The influence of n-6 and n-3 fatty acids on kidney phospholipid composition and on eicosanoid production in aging rats

A Difference in Fatty Acid Composition of Isocaloric High-Fat Diets Alters Metabolic Flexibility in Male C57BL/6JOlaHsd Mice

Poly-unsaturated fatty acids (PUFAs) are considered to be healthier than saturated fatty acids (SFAs), but others postulate that especially the ratio of omega-6 to omega-3 PUFAs (n6/n3 ratio) determines health. Health can be determined with biomarkers, but functional health status is likely better reflected by challenge tests that assess metabolic flexibility. The aim of this study was to determine the effect of high-fat diets with different fatty acid compositions, but similar n6/n3 ratio, on metabolic flexibility. Therefore, adult male mice received isocaloric high-fat diets with either predominantly PUFAs (HFpu diet) or predominantly SFAs (HFs diet) but similar n6/n3 ratio for six months, during and after which several biomarkers for health were measured. Metabolic flexibility was assessed by the response to an oral glucose tolerance test, a fasting and re-feeding test and an oxygen restriction test (OxR; normobaric hypoxia). The latter two are non-invasive, indirect calorimetry-based tests that measure the adaptive capacity of the body as a whole. We found that the HFs diet, compared to the HFpu diet, increased mean adipocyte size, liver damage, and ectopic lipid storage in liver and muscle; although, we did not find differences in body weight, total adiposity, adipose tissue health, serum adipokines, whole body energy balance, or circadian rhythm between HFs and HFpu mice. HFs mice were, furthermore, less flexible in their response to both fasting- re-feeding and OxR, while glucose tolerance was indistinguishable. To conclude, the HFs versus the HFpu diet increased ectopic fat storage, liver damage, and mean adipocyte size and reduced metabolic flexibility in male mice. This study underscores the physiological relevance of indirect calorimetry-based challenge tests.

The protective effect of menhaden oil in the oxidative damage and renal necrosis due to dietary choline deficiency

Weanling rats fed a choline-deficient diet develop kidney oxidative damage, tubular and cortical kidney necrosis, renal failure and animal death. The effect of dietary menhaden oil was assayed on the mentioned sequence correlating oxidative stress with renal structure and function. Rats were fed ad libitum 4 different diets: (a) a choline-deficient diet with corn oil and sunflower hydrogenated oil as a source of fatty acids; (b) the same diet supplemented with choline; (c) a choline-deficient diet with menhaden oil as a source of fatty acids; and (d) the previous diet supplemented with choline. Animals were sacrificed at days 0, 2, 4 and 7. The histopathological study of the kidneys showed that renal necrosis was only observed at day 7 in choline-deficient rats receiving the vegetable oil diet, simultaneously with increased creatinine plasma levels. Homogenate chemiluminescence (BOOH-initiated chemiluminescence) and phospholipid oxidation indicate the development of oxidative stress and damage in choline-deficient rats fed vegetable oils as well as the protective effect of menhaden oil. Rats fed with the fish oil diet showed that oxidative stress and damage develop later, as compared with vegetable oil, with no morphological damage during the experimental period.

Effects of polyunsaturated fatty acids (PUFAs) in the treatment of experimental chronic renal failure

PURPOSE

A diet with polyunsaturated fatty acid (PUFA) supplementation has been reported to reduce renal and cardiac diseases. This study sought to elucidate whether PUFAs derived from plant or marine oils could have beneficial effects on the progression of experimental chronic renal failure (CRF).

METHODS

Experimental CRF was achieved by a 5/6 nephrectomy model. Male Wistar rats were divided into groups and given daily supplements of fish oil (group FO), flaxseed oil (group FXO), or soybean oil (control-group SO) for 30 days. Serum creatinine (sCr), 24-h proteinuria, total cholesterol, triglycerides, and creatinine clearance (CLcr) were measured at day 0 and 30 days after surgery when the rats were euthanized for histological analysis of the remnant kidney.

RESULTS

After 30 days, we observed lower levels of sCr in the groups supplemented with PUFA when compared with the control group (FO: 0.92 ± 0.13; FXO: 1.06 ± 0.28; SO: 1.32 ± 0.47 mg/dL) and significantly slower variations of sCr (ΔsCr) in the groups treated with PUFAs (FO = 0.35 ± 0.16; FXO = 0.47 ± 0.31; OS = 0.72 ± 0.43; mg/dL, P = 0.041). Similarly, the CLcr of both of the groups that received PUFAs was significantly slower than the rats in the control group (FO: 0.45 ± 0.15; FXO: 0.60 ± 0.09; SO: 0.28 ± 0.06 mL/min/day; P = 0.01). The rats that received PUFA supplements also presented significantly less histological lesions compared with the control group.

CONCLUSIONS

These results suggest a beneficial effect of dietary supplementation with flaxseed or fish oil in rats with CRF.

Low n-6:n-3 fatty acid ratio, with fish- or flaxseed oil, in a high fat diet improves plasma lipids and beneficially alters tissue fatty acid composition in mice

BACKGROUND

Health benefits from low n-6:n-3 fatty acid (FA) ratio on cardiovascular risk have been shown. However, the impact of the source of n-3 FAs has not been fully investigated.

AIM

Our purpose was to investigate cardiovascular benefits of oils with a low ratio of n-6:n-3 FAs, but different sources of n-3 FAs in C57BL/6 mice.

METHODS

Twenty-one mice were divided into 3 groups (n=7) and fed a diet supplemented with either a fish or flaxseed oil-based 'designer oils' with an approximate n-6:n-3 FA ratio of 2/1 or with a safflower-oil-based diet with a ratio of 25/1, for 16 weeks. Plasma lipids and fatty acid profile of the liver tissue were characterized.

RESULTS

Compared to baseline, plasma triacylglycerol levels declined (>50%) in all groups by week 4. Plasma cholesterol levels were reduced in both fish and flax groups by 27% and 36%, respectively, as compared to controls at endpoint. The levels of EPA and DHA in liver phospholipids were significantly increased in both fish and flax groups as compared to the control group, with more profound increases in the fish group. Arachidonic acid levels were similarly decreased in the liver tissues from both fish and flax groups as compared to controls.

CONCLUSIONS

Our data suggest that health benefits may be achieved by lowering dietary n-6:n-3 FA even in a high fat diet medium.

Effect of chronic fish oil supplementation on renal function of normal and cachectic rats

In the present study we determined the effect of chronic diet supplementation with n-3 PUFA on renal function of healthy and cachectic subjects by providing fish oil (1 g/kg body weight) to female rats throughout pregnancy and lactation and then to their offspring post-weaning and examined its effect on renal function parameters during their adulthood. The animals were divided into four groups of 5-10 rats in each group: control, control supplemented with fish oil (P), cachectic Walker 256 tumor-bearing (W), and W supplemented with fish oil (WP). Food intake was significantly lower in the W group compared to control (12.66 +/- 4.24 vs 25.30 +/- 1.07 g/day). Treatment with fish oil significantly reversed this reduction (22.70 +/- 2.94 g/day). Tumor growth rate was markedly reduced in the P group (16.41 +/- 2.09 for WP vs 24.06 +/- 2.64 g for W). WP group showed a significant increase in mean glomerular filtration rate compared to P and control (1.520 +/- 0.214 ml min-1 kg body weight-1; P < 0.05). Tumor-bearing groups had low urine osmolality compared to control rats. The fractional sodium excretion decreased in the W group compared to control (0.43 +/- 0.16 vs 2.99 +/- 0.87%; P < 0.05), and partially recovered in the WP group (0.90 +/- 0.20%). In summary, the chronic supplementation with fish oil used in this study increased the amount of fat in the diet by only 0.1%, but caused remarkable changes in tumor growth rate and cachexia, also showing a renoprotective function.

Eicosapentaenoic acid inhibits PDGF-induced mitogenesis and cyclin D1 expression via TGF-beta in mesangial cells

Eicosapentaenoic acid (EPA), an omega-3 polyunsaturated fatty acid derived from fish oil, is efficacious in glomerular diseases where mesangial proliferation is a key event. We examined the mechanisms of action of EPA on platelet-derived growth factor (PDGF)-stimulated rat mesangial cell mitogenesis. EPA dose-dependently inhibited PDGF-stimulated [(3)H]-thymidine incorporation. PDGF-induced PDGF receptor autophosphorylation, an initial event for PDGF signaling, was not affected by 2 micro g/ml EPA. Similarly, PDGF-stimulated activation of extracellular signal-regulated kinase (ERK) was not altered. On the other hand, EPA inhibited cyclin-dependent kinase 4 (CDK4) activation and cyclin D1 protein induction, a critical step for G1/S progression. TGF-beta secretion assessed by ELISA and bioassay was increased by EPA at 18 h. Coincubation with anti-TGF-beta antibody inhibited the EPA-induced suppression of [(3)H]-thymidine incorporation and cyclin D1 expression. SB203580, an inhibitor of p38, a downstream kinase of TGF-beta, did not affect EPA's growth inhibitory effect. These results demonstrate that EPA inhibits PDGF-stimulated mesangial cell mitogenesis and cyclin D1 expression via TGF-beta.

Update on solid-phase extraction for the analysis of lipid classes and related compounds

This article provides information on the different procedures and methodologies developed when solid-phase extraction (SPE) is used for lipid component separation. The analytical systematics, established by different authors and designed to separate groups of compounds and also specific components by using a combination of chromatographic supports and solvents are presented. The review has been divided into three parts, which we consider well defined: edible fats and oils, fatty foods and biological samples. Separations of non-polar and polar lipids is the most extensive systematic, although many other published methods have been established to isolate specific components or a reduced number of components from edible fats and oils, fatty foods or biological samples susceptible to further analysis by other quantitative techniques.

Prevention of acute renal failure

Acute renal failure (ARF) induced by therapeutic agents that are nephrotoxic (e.g., gentamicin, cisplatin, amphotericin, and nonsteroidal anti-inflammatory drugs) or hypotension associated with anesthesia and surgery unfortunately occur with some regularity in small animal practice. Several clinical conditions have been identified that can increase the risk of hospital-acquired ARF in dogs. Recognition of these risk factors allows the clinician to assess the risk/benefit ratio for various drugs and/or procedures. Additionally, initiating protective measures and increasing the monitoring of renal function in those patients that require potentially harmful treatment may decrease the incidence of hospital-acquired ARF.

Omega-3 fatty acids attenuate glomerular capillary hydraulic pressure in rats with renal ablation

To clarify the emerging role of omega-3 fatty acids (FAs) in the regulation of the renal microcirculation, we recently performed micropuncture studies in normal rats maintained on diets enriched with omega-3 FAs. Although those studies suggested that omega-3 FAs alter the renal microcirculation in normal rats, it was not apparent whether this dietary maneuver could modulate intrarenal hemodynamics in the setting of renal disease. Therefore, the present renal micropuncture studies were performed in nephrectomized rats maintained on control diets or diets enriched with omega-3 FAs. Omega-3 FAs abrogated glomerular capillary (56.2 +/- 0.8 vs. 63.9 +/- 2.0 mm Hg) and transcapillary hydraulic pressure (40.9 +/- 1.4 vs. 50.6 +/- 1.3 mm Hg) compared to untreated rats. This effect was attributable to (1) a reduction in mean arterial pressure (138 +/- 3 vs. 163 +/- 2 mm Hg) and (2) a decrease in efferent arteriolar resistance (0.43 +/- 0.06 vs 0.98 +/- 0.19 dyn x seconds x cm-5 x 10(10)). Sclerosis index and albuminuria were also lessened by this dietary maneuver. To further characterize the mechanism of altered renal arteriolar resistance, we then explored the effects of omega-3 FAs on renal prostaglandin synthesis and angiotensin II-stimulated phospholipid turnover. A significant decrease in the urinary excretion of the renal vasoconstrictor, TXA2 (12.8 +/- 2.3 vs. 35.1 +/- 14.0 ng/24 hr), was induced by treatment with omega-3 FAs. Moreover, angiotensin II-stimulated phospholipid turnover was attenuated in intact glomeruli pretreated with omega-3 FAs. We conclude that omega-3 FAs exert favorable effects on experimental renal injury by eliciting a salutary effect on the renal microcirculation of rats subjected to subtotal renal ablation. Moreover, the similarities between these findings and those obtained with sustained inhibition of angiotensin II converting-enzyme suggest that these compounds act through parallel pathways of inhibition.

Effects of vitamin E deficiency and dietary linoleate on serum thromboxane synthesis in male sprague-dawley rats

The aim of the present study was to examine whether vitamin E deficiency and dietary linoleate had additive or synergistic effects on serum thromboxane (TX) status and therefore on thrombogenesis. Eight groups of five male weaning Sprague-Dawley rats were fed semipurified diets containing 3.5 or 18.4% of energy from linoleate (en% linoleate) and 0, 100, 5000, 15,000 ppm vitamin E for 8 weeks. Rats fed no vitamin E had the lowest serum vitamin E while rats fed 15,000 ppm vitamin E had the highest serum vitamin E (p < 0.05). Serum 18:2, n-6 (linoleic acid; LA) and 20:4, n-6 (arachidonic acid; AA) were significantly greater in the 18.4 en% linoleate group than in the 3.5 en% linoleate group (p < 0.05). Serum TXA2, measured as its stable metabolite TXB2, was significantly greater in the vitamin E-deficient rats than in the vitamin E-adequate and vitamin E-supplemented rats (p < 0.05). Serum lipid peroxidation, measured as thiobarbituric acid reactive substances (TBARS), was significantly greater in the 0 and 100 ppm vitamin E groups than in the 5000 and 15,000 ppm vitamin E groups (p < 0.05). No interaction between dietary linoleate and vitamin E deficiency on serum TX status was found. However, it seemed that vitamin E deficiency had a more potent effect on TX synthesis than dietary linoleate. The result suggested that vitamin E deficiency may be prothrombogenic via its effect on TX synthesis.

The potential for dietary polyunsaturated fatty acids in domestic animals

The metabolism and clinical potential for dietary polyunsaturated fatty acids (PUFAs) modifications using oil supplements containing n-3 and n-6 fatty acids are reviewed. Their use in such disorders as renal disease, inflammatory and immune-related disorders, and dermatological conditions in dogs and cats is discussed. The influence of n-3 fatty acid-rich rations on the endotoxin response in horses is described. Progress has been made toward understanding the clinical potential for PUFAs in these species. However, they have not yet been shown to be efficacious in any of the conditions investigated.

Dietary fat composition and age affect synaptosomal and retinal phospholipid fatty acid composition in C57BL/6 mice

The purpose of this study was (i) to determine whether dietary fat-induced differences in neural and retinal membranes occur when dietary fat treatment is implemented in aged animals and (ii) to characterize the effect of long-term differences in dietary fat on neural and retinal membrane composition. For the first objective, young (six-week-old) and old (95-week-old) mice were randomly assigned to beef tallow (TAL) or soybean oil (SBO) diets for eight weeks. For the second objective, young (four-week-old) mice consumed either TAL or SBO diets for 99 weeks. Young and old mice challenged with a change in dietary fat for an eight-week period showed both diet and age effects on neural and retinal phospholipid fatty acid composition (P < 0.05). In addition, significant diet by age interactions were evident. In mice that consumed TAL and SBO diets throughout their life, only retinal phosphatidylethanolamine (PE) 18:2n-6 and neural phosphatidylserine 22:5n-6, PE 18:2n-6 and phosphatidylcholine 18:2n-6 differed between dietary treatments (P < 0.05). Neither the unsaturation index nor the n-6/n-3 ratio was affected by diet. Neural and retinal phospholipid fatty acid composition were responsive to changes in dietary fat even when the treatment was implemented beyond developmental or post-weanling stages. In contrast, when mice consumed TAL or SBO diets throughout their life, fewer differences in phospholipid fatty acid composition were detected, suggesting that the effect of the dietary treatment was mitigated by aging.

Dietary fish oil interferes with renal arachidonic acid metabolism in rats: correlations with renal physiology

Dietary fish oil has been reported to have both beneficial and deleterious effects in animal models of renal disease, which may be related to alterations in renal eicosanoid metabolism. The influence of dietary fish oil on glomerular and renal tubular responses that are linked to arachidonic acid metabolism was examined. Dietary fish oil had antidiuretic and antinatriuretic effects, which correlated with reduced renal cortical endogenous prostaglandin E2 (PGE2). Fish oil altered the renal balance of dienoic prostacyclin (PGI2) to thromboxane (TXA2) in favor of vasodilation, which may explain the observed exaggerated compensatory increases in glomerular function in response to uninephrectomy. Intact rats fed fish oil for 6 months developed proteinuria and impaired glomerular filtration rates (GFR). These deleterious effects were associated with evidence of increased renal lipid peroxidation. These results suggest that dietary fish oil modifies glomerular and renal tubular function in rats, and worsens age-associated proteinuria and declines in GFR. These effects may reflect the impact of dietary fish oil on renal fatty acid composition and arachidonic acid metabolism.

Inhibition of gap junction-mediated intercellular communication by alpha-linolenate

The purpose of this investigation was to assess whether alterations in the fatty acid composition of rat liver epithelial (WB-F344) cell phospholipids would modulate gap junction-mediated intercellular communication (GJIC). WB-F344 cells were grown to confluency in culture medium supplemented with one of seven different fatty acids at a concentration of 50 microM for 48 h. Only alpha-linoleate (18:3 n-3) significantly inhibited GJIC. Saturated fatty acids (12:0, 16:0, and 18:0), a monounsaturated fatty acid (18:1 n-9), and n-6 polyunsaturated fatty acids (18:2 and 20:4) did not affect GJIC. The alpha-linolenate-induced inhibition of GJIC was not due to the activation of protein kinase C or intracellular hydroperoxide production, two lipid-dependent parameters previously shown to inhibit GJIC. In addition, alpha-linolenate did not alter membrane fluidity. Although the mechanism by which alpha-linolenate inhibits GJIC is unclear, changes in the fatty acid composition of cell phospholipids may be of critical importance. Subsequent to supplementation with alpha-linolenate, WB-F344 cell phospholipids had reduced 20:4 n-6 and elevated n-3 fatty acids. The results of this investigation emphasize the importance of current research into the influence of lipids on cell function and identify a new mechanism by which gap junctions can be modulated.

Multiple roles for surface-active phospholipid in hypertension

The elusiveness of the agent responsible for primary hypertension and the diversity of its impact upon the body, as reflected by the widely differing and almost independent avenues of research in this field, indicate that the answer could lie with a particularly common substance in the body acting at various levels of fundamental physiological function. This hypothesis pursues some basic physics of phospholipid whereby a change in quantity or quality can affect the capability to generate extreme surface activity manifest as the numerous properties which this agent can impart to blood and to adjacent surfaces by adsorption. Nine possible roles are traced by which surface-active phospholipid could impinge upon neurogenic control of blood pressure, the effects of circulating relaxing factors, blood rheology, atherosclerosis, and the major renal aspects of control by diuresis and association with the antihypertensive neutral renomedullary lipid. This multi-faceted approach offers mechanisms by which diet can affect blood pressure in addition to the traditional emphasis upon the deposition of atheroma.

Effects of dietary fats on prostanoid production and aortic and plasma fatty acid composition in rats

Male Sprague-Dawley rats were fed diets with 10%, 30%, or 50% of energy derived from fat for two weeks. The fats used were beef tallow, olive oil, peanut oil and butter. Aortic prostacyclin (PGI2) production, platelet aggregation and thromboxane A2 (TXA2) production and plasma and aortic phospholipid (PL) content were measured. Butter- and beef tallow-feeding reduced aortic PGI2 production and collagen-induced TXA2 production in a dose-dependent manner as the level of fat in the diet increased. Neither olive oil nor peanut oil had any effect on aortic PGI2 production or collagen-induced TXA2 production. Butter-feeding also resulted in a decrease in collagen-induced platelet aggregation; however, none of the other fats had any effect on collagen-induced platelet aggregation. The observed decreases in aortic PGI2 and collagen-induced TXA2 production were paralleled by similar decreases in aortic and plasma PL arachidonic acid content and an increase in eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Only the most saturated fats, butter and beef tallow, had significant inhibitory effects on prostanoid production and platelet aggregation.

High linoleic acid diets ameliorate diabetic nephropathy in rats

The value of high polyunsaturated fatty acid (PUFA) diets in preventing diabetic nephropathy in rats was studied. Diabetes was induced by intravenous injection of streptozotocin (SZ), 65 mg/kg. Rats were divided in four groups fed diets containing 11% fat for 38 weeks. Dietary fat derived from four sources: beef tallow (BT; rich in saturated fatty acids), evening primrose oil (EPO; rich in gamma linolenic [GLA] and linoleic acids [LA]), safflower oil (SO; rich in LA), and fish oil (FO; rich in eicosapentaenoic [EPA] and docosahexaenoic [DHA] acids). Ultralente insulin was administered every other day to maintain the blood glucose levels between 11.1 and 22.2 mmol/L (200 and 400 mg/dL). The diets prepared with EPO and SO had a clear beneficial effect on proteinuria, glomerular sclerosis, and tubular abnormalities, as compared with BT. Both diets also increased the ratio of renal cortical production of 6-keto-PGF1 alpha to thromboxane B2 (TXB2), the stable metabolites of PGI2 and TXA2, respectively. They did not induce significant changes in plasma lipid composition. The FO diet did not have an effect on renal disease, but decreased plasma lipids and inhibited eicosanoid synthesis by platelets and kidney cortex. FO feeding was associated with a lowered 6-keto-PGF1 alpha/TXB2 ratio. It is concluded that high LA diets are protective in this model of diabetic nephropathy. The effect may be secondary to modifications of the eicosanoid balance. Diets containing FO have a beneficial effect on plasma lipids in this model.

Formation of PGI3 in the rat during dietary fish oil supplementation

Conflicting results exist in the literature on the conversion of eicosapentaenoic acid (EPA) to trienoic prostaglandins and its influence on the formation of dienoic prostaglandins from arachidonic acid (AA). Tissues from animals fed fish oils produce little, if any, trienoic prostaglandins and reduced amounts of dienoic ones. Excretion of the major urinary metabolite of PGI2 is not reduced in humans taking fish oil, however, and substantial amounts of one derived from PGI3 have been found, by GC/MS. We have addressed this possible species difference by examining the urine of rats fed fish oil for 2.3 dinor-6-keto-PGF1 alpha and its delta 17 analog, formed from PGI2 and PGI3, respectively, and compared them with rats fed corn oil. Fatty acid differences in erythrocyte and aortic lipids were also determined. Rats fed fish oil do make PGI3 from eicosapentaenoic acid in vivo and do not suppress their production of PGI2, despite having more EPA than AA in aortic lipids.

The effect of long-term consumption of fish oil on platelet-activating factor synthesis in rat renal microsomes

The effect of consuming eicosapentaenoic acid (EPA) plus docosahexaenoic acid (DHA) on platelet-activating factor (PAF) biosynthesis by renal acetyl-CoA: 1-O-alkyl-sn-glycero-3-phosphocholine (lysoPAF) acetyltransferase activity was compared in rats fed diets containing fish oil (FO) or sunflower oil (SO) for 11 months. Microsomes from the FO group exhibited a significantly lower formation of [14C]PAF from [1-14C]acetyl-CoA in the absence of exogenously-added lysoPAF. There were no differences between the two groups in the generation of radioactive acylacetyl-glycerophosphocholine (GPC) upon incubation of microsomes without added lysoPAF. Upon addition of lysoPAF, the microsomal synthesis of PAF, but not acylacetyl-GPC, rose considerably. Furthermore, PAF synthesis via microsomal acetyltransferase activity in the FO-fed animals was only 40% that of the SO groups. These findings may bear potential relevance in terms of reducing PAF synthesis in association with renal pathophysiology.