de Azevedo Medeiros Carla Fiama, Neto-Neves Evandro Manoel, Santana Indiara Vieira, Sanches-Lopes Jéssica Maria, Nogueira Renato Corrêa, Batista Rose Inês Matos, Conde-Tella Sandra Oliveira, Montenegro Marcelo F, Tanus-Santos Jose Eduardo
Department of Pharmacology, Ribeirao Preto Medical School, Ribeirao Preto, Sao Paulo, Brazil.
Department of Physiological Sciences, Federal University of Espirito Santo, Vitoria, Espírito Santo, Brazil.
Redox Biol. 2025 Jun 30;85:103748. doi: 10.1016/j.redox.2025.103748.
Nitrite and nitrate bioactivation to nitric oxide (NO) in the enterosalivary cycle of nitrate offers an enormous therapeutic potential for cardiovascular and metabolic diseases and involves xanthine oxidoreductase (XOR), an enzyme widely expressed in the gastrointestinal system. XOR has nitrite reductase activity, reducing nitrite to NO, especially under low pH conditions. Here, we hypothesized that XOR activity critically interacts with acidic gastric pH to cause the blood pressure responses to oral nitrite. To test this hypothesis, rats pretreated with the XOR inhibitor allopurinol (100 mg/kg, by gavage, or vehicle) were treated with N⍵-nitro-l-arginine methyl ester; 60 mg/kg, i.v.) to induce acute hypertension, and received sodium nitrite (1, 5, and 15 mg/kg) in the stomach or in the duodenum. Mean arterial blood pressure (MAP) was monitored invasively. Ozone-based reductive chemiluminescence assays were performed to evaluate plasma nitrite, nitrate, total nitrosylated species and S-nitrosothiols (RSNO) concentrations. Gastric pH was assessed and XOR activity in the stomach and duodenum was assessed by fluorimetry. We found more profound MAP responses to nitrite administered in the duodenum than in the stomach. Importantly, XOR inhibition completely blunted nitrite-induced RSNO formation and hypotensive responses when nitrite is administered in the stomach, whereas XOR inhibition did not affect the responses when nitrite was administered in the duodenum, even though XOR activity is much higher in the duodenum than in the stomach. These results suggest a critical interaction between XOR activity and gastric acidity in mediating RSNO formation and the cardiovascular effects of oral nitrite. These results may help to design better oral nitrite therapeutic formulations.
在硝酸盐的肠-唾液循环中，亚硝酸盐和硝酸盐生物活化生成一氧化氮（NO），这为心血管疾病和代谢性疾病提供了巨大的治疗潜力，且涉及黄嘌呤氧化还原酶（XOR），该酶在胃肠道系统中广泛表达。XOR具有亚硝酸盐还原酶活性，可将亚硝酸盐还原为NO，尤其是在低pH条件下。在此，我们假设XOR活性与胃酸pH值密切相互作用，从而引发口服亚硝酸盐后的血压反应。为验证这一假设，先用XOR抑制剂别嘌呤醇（100mg/kg，经口灌胃，或赋形剂）预处理大鼠，然后用Nω-硝基-L-精氨酸甲酯（60mg/kg，静脉注射）诱导急性高血压，再分别经胃或十二指肠给予亚硝酸钠（1、5和15mg/kg）。通过侵入性监测平均动脉血压（MAP）。采用基于臭氧的还原化学发光分析法评估血浆亚硝酸盐、硝酸盐、总亚硝基化物质和S-亚硝基硫醇（RSNO）浓度。评估胃酸pH值，并通过荧光法评估胃和十二指肠中的XOR活性。我们发现，十二指肠给予亚硝酸盐比胃给予亚硝酸盐引发的MAP反应更显著。重要的是，当经胃给予亚硝酸盐时，XOR抑制完全消除了亚硝酸盐诱导的RSNO形成和降压反应，而当经十二指肠给予亚硝酸盐时，XOR抑制并不影响反应，尽管十二指肠中的XOR活性比胃中的高得多。这些结果表明，XOR活性与胃酸度在介导RSNO形成和口服亚硝酸盐的心血管效应方面存在关键相互作用。这些结果可能有助于设计更好的口服亚硝酸盐治疗制剂。
