Indispensable but Insufficient Role of Renal D-Amino Acid Oxidase in Chiral Inversion of NG-Nitro-D-arginine

• Published in: Chemistry & biodiversity Vol. 7; no. 6; pp. 1413 - 1423
• Main Authors: Xin, Yan-Fei, Li, Xin, Hao, Bin, Gong, Nian, Sun, Wen-Qiang, Konno, Ryuichi, Wang, Yong-Xiang
• Format: Journal Article
• Language: English
• Published: Zürich WILEY-VCH Verlag 01.06.2010; WILEY‐VCH Verlag
• Subjects: Animals; Chiral inversion; D-Amino acid oxidase; D-Amino acids; D-Amino-Acid Oxidase - antagonists & inhibitors; D-Amino-Acid Oxidase - genetics; D-Amino-Acid Oxidase - metabolism; D-Arginine; D‐Arginine, NG‐nitro; Keto Acids - metabolism; Kidney - enzymology; Liver - enzymology; Male; Mice; NG-nitro; Nitroarginine - chemistry; Nitroarginine - metabolism; Rats; Rats, Sprague-Dawley; Sodium Benzoate - pharmacology; Stereoisomerism; Swine
• ISSN: 1612-1872; 1612-1880
• DOI: 10.1002/cbdv.200900275

Unidirectionally chiral inversion of NG‐nitro‐D‐arginine (D‐NNA) to its L‐enantiomer (L‐NNA) occurred in rats, and it was blocked markedly (ca. 80%) by renal vascular ligation, and entirely (100%) by the D‐amino acid oxidase (DAO) inhibitor sodium benzoate, suggesting that renal DAO is essential for the inversion. However, the doses of sodium benzoate administrated were extremely high (e.g., 400 mg/kg) due to its low potency. It is thus possible that sodium benzoate‐mediated blockade of D‐NNA inversion might be due to its nonspecific (or non‐DAO‐related) effects. In addition, after D‐NNA was incubated with the pure enzyme of DAO in vitro without tissue homogenates, L‐NNA was not produced, even though D‐NNA was disposed. We propose that this occurred because D‐NNA was first converted to its corresponding α‐keto acid by DAO and then to L‐NNA by transaminase(s); however, there was no direct evidence for this process. The goal of this study is to further elucidate the process of D‐NNA chiral inversion both in vivo and in in vitro tissue homogenates by comparing mutant ddY/DAO−/− mice that lack DAO activity entirely compared to normal ddY/DAO+/+ mice and Swiss mice. Furthermore, the ability to produce L‐NNA from D‐NNA‐corresponding α‐keto acids (NG‐nitroguanidino‐2‐oxopentanoic acid) produced by porcine kidney‐derived DAO (pkDAO) was also studied in the DAO inhibitor‐pretreated rats. We found that D‐NNA chiral inversion occurred in Swiss mice and ddY/DAO+/+ mice both in vivo and in in vitro kidney homogenates, but not in ddY/DAO−/− mice, correlated to their DAO activities. The α‐keto acid (NG‐nitro‐guanidino‐2‐oxopentanoic acid) from D‐NNA was able to produce L‐NNA, and subsequent vasoconstriction and pressor responses. These results indicate that the role of renal DAO is indispensible but insufficient for chiral inversion of D‐NNA and other neutral and polar D‐amino acids, and unidentified aminotransferase(s) are involved in a subsequent mechanism for the process of chiral inversion.