Inhibition of Human Kallikrein 5 Protease by Triterpenoids from Natural Sources

The host protease KLK5 primes and activates spike proteins to promote human betacoronavirus replication and lung inflammation

Coronaviruses rely on host proteases to activate the viral spike protein, which facilitates fusion with the host cell membrane and the release of viral genomic RNAs into the host cell cytoplasm. The distribution of specific host proteases in the host determines the host, tissue, and cellular tropism of these viruses. Here, we identified the kallikrein (KLK) family member KLK5 as a major host protease secreted by human airway cells and exploited by multiple human betacoronaviruses. KLK5 cleaved both the priming (S1/S2) and activation (S2') sites of spike proteins from various human betacoronaviruses in vitro. In contrast, KLK12 and KLK13 displayed preferences for either the S2' or S1/S2 site, respectively. Whereas KLK12 and KLK13 worked in concert to activate SARS-CoV-2 and MERS-CoV spike proteins, KLK5 by itself efficiently activated spike proteins from several human betacoronaviruses, including SARS-CoV-2. Infection of differentiated human bronchial epithelial cells (HBECs) with human betacoronaviruses induced an increase in KLK5 that promoted virus replication. Furthermore, ursolic acid and other related plant-derived triterpenoids that inhibit KLK5 effectively suppressed the replication of SARS-CoV, MERS-CoV, and SARS-CoV-2 in HBECs and mitigated lung inflammation in mice infected with MERS-CoV or SARS-CoV-2. We propose that KLK5 is a pancoronavirus host factor and a promising therapeutic target for current and future coronavirus-induced diseases.

Ursolic acid ameliorates DNCB-induced atopic dermatitis-like symptoms in mice by regulating TLR4/NF-κB and Nrf2/HO-1 signaling pathways

BACKGROUND

Ursolic acid (UA) is a triterpenoid compound found in natural plants. It has been reported to have anti-inflammatory, antioxidant, and immunomodulatory properties. However, its role in atopic dermatitis (AD) is unknown. This study aimed to evaluate the therapeutic effect of UA in AD mice and explore the underlying mechanisms.

METHODS

Balb/c mice were treated with 2, 4-dinitrochlorobenzene (DNCB) to induce AD-like lesions. During modeling and medication administration, dermatitis scores and ear thickness were measured. Subsequently, histopathological changes, levels of T helper cytokines, and oxidative stress markers levels were evaluated. Immunohistochemistry staining was used to assess changes in the expression of the nuclear factor of kappa B (NF-κB) and NF erythroid 2-related factor 2 (Nrf2). Furthermore, CCK8 assay, reactive oxygen species (ROS) assay, real-time PCR, and western blotting were employed to evaluate the effects of UA on ROS levels, inflammatory mediator production, and the NF-κB and Nrf2 pathways in TNF-α/IFN-γ-stimulated HaCaT cells.

RESULTS

The results showed that UA significantly reduced dermatitis score and ear thickness, effectively inhibited skin proliferation and mast cell infiltration in AD mice, and decreased the expression level of T helper cytokines. Meanwhile, UA improved oxidative stress in AD mice by regulating lipid peroxidation and increasing the activity of antioxidant enzymes. In addition, UA inhibited ROS accumulation and chemokine secretion in TNF-α/IFN-γ-stimulated HaCaT cells. It might exert anti-dermatitis effects by inhibiting the TLR4/NF-κB pathway and activating the Nrf2/HO-1 pathway.

CONCLUSION

Taken together, our results suggest that UA may have potential therapeutic effects on AD and could be further studied as a promising drug for AD treatment.

Involvement of kallikrein-PAR2-proinflammatory pathway in severe trastuzumab-induced cardiotoxicity

Trastuzumab‐induced cardiotoxicity interferes with continued treatment in approximately 10% of patients with ErbB2‐positive breast cancer, but its mechanism has not been fully elucidated. In this study, we recruited trastuzumab‐treated patients with ≥30% reduction in left ventricular ejection fraction (SP) and noncardiotoxic patients (NP). From each of these patients, we established three cases of induced pluripotent stem cell‐derived cardiomyocytes (pt‐iPSC‐CMs). Reduced contraction and relaxation velocities following trastuzumab treatment were more evident in SP pt‐iPSC‐CMs than NP pt‐iPSC‐CMs, indicating the cardiotoxicity phenotype could be replicated. Differences in ATP production, reactive oxygen species, and autophagy activity were observed between the two groups. Analysis of transcripts revealed enhanced kallikrein5 expression and pro‐inflammatory signaling pathways, such as interleukin‐1β, in SP pt‐iPSC‐CMs after trastuzumab treatment. The kallilkrein5‐protease‐activated receptor 2 (PAR2)‐MAPK signaling pathway was more activated in SP pt‐iPSC‐CMs, and treatment with a PAR2‐antagonist suppressed interleukin‐1β expression. Our data indicate enhanced pro‐inflammatory responses through kallikrein5‐PAR2 signaling and vulnerability to external stresses appear to be the cause of trastuzumab‐induced cardiotoxicity in SP.

Pharmacological profiles and therapeutic applications of pachymic acid (Review)

Poria cocos is a saprophytic fungus that grows in diverse species of Pinus. Its sclerotium, called fu-ling or hoelen, has been used in various traditional Chinese medicines and health foods for thousands of years, and in several modern proprietary traditional Chinese medicinal products. It has extensive clinical indications, including sedative, diuretic, and tonic effects. Pachymic acid (PA) is the main lanostane-type triterpenoid in Poria cocos. Evidence suggests that PA has various biological properties such as cytotoxic, anti-inflammatory, antihyperglycemic, antiviral, antibacterial, sedative-hypnotic, and anti-ischemia/reperfusion activities. Although considerable advancements have been made, some fundamental and intricate issues remain unclear, such as the underlying mechanisms of PA. The present study aimed to summarize the biological properties and therapeutic potential of PA. The biosynthetic, pharmacokinetic, and metabolic pathways of PA, and its underlying mechanisms were also comprehensively summarized.

Human Tissue Kallikreins-Related Peptidases Are Targets for the Treatment of Skin Desquamation Diseases

Human tissue Kallikrein-related peptidases (hKLKs) are serine proteases distributed in several tissues that are involved in several biological processes. In skin, many are responsible for skin desquamation in the Stratum Corneum (SC) of the epidermis, specially hKLK5, hKLK7, hKLK6, hKLK8, and hKLK14. In SC, hKLKs cleave proteins of corneodesmosomes, an important structure responsible to maintain corneocytes attached. As part of skin desquamation, hKLKs are also involved in skin diseases with abnormal desquamation and inflammation, such as Atopic Dermatitis (AD), psoriasis, and the rare disease Netherton Syndrome (NS). Many studies point to hKLK overexpression or overactive in skin diseases, and they are also part of the natural skin inflammation process, through the PAR2 cleavage pathway. Therefore, the control of hKLK activity may offer successful treatments for skin diseases, improving the quality of life in patients. Diseases like AD, Psoriasis, and NS have an impact on social life, causing pain, itchy and mental disorders. In this review, we address the molecular mechanisms of skin desquamation, emphasizing the roles of human tissue Kallikrein-related peptidases, and the promising therapies targeting the inhibition of hKLKs.

Synergistic Growth Inhibitory Effects of Eryngium kotschyi Extracts with Conventional Cytotoxic Agents: Cisplatin and Doxorubicin Against Human Endometrium Cancer Cells

BACKGROUND

Endometrial cancer is one of the most common types of cancer. For this reason, various studies have been carried out on its treatment and the effects of natural products on this disease.

OBJECTIVE

This study aimed to examine the growth inhibitory effects of Eryngium kotschyi Boiss. ethyl acetate [EKE] and butanol [EKB] obtained from the main methanol [EKM] extract from the aerial parts on human endometrium carcinoma [RL95-2] cells and their synergistic effect with cisplatin or doxorubicin.

METHODS

RL95-2 cells were treated with E. kotschyi extracts either alone or in combination with cisplatin or doxorubicin. The effects on cell growth were determined using the MTT assay and real-time cell analysis xCELLigence.

RESULTS

The extracts demonstrated growth inhibitory activity, with a certain degree of selectivity against the RL95-2 cell line. Synergistic effects of EKE/cisplatin or doxorubicin at different concentration levels were demonstrated in RL95-2 cells. In some instances, the EKE/doxorubicin combinations resulted in antagonistic effects. The reduction level of cell viability was different and specific to each combination for the RL95-2 cell line.

CONCLUSION

The growth inhibitory activity of cisplatin or doxorubicin, as a single agent, may be modified by combinations of the extracts and be synergistically enhanced in some cases. A significant synergistic effect of EKE on the RL95-2 cell line with cisplatin and doxorubicin was observed. This cytotoxic effect can be investigated in terms of molecular mechanisms. This study is the first of its kind in the literature. The mechanisms involved in this interaction between chemotherapeutic drugs and plant extracts remain unclear and should be further evaluated.

Sodium Bituminosulfonate Used to Treat Rosacea Modulates Generation of Inflammatory Mediators by Primary Human Neutrophils

Background

Sodium bituminosulfonate is derived from naturally occurring sulphur-rich oil shale and is used for the treatment of the inflammatory skin disease rosacea. Major molecular players in the development of rosacea include the release of enzymes that process antimicrobial peptides which, together with reactive oxygen species (ROS) and vascular endothelial growth factor (VEGF), promote pro-inflammatory processes and angiogenesis. The aim of this study was to address the molecular mechanism(s) underlying the therapeutic benefit of the formulation sodium bituminosulfonate dry substance (SBDS), which is indicated for the treatment of skin inflammation, including rosacea.

Methods

We investigated whether SBDS regulates the expression of cytokines, the release of the antimicrobial peptide LL-37, calcium mobilization, proteases (matrix metalloproteinase, elastase, kallikrein (KLK)5), VEGF or ROS in primary human neutrophils. In addition, activity assays with 5-lipoxygenase (5-LO) and recombinant human MMP9 and KLK5 were performed.

Results

We observed that SBDS reduces the release of the antimicrobial peptide LL-37, calcium, elastase, ROS and VEGF from neutrophils. Moreover, KLK5, the enzyme that converts cathelicidin to LL-37, and 5-LO that produces leukotriene (LT)A₄, the precursor of LTB₄, were both inhibited by SBDS with an IC₅₀ of 7.6 µg/mL and 33 µg/mL, respectively.

Conclusion

Since LTB₄ induces LL-37 which, in turn, promotes increased intracellular calcium levels and thereby, ROS/VEGF/elastase release, SBDS possibly regulates the LTB₄/LL-37/calcium – ROS/VEGF/elastase axis by inhibiting 5-LO and KLK5. Additional direct effects on other pro-inflammatory pathways such as ROS generation cannot be ruled out. In summary, SBDS reduces the generation of inflammatory mediators from human neutrophils possibly accounting for its anti-inflammatory effects in rosacea.

Redirecting drug repositioning to discover innovative cosmeceuticals

Skin appearance is essential for self-esteem and quality of life; consequently, skin care products represent a huge market. In particular, cosmeceuticals constitute a hybrid category of skin care formulations, at the interphase of cosmetics and pharmaceuticals, rationally designed to target (patho) physiological mechanisms aiming to enhance skin health and appearance. Cosmeceuticals are marketed as anti-ageing, anti-wrinkle, hair regrowth, skin whitening and wound healing agents with special emphasis on scar-free healing. An overview on recent cutting-edge advances concerning the discovery and development of enhanced performance cosmeceuticals by drug repositioning approaches is presented here. In this context, we propose "target repositioning," a new term, to highlight that druggable protein targets implicated in multiple diseases (hubs in the diseasome) can be exploited to accelerate the discovery of molecularly targeted cosmeceuticals that can promote skin health as an added benefit, which is a novel concept not described before. In this direction, emphasis is placed on the role of mouse models, for often untreatable skin diseases, as well as recent breakthroughs on monogenic rare skin syndromes, in promoting compound repositioning to innovative cosmeceuticals.

Coptis chinensis Franch Directly Inhibits Proteolytic Activation of Kallikrein 5 and Cathelicidin Associated with Rosacea in Epidermal Keratinocytes

Rosacea is a common and chronic inflammatory skin disease that is characterized by dysfunction of the immune and vascular system. The excessive production and activation of kallikerin 5 (KLK5) and cathelicidin have been implicated in the pathogenesis of rosacea. Coptis chinensis Franch (CC) has been used as a medicinal herb in traditional oriental medicine. However, little is known about the efficacy and mechanism of action of CC in rosacea. In this study, we evaluate the effect of CC and its molecular mechanism on rosacea in human epidermal keratinocytes. CC has the capacity to downregulate the expression of KLK5 and cathelicidin, and also inhibits KLK5 protease activity, which leads to reduced processing of inactive cathelicidin into active LL-37. It was determined that CC ameliorates the expression of pro-inflammatory cytokines through the inhibition of LL-37 processing. In addition, it was confirmed that chitin, an exoskeleton of Demodex mites, mediates an immune response through TLR2 activation, and CC inhibits TLR2 expression and downstream signal transduction. Furthermore, CC was shown to inhibit the proliferation of human microvascular endothelial cells induced by LL-37, the cause of erythematous rosacea. These results demonstrate that CC improved rosacea by regulating the immune response and angiogenesis, and revealed its mechanism of action, indicating that CC may be a useful therapeutic agent for rosacea.

Screening of chemical libraries in pursuit of kallikrein-5 specific inhibitors for the treatment of inflammatory dermatoses

Background Aberrant kallikrein activity is observed in a number of inflammatory dermatoses. Up-regulation of kallikrein-5 (KLK5) activity leads to uncontrolled skin desquamation and cleavage of proteinase-activated receptor-2 (PAR2), causing the release of pro-inflammatory cytokines and disruption of epidermal barrier function. This study aimed to identify KLK5-specific small molecule inhibitors which can serve as the foundation of a novel therapeutic for inflammatory skin disorders. Methods Five chemical libraries (13,569 compounds total) were screened against recombinant KLK5 using a fluorogenic enzymatic assay. Secondary validation was performed on the top 22 primary hits. All hits were docked in the KLK5 crystal structure to rationalize their potential interactions with the protein. Results A naturally occurring compound derived from the wood of Caesalpinia sappan (Brazilin) was identified as a novel KLK5 inhibitor (IC50: 20 μM, Ki: 6.4 μM). Docking suggests that the phenolic moiety of Brazilin binds in the S1-pocket of KLK5 and forms a H-bond with S195 side chain. KLK14 was also found to be susceptible to inhibition by Brazilin with a calculated IC50 value of 14.6 μM. Conclusions Natural KLK5 small molecule inhibitors such as Brazilin, are ideal for topical skin disease drug design and remain a promising therapeutic for severe cases of inflammatory skin disorders. Optimized KLK inhibitors may have increased efficacy as therapeutics and warrant further investigation.

The role of kallikreins in inflammatory skin disorders and their potential as therapeutic targets

The skin is a vital organ of the human body, serving numerous protective and functional roles that are essential for survival. Residing in the epidermis are various epidermal proteases responsible for the establishment and regulation of barrier function. The human tissue kallikrein-related peptidase family conserves homeostasis of the skin barrier through their roles in desquamation, antimicrobial defense, innate immune response, and barrier maintenance. The activity of kallikreins is tightly regulated and dysregulation of kallikrein activity is seen to contribute to the formation of several inflammatory skin disorders. This review highlights the roles of kallikreins in skin homeostasis and pathologies. Due to their part in these skin disorders, inhibitors of the skin kallikreins have become attractive therapeutics. Over the past few years, both natural and synthetic inhibitors of several kallikreins have been identified and are undergoing further development as treatments to restore compromised barrier function. This review summarizes the kallikrein inhibitors under development for this purpose. These inhibitors remain promising therapeutics in cases of severe skin inflammation not well managed by current therapies.

Inhibitory Effects of Indole-3-Acetonitrile-4-Methoxy-2-S-Β-d-Glucopyranoside From Nasturtium officinale R. Br on Human Kallikrein 5 and 7 Protease

The stratum corneum tryptic enzyme kallikrein 5 (KLK5) is a serine protease that is involved in the cell renewal and maintenance of the skin barrier functions. The excessive activation of KLK5 causes an exacerbation of dermatoses, such as rosacea and atopic dermatitis. Nasturtium officinale R. Br. (Brassicaceae) is a hardy perennial plant native to Europe and commonly called “Watercress” or “Cresson,” which is one of the brassica vegetables. We aimed to investigate whether the bioactive sulfur-containing compound inhibits the KLK5 protease. The sulfur-containing compounds were evaluated using an enzymatic assay to measure the anti-KLK5 activity. Our study revealed that the sulfur-containing compound inhibits the KLK5 and 7 protease activity. Indole-3-acetonitrile-4-methoxy-2-S-β-d-glucopyranoside may affect the skin barrier and atopic function via the regulation of proteases.

Exonic mutations associated with atopic dermatitis disrupt lympho-epithelial Kazal-type related inhibitor action and enhance its degradation

BACKGROUND

Skin desquamation is facilitated by serine proteases KLK5 and KLK7, which are tightly regulated by lympho-epithelial Kazal-type related inhibitor (LEKTI). LEKTI itself is controlled through degraded by mesotrypsin. Here, we sought to determine whether LEKTI exonic mutations associated with atopic dermatitis (AD) affect the protease inhibitory activity of LEKTI or its susceptibility to mesotrypsin degradation.

METHODS

The inhibitory activities of the LEKTI domain 4 (D4) and D6 WT and AD-associated mutants on the enzyme activities of KLK5 and KLK7 were compared using fluorogenic substrates. A keratinocyte cell culture system using HaCat cells was established to assess the role of D6 WT and D386N on triggering inflammation via the induction of thymic stromal lymphopoietin (TSLP). A degradation assay was used to assess the susceptibility of D4 and D6 mutants to mesotrypsin degradation.

RESULTS

Enzymatic assays revealed that the D6 D386N mutation affected the inhibitory activity of LEKTI on KLK5 but not KLK7. Other exonic mutations on D6 (N368S, V395M, and E420K) and D4 (R267Q) did not alter LEKTI inhibition. The D386N mutation disrupted the role of D6 in suppressing TSLP induction by KLK5 in HaCat cells. Although WT D4 is more susceptible to mesotrypsin degradation than WT D6, the D4 R267Q mutant was more resistant to mesotrypsin degradation, whereas the D6 E420K mutant showed enhanced mesotrypsin-mediated degradation.

CONCLUSION

Exonic mutations in D6, which previously have been associated with AD, may cause a disruption of inhibitory activity on KLK5 or enhance the degradation by mesotrypsin.

Evaluation of a crystallographic surrogate for kallikrein 5 in the discovery of novel inhibitors for Netherton syndrome

The inhibition of kallikrein 5 (KLK5) has been identified as a potential strategy for treatment of the genetic skin disorder Netherton syndrome, in which loss-of-function mutations in the SPINK5 gene lead to down-regulation of the endogenous inhibitor LEKTI-1 and profound skin-barrier defects with severe allergic manifestations. To aid in the development of a medicine for this target, an X-ray crystallographic system was developed to facilitate fragment-guided chemistry and knowledge-based drug-discovery approaches. Here, the development of a surrogate crystallographic system in place of KLK5, which proved to be challenging to crystallize, is described. The biochemical robustness of the crystallographic surrogate and the suitability of the system for the study of small nonpeptidic fragments and lead-like molecules are demonstrated.