Telmisartan shows antihypertensive and several pleiotropic effects that interact with metabolic pathways. In the present study we tested the hypothesis that telmisartan prevents adipogenesis in vitro and weight gain in vivo through activation of peroxisome proliferator-activated receptor (PPAR)-δ–dependent pathways in several tissues. In vitro, telmisartan significantly upregulated PPAR-δ expression in 3T3-L1 preadipocytes in a time- and dose-dependent manner. Other than enhancing PPAR-δ expression by 68.2±17.3% and PPAR-δ activity by 102.0±9.0%, telmisartan also upregulated PPAR-γ expression, whereas neither candesartan nor losartan affected PPAR-δ expression. In vivo, long-term administration of telmisartan significantly reduced visceral fat and prevented high-fat diet-induced obesity in wild-type mice and hypertensive rats but not in PPAR-δ knockout mice. Administration of telmisartan did not influence food intake in mice. Telmisartan influenced several lipolytic and energy uncoupling related proteins (UCPs) and enhanced phosphorylated protein kinase A and hormone sensitive lipase but reduced perilipin expression and finally inhibited adipogenesis in 3T3-L1 preadipocytes. Telmisartan-associated reduction of adipogenesis in preadipocytes was significantly blocked after PPAR-δ gene knockout. Chronic telmisartan treatment upregulated the expressions of protein kinase A, hormone-sensitive lipase, and uncoupling protein 1 but reduced perilipin expression in adipose tissue and increased uncoupling protein 2 and 3 expression in skeletal muscle in wild-type mice but not in PPAR-δ knockout mice. We conclude that telmisartan prevents adipogenesis and weight gain through activation of PPAR-δ–dependent lipolytic pathways and energy uncoupling in several tissues.
Abdominal obesity, which increases cardiometabolic risks, is often associated with hypertension.1 Reduction of high blood pressure significantly lowers cardiovascular mortality.2 Evaluation of antihypertensive drugs for their beneficial effects on weight gain may improve clinical management of obese patients with hypertension.
Angiotensin II receptor blockers (ARBs) are commonly used to lower blood pressure.2 Other than their antihypertensive effects, several clinical trials show that ARB can prevent the onset of type 2 diabetes mellitus.3,4 Recently, clinical and experimental studies have shown that ARBs have effects on weight gain and obesity,5–15 which indicate that ARB could be beneficial for the management of obesity related hypertension. Previous studies suggested that several pleiotropic effects of ARBs include upregulation of uncoupling protein (UCP) 1 and angiotensin II receptor type 1 expression, activation of peroxisome proliferator activated receptor (PPAR)-γ, increase of adiponectin, and promotion of caloric expenditure.5,7,10,14–20 However, the precise mechanisms responsible for the effect of ARBs on fat metabolism remain unresolved. Recent studies suggested that activation of PPAR-δ could prevent high-fat diet-induced obesity in rodents.21–23 In addition, obesity is characterized by increased fat storage and reduced lipolysis in adipose tissue and energy uncoupling.24–27 It is unknown whether ARBs may affect PPAR-δ, lipolytic pathways, and energy uncoupling, such as protein kinase A (PKA); hormone-sensitive lipase (HSL); perilipin, an essential lipid droplet-associated protein; and UCPs.5,24–28 In the present study we tested the hypothesis that telmisartan may prevent adipogenesis in vitro and weight gain in vivo through activation of PPAR-δ–dependent lipolytic pathways and energy uncoupling from rodent models.
Methods
Animal Care
C57BL/6J wild-type mice and PPAR-δ knockout mice were purchased from Jackson Laboratory (Bar Harbor, ME). Twelve-week–old male spontaneously hypertensive rats (SHRs) were obtained from Charles Rivers Laboratories. Animals were given the normal chow diet (ND group) or high-fat diet (HD group). The high-fat diet was obtained from SLAC Laboratory Animal Co, Ltd. Mice and rats were housed in a pathogen-free animal facility and allowed water and food ad libitum. Food intake was similar under these conditions. All of the animals were subject to controlled temperature (22±1°C) and lighting (lights on 6:00 am to 6:00 pm). All of the experimental procedures were performed in accordance with protocols approved by the Institutional Animal Care and Research Advisory Committee.
Long-Term Administration of Telmisartan In Vivo
Mice or SHRs were assigned to the different experimental procedures: (1) mice were fed with normal chow (control) and chow mixed into telmisartan 5 mg/kg daily (telmisartan) for 28 weeks; (2) mice were fed with normal chow or a high-fat diet for 24 weeks, then telmisartan (5 mg/kg daily) was given additionally by oral gavage for 4 weeks; and (3) SHRs on a normal chow or high-fat diet were treated with 5 mg/kg daily telmisartan for 16 weeks. Systolic blood pressure of SHRs was measured by tail cuff, and body weight was quantified weekly. At the end of treatment, the animals were fasted for 12 hours before being euthanized by decapitation. Adipose tissues were assayed. Visceral fat weight was determined via dissection of epididymal, retroperitoneal, and mesenteric fat depots. Representative cross-sections of adipose tissue were analyzed for cell size according to standard techniques, and the rest was frozen and stored at −70°C until further processing.
Biochemical Parameters, Histological Analysis, and Immunohistochemistry
For details, refer to the online Data Supplement, available at http://hyper.ahajournals.org. The immunohistochemical procedure was described in our previous study.29
Immunoblotting
Immunoblots of PPAR-δ, PKA, phosphorylated PKA (p-PKA), HSL, perilipin, UCP-1, UCP-2, UCP-3, palmitoyltransferase-1 (CPT1), cytochrome c oxidase (COX2), and β-actin in tissue were performed using standard techniques. For details, refer to the online Data Supplement.
Preadipocyte Culture and Adipocyte Differentiation Assay
The procedures of preadipocyte culture and adipocyte differentiation assay were described in our previous studies.21,30 For details, refer to the online Data Supplement. Other experiments were performed in isolated preadipocyte cells from visceral adipose tissue of C57BL/6J or PPAR-δ knockout mice in the presence of the 10 μmol/L of telmisartan, 10 μmol/L of candesartan, 10 μmol/L of losartan, and 10 μmol/L of GW0742.
Overexpression of PPAR-δ in 3T3-L1 Preadipocytes
The recombinant adenoviral vectors containing rat PPAR-δ were generated as described.21 For details, refer to the online Data Supplement.
Transfection and Luciferase Assay
PPAR-δ activity was determined by transactivation assays in 3T3-L1 preadipocytes and angiotensin II receptor type 1 knockout PC12W cells (Cell Bank, Chinese Academy of Sciences). Cells were plated in 48-well dishes and transfected by use of the Lipofectamine LTX Reagent (Invitrogen), delivering 150 ng of the full-length coding region of rat PPAR-δ expression plasmid pAdTrack-cytomegalovirus-PPAR-δ, 300 ng of luciferase reporter plasmid tk-peroxisome proliferator response element (PPRE) ×3-luc, and 150 ng of pRL-TK renilla luciferase reporter vector as an internal control. After 6 hours, transfection medium was replaced by 10% FBS/DMEM and cells were treated with varying concentrations of the telmisartan and PPAR-δ agonist GW 0742 and incubated for an additional 24 hours. Cells were assayed for luciferase and renilla activity using the Dual-Glo Luciferase Assay System (Promega) and the Varioskan Flash Type 3001(Thermo Electron Corporation). All of the treatments were performed in triplicate and normalized for renilla activity.
Statistics
Data are expressed as mean±SEM. Statistical significance of differences between mean values was assessed by the Student t test or 1-way ANOVA with a Bonferroni multiple comparison post hoc test, as appropriate. Two-sided P values <0.05 were considered to indicate statistical significance.
Results
Telmisartan Activates PPAR-δ in 3T3-L1 Preadipocytes
First, we examined whether telmisartan affects PPAR-δ protein expression. Compared with control, administration of telmisartan (10 μmol/L), but neither candesartan (10 μmol/L) nor losartan (10 μmol/L), significantly increased PPAR-δ expression in 3T3-L1 preadipocytes. Telmisartan significantly upregulated PPAR-δ expression by 68.2±17.3% (P<0.05; Figure 1A).
Figure 1. Telmisartan activates PPAR-δ in 3T3–L1 preadipocytes and PC12W cells. A, PPAR-δ expression in 3T3–L1 preadipocytes was detected by immunoblotting after treatment without (control [Cont]) or with telmisartan (10 μmol/L; Telm), candesartan (10 μmol/L; Cand), or losartan (10 μmol/L; Losa) for 24 hours; *P<0.05 vs control. B, Dose-dependent effect of telmisartan (▪) for 24 hours or control (□) on PPAR-δ in 3T3–L1 preadipocytes; *P<0.05; **P<0.01 vs control. C, Time-dependent effect of telmisartan (10 μmol/L; ▪) or control (□) on PPAR-δ expression; *P<0.05 vs control. D, Transcriptional activity of PPAR-δ in 3T3–L1 preadipocytes, and PC12W cells were evaluated by luciferase assay after treatment with different concentrations of telmisartan; *P<0.05; **P<0.01 vs control. E, PC12W cells from the same passages were transfected with PPRE-luciferase reporter construct with and without PPAR-δ expression vectors, followed by stimulation with telmisartan (10 μmol/L), GW0742 (10 μmol/L), or losartan (10 μmol/L). Luciferase activity was measured after 24 hours. Experiments were repeated 3 times; *P<0.05; **P<0.01 vs control. F, Effect of telmisartan (10 μmol/L; ▪) on PPAR-γ in 3T3–L1 preadipocytes; *P<0.05 vs control. G, PPAR-δ expression in 3T3–L1 preadipocytes was detected without (control; □) or with telmisartan (10 μmol/L; ▪); or telmisartan in the presence of the PPAR-γ inhibitor GW9662 (10 μmol/L; ▪) for 24 hours; **P<0.001 vs control.
Figure 1B shows the dose-dependent effect of telmisartan on PPAR-δ in 3T3-L1 preadipocytes. We observed that telmisartan concentrations >1 μmol/L significantly increased the PPAR-δ expression in these cells. As indicated in Figure 1C, the effect of telmisartan on PPAR-δ expression was time dependent. Administration of telmisartan for 24 hours significantly increased PPAR-δ in 3T3-L1 preadipocytes. Then, we asked whether the telmisartan-induced upregulation of PPAR-δ protein expression is associated with increased PPAR-δ activity. Treatment of PPRE-transfected 3T3-L1 cells and PC12W cells with telmisartan dose-dependently induced transcriptional activity of PPAR-δ (Figure 1D). Compared with control, telmisartan (10 μmol/L) and PPAR-δ agonist GW0742 (10 μmol/L) significantly increased PPAR-δ activity (2.42±0.10-fold and 5.13±1.25-fold, respectively, P<0.01 versus vehicle-treated cells) in PC12W cells, but losartan did not (Figure 1E). Telmisartan also increased PPAR-γ protein expression in preadipocytes by 34±7% of the control (Figure 1F). On the other hand, an increased PPAR-δ could also be observed after administration of telmisartan in the presence of the PPAR-γ inhibitor GW 9662 (Figure 1G).
PPAR-δ Overexpression or Activation Reduces Adipogenesis
Next, we determined whether PPAR-δ overexpression or activation might play a role in adipogenesis. We examined the effect of overexpression or activation of PPAR-δ on the adipogenesis in vitro. Oil red O staining for detection of adipocyte differentiation was investigated. PPAR-δ overexpression reduced lipid droplets in the cytoplasm from cultured 3T3-L1 preadipocytes (Figure 2A). PPAR-δ overexpression was validated by immunoblotting, as shown in Figure 2B. Administration of GW0742 and telmisartan markedly attenuated adipogenesis (Figure 2C, top) and intracellular triglyceride (TG) levels (GW0742 0.74±0.02 mmol/L and telmisartan 0.69±0.02 mmol/L versus control 0.89±0.03 mmol/L; n=6 for each group; P<0.01) in primary cultured visceral preadipocytes from wild-type mice (Figure 2D), whereas GW0742 and telmisartan failed to influence adipogenesis (Figure 2C, middle) and intracellular TG levels (Figure 2E) in cultured visceral preadipocytes from PPAR-δ knockout mice (GW0742 0.90±0.01 mmol/L and telmisartan 0.96±0.04 mmol/L versus control 0.89±0.07 mmol/L; n=6 for each group; P>0.05). As shown in Figure 2C (bottom), after transfecting PPAR-δ null preadipocytes with the recombinant adenoviral PPAR-δ vector, the inhibitory effects of telmisartan and GW0742 on adipogenesis were rescued compared with control conditions, supporting the importance of PPAR-δ for telmisartan-dependent effects.
Figure 2. Effect of PPAR-δ overexpression or PPAR-δ activation on adipogenesis in adipocytes. A, Lipid droplets were visualized by oil red O staining after differentiation of 3T3–L1 preadipocytes with or without PPAR-δ overexpression; magnification, ×200; representative pictures from 3 to 6 separate experiments are shown. B, PPAR-δ overexpression was validated by immunoblotting. C, Lipid droplets were analyzed in primary cultured visceral adipocytes from wild-type mice (WT; top), from PPAR-δ knockout mice (PPAR-δ−/−; middle) or PPAR-δ null preadipocytes with the adenoviral PPAR-δ vector (PPAR δ−/− rescue; bottom) under control conditions, in the presence of GW0742 or in the presence of telmisartan. 3T3–L1 preadipocytes were stimulated using 3-isobutyl-1-methylxanthine (0.5 mmol/L), dexamethasone (1.0 μmol/L), and insulin (5.0 μg/mL). Magnification, ×400; representative photomicrographs of three separate experiments are shown. D and E, Intracellular TG levels in primary cultured adipocyte from wild-type mice (D) and PPAR-δ knockout mice (E) with or without GW0742 (10 μmol/L) or telmisartan (10 μmol/L) treatment for 24 hours. Values are mean±SEM; n=6 per group; **P<0.01 vs control.
Telmisartan Prevents Weight Gain in Mice Through Activation of PPAR-δ
We further studied whether telmisartan affects body weight and adipose tissue in vivo through PPAR-δ. PPAR-δ gene knockout mice and wild-type mice on a normal chow diet were administrated with telmisartan (5 mg/kg per day) for 28 weeks. Baseline characteristics of wild-type and PPAR-δ knockout mice were included in the online Supplemental Data (Table S1).
Telmisartan significantly reduced body weight, weight of adipose tissue, and adipocyte size in wild-type mice (Figure 3A through 3C). Telmisartan significantly reduced visceral fat from 3.0±0.4 to 1.2±0.2 g (P<0.01; Figure 3B). In contrast, administration of telmisartan for 28 weeks did not influence body weight, adipose tissue weight, and adipocyte size in PPAR-δ gene knockout mice (Figure 3D through 3F). Ectopic fat deposition could be observed in liver from wild-type mice on a high-fat diet (Figure S1). Plasma TG levels and free fatty acid (FFA) levels were significantly lower in wild-type mice treated with telmisartan than in untreated mice (TG: 1.07±0.09 mmol/L versus 1.69±0.16 mmol/L, P<0.01; FFA: 0.55±0.06 mmol/L versus 0.79±0.09 mmol/L, P<0.05; n=8 to 10). In contrast, plasma TG and FFA levels were not significantly different in PPAR-δ gene knockout mice treated with telmisartan and untreated knockout mice (TG: 1.58±0.19 mmol/L versus 1.66±0.18 mmol/L, P>0.05; FFA: 0.78±0.23 mmol/L versus 0.63±0.12 mmol/L, P>0.05; n=5). These findings suggest that long-term administration of telmisartan prevents weight gain and reduces the size of adipocytes and weight of adipose tissue by affecting PPAR-δ in mice.
Figure 3. Telmisartan affects the rise of body weight in wild-type mice but not in PPAR-δ knockout mice. Mice were fed with normal chow (control) and chow plus telmisartan 5 mg/kg daily (telmisartan) for 28 weeks. Effect of telmisartan on rise of body weight (A), weight of adipose tissue (B), and adipocytes size (C) are depicted in wild-type mice. Magnification, ×200; *P<0.05; **P<0.01 vs control; WAT indicates white adipose tissue; Sub, subcutaneous fat. Lack of effect of telmisartan on rise of body weight (D), adipocyte size (E), and adipose tissue weight (F) are depicted in PPAR-δ knockout mice; Magnification, ×200.
Telmisartan Prevents High-Fat Diet-Induced Obesity Through PPAR-δ
As shown in Figure 4A, body weight was significantly higher in wild-type mice on a high-fat diet compared with mice on a normal chow diet. Then telmisartan was added after 24 weeks of a high-fat diet. In these mice, additional administration of telmisartan (5 mg/kg daily) for 1 month significantly reduced body weight in mice despite a continuous high-fat diet but had little effect on body weight in mice on a normal chow diet (Figure 4A). PPAR-δ expression was significantly higher in visceral and subcutaneous fat in wild-type mice treated with telmisartan compared with control mice (Figure 4B and 4C). Furthermore, a similar effect of telmisartan on PPAR-δ expression was also observed in skeletal muscle (Figure 4D). These findings support the idea that telmisartan affects PPAR-δ in several tissues.
Figure 4. Effect of telmisartan on body weight and PPAR-δ expression in adipose tissue from wild-type mice. A, Mice were fed with a normal diet or a high-fat diet for 24 weeks, then telmisartan (5 mg/kg daily) was given additionally by oral gavage for 4 weeks; #P<0.05 vs high fat diet (HD); ND + Tel, ND plus telmisartan; HD + Tel, HD plus telmisartan. PPAR-δ protein expression in visceral (B) and subcutaneous adipose tissue (C) and in skeletal muscle from mice (D) were detected by immunoblotting; *P<0.05 vs ND; #P<0.05 vs HD.
Telmisartan Prevents High-Fat Diet-Induced Obesity in SHRs
Obesity is often associated with hypertension. We further asked whether the effect of telmisartan on obesity and PPAR-δ can also be observed in obese SHRs. SHRs on a normal chow diet and on a high-fat diet were treated by telmisartan (5 mg/kg per day) for 16 weeks. Body weight time dependently increased in SHRs. In contrast, the administration of telmisartan for 16 weeks significantly reduced the rise of body weight in SHRs on a normal chow diet, as well as in SHRs on a high-fat diet (Figure 5A; each P<0.01 compared with controls). Telmisartan also significantly lowered systolic blood pressure in SHRs on a normal chow diet (107±8 mm Hg versus 196±9 mm Hg; P<0.01) or on a high-fat diet (113±6 mm Hg versus 195±8 mm Hg; P<0.01). High-fat diet significantly increased weights of subcutaneous and visceral adipose tissue and the size of adipocytes in obese hypertensive rat. Compared with controls, the weight of adipose tissue and the size of adipocytes were significantly lower in SHRs treated with telmisartan (Figure 5B and 5C). As shown in Figure 5F, PPAR-δ expressions in visceral and subcutaneous fat were significantly higher in SHRs treated with telmisartan compared with controls (Figure 5D and 5E).
Figure 5. Effect of telmisartan on adipose tissue and PPAR-δ expression in SHRs. SHRs were fed with ND, HD, ND plus telmisartan (5 mg/kg per day; ND + Tel), and HD plus telmisartan (5 mg/kg per day; HD + Tel) for 16 weeks. Body weight (A), percentage of adipose tissue vs body weight (B), and vs adipocytes size (C) are shown in these groups; magnification, ×200; *P<0.05; **P<0.01 vs ND; #P<0.05; ##P<0.01 vs HD. PPAR-δ protein expression in visceral fat (D) and subcutaneous fat (E) were detected by immunoblotting; *P<0.05; **P<0.01 vs ND; #P<0.05 vs HD.
Effect of Telmisartan on PPAR-δ–Dependent Lipolytic Pathway and Energy Uncoupling
To evaluate whether the effects on telmisartan are mediated by interaction with lipolytic pathways and energy uncoupling, we measured the PKA, HSL, and perilipin in both adipose tissue and preadipocytes. Furthermore, several energy uncoupling–related molecules were investigated in skeletal muscle. First, we showed p-PKA, HSL, and perilipin in adipose tissue by immunofluorescence (Figure 6A). Second, administration of the PPAR-δ agonist, GW0742, or telmisartan significantly increased the expression of p-PKA and HSL but reduced perilipin expression in cultured preadipocytes from wild-type mice. In contrast, GW0742 and telmisartan had no effect on p-PKA, HSL, and perilipin expression in cultured preadipocytes from PPAR-δ gene knockout mice (Figure 6B). Third, we further observed that administration of telmisartan increased the expression of p-PKA and HSL and reduced the perilipin expression in visceral adipose tissue from wild-type mice. In contrast, telmisartan did not affect the expression of p-PKA, HSL, or perilipin in visceral adipose tissue from PPAR-δ gene knockout mice (Figure 6C). Fourth, chronic administration of telmisartan increased the expression of UCP -1 in brown fat (Figure 6D), UCP-2, and UCP-3 in skeletal muscle (Figure 6E) but had no effect on CPT1 and COX2 in skeletal muscle from wild-type mice (Figure 6F). As expected, telmisartan did not affect the expressions of energy uncoupling–related molecules mentioned above in adipose tissue and skeletal muscle from PPAR-δ gene knockout mice (Figure 6D through 6F).
Figure 6. Effect of telmisartan on lipolysis and energy uncoupling. A, Representative immunofluorescence images showing colocalization of HSL, p-PKA, and perilipin in visceral adipose tissue. Bottom panel of each group shows the negative control performed by omitting the primary antibody. Magnification, ×200. B, Protein expression of PKA, p-PKA, HSL, and perilipin in the primary cultured visceral adipocytes obtained from wild-type mice and PPAR-δ knockout mice in the absence (control) or in the presence of telmisartan (10 μmol/L) or PPAR-δ agonist GW0742 (10 μmol/L) for 24 hours; *P<0.05; **P<0.01 vs control. C, Protein expressions of PKA, p-PKA, HSL, and perilipin in visceral fat from wild-type mice and PPAR-δ knockout mice treated with or without telmisartan (5 mg/kg per day); *P<0.05; **P<0.01 vs control. Wild-type mice and PPAR-δ knockout mice were fed with ND and ND plus telmisartan (5 mg/kg per day; ND + Tel) for 28 weeks. D, UCP-1 protein expression in brown fat. E, UCP-2 and UCP-3 protein expressions in skeletal muscle. F, CPT1 and COX2 protein expressions in skeletal muscle. *P<0.05; **P<0.01 vs normal chow.
Discussion
The major findings of this study are that telmisartan significantly upregulated PPAR-δ expression and activity in 3T3-L1 preadipocytes, activated PPAR-δ–dependent lipolytic pathway, and finally reduced adipogenesis in vitro. The effect of telmisartan on lipolysis was abolished after PPAR-δ gene knockout of preadipocytes. In vivo, long-term administration of telmisartan significantly reduced the rise of body weight and prevented high-fat diet-induced obesity in wild-type mice and hypertensive rats but not in PPAR-δ knockout mice. Telmisartan increased the expression of PPAR-δ and several lipolytic and energy uncoupling–related proteins, including PKA, HSL, and UCPs in adipose tissue and skeletal muscle from wild-type mice and SHRs. This effect of telmisartan could not be observed in PPAR-δ knockout mice.
Currently, it is unclear which drugs may be superior to manage obesity-related hypertension. However, antihypertensive drugs showing antiobese properties may be beneficial for obese subjects with hypertension. ARBs are generally used to lower blood pressure.2 Other than their antihypertensive effect, several ARBs have been shown to prevent the new-onset diabetes mellitus, which is supposed be related to PPAR-γ.17,18 Furthermore, Shimabukuro et al11 showed that the visceral fat area, determined by abdominal computed tomography scan, was reduced in hypertensive patients treated with telmisartan for 24 weeks, whereas treatment of patients with amlodipine did not affect abdominal fat. Chujo et al31 reported that telmisartan treatment decreases visceral fat accumulation and improves serum levels of adiponectin and vascular inflammation markers in Japanese hypertensive patients.
In addition, a recent clinical trial showed that administration of irbesartan significantly reduced waist circumference in hypertensive patients with metabolic syndrome.9 Several experimental studies further demonstrated that mice and rats treated with different ARBs show reduced weight gain.11–14 Although telmisartan was reported to reduce the visceral fat, it did not influence body weight or body mass index either in the Ongoing Telmisartan Alone and in Combination With Ramipril Global Endpoint Trial or in the Prevention Regimen for Effectively Avoiding Second Strokes study.32,33 A recent study suggested that body mass index and waist circumference do not adequately mirror visceral fat accumulations in different racial/ethnic groups.34
The effects of ARB on fat metabolism may be mediated by several pathways, including upregulation of UCP1 and angiotensin II type 2 receptor expression,5,15 activation of PPAR-γ,13,16–18 increase of adiponectin,13 and promotion of caloric expenditure.5,14 However, the underlying mechanisms are a matter of debate. For example, telmisartan is regarded as a partial agonist for PPAR-γ16–18; however, PPAR-γ agonists such as rosiglitazone promote adipocyte differentiation and lead to weight gain.13,35 Furthermore, Clemenz et al36 recently identified the telmisartan as a partial PPAR-α agonist at least in the liver. In addition, Benson et al18 showed that telmisartan can also inhibit the proliferation of cells that lack angiotensin II receptors and cells treated with a PPAR-γ antagonist, suggesting that the antiproliferative effects of telmisartan may involve more than just angiotensin II receptor blockade or activation of PPAR-γ. Therefore, published data and our present findings indicate that the actions of telmisartan were not restricted to PPAR-γ alone, but telmisartan may affect different PPAR subtypes.
Now, the present study including PPAR-δ knockout in vitro and in vivo clearly demonstrates that the effects of telmisartan are mediated by its effect on PPAR-δ. The present findings support results by Wang et al20 showing that activation or overexpression of PPAR-δ can prevent high-fat–induced obesity and weight gain by promoting FFA oxidation in adipose tissue.
First, we demonstrated that telmisartan significantly upregulated PPAR-δ expression and activity in 3T3-L1 preadipocytes. Second, administration of telmisartan, the PPAR-δ agonist, GW0742, or PPAR-δ overexpression reduced accumulation of lipid droplets in cultured preadipocytes. Third, long-term administration of telmisartan increased PPAR-δ expression and reduced weight gain and high-fat–induced obesity in wild-type mice. Fourth, the inhibitory effect of telmisartan on weight gain could not be observed in PPAR-δ knockout mice. Telmisartan may affect PPAR-δ because of its high lipophilicity, which is required to obtain sufficient high penetration rates to bind to intracellular PPAR-δ.17,18 The region where telmisartan may bind to that transcription factor is unknown yet.
Obesity is characterized by increased fat storage in the form of TGs in adipose tissue. In addition, lipolysis has been found to be impaired in obesity.37 In humans, catecholamines and insulin are the most important hormones regulating adipocyte lipolysis. HSL is the predominant lipase effector of catecholamine-stimulated lipolysis in adipocytes.27 HSL-dependent lipolysis in response to catecholamines is mediated by PKA-dependent phosphorylation of perilipin, an essential lipid droplet–associated protein.25 It is believed that phosphorylation of perilipin is important for the translocation of HSL from the cytosol to the lipid droplet, a key event to stimulate lipolysis.24–27
In the present study, we show that either activation of PPAR-δ by GW0742 or by telmisartan significantly increased p-PKA and HSL but reduced perilipin expression in preadipocytes. Furthermore, in wild-type mice, long-term administration of telmisartan increased the expression of PPAR-δ, p-PKA, and HSL but reduced the expression of perilipin in visceral fat. By contrast, the effects of telmisartan on p-PKA and HSL were abolished in PPAR-δ knockout mice. These results indicate that activation of PPAR-δ stimulates the lipolytic pathway. Given the wide expression of PPAR-δ, we showed that the observed effects of telmisartan in adipose tissue could also be obtained in skeletal muscle. Our additional experiments showed that telmisartan upregulated UCP-1 expression in brown fat and expressions of UCP-2 and UCP-3 but had no effect on expressions of CPT1 and COX2 in skeletal muscle. These data supported the notion that the effect of telmisartan is not restricted to fat tissue but a common cellular pathway. In addition, telmisartan can improve insulin sensitivity, supporting the hypothesis that telmisartan may exert additional benefit in the management of obese patients with hypertension.38,39 The beneficial effects of telmisartan may be caused by its lipolysis and energy uncoupling, which is in agreement with recent studies.40,41 Benson et al18 and Schupp et al19 have shown that telmisartan dose-dependently induced fatty acid binding protein 2 expression that is an adipogenic marker through PPAR-γ activation. However, Janke et al16 reported that 1 μmol/L of telmisartan increased lipoprotein lipase expression that is one of the key genes involved in TG breakdown, and 10 μmol/L of telmisartan slightly reduced lipid content in preadipocytes through PPAR-γ activation. In the present study, we showed that 10 μmol/L of telmisartan significantly promoted lipolytic pathway and increased PPAR-δ expression and inhibited adipogenesis in 3T3-L1 preadipocytes through PPAR-δ activation. These somewhat discrepant findings reported in the literature indicate that several pathways may finally determine the effect of telmisartan on adipogenesis by interaction with PPAR-γ and PPAR-δ.
Perspectives
The present study gives experimental evidence that telmisartan prevents lipogenesis and weight gain through activation of PPAR-δ–dependent lipolytic pathways in adipose tissue and energy uncoupling in skeletal muscle. Our data point toward a previously unrecognized role of telmisartan in fat metabolism and energy uncoupling, which may be relevant for the management of obese patients with hypertension. Additional benefit in the treatment of obese patients with hypertension using ARBs including telmisartan would be greatly appreciated and should be investigated in future clinical trials.
Acknowledgments
We thank Drs Theodore W. Kurtz, William J. Arendshorst, and Yu Huang for their helpful comments on this article. We thank Lijuan Wang for technical assistance.
Sources of Funding
This study was supported by Natural Science Foundation of China grant 30890042 (to Z.Z.) and grant 30900706 (to H.H.) and 973 Program of China grant 2006CB503905 (to Z.Y.) and grant 2006CB503804 (to D.L.).
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On the cover: Effect of telmisartan on lipolysis and energy uncoupling. Representative immunofluorescence images showing colocalization of hormone-sensitive lipase (HSL), enhanced phosphorylated protein kinase A (p-PKA), and perilipin in visceral adipose tissue. Magnification, ×200. (See page 869.)
From the Center for Hypertension and Metabolic Diseases (D.Y., H.H., S.M., Z.L., X.F., T.C., L.M., Z.Y., D.L., Z.Z.,), Department of Hypertension and Endocrinology, Daping Hospital, Third Military Medical University, Chongqing Institute of Hypertension, Chongqing, China; Medizinische Klinik IV, Nephrologie (M.T.), Charité Campus Benjamin Franklin, Berlin, Germany.
From the Center for Hypertension and Metabolic Diseases (D.Y., H.H., S.M., Z.L., X.F., T.C., L.M., Z.Y., D.L., Z.Z.,), Department of Hypertension and Endocrinology, Daping Hospital, Third Military Medical University, Chongqing Institute of Hypertension, Chongqing, China; Medizinische Klinik IV, Nephrologie (M.T.), Charité Campus Benjamin Franklin, Berlin, Germany.
From the Center for Hypertension and Metabolic Diseases (D.Y., H.H., S.M., Z.L., X.F., T.C., L.M., Z.Y., D.L., Z.Z.,), Department of Hypertension and Endocrinology, Daping Hospital, Third Military Medical University, Chongqing Institute of Hypertension, Chongqing, China; Medizinische Klinik IV, Nephrologie (M.T.), Charité Campus Benjamin Franklin, Berlin, Germany.
From the Center for Hypertension and Metabolic Diseases (D.Y., H.H., S.M., Z.L., X.F., T.C., L.M., Z.Y., D.L., Z.Z.,), Department of Hypertension and Endocrinology, Daping Hospital, Third Military Medical University, Chongqing Institute of Hypertension, Chongqing, China; Medizinische Klinik IV, Nephrologie (M.T.), Charité Campus Benjamin Franklin, Berlin, Germany.
From the Center for Hypertension and Metabolic Diseases (D.Y., H.H., S.M., Z.L., X.F., T.C., L.M., Z.Y., D.L., Z.Z.,), Department of Hypertension and Endocrinology, Daping Hospital, Third Military Medical University, Chongqing Institute of Hypertension, Chongqing, China; Medizinische Klinik IV, Nephrologie (M.T.), Charité Campus Benjamin Franklin, Berlin, Germany.
From the Center for Hypertension and Metabolic Diseases (D.Y., H.H., S.M., Z.L., X.F., T.C., L.M., Z.Y., D.L., Z.Z.,), Department of Hypertension and Endocrinology, Daping Hospital, Third Military Medical University, Chongqing Institute of Hypertension, Chongqing, China; Medizinische Klinik IV, Nephrologie (M.T.), Charité Campus Benjamin Franklin, Berlin, Germany.
From the Center for Hypertension and Metabolic Diseases (D.Y., H.H., S.M., Z.L., X.F., T.C., L.M., Z.Y., D.L., Z.Z.,), Department of Hypertension and Endocrinology, Daping Hospital, Third Military Medical University, Chongqing Institute of Hypertension, Chongqing, China; Medizinische Klinik IV, Nephrologie (M.T.), Charité Campus Benjamin Franklin, Berlin, Germany.
From the Center for Hypertension and Metabolic Diseases (D.Y., H.H., S.M., Z.L., X.F., T.C., L.M., Z.Y., D.L., Z.Z.,), Department of Hypertension and Endocrinology, Daping Hospital, Third Military Medical University, Chongqing Institute of Hypertension, Chongqing, China; Medizinische Klinik IV, Nephrologie (M.T.), Charité Campus Benjamin Franklin, Berlin, Germany.
From the Center for Hypertension and Metabolic Diseases (D.Y., H.H., S.M., Z.L., X.F., T.C., L.M., Z.Y., D.L., Z.Z.,), Department of Hypertension and Endocrinology, Daping Hospital, Third Military Medical University, Chongqing Institute of Hypertension, Chongqing, China; Medizinische Klinik IV, Nephrologie (M.T.), Charité Campus Benjamin Franklin, Berlin, Germany.
From the Center for Hypertension and Metabolic Diseases (D.Y., H.H., S.M., Z.L., X.F., T.C., L.M., Z.Y., D.L., Z.Z.,), Department of Hypertension and Endocrinology, Daping Hospital, Third Military Medical University, Chongqing Institute of Hypertension, Chongqing, China; Medizinische Klinik IV, Nephrologie (M.T.), Charité Campus Benjamin Franklin, Berlin, Germany.
From the Center for Hypertension and Metabolic Diseases (D.Y., H.H., S.M., Z.L., X.F., T.C., L.M., Z.Y., D.L., Z.Z.,), Department of Hypertension and Endocrinology, Daping Hospital, Third Military Medical University, Chongqing Institute of Hypertension, Chongqing, China; Medizinische Klinik IV, Nephrologie (M.T.), Charité Campus Benjamin Franklin, Berlin, Germany.
Correspondence to Zhiming Zhu, Department of Hypertension and Endocrinology, Daping Hospital, Third Military Medical University, Chongqing 400042, People’s Republic of China. E-mail [email protected]; or Daoyan Liu, Center for Hypertension and Metabolic Diseases, Daping Hospital, Third Military Medical University, Chongqing Institute of Hypertension, Chongqing 400042, People’s Republic of China. E-mail [email protected]
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Telmisartan Prevents Weight Gain and Obesity Through Activation of Peroxisome Proliferator-Activated Receptor-δ–Dependent Pathways
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eLetters should relate to an article recently published in the journal and are not a forum for providing unpublished data. Comments are reviewed for appropriate use of tone and language. Comments are not peer-reviewed. Acceptable comments are posted to the journal website only. Comments are not published in an issue and are not indexed in PubMed. Comments should be no longer than 500 words and will only be posted online. References are limited to 10. Authors of the article cited in the comment will be invited to reply, as appropriate.
Comments and feedback on AHA/ASA Scientific Statements and Guidelines should be directed to the AHA/ASA Manuscript Oversight Committee via its Correspondence page.