The many lives of leptin

Targeting Adipokines: A Promising Therapeutic Strategy for Epilepsy

Epilepsy affects 65 million people globally and causes neurobehavioral, cognitive, and psychological defects. Although research on the disease is progressing and a wide range of treatments are available, approximately 30% of people have refractory epilepsy that cannot be managed with conventional medications. This underlines the importance of further understanding the condition and exploring cutting-edge targets for treatment. Adipokines are peptides secreted by adipocyte's white adipose tissue, involved in controlling food intake and metabolism. Their regulatory functions in the central nervous system (CNS) are multifaceted and identified in several physiology and pathologies. Adipokines play a role in oxidative stress and neuroinflammation which are associated with brain degeneration and connected neurological diseases. This review aims to highlight the potential impacts of leptin, adiponectin, apelin, vaspin, visfatin, and chimerin in the pathogenesis of epilepsy.

The early life growth of head circumference, weight, and height in infants with autism spectrum disorders: a systematic review

BACKGROUNDS

The Autism spectrum disorder (ASD) prevalence has increased significantly over the past two decades. This review summarizes the current knowledge of the association between the early life growth of head circumference (HC), weight, and height with ASD in infants.

METHODS

PubMed, Scopus, Science Direct, and Google Scholar databases were searched up to November 2021 using relevant keywords. All original articles are written in English evaluating the early life growth of HC, weight, and height in infants with ASD were eligible for the present review.

RESULTS

Totally, 23 articles involving 4959 infants were included in this review. Of 13 studies that evaluated HC of infants at birth, 10 studies (83.33%) showed that the HC at the birth of autistic children was similar to that of the average found in the control group. Among 21 studies that evaluated the HC and weight status in infants, 19 studies (90.47%) showed that autistic children had larger HC and weight than the control group or abnormal acceleration of head growth during infancy. Height growth of infants was investigated in 13 studies, of which 10 cases (76.92%) reported that infants with ASD were significantly longer than control groups. Most of he included studies had a good quality.

CONCLUSIONS

The findings suggest that in infants with ASD, without the contribution of birth growth factors and sex of the child, the growth of HC, weight, and height probably was faster than in infants with normal development, in early life. Therefore, these measurements might be useful as initial predictive biomarkers for the risk of developing ASD.

Identification of a novel link between adiposity and visuospatial perception

OBJECTIVE

Recent work has reported a negative association between BMI and performance on the Penn Line Orientation Task. To determine the reliability of this effect, a comprehensive assessment of visual function in individuals with healthy weight (HW) and those with overweight/obesity (OW/OB) was performed.

METHODS

Visual acuity/contrast, Penn Line Orientation Task, and higher-order visuospatial function were measured in 80 (40 with HW, 40 with OW/OB) case-control study participants. Adiposity, fasting glucose, hemoglobin A1c, diet, physical activity, and heart rate variability were also assessed. A subgroup of 22 participants plus 5 additional participants (n = 27) underwent functional magnetic resonance imaging scanning.

RESULTS

Compared with those with HW, individuals with OW/OB performed worse on tasks requiring judgments of line orientation. This effect was mediated by body fat percentage and was unrelated to other measures. Functional magnetic resonance imaging revealed a negative association between BMI and response in the primary visual cortex (V1) during line orientation judgment. Performance was unrelated to V1 response but positively correlated with response in a network of regions, including the lateral occipital cortex, when BMI was accounted for in the model.

CONCLUSIONS

These results demonstrate a selective deficit in line orientation perception associated with adiposity and blunted activation in the V1 that cannot be attributed to visual acuity and does not generalize to other visuospatial tasks.

Body mass index related to executive function and hippocampal subregion volume in subjective cognitive decline

Objective

This study aims to explore whether body mass index (BMI) level affects the executive function and hippocampal subregion volume of subjective cognitive decline (SCD).

Materials and methods

A total of 111 participants were included in the analysis, including SCD (38 of normal BMI, 27 of overweight and obesity) and normal cognitive control (NC) (29 of normal BMI, 17 of overweight and obesity). All subjects underwent the Chinese version of the Stroop Color-Word Test (SCWT) to measure the executive function and a high-resolution 3D T1 structural image acquisition. Two-way ANOVA was used to examine the differences in executive function and gray matter volume in hippocampal subregions under different BMI levels between the SCD and NC.

Result

The subdimensions of executive function in which different BMI levels interact with SCD and NC include inhibition control function [SCWT C-B reaction time(s): F (1,104) = 5.732, p = 0.018], and the hippocampal subregion volume of CA1 [F (1,99) = 8.607, p = 0.004], hippocampal tail [F (1,99) = 4.077, p = 0.046], and molecular layer [F (1,99) = 6.309, p = 0.014]. After correction by Bonferroni method, the population × BMI interaction only had a significant effect on the CA1 (p = 0.004). Further analysis found that the SCWT C-B reaction time of SCD was significantly longer than NC no matter whether it is at the normal BMI level [F (1,104) = 4.325, p = 0.040] or the high BMI level [F (1,104) = 21.530, p < 0.001], and the inhibitory control function of SCD was worse than that of NC. In the normal BMI group, gray matter volume in the hippocampal subregion (CA1) of SCD was significantly smaller than that of NC [F (1,99) = 4.938, p = 0.029]. For patients with SCD, the high BMI group had worse inhibitory control function [F (1,104) = 13.499, p < 0.001] and greater CA1 volume compared with the normal BMI group [F (1,99) = 7.619, p = 0.007].

Conclusion

The BMI level is related to the inhibition control function and the gray matter volume of CA1 subregion in SCD. Overweight seems to increase the gray matter volume of CA1 in the elderly with SCD, but it is not enough to compensate for the damage to executive function caused by the disease. These data provide new insights into the relationship between BMI level and executive function of SCD from the perspective of imaging.

Peripheral versus central insulin and leptin resistance: Role in metabolic disorders, cognition, and neuropsychiatric diseases

Insulin and leptin are classically regarded as peptide hormones that play key roles in metabolism. In actuality, they serve several functions in both the periphery and central nervous system (CNS). Likewise, insulin and leptin resistance can occur both peripherally and centrally. Metabolic disorders such as diabetes and obesity share several key features including insulin and leptin resistance. While the peripheral effects of these disorders are well-known (i.e. cardiovascular disease, hypertension, stroke, dyslipidemia, etc.), the CNS complications of leptin and insulin resistance have come into sharper focus. Both preclinical and clinical findings have indicated that insulin and leptin resistance are associated with cognitive deficits and neuropsychiatric diseases such as depression. Importantly, these studies also suggest that these deficits in neuroplasticity can be reversed by restoration of insulin and leptin sensitivity. In view of these observations, this review will describe, in detail, the peripheral and central functions of insulin and leptin and explain the role of insulin and leptin resistance in various metabolic disorders, cognition, and neuropsychiatric diseases.

Implementation of a Physical Activity Program Protocol in Schoolchildren: Effects on the Endocrine Adipose Tissue and Cognitive Functions

Practicing exercise is one of the best strategies to promote well-being and quality of life, however physical activity in schoolchildren and adolescents is developed in an unpredictable, intermittent way and in short periods. There are relatively few intervention studies investigating the role of physical activity in schoolchildren endocrine function of adipose tissue and cognitive function. One hundred and three boys, divided into two groups: control (n = 51, did not perform additional physical activity) and exercise (n = 52, performed vigorous physical activity after the regular school classes). The exercise group, developed a 6 months physical activity protocol delivered by the physical education teacher during the second semester of the academic course (6 months). Body composition measurements, adherence to the Mediterranean diet, nutritional intake, hematological and biochemical parameters, endocrine function of the adipose tissue and biomarkers of brain molecular function were assessed at enrolment and after 6 months of intervention. No statistically significant differences between both groups were found for age, height and bone mass. Weight and BMI was lower in the exercise group compared to the control group, increasing lean mass and reducing fat mass. 58.68% of children in the exercise group showed high adherence to the Mediterranean Diet compared to 46.32% of the control group. The exercise group was more concerned about their diet consumed more fiber, vitamin B1, B2, B6, B12, D, Niacin, Folic acid, Fe, Zn, Se and Cu. Triglycerides levels and HDL-cholesterol were higher in the exercise group at the end of the study. Leptin, MCP-1, lipocalin-2, adipsin and PAI-1 levels were lower in the exercise group at the end of the exercise protocol. In contrast, adiponectin and osteocrin markedly increased in the exercise group. Moreover, marked increases were recorded in healthy brain state biomarkers (NGF, BDNF, and irisin) in the exercise group, which could have a positive impact on academic performance. Taken together, all the findings reported are consistent with many benefits of the exercise protocol on adipose tissue and brain molecular function, demonstrating the usefulness of early interventions based on physical activity in children to reduce risk factors related to sedentary lifestyle.

Sildenafil ameliorates leptin resistance and normalizes lipid handling in the hypothalamic and adipose tissues of testosterone-exposed pregnant rats

Leptin and hypothalamic-adipose lipid handling are relevant in determining the shift of metabolic activities. There are scanty findings connecting glucose dysregulation as a result of hyperandrogenism during gestation to hypothalamic-adipose axis and leptin resistance. Sildenafil has recently gained attention in the prevention of intra-uterine growth restriction. The present study aimed at demonstrating the effect of sildenafil on leptin resistance and hypothalamic-adipose lipid handling in testosterone-exposed pregnant rats. Three groups of pregnant Wistar rats (n = 5/group) received olive oil (Ctr, S.C.) or testosterone propionate (Tes, 3.0 mg/kg; sc)or testosterone propionate (3.0 mg/kg; sc) and sildenafil (Tes + PDE5, 50 mg/kg; po)from gestational day 14-19. Blood samples, hypothalamus and adipose tissue were excised for biochemical analysis on day 20. Adipose and body weights, plasma leptin and adiponectin, adipose and hypothalamic leptin and triglyceride, adipose uric acid, hypothalamic Nrf2, catalase and nitric oxide were reduced following gestational testosterone exposure. Also, fasting insulin, plasma triglyceride, uric acid, leptin-adiponectin ratio, hypothalamic free fatty acid, total cholesterol, uric acid, aspartate transaminase and cyclic guanine monophosphate were elevated by testosterone exposure to pregnant animals. Sildenafil ameliorated leptin resistance and normalized hypothalamic-adipose lipid handling. Therefore, sildenafil protects against testosterone-induced leptin resistance and adverse hypothalamic-adipose lipid handling in pregnant rats.

Insulin and Leptin/Upd2 Exert Opposing Influences on Synapse Number in Fat-Sensing Neurons

Energy-sensing neural circuits decide to expend or conserve resources based, in part, on the tonic, steady-state, energy-store information they receive. Tonic signals, in the form of adipose tissue-derived adipokines, set the baseline level of activity in the energy-sensing neurons, thereby providing context for interpretation of additional inputs. However, the mechanism by which tonic adipokine information establishes steady-state neuronal function has heretofore been unclear. We show here that under conditions of nutrient surplus, Upd2, a Drosophila leptin ortholog, regulates actin-based synapse reorganization to reduce bouton number in an inhibitory circuit, thus establishing a neural tone that is permissive for insulin release. Unexpectedly, we found that insulin feeds back on these same inhibitory neurons to conversely increase bouton number, resulting in maintenance of negative tone. Our results point to a mechanism by which two surplus-sensing hormonal systems, Upd2/leptin and insulin, converge on a neuronal circuit with opposing outcomes to establish energy-store-dependent neuron activity.

Evaluation of Adipokines Concentration in Iraqi Patients with Major and Minor Beta Thalassemia

Background

Beta thalassemia (β-thalassemia) is a type of inherited blood disorder characterized by the impaired production of beta globin chains. β-Thalassemia can be categorized into three subtypes according to symptom severity: β-thalassemia minor, β-thalassemia intermedia, and β-thalassemia major. Adipose tissue functions as an endocrine gland by synthesizing and secreting an array of bioactive peptides including leptin, adiponectin, and resistin.

Methods

We recruited 30 participants who were transfusion dependent β-thalassemia patients (major) and 30 participants who were non-transfusion dependent β-thalassemia patients (minor). The control group consisted of 20 healthy individuals. Analysis of the demographic profile, hematological profile, biochemical parameters, and serum adipokine concentrations (leptin, adiponectin and resistin) were performed for all participants.

Results

Our results showed that leptin serum levels were significantly lower in the β-thalassemia major group compared with the β-thalassemia minor group or healthy individuals, while serum levels of adiponectin were significantly higher in β-thalassemic patients compared with healthy controls. Serum levels of resistin were significantly higher in β-thalassemic patients compared with the healthy control group. A significant negative correlation was noted between adiponectin and BMI in β-thalassemic patients, whereas leptin was observed to have a significant positive correlation with BMI in the control group. Leptin was observed to have a significant negative correlation with adiponectin and ferritin in the β-thalassemia major group.

Conclusion

The changes we observed in adipokine levels may play a role in the development of the complications related to β-Thalassemia and disease severity.

Obesity as a Risk Factor for Alzheimer's Disease: Implication of Leptin and Glutamate

Obesity is known to induce leptin and insulin resistance. Leptin is a peptide hormone synthesized in adipose tissue that mainly regulates food intake. It has been shown that insulin stimulates the production of leptin when adipocytes are exposed to glucose to encourage satiety; while leptin, via a negative feedback, decreases the insulin release and enhances tissue sensitivity to it, leading to glucose uptake for energy utilization or storage. Therefore, resistance to insulin is closely related to leptin resistance. Obesity in middle age has also been related to Alzheimer's disease (AD). In recent years, the relation between impaired leptin signaling pathway and the onset of AD has been studied. In all this context the role of the blood brain barrier (BBB) is crucial. Slow excitotoxicity happens in AD due to an excess of the neurotransmitter glutamate. Since leptin has been shown to regulate N-methyl-D-aspartate (NMDA) receptors, we want to review the link between these pathological pathways, and how they are affected by other AD triggering factors and its role in the onset of AD.

Food for thought: Leptin regulation of hippocampal function and its role in Alzheimer's disease

Accumulating evidence indicates that diet and body weight are important factors associated with Alzheimer's disease (AD), with a significant increase in AD risk linked to mid-life obesity, and weight loss frequently occurring in the early stages of AD. This has fuelled interest in the hormone leptin, as it is an important hypothalamic regulator of food intake and body weight, but leptin also markedly influences the functioning of the hippocampus; a key brain region that degenerates in AD. Increasing evidence indicates that leptin has cognitive enhancing properties as it facilitates the cellular events that underlie hippocampal-dependent learning and memory. However, significant reductions in leptin's capacity to regulate hippocampal synaptic function occurs with age and dysfunctions in the leptin system are associated with an increased risk of AD. Moreover, leptin is a potential novel target in AD as leptin treatment has beneficial effects in various models of AD. Here we summarise recent advances in leptin neurobiology with particular focus on regulation of hippocampal synaptic function by leptin and the implications of this for neurodegenerative disorders like AD. This article is part of the Special Issue entitled 'Metabolic Impairment as Risk Factors for Neurodegenerative Disorders.'

Leptin resistance and hippocampal behavioral deficits

The adipocyte-derived hormone leptin is an important regulator of body weight and metabolism through activation of brain leptin receptors expressed in regions such as the hypothalamus. Beyond these well described and characterized activities of leptin in the hypothalamus, it is becoming increasingly clear that the central activities of leptin extend to the hippocampus. Indeed, leptin receptors are expressed in the hippocampus where these receptors are proposed to mediate various aspects of hippocampal synaptic plasticity that ultimately impact cognitive function. This concept is supported by studies demonstrating that leptin promotes hippocampal-dependent learning and memory, as well as studies indicating that leptin resistance is associated with deficits in hippocampal-dependent behaviors and in the induction of depressive-like behaviors. The effects of leptin on cognitive/behavioral plasticity in the hippocampus may be regulated by direct activation of leptin receptors expressed in the hippocampus; additionally, leptin-mediated activation of synaptic networks that project to the hippocampus may also impact hippocampal-mediated behaviors. In view of these previous observations, the goal of this review will be to discuss the mechanisms through which leptin facilitates cognition and behavior, as well as to dissect the loci at which leptin resistance leads to impairments in hippocampal synaptic plasticity, including the development of cognitive deficits and increased risk of depressive illness in metabolic disorders such as obesity and type 2 diabetes mellitus (T2DM).

Clarifying the Ghrelin System's Ability to Regulate Feeding Behaviours Despite Enigmatic Spatial Separation of the GHSR and Its Endogenous Ligand

Ghrelin is a hormone predominantly produced in and secreted from the stomach. Ghrelin is involved in many physiological processes including feeding, the stress response, and in modulating learning, memory and motivational processes. Ghrelin does this by binding to its receptor, the growth hormone secretagogue receptor (GHSR), a receptor found in relatively high concentrations in hypothalamic and mesolimbic brain regions. While the feeding and metabolic effects of ghrelin can be explained by the effects of this hormone on regions of the brain that have a more permeable blood brain barrier (BBB), ghrelin produced within the periphery demonstrates a limited ability to reach extrahypothalamic regions where GHSRs are expressed. Therefore, one of the most pressing unanswered questions plaguing ghrelin research is how GHSRs, distributed in brain regions protected by the BBB, are activated despite ghrelin’s predominant peripheral production and poor ability to transverse the BBB. This manuscript will describe how peripheral ghrelin activates central GHSRs to encourage feeding, and how central ghrelin synthesis and ghrelin independent activation of GHSRs may also contribute to the modulation of feeding behaviours.

Leptin resistance elicits depressive-like behaviors in rats

There is a growing appreciation that the complications of obesity extend to the central nervous system (CNS) and include increased risk for development of neuropsychiatric co-morbidities such as depressive illness. The neurological consequences of obesity may develop as a continuum and involve a progression of pathological features which is initiated by leptin resistance. Leptin resistance is a hallmark feature of obesity, but it is unknown whether leptin resistance or blockage of leptin action is casually linked to the neurological changes which underlie depressive-like phenotypes. Accordingly, the aim of the current study was to examine whether chronic administration of a pegylated leptin receptor antagonist (Peg-LRA) elicits depressive-like behaviors in adult male rats. Peg-LRA administration resulted in endocrine and metabolic features that are characteristic of an obesity phenotype. Peg-LRA rats also exhibited increased immobility in the forced swim test, depressive-like behaviors that were accompanied by indices of peripheral inflammation. These results demonstrate that leptin resistance elicits an obesity phenotype that is characterized by peripheral immune changes and depressive-like behaviors in rats, supporting the concept that co-morbid obesity and depressive illness develop as a continuum resulting from changes in the peripheral endocrine and metabolic milieu.

Elevated adiponectin but varied response in circulating leptin levels to falciparum malaria in type 2 diabetics and non-diabetic controls

Background

To investigate effects of falciparum malaria on circulating levels of leptin and adiponectin in type 2 diabetes mellitus (T2DM) and non-diabetic controls in relation to measures of adiposity.

Methods

Levels of leptin and adiponectin were measured in 100 type 2 diabetics and 100 age-matched controls before and during falciparum malaria in a 2-year prospective study. Also, waist circumference (WC), weight, height and hip circumference were measured. Body mass index (BMI) and waist-to-hip ratio (WHR) were computed.

Results

At baseline, diabetics had significantly (p < 0.05) higher WC and BMI but lower WHR, leptin and adiponectin levels. Baseline leptin correlated positively with WC (r = 0.633; p < 0.001) and BMI (r = 0.63; p < 0.001) in diabetics but only BMI (0.562; p < 0.001) in non-diabetic controls. Baseline leptin and adiponectin correlated positively (r = 0.249; p = 0.029) in non-diabetic respondents only. Adiponectin correlated negatively with WC (r = −0.58; p = 0.006) in diabetic males only. During malaria, mean levels of leptin and adiponectin were comparable (p > 0.05) between diabetics and controls. However, compared to baseline levels, significant (p < 0.001) elevation of adiponectin was found in both study groups. In respect of leptin, significant (p < 0.001) rise but decline was observed in diabetics and controls respectively. Malaria-induced leptin correlated negatively with adiponectin (r = −0.694; p < 0.001) in non-diabetic controls only.

Conclusion

Diabetics and controls exhibited increased adiponectin levels due to falciparum malaria but differed in response in terms of leptin levels.

New insights in leptin resistance mechanisms in mice

Leptin resistance is one of the main challenges of obesity. To date, two levels of resistance have been identified, first a decreased rate of leptin uptake into the brain and secondly a diminished central response to leptin. New findings have identified the mechanisms of leptin transport and demonstrated that it can be rescued in obesity, but it did not overcome the problem of central resistance. Alteration in the actions of leptin following diet-induced obesity (DIO) appears to be a multifactorial condition. Several phosphatases are inhibiting leptin signaling pathways in a pathological way. Besides, hypothalamic inflammation alters the neuronal circuits that control metabolism. Recent studies describing both mechanisms (inhibition of leptin signaling and inflammation), have provided key insights to potential new targets for treatment. However, recent data showing that DIO mice may conserve a cellular and physiological response to endogenous leptin, highlights the need to redefine the concept of "leptin resistance".

A novel role of the checkpoint kinase ATR in leptin signaling

In a world with increasing incidences of obesity, it becomes critical to understand the detailed regulation of appetite. To identify novel regulators of the signaling mediated by one of the key hormones of energy homeostasis, leptin, we screened a set of compounds for their effect on the downstream Signal Transducer and Activator of Transcription 3 (STAT3) signaling. Interestingly, cells exposed to inhibitors of the Ataxia Telangiectasia and RAD3-related protein ATR increased their leptin dependent STAT3 activity. This was due to failure of the cells to induce the negative feedback mediator Suppressor of Cytokine Signaling 3 (SOCS3), suggesting that ATR has a previously unknown role in the negative feedback regulation of leptin signaling. This is an important finding not only because it sheds light on additional genes involved in leptin signaling, but also because it brings forward a new potential therapeutic intervention point for increasing leptin signaling in obese individuals.

Leptin Induces a Novel Form of NMDA Receptor-Dependent LTP at Hippocampal Temporoammonic-CA1 Synapses

Hippocampal CA1 pyramidal neurons receive two anatomically distinct glutamatergic inputs that have distinct roles in learning and memory. The hormone leptin markedly influences excitatory synaptic transmission at the indirect Schaffer-collateral pathway to CA1 neurons.

It is well documented that the hormone leptin regulates many central functions and that hippocampal CA1 pyramidal neurons are a key target for leptin action. Indeed, leptin modulates excitatory synaptic transmission and synaptic plasticity at the Schaffer-collateral input to CA1 neurons. However the impact of leptin on the direct temporoammonic (TA) input to CA1 neurons is not known. Here we show that leptin evokes a long-lasting increase [long-term potentiation (LTP)] in excitatory synaptic transmission at TA-CA1 synapses in rat juvenile hippocampus. Leptin-induced LTP was NMDA receptor-dependent and specifically involved the activation of GluN2B subunits. The signaling pathways underlying leptin-induced LTP involve the activation of phosphoinositide 3-kinase, but were independent of the ERK signaling cascade. Moreover, insertion of GluA2-lacking AMPA receptors was required for leptin-induced LTP as prior application of philanthotoxin prevented the effects of leptin. In addition, synaptic-induced LTP occluded the persistent increase in synaptic efficacy induced by leptin. In conclusion, these data indicate that leptin induces a novel form of NMDA receptor-dependent LTP at juvenile TA-CA1 synapses, which has important implications for the role of leptin in modulating hippocampal synaptic function in health and disease.

The integrative role of leptin, oestrogen and the insulin family in obesity-associated breast cancer: potential effects of exercise

Obesity is an established risk factor for postmenopausal breast cancer. The mechanisms through which obesity influences the development and progression of breast cancer are not fully elucidated; however, several factors such as increased oestrogen, concentrations of various members of the insulin family and inflammation that are associated with adiposity are purported to be important factors in this relationship. Emerging research has also begun to focus on the role of adipokines, (i.e. adipocyte secreted factors), in breast cancer. Leptin secretion is directly related to adiposity and is believed to promote breast cancer directly and independently, as well as through involvement with the oestrogen and insulin signalling pathways. As leptin is secreted from white adipose tissue, any intervention that reduces adiposity may be favourable. However, it is also important to consider that energy expenditure through exercise, independent of fat loss, may improve leptin regulation. The purpose of this narrative review was to explore the role of leptin in breast cancer development and progression, identify key interactions with oestrogen and the insulin family, and distinguish the potential effects of exercise on these interactions.

Leptin: A hormone linking activation of neuroendocrine axes with neuropathology

Leptin, a peptide hormone secreted by adipocytes, plays a central role in controlling appetite and weight in both rodents and humans. Basic science and clinical research suggest that this hormone not only affects the regulation of the neuroendocrine axes, but also exerts effects on the central nervous system with subsequent alterations in psychological functions. For instance, leptin suppresses cortisol secretion during stress-related activation of the adrenal axis. As psychiatric disorders like depression are associated with hypercortisolism, leptin is proposed to exert anti-depressant-like effects due to its inhibition of chronically overactive hypothalamo-pituitary-adrenal axis function. Moreover, leptin status of depressed patients could serve as a prognostic marker for therapy response. Besides its influence on neuroendocrine pathways leptin seems to have direct central effects on brain development and neuroplasticity. Low leptin levels have been shown to be associated with increased risk of developing dementia, supporting the idea of a pro-cognitive effect of leptin. These areas may have direct clinical implications and deserve to be studied further in the future.

Serum adiponectin, leptin, and interleukin 6 levels as adipocytokines in children with febrile seizures: The role of adipose tissue in febrile seizures

Proinflammatory and anti-inflammatory cytokines have an important role in the pathogenesis of febrile seizures (FS). Adipocytokines like interleukin 6 (IL-6), leptin, and adiponectin released from adipose tissue play a role in inflammation. This study aimed to assess the probable role of adipose tissue in children with FS. We measured serum IL-6, leptin, and adiponectin levels and evaluated clinical and laboratory findings in children with FS (n = 32) and compared the results with the values of children of the same age with febrile illness without seizures (febrile control, FC; n = 26) and healthy control group (HC; n = 29). The serum levels of white blood cells, C-reactive protein, IL-6, leptin, and adiponectin were found to be significantly higher, while serum hemoglobin (Hb) levels were found to be significantly lower in FS and FC groups than in the HC group (p < 0.001). When we compared the FS with the FC group, the serum Hb levels were significantly lower in the FS group than those in the FC group (p = 0.001). There was no significant difference between the FS and FC group with regard to the serum levels of these adipocytokines (p > 0.05). Our data showed that elevated levels of these adipocytokines as acute phase reactants in FS and FC groups did not contribute to the development of FS.

Leptin inhibits amyloid β-protein fibrillogenesis by decreasing GM1 gangliosides on the neuronal cell surface through PI3K/Akt/mTOR pathway

Leptin is a centrally acting hormone that controls metabolic pathways. Recent epidemiological studies suggest that plasma leptin is protective against Alzheimer's disease. However, the mechanism that underlies this effect remains uncertain. To investigate whether leptin inhibits the assembly of amyloid β-protein (Aβ) on the cell surface of neurons, we treated primary neurons with leptin. Leptin treatment decreased the GM1 ganglioside (GM1) levels in the detergent-resistant membrane microdomains (DRMs) of neurons. The increase in GM1 expression induced by leptin was inhibited after pre-treatment with inhibitors of phosphatidylinositol 3-kinase (LY294002), Akt (triciribine) and the mammalian target of rapamycin (i.e. rapamycin), but not by an inhibitor of extracellular signal-regulated kinase (PD98059). In addition, pre-treatment with these reagents blocked the induction of GM1 in DRMs by leptin. Furthermore, Aβ assembly on the cell surface of neurons was inhibited greatly after treatment with leptin. This reduction was markedly inhibited after pre-treatment with LY294002, triciribine, and rapamycin. These results suggest that leptin significantly inhibits Aβ assembly by decreasing GM1 expression in DRMs of the neuronal surface through the phosphatidylinositol 3-kinase/Akt/mammalian target of rapamycin pathway. These findings highlight the importance of understanding the function of leptin in AD brains. In this study, our aim was to determine whether leptin regulates the expression and localization of GM1 on the neuronal membrane and if it induces the formation of Aβ assembly on the cell surface of neurons. Our results suggest that leptin regulates the expression of GM1 in DRMs of the neuronal membranes. Moreover, leptin does not seem to facilitate fibrillogenesis of exogenously added soluble Aβ from the cell surface of neurons.

The association between serum leptin and post stroke depression: results from a cohort study

BACKGROUND

Depression is a frequent mood disorder that affects around a third of stroke patients and has been associated with poorer outcomes. Our aim was to determine whether there was a relationship between inflammatory markers (leptin) and post-stroke depression (PSD).

METHODS

One hundred and ninety-one ischemic stroke patients admitted to the hospital within the first 24 hours after stroke onset were consecutively recruited and followed up for 3 months. Enzyme-linked immunosorbent assay (ELISA) was used to measure serum levels of leptin at admission. Based on the symptoms, diagnoses of depression were made in accordance with DSM-IV criteria for post-stroke depression at 3 month.

RESULTS

Forty-four patients (23.0%) were diagnosed as having major depression at 3 month. Patients with depression showed higher serum leptin levels at 3 month after stroke (32.2 [IQR, 20.8-57.7] v. 9.9 [IQR, 4.6-13.1]ng/ml, respectively; P = 0.000). Serum levels of leptin ≥20 ng/ml were independently associated with PSD [odds ratio (OR) 20.23, 95% confidence interval (CI) 9.11-51.26, P =  0.000], after adjusting for possible confounders.

CONCLUSIONS

Serum leptin levels elevated at admission were found to be associated with PSD and may provide a new proposal for the treatment of PSD.

A leptin-mediated central mechanism in analgesia-enhanced opioid reward in rats

Opioid analgesics are commonly used in chronic pain management despite a potential risk of rewarding. However, it remains unclear whether opioid analgesia would enhance the opioid rewarding effect thereby contributing to opioid rewarding. Utilizing a rat paradigm of conditioned place preference (CPP) combined with ankle monoarthritis as a condition of persistent nociception, we showed that analgesia induced by either morphine or the nonsteroid anti-inflammatory drug ibuprofen increased CPP scores in arthritic rats, suggesting that analgesia itself had a rewarding effect. However, arthritic rats exhibited a significantly higher CPP score in response to morphine than ibuprofen. Thus, the rewarding effect of morphine was enhanced in the presence of persistent nociception, producing a phenomenon of analgesia-enhanced opioid reward. At the cellular level, administration of morphine activated a cascade of leptin expression, glial activation, and dopamine receptor upregulation in the nucleus accumbens (NAc), while administration of ibuprofen decreased glial activation with no effect on leptin expression in the NAc. Furthermore, the morphine rewarding effect was blocked in leptin deficient ob/ob mice or by neutralizing leptin or interleukin-1β in the NAc without diminishing morphine analgesia. The data indicate that systemic opioid can activate a leptin-mediated central mechanism in the NAc that led to the enhanced opioid rewarding effect. These findings provide evidence for an interaction between opioid analgesia and opioid rewarding, which may have implications in clinical opioid dose escalation in chronic pain management.

Leptin deficiency in vivo enhances the ability of splenic dendritic cells to activate T cells

Leptin is a pleiotropic adipokine that is critical for regulating food intake and energy expenditure and also participates in functions of the immune system, including those of antigen-presenting cells. Here, we assess the effect of leptin deficiency on the function splenic dendritic cells (sDC). sDC from leptin-deficient mice (Lep(ob)) were evaluated ex vivo for phenotype, ability to respond to inflammatory stimuli, to acquire and process antigens and to activate T cells. The data show that Lep(ob) sDC express activation markers similar to controls and respond similarly to LPS activation or anti-CD40 cross-linking. In addition, antigen acquisition and processing by Lep(ob) sDC was similar to controls. However, Lep(ob) sDC elicited higher production of IFN-γ in mixed lymphocyte reactions and increased production of IL-2 by antigen-specific T-cell hybridoma relative to controls. To assess Lep(ob) sDC activation of T cells in vivo, Lep(ob) and control mice were infected systemically with Mycobacterium avium. Lep(ob) mice were significantly better at neutralizing the infection as measured by splenic bacterial load over time. This was mirrored with an increased percentage of activated T cells in M. avium-infected Lep(ob) mice. Thus, although no changes were detected in sDC phenotype, activation, antigen processing or presentation, these DC surprisingly presented an enhanced ability to activate T cells ex vivo and in vivo. These data demonstrate that leptin can modulate DC function and suggest that leptin may dampen T-cell responsiveness in the physiological setting.

Follicular fluid leptin concentrations and expression of leptin and leptin receptor in the equine ovary and in vitro-matured oocyte with reference to pubertal development and breeds

There is no published information about follicular-fluid leptin concentrations or the presence of leptin and leptin receptor in the equine ovary or oocyte. Three groups of mares - adult draft mares, draft fillies and adult Standardbred mares - were included in the study. Leptin and leptin receptor were detected in all immature oocytes by immunofluorescence with higher intensity in oocytes from draft mares compared with draft fillies and Standardbred mares. After in vitro maturation a higher proportion of oocytes reached metaphase II in draft mares than in draft fillies and Standardbred mares, and in all groups both leptin and leptin receptor became localised in the oocyte cortex but with higher immunopositivity in draft mares compared with draft fillies and Standardbred mares. These intensities were confirmed by the expression profiles of leptin and leptin receptor mRNA. Moreover, leptin was detected in ovarian blood vessels in all three types of animal and within the corpora lutea in adult mares. Serum and follicular-fluid concentrations of leptin were similar in draft and Standardbred mares but higher in draft mares than in draft fillies. This study supports the hypothesis that expression of leptin and leptin receptor mRNA and the rate of maturation can be related either to adiposity or to puberty.

Leptin: a biomarker for sleep disorders?

Leptin, a pleiotropic protein hormone produced mainly by fat cells, regulates metabolic activity and many other physiological functions. The intrinsic circadian rhythm of blood leptin is modulated by gender, development, feeding, fasting, sleep, obesity, and endocrine disorders. Hyperleptinemia is implicated in leptin resistance. To determine the specificity and sensitivity of leptin concentrations in sleep disorders, we summarize here the alterations of leptin in four conditions in animal and human studies: short duration of sleep, sleep fragmentation, obstructive sleep apnea (OSA), and after use of continuous positive airway pressure (CPAP) to treat OSA. The presence and causes of contradictory findings are discussed. Though sustained insufficient sleep lowers fasting blood leptin and therefore probably contributes to increased appetite, obesity and OSA independently result in hyperleptinemia. Successful treatment of OSA by CPAP is predicted to decrease hyperleptinemia, making leptin an ancillary biomarker for treatment efficacy. Current controversies also call for translational studies to determine how sleep disorders regulate leptin homeostasis and how the information can be used to improve sleep treatment.

Hormones of adipose tissue and their biologic role in lung cancer

INTRODUCTION

Adipose tissue secretes numerous bioactive peptides, collectively termed "adipocytokines" or "adipokines". Adipokines act in a paracrine, autocrine, or endocrine manner and regulate several physiological and pathological processes. Increasing evidence indicates that adipokines are implicated also in several malignancies, including lung cancer as well.

AIM

The aim of this study is to summarize data concerning adipokines in lung cancer pathogenesis, prognosis and survival; the role of adipokines in lung cancer cachexia is also examined.

MATERIALS AND METHODS

A systematic literature search was performed in the electronic database of Medline. Several studies and review articles met the inclusion criteria.

RESULTS

Leptin and adiponectin are the best studied adipokines. The majority of the relevant studies has investigated the potential correlations mainly between leptin, adiponectin, and sometimes also resistin, and nutritional status, systemic inflammation of lung cancer or lung cancer cachexia and have also assessed their prognostic significance. Few other studies have studied genetic variations in leptin, leptin receptor and adiponectin genes and their association with lung cancer susceptibility and prognosis. The ongoing list of adipokines associated with lung cancer also includes resistin, chemerin, and visfatin.

CONCLUSIONS

Increasing evidence points to the involvement of certain adipocytokines in lung cancer development, progression and prognosis. No conclusive evidence exists so far with regards to the role of adipocytokines in lung cancer cachexia. Future, longitudinal studies are warranted in order to clarify the role of adipocytokines in lung cancer and also uncover adipocytokines as novel therapeutic targets.

Role of leptin resistance in the development of obesity in older patients

Obesity is a global epidemic associated with aging-like cellular processes; in both aging and obesity, resistance to hormones such as insulin and leptin can be observed. Leptin is a circulating hormone/cytokine with central and peripheral effects that is released mainly by subcutaneous white adipose tissue. Centrally, leptin controls food intake, energy expenditure, and fat distribution, whereas it controls (among several others) insulin sensitivity, free fatty acids (FFAs) oxidation, and lipolysis in the periphery. Aging is associated with important changes in both the distribution and the composition of adipose tissue. Fat is redistributed from the subcutaneous to the visceral depot and increased inflammation participates in adipocyte dysfunction. This redistribution of adipose tissue in favor of visceral fat influences negatively both longevity and healthy aging as shown in numerous animal models. These modifications observed during aging are also associated with leptin resistance. This resistance blunts normal central and peripheral functions of leptin, which leads to a decrease in neuroendocrine function and insulin sensitivity, an imbalance in energy regulation, and disturbances in lipid metabolism. Here, we review how age-related leptin resistance triggers metabolic disturbances and affects the longevity of obese patients. Furthermore, we discuss the potential impacts of leptin resistance on the decline of brown adipose tissue thermogenesis observed in elderly individuals.

Alternative splice variants of the rainbow trout leptin receptor encode multiple circulating leptin-binding proteins

In mammals, leptin (Lep) binding proteins (LepBPs) derived from Lep receptor (LepR) gene or protein bind most of the circulating Lep, but to date, information on LepBPs in nonmammalian vertebrate classes is lacking. This study details the characterization of multiple LepBPs in rainbow trout (Oncorhynchus mykiss), an early poikilothermic vertebrate, and presents the complete coding sequences for 3 of them. Size-exclusion chromatography and cross-linking assay identified plasma proteins bound to Lep ranging from 70 to 100 kDa. LepBPs were isolated from plasma by affinity chromatography, and their binding specificity was assessed by a competitive binding assay. A RIA for LepBPs indicates that plasma LepBP levels decline after fasting for 3 weeks. Immunoblotting of LepBPs using antibodies against different LepR epitopes shows that the LepBPs are indeed LepR isoforms. The alternatively spliced LepR transcripts (LepR(S1-3)) that include only the extracellular segment transcribe the 90-kDa LepBP1, the 80-kDa LepBP2, and the 70-kDa LepBP3, respectively. LepR(S1) generally has lower expression than the long-form LepR in most tissues. LepR(S2) is primarily expressed in adipose tissue, whereas LepR(S3) is expressed abundantly in brain and spleen, and moderately in liver and gills. The mRNA levels of hepatic LepR(S3) increase after 2 weeks of fasting. This study demonstrates a mechanism in fish for the generation of LepBPs that differs from that seen in mammals and indicates that the physiologic action of Lep in these poikilothermic vertebrates can be modulated, both centrally and peripherally, by the differentiated, tissue-specific expression of multiple LepBPs.

Molecular cloning and genomic characterization of novel leptin-like genes in salmonids provide new insight into the evolution of the Leptin gene family

In the current study we describe the identification of novel leptin B homologous gene/s in the four salmonid species Atlantic salmon (Salmo salar), rainbow trout (Oncorhynchus mykiss), brown trout (Salmo trutta) and Arctic charr (Salvelinus alpinus). Homology modeling of Salmo salar (Ss) LepB1/B2 suggests that the protein satisfies parameters as long-chain four helical cytokine family and that the basic structural pattern of the protein follows that of human leptin (Zhang et al., 1997). Importantly, the docking studies suggested the SsLepB has binding affinity to the AA residues that identify the leptin binding and FNIII domains of the SsLep receptor (Rønnestad et al., 2010). Phylogenetic analyses support that LepB paralogs have most probably originated by 4R whole genome duplication (WGD) before speciation of the salmonid lineages. LepB1 and LepB2 genes are both present in the two closest relatives, the Atlantic salmon and the brown trout, while rainbow trout and charr have only preserved the long LepB1 variant in their genome. We have defined the sites of SsLepB mRNA expression at key life stages in Atlantic salmon and found that SsLepB1 and SsLepB2, although to different extent, were expressed in redundant and mostly complementary fashion in brain and gills throughout the lifecycle, suggesting that this pair of paralogs is likely undergoing early stages of subfunctionalization. Furthermore, we have quantified the expression profiles of SsLepB genes and of other two recently duplicated salmon leptins (SsLepA1, SsLepA2) during early development and show evidence that in fish, as in mammals and amphibians, leptin could play important roles in growth and development. This study provides an essential groundwork to further elucidate structural and functional evolution of this important hormone in salmonids as well as in other teleosts.

Food for thought: the role of appetitive peptides in age-related cognitive decline

Through their well described actions in the hypothalamus, appetitive peptides such as insulin, orexin and leptin are recognized as important regulators of food intake, body weight and body composition. Beyond these metabolic activities, these peptides also are critically involved in a wide variety of activities ranging from modulation of immune and neuroendocrine function to addictive behaviors and reproduction. The neurological activities of insulin, orexin and leptin also include facilitation of hippocampal synaptic plasticity and enhancement of cognitive performance. While patients with metabolic disorders such as obesity and diabetes have greater risk of developing cognitive deficits, dementia and Alzheimer's disease (AD), the underlying mechanisms that are responsible for, or contribute to, age-related cognitive decline are poorly understood. In view of the importance of these peptides in metabolic disorders, it is not surprising that there is a greater focus on their potential role in cognitive deficits associated with aging. The goal of this review is to describe the evidence from clinical and pre-clinical studies implicating insulin, orexin and leptin in the etiology and progression of age-related cognitive decline. Collectively, these studies support the hypothesis that leptin and insulin resistance, concepts normally associated with the hypothalamus, are also applicable to the hippocampus.

The beneficial effects of leptin on REM sleep deprivation-induced cognitive deficits in mice

Leptin, a 167 amino acid peptide, is synthesized predominantly in the adipose tissues and plays a key role in the regulation of food intake and body weight. Recent studies indicate that leptin receptor is expressed with high levels in many brain regions that may regulate synaptic plasticity. Here we show that deprivation of rapid eye movement (REMD) sleep resulted in impairment of both cue and contextual fear memory. In parallel, surface expression of GluR1 was reduced in the amygdala. Intraperitoneal injection of leptin to the REMD mice rescued memory impairment and reversed surface GluR1 reduction. Using whole-cell recording to evaluate the synaptic function of the thalamus-lateral amygdala (LA) pathway, we found a decrease in frequency and amplitude of miniature excitatory postsynaptic currents (mEPSCs) concomitant with reduced AMPA/NMDA ratios in the REMD mice. By contrast, paired-pulse facilitation (PPF) was increased. The effects of REMD on mEPSCs and AMPA/NMDA ratio could be reversed by leptin treatment, whereas on PPR it could not. Phosphatase and tensin homolog (PTEN), a dual protein/lipid phosphatase, down-regulates the effect of the PI-3 kinase pathway. Fear conditioning increased whereas REMD led to a decrease in the phosphorylated states of PTEN, Akt, and glycogen synthase kinase-3β (GSK3β), and the effects of REMD were reversed by leptin. These results suggest that both pre- and postsynaptic functions of the thalamus-LA pathway were altered by fear conditioning and REMD in opposite directions. Leptin treatment reversed REMD-induced memory deficits primarily by a postsynaptic action by restoring surface expression of GluR1 without affecting PPR.

Selenium and leptin levels in febrile seizure: a case-control study in children

PURPOSE

Febrile seizures (FS) are seizures that occur between the age of 6 and 60 months, but its pathophysiology still is not fully understood. There is limited information about the correlation between levels of selenium and leptin with FS. This study aimed to determine the relationship between serum levels of selenium and leptin in children with FS.

METHODS

This case-control study was conducted in a University Hospital in Shahrekord, Iran, in 2011. The serum levels of selenium and leptin of 25 children with simple febrile seizure (case group) were compared with 25 febrile children without seizure (control group) in acute phase and after three months. The levels of serum selenium and leptin were measured by flame atomic absorption spectrophotometer and enzyme-linked immunosorbent assay method, respectively.

RESULTS

In acute phase, the mean serum level of selenium in case and control groups were 95.88±42.55 and 113.25±54.43 µg/dL, respectively, and difference was not significant (P=0.415), but after three months, this level had a significant increase in both groups (P<0.001). In acute phase, the mean serum leptin level in case and control groups were 0.94±0.5 and 0.98±0.84 ng/mL, respectively, but difference was not significant (P=0.405). After three months, serum leptin level had no significant change in both groups (P=0.882).

CONCLUSION

These observations suggest that serum levels of selenium and leptin have not specific relation with FS but overllay is lower, however, further study is recommended. Also selenium level in stress and acute phase was significantly lower than recovery phase.

Leptin predicts a decline in moderate to vigorous physical activity in minority female children at risk for obesity

What is already known about this subject Physical activity declines as children enter puberty. Leptin is cross-sectionally associated with physical activity, but there are conflicting findings on the magnitude and direction of this association. Leptin concentrations fluctuate during puberty, and may impact energy balance. What this study adds Leptin predicts the decline in physical activity during the start of puberty independent of central adiposity. Based on a median split of leptin, girls with low leptin levels have higher levels of physical activity than girls with high leptin levels at the start of puberty. Leptin levels at the start of puberty may provide a biological basis for the age-related physical activity decline in girls.

BACKGROUND

Leptin may influence moderate to vigorous physical activity (MVPA) at the start of puberty. The direction and magnitude of this association are unclear.

OBJECTIVES

To determine the effect of baseline leptin on MVPA over 1 year in minority girls at high risk for obesity.

METHODS

Data came from TRANSITIONS, a longitudinal observational study on the age-related MVPA decline. Fifty peripubertal girls aged 8-11 years at baseline participated. Baseline leptin (ng mL(-1) ) was collected via a duplicated assay using a double antibody radio immune assay. MVPA (min d(-1) ) was measured using accelerometers for at least four 10-h days on a quarterly basis for up to 1 year.

RESULTS

Continuous leptin was negatively related to MVPA (P = 0.001) independent of central adiposity at baseline and predicted the MVPA decline over 1 year (P = 0.002). For descriptive purposes, baseline leptin was dichotomized at the sample median into 'high leptin' and 'low leptin' categories to determine whether MVPA trajectories differed between these groups. Girls with 'low leptin' at baseline had significantly higher levels of MPVA at baseline, visit 1 and visit 2 compared to girls with 'high leptin'.

CONCLUSIONS

High leptin levels predicted nearly a 12.6% decline in MVPA over 1 year. These findings provide support for the biological basis of declining MVPA as girls enter puberty.

Creation and preliminary characterization of a leptin knockout rat

Leptin, a cytokine-like hormone secreted mainly by adipocytes, regulates various pathways centered on food intake and energy expenditure, including insulin sensitivity, fertility, immune system, and bone metabolism. Here, using zinc finger nuclease technology, we created the first leptin knockout rat. Homozygous leptin null rats are obese with significantly higher serum cholesterol, triglyceride, and insulin levels than wild-type controls. Neither gender produced offspring despite of repeated attempts. The leptin knockout rats also have depressed immune system. In addition, examination by microcomputed tomography of the femurs of the leptin null rats shows a significant increase in both trabecular bone mineral density and bone volume of the femur compared with wild-type littermates. Our model should be useful for many different fields of studies, such as obesity, diabetes, and bone metabolism-related illnesses.

Obesity/hyperleptinemic phenotype impairs structural and functional plasticity in the rat hippocampus

Epidemiological studies estimate that greater than 60% of the adult US population may be categorized as either overweight or obese, and there is a growing appreciation that the complications of obesity extend to the central nervous system (CNS). While the vast majority of these studies have focused on the hypothalamus, more recent studies suggest that the complications of obesity may also affect the structural and functional integrity of the hippocampus. A potential contributor to obesity-related CNS abnormalities is the adipocyte-derived hormone leptin. In this regard, decreases in CNS leptin activity may contribute to deficits in hippocampal synaptic plasticity and suggest that leptin resistance, a well-described phenomenon in the hypothalamus, may also be observed in the hippocampus. Unfortunately, the myriad of metabolic and endocrine abnormalities in diabetes/obesity phenotypes makes it challenging to assess the role of leptin in hippocampal neuroplasticity deficits associated with obesity models. To address this question, we examined hippocampal morphological and behavioral plasticity following lentivirus-mediated downregulation of hypothalamic insulin receptors (hypo-IRAS). Hypo-IRAS rats exhibit increases in body weight, adiposity, plasma leptin and triglyceride levels. As such, hypo-IRAS rats develop a phenotype that is consistent with features of the metabolic syndrome. In addition, hippocampal morphological plasticity and performance of hippocampal-dependent tasks are adversely affected in hypo-IRAS rats. Leptin-mediated signaling is also decreased in hypo-IRAS rats. We will discuss these findings in the context of how hyperleptinemia and hypertriglyceridemia may represent mechanistic mediators of the neurological consequences of impaired hippocampal synaptic plasticity in obesity.

Downregulation of hypothalamic insulin receptor expression elicits depressive-like behaviors in rats

Ongoing epidemiological studies estimate that greater than 60% of the adult US population may be categorized as either overweight or obese. There is a growing appreciation that the complications of obesity extend to the central nervous system (CNS) and may result in increased risk for neurological co-morbidities like depressive illness. One potential mechanistic mediator linking obesity and depressive illness is the adipocyte derived hormone leptin. We previously demonstrated that lentivirus-mediated downregulation of hypothalamic insulin receptors increases body weight, adiposity and plasma leptin levels, which is consistent with features of the metabolic syndrome. Using this novel model of obesity, we examined performance in the forced swim test (FST), the sucrose preference test and the elevated plus maze (EPM), approaches that are often used as measures of depressive-like and anxiety-like behaviors, in rats that received third ventricular injections of either an insulin receptor antisense lentivirus (hypo-IRAS) or a control lentivirus (hypo-Con). Hypo-IRAS rats exhibited significant increases in immobility time and corresponding decreases in active behaviors in the FST and exhibited anhedonia as measured by decreased sucrose intake compared to hypo-Con rats. Hypo-IRAS rats also exhibited increases in anxiety-like behaviors in the EPM. Plasma, hippocampal and amygdalar brain-derived neurotrophic factor (BDNF) levels were reduced in hypo-IRAS rats, suggesting that the obesity/hyperleptinemic phenotype may elicit this behavioral phenotype through modulation of neurotrophic factor expression. Collectively, these data support the hypothesis for an increased risk for mood disorders in obesity, which may be related to decreased expression of hippocampal and amygdalar BDNF.

Subcutaneous administration of leptin normalizes fasting plasma glucose in obese type 2 diabetic UCD-T2DM rats

Leptin has been shown to reduce hyperglycemia in rodent models of type 1 diabetes. We investigated the effects of leptin administration in University of California, Davis, type 2 diabetes mellitus (UCD-T2DM) rats, which develop adult-onset polygenic obesity and type 2 diabetes. Animals that had been diabetic for 2 mo were treated with s.c. injections of saline (control) or murine leptin (0.5 mg/kg) twice daily for 1 mo. Control rats were pair-fed to leptin-treated animals. Treatment with leptin normalized fasting plasma glucose and was accompanied by lowered HbA1c, plasma glucagon, and triglyceride concentrations and expression of hepatic gluconeogenic enzymes compared with vehicle (P < 0.05), independent of any effects on body weight and food intake. In addition, leptin-treated animals exhibited marked improvement of insulin sensitivity and glucose homeostasis compared with controls, whereas pancreatic insulin content was 50% higher in leptin-treated animals (P < 0.05). These effects coincided with activation of leptin and insulin signaling pathways and down-regulation of the PKR-like endoplasmic reticulum (ER) kinase/eukaryotic translation inhibition factor 2α (PERK-eIF2α) arm of ER stress in liver, skeletal muscle, and adipose tissue as well as increased pro-opiomelanocortin and decreased agouti-related peptide in the hypothalamus. In contrast, several markers of inflammation/immune function were elevated with leptin treatment in the same tissues (P < 0.05), suggesting that the leptin-mediated increase of insulin sensitivity was not attributable to decreased inflammation. Thus, leptin administration improves insulin sensitivity and normalizes fasting plasma glucose in diabetic UCD-T2DM rats, independent of energy intake, via peripheral and possibly centrally mediated actions, in part by decreasing circulating glucagon and ER stress.

Obesity/hyperleptinemic phenotype adversely affects hippocampal plasticity: effects of dietary restriction

Epidemiological studies estimate that greater than 60% of the adult US population may be categorized as either overweight or obese and there is a growing appreciation that obesity affects the functional integrity of the central nervous system (CNS). We recently developed a lentivirus (LV) vector that produces an insulin receptor (IR) antisense RNA sequence (IRAS) that when injected into the hypothalamus selectively decreases IR signaling in hypothalamus, resulting in increased body weight, peripheral adiposity and plasma leptin levels. To test the hypothesis that this obesity/hyperleptinemic phenotype would impair hippocampal synaptic transmission, we examined short term potentiation (STP) and long term potentiation (LTP) in the hippocampus of rats that received the LV-IRAS construct or the LV-Control construct in the hypothalamus (hypo-IRAS and hypo-Con, respectively). Stimulation of the Schaffer collaterals elicits STP that develops into LTP in the CA1 region of hypo-Con rats; conversely, hypo-IRAS rats exhibit STP that fails to develop into LTP. To more closely examine the potential role of hyperleptinemia in these electrophysiological deficits, hypo-IRAS were subjected to mild food restriction paradigms that would either: 1) prevent the development of the obesity phenotype; or 2) reverse an established obesity phenotype in hypo-IRAS rats. Both of these paradigms restored LTP in the CA1 region and reversed the decreases in the phosphorylated/total ratio of GluA1 Ser845 AMPA receptor subunit expression observed in the hippocampus of hypo-IRAS rats. Collectively, these data support the hypothesis that obesity impairs hippocampal synaptic transmission and support the hypothesis that these deficits are mediated through the impairment of hippocampal leptin activity.

Time-dependent effects of starvation on serum, pituitary and hypothalamic leptin levels in rats

Leptin is produced by white adipose tissue and other cell types and is involved in both short- and long-term appetite control. Here we studied effects of starvation on serum, pituitary and hypothalamic levels of leptin during 72 h period. Each of the starved groups was sacrificed simultaneously with the group of ad libitum fed animals. The progression of the discrete starvation response phases was monitored by testing the blood glucose, free fatty acid, urea and corticosterone levels. Starvation caused biphasic increase in corticosterone and free fatty acid levels, and significant but transient decrease in urea and glucose levels. Starvation also abolished diurnal rhythm of changes in leptin concentrations in serum and hypothalamic and pituitary tissues. Only 6 h starving period was sufficient to lock serum leptin at low levels, whereas 12 h were needed to silence leptin production/secretion in hypothalamus for the whole examined period. In contrast, leptin production by pituitary tissues of starved animals required 24 h to reach minimum, followed by full recovery by the end of starvation period. These results indicate the tissue specific pattern of leptin release and suggest that the locally produced leptin could activate its receptor in pituitary cells independently of serum levels of this hormone.

Hypothalamic leptin gene therapy prevents weight gain without long-term detrimental effects on bone in growing and skeletally mature female rats

Hypothalamic leptin gene therapy normalizes the mosaic skeletal phenotype of leptin-deficient ob/ob mice. However, it is not clear whether increased hypothalamic leptin alters bone metabolism in animals already producing the hormone. The objective of this study was to evaluate the long duration effects of recombinant adeno-associated virus-rat leptin (rAAV-Lep) hypothalamic gene therapy on weight gain and bone metabolism in growing and skeletally mature leptin-replete female Sprague-Dawley rats. Rats were either unoperated or implanted with cannulas in the third ventricle of the hypothalamus and injected with either rAAV-Lep or rAAV-GFP (control vector encoding green fluorescent protein) and maintained on standard rat chow fed ad libitum for either 5 or 10 weeks (starting at 3 months of age) or 18 weeks (starting at 9 months of age). Tibias, femurs, or lumbar vertebrae were analyzed by micro-computed tomography and/or histomorphometry. In comparison with age-matched rAAV-GFP rats, rAAV-Lep rats maintained a lower body weight for the duration of studies. At 5 weeks after vector administration, rAAV-Lep rats had lower cancellous bone volume and bone marrow adiposity but higher osteoblast perimeter compared with nonoperated controls. However, these values did not differ between the two groups at 10 weeks after vector administration. Differences in cancellous bone volume and architecture were not detected between the rAAV-Lep and rAAV-GFP groups at either time point. Also, rAAV-Lep had no negative effects on bone in the 9-month-old skeletally mature rats at 18 weeks after vector administration. We hypothesize that the transient reductions in bone mass and bone marrow adiposity at 5 weeks after vector administration were due to hypothalamic surgery. We conclude that increased hypothalamic leptin, sufficient to prevent weight gain, has minimal specific effects (rAAV-Lep versus rAAV-GFP) on bone metabolism in normal female rats.

Leptin enhances NMDA-induced spinal excitation in rats: A functional link between adipocytokine and neuropathic pain

Recent studies have shown that leptin (an adipocytokine) played an important role in nociceptive behavior induced by nerve injury, but the cellular mechanism of this action remains unclear. Using the whole-cell patch-clamp recording from rat's spinal cord slices, we showed that superfusion of leptin onto spinal cord slices dose-dependently enhanced N-methyl-d-aspartate (NMDA) receptor-mediated currents in spinal cord lamina II neurons. At the cellular level, the effect of leptin on spinal NMDA-induced currents was mediated through the leptin receptor and the JAK2/STAT3 (but not PI3K or MAPK) pathway, as the leptin effect was abolished in leptin receptor-deficient (db/db) mice and inhibited by a JAK/STAT inhibitor. Moreover, we demonstrated in naïve rats that a single intrathecal administration of leptin enhanced spontaneous biting, scratching, and licking behavior induced by intrathecal NMDA and that repeated intrathecal administration of leptin elicited thermal hyperalgesia and mechanical allodynia, which was attenuated by the noncompetitive NMDA receptor antagonist MK-801. Intrathecal leptin also upregulated the expression of NMDA receptors and pSTAT3 within the rat's spinal cord dorsal horn, and intrathecal MK-801 attenuated this leptin effect as well. Our data demonstrate a relationship between leptin and NMDA receptor-mediated spinal neuronal excitation and its functional role in nociceptive behavior. Since leptin contributes to nociceptive behavior induced by nerve injury, the present findings suggest an important cellular link between the leptin's spinal effect and the NMDA receptor-mediated cellular mechanism of neuropathic pain. A functional link is demonstrated between leptin, an adipocytokine, and the cellular mechanisms of neuropathic pain via enhancement of function and expression of spinal N-methyl-d-aspartate receptors.

The peroxisome proliferator-activated receptor (PPAR) alpha agonist fenofibrate maintains bone mass, while the PPAR gamma agonist pioglitazone exaggerates bone loss, in ovariectomized rats

BACKGROUND

Activation of peroxisome proliferator-activated receptor (PPAR)gamma is associated with bone loss and increased fracture risk, while PPARalpha activation seems to have positive skeletal effects. To further explore these effects we have examined the effect of the PPARalpha agonists fenofibrate and Wyeth 14643, and the PPARgamma agonist pioglitazone, on bone mineral density (BMD), bone architecture and biomechanical strength in ovariectomized rats.

METHODS

Fifty-five female Sprague-Dawley rats were assigned to five groups. One group was sham-operated and given vehicle (methylcellulose), the other groups were ovariectomized and given vehicle, fenofibrate, Wyeth 14643 and pioglitazone, respectively, daily for four months. Whole body and femoral BMD were measured by dual X-ray absorptiometry (DXA), and biomechanical testing of femurs, and micro-computed tomography (microCT) of the femoral shaft and head, were performed.

RESULTS

Whole body and femoral BMD were significantly higher in sham controls and ovariectomized animals given fenofibrate, compared to ovariectomized controls. Ovariectomized rats given Wyeth 14643, maintained whole body BMD at sham levels, while rats on pioglitazone had lower whole body and femoral BMD, impaired bone quality and less mechanical strength compared to sham and ovariectomized controls. In contrast, cortical volume, trabecular bone volume and thickness, and endocortical volume were maintained at sham levels in rats given fenofibrate.

CONCLUSIONS

The PPARalpha agonist fenofibrate, and to a lesser extent the PPARaplha agonist Wyeth 14643, maintained BMD and bone architecture at sham levels, while the PPARgamma agonist pioglitazone exaggerated bone loss and negatively affected bone architecture, in ovariectomized rats.

Leptin-derived peptides that stimulate food intake and increase body weight following peripheral administration

We previously showed that peptides containing leptin sequences 1-33 or 61-90 are taken up by the rat brain. We now report the effects of these peptides on food intake and body weight in mature rats. Peptides were infused intravenously for 4weeks, using Alzet minipumps. Dosages were 20μg/kg/day in experiment I, and 60μg/kg/day in experiment 2. In experiment 1, female rats receiving peptides 1-33 and 61-90 each underwent an approximate doubling of the weight gain of control rats. These peptides also increased food intake in female rats. Peptide 15-32, which has a lesser degree of brain uptake, gave a smaller weight gain. Peptide 83-108, which is not taken up by the brain, had no effect on weight gain or food intake. Similar results were obtained in experiment 2. In male rats, however, none of the peptides caused significant changes in food intake or body weight. This was at least partly due to the fact that all male rats underwent vigorous weight increases. We conclude that peptides 1-33 and 61-90 acted as leptin antagonists, stimulating food intake and body weight increases, at least in female rats. These peptides may lead to clinical applications in conditions such as anorexia and cachexia.