Simmondsin: effects on meal patterns and choice behavior in rats

Food-grade titanium dioxide (E171) differentially affects satiation in mice fed a regular or a high fat diet

Food-grade titanium dioxide (E171) is a widely used food additive and the toxicity after oral consumption is still under research, although it has been already banned in some countries. The consumption of this additive occurs mainly through ultra-processed food products which also contain high amounts of fat. High fat diets (HFD) impair the physiological system controlling satiation and satiety, which are responsible for control of food intake and energy status. The impact of E171 on animal behavior has been poorly explored and here we hypothesize that E171 could worsen the effects on feeding behavior induced by HFD. Therefore, we aimed to evaluate the effects of E171 on the feeding pattern and the behavioral satiety sequence (BSS) of mice fed with a regular diet (RD) or a HFD after 1 and 16 weeks of exposure. The results showed that RD + E171 increased food intake and feeding time, but the prototypical structure of the BSS pattern (feeding→ grooming-activity → resting), was preserved. Conversely, food consumption was not altered in HFD + E171, but the BSS pattern was disrupted as the animals prolonged resting time and spent less time being active. Our findings suggest that E171 delayed the onset of satiation in mice fed with RD but induced the opposite effect in mice fed with HFD.

Combined Omics Analysis Further Unveils the Specific Role of Butyrate in Promoting Growth in Early-Weaning Animals

Abnormal mutations in the microbial structure of early-weaning mammals are an important cause of enteritis. Based on the multiple known beneficial functions of butyrate, we hypothesized that butyrate would alleviate the imbalance of intestinal homeostasis induced by early weaning in animals. However, the mechanisms of action between butyrate and intestinal microbes are still poorly explored. In this study, we aimed to investigate whether butyrate exerts beneficial effects on the structure of the intestinal flora of weanling rabbits and their intestinal homeostasis, growth and development, and we attempted to elucidate the potential mechanisms of action through a combined omics analysis. We found that dietary butyrate upregulated the transcription of tight junction-related proteins in the epithelial barrier and improved the intestinal microbial structure by suppressing harmful bacteria and promoting beneficial ones. Intestinal and plasma metabolomes were also altered. The bile acid secretion, α-linolenic acid, apoptotic, and prostate cancer pathways responded to the positive dietary butyrate-induced metabolic changes in the weanling rabbits, resulting in the inhibition of inflammation, improved antioxidant capacity, increased rates of cell proliferation and survival, and decreased levels of apoptosis. Additionally, dietary butyrate suppressed the release of pro-inflammatory factors and enhanced positive appetite regulation, which increased the average daily gain of the rabbits. These results demonstrated that dietary butyrate can help maintain the integrity of the intestinal epithelial barrier, improve the structural composition of the intestinal microflora, enhance organismal metabolism, inhibit inflammation, reduce post-weaning anorexia, and promote growth and development in early-weaning rabbits. These positive effects of dietary butyrate were exerted via the modulation of the microbe-gut-brain axis.

Effects of diphenyl and p-chloro-diphenyl diselenides on feeding behavior of rats

RATIONALE

The searching for safe and effective antiobesity drugs has been the subject of intense research. Previous studies have shown several pharmacological applications of organoselenium compounds; however, their possible anorectic-like actions have not been investigated.

OBJECTIVE

This study aims to investigate the effects of (PhSe)2 and (p-ClPhSe)2 on feeding behavior of rats and their potential as weight-reducing agents.

METHODS

The effects of intraperitoneal administration of diselenides were investigated through the microstructural pattern of feeding behavior, behavioral satiety sequence (BSS), hypothalamic serotonin (5-HT) uptake, body weight, and epididymal fat content of male rats.

RESULTS

Our findings demonstrated that food intake of fasted rats was reduced by both diselenides (1 and 10 mg/kg). Diphenyl diselenide [(PhSe)2] (1 mg/kg) and p-chloro-diphenyl diselenide [(p-ClPhSe)2] (10 mg/kg) decreased the frequency, mean duration, and mean size of meals compared with the control treatment. The BSS structure was preserved when organoselenium compounds (1 mg/kg) were administered, and it was associated to a displacement to the left when the resting period started indicating a satiating action. Inhibition of 5-HT uptake in the hypothalamus (∼20 %) was also found in rats treated with low doses of (PhSe)2 and (p-ClPhSe)2 (1 mg/kg). Treatments with a high dose of both diselenides (10 mg/kg) carried out for 7 days induced weight loss and epididymal fat reduction in sated rats.

CONCLUSION

This study suggests that diselenides caused a satiating action in rats that could be partially explained by the inhibition of hypothalamic 5-HT uptake. These organoselenium compounds were potential weight-reducing agents when repeatedly administered.

Behavioural contributions to the regulated intake of plant secondary metabolites in koalas

In a given period of time, herbivores often eat less as dietary plant secondary metabolite (PSM) concentrations increase. This reduction in total food intake is interpreted as a need for the herbivore to regulate PSM ingestion in order to avoid toxication. However, regulation of PSM ingestion involves more than the reduction of total intake; it involves an alteration of meal patterns, through a reduction in the number and/or the size of the meals eaten. Despite this, studies of how herbivores alter their meal patterns when offered varying concentrations of PSMs are rare. We investigated whether koalas adjust the number and/or the size of their meals when offered eucalypt foliage varying naturally in concentrations of formylated phloroglucinol compounds (FPCs), a group of PSMs that have previously been shown to inhibit total food intake. High FPC concentrations caused koalas to eat more slowly, eat shorter meals and eat less per meal, which resulted in a reduced total intake. Because increasing FPC concentrations did not cause koalas to alter the number of meals that they ate, clear individual differences between koalas were observed, where some consistently ate fewer larger meals and others ate many smaller meals. Thus, different feeding strategies may still achieve the same outcome of a regulated intake of PSMs. The changes observed match the meal patterns of other herbivores ingesting PSMs known to stimulate nausea and emetic pathways, supporting the idea that feedback signals from nausea are an important way that koalas avoid toxication when eating eucalypt foliage.

PEGylated cholecystokinin prolongs satiation in rats: dose dependency and receptor involvement

BACKGROUND AND PURPOSE

Acute intraperitoneal (i.p.) administration of cholecystokinin (CCK) is known to induce a significant, but short-lasting, reduction in food intake, followed by recovery within hours. Therefore, we had covalently coupled CCK to a 10 kDa polyethylene glycol and showed that this conjugate, PEG-CCK(9), produced a significantly longer anorectic effect than unmodified CCK(9). The present study assessed the dose-dependency of this response and the effect of two selective CCK(1) receptor antagonists, with different abilities to cross the blood-brain barrier (BBB), on PEG-CCK(9)-induced anorexia.

EXPERIMENTAL APPROACH

Food intake was measured, for up to 23 h, after i.p. administration of different doses (2, 4, 8, 16 and 32 microg kg(-1)) of CCK(9) or PEG-CCK(9) in male Wistar rats. Devazepide (100 microg kg(-1)), which penetrates the BBB or 2-NAP (3 mg kg(-1)), which does not cross the BBB, were coadministered i.p. with PEG-CCK(9) (6 microg kg(-1)) and food intake was monitored.

KEY RESULTS

In PEG-CCK(9)-treated rats, a clear dose-dependency was seen for both the duration and initial intensity of the anorexia whereas, for CCK(9), only the initial intensity was dose-dependent. Intraperitoneal administration of devazepide or 2-NAP, injected immediately prior to PEG-CCK(9), completely abolished the anorectic effect of PEG-CCK(9).

CONCLUSIONS AND IMPLICATIONS

The duration of the anorexia for PEG-CCK(9) was dose-dependent, suggesting that PEGylation of CCK(9) increases its circulation time. Both devazepide and 2-NAP completely abolished the anorectic effect of i.p. PEG-CCK(9) indicating that its anorectic effect was solely due to stimulation of peripheral CCK(1) receptors.

PEGylation of cholecystokinin prolongs its anorectic effect in rats

The anorectic compound CCK-9 was coupled to polyethylene glycol 5 kDa, 10 kDa, 20 kDa and 30 kDa, under different reaction conditions. Conjugates were purified by HPLC and characterized by MALDI-TOF MS. A 96% PEGylation yield was obtained in buffer pH 7.5 after 6h reaction at 20 degrees C. The anorectic activity was tested in vivo in rats. A single bolus intra-peritoneal injection of non-modified CCK-9 resulted in a significant initial food intake reduction 30 min after food presentation (87% compared to paired control group). When PEG-CCK-9 conjugates modified with polymers of molecular weight up to 20 kDa were injected, lower but statistically significant initial food intake reductions were obtained (76% for PEG 10 kDa-CCK-9 conjugate compared to control group). The cumulative food intake reduction of non-modified CCK-9 is normalized within 1-2h, whereas the PEG-CCK-9 molecules showed a prolonged anorectic activity lasting for 6h for PEG 5 kDa-CCK-9; 23 h for PEG 10 kDa-CCK-9 and between 8h and 23 h for PEG 20 kDa-CCK-9. For PEG 30 kDa-CCK-9 conjugate, neither an initial nor a cumulative FI reduction was observed. PEG-CCK-9 conjugates show a significantly prolonged anorectic activity in comparison to the non-modified peptide. This effect is most evident for the PEG 10 kDa-CCK-9 conjugate.

Meal pattern of male rats maintained on histidine-, leucine-, or tyrosine-supplemented diet

OBJECTIVE

Food intake is known to be affected by macronutrient composition of the diet, and protein manipulation has been reported to alter food intake, but the effect of individual amino acids on eating behavior has not been fully studied. This study investigated the effect of diet supplementation with three individual amino acids on meal pattern in male rats.

RESEARCH METHODS AND PROCEDURES

Thirty-two Sprague-Dawley rats were randomly divided into four equal groups and fed control diet or histidine (5%)-, leucine (5%)-, or tyrosine (5%)-supplemented diet for 2 weeks and were monitored for their meal pattern.

RESULTS

Total food intake and feeding rate of the different groups were not affected, although other components of meal pattern were altered. Histidine supplementation reduced diurnal meal size by 42% (p < 0.05), whereas that of leucine increased nocturnal meal size by approximately 35% (p < 0.05). Tyrosine supplementation increased food intake of the nocturnal period and decreased that of the diurnal period. Both histidine and tyrosine supplementation elevated fasting plasma insulin levels and suppressed fasting glucose significantly.

DISCUSSION

Individual amino acids were found to alter meal pattern differently. Further investigations are required to dissect the involvement of central and peripheral factors in these alterations.