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D L Laskin

Publications and source records attributed to D L Laskin.

103 records · Page 6Linked to original sources
PubMed1986

Psoralens potentiate ultraviolet light-induced inhibition of epidermal growth factor binding.

The psoralens, when activated by ultraviolet light of 320-400 nm (UVA light), are potent modulators of epidermal cell growth and differentiation. Previously, we reported that, in mammalian cells, these compounds bind to specific saturable high-affinity cellular receptor sites. In the present studies, we demonstrate that binding of psoralens to their receptors followed by UVA light activation is associated with inhibition of epidermal growth factor (EGF) receptor binding. Inhibition of EGF binding, which required UVA light, was rapid and dependent on the dose of UVA light (0.5-2.0 J/cm2), as well as the concentration of psoralens (10 nM to 1 microM). Higher doses of UVA light (2.0-6.0 J/cm2) by themselves were also inhibitory, indicating that psoralens potentiate the UVA-induced inhibition of EGF binding. A number of biologically active analogs of psoralen, including 8-methoxypsoralen, 5-methoxypsoralen, and 4,5',8-trimethylpsoralen, when activated by UVA light, were found to be inhibitors of binding. Inhibition of EGF binding by psoralens was observed in a variety of human and mouse cell culture lines known to possess psoralen receptors. In the epidermal-derived line PAM 212, at least two populations of receptors with different affinities for EGF were found. Psoralens and UVA light selectively inhibited binding to the higher-affinity EGF receptors, an effect analogous to that of the phorbol ester tumor promoters. As observed with phorbol esters, photoactivated psoralens appeared to inhibit EGF binding by an indirect mechanism. These data demonstrate that the psoralens and UVA light have direct biological effects on cell-surface membranes. Since EGF is a growth-regulatory peptide, the ability of psoralens and UVA light to inhibit EGF binding may underlie the biologic effects of these agents in the skin.

Cells, Cultured↗
PubMed1985

A possible mechanism of psoralen phototoxicity not involving direct interaction with DNA.

Psoralens in combination with ultraviolet light (UVA; 320-400 nm) are used in the photochemical treatment of a variety of skin diseases including vitiligo, a skin depigmentational disorder, and psoriasis, a disease of accelerated epidermal cell proliferation. Although it is generally assumed that the major site of action of the psoralens is DNA, we have obtained evidence that another site may be the primary target for these compounds. We have identified specific, saturable, high-affinity binding sites for 8-methoxypsoralen on HeLa cells and have detected specific binding of 8-methoxypsoralen to four other human cell lines and five mouse cell lines. In HeLa cells, specific binding is reversible and independent of the ability of the compound to intercalate into DNA. In addition, binding sites become covalently modified by the psoralen after UVA exposure. Specific binding of 8-[methoxy-3H]methoxypsoralen constitutes 79% of the label bound to the cells. Scatchard analysis indicated two classes of psoralen binding sites: high-affinity sites with a Kd of 19 X 10(-9) M (1.8 X 10(5) sites per cell) and low-affinity sites with a Kd of 4 X 10(-6) M (7.1 X 10(6) sites per cell). Four structurally related psoralen analogs block 8-methoxypsoralen binding in a manner that parallels their biological activity. Based on these findings, we hypothesize that specific binding sites for psoralens on mammalian cells mediate, at least in part, psoralen-induced phototoxicity.

Animals↗
PubMed1985

Stimulation of human neutrophilic granulocyte chemotaxis by monoclonal antibodies.

Two mouse monoclonal antibodies, L12.2 and S5.22, were developed that are specific for human neutrophilic granulocytes and produce a twofold to threefold stimulation of n-formyl-methionine-leucyl-phenylalanine (FMLP)-induced chemotaxis. Stimulation of chemotaxis by the antibodies is specific for FMLP and is concentration dependent. L12.2 appears to be more potent in stimulating chemotaxis and is isotypically distinct from S5.22. In addition, although L12.2 reacts only with mature peripheral blood granulocytes, S5.22 reacts with leukemic cells of both myeloid and monocytic origin and with immature granulocyte precursor cells. This suggests that L12.2 interacts with an antigen that appears late in the differentiation pathway, whereas S5.22 binds to an antigen that is present throughout the myeloid lineage. By means of the under-agarose and Boyden chamber techniques, L12.2, but not S5.22, by itself was also found to be a potent granulocyte chemoattractant. Cells in a gradient of L12.2 display polarized and oriented morphology. L12.2 alone, but not S5.22, also stimulates granulocyte phagocytosis and induces superoxide anion production. Neither L12.2 nor S5.22 affected the release of myeloperoxidase or lysozyme from granulocytes either alone or in combination with FMLP, C5a, or the tumor promoter, 12-O-tetradecanoyl-phorbol-13-acetate (TPA). These results suggest that L12.2 interacts with a single antigenic determinant on granulocytes that is involved in chemotaxis, phagocytosis, and superoxide anion release.

Animals↗
PubMed1983

Antagonist of phorbol ester receptor-mediated chemotaxis in mouse peritoneal macrophages.

Biologically active phorbol ester derivatives displace [3H]phorbol-12, 13-dibutyrate from thioglycollate-elicited mouse peritoneal macrophages in a time-, temperature-, and concentration-dependent manner. Scatchard analysis revealed an apparent Kd of 54.1 nM and 8.0 X 10(5) sites/cell, indicating that these macrophages possess saturable, high-affinity phorbol ester-binding sites. These derivatives also act as chemoattractants for the macrophage at equivalent concentrations. A notable exception to this pattern is phorbol-12,13-diacetate. Phorbol-12,13-diacetate inhibits specific binding of [3H]phorbol-12,13-dibutyrate (concentration required for a 50% inhibition of the maximum specific binding of [3H]phorbol-12,13-dibutyrate, 2.6 microM) and chemotaxis to phorbol-12-myristate, 13-acetate (concentration required for a 50% inhibition of the maximum chemotactic response, 0.39 microM) while exhibiting no activity as a chemoattractant at concentrations up to 10(-5) M. The data indicate that phorbol-12,13-diacetate may be an antagonist for receptor-mediated chemotaxis to phorbol-12-myristate, 13-acetate in the macrophage.

Animals↗
PubMed1981

Induction of chemotaxis in mouse peritoneal macrophages by phorbol ester tumor promoters.

The ability of the tumor promoter, 12-O-tetradecanoylphorbol-13-acetate (TPA), to induce chemotaxis in three different populations of mouse peritoneal macrophages was studied. TPA in the range of 10(-9) to 10(-7) M produced a dose- and time-related increase in chemotaxis in resident, thioglycollate-elicited, and divinyl ether maleic anhydride copolymer-activated macrophages. A maximal response was obtained after 4 hr incubation with 10(-7) M TPA, and this concentration of TPA was as effective as inducing chemotaxis as was endotoxin-activated mouse serum. Orientation of macrophages towards TPA was also observed by microscopy. Within 2 hr, cells exposed to TPA sent out cytoplasmic processes along the TPA gradient. Parallel arrays of cells oriented towards the TPA were observed after 4 hr incubation. Two other diterpene tumor promoters, phorbol-12,13-didecanoate and mezerein, were also chemotactic for the macrophages, as was the peptide epidermal growth factor, which shares a number of effects with TPA on cells in culture. On the other hand, two phorbol esters inactive as tumor promoters, 4-alpha-phorbol-12,13-didecanoate and phorbol, were not chemotactic for macrophages. Retinoic acid, which inhibits tumor promotion, inhibited TPA-induced, but not endotoxin-activated mouse serum-induced chemotaxis. These findings, taken together with previous studies, indicate that phorbol ester tumor promoters are potent modulators of macrophage function.

Animals↗
PubMed1981

Enhancement of macrophage-induced cytotoxicity by phorbol ester tumor promoters.

The potent promoter, 12-O-tetradecanoylphorbol-13-acetate (TPA), markedly enhanced the ability of mouse peritoneal macrophages to inhibit the growth of L5178Y tumor cells as measured by growth in agar. Three populations of macrophages, resident, divinylether maleic anhydride copolymer, and thioglycollate-recruited, were used. In general, TPA reduced both the cocultivation time and the number of macrophages required to induce cytotoxicity in all three macrophage types. With divinylether maleic anhydride copolymer macrophages, TPA enhanced cytotoxicity in a dose-dependent manner in the concentration range of 1.7 to 170 nM at macrophage: tumor cell ratios of 10:1 and 1:1. For reasons that were not apparent, inhibition of cytotoxicity was found at higher cell ratios. With both thioglycollate-elicited and resident macrophages, TPA (170 nM) enhanced cytotoxicity at all ratios tested. Even 1:1 ratios of macrophages:tumor cells, which were not cytotoxic alone, inhibited cell viability by 50% to 60% in the presence of TPA. A correlation was found between the biological activity of related macrocyclic diterpenes and their ability to enhance macrophage-mediated cytotoxicity. Thus, mezerein and phorbol didecanoate enhanced macrophage cytotoxicity, while the biologically inactive analogs, phorbol, 4-O-methyl-12-O-tetradecanoylphorbol-13-acetate, and 4-alpha-phorbol-12, 13-didecanoate were without effect in this assay. Cytotoxicity towards untransformed BALB/c/3T3 cells was also demonstrated using a liquid cloning assay. These target cells were much less sensitive to growth inhibition by the macrophages than were the L5178Y cells. A 50% decrease in survival occurred only after 48 hr incubation and required macrophage: target cell ratios of 100:1. The addition of 170 nM TPA led to a dramatic enhancement of cytotoxicity in these cells at macrophage:target cell ratios of 10:1 and 1:1. The results observed with the phorbol esters in the present studies are compatible with other evidence that these compounds can modulate a variety of macrophage functions.

Animals↗
PubMed1980

Assessment of somatogenotoxicity of povidone-iodine using two in vitro assays.

The mutagenic potential of povidone-iodine (PVP-I) and some related compounds were studied using the L5178Y mouse (TK+/-) lymphoma assay. The established mutagens ethyl methanesulfonate (EMS) and dimethylnitrosamine (DMN) were highly active in this assay, whereas PVP-I, polyvinyl pyrolidone (PVP), potassium iodide (KI), and iodine (I2) were inactive. Furthermore, in the presence of a rat liver microsomal activating fraction (S-9), PVP-I and I2 had only marginal activity as mutagens. Using the Balb/c 3T3 transformation assay we assessed the transformational capacities of these same agents and the positive mutagen N-methyl-N-nitro-N-nitrosoguanidine (MNNG). All concentrations of the compounds tested were inactive in this assay except for PVP-I (5 mg/ml) and MNNG (5 micrograms/ml). However, the response with PVP-I was only marginal. We concluded from these studies that PVP, PVP-I, KI, and I2 did not possess any biologically significant mutagenic or cell transforming ability.

Animals↗
PubMedDate not supplied

Activation of liver macrophages following phenobarbital treatment of rats.

Phenobarbital is a potent inducer of hepatic cytochrome P-450 and is a tumor promoter in the two-stage model of liver carcinogenesis. In the present studies, we show that phenobarbital also induces an accumulation of activated macrophages in the livers of treated rats. These macrophages are larger and more stellate than resident Kupffer cells and are highly vacuolated. In addition, macrophages isolated from livers of phenobarbital-treated rats display increased phagocytosis of sheep red blood cells, chemotaxis toward the complement fragment C5a and enhanced production of hydrogen peroxide. Biologically active mediators released by activated macrophages have been implicated in tumor promotion as well as in the regulation of cytochrome P-450-mediated drug biotransformation. We propose that the activated macrophages that accumulate in the liver following phenobarbital treatment may contribute, at least in part, to the biological responses to this drug.

Animals↗
PubMedDate not supplied

Sinusoidal lining cells and hepatotoxicity.

Treatment of experimental animals with toxic doses of acetaminophen, carbon tetrachloride, phenobarbital, galactosamine, or endotoxin results in an accumulation of macrophages in the liver. These mononuclear phagocytes, as well as hepatic endothelial cells and stellate cells, are activated to release increased amounts of proinflammatory and cytotoxic mediators including hydrogen peroxide, superoxide anion, nitric oxide, bioactive lipids, interleukin 1, platelet activating factor, and tumor necrosis factor alpha. Each of these mediators has the capacity to induce tissue injury directly and/or augment the inflammatory response. When animals are treated with agents that block macrophage functioning and/or mediator release, xenobiotic-induced hepatotoxicity is reduced. In contrast, treatment of animals with macrophage activators augments toxicant-induced liver damage. These data provide direct support for a role of macrophages and inflammatory mediators in hepatotoxicity.

Animals↗
PubMedDate not supplied

Taurine protects rat bronchioles from acute ozone-induced lung inflammation and hyperplasia.

Ozone is a potent respiratory irritant known to induce lung injury in humans and experimental animals. The present studies determined if ozone-induced lung inflammation was modified by pretreatment of animals with taurine, a detoxifying antioxidant. Rats were pretreated for 10 days with 5% taurine in their drinking water (controls received water only) prior to exposure to 2 ppm ozone for 3 h. At 2, 6, 12, 24, 48, and 72 h after ozone exposure, rats were anesthetized and the lungs were perfusion-fixed for histopathologic evaluation. An additional group of rats was used to examine bronchoalveolar lavage cell counts and hydroxyproline levels. A count of bronchoalveolar lavage cells 48 h after ozone exposure showed significantly fewer total inflammatory cells and fewer polymorphonuclear leukocytes accompanied by a reduction in hydroxyproline in the lavage fluid of ozone-exposed rats pretreated with taurine compared to rats that did not receive taurine. Light microscopy revealed an inflammatory cell infiltrate in the lungs of rats exposed to ozone. This was followed by focal hyperplasia in the terminal and respiratory bronchioles. Rats pretreated with taurine and then exposed to ozone showed none of these alterations. In addition, although there was a significant reduction in cell proliferation as measured by DNA precursor incorporation in the lungs of rats pretreated with taurine prior to ozone exposure compared to unsupplemented rats, the distribution of labeled cells was the same in taurine supplemented and unsupplemented groups. Also, significantly higher levels of taurine were found in the plasma, whole blood, and lavage fluid of rats pretreated with dietary taurine compared to rats that received water only. The results suggest that supplemental taurine protects rat lung epithelium from acute ozone-induced lung inflammation and hyperplasia.

Acute Disease↗