Influence of nephron mass in development of chronic renal failure after prolonged warm renal ischemia

Estimating Nephron Number from Biopsies: Impact on Clinical Studies

BACKGROUND

Accumulating evidence supports an association between nephron number and susceptibility to kidney disease. However, it is not yet possible to directly measure nephron number in a clinical setting. Recent clinical studies have used glomerular density from a single biopsy and whole kidney cortical volume from imaging to estimate nephron number and single nephron glomerular filtration rate. However, the accuracy of these estimates from individual subjects is unknown. Furthermore, it is not clear how sample size or biopsy location may influence these estimates. These questions are critical to study design, and to the potential translation of these tools to estimate nephron number in individual subjects.

METHODS

We measured the variability in estimated nephron number derived from needle or virtual biopsies and cortical volume in human kidneys declined for transplantation. We performed multiple needle biopsies in the same kidney, and examined the three-dimensional spatial distribution of nephron density by magnetic resonance imaging. We determined the accuracy of a single-kidney biopsy to predict the mean nephron number estimated from multiple biopsies from the same kidney.

RESULTS

A single needle biopsy had a 15% chance and virtual biopsy had a 60% chance of being within 20% of the whole-kidney nephron number. Single needle biopsies could be used to detect differences in nephron number between large cohorts of several hundred subjects.

CONCLUSIONS

The number of subjects required to accurately detect differences in nephron number between populations can be predicted on the basis of natural intrakidney variability in glomerular density. A single biopsy is insufficient to accurately predict nephron number in individual subjects.

Microvascular rarefaction and hypertension in the impaired recovery and progression of kidney disease following AKI in preexisting CKD states

Acute kidney injury (AKI) is a major complication in hospitalized patients and is associated with elevated mortality rates. Numerous recent studies indicate that AKI also significantly increases the risk of chronic kidney disease (CKD), end-stage renal disease (ESRD), hypertension, cardiovascular disease, and mortality in those patients who survive AKI. Moreover, the risk of ESRD and mortality after AKI is substantially higher in patients with preexisting CKD. However, the underlying mechanisms by which AKI and CKD interact to promote ESRD remain poorly understood. The recently developed models that superimpose AKI on rodents with preexisting CKD have provided new insights into the pathogenic mechanisms mediating the deleterious interactions between AKI and CKD. These studies show that preexisting CKD impairs recovery from AKI and promotes the development of mechanisms of CKD progression. Specifically, preexisting CKD exacerbates microvascular rarefaction, failed tubular redifferentiation, disruption of cell cycle regulation, hypertension, and proteinuria after AKI. The purpose of this review is to discuss the potential mechanisms by which microvascular rarefaction and hypertension contribute to impaired recovery from AKI and the subsequent progression of renal disease in preexisting CKD states.

Characterization of urinary exosomal release of aquaporin-1 and -2 after renal ischemia-reperfusion in rats

Acute kidney injury (AKI) is an important risk factor for the development of chronic kidney disease (CKD), and an alteration in renal water handling has been observed during the transition of AKI to CKD. Urinary exosomal release of aquaporin-1 (AQP1) and AQP2, important proteins for renal water handling, has recently been reported to predict their levels of renal expression. Therefore, we examined the patterns of urinary exosomal release of AQP1 and AQP2, and the exosomal marker proteins tumor susceptibility 101 protein (TSG101) and ALG-2 interacting protein X (Alix), in the acute and chronic phases following induction of AKI by renal bilateral ischemia/reperfusion (I/R) in rats. Blood tests and histological examinations indicated that AKI occurred before at 7 days after renal I/R ( day 7) and that renal fibrosis developed progressively thereafter. Immunoblotting demonstrated significant decreases in the urinary exosomal release of AQP1 and AQP2 during severe AKI. Urinary exosomal release of Alix and TSG101 was significantly increased on day 7. These data were also confirmed in rats with unilateral renal I/R causing more serious AKI. Urinary exosomal release of either the Ser-256- or Ser-269-phosphorylated form of AQP2, both of which are involved in apical trafficking of AQP2, was positively correlated with that of total AQP2. These results suggest that urinary exosomal release of AQP1 and AQP2 is reduced in I/R-induced AKI, whereas that of Alix and TSG101 is increased in the initial phase of renal fibrosis. Furthermore, apical trafficking of AQP2 appears to be related to urinary exosomal release of AQP2.

Progression of Chronic Kidney Disease After Acute Kidney Injury: Role of Self-Perpetuating Versus Hemodynamic-Induced Fibrosis

The relative contribution of self-perpetuating versus hemodynamic-induced fibrosis to the progression of chronic kidney disease (CKD) after acute kidney injury (AKI) is unclear. In the present study, male Sprague-Dawley rats underwent right uninephrectomy and were instrumented with a blood pressure radiotelemeter. Two weeks later, separate groups of rats were subjected to 40 minutes renal ischemia-reperfusion or sham surgery and followed up for 4 or 16 weeks to determine the extent to which glomerulosclerosis and tubulointerstitial fibrosis as a result of the AKI-CKD transition (ie, at 4 weeks post AKI) change over time during the progression of CKD (ie, at 16 weeks post AKI). On average, tubulointerstitial fibrosis was ≈3-fold lower (P<0.05), whereas glomerulosclerosis was ≈6-fold higher (P<0.05) at 16 versus 4 weeks post AKI. At 16 weeks post AKI, marked tubulointerstitial fibrosis was only observed in rats exhibiting marked glomerulosclerosis, proteinuria, and kidney hypertrophy consistent with a hemodynamic pathogenesis of renal injury. Moreover, quantitative analysis between blood pressure and renal injury revealed a clear and modest blood pressure threshold (average 16-week systolic blood pressure of ≈127 mm Hg) for the development of glomerulosclerosis. In summary, modest levels of blood pressure may be playing a substantial role in the progression of renal disease after AKI in settings of preexisting CKD associated with 50% loss of renal mass. In contrast, these data do not support a major role of self-perpetuating tubulointerstitial fibrosis in the progression CKD after AKI in such settings.

Failed Tubule Recovery, AKI-CKD Transition, and Kidney Disease Progression

The transition of AKI to CKD has major clinical significance. As reviewed here, recent studies show that a subpopulation of dedifferentiated, proliferating tubules recovering from AKI undergo pathologic growth arrest, fail to redifferentiate, and become atrophic. These abnormal tubules exhibit persistent, unregulated, and progressively increasing profibrotic signaling along multiple pathways. Paracrine products derived therefrom perturb normal interactions between peritubular capillary endothelium and pericyte-like fibroblasts, leading to myofibroblast transformation, proliferation, and fibrosis as well as capillary disintegration and rarefaction. Although signals from injured endothelium and inflammatory/immune cells also contribute, tubule injury alone is sufficient to produce the interstitial pathology required for fibrosis. Localized hypoxia produced by microvascular pathology may also prevent tubule recovery. However, fibrosis is not intrinsically progressive, and microvascular pathology develops strictly around damaged tubules; thus, additional deterioration of kidney structure after the transition of AKI to CKD requires new acute injury or other mechanisms of progression. Indeed, experiments using an acute-on-chronic injury model suggest that additional loss of parenchyma caused by failed repair of AKI in kidneys with prior renal mass reduction triggers hemodynamically mediated processes that damage glomeruli to cause progression. Continued investigation of these pathologic mechanisms should reveal options for preventing renal disease progression after AKI.

A single-center cohort study to define the role of pretransplant biopsy score in the long-term outcome of kidney transplantation

BACKGROUND

The role of pretransplant biopsy in defining the quality of kidney grafts is still debated. The aim of this study was to investigate the influence of pretransplant biopsy score on long-term graft outcome.

METHODS

In a retrospective cohort study, we analyzed 372 recipients of single kidney transplantation (SKT) from deceased donors between 1997 and 2007, with an available pretransplant biopsy. We evaluated 5- and 10-year graft survival, incidence of delayed graft function, and estimated glomerular filtration rate at 1 and 5 years.

RESULTS

Graft survival at 5 and 10 years was significantly better for recipients with a score of 0 compared to transplants with a score of 1 to 5, whereas we did not observe any significant difference among transplants with a score of 1 through 4. Survival of kidneys with a score of 5 was significantly worse compared to grafts with a score of 1 to 4. In a multivariate Cox model, only pretransplant histological score was significantly associated with graft survival. Transplants with a score of 0 and 5 had the best and the worst graft function, respectively, both at 1 and 5 years, whereas we did not observe any difference among patients with a score of 1 through 4. In a multivariate logistic regression, pretransplant histological score was independently associated with the prevalence of an estimated glomerular filtration rate less than 30 mL/min at 5 years. Finally, delayed graft function rate was significantly higher in recipients with a score of 5 compared to patients with a score of 1 to 4 and score of 0.

CONCLUSIONS

Our data suggest that 1) pretransplant histological score may predict long-term graft outcome and 2) allocation of kidneys with a score of 4 to SKT provides an acceptable long-term graft function and survival.

Inhibition of hyaluronan is protective against renal ischaemia-reperfusion injury

BACKGROUND

Ischaemia-reperfusion injury (IRI) to the kidney is a complex pathophysiological process that leads to acute renal failure and chronic dysfunction in renal allografts. It was previously demonstrated that during IRI, hyaluronan (HA) accumulates in the cortical and external medullary interstitium along with an increased expression of its main receptor, CD44, on inflammatory and tubular cells. The HA-CD44 pair may be involved in persistent post-ischaemic inflammation. Thus, we sought to determine the role of HA in the pathophysiology of ischaemia-reperfusion (IR) by preventing its accumulation in post-ischaemic kidney.

METHODS

C57BL/6 mice received a diet containing 4-methylumbelliferone (4-MU), a potent HA synthesis inhibitor. At the end of the treatment, unilateral renal IR was induced and mice were euthanized 48 h or 30 days post-IR.

RESULTS

4-MU treatment for 14 weeks reduced the plasma HA level and intra-renal HA content at 48 h post-IR, as well as CD44 expression, creatininemia and histopathological lesions. Moreover, inflammation was significantly attenuated and proliferation was reduced in animals treated with 4-MU. In addition, 4-MU-treated mice had a significantly reduced expression of α-SMA and collagen types I and III, i.e. less renal fibrosis, 30 days after IR compared with untreated mice.

CONCLUSION

Our results demonstrate that HA plays a significant role in the pathogenesis of IRI, perhaps in part through reduced expression of CD44. The suppression of HA accumulation during IR may protect renal function against ischaemic insults.

Severe renal mass reduction impairs recovery and promotes fibrosis after AKI

Preexisting CKD may affect the severity of and/or recovery from AKI. We assessed the impact of prior graded normotensive renal mass reduction on ischemia-reperfusion-induced AKI. Rats underwent 40 minutes of ischemia 2 weeks after right uninephrectomy and surgical excision of both poles of the left kidney (75% reduction of renal mass), right uninephrectomy (50% reduction of renal mass), or sham reduction of renal mass. The severity of AKI was comparable among groups, which was reflected by similarly increased serum creatinine (SCr; approximately 4.5 mg/dl) at 2 days, tubule necrosis at 3 days, and vimentin-expressing regenerating tubules at 7 days postischemia-reperfusion. However, SCr remained elevated compared with preischemia-reperfusion values, and more tubules failed to differentiate during late recovery 4 weeks after ischemia-reperfusion in rats with 75% renal mass reduction relative to other groups. Tubules that failed to differentiate continued to produce vimentin, exhibited vicarious proliferative signaling, and expressed less vascular endothelial growth factor but more profibrotic peptides. The disproportionate failure of regenerating tubules to redifferentiate in rats with 75% renal mass reduction associated with more severe capillary rarefaction and greater tubulointerstitial fibrosis. Furthermore, initially normotensive rats with 75% renal mass reduction developed hypertension and proteinuria, 2-4 weeks postischemia-reperfusion. In summary, severe (>50%) renal mass reduction disproportionately compromised tubule repair, diminished capillary density, and promoted fibrosis with hypertension after ischemia-reperfusion-induced AKI in rats, suggesting that accelerated declines of renal function may occur after AKI in patients with preexisting CKD.

Is solitary kidney really more resistant to ischemia? An experimental canine study

PURPOSE

To our knowledge there are no evidence-based medicine data to date to critically judge the vulnerability of a solitary kidney to warm ischemia compared to paired kidneys.

MATERIALS AND METHODS

Ten dogs were exposed to open right nephrectomy to create a solitary kidney model (group 1). Ten dogs with both kidneys were considered group 2. All dogs underwent warm ischemia by open occlusion of the left renal artery for 90 minutes. Dogs were sacrificed at different intervals (3 days to 4 weeks). All dogs were reevaluated by renogram before sacrifice and histopathology of the investigated kidney. The proinflammatory markers CD95 and tumor necrosis factor-α were assessed using real-time polymerase chain reaction.

RESULTS

In group 1 clearance decreased by 20% at 1 week but basal function was regained starting at week 2. In group 2 clearance decreased more than 90% up to week 2. Recovery started at week 3 and by 4 weeks there was a 23% clearance reduction. Histopathological examination in group 1 revealed significant tubular necrosis (60%) at 3 days with regeneration starting at 1 week. In group 2 there was more pronounced tubular necrosis (90%) with regeneration starting at 2 weeks. The expression of proinflammatory markers was up-regulated in each group with higher, more sustained expression in group 2.

CONCLUSIONS

Solitary kidney in a canine model is more resistant to ischemia than paired kidneys based on radiological, pathological and genetic evidence.

Treatment with a novel hypoxia-inducible factor hydroxylase inhibitor (TRC160334) ameliorates ischemic acute kidney injury

BACKGROUND

Hypoxia-inducible factor (HIF) transcriptional system plays a central role in cellular adaptation to low oxygen levels. Preconditional activation of HIF and/or expression of its individual target gene products leading to cytoprotection have been well established in hypoxic/ischemic renal injury. Increasing evidence indicate HIF activation is involved in hypoxic/ischemic postconditioning of heart, brain and kidney. Very few studies evaluated the potential benefits of postischemia HIF activation in renal injury employing a pharmacological agent. We hypothesized that postischemia augmentation of HIF activation with a pharmacological agent would protect renal ischemia/reperfusion injury. For this, TRC160334, a novel HIF hydroxylase inhibitor, was used.

METHODS

TRC160334, a novel HIF hydroxylase inhibitor, was synthesized. Ability of TRC160334 for stabilization of HIF-α and consequent HIF activation was evaluated in Hep3B cells. Efficacy of TRC160334 was evaluated in a rat model of ischemia/reperfusion-induced AKI. Two different treatment protocols were employed, one involved treatment with TRC160334 before onset of ischemia, the other involved treatment after the reperfusion of kidneys.

RESULTS

TRC160334 treatment results in stabilization of HIF-α leading to HIF activation in Hep3B cells. Significant reduction in renal injury was observed by both treatment protocols and remarkable reduction in serum creatinine (23 and 71% at 24 and 48 h, respectively, p < 0.01) was observed with TRC160334 treatment applied after reperfusion. Urine output was significantly improved up to 24 h by both treatment protocols.

CONCLUSION

The data presented here provide pharmacologic evidence for postischemia augmentation of HIF activation by TRC160334 as a promising and clinically feasible strategy for the treatment of renal ischemia/reperfusion injury.

Influence of nephron mass and a phosphorylated 38 mitogen-activated protein kinase inhibitor on the development of early and long-term injury after renal warm ischaemia

BACKGROUND

Renal ischaemia is accompanied by acute and chronic complications. Tumour necrosis factor (TNF) alpha production via p38 mitogen-activated protein kinase (MAPK) is one of the pivotal mechanisms linking ischaemia to inflammation and could be a therapeutic target. FR167653 (FR), an inhibitor of p38 MAPK and TNF-alpha production, may ameliorate renal damage through its effects on TNF-alpha.

METHODS

Warm ischaemia (WI) was induced in male pigs by bilateral clamping of the renal pedicle for 60 min or unilateral renal clamping after contralateral nephrectomy. FR was administered before and during WI, and continuously for 3 h during reperfusion in pigs exposed to the same WI conditions. Experimental groups were compared with sham-operated pigs and those subjected to unilateral nephrectomy without renal ischaemia. Renal function, fibrosis and inflammation were evaluated, and expression of monocyte chemoattractant protein 1, transforming growth factor beta and TNF-alpha was determined after 12 weeks.

RESULTS

FR significantly reduced renal failure in groups subjected to unilateral nephrectomy and bilateral renal ischaemia. Proteinuria was significantly reduced, and inflammation and expression of proinjury proteins were diminished, accompanied by a reduction in renal fibrosis.

CONCLUSION

Control of TNF-alpha production and activity prevents renal damage after prolonged WI.

FR167653 improves renal recovery and decreases inflammation and fibrosis after renal ischemia reperfusion injury

OBJECTIVE

Acute tubular necrosis (ATN) secondary to induced warm ischemia (WI) results in inflammatory and delayed fibrotic processes and remains a common clinical problem with serious consequences. Because tumor necrosis factor-alpha (TNF-alpha) is a prominent proinflammatory factor implicated in the pathophysiology of acute renal ischemia reperfusion injury (IRI), we hypothesized that FR167653 (FR), a potent inhibitor of TNF-alpha and interleukin-1beta production, may reduce IRI.

METHODS

IRI was induced in male pigs by bilateral clamping of the renal pedicle for 90 minutes (WI90), or unilateral renal clamping (90 minutes) after contralateral nephrectomy (1/2Nx90), or unilateral renal clamping without contralateral nephrectomy (WIuni90). FR was administered intravenously 60 minutes before WI (1 mg/kg/h), during WI, and continuously for 3 hours (1 mg/kg/h) during reperfusion in treated groups (FRWI90, FR1/2Nx90, or FRWIuni90). Blood and urine samples were collected between day 1 and 3 months after reperfusion for assessment of renal function. Kidneys were excised and renal tissues were collected at 3 months for morphologic and inflammation evaluation and protein analysis. Experimental groups were compared with sham operated (control) and heminephrectomized (Unif) groups without renal ischemia.

RESULTS

Three WI90 animals (43%) and five 1/2Nx90 (70%) were euthanized and necropsied at day 7 because of no urine production or poor conditions. Mortality was significantly improved after FR treatment. Survival was 100% in the control, Unif, WIuni90, and FR groups. In Unif groups, FR significantly reduced renal failure and bilateral renal ischemia (P < .05). At 3 months, proteinuria was significantly reduced in FR-treated groups (P < .01). Inflammatory cells count was also dramatically diminished in FR-treated pigs (P < .01 for CD3-positive cells). The second aspect of transient ischemia is the fibrotic process determined at 3 months. FR treatment was characterized by a reduction of renal fibrosis, particularly in Unif groups. TNF-alpha protein expression was diminished in FR-treated groups.

CONCLUSION

This is the first evidence that FR reduced the early and long-term effect of WI in the severe ischemia model. This effect was particularly marked against fibrosis and inflammation, which would contribute to deterioration of a patient's renal function.

Vascular endothelial growth factor protein expression in a renal ablation rabbit model under prolonged warm and cold ischemia

BACKGROUND/AIMS

To establish a potential correlation between renal and systemic production of vascular endothelial growth factor (VEGF) protein after prolonged ischemia in a renal ablation model under normothermic and hypothermic conditions.

METHODS

38 uninephrectomized New Zealand rabbits were divided into 5 groups. The rabbits of each group underwent partial nephrectomy under 90 and 60 min of warm and 90 and 120 min of cold ischemia, except for the sham group (S), which served as control. Serum creatinine (SCr) and blood-urea-nitrogen (BUN) levels were assessed. On the 15th postoperative day (POD), the animals were euthanized and the remaining kidneys were evaluated. VEGF immunohistochemistry and serum Western blot analysis were performed.

RESULTS

In comparison to the control group, groups 60W, 90C and 120C showed 1.6-, 1.14- and 1.75-fold decreases, respectively, while the production of VEGF was significantly declined by 7.4-fold in group 90W (p < 0.05). Immunohistochemistry revealed prominent VEGF staining in the above-mentioned three groups, while in group 90W staining was negative. Serum biochemistry and microscopic evaluation verified the same differentiation.

CONCLUSION

Renal and serum VEGF seem to have an analogous expression under conditions of prolonged ischemia. VEGF is overexpressed in hypothermic conditions compared to warm ischemia exceeding 60 min. Hypothermia can be more advantageous in a procedure applying prolonged ischemia.

Recovery from acute renal failure predisposes hypertension and secondary renal disease in response to elevated sodium

Recovery of renal function is a well-characterized feature of models of acute renal failure; however, more recent studies have reported a predisposition to chronic renal disease. This study sought to determine the susceptibility to sodium-dependent hypertension following recovery from ischemic acute renal failure. Following ischemia-reperfusion (I/R) injury, rats were allowed to recover for 35 days on a 0.4% salt diet, then were switched to 4.0% salt diet for an additional 28 days. Blood pressure was significantly increased in postischemic rats switched to high-sodium diet at day 35 (19 ± 9 mmHg) compared with postischemic rats maintained on low-sodium diet. Plasma renin activity and creatinine clearance were not affected by I/R injury. The ischemic injury combined with transfer to 4.0% salt diet resulted in marked renal hypertrophy characterized by interstitial cellular deposition, tubular dilation, and enhanced rates of albumin excretion. Glomerular structure was altered in post-I/R rats switched to high-sodium diet but not in those maintained on low-sodium diets. When rats were acclimated to high-sodium diet before I/R injury, the early injury was similar to that observed in animals acclimated to low-sodium diet, and these animals progressed rapidly toward chronic kidney disease, as evidenced by advancement of albuminuria. These data suggest that the recovery from acute I/R injury is not complete, compromises Na homeostasis, and predisposes hypertension and secondary renal disease.

Effect of prolonged warm ischemia and pneumoperitoneum on renal function in a rat syngeneic kidney transplantation model

BACKGROUND

Laparoscopic donor nephrectomy is associated with several advantages for the donor. However, graft function may be impaired due to use of pneumoperitoneum and prolonged warm ischemia. This study investigated the impact of pneumoperitoneum and prolonged warm ischemia on long-term graft function in a syngeneic rat renal transplant model.

METHODS

A total of 27 Brown Norway rats were randomized for transplantation of kidneys after three different procedures: no insufflation and no warm ischemia (group 1), no insufflation with 20 min of warm ischemia (group 2), and CO2 insufflation and 20 min of warm ischemia (group 3). Glomerular filtration rate (GRF), serum creatinine, urine volume, urine creatinine, and proteinuria were determined monthly for 1 year. One year after transplantation, the grafts were removed for histomorphologic analysis.

RESULTS

No significant differences in GRF, serum creatinine, urine volume, and proteinuria were found among the three groups. Histologic analysis also showed no differences between the groups.

CONCLUSION

Warm ischemia in combination with CO2 pneumoperitoneum, as used in laparoscopic donor nephrectomy, does not result in a negative effect on long-term graft function.

Mammalian Target of Rapamycin Pathway Blockade Slows Progression of Diabetic Kidney Disease in Rats

Recent data suggest that the phosphatidylinositol 3-kinase (PI3-K)/Akt/mammalian target of rapamycin (mTOR) pathway is important in diabetic nephropathy. The effect of mTOR blockade by sirolimus (SRL) in diabetic kidney disease in rats was investigated. Diabetes was induced by streptozotocin in male Sprague-Dawley rats. Sixteen weeks later, diabetic animals were divided into the following groups: diabetes (D; n = 8), diabetes + SRL at 1 mg/kg per d, SRL trough level 2.3 +/- 0.25 ng/ml (D+SRL; n = 7); and diabetes + normoglycemia maintained by insulin implants (D+NG; n = 5). There was an age-matched nondiabetic group (ND; n = 6). All animals were followed for 4 wk. The D group showed glomerular hypertrophy (mean glomerular volume 5.0 +/- 0.4 in D versus 3.3 +/- 0.2 10(6) mu(3) in ND; P < 0.05) without renal hyperplasia (calculated by reverse transcription-PCR of proliferative cell nuclear antigen) and albuminuria (29 +/- 4 in D versus 1.4 +/- 1.5 mg/24 h in ND; P < 0.05). Both D+NG and D+SRL groups had a significant reduction of albuminuria, although glomerular hypertrophy was still present. SRL treatment did not modify the number of infiltrating renal ED1(+) cells. Diabetic animals had greater expression of p-Akt and mTOR, unlike ND rats. NG and SRL treatment reduced p-Akt and normalized mTOR. It is interesting that D+SRL was associated with a significant reduction of renal TGF-beta1 and glomerular connective tissue growth factor. SRL treatment reduced glomerular alpha-smooth muscle actin overexpression and reduced significantly the mesangial matrix accumulation that is characteristic of diabetic nephropathy. In conclusion, mTOR blockade by low-dose SRL has a beneficial effect in diabetic kidney disease, suggesting that the mTOR pathway has an important pathogenic role in diabetic nephropathy.

Glomerular size in early protocol biopsies is associated with graft outcome

Long-term consequences of glomerular enlargement after transplantation are not well understood. The aim is to evaluate the relationship between glomerular volume (Vg) estimated in protocol biopsies, graft function and graft survival. Vg and Banff chronic damage score were evaluated in protocol biopsies at 4 months. Creatinine clearance (CrCl) was estimated by the Cockroft-Gault formula. Vg estimated in 144 patients was 4.8 +/- 2.0 x 10(6)mu(3). It was associated with donor age (r = 0.23, p < 0.01), recipient body mass index (r = 0.17, p = 0.04), delayed graft function (Vg = 5.9 +/- 2.3 vs. 4.6 +/- 1.9 x 10(6)mu(3), p < 0.01) and CrCl (r = 0.17, p = 0.04). The best cutoff of Vg, Banff chronic damage score and CrCl was determined by Cox regression analysis, being 5.0 x 10(6)mu(3) for Vg (relative risk (RR): 2.4, 95% confidence interval (CI): 1.03-5.6), >2 for chronic damage score (RR: 3.4, 95% CI: 1.03-8.9) and 60 mL/min for CrCl (RR: 3.5, 95% CI: 1.04-11.9). These variables were independent predictors of death-censored graft survival. According to Vg and CrCl, four groups of patients were defined. Patients with small glomeruli and high CrCl had a 95% graft survival while patients with large glomeruli and low CrCl had a 45% graft survival at 15 years (p < 0.01). Large glomerular volume, high Banff chronic score and poor early renal function in stable grafts are independently associated with death-censored graft survival.

Risk factors associated with the deterioration of renal function after kidney transplantation

Renal function early after transplantation is associated with a large number of risk factors, including donor age and acute rejection. During the 1990s, donor age increased and the incidence of acute rejection decreased. Renal function between the third and sixth month improved slightly, while renal function deterioration between the third or sixth month and the 12th month improved significantly. This modification coincides with the introduction of mycophenolate mofetil and tacrolimus. The tendency for sustained renal improvement early after transplantation became more evident after the introduction of anti-calcineurin-free regimens. Studies of protocol biopsies have shown that there is an increase of glomerular volume after transplantation and that a larger glomerular volume at 4 months is associated with a better glomerular filtration rate. This adaptation mechanism is impaired in patients with chronic allograft nephropathy or in patients with high cyclosporin levels. Taken together, these data suggest that the steady improvement of renal allograft function may be partly explained by a better glomerular adaptation after transplantation because of the avoidance of the vasoconstrictive effect of anti-calcineurinic agents, and a significant decrease in the prevalence of chronic allograft nephropathy early after transplantation.

Rarefaction of peritubular capillaries following ischemic acute renal failure: a potential factor predisposing to progressive nephropathy

PURPOSE OF REVIEW

Long-term renal complications of acute renal failure have generally not been expected in patients that recover from acute renal failure. However, as the incidence of acute renal failure is rising, the incidence of long-term complications is likely to increase. As a corollary to ischemic acute renal failure, ischemic injury in the setting of transplant is a leading cause of delayed graft function. Unlike acute renal failure in native kidneys, delayed graft function is highly predictive of chronic nephropathy and organ failure. It is generally well accepted that acute reversible injuries mediated by ischemia render grafts susceptible toward future demise. The nature of the susceptibility that is conveyed to grafts following ischemic injury is not well understood.

RECENT FINDINGS

Evidence from animal models suggests that acute injury results in microvascular damage and vessel loss in the kidney, which, as opposed to tubular damage, is largely persistent. In addition, various studies of biopsies of renal transplants suggest that ischemia imposes an early and sustained loss in peritubular capillaries in the transplanted graft. The loss of peritubular capillaries has been associated with nephropathies of diverse etiologies and may represent a single, common pathway towards progressive damage.

SUMMARY

It is hypothesized that rarefaction of peritubular capillaries represents a critical event, following ischemic injury, that permanently alters renal function and predisposes patients to the development of chronic renal insufficiency. Factors that affect vascular reactivity or the structural dynamics of the kidney vascular system following injury may represent future treatment modalities following renal injury.

Estimation of total glomerular number in stable renal transplants

Glomerular number (N(g)) is considered a major determinant of renal function and outcome. In the dog, it has been shown that Ng can be estimated with reasonable precision in vivo by means of a renal biopsy and magnetic resonance imaging (MRI). Thus, this method was applied to study anatomoclinical correlations in stable human renal transplants. Thirty-nine stable renal transplants were included. A protocol renal allograft biopsy was done at 4 mo. Biopsies were evaluated according to Banff criteria. Glomerular volume fraction (Vv(glom/cortex)) was measured by means of a point-counting method, and mean glomerular volume (V(g)) was estimated by means of Weibel and Gomez (V(g)-W&G) and maximal profile area (V(g)-MPA) methods. MRI was used to estimate renal cortical volume (V(cortex)). N(g) was calculated as (Vv(glom/cortex) x V(cortex))/V(g). GFR was estimated by the inulin clearance. Ten age-matched donor biopsies served as controls for V(g). Histologic diagnosis was as follows: normal (n = 20), borderline (n = 7), acute rejection (n = 1), and chronic allograft nephropathy (n = 11). Vv(glom/cortex) was 3.4 +/- 1.1%, V(cortex) was 167 +/- 46 cm(3), V(g)-W&G was 3.2 +/- 1.2 x 10(6) micro m(3), and V(g)-MPA was 3.3 +/- 1.0 x 10(6) micro m(3). V(g)-W&G in donor and recipient biopsies was not different (3.6 +/- 1.1 versus 3.2 +/- 1.2 x 10(6) micro m(3)). Total glomerular number estimated by means of V(g)-W&G (N(g)-W&G) was 0.73 +/- 0.33 x 10(6) and by V(g)-MPA (N(g)-MPA) was 0.74 +/- 0.31 x 10(6). A positive correlation between GFR and N(g)-W&G (r = 0.47, P = 0.002) was observed. Furthermore, the older the donor, the higher V(g)-W&G (r = 0.37, P = 0.01) and the lower N(g)-W&G (r = -0.40, P = 0.01). Total glomerular number can be estimated in stable renal allografts by means of a renal biopsy and MRI. Our data show that N(g) depends on donor age and positively correlates with GFR.

Cyclosporine A sensitizes the kidney to tubulointerstitial fibrosis induced by renal warm ischemia

BACKGROUND

Renal warm ischemic injury and immunosuppression with cyclosporin A (CsA) may contribute to chronic allograft nephropathy after cadaveric transplantation. This study establishes whether CsA can sensitize the kidney to injury and fibrosis induced by renal warm ischemia (RWI).

METHODS

The left kidney of Sprague-Dawley rats was subjected to 30 min of warm ischemia and/or intraperitoneal CsA (15 mg/kg/d) for 30 days (n=6 per group). Renal injury and fibrosis were assessed histologically together with immunohistochemistry for collagen III, transforming growth factor (TGF)-beta1, ED1 (macrophage marker), and alpha-smooth muscle actin. Renal mRNAs for collagen III, TGF-beta 1, matrix metalloproteinase (MMP)-2, and tissue inhibitor of metalloproteinase-1 together with MMP enzyme activity were also determined.

RESULTS

RWI or CsA alone produced only minor effects on renal injury and fibrosis. However, in CsA-treated rats, RWI produced a marked increase in tubulointerstitial fibrosis, as shown by the potentiation of collagen III and TGF-beta1 determined by immunochemistry and mRNA analysis. The up-regulation of tissue inhibitor of metalloproteinase-1 mRNA was associated with a decrease in MMP enzyme activity. In CsA-treated rats, RWI was also associated with an increase in inflammatory infiltrates, elevated immunostain for ED1 (indicating extensive macrophage influx), and elevated immunostain for alpha-smooth muscle actin (indicating myofibroblast activation).

CONCLUSIONS

In the rat, CsA can sensitize the kidney to fibrosis induced by renal warm ischemia. In renal transplantation, when cadaveric donor kidneys have been subjected to a period of warm ischemia, CsA may be an inappropriate choice for immunosuppressive therapy.

Chronic renal hypoxia after acute ischemic injury: effects of L-arginine on hypoxia and secondary damage

Ischemic acute renal failure (ARF) results in the permanent loss of peritubular capillaries and predisposes the progression of chronic renal failure. The present study was undertaken to determine whether renal hypoxia, which may represent an important mediator in disease progression, is persistently exacerbated after recovery from ARF. Rats were subjected to ischemia-reperfusion injury and allowed to recover for 5 or 20 wk. Immunohistochemistry of the hypoxia-sensitive marker 2-pimonidizole at 5 wk revealed an overall increase in incorporation in the outer medullary region after recovery from ARF compared with sham-operated controls. Unilateral nephrectomy, in combination with ischemia-reperfusion injury resulted in greater 2-pimonidizole staining than that observed in the bilateral injury model. In addition, in the unilateral ischemia-nephrectomy model, proteinuria, interstitial fibrosis, and renal functional loss developed significantly faster than in the bilateral model of ARF when animals were allowed to recover for 20 wk. l-Arginine in the drinking water ( approximately 0.5 g/day) increased total renal blood flow approximately 30%, decreased pimonidizole staining, and attenuated manifestations of chronic renal disease. These data suggest that a reduction in the peritubular capillary density after ARF results in a persistent reduction in renal Po(2) and that hypoxia may play an important role in progression of chronic renal disease after ARF.

Renal ischemic injury results in permanent damage to peritubular capillaries and influences long-term function

First published August 9, 2001; 10.1152/ajprenal.00050.2001.—Acute episodes of severe renal ischemia result in acute renal failure (ARF). These episodes are followed by a characteristic recovery and repair response, whereby tubular morphology and renal function appear completely restored within ∼1 mo. However, the chronic effects of such an injury have not been well studied. Male rats were subjected to 60-min bilateral ischemia followed by reperfusion, yielding a characteristic injury. Postischemic animals manifested severe diuresis, peaking at 1 wk postinjury (volume: >45 ml/day, ARF vs. 18 ml/day, sham; P < 0.05). Urine flow subsequently declined but remained significantly elevated vs. sham animals for a 40-wk period. The prolonged alteration in urinary concentrating ability was attributable, in part, to a diminished capacity to generate a hypertonic medullary interstitium. By week 16, proteinuria developed in the post-ARF group and progressed for the duration of the study. Histological examination revealed essentially normal tubular morphology at 4 and 8 wk postinjury but the development of tubulointerstitial fibrosis at 40 wk. Transforming growth factor (TGF)-β1 expression was elevated at 40 wk, but not at 4 and 8 wk postinjury. Microfil analysis revealed an ∼30–50% reduction in peritubular capillary density in the inner stripe of the outer medulla at 4, 8, and 40 wk in post-ARF groups vs. sham animals. In addition, post-ARF rats manifested a significant pressor response to a low dose of ANG II (15 ng · kg−1· min−1). We hypothesize that severe ischemic injury results in a permanent alteration of renal capillary density, contributing to a urinary concentrating defect and the predisposition toward the development of renal fibrosis.

Renal ischemic injury results in permanent damage to peritubular capillaries and influences long-term function

Acute episodes of severe renal ischemia result in acute renal failure (ARF). These episodes are followed by a characteristic recovery and repair response, whereby tubular morphology and renal function appear completely restored within approximately 1 mo. However, the chronic effects of such an injury have not been well studied. Male rats were subjected to 60-min bilateral ischemia followed by reperfusion, yielding a characteristic injury. Postischemic animals manifested severe diuresis, peaking at 1 wk postinjury (volume: >45 ml/day, ARF vs. 18 ml/day, sham; P < 0.05). Urine flow subsequently declined but remained significantly elevated vs. sham animals for a 40-wk period. The prolonged alteration in urinary concentrating ability was attributable, in part, to a diminished capacity to generate a hypertonic medullary interstitium. By week 16, proteinuria developed in the post-ARF group and progressed for the duration of the study. Histological examination revealed essentially normal tubular morphology at 4 and 8 wk postinjury but the development of tubulointerstitial fibrosis at 40 wk. Transforming growth factor (TGF)-beta1 expression was elevated at 40 wk, but not at 4 and 8 wk postinjury. Microfil analysis revealed an approximately 30-50% reduction in peritubular capillary density in the inner stripe of the outer medulla at 4, 8, and 40 wk in post-ARF groups vs. sham animals. In addition, post-ARF rats manifested a significant pressor response to a low dose of ANG II (15 ng x kg(-1) x min(-1)). We hypothesize that severe ischemic injury results in a permanent alteration of renal capillary density, contributing to a urinary concentrating defect and the predisposition toward the development of renal fibrosis.

Protective effect of UR-12670 on chronic nephropathy induced by warm ischaemia in ageing uninephrectomized rats

BACKGROUND

In young animals, renal ischaemia/reperfusion injury and mass reduction are associated with chronic lesions that mimic those found in chronic rejection. We have shown that the phospholipid platelet-activating factor (PAF) participates in young animals in such chronic nephropathy. Here we examine the long-term effects of the orally active PAF antagonist, UR-12670 in ageing uninephrectomized rats exposed to prolonged warm ischaemia.

METHODS

Fifteen- to eighteen-month-old uninephrectomized male Sprague-Dawley rats were allocated into three groups and followed for 16 weeks: UNx, rats without ischaemia; UNxISC, ischaemic kidney (60 min), and UNxISC+UR, ischaemic kidney and UR-12670 from day 0 to the 16th week. Serum creatinine and proteinuria were monitored every 4 weeks. At the end of the study, conventional histology was performed and monocyte-macrophages were identified with the specific monoclonal antibody ED-1.

RESULTS

The UNxISC group had severe acute renal failure with a high mortality rate, which was associated with incomplete restoration of renal function. Renal insufficiency in this group was sustained throughout the follow-up. Both UNx and UNxISC groups developed progressive proteinuria from the 12th week. Though UNxISC+UR group showed similar acute renal failure and mortality rate to the ischaemic non-treated group, serum creatinine decreased to levels similar to UNx group, which were maintained until the end of the study. Treatment of ischaemic kidneys with UR-12670 produced a slight decrease in 24-h proteinuria and a reduction in glomerulosclerosis, the mean tubulointerstitial score and number of monocyte-macrophages to values similar to UNx group.

CONCLUSIONS

The chronic administration of the PAF antagonist UR-12670 attenuates the long-term effects of ischaemia-reperfusion injury in uninephrectomized ageing rats. The beneficial effect of this agent suggests that PAF contributes to the progression to late renal damage in this model.