Ethanol at low concentrations protects glomerular podocytes through alcohol dehydrogenase and 20-HETE

Arachidonic acid metabolism as a therapeutic target in AKI-to-CKD transition

Arachidonic acid (AA) is a main component of cell membrane lipids. AA is mainly metabolized by three enzymes: cyclooxygenase (COX), lipoxygenase (LOX) and cytochrome P450 (CYP450). Esterified AA is hydrolysed by phospholipase A2 into a free form that is further metabolized by COX, LOX and CYP450 to a wide range of bioactive mediators, including prostaglandins, lipoxins, thromboxanes, leukotrienes, hydroxyeicosatetraenoic acids and epoxyeicosatrienoic acids. Increased mitochondrial oxidative stress is considered to be a central mechanism in the pathophysiology of the kidney. Along with increased oxidative stress, apoptosis, inflammation and tissue fibrosis drive the progressive loss of kidney function, affecting the glomerular filtration barrier and the tubulointerstitium. Recent studies have shown that AA and its active derivative eicosanoids play important roles in the regulation of physiological kidney function and the pathogenesis of kidney disease. These factors are potentially novel biomarkers, especially in the context of their involvement in inflammatory processes and oxidative stress. In this review, we introduce the three main metabolic pathways of AA and discuss the molecular mechanisms by which these pathways affect the progression of acute kidney injury (AKI), diabetic nephropathy (DN) and renal cell carcinoma (RCC). This review may provide new therapeutic targets for the identification of AKI to CKD continuum.

Underlying antihypertensive mechanism of egg white-derived peptide QIGLF using renal metabolomics analysis

The kidney is an important target organ in the treatment of hypertension, but the effect of peptide QIGLF with antihypertensive activity on kidneys remains unknown. In the work, we aimed to further understand the hypotensive effects of QIGLF in spontaneously hypertensive rats (SHRs) using widely targeted metabolomics technology to investigate the kidney metabolic profiling variations. After four weeks of oral administration, the results showed different renal metabolomics profiles between QIGLF and model groups. Besides, a total of 10 potential biomarkers were identified, that is, 3-hydroxybutanoate, 20-hydroxyeicosatetraenoic acid, 19(S)-hydroxyeicosatetraenoic acid, 15-oxoETE, L-ornithine, malonate, uridine, uridine 5'-monophosphate, argininosuccinic acid, and N-carbamoyl-L-aspartate. These metabolites might exhibit antihypertensive activity of QIGLF by regulating synthesis and degradation of ketone bodies, arachidonic acid metabolism, pyrimidine metabolism, and arginine biosynthesis. These findings suggest that QIGLF might alleviate hypertension by inhibiting renal inflammation, promoting natriuresis, and regulating renal nitric oxide production.

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.

Effect of body mass index on the association between alcohol consumption and the development of chronic kidney disease

The influence of body mass or metabolic capacity on the association between alcohol consumption and lower risks of developing chronic kidney disease (CKD) is not fully elucidated. We examined whether the body mass index (BMI) affects the association between drinking alcohol and CKD. We defined CKD as an estimated glomerular filtration rate decline < 60 mL/min/1.73 m² and/or positive proteinuria (≥ 1+). Participants were 11,175 Japanese individuals aged 40–74 years without baseline CKD who underwent annual health checkups. Daily alcohol consumption at baseline was estimated using a questionnaire, and the participants were categorized as “infrequent (occasionally, rarely or never),” “light (< 20 g/day),” “moderate (20–39 g/day),” and “heavy (≥ 40 g/day).” Over a median 5-year observation period, 936 participants developed CKD. Compared with infrequent drinkers, light drinkers were associated with low CKD risks; adjusted hazard ratios (95% confidence intervals) were 0.81 (0.69–0.95). Stratified by BMI (kg/m²), moderate drinkers in the low (< 18.5), normal (18.5–24.9), and high (≥ 25.0) BMI groups had adjusted hazard ratios (95% confidence intervals) of 3.44 (1.60–7.42), 0.75 (0.58–0.98), and 0.63 (0.39–1.04), respectively. Taken together, the association between alcohol consumption and CKD incidence was not the same in all the individuals, and individual tolerance must be considered.

Association between alcohol intake and measures of incident CKD: An analysis of nationwide health screening data

To evaluate the association between alcohol intake and incident chronic kidney disease measures as well as the sex differences in this association, we analyzed health screening data of 14,190,878 adults who underwent health screening ≥3 times and had glomerular filtration rate (eGFR) ≥60 mL/min/1.73 m² and normal proteinuria at baseline. eGFR was calculated with the Chronic Kidney Disease Epidemiology Collaboration equation. Proteinuria was defined as ≥1+ dipstick proteinuria and low eGFR as <60 mL/min/1.73 m². The risk of incident proteinuria and low eGFR was analyzed with an extended Cox model with alcohol intake level as a time-varying determinant and the annual change of eGFR with generalized linear model. A J-shape association of alcohol intake with the incident proteinuria was observed in men (adjusted hazard ratio [aHR], 0.961, 95% confidence interval [CI], 0.953–0.970 in men drinking alcohol <10 g/day; aHR 1.139, 95% CI, 1.123–1.154 in men drinking alcohol ≥40 g/day, compared with non-drinking men), and a positive association was seen in women (aHR, 1.034, 95% CI, 1.023–1.044 in women drinking alcohol <10 g/day; aHR, 1.094, 95% CI, 1.034–1.158 in women drinking alcohol ≥40 g/day, compared with non-drinking women). In both sexes, an inverse association of alcohol intake with the annual eGFR decline and incident low eGFR was observed. This study observed a beneficial effect of moderate alcohol intake on incident proteinuria in men and a protective effect of alcohol intake of any amount on the annual eGFR decline and incident low eGFR in both sexes. The long-term implications of these observations need to be elucidated with future studies.

Conflicting roles of 20-HETE in hypertension and renal end organ damage

20-HETE is a cytochrome P450-derived metabolite of arachidonic acid that has both pro- and anti-hypertensive actions that result from modulation of vascular and kidney function. In the vasculature, 20-HETE sensitizes vascular smooth muscle cells to constrictor stimuli and increases myogenic tone. By promoting smooth muscle cell migration and proliferation, as well as by acting on the vascular endothelium to cause endothelial dysfunction, angiotensin converting enzyme (ACE) expression, and inflammation, 20-HETE contributes to adverse vascular remodeling and increased blood pressure. A G protein-coupled receptor was recently identified as the effector for the vascular actions of 20-HETE. In addition, evidence suggests that 20-HETE contributes to hypertension via positive regulation of the renin-angiotensin-aldosterone system, as well as by causing renal fibrosis. On the other hand, 20-HETE exerts anti-hypertensive actions by inhibiting sodium reabsorption by the kidney in both the proximal tubule and thick ascending limb of Henle. This review discusses the pro- and anti-hypertensive roles of 20-HETE in the pathogenesis of hypertension-associated renal disease, the association of gene polymorphisms of cytochrome P450 enzymes with the development of hypertension and renal end organ damage in humans, and 20-HETE related pharmaceutical agents.

Alcohol consumption and incidence of proteinuria: a retrospective cohort study

BACKGROUND

Previous studies report conflicting results of a dose-dependent association between alcohol consumption and incidence of chronic kidney disease. Only a few studies have assessed the clinical impact of > 45-65 g/day of critically high alcohol consumption.

METHODS

This retrospective cohort study included 88,647 males and 88,925 females with dipstick urinary protein ≤ ± and estimated glomerular filtration rate ≥ 60 mL/min/1.73 m² at their first annual health examinations between April 2008 and March 2010 in Japan. The exposure was the self-reported alcohol consumption. The outcome was proteinuria defined as dipstick urinary protein ≥ 1 + or ≥ 2 +.

RESULTS

During median 1.8 years (interquartile range 1.0-2.1) of the observational period, 5416 (6.1%) males and 3262 (3.7%) females developed proteinuria defined as dipstick urinary protein ≥ 1 +. In males, a U-shape association between alcohol consumption and proteinuria was observed in a multivariable-adjusted Poisson regression model [incidence rate ratio (95% confidence interval) of rare, occasional, and daily drinkers with ≤ 19, 20-39, 40-59, and ≥ 60 g/day: 1.00 (reference), 0.86 (0.79-0.94), 0.70 (0.64-0.78), 0.82 (0.75-0.90), 1.00 (0.90-1.11), and 1.00 (0.85-1.17), respectively], whereas a J-shape association was observed in females [1.00 (reference), 0.81 (0.75-0.87), 0.74 (0.64-0.85), 0.93 (0.78-1.11), 1.09 (0.83-1.44), and 1.45 (1.02-2.08), respectively]. Similar associations with dipstick urinary protein ≥ 2 + were shown in males and females.

CONCLUSIONS

Moderate alcohol consumption was associated with lower risk of proteinuria in both males and females. Females with ≥ 60 g/day of high alcohol consumption were at higher risk of proteinuria, whereas males were not. Females were more vulnerable to high alcohol consumption, than males.

Long-term exposure to ethanol downregulates tight junction proteins through the protein kinase Cα signaling pathway in human cerebral microvascular endothelial cells

Brain microvascular endothelial cells (BMECs) are the primary component of the blood-brain barrier (BBB). Tight junction (TJ) proteins, including claudin, occludin and zonula occludens (ZO)-1, ZO-2 and ZO-3, maintain the structural integrity of BMECs. Ethanol activates the assembly and disassembly of TJs, which is a process that is regulated by protein kinase C (PKC). In addition, ethanol treatment leads to the loss of structural integrity, which damages the permeability of the BBB and subsequently affects central nervous system homeostasis, thus allowing additional substances to enter the brain. However, the mechanisms underlying ethanol-induced loss of BBB structure remain unknown. It has been hypothesized that long-term exposure to ethanol reduces the expression of claudin-5, occludin and ZO-1 via the PKC signaling pathway, thereby affecting BBB structural integrity. In the current study, the human cerebral microvascular endothelial cell line, HCMEC/D3, was treated with 50, 100, 200 and 400 mM ethanol for 24, 48 and 72 h. Cell viability was determined using an MTS assay. The expression of claudin-5, occludin and ZO-1 protein and mRNA was measured using western blot analysis and reverse transcription-quantitative polymerase chain reaction, respectively. Following the pretreatment of HCMEC/D3 cells with the PKCα-specific inhibitor, safingol (10 µmol/l), the expression of claudin-5, occludin, ZO-1 and phosphorylated (p)-PKCα was measured using western blot analysis, and PKCα localization was determined by immunofluorescence. With increasing concentrations of ethanol, the expression of claudin-5, occludin and ZO-1 protein decreased, while the expression of claudin-5, occludin and ZO-1 mRNA increased. Exposure to ethanol significantly increased the expression of p-PKCα, whereas no significant effect on the expression of PKCα was observed. Following 48 h treatment with 200 mM ethanol, the expression of claudin-5, occludin and ZO-1 protein was significantly decreased when compared with the control. By contrast, the expression of p-PKCα was increased, and increased translocation of PKCα from the cytoplasm to the nuclear membrane and nucleus was observed. In addition, the results demonstrated that safingol significantly reversed these effects of ethanol. In conclusion, long-term exposure to ethanol downregulates the expression of claudin-5, occludin and ZO-1 protein in HCMEC/D3 s, and this effect may be mediated via activation of PKCα.

Effect of Cytochrome P450 Metabolites of Arachidonic Acid in Nephrology

Thirty-five years ago, a third pathway for the metabolism of arachidonic acid by cytochrome P450 enzymes emerged. Subsequent work revealed that 20-hydroxyeicosatetraenoic and epoxyeicosatrienoic acids formed by these pathways have essential roles in the regulation of renal tubular and vascular function. Sequence variants in the genes that produce 20-hydroxyeicosatetraenoic acid are associated with hypertension in humans, whereas the evidence supporting a role for variants in the genes that alter levels of epoxyeicosatrienoic acids is less convincing. Studies in animal models suggest that changes in the production of cytochrome P450 eicosanoids alter BP. However, the mechanisms involved remain controversial, especially for 20-hydroxyeicosatetraenoic acid, which has both vasoconstrictive and natriuretic actions. Epoxyeicosatrienoic acids are vasodilators with anti-inflammatory properties that oppose the development of hypertension and CKD; 20-hydroxyeicosatetraenoic acid levels are elevated after renal ischemia and may protect against injury. Levels of this eicosanoid are also elevated in polycystic kidney disease and may contribute to cyst formation. Our review summarizes the emerging evidence that cytochrome P450 eicosanoids have a role in the pathogenesis of hypertension, polycystic kidney disease, AKI, and CKD.

The cytoskeleton as a novel target for treatment of renal fibrosis

The incidence of chronic kidney disease (CKD) is increasing, with an estimated prevalence of 12% in the United States (Synder et al., 2009). While CKD may progress to end-stage renal disease (ESRD), which necessitates renal replacement therapy, i.e. dialysis or transplantation, most CKD patients never reach ESRD due to the increased risk of death from cardiovascular disease. It is well-established that regardless of the initiating insult - most often diabetes or hypertension - fibrosis is the common pathogenic pathway that leads to progressive injury and organ dysfunction (Eddy, 2014; Duffield, 2014). As such, there has been extensive research into the molecular and cellular mechanisms of renal fibrosis; however, translation to effective therapeutic strategies has been limited. While a role for the disruption of the cytoskeleton, most notably the actin network, has been established in acute kidney injury over the past two decades, a role in regulating renal fibrosis and CKD is only recently emerging. This review will focus on the role of the cytoskeleton in regulating pro-fibrotic pathways in the kidney, as well as data suggesting that these pathways represent novel therapeutic targets to manage fibrosis and ultimately CKD.

Fluorescence dilution technique for measurement of albumin reflection coefficient in isolated glomeruli

This study describes a high-throughput fluorescence dilution technique to measure the albumin reflection coefficient (σAlb) of isolated glomeruli. Rats were injected with FITC-dextran 250 (75 mg/kg), and the glomeruli were isolated in a 6% BSA solution. Changes in the fluorescence of the glomerulus due to water influx in response to an imposed oncotic gradient was used to determine σAlb. Adjustment of the albumin concentration of the bath from 6 to 5, 4, 3, and 2% produced a 10, 25, 35, and 50% decrease in the fluorescence of the glomeruli. Pretreatment of glomeruli with protamine sulfate (2 mg/ml) or TGF-β1 (10 ng/ml) decreased σAlb from 1 to 0.54 and 0.48, respectively. Water and solute movement were modeled using Kedem-Katchalsky equations, and the measured responses closely fit the predicted behavior, indicating that loss of albumin by solvent drag or diffusion is negligible compared with the movement of water. We also found that σAlb was reduced by 17% in fawn hooded hypertensive rats, 33% in hypertensive Dahl salt-sensitive (SS) rats, 26% in streptozotocin-treated diabetic Dahl SS rats, and 21% in 6-mo old type II diabetic nephropathy rats relative to control Sprague-Dawley rats. The changes in glomerular permeability to albumin were correlated with the degree of proteinuria in these strains. These findings indicate that the fluorescence dilution technique can be used to measure σAlb in populations of isolated glomeruli and provides a means to assess the development of glomerular injury in hypertensive and diabetic models.

Cytochrome P450 and Lipoxygenase Metabolites on Renal Function

Arachidonic acid metabolites have a myriad of biological actions including effects on the kidney to alter renal hemodynamics and tubular transport processes. Cyclooxygenase metabolites are products of an arachidonic acid enzymatic pathway that has been extensively studied in regards to renal function. Two lesser-known enzymatic pathways of arachidonic acid metabolism are the lipoxygenase (LO) and cytochrome P450 (CYP) pathways. The importance of LO and CYP metabolites to renal hemodynamics and tubular transport processes is now being recognized. LO and CYP metabolites have actions to alter renal blood flow and glomerular filtration rate. Proximal and distal tubular sodium transport and fluid and electrolyte homeostasis are also significantly influenced by renal CYP and LO levels. Metabolites of the LO and CYP pathways also have renal actions that influence renal inflammation, proliferation, and apoptotic processes at vascular and epithelial cells. These renal LO and CYP pathway actions occur through generation of specific metabolites and cell-signaling mechanisms. Even though the renal physiological importance and actions for LO and CYP metabolites are readily apparent, major gaps remain in our understanding of these lipid mediators to renal function. Future studies will be needed to fill these major gaps regarding LO and CYP metabolites on renal function.