Membrane damaging effects

Elevated cytoplasmic calcium activates a variety of enzymes with membrane damaging effects. The major enzymes that are involved in activation by calcium include... 

These in vitro cytotoxicity studies are not indicative of in vivo toxicity but rather provide a method to classify the CDs for their potential to destabilize or disrupt cellular membranes. In fact, when whole blood is used instead of erythrocytes for the hemolysis tests, the cytotoxicity of the CDs is diminished 10-fold by the presence of hydrophobic serum components. Thus, the membrane damaging effects of the CDs are observed in vivo only under situations of high concentrations. 

Their biological activity is based on their interaction with membrane phospholipids [8, 9] resulting in increased excretion of glutamate and in enhanced uptake of various substances through stomata. Besides the membrane damaging effect tensides influence markedly the activity of enzymes [10] and enhance the biological activity of insecticides [11] by improving their solubility. 

Cyclodextrins Lessen the Membrane Damaging Effect of Nonionic Tensides... 

Abstract. Nonylphenyl-ethyleneoxide polymers containing 5, 9 and 30 ethyleneoxide groups per molecule build into the hydrophobic fatty acid chains of the cell membrane phospholipid dipalmitoyl-phosphatidyl-choline (DPPC) resulting in a decreased main transition temperature, a decreased enthalpy of the main transition and in enhanced potassium permeability of DPPC liposomes. The a-, jl- and y-cyclodextrins form inclusion complexes with the tenzides lowering their free concentration. The complex formation lessens or sometimes totally prevents the membrane damaging effect of tensides. The effectivity order of cyclodextrins is CD > yCD > aCD. 

Under such conditions in aqueous solutions, the majority of the tenside molecules are in the complexed form. The membrane damaging effect of free tenside at reduced concentration is of course lower. 

Our data do not exclude the possibility that the cyclodextrin-tenside complexes may interact with the DPPC. However, the facts that the cyclodextrins do not show any membrane damaging effect and the tenside-cyclodextrin complex is highly hydrophilic and has considerable dimensions contradict this supposition. 

Szogyi, M., T. Cserhati and J. Szejtli - Cyclodextrins lessen the membrane damaging effect of nonionic tensides 325... 

Our studies are based on the assumption that the in vitro cell membrane-damaging effect of skin-toxic chemicals (Marks and Kingston, 1985) is a crucial event for eye irritation in rabbits, too. 

Elevated cytoplasmic calcium activates a variety of enz3unes, with membrane-damaging effects. The major enz)unes that are involved in activation by calcium include ATPases, phospholipases, proteases, and endonucleases. Thus, increased calcium causes increased mitochondrial permeability and induction of apoptosis and necrosis. Calcium is required for maintenance and fxmction of the cytoskeleton as well (Dahm and Jones, 1996 Delgado-Coello et al., 2006). 

To investigate the safety of thiolated chitosans, several studies have been performed measuring its potential cytotoxicity on various cell lines. The toxicity profiles of chitosan-TBA, for example, were assessed using the red blood cell lysis test. The results showed that thiolated chitosan had a lower membrane damaging effect than the corresponding unmodified control. The safety of thiolated chitosan was further confirmed by metabolic activity (cleavage of dimethyl-thiazolyl-diphenyltetrazo-lium bromide) (MTT) and DNA synthesis (incorporation of 5-bromo-2 -deoxyur-idine [BrdU]) assay on L-929 mouse fibroblast cells. It was found that the toxicity of chitosan-TBA was concentration-dependent [63]. Another thiolated chitosan investigated for cytotoxicity was chitosan-MBA, which was found to be nontoxic because Caco-2 cell viability was around 100% after 4 and 24 h of incubation [25]. 

Chlorine is desirable as a bulk pretreatment biocide for inlet water, but its subsequent removal upstream of the membrane is absolutely necessary ana difficult. NaHSO,3 is a common additive to dechlorinate before membranes. It is customarily added at 3-5 mg/1, an excess over the stoichiometric requirement. NH3 is sometimes added to convert the chlorine to chloramine, a much less damaging biocide. Heavy metals present in seawater seem to amplify the damaging effects of chlorine and other oxidants. 

Kamat, J.P., Boloor, K.K., and Devasagayam, P.A., ChlorophyUin as an effective antioxidant against membrane damage in vitro and ex vivo, Biochim. Biophys. Acta, 1487, 113, 2000. 

Bohm et al. (1995) have studied the protective effect of 3-CAR and LYC against cell membrane damage by N02 showing that LYC is more than twice as effective as 3-CAR. These authors observe two species from the reaction, both in the infrared, assigning them to the radical cation and a radical addition product. 

The cytotoxic and photocytotoxic effects of two water-soluble fullerene derivatives, a dendritic CL mono-adduct and the malonic acid CL tris-adduct were tested on Jurkat cells when irradiated with UVA or UVB light (Rancan et al., 2002). The cell death was mainly caused by membrane damage and it was UV dose-dependent. Tris-malonic acid fullerene was found to be more phototoxic than the dendritic derivative. This result is in contrast to the singlet oxygen quantum yields determined for the two compounds. 

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