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Biomedical subjects

A Raz

Publications and source records attributed to A Raz.

At least 181 records · Page 10Linked to original sources
PubMed1983

Modulation of the metastatic capability in B16 melanoma by cell shape.

The lung colonization of B16-F1 cells grown in flat and spherical configurations was studied. Cells cultivated in vitro as spheroids on a nonadhesive substrate expressed in a reversible fashion a marked increase in their propensity to establish metastases. The altered metastatic capability was accompanied by a reversible reduction in the accessibility of cell surface proteins to external iodination and by a dramatic decrease in the synthesis of vimentin.

Animals↗
PubMed1983

Phospholipase A2 inhibitors. Differential inhibition of fatty acid acylation into kidney lipids by mepacrine and p-bromophenacyl bromide.

Mepacrine and p-bromophenacyl bromide, in addition to their inhibitory effect on lipolysis, are also potent inhibitors of fatty acid acylation into renal medullary lipids. Significant qualitative and quantitative differences in the inhibition by the two drugs were seen. p-Bromophenacyl bromide exerted a non-selective effect inhibiting the incorporation of saturated and unsaturated fatty acids into all phospholipid classes and triacylglycerols. In contrast, mepacrine selectively inhibited the incorporation of both saturated and unsaturated acids into phosphatidylcholine, phosphatidylethanolamine and triglycerides, and concurrently markedly enhanced their incorporation into phosphatidylinositol. Quantitative analysis of these mepacrine effects, together with the known inhibitory effects of this compound on phospholipase A2 and phosphatidylinositol-specific phospholipase C, suggests that mepacrine also inhibits phosphatidic acid phosphatase, thereby shunting the flux of phosphatidic acid away from diglyceride formation and into synthesis of phosphatidylinositol.

Acetophenones↗
PubMed1983

Cultured endothelial cells increase their capacity to synthesize prostacyclin following the formation of a contact inhibited cell monolayer.

The synthesis of the prostaglandins (PG), prostacyclin (PGI2), PGE2, and thromboxane A2 (TXA2), has been investigated in actively growing and contact-inhibited bovine aortic endothelial cell cultures. Cells were stimulated to synthesize prostaglandins by exposure to exogenous arachidonic acid or to the endoperoxide PGH2 and by the liberation of endogenous arachidonic acid from cellular lipids with melittin or ionophore A23187. Increased capacity of the cells to synthesize PGI2 and PGE2 was observed as a function of time in culture, regardless of the type of stimulation. TXA2 production increased with time only upon stimulation of the cells with ionophore A23187. This increased PG synthetic capacity was independent of cell density since it was mainly observed in confluent, nondividing endothelial cell cultures. The fact that increased PGI2 production in confluent cells was also observed with PGH2, a direct stimulator of PGI2 synthetase, implies that this process is independent of the arachidonate concentration within the cells or in the culture medium. This increased capacity is likely to reflect an increased activity of the PG synthetase system associated with the formation of a contact inhibited endothelial cell monolayer. A similar time-dependent increase in the PGI2 production capacity was also observed during growth of cultured bovine corneal endothelial cells.

Animals↗
PubMed1983

Low colony formation in vivo and in culture as exhibited by metastatic melanoma cells selected for reduced homotypic aggregation.

A subpopulation of cells unable to aggregate in the presence of a high concentration of asialofetuin (400 micrograms/ml) has been isolated from the murine B16-F1 melanoma cells which aggregate readily at low asialofetuin concentrations (greater than 0.3 micrograms/ml). Cells of this variant cell lines, designated B16-F1-NA, exhibited also a reduced tendency to undergo homotypic aggregation in the presence of syngeneic serum. In culture, the B16-F1-NA cells spread on solid substrate more than the B16-F1, formed more focal contacts, and proliferated at a slower exponential rate. The pattern of the major cell surface proteins and glycoproteins was similar in the parental and variant cells except for a minor glycoprotein with a molecular weight of 150,000 which was labeled more intensely on the B16-F1 than on the B16-F1-NA cells. Colony formation in semisolid medium and the development of experimental metastases in the lungs of syngeneic mice were markedly reduced in the B16-F1-NA as compared with the parental cells. It is suggested that the ability to undergo aggregation in the presence of glycoproteins is an important property of malignant cells which may influence anchorage-independent growth and the formation of metastases.

Animals↗
PubMed1983

Prostaglandin biosynthesis in submitochondria membrane fractions from rabbit kidney medulla.

We have previously shown (Erman and Raz, 1981; Erman et al, 1982) that mitochondria from rabbit kidney medulla contains prostaglandin synthase activity. Current studies are aimed at localizing this activity in the mitochondrial membrane subfractions. Medullary mitochondria was subfractionated into outer and inner membrane fractions which were characterized by specific enzyme markers. Both outer and inner membrane fractions catalyzed prostaglandin E2 (PGE2) biosynthesis from arachidonic acid. Significantly, the specific activity of prostaglandin synthase in the outer membrane was 9-10 fold higher than in the inner membrane.

Animals↗
PubMed1982

Growth control and cell spreading: differential response in preneoplastic and in metastatic cell variants.

Growth control and sensitivity to changes in cell shape were studied in anchorage-dependent mouse fibroblasts (diploid fibroblasts, 3T3 and 3T6), in DNa tumor-virus-transformed mouse fibroblasts (SVPy 3T3), in four B16 melanoma and five uv-2237 fibrosarcoma cell variants that exhibit distinct metastatic properties. Differential adhesive conditions were established by precoating the plastic plates with poly (2-hydroxyethylmethacrylate) that allowed an accurate and reproducible control of cell shape, from flat to spherical. Mouse fibroblasts that form a continuum between rigorously controlled cells to fully anchorage-independent cells, display a direct correlation between degree of growth control and sensitivity to changes in cell spreading. In contrast, there is no apparent direct correlation between sensitivity of growth control to changes in cellular configuration and the metastatic potential of tumor cells.

Animals↗
PubMed1982

Enzymic coupling of acylhydrolase and prostaglandin synthase activities in subcellular fractions from rabbit renal medulla.

We have recently shown that mitochondrial and plasma-membrane fractions from kidney medulla possess Ca(2+)-stimulated acylhydrolase and prostaglandin synthase activities. The nature of the enzymic coupling between the Ca(2+)-stimulated arachidonic acid release and its subsequent conversion into prostaglandins was investigated in subcellular fractions from rabbit kidney medulla. Plasma-membrane, mitochondrial and microsomal fractions were found to have similar apparent K(m) values for conversion of added exogenous arachidonate into prostaglandins. The rate of prostaglandin biosynthesis (V(max.)) from added arachidonic acid in the microsomal fraction was approx. 2-fold higher than in the other subcellular fractions. In contrast, prostaglandin E(2) synthesis from endogenous arachidonate in plasma-membrane and mitochondrial fractions was 3-4-fold higher than in microsomes. Furthermore, Ca(2+) stimulated endogenous arachidonate deacylation and prostaglandin E(2) generation in the former two fractions but not in microsomes. In mitochondrial or crude plasma-membrane fractions, in which prostaglandin biosynthesis was inhibited with aspirin, arachidonate released from these fractions was converted into prostaglandins by the microsomal prostaglandin synthase. Thus an intracellular prostaglandin generation process that involves inter-fraction transfer of arachidonic acid can operate. Prostaglandin generation by such an inter-fraction process is, however, less efficient than by an intra-fraction process, where arachidonic acid released by mitochondria or crude plasma membranes is converted into prostaglandins by prostaglandin synthase present in the same fraction. This demonstrates the presence of a tight intra-fraction enzymic coupling between Ca(2+)-stimulated acylhydrolase and prostaglandin synthase enzyme systems in both mitochondrial and plasma-membrane fractions.

Animals↗
PubMed1982

Different pools of esterified arachidonic acid in rabbit kidney medulla: relationship to Ca2+-stimulated prostaglandin biosynthesis.

We investigated the effect of Ca2+ ions on renal medulla metabolism of endogenous esterified arachidonic acid in contrast to that of radioactive arachidonate incorporated into medullary lipids. Some striking differences between the release of unlabeled prostaglandin E2 and of 14C-labeled prostaglandin E2 and arachidonic acid were seen in incubations in absence or presence of Ca2+ ions. These differences indicated that exogenous [14C] arachidonate incubated with medulla slices is incorporated into both Ca2+-sensitive and Ca2+-insensitive lipid pools of esterified arachidonate and furthermore, the Ca2+-sensitive pool is itself heterogeneous and consists of at least 2 functionally different lipid pools of esterified arachidonate. The first Ca2+-sensitive pool is characterized by a higher arachidonate turnover rate and incorporates more rapidly added radioactive arachidonate. The acylhydrolase activity which releases arachidonate from this pool is not efficiently coupled to prostaglandin endoperoxide synthase. In contrast, the second Ca2+-sensitive lipid pool has a slower arachidonate turnover rate and, consequently, a slower incorporation of added 14C-acid. The acylhydrolase activity associated with this pool is more tightly coupled to prostaglandin endoperoxide synthase, so that a higher portion of released arachidonate is converted to prostaglandin E2. Studies on arachidonic acid metabolic transformations using exogenously radioactive free acid added to tissues should therefore be interpreted with caution because the results obtained may not reflect accurately the metabolic fate of endogenous, lipid-esterified arachidonate which is released and metabolized under physiological conditions in vivo.

Animals↗
PubMed1982

B16 melanoma cell variants: irreversible inhibition of growth and induction of morphologic differentiation by anthracycline antibiotics.

The interaction of doxorubicin and N-trifluoroacetyladriamycin-14-valerate (AD32) with B16 melanoma cell variants that exhibit distinct metastatic properties was explored. The addition of the two drugs to cell monolayers at noncytolytic concentrations for 16 hours resulted in irreversible inhibition of proliferation of tumor cells and loss of their tumorigenicity after injection into inbred C57BL/6 mice. Cessation of melanoma cell proliferation was accompanied by cellular and nuclear hypertrophy and the development of axon-like processes. As assessed by drug-specific cytofluorescence, after 16-hour exposure of the cells to doxorubicin and AD32, the drugs were localized in the nuclei. Incubation of drug-treated cell monolayers for 6 additional days in drug-free culture medium led to the complete disappearance of nuclear stain. The highly metastatic B16-F10-B2 cell line was the most sensitive to the drugs' effects, whereas the other two malignant melanoma cell lines, although differing in their metastatic capabilities, exhibited similar sensitivities to the drugs' effects. Doxorubicin was notably more potent than AD32 in its growth inhibitory effect on the three tested melanoma cell variants. The possible mutagenic effect of anthracycline drugs on tumor cells was discussed.

Animals↗
PubMed1982

Analysis of the fate of systemically administered liposomes and implications for their use in drug delivery.

Functional and ultrastructural studies of liposomes injected i.v. into inbred C57BL/6N mice were performed to determine whether free liposomes can traverse capillaries. In the liver and spleen, organs with discontinuous (sinusoidal) capillaries, ultrastructural and cell fractionation studies revealed that small (300- to 800-A diameter), sonicated, unilamellar liposomes were more efficient in penetrating liver sinusoids to interact with hepatocytes than were large (0.5- to 10-micrometers) multilamellar liposomes. Ultrastructural studies of the behavior of liposomes in the continuous capillaries of the lungs revealed that circulating phagocytic cells engulf the liposomes in the capillaries. Transcapillary migration of free liposomes was not observed. We conclude that free liposomes are unable to extravasate to reach the alveoli for subsequent engulfment by alveolar macrophages. Instead, liposomes in the lung capillaries are engulfed by circulating blood phagocytes which subsequently migrate to the alveoli to become alveolar macrophages. Experiments on the recruitment of blood monocytes into the lungs subjected to whole- or partial-body X-radiation confirmed that transfer of i.v.-injected liposomes to the alveolar compartment was mediated by blood monocytes. The inability of liposomes to escape from continuous capillaries and their rapid uptake by circulating and fixed phagocytic cells calls into question the feasibility of using liposomes to "target" drugs to cells in extravascular tissues.

Animals↗
PubMed1982

Altered organization of cell-substrate contacts and membrane-associated cytoskeleton in tumor cell variants exhibiting different metastatic capabilities.

The pattern of cell-substrate attachment and the organization of actin-containing microfilament bundles were analyzed in tumor cell variants of the K-1735 melanoma and UV-2237 fibrosarcoma series exhibiting distinct metastatic phenotypes. In both tumors, the low-metastatic cells were relatively flat, with well-developed focal contacts. Visualization of the cellular organization of actin and vinculin by fluorescence microscopy indicated that the low-metastatic cells contained prominent stress fibers which terminated in large vinculin-containing focal contacts. The high-metastatic cells were characterized by poor organization of vinculin and adhesion plaques as well as by low number and disarray of actin bundles. These results are compatible with the notion that cytoskeletal organization may be involved in cytodynamic processes related to tumor cell dissemination and implantation.

Animals↗
PubMed1981

Evidence for different purinergic receptors for ATP and ADP in rabbit kidney and heart.

ATP and ADP stimulated the release of specific prostaglandin products from the perfused rabbit kidney heart. The two nucleotides produced the same qualitative profile of prostaglandin products. In kidney, prostaglandin E2 was the major product, whereas in heart 6-keto prostaglandin F1 alpha and prostaglandin E2 predominated. ATP was a slightly more potent than ADP. ATP administered into the perfused heart to kidney was rapidly hydrolyzed to ADP and AMP. The prostaglandin E2 generating activity of ATP was increased 6-10 fold when ATP was given together with AMP-PCP or AMP-PNP which competitively inhibit the activity of vascular ATPase. Thus, the rapid hydrolysis of ATP reduces its agonistic activity for prostaglandin release. ATP and ADP administered together at maximal stimulating doses produced an additive response for prostaglandin E2 release. These results and the results of tachyphylaxis experiments indicate that ATP and ADP interact independently with different types of purinergic receptors.

Adenosine Diphosphate↗
PubMed1981

Testosterone potentiation of ionophore and ADP induced platelet aggregation: relationship to arachidonic acid metabolism.

The role of arachidonic acid oxygenated products in human platelet aggregation induced by the ionophore A23187 was investigated. The ionophore produced an increased release of both saturated and unsaturated fatty acids and a concomitant increased formation of TxA2 and other arachidonate products. TxA2 (and possibly other cyclo oxygenase products) appears to have a significant role in ionophore-induced aggregation only when low concentrations (less than 1 micro M ) of the ionophore are employed. Testosterone added to rat or human platelet-rich plasma (PRP) was shown previously to potentiate platelet aggregation induced by ADP, adrenaline, collagen and arachidonic acid (1, 2). We show that testosterone also potentiates ionophore induced aggregation in washed platelets and in PRP. This potentiation was dose and time dependent and resulted form increased lipolysis and concomitant generation of TxA2 and other prostaglandin products. The testosterone potentiating effect was abolished by preincubation of the platelets with indomethacin.

Adenosine Diphosphate↗
PubMed1981

Selective induction of de novo prostaglandin biosynthesis in rabbit kidney cortex.

Ureter-obstructed kidney develops during perfusion an enhanced responsiveness to bradykinin-stimulated prostaglandin release. This enhanced prostaglandin generation results from de novo synthesis of prostaglandin synthetase and acylhydrolase enzymes during the perfusion and is therefore unaffected by acetylsalicylic acid (aspirin) inhibition of prostaglandin synthesis prior to initiation of perfusion. Studies were carried out to identify the renal cellular site in which the newly synthesizing prostaglandin generating system is localized. Kidneys with or without aspirin treatment were perfused for either 1 or 5 h. Following perfusion, medullary and cortical slices were incubated and prostaglandin E2 production measured. Medullary slices showed similar prostaglandin E2 biosynthetic activity in kidneys perfused for 1 or 5 h. Furthermore, medullary prostaglandin generation was inhibited (90-95%) by aspirin pre-treatment and did not increase during subsequent perfusion for 5 h. In contrast, cortical slices from kidneys pretreated with aspirin regained their full activity after 5 h or perfusion, this regeneration being abolished by infusion of the protein synthesis inhibitor, cycloheximide. The same differences in activities between medulla and cortex were also seen when microsomal fractions were compared. The perfusion-induced formation of prostaglandin synthetase activity is thus specifically localized in the cortex and can be detected in cortical microsomes. This cortical activity is unique in that endogenous arachidonic acid released from esterified lipids is converted to prostaglandins, whereas exogenous added arachidonic acid is not. It thus appears that the induced cortical acylhydrolase and prostaglandin synthetase activities are tightly coupled and that the true molecular form or precursor arachidonate for this prostaglandin generating system is esterified and not free arachidonate.

Animals↗
PubMed1981

Prostaglandin biosynthesis and lipolysis in subcellular fractions from rabbit kidney medulla.

Three separate prostaglandin-generating activities are associated with plasma membranes, mitochondria and microsomal fractions from rabbit kidney medulla. In the plasma membranes and mitochondria, but not in microsomal fractions, Ca2+ ions stimulate the activity of phospholipase A2, yielding selective release of arachidonic acid and linoleic acid and concomitant increase in prostaglandin E2 formation.

Animals↗