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

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.

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.

Effects of different dietary amounts of LCPUFA n3 and vitamin B6 on lipid composition and antioxidant defences in rat kidney

Our previous report demonstrated that, when vitamin deficiency is associated with high contents of long chain polyunsaturated fatty acids (LCPUFA) n3, lipid peroxidation susceptibility in rat heart and liver increases. In this paper, we evaluated the effect of the same dietary administration on lipid composition and antioxidant defenses of rat kidney. Results showed that vitamin B(6) deficiency, when associated with a fish oil diet, as compared to vegetable oil condition, increased relative kidney weight and decreased pyridoxal-5P contents. The different LCPUFA n3 dietary contents produced, on kidney phospholipids, effects interlaced with those of vitamin B(6) deficiency; in particular fish oil and vitamin B(6) deficient diet caused a significant decrease of arachidonic acid showing that the processes of elongation and desaturation of linoleic acid were slowed. Also, peroxidation susceptibility was higher, as demonstrated both by increased TBARS formation and glutathione peroxidase activity, and by decreased vitamin E contents and reduced glutathione/oxidized glutathione ratio.

Effects of dietary polyunsaturated fatty acid supplementation in early renal insufficiency in dogs

Dietary supplementation with polyunsaturated fatty acids (PUFAs) alters the course of experimental kidney disease in dogs. In particular, supplementation with omega-6 PUFAs hastens the decline of kidney function, and omega-3 PUFAs are renoprotective. We investigated the early stages of renal insufficiency to determine whether PUFA supplementation altered the magnitude of hypercholesterolemia or glomerular hemodynamics. Two months after 11/12 nephrectomy, dogs were randomly divided into three groups of 6 animals each. Each group of dogs was then fed a low-fat basal diet supplemented with one of three sources of lipid to achieve a final concentration of 15% added fat. Fat sources were rich in omega-3 PUFAs (menhaden fish oil, group FO), omega-6 PUFAs (safflower oil, group SO), or saturated fatty acids (beef tallow, group C). Early in renal insufficiency, before significant kidney damage, group FO had a lower (P<.05) serum cholesterol concentration and tended to have a lower urinary prostaglandin E2 (PGE2) and thromboxane A2 (TxA2) excretion than group C. In contrast, group SO had a higher mean glomerular capillary pressure (P<.05) and more glomerular enlargement (P<.05) and tended to have higher eicosanoid excretion rates than group C. These differences in lipid metabolism, glomerular hypertension and hypertrophy, and urinary eicosanoid metabolism could explain, in part, the beneficial effects of omega-3 PUFAs and the detrimental effects of omega-6 PUFAs when administered on a long-term basis in this model of renal insufficiency.

Beneficial effects of chronic administration of dietary omega-3 polyunsaturated fatty acids in dogs with renal insufficiency

Dietary supplementation with polyunsaturated fatty acids (PUFA) alters the course of experimental renal disease in rats. However, chronic renal disease in other laboratory animals and in human beings frequently responds differently to experimental manipulations. We investigated the effects of variations in dietary PUFA composition on the chronic course of induced renal disease in dogs. Two months after 15/16 nephrectomy, dogs were randomly divided into three groups of seven animals each. For the next 20 months, each group of dogs was fed a low-fat basal diet supplemented with one of three sources of lipid to achieve a final concentration of 15% added fat. Fat sources provided omega-3 PUFA (menhaden fish oil, group FO), omega-6 PUFA (safflower oil, group SO), or saturated fatty acids (beef tallow, group BT). Throughout the dietary trial, the magnitude of proteinuria and the plasma concentrations of creatinine, cholesterol, and triglyceride were lower in group FO. The mean overall glomerular filtration rate was 0.89+/-0.18 ml/min per kilogram of body weight in group SO, a value that was significantly less (p < 0.05) than the corresponding values for groups BT and FO (1.21+/-0.18 and 1.43+/-0.20 ml/min/kg, respectively). Renal interstitial fibrosis also was significantly elevated in group SO. The extents of mesangial matrix expansion, glomerulosclerosis, and renal interstitial cellular infiltrate were similar in groups BT and SO, but lower (p < 0.05) in group FO. We conclude that supplementation with omega-6 PUFA enhanced renal injury; supplementation with omega-3 PUFA was renoprotective.

Studies on the impact of dietary fat composition on proteinuria in diabetic rats

Rats with streptozotocin diabetes were pair-fed diets containing 20% beef tallow (BT), fish oil (FO), or safflower oil (SO) for up to six months. After one month, differences in glucose control were not observed but rats fed FO had more renal hypertrophy. FO reduced glomerular prostaglandin E2 and 6-keto F1 alpha, and BT increased thromboxane B2 production, but there were no differences in glomerular filtration rate (GFR) or renal plasma flow (RPF). Animals fed BT needed more insulin after two months than rats fed FO followed by SO. After six months, diabetic rats fed FO had larger relative kidney weights than SO or BT, but a similar pattern was present in non-diabetic controls fed the same diets. Diabetic rats fed BT had more proteinuria than diabetic rats fed SO but not FO. However, FO-fed controls had more proteinuria than controls fed SO and similar levels of proteinuria as diabetic rats fed FO. The composition of dietary fat alters glucose tolerance in diabetic rats after two months. BT increases glomerular thromboxane production and hastens proteinuria compared to SO. FO enhances renal growth and proteinuria, but this effect is independent of the diabetic condition.

Lipid abnormalities in the nephrotic syndrome: causes, consequences, and treatment

Hyperlipidemia so commonly complicates heavy proteinuria that it has come to be regarded as an integral feature of the nephrotic syndrome (NS). Characteristically, total plasma cholesterol and triglyceride levels are elevated, as are very-low-density lipoprotein (VLDL) and low-density lipoprotein (LDL) cholesterol. Although high-density lipoprotein (HDL) concentrations may be normal, HDL subtypes are abnormally distributed, with a reduction of HDL2 and an increase in HDL3. In addition, lipoprotein (a) [Lp (a)] levels may be elevated. The mechanisms underlying these abnormalities are multifactorial, involving both increased rates of lipoprotein synthesis and defective clearance and catabolism of circulating particles. Although recent dietary and therapeutic studies have demonstrated that nephrotic hyperlipidemia can be effectively treated, the need for such intervention has not been clearly established. This pattern of lipoprotein abnormality is associated with an increased risk of cardiovascular disease in the general population, and several studies have suggested that nephrotic individuals are more likely to develop atherosclerosis. However, no prospective trials have evaluated the relationship between deranged lipid metabolism and coronary or cerebral artery disease in patients with NS. In addition, although recent experimental studies suggest that lipid abnormalities may accelerate renal injury and that lipid-lowering agents may protect renal function, there is little current evidence to suggest that such intervention is of value in preserving residual renal function in humans. Further studies are clearly required to assess the potential long-term benefits of lipid-lowering intervention in individuals with NS. In the meantime, based on data generated from other population groups, a rational approach to the clinical management of hyperlipidemia in these patients is presented.