Mingyan Xiang

Breast milk levels of zinc and ω‐6 polyunsaturated fatty acids and growth of healthy Chinese infants

Aim: To examine the concentrations of zinc and ω‐6 polyunsaturated fatty acids (ω‐6 PUFAs) in breast milk, the impact of zinc on ω‐6 PUFA metabolism, and the growth rate of infants.

A pilot study investigating the effects of Yakult fermented milk drink (L. casei Shirota) on salivary IFN-y, sIgA, IgA1 and IgA2 in healthy volunteers

This pilot study investigated the effects on salivary cytokine and sIgA before and after daily consumption of Lactobacillus casei Shirota (LcS) in nine healthy adult volunteers. Subjects were asked to consume two bottles each day of a fermented milk drink containing a total of 1.3 · 1010 live cells of LcS (Yakult), for 4 weeks. Volunteers were asked to avoid food and drink for at least 1 h before morning unstimulated saliva samples were collected over a 5 min period. Samples were collected at baseline, at week 1, 2 and 4 of LcS consumption, and 2 weeks after cessation of consumption. We found a significant transient increase in salivary IFN-g levels, but were unable to detect IL-12, and an increase in salivary sIgA, IgA1 and IgA2 secretion. Baseline salivary IFN-g was below the assay detection limits. However, at week 1, 4/9 subjects had detectable salivary IFN-g levels, 8/9 (P<0.01) at week 2 and 3/9 at week 4. None had detectable IFN-g levels at week 6. IFN-g concentrations ranged from 35.3 to 92.0 pg/ml. There was a significant (P<0.02) increase in salivary sIgA secretion rate at week 4 (Fig. A). At week 6, the sIgA secretion rate was greater than baseline. The IgA1 secretion rate was significantly greater than baseline at week 4 (P<0.05) and week 6 (P<0.02) (Fig. B). The IgA2 secretion was also significantly increased at week 4 (P<0.05) and week 6 (P<0.01) (Fig. B) and the IgA1:IgA2 ratio significantly greater at week 2 (P<0.01). This pilot study demonstrates that LcS can induce increased salivary IFN-g, sIgA, IgA1 and IgA2 secretion in healthy adults, which may improve mucosal immunity in the upper respiratory tract and provide health related benefits. A larger detailed study investigating cytokine networks, immunoglobulins and T cell responses in different immune system compartments in parallel with a placebo control group would define more rigorously and precisely the immunological effects of LcS (Yakult).

Relation between visfatin as a novel adipokine and AMP-activated protein kinase in obesity

Obesity is a serious public health problem because it increases the risk of chronic diseases such as diabetes mellitus, cardiovascular disease, stroke and some cancers. Visfatin, known as pre-B cell colony-enhancing factor (PBEF) and nicotinamide phosphoribosyltransferase (Nampt), is regarded as a novel adipokine that improves glucose tolerance and may play a role in the development of obesityassociated insulin resistance and type 2 diabetes mellitus (T2DM). Visfatin/PBEF/Nampt is preferentially expressed by visceral adipose tissue compared with subcutaneous fat. AMP-activated protein kinase (AMPK) is a major regulator of energy metabolism at both the cell and the whole body level. Many studies have suggested a role for AMPK in the physiological regulation of fatty acid and glucose metabolism, and in the regulation of appetite and of body weight. Therefore, AMPK is considered as a major player in the development of obesity. The model of diet-induced obesity (DIO) in rats has many features in common with human obesity and can serve as a model to study the pathogenesis and treatment of obesity. In Wistar rats, a half of the rats became hyperphagic and developed DIO, whereas the rest were diet-resistant (DR) when the rats were fed with a high fat (44% fat) diet. The present study investigated the relationship between visfatin and activated and inactivated AMPK (p-AMPK:AMPK) in DIO and DR rats. Male Wistar rats (n = 20) at 4 weeks of age were fed rat chow for 3 days and were switched to high fat diet (3.98 kcal/g with 44% as fat) for 10 weeks. At the end of this period, 7 highest and 7 lowest abdominal fat pads (% body weight) gainers were retrospectively identified as DIO and DR, respectively. It was found that plasma visfatin in the DIO rats increased by 18% compared to the DR rats. Furthermore, visfatin of the visceral adipose tissue in the DIO rats was significantly higher than that of the DR rats. However, AMPK of the visceral adipose tissue in the DIO rats was significantly lower than that of the DR rats. A significant negative correlation was found between the visfatin and AMPK of visceral adipose tissue (r = 0.58, P<0.05; Fig.). These results indicate that the elevated visfatin expression and lowered AMPK activity in visceral adipose tissue may be related to the development of obese condition in rats. Visfatin may play a role in obesity development by down-regulating AMPK activity.

Effect of exercise on visfatin and AMP-activated protein kinase expression in obesity

Obesity is considered as a chronic condition of clinical significance, obese individuals are subject to a high level of stigmatization resulting in discrimination. Visfatin, known as pre-B cell colony-enhancing factor (PBEF) and nicotinamide phosphoribosyltransferase (Nampt), has been identified as a new adipocytokine affecting insulin resistance by binding to the insulin receptor. AMPK plays a central role in the development and therapy of metabolic disorders such as diabetes and obesity, and has been recognized as a possible drug target. Understanding the molecular events initiated by regular exercise can be studied in laboratory animals such as rodents. The model of diet-induced obesity (DIO) in rats has many features in common with human obesity and can serve as a useful model to study the pathogenesis and treatment of obesity. The present study investigated the relationship between visfatin and AMPK in DIO and DIOswimming rats. Male Sprague-Dawley rats (n = 110) at 3 weeks of age were randomly assigned into groups. Ten rats were fed rat chow during the study as the control and 100 rats were fed both rat chow plus high fat diet [HFD, 5.58 kcal/g (23.35 kJ/g) with 66.5% as fat/ lard] ad libitum for 14 weeks. At the end of this period, 44 rats developed DIO which was assessed by the Lee obesity index. The DIO rat’s Lee obesity index was more than the average Lee obesity index plus 2 SD of the chow-fed control rats. At week 15, 10 chow-fed control rats were kept on the rat chow, 11 DIO rats were kept on the rat chow plus HFD ad libitum and the other 11 DIO rats were also kept on the rat chow plus HFD ad libitum and trained to swim at 28–30 C for 40 min/d and 6 days/week for 5 weeks (DIO-swimming). Other rats were used in other studies (data not presented). Plasma visfatin concentration in DIO-swimming rats and chow-fed control rats tended to be (or was significantly) lower than that of DIO rats. DIO-swimming rats had significantly lower visfatin expression in the visceral adipose tissue than DIO rats, however, they had significantly higher visfatin expression than chow-fed control rats (Figure). Moreover, the activity of AMPK in the visceral adipose tissue was significantly (or tended to be) higher in both DIO-swimming and chowfed control rats than DIO rats (Figure). These results indicate that exercise which can be part of lifestyle modification, may inactive visfatin and activate AMPK in several ways contributing to glucose and fat oxidation. Visfatin and AMPK may play important roles in the development of obesity.

Effect of high-dose creatine supplementation on endogenous creatine synthesis during exercise

Creatine (Cre) has become one of the most popular ergogenic sport supplements used today. Cre supplementation can improve athletic performance and cellular bioenergetics. A routine oral Cre protocol recommended for humans is a loading dose of 20 g/d (0.3 g/kg/d, 67 kg body weight) for 5–7 days, followed by a long-term maintenance dose of 2–5 g/d (0.03–0.075 g/kg/d). The doses of 1.5 g/kg/d and 0.15 g/kg/d for rats were calculated from the recommended loading dose of 20 g/d (0.3 g/kg/d) and the maintainable dose of 2 g/d (0.03 g/kg/d) for human subjects according to Calabrese. Thus the amounts of 1.5 and 6.0 g/kg/d Cre were considered to be highor higher-dose in the rat study. The L-arginine:glycine amidinotransferase (L-AGAT) in kidneys is regarded as a key enzyme in the endogenous Cre synthesis in mammals, and the guanidinoacetic acid (GAA) is the precursor in this synthesis. The aim of the present study was to determine the effect of supplementation with 0, 1.5 and 6.0 g Cre /kg body weight per day for 2 weeks on the L-AGAT activity in the kidneys, the GAA concentration in the livers, and serum Cre and creatinine in swim-trained male Sprague–Dawley rats. L-AGAT activity and the GAA concentration were determined spectroscopically. Cre and creatinine in serum were also measured using an autoanalyser (7170A Hitachi Ltd., Japan). Treatment groups rats (n = 10 per group) were trained to swim for 2 h/d and 6 days/week for 2 weeks. The control group rats (without Cre supplementation, n = 10) were sedentary for 2 weeks. In the comparison between the swimtrained group without Cre supplementation and the control group, L-AGAT activity and GAA concentration in the swim-trained group increased (%) by 15.4 (P<0.01) and 26.7 (P<0.01). In three swim-trained groups, the L-AGAT activity and the GAA concentration decreased (%) by 61.7 (P<0.01) and 69.7 (P<0.01), and 16.6 (P<0.01) and 45.8 (P<0.01), respectively, in the groups supplemented with 1.5 and 6.0 g Cre/kg per day for 2 weeks compared to the group without Cre supplementation. Serum Cre and creatinine concentrations in the group receiving 6.0 g Cre/kg per day increased significantly. L-AGAT activity was positively correlated with the concentration of GAA (n = 30, r = 0.84, P<0.001); however, negatively correlated with serum Cre (n = 30, r = 0.72, P<0.001). These results indicate that in rats L-AGAT activity and GAA concentration could be markedly enhanced by exercise, implying that exercise may benefit endogenous Cre synthesis due to more Cre needed during exercise. The L-AGAT activity and GAA concentration, however, could be rapidly reduced by supplementation with 1.5–6.0 g Cre/kg per d, which is equivalent to 20–80 g Cre/d (67 kg body weight) in human subjects, suggesting that high-dose Cre supplementation may result in depression of endogenous Cre metabolism and may have potential adverse effects on the exercise-trained body. Little is known about the effect of high-dose Cre supplementation on the immune system; the results of a follow-up study of immune function will be of interest.