What have we learned about the kallikrein-kinin and renin-angiotensin systems in neurological disorders?

A comprehensive review on current understanding of bradykinin in COVID-19 and inflammatory diseases

Bradykinin, a member of the kallikrein–kinin system (KKS), is a potent, short-lived vasoactive peptide that acts as a vasodilator and an inflammatory mediator in a number of signaling mechanisms. Bradykinin induced signaling is mediated through kinin B1 (BDKRB1) and B2 (BDKRB2) transmembrane receptors coupled with different subunits of G proteins (G_αi/G_α0, G_αq and G_β1γ2). The bradykinin-mediated signaling mechanism activates excessive pro-inflammatory cytokines, including IL-6, IL-1β, IL-8 and IL-2. Upregulation of these cytokines has implications in a wide range of clinical conditions such as inflammation leading to fibrosis, cardiovascular diseases, and most recently, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). In SARS-CoV-2 infection, bradykinin is found to be at raised levels and is reported to trigger a diverse array of symptoms. All of this brings bradykinin to the core point as a molecule of immense therapeutic value. Our understanding of its involvement in various pathways has expanded with time. Therefore, there is a need to look at the overall picture that emerges from the developments made by deciphering the bradykinin mediated signaling mechanisms involved in the pathological conditions. It will help devise strategies for developing better treatment modalities in the implicated diseases. This review summarizes the current state of knowledge on bradykinin mediated signaling in the diverse conditions described above, with a marked emphasis on the therapeutic potential of targeting the bradykinin receptor.

Successful Treatment of Noise-Induced Hearing Loss by Mesenchymal Stromal Cells: An RNAseq Analysis of Protective/Repair Pathways

Mesenchymal stromal cells (MSCs) are an adult derived stem cell-like population that has been shown to mediate repair in a wide range of degenerative disorders. The protective effects of MSCs are mainly mediated by the release of growth factors and cytokines thereby modulating the diseased environment and the immune system. Within the inner ear, MSCs have been shown protective against tissue damage induced by sound and a variety of ototoxins. To better understand the mechanism of action of MSCs in the inner ear, mice were exposed to narrow band noise. After exposure, MSCs derived from human umbilical cord Wharton's jelly were injected into the perilymph. Controls consisted of mice exposed to sound trauma only. Forty-eight hours post-cell delivery, total RNA was extracted from the cochlea and RNAseq performed to evaluate the gene expression induced by the cell therapy. Changes in gene expression were grouped together based on gene ontology classification. A separate cohort of animals was treated in a similar fashion and allowed to survive for 2 weeks post-cell therapy and hearing outcomes determined. Treatment with MSCs after severe sound trauma induced a moderate hearing protective effect. MSC treatment resulted in an up-regulation of genes related to immune modulation, hypoxia response, mitochondrial function and regulation of apoptosis. There was a down-regulation of genes related to synaptic remodeling, calcium homeostasis and the extracellular matrix. Application of MSCs may provide a novel approach to treating sound trauma induced hearing loss and may aid in the identification of novel strategies to protect hearing.

A modular map of Bradykinin-mediated inflammatory signaling network

Bradykinin, a member of the kallikrein-kinin system (KKS), is associated with an inflammatory response pathway with diverse vascular permeability functions, including thrombosis and blood coagulation. In majority, bradykinin signals through Bradykinin Receptor B2 (B2R). B2R is a G protein-coupled receptor (GPCR) coupled to G protein family such as Gα_qs, Gα_q/Gα_11, Gα_i1, and Gβ1_γ2_. B2R stimulation leads to the activation of a signaling cascade of downstream molecules such as phospholipases, protein kinase C, Ras/Raf-1/MAPK, and PI3K/AKT and secondary messengers such as inositol-1,4,5-trisphosphate, diacylglycerol and Ca²⁺ ions. These secondary messengers modulate the production of nitric oxide or prostaglandins. Bradykinin-mediated signaling is implicated in inflammation, chronic pain, vasculopathy, neuropathy, obesity, diabetes, and cancer. Despite the biomedical importance of bradykinin, a resource of bradykinin-mediated signaling pathway is currently not available. Here, we developed a pathway resource of signaling events mediated by bradykinin. By employing data mining strategies in the published literature, we describe an integrated pathway reaction map of bradykinin consisting of 233 reactions. Bradykinin signaling pathway events included 25 enzyme catalysis reactions, 12 translocations, 83 activation/inhibition reactions, 11 molecular associations, 45 protein expression and 57 gene regulation events. The pathway map is made publicly available on the WikiPathways Database with the ID URL: https://www.wikipathways.org/index.php/Pathway:WP5132. The bradykinin-mediated signaling pathway map will facilitate the identification of novel candidates as therapeutic targets for diseases associated with dysregulated bradykinin signaling.

Bradykinin Activates the Bradykinin B2 Receptor to Ameliorate Neuronal Injury in a Rat Model of Spinal Cord Ischemia-Reperfusion Injury

Bradykinin and bradykinin B2 receptors (B2R) play important roles in both the peripheral and central nervous systems. The aim of this study was to explore the changes of bradykinin and B2R in spinal cord ischemic injury (SCII) and whether bradykinin treatment would improve the neurologic function of SCII rats. The rats were divided into the sham group, the SCII group, and three doses of bradykinin (50, 100, 150 μg/kg) groups. The neurologic function was assessed by the Basso, Beattie, and Bresnahan (BBB) score at -1, 1, 3, 5, and 7 days postsurgery. Bradykinin concentration in serum and IL-6, TNF-α, and MCP-1 levels in the spinal cord were detected by ELISA. The mRNA expressions of B2R, IL-6, TNF-α, MCP-1, COX-2, and iNOS in the spinal cord were determined by RT-PCR. The protein expressions of B2R, COX-2, iNOS, p65, and p-p65 were detected by Western blot. Immunohistochemical staining was used to examine B2R expression in the L4-6 segments of the spinal cord. Bradykinin levels in serum and B2R expression in the spinal cord were downregulated in SCII rats. Bradykinin treatment significantly improved the hind limb motor function of SCII rats and increased B2R expression, inhibiting COX-2, iNOS, and p-p65 expression in the spinal cord of SCII rats together with a decrease of the inflammatory mediators of IL-6, TNF-α, and MCP-1 levels. Bradykinin administration activated B2R in the spinal cord of SCII rats, which may improve hind limb locomotor recovery by regulating the NF-κB signaling pathway to inhibit the inflammatory response. These findings may provide a theoretical basis for the clinical application of bradykinin in SCII.

Involvement of Bradykinin Receptor 2 in Nerve Growth Factor Neuroprotective Activity

Neurotrophin nerve growth factor (NGF) has been demonstrated to upregulate the gene expression of bradykinin receptor 2 (B2R) on sensory neurons, thus facilitating nociceptive signals. The aim of the present study is to investigate the involvement of B2R in the NGF mechanism of action in nonsensory neurons in vitro by using rat mixed cortical primary cultures (CNs) and mouse hippocampal slices, and in vivo in Alzheimer’s disease (AD) transgenic mice (5xFAD) chronically treated with NGF. A significant NGF-mediated upregulation of B2R was demonstrated by microarray, Western blot, and immunofluorescence analysis in CNs, indicating microglial cells as the target of this modulation. The B2R involvement in the NGF mechanism of action was also demonstrated by using a selective B2R antagonist which was able to reverse the neuroprotective effect of NGF in CNs, as revealed by viability assay, and the NGF-induced long-term potentiation (LTP) in hippocampal slices. To confirm in vitro observations, B2R upregulation was observed in 5xFAD mouse brain following chronic intranasal NGF treatment. This study demonstrates for the first time that B2R is a key element in the neuroprotective activity and synaptic plasticity mediated by NGF in brain cells.

Kininogen Level in the Cerebrospinal Fluid May Be a Potential Biomarker for Predicting Epileptogenesis

Purpose: Epilepsy is a highly disabling neurological disorder. Brain insult is the most critical cause of epilepsy in adults. This study aimed to find reliable and efficient biomarkers for predicting secondary epilepsy. Materials and methods: The LiCl-pilocarpine (LiCl-Pilo) chronic epilepsy rat model was used, and rat cerebrospinal fluid (CSF) was collected 5 days after status epilepticus (SE). The CSF was analyzed using the label-free LC-ESI-Q-TOF-MS/MS. Differential expression of proteins was confirmed using enzyme-linked immunosorbent assay (ELISA) and Western blotting. The corresponding protein level in the CSF of patients with encephalitis in the postacute phase was determined using ELISA and compared between patients with and without symptomatic epilepsy after encephalitis during a 2-year follow-up. Results: The proteomics and ELISA results showed that the protein level of kininogen (KNG) was obviously elevated in both CSF and hippocampus, but not in serum, 5 days after the onset of SE in LiCl-Pilo chronic epilepsy model rats. In patients with encephalitis, the protein level of KNG in the CSF in the postacute phase was significantly elevated in patients with a recurrent epileptic seizure during a 2-year follow-up than in patients without a recurrent seizure. Conclusion: KNG in the CSF may serve as a potential biomarker for predicting epileptogenesis in patients with encephalitis.

Implication of the Kallikrein-Kinin system in neurological disorders: Quest for potential biomarkers and mechanisms

Neurological disorders represent major health concerns in terms of comorbidity and mortality worldwide. Despite a tremendous increase in our understanding of the pathophysiological processes involved in disease progression and prevention, the accumulated knowledge so far resulted in relatively moderate translational benefits in terms of therapeutic interventions and enhanced clinical outcomes. Aiming at specific neural molecular pathways, different strategies have been geared to target the development and progression of such disorders. The kallikrein-kinin system (KKS) is among the most delineated candidate systems due to its ubiquitous roles mediating several of the pathophysiological features of these neurological disorders as well as being implicated in regulating various brain functions. Several experimental KKS models revealed that the inhibition or stimulation of the two receptors of the KKS system (B1R and B2R) can exhibit neuroprotective and/or adverse pathological outcomes. This updated review provides background details of the KKS components and their functions in different neurological disorders including temporal lobe epilepsy, traumatic brain injury, stroke, spinal cord injury, Alzheimer's disease, multiple sclerosis and glioma. Finally, this work will highlight the putative roles of the KKS components as potential neurotherapeutic targets and provide future perspectives on the possibility of translating these findings into potential clinical biomarkers in neurological disease.

Excess of Aminopeptidase A in the Brain Elevates Blood Pressure via the Angiotensin II Type 1 and Bradykinin B2 Receptors without Dipsogenic Effect

Aminopeptidase A (APA) cleaves angiotensin (Ang) II, kallidin, and other related peptides. In the brain, it activates the renin angiotensin system and causes hypertension. Limited data are available on the dipsogenic effect of APA and pressor effect of degraded peptides of APA such as bradykinin. Wistar-Kyoto rats received intracerebroventricular (icv) APA in a conscious, unrestrained state after pretreatment with (i) vehicle, (ii) 80 μg of telmisartan, an Ang II type-1 (AT1) receptor blocker, (iii) 800 nmol of amastatin, an aminopeptidase inhibitor, and (iv) 1 nmol of HOE-140, a bradykinin B2 receptor blocker. Icv administration of 400 and 800 ng of APA increased blood pressure by 12.6 ± 3.0 and 19.0 ± 3.1 mmHg, respectively. APA did not evoke drinking behavior. Pressor response to APA was attenuated on pretreatment with telmisartan (vehicle: 22.1 ± 2.2 mmHg versus telmisartan: 10.4 ± 3.2 mmHg). Pressor response to APA was also attenuated with amastatin and HOE-140 (vehicle: 26.5 ± 1.1 mmHg, amastatin: 14.4 ± 4.2 mmHg, HOE-140: 16.4 ± 2.2 mmHg). In conclusion, APA increase in the brain evokes a pressor response via enzymatic activity without dipsogenic effect. AT1 receptors and B2 receptors in the brain may contribute to the APA-induced pressor response.

Kinin Peptides Enhance Inflammatory and Oxidative Responses Promoting Apoptosis in a Parkinson's Disease Cellular Model

Kinin peptides ubiquitously occur in nervous tissue and participate in inflammatory processes associated with distinct neurological disorders. These substances have also been demonstrated to promote the oxidative stress. On the other hand, the importance of oxidative stress and inflammation has been emphasized in disorders that involve the neurodegenerative processes such as Parkinson's disease (PD). A growing number of reports have demonstrated the increased expression of kinin receptors in neurodegenerative diseases. In this study, the effect of bradykinin and des-Arg¹⁰-kallidin, two representative kinin peptides, was analyzed with respect to inflammatory response and induction of oxidative stress in a PD cellular model, obtained after stimulation of differentiated SK-N-SH cells with a neurotoxin, 1-methyl-4-phenylpyridinium. Kinin peptides caused an increased cytokine release and enhanced production of reactive oxygen species and NO by cells. These changes were accompanied by a loss of cell viability and a greater activation of caspases involved in apoptosis progression. Moreover, the neurotoxin and kinin peptides altered the dopamine receptor 2 expression. Kinin receptor expression was also changed by the neurotoxin. These results suggest a mediatory role of kinin peptides in the development of neurodegeneration and may offer new possibilities for its regulation by using specific antagonists of kinin receptors.

The novel nonapeptide acein targets angiotensin converting enzyme in the brain and induces dopamine release

BACKGROUND AND PURPOSE

Using an in-house bioinformatics programme, we identified and synthesized a novel nonapeptide, H-Pro-Pro-Thr-Thr-Thr-Lys-Phe-Ala-Ala-OH. Here, we have studied its biological activity, in vitro and in vivo, and have identified its target in the brain.

EXPERIMENTAL APPROACH

The affinity of the peptide was characterized using purified whole brain and striatal membranes from guinea pigs and rats . Its effect on behaviour in rats following intra-striatal injection of the peptide was investigated. A photoaffinity UV cross-linking approach combined with subsequent affinity purification of the ligand covalently bound to its receptor allowed identification of its target.

KEY RESULTS

The peptide bound with high affinity to a single class of binding sites, specifically localized in the striatum and substantia nigra of brains from guinea pigs and rats. When injected within the striatum of rats, the peptide stimulated in vitro and in vivo dopamine release and induced dopamine-like motor effects. We purified the target of the peptide, a ~151 kDa protein that was identified by MS/MS as angiotensin converting enzyme (ACE I). Therefore, we decided to name the peptide acein.

CONCLUSION AND IMPLICATIONS

The synthetic nonapeptide acein interacted with high affinity with brain membrane-bound ACE. This interaction occurs at a different site from the active site involved in the well-known peptidase activity, without modifying the peptidase activity. Acein, in vitro and in vivo, significantly increased stimulated release of dopamine from the brain. These results suggest a more important role for brain ACE than initially suspected.

Renin inhibitor aliskiren exerts beneficial effect on trabecular bone by regulating skeletal renin-angiotensin system and kallikrein-kinin system in ovariectomized mice

SUMMARY

The skeletal renin-angiotensin system contributes to the development of osteoporosis. The renin inhibitor aliskiren exhibited beneficial effects on trabecular bone of osteoporotic mice, and this action might be mediated through angiotensin and bradykinin receptor pathways. This study implies the potential application of renin inhibitor in the management for postmenopausal osteoporosis.

INTRODUCTION

The skeletal renin-angiotensin system plays key role in the pathological process of osteoporosis. The present study is designed to elucidate the effect of renin inhibitor aliskiren on trabecular bone and its potential action mechanism in ovariectomized (OVX) mice.

METHODS

The OVX mice were treated with low dose (5 mg/kg) or high dose (25 mg/kg) of aliskiren or its vehicle for 8 weeks. The bone turnover markers were measured by ELISA. The structural parameters of trabecular bone at lumbar vertebra (LV) and distal femoral metaphysis were measured by micro-CT. The expression of messenger RNA (mRNA) and protein was studied by RT-PCR and immunoblotting, respectively.

RESULTS

Aliskiren treatment reduced urinary excretion of calcium and serum level of tartrate-resistant acid phosphatase in OVX mice. The treatment with aliskiren significantly increased bone volume (BV/TV) and connectivity density (Conn.D) of trabecular bone at LV-2 and LV-5 as well as dramatically enhanced BV/TV, Conn.D, bone mineral density (BMD/BV) and decreased bone surface (BS/BV) at the distal femoral end. Aliskiren significantly down-regulated the expression of angiotensinogen, angiotensin II (Ang II), Ang II type 1 receptor, bradykinin receptor (BR)-1, and osteocytic-specific gene sclerostin as well as the osteoclast-specific genes, including carbonic anhydrase II, matrix metalloproteinase-9, and cathepsin K.

CONCLUSIONS

This study revealed that renin inhibitor aliskiren exhibited the beneficial effects on trabecular bone of ovariectomy-induced osteoporotic mice, and the underlying mechanism for this action might be mediated through Ang II and BR signaling pathways in bone.

Involvement of Kallikrein-Related Peptidases in Normal and Pathologic Processes

Human kallikrein-related peptidases (KLKs) are a subgroup of serine proteases that participate in proteolytic pathways and control protein levels in normal physiology as well as in several pathological conditions. Their complex network of stimulatory and inhibitory interactions may induce inflammatory and immune responses and contribute to the neoplastic phenotype through the regulation of several cellular processes, such as proliferation, survival, migration, and invasion. This family of proteases, which includes one of the most useful cancer biomarkers, kallikrein-related peptidase 3 or PSA, also has a protective effect against cancer promoting apoptosis or counteracting angiogenesis and cell proliferation. Therefore, they represent attractive therapeutic targets and may have important applications in clinical oncology. Despite being intensively studied, many gaps in our knowledge on several molecular aspects of KLK functions still exist. This review aims to summarize recent data on their involvement in different processes related to health and disease, in particular those directly or indirectly linked to the neoplastic process.