The senotherapeutic nicotinamide riboside raises platelet nicotinamide adenine dinucleotide levels but cannot prevent storage lesion.

BACKGROUND: Supplementation of the nicotinamide adenine dinucleotide (NAD) precursor nicotinamide riboside (NR) has recently been shown to increase life-span of cells, tissues, and entire organisms. [Correction added on 13 December 2019, after first online publication: In the preceding sentence, "adenine nicotinamide" was revised to "nicotinamide adenine."] The impact of NR on platelet longevity has not been tested. STUDY DESIGN AND METHODS: A pool-and-split design of buffy coat derived platelet concentrates (PCs) was used. One arm was treated with cumulative doses of NR-triflate, the control arm with sodium triflate. Storage lesion was monitored for 23 days. Platelet metabolic and functional parameters were tested. Clearance of human platelets was measured in a mouse model of transfusion. RESULTS: Total intracellular NAD levels in platelets decreased two-fold from 4.8 ± 0.5 fmol (mean ± SD, n = 6) to 2.1 ± 1.8 fmol per 103 control cells, but increased almost 10-fold to 41.5 ± 4.1 fmol per 103 NR treated platelets. This high intracellular NAD level had no significant impact on platelet count, mean platelet volume, swirling, nor on lactate and glucose levels. Platelet aggregation and integrin αIIb ß3 activation declined steadily and comparably in both conditions. GPIbα levels were slightly lower in NR-treated platelets compared to control, but this was not caused by reduced receptor shedding because glycocalicin increased similarly. Apoptotic markers cytochrome c, Bcl-xL, cleaved caspase-3, and Bak were not different throughout storage for both conditions. Platelet survival in a mouse model of transfusion was not different between NR-treated and control platelets. CONCLUSION: Platelets carry the cellular machinery to metabolize NR into NAD at rates comparable to other eukaryotic cells. Unlike those cells, platelet life-span cannot be prolonged using this strategy.

Psoralen and Ultraviolet A Light Treatment Directly Affects Phosphatidylinositol 3-Kinase Signal Transduction by Altering Plasma Membrane Packing.

Psoralen and ultraviolet A light (PUVA) are used to kill pathogens in blood products and as a treatment of aberrant cell proliferation in dermatitis, cutaneous T-cell lymphoma, and graft-versus-host disease. DNA damage is well described, but the direct effects of PUVA on cell signal transduction are poorly understood. Because platelets are anucleate and contain archetypal signal transduction machinery, they are ideally suited to address this. Lipidomics on platelet membrane extracts showed that psoralen forms adducts with unsaturated carbon bonds of fatty acyls in all major phospholipid classes after PUVA. Such adducts increased lipid packing as measured by a blue shift of an environment-sensitive fluorescent probe in model liposomes. Furthermore, the interaction of these liposomes with lipid order-sensitive proteins like amphipathic lipid-packing sensor and α-synuclein was inhibited by PUVA. In platelets, PUVA caused poor membrane binding of Akt and Bruton's tyrosine kinase effectors following activation of the collagen glycoprotein VI and thrombin protease-activated receptor (PAR) 1. This resulted in defective Akt phosphorylation despite unaltered phosphatidylinositol 3,4,5-trisphosphate levels. Downstream integrin activation was furthermore affected similarly by PUVA following PAR1 (effective half-maximal concentration (EC50), 8.4 ± 1.1 versus 4.3 ± 1.1 µm) and glycoprotein VI (EC50, 1.61 ± 0.85 versus 0.26 ± 0.21 µg/ml) but not PAR4 (EC50, 50 ± 1 versus 58 ± 1 µm) signal transduction. Our findings were confirmed in T-cells from graft-versus-host disease patients treated with extracorporeal photopheresis, a form of systemic PUVA. In conclusion, PUVA increases the order of lipid phases by covalent modification of phospholipids, thereby inhibiting membrane recruitment of effector kinases.