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-Met-enkephalin is a neuropeptide known to exert protective effects in various experimental models of autoimmune and inflammatory diseases. These effects are mediated through opioid receptors and can be abolished by the opioid receptor antagonist naltrexone. Investigation of peptide enantiomerism and the incorporation of d-amino acids are crucial for designing novel peptides with altered structural and biological properties compared with their native l-forms. Since no data are currently available on the properties or biological activity of the d-Met-enkephalin enantiomer, we evaluated its hepatoprotective potential in a mouse model of acetaminophen-induced hepatotoxicity. Male CBA mice were treated with d-Met-enkephalin, and hepatoprotection was assessed by measuring plasma alanine aminotransferase (ALT) and aspartate amino-transferase (AST) activities, along with histological liver necrosis scores. The peptide’s secondary structure and antisense peptide binding were analysed using circular dichroism and fluorescence spectroscopy, respectively. -Met-enkephalin demonstrated dose-dependent hepatoprotective effects within the range of 0.5–20 mg kg–1, with maximal protection observed at 5 mg kg , a dose comparable to that of the l-enantiomer (7.5 mg kg ). This preservation of biological activity may be attributed to the presence of the achiral amino acid glycine at positions 2 and 3, which maintains the functional conformation of the d-enantiomer. The role of opioid receptor involvement was further examined through direct receptor blockade using naltrexone and indirect inhibition with the antisense peptide IPPKY.

Group 2 innate lymphoid cells are shown to have a critical role in energy homeostasis by producing methionine-enkephalin peptides in response to interleukin 33, thus promoting the beiging of white adipose tissue; increased numbers of beige (also known as brown-like or brite) fat cells in white adipose tissue leads to increased energy expenditure and decreased adiposity. Innate lymphoid cells drive energy up, adiposity down The immune system is now thought to be involved in the development of obesity, together with genetic and environmental factors. Recent research identified group 2 innate lymphoid cells (ILC2s) in adipose tissue as a factor in the development of obesity in mice. David Artis and colleagues show here that ILC2s play a critical role in energy homeostasis by producing methionine-enkephalin peptides in response to interleukin-33. This promotes the emergence of beige adipocytes, a specialized adipocyte population arising from white adipose tissue. This 'beiging' process leads to increased energy expenditure and decreased adiposity. Obesity is an increasingly prevalent disease regulated by genetic and environmental factors. Emerging studies indicate that immune cells, including monocytes, granulocytes and lymphocytes, regulate metabolic homeostasis and are dysregulated in obesity 1 , 2 . Group 2 innate lymphoid cells (ILC2s) can regulate adaptive immunity 3 , 4 and eosinophil and alternatively activated macrophage responses 5 , and were recently identified in murine white adipose tissue (WAT) 5 where they may act to limit the development of obesity 6 . However, ILC2s have not been identified in human adipose tissue, and the mechanisms by which ILC2s regulate metabolic homeostasis remain unknown. Here we identify ILC2s in human WAT and demonstrate that decreased ILC2 responses in WAT are a conserved characteristic of obesity in humans and mice. Interleukin (IL)-33 was found to be critical for the maintenance of ILC2s in WAT and in limiting adiposity in mice by increasing caloric expenditure. This was associated with recruitment of uncoupling protein 1 (UCP1) + beige adipocytes in WAT, a process known as beiging or browning that regulates caloric expenditure 7 , 8 , 9 . IL-33-induced beiging was dependent on ILC2s, and IL-33 treatment or transfer of IL-33-elicited ILC2s was sufficient to drive beiging independently of the adaptive immune system, eosinophils or IL-4 receptor signalling. We found that ILC2s produce methionine-enkephalin peptides that can act directly on adipocytes to upregulate Ucp1 expression in vitro and that promote beiging in vivo . Collectively, these studies indicate that, in addition to responding to infection or tissue damage, ILC2s can regulate adipose function and metabolic homeostasis in part via production of enkephalin peptides that elicit beiging.

Enkephalins are endogenous opioid pentapeptides that play a role in neurotransmission and pain modulation in vertebrates. However, the distribution pattern of enkephalinergic neurons in the brains of reptiles has been understudied. This study reports the organization of the methionine-enkephalin (M-ENK) and leucine-enkephalin (L-ENK) neuronal systems in the central nervous system of the gecko Hemidactylus frenatus using an immunofluorescence labeling method. Although M-ENK and L-ENK-immunoreactive (ir) fibers extended throughout the pallial and subpallial subdivisions, including the olfactory bulbs, M-ENK and L-ENK-ir cells were found only in the dorsal septal nucleus. Enkephalinergic perikarya and fibers were highly concentrated in the periventricular and lateral preoptic areas, as well as in the anterior and lateral subdivisions of the hypothalamus, while enkephalinergic innervation was observed in the hypothalamic periventricular nucleus, infundibular recess nucleus and median eminence. The dense accumulation of enkephalinergic content was noticed in the pars distalis of the hypophysis. In the thalamus, the nucleus rotundus and the dorsolateral, medial, and medial posterior thalamic nuclei contained M-ENK and L-ENK-ir fibers, whereas clusters of M-ENK and L-ENK-ir neurons were observed in the pretectum, mesencephalon, and rhombencephalon. The enkephalinergic fibers were also seen in the area X around the central canal, as well as the dorsal and ventral horns. The widespread distribution of enkephalin-containing neurons within the central nervous system implies that enkephalins regulate a variety of functions in the gecko, including sensory, behavioral, hypophysiotropic, and neuroendocrine functions.

Enkephalins are opioid peptides that modulate analgesia, reward, and stress. In vivo detection of enkephalins remains difficult due to transient and low endogenous concentrations and inherent sequence similarity. To begin to address this, we previously developed a system combining in vivo optogenetics with microdialysis and a highly sensitive mass spectrometry-based assay to measure opioid peptide release in freely moving rodents (Al-Hasani et al., 2018, eLife). Here, we show improved detection resolution and stabilization of enkephalin detection, which allowed us to investigate enkephalin release during acute stress. We present an analytical method for real-time, simultaneous detection of Met- and Leu-enkephalin (Met-Enk and Leu-Enk) in the mouse nucleus accumbens shell (NAcSh) after acute stress. We confirm that acute stress activates enkephalinergic neurons in the NAcSh using fiber photometry and that this leads to the release of Met- and Leu-Enk. We also demonstrate the dynamics of Met- and Leu-Enk release as well as how they correlate to one another in the ventral NAc shell, which was previously difficult due to the use of approaches that relied on mRNA transcript levels rather than posttranslational products. This approach increases spatiotemporal resolution, optimizes the detection of Met-Enk through methionine oxidation, and provides novel insight into the relationship between Met- and Leu-Enk following stress.

The Diabetes and Antenatal Milk Expressing (DAME) randomised controlled trial (RCT) was conducted in 2011–2015, at six sites in Melbourne, Australia to explore the effect of advising women with diabetes in pregnancy to express breast milk from 36 weeks gestation. Infants whose mothers were randomised to express in pregnancy were more likely to be exclusively breast milk fed during their hospital stay, and there was no evidence of harm. This paper explores women's views and experiences of antenatal expressing. In this two‐arm RCT, 635 women with diabetes in pregnancy who were otherwise of low medical risk were randomised at 36–37 weeks gestation to usual care (not expressing, n = 316), or the intervention, where women were advised to hand express for 10 min twice daily until birth (n = 319). Semistructured face‐to‐face interviews were conducted with 10 women who expressed antenatally. They were asked about their experiences of antenatal expressing, including how they felt about the overall experience, the amount of breast milk they expressed, making time to express, and their experience of breastfeeding. Thematic analysis of the in‐depth interviews identified six themes: (1) learning and adapting expressing, (2) feelings and sensations associated with expressing, (3) support, (4) dis/empowerment, (5) health, and (6) the value of breast milk. Women had both positive and negative experiences of antenatal expressing. If health professionals are advising antenatal expressing to women, it is important they understand the range of outcomes and experiences. Key messages Women's experiences of antenatal expressing were both positive and negative; it is important to understand the range of experiences. Women should be advised that some women express little or no breast milk antenatally and therefore be reassured if they are concerned. For women with diabetes in pregnancy, their diabetes management is a significant time burden, and should be considered when discussing antenatal expressing with women. Maternity care providers need to follow‐up with pregnant women advised to express, to provide education, reassurance, and reassess expressing techniques. Maternity care providers need to manage and prioritise the use of expressed breast milk.

The objective of this study was to evaluate the effect of low-dose naltrexone (LDN) as a carboplatin chemotherapy-associated drug in female dogs with mammary carcinoma in benign mixed tumors (MC-BMT) after mastectomy and to assess its association with quality of life and survival rates. Sixty female dogs were included in this study, all of which had histopathological diagnosis of MC-BMT and were divided into three groups: G1 (control), consisting of animals submitted only to mastectomy with or without regional metastasis; G2, composed of treated animals that did not present with metastasis; and G3, treated dogs that presented with metastasis. G2 and G3 were also subdivided according to the treatment administered: chemotherapy alone (MC-BMT(-) C/MC-BMT(+) C) or LDN and chemotherapy (MC-BMT(-) C+LDN/MC-BMT(+) C+LDN). All animals were subjected to clinical evaluation, mastectomy, peripheral blood lymphocyte immunophenotyping, beta-endorphin and met-enkephalin quantification, and evaluation of survival rates and quality of life scores. The results showed higher serum concentrations of beta-endorphin and met-enkephalin, fewer chemotherapy-related side effects, and better quality of life and survival rates in the LDN-treated groups than in LDN-untreated groups (P < 0.05). Evaluation of clinical and pathological parameters indicated a significant association between the use of LDN and both prolonged survival and enhanced quality of life. These results indicate that LDN is a viable chemotherapy-associated treatment in female dogs with MC-BMT, maintaining their quality of life and prolonging survival rates.

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a newly identified tick-borne virus with a high case fatality rate. Currently, no specific antiviral drugs are available for its treatment. Methionine enkephalin (MENK) has the ability to enhance immune cell function nonspecifically. This study investigated the mechanism by which MENK regulates macrophages to exert antiviral effects against SFTSV infection. An SFTSV-infected RAW264.7 macrophage model pretreated with MENK was developed. RNA sequencing was employed to analyze transcriptomic alterations and identify differentially expressed genes (DEGs). Subsequent experimental validation based on bioinformatics analysis was performed on key DEGs. The DEGs between the MENK-SFTSV and SFTSV groups were mainly enriched in several signaling pathways, including the Toll-like receptor (TLR) signaling pathway (ko04620), IL-17 signaling pathway (ko04657), TNF signaling pathway (ko04668), and interaction between viral proteins and cytokines and their receptors (ko04061). Key genes included TLR7, TLR3, TLR8, TLR9, activator protein-1 (AP-1), IL-17RA, TNF-α, IL-1β, CCR5, and CXCL10, all of which successfully docked with the MENK molecule. Compared with the TLR7 agonist imiquimod (IMQ), MENK demonstrated a greater advantage in modulating macrophages to resist SFTSV infection. MENK and the TLR7 agonist imiquimod can upregulate the expressions of TLR7, TLR3, AP-1, and IL-17RA. In addition, MENK significantly upregulated the levels of TLR9, TLR8, IL-1β, TNF-α, CCR5, and CXCL10. MENK upregulated the expression levels of the pattern recognition receptors and cytokine receptors; promoted the nuclear transcription to modulate cellular immune responses; and increased the levels of the cytokines to induce inflammatory responses against SFTSV infection. Notably, MENK possessed unique advantages and exhibited efficacy comparable to IMQ in restoring antiviral immunity, suggested that MENK emerged as a promising host-directed therapeutic candidate or vaccine prototype against SFTSV infection, warranting further preclinical and clinical investigation.

Quercetin and resveratrol are polyphenolic compounds, members of the flavonoid and the stilbene family, respectively, both medicinally important as dietary anticancer and antioxidant agents. They are present in a variety of foods—including fruits, vegetables, tea, wine, as well as other dietary supplements—and are responsible for various health benefits. Different quercetin and resveratrol esters of Leu/Met-enkephalin and tetrapeptide Leu-Ser-Lys-Leu (LSKL) were synthesized as model systems for monitoring the influence of the peptides on biological activity of resveratrol and quercetin. General formula of the main peptidyl-quercetin derivatives is 2-[3-(aa)n-4-hydroxyphenyl]-3,5,7-tri-hydroxy-4H-1-benzopyran-4-on, and the general formula of the main peptidyl-resveratrol derivatives is (E)-5-[4-(aa)n)styryl]benzene-1,3-diol. The antioxidant and anticancer activities of prepared compounds were investigated. Significant anticancer activity was obtained for the LSKL-based both quercetin and resveratrol derivatives. All prepared compounds exhibit antioxidant activity, in particular quercetin derivative containing Met-enkephalin.

To evaluate the impact of slow-tempo music listening periods in mechanically ventilated intensive care unit patients. A randomized crossover study was performed in a 16-bed, adult critical care unit at a tertiary care hospital. Still-sedated patients, mandating at least 3 more days of mechanical ventilation, were included. The intervention consisted in two 1-hour daily periods of music-vs-sham-MP3 listening which were performed on Day 1 or 3 post-inclusion, with a Day 2 wash-out. “Before-after” collection of vital signs, recording of daily sedative drug consumption and measurement of stress and inflammatory blood markers were performed. Of 55 randomized patients, 49 were included in the final analyses. Along with music listening, (i) vital signs did not consistently change, whereas narcotic consumption tended to decrease to a similar sedation (P = .06 vs sham-MP3); (ii) cortisol and prolactin blood concentrations decreased, whereas Adreno Cortico Trophic Hormone (ACTH)/cortisol ratio increased (P = .02; P = .038; and P = .015 vs sham-MP3, respectively), (iii) cortisol responders exhibited reversed associated changes in blood mehionine (MET)-enkephalin content (P = .01). In the present trial, music listening is a more sensitive stress-reliever in terms of biological vs clinical response. The hypothalamus-pituitary adrenal axis stress axis is a quick sensor of music listening in responding mechanically ventilated intensive care unit patients, through a rapid reduction in blood cortisol.

Rat sialorphin (Gln-His-Asn-Pro-Arg) is a natural blocker of neprilysin (NEP) that belongs to the family of endogenous opioid peptide-degrading enzymes. Studies have confirmed the efficiency of sialorphin in blocking the activity of NEP, both in vitro and in vivo. It has been demonstrated that this inhibitor has a strong analgesic, anti-inflammatory, immunological and metabolic effect either directly or indirectly by affecting the level of Met/Leu-enkephalins. In this work, sialorphin and their 12 analogues were synthesised using the solid-phase method. The effect of the peptides on the degradation of Met-enkephalin by NEP and metabolic degradation in human plasma was investigated in vitro. We show that the change in the N-terminal amino acid configuration from l to d in almost all peptides, except d-Arg-His-Asn-Pro-Arg (peptide XI), led to the abolition of their inhibitory activity. With molecular modelling technique we explained the structural properties of the l and d-arginine located on the N-terminal part of the peptide. The detailed analysis of the protein binding pocket allowed us to explain why d-arginine is so unique among all d residues. Peptide XI showed the highest stability among the tested peptides in human plasma. For instance sialorphin after a 2-hour incubation in human plasma was almost completely decomposed, while the level of peptide XI dropped to 45% after 48 h under these conditions.