Functionalising silk hydrogels with hetero- and homotypic nanoparticles.

Despite many reports detailing silk hydrogels, the development of composite silk hydrogels with homotypic and heterotypic silk nanoparticles and their impact on material mechanics and biology have remained largely unexplored. We hypothesise that the inclusion of nanoparticles into silk-based hydrogels enables the formation of homotropic and heterotropic material assemblies. The aim was to explore how well these systems allow tuning of mechanics and cell adhesion to ultimately control the cell-material interface. We utilised nonporous silica nanoparticles as a standard reference and compared them to nanoparticles derived from Bombyx mori silk and Antheraea mylitta (tasar) silk (approximately 100-150 nm in size). Initially, physically cross-linked B. mori silk hydrogels were prepared containing silica, B. mori silk nanoparticles, or tasar silk nanoparticles at concentrations of either 0.05% or 0.5% (w/v). The initial modulus (stiffness) of these nanoparticle-functionalised silk hydrogels was similar. Stress relaxation was substantially faster for nanoparticle-modified silk hydrogels than for unmodified control hydrogels. Increasing the concentrations of B. mori silk and silica nanoparticles slowed stress relaxation, while the opposite trend was observed for hydrogels modified with tasar nanoparticles. Cell attachment was similar for all hydrogels, but proliferation during the initial 24 h was significantly improved with the nanoparticle-modified hydrogels. Overall, this study demonstrates the manufacture and utilisation of homotropic and heterotropic silk hydrogels.

Ethanolic extract of Halymenia durvillei induced G2/M arrest and altered the levels of cell cycle regulatory proteins of MDA-MB-231 triple-negative breast cancer cells.

Background and purpose: The GC-MS analysis reported n-hexadecanoic acid or palmitic acid as a major component of the ethanolic extract of Halymenia durvillei (HDET). This compound shows cytotoxic effects against various human cancer cells. The present study investigated the effect of HDET on the viability and proliferation of MDA-MB-231, a triple-negative breast cancer (TNBC) cell line. Experimental approach: Cell proliferation and cell cycle analysis were determined by flow cytometry and cell cycle regulatory protein expression levels were then determined by Western blotting. The presence of reactive oxygen species (ROS) was evaluated by dichlorofluorescein, followed by analyzing changes in gene expression of antioxidant enzymes using a real-time polymerase chain reaction. Findings/Results: HDET dose-dependently reduced cell viability with the 50% inhibitory concentration (IC50) of 269.4 ± 31.2 µg/mL at 24 h. The cell proliferation assays showed increased succinimidyl ester fluorescent intensity after treatment with ≥ 100 µg/mL of HDET, indicating the inhibition of cell proliferation. Cell cycle analysis using propidium iodide staining showed an increased percentage of cells in the G2/M phase. HDET also decreased the levels of cell cycle regulatory proteins including cyclin D1 and increased the level of p21. HDET promoted oxidative stress by increasing ROS levels along with the reduction of catalase expression. However, HDET did not induce apoptosis and caspase activation in TNBC cells. Conclusion and implications: These findings suggest that HDET which is rich in palmitic acid may serve as a potential therapeutic agent to target TNBC via arrest cell cycle progression at the G2/M phase.

Microfibre-Functionalised Silk Hydrogels.

Silk hydrogels have shown potential for tissue engineering applications, but several gaps and challenges, such as a restricted ability to form hydrogels with tuned mechanics and structural features, still limit their utilisation. Here, Bombyx mori and Antheraea mylitta (Tasar) silk microfibres were embedded within self-assembling B. mori silk hydrogels to modify the bulk hydrogel mechanical properties. This approach is particularly attractive because it creates structured silk hydrogels. First, B. mori and Tasar microfibres were prepared with lengths between 250 and 500 µm. Secondary structure analyses showed high beta-sheet contents of 61% and 63% for B. mori and Tasar microfibres, respectively. Mixing either microfibre type, at either 2% or 10% (w/v) concentrations, into 3% (w/v) silk solutions during the solution-gel transition increased the initial stiffness of the resulting silk hydrogels, with the 10% (w/v) addition giving a greater increase. Microfibre addition also altered hydrogel stress relaxation, with the fastest stress relaxation observed with a rank order of 2% (w/v) > 10% (w/v) > unmodified hydrogels for either fibre type, although B. mori fibres showed a greater effect. The resulting data sets are interesting because they suggest that the presence of microfibres provided potential 'flow points' within these hydrogels. Assessment of the biological responses by monitoring cell attachment onto these two-dimensional hydrogel substrates revealed greater numbers of human induced pluripotent stem cell-derived mesenchymal stem cells (iPSC-MSCs) attached to the hydrogels containing 10% (w/v) B. mori microfibres as well as 2% (w/v) and 10% (w/v) Tasar microfibres at 24 h after seeding. Cytoskeleton staining revealed a more elongated and stretched morphology for the cells growing on hydrogels containing Tasar microfibres. Overall, these findings illustrate that hydrogel stiffness, stress relaxation and the iPSC-MSC responses towards silk hydrogels can be tuned using microfibres.

Allyl ether of mansonone G as a potential anticancer agent for colorectal cancer.

Mansonone G (MG), a 1,2-naphthoquinone isolated from the heartwood of Mansonia gagei Drumm, exhibited several pharmacological activities such as anti-bacterial, anti-estrogenic and anti-adipogenic effect. This study evaluated the cytotoxicity of MG and its derivatives as well as determined the mechanism(s) underlying the cytotoxic activity of the most potent MG derivative on two CRC cell lines, HCT-116 cells carrying p53 wild-type and HT-29 cells carrying p53 mutant. We found that MG and its derivatives could inhibit viability of HCT-116 and HT-29 cells in a concentration-dependent manner. Of all semi-synthetic derivatives of MG, allyl ether mansonone G (MG7) was the most potent cytotoxic agent toward cancer cells and less toxic to normal cells. MG7 could induce ROS generation which was associated with cytotoxicity and apoptosis in both HCT-116 and HT-29 cells. Western blot analysis revealed that MG7 downregulated the expression of Bcl-2 and Bcl-xL proteins in both CRC cell lines and upregulated the expression of BAK protein in HT-29 cells. Moreover, MG7 inhibited AKT signaling pathway in both CRC cell lines and modulated ERK1/2 signaling pathway by inhibiting ERK1/2 phosphorylation in HCT-116 cells and activating ERK1/2 phosphorylation in HT-29 cells. Molecular docking revealed that MG7 could bind to the ATP-binding pocket of AKT and ERK1 via hydrophobic interactions.

Smart Silk Origami as Eco-sensors for Environmental Pollution.

Origami folding is an easy, cost-effective, and scalable fabrication method for changing a flat material into a complex 3D functional shape. Here, we created semicrystalline silk films doped with iron oxide particles by mold casting and annealing. The flat silk films could be loaded with natural dyes and folded into 3D geometries using origami principles following plasticization. They performed locomotion under a magnetic field, were reusable, and displayed colorimetric stability. The critical parameters for the design of the semi-autonomous silk film, including ease of folding, shape preservation, and locomotion in the presence of a magnetic field, were characterized, and pH detection was achieved by eye and by digital image colorimetry with a response time below 1 min. We demonstrate a practical application─a battery-free origami silk boat─as a colorimetric sensor for waterborne pollutants, which was reusable at least five times. This work introduces silk eco-sensors and merges responsive actuation and origami techniques.

Impact of silk hydrogel secondary structure on hydrogel formation, silk leaching and in vitro response.

Silk can be processed into a broad spectrum of material formats and is explored for a wide range of medical applications, including hydrogels for wound care. The current paradigm is that solution-stable silk fibroin in the hydrogels is responsible for their therapeutic response in wound healing. Here, we generated physically cross-linked silk fibroin hydrogels with tuned secondary structure and examined their ability to influence their biological response by leaching silk fibroin. Significantly more silk fibroin leached from hydrogels with an amorphous silk fibroin structure than with a beta sheet-rich silk fibroin structure, although all hydrogels leached silk fibroin. The leached silk was biologically active, as it induced vitro chemokinesis and faster scratch assay wound healing by activating receptor tyrosine kinases. Overall, these effects are desirable for wound management and show the promise of silk fibroin and hydrogel leaching in the wider healthcare setting.

Silk Hydrogel Substrate Stress Relaxation Primes Mesenchymal Stem Cell Behavior in 2D.

Tissue-mimetic silk hydrogels are being explored for diverse healthcare applications, including stem cell delivery. However, the impact of stress relaxation of silk hydrogels on human mesenchymal stem cell (MSC) biology is poorly defined. The aim of this study was to fabricate silk hydrogels with tuned mechanical properties that allowed the regulation of MSC biology in two dimensions. The silk content and stiffness of both elastic and viscoelastic silk hydrogels were kept constant to permit direct comparisons. Gene expression of IL-1ß, IL-6, LIF, BMP-6, BMP-7, and protein tyrosine phosphatase receptor type C were substantially higher in MSCs cultured on elastic hydrogels than those on viscoelastic hydrogels, whereas this pattern was reversed for insulin, HNF-1A, and SOX-2. Protein expression was also mechanosensitive and the elastic cultures showed strong activation of IL-1ß signaling in response to hydrogel mechanics. An elastic substrate also induced higher consumption of glucose and aspartate, coupled with a higher secretion of lactate, than was observed in MSCs grown on viscoelastic substrate. However, both silk hydrogels changed the magnitude of consumption of glucose, pyruvate, glutamine, and aspartate, and also metabolite secretion, resulting in an overall lower metabolic activity than that found in control cells. Together, these findings describe how stress relaxation impacts the overall biology of MSCs cultured on silk hydrogels.

Intracellular nickel accumulation induces apoptosis and cell cycle arrest in human astrocytic cells.

Nickel, a heavy metal found in electronic wastes and fume from electronic cigarettes, induces neuronal cell death and is associated with neurocognitive impairment. Astrocytes are the first line of defense against nickel after entering the brain; however, the effects of nickel on astrocytes remain unknown. Herein, we investigated the effect of nickel exposure on cell survival and proliferation and the underlying mechanisms in U-87 MG human astrocytoma cells and primary human astrocytes. Intracellular nickel levels were elevated in U-87 MG cells in a dose- and time-dependent manner after exposure to nickel chloride. The median toxic concentrations of nickel in astrocytoma cells and primary human astrocytes were 600.60 and >1000 µM at 48 h post-exposure, respectively. Nickel exposure triggered apoptosis in concomitant with the decreased expression of anti-apoptotic B-cell lymphoma protein (Bcl-2) and increased caspase-3/7 activity. Nickel induced reactive oxygen species formation. Additionally, nickel suppressed astrocyte proliferation in a dose- and time-dependent manner by delaying G2 to M phase transition through the upregulation of cyclin B1 and p27 protein expression. These results indicate that nickel-induced cytotoxicity of astrocytes is mediated by the activation of apoptotic pathway and disruption of cell cycle regulation.

Silk Nanoparticle Manufacture in Semi-Batch Format.

Silk nanoparticles have demonstrated utility across a range of biomedical applications, especially as drug delivery vehicles. Their fabrication by bottom-up methods such as nanoprecipitation, rather than top-down manufacture, can improve critical nanoparticle quality attributes. Here, we establish a simple semi-batch method using drop-by-drop nanoprecipitation at the lab scale that reduces special-cause variation and improves mixing efficiency. The stirring rate was an important parameter affecting nanoparticle size and yield (400 < 200 < 0 rpm), while the initial dropping height (5.5 vs 7.5 cm) directly affected nanoparticle yield. Varying the nanoparticle standing time in the mother liquor between 0 and 24 h did not significantly affect nanoparticle physicochemical properties, indicating that steric and charge stabilizations result in high-energy barriers for nanoparticle growth. Manufacture across all tested formulations achieved nanoparticles between 104 and 134 nm in size with high ß-sheet content, spherical morphology, and stability in aqueous media for over 1 month at 4 °C. This semi-automated drop-by-drop, semi-batch silk desolvation offers an accessible, higher-throughput platform for standardization of parameters that are difficult to control using manual methodologies.

Cadmium induces CCL2 production in glioblastoma cells via activation of MAPK, PI3K, and PKC pathways.

Cadmium (Cd) is accumulated in human astrocytes and induces the production of interleukin (IL)-6 and IL-8. Astrocytes are one of the major sources of chemokine C-C motif ligand 2 (CCL2; known as monocyte chemoattractant protein-1 [MCP-1]), in the brain. Elevated CCL2 levels are associated with cognitive impairment as well as the migration and invasion of glioblastoma cells. The present study hypothesized that non-toxic concentrations of Cd (as cadmium chloride [CdCl2]) could up-regulate CCL2 production in U-87 MG human glio-blastoma cells. The results showed that after exposure of the U-87 MG cells to CdCl2 at 1 and 10 µM, there was an up-regulation of CCL2 mRNA expression after 3 h of exposure and increased CCL2 secretion after 6 and 24 h. The study also found that inhibition of MAPK pathways, including ERK1/2, p38, and JNK by U0126, SB203580 and SP600125, respectively, reduced Cd-induced CCL2 secretion by the cells. Moreover, when cells were pretreated with Ro 32-0432 (an inhibitor of calcium-dependent PKC) and LY294002 (a PI3K inhibitor), this also resulted in a down-regulation of any Cd-induced CCL2 expression. Taken together, the results of this study allow for the conclusion to be made that CCL2 up-regulation in U-87 MG cells induced by Cd is mediated, in part, by an activation of MAPK, PI3K/Akt, and PKC pathways.

Dose-Dependent Acute Circulatory Fates Elicited by Cadmium Are Mediated by Differential Engagements of Cardiovascular Regulatory Mechanisms in Brain.

Whereas cadmium is a toxicant that has been shown to cause cardiovascular toxicity and mortality in mammals, few mechanistic studies address its acute circulatory actions. The present study assessed the hypothesis that cadmium effects dose-dependent acute circulatory fates via differential participation of the cardiovascular regulatory mechanisms in brain. In Sprague-Dawley rats maintained under propofol anesthesia, cadmium acetate (8 mg/kg, iv) induced significantly high mortality rate within 10 min, concomitant with progressive decline toward zero level of mean arterial pressure (MAP), heart rate (HR), baroreflex-mediated sympathetic vasomotor tone, and carotid blood flow (CBF). There were concurrent tissue anoxia, cessation of microvascular perfusion, reduction of mitochondrial membrane potential and ATP production, and necrotic cell death in the rostral ventrolateral medulla (RVLM), the brain stem site that maintains blood pressure and sympathetic vasomotor tone. On the other hand, a lower-dose of cadmium (4 mg/kg, iv) resulted in only a transient decrease in MAP that was mirrored by an increase in CBF and baroreflex-mediated sympathetic vasomotor tone, minor changes in HR, along with transient hypoxia, and apoptotic cell death in RVLM. We conclude that cadmium elicits dose-dependent acute cardiovascular effects with differential underlying biochemical and neural mechanisms. At a higher-dose, cadmium induces high mortality by effecting acute cardiovascular collapse via anoxia, diminished tissue perfusion, mitochondrial dysfunction and bioenergetics failure that echo failure of cerebral autoregulation, leading to necrosis, and loss of functionality in RVLM. On the other hand, a lower-dose of cadmium elicits low mortality, transient decrease in arterial pressure, and hypoxia and apoptosis in RVLM that reflect sustained cerebral autoregulation.

Cadmium induces apoptotic program imbalance and cell cycle inhibitor expression in cultured human astrocytes.

Cadmium is a highly neurotoxic heavy metal impairing neurogenesis and induces neurodegenerative disorders. Toxic concentrations of cadmium induce astrocytic apoptosis by depleting intracellular glutathione levels, elevating intracellular calcium levels, altering mitochondria membrane potentials, and activating JNK and PI3K/Akt signaling pathways. Cadmium suppresses cell proliferation in kidney epithelial cells, lung fibroblasts, and primary myelocytes; however, cadmium's effects on proteins regulating oxidative stress, apoptosis, and cell proliferation in astrocytes are less known. The present study hypothesized that cadmium alters levels of antioxidant enzymes, apoptotic regulator proteins, and cell cycle inhibitor proteins, resulting in apoptosis and cell cycle arrest. Concentrations ≥20 µM cadmium induced apoptosis and led to intracellular changes including DNA fragmentation, reduced mRNA expression of antioxidant enzymes (i.e., catalase and glutathione S transferase-A4), downregulation of B-cell lymphoma 2 (Bcl-2), and upregulation of Bcl-2-associated X protein (Bax). Moreover, cadmium suppressed astrocytic proliferation by inducing S and G2/M phase cell cycle arrest and promoting p53, p21, and p27 expression. In conclusion, this study provides mechanistic insight into cadmium-induced cytotoxicity of astrocytes and highlights potential targets for prevention of cadmium-induced apoptosis and cell cycle arrest.

Cysteinyl leukotriene receptor antagonists induce apoptosis and inhibit proliferation of human glioblastoma cells by downregulating B-cell lymphoma 2 and inducing cell cycle arrest.

Glioblastoma is the most aggressive type of brain cancer with the highest proliferation, invasion, and migration. Montelukast and zafirlukast, 2 widely used leukotriene receptor antagonists (LTRAs) for asthma treatment, inhibited invasion and migration of glioblastoma cell lines. Montelukast induces apoptosis and inhibits cell proliferation of various cancer cells. Herein, apoptotic and antiproliferative effects of montelukast and zafirlukast were investigated in 2 glioblastoma cell lines, A172 and U-87 MG. Both LTRAs induced apoptosis and inhibited cell proliferation of glioblastoma cells in a concentration-dependent manner. Montelukast was more cytotoxic and induced higher levels of apoptosis than zafirlukast in A172 cells, but not in U-87 MG cells. Both drugs decreased expression of B-cell lymphoma 2 (Bcl-2) protein without affecting Bcl-2-associated X (Bax) levels. LTRAs also reduced the phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2). In contrast, zafirlukast showed a greater antiproliferative effect than montelukast and induced G0/G1 cell cycle arrest by upregulating p53 and p21 expression. These results suggested the therapeutic potential of LTRAs in glioblastoma.

Cadmium-induced IL-6 and IL-8 expression and release from astrocytes are mediated by MAPK and NF-κB pathways.

Chronic exposure to cadmium has been linked to brain cancers, learning disabilities and memory deficits. Previous studies of cadmium toxicity in the central nervous system report cadmium induces oxidative stress in neurons and astrocytes. In the peripheral system, cadmium promotes interleukin-6 (IL-6) and IL-8 production and release. Elevation of IL-6 expression is linked to the pathogenesis of neurodegenerative diseases and astrogliosis. IL-8 plays a role in angiogenesis of gliomas and neurodegenerative diseases. Herein, the effects of non-toxic concentrations of cadmium on the production of IL-6 and IL-8 and the underlying mechanisms were investigated. U-87 MG human astrocytoma cells and primary human astrocytes were exposed to cadmium chloride. At 24h post-exposure to 1 and 10µM, levels of intracellular cadmium in U-87 MG cells were 11.89±3.59 and 53.08±7.59µg/g wet weight, respectively. These concentrations had minimal effects on cell morphology and viability. IL-6 and IL-8 mRNA levels and secretion increased in dose- and time-dependent manners post cadmium exposure. Acute exposure to cadmium increased phosphorylation of ERK1/2, p38 MAPK, and p65 NF-κB. Pretreatment with U0126-an inhibitor of MEK1 and MEK2 kinases-SB203580-a p38 MAPK inhibitor-and SC-514-an IKKß inhibitor-suppressed cadmium-induced IL-8 expression and release. Upregulation of cadmium-induced IL-6 was inhibited by U0126 and SC-514, but not SB203580. On the other hand, SP600125-a JNK inhibitor-and celecoxib-a selective COX-2 inhibitor-had no effect on production of both cytokines. In conclusion, non-toxic concentrations of cadmium can stimulate IL-6 and IL-8 release through MAPK phosphorylation and NF-κB activation. Suppressing IL-6 and IL-8 production could be novel approaches to prevent cadmium-induced angiogenesis in gliomas and inflammation in the brain.