The autonomic nervous system regulates postprandial hepatic lipid metabolism

Eating Increases and Exercise Decreases Disease Activity in Patients With Symptomatic Dermographism

BACKGROUND

Eating can increase disease activity in patients with symptomatic dermographism , the most common subtype of chronic inducible urticaria, but it is unclear how common this is. The effects of exercising on symptomatic dermographism disease activity have also not yet been determined.

OBJECTIVE

To assess the impact of exercise and nonspecific carbohydrate-rich food intake on the severity and intensity of symptomatic dermographism after exercise and nonspecific carbohydrate-rich food intake.

METHODS

We assessed disease activity by FricTest provocation testing in 75 symptomatic dermographism patients before and after eating, exercising, or both. We determined the rates of food-dependent (FD) symptomatic dermographism and food-exacerbated (FE) symptomatic dermographism. By comparing post- and pre-exercise FricTest scores, we identified complete responders: that is, patients with a negative FricTest response after exercising and partial responders. Finally, we evaluated whether exercise protects patients with FD-symptomatic dermographism or FE-symptomatic dermographism from eating-induced worsening of symptomatic dermographism.

RESULTS

Of 64 symptomatic dermographism patients, eight had FD-symptomatic dermographism (13%), 42 had FE-symptomatic dermographism (66%), and 14 patients showed no negative impact of eating on disease activity (21%). Physical exercise reduced FricTest skin provocation test responses in 83% of 58 patients. Exercising protected patients with FD/FE-symptomatic dermographism from worsening of symptomatic dermographism owing to eating in half of cases, with higher rates for exercise after eating (67%) compared with exercise before eating (35%).

CONCLUSIONS

Our study shows that eating often worsen symptomatic dermographism symptoms, and exercise often improves it. Our findings might aid patients in controlling symptoms better.

Effect of Prior Exercise on Postprandial Lipemia: An Updated Meta-Analysis and Systematic Review

The purpose of this systematic review was to synthesize the results from current literature examining the effects of prior exercise on the postprandial triglyceride (TG) response to evaluate current literature and provide future direction. A quantitative review was performed using meta-analytic methods to quantify individual effect sizes. A moderator analysis was performed to investigate potential variables that could influence the effect of prior exercise on postprandial TG response. Two hundred and seventy-nine effects were retrieved from 165 studies for the total TG response and 142 effects from 87 studies for the incremental area under the curve TG response. There was a moderate effect of exercise on the total TG response (Cohen's d = -0.47; p < .0001). Moderator analysis revealed exercise energy expenditure significantly moderated the effect of prior exercise on the total TG response (p < .0001). Exercise modality (e.g., cardiovascular, resistance, combination of both cardiovascular and resistance, or standing), cardiovascular exercise type (e.g., continuous, interval, concurrent, or combined), and timing of exercise prior to meal administration significantly affected the total TG response (p < .001). Additionally, exercise had a moderate effect on the incremental area under the curve TG response (Cohen's d = -0.40; p < .0001). The current analysis reveals a more homogeneous data set than previously reported. The attenuation of postprandial TG appears largely dependent on exercise energy expenditure (∼2 MJ) and the timing of exercise. The effect of prior exercise on the postprandial TG response appears to be transient; therefore, exercise should be frequent to elicit an adaptation.

Sleep Deficiency Is Associated With Exacerbation of Symptoms and Impairment of Anorectal and Autonomic Functions in Patients With Functional Constipation

Objective

Sleep deficiency (SD) is commonly seen in patients with functional constipation (FC). Our aim was to determine whether the presence of SD would influence symptoms, anorectal motility, sensation, and autonomic function in FC patients.

Materials and Methods

A total of 85 FC patients with SD and 193 FC patients without SD underwent high-resolution anorectal manometry. SD was assessed by using the Pittsburgh Sleep Quality Index (PSQI) score. Participants were required to fill in the entire questionnaires, including Patients' Constipation-symptoms, State-Trait Anxiety Inventory, and Hamilton Depression Scale. Autonomic dysfunction was studied by recording the heart rate variability. Multiple logistic regression was performed to explore the potential risk factors for anorectal function.

Results

Functional constipation patients with SD had a higher total score of constipation symptom (P < 0.001), in comparison with those without SD. FC patients with SD demonstrated significantly lower threshold volume for first sensation (P < 0.001) and urge (P < 0.001), as compared to those without SD. The PSQI score positively correlated with constipation symptom total score (P < 0.001), and negatively correlated with threshold volume for first sensation (P < 0.001) and urge (P < 0.001). FC patients with SD had a reduced vagal activity (P = 0.016) and a higher sympathetic activity as compared to those without SD (P = 0.003). Multivariate logistic regression revealed that SD, anxiety and depression were independent risk factors for anorectal function, with SD exhibiting the highest degree of association with first sensation (OR: 4.235).

Conclusion

Sleep deficiency is associated with worse constipation related symptoms, altered anorectal function and perception, and impaired autonomic function in FC patients.

How exposure to chronic stress contributes to the development of type 2 diabetes: A complexity science approach

Chronic stress contributes to the onset of type 2 diabetes (T2D), yet the underlying etiological mechanisms are not fully understood. Responses to stress are influenced by earlier experiences, sex, emotions and cognition, and involve a complex network of neurotransmitters and hormones, that affect multiple biological systems. In addition, the systems activated by stress can be altered by behavioral, metabolic and environmental factors. The impact of stress on metabolic health can thus be considered an emergent process, involving different types of interactions between multiple variables, that are driven by non-linear dynamics at different spatiotemporal scales. To obtain a more comprehensive picture of the links between chronic stress and T2D, we followed a complexity science approach to build a causal loop diagram (CLD) connecting the various mediators and processes involved in stress responses relevant for T2D pathogenesis. This CLD could help develop novel computational models and formulate new hypotheses regarding disease etiology.

Ameliorating Effects of Transcutaneous Electrical Acustimulation at Neiguan (PC6) and Zusanli (ST36) Acupoints Combined with Adaptive Biofeedback Training on Functional Outlet Obstruction Constipation

BACKGROUND

Stimulant laxatives are still considered the most common treatment for functional outlet obstruction constipation (FOOC). However, the effectiveness of laxatives is unsatisfactory, and the long-term use of laxatives may cause certain adverse events. With this in mind, it is, however, paramount that novel complementary treatment(s) and/or other forms of alternative medicine are adequately investigated.

AIMS

The study aims to explore the effects and potential mechanism(s) of transcutaneous electrical acustimulation (TEA) combined with adaptive biofeedback training (ABT) on FOOC.

METHODS

A total of forty-five patients with FOOC were recruited and were randomly assigned to receive either Macrogol 4000 Powder (MAC, 10 g bid) (group A, n = 15) only, ABT + MAC + Sham-TEA (group B, n = 15), or TEA + ABT + MAC (group C, n = 15) in a six-week study. Individual patients' constipation-symptoms (PAC-SYM) and constipation-quality of life (PAC-QOL) were both assessed and scored. Serum acetylcholine (Ach) and nitric oxide (NO) were measured from drawn blood samples while individual patients' heart rate variability (HRV) was calculated at baseline and after each corresponding therapy. Anorectal manometry and balloon expulsion test were both performed before and after treatment.

RESULTS

Firstly, participants in group C had significantly lower scores of PAC-SYM, PAC-QOL, and a decreased anal defecating pressure (ADP) as compared to participants in group B (all p < 0.050). These results, however, suggest the TEAs effect. Secondly, the low-frequency band (LF)/(LF + HF) ratio in groups B and C were decreased as compared to group A (p=0.037, p=0.010, respectively) regarding HRV. On the other hand, the high-frequency band (HF)/(LF + HF) ratio in groups B and C showed an opposite outcome. Finally, the serum Ach in groups B and C was significantly higher as compared to group A (p=0.023, p=0.012, respectively). Of significant importance, the serum NO in groups B and C were notably low as compared to group A (p=0.001, p < 0.001, respectively).

CONCLUSIONS

TEA, combined with ABT, effectively improves constipation symptoms as well as QOL in FOOC patients. It is, however, achieved by decreasing ADP, which mechanisms are mediated via the autonomic and enteric mechanisms.

Ameliorating Effects of Transcutaneous Electrical Acustimulation Combined With Deep Breathing Training on Refractory Gastroesophageal Reflux Disease Mediated via the Autonomic Pathway

AIMS

To investigate the effects and possible mechanisms of transcutaneous electrical acustimulation (TEA) combined with deep breathing training (DBT) on refractory gastroesophageal reflux disease (rGERD).

METHODS

Twenty-one patients with rGERD were recruited and randomly assigned to receive either only esomeprazole (ESO, 20 mg bid) (group A, n = 7), TEA + DBT + ESO (group B, n = 7), or sham-TEA + DBT + ESO (group C, n = 7) in a four-week study. The reflux diagnostic questionnaire (RDQ) score and heart rate variability (HRV) were recorded and evaluated at baseline and at the end of each treatment. Blood samples were collected for the measurement of serum acetylcholine (Ach) and nitric oxide (NO). Esophageal manometry and 24-hour pH monitoring were performed before and after the treatment.

RESULTS

After treatment, 1) the participants in group B had significantly lower scores of RDQ and DeMeester and increased lower esophageal sphincter pressure (LESP) than those in group C (all p < 0.05), suggesting the role of TEA; 2) low frequency band (LF)/(LF + HF) ratio in groups B and C was decreased, compared with group A (p = 0.010, p = 0.042, respectively); high frequency band (HF)/(LF + HF) ratio in B and C groups was significantly increased, compared with group A (p = 0.010, p = 0.042, respectively); 3) The serum Ach in groups B and C was significantly higher than group A (p = 0.022, p = 0.046, respectively); the serum NO in groups B and C was significantly lower than group A (p = 0.010, p = 0.027, respectively).

CONCLUSIONS

TEA combined with the DBT can effectively improve the reflux symptoms in rGERD patients by increasing LESP and reducing gastroesophageal reflux, which may be mediated via the autonomic and enteric mechanisms.

Effects of Light-at-Night on the Rat Liver - A Role for the Autonomic Nervous System

Exposure to light at night (LAN) has been associated with serious pathologies, including obesity, diabetes and cancer. Recently we showed that 2 h of LAN impaired glucose tolerance in rats. Several studies have suggested that the autonomic nervous system (ANS) plays an important role in communicating these acute effects of LAN to the periphery. Here, we investigated the acute effects of LAN on the liver transcriptome of male Wistar rats. Expression levels of individual genes were not markedly affected by LAN, nevertheless pathway analysis revealed clustered changes in a number of endocrine pathways. Subsequently, we used selective hepatic denervations [sympathetic (Sx), parasympathetic (Px), total (Tx, i.e., Sx plus Px), sham] to investigate the involvement of the ANS in the effects observed. Surgical removal of the sympathetic or parasympathetic hepatic branches of the ANS resulted in many, but small changes in the liver transcriptome, including a pathway involved with circadian clock regulation, but it clearly separated the four denervation groups. On the other hand, analysis of the liver metabolome was not able to separate the denervation groups, and only 6 out of 78 metabolites were significantly up- or downregulated after denervations. Finally, removal of the sympathetic and parasympathetic hepatic nerves combined with LAN exposure clearly modulated the effects of LAN on the liver transcriptome, but left most endocrine pathways unaffected.

Conclusion: One-hour light-at-night acutely affects the liver transcriptome. Part of this effect is mediated via the nervous innervation, as a hepatectomy modulated and reduced the effect of LAN on liver transcripts.

Acute peat smoke inhalation sensitizes rats to the postprandial cardiometabolic effects of a high fat oral load

Wildland fire emissions cause adverse cardiopulmonary outcomes, yet controlled exposure studies to characterize health impacts of specific biomass sources have been complicated by the often latent effects of air pollution. The aim of this study was to determine if postprandial responses after a high fat challenge, long used clinically to predict cardiovascular risk, would unmask latent cardiometabolic responses in rats exposed to peat smoke, a key wildland fire air pollution source. Male Wistar Kyoto rats were exposed once (1 h) to filtered air (FA), or low (0.36 mg/m³ particulate matter) or high concentrations (3.30 mg/m³) of peat smoke, generated by burning peat from an Irish bog. Rats were then fasted overnight, and then administered an oral gavage of a HF suspension (60 kcal% from fat), mimicking a HF meal, 24 h post-exposure. In one cohort, cardiac and superior mesenteric artery function were assessed using high frequency ultrasound 2 h post gavage. In a second cohort, circulating lipids and hormones, pulmonary and systemic inflammatory markers, and circulating monocyte phenotype using flow cytometry were assessed before or 2 or 6 h after gavage. HF gavage alone elicited increases in circulating lipids characteristic of postprandial responses to a HF meal. Few effects were evident after peat exposure in un-gavaged rats. By contrast, exposure to low or high peat caused several changes relative to FA-exposed rats 2 and 6 h post HF gavage including increased heart isovolumic relaxation time, decreased serum glucose and insulin, increased CD11 b/c-expressing blood monocytes, increased serum total cholesterol, alpha-1 acid glycoprotein, and alpha-2 macroglobulin (p = 0.063), decreased serum corticosterone, and increased lung gamma-glutamyl transferase. In summary, these findings demonstrate that a HF challenge reveals effects of air pollution that may otherwise be imperceptible, particularly at low exposure levels, and suggest exposure may sensitize the body to mild inflammatory triggers.

Long-term outcomes of patients undergoing simultaneous liver transplantation and sleeve gastrectomy

Obesity is increasingly common before and after liver transplantation (LT), yet optimal management remains unclear. The aim of this study was to analyze the long-term outcomes for obese patients undergoing LT, including a noninvasive weight loss program and combined LT and sleeve gastrectomy (SG). Since 2006, all patients referred for LT with a body mass index (BMI) ≥35 kg/m² were enrolled. Patients who achieved weight loss (BMI <35) underwent LT alone, and those who did not underwent simultaneous LT + SG. Analysis of long-term outcomes for patients ≥3 years posttransplant was performed. Since 2006, there were 36 in the weight loss intervention (LT cohort) and 13 in the LT + SG cohort with >3 years of follow-up, whereas overall, a total of 29 patients underwent LT + SG. Patients in the LT cohort had less severe obesity at enrollment (40.0 ± 2.7 vs. LT + SG cohort 46.0 ± 4.5; P < 0.001). In the LT cohort, 83.3% (30 of 36) achieved >10% loss in total body weight (TBW) pre-LT. Three years posttransplant, 29.4% of patients in the LT cohort maintained >10% loss in TBW, whereas 100% of the LT + SG patients did (P < 0.001). Patients who underwent LT + SG maintained a significantly higher percentage of total body weight loss after 3 years of follow-up (LT cohort 3.9 ± 13.3% vs. LT + S G cohort 34.8 ± 17.3%; P < 0.001). Patients in the LT + SG also had a lower prevalence of hypertension, insulin resistance, and hepatic steatosis and required fewer antihypertensive medications and lipid agents at last follow-up.

CONCLUSION

Whereas weight loss before transplantation was achieved by obese patients, weight regain was common in the LT cohort. Combined LT + SG resulted in more effective and more durable weight loss, as well as fewer metabolic complications at last follow-up. (Hepatology 2018).

Multiple effects of cold exposure on livers of male mice

Cold exposure of mice is a common method to stimulate brown adipose tissue (BAT) activity and induce browning of white adipose tissue (WAT) that has beneficial effects on whole-body lipid metabolism, including reduced plasma triglyceride (TG) concentrations. The liver is a key regulatory organ in lipid metabolism as it can take up as well as oxidize fatty acids. The liver can also synthesize, store and secrete TGs in VLDL particles. The effects of cold exposure on murine hepatic lipid metabolism have not been addressed. Here, we report the effects of 24-h exposure to 4°C on parameters of hepatic lipid metabolism of male C57BL/6J mice. Cold exposure increased hepatic TG concentrations by 2-fold (P < 0.05) but reduced hepatic lipogenic gene expression. Hepatic expression of genes encoding proteins involved in cholesterol synthesis and uptake such as the LDL receptor (LDLR) was significantly increased upon cold exposure. Hepatic expression of Cyp7a1 encoding the rate-limiting enzyme in the classical bile acid (BA) synthesis pathway was increased by 4.3-fold (P < 0.05). Hepatic BA concentrations and fecal BA excretion were increased by 2.8- and 1.3-fold, respectively (P < 0.05 for both). VLDL-TG secretion was reduced by approximately 50% after 24 h of cold exposure (P < 0.05). In conclusion, cold exposure has various, likely intertwined effects on the liver that should be taken into account when studying the effects of cold exposure on whole-body metabolism.

The role of the daily feeding rhythm in the regulation of the day/night rhythm in triglyceride secretion in rats

Plasma triglyceride (TG) levels show a clear daily rhythm, however, thus far it is still unknown whether this rhythm results from a daily rhythm in TG production, TG uptake or both. Previous studies have shown that feeding activity affects plasma TG concentrations, but it is not clear how the daily rhythm in feeding activity affects plasma TG concentrations. In the present study, we measured plasma TG concentrations and TG secretion rates in rats at 6 Zeitgeber times to investigate whether plasma TG concentrations and TG secretion show a daily rhythm. We found that plasma TG concentrations and TG secretion show a significant day/night rhythm. Next, we removed the daily rhythm in feeding behavior by introducing a 6-meals-a-day (6M) feeding schedule to investigate whether the daily rhythm in feeding behavior is necessary to maintain the daily rhythm in TG secretion. We found that the day/night rhythm in TG secretion was abolished under 6M feeding conditions. Hepatic apolipoprotein B (ApoB) and microsomal TG transfer protein (Mttp), which are both involved in TG secretion, also lost their daily rhythmicity under 6M feeding conditions. Together, these results indicate that: (1) the daily rhythm in TG secretion contributes to the formation of a day/night rhythm in plasma TG levels and (2) a daily feeding rhythm is essential for maintaining the daily rhythm in TG secretion.

Hepatic lipid metabolism and non-alcoholic fatty liver disease in aging

Aging is associated with dysregulation of glucose and lipid metabolism. Various factors that contribute to the dysregulation include both modifiable (e.g. obesity, insulin resistance) and non-modifiable risk factors (age-associated physiologic changes). Although there is no linear relationship between aging and prevalence of non-alcoholic fatty liver disease, current data strongly suggests that advanced age leads to more severe histological changes and poorer clinical outcomes. Hepatic lipid accumulation could lead to significant hepatic and systemic consequences including steatohepatitis, cirrhosis, impairment of systemic glucose metabolism and metabolic syndrome, thereby contributing to age-related diseases. Insulin, leptin and adiponectin are key regulators of the various physiologic processes that regulate hepatic lipid metabolism. Recent advances have expanded our understanding in this field, highlighting the role of novel mediators such as FGF 21, and mitochondria derived peptides. In this review, we will summarize the mediators of hepatic lipid metabolism and how they are altered in aging.

Farnesoid X receptor: A "homeostat" for hepatic nutrient metabolism

The Farnesoid X receptor (FXR) is a nuclear receptor activated by bile acids (BAs). BAs are amphipathic molecules that serve as fat solubilizers in the intestine under postprandial conditions. In the post-absorptive state, BAs bind FXR in the hepatocytes, which in turn provides feedback signals on BA synthesis and transport and regulates lipid, glucose and amino acid metabolism. Therefore, FXR acts as a homeostat of all three classes of nutrients, fats, sugars and proteins. Here we re-analyze the function of FXR in the perspective of nutritional metabolism, and discuss the role of FXR in liver energy homeostasis in postprandial, post-absorptive and fasting/starvation states. FXR, by regulating nutritional metabolism, represses autophagy in conditions of nutrient abundance, and controls the metabolic needs of proliferative cells. In addition, FXR regulates inflammation via direct effects and via its impact on nutrient metabolism. These functions indicate that FXR is an attractive therapeutic target for liver diseases.

Hypothalamic kappa opioid receptor mediates both diet-induced and melanin concentrating hormone-induced liver damage through inflammation and endoplasmic reticulum stress

The opioid system is widely known to modulate the brain reward system and thus affect the behavior of humans and other animals, including feeding. We hypothesized that the hypothalamic opioid system might also control energy metabolism in peripheral tissues. Mice lacking the kappa opioid receptor (κOR) and adenoviral vectors overexpressing or silencing κOR were stereotaxically delivered in the lateral hypothalamic area (LHA) of rats. Vagal denervation was performed to assess its effect on liver metabolism. Endoplasmic reticulum (ER) stress was inhibited by pharmacological (tauroursodeoxycholic acid) and genetic (overexpression of the chaperone glucose-regulated protein 78 kDa) approaches. The peripheral effects on lipid metabolism were assessed by histological techniques and western blot. We show that in the LHA κOR directly controls hepatic lipid metabolism through the parasympathetic nervous system, independent of changes in food intake and body weight. κOR colocalizes with melanin concentrating hormone receptor 1 (MCH-R1) in the LHA, and genetic disruption of κOR reduced melanin concentrating hormone-induced liver steatosis. The functional relevance of these findings was given by the fact that silencing of κOR in the LHA attenuated both methionine choline-deficient, diet-induced and choline-deficient, high-fat diet-induced ER stress, inflammation, steatohepatitis, and fibrosis, whereas overexpression of κOR in this area promoted liver steatosis. Overexpression of glucose-regulated protein 78 kDa in the liver abolished hypothalamic κOR-induced steatosis by reducing hepatic ER stress.

CONCLUSIONS

This study reveals a novel hypothalamic-parasympathetic circuit modulating hepatic function through inflammation and ER stress independent of changes in food intake or body weight; these findings might have implications for the clinical use of opioid receptor antagonists. (Hepatology 2016;64:1086-1104).

When to eat? The influence of circadian rhythms on metabolic health: are animal studies providing the evidence?

As obesity and metabolic diseases rise, there is need to investigate physiological and behavioural aspects associated with their development. Circadian rhythms have a profound influence on metabolic processes, as they prepare the body to optimise energy use and storage. Moreover, food-related signals confer temporal order to organs involved in metabolic regulation. Therefore food intake should be synchronised with the suprachiasmatic nucleus (SCN) to elaborate efficient responses to environmental challenges. Human studies suggest that a loss of synchrony between mealtime and the SCN promotes obesity and metabolic disturbances. Animal research using different paradigms has been performed to characterise the effects of timing of food intake on metabolic profiles. Therefore the purpose of the present review is to critically examine the evidence of animal studies, to provide a state of the art on metabolic findings and to assess whether the paradigms used in rodent models give the evidence to support a 'best time' for food intake. First we analyse and compare the current findings of studies where mealtime has been shifted out of phase from the light-dark cycle. Then, we analyse studies restricting meal times to different moments within the active period. So far animal studies correlate well with human studies, demonstrating that restricting food intake to the active phase limits metabolic disturbances produced by high-energy diets and that eating during the inactive/sleep phase leads to a worse metabolic outcome. Based on the latter we discuss the missing elements and possible mechanisms leading to the metabolic consequences, as these are still lacking.

Non-alcoholic fatty liver disease as a consequence of autonomic imbalance and circadian desynchronization

The circadian system, headed by the suprachiasmatic nucleus, synchronizes behaviour and metabolism according to the external light-dark cycle through neuroendocrine and autonomic signals. Metabolic diseases, such as steatosis, obesity and glucose intolerance, have been associated with conditions of circadian misalignment wherein the feeding schedule has been moved to the resting phase. Here we describe the physiological processes involved in liver lipid accumulation and show how they follow a circadian pattern importantly regulated by both the autonomic nervous system and the feeding-fasting cycle. We propose that an unbalanced activity of the sympathetic-parasympathetic branches between organs induced by circadian misalignment provides the conditions for the development and progression of non-alcoholic fatty liver disease.

Hypothalamic innate immune reaction in obesity

Findings from rodent and human studies show that the presence of inflammatory factors is positively correlated with obesity and the metabolic syndrome. Obesity-associated inflammatory responses take place not only in the periphery but also in the brain. The hypothalamus contains a range of resident glial cells including microglia, macrophages and astrocytes, which are embedded in highly heterogenic groups of neurons that control metabolic homeostasis. This complex neural-glia network can receive information directly from blood-borne factors, positioning it as a metabolic sensor. Following hypercaloric challenge, mediobasal hypothalamic microglia and astrocytes enter a reactive state, which persists during diet-induced obesity. In established mouse models of diet-induced obesity, the hypothalamic vasculature displays angiogenic alterations. Moreover, proopiomelanocortin neurons, which regulate food intake and energy expenditure, are impaired in the arcuate nucleus, where there is an increase in local inflammatory signals. The sum total of these events is a hypothalamic innate immune reactivity, which includes temporal and spatial changes to each cell population. Although the exact role of each participant of the neural-glial-vascular network is still under exploration, therapeutic targets for treating obesity should probably be linked to individual cell types and their specific signalling pathways to address each dysfunction with cell-selective compounds.

Fasting-induced changes in hepatic thyroid hormone metabolism in male rats are independent of autonomic nervous input to the liver

During fasting, profound changes in the regulation of the hypothalamus-pituitary-thyroid axis occur in order to save energy and limit catabolism. In this setting, serum T3 and T4 are decreased without an appropriate TSH and TRH response reflecting central down-regulation of the hypothalamus-pituitary-thyroid axis. Hepatic thyroid hormone (TH) metabolism is also affected by fasting, because type 3 deiodinase (D3) is increased, which is mediated by serum leptin concentrations. A recent study showed that fasting-induced changes in liver TH sulfotransferases (Sults) and uridine 5'-diphospho-glucuronosyltransferase (Ugts) depend on a functional melanocortin system in the hypothalamus. However, the pathways connecting the hypothalamus and the liver that induce these changes are currently unknown. In the present study, we investigated in rats whether the fasting-induced changes in hepatic TH metabolism are regulated by the autonomic nervous system. We selectively cut either the sympathetic or the parasympathetic input to the liver. Serum and liver TH concentrations, deiodinase expression, and activity and Sult and Ugt expression were measured in rats that had been fasted for 36 hours or were fed ad libitum. Fasting decreased serum T3 and T4 concentrations, whereas intrahepatic TH concentrations remained unchanged. D3 expression and activity increased, as was the expression of constitutive androstane receptor, Sult1b1, and Ugt1a1, whereas liver D1 was unaffected. Neither sympathetic nor parasympathetic denervation affected the fasting-induced alterations. We conclude that fasting-induced changes in liver TH metabolism are not regulated via the hepatic autonomic input in a major way and more likely reflect a direct effect of humoral factors on the hepatocyte.

Acetylcholinesterase (AChE) inhibition aggravates fasting-induced triglyceride accumulation in the mouse liver

Although fasting induces hepatic triglyceride (TG) accumulation in both rodents and humans, little is known about the underlying mechanism. Because parasympathetic nervous system activity tends to attenuate the secretion of very-low-density-lipoprotein-triglyceride (VLDL-TG) and increase TG stores in the liver, and serum cholinesterase activity is elevated in fatty liver disease, the inhibition of the parasympathetic neurotransmitter acetylcholinesterase (AChE) may have some influence on hepatic lipid metabolism. To assess the influence of AChE inhibition on lipid metabolism, the effect of physostigmine, an AChE inhibitor, on fasting-induced increase in liver TG was investigated in mice. In comparison with ad libitum-fed mice, 30 h fasting increased liver TG accumulation accompanied by a downregulation of sterol regulatory element-binding protein 1 (SREBP-1) and liver-fatty acid binding-protein (L-FABP). Physostigmine promoted the 30 h fasting-induced increase in liver TG levels in a dose-dependent manner, accompanied by a significant fall in plasma insulin levels, without a fall in plasma TG. Furthermore, physostigmine significantly attenuated the fasting-induced decrease of both mRNA and protein levels of SREBP-1 and L-FABP, and increased IRS-2 protein levels in the liver. The muscarinic receptor antagonist atropine blocked these effects of physostigmine on liver TG, serum insulin, and hepatic protein levels of SREBP-1 and L-FABP. These results demonstrate that AChE inhibition facilitated fasting-induced TG accumulation with up regulation of the hepatic L-FABP and SREBP-1 in mice, at least in part via the activation of muscarinic acetylcholine receptors. Our studies highlight the crucial role of parasympathetic regulation in fasting-induced TG accumulation, and may be an important source of information on the mechanism of hepatic disorders of lipid metabolism.

Hypothalamic control of hepatic lipid metabolism via the autonomic nervous system

Our body is well designed to store energy in times of nutrient excess, and release energy in times of food deprivation. This adaptation to the external environment is achieved by humoral factors and the autonomic nervous system. Claude Bernard, in the 19th century, showed the importance of the autonomic nervous system in the control of glucose metabolism. In the 20th century, the discovery of insulin and the development of techniques to measure hormone concentrations shifted the focus from the neural control of metabolism to the secretion of hormones, thus functionally "decapitating" the body. Just before the end of the 20th century, starting with the discovery of leptin in 1994, the control of energy metabolism went back to our heads. Since the start of 21st century, numerous studies have reported the involvement of hypothalamic pathways in the control of hepatic insulin sensitivity and glucose production. The autonomic nervous system is, therefore, acknowledged to be one of the important determinants of liver metabolism and a possible treatment target. In this chapter, we review research to date on the hypothalamic control of hepatic lipid metabolism.

The hypothalamic neural-glial network and the metabolic syndrome

Despite numerous educational interventions and biomedical research efforts, modern society continues to suffer from obesity and its associated metabolic diseases, such as type 2 diabetes mellitus, and these diseases show little sign of abating. One reason for this is an incomplete understanding of the pathology of the metabolic syndrome, which obstructs the development of effective therapeutic strategies. While hypothalamic neuropathy is a potential candidate that may contribute to the pathogenesis of the metabolic syndrome, the specific causes of hypothalamic neuropathy remain largely unknown. During different stages of high-calorie diet-induced metabolic syndrome, the hypothalamus undergoes gliosis and angiogenesis, both of which potentially reflect ongoing inflammatory processes. This overview discusses current data suggesting a role for hypothalamic inflammation-like processes in diet-induced metabolic diseases and provides a perspective on how to unravel molecular mechanisms of "hypothalamic inflammation" in order to develop anti-obesity therapeutic strategies.

Combination of grape seed proanthocyanidin extract and docosahexaenoic acid-rich oil increases the hepatic detoxification by GST mediated GSH conjugation in a lipidic postprandial state

The ingestion of dietary lipids leads to oxidative stress. This postprandial oxidative stress may potentiate the adverse effects of postprandial hyperlipidaemia. Proanthocyanidins have been shown to alleviate oxidative stress and hypertriglyceridaemia associated with the postprandial state. Additionally, omega-3 polyunsaturated fatty acids (PUFAs) also have beneficial effects on lipoprotein metabolism and oxidative stress. The present study was designed to investigate the possible additive effects in liver of an acute dose of grape seed proanthocyanidins extract (GSPE) and oil rich in docosahexaenoic acid (DHA-OR) on lipidic postprandial oxidative stress in Wistar rats. GSPE+DHA-OR modifies the hepatic antioxidant enzymatic activities (GST and GPx), clearly showing that this combination increases the detoxification of postprandial xenobiotics via the GST action mediated hepatic GSH conjugation. In conclusion, this study provides evidence that the combination of GSPE and DHA-OR ameliorate the transient imbalance between the lipid hydroperoxide level and antioxidant status related to a lipidic postprandial state.

Effect of prior exercise on postprandial lipemia: an updated quantitative review

Reducing postprandial triglycerides (TG) can lower the risk for cardiovascular disease. The purpose of this study was to perform a meta-analytic review of the literature to estimate the effect of prior exercise on postprandial lipemia. A total of 121 effects were found from 76 studies for the total TG response and 70 effects from 44 studies for the incremental area under the curve (iAUC) TG response. The weighted mean effect was moderate for the total TG response, Cohen's d = −0.60 ( P < 0.0001), and for the iAUC response, Cohen's d = −0.59 ( P < 0.0001). Moderator analysis revealed women exhibited a larger reduction ( P < .01) in the total TG response following exercise ( d = −0.96) than men ( d = −0.57); high-intensity interval training induced a larger reduction ( P < .05) in the iAUC response ( d = −1.49) than aerobic ( d = −0.58) or resistance ( d = −0.13) exercise, and participants maintaining an energy deficit following exercise exhibited a greater reduction in the iAUC response ( d = −0.67) compared with participants in energy balance ( d = −0.28). We conclude that prior acute exercise reduces postprandial lipemia, with the magnitude of effect influenced by sex, type of exercise, and energy deficit following exercise.

The gut-liver axis

PURPOSE OF REVIEW

The liver adaptively responds to extra-intestinal and intestinal inflammation. In recent years, the role of the autonomic nervous system, intestinal failure and gut microbiota has been investigated in the development of hepatic, intestinal and extra-intestinal disease.

RECENT FINDINGS

The autonomic nervous system can be stimulated via enteral fat leading to cholecystokinin release, stimulating receptors in the gut and in the brain. This promotes bowel integrity, dampening the inflammatory response to food antigens. Consensus exists that intravenously administered long-chain fatty acids can cause liver damage but randomized-controlled trials are lacking. Disruption of the enterohepatic circulation of bile salts can give rise to cholestasis and nonalcoholic fatty liver disease, which may progress to fibrosis and cirrhosis. Reduced intestinal availability of bile salts reduces stimulation of the farnesoid X receptor. This may induce hepatic bile salt overload and associated hepatotoxicity through reduced action of intestinal fibroblast growth factor 19. Evidence is put forward to suggest that the intestinal microbiota is associated with liver abnormalities.

SUMMARY

Enteral lipids reduce inflammation and liver damage during stress or systemic inflammation, whereas parenteral lipid is associated with liver damage. Maintaining the enterohepatic circulation of bile salts limits hepatic cholestasis through an farnesoid X receptor feedback pathway. Changes in gut microbiota composition may induce liver disease.