Specific inhibition of hepatic fatty acid synthesis exerted by dietary linoleate and linolenate in essential fatty acid adequate rats

Dietary linoleate and linolenate were investigated for their ability to specifically inhibit liver and adipose tissue lipogenesis in meal-fed (access to food 900-1,200 hr), essential fatty acid (EFA) adequate rats. Supplementing a high carbohydrate diet containing 2.5% safflower oil with 3% palmitate 16∶0, oleate 18∶1, or linoleate 18∶2 did not affect in vivo liver or adipose tissue fatty acid synthesis. However, 18∶2 addition to the basal diet did result in a significant (P<0.05) decline of liver fatty acid synthetase (FAS) and glucose-6-phosphate dehydrogenase (G6PD) activities. When the safflower oil content of the basal diet was reduced to 1%, the addition of 3% 18∶2 or linolenate 18∶3 significantly (P<0.05) depressed hepatic FAS, G6PD, and in vivo fatty acid synthesis by 50%. Addition of 18∶1 caused no depression in hepatic FAS activity but did result in a significant (P<0.05) decline in liver G6PD activity and fatty acid synthesis which was intermediate between basal and basal +18∶2-or+18∶3-fed animals. Adipose tissue rates of lipogenesis were completely unaffected by dietary fatty acid supplementation. Similarly, the addition of 3 or 5% 18∶3 to a basal diet for only one meal resulted in no change in lipogenesis relative to that in animals fed the basal diet. The data indicate that, like rats fed EFA-deficient diets, dietary 18∶2 and 18∶3 exert a specific capacity to depress rat liver FAS and G6PD activities and rate of fatty acid synthesis. Michigan Agricultural Experiment station Journal Article No. 7581. D.R. Romsos is the recipient of Career Development Award K04 AM 00112     

Influence of fasting-refeeding and dietary linoleate on liver glucose-6-phosphate dehydrogenase and phospholipid fatty acid composition in rats adapted to a purified diet

Responses to refeeding after fasting were studied in male rats fed a purified casein-sucrose diet containing 5% safflower oil. After a 48 hr fast, the rats were fed either the same diet or the same diet minus oil (fat-free diet). These experiments were designed to distinguish changes due to fasting and refeeding alone without a change of diet from those changes caused by refeeding a diet of different composition. In the first experiment, rats were refed for 3 or 7 days. In rats refed either diet, liver glucose-6-phosphate dehydrogenase (G6PD) activity was elevated above refasting levels, but after 7 days, activity in rats refed the 5% safflower oil diet was significantly lower than in those refed the fatfree diet. The amount of liver arachidonate in rats refed the safflower oil diet was the same during refeeding as before fasting. In the second experiment, rats were refed the fat-free diet for 1, 2, 3, or 7 days. Liver G6PD and fatty acid synthetase were measured, as well as fatty acids in liver total lipids and phospholipids. G6PD activity increased above prefasting levels after one day refeeding and continued to increase, for 7 days. Fatty acid synthetase activity increased for the first 3 days of refeeding, with no additional increase after 7 days. In all rats refed the fat-free diet, the proportions of arachidonate and linoleate in liver phospholipids diminished with time, and eicosatrienoate appeared. These results show that (a) maintenance of liver phospholipid arachidonate did not prevent increased G6PD activity in early refeeding, but the elevated G6PD activity later declined when phospholipid arachidonate was maintained by feeding a source of linoleate; (b) the metabolic state of fastedrefed rats had not returned to prefasting conditions even after 7 days of refeeding a linoleate-rich diet to which the rats were adapted before fasting.     

Zinc deficiency and activities of lipogenic and glycolytic enzymes in liver of rats fed coconut oil or linseed oil

In previous studies, zinc-deficient rats force-fed a diet with coconut oil as the major dietary fat developed a fatty liver, whereas zinc-deficient rats force-fed a diet with linseed oil did not. The present study was conducted to elucidate the reason for this phenomenon. In a bifactorial experiment, rats were fed zinc-adequate or zinc-deficient diets containing either a mixture of coconut oil (70 g/kg) and safflower oil (10 g/kg) (“coconut oil diet”) or linseed oil (80 g/kg) (“linseed oil diet”) as a source of dietary fat, and activities of lipogenic and glycolytic enzymes in liver were determined. In order to ensure adequate food intake, all the rats were force-fed. Zinc-deficient rats on the coconut oil diet developed a fatty liver, characterized by elevated levels of triglycerides with saturated and monounsaturated fatty acids. These rats also had markedly elevated activities of the lipogenic enzymes acetyl-CoA carboxylase, fatty acid synthase (FAS), glucose-6-phosphate dehydrogenase (G6PDH), 6-phosphogluconate dehydrogenase (6PGDH), and citrate cleavage enzyme, whereas activities of malic enzyme and glycolytic enzymes were not different compared with zinc-adequate rats on the coconut oil diet. In contrast, rats receiving the linseed oil diet had similar triglyceride concentrations regardless of zinc status, and activities of lipogenic enzymes and glycolytic enzymes were not different between the two groups. Zinc-deficient rats fed either type of dietary fat exhibited statistically significant correlations between activities of FAS, G6PDH, 6PGDH and concentrations of saturated and monounsaturated fatty acids in liver. The concentrations of serum lipids were elevated in zinc-deficient rats fed either type of dietary fat. These results demonstrate that fatty liver in zinc-deficient rats on the coconut oil diet is caused by elevated activities of lipogenic enzymes, and not by disturbed lipid secretion from liver. Dietary linseed oil prevents both the elevation of lipogenic enzyme activity and fatty liver in zinc-deficient rats.     

The hypotriglyceridemic effect of eicosapentaenoic acid in rats is reflected in increased mitochondrial fatty acid oxidation followed by diminished lipogenesis

The effect of eicosapentaenoic acid (EPA) on fatty acid oxidation and on key enzymes of triglyceride metabolism and lipogenesis was investigated in the liver of rats. Repeated administration of EPA to normolipidemic rats resulted in a time-dependent decrease in plasma triglycerides, phospholipids and cholesterol. The triglyceride-lowering effect was observed after one day of feeding whereas lowering of plasma cholesterol and phospholipids was observed after five days of treatment. The triglyceride content of liver was reduced after two-day treatment. At that time, increased mitochondrial fatty acid oxidation occurred whereas mitochondrial and microsomal glycerophosphate acyltransferase was inhibited. The phosphatidate phosphohydrolase activity was unchanged. Adenosine triphosphate:citrate lyase, acetyl-CoA carboxylase, fatty acid synthetase and glucose-6-phosphate dehydrogenase were inhibited during the 15 d of EPA treatment whereas peroxisomal β-oxidation was increased. At one day of feeding, however, when the hypotriglyceridemic effect was established, the lipogenic enzyme activities were reduced to the same extent in palmitic acid-treated animals as in EPA-treated rats. In cultured rat hepatocytes, the oxidation of [¹⁴C]palmitic acid to carbon dioxide and acid-soluble products was stimulated in the presence of EPA. These results suggest that the instant hypolipidemia in rats given EPA could be explained at least in part by a sudden increase in mitochondrial fatty acid oxidation, thereby reducing the availability of fatty acids for lipid synthesis in the liver for export,e.g., in the form of very low density lipoproteins, even before EPA induced peroxisomal fatty acid oxidation, reduced triglyceride biosynthesis and diminished lipogenesis.     

Insulin Stimulates Lipogenesis and Attenuates Beta-Oxidation in White Adipose Tissue of Fed Rainbow Trout

As lipid deposition tissue in fish, the white adipose tissue (WAT) has important functions related to reproduction and the challenges of long-term fasting. In the study reported here, we infused fish fed a high-carbohydrate diet with two doses of insulin for 5 days in order to explore the effects of this hormone on lipogenesis and beta-oxidation-related enzymes. We demonstrated the presence of some of the main lipogenic enzymes at molecular, protein and activity levels (ATP-citrate lyase and fatty acid synthase). However, while ATP-citrate lyase was unexpectedly down-regulated, fatty acid synthase was up-regulated (at protein and activity levels) in an insulin dose-dependent manner. The main enzymes acting as NADPH donors for lipogenesis were also characterized at biochemical and molecular levels, although there was no evidence of their regulation by insulin. On the other hand, lipid oxidation potential was found in this tissue through the measurement of gene expression of enzymes involved in β-oxidation, highlighting two carnitine palmitoyltransferase isoforms, both down-regulated by insulin infusion. We found that insulin acts as an important regulator of trout WAT lipid metabolism, inducing the final stage of lipogenesis at molecular, protein and enzyme activity levels and suppressing β-oxidation at least at a molecular level. These results suggest that WAT in fish may have a role that is important not only as a lipid deposition tissue but also as a lipogenic organ (with possible involvement in glucose homeostasis) that could also be able to utilize the lipids stored as a local energy source.     

Lipid abnormalities in pancreatic tissue of streptozotocin-induced diabetic rats

Pancreatic lipid and fatty acid composition was determined in streptozotocin-induced diabetic rats and compared to control and insulin-treated diabetic rats. A pronounced decrease of total fatty acids was recorded and mainly accounted for by a drop of fatty acids in glycerides. Cholesterol, on the other hand, was significantly increased two- to three-fold, leading to an elevated cholesterol/phospholipid ratio. Morpho-cytochemical studies confirmed these findings because the multiple lipid droplets present in acinar cells of diabetic animals were found to be of cholesterol nature. The major alterations in phospholipid-fatty acid composition were characterized by an increase of linoleate coupled to a decrease of monounsaturates and arachidonate, suggesting defective metabolism of saturates and of linoleate. This was further supported by fatty acid ratios that suggested low Δ5 and Δ9 desaturation. Daily administration of insulin for 10 days restored and overcorrected the various lipid alterations. This study suggests that there are alterations in lipid composition and metabolism in the exocrine pancreas of chronic streptozotocin-induced diabetic rats. Their possible role in the mechanism regulating pancreatic function and secretion remains to be elucidated.     

Water-soluble organosulfur compounds of garlic inhibit fatty acid and triglyceride syntheses in cultured rat hepatocytes

The putative hypolipidemic effect of garlic remains controversial. To gain further insight into the effect of garlic on lipid metabolism, the present study determined the inhibitory effects of water-soluble organosulfur compounds present in garlic on triglyceride (TG) and fatty acid synthesis in cultured rat hepatocytes. When incubated at 0.05 to 4.0 mmol/L with cultured hepatocytes, S-allyl cysteine (SAC) and S-propyl cysteine (SPC) decreased [2-¹⁴C]acetate incorporation into triglyceride in a concentration-dependent fashion achieving a maximal inhibition at 4.0 mmol/L of 43 and 51%, respectively. The rate of [2-¹⁴C]acetate incorporation into phosphlipids was depressed to a similar extent by SAC and SPC. SPC, SAC, S-ethyl cysteine (SEC), and γ-glutamyl-S-methyl cysteine decreased [2-¹⁴C]acetate incorporation into fatty acid synthesis by 81, 59, 35, and 40%, respectively, at 2.0–4.0 mmol/L concentrations. Alliin, γ-glutamyl-S-allyl cysteine, γ-glutamyl-S-propyl cysteine S-allyl-N-acetyl cysteine, S-allylsulfonyl alanine, and S-methyl cysteine had no effect on fatty acid synthesis. The activities of lipogenic enzymes, fatty acid synthase (FAS), and glucose-6-phosphate dehydrogenase (G6PDH) were measured in cultured hepatocytes treated with the inhibitors. The activity of FAS in cells treated with 4.0 mmol/L SAC and SPC, respectively, was 32 and 27% lower than that of non-treated cells. Neither SAC nor SPC affected G6PDH activity. The results indicate that SAC, SEC, and SPC inhibit lipid biosynthesis in cultured rat hepatocytes, and further suggest that these S-alk(en)yl cysteines of garlic impair triglyceride synthesis in part due to decreased de novo fatty acid synthesis resulting from inhibition on FAS. Whether tissue concentrations of active garlic components can achieve levels required to inhibit TG synthesis in vivo warrants further investigation.     

Suppression of hepatocyte fatty acid synthesis by albumin-bound linoleate involves depolymerization of acetyl-CoA carboxylase filaments

Digitonin treatment of chick liver cells in monolayer culture results in plasma membrane perforations due to digitonin removal of membrane cholesterol. The amount and rate of acetyl-CoA carboxylase activity that escapes from the hepatocyte during digitonin treatment is positively related to the amount of protomeric carboxylase in the cells. Incubation of chick liver cells in culture with albuminbound linoleate (60 min) caused a 3-fold increase in the amount of carboxylase activity released during exposure of cells to digitonin. Concomitant with the enhanced release of carboxylase activity was an 85% reduction in fatty acid synthesis induced by linoleate. Apparently, acute suppression of hepatocyte fatty acid synthesis by media free fatty acids resulted, in part, from a change in carboxylase conformation from the active polymeric state to the inactive protomeric form.     

Lipogenic enzyme activities in primary cultures of adult mouse hepatocytes

The effects of various unsaturated fatty acids such as oleic (18∶1n−9), linoleic (18∶2n−6) and arachidonic (20∶4n−6) on the activities of fatty acid synthetase (FAS), malic enzyme (ME), glucose-6-phosphate dehydrogenase (G6PDH) and 6-phosphogluconate dehydrogenase (6PGDH) all were determined in primary cultures of mouse hepatocytes. Activities of FAS and ME were found to decrease with time in culture regardless of whether hepatocyte donors were fed diets containing polyunsaturated fatty acid-free hydrogenated cottonseed oil (HCTO) or corn oil (CO). On the other hand, while G6PDH activity also declined in cultured hepatocytes obtained from HCTO-fed mice, the activity of this enzyme increased in cells cultured from CO-fed mice. 6PGDH activity was found to increase in hepatocytes obtained from both diet groups. Neither 18∶2 nor 20∶4 when added to media could alter FAS or ME activities compared with those observed with either 18∶1-containing or fatty acid-free media. Since lactic dehydrogenase activity and the rate of incorporation of [³H] leucine into FAS protein were unaltered with time in hepatocyte cultures, the decreased activities of FAS and ME cannot be attributed to a loss in cell viability during culture but rather appear to be specific for those enzymes which respond to diet hormones in vivo. Examination of the fatty acid contents of the cells after the culture period showed that the values for the ratios of 16∶0/16∶1 and of 18∶0/18∶1 were elevated when either 18∶2 or 20∶4 was added to the medium even though there was no evidence for elongation of the added 18∶2 or for 20∶4 being converted to 22∶4. This result suggest that Δ9-desaturase activity was inhibited by these polyunsaturated fatty acids and that conversion of 18∶2 to 20∶4 was not required for such action. The rate of synthesis determined by the relative rate of incorporation of [³H]leucine into FAS was two to five times higher in hepatocytes prepared from mice fed the HCTO diet than in hepatocytes from mice fed the CO diet. We have concluded that the mechanisms for long-term regulation may not be contained entirely within the liver.     

Effect of cold environment on hepatic microsomal Δ6 and Δ9 desaturase activity of male rats

Male rats maintained at 24 C and then shifted to 5 C for 5 days increased food intake and decreased in growth rate and food conversion. No modification was observed in Δ6 desaturase activity, while Δ9 desaturase activity decreased after this period of time. These results were confirmed by liver microsomal and mitochondrial fatty acid composition. The phospholipid composition of liver microsomes was unaltered, whereas in mitochondria, phosphatidylcholine and sphingomyelin decreased and phosphatidylethanolamine increased due to the cold environment. The influence of food intake and weight changes on fatty acid metabolism was studied using (i) rats maintained at 5 C with restricted food intake to match the food intake of those kept at 24 C with food ad libitum and (ii) rats maintained at 24 C whose food intake was also restricted so that their growth rate would be the same as that of rats maintained at 5 C with food ad libitum, respectively. These results indicate that the negative metabolic balance state of these cold conditions is not an active factor modifier of Δ6 desaturase activity, whereas it decreases Δ9 desaturase activity, reflecting the lipogenic characteristics of the latter enzyme.     

Effect of dietary fatty acids on Δ5 desaturase activity and biosynthesis of arachidonic acid in rat liver microsomes

The effect of different fatty acids supplemented to a fat-free diet on the activity of Δ5 desaturase was studied. Fat-free diet produces a reduction in the conversion of eicosa-8,11,14-trienoic acid to arachidonic acid. The addition of thecis-ω6 acids, linoleic, γ-linolenic or arachidonic to the diet produces an increase of eicosatrienoic acid desaturation, shifting Δ5 desaturase activity towards the controls on a balanced diet. This reactivation is apparently produced by induction of enzyme biosynthesis since linoleate effect was suppressed by simultaneous cycloheximide injection. On the contrary, no changes in Δ5 desaturation activity were found when the diet was supplemented with palmitic or 9-trans,12-trans-linoleic acid. The changes on the activity of Δ5 desaturase were compared with the fatty acid composition of plasma and liver microsomes.     

Linoleic acid metabolism in the spontaneously diabetic rat: Δ6-desaturase activity vs. product/precursor ratios

The activity of Δ6-desaturase of linoleic acid, a rate-limiting step in the formation of arachidonic acid, is decreased in animal models of severe, uncontrolled diabetes. The aim of the study was to measure the activity of liver microsomal Δ6-desaturase of spontaneously diabetic BioBreeding/Edinburgh rats receiving subcutaneous insulin daily and of genetically related nondiabetic animals. The activity of Δ6-desaturase was then compared with indices of activity (plasma lipid fatty acid product/precursor ratios) frequently used in human studies. Diabetic rats treated with insulin had 75±8% of the activity of microsomal Δ6-desaturase of nondiabetic controls (P<0.05). Insulin withdrawal tended to reduce the activity further (61% of control), although the activity did not differ from insulin-treated diabetic rats. The ratio of plasma phospholipid or cholesteryl ester γ-linolenic over linoleic acid was not decreased in insulin-treated diabetic rats. By contrast, the ratio of γ-linolenic over linoleic acid of microsomes was almost three-fold higher in insulin-treated diabetic rats (P<0.05). The γ-linolenic over linoleic acid ratio as an index of activity gave inconsistent results in insulin-deprived rats. The ratio of γ-linolenic over linoleic acid of cholesteryl esters did not differ between control and diabetic rats, nor did it correlate with microsomal Δ6-desaturase activity. Furthermore, the index of Δ6-desaturase activity, derived from the fatty acid composition of microsomal phospholipids, did not correlate with microsomal Δ6-desaturase activity. Diabetes, even when controlled by regular insulin injections, reduces the metabolism of linoleic acid, but the effect is less than previously published. The fatty acid compositions of plasma and liver microsomal lipids are not reliable indices of Δ6-desaturase activity in diabetes.     

Long-term feeding of dietary oils alters lipid metabolism, lipid peroxidation, and antioxidant enzyme activities in a teleost (Anabas testudineus bloch)

Anabas testudineus (climbing perch), average body weight 21±1 g, were maintained in culture tanks and fed a 35% protein feed plus an additional supplementation of three dietary oils (20% each of coconut oil, palm oil, or cod liver oil). Body weight gain was similar among all groups. However, several hepatic lipogenic enzymes such as malic enzyme (ME), NADP-isocitrate dehydrogenase (ICDH), glucose-6-phosphate dehydrogenase (G6PDH), 6-phosphogluconate dehydrogenase (6PGDH) and β-hydroxy-β-methyl glutaryl CoA reductase (HMG CoA reductase) were assayed, and they responded differently. Hepatic ME and G6PDH activities showed a significant decrease in the coconut oil and palm oil groups, but there was no significant change in ICDH activity. The 6PGDH activities were reduced, whereas HMG CoA reductase activity was increased in the palm oil-treated group. Cholesterol synthesis in the liver and muscle increased in the palm oil-treated group, but liver phospholipids did not show any significant change in fish supplemented with oils rich in saturated fatty acids. Triacyl-glycerol and free fatty acid concentrations were high in the coconut oil- and palm oil-supplemented groups. Lipid peroxidation products such as thiobarbituric acid-reactive substances and conjugated dienes decreased in the same two groups. Antioxidant potential was high in all groups as evidenced by increased activity of superoxide dismutase, glutathione peroxidase, and glutathione content. The results of this study indicate that in fish, dietary lipids depress hepatic lipogenic activity as well as lipid peroxidation products by maintaining high levels of antioxidant enzymes.     

The effect of dietary vitamin E supply and a moderately oxidized oil on activities of hepatic lipogenic enzymes in rats

Diets rich in polyunsaturated fatty acids (PUFA) are well known to suppress hepatic lipogenic enzymes compared to fat-free diets or diets rich in saturated fatty acids. However, the mechanism underlying suppression of lipogenic enzymes is not quite clear. The present study was undertaken to investigate whether lipid peroxidation products are involved in suppression of lipogenic enzymes. Therefore, an experiment with growing male rats assigned to six groups over a period of 40 d was carried out. Rats received semisynthetic diets containing 9.5% coconut oil and 0.5% fresh soybean oil (coconut oil diet, peroxide value 5.1 meq O₂/kg oil), 10% fresh soybean oil (fresh soybean oil diet, peroxide value 0.5 meq O₂/kg oil), or 10% thermally treated soybean oil (oxidized soybean oil diet, peroxide value 74 meq O₂/kg oil). To modify the antioxidant state of the rats, we varied the vitamin E supply (11 and 511 mg α-tocopherol equivalents per kg of diet) according to a bi-factorial design. Food intake and body weight gain were not influenced by dietary fat and vitamin E supply. Activities of hepatic lipogenic enzymes were markedly influenced by the dietary fat. Feeding either fresh or oxidized soybean oil diets markedly reduced activities of fatty acid synthase, (FAS), acetyl CoA-carboxylase, (AcCX), glucose-6-phosphate dehydrogenase, (G6PDH), 6-phosphogluconate dehydrogenase, and ATP citrate lyase (ACL) relative to feeding the coconut oil diet. Moreover, feeding oxidized soybean oil slightly, but significantly, lowered activities of FAS, AcCX, and ACL compared to feeding fresh soybean oil. Activities of hepatic lipogenic enzymes were reflected by concentrations of triglycerides in liver and plasma. Rats fed the coconut oil diet had markedly higher triglyceride concentrations in liver and plasma than rats consuming fresh or oxidized soybean oil diets, and rats fed oxidized soybean oil had lower concentrations than rats fed fresh soybean oil. The vitamin E supply of the rats markedly influenced concentrations of thiobarbituric acid-reactive substances in liver, but it did not influence activities of hepatic lipogenic enzymes. Because the vitamin E supply had no effect, and ingestion of an oxidized oil had only a minor effect, on activities of hepatic lipogenic enzymes, it is strongly suggested that neither exogenous nor endogenous lipid peroxidation products play a significant role in the suppression of hepatic lipogenic enzymes by diets rich in PUFA. Therefore, we assumed that dietary PUFA themselves are involved in regulatio of hepatic lipogenic enzymes. Nevertheless, the study shows that ingestion of oxidized oils, regardless of the vitamin E supply, also affects hepatic lipogenesis, and hence influences triglyceride levels in liver and plasma.     

Fatty acid and sterol synthesis by rat small intestine in vitro

Slices of rat jejunum were incubated with [2-¹⁴C]pyruvate, [1-¹⁴C]acetate, or [³H]H₂O to determine lipogenic activity. Under all conditions studied, pyruvate acted as a better precursor than acetate for fatty acid synthesis but not for the synthesis of sterol. Exogenous glucose significantly (P≤0.05) increased the conversion of both pyruvate and acetate to fatty acids. By contrast, fasting resulted in a decrease (p≤0.05) in lipogenic activity. The highest levels of lipogenesis were observed when [³H]H₂O + glucose at a concentration of 20 mM was used. From such experiments, the absolute rate of fatty acid synthesis in the tissue preparation was calculated: 734±54 nmoles acetyl units incorporated into fatty acids/g tissue/hr.     

Effect of tumor necrosis factor-α on triglyceride and phospholipid content and fatty acid composition of liver and carcass in rats

We have previously shown that a continuous infusion of tumor necrosis factor-α (TNF-α) in rats results in an increase in plasma triglyceride (TG), liver protein and DNA, and at the same time a reduction in muscle protein. However, there is no information on the associated effects of TNF-α on liver and muscle lipids. The present study, therefore, determined the effect of TNF-α on the TG and phospholipid (PL) content and their fatty acid composition, in the liver and carcass of rats and correlated with the plasma levels of insulin, corticosterone, and catecholamaines. Total parenteral nutrition that met the daily nutrient requirements was continuously infused for 10 d through a central vein catheter in two groups of rats, one receiving infused TNF-α (100 μg/kg/d) and a control group. Hepatic TG and PL, expressed either as mg/g dry weight or total organ content, were significantly increased in the TNF-α-infused group compared with controls. Livers of TNF-α infused rats contained significantly less saturated and monounsaturated fatty acids and significantly more polyunsaturated fatty acids (PUFA) of the ω3 and ω6 series than controls. The carcass, on the other hand, contained significantly more monounsaturated and significantly less polyunsaturated fatty acids of the ω6 series than controls. There were no changes in corticosterone level. Although plasma glucose levels were comparable between control and TNF-α infused rats, the latter had a marked increase in insulin levels, demonstrating insulin resistance. In addition TNF-α infused rats had raised norepinephrine levels. The fall in carcass and rise in liver TG and PL are consistent with the presence of insulin resistance and raised norepinephrine levels. However, the increase in PUFA content of the liver, especially the increase in 20∶4ω6 levels in liver PL and TG, is likely to be the effect of TNF-α and suggests increased activity of Δ5-desaturase.     

The effect of kind of dietary carbohydrate upon the composition of liver fatty acids of the rat

Weanling male rats were fed fat-free diets containing either starch, sucrose, glucose or maltose as principal ingredient. One fourth of each group was fed oral supplements of linoleate. Subgroups of the fat-free groups were killed at 1, 3 and 6 weeks and the lmoleate supplemented group also at 6 weeks. Liver fatty acids were analyzed by gas chromatography. All groups showed changes in fatty acid composition characteristic of essential fatty acid deficiency, and linoleate reversed these changes. The three sugars induced similar compositions of liver fatty acids, but starch stimulated appearance of higher proportions of several odd-chain fatty acids. These included 15:0, 15:1, 17:0, 17:1, 17:2, 19:0, 19:1, 19:2, 19:3 and 19:4. These changes could not be accounted for by their content in the dietary starch. Presented at the AOCS meeting, Houston, April, 1965. Visitor under the AID Program of the United States State Department.     

Effect of eicosa-5,8,11,14-tetraynoic acid on fatty acid composition of selected organs in the rat

Eicosa-5,8,11,14-tetraynoic acid or arachidonic acid or no supplement (controls) was given orally to rats maintained on a fat free diet and the fatty acid composition of total lipids of several organs determined. No changes were noted in the total fatty acid concentrations of the organs examined in the various groups. A decrease in the amount of arachidonic acid, 22∶4ω6 and 22∶5ω6 (as percent of total fatty acids), and an increase in the amount of 20∶3ω6 and linoleate were observed in total lipids of several organs. In the group receiving the arachidonate supplement, there was less linoleate and 20∶3ω6 and more arachidonate than in the controls. Both eicosa-5,8,11,14-tetraynoic acid and arachidonate supplements resulted in a decrease in 20∶3ω9 in most organs studied. Generally, the most marked changes were seen in liver but, of the other organs examined (heart, kidney, testis, brain, and adrenals), only the adrenals failed to show any significant differences between the controls and each of the two supplemented groups. Although the experimental conditions preclude conclusive interpretation of the changes observed, it is suggested that eicosa-5,8,11,14-tetraynoic acid was effective in inhibiting the conversion of linoleate to arachidonate and the conversion of arachidonate to 22∶4 and 22∶5.     

Effect of nutritional status on the fatty acid composition of rat liver and cultured hepatocytes

The lipid concentration and fatty acid composition of the whole liver and of cultured hepatocytes isolated from the livers of rats fed ad libitum (fed), fasted for 24 hr (fasted), or fasted for 48 hr and then refed a fat-free, high carbohydrate diet for 48 hr (refed) was studied. Hepatocytes were maintained as monolayer cultures in serum-free, lipid-free media and their fatty acid composition was analyzed at 3, 24, 48, 72 and 96 hr. The livers of fed animals, as well as their hepatocytes, contained less total lipid than those from animals on either of the other dietary regimes. Livers of fasted animals had three times the amount of lipid found in the livers of fed animals, and the livers of refed animals contained five times the amount of lipid as the livers of fed animals (all based on mg lipid/g wet weight of liver). The fatty acid composition of hepatocytes after 3 hr of culturing was very similar to that of fresh liver when compared in each of the dietary regimes. However, while the fatty acid compositions of livers and hepatocytes from fed and fasted animals were similar, the pattern in liver of refed animals was quite distinct from that of the fed animals. In the fed and fasted animals palmitic acid (16∶0), stearic acid (18∶0), oleic acid (18∶1[n-9]), linoleic acid (18∶2[n-6]) and arachidonic acid (20∶4[n-6]) were the major fatty acids of the liver; in refed animals 16∶0, palmitoleic acid (16∶1[n-7]), 18∶0, 18∶1(n-9) andcis-vaccenic acid (the n-7 isomer of oleic acid) were the major fatty acids. During maintenance in culture the 18∶1(n-9) content of the hepatocytes increased in cells from livers of animals on all three dietary regimes. The polyunsaturated fatty acid content was similar in fresh livers and isolated hepatocytes in all samples when compared on the basis of μg fatty acid/mg of hepatocyte or liver protein. It was also found that the polyunsaturated fatty acid content of hepatocytes was remarkedly stable with time of culture when the cells were incubated in serum-free, lipid-free medium. Thus, isolated hepatocytes maintained in serum-free medium appear to be a possible system for the evaluation of the effects of prior nutritional status on fatty acid metabolism in the whole animal, not subject to hormonal and other somatic influences which often complicate the interpretation of such nutritional studies.