Protease inhibitors and carcinogenesis: a review

Mitigation of antinutritional factors and protease inhibitors of defatted winged bean-seed proteins using thermal and hydrothermal treatments: Denaturation/unfolding coupled hydrolysis mechanism

The inactivation of antinutritional factors, protease inhibitors within winged bean protein was induced by two respective method treatments. The physical method based on steam vapor that was conducted using an autoclave and chemical method consisting on pH-gradients of buffer solutions prepared at respective acidic pH, neutral pH and alkaline pH ranges. The activity of remaining protease inhibitors of bowman birk inhibitor (BBI), and kunitz-trypsin inhibitor (KTI) after and before treatments was enzymatically confirmed using relevant antagonistic trypsin and combined trypsin-α-chymotrypsin digests. The resulting molecular assembly indicating an interval molecular relaxation range of °0.16 < °DA < °0.2 corresponding to reconformation in protein units with volume-mass changes of -2.17 < ∂v' < +2.17 and with denaturation/unfolding efficiency based on heat capacity ΔCp of 36.36 < DE/UF% < 54.67. These structural changes had a great benefit in determining and producing functional protein hydrolysates.

Bioactive Composition, Antioxidant Activity, and Anticancer Potential of Freeze-Dried Extracts from Defatted Gac (Momordica cochinchinensis Spreng) Seeds

Background: Gac (Momordica cochinchinensis Spreng) seeds have long been used in traditional medicine as a remedy for numerous conditions due to a range of bioactive compounds. This study investigated the solvent extraction of compounds that could be responsible for antioxidant activity and anticancer potential. Methods: Defatted Gac seed kernel powder was extracted with different solvents: 100% water, 50% methanol:water, 70% ethanol:water, water saturated butanol, 100% methanol, and 100% ethanol. Trypsin inhibitors, saponins, phenolics, and antioxidant activity using the 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS), the 2,2-diphenyl-1-picrylhydrazyl (DPPH) and the ferric reducing antioxidant power (FRAP) assays; and anticancer potential against two melanoma cancer cell lines (MM418C1 and D24) were analysed to determine the best extraction solvents. Results: Water was best for extracting trypsin inhibitors (581.4 ± 18.5 mg trypsin/mg) and reducing the viability of MM418C1 and D24 melanoma cells (75.5 ± 1.3 and 66.9 ± 2.2%, respectively); the anticancer potential against the MM418C1 cells was highly correlated with trypsin inhibitors (r = 0.92, p < 0.05), but there was no correlation between anticancer potential and antioxidant activity. The water saturated butanol had the highest saponins (71.8 ± 4.31 mg aescin equivalents/g), phenolic compounds (20.4 ± 0.86 mg gallic acid equivalents/g), and antioxidant activity, but these measures were not related to anticancer potential. Conclusions: Water yielded a Gac seed extract, rich in trypsin inhibitors, which had high anticancer potential against two melanoma cell lines.

Trypsin Inhibitors from Cajanus cajan and Phaseolus limensis Possess Antioxidant, Anti-Inflammatory, and Antibacterial Activity

Protease inhibitors are one of the most promising and investigated subjects for their role in pharmacognostic and pharmacological studies. This study aimed to investigate antioxidant, anti-inflammatory, and antimicrobial activities of trypsin inhibitors (TIs) from two plant sources (Cajanus cajan and Phaseolus limensis). TI was purified from C. cajan (PUSA-992) by ammonium sulfate precipitation followed by ion exchange chromatography. TI from Phaseolus limensis (lima bean trypsin inhibitor; LBTI) was procured from Sigma-Aldrich, St. Louis, Missouri, United States. The antioxidant activity was analyzed by ferric ion reducing antioxidant power (FRAP) and 2,2-diphenyl-1-picrylhydrazyl (DPPH). The anti-inflammatory property of TIs was determined by inhibition of albumin denaturation assay. Ascorbic acid and aspirin were used as standards for antioxidant and anti-inflammatory assays, respectively. These TIs were tested against various bacterial and fungal strains. The TIs showed DPPH radical-scavenging activity in a concentration-dependent manner with IC₅₀ values comparable to ascorbic acid. The FRAP values were also observed comparable to ascorbic acid and followed the trend of dose-dependent manner. The half maximal inhibitory concentration (IC₅₀) values of CCTI and LBTI in anti-inflammatory test showed that LBTI is more potent than CCTI. The TIs showed potent antibacterial activity, but apparently no action against fungi. This study has reported the biological properties of CCTI and LBTI for the first time. The results show that TIs possess the ability to inhibit diseases caused by oxidative stress, inflammation, and bacterial infestation.

Structural and Biophysical Characterization of Cajanus cajan Protease Inhibitor

CONTEXT

A large number of studies have proven that Protease inhibitors (PIs), specifically serine protease inhibitors, show immense divergence in regulation of proteolysis by targeting their specific proteases and hence, they play a key role in healthcare.

OBJECTIVE

We aimed to access in-vitro anticancer potential of PI from Cajanus cajan (CCPI). Also, crystallization of CCPI was targetted alongwith structure determination and its structure-function relationship.

MATERIALS AND METHODS

CCPI was purified from Cajanus cajan seeds by chromatographic techniques. The purity and molecular mass was determined by SDS-PAGE. Anticancer potential of CCPI was determined by MTT assay in normal HEK and cancerous A549 cells. The crystallization screening of CCPI was performed by commercially available screens. CCPI sequence was subject to BLASTp with homologous PIs. Progressive multiple alignment was performed using clustalw2 and was modelled using ab initio protocol of I-TASSER.

RESULTS

The results showed ~14kDa CCPI was purified in homogeneity. Also, CCPI showed low cytotoxic effects of in HEK i.e., 27% as compared with 51% cytotoxicity in A549 cells. CCPI crystallized at 16°C using 15% PEG 6000 in 0.1M potassium phosphate buffer (pH 6.0) in 2-3weeks as rod or needles visualized as clusters under the microscope. The molecular modelling revealed that it contains 3 beta sheets, 3 beta hairpins, 2 β-bulges, 6 strands, 3 helices, 1helix-helix interaction, 41 β-turns and 27 γ-turns.

DISCUSSION AND CONCLUSION

The results indicate that CCPI may help to treat cancer in vivo aswell. Also, this is the first report on preliminary crystallization and structural studies of CCPI.

Allium sativum Protease Inhibitor: A Novel Kunitz Trypsin Inhibitor from Garlic Is a New Comrade of the Serpin Family

PURPOSE

This study was aimed to purify and characterize the Protease inhibitor (PI) from a plant Allium sativum (garlic) with strong medicinal properties and to explore its phytodrug potentials.

METHODS

Allium sativum Protease Inhibitor (ASPI) was purified using ammonium sulphate fractionation and Fast Protein Liquid Chromatography on anion exchanger Hi-Trap DEAE column. The purified protein was analyzed for its purity and molecular weight by SDS PAGE. The confirmation of presence of trypsin inhibiting PI was performed by MALDI TOF-TOF and analyzed by MASCOT database. The ASPI was further investigated for its kinetic properties and stability under extreme conditions of pH, temperature and chemical denaturants. Secondary structure was determined by Circular Dichorism (CD) spectroscopy.

RESULTS

ASPI of ~15 kDa inhibited trypsin and matched "truncated kunitz Trypsin Inhibitor (Glycine max)" in MASCOT database. The purified ASPI showed 30376.1371 U/mg specific activity with a fold purity of 159.92 and yield ~93%. ASPI was quite stable in the range of pH 2-12 showing a decline in the activity around pH 4-5 suggesting that the pI value of the protein as ASPI aggregates in this range. ASPI showed stability to a broad range of temperature (10-80°C) but declined beyond 80°C. Further, detergents, oxidizing agents and reducing agents demonstrated change in ASPI activity under varying concentrations. The kinetic analysis revealed sigmoidal relationship of velocity with substrate concentration with Vmax 240.8 (μM/min) and Km value of 0.12 μM. ASPI showed uncompetitive inhibition with a Ki of 0.08±0.01 nM). The Far UV CD depicted 2.0% α -helices and 51% β -sheets at native pH.

CONCLUSIONS

To conclude, purified ~15 kDa ASPI exhibited fair stability in wide range of pH and temperature Overall, there was an increase in purification fold with remarkable yield. Chemical modification studies suggested the presence of lysine and tryptophan residues as lead amino acids present in the reactive sites. Therefore, ASPI with trypsin inhibitory property has the potential to be used as a non-cytotoxic clinical agents.

Selective isolation of trypsin inhibitor and lectin from soybean whey by chitosan/tripolyphosphate/genipin co-crosslinked beads

Selective isolation of Kunitz trypsin inhibitor (KTI) and lectin from soybean whey solutions by different types of chitosan beads was investigated. The chitosan beads were co-crosslinked with tripolyphosphate/genipin in solutions at pH 5, 7 or 9 (CB5, CB7, CB9). The maximum adsorption ratios of chitosan beads to KTI and lectin were observed at pH 4.4 and 5.4, respectively; highly selective separation was also demonstrated at these pHs. The adsorption ratios increased with temperature, rising between 5 and 25 °C. CB9 produced the best adsorption ratio, followed by CB7 then CB5. The critical interaction governing absorption of chitosan beads to KTI and lectin could be hydrogen bonding. At pH 9, KTI and lectin desorbed efficiently from CB7 with desorption ratios of 80.9% and 81.4%, respectively. The desorption was most likely caused predominantly by electrostatic repulsion. KTI and lectin can effectively be selectively isolated from soybean whey using this novel separation technique.

Structure of the proteasome

The ubiquitin-proteasomal system is an essential element of the protein quality control machinery in cells. The central part of this system is the 20S proteasome. The proteasome is a barrel-shaped multienzyme complex, containing several active centers hidden at the inner surface of the hollow cylinder. So, the regulation of the substrate entry toward the inner proteasomal surface is a key control mechanism of the activity of this protease. This chapter outlines the knowledge on the structure of the subunits of the 20S proteasome, the binding and structure of some proteasomal regulators and inducible proteasomal subunits. Therefore, this chapter imparts the knowledge on proteasomal structure which is required for the understanding of the following chapters.

Calliandra selloi Macbride trypsin inhibitor: isolation, characterization, stability, spectroscopic analyses

A trypsin inhibitor was purified from Calliandra selloi Macbride seeds (CSTI). SDS-PAGE under non-reducing conditions showed a single band of approximately 20,000 Da, while under reducing conditions two bands of 16,000 and 6000 Da were observed, indicating that CSTI consists of two polypeptide chains. Molecular masses of 20,078 and 20,279 were obtained by mass spectrometry, although only one pI of 4.0 was observed and one peak was obtained by reversed phase chromatography. Amino-terminal sequence analysis showed homology to Kunitz-type inhibitors. CSTI was able to inhibit trypsin (Ki 2.21 x 10(-7)M), alpha-chymotrypsin (Ki 4.95 x 10(-7)M) and kallikrein (Ki 4.20 x 10(-7)M) but had no effect on elastase. Trypsin inhibitory activity was stable over a wide range of pH and temperature. CSTI was particularly susceptible to DTT treatment, followed by addition of iodoacetamide. Far-UV circular dichroism measurements revealed that CSTI is a beta-II protein. Thermal unfolding showed a two-state transition with a midpoint at 68 degrees C. Far-UV CD spectra of CSTI at pH extremes showed little changes, while more pronounced differences in near-UV CD spectra were detected. Remarkably, treatment with 1mM DTT caused very slight changes in the far-UV CD spectrum, and only after carbamidomethylation was there was a marked loss observed in secondary structure.

Biochemical characterization, stability studies and N-terminal sequence of a bi-functional inhibitor from Phaseolus aureus Roxb. (Mung bean)

Herein, we report the purification and biochemical characterization of a novel bi-functional protein proteinase/amylase inhibitor from the dietary leguminous pulse Phaseolus aureus Roxb. (Vigna radiata L.) by means of acetic acid precipitation, salt fractionation, ion-exchange chromatography (DEAE-cellulose) and affinity chromatography on trypsin-sepharose column. P. aureus inhibitor is a bi-functional inhibitor since it exhibits inhibitory activity towards trypsin-like and alpha-chymotrypsin-like serine proteinases as well as against alpha-amylases. It is a helix-rich protein (Mr 13,600) containing approximately eight tyrosines, one tryptophan and two cystines. N-terminal sequence alignment reveals no homology to other proteinase inhibitors reported from Phaseolus sp. thereby confirming that it is a novel inhibitor. Inhibitory activity measurements show that the inhibitor is quite stable even at extremely high temperatures and is only slightly affected by pH changes. Circular dichroism (CD) conformational studies revealed some changes in its near- as well as far-ultraviolet spectrum at extremes of pH and temperature. Treatments with trypsin for varying time periods did not alter its proteolytic inhibitory activity but caused some reduction in its amylase inhibitory activity.

Frog albumin is expressed in skin and characterized as a novel potent trypsin inhibitor

A novel potent trypsin inhibitor was purified and characterized from frog Bombina maxima skin. A full-length cDNA encoding the protein was obtained from a cDNA library constructed from the skin. Sequence analysis established that the protein actually comprises three conserved albumin domains. B.maxima serum albumin was subsequently purified, and its coding cDNA was further obtained by PCR-based cloning from the frog liver. Only two amino acid variations were found in the albumin sequences from the skin and the serum. However, the skin protein is distinct from the serum protein by binding of a haem b (0.95 mol/mol protein). Different from bovine serum albumin, B. maxima albumin potently inhibited trypsin. It bound tightly with trypsin in a 1:1 molar ratio. The equilibrium dissociation constants (KD) obtained for the skin and the serum proteins were 1.92 x 10(-9) M and 1.55 x 10(-9) M, respectively. B. maxima albumin formed a noncovalent complex with trypsin through an exposed loop formed by a disulfide bond (Cys53-Cys62), which comprises the scissile bond Arg58(P1)-His59(P1'). No inhibitory effects on thrombin, chymotrypsin, elastase, and subtilisin were observed under the assay conditions. Immunohistochemical study showed that B. maxima albumin is widely distributed around the membranes of epithelial layer cells and within the stratum spongiosum of dermis in the skin, suggesting that it plays important roles in skin physiological functions, such as water economy, metabolite exchange, and osmoregulation.

Vitamins, Phytochemicals, Diets, and Their Implementation in Cancer Chemoprevention

With progressive "Westernization" of the dietary pattern in Asian countries, such as Korea and Japan, unhealthy signs, such as increases in obesity and incidence rate of cancers, are starting to appear in recent statistics. These results support the hypothesis that a dietary pattern of low fats and high antioxidants based on plant foods will reduce the risk of cancer Recently, antioxidative vitamins and phenolic phytochemicals derived from our daily diet have received much attention because of their potential chemopreventive activities. Their chemopreventive mechanisms have been suggested mainly due to their protective effects against oxidative DNA damage. However. several studies have shown that dietary antioxidant supplements, such as vitamins and phenolic phytochemicals, are not beneficial; they may rather, cause DNA damage. These results suggest that a metabolomics approach might demonstrate that antioxidant rich whole diets play a more important role, rather than individual antioxidants in cancer prevention. On the other hand, the chemopreventive mechanisms of dietary vitamins and phenolic phytochemicals may be associated with the inhibition of other carcinogenic processes, particularly tumor promotion, rather than that of tumor initiation. In this article, possible cancer-preventive mechanisms of dietary vitamins and phenolic phytochemicals, are reviewed.

One-step purification of Kunitz soybean trypsin inhibitor

A fast and simple method for the extraction and purification of Kunitz trypsin inhibitor from soybean seeds is described. The first step consisted in the heat treatment of whole soybean seeds in water at 60 degrees C for 90 min. It was found that 8.4% of total trypsin inhibitory activity of the seeds was secreted during heat treatment. The aqueous medium was loaded onto an affinity chromatography column with immobilized trypsin. The retained fraction, eluted with 0.01 N HCl, contained the purified Kunitz trypsin inhibitor, which was subsequently stabilized by freeze-drying without loss of activity. From 1g soybean seeds, 0.7 mg inhibitor with a specific trypsin inhibitory (TI) activity of 11,430 TIU/mg was obtained. The yield was greater than that obtained with established procedures. Due to the ease of the procedure proposed, the method is readily scalable to pilot plant or industrial preparations.

Effects of native and cleaved forms of alpha1-antitrypsin on ME 1477 tumor cell functional activity

Tumor cells synthesize and release a variety of substances, including proteases and protease inhibitors involved in cell growth and proliferation. alpha1-Antitrypsin (AAT) is a serine proteinase inhibitor synthesized primarily in the liver, but also in extra-hepatic tissues and cells, including tumor cells. AAT exists not only in a native, active inhibitory form, but also in several, non-inhibitory forms, such as cleaved and/or degraded. This study was designed to investigate the synthesis of AAT by melanoma cells, ME 1477, and the effects of native, cleaved and C-terminal fragment of AAT (C-36) on cell functional activity. We found that ME 1477 cells synthesize and secrete AAT with the same apparent molecular mass as described for AAT purified from plasma, but with no measurable inhibitory activity. As determined by Western blot after immunoprecipitation of [32S]-labeled AAT, exogenous native or modified forms of AAT added to the cells at a concentration of 10 microM did not change AAT synthesis. Moreover, cells exposed to native AAT show decreased [3H]-thymidine incorporation by 53% and tissue inhibitor of metalloproteinases (TIMP)-1 levels by 36%. In contrast, cells treated with C-36 peptide significantly increased metalloproteinase activity, and [3H]-thymidine incorporation by 35%. Specifically, pro-collagenase-1 levels were found to be increased by 1.4-fold and decreased by 1.5-fold in cells treated with C-36 peptide and native AAT, respectively. Cleaved form of AAT had no significant effects on parameters measured. Data obtained from this study suggest that specific forms of AAT have multiple effects on tumor cell viability and play diverse roles in tumorogenesis.

Multiple effects of alpha1-antitrypsin on breast carcinoma MDA-MB 468 cell growth and invasiveness

The degradation of extracellular matrix during cancer invasion results from the action of several protease and protease inhibitor systems. Alpha(1)-Antitrypsin (AAT) is a serine proteinase inhibitor produced by various tumour cells, and its plasma concentration rises during inflammation, infection and malignant diseases. AAT is found in a native, inhibitory active form, but also in other, non-inhibitory forms including cleaved and/or degraded. To test a hypothesis that AAT dependent on its molecular form may have multiple effects on tumour cell behaviour, breast cancer cells, MDA-MB 468, were cultured alone or stimulated with a native AAT or its C-terminal fragment (C-36) at a concentration of 5 micromol/l for 2, 24 and 48 hours. Native AAT added to the cells for 2 hours enhanced transforming growth factor beta 1 (TGFbeta1) levels by 50%, but inhibited cell proliferation (by 61%), reduced interleukin 6 (IL-6) levels (by 87%) and activity (by about 66%), compared with non-stimulated cells. Native AAT showed similar, but less pronounced, effects when added to the cells for 24 and 48 hours. Under the same experimental conditions the cells exposed to the C-36 peptide significantly increased in proliferation, invasiveness and showed higher IL-6 levels. In addition, cells treated with the C-36 for 48 hours increased in NFkappaB (nuclear factor kappa B) activity. These results indicate that AAT, dependent on its molecular form, can both suppress and induce breast tumour cell biological activity in vitro.

The effects of a protease inhibitor fraction from tepary bean (Phaseolus acutifolius) on in vitro cell proliferation and cell adhesion of transformed cells

Some protease inhibitors (PI), such as the soybean Bowman-Birk protease inhibitor (SBBI), have been described as anticarcinogenic agents. Although PI are ubiquitous compounds in living organisms, the anticarcinogenic potential of PIs other than SBBI remain poorly explored. We evaluated the antiproliferative effect of a protein fraction from tepary bean (Phaseolus acutifolius) seeds with protease inhibitor activity (TPIF), on normal and on malignant cells. TPIF was obtained after precipitation with ammonium sulfate and gel filtration, and its bioactivity was assayed in vitro on HeLa cells, normal 3T3 fibroblasts and 3T3/v-mos transformed fibroblasts. TPIF showed antiproliferative and cytotoxic effects on 3T3/v-mos transformed fibroblasts in a dose-dependent way. On the contrary, TPIF was only cytostatic for normal 3T3 cells at the highest doses assayed, and had no effect on epithelial HeLa cells proliferation. Sublethal TPIF doses also stimulated cell adhesion of poorly adherent 3T3/v-mos cell line.

Structural basis of the endoproteinase-protein inhibitor interaction

Proteolytic enzymes are potentially hazardous to their protein environment, so that their activity must be carefully controlled. Living organisms use protein inhibitors as a major tool to regulate the proteolytic activity of proteinases. Most of the inhibitors for which 3D structures are available are directed towards serine proteinases, interacting with the active sites in a 'canonical' i.e. substrate-like manner via an exposed reactive site loop of conserved conformation. More recently, some non-canonically binding serine proteinase inhibitors directed against coagulation factors, in particular thrombin, a few cysteine proteinase inhibitors inhibitory towards papain-like proteinases, and three zinc endopeptidase inhibitors directed against metzincins and thermolysin have been characterised in the free and complexed state, displaying novel mechanisms of inhibition with their target proteinases. These different interaction modes are presented and briefly discussed with respect to the different strategies applied by nature.

Endoproteinase-protein inhibitor interactions

Nature uses protein inhibitors as important tools to regulate the proteolytic activity of their target proteinases. Most of these inhibitors for which 3D structures are available are directed towards serine proteinases, interacting with their active-sites in a substrate-like "canonical" manner via an exposed reactive-site loop of conserved conformation. More recently, some non-canonically binding serine proteinase inhibitors, two cysteine proteinase inhibitors, and three zinc endopeptidase inhibitors have been characterized in the free and complexed state, displaying novel mechanisms of inhibition with their target proteinases. These different interaction modes are briefly discussed, with particular emphasis on the interaction between matrix metalloproteinases (MMPs) and their endogenous tissue inhibitors of metalloproteinases (TIMPs).