Endothelin B receptors preserve renal blood flow in a normotensive model of endotoxin-induced acute kidney dysfunction

B-type natriuretic peptide is upregulated by c-Jun N-terminal kinase and contributes to septic hypotension

B-type natriuretic peptide (BNP) is secreted by ventricular cardiomyocytes in response to various types of cardiac stress and has been used as a heart failure marker. In septic patients, increased BNP suggests poor prognosis; however, no causal link has been established. Among various effects, BNP decreases systemic vascular resistance and increases natriuresis that leads to lower blood pressure. We previously observed that JNK inhibition corrects cardiac dysfunction and suppresses cardiac BNP mRNA in endotoxemia. In this study, we investigated the transcriptional mechanism that regulates BNP expression and the involvement of plasma BNP in causing septic hypotension. Our in vitro and in vivo findings confirmed that activation of JNK signaling increases BNP expression in sepsis via direct binding of c-Jun in activating protein–1 (AP-1) regulatory elements of the Nppb promoter. Accordingly, genetic ablation of BNP, as well as treatment with a potentially novel neutralizing anti-BNP monoclonal antibody (19B3) or suppression of its expression via administration of JNK inhibitor SP600125 improved cardiac output, stabilized blood pressure, and improved survival in mice with polymicrobial sepsis. Therefore, inhibition of JNK signaling or BNP in sepsis appears to stabilize blood pressure and improve survival.

Nicotine reverses the enhanced renal vasodilator capacity in endotoxic rats: Role of α7/α4β2 nAChRs and HSP70

BACKGROUND

Nicotine alleviates renal inflammation and injury induced by endotoxemia. This study investigated (i) the nicotine modulation of hemodynamic and renal vasodilatory responses to endotoxemia in rats, and (ii) roles of α7 or α4β2-nAChRs and related HSP70/TNFα/iNOS signaling in the interaction.

METHODS

Endotoxemia was induced by ip lipopolysaccharide (5 mg/kg/day, for 2 days) and changes in systolic blood pressure and vasodilator responsiveness of isolated perfused kidney to acetylcholine or 5'-N-ethylcarboxamidoadenosine (NECA, adenosine receptor agonist) were evaluated.

RESULTS

Lipopolysaccharide had no effect on serum creatinine, reduced blood pressure, and increased renal vasodilations induced by acetylcholine or NECA in male and female preparations. Immunohistochemical analyses showed that lipopolysaccharide reduced renal HSP70 expression, but increased α7-nAChRs, α4β2-nAChRs and iNOS expressions. The co-administration of aminoguanidine (iNOS inhibitor), pentoxifylline (TNFα inhibitor), or nicotine attenuated lipopolysaccharide mediation of renal vasodilations and elevations in α7/α4β2-nAChR and iNOS expressions. Nicotine also reversed the downregulating effect of lipopolysaccharide on HSP70 expression. α7-nAChRs (methyllycaconitine citrate, MLA) or α4β2-nAChRs (dihydro-β-erythroidine, DHβE) blockade potentiated the lipopolysaccharide enhancement of renal vasodilations, and abolished the depressant effect of nicotine on lipopolysaccharide responses. A similar abolition of nicotine effects was seen after HSP70 inhibition by quercetin. Alternatively, lipopolysaccharide hypotension was eliminated in rats treated with DHβE/nicotine or quercetin/nicotine regimen in contrast to no effect for nicotine alone or combined with MLA.

CONCLUSIONS

These findings establish that nicotine offsets lipopolysaccharide facilitation of renal vasodilations possibly through a crosstalk between HSP70 and nAChRs of the α7 and α4β2 types.

Endothelin and tubulointerstitial renal disease

All components of the endothelin (ET) system are present in renal tubular cells. In this review, we summarize current knowledge about ET and the most common tubular diseases: acute kidney injury (AKI) and polycystic kidney disease. AKI originally was called acute tubular necrosis, pointing to the most prominent morphologic findings. Similarly, cysts in polycystic kidney disease, and especially in autosomal-dominant polycystic kidney disease, are of tubular origin. Preclinical studies have indicated that the ET system and particularly ETA receptors are involved in the pathogenesis of ischemia-reperfusion injury, although these findings have not been translated to clinical studies. The ET system also has been implicated in radiocontrast-dye-induced AKI, however, ET-receptor blockade in a large human study was not successful. The ET system is activated in sepsis models of AKI; the effectiveness of ET blocking agents in preclinical studies is variable depending on the model and the ET-receptor antagonist used. Numerous studies have shown that the ET system plays an important role in the complex pathophysiology associated with cyst formation and disease progression in polycystic kidney disease. However, results from selective targeting of ET-receptor subtypes in animal models of polycystic kidney disease have proved disappointing and do not support clinical trials. These studies have shown that a critical balance between ETA and ETB receptor action is necessary to maintain structure and function in the cystic kidney. In summary, ETs have been implicated in the pathogenesis of several renal tubulointerstitial diseases, however, experimental animal findings have not yet led to use of ET blockers in human beings.

The role of endothelin-1 and endothelin receptor antagonists in inflammatory response and sepsis

Endothelin-1 (ET-1) is a potent endogenous vasoconstrictor, mainly secreted by endothelial cells. It acts through two types of receptors: ETA and ETB. Apart from a vasoconstrictive action, ET-1 causes fibrosis of the vascular cells and stimulates production of reactive oxygen species. It is claimed that ET-1 induces proinflammatory mechanisms, increasing superoxide anion production and cytokine secretion. A recent study has shown that ET-1 is involved in the activation of transcription factors such as NF-κB and expression of proinflammatory cytokines including TNF-α, IL-1, and IL-6. It has been also indicated that during endotoxaemia, the plasma level of ET-1 is increased in various animal species. Some authors indicate a clear correlation between endothelin plasma level and morbidity/mortality rate in septic patients. These pathological effects of ET-1 may be abrogated at least partly by endothelin receptor blockade. ET-1 receptor antagonists may be useful for prevention of various vascular diseases. This review summarises the current knowledge regarding endothelin receptor antagonists and the role of ET-1 in sepsis and inflammation.

Influence of specific endothelin-1 receptor blockers on hemodynamic parameters and antioxidant status of plasma in LPS-induced endotoxemia

BACKGROUND

The potent vasoconstrictor endothelin-1 has been implicated in the pathogenesis of plasma oxidative stress seen in sepsis. The selective endothelin receptor blockers BQ123 and BQ788 were used to investigate the importance of selective endothelin receptor blockage in modulating oxidative stress during endotoxemia.

METHODS

The study was performed on male Wistar rats (n = 6 per group) divided into groups: (1) saline, (2) lipopolysaccharide (LPS) (15 mg/kg)-saline, (3) BQ123 (0.5 mg/kg)-LPS, (4) BQ123 (1 mg/kg)-LPS, (5) BQ788 (3 mg/kg)-LPS. The endothelin receptor type A(ETA-R) or type B (ETB-R) antagonist was injected intravenously 30 min before LPS administration. Blood pressure was monitored and blood was taken before, 90 min and 300 min after saline or LPS administration.

RESULTS

Injection of LPS alone resulted in a decrease in mean arterial pressure (MAP) (p < 0.05), a decrease in ferric reducing ability of plasma (FRAP) value (p < 0.01) and a marked increase in plasma tumor necrosis factor α (TNF-α) and thiobarbituric acid reactive substances (TBARS) (p < 0.001, p < 0.001, respectively). Administration of BQ123 before LPS administration deteriorated MAP in a dose dependent way. Moreover, BQ123 (1 mg/kg) decreased plasma level of TBARS and TNF-α (p < 0.01 and p < 0.05, respectively) and increased FRAP value (p < 0.001). On the contrary, BQ788 prevented LPS-induced decrease in MAP(p < 0.001) and led to a significant reduction in plasma TBARS concentration (p < 0.01).

CONCLUSIONS

Our study showed that blockage of ETB-R during endotoxemia improved blood hemodynamics and decreased plasma lipid peroxidation. Blockage of ETA-R improved plasma antioxidant status and decreased lipid peroxidation and TNF-α production, but it deteriorated hemodynamic conditions.

Pharmacological targets in the renal peritubular microenvironment: implications for therapy for sepsis-induced acute kidney injury

One of the most frequent and serious complications to develop in septic patients is acute kidney injury (AKI), a disorder characterized by a rapid failure of the kidneys to adequately filter the blood, regulate ion and water balance, and generate urine. AKI greatly worsens the already poor prognosis of sepsis and increases cost of care. To date, therapies have been mostly supportive; consequently there has been little change in the mortality rates over the last decade. This is due, at least in part, to the delay in establishing clinical evidence of an infection and the associated presence of the systemic inflammatory response syndrome and thus, a delay in initiating therapy. A second reason is a lack of understanding regarding the mechanisms leading to renal injury, which has hindered the development of more targeted therapies. In this review, we summarize recent studies, which have examined the development of renal injury during sepsis and propose how changes in the peritubular capillary microenvironment lead to and then perpetuate microcirculatory failure and tubular epithelial cell injury. We also discuss a number of potential therapeutic targets in the renal peritubular microenvironment, which may prevent or lessen injury and/or promote recovery.

Endothelin receptor A antagonism attenuates renal medullary blood flow impairment in endotoxemic pigs

Background

Endothelin-1 is a potent endogenous vasoconstrictor that contributes to renal microcirculatory impairment during endotoxemia and sepsis. Here we investigated if the renal circulatory and metabolic effects of endothelin during endotoxemia are mediated through activation of endothelin-A receptors.

Methods and Findings

A randomized experimental study was performed with anesthetized and mechanically ventilated pigs subjected to Escherichia coli endotoxin infusion for five hours. After two hours the animals were treated with the selective endothelin receptor type A antagonist TBC 3711 (2 mg⋅kg⁻¹, n = 8) or served as endotoxin-treated controls (n = 8). Renal artery blood flow, diuresis and creatinine clearance decreased in response to endotoxemia. Perfusion in the cortex, as measured by laser doppler flowmetry, was reduced in both groups, but TBC 3711 attenuated the decrease in the medulla (p = 0.002). Compared to control, TBC 3711 reduced renal oxygen extraction as well as cortical and medullary lactate/pyruvate ratios (p<0.05) measured by microdialysis. Furthermore, TBC 3711 attenuated the decline in renal cortical interstitial glucose levels (p = 0.02) and increased medullary pyruvate levels (p = 0.03). Decreased creatinine clearance and oliguria were present in both groups without any significant difference.

Conclusions

These results suggest that endothelin released during endotoxemia acts via endothelin A receptors to impair renal medullary blood flow causing ischemia. Reduced renal oxygen extraction and cortical levels of lactate by TBC 3711, without effects on cortical blood flow, further suggest additional metabolic effects of endothelin type A receptor activation in this model of endotoxin induced acute kidney injury.

Urotensin-II receptor antagonism does not improve renal haemodynamics or function in rats with endotoxin-induced acute kidney injury

1. Urotensin-II (U-II) is a vasoactive peptide that influences renal haemodynamics and kidney function. The aim of the present study was to examine the effects of the selective U-II receptor antagonist, urantide, on renal haemodynamics, oxygenation and function in endotoxaemic rats. 2. Endotoxaemia was induced in Sprague-Dawley rats by an intraperitoneal dose of lipopolysaccharide (LPS; Escherichia coli O127:B8, 7.5 mg/kg). At 16 h after endotoxin was given, renal clearance experiments were carried out in thiobutabarbital anaesthetized rats. Group 1, sham-saline; group 2, sham-urantide; group 3 LPS-saline; and group 4, LPS-urantide received isotonic saline or urantide (0.2 mg/kg bolus intravenously, followed by an infusion of 1.2 mg/kg/h throughout) after baseline measurements. Kidney function, renal blood flow (RBF), and cortical and outer medullary perfusion (laser-Doppler flowmetry) and oxygen tension (Clark-type microelectrodes) were analysed during 2 h of drug administration. 3. At baseline, endotoxaemic rats showed approximately 50% reductions in glomerular filtration rate (GFR) and RBF (P < 0.05), a decline in cortical and outer medullary perfusion and pO(2) (P < 0.05), and a significant increase in mean arterial pressure (MAP; P < 0.05) compared with saline-injected controls. In sham animals, urantide in a dose that did not significantly influence MAP or RBF, increased GFR (P < 0.05 time × treatment interaction) and filtration fraction (P < 0.05 treatment effect). However, urantide had no statistically significant effects on any of the investigated variables in endotoxaemic rats. 4. These findings show that U-II, through the UT receptor, does not contribute to abnormalities in renal haemodynamics and function in endotoxaemic rats.

Lipopolysaccharide reduces sodium intake and sodium excretion in dehydrated rats

The objective of this study was to find out if lipopolysaccharide (LPS) administered intraperitoneally affects sodium and water intake and renal excretion in dehydrated rats. LPS (0.3-5 mg/kg b.w.) inhibited 0.3M NaCl intake induced by subcutaneous injection of the diuretic furosemide (FURO, 10 mg/kg b.w.) combined with the angiotensin converting enzyme inhibitor, captopril (CAP, 5 mg/kg b.w.). Only the highest doses of LPS (2.5 and 5 mg/kg) inhibited water intake induced by FURO/CAP. LPS (0.6 mg/kg) reduced urinary volume and sodium excretion, but had no effect on mean arterial pressure or heart rate of rats treated with FURO/CAP. LPS (0.3-5.0 mg/kg) abolished intracellular thirst and reduced by 50% the urine sodium concentration of rats that received 2 ml of 2M NaCl by gavage. LPS (0.3-5.0 mg/kg) also reduced thirst in rats treated with FURO alone (10 mg/rat sc). The results suggest that LPS has a preferential, but not exclusive, inhibitory effect on sodium intake and on intracellular thirst. The inhibition of hydro-mineral intake and the antinatriuresis caused by LPS in dehydrated rats may contribute to the multiple effects of the endotoxin on fluid and electrolyte balance and be part of the strategy to cope with infections.

Ablation of transient receptor potential vanilloid 1 abolishes endothelin-induced increases in afferent renal nerve activity: mechanisms and functional significance

Endothelin 1 (ET-1) and its receptors, ETA and ETB, play important roles in regulating renal function and blood pressure, and these components are expressed in sensory nerves. Activation of transient receptor potential vanilloid (TRPV) 1 channels expressed in sensory nerves innervating the renal pelvis enhances afferent renal nerve activity (ARNA), diuresis, and natriuresis. We tested the hypothesis that ET-1 increases ARNA via activation of ETB, whereas ETA counterbalances ETB in wild-type (WT) but not TRPV1-null mutant mice. ET-1 alone or with BQ123, an ETA antagonist, perfused into the left renal pelvis increased ipsilateral ARNA in WT but not in TRPV1-null mutant mice, and ARNA increases were greater in the latter. [Ala1, 3,11,15]-endothelin 1, an ETB agonist, increased ARNA that was greater than that induced by ET-1 in WT mice only. [Ala1, 3,11,15]-endothelin 1-induced increases in ARNA were abolished by chelerythrine, a protein kinase C inhibitor, but not by H89, a protein kinase A inhibitor. Chelerythrine, H89, and BQ788, an ETB antagonist, did not affect ARNA triggered by capsaicin in WT mice. Substance P release from the renal pelvis was increased by [Ala1, 3,11,15]-endothelin 1 in WT mice only, and the increase was abolished by chelerythrine but not by H89. Chelerythrine, H89, and BQ788 did not affect capsaicin-induced substance P release. Our data show that ET1 increases ARNA via activation of ETB, whereas ETA counterbalances ETB in WT but not in TRPV1-null mutant mice, suggesting that TRPV1 mediates ETB-dependent increases in ARNA, diuresis, and natriuresis possibly via the protein kinase C pathway.

Low-dose dexamethasone-supplemented fluid resuscitation reverses endotoxin-induced acute renal failure and prevents cortical microvascular hypoxia

There is growing evidence that impairment in intrarenal oxygenation and hypoxic injury might contribute to the pathogenesis of septic renal failure. An important molecule known to act on the renal microvascular tone and therefore consequently being involved in the regulation of intrarenal oxygen supply is NO. The main production of NO under septic conditions derives from iNOS, an enzyme that can be blocked by dexamethasone (DEX). In an animal model of endotoxin-induced renal failure, we tested the hypothesis that inhibition of iNOS by low-dose DEX would improve an impaired intrarenal oxygenation and kidney function. Twenty-two male Wistar rats received a 30-min intravenous infusion of LPS (2.5 mg/kg) and consecutively developed endotoxemic shock. Two hours later, in 12 animals, fluid resuscitation was initiated. Six rats did not receive resuscitation; four animals served as time control. In addition to the fluid, six animals received a bolus of low-dose DEX (0.1 mg/kg). In these animals, the renal iNOS mRNA expression was significantly suppressed 3 h later. Dexamethasone prevented the appearance of cortical microcirculatory hypoxic areas, improved renal oxygen delivery, and significantly restored oxygen consumption. Besides a significant increase in MAP and renal blood flow, DEX restored kidney function and tubular sodium reabsorption to baseline values. In conclusion, treatment with low-dose DEX in addition to fluid resuscitation reversed endotoxin-induced renal failure associated by an improvement in intrarenal microvascular oxygenation. Therefore, low-dose DEX might have potential application in the prevention of septic acute renal failure.

Rapid and segmental specific dysregulation of AQP2, S256-pAQP2 and renal sodium transporters in rats with LPS-induced endotoxaemia

BACKGROUND

Acute renal failure (ARF) is a frequent complication of sepsis. Characteristics of ARF in sepsis are impaired urinary concentration, increased natriuresis and decreased glomerular filtration rate (GFR), in which inducible nitric oxide synthase (iNOS) has been revealed to play a role. Aims. We aimed to investigate renal water and sodium excretion and in parallel the segmental regulation of renal AQP2 and major sodium transporters in rats with acute LPS-induced endotoxaemia. Next, we aimed to examine the changes of iNOS expression and activated macrophage infiltration in the kidney and the effects of iNOS inhibition on AQP2 and NKCC2 expression in LPS rats.

METHODS

Rats were treated with LPS (i.p.) or with LPS + iNOS inhibitor L-NIL, and 6 h later kidneys were subjected to semiquantitative immunoblotting and immunohistochemistry.

RESULTS

Polyuria and increased natriuresis were seen 6 h after LPS injection alongside downregulation of both AQP2 and S256-phosphorylated AQP2 in CTX/OSOM and ISOM but not in inner medulla (IM). Thick ascending limb sodium transporters NHE3 and NKCC2 were downregulated in ISOM and NaPi2 was decreased in CTX/OSOM, whereas NCC and ENaC were not consistently downregulated. Immunolabelling intensity of iNOS was increased in vascular structures and transitional epithelium, and an infiltration of activated macrophages was seen in CTX and ISOM. L-NIL co-treatment prevented the downregulation of NKCC2 but not AQP2 in LPS rats.

CONCLUSIONS

Early downregulation of AQP2 and sodium transporters takes place segmentally in the kidney after LPS administration. In addition, an infiltration of activated macrophages and increased iNOS expression may play a role in the urinary concentrating defect in acute LPS-induced entotoxaemia.