Human plasma kallikrein: roles in coagulation, fibrinolysis, inflammation pathways, and beyond

Substitution of reactive centre loop residues from C1 esterase inhibitor increases the inhibitory specificity of alpha-1 antitrypsin for plasma kallikrein

C1 esterase inhibitor (C1INH) is a member of the serpin superfamily of proteins and controls plasma kallikrein (Pka). Purified C1INH concentrates are effective in controlling C1INH deficiency (hereditary angioedema, HAE). Because C1INH is a relatively slow inhibitor of Pka, we sought to develop a more effective inhibitor by exchanging reactive centre loop (RCL) residues in another serpin, alpha-1 antitrypsin (AAT) variant M358R, with the corresponding residues of C1INH. Novel, soluble, N-terminally hexahistidine-tagged variants were expressed in E. coli, purified by nickel chelate chromatography, and characterized kinetically. AAT/C1INH loop exchange mutants were designated by the RCL residues exchanged using the reactive centre P1-P1' convention. Maximal exchange mutant AC (10-4') inhibited Pka 78-fold and activated Factor XI (FXIa) 350-fold less rapidly than AAT M358R. Eleven additional variants were expressed, restoring AAT residues stepwise. The most selective variant was AC (10-3/4'), which restored AAT residues from P2-P3' compared to AC (10-4'), and inhibited Pka 1.9-fold more rapidly, and FXIa 1.6-fold less rapidly, for a gain in selectivity of 2.8-fold (p < 0.0001), without increasing the stoichiometry of inhibition (SI). The most active variant was AC (10-3), in which both the rate of Pka and FXIa inhibition were elevated relative to AAT M358R values, without SI elevation. Other variants exhibited slower reaction rates and/or elevated SI values. These results indicate that RCL exchanges can be productively employed to change serpin specificity and selectivity, but that the most effective exchanges may not be contiguous due to cooperativity between RCL residues.

Omega-3 Fatty Acids and Exercise in Obesity Management: Independent and Synergistic Benefits in Metabolism and Knowledge Gaps

Obesity is a significant global health issue, profoundly affecting metabolic and cardiovascular health and other related chronic conditions. In Chile, the prevalence of obesity is among the highest within the Organisation for Economic Cooperation and Development (OECD) countries, highlighting a critical public health challenge. This narrative review examines current evidence on the independent and potential synergistic roles of omega-3 fatty acids and exercise in managing obesity-related metabolic dysfunction. Omega-3 fatty acids, particularly eicosapentaenoic acid (EPA), have been shown to lower triglyceride levels, enhance lipid metabolism, and modulate inflammation via pathways involving peroxisome proliferator-activated receptors (PPARs) and sterol regulatory element-binding protein-1c (SREBP-1c). Exercise interventions, such as moderate-intensity continuous training (MICT) and high-intensity interval training (HIIT), provide distinct yet complementary metabolic benefits. Specifically, MICT improves body fat distribution and mitochondrial efficiency, whereas HIIT has notable effects on metabolic adaptability and insulin signaling. Additionally, emerging evidence points toward a potential role of the kinin-kallikrein system, particularly kallikrein 7 (KLK7), in obesity-associated insulin resistance. Despite these promising findings, several knowledge gaps persist regarding optimal dosing, intervention timing, population-specific effects, and the exact mechanisms behind the potential synergistic interactions between omega-3 supplementation and structured exercise. This review emphasizes the importance of conducting further research, particularly controlled clinical trials, to clarify these combined interventions' effectiveness and establish targeted therapeutic strategies tailored to individual metabolic profiles.

Structure-based identification of bioactive phytochemicals targeting kallikrein-related peptidase 2 for prostate cancer therapy

Kallikrein-related peptidase 2 (KLK2) is a serine protease exhibiting antiangiogenic properties through proteolytic activity. KLK2 is overexpressed in prostate cancer and plays a pivotal role in cancer progression, establishing it as a potential therapeutic target. Despite the promising results of small molecule inhibitors targeting KLK2 in prostate cancer treatment, there are still many challenges in the development and application of these inhibitors. As a consequence, very few KLK2 inhibitors have advanced to clinical trials because of issues with specificity and selectivity. Moreover, the precise mechanisms underlying KLK2's interactions with small molecule inhibitors remain inadequately understood. This study used structure-based virtual screening of a phytochemical library and found three compounds, Phaseolin, Withaphysalin D, and Nicandrenone, as potential KLK2 inhibitors. These compounds exhibited high binding affinities (-8.9 to -8.8 kcal/mol), favorable pharmacokinetic profiles, and stable interactions with KLK2's catalytic residues (including His65) in docking studies. Their binding was further validated through MM-PBSA free energy calculations, which confirmed energetically favorable interactions with KLK2. The findings suggest that these phytochemicals have a high potential to be exploited as novel KLK2 inhibitors with improved efficacy. While experimental validation of enzymatic inhibition and antitumor efficacy is required, this study provides a structural and mechanistic foundation for advancing these candidates into preclinical testing. These results also highlight the use of phytochemical libraries and dynamics-driven virtual screening in developing targeted therapies for prostate cancer.

Preventive administration of shengmaiyin: a novel approach to counteract heatstroke-induced coagulopathy in rats

Background

Coagulation disorders play a pivotal role in the elevated mortality rates associated with exertional heatstroke (EHS).

Purpose

To investigate the impact of Shengmai Yin Oral Liquid (SMY) on heatstroke-induced coagulopathy (HIC) in rats with EHS and to elucidate the underlying mechanisms.

Methods

A cohort of eighteen male SPF-grade SD rats, each implanted with a telemetric temperature capsule, were randomly allocated to three groups: a normal control (NC) group, an EHS group, and an SMY group (n = 6 per group). The SMY group received SMY orally at a dosage of 20g/(Kg·day) for a period of five consecutive days. Both the EHS and SMY groups were subjected to exercise in a climate-controlled chamber maintained at 40°C with 70% relative humidity until signs of exhaustion and a core body temperature of 42°C were reached, with the duration and distance of their exercise being meticulously documented. Histopathological assessments were performed on the liver, kidney, lung, duodenum, and heart of the rats. Blood samples were collected to measure prothrombin time (PT), activated partial thromboplastin time (APTT), platelet count, and levels of lactic acid (Lac), thrombomodulin (TM), thrombospondin-1 (TSP-1), von Willebrand factor (vWF), and plasminogen activator inhibitor-1 (PAI-1). Plasma samples were subjected to data-independent acquisition (DIA)-based quantitative proteomics analysis, and differentially expressed proteins identified were further authenticated using parallel reaction monitoring (PRM) and Enzyme-Linked Immunosorbent Assay (ELISA).

Results

The SMY group exhibited a significantly extended running distance and time before reaching a core temperature of 42°C compared to the EHS group. Histopathological examination revealed thrombosis in the liver, kidney, lung, duodenum, and heart of rats in the EHS group, whereas no significant thrombosis was observed in the SMY group. The EHS group showed significantly prolonged PT and APTT, increased Lac, decreased platelet count, and elevated plasma levels of TM, vWF, TSP-1, and PAI-1 compared to the NC group (P < 0.05). In contrast, the SMY group demonstrated a significant reduction in APTT, an increase in platelet count, and decreased plasma levels of TM, vWF, PAI-1, and TSP-1 compared to the EHS group (P < 0.05). Among the 1,189 proteins identified, 56 differentially expressed proteins (DEPs) were associated with SMY's protective effects against HIC, primarily involved in the upregulation of the relaxin signaling pathway, protein digestion and absorption, platelet activation, and ECM-receptor interaction signaling pathways, as well as the downregulation of the spliceosome and ribosome signaling pathways. PRM quantitative analysis indicated that SMY may upregulate the expression of Nucleobindin-1 (Nucb1), Procollagen C-endopeptidase enhancer 1 (Pcolce), and lectin galactoside-binding soluble 1 (Lgals1), and downregulate the expression of Xpnpep2. Subsequent ELISA validation confirmed a significant increase in plasma Xpnpep2 levels in EHS rats, an effect that was substantially reduced by pre-treatment with SMY.

Conclusion

SMY demonstrates the capacity to mitigate HIC by lessening the impact of vascular endothelial damage and moderating the consumption of coagulation factors and platelets. This salutary influence is correlated with the downregulation of XPNPEP2 expression.

Enhancement of plasma kallikrein specificity of antitrypsin variants identified by phage display and partial reversion

BACKGROUND

The naturally occurring variant Alpha-1 Antitrypsin M358R (AAT M358R), modified at the P1 position of the reactive center loop (RCL), shifts its inhibitory protease target from neutrophil elastase to multiple coagulation and contact proteases, including activated plasma kallikrein (Pka; KLKB1). Our aim was to increase the specificity of AAT M358R for Pka as a potential novel therapeutic agent to treat pathological swelling arising from elevated Pka levels in patients with Hereditary Angioedema.

RESULTS

Two AAT M358R T7Select phage display libraries randomized at RCL positions P7-P3 and P2-P3' were iteratively probed with Pka. The most abundant Pka-inhibitory motifs from phage display were P7-P3, QLIPS; and P2-P3', VRRAY (mutated residues in bold). AAT variants expressing these motifs, alone or in combination, as well as six less-mutated P7-P3 revertant proteins were expressed, purified, and characterized kinetically. Variants AAT M358R (QLIPS) (designated 7-QLIPS-3) and 7-FLEPS-3 exhibited significantly enhanced selectivity for Pka (over factor XIa) by factors of 6.9 and 9.2, respectively, without increasing the stoichiometry of inhibition (SI) or decreasing the inhibition rate relative to AAT M358R. No other variants matched this profile.

CONCLUSIONS

Pro substitution at P4 was found to be important for enhanced inhibition of Pka by AAT M358R. Two novel variants with this substitution are more rapid and selective inhibitors of Pka than AAT M358R and may provide better control of Pka in vivo than existing HAE therapeutics.

Platform-dependent effects of genetic variants on plasma APOL1 and their implications for kidney disease

Mutations in apolipoprotein L1 (APOL1) are strongly associated with an increased risk of kidney disease in individuals of African ancestry, yet the underlying mechanisms remain largely unknown. Plasma proteomics provides opportunities to elucidate mechanisms of disease by studying the effects of disease-associated variants on circulating protein levels. Here, we examine the genetic drivers of circulating APOL1 in individuals of African and European ancestry from four independent cohorts (UK Biobank, AASK, deCODE and Health ABC) employing three proteomic technologies (Olink, SomaLogic and mass spectrometry). We find that disease-associated APOL1 G1 and G2 variants are strong pQTLs for plasma APOL1 in Olink and SomaLogic, but the direction of their effects depends on the proteomic platform. We identify an additional APOL1 missense variant (rs2239785), common in Europeans, exhibiting the same platform-dependent directional discrepancy. Similarly, variants in the kallikrein-kinin pathway ( KLKB1 , F12 , KNG1 ) and their genetic interactions exhibit strong trans -pQTL effects for APOL1 measured by Olink, but not SomaLogic. To explain these discrepancies, we propose a model in which APOL1 mutations and the kallikrein-kinin pathway influence the relative abundance of two distinct APOL1 forms, corresponding to APOL1 bound to trypanolytic factors 1 and 2, which are differentially recognized by different proteomic platforms. We hypothesize that this shift in relative abundance of APOL1 forms may contribute to the development of kidney disease.

Impact of High Glucose on Bone Collagenous Matrix Composition, Structure, and Organization: An Integrative Analysis Using an Ex Vivo Model

Diabetes mellitus is a widespread metabolic disorder linked to numerous systemic complications, including adverse effects on skeletal health, such as increased bone fragility and fracture risk. Emerging evidence suggests that high glucose may disrupt the extracellular matrix (ECM) of bone, potentially altering its composition and organization. Collagen, the primary organic component of the ECM, is critical for maintaining structural integrity and biomechanical properties. However, definitive evidence and a comprehensive understanding of the molecular mechanisms through which high glucose impacts the ECM and collagen remain elusive. This study employed an ex vivo embryonic chicken femur model to investigate the effects of high glucose on the collagenous matrix. A comprehensive approach integrating histological evaluation, histomorphometry, ATR-FTIR spectroscopy, and proteomics was adopted to unravel structural, biochemical, and molecular changes in the ECM. Histomorphometric analysis revealed disrupted collagen fibril architecture, characterized by altered fibril diameter, alignment, and spatial organization. ATR-FTIR spectroscopy highlighted biochemical modifications, including non-enzymatic glycation that impaired collagen crosslinking and reduced matrix integrity. Proteomic profiling unveiled significant alterations in ECM composition and function, including downregulation of key collagen crosslinking enzymes and upregulation of inflammatory and coagulation pathways. High glucose profoundly disrupts the collagenous matrix of bone, weakening its structural integrity and organization. These findings emphasize the critical impact of high glucose environments on extracellular matrix composition and bone quality, offering insights into the mechanisms behind diabetic bone fragility and guiding future research toward targeted therapeutic strategies.

Understanding COVID-19 outcome: Exploring the prognostic value of soluble biomarkers indicative of endothelial impairment

Host proteins released by the activated endothelial cells during SARS-CoV-2 infection are implicated to be involved in coagulation and endothelial dysfunction. However, the underlying mechanism that governs the vascular dysfunction and disease severity in COVID-19 remains obscure. The study evaluated the serum levels of Bradykinin, Kallikrein, SERPIN A, and IL-18 in COVID-19 (N-42 with 20 moderate and 22 severe) patients compared to healthy controls (HC: N-10) using ELISA at the day of admission (DOA) and day 7 post-admission. The efficacy of the protein levels in predicting disease severity was further determined using machine learning models. The levels of bradykinins and SERPIN A were higher (P ≤ 0.001) in both severe and moderate cases on day 7 post-admission compared to DOA. All the soluble proteins studied were found to elevated (P ≤ 0.01) in severe compared to moderate in day 7 and were positively correlated (P ≤ 0.001) with D-dimer, a marker for coagulation. ROC analysis identified that SERPIN A, IL-18, and bradykinin could predict the clinical condition of COVID-19 with AUC values of 1, 0.979, and 1, respectively. Among the models trained using univariate model analysis, SERPIN A emerged as a strong prognostic biomarker for COVID-19 disease severity. The serum levels of SERPIN A in conjunction with the coagulation marker D-dimer, serve as a predictive indicator for COVID-19 clinical outcomes. However, studies are required to ascertain the role of these markers in disease virulence.

Unveiling therapeutic frontiers: DON/DRP-104 as innovative Plasma kallikrein inhibitors against carcinoma-associated hereditary angioedema shocks - a comprehensive molecular dynamics exploration

Human plasma kallikrein (PKa) is a member of the serine protease family and serves as a key mediator of the kallikrein-kinin system (KKS), which is known for its regulatory roles in inflammation, vasodilation, blood pressure, and coagulation. Genetic dysregulation of KKS leads to Hereditary Angioedema (HAE), which is characterized by spontaneous, painful swelling in various body regions. Importantly, HAE frequently coexists with various cancers. Despite substantial efforts towards the development of PKa inhibitors for HAE, there remains a need for bifunctional agents addressing both anti-cancer and anti-HAE aspects, especially against carcinoma-associated comorbid HAE conditions. Consequently, we investigated the therapeutic potential of the anti-glutamine prodrug, isopropyl(S)-2-((S)-2-acetamido-3-(1H-indol-3-yl)-propanamido)-6-diazo-5-oxo-hexanoate (DRP-104), and its active form, 6-Diazo-5-oxo-l-norleucine (DON), recognized for their anti-cancer properties, as novel PKa inhibitors. Utilizing structure-based in silico methods, we conducted a comparative analysis with berotralstat, a clinically approved HAE prophylactic, and sebetralstat, an investigational HAE therapeutic agent, in Phase 3 clinical trials. Inhibiting PKa with DON resulted in relatively heightened structural stability, rigidity, restricted protein folding, and solvent-accessible loop exposure, contributing to increased intra-atomic hydrogen bond formation. Conversely, PKa inhibition with DRP-104 induced restricted residue flexibility and significantly disrupted the critical SER195-HIS57 arrangement in the catalytic triad. Both DON and DRP-104, along with the reference drugs, induced strong cooperative intra-residue motion and bidirectional displacement in the PKa architecture. The results revealed favorable binding kinetics of DON/DRP-104, showing thermodynamic profiles that were either superior or comparable to those of the reference drugs. These findings support their consideration for clinical investigations into the management of carcinoma-associated HAE.

Selective Detection of Active Extracellular Granzyme A by Using a Novel Fluorescent Immunoprobe with Application to Inflammatory Diseases

Granzymes (Gzms), a family of serine proteases, expressed by immune and nonimmune cells, present perforin-dependent and independent intracellular and extracellular functions. When released in the extracellular space, GzmA, with trypsin-like activity, is involved in the pathophysiology of different inflammatory diseases. However, there are no validated specific systems to detect active forms of extracellular GzmA, making it difficult to assess its biological relevance and potential use as a biomarker. Here, we have developed fluorescence-energy resonance-transfer (FRET)-based peptide probes (FAM-peptide-DABCYL) to specifically detect GzmA activity in tissue samples and biological fluids in both mouse and human samples during inflammatory diseases. An initial probe was developed and incubated with GzmA and different proteases like GzmB and others with similar cleavage specificity as GzmA like GzmK, thrombin, trypsin, kallikrein, or plasmin. After measuring fluorescence, the probe showed very good specificity and sensitivity for human and mouse GzmA when compared to GzmB, its closest homologue GzmK, and with thrombin. The specificity of this probe was further refined by incubating the samples in a coated plate with a GzmA-specific antibody before adding the probe. The results show a high specific detection of soluble GzmA even when compared with other soluble proteases with very similar cleavage specificity like thrombin, GzmK, trypsin, kallikrein, or plasmin, which shows nearly no fluorescence signal. The high specific detection of GzmA was validated, showing that using pure proteins and serum and tissue samples from GzmA-deficient mice presented a significant reduction in the signal compared with WT mice. The utility of this system in humans was confirmed, showing that GzmA activity was significantly higher in serum samples from septic patients in comparison with healthy donors. Our results present a new immunoprobe with utility to detect extracellular GzmA activity in different biological fluids, confirming the presence of active forms of the soluble protease in vivo during inflammatory and infectious diseases.

The secretory leukocyte protease inhibitor (SLPI) in pathophysiology of non-communicable diseases: Evidence from experimental studies to clinical applications

Non-communicable diseases (NCDs) are a worldwide health issue because of their prevalence, negative impacts on human welfare, and economic costs. Protease enzymes play important roles in viral and NCD diseases. Slowing disease progression by inhibiting proteases using small-molecule inhibitors or endogenous inhibitory peptides appears to be crucial. Secretory leukocyte protease inhibitor (SLPI), an inflammatory serine protease inhibitor, maintains protease/antiprotease balance. SLPI is produced by host defense effector cells during inflammation to prevent proteolytic enzyme-induced tissue damage. The etiology of noncommunicable illnesses is linked to SLPI's immunomodulatory and tissue regeneration roles. Disease phases are associated with SLPI levels and activity changes in regional tissue and circulation. SLPI has been extensively evaluated in inflammation, but rarely in NCDs. Unfortunately, the thorough evaluation of SLPI's pathophysiological functions in NCDs in multiple research models has not been published elsewhere. In this review, data from PubMed from 2014 to 2023 was collected, analysed, and categorized into in vitro, in vivo, and clinical studies. According to the review, serine protease inhibitor (SLPI) activity control is linked to non-communicable diseases (NCDs) and other illnesses. Overexpression of the SLPI gene and protein may be a viable diagnostic and therapeutic target for non-communicable diseases (NCDs). SLPI is also cytoprotective, making it a unique treatment. These findings suggest that future research should focus on these pathways using advanced methods, reliable biomarkers, and therapy approaches to assess susceptibility and illness progression. Implications from this review will help pave the way for a new therapeutic target and diagnosis marker for non-communicable diseases.