obesity is known to present an inflammatory process of low grade , with elevated levels of cytokines such as interleukin 6 ( il-6 ) , tumor necrosis factor alpha ( tnf- ) , and interleukin 1 beta ( il-1 ) , contributing to the pathogenesis of important disturbances of the obese condition , as insulin resistance and metabolic defects . this inflammatory state has been described to induce elevated signaling through the toll - like receptors tlr2 and tlr4 , with activation of the nuclear factor b ( nfb ) pathway in muscle , liver , and adipose tissue [ 14 ] . in this inflammatory pathway , tlr2/4 binding to the myeloid differentiation factor-88 ( myd88 ) leads , after some intermediate steps , to the recruitment of the tumor necrosis factor receptor - associated factor-6 ( traf6 ) . its interactions with several proteins leads to phosphorylation of the inhibitory factor ib , which is then targeted for proteosomal degradation , releasing nfb , whose p65 subunit undergoes phosphorylation and translocates to the nucleus , where it binds to its target genes to produce proinflammatory cytokines . importantly , prolonged intake of saturated or trans fats has also been associated with nfb / myd88 pathway - mediated induction of inflammatory cytokines in the hypothalamus and cytokine - induced impairment of central insulin hypophagia [ 610 ] . the hypothalamus is a key regulator of energy homeostasis , through the production of orexigenic and anorexigenic neuropeptides targeted by the peripheral hormones leptin and insulin , which exert a pivotal control food intake and energy expenditure . we have shown that the disruption of these hypothalamic mechanisms , including insulin , leptin , and serotonin systems , is associated with obesity [ 1116 ] . the consequences of the dietary consumption of excess polyunsaturated fats to the central control of energy homeostasis have been addressed by few studies . we have recently explored this matter and found that a high - fat diet containing soy oil , a source of omega-6 polyunsaturated fatty acids ( pufas ) , induced an obesogenic profile of hypothalamic neuronal activation , as evaluated by c - fos immunoreactivity . on the other hand , a fish oil - enriched diet , a source of omega-3 pufas , abolished serotonin - induced hypophagia and impaired hypothalamic serotonin turnover and 5-ht 2c receptor levels . we have also shown that the high - fat soy - oil diet inhibited insulin - induced hypophagia and akt serine phosphorylation , while the fish - oil diet prevented these alterations . whether these divergent effects of the diets are linked to differential inflammatory signaling in the hypothalamus has not been explored . the aim of the present study was to investigate in rats the effects of the long - term consumption of high - fat diets , enriched with either soy oil ( n-6 pufas ) or fish oil ( n-3 pufas ) , on the hypothalamic expression of proteins involved in the inflammatory pathway . additionally , liver and muscle tissue were studied , since little is known about the effects of polyunsaturated fat diets on the modulation of inflammatory status in these tissues . the experimental research committee of the federal university of so paulo approved all animal procedures . they were housed five per cage under 12  h light - dark cycle , at 22  1c , and with free access to food and water . the 2-month - old male wistar rats were randomly assigned to receive one of three ad libitum diet treatments for 8 weeks : balanced chow ( 2.8  kcal / g , 15%  kcal from fat , nuvilab , brazil ) or high - fat diets ( 3.5  kcal / g , 50% kcal from fat ) enriched with 20% ( w / w ) of either soy oil ( liza , cargill agrcola , brazil ) or fish oil ( ropufa  75  -3 , roche , dsm nutritional products , brazil ) to the standard chow . casein was added to both high - fat diets ( 20% , w / w ) , to achieve the same protein content of the control chow , and butylated hydroxytoluene ( 0.02% of added oil ) was added as an antioxidant agent . the fatty acid composition of the diets was determined by gas chromatography , as previously detailed [ 12 , 18 ] . the data showed a high percentage of n-3 pufas in the fish diet , mainly eicosapentaenoic acid ( epa ) and docosahexaenoic acid ( dha ) , whereas the soy and the control diets had high percentages of n-6 pufas , mainly linoleic acid ( la ) . at the end of the 8-week diet treatment , serum nonesterified free fatty acids ( nefa ) levels were quantified by colorimetric method ( zenbio , nc , usa ) . serum endotoxin was assayed using chromogenic limulus amebocyte lysate kit ( cambrex bio science , md , usa ) , as previously detailed . the hypothalamus , liver , and gastrocnemius muscle were homogenized and centrifuged at 12 ,  000  g for 40  min at 4c . protein concentration of the supernatants was determined using bca assay ( bio - rad , hercules , california , usa ) with bovine serum albumin as standard . tnf- , il-1 , il-6 , and il-10 contents were assayed by elisa in 100  l aliquots ( duoset elisa , r&d systems , minneapolis , mn , usa ) , following the recommendations of the manufacturer . the hypothalamus was homogenized in solubilization buffer containing protease inhibitors and centrifuged at 12,000  g for 35  min at 4c . 75  g of protein was resolved in 8 or 10% sds - page and electrotransferred to nitrocellulose membranes . the membranes were incubated overnight at 4c with primary antibody against tnf-r , il-6r , il-10r , tlr2 , tlr4 , myd88 , traf6 , nfbp50 , or nfbp65 ( santa cruz biotechnology , ca , usa ) . the bands detected by chemiluminescence were quantified by optical densitometry of developed autoradiographs ( scion image software , scion corporation , frederick , usa ) . for the evaluation of protein loading , the statistical analysis was performed using the graphpad prism statistics software package version 5.0 for windows ( graphpad software , san diego , ca , usa ) . comparisons among control , soy , and fish groups were performed by one - way anova followed by tukey 's test for multiple comparisons . at the end of diet treatment , body mass was significantly higher in the soy group than that in both the control ( + 45% ) and the fish oil ( + 42% ) groups ( figure 1(a ) ) . the fish oil group had significantly lower serum nefa levels than both the control ( 22% ) and the soy oil ( 39% ) groups ( figure 1(b ) ) . the fish oil group had reduced hypothalamic protein levels of tnf- ( 61% ) and il-6 ( 49% ) when compared to the control group ( figures 2(a)-2(b ) ) . levels of il-10 , il1- , tnf-r , and il-6r were similar among the studied groups ( figures 2(c)2(f ) ) . il-10r levels were 21% higher in the fish than in the control group ( figure 2(g ) ) . no significant differences were observed among the groups in hypothalamic protein levels of tlr2 , tlr4 , myd88 , and nfbp50 ( figures 3(a)3(c ) and 3(e ) ) . traf6 levels were higher in the soy than those in the control and fish oil groups ( 25% and 27% , resp . , figure 3(d ) ) while nfbp65 levels were 73% higher in the soy than those in the control group ( figure 3(f ) ) . il-6 were significantly lower in the fish oil than those in the control group ( figures 4(a)-4(b ) ) while muscle il-10 levels were increased in both the soy and the fish groups ( figure 4(c ) ) . liver levels of tnf- and il-6 were significantly lower in both the fish and the soy groups than those in the control group ( figures 4(d)-4(e ) ) while liver il-10 levels were similar among groups ( figure 4(f ) ) . since hypothalamic inflammation induced by intake of saturated and trans fat diets has been associated with hypothalamic leptin and insulin resistance and obesity , the main objective of the present study was to ascertain the effect of high - fat pufa diets on inflammatory parameters in the hypothalamus of rats . we compared diets prepared with soy and fish oils , used to promote diet enrichment with either n-6 or n-3 series pufas , as previously determined [ 1618 ] . the soy diet induced increased hypothalamic levels of traf6 and nfbp65 , findings indicative of local stimulation of the nfb pathway . on the other hand , the fish diet led to diminished hypothalamic levels of traf6 and of the inflammatory cytokines tnf- and il-6 , along with enhanced levels of the receptor protein for il-10 , an anti - inflammatory cytokine . these findings agree with the report of induction of inflammatory process after intracerebroventricular administration of the n-6 pufa linoleic acid but not of the n-3 pufa linolenic acid to rats for 3 days . interestingly , unlike the effects of saturated fat - feeding [ 69 ] , in the present experiments , the levels of tnf- , il-1 , and il-6 , as well as of their receptor proteins , were not altered in the hypothalamus of the soy - diet rats , in agreement with previous data . intermediates of the nfb pathway have been shown to affect insulin signal transmission , as ikk was able to both induce serine phosphorylation of irs-1 and upregulate socs3 ( suppressor of cytokine signaling ) in the hypothalamus of mice fed high - fat saturated diet . moreover , the inclusion of an n-3-rich oil in a saturated high - fat diet reversed the diet - induced hypothalamic inflammation and improved insulin and leptin signaling , through binding to the transmembrane g - protein - coupled receptor 120 ( gpr120 ) [ 20 , 21 ] . since hypothalamic inflammation has been associated with central insulin resistance [ 610 ] , the present data are also in line with our previous work , reporting impairment of hypothalamic insulin signaling and abolition of insulin hypophagia by the soy diet while the fish diet exerted a protective effect . the present results thus showed that a pufa - rich hyperlipidic diet based on soy oil induced an inflammatory process in the hypothalamic tissue , in a fashion similar to previously reported for saturated diets . this inflammatory status probably contributed to the impairment of feeding - controlling mechanisms and body adiposity previously reported as well as the increased body mass herein observed . on the other hand , the hypothalamus was spared of the inflammation induced by the soy diet when the excess fat was substituted for fish oil , in agreement with our earlier findings of normal insulin - induced hypophagia . differently from the hypothalamic tissue , in liver and muscle both the soy and the fish diets led to reduced levels of proinflammatory proteins . this agrees with data in human skeletal muscle , in which modulation of inflammatory mediators by la ( 18  :  2n-6 ) and dha acid ( 22  :  6n-3 ) has been associated with increased muscle fat oxidation and glucose uptake . other authors have also shown that n-3 pufas reduced several proinflammatory markers in human heart muscle [ 23 , 24 ] . in liver , omega-3 fatty acids have been shown to reduce inflammatory mediators to prevent hepatic insulin resistance . the results showed that the high - fat soy diet induced activation of the hypothalamic nfb inflammatory pathway , probably predisposing to the disturbances leading to obesity . on the other hand , the high - fat fish diet improved the central and the peripheral inflammatory profile via reduction of intracellular inflammatory mediators , suggesting a protection against obesity .
whether pufa diets affect inflammatory mediators in central and peripheral sites is not clear . 
 we investigated the effect of high - fat pufa diets on the expression of proteins involved in inflammatory pathways in hypothalamus , muscle , and liver . 
 male rats were fed for 2 months with either chow or high - fat diets enriched with either soy ( n-6 pufas ) or fish oil ( n-3 pufas ) . 
 the fish group had normal body weight , low serum nefa , reduced hypothalamic levels of tnf- , il-6 , and traf6 , and increased levels of il-10 receptor . in contrast , the soy group had increased body weight and hypothalamic levels of traf6 and nfbp65 . in muscle , the fish diet reduced tnf- and il-6 levels . both pufa diets increased muscle il-10 levels and reduced liver tnf- and il-6 levels . 
 the data showed that the high - fat soy diet induced activation of the hypothalamic nfb inflammatory pathway , a feature predisposing to feeding and energy expenditure disturbances associated with the development of obesity . on the other hand 
 , the high - fat fish diet improved the central and the peripheral inflammatory profile via reduction of intracellular inflammatory mediators , suggesting a protection against obesity .