Uremia is typically defined as the signs that result as a consequence of the loss of kidney function. Uremia is caused by the accumulation of organic waste products as well as the impairment of metabolic and endocrine renal functions. The most common cause of uremia is CKD, but other conditions such as AKI, lower urinary tract obstruction, and rupture of the urinary tract may cause it.1 In human medicine, it has been reported that persistent chronic inflammation in patients with CKD is a major contributing factor for increased morbidity and mortality rates.2 Factors contributing to this inflammatory process are retention of mediators such as circulating cytokines and pro-oxidants with declining kidney function as well as increased tissue production of inflammatory mediators caused by uremia, oxidative stress, and other factors such as overhydration.2,3
In human medicine, 1% of hospital admissions are the result of AKI, and up to 7% of patients hospitalized for other conditions develop AKI.4 In veterinary medicine, the incidence of AKI in hospital admissions is unknown, but studies5,6,a conducted to investigate hospital-acquired AKI found that the prevalence is between 9% and 14.6%. In addition, the extent of the increase in azotemia can be used as a predictor for death of dogs and cats.5,7 Despite the availability of both intermittent hemodialysis and continuous renal replacement therapy, the mortality rate still remains high in humans and domestic animals. In a recent study8 of cats and dogs with AKI treated by means of intermittent hemodialysis, it was found that although there was a high mortality rate for dogs prior to discharge from the hospital, the overall rate of survival to discharge from the hospital was 53%, which is similar to values reported for human patients.
It is currently believed that inflammation plays a major role in the pathophysiology of AKI, both for initiation of AKI and also in the extension phase. It is thought that the initial insult to the kidneys results in morphological and functional changes in vascular endothelial cells and the tubular epithelium. Subsequently, renal endothelial cells and proximal tubular epithelial cells produce cytokines and chemokines that lead to infiltration of inflammatory cells (eg, neutrophils, lymphocytes, macrophages, and natural killer cells) into the kidneys. Inflammatory cells then additionally produce proinflammatory and anti-inflammatory cytokines that may contribute to the already existing inflammation.4
Proinflammatory cytokines include many cytokines characterized as inducible and belonging to various families. Proinflammatory cytokines include IL-1, IL-2, IL-6, IL-8, members of the TNF family, IFN-γ, and others. Anti-inflammatory cytokines, such as IL-10 or TGF-β, typically control or decrease inflammatory processes.9
In several studies of AKI in experimental settings in mice or rats as well as clinical studies in human patients with AKI, investigators have detected increased concentrations of proinflammatory and antiinflammatory cytokines and mediators. Studies10,11 of mice with ischemic AKI have found that IL-2, IL-6, IL-10, IFN-γ, and TGF-β concentrations are increased in renal tissue. Similar results were obtained in another study,12 with elevated concentrations of IL-1α, IL-1β, IL-6, and IL-18 in renal tissue of mice with cisplatin-induced AKI. Fewer studies have been conducted to evaluate inflammatory mediators in humans with AKI. Investigators of 1 study13 found that human patients with AKI have significantly higher plasma concentrations of IL-1β, IL-6, IL-8, TNF-α, C-reactive protein, and IL-10, compared with concentrations in healthy people and patients with CKD. Additionally, concentrations of IL-6, IL-8, and the anti-inflammatory cytokine IL-10 were significantly higher in nonsurvivors.13 Other studies14,15 have revealed that concentrations of IL-2, IL-6, and TNF-α are markedly higher in patients with AKI and are significantly associated with mortality rates.
The enzyme 5-LO is primarily expressed in leukocytes and is the key enzyme in the biosynthesis of leukotrienes, which are considered potent mediators of inflammation.16 Lipoxygenase enzymes have also been implicated in renal vasoconstriction and inflammation in AKI, and lipoxygenase interaction products (lipoxins) have been found to be beneficial in AKI.17,18 One of the key enzymes that generates nitric oxide from L-arginine is iNOS; iNOS-derived nitric oxide plays an important role in inflammatory conditions. In rats, induced ischemic AKI results in major damage to the kidneys and a concomitant increase in the iNOS concentration.19
On the basis of these findings in human medicine and experimental studies, we hypothesized that uremia is an inflammatory condition in dogs, the degree of inflammation is associated with the severity of azotemia, and the degree of inflammation is more pronounced in dogs with AKI than in dogs with CKD. The purpose of the study reported here was to assess the inflammatory status of dogs with impaired renal function attributable to various causes by measuring the expression of inflammatory cytokines and enzymes in venous blood samples.
Materials and Methods
Animals
Dogs with azotemia attributable to AKI or stable CKD that were evaluated at the small animal clinic of the Vetsuisse Faculty, University of Bern, between January 1 and December 31, 2010, were eligible for inclusion in this prospective study. All dogs enrolled in this study were also included in other experiments that focused on leptospirosis-associated pulmonary hemorrhage syndrome.b Acute kidney injury was defined as acute onset of renal azotemia or evidence of acute tubular damage and compatible historical, clinical, clinicopathologic, and radiographic findings. Chronic kidney disease was defined as stable azotemia for at least 1 month, inability to concentrate urine, and compatible abdominal ultrasonography findings. Exclusion criteria included known or suspected acute-on-chronic kidney disease, glomerulonephropathies, and azotemia attributable to prerenal and postrenal causes.
Dogs with AKI were classified into 5 grades as defined in IRIS guidelines20: I = nonazotemic AKI (serum creatinine concentration < 140 μmol/L), II = mild AKI (serum creatinine concentration, 141 to 220 μmol/L), III = moderate AKI (serum creatinine concentration, 221 to 445 μmol/L), IV = moderate-to-severe AKI (serum creatinine concentration, 446 to 890 μmol/L), and V = severe AKI (serum creatinine concentration, > 890 μmol/L). Dogs with stable CKD were classified into 4 stages as defined in IRIS guidelines21: I = nonazotemic CKD (serum creatinine concentration, < 125 μmol/L), II = mild renal azotemia (serum creatinine concentration, 125 to 179 μmol/L), III = moderate renal azotemia (serum creatinine concentration, 180 to 439 μmol/L), and IV = severe renal azotemia (serum creatinine concentration, > 440 μmol/L).
A control group was included in the study; it consisted of 10 healthy dogs owned by staff or volunteers. Dogs were confirmed to be healthy on the basis of results of physical examination, a CBC, biochemical analysis, and urinalysis.
Owners provided informed consent for inclusion of their dogs in the study. The study was approved by the Animal Experimental Ethics Committee of the Small Animal Teaching Hospital of the Vetsuisse Faculty at the University of Bern.
Procedures
Demographic and laboratory characteristics, including results for a CBC, biochemical analysis, and urinalysis, were evaluated for every dog. Expression of the anti-inflammatory cytokines IL-10 and TGF-β as well as the proinflammatory cytokines IL-1α, IL-1β, IL-8, and TNF-α were measured in venous blood samples collected at the time of initial evaluation. Additionally, expression of the enzymes 5-LO and iNOS was also evaluated. Each cytokine and enzyme was analyzed by measuring mRNA expression with a real-time PCR assay as described elsewhere.b Briefly, mRNA was extracted from whole blood with a commercially available kitc used in accordance with the manufacturer's protocol. The RNA was converted to cDNA with a synthesis kit.d Specific primers were used as previously described.b The real-time PCR assay was developed and evaluated on a real-time DNA detection system.e The mRNA expression was calculated relative to that for the housekeeping gene ubiquitin, which was used as a control sample.
Data analysis
Statistical analysis was performed with commercial software.f Given that most data were not normally distributed, nonparametric tests were used. Continuous data were compared by means of the Mann-Whitney rank-sum test. Regression analysis was performed by means of Spearman rank correlation. The proportion of dogs with higher inflammatory biomarker expression was evaluated by comparing values for dogs with AKI or CKD with the range of values for the healthy dogs. Values of P ≤ 0.05 were considered significant.
Results
Forty-six dogs met the criteria for AKI, and 8 dogs met the criteria for CKD. In this population, AKI was attributed to leptospirosis (n = 32 [69.6%]), grape ingestion (3 [6.5%]), and other intoxications (2 [4.3%]); 9 (19.6%) dogs had AKI of unknown origin.
Dogs in the AKI group ranged from 0.17 to 12.3 years of age (median, 4.8 years), dogs in the CKD group ranged from 0.75 to 10.6 years of age (median, 6.5 years), and dogs in the healthy group ranged from 1 to 11.1 years of age (median, 3.9 years). In the AKI group, 1 dog was classified as IRIS grade I, 10 dogs as IRIS grade III, 19 dogs as IRIS grade IV, and 16 dogs as IRIS grade V. In the CKD group, 1 dog was classified as IRIS stage III, and the remaining 7 dogs were classified as IRIS stage IV.
Clinicopathologic variables for all dogs were summarized (Table 1). The PCV was markedly higher for dogs with AKI than for dogs with CKD and for healthy dogs than for dogs with AKI or CKD. Number of platelets was markedly lower for dogs with AKI, compared with the number of platelets for healthy dogs. The WBC counts were elevated for dogs with AKI, compared with results for dogs with CKD or healthy dogs. Band cell and neutrophil counts were markedly higher for dogs with AKI, compared with counts for healthy dogs, and neutrophil counts were markedly higher for dogs with AKI, compared with counts for dogs with CKD. The WBC, band cell, and neutrophil counts were significantly higher for dogs with AKI attributable to an infectious cause, compared with counts for dogs with AKI attributable to other causes. By definition, serum urea and creatinine concentration were also markedly higher for dogs with AKI or CKD than for healthy dogs.
Dogs with AKI or CKD had significant increases in mRNA expression of IL-1α (P < 0.001), IL-1β (P < 0.001), and 5-LO (P = 0.004), compared with mRNA expression for healthy dogs. Dogs with AKI had a significant (P = 0.005) increase in TGF-β expression, compared with mRNA expression for healthy dogs; TGF-β expression did not differ significantly between dogs with CKD and healthy dogs. There was no significant difference in cytokine or enzyme mRNA expression between dogs with AKI and dogs with CKD (Figure 1). However, dogs with AKI had more variability in expression of most cytokines and enzymes, in particular IL-1α, IL-8, 5-LO, and iNOS. Regression analysis revealed no correlation between IL-1α expression and serum creatinine concentration for dogs with CKD or AKI (Figure 2). Additionally, no correlation was detected among the various causes of AKI when evaluated separately and for the comparison between infectious causes (eg, leptospirosis) and noninfectious causes of AKI. To provide a better assessment of a possible correlation between inflammatory markers and the degree of azotemia, dogs with CKD and AKI were allocated into quartiles (on the basis of serum creatinine and urea concentrations) and also were grouped in accordance with the stage or grade of CKD or AKI, respectively. No correlation between the degree of azotemia and expression of IL-1α, IL-1β, and TGF-β was detected for these additional classifications (Figure 3).
Box-and-whisker plots of relative mRNA expression of cytokines and enzymes in whole blood of 46 dogs with AKI (black bars), 8 dogs with CKD (gray bars), and 10 healthy dogs (white bars). The mRNA expression was calculated relative to that for the housekeeping gene ubiquitin. Each box represents the interquartile range, the horizontal line in each box represents the median, the whiskers represent 1.5 times the interquartile range, and circles represent outliers.
Citation: American Journal of Veterinary Research 77, 2; 10.2460/ajvr.77.2.218
Relative mRNA expression of IL-1α in relation to the serum creatinine concentration for 46 dogs with AKI (white squares) and 8 dogs with CKD (black circles). The mRNA expression was calculated relative to that for the housekeeping gene ubiquitin. The lines of best fit for dogs with AKI (gray line; r2 = 0.069; P = 0.089) and dogs with CKD (black line; r2 = 0.33; P = 0.14) revealed that there was no correlation between the variables.
Citation: American Journal of Veterinary Research 77, 2; 10.2460/ajvr.77.2.218
Box-and-whisker plots of relative mRNA expression of IL-Iα (A), IL-1 β (B), TGF-β (C), and 5-LO (D) for 10 healthy dogs, 54 dogs with azotemia, 8 dogs with CKD, 10 dogs with AKI grade III, 19 dogs with AKI grade IV, and 16 dogs with AKI grade V. The mRNA expression was calculated relative to that for the housekeeping gene ubiquitin. Grades of AKI were classified as defined in IRIS guidelines.20 See Figure 1 for remainder of key.
Citation: American Journal of Veterinary Research 77, 2; 10.2460/ajvr.77.2.218
Median (interquartile range) values of laboratory variables measured in blood samples obtained from 46 dogs with AKI, 8 dogs with CKD, and 10 healthy dogs at initial evaluation.
| Variable | AKI | CKD | Healthy |
|---|---|---|---|
| PCV (%) | 32.5 (28.0–40.0)a | 23.5 (14.8–30.5)b | 43 (41–46.5)c |
| Platelet count (109 platelets/L) | 166.0 (90.8–256.3)a | 205.5 (101.8–261.8)a,b | 226 (202.3–278.5)b |
| WBC count (109 cells/L) | 14.7 (11.7–19)a | 8.9 (7.1–13.8)b | ll.2 (7.1–11.6)b |
| Band cell count (109 cells/L) | 0.47 (0.11–1)a | 0.04 (0–0.24)a,b | 0.05 (0.05–0.08)b |
| Segmented cell count (109 cells/L) | 11.23 (9.47–15.39)a | 6.81 (4.61–8.51)b | 5.97 (4.07–6.61)b |
| Creatinine (μmol/L) | 785.5 (449.5–1,044)a | 866.5 (679–1,246)a | 80.5 (70.3–92.3)b |
| Urea (mmol/L) | 55.8 (39.7–73.1)a | 77.4 (54.5–83.7)a | 6.5 (4.6–7.2)b |
Within a row, values with different superscript letters differ significantly (P < 0.05).
Expression of various inflammatory biomarkers was higher in 2 to 35 of the 46 (4.3% to 76.1%) dogs in the AKI group and 1 to 7 of the 8 dogs in the CKD group, compared with expression for the healthy dogs (Figure 4). Of the 46 dogs with AKI, 17 (37.0%) had higher IL-8 mRNA expression, compared with expression for the healthy dogs; none of the 8 dogs with CKD had higher IL-8 expression, compared with expression for the healthy dogs. These proportions differed significantly (P = 0.047) between the AKI and CKD groups. Also, a significantly (P = 0.02) higher proportion of dogs with CKD (3/8) than with AKI (2/46) had elevated TNF-α expression. Interestingly, none of the dogs with AKI or CKD had lower expression of inflammatory biomarkers, compared with expression for healthy dogs.
Proportions of dogs with AKI (black bars) and CKD (gray bars) that had higher cytokine expression than did healthy dogs. *†Proportion differs significantly (*P = 0.047; †P = 0.02) from the proportion of dogs with CKD.
Citation: American Journal of Veterinary Research 77, 2; 10.2460/ajvr.77.2.218
Discussion
On the basis of results for the study reported here, uremia appeared to be an inflammatory condition with dysregulation of cytokines and enzymes in dogs with stable CKD as well as in dogs with AKI, which thus confirmed our hypothesis. Expression of the proinflammatory biomarkers IL-1α, IL-1β, and 5-LO as well as the anti-inflammatory marker TGF-β was elevated in uremic dogs, and expression of TGF-β was also significantly increased for dogs with AKI, compared with expression for dogs with CKD. The IL-1 molecule comprises a major proinflammatory family of cytokines that acts mainly through the induction of proinflammatory cytokines and mediators. The initial inflammatory response is induced by IL-1 α derived from damaged cells. Subsequently, resident macrophages respond to IL-1α and produce IL-1β, which is then responsible for the propagation of the inflammatory response.22–24 The enzyme 5-LO is implicated as an inflammatory enzyme in renal injury, but it does not appear to be a biomarker of inflammation commonly used for patients with AKI.18 Considering that 5-LO expression was clearly higher in dogs with impaired renal function, it might be useful as part of a biomarker panel, especially considering that lipoxins are of benefit as a treatment for ischemic AKI.19
The kidneys are a site of TGF-β production and TGF-β action. It is known that TGF-β plays a key role in chronic progressive renal disease by mediating fibrogenesis as well as apoptosis and epithelial-to-mesenchymal transdifferentiation.25 Therefore, increased expression of TGF-β in dogs with CKD was not surprising. Expression of TGF-β was also significantly higher in dogs with AKI, compared with expression in dogs with CKD. Expression of TGF-β was elevated within 3 days and remained elevated for up to 7 days after experimental induction of ischemic AKI in rats.26 The role of TGF-β in AKI is not completely clear, but TGF-β activity appears to influence cellular proliferation after an initial insult, although definitive evidence is lacking that TGF-β plays a substantial role in the renal repair response. In contrast, TGF-β activity promotes renal fibrogenesis and renal blood vessel loss following AKI and therefore may predispose the kidneys to the development of CKD.26
The reason that expression of other inflammatory cytokines (eg, TNF-α) that have been elevated in experiments and clinical studies of AKI was not different between diseased and healthy dogs of the present study was not clear. Also, no correlation was detected between laboratory variables, especially the degree of azotemia and cytokine gene expression, which was in contrast to the assumption for the second hypothesis. Additionally, except for expression of TGF-β, no difference was detected between dogs with AKI and CKD, which supported the third hypothesis only for TGF-β expression.
A potential explanation was the timing of cytokine determination in the overall course of disease. The interval between onset of clinical signs and initial evaluation differed among dogs with AKI. Therefore, it was possible that differences in expression of early and late inflammatory markers may have been missed. It is also important to mention that inflammatory cytokine and enzyme biological processes are extremely complex in disease states, and a lack of correlation between gene expression of cytokines and their bioactivity has been reported.27 Of course, this hypothesis should be confirmed with the measurement of plasma concentrations of cytokines. In some diseases, measurement of cytokines in samples other than plasma might be useful. For example, measurement of urinary IL-6 concentrations reflects disease states better than does circulating plasma IL-6 concentrations,28 and assessment of inflammatory cytokine concentrations in bronchial alveolar lavage fluid has better prognostic value than does assessment of concentrations in plasma.29,30 Furthermore, in most experimental studies of AKI, cytokine concentrations have been measured directly in renal tissue. This procedure is not without risk and thus is not routinely performed in veterinary medicine. Measuring cytokine expression in urine instead of plasma may provide a better understanding of the inflammatory process for AKI. However, given that 27 of 46 (59%) dogs in the present study were oliguric or anuric, a urine sample was not available for most of the dogs with renal impairment.
It is also possible that the differences in plasma cytokine expression between groups were too small to be detected by the methods used in the present study or that variations were attributable to heterogeneity of the disease groups. A similar observation has been made for plasma concentrations of IL-1β in another study.31 Other limitations for the study reported here included the sample size of the groups; however, statistical power should have been sufficient to detect major, clinically relevant differences. Another factor was that the degree of inflammation was multifactorial and caused by a combination of primary (etiology) and secondary (complications) variables. The fact that most of the dogs with AKI had leptospirosis might also have biased the results.
The inflammatory process is extremely complex, and it is possible that biomarkers other than the ones we evaluated in the present study would have better represented inflammation in AKI. Interleukin-6 is an important proinflammatory cytokine in the kidneys, and release of IL-6 is stimulated by TNF-α. In several studies,14,16,31,32 plasma IL-6 concentrations were increased in patients with AKI and could be used to predict death. In addition, urinary IL-6 concentrations have been proposed as an early marker for acute renal allograft rejection.33 Unfortunately, results of several attempts to measure IL-6 concentrations with various primers have failed to meet quality requirements. Furthermore, IL-18, a proinflammatory cytokine induced in the proximal tubules after injury, appears to be a potential biomarker for AKI. Urinary IL-18 concentrations are increased in mice with ischemic AKI and also in human patients with acute tubular necrosis and delayed graft function, compared with concentrations of patients with other renal diseases.34 In addition, IL-18 concentrations can be used as a marker for early detection of AKI and also to predict risk of death after AKI.35
For the study reported here, a clear increase in mRNA expression of the cytokines IL-1α, IL-1β, and TGF-β and the enzyme 5-LO was detected in blood samples obtained from dogs with renal disease, which suggested that these markers are part of an inflammatory response for AKI or CKD and therefore should be included in a biomarker panel. Although no difference in expression was detected between dogs with AKI or CKD, dogs with AKI more frequently had elevated IL-8 mRNA expression and dogs with CKD had elevated TNF-α expression, which suggested an association with the type of renal disease. Further studies are needed to assess cytokine expression in other samples such as urine or renal parenchyma within the same disease groups and to evaluate clinical factors such as hydration status on the degree of inflammation. Additions to this panel of biomarkers and their sequential measurement over the time course of the disease might also provide information that would aid in the understanding of the inflammatory status of critically ill dogs with AKI.
ABBREVIATIONS
| 5-LO | 5-lipoxygenase |
| AKI | Acute kidney injury |
| CKD | Chronic kidney disease |
| IL | Interleukin |
| iNOS | Inducible nitric oxide synthase |
| IRIS | International Renal Interest Society |
| TGF | Transforming growth factor |
| TNF | Tumor necrosis factor |
Footnotes
Eatroff AE, Langston C. Acute kidney injury in dogs hospitalized in the intensive care unit: a prospective study, in Proceedings (abstr). 30th Am Coll Vet Intern Med Forum 2012;798.
Maissen-Villiger C. Expression profile of cytokines and enzymes mRNA in blood leukocytes of dogs with leptospirosis and its associated pulmonary hemorrhage syndrome. Doctoral thesis, Department of Clinical Veterinary Medicine, Vetsuisse Faculty, University of Bern, Switzerland, 2015.
RNeasy protect animal blood kit, Qiagen, Hombrechtikon, Switzerland.
SuperScript VILO cDNA synthesis kit, Invitrogen, Basel, Switzerland.
Rotor-Gene 6000, Corbett Research Pty Ltd, Sydney, Australia.
NCSS software, NCSS LLC, Kaysville, Utah.
References
1. Squires R. Uraemia. In: Elliott J, Grauer G, eds. BSAVA manual of canine and feline nephrology and urology. 2nd ed. Gloucester, England: British Small Animal Veterinary Association, 2007;54–68.
2. Schindler R. Causes and therapy of microinflammation in renal failure. Nephrol Dial Transplant 2004; 19: 34–40.
3. Carrero JJ, Stenvinkel P. Inflammation in end-stage renal disease—what have we learned in 10 years? Semin Dial 2010; 23: 498–509.
4. Akcay A, Nguyen Q, Edelstein CL. Mediators of inflammation in acute kidney injury [published online ahead of print]. Mediators Inflamm doi: 10.1155/2009/137072.
5. Thoen M, Kerl M. Characterization of acute kidney injury in hospitalized dogs and evaluation of a veterinary acute kidney injury staging system. J Vet Emerg Crit Care (San Antonio) 2011; 21: 648–657.
6. Kenney EM, Rozanski EA, Rush JE, et al. Association between outcome and organ system dysfunction in dogs with sepsis: 114 cases (2003–2007). J Am Vet Med Assoc 2010; 236: 83–87.
7. Harison E, Langston C, Palma D, et al. Acute azotemia as a predictor of mortality in dogs and cats. J Vet Intern Med 2012; 26: 1093–1098.
8. Eatroff AE, Langston CE, Chalhoub S, et al. Long-term outcome of cats and dogs with acute kidney injury treated with intermittent hemodialysis: 135 cases (1997–2010). J Am Vet Med Assoc 2012; 241: 1471–1478.
9. Abbas A, Lichtman A, Pillai S. Cytokines. In: Cellular and molecular immunology. 6th ed. Philadelphia: Saunders Elsevier, 2007;267–301.
10. Goes N, Urmson J, Ramassar V, et al. Ischemic acute tubular necrosis induces an extensive local cytokine response. Evidence for induction of interferon-gamma, transforming growth factor-beta 1, granulocyte-macrophage colony-stimulating factor, interleukin-2, and interleukin-10. Transplantation 1995; 59: 565–572.
11. Kielar ML, John R, Bennett M, et al. Maladaptive role of IL-6 in ischemic acute renal failure. JAm Soc Nephrol 2005; 16: 3315–3325.
12. Faubel S, Lewis EC, Reznikov L, et al. Cisplatin-induced acute renal failure is associated with an increase in the cytokines interleukin (IL)-1beta, IL-18, IL-6, and neutrophil infiltration in the kidney. J Pharmacol Exp Ther 2007; 322: 8–15.
13. Simmons EM, Himmelfarb J, Sezer MT, et al. Plasma cytokine levels predict mortality in patients with acute renal failure. Kidney Int 2004; 65: 1357–1365.
14. Ficek R, Kokot F, Chudek J, et al. Plasma concentrations of tumor necrosis factor alpha may predict the outcome of patients with acute renal failure. Kidney Blood Press Res 2006; 29: 203–209.
15. Kadiroglu AK, Sit D, Atay AE, et al. The evaluation of effects of demographic features, biochemical parameters, and cytokines on clinical outcomes in patients with acute renal failure. Ren Fail 2007; 29: 503–508.
16. Steinhilber D. 5-Lipoxygenase: a target for antiinflammatory drugs revisited. Curr Med Chem 1999; 6: 71–85.
17. Imig JD. Eicosanoids and renal vascular function in diseases. Clin Sci 2006; 111: 21–34.
18. Kieran NE, Maderna P, Godson C. Lipoxins: potential antiinflammatory, proresolution, and antifibrotic mediators in renal disease. Kidney Int 2004; 65: 1145–1154.
19. Villanueva S, Cespedes C, Gonzalez AA, et al. Effect of ischemic acute renal damage on the expression of COX-2 and oxidative stress-related elements in rat kidney. Am J Physiol Renal Physiol 2007; 292: F1364–F1371.
20. IRIS. IRIS grading of AKI. Available at: www.iris-kidney.com/guidelines/grading.shtml. Accessed Jan 10, 2015.
21. IRIS. IRIS staging of CKD. Available at: www.iris-kidney.com/guidelines/staging.shtml. Accessed Jan 10, 2015.
22. Rider P, Carmi Y, Guttman O, et al. IL-1alpha and IL-1beta recruit different myeloid cells and promote different stages of sterile inflammation. J Immunol 2011; 187: 4835–4843.
23. Dinarello CA. Interleukin-1 in the pathogenesis and treatment of inflammatory diseases. Blood 2011; 117: 3720–3732.
24. Ortega LM, Fornoni A. Role of cytokines in the pathogenesis of acute and chronic kidney disease, glomerulonephritis, and end-stage kidney disease. Int J Interferon Cytokine Mediator Res 2010; 2: 49–62.
25. Böttinger EP, Bitzer M. TGF-beta signaling in renal disease. J Am Soc Nephrol 2002; 13: 2600–2610.
26. Spurgeon KR, Donohoe DL, Basile DP. Transforming growth factor-beta in acute renal failure: receptor expression, effects on proliferation, cellularity, and vascularization after recovery from injury. Am J Physiol Renal Physiol 2005; 288: 568–577.
27. Himmelfarb J, Le P, Klenzak J, et al. Impaired monocyte cytokine production in critically ill patients with acute renal failure. Kidney Int 2004; 66: 2354–2360.
28. Otto G, Braconier J, Andreasson A, et al. Interleukin-6 and disease severity in patients with bacteremic and nonbacteremic febrile urinary tract infection. J Infect Dis 1999; 179: 172–179.
29. Pittet JF, Mackersie RC, Martin TR, et al. Biological markers of acute lung injury: prognostic and pathogenetic significance. Am J Respir Crit Care Med 1997; 155: 1187–1205.
30. Pugin J, Ricou B, Steinberg KP, et al. Proinflammatory activity in bronchoalveolar lavage fluids from patients with ARDS, a prominent role for interleukin-1. Am J Respir Crit Care Med 1996; 153: 1850–1856.
31. Himmelfarb J, McMonagle E, Freedman S, et al. Oxidative stress is increased in critically ill patients with acute renal failure. J Am Soc Nephrol 2004; 15: 2449–2456.
32. Ahlström A, Hynninen M, Tallgren M, et al. Predictive value of interleukins 6, 8 and 10, and low HLA-DR expression in acute renal failure. Clin Nephrol 2004; 61: 103–110.
33. Han WK, Bonventre JX. Biologic markers for the early detection of acute kidney injury. Curr Opin Crit Care 2004; 10: 476–482.
34. Parikh CR, Jani A, Melnikov VY, et al. Urinary interleukin-18 is a marker of human acute tubular necrosis. Am J Kidney Dis 2004; 43: 405–414.
35. Coca SG, Parikh CR. Urinary biomarkers for acute kidney injury: perspectives on translation. Clin J Am Soc Nephrol 2008; 3: 481–490.
