NAD+ metabolism: A therapeutic target for age-related metabolic disease

Abstract

Nicotinamide adenine dinucleotide (NAD) is a central metabolic cofactor by virtue of its redox capacity, and as such regulates a wealth of metabolic transformations. However, the identification of the longevity protein silent regulator 2 (Sir2), the founding member of the sirtuin protein family, as being NAD⁺-dependent reignited interest in this metabolite. The sirtuins (SIRT1-7 in mammals) utilize NAD⁺ to deacetylate proteins in different subcellular compartments with a variety of functions, but with a strong convergence on optimizing mitochondrial function. Since cellular NAD⁺ levels are limiting for sirtuin activity, boosting its levels is a powerful means to activate sirtuins as a potential therapy for mitochondrial, often age-related, diseases. Indeed, supplying excess precursors, or blocking its utilization by poly(ADP-ribose) polymerase (PARP) enzymes or CD38/CD157, boosts NAD⁺ levels, activates sirtuins and promotes healthy aging. Here, we discuss the current state of knowledge of NAD⁺ metabolism, primarily in relation to sirtuin function. We highlight how NAD⁺ levels change in diverse physiological conditions, and how this can be employed as a pharmacological strategy.     

Mitochondrial cyclophilin-D as a potential therapeutic target for post-myocardial infarction heart failure

The pharmacological inhibition or genetic ablation of cyclophilin-D (CypD), a critical regulator of the mitochondrial permeability transition pore (mPTP), confers myocardial resistance to acute ischemia-reperfusion injury, but its role in post-myocardial infarction (MI) heart failure is unknown. The aim of this study was to determine whether mitochondrial CypD is also a therapeutic target for the treatment of post-MI heart failure. Wild-type (WT) and CypD(-/-) mice were subjected to either sham surgery or permanent ligation of the left main coronary artery to induce MI, and were assessed at either 2 or 28 days to determine the long-term effects of CypD ablation. After 2 days, myocardial infarct size was smaller and left ventricular (LV) function was better preserved in CypD(-/-) mice compared to WT mice. After 28 days, when compared to WT mice, in the CypD(-/-) mice, mortality was halved, myocardial infarct size was reduced, LV systolic function was better preserved, LV dilatation was attenuated and in the remote non-infarcted myocardium, there was less cardiomyocyte hypertrophy and interstitial fibrosis. Finally, ex vivo fibroblast proliferation was found to be reduced in CypD(-/-) cardiac fibroblasts, and in WT cardiac fibroblasts treated with the known CypD inhibitors, cyclosporin-A and sanglifehrin-A. Following an MI, mice lacking CypD have less mortality, smaller infarct size, better preserved LV systolic function and undergo less adverse LV remodelling. These findings suggest that the inhibition of mitochondrial CypD may be a novel therapeutic treatment strategy for post-MI heart failure.     

Effects of iloprost,a PGI2 derivative,on ischemic myocardial energy and carbohydrate metabolism in dogs

Effects of iloprost, which is a stable prostacyclin analogue, on the ischemic myocardium were examined in the open-chest dog heart, in terms of biochemical parameters. Ischemia was initiated by ligating the left anterior descending coronary artery. When the coronary artery was ligated for 3 min, the levels or glycogen, fructose-1,6-diphosphate (FDP), adenosine triphosphate and creatinephosphate decreased, and the levels of glucose-6-phosphate (G6P), fructose-6-phosphate (F6P), lactate, adenosine diphosphate and adenosine monophosphate increased. During ischemia, therefore, energy charge potential was significantly decreased from 0.89±0.01 to 0.82±0.01, and ([G6P]+[F6P])/[FDP] and [lactate]/[pyruvate] ratios were significantly increased from 1.75±0.30 to 29.05±5.70 and 13±3 to 393±112, respectively. Iloprost (0.1, 0.3, or 1 g·kg^–1) was injected intravenously 5 min before the onset of ischemia. Iloprost (0.1, 0.3, and 1 g·kg^–1) reduced the ischemia-induced decrease in energy charge potential to 94, 74, and 86%, respectively, the increase in ([G6P]+[F6P]/[FDP] to 38, 29, 32%, respectively, and the increase in [lactate]/[pyruvate] to 67, 45, 65%, respectively. These results suggest that iloprost lessens the myocardial metabolic derangements produced by ischemia, and the most potent effect was obtained at the dose of 0.3 g·kg^–1.     

ICAM-1 in acute myocardial infarction: a potential therapeutic target

Current treatments for AMI centre on prompt restoration of epicardial coronary blood flow. Despite improvements, AMI is still associated with significant morbidity and mortality. Novel approaches are therefore keenly sought. Intercellular adhesion molecule-1 (ICAM-1, CD54) is a member of the immunoglobulin superfamily. It is implicated in neutrophil and monocyte-endothelial cell adhesion, processes contributing to myocardial neutrophil infiltration and microvascular coronary slow flow, both viewed as important to the pathophysiologic responses in AMI. ICAM-1 would therefore appear an important potential therapeutic target in this context, and is the subject of this review.     

Free fatty acid metabolism during myocardial ischemia and reperfusion

Long chain free fatty acids (FFA) are the preferred metabolic substrates of myocardium under aerobic conditions. However, under ischemic conditions long chain FFA have been shown to be harmful both clinically and experimentally. Serum levels of free fatty acids frequently are elevated in patients with myocardial ischemia. The proposed mechanisms of the detrimental effects of free fatty acids include: (1) accumulation of toxic intermediates of fatty acid metabolism, such as long chain acyl-CoA thioesters and long chain acylcarnitines, (2) inhibition of glucose utilization, particularly glycolysis, during ischemia and/or reperfusion, and (3) uncoupling of oxidative metabolism from electron transfer. The relative importance of these mechanisms remains controversial. The primary site of FFA-induced injury appears to be the sarcolemmal and intracellular membranes and their associated enzymes. Inhibitors of free fatty acid metabolism have been shown experimentally to decrease the size of myocardial infarction and lessen postischemic cardiac dysfunction in animal models of regional and global ischemia. The mechanism by which FFA inhibitors improve cardiac function in the postischemic heart is controversial. Whether the effects are dependent on decreased levels of long chain intermediates and/or enhancement of glucose utilization is under investigation. Manipulation of myocardial fatty acid metabolism may prove beneficial in the treatment of myocardial ischemia, particularly during situations of controlled ischemia and reperfusion, such as percutaneous transluminal coronary angioplasty and coronary artery bypass grafting. (Mol Cell Biochem 166: 85-94, 1997)     

Glutamate metabolism in cerebral mitochondria after ischemia and post‐ischemic recovery during aging: relationships with brain energy metabolism

Glutamate is involved in cerebral ischemic injury, but its role has not been completely clarified and studies are required to understand how to minimize its detrimental effects, contemporarily boosting the positive ones. In fact, glutamate is not only a neurotransmitter, but primarily a key metabolite for brain bioenergetics. Thus, we investigated the relationships between glutamate and brain energy metabolism in an in vivo model of complete cerebral ischemia of 15 min and during post‐ischemic recovery after 1, 24, 48, 72, and 96 h in 1‐year‐old adult and 2‐year‐old aged rats. The maximum rates (V _max) of glutamate dehydrogenase (GlDH ), glutamate‐oxaloacetate transaminase, and glutamate‐pyruvate transaminase were assayed in somatic mitochondria (FM ) and in intra‐synaptic ‘Light’ mitochondria and intra‐synaptic ‘Heavy’ mitochondria ones purified from cerebral cortex, distinguishing post‐ and pre‐synaptic compartments. During ischemia, none of the enzymes were modified in adult animals. In aged ones, glutamate‐oxaloacetate transaminase was increased in FM and GlDH in intra‐synaptic ‘Heavy’ mitochondria, stimulating glutamate catabolism. During post‐ischemic recovery, FM did not show modifications at both ages while, in intra‐synaptic mitochondria of adult animals, glutamate catabolism was increased after 1 h of recirculation and decreased after 48 and 72 h, whereas it remained decreased up to 96 h in aged rats. These results, with those previously published about Krebs’ cycle and Electron Transport Chain (Villa et al ., [2013] Neurochem. Int . 63, 765–781), demonstrate that: (i) V _max of energy‐linked enzymes are different in the various cerebral mitochondria, which (ii) respond differently to ischemia and post‐ischemic recovery, also (iii) with respect to aging.

     

The pyruvate dehydrogenase complex as a therapeutic target for age-related diseases

Considerable research has been conducted on mitochondrial biology as it pertains to aging. However, relatively little attention has been accorded the pyruvate dehydrogenase complex (PDC) relative to how we grow old and acquire age-related diseases. The purpose of this review is threefold: first, to describe the physiological chemistry of the PDC and define its place in normal cellular bioenergetics; second, to compare and contrast the pathogenesis and clinical features of congenital PDC deficiency with discrete examples of age-associated dysfunction of the complex; and third, to summarize recent findings in Caenorhabditis elegans that shed additional new light on the significance of the PDC to the aging process.     

大鼠心肌整体缺血及离体再灌注致生物膜的损伤作用

目的和方法：利用整体大鼠异丙肾上腺素损伤（ISO）和离体大鼠全心停灌／再灌（I／R）两种模型,观察了心肌缺血和缺血／再灌注对心肌生物膜－线粒体膜及肌纤维膜损伤的影响。结果：ISO（5mg/kg,皮下注射）和I／R（20min/20min)可导致大鼠心脏生物膜产生严重损伤,表现为心肌线粒体脂质过氧化产物明显增加,线粒体磷脂酶A2（PLA2）激活,从而导致线粒体膜磷脂（PL）含量减少,磷脂分解产物游离脂肪酸（FFA）增加,膜脂流动性（LFU）降低,线粒体Ca^2 -ATPase及肌纤维膜Na^ ,K^ -ATPase活性降低,线粒体呼吸功能降低、呼吸链氧化磷酸化解偶联,高能磷酸化合物生成减少。结论：整体ISO和离体I／R可导致大鼠心肌线粒体、肌纤维膜结构和功能损伤。     

Dihydrofolate reductase as a therapeutic target

The folate antagonists are an important class of therapeutic compounds, as evidenced by their use as antiinfective, antineoplastic, and antiinflammatory drugs. Thus far, all of the clinically useful drugs of this class have been inhibitors of dihydrofolate reductase (DHFR), a key enzyme in the synthesis of thymidylate, and therefore, of DNA. The basis of the antiinfective selectivity of these compounds is clear; the antifolates trimethoprim and pyrimethamine are potent inhibitors of bacterial and protozoal DHFRs, respectively, but are only weak inhibitors of mammalian DHFRs. These species-selective agents apparently exploit the differences in the active site regions of the parasite and host enzymes. Methotrexate is the DHFR inhibitor used most often in a clinical setting as an anticancer drug and as an antiinflammatory and immunosuppressive agent. Considerable progress has been made recently in understanding the biochemical basis for the selectivity of this drug and the biochemical mechanism (or mechanisms) responsible for the development of resistance to treatment with the drug. This understanding has led to a new generation of DHFR inhibitors that are now in clinical trials.     

CD38 as a therapeutic target

The CD38 molecule is well represented on cell surfaces in many cases of a variety of lymphoid tumors, notably multiple myeloma, AIDS-associated lymphomas, and post-transplant lymphoproliferations. As such, this molecule is a promising target for antibody therapy. After early disappointments, improved anti-CD38 antibodies of strong cytolytic potential have been described by 3 groups. First, a human IgG monoclonal anti-CD38 antibody raised in mice transgenic for human Ig has been found to induce potent complement and cellular cytotoxicities against both myeloma cell lines and fresh harvests from myeloma marrow and leukemic blood. This antibody also exhibits the singular property of inhibiting the CD38 cyclase activity. Second, a series of CD38-specific human antibodies, with high affinities and high ADCC activities against cell lines and primary cultures of myeloma, has been selected from a unique phage-display library. Finally, to enhance specificity for myeloma cells, bispecific domain antibodies targeting both CD38 and CD138 have been developed. As they lack any Fc module, these constructs rely on cytotoxicity for delivering a toxin to tumor cells. The list of candidate CD38-bearing neoplasms as targets for these antibody constructs can now be expanded to include acute promyelocytic leukemia, and possibly other myeloid leukemias, in which surface CD38 can be induced by retinoid treatment. One caveat here is that evidence has been produced to suggest that CD38 promotes pulmonary manifestations of the hazardous retinoic acid syndrome.     

Evaluating DAPK as a therapeutic target

Death associated protein kinase 1 (DAPK) is an important serine/theoreine kinase involved in various cellular processes such as apoptosis, autophagy and inflammation. DAPK expression and activity are misregulated in multiple diseases including cancer, neuronal death, stoke, et al. Methylation of the DAPK gene is common in many types of cancer and can lead to loss of DAPK expression. In this review, we summarize the pathological status and functional roles of DAPK in disease and compare the published reagents that can manipulate the expression or activity of DAPK. The pleiotropic functions of DAPK make it an intriguing target and the barriers and opportunities for targeting DAPK for future clinical application are discussed.     

Mammalian target of rapamycin as a therapeutic target in leukemia

Reflecting its critical role in integrating cell growth and division with the cellular nutritional environment, the mammalian target of rapamycin *(mTOR) is a highly conserved downstream effector of the phosphatidylinositol 3-kinase (PI3K)/Akt (protein kinase B) signaling pathway. mTOR activates both the 40S ribosomal protein S6 kinase (p70s6k) and the eukaryotic initiation factor 4E-binding protein-1. As a consequence of inhibiting its downstream messengers, mTOR inhibitors prevent cyclin-dependent kinase (CDK) activation, inhibit retinoblastoma protein phosphorylation, and accelerate the turnover of cyclin D1, leading to a deficiency of active CDK4/cyclin D1 complexes, all of which may help cause GI phase arrest. Constitutive activation of the PI3K/Akt kinases occur in human leukemias. FLT3, VEGF, and BCR-ABL mediate their activities via mTOR. New rapamycin analogs including CCI-779, RAD001, and AP23573, are entering clinical studies for patients with hematologic malignancies.     

Cardiac telocytes were decreased during myocardial infarction and their therapeutic effects for ischaemic heart in rat

Recently, cardiac telocytes were found in the myocardium. However, the functional role of cardiac telocytes and possible changes in the cardiac telocyte population during myocardial infarction in the myocardium are not known. In this study, the role of the recently identified cardiac telocytes in myocardial infarction (MI) was investigated. Cardiac telocytes were distributed longitudinally and within the cross network of the myocardium, which was impaired during MI. Cardiac telocytes in the infarction zone were undetectable from approximately 4 days to 4 weeks after an experimental coronary occlusion was used to induce MI. Although cardiac telocytes in the non‐ischaemic area of the ischaemic heart experienced cell death, the cell density increased approximately 2 weeks after experimental coronary occlusion. The cell density was then maintained at a level similar to that observed 1–4 days after left anterior descending coronary artery (LAD)‐ligation, but was still lower than normal after 2 weeks. We also found that simultaneous transplantation of cardiac telocytes in the infarcted and border zones of the heart decreased the infarction size and improved myocardial function. These data indicate that cardiac telocytes, their secreted factors and microvesicles, and the microenvironment may be structurally and functionally important for maintenance of the physiological integrity of the myocardium. Rebuilding the cardiac telocyte network in the infarcted zone following MI may be beneficial for functional regeneration of the infarcted myocardium.     

Neuroprotection by estrogen in the brain: the mitochondrial compartment as presumed therapeutic target

Neuroprotection by estrogen in the CNS is well-documented and comprises the intricate regulation of cell–cell communication between neurons and supportive non-neuronal glial cells. It is assumed that these interactions are essential for cell survival under pathological and toxic conditions by regulating the allocation of trophic molecules, e.g., growth factors, controlling relevant intracellular anti-apoptotic and death cascades, and attenuating inflammatory processes. Malfunction and disturbance of mitochondria are doubtlessly associated with brain cell degeneration during neurotoxic and neurodegenerative processes. Estrogen has been documented as protective agent in the brain by stimulating growth factor supply and cell-intrinsic pro-/anti-apoptotic signaling pathways. In recent years, an additional estrogen-dependent safe-guarding strategy comes into the focus of neuronal protection. The mitochondrial compartment appears to be regulated by estrogen at the level of ATP and reactive oxygen species production as well as under a structural-functional viewpoint. In the present article, we would like to highlight recent data which demonstrate that sex steroids can directly and indirectly interfere with mitochondrial properties via non-nuclear, presumably mitochondria-intrinsic and nuclear signaling mechanisms. This enables mitochondria to cope with pathological processes and provide stabile local energy homeostasis and an anti-apoptotic base setting in the brain which, in turn, is a prerequisite for neuronal survival.     

SIK2对心肌缺血/再灌注损伤大鼠能量代谢的影响及其机制*

目的: 探究盐诱导激酶2(SIK2)对大鼠心肌能量代谢的影响及其机制。方法: 通过结扎冠脉左前降支建立大鼠急性心梗模型,实验分为假手术组(Sham)、缺血再灌注组(I/R)、SIK2抑制组(I/R+Bosutinib)(10 mg/kg处理24 h)。心脏超声检测各组大鼠心脏结构和功能;HE染色观察大鼠心肌细胞病理学变化;ELISA检测各组大鼠心肌组织中腺苷三磷酸(ATP)、乳酸(LA)的含量;蛋白印迹法(WB)检测各组大鼠心肌组织中SIK2、p-DRP1(Ser616)、DRP1、p-AKT、AKT、p-mTOR、mTOR蛋白表达水平。结果: 与Sham组相比,I/R组心肌细胞病理损伤加重且SIK2蛋白表达增加(P<0.05);与I/R组相比,I/R+Bosutinib组SIK2表达降低且心肌病理损伤减轻。与Sham组相比,I/R组LVEF、FS降低(P<0.05);与I/R组相比,I/R+Bosutinib组LVEF、FS增高(P< 0.05),各组IVS、LVPW无明显差异(P>0.05)。与Sham组相比,I/R组ATP含量减少,LA含量增加(P<0.05),与I/R组相比,I/R+Bosutinib组ATP含量增加,LA含量减少(P<0.05)。与Sham组相比,I/R组p-DRP1(Ser616)表达增多,p-AKT、p-mTOR蛋白表达减少(P<0.05);与I/R组相比,I/R+Bosutinib组p-DRP1(Ser616)蛋白表达减少,p-AKT、p-mTOR蛋白表达增多(P<0.05);各组mTOR、AKT、DRP1蛋白无明显差异(P>0.05)。结论: SIK2可能通过AKT/mTOR信号通路及促进线粒体裂变抑制能量代谢,抑制SIK2可提高心肌能量代谢水平进而减轻心肌缺血/再灌注损伤。