Neutrophils and acute ischemia-reperfusion injury.

Leukocyte infiltration in response to I/R injury is a well-known but poorly understood phenomenon. The contribution of neutrophils in this process is still controversial. Despite numerous data, little is known about exact numbers of infiltrating neutrophils. The role of monocytes/macrophages in this process is even more unclear. The role neutrophils in the kidney and other organs was reviewed. The variability in models and methods for neutrophil quantification were examined, along with carrying out a critical overview of depletion and anti-adhesion approaches. Nevertheless, the exact role attributed to neutrophils in the I/R process remains unclear.

Differences in osteopontin up-regulation between proximal and distal tubules after renal ischemia/reperfusion.

BACKGROUND: Osteopontin (OPN) is a highly acidic phosphoprotein containing an arginine-glycine-aspartic acid (RGD) cell adhesion motif. High OPN expression has been found in tissues with high cell turnover, and OPN up-regulation has been demonstrated in several models of renal injury, suggesting a possible role in tissue remodeling and repair. However, its exact function in the kidney remains unknown. In this study, the possible contribution of OPN to regeneration and repair in the kidney was explored by studying the time course and subcellular localization of OPN up-regulation after renal ischemia/reperfusion injury in different nephron segments and by investigating its relationship with tubular morphology. METHODS: Rats that underwent 60 minutes of left renal ischemia and a right nephrectomy sacrificed at 10 different time points (from 1 hr to 10 days after reperfusion) were compared with uninephrectomized rats at each time point. In renal tissue sections immunostained for OPN, proximal (PTs) and distal tubules (DTs) in both the renal cortex and outer stripe of the outer medulla (OSOM) were scored for the degree of OPN expression and tubular morphology. RESULTS: Kidneys of uninephrectomized rats showed no injury, and the localization and intensity of their OPN expression remained unaltered compared with normal rats. After ischemia/reperfusion, morphological damage was most severe in PTs of the OSOM, but all examined nephron segments showed a significant increase in OPN expression. The time course of OPN up-regulation was different in PTs and DTs. DTs in both cortex and OSOM rapidly increased their OPN expression, with a maximum at 24 hours after reperfusion followed by a slow decrease. In contrast, PTs showed a delayed increase in OPN staining, with a maximum after five to seven days, higher in the OSOM than in the cortex. In OSOM PTs, OPN expression was predominantly associated with morphological regeneration, whereas DTs showed a substantial OPN up-regulation without major morphological damage. PTs and DTs displayed a different subcellular OPN staining pattern: OPN staining in DTs was located to the apical side of the cell; PTs, however, presented a vesicular, perinuclear staining pattern. CONCLUSIONS: Our study found a different pattern of OPN up-regulation after renal ischemia/reperfusion in PTs versus DTs, both with regard to time course and subcellular localization. DTs show an early and persistent increase in OPN staining in the absence of major morphological injury, whereas OPN staining in PTs is delayed and is mostly associated with morphological regeneration. PTs show a vesicular, perinuclear OPN staining pattern, whereas DTs show OPN staining at the apical cell side.

Chronic reduction in renal mass in the rat attenuates ischemia/reperfusion injury and does not impair tubular regeneration.

It is not known whether a kidney with chronic structural and functional changes is more vulnerable to an acute renal insult, and whether its regeneration capacity after injury is altered. To study this question, Lewis rats were submitted 10 wk after 5/6 nephrectomy to an ischemic insult of 60 min (remnant kidney [RK] group). Functional and morphologic data of the RK group were compared with data obtained in 10-wk uninephrectomized (1K) and normal (2K) Lewis rats with unilateral and bilateral renal ischemia, respectively. The acute postischemic decrease in creatinine clearance was smallest in the RK group, followed by the 2K and 1K groups, respectively. At days 1 and 3, fewer proximal tubules in the outer stripe of the outer medulla of the RK and 2K groups had undergone acute tubular necrosis compared with the 1K group. The mean percentage of tubules with signs of regeneration was maximal at day 3 in the three experimental groups. At day 10, regeneration was almost complete in the three groups. The number of leukocytes (OX1+ cells) present in the RK before ischemia did not increase after ischemia/reperfusion injury (377 +/- 146 cells/mm2 at day 0) in contrast to the 1K and 2K groups. In the latter groups, the number of leukocytes had increased gradually, reaching a maximum at day 15 (1K: 960 +/- 308 cells/mm2) and day 10 (2K: 668 +/- 164 cells/mm2), respectively. In conclusion, this study has shown that an RK exhibiting chronic morphologic changes of interstitial fibrosis and tubular atrophy is protected against ischemia/reperfusion injury, and that its regeneration capacity is preserved. The reperfusion injury is not followed by further accumulation of leukocytes, which were already present in the RK before ischemia.

The low countries - 16th/17th century.

Andreas Vesalius and Jan Baptist Van Helmont are the two major personalities who contributed substantially and in a different way to the early development of renal anatomy/physiology of the 16th/17th century in the Southern Low Countries. The importance of A. Vesalius' publication 'de humani corporis fabrica libri septem' cannot be overestimated. The kidney was an intriguing organ to Vesalius, the function of which he could not fully grasp. J.B. Van Helmont was the first to demonstrate the importance of the measurement of the specific gravity of the urine and relating it to physiological and pathophysiological conditions. He made accurate clinical observations supported by autopsy examinations concerning the role of the kidney in the generation of dropsy.

Anti-B7-1 blocks mononuclear cell adherence in vasa recta after ischemia.

BACKGROUND: Blocking the costimulatory pathway by CTLA-4 Ig, reactive with both B7-1 and B7-2 costimulatory molecules, protects the kidney during acute ischemia/reperfusion injury. This study investigated whether and how B7-1 and/or B7-2 proteins are involved in renal ischemia/reperfusion injury (IRI). METHODS: Uninephrectomized rats were submitted to warm renal ischemia (30 min) and received control monoclonal antibody (mAb; 17E3), anti-B7-1 (3H5), anti-B7-2 (24F), a combination of anti-B7-1/B7-2, or CTLA-4 Ig. Renal function, morphology, and the kinetics of inflammatory cells were studied for a ten-day period. Binding sites of the injected antibodies were detected by secondary staining with anti-mouse Ab. RESULTS: Compared with controls, acute renal failure (ARF) in the anti-B7-1 group was attenuated both functionally and morphologically. Anti-B7-1/B7-2 and CTLA-4 Ig also were protective in IRI. ARF was not altered by anti-B7-2 treatment. Two hours after reperfusion, B7-1 was expressed along the endothelial cells of the ascending vasa recta. Expression of B7-1 increased over time during the first 24 hours and decreased thereafter. Two hours after reperfusion, adherence/accumulation of T cells and monocytes/macrophages was found in the vasa recta of the ischemic kidney. Anti-B7-1-treated animals had fewer T cells and monocytes/macrophages in the vasa recta compared with controls. Leukocyte accumulation in these vessels after anti-B7-2 treatment was not different from IRI controls. CONCLUSION: These observations strongly support the key role of the B7-1 protein in the protection of renal IRI through inhibition of T cell and monocyte adherence at the level of the ascending vasa recta.

Antibodies to both ICAM-1 and LFA-1 do not protect the kidney against toxic (HgCl2) injury.

BACKGROUND: The role of inflammatory leukocytes in acute renal failure (ARF) remains controversial and appears largely uninvestigated in toxic (in contrast to ischemic) ARF. METHODS: Female Wistar rats were injected with monoclonal antibodies (mAbs) directed to both the leukocyte function-associated antigen 1 (LFA-1) and the intercellular adhesion molecule 1 (ICAM-1). Doses (6 mg/kg of each mAb) were given 24 hours prior to the induction of acute tubular necrosis (ATN) by mercuric chloride administration (2 mg/kg, subcutaneously, day 0) and subsequently every 48 hours. Control rats similarly received either control antibody (12 mg/kg) or vehicle prior to and following the induction of ATN. Renal function was also measured from male Lewis rats that were similarly treated with anti-adhesion antibodies during exposure to 30 minutes of unilateral renal ischemia. RESULTS: Injected antibodies were demonstrated on peripheral blood leukocytes (flow cytometrical detection of mouse anti-LFA-1) and on endothelium (immunohistochemical staining of mouse anti-ICAM-1) and were measured in serum (enzyme-linked immunosorbent assay). Macrophages and T cells were prominent in the kidney of control treatment rats after HgCl2 injection, but anti-adhesion treatment clearly had prevented their infiltration. Notwithstanding, renal tubular injury was equally pronounced in all mercuric chloride treatment groups and so was the decline in renal function (serum creatinine, proteinuria). Tubular epithelial cell proliferation seemed slightly less pronounced and delayed in anti-adhesion treated rats. Kidneys from ischemia exposed rats were, however, functionally protected by identical anti-ICAM-1/anti-LFA-1 treatment. CONCLUSION: Prevention of cellular infiltration by mAbs to LFA-1 and ICAM-1 has no effect on renal morphology, function, or regeneration following mercuric chloride-induced ARF in the rat. This result contrasts with the functional protection of the rat kidney to ischemia/reperfusion injury by virtue of an identical antibody treatment protocol. Resolving that controversy should bring better insight in fundamental processes underlying different types of ARF, and will be the subject of further study.

TIMP-1 gene expression and PAI-1 antigen after unilateral ureteral obstruction in the adult male rat.

BACKGROUND: Sustained obstruction of urinary flow invariably leads to inflammation, loss of functional renal structures and progressive deposition of extracellular matrix proteins, culminating in renal fibrosis. Although increased renal tissue inhibitor of matrix metalloproteinase (TIMP-1) expression is one of the early events following experimental hydronephrosis, little is known about its cellular source. Both the recruited macrophage and the resident/recruited (myo)fibroblast have been postulated to be candidate TIMP-1 transcribing cells. Currently, data concerning plasminogen activator inhibitor type 1 (PAI-1) expression in the ligated kidney are unavailable. Our study concentrated on the localization of TIMP-1 expressing cells and PAI-1 immunoreactive cells in the obstructed rat kidney. METHODS: Rats were sacrificed 1, 5, 10, 15, 20 and 26 days after unilateral ureteral obstruction (UUO) or sham-surgery (SOR). Leukocyte (OX-1+), macrophage (ED1+) and neutrophil infiltration were analyzed using specific antibodies or nuclear morphology. alpha-Smooth muscle actin (alpha-SMA) immunostaining was measured morphometrically. Mitotic figures and nuclei with an apoptotic morphology were quantified in hematoxylin-eosin (H&E)-stained sections. TIMP-1 mRNA transcribing cells were localized with in situ hybridization (ISH) and identified by subsequent immunostainings for alpha-SMA and macrophages. PAI-1 antigenicity was evaluated immunohistochemically in SOR, contralateral unobstructed kidneys (CUK), and UUO kidneys. RESULTS: The number of leukocytes and macrophages in the ligated rat kidney increased progressively in time, starting from day 5 post-surgery when compared with CUKs. Neutrophil accumulation in UUO kidneys became apparent from day 5 and large intraluminal leukocyte clusters (neutrophils and macrophages) were found in the lumen of distended tubules, especially at later stages post-obstruction, when collected urine and tissue samples proved to be sterile upon culture. From day 5 on, the number of apoptotic cells started to predominate the number of mitotic cells in the obstructed kidneys. Interstitial alpha-SMA immunoreactivity in the ligated kidney expanded from day 5 on and was most pronounced in the inner stripe of the outer medulla. As early as 24 hours post-ligation, TIMP-1 mRNA transcribing interstitial cells were detected with ISH, while tubular TIMP-1 expression was sparse. Since at that point in time, no interstitial alpha-SMA expressing cells and only few ED1+ macrophages were present, the bulk of the TIMP-1 mRNA transcription occurred in other interstitial cells. Throughout the study period numerous interstitial TIMP-1 expressing cells were detectable in obstructed kidneys and from day 5 after ligation on, we could identify alpha-SMA+ and to a lesser degree ED1+ macrophages as TIMP-1 transcribing cells. In addition, dilated tubules containing intraluminal leukocyte casts were surrounded by a corona of intact neutrophils in H&E-stained sections and ISH showed that similar tubules were encircled by TIMP-1 mRNA expressing cells. PAI-1 immunoreactivity appeared to diminish in the early phase following urinary outlet obstruction, but emerged in damaged tubules from day 5 to 10 on. In later stages post-ligation, PAI-1+ cells and PAI-1 immunoreactive material were found embedded in the extracellular matrix. CONCLUSIONS: Our results confirm that TIMP-1 is active in the early phase of the fibrotic process and we demonstrated that initially TIMP-1 mRNA is transcribed by very few ED1+ macrophages but mainly by other, presently unidentified, interstitial cells. During later stages of post-ligation, both TIMP-1 (transcribed among others by alpha-SMA+ myofibroblasts, ED1+ macrophages, and possibly neutrophils) and PAI-1 are involved in the progression of tubulointerstitial scarring.

Identification and kinetics of leukocytes after severe ischaemia/reperfusion renal injury.

BACKGROUND: Leukocyte adhesion/infiltration in response to renal ischaemia/reperfusion (I/R) injury is a well-known but poorly understood phenomenon. The identification, kinetics, and exact role of these inflammatory cells in I/R injury and regeneration are still matters of debate. METHODS: Uninephrectomized rats were submitted to 60 min renal ischaemia by clamping of renal vessels. RESULTS: Severe acute renal failure was observed, with maximum functional impairment on day 2. By 12 h after the ischaemic event, up to 80% of proximal tubular cells in the outer stripe of outer medulla (OSOM) were already severely damaged. Proliferation (proliferating cell nuclear antigen (PCNA) staining) started after 24 h, reaching maximum activity on day 3. Regeneration of tubular morphology started on the 3rd day, and after 10 days 50% of tubules had regenerated completely. Interstitial leukocytes (OX-1 immunohistochemical staining) were already prominent at day 1, thereafter gradually increasing with time. The so-called neutrophil-specific identification methods (myeloperoxidase (MPO), chloroacetate esterase, mAb HIS-48) proved to be non-specific, since they also stained for macrophages, as demonstrated by flow cytometry and the combination of these stainings with the macrophage-specific ED-1 staining. MPO activity was already significantly increased at 1 h post-I/R (439+/-34%, P<0.005), reaching its maximum activity after 12 h of I/R (1159+/-138%, P<0.0005), declining thereafter. On the other hand, neutrophil presence investigated by H&E staining revealed only a few neutrophils in glomeruli, medullary rays, and OSOM at 24 h after the ischaemic event (4.7+/-4.2 cells/mm(2) vs controls=2.3+/-2.0 cells/mm(2) (n.s.)), and remained unchanged over the next 10 days. In contrast, significant monocyte/macrophage adhesion/infiltration (ED-1 staining) occurred at the OSOM at 24 h post-ischaemia (at 24 h, 120+/-46 cells/mm(2) vs. sham=18+/-4 cells/mm(2) (P<0.05)), became prominent at day 5 (1034+/-161 cells/mm(2) vs sham=18+/-18 cells/mm(2) (P<0.05)), and almost disappeared after 10 days. CD4(+) cells (W3/25) gradually increased from day 5, reaching a maximum at day 10. A few CD8(+) cells (OX-8) were apparent from days 3 until 10, but no B-cells (OX-33) were observed. CONCLUSIONS: After severe warm I/R renal injury, a pronounced acute tubular necrosis occurs during the first 12-24 h in the absence of a marked cellular infiltrate, but with an important renal MPO activity, reflecting the activation of the adhering inflammatory cells (polymorphonuclear cells (PMNs) and mainly monocytes/macrophages). Only later at the time and site (OSOM) of regeneration a sequential accumulation of monocytes/macrophages and T cells becomes prominent, in contrast with the low number of neutrophils found in the kidney during the 10-day post-ischaemic period. The non-specificity of the so-called neutrophil-specific identification methods (MPO activity, naphthol AS-D chloroacetate esterase, or mAb HIS-48 staining), cross-reacting with monocytes/macrophages, explains the controversy in literature concerning the number of PMNs in post-ischaemic injury.