Broad-spectrum Protease Inhibitor Research Articles

Identification of Potent, Broad-Spectrum Coronavirus Main Protease Inhibitors for Pandemic Preparedness.

The COVID-19 pandemic highlights the ongoing risk of zoonotic transmission of coronaviruses to global health. To prepare for future pandemics, it is essential to develop effective antivirals targeting a broad range of coronaviruses. Targeting the essential and clinically validated coronavirus main protease (Mpro), we constructed a structurally diverse Mpro panel by clustering all known coronavirus sequences by Mpro active site sequence similarity. Through screening, we identified a potent covalent inhibitor that engaged the catalytic cysteine of SARS-CoV-2 Mpro and used structure-based medicinal chemistry to develop compounds in the pyrazolopyrimidine sulfone series that exhibit submicromolar activity against multiple Mpro homologues. Additionally, we solved the first X-ray cocrystal structure of Mpro from the human-infecting OC43 coronavirus, providing insights into potency differences among compound-target pairs. Overall, the chemical compounds described in this study serve as starting points for the development of antivirals with broad-spectrum activity, enhancing our preparedness for emerging human-infecting coronaviruses.

The Prominence of the Broad-Spectrum Protease inhibitor gene A2ML1 as a potential biomarker in cervical cancer diagnostics using Immunotherapeutic and Multi-Omics approaches

One of the venereal tumors that threaten human life is cervical cancer. A2ML1 is detected in advanced-stage cancer patients and is found to be strongly associated with cervical cancer. A2ML1 was shown to be substantially expressed in cervical cancer in this study, which used data from the TCGA database. Those with high A2ML1 expression had a lower chance of survival than patients with low A2ML1 expression. Both univariate and multivariate Cox regression analyses were utilized to investigate the relationship between clinical variables and overall survival rates. An investigation into the link between A2ML1 and immune infiltration was subsequently conducted. Utilizing the immune cell database, research was conducted to investigate the dispersion of 24 immune cells and their correlation to A2ML1 expression. In addition to this, the favorable correlation between immune cells and A2ML1 was validated using all three immune cell methodologies. The Genomics of Drug Sensitivity in Cancer database was used to confirm the idea that there is a link between A2ML1 expression and the efficacy of chemotherapy or immunotherapy. The findings demonstrated that A2ML1 is a potential biomarker for cervical cancer diagnostics. This biomarker may be used to chaperone immunotherapy, as well as to explain the elucidates of cervical cancer caused by the immunological microenvironment.

A2M possesses anti-bacterial functions by recruiting and enhancing phagocytosis through GRP78 in an echinoderm

Alpha-2-macroglobulin (A2M) is an extracellular macromolecule mainly known for its role as a broad-spectrum protease inhibitor in mammals. However, the immune recognition and regulation mechanisms of A2M in invertebrates are still not well investigated. In the current study, the role of sea cucumber Apostichopus japonicus A2M in the regulation of innate immune responses was explored. We found that AjA2M promotes phagocytosis of Vibrio splendidus in coelomocytes of sea cucumber. Then two major functional structural domains of AjA2M, the thioester domain (TED) and the receptor-binding structural domain (RBD) were cloned. It was found that the AjA2M-TED binds to pathogens while causing Vibrio splendidus aggregation; the AjA2M-RBD interacts with the Glucose Regulated Protein 78 (AjGRP78), subsequently AjGRP78 accelerates the degradation of Vibrio splendidus in lysosomes by facilitating polymerisation and rearrangement of the cytoskeleton. Collectively, the findings together suggest that A2M-GRP78 axis mediates immune signaling pathway of phagocytosis and AjA2M has been characterized to play an essential crucial role in antibacterial immune responses of invertebrates.

Organotypic lung tissue culture as a preclinical model to study host- influenza A viral infection: A case for repurposing of nafamostat mesylate

Reliable and effective models for recapitulation of host-pathogen interactions are imperative for the discovery of potential therapeutics. Ex vivo models can fulfill these requirements as the multicellular native environment in the tissue is preserved and be utilized for toxicology, vaccine, infection and drug efficacy studies due to the presence of immune cells. Drug repurposing involves the identification of new applications for already approved drugs that are not related to the prime medical indication and emerged as a strategy to cope with slow pace of drug discovery due to high costs and necessary phases to reach the patients. Within the scope of the study, broad-spectrum serine protease inhibitor nafamostat mesylate was repurposed to inhibit influenza A infection and evaluated by a translational ex vivo organotypic model, in which human organ-level responses can be achieved in preclinical safety studies of potential antiviral agents, along with in in vitro lung airway culture. The safe doses were determined as 10 µM for in vitro, whereas 22 µM for ex vivo to be applied for evaluation of host-pathogen interactions, which reduced virus infectivity, increased cell/tissue viability, and protected total protein content by reducing cell death with the inflammatory response. When the gene expression levels of specific pro-inflammatory, anti-inflammatory and cell surface markers involved in antiviral responses were examined, the significant inflammatory response represented by highly elevated mRNA gene expression levels of cytokines and chemokines combined with CDH5 downregulated by 5.1-fold supported the antiviral efficacy of NM and usability of ex vivo model as a preclinical infection model.

Efficacy and safety of Nafamostat mesylate in patients with end-stage renal failure.

Recent studies on dialysis anticoagulation therapy in patients with renal failure have shown that Nafamostat mesylate, a broad-spectrum potent serine protease inhibitor, has strong anticoagulation and anti-fiber activity. To evaluate the efficacy and safety of Nafamostat mesylate in patients with end-stage renal failure. Seventy-five patients with end-stage renal failure who received hemodialysis at our hospital between January 2020 and August 2021 were selected and divided into the observation group (Nafamostat mesylate for injection, n = 33) and control group (heparin sodium injection, n = 32). General patient data, indicators of clinical efficacy, dialyzer hemocoagulation parameters, coagulation function indices, and hemoglobin concentration and platelet count before and after treatment, and the occurrence of adverse reactions after treatment were compared between the two groups. The two groups showed no significant differences in general patient data (P > 0.05). The post-treatment effectiveness rate in the control group was lower than that in the observation group (P < 0.05). The two groups showed no significant difference in the number of patients in grade I (P > 0.05), while the number of patients in grade 0 was lower in the control group, and the number of patients in grades II and III was higher in the control group (P < 0.05). The post-treatment prothrombin time, activated partial thromboplastin time, thrombin time, and international normalized ratio values in the control group were higher than those in the observation group, while the fibrinogen level in the control group was lower than that in the observation group (P < 0.05). The two groups showed no significant difference in the platelet count and hemoglobin level before and after treatment (P > 0.05). The total number of post-treatment adverse reactions in the observation group was lower than that in the control group (P < 0.05). Treatment of patients showing end-stage renal failure with Nafamostat mesylate can significantly improve therapeutic efficacy and has high safety and clinical value.

Engineering New Protease Inhibitors Using α2-Macroglobulin.

Protease inhibitors of the alpha-macroglobulin family (αM) have a unique mechanism that allows them to trap proteases that is dependent not on the protease's class, but rather on its cleavage specificity. Proteases trigger a conformational change in the αM protein by cleaving within a "bait region," resulting in the sequestering of the protease inside the αM molecule. This nonspecific inhibitory mechanism appears to have arisen early in the αM family, and the broad protease-trapping capacity that it allows may play a role in pathogen defense.Human α2-macroglobulin (A2M) is a tetrameric αM whose bait region is permissive to cleavage by most proteases, making it a broad-spectrum protease inhibitor. Recent work has demonstrated that the inhibitory capacity of A2M derives directly from its bait region sequence: modifying the bait region sequence to introduce or remove protease cleavage sites will modify A2M's inhibition of the relevant proteases accordingly. Thus, changing the amino acid sequence of the bait region presents an effective avenue for protein engineering of new protease inhibitors if the substrate specificity of the target protease is known. The design of new A2M-based protease inhibitors with tailored inhibitory capacities has potential applications in basic research and the clinic. In this chapter, we describe the general approach and considerations for the bait region engineering of A2M.

Nafamostat mesilate prevented caerulein-induced pancreatic injury by targeting HDAC6-mediated NLRP3 inflammasome activation.

Nafamostat mesilate (NM), a synthetic broad-spectrum serine protease inhibitor, has been commonly used for treating acute pancreatitis (AP) and other inflammatory-associated diseases in some East Asia countries. Although the potent inhibitory activity against inflammation-related proteases (such as thrombin, trypsin, kallikrein, plasmin, coagulation factors, and complement factors) is generally believed to be responsible for the anti-inflammatory effects of NM, the precise target and molecular mechanism underlying its anti-inflammatory activity in AP treatment remain largely unknown. The protection of NM against pancreatic injury and inhibitory effect on the NOD-like receptor protein 3 (NLRP3) inflammasome activation were investigated in an experimental mouse model of AP. To decipher the molecular mechanism of NM, the effects of NM on nuclear factor kappa B (NF-κB) activity and NF-κB mediated NLRP3 inflammasome priming were examined in lipopolysaccharide (LPS)-primed THP-1 cells. Additionally, the potential of NM to block the activity of histone deacetylase 6 (HDAC6) and disrupt the association between HDAC6 and NLRP3 was also evaluated. NM significantly suppressed NLRP3 inflammasome activation in the pancreas, leading to a reduction in pancreatic inflammation and prevention of pancreatic injury during AP. NM was found to interact with HDAC6 and effectively inhibit its function. This property allowed NM to influence HDAC6-dependent NF-κB transcriptional activity, thereby blocking NF-κB-driven transcriptional priming of the NLRP3 inflammasome. Furthermore, NM exhibited the potential to interfere the association between HDAC6 and NLRP3, impeding HDAC6-mediated intracellular transport of NLRP3 and ultimately preventing NLRP3 inflammasome activation. Our current work has provided valuable insight into the molecular mechanism underlying the immunomodulatory effect of NM in the treatment of AP, highlighting its promising application in the prevention of NLRP3 inflammasome-associated inflammatory pathological damage.

Efficacy and safety of nafamostat mesilate anticoagulation in blood purification treatment of critically ill patients: a systematic review and meta-analysis

Background Nafamostat mesilate (NM), a broad-spectrum and potent serine protease inhibitor, can be used as an anticoagulant during extracorporeal circulation, as well as a promising drug effective against coronavirus disease 2019 (COVID-19). We conducted a systematic meta-analysis to evaluate the safety and efficacy of NM administration in critically ill patients who underwent blood purification therapy (BPT). Methods The Cochrane Library, Web of Science and PubMed were comprehensively searched from inception to August 20, 2021, for potential studies. Results Four randomized controlled trials (RCTs) and seven observational studies with 2723 patients met the inclusion criteria. The meta-analysis demonstrated that conventional therapy (CT) significantly increased hospital mortality compared with NM administration (RR = 1.25, p = 0.0007). In subgroup analyses, the in-hospital mortality of the NM group was significantly lower than that of the anticoagulant-free (NA) group (RR = 1.31, p = 0.002). The CT interventions markedly elevated the risk ratio of bleeding complications by 45% (RR = 1.45, p = 0.010) compared with NM interventions. In another subgroup analysis, NM used exhibited a significantly lower risk of bleeding complications than those of the low-molecular-weight heparin (LMWH) used (RR = 4.58, p = 0.020). The filter lifespan was decreased significantly (MD = −10.59, p < 0.0001) in the NA groups compared with the NM groups. Due to the poor quality of the included RCTs, these results should be interpreted with caution. Conclusion Given the better survival outcomes, lower risk of bleeding, NM anticoagulation seems to be a safe and efficient approach for BPT patients and could yield a favorable filter lifespan. More multi-center RCTs with large samples are required for further validation of this study.

Ulinastatin Alleviates Rhabdomyolysis-Induced Acute Kidney Injury by Suppressing Inflammation and Apoptosis via Inhibiting TLR4/NF-κB Signaling Pathway.

Acute kidney injury (AKI) is an important complication of rhabdomyolysis (RM), but there is lack of effective treatments. Ulinastatin (UTI) is a broad-spectrum serine protease inhibitor isolated and purified from human urine with strong anti-inflammatory and cytoprotective actions. The aim of this research was to investigate the effect and potential mechanism of UTI on RM-induced AKI (RM-AKI). We established RM-induced AKI model and myoglobin (Mb)-stimulated NRK-52E cell model. In vivo, twenty-four rats were randomly divided into three groups (n = 8): control, RM-AKI, and RM-AKI + UTI. In vitro, the NRK-52E cells were divided into six groups according to the different treatment method. Mb-stimulated NRK-52E cells were treated with UTI or si-TLR4 transfection to characterize the mechanisms of UTI in RM-AKI. Indicators of the kidney injury, cell viability, cell cycle, oxidative stress, inflammation, apoptosis, and TLR4/NF-κB signaling pathway were assessed. In vivo and in vitro, UTI significantly decreased the expression of TLR4 and p65. In vivo, UTI significantly improved renal function and reduced inflammatory reaction and kidney injury. In vitro, UTI protected NRK-52E cells from Mb stimulation by suppressing cell cytotoxicity, cell cycle inhibition, overproduction of ROS, inflammation, and apoptosis. Additionally, UTI played a protective role by downregulating the TLR4 expression. The results indicate that UTI alleviates RM-AKI by suppressing the inflammatory response and apoptosis via inhibiting TLR4/NF-κB signaling pathway. Our study provides a new mechanism for the protective effect of UTI on RM-AKI.

Multi-omics analyses of the ulcerative colitis gut microbiome link Bacteroides vulgatus proteases with disease severity.

Ulcerative colitis (UC) is driven by disruptions in host-microbiota homeostasis, however current treatments exclusively target host inflammatory pathways. To understand how host-microbiota interactions become disrupted in UC, we collected and analyzed six fecal or serum based –omic datasets (metaproteomic, metabolomic, metagenomic, metapeptidomic, and amplicon sequencing profiles of fecal samples and proteomic profiles of serum samples) from 40 UC patients at a single inflammatory bowel disease centre, as well as various clinical, endoscopic, and histologic measures of disease activity. A validation cohort of 210 samples (73 UC, 117 Crohn’s disease (CD), 20 healthy controls) was collected and analyzed separately and independently. Data integration across both cohorts showed that a subset of the clinically active UC patients had an over-abundance of proteases that originated from the bacterium, Bacteroides vulgatus. To test whether B. vulgatus proteases contribute to UC disease activity, we first profiled B. vulgatus proteases found in patients and bacterial cultures. Use of a broad-spectrum protease inhibitor improved B. vulgatus-induced barrier dysfunction in vitro, and prevented colitis in B. vulgatus monocolonized, IL-10 deficient mice. Furthermore, transplantation of feces from UC patients with a high abundance of B. vulgatus proteases into germ-free mice induced colitis dependent on protease activity. These results, stemming from a multi-omics approach, improve understanding of functional microbiota alterations that drive UC and provides a resource for identifying other pathways that could be inhibited as a strategy to treat this disease.

Investigating Constraints Along the Plant Secretory Pathway to Improve Production of a SARS-CoV-2 Spike Vaccine Candidate.

Given the complex maturation requirements of viral glycoproteins and the challenge they often pose for expression in plants, the identification of host constraints precluding their efficient production is a priority for the molecular farming of vaccines. Building on previous work to improve viral glycoprotein production in plants, we investigated the production of a soluble SARS-CoV-2 spike comprising the ectopic portion of the glycoprotein. This was successfully transiently expressed in N. benthamiana by co-expressing the human lectin-binding chaperone calreticulin, which substantially increased the accumulation of the glycoprotein. The spike was mostly unprocessed unless the protease furin was co-expressed which resulted in highly efficient processing of the glycoprotein. Co-expression of several broad-spectrum protease inhibitors did not improve accumulation of the protein any further. The protein was successfully purified by affinity chromatography and gel filtration, although the purified product was heterogenous and the yields were low. Immunogenicity of the antigen was tested in BALB/c mice, and cellular and antibody responses were elicited after low dose inoculation with the adjuvanted protein. This work constitutes an important proof-of-concept for host plant engineering in the context of rapid vaccine development for SARS-CoV-2 and other emerging viruses.

Discovery of diminazene as a dual inhibitor of SARS-CoV-2 human host proteases TMPRSS2 and furin using cell-based assays.

The proteases TMPRSS2 (transmembrane protease serine 2) and furin are known to play important roles in viral infectivity including systematic COVID-19 infection through priming of the spike protein of SARS-CoV-2 and related viruses. To discover small-molecules capable of inhibiting these host proteases, we established convenient and cost-effective cell-based assays employing Vero cells overexpressing TMPRSS2 and furin. A cell-based proteolytic assay for broad-spectrum protease inhibitors was also established using human prostate cancer cell line LNCaP. Evaluation of camostat, nafamostat, and gabexate in these cell-based assays confirmed their known TMPRSS2 inhibitory activities. Diminazene, a veterinary medicinal agent and a known furin inhibitor was found to inhibit both TMPRSS2 and furin with IC50s of 1.35 and 13.2 μM, respectively. Establishment and the use of cell-based assays for evaluation TMPRSS2 and furin inhibitory activity and implications of dual activity of diminazene vs TMPRSS2 and furin are presented.

Alpha-2-Macroglobulin in Inflammation, Immunity and Infections.

Alpha-2-macroglobulin is an extracellular macromolecule mainly known for its role as a broad-spectrum protease inhibitor. By presenting itself as an optimal substrate for endopeptidases of all catalytic types, alpha-2-macroglobulin lures active proteases into its molecular cage and subsequently ‘flags’ their complex for elimination. In addition to its role as a regulator of extracellular proteolysis, alpha-2-macroglobulin also has other functions such as switching proteolysis towards small substrates, facilitating cell migration and the binding of cytokines, growth factors and damaged extracellular proteins. These functions appear particularly important in the context of immune-cell function. In this review manuscript, we provide an overview of all functions of alpha-2-macroglobulin and place these in the context of inflammation, immunity and infections.

Therapeutic Approaches in Modulating the Inflammatory and Immunological Response in Patients With Sepsis, Acute Respiratory Distress Syndrome, and Pancreatitis: An Expert Opinion Review.

Immunomodulation has long been an adjunct approach in treating critically ill patients with sepsis, acute respiratory distress syndrome (ARDS), and acute pancreatitis (AP). Hyperactive immune response with immunopathogenesis leads to organ dysfunction and alters the clinical outcomes in critically ill. Though the immune response in the critically ill might have been overlooked, it has gathered greater attention during this novel coronavirus disease 2019 (COVID-19) pandemic. Modulating hyperactive immune response, the cytokine storm, especially with steroids, has shown to improve the outcomes in COVID-19 patients. In this review, we find that immune response pathogenesis in critically ill patients with sepsis, ARDS, and AP is nearly similar. The use of immunomodulators such as steroids, broad-spectrum serine protease inhibitors such as ulinastatin, thymosin alpha, intravenous immunoglobulins, and therapies such as CytoSorb and therapeutic plasma exchange may help in improving the clinical outcomes in these conditions. As the experience of the majority of physicians in using such therapeutics may be limited, we provide our expert comments regarding immunomodulation to optimize outcomes in patients with sepsis/septic shock, ARDS, and AP.

Crystal structure of nafamostat dimesylate.

Nafamostat dimesylate {systematic name: [amino({6-[(4-{[amino(iminiumyl)methyl]amino}phenyl)carbonyloxy]naphthalen-2-yl})methylidene]azanium bis(methanesulfonate)}, C19H19N5O2 2+·2CH3O3S-, is a broad-spectrum serine protease inhibitor and has been applied clinically as an anti-coagulant agent during hemodialysis and for treatment of severe acute pancreatitis (SAP). Since nafamostat contains flexible moieties, it is necessary to determine the conformation to understand the structure-activity relationships. The divalent cation has a screw-like motif. The guanidinium group is approximately perpendicular to the naphthyl ring system, subtending a dihedral angle of 84.30 (14)°. In the crystal, the nafamostat mol-ecules form columnar structures surrounded by a hydro-philic region.

Interaction of Penaeus vannamei hemocyanin and α2-macroglobulin modulates the phenoloxidase activity

Prophenoloxidase (proPO)-activating system is a critical innate immune defense in invertebrates. However, the mechanisms involved in regulating the phenoloxidase (PO) activity in shrimp hemolymph remain ill-defined. Our previous studies showed that Penaeus vannamei hemocyanin (HMC) and α2-macroglobulin (α2M), two key regulators of proPO-activating system in plasma, might interact with each other, indicating that this interaction could be implicated in controlling PO activity. Herein, we further confirmed that HMC specifically bind to α2M using Pull down and Far-Western blot analyses. Further studies demonstrated that HMC could directly interact with the receptor binding domain of α2M. In addition, HMC and α2M followed similar expression pattern upon Vibrio parahaemolyticus infection, suggesting the interaction of HMC and α2M might have a role in immune response. Finally, we found that α2M, as a broad-spectrum proteinase inhibitor, suppressed the serum PO activity in vitro, while hemocyanin could partially restore this inhibitory effect. In sum, the present data indicate that HMC interacts with α2M and therefore modulates the PO activity. This finding contributes to better understanding of stable state maintenance of PO activity in shrimp.

A structure-guided taxonomicbased approach to the design of broad-spectrum coronavirus protease inhibitors

A structure-guided taxonomicbased approach to the design of broad-spectrum coronavirus protease inhibitors

The analgesic effects of ulinastatin either as a single agent or in combination with sufentanil: A novel therapeutic potential for postoperative pain

Ulinastatin is a broad-spectrum protease inhibitor widely used for the treatment of various inflammation-related diseases owing to its recognized excellent anti-inflammatory and cytoprotective properties. However, whether ulinastatin can relieve postoperative pain remains unclear. In this study, we evaluated the analgesic effects of ulinastatin administered either as a single agent or in combination with sufentanil in a validated preclinical rat model of postoperative pain induced by plantar incision. We found that incisional surgery on the hind paw of these rats induced sustained ipsilateral mechanical pain hypersensitivity that lasted for at least 10 days. A single intraperitoneal (i.p.) injection of ulinastatin prevented the development and reversed the maintenance of incision-induced mechanical pain hypersensitivity in a dose-dependent manner. However, ulinastatin had no effect on the baseline nociceptive threshold. Moreover, repeated i.p. injections of ulinastatin persistently attenuated incision-induced mechanical pain hypersensitivity and promoted recovery from the surgery. The rats did not develop any analgesic tolerance over the course of repeated injections of ulinastatin. A single i.p. injection of ulinastatin was also sufficient to inhibit the initiation and maintenance of incision-induced hyperalgesic priming when the rats were subsequently challenged with an ipsilateral intraplantar prostaglandin E2 injection. Furthermore, the combined administration of ulinastatin and sufentanil significantly enhanced the analgesic effect of sufentanil on postoperative pain, which involved mechanisms other than a direct influence on opioid receptors. These findings demonstrated that ulinastatin had a significant analgesic effect on postoperative pain and might be a novel pharmacotherapeutic agent for managing postoperative pain either alone or as an adjuvant.

Development of selective protease inhibitors via engineering of the bait region of human α2-macroglobulin

Human α2-macroglobulin (A2M) is an abundant protease inhibitor in plasma, which regulates many proteolytic processes and is involved in innate immunity. A2M’s unique protease-trapping mechanism of inhibition is initiated when a protease cleaves within the exposed and highly susceptible “bait region.” As the wild-type bait region is permissive to cleavage by most human proteases, A2M is accordingly a broad-spectrum protease inhibitor. In this study, we extensively modified the bait region in order to identify any potential functionally important elements in the bait region sequence and to engineer A2M proteins with restrictive bait regions, which more selectively inhibit a target protease. A2M in which the bait region was entirely replaced by glycine-serine repeats remained fully functional and was not cleaved by any tested protease. Therefore, this bait region was designated as the “tabula rasa” bait region and used as the starting point for further bait region engineering. Cleavage of the tabula rasa bait region by specific proteases was conveyed by the insertion of appropriate substrate sequences, e.g., basic residues for trypsin. Screening and optimization of tabula rasa bait regions incorporating matrix metalloprotease 2 (MMP2) substrate sequences produced an A2M that was specifically cleaved by MMPs and inhibited MMP2 cleavage activity as efficiently as wild-type A2M. We propose that this approach can be used to develop A2M-based protease inhibitors, which selectively inhibit target proteases, which might be applied toward the clinical inhibition of dysregulated proteolysis as occurs in arthritis and many types of cancer.

Ulinastatin Exhibits Antinociception in Rat Models of Acute Somatic and Visceral Pain Through Inhibiting the Local and Central Inflammation.

IntroductionUlinastatin, a broad-spectrum serine protease inhibitor, has been widely used to treat various diseases clinically. However, so far, the antinociceptive effect of ulinastatin remains less studied experimentally and the underlying mechanisms of ulinastatin for pain relief remain unclear. This study aimed to find evidence of the analgesic effect of ulinastatin on acute somatic and visceral pain.MethodsThe analgesic effect of ulinastatin on acute somatic and visceral pain was evaluated by using formalin and acetic acid-induced writhing test. The analgesic mechanism of ulinastatin was verified by detecting the peripheral inflammatory cell infiltration and spinal glial activation with hematoxylin-eosin (H&E) and immunohistochemistry staining.ResultsWe found that both of intraperitoneal (i.p.) pre-administration and post-administration of ulinastatin could reduce the total number of flinching and the licking duration following intraplantar formalin injection in a dose-related manner. However, the inhibitory effect of ulinastatin existed only in the second phase (Phase 2) of formalin-induced spontaneous pain response, with no effect in the first phase (Phase 1). The formalin-induced edema and ulcer were also improved by i.p. administration of ulinastatin. Moreover, i.p. administration of ulinastatin was also able to delay the occurrence of acetic acid-induced writhing and reduced the total number of writhes dose-dependently. We further demonstrated that ulinastatin significantly decreased the local inflammatory cell infiltration in injured paw and peritoneum tissue under formalin and acetic acid test separately. The microglial and astrocytic activation in the spinal dorsal horn induced by intraplantar formalin and i.p. acetic acid injection were also dramatically inhibited by i.p. administration of ulinastatin.ConclusionOur results for the first time provided a new line of evidence showing that ulinastatin could attenuate acute somatic and visceral pain by inhibiting the peripheral and spinal inflammatory reaction.