Sequential three-dimensional time-of-flight MR angiography of the carotid arteries: value of variable excitation and postprocessing in reducing venetian blind artifact

OBJECTIVE

Multiple overlapping three-dimensional (3D) time-of-flight carotid MR angiography potentially combines many of the desirable features of two-dimensional (2D) and single-volume 3D MR angiographic imaging techniques. Yet the maximum-intensity-projection images from such acquisitions are often degraded by artifact due to nonuniform signal intensity of contiguous imaging volumes and inadequate, yet arduous, postprocessing. The former has been termed venetian blind artifact. To date, the severity of the artifact has been minimized by the use of very thin slabs with a large percentage of overlap. However, the artifact typically is still appreciable, and the required acquisition and postprocessing times are increased. The purpose of this study was to examine the value of technical modifications of both the multislab acquisition and postprocessing procedures to reduce this artifact on images of healthy volunteers.

SUBJECTS AND METHODS

Spatially variable RF pulses along the direction of flow were applied as excitation pulses in the multislab time-of-flight MR angiographic acquisitions to compensate for the nonuniform blood signal intensity caused by spin saturation. An automatic postprocessing technique was used to optimally combine the image data in overlapping slices by selecting the higher-intensity pixel of the two on a pixel-by-pixel basis. Ratios of the standard deviation of signal intensity to the mean signal intensity were computed as a function of RF profile and postprocessing method along the long axes of the arteries to measure the uniformity of the signal intensity of the blood. The spatially variable and sinc RF pulse acquisitions, combined with automatic and conventional manual postprocessing, were compared.

RESULTS

Compared with the sinc pulse acquisition, the MR angiograms acquired with spatially variable excitation pulses improved the signal uniformity of the arteries with thicker volumes and less overlap, thereby reducing the acquisition time by 25% for similar spatial coverage. When used with the automatic postprocessing technique, the severity of the venetian blind artifact on maximum-intensity-projection images was minimized and the postprocessing time was reduced by roughly a factor of 5.

CONCLUSION

The combined use of spatially variable excitation pulses and an automatic postprocessing technique can improve the uniformity of the signal from blood across the slab and allow thicker slabs to be acquired with less overlap. Data acquisition and postprocessing times can be reduced significantly. This work suggests it may be possible to easily produce overlapping 3D MR angiograms that should be superior to conventional 2D and 3D studies.

Structure-function analysis of CYP2A10 and CYP2A11, P450 cytochromes that differ in only eight amino acids but have strikingly different activities toward testosterone and coumarin

Cytochrome P450 NMa, which was first identified in this laboratory in rabbit nasal microsomes, is now known to represent two distinct gene products, P450s 2A10 and 2A11. In the present study, chimeric and site-directed mutants of 2A11 were constructed to determine which of the eight different amino acid residues are responsible for the much greater activity of 2A10 toward coumarin and testosterone. Mutation of Arg62 and Asp63 of 2A11 to the corresponding residues in 2A10, or mutation of Thr120 to Ser, as found in 2A10, did not change the activities. However, mutation of Arg62, Asp63, Gln104, Ala117, and Thr120 of 2A11 to the corresponding residues in 2A10 resulted in a protein that is as active as 2A10 in coumarin hydroxylation and approximately half as active as 2A10 in androstenedione formation. Mutation of Arg372 in 2A11 to His, as found in 2A10, resulted in a significant increase in the rate of hydroxylation of testosterone, but not of coumarin. Our findings indicate that the identify of the amino acid at position 104 and/or 117 is important for activity with testosterone and for regioselectivity at the 17 position, as well as for optimal activity with coumarin. In contrast, the identity of the residue at position 372 is important for optimal activity with testosterone but not the regioselectivity at the 17 position and does not influence the activity with coumarin.

Direct structural observation of an acyl-enzyme intermediate in the hydrolysis of an ester substrate by elastase

The method of X-ray crystallographic cryoenzymology has been used to determine the crystal structure of a kinetically significant species on the reaction pathway of a crystalline enzyme. The structure of a specific acyl-enzyme intermediate in the elastase-catalyzed hydrolysis of the N-carbobenzoxy-L-alanine p-nitrophenyl ester has been determined and refined against X-ray diffraction data at 2.3-A resolution. The difference Fourier electron density map clearly shows electron density for the trapped acyl-enzyme. The acyl-enzyme was formed at -26 degrees C and was stabilized at -55 degrees C during data collection, taking advantage of the glass transition in protein dynamics that occurs at around -50 degrees C.

Fragile X induction systems in CVS cultures: effect on cytogenetic, PCR, and genomic Southern Blot DNA analyses of the FMR-1 gene

Low fragile X frequencies have been commonly observed in chorionic villus sample (CVS) cultures, compared to subsequent analysis in whole blood or products of conception (POC). To investigate possible mechanisms for this effect, CVS cultures from a previously identified fragile X positive male, were restudied and compared to subsequent POC cultures from lung, muscle, skin, and thymus. Cultures were exposed, for the last 24 hours before harvesting, to FUdR, excess thymidine, and a combination of both. For CVS, only those cultures that were exposed to a combination of FUdR and excess thymidine showed positive cytogenetic findings (1/90 or 1.1%), agreeing with our original positive cytogenetic results (2/86 or 2.3%) for cultures exposed to excess thymidine. Fragile X frequencies in the POC tissues from this fetus increased to an average of 14%. PCR analyses showed full mutations (> 200 CGG repeats) in uninduced CVS cultures but induced cultures exhibited apparently smaller sizes in the range of 120-180 repeats. The results showed variability. In one instance, the banding pattern from one of the uninduced cultures was similar to the results where cultures were exposed to a double induction system. When PCR analyses were conducted on induced POC cultures, full mutations were observed in virtually all samples. Southern blot genomic analysis using probe StB12.3 showed an unmethylated full mutation in CVS cultures. Southern blot patterns from cultures of muscle revealed size variations of DNA bands in the premutation range representing unmethylated DNA as well as methylated full mutations. Finally, variations were also observed in lung and skin cultures, compared to CVS and muscle.(ABSTRACT TRUNCATED AT 250 WORDS)

SPARC (secreted protein acidic and rich in cysteine) regulates endothelial cell shape and barrier function

SPARC (secreted protein acidic and rich in cysteine) can be selectively expressed by the endothelium in response to certain types of injury and induces rounding in adherent endothelial cells in vitro. To determine whether SPARC might influence endothelial permeability, we studied the effect of exogenous SPARC on the movement of 14C-labeled bovine serum albumin across postconfluent bovine pulmonary artery endothelial cells. SPARC increased (P < 0.02) transendothelial albumin flux in a dose-dependent manner at concentrations > or = 0.5 microgram/ml. At a fixed dose (15 micrograms/ml), exposure times > or = 1 h augmented (P < 0.005) albumin flux by 1.3- to 3.6-fold; this increase was blocked by anti-SPARC antibodies but not by inhibition of protein synthesis. Barrier dysfunction was not associated with loss of cell viability. Monolayers exposed to SPARC exhibited a rounded morphology and intercellular gaps. Prior stabilization of F-actin with phallicidin protected against the changes in barrier function (P = 0.0001) that were otherwise induced by SPARC. Bovine aortic and retinal microvascular endothelia also responded to SPARC. We propose that SPARC regulates endothelial barrier function through F-actin-dependent changes in cell shape, coincident with the appearance of intercellular gaps, that provide a paracellular pathway for extravasation of macromolecules.

[Studies on the induction of L-phenylalanine ammonia lyase(PAL) in Rhodotorula glutinis and transformation of phenylalanine from trans-cinnamic acid]

The induction of PAL in Rhodotorula glutinis and transformation of L-phenylalanine from trans-cinnamic acid were studied. The optimum medium for PAL induction was composed of (g/L) 10.0 yeast extract, 10.0 peptone, 5.0 NaCl, 0.5 KH2 PO4, 0.5 phenylalanine 1.0 (NH4)2SO4 and 5.0 glucose, pH 6.0-6.5. The cultivation temperature was 30.0 degrees C. In the process of transformation, the effect of [NH4]+ on initial velocity was in accordance with Michaelis-Menten rate expression in which Km and Vmax were 16.85 mol/L and 5.96 g.L-1.h-1 for ammonia and the optimum pH was 10.0. Substrate activation and inhibition were observed at low and high concentration of cinnamic acid. The yield of phenylalanine from cinnamic acid reached more than 60.0%.

Lipopolysaccharide (LPS)-binding protein and soluble CD14 function as accessory molecules for LPS-induced changes in endothelial barrier function, in vitro

Bacterial LPS induces endothelial cell (EC) injury both in vivo and in vitro. We studied the effect of Escherichia coli 0111:B4 LPS on movement of 14C-BSA across bovine pulmonary artery EC monolayers. In the presence of serum, a 6-h LPS exposure augmented (P < 0.001) transendothelial 14C-BSA flux compared with the media control at concentrations > or = 0.5 ng/ml, and LPS (10 ng/ml) exposures of > or = 2-h increased (P < 0.005) the flux. In the absence of serum, LPS concentrations of up to 10 micrograms/ml failed to increase 14C-BSA flux at 6 h. The addition of 10% serum increased EC sensitivity to the LPS stimulus by > 10,000-fold. LPS (10 ng/ml, 6 h) failed to increase 14C-BSA flux at serum concentrations < 0.5%, and maximum LPS-induced increments could be generated in the presence of > or = 2.5%. LPS-binding protein (LBP) and soluble CD14 (sCD14) could each satisfy this serum requirement; either anti-LBP or anti-CD14 antibody each totally blocked (P < 0.00005) the LPS-induced changes in endothelial barrier function. LPS-LBP had a more rapid onset than did LPS-sCD14. The LPS effect in the presence of both LBP and sCD14 exceeded the effect in the presence of either protein alone. These data suggest that LBP and sCD14 each independently functions as an accessory molecule for LPS presentation to the non-CD14-bearing endothelial surface. However, in the presence of serum both molecules are required.

Analogous inhibitors of elastase do not always bind analogously

It has been assumed that the structure of a single inhibitor complex is sufficient to define the available subsites of an enzyme that has a unique binding site and a uniquely defined mode for ligand binding--the specificity for these subsites can thus be probed by kinetic experiments. Elastase is an enzyme for which these traditional assumptions, which underlie such structural and kinetic studies, do not hold. Three new crystal structures of elastase complexed to chemically similar inhibitors with similar binding affinities reveal a diversity of binding modes as well as two new subsites on elastase. The existence of multiple binding sites and different binding modes for such similar inhibitors indicates that researchers must proceed with caution when using kinetics to map out protein subsites.

Bioconcentration of cadmium in water hyacinth (Eichhornia crassipes) in relation to thiol group content

To study the bioconcentration of cadmium in water hyacinth, the plants were exposed to water containing 2 microg Cd2+/ml for extended periods of time. Three strains from several exposures during a 30-day period were sampled for the analyses of cadmium and thiol group. The data showed that the plant concentrates cadmium mainly in the roots and that the cadmium uptake is proportional to the increase of the thiol group content. The latter suggests the possibility of using the thiol group content to assess the bioconcentration of heavy metal ions in water hyacinth and as a general parameter for monitoring the heavy metal pollution of water. A simple two-compartmental model was used to simulate the kinetics of cadmium uptake. The calculated bioconcentration factor matches the one derived directly from experimental data, indicating the adequacy of the model.

Relationship of articular soft tissue contour and shape to the underlying eminence and slope profile in young adult temporomandibular joints

This study examined whether the overall shape of the articular soft tissue overlying the posterior slope and articular eminence of the temporal bone could be predicted by the underlying osseous contour in a histologic model of 51 central sagittal sections of young adult temporomandibular joints. Articular soft tissue and bone contours were traced, and osseous landmarks identified on the basis of joint geometry. Soft tissue thickness measurements were made under low power light microscopy. Seven categories of articular soft tissue pattern were identified. The soft tissue uniformly followed the osseous contour in only one (14%). A progressive increase in soft tissue thickness from the middle of the posterior slope to the articular crest was the most common pattern (35%) but did not describe most of the sample that was more asymmetric. Pattern was poorly predicted by the shape and slope of the temporal bone outline or by dental factors that describe anterior guidance and did not relate to disk displacement. The articular soft tissue compensated for flatter eminence slopes and osseous irregularities and maintained an intact surface. This study has clinical implications for radiographic interpretation of disk space, condyle translation pathways, and the integrity of the functional articular surface.

Contour mapping of the TMJ temporal component and the relationship to articular soft tissue thickness and disk displacement

The osseous architecture of central sagittal histologic sections of the temporal component of 51 temporomandibular joints of young adults at autopsy was studied to determine if this predicted the thickness of the overlying articular soft tissue and disk displacement. Geometric groupings of fossa-eminence shapes were generated using a hierarchical cluster analysis of the osseous fossa-eminence sigmoid curve, size, and slope. Six cluster groups were evolved and tested for relationship to soft tissue thickness measured at the eminence crest, mid-point of the eminence slope, closed pack location of the condyle, the inflection point, and the depth of the fossa. Soft tissue thickness at the inflection point and depth of the fossa was remarkably constant between cluster groups. Increased soft tissue thickness at the eminence crest and lower part of the posterior slope was weakly correlated to a flatter eminence slope and curve, explaining 10% to 20% of the variance (r2). There were no relationships between the parameters studied to the fossa curvature. An ANOVA showed no statistical difference in the posterior slope angle between the categories of disk position (p = 0.715) or to the six cluster groupings. The results suggest that the osseous contours seen on radiographs may not accurately predict the actual articular surface of the temporal component.

Rapid fragile X carrier screening and prenatal diagnosis using a nonradioactive PCR test

OBJECTIVE

To develop a rapid, nonradioactive test using the polymerase chain reaction (PCR) capable of detecting full fragile X mutations, premutations, and resolving normal alleles and to apply this to prenatal diagnosis and carrier screening of pregnant women at risk for fragile X carrier status.

DESIGN

Prenatal and blood sample PCR analysis with confirmation by direct Southern blotting and cytogenetic techniques.

SETTING

Samples sent to a DNA diagnostic research laboratory at a tertiary referral center.

PARTICIPANTS

Pregnant women with a family history of undiagnosed mental retardation or known fragile X syndrome and controls.

RESULTS

A rapid, nonradioactive PCR screening protocol for the fragile X mental retardation-1 gene for both normal and mutant alleles was developed. Analysis of 570 control X chromosomes showed a modal number of 30 CGG repeats (range, 12 to 52 repeats) and a calculated heterozygosity of approximately 80%. No excess of homozygosity was found, indicating the test was accurate for normal allele resolution. In addition, 150 unrelated pregnant women were screened. Within known fragile X families, five of 20 pregnant women were diagnosed as carriers. Two new fragile X families were diagnosed among relatives of 130 females with family histories of undiagnosed mental retardation, although no carriers were identified. Prenatal PCR testing of 28 carriers accurately detected nine fetuses with full mutations.

CONCLUSIONS

This rapid, nonradioactive PCR protocol allows accurate resolution of normal alleles as well as simultaneous detection of carrier alleles and full mutations. With this approach, efficient screening of pregnant women at risk for fragile X carrier status, subsequent genetic counseling of identified carriers, and reliable prenatal diagnosis can be offered.

Evidence that methylation of the FMR-I locus is responsible for variable phenotypic expression of the fragile X syndrome

DNA at the FMR-1 locus was analyzed by Southern blot using probe StB12.3 in an unusual fragile X family with six brothers, three of whom are affected with fragile X to varying degrees, two of whom are nonpenetrant carriers, and one of whom is unaffected. Fragile X chromosome studies, detailed physical examinations, and psychological testing were completed on all six. Two of the affected brothers and the two nonpenetrant brothers were found to be methylation mosaics. The three affected males spanned the phenotypic and cognitive spectrum of the fragile X syndrome. A correlation was seen between the degree of methylation and the phenotypic expression identified in the three affected males. The two males initially classified as nonpenetrant were found to have mild phenotypic expression which consisted of minor cognitive deficits and a partial physical phenotype. These two, who were negative on fragile X chromosome studies, were found on DNA analysis to have large broad smears, with approximately 97% of the DNA unmethylated. The results described here indicate that some "nonpenetrant" carrier males may have varying amounts of methylation of the FMR-1 region, which can result in mild expression of the fragile X syndrome. The apparently mild phenotypic and cognitive expression of the fragile X syndrome in the two males, initially classified as nonpenetrant, who are mosaic for hypermethylation of an expansion of the CGG repeat in the premutation range, indicates that expression of the syndrome is not confined to males with large, hypermethylated expansions (full mutation) but has instead a gradient effect with a threshold for the full expression of the phenotype.

Bacterial lipopolysaccharide induces actin reorganization, intercellular gap formation, and endothelial barrier dysfunction in pulmonary vascular endothelial cells: concurrent F-actin depolymerization and new actin synthesis

Bacterial lipopolysaccharide (LPS) influences pulmonary vascular endothelial barrier function in vitro. We studied whether LPS regulates endothelial barrier function through actin reorganization. Postconfluent bovine pulmonary artery endothelial cell monolayers were exposed to Escherichia coli 0111:B4 LPS 10 ng/ml or media for up to 6 h and evaluated for: 1) transendothelial 14C-albumin flux, 2) F-actin organization with fluorescence microscopy, 3) F-actin quantitation by spectrofluorometry, and 4) monomeric G-actin levels by the DNAse 1 inhibition assay. LPS induced increments in 14C-albumin flux (P < 0.001) and intercellular gap formation at > or = 2-6 h. During this same time period the endothelial F-actin pool was not significantly changed compared to simultaneous media controls. Mean (+/- SE) G-actin (micrograms/mg total protein) was significantly (P < 0.002) increased compared to simultaneous media controls at 2, 4, and 6 h but not at 0.5 or 1 h. Prior F-actin stabilization with phallicidin protected against the LPS-induced increments in G-actin (P = 0.040) as well as changes in barrier function (P < 0.0001). Prior protein synthesis inhibition unmasked an LPS-induced decrement in F-actin (P = 0.0044), blunted the G-actin increment (P = 0.010), and increased LPS-induced changes in endothelial barrier function (P < 0.0001). Therefore, LPS induces pulmonary vascular endothelial F-actin depolymerization, intercellular gap formation, and barrier dysfunction. Over the same time period, LPS increased total actin (P < 0.0001) and new actin synthesis (P = 0.0063) which may be a compensatory endothelial cell response to LPS-induced F-actin depolymerization.

Construction of multiple copy of alpha-domain gene fragment of human liver metallothionein IA in tandem arrays and its expression in transgenic tobacco plants

Metallothioneins (MT) are low molecular weight, cysteine-rich, metal-binding proteins. An MT molecule contains two domains which appear to act independently--an alpha-domain, which is characterized by cadmium-binding, and a beta-domain, which binds preferentially to copper. Based on this conception, DNA duplex encoding the alpha-domain (106 bp) of human MT-IA was constructed from a chemically-synthesized oligomer by repair synthesis and enzymatic ligation and cloned into pUC19. The genes cloned were sequenced and found to be in the correct order as designed. Synthetic directional adapters were attached to the terminals of the alpha-domain gene fragment of human MT-IA to establish complete control over fragment orientation during ligation. The use of these directional adapters thereby ensured the production of multiple copies of the alpha-domain in tandem arrays. The successive alpha-domains were linked by a peptide linker consisting of 10 residues. A chimeric gene containing 12 cloned tandemly repeated copies of the 106 bp alpha-domain DNA was introduced into tobacco cells on a disarmed Ti-plasmid of Agrobacterium tumefaciens. A total of 10 different transgenic tobacco plants were generated, of which two showed root and shoot growth unaffected by up to 200 mg/l kanamycin and 100 microM cadmium, whereas root growth of control plants was severely inhibited and leaf chlorosis developed on media containing only 10 microM cadmium.

Isolation and heterologous expression of cloned cDNAs for two rabbit nasal microsomal proteins, CYP2A10 and CYP2A11, that are related to nasal microsomal cytochrome P450 form a

Nasal microsomal P450 form a (NMa), a major cytochrome P450 isozyme in rabbit olfactory and respiratory nasal mucosa with high activity toward a variety of odorants and environmental toxicants, was previously purified to electrophoretic homogeneity from rabbit nasal microsomes. In the present study, a cDNA library constructed from poly(A)+ RNA from rabbit respiratory nasal mucosa was screened with antibodies to P450 NMa, and five immunopositive clones were isolated and characterized. Sequence analysis indicated that the clones encode two highly similar P450s that contain 494 amino acid residues, with the first 20 corresponding to P450 NMa, and differ from each other in only 8 residues scattered throughout the polypeptide chains. On the basis of structural homology the two proteins are designated as CYP2A10 and CYP2A11 and are the first members of the P450 2A subfamily to be identified in nasal tissue. Genomic blot analysis indicated that 2A10 and 2A11 are apparently not allelic variants. Both genes are expressed in liver and lung as well as in nasal tissues, as judged by RNA blot analysis, but the relative levels of the two mRNAs differ. Both enzymes were partially purified after expression of the cDNAs in Escherichia coli and shown to catalyze the oxygenation of a variety of substrates, including ethanol and procarcinogens such as N-nitrosodiethylamine and phenacetin. P450 2A10 is generally more active than P450 2A11 and strikingly so in the conversion of testosterone to androstenedione.

Maturation induced internalization of beta 1-integrin by Xenopus oocytes and formation of the maternal integrin pool

A pool of beta 1-integrin, ready to be inserted into the cleavage membranes, is present in the cytoplasm of the Xenopus egg, while its plasma membrane is devoid of this membrane protein (Gawantka et al., 1992). The underlying mechanisms that lead to this specific pattern of beta 1-integrin distribution in the egg have been investigated. beta 1-Integrin is present on the oocyte membrane throughout oogenesis. During maturation the oocyte membrane is cleared of beta 1-integrin via internalization of the protein by the oocyte. Synthesis of beta 1-integrin precursor is stimulated moderately in the maturing oocyte. At the same time processing of the precursor into the mature form of beta 1-integrin and its complexing with a putative alpha-chain is greatly accelerated. This way a maternal integrin pool accumulates in the mature oocyte. It is localized in conspicuous yolk free patches which contain large amounts of endoplasmic reticulum, Golgi complexes and smooth vesicles. We suggest that membrane vesicles harbouring the beta 1-integrin are generated in these cytoplasmic regions and that this store of vesicles provides the material source for the rapid membrane formation during cleavage.

Immunohistochemical localization of a cytochrome P-450 isozyme in human nasal mucosa: age-related trends

Immunoperoxidase staining with an antibody to cytochrome P-450 (NMa) was used to investigate the localization of this isozyme in the human nasal mucosa. Olfactory mucosa was identified by staining of olfactory receptor cells with an antibody to olfactory marker protein. Immunoreactivity to NMa was localized in sustentacular cells in the olfactory epithelium, and in Bowman's gland acinar cells and vascular endothelial cells in the lamina propria. In the respiratory mucosa, ciliated epithelial cells, as well as serous gland acinar cells and vascular endothelial cells in the lamina propria, were immunoreactive for this isozyme. An age-related decrement in the intensity and extent of immunoreactivity within these cells was noted in nasal tissue from patients 60 years of age and over when compared with that of patients under 60 years of age. These results identify sites of xenobiotic metabolism or activation in human nasal mucosa.

TNF-alpha induces endothelial cell F-actin depolymerization, new actin synthesis, and barrier dysfunction

Tumor necrosis factor-alpha (TNF-alpha) influences pulmonary vascular endothelial barrier function in vitro. We studied whether recombinant TNF-alpha (rTNF-alpha) regulates endothelial barrier function through actin reorganization. Postconfluent bovine pulmonary artery endothelial cell monolayers were exposed to human rTNF-alpha (1,000 U/ml) and evaluated for 1) transendothelial [14C]albumin flux, 2) F-actin organization with fluorescence microscopy, 3) F-actin quantitation by spectrofluorometry, and 4) monomeric G-actin levels by the deoxyribonuclease I inhibition assay. rTNF-alpha induced increments in [14C]albumin flux (P < 0.04) and intercellular gap formation at > or = 2-6 h. During this same time, the endothelial F-actin pool decreased (P = 0.0064), with reciprocal increases in the G-actin pool (P < 0.0001). Prior F-actin stabilization with phallicidin protected against the rTNF-alpha-induced increments in G-actin (P < 0.002) as well as changes in barrier function (P < 0.01). Prior protein synthesis inhibition enhanced the rTNF-alpha-induced decrement in F-actin (P < 0.0001), blunted the G-actin increment (P < 0.002), and increased rTNF-alpha-induced changes in endothelial barrier function (P < 0.003). Therefore, rTNF-alpha induces pulmonary vascular endothelial F-actin depolymerization, intercellular gap formation, and barrier dysfunction. rTNF-alpha also increased total actin (P < 0.02) and new actin synthesis (P < 0.002), which may be a compensatory endothelial cell response to rTNF-alpha-induced F-actin depolymerization.

Flavone improves functional recovery after ischemia in isolated reperfused rabbit hearts

The effects of flavone (2-phenyl-1,4-benzopyrone), a modulator of the cytochrome P-450 monooxygenase system, on myocardial postischemic reperfusion recovery were examined in the present study. Left ventricular functional recovery was evaluated in isolated, crystalloid-perfused rabbit hearts after 2 hours of modestly hypothermic (34 degrees C) global ischemia. Four groups (n = 8 in each group) were studied and compared: a vehicle control group, a second group pretreated with flavone (8 x 10(-6) mol/L) before ischemia, a third group pretreated with flavone followed by SKF 525-A (1.7 x 10(-5) mol/L), an inhibitor of cytochrome P-450, and a fourth group pretreated with flavone followed by indomethacin (1 x 10(-6) mol/L), an inhibitor of cyclooxygenase. At 15, 30, and 45 minutes after reperfusion, recovery of left ventricular developed pressure in the control group averaged (mean +/- standard deviation) only 2.60% +/- 12.7%, 35.5% +/- 15.0%, and 42.9% +/- 13.5% of baseline, respectively. In the flavone-treated group, recovery was significantly better, averaging 67.7% +/- 10.7%, 73.9% +/- 9.3%, and 73.6% +/- 7.6% of baseline at the same time periods. Recovery of peak positive rate of pressure rise in the control group averaged 27.4% +/- 15.2%, 38.6% +/- 19.2%, and 45.4% +/- 18.6% of baseline at 15, 30, and 45 minutes of reperfusion, respectively. In the flavone-treated group recovery values were significantly higher, averaging 67.8% +/- 9.6%, 77.3% +/- 8.5%, and 77.0% +/- 9.0% of baseline. End-diastolic pressures were significantly lower in the flavone-treated group compared with the control group at all reperfusion time points. Myocardial oxygen consumption was significantly higher in the flavone-treated group at 30 and 45 minutes of reperfusion, as well. The improvement resulting from flavone infusion was abolished completely by SKF 525-A, providing support for the interpretation that the effects of flavone were mediated through the cytochrome P-450 system. The cyclooxygenase inhibitor indomethacin midly attenuated the effects of flavone pretreatment, suggesting that the effects of flavone were only minimally related to metabolites of cyclooxygenase. We conclude that pretreatment with flavone represents a promising approach to myocardial protection that may be due to modulation of the myocardial cytochrome P-450 system.

Effects of repeated administration of cocaine to the fetal sheep in the last days of pregnancy

OBJECTIVE

There are no reports on the direct effects of repeated cocaine administration to the fetus in late pregnancy. The aim of our study was therefore to examine the effects of repeated fetal exposure to cocaine on fetal development.

STUDY DESIGN

Ten fetal sheep were instrumented at 123 +/- 1 days' gestation. Five fetuses received a single daily intravenous injection of cocaine (2 mg/kg) commencing at 130 to 131 days of gestation until delivery at 132 to 144 days of gestation; those fetuses were compared with fetuses that did not receive cocaine (n = 5).

RESULTS

Basal fetal arterial blood gas values, blood pressure, heart rate, and nuchal and diaphragmatic activities did not change in the days preceding labor. Fetal arterial PO2 fell after cocaine administration, but this was significant only on the first day. Cocaine induced consistent significant alterations in fetal pH and PCO2, blood pressure, and heart rate. During labor cocaine stimulated diaphragmatic and nuchal muscle activity when compared with the other days. There was no increase in diaphragmatic and nuchal muscle activity in the controls.

CONCLUSION

Our studies indicate that in fetal sheep the cardiovascular and blood gas response to cocaine in late pregnancy is not altered by repeated exposure to cocaine and that cocaine stimulates fetal breathing during labor.

Cytochromes P450 NMa, NMb (2G1), and LM4 (1A2) are differentially expressed during development in rabbit olfactory mucosa and liver

Mammalian olfactory mucosa has a high concentration of cytochrome P450 monooxygenases (P450). The major olfactory P450 isoforms in adult rabbits include P450 NMa, which is found in both olfactory and respiratory mucosa, as well as in liver at a low level, P450 NMb (2G1), which is olfactory specific, and P450 form 4 (1A2), which is found only in liver and olfactory mucosa. In the present study, we have found that the developmental expression of olfactory P450 in rabbits is not coordinated with the ontogenesis of hepatic P450. These three P450 isoforms were detected immunochemically and found to be at a relatively high level in olfactory but not hepatic microsomes in the first 2 weeks after birth. In the liver, NMb is not detectable at any age and NMa is not detectable until the fourth week. P450 1A2 is not detectable until the third week, but its level increases rapidly in the fourth week. These P450 isoforms are also detectable in prenatal olfactory tissue at 2 days before birth, indicating that direct exposure to air is not a prerequisite for their early expression in this tissue and that the early appearance of these enzymes may be controlled by both endogenous and environmental factors. In addition, the developmental expression of 2E1, a minor olfactory P450 isoform, also occurs earlier in olfactory mucosa than in liver, and the same conclusion can be made about the expression of NADPH-P450 reductase, which is detectable in olfactory microsomes but not in hepatic microsomes from prenatal rabbits. Thus, the regulatory mechanisms that control basal prenatal expression in the olfactory tissue may be common for multiple P450 isoforms and perhaps also for other biotransformation enzymes. The tissue-specific early onset of expression of multiple forms of P450 in olfactory tissue suggests that these enzymes may play an important role in the neonatal period, when olfactory ability is vital for the survival of the newborn. The presence of relatively high levels of biotransformation enzymes in the olfactory mucosa may also have important implications for neonatal inhalation toxicology.

Metabolism of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), a tobacco-specific carcinogen, by rabbit nasal microsomes and cytochrome P450s NMa and NMb

Rabbit nasal olfactory and respiratory microsomes were found to catalyze the alpha-hydroxylation of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) with specific activities of 262 and 136 pmol/min/mg protein in the formation of keto aldehyde, and of 318 and 190 pmol/min/mg protein in the formation of keto alcohol respectively. The formation of NNK-N-oxide was observed in experiments with rabbit olfactory and respiratory microsomes, but not with rat nasal microsomes. However, the rat nasal microsomes had higher activity in catalyzing the alpha-hydroxylation of NNK. In a reconstituted system, rabbit P450NMa, a major constitutive P450 isozyme in nasal microsomes, displayed high activities in the formation of the keto aldehyde and the keto alcohol with apparent Km values of 15 and 9 microM respectively. In comparison, rabbit olfactory specific P450NMb had a low activity in catalyzing the formation of keto aldehyde (Km = 186 microM) and no activity in the formation of keto alcohol. The P450NMa-catalyzed oxidation of NNK was inhibited by nicotine and diallyl sulfide. Kinetic studies indicated that nicotine is a competitive inhibitor. These results demonstrate that enzymes in rabbit nasal microsomes, especially P450NMa, efficiently catalyze the bioactivation of NNK.

Induction of P-450 cytochromes 2E2, 1A1, and 1A2 by imidazole in neonatal rabbits

Cytochrome P-450 2E1 is induced in adult rabbits by treatment with alcohol, imidazole, and a variety of other agents, as shown earlier in this laboratory, but it is not known whether the highly homologous P-450 2E2 is similarly induced. In this study, the effects of imidazole on 2E2 expression were examined in neonatal rabbits, in which 2E1 is not detectable. Treatment of the animals with imidazole on days 8 through 11 after birth caused a 3-fold increase in the content of total P-450 in liver microsomes. In contrast, the microsomal content of cytochrome b5 and NADPH-P450 reductase was not changed. Immunoblot analysis revealed a significant increase in the level of P-450 2E2 (3-fold) as well as 1A1 (> 10-fold) and 1A2 (> 2-fold) in hepatic microsomes from imidazole-treated neonatal rabbits. The rates of microsomal N-demethylation of N-nitrosodimethylamine and O-deethylation of 7-ethoxyresorufin were similarly increased from 1.3 and 0.03 nmol/min/mg protein, respectively, to 5.6 and 0.24 nmol/min/mg protein, respectively, by imidazole treatment. Blot analysis indicated that the levels of 2E2, 1A1, and 1A2 mRNAs are not increased by imidazole treatment and that 2E1 mRNA is not detectable in either untreated or imidazole-treated neonates. The induction of P-450 2E2 was confirmed by NH2-terminal amino acid sequence analysis of immunopurified 2E protein from hepatic microsomes of imidazole-treated neonatal rabbits.(ABSTRACT TRUNCATED AT 250 WORDS)