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Obesity Research Center, Departments of Medicine and Biochemistry, Boston University School of Medicine, Boston, MA 02118
2To whom correspondence should be addressed. E-mail: wguo{at}bu.edu.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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, steroid regulatory binding element protein (SREBP)-1c and CCAAT element binding protein (C/EBP
) at both the mRNA and protein levels. Expression of differentiation markers, including adipocyte fatty acid binding protein (ALBP), glycerol-3-phosphate dehydrogenase (GPDH) and leptin, was also significantly diminished by octanoate. However, octanoate did not prevent the decrease in preadipocyte factor-1 (Pref-1) expression that occurs during adipogenesis, nor did it inhibit the early induction of C/EBPß,
. Treatment with synthetic PPAR ligands partially offset the inhibitory effect of octanoate on differentiation. Ectopic expression of PPAR2 in 3T3-L1 cells partially restored lipid accretion and GPDH activity in octanoate-treated cells. Adding octanoate together with troglitazone attenuated the effects of troglitazone on adipocyte differentiation in both normal 3T3-L1 cells and engineered 3T3-L1 cells that expressed ectopic PPAR2, implying that octanoate might compete against troglitazone for its binding to PPAR. These results suggest that octanoate may block adipogenesis at least in part by its influence on the expression/activation of PPAR.
KEY WORDS: • medium-chain fatty acids • preadipocytes • adipogenesis • transcription factors
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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). Because medium-chain fatty acids (MCFA) can be activated within mitochondria for ß-oxidation independently of carnitine palmitoyl coenzyme A transferase-I (2
–5
), they are generally believed to be oxidized rapidly, without sustained metabolic effects on host cells. Because of their high water solubility, MCT-derived fatty acids are rapidly absorbed and delivered to the liver via the portal vein (6
). Therefore, reduced weight gain resulting from MCT feeding often has been attributed to hepatic oxidation of MCFA, resulting in reduced fatty acid delivery to adipose tissue. However, this accounts only partially for the effects of MCT on adipose tissue development. Because MCT feeding leads to the appearance of MCFA in chylomicrons (7
,8
) and adipose tissue (9
–12
), as well as altered lipogenesis in adipose tissue (13
,14
), it is likely that the influence of MCFA on adipose tissue may be more substantial than previously appreciated.
We recently showed that cultured preadipocytes treated with octanoate accumulated less triglyceride and had lower glycerol-3-phosphate dehydrogenase (GPDH) activity than cells treated with oleate, suggesting that octanoate may inhibit differentiation (15
). We report here that octanoate indeed blocks differentiation of 3T3-L1 preadipocytes through inhibition of the expression of key adipogenic transcription factors. These data support the possibility that partial replacement of dietary fat with MCT might be a valuable tool for the treatment of obesity.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Fatty acids (FA), bovine serum albumin (BSA), cell culture media and related reagents were purchased from Sigma Chemical (St. Louis, MO). Monoclonal antibodies for peroxisome proliferator-activated receptor (PPAR), polyclonal antibodies for steroid regulatory binding element protein (SREBP)-1c and CCAAT element binding protein (C/EBP) and the luminol reagent were from Santa Cruz Biotechnology (Santa Cruz, CA). Trizol reagent for RNA isolation was obtained from Invitrogen (Carlsbad, CA). Antiadipocyte fatty acid binding protein (ALBP) primary antibody was kindly provided by Dr. D. Bernlohr (University of Minnesota, Minneapolis/St. Paul, MN). Troglitazone was purchased from Biomol (Plymouth, PA). All other cell culture supplies were from FisherSci (Augawa, MA).
3T3-L1 preadipocytes were obtained from American Type Culture Collection (Manassas, VA) and subcultured in high glucose Dulbecco’s minimum essential medium (DMEM) with 10% calf serum, penicillin (100 IU), and streptomycin (100 IU) for up to 20 passages. No significant variance in differentiation capacity was found among generations. Differentiation was induced using DMEM with 10% fetal bovine serum supplemented with MDI [methylisobutylxanthine (M; 0.5 mmol/L), dexamethasone (D; 1 µmol/L) and insulin (I; 10 nmol/L)]. In separate experiments, differentiation was induced by indomethacin (125 µmol/L)/insulin (10 nmol/L) or by insulin (10 nmol/L) alone. After 48 h, medium was changed to DMEM with 10% fetal bovine serum and insulin (10 nmol/L). Octanoate and oleate were prepared in DMEM with BSA (FA/BSA = 5) and added to cells at the beginning of the differentiation protocols. Up to 3 mmol/L octanoate was added to cell cultures, which is within the range of the 2–5 mmol/L octanoate generally used in cell culture studies (16
). For incubations with 2 mmol/L octanoate, 
99% of the added octanoate was recovered from culture medium after 48 h, indicating that cellular consumption of octanoate (esterification, oxidation) was rather limited. Selected cultures were examined after exposure to trypan blue. No toxic effects of octanoate were found. Additional cytotoxicity testing was conducted using Annexin V staining with the Vybrant Apoptosis Assay Kit (Molecular Probes, Eugene, OR), and no adverse effects on cell viability were found for cells treated with up to 3 mmol/L octanoate (data not shown). We found previously that adipocytes incubated with octanoate can store 20 mol/100 mol octanoate within a few hours (15
). Others also report that storage of MCFA can reach up to 30 mol/100 mol in MCT-fed rats (17
). Because MCFA are released rapidly during lipolysis both from endogenous (15
) and exogenous (18
) sources, it is likely that the local concentrations of MCFA in adipose tissue are much higher than the typical blood FA concentrations of 0.5–1.5 mmol/L. For this reason, the effects of octanoate on adipogenesis were studied in the range of 0.5–3 mmol/L in this work.
3T3-L1 preadipocytes stably transfected with a dominant positive form of C/EBPß were prepared and differentiated as previously reported (19
). Octanoate was added as described above. The preparation of 3T3-L1 cells stably transfected with PPAR2 will be published elsewhere (S.R. Farmer, unpublished data). These cells were grown to confluence in DMEM with 10% calf serum and 10 nmol/L insulin. Cells were induced to differentiate as in the MDI protocol described above, except that methylisobutylxanthine was not added. Octanoate and troglitazone were added together or separately in selected cultures.
Primary rat preadipocytes were isolated from male Sprague-Dawley rats and differentiated as described previously (15
). Octanoate and oleate were added to the differentiation medium as described above. BSA alone was added to the control cultures. Cells were harvested for mRNA analysis 16 h after the initiation of differentiation.
Cultures were washed four times with ice-cold PBS and lysed with protease inhibitors. Proteins were further purified by ethanol precipitation, quantified using Bradford reagent from BioRad (Hercules, CA), and separated by SDS-PAGE electrophoresis. Protein was transferred to Immobilon polyvinylidene difluoride membranes and the membranes were stained to visualize banding and confirm protein integrity before probing. Blotting membranes were blocked for 1 h at room temperature in Tris-buffered saline containing 5% milk, 1.0% BSA, and 0.1% Tween 20. Incubation with primary antibody was for 2 h at 24° for ALBP (1:5000), SREBP-1c (1:200), C/EBP (1:200) and PPAR (1:100). Blots were washed and then incubated with secondary antibody conjugated to horseradish peroxidase (1:1000–1:2500) for 45 min at 24°C. Visualization of secondary antibody binding was performed by chemiluminesense. Linearity of protein loading was confirmed over the range of the loading levels of proteins being assayed.
Total RNA was isolated from preadipocytes using TRIzol reagent from Invitrogen. Messenger RNA was assayed by multiplex competimer-based reverse transcriptase-polymerase chain reaction (RT-PCR) using 18S or hypoxanthine phosphoribosyl transferase (HPRT) as the internal control (20
). All PCR primers were synthesized by Life Technologies. Primers were designed using the Primer-3 program based on the published sequences in the gene banks. Detailed primer sequences and the linear ranges of PCR cycle numbers are shown in Table 1
. All RT-PCR products were analyzed by 1.5% agarose gel electrophoresis. DNA contamination was excluded by PCR experiments without reverse transcription.
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Cellular DNA, triglyceride and GPDH activity, were measured as described (15
). Lipid droplets were stained with Oil-red-O (21
).
Data are shown are means ± SEM. Statistical analyses used one-way ANOVA and Duncan’s multiple comparison test to identify differences between the groups. Differences were considered significant when P < 0.05.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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We showed previously that confluent 3T3-L1 preadipocytes treated with octanoate accumulated much less triglyceride than cells treated with oleate (15
). Whether octanoate actually inhibited the differentiation process remained unclear. In this study, preadipocytes were differentiated using the standard MDI treatment protocol along with the fatty acids being tested. By d 8, most of the control cells had accumulated lipid droplets (Fig. 1A
). Within the same time interval, cells exposed to 0.1 mmol/L oleate accumulated more and larger lipid droplets than control cells (Fig. 1
B), consistent with reports that long-chain fatty acids (LCFA) potentiate preadipocyte differentiation (22
). Adding octanoate with oleate blocked lipid accumulation (Fig. 1
C). In the absence of oleate, octanoate further inhibited lipid storage (Fig. 1
D–F). Intracellular triglyceride levels measured enzymatically were consistent with the observed morphology (Fig. 1
G). The inhibitory effects of octanoate on lipid accretion were not irreversible. Triglyceride accumulation resumed after octanoate was removed (Fig. 1
G, column 8), suggesting that octanoate did not prevent the initiation of the differentiation program induced by MDI treatment because parallel cultures without MDI treatment did not accumulate lipids (not shown).
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, SREBP-1c, preadipocyte factor-1 (Pref-1) and ALBP.">Effects of octanoate on expression of PPAR, C/EBP, SREBP-1c, preadipocyte factor-1 (Pref-1) and ALBP.
Adipocyte differentiation involves a series of programmed changes in gene expression. To determine whether reduced lipid accretion resulted from an octanoate-mediated alteration in the differentiation program, the expression of a number of adipogenic genes was studied by semiquantitative RT-PCR. Treatment with octanoate reduced the mRNA levels of major adipogenic transcription factors, including PPAR, C/EBP and SREBP-1c (Fig. 2
). Effects of octanoate on these factors were specific because the levels of the housekeeping genes, HPRT mRNA and 18S rRNA (Fig. 2)
, were unaffected. Furthermore, octanoate-associated attenuation of PPAR, C/EBP and SREBP-1c mRNAs was accompanied by a decrease in the abundance of the corresponding proteins (Fig. 3
). In the control cells, PPAR existed mainly in the nonphosphorylated form, and the ratio of the phosphorylated to the nonphosphorylated form increased substantially in octanoate-treated cells. This was especially evident in the case of 1 mmol/L octanoate, with which the total PPAR protein level was moderately reduced, but the phosphorylated form was substantially increased, suggesting that inactivation of PPAR may be one means by which octanoate inhibited adipogenesis (23
). At higher concentrations of octanoate, the density of the phosphorylated form was reduced, likely as a result of the overall suppression of PPAR expression.
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) and protein levels (P = 0.13; Fig. 3
) of ALBP were reduced only slightly by octanoate. Why ALBP was not reduced more extensively is not clear, but may be related to interactions between octanoate and ALBP because fatty acid binding generally reduces ALBP degradation (24
). Octanoate treatment did not prevent the decrease in Pref-1 expression (Fig. 2)
, the irreversible molecular checkpoint for the initiation of differentiation (25
). Thus, octanoate did not block the differentiation program through the maintenance of Pref-1 expression. Effects of octanoate treatment on the expression of GPDH and leptin.
GPDH and leptin increase late during differentiation. We previously found that octanoate treatment reduced GPDH activity (15
). In this work, we showed that GPDH mRNA was also drastically reduced by octanoate (Fig. 4
). Leptin is an adipocyte-specific hormone that has many metabolic functions (26
). Its production is associated with increasing fat mass (27
) and lipogenesis (28
). Therefore, it is not surprising that octanoate-treated cells had less leptin mRNA because they had reduced fat storage.
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ligands offset the effects of octanoate on preadipocyte differentiation.">Synthetic PPAR ligands offset the effects of octanoate on preadipocyte differentiation.
The transactivating activity of PPAR, a major transcription factor for genes involved in differentiation and lipid metabolism, is modulated by natural or synthetic ligands (29
–34
). To determine whether the inhibitory effects of octanoate can be overcome through the activation of PPAR, a synthetic PPAR ligand, troglitazone, was added to the differentiation medium with or without octanoate. By d 8, cellular triglyceride accumulation followed the order: troglitazone > troglitazone + octanoate > octanoate (Fig. 5
). Expression of adipogenic genes in these cells also followed the same order, and similar results were observed in cells treated with two other PPAR ligands, ciglitazone and rosiglitazone (data not shown). Therefore, inhibitory effects of octanoate on 3T3-L1 preadipocyte differentiation could be restored in part by PPAR synthetic ligands.
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C/EBPß and C/EBP play vital roles in the initiation of adipogenesis (35
), including activation of PPAR and C/EBP expression (19
,36
). In this work, we found no inhibitory effect of octanoate on the early expression of C/EBPß,. As shown in Figure 6
, C/EBPß (activated form, upper panels) appeared within 2 h of adding MDI, reached the peak level in 4–8 h and declined to trace levels by 24 h. The negative isoform of C/EBPß was not detected in these experiments. Changes in C/EBP paralleled those of C/EBPß, but declined somewhat earlier than C/EBPß (Fig. 6
, lower panels). The rapid early appearance and subsequent rapid decrease are consistent with the previously published time courses of C/EBPß, expression (19
,37
), and octanoate did not affect the protein abundance of these two transcription factors. In a separate experiment, we found that ectopic expression of the active isoform of C/EBPß in 3T3-L1 cells could not restore differentiation in octanoate-treated cells (data not shown). Therefore, C/EBPß, are unlikely to be the targets of octanoate. Nevertheless, the possibility that octanoate attenuated the activity of these early transcription factors still cannot be excluded.
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2 restored adipocyte differentiation in octanoate-treated cells.
We next studied the effects of octanoate on differentiation of 3T3-L1 preadipocytes ectopically expressing PPAR2. By d 8 after the initiation of differentiation, control cells did not show appreciable lipid accumulation (Fig. 7A
). In contrast, cells treated with 2 mmol/L octanoate alone (Fig. 7
B) or in combination with 5 µmol/L troglitazone (Fig. 7
D) acquired significant amounts of triglycerides, although somewhat less than in cells treated with troglitazone alone (Fig. 7
C). The extent of differentiation evaluated by measuring cellular GPDH activity (Fig. 7
E) and triglyceride level (Fig. 7
F) was consistent with the morphological appearance of the cells (Fig. 7
, A–D). The PPAR mRNA levels in these cells were not affected by exposure to octanoate (not shown), likely due to the high level of ectopic expression of this gene. These data showed that in 3T3-L1 cells overexpressing PPAR2, octanoate did not inhibit lipid accretion and GPDH activation, two biochemical markers of adipocyte differentiation. Moreover, octanoate added alone promoted adipogenesis compared with control cells (Fig. 7
, B vs. A). Adding octanoate with troglitazone moderately reduced cellular GPDH activity, suggesting that octanoate and troglitazone compete, attenuating the potency of troglitazone as a differentiation inducer.
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To test the physiologic relevance of the above findings in primary cultured rat preadipocytes, octanoate or oleate was added to the differentiation medium at various concentrations. Treatment with octanoate (1 mmol/L) reduced the expression of PPAR and C/EBP compared with the control without added fatty acid (Figure 8
). In contrast, treatment with oleate (0.1 mmol/L) increased the expression of these genes. Octanoate treatment also suppressed the expression of SREBP-1c and leptin in these cells (not shown). Similar results were found in primary cultured rat preadipocytes treated with octanoate at other concentrations (0.5–2 mmol/L, not shown).
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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). Some of these studies also reported no effects of MCFA on adipogenic gene expression (22
,39
). The discrepancy between our data and those of others is likely because others compared MCFA and LCFA at the same low concentrations. However, because of their high water solubility, the partitioning of MCFA into the exogenous aqueous phase is expected to be greater than into the cell membrane, whereas the opposite is true for LCFA. It has been demonstrated that the values of Km and Vmax for fatty acid uptake are 90% lower for MCFA than for LCFA (40
). Therefore, although LCFA may enhance adipocyte differentiation at rather low concentrations (22
), octanoate at similar low concentrations may not have significant effects. In this work, we present evidence that exposure of preadipocytes to octanoate significantly down-regulated the expression of PPAR, C/EBP and SREBP-1c at both the mRNA and protein levels, without blocking MDI-induced changes in Pref-1 (Fig. 2)
or C/EBPß, (Fig. 6)
. Additionally, octanoate-treated cells adopted a rounded morphology characteristic of the first phase of adipogenesis (Fig. 1)
. Together, these findings suggest that octanoate blocks adipogenesis within the differentiation program at a step before the induction of PPAR and C/EBP but downstream from Pref-1 and C/EBPß,. The concentrations of octanoate used in this study (1–3 mmol/L for 3T3-L1 preadipocytes, and 0.5–2 mmol/L for primary rat preadipocytes) are relatively high compared with fatty acid concentrations commonly used in other studies (41
). However, in both cell types, differentiation was substantially inhibited at 1 mmol/L octanoate, suggesting that effective concentrations of octanoate could be even lower. Because a plasma octanoate concentration between 0.4 and 0.8 mmol/L is tolerated in vivo (42
), the in vitro effects of octanoate found in this work are, in principle, achievable in vivo. Moreover, local concentrations may be higher when special delivery techniques are used. Indeed, methods for transdermal delivery of MCT have been established (43
). Therefore, the findings in this study are potentially relevant for the regulation of adipose tissue development.
The mechanisms that regulate the expression of the early adipogenic transcription factors include cAMP-associated induction of C/EBPß, and dexamethasone-associated reduction of Pref-1, respectively. Octanoate appears to have no inhibitory effect on the hormone-mediated changes in the expression of these early factors (44
,45
). In fact, ectopic overexpression of C/EBPß did not overcome the inhibitory effects of octanoate. It appears that octanoate inhibited adipogenesis at a step between the early induction of C/EBPß, and the expression/activation PPAR and C/EBP.
Because octanoate belongs to the FA family, potential targets of the inhibitory action of octanoate are transcription factors that are regulated by lipids. SREBP are basic helix-loop-helix transcription factors that regulate expression of enzymes and other proteins involved in cholesterol and fatty acid synthesis. Because the SREBP-1c isoform has been shown to regulate adipogenesis (29
,46
–53
), it is tempting to suggest that inhibition of SREBP-1c expression (Figs. 2
, 3)
may be one means by which octanoate blocks adipogenesis. Recently it was reported that FA inhibit the expression of SREBP-1c by competitively blocking the activation of liver X receptor (LXR) (54
). Although LXR is expressed mainly in the liver, LXRß is expressed ubiquitously (55
). Therefore, it remains possible that octanoate may interact with LXR, causing suppression of SREBP-1c, which in turn inhibits adipogenesis. On the other hand, in spite of the pivotal role of SREBP-1c in mediating lipogenesis in the liver (56
), its real function in adipocytes has been questioned, especially because SREBP-1c null mice have normal adipose tissue mass as well as normal expression levels of lipogenic enzymes (57
). Moreover, the expression of SREBP-1c may occur after that of PPAR during adipogenesis (58
). Therefore, the lowering of SREBP-1c by octanoate documented in this study may be a marker of inhibition of adipogenesis. Whether SREBP-1c is a cause or an effect of decreased adipogenesis remains to be determined.
A second ligand-dependent nuclear transcription factor that may be involved in early adipogenesis is PPAR (59
–61
). However, we found that abundant PPAR expression appeared after, instead of before the appearance of PPAR (data not shown). Therefore, it is unlikely that the inhibition on PPAR by octanoate is mediated by PPAR. Another possibility is that octanoate may activate PPAR to increase the oxidative disposal of LCFA, the endogenous ligand or ligand precursors for PPAR. By incubating cells with octanoate and oleate together, we found that lipid accretion was increased but not the expression of differentiation-dependent genes (data not shown), indicating that oleate was passively stored as cellular lipid without switching on adipogenesis. Therefore, availability of LCFA, which presumably activate both PPAR and PPAR (32
,62
), could not fully restore adipogenesis in the presence of octanoate.
Although other mechanisms remain possible, our data point to PPAR as one of the major targets of octanoate, not only because octanoate reduced the expression of PPAR and increased its phosphorylation, but also because synthetic PPAR ligands partially overcame the inhibitory effects of octanoate. Moreover, octanoate seems to enhance differentiation in 3T3-L1 cells ectopically overexpressing PPAR2, although to a lesser extent than troglitazone. These results suggest that octanoate may act as a partial ligand for PPAR. In the absence of more active endogenous or synthetic ligands and/or in the presence of ectopic PPAR2, octanoate may partially activate this transcription factor and enhance differentiation (Fig. 7
, B vs. A). On the other hand, binding of octanoate to PPAR would likely compete with the binding of more potent ligands, especially when the exogenous octanoate concentration is substantially higher than that of the active ligands. In normal preadipocytes, endogenous ligands are produced as the differentiation program progresses. Therefore, the binding of octanoate to PPAR at an early stage may effectively prevent subsequent activation of PPAR by more potent endogenous ligands, and as a result, octanoate inhibits adipocyte differentiation.
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ACKNOWLEDGMENTS |
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2. |
FOOTNOTES |
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3 Abbreviations used: ALBP, adipocyte fatty acid binding protein; BSA, bovine serum albumin; C/EBP, CCAAT element binding protein; DMEM, Dulbecco’s modified Eagle’s medium; FA, fatty acid; GPDH, glycerol-3-phosphate dehydrogenase; HPRT, hypoxanthine phosphoribosyl transferase; LCFA, long-chain fatty acids; LXR, liver X receptor; MCFA, medium-chain fatty acids; MCT, medium-chain triglycerides; MDI, methylisobutylxanthine, dexamethasone, insulin; PPAR, peroxisome proliferator-activated receptor; Pref-1, preadipocyte factor-1; RT-PCR, reverse transcriptase-polymerase chain reaction; SREBP, steroid regulatory element binding protein.
Manuscript received 23 October 2001. Initial review completed 7 December 2001. Revision accepted 29 January 2002.
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LITERATURE CITED |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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1.
Geliebter, A., Torbay, N., Bracco, E. F., Hashim, S. A. & Van Itallie, T. B. (1983) Overfeeding with medium-chain triglyceride diet results in diminished deposition of fat. Am. J. Clin. Nutr. 37:1-4.
2. Metges, C. C. & Wofram, G. (1991) Medium- and long-chain triglycerides labeled with 13C: a comparison of oxidation after oral or parenteral administration in humans. J. Nutr. 121:31-36.
3.
Schwabe, A. D., Bennett, L. R. & Bowman, L. P. (1964) Octanoic acid absorption and oxidation in humans. J. Appl. Physiol. 19:335-337.
4. Pegorier, J. P., Duee, P. H., Herbin, C., Laulan, P. Y., Blade, C., Peret, J. & Girard, J. (1988) Fatty acid metabolism in hepatocytes isolated from rats adapted to high fat diets containing long- or medium-chain triglycerides. Biochem. J. 249:801-806.[Medline]
5. Crozier, G. L. (1988) Medium-chain triglyceride feeding over the long term: the metabolic fate of [1-14C] octanoate and [1-14C] oleate in isolated rat hepatocytes. J. Nutr. 118:297-304.
6. Bach, A. C., Ingenbleek, Y. & Frey, A. (1996) The usefulness of dietary medium chain triglycerides in body weight control: fact or fancy?. J. Lipid Res. 37:708-726.[Abstract]
7. Sigalet, D. & Martin, G. (1999) Lymphatic absorption of glucose and fatty acids as determined by direct measurement. J. Pediatr. Surg. 34:39-43.[Medline]
8.
Swift, L. L., Hill, J. O., Peters, J. C. & Greene, H. L. (1990) Medium chain fatty acids: evidence for incorporation into chylomicron triglycerides in humans. Am. J. Clin. Nutr. 52:834-836.
9.
Sarda, P., Lepage, g., Roy, C. C. & Chessex, P. (1987) Storage of medium chain triglycerides in adipose tissue of orally fed infants. Am. J. Nutr. 45:399-405.
10. Lee, K. T., Akoh, C. C., Flatt, W. P. & Lee, J. H. (2000) Nutritional effects of enzymatically modified soybean oil with caprylic acid versus physical mixture analogue in obese Zucker rats. J. Agric. Food Chem. 48:5696-5701.[Medline]
11.
Johnson, R. Y., Young, S. K., Cotter, R., Lin, L. & Rowe, W. B. (1990) Medium-chain triglyceride lipid emulsion: metabolism and tissue distribution. Am. J. Clin. Nutr. 52:502-5.–8.
12. Hill, J. O., Peters, J. C., Yakubu, F., Greene, H. & Swift, L. (1993) Lipid accumulation and body fat distribution is influenced by type of dietary fat fed to rats. Intl. J. Obes. 17:223-236.
13. Willey, J. H. & Leveille, G. A. (1973) Metabolic consequences of dietary medium-chain triglycerides in the rat. J. Nutr. 103:829-835.
14. Lavau, M. & Hashim, S. A. (1977) Effects of medium-chain triglycerides on lipogenesis and body fat in the rat. J. Nutr. 108:613-620.
15. Guo, W., Choi, J.-K., Kirkland, J. L., Corkey, B. E. & Hamilton, J. A. (2000) Esterification of free fatty acids in adipocytes: a comparison between octanoate and oleate. Biochem. J. 349:463-471.[Medline]
16.
Roncero, C. & Gooridge, A. G. (1992) Hexanoate and octanoate inhibit transcription of the malic enzyme and fatty acid synthase genes in chick embryo hepatocytes in culture. J. Biol. Chem. 267:14918-14927.
17. Deckelbaum, R. J., Hamilton, J. A., Moser, A., Bengtsson-Olivecrona, G., Buttbul, E., Carpentier, Y., Gutman, A. & Olivecrona, T. (1990) Medium chain versus long chain triacylglycerol emulsion hydrolysis by lipoprotein lipase and hepatic lipase: implications for the mechanisms of lipase action. Biochemistry 29:1136-1142.[Medline]
18. Kinkela, T., Chanussot, F., Bach, A., Max, J. P., Schirardin, H. & Debry, G. (1983) Effects of diets containing medium chain and long chain triglycerides in the genetically obese Zucker fa/fa rats. Comparison of fatty acids and triglycerides in the liver and adipose tissues. Ann. Nutr. Metab. 27:404-414.[Medline]
19.
Hamm, J. K., Park, B. H. & Farmer, S. R. (2001) A role for C/EBPß in regulating peroxisome proliferator-activated receptor activity during adipogenesis in 3T3–L1 preadipocytes. J. Biol. Chem. 276:18464-18471.
20. Thellin, O. Z., W. Lakaye, B., De Borman, B., Coumans, B., Hennen, G., Grisar, T., Igout, A. & Heinen, E. (1999) Housekeeping genes as internal standards: use and limits. J. Biotechnol. 75:291-295.[Medline]
21. Wu, Z., Bucher, N. L. & Farmer, S. R. (1996) Induction of peroxisome proliferator-activated receptor gamma during the conversion of 3T3 fibroblasts into adipocytes is mediated by C/EBPß, C/EBPä, and glucocorticoids. Mol. Cell. Biol. 16:4128-4136.[Abstract]
22. Amri, E. Z., Bertrand, B., Ailhaud, G. & Grimaldi, P. (1991) Regulation of adipose cell differentiation. I. Fatty acids are inducers of the ALBP gene expression. J. Lipid Res. 32:1449-1456.[Abstract]
23.
Reginato, M. J., Krakow, S. L., Bailey, S. T. & Lazar, M. A. (1998) Prostaglandins promote and block adipogenesis through opposing effects on peroxisome proliferator activated receptor . J. Biol. Chem. 273:1855-1858.
24. Honma, Y., Niimi, M., Ychiumi, T., Takahashi, Y. & Odani, S. (1994) Evidence for conformational change of fatty acid binding protein accompanying binding of hydrophobic ligands. Biochem. J. 116:1025-1029.
25.
Xing, H., Northrop, J. P., Grove, J. R., Kilpatrick, K. E., Su, J. L. & Ringold, G. M. (1997) TNF-mediated inhibition and reversal of adipocyte differentiation is accompanied by suppressed expression of PPAR without effects on Pref-1 expression. Endocrinology 138:2776-2783.
26. Reidy, S. P. & Weber, J.-M. (2000) Leptin: an essentially regulator of lipid metabolism. Comp. Biochem. Physiol. A 125:285-297.
27. Raclot, T., Groscolas, R., Langin, D. & Ferrs, P. (1997) Site-specific regulation of gene expression by n-3 polyunsatuated fatty acids in rat white adipose tissues. J. Lipid Res. 38:1963-1972.[Abstract]
28. Stumvoll, M., Fritsche, A., Tschritter, O., Rainer, L., Wahl, H. G., Renn, W. & Haring, H. (2000) Leptin levels in humans are acutely suppressed by isoproterenol despite acipmox-induced inhibition of lipolysis, but not by fatty acids. Metabolism 49:335-339.[Medline]
29.
Kim, J. B., Wright, H. M., Wright, M. & Spiegelman, B. M. (1998) ADD1/SREBP1 activates PPAR through the production of endogenous ligand. Proc. Natl. Acad. Sci. U.S.A. 95:4333-4337.
30.
Forman, B. M., Tontonoz, P., Jasmine, C., Brum, R. P., Spiegelman, B. M. & Evans, R. M. (1995) 15-Deoxy-ä 12, 14-prostaglandin J2 is a ligand for the adipocyte determination factor PPAR. Cell 83:803-812.[Medline]
31.
Kliewer, S. A., Lenhard, J. M., Willson, T. M., Patel, I., Morris, D. C. & Lehmann, J. M. (1995) A prostaglandin J2 metabolite binds peroxisome proliferator-activated receptor and promotes adipocyte differentiation. Cell 83:813-819.[Medline]
32.
Kliewer, S. A., Sundseth, S. S., Jones, S. A., Brown, P. J., Wisely, G. B., Koble, C. S., Devchand, P., Wahli, W., Willson, T. M., Lenhard, J. M. & Lehmann, J. M. (1997) Fatty acids and eicosanoids regulate gene expression through direct interactions with peroxisome proliferator-activated receptors and . Proc. Natl. Acad. Sci. U.S.A. 94:4318-43232.
33.
Oberfield, J. L., Collins, J. L., Holmes, C. R., Goreham, D. M., Cooper, J. P., Cobb, J. E., Lengard, J. M., Hull-Ryde, E. A., Mohr, C. P., Blanchard, S. G., Parks, D. J., Moore, L. B., Lehmann, J. M., Plunket, K., Millder, B., Milburn, M. V., Kliewer, S. A. & Willson, T. M. (1999) A peroxisome proliferator-activated receptor ligand inhibits adipocyte differentiation. Proc. Natl. Acad. Sci. U.S.A. 96:6102-6106.
34.
Wright, H. M., Clish, C. B., Mikami, T., Hauser, S, Yanagi, K., Hiramatsu, R., Serhan, C. N. & Spiegelman, B. M. (2000) A synthetic antagonist for the peroxisome proliferator-activated receptor inhibits adipocyte differentiation. J. Biol. Chem. 21:1873-1877.
35.
Darlington, G. J., Ross, S. E. & MacDougald, O. A. (1998) The role of C/EBP genes in adipocyte differentiation. J. Biol. Chem. 273:30057-30060.
36.
Wu, Z., Xie, Y., Bucher, N. L. & Farmer, S. R. (1995) Conditional ectopic expression of C/EBPß in NIH-3T3 cells induces PPAR and stimulates adipogenesis. Genes Dev. 9:2350-2363.
37.
Mandrup, S. & Land, M. D. (1997) Expression of C/EBP and PPAR family members during differentiation of 3T3–L1 preadipocytes. J. Biol. Chem. 272:5367-5370.
38. Grimaldi, P. A., Teboul, L., Gaillard, D., Armengod, A. V. & Amri, E. Z. (1999) Long chain fatty acids as modulators of gene transcription in preadipose cells. Mol. Cell. Biochem. 192:63-68.[Medline]
39. Ding, S.-T. & Mersmann, H. J. (2001) Fatty acid modulate porcine adipocyte differentiation and transcripts for transcription factors and adipocyte-characteristic proteins. J. Nutr. Biochem. 12:101-108.[Medline]
40.
DeGrella, R. F. & Light, R. J. (1980) Uptake and metabolism of fatty acids by dispersed adult rat heart myocytes. I. Kinetics of homologous fatty acids. J. Biol. Chem. 255:9731-9738.
41. Pahl-Wostl, C. & Seelig, J. (1987) Ketogenesis in the liver followed by 13C NMR spectroscopy. Infusion of [1-13C] octanoate. Biol. Chem. 368:305-314.
42. Miles, J., Cattalini, M., Sharbrough, F., Wold, L., Wharen, R., Gerich, J. & Haymond, M. (1991) Metabolic and neurologic effects of an intravenous medium chain triglyceride emulsion. J. Parenter. Enteral Nutr. 15:37-41.[Abstract]
43. Schwarz, J., Weisspapir, M. & Friedmen, D. (1995) Enhanced transdermal delivery of diazepam by submicron emulsion (SME) creams. Pharm. Res. 12:687-692.[Medline]
44. Chen, X.-L., Dean, R. G. & Hausman, G. J. (1999) Expression of leptin mRNA and CCAAT-enhancer binding proteins in response to insulin deprivation during preadipocyte differentiation in primary cultures of porcine stromal-vascular cells. Domest. Anim. Endocrinol. 17:389-401.[Medline]
45. Hausman, G. J., Hausman, D. B. & Martin, R. J. (1992) Biochemical and cytochemical studies of preadipocyte differentiation in serum free cultures of porcine stromal-vascular cells: the interaction of dexamethasone and growth hormone. Acta Anat. 143:322-339.[Medline]
46.
Latasa, M. J., Moon, Y. S., Kim, K. H. & Sul, H. S. (2000) Nutritional regulation of the fatty acid synthase promoter in vivo: sterol regulatory element binding protein functions through an upstream region containing a sterol regulatory element. Proc. Natl. Acad. Sci. U.S.A. 97:10619-10624.
47. Schoonjans, K., Gelman, L., Haby, C., Briggs, M. & Auwerx, J. (2000) Induction of LPL gene expression by sterols is mediated by a sterol regulatory element and is independent of the presence of multiple E boxes. J. Mol. Biol. 304:323-334.[Medline]
48.
Tabor, D. E., Kim, J. B., Spiegelman, B. M. & Edwards, P. A. (1999) Identification of conserved cis-elements and transcription factors required for sterol-regulated transcription of stearoyl-CoA desaturase 1 and 2. J. Biol. Chem. 274:20603-20610.
49.
Yahagi, N., Shimano, H., Hasty, A. H., Amemiya-Kudo, M., Okazaki, H., Tamura, Y., Iizuka, Y., Shionoiri, F., Ohashi, K., Osuga, J., Harada, K., Gotoda, T., Nagai, R., Ishibashi, S. & Yamada, N. (1999) A crucial role of sterol regulatory element-binding protein-1 in the regulation of lipogenic gene expression by polyunsaturated fatty acids. J. Biol. Chem. 274:35840-35844.
50.
Ericsson, J., Jackson, S. M., Kim, J. B., Spiegelman, B. M. & Edwards, P. A. (1997) Identification of glycerol-3-phosphate acyltransferase as an adipocyte determination and differentiation factor 1- and sterol regulatory element-binding protein-responsive gene. J. Biol. Chem. 272:7298-7305.
51. Sul, H. S., Latasa, M. J., Moon, Y. & Kim, K. H. (2000) Regulation of the fatty acid synthase promoter by insulin. J. Nutr. 130:315S-320S.
52. Fajas, L., Fruchart, J. C. & Auwerx, J. (1998) Transcriptional control of adipogenesis. Curr. Opin. Lipidol. 8:59-66.
53.
Fajas, L., Schoonjans, K., Gelman, L., Kim, J. B., Najib, J., Martin, G., Fruchart, J., Briggs, M., Spiegelman, B. M. & Auwerx, J. (1999) Regulation of peroxisome proliferator-activated receptor expression by adipocyte differentiation and determination factor 1/sterol regulatory element binding protein 1: implications for adipocyte differentiation and metabolism. Mol. Cell. Biol. 19:5495-5503.
54.
Ou, J., Tu, H., Shan, B., Luk, A., DeBose-Boyd, R. A., Bashmakov, Y., Goldstein, J. L. & Brown, M. S. (2001) Unsaturated fatty acids inhibit transcription of the sterol regulatory element-binding protein 1c (SREBP-1c) gene by antagonizing ligand-dependent activation of LXR. Proc. Natl. Acad. Sci. U.S.A. 98:6027-6032.
55.
Janowski, B. A., Grogan, M. J., Jones, S. A., Wisely, G. B., Kliewer, S. A., Corey, E. J. & Mangelsdorf, D. J. (1999) Structural requirements of ligands for the oxysterol liver X receptors LXR and LXRß. Proc. Natl. Acad. Sci. U.S.A. 96:266-271.
56. Horton, J. D. & Shimomura, I. (1999) Sterol regulatory element-binding protein: activators of cholesterol and fatty acid biosynthesis. Curr. Opin. Lipidol. 10:143-150.[Medline]
57. Shimano, H., Shimomura, I., Hammer, R. E., Herz, J., Goldstein, J. L., Brown, M. S. & Horton, J. D. (1997) Elevated levels of SREBP-2 and cholesterol synthesis in livers of mice homozygous for a targeted disruption of the SREBP-1 gene. J. Clin. Investig. 100:2115-2124.[Medline]
58.
Caron, M., Auclair, M., Vigouroux, C., Glorian, M., Forest, C. & Capeau, J. (2001) The HIV protease inhibitor indinavir impairs sterol regulatory element-binding protein-1 intranuclear localization, inhibits preadipocytes differentiation, and induces insulin resistance. Diabetes 50:1378-1388.
59.
Bastie, C., Holst, D., Gaillard, D., Jehl-Pietri, C. & Grimaldi, P. A. (1999) Expression of peroxisome proliferator-activated receptor PPAR promotes induction of PPAR and adipocyte differentiation in 3T3C2 fibroblasts. J. Biol. Chem. 274:21920-21925.
60.
Berger, J., Leibowitz, M. D., Doebber, T. W., Elbrecht, A., Zhang, B., Zhou, G., Chhabi Biswas, C., Cullinan, C. A., Hayes, N. S., Li, Y., Tanen, M. T., Ventre, J., Wu, M. S., Berger, G. D., Mosley, R., Marquis, R., Santini, C., Sahoo, S. P., Tolman, R. L., Smith, R. G. & Moller, D. E. (1999) Novel peroxisome proliferator-activated receptor (PPAR) and PPAR ligands produce distinct biological effects. J. Biol. Chem. 274:6718-6725.
61.
Hansen, J. B., Zhang, H., Rasmussen, T. H., Petersen, R. K., Flindt, E. N. & Kristiansen, K. (2001) Peroxisome proliferator-activated receptor (PPAR)-mediated regulation of preadipocyte proliferation and gene expression is dependent on cAMP signaling. J. Biol. Chem. 276:3175-3182.
62.
Froman, B. M., Chen, J. & Evens, R. M. (1997) Hypolipidemic drugs, polyunsaturated fatty acids, and eicosanoids are ligands for peroxisome proliferator-activated receptors and . Proc. Natl. Acad. Sci. U.S.A. 94:4312-4317.
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