Amino Acids (v.45, #1)

The peripheral nervous system is connected with lymphoid organs through sensory nerves that mediate pain reflexes and may influence immune responses through the release of neuropeptides such as calcitonin gene-related peptide (CGRP). Local and systemic levels of CGRP increase rapidly during inflammatory responses. CGRP inhibits effector functions of various immune cells and dampens inflammation by distinct pathways involving the amplification of IL-10 production and/or the induction of the transcriptional repressor inducible cAMP early repressor (ICER). Thus, available evidence suggests that, in neuro-immunological interactions, CGRP mediates a potent peptidergic anti-inflammatory pathway.
Keywords: Neuro-immunological communication; Inflammatory disorders; CGRP; Sensory nerves; ICER; IL-10; Signal transduction

Endogenous opioids are synthesized in vivo to modulate pain mechanisms and inflammatory pathways. Endogenous and exogenous opioids mediate analgesia in response to painful stimuli by binding to opioid receptors on neuronal cells. However, wide distribution of opioid receptors on tissues and organ systems outside the CNS, such as the cells of the immune system, indicate that opioids are capable of exerting additional effects in the periphery, such as immunomodulation. The increased prevalence of infections in opioid abuser-based epidemiological studies further highlights the immunosuppressive effects of opioids. In spite of their many debilitating side effects, prescription opioids remain a gold standard for treatment of chronic pain. Therefore, given the prevalence of opioid use and abuse, opioid-mediated immune suppression presents a serious concern in our society today. It is imperative to understand the mechanisms by which exogenous opioids modulate immune processes. In this review, we will discuss the role of opioid receptors and their ligands in mediating immune-suppressive functions. We will summarize recent studies on direct and indirect opioid modulation of the cells of the immune system, as well as the role of opioids in exacerbation of certain disease states.
Keywords: Opioid; Opioid receptors; Immunosuppression; Morphine

Vasoactive intestinal peptide (VIP), a 28-amino acid neuropeptide/neurotransmitter, is widely distributed in both the central and peripheral nervous system. VIP is released by both neurons and immune cells. Various cell types, including immune cells, express VIP receptors. VIP has pleiotropic effects as a neurotransmitter, immune regulator, vasodilator and secretagogue. This review is focused on VIP production and effects on immune cells, VIP receptor signaling as related to immune functions, and the involvement of VIP in inflammatory and autoimmune disorders. The review addresses present clinical use of VIP and future therapeutic directions.
Keywords: Vasoactive intestinal peptide; Autoimmunity; Inflammation; Neuroinflammation; Neuropeptides/neurotransmitters

The intriguing mission of neuropeptide Y in the immune system by Mirjana Dimitrijević; Stanislava Stanojević (41-53).
For many years, the central nervous system and the immune system were considered two autonomous entities. However, extensive research in the field of neuroimmunomodulation during the past decades has demonstrated the presence of different neuropeptides and their respective receptors in the immune cells. More importantly, it has provided evidence for the direct effects of neuropeptides on the immune cell functions. Neuropeptide Y (NPY) is generally considered the most abundant peptide in the central and peripheral nervous system. However, it is also distinguished by exhibiting pleiotropic functions in many other physiological systems, including the immune system. NPY affects the functions of the cells of the adaptive and innate immunity. In this respect, NPY is known to modulate immune cell trafficking, T helper cell differentiation, cytokine secretion, natural killer cell activity, phagocytosis and the production of reactive oxygen species. The specific Y receptors have been found in immune cells, and their expression is amplified upon immune stimulation. Different Y receptor subtypes may mediate an opposite effect of NPY on the particular function, thus underlining its regulatory role. Since the immune cells are capable of producing NPY upon appropriate stimulation, this peptide can regulate immune cell functions in an autocrine/paracrine manner. NPY also has important implications in several immune-mediated disorders, which affirms the clear need for further investigation of its role in either the mechanisms of the disease development or its possible therapeutic capacity. This review summarises the key points of NPY’s mission throughout the immune system.
Keywords: Neuropeptide Y; Y receptors; Immune cells; Infection; Inflammation; Autoimmunity

Adrenergic modulation of immune cells: an update by Franca Marino; Marco Cosentino (55-71).
Sympathoadrenergic pathways are crucial to the communication between the nervous system and the immune system. The present review addresses emerging issues in the adrenergic modulation of immune cells, including: the specific pattern of adrenoceptor expression on immune cells and their role and changes upon cell differentiation and activation; the production and utilization of noradrenaline and adrenaline by immune cells themselves; the dysregulation of adrenergic immune mechanisms in disease and their potential as novel therapeutic targets. A wide array of sympathoadrenergic therapeutics is currently used for non-immune indications, and could represent an attractive source of non-conventional immunomodulating agents.
Keywords: Noradrenaline; Adrenaline; Adrenoceptors; Immune cells; Human disease

Research done in the past years pointed to a novel function of cholinergic transmission. It has been shown that cholinergic transmission can modulate various aspects of the immune function, whether innate or adaptive. Cholinergic transmission affects immune cell proliferation, cytokine production, T helper differentiation and antigen presentation. Theses effects are mediated by cholinergic muscarinic and nicotinic receptors and other cholinergic components present in immune cells, such as acetylcholinesterase (AChE) and cholineacetyltransferase. The α7 nicotinic acetylcholine receptor was designated anti-inflammatory activity and has shown promise in pre-clinical models of inflammatory disorders. We herein describe the various components of the immune cholinergic system, and specifically the immune suppressive effects of α7 activation. This activation can be accomplished either by direct stimulation or indirectly, by inhibition of AChE. Thus, the presence of the immune cholinergic system can pave the way for novel immunomodulatory agents, or to the broadening of use of known cholinergic agents.
Keywords: Multiple sclerosis; Myasthenia gravis; Neuroinflammation ; Acetylcholinesterase inhibitors; α7 nicotinic acetylcholine receptor

GABA is an effective immunomodulatory molecule by Zhe Jin; Suresh Kumar Mendu; Bryndis Birnir (87-94).
In recent years, it has become clear that there is an extensive cross-talk between the nervous and the immune system. Somewhat surprisingly, the immune cells themselves do express components of the neuronal neurotransmitters systems. What role the neurotransmitters, their ion channels, receptors and transporters have in immune function and regulation is an emerging field of study. Several recent studies have shown that the immune system is capable of synthesizing and releasing the classical neurotransmitter GABA (γ-aminobutyric acid). GABA has a number of effects on the immune cells such as activation or suppression of cytokine secretion, modification of cell proliferation and GABA can even affect migration of the cells. The immune cells encounter GABA when released by the immune cells themselves or when the immune cells enter the brain. In addition, GABA can also be found in tissues like the lymph nodes, the islets of Langerhans and GABA is in high enough concentration in blood to activate, e.g., GABA-A channels. GABA appears to have a role in autoimmune diseases like multiple sclerosis, type 1 diabetes, and rheumatoid arthritis and may modulate the immune response to infections. In the near future, it will be important to work out what specific effects GABA has on the function of the different types of immune cells and determine the underlying mechanisms. In this review, we discuss some of the recent findings revealing the role of GABA as an immunomodulator.
Keywords: GABA; GABA-A; Neurotransmitter; Immunomodulation; Autoimmune disease; Immune cells

Studies of the last 40 years have brought to light an important physiological network, the endocannabinoid system. Endogenous and exogenous cannabinoids mediate their effects through activation of specific cannabinoid receptors. This modulatory homoeostatic system operates in the regulation of brain function and also in the periphery. The cannabinoid system has been shown to be involved in regulating the immune system. Studies examining the effect of cannabinoid-based drugs on immunity have shown that many cellular and cytokine mechanisms are modulated by these agents, thus raising the hypothesis that these compounds may be of value in the management of chronic inflammatory diseases. The special properties of endocannabinoids as neurotransmitters, their pleiotropic effects and the impact on immune function show that the endocannabinoid system represents a revolving plate of neural and immune interactions. In this paper, we outline current information on immune effects of cannabinoids in health and disease.
Keywords: Endocannabinoid system; Immune cells; Cannabinoids; Immunomodulation

Functional implications of hippocampal adult neurogenesis in intellectual disabilities by Meritxell Pons-Espinal; Maria Martinez de Lagran; Mara Dierssen (113-131).
The development of strategies capable to promote nervous system plasticity in adulthood is nowadays an important aim in neuroscience to improve not only cognitive abilities but also to ameliorate pathological dysfunctions. Several studies have demonstrated that adult neurogenesis is regulated by many physiological and pathological stimuli at almost every stage, from proliferation of neuronal precursors until integration and activation of newly formed neurons in the preexisting network. We review the process of generating functional neurons from precursors in the adult brain and its implications in intellectual disability disorders.

Extracellular glutamate should be maintained at low levels to conserve optimal neurotransmission and prevent glutamate neurotoxicity in the brain. Excitatory amino acid transporters (EAATs) play a pivotal role in removing extracellular glutamate in the central nervous system (CNS). Excitatory amino acid carrier 1 (EAAC1) is a high-affinity Na+-dependent neuronal EAAT that is ubiquitously expressed in the brain. However, most glutamate released in the synapses is cleared by glial EAATs, but not by EAAC1 in vivo. In the CNS, EAAC1 is widely distributed in somata and dendrites but not in synaptic terminals. The contribution of EAAC1 to the control of extracellular glutamate levels seems to be negligible in the brain. However, EAAC1 can transport not only extracellular glutamate but also cysteine into the neurons. Cysteine is an important substrate for glutathione (GSH) synthesis in the brain. GSH has a variety of neuroprotective functions, while its depletion induces neurodegeneration. Therefore, EAAC1 might exert a critical role for neuroprotection in neuronal GSH metabolism rather than glutamatergic neurotransmission, while EAAC1 dysfunction would cause neurodegeneration. Despite the potential importance of EAAC1 in the brain, previous studies have mainly focused on the glutamate neurotoxicity induced by glial EAAT dysfunction. In recent years, however, several studies have revealed regulatory mechanisms of EAAC1 functions in the brain. This review will summarize the latest information on the EAAC1-regulated neuroprotective functions in the CNS.
Keywords: Glutathione; Cysteine uptake; EAAC1; GTRAP3-18; Neurodegeneration

Panurgines, novel antimicrobial peptides from the venom of communal bee Panurgus calcaratus (Hymenoptera: Andrenidae) by Sabína Čujová; Jiřina Slaninová; Lenka Monincová; Vladimír Fučík; Lucie Bednárová; Jitka Štokrová; Oldřich Hovorka; Zdeněk Voburka; Jakub Straka; Václav Čeřovský (143-157).
Three novel antimicrobial peptides (AMPs), named panurgines (PNGs), were isolated from the venom of the wild bee Panurgus calcaratus. The dodecapeptide of the sequence LNWGAILKHIIK-NH2 (PNG-1) belongs to the category of α-helical amphipathic AMPs. The other two cyclic peptides containing 25 amino acid residues and two intramolecular disulfide bridges of the pattern Cys8–Cys23 and Cys11–Cys19 have almost identical sequence established as LDVKKIICVACKIXPNPACKKICPK-OH (X=K, PNG-K and X=R, PNG-R). All three peptides exhibited antimicrobial activity against Gram-positive bacteria and Gram-negative bacteria, antifungal activity, and low hemolytic activity against human erythrocytes. We prepared a series of PNG-1 analogs to study the effects of cationicity, amphipathicity, and hydrophobicity on the biological activity. Several of them exhibited improved antimicrobial potency, particularly those with increased net positive charge. The linear analogs of PNG-K and PNG-R having all Cys residues substituted by α-amino butyric acid were inactive, thus indicating the importance of disulfide bridges for the antimicrobial activity. However, the linear PNG-K with all four cysteine residues unpaired, exhibited antimicrobial activity. PNG-1 and its analogs induced a significant leakage of fluorescent dye entrapped in bacterial membrane-mimicking large unilamellar vesicles as well as in vesicles mimicking eukaryotic cell membrane. On the other hand, PNG-K and PNG-R exhibited dye-leakage activity only from vesicles mimicking bacterial cell membrane.
Keywords: Antimicrobial peptides; Wild bee venom; CD spectroscopy; Large unilamellar vesicles; Electron microscopy

Photophysics of novel coumarin-labeled depsipeptides in solution: sensing interactions with SDS micelle via TICT model by Suvendu Biswas; Ilker Avan; Akash K. Basak; Nader E. Abo-Dya; Abdullah Asiri; Alan R. Katritzky (159-170).
N-Acylbenzotriazoles enable the synthesis (6992 % yield) of blue to green fluorescent coumarin-labeled depsidipeptides 8a–f (quantum yields 0.0040.97) and depsitripeptides 12a–d (quantum yields 0.020.96). Detailed photophysical studies of fluorescent coumarin-labeled depsipeptides 8a–f and 12a–d are reported for both polar protic and polar aprotic solvents. 7-Methoxy and 7-diethylaminocoumarin-3-ylcarbonyl depsipeptides 8c,f and 12d are highly solvent sensitive. These highly fluorescent compounds could be useful for peptide assays. Further photophysical studies of 7-diethylaminocoumarin-labeled depsipeptides 8c,12d within the micellar microenvironment of SDS reflect their ability to bind with the biological membrane, suggesting potential applications in the fields of bio- and medicinal chemistry.
Keywords: Coumarin; Peptidomimetics; Depsipeptides; SDS; Micelle; TICT

Side-effects of analgesic kyotorphin derivatives: advantages over clinical opioid drugs by Marta M. B. Ribeiro; Sónia Sá Santos; David S. C. Sousa; Margarida Oliveira; Sara M. Santos; Montserrat Heras; Eduard Bardaji; Isaura Tavares; Miguel A. R. B. Castanho (171-178).
The adverse side-effects associated with opioid administration restrain their use as analgesic drugs and call for new solutions to treat pain. Two kyotorphin derivatives, kyotorphin-amide (KTP–NH2) and ibuprofen–KTP–NH2 (IbKTP–NH2) are promising alternatives to opioids: they trigger analgesia via an indirect opioid mechanism and are highly effective in several pain models following systemic delivery. In vivo side-effects of KTP–NH2 and IbKTP–NH2 are, however, unknown and were evaluated in the present study using male adult Wistar rats. For comparison purposes, morphine and tramadol, two clinically relevant opioids, were also studied. Results showed that KTP-derivatives do not cause constipation after systemic administration, in contrast to morphine. Also, no alterations were observed in blood pressure or in food and water intake, which were only affected by tramadol. A reduction in micturition was detected after KTP–NH2 or tramadol administrations. A moderate locomotion decline was detected after IbKTP–NH2-treatment. The side-effect profile of KTP–NH2 and IbKTP–NH2 support the existence of opioid-based mechanisms in their analgesic actions. The conjugation of a strong analgesic activity with the absence of the major side-effects associated to opioids highlights the potential of both KTP–NH2 and IbKTP–NH2 as advantageous alternatives over current opioids.
Keywords: Kyotorphin; Analgesic peptides; Opioids; Side-effects; Morphine; Constipation

Efficacy of l-proline administration on the early responses during cutaneous wound healing in rats by Thangavel Ponrasu; Sankar Jamuna; Arulanandham Mathew; Karuppanan Natarajan Madhukumar; Moorthy Ganeshkumar; Kuttalam Iyappan; Lonchin Suguna (179-189).
Proline (Pro) plays a versatile role in cell metabolism and physiology. Pro and hydroxypro are major imino acids present in collagen, an important connective tissue protein, essential for wound healing, which is a primary response to tissue injury. This study explains the role of l-pro on cutaneous wound healing in rats when administered both topically and orally. Open excision wounds were made on the back of rats, and 200 μl (200 mg) of pro was administered topically and orally once daily to the experimental rats until the wounds healed completely. The control wounds were left untreated. Granulation tissues formed were removed after day 4 and 8 of post excision wounding, and biochemical parameters such as total protein, collagen, hexosamine, and uronic acid were estimated. Levels of enzymatic and non-enzymatic antioxidants such as catalase, superoxide dismutase, glutathione peroxidase, ascorbic acid, and reduced glutathione were evaluated along with lipid peroxides in the granulation tissues. Tensile strength and period of epithelialization were also measured. It was observed that the treated wounds healed very fast as evidenced by augmented rates of epithelialization and wound contraction, which was also confirmed by histological examinations. The results strappingly authenticate the beneficial effects of the topical administration of l-proline in the acceleration of wound healing than the oral administration and control.
Keywords: l-Proline; Collagen; Excision wound; Tensile strength; Epithelialization

An amino acid mixture improves glucose tolerance and lowers insulin resistance in the obese Zucker rat by Jeffrey R. Bernard; Yi-Hung Liao; Zhenping Ding; Daisuke Hara; Maximilian Kleinert; Jeffrey L. Nelson; John L. Ivy (191-203).
The purpose of this investigation was to test an amino acid mixture on glucose tolerance in obese Zucker rats [experiment (Exp)-1] and determine whether differences in blood glucose were associated with alterations in muscle glucose uptake [experiment (Exp)-2]. Exp-1 rats were gavaged with either carbohydrate (OB-CHO), carbohydrate plus amino acid mixture (OB-AA-1), carbohydrate plus amino acid mixture with increased leucine concentration (OB-AA-2) or water (OB-PLA). The glucose response in OB-AA-1 and OB-AA-2 were similar, and both were lower compared to OB-CHO. This effect of the amino acid mixtures did not appear to be solely attributable to an increase in plasma insulin. Rats in Exp-2 were gavaged with carbohydrate (OB-CHO), carbohydrate plus amino acid mixture (OB-AA-1) or water (OB-PLA). Lean Zuckers were gavaged with carbohydrate (LN-CHO). Fifteen minutes after gavage, a radiolabeled glucose analog was infused through a catheter previously implanted in the right jugular vein. Blood glucose was significantly lower in OB-AA-1 compared to OB-CHO while the insulin responses were similar. Glucose uptake was greater in OB-AA-1 compared with OB-CHO, and similar to that in LN-CHO in red gastrocnemius muscle (5.15 ± 0.29, 3.8 ± 0.27, 5.18 ± 0.34 µmol/100 g/min, respectively). Western blot analysis showed that Akt substrate of 160 kDa (AS160) phosphorylation was enhanced for OB-AA-1 and LN-CHO compared to OB-CHO. These findings suggest that an amino acid mixture improves glucose tolerance in an insulin resistant model and that these improvements are associated with an increase in skeletal muscle glucose uptake possibly due to improved intracellular signaling.
Keywords: Oral glucose tolerance test; Isoleucine; Leucine; Akt substrate of 160 kDa (AS160); Skeletal muscle