remains a puzzle. We systematically investigated the Middle East respiratory syndrome-coronavirus (MERS-CoV) macro domain for its ligand selectivity and binding properties by structural and biophysical approaches. Of interest, NAD, which is considered not to interact with macro domains, was co-crystallized with the MERS-CoV macro domain. Further studies at physiological temperature revealed that NAD has similar binding ability with ADPR because of the accommodation of the thermal-tunable binding pocket. This study provides the biochemical and structural bases of the detailed ligand-binding mode of the MERS-CoV macro domain. In addition, our observation of enhanced binding affinity of the MERS-CoV macro domain to NAD at physiological temperature highlights the need for further study to reveal the biological functions.

Untargeted analysis of plasma samples from pre-eclamptic women reveals polar and apolar changes in the metabolome

IntroductionPre-eclampsia is a hypertensive gestational disorder that affects approximately 5% of all pregnancies.ObjectivesAs the pathophysiological processes of pre-eclampsia are still uncertain, the present case–control study explored underlying metabolic processes characterising this disease.MethodsMaternal peripheral plasma samples were collected from pre-eclamptic (n = 32) and healthy pregnant women (n = 35) in the third trimester. After extraction, high-resolution mass spectrometry-based untargeted metabolomics was used to profile polar and apolar metabolites and the resulting data were analysed via uni- and multivariate statistical approaches.ResultsThe study demonstrated that the metabolome undergoes substantial changes in pre-eclamptic women. Amongst the most discriminative metabolites were hydroxyhexacosanoic acid, diacylglycerols, glycerophosphoinositols, nicotinamide adenine dinucleotide metabolites, bile acids and products of amino acid metabolism.ConclusionsThe putatively identified compounds provide sources for novel hypotheses to help understanding of the underlying biochemical pathology of pre-eclampsia.

Maternal Nicotinamide Riboside Enhances Postpartum Weight Loss, Juvenile Offspring Development, and Neurogenesis of Adult Offspring (P11-003-19)

ObjectivesWe tested the hypothesis that postpartum constitutes a metabolic stress to the nicotinamide adenine dinucleotide (NAD) system and that supplementation of mothers during postpartum with nicotinamide riboside (NR) might improve health outcomes to mothers and offspring. MethodsMales impregnated female C57BL6 mice and Fisher 344 rats, who were fed a normal chow (NC) diet until they produced litters. At parturition, females were sorted into cages with pups, where they were either fed NC or NC supplemented with 3 grams of NR/kg of the diet. Lactation was measured at days 7, 14 & 21. Maternal weight change was measured from the day of parturition to the day of weaning. At weaning, offspring were moved to cages with NC. Some mothers and pups were sacrificed at day 14. Pups were analyzed at various times into adulthood for physiological, physical, neurodevelopmental and neurobehavioral phenotypes. ResultsWe discovered that postpartum rewires the maternal NAD system such that the liver NAD metabolome is depressed to circulate higher levels of NAD metabolites in blood. The mammary in a lactating dam is increased by > 20-fold in levels of NAD and NADP. When postpartum female rodents are supplemented with NR, they maintain their liver NAD metabolome and superinduce blood and mammary NAD while also circulating more prolactin. This superinduces mammary biosynthetic programs. NR-supplemented mothers produce more milk, are advantaged in post-gestational weight loss and produce larger weanlings than NC-fed mothers. Offspring of NR-supplemented mothers have striking advantages in glycemic control, motor activity and motor learning as juveniles. Adult offspring of NR-supplemented mothers retained greater physical capabilities, were less anxious, had less depressive-like behavior and greater spatial memory than offspring of NC-fed mothers. NR-supplemented mothers produce more BDNF in their milk and offspring of NR-supplemented mothers have an advantage in adult hippocampal neurogenesis. ConclusionsThe data show that NAD limits multiple maternal functions including lactation and expression of BDNF into milk and that improved maternal micronutrition has lasting neurodevelopmental, physical and neurobehavioral benefits to offspring. Funding SourcesChromaDex & Roy J Carver Trust. Supporting Tables, Images and/or Graphs▪

Why Is Mom Stressed: Homeorhesis as the Potential Problem and Nicotinamide Riboside as the Potential Solution

The remodeling of female mammalian physiology to support the development of a fertilized egg into an externally breathing individual and then to provide all the nutrition to this individual while remodeling back to nearly her pregestational state is without parallel in male mammalian physiological transitions. While it is common parlance to refer to postpartum depression as a not infrequent stress in women, the postpartum physiological changes after every birth constitute profound metabolic stresses that are understudied and have important nutritional, behavioral, and neurodevelopmental implications for the maternal and neonatal health of every mammalian species. We discovered that the postpartum liver of a lactating female mouse has a depressed nicotinamide adenine dinucleotide (NAD) metabolome linked to circulation of higher levels of NAD metabolites in support of a >20-fold increase in NAD coenzymes in the mammary. Furthermore, by supporting a new mother’s apparent higher demand for NAD precursors, we increased circulation of prolactin, superinduced mammary biosynthetic programs, increased her time of arched-back nursing, enhanced mammary production of brain-derived neurotrophic factor, promoted postgestational weight loss, advanced the neurobehavioral development of her offspring, and allowed them to mature as stronger and more resilient adults with advantages in hippocampal neurogenesis and body composition. These results show that a new mother’s capacity for biosynthesis and functionally important nurturing is apparently limited by NAD. Here, we discuss homeorhetic flow of resources from a new mother to her offspring in the context of NAD metabolism and suggest avenues for future investigation.

Brain bioenergetics and redox state measured by 31P magnetic resonance spectroscopy in unaffected siblings of patients with psychotic disorders

BackgroundBrain bioenergetic anomalies and redox dysregulation have been implicated in the pathophysiology of psychotic disorders. The present study examined brain energy-related metabolites and the balance between nicotinamide adenine dinucleotide metabolites (oxidized NAD+ and reduced NADH) using 31P-magnetic resonance spectroscopy (31P-MRS) in unaffected siblings, compared to first episode psychosis (FEP) patients and healthy controls. Methods21 unaffected siblings, 32 FEP patients (including schizophrenia spectrum and affective psychoses), and 21 controls underwent 31P-MRS in the frontal lobe (6×6×4cm3) on a 4T MR scanner, using custom-designed dual-tuned surface coil with outer volume suppression. Brain parenchymal pH and steady-state metabolite ratios of high energy phosphate compounds were measured. NAD+ and NADH levels were determined using a 31P-MRS fitting algorithm. 13 unaffected sibling-patient pairs were related; other patients and siblings were unrelated. ANCOVA analyses were used to examine 31P-MRS measures, with age and gender as covariates. ResultsThe phosphocreatine/adenosine triphosphate ratio was significantly reduced in both unaffected siblings and FEP patients, compared to controls. NAD+/NADH ratio was significantly reduced in patients compared to siblings and controls, with siblings showing a reduction in NAD+/NADH compared to controls that was not statistically significant. Compared to patients and controls, siblings showed significantly reduced levels of NAD+. Siblings did not differ from patients or controls on brain pH. DiscussionOur results indicate that unaffected siblings show some, but not all the same abnormalities in brain energy metabolites and redox state as FEP patients. Thus, 31P-MRS studies may identify factors related both to risk and expression of psychosis.

Mitochondrial NAD(P)H In vivo: Identifying Natural Indicators of Oxidative Phosphorylation in the (31)P Magnetic Resonance Spectrum.

Natural indicators provide intrinsic probes of metabolism, biogenesis and oxidative protection. Nicotinamide adenine dinucleotide metabolites (NAD(P)) are one class of indicators that have roles as co-factors in oxidative phosphorylation, glycolysis, and anti-oxidant protection, as well as signaling in the mitochondrial biogenesis pathway. These many roles are made possible by the distinct redox states (NAD(P)+ and NAD(P)H), which are compartmentalized between cytosol and mitochondria. Here we provide evidence for detection of NAD(P)+ and NAD(P)H in separate mitochondrial and cytosol pools in vivo in human tissue by phosphorus magnetic resonance spectroscopy (31P MRS). These NAD(P) pools are identified by chemical standards (NAD+, NADP+, and NADH) and by physiological tests. A unique resonance reflecting mitochondrial NAD(P)H is revealed by the changes elicited by elevation of mitochondrial oxidation. The decline of NAD(P)H with oxidation is matched by a stoichiometric rise in the NAD(P)+ peak. This unique resonance also provides a measure of the improvement in mitochondrial oxidation that parallels the greater phosphorylation found after exercise training in these elderly subjects. The implication is that the dynamics of the mitochondrial NAD(P)H peak provides an intrinsic probe of the reversal of mitochondrial dysfunction in elderly muscle. Thus, non-invasive detection of NAD(P)+ and NAD(P)H in cytosol vs. mitochondria yields natural indicators of redox compartmentalization and sensitive intrinsic probes of the improvement of mitochondrial function with an intervention in human tissues in vivo. These natural indicators hold the promise of providing mechanistic insight into metabolism and mitochondrial function in vivo in a range of tissues in health, disease and with treatment.

From Eggs to Hearts: What Is the Link between Cyclic ADP‐Ribose and Ryanodine Receptors?

It was first proposed that cyclic ADP-ribose (cADPR) could activate ryanodine receptors (RyR) in 1991. Following a subsequent report that cADPR could activate cardiac RyR (RyR2) reconstituted into artificial membranes and stimulate Ca(2+) -release from isolated cardiac SR, there has been a steadily mounting stockpile of publications proclaiming the physiological and pathophysiological importance of cADPR in the cardiovascular system. It was only 2 years earlier, in 1989, that cADPR was first identified as the active metabolite of nicotinamide adenine dinucleotide (NAD), responsible for triggering the release of Ca(2+) from crude homogenates of sea urchin eggs. Twenty years later, can we boast of being any closer to unraveling the mechanisms by which cADPR modulates intracellular Ca(2+) -release? This review sets out to examine the mechanisms underlying the effects of cADPR and ask whether cADPR is an important signaling molecule in the heart.

Accumulation of poly(ADP-ribose) polymerase inhibitors in children with chronic renal failure

Nicotinamide, N-methyl-2-pyridone-5-carboxamide (Met2PY) and N-methyl-4-pyridone-3-carboxamide (Met4PY) are biological metabolites of the intracellular coenzyme nicotinamide adenine dinucleotide (NAD) that can potentially inhibit poly(ADP-ribose) polymerase 1 (PARP-1; DNA repair enzyme). Our research was aimed at establishing whether chronic renal failure (CRF) in children leads to the elevation of plasma NAD metabolites sufficient to inhibit PARP-1 activity. Nicotinamide, Met2PY and Met4PY plasma and erythrocyte concentrations were measured in 25 children with CRF and in 19 healthy children. The effect of these NAD metabolites on PARP-1 activity was studied in vitro. We found that plasma concentration of all NAD metabolites (nicotinamide, Met2PY, Met4PY) in children with CRF could reach the concentration of 2, 30 and 10 microM as compared to 0.2, 1 and 0.5 microM, respectively, in healthy children. The concentration of nicotinamide metabolites correlated positively with plasma creatinine concentration and negatively with creatinine clearance in children with CRF. We found that Met2PY, Met4PY and nicotinamide inhibited in vitro PARP-1 activity with IC50 values of 2.1, 0.18 and 0.12 mM, respectively. Our data indicate that NAD metabolites accumulate in plasma of children with CRF and their combined effect could lead to the inhibition of PARP-1 activity. NAD metabolites could be particularly harmful in children due to higher DNA turnover than in adults.

Calcium-Induced Calcium Release and Cyclic ADP-Ribose-Mediated Signaling in the Myocytes from Small Coronary Arteries

Cyclic ADP-ribose (cADPR), an endogenous metabolite of nicotinamide adenine dinucleotide, was first reported to be present in sea urchin eggs and to possess Ca mobilizing activity (Clapper et al., 1987; Lee et al., 1989). Recent studies have indicated that cADPR is produced in a variety of mammalian tissues and cells, including heart, liver, spleen, brain and red blood cells, pituitary cells, as well as renal epithelial cells (Beers et al., 1995; Koshiyama et al., 1991; Takesawa et al., 1993; White et al., 1993). Basal concentrations of cADPR in cardiac muscle, liver, and brain are estimated to be 100–200 nM (Galione, 1994; Lee, 1994). Like sea urchin eggs, cADPR also causes Ca release from the endoplasmic reticulum in these mammalian tissues and cells. It mobilizes intracellular Ca by a mechanism completely independent of inositol 1,4,5trisphosphate (IP3), since the IP3 receptor antagonist heparin cannot block the effect of cADPR (Galione,

7-Deaza cyclic adenosine 5′-diphosphate ribose: first example of a Ca 2+-mobilizing partial agonist related to cyclic adenosine 5′-diphosphate ribose

Cyclic adenosine 5'-diphosphate ribose (cADPR), a naturally occurring metabolite of nicotinamide adenine dinucleotide (NAD+), mobilizes Ca2+ from non-mitochondrial stores in a variety of mammalian and invertebrate tissues. It has been shown that cADPR activates ryanodine-sensitive Ca(2+)-release channels, working independently of inositol 1,4,5-trisphosphate (IP3) to mobilize intracellular Ca2+ stores. In some systems, cADPR has been shown to be more potent than IP3. The chemo-enzymatic synthesis of structurally modified analogues of cADPR can provide pharmacological tools for probing this new Ca(2+)-signaling pathway. In this work, we describe the synthesis and evaluation of a structural mimic of cADPR with different Ca(2+)-releasing properties. 7-Deaza cyclic adenosine 5'-diphosphate ribose (7-deaza cADPR), a novel cADPR analogue modified in the purine ring, was synthesized and its ability to release Ca2+ from non-mitochondrial pools in homogenates made from sea urchin eggs was investigated. 7-Deaza cADPR was more effective in releasing Ca2+ than cADPR, but it only released approximately 66% of the Ca2+ released by a maximal concentration of cADPR. It was also more resistant to hydrolysis than cADPR. If we administered increasing concentrations of 7-deaza cADPR at the same time as a maximal concentration of cADPR, the induction of Ca2+ release by cADPR was antagonized. 7-Deaza cADPR has a Ca(2+)-release profile consistent with that of a partial agonist, and it is the first reported example of such a compound to act at the cADPR receptor. The imidazole ring of cADPR is clearly important in stimulating the Ca(2+)-release machinery, and the present results demonstrate that structural modification of a site other than position 8 of the purine ring can affect the efficacy of Ca2+ release. 7-Deaza cADPR represents a significant step forwards in designing modulators of the cADPR signaling pathway.

Characterization of cyclic adenosine diphosphate-ribose-induced Ca2+ release in T lymphocyte cell lines.

Ca2+ release from intracellular stores is one of the major events transducing extracellular signals into living cells. Recently, a metabolite of nicotinamide adenine dinucleotide+ (NAD+), termed "cyclic adenosine diphosphate-ribose" (cADPr), has been described to release Ca2+ from caffeine-sensitive internal stores of cells. Jurkat T cells possess intracellular Ca2+ stores sensitive to caffeine, so a potential involvement of cADPr in Ca2+ signaling was investigated. cADPr released Ca2+ in a dose-dependent manner from intracellular stores of permeabilized Jurkat T cells. Half maximal release was obtained at 2.25 microM cADPr. Prior addition of D-myo-inositol 1,4,5-trisphosphate (Ins(1,4,5)P3) or thapsigargin did not influence cADPr-induced Ca2+ release, indicating the presence of different Ca2+ pools sensitive to Ins(1,4,5)P3 and cADPr. The specificity of the response was confirmed using the inhibitors ruthenium red, 8-NH2-cADPr, and 8-Br-cADPr. All three compounds blocked cADPr-induced, but not Ins(1,4,5)P3-induced, Ca2+ release in a dose-dependent manner. Cyclic GMP (cGMP)-induced Ca2+ release was also partly antagonized by ruthenium red, indicating involvement of a cGMP-dependent step in the formation of cADPr. The presence of endogenous cADPr was analyzed directly by HPLC. Sequential separation on strong anion exchange HPLC and reverse-phase, ion-pair HPLC resulted in a single symmetric peak co-eluting with standard cADPr. The identity of this endogenous material was further confirmed by its ability to release Ca2+ in saponin-permeabilized Jurkat T cells.

Functional Expression of Soluble Forms of Human CD38 in Escherichia coli and Pichia pastoris

Cyclic adenosine diphosphate (ADP)-ribose (cADPR), a metabolite of nicotinamide adenine dinucleotide (NAD +), mobilizes calcium from intracellular stores in many cells, The synthesis of cADPR from NAD(+) and its subsequent hydrolysis to ADPR is catalyzed by an ADP-ribosyl cyclase and a cADPR hydrolase, respectively, The ADP-ribosyl cyclase cloned from the ovotestis of the marine invertebrate Aplysia californica has amino acid sequence homology to the human lymphocyte surface antigen CD38, CD38 has been shown to catalyze both the formation and the hydrolysis of cADPR. In this study, we produced soluble, enzymatically active CD38 using recombinant expression techniques in bacteria and yeast, We engineered a gene coding for a soluble form of CD38 by excision of the region of the gene coding for the N-terminal amino acids representing the putative membrane spanning sequence and short putative intracellular sequence. For expression in bacteria ( Escherichia coli), this construct was cloned into the pFlag-1 plasmid which allows induced, periplasmic expression and relatively simple purification of the soluble CD38, For expression in yeast ( Pichia pastoris) the CD38 sequence was further modified to eliminate four putative N-linked glycosylation sites and the resulting construct was expressed as a secreted protein, Both systems produce soluble enzymes of approximately 30 kDa and both recombinant enzymes display similar cyclase and hydrolase activities.

Cyclic ADP-ribose, the ADP-ribosyl cyclase pathway and calcium signalling

Cyclic adenosine diphosphate-ribose, an endogenous metabolite of nicotinamide adenine dinucleotide was first characterized as a potent Ca 2+ mobilizing agent in sea urchin eggs. Mounting evidence points to it being an endogenous activator of Ca 2+-induced Ca 2+ release by non-skeletal muscle ryanodine receptors in several invertebrate and mammalian cell types. Cyclic adenosine diphosphate-ribose is synthesized by adenosine diphosphate-ribosyl cyclases, which have been found to be widespread enzymes. Recent data suggests that cyclic adenosine diphosphate-ribose may function as a second messenger in sea urchin eggs at fertilization and in stimulus secretion coupling in pancreatic β-cells. A second messenger role for cyclic adenosine diphosphate-ribose requires that its intracellular levels be under the control of extracellular stimuli. Another second messenger, cGMP, stimulates the synthesis of cyclic adenosine diphosphate-ribose from nicotinamide adenine dinucleotide by activating the adenosine diphosphate-ribosyl cyclase pathway in sea urchin eggs and egg homogenates, suggesting that cyclic adenosine diphosphate-ribose may be an intracellular messenger for cell surface receptors or nitric oxide, which activate cGMP-producing guanylate cyclases. Cyclic adenosine diphosphate-ribose may have a similar role to inositol trisphosphate in controlling intracellular calcium signalling with these two calcium-mobilizing second messengers activating ryanodine receptors and inositol trisphosphate receptors respectively.

Formation and Hydrolysis of Cyclic ADP-Ribose Catalyzed by Lymphocyte Antigen CD38

CD38 is a 42-kilodalton glycoprotein expressed extensively on B and T lymphocytes. CD38 exhibits a structural homology to Aplysia adenosine diphosphate (ADP)-ribosyl cyclase. This enzyme catalyzes the synthesis of cyclic ADP-ribose (cADPR), a metabolite of nicotinamide adenine dinucleotide (NAD+) with calcium-mobilizing activity. A complementary DNA encoding the extracellular domain of murine CD38 was constructed and expressed, and the resultant recombinant soluble CD38 was purified to homogeneity. Soluble CD38 catalyzed the formation and hydrolysis of cADPR when added to NAD+. Purified cADPR augmented the proliferative response of activated murine B cells, potentially implicating the enzymatic activity of CD38 in lymphocyte function.

Synthesis and Degradation of Cyclic ADP-Ribose by NAD Glycohydrolases

Cyclic adenosine diphosphoribose (cADPR), a recently discovered metabolite of nicotinamide adenine dinucleotide (NAD), is a potent calcium-releasing agent postulated to be a new second messenger. An enzyme that catalyzes the synthesis of cADPR from NAD and the hydrolysis of cADPR to ADP-ribose (ADPR) was purified to homogeneity from canine spleen microsomes. The net conversion of NAD to ADPR categorizes this enzyme as an NAD glycohydrolase. NAD glycohydrolases are ubiquitous membrane-bound enzymes that have been known for many years but whose function has not been identified. The results presented here suggest that these enzymes may function in the regulation of calcium homeostasis by the ability to synthesize and degrade cADPR.

Calcium Mobilization by Dual Receptors During Fertilization of Sea Urchin Eggs

Fertilization is accompanied by a transient increase in the concentration of intracellular Ca2+, which serves as a signal for initiating development. Some of the Ca2+ appears to be released from intracellular stores by the binding of inositol trisphosphate (IP3) to its receptor. However, in sea urchin eggs, other mechanisms appear to participate. Cyclic adenosine diphosphate--ribose (cADPR), a naturally occurring metabolite of nicotinamide adenine dinucleotide, is as potent as IP3 in mobilizing Ca2+ in sea urchin eggs. Experiments with antagonists of the cADPR and IP3 receptors revealed that both Ca2+ mobilizing systems were activated during fertilization. Blockage of either of the systems alone was not sufficient to prevent the sperm-induced Ca2+ transient. This study provides direct evidence for a physiological role of cADPR in the Ca2+ signaling process.