Biomedical subjects

A Constantinescu

Publications and source records attributed to A Constantinescu.

At least 19 recordsLinked to original sources

PubMed2005

Changes of the nutrient loads of the Danube since the late eighties: An analysis based on long term changes along the whole Danube River and its main tributaries.

The Danube nutrient loads are affected by human impacts mainly from agriculture and wastewater discharges. Knowledge about the Danube nutrient loads and the changes of these loads over time is essential for understanding the changes within the ecosystem of the Black Sea, induced by these loads. The paper shows the long term changes of the nutrient load along the Danube estimated by measurements from different countries and institutions. The results show large differences between Dissolved Inorganic Nitrogen (DIN) and Total Phosphorus (TP). For TP, the Danube River loads show a strong decrease since 1988-1992, especially in the Middle and Lower basin. This change is probably partly connected to the dramatic economic changes in the Middle and Eastern European countries following the collapse of the communist system. The DIN load does not show a decreasing trend in the last decade. The data indicate that there may be a decreasing trend in the anthropogenic emissions, but that such a trend is counteracted by a significantly increasing trend of the Danube discharge in the last decade. The accuracy of the available data is analysed in the paper as well.

Environmental Monitoring↗

PubMed2004

Hypoxic rise in cytosolic calcium and renal proximal tubule injury mediated by a nickel-sensitive pathway.

In the kidney, cell injury resulting from ischemia and hypoxia is thought to be due, in part, to increased cytosolic Ca(2+) levels, [Ca(2+)]i, leading to activation of lytic enzymes, cell dysfunction, and necrosis. We report evidence of a progressive and exponential increase in [Ca(2+)]i (from 245 +/- 10 to 975 +/- 100 nM at 45 mins), cell permeabilization and propidium iodide (PI) staining of the nucleus, and partial loss of cell transport functions such as Na(+)-gradient-dependent uptakes of (14)C-alpha-methylglucopyranoside and inorganic phosphate ((32)Pi) in proximal convoluted tubules of adult rabbits subjected to hypoxia. The rise in [Ca(2+)]i depended on the presence of extracellular [Ca(2+)] and could be blocked by 50 microM Ni(2+)but not by verapamil (100 microM). Presence of 50 microM Ni(2+) also reduced the hypoxia-induced morphological and functional injuries. We also used HEK 293 cells, a kidney cell line, incubated in media without glucose and exposed for 3.5 hrs to 1% O(2)-5% CO(2) and then returned to glucose-containing media for another 3.5 hrs in an air-5% CO(2) atmosphere and finally exposed for 1 min to media containing 1 microM PI. NiCl(2) (50 microM) or pentobarbital (300 microM) more than phenobarbital (1.5 mM), when present in the incubation medium during both the hypoxic and the reoxygenation periods, induced significant (P < 0.001) reductions in the number of cell nuclei stained with PI, similar to their relative potency as inhibitors of T channels. Our findings indicate that hypoxia-induced alterations in calcium level and subsequent cell injury in the proximal convoluted tubule and in HEK cells involve a nickel-sensitive and dihydropyridine insensitive pathway or channel.

Animals↗

PubMed2003

Solving the ultranonlocality problem in time-dependent spin-density-functional theory.

It has been known for some time that the exchange-correlation potential in time-dependent density-functional theory is an intrinsically nonlocal functional of the density as soon as one goes beyond the adiabatic approximation. In this paper we show that a much more severe nonlocality problem, with a completely different physical origin, plagues the exchange-correlation potentials in time-dependent spin-density functional theory. We show how the use of the spin current density as a basic variable solves this problem, and we provide an explicit local expression for the exchange-correlation fields as functionals of the spin currents.

Journal Article↗

PubMed2001

Tumor oximetry: demonstration of an enhanced dynamic mapping procedure using fluorine-19 echo planar magnetic resonance imaging in the Dunning prostate R3327-AT1 rat tumor.

PURPOSE: We have developed an enhanced approach to measuring regional oxygen tension (pO(2)) dynamics in tumors. The technique is demonstrated in a group of 8 Dunning prostate rat tumors (R3327-AT1) with respect to respiratory challenge. METHODS AND MATERIALS: Hexafluorobenzene was injected directly into the tumors of anesthetized rats. (19)F nuclear magnetic resonance echo planar imaging relaxometry was performed to obtain maps of regional tumor oxygenation under baseline conditions and when the inhaled gas was changed to oxygen or carbogen. RESULTS: Sequential pO(2) maps required 8 min, with a typical precision of 1-3 torr at 30-100 individual regions across a tumor. When rats breathed 33% oxygen, distinct heterogeneity was observed for baseline oxygenation in each tumor with pO(2) values ranging from hypoxic to greater than 100 torr. Larger tumors showed significantly lower baseline pO(2). Respiratory challenge with oxygen or carbogen produced significant increases in tumor oxygenation with a close correlation between the response to each gas at individual locations. Regions of both small and large tumors responded to respiratory challenge, but the rate was generally much faster in initially well-oxygenated regions. CONCLUSIONS: Regional pO(2) was assessed quantitatively and the response of multiple individual tumor regions observed simultaneously with respect to interventions.

Animals↗

PubMed2001

Annexin V binds to positively selected B cells.

Recombinant annexin V (rAnV) has been used in flow cytometry to identify cells undergoing apoptosis, based on its ability to bind to phosphatidylserine, a negatively charged lipid normally restricted to the cytoplasmic face of the plasma membrane but externalized early during apoptosis. When we stained murine bone marrow (BM) cells with fluorescently labeled rAnV, we found that a surprisingly large fraction of BM B cells bearing selectable transgenic Ag receptors bind significant amounts of rAnV, but that these cells are not apoptotic. Here, we show that binding of rAnV to developing B cells in normal mice correlates with B cell receptor-dependent selection events at several stages of development within both B-1 and B-2 cell subsets. In fact, nearly all B-1 B cells and splenic marginal zone B cells bind rAnV, suggesting that the externalization of phosphatidylserine occurs once mature B cells are selected through BCR-mediated signaling. However, this plasma membrane alteration is apparently not shared by all lymphocytes, because we did not find a parallel population of rAnV-binding viable T cells in vivo in normal or TCR transgenic mice. We also show that BM stromal cell lines can influence the extent of rAnV binding by viable BM B cells during coculture in vitro. We suggest that rAnV detects a potentially important membrane alteration that occurs as B cells develop in the BM and are readied for export to the peripheral lymphoid organs and again among mature B cells recruited to the marginal zone or the B-1 compartment.

Animals↗

PubMed2001

Bone phenotype of the aromatase deficient mouse.

Estrogens are important for normal bone growth and metabolism. The mechanisms are incompletely understood. Thus, we have undertaken characterization of the skeletal phenotype of aromatase (ArKO) deficient mice. No abnormalities have been noted in skeletal patterning in newborns. Adult ArKO mice show decreased femur length and decreased peak Bone Mineral Density (BMD) with accelerated bone loss by 7 months of age in females. Magnetic resonance microscopy (MR) and microCT (microCT) imaging disclosed decreased cancellous connectivity and reduced cancellous bone volume in ArKO females. Bone formation rate (BFR) is increased in ArKO females and decreased in ArKO males. Estradiol therapy reverses these changes. This anabolic effect of estradiol in the male skeleton is supported by 18-F- Positron Emission Tomography (PET) imaging, which clearly demonstrates decreased spinal uptake, but marked increase after estradiol therapy. Serum IGF-1 levels are high in young female ArKO mice but low in young ArKO males. The reduced BMD in ArKO females, despite the presence of elevated serum IGF 1, suggests that other mechanism(s) are operative. There is increased B-cell lymphopoiesis in adult female ArKO bone marrow cells. These results show that ArKO mice show the effects of estrogen deficiency on bone growth, mass, metabolism, microarchitecture and the hematopoietic microenvironment.

Animals↗

PubMed2001

Prognostic radiology: quantitative assessment of tumor oxygen dynamics by MRI.

It is generally recognized that tumor hypoxia has a strong influence over therapeutic outcome in the clinic. The authors have developed an oximetry approach using 19F echo planar magnetic resonance imaging-FREDOM (Fluorocarbon Relaxometry using Echoplanar imaging for Dynamic Oxygen Mapping), which reveals dynamic changes based on sequential maps of regional tumor PO2. Preclinical investigations focused on diverse sublines of the Dunning prostate R3327 tumor. As expected, intratumoral heterogeneity was considerable. However, large tumors (>3.5 cm3) were significantly less well oxygenated than smaller tumors (<2 cm3). Faster growing, less differentiated tumors were less well oxygenated than size-matched tumors of slower growing sublines. The greatest potential of this technique is the ability to follow the fate of individual tumor regions with respect to interventions. For each subline, there was a significant response to respiratory challenge with oxygen for initially well-oxygenated regions (baseline PO2 > 10 mm Hg). More interestingly, subline dependent behavior was found for initially hypoxic regions that correlated with rate of growth. The authors believe the FREDOM approach is essentially ripe for translation to the clinic. This approach could help to identify patients with hypoxic tumors and indicate the feasibility of manipulating tumor characteristics through adjuvant interventions to improve therapeutic response.

Animals↗

PubMed2001

Tumor oxygen dynamics with respect to growth and respiratory challenge: investigation of the Dunning prostate R3327-HI tumor.

We recently described a novel approach to measuring regional tumor oxygen tension using (19)F nuclear magnetic resonance echo planar imaging relaxometry (FREDOM) of hexafluorobenzene. We have now applied this technique to evaluate in detail the oxygen tension dynamics in the relatively slowly growing, moderately well-differentiated Dunning prostate R3327 HI rat tumor with respect to tumor growth and respiratory challenge. Seven individual tumors were assessed repeatedly over a period of 5 weeks ( approximately 4 volume doubling times). For small tumors (<1 cm(3)), the mean pO(2) ranged from 28 to 44 Torr under baseline conditions, decreasing to less than 10 Torr when the tumors reached 5 to 6 cm(3), with a strong inverse correlation between the baseline tumor oxygen tension and the tumor size. The hypoxic fraction (defined as the percentage of the voxels with pO(2) <10 Torr) increased significantly with tumor growth. Administration of oxygen or carbogen produced a significant increase (P < 0.0001) in tumor oxygenation at all stages of tumor growth. Most interestingly, even regions of these tumors that were initially poorly oxygenated responded rapidly, and significantly, to respiratory intervention, in contrast to the behavior of the faster-growing rat prostate tumors investigated previously.

Animals↗

PubMed2000

Enhancing hepatocyte adhesion by pulsed plasma deposition and polyethylene glycol coupling.

Decreased hepatocyte adhesion to polymeric constructs limits the function of tissue engineered hepatic assist devices. We grafted adhesion peptides (RGD and YIGSR) to polycaprolactone (PCL) and poly-L-lactic acid (PLLA) in order to mimic the in vivo extracellular matrix and thus enhance hepatocyte adhesion. Peptide grafting was done by a novel technique in which polyethylene glycol (PEG)-adhesion peptide was linked to allyl-amine coated on the surface of PCL and PLLA by pulsed plasma deposition (PPD). Peptide grafting density, quantified by radio-iodinated tyrosine in YIGSR, was 158 fmol/cm(2) on PLLA and 425 fmol/cm(2) on PCL surfaces. The adhesion of hepatocytes was determined by plating 250,000 hepatocytes/well (test substrates were coated on 12 well plates) and quantifying the percentage of adhered cells after 6 h by MTT assay. Adhesion on PCL surfaces was significantly enhanced (p < 0.05) by both YIGSR (percentage of adhered cells = 53 +/- 7%) and RGD (53 +/- 12%) when compared to control surfaces (31 +/- 8%). Hepatocyte adhesion on PLLA was significantly (p < 0.05) enhanced on PLLA-PEG-RGD surfaces (76 +/- 14%) compared to control surfaces (42 +/- 19%) and more (68 +/- 25%) but not statistically significant (p = 0.15) on PLLA-PEG-YIGSR surfaces compared to control surfaces. These results indicate that hepatocyte adhesion to PCL and PLLA based polymeric surfaces can be enhanced by a novel adhesion peptide grafting technique using pulsed plasma deposition and PEG cross-linking.

Animals↗

PubMed1999

Ethanol-induced translocation of cAMP-dependent protein kinase to the nucleus. Mechanism and functional consequences.

Ethanol induces translocation of the catalytic subunit (Calpha) of cAMP-dependent protein kinase (PKA) from the Golgi area to the nucleus in NG108-15 cells. Ethanol also induces translocation of the RIIbeta regulatory subunit of PKA to the nucleus; RI and Cbeta are not translocated. Nuclear PKA activity in ethanol-treated cells is no longer regulated by cAMP. Gel filtration and immunoprecipitation analysis confirm that ethanol blocks the reassociation of Calpha with RII but does not induce dissociation of these subunits. Ethanol also reduces inhibition of Calpha by the PKA inhibitor PKI. Pre-incubation of Calpha with ethanol decreases phosphorylation of Leu-Arg-Arg-Ala-Ser-Leu-Gly (Kemptide) and casein but has no effect on the phosphorylation of highly charged molecules such as histone H1 or protamine. cAMP-response element-binding protein (CREB) phosphorylation by Calpha is also increased in ethanol-treated cells. This increase in CREB phosphorylation is inhibited by the PKA antagonist (R(p))-cAMPS and by an adenosine receptor antagonist. These results suggest that ethanol affects a cascade of events allowing for sustained nuclear localization of Calpha and prolonged CREB phosphorylation. These events may account for ethanol-induced changes in cAMP-dependent gene expression.

Animals↗

PubMed1999

Transient adhesion of platelets in pump-oxygenator systems: influence of SMA and nitric oxide treatments.

We employed gamma scintigraphy to quantify the transient accumulations of platelets in pump-oxygenator systems employed in cardiopulmonary bypass (CPB). A flat sheet microporous polypropylene membrane oxygenator (Cobe Duo) was employed, with and without siloxane/caprolactone oligomer coating (SMA) (n = 8 each). The effect of nitric oxide gas infusion on platelet deposition was also evaluated for the uncoated Cobe Duo system (n = 10 each). Scintigraphic images of radiolabelled cells were obtained and converted to numbers of all platelets, labeled and unlabeled, adhering to the pump and oxygenator surfaces. These numbers were compared, by study group, for a 90-min period of normothermic CPB in the adult pig, employing standard prime and anticoagulation regimens. Platelets adhered in large numbers to control oxygenators, reaching maxima (> 20% of the circulating platelet mass) 30 min following institution of CPB, and decreasing for the duration of CPB. SMA treatment significantly decreased platelet adhesion following a 5-10-min transient accumulation period. Nitric oxide infusion significantly reduced platelet adhesion throughout the CPB period. Platelet accumulations on the high fluid shear centrifugal pump surfaces increased monotonically to maxima at about the same time as for the oxygenators, but did not decrease thereafter. Higher platelet surface densities were observed on the centrifugal pump surfaces than on the oxygenator surfaces. CPB with the untreated circuit tended to reduce circulating platelet counts vs theoretical values based on hemodilution alone. In contrast, SMA significantly increased the circulating platelet count versus the untreated control group. These results indicate that platelet adherence to the foreign surfaces of CPB equipment are influenced in characteristic ways by time and fluid shear. SMA treatment and nitric oxide infusion both reduce platelet adhesion to oxygenator surfaces. SMA treatment spares these cells for the circulation.

Animals↗

PubMed1999

Regional tumor oxygenation and measurement of dynamic changes.

We recently described a novel approach to measuring regional tumor oxygen tension using (19)F pulse burst saturation recovery (PBSR) nuclear magnetic resonance (NMR) echo planar imaging (EPI) relaxometry of hexafluorobenzene. We now compare oxygen tension measurements in a group of size-matched R3327-AT1 Dunning prostate rat tumors made using this new method with those using a traditional polarographic method: the Eppendorf histograph. Similar oxygen tension distributions were found using the two methods, and both techniques showed that tumors with volume greater than 3.5 cm(3) were significantly (P < 0.0001) less well oxygenated than smaller tumors (volume less than 2 cm(3)). Using the (19)F EPI approach, we also examined the response to respiratory challenge. Increasing the concentration of inspired oxygen from 33% to 100% O(2) produced a significant increase (P < 0.0001) in tumor oxygenation for a group of small tumors. In contrast, no change was observed in the mean pO(2) for a group of large tumors. Consideration of individual tumor regions irrespective of tumor size showed a strong correlation between the maximum pO(2) observed when breathing 100% O(2) compared with mean baseline pO(2). These results further demonstrate the usefulness of (19)F EPI to assess changes in regional tumor oxygenation.

Adenocarcinoma↗

PubMed1998

Regional tumor oxygen tension: fluorine echo planar imaging of hexafluorobenzene reveals heterogeneity of dynamics.

PURPOSE: Therapeutic success could be enhanced if therapy were tailored to the characteristics of specific tumors. We have been developing novel approaches to measuring tumor oxygen tension in vivo, and recently reported a method based on 19F nuclear magnetic resonance (NMR) spin lattice echo planar imaging (EPI) relaxometry of hexafluorobenzene (HFB). We have now examined the feasibility of monitoring dynamic changes in regional tumor oxygenation in response to respiratory challenge. Preliminary data in one tumor show distinct differences before and subsequent to irradiation. METHODS AND MATERIALS: Dunning prostate adenocarcinoma R3327-AT1 was grown in the form of pedicles on the foreback of male Copenhagen rats. When the tumors reached approximately 1 cm diameter, HFB (40 microl) was administered by direct intratumoral injection deliberately dispersed to interrogate both central and peripheral regions. Local pO2 was determined using pulse burst saturation recovery 19F NMR EPI on the basis of the spin lattice relaxation rate. RESULTS: Interrogation of both central and peripheral regions of tumors showed bimodal distribution for oxygenation, including many voxels with pO2 < 15 torr. Altering the inspired gas to 100% O2 produced significant elevation for regions with initially high pO2 (P < 0.01), but the temporal course of dynamic changes varied for each voxel. Many voxels with low pO2 showed little response. Following irradiation (20 Gy), tumor oxygenation was significantly elevated and remained high for at least 10 h. CONCLUSION: We believe this method provides a valuable new approach to investigate tumor oximetry that may extend our understanding of tumor physiology, and could have prognostic value.

Animals↗

PubMed1998

Regional tumor oximetry: 19F NMR spectroscopy of hexafluorobenzene.

PURPOSE: An accurate method for monitoring oxygen tension (pO2) of individual tumors could be valuable for optimizing treatment plans. We have recently shown that 19F nuclear magnetic resonance (NMR) spin-lattice relaxometry of hexafluorobenzene (HFB) provides a highly sensitive indicator of tumor oxygenation. We have now refined the methodology to provide enhanced precision, and applied the method to investigate dynamic changes in tumor oxygenation. METHODS AND MATERIALS: Dunning prostate adenocarcinoma R3327-AT1 was grown in the form of pedicles on the foreback of male Copenhagen rats. When the tumors reached approximately equal to 1 cm diameter, HFB (20 microl) was administered, either centrally or peripherally, by direct intratumoral (i.T) injection. Local pO2 was determined using pulse-burst saturation recovery (PBSR) 19F NMR spectroscopy on the basis of the spin-lattice relaxation rate, R1. RESULTS: Interrogation of the central region of tumors provided typical values in the range pO2 = 1.4-6.4 mmHg, with a typical stability of +/-2 mmHg over a period of 20 min, when rats breathed 33% O2. Altering the inhaled gas to oxygen or carbogen (95% O2/5% CO2) produced no significant change. In contrast, interrogation of tumor periphery indicated baseline pO2 in the range 7.9-78.9 mmHg. Altering inspired gas produced significant changes (p < 0.0001) with O2 or carbogen, although the change was generally greater with carbogen. In each case, pO2 returned to baseline within 16 min of returning the inhaled gas to baseline. CONCLUSION: We believe this method provides a valuable new approach with the requisite precision and accuracy to investigate tumor pO2.

Animals↗

PubMed1998

SPECT electronic collimation resolution enhancement using chi-square minimization.

An electronic collimation technique is developed which utilizes the chi-square goodness-of-fit measure to filter scattered gammas incident upon a medical imaging detector. In this data mining technique, Compton kinematic expressions are used as the chi-square fitting templates for measured energy-deposition data involving multiple-interaction scatter sequences. Fit optimization is conducted using the Davidon variable metric minimization algorithm to simultaneously determine the best-fit gamma scatter angles and their associated uncertainties, with the uncertainty associated with the first scatter angle corresponding to the angular resolution precision for the source. The methodology requires no knowledge of materials and geometry. This pattern recognition application enhances the ability to select those gammas that will provide the best resolution for input to reconstruction software. Illustrative computational results are presented for a conceptual truncated-ellipsoid polystyrene position-sensitive fibre head-detector Monte Carlo model using a triple Compton scatter gamma sequence assessment for a 99mTc point source. A filtration rate of 94.3% is obtained, resulting in an estimated sensitivity approximately three orders of magnitude greater than a high-resolution mechanically collimated device. The technique improves the nominal single-scatter angular resolution by up to approximately 24 per cent as compared with the conventional analytic electronic collimation measure.

Algorithms↗

PubMed1998

Analytic treatment of resolution precision in electronically collimated SPECT imaging involving multiple-interaction gamma rays.

The widely applied single-interaction analytic expression characterizing the energy resolution component of the angular resolution precision for an electronically collimated point source is extended to include multiple-interaction Compton scatter sequences as well as sequences terminated by photoelectric absorption. The analytic formulation is developed using the statistical variance of the mean for components comprising composite, multivariate resolution precision estimators. It is demonstrated that enhanced resolution precision in the incident interaction scatter angle is attained when use is made of information from multiple interactions. An improvement in the resolution precision of up to approximately 40% is observed for triple Compton scatter. Comparison of the analytic estimates with Monte Carlo/chi-square results shows good agreement.

Chi-Square Distribution↗

PubMed1997

New energy transfer dyes for DNA sequencing.

We have synthesized a set of four energy transfer dyes and demonstrated their use in automated DNA sequencing. The donor dyes are the 5- or 6-carboxy isomers of 4'-aminomethylfluorescein and the acceptor dyes are a novel set of four 4,7-dichloro-substituted rhodamine dyes which have narrower emission spectra than the standard, unsubstituted rhodamines. A rigid amino acid linker, 4-aminomethylbenzoic acid, was used to separate the dyes. The brightness of each dye in an automated sequencing instrument equipped with a dual line argon ion laser (488 and 514 nm excitation) was 2-2.5 times greater than the standard dye-primers with a 2 times reduction in multicomponent noise. The overall improvement in signal-to-noise was 4- to 5-fold. The utility of the new dye set was demonstrated by sequencing of a BAC DNA with an 80 kb insert. Measurement of the extinction coefficients and the relative quantum yields of the dichlororhodamine components of the energy transfer dyes showed their values were reduced by 20-25% compared with the dichlororhodamine dyes alone.

Base Sequence↗

PubMed1997

Changes in locus-specific V(D)J recombinase activity induced by immunoglobulin gene products during B cell development.

The process of V(D)J recombination is crucial for regulating the development of B cells and for determining their eventual antigen specificity. Here we assess the developmental regulation of the V(D)J recombinase directly, by monitoring the double-stranded DNA breaks produced in the process of V(D)J recombination. This analysis provides a measure of recombinase activity at immunoglobulin heavy and light chain loci across defined developmental stages spanning the process of B cell development. We find that expression of a complete immunoglobulin heavy chain protein is accompanied by a drastic change in the targeting of V(D)J recombinase activity, from being predominantly active at the heavy chain locus in pro-B cells to being exclusively restricted to the light chain loci in pre-B cells. This switch in locus-specific recombinase activity results in allelic exclusion at the immunoglobulin heavy chain locus. Allelic exclusion is maintained by a different mechanism at the light chain locus. We find that immature, but not mature, B cells that already express a functional light chain protein can undergo continued light chain gene rearrangement, by replacement of the original rearrangement on the same allele. Finally, we find that the developmentally regulated targeting of V(D)J recombination is unaffected by enforced rapid transit through the cell cycle induced by an E mu-myc transgene.

Animals↗