Hemolysis of erythrocytes and fluorescence polarization changes elicited by peptide toxins, aliphatic alcohols, related glycols and benzylidene derivatives

Safety Assessment of Alkyl Benzoates as Used in Cosmetics

The functions of alkyl benzoates in cosmetics include fragrance ingredients, skin-conditioning agents—emollient, skin-conditioning agents—miscellaneous, preservatives, solvents, and plasticizers. The Cosmetic Ingredient Review Expert Panel reviewed the relevant animal and human data and noted gaps in the available safety data for some of the alkyl benzoates. Similar structure activity relationships, biologic functions, and cosmetic product usage allowed the available data of many of the alkyl benzoates to be extended to the entire group. Carcinogenicity data were not available, but available data indicated that these alkyl benzoate cosmetic ingredients are not genotoxic. Also benzoic acid and tested component alcohols were not reproductive or developmental toxicants, are not genotoxic in almost all assays, and are not carcinogenic. These ingredients were determined to be safe in the present practices of use and concentration.

Safety Assessment of 1,2-Glycols as Used in Cosmetics

Caprylyl glycol and related 1,2-glycols are used mostly as skin and hair conditioning agents and viscosity agents in cosmetic products, and caprylyl glycol and pentylene glycol also function as cosmetic preservatives. The Cosmetic Ingredient Review (CIR) Expert Panel noted that, while these ingredients are dermally absorbed, modeling data predicted decreased skin penetration of longer chain 1,2-glycols. Because the negative oral toxicity data on shorter chain 1,2-glycols and genotoxicity data support the safety of the 1,2-glycols reviewed in this safety assessment, the Panel concluded that these ingredients are safe in the present practices of use and concentration described in this safety assessment.

Chlorodinitrobenzene-mediated damage in the human erythrocyte membrane leads to haemolysis

1-chloro-2,4-dinitrobenzene (CDNB), an intracellular glutathione-depleting agent, has been shown to have an adverse effect on erythrocyte membrane integrity. In the current study, we have demonstrated that CDNB caused haemolysis of human red blood cells (RBC) at higher concentrations (>or= 5 mM). The haemolysis induced by CDNB was preceded by the leakage of K(+) from the cells suggesting the colloid-osmotic nature of this lysis. The inclusion of molecules of increasing size in the extracellular media inhibited both the rate and extent of haemolysis thus supporting the proposal of CDNB-induced pore formation. The size of membrane lesions increased with an increase in the concentration of CDNB. SDS-PAGE demonstrated that CDNB causes the polymerisation and/or fragmentation of membrane proteins. Although CDNB has been shown to cause a drastic reduction in membrane thiols, our data suggest that the CDNB-induced formation of membrane disulfide bonds as a prima facie cause of permeability enhancement is unlikely.

Modulation of the susceptibility of human erythrocytes to snake venom myotoxic phospholipases A(2): role of negatively charged phospholipids as potential membrane binding sites

Cerrophidion (Bothrops) godmani myotoxins I (CGMT-I) and II (CGMT-II), Asp-49 and Lys-49 phospholipases A(2) (PLA2s), which drastically differ in enzymatic activity, were devoid of direct hemolytic effects on erythrocytes (RBC) from different species despite the fact that enzymatically active CGMT-I was able to hydrolyze RBC membrane phospholipids and disrupt liposomes prepared from RBC lipids. Human RBC did not become susceptible to the toxins after treatment with neuraminidase or after altering membrane fluidity with cholesterol or sublytic concentrations of detergent. Unlike normal RBC, significant hemolysis was induced by CGMT-II and another similar Lys-49 isoform, B. asper MT-II (BAMT-II), in RBC enriched with phosphatidylserine (PS). Hemolysis was greater in RBC preincubated with pyridyldithioethylamine (PDA), a potent inhibitor of aminophospholipid transport. RBC enriched with phosphatidic acid (PA) also became susceptible to the myotoxins but was unaffected by PDA. Cells enriched with phosphatidylcholine (PC) remained resistant to the action of the toxins. BAMT-II also induced damage in black lipid membranes prepared with PS but not PC alone. When RBC binding of BAMT-II was measured by enzyme-linked immunosorbent assay, it was observed that PS- and PA-enriched erythrocytes were always able to capture more toxin than normal and PC-enriched RBC. This effect was significantly improved by PDA (in the case of PS) and it was observed either in the presence or in the absence of calcium in the medium. These data suggest that negatively charged lipids in the outer leaflet of cell membranes constitute myotoxic PLA2 binding sites. The scarcity of anionic phospholipids in the outer leaflet of RBC could explain their resistance to the action of these PLA2s.

SMAP-29: a potent antibacterial and antifungal peptide from sheep leukocytes

SMAP-29 is a cathelicidin-derived peptide deduced from sheep myeloid mRNA. The C-terminally amidated form of this peptide was chemically synthesized and shown to exert a potent antimicrobial activity. Antibiotic-resistant clinical isolates highly susceptible to this peptide include MRSA and VREF isolates, that are a major worldwide problem, and mucoid Pseudomonas aeruginosa associated with chronic respiratory inflammation in CF patients. In addition, SMAP-29 is also active against fungi, including Cryptococcus neoformans isolated from immunocompromised patients. SMAP-29 causes significant morphological alterations of the bacterial surfaces, as shown by scanning electron microscopy, and is also hemolytic against human, but not sheep erythrocytes. Its potent antimicrobial activity suggests that this peptide is an excellent candidate as a lead compound for the development of novel antiinfective agents.

Accidental cell death and generation of reactive oxygen intermediates in human lymphocytes induced by thionins from Viscum album L

The cytotoxic mechanisms of thionins from Viscum album L., the viscotoxins, were investigated in human granulocytes and lymphocytes. The time course of viscotoxin effects indicate accidental cell death, i.e. membrane permeabilization, degradation of cytoplasm and chromatin, swelling of mitochondria with loss of their cristae, and generation of reactive oxygen intermediates within 1-2 h, followed by secondary apoptosis-associated events. The viscotoxin homologue purothionin from whole-wheat flour and viscotoxin B, however, did not induce cell death in cultured lymphocytes. Cytotoxicity of cationic and amphipathic viscotoxin was prevented only by cleavage of its disulphide bridges.

Mechanisms by which thionin induces susceptibility of S49 cell membranes to extracellular phospholipase A2

Whereas cells normally resist attack by PLA2, they become susceptible under certain pathological conditions. To ascertain the regulatory mechanisms that induce cellular susceptibility to PLA2, the effect of thionin on S49 cells was examined in the presence of PLA2. Thionin alone was unable to evoke hydrolysis of the lipid bilayer. Likewise, the addition of PLA2 alone caused production of only a minimal amount of free fatty acid. However, thionin and PLA2 together resulted in significant hydrolysis of the cell membrane. Thionin caused perturbation of the bilayer structure as suggested by the changes in the emission spectra of laurdan and the permeability of the membrane to propidium iodide. These changes correlated quantitatively with the susceptibility of the lipid bilayer to PLA2. Furthermore, thionin induced a modest increase in intracellular Ca2+. The source of this Ca2+ was the extracellular fluid since EDTA in the extracellular medium inhibited the Ca2+ influx. Moreover, cobalt chloride, a universal Ca2+ channel blocker, prevented the rise in intracellular Ca2+, the uptake of propidium iodide, and the susceptibility to PLA2 induced by thionin. In contrast, the changes in the laurdan emission caused by the thionin were not affected by the cobalt. Furthermore, incubation of the cells with the calcium ionophore A23187 also caused the cells to become susceptible to PLA2. We hypothesize that thionin causes S49 cell membranes to become susceptible to PLA2 by a Ca2+-dependent perturbation of the bilayer structure.

Interaction of Escherichia coli heat-stable enterotoxin B with cultured human intestinal epithelial cells

Binding of Escherichia coli heat-stable enterotoxin B (STb) to the human intestinal epithelial cell lines T84 and HT29 and to polarized T84 cells was studied to define the initial interaction of this peptide toxin with target cells. Equilibrium and competitive binding isotherms showed that 125I-STb bound specifically to T84 and HT29 cells; however, the toxin-epithelial cell interactions could be characterized by low-affinity binding (< or = 10(5) M(-1)) to a high number of binding sites (> or = 10(6) per cell). STb binding to T84 and HT29 cells as a function of 125I-STb concentration did not approach saturation at levels well above the effective biological concentration of STb for fluid secretion. Treatment of the 125I-STb-bound T84 and HT29 cells with an acidic saline solution to remove surface-bound toxin revealed that only approximately 55% +/- 10% of 125I-STb could be removed by this treatment at 4 degrees C, suggesting that approximately half of the bound STb was stably associated with the plasma membrane and/or internalized into the cytoplasm. Similar results were obtained when binding and internalization experiments were conducted at 22 and 37 degrees C. Immunofluorescence studies demonstrated that the strongest signal for STb appeared in the plasma membrane even after acid treatment. Toxin-treated cells also displayed diffuse cytoplasmic staining, indicating that once cell bound, STb did not appear to preferentially associate with membrane vesicles or cellular organelles. Binding and subsequent internalization of 125I-STb were not affected by treatment of the cells with trypsin, endoglycosidase F/peptide N-glycosidase F, Vibrio cholerae neuraminidase, tunicamycin, or 5 mM sodium chlorate, which blocks sulfation of surface proteoglycans. In addition, the internalization process was not altered by preincubation of the cells with the cytoskeleton inhibitors cytochalasin D and colchicine or cellular perturbants (i.e., 0.45 M sucrose and 5 mM sodium azide), indicating that cell surface proteins or carbohydrates did not function as STb receptors. The binding of 125I-STb to polarized T84 cells was also examined, and the total and nonspecific binding isotherms were found to overlap, indicating that the apical surface of polarized T84 cells did not contain a specific receptor for STb. In comparison to undifferentiated cells, twice the amount of bound STb (approximately 80% +/- 10%) was removable from polarized T84 cells after treatment with acidic solution. The percentage of surface-bound STb to polarized T84 cells did not vary significantly with the transepithelial electrical resistance of the cells or when STb was applied basolaterally. Together, our results indicate that STb binds with relatively low affinity to the plasma membrane of cultured intestinal epithelial cells and polarized T84 cells, probably to membrane lipids, and becomes stably associated with the lipid bilayer. The fact that a significant portion of the bound STb becomes free in the cytoplasm, even at a low temperature, suggests that the bound toxin may directly traverse the membrane bilayer.

Thionins: properties, possible biological roles and mechanisms of action

Thionins are low-molecular-weight proteins (M(r) ca. 5000) occurring in seeds, stems, roots and leaves of a number of plant species. The different members of this family of plant proteins show both sequence and structural homology, and are toxic to bacteria, fungi, yeasts and various naked cells in vitro. Toxicity requires an electrostatic interaction of the positively charged thionin with the negatively charged phospholipids making up the membrane, followed by either pore formation or a specific interaction with a certain lipid domain. This domain might be composed of phosphoinositides, which mediate transduction of environmental signals in eukaryotes. Their in vitro toxicity to plant pathogenic bacteria and fungi could reflect a direct role in plant defence, although, in view of the many divergent activities displayed by thionins both in vitro and in vivo, a biological role other than inhibition of microbial growth is equally plausible.

Enhancement of adenylate cyclase activity in S49 lymphoma cell membranes by the toxin thionin from Pyrularia pubera

We investigated the mode of action of Pyrularia thionin on adenylate cyclase in S49 lymphoma cell membranes. Thionin increased the forskolin-induced cAMP production in both wild-type and cyc- variant cell membranes. Thionin increased the apparent efficacy, but not potency, of the stimulation of adenylate cyclase by forskolin. Our results also indicated that the stimulatory G protein (Gs) was not involved in the action of thionin on adenylate cyclase; however, thionin appeared to reduce the effect of Gi on adenylate cyclase. We examined the effect of thionin on the temperature dependence of adenylate cyclase activity. The effect of thionin was not quantitatively the same at all temperatures. The effect was greatest in the range of about 30 degrees C to 50 degrees C. In addition, cardiotoxin, a structurally distinct peptide that alters the properties of biological membranes similarly to thionin, also enhanced the activity of adenylate cyclase. It seems reasonable to suspect that thionin influences the activity of adenylate cyclase indirectly by acting on the membrane.

Effect of small doses of ethylene glycol monomethyl ether on the acetylcholinesterase and delta-aminolevulinic acid dehydratase activity in erythrocytes, blood and bone marrow of rats

The effect of small doses of ethylene glycol monomethyl ether (EGMME) on the activity of acetylcholinesterase (ACHE) in erythrocytes and whole blood as well as on the delta-aminolevulinic acid dehydratase (ALA-D) in blood and bone marrow was studied in Wistar rats. Significant reduction in the activity of both enzymes was noted three days after ip administration of 200 mg/kg b.w. EGMME whereas seven days later the activity of both enzymes returned to the control levels. Activity of ALA-D in blood appeared to be most sensitive to EGMME, and reacted even to the lowest dose, which did not significantly alter activity of ACHE or ALA-D in bone marrow. Haematological parameters in all treated groups remained unaltered.

Possible mechanisms of action of cobra snake venom cardiotoxins and bee venom melittin

Cobra snake venom cardiotoxins and bee venom melittin share a number of pharmacological properties in intact tissues including hemolysis, cytolysis, contractures of muscle, membrane depolarization and activation of tissue phospholipase C and, to a far lesser extent, an arachidonic acid-associated phospholipase A2. The toxins have also been demonstrated to open the Ca2+ release channel (ryanodine receptor) and alter the activity of the Ca(2+)+Mg(2+)-ATPase in isolated sarcoplasmic reticulum preparations derived from cardiac or skeletal muscle. However, a relationship of these actions in isolated organelles to contracture induction has not yet been established. The toxins also bind to and, in some cases, alter the function of a number of other proteins in disrupted tissues. The most difficult tasks in understanding the mechanism of action of these toxins have been dissociating the primary from secondary effects and distinguishing between effects that only occur in disrupted tissues and those that occur in intact tissue. The use of cardiotoxin and melittin fractions contaminated with trace ('undetectable') amounts of venom-derived phospholipases A2 has continued to be common practice, despite the problems associated with the synergism between the toxins and enzymes and the availability of methods to overcome this problem. With adequate precautions taken with regard to methodology and interpretation of results, the cobra venom cardiotoxins and bee venom melittin may prove to be useful probes of a number of cell processes, including lipid metabolism and Ca2+ regulation in skeletal and cardiac muscle.

Binding properties of Pyrularia thionin and Naja naja kaouthia cardiotoxin to human and animal erythrocytes and to murine P388 cells

Pyrularia thionin and snake venom cardiotoxin are strongly basic peptides which induce hemolysis, depolarization of muscle cells and activation of endogenous phospholipase A2. An earlier study of the hemolysis reaction indicated that the two peptides bind to and compete for the same site on human erythrocytes. A recent study examined the hemolysis induced by both peptides as the phosphate and Ca2+ content of the reaction mixture was varied. The results of the recent study (VERNON, L. P. and ROGERS, A., Toxicon 30, 701-709) agree with this companion study on the binding of 125I-labeled pyrularia thionin and cardiotoxin to erythrocytes under the same conditions. Added phosphate ion at 5 mM and removal of membrane-bound Ca2+ by treatment with 10 mM EGTA make more binding sites of the same affinity available to both peptides, which are shown to bind in a competitive fashion to the same site. Addition of 10 mM Ca2+ to the medium decreases peptide binding due to competitive binding of Ca2+ to the same site on the membrane. For human erythrocytes the number of binding sites/cell for the thionin ranged from 0.7 to 1.7 x 10(5) and for cardiotoxin from 0.82 to 1.6 x 10(5). The calculated dissociation constants (Kd) from the Scatchard plots ranged from 0.43 to 1.1 microM for the thionin and from 0.40 to 0.98 microM for the cardiotoxin. The binding sites for thionin and cardiotoxin with sheep erythrocytes were 1.7 and 2.0 x 10(4) sites/cell, respectively, and both cow and horse erythrocytes demonstrated 2.7 x 10(4) sites/cell for the thionin. Binding studies with murine P388 cells showed 7.0 and 9.5 x 10(6) sites per cell for Pyrularia thionin and cardiotoxin, respectively.

Effect of calcium and phosphate ions on hemolysis induced by Pyrularia thionin and Naja naja kaouthia cardiotoxin

Pyrularia thionin is a strongly basic bioactive peptide of 47 amino acids isolated from nuts of Pyrularia pubera. It is hemolytic, cytotoxic and activates an endogenous phospholipase A2 in 3T3 cells. Earlier studies have shown that the cardiotoxin from Naja naja kaouthia has similar activities and binds to the same site as Pyrularia thionin. Since the peptides appear to bind to the phospholipids of cell membranes to elicit their cellular responses, the effect of modifying the electrostatic environment was studied by separately adding phosphate ion and Ca2+, and by removing Ca2+ from the membrane by treatment with EGTA. Analysis of erythrocyte hemolysis for both Pyrularia thionin and cardiotoxin shows that the reactions follow Michaelis-Menten kinetics, with the peptides serving as the substrate. The basal rate of hemolysis in physiological saline is markedly increased by the addition of phosphate in the 5-10 mM range and also by removing membrane-bound Ca2+ by incubation of the cells with 10 mM EGTA. These treatments do not change the apparent K(m) values, but increase the V(max), indicating that more binding sites are made available by these treatments. On the other hand, added Ca2+ in the 5-10 mM range competitively inhibits the reaction by inhibiting the binding of the peptide to the membrane.

Membrane structure, toxins and phospholipase A2 activity

The phospholipid-hydrolyzing enzyme phospholipase A2 (PLA2) (EC 3.1.1.4) exists in several forms which can be located in the cytosol or on cellular membranes. We review briefly cellular regulatory mechanisms involving covalent modification by protein kinase C and the action of Ca2+, cytokines, G proteins and other cellular proteins. The major focus is the role of phospholipid structure on PLA2 activity, including (1) the mechanism of PLA2 action on synthetic phospholipid bilayers, (2) perturbation of synthetic and cellular membranes with lipophilic agents and membrane-interactive peptides and (3) the ability of these agents to activate endogenous PLA2 activity, with emphasis on the venom and plant toxins melittin, cardiotoxin and Pyrularia thionein.