J Nutr Sci Vitaminol, 62, 277–280, 2016

Note Decreases the Suppressive Effect of on Food Intake and Fat Accumulation

Riku Asahi1, Kaoru Tanaka1, Takahiko J. Fujimi1, Nobuyuki Kanzawa2 and Shigeru Nakajima1

1 Department of Registered Dietitians, Faculty of Health and Nutrition, Bunkyo University, 1100 Namegaya, Chigasaki, Kanagawa 253–8550, Japan 2 Department of Materials and Life Science, Faculty of Science and Technology, Sophia University, 7–1 Kioi, Chiyoda-ku, Tokyo 102–8554, Japan (Received November 9, 2015)

Summary We recently suggested that proline might decrease the suppressive effect of his- tidine on food intake. Our purpose in the present study was to investigate the influence of proline on the suppressive effect of histidine on food intake and accumulation of body fat. Male Wistar rats were divided into four groups and allowed free access to the following diets for 3 wk: control (C), 5% proline (P), 5% histidine (H), or 5% histidine plus 10% proline (HP) diets. Food intake for 7 d and retroperitoneal fat tissue weight at the end of the experimental period of the HP diet group were greater than those of the H diet group, whereas no signifi- cant difference existed between the HP diet group and the C diet group. Our results indicate that proline inhibits the influence of histidine on food intake and accumulation of body fat. Key Words histidine, proline, food intake, body fat, inhibition

A common factor in metabolic syndrome is visceral food intake using the cafeteria method, where rats are obesity, which is associated with hyperlipidemia, hyper- allowed to choose two diets (18). Intake of the histidine piesia and hyperglycemia. Fat accumulation in adipose diet was significantly lower than that of the histidine tissues is caused by a decreased basal metabolic rate plus proline diet. These results strongly suggested that due to a lack of exercise and excessive caloric intake (1). proline reduced the suppressive effect of histidine on Therefore, the prevention and resolution of obesity may food intake. However in the cafeteria method, the pref- play a role in preventing the development of metabolic erence of diet influences the selection of diet and food syndrome. intake. Furthermore, it is difficult to see the influence of Many substances are known to regulate ingestive each diet, since two different diets were set in the same behavior, including histamine. Hypothalamic neuronal cage. The purpose of this study was to clarify the influ- histamine has anti-obesity effects such as suppressed ence of proline on suppressive effect of histidine on food food intake (2–6), increased lipolysis in white adi- intake using a single diet in an animal experiment. pose tissue (WAT), and increased energy consumption through increased expression of uncoupling 1 Materials and Methods (UCP1) in brown adipose tissue (BAT) (7–9). Histamine Animal experimental procedures. Five-week-old male cannot cross the blood-brain barrier (BBB), which is in Wistar rats (n524) were purchased from CLEA Japan, contrast to histidine, a precursor in the synthesis of his- Inc. (Tokyo, Japan). The animals were housed in individ- tamine (10). When histidine is absorbed and crosses the ual stainless steel cages with wire mesh bottoms in a tem- BBB, it is converted into histamine by histidine decar- perature- (2362˚C) and light-controlled room (lights on boxylase (HDC) within neuronal cell bodies located in from 2:00 AM to 2:00 PM). The rats were acclimated to the tuberomammillary nucleus (TMN) of the hypothal- the experimental conditions and given free access to the amus (11). We previously reported on the anti-obesity control diet (C diet) for 4 d. The components of diets are effect of histidine using nutrition surveys in humans shown in Table 1. After the rats were acclimated to the and animal experiments (12–16). Oral histidine admin- C diet, they were assigned to one of four groups (n56/ istration in rats suppressed food intake and the accumu- group) on the basis of body weight (average initial body lation of body fat (16). In the human nutrition survey, weight5140 g, range5134–147 g) and allowed free there was a negative correlation between energy intake access to water and the experimental diets for 3 wk: 25% and histidine/protein intake (17). However, this sup- casein (C) diet, 20% casein plus 5% proline (P) diet, 20% pressive effect decreased under conditions of high pro- casein plus 5% histidine (H) diet and 20% casein plus line/protein intake. Recently, we also reported the influ- 5% histidine and 10% proline (HP) diet (Table 1). Food ence of proline on the suppressive effect of histidine on intake and body weight were recorded daily. At the end of the experimental period, the rats were anesthetized E-mail: [email protected] using somnopentyl (Kyoritsuseiyaku Co., Ltd., Japan)

277 278 Asahi R et al. injection, whole blood was collected from the heart, and Results the retroperitoneal fat and epididymal fat removed and The content of nitrogen sources (protein and free weighed. The animal use committee of Bunkyo Univer- amino acids) in the C diet, P diet and H diet were set to sity approved the study (approval number: 10-2), and the same level (Table 1). Since a significant suppression animals were maintained in accordance with university effect on food intake of histidine had been observed at a guidelines for the care and use of laboratory animals. concentration of 5%, the concentration of histidine in Statistical analysis. Data are presented as means6 this experiment was set at 5% (16). The concentration standard error of the mean. The significance of differ- of proline was also set to the same 5% concentration ences among the group was determined by one-way to see the influence of proline under the same protein analysis of variance (ANOVA) with Ryan’s multiple- content conditions. We also prepared a diet contain- range test. p,0.05 was considered a statistically signifi- ing both proline and histidine. In previous research, a cant difference. high proline/histidine content ratio in the diet suggested that proline decreased the suppressive effect of histidine on food intake and proline content added 2 volumes of Table 1. Composition of the experimental diets. additive amount of histidine in the histidine diet in the cafeteria method (17, 18); thus, we examined the influ- Components C diet P diet H diet HP diet ence of proline by supplementing with 5% histidine and (g/kg) 10% proline (Table 1). Histidine — — 50 50 Food intake was significantly greater in the HP diet Proline — 50 — 100 group than in the H diet group on days 3 to 6, while food Casein 250 200 200 200 intake in the H diet group was significantly lower than 3 3 3 3 in the C diet group on each day. Moreover, the C and P Cornstarch 377 377 377 277 diet groups did not significantly differ in food intake (Fig. Corn oil 100 100 100 100 1). Total food intake and body weight gain over the 7 d Sucrose 210 210 210 210 showed a similar tendency; the HP diet group values Vitamin mixture1 10 10 10 10 1 were significantly higher than those of the H diet group, Mineral mixture 40 40 40 40 while there were no significant differences between the Cellulose 10 10 10 10 C and P diet groups (Table 2). However, there was little 1 Based on the American Institute of Nutrition dietary difference among the four diet groups in food intake and allowance for rats (AIN-76). body weight gain beginning on day 8, and both total

Fig. 1. Food intake in rats fed a control diet (C), 5% proline diet (P), 5% histidine diet (H) and 5% histidine plus 10% pro- line diet (HP) for 7 d. Each column represents the mean value of six rats; vertical bars represent the standard error of the mean. Different letters above the bars indicate mean values that were significantly different from each other (p,0.05) using ANOVA by Ryan’s multiple-range test.

Table 2. Food intake and body weight gain in rats in each diet regimen.1

C diet P diet H diet HP diet

Food intake (g/7 d) 104.862.8a 97.561.9a 81.961.3b 87.260.8c Body weight gain (g/7 d) 56.662.1a 52.260.6a 43.261.1b 47.361.3c

1 Data are expressed as mean6standard error of mean (n56). Different letters indicate mean values that were significantly different from each other (p,0.05) using ANOVA by Ryan’s multiple-range test. Inhibitory Effect of Proline on Histidine 279

Fig. 2. Retroperitoneal (A) and epididymal (B) fat weights in rats fed experimental diets for 3 wk. C, P, H and HP are the control diet, 5% proline diet, 5% histidine diet, and 5% histidine plus 10% proline diet, respectively. Each column repre- sents the mean value of six rats, and vertical bars represent the standard error of the mean. Different letters above the bars indicate mean values that were significantly different from each other (p,0.05) using ANOVA by Ryan’s multiple-range test. food intake and body weight gain over the 3 wk dura- which the proline content was two-fold greater than tion did not significantly differ between the H and HP the histidine content of the H diet group, was increased diet groups (data not shown). compared to the H diet group (Fig. 1), indicating a The HP, C, and P diet groups did not differ in retroper- reduction in the feeding suppression effect of histidine. itoneal fat weight. However, the weight of retroperito- In our previous study using the cafeteria method, intake neal fat in the H diet group was significantly lower than of a high proline/histidine ratio diet was significantly that of the other groups (Fig. 2A). This finding supports increased compared to a low ratio diet, supporting the that of a previous study in which the retroperitoneal fat results of this experiment. However, prior to the second weight of the H diet group was significantly less than day, it was thought that differences in the protein con- that of the C diet group (16). The epididymal fat weight tents were responsible for the lack of significant differ- of the HP diet group showed an increasing tendency ences in food intake between the H and HP diet group. compared to the H diet group; however, this difference Changes in dietary protein contents have been reported was not significant (Fig. 2B). to decrease early food intake in animal experiments (21, 22). Therefore, we consider that protein contents may Discussion influence the dietary intake of the HP diet group (pro- Histidine can pass the BBB and enter the brain, where tein contents 35.3%) because the tested animals in our it is taken up into histamine-containing neurons and experiments were initially maintained on the C diet with is converted to histamine by HDC. The released hista- a protein content of 25.3%. mine controls ingestive behavior through histamine H1 Furthermore, we consider that the addition of proline receptors, which belong to a family of G protein (gua- had no effect on ingestion behavior because food intake nine nucleotide-binding regulatory ) coupled was the same between the C diet and P diet groups. receptors (3, 19, 20), and induces anti-obesity effects In addition, it is discussed that the proline alone has such as feeding suppression, lipolysis in white adipose no food intake enhancement effect since the previous tissue (intracerebroventricular injection of histamine research showed a 0% to 5% proline concentration diet promotes glycerol release from white adipose tissue), has no influence on the food intake (18, 23). This study and weight reduction (2–4). Moreover, histaminergic also revealed the food intake of the P diet group with 5% neurons are known to participate in regulating heat pro- proline concentration did not increase day by day. On duction (thermoregulation) and energy consumption. the other hand, in the P diet, histidine contained in the Expression of UCP1 in brown adipose tissues of diet- casein of the diet did not show any obvious food intake induced obese (DIO) or diabetic (db/db) mice increased enhancement effect despite the high proline/histidine when histamine was administered to the cerebral ventri- ratio, since the histidine concentration was low. From cle, and histamine H1 receptor knockout mouse showed this result, not only the proline/histidine ratio, but also a decreased suppressive effect on food intake and expres- the histidine and proline concentration is considered to sion of UCP1 (7). On the other hand, intake of histidine, be important. which is a precursor of histamine, also affects the hista- Moreover, total food intake and total body weight gain mine neuron system, and the expression level of UCP1 over the experimental period did not significantly differ; increased and food intake decreased when a histidine however, retroperitoneal fat weight differed between diet of 5% concentration was provided to Wistar rats for groups (Fig. 2). We suggest that proline inhibited the 8 d (16). lipolysis action of histidine in the presence of both his- In this study, food intake of the HP diet group, in tidine and proline since a significant increase in fat was 280 Asahi R et al. observed in the HP diet group compared to the H diet 9) Yoshimatsu H, Itateyama E, Kondou S, Tajima D, group. 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