Angiotensin-(1-7)/Mas receptor as an antinociceptive agent in cancer-induced bone pain

Current understanding of the link between angiotensin-converting enzyme and pain perception

The renin-angiotensin system (RAS) is known to affect diverse physiological processes that affect the functioning of many key organs. Angiotensin-converting enzyme (ACE) modulates a variety of bioactive peptides associated with pain. ACE inhibitors (ACEis) have found applications in the treatment of cardiovascular, kidney, neurological and metabolic disorders. However, ACEis also tend to display undesirable effects, resulting in increased pain sensitization and mechanical allodynia. In this review, we provide comprehensive discussion of preclinical and clinical studies involving the evaluation of various clinically approved ACEis. With the emerging knowledge of additional factors involved in RAS signaling and the indistinct pharmacological role of ACE substrates in pain, extensive studies are still required to elucidate the mechanistic role of ACE in pain perception.

Regulation of vascular angiotensin II type 1 and type 2 receptor and angiotensin-(1-7)/MasR signaling in normal and hypertensive pregnancy

Normal pregnancy (Norm-Preg) is associated with a slight reduction in blood pressure (BP) and decreased BP response to vasoconstrictor stimuli such as angiotensin II (Ang II), although the renin-angiotensin-aldosterone system (RAAS) is upregulated. Preeclampsia (PE) is a complication of pregnancy manifested as hypertension-in-pregnancy (HTN-Preg), and dysregulation of angiotensin biosynthesis and signaling have been implicated. Ang II activates vascular Ang II type-1 receptor (AT1R) and Ang II type-2 receptor (AT2R), while angiotensin-(1-7) promotes Ang-(1-7)/MasR signaling. The role of AT1R in vasoconstriction and the activated cellular mechanisms are well-characterized. The sensitivity of vascular AT1R to Ang II and consequent activation of vasoconstrictor mechanisms decrease during Norm-Preg, but dramatically increase in HTN-Preg. Placental ischemia in late pregnancy could also initiate the release of AT1R agonistic autoantibodies (AT1AA) with significant impact on endothelial dysfunction and activation of contraction pathways in vascular smooth muscle including [Ca2+]c and protein kinase C. On the other hand, the role of AT2R and Ang-(1-7)/MasR in vascular relaxation, particularly during Norm-Preg and PE, is less clear. During Norm-Preg, increases in the expression/activity of vascular AT2R and Ang-(1-7)/MasR promote the production of endothelium-derived relaxing factors such as nitric oxide (NO), prostacyclin and endothelium-derived hyperpolarizing factor leading to generalized vasodilation. Aortic segments of Preg rats show prominent endothelial AT2R staining and increased relaxation and NO production in response to AT2R agonist CGP42112A, and treatment with AT2R antagonist PD123319 enhances phenylephrine-induced contraction. Decreased vascular AT2R and Ang-(1-7)/MasR expression and receptor-mediated mechanisms of vascular relaxation have been suggested in HTN-Preg animal models, but their role in human PE needs further testing. Changes in angiotensin-converting enzyme-2 (ACE2) have been observed in COVID-19 patients, and whether ACE2 influences the course of COVID-19 viral infection/immunity in Norm-Preg and PE is an intriguing area for research.

PNA6, a Lactosyl Analogue of Angiotensin-(1-7), Reverses Pain Induced in Murine Models of Inflammation, Chemotherapy-Induced Peripheral Neuropathy, and Metastatic Bone Disease

Pain is the most significant impairment and debilitating challenge for patients with bone metastasis. Therefore, the primary objective of current therapy is to mitigate and prevent the persistence of pain. Thus, cancer-induced bone pain is described as a multifaceted form of discomfort encompassing both inflammatory and neuropathic elements. We have developed a novel non-addictive pain therapeutic, PNA6, that is a derivative of the peptide Angiotensin-(1-7) and binds the Mas receptor to decrease inflammation-related cancer pain. In the present study, we provide evidence that PNA6 attenuates inflammatory, chemotherapy-induced peripheral neuropathy (CIPN) and cancer pain confined to the long bones, exhibiting longer-lasting efficacious therapeutic effects. PNA6, Asp-Arg-Val-Tyr-Ile-His-Ser-(O-β-Lact)-amide, was successfully synthesized using solid phase peptide synthesis (SPPS). PNA6 significantly reversed inflammatory pain induced by 2% carrageenan in mice. A second murine model of platinum drug-induced painful peripheral neuropathy was established using oxaliplatin. Mice in the oxaliplatin-vehicle treatment groups demonstrated significant mechanical allodynia compared to the oxaliplatin-PNA6 treatment group mice. In a third study modeling a complex pain state, E0771 breast adenocarcinoma cells were implanted into the femur of female C57BL/6J wild-type mice to induce cancer-induced bone pain (CIBP). Both acute and chronic dosing of PNA6 significantly reduced the spontaneous pain behaviors associated with CIBP. These data suggest that PNA6 is a viable lead candidate for treating chronic inflammatory and complex neuropathic pain.

Angiotensin-Related Peptides and Their Role in Pain Regulation

Angiotensin (Ang)-generating system has been confirmed to play an important role in the regulation of fluid balance and blood pressure and is essential for the maintenance of biological functions. Ang-related peptides and their receptors are found throughout the body and exhibit diverse physiological effects. Accordingly, elucidating novel physiological roles of Ang-generating system has attracted considerable research attention worldwide. Ang-generating system consists of the classical Ang-converting enzyme (ACE)/Ang II/AT1 or AT2 receptor axis and the ACE2/Ang (1-7)/MAS1 receptor axis, which negatively regulates AT1 receptor-mediated responses. These Ang system components are expressed in various tissues and organs, forming a local Ang-generating system. Recent findings indicate that changes in the expression of Ang system components under pathological conditions are involved in the development of neuropathy, inflammation, and their associated pain. Here, we summarized the effects of changes in the Ang system on pain transmission in various organs and tissues involved in pain development process.

Screening of potential pain genes in pancreatic ductal adenocarcinoma (PDAC) based on bioinformatics methods

Background

We aimed to identify cancer pain genes in pancreatic ductal adenocarcinoma (PDAC) using bioinformatic tools to provide evidence for pain treatment in PDAC patients.

Methods

The GSE50570 data were obtained from the high-throughput Gene Expression Omnibus (GEO) database and subsequently analyzed. A volcano map, principal component analysis (PCA) map, box plot, and heat map were drawn, and a Venn diagram was constructed by comparison with human secreted histone genes. The differentially expressed secreted histone genes in PDAC were obtained. Then, Gene Ontology (GO) functional annotation and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses were performed, followed by protein-protein interaction (PPI) network analysis and key genetic screening.

Results

In comparison to normal samples, the expression of 81 secreted protein-related genes was downregulated, and the expression of 12 secreted protein-related genes was upregulated in PDAC. According to the GO and KEGG enrichment analysis results, these differentially expressed genes are mainly involved in the PI3K-Akt signaling pathway, protein digestion and absorption, extracellular matrix (ECM) receptor interaction, AGE-RAGE (advanced glycation endproducts-the Receptor of Advanced Glycation Endproducts) signaling pathway, relaxin signaling pathway, interleukin-17 (IL-17) signaling pathway, and transforming growth factor-β (TGF-β) signaling pathway, affecting the different manifestations of PDAC cancer pain. We used Cytoscape software to construct a protein interaction network of common differentially expressed genes and obtained three clusters with high scores. Our literature review found that several genes, including PTGS2, VCAN, and CCL2, were directly related to cancer pain occurrence.

Conclusions

By data mining the PDAC tumor expression, dozens of differentially expressed genes were identified in this study, several of which have been associated with the frequency and severity of cancer pain. This study provides an important foundation for the pain treatment of PDAC tumor patients.

Angiotensin type 2 receptor antagonism as a new target to manage gout

BACKGROUND

There is a growing search for therapeutic targets in the treatment of gout. The present study aimed to evaluate the analgesic and anti-inflammatory potential of angiotensin type 2 receptor (AT₂R) antagonism in an acute gout attack mouse model.

METHODS

Male wild-type (WT) C57BL/6 mice either with the AT₂R antagonist, PD123319 (10 pmol/joint), or with vehicle injections, or AT₂R KO mice, received intra-articular (IA) injection of monosodium urate (MSU) crystals (100 µg/joint), that induce the acute gout attack, and were tested for mechanical allodynia, thermal hyperalgesia, spontaneous nociception and ankle edema development at several times after the injections. To test an involvement of AT₂R in joint pain, mice received an IA administration of angiotensin II (0.05-5 nmol/joint) with or without PD123319, and were also evaluated for pain and edema development. Ankle joint tissue samples from mice undergoing the above treatments were assessed for myeloperoxidase activity, IL-1β release, mRNA expression analyses and nitrite/nitrate levels, 4 h after injections.

RESULTS

AT₂R antagonism has robust antinociceptive effects on mechanical allodynia (44% reduction) and spontaneous nociception (56%), as well as anti-inflammatory effects preventing edema formation (45%), reducing myeloperoxidase activity (54%) and IL-1β levels (32%). Additionally, Agtr2^tm1a mutant mice have largely reduced painful signs of gout. Angiotensin II administration causes pain and inflammation, which was prevented by AT₂R antagonism, as observed in mechanical allodynia 4 h (100%), spontaneous nociception (46%), cold nociceptive response (54%), edema formation (83%), myeloperoxidase activity (48%), and IL-1β levels (89%). PD123319 treatment also reduces NO concentrations (74%) and AT₂R mRNA levels in comparison with MSU untreated mice.

CONCLUSION

Our findings show that AT₂R activation contributes to acute pain in experimental mouse models of gout. Therefore, the antagonism of AT₂R may be a potential therapeutic option to manage gout arthritis.

Angiotensin-(1-7) improves cognitive function and reduces inflammation in mice following mild traumatic brain injury

Introduction

Traumatic brain injury (TBI) is a leading cause of disability in the US. Angiotensin 1-7 (Ang-1-7), an endogenous peptide, acts at the G protein coupled MAS1 receptors (MASR) to inhibit inflammatory mediators and decrease reactive oxygen species within the CNS. Few studies have identified whether Ang-(1-7) decreases cognitive impairment following closed TBI. This study examined the therapeutic effect of Ang-(1-7) on secondary injury observed in a murine model of mild TBI (mTBI) in a closed skull, single injury model.

Materials and methods

Male mice (n = 108) underwent a closed skull, controlled cortical impact injury. Two hours after injury, mice were administered either Ang-(1-7) (n = 12) or vehicle (n = 12), continuing through day 5 post-TBI, and tested for cognitive impairment on days 1-5 and 18. pTau, Tau, GFAP, and serum cytokines were measured at multiple time points. Animals were observed daily for cognition and motor coordination via novel object recognition. Brain sections were stained and evaluated for neuronal injury.

Results

Administration of Ang-(1-7) daily for 5 days post-mTBI significantly increased cognitive function as compared to saline control-treated animals. Cortical and hippocampal structures showed less damage in the presence of Ang-(1-7), while Ang-(1-7) administration significantly changed the expression of pTau and GFAP in cortical and hippocampal regions as compared to control.

Discussion

These are among the first studies to demonstrate that sustained administration of Ang-(1-7) following a closed-skull, single impact mTBI significantly improves neurologic outcomes, potentially offering a novel therapeutic modality for the prevention of long-term CNS impairment following such injuries.

Modelling skeletal pain harnessing tissue engineering

Bone pain typically occurs immediately following skeletal damage with mechanical distortion or rupture of nociceptive fibres. The pain mechanism is also associated with chronic pain conditions where the healing process is impaired. Any load impacting on the area of the fractured bone will stimulate the nociceptive response, necessitating rapid clinical intervention to relieve pain associated with the bone damage and appropriate mitigation of any processes involved with the loss of bone mass, muscle, and mobility and to prevent death. The following review has examined the mechanisms of pain associated with trauma or cancer-related skeletal damage focusing on new approaches for the development of innovative therapeutic interventions. In particular, the review highlights tissue engineering approaches that offer considerable promise in the application of functional biomimetic fabrication of bone and nerve tissues. The strategic combination of bone and nerve tissue engineered models provides significant potential to develop a new class of in vitro platforms, capable of replacing in vivo models and testing the safety and efficacy of novel drug treatments aimed at the resolution of bone-associated pain. To date, the field of bone pain research has centred on animal models, with a paucity of data correlating to the human physiological response. This review explores the evident gap in pain drug development research and suggests a step change in approach to harness tissue engineering technologies to recapitulate the complex pathophysiological environment of the damaged bone tissue enabling evaluation of the associated pain-mimicking mechanism with significant therapeutic potential therein for improved patient quality of life.

Graphical abstract

Rationale underlying novel drug testing platform development. Pain detected by the central nervous system and following bone fracture cannot be treated or exclusively alleviated using standardised methods. The pain mechanism and specificity/efficacy of pain reduction drugs remain poorly understood. In vivo and ex vivo models are not yet able to recapitulate the various pain events associated with skeletal damage. In vitro models are currently limited by their inability to fully mimic the complex physiological mechanisms at play between nervous and skeletal tissue and any disruption in pathological states. Robust innovative tissue engineering models are needed to better understand pain events and to investigate therapeutic regimes.

Demystifying the dual role of the angiotensin system in neuropathic pain

Neuropathic Pain is caused by damage to a nerve or disease of the somatosensory nervous system. Apart from the blood pressure regulating actions of angiotensin ligands, studies have shown that it also modulates neuropathic pain. In the animal models including surgical, chemotherapeutic, and retroviral-induced neuropathic pain, an increase in the levels of angiotensin II has been identified and it has been proposed that an increase in angiotensin II may participate in the induction of neuropathic pain. The pain-inducing actions of the angiotensin system are primarily due to the activation of AT₁ and AT₂ receptors, which trigger the diverse molecular mechanisms including the induction of neuroinflammation to initiate and maintain the state of neuropathic pain. On the other hand, the pain attenuating action of the angiotensin system has been attributed to decreasing in the levels of Ang_(1-7), and Ang IV and an increase in the levels of bradykinin. Ang_(1-7) may attenuate neuropathic pain via activation of the spinal Mas receptor. However, the detailed molecular mechanism involved in Ang_(1-7) and Ang IV-mediated pain attenuating actions needs to be explored. The present review discusses the dual role of angiotensin ligands in neuropathic pain along with the possible mechanisms involved in inducing or attenuating the state of neuropathic pain.

COVID-19 in Joint Ageing and Osteoarthritis: Current Status and Perspectives

COVID-19 is a trending topic worldwide due to its immense impact on society. Recent trends have shifted from acute effects towards the long-term morbidity of COVID-19. In this review, we hypothesize that SARS-CoV-2 contributes to age-related perturbations in endothelial and adipose tissue, which are known to characterize the early aging process. This would explain the long-lasting symptoms of SARS-CoV-2 as the result of an accelerated aging process. Connective tissues such as adipose tissue and musculoskeletal tissue are the primary sites of aging. Therefore, current literature was analyzed focusing on the musculoskeletal symptoms in COVID-19 patients. Hypovitaminosis D, increased fragility, and calcium deficiency point towards bone aging, while joint and muscle pain are typical for joint and muscle aging, respectively. These characteristics could be classified as early osteoarthritis-like phenotype. Exploration of the impact of SARS-CoV-2 and osteoarthritis on endothelial and adipose tissue, as well as neuronal function, showed similar perturbations. At a molecular level, this could be attributed to the angiotensin-converting enzyme 2 expression, renin-angiotensin system dysfunction, and inflammation. Finally, the influence of the nicotinic cholinergic system is being evaluated as a new treatment strategy. This is combined with the current knowledge of musculoskeletal aging to pave the road towards the treatment of long-term COVID-19.

Participation of angiotensin-(1-7) in exercise-induced analgesia in rats with neuropathic pain

Exercise reduces neuropathic pain in animals and humans. Recent studies indicate that training exercise favors the synthesis and action of angiotensin-(1-7) (Ang-(1-7)), a vasoactive peptide of the renin-angiotensin system (RAS), in various tissues. Interestingly, Ang-(1-7) also relieves neuropathic pain; however, it remains to be elucidated whether exercise mitigates this type of pain through Ang-(1-7). In this study, we investigated the role of Ang-(1-7) in exercise-induced analgesia in a neuropathic pain model. Male Wistar rats were ligated of lumbar spinal nerves (L5 and L6) or sham-operated. Then, they were subjected to acute (2-h) or chronic (4-week) exercise protocols. Tactile allodynia was evaluated before and after each exercise intervention. Microosmotic pumps were implanted subcutaneously for the release of Ang-(1-7) or A779 (selective Mas receptor (MasR; Ang-(1-7) receptor) antagonist). Plasma levels of Ang II and Ang-(1-7) were quantified by HPLC. Spinal nerve ligation (SNL) produced tactile allodynia. Both acute and chronic exercise reversed this neuropathic behavior. A779 treatment prevented the antiallodynic effect induced by each exercise protocol. SNL increased the plasma Ang II/Ang-(1-7) ratio; however, exercise did not modify it. Acute treatment with Ang-(1-7) via MasR mimicked exercise-mediated antinociception. Collectively, these results suggest that activation of the Ang-(1-7)/MasR axis of the RAS represents a potential novel mechanism by which exercise attenuates neuropathic pain in rats.

Shedding Light on the Pharmacological Interactions between μ-Opioid Analgesics and Angiotensin Receptor Modulators: A New Option for Treating Chronic Pain

The current protocols for neuropathic pain management include µ-opioid receptor (MOR) analgesics alongside other drugs; however, there is debate on the effectiveness of opioids. Nevertheless, dose escalation is required to maintain their analgesia, which, in turn, contributes to a further increase in opioid side effects. Finding novel approaches to effectively control chronic pain, particularly neuropathic pain, is a great challenge clinically. Literature data related to pain transmission reveal that angiotensin and its receptors (the AT1R, AT2R, and MAS receptors) could affect the nociception both in the periphery and CNS. The MOR and angiotensin receptors or drugs interacting with these receptors have been independently investigated in relation to analgesia. However, the interaction between the MOR and angiotensin receptors has not been excessively studied in chronic pain, particularly neuropathy. This review aims to shed light on existing literature information in relation to the analgesic action of AT1R and AT2R or MASR ligands in neuropathic pain conditions. Finally, based on literature data, we can hypothesize that combining MOR agonists with AT1R or AT2R antagonists might improve analgesia.

Synthesis, Physicochemical Characterization, In Vitro 2D/3D Human Cell Culture, and In Vitro Aerosol Dispersion Performance of Advanced Spray Dried and Co-Spray Dried Angiotensin (1-7) Peptide and PNA5 with Trehalose as Microparticles/Nanoparticles for Targeted Respiratory Delivery as Dry Powder Inhalers

The peptide hormone Angiotensin (1—7), Ang (1—7) or (Asp-Arg-Val-Tyr-Ile-His-Pro), is an essential component of the renin–angiotensin system (RAS) peripherally and is an agonist of the Mas receptor centrally. Activation of this receptor in the CNS stimulates various biological activities that make the Ang (1—7)/MAS axis a novel therapeutic approach for the treatment of many diseases. The related O-linked glycopeptide, Asp-Arg-Val-Tyr-Ile-His-Ser-(O-β-D-Glc)-amide (PNA5), is a biousian revision of the native peptide hormone Ang (1—7) and shows enhanced stability in vivo and greater levels of brain penetration. We have synthesized the native Ang (1—7) peptide and the glycopeptide, PNA5, and have formulated them for targeted respiratory delivery as inhalable dry powders. Solid phase peptide synthesis (SPPS) successfully produced Ang (1—7) and PNA5. Measurements of solubility and lipophilicity of raw Ang (1—7) and raw PNA5 using experimental and computational approaches confirmed that both the peptide and glycopeptide have high-water solubility and are amphipathic. Advanced organic solution spray drying was used to engineer the particles and produce spray-dried powders (SD) of both the peptide and the glycopeptide, as well as co-spray-dried powders (co-SD) with the non-reducing sugar and pharmaceutical excipient, trehalose. The native peptide, glycopeptide, SD, and co-SD powders were comprehensively characterized, and exhibited distinct glass transitions (T_g) consistent with the amorphous glassy state formation with T_gs that are compatible with use in vivo. The homogeneous particles displayed small sizes in the nanometer size range and low residual water content in the solid-state. Excellent aerosol dispersion performance with a human DPI device was demonstrated. In vitro human cell viability assays showed that Ang (1—7) and PNA5 are biocompatible and safe for different human respiratory and brain cells.

COVID-Pain: Acute and Late-Onset Painful Clinical Manifestations in COVID-19 - Molecular Mechanisms and Research Perspectives

Although the respiratory manifestations of COVID-19 are predominant, signs and symptoms of an extra-pulmonary involvement are usually encompassed among the clinical picture of the disease. Several painful manifestations can occur during the acute phase but also as short- or long-term complications. Myalgia, joint pain, sore throat, abdominal pain, chest pain, and headache usually accompany respiratory symptoms, but they can also occur as isolated clinical findings or can be expressed regardless of the severity of COVID-19. On these premises, given the vast spectrum of clinical manifestations and the complexity of their pathogenesis, it would be more appropriate to refer to "COVID-pain", an umbrella term useful for encompassing all these clinical manifestations in a separate chapter of the disease. In this scenario, we addressed the topic from a molecular perspective, trying to provide explanations for the underlying pathophysiological processes. Consequently, this narrative review is aimed at dissecting the mechanisms of acute and chronic painful manifestations, summarizing fundamental concepts on the matter, controversies, current research gaps, and potential developments in this field.

Ramipril Alleviates Oxaliplatin-Induced Acute Pain Syndrome in Mice

Oxaliplatin is a key drug for colorectal cancer that causes OXP-induced peripheral neuropathy, a dose-limiting effect characterized by cold and tactile hyperesthesia. The relationship between the sensory nervous system and modulation of the renin-angiotensin system has been described, focusing on pain and neurodegeneration in several animal models. We assessed the effect of the RAS modulator, ramipril, an angiotensin converting-enzyme inhibitor in a mouse model of OXP-induced acute pain syndrome. OXP was administered in Swiss mice at a cumulative dose of 15 mg/kg (3 x 5 mg/kg/3 days, i.p.). RAM was administered i.p. every day from 24 h before the first OXP injection until the end of the experiments. We evaluated OIAS development and treatment effects by sensorimotor tests, intraepidermal nerve fiber and dorsal root ganglia-neuron immunohistochemical analyses, and sciatic nerve ultrastructural analysis. OXP-treated mice showed tactile allodynia and cold hypersensitivity, without motor impairment and evidence of nerve degeneration. RAM prevented cold sensitivity and improved recovery of normal tactile sensitivity in OXP-treated mice. Our finding that RAM alleviates OXP-induced pain is a step towards evaluating its therapeutic potential in patients receiving OXP treatment.

ACE2/Angiotensin-(1-7)/Mas Receptor Axis in Human Cancer: Potential Role for Pediatric Tumors

BACKGROUND

Pediatric tumors remain the highest cause of death in developed countries. Research on novel therapeutic strategies with lesser side effects is of utmost importance. In this scenario, the role of Renin-Angiotensin System (RAS) axes, the classical one formed by angiotensinconverting enzyme (ACE), Angiotensin II and AT1 receptor and the alternative axis composed by ACE2, Angiotensin-(1-7) and Mas receptor, have been investigated in cancer.

OBJECTIVE

This review aimed to summarize the pathophysiological role of RAS in cancer, evidence for anti-tumor effects of ACE2/Angiotensin-(1-7)/Mas receptor axis and future therapeutic perspectives for pediatric cancer.

METHODS

Pubmed, Scopus and Scielo were searched in regard to RAS molecules in human cancer and pediatric patients. The search terms were "RAS", "ACE", "Angiotensin-(1-7)", "ACE2", "Angiotensin II", "AT1 receptor", "Mas receptor", "Pediatric", "Cancer".

RESULTS

Experimental studies have shown that Angiotensin-(1-7) inhibits the growth of tumor cells and reduces local inflammation and angiogenesis in several types of cancer. Clinical trials with Angiotensin-( 1-7) or TXA127, a pharmaceutical grade formulation of the naturally occurring peptide, have reported promising findings, but not enough to recommend medical use in human cancer. In regard to pediatric cancer, only three articles that marginally investigated RAS components were found and none of them evaluated molecules of the alternative RAS axis.

CONCLUSION

Despite the potential applicability of Angiotensin-(1-7) in pediatric tumors, the role of this molecule was never tested. Further clinical trials are necessary, also including pediatric patients, to confirm safety and efficiency and to define therapeutic targets.

Angiotensin receptors and neuropathic pain

Growing evidence implicates the renin-angiotensin system (RAS) in multiple facets of neuropathic pain (NP). This narrative review focuses primarily on the major bioactive RAS peptide, Angiotensin II (Ang II), and its receptors, namely type 1 (AT1R) and type 2 (AT2R). Both receptors are involved in the development of NP and represent potential therapeutic targets. We first discuss the potential role of Ang II receptors in modulation of NP in the central nervous system. Ang II receptor expression is widespread in circuits associated with the perception and modulation of pain, but more studies are required to fully characterize receptor distribution, downstream signaling, and therapeutic potential of targeting the central nervous system RAS in NP. We then describe the peripheral neuronal and nonneuronal distribution of the RAS, and its contribution to NP. Other RAS modulators (such as Ang (1-7)) are briefly reviewed as well. AT1R antagonists are analgesic across different pain models, including NP. Several studies show neuronal protection and outgrowth downstream of AT2R activation, which may lead to the use of AT2R agonists in NP. However, blockade of AT2R results in analgesia. Furthermore, expression of the RAS in the immune system and a growing appreciation of neuroimmune crosstalk in NP add another layer of complexity and therapeutic potential of targeting this pathway. A growing number of human studies also hint at the analgesic potential of targeting Ang II signaling. Altogether, Ang II receptor signaling represents a promising, far-reaching, and novel strategy to treat NP.

Global prevalence and pathogenesis of headache in COVID-19: A systematic review and meta-analysis

Background: This study was conducted to determine the prevalence of headache in coronavirus disease 2019 (COVID-19) and to assess its association as a predictor for COVID-19. This study also aimed to discuss the possible pathogenesis of headache in COVID-19. Methods: Available articles from PubMed, Scopus, and Web of Science were searched as of September 2 nd, 2020. Data on characteristics of the study, headache and COVID-19 were extracted following the PRISMA guidelines. Biases were assessed using the Newcastle-Ottawa scale. The cumulative prevalence of headache was calculated for the general population (i.e. adults and children). The pooled odd ratio (OR) with 95% confidence intervals (95%CI) was calculated using the Z test to assess the association between headache and the presence of COVID-19 cases. Results: We included 104,751 COVID-19 cases from 78 eligible studies to calculate the global prevalence of headache in COVID-19 and 17 studies were included to calculate the association of headache and COVID-19. The cumulative prevalence of headache in COVID-19 was 25.2% (26,464 out of 104,751 cases). Headache was found to be more prevalent, approximately by two-fold, in COVID-19 patients than in non-COVID-19 patients with symptoms of other respiratory viral infections, OR: 1.73; 95% CI: 1.94, 2.5 with p=0.04. Conclusion: Headache is common among COVID-19 patients and seems to be more common in COVID-19 patients compared to those with the non-COVID-19 viral infection. No definitive mechanisms on how headache  emerges in COVID-19 patients but several possible hypotheses have been proposed. However, extensive studies are warranted to elucidate the mechanisms. PROSPERO registration: CRD42020210332 (28/09/2020).

Global prevalence and pathogenesis of headache in COVID-19: A systematic review and meta-analysis

Background: This study was conducted to determine the prevalence of headache in coronavirus disease 2019 (COVID-19) and to assess its association as a predictor for COVID-19. This study also aimed to discuss the possible pathogenesis of headache in COVID-19. Methods: Available articles from PubMed, Scopus, and Web of Science were searched as of September 2 nd, 2020. Data on characteristics of the study, headache and COVID-19 were extracted following the PRISMA guidelines. Biases were assessed using the Newcastle-Ottawa scale. The cumulative prevalence of headache was calculated for the general population (i.e. adults and children). The pooled odd ratio (OR) with 95% confidence intervals (95%CI) was calculated using the Z test to assess the association between headache and the presence of COVID-19 cases. Results: We included 104,751 COVID-19 cases from 78 eligible studies to calculate the global prevalence of headache in COVID-19 and 17 studies were included to calculate the association of headache and COVID-19. The cumulative prevalence of headache in COVID-19 was 25.2% (26,464 out of 104,751 cases). Headache was found to be more prevalent, approximately by two-fold, in COVID-19 patients than in non-COVID-19 patients (other respiratory viral infections), OR: 1.73; 95% CI: 1.94, 2.5 with p=0.04. Conclusion: Headache is common among COVID-19 patients and seems to be more common in COVID-19 patients compared to those with the non-COVID-19 viral infection. No definitive mechanisms on how headache  emerges in COVID-19 patients but several possible hypotheses have been proposed. However, extensive studies are warranted to elucidate the mechanisms. PROSPERO registration: CRD42020210332 (28/09/2020).

Glycopeptide drugs: A pharmacological dimension between "Small Molecules" and "Biologics"

Peptides are an important class of molecules with diverse biological activities. Many endogenous peptides, especially neuropeptides and peptide hormones, play critical roles in development and regulating homeostasis. Furthermore, as drug candidates their high receptor selectivity and potent binding leads to reduced off-target interactions and potential negative side effects. However, the therapeutic potential of peptides is severely hampered by their poor stability in vivo and low permeability across biological membranes. Several strategies have been successfully employed over the decades to address these concerns, and one of the most promising strategies is glycosylation. It has been demonstrated in numerous cases that glycosylation is an effective synthetic approach to improve the pharmacokinetic profiles and membrane permeability of peptides. The effects of glycosylation on peptide stability and peptide-membrane interactions in the context of blood-brain barrier penetration will be explored. Numerous examples of glycosylated analogues of endogenous peptides targeting class A and B G-protein coupled receptors (GPCRs) with an emphasis on O-linked glycopeptides will be reviewed. Notable examples of N-, S-, and C-linked glycopeptides will also be discussed. A small section is devoted to synthetic methods for the preparation of glycopeptides and requisite amino acid glycoside building blocks.

The search for translational pain outcomes to refine analgesic development: Where did we come from and where are we going?

Pain measures traditionally used in rodents record mere reflexes evoked by sensory stimuli; the results thus may not fully reflect the human pain phenotype. Alterations in physical and emotional functioning, pain-depressed behaviors and facial pain expressions were recently proposed as additional pain outcomes to provide a more accurate measure of clinical pain in rodents, and hence to potentially enhance analgesic drug development. We aimed to review how preclinical pain assessment has evolved since the development of the tail flick test in 1941, with a particular focus on a critical analysis of some nonstandard pain outcomes, and a consideration of how sex differences may affect the performance of these pain surrogates. We tracked original research articles in Medline for the following periods: 1973-1977, 1983-1987, 1993-1997, 2003-2007, and 2014-2018. We identified 606 research articles about alternative surrogate pain measures, 473 of which were published between 2014 and 2018. This indicates that preclinical pain assessment is moving toward the use of these measures, which may soon become standard procedures in preclinical pain laboratories.

Angiotensin-(1-7) induces beige fat thermogenesis through the Mas receptor

OBJECTIVE

Angiotensin-(1-7) [Ang-(1-7)], a component of the renin angiotensin system, is a vasodilator that exerts its effects primarily through the Mas receptor. The discovery of the Mas receptor in white adipose tissue (WAT) suggests an additional role for this peptide. The aim of the present study was to assess whether Ang-(1-7) can induce the expression of thermogenic genes in white adipose tissue and increase mitochondrial respiration in adipocytes.

MATERIALS/METHODS

Stromal Vascular fraction (SVF)-derived from mice adipose tissue was stimulated for one week with Ang-(1-7), then expression of beige markers and mitochondrial respiration were assessed. Mas^+/+ and Mas^-/- mice fed a control diet or a high fat-sucrose diet (HFSD) were exposed to a short or long term infusion of Ang-(1-7) and body weight, body fat, energy expenditure, cold resistance and expression of beige markers were assessed. Also, transgenic rats overexpressing Ang-(1-7) were fed with a control diet or a high fat-sucrose diet and the same parameters were assessed. Ang-(1-7) circulating levels from human subjects with different body mass index (BMI) or age were measured.

RESULTS

Incubation of adipocytes derived from SVF with Ang-(1-7) increased the expression of beige markers. Infusion of Ang-(1-7) into lean and obese Mas^+/+mice also induced the expression of Ucp1 and some beige markers, an effect not observed in Mas^-/- mice. Mas^-/- mice had increased body weight gain and decreased cold resistance, whereas rats overexpressing Ang-(1-7) showed the opposite effects. Overexpressing rats exposed to cold developed new thermogenic WAT in the anterior interscapular area. Finally, in human subjects the higher the BMI, low circulating concentration of Ang-(1-7) levels were detected. Similarly, the circulating levels of Ang-(1-7) peptide were reduced with age.

CONCLUSION

These data indicate that Ang-(1-7) stimulates beige markers and thermogenesis via the Mas receptor, and this evidence suggests a potential therapeutic use to induce thermogenesis of WAT, particularly in obese subjects that have reduced circulating concentration of Ang-(1-7).

Downregulation of spinal angiotensin converting enzyme 2 is involved in neuropathic pain associated with type 2 diabetes mellitus in mice

We have previously reported that the spinal angiotensin (Ang) system is involved in the modulation of streptozotocin (STZ)-induced diabetic neuropathic pain in mice. An important drawback of this model however is the fact that the neuropathic pain is independent of hyperglycemia and produced by the direct stimulation of peripheral nerves. Here, using the leptin deficient ob/ob mouse as a type 2 diabetic model, we examined whether the spinal Ang system was involved in naturally occuring diabetic neuropathic pain. Blood glucose levels were increased in ob/ob mice at 5-15 weeks of age. Following the hyperglycemia, persistent tactile and thermal hyperalgesia were observed at 11-14 and 9-15 weeks of age, respectively, which was ameliorated by insulin treatment. At 12 weeks of age, the expression of Ang-converting enzyme (ACE) 2 in the spinal plasma membrane fraction was decreased in ob/ob mice. Spinal ACE2 was expressed in neurons and microglia but the number of NeuN-positive neurons was decreased in ob/ob mice. In addition, the intrathecal administration of Ang (1-7) and SB203580, a p38 MAPK inhibitor, attenuated hyperalgesia in ob/ob mice. The phosphorylation of spinal p38 MAPK was also attenuated by Ang (1-7) in ob/ob mice. These inhibitory effects of Ang (1-7) were prevented by A779, a Mas receptor antagonist. In conclusion, we revealed that the Ang (1-7)-generating system is downregulated in ob/ob mice and is accompanied by a loss of ACE2-positive neurons. Furthermore, Ang (1-7) decreased the diabetic neuropathic pain through inhibition of p38 MAPK phosphorylation via spinal Mas receptors.

Lactation Leads to Modifications in Maternal Renin-Angiotensin System in Later Life

The objective of this study was to evaluate whether the renin-angiotensin system (RAS) is associated with maternal cardioprotective phenotype observed in post-lactated mice later in life. Following the delivery, CD-1 female mice were randomized to one of the following groups: lactated (nursed pups for 3 weeks, n = 10) or non-lactated (pups were removed after birth, n = 10). The mice were sacrificed 6 months after the delivery, and tissues were collected. Protein levels of angiotensinogen, angiotensin type 1 and 2 receptors (AT1R, AT2R), angiotensin converting enzymes (ACE, ACE2), and MAS receptor were determined using Western blot. Results were analyzed using Student's t-test and Mann-Whitney test as appropriate (significance: P < 0.05). Angiotensinogen levels were significantly lower in the liver (P = 0.0002), and ACE was significantly decreased in the lungs (P = 0.04) and kidney (P = 0.001) from lactated mice as compared to non-lactated. The levels of AT2R in the kidney (P = 0.02) and visceral adipose tissue (VAT, P = 0.04), the ACE 2 in the VAT (P = 0.03) and heart (P = 0.04), and MAS receptor in VAT (P = 0.02) were significantly elevated in tissues from lactated mice. No other differences were found. Lactation led to the upregulation and downregulation of selected RAS components in lactated mice as compared to non-lactated group and may be a contributing factor to maternal cardioprotective phenotype later in life. Further studies are needed to dissect the mechanisms between lactation and the long-term maternal cardiometabolic benefits, which could lead to the therapies to prevent cardiovascular disease in women.

Interaction of Sex Hormones and the Renin-Angiotensin System in Ovariectomized Rats Subjected to Ischemia-Reperfusion Induction

Backgrounds:

Ischemia-reperfusion (IR) injuries occur in a variety of clinical conditions, which lead to kidney damage. Most of the tissue damages after IR are due to the activation of the renin–angiotensin system (RAS). Hence, in this study, the interaction of sex hormones and RAS in ovariectomized (OV) rats subjected to IR induction has been studied.

Materials and Methods:

The animals were divided into different groups. Groups 1 (OV + E, OV rat + estradiol) and 2 (OV rat) each one consisted of three separate IR-induced subgroups treated with losartan, angiotensin 1–7 (Ang 1–7), and their combination, Group 3, as control and Group 4, as sham. Next, 72 h after IR, blood samples were collected, the right kidneys were homogenized, and left kidneys were fixed in 10% formalin.

Results:

Findings show that serum blood urea nitrogen, creatinine, and kidney tissue damage score levels increased significantly with induction of IR (P < 0.05). Mean serum levels of these factors in OV + E groups are higher than those of the OV. The presence or absence of estradiol did not affect the levels of antioxidants in the different groups receiving Los, Ang 1–7, and their combination. Los, Ang 1–7, and their combination reduced serum and kidney malondialdehyde levels in both OV and OV + E groups.

Conclusion:

Estrogen not only fails to improve renal functioning but it can also exacerbate it. While the treatments used in this study, in the absence of estradiol, it had a better effect on kidney damages and improved its functions.

The endocannabinoid system: Novel targets for treating cancer induced bone pain

Treating Cancer-induced bone pain (CIBP) continues to be a major clinical challenge and underlying mechanisms of CIBP remain unclear. Recently, emerging body of evidence suggested the endocannabinoid system (ECS) may play essential roles in CIBP. Here, we summarized the current understanding of the antinociceptive mechanisms of endocannabinoids in CIBP and discussed the beneficial effects of endocannabinoid for CIBP treatment. Targeting non-selective cannabinoid 1 receptors or selective cannabinoid 2 receptors, and modulation of peripheral AEA and 2-AG, as well as the inhibition the function of fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL) have produced analgesic effects in animal models of CIBP. Management of ECS therefore appears to be a promising way for the treatment of CIBP in terms of efficacy and safety. Further clinical studies are encouraged to confirm the possible translation to humans of the very promising results already obtained in the preclinical studies.

The effect of angiotensin 1-7 and losartan on renal ischemic/reperfusion injury in male rats

Ischemia/reperfusion (I/R) is a major cause of acute kidney injury. Several studies have shown that renin angiotensin (Ang) system and activation of Ang II type 1 receptor (AT1) are involved in various forms of kidney diseases. Likewise, Ang 1-7 as a physiologic antagonist of AT1 and losartan could possibly protect the kidney against I/R damage. Therefore, we investigated renal injury by administering the drugs before and after I/R. Fifty-four male Wistar rats were randomly assigned to five groups as follows. 1, Sham operated; 2, saline group (as a control group); 3, losartan group; 4, Ang 1-7group; and 5, Ang 1-7 + losartan simultaneously. It should be noted that groups 2-5 consisted of two separate I/R-induced subgroups both receiving medication where the first groups received the treatment 15 min before induction of I/R while the medications were given to the second groups immediately after induction of I/R. Twenty four h after I/R, blood samples were collected, and then levels of serum urea nitrogen (BUN), creatinine (Cr), nitrite, malondialdehyde (MDA), lactate dehydrogenase (LDH) and total antioxidant capacity (TAC) were measured. Likewise, nitrite, MDA and TAC were measured in the homogenized kidney tissues. After the induction of I/R, the BUN, Cr, LDH, and kidney tissue damage score increased. Administration of Ang 1-7 alone or simultaneously with losartan decreased the levels of aforementioned factors. Also, kidney MDA and nitrate levels significantly increased after I/R induction (P < 0.05). According to the results of this study, it can be claimed that the effect of losartan in the presence of Mas receptor is statistically significant and kidney damage dramatically decreases.

AHU377+Valsartan (LCZ696) Modulates Renin-Angiotensin System (RAS) in the Cardiac of Female Spontaneously Hypertensive Rats Compared With Valsartan

BACKGROUND

Hypertension is a major cause of death and morbidity worldwide and is increasing in prevalence. The Renin-angiotensin system (RAS) is the most common mechanism involved in the pathophysiology of hypertension. Understanding the mechanism of the pathophysiologic processes will help direct potential therapeutic strategies to treat hypertension and improve cardiac function. Recently, a novel drug LCZ696 containing both an angiotensin receptor blocker valsartan and a neprilysin inhibitor (AHU377) has shown a promising effect on the treatment of hypertension. However, the effects of LCZ696 on the expression of main components of RAS, namely, angiotensin-converting enzyme (ACE), angiotensin-converting enzyme 2 (ACE2), angiotensin II type 1 receptor (AT1 R), angiotensin II type 2 receptor (AT2 R), and angiotensin (1-7) receptor/Mas receptor (MasR) remain unclear. The aim of the present study was to evaluate the effects of LCZ696 on the protective arms of RAS in the cardiac tissue when compared with valsartan under the equal inhibition of AT1 R. We hypothesized that the superior effects of LCZ696 may contribute to its greater effect on the RAS than valsartan.

MATERIALS AND METHODS

Sixteen-week-old female spontaneously hypertensive rats (SHRs) were used in this study. Wistar-Kyoto (WKY) rats were used as controls. All rats were randomly divided into LCZ696 (n = 10), valsartan (n = 10), SHR (n = 10), and WKY (n = 10) groups under a 12-hour dark and 12-hour light cycle and provided with regular chow diet and water. The tail-cuff method was performed to measure blood pressure. Cardiac function was assessed by echocardiography.

RESULTS

The blood pressure value was lower in LCZ696 than valsartan in SHR after 12 weeks of treatment. Further, LCZ696 inhibits the ACE and AT1 R protein expression in the cardiac of SHR and significantly upregulate the protective axis of RAS components, including ACE2, MasR, and AT2 R. Left ventricular AT2 R messenger RNA (mRNA) expression was higher in the LCZ696+SHR group compared with valsartan. In addition, real-time polymerase chain reaction analysis revealed that LCZ696 enhanced the mRNA expression of antihypertensive components AT2 R, ACE2, and MasR and decreased the expression of AT1 R. However, only AT2 R and ACE2 mRNA expressions have a statistical difference between the LCZ696 and valsartan groups. No difference was observed in the mRNA expression of ACE and MasR. The stronger positive signal of transforming growth factor β in the left ventricle was inhibited in each administrated group compared with SHR groups.

CONCLUSIONS

LCZ696 ameliorates the vasoconstrictor axis of the RAS AT1 R and stimulate the protective arm effectors, ACE2 and AT2 R, as well as reverses the compensatory upregulation of neuronal nitric oxide synthase and endothelial nitric oxide synthase in SHR. These findings suggest the mechanistic insight of the cardiac-protective and greater hypotensive effects of LCZ696.

Core Outcome Measures in Preclinical Assessment of Candidate Analgesics

All preclinical procedures for analgesic drug discovery involve two components: 1) a "pain stimulus" (the principal independent variable), which is delivered to an experimental subject with the intention of producing a pain state; and 2) a "pain behavior" (the principal dependent variable), which is measured as evidence of that pain state. Candidate analgesics are then evaluated for their effectiveness to reduce the pain behavior, and results are used to prioritize drugs for advancement to clinical testing. This review describes a taxonomy of preclinical procedures organized into an "antinociception matrix" by reference to their types of pain stimulus (noxious, inflammatory, neuropathic, disease related) and pain behavior (unconditioned, classically conditioned, operant conditioned). Particular emphasis is devoted to pain behaviors and the behavioral principals that govern their expression, pharmacological modulation, and preclinical-to-clinical translation. Strengths and weaknesses are compared and contrasted for procedures using each type of behavioral outcome measure, and the following four recommendations are offered to promote strategic use of these procedures for preclinical-to-clinical analgesic drug testing. First, attend to the degree of homology between preclinical and clinical outcome measures, and use preclinical procedures with behavioral outcome measures homologous to clinically relevant outcomes in humans. Second, use combinations of preclinical procedures with complementary strengths and weaknesses to optimize both sensitivity and selectivity of preclinical testing. Third, take advantage of failed clinical translation to identify drugs that can be back-translated preclinically as active negative controls. Finally, increase precision of procedure labels by indicating both the pain stimulus and the pain behavior in naming preclinical procedures.

Peripherally restricted cannabinoid 1 receptor agonist as a novel analgesic in cancer-induced bone pain

Many malignant cancers, including breast cancer, have a propensity to invade bones, leading to excruciating bone pain. Opioids are the primary analgesics used to alleviate this cancer-induced bone pain (CIBP) but are associated with numerous severe side effects, including enhanced bone degradation, which significantly impairs patients' quality of life. By contrast, agonists activating only peripheral CB1 receptors (CB1Rs) have been shown to effectively alleviate multiple chronic pain conditions with limited side effects, yet no studies have evaluated their role(s) in CIBP. Here, we demonstrate for the first time that a peripherally selective CB1R agonist can effectively suppress CIBP. Our studies using a syngeneic murine model of CIBP show that both acute and sustained administration of a peripherally restricted CB1R agonist, 4-{2-[-(1E)-1[(4-propylnaphthalen-1-yl)methylidene]-1H-inden-3-yl]ethyl}morpholine (PrNMI), significantly alleviated spontaneous pain behaviors in the animals. This analgesic effect by PrNMI can be reversed by a systemic administration but not spinal injection of SR141716, a selective CB1R antagonist. In addition, the cancer-induced bone loss in the animals was not exacerbated by a repeated administration of PrNMI. Furthermore, catalepsy and hypothermia, the common side effects induced by cannabinoids, were measured at the supratherapeutic doses of PrNMI tested. PrNMI induced mild sedation, yet no anxiety or a decrease in limb movements was detected. Overall, our studies demonstrate that CIBP can be effectively managed by using a peripherally restricted CB1R agonist, PrNMI, without inducing dose-limiting central side effects. Thus, targeting peripheral CB1Rs could be an alternative therapeutic strategy for the treatment of CIBP.

A Novel Angiotensin-(1-7) Glycosylated Mas Receptor Agonist for Treating Vascular Cognitive Impairment and Inflammation-Related Memory Dysfunction

Increasing evidence indicates that decreased brain blood flow, increased reactive oxygen species (ROS) production, and proinflammatory mechanisms accelerate neurodegenerative disease progression such as that seen in vascular contributions to cognitive impairment and dementia (VCID) and Alzheimer's disease and related dementias. There is a critical clinical need for safe and effective therapies for the treatment and prevention of cognitive impairment known to occur in patients with VCID and chronic inflammatory diseases such as heart failure (HF), hypertension, and diabetes. This study used our mouse model of VCID/HF to test our novel glycosylated angiotensin-(1-7) peptide Ang-1-6-O-Ser-Glc-NH2 (PNA5) as a therapy to treat VCID and to investigate circulating inflammatory biomarkers that may be involved. We demonstrate that PNA5 has greater brain penetration compared with the native angiotensin-(1-7) peptide. Moreover, after treatment with 1.0/mg/kg, s.c., for 21 days, PNA5 exhibits up to 10 days of sustained cognitive protective effects in our VCID/HF mice that last beyond the peptide half-life. PNA5 reversed object recognition impairment in VCID/HF mice and rescued spatial memory impairment. PNA5 activation of the Mas receptor results in a dose-dependent inhibition of ROS in human endothelial cells. Last, PNA5 treatment decreased VCID/HF-induced activation of brain microglia/macrophages and inhibited circulating tumor necrosis factor α, interleukin (IL)-7, and granulocyte cell-stimulating factor serum levels while increasing that of the anti-inflammatory cytokine IL-10. These results suggest that PNA5 is an excellent candidate and "first-in-class" therapy for treating VCID and other inflammation-related brain diseases.

The Role of Angiotensin–(1-7) in Cancer

The rationale to investigate the role of angiotensin-(1-7) [Ang-(1-7)] in cancer relies on the fact that the heptapeptide inhibits the growth of several cell lines. The first studies showed that Ang-(1-7) accelerated hematopoietic recovery in the peripheral blood and bone marrow after chemotherapy and inhibits lung cancer cell growth through the activation of Mas receptor. In this chapter, we summarize studies on the role of Ang-(1-7) in different types of cancer, especially lung, breast, prostate, hepatocellular cancers and in gliobalstoma multiforme (GBM). The antitumor effect of Ang-(1-7) was due to reduction of angiogenesis, cancer-associated fibrosis, osteoclastogenesis, tumor-induced inflammation, and metastasis as well as inhibition of cancer cell growth and proliferation. In clinical trials, Ang-(1-7) was well tolerated with limited toxic or quality-of-life side effects and showed clinical benefit in cancer patients with solid tumors. Further clinical trials are needed to confirm safety, to determine doses and clinical indications.

Angiotensin II Triggers Peripheral Macrophage-to-Sensory Neuron Redox Crosstalk to Elicit Pain

Injury, inflammation, and nerve damage initiate a wide variety of cellular and molecular processes that culminate in hyperexcitation of sensory nerves, which underlies chronic inflammatory and neuropathic pain. Using behavioral readouts of pain hypersensitivity induced by angiotensin II (Ang II) injection into mouse hindpaws, our study shows that activation of the type 2 Ang II receptor (AT2R) and the cell-damage-sensing ion channel TRPA1 are required for peripheral mechanical pain sensitization induced by Ang II in male and female mice. However, we show that AT2R is not expressed in mouse and human dorsal root ganglia (DRG) sensory neurons. Instead, expression/activation of AT2R on peripheral/skin macrophages (MΦs) constitutes a critical trigger of mouse and human DRG sensory neuron excitation. Ang II-induced peripheral mechanical pain hypersensitivity can be attenuated by chemogenetic depletion of peripheral MΦs. Furthermore, AT2R activation in MΦs triggers production of reactive oxygen/nitrogen species, which trans-activate TRPA1 on mouse and human DRG sensory neurons via cysteine modification of the channel. Our study thus identifies a translatable immune cell-to-sensory neuron signaling crosstalk underlying peripheral nociceptor sensitization. This form of cell-to-cell signaling represents a critical peripheral mechanism for chronic pain and thus identifies multiple druggable analgesic targets.SIGNIFICANCE STATEMENT Pain is a widespread health problem that is undermanaged by currently available analgesics. Findings from a recent clinical trial on a type II angiotensin II receptor (AT2R) antagonist showed effective analgesia for neuropathic pain. AT2R antagonists have been shown to reduce neuropathy-, inflammation- and bone cancer-associated pain in rodents. We report that activation of AT2R in macrophages (MΦs) that infiltrate the site of injury, but not in sensory neurons, triggers an intercellular redox communication with sensory neurons via activation of the cell damage/pain-sensing ion channel TRPA1. This MΦ-to-sensory neuron crosstalk results in peripheral pain sensitization. Our findings provide an evidence-based mechanism underlying the analgesic action of AT2R antagonists, which could accelerate the development of efficacious non-opioid analgesic drugs for multiple pain conditions.

Dimerization of AT2 and Mas Receptors in Control of Blood Pressure

PURPOSE OF REVIEW

Angiotensin type 2 receptor (AT2R) and receptor Mas (MasR) are part of the "protective arm" of the renin angiotensin system. Gene and pharmacological manipulation studies reveal that AT2R and MasR are involved in natriuretic, vasodilatory, and anti-inflammatory responses and in lowering blood pressure in various animal models under normal and pathological conditions such as salt-sensitive hypertension, obesity, and diabetes. The scope of this review is to discuss co-localization and heterodimerization as potential molecular mechanisms of AT2R- and MasR-mediated functions including antihypertensive activities.

RECENT FINDINGS

Accumulating evidences show that AT2R and MasR are co-localized, make a heterodimer, and are functionally interdependent in producing their physiological responses. Moreover, ang-(1-7) preferably may be an AT1R-biased agonist while acting as a MasR agonist. The physical interactions of AT2R and MasR appear to be an important mechanism by which these receptors are involved in blood pressure regulation and antihypertensive activity. Whether heteromers of these receptors influence affinity or efficacy of endogenous or synthetic agonists remains a question to be considered.

Inhibitory effect of angiotensin (1-7) on angiotensin III-induced nociceptive behaviour in mice

We have previously demonstrated that the intrathecal (i.t.) administration of angiotensin (Ang) II into mice produces a nociceptive behaviour consisting of scratching, biting and licking accompanied by the phosphorylation of p38 MAPK in the spinal cord, which was mediated through AT1 receptors. Both the p38 MAPK phosphorylation and subsequent nociceptive behaviour were attenuated by the i.t. co-administration of Ang (1-7), an N-terminal fragment of Ang II, that acted via Mas receptors. On the other hand, a C-terminal fragment of Ang II, namely Ang III, was also shown to induce a nociceptive behaviour by acting upon AT1 receptors on spinal astrocytes and neurons, and was found to be more potent than Ang II. However, the inhibitory effect of Ang (1-7) on the Ang III-induced nociceptive behaviour remains unclear. Thus, here we examined whether Ang (1-7) can attenuate the Ang III-induced nociceptive behaviour and activation of spinal p38 MAPK. The i.t. administration of Ang (1-7) (1-100fmol) dose-dependently attenuated the Ang III (1pmol)-induced nociceptive behaviour in mice. Moreover, the inhibitory effect of Ang (1-7) at a dose of 100fmol was prevented by A779 (30fmol), a Mas receptor antagonist. Western blot analysis showed that the phosphorylation of p38 MAPK induced by the i.t. administration of Ang III (1pmol) was also attenuated by Ang (1-7) (100fmol), and this inhibition was prevented by A779 (30fmol). Furthermore, we showed that in the lumbar superficial dorsal horn, Mas receptors are expressed in neurons and microglia but absent from astrocytes. Together, these results suggest that the i.t. administration of Ang (1-7) attenuates the nociceptive behaviour and accompanying p38 MAPK phosphorylation induced by Ang III, and that this effect is likely mediated through Mas receptors on spinal neurons.

Significance of angiotensin 1-7 coupling with MAS1 receptor and other GPCRs to the renin-angiotensin system: IUPHAR Review 22

Angiotensins are a group of hormonal peptides and include angiotensin II and angiotensin 1-7 produced by the renin angiotensin system. The biology, pharmacology and biochemistry of the receptors for angiotensins were extensively reviewed recently. In the review, the receptor nomenclature committee was not emphatic on designating MAS1 as the angiotensin 1-7 receptor on the basis of lack of classical G protein signalling and desensitization in response to angiotensin 1-7, as well as a lack of consensus on confirmatory ligand pharmacological analyses. A review of recent publications (2013-2016) on the rapidly progressing research on angiotensin 1-7 revealed that MAS1 and two additional receptors can function as 'angiotensin 1-7 receptors', and this deserves further consideration. In this review we have summarized the information on angiotensin 1-7 receptors and their crosstalk with classical angiotensin II receptors in the context of the functions of the renin angiotensin system. It was concluded that the receptors for angiotensin II and angiotensin 1-7 make up a sophisticated cross-regulated signalling network that modulates the endogenous protective and pathogenic facets of the renin angiotensin system.