The anti-inflammatory peptide Ac-SDKP: Synthesis, role in ACE inhibition, and its therapeutic potential in hypertension and cardiovascular diseases

The anti-inflammatory and tolerogenic potential of small spleen peptides

Maintaining peripheral immune tolerance and preventing harmful autoimmune reactions is a fundamental task of the immune system. However, these essential functions are significantly compromised during autoimmune disorders, creating a major challenge in treating these conditions. In this context, we provide an overview of research on small spleen polypeptides (SSPs) that naturally regulate peripheral immune tolerance. Alongside outlining the observed effects of SSPs, we summarize here the findings on the cellular and molecular mechanisms that underlie their regulatory impact. Specifically, SSPs have demonstrated remarkable effectiveness in halting the progression of developing or established autoimmune disorders like psoriasis or arthritis in animal models. They primarily target dendritic cells (DCs), swiftly prompting the production of extracellular ATP, which is then degraded and sensed by adenosine receptors. This process triggers the mTOR signaling cascade, similar to powerful immune triggers, but instead of a rapid and intense reaction, it leads to a moderate yet significant activation of the mTOR signaling cascade. This induces a tolerogenic state in dendritic cells, ultimately leading to the generation of Foxp3+ immunosuppressor Treg cells. In addition, SSPs may indirectly attenuate the autoimmune response by reducing extracellular ATP synthesis in non-immune cells, such as endothelial cells, when exposed to elevated levels of proinflammatory cytokines. SSPs thus have the potential to contribute to the restoration of peripheral immune tolerance and may offer valuable therapeutic benefits in treating autoimmune diseases.

A deep learning model for anti-inflammatory peptides identification based on deep variational autoencoder and contrastive learning

As a class of biologically active molecules with significant immunomodulatory and anti-inflammatory effects, anti-inflammatory peptides have important application value in the medical and biotechnology fields due to their unique biological functions. Research on the identification of anti-inflammatory peptides provides important theoretical foundations and practical value for a deeper understanding of the biological mechanisms of inflammation and immune regulation, as well as for the development of new drugs and biotechnological applications. Therefore, it is necessary to develop more advanced computational models for identifying anti-inflammatory peptides. In this study, we propose a deep learning model named DAC-AIPs based on variational autoencoder and contrastive learning for accurate identification of anti-inflammatory peptides. In the sequence encoding part, the incorporation of multi-hot encoding helps capture richer sequence information. The autoencoder, composed of convolutional layers and linear layers, can learn latent features and reconstruct features, with variational inference enhancing the representation capability of latent features. Additionally, the introduction of contrastive learning aims to improve the model's classification ability. Through cross-validation and independent dataset testing experiments, DAC-AIPs achieves superior performance compared to existing state-of-the-art models. In cross-validation, the classification accuracy of DAC-AIPs reached around 88%, which is 7% higher than previous models. Furthermore, various ablation experiments and interpretability experiments validate the effectiveness of DAC-AIPs. Finally, a user-friendly online predictor is designed to enhance the practicality of the model, and the server is freely accessible at http://dac-aips.online .

Synthesis, biological evaluation, and molecular modelling of substituted thiazolyl thiourea derivatives: A new class of prolyl oligopeptidase inhibitors

Prolyl oligopeptidase (POP) is a compelling therapeutic target associated with aging and neurodegenerative disorders due to its pivotal role in neuropeptide processing. Despite initial promise demonstrated by early-stage POP inhibitors, their progress in clinical trials has been halted at Phase I or II. This impediment has prompted the pursuit of novel inhibitors. The current study seeks to contribute to the identification of efficacious POP inhibitors through the design, synthesis, and comprehensive evaluation (both in vitro and in silico) of thiazolyl thiourea derivatives (5a-r). In vitro experimentation exhibited that the compounds displayed significant higher potency as POP inhibitors. Compound 5e demonstrated an IC50 value of 16.47 ± 0.54 μM, representing a remarkable potency. A meticulous examination of the structure-activity relationship indicated that halogen and methoxy substituents were the most efficacious. In silico investigations delved into induced fit docking, pharmacokinetics, and molecular dynamics simulations to elucidate the intricate interactions, orientation, and conformational changes of these compounds within the active site of the enzyme. Moreover, our pharmacokinetic assessments confirmed that the majority of the synthesized compounds possess attributes conducive to potential drug development.

Small Spleen Peptides (SSPs) Shape Dendritic Cell Differentiation through Modulation of Extracellular ATP Synthesis Profile

Restoring peripheral immune tolerance is crucial for addressing autoimmune diseases. An ancient mechanism in maintaining the balance between inflammation and tolerance is the ratio of extracellular ATP (exATP) and adenosine. Our previous research demonstrated the effectiveness of small spleen peptides (SSPs) in inhibiting psoriatic arthritis progression, even in the presence of the pro-inflammatory cytokine TNFα, by transforming dendritic cells (DCs) into tolerogenic cells and fostering regulatory Foxp3+ Treg cells. Here, we identified thymosins as the primary constituents of SSPs, but recombinant thymosin peptides were less efficient in inhibiting arthritis than SSPs. Since Tβ4 is an ecto-ATPase-binding protein, we hypothesized that SSPs regulate exATP profiles. Real-time investigation of exATP levels in DCs revealed that tolerogenic stimulation led to robust de novo exATP synthesis followed by significant degradation, while immunogenic stimulation resulted in a less pronounced increase in exATP and less effective degradation. These contrasting exATP profiles were crucial in determining whether DCs entered an inflammatory or tolerogenic state, highlighting the significance of SSPs as natural regulators of peripheral immunological tolerance, with potential therapeutic benefits for autoimmune diseases. Finally, we demonstrated that the tolerogenic phenotype of SSPs is mainly influenced by adenosine receptors, and in vivo administration of SSPs inhibits psoriatic skin inflammation.

Novel role of cardiovascular MRI to contextualise tuberculous pericardial inflammation and oedema as predictors of constrictive pericarditis

Tuberculosis (TB) and human immunodeficiency virus/acquired immunodeficiency syndrome have reached epidemic proportions, particularly affecting vulnerable populations in low- and middle-income countries of sub-Saharan Africa. TB pericarditis is the commonest cardiac manifestation of TB and is the leading cause of constrictive pericarditis, a reversible (by surgical pericardiectomy) cause of diastolic heart failure in endemic areas. Unpacking the complex mechanisms underpinning constrictive haemodynamics in TB pericarditis has proven challenging, leaving various basic and clinical research questions unanswered. Subsequently, risk stratification strategies for constrictive outcomes have remained unsatisfactory. Unique pericardial tissue characteristics, as identified on cardiovascular magnetic resonance imaging, enable us to stage and quantify pericardial inflammation and may assist in identifying patients at higher risk of tissue remodelling and pericardial constriction, as well as predict the degree of disease reversibility, tailor medical therapy, and determine the ideal timing for surgical pericardiectomy.

Ac-SDKP attenuates ER stress-stimulated collagen production in cardiac fibroblasts by inhibiting CHOP-mediated NF-κB expression

Inflammation and cardiac fibrosis are prevalent pathophysiologic conditions associated with hypertension, cardiac remodeling, and heart failure. Endoplasmic reticulum (ER) stress triggers the cells to activate unfolded protein responses (UPRs) and upregulate the ER stress chaperon, enzymes, and downstream transcription factors to restore normal ER function. The mechanisms that link ER stress-induced UPRs upregulation and NF-κB activation that results in cardiac inflammation and collagen production remain elusive. N-Acetyl-Ser-Asp-Lys-Pro (Ac-SDKP), a natural tetrapeptide that negatively regulates inflammation and fibrosis, has been reported. Whether it can inhibit ER stress-induced collagen production in cardiac fibroblasts remains unclear. Thus, we hypothesized that Ac-SDKP attenuates ER stress-stimulated collagen production in cardiac fibroblasts by inhibiting CHOP-mediated NF-κB expression. We aimed to study whether Ac-SDKP inhibits tunicamycin (TM)-induced ER stress signaling, NF-κB signaling, the release of inflammatory cytokine interleukin-6, and collagen production in human cardiac fibroblasts (HCFs). HCFs were pre-treated with Ac-SDKP (10 nM) and then stimulated with TM (0.25 μg/mL). We found that Ac-SDKP inhibits TM-induced collagen production by attenuating ER stress-induced UPRs upregulation and CHOP/NF-κB transcriptional signaling pathways. CHOP deletion by specific shRNA maintains the inhibitory effect of Ac-SDKP on NF-κB and type-1 collagen (Col-1) expression at both protein and mRNA levels. Attenuating ER stress-induced UPR sensor signaling by Ac-SDKP seems a promising therapeutic strategy to combat detrimental cardiac inflammation and fibrosis.

Structural insights into the inhibitory mechanism of angiotensin-I-converting enzyme by the lactotripeptides IPP and VPP

Human somatic angiotensin-1-converting enzyme (sACE) is composed of a catalytic N-(nACE) and C-domain (cACE) of similar size with different substrate specificities. It is involved in the regulation of blood pressure by converting angiotensin I to the vasoconstrictor angiotensin II and has been a major focus in the development of therapeutics for hypertension. Bioactive peptides from various sources, including milk, have been identified as natural ACE inhibitors. We report the structural basis for the role of two lacototripeptides, Val-Pro-Pro and Ile-Pro-Pro, in domain-specific inhibition of ACE using X-ray crystallography and kinetic analysis. The lactotripeptides have preference for nACE due to altered polar interactions distal to the catalytic zinc ion. Elucidating the mechanism of binding and domain selectivity of these peptides also provides important insights into the functional roles of ACE.

Diabetic Pneumopathy- A Novel Diabetes-associated Complication: Pathophysiology, the Underlying Mechanism and Combination Medication

BACKGROUND

The "diabetic lung" has been identified as a possible target organ in diabetes, with abnormalities in ventilation control, bronchomotor tone, lung volume, pulmonary diffusing capacity, and neuroadrenergic bronchial innervation.

OBJECTIVE

This review summarizes studies related to diabetic pneumopathy, pathophysiology and a number of pulmonary disorders including type 1 and type 2 diabetes.

METHODS

Electronic searches were conducted on databases such as Pub Med, Wiley Online Library (WOL), Scopus, Elsevier, ScienceDirect, and Google Scholar using standard keywords "diabetes," "diabetes Pneumopathy," "Pathophysiology," "Lung diseases," "lung infection" for review articles published between 1978 to 2023 very few previous review articles based their focus on diabetic pneumopathy and its pathophysiology.

RESULTS

Globally, the incidence of diabetes mellitus has been rising. It is a chronic, progressive metabolic disease. The "diabetic lung" may serve as a model of accelerated ageing since diabetics' rate of respiratory function deterioration is two to three-times higher than that of normal, non-smoking people.

CONCLUSION

Diabetes-induced pulmonary dysfunction has not gained the attention it deserves due to a lack of proven causality and changes in cellular properties. The mechanism underlying a particular lung illness can still only be partially activated by diabetes but there is evidence that hyperglycemia is linked to pulmonary fibrosis in diabetic people.

N-Methyl-(2S,4R)-trans-4-hydroxy-L-proline isolated Sideroxylon obtusifolium attenuates TPA-induced irritant contact dermatitis in mice

Dermatitis is defined as a set of inflammatory diseases that affect the skin, with varied causes. Among the different types of dermatitis, contact dermatitis is the most prevalent. Although the current therapy is often effective, it is associated with adverse effects and the possibility of drug tolerance. N-Methyl-(2S, 4R)-trans-4-hydroxy-L-proline is a L-proline amino acid derivative found in the leaves of Sideroxylon obtusifolium, a species traditionally used to treat inflammatory diseases. The aim of this study was to investigate the topical anti-inflammatory effect of N-methyl-(2S, 4R)-trans-4-hydroxy-L-proline (NMP) in 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced irritant contact dermatitis in mice. Topically administered NMP, at doses of 0.03 - 0.50 mg/ear, reduced TPA-induced ear edema and neutrophil migration, as evidenced by low tissue myeloperoxidase activity and verified by histological examination. In addition, NMP (0.06 mg/ear) reduced tissue levels of pro-inflammatory cytokines (TNF-α, IL-6, IL-1β, INF-γ and MCP-1) and of the anti-inflammatory cytokine IL-10, and reduced gene expression of TNF-α, IL-6 and IL-1β increased by TPA. The data suggest that N-methyl-(2S, 4R)-trans-4-hydroxy-L-proline acts as a topical anti-inflammatory agent that decreases the expression of inflammatory cytokines, making it useful for the treatment of skin inflammation. Further investigations are necessary for its development as a therapeutic agent.

Ac-SDKP promotes KIF3A-mediated β-catenin suppression through a ciliary mechanism to constrain silica-induced epithelial-myofibroblast transition

Kinesin family member 3 A (KIF3A) decrease have been reported in silicotic patients and rats. However, the detailed mechanisms of KIF3A in silicosis remain unknown. In this study, we demonstrated that KIF3A effectively blocked the expression of β-catenin and downstream myocardin-related transcription factor (MRTF)-A/serum response factor (SRF) signaling, thus inhibiting silica-induced epithelial-myofibroblast transition (EMyT). Moreover, KIF3A was identified as a downstream mediator of an antifibrotic tetrapeptide N-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP). Knockdown of KIF3A expression reactivated β-catenin/myocardin-related transcription factor (MRTF)-A/serum response factor (SRF) signaling that was attenuated by Ac-SDKP in vitro. Collectively, our findings suggest that Ac-SDKP plays its anti-fibrosis role via KIF3A-mediated β-catenin suppression, at least in part, in both in vivo model of silicosis and in vitro model of EMyT.

Association between angiotensin-converting enzyme inhibitor-induced cough and the risk of lung cancer: a Mendelian randomization study

Background: Observational studies and meta-analyses have demonstrated a positive correlation between the use of angiotensin-converting enzyme inhibitors (ACEIs) and lung cancer. However, the findings remain controversial; furthermore, the relationship between ACEI-induced cough and lung cancer development remains unknown. We used Mendelian randomization (MR) to verify the association between ACEI use, ACEI-induced cough, and the risk of lung cancer. Methods: We performed a two-sample MR analysis to determine the unconfounded relationships between ACE inhibition, which mimics the effects of ACEIs, and genetic proxies for ACEI-induced cough and lung cancer. Single nucleotide polymorphisms that imitate ACE receptors and ACEI-induced cough were collected and integrated into a meta-analysis of existing genome-wide association studies for various lung cancers. The relationship was quantified using inverse variance weighting, weighted median, and MR-Egger methods. Results: A statistically significant association was observed between ACE inhibition and the risk of small cell lung cancer for Europeans (excluding rs118121655/rs80311894). Associations were identified between ACEI-induced cough and the risk of lung cancer for Europeans, although not for Asians, and between ACEI-induced cough and lung adenocarcinoma (excluding rs360206). Conclusion: Our findings reveal a relationship between ACE inhibition and lung cancer development, as well as a significant association between ACEI-induced cough and a higher risk of lung cancer for Europeans. Patients with hypertension who experience dry cough as a side effect of ACEI use should consider switching to an alternative antihypertensive treatment.

The Prolyl Oligopeptidase Inhibitor KYP-2047 Is Cytoprotective and Anti-Inflammatory in Human Retinal Pigment Epithelial Cells with Defective Proteasomal Clearance

Increased oxidative stress, dysfunctional cellular clearance, and chronic inflammation are associated with age-related macular degeneration (AMD). Prolyl oligopeptidase (PREP) is a serine protease that has numerous cellular functions, including the regulation of oxidative stress, protein aggregation, and inflammation. PREP inhibition by KYP-2047 (4-phenylbutanoyl-L-prolyl1(S)-cyanopyrrolidine) has been associated with clearance of cellular protein aggregates and reduced oxidative stress and inflammation. Here, we studied the effects of KYP-2047 on inflammation, oxidative stress, cell viability, and autophagy in human retinal pigment epithelium (RPE) cells with reduced proteasomal clearance. MG-132-mediated proteasomal inhibition in ARPE-19 cells was used to model declined proteasomal clearance in the RPEs of AMD patients. Cell viability was assessed using LDH and MTT assays. The amounts of reactive oxygen species (ROS) were measured using 2',7'-dichlorofluorescin diacetate (H2DCFDA). ELISA was used to determine the levels of cytokines and activated mitogen-activated protein kinases. The autophagy markers p62/SQSTM1 and LC3 were measured with the western blot method. MG-132 induced LDH leakage and increased ROS production in the ARPE-19 cells, and KYP-2047 reduced MG-132-induced LDH leakage. Production of the proinflammatory cytokine IL-6 was concurrently alleviated by KYP-2047 when compared with cells treated only with MG-132. KYP-2047 had no effect on autophagy in the RPE cells, but the phosphorylation levels of p38 and ERK1/2 were elevated upon KYP-2047 exposure, and the inhibition of p38 prevented the anti-inflammatory actions of KYP-2047. KYP-2047 showed cytoprotective and anti-inflammatory effects on RPE cells suffering from MG-132-induced proteasomal inhibition.

Amphibian-derived wound healing peptides: chemical molecular treasure trove for skin wound treatment

Amphibian-derived wound healing peptides thus offer new intervention measures and strategies for skin wound tissue regeneration. As novel drug lead molecules, wound healing peptides can help analyze new mechanisms and discover new drug targets. Previous studies have identified various novel wound healing peptides and analyzed novel mechanisms in wound healing, especially competing endogenous RNAs (ceRNAs) (e.g., inhibition of miR-663a promotes skin repair). In this paper, we review amphibian-derived wound healing peptides, including the acquisition, identification, and activity of peptides, a combination of peptides with other materials, and the analysis of underlying mechanisms, to better understand the characteristics of wound healing peptides and to provide a molecular template for the development of new wound repair drugs.

The Pathophysiological Role of Thymosin β4 in the Kidney Glomerulus

Diseases affecting the glomerulus, the filtration unit of the kidney, are a major cause of chronic kidney disease. Glomerular disease is characterised by injury of glomerular cells and is often accompanied by an inflammatory response that drives disease progression. New strategies are needed to slow the progression to end-stage kidney disease, which requires dialysis or transplantation. Thymosin β4 (Tβ4), an endogenous peptide that sequesters G-actin, has shown potent anti-inflammatory function in experimental models of heart, kidney, liver, lung, and eye injury. In this review, we discuss the role of endogenous and exogenous Tβ4 in glomerular disease progression and the current understanding of the underlying mechanisms.

Knockout of ACE-N facilitates improved cardiac function after myocardial infarction

Angiotensin-converting enzyme (ACE) hydrolyzes N-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP) into inactive fragments through its N-terminal site (ACE-N). We previously showed that Ac-SDKP mediates ACE inhibitors' cardiac effects. Whether increased bioavailability of endogenous Ac-SDKP caused by knocking out ACE-N also improves cardiac function in myocardial infarction (MI)-induced heart failure (HF) is unknown. Wild-type (WT) and ACE-N knockout (ACE-NKO) mice were subjected to MI by ligating the left anterior descending artery and treated with vehicle or Ac-SDKP (1.6 mg/kg/day, s.c.) for 5 weeks, after which echocardiography was performed and left ventricles (LV) were harvested for histology and molecular biology studies. ACE-NKO mice showed increased plasma Ac-SDKP concentrations in both sham and MI group compared to WT. Exogenous Ac-SDKP further increased its circulating concentrations in WT and ACE-NKO. Shortening (SF) and ejection (EF) fractions were significantly decreased in both WT and ACE-NKO mice post-MI, but ACE-NKO mice exhibited significantly lesser decrease. Exogenous Ac-SDKP ameliorated cardiac function post-MI only in WT but failed to show any additive improvement in ACE-NKO mice. Sarcoendoplasmic reticulum calcium transport ATPase (SERCA2), a marker of cardiac function and calcium homeostasis, was significantly decreased in WT post-MI but rescued with Ac-SDKP, whereas ACE-NKO mice displayed less loss of SERCA2 expression. Our study demonstrates that gene deletion of ACE-N resulted in improved LV cardiac function in mice post-MI, which is likely mediated by increased circulating Ac-SDKP and minimally reduced expression of SERCA2. Thus, future development of specific and selective inhibitors for ACE-N could represent a novel approach to increase endogenous Ac-SDKP toward protecting the heart from post-MI remodeling.

Cordyceps militaris Inhibited Angiotensin-Converting Enzyme through Molecular Interaction between Cordycepin and ACE C-Domain

One of the most important therapeutic modalities for the management of hypertension is the inhibition of the angiotensin-converting enzyme (ACE). Cordyceps militaris has received substantial attention because to its therapeutic potential and biological value. To gather information about the antihypertensive properties of C. militaris, the ACE inhibitory activity was evaluated. An ethanolic extract of the fruiting body of C. militaris was obtained, and the extract was separated by UHPLC method with a fluorescence detector for the quantification of cordycepin and adenosine. The ethanolic extract had a considerably higher cordycepin level. Additionally, an in vitro kinetic analysis was carried out to find out how much C. militaris extract inhibited ACE. This extract exhibited non-competitive inhibition on ACE. The Ki value of the C. militaris extract against ACE was found to be 8.7 µg/mL. To the best of our knowledge, this is the first report of the analysis of a protein cavity together with molecular docking carried out to comprehend the intermolecular interactions between cordycepin and the ACE C-domain, which impact the spatial conformation of the enzyme and reduce its capacity to break down the substrate. According to a molecular docking, hydrogen bonding interactions between the chemicals and the ACE S2’ subsite are primarily responsible for cordycepin inhibition at the ACE C domain. All these findings suggest that C. militaris extract are a kind of natural ACE inhibitor, and cordycepin has the potential as an ACE inhibitor.

An analytical quality by design approach towards a simple and novel HPLC-UV method for quantification of the antifibrotic peptide N-acetyl-seryl-aspartyl-lysyl-proline

N-acetyl-seryl-aspartyl-lysyl proline (Ac-SDKP) is a tetrapeptide possessing anti-fibrotic, angiogenic, anti-inflammatory, anti-apoptotic, and immunomodulatory properties. Currently, the main method to quantify the peptide is liquid chromatography-tandem mass spectrometry (LC-MS/MS) and enzyme-linked immunosorbent assay (ELISA), both of which are labour intensive and require expensive equipment and consumables. Furthermore, these techniques are generally utilised to detect very low or trace concentrations, such as in biological samples. The use of high concentrations of analyte might overload the extraction column or the separation column in LC-MS/MS or the ELISA plates, so the response could be a non-linear relationship at high analyte concentrations. Thus, they are not ideal for formulation development where detection of dose-equivalent concentrations is typically required. Therefore, a cost-effective, simple, and accurate quantification method for the peptide at a higher concentration needs to be developed. In this study, a simple and novel HPLC-UV method is proposed and validated using an Analytical Quality by Design (AQbD) approach. The method is first screened and optimised using chromatographic responses including capacity factor, resolution, tailing factor, and theoretical plate counts, fulfilling the International Council for Harmonisation (ICH) Q2 (R1) guidelines. The resultant optimised chromatography conditions utilised 10 mM phosphate buffer at pH 2.5 and acetonitrile as mobile phases, starting at 3% (v/v) acetonitrile and 97% (v/v) buffer and increasing to 9.7% (v/v) acetonitrile and 90.3% (v/v) buffer over 15 minutes at a flow rate of 1 mL/min at the column temperature of 25 °C. The injection volume is set at 10 μL and the VWD detector wavelength is 220 nm. The method established is suitable for detecting the peptide at a relatively high concentration, with a quantifiable range from 7.8 μg/mL to 2.0 mg/mL. In addition, the use of a relatively simple HPLC-UV approach could significantly reduce costs and allow easier access to quantify the peptide concentration. A limitation of this method is lower sensitivity compared with using LC-MS/MS and ELISA methods but running costs are lower and the methodology is simpler. The method is capable to quantify the peptide in various tested matrix solutions, with successful quantitation of the peptide in samples obtained from in vitro drug release study in PBS and from a chitosan-TPP nanogels formulation. Therefore, the method developed here offers a complementary approach to the existing quantification methods, quantifying this peptide at increased concentrations in simple to intermediately complex matrix solutions, such as HBSS, DMEM and FluoroBrite cell culture media.

Ac-SDKP peptide improves functional recovery following spinal cord injury in a preclinical model

Damage to the spinal cord triggers a local complex inflammatory reaction that results in irreversible impairments or complete loss of motor function. The evidence suggested that inhibiting the pro-inflammatory macrophage/microglia (M1 subsets) and stimulating the anti-inflammatory macrophage/microglia (M2 subsets) are potential strategies for the treatment of neuroinflammation-related diseases. We evaluated the potentially protective effect of Ac-SDKP as an endogenous tetrapeptide on rat spinal cord injury (SCI). Wistar rats were subjected to a weight-drop contusion model and were treated with Ac-SDKP (0.8 mg/kg) given subcutaneously once a day for 7 days starting at two clinically relevant times, at 2 h or 6 h post-injury. The effect of Ac-SDKP was assessed by motor functional analysis, real-time PCR (CD86 and CD206 mRNA), western blot (caspase-3), ELISA (TNF-a, IL-10), and histological analysis (toluidine blue staining). Ac-SDKP improved locomotor recovery and rescue motor neuron loss after SCI. Moreover, a decreased in TNF-a level as well as caspase 3 protein levels occurred in the lesion epicenter of the spinal cord following treatment. In addition, CD206 mRNA expression level increased significantly in Ac-SDKP treated rats compared with SCI. Together these data suggest that Ac-SDKP might be a novel immunomodulatory drug. It may be beneficial for the treatment of SCI with regards to increasing CD206 gene expression and suppress inflammatory cytokine to improve motor function and reducing histopathological lesion.

Amphibian-derived peptide homodimer promotes regeneration of skin wounds

Despite the increasing treatments in skin wound repair, existing therapeutic drugs cannot meet current needs. As such, skin wound repair remains a considerable clinical challenge, and thus the discovery of new pro-healing agents is crucial. Here, we identified the first naturally occurring peptide homodimer named as OA-GP11 dimer (OA-GP11d) from Odorrana andersonii (odorous frog) through the combinational methods of peptidomics and genomics. OA-GP11d was linked by the intramolecular disulfide formed by the 10^th cysteine residues from the monomer of peptide with sequence of GPLSGINAECM, which effectively promoted the repair of full-thickness and burn wounds in mice. The underlying molecular mechanisms revealed that OA-GP11d not only accelerated the migration and cell-scratch healing of mouse keratinocytes, but also activated the mitogen-activated protein kinases (MAPKs) signaling pathway (phosphorylation of p38 and ERK subgroups) in immortalized human keratinocytes (HaCaT). Besides, OA-GP11d reduced the phosphorylation of nuclear factor-κB (NF-κB) and inhibitor of NF-κB (I-κB) induced by lipopolysaccharide stimulation in mouse macrophages, and inhibited the release of associated inflammatory factors tumor necrosis factor (TNF)-α and interleukin (IL)-6. OA-GP11d is the first identified naturally occurring peptide dimer with significant pro-healing potency. Our results highlight the importance of amphibians as a source of novel pro-healing agents and suggest OA-GP11d as a potential new pro-regenerative drug candidate.

Recent Advances in Diabetic Kidney Diseases: From Kidney Injury to Kidney Fibrosis

Diabetic kidney disease (DKD) is the leading cause of chronic kidney disease and end-stage renal disease. The natural history of DKD includes glomerular hyperfiltration, progressive albuminuria, declining estimated glomerular filtration rate, and, ultimately, kidney failure. It is known that DKD is associated with metabolic changes caused by hyperglycemia, resulting in glomerular hypertrophy, glomerulosclerosis, and tubulointerstitial inflammation and fibrosis. Hyperglycemia is also known to cause programmed epigenetic modification. However, the detailed mechanisms involved in the onset and progression of DKD remain elusive. In this review, we discuss recent advances regarding the pathogenic mechanisms involved in DKD.

Potential Role of Adult Hippocampal Neurogenesis in Traumatic Brain Injury

Traumatic brain injury (TBI) is a serious cause of disability and death among young and adult individuals, displaying complex pathophysiology including cellular and molecular mechanisms that are not fully elucidated. Many experimental and clinical studies investigated the potential relationship between TBI and the process by which neurons are formed in the brain, known as neurogenesis. Currently, there are no available treatments for TBI's long-term consequences being the search for novel therapeutic targets, a goal of highest scientific and clinical priority. Some studies evaluated the benefits of treatments aimed at improving neurogenesis in TBI. In this scenario, herein, we reviewed current pre-clinical studies that evaluated different approaches to improving neurogenesis after TBI while achieving better cognitive outcomes, which may consist in interesting approaches for future treatments.

Anti-inflammatory peptides and metabolomics-driven biomarkers discovery from sea cucumber protein hydrolysates

The hydrolysates from Apostichopus japonicus sea cucumber are an important source of nitrogen that may be added to foods. We evaluated the effect of A. japonicus hydrolysates on inflammation-associated leukocyte recruitment. The results revealed that leukocyte migration to the site of injury was significantly blocked by AJH-1 (<10 kDa), suggesting a protective effect against CuSO₄ -induced neuromast damage in a zebrafish model. Based on liquid chromatography/time-of-flight/mass spectrometry, and metabolomic analysis, the nine biomarker candidates in AJH-1 were Val, Ala-Pro-Arg, Gly-Lys, Asp propyl ester, Glu methyl ester, His butyl ester, Ile-Ala-Ala-Lys, Tyr-Lys, and Asn-Pro-Gly-Lys. We used molecular docking to predict the binding affinity and docked position of the peptides onto the angiotensin converting enzyme (ACE). All the identified peptides had adequate binding affinity toward ACE, especially peptides Ala-Pro-Arg and Gly-Lys. These peptides may be used in the development of therapeutic foods. PRACTICAL APPLICATION: The study revealed the anti-inflammatory properties of the fractionated sea cucumber protein hydrolysate (<10 kDa). The characteristic peptides may be used as functional ingredients in nutraceutical foods and beverages.

Novel roles of the renal angiotensin-converting enzyme

The observation that all components of the renin angiotensin system (RAS) are expressed in the kidney and the fact that intratubular angiotensin (Ang) II levels greatly exceed the plasma concentration suggest that the synthesis of renal Ang II occurs independently of the circulating RAS. One of the main components of this so-called intrarenal RAS is angiotensin-converting enzyme (ACE). Although the role of ACE in renal disease is demonstrated by the therapeutic effectiveness of ACE inhibitors in treating several conditions, the exact contribution of intrarenal versus systemic ACE in renal disease remains unknown. Using genetically modified mouse models, our group demonstrated that renal ACE plays a key role in the development of several forms of hypertension. Specifically, although ACE is expressed in different cell types within the kidney, its expression in renal proximal tubular cells is essential for the development of high blood pressure. Besides hypertension, ACE is involved in several other renal diseases such as diabetic kidney disease, or acute kidney injury even when blood pressure is normal. In addition, studies suggest that ACE might mediate at least part of its effect through mechanisms that are independent of the Ang I conversion into Ang II and involve other substrates such as N-acetyl-seryl-aspartyl-lysyl-proline (AcSDKP), Ang-(1-7), and bradykinin, among others. In this review, we summarize the recent advances in understanding the contribution of intrarenal ACE to different pathological conditions and provide insight into the many roles of ACE besides the well-known synthesis of Ang II.

Renin-angiotensin system and inflammation update

The most classical view of the renin-angiotensin system (RAS) emphasizes its role as an endocrine regulator of sodium balance and blood pressure. However, it has long become clear that the RAS has pleiotropic actions that contribute to organ damage, including modulation of inflammation. Angiotensin II (Ang II) activates angiotensin type 1 receptors (AT1R) to promote an inflammatory response and organ damage. This represents the pathophysiological basis for the successful use of RAS blockers to prevent and treat kidney and heart disease. However, other RAS components could have a built-in capacity to brake proinflammatory responses. Angiotensin type 2 receptor (AT2R) activation can oppose AT1R actions, such as vasodilatation, but its involvement in modulation of inflammation has not been conclusively proven. Angiotensin-converting enzyme 2 (ACE2) can process Ang II to generate angiotensin-(1-7) (Ang-(1-7)), that activates the Mas receptor to exert predominantly anti-inflammatory responses depending on the context. We now review recent advances in the understanding of the interaction of the RAS with inflammation. Specific topics in which novel information became available recently include intracellular angiotensin receptors; AT1R posttranslational modifications by tissue transglutaminase (TG2) and anti-AT1R autoimmunity; RAS modulation of lymphoid vessels and T lymphocyte responses, especially of Th17 and Treg responses; interactions with toll-like receptors (TLRs), programmed necrosis, and regulation of epigenetic modulators (e.g. microRNAs and bromodomain and extraterminal domain (BET) proteins). We additionally discuss an often overlooked effect of the RAS on inflammation which is the downregulation of anti-inflammatory factors such as klotho, peroxisome proliferator-activated receptor γ co-activator 1α (PGC-1α), transient receptor potential ankyrin 1 (TRPA1), SNF-related serine/threonine-protein kinase (SNRK), serine/threonine-protein phosphatase 6 catalytic subunit (Ppp6C) and n-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP). Both transcription factors, such as nuclear factor κB (NF-κB), and epigenetic regulators, such as miRNAs are involved in downmodulation of anti-inflammatory responses. A detailed analysis of pathways and targets for downmodulation of anti-inflammatory responses constitutes a novel frontier in RAS research.

Ac-SDKP Attenuates Activation of Lung Macrophages and Bone Osteoclasts in Rats Exposed to Silica by Inhibition of TLR4 and RANKL Signaling Pathways

Background

Silica-induced inflammatory activation is associated with silicosis and various non-respiratory conditions. The present study was designed to examine the anti-inflammatory effects of N-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP) on lung macrophages and bone osteoclasts after silica inhalation in rats.

Methods

Wistar rats and NR8383 and RAW 264.7 cell lines were used in the present study. The receptor activator of nuclear factor kappa-B ligand (RANKL) and toll-like receptor 4 (TLR4) signaling pathways was measured in the lung tissue of rats or NR8383/RAW 264.7 cells exposed to silica. The microarchitecture of the trabecular bone in the tibia and femur was evaluated in silicotic rats. Furthermore, the roles of Ac-SDKP on silicotic rats, silica-treated NR8383/RAW 264.7 cells, and RANKL-induced osteoclast differentiation were studied.

Results

The data indicated that silica inhalation might activate the RANKL and TLR4 signaling pathways in lung macrophages, thus inducing the lung inflammatory and proteolytic phenotype of macrophages and osteoclasts in lung and bone. Ac-SDKP maintained the lung elastin level by inhibiting lung inflammation and macrophage activation via the RANKL and TLR4 signaling pathways. Ac-SDKP also attenuated the reduction in femoral bone mineral density in silicotic rats by inhibiting osteoclast differentiation via the RANKL signaling pathway.

Conclusion

Our findings support the hypothesis that inhalation of crystalline silica induces activation of lung macrophages and bone osteoclasts via the RANKL and TLR4 signaling pathways. Ac-SDKP has the potential to stabilize lung homeostasis and bone metabolism.

Mep1a contributes to Ang II-induced cardiac remodeling by promoting cardiac hypertrophy, fibrosis and inflammation

Pathological cardiac remodeling, characterized by excessive deposition of extracellular matrix proteins and cardiac hypertrophy, leads to the development of heart failure. Meprin α (Mep1a), a zinc metalloprotease, previously reported to participate in the regulation of inflammatory response and fibrosis, may also contribute to cardiac remodeling, although whether and how it participates in this process remains unknown. Here, in this work, we investigated the role of Mep1a in pathological cardiac remodeling, as well as the effects of the Mep1a inhibitor actinonin on cardiac remodeling-associated phenotypes. We found that Mep1a deficiency or chemical inhibition both significantly alleviated TAC- and Ang II-induced cardiac remodeling and dysfunction. Mep1a deletion and blocking both attenuated TAC- and Ang II-induced heart enlargement and increases in the thickness of the left ventricle anterior and posterior walls, and reduced expression of pro-hypertrophic markers, including atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), and myosin heavy chain beta (β-MHC). In addition, Mep1a deletion and blocking significantly inhibited TAC- and Ang II-induced cardiac fibroblast activation and production of extracellular matrix (ECM). Moreover, in Mep1a^-/- mice and treatment with actinonin significantly reduced Ang II-induced infiltration of macrophages and proinflammatory cytokines. Notably, we found that in vitro, Mep1a is expressed in cardiac myocytes and fibroblasts and that Mep1a deletion or chemical inhibition both markedly suppressed Ang II-induced hypertrophy of rat or mouse cardiac myocytes and activation of rat or mouse cardiac fibroblasts. In addition, blocking Mep1a in macrophages reduced Ang II-induced expression of interleukin (IL)-6 and IL-1β, strongly suggesting that Mep1a participates in cardiac remodeling processes through regulation of inflammatory cytokine expression. Mechanism studies revealed that Mep1a mediated ERK1/2 activation in cardiac myocytes, fibroblasts and macrophages and contributed to cardiac remodeling. In light of our findings that blocking Mep1a can ameliorate cardiac remodeling via inhibition of cardiac hypertrophy, fibrosis, and inflammation, Mep1a may therefore serve as a strong potential candidate for therapeutic targeting to prevent cardiac remodeling.

Discovery of a novel short peptide with efficacy in accelerating the healing of skin wounds

Despite extensive efforts to develop efficacious therapeutic approaches, the treatment of skin wounds remains a considerable clinical challenge. Existing remedies cannot sufficiently meet current needs, so the discovery of novel pro-healing agents is of growing importance. In the current research, we identified a novel short peptide (named RL-QN15, primary sequence 'QNSYADLWCQFHYMC') from Rana limnocharis skin secretions, which accelerated wound healing in mice. Exploration of the underlying mechanisms showed that RL-QN15 activated the MAPK and Smad signaling pathways, and selectively modulated the secretion of cytokines from macrophages. This resulted in the proliferation and migration of skin cells and dynamic regulation of TGF-β1 and TGF-β3 in wounds, which accelerated re-epithelialization and granulation tissue formation and thus skin regeneration. Moreover, RL-QN15 showed significant therapeutic potency against chronic wounds, skin fibrosis, and oral ulcers. Our results highlight frog skin secretions as a potential treasure trove of bioactive peptides with healing activity. The novel peptide (RL-QN15) identified in this research shows considerable capacity as a candidate for the development of novel pro-healing agents.

A long-acting isomer of Ac-SDKP attenuates pulmonary fibrosis through SRPK1-mediated PI3K/AKT and Smad2 pathway inhibition

Idiopathic pulmonary fibrosis (IPF) is a progressive, life-threatening lung disease with a poor prognosis. N-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP) is a critical negative regulator of fibrosis development. However, it's extremely short half-life greatly limits its applications. Previously, we reported an Ac-SDKP analog peptide in which Asp and Lys residues were replaced with D-amino acids (Ac-SD_D K_D P). Ac-SD_D K_D P exhibits better resistance to angiotensin-1-converting enzyme (ACE)-mediated degradation and a longer half-life than Ac-SDKP in rat and human sera. The objective of this study was to explore the potential application of Ac-SD_D K_D P for the treatment of IPF and to clarify the underlying mechanisms. We found that Ac-SD_D K_D P exerted similar antifibrotic effects as Ac-SDKP on human fetal lung fibroblast-1 (HFL-1) proliferation, α-smooth muscle actin (α-SMA), collagen I and collagen III expression, and Smad-2 phosphorylation in vitro. In vivo, Ac-SD_D K_D P exhibited significantly greater protective effects against bleomycin-induced pulmonary fibrosis than Ac-SDKP in mice. α-SMA, CD45, collagen I and collagen III expression, and Smad-2 phosphorylation were significantly decreased in the lungs of Ac-SD_D K_D P-treated but not Ac-SDKP-treated mice. Furthermore, a pull-down experiment was used to screen for molecules that interact with Ac-SDKP. Co-immunoprecipitation (Co-IP) and computer-based molecular docking experiments demonstrated an interaction between Ac-SDKP or Ac-SD_D K_D P (Ac-SDKP/Ac-SD_D K_D P) and serine/arginine-rich protein-specific kinase 1 (SRPK1) that caused inhibition SRPK1-mediated phosphatidylinositol-3 kinase/ serine/threonine kinase (PIK3/AKT) signaling pathway activation and Smad2 phosphorylation and thereby attenuated lung fibrosis. Our data suggest that long-acting Ac-SD_D K_D P may potentially be an effective drug for the treatment of pulmonary fibrosis. The interacting molecule and antifibrotic mechanism of Ac-SDKP/Ac-SD_D K_D P were also identified, providing an experimental and theoretical foundation for the clinical application of the drug.

Novel antihypertensive action of rutin is mediated via inhibition of angiotensin converting enzyme/mineralocorticoid receptor/angiotensin 2 type 1 receptor (ATR1) signaling pathways in uninephrectomized hypertensive rats

Hypertension is the most common cardiovascular disease that affects approximately 26% of adult population, worldwide. Rutin is one of the important flavonoids that is consumed in the daily diet, and found in many food items, vegetables, and beverages. Uninephrectomy (UNX) of the left kidney was performed, followed by induction of hypertension. The rats were randomly divided into four groups of 10 rats: group 1-Sham-operated rats; group 2-UNX rats, group 3-UNX-L-NAME (40 mg/kg) plus rutin (100 mg/kg bwt), and groups 4-UNX-L-NAME plus lisinopril (10 mg/kg bwt), orally for 3 weeks. Results revealed significant heightening of arterial pressure and oxidative stress indices, while hypertensive rats treated with rutin had lower expressions of angiotensin converting enzyme (ACE) and mineralocorticoid receptor in uninephrectomized rats. Together, rutin as a novel antihypertensive flavonoid could provide an unimaginable benefits for the management of hypertension through inhibition of angiotensin converting enzyme and mineralocorticoid receptor. PRACTICAL APPLICATIONS: Hypertension has been reported to be the most common cardiovascular disease, affecting approximately 26% of the adult population worldwide with predicted prevalence to increase by 60% by 2025. Recent advances in phytomedicine have shown flavonoids to be very helpful in the treatment of many diseases. Flavonoids have been used in the treatment and management of cardiovascular diseases, obesity and hypertension. The study revealed that rutin, a known flavonoid inhibited angiotensin converting enzyme (ACE), angiotensin 2 type 1 receptor (ATR1), and mineralocorticoid receptor (MCR), comparable to the classic ACE inhibitor, Lisinopril, indicating the novel antihypertensive property of rutin. Therefore, flavonoids such as rutin found in fruits and vegetables could, therefore, serve as an antihypertensive drug regimen. Combining all, functional foods rich in flavonoids could be used as potential therapeutic candidates for managing uninephrectomized hypertensive patients.

Poricoic acid A as a modulator of TPH-1 expression inhibits renal fibrosis via modulating protein stability of β-catenin and β-catenin-mediated transcription

Background

Renal fibrosis is the common feature of chronic kidney disease (CKD). However, few drugs specifically target fibrogenesis due to the lack of an effective therapeutic target. Hence, it is urgent to find a therapeutic strategy that inhibits renal fibrosis. Here, we identified that poricoic acid A (PAA) as the modulator of tryptophan hydroxylase-1 (TPH-1), the key enzyme in tryptophan metabolism, exerted potent anti-fibrotic effects in the kidney.

Methods

Lentiviral vector, luciferase reporter activity assay and co-immunoprecipitation were used. The animal model of unilateral ureteral obstruction and adenine-induced chronic renal failure as well as transforming growth factor (TGF)-β1-treated epithelial cells NRK-52E and fibroblasts NRK-49F were used.

Results

TPH-1 was gradually decreased during CKD progression, while PAA treatment significantly increased TPH-1 expression to suppress renal fibrosis. Pharmacological overexpression of TPH-1 by PAA treatment exhibited anti-fibrosis and was linked to Wnt/β-catenin signaling activity. TPH-1 exhibited anti-fibrotic effects by suppressing epithelial cell injury and fibroblast activation, and PAA promoted TPH-1 expression and then suppressed the Wnt/β-catenin signaling pathway via regulating the protein stability of β-catenin and β-catenin-mediated transcription. TPH-1 overexpression enhanced the anti-fibrotic effects of PAA, while TPH-1 deficiency weakened the anti-fibrotic effects of PAA, indicating that TPH-1 was required for the anti-fibrotic effects of PAA.

Conclusion

PAA as a modulator of TPH-1 expression attenuated renal fibrosis through regulating the Wnt/β-catenin signaling pathway by acting on the protein stability of β-catenin and β-catenin-mediated transcription. TPH-1 was required for PAA to exert anti-fibrosis.

N-Acetyl-Seryl-Aspartyl-Lysyl-Proline Mitigates Experimental Colitis Through Inhibition of Intestinal Mucosal Inflammatory Responses via MEK-ERK Signaling

N-acetyl-seryl-aspartyl-lysyl-proline (AcSDKP) is an endogenous immunomodulatory peptide that is generated from thymosin β4 (Tβ4) through stepwise hydrolysis, involving meprin-α and prolyl endopeptidase (PREP). It is well acknowledged that AcSDKP exerts beneficial effects on multiple cardiovascular and renal diseases. However, the functional role of AcSDKP in inflammatory bowel disease (IBD) remains poorly understood. Here, we aimed to assess the content of AcSDKP in patients with IBD and investigate the impact of AcSDKP on intestinal inflammation in IBD. We found that in the inflamed mucosal specimens of patients with ulcerative colitis, the expression levels of Tβ4 and meprin-α were decreased, while PREP was expressed at similar levels to non-inflamed mucosa. In vitro, AcSDKP inhibited the expression of proinflammatory factors in intestinal epithelial cells partially by reducing the activation of MEK-ERK signaling. In vivo studies showed that transgenic mice, with lower levels of AcSDKP, were more vulnerable to dextran sulfate sodium (DSS)-induced colitis and exhibited more severe intestinal inflammatory responses. On the other hand, exogenous AcSDKP infusion significantly attenuated the clinical symptoms and intestinal mucosal inflammation in DSS-induced mice. In conclusion, results from this study demonstrated the anti-inflammatory function of AcSDKP within the intestine and suggest that AcSDKP has a promising therapeutic potential for IBD treatment.

The immunopathogenesis of tuberculous pericarditis

Tuberculous pericarditis is a severe form of extrapulmonary tuberculosis and is the commonest cause of pericardial effusion in high incidence settings. Mortality ranges between 8 and 34%, and it is the leading cause of pericardial constriction in Africa and Asia. Current understanding of the disease is based on models derived from studies performed in the 1940-50s. This review summarises recent advances in the histology, microbiology and immunology of tuberculous pericarditis, with special focus on the effect of Human Immunodeficiency Virus (HIV) and the determinants of constriction.

Considerations for Docking of Selective Angiotensin-Converting Enzyme Inhibitors

The angiotensin-converting enzyme (ACE) is a two-domain dipeptidylcarboxypeptidase, which has a direct involvement in the control of blood pressure by performing the hydrolysis of angiotensin I to produce angiotensin II. At the same time, ACE hydrolyzes other substrates such as the vasodilator peptide bradykinin and the anti-inflammatory peptide N-acetyl-SDKP. In this sense, ACE inhibitors are bioactive substances with potential use as medicinal products for treatment or prevention of hypertension, heart failures, myocardial infarction, and other important diseases. This review examined the most recent literature reporting ACE inhibitors with the help of molecular modeling. The examples exposed here demonstrate that molecular modeling methods, including docking, molecular dynamics (MD) simulations, quantitative structure-activity relationship (QSAR), etc, are essential for a complete structural picture of the mode of action of ACE inhibitors, where molecular docking has a key role. Examples show that too many works identified ACE inhibitory activities of natural peptides and peptides obtained from hydrolysates. In addition, other works report non-peptide compounds extracted from natural sources and synthetic compounds. In all these cases, molecular docking was used to provide explanation of the chemical interactions between inhibitors and the ACE binding sites. For docking applications, most of the examples exposed here do not consider that: (i) ACE has two domains (nACE and cACE) with available X-ray structures, which are relevant for the design of selective inhibitors, and (ii) nACE and cACE binding sites have large dimensions, which leads to non-reliable solutions during docking calculations. In support of the solution of these problems, the structural information found in Protein Data Bank (PDB) was used to perform an interaction fingerprints (IFPs) analysis applied on both nACE and cACE domains. This analysis provides plots that identify the chemical interactions between ligands and both ACE binding sites, which can be used to guide docking experiments in the search of selective natural components or novel drugs. In addition, the use of hydrogen bond constraints in the S₂ and S₂′ subsites of nACE and cACE are suggested to guarantee that docking solutions are reliable.

Interaction of N-acetyl-seryl-aspartyl-lysyl-proline with the angiotensin-converting enzyme 2-angiotensin-(1-7)-Mas axis attenuates pulmonary fibrosis in silicotic rats

NEW FINDINGS

What is the central question of this study? What are the effects of the antifibrotic peptide acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP) on the angiotensin-converting enzyme 2 (ACE2)-angiotensin-(1-7)-Mas axis during the occurrence and progression of silicosis? What is the main finding and its importance? Ac-SDKP inhibited lung fibrosis in rats exposed to silica by activation of the ACE2-angiotensin-(1-7)-Mas axis. Angiotensin-(1-7) potentially promotes Ac-SDKP by increasing the level of meprin α, the major synthetase of Ac-SDKP. Thus, the interaction Ac-SDKP and angiotesin-(1-7) in silicosis could provide a new therapeutic strategy.

ABSTRACT

The central role of angiotensin-converting enzyme (ACE) in the occurrence and progression of silicosis has been established. The antifibrotic peptide acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP) can be degraded by ACE. The ACE2-angiotensin-(1-7)-Mas axis is protective and acts to counterbalance the detrimental effects of ACE-angiotensin II (Ang II)-Ang II type 1 receptor and exerts antifibrotic effects. Here, we demonstrate an interaction between Ac-SDKP and Ang-(1-7) in the inhibition of collagen deposition and myofibroblast differentiation in rats exposed to silica. Treatment with Ac-SDKP increased the level of ACE2-Ang-(1-7)-Mas in rats or in cultured fibroblasts and decreased the levels of collagen type I and α-smooth muscle actin. Furthermore, exogenous Ang-(1-7) had similar antifibrotic effects and increased the level of meprin α, a major Ac-SDKP synthetase, both in vivo and in vitro. Compared with non-silicotic patients exposed to silica, the level of serum ACE was increased in patients with silicosis phase III; the levels of Ang II and Ang-(1-7) were high in patients with silicosis phase II; and the level of Ac-SDKP was high in the silicosis phase III group. These data imply that Ac-SDKP and Ang-(1-7) have an interactive effect as regulatory peptides of the renin-angiotensin system and exert antifibrotic effects.

Advances in Structural Biology of ACE and Development of Domain Selective ACE-inhibitors

BACKGROUND

The Angiotensin-I converting enzyme (ACE) is one of the most important components of the renin-angiotensin-aldosterone system controlling blood pressure and renal functions. Inhibitors of ACE are first line therapeutics used in the treatment of hypertension and related cardiovascular diseases. Somatic ACE consists of two homologous catalytic domains, the C- and N-domains. Recent findings have shown that although both domains are highly homologous in structure, they may have different physiological functions. The C-domain is primarily involved in the control of blood pressure, in contrast to the N-domain that is engaged in the regulation of hematopoietic stem cell proliferation. The currently available ACE inhibitors have some adverse effects that can be attributed to the non-selective inhibition of both domains. In addition, specific Ndomain inhibitors have emerged as potential antifibrotic drugs. Therefore, ACE is still an important drug target for the development of novel domain-selective drugs not only for the cardiovascular system but also for other systems.

OBJECTIVE

Detailed structural information about interactions in the protein-ligand complex is crucial for rational drug design. This review highlights the structural information available from crystallographic data which is essential for the development of domain selective inhibitors of ACE.

METHODS

Over eighty crystal complexes of ACE are placed into the Protein Database. An overview of X-ray ACE complexes with various inhibitors in C- and N-domains and an analysis of their binding mode have given mechanistic explanation of the structural determinants of selective ligand binding. In addition, ACE domain selective inhibitors with dual modes of action in complexes with ACE are also discussed.

CONCLUSION

Selectivity of ACE inhibitors for the N- and C-domain is controlled by subtle differences in the amino-acids forming the active site. Reported studies of crystal complexes of inhibitors in the C- and N-domains revealed that most selective inhibitors interact with non-conserved amino-acids between domains and have distinct interactions with the residues in the S2 and S2' subsites of the ACE catalytic site. Moreover, unusual binding of the second molecule of inhibitors in the binding cavity opens new possibilities of exploiting more distant regions of the catalytic center in structure-based design of novel drugs.

Angiotensin-converting enzyme inhibitory peptides from Lactobacillus delbrueckii QS306 fermented milk

Angiotensin-converting enzyme inhibitory peptides were isolated and identified from milk fermented using Lactobacillus delbrueckii QS306. The peptide with the highest angiotensin-converting enzyme inhibitory activity (C5) was purified using ultrafiltration with 10 and 3 kDa molecular mass cut-off membranes, Sephadex G-15 (Sigma-Aldrich, St. Louis, MO) gel filtration chromatography, reversed-phase HPLC, and Orbitrap Elite (Thermo Fisher Scientific Inc., Waltham, MA) liquid chromatography-tandem mass spectrometry. We obtained peptide LPYPY by microbial fermentation, which was derived from κ-casein f (AA 77-81). We synthesized LPYPY using an Fmoc solid-phase synthesis method and explored the secondary structure of the pentapeptide. The half maximal inhibitory concentration for the angiotensin-converting enzyme inhibitory activity of LPYPY was 12.87 μg/mL. The results provide additional information for ongoing research and the development of functional foods having antihypertensive effects.

ACE inhibitor suppresses cardiac remodeling after myocardial infarction by regulating dendritic cells and AT2 receptor-mediated mechanism in mice

Dendritic cells (DCs) play a complex role in the progression of myocardial infarction (MI). The impact of angiotensin-converting enzyme (ACE) inhibitor therapy, partly via affecting DCs maturation and recruitment, was tested on a MI mouse model. Furthermore, the cardioprotective effects of ACEI were enhanced through attenuating migration of DCs from the spleen into peripheral circulation, thereby inhibiting DCs maturation and tissue inflammation. ACEI repress DCs immune inflammatory response through down-regulating DCs maturation surface markers and regulating inflammatory cytokines, which led to a higher survival rate, improved function and remodeling through decreased inflammatory response after MI. However, inhibition of AT₂R activation, resulted in a reduction of ACEI effects on DCs. The potent anti-inflammatory effect of ACEI can partially be attributed to its impact on DCs through activation of AT₂R, which may provide a new target mechanism for ACEI therapy after MI.

d-amino acid modification protects N-Acetyl-seryl-aspartyl-lysyl-proline from physiological hydroxylation and increases its antifibrotic effects on hepatic fibrosis

N-Acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP) is a critical negative regulator of fibrosis development in the liver. However, its extremely short half-life in vivo greatly compromises its potential applications. Here, we report an Ac-SDKP analog peptide with d-amino acid replacement (Ac-SD_D K_D P). The stability of Ac-SD_D K_D P and its prevention of liver fibrosis were investigated in vitro and in vivo. The stabilities of Ac-SDKP and Ac-SD_D K_D P exposed to angiotensin-1-converting enzyme (ACE) and their half-lives in rats and human sera were determined by high-performance liquid chromatography. The inhibitory effects of Ac-SDKP and Ac-SD_D K_D P on the proliferation and activation of hepatic stellate cells (HSC-T6) were evaluated using the Cell Counting Kit-8, Western blotting, reverse transcription quantitative polymerase chain reaction, and immunofluorescence assays. Finally, the protective effects of Ac-SDKP and Ac-SD_D K_D P on carbon tetrachloride (CCl₄ )-induced liver fibrosis in rats were compared. d-Amino acid replacement significantly enhanced the stability of the peptide to ACE and prolonged the half-life of Ac-SDKP in rats and human sera. The Ac-SDKP-mediated inhibition of HSC-T6 cell proliferation was well preserved, and Ac-SD_D K_D P exerted inhibitory effects comparable to Ac-SDKP on α-smooth muscle actin (α-SMA), collagen I and III expression, and phosphorylated-Smad-2 expression. After intraperitoneal (i.p.) administration, Ac-SD_D K_D P exhibited significantly greater protection than Ac-SDKP against CCl₄ -induced liver fibrosis in rats. The serum alanine aminotransferase, aspartate aminotransferase, albumin, and total protein levels of the Ac-SD_D K_D P-treated rats were significantly lower than those of the Ac-SDKP-treated rats. α-SMA, CD45, and collagen I and III expression, as well as Smad-2 phosphorylation were significantly attenuated in the livers of the Ac-SD_D K_D P-treated rats compared to those of the Ac-SDKP-treated rats. Furthermore, we showed that the Ac-SD_D K_D P concentration in the rat liver increased to a physiological level of 60 min after i.p. administration, although i.p. administration of Ac-SDKP failed to enhance the peptide concentration in the rat liver. Our findings indicate that d-amino acid replacement is a simple and effective method to enhance the stability of Ac-SDKP. Ac-SD_D K_D P represents potential application of Ac-SDKP in fibrosis treatment and provides a new potential treatment strategy for liver fibrosis. © 2019 IUBMB Life, 71(9):1302-1312, 2019.