Cholecystokinin Plays a Novel Protective Role in Diabetic Kidney Through Anti-inflammatory Actions on Macrophage Anti-Inflammatory Effect of Cholecystokinin

Inflammatory process is involved in the pathogenesis of diabetic nephropathy. In this article, we show that cholecystokinin (CCK) is expressed in the kidney and exerts renoprotective effects through its anti-inflammatory actions. DNA microarray showed that CCK was upregulated in the kidney of diabetic wild-type (WT) mice but not in diabetic intracellular adhesion molecule-1 knockout mice. We induced diabetes in CCK-1 receptor (CCK-1R) and CCK-2R double-knockout (CCK-1R,-2R) mice, and furthermore, we performed a bone marrow transplantation study using CCK-1R mice to determine the role of CCK-1R on macrophages in the diabetic kidney. Diabetic CCK-1R,-2R mice revealed enhanced albuminuria and inflammation in the kidney compared with diabetic WT mice. In addition, diabetic WT mice with CCK-1R bone marrow–derived cells developed more albuminuria than diabetic CCK-1Rmice with WT bone marrow– derived cells. Administration of sulfated cholecystokinin octapeptide (CCK-8S) ameliorated albuminuria, podocyte loss, expression of proinflammatory genes, and infiltration of macrophages in the kidneys of diabetic rats. Furthermore, CCK-8S inhibited both expression of tumor necrosis factor-a and chemotaxis in cultured THP-1 cells. These results suggest that CCK suppresses the activation of macrophage and expression of proinflammatory genes in diabetic kidney. Our findings may provide a novel strategy of therapy for the early stage of diabetic nephropathy. As the incidence of diabetes continues to increase in almost all areas of developing and developed countries, diabetic nephropathy has become the most common cause of end-stage renal disease worldwide (1). In addition, accumulating evidence suggests that the development of diabetic nephropathy leads directly to increased cardiovascular mortality (2). Recent studies have suggested that the inflammatory process plays a crucial role in the pathogenesis of diabetic nephropathy (3). We previously focused on the relationship between intracellular adhesion molecule-1 (ICAM-1) expression and macrophage infiltration in the diabetic kidney. We reported that ICAM-1 was overexpressed on endothelial cells and mediated macrophage infiltration in the diabetic kidney (4). Furthermore, we demonstrated that blockade of macrophage infiltration using anti–ICAM-1 antibody (4) or ICAM-1 knockout (ICAM-1) mice (5) ameliorated diabetic renal injury, suggesting that the inflammatory axis of ICAM-1 activation to macrophage infiltration plays a pivotal role in the development of diabetic nephropathy. In the current study, we performed a comprehensive, microarray-based analysis to clarify the genes responsible for the difference in urinary albumin excretion between diabetic ICAM-1 mice and diabetic wild-type (WT) mice. Unexpectedly, we found that cholecystokinin (CCK) mRNA expression was increased in the diabetic kidney of WT mice, whereas no significant increase was observed in nondiabetic WT mice. CCK is a peptide hormone discovered in the small intestine (6,7) and is secreted from endocrine I cells of the duodenum and the jejunum into the bloodstream after a meal (8). CCK is well known as a regulator in the digestive tract and as a neurotransmitter in the nervous system (9,10). In addition to these well-known effects of CCK, antiinflammatory effects of CCK have been reported (11–14). To examine the role of CCK in the pathogenesis of diabetic nephropathy, diabetes was induced in CCK-1 receptor (CCK-1R) and CCK-2 receptor (CCK-2R) double-knockout (CCK-1R,-2R) mice. It is noteworthy that diabetic CCK-1R,-2R mice exhibited increased albuminuria and showed increased levels of proinflammatory genes in the kidney cortex. Therefore, we speculated CCK had renoprotective effects, and we further examined the effects of From the Department of Medicine and Clinical Science, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama, Japan; the Center for Innovative Clinical Medicine, Okayama University Hospital, Okayama, Japan; the Department of Nutrition and Physiology, Tokyo Kasei University, Tokyo, Japan; the Department of Primary Care and Medical Education, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama, Japan; the Department of Diabetic Nephropathy, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama, Japan; the Department of Gastroenterology, National Kyushu Cancer Center, Fukuoka, Japan; and the Department of Hematology and Oncology, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama, Japan. Corresponding author: Kenichi Shikata, [email protected]. Received 24 March 2011 and accepted 19 December 2011. DOI: 10.2337/db11-0402 This article contains Supplementary Data online at http://diabetes .diabetesjournals.org/lookup/suppl/doi:10.2337/db11-0402/-/DC1. 2012 by the American Diabetes Association. Readers may use this article as long as the work is properly cited, the use is educational and not for profit, and the work is not altered. See http://creativecommons.org/licenses/by -nc-nd/3.0/ for details.