Blood NAD levels are reduced in very old patients hospitalized for heart failure

Highlights

• NAD coenzyme is a key player in energy metabolism and signaling that isdepleted in many tissues with aging

• Blood NAD levels measured in a healthy population of 151 voluntary donors aged 19 to 68 years was 23.4 (SD 4.05) μmol/L

• Correlation between blood NAD levels and age differed between males and females with a trend toward reduction in males only

• Blood NAD levels were lower in elderly patients hospitalized for heart failure with a mean at 20.7 (SD 3.6) μmol/L (p=0.007)

• Our study suggests that administration of NAD precursors to this type of patients should be tested for clinical benefits

Abstract

Background

Age-associated decline in nicotinamide adenine dinucleotide (NAD) tissue levels has emerged as potential driving mechanism in the establishment of energy metabolism perturbations in the context of chronic diseases, notably heart failure.

Objective

The aim of this study was to measure the blood NAD levels in a healthy blood donor population and in a population of elderly patients hospitalized for decompensated heart failure.

Method

Whole blood sample was collected from 151 healthy voluntary blood donors, aged 19 to 68 years, and from 19 patients aged 75 to 101 years and hospitalized for decompensated heart failure in a geriatric ward. Metabolites were extracted by the hot buffered ethanol procedure and NAD was quantified in triplicate for each sample.

Results

The mean concentration of NAD in blood of healthy donors was 23.4 (SD 4.05) μmol/L. There was no significant correlation between NAD levels and donors' age nor sex in the healthy population when studied as a whole. However, the linear regression curves of NAD concentration plotted against age differed between males and females (p = 0.0283) with a trend in males to decline with age that was not observed in females. The mean concentration of NAD in whole blood samples of the geriatric population was 20.7 (SD 3.6) μmol/L (p = 0.007 versus the healthy blood donor population). There were no differences between males and females (p = 0.7) nor between patients with ejection fraction inferior or superior to 50% (p = 0.86) in the geriatric population.

Conclusion

This study highlighted a diminution of NAD blood levels for elderly patients hospitalized for decompensated heart failure in comparison to a healthy population, suggesting that new therapeutics to restore NAD stock and energy metabolism would be a major progress in the management of this type of geriatric patients.

Introduction

Aging is characterized by a progressive decline in the ability of bioenergetic systems to sustain body needs due notably to systemic metabolic imbalance and mitochondrial dysfunction at the tissue level (Jang et al., 2018). Age-associated decline in nicotinamide adenine dinucleotide (NAD) tissue levels has recently emerged as a potential driving mechanism in the establishment of energy metabolism perturbations in the context of aging and in chronic degenerative diseases (Yaku et al., 2018; Lee et al., 2019). NAD is a major electron carrier coenzyme for all energy substrates oxidation, including glucose, fatty acids and ketone bodies. In its reduced form, NADH coenzyme is the major electron donor to the mitochondrial electron transport chain, providing the energy required to build the proton gradient in the mitochondrial intermembrane space whose driving force is used in turn by the ATP synthase to generate ATP. In its phosphorylated NADP(H) is the major coenzyme for reactive oxygen species (ROS) detoxification systems. In all these processes in which NAD(P) is used as a coenzyme, the total pool of NAD(P), i.e. the sum of oxidized NAD(P)⁺ and reduced NAD(P)H, is not changed.

However, in its oxidized form, NAD⁺ is also used as a substrate by a number of signaling pathways that regulate energy metabolism at the transcriptional and enzymatic levels (Sirtuins 1 to 7), the repair of DNA lesions induced by ROS (PARP1) or Ca²⁺ release from intracellular stores, notably the sarco-endoplasmic reticulum (CD38 ADPribose cyclase) (Mericskay, 2016). All these signaling pathways irreversibly cleave the NAD⁺ molecule into nicotinamide and ADP-ribose moieties. In physiological condition, the steady-state tissue level of total NAD (sum of NAD⁺ and NADH) is maintained through compensative NAD biosynthetic pathways. These pathways start with different precursors that include the tryptophane amino acid through the de novo pathway or the vitamins B3, i.e. the nicotinamide, the nicotinic acid and the nicotinamide riboside through three different salvage pathways (Belenky et al., 2007). In the body, the heart is a major energy consuming organ that is able to use all kind of substrates, including glucose, fatty acids and ketone bodies, all of them relying on NAD⁺ coenzyme to be oxidized. Mitochondrial oxidative metabolism represents the major source of ATP production in the cardiac cells and contains a major fraction of the NAD pool. In heart disease, a severe mitochondrial dysfunction occurs and there is a mismatch between the energy demand and bioenergetic capacities of the myocardium (Zhou and Tian, 2018). In chronic heart failure, the elevated cytosolic concentration of sodium (Na⁺) in the failing myocytes accelerates Ca²⁺ efflux via mitochondrial Na⁺/Ca²⁺ exchange and consequently, because of the role of Ca²⁺ in the stimulation of Krebs cycle enzymes and oxidative phosphorylation metabolism, the NADH/NAD⁺ redox potential decreases (Liu and O'Rourke, 2008). This mismatch between calcium flux perturbations, energy demand and contractility ends up in the generation of high oxidative stress that further contribute to the deterioration of cardiac cell survival and function (Dietl and Maack, 2017). Beyond the alterations in the redox state of the coenzyme, the total pool of NAD can be depressed in upon cardiac injury. Acute ischemic injury was shown to severely depressed myocardial, and notably mitochondrial pool of NAD by 30% through the activation of a NAD glycohydrolase associated to the mitochondrial outer membrane (Lisa et al., 2001). Recently, some studies showed that also, in chronic heart failure, myocardial NAD levels were reduced by 25 to 30% and that restoring NAD levels with NAD precursors supplementation would preserve cardiac NAD levels and cardiac function in preclinical models (Diguet et al., 2018; Vignier et al., 2018; Lee et al., 2016; Horton et al., 2016). We notably identified a new type of metabolic shift for the NAD biosynthetic pathways in the context of dilated cardiomyopathy leading to heart failure, with a repression of the nicotinamide phosphoribosyl transferase (NAMPT), a key enzyme for the recycling of the nicotinamide released by NAD signaling pathways and the activation of the nicotinamide riboside kinase 2 (NMRK2) (Diguet et al., 2018).

Heart failure is also a systemic syndrome presenting complex interactions with other diseases, directly altering the function of numerous peripheric organs such as the kidneys and the liver because of the reduction in blood perfusion and conversely, heart failure prevalence and outcome is modified by the presence of comorbidities such as arterial hypertension, kidney failure, diabetes or obesity. Most of these disease conditions have also been shown to present alterations in tissue NAD levels or redox states (Kane and Sinclair, 2018).

NAD metabolism is not only regulated at the tissue level by the bioenergetic activity of the cells and the rate of NAD consumption by NAD signaling pathways but also at the systemic level by the circulation of NAD and precursors. Blood NAD levels are often measured in clinical studies aiming at evaluating the efficacy of NAD precursors treatment in different condition (Dollerup et al., 2018; Conze et al., 2019; Trammell et al., 2016; Airhart et al., 2017).

Here, we thought to address whether we could detect a change in blood NAD levels: first in a healthy blood donor population following age and sex; second in a population of elderly patients hospitalized for decompensated heart failure, in order to determine whether this type of patients might present an alteration in blood NAD levels and might be in need of NAD precursor supplementation.