Basic ResearchLuminal Alkalinization Attenuates Proteinuria-Induced Oxidative Damage in Proximal Tubular CellsSouma, Tomokazu*,†; Abe, Michiaki*,‡; Moriguchi, Takashi†; Takai, Jun†; Yanagisawa-Miyazawa, Noriko*; Shibata, Eisuke*; Akiyama, Yasutoshi*; Toyohara, Takafumi*; Suzuki, Takehiro*; Tanemoto, Masayuki*; Abe, Takaaki*; Sato, Hiroshi*; Yamamoto, Masayuki†; Ito, Sadayoshi* Author Information *Division of Nephrology, Endocrinology, and Vascular Medicine, Department of Medicine, and †Department of Medical Biochemistry, Tohoku University Graduate School of Medicine, Sendai, Japan, and ‡Department of Nephrology, Sendai Shakaihoken Hospital, Sendai, Japan Correspondence: Dr. Tomokazu Souma, Division of Nephrology, Endocrinology, and Vascular Medicine, Department of Medicine, Tohoku University Graduate School of Medicine, 2-1 Seiryo-machi, Aoba-ku, Sendai 980-8575, Japan. Phone: +81-22-717-7163; Fax: +81-22-717-7168; E-mail: [email protected]; or Dr. Michiaki Abe, Division of Nephrology, Endocrinology, and Vascular Medicine, Department of Medicine, Tohoku University Graduate School of Medicine, 2-1 Seiryo-machi, Aoba-ku, Sendai 980-8575, Japan. Phone: +81-22-717-7163; Fax: +81-22-717-7168; E-mail: [email protected] Received November 10, 2009 Accepted October 25, 2010 Journal of the American Society of Nephrology 22(4):p 635-648, April 2011. | DOI: 10.1681/ASN.2009111130 Buy Metrics Abstract A highly acidic environment surrounds proximal tubular cells as a result of their reabsorption of HCO3−. It is unclear whether this luminal acidity affects proteinuria-induced progression of tubular cell damage. Here, we investigated the contribution of luminal acidity to superoxide (O2·−) production induced by oleic acid–bound albumin (OA-Alb) in proximal tubular cells. Acidic media significantly enhanced OA-Alb–induced O2·− production in the HK-2 proximal tubular cell line. Simultaneous treatment with both OA-Alb and acidic media led to phosphorylation of the intracellular pH sensor Pyk2. Highly phosphorylated Pyk2 associated with activation of Rac1, an essential subcomponent of NAD(P)H oxidase. Furthermore, knockdown of Pyk2 with siRNA attenuated the O2·− production induced by cotreatment with OA-Alb and acid. To assess whether luminal alkalinization abrogates proteinuria-induced tubular damage, we studied a mouse model of protein-overload nephropathy. NaHCO3 feeding selectively alkalinized the urine and dramatically attenuated the accumulation of O2·−-induced DNA damage and proximal tubular injury. Overall, these observations suggest that luminal acidity aggravates proteinuria-induced tubular damage and that modulation of this acidic environment may hold potential as a therapeutic target for proteinuric kidney disease. Copyright © 2011 The Authors. Published by Wolters Kluwer Health, Inc. All rights reserved.