n-3 fatty acids reduce proteinuria in patients with chronic glomerular disease

Renoprotective effects of docosahexaenoic acid in cats with early chronic kidney disease due to polycystic kidney disease: a pilot study

OBJECTIVES

Lipids containing n-3 fatty acids have been reported to have protective effects on renal function, with docosahexaenoic acid (DHA) expected to be particularly effective. However, no reports have demonstrated the renoprotective effects of DHA-enriched lipids in cats with chronic kidney disease (CKD). Therefore, the aim of this pilot study was to examine the renoprotective effects of DHA-enriched fish oil in cats.

METHODS

Five healthy cats and five cats with early non-azotaemic CKD due to autosomal dominant polycystic kidney disease (PKD) were orally administered DHA-enriched fish oil in liquid form (250 or 500 mg/kg body weight [BW] and 250 mg/kg BW of DHA, respectively) for 28 days. Inappropriately dilute urine and markedly increased urinary N-acetyl-d-glucosamine (NAG) index were detected in cats with PKD before DHA-enriched fish oil administration. Changes in the fatty acid composition ratio in the blood of all 10 cats were assessed after orally administering 250 mg/kg of DHA.

RESULTS

Post-administration, no adverse clinical effects were observed, and blood and urine tests were within the reference intervals in healthy cats. Cats with PKD showed significantly decreased serum symmetric dimethylarginine (SDMA), urine protein:creatinine ratio (UPC) and urinary NAG index at post-administration. Furthermore, oral administration of DHA-enriched fish oils significantly decreased the blood concentration ratio of arachidonic acid (AA) in cats with PKD post-administration. Furthermore, the concentration ratio of DHA in the blood significantly increased in both healthy cats and cats with PKD, and the DHA:AA ratio also increased.

CONCLUSIONS AND RELEVANCE

Oral administration of DHA-enriched fish oils for 28 days significantly decreased blood AA levels and significantly increased DHA concentration and DHA:AA ratios in cats with PKD, and improved the SDMA, UPC and urinary NAG index, suggesting its potential for renoprotective effects in cats with early non-azotaemic CKD due to PKD.

Association of Dietary Intakes and Genetically Determined Serum Concentrations of Mono and Poly Unsaturated Fatty Acids on Chronic Kidney Disease: Insights from Dietary Analysis and Mendelian Randomization

Polyunsaturated fatty acid (PUFA) intake is generally associated with better renal function, while the association of monounsaturated fatty acids (MUFAs) remains unconfirmed. Mendelian randomization (MR) analysis was used to obtain unconfounded estimates of the causal association of dietary intake and genetically determined serum PUFA and MUFA levels with measures of renal function. Data from participants of the National Health and Nutrition Examination Surveys (NHANES) from 2005 to 2010 were used. Data from the largest genome-wide association studies (GWAS) on MUFAs, PUFAs, eGFR, and chronic kidney disease (CKD) were analysed for the entire sample. A total of 16,025 participants were included. eGFR improved across increasing quartiles of total PUFA intake from 86.3 ± 0.5 (Q1) to 96.2 ± 0.5 mL/min/1.73 m² (Q4), (p < 0.001). Conversely, there was no association between MUFA intake and measures of renal function (all p > 0.21). In multivariable models, the top quartile of PUFA intake had a 21% lower risk for CKD, but there was no significant association between CKD risk and MUFA intake. Genetically determined serum MUFA (heptadecenoate (17:1), myristoleic acid (14:1), and palmitoleic acid (16:1)) and PUFA (α-linolenic acid and eicosapentaenoic acid) concentrations had no significant association with eGFR and CKD risk. Additionally, no association was found in the analyses stratified by diabetes status. Higher dietary PUFA intake is associated with lower risk of CKD, while there was no association with serum levels of MUFAs or PUFAs. Additional studies including clinical trials are warranted.

Fish oil replacement prevents, while docosahexaenoic acid-derived protectin DX mitigates end-stage-renal-disease in atherosclerotic diabetic mice

Diabetic nephropathy (DN) remains the major cause of end-stage renal disease (ESRD). We used high-fat/high-sucrose (HFHS)-fed LDLr^-/- /ApoB^100/100 mice with transgenic overexpression of IGFII in pancreatic β-cells (LRKOB100/IGFII) as a model of ESRD to test whether dietary long chain omega-3 polyunsaturated fatty acids LCω3FA-rich fish oil (FO) could prevent ESRD development. We further evaluated the potential of docosahexaenoic acid (DHA)-derived pro-resolving lipid mediators, 17-hydroxy-DHA (17-HDHA) and Protectin DX (PDX), to reverse established ESRD damage. HFHS-fed vehicle-treated LRKOB100/IGFII mice developed severe kidney dysfunction leading to ESRD, as revealed by advanced glomerular fibrosis and mesangial expansion along with reduced percent survival. The kidney failure outcome was associated with cardiac dysfunction, revealed by reduced heart rate and prolonged diastolic and systolic time. Dietary FO prevented kidney damage, lean mass loss, cardiac dysfunction, and death. 17-HDHA reduced podocyte foot process effacement while PDX treatment alleviated kidney fibrosis and mesangial expansion as compared to vehicle treatment. Only PDX therapy was effective at preserving the heart function and survival rate. These results show that dietary LCω3FA intake can prevent ESRD and cardiac dysfunction in LRKOB100/IGFII diabetic mice. Our data further reveals that PDX can protect against renal failure and cardiac dysfunction, offering a potential new therapeutic strategy against ESRD.

Effects of fish oil during hemodialysis on nutritional status and quality of life: a randomized double-blinded trial

Background

Supplementation of fish oil has been shown to exert beneficial effects in patients undergoing hemodialysis. The aim of this study was to investigate the efficacy of fish oil in improving the quality of life of these patients through a randomized, double-blinded clinical trial.

Methods

Among the 103 patients enrolled in the study, a total of 74 patients were randomized to receive fish oil (intervention group) or placebo (n=37 per group). Patients received identical soft-gel capsules, with each capsule containing either 1000 mg fish oil or placebo for 4 months. Personnel responsible for data collection and analyses were blinded to the grouping.

Results

The reduction of protein-energy wasting (PEW) in the intervention group was significantly more prominent compared to the placebo group (P=0.023). The intervention group demonstrated significant increase in midarm circumference, arm muscle circumference, and triceps skinfold thickness after fish oil intake. The intervention group also exhibited significant differences from the placebo group in creatinine, uric acid, and serum calcium levels. Significant improvement was seen regarding the physical role and energy/figure in the intervention group.

Conclusions

Our study demonstrated that fish oil intake in patient undergoing hemodialysis can significantly reduce PEW, and improve physical and biochemical parameters and quality of life, which could provide guidance to clinical management of these patients.

Omega-3 Supplementation in the Prevention of Contrast Induced Nephropathy in Patients Undergoing Elective Percutaneous Coronary Intervention: A Randomized Placebo-Controlled Trial

Purpose: Contrast-induced nephropathy (CIN) is the third cause of hospital-acquired renal failure and is associated with significant morbidity and mortality. Several studies have revealed the protective role of omega-3 in prevention and treatment of some kidney injuries. This study was conducted to examine the effect of omega-3 supplementation on the markers of renal function and to evaluate its potential in the prevention of CIN in patients undergoing elective percutaneous coronary intervention (PCI). Methods: In this double-blind, randomized clinical trial, 85 eligible patients scheduled for PCI was randomly divided into omega-3 (a single 3750 mg dose of omega-3 as well as routine hydration therapy within 12 hours before PCI) or control (placebo plus routine hydration therapy) groups. Serum creatinine (SCr) and cystatin C levels were measured at baseline and 24 hours after PCI. Results: Our results indicated that post- PCI cystatin C levels were significantly decreased in the omega-3 group compared to the control group (P < 0.001). Although less upward manner was seen in the level of 24-hour creatinine in the omega-3 group, it did not reach the significance level (P = 0.008). Conclusion: The positive effect of omega-3 on cystatin C levels showed that it may have a protective role in the prevention of CIN in post-PCI patients with normal kidney function. However, to better assess this effect, it is highly recommended to design future studies with higher doses and longer duration of therapy with omega-3 plus long-term follow up.

Kidney Lipidomics by Mass Spectrometry Imaging: A Focus on the Glomerulus

Lipid disorders have been associated with glomerulopathies, a distinct type of renal pathologies, such as nephrotic syndrome. Global analyses targeting kidney lipids in this pathophysiologic context have been extensively performed, but most often regardless of the architectural and functional complexity of the kidney. The new developments in mass spectrometry imaging technologies have opened a promising field in localized lipidomic studies focused on this organ. In this article, we revisit the main works having employed the Matrix Assisted Laser Desorption Ionization Time of Flight (MALDI-TOF) technology, and the few reports on the use of TOF-Secondary Ion Mass Spectrometry (TOF-SIMS). We also present a first analysis of mouse kidney cortex sections by cluster TOF-SIMS. The latter represents a good option for high resolution lipid imaging when frozen unfixed histological samples are available. The advantages and drawbacks of this developing field are discussed.

The omega-3 index in patients with heart failure: A prospective cohort study

BACKGROUND

Epidemiologic studies on the omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in heart failure are scarce, while one large intervention trial demonstrated a modest benefit.

METHODS

This is a secondary analysis from the Interdisciplinary Network Heart Failure (INH) program. Patients hospitalized for systolic heart failure were enrolled and followed for 36 months. At baseline, whole blood samples from 899 patients were analyzed for fatty acid composition using a standardized analytical procedure (HS-Omega-3 Index®, O3-I). Associations of the O3-I with markers of heart failure severity, clinical characteristics, biomarkers, and mortality were analyzed.

RESULTS

The mean O3-I was 3.7 ± 1.0%. Patient mean age was 68 ± 12 years (72% male, 43% in New York Heart Association (NYHA) class III or IV, mean LVEF 30 ± 8%). During follow-up 258 patients (28.7%) died. After adjustment for potential confounders, the O3-I showed weak associations with uncured malignancy, end-systolic diameter of the left atrium, left ventricular end-diastolic and end-systolic diameters, and blood lipids and other laboratory parameters (all p < 0.05), but not with NYHA class, left ventricular ejection fraction, and the underlying cause of heart failure. The O3-I did not predict the 3-year mortality risk.

CONCLUSIONS

Our results show a marked depletion of omega-3 fatty acids in patients hospitalized for decompensated heart failure (suggested target range 8-11%). Although the O3-I was associated with a panel of established risk indicators in heart failure, it did not predict mortality risk.

CLINICAL TRIAL REGISTRATION

www.controlled-trials.com; ISRCTN23325295.

Lipid Mediators in Inflammation

Lipids are potent signaling molecules that regulate a multitude of cellular responses, including cell growth and death and inflammation/infection, via receptor-mediated pathways. Derived from polyunsaturated fatty acids (PUFAs), such as arachidonic acid (AA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), each lipid displays unique properties, thus making their role in inflammation distinct from that of other lipids derived from the same PUFA. This diversity arises from their synthesis, which occurs via discrete enzymatic pathways and because they elicit responses via different receptors. This review will collate the bioactive lipid research to date and summarize the major pathways involved in their biosynthesis and role in inflammation. Specifically, lipids derived from AA (prostanoids, leukotrienes, 5-oxo-6,8,11,14-eicosatetraenoic acid, lipoxins, and epoxyeicosatrienoic acids), EPA (E-series resolvins), and DHA (D-series resolvins, protectins, and maresins) will be discussed herein.

NLRP3 inflammasome as a novel target for docosahexaenoic acid metabolites to abrogate glomerular injury

The nucleotide-binding oligomerization domain-like receptor containing pyrin domain 3 (NLRP3) inflammasome has been implicated in podocyte injury and glomerular sclerosis during hyperhomocysteinemia (hHcys). However, it remains unclear whether the NLRP3 inflammasome can be a therapeutic target for treatment of hHcys-induced kidney injury. Given that DHA metabolites-resolvins have potent anti-inflammatory effects, the present study tested whether the prototype, resolvin D1 (RvD1), and 17S-hydroxy DHA (17S-HDHA), an intermediate product, abrogate hHcys-induced podocyte injury by targeting the NLRP3 inflammasome. In vitro, confocal microscopy demonstrated that 17S-HDHA (100 nM) and RvD1 (60 nM) prevented Hcys-induced formation of NLRP3 inflammasomes, as shown by reduced colocalization of NLRP3 with apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC) or caspase-1. Both DHA metabolites inhibited Hcys-induced caspase-1 activation and interleukin-1β production. However, DHA had no significant effect on these Hcys-induced changes in podocytes. In vivo, DHA lipoxygenase metabolites substantially inhibited podocyte NLRP3 inflammasome formation and activation and consequent glomerular sclerosis in mice with hHcys. Mechanistically, RvD1 and 17S-HDHA were shown to suppress Hcys-induced formation of lipid raft redox signaling platforms and subsequent O₂^·- production in podocytes. It is concluded that inhibition of NLRP3 inflammasome activation is one of the important mechanisms mediating the beneficial action of RvD1 and 17S-HDHA on Hcys-induced podocyte injury and glomerular sclerosis.

Omega-3 Polyunsaturated Fatty Acids Attenuate Fibroblast Activation and Kidney Fibrosis Involving MTORC2 Signaling Suppression

Epidemiologic studies showed the correlation between the deficiency of omega-3 polyunsaturated fatty acids (n-3 PUFAs) and the progression of chronic kidney diseases (CKD), however, the role and mechanisms for n-3 PUFAs in protecting against kidney fibrosis remain obscure. In this study, NRK-49F cells, a rat kidney interstitial fibroblast cell line, were stimulated with TGFβ1. A Caenorhabditis elegans fat-1 transgenic mouse model in which n-3 PUFAs are endogenously produced from n-6 PUFAs owing to the expression of n-3 fatty acid desaturase were deployed. Docosahexaenoic acid (DHA), one member of n-3 PUFAs family, could suppress TGFβ1-induced fibroblast activation at a dose and time dependent manner. Additionally, DHA could largely inhibit TGFβ1-stimulated Akt but not S6 or Smad3 phosphorylation at a time dependent manner. To decipher the role for n-3 PUFAs in protecting against kidney fibrosis, fat-1 transgenic mice were operated with unilateral ureter obstruction (UUO). Compared to the wild types, fat-1 transgenics developed much less kidney fibrosis and inflammatory cell accumulation accompanied by less p-Akt (Ser473), p-Akt (Thr308), p-S6 and p-Smad3 in kidney tissues at day 7 after UUO. Thus, n-3 PUFAs can attenuate fibroblast activation and kidney fibrosis, which may be associated with the inhibition of mTORC2 signaling.

Omega-3 fatty acid supplementation as an adjunctive therapy in the treatment of chronic kidney disease: a meta-analysis

The aim of this study was to evaluate the benefits and risks of omega-3 fatty acid supplementation in patients with chronic kidney disease. A systematic search of articles in PubMed, Embase, the Cochrane Library, and reference lists was performed to find relevant literature. All eligible studies assessed proteinuria, the serum creatinine clearance rate, the estimated glomerular filtration rate, or the occurrence of end-stage renal disease. Standard mean differences with 95% confidence intervals for continuous data were used to estimate the effects of omega-3 fatty acid supplementation on renal function, as reflected by the serum creatinine clearance rate, proteinuria, the estimated glomerular filtration rate, and relative risk. Additionally, a random-effects model was used to estimate the effect of omega-3 fatty acid supplementation on the risk of end-stage renal disease. Nine randomized controlled trials evaluating 444 patients with chronic kidney disease were included in the study. The follow-up duration ranged from 2 to 76.8 months. Compared with no or low-dose omega-3 fatty acid supplementation, any or high-dose omega-3 fatty acid supplementation, respectively, was associated with a lower risk of proteinuria (SMD: -0.31; 95% CI: -0.53 to -0.10; p=0.004) but had little or no effect on the serum creatinine clearance rate (SMD: 0.22; 95% CI: -0.40 to 0.84; p=0.482) or the estimated glomerular filtration rate (SMD: 0.14; 95% CI: -0.13 to 0.42; p=0.296). However, this supplementation was associated with a reduced risk of end-stage renal disease (RR: 0.49; 95% CI: 0.24 to 0.99; p=0.047). In sum, omega-3 fatty acid supplementation is associated with a significantly reduced risk of end-stage renal disease and delays the progression of this disease.

Effects of v-3 essential fatty acids against formaldehyde-induced nephropathy in rats

The aim of this study was to examine the toxicity of formaldehyde (FA) on the kidney and the protective effects of v-3 essential fatty acids against these toxic effects. Twenty-one male Wistar rats were divided into three groups. Rats in Group I comprised the controls, while the rats in Group II were injected every other day with FA. Rats in Group III received v-3 fatty acids daily while exposed to FA. At the end of the 14-day experimental period, all rats were killed by decapitation and the kidneys removed. Some of the kidney tissue specimens were used for determination of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) activities, and malondialdehyde (MDA) levels. The remaining kidney tissue specimens were used for light microscopic evaluation. The levels of SOD and GSH-Px were significantly decreased, and MDA levels were significantly increased in rats treated with FA compared with those of the controls. Furthermore, in the microscopic examination of this group, glomerular and tubular degeneration, vascular congestion and tubular dilatation were observed. However, increased SOD and GSH-Px enzyme activities, and decreased MDA levels were detected in the rats administered v-3 fatty acids while exposed to FA. Additionally, kidney damage caused by FA was decreased and structural appearance was similar to that of the control rats in this group. In conclusion, it was determined that FA-induced kidney damage was prevented by administration of v-3 essential fatty acids.

Effect of ω-3 polyunsaturated fatty acids on the growth of IEC-6 cells injured by heavy metals

Environmental pollution is a current area of focus worldwide, particularly heavy metal pollution. Feasible prevention or therapeutic strategies are required. Exploration of the correlation between ω-3 polyunsaturated fatty acids (ω-3 PUFAs) and intestinal epithelial cells injured by heavy metals may be of significance for intestinal health. In the present study, the effects of ω-3 PUFAs on the rat intestinal crypt cell line (IEC-6) injured by heavy metals and its mechanisms were determined according to the evaluation of cell viability and expression levels of reactive oxygen species (ROS), epidermal growth factor (EGF) and interleukin-6 (IL-6). The results demonstrated that ω-3 PUFAs can improve the viability of IEC-6 cells injured by heavy metals and the expression level of ROS was correlated with oxidative damage; the increased expression level of inflammatory factors is associated with cell apoptosis. In the present study, ω-3 PUFAs significantly decreased the expression levels of ROS, EGF and IL-6. This indicates that the protective action of ω-3 PUFAs was associated with a decrease of oxidative damage and pro-inflammatory cytokine expression against the damage of heavy metals.

Long-chain polyunsaturated fatty acid sources and evaluation of their nutritional and functional properties

Recent studies have clearly shown the importance of polyunsaturated fatty acids (as essential fatty acids) and their nutritional value for human health. In this review, various sources, nutritional properties, and metabolism routes of long-chain polyunsaturated fatty acids (LC-PUFA) are introduced. Since the conversion efficiency of linoleic acid (LA) to arachidonic acid (AA) and also α-linolenic acid (ALA) to docosahexaenoic acid (DHA) and eicosatetraenoic acid (EPA) is low in humans, looking for the numerous sources of AA, EPA and EPA fatty acids. The sources include aquatic (fish, crustaceans, and mollusks), animal sources (meat, egg, and milk), plant sources including 20 plants, most of which were weeds having a good amount of LC-PUFA, fruits, herbs, and seeds; cyanobacteria; and microorganisms (bacteria, fungi, microalgae, and diatoms).

Endogenous synthesis of n-3 PUFA modifies fatty acid composition of kidney phospholipids and eicosanoid levels in the fat-1 mouse

The goal of the present study was to determine whether endogenous synthesis of n-3 polyunsaturated fatty acids (PUFA) in the fat-1 mouse is comparable to fish oil feeding with respect to kidney n-3 PUFA composition and eicosanoid levels. Wild-type and heterozygous fat-1 mice, capable of synthesizing n-3 PUFA endogenously, were given diets enriched in either n-3 or n-6 PUFA in a 2×2 factorial design and terminated after 12 weeks. Kidney phospholipid fatty acids were analysed by gas chromatography. Kidney eicosanoids were analysed by liquid chromatography tandem mass spectrometry. Relative to control mice fed n-6 PUFA, n-3 PUFA fed and fat-1 mice had higher levels of kidney phospholipid n-3 PUFA, and lower levels of n-6 PUFA and eicosanoids. However, mice fed n-3 PUFA mice had higher levels of n-3 PUFA and lower levels of eicosanoids as compared to fat-1 mice. In conclusion, diet feeding had a greater impact on kidney fatty acid composition and eicosanoid levels than the genetic effect of the fat-1 gene. However, the fat-1 mouse remains a close approximation that can be used as a complementary model to study the role of n-3 PUFA in the kidney.

Emerging importance of omega-3 fatty acids in the innate immune response: molecular mechanisms and lipidomic strategies for their analysis

The beneficial health properties of dietary omega-3 polyunsaturated fatty acids, particularly eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) have long been known and their metabolic dysfunction has been linked to a range of diseases including various inflammatory disorders, cardiovascular diseases, and cancer. However, the molecular mechanisms underlying their health benefits have remained unclear. Recent technological advances in lipidomic analytical strategies have resulted in the discovery of a range of bioactive mediators derived from EPA and DHA that possess potent anti-inflammatory and pro-resolving properties and that may be responsible, at least in part, for the beneficial effects observed. These mediators include resolvins, protectins and maresins, as well as EPA derivatives of classical arachidonic acid derived eicosanoids, such as prostaglandin E3 . The aim of this review is to provide an overview of the biosynthetic pathways and biological properties of these omega-3 mediators, with a particular focus on the emerging importance of the counter-regulatory role of omega-3 and -6 fatty acids in the spatial and temporal regulation of the inflammatory response. It will also provide an insight into a range of lipidomic approaches, which are currently available to analyse these fatty acids and their metabolites in biological matrices.

Plasma phospholipid fatty acid and ex vivo neutrophil responses are differentially altered in dogs fed fish- and linseed-oil containing diets at the same n-6:n-3 fatty acid ratio

The effect of diets containing either 18-carbon n-3 fatty acids (FA) or 20/22-carbon n-3 FA on canine plasma and neutrophil membrane fatty acid composition, superoxide and leukotriene B₄ and B₅ production when fed at the same n-6:n-3 fatty acid ratio was investigated. Four groups of ten dogs each were fed a low fat basal diet supplemented with safflower oil (SFO), beef tallow (BTO), linseed oil (LSO), or Menhaden fish oil (MHO) for 28 days. Dietary fat provided 40.8% of energy and the n-6:n-3 of the diets were ~100:1, 9.7:1, 0.38:1, and 0.34:1 for the SFO, BTO, LSO and MHO groups, respectively. The MHO and LSO groups had increased incorporation of EPA and DPA in both the plasma and neutrophil membranes compared to the BTO and SFO groups. DHA was observed in the MHO but not in the LSO group. Neutrophils from the MHO diet fed dogs had less LTB₄ and greater LTB₅ than the other three groups. The LSO group also showed a reduction in LTB₄ and greater LTB₅ production compared to the SFO and BTO groups. Both LSO and MHO groups had lower superoxide production compared to the SFO and BTO groups. Diets containing 18 or 20/22 carbon n-3 FA fed at the same n-6:n-3 resulted in differential incorporation of long chain n-3 FA into neutrophil membranes. Thus, fatty acid type and chain length individually affect neutrophil membrane structure and function and these effects exist independent of dietary total n-6:total n-3 FA ratios.

Consumption of long-chain n-3 PUFA, α-linolenic acid and fish is associated with the prevalence of chronic kidney disease

Due to the anti-inflammatory properties of PUFA, it has been suggested that they may protect against kidney damage in adults. However, relatively few epidemiological studies have examined this hypothesis in human subjects. We investigated the association between dietary intakes of PUFA (n-3, n-6 and α-linolenic acid), fish and the prevalence of chronic kidney disease (CKD). A total of 2600 Blue Mountains Eye Study (1997-9) participants aged ≥ 50 years were analysed. Dietary data were collected using a semi-quantitative FFQ, and PUFA and fish intakes were calculated. Baseline biochemistry including serum creatinine was measured. Moderate CKD was defined as an estimated glomerular filtration rate of < 60 ml/min per 1·73 m2. Participants in the highest quartile of long-chain n-3 PUFA intake had a significantly reduced likelihood of having CKD compared with those in the lowest quartile of intake (multivariable-adjusted OR 0·69, 95 % CI 0·49, 0·99). α-Linolenic acid intake was positively associated with CKD (OR, per standard deviation increase in α-linolenic acid, 1·18, 95 % CI 1·05, 1·32). Total n-3 PUFA or total n-6 PUFA were not significantly associated with CKD. The highest compared with the lowest quartile of fish consumption was associated with a reduced likelihood of CKD (OR 0·68, 95 % CI 0·48, 0·97; P for trend = 0·02). The present study shows that an increased dietary intake of long-chain n-3 PUFA and fish reduces the prevalence of CKD. Hence, a diet rich in n-3 PUFA and fish could have a role in maintaining healthy kidney function, in addition to roles of these nutrients in the prevention and modulation of other diseases.

Old and new generation lipid mediators in acute inflammation and resolution

Originally regarded as just membrane constituents and energy storing molecules, lipids are now recognised as potent signalling molecules that regulate a multitude of cellular responses via receptor-mediated pathways, including cell growth and death, and inflammation/infection. Derived from polyunsaturated fatty acids (PUFAs), such as arachidonic acid (AA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), each lipid displays unique properties, thus making their role in inflammation distinct from that of other lipids derived from the same PUFA. The diversity of their actions arises because such metabolites are synthesised via discrete enzymatic pathways and because they elicit their response via different receptors. This review will collate the bioactive lipid research to date and summarise the findings in terms of the major pathways involved in their biosynthesis and their role in inflammation and its resolution. It will include lipids derived from AA (prostanoids, leukotrienes, 5-oxo-6,8,11,14-eicosatetraenoic acid, lipoxins and epoxyeicosatrienoic acids), EPA (E-series resolvins), and DHA (D-series resolvins, protectins and maresins).

Omega-3 polyunsaturated fatty acids in the treatment of kidney disease

After more than 25 years of published investigation, including randomized controlled trials, the role of omega-3 polyunsaturated fatty acids in the treatment of kidney disease remains unclear. In vitro and in vivo experimental studies support the efficacy of omega-3 polyunsaturated fatty acids on inflammatory pathways involved with the progression of kidney disease. Clinical investigations have focused predominantly on immunoglobulin A (IgA) nephropathy. More recently, lupus nephritis, polycystic kidney disease, and other glomerular diseases have been investigated. Clinical trials have shown conflicting results for the efficacy of omega-3 polyunsaturated fatty acids in IgA nephropathy, which may relate to varying doses, proportions of eicosapentaenoic acid and docosahexaenoic acid, duration of therapy, and sample size of the study populations. Meta-analyses of clinical trials using omega-3 polyunsaturated fatty acids in IgA nephropathy have been limited by the quality of available studies. However, guidelines suggest that omega-3 polyunsaturated fatty acids should be considered in progressive IgA nephropathy. Omega-3 polyunsaturated fatty acids decrease blood pressure, a known accelerant of kidney disease progression. Well-designed, adequately powered, randomized, controlled clinical trials are required to further investigate the potential benefits of omega-3 polyunsaturated fatty acids on the progression of kidney disease and patient survival.

Evaluation of phosphorus, protein, and n-3 fatty-acid content in 15 marine fish species identifies the species most beneficial to renal patients

OBJECTIVE

Among 15 marine fish species, we sought to identify those most beneficial to renal patients by evaluating their phosphorus (P), protein (PC), and n-3 fatty-acid (n-3 PUFA) content.

DESIGN

These 15 species are all edible. They were obtained and sampled randomly, and were filleted to obtain 100g, enabling us to perform the analysis in triplicate. Crude protein was analyzed with a Kjeltec, and minerals were analyzed using atomic absorption spectrophotometry.

RESULTS

The PC values (g/100g) ranged from 14.3 (blue runner; BR) to 22.8 (California butterfly ray). The fish with the highest P (mg/100g) content were spotted sea trout (ST), gafftopsail fish (CF) (289), and BR (274), followed by smalltail shark (272). The species with the lowest ratio of P:n-3 PUFA was dollar fish (DF) (0.28), followed by BR, ST, and vermilion snapper (range, 0.28 to 0.67). The highest ratio of P:n-3 PUFA was found in the small-tail shark (11.6). Fish with a high n-3 PUFA/g PC content were DF (41.7), BR (38.05), ST (34.8), and CF (22.5). There was a tendency of P to increase as muscle fat increased (mg P/100g), i.e., lean fish (194), semifatty fish (239), and fatty fish (262).

CONCLUSIONS

The regular inclusion in the diet, at least three times a week, of the species DF, BR, CF, ST, caitipa mojarra, vermillion snapper, and pot snapper can be considered beneficial to the general health status of renal patients.

Modulation of lipid rafts by Omega-3 fatty acids in inflammation and cancer: implications for use of lipids during nutrition support

Current understanding of biologic membrane structure and function is largely based on the concept of lipid rafts. Lipid rafts are composed primarily of tightly packed, liquid-ordered sphingolipids/cholesterol/saturated phospholipids that float in a sea of more unsaturated and loosely packed, liquid-disordered lipids. Lipid rafts have important clinical implications because many important membrane-signaling proteins are located within the raft regions of the membrane, and alterations in raft structure can alter activity of these signaling proteins. Because rafts are lipid-based, their composition, structure, and function are susceptible to manipulation by dietary components such as omega-3 polyunsaturated fatty acids and by cholesterol depletion. We review how alteration of raft lipids affects the raft/nonraft localization and hence the function of several proteins involved in cell signaling. We focus our discussion of raft-signaling proteins on inflammation and cancer.

Treatment of severe IgA nephropathy with omega-3 fatty acids: the effect of a "very low dose" regimen

BACKGROUND

The effect of a "very low dose" of purified omega-3 fatty acids (PFA) in the progression of severe IgA nephropathy (IgAN) was tested, in a randomized, prospective, controlled trial.

METHODS

Fourteen patients were assigned to receive a "very low dose" of PFA (0.85 g EPA and 0.57 g PHA) and 14 patients were treated symptomatically and used as controls. Both groups were similar in terms of serum creatinine (Scr) and glomerular filtration rate (GFR) at baseline. Patients were treated for 4 years. The primary end-points were an increase of 50% or more in Scr or a decrease of 50% or more in GFR at the end of the study.

RESULTS

During treatment, 1 patient (7%) in the PFA group and 6 (43%) in the control group had an increase of 50% or more in their Scr (p<0.01). Also, 1 patient (7%) in the PFA group and 7 (50%) in the control group had a decrease of 50% or more in GFR (p<0.007). The mean annual change in Scr was 0.2 mg/dL in the PFA group and 1.0 mg/dL in the control group (p<0.01). The mean annual change in GFR was -1.4 mL/min in the PFA group and -3.0 mL/min in the control group (p <0.001). One patient in the PFA group (7%) and 6 patients in the control group (43%) (p<0.01) developed end-stage renal disease during the period of observation.

CONCLUSIONS

A "very low dose" of PFA is also effective in slowing renal progression in high-risk patients with IgAN and particularly those with advanced renal disease.

EPA and DHA reduce LPS-induced inflammation responses in HK-2 cells: Evidence for a PPAR-γ–dependent mechanism

BACKGROUND

Recent studies have shown that fish oil, containing omega-3 polyunsaturated fatty acids (omega-3 PUFAs) eicosapentaenoic acid (EPA) (C20:5 omega 3), and docosahexaenoic acid (DHA) (C22:6 omega 3) retard the progression of renal disease, especially in IgA nephropathy (IgAN). Despite increasing knowledge of the beneficial effects of fish oils, little is known about the mechanisms of action of omega-3 PUFAs. It has been reported that activation of peroxisome proliferator-activated receptors (PPARs) inhibits production of proinflammatory cytokines. Both EPA and DHA have been shown to activate PPARs. The aim of this study was to examine if omega-3 PUFAs have anti-inflammatory effects via activation of PPARs in human renal tubular cells.

METHODS

An immortalized human proximal tubular cell line [human kidney-2 (HK-2) cells] was used in all experiments. Conditioned media was collected from omega-3 PUFAs- treated cells and subjected to enzyme-linked immunosorbent assay (ELISA). Total cellular RNA was isolated from the above cells for real-time quantitative polymerase chain reaction (PCR). Nuclear Extracts were prepared from the HK-2 cells for transcription factor activation assay.

RESULTS

Both EPA and DHA at 10 micromol/L and 100 micromol/L concentrations effectively decreased lipopolysaccharide (LPS)-induced nuclear factor-kappaB (NF-kappaB) activation and monocyte chemoattractant protein-1 (MCP-1) expression. EPA and DHA also increased both PPAR-gamma mRNA and protein activity (two- to threefold) in HK-2 cells. A dose of 100 micromol/L bisphenol A diglycidyl ether (BADGE) abolished the PPAR-gamma activation induced by both EPA and DHA and removed the inhibitory effect of EPA and DHA on LPS-induced NF-kappaB activation in HK-2 cells. Overexpression of PPAR-gamma further inhibited NF-kappaB activation compared to the control cells in the presence of EPA and DHA.

CONCLUSION

Our data demonstrate that both EPA and DHA down-regulate LPS-induced activation of NF-kappaB via a PPAR-gamma-dependent pathway in HK-2 cells. These results suggest that PPAR-gamma activation by EPA and DHA may be one of the underlying mechanisms for the beneficial effects of fish oil.

The role of fish oil/omega-3 fatty acids in the treatment of IgA nephropathy

Beneficial effects of omega-3 polyunsaturated fatty acids (n-3 PUFA) have been reported in recent epidemiologic studies and randomized clinical trials in a variety of cardiovascular and autoimmune diseases. Fish and marine oils are the most abundant and convenient sources of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), the two major n-3 fatty acids that serve as substrates for cyclooxygenase and lipoxygenase pathways leading to less potent inflammatory mediators than those produced through the n-6 PUFA substrate, arachidonic acid. N-3 PUFA can also suppress inflammatory and/or immunologic responses through eicosanoid-independent mechanisms. Although the pathophysiology of IgA nephropathy is incompletely understood, it is likely that n-3 PUFA prevents renal disease progression by interfering with a number of effector pathways triggered by mesangial immune-complex deposition. In addition, potential targets of n-3 PUFA relevant to renal disease progression could be similar to those involved in preventing the development and progression of cardiovascular disease by lowering blood pressure, reducing serum lipid levels, decreasing vascular resistance, or preventing thrombosis. In IgA nephropathy, efficacy of n-3 PUFA contained in fish oil supplements has been tested with varying results. The largest randomized clinical trial performed by our collaborative group provided strong evidence that treatment for 2 years with a daily dose of 1.8 g of EPA and 1.2 g of DHA slowed the progression of renal disease in high-risk patients. These benefits persisted after 6.4 years of follow up. With safety, composition, and dosing convenience in mind, we can recommend two products that are available as pharmaceutical-grade fish-oil concentrates, Omacor (Pronova Biocare, Oslo, Norway) and Coromega (European Reference Botanical Laboratories, Carlsbad, CA).

Docosahexaenoic acid: membrane properties of a unique fatty acid

Docosahexaenoic acid (DHA) with 22-carbons and 6 double bonds is the extreme example of an omega-3 polyunsaturated fatty acid (PUFA). DHA has strong medical implications since its dietary presence has been positively linked to the prevention of numerous human afflictions including cancer and heart disease. The PUFA, moreover, is essential to neurological function. It is remarkable that one simple molecule has been reported to affect so many seemingly unrelated biological processes. Although details of a molecular mode of action remain elusive, DHA must be acting at a fundamental level common to many tissues that is related to the high degree of conformational flexibility that the multiple double bonds have been identified to confer. One likely target for DHA action is at the cell membrane where the fatty acid is known to readily incorporate into membrane phospholipids. Once esterified into phospholipids DHA has been demonstrated to significantly alter many basic properties of membranes including acyl chain order and "fluidity", phase behavior, elastic compressibility, permeability, fusion, flip-flop and protein activity. It is concluded that DHA's interaction with other membrane lipids, particularly cholesterol, may play a prominent role in modulating the local structure and function of cell membranes.

Higher intakes of fish protein are related to a lower risk of microalbuminuria in young Swedish type 1 diabetic patients

OBJECTIVE

To examine the influence of dietary intake from various protein and fat sources on the occurrence of microalbuminuria in type 1 diabetic patients.

RESEARCH DESIGN AND METHODS

In this nested case control study, 1,150 patients with diabetes duration >5 years reported dietary habits for the previous 12 months and submitted urinary samples for the analysis of albumin excretion rate (AER). A total of 75 cases of albuminuria (overnight AER > or = 15 microg/min) were identified and compared with 225 duration-matched control subjects.

RESULTS

Neither mean protein, fat intake, average fish protein intake (control subjects 4.56 +/- 3.83 g/day and cases 3.82 +/- 2.87 g/day; P = 0.12), nor intake of meat and vegetable protein differed between the cases of albuminuria and the control subjects. High consumers of fish protein (greater than the 75th percentile) (12 cases and 63 control subjects, mean intake 9.35 g fish protein/day, i.e., approximately 53 g fish/day) had lower odds ratios (ORs) for microalbuminuria than individuals consuming less fish protein (mean 2.72 g/day) (crude OR 0.49 and 95% CI 0.25-0.97). When adjusted for known confounding factors, such as HbA1c, mean arterial pressure, diabetes duration, age, sex, smoking, BMI, country region, and total energy, individuals with a high intake of fish protein and fish fat showed a reduction in the risk for microalbuminuria (OR 0.22 and 0.31, respectively; 95% CI 0.09-0.56 and 0.13-0.76, respectively). When fish protein and fat were adjusted for each other, a high intake of fish protein but not of fish fat was still significantly associated with a decrease in the risk for microalbuminuria.

CONCLUSIONS

Total protein and fat intake were not associated with the presence of microalbuminuria, but a diet including a high amount of fish protein seemed to lessen the risk.

Omega-3 polyunsaturated fatty acids in adolescents: knowledge and consumption

OBJECTIVE

To assess adolescents' knowledge about n-3 polyunsaturated fatty acids (PUFA) and their dietary intake of these important nutrients.

METHODS

A questionnaire consisting of 12 questions assessing the knowledge and intake of n-3 PUFA and of a 24-h dietary recall was administered to 1117 ninth-grade adolescents (52% girls and 48% boys) attending five public schools. The adolescents were subsequently provided with verbal and written information on the health benefits, requirements, and dietary sources of n-3 PUFA. Dietary recalls were analyzed for energy and n-3 PUFA intake. Descriptive statistics, Student's t-tests, Chi-square analysis, and multiple regression analysis were used to assess adolescents' knowledge about n-3 PUFA as well as to examine relationships of independent variables with n-3 PUFA intake.

RESULTS

Most adolescents (89%) believed that eating fish, a main source of very long chain (VLC) n-3 PUFA, is healthy and may prevent heart disease (59%), but only a few knew about n-3 PUFA's role in alleviating inflammation (29%) and its potential for cancer prevention (25%). Many were aware of marine sources of n-3 PUFA, such as salmon (67%), tuna (46%), mackerel (30%), and herring (26%), but only 36% knew about adequate intake of VLC n-3 PUFA. The main source of n-3 PUFA information was parents (58%), whereas only 21% of adolescents reported that their care providers had discussed health benefits of n-3 PUFA with them. About one-third of adolescents consumed fish at least once a week, and 29% consumed fish once a month. Dislike (22% of participants) and allergy (3%) were the main reasons for rarely (< or = 3 times/year; 18%) or never (17%) consuming fish. Only one adolescent reported daily consumption of a fish concentrate supplement. Daily consumption of linolenic acid was higher in boys (0.38 +/- 0.02 g) than in girls (0.31 +/- 0.01 g; p =.002). Total intake of n-3 PUFA represented only 30% of the presently available (Canadian) recommended daily allowance (CRDA) for 14- to 15-year-old boys (1.4 g/day) and 29% of the CRDA for 14- to 15-year-old girls (1.2 g/day).

CONCLUSIONS

Adolescents are aware of some of the health benefits of n-3 PUFA but lack concrete information about dietary requirements of n-3 PUFA and about n-3 PUFA content of various dietary sources.

Human requirement for N-3 polyunsaturated fatty acids

The diet of our ancestors was less dense in calories, being higher in fiber, rich in fruits, vegetables, lean meat, and fish. As a result, the diet was lower in total fat and saturated fat, but contained equal amounts of n-6 and n-3 essential fatty acids. Linoleic acid (LA) is the major n-6 fatty acid, and alpha-linolenic acid (ALA) is the major n-3 fatty acid. In the body, LA is metabolized to arachidonic acid (AA), and ALA is metabolized to eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). The ratio of n-6 to n-3 essential fatty acids was 1 to 2:1 with higher levels of the longer-chain polyunsaturated fatty acids (PUFA), such as EPA, DHA, and AA, than today's diet. Today this ratio is about 10 to 1:20 to 25 to 1, indicating that Western diets are deficient in n-3 fatty acids compared with the diet on which humans evolved and their genetic patterns were established. The n-3 and n-6 EPA are not interconvertible in the human body and are important components of practically all cell membranes. The N-6 and n-3 fatty acids influence eicosanoid metabolism, gene expression, and intercellular cell-to-cell communication. The PUFA composition of cell membranes is, to a great extent, dependent on dietary intake. Therefore, appropriate amounts of dietary n-6 and n-3 fatty acids need to be considered in making dietary recommendations. These two classes of PUFA should be distinguished because they are metabolically and functionally distinct and have opposing physiological functions; their balance is important for homeostasis and normal development. Studies with nonhuman primates and human newborns indicate that DHA is essential for the normal functional development of the retina and brain, particularly in premature infants. A balanced n-6/n-3 ratio in the diet is essential for normal growth and development and should lead to decreases in cardiovascular disease and other chronic diseases and improve mental health. Although a recommended dietary allowance for essential fatty acids does not exist, an adequate intake (AI) has been estimated for n-6 and n-3 essential fatty acids by an international scientific working group. For Western societies, it will be necessary to decrease the intake of n-6 fatty acids and increase the intake of n-3 fatty acids. The food industry is already taking steps to return n-3 essential fatty acids to the food supply by enriching various foods with n-3 fatty acids. To obtain the recommended AI, it will be necessary to consider the issues involved in enriching the food supply with n-3 PUFA in terms of dosage, safety, and sources of n-3 fatty acids.

Suppressive effects of fish oil on mesangial cell proliferation in vitro and in vivo

BACKGROUND

Mesangial cell proliferation is a characteristic feature of IgA nephropathy and many other forms of glomerulonephritis. Recent clinical studies have shown that dietary fish oil supplementation retards renal disease progression in patients with IgA nephropathy. The mechanism by which this effect occurs is unknown.

METHODS

The anti-Thy 1.1 (ATS) model of mesangial proliferative glomerulonephritis was employed to test the hypothesis that dietary fish oil supplementation reduces mesangial cell proliferation following acute injury. Subcultured rat mesangial cells were used to determine the in vitro effects of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), the primary components of fish oil, on proliferation.

RESULTS

Following antithymocyte serum (ATS) administration, proteinuria was significantly decreased in animals treated with fish oil compared with sesame oil-treated controls. In ATS rats given fish oil, there was less mesangial cell and matrix expansion, mesangiolysis, or basement membrane disruption (delta% = -40%). ATS rats receiving fish oil had less glomerular cell proliferation (PCNA-delta% = -50%) and a reduction of alpha-smooth muscle actin expression (delta% = -27%) by mesangial cells. In subcultured rat mesangial cells, DHA, but not EPA, significantly inhibited proliferation.

CONCLUSIONS

Fish oil inhibits mesangial cell activation and proliferation in ATS glomerulonephritis, reduces proteinuria, and decreases histologic evidence of glomerular damage. In vitro, the antiproliferative effects of fish oil are more likely related to the action of DHA. We suggest that orally administered fish oil, or purified DHA, may have a suppressive effect in acute phases or relapses of glomerulopathies by inhibiting activation and proliferation of mesangial cells.

Serum lipid concentrations and mean life span are modulated by dietary polyunsaturated fatty acids in the senescence-accelerated mouse

The senescence-accelerated mouse (SAMP8) is an animal model used in studies of aging. This study was undertaken to investigate the effects of dietary PUFA on longevity (Experiment 1) and serum lipid concentrations (Experiment 2) in SAMP8 mice. Male mice were fed either an (n-3) PUFA-rich (9 g/100 g perilla oil) or an (n-6) PUFA-rich (9 g/100 g safflower oil) diet beginning at 6 wk of age. Experiment 1: The groups did not differ in body weight gain, but those fed perilla oil had significantly lower scores of senescence relative to those fed safflower oil (P<0.05). The mean life span of mice fed perilla oil was 357+/-21 d and of those fed safflower oil, 426+/-24 d (P<0.05). Pathological studies revealed that the incidence of tumors was significantly lower in the perilla oil group than in the safflower oil group (P<0.05). Approximately half the mice fed perilla oil had died after 10 mo, and the direct causes closely connected with death could not be specified. Experiment 2: The serum total cholesterol, HDL cholesterol, triglyceride and phospholipid concentrations were significantly lower in the perilla oil group than in the safflower oil group (P<0.01). A marked decrease of serum HDL cholesterol and apolipoprotein A-II (ApoA-II)concentrations in advanced age were observed in the mice fed perilla oil (P<0.01). Ten-month-old mice fed perilla oil had a significantly greater ratio of apolipoprotein A-I (ApoA-I) to ApoA-II than those fed safflower oil. Separation of HDL subfractions revealed that the smaller HDL species were much more abundant than the larger HDL species in both dietary oil groups. These findings suggest that dietary (n-3) and (n-6) PUFA differ in their effects on serum lipid metabolism which may modulate the mean life span of SAMP8 mice fed each dietary oil.

Essential fatty acids in health and chronic disease

Human beings evolved consuming a diet that contained about equal amounts of n-3 and n-6 essential fatty acids. Over the past 100-150 y there has been an enormous increase in the consumption of n-6 fatty acids due to the increased intake of vegetable oils from corn, sunflower seeds, safflower seeds, cottonseed, and soybeans. Today, in Western diets, the ratio of n-6 to n-3 fatty acids ranges from approximately 20-30:1 instead of the traditional range of 1-2:1. Studies indicate that a high intake of n-6 fatty acids shifts the physiologic state to one that is prothrombotic and proaggregatory, characterized by increases in blood viscosity, vasospasm, and vasoconstriction and decreases in bleeding time. n-3 Fatty acids, however, have antiinflammatory, antithrombotic, antiarrhythmic, hypolipidemic, and vasodilatory properties. These beneficial effects of n-3 fatty acids have been shown in the secondary prevention of coronary heart disease, hypertension, type 2 diabetes, and, in some patients with renal disease, rheumatoid arthritis, ulcerative colitis, Crohn disease, and chronic obstructive pulmonary disease. Most of the studies were carried out with fish oils [eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)]. However, alpha-linolenic acid, found in green leafy vegetables, flaxseed, rapeseed, and walnuts, desaturates and elongates in the human body to EPA and DHA and by itself may have beneficial effects in health and in the control of chronic diseases.

Gene expression of 5-lipoxygenase and LTA4 hydrolase in renal tissue of nephrotic syndrome patients

Leukotrienes (LT) of the 5-lipoxygenase pathway constitute a class of potent biological lipid mediators of inflammation implicated in the pathogenesis of different models of experimental glomerulonephritis. The key enzyme, 5-lipoxygenase (5-LO), catalyses oxygenation of arachidonic acid to generate the primary leukotriene LTA4. This LT, in turn, serves as a substrate for either LTA4 hydrolase, to form the potent chemoattractant LTB4, or LTC4 synthase, to produce the powerful vasoconstrictor LTC4. To investigate the potential role of LT in the pathogenesis of human glomerulonephritis with nephrotic syndrome, we examined the gene expression of 5-LO and LTA4 hydrolase in renal tissue of 21 adult patients with nephrotic syndrome and 11 controls. The patients consisted of 11 cases of membranous nephropathy (MN), seven focal and segmental glomerulosclerosis (FSGS), two non-IgA mesangial glomerulonephritis and one minimal change disease. Total RNA purified from renal tissue was reverse transcribed into cDNA and amplified with specific primers in a polymerase chain reaction (RT-PCR). Eight patients' renal tissue, four MN and four FSGS, co-expressed 5-LO and LTA4 hydrolase. In situ hybridization analysis revealed 5-LO expression and distribution limited to the interstitial cells surrounding the peritubular capillaries. Comparative clinical and immunohistological data showed that these eight patients had impaired renal function and interstitial changes that significantly correlated with 5-LO expression. These findings suggest that leukotrienes may play an important role in the pathogenesis of MN and FSGS. These results are also relevant to elucidating the pathophysiologic mechanisms which underlie progression to renal failure in these diseases.

Immunonutrition: the role of omega-3 fatty acids

The dietary fatty acids of the omega-3 series are rapidly incorporated into cell membranes and profoundly influence biological responses. These lipids influence membrane stability, membrane fluidity, cell mobility, the formation of receptors, binding of ligands to their receptors, activation of intracellular signaling pathways either directly or through the formation of eicosanoids, gene expression, and cell differentiation. In general, eicosanoids formed from the omega-3 fatty acids are much less potent in causing biological responses than those formed from the omega-6 fatty acids, including stimulation of cytokine production and inflammatory responses. In well-controlled clinical studies, consumption of omega-3 fatty acids has resulted in reduction of cardiovascular diseases including arrhythmias and hypertension, protection from renal disease, improvement in rheumatoid arthritis, improvement in inflammatory bowel diseases, reduced episodes of rejection, and protection from infection. The interactions between the omega-3 fatty acids and pharmacologic drugs that alter intracellular signaling pathways are only now being studied.

Lack of renal effects of fish oil administration in patients with advanced cirrhosis and impaired glomerular filtration

The treatment of renal failure in cirrhotic patients with ascites remains unsatisfactory. Recent studies have shown that the dietary supplementation with fish oil improves the renal function of normal subjects, as well as that of patients with renal failure of different etiologies. We have investigated the renal effects of a daily supplementation for 1 month of 12 g fish oil (27% C20:5 n-3 eicosapentanoic acid [EPA], and 23% C22:6 n-3 docosahexanoic acid [DHA]) in a prospective study of cirrhotic patients with ascites, nine with normal renal function (group 1) and eight with renal failure (glomerular filtration rate [GFR] < 60 mL/min, group 2). Compliance with the dietary regimen was confirmed by fatty acid chromatography that showed increased plasma concentration of EPA (from 1.5 +/- 0.7% to 3.7 +/- 0.8%, P = .024, in group 1; and from 0.53 +/- 0.3% to 2.9 +/- 0.8%, P = .03, in group 2) and of DHA (from 2.1 +/- 0.4% to 3.4 +/- 0.3%, P = .008, in group 1; and from 1.45 +/- 0.5% to 3.8 +/- 0.4%, P = .05, in group 2). At the end of the study, in patients from group 1, the glomerular filtration rate increased by 19% (from 94 +/- 8 to 113 +/- 13 mL/min, P = .039), and the urine flow increased by 39% (from 0.85 +/- 0.14 to 1.12 +/- 0.2 mL/min, P = .039), while no changes occurred in the renal function of patients from group 2. No changes were observed in the urinary excretion of prostaglandin (PG) E2 or of 6-keto prostaglandin-1-alpha (6-K-PGF1-alpha) nor in plasma renin activity (PRA) or the plasma concentration of aldosterone (PA) or antidiuretic hormone (ADH) in both groups. As far as undesirable effects of fish oils were considered, the mean arterial pressure (MAP) decreased in both groups (group 1: from 88.6 +/- 2 to 85.3 +/- 2 mm Hg, P = .015; group 2: from 88.2 +/- 3 to 82.8 +/- 3 mm Hg, P = .05), and bleeding time displayed a significant increase when patients were considered collectively (from 744 +/- 89 to 872 +/- 106 seconds, P = .0068). In conclusion, the administration of fish oil for 1 month was unable to improve renal function in cirrhotic patients with ascites and renal failure. The occurrence of undesirable effects, such as the reduction of arterial pressure and the prolongation of bleeding time, argues against the use of fish oils in these patients.

Pharmacology of immunosuppressive medications used in renal diseases and transplantation

As understanding of the molecular basis for the immune response has expanded rapidly, so have the possibilities for designing therapeutic interventions that are more effective, more specific, and safer than current treatment options. The promise of therapeutic advances in the future is based on the rapidly expanding insights into the pathogenesis of abnormal immunologic reactions. Nowhere is the understanding of molecular mechanisms, pathophysiology, and targeted therapy more relevant than in the field of renal transplantation, which makes up much of the clinical database for the use of immunosuppressive therapy for renal disease. Despite the recent advances in basic immunology, clinical validation of new agents and approaches is lacking for most drugs at present. This review will focus in the pharmacology of agents used in the therapy of immunologic renal disease and in renal transplantation. It should be recognized that clinical pharmacology and experience with newer agents is limited, and potential utility is based largely on experimental data.

n-3 polyunsaturated fatty acids: update 1995

Epidemiologic and biochemical studies have suggested an anti-inflammatory effect of n-3 fatty acids. Beneficial therapeutic effects reported from small patient groups need to be confirmed in large-cohort controlled clinical trials. There is a growing number of clinical trials of n-3 fatty acid supplementation in disease. Clinical benefits have been moderate in patients with rheumatoid arthritis and with arterial hypertension. Clearly negative results have been reported during the past 2 years for patients with lupus nephritis and for patients with psoriasis or with atopic dermatitis. Such trials have now been completed. For patients with coronary artery disease following coronary angioplasty, earlier results of a large meta-analysis, could not be confirmed. For patients with IgA-nephropathy and for patients following kidney transplantation, a clear benefit was seen in patients receiving fish oil. These promising results are currently pursued in follow-up phase III clinical trials.

Lipid-lowering therapy in patients with renal disease

A growing number of clinical trials have examined the effects of different lipid lowering strategies in patients with renal disease. We carried out a meta-analysis to compare and contrast the relative efficacy of various antilipemic therapies in different renal disease settings. Studies that investigated one or more therapies designed to lower serum lipids were combined using weighted multiple linear regression. The analysis adjusted treatment effects for differences in baseline lipid levels and possible placebo effects. The results showed that antilipemic therapies generally had similar effects on lipids in different renal disease settings. In nephrotic syndrome the greatest and most consistent reductions in low density lipoprotein cholesterol (LDL) were seen with 3-hydroxy-3-methylglutaryl co-enzyme A (HMG-CoA) reductase inhibitors (regression coefficient with 95% confidence interval in mg/dl = -63, -79 to -46). Similar results were seen for LDL in renal transplant (-51, -57 to -45), renal insufficiency (-62, -82 to -42), hemodialysis (-65, -80 to -50) and continuous ambulatory peritoneal dialysis (CAPD) patients (-84, -104 to -64). Fibric acid analogues had less effect on LDL, but caused greater reductions in triglycerides: -132, -178 to -87, in nephrotic syndrome; -69, -93 to -45 in transplant: -107, -169 to -45 in renal insufficiency; -72, -120 to -24 in hemodialysis; and -96, -162 to -30 in CAPD. In general, the effects of diet and other therapies were less consistent. Despite possible limitations of this meta-analysis, the results provide a useful framework for choosing antilipemic therapy, and point to areas for future long-term studies examining the safety and efficacy of lipid lowering strategies in patients with renal disease.

A controlled trial of fish oil in IgA nephropathy. Mayo Nephrology Collaborative Group

BACKGROUND

The n-3 fatty acids in fish oil affect eicosanoid and cytokine production and therefore have the potential to alter renal hemodynamics and inflammation. The effects of fish oil could prevent immunologic renal injury in patients with IgA nephropathy.

METHODS

In a multicenter, placebo-controlled, randomized trial we tested the efficacy of fish oil in patients with IgA nephropathy who had persistent proteinuria. The daily dose of fish oil was 12 g; the placebo was a similar dose of olive oil. Serum creatinine concentrations, elevated in 68 percent of the patients at base line, and creatinine clearance were measured for two years. The primary end point was an increase of 50 percent or more in the serum creatinine concentration at the end of the study.

RESULTS

Fifty-five patients were assigned to receive fish oil, and 51 to receive placebo. According to Kaplan-Meier estimation, 3 patients (6 percent) in the fish-oil group and 14 (33 percent) in the placebo group had increases of 50 percent or more in their serum creatinine concentrations during treatment (P = 0.002). The annual median changes in the serum creatinine concentrations were 0.03 mg per deciliter (2.7 mumol per liter) in the fish-oil group and 0.14 mg per deciliter (12.4 mumol per liter) in the placebo group. Proteinuria was slightly reduced and hypertension was controlled to a comparable degree in both groups. The cumulative percentage of patients who died or had end-stage renal disease was 40 percent in the placebo group after four years and 10 percent in the fish-oil group (P = 0.006). No patient discontinued fish-oil treatment because of adverse effects.

CONCLUSIONS

In patients with IgA nephropathy, treatment with fish oil for two years retards the rate at which renal function is lost.

n-3 fatty acids and renal diseases

There are numerous biologic rationales for the use of n-3 fatty acids in renal diseases, including a possible increase in the renal vasodilatory capacity by a rearrangement of renal prostanoid production, a reduction in the production of proinflammatory leukotrienes, a reduction in the transcapillary escape rate of albumin, and actions limiting cyclosporine-related nephrotoxicity. Studies of animal models of renal disease, mostly of immune-renal disease, support the idea of the possible usefulness of these compounds. The most promising areas of clinical investigation include the reduction of proteinuria in some chronic glomerular diseases, the treatment of immunoglobulin A nephropathy, and the prevention of cyclosporine-induced nephrotoxicity. However, the results of larger clinical studies, some of which are ongoing, are necessary to support the use of n-3 fatty acids in human renal diseases.