Regulation of polyunsaturated fatty acid metabolism in tissue phospholipids of obese (fa/fa) and lean (Fa/-) Zucker rats. 1. Effect of dietary lipids on cardiac tissue

Comparative actions of omega-3 fatty acids on in-vitro lipid droplet formation

Storage of fat into lipid droplets (LDs) is the key step in adipogenesis. Previously the omega-3 polyunsaturated fatty acid (n-3PUFA) eicosapentaenoic acid (EPA; C20:5n-3) has been shown to suppress LD formation, yet the actions of other n-3PUFA is unknown. Here, we examined the impact of the three major long chain n-3PUFA; EPA, docosapentaenoic acid (DPA; C22:5n-3) and docosahexaenoic acid (DHA; C22:6n-3) on LD formation in 3T3-L1 adipocytes. Cells were supplemented with 100µM fatty acid during differentiation. All n-3PUFA significantly reduced LD formation and the metabolic disorder marker, SCD1, in comparison to stearic acid (STA; C18:0). This action was more potent for DHA than either EPA or DPA. Furthermore, DHA significantly increased lipolysis and ATGL gene and protein expression but reduced the gene expression of three proteins related to LD formation (Perilipin A, Caveolin-1 and Cidea), compared with other n-3PUFA. Thus, DHA, above EPA and DPA, markedly suppressed fat storage in LDs in in-vitro adipocytes.

Abnormal immune responses in fa/fa Zucker rats and effects of feeding conjugated linoleic acid

OBJECTIVE

The objective of this study was to characterize immune function in the fa/fa Zucker rat, and to determine the effects of feeding conjugated linoleic acid (CLA) isomers on immune function.

METHODS AND PROCEDURES

Lean and fa/fa Zucker rats were fed for 8 weeks nutritionally complete diets with different CLA isomers (%wt/wt): control (0%), c9t11 (0.4%), t10c12 (0.4%), or MIX (0.4% c9t11 + 0.4% t10c12). Isolated splenocytes were used to determine phospholipid (PL) fatty acid composition and cell phenotypes, or stimulated with mitogen to determine their ability to produce cytokines, immunoglobulins (Ig), and nitric oxide (NO).

RESULTS

Splenocyte PL of fa/fa rats had a higher proportion of total monounsaturated fatty acids and n -3 polyunsaturated fatty acids (PUFA), and lower n -6 PUFA and n -6-to-n -3 PUFA ratio (P < 0.05). Feeding CLA increased the content of CLA isomers into PL, but there were lower proportions of each CLA isomer in fa/fa rats. Splenocytes of fa/fa rats produced more amounts of IgA, IgG, and IgM, NO, and interleukin-1beta (IL-1beta), IL-6, and tumor necrosis factor-alpha (TNF-alpha) (P < 0.05). Obese rats fed the t10c12 diet produced less TNF-alpha and IL-1beta (lippopolysaccharide (LPS), P < 0.05). Splenocytes of fa/fa rats produced less concanavalin A (ConA)-stimulated IL-2 (P < 0.0001) than lean rats, except fa/fa rats fed the c9t11 diet (P < 0.05).

DISCUSSION

The c9t11 and t10c12 CLA isomers were incorporated into the membrane PL of the fa/fa Zucker rat, but to a lesser extent than lean rats. Splenocytes of obese rats responded in a proinflammatory manner and had reduced T-cell function and feeding the t10c12 and c9t11 CLA isomers may improve some of these abnormalities by distinct methods.

Overfeeding-induced ovarian dysfunction in broiler breeder hens is associated with lipotoxicity

In mammals, triacylglycerol (TAG) accumulation in nonadipose tissue, termed lipotoxicity, develops with obesity and can provoke insulin resistance, overt diabetes, and ovarian dysfunction. Leptin, an adipose tissue hormone, may mediate these effects. Feed-satiated broiler breeder hens manifest lipotoxicity-like symptoms. Changes in body and organ weights, hepatic and plasma TAG, nonesterified fatty acids (NEFA), ovarian morphology, and egg production in response to acute voluntary increases of feed intake were measured in 2 studies with Cobb 500 broiler breeder hens provided with either 145 or > or = 290 g of feed/d per hen for 10 d. In both studies, no hen fed 145 g of feed/d exhibited ovarian abnormalities, whereas approximately 50% of feed-satiated hens did. Egg production in feed-satiated hens was reduced from 73.3 to 55.8% (P = 0.001). Morphology indicated that apoptosis-induced atresia occurred in the hierarchical follicles. Fractional weight of yolk increased from 29.3 to 30.6% (P = 0.016) and no longer correlated to egg weight. Body, liver, and abdominal adipose weights were significantly greater (P < 0.05) in feed-satiated hens, as were plasma concentrations of glucose, NEFA, TAG, insulin, and leptin (P < 0.05). Feed-satiated hens with abnormal ovaries had significantly more liver and abdominal fat, greater plasma leptin and TAG concentrations, and more saturated fatty acids in plasma NEFA than did feed-satiated hens with normal ovaries. Differences in severity of lipotoxic metabolic and hormonal responses among feed-satiated hens were closely linked to the incidence of ovarian abnormalities and granulosa cell susceptibility to apoptosis and necrosis.

Olive oil and modulation of cell signaling in disease prevention

Epidemiological studies show that populations consuming a predominantly plant-based Mediterranean-style diet exhibit lower incidences of chronic diseases than those eating a northern European or North American diet. This observation has been attributed to the greater consumption of fruits and vegetables and the lower consumption of animal products, particularly fat. Although total fat intake in Mediterranean populations can be higher than in other regions (ca. 40% of calories), the greater proportion is derived from olive oil and not animals. Increased olive oil consumption is implicated in a reduction in cardiovascular disease, rheumatoid arthritis, and, to a lesser extent, a variety of cancers. Olive oil intake also has been shown to modulate immune function, particularly the inflammatory processes associated with the immune system. Olive oil is a nonoxidative dietary component, and the attenuation of the inflammatory process it elicits could explain its beneficial effects on disease risk since oxidative and inflammatory stresses appear to be underlying factors in the etiology of these diseases in man. The antioxidant effects of olive oil are probably due to a combination of its high oleic acid content (low oxidation potential compared with linoleic acid) and its content of a variety of plant antioxidants, particularly oleuropein, hydroxytyrosol, and tyrosol. It is also possible that the high oleic acid content and a proportionate reduction in linoleic acid intake would allow a greater conversion of alpha-linolenic acid (18:3n-3) to longer-chain n-3 PUFA, which have characteristic health benefits. Adoption of a Mediterranean diet could confer health benefits in high-risk populations.

Cognitive aging, childhood intelligence, and the use of food supplements: possible involvement of n-3 fatty acids

BACKGROUND

Food supplement use is widely promoted, but little is known about the cognitive effects of food supplements.

OBJECTIVE

We examined the effects of food supplement use on cognitive aging.

DESIGN

This was an observational study of subjects born in 1936 whose mental ability was tested in 1947 and who were followed up in 2000-2001, at which time cognition, diet, food supplement use, and risk factors for vascular disease were assessed. In a nested case-control study, fish-oil users were matched with nonusers, and cognitive function was related to erythrocyte n-3 fatty acid composition.

RESULTS

Childhood intelligence quotient (IQ) did not differ significantly by category of food supplement use (ie, none, fish oil, vitamins, and other). At the age of 64 y, cognitive function was higher in food supplement users than in nonusers before adjustment for childhood IQ. After adjustment for childhood IQ, digit symbol (mental speed) test scores were higher in food supplement users. Fish-oil supplement users consumed more vitamin C and vegetable and cereal fiber than did non-supplement-users. In a nested case-control study, erythrocyte membrane n-3 content was higher in fish-oil supplement users than in nonusers, but cognitive function did not differ significantly between groups. Total erythrocyte n-3 fatty acids and the ratio of docosahexaenoic acid to arachidonic acid was associated with better cognitive function in late life before and after adjustment for childhood IQ.

CONCLUSIONS

Food supplement use and erythrocyte n-3 content are associated with better cognitive aging. If associations with n-3 content are causal, optimization of n-3 and n-6 fatty acid intakes could improve retention of cognitive function in old age.

Glucose oversupply increases Delta9-desaturase expression and its metabolites in rat skeletal muscle

AIM/HYPOTHESIS

Previous studies have shown that prolonged glucose infusion causes insulin resistance and triglyceride accumulation in rat skeletal muscle. In this study, we investigated a possible relationship between insulin resistance and the composition of different accumulated lipid fractions in rat skeletal muscle.

METHODS

Continuous glucose infusion was carried out in rats for 7 days. Lipids were extracted from skeletal muscle, separated by thin layer chromatography and fatty acid composition of phospholipids, triglycerides, diglycerides, free fatty acids and cholesterol esters fractions was analysed by gas chromatography. Delta9-Desaturase mRNA was measured by real time polymerase chain reaction. The enzyme activity was measured in the microsomal fractions.

RESULTS

Prolonged glucose infusion (5 days) increased the relative content of palmitoleic acid (16:1 N7) several-fold (2.3- to 5.8-fold) in four out of five lipid fractions and enhanced oleic acid (18:1 N9) two-fold in three lipid fractions suggesting increased Delta9-desaturase activity while the content of several polyunsaturated fatty acids was reduced. In parallel, Delta9-Desaturase mRNA contents and enzyme activities in skeletal muscle were increased 10-fold, 75-fold, 2.6-fold and 7.7-fold after 2 and 5 days of glucose infusion, respectively.

CONCLUSION/INTERPRETATION

Our results suggest that long-term glucose oversupply induces a rapid increase in Delta9-desaturase expression and enzyme activity in skeletal muscle which leads to fast and specific changes in fatty acid metabolism possibly contributing to the insulin resistance in this animal model.

Effects of arachidonic acid plus zinc on glucose disposal in genetically diabetic (ob/ob) mice

AIM

The present study is designed to determine whether arachidonic acid (AA) plus zinc improves clinical signs of diabetes in genetically diabetic ob/ob mice.

METHODS

In the first study, effects of acute administration of AA plus zinc on glucose disposal were determined in ob/ob and lean mice (n = 6 each). In the second study, ob/ob and lean mice were treated with increasing doses of AA plus zinc for 2 weeks (n = 5 each). Postprandial and fasting blood glucose concentrations, three-hour-area-average above fasting glucose concentration (TAFGC), water and food intake, body weight and plasma insulin concentrations were measured.

RESULTS

Acute administration of AA plus zinc significantly increased glucose disposal in ob/ob mice. In the second study, postprandial and fasting blood glucose concentrations, TAFGC, and water and food intake in ob/ob mice treated with AA plus zinc for 2 weeks were significantly decreased compared with those in mice given no AA. Plasma insulin concentrations in both lean and ob/ob mice were not changed by AA treatment in drinking water.

CONCLUSIONS

AA plus zinc in drinking water is effective in decreasing blood glucose levels in obese mice. These results indicate that use of these compounds should be considered as a dietary supplement to control hyperglycaemia in patients with type II diabetes.

Exercise training reduces skeletal muscle membrane arachidonate in the obese (fa/fa) Zucker rat

Compared with the lean (Fa/-) genotype, obese (fa/fa) Zucker rats have a relative deficiency of muscle phospholipid arachidonate, and skeletal muscle arachidonate in humans is positively correlated with insulin sensitivity. To assess the hypothesis that the positive effects of exercise training on insulin sensitivity are mediated by increased muscle arachidonate, we randomized 20 lean and 20 obese weanling male Zucker rats to sedentary or treadmill exercise groups. After 9 wk, fasting serum, three skeletal muscles (white gastrocnemius, soleus, and extensor digitorum longus), and heart were obtained. Fasting insulin was halved by exercise training in the obese rat. In white gastrocnemius and extensor digitorum longus (fast-twitch muscles), but not in soleus (a slow-twitch muscle) or heart, phospholipid arachidonate was lower in obese than in lean rats (P < 0.001). In all muscles, exercise in the obese rats reduced arachidonate (P < 0.03, by ANOVA contrast). We conclude that improved insulin sensitivity with exercise in the obese genotype is not mediated by increased muscle arachidonate and that reduced muscle arachidonate in obese Zucker rats is unique to fast-twitch muscles.

Phospholipid fatty acid composition in type I and type II rat muscle

The fatty acid composition of the membrane phospholipids phosphatidylcholine (PC) and phosphatidylethanolamine in insulin-sensitive Type I (soleus) and insulin-resistant Type II (EDL) muscle is not known. In the present studies, soleus and EDL muscles were removed from 250-300 g Sprague-Dawley rats, and the fatty acid composition of total and individual phospholipid (PL) species was quantitated. As expected, triglyceride content was increased twofold in soleus muscle. No quantitative differences in the individual PL species or cholesterol content were found between the two muscles. However, a striking difference in PL fatty acid composition was observed in the PC fraction. An increase in 16:0 with decreases in 18:0, 18:1, 22:5n-3, and 22:6n-3 (P < 0.001 for each) was observed in the PC fraction of EDL compared to that from soleus, consistent with reduced elongation of PC fatty acids. Inhibition of fatty acid oxidation with the carnitine palmitoyl transferase-1 inhibitor, etomoxir, did not alter the fatty acid pattern in either muscle. We conclude that an alteration in PL fatty acid composition consistent with reduced elongation of both saturated and unsaturated fatty acids is observed in Type II muscle. The restriction of these alterations to the PC fraction has important implications.

Adipose tissue stearoyl-CoA desaturase mRNA is increased by obesity and decreased by polyunsaturated fatty acids

Stearoyl-CoA desaturase (SCD) is a key regulatory enzyme in the synthesis of unsaturated fatty acids. Although regulation of hepatic SCD by obesity and polyunsaturated fatty acids (PUFA) has been well investigated, no studies have addressed whether similar regulation occurs in adipose tissue. We addressed these questions by feeding control (12% corn oil) and high-PUFA (48% corn oil) diets to lean and obese Zucker rats and analyzing SCD mRNA levels in adipose tissue and liver. We report that SCD mRNA content was dramatically elevated in adipose tissue of obese vs. lean rats on both diets and was significantly decreased by PUFA in both genotypes. Interestingly, we demonstrate that SCD expression was directly downregulated in a dose dependent manner by PUFA in 3T3-L1 adipocytes. We conclude that 1) obese Zucker rats overexpress the SCD gene in both liver and adipose tissue and 2) PUFA directly suppress SCD expression in adipocytes. Further studies will elucidate the mechanisms responsible for obesity- and PUFA-mediated regulation of SCD in adipose cells.

Effect of dietary lipids and endocrine changes on polyunsaturated fatty acids in phospholipids of pancreas and brown adipose tissue of obese and lean rats

Obese (fa/fa) rats fed on control diet have lower proportions of linoleic acid (18:2n-6) and/or arachidonic acid (20:4n6) in IBAT and pancreas phospholipids compared with lean (Fa/-) rats. Lower stearic acid (18:0) to oleic acid (18:1n-9) mean ratios in fa/fa compared with Fa/- suggest enhanced delta 9-desaturase activity in the former. 18:2/20:4 mean ratios in pancreas, but not IBAT, are indicative of a reduced delta 6-desaturase activity in fa/fa rats. Absolute amounts of phospholipids (mg/unit tissue wt) were 2-fold greater in IBAT of fa/fa compared with Fa/- rats, irrespective of their diet. This was reflected in greater absolute amounts of 18:2n-6 and 20:4n-6 only in HSO and HTO fa/fa groups, but not in the control group. Adrenalectomy (Adx) or T3 treatment also modified phospholipid fatty acid composition of IBAT and pancreas phospholipids in animals fed on the control diet with fa/fa rats more sensitive to endocrine induced changes. In fa/fa rats T3 treatment increased docosahexaenoic acid (22:6n-3) in IBAT of both phenotypes compared with the control, but this effect was evident only in fa/fa and not Fa/- pancreas. T3 treatment also increased docosapentaenoic acid (22:5n-3) in IBAT from, both phenotypes, but no 22:5n-3 was evident in the pancreatic tissue of these animals. ADX also increased 22:6n-3 in the IBAT of fa/fa (Fa/- values were less than 1%) but not in the pancreas of fa/fa or Fa/-. ADX modified the relative proportions of 18:0 to 18:1 and 18:2 to 20:4 in IBAT and pancreas of fa/fa in a way that indicated decreased delta 9-desaturase and increased delta 6-desaturase activities; these effects tended toward normal again in pancreas of fa/fa rats on corticosterone replacement (CST).

Phospholipid fatty acid composition and vitamin E levels in the retina of obese (fa/fa) and lean (FA/FA) Zucker rats

We have compared the fatty acid composition of the major classes of phospholipids in the retina of lean (FA/FA) and genetically obese (fa/fa) male Zucker rats. In all phospholipid fractions, there was a higher ratio of n-3 to n-6 fatty acids in obese animals whereas the total content of polyunsaturated fatty acids (PUFA) was unaffected by the genotype. Lower percentages of arachidonic acid (20:4(n-6)) were present in the phosphatidylcholine, phosphatidylinositol and phosphatidylserine fractions in the retina of obese rats. This was associated with a higher level of docosahexaenoic acid (22:6(n-3)) in these fractions. In addition, increased levels of dihomo-gamma-linolenic acid (20:3(n-6)) were present in the retinal phosphatidylcholine and phosphatidylethanolamine of obese animals. These results indicate that modifications of phospholipid fatty acid composition which have previously been reported in peripheral tissues of obese Zucker rats also affect the retina. Furthermore, the retinal levels of vitamin E were higher in obese than in lean rats suggesting differences in the tissue antioxidant status between these two genotypes.

The relation between insulin sensitivity and the fatty-acid composition of skeletal-muscle phospholipids

BACKGROUND

Insulin resistance and hyperinsulinemia are features of obesity, non-insulin-dependent diabetes mellitus, and other disorders. Skeletal muscle is a major site of insulin action, and insulin sensitivity may be related to the fatty-acid composition of the phospholipids within the muscle membranes involved in the action of insulin.

METHODS

We determined the relation between the fatty-acid composition of skeletal-muscle phospholipids and insulin sensitivity in two groups of subjects. In one study, we obtained samples of the rectus abdominis muscle from 27 patients undergoing coronary artery surgery; fasting serum insulin levels provided an index of insulin sensitivity. In the second study, a biopsy of the vastus lateralis muscle was performed in 13 normal men, and insulin sensitivity was assessed by euglycemic-clamp studies.

RESULTS

In the patients undergoing surgery, the fasting serum insulin concentration (a measure of insulin resistance) was negatively correlated with the percentage of individual long-chain polyunsaturated fatty acids in the phospholipid fraction of muscle, particularly arachidonic acid (r = -0.63, P < 0.001); the total percentage of C20-22 polyunsaturated fatty acids (r = -0.68, P < 0.001); the average degree of fatty-acid unsaturation (r = -0.61, P < 0.001); and the ratio of the percentage of C20:4 n-6 fatty acids to the percentage of C20:3 n-6 fatty acids (r = -0.55, P < 0.01), an index of fatty-acid desaturase activity. In the normal men, insulin sensitivity was positively correlated with the percentage of arachidonic acid in muscle (r = 0.76, P < 0.01), the total percentage of C20-22 polyunsaturated fatty acids (r = 0.76, P < 0.01), the average degree of fatty-acid unsaturation (r = 0.62, P < 0.05), and the ratio of C20:4 n-6 to C20:3 n-6 (rho = 0.76, P = 0.007).

CONCLUSIONS

Decreased insulin sensitivity is associated with decreased concentrations of polyunsaturated fatty acids in skeletal-muscle phospholipids, raising the possibility that changes in the fatty-acid composition of muscles modulate the action of insulin.