Red peppers with different pungencies and bioactive compounds differentially modulate energy and glucose metabolism in ovariectomized rats fed high fat diets
Introduction
Koreans have a much lower average body mass index (BMI) than most of the developed world with only 31.3% of the adult population having a BMI above 25 (Rhee, Park, Kim, & Woo, 2013). In contrast, among adult Americans 72.3% of men and 64.1% of women have BMIs of 25 or more (Flegal, Carroll, Kit, & Ogden, 2012). Undoubtedly, many dietary and lifestyle factors as well as genetic differences contribute to the difference, but the high consumption of red pepper in the Korean diet could be one contributing factor.
Koreans have traditionally consumed relatively large amounts of red pepper, which has been show to improve energy balance via elevating resting energy expenditure (Kim and Park, 2005, Yu et al., 2012). Many human and animal studies have investigated the modulation of energy intake and expenditure by capsaicin, a major component of red pepper (Kwon et al., 2013, Saito and Yoneshiro, 2013). Red pepper intake has increased from 5.2 g/day in 1998 to 7.2 g/day in 2005 in Korea, and the increased intake might be associated with the low prevalence of obesity in the Korean population. Kim and Park (2005) revealed that red pepper intake was positively correlated with energy intake (r = 0.05) in 100 female undergraduate students; but despite the increased energy intake, it was negatively correlated with waist circumferences (r = −0.2) and fat mass (r = −0.2) as measured by bioelectrical impedance analysis, suggesting that red pepper intake might decrease fat mass by increasing energy expenditure. In our previous study (Kwon et al., 2013) 0.025% capsaicin intake decreased body weight gain, visceral fat accumulation, and serum leptin levels without modulating energy intake in diabetic rats. In addition, capsiate, a non-pungent capsinoid, also improved energy homeostasis. Snitker et al. (2009) reported that oral intake of 6 mg/day of non-pungent capsinoids resulted in abdominal fat loss by increasing fat oxidation in 40 obese men and 40 obese women. Another non-pungent capsinoid, dihydrocapsiate (3 or 9 mg/day), is reported to have caused a small thermogenic effect of about 50 kcal/day for 1 month in seventy-eight healthy men. Although no study has reported a direct effect on energy homeostasis, serum levels of β-carotene, another red pepper component, are negatively associated with abdominal fat mass in children (Canas et al., 2012) and β-carotene suppresses fat accumulation in 3T3-L1 adipocytes (Lobo et al., 2010). Overall, all of the major red pepper components including capsaicinoids, capsinoids, and carotenoids have the potential to modulate energy and glucose metabolism in experimental animals and humans.
Different varieties of red peppers contain different combinations of carotenoids, capsaicinoids and capsinoids which give the peppers various colors and pungencies and possibly different effects on energy and glucose homeostasis. However, few studies have investigated the effects of different types of red pepper on energy and glucose homeostasis in experimental animals. Therefore, we hypothesized that different varieties of red peppers having more or less pungency and different colors due to carotenoid content might differently modulate energy and glucose homeostasis in diet-induced obese rats. The objective of the study was to test the hypothesis using three varieties of red pepper from Young Yang County (Gungsangbuk-Do, Korea) according to the intensity of pungency: less pungent red pepper (LSP; Geumdang), moderately pungent red pepper (MSP; Chilsung) and severely pungent red pepper (SSP; Subicho) in ovariectomized (OVX) rats fed a high fat diet and also to explore possible mechanisms. OVX rats have similar symptoms as post-menopausal women with increased visceral fat mass and bone loss (Santollo, Wiley, & Eckel, 2007), making them a good model for studying dietary interventions for preventing obesity and related pathologies.
Section snippets
Extraction and lyophilization
Three varieties of red pepper powders (LSP, MSP, and SSP) were extracted with 70% ethanol by shaking for 24 h at 25 °C, centrifuged, and supernatants lyophilized (Il Shin) 8000g for 30 min.
Analysis of bioactive compounds
Bioactive components in the red pepper extracts were analyzed by HPLC using a YMC ODS-AM (250 mm × 4.6 mm I.D.; particle size, 5 μm) reversed-phase column (JASCO-ChromNAV, Japan). The mobile phase consisted of solvents, 0.1% acetic acid in water (A) and 0.1% acetic acid in acetonitrile (B). The following gradient was
Bioactive components of red peppers
As expected from the pungency, the contents of capsaicin, dihydrocapsaicin and total capsaicinoid concentrations were in an ascending order of LSP < MSP < SSP (Table 1). Capsiate was not detected in any of the red pepper extracts. In red peppers, β-carotene, zeaxanthin, capsanthin, total carotenoids and chlorogenic acid were present in inverse concentrations as capsaicin contents (Table 1). The contents of total flavonoid and total phenolic compounds were higher in descending order of SSP > LSP > MSP (
Discussion
Consistent with our hypothesis, we found that different varieties of red pepper with different pungencies had different concentrations of bioactive compounds which were associated with differential effects on body weight regulation and blood glucose control. The more pungent red peppers, as expected, had higher concentrations of capsaicin and capsaicinoids. However, the higher pungency red peppers had lower concentration of carotenoids. The more pungent peppers were more effective for
Conclusion
Different varieties of red pepper differently modulated energy and glucose metabolism due to different compositions of bioactive compounds such as carotenoids, capsaicinoids, and capsinoids in OVX rats fed a high fat diet. MSP and SSP decreased visceral fat mass but increased brown adipose tissues, resulting in a greater increase in energy expenditure and improved glucose tolerance by potentiating glucose-stimulated insulin secretion and increasing β-cell mass, However, LSP enhanced insulin
Authors’ contribution
HJY, DYK and SP designed research; HJY, MJK, DSK, SK, MNR, LJJ and BKS conducted animal study and biochemical assays; SP DYK and JWD analyzed data and wrote the paper. SP had primary responsibility for final content. All authors contributed to writing drafting of the manuscript and approved the final version of manuscript.
Conflict of interest declaration
The authors declare that there are no conflicts of interest.
Acknowledgements
This work was supported by “Food Functionality Evaluation program” under the Ministry of Food, Agriculture, Forestry and Fisheries and the Korea Science and Engineering Foundation in Korea and partly by Young Yang County.
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