The induction of apoptosis is a common feature of the cytotoxic action of ether-linked glycerophospholipids in human leukemic cells

The ability of 2 recent ether-lipid derivatives, aza-phospholipids BN52205 and BN52211, to induce apoptosis in different leukemia cell lines was investigated using I-octadecyl-2-methyl-rac-glycero-3- phosphocholine (ET-18-OCH3) as a positive control. HL60, K562, Molt-4 and U937 cells were exposed for 24 hr to 20 microM of drug. The 2 aza-derivatives were as cytotoxic as ET-18-OCH3: BN52205 and BN52211 selectively induced apoptotic death in HL60, Molt-4 and U937 cells, but not in the K562-resistant cell line. Around 50% of DNA was fragmented in HL60 cells after exposure to the aza-derivatives, and 34% and 20% of DNA was fragmented in Molt-4 and U937 cells respectively. Similar results were obtained when cells were exposed to ET-18-OCH3. Our data confirm that ether lipids induce apoptosis in a variety of human leukemic cells, providing a possible explanation for their selectivity and mechanism of action.

Conformational polymorphism of the amyloidogenic and neurotoxic peptide homologous to residues 106-126 of the prion protein

Prion-related encephalopathies are characterized by cerebral accumulation of a post-translationally modified form of the cellular prion protein (PrPC), designated PrPSc. Evidence suggests that the conversion from PrPC to PrPSc involves changes in the secondary structure leading to an increase in beta-sheet content. We have previously shown that a synthetic peptide homologous to residues 106-126 of human PrP, belonging to a predicted alpha-helical domain, exhibits a beta-sheet conformation, forms amyloid-like fibrils, and is neurotoxic in vitro. The present study investigated how different chemicophysical conditions such as pH and ionic strength or a membrane-like environment influenced the secondary structure of this peptide. PrP 106-126 exhibited a predominantly beta-sheet structure in 200 mM phosphate buffer, pH 5.0, but a combination of beta-sheet and random coil structure in 200 mM phosphate buffer, pH 7.0, or in deionized water. The addition of trifluoroethanol (50% final concentration) to solutions of peptide in deionized water induced the appearance of an alpha-helical secondary structure, but did not modify the beta-sheet conformation of the peptide dissolved in 200 mM phosphate buffer, pH 5.0. In the presence of micelles formed by a 5% solution of sodium dodecyl sulfate, PrP 106-126 showed a high content of alpha-helix. When the peptide was dissolved in 5 mM phosphate buffer, pH 7.4, and incubated with liposomes, it changed from a prevalently random coil structure to a beta-sheet conformation. The environment-dependent conformational polymorphism of PrP 106-126 and its marked tendency to form stable beta-sheet structures at acidic pH could account for the shift from alpha-helix to beta-sheet associated with the conversion of PrPC to PrPSc, which occurs most likely in the endosomal-lysosomal compartment.

Analytical validity of electrochemical determination of lecithin for establishing foetal lung maturity in normal and complicated pregnancies

An electrochemical assay of lecithin for the prediction of foetal lung maturity in normal and complicated pregnancies has been analytically evaluated. The method is based on sequential enzymatic reactions causing the stoichiometric transformation of lecithin to hydrogen peroxide, which reacts with an organo-fluoro compound in the presence of peroxidase. The rupture of the C-F bond releases fluoride ions, that are detected by a selective electrode. The correlation between the lecithin concentration in amniotic fluid, measured electrochemically, and the fluorescence polarization (FP) value, chosen as reference method, was determined. Correlation studies were performed on rat amniotic fluids, on 67 samples from human normal pregnancies, and on seven samples from complicated pregnancies. The relationships between the FP value and the lecithin concentration were linear, and the correlation coefficients were 0.987 for rat and 0.884 for human amniotic fluids. Concordance was good for predicting foetal lung maturity in complicated pregnancies.

Protein kinase C is not involved in cholesterol-induced resistance to synthetic ether lipids

The possible role of protein kinase C in cholesterol-induced resistance to ether lipids was investigated. The enrichment of HL60 cells in cholesterol (CHOL) (HL60-CHOL) resulted in a significant increase in the ID50 values for 1-octadecyl-2-methyl-rac-glycero- 3-phosphocholine (ET-18-OMe) (3.75 +/- 0.7 microM and 6.69 +/- 0.5 microM for HL60 and HL60-CHOL, respectively). In the same conditions, HL60 and HL60-CHOL cells showed comparable levels of both cytosolic and membrane-associated protein kinase C activity. Phorbol ester (PMA) stimulation induced protein kinase C to translocate from the cytosol to the plasma membrane in both cell types and with similar kinetics (272 +/- 32% and 299 +/- 41% increase in HL60 and HL60-CHOL, respectively after 100 ng/ml PMA for 10 min). Pretreatment of the two cell types with 50 microM ET-18-OMe resulted in comparable levels of PKC inhibition after phorbol ester stimulation. These results suggested that alterations in plasma membrane lipid composition induced by CHOL do not result in major changes in protein kinase C activity. Thus, protein kinase C does not appear to be involved in cholesterol-induced resistant phenotype in HL60 cells.

Molecular characteristics of a protease-resistant, amyloidogenic and neurotoxic peptide homologous to residues 106-126 of the prion protein

In the prion-related encephalopathies the prion protein is converted to an altered form, known as PrPSc, that is partially resistant to protease digestion. This abnormal isoform accumulates in the brain and its protease-resistant core aggregates extracellularly into amyloid fibrils. We have investigated the conformational properties, aggregation behaviour and sensitivity to protease digestion of a synthetic peptide homologous to residues 106-126 of human PrP, which was previously found to form amyloid-like fibrils in vitro and displayed neurotoxic activity toward primary cultures of rat hippocampal neurons. A scrambled sequence of peptide PrP 106-126 was used as a control. By circular dichroism, PrP 106-126 exhibited a secondary structure composed largely of beta-sheet, whereas the scrambled sequence of PrP 106-126 showed a random coil structure. The beta-sheet content of PrP 106-126 was much higher in 200 mM phosphate buffer at pH 5.0 than in the same buffer at pH 7.0. Laser light scattering analysis showed that PrP 106-126 aggregated immediately after dissolution in 20 mM or 200 mM phosphate buffer, pH 5.0 and 7.0, whereas scrambled PrP 106-126 did not. PrP 106-126 aggregates had an average hydrodinamic diameter of 100 nm and an average molecular weight of 12 x 10(6) +/- 30% Daltons, corresponding to the aggregation of 6000 +/- 30% molecules. Peptide PrP 106-126 showed partial resistance to digestion with Proteinase K and Pronase, whereas scrambled PrP 106-126 was completely degraded by incubation with the enzymes at 37 degrees C for 30 minutes.

Effect of paf antagonists on the cytotoxic activity of antineoplastic ether phospholipids

The capability of the methoxy-substituted 1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine (ET-18-OCH3 or Edelfosine) and the two aza-alkylphospholipids BN 52205 and BN 52211 to bind to the PAF receptor was analysed in rabbit platelet membranes. Ether phospholipid concentrations were tested between 10(-5) M and 10(-11) M. The results indicate that ether phospholipids are not able to bind to the PAF receptor and do not prevent PAF binding to its receptor. Moreover, the cytotoxic effect of three potent PAF antagonists, BN 52021, BN 50730 and BN 50739, were analysed in HL60 promyelocytic cells. These cells were pre-and co-treated with PAF antagonists and ether phospholipids. The data show that the three PAF antagonists failed to counteract the activity of ET-18-OCH3, BN 52205 and BN 52211 thus demonstrating that the cytotoxic effect of these new anti-neoplastic drugs is not mediated by the PAF receptor.

The effect of culture medium composition on ether lipid cytotoxic activity

The effect of a serum-free medium (TNB-100), compared to RPMI 1640 containing 10% fetal bovine serum (FBS), on the lipid composition of HL60 and K562 leukemic cells was investigated. The 10% FBS RPMI medium contained approximately three times more phospholipids (PL), about three times more protein and eight times more cholesterol (CHOL) than did the TNB-100 medium. Cells cultured in TNB-100 medium, referred to as HL60-TNB and K562-TNB cells, were significantly lower in PL and CHOL than 10% FBS RPMI cells, with about a threefold higher PL-to-CHOL ratio; however, these cells were significantly higher in protein content. Cells grown in TNB-100 were also significantly more fluid than 10% FBS RPMI cells and were more sensitive to the fluidizing action of the ether lipid 1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine. The 50% inhibitory dose of the drug was about 50% lower in TNB-grown cells than in 10% FBS RPMI cells.

Induction of apoptosis in human leukemic cells by the ether lipid 1-octadecyl-2-methyl-rac-glycero-3-phosphocholine. A possible basis for its selective action

Ether-linked glycerophospholipids (ether lipids, EL) are membrane-interactive drugs selectively cytotoxic toward neoplastic cells compared with normal cells. No conclusive explanation has yet been provided for this selectivity. We now present data indicating that the drug 1-octadecyl-2-methyl-rac-glycero-3-phosphocholine (ET-18-OMe) induces apoptosis, or programmed cell death, in human leukemic cells. Apoptotic death is induced selectively by ET-18-OMe in HL60 cells, which are sensitive to the drug's cytotoxic action, but not in the resistant K562 cell line. Enrichment of HL60 cells with cholesterol (HL60-CHOL cells) significantly protects the cells from the cytotoxic effect and from the induction of apoptosis by ET-18-OMe; the percentage of fragmented DNA is only 17% for HL60-CHOL, compared with 50% in native HL60 cells after exposure to 20 microns ET-18-OMe for 24 hr. Our study provides a possible explanation for differences in sensitivity to EL among different cell types and illustrates an indirect interaction of EL with cellular DNA.

Fetal lung maturity evaluation with fluorescence polarization of the amniotic fluid

Fluorescence polarization of the amniotic fluid from 39 high risk pregnancies requiring preterm delivery was measured in order to assess the maturity of the fetal lung. The study population included 15 cases of intrauterine growth retardation, ten maternal hypertension, five maternal Hodgkin's disease, three placenta previa, two fetal malformation, two polyamnios, one untreated diabetes, one maternal nephropathy. All patients underwent a single amniocentesis before deciding whether to deliver a preterm baby and FP of the amniotic fluid was done within two hours from amniocentesis. In five cases this was > 0.311, the cut-off limit taken as an indicator of fetal pulmonary status, and three of these developed respiratory distress syndrome. In 34 cases FP values were < or = 0.311; in spite of the apparent lung maturity two of these newborns developed respiratory distress syndrome. On the basis of these results the FP sensitivity was calculated as 60%, specificity 94% and the overall accuracy 90%.

Membrane cholesterol content and sensitivity of human carcinoma-cells to antineoplastic ether phospholipids

Ether phospholipids represent a new class of anti-cancer drugs which appear to exert their tumoricidal activity through a direct and indirect cytotoxic effect against tumor cells of different origins. The chemotherapeutic interest in these new drugs is based on the finding that, contrary to the majority of anti-cancer drugs, ether phospholipids do not interfere with DNA synthesis, are anti-invasive and induce tumor cell differentiation. There is increasing experimental evidence that the direct cytotoxic effect of these new drugs is mediated by the cell membrane. We have measured the lipid membrane composition of three human carcinoma cell lines that have been found to possess different sensitivity to the tumoricidal activity of four antitumor ether phospholipids. A statistically significant difference has been found in the membrane cholesterol content of the three cell lines and a positive correlation has been established between the membrane cholesterol level and the carcinoma cell sensitivity to ether phospholipids. These findings emphasize previous data obtained with leukemic cells and reinforce the interest in ether phospholipids whose cytotoxic properties may represent a new step towards a more promising anti-cancer chemotherapy.

A novel pharmacological approach for paraquat poisoning in rat and A549 cell line using ambroxol, a lung surfactant synthesis inducer

Paraquat (PQ) is a widely used herbicide that causes acute adult respiratory distress syndrome (ARDS) and chronic lung damage (diffuse fibrosis). One of the earliest biochemical effects induced by PQ is damage to type II pneumocytes with consequent depletion of surfactant. With the aim of counteracting the toxic effects of PQ, a series of investigations were performed into the possible protective effect of the drug ambroxol, which induces the synthesis of surfactant in lung alveolar type II cells. The number of survivors and survival time of rats treated ip with 35 mg PQ/kg was significantly increased by 3 days of ambroxol pretreatment and by ambroxol treatment 30 min or 2 hr after PQ. Total phospholipid content in lung and bronchoalveolar lavage fluid (BALF) was significantly reduced 30 hr after treatment with PQ alone. The association of ambroxol with PQ significantly antagonized this reduction. In BALF the ratio between palmitic acid and stearic acid concentrations was significantly lower in animals treated with PQ alone but was returned to normal by the association with ambroxol. The cell line A549, exposed in vitro to PQ concentrations from 0.5 x 10(-4) to 2 x 10(-3) M, showed a significant dose-dependent loss of viability. Cells pretreated with ambroxol (10 mg/ml) were more resistant to PQ and their viability started to decrease significantly only from a PQ concentration of 0.8 x 10(-3) M. Membrane microviscosity was measured on the same cells. Cells treated with PQ alone showed a reduction of membrane microviscosity, which was significantly counteracted by ambroxol pretreatment. The curves of modification of membrane microviscosity of cells treated with PQ and with ambroxol plus PQ paralleled those of cell viability, indicating that the stimulation of surfactant synthesis in vitro may be a prerequisite for counteracting some of the early effects of PQ.

Total Urinary Hydroxyproline Determined with Rapid and Simple High-Performance Liquid Chromatography

A precolumn derivatization method was optimized for rapid and specific analysis of total urinary hydroxyproline by HPLC. After an overnight hydrolysis, urine samples dried and reconstituted with the internal standard cysteic acid (in sodium hydrogen carbonate, pH 9.3) were derivatized with N,N-diethyl-2,4-dinitro-5-fluoroaniline (FDNDEA) at 100 degrees C for 20 min. The DNDEA-hydroxyproline adduct was separated on an Ultrasphere ODS column with a mobile phase of acetate buffer (containing triethylamine, 6 mL/L, pH 4.3) and acetonitrile (80/20, by vol), and was detected at 360 nm. A single run took 18 min with a hydroxyproline retention time of 7.3 min. The assay showed a linear response to hydroxyproline concentrations from 5 to 100 mg/L with a detection limit of 0.8 ng injected, corresponding to 2 mg/L in urine. Mean (SD) analytical recovery was 94.2 (13)% and 104 (9)% at 10 and 50 mg/L, respectively. Within-run and between-run CVs (n = 10) were 3.74% and 4.33%, respectively, for 25 mg/L. Results for samples (n = 50) analyzed by HPLC (y) vs ion-exchange chromatography with postcolumn ninhydrin reaction (x) correlated well: y = 0.98x + 1.02 (r = 0.985, Sxy = 3.13). In another comparison, involving 173 samples, a colorimetric procedure (Hypronosticon, x) gave slightly higher values than the HPLC method (y): y = 0.83x + 2.21 (r = 0.937, Sxy = 4.6).

Total urinary hydroxyproline determined with rapid and simple high-performance liquid chromatography

A precolumn derivatization method was optimized for rapid and specific analysis of total urinary hydroxyproline by HPLC. After an overnight hydrolysis, urine samples dried and reconstituted with the internal standard cysteic acid (in sodium hydrogen carbonate, pH 9.3) were derivatized with N,N-diethyl-2,4-dinitro-5-fluoroaniline (FDNDEA) at 100 degrees C for 20 min. The DNDEA-hydroxyproline adduct was separated on an Ultrasphere ODS column with a mobile phase of acetate buffer (containing triethylamine, 6 mL/L, pH 4.3) and acetonitrile (80/20, by vol), and was detected at 360 nm. A single run took 18 min with a hydroxyproline retention time of 7.3 min. The assay showed a linear response to hydroxyproline concentrations from 5 to 100 mg/L with a detection limit of 0.8 ng injected, corresponding to 2 mg/L in urine. Mean (SD) analytical recovery was 94.2 (13)% and 104 (9)% at 10 and 50 mg/L, respectively. Within-run and between-run CVs (n = 10) were 3.74% and 4.33%, respectively, for 25 mg/L. Results for samples (n = 50) analyzed by HPLC (y) vs ion-exchange chromatography with postcolumn ninhydrin reaction (x) correlated well: y = 0.98x + 1.02 (r = 0.985, Sxy = 3.13). In another comparison, involving 173 samples, a colorimetric procedure (Hypronosticon, x) gave slightly higher values than the HPLC method (y): y = 0.83x + 2.21 (r = 0.937, Sxy = 4.6).

Modulation of ATPase activity by cholesterol and synthetic ether lipids in leukemic cells

Synthetic ether lipids (EL) exert their antiproliferative action on leukemic cells through localization in the plasma membrane with subsequent biochemical effects which are still being elucidated. In the present study, the modulation of membrane-linked ATPase activity was investigated in relation to changes in membrane fluidity of HL60 and K562 human leukemic cells. Incubation of HL60 and K562 cells with EL under non-cytotoxic conditions caused significant membrane fluidization which was related to the membrane cholesterol (CHOL) levels. HL60 cells, which are sensitive to the cytotoxic action of EL, had a lower basal CHOL content. When HL60 cells were loaded with CHOL, Na+, K(+)-ATPase activity was reduced significantly compared to that of untreated cells. In contrast, CHOL-deprived K562 cells had twice the Na+,K(+)-ATPase activity of unmodified K562 cells. Na+K(+)- and Mg(2+)-ATPase activities were stimulated significantly in both cell lines by EL at concentrations lower than 20 microM. This stimulation was greater in cells richer in CHOL, such as K562 cells and CHOL-enriched HL60 cells. In contrast, Na+,K(+)-ATPase in both cell lines was inhibited by EL above 20 microM regardless of the CHOL content. Mg(2+)-ATPase activity was not related to cell CHOL content and was not inhibited by EL above 20 microM.

Effect of tyrosine on the potentiation by aspartame and phenylalanine of metrazol-induced convulsions in rats

Male rats were treated by oral intubation with tyrosine (Tyr), at doses of 0.5 and 1.0 g/kg body weight, alone or together with 1 g aspartame (APM)/kg body weight, or an equivalent dose of phenylalanine (Phe; 0.5 g/kg body weight); the effects on seizures induced by an effective dose of metrazol (ED50) were observed. Tyr (0.5 g/kg body weight) had a protective effect against the Phe-potentiation of metrazol-induced clonic-tonic convulsions. At the same dose Tyr had no effect on the seizure-promoting activity of APM, but at 1 g/kg it reduced the proconvulsant potential of the sweetener. Analysis of the brain and plasma amino acid concentrations indicated that the Tyr to Phe ratio tended to be enhanced in Tyr-Phe treated rats compared with those treated with Phe alone. This ratio remained essentially constant in the brain of APM-treated rats, compared with those treated with APM plus 1 g Tyr/kg body weight, whereas an increase in this ratio in the plasma was observed. These results confirm that Tyr antagonizes the proconvulsant effect of Phe and APM and they further suggest that no simple relationship exists between the relative brain concentrations of the two amino acids and the response to metrazol convulsions.

Increased ether lipid cytotoxicity by reducing membrane cholesterol content

Ether-linked glycerophospholipids (ether lipids, EL) are selectively toxic and anti-proliferative agents against cancer cells in vitro. The reason for such selectivity is not completely clear. Their mechanism of action is mediated through an interaction with the plasma membrane and the membrane lipid composition may modulate it. As a continuation of previous reports, we now present data showing that cholesterol concentration modulates EL toxicity in the K562, U937 and MOLT4 leukemic cell lines in vitro. Cells become sensitive to otherwise ineffective doses of EL when their cholesterol content is lowered. Cell cholesterol levels were reduced by exposure to an egg lipid mixture (neutral glycerides, phosphatidylcholine and phosphatidylethanolamine, AL721). The data contribute to an understanding of the EL mechanism of action on membranes and suggest that the cellular cholesterol concentration must be considered a major factor in modulating the cytotoxic effects of EL.

Interspecies and interstrain studies on the increased susceptibility to metrazol-induced convulsions in animals given aspartame

The ability of aspartame (APM) to increase the susceptibility to metrazol-induced convulsions was studied in two strains of mice (CD1 and DBA/2J) and in guinea-pigs. Rats were included as known positive controls. Plasma and brain levels of phenylalanine (Phe) and tyrosine (Tyr) were measured in CD1 mice and guinea-pigs at various intervals after a dose of 1 g APM/kg body weight (administered orally to mice and ip to guinea-pigs). In mice, peak levels of Phe and Tyr were observed in plasma after 30 min and in brain after 60 min. In guinea-pigs peak plasma levels of Phe and Tyr occurred 30 min after treatment. Phe was at a maximum in guinea-pig brain after 30 min, while Tyr levels reached a peak at 120 min. In further experiments Phe and Tyr levels were measured 1 hr after APM doses of 0.5, 0.75 or 1 g/kg. In CD1 mice, plasma Phe and Tyr levels were increased significantly only at the highest dose, whereas in brain, Tyr concentrations were significantly increased by 0.75 or 1 g APM/kg and Phe was significantly increased by all three doses. In the guinea-pig, plasma Phe and Tyr were increased significantly only by 1 g APM/kg and in brain this dose significantly raised only the Phe levels. Monoamine and metabolite levels were determined in the brain striata of CD1 and DBA/2J mice 1 hr after the oral administration of 1 or 2 g APM/kg body weight; no differences from control values were found in either strain. The studies of potentiation of metrazol-induced convulsions showed that APM, at doses of up to 2 g/kg body weight, had no such effect in mice or guinea-pigs. In contrast, as expected, the potentiation was significant in the rat at 1 g/kg.

Serum amino acid analysis with pre-column derivatization: comparison of the o-phthaldialdehyde and N,N-diethyl-2,4-dinitro-5-fluoroaniline methods

We compared two pre-column derivatization methods, o-phthaldialdehyde (OPA) and N,N-diethyl-2,4-dinitro-5-fluoroaniline (FDNDEA), for analysis of serum amino acids by reversed-phase high-performance liquid chromatography. Separations took 102 and 106 min for FDNDEA and OPA (reconditioning included), respectively, allowing a very good resolution of 30 amino acids by the former process and 38 by the latter. Linearity, within- and between-day variability and advantages in terms of accuracy and speed were studied for both methods. Twenty serum samples from healthy volunteers were assayed with OPA, FDNDEA and with the reference method of ion-exchange and post-column ninhydrin reaction (amino acid analyser), which took 170 min. The correlation between OPA and ninhydrin was good for all the amino acids (r = 0.959) except for the last-eluting lysine. Good agreement was found for FDNDEA (r = 0.987), which appeared in general to be a highly reproducible technique. Both pre-column methods were more sensitive than the post-column ninhydrin method.

Determination of argininosuccinate lyase and arginase activities with an amino acid analyzer

The measurement of argininosuccinate lyase (ASase) and arginase, both in liver and erythrocytes, was developed by using a commercial amino acid analyzer. The method is based upon the use of two different substrates, argininosuccinate and arginine for ASase and arginase, respectively, and the measurement of only one final metabolite: ornithine. The use of ornithine as a marker of biological activity of ASase is related to the fact that in the urea cycle, the specific activity of arginase is much higher than that of ASase; thus, during in vitro determinations, arginine, which is the product of ASase, is rapidly converted to ornithine. The sensitivity of the methods is very high since we were able to detect both activities using very diluted rat liver homogenates (0.10 mg protein/ml) or few microliters of human blood. In rat liver the Vmax for ASase and arginase were respectively 0.54 and 140 mumol/h/mg protein; the apparent Km values 1.25 and 13.5 mM. In human erythrocytes the Vmax for the same enzymes were 7.2 and 170 nmol/h/mg Hb and the apparent Km values were 0.66 and 9.5 mM. In 10 healthy volunteers the specific activity of ASase and arginase determined in blood were respectively 8.60 +/- 0.46 and 124.1 +/- 14.5 nmol/h/mg Hb. The results obtained from 2 patients suffering from argininosuccinic aciduria were also reported. In these latter cases while ASase was not detectable in blood, arginase activity was at the lowest end of the confidence limits determined in healthy volunteers.

Fluorescence polarization changes with gestational age in amniotic fluid of rabbit and guinea pig

The variation of amniotic fluid microviscosity with gestational age was measured in rat, rabbit, and guinea pig. In rat, the changes followed the same pattern as known for women, microviscosity being high during early and mid-gestation and markedly lowering 12 h before delivery. Surprisingly, an opposite trend was observed in rabbit and guinea pig amniotic fluid. Moreover, the lecithin to sphingomyelin ratio markedly rose in late gestation in all species considered. Qualitative and quantitative analysis of lipids and phospholipids were performed in woman and rabbit amniotic fluids at early and late gestational ages. Among all the parameters measured, the most important differences that can influence the amniotic fluid microviscosity are the presence of very high levels of lysophosphatidylcholine both in early and late gestation in rabbit (much higher than in woman) and the cholesterol to total phospholipid ratio which decreased with gestational age in woman but remained stable in rabbit. The Arrhenius plot of the logarithm of microviscosity against the reciprocal of absolute temperature of mature and immature amniotic fluids from woman and rabbit was also determined. The temperature profiles confirmed the differences in lipid profile between woman and rabbit in early and late gestation which could be quantified on a physicochemical basis by determining the activation energy (delta E) at 25 degrees and 37 degrees C for each curve. This confirmed the opposite patterns in woman and rabbit and showed that amniotic fluid from the immature rabbit was the most fluid.

Role of cell cholesterol in modulating antineoplastic ether lipid uptake, membrane effects and cytotoxicity

Membrane-interactive ether lipids (EL) exert toxic and antiproliferative effects on cancer cells in vitro. They appear to be selectively more toxic to cancer cells than to normal cells and thus they are ideal candidates for bone-marrow purging procedures. However, no conclusive explanation has yet been provided for this property. We now present some data indicating that the cholesterol concentration in the incubation medium modulates EL toxicity against the HL60 leukemic cell line in vitro. Furthermore, model membranes richer in cholesterol take up EL more slowly, and cell cholesterol enrichment of HL60 cells counteracts EL biophysical membrane interaction, but not toxicity, in our experimental model. However, the K562 cell line, a leukemia line less sensitive to EL toxic action, has higher levels of cell cholesterol. Our data provide evidence to explain differences in sensitivity to EL among different cell types and contribute to the understanding of the mechanism of action of EL.