Role of nitric oxide and prostaglandin E2 in acute renal hypoperfusion

Optimising renal cancer patients for nephron-sparing surgery: a review of pre-operative considerations and peri-operative techniques for partial nephrectomy

Nonmodifiable factors including pre-operative renal function and amount of healthy renal tissue preserved are the most important predictive factors that determine renal function after partial nephrectomy. Ischaemia time is an important modifiable risk factor and cold ischaemia time should be used if longer ischaemia time is anticipated. New techniques may have a role in maximising postoperative kidney function, but more robust studies are required to understand their potential benefits and risks.

Oat1/3 restoration protects against renal damage after ischemic AKI

Expression of proximal tubular organic anion transporters Oat1 and Oat3 is reduced by PGE2 after renal ischemia and reperfusion (I/R) injury. We hypothesized that impaired expression of Oat1/3 is decisively involved in the deterioration of renal function after I/R injury. Therefore, we administered probenecid, which blocks proximal tubular indomethacin uptake, to abolish the indomethacin-mediated restoration of Oat1/3 regulation and its effect on renal functional and morphological outcome. Ischemic acute kidney injury (iAKI) was induced in rats by bilateral clamping of renal arteries for 45 min with 24-h follow-up. Low-dose indomethacin (1 mg/kg) was given intraperitoneally (ip) at the end of ischemia. Probenecid (50 mg/kg) was administered ip 20 min later. Indomethacin restored the expression of Oat1/3, PAH net secretion, and PGE2 clearance. Additionally, indomethacin improved kidney function as measured by glomerular filtration rate (GFR), renal perfusion as determined by corrected PAH clearance, and morphology, whereas it reduced renal cortical apoptosis and nitric oxide production. Notably, indomethacin did not affect inflammation parameters in the kidneys (e.g., monocyte chemoattractant protein-1, ED1+ cells). On the other hand, probenecid blocked the indomethacin-induced restoration of Oat1/3 and moreover abrogated all beneficial effects. Our study indicates that the beneficial effect of low-dose indomethacin in iAKI is not due to its anti-inflammatory potency, but in contrast to its restoration of Oat1/3 expression and/or general renal function. Inhibition of proximal tubular indomethacin uptake abrogates the beneficial effect of indomethacin by resetting the PGE2-mediated Oat1/3 impairment, thus reestablishing renal damage. This provides evidence for a mechanistic effect of Oat1/3 in a new model of the induction of renal damage after iAKI.

Meclofenamate elicits a nephropreventing effect in a rat model of ischemic acute kidney injury by suppressing indoxyl sulfate production and restoring renal organic anion transporters

Indoxyl sulfate (IS), a putative low-molecular weight uremic toxin, is excreted in the urine under normal kidney function, but is retained in the circulation and tissues during renal dysfunction in acute kidney injury and chronic kidney disease. IS, which is one of the most potent inducers of oxidative stress in the kidney and cardiovascular system, is enzymatically produced in the liver from indole by cytochrome P450-mediated hydroxylation to indoxyl, followed by sulfotransferase-mediated sulfate conjugation. We used rat liver S9 fraction to identify inhibitors of IS production. After testing several compounds, including phytochemical polyphenols, we identified meclofenamate as a potent inhibitor of IS production with an apparent IC50 value of 1.34 μM. Ischemia/reperfusion (I/R) of rat kidney caused a marked elevation in the serum IS concentration 48 hours after surgery. However, intravenous administration of meclofenamate (10 mg/kg) significantly suppressed this increase in the serum level of IS. Moreover, IS concentrations in both kidney and liver were dramatically elevated by renal I/R treatment, but this increase was blocked by meclofenamate. Serum creatinine and blood urea nitrogen were markedly elevated in rats after renal I/R treatment, but these increases were significantly restored by administration of meclofenamate. Renal expression of both basolateral membrane-localized organic anion transporters rOAT1 and rOAT3 was downregulated by I/R treatment. However, expression of rOAT1 and rOAT3 recovered after administration of meclofenamate, which is associated with the inhibition of I/R-evoked elevation of prostaglandin E2. Our results suggest that meclofenamate inhibits hepatic sulfotransferase-mediated production of IS, thereby suppressing serum and renal accumulation of IS. Meclofenamate also prevents the prostaglandin E2-dependent downregulation of rOAT1 and rOAT3 expression. In conclusion, meclofenamate was found to elicit a nephropreventive effect in ischemic acute kidney injury.

Differential effect of COX1 and COX2 inhibitors on renal outcomes following ischemic acute kidney injury

BACKGROUND/AIMS

We have previously shown that 1 mg/kg indomethacin improves expression and functionality of renal organic anion transporters Oat1 and Oat3 after renal ischemia and furthermore improves renal outcome after ischemia. As we detected differential effects of COX1 or COX2 inhibitors on organic anion transport after ischemia and reperfusion in culture, we investigated the effect of the SC560 (COX1 inhibitor) and SC58125 (COX2 inhibitor) on expression of Oat1/3 and renal outcome after ischemic acute kidney injury (iAKI).

METHODS

iAKI was induced in rats by bilateral clamping of renal arteries for 45 min. SC560 or SC58125 (1 mg/kg each) were given intraperitoneally as soon as reperfusion started. Sham-treated animals served as controls. Oat1/3 were determined by qPCR and Western blot. Glomerular filtration rate (GFR), p-aminohippurate (PAH) clearance and PAH extraction ratio was determined. All parameters were detected 24 h after ischemia. Renal plasma flow was calculated.

RESULTS

In clamped animals SC560 (COX1 inhibitor) restored expression of Oat1/3, as well as renal perfusion. Additionally, SC560 substantially improved kidney function as measured by GFR. Application of the COX2 inhibitor SC58125 did not exert these beneficial effects.

CONCLUSION

Our study indicates that COX1 inhibitor SC560 applied after ischemia prevents ischemia-induced downregulation of Oat1/3 during reperfusion and has a substantial protective effect on kidney function. Whether and to what particular extent this apparent improvement of function is mechanistically due to beneficial effects on tubular function, renal perfusion or glomerular filtration will be the scope of future studies.

Annexin A1 modulates macula densa function by inhibiting cyclooxygenase 2

Annexin A1 (ANXA1) exerts anti-inflammatory effects through multiple mechanisms including inhibition of prostaglandin synthesis. Once secreted, ANXA1 can bind to G protein-coupled formyl peptide receptors (Fpr) and activate diverse cellular signaling pathways. ANXA1 is known to be expressed in cells of the juxtaglomerular apparatus, but its relation to the expression of cyclooxygenase 2 (COX-2) in thick ascending limb and macula densa cells has not been elucidated. We hypothesized that ANXA1 regulates the biosynthesis of COX-2. ANXA1 abundance in rat kidney macula densa was extensively colocalized with COX-2 (95%). Furosemide, an established stimulus for COX-2 induction, caused enhanced expression of both ANXA1 and COX-2 with maintained colocalization (99%). In ANXA1-deficient mice, COX-2-positive cells were more numerous than in control mice (+107%; normalized to glomerular number; P < 0.05) and renin expression was increased (+566%; normalized to glomerular number; P < 0.05). Cultured macula densa cells transfected with full-length rat ANXA1 revealed downregulation of COX-2 mRNA (−59%; P < 0.05). Similarly, treatment with dexamethasone suppressed COX-2 mRNA in the cells (−49%; P < 0.05), while inducing ANXA1 mRNA (+56%; P < 0.05) and ANXA1 protein secretion. Inhibition of the ANXA-1 receptor Fpr1 with cyclosporin H blunted the effect of dexamethasone on COX-2 expression. These data show that ANXA1 exerts an inhibitory effect on COX-2 expression in the macula densa. ANXA1 may be a novel intrinsic modulator of renal juxtaglomerular regulation by inhibition of PGE2 synthesis.

Affirmative effects of iloprost on apoptosis during ischemia-reperfusion injury in kidney as a distant organ

OBJECTIVE

Apoptosis and its regulatory mechanisms take part in renal ischemia-reperfusion (I/R) injury which can result in acute renal failure and the inhibition of the caspase is considered as a new therapeutic strategy. In this context, we investigated the antiapoptotic and cytoprotective effects of iloprost, a prostacyclin analog, in kidney as a distant organ.

METHODS

Wistar albino rats were randomized into five groups (n = 12 in each) as sham, ischemia, I/R, iloprost (10 μg kg(-1)), and I/R + iloprost (10 μg kg(-1)). A 4 h reperfusion procedure was carried out after 4 h of ischemia. Caspase-8 was evaluated for death receptor-induced pathways, whereas caspase-9 was evaluated for mitochondria-dependent pathways and caspase-3 was investigated for overall apoptosis. Superoxide dismutase (SOD) enzyme activity and nitrite content as an indicator of nitric oxide (NO) production were also analyzed in kidney tissues.

RESULTS

Caspases-3, -8, and -9 were all significantly elevated in both ischemia and I/R groups compared to the sham group; however, treatment with iloprost reduced caspases-3, -8, and -9. SOD enzyme activity was attenuated by iloprost when compared to ischemic rats. The different effects of NO were found which change according to the present situation in ischemia, I/R, and treatment with iloprost.

CONCLUSIONS

These findings suggested that iloprost prevents apoptosis in both receptor-induced and mitochondria-dependent pathways in renal I/R injury and it may be considered as a cytoprotective agent for apoptosis. Understanding the efficiency of iloprost on the pathways for cell death may lead to an opportunity in the therapeutic approach for renal I/R injury.

Low-dose indomethacin after ischemic acute kidney injury prevents downregulation of Oat1/3 and improves renal outcome

We have previously shown that expression of renal organic anion transporters Oat1 and Oat3 is diminished by prostaglandin E2 (PGE2) and that both transporters are downregulated after renal ischemia. Because PGE2 is increased after renal ischemia and is generated by cyclooxygenases (COX), we investigated the effect of the COX inhibitor indomethacin on expression of Oat1/3 after ischemic acute kidney injury (iAKI). iAKI was induced in rats by bilateral clamping of renal arteries for 45 min. Indomethacin (1 mg/kg) was given intraperitoneally as soon as reperfusion started. Sham-treated animals served as controls. Oat1/3 were determined by qPCR and Western blot. PGE2 in blood and urine was measured by enzyme-linked immunosorbent assay. Invasion of monocytes/macrophages was determined. Glomerular filtration rate and renal plasma flow were determined. All parameters were detected 24 h after ischemia. PAH net secretion, as well as clearance and secretion of PGE2 were calculated. In clamped animals, indomethacin restored expression of Oat1/3, as well as PAH net secretion, PGE2 clearance, or PGE2 secretion. Additionally, indomethacin substantially improved kidney function as measured by glomerular filtration and PAH clearance. Indomethacin did not affect ischemia-induced invasion of monocytes/macrophages. In conclusion, our study indicates that low-dose indomethacin applied after ischemia prevents ischemia-induced downregulation of Oat1/3 during reperfusion and has a substantial protective effect on kidney function after iAKI. The beneficial effect of low-dose indomethacin on renal outcome is likely due to an effect different from inhibition of inflammation. In accordance to the decreased PAH net secretion, renal excretion of an endogenous organic anion (PGE2) is also impaired after ischemia and reperfusion.

15-Deoxy-delta(12,14)-prostaglandin J(2) down-regulates CXCR4 on carcinoma cells through PPARgamma- and NFkappaB-mediated pathways

The chemokine receptor CXCR4 plays a key role in the metastasis of colorectal cancer and its growth at metastatic sites. Here, we have investigated the mechanisms by which CXCR4 on cancer cells might be regulated by eicosanoids present within the colorectal tumor microenvironment. We show that prostaglandins PGE(2), PGA(2), PGD(2), PGJ(2) and 15dPGJ(2) each down-regulates CXCR4 receptor expression on human colorectal carcinoma cells to differing degrees. The most potent of these were PGD(2) and its metabolites PGJ(2) and 15dPGJ(2). Down-regulation was most rapid with the end-product 15dPGJ(2) and was accompanied by a marked reduction in CXCR4 mRNA. 15dPGJ(2) is known to be a ligand for the nuclear receptor PPARgamma. Down-regulation of CXCR4 was also observed with the PPARgamma agonist rosiglitazone, while 15dPGJ(2)-induced CXCR4 down-regulation was substantially diminished by the PPARgamma antagonists GW9662 and T0070907. These data support the involvement of PPARgamma. However, the 15dPGJ(2) analogue CAY10410, which can act on PPARgamma but which lacks the intrinsic cyclopentenone structure found in 15dPGJ(2), down-regulated CXCR4 substantially less potently than 15dPGJ(2). The cyclopentenone grouping is known to inhibit the activity of NFkappaB. Consistent with an additional role for NFkappaB, we found that the cyclopentenone prostaglandin PGA(2) and cyclopentenone itself could also down-regulate CXCR4. Immunolocalization studies showed that the cellular context was sufficient to trigger a focal nuclear pattern of NFkappaB p50 and that 15dPGJ(2) interfered with this p50 nuclear localization. These data suggest that 15dPGJ(2) can down-regulate CXCR4 on cancer cells through both PPARgamma and NFkappaB. 15dPGJ(2), present within the tumor microenvironment, may act to down-regulate CXCR4 and impact upon the overall process of tumor expansion.

Downregulation of organic anion transporters OAT1 and OAT3 correlates with impaired secretion ofpara-aminohippurate after ischemic acute renal failure in rats

Ischemic acute renal failure (iARF) was described to reduce renal extraction of the organic anion para-aminohippurate (PAH) in humans. The rate-limiting step of renal organic anion secretion is its basolateral uptake into proximal tubular cells. This process is mediated by the organic anion transporters OAT1 and OAT3, which both have a broad spectrum of substrates including a variety of pharmaceutics and toxins. Using a rat model of iARF, we investigated whether impairing the secretion of the organic anion PAH might be associated with downregulation of OAT1 or OAT3. Inulin and PAH clearance was determined starting from 6 up to 336 h after ischemia-reperfusion (I/R) injury. Net secretion of PAH was calculated and OAT1 as well as OAT3 expression was analyzed by RT-PCR and Western blotting. Inulin and PAH clearance along with PAH net secretion were initially diminished after I/R injury with a gradual recovery during follow-up. This initial impairment after iARF was accompanied by decreased mRNA and protein levels of OAT1 and OAT3 in clamped animals compared with sham-operated controls. In correlation to the improvement of kidney function, both mRNA and protein levels of OAT1 and OAT3 were upregulated during the follow-up. Thus decreased expression of OAT1 and OAT3 is sufficient to explain the decline of PAH secretion after iARF. As a result, this may have substantial impact on excretion kinetics and half-life of organic anions. As a consequence, the biological effects of a variety of organic anions may be affected after iARF.

Angiotensin II-induced calcium signaling in the afferent arteriole from rats with two-kidney, one-clip hypertension

The aim of this study was to investigate ANG II-induced Ca2+signaling in freshly isolated afferent arterioles (AA) from two-kidney, one-clip hypertensive (2K1C) rats, which have an elevated plasma and renal ANG II level, and different perfusion pressure and vascular tone in the clipped and nonclipped kidney. The Ca2+responses in vessels from 2K1C and control rats were similar in all groups ( P > 0.1). The intracellular Ca2+(Cai2+) response in the afferent arteriole after 10−8M ANG II stimulation was 0.57 ± 0.10, 0.50 ± 0.07, 0.48 ± 0.04, and 0.36 ± 0.05 in the control, sham, nonclipped, and clipped kidney, respectively. These data were consistent with the finding of unchanged AT1aR mRNA levels in AAs from all groups. Although the absolute values were similar, the dose-response curves to ANG II were different. In the control, sham, and nonclipped kidney from 2K1C, the dose-response curve leveled off between 10−8and 10−6M ANG II. In the clipped kidney, the dose-response curve was linear, with a significantly increased response at 10−6M compared with 10−8M ANG II ( P < 0.05). Inhibition of cyclooxygenase-1 (COX-1) with indomethacin enhanced the ANG II response in the nonclipped (Δ0.30 ± 0.09) and clipped (Δ0.30 ± 0.09) kidneys from 2K1C ( P < 0.005), but not in control rats (Δ−0.02 ± 0.11, P > 0.8). Conclusively, the ANG II-induced Cai2+response was reduced by COX-1-derived prostaglandins in 2K1C, in contrast to control animals, where the COX-1 inhibition had no effect. COX-2 inhibition with NS-398 did not increase the ANG II-mediated Cai2+response in any of the groups.

Prostaglandin E2 inhibits its own renal transport by downregulation of organic anion transporters rOAT1 and rOAT3

Prostaglandin E2 (PGE2) is the principal mediator of fever and inflammation. Recently, evidence emerged that during febrile response, PGE2 that is generated in the periphery enters the hypothalamus and contributes to the maintenance of fever. In a rat model of fever generation, peripheral PGE2 is increased, whereas clearance by metabolism of peripheral PGE2 is downregulated. The major route of PGE2 excretion is via the renal proximal tubular organic anion secretory system, where basolateral uptake that is mediated by renal organic anion transporter 1 (rOAT1) and rOAT3 is rate limiting. Therefore, it was hypothesized that PGE2 itself will abolish its excretion by rOAT1 or rOAT3. Fluorescein was used as a prototypic organic anion, and NRK-52E cells from rat served as a proximal tubular model system. PGE2 time-dependently downregulates basolateral organic anion uptake, without affecting cell volume or cell protein, recirculation of counter ions, or proximal tubular transport systems in general. In addition, PGE2 diminishes expression of both rOAT1 and rOAT3. Both organic anion uptake and expression of rOAT1 and rOAT3 are dose-dependently downregulated by PGE2. These findings suggest that during fever or inflammation, renal secretory transport of PGE2 is reduced, contributing to elevated PGE2 levels in blood. These data fit into the hypothetical concept of peripheral PGE2's playing a significant role in fever. The described regulatory mechanism may also be of relevance in chronic inflammatory events. Moreover, the data presented could explain why increased plasma urate levels occur in diseases that go along with increased levels of PGE2.

Nitrite-derived nitric oxide formation following ischemia-reperfusion injury in kidney

Nitric oxide (NO) is synthesized from l-arginine by nitric oxide synthase (NOS), and nitrite and nitrate are believed to be waste forms of NO. We previously reported an enzyme-independent pathway of NO generation from nitrite in acidic conditions. In this study, we show nitrite-derived NO formation in renal ischemia-reperfusion injury using electron paramagnetic resonance (EPR) spectroscopy. In this experiment, we utilized a stable isotope of [(15)N]nitrite as a source of nitrite to distinguish l-arginine-derived NO from [(15)N]nitrite-derived (15)NO. Intravenous infusion of a stable isotope of [(15)N]nitrite ((15)NO(2)(-)) facilitated the formation of Hb(15)NO during renal ischemia, which demonstrated that the origin of NO was nitrite. The EPR signal of Hb(15)NO in kidney appeared after 40 min of renal ischemia, and renal reperfusion decreased the Hb(15)NO level in the kidney and increased it in blood by contrast. In addition, the amount of HbNO was nitrite concentration dependent, and this formation was NOS independent. Our findings suggest that nitrite can be an alternative source of NO in ischemic kidney and that it binds with hemoglobin and then is spread by the circulation after reperfusion.