Pharmacognosy Magazine

ORIGINAL ARTICLE
Year
: 2016  |  Volume : 12  |  Issue : 46  |  Page : 120--127

In vitro screening and evaluation of 37 traditional chinese medicines for their potential to activate peroxisome proliferator-activated receptors-γ


Die Gao, Yonglan Zhang, Fengqing Yang, Yexin Lin, Qihui Zhang, Zhining Xia 
 Department of Pharmacy, College of Chemistry and Chemical Engineering, Chongqing University, Chongqing 400030, P.R. China

Correspondence Address:
Zhining Xia
College of Chemistry and Chemical Engineering, Chongqing University, Chongqing 400030
P.R. China

Abstract

Background: Peroxisome proliferator-activated receptors (PPAR)-γ is widely used as an attractive target for the treatment of type 2 diabetes mellitus. Thiazolidinediones, the agonists of PPARγ, has been popularly utilized as insulin sensitizers in the therapy of type 2 diabetes whereas numerous severe side-effects may also occur concomitantly. Objective: The PPARγ activation activity of different polar extracts, including petroleum ether, ethyl acetate, n-butanol, residual of ethanol, the precipitate part of water and the supernatant of water extracts, from 37 traditional Chinese medicines were systematically evaluated. Materials and Methods: HeLa cells were transiently co-transfected with the re-constructed plasmids of GAL4-PPARγ-ligand binding domain and pGL4.35. The activation of PPARγ by different polarity extracts were evaluated based on the PPARγ transactivation assay and rosiglitazone was used as positive control. Results: Seven medicines (root bark of Lycium barbarum, Anoectochilus sroxburghii, the rhizome of Phragmites australis, Pterocephalus hookeri, Polygonatum sibiricum, fruit of Gleditsia sinensis, and Epimedium brevicornu) were able to significantly activate PPARγ. Conclusion: As seven medicines were able to activate PPARγ, the anti-diabetic activity of them is likely to be mediated by this nuclear receptor.



How to cite this article:
Gao D, Zhang Y, Yang F, Lin Y, Zhang Q, Xia Z. In vitro screening and evaluation of 37 traditional chinese medicines for their potential to activate peroxisome proliferator-activated receptors-γ.Phcog Mag 2016;12:120-127


How to cite this URL:
Gao D, Zhang Y, Yang F, Lin Y, Zhang Q, Xia Z. In vitro screening and evaluation of 37 traditional chinese medicines for their potential to activate peroxisome proliferator-activated receptors-γ. Phcog Mag [serial online] 2016 [cited 2021 Jun 20 ];12:120-127
Available from: http://www.phcog.com/text.asp?2016/12/46/120/177909


Full Text

Summary

Lots of the tested medicinal products had activation effects on activating PPARγ Ethyl acetate extracts of root bark of L.barbarum, rhizome of P.saustralis and fruit of G.siasinensis showed good PPARγ activation effect similar or higher than that of positive control, 0.5 μg/mL rosiglitazone Petroleum ether extracts of A.roxburghii, P. hookeri, P. sibiricum, E.brevicornu also can significantly activate PPARγ, the effects of them were higher than t0.5 μg/mL rosiglitazone Schisandra chinensis (Turcz.) Baill., the fruit Cornus officinalis Siebold and Zucc., Alisma plantago-aquatica L. and the root of Trichosanthes Kirilowii Maxim., traditional anti-diabetic mediciness in China, had no effects on the activation of PPARγ.

[Inline:1]

 Introduction



Diabetes mellitus is a metabolic disease characterized by insulin resistance coupled with a lackage of enough insulin to control blood glucose.[1] It is well-known that chronic hyperglycemia results in many diabetic complications such as diabetic nephropathy, obesity, and atherosclerosis.[2]

Peroxisome proliferator-activated receptors (PPARs) have been implicated to participate in many critical physiological and pathological processes, especially in the treatment of diabetes mellitus, obesity, and atherosclerosis.[3],[4] They play important roles in the expression of various genes which are crucial to lipid and glucose metabolism.[5] There are three PPAR subtypes, PPARα, PPARβ/δ, and PPARγ, which have respective expression patterns and regulate different biological processes based on the requirement of a specific tissue.[6] PPARγ is expressed in adipose cells as well as islet beta cells.[7] Activation of PPARγ can improve insulin sensitization and reduce the risk of the insulin resistance in adipose tissue, liver tissue, and et al.[8],[9] The activation of it affects the glucose homeostasis and lipid metabolism as well as inflammation.[10] Increasing evidence indicated that the activation of PPARγ can promote the adipocyte differentiation, decrease the accumulation of glucose in adipose tissue.[11],[12] Moreover, PPARγ plays an important role in the regulation of pancreatic functions and activation of PPARγ can decrease β-cell apoptosis.[13] It is also known that PPARγ affects glucose-stimulated insulin secretion.[14],[15] Therefore, the screening of drugs which can activate PPARγ has great significance in the treatment of diabetes mellitus and related metabolic syndromes.

Thiazolidinediones (TZDs), the agonists of PPARγ, had been demonstrated to have a variety of clinical effects such as enhancing insulin sensitivity and improving glucose tolerance.[16],[17] However, recently evidence demonstrates that TZDs had several side-effects such as cardiovascular risks, liver damage, weight gain, and peripheral edema.[18],[19] On the other hand, traditional Chinese medicines (TCMs) with fewer side-effects have proven historically to be a potential source for drug discovery. Therefore, numbers of researches have been done to explore the activators of PPARγ from TCMs.[10],[20]

In previous study, we developed a cell-based PPARs screening model. The model is a stable and effective assay tool to characterize the interactions between PPAR subtype and PPARs activating drugs. Only when a drug bound and activated GAL4-PPARγ-ligand binding domain (LBD) could the luciferase be expressed. The Z'-factor, which was a useful tool and a statistical characteristic of any given assay, was used to evaluate the reliability and the stability of our model. When the value of Z'-factor was between 0.5 and 1, suggesting that the model was suitable for drug screening. The value of Z'-factor of our model was 0.64.[21]

Herein, this study aimed to preliminary screen and to evaluate the activation of PPARγ by different polarity extracts from 37 TCMs on the basis of PPARγ transactivation assay, laying the basis of further identifying the effects of active extracts on PPARγ-mediated gene expression, and biological responses and isolating the active compounds from active extracts.

 Materials and Methods



Cells and reagents

HeLa cells were purchased from the Cell Center of the Chinese Academy of Medicinal Sciences (Shanghai, China). Fetal bovine serum (FBS) and Dulbecco's modified Eagle's medium (DMEM) were products of Gibco BRL (Gaithersburg, MD, USA). FUGene® HD Transfection Reagent and Bright-Glo ™ Luciferase Assay were purchased from Promega (Madison, WI, USA). Dimethyl sulfoxide (DMSO), penicillin, streptomycin, and rosiglitazone were provided from Sigma-Aldrich Chemical Co, Ltd (St. Louis, MO, USA).

Plasmid construction

pGL4.35 (luc2P/9XGAL4UAS/Hygro) Vector (Product No. E1370) and GAL4-GR Vector (Product No. E1581) were from Promega Corporation (Madison, WI, USA). The synthetic PPARγ-LBD gene sequences were inserted into GAL4-GR vector, and the sequencing of PPARγ-LBD genes was analyzed by restriction enzyme digestion (XhoI and XbaI) and gel electrophoresis. Then PPARγ-LBD replaced glucocorticoid receptor-LBD (GR-LBD) gene fusion in original GAL4-GR Vector and then formed the GAL4-PPARγ-LBD fusion protein. The pGL4.35 (luc2P/9XGAL4UAS/Hygro) vector containing GAL4 special response element of firefly luciferase was used as reporter gene.

Collection of medicines material

The TCMs were obtained from the local drug stores, TCMs markets or production place [Table 1]. Further identification of the specimens was authenticated by Professor GuoyueZhong (Jiangxi University of TCM). All voucher specimens have been deposited at Chongqing Academy of Chinese Materia Medica, Chongqing, China.{Table 1}

Preparation of different polarity extracts

The dried materials of 37 TCMs were ground into fine powder in a pulverizer, respectively. Reflux extraction was conducted in turn by petroleum ether, 70% ethanol, and water. Then, 70% ethanol extract was liquid-liquid extracted by ethyl acetate, while the concentrated segments of water were treated with absolute ethanol until the absolute ethanol reached to 60%. Afterward, the precipitate and the supernatant were collected, respectively. Finally, petroleum ether, ethyl acetate, the residual of ethanol, the precipitate, and the supernatant of water extracts were obtained. Each part was concentrated to dryness in a vacuum to afford samples for biological tests.

The positive drugs, petroleum ether, and ethyl acetate extracts were dissolved in DMSO. The residual of ethanol, the precipitate part of water, and the supernatant of water extracts were dissolved in water. All of them were stored at −20°C.

Cell culture

HeLa cells were grown in DMEM, containing 10% FBS and antibiotics (100 units/mL penicillin and 100 μg/mL streptomycin). All cells were cultivated at 37°C in 5%CO2 atmosphere.

 In Vitro Peroxisome Proliferator-Activated Receptors γ Transactivation Bioassay



HeLa cells were seeded into 6 well-plates at a density of 2 × 105 cells/well in DMEM containing 10% FBS, 100 units/mL penicillin, and 100 μg/mL streptomycin for 24 h. Then, 0.4 μg GAL4-PPARγ-LBD vector and 1.6 μg of pGL4.35 vector were transiently co-transfections into cells under the condition of FuGENE® HD Transfection reagent. After an overnight culture, the cells were replaced into 96 well-plates with new culture medium. 24 h later, negative control, 0.5 μg/mL rosiglitazone, or test samples were added, respectively. After 24 h, the luciferase activity was detected with Bright-Glo ™.

Statistical analysis

Each of these samples was measured in triplicate at various concentrations. Each concentration was tested for sextuplicate. All data are expressed as the mean ± standard deviation. The results were analyzed by one-way, and significant differences were determined by the origin 8.0. Statistical significance is displayed as P < 0.05.

 Results



The dose relationship between positive drug and the activation of peroxisome proliferator-activated receptors γ

To select an appropriate concentration of positive drug, the activation of PPARγ by rosiglitazone was tested (concentration from 0.5 μg/mL to 4.0 μg/mL) by PPARγ transactivation bioassay. The fold activation of rosiglitazone in dose-dependence manner is shows in [Figure 1]. The maximum fold on the activation of PPARγ was 1 μg/mL, and the range of fold activation was from 3.8-to 5.8-folds activation compared to vehicle control (DMSO). On the other hand, there was little change of the fold activation when the concentration of rosiglitazone exceeded 0.5 μg/mL (the range of fold activation was from 3.2 to 5.1 folds activation). Hence, we chose 0.5 μg/mL rosiglitazone as a positive control in later experiments.{Figure 1}

Effects of different polarity extracts on the activation of peroxisome proliferator-activated receptors γ

The activation of PPARγ resulted from 185 different kinds of prepared extracts from selected TCMs were tested for six concentrations, respectively. The results [Table 2] indicated that nine extracts resulted in stronger activation on PPARγ than rosiglitazone based on the comparisons of the maximum folds on the activation of PPARγ.{Table 2}

Ethyl acetate extract of root bark of Lyciumbarbarum had the strongest effect on activating PPARγ in all extracts. The maximum fold was 7.11-fold (50 μg/mL), which equal to 207% of positive drug [Figure 2]a. Besides, ethyl acetate extracts of rhizome of Phragmitesaustralis and fruit of Gleditsiasinensis also could significantly activate PPARγ. The maximum fold on the activation of PPARγ by rhizome of P. saustralis was 5.69 fold, which was 137% of 0.5 μg/mL rosiglitazone [Figure 2]b. The maximum fold activation of the fruit of G. sinensis was 5.02-fold, about 105% that of positive control [Figure 2]c.{Figure 2}

Petroleum ether extracts of Anoectochilusroxburghii, Pterocephalushookeri, Polygonatumsibiricum, Epimediumbrevicornu also can significantly activate PPARγ. The maximum folds on the activation of PPARγ by them were higher than that of positive drug. The maximum fold to activate PPARγ by A. sroxburghii was 5.15 fold, about 160% compared to 0.5 μg/mL rosiglitazone [Figure 3]a. The maximum fold to activate PPARγ by P. hookeri was 4.06 fold, 121% of positive control [Figure 3]b. The maximum folds on the activation of PPARγ by P. sibiricum and E. brevicornu were 4.67 fold and 5.76 fold, which equaled to 117% and 104% of 0.5 μg/mL rosiglitazone [Figure 3]c and [Figure 3]d.{Figure 3}

In addition, the residual of ethanol and the supernatant of water extracts of P. hookeri also had remarkable activation effects on PPARγ [Figure 4]a and [Figure 4]b. The maximum folds on the activation of PPARγ by them were similar to positive drug. The maximum folds to activate PPARγ by the residual of ethanol and the supernatant of water extracts were 3.65 fold and 3.61 fold, which were 107% and 104% that of positive control, respectively.{Figure 4}

However, traditionally anti-diabetic medicine including Schisandra chinensis, the fruit of Calendula officinalis, Alismaplantago-aquatica and the root of Trichosantheskirilowii, had no effects on the activation of PPARγ.

 Discussion



Nuclear receptors are large family of receptors which allow an access to the control of gene regulation. The family contains steroid receptors, metabolic receptors, retinoid receptors, Vitamin D receptor and et al.[22],[23] They play important roles in normal development, reproduction, and metabolism.[24],[25],[26] Most nuclear receptors, share a similar basic structure that contains two important domains named LBD and DNA-binding domain. The two domains are crucial for the regulation of the transcription of nuclear receptors. Especially, the LBD fulfills the functions of ligand binding, dimerization, and recruitment of co-regulators.[27],[28],[29] Ligand binding and activation of nuclear receptor induces a conformational change of it and participates in the regulation of transcription via many approaches such as activation of phosphorylation of the receptor, replacement of corepressors by coactivators and et al.[30],[31]

Considering that nuclear receptor family binds to a wide range of lipophilic ligands derived from daily life, targeting nuclear receptors have been a major source for the development of new drugs.[32] It is noteworthy that researchers have found some active compounds from traditional medicines which are the ligands for some of these nuclear receptors.[23],[33] For example, honoliol, a compound isolated from magnolia bark, is a partial PPARγ agonist which binds directly to PPARγ LBD.[20] On accounting that honokiol can prevent hyperglycemia and weight gain in mice, it becomes a clinically interesting compound which has opportunity to replace TZDs.

In the past few decades, the prevalence of diabetes mellitus has increased, especially type 2 diabetes. Type 2 diabetes mellitus are closely related to unhealthy diet, sedentary lifestyle, as well as the rise of obesity in the population, which in turn impel the search for new preventive and treatment strategies.[34],[35] In recent years, metabolic receptors from nuclear receptor family get more and more attention due to their regulation of metabolic homeostasis.[36],[37] It is noteworthy that PPARγ, which belongs to PPAR family, is widely used as an important target for the treatment of diabetes mellitus. Ligand binding of PPARγ can induce the expression of a lot of genes which in turns changes the lipids and glucose metabolism.[38],[39] However, common agonists of PPARγ such as TZDs, have many serious side-effects such as cardiovascular risks, liver damage, weight gain, and peripheral edema.[40] Hence, significant research efforts have recently been undertaken to explore the potential drugs of activating PPARγ with less adverse effects.[40],[41],[42],[43] TCMs seem to be an ideal replacement of TZDs for the treatment of hyperglycemia, insulin resistance, and the diabetic complications with less adverse effects.[44],[45],[46]

Based on the cell-based PPARs screening model.[47] In this study, thirty-seven traditionally used anti-diabetic TCMs were selected and to evaluate their activation activities of PPARγ. The activations of PPARγ-LBD by different polarity extracts from 37 TCMs were evaluated. The results indicated that the ethyl acetate extracts of root bark of L. barbarum, rhizome of P. saustralis and fruit of G. sinensis could significantly activate PPARγ. The activities of them were higher than that of 0.5 μg/mL rosiglitazone. Besides, petroleum ether extracts of A. sroxburghii, P. hookeri, P.sibiricum, E. brevicornu also can significantly activate PPARγ. The activities of them were also higher than that of 0.5 μg/mL rosiglitazone. Furthermore, the residual of ethanol and the supernatant of water extracts of P. hookeri had remarkable activation effects on PPARγ. Thus, three extracts (petroleum ether, the residual of ethanol and the supernatant of water) of P.hookeri were found to have a significant effect on the activation of PPARγ compared to 0.5 μg/mL rosiglitazone. On the other hand, previous studies showed that P. hookeri had good anti-inflammatory effects, and it was used to treat inflammation and analgesic in Tibet of China.[48] Other evidence also demonstrated that the ligands of PPARγ can treat inflammation in the development of diabetes mellitus.[49],[50] Therefore, it is speculated that the significant activation of PPARγ by P. hookeri might be related to its remarkable anti-inflammatory activity.

On the contrary, we found that all extracts of S. chinensis, C. officinalis, A.plantago-aquatica, and the root of T. kirilowii could not activate PPARγ. Previous studies showed that extracts of S. chinensis were effective when used as aldosereductase inhibitors for the treatment of diabetes mellitus.[51] The petroleum ether extract of it had PTP1B and alpha-glucosidase inhibitory activities. Moreover, schisandrols A and B, schisandrins A and B from S. chinensis were the ligands of pregnane X receptor, a xenobiotic receptor from nuclear receptor family.[23] Thus, it was speculated that the anti-diabetic effect of S.chinensis was through activating mulitiple targets except for PPARγ. Similar to S.chinensis, the anti-diabetic effects of C. officinalis, A. plantago-aquatica and the root of T. kirilowii were not through activating PPARγ.

Momordicacharantia also named “bitter gourd” had been found to be able to activate PPARα and PPARγ in vitro.[52] In our study, we also found it can activate PPARγ. Furthermore, extracts of Panaxginseng, Salviamiltiorrhiza, and Gynostemmapentaphyllum also can activate PPARγ.[23],[53] The results were consistent with the previous study. However, among these chosen TCMs, only a few of them had been studied with regard to the PPARγ activation through a PPARγ transactivation assay in vitro. Our study firstly evaluated the PPARγ activation by different polarity extracts from 37 TCMs with a PPARγ transactivation assay, providing the basis of clarifying the specific mechanism, looking for other targets of activating extracts and screening the active compounds. Further studies will be focused on studying the specific mechanisms of active extracts on activating PPARγ and screening of the active compounds through bio-guided separation.

 Conclusion



In summary, we have established that petroleum ether extracts of A. sroxburghii, P.hookeri, P.sibiricum, E. brevicornu, ethyl acetate extracts of root bark of L. barbarum, rhizome of P. saustralis and fruit of G. sinensis can significantly activate PPARγ as shown by specific activation of a PPARγ-LBD luciferase receptor assay. Hence, the anti-diabetic activity of them could in part be mediated by this nuclear receptor. Additional research will be necessary to further identify the effects of active extracts such as ethyl acetate extract of root bark of L. barbarum on PPARγ-mediated gene expression and biological responses. Moreover, further studies also will be done to identify the active compounds of PPARγ-LBD.

Financial support and sponsorship

Financial Support of this paper is provided by The National Natural Science Foundation of China (Grant No. 21175159, No. 21275169 and No. 81202886) and The International Cooperation Project of Ministry of Science and Technology of China (Grant No. 2010DFA32680).

Conflicts of interest

There are no conflicts of interest.

References

1Janani C, Ranjitha Kumari BD. PPAR gamma gene - A review. Diabetes Metab Syndr Clin Res Rev 2014;438:1-5.
2Zephy D, Ahmad J. Type 2 diabetes mellitus: Role of melatonin and oxidative stress. Diabetes Metab Syndr 2015;9:127-31.
3Wahli W, Michalik L. PPARs at the crossroads of lipid signaling and inflammation. Trends Endocrinol Metab 2012;23:351-63.
4Wang Yx. PPARs: Diverse regulators in energy metabolism and metabolic diseases. Cell Res 2010;20:124-37.
5Abbas A, Blandon J, Rude J, Elfar A, Mukherjee D. PPAR-agonist in treatment of diabetes: Cardiovascular safety considerations. Cardiovasc Hematol Agents Med Chem 2012;10:124-34.
6Montagner A, Rando G, Degueurce G, Leuenberger N, Michalik L, Wahli W. New insights into the role of PPARs. Prostaglandins Leukot Essent Fatty Acids 2011;85:235-43.
7Dubois M, Pattou F, Kerr-Conte J, Gmyr V, Vandewalle B, Desreumaux P, et al. Expression of peroxisome proliferator-activated receptor gamma (PPAR gamma) in normal human pancreatic islet cells. Diabetologia 2000;43:1165-9.
8Amin RH, Mathews ST, Camp HS, Ding L, Leff T. Selective activation of PPARγ in skeletal muscle induces endogenous production of adiponectin and protects mice from diet-induced insulin resistance. Am J Physiol Endocrinol Metab 2010;298:E28-37.
9Grygiel-Gorniak B. Peroxisome proliferator-activated receptors and their ligands: Nutritional and clinical implications – A review. Nut J 2014;13:17.
10Wang L, Waltenberger B, Pferschy-Wenzig EM, Blunder M, Liu X, Malainer C, et al. Natural product agonists of peroxisome proliferator-activated receptor gamma (PPARgamma): A review. Biochem Pharmacol 2014;92:73-89.
11Morales-Garcia JA, Luna-Medina R, Alfaro-Cervello C, Cortes-Canteli M, Santos A, Garcia-Verdugo JM, et al. Peroxisome proliferator-activated receptor ? ligands regulate neural stem cell proliferation and differentiation in vitro and in vivo. Glia 2011;59:293-307.
12Grimaldi PA. The roles of PPARs in adipocyte differentiation. Prog Lipid Res 2001;40:269-81.
13Lin CY, Gurlo T, Haataja L, Hsueh WA, Butler PC. Activation of peroxisome proliferator-activated receptor-gamma by rosiglitazone protects human islet cells against human islet amyloid polypeptide toxicity by a phosphatidylinositol 3 '-kinase-dependent pathway. J Clin Endocrinol Metab 2005;90:6678-86.
14Kim HS, Hwang YC, Koo SH, Park KS, Lee MS, Kim KW, et al. PPAR-gamma activation increases insulin secretion through the up-regulation of the free fatty acid receptor GPR40 in pancreatic ß-cells. PLoS One 2013;8:e50128.
15Kim HI, Kim JW, Kim SH, Cha JY, Kim KS, Ahn YH. Identification and functional characterization of the peroxisomal proliferator response element in rat GLUT2 promoter. Diabetes 2000;49:1517-24.
16Durbin RJ. Thiazolidinedione therapy in the prevention/delay of type 2 diabetes in patients with impaired glucose tolerance and insulin resistance. Diabetes Obes Metab 2004;6:280-5.
17Boyle PJ, King AB, Olansky L, Marchetti A, Lau H, Magar R, et al. Effects of pioglitazone and rosiglitazone on blood lipid levels and glycemic control in patients with type 2 diabetes mellitus: A retrospective review of randomly selected medical records. Clin Ther 2002;24:378-96.
18Shah P, Mudaliar S. Pioglitazone: Side effect and safety profile. Expert Opin Drug Saf 2010;9:347-54.
19Dunn FL, Higgins LS, Fredrickson J, DePaoli AM; INT- study group. Selective modulation of PPARγ activity can lower plasma glucose without typical thiazolidinedione side-effects in patients with Type 2 diabetes. J Diabetes Complications 2011;25:151-8.
20Atanasov AG, Wang JN, Gu SP, Bu J, Kramer MP, Baumgartner L, et al. Honokiol: A non-adipogenic PPAR gamma agonist from nature. Biochim Biophys Acta 2013;1830:4813-9.
21Xia ZN, Lin YX, Guo LX, Yang FQ, Xu P, Zhang YL, et al. Development of a cell-based high-throughput peroxisome proliferator-activated receptors (PPARs) screening model and its application for evaluation of the extracts from rhizoma Coptis. J Asian Nat Prod Res 2013;15:225-34.
22Cookman CJ, Belcher SM. Classical nuclear hormone receptor activity as a mediator of complex concentration response relationships for endocrine active compounds. Curr Opin Pharmacol 2014;19:112-9.
23Li L, Bonneton F, Chen XY, Laudet V. Botanical compounds and their regulation of nuclear receptor action: The case of traditional Chinese medicine. Mol Cell Endocrinol 2015;401:221-37.
24Gonzalez-Sanchez E, Firrincieli D, Housset C, Chignard N. Nuclear receptors in acute and chronic cholestasis. Dig Dis 2015;33:357-66.
25Moschetta A. Nuclear receptors and cholesterol metabolism in the intestine. Atheroscler Suppl 2015;17:9-11.
26Polvani S, Tarocchi M, Tempesti S, Galli A. Nuclear receptors and pathogenesis of pancreatic cancer. World J Gastroenterol 2014;20:12062-81.
27Vincent ZA, Aurelien GA, Michielin O. Peroxisome proliferator-activated receptor structures: Ligand specificity, molecular switch and interactions with regulators. Biochim Biophys Acta Mol Cell Biol Lipids 2007;1771:915-25.
28Kojetin DJ, Burris TP. Small molecule modulation of nuclear receptor conformational dynamics: Implications for function and drug discovery. Mol Pharmacol 2013;83:1-8.
29Rochel N, Moras D. Ligand binding domain of Vitamin D receptors. Curr Top Med Chem 2006;6:1229-41.
30Weatherman RV, Fletterick RJ, Scanlan TS. Nuclear-receptor ligands and ligand-binding domains. Annu Rev Biochem 1999;68:559-81.
31Feige JN, Gelman L, Michalik L, Desvergne B, Wahli W. From molecular action to physiological outputs: Peroxisome proliferator-activated receptors are nuclear receptors at the crossroads of key cellular functions. Prog Lipid Res 2006;45:120-59.
32Gronemeyer H, Gustafsson JA, Laudet V. Principles for modulation of the nuclear receptor superfamily. Nat Rev Drug Discov 2004;3:950-64.
33Guo D, Wang J, Wang X, Luo H, Zhang H, Cao D, et al. Double directional adjusting estrogenic effect of naringin from Rhizoma drynariae (Gusuibu). J Ethnopharmacol 2011;138:451-7.
34Pulgaron ER, Delamater AM. Obesity and type 2 diabetes in children: Epidemiology and treatment. Curr Diab Rep 2014;14:508.
35Van Buren DJ, Tibbs TL. Lifestyle interventions to reduce diabetes and cardiovascular disease risk among children. Curr Diab Rep 2014;14:557.
36Chawla A, Repa JJ, Evans RM, Mangelsdorf DJ. Nuclear receptors and lipid physiology: Opening the X-files. Science 2001;294:1866-70.
37Senese R, Lasala P, Lseanza C, de Lange P. New avenues for regulation of lipid metabolism by thyroid hormones and analogs. Front Physiol 2014;5:475.
38Houseknecht KL, Cole BM, Steele PJ. Peroxisome proliferator-activated receptor gamma (PPAR gamma) and its ligands: A review. Domest Anim Endocrinol 2002;22:1-23.
39Kliewer SA, Xu HE, Lambert MH, Willson TM. Peroxisome proliferator-activated receptors: From genes to physiology. Recent Prog Horm Res 2001;56:239-63.
40Kung J, Henry RR. Thiazolidinedione safety. Expert Opin Drug Saf 2012;11:565-79.
41Rubenstrunk A, Hanf R, Hum DW, Fruchart JC, Staels B. Safety issues and prospects for future generations of PPAR modulators. Biochim Biophys Acta 2007;1771:1065-81.
42Sood V, Colleran K, Burge MR. Thiazolidinediones: A comparative review of approved uses. Diabetes Technol Ther 2000;2:429-40.
43Higgins LS, DePaoli AM. Selective peroxisome proliferator-activated receptor gamma (PPAR gamma) modulation as a strategy for safer therapeutic PPAR gamma activation. Am J Clin Nutr 2010;91:267S-72S.
44Gupta RK, Kesari AN, Murthy PS, Chandra R, Tandon V, Watal G. Hypoglycemic and antidiabetic effect of ethanolic extract of leaves of Annona squamosa L. in experimental animals. J Ethnopharmacol 2005;99:75-81.
45Modak M, Dixit P, Londhe J, Ghaskadbi S, Devasagayam TP. Indian herbs and herbal drugs used for the treatment of diabetes. J Clin Biochem Nutr 2007;40:163-73.
46Malviya N, Jain S, Malviya S. Antidiabetic potential of medicinal plants. Acta Pol Pharm 2010;67:113-8.
47Xia ZN, Lin YX, Guo LX, Yang FQ, Xu P, Zhang YL, et al. Development of a cell-based high-throughput peroxisome proliferator-activated receptors (PPARs) screening model and its application for evaluation of the extracts from rhizoma Coptis. J Asian Nat Prod Res 2013;15:225-34.
48Zhang L, Hu JJ, Lin JW, Fang WS, Du GH. Anti-inflammatory and analgesic effects of ethanol and aqueous extracts of Pterocephalushookeri (C.B. Clarke) Höeck. J Ethnopharmacol 2009;123:510-4.
49Donath MY, Shoelson SE. Type 2 diabetes as an inflammatory disease. Nat Rev Immunol 2011;11:98-107.
50Varga T, Czimmerer Z, Nagy L. PPARs are a unique set of fatty acid regulated transcription factors controlling both lipid metabolism and inflammation. Biochim Biophys Acta 2011;1812:1007-22.
51Li WL, Zheng HC, Bukuru J, De Kimpe N. Natural medicines used in the traditional Chinese medical system for therapy of diabetes mellitus. J Ethnopharmacol 2004;92:1-21.
52Chao CY, Huang CJ. Bitter gourd (Momordica charantia) extract activates peroxisome proliferator-activated receptors and upregulates the expression of the acyl CoA oxidase gene in H4IIEC3 hepatoma cells. J Biomed Sci 2003;10 (6 Pt 2):782-91.
53Gong Z, Huang C, Sheng X, Zhang Y, Li Q, Wang MW, et al. The role of tanshinone IIA in the treatment of obesity through peroxisome proliferator-activated receptor gamma antagonism. Endocrinology 2009;150:104-13.