Biomedical subjects

N Milosevic

Publications and source records attributed to N Milosevic.

6 recordsLinked to original sources

PubMed2002

Semiclassical Dirac theory of tunnel ionization.

We present analytic tunnel ionization rates for hydrogenlike ions in ultrahigh intensity laser fields, as obtained from a semiclassical solution of the three-dimensional Dirac equation. This presents the first quantitative determination of tunneling in atomic ions in the relativistic regime. Our theory opens the possibility to study strong laser field processes with highly charged ions, where relativistic ionization plays a dominant role.

Journal Article↗

PubMed2001

Attosecond metrology.

The generation of ultrashort pulses is a key to exploring the dynamic behaviour of matter on ever-shorter timescales. Recent developments have pushed the duration of laser pulses close to its natural limit-the wave cycle, which lasts somewhat longer than one femtosecond (1 fs = 10-15 s) in the visible spectral range. Time-resolved measurements with these pulses are able to trace dynamics of molecular structure, but fail to capture electronic processes occurring on an attosecond (1 as = 10-18 s) timescale. Here we trace electronic dynamics with a time resolution of </= 150 as by using a subfemtosecond soft-X-ray pulse and a few-cycle visible light pulse. Our measurement indicates an attosecond response of the atomic system, a soft-X-ray pulse duration of 650 +/- 150 as and an attosecond synchronism of the soft-X-ray pulse with the light field. The demonstrated experimental tools and techniques open the door to attosecond spectroscopy of bound electrons.

Journal Article↗

PubMed2001

Immobilisation on polystyrene of diazirine derivatives of mono- and disaccharides: biological activities of modified surfaces.

The potential of surface glycoengineering for biomaterials and biosensors originates from the importance of carbohydrate-protein interactions in biological systems. The strategy employed here utilises carbene generated by illumination of diazirine to achieve covalent bonding of carbohydrates. Here, we describe the synthesis of an aryl diazirine containing a disaccharide (lactose). Surface analysis techniques [X-ray photoelectron spectroscopy (XPS) and time of flight secondary ion mass spectroscopy (ToF-SIMS)] demonstrate its successful surface immobilisation on polystyrene (PS). Results are compared to those previously obtained with an aryl diazirine containing a monosaccharide (galactose). The biological activity of galactose- or lactose-modified PS samples is studied using rat hepatocytes, Allo A lectin and solid-phase semi-synthesis with alpha-2,6-sialyltransferase. Allo A shows some binding to galactose-modified PS but none to lactose-modified surfaces. Similar results are obtained with rat hepatocytes. In contrast, sialylation of lactose-modified PS is achieved but not with galactose-modified surfaces. The different responses indicate that the biological activity depends not only on the carbohydrate per se but also on the structure and length of the spacer.

Animals↗

PubMed2000

Lead stimulates intercellular signalling between hepatocytes and Kupffer cells.

The role of intercellular signalling between liver cells in lead (Pb)(1)-induced liver toxicity was investigated in cocultures of freshly isolated and cultured rat hepatocytes and Kupffer cells. The Kupffer cells (seeded onto culture dish inserts), the hepatocytes or the two in cocultures were exposed to Pb acetate (2-50 microM) in combination with lipopolysaccharide (0.1-1000 ng/ml). In hepatocyte cultures, the combined Pb/lipopolysaccharide treatment induced no significant increase in the release of the proinflammatory cytokine tumor necrosis factor-alpha (TNF-alpha) whereas in Kupffer cell cultures and in cocultures, at low lipopolysaccharide levels (0.1 and 1 ng/ml), TNF-alpha release was synergistically increased (up to 30-fold) when compared to lipopolysaccharide exposure alone. This stimulation of Kupffer cell-derived TNF-alpha release was specific for Pb or not detectable with mercury and cadmium. As a response to the Pb/lipopolysaccharide induced release of TNF-alpha, the cocultured hepatocytes increased their nitric oxide (NO) content sixfold when compared with lipopolysaccharide alone and downregulated the negatively regulated acute phase protein albumin. This downregulation was also detectable without lipopolysaccharide and without TNF-alpha release, indicating that Pb induces additional thus far unidentified Kupffer cell-derived factors, which interact with the cocultured hepatocytes. At the time of TNF-alpha release, the viability of the hepatocytes and the Kupffer cells was not affected. However, after a 48-h treatment period, Pb induced a Kupffer cell specific toxicity without affecting the hepatocytes. Loss of hepatocyte viability after lipopolysaccharide/Pb stimulation was only detectable in the presence of cocultured Kupffer cells together with human-derived granulocytes. It is concluded that Pb stimulates intercellular signalling between Kupffer cells and hepatocytes which is synergistically enhanced in the presence of low lipopolysaccharide levels. The released Kupffer cell-derived signals (e.g. cytokines) promotes most likely proteolytic hepatocyte killing in combination with a direct cellular interaction between the granulocytes and the hepatocytes.

Acetates↗

PubMed1999

Kupffer cell-mediated differential down-regulation of cytochrome P450 metabolism in rat hepatocytes.

Nonparenchymal cells, particularly Kupffer cells, might play an important role in the modulation of xenobiotic metabolism in liver and its pharmacological and toxicological consequences. This intercellular communication via the exchange of soluble factors was investigated in primary rat Kupffer cells and hepatocytes. Freshly isolated rat Kupffer cells were seeded onto cell culture inserts and cocultured with 5 day old serum-free rat hepatocyte monolayer cultures at a ratio of 1:1 for 2 days. Hepatocyte cultures, Kupffer cell cultures or cocultures were treated with 0.1 ng/ml-10 microg/ml lipopolysaccharide (LPS). Within this concentration range, no significant toxicity was observed in either cell type. In LPS-exposed cocultures, tumor necrosis factor alpha (TNFalpha) levels rose up to 5 ng/ml within 5 h; nitric oxide (NO) levels increased up to 70 microM within 48 h of treatment, both in a dose-dependent fashion. The release of negative (albumin) and positive (alpha1-acid-glycoprotein) acute phase proteins from the hepatocytes was strongly down- and up-regulated, respectively. The simultaneous treatment of the cocultures with phenobarbital and LPS (10 ng/ml) or 3-methylcholanthrene and LPS (10 ng/ml) resulted in a strong down-regulation (85%) of the phenobarbital-induced cytochrome P450 (CYP) isoform CYP2B1 in the hepatocytes whereas the 3-methylcholanthrene-induced isoform CYP1A1 was only weakly affected (15%). This specific down-regulation of CYP2B1 was mediated exclusively by TNFalpha, released from the Kupffer cells. It was not linked with NO release from or inducible NO synthase activity in the hepatocytes. The TNFalpha release was not affected by the two xenobiotics. Acetaminophen tested in these cocultures showed no direct interaction with the Kupffer cells. The use of liver cell cocultures is therefore a useful approach to investigate the influence of intercellular communication on xenobiotic metabolism in liver.

Acetaminophen↗

PubMed1999

[Cocultures between primary parenchymal and nonparenchymal liver cells improve the reliability of results from in vitro toxicity testing]

Conventional homotypic hepatocyte cultures do not include the possible contribution of nonparenchymal liver cells, particularly Kupffer cells, to the pharmacological and toxicological consequences after exposure to xenobiotics. Therefore the exchange of soluble factors between liver cells was investigated in cocultures between primary, freshly isolated cultured rat hepatocytes and Kupffer cells. Cocultures were exposed to endotoxins in combination with phenobarbital, 3-methylcholanthrene or lead. A strong but selective down-regulation of xenobiotic induced cytochrome P450 isoforms was detectable, mediated exclusively by TNFalphareleased from the Kupffer cells. Pb synergistically increased this endotoxin induced TNFalpha-release. The results indicate that cocultures improve the reliability of data obtained from organ specific cell cultures and that they simulate much closer the situation in the intact liver.

Journal Article↗