Anorexigenic neuropeptides as anti-obesity and neuroprotective agents: exploring the neuroprotective effects of anorexigenic neuropeptides

Since 1975, the incidence of obesity has increased to epidemic proportions, and the number of patients with obesity has quadrupled. Obesity is a major risk factor for developing other serious diseases, such as type 2 diabetes mellitus, hypertension, and cardiovascular diseases. Recent epidemiologic studies have defined obesity as a risk factor for the development of neurodegenerative diseases, such as Alzheimer's disease (AD) and other types of dementia. Despite all these serious comorbidities associated with obesity, there is still a lack of effective antiobesity treatment. Promising candidates for the treatment of obesity are anorexigenic neuropeptides, which are peptides produced by neurons in brain areas implicated in food intake regulation, such as the hypothalamus or the brainstem. These peptides efficiently reduce food intake and body weight. Moreover, because of the proven interconnection between obesity and the risk of developing AD, the potential neuroprotective effects of these two agents in animal models of neurodegeneration have been examined. The objective of this review was to explore anorexigenic neuropeptides produced and acting within the brain, emphasizing their potential not only for the treatment of obesity but also for the treatment of neurodegenerative disorders.

Peripheral administration of lipidized NPAF and NPFF analogs does not influence central food intake regulation but induces anxiety-like behavior

RF-amide peptides influence multiple physiological processes, including the regulation of appetite, stress responses, behavior, and reproductive and endocrine functions. In this study, we examined the roles of neuropeptide FF receptors (NPFFR1 and NPFFR2) by generating several lipidized analogs of neuropeptide AF (NPAF) and 1DMe, a stable analog of neuropeptide FF (NPFF). These analogs were administered peripherally for the first time to investigate their effects on food intake and other potential physiological outcomes. Lipidized NPAF and 1DMe analogs exhibited enhanced stability and increased pharmacokinetics. These analogs demonstrated preserved high affinity for NPFFR2 in the nanomolar range, while the binding affinity for NPFFR1 was tens of nanomoles. They activated the ERK and Akt signaling pathways in cells overexpressing the NPFFR1 and NPFFR2 receptors. Acute food intake in fasted mice decreased after the peripheral administration of oct-NPAF or oct-1DMe. However, this effect was not as pronounced as that observed after the injection of palm11-PrRP31, a potent anorexigenic compound used as a comparator that binds to GPR10 and the NPFFR2 receptor with high affinity. Neither oct-1DMe nor oct-NPAF decreased food intake or body weight in mice with diet-induced obesity during long-term treatment. In mice treated with oct-1DMe, we observed decreased activity in the central zone during the open field test and decreased activity in the open arms of the elevated plus maze. Furthermore, we observed a decrease in plasma noradrenaline levels and an increase in plasma corticosterone levels, as well as an increase in Crh expression in the hypothalamus. Moreover, neuronal activity in the hypothalamus was increased after treatment with oct-1DMe. In this study, we report that oct-1DMe did not have any long-term effects on the central regulation of food intake; however, it caused anxiety-like behavior.

An analogue of the Prolactin Releasing Peptide reduces obesity and promotes adult neurogenesis

Hypothalamic Adult Neurogenesis (hAN) has been implicated in regulating energy homeostasis. Adult-generated neurons and adult Neural Stem Cells (aNSCs) in the hypothalamus control food intake and body weight. Conversely, diet-induced obesity (DIO) by high fat diets (HFD) exerts adverse influence on hAN. However, the effects of anti-obesity compounds on hAN are not known. To address this, we administered a lipidized analogue of an anti-obesity neuropeptide, Prolactin Releasing Peptide (PrRP), so-called LiPR, to mice. In the HFD context, LiPR rescued the survival of adult-born hypothalamic neurons and increased the number of aNSCs by reducing their activation. LiPR also rescued the reduction of immature hippocampal neurons and modulated calcium dynamics in iPSC-derived human neurons. In addition, some of these neurogenic effects were exerted by another anti-obesity compound, Liraglutide. These results show for the first time that anti-obesity neuropeptides influence adult neurogenesis and suggest that the neurogenic process can serve as a target of anti-obesity pharmacotherapy.

Lipidization as a tool toward peptide therapeutics

Peptides, as potential therapeutics continue to gain importance in the search for active substances for the treatment of numerous human diseases, some of which are, to this day, incurable. As potential therapeutic drugs, peptides have many favorable chemical and pharmacological properties, starting with their great diversity, through their high affinity for binding to all sort of natural receptors, and ending with the various pathways of their breakdown, which produces nothing but amino acids that are nontoxic to the body. Despite these and other advantages, however, they also have their pitfalls. One of these disadvantages is the very low stability of natural peptides. They have a short half-life and tend to be cleared from the organism very quickly. Their instability in the gastrointestinal tract, makes it impossible to administer peptidic drugs orally. To achieve the best pharmacologic effect, it is desirable to look for ways of modifying peptides that enable the use of these substances as pharmaceuticals. There are many ways to modify peptides. Herein we summarize the approaches that are currently in use, including lipidization, PEGylation, glycosylation and others, focusing on lipidization. We describe how individual types of lipidization are achieved and describe their advantages and drawbacks. Peptide modifications are performed with the goal of reaching a longer half-life, reducing immunogenicity and improving bioavailability. In the case of neuropeptides, lipidization aids their activity in the central nervous system after the peripheral administration. At the end of our review, we summarize all lipidized peptide-based drugs that are currently on the market.

High-Fat Diet Induces Resistance to Ghrelin and LEAP2 Peptide Analogs in Mice

Recent data suggest that the orexigenic peptide ghrelin and liver-expressed antimicrobial peptide 2 (LEAP2) have opposing effects on food intake regulation. Although circulating ghrelin is decreased in obesity, peripheral ghrelin administration does not induce food intake in obese mice. Limited information is available on ghrelin resistance in relation to LEAP2. In this study, the interplay between ghrelin and LEAP2 in obesity induced by a high-fat (HF) diet in mice was studied. First, the progression of obesity and intolerance to glucose together with plasma levels of active and total ghrelin, leptin, as well as liver LEAP2 mRNA expression at different time points of HF diet feeding was examined. In addition, the impact of switch from a HF diet to a standard diet on plasma ghrelin and LEAP2 production was studied. Second, sensitivity to the stable ghrelin analogue [Dpr3]Ghrelin or our novel LEAP2 analogue palm-LEAP2(1-14) during the progression of HF diet-induced obesity and after the switch for standard diet was investigated. Food intake was monitored after acute subcutaneous administration. HF diet feeding decreased both active and total plasma ghrelin and increased liver LEAP2 mRNA expression along with intolerance to glucose and the switch to a standard diet normalized liver LEAP2 mRNA expression and plasma level of active ghrelin, but not of total ghrelin. Additionally, our study demonstrates that a HF diet causes resistance to [Dpr3]Ghrelin, reversible by switch to St diet, followed by resistance to palm-LEAP2(1-14). Further studies are needed to determine the long-term effects of LEAP2 analogues on obesity-related ghrelin resistance.

Feeding High-Fat Diet Accelerates Development of Peripheral and Central Insulin Resistance and Inflammation and Worsens AD-like Pathology in APP/PS1 Mice

Alzheimer's disease (AD) is a progressive brain disorder characterized by extracellular amyloid-β (Aβ) plaques, intracellular neurofibrillary tangles formed by hyperphosphorylated Tau protein and neuroinflammation. Previous research has shown that obesity and type 2 diabetes mellitus, underlined by insulin resistance (IR), are risk factors for neurodegenerative disorders. In this study, obesity-induced peripheral and central IR and inflammation were studied in relation to AD-like pathology in the brains and periphery of APP/PS1 mice, a model of Aβ pathology, fed a high-fat diet (HFD). APP/PS1 mice and their wild-type controls fed either a standard diet or HFD were characterized at the ages of 3, 6 and 10 months by metabolic parameters related to obesity via mass spectroscopy, nuclear magnetic resonance, immunoblotting and immunohistochemistry to quantify how obesity affected AD pathology. The HFD induced substantial peripheral IR leading to central IR. APP/PS1-fed HFD mice had more pronounced IR, glucose intolerance and liver steatosis than their WT controls. The HFD worsened Aβ pathology in the hippocampi of APP/PS1 mice and significantly supported both peripheral and central inflammation. This study reveals a deleterious effect of obesity-related mild peripheral inflammation and prediabetes on the development of Aβ and Tau pathology and neuroinflammation in APP/PS1 mice.

Obesity, Cardiovascular and Neurodegenerative Diseases: Potential Common Mechanisms

The worldwide increase in the incidence of obesity and cardiovascular and neurodegenerative diseases, e.g. Alzheimer's disease, is related to many factors, including an unhealthy lifestyle and aging populations. However, the interconnection between these diseases is not entirely clear, and it is unknown whether common mechanisms underlie these conditions. Moreover, there are currently no fully effective therapies for obesity and neurodegeneration. While there has been extensive research in preclinical models addressing these issues, the experimental findings have not been translated to the clinic. Another challenge relates to the time of onset of individual diseases, which may not be easily identified, since there are no specific indicators or biomarkers that define disease onset. Hence knowing when to commence preventive treatment is unclear. This is especially pertinent in neurodegenerative diseases, where the onset of the disease may be subtle and occur decades before the signs and symptoms manifest. In metabolic and cardiovascular disorders, the risk may occur in-utero, in line with the concept of fetal programming. This review provides a brief overview of the link between obesity, cardiovascular and neurodegenerative diseases and discusses potential common mechanisms including the role of the gut microbiome.

NPFFR2-deficient mice fed a high-fat diet develop strong intolerance to glucose

A previous study on neuropeptide FF receptor 2 (NPFFR2)-deficient mice has demonstrated that NPFFR2 is involved in the control of energy balance and thermogenesis. Here, we report on the metabolic impact of NPFFR2 deficiency in male and female mice that were fed either a standard diet (STD) or a high-fat diet (HFD) and each experimental group consisted of ten individuals. Both male and female NPFFR2 knockout (KO) mice exhibited severe glucose intolerance that was exacerbated by a HFD diet. In addition, reduced insulin pathway signaling proteins in NPFFR2 KO mice fed a HFD resulted in the development of hypothalamic insulin resistance. HFD feeding did not cause liver steatosis in NPFFR2 KO mice of either sex, but NPFFR2 KO male mice fed a HFD had lower body weights, white adipose tissues, and liver and lower plasma leptin levels compared with their wild-type (WT) controls. Lower liver weight in NPFFR2 KO male mice compensated for HFD-induced metabolic stress by increased liver PPARα and plasma FGF21 hepatokine, which supported fatty acid β-oxidation in the liver and white adipose tissue. Conversely, NPFFR2 deletion in female mice attenuated the expression of Adra3β and Pparγ, which inhibited lipolysis in adipose tissue.

Metabolomic Study of Aging in fa/fa Rats: Multiplatform Urine and Serum Analysis

Zucker fatty (fa/fa) rats represent a well-established and widely used model of genetic obesity. Because previous metabolomic studies have only been published for young fa/fa rats up to 20 weeks of age, which can be considered early maturity in male fa/fa rats, the aim of our work was to extend the metabolomic characterization to significantly older animals. Therefore, the urinary profiles of obese fa/fa rats and their lean controls were monitored using untargeted NMR metabolomics between 12 and 40 weeks of age. At the end of the experiment, the rats were also characterized by NMR and LC-MS serum analysis, which was supplemented by a targeted LC-MS analysis of serum bile acids and neurotransmitters. The urine analysis showed that most of the characteristic differences detected in young obese fa/fa rats persisted throughout the experiment, primarily through a decrease in microbial co-metabolite levels, the upregulation of the citrate cycle, and changes in nicotinamide metabolism compared with the age-related controls. The serum of 40-week-old obese rats showed a reduction in several bile acid conjugates and an increase in serotonin. Our study demonstrated that the fa/fa model of genetic obesity is stable up to 40 weeks of age and is therefore suitable for long-term experiments.

GPR160 is not a receptor of anorexigenic cocaine- and amphetamine-regulated transcript peptide

COCAINE: and amphetamine-regulated transcript peptide (CARTp) is an anorexigenic neuropeptide whose receptor is undisclosed. Previously, we reported the specific binding of CART(61-102) to pheochromocytoma PC12 cells, where CART(61-102) affinity and the number of binding sites per cell corresponded to ligand-receptor binding. Recently, Yosten et al. designated orphan GPR160 as the CARTp receptor, because the GPR160 antibody abolished neuropathic pain and anorexigenic effects induced by CART(55-102) and exogenous CART(55-102) coimmunoprecipitated with GPR160 in KATOIII cells. As no direct evidence that CARTp is a ligand for GPR160 has been described, we decided to verify this hypothesis by testing CARTp affinity to the GPR160 receptor. We investigated the GPR160 expression in PC12 cells since it is cell line known to specifically bind CARTp. Moreover, we examined the specific CARTp binding in THP1 cells, with high endogenous GPR160 expression and GPR160-transfected cell lines U2OS and U-251 MG. In PC12 cells, the GPR160 antibody did not compete for specific binding with ¹²⁵I-CART(61-102) or with ¹²⁵I-CART(55-102), and GPR160 mRNA expression and GPR160 immunoreactivity were not detected. Moreover, THP1 cells did not show any ¹²⁵I-CART(61-102) or ¹²⁵I-CART(55-102) specific binding despite GPR160 detection by fluorescent immunocytochemistry (ICC). Finally, no ¹²⁵I-CART(61-102) or ¹²⁵I-CART(55-102) specific binding in the GPR160-transfected cell lines U2OS and U-251 MG, selected due to their negligible endogenous expression of GPR160, was detected, despite the detection of GPR160 by fluorescent ICC. Our binding studies clearly demonstrated that GPR160 cannot be a receptor for CARTp. Further studies are needed to identify true CARTp receptors.

Search for lipidized PrRP analogs with strong anorexigenic effect: In vitro and in vivo studies

Prolactin-releasing peptide (PrRP) is an anorexigenic neuropeptide that attenuates food intake and increases energy expenditure. We designed three series of new lipidized PrRP31 analogs of different lengths of fatty acids attached at amino acids 1 or 11 directly or via linkers, part of them acetylated at the N-terminus and/or modified with dichlorophenylalanine (PheCl₂) at the C-terminus. We tested their affinity for and activation of signaling pathways relevant to receptors GPR10, NPFF-R2, and NPFF-R1, effect on food intake in fasted or freely fed mice and rats, and stability in rat plasma. We aimed to select a strong dual GPR10/NPFF-R2 agonist whose affinity for NPFF-1 was not enhanced. The selected potent analog was then tested for body weight-lowering potency after chronic administration in mice with diet-induced obesity. PrRP31 analogs lipidized by monocarboxylic fatty acids showed strong dual affinity for both GPR10 and NPFF-R2 and activated MAPK/ERK1/2, Akt and CREB in cells overexpressing GPR10 and NPFF-R2. The selected analog stabilized at N- and C-termini and palmitoylated through the TTDS linker to Lys¹¹ is a powerful dual agonist GPR10/NPFF-R2 at not enhanced affinity for NPFF-R1. It showed strong anti-obesity properties in mice with diet-induced obesity and became a potential compound for further studies.

A Novel Truncated Liver Enriched Antimicrobial Peptide-2 Palmitoylated at its N-Terminal Antagonizes Effects of Ghrelin

Ghrelin is secreted in the stomach during fasting and targets the growth hormone secretagogue receptor (GHSR1a) in the hypothalamus and brainstem to exert its orexigenic effect. Recently, liver enriched antimicrobial peptide-2 (LEAP2) was identified as an endogenous high-affinity GHSR1a antagonist. LEAP2 is a 40-amino acid peptide with two disulfide bridges and GHRS1a affinity in the N-terminal hydrophobic part. In this study, we tested modified truncated N-terminal peptide LEAP2 (1-14), along with its myristoylated, palmitoylated, and stearoylated analogs, to determine their affinity to and activation of GHSR1a and their anorexigenic effects after acute peripheral administration. The lipidized analogs bound GHSR1a with affinity similar to that of natural LEAP2, and lipidization significantly enhanced the affinity of LEAP2(1-14) to GHSR1a. According to the beta-lactamase reporter gene response, the natural GHSR1a agonist ghrelin activated the receptor with nanomolar EC₅₀ LEAP2(1-14) analogs behaved as inverse agonists of GHSR1a and suppressed internal activity of the receptor with EC₅₀ values in the 10^-8 M range. LEAP2(1-14) analogs significantly lowered acute food intake in overnight fasted mice, and palmitoylated LEAP2(1-14) was the most potent. In free-fed mice, all LEAP2(1-14) analogs significantly decreased the orexigenic effect of the stable ghrelin analog [Dpr³]Ghrelin. Moreover, palmitoylated LEAP2(1-14) inhibited the growth hormone (GH) release induced by [Dpr³] Ghrelin and exhibited an increased stability in rat plasma compared with LEAP2(1-14). In conclusion, palmitoylated LEAP2(1-14) had the most pronounced affinity for GHSR1a, had an anorexigenic effect, exhibited stability in rat plasma, and attenuated [Dpr³]Ghrelin-induced GH release. Such properties render palmitoylated LEAP2(1-14) a promising substance for antiobesity treatment. SIGNIFICANCE STATEMENT: The agonist and antagonist of one receptor are rarely found in one organism. For ghrelin receptor (growth hormone secretagogue receptor, GHSR), endogenous agonist ghrelin and endogenous antagonist/inverse agonist liver enriched antimicrobial peptide-2 (LEAP2) co-exist and differently control GHSR signaling. As ghrelin has a unique role in food intake regulation, energy homeostasis, and cytoprotection, lipidized truncated LEAP2 analogs presented in this study could serve not only to reveal the relationship between ghrelin and LEAP2 but also for development of potential anti-obesity agents.

Age-related metabolic and neurodegenerative changes in SAMP8 mice

The most important risk factor for the development of sporadic Alzheimer’s disease (AD) is ageing. Senescence accelerated mouse prone 8 (SAMP8) is a model of sporadic AD, with senescence accelerated resistant mouse (SAMR1) as a control. In this study, we aimed to determine the onset of senescence-induced neurodegeneration and the related potential therapeutic window using behavioral experiments, immunohistochemistry and western blotting in SAMP8 and SAMR1 mice at 3, 6 and 9 months of age. The Y-maze revealed significantly impaired working spatial memory of SAMP8 mice from the 6^th month. With ageing, increasing plasma concentrations of proinflammatory cytokines in SAMP8 mice were detected as well as significantly increased astrocytosis in the cortex and microgliosis in the brainstem. Moreover, from the 3^rd month, SAMP8 mice displayed a decreased number of neurons and neurogenesis in the hippocampus. From the 6^th month, increased pathological phosphorylation of tau protein at Thr231 and Ser214 was observed in the hippocampi of SAMP8 mice. In conclusion, changes specific for neurodegenerative processes were observed between the 3^rd and 6^th month of age in SAMP8 mice; thus, potential neuroprotective interventions could be applied between these ages.

MALDI Mass Spectrometry Imaging of Lipids on Free-Floating Brain Sections and Immunohistochemically Colocalized Markers of Neurodegeneration

In mass spectrometry imaging (MSI), the essential steps in sample preparation include collection and storage. The most widely used preservation procedure for MSI consists in freezing samples and storing them at temperatures below -80 °C. On the other hand, the most common method for preserving biological samples in clinical practice is their fixation in paraformaldehyde. The storage of free-floating sections is a particular type of the preservation of paraformaldehyde-fixed tissues that is used in immunohistochemistry. This chapter describes the approach of the multimodal imaging of free-floating brain sections using the MSI of lipids and the immunohistochemistry of neurodegeneration markers.

Lipidized Prolactin-Releasing Peptide as a New Potential Tool to Treat Obesity and Type 2 Diabetes Mellitus: Preclinical Studies in Rodent Models

Obesity and type 2 diabetes mellitus (T2DM) are preconditions for the development of metabolic syndrome, which is reaching pandemic levels worldwide, but there are still only a few anti-obesity drugs available. One of the promising tools for the treatment of obesity and related metabolic complications is anorexigenic peptides, such as prolactin-releasing peptide (PrRP). PrRP is a centrally acting neuropeptide involved in food intake and body weight (BW) regulation. In its natural form, it has limitations for peripheral administration; thus, we designed analogs of PrRP lipidized at the N-terminal region that showed high binding affinities, increased stability and central anorexigenic effects after peripheral administration. In this review, we summarize the preclinical results of our chronic studies on the pharmacological role of the two most potent palmitoylated PrRP31 analogs in various mouse and rat models of obesity, glucose intolerance, and insulin resistance. We used mice and rats with diet-induced obesity fed a high-fat diet, which is considered to simulate the most common form of human obesity, or rodent models with leptin deficiency or disrupted leptin signaling in which long-term food intake regulation by leptin is distorted. The rodent models described in this review are models of metabolic syndrome with different severities, such as obesity or morbid obesity, prediabetes or diabetes and hypertension. We found that the effects of palmitoylated PrRP31 on food intake and BW but not on glucose intolerance require intact leptin signaling. Thus, palmitoylated PrRP31 analogs have potential as therapeutics for obesity and related metabolic complications.

Palmitoylated prolactin-releasing peptide reduced Aβ plaques and microgliosis in the cerebellum: APP/PS1 mice study

BACKGROUND

Prolactin-releasing peptide (PrRP) is a potential drug for the treatment of obesity and associated type 2 diabetes mellitus (T2DM) due to its strong anorexigenic and antidiabetic properties. In our recent study, the lipidized PrRP analog palm11-PrRP31 was proven to exert beneficial effects in APP/PS1 mice, a model of Alzheimer´s disease (AD)-like amyloid-β (Aβ) pathology, reducing the Aβ plaque load, microgliosis and astrocytosis in the hippocampus and cortex.

OBJECTIVE

In this study, we focused on the neuroprotective and anti-inflammatory effects of palm11-PrRP31 and its possible impact on synaptogenesis in the cerebellum of APP/PS1 mice, because others have suggested that cerebellar Aβ plaques contribute to cognitive deficits in AD.

METHODS

APP/PS1 mice were treated subcutaneously with palm11-PrRP31 for 2 months, then immunoblotting and immunohistochemistry were used to quantify pathological markers connected to AD, compared to control mice.

RESULTS

In the cerebella of 8 months old APP/PS1 mice, we found widespread Aβ plaques surrounded by activated microglia detected by ionized calcium-binding adapter molecule (Iba1), but no increase in astrocytic marker glial fibrillary acidic protein (GFAP) compared to controls. Interestingly, no difference in both presynaptic markers syntaxin1A and postsynaptic marker spinophilin was registered between APP/PS1 and control mice. Palm11-PrRP31 treatment significantly reduced the Aβ plaque load and microgliosis in the cerebellum. Furthermore, palm11-PrRP31 increased synaptogenesis and attenuated neuroinflammation and apoptosis in the hippocampus of APP/PS1 mice.

CONCLUSION

These results suggest palm11-PrRP31 is a promising agent for the treatment of neurodegenerative disorders.

Cholecystokinin system is involved in the anorexigenic effect of peripherally applied palmitoylated prolactin-releasing peptide in fasted mice

Prolactin-releasing peptide (PrRP) has been proposed to mediate the central satiating effects of cholecystokinin (CCK) through the vagal CCK1 receptor. PrRP acts as an endogenous ligand of G protein-coupled receptor 10 (GPR10), which is expressed at the highest levels in brain areas related to food intake regulation, e.g., the paraventricular hypothalamic nucleus (PVN) and nucleus of the solitary tract (NTS). The NTS and PVN are also significantly activated after peripheral CCK administration. The aim of this study was to determine whether the endogenous PrRP neuronal system in the brain is involved in the central anorexigenic effect of the peripherally administered CCK agonist JMV236 or the CCK1 antagonist devazepide and whether the CCK system is involved in the central anorexigenic effect of the peripherally applied lipidized PrRP analog palm-PrRP31 in fasted lean mice. The effect of devazepide and JMV236 on the anorexigenic effects of palm-PrRP31 as well as devazepide combined with JMV236 and palm-PrRP31 on food intake and Fos cell activation in the PVN and caudal NTS was examined. Our results suggest that the anorexigenic effect of JMV236 is accompanied by activation of PrRP neurons of the NTS in a CCK1 receptor-dependent manner. Moreover, while the anorexigenic effect of palm-PrRP31 was not affected by JMV236, it was partially attenuated by devazepide in fasted mice. The present findings indicate that the exogenously influenced CCK system may be involved in the central anorexigenic effect of peripherally applied palm-PrRP31, which possibly indicates some interaction between the CCK and PrRP neuronal systems.

Aging and high-fat diet feeding lead to peripheral insulin resistance and sex-dependent changes in brain of mouse model of tau pathology THY-Tau22

Background

Obesity leads to low-grade inflammation in the adipose tissue and liver and neuroinflammation in the brain. Obesity-induced insulin resistance (IR) and neuroinflammation seem to intensify neurodegeneration including Alzheimer’s disease. In this study, the impact of high-fat (HF) diet-induced obesity on potential neuroinflammation and peripheral IR was tested separately in males and females of THY-Tau22 mice, a model of tau pathology expressing mutated human tau protein.

Methods

Three-, 7-, and 11-month-old THY-Tau22 and wild-type males and females were tested for mobility, anxiety-like behavior, and short-term spatial memory in open-field and Y-maze tests. Plasma insulin, free fatty acid, cholesterol, and leptin were evaluated with commercial assays. Liver was stained with hematoxylin and eosin for histology. Brain sections were 3′,3′-diaminobenzidine (DAB) and/or fluorescently detected for ionized calcium-binding adapter molecule 1 (Iba1), glial fibrillary acidic protein (GFAP), and tau phosphorylated at T231 (pTau (T231)), and analyzed. Insulin signaling cascade, pTau, extracellular signal-regulated kinase 1/2 (ERK1/2), and protein phosphatase 2A (PP2A) were quantified by western blotting of hippocampi of 11-month-old mice. Data are mean ± SEM and were subjected to Mann-Whitney t test within age and sex and mixed-effects analysis and Bonferroni’s post hoc test for age comparison.

Results

Increased age most potently decreased mobility and increased anxiety in all mice. THY-Tau22 males showed impaired short-term spatial memory. HF diet increased body, fat, and liver weights and peripheral IR. HF diet-fed THY-Tau22 males showed massive Iba1+ microgliosis and GFAP+ astrocytosis in the hippocampus and amygdala. Activated astrocytes colocalized with pTau (T231) in THY-Tau22, although no significant difference in hippocampal tau phosphorylation was observed between 11-month-old HF and standard diet-fed THY-Tau22 mice. Eleven-month-old THY-Tau22 females, but not males, on both diets showed decreased synaptic and postsynaptic plasticity.

Conclusions

Significant sex differences in neurodegenerative signs were found in THY-Tau22. Impaired short-term spatial memory was observed in 11-month-old THY-tau22 males but not females, which corresponded to increased neuroinflammation colocalized with pTau(T231) in the hippocampi and amygdalae of THY-Tau22 males. A robust decrease in synaptic and postsynaptic plasticity was observed in 11-month-old females but not males. HF diet caused peripheral but not central IR in mice of both sexes.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-021-02190-3.

GPR10 gene deletion in mice increases basal neuronal activity, disturbs insulin sensitivity and alters lipid homeostasis

G-protein-coupled receptor GPR10 is expressed in brain areas regulating energy metabolism. In this study, the effects of GPR10 gene deficiency on energy homeostasis in mice of both sexes fed either standard chow or a high-fat diet (HFD) were studied, with a focus on neuronal activation of PrRP neurons, and adipose tissue and liver metabolism. GPR10 deficiency in males upregulated the phasic and tonic activity of PrRP neurons in the nucleus of the solitary tract. GPR10 knockout (KO) males on a standard diet displayed a higher body weight than their wild-type (WT) littermates due to an increase in adipose tissue mass; however, HFD feeding did not cause weight differences between genotypes. Expression of lipogenesis genes was suppressed in the subcutaneous adipose tissue of GPR10 KO males. In contrast, GPR10 KO females did not differ in body weight from their WT controls, but showed elevated expression of lipid metabolism genes in the liver and subcutaneous adipose tissue compared to WT controls. An attenuated non-esterified fatty acids change after glucose load compared to WT controls suggested a defect in insulin-mediated suppression of lipolysis in GPR10 KO females. Indirect calorimetry did not reveal any differences in energy expenditure among groups. In conclusion, deletion of GPR10 gene resulted in changes in lipid metabolism in mice of both sexes, however in different extent. An increase in adipose tissue mass observed in only GPR10 KO males may have been prevented in GPR10 KO females owing to a compensatory increase in the expression of metabolic genes.

Iodination of CART(61-102) peptide: Preserved binding and anorexigenic activity in mice

CART (cocaine- and amphetamine-regulated transcript) peptides are involved in food intake regulation, stress, and other physiological functions. Although CART peptides have been known for over 25 years, their receptor(s) have not yet been characterized. In this short review, we will summarize our previous studies, where we reported specific binding of ¹²⁵ I-CART(61-102) to PC12 rat pheochromocytoma cells. Competitive binding experiments performed with mono- and di-iodinated peptides and their isoforms with oxidized Met⁶⁷ resulted in nanomolar binding affinity. Moreover, in our previous study, CART(61-102), as well as di-iodinated CART(61-102), have shown a strong anorexigenic effect in fasted lean mice after intracerebroventricular administration. In conclusion, from our previous studies, iodination of CART(61-102) resulted in mono- and di-iodinated analogs with or without oxidized Met⁶⁷ . All analogs revealed a high affinity to binding sites at PC12 cells and preserved biological activity.

Lipidized Prolactin-Releasing Peptide Agonist Attenuates Hypothermia-Induced Tau Hyperphosphorylation in Neurons

Alzheimer's disease (AD) is one of the most prevalent neurodegenerative diseases, characterized by the accumulation of extracellular amyloid plaques and intraneuronal neurofibrillary tangles. These tangles mainly consist of hyperphosphorylated tau protein. As it induces tau hyperphosphorylation in vitro and in vivo, hypothermia is a useful tool for screening potential neuroprotective compounds that ameliorate tau pathology. In this study, we examined the effect of prolactin-releasing peptide (PrRP), its lipidized analog palm11-PrRP31 and glucagon-like-peptide-1 agonist liraglutide, substances with anorexigenic and antidiabetic properties, on tau phosphorylation and on the main kinases and phosphatases involved in AD development. Our study was conducted in a neuroblastoma cell line SH-SY5Y and rat primary neuronal cultures under normothermic and hypothermic conditions. Hypothermia induced a significant increase in tau phosphorylation at the pThr212 and pSer396/pSer404 epitopes. The palmitoylated analogs liraglutide and palm11-PrRP31 attenuated tau hyperphosphorylation, suggesting their potential use in the treatment of neurodegenerative diseases.

Mass spectrometry imaging of free-floating brain sections detects pathological lipid distribution in a mouse model of Alzheimer's-like pathology

Mass spectrometry imaging (MSI) is a modern analytical technique capable of monitoring the spatial distribution of compounds within target tissues. Collection and storage are important steps in sample preparation. The recommended and most widely used preservation procedure for MSI is freezing samples in isopentane and storing them at temperatures below -80 °C. On the other hand, the most common and general method for preserving biological samples in clinical practice is fixation in paraformaldehyde. Special types of samples prepared from these fixed tissues that are used for histology and immunohistochemistry are free-floating sections. It would be very beneficial if the latter procedure could also be applicable for the samples intended for subsequent MSI analysis. In the present work, we optimized and evaluated paraformaldehyde-fixed free-floating sections for the analysis of lipids in mouse brains and used the sections for the study of lipid changes in double transgenic APP/PS1 mice, a model of Alzheimer's-like pathology. Moreover, we examined the neuroprotective properties of palm¹¹-PrRP31, an anorexigenic and glucose-lowering analog of prolactin-releasing peptide, and liraglutide, a type 2 diabetes drug. From the free-floating sections, we obtained lipid images without interference or delocalization, and we demonstrated that free-floating sections can be used for the MSI of lipids. In the APP/PS1 mice, we observed a changed distribution of various lipids compared to the controls. The most significant changes in lipids in the brains of APP/PS1 mice compared to wild-type controls were related to gangliosides (GM2 36:1, GM3 36:1) and phosphatidylinositols (PI 38:4, 36:4) in regions where the accumulation of senile plaques occurred. In APP/PS1 mice peripherally treated with palm¹¹-PrRP31 or liraglutide for 2 months, we found that both peptides reduced the amount and space occupied by lipids, which were linked to the senile plaques. These results indicate that palm¹¹-PrRP31 as well as liraglutide might be potentially useful in the treatment of neurodegenerative diseases.

Synergistic effect of leptin and lipidized PrRP on metabolic pathways in ob/ob mice

Lack of leptin production in ob/ob mice results in obesity and prediabetes that could be partly reversed by leptin supplementation. In the hypothalamus, leptin supports the production of prolactin-releasing peptide (PrRP), an anorexigenic neuropeptide synthesized and active in the brain. In our recent studies, the palmitoylated PrRP analog palm11-PrRP31 showed a central anorexigenic effect after peripheral administration. This study investigates whether PrRP could compensate for the deficient leptin in ob/ob mice. In two separate experiments, palm11-PrRP31 (5 mg/kg) and leptin (5 or 10 μg/kg) were administered subcutaneously twice daily for 2 or 8 weeks to 8- (younger) or 16-(older) week-old ob/ob mice, respectively, either separately or in combination. The body weight decreasing effect of palm11-PrRP31 in both younger and older ob/ob mice was significantly powered by a subthreshold leptin dose, the combined effect could be then considered synergistic. Leptin and palm11-PrRP31 also synergistically lowered liver weight and blood glucose in younger ob/ob mice. Reduced liver weight was linked to decreased mRNA expression of lipogenic enzymes. In the hypothalamus of older ob/ob mice, two main leptin anorexigenic signaling pathways, namely, Janus kinase, signal transducer and activator of transcription-3 activation and AMP-activated protein kinase de-activation, were induced by leptin, palm11-PrRP31, and their combination. Thus, palm11-PrRP31 could partially compensate for leptin deficiency in ob/ob mice. In conclusion, the results demonstrate a synergistic effect of leptin and our lipidized palm11-PrRP31 analog.

Pathophysiology of NAFLD and NASH in Experimental Models: The Role of Food Intake Regulating Peptides

Obesity, diabetes, insulin resistance, sedentary lifestyle, and Western diet are the key factors underlying non-alcoholic fatty liver disease (NAFLD), one of the most common liver diseases in developed countries. In many cases, NAFLD further progresses to non-alcoholic steatohepatitis (NASH), fibrosis, cirrhosis, and to hepatocellular carcinoma. The hepatic lipotoxicity and non-liver factors, such as adipose tissue inflammation and gastrointestinal imbalances were linked to evolution of NAFLD. Nowadays, the degree of adipose tissue inflammation was shown to directly correlate with the severity of NAFLD. Consumption of higher caloric intake is increasingly emerging as a fuel of metabolic inflammation not only in obesity-related disorders but also NAFLD. However, multiple causes of NAFLD are the reason why the mechanisms of NAFLD progression to NASH are still not well understood. In this review, we explore the role of food intake regulating peptides in NAFLD and NASH mouse models. Leptin, an anorexigenic peptide, is involved in hepatic metabolism, and has an effect on NAFLD experimental models. Glucagon-like peptide-1 (GLP-1), another anorexigenic peptide, and GLP-1 receptor agonists (GLP-1R), represent potential therapeutic agents to prevent NAFLD progression to NASH. On the other hand, the deletion of ghrelin, an orexigenic peptide, prevents age-associated hepatic steatosis in mice. Because of the increasing incidence of NAFLD and NASH worldwide, the selection of appropriate animal models is important to clarify aspects of pathogenesis and progression in this field.

High-fructose drinks affect microRNAs expression differently in lean and obese mice

High fructose intake from soft drinks and sweets is assumed to have a negative impact on human health. Yet in spite of intensive research, the molecular mechanisms of these effects have not been fully elucidated yet, for example, the effect of high fructose intake could be different in normal and obese individuals. Four groups of mice were used in this study: control groups of lean mice and mice with obesity induced by a high-fat diet, then both of these groups with or without fructose administration in drinks. In plasma of each group, triacylglycerol, cholesterol, free fatty acids, alanine aminotransferase, insulin and adiponectin were measured. The expression levels of selected microRNAs (miRNAs) in plasma, the liver, white adipose tissue, brown adipose tissue and subcutaneous adipose tissue were quantified. In both lean and obese mice, high fructose intake increased cholesterol amount in the liver, up-regulated hepatic miR-27a, down-regulated miR-33a in white adipose tissue and increased plasmatic level of miR-21. The effect of high fructose intake on other miRNAs in the liver, plasma and adipose tissues differed in normal and obese mice. Fructose intake led to hepatic hypercholesterolemia and aberrant expression of several miRNAs participating in lipid metabolism, adipocytes differentiation and nonalcoholic fatty liver disease promotion. The effect of fructose on miRNAs expression differed in normal and obese mice. Nevertheless, plasmatic miR-21, which was induced by fructose in both lean and obese mice, may be considered as a potential biomarker of excessive fructose intake.

Metabolomic Study of Obesity and Its Treatment with Palmitoylated Prolactin-Releasing Peptide Analog in Spontaneously Hypertensive and Normotensive Rats

In this study, the combination of metabolomics and standard biochemical and biometric parameters was used to describe the metabolic effects of diet-induced obesity and its treatment with the novel antiobesity compound palm¹¹-PrRP31 (palmitoylated prolactin-releasing peptide) in spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto rats (WKY). The results showed that SHR on a high-fat (HF) diet were normoglycemic with obesity and hypertension, while WKY on the HF diet were normotensive and obese with prediabetes. NMR-based metabolomics revealed mainly several microbial cometabolites altered by the HF diet, particularly in urine. The HF diet induced similar changes in both models. However, two groups of genotype-specific metabolites were defined: metabolites specific to the genotype at baseline (e.g., 1-methylnicotinamide, phenylacetylglycine, taurine, methylamine) and metabolites reacting specifically to the HF diet in individual genotypes (2-oxoglutarate, dimethylamine, N-butyrylglycine, p-cresyl sulfate). The palm¹¹-PrRP31 lowered body weight and improved biochemical and biometric parameters in both strains, and it improved glucose tolerance in WKY rats on the HF diet. In urine, the therapy induced significant decrease of formate and 1-methylnicotinamide in SHR and alanine, allantoin, dimethylamine, and N-butyrylglycine in WKY. Altogether, our study confirms the effectiveness of palm¹¹-PrRP31 for antiobesity treatment.

The impact of anorexigenic peptides in experimental models of Alzheimer's disease pathology

Alzheimer's disease (AD) is the most prevalent neurodegenerative disorder in the elderly population. Numerous epidemiological and experimental studies have demonstrated that patients who suffer from obesity or type 2 diabetes mellitus have a higher risk of cognitive dysfunction and AD. Several recent studies demonstrated that food intake-lowering (anorexigenic) peptides have the potential to improve metabolic disorders and that they may also potentially be useful in the treatment of neurodegenerative diseases. In this review, the neuroprotective effects of anorexigenic peptides of both peripheral and central origins are discussed. Moreover, the role of leptin as a key modulator of energy homeostasis is discussed in relation to its interaction with anorexigenic peptides and their analogs in AD-like pathology. Although there is no perfect experimental model of human AD pathology, animal studies have already proven that anorexigenic peptides exhibit neuroprotective properties. This phenomenon is extremely important for the potential development of new drugs in view of the aging of the human population and of the significantly increasing incidence of AD.

Liraglutide and a lipidized analog of prolactin-releasing peptide show neuroprotective effects in a mouse model of β-amyloid pathology

Obesity and type 2 diabetes mellitus (T2DM) are important risk factors for Alzheimer's disease (AD). Drugs originally developed for T2DM treatment, e.g., analog of glucagon-like peptide 1 liraglutide, have shown neuroprotective effects in mouse models of AD. We previously examined the neuroprotective properties of palm¹¹-PrRP31, an anorexigenic and glucose-lowering analog of prolactin-releasing peptide, in a mouse model of AD-like Tau pathology, THY-Tau22 mice. Here, we demonstrate the neuroprotective effects of palm¹¹-PrRP31 in double transgenic APP/PS1 mice, a model of AD-like β-amyloid (Aβ) pathology. The 7-8-month-old APP/PS1 male mice were subcutaneously injected with liraglutide or palm¹¹-PrRP31 for 2 months. Both the liraglutide and palm¹¹-PrRP31 treatments reduced the Aβ plaque load in the hippocampus. Palm¹¹-PrRP31 also significantly reduced hippocampal microgliosis, consistent with our observations of a reduced Aβ plaque load, and reduced cortical astrocytosis, similar to the treatment with liraglutide. Palm¹¹-PrRP31 also tended to increase neurogenesis, as indicated by the number of doublecortin-positive cells in the hippocampus. After the treatment with both anorexigenic compounds, we observed a significant decrease in Tau phosphorylation at Thr231, one of the first epitopes phosphorylated in AD. This effect was probably caused by elevated activity of protein phosphatase 2A subunit C, the main Tau phosphatase. Both liraglutide and palm¹¹-PrRP31 reduced the levels of caspase 3, which has multiple roles in the pathogenesis of AD. Palm¹¹-PrRP31 increased protein levels of the pre-synaptic marker synaptophysin, suggesting that palm¹¹-PrRP31 might help preserve synapses. These results indicate that palm¹¹-PrRP31 has promising potential for the treatment of neurodegenerative diseases.

In Vitro and In Vivo Characterization of Novel Stable Peptidic Ghrelin Analogs: Beneficial Effects in the Settings of Lipopolysaccharide-Induced Anorexia in Mice

Ghrelin, the only known orexigenic gut hormone produced primarily in the stomach, has lately gained attention as a potential treatment of anorexia and cachexia. However, its biologic stability is highly limited; therefore, a number of both peptide and nonpeptide ghrelin analogs have been synthesized. In this study, we provide in vitro and in vivo characterization of a series of novel peptide growth hormone secretagogue receptor (GHS-R1a) agonists, both under nonpathologic conditions and in the context of lipopolysaccharide (LPS)-induced anorexia. These analogs were based on our previous series modified by replacing the Ser³ with diaminopropionic acid (Dpr), the N-terminal Gly with sarcosine, and Phe⁴ with various noncoded amino acids. New analogs were further modified by replacing the n-octanoyl bound to Dpr³ with longer or unsaturated fatty acid residues, by incorporation of the second fatty acid residue into the molecule, or by shortening the peptide chain. These modifications preserved the ability of ghrelin analogs to bind to the membranes of cells transfected with GHS-R1a, as well as the GHS-R1a signaling activation. The selected analogs exhibited long-lasting and potent orexigenic effects after a single s.c. administration in mice. The stability of new ghrelin analogs in mice after s.c. administration was significantly higher when compared with ghrelin and [Dpr³]ghrelin, with half-lives of approximately 2 hours. A single s.c. injection of the selected ghrelin analogs in mice with LPS-induced anorexia significantly increased food intake via the activation of orexigenic pathways and normalized blood levels of proinflammatory cytokines, demonstrating the anti-inflammatory potential of the analogs.

Prolactin-releasing peptide improved leptin hypothalamic signaling in obese mice

The situation following anti-obesity drug termination is rarely investigated, eventhough a decrease in body weight needs to be sustained. Therefore, this study examined the impact of twice-daily peripheral administration of 5 mg/kg [N-palm-γGlu-Lys¹¹] prolactin-releasing peptide 31 (palm¹¹-PrRP31) in mice with diet-induced obesity (DIO from consuming a high-fat diet) after 28 days of treatment (palm¹¹-PrRP31 group) and after 14 days of peptide treatment followed by 14 days of discontinuation (palm¹¹-PrRP31 + saline group). At the end of the treatment, cumulative food intake, body weight and subcutaneous fat weight/body weight ratio and leptin plasma level were reduced significantly in both the palm¹¹-PrRP31 group and the palm¹¹-PrRP31 + saline group compared to the saline control group. This reduction correlated with significantly increased FOSB, a marker of long-term neuronal potentiation, in the nucleus arcuatus and nucleus tractus solitarii, areas known to be affected by the anorexigenic effect of palm¹¹-PrRP31. Moreover, activation of leptin-related hypothalamic signaling was registered through an increase in phosphoinositide-3-kinase, increased phosphorylation of protein kinase B (PKB, AKT) and enhanced extracellular signal-regulated kinase 1/2 phosphorylation. Besides, lowered apoptotic markers c-JUN N-terminal kinase and c-JUN phosphorylation were registered in the hypothalami of both palm¹¹-PrRP31-treated groups. This study demonstrates that palm¹¹-PrRP31 positively affects feeding and leptin-related hypothalamic signaling, not only after 28 days of treatment but even 14 days after the termination of a 14-day long treatment without the yo-yo effect.

Potential neuroprotective and anti-apoptotic properties of a long-lasting stable analog of ghrelin: an in vitro study using SH-SY5Y cells

Neurodegenerative disorders, such as Alzheimer's disease (AD) and Parkinson's disease (PD), are increasing in prevalence. Currently, there are no effective and specific treatments for these disorders. Recently, positive effects of the orexigenic hormone ghrelin on memory and learning were demonstrated in mouse models of AD and PD. In this study, we tested the potential neuroprotective properties of a stable and long-lasting ghrelin analog, Dpr(3)ghrelin (Dpr(3)ghr), in SH-SY5Y neuroblastoma cells stressed with 1.2 mM methylglyoxal (MG), a toxic endogenous by-product of glycolysis, and we examined the impact of Dpr(3)ghr on apoptosis. Pre-treatment with both 10(-5) and 10(-7) M Dpr(3)ghr resulted in increased viability in SH-SY5Y cells (determined by MTT staining), as well as reduced cytotoxicity of MG in these cells (determined by LDH assay). Dpr(3)ghr increased viability by altering pro-apoptotic and viability markers: Bax was decreased, Bcl-2 was increased, and the Bax/Bcl-2 ratio was attenuated. The ghrelin receptor GHS-R1 and Dpr(3)ghr-induced activation of PBK/Akt were immuno-detected in SH-SY5Y cells to demonstrate the presence of GHS-R1 and GHS-R1 activation, respectively. We demonstrated that Dpr(3)ghr protected SH-SY5Y cells against MG-induced neurotoxicity and apoptosis. Our data suggest that stable ghrelin analogs may be candidates for the effective treatment of neurodegenerative disorders.

Impact of novel palmitoylated prolactin-releasing peptide analogs on metabolic changes in mice with diet-induced obesity

Analogs of anorexigenic neuropeptides, such as prolactin-releasing peptide (PrRP), have a potential as new anti-obesity drugs. In our previous study, palmitic acid attached to the N-terminus of PrRP enabled its central anorexigenic effects after peripheral administration. In this study, two linkers, γ-glutamic acid at Lys¹¹ and a short, modified polyethylene glycol at the N-terminal Ser and/or Lys¹¹, were applied for the palmitoylation of PrRP31 to improve its bioavailability. These analogs had a high affinity and activation ability to the PrRP receptor GPR10 and the neuropeptide FF2 receptor, as well as short-term anorexigenic effect similar to PrRP palmitoylated at the N-terminus. Two-week treatment with analogs that were palmitoylated through linkers to Lys¹¹ (analogs 1 and 2), but not with analog modified both at the N-terminus and Lys¹¹ (analog 3) decreased body and liver weights, insulin, leptin, triglyceride, cholesterol and free fatty acid plasma levels in a mouse model of diet-induced obesity. Moreover, the expression of uncoupling protein-1 was increased in brown fat suggesting an increase in energy expenditure. In addition, treatment with analogs 1 and 2 but not analog 3 significantly decreased urinary concentrations of 1-methylnicotinamide and its oxidation products N-methyl-2-pyridone-5-carboxamide and N-methyl-4-pyridone-3-carboxamide, as shown by NMR-based metabolomics. This observation confirmed the previously reported increase in nicotinamide derivatives in obesity and type 2 diabetes mellitus and the effectiveness of analogs 1 and 2 in the treatment of these disorders.

The effects of liraglutide in mice with diet-induced obesity studied by metabolomics

Liraglutide is the glucagon-like peptide-1 receptor agonist widely used for the treatment of type 2 diabetes mellitus. Recently, it has been demonstrated to decrease cardiovascular morbidity and mortality in patients with type 2 diabetes and high cardiovascular risk. Although the major modes of liraglutide action are well-known, its detailed action at the metabolic level has not been studied. To this end, we explored the effect of 2-week liraglutide treatment in C57BL/6 male mice with obesity and diabetes induced by 13 weeks of high-fat diet using NMR spectroscopy to capture the changes in urine metabolic profile induced by the therapy. The liraglutide treatment decreased body and fat pads weight along with blood glucose and triglyceride levels. NMR spectroscopy identified 11 metabolites significantly affected by liraglutide treatment as compared to high-fat diet-fed control group. These metabolites included ones involved in nicotinamide adenine dinucleotide metabolism, β-oxidation of fatty acids and microbiome changes. Although majority of the metabolites changed after liraglutide treatment were similar as the ones previously identified after vildagliptin administration in a similar mouse model, the changes in creatinine, taurine and trigonelline were specific for liraglutide administration. The significance of these changes and its possible use in the personalization of antidiabetic therapy in humans requires further research.

The role of food intake regulating peptides in cardiovascular regulation

Obesity is a risk factor that worsens cardiovascular events leading to higher morbidity and mortality. However, the exact mechanisms of relation between obesity and cardiovascular events are unclear. Nevertheless, it has been demonstrated that pharmacological therapy for obesity has great potential to improve some cardiovascular problems. Therefore, it is important to determine the common mechanisms regulating both food intake and blood pressure. Several hormones produced by peripheral tissues work together with neuropeptides involved in the regulation of both food intake and blood pressure. Anorexigenic (food intake lowering) hormones such as leptin, glucagon-like peptide-1 and cholecystokinin cooperate with α-melanocyte-stimulating hormone, cocaine- and amphetamine-regulated peptide as well as prolactin-releasing peptide. Curiously their collective actions result in increased sympathetic activity, especially in the kidney, which could be one of the factors responsible for the blood pressure increases seen in obesity. On the other hand, orexigenic (food intake enhancing) peptides, especially ghrelin released from the stomach and acting in the brain, cooperates with orexins, neuropeptide Y, melanin-concentrating hormone and galanin, which leads to decreased sympathetic activity and blood pressure. This paradox should be intensively studied in the future. Moreover, it is important to know that the hypothalamus together with the brainstem seem to be major structures in the regulation of food intake and blood pressure. Thus, the above mentioned regions might be essential brain components in the transmission of peripheral signals to the central effects. In this short review, we summarize the current information on cardiovascular effects of food intake regulating peptides.

Urinary metabolomic profiling in mice with diet-induced obesity and type 2 diabetes mellitus after treatment with metformin, vildagliptin and their combination

Metformin, vildagliptin and their combination are widely used for the treatment of diabetes, but little is known about the metabolic responses to these treatments. In the present study, NMR-based metabolomics was applied to detect changes in the urinary metabolomic profile of a mouse model of diet-induced obesity in response to these treatments. Additionally, standard biochemical parameters and the expression of enzymes involved in glucose and fat metabolism were monitored. Significant correlations were observed between several metabolites (e.g., N-carbamoyl-β-alanine, N1-methyl-4-pyridone-3-carboxamide, N1-methyl-2-pyridone-5-carboxamide, glucose, 3-indoxyl sulfate, dimethylglycine and several acylglycines) and the area under the curve of glucose concentrations during the oral glucose tolerance test. The present study is the first to present N-carbamoyl-β-alanine as a potential marker of type 2 diabetes mellitus and consequently to demonstrate the efficacies of the applied antidiabetic interventions. Moreover, the elevated acetate level observed after vildagliptin administration might reflect increased fatty acid oxidation.

Prolactin-releasing peptide: a new tool for obesity treatment

Obesity is an escalating epidemic, but an effective noninvasive therapy is still scarce. For obesity treatment, anorexigenic neuropeptides are promising tools, but their delivery from the periphery to the brain is complicated because peptides have a low stability and limited ability to cross the blood-brain barrier. In this review, we summarize results of several studies with our newly designed lipidized analogs of prolactin-releasing peptide (PrRP). PrRP is involved in feeding and energy balance regulation as demonstrated by obesity phenotypes of both PrRP- and PrRP-receptor-knockout mice. Lipidized PrRP analogs showed binding affinity and signaling in PrRP receptor-expressing cells similar to natural PrRP. Moreover, these analogs showed high binding affinity also to anorexigenic neuropeptide FF (NPFF)-2 receptor. Acute peripheral administration of myristoylated and palmitoylated PrRP analogs to mice and rats induced strong and long-lasting anorexigenic effects and neuronal activation in the brain areas involved in food intake regulation. Two-week-long subcutaneous administration of palmitoylated PrRP31 and myristoylated PrRP20 lowered food intake, body weight, improved metabolic parameters and attenuated lipogenesis in mice with diet-induced obesity. A strong anorexigenic, body weight-reducing and glucose tolerance-improving effect of palmitoylated-PrRP31 was shown also in diet-induced obese rats after its repeated 2-week-long peripheral administration. Thus, the strong anorexigenic and body weight-reducing effects of palmitoylated PrRP31 and myristoylated PrRP20 make these analogs attractive candidates for antiobesity treatment. Moreover, PrRP receptor might be a new target for obesity therapy.

Palmitoylated PrRP analog decreases body weight in DIO rats but not in ZDF rats

Anorexigenic neuropeptides produced and acting in the brain have the potential to decrease food intake and ameliorate obesity, but are ineffective after peripheral application, owing to a limited ability to cross the blood-brain barrier. We have designed lipidized analogs of prolactin-releasing peptide (PrRP), which is involved in energy balance regulation as demonstrated by obesity phenotypes of both Prrp-knockout and Prrp receptor-knockout mice. The aim of this study was to characterize the subchronic effect of a palmitoylated PrRP analog in two rat models of obesity and diabetes: diet-induced obese Sprague-Dawley rats and leptin receptor-deficient Zucker diabetic (ZDF) rats. In the rats with diet-induced obesity (DIO), a two-week intraperitoneal treatment with palmitoylated PrRP lowered food intake by 24% and body weight by 8%. This treatment also improved glucose tolerance and tended to decrease leptin levels and adipose tissue masses in a dose-dependent manner. In contrast, in ZDF rats, the same treatment with palmitoylated PrRP lowered food intake but did not significantly affect body weight or glucose tolerance, probably in consequence of severe leptin resistance due to a nonfunctional leptin receptor. Our data indicate a good efficacy of lipidized PrRP in DIO rats. Thus, the strong anorexigenic, body weight-reducing, and glucose tolerance-improving effects make palmitoylated PrRP an attractive candidate for anti-obesity treatment.

Effect of palmitoylated prolactin-releasing peptide on food intake and neural activation after different routes of peripheral administration in rats

Obesity is an escalating epidemic, but an effective non-invasive therapy is still scarce. For obesity treatment, anorexigenic neuropeptides are promising tools, but their delivery from the periphery to the brain is complicated by their peptide character. In order to overcome this unfavorable fact, we have applied the lipidization of neuropeptide prolactin-releasing peptide (PrRP), whose strong anorexigenic effect was demonstrated. A palmitoylated analog of human PrRP (h palm-PrRP31) was injected in free-fed Wistar rats by three routes: subcutaneous (s.c.), intraperitoneal (i.p) (both 5 mg/kg) and intravenous (i.v.) (from 0.01 to 0.5 mg/kg). We found a circulating compound in the blood after all three applications with the highest concentration after i.v. administration. This corresponds to the effect on food intake, which was also strongest after i.v. injection. Moreover, this is in agreement with the fact that the expression of c-Fos in specific brain regions involved in food intake regulation was also highest after intravenous application. Pharmacokinetic data are further supported by results obtained from dynamic light scattering and CD spectroscopy. Human palm-PrRP31 analog showed a strong tendency to micellize, and formation of aggregates suggested lower availability after i.p. or s.c. application. We have demonstrated that palm-PrRP influenced food intake even in free fed rats. Not surprisingly, the maximal effect was achieved after the intravenous application even though two orders of magnitude lower dose was used compared to both two other applications. We believe that palm-PrRP could have a potential as an antiobesity drug when its s.c. application would be improved.

Peripheral administration of palmitoylated prolactin-releasing peptide induces Fos expression in hypothalamic neurons involved in energy homeostasis in NMRI male mice

Energy homeostasis is the result of a balance between energy intake and expenditure, and the hypothalamus plays a key role in the regulation of these processes. The hypothalamic prolactin-releasing peptide (PrRP) is involved in food intake regulation and energy homeostasis, although only its lipidized analogs exert central anorexigenic effects after peripheral administration. The aim of the present study was to delineate the extent of the Fos expression as a marker of neuronal activation within the hypothalamic structures involved in food intake regulation after peripherally administered palmitoylated PrRP31 (palm-PrRP31) and to determine whether the anorexigenic effect of peripherally administered palm-PrRP31 influence the activity of hypocretin (HCRT) and oxytocin (OXY) neurons, i.e., the neuropeptides crucially involved in the regulation of energy homeostasis. The data confirmed an anorexigenic effect of palm-PrRP31 treatment (5mg/kg, s.c.) in mice. In the palm-PrRP31-treated animals, a significant increase in Fos expression was observed in the hypothalamic paraventricular (PVN), dorsomedial (DMN), and arcuate (Arc) nuclei and in the neurons of the nucleus of the solitary tract (NTS). Moreover, significant Fos expression was observed in the lateral hypothalamic area (LHA) HCRT neurons and PVN OXY neurons after palm-PrRP31 administration. The present findings may indicate that palm-PrRP31 may be involved in energy homeostasis via the activation of several hypothalamic structures. Fos activation of the hypothalamic OXY and HCRT neurons in the PVN and LHA emphasizes the importance of the areas mentioned in the central action of palm-PrRP31.

Strategy for NMR metabolomic analysis of urine in mouse models of obesity--from sample collection to interpretation of acquired data

The mouse model of monosodium glutamate induced obesity was used to examine and consequently optimize the strategy for analysis of urine samples by NMR spectroscopy. A set of nineteen easily detectable metabolites typical in obesity-related studies was selected. The impact of urine collection protocol, choice of (1)H NMR pulse sequence, and finally the impact of the normalization method on the detected concentration of selected metabolites were investigated. We demonstrated the crucial effect of food intake and diurnal rhythms resulting in the choice of a 24-hour fasting collection protocol as the most convenient for tracking obesity-induced increased sensitivity to fasting. It was shown that the Carr-Purcell-Meiboom-Gill (CPMG) experiment is a better alternative to one-dimensional nuclear Overhauser enhancement spectroscopy (1D-NOESY) for NMR analysis of mouse urine due to its ability to filter undesirable signals of proteins naturally present in rodent urine. Normalization to total spectral area provided comparable outcomes as did normalization to creatinine or probabilistic quotient normalization in the CPMG-based model. The optimized approach was found to be beneficial mainly for low abundant metabolites rarely monitored due to their overlap by strong protein signals.

Obesity-related hypertension: possible pathophysiological mechanisms

Hypertension is one of the major risk factors of cardiovascular diseases, but despite a century of clinical and basic research, the discrete etiology of this disease is still not fully understood. The same is true for obesity, which is recognized as a major global epidemic health problem nowadays. Obesity is associated with an increasing prevalence of the metabolic syndrome, a cluster of risk factors including hypertension, abdominal obesity, dyslipidemia, and hyperglycemia. Epidemiological studies have shown that excess weight gain predicts future development of hypertension, and the relationship between BMI and blood pressure (BP) appears to be almost linear in different populations. There is no doubt that obesity-related hypertension is a multifactorial and polygenic trait, and multiple potential pathogenetic mechanisms probably contribute to the development of higher BP in obese humans. These include hyperinsulinemia, activation of the renin-angiotensin-aldosterone system, sympathetic nervous system stimulation, abnormal levels of certain adipokines such as leptin, or cytokines acting at the vascular endothelial level. Moreover, some genetic and epigenetic mechanisms are also in play. Although the full manifestation of both hypertension and obesity occurs predominantly in adulthood, their roots can be traced back to early ontogeny. The detailed knowledge of alterations occurring in the organism of experimental animals during particular critical periods (developmental windows) could help to solve this phenomenon in humans and might facilitate the age-specific prevention of human obesity-related hypertension. In addition, better understanding of particular pathophysiological mechanisms might be useful in so-called personalized medicine.

Structural and functional study of the GlnB22-insulin mutant responsible for maturity-onset diabetes of the young

The insulin gene mutation c.137G>A (R46Q), which changes an arginine at the B22 position of the mature hormone to glutamine, causes the monogenic diabetes variant maturity-onset diabetes of the young (MODY). In MODY patients, this mutation is heterozygous, and both mutant and wild-type (WT) human insulin are produced simultaneously. However, the patients often depend on administration of exogenous insulin. In this study, we chemically synthesized the MODY mutant [GlnB22]-insulin and characterized its biological and structural properties. The chemical synthesis of this insulin analogue revealed that its folding ability is severely impaired. In vitro and in vivo tests showed that its binding affinity and biological activity are reduced (both approximately 20% that of human insulin). Comparison of the solution structure of [GlnB22]-insulin with the solution structure of native human insulin revealed that the most significant structural effect of the mutation is distortion of the B20-B23 β-turn, leading to liberation of the B chain C-terminus from the protein core. The distortion of the B20-B23 β-turn is caused by the extended conformational freedom of the GlnB22 side chain, which is no longer anchored in a hydrogen bonding network like the native ArgB22. The partially disordered [GlnB22]-insulin structure appears to be one reason for the reduced binding potency of this mutant and may also be responsible for its low folding efficiency in vivo. The altered orientation and flexibility of the B20-B23 β-turn may interfere with the formation of disulfide bonds in proinsulin bearing the R46Q (GlnB22) mutation. This may also have a negative effect on the WT proinsulin simultaneously biosynthesized in β-cells and therefore play a major role in the development of MODY in patients producing [GlnB22]-insulin.

Deficient hippocampal insulin signaling and augmented Tau phosphorylation is related to obesity- and age-induced peripheral insulin resistance: a study in Zucker rats

Background

Insulin signaling and Tau protein phosphorylation in the hippocampi of young and old obese Zucker fa/fa rats and their lean controls were assessed to determine whether obesity-induced peripheral insulin resistance and aging are risk factors for central insulin resistance and whether central insulin resistance is related to the pathologic phosphorylation of the Tau protein.

Results

Aging and obesity significantly attenuated the phosphorylation of the insulin cascade kinases Akt (protein kinase B, PKB) and GSK-3β (glycogen synthase kinase 3β) in the hippocampi of the fa/fa rats. Furthermore, the hyperphosphorylation of Tau Ser396 alone and both Tau Ser396 and Thr231 was significantly augmented by aging and obesity, respectively, in the hippocampi of these rats.

Conclusions

Both age-induced and obesity-induced peripheral insulin resistance are associated with central insulin resistance that is linked to hyperTau phosphorylation. Peripheral hyperinsulinemia, rather than hyperglycemia, appears to promote central insulin resistance and the Tau pathology in fa/fa rats.

Triazole GHS-R1a antagonists JMV4208 and JMV3002 attenuate food intake, body weight, and adipose tissue mass in mice

The only peripherally released orexigenic hormone, ghrelin, plays a key role in food intake and body weight regulation. Antagonizing the ghrelin receptor, GHS-R1a, represents a promising approach for anti-obesity therapy. In our study, two novel GHS-R1a antagonists JMV4208 and JMV3002, which are trisubstituted 1,2,4-triazoles, decreased food intake in fasted lean mice in a dose-dependent manner, with ED50 values of 5.25 and 2.05 mg/kg, respectively. Both compounds were stable in mouse blood, with half-lives of 90 min (JMV4208) and 60 min (JMV3002), and disappeared from the blood 8h after administration. Fourteen days of treatment with the ghrelin antagonists (20 mg/kg twice a day) decreased food intake, body weight and adipose tissue mass in mice with diet-induced obesity (DIO). These results are likely attributable to an impact on food intake reduction and an attenuated expression of the lipogenesis-promoting enzymes (acetyl-CoA carboxylase 1 in subcutaneous fat and fatty acid synthase in subcutaneous and intraperitoneal fat). The decrease in fat mass negatively impacted circulating leptin levels. These data suggest that JMV4208 and JMV3002 could be useful therapeutic agents for the treatment of obesity.

Changes in FGF21 serum concentrations and liver mRNA expression in an experimental model of complete lipodystrophy and insulin-resistant diabetes

Patients with obesity and type 2 diabetes often display high levels of the anti-diabetic factor fibroblast growth factor-21 (FGF21), suggesting that the overproduction of FGF21 may result from increased adiposity in an attempt by white adipose tissue (WAT) to counteract insulin resistance. However, the production of FGF21 diabetes in the absence of WAT has not been examined. In this study, we investigated the effects of lipodystrophy in A-ZIP F-1 mice on FGF21 production in relation to diabetes. A-ZIP F-1 mice displayed high FGF21 plasma levels resulting from enhanced FGF21 mRNA expression in the liver. Concomitant enhancement of FGF21 receptor (FGFR1) and glucose transporter 1 (GLUT-1) mRNA expression was observed in the muscles of A-ZIP F-1 mice. Furthermore, the activation of hypothalamic NPY and AgRP mRNA expression positively correlated with plasma levels of FGF21 but not active ghrelin. Our study demonstrates that an increased FGF21 plasma level in lipodystrophic A-ZIP F-1 mice results mainly from up-regulated liver production but does not suffice to overcome the lipodystrophy-induced severe type 2-diabetes and insulin resistance in the liver linked to the augmented liver fat deposition.