Vascular and anti‐platelet actions of 1,2‐ and 1,3‐glyceryl dinitrate

Abstract

1. The aim of this study was to investigate whether two metabolites of glyceryl trinitrate (GTN), 1,2 and 1,3-glyceryl dinitrate (1,2-GDN and 1,3-GDN) could account for the pharmacological effects of GTN. To this end the formation of nitric oxide (NO) from 1,2- and 1,3-GDN in the presence of bovine aortic smooth muscle cells (SMC) or endothelial cells (EC) was studied. The effects of various thiols on NO formation from these dinitrates was also evaluated. 2. 1,2-GDN or 1,3-GDN (10(-10)-10(-5) M) caused a dose-dependent relaxation of rabbit aortic strips denuded of endothelium and precontracted with phenylephrine. The dinitrates were less than one tenth as potent as GTN. 3. Incubation of 1,2-GDN or 1,3-GDN (75-2400 microM) with SMC for 30 min led to a concentration-dependent increase in nitrite (NO2-) formation but this increase was less than that produced from GTN. Likewise incubation of 1,2-GDN or 1,3-GDN with N-acetylcysteine (NAC), glutathione (GSH) or thiosalicylic acid (TSA) (all at 1 mM) for 30 min at 37 degrees C produced a concentration-dependent increase in NO2- formation. 4. Platelet aggregation induced by thrombin (40 mu ml-1) was not modified by high concentrations of 1,2-GDN or 1,3-GDN (175-700 microM). However, aggregation was inhibited when platelets were exposed to 1,2-GDN or 1,3-GDN (700 microM) in the presence of SMC (0.24-1.92 x 10(5) cells) or EC (0.8-3.2 x 10(5) cells). These effects were abrogated by co-incubation with oxyhaemoglobin (OxyHb, 10 microM) indicating that they were due to NO release. The concentrations of the dinitrates required to inhibit platelet aggregation by 50% were about 15 times higher than for GTN in the presence of the same numbers of SMC or EC.5. When NAC or TSA (both at 0.5 mM) were co-incubated with platelets for 3 min in the presence of1,2-GDN or 1,3-GDN, a concentration-dependent inhibition of platelet aggregation was observed. These anti-platelet effects were abolished by co-incubation with OxyHb (10 microM). Glutathione had no potentiating effects.6. Thus the dinitrate metabolites of GTN are metabolized to NO by SMC or EC and are acted upon by thiols to form NO at concentrations about 10 times higher than those of GTN. In vivo, after oral or intravenous GTN, GDN levels are reached which are more than 10 times higher than those of GTN.These data support the notion that part of the effects of GTN are due to the generation of NO from 1,2-GDN and 1,3-GDN by the cells of the vascular wall.

Modulation of Prostaglandin Biosynthesis by Nitric Oxide and Nitric Oxide Donors

“…Chong and Fung (1991) also reported that among aliphatic and aromatic thiols tested, NAC, mercaptosuccinic acid, and TSA were the most potent generators of NO from GTN in buffer with an order of potency of NAC Ͻ mercaptosuccinic acid Ͻ TSA. Later studies then showed that this correlated with their efficacy in increasing the antiplatelet effects of GTN (Salvemini et al, 1993b) and in potentiating the in vivo hemodynamic effects of organic nitrates (Lawson et al, 1991;Salvemini et al, 1993b,c). Glutathione does not release NO and releases only nitrite, which is devoid of biological effects (except perhaps at very high doses).…”

“…Glutathione does not release NO and releases only nitrite, which is devoid of biological effects (except perhaps at very high doses). Thus, glutathione does not potentiate the pharmacological actions of organic nitrates (Feelisch, 1991;Salvemini et al, 1993b).…”

Repurposing Drugs in Oncology (ReDO)—nitroglycerin as an anti-cancer agent

“…Note that all forms of NTG delivery are prone to high-levels of inter and intra-patient variability [ 3 ]. The two main metabolites of NTG are 1,2 and 1,3-glyceryl dinitrate (1,2-GDN and 1,3-GDN), which achieve higher plasma concentrations than the parent compound but which have lower vasodilatory activity; nevertheless these metabolites contribute to the pharmacological effects of NTG administration [ 5 ].…”

Nitroglycerin [BAT Value Documentation, 1998]

“…Clinical investigations show that after ingestion, nitroglycerin cannot be detected in plasma or the concentrations are very low (16,81,83,106). Metabolites such as glycerol dinitrate are, however, detectable (57,83 (91) found that the glycerol dinitrate levels were up to 10 times higher than the nitroglycerin levels after oral and dermal administration of nitroglycerin. The plasma concentrations of glycerol-1,2-dinitrate are higher than those of glycerol-1,3-dinitrate after oral administration of nitroglycerin (81).…”