Effect of electric pulses and antiproliferative drugs on cultured bovine retinal pigment epithelial cells

Mitomycin C enhanced the antitumor efficacy of Rocaglamide in colorectal cancer

Rocaglamide (ROC), a natural phytochemical isolated from Aglaia species, is a translational inhibitor of de novo c-FLIP synthesis, which relieves the inhibition of c-FLIP dimerization with procasoase-8 and downstream activation. Unfortunately, a lot of cancer cells, especially colorectal cancer cells (CRC), exhibit marked resistance to Rocaglamide-induced cell death. Research has demonstrated that mitomycin C (MMC) has broad-spectrum anti-tumor activity that it can synergize with a wide range of clinical drugs to inhibit tumor growth. The current study investigated whether MMC combined with ROC could sensitize CRC cells with different ROC resistance to apoptosis. HCT116 and HT29, two different CRC cells, were treated with ROC and/or MMC, and the induction of apoptosis, inhibition of cell migration and invasion, arrest of cell cycle, induction of reactive oxygen species, and effects on Bcl-2 family signaling pathway were investigated. The results showed that low concentration of MMC combined with ROC significantly promoted HCT116 and HT29 cell apoptosis and inhibited cell proliferation by downregulating the expression of Bcl-2 and c-FLIP, upregulating the expression of Bax, activating the caspase cascade (involving the mitochondrial apoptosis pathway), arresting cell cycle in G1 phase, and increasing the level of reactive oxygen species (ROS). In addition, the viability and morphology of MRC-5 cells were not significantly affected by the combined treatment with ROC and MMC, indicating its safety. Therefore, it is concluded that the combination treatment of ROC and MMC is a highly effective tumor therapy and may offer a promising therapeutic strategy for the treatment of CRC.

Bioelectric Potential in Next-Generation Organoids: Electrical Stimulation to Enhance 3D Structures of the Central Nervous System

Pluripotent stem cell-derived organoid models of the central nervous system represent one of the most exciting areas in in vitro tissue engineering. Classically, organoids of the brain, retina and spinal cord have been generated via recapitulation of in vivo developmental cues, including biochemical and biomechanical. However, a lesser studied cue, bioelectricity, has been shown to regulate central nervous system development and function. In particular, electrical stimulation of neural cells has generated some important phenotypes relating to development and differentiation. Emerging techniques in bioengineering and biomaterials utilise electrical stimulation using conductive polymers. However, state-of-the-art pluripotent stem cell technology has not yet merged with this exciting area of bioelectricity. Here, we discuss recent findings in the field of bioelectricity relating to the central nervous system, possible mechanisms, and how electrical stimulation may be utilised as a novel technique to engineer “next-generation” organoids.

Effects of electrical stimulation on cell proliferation and apoptosis

The application of exogenous electrical stimulation (ES) to cells in order to manipulate cell apoptosis and proliferation has been widely investigated as a possible method of treatment in a number of diseases. Alteration of the transmembrane potential of cells via ES can affect various intracellular signaling pathways which are involved in the regulation of cellular function. Controversially, several types of ES have proved to be effective in both inhibiting or inducing apoptosis, as well as increasing proliferation. However, the mechanisms through which ES achieves this remain fairly unclear. The aim of this review was to comprehensively summarize current findings from in vitro and in vivo studies on the effects of different types of ES on cell apoptosis and proliferation, highlighting the possible mechanisms through which ES induced these effects and define the optimum parameters at which ES can be used. Through this we hope to provide a greater insight into how future studies can most effectively use ES at the clinical trial stage.

Electroporation enhances mitomycin C cytotoxicity on T24 bladder cancer cell line: a potential improvement of intravesical chemotherapy in bladder cancer

Intravesical mitomycin instillation combined with electric pulses is being used experimentally for the treatment of T1 bladder tumors, in patients unfit for surgery. Electroporation may enhance the uptake of chemotherapeutics by permeabilization of cell membranes. We investigated if electroporation improves the cytotoxicity of mitomycin. In two cell lines, T24 (bladder cancer cell line) and DC3F (Chinese hamster fibroblast), exposure to different concentrations of mitomycin (0.01-2000μM) was tested with and without electroporation (6 pulses of 1kV/cm, duration: 99μs, frequency: 1Hz). Cell viability was assessed by colorimetric assay (MTT). For both cell lines, mitomycin's IC_50 was approximately 1000μM in both pulsed and unpulsed cells. On T24 cells, electroporation and mitomycin caused (relative reduction) RR of survival of: 25%, 31% and 29%, by concentrations 0μM, 500μM and 1000μM respectively. For DC3F cells, the RRs of survival were: 28%, 29%, and 33%, by concentrations 0μM, 500μM and 1000μM respectively. In conclusion, electroporation and mitomycin together are about 30% more effective than mitomycin alone. The results help to elucidate the additive effect of mitomycin and electric pulses and support the use of this combination in the treatment of bladder cancer.

Mitomycin C, Ceramide, and 5-Fluorouracil Inhibit Corneal Haze and Apoptosis After PRK

PURPOSE

To investigate the effects of mitomycin C (MMC), ceramide, and 5-fluororacil (5-FU) on haze after photorefractive keratectomy (PRK) and exposure to ultraviolet B (UVB) radiation.

METHODS

The right eyes of 42 New Zealand white rabbits were treated with PRK to correct -10 diopter with a 5-mm optical zone. Sponges soaked in 0.02% MMC, 10 or 40 micromol/L ceramide, or 0.5% 5-FU were applied to the right eyes of 6 rabbits each, and a tarsorrhaphy was performed. Eight weeks after complete healing, topical 0.02% MMC or 0.5% 5-FU was applied twice daily to the right eyes of 6 rabbits that had previously received PRK but no topical medication. The control group of 6 rabbits was treated only with PRK. Three weeks after PRK, all the laser-treated eyes were exposed to 100 mJ/cm UVB radiation. Corneal haze was assessed biomicroscopically every 2 weeks using the Fantes scale. Eyes were enucleated 2, 7, and 13 weeks after PRK, and tissue specimens were stained with hematoxylin and eosin and with Apostain.

RESULTS

Corneal haze was observed in all rabbits after PRK and was aggravated by UVB irradiation. When applied immediately after PRK, MMC induced corneal opacity and apoptosis of keratocytes, but, at later times, this reagent significantly suppressed opacity, Apostain-positive keratocytes and reactivation of keratocytes, even after UVB irradiation. In contrast, ceramide and 5-FU suppressed corneal opacity after PRK, but this effect was not sustained after UVB irradiation.

CONCLUSIONS

MMC is a potent inhibitor of haze induced by PRK and UVB irradiation. Throughout the process of corneal wound healing, the severity of apoptosis and reactivation of keratocytes was closely correlated with haze formation.

Ascorbic acid reversibly inhibits proliferation of retinal pigment epithelial cells

PURPOSE

Proliferation control in adult retinal pigment epithelial (ARPE) cells is an essential factor in the clinical management of proliferative vitreoretinopathy (PVR). Factors which inhibit PVR and which are without toxic potential are therefore of interest in controlling proliferation. The aim of the present study was to gain insight into a possible function of high intraocular ascorbic acid levels as a physiological modulator of proliferation.

METHODS

Adult retinal pigment epithelial cells were incubated in vitro with increasing concentrations of ascorbic acid (0.5-4 mmol, pH 7.4). Cell proliferation was assayed by the bromide-deoxy-uridine (BrdU) assay. The culture medium (CM) containing ascorbic acid was replaced with normal CM and the recovery of proliferation was measured after 24 hours. In order to be able to distinguish between proliferation inhibition, apoptosis, necrosis and recovery of proliferation, we performed TUNEL assays and fluorescence analysis cell-counter (FAC) analysis.

RESULTS

Ascorbic acid significantly inhibits ARPE cell proliferation if it is present in concentrations above 2 mmol. Proliferation resumed in all ARPE cell cultures after pre-incubation with ascorbic acid, indicating that direct toxicity of ascorbic acid is a negligible factor. The time-point and extent of recovery in proliferation was dependent on the initial ascorbic acid concentration. Fluorescence-labelled cell counts on apoptosis markers (FAC) data showed some induction of apoptosis and necrosis after incubation with 4 mmol ascorbic acid.

CONCLUSIONS

Ascorbic acid has a dose-dependent influence on the proliferation of vital ARPE cells. This possibly reflects the role of ascorbic acid at a physiological level within the vitreous cavity in preventing proliferative vitreoretinopathy (PVR). These findings may stimulate the development of new strategies in the clinical treatment of PVR.

The cell cycle distribution of cultured human retinal pigmented epithelial cells under exposure of anti-proliferative drugs

It has been well documented that RPE cells play an important role in the formation of proliferative vitreoretinopathy (PVR). We studied the effects of four most widely used anti-proliferative drugs, i.e., 5-fluorouracil (5-FU), daunomycin (DM), mitomycin C (MMC) and dexamethasone (DEX) in an in vitro model system (cultured human RPE). The cells treated with indicated concentrations of drugs for 48 h were harvested for DNA content analysis. In addition, a time course study with constant dosage of drugs was performed. The results revealed that, after incubation for 48 h, an increased percentage (31.1%) of S phase cells was noted with exposure to MMC (10 ng/ml). It was confirmed by 5-bromodeoxyuridine (BrdU) incorporation test that this increase does not result from higher transition rate from G1 to S phase. The cells of G2/M phase markedly increased from 13.8% to 29.7% with 10 ng/ml DM. We also demonstrated that 5-FU and MMC treatment led to cell accumulation at S phase and DM treatment resulted in cell accumulation at G2/M phase, These findings were compatible with their pharmacological mechanisms. Development of an in vitro model using cultured human RPE to study the effects of various anti-proliferative drugs on cell cycle can provide a rapid, safe and inexpensive method for selection of drugs used for management of PVR.

A comparative study of effects of antiproliferative drugs on human retinal pigment epithelial cells in vitro

The effects of various antiproliferative drugs have been tested in numerous cell types in vitro, but a comparison of effects of these drugs on cultured human retinal pigment epithelium (RPE) has not been reported. We studied the effects of four most widely used antiproliferative drugs (5-FU, daunomycin, mitomycin and dexamethasone) in a new in vitro model system (cultured human RPE). Various concentrations and exposure periods were tested in four human RPE cell lines. 5-FU showed a dose-dependant growth inhibition, with an ID50 of 5.35 +/- 2.38 x 10(-7) M after 4 days culture. A decrease of cell number occurred relatively later, the slope of the dose-response curve was less steep than that of others. Mitomycin C showed an immediate and strong growth inhibition and cytotoxic effects, with an ID50 of 3.73 +/- 0.71 X 10(-9) M. RPE cultured with daunomycin showed an abrupt decrease of cell number from 10(-9) M to 10(-8) M, the ID50 value was 1.07 +/- 0.23 x 10(-8) M. Dexamethasone showed a biphasic effect; it stimulated cell growth at 10(-7) to 10-6 M and inhibited cell growth at 10(-4) M or higher, with an ID50 of 6.05 +/- 1.61 x 10(-3) M. The advantages and disadvantages of these drugs and the prospective clinical application of these drugs for management of proliferative vitreoretinopathy (PVR) were discussed. Development of an in vitro model using cultured human RPE to study the effects of various antiproliferative drugs can provide a rapid, safe and inexpensive method for selection of drugs used for management of proliferative vitreoretinopathy.

Targeted gene transfer to corneal stroma in vivo by electric pulses

This study was conducted to develop a method of targeted gene transfer by electric pulses to a selected area of corneal stroma in vivo. Plasmid DNA with a green fluorescent protein (GFP) gene under a cytomegalovirus promoter was injected through the corneal pocket into the corneal stroma of the adult Brown Norway rat, and various intensities of electric pulses ranging from 10 to 30 V were delivered to the corneal epithelial side with an electric probe. Direct stereomicroscopy of the fluorescent using real-time imaging was used to determine in vivo gene expression on days 1, 2, 4, 6, 8, 10, 15, and 20 after gene transfer. Transgene expression was detected in the corneal stroma as early as day 1 and until day 15. The most intense expression was noted on days 4 and 6. Gene transfer was most effective using eight electric pulses of 20 V for 50 msec. Histologic study disclosed GFP expression in keratocytes within the targeted area. There was no apparent cell damage in the gene transferred cells. No apparent inflammation was found in the anterior chamber or trabecular cells when electric pulses less than 30 V were used. In summary, the present technique transferred the gene of interest to a highly selected area of corneal stroma with no apparent damage. This method will likely be useful not only for developing gene therapy for corneal diseases but also for corneal research in general.

Mechanism of growth inhibitory effect of Mitomycin-C on cultured human retinal pigment epithelial cells: apoptosis and cell cycle arrest

PURPOSE

To investigate the therapeutic potential of Mitomycin-C (MMC) in the management of proliferative vitreoretinopathy, the antiproliferative effect of MMC on cultured human retinal pigment epithelial (RPE) cells were investigated in vitro.

METHODS

Drug sensitivities of cultured human RPE cells to MMC were determined using the tetrazolium dye assay. In order to detect the presence of apoptosis, DNA fragmentation was assessed by DAPI staining, and TdT-dUTP nick-end labeling (TUNEL) assay. The relative amount of DNA fragmentation was quantified by flow cytometric analysis. To analyze the cell cycle response of RPE cells to MMC, flow cytometric analysis of propidium iodide stained nuclei was performed. The levels of proteins related to DNA damage in the RPE cells were then determined by Western blot analysis.

RESULTS

MMC inhibited cell proliferation in a dose-dependent manner. The majority of RPE cells following treatment with 10 microg/ml of MMC exhibited fragmented nuclei as observed by DAPI staining and TUNEL assay. Cell cycle analysis demonstrated an accumulation of cells arrested in S and G2/M phase following treatment with 1 microg/ml of MMC. At 10 microg/ml of MMC, a dramatic increase of the cell population in the sub G1 peak, which can be considered a marker of cell death by apoptosis, was observed by flow cytometry. Western blot analysis of p53 and p21 revealed a gradual increase in the level of these proteins when RPE cells were exposed to increasing concentrations of MMC.

CONCLUSIONS

This study demonstrated that the response of RPE cells to MMC was bi-directional: 1) partial arrest of the cell cycle at S, G2/M phase, and 2) induction of apoptotic cell death.

The comparative benefits of glaucoma filtering surgery with an electric-pulse targeted drug delivery system demonstrated in an animal model

PURPOSE

To evaluate the safety and effectiveness of glaucoma filtering surgery performed with the adjunctive use of bleomycin administered in conjunction with electric pulses (EP).

DESIGN

Experimental study in rabbits. CONTROLS AND METHODS: Trabeculectomies were performed on pigmented rabbits (2 to 2.5 kg) using the following adjunctive treatments: 5 microM of topical bleomycin and EP (5V, 50 msec, 8 pulses) (group A: B+E+, n=15); bleomycin but no EP (group B: B+E-, n=15); 5 ,uM mitomycin C (MMC) and EP (group C: M+E+, n= 10); MMC but no EP (group D: M+E-, n=10); EP alone (group E: E+, n=10); and no adjunctive treatment (group F: E-, negative control, n=10).

MAIN OUTCOME MEASURES

Intraocular pressure (IOP) was measured regularly for 60 days after the operation. Bleb formation and the condition of the conjunctiva, cornea, and retina were also regularly evaluated. Histologic studies were performed by light microscopy, and retinal functions were evaluated by electroretinography.

RESULTS

Postoperative IOP was significantly lower than the preoperative level in all the animals until day 7. However, in groups E and F (the negative control) it returned to the preoperative level after day 7, and in groups B, C, and D after 15 days. The IOP of group A remained lower even on day 40. The average amount IOP was lowered or increased on day 20 was -6.4 mmHg (P < 0.05) in group A; -0.2 mmHg in group B; +1.2 mmHg in group C; and -3.25 mmHg in group D. The survival rate of the filtering blebs on day 20 was significantly higher in group A than in the other groups. Clinical and histologic studies uncovered no pathologic findings in any intra- or paraocular tissues. Electroretinographic evaluation of retinal function in group A showed no apparent change over the 60 days of the study.

CONCLUSION

Glaucoma filtering surgery in rabbits with the adjunctive use of bleomycin in conjunction with EP significantly lowered IOP for up to 40 days without clinically, morphologically, or functionally harming intraocular tissues.

Synergistic effect of electric pulses and bleomycin on cultured rabbit subconjunctival fibroblasts

BACKGROUND

The combined effect of electric pulses (EP) and antiproliferative agents on the proliferation of rabbit Tenon's capsule fibroblasts was investigated.

METHODS

Rabbit Tenon's capsule fibroblasts were cultured. Some of these cells were exposed to various intensities of EP alone (500-2500 V/cm). Other cells were then exposed for 30 min to an antiproliferative agent: bleomycin (BLM; 0.0005-50 mumol/l), mitomycin C (MMC; 0.0005-50 mumol/l), 5-fluorouracil (5-FU; 0.05-5000 mumol/l), or streptomycin (SM; 0.0005-50 mumol/l) with or without EP (2000 V/cm, 99 mus, eight pulses). Cell proliferation was assessed by cell counting on day 3 and by a 3H-thymidine uptake assay. DNA fragmentation was assessed by flow-cytometric analysis and agarose gel electrophoresis.

RESULTS

A significant reduction in the cell number was observed only at 2500 V/cm (P < 0.05). BLM, MMC and 5-FU treatment inhibited cell proliferation in a dose-dependent manner either with or without EP (ID50: BLM alone, 0.029 mumol/l; BLM and EP, 0.00022 mumol/l; MMC alone, 41.6 mumol/l; MMC and EP, 27.5 mumol/l; 5-FU alone, 1045 mumol/l; 5-FU and EP, 690.2 mumol/l; P < 0.05). EP treatment induced an inhibitory effect of BLM on cell proliferation which was 100 times more prominent than BLM alone (0.0005 mumol/l of BLM alone 103.4 +/- 4.4%, 0.0005 mumol/l of BLM and EP 26.0 +/- 4.4%; P = 0.021). BLM treatment with EP also augmented the apoptotic-like DNA fragmentation in both a flow-cytometric DNA histogram and agarose gel-electrophoresis.

CONCLUSION

EP treatment enhanced the inhibitory effect of BLM on the cell proliferation of Tenon's capsule fibroblasts of rabbits. The combination of electric pulses and antiproliferative drug treatments may therefore reduce the necessary dose of antiproliferative agents in filtering surgery.