Monocyte chemoattractant protein-1 (MCP-1/chemokine (C–C motif) ligand 2) is a member of the C–C chemotactic cytokine (chemokine) family, produced by multiple cell types constitutively or after induction(Reference Deshmane, Kremlev and Amini1). The circulating level of MCP-1 was found to be approximately 50 % higher in obese mice(Reference Sartipy and Loskutoff2) and in human subjects with type 2 diabetes(Reference Nomura, Shouzu and Omoto3) in comparison with controls. MCP-1 recruits monocytes into adipose tissues and enhances obesity-associated chronic inflammation(Reference Kamei, Tobe and Suzuki4) and insulin resistance(Reference Fantuzzi5). It also facilitates the expansion and remodelling of the adipose tissue during the development of obesity through an angiogenic effect on the endothelial cells(Reference Salcedo, Ponce and Young6); furthermore, this chemokine can decrease the liposynthesis ability of adipocytes(Reference Sartipy and Loskutoff2) and subsequently elevate the NEFA level in the circulation(Reference Kamei, Tobe and Suzuki4), exerting lipotoxicity in the periphery(Reference Unger7). Therefore, inhibiting MCP-1 overproduction has become a preventive strategy for obesity-induced type 2 diabetes.
Our previous study has shown that an ethanol–water extract from bamboo (BEX, Phyllostachys edulis) efficiently protected murine muscle C2C12 cells from lipotoxicity(Reference Panee, Liu and Lin8), an obesity-related condition leading to inflammation and insulin resistance(Reference Boden, She and Mozzoli9, Reference Shi, Kokoeva and Inouye10). In the present study, it is further revealed that the BEX as a dietary supplement significantly decreased the circulating level of MCP-1 in mice treated with a diet containing a high level of saturated fat, with concurrence of decreased weight of the mesenteric fat depot.
Experimental methods
Bamboo extract
The BEX used in the present study was provided by Golden Basin LLC (Kailua, HI, USA). It is prepared from fresh leaves and small branches of bamboo (P. edulis) in Hunan Province, China, through a patented ethanol–water extraction procedure (Chinese invention patent, CN 1287848A).
Animals
Male C57BL/6J mice at 4 weeks of age were purchased from Jackson Laboratories (Bar Harbor, MN, USA). The animals were housed three to four per cage and had ad libitum access to water and food. The room temperature was controlled at 20°C, and lighting was turned on and off with 12 h intervals. Institutional and national guidelines for the care and use of animals were followed, and all experimental procedures involving animals were approved by the Institutional Animal Care and Use Committee at the University of Hawaii (Honolulu, HI, USA).
Dietary treatment
After 1 week of acclimatisation with regular rodent chow, mice were fed a standard diet (10 % energy from fat) or a high-fat diet (60 % energy from fat) with or without the BEX supplement (11 g dry mass per 17 000 kJ) for 6 months. A total of ten mice were used in each dietary group. Body weight and food consumption were measured weekly. All diets were purchased from Research Diets (New Brunswick, NJ, USA). The dietary composition is listed in Table 1.
BEX, bamboo extract.
Measurement of the abdominal fat pads
After euthanisation, epididymal fat, perirenal fat and mesenteric fat were collected and weighed.
Serum monocyte chemoattractant protein-1 quantification
Blood was collected through cardiac puncture. MCP-1 concentrations in the sera were measured using a Cytometric Bead Array – Mouse MCP-1 Flex Set (BD Biosciences, Bedford, MA, USA).
Statistical analysis
Statistical analysis was performed by two-way ANOVA with Bonferroni's post hoc test using the software Prism 4.0a (GraphPad Software, Inc., La Jolla, CA, USA) and Stata 11.0 (StataCorp LP, College Station, TX, USA) (Table 2). The weekly record of body weight was analysed using linear regression with Huber correction and random-effects regression to account for multiple measurements per mouse. P ≤ 0·05 was considered statistically significant.
BEX, bamboo extract.
a,b,c Mean values within a row with unlike superscript letters were significantly different (P < 0·05).
* Energy intake is the average of the weekly measurements.
Results
Table 2 summarises the major findings of the present study. During the 6 months of treatment, the high dietary fat content increased the daily energy intake by approximately 30 % (P < 0·0001). The BEX supplement did not affect the energy intake. The body weight of mice at both start and end points is shown. High-fat diets resulted in an average of 60 % increase in body weight (P < 0·0001) at the end point. When the weekly record of the body weight (data not shown) was analysed, the BEX supplement in the high-fat diet was found to slightly decrease ( − 3 %, P < 0·01) the weight gain of mice.
The high dietary fat content also increased the total weight of the abdominal fat by approximately threefold. When the weight of the individual fat depot was analysed, the BEX was found to increase the epididymal fat by 20 % (0·37 g, P < 0·05) and decrease the mesenteric fat by 24 % (0·52 g, P < 0·01), but did not affect the total weight of the visceral fat. An interaction between the fat content and the BEX was found to play an important role in regulating the weight of the mesenteric fat depot (P < 0·01).
Most interestingly, the BEX supplement dramatically decreased high-fat, diet-induced elevated MCP-1 concentration in the serum ( − 49 %, P < 0·05), and whether this is related to modulated endocrine properties of the visceral fat, especially the mesenteric fat, is to be studied.
Discussion
Using the same diet containing a high level of saturated fat, Yu et al. (Reference Yu, Kim and Kwon11) treated C57BL/6 mice for 3 months and compared the MCP-1 expression and secretion in four types of adipose tissues: mesenteric, epididymal, perirenal and subcutaneous. While the amounts of MCP-1 released by the epididymal, perirenal and subcutaneous fat depots were approximately the same, this level quadruplicated in the mesenteric fat. Mesenteric adipose tissue-conditioned medium also induced the highest degree of macrophage migration and stimulated pro-inflammatory cytokine production in macrophages. These findings indicate that in comparison with the other fat depots, the mesenteric fat tissue has a more pronounced role in obesity-associated inflammation. The present study showed that the BEX supplement in a high-fat diet decreased the weight of the mesenteric fat by 0·52 g, and therefore it may attenuate MCP-1 secretion from this tissue and subsequently contribute to the decrease in MCP-1 in the circulation. Although the BEX increased the weight of the epididymal fat by 0·37 g, this may not compensate the change caused by the mesenteric fat due to the dramatic difference between the MCP-1 secretion abilities of these two fat depots. This suggests that the BEX may alter the distribution of fat storage in the visceral adipose tissues and lower MCP-1 secretion as a final result. Although white adipose tissue is a major source of MCP-1(Reference Sartipy and Loskutoff2), this chemokine is also produced in other tissues(Reference Heymann, Trautwein and Tacke12–Reference Marino, Scuderi and Provenzano14), and therefore a systematic study is needed to evaluate the tissue-specific effect of BEX.
Other natural products that inhibit the overproduction of MCP-1 in obese/diabetic rodents and in cell culture models include traditional Asian medicine(Reference Zhang, Chen and Deng15–Reference Lee, Kang and Kim18), extracts from herbs(Reference Kang, Hirai and Goto19), spices(Reference Jain, Rains and Croad20, Reference Woo, Kang and Kawada21), fruits and vegetables(Reference Abe, Saito and Kubo22–Reference Zhu, Yong and Wu25). Due to the use of different models and experimental procedures, and variable purity of the extracts, it is difficult to perform an accurate comparison between the efficacy of BEX and other reported natural products. The daily dose of BEX used in the present study was 773 mg/kg body weight for mouse, and this corresponds to 63 mg/kg body weight for human subjects (3·8 g/d for a 60 kg adult) when the body surface area normalisation method is used for an allometric dose translation(Reference Reagan-Shaw, Nihal and Ahmad26).
The BEX used in the present study consists of approximately 50 % water, 20 % saccharides, 10 % protein and 20 % other components. The active component(s) contributing to the effects described earlier are to be further determined. The extraordinary abundance of the raw material is a major advantage of this natural product. P. edulis is known for its fast growth, wide geographical distribution and easy propagation. The raw materials (small branches and leaves) used for BEX production are by-products of the bamboo timber industry. Therefore, the present study suggests a potential nutraceutical application of a rich and environmentally friendly natural resource.
Acknowledgements
We thank Dr Leigh Anne Shafer who is funded by the University of Hawaii RCMI Programme for assistance with statistical analysis. The present study was supported by grant no. R21 AT003874-02 (J. P.) and R21 AT005139-01 (J. P.) from the NCCAM and ORWH, 5G12RR003061-23 from the NCRR, and 5P20 MD000173-08 from the NCMHD. The contents of this paper are solely the responsibility of the authors and do not necessarily represent the official views of the funding agencies or the National Institutes of Health. J. K. H. contributed to the MCP-1 measurement and data analysis; W. L. contributed to the animal management; M. J. B. contributed to the general consultation; J. P. contributed to the study design, data analysis and manuscript writing. The authors declare that there are no conflicts of interest.