Lipopolysaccharide-induced anorexia following hepatic portal vein and vena cava administration

3,5-Dimethyl-2,4,6-trimethoxychalcone Lessens Obesity and MAFLD in Leptin-Deficient ob/ob Mice

Chalcones constitute an important group of natural compounds abundant in fruits and comestible plants. They are a subject of increasing interest because of their biological activities, including anti-diabetic and anti-obesity effects. The simple chalcone structural scaffold can be modified at multiple sites with different chemical moieties. Here, we generated an artificial chalcone, i.e., 3,5-dimethyl-2,4,6-trimethoxychalcone (TriMetChalc), derived from 2',4'-Dihydroxy-6'-methoxy-3',5'-dimethylchalcone (DMC). DMC is a major compound of Cleistocalyx operculatus, a plant widely used in Asia for its anti-hyperglycemic activity. Using ob/ob mice as an obesity model, we report that, after 3 weeks of per os administration, TriMetChalc modified food intake through the specific activation of brain structures dedicated to the regulation of energy balance. TriMetChalc also decreased weight gain, glucose intolerance, and hepatic steatosis. Moreover, through extensive liver lipidomic analysis, we identified TriMetChalc-induced modifications that could contribute to improving the liver status of the animals. Hence, TriMetChalc is a chalcone derivative capable of reducing food intake and the addition of glucose intolerance and hepatic steatosis in a mouse model of obesity. In light of these results, we believe that TriMetChalc action deserves to be more deeply evaluated over longer treatment periods and/or in combination with other chalcones with protective effects on the liver.

Circulating glucagon-like peptide-1 (GLP-1) inhibits eating in male rats by acting in the hindbrain and without inducing avoidance

To address the neural mediation of the eating-inhibitory effect of circulating glucagon-like peptide-1 (GLP-1), we investigated the effects of 1) intra-fourth ventricular infusion of the GLP-1 receptor antagonist exendin-9 or 2) area postrema lesion on the eating-inhibitory effect of intrameal hepatic portal vein (HPV) GLP-1 infusion in adult male rats. To evaluate the physiological relevance of the observed effect we examined 3) the influence of GLP-1 on flavor acceptance in a 2-bottle conditioned flavor avoidance test, and 4) measured active GLP-1 in the HPV and vena cava (VC) in relation to a meal and in the VC after HPV GLP-1 infusion. Intrameal HPV GLP-1 infusion (1 nmol/kg body weight-5 min) specifically reduced ongoing meal size by almost 40% (P < .05). Intra-fourth ventricular exendin-9 (10 μg/rat) itself did not affect eating, but attenuated (P < .05) the satiating effect of HPV GLP-1. Area postrema lesion also blocked (P < .05) the eating-inhibitory effect of HPV GLP-1. Pairing consumption of flavored saccharin solutions with HPV GLP-1 infusion did not alter flavor acceptance, indicating that HPV GLP-1 can inhibit eating without inducing malaise. A regular chow meal transiently increased (P < .05) HPV, but not VC, plasma active GLP-1 levels, whereas HPV GLP-1 infusion caused a transient supraphysiological increase (P < .01) in VC GLP-1 concentration 3 minutes after infusion onset. The results implicate hindbrain GLP-1 receptors and the area postrema in the eating-inhibitory effect of circulating GLP-1, but question the physiological relevance of the eating-inhibitory effect of iv infused GLP-1 under our conditions.

Modification of energy balance induced by the food contaminant T-2 toxin: a multimodal gut-to-brain connection

T-2 toxin is one of the most toxic Fusarium-derived trichothecenes found on cereals and constitutes a widespread contaminant of agricultural commodities as well as commercial foods. Low doses toxicity is characterized by reduced weight gain. To date, the mechanisms by which this mycotoxin profoundly modifies feeding behavior remain poorly understood and more broadly the effects of T-2 toxin on the central nervous system (CNS) have received limited attention. Through an extensive characterization of sickness-like behavior induced by T-2 toxin, we showed that its per os (p.o.) administration affects not only feeding behavior but also energy expenditure, glycaemia, body temperature and locomotor activity. Using c-Fos expression mapping, we identified the neuronal structures activated in response to T-2 toxin and observed that the pattern of neuronal populations activated by this toxin resembled that induced by inflammatory signals. Interestingly, part of neuronal pathways activated by the toxin were NUCB-2/nesfatin-1 expressing neurons. Unexpectedly, while T-2 toxin induced a strong peripheral inflammation, the brain exhibited limited inflammatory response at a time point when anorexia was ongoing. Unilateral vagotomy partly reduced T-2 toxin-induced brainstem neuronal activation. On the other hand, intracerebroventricular (icv) T-2 toxin injection resulted in a rapid (<1h) reduction in food intake. Thus, we hypothesized that T-2 toxin could signal to the brain through neuronal and/or humoral pathways. The present work provides the first demonstration that T-2 toxin modifies feeding behavior by interfering with central neuronal networks devoted to central energy balance. Our results, with a particular attention to peripheral inflammation, strongly suggest that inflammatory mediators partake in the T-2 toxin-induced anorexia and other symptoms. In view of the broad human and breeding animal exposure to T-2 toxin, this new mechanism may lead to reconsider the impact of the consumption of this toxin on human health.

Advances in deoxynivalenol toxicity mechanisms: the brain as a target

Deoxynivalenol (DON), mainly produced by Fusarium fungi, and also commonly called vomitoxin, is a trichothecene mycotoxin. It is one of the most abundant trichothecenes which contaminate cereals consumed by farm animals and humans. The extent of cereal contamination is strongly associated with rainfall and moisture at the time of flowering and with grain storage conditions. DON consumption may result in intoxication, the severity of which is dose-dependent and may lead to different symptoms including anorexia, vomiting, reduced weight gain, neuroendocrine changes, immunological effects, diarrhea, leukocytosis, hemorrhage or circulatory shock. During the last two decades, many studies have described DON toxicity using diverse animal species as a model. While the action of the toxin on peripheral organs and tissues is well documented, data illustrating its effect on the brain are significantly less abundant. Yet, DON is known to affect the central nervous system. Recent studies have provided new evidence and detail regarding the action of the toxin on the brain. The purpose of the present review is to summarize critical studies illustrating this central action of the toxin and to suggest research perspectives in this field.

The food-contaminant deoxynivalenol modifies eating by targeting anorexigenic neurocircuitry

Physiological regulations of energy balance and body weight imply highly adaptive mechanisms which match caloric intake to caloric expenditure. In the central nervous system, the regulation of appetite relies on complex neurocircuitry which disturbance may alter energy balance and result in anorexia or obesity. Deoxynivalenol (DON), a trichothecene, is one of the most abundant mycotoxins found on contaminated cereals and its stability during processing and cooking explains its widespread presence in human food. DON has been implicated in acute and chronic illnesses in both humans and farm animals including weight loss. Here, we provide the first demonstration that DON reduced feeding behavior and modified satiation and satiety by interfering with central neuronal networks dedicated to food intake regulation. Moreover, our results strongly suggest that during intoxication, DON reaches the brain where it modifies anorexigenic balance. In view of the widespread human exposure to DON, the present results may lead to reconsider the potential consequences of chronic DON consumption on human eating disorders.

Effects of grain-pellet and alfalfa-pellet subacute ruminal acidosis (SARA) challenges on feeding behaviour of lactating dairy cows

Li, S., Khafipour, E., Krause, D. O., González, L. A. and Plaizier, J. C. 2011. Effects of grain-pellet and alfalfa-pellet subacute ruminal acidosis (SARA) challenges on feeding behaviour of lactating dairy cows. Can. J. Anim. Sci. 91: 323–330. The effects of two nutritional challenges aimed at inducing subacute ruminal acidosis (SARA) on the feeding behaviour of lactating dairy cows were investigated in two separate experiments. Both experiments included eight tie-stall-housed cows that were fed once daily. Feeding behaviour of individual cows was monitored by continuously weighing the feed in the mangers. In each experiment, ruminal pH was monitored in four rumen cannulated cows. In the first experiment, cows received a control diet containing 50% mixed concentrate and 50% alfalfa and barley silage (DM basis) during weeks 1 to 5 of two subsequent 6-wk periods. During week 6 of both periods, a grain-pellet SARA challenge (GPSC) was conducted by replacing 21% of DM of the basal diet with wheat-barley pellets. Data obtained in week 4 were taken as a control. In the second experiment, cows received a control diet containing 50% of DM as mixed concentrate and 50% of DM as chopped alfalfa hay during the first week of a 5-wk period. Between week 2 and week 5, an alfalfa-pellet SARA challenge (APSC) was conducted by replacing alfalfa hay in the control diet with alfalfa pellets at a rate of 8% per week. Week 1 and week 5 were considered as the control and SARA challenge, respectively. In the first experiment, the GPSC reduced the meal duration from 48.9 to 38.6 min meal−1 and the eating time from 6.7 to 5.5 h d−1. Meal criteria, meal frequency, meal size, and eating rate were not affected. In the second experiment, the APSC did not affect the meal criterion, meal duration, and eating time per day, but increased dry matter intake from 18.7 to 24.3 kg d−1, meal frequency from 8.2 to 9.4 meals d−1, meals size from 2.4 to 2.7 kg DM, and eating rate from 54.8 to 67.6 g DM min−1. The duration of the first meal after feed delivery was reduced from 154.5 to 103.6 min by the GPSC and from 146.7 to 112.2 min by the APSC. This reduction in the duration of the first meal was accompanied by a reduction in the drop of the ruminal pH during the GPSC, but not during the APSC. Only the APSC increased eating rate of the first meal. Other parameters of this first meal were not affected by both challenges.

Leptin: at the crossroads of energy balance and systemic inflammation

In addition to playing a central role in energy homeostasis, leptin is also an important player in the inflammatory response. Systemic inflammation is accompanied by fever (less severe cases) or hypothermia (more severe cases). In leptin-irresponsive mutants, the hypothermia of systemic inflammation is exaggerated, presumably due to the enhanced production and cryogenic action of tumor necrosis factor (TNF)-alpha. Mechanisms that exaggerate hypothermia can also attenuate fever, particularly in a cool environment. Another common manifestation of systemic inflammation is behavioral depression. Along with the production of interleukin (IL)-1beta, this manifestation is exaggerated in leptin-irresponsive mutants. The enhanced production of TNF-alpha and IL-1beta may be due, at least in part, to insufficient activation of the anti-inflammatory hypothalamo-pituitary-adrenal axis by immune stimuli in the absence of leptin signaling. In experimental animals and humans that are responsive to leptin, suppression of leptin production under conditions of negative energy balance (e.g., fasting) can exaggerate both hypothermia and behavioral depression. Since these manifestations aid energy conservation, exaggeration of these manifestations under conditions of negative energy balance is likely to be beneficial.

Hypothalamic integration of immune function and metabolism

The immune and neuroendocrine systems are closely involved in the regulation of metabolism at peripheral and central hypothalamic levels. In both physiological (meals) and pathological (infections, traumas and tumors) conditions immune cells are activated responding with the release of cytokines and other immune mediators (afferent signals). In the hypothalamus (central integration), cytokines influence metabolism by acting on nucleus involved in feeding and homeostasis regulation leading to the acute phase response (efferent signals) aimed to maintain the body integrity. Peripheral administration of cytokines, inoculation of tumor and induction of infection alter, by means of cytokine action, the normal pattern of food intake affecting meal size and meal number suggesting that cytokines acted differentially on specific hypothalamic neurons. The effect of cytokines-related cancer anorexia is also exerted peripherally. Increase plasma concentrations of insulin and free tryptophan and decrease gastric emptying and d-xylose absorption. In addition, in obesity an increase in interleukin (IL)-1 and IL-6 occurs in mesenteric fat tissue, which together with an increase in corticosterone, is associated with hyperglycemia, dyslipidemias and insulin resistance of obesity-related metabolic syndrome. These changes in circulating nutrients and hormones are sensed by hypothalamic neurons that influence food intake and metabolism. In anorectic tumor-bearing rats, we detected upregulation of IL-1beta and IL-1 receptor mRNA levels in the hypothalamus, a negative correlation between IL-1 concentration in cerebro-spinal fluid and food intake and high levels of hypothalamic serotonin, and these differences disappeared after tumor removal. Moreover, there is an interaction between serotonin and IL-1 in the development of cancer anorexia as well as an increase in hypothalamic dopamine and serotonin production. Immunohistochemical studies have shown a decrease in neuropeptide Y (NPY) and dopamine (DA) and an increase in serotonin concentration in tumor-bearing rats, in first- and second-order hypothalamic nuclei, while tumor resection reverted these changes and normalized food intake, suggesting negative regulation of NPY and DA systems by cytokines during anorexia, probably mediated by serotonin that appears to play a pivotal role in the regulation of food intake in cancer. Among the different forms of therapy, nutritional manipulation of diet in tumor-bearing state has been investigated. Supplementation of tumor bearing rats with omega-3 fatty acid vs. control diet delayed the appearance of tumor, reduced tumor-growth rate and volume, negated onset of anorexia, increased body weight, decreased cytokines production and increased expression of NPY and decreased alpha-melanocyte-stimulating hormone (alpha-MSH) in hypothalamic nuclei. These data suggest that omega-3 fatty acid suppressed pro-inflammatory cytokines production and improved food intake by normalizing hypothalamic food intake-related peptides and point to the possibility of a therapeutic use of these fatty acids. The sum of these data support the concept that immune cell-derived cytokines are closely related with the regulation of metabolism and have both central and peripheral actions, inducing anorexia via hypothalamic anorectic factors, including serotonin and dopamine, and inhibiting NPY leading to a reduction in food intake and body weight, emphasizing the interconnection of the immune and neuroendocrine systems in regulating metabolism during infectious process, cachexia and obesity.

Current perspectives on behavioural and cellular mechanisms of illness anorexia

Here we review our current understanding of the integration of immune, neural, metabolic and endocrine signals involved in the generation of anorexia during acute infection, with the focus on anorexia elicited by peripheral administration of bacterial lipopolysaccharide (LPS). We chose to limit this review to peripheral LPS-anorexia because the mechanisms underlying this response may also be valid for anorexia during other types of acute or chronic infections, with slight differences in the duration of anorexia, levels of circulating concentrations of pro-inflammatory cytokines and hypermetabolism. Evidence so far indicates that LPS-anorexia is a complex response beneficial to host defence that involves both peripheral and central action of pro-inflammatory cytokines, other immune factors, such as prostanoids, and neurotransmitters, such as serotonin. One interesting characteristic of LPS-anorexia is its sexual differentiation, an aspect mainly mediated by the gonadal hormone estradiol. Understanding the behavioural and molecular mechanisms of LPS-anorexia may even provide useful leads for identifying mechanisms of eating disorders in humans.

Systemic administration of lipopolysaccharide increases plasma leptin levels: blockade by soluble interleukin-1 receptor

Lipopolysaccharide (LPS) is known to produce several central and neuroendocrine effects and some of these effects are believed to be mediated through cytokines and other proteins. One such protein, leptin, produced by adipose tissue has been shown to cause anorexia, a central effect associated with LPS treatment. This raised the possibility that LPS-induced effects on feeding behavior may be mediated through leptin. This study was done to investigate the effects of systemic administration of LPS on plasma leptin levels in rats and the possible involvement of interleukin-1 (IL-1) in this mechanism. Adult male rats were implanted with indwelling jugular catheters and after collecting two pretreatment blood samples, the animals were injected (i.p.) with saline, 5 microg, 10 microg, or 25 microg/kg BW of LPS, or treated with 25 microg of soluble IL-1 receptor (sIL-1R) 5 min before and 90 min after 25 microg/kg BW of LPS. Posttreatment blood samples were collected at 30 min intervals for a period of 6 h. Plasma leptin concentrations were measured by radioimmunoassay. Treatment with saline did not produce any change in plasma leptin levels. In contrast, each of the three doses of LPS produced a dose-dependent increase in plasma leptin levels within 120 min. Leptin levels remained elevated for the next 4 h. Treatment with sIL-1 R completely blocked the LPS-induced increase in leptin levels, indicating that this effect is in fact mediated through IL-1. These results indicate that leptin could be a possible mediator of LPS-induced effects on feeding.