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Biochemical and Molecular Actions of Nutrients

Palmitate Activates the NF-B Transcription Factor and Induces IL-6 and TNF Expression in 3T3-L1 Adipocytes¹

Department of Animal Sciences, Center for Comparative Medicine, Purdue University, West Lafayette, IN 47907-2054

²To whom correspondence should be addressed. E-mail: spurloc0{at}purdue.edu.

	ABSTRACT

TOP ABSTRACT MATERIALS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 
Fatty acids and their metabolites regulate gene expression and immunological pathways. Furthermore, obese individuals frequently have increased circulating fatty acid concentrations, and localized inflammation in adipose tissue may facilitate the systemic inflammation associated with the insulin resistance of obesity. Although palmitate induces inflammation (i.e., activates proinflammatory pathways) in myotubes, the effects of fatty acids on inflammatory processes in adipocytes have not been established. Therefore, we examined the potential for palmitate, laurate, and docosahexaenoic acid (DHA) to modulate inflammation in 3T3-L1 adipocytes. Palmitate, but not DHA or laurate, induced nuclear factor B (NF-B)-driven luciferase activity and interleukin-6 (IL-6) expression (P < 0.05). Inhibition of fatty acyl Co-A synthase (FACS) with triacsin C suppressed palmitate-induced NF-B activation (P < 0.05), but caused an additive increase in palmitate-induced IL-6 expression (P < 0.05). Disrupting mitogen-activated protein kinase/Erk kinase (MEK) and protein kinase C (PKC) activity with U0126 and Bisindolylmaleimide (Bis), respectively, suppressed palmitate-induced IL-6 expression (P < 0.05), but had no effect on NF-B reporter gene activity (P > 0.05). However, the phosphoinositide-3 kinase (PI3K) inhibitor, wortmannin, alone and additively with palmitate, activated the NF-B reporter gene and induced IL-6 expression (P < 0.05). Palmitate also induced the mRNA expression of tumor necrosis factor (TNF) (P < 0.05), but the increase in mRNA abundance was not reflected in a greater protein concentration in the media (P > 0.05). These data indicate that palmitate induces inflammation in adipocytes, and that this is not a generalized effect of all SFA. Furthermore, PI3K may act constitutively to suppress inflammation. Consequently, inhibition of this enzyme may promote and exacerbate the inflammation in adipose tissue that is associated with obesity and insulin resistance.

KEY WORDS: • NF-B • fatty acids • cytokines • adipocyte • inflammation

The potential contribution of fatty acids to the mechanisms underlying impaired glucose metabolism has been described in the so-called Randle effect (1). In addition, fatty acids suppress insulin-stimulated glucose uptake in multiple cell types (2), and it is well established that metabolic disorders, including dyslipidemias, obesity, and diabetes, are often accompanied by elevated serum concentrations of fatty acids (3). Because these diseases are also characterized by marked increases in serum concentrations of inflammatory mediators, including tumor necrosis factor (TNF),³ interleukin-6 (IL-6), sialic acid, and C-reactive protein (4–6), they are commonly referred to as inflammatory states (7,8).

Recent publications showed that palmitate induces insulin resistance in myotube models (9,10), and that the nuclear factor B (NF-B) transcription factor is a key mediator of this effect (10,11). However, insulin-induced glycogen synthesis and activation of Akt/protein kinase B (PKB) are not responsive to palmitate in 3T3-L1 adipocytes (9), but are clearly suppressed by this fatty acid in myotubes (10). Therefore it is apparent that the mechanisms underlying fatty acid–induced insulin resistance in myofibers and adipocytes may differ.

Adipose tissue is a major source of proinflammatory cytokines, particularly in obesity (8). Considering this link between obesity and adipose production of inflammatory mediators, it is of great interest that lauric acid (12) and palmitate (11) induce cyclooxygenase (i.e., COX-2) and IL-6 expression in macrophages and muscle, respectively. Some fatty acids also oppose insulin-mediated glucose uptake (13) and activate inhibitor B kinase (IKK) (14), the kinase that marks inhibitor B (IB) for proteolytic degradation to enable NF-B function. Whether the same regulatory linkages exist in the adipocyte has not been addressed experimentally. We showed previously that NF-B is a major inflammatory mediator in primary porcine adipocytes (15) and in 3T3-L1 adipocytes (16). Thus, considering that palmitate activates NF-B in myotube cultures (10,11), we hypothesized that fatty acids would activate NF-B in the adipocyte and induce TNF and IL-6 production. The data presented herein indicate clearly that palmitate, at physiological concentrations, activates NF-B and induces proinflammatory cytokine production in adipocytes. Furthermore, the importance of specific kinase-regulated pathways is indicated.

	MATERIALS AND METHODS

TOP ABSTRACT MATERIALS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 
    3T3-L1 adipocyte culture. Cells (3T3-L1) were obtained from the American Type Culture Collection and were grown in 24-well plates according to standard conditions. Briefly, cells were grown in 5% CO₂ in DMEM (GIBCO) containing 10% calf serum (GIBCO) in the presence of a 1% penicillin/streptomycin mixture (Invitrogen). At 2 d postconfluence (d 0), cells were induced to differentiate with a medium containing 10% fetal bovine serum (FBS; GIBCO), 1.7 µmol/L insulin, 1 µmol/L dexamethasone, and 0.5 mmol/L isobutylmethylxanthine for 48 h. Thereafter, fresh medium containing only insulin was added every 2 d for another 4 d. On d 8, cells were fully differentiated and the medium was changed to an insulin-free medium containing 10% FBS.

    Cell transfection and reporter assay. On d 5 after induction of differentiation, cells were transfected with Fugene 6 reagent (Roche) for 48 h with pNF-B-Luc plasmid (0.25 µg/well), with the firefly luciferase gene under the control of 5 repeats of the NF-B (TGGGGACTTTCCGC) enhancer element (Stratagene). Transfection efficiency was normalized by cotransfecting cells (0.05 µg/well) with pRL-CMV vector (Promega), a plasmid encoding the renilla luciferase gene under the CMV promoter. For all experiments, the firefly luciferase luminescence was normalized with the renilla using the Dual luciferase assay system (Promega). Experiments on the fully differentiated cells were conducted on d 8. Cells were pretreated with serum-poor medium (0.25% FBS) for 12 h before treatments were applied. Media and the cell lysate were recovered for ELISA and the luciferase assay, respectively. A fatty acid–bovine serum albumin (BSA) complex (ratio 3:1) was prepared according to the method of Rakatzi et al. (17). Briefly, 45 µmol of palmitate was converted into its sodium salt in the presence of 0.1 mol/L NaOH. This was added to a prewarmed 10% fatty acid–free BSA solution. The solution was sonicated in quick bursts, allowed to cool to room temperature, and then sterile filtered.

    Cytokine ELISA. Media concentrations of IL-6 and TNF were measured using mouse-specific ELISA kits (Pierce Endogen) according to the manufacturer’s protocols.

    Real time quantitative PCR. Total RNA was recovered from cells using the Trizol reagent (Invitrogen) and Dnase treated using Turbo Dnase® (Ambion). RNA was reverse transcribed using the Superscript^TM first-strand cDNA synthesis kit (Invitrogen). Primer sequences for mouse IL-6 were 5'-AACGATGATGCACTTGCAGA-3' and 5'-GAGCATTGGAAATTGGGGTA-3', for the sense and antisense primers, respectively (18). Sense and antisense primers for ß-actin and TNF were, for ß-actin, 5'-ATG GGT CAG AAG GAC TCC TAC G-3' and 5'-AGT GGT ACG ACC AGA GGC ATA C-3', respectively, and for TNF, 5'-TCC CCA AAG GGA TGA GAA GTT C-3' and 5'-TCA TAC CAG GGT TTG AGC TCA G-3', respectively, as reported earlier (19). Thermal cycling conditions for the PCR reactions were 94°C for 5 min followed by 40 cycles of 94°C for 45 s, 61°C for 30 s, and 72°C for 30 s. Polymerase reaction products amplified by these primers (283, 308, and 411 bp for IL-6, ß-actin, and TNF, respectively) were cloned into pGEMT vector (Promega) and sequenced for verification. Real-time reactions were carried out on an iCycler real-time machine (Biorad) using the IQ^TM SYBR® Green Supermix kit (Biorad). The abundance of each gene product was calculated by regressing against the standard curve generated in the same reaction with their respective plasmids. The IL-6 and TNF values for each sample were normalized to ß-actin.

    Statistical analyses. Data were examined for normality and analyzed using the mixed-model analysis of a split-plot design. The fixed effect was the treatment, and the random effect was the replicate. The main effects (treatment and replicate) were tested against the treatment x replicate interaction term. When protected by a significant F-test, mean separation was accomplished using the least-squares mean separation (pdiff) procedure (20). Differences were considered significant at P < 0.05. Values in the text are means ± SEM.

	RESULTS

TOP ABSTRACT MATERIALS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 
The NF-B transcription factor is critical for the activation for cytokine gene expression; to characterize its regulation by fatty acids, we tested the potential for DHA, laurate, and palmitate to activate an NF-B–driven luciferase reporter gene construct. We also used Escherichia coli–derived LPS as a positive control. LPS and palmitate caused 2.5- and 3.5-fold increases, respectively, in luciferase activity (P < 0.05), whereas DHA and laurate had no effect (Fig. 1A). Thereafter, we examined the induction of cytokine release by these treatments (Fig. 1B). Both LPS and palmitate increased the accumulation of IL-6 in the culture media (P < 0.05); consistent with the lack of stimulation of NF-B reporter gene activity, DHA and laurate again had no effect. Because DHA antagonizes the onset and progression of inflammation in some cell types (21), we determined the extent to which DHA modulates inflammatory responses to LPS and palmitate in adipocytes (Fig. 2A). DHA attenuated (P < 0.05) the induction of the NF-B reporter gene by palmitate, but did not antagonize the LPS response. Furthermore, the attenuation of palmitate- or LPS-induced NF-B activation by DHA occurred without a concomitant reduction in IL-6 mRNA abundance (Fig. 2B).

View larger version (13K): [in this window] [in a new window]   FIGURE 1 Activation of an NF-B–driven luciferase reporter construct and induction of IL-6 media accumulation by fatty acids. (A) Fully differentiated 3T3-L1 adipocytes kept in a serum-poor medium (0.25% FBS) overnight were treated as indicated with LPS (100 µg/L), and 250 µmol/L DHA, palmitate, and laurate for 24 h. Firefly luminescence was normalized to renilla. Data are expressed relative to control. (B) Media IL-6 concentration in adipocytes treated as in A. Bars represent means + SEM, n = 4 replicates. Means without a common letter differ, P < 0.05.

View larger version (13K): [in this window] [in a new window]   FIGURE 2 Regulation of LPS and palmitate-induced NF-B luciferase activity and IL-6 media accumulation by DHA. Adipocytes in a serum-poor medium were pretreated for 6 h with 250 µmol/L DHA, and thereafter treated as indicated with LPS (100 µg/L) and 250 µmol/L palmitate for 24 h. (A) Normalized firefly luciferase activity. (B) Media IL-6 concentration. Bars represent means + SEM, n = 3 (A) or 4 (B) replicates. Means without a common letter differ, P < 0.05.

View larger version (16K): [in this window] [in a new window]   FIGURE 3 Dose dependency of induction of IL-6 and TNF protein accumulation and mRNA expression by palmitate. Adipocytes were treated in serum-poor medium with palmitate (0.125, 250, and 500 µmol/L) for 24 h. Media and mRNA were collected. (A) IL-6 mRNA expression. Expression was normalized to ß-actin. (B) Media IL-6 concentration. (C) TNF mRNA expression. TNF mRNA was normalized to ß-actin. (D) TNF accumulation in the media. Bars represent means + SEM, n = 4 replicates. Means without a common letter differ, P < 0.05.

View larger version (12K): [in this window] [in a new window]   FIGURE 4 Regulation of palmitate-induced NF-B luciferase activity and IL-6 media accumulation by triacsin C. 3T3-L1 adipocytes in serum-poor medium were pretreated for 2 h with 10 µmol/L triacsin C and thereafter treated as indicated with 250 µmol/L palmitate for 24 h. (A) NF-B luciferase activation. (B) Media IL-6 concentration. Bars represent means + SEM, n = 6 replicates. Means without a common letter differ, P < 0.05.

View larger version (13K): [in this window] [in a new window]   FIGURE 5 Regulation of palmitate-induced NF-B activation and IL-6 media accumulation by kinase inhibitors. Pharmacological inhibitors to MEK (U0126), PKC (Bis), and PI3K (wortmannin) were used to pretreat cells for 1 h at concentrations of 15, 20, and 1 µmol/L, respectively, before adding palmitate (250 µmol/L) for 24 h. (A) Normalized NF-B luciferase activation. (B) Media IL-6 concentration. Bars represent means + SEM, n = 3 (A) or 6 (B) replicates. Means without a common letter differ, P < 0.05.

	DISCUSSION

TOP ABSTRACT MATERIALS AND METHODS RESULTS DISCUSSION LITERATURE CITED

Collectively, the data indicate that the mechanism by which palmitate activates NF-B in adipocytes is independent of that by which IL-6 release into the culture medium is induced. DHA disrupted NF-B activation by palmitate, whereas it was inconsequential in stimulating IL-6 release. Similarly, the kinase inhibitor data indicate that activation of NF-B was largely independent of MEK and PKC activity, but IL-6 release was blocked by inhibition of either kinase. Finally, the activation of NF-B by palmitate required FACS activity (and presumably, formation of palmitoyl CoA), whereas the stimulation of IL-6 release was enhanced by inhibition of this enzyme. However, when the regulation of NF-B and IL-6 were discordant, we acknowledge the possibility that NF-B or cytokine mRNA changes were perhaps transient. Nonetheless, it is quite likely that dietary and pharmacological strategies aimed at alleviating inflammation in adipocytes must of necessity target multiple inflammatory pathways.

Mechanistically, several points are pertinent to the activation of NF-B and induction of IL-6. Palmitate is readily incorporated into diacylyglycerol and activates PKC in some cell types (29–30). Furthermore, the activation of IKK, a pivotal step in the activation of NF-B, by PKC in 3T3-L1 adipocytes is well established (14). Palmitate is also required for ceramide synthesis (9), and ceramide activates NF-B in macrophages (31). However, the IL-6 promoter is regulated by multiple transcription factors, including C/CAAT enhancer binding protein, activator protein-1 (AP-1), and cyclic AMP response element binding protein, with NF-B acting as the terminal signal for the activation of the enhanceosome (32). In the present study, the palmitate-induced accumulation of IL-6 was regulated independently of NF-B activation, and earlier work in our laboratory, albeit with a primary pig adipocyte model, showed a clear disruption of the LPS-induced IL-6 expression by inhibition of MEK with no apparent reduction in NF-B activation. This seemingly indicates the importance of AP-1 or other components of the enhanceosome in the regulation of IL-6 production in adipocytes. Thus, strategies to control IL-6 production in these cells must extend beyond the regulation of NF-B; given that the accumulation of IL-6 in the media was blocked by inhibition of MEK or PKC, these pathways may be particularly important to the overall control of inflammation in adipocytes.

Weigert et al. (11) showed that free (i.e., nonacylated) palmitate per se is responsible for the induction of IL-6 expression in human myotubes, and because activation of NF-B was required for the IL-6 response, it would seem that free palmitate also led to the activation of NF-B. However, in our adipocyte model, disrupting acylation of palmitate with the FACS inhibitor actually antagonized the NF-B–driven reporter gene activity while augmenting the accumulation of IL-6 in the culture media. As noted above, these findings in adipocytes indicate the discoordinate regulation of NF-B and IL-6 production, and underscore the importance of other pathways. These potential regulatory differences between adipocytes and myocytes also highlight the necessity of detailed mechanistic studies of inflammation in specific cell types.

An additional major finding of this study pertains to the regulation of NF-B and IL-6 production by palmitate and wortmannin. Lee et al. (21) determined that lauric acid activated NF-B and induced COX-2 expression via a Tlr4 signaling pathway that is coupled to PI3K-Akt signaling in RAW264.7 macrophages. Our findings in 3T3-L1 adipocytes are inconsistent with these results obtained using the RAW264.7 macrophage and 293T cell models. In adipocytes, lauric acid was an ineffective activator of NF-B and did not induce IL-6 accumulation in the medium. However, palmitate and wortmannin, a potent inhibitor of PI3K, acted additively to stimulate both NF-B reporter gene activity and IL-6 accumulation in the medium. Others (33) obtained similar results in that inhibition of the PI3K-Akt pathways enhances the transcriptional activity of NF-B (p65) in human monocytic cells. Thus, inhibition of PI3K, rather than activation, is associated with activation of NF-B and the induction of IL-6 in adipocytes and human monocytes. It is possible that palmitate partially inhibits PI3K, and that wortmannin further suppresses activity of this enzyme. This is consistent with the induction of insulin resistance by palmitate, and we are currently testing this hypothesis.

Finally, we also determined that palmitate induces the mRNA expression of TNF in adipocytes. However, the release of this proinflammatory cytokine into the culture medium was actually attenuated by palmitate in a dose-dependent manner, at least within the time line of the experiments conducted. Although we cannot rule out the possibility that degradation of the cytokine in the media affected measurable concentrations at the chosen endpoint, several additional points are pertinent. Xu et al. (34) showed that obesity is associated with suppressed cleavage of transmembrane TNF from adipocytes. It seems possible that although the higher concentrations of palmitate induced TNF expression, there was a concomitant disruption of transmembrane cleavage that was reflected in lower concentrations in the media. It is also possible that IL-6 released into the culture medium acted directly or indirectly in autocrine fashion to suppress palmitate-induced release of TNF into the culture medium. IL-6 was shown previously to exert an anti-inflammatory effect through suppression of TNF production in skeletal muscle (35). However, these possibilities must be addressed directly in adipocytes.

In summary, the data presented herein support 3 major points regarding inflammation in adipocytes. First, the induction of markers of inflammation by palmitate, but not laurate or DHA, indicates that fatty acid–induced inflammation in adipocytes is not a generalized feature of fatty acids, but rather a specific one. Second, that the activation of the NF-B and the induction of IL-6 release into the media are differentially regulated by inhibition of FACS indicates that 2 independent mechanisms are responding to acylated vs. nonacylated (free) palmitate. Finally, our data indicate clearly that the PI3K pathway is linked directly to the regulation of inflammation in adipocytes. The relevance of these findings in vivo remains to be determined, but our results implicate palmitate in the inflammation in adipose tissue that accompanies obesity.

	ACKNOWLEDGMENTS

 
The authors are grateful to Paul Collodi, Young-Cheul Kim, and Jill Hutchcroft for helpful discussions of the data and their evaluations of the manuscript. We also appreciate the advice of Young-Cheul Kim and Nick Gabler with respect to the 3T3-L1 culture system.

	FOOTNOTES

 
¹ Supported by Purdue University Agricultural Research Program # 2005–17559.

³ Abbreviations used: AP-1, activator protein-1; Bis, Bisindolylmaleimide; BSA, bovine serum albumin; COX, cyclooxygenase; DHA, docosahexaenoic acid; FACS, fatty acyl Co-A synthase; FBS, fetal bovine serum; IB, inhibitor B; IKK, inhibitor B kinase; IL-6, interleukin-6; MEK, mitogen-activated protein kinase/Erk kinase; NF-B, nuclear factor B; PI3K, phosphoinositide-3 kinase; PKB, protein kinase B; PKC, protein kinase C; TNF, tumor necrosis factor .

Manuscript received 15 February 2005. Initial review completed 3 March 2005. Revision accepted 17 May 2005.

	LITERATURE CITED

TOP ABSTRACT MATERIALS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 

1. Randle, P. J., Priestman, D. A., Mistry, S. C. & Halsall, A. (1994) Glucose fatty acid interactions and the regulation of glucose disposal. J. Cell. Biochem. 55(suppl.):1-11.

2. Arner, P. (2002) Insulin resistance in type 2 diabetes: role of fatty acids. Diabetes Metab. Res. Rev. 2(suppl.):S5-S9.

3. Mook, S., Halkes, C.J.C., Bilecen, S. & Cabezas, M. C. (2004) In vivo regulation of plasma free fatty acids in insulin resistance. Metabolism 53:1197-1201.[Medline]

4. Ekin, S., Mert, N., Gunduz, H. & Meral, I. (2003) Serum sialic acid levels and selected mineral status in patients with type 2 diabetes mellitus. Biol. Trace Elem. Res. 94:193-201.[Medline]

5. Lo, H. C., Lin, S. C., Wang, Y. M., Lo, H. C., Lin, S. C. & Wang, Y. M. (2004) The relationship among serum cytokines, chemokine, nitric oxide, and leptin in children with type 1 diabetes mellitus. Clin. Biochem. 37:666-672.[Medline]

6. Crook, M. (2004) Type 2 diabetes mellitus: a disease of the innate immune system?. An update. Diabet. Med. 21:203-207.

7. Chase, H. P., Cooper, S., Osberg, I., Stene, L. C., Barriga, K., Norris, J., Eisenbarth, G. S. & Rewers, M. (2004) Elevated C-reactive protein levels in the development of type 1 diabetes. Diabetes 53:2569-2573.[Abstract/Free Full Text]

8. Maachi, M., Pieroni, L., Bruckert, E., Jardel, C., Fellahi, S., Hainque, B., Capeau, J. & Bastard, J. P. (2004) Systemic low-grade inflammation is related to circulating and adipose tissue TNFalpha, leptin and IL-6 levels in obese women. Int. J. Obes. Relat. Metab. Disord. 28:993-997.[Medline]

9. Chavez, J. A. & Summers, S. A. (2003) Characterizing the effects of saturated fatty acids on insulin signaling and ceramide and diacylglycerol accumulation in 3T3–L1 adipocytes and C2C12 myotubes. Arch. Biochem. Biophys. 419:101-109.[Medline]

10. Sinha, S., Perdomo, G., Brown, N. F. & O’Doherty, R. M. (2004) Fatty acid-induced insulin resistance in L6 myotubes is prevented by inhibition of activation and nuclear localization of nuclear factor kappa B. J. Biol. Chem. 279:41294-41301.[Abstract/Free Full Text]

11. Weigert, C., Brodbeck, K., Staiger, H., Kausch, C., Machicao, F., Haring, H. U. & Schleicher, E. D. (2004) Palmitate, but not unsaturated fatty acids, induces the expression of interleukin-6 in human myotubes through proteasome-dependent activation of nuclear factor-kappaB. J. Biol. Chem. 279:23942-23952.[Abstract/Free Full Text]

12. Lee, J. Y., Sohn, K. H., Rhee, S. H. & Hwang, D. (2001) Saturated fatty acids, but not unsaturated fatty acids, induce the expression of cyclooxygenase-2 mediated through Toll-like receptor 4. J. Biol. Chem. 276:16683-16689.[Abstract/Free Full Text]

13. Van Epps-Fung, M., Williford, J., Wells, A. & Hardy, R. W. (1997) Fatty acid-induced insulin resistance in adipocytes. Endocrinology 138:4338-4345.[Abstract/Free Full Text]

14. Gao, Z., Zhang, X., Zuberi, A., Hwang, D., Quon, M. J., Lefevre, M. & Ye, J. (2004) Inhibition of insulin sensitivity by free fatty acids requires activation of multiple serine kinases in 3T3–L1 adipocytes. Mol. Endocrinol. 18:2024-2034.[Abstract/Free Full Text]

15. Ajuwon, K. M., Jacobi, S. K., Kuske, J. L. & Spurlock, M. E. (2004) Interleukin-6 and interleukin-15 are selectively regulated by lipopolysaccharide and interferon-gamma in primary pig adipocytes. Am. J. Physiol. 286:R547-R553.

16. Ajuwon, K. M. & Spurlock, M. E. (2005) Adiponectin inhibits LPS-induced NF-B activation and IL-6 production, and increases PPAR2 expression in adipocytes. Am. J. Physiol. 288:R1220-R1225.

17. Rakatzi, I., Mueller, H., Ritzeler, O., Tennagels, N. & Eckel, J. (2004) Adiponectin counteracts cytokine- and fatty acid-induced apoptosis in the pancreatic beta-cell line INS-1. Diabetologia 47:249-258.[Medline]

18. Gobert, A. P., Bambou, J. C., Werts, C., Balloy, V., Chignard, M., Moran, A. P. & Ferrero, R. L. (2004) Helicobacter pylori heat shock protein 60 mediates interleukin-6 production by macrophages via a toll-like receptor (TLR)-2-, TLR-4-, and myeloid differentiation factor 88-independent mechanism. J. Biol. Chem. 279:245-250.[Abstract/Free Full Text]

19. Jhun, B. S., Jin, Q., Oh, Y. T., Kim, S. S., Kong, Y., Cho, Y. H., Ha, J., Baik, H. H. & Kang, I. (2004) 5-Aminoimidazole-4-carboxamide riboside suppresses lipopolysaccharide-induced TNF-alpha production through inhibition of phosphatidylinositol 3-kinase/Akt activation in RAW 264.7 murine macrophages. Biochem. Biophys. Res. Commun. 318:372-380.[Medline]

20. SAS Institute Inc (1999) 5-Aminoimidazole-4-carboxamide riboside suppresses lipopolysaccharide-induced TNF-alpha production through inhibition of phosphatidylinositol 3-kinase/Akt activation in RAW 264.7 murine macrophages. SAS User’s Guide (version 8) SAS Institute Cary, NC.

21. Lee, J. Y., Ye, J., Gao, Z., Youn, H. S., Lee, W. H., Zhao, L., Sizemore, N. & Hwang, D. H. (2003) Reciprocal modulation of Toll-like receptor-4 signaling pathways involving MyD88 and phosphatidylinositol 3-kinase/AKT by saturated and polyunsaturated fatty acids. J. Biol. Chem. 278:37041-37051.[Abstract/Free Full Text]

22. Zhao, S., Yang, Y. N. & Song, J. G. (2004) Ceramide induces caspase-dependent and -independent apoptosis in A-431 cells. J. Cell Physiol. 199:47-56.[Medline]

23. Nalecz, K. A., Miecz, D., Berezowski, V. & Cecchelli, R. (2004) Carnitine: transport and physiological functions in the brain. Mol. Aspects Med. 25:551-567.[Medline]

24. Lee, J. Y., Zhao, L., Youn, H. S., Weatherill, A. R., Tapping, R., Feng, L., Lee, W. H., Fitzgerald, K. A. & Hwang, D. H. (2004) Saturated fatty acid activates but polyunsaturated fatty acid inhibits Toll-like receptor 2 dimerized with Toll-like receptor 6 or 1. J. Biol. Chem. 279:16971-16979.[Abstract/Free Full Text]

25. Rotter, V., Nagaev, I. & Smith, U. (2003) Interleukin-6 (IL-6) induces insulin resistance in 3T3–L1 adipocytes and is, like IL-8 and tumor necrosis factor-alpha, overexpressed in human fat cells from insulin-resistant subjects. J. Biol. Chem. 278:45777-45784.[Abstract/Free Full Text]

26. Lin, Y., Lee, H., Berg, A. H., Lisanti, M. P., Shapiro, L. & Scherer, P. E. (2000) The lipopolysaccharide-activated toll-like receptor (TLR)-4 induces synthesis of the closely related receptor TLR-2 in adipocytes. J. Biol. Chem. 275:24255-24263.[Abstract/Free Full Text]

27. Fasshauer, M., Klein, J., Lossner, U. & Paschke, R. (2003) Interleukin (IL)-6 mRNA expression is stimulated by insulin, isoproterenol, tumour necrosis factor alpha, growth hormone, and IL-6 in 3T3–L1 adipocytes. Horm. Metab. Res. 35:147-152.[Medline]

28. Ducluzeau, P. H., Fletcher, L. M., Vidal, H., Laville, M. & Tavare, J. M. (2002) Molecular mechanisms of insulin-stimulated glucose uptake in adipocytes. Diabetes Metab. 28:85-92.[Medline]

29. Eitel, K., Staiger, H., Rieger, J., Mischak, H., Brandhorst, H., Brendel, M. D., Bretzel, R. G., Haring, H. U. & Kellerer, M. (2003) Protein kinase C delta activation and translocation to the nucleus are required for fatty acid-induced apoptosis of insulin-secreting cells. Diabetes 52:991-997.[Abstract/Free Full Text]

30. Montell, E., Turini, M., Marotta, M., Roberts, M., Noe, V., Ciudad, C. J., Mace, K. & Gomez-Foix, A. M. (2001) DAG accumulation from saturated fatty acids desensitizes insulin stimulation of glucose uptake in muscle cells. Am. J. Physiol. 280:E229-E237.

31. Wu, D., Marko, M., Claycombe, K., Paulson, K. E. & Meydani, S. N. (2003) Ceramide-induced and age-associated increase in macrophage COX-2 expression is mediated through up-regulation of NF-kappa B activity. J. Biol. Chem. 278:10983-10992.[Abstract/Free Full Text]

32. Vanden Berghe, W., Vermeulen, L., De Wilde, G., De Bosscher, K., Boone, E. & Haegeman, G. (2000) Signal transduction by tumor necrosis factor and gene regulation of the inflammatory cytokine interleukin-6. Biochem. Pharmacol. 60:1185-1195.[Medline]

33. Guha, M. & Mackman, N. (2002) The phosphatidylinositol 3-kinase-Akt pathway limits lipopolysaccharide activation of signaling pathways and expression of inflammatory mediators in human monocytic cells. J. Biol. Chem. 277:32124-32132.[Abstract/Free Full Text]

34. Xu, H., Uysal, K. T., Becherer, J. D., Arner, P. & Hotamisligil, G. S. (2002) Altered tumor necrosis factor-alpha (TNF-alpha) processing in adipocytes and increased expression of transmembrane TNF-alpha in obesity. Diabetes 51:1876-18783.[Abstract/Free Full Text]

35. Pedersen, B. K., Steensberg, A., Keller, P., Keller, C., Fischer, C., Hiscock, N., van Hall, G., Plomgaard, P. & Febbraio, M. A. (2003) Muscle-derived interleukin-6: lipolytic, anti-inflammatory and immune regulatory effects. Pflugers Arch. 446:9-16.[Medline]

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