Hemodynamic role of arachidonate 12- and 5-lipoxygenases in nephrotoxic serum nephritis

The Dysregulation of Eicosanoids and Bile Acids Correlates with Impaired Kidney Function and Renal Fibrosis in Chronic Renal Failure

Chronic renal failure (CRF) is an irreversible deterioration of the renal functions that characterized by fluid electrolyte unbalance and metabolic-endocrine dysfunctions. Increasing evidence demonstrated that metabolic disturbances, especially dyslipidemia and profound changes in lipid and lipoprotein metabolism were involved in CRF. Identification of lipids associated with impaired kidney functions may play important roles in the understanding of biochemical mechanism and CRF treatment. Ultra-performance liquid chromatography coupled with high-definition mass spectrometry-based lipidomics was performed to identify important differential lipids in adenine-induced CRF rats and investigate the undergoing anti-fibrotic mechanism of Polyporus umbellatus (PPU) and ergone (ERG). Linear correlation analysis was performed between lipid species intensities and creatinine levels in serum. Adenine-induced rats exhibited declining kidney function and renal fibrosis. Compared with control rats, a panel of lipid species was identified in the serum of CRF rats. Our further study demonstrated that eight lipids, including leukotrienes and bile acids, presented a strong linear correlation with serum creatinine levels. In addition, receiver operating characteristics analysis showed that eight lipids exhibited excellent area under the curve for differentiating CRF from control rats, with high sensitivity and specificity. The aberrant changes of clinical biochemistry data and dysregulation of eight lipids could be significantly improved by the administration of PPU and ergone. In conclusion, CRF might be associated with the disturbance of leukotriene metabolism, bile acid metabolism and lysophospholipid metabolism. The levels of eicosanoids and bile acids could be used for indicating kidney function impairment in CRF. PPU could improve renal functions and either fully or partially reversed the levels of eicosanoids and bile acids.

Elevated lipoxygenase and cytochrome P450 products predict progression of chronic kidney disease

BACKGROUND

The clinical relevance of arachidonic acid (AA) metabolites in chronic kidney disease (CKD) progression is poorly understood. We aimed to compare the concentrations of 85 enzymatic pathway products of AA metabolism in patients with CKD who progressed to end-stage kidney disease (ESKD) versus patients who did not in a subcohort of Chronic Renal Insufficiency Cohort (CRIC) and to estimate the risk of CKD progression and major cardiovascular events by levels of AA metabolites and their link to enzymatic metabolic pathways.

METHODS

A total 123 patients in the CRIC study who progressed to ESKD were frequency matched with 177 nonprogressors and serum eicosanoids were quantified by mass spectrometry. We applied serum collected at patients' Year 1 visit and outcome of progression to ESKD was ascertained over the next 10 years. We used logistic regression models for risk estimation.

RESULTS

Baseline 15-hydroxyeicosatetraenoate (HETE) and 20-HETE levels were significantly elevated in progressors (false discovery rate Q ≤ 0.026). The median 20-HETE level was 7.6 pmol/mL [interquartile range (IQR) 4.2-14.5] in progressors and 5.4 pmol/mL (IQR 2.8-9.4) in nonprogressors (P < 0.001). In an adjusted model, only 20-HETE independently predicted CKD progression. Each 1 standard deviation increase in 20-HETE was independently associated with 1.45-fold higher odds of progression (95% confidence interval 1.07-1.95; P = 0.017). Principal components of lipoxygenase (LOX) and cytochrome P450 (CYP450) pathways were independently associated with CKD progression.

CONCLUSIONS

We found higher odds of CKD progression associated with higher 20-HETE, LOX and CYP450 metabolic pathways. These alterations precede CKD progression and may serve as targets for interventions aimed at halting progression.

Gene expression of 5-, 12-, and 15-lipoxygenases and leukotriene receptors along the rat nephron

The arachidonate signaling pathways comprise prostanoids formed by cyclooxygenases, EETs, and HETEs formed by cytochrome P-450 (CYP) enzymes and HETEs and leukotrienes generated by lipoxygenases. Whereas the intrarenal localization of cyclooxygenases and of some CYP enzymes along the nephron has already been determined, the localization of lipoxygenases and leukotriene-forming enzymes together with leukotriene receptors in the kidney is less clear. This study therefore aimed to determine the expression of 5-, 12-, and 15-lipoxygenases as well as the leukotriene receptors along the rat nephron. The kidneys were dissected into cortex and outer and inner medulla, and the microdissected nephron segments were collected after a collagenase digestion. mRNA abundance was determined by RT-PCR and real-time PCR. 15-LOX mRNA showed a characteristic expression pattern along the distal nephron. 12-LOX mRNA was only found in the glomerulus. Similarly, 5-LOX mRNAs together with 5-LOX-activating protein mRNAs were expressed in the glomerulus and also in the vasa recta. The leukotriene A4 hydrolase was found in all nephron segments, whereas leukotriene C4 synthase mRNA could not be found in any nephron segment. The leukotriene receptor B4 and the cysteinyl leukotriene receptor type 1 were selectively expressed in the glomerulus, whereas cysteinyl receptor type 2 was not found in any nephron segment. Our data suggest that the glomerulus is a major source and target for 5- and 12-HETE and for leukotrienes. The collecting duct system, on the other hand, appears to be a major source of 15-HETE.

Lipoxin A4 inhibits TNF-α-induced production of interleukins and proliferation of rat mesangial cells

BACKGROUND

Studies have shown that lipoxin A(4) (LXA(4)) and its analogues inhibited proliferation of glomerular mesangial cells induced by leukotriene D(4) (LTD(4)) or platelet-derived growth factor (PDGF), reduced the production of proinflammatory cytokines such as interleukin (IL)-1beta and IL-6 in renal tissue of ischemic injury. In the present studies, we examine whether LXA(4) have inhibitory effects on tumor necrosis factor-alpha (TNF-alpha)-induced productions of IL-1beta and IL-6 and proliferation of glomerular mesangial cells of rat, and explore the molecular mechanisms of signal pathway of LXA(4).

METHODS

Cultured glomerular mesangial cells were treated with TNF-alpha (10 ng/mL), with or without preincubation with LXA(4) at the different concentrations. Cell proliferation was assessed by [(3)H]-thymidine incorporation. Proteins of IL-1beta and IL-6 in supernatant were analyzed by enzyme-linked immunosorbent assay (ELISA). Expressions of mRNA of IL-1beta and IL-6 were determined by real-time polymerase chain reaction (PCR) and cyclin E by reverse transcription (RT)-PCR. Proteins of cyclin E, threonine phosphorylated Akt(1) at 308 site (Thr(308)) and p27(kip1) were analyzed by Western blotting studies. Activities of signal transducers and activators of transcription-3 (STAT(3)), nuclear factor-kappaB (NF-kappaB) were determined by electrophroretic mobility shift assay (EMSA). Expression of Src homology (SH) 2-containing protein-tyrosine phosphatase (SHP-2) was assessed by immunoprecipitation and immunoblotting.

RESULTS

TNF-alpha-stimulated proliferation, release of proteins and expressions of mRNA of IL-1beta and IL-6 in mesangial cells were inhibited by LXA(4) in a dose-dependent manner. The marked increments in mRNA expression and protein synthesis of cyclin E induced by TNF-alpha in parallel with proliferation of mesangial cells were down-regulated by LXA(4). LXA(4) antagonized the phosphorylation of SHP-2 and activity of NF-kappaB induced by TNF-alpha. Pretreatment of the cells with NF-kappaB inhibitor pyrrolidine dithio-carbamate (PDTC) blocked the productions of IL-1beta, IL-6, and activation of NF-kappaB induced by TNF-alpha. Stimulation of mesangial cells with TNF-alpha resulted in enhanced DNA-binding activity of STAT(3). This increment was inhibited by LXA(4) in a dose-dependent manner. Threonine phosphorylated Akt(1) protein at 308 site stimulated by TNF-alpha was reduced by LXA(4.) TNF-alpha-induced decrement in expression of p27(kip1) protein was ameliorated by LXA(4) in a dose-dependent manner.

CONCLUSION

TNF-alpha-induced proliferation and increment of cyclin E of rat mesangial cells can be inhibited by LXA(4), and these inhibitory effects might be through the mechanisms of STAT(3) and Akt(1)/p27(kip1) pathway-dependent signal transduction. LXA(4) also antagonized TNF-alpha-stimulated IL-1beta and IL-6 synthesis, and these antagonisms were related to SHP-2 and NF-kappaB pathway-dependent signal transduction.

The effects of donor brain death on renal function and arachidonic acid metabolism in a large animal model of hypothermic preservation injury

BACKGROUND

Donor brain death (BD) has been implicated as a risk factor for the poor performance of kidneys after transplantation in small but not large animal models. This study determined the effects of donor BD on renal function and lipid mediator metabolism in a large animal model of renal hypothermic preservation injury.

METHODS

Adult beagle donors were subjected to explosive BD for 16 hr. After BD, the kidneys were removed, cold stored for 24 hr in cold University of Wisconsin solution, and allotransplanted into recipient dogs for either 4 hr (group 1) or 7 days (group 2). Controls for both groups consisted of kidneys obtained from living donors. Renal allograft function and tissue arachidonic acid (AA) metabolism were determined after reperfusion.

RESULTS

Short-term renal function after transplantation was generally unaffected by BD. Renal blood flow decreased after reperfusion but was not altered during the 16-hr BD period. Neutrophil infiltration significantly increased in kidneys from brain-dead donors before storage and after 4 hr of reperfusion. Renal cortex and medulla AA metabolism were not significantly affected by BD after short-term reperfusion except when thiol-ether leukotrienes (LTC(4)/D(4)/E(4)) were increased with BD. Serum creatinine was elevated during 7 days, but, surprisingly, BD significantly attenuated this injury.

CONCLUSION

BD in large mammals does not significantly affect renal allograft function or AA metabolism after transplantation. The role of BD in human renal preservation injury and inflammation should be reevaluated.

Innate immune responses in viral encephalitis

The innate immune system is multifaceted, comprised of preformed factors, cells, and many proteins and lipid mediators produced by those cells. In the CNS these are critical in initiation and amplification of the inflammatory response and in the subsequent elicitation of the specific T cell response to viral encephalitis. Cells that are resident in brain parenchyma and peripheral cells that are recruited both play key roles in the hosts's responses. Unlike the peripheral compartments, in the CNS, non-cytolytic means of eliminating viral infections have been critical, since, in contrast to columnar epithelial cells, neurons are non-renewing. When the innate immune responses are inefficient or absent in viral encephalitis, pathology is more likely. Much more work remains to elucidate all of the critical cells and their mediators, as well as to develop new therapies for infections of the CNS.

Role of intracellular signalling pathways in hydrogen peroxide-induced injury to rat glomerular mesangial cells

1. Brief exposure of cultured rat glomerular mesangial cells (GMC) to H2O2 in nominally bicarbonate-free solution induced a rapid dose dependent, dantrolene-inhibitable increase in intracellular free Ca2+ from 65 +/- 6 to 203 +/- 14 nmol/L and a prolonged release of [14C]-arachidonic acid [14C]-AA which preceded the onset of cell membrane damage assessed by trypan-blue uptake. 2. Ca2+ responses were potentiated in HCO3-/CO2 containing buffers and reached values of 1145 +/- 100 nmol/L at 1 mmol/L H2O2. In HCO3-/CO2 solutions, but not HEPES buffer, H2O2-induced Ca2+ increases were markedly attenuated by verapamil (100 mumol/L) or removal of extracellular calcium. 3. Enhanced release of [14C]-AA was partially attenuated by inhibitors of key intracellular signalling mechanisms including the phospholipase-A2 (PLA2) inhibitor mepacrine (100 mumol/L), the NADPH oxidase inhibitor diphenyliodonium (10 mumol/L), the mitochondrial calcium-cycling inhibitor ruthenium red (10 mumol/L) and the iron chelator dipyridyl (100 mumol/L). Release was unaffected by protein kinase C inhibition with H7 (100 mumol/L), inositol triphosphate antagonism with neomycin (1 mmol/L) or overnight treatment with the G-protein antagonist pertussis toxin (5 micrograms/mL). 4. Several structurally diverse lipoxygenase inhibitors, including esculetin, baicalein and phenidone, over the dose range 1-100 mumol/L, also prevented [14C]-AA release and markedly protected against cell membrane damage. No drug directly scavenged H2O2 assessed by UV absorption. 5. These results indicate that H2O2 activates in GMC a complex series of interrelated pathological mechanisms which in turn contribute to a prolongation of oxidative damage beyond the time of the initial exposure. These include an increase in intracellular calcium which, depending upon conditions, appears to be mediated by release from intracellular stores as well as Ca2+ entry from the extracellular space. In turn there is a sustained release of arachidonic acid, which may partly depend on prolonged activation of PLA2 but not phospholipase C. 6. Release of [14C]-AA could be attenuated by inhibitors of NADPH oxidase, mitochondrial calcium-cycling, iron chelators and a structurally diverse range of lipoxygenase inhibitors in association with protection from H2O2-mediated cell membrane damage.

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.

Fibrinogen mediates platelet-polymorphonuclear leukocyte cooperation during immune-complex glomerulonephritis in rats

The metabolic and functional alterations which occur during the acute phase of nephrotoxic nephritis (NTN) in rats, a model of immune-mediated glomerulonephritis, result from a cooperative interaction between PMNs and platelets (PLTs). In consequence, we hypothesized that fibrinogen (Fg) might play a critical role in this process and, accordingly, we found that defibrination of animals decreased both the acute phase proteinuria in NTN (approximately 70%) as well as the influx of PLTs and PMNs into the glomerulus (approximately 40-50%). In contrast, blockade of the PLT Fg receptor, alpha IIb beta 3, with the RGD peptidomimetic SC-49992 decreased proteinuria (approximately 90%) without substantially altering the influx of PMNs or PLTs. Immunocytochemistry showed a marked increase in beta 3 integrin expression in inflamed glomeruli which was prevented either by PMN or PLT depletion before disease induction. FACS and immunocytochemical analysis of glomerular cell dissociates demonstrated that beta 3 integrin expression was predominantly on intraglomerular PLTs. In vitro, activated PLTs stimulated the PMN respiratory burst, an interaction which could be inhibited by Fg receptor blockade. In sum, acute NTN is accompanied by a marked increase in glomerular beta 3 integrin expression predominantly due to the influx of PLTs which localize to the glomerulus in a PMN-dependent fashion. Fg appears to serve a major role as a coactivating stimulus for PLT-PMNs in situ via alpha IIb beta 3, potentially mediating the PMN respiratory burst which contributes to proteinuria. Fg may also play a subsidiary role in PMN/PLT comigration.