Biomedical subjects

D Schwarz

Publications and source records attributed to D Schwarz.

At least 19 recordsLinked to original sources

PubMed2007

Genotype and phenotype relationship in drug metabolism.

Pharmacogenetics, one of the fields of clinical pharmacology, studies how genetic factors influence drug response. If hereditary traits are taken into account appropriately before starting drug treatment, the type of drug and its dosage can be tailored to the individual patient's needs. Today, the relationships between dosage requirements and genetic variations in drug-metabolizing enzymes such as cytochrome P450 (CYP) 2D6, CYP2C9, and CYP2C19 or in drug transporters such as p-glycoprotein (ABCB1) and OATP-C (SLC21A6) are substantiated best. A standard dose will bring about more adverse effects than usual if enzymatic activity is lacking or feeble. Sometimes, however, therapeutic response might be better because of higher concentrations: proton pump inhibitors for eradication of Helicobacter pylori are more efficacious in carriers of a deficient CYP2C19 variant. In some cases, genetic tests can help distinguish between responders and nonresponders of a specific drug treatment, and genotype-based dosage is possible.

Animals↗

PubMed2006

[Hippocampus, structure of the brain and schizophrenia].

Schizophrenia is a clinically heterogeneous state without clearly defined pathogenesis. This limits the classification approaches with consequent lack of ability for individual treatment strategies. It becomes evident that hippocampus is a key structure in the neuropathology of schizophrenia and a concept of hippocampal reduction as an endophenotype of schizophrenia was established. The biggest support came from MRI volumetric studies. Despite that, due to some inconsistent findings, clinical consequences of hippocampal shrinkage are not yet clear. Contemporary methods of brain imaging (computation morphometry, voxel-based morphometry) could help us to outline the concept of schizophrenia and to clarify the clinical consequences of brain structure changes.

Brain↗

PubMed2002

Realtime transfer of live video images in parallel with three-dimensional modelling of the surgical field in computer-assisted telesurgery.

We have carried out three-dimensional, computer-assisted, functional endoscopic sinus telesurgery. Surgeons at different locations up to 300 km apart could not only see and transfer video images but also transfer three-dimensional computer models and manipulate them in realtime during surgery. Two different approaches were used. In the first telesurgery procedure we used M-JPEG compression and transmitted the data using fibre optic connections (ATM OC-3) at a bandwidth of 155 Mbit/s. In the second telesurgery procedure video images were transmitted over four E1 digital lines, amounting to about 8 Mbit/s of bandwidth, with better compression standards, such as MPEG1 and 2. We found that MPEG2 video compression produced the best picture quality for the operating field and endoscopic cameras. For conferencing and consultation between two or more connected sites during the surgery, we used JPEG and MPEG1 video compression with audio. The main feature of our three-dimensional telesurgery was the use of three-dimensional modelling of the operative field. This is important for emergency surgical interventions. We do not advocate that inexperienced surgeons operate on patients, not even with the guidance of a remote surgeon. However, three-dimensional telesurgery may become very valuable for experienced surgeons in the future.

Adult↗

PubMed2001

Violent injuries among adolescents: declining morbidity and mortality in an urban population.

STUDY OBJECTIVE: Adolescent homicide rates are decreasing nationally for unclear reasons. We explore changes in intentional injury morbidity and mortality within the context of other injuries and specific causes. METHODS: We performed surveillance of hospital, medical examiner, and vital records for nonfatal injury among adolescents age 10 to 19 years living in the District of Columbia from June 15, 1996, to June 15, 1998, and fatal injury from 1989 to 1998. RESULTS: Over the 2-year study period, 15,190 adolescents were seen for injury, resulting in an event-based rate of 148 injuries per 1,000 adolescents per year; 7% required hospitalization, and 0.8% died. Interpersonal intentional injuries accounted for 25% of all injuries, 45% of hospitalizations, and 85% of injury deaths. Assault morbidity decreased with no change noted for unintentional and self-inflicted injury. Firearm injuries, stabs, and assaults with other objects showed the largest decrease, with no decrease in unarmed assaults. Injury mortality peaked in 1993 and has declined since. Firearms caused 72% to 90% of all injury deaths from 1989 to 1998, most the result of homicide. CONCLUSION: There has been a decline in intentional injury rates over the study periods related to decreased weapon injury; data suggest a change in the lethality of fighting methods but no change in unarmed fighting behavior.

Adolescent↗

PubMed2001

Co-expression of human cytochrome P4501A1 (CYP1A1) variants and human NADPH-cytochrome P450 reductase in the baculovirus/insect cell system.

1. Three human cytochrome P4501A1 (CYP1A1) variants, wild-type (CYP1A1.1), CYP1A1.2 (1462V) and CYP1A1.4 (T461N), were co-expressed with human NADPH-P450 reductase (OR) in Spodoptera frugiperda (Sf9) insect cells by baculovirus co-infection to elaborate a suitable system for studying the role of CYPA1 polymorphism in the metabolism of exogenous and endogenous substrates. 2. A wide range of conditions was examined to optimize co-expression with regard to such parameters as relative multiplicity of infection (MOI), time of harvest, haem precursor supplementation and post-translational stabilization. tinder optimized conditions, almost identical expression levels and molar OR/CYP1A1 ratios (20:1) were attained for all CYP1A1 variants. 3. Microsomes isolated from co-infected cells demonstrated ethoxyresorufin deethlylase activities (nmol/min(-1) nmol(-1) CYP1A1) of 16.0 (CYP1A1.1), 20.5 (CYP1A1.2) and 22.5 (CYP1A1.4). Pentoxyresorufin was dealkylated approximately 10-20 times slower with all enzyme variants. 4. All three CYP1A1 variants were active in metabolizing the precarcinogen benzo[a]pyrene (B[a]P), with wild-type enzyme showing the highest activity, followed by CYP1A1.4 (60%) and CYP1A1.2 (40%). Each variant produced all major metabolites including B[a]P-7,8-dihydrodiol, the precursor of the ultimate carcinogenic species. 5. These studies demonstrate that the baculovirus-mediated co-expression-by-co-infection approach all CYP1A1 variants yields functionally active enzyme systems with similar molar OR/CYP1A1 ratios, thus providing suitable preconditions to examine the metabolism of and environmental chemicals by the different CY1A1 variants.

Animals↗

PubMed2001

Differential metabolism of benzo[a]pyrene and benzo[a]pyrene-7,8-dihydrodiol by human CYP1A1 variants.

Cytochrome P450 1A1 (CYP1A1) plays a key role in the metabolism of carcinogens, such as benzo[a]pyrene (B[a]P) and metabolites to ultimate carcinogens. Three human allelic variants, namely wild-type (CYP1A1.1), CYP1A1.2 (I462V) and CYP1A1.4 (T461N), were coexpressed by coinfection of baculovirus-infected insect cells with human NADPH-P450 reductase. These recombinant enzymes (in microsomal membranes) were used to analyze whether CYP1A1 polymorphisms affect catalytic activities towards B[a]P and B[a]P-7,8-dihydrodiol. The complete spectrum of phase I metabolites, including the tetrahydrotetrols resulting from hydrolysis of the ultimate carcinogen, B[a]P-7,8-dihydrodiol-9,10-epoxide, was examined by HPLC. Wild-type enzyme showed the highest total metabolism of B[a]P, CYP1A1.2 was approximately 50%, and CYP1A1.4 approximately 70%. Km values for all metabolites with CYP1A1.2 were generally significantly lower than with wild-type enzyme (e.g. B[a]P-7,8-diol formation: 13.8 microM for wild-type, 3.5 microM for CYP1A1.2 and 7.7 microM for CYP1A1.4). Addition of epoxide hydrolase markedly increases the relative diol-to-phenol activities by all three variants. However, CYP1A1.4 exhibits the greatest efficiency to produce diol species. Each variant produced the diol epoxides from B[a]P-7,8-dihydrodiol. CYP1A1.1 exhibited with 10.4 pmol/min/pmol CYP1A1 the greatest total rate for 7,8-diol metabolites followed by CYP1A1.2 (7.2 pmol/min/pmol CYP1A1) and CYP1A1.4 (5.5 pmol/min/pmol CYP1A1). All enzyme variants produced about three times more diol epoxide 2-derived metabolites than diol epoxide 1-derived ones, whereby both rare allelic variants exhibited statistically significantly increased formation of diol epoxide 2. This study showed that the three CYP1A1 variants had different enzyme kinetics properties to produce both the diol metabolites from B[a]P and the ultimate mutagenic species diol epoxide 2 from B[a]P-7,8-dihydrodiol, which must be considered in the evaluation of individual susceptibility to cancer.

Animals↗

PubMed2000

Curvature properties of novel forms of phosphatidylcholine with branched acyl chains.

We studied the properties of a series of phosphatidylcholine molecules with branched acyl chains. These lipids have previously been shown to have marked stimulatory effects on the side-chain cleavage activity of cytochrome P450SCC (CYP11A1), an enzyme of the inner mitochondrial membrane. The synthetic lipids used were diacyl phosphatidylcholines with the decanoyl, dodecanoyl or tetradecanoyl chain having a hexyl, octyl or decyl straight chain aliphatic branch at the 2-position. All three lipids lowered the bilayer to hexagonal phase transition temperature of dielaidoyl phosphatidylethanolamine, the lipids with longer acyl chains being more effective in this regard. As pure lipids all of the forms were found by X-ray diffraction to be predominantly in the hexagonal phase (HII) over the entire temperature range of 7-75 degrees C. The properties of the HII phase were unusual with regard to the small size of the lattice spacings and the small temperature dependence of the spacings. We used tetradecane to relieve hydrocarbon packing constraints to determine the intrinsic radius of curvature of the lipid monolayer. The elastic bending modulus was measured in the presence of tetradecane by introducing an osmotic gradient across the hexagonal phase cylinders with aqueous solutions of poly(ethylene glycol). The elastic bending modulus was found to be higher than that observed with other lipids and to increase with temperature. Both the small intrinsic radius of curvature and the high elastic bending modulus indicate that the presence of these lipids in bilayer membranes will impose a high degree of negative curvature strain.

Calorimetry, Differential Scanning↗

PubMed2000

Allelic variants of human cytochrome P450 1A1 (CYP1A1): effect of T461N and I462V substitutions on steroid hydroxylase specificity.

Steroid hydroxylation specificities were determined for the wild-type and the two allelic variants of the polymorphic human cytochrome P450 1A1 (CYP1A1) that were associated with amino acid exchanges near the active site of the enzyme. All three variants were expressed in insect cells using recombinant baculoviruses. Each variant protein was spectrally and enzymatically active, as judged by the ability of the prepared microsomes to catalyse O-dealkylation of ethoxyresorufin and pentoxyresorufin in cumene hydroperoxide-mediated reactions. With progesterone and testosterone as substrate, all variants of CYP1A1 exhibited high, but different steroid hydroxylation activities (8-40 pmol hydroxysteroid/min/pmol CYP1A1, i.e. approximately 800-4000 pmol/min/mg microsomal protein). All three variants exclusively catalysed 6beta-hydroxylation of both steroids. In addition, towards progesterone as substrate, all variants also catalysed 16alpha-hydroxylations with approximately half of the rate of 6beta-hydroxylation activity. With progesterone as substrate for hydroxylation in 6beta position, CYP1A1 T461N had the lowest catalytic efficiency (Vmax/Km) followed by the CYP1A1 I462V variant and the wild-type enzyme. For 16alpha-hydroxylation of progesterone, the catalytic efficiencies of the three variants are not statistically significantly different. With testosterone as substrate the CYP1A1 1462V variant catalysed 6beta-hydroxylation with an efficiency considered not significantly different compared to the wild-type, although both the apparent Km and Vmax were significantly decreased. In contrast, the CYP1A1 T461N variant exhibited significantly decreased catalytic efficiencies compared to both the 1462V variant and the wild-type enzyme. These results indicate that all three naturally occurring allelic variants of human CYP1A1 hydroxylate steroid hormones with varying efficiencies in a stereo- and regioselective manner, whereby the CYP1A1 T461N variant exhibited the lowest catalytic efficiency.

Alleles↗

PubMed1999

Complex formation in vesicle-reconstituted mitochondrial cytochrome P450 systems (CYP11A1 and CYP11B1) as evidenced by rotational diffusion experiments using EPR and ST-EPR.

Rotational diffusion measurements using EPR and saturation transfer EPR were applied to analyze complex formation between the electron-transfer components of the mitochondrial steroid-hydroxylating cytochrome P450 systems (CYP11A1 and CYP11B1) in phosphatidylcholine/phosphatidylethanolamine/cardiolipin vesicles prepared by octyl glucoside dialysis/adsorption. Octyl glucoside reconstitution of P450SCC results in large vesicles, which have an advantage over small vesicles in that vesicle tumbling does not contribute to measured rotational diffusion rates. Immobilization of spin-labeled adrenodoxin by both P450SCC and adrenodoxin reductase indicates equimolar complexation between P450SCC and adrenodoxin as well as between adrenodoxin reductase and adrenodoxin. Combination of rotational diffusion and antibody cross-linking confirmed the complexation of adrenodoxin with P450SCC and for the first time provided direct evidence of a complex between P450SCC and P45011beta in the membrane. In contrast, no evidence was found for the existence of adrenodoxin reductase-P450SCC complexes or a ternary complex of all three proteins. Thus, these experiments confirm the shuttle mechanism of electron transfer to vesicle-reconstituted P450SCC and P45011beta.

Adrenodoxin↗

PubMed1999

Enzymatic properties of vesicle-reconstituted human cytochrome P450SCC (CYP11A1) differences in functioning of the mitochondrial electron-transfer chain using human and bovine adrenodoxin and activation by cardiolipin.

The recently reported heterologous expression and purification of both human cytochrome P450SCC and adrenodoxin [Woods, S.T., Sadleir, J., Downs, T., Triantopoulos, T., Haedlam, M.J. & Tuckey, R.C. (1998) Arch. Biochem. Biophys. 353, 109-115] has enabled us to perform studies with the membrane-reconstituted human enzymes to better understand the side-chain cleavage reaction in humans. Human P450SCC was successfully reconstituted into dioleoylphosphatidylcholine vesicles with and without cardiolipin and its enzymatic properties characterized in the membrane-bound state. Enhancement of the P450SCC activity and significant activation by cardiolipin were observed when human adrenodoxin instead of bovine adrenodoxin was used as electron donor. In the absence of cardiolipin, Km for cholesterol was decreased twice in the case of human adrenodoxin indicating enhanced cholesterol binding. On the other hand, in the presence of cardiolipin in the membrane both Km and V for cholesterol were decreased with human adrenodoxin as electron donor. Kinetic analysis of the interaction between human P450SCC and its redox partners provided evidence for enhanced binding of the human electron donor to human P450SCC indicated by both an increased V and decreased Kd for human adrenodoxin compared with the values with bovine adrenodoxin. Because no similar effects were observed in Tween 20 micelles, these results suggest that the phospholipid membrane may play an important role in the interaction of human adrenodoxin with human P450SCC.

Adrenodoxin↗

PubMed1999

A new paradigm of injury intentionality.

OBJECTIVE: To improve understanding of processes leading to injury and assess more specifically the degree of intentionality. METHODS: A new paradigm was developed that characterizes the act of inflicting injury (self, other, not inflicted) and the motive. Motives are determined for the act of injury and for the outcome. To test this, 986 cases of adolescent injuries in seven hospitals were reviewed. Three investigators independently classified all cases using the new paradigm and three used standard definitions of intent. Inter-rater reliability was measured. RESULTS: Of injuries inflicted by others, 61% were intentional using the standard classification. In the new paradigm 67% were intended acts and 59% involved intentional motive for outcome. Altogether 87% of sports injuries were coded as unintentional acts compared with 96% using standard methods. Using standard classification there was 93% agreement between paired raters, with an average kappa of 0.86. In the new paradigm questions on intentionality of act, outcome, and infliction of act, the agreement was 89%, 91%, 88%, with a kappa of 0.79, 0.80, 0.76, respectively. CONCLUSIONS: This paradigm defines a spectrum of injury intent, enhances understanding of the causal sequence of injury, and has important implications for research and prevention.

Adolescent↗

PubMed1998

Branched phosphatidylcholines stimulate activity of cytochrome P450SCC (CYP11A1) in phospholipid vesicles by enhancing cholesterol binding, membrane incorporation, and protein exchange.

Phosphatidylcholines (PCs) with branched fatty acyl chains substituted in the two positions of the main chains (branched PCs) have been shown to be potent activators of the side chain cleavage activity of cytochrome P450SCC (CYP11A1) (Schwarz, D., Kisselev, P., Wessel, R., Jueptner, O., and Schmid, R. D. (1996) J. Biol. Chem. 271, 12840-12846). The present study reports on the effect of a series of branched PC on cholesterol binding, membrane integration, and protein exchange in large unilamellar vesicles prepared by an extrusion technique. Enzyme kinetics using vesicles as well as optical titration using a micelle system with the detergent Tween 20 demonstrate that activation is correlated with the fraction of P450SCC in the high spin form. The potency of branched PCs both to activate the enzyme and to induce spin state changes increases with increasing lengths of both the branched and main fatty acyl chains. We found that the extent as well as the rate of integration of P450SCC into vesicle membranes studied by gel chromatography and stopped flow kinetics were increased by branched PC. Finally, it is demonstrated by measurement of the enzymatic activity in primary and secondary vesicles that branched PCs are potent in retaining a very rapid exchange of P450SCC between vesicles, in contrast to cardiolipin, that partially inhibits this exchange process. The data suggest that different properties of P450SCC in membrane systems including cholesterol binding, membrane integration, and protein exchange are affected by branched PCs and probably by other phospholipids, too, and therefore must be considered in an explanation of the observed high stimulation of activity.

Animals↗

PubMed1998

Ethical issues in radiation protection, continued.

Shrader-Frechette and Persson (1997) reviewed ethical thinking on (1) Equity vs. Efficiency, (2) Health vs. Economics, (3) Individual Rights vs. Societal Benefits, (4) Due Process vs. Necessary Sacrifice, and (5) Stakeholder Consent vs. Management Decisions. This discussion offers reasoned conclusions pertaining to these five topics. In addition, ethical aspects are discussed as to (6) Psychological Harm Through Fear of Radiation, (7) Economical-ecological Harm Through Fear of Radiation, and (8) Science: the Question of Truth.

Ethics↗

PubMed1997

Evidence that nonbilayer phase propensity of the membrane is important for the side chain cleavage activity of cytochrome P450SCC.

To analyze whether specific protein-lipid interactions or physical features of the membrane contribute to cytochrome P450SCC (CYP11A1) activation by lipids, dimyristoylphosphatidylcholine/cardiolipin and dimyristoylphosphatidylcholine/branched phosphatidylcholine vesicles of defined acyl chain structure were studied for their ability to stimulate the side chain cleavage activity of the enzyme. Activation was found to increase with the mole percent of nonbilayer lipids in the system and the chain lengths of both the branched and main fatty acyl chains of the activator lipid. Unsaturation provided by dioleoylphosphatidylcholine as host lipid leads to a further increase in the potency of the branched phosphatidylcholines to activate the enzyme. The observed activation can be qualitatively interpreted in terms of the effect of these lipids on the hydrophobic volume of the membrane. Using differential scanning calorimetry, we showed that the branched phosphatidylcholines perturb the bilayer membrane structure of dimyristoylphosphatidylcholine and lower the bilayer to hexagonal phase transition temperature of dielaidoylphosphatidylethanolamine, i.e., promote hexagonal phase formation. We also examined the effect of eicosane on both the cytochrome P450SCC activity and the lipid polymorphism and found that eicosane increases both the activity and the hexagonal phase propensity of the vesicle membrane. Because of these correlations, we conclude that the nonbilayer phase propensity of the membrane rather than specific binding of activator lipids to the enzyme explains best the observed activation of enzymatic activity by the lipids.

Alkanes↗

PubMed1997

Possible involvement of nonbilayer lipids in the stimulation of the activity of cytochrome P450SCC (CYP11A1) and its propensity to induce vesicle aggregation.

Phosphatidylcholines with saturated branched fatty acyl chains substituted in the 2-positions of the main chains have a significant stimulating effect on both the side chain cleavage activity of cytochrome P450SCC and the ability of P450SCC to induce a specific vesicle aggregation in lipid-vesicle reconstituted systems. Stimulation increases with increasing content of the branched phosphatidylcholines and is sensitive to its acyl chain structure and composition. Because branched phosphatidylcholines containing 2-alkyl substituted fatty acid chains belong to a new class of phosphatidylcholines forming inverted nonbilayer phases the results indicate that nonbilayer lipids might play an important role in the function of mitochondrial P450SCC.

Cholesterol Side-Chain Cleavage Enzyme↗

PubMed1996

Alpha-branched 1,2-diacyl phosphatidylcholines as effectors of activity of cytochrome P450SCC (CYP11A1). Modeling the structure of the fatty acyl chain region of cardiolipin.

Cardiolipin has been shown to be the most effective activator of cholesterol side chain cleavage activity of cytochrome P450SCC, and evidence has been provided for a lipid effector site on the enzyme. Results suggested the headgroup of cardiolipin as major determinant of lipid interaction with P450SCC (Lambeth, J. D. (1981) J. Biol. Chem. 256, 4757-4762). The role of unsaturation is contradictory and open to question (Igarashi, Y. and Kimura, T. (1986) Biochemistry 25, 6461-6466). We synthesized phosphatidylcholines with fully saturated branched fatty acyl chains substituted in the 2-positions of the main chains and studied the influence of these lipids on the activity and other properties of P450SCC in vesicle-reconstituted systems. These saturated branched lipids, with regard to the fatty acyl moiety in molecular shape similar to cardiolipin but with the headgroup of phosphatidylcholines retained, showed a stimulatory efficiency higher than any other phospholipid and at least comparable to cardiolipin. Activation is sensitive to the acyl chain structure and composition. Results suggest that the shape of the molecule at least partially plays an important role in the process of stimulation of the activity of P450SCC. Because binding of cholesterol was increased by the branched lipids monitored optically by the fraction of P450SCC in the high spin form, it was concluded that these lipids, like cardiolipin and other lipids, exert their effects by regulating the binding of cholesterol to P450SCC. These data suggest that polymorphic lipids such as branched phosphatidylcholines and cardiolipin might influence P450SCC function by maintenance of the membrane curvature at a value optimal for activity.

Acylation↗

PubMed1996

Delayed repair: the role of glutathione in a rat incisional wound model.

Glutathione is a low molecular weight tripeptide that is a major intracellular antioxidant, modulates DNA synthesis, and may regulate signal transduction mechanisms. Our previous studies in rats suggested that intracellular stores of glutathione were sensitive to skin ischemia and, therefore, may regulate the early temporal course of wound healing. A 4-cm incision was placed on a rat's back and in vivo wound strength was measured over time. Animals were depleted of glutathione using L-buthionine-(S,R)-sulfoximine (BSO), an inhibitor of the enzyme gamma-glutamylcysteine synthetase. Some animals were treated in combination with allopurinol/BSO or with allopurinol alone. The data demonstrated at 4 days that BSO treatment produced a fourfold reduction in glutathione (3.51 +/- 1.78) over baseline (16.15 +/- 2.18) levels and twofold reduction (5.0 +/- 1.1) over untreated sham controls (11.1 +/- 2.3) (P < 0.05). Allopurinol provided no protection to glutathione levels. BSO treatment alone reduced wound burst strength compared to the other groups (P < 0.05). Allopurinol treatment enhanced wound strength over sham controls and BSO groups at 9 days after wounding (P < 0.05). Hydroxyproline content in wounds accumulated faster by Day 4 in the BSO-treatment groups compared to sham controls (P < 0.05), whereas the BSO-treatment groups had lower hydroxyproline levels measured at Day 6 (P < 0.05). These data provide the first evidence that wound healing is related to the temporal course of glutathione metabolism. The effect may not be related to oxidant stress since allopurinol provided enhanced wound burst strength without protecting wound glutathione levels.

Allopurinol↗

PubMed1996

Right ventricular nerve sheath tumour and patent foramen ovale presenting with transient ischemic attack.

A 66-year-old man presented with dyspnea and a transient ischemic attack. Echocardiography revealed a right ventricular mass and patent foramen ovale. During surgery the mass was found to be a malignant nerve sheath tumour. Several weeks later, the patient developed small bowel obstruction, and laparotomy disclosed multiple metastases involving the small and large bowel. The paper describes the clinical course and management of this patient and reviews the pertinent literature.

Aged↗