Flavonoid-Quinoxaline Hybrid Compounds as Cathepsin Inhibitors Against Fascioliasis.

Fasciola hepatica is a parasitic trematode that infects livestock animals and humans, causing significant health and economic burdens worldwide. The extensive use of anthelmintic drugs has led to the emergence of resistant parasite strains, posing a threat to treatment success. The complex life cycle of the liver fluke, coupled with limited funding and research interest, have hindered progress in drug discovery. Our group has been working in drug development against this parasite using cathepsin proteases as molecular targets, finding promising compound candidates with in vitro and in vivo efficacy. Here, we evaluated hybrid molecules that combine two chemotypes, chalcones and quinoxaline 1,4-di- N-oxides, previously found to inhibit F. hepatica cathepsin Ls and tested their in vitro activity with the isolated targets and the parasites in culture. These molecules proved to be good cathepsin inhibitors and to kill the juvenile parasites at micromolar concentrations. Also, we performed molecular docking studies to analyze the compounds-cathepsins interface, finding that the best inhibitors interact at the active site cleft and contact the catalytic dyad and residues belonging to the substrate binding pockets. We conclude that the hybrid compounds constitute promising scaffolds for the further development of new fasciolicidal compounds.

Specific photodamage on HT-29 cancer cells leads to endolysosomal failure and autophagy blockage by cathepsin depletion.

Endolysosomes perform a wide range of cellular functions, including nutrient sensing, macromolecule digestion and recycling, as well as plasma membrane repair. Because of their high activity in cancerous cells, endolysosomes are attractive targets for the development of novel cancer treatments. Light-activated compounds termed photosensitizers (PS) can catalyze the oxidation of specific biomolecules and intracellular organelles. To selectively damage endosomes and lysosomes, HT-29 colorectal cancer cells were incubated with nanomolar concentrations of meso-tetraphenylporphine disulfonate (TPPS2a), an amphiphilic PS taken up via endocytosis and activated by green light (522 nm, 2.1 J.cm-1). Several cellular responses were characterized by a combination of immunofluorescence and immunoblotting assays. We showed that TPPS2a photosensitization blocked autophagic flux without extensive endolysosomal membrane rupture. Nevertheless, there was a severe functional failure of endolysosomes due to a decrease in CTSD (cathepsin D, 55%) and CTSB (cathepsin B, 52%) maturation. PSAP (prosaposin) processing (into saposins) was also considerably impaired, a fact that could be detrimental to glycosphingolipid homeostasis. Therefore, photosensitization of HT-29 cells previously incubated with a low concentration of TPPS2a promotes endolysosomal dysfunction, an effect that can be used to improve cancer therapies.

NAIP/NLRC4 inflammasome participates in macrophage responses to Trypanosoma cruzi by a mechanism that relies on cathepsin-dependent caspase-1 cleavage.

Inflammasomes are large protein complexes that, once activated, initiate inflammatory responses by activating the caspase-1 protease. They play pivotal roles in host defense against pathogens. The well-established role of NAIP/NLRC4 inflammasome in bacterial infections involves NAIP proteins functioning as sensors for their ligands. However, recent reports have indicated the involvement of NLRC4 in non-bacterial infections and sterile inflammation, even though the role of NAIP proteins and the exact molecular mechanisms underlying inflammasome activation in these contexts remain to be elucidated. In this study, we investigated the activation of the NAIP/NLRC4 inflammasome in response to Trypanosoma cruzi, the protozoan parasite responsible for causing Chagas disease. This parasite has been previously demonstrated to activate NLRP3 inflammasomes. Here we found that NAIP and NLRC4 proteins are also required for IL-1ß and Nitric Oxide (NO) release in response to T. cruzi infection, with their absence rendering macrophages permissive to parasite replication. Moreover, Nlrc4 -/- and Nlrp3 -/- macrophages presented similar impaired responses to T. cruzi, underscoring the non-redundant roles played by these inflammasomes during infection. Notably, it was the live trypomastigotes rather than soluble antigens or extracellular vesicles (EVs) secreted by them, that activated inflammasomes in a cathepsins-dependent manner. The inhibition of cathepsins effectively abrogated caspase-1 cleavage, IL-1ß and NO release, mirroring the phenotype observed in Nlrc4 -/-/Nlrp3 -/- double knockout macrophages. Collectively, our findings shed light on the pivotal role of the NAIP/NLRC4 inflammasome in macrophage responses to T. cruzi infection, providing new insights into its broader functions that extend beyond bacterial infections.

In vitro and in vivo studies on a group of chalcones find promising results as potential drugs against fascioliasis.

About a third of the world population is infected by helminth parasites implicated in foodborne trematodiasis. Fascioliasis is a worldwide disease caused by trematodes of the genus Fasciola spp. It generates huge economic losses to the agri-food industry and is currently considered an emerging zoonosis by the World Health Organization (WHO). The only available treatment relies on anthelmintic drugs, being triclabendazole (TCBZ) the drug of choice to control human infections. The emergence of TCBZ resistance in several countries and the lack of an effective vaccine to prevent infection highlights the need to develop new drugs to control this parasitosis. We have previously identified a group of benzochalcones as inhibitors of cathepsins, which have fasciolicidal activity in vitro and are potential new drugs for the control of fascioliasis. We selected the four most active compounds of this group to perform further preclinical studies. The compound's stability was determined against a liver microsomal enzyme fraction, obtaining half-lives of 34-169 min and low intrinsic clearance values (<13 µL/min/mg), as desirable for potential new drugs. None of the compounds were mutagenic or genotoxic and no in vitro cytotoxic effects were seen. Compounds C31 and C34 showed the highest selectivity index against liver fluke cathepsins when compared to human cathepsin L. They were selected for in vivo efficacy studies observing a protective effect, similar to TCBZ, in a mouse model of infection. Our findings strongly encourage us to continue the drug development pipeline for these molecules.

Lysosomal cathepsins act in concert with Gasdermin-D during NAIP/NLRC4-dependent IL-1ß secretion.

The NAIP/NLRC4 inflammasome is classically associated with the detection of bacterial invasion to the cytosol. However, recent studies have demonstrated that NAIP/NLRC4 is also activated in non-bacterial infections, and in sterile inflammation. Moreover, in addition to the well-established model for the detection of bacterial proteins by NAIP proteins, the participation of other cytosolic pathways in the regulation of NAIP/NLRC4-mediated responses has been reported in distinct contexts. Using pharmacological inhibition and genetic deletion, we demonstrate here that cathepsins, well known for their involvement in NLRP3 activation, also regulate NAIP/NLRC4 responses to cytosolic flagellin in murine and human macrophages. In contrast to that observed for NLRP3 agonists, cathepsins inhibition did not reduce ASC speck formation or caspase-1 maturation in response to flagellin, ruling out their participation in the effector phase of NAIP/NLRC4 activation. Moreover, cathepsins had no impact on NF-κB-mediated priming of pro-IL-1ß, thus suggesting these proteases act downstream of the NAIP/NLRC4 inflammasome activation. IL-1ß levels secreted in response to flagellin were reduced in the absence of either cathepsins or Gasdermin-D (GSDMD), a molecule involved in the induction of pyroptosis and cytokines release. Notably, IL-1ß secretion was abrogated in the absence of both GSDMD and cathepsins, demonstrating their non-redundant roles for the optimal IL-1ß release in response to cytosolic flagellin. Given the central role of NAIP/NLRC4 inflammasomes in controlling infection and, also, induction of inflammatory pathologies, many efforts have been made to uncover novel molecules involved in their regulation. Thus, our findings bring together a relevant contribution by describing the role of cathepsins as players in the NAIP/NLRC4-mediated responses.

Enzymes in the time of COVID-19: An overview about the effects in the human body, enzyme market, and perspectives for new drugs.

The rising pandemic caused by a coronavirus, resulted in a scientific quest to discover some effective treatments against its etiologic agent, the severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2). This research represented a significant scientific landmark and resulted in many medical advances. However, efforts to understand the viral mechanism of action and how the human body machinery is subverted during the infection are still ongoing. Herein, we contributed to this field with this compilation of the roles of both viral and human enzymes in the context of SARS-CoV-2 infection. In this sense, this overview reports that proteases are vital for the infection to take place: from SARS-CoV-2 perspective, the main protease (Mpro ) and papain-like protease (PLpro ) are highlighted; from the human body, angiotensin-converting enzyme-2, transmembrane serine protease-2, and cathepsins (CatB/L) are pointed out. In addition, the influence of the virus on other enzymes is reported as the JAK/STAT pathway and the levels of lipase, enzymes from the cholesterol metabolism pathway, amylase, aspartate aminotransferase, alanine aminotransferase, lactate dehydrogenase, and glyceraldehyde 3-phosphate dehydrogenase are also be disturbed in SARS-CoV-2 infection. Finally, this paper discusses the importance of detailed enzymatic studies for future treatments against SARS-CoV-2, and how some issues related to the syndrome treatment can create opportunities in the biotechnological market of enzymes and the development of new drugs.

Analysis of cathepsin S expression in gastric adenocarcinoma and in Helicobacter pylori infection.

BACKGROUND: Recent experimental studies have suggested a potential link between cathepsin S (CTTS) and gastric adenocarcinoma progression. Herein, we aimed to evaluate the expression of CTTS in gastric adenocarcinoma in patients who underwent curative-intent surgical resection. METHODS: This was a cross-sectional study that included two groups: gastric adenocarcinoma (n = 42) and gastritis (n = 50). The gastritis group was then subdivided into H. pylori-positive (n = 25) and H. pylori-negative (n = 25) groups. Gastric tissue samples were analysed to determine CTTS expression through immunohistochemistry. Samples were obtained by oesophagogastroduodenoscopy or surgical specimens. RESULTS: In patients with gastritis, the age ranged from 18 to 78 years. Among them, 34% were male, and 66% were female. In patients with gastric adenocarcinoma, the age ranged from 37 to 85 years. Among them, 50% were male. When comparing the expression of CTTS between the two groups, only 16% of the gastritis samples had an expression higher than 25%. Alternatively, among patients with gastric adenocarcinoma, 19% had expression between 25-50%, 14.3% between 51-75%, and 26.2% had expression higher than 75% (p < 0.001). In the gastritis group, CTTS expression was significantly higher in patients with a positive test for H. pylori than negative test for H. pylori: 87.5% and 38.5%, respectively (p<0.001). There was no statistically significant association between CTTS positivity and clinicopathological variables, including tumour staging, histological type, angiolymphatic invasion, recurrence, current status and death. CONCLUSION: CTTS expression is higher in gastric adenocarcinoma samples. Patients with gastritis due to H. pylori also show a higher expression of CTTS than patients with negative results for this bacterium.

P2X7 Receptor Triggers Lysosomal Leakage Through Calcium Mobilization in a Mechanism Dependent on Pannexin-1 Hemichannels.

The P2X7 receptor is a critical purinergic receptor in immune cells. Its activation was associated with cathepsin release into macrophage cytosol, suggesting its involvement in lysosomal membrane permeabilization (LMP) and leakage. Nevertheless, the mechanisms by which P2X7 receptor activation induces LMP and leakage are unclear. This study investigated cellular mechanisms associated with endosomal and lysosomal leakage triggered by P2X7 receptor activation. We found that ATP at 500 µM and 5 mM (but not 50 µM) induced LMP in non-stimulated peritoneal macrophages. This effect was not observed in P2X7-deficient or A740003-pretreated macrophages. We found that the P2X7 receptor and pannexin-1 channels mediate calcium influx that might be important for activating specific ion channels (TRPM2 and two-pore channels) on the membranes of late endosomes and lysosomes leading to LMP leakage and consequent cathepsin release. These findings suggest the critical role of the P2X7 receptor in inflammatory and infectious diseases via lysosomal dysfunction.

Association of Retromer Deficiency and Tau Pathology in Down Syndrome.

Retromer deficiency is reported in Down syndrome and correlates with amyloidosis, however, its association with tau neuropathology remains unclear. Down syndrome and control brain tissues were evaluated for phosphorylated tau, tau modulators, and cathepsin-D activity. Several kinases and phosphatase PP2A were unchanged, but tau phosphorylation was elevated, and cathepsin-D activity decreased in aged patients with Down syndrome. Retromer proteins positively associated with soluble tau, whereas pathogenic tau negatively correlated with retromer proteins and cathepsin-D activity. Retromer deficiency and consequent reduction of cathepsin-D activity may contribute to pathogenic tau accumulation, thus, retromer represents a viable therapeutic target against tau pathology in Down syndrome. ANN NEUROL 2022;91:561-567.

Cathepsin S as an early biomarker for cardiovascular disease in chronic kidney disease patients.

INTRODUCTION: A high incidence of cardiovascular disease (CVD) events and premature mortality is observed in patients with chronic kidney disease (CKD). Thus, new biomarkers that may help predict the development of CVD in early stages of CKD are being investigated along with other traditional risk factors. OBJECTIVE: To investigate cathepsin S as an early biomarker for CVD in patients with CKD. METHODS: A total of 64 patients with CKD were included and classified into 2 groups: CKD patients with established CVD and CKD patients with non-established CVD. All patients were submitted to routine investigations including complete blood count, random blood sugar, glycated hemoglobin (HbA1c), serum electrolytes, urea, creatinine, total protein, total albumin, calcium total, phosphorous, uric acid, vitamin D, parathormone, lipid profile, liver function test, measurement of serum cathepsin S (Cat S), and 2D Echo of the heart. RESULTS: The level of serum Cat S was increased in CKD patients with CVD (p <0.05) as well as in later stages of CKD (p <0.05). CVD was also more common in patients in early stage CKD. In early stages CKD, Cat S and CVD were positively correlated. CONCLUSION: These findings suggest that serum Cat S might be useful as an early biomarker for CVD in CKD patients.

Recruitment of lysosomal cathepsins B, L and D as digestive enzymes in Coleoptera.

The recruitment of the lysosomal cathepsins B (CAB), L (CAL) and D (CAD) as luminal digestive enzymes was investigated in 3 species of beetles. Gene expression was determined by RNA-seq in different regions of the midgut and in the carcasses from the transcriptomes of Dermestes maculatus, Tenebrio molitor and Zabrotes subfasciatus. These data together with phylogenetic analyses, allowed us to identify the sequences of the gene coding for digestive and lysosomal CABs, CADs and CALs in T. molitor and Z. subfasciatus and observe the absence of digestive cathepsins in D. maculatus. Comparisons of structures based on the overall similarity of modelled structures were performed and subsite residues in the lysosomal and digestive CALs were identified by molecular docking. The data showed that S2 subsites are very variable, probably as an adaption to a luminal digestive role. The survey of sequences of the gene coding for cathepsins in the genomes of 13 beetle species from different phylogenetic groups showed that expansion of CAL and CAB genes occurred only in the Cucujiformia clade. Several digestive CABs have a reduced occluding loop, probably to act as digestive enzymes. Pollen-feeding was proposed to be the selective pressure to recruit cathepsins as digestive enzymes in Cucujiformia beetles.

Disclosing the involvement of proteases in an eczema murine animal model: Perspectives for protease inhibitor-based therapies.

Eczema is a skin condition characterized by itchy and inflammatory patches. The accumulation of neutrophils and the imbalance between enzymes and their inhibitors appears to be related to this condition. We proposed a neutrophil elastase (NE)-based eczema model in mice in order to verify histopathological features as well as the expression and activity of proteases and inhibitors. Mice skins were topically administered with human NE (0-2 pmol/cm2) for 24-168 h. It was observed thickening of epidermis, parakeratosis, spongiosis and leukocyte infiltration. Also, NE-treated skins presented high activity of epidermal kallikreins 5 and 7, and cathepsin B on synthetic substrates, and expression evaluated by RT-qPCR. The proteolytic activity was inhibited by soybean trypsin inhibitor, CA074 and Caesalpinia echinata kallikrein inhibitor (CeKI). The topic application of CeKI reversed eczema phenotype in NE-treated skins. Elafin expression was shown to be increased in NE-treated skins. These results suggest that the NE may trigger morphological and biochemical changes in skin similar to those observed in eczematous diseases. In addition to the establishment of this in vivo model, this work opens perspectives for the use of protease inhibitor-based drugs for the management of this skin condition.

Dano fotoinduzido no sistema endolisossomal: modulação da autofagia e metabolismo de lipídios em células de câncer colorretal / Endo-lysosomal system photodamage: modulation of autophagy and lipid metabolism in colorectal cancer cells

O câncer colorretal (CCR) é o terceiro câncer mais diagnosticado em humanos. O CCR causou mais de 900.000 mortes em 2020 e foi estimado, para o período entre 2020 - 2025, um incremento de 13.5 % no número de casos novos de acordo com a plataforma Web Global Cancer Observatory. A Terapia Fotodinâmica (PDT) é uma alternativa terapêutica promissora. Conhecer as vias de sinalização de morte celular, assim como, as respostas associadas com a resistência ao dano foto-oxidativo, são relevantes para incrementar a eficiência da PDT. Neste trabalho, investigamos como as células de adenocarcinoma colorretal HT 29 respondem ao dano fotoinduzido gerado pelo fotossensibilizador (FS) meso-tetrafenilporfirina dissulfônado (TPPS2a), uma molécula que é ativada pela irradiação com luz em 522 nm. Como esperado, após irradiação (2.1 J cm-2) foi verificado que com o incremento do TPPS2a houve diminuição da viabilidade celular. A concentração do FS escolhida para darmos seguimento ao estudo foi a necessária para reduzir em 30 % a sobrevida celular (DL30; 148 nM). Abordagens moleculares nos permitiram identificar que nas células fotossensibilizadas a redução na maturação da catepsina D (CTSD, 55 %) e da catepsina B (CTSB, 52 %) contribuem com a disfunção endolisossomal. Além disso, comprovamos que as células fotossensibilizadas tiveram, pela menor quantidade de CTSD ativa, o processamento da prosaposina (PSAP) significativamente afetado. Células coletadas após 24 horas de irradiação expressaram 7 vezes mais PSAP do que as amostras dos grupos controle, sugerindo que as reações de oxidação causadas pelo TPPS2a podem ocasionar o acúmulo de glicoesfingolipídios nos endossomos e nos lisossomos, mimetizando o fenótipo observado em doenças de armazenamento lisossomal. Imagens de células HT 29 com expressão estável da proteína LGALS3 fusionada ao marcador EFGP mostraram que, após 24 horas de irradiação, as células não ativaram a lisofagia para remover os endossomos e os lisossomos danificados. A ausência do recrutamento da LGALS3 também apontou que as membranas dos endossomos e dos lisossomos não apresentam rupturas permanentes que permitam a passagem de uma molécula de 26 kDa. Experimentos complementares de análise da expressão proteica dos marcadores autofágicos LC3-II e p62/SQSTM1 (referida como p62) confirmaram o bloqueio do fluxo autofágico nas células fotosenssibilizadas. Pelo envolvimento do sistema endolisossomal no tráfego de membranas e no fluxo de lipídios, o aumento da transcrição da Hidroximetilglutaril-CoA reductase (HMGCR) (≈ 1.6 vezes) uma enzima envolvida na síntese de novo do colesterol - sugeriu que a disfunção dos endossomos e dos lisossomos altera a distribuição de colesterol. Não obstante, para manter a homeostase lipídica nas células fotossensibilizadas este não foi o único mecanismocompensatório acionado, uma vez que houve um incremento sutil; porém, significativo (1.2 vezes) na transcrição da ceramidase ácida (ASAH1). Em conjunto, nossos dados apontam que a fotossensibilização com TPPS2a constitui uma ferramenta promissora para causar dano no sistema endolisossomal, inibindo a autofagia e permitindo o estudo das respostas metabólicas em células expostas a estresse oxidativo

Colorectal cancer (CRC) is the third most commonly diagnosed cancer in humans. CRC caused more than 900,000 deaths in 2020 and it was estimated for the period 2020 - 2025, an increase of 13.5 % in the number of new cases according to the Global Cancer Observatory Web platform. Photodynamic Therapy (PDT) is a promising therapeutic alternative. Understandings of cell death signaling pathways as well as the adaptive responses associated with resistance to photo-oxidative damage are relevant to optimize the effectiveness of PDT. For this purpose, in this research, we investigated how HT-29 colorectal adenocarcinoma cells respond to photosensitization reactions generated by TPPS2a, a molecule activated by irradiation with light at 522 nm. PS concentrations displayed increased inhibitory effect on cell viability after irradiation (2.1 J cm-2). The lethal dose selected to photosensibilize cells was the TPPS2a concentration able to reduce 30 % of cell survival (LD30; 148 nM). By molecular methods, we observed a reduction in cathepsin D (CTSD, 55 %) and cathepsin B (CTSB, 52 %) maturation, depletion that may contribute to endo-lysosomal dysfunction in photosensitized cells. It is widely known that endo-lysosomal cathepsins are crucial in protein turnover and degradation. Thus, we focused on the consequence of CTSD reduction. Literature data indicate that CTSD plays a key role in prosaposin (PSAP) processing to the four saposins (SAPs) that are required in glycosphingolipids breakdown. In fact, our results in photosensitized cells showed that, due to the lower amount of active CTSD, PSAP processing was significantly affected. Cells collected after irradiation expressed 7 times more PSAP than cells from the control groups. This data suggest that oxidative photodamage induced by TPPS2a may result in glycosphingolipid-accumulating endosomes and lysosomes, phenotype which mimics lysosomal storage diseases. Furthermore, we monitored by fluorescence microscopy a form of selective autophagy which detects and removes damaged endosomes and lysosomes known as lysophagy. Images of HT-29 cells expressing Galectin 3/LGALS3 fused to EFGP showed that photosensitized cells did not activate lysophagy. The absence of LGALS3 recruitment also indicated that the membranes of endosomes and lysosomes do not present ruptures which allow the passage of proteins with a molecular weight up to at least 26 kDa. Protein expression analysis of the autophagic markers LC3-II and p62/SQSTM1 (referred as p62) confirmed autophagic flux blockade in cells challenged with photoactivated TPPS2a. The endo-lysosomal system plays a key role in membrane trafficking and lipid flux. At the transcriptional level, 1.6-fold increase in gene expression of Hydroxymethylglutaryl-CoA reductase (HMGCR) - an enzyme involved in the synthesis de novo of cholesterol - indicated that endosomes and lysosomes dysfunction alters the distribution of cholesterol in cellschallenged with photoactivated TPPS2a. However, to maintain lipid homeostasis in photosensitized cells, this was not the only compensatory mechanism triggered, since there was a slightly increase (1.2-fold) in the transcription of acid ceramidase (ASAH1). Taken together, our data showed that photosensitization with TPPS2a constitutes a promising tool to damage the endolysosomal system, to inhibit autophagy and to study metabolic responses in cells exposed to oxidative stress

Lysosomal cathepsin creates chimeric epitopes for diabetogenic CD4 T cells via transpeptidation.

The identification of the peptide epitopes presented by major histocompatibility complex class II (MHCII) molecules that drive the CD4 T cell component of autoimmune diseases has presented a formidable challenge over several decades. In type 1 diabetes (T1D), recent insight into this problem has come from the realization that several of the important epitopes are not directly processed from a protein source, but rather pieced together by fusion of different peptide fragments of secretory granule proteins to create new chimeric epitopes. We have proposed that this fusion is performed by a reverse proteolysis reaction called transpeptidation, occurring during the catabolic turnover of pancreatic proteins when secretory granules fuse with lysosomes (crinophagy). Here, we demonstrate several highly antigenic chimeric epitopes for diabetogenic CD4 T cells that are produced by digestion of the appropriate inactive fragments of the granule proteins with the lysosomal protease cathepsin L (Cat-L). This pathway has implications for how self-tolerance can be broken peripherally in T1D and other autoimmune diseases.

Small molecules under development for psoriasis: on the road to the individualized therapies.

Psoriasis is an incurable cutaneous illness characterized by the presence of well-delimited reddish plaques and silvery-white dry scales. So far, there is a limited understanding of its pathogenesis, though recent discoveries on the immunological, genetic and molecular aspects of this disease have significantly contributed to the identification of new targets and the development of novel drugs. Despite these advances, many patients are still dissatisfied, so to improve patient satisfaction, reliability, and clinical outcomes, the individualization of the treatments for this disease becomes a necessity. This review summarizes recent findings related to psoriasis pathogenesis and describes new small molecules and targets recently identified as promising for treatments. Additionally, the current status, challenges and the future directions for achieving individualized therapy for this disease and the need for more collaborative studies are discussed. The individualization of treatments for psoriasis, rather than a goal, is analyzed as a process where a dynamic integration between the needs and characteristics of the patients, the pharmacological progress, and the clinical decisions takes place.

Recombinant expression, characterization and phylogenetic studies of novels cystatins-like proteins of sweet orange (Citrus sinensis) and clementine (Citrus clementina).

Phytocystatins are plant cystatins that are related to several physiological processes regulating endogenous cysteine proteases involved in seed development and germination, programmed cell death and response to stress conditions. In addition, phytocystatins can act in plant defense against exogenous peptidases from herbivorous insects, pathogens and nematodes. Considering that Citrus fruits are important to human nutrition and represent a high value crop in worldwide agriculture, in the present work, we performed the identification of putative cystatins from Citrus sinensis and from Citrus clementine and submitted them to phylogenetic analysis. Six cystatins from each species were identified as orthologous and classified into three well supported phylogenetic groups. Five cystatins representative of the phylogenetic groups were recombinantly expressed and the in vitro studies revealed them to be potent inhibitors against the cysteine peptidases papain, legumain, human cathepsins (B, L, S, K) and a cathepsin B-like from Diaphorina citri (the Asian Citrus psyllid). Our findings provide the C. clementina and C. sinensis cystatins classification and an enzyme-inhibitor interactions profile, which may reflect an evolutionary process of Citrus cystatins related to gene functions as initial germination rates and seedlings development as well associated to plant defense against pathogens, as insects and nematodes.

Schistosoma mansoni cathepsin D1: Biochemical and biophysical characterization of the recombinant enzyme expressed in HEK293T cells.

Schistosomes express a variety of aspartyl proteases (APs) with distinct roles in the helminth pathophysiology, among which degradation of host haemoglobin is key, since it is the main amino acid source for these parasites. A cathepsin D-like AP from Schistosoma mansoni (SmCD1) has been used as a model enzyme for vaccine and drug development studies in schistosomes and yet a reliable expression system for readily producing the recombinant enzyme in high yield has not been reported. To contribute to further advancing the knowledge about this valuable antischistosomal target, we developed a transient expression system in HEK 293T mammalian cells and performed a biochemical and biophysical characterization of the recombinant enzyme (rSmCD1). It was possible to express a recombinant C-terminal truncated form of SmCD1 (rSmCD1ΔCT) and purify it with high yield (16 mg/L) from the culture supernatant. When analysed by Size-Exclusion Chromatography and multi-angle laser light scattering, rSmCD1ΔCT behaved as a dimer at neutral pH, which is unusual for cathepsins D, turning into a monomer after acidification of the medium. Through analytical ultrancentrifugation, the dimer was confirmed for free rSmCD1ΔCT in solution as well as stabilization of the monomer during interaction with pepstatin. The mammalian cell expression system used here was able to produce rSmCD1ΔCT with high yields allowing for the first time the characterization of important kinetic parameters as well as initial description of its biophysical properties.

Cyclopalladated compounds containing 2,6-lutidine: Synthesis, spectral and biological studies.

Bridge splitting reactions between [Pd(C2,N-dmba)(µ-X)]2 (dmba = N,N-dimethylbenzylamine; X = Cl, I, N3, NCO) and 2,6-lutidine (lut) in the 1:2 molar ratio at room temperature afforded cyclopalladated compounds of general formulae [Pd(C2,N-dmba)(X)(lut)] {X = Cl- (1), I-(2), NNN-(3), NCO-(4)}, which were characterized by elemental analyses and infrared (IR), 1H NMR spectroscopy. The molecular structures of all synthesized palladacycles have been solved by single-crystal X-ray crystallography. The cytotoxicity of the cyclopalladated compounds has been evaluated against a panel of murine {mammary carcinoma (4T1) and melanoma (B16F10-Nex2)} and human {melanoma (A2058, SK-MEL-110 and SK-MEL-5) tumor cell lines. All complexes were about 10 to 100-fold more active than cisplatin, depending on the tested tumor cell line. For comparison purposes, the cytotoxic effects of 1-4 towards human lung fibroblasts (MRC-5) have also been tested. The late apoptosis-inducing properties of 1-4 compounds in SK-MEL-5 cells were verified 24 h incubation using annexin V-Fluorescein isothiocyanate (FITC)/propidium iodide (PI). The binding properties of the model compound 1 on human serum albumin (HSA) and calf thymus DNA (ct-DNA) have been studied using circular dichroism and fluorescence spectroscopy. Docking simulations have been carried out to gain more information about the interaction of the palladacycle and HSA. The ability of compounds 1-4 to inhibit the activity of cathepsin B and L has also been investigated in this work.