Elevated cysteinyl leukotriene excretion in experimental glomerulonephritis

Glomerular Biomechanical Stress and Lipid Mediators during Cellular Changes Leading to Chronic Kidney Disease

Hyperfiltration is an important underlying cause of glomerular dysfunction associated with several systemic and intrinsic glomerular conditions leading to chronic kidney disease (CKD). These include obesity, diabetes, hypertension, focal segmental glomerulosclerosis (FSGS), congenital abnormalities and reduced renal mass (low nephron number). Hyperfiltration-associated biomechanical forces directly impact the cell membrane, generating tensile and fluid flow shear stresses in multiple segments of the nephron. Ongoing research suggests these biomechanical forces as the initial mediators of hyperfiltration-induced deterioration of podocyte structure and function leading to their detachment and irreplaceable loss from the glomerular filtration barrier. Membrane lipid-derived polyunsaturated fatty acids (PUFA) and their metabolites are potent transducers of biomechanical stress from the cell surface to intracellular compartments. Omega-6 and ω-3 long-chain PUFA from membrane phospholipids generate many versatile and autacoid oxylipins that modulate pro-inflammatory as well as anti-inflammatory autocrine and paracrine signaling. We advance the idea that lipid signaling molecules, related enzymes, metabolites and receptors are not just mediators of cellular stress but also potential targets for developing novel interventions. With the growing emphasis on lifestyle changes for wellness, dietary fatty acids are potential adjunct-therapeutics to minimize/treat hyperfiltration-induced progressive glomerular damage and CKD.

Kidney in the net of acute and long-haul coronavirus disease 2019: a potential role for lipid mediators in causing renal injury and fibrosis

PURPOSE OF REVIEW

Severe COVID-19 disease is often complicated by acute kidney injury (AKI), which may transition to chronic kidney disease (CKD). Better understanding of underlying mechanisms is important in advancing therapeutic approaches.

RECENT FINDINGS

SARS-CoV-2-induced endothelial injury initiates platelet activation, platelet-neutrophil partnership and release of neutrophil extracellular traps. The resulting thromboinflammation causes ischemia-reperfusion (I/R) injury to end organs. Severe COVID-19 induces a lipid-mediator storm with massive increases in thromboxane A2 (TxA2) and PGD2, which promote thromboinflammation and apoptosis of renal tubular cells, respectively, and thereby enhance renal fibrosis. COVID-19-associated AKI improves rapidly in the majority. However, 15-30% have protracted renal injury, raising the specter of transition from AKI to CKD.

SUMMARY

In COVID-19, the lipid-mediator storm promotes thromboinflammation, ischemia-reperfusion injury and cytotoxicity. The thromboxane A2 and PGD2 signaling presents a therapeutic target with potential to mitigate AKI and transition to CKD. Ramatroban, the only dual antagonist of the thromboxane A2/TPr and PGD2/DPr2 signaling could potentially mitigate renal injury in acute and long-haul COVID. Urgent studies targeting the lipid-mediator storm are needed to potentially reduce the heavy burden of kidney disease emerging in the wake of the current pandemic.

Radioprotective effects of montelukast, a selective leukotriene CysLT1 receptor antagonist, against nephrotoxicity induced by gamma radiation in mice

PURPOSE

In this study, we evaluated the renal protective effects of montelukast (MLK) against ionizing radiation (IR) induced nephrotoxicity in mice.

MATERIALS AND METHODS

Radioprotective effects of MLK were assessed by biochemical analysis including measurements of kidney malondialdehyde (MDA), reduced glutathione (GSH), and serum creatinine and urea levels. Besides, for further evaluation of protective effects of MLK on renal system, ^99m Tc-dimercaptosuccinic acid (DMSA) has been applied. The total antioxidant capacity of MLK was measured by using 1,1-diphenyl-2-picryl hydrazyl radical reagents and compared with butylated hydroxyl toluene standard antioxidant.

RESULTS

The biochemical evaluation revealed that better results have been achieved for the groups administered with MLK than the only radiation group. Besides only IR-treated mice group, those treated with MLK demonstrated a significant decrease in urea and creatinine levels. Statistically, significant differences of MDA and SHG levels (P < .05) were found between the radiation group and MLK plus IR-treated group. Also, ^99m Tc-DMSA kidney uptake value (%ID/g) was observed lower for MLK plus IR-treated mice group than only radiation-treated mice group.

CONCLUSIONS

According to our findings, MLK has a potential role to be used as a renal protective agent against gamma radiation in radiotherapy.

Leukotrienes and kidney diseases

Purpose of review

This review will critically highlight the role of leukotrienes as mediators of renal diseases and drug nephrotoxicity. It will also discuss the recently identified mechanism of cysteinyl leukotrienes induction and action, and will propose clinical implementation of these findings.

Recent findings

Since last reviewed in 1994, leukotrienes were shown to mediate drug-associated nephrotoxicity, transplant rejection and morbidity in several models of renal diseases. Although leukotrienes may be released by various infiltrating leukocytes, a recent study demonstrated that cytotoxic agents trigger production of leukotriene C₄ (LTC₄) in mouse kidney cells by activating a biosynthetic pathway based on microsomal glutathione-S-transferase 2 (MGST2). LTC₄ then elicits nuclear accumulation of hydrogen peroxide-generating NADPH oxidase 4, leading to oxidative DNA damage and cell death. LTC₄ inhibitors, commonly used as systemic asthma drugs, alleviated drug-associated damage to proximal tubular cells and attenuated mouse morbidity.

Summary

Cysteinyl leukotrienes released by mast cells trigger the symptoms of asthma, including bronchoconstriction and vasoconstriction. Therefore, effective leukotriene inhibitors were approved as orally administered asthma drugs. The findings that leukotrienes mediate the cytotoxicity of nephrotoxic drugs, and are involved in numerous renal diseases, suggest that such asthma drugs may ameliorate drug-induced nephrotoxicity, as well as some renal diseases.

Urinary leukotriene E4 is associated with renal function but not with endothelial function in type 2 diabetes

Leukotrienes are inflammatory and vasoactive mediators implicated in endothelium-dependent relaxations and atherosclerosis. Urinary leukotriene E₄ (U-LTE₄) is a validated disease marker of asthma and increases also in diabetes and acute coronary syndromes. The aim of the present study was to evaluate the association of U-LTE₄ and CRP with endothelial function. Urine samples were obtained from 30 subjects (80% males; median age 65) with type 2 diabetes of at least two years duration and a median glomerular filtration rate (eGFR) of 71 (14–129) mL/min. Reactive hyperemia index (RHI) was used as a measure of microvascular endothelial function, whereas macrovascular endothelial function was determined be means of flow-mediated dilatation of the brachial artery (FMD). Decreased renal function was associated with lower concentrations of U-LTE₄. In addition, U-LTE₄ was correlated with serum creatinine (R = −0.572; P = 0.001) and eGFR (R = 0.517; P = 0.0036). A stepwise multiple linear regression analysis identified eGFR as an independent predictor of U-LTE₄ concentrations. In conclusion, the present results did not establish an association of U-LTE₄ with endothelial dysfunction. However, eGFR was an independent predictor of U-LTE₄, but not CRP, in this cohort, suggesting that GFR should be considered in biomarker studies of U-LTE₄.

Montelukast reduces ischaemia/reperfusion-induced bladder dysfunction and oxidant damage in the rat

The present study aimed to investigate the possible beneficial effects of the cysteinyl leukotriene-1 receptor antagonist montelukast on contractility and oxidant damage after ischaemia/reperfusion (I/R) of rat urinary bladder. The abdominal aorta of Sprague-Dawley rats was occluded to induce I/R. Montelukast (10 mg kg(-1)) or saline was administered intraperitoneally before I/R. In the sham-operated group, the abdominal aorta was left intact and the animals were treated with montelukast or saline. After decapitation, the bladder was removed and the tissue was either used for functional studies or stored for biochemical assays. In the I/R group, the isometric contractile responses of the bladder strips to carbachol (10(-8)-10(-4) M) were lower than those of the control group and were reversed by treatment with montelukast. Lipid peroxidation and myeloperoxidase activity of the bladder tissues in the I/R group were greater than in the sham-operated group. Montelukast treatment in the I/R group decreased these parameters compared with I/R alone. Similarly, the significant decrease in tissue glutathione level in the I/R group compared with controls was also prevented by montelukast. Treatment with montelukast almost completely reversed the low contractile responses of rat urinary bladder to carbachol and prevented oxidative tissue damage following I/R.

Oxidative renal damage in pyelonephritic rats is ameliorated by montelukast, a selective leukotriene CysLT1 receptor antagonist

Urinary tract infections may induce severe inflammation, transient impairment in renal function and scar formation, ranging in severity from acute symptomatic pyelonephritis to chronic pyelonephritis, which have a potential to lead to renal failure and death. The present study aimed to investigate the possible protective effect of montelukast, a selective antagonist of cysteinyl leukotriene receptor 1 (leukotriene CysLT1), against Escherichia coli-induced oxidative injury and scarring in renal tissue. Wistar rats were injected 0.1 ml of E. coli (ATCC 25922 10(10) cfu/ml) or saline into left renal medullae. Six rats were assigned as the sham group and were given 0.1 ml 0.9% NaCl. Pyelonephritic rats were treated with either saline or montelukast immediately after surgery and at daily intervals. Twenty-four hours or one week after E. coli injection, rats were decapitated and the kidney samples were taken for histological examination or determination of renal malondialdehyde, glutathione (GSH) levels, myeloperoxidase (MPO) activity, and collagen contents. Formation of reactive oxygen species in renal tissue samples was monitored by using chemiluminescence technique with luminol and lucigenin probes. Creatinine, blood urea nitrogen and lactate dehydrogenase (LDH) activity were measured in the serum samples. E. coli inoculation caused significant increases in malondialdehyde level, MPO activity, chemiluminescence levels and collagen content, while GSH level was decreased in the renal tissues (p<0.05-0.001). On the other hand, serum TNF-alpha, LDH, blood urea nitrogen and serum creatinine levels were elevated in the pyelonephritic rats as compared to control group. Leukotriene CysLT1 receptor antagonist montelukast reversed all these biochemical indices, as well as histopathological alterations, that were induced by acute pyelonephritis. It seems likely that montelukast protects kidney tissue by inhibiting neutrophil infiltration, balancing oxidant-antioxidant status, and regulating the generation of inflammatory mediators suggesting a future role for leukotriene CysLT1 receptor antagonists in the treatment of pyelonephritis.

Induction of leukotriene C4 synthase after the differentiation of rat basophilic leukemia cells with retinoic acid and a low dose of actinomycin D and its suppression with methylprednisolone

Leukotriene C(4) synthase (LTC(4) S) is a pivotal enzyme for generation of cysteinyl-leukotrienes (cysLTs). LTC(4) S activity in rat basophilic leukemia-1 (RBL-1) cells increased after culture in the presence of retinoic acid (RA) analogues, which was inhibited by cycloheximide or actinomycin D (ACD). Unexpectedly, the co-addition of a low dose of ACD with RA further potentiated the upregulation of the LTC(4) S activity. Daunorubicin and mitomycin C also had a similar effect. When stimulated with calcium ionophore A23187, control cells did not produce cysLTs, but RA-treated cells generated cysLTs and the co-addition of ACD further increased. While LTC(4) S mRNA and protein increased in the cells treated with RA, the co-addition of ACD further potentiated both in proportion to the LTC(4) S activity. The effect of ACD was considered to enhance the transcription rate of LTC(4) S gene, but not the mRNA-stability. The addition of methylprednisolone (MP) inhibited generation of cysLTs from the cells with A23187-stimulation and also did LTC(4) S activity, but did not inhibit 5-lipoxygenase (5-LOX). The suppression of LTC(4) S with MP showed a dependent manner on the time-point and duration of MP-treatment after RA-addition which was correlated with reduction in LTC(4) S mRNA and protein. The cells cultured with RA plus ACD contained more histamine, chymase activity, and granules in the cytoplasm than the control cells, suggesting differentiation to mature mast cells. In consideration of RA-differentiation therapy, it may be of pathophysiological relevance that the antineoplastic agents potentiate RA-induced, steroid-sensitive, induction of LTC(4) S in RBL-1 cells.

cDNA cloning and expression of rat leukotriene C(4) synthase: elevated expression in rat basophilic leukemia-1 cells after treatment with retinoic acid

Leukotriene C(4) synthase (LTC(4) S) is considered a pivotal enzyme for generation of potent proinflammatory mediators, cysteinyl-leukotrienes (cysLTs). LTC(4) S cDNA was cloned in rat basophilic leukemia-1 (RBL-1) cells, and exhibited 84.8% and 94.5% identity with the reported human and mouse LTC(4) S cDNA sequences, respectively. Homology between the rat LTC(4) S amino acid sequence and the corresponding sequences from the other species was 86.5% and 95.3% with human and mouse sequences, respectively. Rat LTC(4) S thus showed extensive homology with both mouse and human cDNA sequences. The active enzyme as assessed by LTC(4) S activity was expressed in COS-7 cells. While RBL-1 cells after the culture for 48 h in the presence of 0.1 microg/ml all trans -retinoic acid (RA) exhibited 27 times higher LTC(4) S activity than control cells, Northern-blot analysis of RA-treated cells showed upregulation of LTC(4) S mRNA. Polyclonal antibody was raised against the synthesized peptide deduced from the nucleotide sequence. Thus, Western-blot analysis of RBL-1 cells treated with RA and COS-7 cells transfected with pcDNA-LTC(4) S commonly showed a band at approximately 18 kDa in each solubilized enzyme solution, but either control cells did not. This cDNA probe and antibody may be useful for investigating the roles of cysLTs in various experimental models of rats.

Molecular identification of a rat novel organic anion transporter moat1, which transports prostaglandin D(2), leukotriene C(4), and taurocholate

We have isolated a rat novel multispecific organic anion transporter, moat1. The isolated clones were originated by alternative splicing of the moat1 mRNA. The nucleotide sequences predict a protein of 682 amino acids with moderate sequence similarity to LST-1, the oatp family, and the prostaglandin transporter. Northern blot analysis of rat moat1 identified a predominant transcript of 4.4 kilonucleotides in all tissues. Northern blot and in situ hybridization analyses of rat brain further indicated that moat1 mRNA is widely distributed in neuronal cells of the central nervous system, especially in the hippocampus and cerebellum. moat1 transports prostaglandin D(2) (K(m); 35.5 nM), leukotriene C(4) (K(m); 3.2 microM) and taurocholate (K(m); 17.6 microM) in a sodium-independent manner. moat1 also transports prostaglandin E(1), E(2), thromboxane B(2), and iloprost but not dehydroepiandrosterone sulfate and digoxin, of which the substrate specificity is similar, but definitively different from those of any other organic anion transporters.

The role of selectins in glomerular leukocyte recruitment in rat anti-glomerular basement membrane glomerulonephritis

Leukocytes play a central role in the pathogenesis of anti-glomerular basement membrane glomerulonephritis (anti-GBM GN). Understanding the mechanisms underlying their recruitment in the glomerulus is of critical importance, because this may lead to more specific anti-inflammatory drug design. The requirement for integrins, especially from the beta2 group, and their Ig superfamily counter-receptors has been established, however, the role of selectins remains controversial. An intravital microscopy technique was developed to study concomitantly the glomerular and venular leukocyte kinetics and the hemodynamic alterations in a rat model of anti-GBM GN, induced by injection of 10 mg of nephrotoxic serum (NTS). Histologic studies of the kidney were performed in parallel and urinary protein excretion was measured. The animals received NTS alone or were pretreated with either a monoclonal antibody against the beta2 integrin CD11b (OX42, 4 mg/kg) or fucoidan F7 (FF7, 8 mg/kg), an oligosaccharide that blocks both L- and P-selectin function. Administration of NTS resulted in a time-dependent increase in the number of adherent leukocytes in the glomeruli and a parallel decrease of the perfused glomerular capillary area. Substantial proteinuria was observed. Pretreatment with OX42 significantly attenuated these changes. FF7 almost abolished the rolling of the leukocytes in the venules, thus demonstrating efficient anti-selectin activity. Nevertheless, FF7 had no influence on the glomerular events or on the development of proteinuria. These results confirm that glomerular leukocyte adhesion in anti-GBM GN is CD11b-dependent. However, selectin-mediated interaction between the leukocytes and the glomerular capillary endothelium does not appear to be a prerequisite for leukocyte adhesion in the glomerulus. These results therefore question the potential utility of anti-selectin therapy in the treatment of anti-GBM GN.

gamma-glutamyl leukotrienase, a gamma-glutamyl transpeptidase gene family member, is expressed primarily in spleen

We have recently identified a mouse enzyme termed gamma-glutamyl leukotrienase (GGL) that converts leukotriene C4 (LTC4) to leukotriene D4 (LTD4). It also cleaves some other glutathione (GSH) conjugates, but not GSH itself (Carter, B. Z., Wiseman, A. L., Orkiszewski, R., Ballard, K. D., Ou, C.-N., and Lieberman, M. W. (1997) J. Biol. Chem. 272, 12305-12310). We have now cloned a full-length mouse cDNA coding for GGL activity and the corresponding gene. GGL and gamma-glutamyl transpeptidase constitute a small gene family. The two cDNAs share a 57% nucleotide identity and 41% predicted amino acid sequence identity. Their corresponding genes have a similar intron-exon organization and are located 3 kilobases apart. A search of Genbank and reverse transcription-polymerase chain reaction analysis failed to identify additional family members. Mapping of the GGL transcription start site revealed that the GGL promoter is TATA-less but contains an initiator, a control element for transcription initiation. Northern blots for GGL expression were negative. As judged by ribonuclease protection, in situ hybridization, and measurement of enzyme activity, spleen had the highest level of GGL expression. GGL is also expressed in thymic lymphocytes, bronchiolar epithelial cells, pulmonary interstitial cells, renal proximal convoluted tubular cells, and crypt cells of the small intestine as well as in cerebral, cerebellar, and brain stem neurons but not in glial cells. GGL is widely distributed in mice, suggesting an important role for this enzyme.

Leukotriene D4 and cystinyl-bis-glycine metabolism in membrane-bound dipeptidase-deficient mice

We have developed mice deficient in membrane-bound dipeptidase (MBD, EC 3.4.13.19), the enzyme believed to be responsible for the conversion of leukotriene D4 (LTD4) to leukotriene E4 (LTE4). The MBD mutation generated by us was demonstrated to be a null mutation by Northern blot analysis and the absence of beta-lactamase activity in lung, kidney, small intestine, and heart. MBD gene deletion had no effect on viability or fertility. The mutant mice retain partial ability to convert LTD4 to LTE4, ranging from 80-90% of the wild-type values in small intestine and liver to 16% in kidney and 40% in lung, heart, and pancreas. MBD is also believed to function consecutively after gamma-glutamyl transpeptidase to cleave cystinyl-bis-glycine (cys-bis-gly) generated from glutathione cleavage. Our data indicate that kidney homogenates from MBD-deficient mice retain approximately 40% of their ability to cleave cys-bis-gly, consistent with only modest elevations (3-5-fold) of cys-bis-gly in urine from MBD-deficient mice. These observations demonstrate that the conversion of LTD4 to LTE4 and the degradation of cys-bis-gly are catalyzed by at least two alternative pathways (one of which is MBD) that complement each other to varying extents in different tissues.

Inhibition of leukotriene biosynthesis improves renal function in experimental glomerulonephritis

The development of renal dysfunction in experimental glomerulonephritis (GN) is mediated in part by enhanced leukotriene (LT) formation. In our studies the pathophysiological role of LTs was investigated through pharmacological inhibition of LT biosynthesis in a rat model of nephrotoxic serum nephritis. MK-0591, an indirect inhibitor of 5-lipoxygenase activity, was co-administered to rats injected with nephrotoxic rabbit serum, followed by assessment of renal function, morphology and microsomal LTC4 synthase activity on day 7. A significant improvement in glomerular function was noted (p < 0.05), together with a 50% reduction in proteinuria (p < 0.01) in animals receiving MK-0591 (60 mg kg-1 day-1). In addition, the fall in renal LTC4 synthase activity which occurred in nephritic rats (to 74% of control values, p < 0.01) was prevented in drug-treated animals. Based on these results, it appears that inhibition of LT biosynthesis protects against both renal impairment and alterations in LTC4 synthase activity during the development of experimental GN, and may provide a useful therapeutic adjunct in the treatment of this disease.

Renal leukotriene C4 synthase: characterization, partial purification and alterations in experimental glomerulonephritis

Cysteinyl leukotrienes (LT) play an important role in the development of experimental glomerulonephritis (GN). We have partially purified and characterized LTC4 synthase, the enzyme responsible for cysteinyl LT formation, from rat renal microsomes and have investigated this enzyme activity in nephritic rats. LTC4 formation, measured in vitro, was linear for > 10 min at 25 degrees C in the presence of 50 mM serine borate (an inhibitor of gamma-glutamyl transpeptidase), with Km values for LTA4 and GSH of 56 microM and 8.5 mM, respectively. Detergent solubilization and anion-exchange chromatography of microsomal proteins resulted in a 7-fold increase in enzyme specific activity. Enzymatic and immunoblot analysis demonstrated that cytosolic and microsomal glutathione S-transferase (GST) activities were distinct from LTC4 synthase activity. Comparison of LTC4 synthase activity in nephritic rats over 21 days revealed an initial increase over the first 24 h following injection of nephrotoxic sera, followed by a subsequent decline until day 7 and a gradual recovery by day 21. Inhibition of LT biosynthesis with MK-0591 (10 mg kg-1 d-1) reduced GN-associated proteinuria by 72% (P < 0.05). These results suggest a potential mechanism for enhanced cysteinyl LT formation in the development of experimental GN and further support their causal role in the etiology of this disease.