Continuous spectrofluorometric measurements of uptake by cultured cells of 12-(1-pyrene)-dodecanoic acid from its complex with albumin

Uptake of a fluorescent-labeled fatty acid by spiroplasma floricola cells

12-(1-pyrene)dodecanoic fatty acid (P12) uptake by Spiroplasma floricola BNR-1 cells was characterized with regard to its kinetics, specificity, metabolism and susceptibility to protein and lipid inhibitors. The uptake process depended on temperature and pH, and exhibited biphasic saturation kinetics with a very low (2.7 microM) and a high (37 microM) apparent Km value. Lauric, myristic, palmitic, stearic and oleic fatty acids did not compete with P12 for transport. The fluorescence of P12 was exclusively recovered in the neutral lipid fraction, suggesting that this fatty acid is not further utilized for phospholipid biosynthesis. Valinomycin, carbonylcyanide m-chlorophenyldrazone (CCCP), dicyclohexylcarbodiimide (DCCD), and pronase strongly reduced P12 uptake by cells, but not by membrane vesicles, affecting the high affinity (low Km) component of the uptake system. Uptake of P12 by cells, as well as by membrane vesicles, was very sensitive to glutaraldehyde, chlorpromazine, phospholipase A21 and ascorbate with FeCl3, which affected the low affinity (high Km) component of a transport system. Digitonin stimulated P12 uptake. We suggest that the incorporation of P12 into spiroplasma cell membrane is a two-step process: a high specificity energy-dependent and protease-sensitive binding to the outer surface of membrane, and a low specificity and energy-independent diffusion and partition into the membrane lipid environment.

Influence of chain length of pyrene fatty acids on their uptake and metabolism by Epstein-Barr-virus-transformed lymphoid cell lines from a patient with multisystemic lipid storage myopathy and from control subjects

The uptake and intracellular metabolism of 4-(1-pyrene)butanoic acid (P4), 10-(1-pyrene)decanoic acid (P10) and 12-(1-pyrene)dodecanoic acid (P12) were investigated in cultured lymphoid cell lines from normal individuals and from a patient with multisystemic lipid storage myopathy (MLSM). The cellular uptake was shown to be dependent on the fatty-acid chain length, but no significant difference in the uptake of pyrene fatty acids was observed between MLSM and control lymphoid cells. After incubation for 1 h the distribution of fluorescent fatty acids taken up by the lymphoid cell lines also differed with the chain length, most of the fluorescence being associated with phospholipid and triacylglycerols. In contrast with P10 and P12, P4 was not incorporated into neutral lipids. When the cells were incubated for 24 h with the pyrene fatty acids, the amount of fluorescent lipids synthesized by the cells was proportional to the fatty acid concentration in the culture medium. After a 24 h incubation in the presence of P10 or P12, at any concentration, the fluorescent triacylglycerol content of MLSM cells was 2-5-fold higher than that of control cells. Concentrations of pyrene fatty acids higher than 40 microM seemed to be more toxic for mutant cells than for control cells. This cytotoxicity was dependent on the fluorescent-fatty-acid chain length (P12 greater than P10 greater than P4). Pulse-chase experiments permitted one to demonstrate the defect in the degradation of endogenously biosynthesized triacylglycerols in MLSM cells (residual activity was around 10-25% of controls on the basis of half-lives and initial rates of P10- or P12-labelled-triacylglycerol catabolism); MLSM lymphoid cells exhibited a mild phenotypic expression of the lipid storage (less severe than that observed in fibroblasts). P4 was not utilized in the synthesis of triacylglycerols, and thus did not accumulate in MLSM cells: this suggests that natural short-chain fatty acids might induce a lesser lipid storage in this disease.

Enzymatic synthesis of pyrene-labeled polyphosphoinositides and their behavior in organic solvents and phosphatidylcholine bilayers

A method is reported for the synthesis of pyrene-labeled analogues of phosphatidylinositol 4-phosphate (Pyr-PIP) and phosphatidylinositol 4,5-biphosphate (Pyr-PIP2) from sn-2-(pyrenyl-decanoyl)phosphatidylinositol (Pyr-PI) using partially purified PI and PIP kinase preparations. Phosphorylation of Pyr-PI and Pyr-PIP was extensive (more than 50%) provided that the ATP concentration was high and that stabilizing agents such as sucrose and polyethylene glycol were present in the incubation medium. Pyr-PIP and Pyr-PIP2 were isolated by chromatography on immobilized neomycin. The identity of the products was established by thin-layer chromatography, UV-absorption spectroscopy, and spectrofluorometry. The pyrene excimer/monomer fluorescence technique revealed that, in contrast to Pyr-PI, Pyr-PIP and Pyr-PIP2 formed clusters in organic solvents. By use of the same technique for model membranes, it was shown that in phosphatidylcholine bilayers the collision frequency of the three fluorescent phosphoinositides decreased in the order PI greater than PIP greater than PIP2. Addition of Ca2+ at concentrations above 0.1 mM increased the collision frequency of Pyr-PIP2 and, to a much lesser extent, Pyr-PIP; Ca2+ had no effect on Pyr-PI.

Uptake and degradation of virus-associated fluorescent sulfatide by skin fibroblasts

A fluorescent derivative of cerebroside sulfate, pyrene-dodecanoyl sphingosylgalactosylsulfate (P12-CS) was incorporated into the envelope of vesicular stomatitis virus (VSV). When the P12-CS-containing virus was incubated for 24 h with skin fibroblasts, up to 40% of the sulfatide was located in the cells--a value at least 10 fold greater than that observed using sulfatide suspensions without virus. In a similar experiment, in which the 24 h 'pulse' was followed by a 48 h 'chase', about 15-20% of the virus-associated fluorescence was recovered in the skin fibroblasts. Of the latter, about one-third was present as desulfated degradation products of P12-CS. The high uptake and degradation of the virus-associated sulfatide by intact skin fibroblasts suggested that enveloped viruses could be used for introducing other lipids into cells. This could be utilized for studying lipid catabolism and diagnosing lipid storage disorders in intact living cells.

Analysis of cellular heterogeneity in the response of human leukemic cells to photosensitization induced by pyrene-containing fatty acid

Incubation of cells with 12-(1-pyrene) dodecanoic acid (P12) followed by irradiation with ultraviolet light at 366 nm (UVA) resulted in cytotoxicity. We compared the photosensitivity to UVA irradiation of various human myelo-monocytic leukemic cell lines, their intra- and inter-clonal variability and correlated their photosensitivity to P12-uptake and metabolism. The fluorescence properties of pyrene were utilized for flow cytometric analysis of cell distribution with respect to P12-uptake as well as for sorting subpopulations differing in their fluorescence. Spectrofluorometric analysis of the total cell-associated fluorescence and of the cellular lipids-associated fluorescence were also carried out. Considerable heterogeneity in P12-uptake and photosensitivity was found not only among cell lines, but also in the response of different clones and among the individual cells in specific clonal populations. Within a clone, photosensitivity was related to the amount of P12 taken up by the individual cells, while among different cell lines and their clones the photosensitivity was correlated with the proportion of cellular pyrene-linked phospholipids. The larger the fraction of pyrene-linked phospholipids within the cell--the more sensitive it was to UVA-irradiation. Photosensitivity could be affected by changing the proportion of cellular pyrene-linked phospholipids. Cells treated with cAMP showed an increase in total P12-uptake, but the proportion of pyrene-linked phospholipids was reduced, resulting in lower photosensitivity. These findings, demonstrating that by manipulating lipid metabolism photosensitivity can be modified, may prove useful in a clinical setting for selective photosensitization of malignant cells.

Flow cytofluorometric analysis of the uptake of the fluorescent fatty acid pyrene-dodecanoic acid by human peripheral blood cells

The fluorescence activated cell sorter (FACS) was used for measuring the uptake of the fluorescent fatty acid derivative 12-(1-pyrene) dodecanoic acid (P12) by human peripheral blood cells. The results indicate that blood cells differ widely in their ability to take up P12, with polymorphonuclear cells showing the greatest uptake, followed by lymphocytes, platelets, and RBCs. These differences in P12 uptake provide a potential additional parameter for differential cell counting. Using the ability of the FACS to "gate out" nonrelevant cells, it was possible to measure the rate of P12 uptake by each respective cell type even when admixed with other cells. Thus elaborate physical separation procedures could be avoided, and contaminating cells did not influence the results. Differences in P12 uptake were also utilized to separate blood cells into pure subpopulations of specific cell types.

Spectrofluorometric measurements of the dispersion state of pyrenedodecanoic acid and its uptake by cultured cells and liposomes

Pyrene dodecanoic acid (P12), a medium-chain fatty acid to which the fluorescent probe pyrene is covalently linked, showed a considerable increase in fluorescence when the probe was introduced into a hydrophobic environment. Also, when closely packed in an aggregate, an energy transfer between two adjacent molecules of pyrene occurred, resulting in a shift of the peak of the emission spectrum from 378 nm ('monomeric') to 475 nm ('excimeric'). These two respective properties were utilized for the following: (a) A spectrofluorometric measurement of the critical micellar concentration (CMC) of the pyrene fatty acid, defined as the concentration at which the 475 nm emission peak appeared as a consequence of the aggregation of P12 molecules in aqueous solution to form micelles; the CMC of P12 was found to be in the range of 1 to 2 microM. (b) The penetration of P12, from an aqueous solution or dispersion, into unilamellar phospholipid vesicles was determined by monitoring the increase of the fluorescence at 378 nm. The fluorescence increase was time-dependent and proportional to the respective concentrations of P12 or phospholipid vesicles. Substituting the neutral phosphatidylcholine with the negatively-charged phosphatidylserine vesicles resulted in a slower rate as well as lesser total uptake of P12. (c) The uptake of P12 by cells was accompanied by an increase in the monomeric fluorescence emission intensity. Using cells in suspension, this could be followed continuously in a spectrofluorometer equipped with a recorder. The uptake was found to be time-dependent and proportional to P12 concentration.