COX-2 activity transiently contributes to increased water and NaCl excretion in the polyuric phase after release of ureteral obstruction

Obstructive uropathy: Overview of the pathogenesis, etiology and management of a prevalent cause of acute kidney injury

Obstructive uropathy is defined as the structural or functional interruption of urinary outflow at any level in the urinary tract. It is regarded as one of the most prevalent causes of acute kidney injury (AKI), accounting for 5%-10% of cases. Acute severe obstruction of the urinary tract is a potentially threatening situation for the kidneys and therefore requires prompt identification and management to relieve obstruction. The aim of the present article is to review and synthesize available evidence on obstructive uropathy, providing a clinical guideline for clinicians. A literature review on obstructive uropathy in the context of AKI was performed, focusing on the least clarified aspects regarding diagnosis and management. Recent literature searching was conducted in English and top-level evidence articles including systematic reviews, metanalyses and large series were prioritized. Acute obstruction of the urinary tract is a diagnostic and therapeutical challenge that may lead to important clinical complications together with direct structural and hemodynamic damage to the kidney. Early recognition of the leading cause and its exact location is essential to ensure prompt urinary drainage together with the most suitable drainage technique selection. A multidisciplinary approach, including urologists, nephrologists, and other medical specialties, is best suited to correctly manage concomitant hemodynamic changes, fluid and electrolyte imbalances, and other related issues. Obstructive uropathy is one of the leading causes of AKI. Recognition of patients suitable for early diversion and feasibility or adequate selection of the indicated technique is sometimes challenging. A thorough understanding of the physiopathology behind the development of urinary obstruction is vital for correct diagnosis and management.

Obstructive nephropathy and molecular pathophysiology of renal interstitial fibrosis

The kidneys play a key role in maintaining total body homeostasis. The complexity of this task is reflected in the unique architecture of the organ. Ureteral obstruction greatly affects renal physiology by altering hemodynamics, changing glomerular filtration and renal metabolism, and inducing architectural malformations of the kidney parenchyma, most importantly renal fibrosis. Persisting pathological changes lead to chronic kidney disease, which currently affects ∼10% of the global population and is one of the major causes of death worldwide. Studies on the consequences of ureteral obstruction date back to the 1800s. Even today, experimental unilateral ureteral obstruction (UUO) remains the standard model for tubulointerstitial fibrosis. However, the model has certain limitations when it comes to studying tubular injury and repair, as well as a limited potential for human translation. Nevertheless, ureteral obstruction has provided the scientific community with a wealth of knowledge on renal (patho)physiology. With the introduction of advanced omics techniques, the classical UUO model has remained relevant to this day and has been instrumental in understanding renal fibrosis at the molecular, genomic, and cellular levels. This review details key concepts and recent advances in the understanding of obstructive nephropathy, highlighting the pathophysiological hallmarks responsible for the functional and architectural changes induced by ureteral obstruction, with a special emphasis on renal fibrosis.

Increased COX-2 after ureter obstruction attenuates fibrosis and is associated with EP2 receptor upregulation in mouse and human kidney

AIM

Cyclooxygenase-2 (COX-2) activity protects against oxidative stress and apoptosis early in experimental kidney injury. The present study was designed to test the hypothesis that COX-2 activity attenuates fibrosis and preserves microvasculature in injured kidney. The murine unilateral ureteral-obstruction (UUO) model of kidney fibrosis was employed and compared with human nephrectomy tissue with and without chronic hydronephrosis.

METHODS

Fibrosis and angiogenic markers were quantified in kidney tissue from wild-type and COX-2^-/- mice subjected to UUO for 7 days and in human kidney tissue. COX-enzymes, prostaglandin (PG) synthases, PG receptors, PGE₂ , and thromboxane were determined in human tissue.

RESULTS

COX-2 immunosignal was observed in interstitial fibroblasts at baseline and after UUO. Fibronectin, collagen I, III, alpha-smooth muscle actin, and fibroblast specific protein-1 mRNAs increased significantly more after UUO in COX-2^-/- vs wild-type mice. In vitro, fibroblasts from COX-2^-/- kidneys showed higher matrix synthesis. Compared to control, human hydronephrotic kidneys showed (i) fibrosis, (ii) no significant changes in COX-2, COX-1, PGE₂ -, and prostacyclin synthases, and prostacyclin and thromboxane receptor mRNAs, (iii) increased mRNA and protein of PGE₂ -EP₂ receptor level but unchanged PGE₂ tissue concentration, and (iv) two- to threefold increased thromboxane synthase mRNA and protein levels, and increased thromboxane B₂ tissue concentration in cortex and outer medulla.

CONCLUSION

COX-2 protects in the early phase against obstruction-induced fibrosis and maintains angiogenic factors. Increased PGE₂ -EP₂ receptor in obstructed human and murine kidneys could contribute to protection.

Aquaporin1-3 expression in normal and hydronephrotic kidneys in the human fetus

BACKGROUND

Decreased expression of the renal aquaporin (AQP) protein family is associated with hydronephrosis in adult humans and animals. However, the expression of AQPs, especially subtypes AQP1-3, which play a core role in the urinary concentration function, in hydronephrotic human fetuses is not clear. The aim of this study is to investigate the expression of the AQP1-3 in normal and hydronephrotic human fetal kidneys.

METHODS

Twenty-one normal and six hydronephrotic kidney (HK) samples were harvested from abortive fetuses. Meanwhile, seven normal adult human kidney samples were collected as positive controls. Quantitative real-time PCR, western blotting, and immunohistochemistry were used to analyze the expression of AQP1-3.

RESULTS

Both the protein and messenger mRNA expression levels of AQP1-3 increased with gestational age in the normal fetuses, but the levels were significantly lower than those in the adult tissues and significantly higher than those in the hydronephrotic fetuses at the same gestational age.

CONCLUSIONS

The increased expression of AQP1-3 with gestational age in the fetal kidney may indicate maturation of the urinary concentrating ability. The lower expression of AQP1-3 in HKs may reflect a maturation obstacle with regard to urinary concentration in human hydronephrotic fetuses.

Vasopressin-Independent Regulation of Aquaporin-2 by Tamoxifen in Kidney Collecting Ducts

Arginine vasopressin (AVP) mediates water reabsorption in the kidney collecting ducts through regulation of aquaporin-2 (AQP2). Also, estrogen has been known to regulate AQP2. Consistently, we previously demonstrated that tamoxifen (TAM), a selective estrogen receptor modulator, attenuates the downregulation of AQP2 in lithium-induced nephrogenic diabetes insipidus (NDI). In this study, we investigated the AVP-independent regulation of AQP2 by TAM and the therapeutic effect of TAM on the dysregulation of AQP2 and impaired urinary concentration in a unilateral ureteral obstruction (UUO) model. Primary cultured inner medullary collecting duct (IMCD) cells from kidneys of male Sprague-Dawley rats were treated with TAM. Rats subjected to 7 days of UUO were treated with TAM by oral gavage. Changes of intracellular trafficking and expression of AQP2 were evaluated by quantitative PCR, Western blotting, and immunohistochemistry. TAM induced AQP2 protein expression and intracellular trafficking in primary cultured IMCD cells, which were independent of the vasopressin V2 receptor (V2R) and cAMP activation, the critical pathways involved in AVP-stimulated regulation of AQP2. TAM attenuated the downregulation of AQP2 in TGF-β treated IMCD cells and IMCD suspensions prepared from UUO rats. TAM administration in vivo attenuated the downregulation of AQP2, associated with an improvement of urinary concentration in UUO rats. In addition, TAM increased CaMKII expression, suggesting that calmodulin signaling pathway is likely to be involved in the TAM-mediated AQP2 regulation. In conclusion, TAM is involved in AQP2 regulation in a vasopressin-independent manner and improves urinary concentration by attenuating the downregulation of AQP2 and maintaining intracellular trafficking in UUO.

Melatonin therapy protects against renal injury before and after release of bilateral ureteral obstruction in rats

AIM

Blockage of the urinary tract is often connected with renal function impediment, including reductions in glomerular filtration rate (GFR) and the power to control sodium as well as water elimination through urination. Melatonin, known to be the primary product of the pineal gland, prevents renal damage caused by ischemic reperfusion. However, the effects of melatonin on urinary obstruction, as well as release of obstruction induced kidney injury are still largely unknown. The aim of present study was to investigate the effect of melatonin on mediating protection against renal injury triggered from either bilateral ureteral obstruction (BUO) or BUO release (BUO-R).

MAIN METHODS

Adult male Sprague-Dawley rats (n = 60) were clustered into six treatment groups: sham treated-1; BUO-non-treated (24 h BUO only); BUO + melatonin; sham treated-2; BUO-48hR (24 h of BUO and then release for 2 days); and BUO-48hR + melatonin. Kidney tissues, blood and urine samples were obtained for further assessment.

KEY FINDINGS

It was found that melatonin treatment remarkably promoted the recovery of the handling capacity of urinary excretion of water as well as sodium in BUO and BUO-48hR models. Melatonin treatment partially inhibited inflammatory cytokine expression and the downregulation of aquaporin (AQPs, AQP-1, -2 and -3) expression in these two models. Moreover, the cytoarchitecture of BUO rats exposed to melatonin was well preserved.

SIGNIFICANCE

Melatonin treatment potently prevents BUO or BUO-R induced renal injury, which may be partially attributed to restoring the expression of AQPs and inhibition of inflammatory response, as well as preserving renal ultrastructural integrity.

Role of mitochondrial oxidative stress in modulating the expressions of aquaporins in obstructive kidney disease

Downregulation of aquaporins (AQPs) in obstructive kidney disease has been well demonstrated with elusive mechanisms. Our previous study indicated that mitochondrial dysfunction played a crucial role in this process. However, it is still uncertain how mitochondrial dysfunction affected the AQPs in obstructive kidney disease. This study investigated the role of mitochondria-derived oxidative stress in mediating obstruction-induced downregulation of AQPs. After unilateral ureteral obstruction for 7 days, renal superoxide dismutase 2 (SOD2; mitochondria-specific SOD) was reduced by 85%. Meanwhile, AQP1, AQP2, AQP3, and AQP4 were remarkably downregulated as determined by Western blotting and/or quantitative real-time PCR. Administration of the SOD2 mimic manganese (III) tetrakis(4-benzoic acid)porphyrin chloride (MnTBAP) significantly attenuated AQP2 downregulation in line with complete blockade of thiobarbituric acid-reactive substances elevation, whereas the reduction of AQP1, AQP3, and AQP4 was not affected. The cyclooxygenase (COX)-2/prostaglandin (PG) E2 pathway has been well documented as a contributor of AQP reduction in obstructed kidney; thus, we detected the levels of COX-1/2 and microsomal prostaglandin E synthase 1 (mPGES-1) in kidney and PGE2 secretion in urine. Significantly, MnTBAP partially suppressed the elevation of COX-2, mPGES-1, and PGE2. Moreover, a marked decrease of V2 receptor was significantly restored after MnTBAP treatment. However, the fibrotic response and renal tubular damage were unaffected by MnTBAP in obstructed kidneys. Collectively, these findings suggested an important role of mitochondrial oxidative stress in mediating AQP2 downregulation in obstructed kidney, possibly via modulating the COX-2/mPGES-1/PGE2/V2 receptor pathway.

Postobstructive diuresis in cats with naturally occurring lower urinary tract obstruction: incidence, severity and association with laboratory parameters on admission

OBJECTIVES

The objectives of this retrospective study were to investigate the actual incidence of postobstructive diuresis after relief of urethral obstruction in cats, as well as to identify changes in blood and urine parameters that might be associated with postobstructive diuresis (POD), and to assess the impact of fluid therapy.

METHODS

The medical records of 57 male cats with urethral obstruction that were treated with an indwelling urinary catheter were retrospectively analysed. Absolute urine output in ml/kg/h every 4 h and the incidence of cats with polyuria (urine volume >2 ml/kg/h) at any time point over a 48 h period after the re-establishment of urine flow were investigated. In addition, postobstructive diuresis in relation to fluid therapy (PODFR) was defined as urine output greater than the administered amount of intravenous fluids on at least two subsequent time points. Polyuria and PODFR were investigated for their association with blood and urine laboratory parameters.

RESULTS

After 4 h, 74.1% (40/54) of the cats had polyuria, with a urine output of >2 ml/kg/h. Metabolic acidosis was present in 46.2% of the cats. Venous blood pH and bicarbonate were inversely correlated with urine output in ml/kg/h after 4 h. The overall incidence of POD within 48 h of catheterisation was 87.7%. There was a significant correlation between intravenous fluid rate at time point x and urine output at time point x + 1 at all the time points except for the fluid rate at time point 0 and the urine output after 4 h. PODFR was seen in 21/57 cats (36.8%).

CONCLUSIONS AND RELEVANCE

POD is a frequent finding in cats treated for urethral obstruction, and can be very pronounced. Further studies are required to determine whether or not a change in venous blood pH actually interferes with renal concentrating ability. The discrepancy between the frequency of cats with polyuria and PODFR (87.7% vs 36.8%) in the present study indicates that administered intravenous fluid therapy might be the driving force for the high incidence of polyuria in some cats with naturally occurring obstructive feline lower urinary tract disease.

Inhibition of mitochondrial complex-1 restores the downregulation of aquaporins in obstructive nephropathy

Obstructive kidney disease is a common complication in the clinic. Downregulation of aquaporins (AQPs) in obstructed kidneys has been thought as a key factor leading to the polyuria and impairment of urine-concentrating capability after the release of kidney obstruction. The present study was to investigate the role of mitochondrial complex-1 in modulating AQPs in obstructive nephropathy. Following 7-day unilateral ureteral obstruction (UUO), AQP1, AQP2, AQP3, and vasopressin 2 (V₂) receptor were remarkably reduced as determined by qRT-PCR and/or Western blotting. Notably, inhibition of mitochondrial complex-1 by rotenone markedly reversed the downregulation of AQP1, AQP2, AQP3, and V₂ In contrast, AQP4 was not affected by kidney obstruction or rotenone treatment. In a separate study, rotenone also attenuated AQPs' downregulation after 48-h UUO. To study the potential mechanisms in mediating the rotenone effects on AQPs, we examined the regulation of the COX-2/microsomal prostaglandin E synthase (mPGES)-1/PGE₂/EP pathway and found that COX-2, mPGES-1, and renal PGE₂ content were all significantly elevated in obstructive kidneys, which was not affected by rotenone treatment. For EP receptors, EP₂ and EP₄ but not EP₁ and EP₃ were upregulated in obstructive kidneys. Importantly, rotenone strikingly suppressed EP₁ and EP₄ but not EP₂ and EP₃ receptors. However, treatment of EP₁ antagonist SC-51322 could not affect AQPs' reduction in obstructed kidneys. Collectively, these findings suggested an important role of mitochondrial dysfunction in modulating AQPs and V₂ receptor in obstructive nephropathy possibly via prostaglandin-independent mechanisms.

Physiology and pathophysiology of cyclooxygenase-2 and prostaglandin E2 in the kidney

The cyclooxygenase (COX) enzyme system is the major pathway catalyzing the conversion of arachidonic acid into prostaglandins (PGs). PGs are lipid mediators implicated in a variety of physiological and pathophysiological processes in the kidney, including renal hemodynamics, body water and sodium balance, and the inflammatory injury characteristic in multiple renal diseases. Since the beginning of 1990s, it has been confirmed that COX exists in 2 isoforms, referred to as COX-1 and COX-2. Even though the 2 enzymes are similar in size and structure, COX-1 and COX-2 are regulated by different systems and have different functional roles. This review summarizes the current data on renal expression of the 2 COX isoforms and highlights mainly the role of COX-2 and PGE2 in several physiological and pathophysiological processes in the kidney.

NSAIDs Alter Phosphorylated Forms of AQP2 in the Inner Medullary Tip

Vasopressin increases urine concentration through activation of aquaporin-2 (AQP2) in the collecting duct. Nonsteroidal anti-inflammatory drugs (NSAIDs) block prostaglandin E2 synthesis, and may suppress AQP2 producing a urine concentrating defect. There are four serines in AQP2 that are phosphorylated by vasopressin. To determine if chronic use of NSAIDs changes AQP2's phosphorylation at any of these residues, the effects of a non-selective NSAID, ibuprofen, and a COX-2-selective NSAID, meloxicam, were investigated. Daily ibuprofen or meloxicam increased the urine output and decreased the urine osmolality significantly by days 7 through 14. Concomitantly, meloxicam significantly reduced total AQP2 protein abundance in inner medulla (IM) tip to 64% of control and base to 63%, respectively. Ibuprofen significantly decreased total AQP2 in IM tip to 70% of control, with no change in base. Meloxicam significantly increased the ratios of p256-AQP2 and p261-AQP2 to total AQP2 in IM tip (to 44% and 40%, respectively). Ibuprofen increased the ratio of p256-AQP2 to total AQP2 in IM tip but did not affect p261-AQP2/total AQP2 in tip or base. Both ibuprofen and meloxicam increased p264-AQP2 and p269-AQP2 ratios in both tip and base. Ibuprofen increased UT-A1 levels in IM tip, but not in base. We conclude that NSAIDs reduce AQP2 abundance, contributing to decreased urine concentrating ability. They also increase some phosphorylated forms of AQP2. These changes may partially compensate for the decrease in AQP2 abundance, thereby lessening the decrease in urine osmolality.

A novel therapeutic effect of statins on nephrogenic diabetes insipidus

Statins competitively inhibit hepatic 3-hydroxy-3-methylglutaryl-coenzyme A reductase, resulting in reduced plasma total and low-density lipoprotein cholesterol levels. Recently, it has been shown that statins exert additional ‘pleiotropic’ effects by increasing expression levels of the membrane water channels aquaporin 2 (AQP2). AQP2 is localized mainly in the kidney and plays a critical role in determining cellular water content. This additional effect is independent of cholesterol homoeostasis, and depends on depletion of mevalonate-derived intermediates of sterol synthetic pathways, i.e. farnesylpyrophosphate and geranylgeranylpyrophosphate. By up-regulating the expression levels of AQP2, statins increase water reabsorption by the kidney, thus opening up a new avenue in treating patients with nephrogenic diabetes insipidus (NDI), a hereditary disease that yet lacks high-powered and limited side effects therapy. Aspects related to water balance determined by AQP2 in the kidney, as well as standard and novel therapeutic strategies of NDI are discussed.

Lithium induces microcysts and polyuria in adolescent rat kidney independent of cyclooxygenase-2

In patients, chronic treatment with lithium leads to renal microcysts and nephrogenic diabetes insipidus (NDI). It was hypothesized that renal cyclooxygenase‐2 (COX‐2) activity promotes microcyst formation and NDI. Kidney microcysts were induced in male adolescent rats by feeding dams with lithium (50 mmol/kg chow) from postnatal days 7–34. Lithium treatment induced somatic growth retardation, renal microcysts and dilatations in cortical collecting duct; it increased cortical cell proliferation and inactive pGSK‐3β abundance; it lowered aquaporin‐2 (AQP2) protein abundance and induced polyuria with decreased ability to concentrate the urine; and it increased COX‐2 protein level in thick ascending limb. Concomitant treatment with lithium and a specific COX‐2 inhibitor, parecoxib (5 mg/kg per day, P10–P34), did not prevent lithium‐induced microcysts and polyuria, but improved urine concentrating ability transiently after a 1‐desamino‐8‐D‐arginine vasopressin challenge. COX‐2 inhibition did not reduce cortical lithium‐induced cell proliferation and phosphorylation of glycogen synthase kinase‐3β (GSK‐3β). COX‐1 protein abundance increased in rat kidney cortex in response to lithium. COX‐1 immunoreactivity was found in microcyst epithelium in rat kidney. A human nephrectomy specimen from a patient treated for 28 years with lithium displayed multiple, COX‐1‐immunopositive, microcysts. In chronic lithium‐treated adolescent rats, COX‐2 is not colocalized with microcystic epithelium, mitotic activity, and inactive pGSK‐3β in collecting duct; a blocker of COX‐2 does not prevent cell proliferation, cyst formation, or GSK‐3β inactivation. It is concluded that COX‐2 activity is not the primary cause for microcysts and polyuria in a NaCl‐substituted rat model of lithium nephropathy. COX‐1 is a relevant candidate to affect the injured epithelium.

Long‐term use of lithium is associated with development of microcysts in the kidney. In this study the role for cyclooxygenase‐2 (COX‐2)‐derived prostaglandins in cyst formation was tested in a rat model. Inhibition of COX‐2 did not resolve or prevent kidney injury. COX‐1 was associated with the cyst epithelium and is more likely to play a functional role.

Aquaporin-2 regulation in health and disease

Aquaporin-2 (AQP2), the vasopressin-regulated water channel of the renal collecting duct, is dysregulated in numerous disorders of water balance in people and animals, including those associated with polyuria (urinary tract obstruction, hypokalemia, inflammation, and lithium toxicity) and with dilutional hyponatremia (syndrome of inappropriate antidiuresis, congestive heart failure, cirrhosis). Normal regulation of AQP2 by vasopressin involves 2 independent regulatory mechanisms: (1) short-term regulation of AQP2 trafficking to and from the apical plasma membrane, and (2) long-term regulation of the total abundance of the AQP2 protein in the cells. Most disorders of water balance are the result of dysregulation of processes that regulate the total abundance of AQP2 in collecting duct cells. In general, the level of AQP2 in a collecting duct cell is determined by a balance between production via translation of AQP2 mRNA and removal via degradation or secretion into the urine in exosomes. AQP2 abundance increases in response to vasopressin chiefly due to increased translation subsequent to increases in AQP2 mRNA. Vasopressin-mediated regulation of AQP2 gene transcription is poorly understood, although several transcription factor-binding elements in the 5' flanking region of the AQP2 gene have been identified, and candidate transcription factors corresponding to these elements have been discovered in proteomics studies. Here, we review progress in this area and discuss elements of vasopressin signaling in the collecting duct that may impinge on regulation of AQP2 in health and in the context of examples of polyuric diseases.

Is there a role for PGE2 in urinary concentration?

Prostanoids are prominent, yet complex, components in the maintenance of body water homeostasis. Recent functional and molecular studies have revealed that the local lipid mediator PGE2 is involved both in water excretion and absorption. The biologic actions of PGE2 are exerted through four different G-protein-coupled receptors; designated EP1-4, which couple to separate intracellular signaling pathways. Here, we discuss new developments in our understanding of the actions of PGE2 that have been uncovered utilizing receptor specific agonists and antagonists, EP receptor and PG synthase knockout mice, polyuric animal models, and the new understanding of the molecular regulation of collecting duct water permeability. The role of PGE2 in urinary concentration comprises a variety of mechanisms, which are not fully understood and likely depend on which receptor is activated under a particular physiologic condition. EP3 and microsomal PG synthase type 1 play a role in decreasing collecting duct water permeability and increasing water excretion, whereas EP2 and EP4 can bypass vasopressin signaling and increase water reabsorption through two different intracellular signaling pathways. PGE2 has an intricate role in urinary concentration, and we now suggest how targeting specific prostanoid receptor signaling pathways could be exploited for the treatment of disorders in water balance.

Disruption of cyclooxygenase-2 prevents downregulation of cortical AQP2 and AQP3 in response to bilateral ureteral obstruction in the mouse

Bilateral ureteral obstruction (BUO) in rats is associated with increased cyclooxygenase type 2 (COX-2) expression, and selective COX-2 inhibition prevents downregulation of aquaporins (AQPs) in response to BUO. It was hypothesized that a murine model would display similar changes in renal COX-2 and AQPs upon BUO and that targeted disruption of COX-2 protects against BUO-induced suppression of collecting duct AQPs. COX-2(-/-) and wild-type littermates (C57BL/6) were employed to determine COX-1, -2, AQP2, and AQP3 protein abundances and localization after BUO. In a separate series, sham and BUO wild-type mice were treated with a selective COX-2 inhibitor, parecoxib. The COX-2 protein level increased in wild-type mice in response to BUO and was not detectable in COX-2(-/-). COX-1 protein abundance was increased in sham-operated and BUO mice. Total AQP2 and -3 mRNA and protein levels decreased significantly after BUO in the cortex+outer medulla (C+OM) and inner medulla (IM). The decrease in C+OM AQP2 and -3 levels was attenuated/prevented in COX-2(-/-) mice, whereas there was no change in the IM. In parallel, inhibition of COX-2 by parecoxib rescued C+OM AQP3 and IM AQP2 protein level in wild-type mice subjected to BUO. In summary, 1) In C57BL/6 mice, ureteral obstruction increases renal COX-2 expression in interstitial cells and lowers AQP2/-3 abundance and 2) inhibition of COX-2 activity by targeted disruption or pharmacological blockade attenuates obstruction-induced AQP downregulation. In conclusion, COX-2-derived prostaglandins contribute to downregulation of transcellular water transporters in the collecting duct and likely to postobstruction diureses in the mouse.

Plant ureases and related peptides: understanding their entomotoxic properties

Recently, ureases were included in the arsenal of plant defense proteins, alongside many other proteins with biotechnological potential such as insecticides. Isoforms of Canavalia ensiformis urease (canatoxin—CNTX and jack bean urease—JBURE-I) are toxic to insects of different orders. This toxicity is due in part to the release of a 10 kDa peptide from the native protein, by cathepsin-like enzymes present in the insect digestive tract. The entomotoxic peptide, Jaburetox-2Ec, exhibits potent insecticidal activity against several insects, including many resistant to the native ureases. JBURE-I and Jaburetox-2Ec cause major alterations of post-feeding physiological processes in insects, which contribute to, or can be the cause of, their entomotoxic effect. An overview of the current knowledge on plant urease processing and mechanisms of action in insects is presented in this review.

Cyclooxygenase inhibitors protect D-galactosamine/lipopolysaccharide induced acute hepatic injury in experimental mice model

We investigated the protective effects of two non-steroid anti-inflammatory drugs, indomethacin (COX-1 and COX-2 inhibitors) and nimesulide (specific COX-2 inhibitor) on the hepatic injury induced by lipopolysaccharide in d-galactosamine sensitized (Gal/LPS) mice. ICR male mice were injected with a single dose of Gal/LPS with or without pre-treatment of 3mg/kg indomethacin or 30 mg/kg nimesulide (single i.p. injection). Sixteen hours later, blood and liver tissues of mice were collected for histological, molecular, and biochemical analyses. Our results showed marked reduction of hepatic necrosis, serum ALT, and tissue TBARS levels in both indomethacin- and nimesulide-pre-treated mice when compared with Gal/LPS-treated mice. Western blot and RT-PCR analysis showed decreased levels of iNOS mRNA, iNOS protein, and nitrotyrosine formation in both COX inhibitor pre-treated groups when compared with Gal/LPS-treated group. There was an inverse relationship between COX-1 and COX-2 expressions, as well as between COX-2 and C/EBP-α expressions in COX inhibitors groups, Gal/LPS and control groups. COX inhibitors reduced the expression of TNF-α mRNA and the activity of NF-κB which were elevated by Gal/LPS treatment. We conclude that COX inhibitors protected the liver from Gal/LPS-induced hepatotoxicity. COX inhibitors could be considered as potential agents in the prevention of acute liver failure and sepsis.

Bilateral ureteral obstruction induces early downregulation and redistribution of AQP2 and phosphorylated AQP2

Bilateral ureteral obstruction (BUO) is characterized by impairment of urine flow from the kidneys and altered expression of specific membrane proteins in the kidney involved in regulation of renal water and salt transport. Importantly, 24-h BUO reduces the abundance of the collecting duct water channel aquaporin-2 (AQP2) and AQP2 phosphorylated at serine 256 (AQP2pS256). To investigate the mechanism behind downregulation of AQP2 in BUO, rats were subjected to BUO and examined after 2, 6, 12, and 24 h. Q-PCR and immunoblotting showed significantly decreased AQP2 mRNA expression after 2-h BUO and decreased abundance of total AQP2 after 12 and 24 h. In parallel, immunohistochemistry showed weaker labeling of AQP2 at the apical surface of inner medullary collecting ducts (IMCD) compared with controls. The abundance of AQP2pS256 was significantly reduced from 6-h BUO and was confirmed by immunohistochemistry. Importantly, immunoblotting showed reduced abundance of AQP2pS261 after 12- and 24-h BUO mimicking total AQP2. Immunohistochemistry demonstrated early changed intracellular localization of AQP2pS261 in BUO, and colocalization studies showed redistribution from the apical membrane to early endosomes and lysosomes. In conclusion, BUO induces a very early regulation of AQP2 both at the level of abundance and on cellular localization. AQP2 and AQP2 phosphorylated at ser261 redistribute to more intracellular localizations and colocalize with the early endosomal marker EEA1 and the lysosomal marker cathepsin D, suggesting that early downregulation of AQP2 could in part be caused by degradation of AQP2 through a lysosomal degradation pathway.

Induction of the renal stanniocalcin-1 gene in rodents by water deprivation

Stanniocalcin-1 (STC-1) is made by kidney collecting duct cells for targeting of nephron mitochondria to promote respiratory uncoupling and calcium uniport activity. However, the purpose of these actions and how the renal gene is regulated are poorly understood. This study has addressed the latter issue by monitoring renal STC-1 gene expression in different models of kidney function. Unilateral nephrectomy and over-hydration had no bearing on renal gene activity in adult Wistar rats. Dehydration, on the other hand, had time-dependent stimulatory effects in male and female kidney cortex, where STC-1 mRNA levels increased 8-fold by 72h. Medullary gene activity was significantly increased as well, but muted in comparison ( approximately 2-fold). Gene induction was accompanied by an increase in mitochondrial sequestration of STC-1 protein. Aldosterone and angiotensin II had no bearing on STC-1 gene induction, although there was evidence of a role for arginine vasopressin. Gene induction was unaltered in integrin alpha1 knockout mice, which have an impaired tonicity enhancer binding protein (TonEBP) response to dehydration. The STC-1 gene response could be cytoprotective in intent, as dehydration entails a fall in renal blood flow and a rise in medullary interstitial osmolality. Alternatively, STC-1 could have a role in salt and water balance as dehydration necessitates water conservation as well as controlled natriuresis and kaliuresis.

Nonsteroidal Anti-Inflammatory Drugs and the Kidney

Non-steroidal anti-inflammatory drugs (NSAIDs) inhibit the isoenzymes COX-1 and COX-2 of cyclooxygenase (COX). Renal side effects (e.g., kidney function, fluid and urinary electrolyte excretion) vary with the extent of COX-2-COX-1 selectivity and the administered dose of these compounds. While young healthy subjects will rarely experience adverse renal effects with the use of NSAIDs, elderly patients and those with co-morbibity (e.g., congestive heart failure, liver cirrhosis or chronic kidney disease) and drug combinations (e.g., renin-angiotensin blockers, diuretics plus NSAIDs) may develop acute renal failure. This review summarizes our present knowledge how traditional NSAIDs and selective COX-2 inhibitors may affect the kidney under various experimental and clinical conditions, and how these drugs may influence renal inflammation, water transport, sodium and potassium balance and how renal dysfunction or hypertension may result.

Urinary tract obstruction induces transient accumulation of COX-2-derived prostanoids in kidney tissue

Inhibitors of cyclooxygenase (COX)-2 prevent suppression of aquaporin-2 and reduce polyuria in the acute phase after release of bilateral ureteral obstruction (BUO). We hypothesized that BUO leads to COX-2-mediated local accumulation of prostanoids in inner medulla (IM) tissue. To test this, rats were subjected to BUO and treated with selective COX-1 or COX-2 inhibitors. Tissue was examined at 2, 6, 12, and 24 h after BUO. COX-2 protein abundance increased in IM 12 and 24 h after onset of BUO but did not change in cortex. COX-1 did not change at any time points in any region. A full profile of all five primary prostanoids was obtained by mass spectrometric determination of PGE(2), PGF(2alpha), 6-keto-PGF(1alpha), PGD(2), and thromboxane (Tx) B(2) concentrations in kidney cortex/outer medulla and IM fractions. IM concentration of PGE(2), 6-keto-PGF(1alpha), and PGF(2alpha) was increased at 6 h BUO, and PGE(2) and PGF(2alpha) increased further at 12 h BUO. TxB(2) increased after 12 h BUO. 6-keto-PGF(1alpha) remained significantly increased after 24 h BUO. The COX-2 inhibitor parecoxib lowered IM PGE(2,) TxB(2), 6-keto-PGF(1alpha), and PGF(2alpha) below vehicle-treated BUO and sham rats at 6, 12 and, 24 h BUO. The COX-1 inhibitor SC-560 lowered PGE(2), PGF(2alpha), and PGD(2) in IM compared with untreated 12 h BUO, but levels remained significantly above sham. In cortex tissue, PGE(2) and 6-keto-PGF(1alpha) concentrations were elevated at 6 h only. In conclusion, COX-2 activity contributes to the transient increase in prostacyclin metabolite 6-keto-PGF(1alpha) and TxB(2) concentration in the kidney IM, and COX-2 is the predominant isoform that is responsible for accumulation of PGE(2) and PGF(2alpha) with minor, but significant, contributions from COX-1. PGD(2) synthesis is mediated exclusively by COX-1. In BUO, therapeutic interventions aimed at the COX-prostanoid pathway should target primarily COX-2.

Severe toxicity and cyclooxygenase (COX)-2 mRNA increase by lithium in the neonatal mouse kidney

Functions of the kidney of mammals are immature during the neonatal period, and the neonatal kidney could be susceptible to chemicals, including drugs and environmental toxicants. Among these chemicals, cyclooxygenase (COX)-inducing chemicals should be given attentions as the potential kidney toxicants during the period, and we hypothesized that lithium chloride (LiCl) has such toxicity. Neonatal mice of C57BL/J strain were intraperitoneally injected with LiCl (2 mmol/kg body weight) daily until 21 days of age, and examined on 7 days and 21 days of age. Neonatal treatment of LiCl caused a significant increase in COX-2 mRNA and a decrease in mRNAs of aquaporins on day 7 of age. Osmolarity of urine from LiCl-treated neonates was significantly lower than that of control neonate. Most of the LiCl-treated neonates died during the second week of age. Histological examination revealed renal cysts on day 7 and hydronephrosis on day 21. in the surviving neonates. The present results showed that the kidney of mouse neonates is vulnerable to lithium, and suggested the possibility that COX-2 upregulation is responsible for the severe renal toxicity including hydronephrosis.

Cyclooxygenase 2 inhibition exacerbates AQP2 and pAQP2 downregulation independently of V2 receptor abundance in the postobstructed kidney

Previously we demonstrated that ANG II receptor (AT1R) blockade attenuates V2 receptor (V2R), AQP2, and pS256-AQP2 downregulation in the postobstructed kidney and partially reverses obstruction-induced inhibition of cAMP generation and cyclooxygenase 2 (COX-2) induction. Therefore, we speculated whether the effects of AT1R blockade on V2R and the vasopressin-regulated pathway are attributable to attenuated COX-2 induction. To examine this, rats were subjected to 24-h bilateral ureteral obstruction (BUO) followed by 48-h release and treated with the COX-2 inhibitor parecoxib or saline. Control rats were sham-operated. Parecoxib treatment significantly reduced urine output 24 h after release of BUO whereas urine osmolality and solute-free water reabsorption was comparable between saline- and parecoxib-treated BUO rats. Immunoblotting revealed a significant decrease in AQP2 and pS256-AQP2 abundance to 20 and 23% of sham levels in parecoxib-treated BUO rats compared with 40 and 55% of sham levels in saline-treated BUO rats. Immunohistochemistry confirmed the exacerbated AQP2 and pS256-AQP2 downregulation in parecoxib-treated BUO rats. Finally, parecoxib treatment had no effect on V2R downregulation and the inhibited, vasopressin-stimulated cAMP generation in inner medullary membrane fractions from the postobstructed kidney. In conclusion, COX-2 inhibition exacerbates AQP2 and pS256-AQP2 downregulation 48 h after release of 24-h BUO independently of V2R abundance and vasopressin-stimulated cAMP generation. The results indicate that COX-2 inhibition does not mimic AT1R blockade-mediated effects and that AT1R-mediated AQP2 regulation in the postobstructed kidney collecting duct is independent of COX-2 induction.

Potential involvement of P2Y2 receptor in diuresis of postobstructive uropathy in rats

AVP resistance of the medullary collecting duct (mCD) in postobstructive uropathy (POU) has been attributed to increased production of PGE2. P2Y2 receptor activation causes production of PGE2 by the mCD. We hypothesize that increased P2Y2 receptor expression and/or activity may contribute to the diuresis of POU. Sprague-Dawley rats were subjected to bilateral ureteral obstruction for 24 h followed by release (BUO/R, n = 17) or sham operation (SHM/O, n = 15) and euthanized after 1 wk or 12 days. BUO/R rats developed significant polydipsia, polyuria, urinary concentration defect, and increased urinary PGE2 and decreased aquaporin-2 protein abundance in the inner medulla compared with SHM/O rats. After BUO/R, the relative mRNA expression of P2Y2 and P2Y6 receptors was increased by 2.7- and 4.9-fold, respectively, without significant changes in mRNA expression of P2Y1 or P2Y4 receptor. This was associated with a significant 3.5-fold higher protein abundance of the P2Y2 receptor in BUO/R than SHM/O rats. When freshly isolated mCD fractions were challenged with different types of nucleotides (ATPgammaS, ADP, UTP, or UDP), BUO/R and SHM/O rats responded to only ATPgammaS and UTP and released PGE2, consistent with involvement of the P2Y2, but not P2Y6, receptor. ATPgammaS- or UTP-stimulated increases in PGE2 were much higher in BUO/R (3.20- and 2.28-fold, respectively, vs. vehicle controls) than SHM/O (1.68- and 1.30-fold, respectively, vs. vehicle controls) rats. In addition, there were significant 2.4- and 2.1-fold increases in relative mRNA expression of prostanoid EP1 and EP3 receptors, respectively, in the inner medulla of BUO/R vs. SHM/O rats. Taken together, these data suggest that increased production of PGE2 by the mCD in POU may be due to increased expression and activity of the P2Y2 receptor. Increased mRNA expression of EP1 and EP3 receptors in POU may also help accentuate PGE2-induced signaling in the mCD.

Invitro effect of Canavalia ensiformis urease and the derived peptide Jaburetox-2Ec on Rhodnius prolixus Malpighian tubules

Ureases are metalloenzymes that are widespread among plants, fungi and bacteria. Urease isoforms (jack bean urease-JBU and canatoxin) from Canavalia ensiformis seeds are toxic to insects and fungi, suggesting a role in plant defense. The entomotoxic effect is due to the release of a 10-kDa peptide by cathepsin-like enzymes in the insect's midgut. Urease causes a decrease in post-feeding weight loss in Rhodnius prolixus, suggesting an effect on water balance. To investigate how this impairment occurs, we have evaluated the action of JBU and the urease-derivated peptide Jaburetox-2Ec on R. prolixus Malpighian tubules and also investigated the involvement of second messengers. JBU and Jaburetox-2Ec affect serotonin-induced secretion from Malpighian tubules. This effect is not cAMP-dependent, but the Jaburetox-2Ec effect is cGMP-dependent. Eicosanoid metabolites and calcium ions appear to be involved in JBU effect on diuresis, but are not involved in the action of Jaburetox-2Ec. Jaburetox-2Ec, but not JBU, causes a change in the transepithelial potential of the tubules. Canatoxin has a similar effect on tubules secretion, decreasing the secretion rate, but the urease from Helicobacter pylori has no significant effect. These data are helpful in our understanding of the actions of ureases and derived peptides on insects, and also reinforces the potential use of these proteins as biopesticides.

Angiotensin II regulates V2 receptor and pAQP2 during ureteral obstruction

Release of bilateral ureteral obstruction (BUO) is associated with nephrogenic diabetes insipidus (NDI) and a reduced abundance of the vasopressin-regulated aquaporins. To evaluate the role of the vasopressin type 2 receptor (V2R), we determined V2R abundance in kidneys from rats subjected to 24-h BUO or 24-h unilateral ureteral obstruction (UUO) followed by 48-h release. Because angiotensin II type 1 (AT1) receptor blockade attenuates postobstructive polyuria and aquaporin-2 (AQP2) downregulation, we examined the effect of AT1 receptor blockade on AQP2 phosphorylated at serine 256 (pS256-AQP2) and V2 receptor complex abundance in kidney inner medulla (IM). Furthermore, cAMP generation in sodium fluoride- and forskolin-stimulated inner medullary membrane fractions was studied after release of BUO. V2R was significantly reduced to 12% of sham levels in IM and to 52% of sham levels in cortex and outer stripe of outer medulla (OSOM) from BUO rats. In UUO rats, V2R abundance in the obstructed kidney IM decreased to 35% of sham levels, whereas it was comparable to sham levels in the nonobstructed kidney IM. No significant change was observed in cortex and OSOM. AT1 receptor blockade attenuated V2R, pS256-AQP2, and G(s)alpha protein downregulation in IM and partially reversed the obstruction-induced inhibition of sodium fluoride- and forskolin-stimulated cAMP generation in inner medullary membrane fractions from BUO rats. In conclusion, V2R downregulation plays a pivotal role in development of NDI after release of BUO. In addition, we have shown that angiotensin II regulates the V2 receptor complex and pS256-AQP2 in postobstructive kidney IM, probably by stimulating cAMP generation.

N-acetylcysteine protects against renal injury following bilateral ureteral obstruction

Background. Obstructive nephropathy decreases renal blood flow (RBF) and glomerular filtration rate (GFR), causing tubular abnormalities, such as urinary concentrating defect, as well as increasing oxidative stress. This study aimed to evaluate the effects of N-acetylcysteine (NAC) on renal function, as well as on the protein expression of aquaporin 2 (AQP2) and endothelial nitric oxide synthase (eNOS), after the relief of bilateral ureteral obstruction (BUO).

Methods. Adult male Wistar rats were divided into four groups: sham (sham operated); sham operated + 440 mg/kg body weight (BW) of NAC daily in drinking water, started 2 days before and maintained until 48 h after the surgery; BUO (24-h BUO only); BUO + NAC-pre (24-h BUO plus 440 mg/kg BW of NAC daily in drinking water started 2 days before BUO); and BUO + NAC-post (24-h BUO plus 440 mg/kg BW of NAC daily in drinking water started on the day of BUO relief). Experiments were conducted 48 h after BUO relief.

Results. Serum levels of thiobarbituric reactive substances, which are markers of lipid peroxidation, were significantly lower in NAC-treated rats than in the BUO group rats. The administration of NAC provided significant protection against post-BUO GFR drops and reductions in RBF. Renal cortices and BUO rats presented decreased eNOS protein expression of eNOS in the renal cortex of BUO group rats, whereas it was partially recovered in BUO + NAC-pre group rats. Urine osmolality was significantly lower in BUO rats than in sham group rats or NAC-treated rats, the last also presenting less interstitial fibrosis. Post-BUO downregulation of AQP2 protein expression was averted in the BUO + NAC-pre group rats.

Conclusions. This study demonstrates that NAC administration ameliorates the renal function impairment observed 48 h after the relief of 24-h BUO. Oxidative stress is important for the suppression of GFR, RBF, tissue AQP2 and eNOS in the polyuric phase after the release of BUO.