• Toxicological Research
• /
• 제16권4호
• /
• pp.311-315
• /
• 2000

Previous studies showed that benzoquinone derivatives inhibited platelet aggregation. but there is no information available on their cytotoxicity to platelets. 1n the present study. washed platelets isolated from rats were treated with 1.4-benzoquinone. a representative benzoquinone derivative. to examine its antiaggregating effect and cytotoxicity. 1.4-Benzoquinone significantly inhibited thrombin-induced platelet aggregation. Consistent with this finding. 1.4-benzoquinone suppressed cytosolic calcium increase induced by thrombin. To examine the cytotoxicity by 1 A-benzoquinone in platelets. turbidometry and lactate dehydrogenase release were measured. Treatment with 1.4-benzoquinone resulted in slight cytotoxicity (30% release at 60 min) to platelets. However. the cytotoxicity was not correlated with increase of cytosolic calcium levels in platelets. All these data suggested that 1.4-benzoquinone inhibited thrombin-induced platelet aggregation mediated by inhibition elf calcium level increase and that 1.4-benzoquinone reveals cytotoxicity to some extent without alteration of calcium level in platelets.

• Maxillofacial Plastic and Reconstructive Surgery
• /
• 제27권1호
• /
• pp.24-31
• /
• 2005

Recently, Platelet rich plasma(PRP) is commonly used because it is now well known that platelets have many functions beyond that of simple hemostasis in aspect of containing autogenous source of several growth factors. It could be responsible for increasing cell mitosis, increasing collagen production, recruiting other cells to the site of injury, initiating vascular ingrowth, and inducing cell differentiation, enhancing bone formation capacity and easily handling to clinician. However, in spite of these clinical advantages, still the theory behind the use of PRP is compelling. This study was to determine preparation techniques used to increase the concentration of platelets and growth factors are all crucial steps in early wound healing of bone graft which may lead to a more rapid and denser bone regenerate. 200 volunteers were sampled and PRP were prepared according to each evaluation item in this study. Higher concentration of platelets have been gained in double centrifugation. 2000 and 2500 rpm showed proper concentration of platelets at first centrifugation and 5000 rpm in second. Timing for 2 minutes was showed good concentration of platelets in high and low centrifugation speed. It was better concentration of platelets in 20 or 30 ml volume during centrifugation. In histomorphologic findings, degrnulated and high concentraion of platelets were found in low centrifugation speed.

• Toxicological Research
• /
• 제11권2호
• /
• pp.303-308
• /
• 1995

Nitric oxide, a physiological transmitter, is reported to mediate cellular injury in various tissues. Its reactivity to free radical is believed to be one of the reasons for its involvement in cytotoxicity. Menadione, a representative quinone, is cytotoxic to several cell systems including isolated hepatocyte, endothelial cell and red blood cells. Its toxic mechanism is related to oxidative stress, mediated by toxic free radicals. Our previous studies demonstrated that menadione induced cell lysis and increase of oxygen consumption in platelets. It has been reported that platelets have nitric oxide producing enzyme, nitric oxide synthase. Thus, we have investigated to manifest the role of nitric oxide.in menadione-induced cytotoxicity in rat platelets. Menadione induced cytotoxicity in platelets was unaffected by $N^G$-nitro-arginine methyl ester (L-NAME), selective and competitive inhibitor of nitric oxide synthase. We also invesitgated the role of extracellular nitric oxide in menadione-induced cytotoxicity of platelets by addition with sodium nitroprusside (SNP). SNP did not affect platelet cytotoxicity by menadione. These results suggested that nitric oxide which was generated endogeneously or exogeneously might have a negligible role in menadione-induced cytotoxicity in rat platelets.

• Archives of Pharmacal Research
• /
• 제19권1호
• /
• pp.12-17
• /
• 1996

Our previous studies demonstrate that menadione (MEN) is cytotoxic to platelets of rats by depleting glutathione (GSH). In order to clarify whether GSH has a role in protecting against menadione-induced cytotoxicity, the effect of GSH depletors as well as GSH precusors on menadione-induced cytotoxicity was investigated. Cysteine and dithiothreitol (DTT) prevent MEN-induced cytotoxicity in a dose-dependent manner, as determined by LDH leakage and change in turbidity. When platelets were treated with 1-chloro-2,4-dinitrobenzene (CDNB) and diethylmaleate (DEM), both of which deplete intracellular GSH, MEN-induced cytotoxicity was potentiated in the CDNB-treated paltelets, but not in the DEM-treated platelets. These data suggest that the GSH in platelets plays an important role in protecting against cytotoxicity induced by menadione.

• Steel and Composite Structures
• /
• 제32권6호
• /
• pp.821-832
• /
• 2019

An analysis on thermal buckling and postbuckling of composite laminated plates reinforced with a low amount of graphene platelets is performed in the current investigation. It is assumed that graphaene platelets are randomly oriented and uniformly dispersed in each layer of the composite media. Elastic properties of the nanocomposite media are obtained by means of the modified Halpin-Tsai approach which takes into account the size effects of the graphene reinforcements. By means of the von $K{\acute{a}}rm{\acute{a}}n$ type of geometrical nonlinearity, third order shear deformation theory and nonuniform rational B-spline (NURBS) based isogeometric finite element method, the governing equations for the thermal postbuckling of nanocomposite plates in rectangular shape are established. These equations are solved by means of a direct displacement control strategy. Numerical examples are given to study the effects of boundary conditions, weight fraction of graphene platelets and distribution pattern of graphene platelets. It is shown that, with introduction of a small amount of graphene platelets into the matrix of the composite media, the critical buckling temperature of the plate may be enhanced and thermal postbuckling deflection may be alleviated.

• Toxicological Research
• /
• 제11권2호
• /
• pp.295-302
• /
• 1995

Menadione-ghitathione conjugate (MEN-SG), a metabolite of menadione, is known to be a redoxcycler in rat hepatocyte subcellular fraction. Therefore, it was assumed that MEN-SG could exert cytotoxlclty to ral platelets, another target tissue of menadione. We first synthesized MEN-SG, the identity of which was verified by mass, $^1{H}$-NMR and UV-visible spectra. In addition, the stability of MEN-SG was investigated in biological assay system. MEN-SG was degraded in a time-dependent manner in DMSO which had been used as a vehicle and thus, tris-HCl buffer was used as a vehicle of MEN-SG despite the low solubility in it. Perchloric acid as well as platelets itself did not affect the stability of MEN-SG. Our next attempt was the evaluation of cytotoxicity of MEN-SG in rat platelets. MEN-SG did not induce cytotoxicity to rat platelets measured by two different methods, LDH release and turbidity changes. The extents of oxygen consumption by MEN-SG in intact platelets were significantly lower than those by menadione, though it had been observed that oxygen consumptions by menadione and MENSG were similar in subcellular fractioas of platelets. These results suggest that MEN-SG is not toxic to rat platelets despite its redox cycling capacity and glutathione conjugation reaction of menadione could be regarded as a detoxification process.

• Toxicological Research
• /
• 제13권3호
• /
• pp.229-235
• /
• 1997

The elevation of intracellular calcium in various tissues due to oxidative stress induced by either menadione or adriamycin has been well documented. The increase of calcium level in platelets results in aggregation of platelets. To test the hypothesis that chemically induced calcium elevations can play a role in platelet aggregation, we have studied the effects of menadione and adriamycin on aggregation of platelets isolated from female rats. Treatment with menadione and adriamycin to platelet rich plasma (PRP) appeared to induce platelet aggregations up to 60%, as determined by aggregometry. However, exposure of PRP to rnenadione or adriamycin led to a loss of viability, as measured by lactate dehydrogenase (LDH) leakage. Morphological studies of platelets revealed that, when PRP was treated with menadione, aggregates of platelets were not observed and the numbers of platelets were decreased significantly. This suggests that menadione and adriamycin decreased turbidity by inducing platelet lysis rather than platelet aggregation. These cellular toxicities induced by menadione or adriamycin was not correlated with oxygen consumption rate but with depletion of protein thiols, suggesting that protein thiols might play an important role in chemical-induced platelet toxicity.

• Archives of Plastic Surgery
• /
• 제36권1호
• /
• pp.19-23
• /
• 2009

Purpose: Platelet transplantation is a novel therapeutic strategy for acceleration of wound healing. When applying platelets, efficacy of adding thrombin to stimulate growth factor release from platelets has already been proved. However, no quantitative data of the thrombin treatment has been reported. The purpose of this study was to determine the optimal thrombin concentration to maximize growth factor release of platelets. In particular, this study was designed to quantify levels of platelet derived growth factor(PDGF)-BB, which is a major growth factor contained in the platelets, in vitro. Methods: Fresh platelets were obtained from a blood bank. They were suspended in DMEM/F - 12 and incubated with thrombin of various concentrations. The concentrations of thrombin tested were 0, 6.25, 12.5, 25, 50, 100, 200, and 400 IU/ml. After 30 minutes, 1, 3, 5, and 7 days, the levels of PDGF - BB were measured using enzyme linked immunosorbent assay. Platelets from four donors were included in this study. Each sample was tested in triplicate and the mean value was used as a data for each sample. Results: The addition of thrombin increased the level of PDGF - BB. Increases in storage time of platelets resulted in decreased levels of PDGF - BB. Higher levels of PDGF were detected in consort with increased thrombin concentrations. However, there was no significant difference between samples of 200 and 400 IU/ml concentrations. Conclusion: The results indicate that adding thrombin accelerates the release of growth factors from platelets and the optimal thrombin concentration to maximize this function is 200 IU/ml.

• 약학회지
• /
• 제41권6호
• /
• pp.749-755
• /
• 1997

It has been reported that dose-dependent $Ca^{2+}$ increase by menadione in platelets could be measured by fluorescent dye, quin-2. The problems will be described here rel ating to measuring $Ca^{2+}$ in menadione-exposed platelets using fura-2 and fluo-3, widely used fluorescent indicators. Additions of menadione to fura-2 loaded platelets and their lysates resulted in marked reduction in fluorescence intensity at both 340nm ($Ca^{2+}$-unbound form) 380nm ($Ca^{2+}$-undbound form) excitation wavelengths. Fura-2 excitation spectra were overlapped with UV-visible absorption spectra of menadione, suggesting that light absorption by menadione itself could quench fluorescence generated by fura-2. Next approach was to use fluo-3 which has the higher wavelength (490nm) of excitation. Previous work demonstrated that treatment with probenecid to platelets was required to prevent fluo-3 dye leakage. However, probenecid itself was proven to be inadequate to measure the concentration of intracellular $Ca^{2+}$; by reducing menadione-induced cytotoxicity in platelets. Our results suggest that it is not feasible to measure $Ca^{2+}$ in platelets by using fura-2 and fluo-3 in the presence of probenecid, and cautions should be taken to measure changes of intracellular $Ca^{2+}$ levels by fluorescent dyes following chemical exposure.

• Steel and Composite Structures
• /
• 제38권3호
• /
• pp.337-353
• /
• 2021

Micro-electro-mechanical systems (MEMS) are widely employed in sensors, biomedical devices, optic sectors, and micro-accelerometers. New reinforcement materials such as carbon nanotubes as well as graphene platelets provide stiffer structures with controllable mechanical specifications by changing the graphene platelet features. This paper deals with buckling analyses of functionally graded graphene platelets micro plates with two piezoelectric layers subjected to external applied voltage. Governing equations are based on Kirchhoff plate theory assumptions beside the modified couple stress theory to incorporate the micro scale influences. A uniform temperature change and external electric field are regarded along the micro plate thickness. Moreover, an external in-plane mechanical load is uniformly distributed along the micro plate edges. The Hamilton's principle is employed to extract the governing equations. The material properties of each composite layer reinforced with graphene platelets of the considered micro plate are evaluated by the Halpin-Tsai micromechanical model. The governing equations are solved by the Navier's approach for the case of simply-supported boundary condition. The effects of the external applied voltage, the material length scale parameter, the thickness of the piezoelectric layers, the side, the length and the weight fraction of the graphene platelets as well as the graphene platelets distribution pattern on the critical buckling temperature change and on the critical buckling in-plane load are investigated. The outcomes illustrate the reduction of the thermal buckling strength independent of the graphene platelets distribution pattern while meanwhile the mechanical buckling strength is promoted. Furthermore, a negative voltage, -50 Volt, strengthens the micro plate stability against the thermal buckling occurrence about 9% while a positive voltage, 50 Volt, decreases the critical buckling load about 9% independent of the graphene platelet distribution pattern.