n-3 fatty acids reduce plasma 20-hydroxyeicosatetraenoic acid and blood pressure in patients with chronic kidney disease

Beneficial Effects of Omega-3 Fatty Acids on Obesity and Related Metabolic and Chronic Inflammatory Diseases

Omega-3 polyunsaturated fatty acids (n-3 PUFAs) are known to help resolve inflammation through generation of anti-inflammatory eicosanoids and specialized pro-resolving mediators, including resolvins, protectins, and maresins. Through binding to the GPR120/FFAR4 receptor, their beneficial effects result from phospholipid membrane remodeling, impairment of inflammatory signaling molecules clustering, subsequent inhibition of NF-κB and inflammasome activation, and a reduction in oxidative stress. Obesity, a chronic inflammatory disease that contributes to metabolic disorders, is alleviated by n-3 PUFAs. In the adipose tissue (AT) of individuals with obesity, n-3 PUFAs counteract hypoxia, inhibit immune cell infiltration and AT inflammation, improve insulin sensitivity, and reduce fat mass. Beyond AT, n-3 PUFAs also alleviate other metabolic disorders such as metabolic-associated steatotic liver disease (MASLD), gut dysbiosis, and/or renal dysfunction. In cardiovascular disease (CVD), they are mainly recommended as a secondary prevention for patients with coronary heart disease risks. This review provides an in-depth analysis of the benefits of n-3 PUFAs in obesity and related metabolic diseases, examining both the mechanistic and clinical aspects. Additionally, it also explores the effects of n-3 PUFAs in obesity-related chronic inflammatory conditions, including inflammatory bowel disease, psoriasis, rheumatoid arthritis, osteoarthritis, and multiple sclerosis, by targeting specific pathophysiological mechanisms. Clinical applications and limitations of n-3 PUFAs are discussed based on findings from human clinical trials.

Emerging Roles and Therapeutic Applications of Arachidonic Acid Pathways in Cardiometabolic Diseases

Cardiometabolic disease has become a major health burden worldwide, with sharply increasing prevalence but highly limited therapeutic interventions. Emerging evidence has revealed that arachidonic acid derivatives and pathway factors link metabolic disorders to cardiovascular risks and intimately participate in the progression and severity of cardiometabolic diseases. In this review, we systemically summarized and updated the biological functions of arachidonic acid pathways in cardiometabolic diseases, mainly focusing on heart failure, hypertension, atherosclerosis, nonalcoholic fatty liver disease, obesity, and diabetes. We further discussed the cellular and molecular mechanisms of arachidonic acid pathway-mediated regulation of cardiometabolic diseases and highlighted the emerging clinical advances to improve these pathological conditions by targeting arachidonic acid metabolites and pathway factors.

Antioxidants for adults with chronic kidney disease

BACKGROUND

Chronic kidney disease (CKD) is a significant risk factor for cardiovascular disease (CVD) and death. Increased oxidative stress in people with CKD has been implicated as a potential causative factor. Antioxidant therapy decreases oxidative stress and may consequently reduce cardiovascular morbidity and death in people with CKD. This is an update of a Cochrane review first published in 2012.

OBJECTIVES

To examine the benefits and harms of antioxidant therapy on death and cardiovascular and kidney endpoints in adults with CKD stages 3 to 5, patients undergoing dialysis, and kidney transplant recipients.

SEARCH METHODS

We searched the Cochrane Kidney and Transplant Register of Studies until 15 November 2022 using search terms relevant to this review. Studies in the Register are identified through searches of CENTRAL, MEDLINE, and EMBASE, conference proceedings, the International Clinical Trials Registry Platform (ICTRP) Search Portal, and ClinicalTrials.gov.

SELECTION CRITERIA

We included all randomised controlled trials investigating the use of antioxidants, compared with placebo, usual or standard care, no treatment, or other antioxidants, for adults with CKD on cardiovascular and kidney endpoints.

DATA COLLECTION AND ANALYSIS

Titles and abstracts were screened independently by two authors who also performed data extraction using standardised forms. Results were pooled using random effects models and expressed as risk ratios (RR) or mean difference (MD) with 95% confidence intervals (CI). Confidence in the evidence was assessed using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach.

MAIN RESULTS

We included 95 studies (10,468 randomised patients) that evaluated antioxidant therapy in adults with non-dialysis-dependent CKD (31 studies, 5342 patients), dialysis-dependent CKD (41 studies, 3444 patients) and kidney transplant recipients (21 studies, 1529 patients). Two studies enrolled dialysis and non-dialysis patients (153 patients). Twenty-one studies assessed the effects of vitamin antioxidants, and 74 assessed the effects of non-vitamin antioxidants. Overall, the quality of included studies was moderate to low or very low due to unclear or high risk of bias for randomisation, allocation concealment, blinding, and loss to follow-up. Compared with placebo, usual care, or no treatment, antioxidant therapy may have little or no effect on cardiovascular death (8 studies, 3813 patients: RR 0.94, 95% CI 0.64 to 1.40; I² = 33%; low certainty of evidence) and probably has little to no effect on death (any cause) (45 studies, 7530 patients: RR 0.95, 95% CI 0.82 to 1.11; I² = 0%; moderate certainty of evidence), CVD (16 studies, 4768 patients: RR 0.79, 95% CI 0.63 to 0.99; I² = 23%; moderate certainty of evidence), or loss of kidney transplant (graft loss) (11 studies, 1053 patients: RR 0.88, 95% CI 0.67 to 1.17; I² = 0%; moderate certainty of evidence). Compared with placebo, usual care, or no treatment, antioxidants had little to no effect on the slope of urinary albumin/creatinine ratio (change in UACR) (7 studies, 1286 patients: MD -0.04 mg/mmol, 95% CI -0.55 to 0.47; I² = 37%; very low certainty of evidence) but the evidence is very uncertain. Antioxidants probably reduced the progression to kidney failure (10 studies, 3201 patients: RR 0.65, 95% CI 0.41 to 1.02; I² = 41%; moderate certainty of evidence), may improve the slope of estimated glomerular filtration rate (change in eGFR) (28 studies, 4128 patients: MD 3.65 mL/min/1.73 m², 95% CI 2.81 to 4.50; I² = 99%; low certainty of evidence), but had uncertain effects on the slope of serum creatinine (change in SCr) (16 studies, 3180 patients: MD -13.35 µmol/L, 95% CI -23.49 to -3.23; I² = 98%; very low certainty of evidence). Possible safety concerns are an observed increase in the risk of infection (14 studies, 3697 patients: RR 1.30, 95% CI 1.14 to 1.50; I² = 3%; moderate certainty of evidence) and heart failure (6 studies, 3733 patients: RR 1.40, 95% CI 1.11 to 1.75; I² = 0; moderate certainty of evidence) among antioxidant users. Results of studies with a low risk of bias or longer follow-ups generally were comparable to the main analyses.

AUTHORS' CONCLUSIONS

We found no evidence that antioxidants reduced death or improved kidney transplant outcomes or proteinuria in patients with CKD. Antioxidants likely reduce cardiovascular events and progression to kidney failure and may improve kidney function. Possible concerns are an increased risk of infections and heart failure among antioxidant users. However, most studies were of suboptimal quality and had limited follow-up, and few included people undergoing dialysis or kidney transplant recipients. Furthermore, the large heterogeneity in interventions hampers drawing conclusions on the efficacy and safety of individual agents.

Modulation of endothelium function by fatty acids

The endothelium acts as the barrier that prevents circulating lipids such as lipoproteins and fatty acids into the arterial wall; it also regulates normal functioning in the circulatory system by balancing vasodilation and vasoconstriction, modulating the several responses and signals. Plasma lipids can interact with endothelium via different mechanisms and produce different phenotypes. Increased plasma-free fatty acids (FFAs) levels are associated with the pathogenesis of atherosclerosis and cardiovascular diseases (CVD). Because of the multi-dimensional roles of plasma FFAs in mediating endothelial dysfunction, increased FFA level is now considered an essential link in the onset of endothelial dysfunction in CVD. FFA-mediated endothelial dysfunction involves several mechanisms, including dysregulated production of nitric oxide and cytokines, metaflammation, oxidative stress, inflammation, activation of the renin-angiotensin system, and apoptosis. Therefore, modulation of FFA-mediated pathways involved in endothelial dysfunction may prevent the complications associated with CVD risk. This review presents details as to how endothelium is affected by FFAs involving several metabolic pathways.

Regulation of hepatic coenzyme Q biosynthesis by dietary omega-3 polyunsaturated fatty acids

Dietary fats are important for human health, yet it is not fully understood how different fats affect various health problems. Although polyunsaturated fatty acids (PUFAs) are generally considered as highly oxidizable, those of the n-3 series can ameliorate the risk of many age-related disorders. Coenzyme Q (CoQ) is both an essential component of the mitochondrial electron transport chain and the only lipid-soluble antioxidant that animal cells can synthesize. Previous work has documented the protective antioxidant properties of CoQ against the autoxidation products of PUFAs. Here, we have explored in vitro and in vivo models to better understand the regulation of CoQ biosynthesis by dietary fats. In mouse liver, PUFAs increased CoQ content, and PUFAs of the n-3 series increased preferentially CoQ₁₀. This response was recapitulated in hepatic cells cultured in the presence of lipid emulsions, where we additionally demonstrated a role for n-3 PUFAs as regulators of CoQ biosynthesis via the upregulation of several COQ proteins and farnesyl pyrophosphate levels. In both models, n-3 PUFAs altered the mitochondrial network without changing the overall mitochondrial mass. Furthermore, in cellular systems, n-3 PUFAs favored the synthesis of CoQ₁₀ over CoQ₉, thus altering the ratio between CoQ isoforms through a mechanism that involved downregulation of farnesyl diphosphate synthase activity. This effect was recapitulated by both siRNA silencing and by pharmacological inhibition of farnesyl diphosphate synthase with zoledronic acid. We highlight here the ability of n-3 PUFAs to regulate CoQ biosynthesis, CoQ content, and the ratio between its isoforms, which might be relevant to better understand the health benefits associated with this type of fat. Additionally, we identify for the first time zoledronic acid as a drug that inhibits CoQ biosynthesis, which must be also considered with respect to its biological effects on patients.

Targeted analysis of eicosanoids derived from cytochrome P450 pathway by high-resolution multiple-reaction monitoring mass spectrometry

Cytochrome P450 (CYP450) pathway is one of the critical enzymatic via eicosanoid biosynthesis. Nevertheless, their metabolites are far less explored. This pathway plays a crucial role in converting arachidonic acid to hydroxyeicosatetraenoic (HETEs), epoxyeicosatrienoic (EETs), dihydroxyeicosatetraenoic acids (DiHETEs), and dihydroxyeicosatrienoic acids (DiHETrEs), which mediate several physiological and pathological functions. However, CYP450-derived eicosanoids are structurally complex, making those analyses a challenge in lipidomics studies. Herein, a high-resolution multiple-reaction monitoring (MRM^HR ) method has been proposed as a powerful tool for the simultaneous analysis of CYP450-eicosanoids on different biological samples. The developed liquid chromatography (LC)-MRM^HR method was partially validated according to the Food and Drug Administration (FDA) criteria, demonstrating adequate specificity, linearity, precision, and accuracy. Besides, several biological samples were analyzed to guarantee the feasibility of the method. The proposed strategy may improve the understanding of CYP450-derived eicosanoids in biological systems, which could be fundamental to reveal new aspects of those in physiologic and pathologic conditions.

A systematic review for the efficacy of coenzyme Q10 in patients with chronic kidney disease

BACKGROUND

The effects of coenzyme Q10 (CoQ10) supplementation in chronic kidney disease (CKD) patients remain controversial.

OBJECTIVE

A systematic review of current evidence was performed to systematically and comprehensively summarize the effects of CoQ10 on cardiovascular outcomes, oxidative stress, inflammation, lipid profiles, and glucose metabolism.

METHODS

MEDLINE, EMBASE, and the Cochrane Library database (Cochrane Central Register of Controlled Trials) were searched to identify eligible studies investigating the effects of CoQ10 supplementation on patients with CKD.

RESULTS

Twelve independent studies (including seventeen publications) were included in this systematic review. For CKD patients, six studies reported variable cardiovascular outcomes, which yielded inconsistent results. Regarding oxidative stress and inflammation, pooled analysis showed that CoQ10 supplementation significantly reduced malonaldehyde (WMD: - 1.15 95% CI - 1.48 to - 0.81) and high-sensitivity C reactive protein levels (WMD: - 1.18 95% CI - 2.21 to - 0.15). Regarding glucose metabolism, we found that CoQ10 supplementation resulted in significant improvements in HbA1c (WMD: - 0.80; 95% CI: - 1.35 to - 0.24) and QUICKI (WMD: 0.02; 95% CI: 0.01 to 0.03). The pooled results indicated that CoQ10 supplementation had no effects on total cholesterol, or LDL-cholesterol, or on HDL-cholesterol, and triglycerides.

CONCLUSIONS

Our systematic review demonstrated that CoQ10 supplementation might have promising effects on oxidative stress. This work provided some clues that CoQ10 supplementation might have the potential to improve inflammation levels, glucose metabolism, cardiac structure, and cardiac biomarkers. However, the effects of CoQ10 supplementation should be confirmed in larger high-quality studies.

Trace Elements and Fatty Acid Profile of Argyrosomus regius (Asso, 1801) from Mediterranean Aquaculture

Although Argyrosomus regius (Asso, 1801) counts among the most appreciated and increasingly consumed fish species in Europe, little information is available on its flesh quality. This research concerns both healthy aquatic resource diversification and good nutritional quality. It is the first study to evaluate the quality of A. regius flesh from Mediterranean aquaculture. It aims to assess the concentration of 19 trace elements and to determine the fatty acid profile of this fish farmed in the Mediterranean Sea and to discuss human exposure risks. The nutritional intake of oligoelements (selenium (Se), zinc (Zn), and chromium (Cr)) and the mean concentrations of contaminants (arsenic (As), barium (Ba), cadmium (Cd), lead (Pb), and tin (Sn)) in A. regius muscles are, respectively, above and below recommended regulatory standards set by the international legislation. Additionally, the low fat content in its muscle mass and its high level of docosahexaenoic acid (C22: 6 n-3; DHA) and, to a lesser extent, eicosapentaenoic acid (C20: 5 n-3; EPA) confers satisfying nutritional qualities. This study allowed to conclude that meager can be considered as a source of seafood with good nutritional qualities for human health.

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.

Omega-3 fatty acids decrease oxidative stress and inflammation in macrophages from patients with small abdominal aortic aneurysm

Abdominal aortic aneurysm (AAA) is associated with inflammation and oxidative stress, the latter of which contributes to activation of macrophages, a prominent cell type in AAA. Omega-3 polyunsaturated fatty acids (n-3 PUFAs) have been reported to limit oxidative stress in animal models of AAA. The aim of this study was to evaluate the effect of the n-3 PUFA docosahexaenoic acid (DHA) on antioxidant defence in macrophages from patients with AAA. Cells were obtained from men with small AAA (diameter 3.0–4.5 cm, 75 ± 6 yr, n = 19) and age- matched male controls (72 ± 5 yr, n = 41) and incubated with DHA for 1 h before exposure to 0.1 µg/mL lipopolysaccharide (LPS) for 24 h. DHA supplementation decreased the concentration of tumour necrosis factor-α (TNF-α; control, 42.1 ± 13.6 to 5.1 ± 2.1 pg/ml, p < 0.01; AAA, 25.2 ± 9.8 to 1.9 ± 0.9 pg/ml, p < 0.01) and interleukin-6 (IL-6; control, 44.9 ± 7.7 to 5.9 ± 2.0 pg/ml, p < 0.001; AAA, 24.3 ± 5.2 to 0.5 ± 0.3 pg/ml, p < 0.001) in macrophage supernatants. DHA increased glutathione peroxidase activity (control, 3.2 ± 0.3 to 4.1 ± 0.2 nmol/min/ml/μg protein, p = 0.004; AAA, 2.3 ± 0.5 to 3.4 ± 0.5 nmol/min/ml/μg protein, p = 0.008) and heme oxygenase-1 mRNA expression (control, 1.5-fold increase, p < 0.001). The improvements in macrophage oxidative stress status serve as a stimulus for further investigation of DHA in patients with AAA.

Metabolomics biomarkers and the risk of overall mortality and ESRD in CKD: Results from the Progredir Cohort

INTRODUCTION

Studies on metabolomics and CKD have primarily addressed CKD incidence defined as a decline on eGFR or appearance of albuminuria in the general population, with very few evaluating hard outcomes. In the present study, we investigated the association between metabolites and mortality and ESRD in a CKD cohort.

SETTING AND METHODS

Data on 454 participants of the Progredir Cohort Study, Sao Paulo, Brazil were used. Metabolomics was performed by GC-MS (Agilent MassHunter) and metabolites were identified using Agilent Fiehn GC/MS and NIST libraries. After excluding metabolites present in <50% of participants, 293 metabolites were analyzed. An FDR q value <0.05 criteria was applied in Cox models on the composite outcome (mortality or incident renal replacement therapy) adjusted for batch effect, resulting in 34 metabolites associated with the outcome. Multivariable-adjusted Cox models were then built for the composite outcome, death, and ESRD incident events. Competing risk analysis was also performed for ESRD.

RESULTS

Mean age was 68±12y, mean eGFR-CKDEPI was 38.4±14.6 ml/min/1.73m2 and 57% were diabetic. After adjustments (GC-MS batch, sex, age, DM and eGFR), 18 metabolites remained significantly associated with the composite outcome. Nine metabolites were independently associated with death: D-malic acid (HR 1.84, 95%CI 1.32-2.56, p = 0.0003), acetohydroxamic acid (HR 1.90, 95%CI 1.30-2.78, p = 0.0008), butanoic acid (HR 1.59, 95%CI 1.17-2.15, p = 0.003), and docosahexaenoic acid (HR 0.58, 95%CI 0.39-0.88, p = 0.009), among the top associations. Lactose (SHR 1.49, 95%CI 1.04-2.12, p = 0.03), 2-O-glycerol-α-D-galactopyranoside (SHR 1.76, 95%CI 1.06-2.92, p = 0.03), and tyrosine (SHR 0.52, 95%CI 0.31-0.88, p = 0.02) were associated to ESRD risk, while D-threitol, mannitol and myo-inositol presented strong borderline associations.

CONCLUSION

Our results identify specific metabolites related to hard outcomes in a CKD population. These findings point to the need of further exploration of these metabolites as biomarkers in CKD and the understanding of the underlying biological mechanisms related to the observed associations.

A rapid UPLC-MS/MS assay for eicosanoids in human plasma: Application to evaluate niacin responsivity

A rapid and sensitive method using ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was developed to simultaneously quantify hydroxyeicosatetraenoic (HETE), dihydroxyeicosatrienoic (DiHETrE), epoxyeicosatrienoic acid (EET), and prostaglandin metabolites of arachidonic acid in human plasma. Sample preparation consisted of solid phase extraction with Oasis HLB (30mg) cartridges for all metabolites. Separation of HETEs, EETs, and DiHETrEs was achieved on an Acquity UPLC BEH C18, 1.7µm (100×2.1mm) reversed-phase column (Waters Corp, Millford, MA) with negative electrospray ionization mass spectrometric detection. A second injection of the same extracted sample allowed for separation and assessment of prostaglandin metabolites under optimized UPLC-MS/MS conditions. Additionally, the endogenous levels of these metabolites in five different matrices were determined in order to select the optimal matrix for assay development. Human serum albumin was shown to have the least amount of endogenous metabolites, a recovery efficiency of 79-100% and a matrix effect of 71 - 100%. Linear calibration curves ranging from 0.416 to 66.67ng/ml were validated. Inter-assay and intra-assay variance was less than 15% at most concentrations. This method was successfully applied to quantify metabolite levels in plasma samples of healthy control subjects receiving niacin administration to evaluate the association between niacin administration and eicosanoid plasma level response.

Strategies to decrease oxidative stress biomarker levels in human medical conditions: A meta-analysis on 8-iso-prostaglandin F2α

The widespread detection of elevated oxidative stress levels in many medical conditions has led to numerous efforts to design interventions to reduce its effects. Efforts have been wide-ranging, from dietary changes to administration of antioxidants, supplements, e.g., omega-3-fatty acids, and many medications. However, there is still no systemic assessment of the efficacy of treatments for oxidative stress reduction across a variety of medical conditions. The goal of this meta-analysis is, by combining multiple studies, to quantitate the change in the levels of the popular oxidative stress biomarker 8-iso-prostaglandin F2α (8-iso-PGF2α) after a variety of treatment strategies in human populations. Nearly 350 unique publications with 180 distinct strategies were included in the analysis. For each strategy, the difference between pre- or placebo and post-treatment levels calculated using Hedges' g value of effect. In general, administration of antibiotics, antihyperlipidemic agents, or changes in lifestyle (g = - 0.63, - 0.54, and 0.56) had the largest effect. Administration of supplements, antioxidants, or changes in diet (g = - 0.09, - 0.28, - 0.12) had small quantitative effects. To fully interpret the effectiveness of these treatments, comparisons to the increase in g value for each medical condition is required. For example, antioxidants in populations with coronary artery disease (CAD) reduce the 8-iso-PGF2α levels by g = - 0.34 ± 0.1, which is quantitatively considered a small effect. However, CAD populations, in comparison to healthy populations, have an increase in 8-iso-PGF2α levels by g = 0.38 ± 0.04; therefore, the overall reduction of 8-iso-PGF2α levels is ≈ 90% by this treatment in this specific medical condition. In conclusion, 8-iso-PGF2α levels can be reduced not only by antioxidants but by many other strategies. Not all strategies are equally effective at reducing 8-iso-PGF2α levels. In addition, the effectiveness of any strategy can be assessed only in relation to the medical condition investigated.

Musings about the role dietary fats after 40 years of fatty acid research

Since the 1950's nutrition recommendations have focussed on the replacement of saturated fats in the diet with polyunsaturated fats, a strategy that continues to this day. Despite supporting evidence from clinical trials for the advantages of Mediterranean diets, there has been less attention paid to the role of monounsaturated fats. It has been known for many years that diets high in linoleic acid (LA) compete for the incorporation of omega 3 fatty acids into tissues. What is also clear is that diets rich in LA are not free from concerns and the discovery of oxlams, oxygenated derivatives of LA, having potent inflammatory effects may help us question the dogma of LA rich diets. Given that dietary oleic acid a prime constituent of Mediterranean diets can be metabolised to Mead acid (ETrA) has in the past been a cause for concern, but new data showing the anti-inflammatory effects of ETrA suggest that there is a need for further research about the benefits of monounsaturated oils on human health. Finally, there is a need to re-examine how dietary fats are monitored in clinical studies. The current method of focussing on esterified fatty acids may be too insensitive to detect clinically important changes.

The effect of n-3 fatty acids and coenzyme Q10 supplementation on neutrophil leukotrienes, mediators of inflammation resolution and myeloperoxidase in chronic kidney disease

BACKGROUND

Neutrophils release leukotriene (LT)B₄ and myeloperoxidase (MPO) that may be important mediators of chronic inflammation in chronic kidney disease (CKD). The n-3 fatty acids (n-3 FA) eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) have the potential to attenuate inflammation through production of LTB₅ and the Specialized Proresolving Lipid Mediators (SPM) that promote the resolution of inflammation. In animal models, coenzyme Q10 (CoQ) also attenuates inflammation by reducing MPO and LTB₄.

OBJECTIVE

This study evaluated the independent and combined effects of n-3 FA and CoQ supplementation on neutrophil leukotrienes, the pro-inflammatory eicosanoid 5-hydroxyeicosatetraenoic acid (5-HETE), SPM, and plasma MPO, in patients with CKD.

DESIGN

In a double-blind, placebo-controlled intervention of factorial design, 85 patients with CKD were randomized to either n-3 FA (4 g), CoQ (200 mg), both supplements, or control (4 g olive oil), daily for 8 weeks. Plasma MPO and calcium ionophore-stimulated neutrophil release of LTs, 5-HETE and SPM were measured at baseline and after 8 weeks.

RESULTS

Seventy four patients completed the intervention. n-3 FA, but not CoQ, significantly increased neutrophil LTB₅ (P < 0.0001) and the SPM 18-hydroxyeicosapentaenoic acid (18-HEPE), resolvin E1 (RvE1), resolvin E2 (RvE2) and resolvin E3 (RvE3) that derive from EPA, as well as 17-hydroxydocosahexaenoic acid (17-HDHA) and resolvin D5 (RvD5) that derive from DHA (all P < 0.01). Neutrophil LTB4 and its metabolites, and 5-HETE were not significantly altered by n-3 FA or CoQ. Plasma MPO was significantly reduced with n-3 FA alone (P = 0.013) but not when given in combination with CoQ.

CONCLUSION

n-3 FA supplementation in patients with CKD leads to increased neutrophil release of LTB₅ and several SPM, as well as a reduction in plasma MPO that may have important implications for limiting chronic inflammation.

Is renal tubular cadmium toxicity clinically relevant?

Background

Exposure to cadmium (Cd) has been associated with the development of hypertension, especially in women, but the mechanism of such an association is not understood. We hypothesize that Cd exposure alters renal production of 20-hydroxyeicosatetraenoic acid (20-HETE), which plays an indispensable role in renal salt balance and blood pressure control.

Methods

We examined long-term Cd exposure in relation to urinary 20-HETE excretion levels, tubular dysfunction and blood pressure measures, using data from a population-based, cross-sectional study that included 115 normotensive and 110 hypertensive women, 33-55 years of age, who lived in Cd contamination areas in Thailand.

Results

The mean [standard deviation (SD)] blood Cd level of the study subjects was 3.57 (3.3) µg/L, while the mean (SD) urinary Cd and urinary 20-HETE levels were 0.58 (0.47) µg/g creatinine and 1651 (4793) pg/mL, respectively. Elevated 20-HETE levels were associated with a 90% increase in prevalence odds of hypertension (P = 0.029), four times greater odds of having higher urinary Cd levels (P = 0.030) and a 53% increase in odds of having higher levels of tubular dysfunction (P = 0.049), evident from an increase in urinary excretion of β2-microglobulin. In normotensive subjects, an increase in urinary 20-HETE levels from tertile 1 to tertile 3 was associated with a systolic blood pressure increase of 6 mmHg (95% confidence interval 0.3-12, P = 0.040).

Conclusions

This is the first report that links urinary 20-HETE levels to blood pressure increases in Cd-exposed women, thereby providing a plausible mechanism for associated development of hypertension.

The polyunsaturated fatty acid balance in kidney health and disease: A review

Epidemiological studies show that circulating polyunsaturated fatty acids contribute to preserve renal function. In renal disease states there is generally a lack of omega-3 long chain polyunsaturated fatty acids (n-3 LCPUFA) as measured in biological samples, but despite intense research for more than 30 years, it is still unclear how and to what extent their supplementation would benefit kidney disorders. Studies evaluating the n-6 series and the kidney are less frequent. The last compilation of clinical trials with n-3 LCPUFA supplements focusing on renal function and damage dates back to 2012. We here discuss n-3 and n-6 fatty acids in relation to the kidney summarizing single- and double blind randomized controlled trials performed between 2012 and 2016. Nine were sub-studies/post-hoc analyses of previous parent trials. Twelve out of the twenty trials reported on fatty acid profile or fatty acid species. Factors that may explain inconsistent results obtained after supplementation with the n-3 LCPUFA EPA and DHA in kidney disease are discussed such as baseline levels determining response, drug interaction. The need of evaluating fatty acid status before and after intervention is emphasized, to match changes in outcome measure with changes of any fatty acid potentially involved.

Omega 3 Polyunsaturated Fatty Acids Improve Endothelial Dysfunction in Chronic Renal Failure: Role of eNOS Activation and of Oxidative Stress

Background: Endothelial dysfunction is a key vascular alteration in chronic kidney disease (CKD). Omega 3 (n-3) polyunsaturated fatty acids (PUFA) reduce vascular oxidative stress and inflammation. We investigated whether n-3 PUFA could reverse endothelial dysfunction in CKD by improving endothelial nitric oxide synthase (eNOS) function and oxidative stress. Methods: 5/6 nephrectomized male Wistar rats (CKD; n = 10) and sham operated animals (SHAM; n = 10) were treated for 6 weeks with standard diet. An additional group of CKD rats were fed an n-3 PUFA enriched diet (CKD + PUFA; n = 10). We then measured endothelium-dependent (EDD) and -independent vasodilation, markers of endothelial function and of oxidative stress in thoracic aortas. Results: Compared to SHAM, in CKD aortas EDD and eNOS expression were reduced (p < 0.05) and 3-nitrotyrosine levels were increased, while expression of NADPH oxidase subunits NOX4 and p22^phox was similar. In-vitro incubation with Tiron failed to reverse endothelial dysfunction in CKD. In CKD + PUFA, EDD improved (p < 0.05) compared with CKD rats, while blockade of eNOS by L-NAME worsened EDD. These effects were accompanied by increased (p < 0.05) eNOS and reduced (p < 0.05) expression of NOX4 and 3-nitrotyrosine levels. Conclusion: Collectively, these findings indicate that n-3 PUFA improve endothelial dysfunction by restoring NO bioavailability in CKD.

Naturally Occurring Compounds: New Potential Weapons against Oxidative Stress in Chronic Kidney Disease

Oxidative stress is a well-described imbalance between the production of reactive oxygen species (ROS) and the antioxidant defense system of cells and tissues. The overproduction of free radicals damages all components of the cell (proteins, lipids, nucleic acids) and modifies their physiological functions. As widely described, this condition is a biochemical hallmark of chronic kidney disease (CKD) and may dramatically influence the progression of renal impairment and the onset/development of major systemic comorbidities including cardiovascular diseases. This state is exacerbated by exposure of the body to uremic toxins and dialysis, a treatment that, although necessary to ensure patients' survival, exposes cells to non-physiological contact with extracorporeal circuits and membranes with consequent mitochondrial and anti-redox cellular system alterations. Therefore, it is undeniable that counteracting oxidative stress machinery is a major pharmacological target in medicine/nephrology. As a consequence, in recent years several new naturally occurring compounds, administered alone or integrated with classical therapies and an appropriate lifestyle, have been proposed as therapeutic tools for CKD patients. In this paper, we reviewed the recent literature regarding the "pioneering" in vivo testing of these agents and their inclusion in small clinical trials performed in patients affected by CKD.

20-HETE Signals Through G-Protein-Coupled Receptor GPR75 (Gq) to Affect Vascular Function and Trigger Hypertension

RATIONALE

20-Hydroxyeicosatetraenoic acid (20-HETE), one of the principle cytochrome P450 eicosanoids, is a potent vasoactive lipid whose vascular effects include stimulation of smooth muscle contractility, migration, and proliferation, as well as endothelial cell dysfunction and inflammation. Increased levels of 20-HETE in experimental animals and in humans are associated with hypertension, stroke, myocardial infarction, and vascular diseases.

OBJECTIVE

To date, a receptor/binding site for 20-HETE has been implicated based on the use of specific agonists and antagonists. The present study was undertaken to identify a receptor to which 20-HETE binds and through which it activates a signaling cascade that culminates in many of the functional outcomes attributed to 20-HETE in vitro and in vivo.

METHODS AND RESULTS

Using crosslinking analogs, click chemistry, binding assays, and functional assays, we identified G-protein receptor 75 (GPR75), currently an orphan G-protein-coupled receptor (GPCR), as a specific target of 20-HETE. In cultured human endothelial cells, 20-HETE binding to GPR75 stimulated Gα_q/11 protein dissociation and increased inositol phosphate accumulation and GPCR-kinase interacting protein-1-GPR75 binding, which further facilitated the c-Src-mediated transactivation of epidermal growth factor receptor. This results in downstream signaling pathways that induce angiotensin-converting enzyme expression and endothelial dysfunction. Knockdown of GPR75 or GPCR-kinase interacting protein-1 prevented 20-HETE-mediated endothelial growth factor receptor phosphorylation and angiotensin-converting enzyme induction. In vascular smooth muscle cells, GPR75-20-HETE pairing is associated with Gα_q/11- and GPCR-kinase interacting protein-1-mediated protein kinase C-stimulated phosphorylation of MaxiKβ, linking GPR75 activation to 20-HETE-mediated vasoconstriction. GPR75 knockdown in a mouse model of 20-HETE-dependent hypertension prevented blood pressure elevation and 20-HETE-mediated increases in angiotensin-converting enzyme expression, endothelial dysfunction, smooth muscle contractility, and vascular remodeling.

CONCLUSIONS

This is the first report to identify a GPCR target for an eicosanoid of this class. The discovery of 20-HETE-GPR75 pairing presented here provides the molecular basis for the signaling and pathophysiological functions mediated by 20-HETE in hypertension and cardiovascular diseases.

n-3 Fatty Acid Supplementation and Leukocyte Telomere Length in Patients with Chronic Kidney Disease

DNA telomere shortening associates with the age-related increase cardiovascular disease (CVD) risk. Reducing oxidative stress, could modify telomere erosion during cell replication, and CVD risk in patients with chronic kidney disease (CKD). The effect of n-3 fatty acids and coenzyme Q10 (CoQ) on telomere length was studied in a double-blind placebo-controlled trial in CKD. Eighty-five CKD patients were randomized to: n-3 fatty acids (4 g); CoQ (200 mg); both supplements; or control (4 g olive oil), daily for 8 weeks. Telomere length was measured in neutrophils and peripheral blood mononuclear cells (PBMC) at baseline and 8 weeks, with and without correction for cell counts. Main and interactive effects of n-3 fatty acids and CoQ on telomere length were assessed adjusting for baseline values. F₂-isoprostanes were measured as markers of oxidative stress. There was no effect of n-3 fatty acids or CoQ on neutrophil or PBMC telomere length. However, telomere length corrected for neutrophil count was increased after n-3 fatty acids (p = 0.015). Post-intervention plasma F₂-isoprostanes were negative predictors of post-intervention telomere length corrected for neutrophil count (p = 0.025).The effect of n-3 fatty acids to increased telomere length corrected for neutrophil count may relate to reduced oxidative stress and increased clearance of neutrophils with shorter telomeres from the circulation. This may be a novel mechanism of modifying CVD risk in CKD patients.