Substance P ameliorates tumor necrosis factor-alpha-induced endothelial cell dysfunction by regulating eNOS expression in vitro

Substance P reversibly compromises the integrity and function of blood-brain barrier

BACKGROUND

Substance P (SP) plays a role in vasodilatation and tissue integrity through its receptor, neurokinin 1 (NK1R). However, its specific effect on blood-brain barrier (BBB) remains unknown.

METHODS

The impact of SP on the integrity/function of human BBB model in vitro, composed of brain microvascular endothelial cells (BMECs), astrocytes and pericytes, was assessed by measurements of transendothelial electrical resistance and paracellular flux of sodium fluorescein (NaF), respectively in the absence/presence of specific inhibitors targeting NK1R (CP96345), Rho-associated protein kinase (ROCK; Y27632) and nitric oxide synthase (NOS; N(G)-nitro-L-arginine methyl ester). Sodium nitroprusside (SNP), a NO donor, was employed as a positive control. The levels of tight junction proteins, zonula occludens-1, occludin and claudin-5 alongside RhoA/ROCK/myosin regulatory light chain-2 (MLC2) and extracellular signal‑regulated protein kinase (Erk1/2) proteins were detected by western analyses. Subcellular localisations of F-actin and tight junction proteins were visualized by immunocytochemistry. Flow cytometry was used to detect transient calcium release.

RESULTS

Exposure to SP increased RhoA, ROCK2 and phosphorylated serine-19 MLC2 protein levels and Erk1/2 phosphorylation in BMECs which were abolished by CP96345. These increases were independent of the changes in intracellular calcium availability. SP perturbed BBB in a time-dependent fashion through induction of stress fibres. Changes in tight junction protein dissolution or relocalisation were not involved in SP-mediated BBB breakdown. Inhibition of NOS, ROCK and NK1R mitigated the effect of SP on BBB characteristics and stress fibre formation.

CONCLUSION

SP promoted a reversible decline in BBB integrity independent of tight junction proteins expression or localisation.

Substance P Alleviates Retinal Pigment Epithelium Dysfunction Caused by High Glucose-Induced Stress

When the retina is constantly affected by high glucose (HG) due to diabetes, the barrier function of the retinal pigment epithelium (RPE) is impaired, accompanied by unnecessary vascularization. This eventually leads to the development of diabetic retinopathy (DR). This study investigated the recovery effect of substance P (SP) on RPE injured by HG. RPE was treated with HG for 24 h, and HG-induced cellular injuries were confirmed. SP was added to the dysfunctional RPE. Compared to RPE in low glucose (LG) conditions, HG-damaged RPE had large, fibrotic cell shapes, and its cellular viability decreased. HG treatment reduced tight junction protein expression levels and caused oxidative stress by interrupting the antioxidant system; this was followed by inflammatory factor intracellular adhesion molecule-1 (ICAM-1), Monocyte chemotactic protein-1 (MCP-1), and angiogenesis factor vascular endothelial growth factor (VEGF) expression. SP treatment contributed to RPE recovery by enhancing cell viability, tight junction protein expression, and RPE function under HG conditions, possibly by activating the Akt signaling pathway. Importantly, SP treatment reduced ICAM-1, MCP-1, and VEGF expression. Collectively, SP activated survival signals to suppress oxidative stress and improve retinal barrier function in RPE, accompanied by immune suppression. This suggests the possible application of SP to diabetic retinal injuries.

The neuropeptide substance P/neurokinin-1 receptor system and diabetes: From mechanism to therapy

Diabetes is a significant public health issue known as the world's fastest-growing disease condition. It is characterized by persistent hyperglycemia and subsequent chronic complications leading to organ dysfunction and, ultimately, the failure of target organs. Substance P (SP) is an undecapeptide that belongs to the family of tachykinin (TK) peptides. The SP-mediated activation of the neurokinin 1 receptor (NK1R) regulates many pathophysiological processes in the body. There is also a relation between the SP/NK1R system and diabetic processes. Importantly, deregulated expression of SP has been reported in diabetes and diabetes-associated chronic complications. SP can induce both diabetogenic and antidiabetogenic effects and thus affect the pathology of diabetes destructively or protectively. Here, we review the current knowledge of the functional relevance of the SP/NK1R system in diabetes pathogenesis and its exploitation for diabetes therapy. A comprehensive understanding of the role of the SP/NK1R system in diabetes is expected to shed further light on developing new therapeutic possibilities for diabetes and its associated chronic conditions.

Substance P-Mediated Vascular Protection Ameliorates Bone Loss

Estrogen deficiency causes bone loss via diverse pathological cellular events. The involvement of the vasculature in bone formation has been widely studied, and type H vasculature has been found to be closely related to bone healing. Ovariectomy- (OVX-) induced estrogen deficiency reduces type H vessel density and promotes reduction of bone density. Analysis of early events after OVX showed that estrogen deficiency preferentially induces oxidative stress, which might provoke endothelial dysfunction and reduce angiogenic factors systemically and locally. The instability of the vascular potential is expected to promote bone loss under estrogen deficiency. Substance P (SP) is an endogenous neuropeptide that controls inflammation and prevents cell death under pathological conditions. SP can elevate nitric oxide production in endothelial cells and inhibit endothelial dysfunction. This study is aimed at investigating the preventive effects of systemically injected SP on OVX-induced vascular loss and osteoporosis onset. SP was systemically administered to OVX rats twice a week for 4 weeks, immediately after OVX induction. OVX conditions could decrease antioxidant enzyme activity, type H vessels, and angiogenic growth factors in the bone marrow, followed by inflammation and bone loss. However, pretreatment with SP could block type H vessel loss, accompanied by the enrichment of nitric oxide and sustained angiogenic factors. SP-mediated early vascular protection inhibits bone density reduction. Altogether, this study suggests that early administration of SP can block osteoporosis development by modulating oxidative stress and protecting the bone vasculature and angiogenic paracrine potential at the initial stage of estrogen deficiency.

Effects of substance P on human cerebral microvascular endothelial cell line hCMEC/D3 are mediated exclusively through a truncated NK-1 receptor and depend on cell confluence

The neuropeptide substance P (SP) mediates pain transmission, immune modulation, vasodilation and neurogenic inflammation. Its role in the peripheral nervous system has been well characterised. However, its actions on the blood-brain barrier (BBB) are less clear and warrant further study. The aim of this study was to characterise the effect of SP on the brain microvascular endothelial cells using the immortalized human brain microvascular endothelial cell line hCMEC/D3. As part of our studies, we have evaluated changes in expression, at mRNA and protein levels, of genes involved in the function of the blood-brain barrier such as occludin, induced by exposure to SP. We show that the effect of SP is dependent on cell confluence status. Thus, at low confluence but not at full confluence, SP treatment reduced occludin expression. The expression of the SP receptor, neurokinin-1 receptor (NK-1R) (the truncated form of the receptor expressed exclusively in this cell line) was also modulated in a similar pattern. SP treatment stimulated extracellular signal-regulated kinase (Erk2) phosphorylation which was not associated to changes in Interleukin-6 (IL-6), Interleukin-8 (IL-8), or Intercellular Adhesion Molecule 1 (ICAM-1) protein expression. In addition, SP treatment effectively recovered nitric oxide production on cells exposed to tumour necrosis factor alpha (TNF-α). SP did not trigger intracellular calcium release in hCMEC/D3 cells. We conclude that hCMEC/D3 cells are partially responsive to SP, that the effects are mediated through the truncated form of the receptor and are dependent on the confluence status of these cells.

Substance P, A Promising Therapeutic Target in Musculoskeletal Disorders

A large number of studies have focused on the role of substance P (SP) and the neurokinin-1 receptor (NK1R) in the pathogenesis of a variety of medical conditions. This review provides an overview of the role of the SP-NK1R pathway in the pathogenesis of musculoskeletal disorders and the evidence for its role as a therapeutic target for these disorders, which are major public health problems in most countries. To summarize, the brief involvement of SP may affect tendon healing in an acute injury setting. SP combined with an adequate conjugate can be a regenerative therapeutic option in osteoarthritis. The NK1R antagonist is a promising agent for tendinopathy, rheumatoid arthritis, and osteoarthritis. Research on the SP-NK1R pathway will be helpful for developing novel drugs for osteoporosis.

Substance-P Inhibits Cardiac Microvascular Endothelial Dysfunction Caused by High Glucose-Induced Oxidative Stress

Diabetes is characterized by high glucose (HG) levels in the blood circulation, leading to exposure of the vascular endothelium to HG conditions. Hyperglycemia causes oxidative stress via excessive reactive oxygen species (ROS) production in the endothelium, which leads to cellular dysfunction and the development of diabetic vascular diseases. Substance-P (SP) is an endogenous peptide involved in cell proliferation and migration by activating survival-related signaling pathways. In this study, we evaluated the role of SP in cardiac microvascular endothelial cells (CMECs) in HG-induced oxidative stress. CMECs were treated with diverse concentrations of glucose, and then the optimal dose was determined. Treatment of CMECs with HG reduced their viability and induced excessive ROS secretion, inactivation of PI3/Akt signaling, and loss of vasculature-forming ability in vitro. Notably, HG treatment altered the cytokine profile of CMECs. However, SP treatment inhibited the HG-mediated aggravation of CMECs by restoring viability, free radical balance, and paracrine potential. SP-treated CMECs retained the capacity to form compact and long stretching-tube structures. Collectively, our data provide evidence that SP treatment can block endothelial dysfunction in hyperglycemia and suggest the possibility of using SP for treating diabetic complications as an antioxidant.

Substance P ameliorates TNF-α-mediated impairment of human aortic vascular cells in vitro

Vascular diseases are caused by endothelial dysfunction due to inflammation. On endothelial injury, the expression of extracellular matrix (ECM) is enhanced and nitric oxide (NO) bioavailability becomes deficient. This condition affects endothelial metabolism and leads to vascular destruction. The aim of this investigation was to determine whether substance P (SP) is able to protect the endothelium against inflammatory stress. To this end, aortic endothelial cells were pre-treated with SP, followed by tumour necrosis factor α (TNF-α), and cellular responses were evaluated using a combination of cell biology and quantification assays, as well as western blot analyses. Our results show that TNF-α enhanced ECM expression and reduced NO production within 4 hours, promoting immune cell adhesion to the endothelium and monocyte chemoattractant protein-1 (MCP-1) secretion from aortic smooth muscle cells. However, SP treatment ameliorated TNF-α-induced endothelial impairment by maintaining low ECM levels. Our data suggest that this protective effect is mediated by Akt activation and NO-enriched conditions. The inhibition of aortic endothelial cell injury by SP also reduced MCP-1 production in aortic smooth muscle cells. Together, our data indicate that SP can protect aortic endothelial and smooth muscle cells from inflammatory injury, which suggests that SP may prevent cardiovascular disease.

Substance P blocks β-aminopropionitrile-induced aortic injury through modulation of M2 monocyte-skewed monocytopoiesis

Aortic injuries, including aortic aneurysms and dissections, are fatal vascular diseases with distinct histopathological features in the aortic tissue such as inflammation-induced endothelial dysfunction, infiltration of immune cells, and breakdown of the extracellular matrix. Few treatments are available for treating aortic aneurysms and dissections; thus, basic and clinical studies worldwide have been attempted to inhibit disease progression. Substance P (SP) exerts anti-inflammatory effects and promotes restoration of the damaged endothelium, leading to vasculature protection and facilitation of tissue repair. This study was conducted to explore the protective effects of systemically injected SP on thoracic aortic injury (TAI). A TAI animal model was induced by orally administering β-aminopropionitrile to rats for 6 weeks. β-aminopropionitrile blocked crosslinking ECM in aorta to cause structural alteration with inflammation within 1 week and then, induced aortic dissection within 4 weeks of initiating treatment, leading to mortality within 6 weeks. Treatment of TAI rats with SP-induced anti-inflammatory responses systemically and locally, possibly by enriching anti-inflammatory M2 monocytes in the spleen and peripheral blood at early phase of aortic injury due to β-aminopropionitrile. SP-induced immune suppression finally prevented the development of aortic dissection by limiting inflammation-mediated aortic destruction. Taken together, these results suggest that SP treatment can block aortic injury by controlling the immune-cell profile and suppressing proinflammatory responses during the initial stage of vascular disease progression.

Substance P blocks ovariectomy-induced bone loss by modulating inflammation and potentiating stem cell function

Osteoporosis is an age-related disease caused by imbalanced bone remodeling resulting from excessive bone resorption. Osteoporosis is tightly linked with induction of chronic inflammation, which activates osteoclasts and impairs osteoprogenitor in bone marrow. T helper 17 (Th17) cells have been recently recognized as one of major inducers in the pathophysiology of bone loss by secreting IL-17. Thus, modulation of Th17 development is anticipated to affect the progression of osteoporosis.

Substance P (SP) is reported to provide anti-inflammatory effects by controlling immune cell profile and also, promote restoration of damaged stem cell niches—the bone marrow—by repopulating BMSCs or potentiating its paracrine ability. This study aimed to explore the therapeutic effects of systemically injected SP on ovariectomy (OVX)-induced osteoporosis.

Resultantly, SP injection obviously blocked OVX-induced impairment of bone microarchitecture and reduction of the mineral density. In osteoporotic condition, SP could ameliorate chronic inflammation by promoting Treg cell polarization and inhibiting the development of osteoclastogenic Th17 cells. Moreover, SP could rejuvenate stem cell and enable stem cells to repopulate and differentiate into osteoblast.

Collectively, our study strongly suggests that SP treatment can block osteoporosis and furthermore, SP treatment provides therapeutic effect on chronic disease with inflammation and stem cell dysfunction.

Substance-P Restores Cellular Activity of ADSC Impaired by Oxidative Stress

Oxidative stress induces cellular damage, which accelerates aging and promotes the development of serious illnesses. Adipose-derived stem cells (ADSCs) are novel cellular therapeutic tools and have been applied for tissue regeneration. However, ADSCs from aged and diseased individuals may be affected in vivo by the accumulation of free radicals, which can impair their therapeutic efficacy. Substance-P (SP) is a neuropeptide that is known to rescue stem cells from senescence and inflammatory attack, and this study explored the restorative effect of SP on ADSCs under oxidative stress. ADSCs were transiently exposed to H2O2, and then treated with SP. H2O2 treatment decreased ADSC cell viability, proliferation, and cytokine production and this activity was not recovered even after the removal of H2O2. However, the addition of SP increased cell viability and restored paracrine potential, leading to the accelerated repopulation of ADSCs injured by H2O2. Furthermore, SP was capable of activating Akt/GSK-3β signaling, which was found to be downregulated following H2O2 treatment. This might contribute to the restorative effect of SP on injured ADSCs. Collectively, SP can protect ADSCs from oxidant-induced cell damage, possibly by activating Akt/GSK-3β signaling in ADSCs. This study supports the possibility that SP can recover cell activity from oxidative stress-induced dysfunction.

Substance P Improves Renal Ischemia Reperfusion Injury Through Modulating Immune Response

Substance P (SP), an injury-inducible messenger that mobilizes bone marrow stem cells and modulates the immune response, has been suggested as a novel target for therapeutic agents. We evaluated the role of SP as an immune cell modulator during the progression of renal ischemic/reperfusion injury (IRI). Unilateral IRI induced the transient expression of endogenous SP and the infiltration of CCR7⁺ M1 macrophages in injured kidneys. However, SP altered the intrarenal macrophage polarization from CCR7⁺ M1 macrophages to CD206⁺ M2 macrophages in injured kidneys. SP also modulated bone marrow-derived neutrophils and mesenchymal stromal cells after IRI. SP treatment for 4 weeks starting one week after unilateral IRI significantly preserved kidney size and length and normal tubular structures and alleviated necrotic tubules, inflammation, apoptosis, and tubulointerstitial fibrosis. The beneficial effects of SP were accompanied by attenuation of intrarenal recruitment of CD4, CD8, and CD20 cells and abnormal angiogenesis. The immunomodulatory effect of SP suggested that SP could be a promising therapeutic target for preventing the progression of acute kidney injury to chronic kidney disease.

Substance P accelerates wound repair by promoting neovascularization and preventing inflammation in an ischemia mouse model

AIMS

Arterial insufficiency ulcers are frequent complications of peripheral artery disease and infection or long-term neglect of the ulcer can eventually lead to amputation of the affected body part. An ischemic environment, caused by interrupted blood flow, affects the supply of nutrients and elongates the inflammation period, inducing tissue degeneration. Thus, the modulation of neovascularization and inflammation could be an ideal therapeutic strategy for ischemic wound healing. This study aimed to elucidate whether systemically administered substance P (SP) could promote ischemic wound repair in mice by restoring blood perfusion and suppressing inflammation.

MAIN METHODS

The effects of SP were assessed by analyzing wound size, blood flow, epidermal and dermal layer regeneration, vessel formation, and the inflammatory cytokine profiles in a hind-limb ischemia non-clinical mouse model.

KEY FINDINGS

SP-treated mice exhibited dramatically rapid wound healing and restoration of blood flow within the ischemic zone, compared with saline-treated mice. Notably, SP-treated mice showed enhanced pericyte-covered vasculature compared to saline-treated mice. Moreover, anti-inflammatory effects were detected in mice in the SP-treated group, including suppression of inflammation-mediated spleen enlargement, reduction of tumor necrosis factor-alpha, and promotion of circulatory interleukin-10 levels.

SIGNIFICANCE

These results suggest that SP could be a possible therapeutic candidate for patients with peripheral artery disease, including those with ischemic ulcers.