The cationic cell-penetrating KT2 peptide promotes cell membrane defects and apoptosis with autophagy inhibition in human HCT 116 colon cancer cells

The anticancer activity of cationic antimicrobial peptides (AMPs) has become more interesting because some AMPs have selective recognition against cancer cells. However, their antitumor properties and underlying mechanisms in cancer cells have not been clearly understood. In this study, we evaluated the effects of KT2 (lysine/tryptophan-rich AMP) on the cellular uptake and internalization mechanism, cell viability, surface charge of the cell membrane, membrane integrity, apoptotic cell death, and autophagy in human HCT 116 colon cancer cells. We found that KT2 interacted with the cell membrane of HCT 116 cells and was internalized into HCT 116 cells via clathrin-mediated and caveolae-mediated endocytosis mechanisms. The interaction of KT2 with cells caused cell membrane structure change, elevated membrane permeability, and KT2 also affected the lipid component. The results of atomic force microscopy showed cellular membrane defects of KT2-treated cells. The internalized KT2 induced nuclear condensation and apoptotic cell death. It elevated the apoptotic factor levels including those of cytochrome c and apoptosis-inducing factor. Furthermore, KT2 inhibited autophagy by the suppression of autophagy-related 5, autophagy-related 7, autophagy-related 16 like 1, and Beclin-1 proteins. In conclusion, these results revealed the cytotoxicity of cationic KT2 against HCT 116 cells and may help to clarify the interactions between cationic AMPs and cancer cells.     

An Investigation of Antioxidant and Anti-inflammatory Activities from Blood Components of Crocodile (Crocodylus siamensis)

Antioxidant and anti-inflammatory activities were found from Crocodylus siamensis (C. siamensis) blood. The 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) radical scavenging, nitric oxide scavenging, hydroxyl radical scavenging and linoleic peroxidation assays were used to investigate the antioxidant activities of the crocodile blood. Results show that crocodile blood components had antioxidant activity, especially hemoglobin (40.58 % nitric oxide radical inhibition), crude leukocyte extract (78 % linoleic peroxidation inhibition) and plasma (57.27 % hydroxyl radical inhibition). Additionally, the anti-inflammatory activity of the crocodile blood was studied using murine macrophage (RAW 264.7) as a model. The results show that hemoglobin, crude leukocyte extract and plasma were not toxic to RAW 264.7 cells. Also they showed anti-inflammatory activity by reduced nitric oxide (NO) and interleukin 6 (IL-6) productions from lipopolysaccharide (LPS)-stimulated cells. The NO inhibition percentages of hemoglobin, crude leukocyte extract and plasma were 31.9, 48.24 and 44.27 %, respectively. However, only crude leukocyte extract could inhibit IL-6 production. So, the results of this research directly indicate that hemoglobin, crude leukocyte extract and plasma of C. siamensis blood provide both antioxidant and anti-inflammatory activities, which could be used as a supplementary agent in pharmaceutical products.     

Monosodium Glutamate Dietary Consumption Decreases Pancreatic β-Cell Mass in Adult Wistar Rats

Background

The amount of dietary monosodium glutamate (MSG) is increasing worldwide, in parallel with the epidemics of metabolic syndrome. Parenteral administration of MSG to rodents induces obesity, hyperglycemia, hyperlipidemia, insulin resistance, and type 2 diabetes. However, the impact of dietary MSG is still being debated. We investigated the morphological and functional effects of prolonged MSG consumption on rat glucose metabolism and on pancreatic islet histology.

Methods

Eighty adult male Wistar rats were randomly subdivided into 4 groups, and test rats in each group were supplemented with MSG for a different duration (1, 3, 6, or 9 months, n=20 for each group). All rats were fed ad libitum with a standard rat chow and water. Ten test rats in each group were provided MSG 2 mg/g body weight/day in drinking water and the 10 remaining rats in each group served as non-MSG treated controls. Oral glucose tolerance tests (OGTT) were performed and serum insulin measured at 9 months. Animals were sacrificed at 1, 3, 6, or 9 months to examine the histopathology of pancreatic islets.

Results

MSG-treated rats had significantly lower pancreatic β-cell mass at 1, 6 and 9 months of study. Islet hemorrhages increased with age in all groups and fibrosis was significantly more frequent in MSG-treated rats at 1 and 3 months. Serum insulin levels and glucose tolerance in MSG-treated and untreated rats were similar at all time points we investigated.

Conclusion

Daily MSG dietary consumption was associated with reduced pancreatic β-cell mass and enhanced hemorrhages and fibrosis, but did not affect glucose homeostasis. We speculate that high dietary MSG intake may exert a negative effect on the pancreas and such effect might become functionally significant in the presence or susceptibility to diabetes or NaCl; future experiments will take these crucial cofactors into account.     

Antimicrobial peptides derived from goose egg white lysozyme

Peptide fragments possessing antimicrobial activity were obtained by protease digestion of goose egg white lysozyme. Digested peptide purified from RP-HPLC which showed no lysozyme activity exhibited bactericidal activity toward Gram-negative and Gram-positive bacteria. LC/MS–MS and automated Edman degradation revealed the amino acid sequence to be Thr-Ala-Lys-Pro-Glu-Gly-Leu-Ser-Tyr. This sequence corresponds to amino acid positions 20–28, located at the N-terminal outer part of goose lysozyme. The peptide acted on bacterial membrane as shown by scanning electron microscopy. The mechanism of action could be explained from a helical structure that may be formed by the centered Pro residue and the terminal Lys residue after the peptide attaches to a cell membrane. This is the first study to report that a peptide derived from the protease digests of G-type lysozyme possesses antimicrobial activity with broad spectrum activity. Our result is comparative to the previous reports of Chicken lysozyme and T4 phage lysozyme, which showed antimicrobial activity after digestion with protease. These results might contribute to the usage of antimicrobial peptides engineered by genetic or chemical synthesis.     

The Effects of Temperature and pH on Secondary Structure and Antioxidant Activity of Crocodylus siamensis Hemoglobin

Crocodylus siamensis hemoglobin (cHb) was purified by gel filtration chromatography and visualized by SDS-PAGE. Effects of temperature and pH on secondary structure and conformation changes of cHb were studied using circular dichroism spectropolarimeter and fourier transform infrared spectrophotometer. The secondary structure of intact cHb was mainly α-helices. cHb was not heat stable when heated at 65 °C and cooled down to original temperature, indicating the irreversible unfolding process. The stability of cHb at different pH ranging from 2.5 to 10.5 was determined. The maximum value of the α-helix content was found at pH 3.5 and tended to decrease at strong acid and strong base. The antioxidant activities of heat treated cHb and cHb in solution with pH range 2.5 to 10.5 were tested by DPPH radical scavenging assay. cHb at pH 4.5, having highest β-turn structure, showed highest radical scavenging activity. In contrast to pH, heat had no effect on antioxidant activity of cHb.     

Cloning,Expression, and Characterization of Siamese Crocodile (<Emphasis Type="Italic">Crocodylus siamensis</Emphasis>) Hemoglobin from <Emphasis Type="Italic">Escherichia coli</Emphasis> and <Emphasis Type="Italic">Pichia pastoris</Emphasis>

Recombinant Crocodylus siamensis hemoglobin (cHb) has been constructed and expressed using Escherichia coli as the expression system in conjunction with a trigger factor from the Cold-shock system as the fusion protein. While successful processing as soluble protein in E. coli was achieved, the net yields of active protein from downstream purification processes remained still unsatisfactory. In this study, cHb was constructed and expressed in the eukaryotic expression system Pichia pastoris. The results showed that cHb was excreted from P. pastoris as a soluble protein after 72 h at 25 °C. The amino acid sequence of recombinant cHb was confirmed using LC–MS/MS. Indeed, the characteristic of Hb was investigated by external heme incorporation. The UV–Vis profile showed a specific pattern of the absorption at 415 nm, indicating the recombinant cHb was formed complex with heme, resulting in active oxyhemoglobin (OxyHb). This result suggests that the heme molecules were fully combined with heme binding site of the recombinant cHb, thus producing characteristic red color for the OxyHb at 540 and 580 nm. The results revealed that the recombinant cHb was prosperously produced in P. pastoris and exhibited a property as protein–ligand binding. Thus, our work described herein offers a great potential to be applied for further studies of heme-containing protein expression. It represents further pleasing option for protein production and purification on a large scale, which is important for determination and characterization of the authenticity features of cHb proteins.     

Complete amino acid sequence of three reptile lysozymes

To study the structure and function of reptile lysozymes, we have reported their purification, and in this study we have established the amino acid sequence of three egg white lysozymes in soft-shelled turtle eggs (SSTL A and SSTL B from Trionyx sinensis, ASTL from Amyda cartilaginea) by using the rapid peptide mapping method. The established amino acid sequence of SSTL A, SSTL B, and ASTL showed substitutions of 43, 42, and 44 residues respectively when compared with the HEWL (hen egg white lysozyme) sequence. In these reptile lysozymes, SSTL A had one substitution compared with SSTL B (Gly126Asp) and had an N-terminal extra Gly and 11 substitutions compared with ASTL. SSTL B had an N-terminal extra Gly and 10 residues different from ASTL. The sequence of SSTL B was identical to soft-shelled turtle lysozyme from STL (Trionyx sinensis japonicus). The Ile residue at position 93 of ASTL is the first report in all C-type lysozymes. Furthermore, amino acid substitutions (Phe34His, Arg45Tyr, Thr47Arg, and Arg114Tyr) were also found at subsites E and F when compared with HEWL. The time course using N-acetylglucosamine pentamer as a substrate exhibited a reduction of the rate constant of glycosidic cleavage and increase of binding free energy for subsites E and F, which proved the contribution for amino acids mentioned above for substrate binding at subsites E and F. Interestingly, the variable binding free energy values occurred on ASTL, may be contributed from substitutions at outside of subsites E and F.     

Antimicrobial Action of the Cyclic Peptide Bactenecin on Burkholderia pseudomallei Correlates with Efficient Membrane Permeabilization

Burkholderia pseudomallei is a category B agent that causes Melioidosis, an acute and chronic disease with septicemia. The current treatment regimen is a heavy dose of antibiotics such as ceftazidime (CAZ); however, the risk of a relapse is possible. Peptide antibiotics are an alternative to classical antibiotics as they exhibit rapid action and are less likely to result in the development of resistance. The aim of this study was to determine the bactericidal activity against B. pseudomallei and examine the membrane disrupting abilities of the potent antimicrobial peptides: bactenecin, RTA3, BMAP-18 and CA-MA. All peptides exhibited >97% bactericidal activity at 20 µM, with bactenecin having slightly higher activity. Long term time-kill assays revealed a complete inhibition of cell growth at 50 µM bactenecin and CA-MA. All peptides inhibited biofilm formation comparable to CAZ, but exhibited faster kinetics (within 1 h). Bactenecin exhibited stronger binding to LPS and induced perturbation of the inner membrane of live cells. Interaction of bactenecin with model membranes resulted in changes in membrane fluidity and permeability, leading to leakage of dye across the membrane at levels two-fold greater than that of other peptides. Modeling of peptide binding on the membrane showed stable and deep insertion of bactenecin into the membrane (up to 9 Å). We propose that bactenecin is able to form dimers or large β-sheet structures in a concentration dependent manner and subsequently rapidly permeabilize the membrane, leading to cytosolic leakage and cell death in a shorter period of time compared to CAZ. Bactenecin might be considered as a potent antimicrobial agent for use against B. pseudomallei.