Sang-Kyung Jo

BACKGROUND: Although neutrophils and T cells are important in mediating renal injury following ischaemia/reperfusion, the role of macrophages is still unknown. Using liposomal clodronate (LC), we investigated the effect of systemic monocyte-macrophage depletion on renal damage in ischaemic acute renal failure in rats. METHODS: Male Sprague-Dawley rats were injected by LC or liposomal vehicle and underwent bilateral renal pedicle clamping (40 min) or sham ischaemia. Biochemical and histological renal damage was assessed and gene expression kinetics of tumour necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta), IL-6 and monocyte chemoattractant protein-1 (MCP-1) using quantitative real-time reverse transcription-polymerase chain reaction were conducted at 4, 24 and 72 h after reperfusion. RESULTS: The percentage of peripheral blood monocytes and ectodysplasin-1-positive cells in liver decreased significantly in LC-treated animals at 24 h. Systemic monocyte-macrophage depletion resulted in (a) less severe tubular necrosis, (b) reduced inflammation and (c) reduced apoptosis of renal tubular epithelial cells. Gene expression kinetics showed that IL-6 gene expression peaked early at 4 h after reperfusion, followed by TNF-alpha, IL-1beta and MCP-1 expressions, which peaked at 24 h. Systemic monocyte-macrophage depletion significantly reduced these cytokine and chemokine gene expressions. CONCLUSIONS: These results suggest that macrophages are an important mediator in the initiation period of ischaemia/reperfusion injury and strategies that limit initial macrophage infiltration or activation can be useful in the treatment of acute renal failure.

Large macromolecular MRI contrast agents with albumin or dendrimer cores are useful for imaging blood vessels. However, their prolonged retention is a major limitation for clinical use. Although smaller dendrimer-based MRI contrast agents are more quickly excreted by the kidneys, they are also able to visualize vascular structures better than Gd-DTPA due to less extravasation. Additionally, unlike Gd-DTPA, they transiently accumulate in renal tubules and thus also can be used to visualize renal structural and functional damage. However, these dendrimer agents are retained in the body for a prolonged time. The purpose of this study was to obtain information from which a macromolecular dendrimer-based MRI contrast agents feasible for use in further clinical studies could be chosen. Six small dendrimer-based MRI contrast agents were synthesized, and their pharmacokinetics, whole-body retention, and dynamic MRI were evaluated in mice to determine an optimal agent in comparison to Gd-[DTPA]-dimeglumine. Diaminobutane (DAB) dendrimer-based agents cleared more rapidly from the body than polyamidoamine (PAMAM) dendrimer-based agents with the same numbers of branches. Smaller dendrimer conjugates were more rapidly excreted from the body than the larger dendrimer conjugates. Since PAMAM-G2, DAB-G3, and DAB-G2 dendrimer-based contrast agents showed relatively rapid excretion, these three conjugates might be acceptable for use in further clinical applications.

INTRODUCTION: Acute kidney injury (AKI) is a major risk factor in the development of chronic kidney disease (CKD). However, the mechanisms linking AKI to CKD remain unclear. We examined the alteration of macrophage phenotypes during an extended recovery period following ischemia/reperfusion injury (IRI) and determine their roles in the development of fibrosis. METHODS: The left renal pedicle of mice was clamped for 40 min. To deplete monocyte/macrophage, liposome clodronate was injected or CD11b-DTR and CD11c-DTR transgenic mice were used. RESULTS: Throughout the phase of IRI recovery, M2-phenotype macrophages made up the predominant macrophage subset. On day 28, renal fibrosis was clearly shown with increased type IV collagen and TGF-β. The depletion of macrophages induced by the liposome clodronate injection improved renal fibrosis with a reduction of kidney IL-6, type IV collagen, and TGF-β levels. Additionally, the adoptive transfer of the M2c macrophages partially reversed the beneficial effect of macrophage depletion, whereas the adoptive transfer of the M1 macrophages did not. M2 macrophages isolated from the kidneys during the recovery phase expressed 2.5 fold higher levels of TGF-β than the M1 macrophages. The injection of the diphtheria toxin into CD11b or CD11c-DTR transgenic mice resulted in lesser depletion or no change in M2 macrophages and had little impact on renal fibrosis. CONCLUSION: Although M2 macrophages are known to be indispensible for short-term recovery, they are thought to be main culprit in the development of renal fibrosis following IRI.

Agonists of the sphingosine-1-phosphate receptor (S1PR) attenuate kidney ischemia-reperfusion injury (IRI). Previous studies suggested that S1P1R-induced lymphopenia mediates this protective effect, but lymphocyte-independent mechanisms could also contribute. Here, we investigated the effects of S1PR agonists on kidney IRI in mice that lack T and B lymphocytes (Rag-1 knockout mice). Administration of the nonselective S1PR agonist FTY720 or the selective S1P1R agonist SEW2871 reduced injury in both Rag-1 knockout and wild-type mice. In vitro, SEW2871 significantly attenuated LPS- or hypoxia/reoxygenation-induced apoptosis in cultured mouse proximal tubule epithelial cells, supporting a direct protective effect of S1P1R agonists via mitogen-activated protein kinase and/or Akt pathways. S1P1Rs in the proximal tubule mediated IRI in vivo as well: Mice deficient in proximal tubule S1P1Rs experienced a greater decline in renal function after IRI than control mice and their kidneys were no longer protected by SEW2871 administration. In summary, S1PRs in the proximal tubule are necessary for stress-induced cell survival, and S1P1R agonists are renoprotective via direct effects on the tubule cells. Selective agonists of S1P1Rs may hold therapeutic potential for the prevention and treatment of acute kidney injury.