MP38-02: Impaired Nicotinamide Adenine Dinucleotide (NAD+) Mediating Endothelium-Independent Relaxation With Aging On Human Corpus Cavernosum

Serap Gur*, Ankara, Turkey, Suresh C. Sikka, Sudha Talwar, New Orleans, LA, Didem Yilmaz-Oral, Adana, Turkey, Asim Abdel-Mageed, Wayne JG Hellstrom, New Orleans, LA

Introduction: Nicotinamide adenine dinucleotide (NAD+), a small-molecule cofactor for NAD+-dependent enzymes, such as the sirtuins (SIRT) is a coenzyme for redox reactions, making it central to energy metabolism. SIRT-stimulation by hydrogen sulfide (H2S) reverses redox changes. Remarkably, ageing is accompanied by a gradual decline in tissue and cellular NAD+ levels leading to a slow rate of glycolysis, mitochondrial electron transport, and ATP formation. This study aimed to evaluate the effect of aging on  NAD+-induced relaxation of human CC.

Methods: Human CC from ED patients (n=12) undergoing penile prosthesis surgery were processed for organ bath. After precontraction with phenylephrine (Phe, 10µM), concentration-response curves were performed for NAD+ (10nM-100µM) on CC from middle-aged and aged individuals. Underlying mechanisms of relaxation were evaluated by inhibitory agents, namely L-NAME [an inhibitor of NOS], ODQ (a soluble guanylyl cyclase inhibitor), and tetraethylammonium (TEA, non-selective K+ channel blocker). The relaxation responses to electrical field stimulation (EFS), acetylcholine (ACh), sodium hydrogen sulfur (NaHS, a donor of H2S), adenosine (Ado), and contractile response to EFS were examined in the presence or absence of NAD+(10µM). Cellular localization of eNOS, nNOS, and VEGF expressions was performed by Western blotting and immunofluorescence. For the primary cell culture of human penile tissue samples, the cells in growth media for 2 weeks were characterized for smooth muscle cell protein marker, treated with 500µM of NAD+ either 6 hours or 24 hours, and cell lysate was quantitated for eNOS, nNOS, VEGF, and GAPDH expressions.

Results: NAD+ reduced the maximal contractile response induced by Phe (46.2±9.9%). The NAD+-induced relaxations were not affected by inhibitors. NAD+ induced relaxations were significantly lower (11.1±5.3%, p= 0.0270) in the aged (75.6±1.2 years) group when compared (40.7 ±6.9%) middle-aged (63.0±4.0 years) group. NAD+-evoked relaxations of HCC were augmented with NaHS and Ado incubations. Using Western blot analysis, confocal imaging, and cell-culture experiments for eNOS, nNOS, and VEGF, NAD+ could not change impairment in samples.

Conclusions: Our studies have elucidated a decreased relaxation of NAD+ on HCC tissues from aged men. The relaxation response to NAD+ is independent of the activation of the NO-cGMP system. NAD+-involved molecular targets can be through actions at H2S and Ado- receptor mechanisms in HCC. Collectively, NAD+ repletion as a promising therapeutic approach may preserve penile biogenesis and integrity during aging.

Source of Funding: None