The nitroxyl donor, Angeli's salt, inhibits inflammatory hyperalgesia in rats.

Nitric oxide modulates pain development. However, there is no evidence on the effect of nitroxyl (HNO/NO⁻) in nociception. Therefore, we addressed whether nitroxyl inhibits inflammatory hyperalgesia and its mechanism using the nitroxyl donor Angeli's salt (AS; Na2N2O3). Mechanical hyperalgesia was evaluated using a modified Randall and Selitto method in rats, cytokine production by ELISA and nitroxyl was determined by confocal microscopy in DAF (a cell permeable reagent that is converted into a fluorescent molecule by nitrogen oxides)-treated dorsal root ganglia neurons in culture. Local pre-treatment with AS (17-450 µg/paw, 30 min) inhibited the carrageenin-induced mechanical hyperalgesia in a dose- and time-dependent manner with maximum inhibition of 97%. AS also inhibited carrageenin-induced cytokine production. AS inhibited the hyperalgesia induced by other inflammatory stimuli including lipopolysaccharide, tumor necrosis factor-α, interleukin-1ß and prostaglandin E2. Furthermore, the analgesic effect of AS was prevented by treatment with ODQ (a soluble guanylate cyclase inhibitor), KT5823 (a protein kinase G [PKG] inhibitor) or glybenclamide (an ATP-sensitive K⁺ channel blocker), but not with naloxone (an opioid receptor antagonist). AS induced concentration-dependent increase in fluorescence intensity of DAF-treated neurons in a l-cysteine (nitroxyl scavenger) sensitive manner. l-cysteine did not affect the NO⁺ donor S-Nitroso-N-acetyl-DL- penicillamine (SNAP)-induced anti-hyperalgesia or fluorescence of DAF-treated neurons. This is the first study to demonstrate that nitroxyl inhibits inflammatory hyperalgesia by reducing cytokine production and activating the cGMP/PKG/ATP-sensitive K⁺ channel signaling pathway in vivo.

Enhanced responsiveness to nitric oxide, nitroxyl anions, and nitrergic transmitter by 3-(5'-hydroxymethyl-2'-furyl)-1-benzyl indazole in the rat anococcygeus muscle.

The effects of 3-(5'-hydroxymethyl-2'-furyl)-1-benzyl indazole (YC-1) on responses to sodium nitroprusside (SNP), S-nitroso-N-acetyl-penicillamine (SNAP), the nitroxyl anion donor Angeli's salt, and nitrergic nerve stimulation, as well as the release of NO from nitrergic nerves, were studied in the rat isolated anococcygeus muscle. YC-1 (1-100 microM) produced concentration-dependent relaxations in contracted muscles, which were partially but significantly reduced by the inhibitor of soluble guanylate cyclase (sGC), 1H-[1,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one (ODQ, 1 and 10 microM). At a concentration that did not affect tissue tension, YC-1 (1 microM) significantly enhanced relaxations to SNP, SNAP, and Angeli's salt but did not affect relaxations to papaverine (10 microM). Nitrergic relaxations elicited by short periods (1 Hz for 10 s, 15 V) and long periods of EFS (5 Hz for 5 min, 15 V) were also enhanced by YC-1. YC-1 (100 microM), in an l-NAME and tetrodotoxin-insensitive manner, also increased the amount of NO detected in the organ bath media after the tissue was field stimulated (5 Hz for 5 min), which may have resulted from the electrolytic degradation of YC-1, as this effect was also seen in the absence of tissue. In summary, YC-1 enhanced relaxations to donors of NO, Angeli's salt, and nitrergic nerve stimulation in the rat anococcygeus muscle; however, the enhanced release of NO by YC-1 following nitrergic nerve stimulation was not a tissue-dependent effect.