Humanin Nanoparticles for Reducing Pathological Factors Characteristic of Age-Related Macular Degeneration

BACKGROUND

Humanin is a novel neuronal peptide that has displayed potential in the treatment of Alzheimer's Disease through the suppression of inflammatory IL-6 cytokine receptors. Such receptors are found throughout the body, including the eye, suggesting its other potential applications. Age-related Macular Degeneration (AMD) is the leading cause of blindness in the developing world. There is no cure for this disease, and current treatments have several negative side effects associated with them, making finding other treatment options desirable.

OBJECTIVE

In this study, the potential applications in treating AMD for a more potent humanin derivative, AGA-HNG, were studied.

METHODS

AGA-HNG was synthesized and encapsulated in chitosan Nanoparticles (NPs), which were then characterized for their size, Encapsulation Efficiency (EE), and drug release. Their ability to suppress VEGF secretion and protect against oxidative apoptosis was studied in vitro using ARPE-19 cells. The chitosan NPs exhibited similar anti-VEGF properties and oxidative protection as the free protein while exhibiting superior pharmaceutical characteristics including biocompatibility and drug release.

RESULTS

Drug-loaded NPs exhibited a radius of 346nm with desirable pharmacokinetic properties including a stable surface charge (19.5 ± 3.7 mV) and steady drug release capacity. AGA-HNG showed great promise in mediating apoptosis in hypoxic cells. They were also able to significantly reduce VEGF expression in vitro with reduced cellular toxicity compared to the free drug.

CONCLUSION

The ability of this drug delivery system to reduce retinal apoptosis with desirable pharmacokinetic and biocompatible properties makes this a promising therapeutic option for AMD.

A structural view of the dissociation of Escherichia coli tryptophanase

Tryptophanase (Trpase) is a pyridoxal 5'-phosphate (PLP)-dependent homotetrameric enzyme which catalyzes the degradation of L-tryptophan. Trpase is also known for its cold lability, which is a reversible loss of activity at low temperature (2°C) that is associated with the dissociation of the tetramer. Escherichia coli Trpase dissociates into dimers, while Proteus vulgaris Trpase dissociates into monomers. As such, this enzyme is an appropriate model to study the protein-protein interactions and quaternary structure of proteins. The aim of the present study was to understand the differences in the mode of dissociation between the E. coli and P. vulgaris Trpases. In particular, the effect of mutations along the molecular axes of homotetrameric Trpase on its dissociation was studied. To answer this question, two groups of mutants of the E. coli enzyme were created to resemble the amino-acid sequence of P. vulgaris Trpase. In one group, residues 15 and 59 that are located along the molecular axis R (also termed the noncatalytic axis) were mutated. The second group included a mutation at position 298, located along the molecular axis Q (also termed the catalytic axis). Replacing amino-acid residues along the R axis resulted in dissociation of the tetramers into monomers, similar to the P. vulgaris Trpase, while replacing amino-acid residues along the Q axis resulted in dissociation into dimers only. The crystal structure of the V59M mutant of E. coli Trpase was also determined in its apo form and was found to be similar to that of the wild type. This study suggests that in E. coli Trpase hydrophobic interactions along the R axis hold the two monomers together more strongly, preventing the dissociation of the dimers into monomers. Mutation of position 298 along the Q axis to a charged residue resulted in tetramers that are less susceptible to dissociation. Thus, the results indicate that dissociation of E. coli Trpase into dimers occurs along the molecular Q axis.

Humanin Derivatives Inhibit Necrotic Cell Death in Neurons

Humanin and its derivatives are peptides known for their protective antiapoptotic effects against Alzheimer's disease. Herein, we identify a novel function of the humanin-derivative AGA(C8R)-HNG17 (namely, protection against cellular necrosis). Necrosis is one of the main modes of cell death, which was until recently considered an unmoderated process. However, recent findings suggest the opposite. We have found that AGA(C8R)-HNG17 confers protection against necrosis in the neuronal cell lines PC-12 and NSC-34, where necrosis is induced in a glucose-free medium by either chemohypoxia or by a shift from apoptosis to necrosis. Our studies in traumatic brain injury models in mice, where necrosis is the main mode of neuronal cell death, have shown that AGA(C8R)-HNG17 has a protective effect. This result is demonstrated by a decrease in a neuronal severity score and by a reduction in brain edema, as measured by magnetic resonance imaging (MRI). An insight into the peptide's antinecrotic mechanism was attained through measurements of cellular ATP levels in PC-12 cells under necrotic conditions, showing that the peptide mitigates a necrosis-associated decrease in ATP levels. Further, we demonstrate the peptide's direct enhancement of the activity of ATP synthase activity, isolated from rat-liver mitochondria, suggesting that AGA(C8R)-HNG17 targets the mitochondria and regulates cellular ATP levels. Thus, AGA(C8R)-HNG17 has potential use for the development of drug therapies for necrosis-related diseases, for example, traumatic brain injury, stroke, myocardial infarction, and other conditions for which no efficient drug-based treatment is currently available. Finally, this study provides new insight into the mechanisms underlying the antinecrotic mode of action of AGA(C8R)-HNG17.

Structures of Escherichia coli tryptophanase in holo and 'semi-holo' forms

Two crystal forms of Escherichia coli tryptophanase (tryptophan indole-lyase, Trpase) were obtained under the same crystallization conditions. Both forms belonged to the same space group P43212 but had slightly different unit-cell parameters. The holo crystal form, with pyridoxal phosphate (PLP) bound to Lys270 of both polypeptide chains in the asymmetric unit, diffracted to 2.9 Å resolution. The second crystal form diffracted to 3.2 Å resolution. Of the two subunits in the asymmetric unit, one was found in the holo form, while the other appeared to be in the apo form in a wide-open conformation with two sulfate ions bound in the vicinity of the active site. The conformation of all holo subunits is the same in both crystal forms. The structures suggest that Trpase is flexible in the apo form. Its conformation partially closes upon binding of PLP. The closed conformation might correspond to the enzyme in its active state with both cofactor and substrate bound in a similar way as in tyrosine phenol-lyase.

Regulation of autophagy by α1-antitrypsin: "a foe of a foe is a friend"

Autophagy is involved in both the cell protective and the cell death process but its mechanism is largely unknown. The present work unravels a novel intracellular mechanism by which the serpin α1-antitrypsin (AAT) acts as a novel negative regulator of autophagic cell death. For the first time, the role of intracellularly synthesized AAT, other than in liver cells, is demonstrated. Autophagic cell death was induced by N-α-tosyl-L-phenylalanine chloromethyl ketone (TPCK) and tamoxifen. By utilizing a fluorescently tagged TPCK analog, AAT was "fished out" (pulled out) as a TPCK intracellular protein target. The interaction was further verified by competition binding experiments. Both inducers caused downregulation of AAT expression associated with activation of trypsin-like proteases. Furthermore, silencing AAT by siRNA induced autophagic cell death. Moreover, AAT administration to cultured cells prevented autophagic cell death. This new mechanism could have implications in the treatment of diseases by the regulation of AAT levels in which autophagy has a detrimental function. Furthermore, the results imply that the high synthesis of endogenous AAT by cancer cells could provide a novel resistance mechanism of cancer against autophagic cell death.

Cardiolipin plays a role in KCN-induced necrosis

Cardiolipin (CL) is a unique anionic, dimeric phospholipid found almost exclusively in the inner mitochondrial membrane and is essential for the function of numerous enzymes that are involved in mitochondrial energy metabolism. While the role of cardiolipin in apoptosis is well established, its involvement in necrosis is enigmatic. In the present study, KCN-induced necrosis in U937 cells was used as an experimental model to assess the role of CL in necrosis. KCN addition to U937 cells induced reactive oxygen species (ROS) formation, while the antioxidants inhibited necrosis, indicating that ROS play a role in KCN-induced cell death. Further, CL oxidation was confirmed by the monomer green fluorescence of 10-N-nonyl acridine orange (NAO) and by TLC. Utilizing the red fluorescence of the dimeric NAO, redistribution of CL in mitochondrial membrane during necrosis was revealed. We also showed that the catalytic activity of purified adenosine triphosphate (ATP) synthase complex, known to be modulated by cardiolipin, decreased following KCN treatment. All these events occurred at an early phase of the necrotic process prior to rupture of the cell membrane. Furthermore, CL-deficient HeLa cells were found to be resistant to KCN-induced necrosis as compared with the wild type cells. We suggest that KCN, an effective reversible inhibitor of cytochrome oxidase and thereby of the respiratory chain leads to ROS increase, which in turn oxidizes CL (amongst other membrane phospholipids) and leads to mitochondrial membrane lipid reorganization and loss of CL symmetry. Finally, the resistance of CL-deficient cells to necrosis further supports the notion that CL, which undergoes oxidation during necrotic cell death, is an integral part of the milieu of events taking place in mitochondria leading to membrane disorganization and mitochondrial dysfunction.

Structural insights into cold inactivation of tryptophanase and cold adaptation of subtilisin S41

A wide variety of enzymes can undergo a reversible loss of activity at low temperature, a process that is termed cold inactivation. This phenomenon is found in oligomeric enzymes such as tryptophanase (Trpase) and other pyridoxal phosphate dependent enzymes. On the other hand, cold-adapted, or psychrophilic enzymes, isolated from organisms able to thrive in permanently cold environments, have optimal activity at low temperature, which is associated with low thermal stability. Since cold inactivation may be considered "contradictory" to cold adaptation, we have looked into the amino acid sequences and the crystal structures of two families of enzymes, subtilisin and tryptophanase. Two cold adapted subtilisins, S41 and subtilisin-like protease from Vibrio, were compared to a mesophilic and a thermophilic subtilisins, as well as to four PLP-dependent enzymes in order to understand the specific surface residues, specific interactions, or any other molecular features that may be responsible for the differences in their tolerance to cold temperatures. The comparison between the psychrophilic and the mesophilic subtilisins revealed that the cold adapted subtilisins have a high content of acidic residues mainly found on their surface, making it charged. The analysis of the Trpases showed that they have a high content of hydrophobic residues on their surface. Thus, we suggest that the negatively charged residues on the surface of the subtilisins may be responsible for their cold adaptation, whereas the hydrophobic residues on the surface of monomeric Trpase molecules are responsible for the tetrameric assembly, and may account for their cold inactivation and dissociation.

The reactivation of DnaA(L366K) requires less acidic phospholipids supporting their role in the initiation of chromosome replication in Escherichia coli

DnaA(L366K), in concert with a wild-type DnaA (wtDnaA) protein, restores the growth of Escherichia coli cells arrested in the absence of adequate levels of cellular acidic phospholipids. In vitro and in vivo studies showed that DnaA(L366K) alone does not induce the initiation of replication, and wtDnaA must also be present. Hitherto the different behavior of wt and mutant DnaA were not understood. We now demonstrate that this mutant may be activated at significantly lower concentrations of acidic phospholipids than the wild-type protein, and this may explain the observed growth restoration in vivo.

The structure of apo tryptophanase fromEscherichia colireveals a wide-open conformation

The crystal structure of apo tryptophanase from Escherichia coli (space group F222, unit-cell parameters a = 118.4, b = 120.1, c = 171.2 A) was determined at 1.9 A resolution using the molecular-replacement method and refined to an R factor of 20.3% (R(free) = 23.2%). The structure revealed a significant shift in the relative orientation of the domains compared with both the holo form of Proteus vulgaris tryptophanase and with another crystal structure of apo E. coli tryptophanase, reflecting the internal flexibility of the molecule. Domain shifts were previously observed in tryptophanase and in the closely related enzyme tyrosine phenol-lyase, with the holo form found in an open conformation and the apo form in either an open or a closed conformation. Here, a wide-open conformation of the apo form of tryptophanase is reported. A conformational change is also observed in loop 297-303. The structure contains a hydrated Mg(2+) at the cation-binding site and a Cl(-) ion at the subunit interface. The enzyme activity depends on the nature of the bound cation, with smaller ions serving as inhibitors. It is hypothesized that this effect arises from variations of the coordination geometry of the bound cation.

Intrinsic fluorescence polarization of amniotic fluid: II. Toward a noninvasive method for the determination of fetal lung maturity

The present study compares two methods for the determination of fetal lung maturity: the novel intrinsic fluorescence polarization ratio (IFPR) and the commercial TDx-FLMII. Amniotic fluid (AF) samples were collected from 69 women during the second and third trimesters of singleton pregnancies. Thirty-three samples were tested for IFPR only after centrifugation, and the rest were examined both before and after centrifugation. Of the latter 33 samples, 29 were assessed for lung maturity with the TDx-FLMII method as well. The results showed that IFPR values decreased with the advance in gestational age (r = 0.77, p < 0.05, n = 69). A significant correlation was found between IFPR of centrifuged and noncentrifuged samples (r = 0.94, p < 0.05, n = 36). A significant correlation was demonstrated between IFPR and TDx-FLMII values of centrifuged (r = 0.75, p < 0.05, n = 29) and noncentrifuged (r = 0.63, p < 0.05, n = 29) samples and moreover, samples considered mature by TDx-FLMII had low values of IFPR (n = 10). It can be concluded that the IFPR method can utilize noncentrifuged AF, thus suggested as a potential noninvasive method.

Membrane-catalyzed nucleotide exchange on DnaA. Effect of surface molecular crowding

DnaA is the initiator protein for chromosomal replication in bacteria; its activity plays a central role in the timing of the primary initiations within the Escherichia coli cell cycle. A controlled, reversible conversion between the active ATP-DnaA and the inactive ADP forms modulates this activity. In a DNA-dependent manner, bound ATP is hydrolyzed to ADP. Acidic phospholipids with unsaturated fatty acids are capable of reactivating ADP-DnaA by promoting the release of the tightly bound ADP. The nucleotide dissociation kinetics, measured in the present study with the fluorescent derivative 3'-O-(N-methylantraniloyl)-5'-adenosine triphosphate, was dependent on the density of DnaA on the membrane in a cooperative manner: it increased 5-fold with decreased protein density. At all surface densities the nucleotide was completely released, presumably due to protein exchange on the membrane. Distinct temperature dependences and the effect of the crowding agent Ficoll suggest that two functional states of DnaA exist at high and low membrane occupancy, ascribed to local macromolecular crowding on the membrane surface. These novel phenomena are thought to play a major role in the mechanism regulating the initiation of chromosomal replication in bacteria.

Crystallization and preliminary X-ray analysis of the apo form of Escherichia coli tryptophanase

Tryptophanase from Escherichia coli is a pyridoxal phosphate-dependent homotetrametic enzyme with a subunit weight of 52 kDa. It has been crystallized in the apo form by the hanging-drop vapour-diffusion method using polyethylene glycol 400 as a precipitant and magnesium chloride as an additive. The crystals belong to the orthorhombic space group F222, with unit-cell parameters a = 118.4, b = 120.1, c = 171.2 A. A 97.8% complete data set to 1.9 A resolution was collected at a rotating-anode source from a single frozen crystal. Packing-density considerations agree with a monomer in the asymmetric unit with a solvent content of 55%. Tryptophanase mutants W330F and Y74F were crystallized under the same conditions and the crystals diffracted to a resolution limit of 1.9 A. Data sets of wild-type crystals soaked with L-tryptophan or pyridoxal phosphate were collected, as well as of Y74F mutant soaked with both.

Intrinsic fluorescence polarization of amniotic fluid: evaluation of human fetal lung maturity

This article reports a novel approach for the evaluation of fetal lung maturity based on fluorescence polarization (FP). The technique determines the intrinsic fluorescence polarization ratio (IFPR) of the amniotic fluid (AF). In vitro measurements of the IFPR indicate a clear dichotomy: high values for young pregnancies and low values for mature pregnancies. The new method has the potential to be a noninvasive procedure because the excitation of the AF and the collection of its fluorescence emission can be performed through the intact cervical amniotic membranes.

Phosphatidylethanolamine and phosphatidylglycerol are segregated into different domains in bacterial membrane. A study with pyrene-labelled phospholipids

To detect and characterize membrane domains that have been proposed to exist in bacteria, two kinds of pyrene-labelled phospholipids, 2-pyrene-decanoyl-phosphatidylethanolamine (PY-PE) and 2-pyrene-decanoyl-phosphatidylglycerol (PY-PG) were inserted into Escherichia coli or Bacillus subtilis membrane. The excimerization rate coefficient, calculated from the excimer-to-monomer ratio dependencies on the probe concentration, was two times higher for PY-PE than for PY-PG at 37 degrees C. This was ascribed to different local concentrations rather than to differences in mobility. The extent of mixing between the two fluorescent phospholipids, estimated by formation of their heteroexcimer, was found very low both in E. coli and B. subtilis, in contrast to model membranes. In addition, these two pyrene derivatives exhibited different temperature phase transitions and different detergent extractability, indicating that the surroundings of these phospholipids in bacterial membrane differ in organization and order. Inhibition of protein synthesis, leading to condensation of nucleoid and presumably to dissipation of membrane domains, indeed resulted in increased formation of heteroexcimers, broadening of phase transitions and equal detergent extractability of both probes. It is proposed that in bacterial membranes these phospholipids are segregated into distinct domains that differ in composition, proteo-lipid interaction and degree of order; the proteo-lipid domain being enriched by PE.

Low-frequency electromagnetic fields induce a stress effect upon higher plants, as evident by the universal stress signal, alanine

15N NMR analysis reveals alanine production in Duckweed plants exposed to low intensity sinusoidally varying magnetic fields (SVMF) at 60 and 100Hz, and fed by 15N-labeled ammonium chloride. Alanine does not accumulate in the absence of SVMF. Addition of vitamin C, a radical scavenger, reduced alanine production by 82%, indicating the roll of free radicals in the process. Alanine accumulation in plants and animals in response to exposure to a variety of stress conditions, including SVMF, is a general phenomenon. It is proposed that alanine is a universal first stress signal expressed by cells.

Coexistence of domains with distinct order and polarity in fluid bacterial membranes

In this study we sought the detection and characterization of bacterial membrane domains. Fluorescence generalized polarization (GP) spectra of laurdan-labeled Escherichia coli and temperature dependencies of both laurdan's GP and fluorescence anisotropy of 1,3-diphenyl-1,3,5-hexatriene (DPH) (rDPH) affirmed that at physiological temperatures, the E. coli membrane is in a liquid-crystalline phase. However, the strong excitation wavelength dependence of rlaurdan at 37 degrees C reflects membrane heterogeneity. Time-resolved fluorescence emission spectra, which display distinct biphasic redshift kinetics, verified the coexistence of two subpopulations of laurdan. In the initial phase, <50 ps, the redshift in the spectral mass center is much faster for laurdan excited at the blue edge (350 nm), whereas at longer time intervals, similar kinetics is observed upon excitation at either blue or red edge (400 nm). Excitation in the blue region selects laurdan molecules presumably located in a lipid domain in which fast intramolecular relaxation and low anisotropy characterize laurdan's emission. In the proteo-lipid domain, laurdan motion and conformation are restricted as exhibited by a slower relaxation rate, higher anisotropy and a lower GP value. Triple-Gaussian decomposition of laurdan emission spectra showed a sharp phase transition in the temperature dependence of individual components when excited in the blue but not in the red region. At least two kinds of domains of distinct polarity and order are suggested to coexist in the liquid-crystalline bacterial membrane: a lipid-enriched and a proteolipid domain. In bacteria with chloramphenicol (Cam)-inhibited protein synthesis, laurdan showed reduced polarity and restoration of an isoemissive point in the temperature-dependent spectra. These results suggest a decrease in membrane heterogeneity caused by Cam-induced domain dissipation.

On the regulatory role of dipeptidyl peptidase IV (=CD=adenosine deaminase complexing protein) on adenosine deaminase activity

The molecular mechanism controlling the variable activity of the malignancy marker adenosine deaminase (ADA) is enigmatic. ADA activity was found to be modulated by the membrane-bound adenosine deaminase complexing protein (CP=DPPIV=CD26). The role of lipid-protein interactions in this modulation was sought. While direct solubilization of ADA in vesicles resulted in loss of ADA activity, the binding of ADA to CP reconstituted in vesicles restored the specific activity. The activity of ADA, free or bound to CP in solution, resulted in continuous linear Arrhenius plots. However, ADA bound to reconstituted CP exhibited two breaks associated with approximately 30% increased activity, at 25 and 13 degrees C, yielding three lines with similar apparent activation energies (E(a)). Continuum solvent model calculations of the free energy of transfer of the transmembrane helix of CP from the aqueous phase into membranes of various widths show that the most favorable orientations of the helix above and below the main phase transition may be different. We suggest that the 20% change in the thickness of the bilayer below and above the main phase transition may modify the orientation of CP in the membrane, thereby affecting substrate accessibility of ADA. This could account for ADA's reduced activity associated with increased membrane fluidity in transformed vs. normal fibroblasts.

Nature of Interaction between basic fibroblast growth factor and the antiangiogenic drug 7,7-(carbonyl-bis[imino-N-methyl-4,2-pyrrolecarbonylimino[N-methyl-4,2-pyrrole]-carbonylimino])-bis-(1,3-naphtalene disulfonate). II. Removal of polar interactions affects protein folding

Fibroblast growth factor-2 (basic FGF), a potent inducer of angiogenesis, and the naphthalene sulfonic distamycin A derivative, 7,7-(carbonyl-bis[imino-N-methyl-4,2-pyrrolecarbonylimino[N-methyl-4,2-pyrrole]-carbonylimino])-bis-(1,3-naphtalene disulfonate) (PNU145156E), which exhibits in vivo antiangiogenic activity, form a tight reversible (1:1) complex. PNU145156E binds to the heparin and the selenate-binding sites on bFGF. The cis bFGF-heparin (2:1) complex, essential for the activation of the angiogenic process, is thus prevented. The nature of the forces involved in bFGF:PNU145156E complex, using the wild-type and the K128Q, K138Q, K134Q, and K128Q-K138Q point mutated bFGFs was sought. Based on thermodynamic analysis of the complexation constants, protein temperature stability profiles by ultraviolet absorption, circular dichroism measurements, fluorescence Förster energy-transfer, and anisotropy studies, in harmony with the published x-ray crystallographic structure, the following molecular interactions are proposed: reduced coulombic interactions, hence loosening of the complex by the removal of charged polar groups from the bFGF-heparin binding cleft resulted in decreased binding constants and in a change in the binding mode from polar to nonpolar. Concomitantly, upon mutation, the protein was rendered more compact, less flexible, and less aqueously exposed compared with the wild type. These were further pronounced with the double mutant: weaker dominantly nonpolar protein-drug interactions were accompanied by conspicuous folding. With heparin, however, wild-type bFGF forms a tighter complex with a more compact structure.

Cold-induced enzyme inactivation: how does cooling lead to pyridoxal phosphate-aldimine bond cleavage in tryptophanase?

The phenomenon of cold scission or cold lability, which entails a widespread variety of oligomeric enzymes, is still enigmatic. The effect of cooling on the activity and the quaternary structure of the pyridoxal 5'-phosphate (PLP)-dependent enzyme, tryptophanase (Tnase), was studied utilizing single photon counting time-resolved spectrofluorometry. Upon cooling of holo-wild-type (wt) Tnase and its W330F mutant from 25 degrees C to 2 degrees C, a reduction in PLP fluorescence lifetime and rotational correlation time as well as inactivation and dissociation from tetramers to dimers were observed for both enzymes. Fluorescence anisotropy invariably decreased as a consequence of cooling, whether it was accompanied by a slight decrease in activity without significant dissociation, or by a substantial decrease in activity that was associated with either a partial or major dissociation. These results support the suggested conformational change that precedes the PLP-aldimine bond scission. It is proposed that cold inactivation is initiated by the weakening of hydrophobic interactions, leading to conformational changes which are the driving force for the aldimine bond cleavage.

Effect of sinusoidally varying magnetic fields on cell proliferation and adenosine deaminase specific activity

The effect of sinusoidally varying magnetic fields (SVMF) on chick embryo fibroblasts (CEF) was examined by two independent methods: 1) measurement of cell proliferation at 0.06-0.7 mT (100, 60 and 50 Hz) using a colorimetric assay (MTT); 2) monitoring of specific activity of adenosine deaminase (ADA) at 0.3 and 0.7 mT, 60 Hz. Both increased cell proliferation and reduced ADA specific activity are associated with cell transformation. The MTT test showed an increase in cell proliferation of up to 64% after a 24 h exposure to SVMF at 100 Hz, 0.7 mT. Cell proliferation at constant frequency (100 Hz) depended on SVMF intensity. Cell proliferation at constant intensity (0.7 mT) increased with increasing field frequency. At 0.7 mT, 60 Hz cell proliferation increased by 31%, 28%, and 26% when measured by hemocytometry, 3H-thymidine incorporation, and the MTT assay, respectively. ADA specific activity in CEF decreased by circa 48% on exposure to SVMF at 60 Hz, 0.3 mT for 24 h; only a statistically insignificant trend was seen at 0.7 mT, 60 Hz. Our findings showed that CEF cell proliferation and ADA specific activity were modified by SVMF. Both methods, independently, qualitatively detect a magnetic field effect.

Transcription- and translation-dependent changes in membrane dynamics in bacteria: testing the transertion model for domain formation

Cell cycle events have been proposed to be triggered by the formation of membrane domains in the process of coupled transcription, translation and insertion ('transertion') of nascent membrane and exported proteins. Disruption of domain structure should lead to changes in membrane dynamics. Membrane viscosity of Escherichia coli and Bacillus subtilis decreased after inhibition of protein synthesis by chloramphenicol or puromycin, or of RNA initiation by rifampicin, but not after inhibition of RNA elongation by streptolydigin or amino acid starvation of a stringent strain. The decrease caused by inhibitors of protein synthesis was prevented by streptolydigin if added simultaneously, but was not reversed if added later. The drug-induced decrease in membrane viscosity is energy dependent: it did not happen in KCN-treated cells. All treatments decreasing membrane viscosity also induced nucleoid compaction and fusion. Inhibition of macromolecular synthesis without membrane perturbation caused nucleoids to expand. Changes in membrane dynamics were also displayed during a nutritional shift-down transition that causes imbalance in macromolecular syntheses. The results are consistent with the transertion model, predicting dissipation of membrane domains by termination of protein synthesis or detachment of polysomes from DNA; domain structure is conserved if the transertion process is 'frozen'.

Enhanced proliferation caused by a low frequency weak magnetic field in chick embryo fibroblasts is suppressed by radical scavengers

Sinusoidal varying magnetic fields (SVMF) were reported by us to enhance the proliferation of chick embryo fibroblasts (CEF). The mechanism through which SVMF affects biological systems is still enigmatic. While the SVMF examined by us (50, 60, and 100 Hz/0.06-0.7 mT) were all below kT, they may have the potential of altering chemical processes in which excited radicals are involved. We tested this hypothesis by subjecting CEF to radical scavengers during exposure to a magnetic field of 100 Hz and 0.7 mT for 24 h. Cell proliferation was evaluated by MTT colorimetric assay. In the presence of catalase, superoxide dismutase, or vitamin E, the SVMF enhanced cell proliferation was reduced by 79, 67, and 82%, respectively. The addition of exogenous radical scavengers to the cells during the exposure to magnetic field significantly suppressed the enhancement in cell proliferation caused by the field.

Pyridoxal phosphate binding to wild type, W330F, and C298S mutants of Escherichia coli apotryptophanase: unraveling the cold inactivation

The mechanism of pyridoxal phosphate (PLP) binding to apotryptophanase was investigated using stopped-flow kinetics with wild type (WT), W330F and C298S mutants. Based on the dependence of the rate constants on PLP concentrations for the fast and slow phases detected, two mechanistic schemes were proposed. For the WT and C298S mutant, the slow process is due to an isomerization of the aldimine complex after its formation, and not to the binding to an alternative conformation of the apoenzyme, which is the case proposed for the W330F mutant. It is suggested that during the cold inactivation process a conformational change precedes the aldimine bond cleavage. For the W330F apotryptophanase, another conformational change occurs subsequent to the aldimine bond cleavage.

Nature of interaction between basic fibroblast growth factor and the antiangiogenic drug 7,7-(Carbonyl-bis[imino-N-methyl-4, 2-pyrrolecarbonylimino[N-methyl-4,2-pyrrole]-carbonylimino] )bis-(1, 3-naphthalene disulfonate)

PNU145156E (7,7-(carbonyl-bis[imino-N-methyl-4, 2-pyrrolecarbonylimino[N-methyl-4,2-pyrrole]-carbonylimino]) -bis-(1, 3-naphthalene disulfonate)) is a naphthalene sulfonic distamycin A derivative that interacts with heparin-binding growth factors. Because PNU145156E inhibits tumor angiogenesis, it was selected for clinical development. Picosecond time-resolved fluorescence emission and anisotropy were used to characterize the binding of PNU145156E to the basic fibroblast growth factor (a protein associated with tumor angiogenesis). A decrease in PNU145156E fluorescence lifetime was observed as a function of human basic fibroblast growth factor (bFGF) concentration. Nonlinear least-squares fitting of the binding isotherm yielded Kd = 145 nM for a single class of binding sites. Time-resolved anisotropy gave Kd = 174 nM. Kd = 150 nM was independently verified by quantitative high-performance affinity chromatography. The displaced volume of the complex, calculated from its rotational correlation time, fitted a sphere of 1:1 stoichiometry. These results account for the formation of a tight yet reversible PNU145156E:bFGF complex. An evaluation of PNU145156E fluorescence lifetimes in various solvents has highlighted the forces involved in stabilizing the complex. These are mostly electrostatic-hydrophobic in nature, with a relatively low contribution from hydrogen bonding. Both polar and nonpolar groups are involved on the protein-binding site within a largely hydrophobic cleft. A potential binding trajectory, based on a combination of these results with site-directed chemical modification and known bFGF x-ray structure, is suggested.

Cold inactivation and dissociation into dimers of Escherichia coli tryptophanase and its W330F mutant form

The kinetics and mechanism of reversible cold inactivation of the tetrameric enzyme tryptophanase have been studied. Cold inactivation is shown to occur slowly in the presence of K+ ions and much faster in their absence. The W330F mutant tryptophanase undergoes rapid cold inactivation even in the presence of K+ ions. In all cases the inactivation is accompanied by a decrease of the coenzyme 420-nm CD and absorption peaks and a shift of the latter peak to shorter wavelengths. The spectral changes and the NaBH4 test indicate that cooling of tryptophanase leads to breaking of the internal aldimine bond and release of the coenzyme. HPLC analysis showed that the ensuing apoenzyme dissociates into dimers. The dissociation depends on the nature and concentration of anions in the buffer solution. It readily occurs at low protein concentrations in the presence of salting-in anions Cl-, NO3- and I-, whereas salting-out anions, especially HPO4(2-), hinder the dissociation. K+ ions do not influence the dissociation of the apoenzyme, but partially protect holotryptophanase from cold inactivation. Thus, the two processes, cold inactivation of tryptophanase and dissociation of its apoform into dimers exhibit different dependencies on K+ ions and anions.

Alterations in membrane lipid dynamics of leukemic cells undergoing growth arrest and differentiation: dependency on the inducing agent

The effect of various differentiation inducers on membrane cell dynamics was studied using HL-60 and K562 leukemic cell lines. Membrane lipid dynamics was measured by the steady-state fluorescence polarization (P) method utilizing either 1,6-diphenyl-1,3,5-hexatriene (DPH) or the trimethyl ammonium derivative of DPH (TMA-DPH), which ascertains anchorage of the label to the membrane-water-lipid interface. Decrease in membrane microfluidity was observed in HL-60 cells undergoing differentiation into macrophages by 1,25-dihydroxyvitamin D3 and by K562 cells induced to differentiate by DMSO. Sodium butyrate caused an increase in membrane fluidity in K562 cells undergoing differentiation into erythroid-like cells while in HL-60 cells a dual effect was observed. At 0.4 mM concentration, in which the cells were induced to differentiate along the monocyte pathway, a decrease in membrane fluidity was observed, while at 1 mM concentration an increase in membrane fluidity occurred. Interferon-gamma (IFN-gamma) induced an increase in membrane fluidity in both cell lines. Using HL-60 cells fluorescently labeled by TMA-DPH, similar results indicating fluidization of the membrane following IFN-gamma treatment were obtained. Advanced fluorescence lifetime measurements, evaluated either by phase modulation spectrofluorometry or by single photon correlation fluorometry confirmed that the decrease in fluorescence polarization by IFN-gamma resulted from membrane fluidization and not from elongation of the probe's excited state lifetime. It is suggested that the inducer mode of action, and not the differentiation route, determine the outcome of changes in membrane microviscosity.

The CP-I subunit of adenosine deaminase complexing protein from calf kidney is identical to human, mouse, and rat dipeptidyl peptidase IV

The CP-I subunit of calf kidney adenosine deaminase complexing protein (ADCP), isolated by affinity chromatography based on Sepharose-4B immobilized adenosine deaminase, is identical with dipeptidyl peptidase IV. This finding is based on the following results: (a) Its M(r) = 110 kD, as determined by sodium dodecyl sulphate polyacrylamide gel electrophoresis; (b) its catalytic activity toward Gly-Pro-p-nitroanilide; (c) its inhibition by serine protease inhibitor; and (d) by two peptide sequences resulting from its trypsin proteolysis. Accordingly, the CP-I subunit of ADCP isolated from bovine kidney is DPPIV (CD26). Thus, as anticipated, the high affinity between ADA subunits prevails even when they originate in different species.

Probing the active site of adenosine deaminase by a pH responsive fluorescent competitive inhibitor

The adenine analog erythro-9-(2-hydroxy-3-nonyl)adenine, EHNA, a tight reversible inhibitor (KI = 1.6 x 10(-9) M) of adenosine deaminase (EC 3.5.4.4) (ADase), was modified into the fluorescent etheno derivative epsilon-EHNA. The latter is a competitive inhibitor of adenosine deaminase [KI = (2.80 +/- 0.01)10(-6) M], having the fluorescent properties of epsilon-adenines. Affinity to the active site, monitored by both steady-state and dynamic fluorescence polarization, was confirmed by competition experiments with 2'-deoxycoformycin, the substrate adenosine and EHNA. The epsilon-adenine moiety of epsilon-EHNA librates at the shallow active site of ADase. The low absorptivity of epsilon-EHNA required the measurement of fluorescence excitation spectra. Computer subtraction of fluorescence excitation spectrum of ADase from that of its equimolar complex with epsilon-EHNA revealed the corrected excitation spectrum of epsilon-EHNA at the active site of the enzyme. This spectrum mimics that of epsilon-EHNA at pH 5.5 in buffer solution, implying its protonation at the active site of the enzyme. These results are in agreement with the presence of acidic amino acids that are essential to the catalytic mechanism.

Distamycin-A derivatives potentiate tumor-necrosis-factor activity via the modulation of tyrosine phosphorylation

The cytotoxic activities of 2 novel distamycin-A derivatives, FCE 24517 and FCE 25450A, alone and in combination with tumor-necrosis factor-alpha (TNF), were studied. Both drugs, especially FCE 25450A, analyzed extensively here, inhibited the growth of HL60 promyelocytic cells, and human SV80 and murine L929 transformed fibroblasts in a dose-dependent manner. The growth-inhibitory potential of sequential exposure to the distamycin-A analogs and TNF was determined. A 4-hr treatment of L929 fibroblasts with 100-1,000 ng/ml FCE 25450A, followed by 2 ng/ml TNF, resulted in a synergistic anti-proliferative effect. The synergism of FCE 24517 with TNF was less profound. Experiments to elucidate the mechanism underlying the cooperation revealed that FCE 25450A pre-treatment almost completely abolished the elevated tyrosine phosphorylation of a 137-kDa and other membranal proteins and prevented the de-phosphorylation of another protein band observed in L929 cells in the presence of TNF. FCE 25450A alone induced no changes in the phosphotyrosine profile of the cells. The effect of FCE 25450A was counteracted by the tyrosine-phosphatase inhibitor orthovanadate. In parallel, the inhibitor also diminished the antiproliferative action of the FCE 25450A/TNF combination. These findings suggest that, beyond their cytotoxic effects as single agents, the distamycin derivatives increase the sensitivity of cells to TNF. This effect is governed via the inhibition of TNF-induced tyrosine phosphorylation of specific proteins which are probably involved in the development of TNF resistance. Thus, protein de-phosphorylation might provide an additional mechanism of action of these novel distamycin-A-derived drugs.

Interaction of a novel fluorescent analog of interferon-gamma with transformed cells

A fluorescent analog of human recombinant interferon-gamma (IFN-gamma) was prepared for the first time. The recovered pyrene-labeled IFN-gamma (py-IFN-gamma), with an estimated seven pyrene molecules per IFN-gamma, retained over half of its original biological activity. Binding of py-IFN-gamma to human amnion WISH cells showed appreciable enhancement in fluorescence polarization from 0.055 to 0.215 and in fluorescence lifetime from 56 to 80 ns. The ratio of the vibronic peaks did not change, indicating that the pyrene molecules remained in water environment even after binding. Py-IFN-gamma provides a novel tool for unraveling the mechanism of the initial interaction between this antiproliferative lymphokine and its target, cancer cell membrane receptors. Its fluorescence could provide the means to follow receptor recycling when it occurs.

Novel fluorescence-photochrome labeling method in the study of biomembrane dynamics

A novel photochrome-fluorescence method (PFLM) based on monitoring fluorescence parameters and kinetics of photochrome photoisomerization of para-substituted stilbenes (PSS) has been proposed. It was shown that PSS exhibits fluorescence characteristics which are similar to ones of typical membrane fluorescence probes such as diphenylhexatriene (DPH). A study of kinetics of PSS trans-cis and cis-trans photoisomerization makes it possible to estimate, under certain conditions, the rotational correlation time of the stilbene fragments in the excited state of PSS for the fixed angle 180 degrees. In viscous media this process is a rate-determining stage. Taken together, the both techniques, fluorescence and photochrome, make it possible to establish a detailed mechanism and measure quantitative parameters of stilbene probe (PSS) mobility in a membrane. The PFLM was applied to the study of E. coli membrane dynamics.

Interactions of Escherichia coli tryptophanase with quasisubstrates and monovalent cations studied by the circular dichroism and fluorescence methods

The reaction of tryptophanase and its W330F and W248F mutant forms with quasi-substrates forming an external pyridoxal phosphate aldimine or quinonoid is accompanied by the appearance of a positive circular dichroism (CD) peak at 290 nm. The peak seems to arise from a Tyr residue undergoing reorientation during the reaction. The peak does not appear upon formation of non-covalent Michaelis complexes of the enzyme with quasi-substrates such as indolepropionate, beta-phenyllactate and alpha-methylphenylalanine. The non-covalent complexes and external aldimines exhibit similar absorption spectra but can be distinguished by their CD and by the intensity of their fluorescence. Formation of the non-covalent complexes leads to an increase in positive CD at 420 nm while formation of the external aldimines leads to disappearance of the positive CD at 420 nm and its replacement by negative CD; it also leads to strong quenching of the coenzyme fluorescence at 500 nm. The quantum yield of fluorescence of the external aldimines is 6-times lower than that of the internal aldimine. Activating cations (K+, NH4+) strongly diminish the intensity of a negative protein CD band at 275 nm. From a comparison of the intensity of this band in the spectra of the wild-type holo- and apoenzyme and in the tryptophan mutants, it was deduced that the band belongs to a Tyr residue, which may be a part of the cation-binding site or located in its immediate vicinity.

Purinergically induced membrane fluidization in ciliary cells: characterization and control by calcium and membrane potential

To examine the role of membrane dynamics in transmembrane signal transduction, we studied changes in membrane fluidity in mucociliary tissues from frog palate and esophagus epithelia stimulated by extracellular ATP. Micromolar concentrations of ATP induced strong changes in fluorescence polarization, possibly indicating membrane fluidization. This effect was dosage dependent, reaching a maximum at 10-microM ATP. It was dependent on the presence of extracellular Ca2+ (or Mg2+), though it was insensitive to inhibitors of voltage-gated calcium channels. It was inhibited by thapsigargin and by ionomycin (at low extracellular Ca2+ concentration), both of which deplete Ca2+ stores. It was inhibited by the calcium-activated potassium channel inhibitors quinidine, charybdotoxin, and apamine and was reduced considerably by replacement of extracellular Na+ with K+. Hyperpolarization, or depolarization, of the mucociliary membrane induced membrane fluidization. The degree of membrane fluidization depended on the degree of hyperpolarization or depolarization of the ciliary membrane potential and was considerably lower than the effect induced by extracellular ATP. These results indicate that appreciable membrane fluidization induced by extracellular ATP depends both on an increase in intracellular Ca2+, mainly from its internal stores, and on hyperpolarization of the membrane. Calcium-dependent potassium channels couple the two effects. In light of recent results on the enhancement of ciliary beat frequency, it would appear that extracellular ATP-induced changes both in ciliary beat frequency and in membrane fluidity are triggered by similar signal transduction pathways.