Histidine induces lipolysis through sympathetic nerve in white adipose tissue

Light-responsive adipose-hypothalamus axis controls metabolic regulation

Light is fundamental for biological life, with most mammals possessing light-sensing photoreceptors in various organs. Opsin3 is highly expressed in adipose tissue which has extensive communication with other organs, particularly with the brain through the sympathetic nervous system (SNS). Our study reveals a new light-triggered crosstalk between adipose tissue and the hypothalamus. Direct blue-light exposure to subcutaneous white fat improves high-fat diet-induced metabolic abnormalities in an Opsin3-dependent manner. Metabolomic analysis shows that blue light increases circulating levels of histidine, which activates histaminergic neurons in the hypothalamus and stimulates brown adipose tissue (BAT) via SNS. Blocking central actions of histidine and denervating peripheral BAT blunts the effects of blue light. Human white adipocytes respond to direct blue light stimulation in a cell-autonomous manner, highlighting the translational relevance of this pathway. Together, these data demonstrate a light-responsive metabolic circuit involving adipose-hypothalamus communication, offering a potential strategy to alleviate obesity-induced metabolic abnormalities.

Study of Effect of Sympathetic Nerve on Children's Brain Diseases Based on Analysis of Magnetic Resonance Imaging Kurtosis

BACKGROUND

We evaluated the improvement in the gray and white matter functional areas in children with cerebral palsy (CP) after common carotid artery sympathetic neural network ablation. We also analyzed the relationship between the values of the diffusion kurtosis imaging (DKI) parameters and clinical signs in children with CP.

METHODS

We collected data from 22 children with unilateral spastic CP who had undergone common carotid sympathetic neural network ablation in our hospital from January 1, 2014 to December 1, 2018, using magnetic resonance kurtosis imaging technology parameters.

RESULTS

The study found that the changes from preoperatively to postoperatively in the kurtosis fractional anisotropy (KFA) values for the frontal lobe, parietal lobe, temporal lobe, internal sac forelimb, and corpus callosum were statistically significant. However, the changes in the internal sac forelimb, corpus callosum, and KFA values were not statistically significant. The changes from preoperatively to postoperatively in the mean kurtosis (MK) values for the frontal lobe, parietal lobe, temporal lobe, hindlimb of the internal capsule, corpus callosum, and caudate nucleus were statistically significant. However, the MK values for the forelimb, corpus callosum, and thalamus were not statistically significant. The 66-item gross motor function measure scores correlated negatively with the KFA value and positively with the MK value.

CONCLUSION

Therefore, it can be concluded that DKI technology can more accurately reflect the gray and white matter damage in children with CP, and the DKI parameters can be used as a monitoring and evaluation index for children with CP.

Loss of histaminergic modulation of thermoregulation and energy homeostasis in obese mice

Histamine acts centrally to increase energy expenditure and reduce body weight by mechanisms not fully understood. It has been suggested that in the obese state hypothalamic histamine signaling is altered. Previous studies have also shown that histamine acting in the preoptic area controls thermoregulation. We aimed to study the influence of preoptic histamine on body temperature and energy homeostasis in control and obese mice. Activating histamine receptors in the preoptic area by increasing the concentration of endogenous histamine or by local injection of specific agonists induced an elevation of core body temperature and decreased respiratory exchange ratio (RER). In addition, the food intake was significantly decreased. The hyperthermic effect was associated with a rapid increase in mRNA expression of uncoupling proteins in thermogenic tissues, the most pronounced being that of uncoupling protein (UCP) 1 in brown adipose tissue and of UCP2 in white adipose tissue. In diet-induced obese mice histamine had much diminished hyperthermic effects as well as reduced effect on RER. Similarly, the ability of preoptic histamine signaling to increase the expression of uncoupling proteins was abolished. We also found that the expression of mRNA encoding the H1 receptor subtype in the preoptic area was significantly lower in obese animals. These results indicate that histamine signaling in the preoptic area modulates energy homeostasis by regulating body temperature, metabolic parameters and food intake and that the obese state is associated with a decrease in neurotransmitter's influence.

Histamine in neurotransmission and brain diseases

Apart from its central role in the mediation of allergic reactions, gastric acid secretion and inflammation in the periphery, histamine serves an important function as a neurotransitter in the central nervous system. The histaminergic neurons originate from the tuberomamillary nucleus of the posterior hypothalamus and send projections to most parts of the brain. The central histamine system is involved in many brain functions such as arousal, control of pituitary hormone secretion, suppression ofeating and cognitive functions. The effects of neuronal histamine are mediated via G-protein-coupled H1-H4 receptors. The prominent role of histamine as a wake-promoting substance has drawn interest to treat sleep-wake disorders, especially narcolepsy, via modulation of H3 receptor function. Post mortem studies have revealed alterations in histaminergic system in neurological and psychiatric diseases. Brain histamine levels are decreased in Alzheimer's disease patients whereas abnormally high histamine concentrations are found in the brains of Parkinson's disease and schizophrenic patients. Low histamine levels are associated with convulsions and seizures. The release of histamine is altered in response to different types of brain injury: e.g. increased release of histamine in an ischemic brain trauma might have a role in the recovery from neuronal damage. Neuronal histamine is also involved in the pain perception. Drugs that increase brain and spinal histamine concentrations have antinociceptive properties. Histaminergic drugs, most importantly histamine H3 receptors ligands, have shown efficacy in many animal models of the above-mentioned disorders. Ongoing clinical trials will reveal the efficacy and safety of these drugs in the treatment of human patients.

Metabolic regulatory network alterations in response to acute cold stress and ginsenoside intervention

Acute stress may trigger systemic biochemical and physiological changes in living organisms, leading to a rapid loss of homeostasis, which can be gradually reinstated by self-regulatory mechanisms and/or drug intervention strategy. However, such a sophisticated metabolic regulatory process has so far been poorly understood, especially from a holistic view. Urinary metabolite profiling of Sprague-Dawley rats exposed to cold temperature (-10 degrees C) for 2 h using GC/MS in conjunction with modern multivariate statistical techniques revealed drastic biochemical changes as evidenced by fluctuations of urinary metabolites and demonstrated the protective effect of total ginsenosides (TGs) in ginseng extracts on stressed rats. The metabonomics approach enables us to visualize significant alterations in metabolite expression patterns as a result of stress-induced metabolic responses and post-stress compensation, and drug intervention. Several major metabolic pathways including catecholamines, glucocorticoids, the tricarboxylic acid (TCA) cycle, tryptophan (nicotinate), and gut microbiota metabolites were identified to be involved in metabolic regulation and compensation required to restore homeostasis.

Alterations of lipid metabolism and gene expression in rat adipocytes during chronic olanzapine treatment

Although antipsychotics are established drugs in schizophrenia treatment, they are admittedly known to induce side effects favoring the onset of obesity and worsening its complications. Despite potential involvement of histamine receptor antagonism, or of other neurotransmitter systems, the mechanism by which antipsychotic drugs increase body weight is not elucidated. The aim of the present study was to investigate whether chronic antipsychotic treatments can directly alter the regulation of two main functions of white adipose tissue: lipolysis and glucose utilization. The influence of a classical antipsychotic (haloperidol) was compared to that of two atypical antipsychotics, one known to favor weight gain (olanzapine), the other not (ziprasidone). Cell size, lipolytic capacity and glucose transport activity were determined in white adipocytes of rats subjected to 5-week oral treatment with these antipsychotics. Gene expression of adipocyte proteins involved in glucose transport or fat storage and mobilization, such as glucose transporters (GLUT1 and GLUT4), leptin, matrix metallo-proteinase-9 (MMP9), hormone-sensitive lipase (HSL) and fatty acid synthase (FAS) was also evaluated. Adipocytes from chronic olanzapine-treated rats exhibited decreased lipolytic activity, lowered HSL expression and increased FAS expression. These changes were concomitant to enlarged fat deposition and adipocyte size. Alterations were observed in adipocytes from olanzapine-treated rats whereas the other antipsychotics did not induce any notable disorder. Our results therefore show evidence of an effect of chronic antipsychotic treatment on rat adipocyte metabolism. Thus, impairment of fat cell lipolysis should be considered as a side effect of certain antipsychotics, leading, along with the already documented hyperphagia, to the excessive weight gain observed in patients under prolonged treatment..

Thematic review series: adipocyte biology. Sympathetic and sensory innervation of white adipose tissue

During our study of the reversal of seasonal obesity in Siberian hamsters, we found an interaction between receptors for the pineal hormone melatonin and the sympathetic nervous system (SNS) outflow from brain to white adipose tissue (WAT). This ultimately led us and others to conclude that the SNS innervation of WAT is the primary initiator of lipid mobilization in these as well as other animals, including humans. There is strong neurochemical (norepinephrine turnover), neuroanatomical (viral tract tracing), and functional (sympathetic denervation-induced blockade of lipolysis) evidence for the role of the SNS in lipid mobilization. Recent findings suggest the presence of WAT sensory innervation based on strong neuroanatomical (viral tract tracing, immunohistochemical markers of sensory nerves) and suggestive functional (capsaicin sensory denervation-induced WAT growth) evidence, the latter implying a role in conveying adiposity information to the brain. By contrast, parasympathetic nervous system innervation of WAT is characterized by largely negative neuroanatomical evidence (viral tract tracing, immunohistochemical and biochemical markers of parasympathetic nerves). Functional evidence (intraneural stimulation and in situ microdialysis) for the role of the SNS innervation in lipid mobilization in human WAT is convincing, with some controversy regarding the level of sympathetic nerve activity in human obesity.

Ghrelin regulates adiposity in white adipose tissue and UCP1 mRNA expression in brown adipose tissue in mice

To examine the involvement of ghrelin in obesity, we investigated the effects of treatment with peripherally administered ghrelin on food intake, adiposity, and expression of uncoupling protein (UCP) mRNA in brown (BAT) and white (WAT) adipose tissue in mice. Acute bolus administration of ghrelin at a dose of 120 nmol/kg increased cumulative food intake over 4 and 24 h as compared to controls (p<0.05 for each), whereas 12 nmol/kg/day ghrelin showed no remarkable effect (p>0.1). Chronic repeated treatment with 12 nmol/kg/day ghrelin for 7 days increased body weight and adiposity assessed by the weight of adipose tissue, triglyceride content in WAT (p<0.05 for each versus control). In addition, the same treatment decreased and increased mRNA expression of BAT UCP1 and WAT UCP2, respectively (p<0.05 for each). In conclusion, ghrelin can regulate body weight, adiposity and UCPs mRNA expression in mice. The present results provide evidence for a new regulatory loop involving ghrelin and UCP, and add novel insights into the regulatory mechanisms of obesity.

Assessment of pharmacology and potential anti-obesity properties of H3receptor antagonists/inverse agonists

Histamine is a key neurotransmitter that alters central nervous system functions in both behavioural and homeostatic contexts through its actions on the histamine (H) subreceptors H(1), H(2) and H(3) G-protein-coupled receptors. H(3)receptors have a diverse central nervous system distribution where they function as both homo- and hetero-receptors to modulate the synthesis and/or release of several neurotransmitters. H(3) receptors are constitutively active, which implies that antagonists of H(3) receptors may also function as inverse agonists to alter the basal state of the receptor and uncouple constitutive receptor-G-protein interactions. Reference H(3) antagonists such as thioperamide and ciproxifan, administered either centrally or systemically, have been shown to cause changes in food consumption and/or body weight in proof-of-concept studies. More recently, several non-imidazole-based H(3) antagonists/inverse agonists have also been described with efficacy in at least one animal model of human obesity. Considerable preclinical effort remains necessary before such compounds achieve therapeutic success or failure. Moreover, ongoing research in a number of laboratories has shed new insights into the effects of H(3) ligands in the control of feeding, appetite and body weight, which offer different results and conclusions. The goal of this review is to appraise these findings and forecast whether any H(3) antagonists/inverse agonists will provide clinical utility to treat human obesity.

High leptin level is accompanied with decreased long leptin receptor transcript in histamine deficient transgenic mice

Leptin is a multifunctional cytokine and hormone that primarily acts in the hypothalamus and plays a key role in regulation of food intake and energy expenditure. Leptin acts through its receptor (OBR), the product of db gene that activates the Jak/STAT pathway predominantly. To exert its functions, leptin interacts with histamine as well. Histamine is a downstream effector of leptin as its release, metabolism is enhanced by leptin and hypothalamic histamine reduces food intake. In a bi-directional regulatory loop histamine also influences leptin concentration by inhibiting its expression. In this study we demonstrate that histamine deficiency elevates serum leptin level and decreases full-length leptin receptor isoform with a slight increase of the short one and results in mild late onset obesity. These observation can help to elucidate further the bi-lateral interaction of leptin and histamine, and therefore provide useful data to understand the pathomechanism of obesity.

Histidine supplementation suppresses food intake and fat accumulation in rats

OBJECTIVE

Histamine, a derivative of histidine, decreases food intake and body fat by activation of histamine neurons. Our objective was to clarify the effect of dietary histidine, in particular, on food intake and/or body fat accumulation in rats.

METHODS

Male Wistar rats were assigned to one of four groups after acclimation and allowed free access to diets containing 20% casein (0% histidine), 20% casein plus 1.0% histidine, 20% casein plus 2.5% histidine, or 20% casein plus 5% histidine for 8 d.

RESULTS

Food intake and body weight were recorded daily and compared between groups. During the experimental period, food intake decreased according to the increases in dietary histidine. There was a negative and significant (P < 0.01) correlation between dietary histidine (grams per 8 d) and retroperitoneal fat pad (grams per 100 g of body weight). Uncoupling protein-1 mRNA in brown adipose tissue increased with increases in dietary histidine.

CONCLUSION

Our results indicate that dietary histidine suppresses food intake and fat accumulation in rats.

Skin Reactivity to Histamine and Codeine in Unselected 9-Year-Old Children from Italy, Poland and Libya

BACKGROUND

Previous studies have shown that histamine skin reactivity (the dimensions of a skin wheal elicited by a prick with histamine 10 mg/ml) in unselected school children has increased in Italy during the past two decades and is higher in Italy than in Poland. Hence this variable can probably be influenced by a changing or different lifestyle. The aim of this study was to compare skin reactivity to histamine and codeine (a marker of histamine releasability from mast cells) in schoolchildren from countries with different lifestyles.

METHODS

Six previously unstudied unselected populations of 9-year-old schoolchildren (two each from Poland, Italy, and Libya; n = 863 subjects; 49.0% males) were pricked with two concentrations of histamine (10 and 1 mg/ml) and codeine (90 and 9 mg/ml).

RESULTS

The higher concentrations of both pharmacologic agents tested yielded significantly different wheal areas in the three countries: Poland < Italy < Libya (histamine, 11.8, 16.1 and 20.7 mm2; codeine, 9.2, 13.2 and 16.2 mm2; p < 0.001 for all comparisons). The lower concentrations elicited almost matching results. Histamine wheal areas correlated closely with areas elicited by codeine in the same individual: angular coefficients of the histamine to codeine regression lines were 0.535, Italy; 0.551, Libya; 0.612, Poland; and 0.581 for the whole population. More histamine was needed to produce a wheal in Poland than in Libya: a 20-mm2 wheal required an injected histamine concentration of about 8.8 mg/ml in Libya, 29.5 mg/ml in Italy and 102.1 mg/ml in Poland.

CONCLUSION

More studies are necessary to explain the observed international differences in skin histamine reactivity and their effect on the prevalence of positive allergen skin tests.

l-Histidine stimulates sympathetic nerve activity to brown adipose tissue in rats

Hypothalamic neuronal histamine is involved in the central regulation of energy expenditure through the activation of sympathetic nerves innervating brown adipose tissue (BAT). The present study examined the effect of L-histidine, a precursor of neuronal histamine, on BAT sympathetic nerve activity in rats. Infusion of histamine at a dose of 1 nmol/rat into the third cerebroventricle significantly increased BAT sympathetic nerve activity as compared with the effect of phosphate buffered saline (P < 0.05). Intraperitoneal (i.p.) injection of L-histidine (0.3 mmol/rat) also significantly increased BAT sympathetic nerve activity as compared with the effect of PBS (P < 0.05). Pretreatment with an i.p. bolus injection of 224 micromol/kg alpha-fluoromethylhistidine, a suicide inhibitor of the histamine synthesizing enzyme histidine decarboxylase, blocked the stimulatory effect of l-histidine on BAT sympathetic nerve activity. These results indicate that L-histidine regulates BAT sympathetic nerve activity through its conversion into neuronal histamine in the hypothalamus.

Functional heterogeneity of the responses of histaminergic neuron subpopulations to various stress challenges

In rats, the cell bodies of the histaminergic neuronal system are clustered in five distinct cell groups (E1-E5) within the posterior hypothalamus. On the basis of tract tracing studies, these histaminergic subgroups have been regarded as one functional unit. In addition to its well-characterized role in arousal, locomotor activity, metabolism, feeding, drinking and behaviour, as well as in coordination of autonomic functions, histamine has been implicated in regulation of the hypothalamo-pituitary-adrenocortical axis during stress. To address the capacity of different histaminergic subgroups to respond to various challenges, we revealed c-Fos, the immediate early gene marker of activated neurons, in histamine synthesizing neurons by combining c-Fos immunocytochemistry with in situ hybridization of histidine decarboxylase (HDC) mRNA. Compared to the negligible colocalization of these markers in control rats, restraint, insulin-induced hypoglycaemia and foot shock resulted in specific activation of histamine synthesizing neurons of the E4 and E5 subgroup in the tuberomammillary region. Up to 36% of HDC mRNA-expressing cells show c-Fos immunoreactivity in the E5 region. In addition, some neurons of the E1, E2 and E3 histaminergic groups were activated after restraint stress. Many less c-Fos-positive histaminergic neurons were detected after immobilization and dehydration. Ether stress, acute hyperosmotic stimulus or injection of bacterial lipopolysaccharide did not activate hypothalamic HDC-positive neurons. These results suggest, for the first time, the functional heterogeneity of histaminergic neuron population, the components of which are recruited in a stressor- and subgroup-specific manner.

Hyperleptinemia, visceral adiposity, and decreased glucose tolerance in mice with a targeted disruption of the histidine decarboxylase gene

Histamine has been referred to as an anorexic factor that decreases appetite and fat accumulation and affects feeding behavior. Tuberomammillary histaminergic neurons have been implicated in central mediation of peripheral metabolic signals such as leptin, and centrally released histamine inhibits ob gene expression. Here we have characterized the metabolic phenotype of mice that completely lack the ability to produce histamine because of targeted disruption of the key enzyme in histamine biosynthesis (histidine decarboxylase, HDC). Histochemical analyses confirmed the lack of HDC mRNA, histamine immunoreactivity, and histaminergic innervation throughout the brain of gene knockout mouse. Aged histamine-deficient (HDC-/-) mice are characterized by visceral adiposity, increased amount of brown adipose tissue, impaired glucose tolerance, hyperinsulinemia, and hyperleptinemia. Histamine-deficient animals are not hyperphagic but gain more weight and are calorically more efficient than wild-type controls. These metabolic changes presumably are due to the impaired regulatory loop between leptin and hypothalamic histamine that results in orexigenic dominance through decreased energy expenditure, attenuated ability to induce uncoupling protein-1 mRNA in the brown adipose tissue and defect in mobilizing energy stores. Our results further support the role of histamine in regulation of energy homeostasis.