g width=387.31501159668 height=232.08500289917  />(e)(f)(g)(h)

Figure 2. Effect of treatment with selective PPARδ agonists (GW501516 and HS00098) on serum cholesterol (CHO) (a); high density lipoprotein cholesterol (HDLc) (b); low density lipoprotein cholesterol (LDLc) (c); triglyceride (TG) (d); blood glucose (BG) (e); insulin (f); Apo-A1 (g); and Apo-B100 (h) in diet-induced obese rhesus monkeys. All data are expressed as mean (SD). Each dose was administered for 1 month. Initially and at the end of each month after drug treatment, the data were compared with the control group and analyzed by ANOVA with repeated measures followed by Dunnett’s post hoc test. The values were considered to be significant (*) when a value of P < 0.05 was achieved. N = 5 animals/group.

both drugs could induce weight loss. Although the weight gain of the HS00098 subjects was lower than that of the GW501516 group, it is difficult to determine the cause considering the decreased food intake of the HS00098 animals.

Studies have revealed that PPARδ controls an array of metabolic genes involved in glucose homeostasis and fatty acid synthesis/storage, and mobilization and catabolism in a tissue-specific manner. A number of studies have also shown that PPARδ agonists regulate food intake, body weight, insulin sensitivity, and adiposity [8,24-30]. Transgenic mice, in which constitutively active PPARδ is expressed in muscle, are highly resistant to high-fat, diet-induced obesity [13]. Several synthetic ligands, namely GW501516, GW7042 and L165041, have also been developed, each exhibiting different efficacies in ameliorating symptoms of metabolic disorders [12,29,31,32]. GW501516, a selective PPARδ agonist, promotes fatty acid oxidation and utilization, and reduces lipid accumulation in adipocytes, skeletal muscle, and in the liver in diet-induced obese ob/ob [30], and db/db mice [29]. In fact, GW501516, a high affinity synthetic agonist, has been shown to reduce weight gain and decrease circulating TGs in mice fed a high fat diet or ob/ob mice [14,33]. The results from the GW501516 group in this study and also in a similar report proved that HS00098 (an investigational drug and a PPARδ agonist) had an even stronger effect than the GW501516.

In humans, lipid homeostasis is a delicate balance among dietary intake, de novo synthesis, and catabolism. The increased incidence of cardiovascular disease in Westernized nations has been linked to dyslipidemias associated with changes in the fat content of the diet [34]. Obesity, insulin resistance, and hypertension are comorbidities with these lipid disorders; these together are known as the metabolic syndrome X [35]. Individuals with this condition have high serum triglycerides and abnormally low levels of HDLc [35,36]. This lipid profile is accompanied by an increase in the proportion of small-dense LDL particles, which tend to accumulate in the arterial wall leading to the formation of atherosclerotic cholesterol-laden foam cells [37]. HDL plays a protective role through the process of reverse cholesterol transport whereby cholesterol is removed from the peripheral cells, including the macrophage-derived foam cells, and returned to the liver [38]. Agents that raise the levels of HDL through reverse cholesterol transport could provide a new therapeutic option for the prevention of atherosclerotic cardiovascular disease [2]. Our data showed that both GW501516 and HS00098 reduced circulating TG, T-CHO, Apo-B100, and LDLc and prevented the decline of HDLc, apoA-1, and insulin levels, thereby suggesting that GW 501516 and HS00098 regulated the lipid homeostasis. The data from the test group HS00098 were more pronounced than those from the test group GW501516, thereby suggesting that the effect of HS00098 on serum profiles was stronger than the effect of GW501516. This implied that HS00098 played an important role in ameliorating the serum lipid profiles of high-fat diet-induced obese rhesus monkeys. Collectively, this data suggested that HS00098 and GW501516 increased fat combustion and may provide a means to regulate adiposity.

The effect of GW501516 on glucose homeostasis has been studied in several mouse models of insulin resistance/ type II diabetes. In C57BL/6 mice fed a high fat diet, coadministration of this PPARδ agonist at 3 mg·kg−1·day−1 for 2 months increased the metabolic rate, reduced fatty liver, and decreased lipid accumulation and increased mitochondrial biogenesis in muscle. The circulating insulin levels also declined, whereas the improvement in glucose tolerance and insulin sensitivity determined by the glucose and insulin tolerant test (GTT and ITT) was moderate [33]. The effect appeared to be dose-dependent at 10 mg·kg−1·day−1, wherein the ability of GW501516 to lower blood glucose levels and enhance glucose tolerance became apparent [14]. Interestingly, in addition to improving glucose homeostasis, GW501516 treatment normalized pancreatic islet hypertrophy and increased glucose-stimulated insulin secretion in ob/ob mice [33]. GW501516 did not induce insulin release in isolated islets [39], thereby suggesting that the increased insulin secretion was secondary to improved islet function. Our investigation shows that HS00098 and GW501516 played a role in maintaining blood glucose level stabilization, while it was unstable in the control group. At the same time, compared with the control group, the ascending amplitude of GW501516 and HS00098 group was significantly lower, and the ascending/declining amplitude was similar. The results suggested that GW501516 and HS00098, as PPARδ agonists, played an important role in reducing the insulin level in obese rhesus monkeys and that the two drugs functioned in synergistic competetion with insulin. In addition, the results showed that the 2 drugs regulated the insulin level depending on the concentration of drugs, and it can be seen that HS00098 regulated the insulin level at the 1 mg/kg dosage but GW501516 was effective at the 3 mg/kg dosage. This also suggested that high levels of HS00098 (1 mg/kg) activated PPARδ expression and then synergistically competed with insulin, thereby leading to a lower level of insulin. However, according to the previous report that PPARδ can increase insulin sensitivity [30], HS00098 also had a similar role.

In summary, the above results suggested that the investigational drug (HS00098) can effectively reduce blood lipids and maintain the blood glucose levels of diet-induced obese rhesus monkeys depending on the dose.

5. ACKNOWLEDGEMENTS

Wen Zeng, Zheng-Li Chen and An-Chun Cheng designed research; Qi-Hui Luo and Zheng-Li Chen performed research; An-Chun Cheng and Wen Zeng contributed new analytical tools and reagents; Qi-Hui Luo, Chun-Mei Zhu and Feng-Jun Bi analyzed data; Qi-Hui Luo and Zheng-Li Chen wrote the paper. Zheng-Li Chen is the Corresponding author.

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NOTES

*The study was supported by the Program for Changjiang Scholars and Innovative Research Team in University (IRT0848), the Youth Foundation of Sichuan Province Sci & Tech Bureau, China (08ZQ026-061), the National and Sichuan Province Innovation Funds for Moderate Scale Science and Technology Corporation (06C26215101716), Sichuan Province Basic Research Program (2008JY0100/ 2008JY0102) and Program for Key Disciplines Construction of Sichuan Province (SZD0418).

#Corresponding author.

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