Carotid-compression technique for the insertion of guiding catheters

Inserting a guiding catheter into a tortuous artery for neurointerventional procedures can be difficult. In our technique, the carotid artery is manually compressed to stabilize and/or straighten the inserted wire before advancing the guiding catheter. Although this technique is not risk-free and care must be taken to avoid vascular injury by excessive compression, it is useful for the insertion of a guiding catheter into the carotid artery.

Relationship between regional cerebral metabolism and consciousness disturbance in traumatic diffuse brain injury without large focal lesions: an FDG-PET study with statistical parametric mapping analysis

BACKGROUND

The cerebral metabolism of patients in the chronic stage of traumatic diffuse brain injury (TDBI) has not been fully investigated.

AIM

To study the relationship between regional cerebral metabolism (rCM) and consciousness disturbance in patients with TDBI.

METHODS

52 patients with TDBI in the chronic stage without large focal lesions were enrolled, and rCM was evaluated by fluorine-18-fluorodeoxyglucose positron emission tomography (FDG-PET) with statistical parametric mapping (SPM). All the patients were found to have disturbed consciousness or cognitive function and were divided into the following three groups: group A (n = 22), patients in a state with higher brain dysfunction; group B (n = 13), patients in a minimally conscious state; and group C (n = 17), patients in a vegetative state. rCM patterns on FDG-PET among these groups were evaluated and compared with those of normal control subjects on statistical parametric maps.

RESULTS

Hypometabolism was consistently indicated bilaterally in the medial prefrontal regions, the medial frontobasal regions, the cingulate gyrus and the thalamus. Hypometabolism in these regions was the most widespread and prominent in group C, and that in group B was more widespread and prominent than that in group A.

CONCLUSIONS

Bilateral hypometabolism in the medial prefrontal regions, the medial frontobasal regions, the cingulate gyrus and the thalamus may reflect the clinical deterioration of TDBI, which is due to functional and structural disconnections of neural networks rather than due to direct cerebral focal contusion.

Evidence for white matter disruption in traumatic brain injury without macroscopic lesions

BACKGROUND

Non-missile traumatic brain injury (nmTBI) without macroscopically detectable lesions often results in cognitive impairments that negatively affect daily life.

AIM

To identify abnormal white matter projections in patients with nmTBI with cognitive impairments using diffusion tensor magnetic resonance imaging (DTI).

METHODS

DTI scans of healthy controls were compared with those of 23 patients with nmTBI who manifested cognitive impairments but no obvious neuroradiological lesions. DTI was comprised of fractional anisotropy analysis, which included voxel-based analysis and confirmatory study using regions of interest (ROI) techniques, and magnetic resonance tractography of the corpus callosum and fornix.

RESULTS

A decline in fractional anisotropy around the genu, stem and splenium of the corpus callosum was shown by voxel-based analysis. Fractional anisotropy values of the genu (0.47), stem (0.48), and splenium of the corpus callosum (0.52), and the column of the fornix (0.51) were lower in patients with nmTBI than in healthy controls (0.58, 0.61, 0.62 and 0.61, respectively) according to the confirmatory study of ROIs. The white matter architecture in the corpus callosum and fornix of patients with nmTBI were seen to be coarser than in the controls in the individual magnetic resonance tractography.

CONCLUSIONS

Disruption of the corpus callosum and fornix in patients with nmTBI without macroscopically detectable lesions is shown. DTI is sensitive enough to detect abnormal neural fibres related to cognitive dysfunction after nmTBI.

p53-Independent ceramide formation in human glioma cells during gamma-radiation-induced apoptosis

Although the p53 tumor-suppressor gene product plays a critical role in apoptotic cell death induced by DNA-damaging chemotherapeutic agents, human glioma cells with functional p53 were more resistant to gamma-radiation than those with mutant p53. U-87 MG cells with wild-type p53 were resistant to gamma-radiation. U87-W E6 cells that lost functional p53, by the expression of type 16 human papillomavirus E6 oncoprotein, became susceptible to radiation-induced apoptosis. The formation of ceramide by acid sphingomyelinase (A-SMase), but not by neutral sphingomyelinase, was associated with p53-independent apoptosis. SR33557 (2-isopropyl-1-(4-[3-N-methyl-N-(3,4-dimethoxybphenethyl)amino]propyloxy)benzene-sulfonyl) indolizine, an inhibitor of A-SMase, suppressed radiation-induced apoptotic cell death. In contrast, radiation-induced A-SMase activation was blocked in glioma cells with endogenous functional p53. The expression of acid ceramidase was induced by gamma-radiation, and was more evident in cells with functional p53. N-oleoylethanolamine, which is known to inhibit ceramidase activity, unexpectedly downregulated acid ceramidase and accelerated radiation-induced apoptosis in U87-W E6 cells. Moreover, cells with functional p53 could be sensitized to gamma-radiation by N-oleoylethanolamine, which suppressed radiation-induced acid ceramidase expression and then enhanced ceramide formation. Sensitization to gamma-radiation was also observed in U87-MG cells depleted of functional p53 by retroviral expression of small interfering RNA. These results indicate that ceramide may function as a mediator of p53-independent apoptosis in human glioma cells in response to gamma-radiation, and suggest that p53-dependent expression of acid ceramidase and blockage of A-SMase activation play pivotal roles in protection from gamma-radiation of cells with endogenous functional p53.

Segmental high intensity on T1-weighted hepatic MR images

BACKGROUND

We investigated the diagnostic importance of segmental high-intensity (SHI) areas not corresponding to mass lesions on T1-weighted magnetic resonance (MR) images.

METHODS

We conducted a retrospective investigation of hepatic MR images obtained from 634 patients during a 4-year period at our institution. Images were compared with findings reported in the patients' medical records. There were 16 patients (2.5%) with SHI areas not corresponding to a mass lesion. We compared MR images with plain computed tomographic (CT) scans (n = 16), angiograms (n = 12), and histologic findings (n = 10).

RESULTS

The segments with intrahepatic bile duct dilatation showed hyperintensity on T1-weighted images. In six of 16 patients, the biliary duct was more dilated in the area of hyperintensity than in areas without hyperintensity. The SHI areas appeared as areas of low attenuation (n = 13), high attenuation (n = 1), or isoattenuation (n = 2) on plain CT scans. Histologically, these areas showed ductular proliferation and deposition of bile pigment within the hepatocytes.

CONCLUSION

Segmental areas of increased signal intensity on T1-weighted images were probably due to intrahepatic cholestasis.

Discrepancy between lesion distributions on methionine PET and MR images in patients with glioblastoma multiforme: insight from a PET and MR fusion image study

OBJECTIVE

To examine (11)C-methyl methionine (MET) accumulation on positron emission tomographic (PET) imaging of glioblastoma multiforme to determine the distribution of metabolic abnormality compared with magnetic resonance imaging (MRI).

METHODS

Contemporaneous MRI was superimposed on corresponding MET-PET images in 10 patients with newly diagnosed glioblastoma multiforme before treatment. Differences between the extended area of MET accumulation on PET imaging (MET area), the gadolinium (Gd) enhanced area on T1 weighted images (Gd area), and the abnormal high signal intensity area on T2 weighted images (T2-high area) were assessed.

RESULTS

The MET area was larger than the Gd area and included the entire Gd area. The discrepancy in volume between the MET and Gd areas became greater with increasing tumour diameter. On average, 58.6% of the MET area was located within the Gd area, 90.1% within 10 mm outside the Gd area, 98.1% within 20 mm, and 99.8% within 30 mm. A newly developed Gd area had emerged in five of the 10 cases up to the time of study. In three of the five cases this was in the MET area even after complete surgical resection of the Gd area on the initial MRI; in the remaining two it originated in the residual Gd area after surgery. In all cases, the T2-high area was larger than the MET area. The MET area extended partly beyond the T2-high area in nine cases, and was completely within it in one.

CONCLUSIONS

Glioblastoma multiforme cells may extend over the Gd area and more widely with increasing tumour size on Gd-MRI. The T2-high area includes the greater part of the tumour but not its entire area. The methods reported may be useful in planning surgical resection, biopsy, or radiosurgery.

Considerations in the surgical treatment of superior-wall type aneurysm at the proximal (M1) segment of the middle cerebral artery

OBJECTIVE

To present our experience and analyze the risks of neck clipping for superior-wall type aneurysms of the proximal segment of the middle cerebral artery (M1-Sup aneurysm).

METHODS

Of 14 patients with M1-Sup aneurysms, 4 suffered postoperative infarctions in the territory of the lenticulostriate arteries (LSA) or fronto-orbital arteries. We re-examined our intraoperative findings and clinical records in an effort to identify possible causes.

RESULTS

The patency of the LSA was confirmed at the end of surgery in all 14 cases. We posit that temporary occlusion of the LSA by a permanent clip resulted in delayed obstruction of the LSA in 3 patients. Other possibilities we considered were relatively long temporary occlusion of the M1, slipping of the clips and twisting of the clip blades after release of the brain retractors.

CONCLUSION

M1-Sup aneurysms are some of the most complicated aneurysms; they carry the risk of perforator injury during neck clipping. Surgical considerations to avoid perforator injury are discussed.

Molecular mechanisms of TNF-α-induced ceramide formation in human glioma cells:P53-mediated oxidant stress-dependent and -independent pathways

The present study was designed to examine the roles of p53, reactive oxygen species (ROS), and ceramide, and to determine their mutual relationships during tumor necrosis factor (TNF)-alpha-induced apoptosis of human glioma cells. In cells possessing wild-type p53, TNF-alpha stimulated ceramide formation via the activation of both neutral and acid sphingomyelinases (SMases), accompanied by superoxide anion (O2-*) production, and induced mitochondrial depolarization and cytochrome c release, whereas p53-deficient cells were partially resistant to TNF-alpha and lacked O2-* generation and neutral SMase activation. Restoration of functional p53 sensitized glioma cells expressing mutant p53 to TNF-alpha by accumulation of O2-*. z-IETD-fmk (benzyloxycarbonyl-Ile-Glu-Thr-Asp fluoromethyl ketone), but not z-DEVD-fmk (benzyloxycarbonyl-Asp-Glu-Val-Asp fluoromethyl ketone), blocked TNF-alpha-induced ceramide formation through both SMases as well as O2-* generation. Caspase-8 was processed by TNF-alpha regardless of p53 status of cells or the presence of antioxidants. Two separate signaling cascades, p53-mediated ROS-dependent and -independent pathways, both of which are initiated by caspase-8 activation, thus contribute to ceramide formation in TNF-alpha-induced apoptosis of human glioma cells.

A novel case with germline p53 gene mutation having concurrent multiple primary colon tumours

During a search for causative genes in patients with concurrent multiple primary colon tumours, we found a novel case with a germline mutation of the p53 gene, from GCC (Ala) to GTC (Val) at codon 189. Of the six primary colon tumours that this patient had, one large advanced carcinoma exhibited a somatic p53 mutation and a somatic APC mutation, in addition to the germline p53 mutation. Two early carcinomas and three adenomas had somatic APC mutations but no somatic p53 mutation or loss of the p53 allele. K-ras-2 mutations were detected in an advanced carcinoma and an early carcinoma. The present results suggest that a patient with a certain type of germline p53 mutation is predisposed to concurrent multiple colon tumours. It is also suggested that in such a patient, a somatic APC mutation is involved in tumour formation and that an additional somatic p53 mutation contributes to tumour progression.

Structure-based generation of a new class of potent Cdk4 inhibitors: new de novo design strategy and library design

As a first step in structure-based design of highly selective and potent Cdk4 inhibitors, we performed structure-based generation of a novel series of Cdk4 inhibitors. A Cdk4 homology model was constructed according to X-ray analysis of an activated form of Cdk2. Using this model, we applied a new de novo design strategy which combined the de novo design program LEGEND with our in-house structure selection supporting system SEEDS to generate new scaffold candidates. In this way, four classes of scaffold candidates including diarylurea were identified. By constructing diarylurea informer libraries based on the structural requirements of Cdk inhibitors in the ATP binding pocket of the Cdk4 model, we were able to identify a potent Cdk4 inhibitor N-(9-oxo-9H-fluoren-4-yl)-N'-pyridin-2-ylurea 15 (IC(50) = 0.10 microM), together with preliminary SAR. We performed a docking study between 15 and the Cdk4 model and selected a reasonable binding mode which is consistent with the SAR. Further modification based on the proposed binding mode provided a more potent compound, N-[(9bR)-5-oxo-2,3,5,9b-tetrahydro-1H-pyrrolo[2,1-a]isoindol-9-yl]-N'-pyridin-2-ylurea 26a (IC(50) = 0.042 microM), X-ray analysis of which was accomplished by the soaking method. The predicted binding mode of 15 in Cdk4 was validated by X-ray analysis of the Cdk2-26a complex.

The clinical utility of contrast-enhanced 3D MR angiography for cerebrovascular disease

The purpose of this study was to evaluate the usefulness of contrast-enhanced 3D MR angiography (CE-MRA) with an automated bolus-detection algorithm (SmartPrep technique) and the specialized phased-array coils for the patients suspected cerebrovascular disease. Forty-three patients with brain attack were examined with CE-MRA. A tracker volume of SmartPrep technique was placed along the ascending aorta in the coronal image. After the bolus injection of gadolinium, an increase in signal that corresponded to the arrival of gadolinium was used to trigger centric re-ordered spoiled gradient echo arterial selective MRA with imaging time of 20-40 sec. We were able to achieve a 100% successful triggering rate of SmartPrep technique and selectively arterial-phase carotid and vertebral arteries with almost no venous contamination could be delineated. These techniques enabled high resolution imaging of entire craniocervical arteries from aortic arch to the circle of Willis. This CE-MRA was useful to evaluate both occlusion of arteries and the collateral pathways and to measure stenosis and residual flow of dissection accurately. CE-MRA was a reliable less-invasive alternative to investigate the patients of cerebrovascular disease.

Cloning and overexpression of the oah1 gene encoding O-acetyl-L-homoserine sulfhydrylase of Thermus thermophilus HB8 and characterization of the gene product

The oah1 gene of an extremely thermophilic bacterium, Thermus thermophilus HB8, was cloned, sequenced, and overexpressed in Escherichia coli cells. The gene product having a high O-acetyl-L-homoserine sulfhydrylase (EC 4.2.99.10) activity was purified to homogeneity, with a recovery of approximately 40% and a purification ratio of 81-fold, both calculated from the cell-homogenate. The protein showed molecular masses of approximately 163000 (for the native form) and 47000 (for the subunit). The isoelectric point was pH 6.0. The optimum temperature and pH for the activity were approximately 70 degrees C and pH 7.8, respectively. The enzyme was also shown to be very stable at high temperature (90% activity remaining at 90 degrees C for 60 min at pH 7.8) and in a wide range of pH (pH 4-12 at room temperature). The absorption spectrum showed a peak at 425 nm, and hydroxylamine hydrochloride (0.1 mM) inhibited approximately 90% of the activity, suggesting formation of a Schiff base with pyridoxal 5'-phosphate. The enzyme showed an apparent K(m) value of 6.8 mM for O-acetyl-L-homoserine, a V(max) value of 165 micromol/min per mg of protein at a fixed sulfide concentration of 5 mM, and also an apparent K(m) value of approximately 1.3 mM for sulfide (with 25 mM acetylhomoserine). L-Methionine (1 mM) inhibited the enzyme activity by 67%. Based on these findings, it was discussed that this enzyme might be inactive under ordinary conditions but might become active as an alternative homocysteine synthase in T. thermophilus HB8, only under such conditions as deficiency in transsulfuration, bringing about a sufficient amount of sulfide available in the cell.

Cerebral ischemic complications following intracranial bleeding in patients with moyamoya disease--three case reports

Three patients with bleeding-type moyamoya disease suffered ischemic complications following their first episode of intracranial bleeding. The patients presented with intraventricular hemorrhage and suffered cerebral infarction on the 14th, 16th, and 11th days after the ictus, respectively. The clinical records revealed no obvious hypotension before progression to infarction and suggested that dehydration accelerated by the administration of hyperosmotic drugs was a contributing factor to the infarction. Two patients underwent superficial temporal artery-middle cerebral artery anastomoses in the chronic stages and have never experienced further ischemic complications. The other patient died despite receiving intensive care. Hemodynamic reserve may be severely impaired in patients with bleeding-type moyamoya disease. Adequate control of hydration is important to prevent cerebral infarction after intracranial bleeding in patients with moyamoya disease.

Alterations of repeated sequences in 5' upstream and coding regions in colorectal tumors from patients with hereditary nonpolyposis colorectal cancer and Turcot syndrome

One of the characteristics of tumors from patients with germline mutations of DNA mismatch repair genes is instability at microsatellite regions (MSI). We analysed alterations at repeated sequences of coding regions, as well as those of 5' upstream regions, in 29 MSI-High colorectal tumors from patients with hereditary nonpolyposis colorectal cancer (HNPCC) and Turcot syndrome. We found that repeated sequences in 5' upstream regions were altered in these tumors, at considerable frequencies. The (A)10 repeat in the promoter region (position -178 to approximately -169) of the GAPDH gene was altered in 17% of the tumors. The (A)10(TA)9 in the 5' upstream region (position -318 to approximately -291) of the mitochondrial isoleucyl tRNA synthetase gene (IleRS-A), coded in nuclear DNA, was altered in 59% of the tumors, whereas (A)9 in the 5' upstream region (position -859 to approximately -851) of cytoplasmic isoleucyl tRNA synthetase gene (IleRS-B) was not altered. Alteration at repeated sequences in the coding regions were 72% at TGFbetaRII(A)10, 24% at IGFIIR(G)8, 45% at BAX(G)8, 55% at E2F4(CAG)13, 66% at caspase-5 (A)10, 31% at MBD4(A)10, 55% at hMSH3(A)8 and 34% at hMSH6(C)8. The number of altered genes increased with the advancement of carcinoma according to Dukes categories: mean numbers of altered genes within these 10 genes were 2.6 for Dukes A, 4.7 for Dukes B and 7.8 for Dukes C. The mean number for adenomas was 2.0. These results suggest that the MSI phenotype also causes alteration of 5' upstream regions which may affect apoptosis and some mitochondrial functions in HNPCC and Turcot tumors, and that accumulation of altered genes with repeated sequences is associated with the progression of HNPCC and Turcot colorectal tumors.

Spinal injuries in snowboarders: risk of jumping as an integral part of snowboarding

BACKGROUND

The purpose of this study was to clarify the occurrence rate and characteristics of spinal injuries caused by snowboarding that were sustained at the Okumino skiing area in Gifu Prefecture, Japan, from 1988 to 2000.

METHODS

This study was a retrospective review of 13,490 cases of snowboard- or ski-related injury treated at Sumi Memorial Hospital over this period.

RESULTS

A total of 7,188 patients sustained snowboard-related injuries, and 238 of these had spinal injuries caused by snowboarding (3.3%), whereas 6,302 patients sustained ski-related injuries, and 86 of these had spinal injuries caused by skiing (1.4%). Although there were no significant differences in the difficulty of slope, location of vertebral fracture, or spinal cord injury between snowboarders and skiers, the incidence of transverse process fractures was significantly higher in snowboard-related than in skiing-related injury (p < 0.05). In addition, there was a significantly higher incidence of spinal injury among beginner snowboarders than among beginner skiers (p = 0.04). Furthermore, intermediate or expert snowboarders were more likely to be injured because of jumping than beginners (p < 0.001), whereas about 70% of spinal injuries caused by skiing resulted from a simple fall.

CONCLUSION

Spinal injuries sustained while snowboarding are increasing considerably in incidence and are characterized as complex injuries. We must educate young snowboarders of the risk of this sport, to prevent these serious injuries.

Somatic mutation rate of the APC gene

BACKGROUND

Somatic inactivation of the wild-type APC gene is involved in the development of adenoma of familial adenomatous polyposis. This situation is also true in sporadic adenomas. It is of biological interest to know the somatic mutation rate of the APC gene.

METHODS

The number of stem cells of the colon (N) and somatic mutation rate of the APC gene in a stem cell in a year (m) can induce age-specific incidence of adenomas. The number of stem cells was estimated as 10(8) according to previous reports. In the general population, expected adenomas at the end of age n years will be approximately Nm2n2/4. In patients with polyposis, the expected number of adenomas will be Nmn/2. By setting several figures for m, the expected incidence of adenomas was compared with the actual occurrences.

RESULTS

If the mutation rate was set between 2/10(6) and 3/10(6) mutations/stem cell/year, the calculated numbers were well fitted to the actual data. Expected adenomas in polyposis patients at the age of 20 and 40 years were 2000 and 4000 and these were within actual experiences.

CONCLUSIONS

This is the first study to estimate the somatic mutation rate of the APC gene. The estimated somatic mutation rate of the APC gene was between 2/10(6) and 3/10(6) mutations/stem cell/year.

Cerebral hemodynamic parameters for patients with neurological improvements after extracranial-intracranial arterial bypass surgery: evaluation using positron emission tomography

OBJECTIVE

The purpose of this study was to clarify the hemodynamic features of patients who experienced improved neurological function after extracranial-intracranial arterial bypass surgery. With this aim, we retrospectively analyzed the results of their pre- and postoperative positron emission tomographic studies.

METHODS

This study included 16 patients who exhibited stable neurological dysfunction just before extracranial-intracranial bypass surgery. All underwent pre- and postoperative positron emission tomographic studies. They were divided into groups, i.e., patients who did (Group 1, n = 6) or did not (Group 2, n = 10) manifest postoperative improvements in neurological functions. Positron emission tomographic parameters obtained in the middle cerebral artery territories were compared between the two groups.

RESULTS

Comparison of the preoperative hemodynamic values on the affected side and the contralateral side demonstrated that the mean regional cerebral blood flow values were significantly lower on the affected side in both groups (Group 1, P < 0.005; Group 2, P < 0.05). For Group 1 patients, the mean regional oxygen extraction fraction (rOEF) and regional cerebral blood volume values were significantly higher on the affected side than on the contralateral side (P < 0.01 and P < 0.05, respectively). For Group 2 patients, the mean regional cerebral metabolic rate of oxygen (rCMRO2) value was significantly lower on the affected side than on the contralateral side (P < 0.05). The mean rOEF and rCMRO2 values on the affected side were significantly higher for Group 1 patients, compared with Group 2 patients, before surgery (P < 0.05 and P < 0.05, respectively). The preoperative regional cerebral blood flow and regional cerebral blood volume values on the affected side were similar for the two groups. Postoperative changes in mean regional cerebral blood flow and mean rOEF on the affected side were statistically significant for both groups. The mean rCMRO2 on the affected side for Group 2 was significantly lower than that for Group 1, even after bypass surgery (P < 0.05).

CONCLUSION

Bypass surgery may improve neurological function for patients with significantly elevated rOEF values and rCMRO2 values near the normal level. These hemodynamic parameters may be useful for the identification of candidates for extracranial-intracranial bypass surgery.

Occurrence of transsulfuration in synthesis of L-homocysteine in an extremely thermophilic bacterium, Thermus thermophilus HB8

A cell extract of an extremely thermophilic bacterium, Thermus thermophilus HB8, cultured in a synthetic medium catalyzed cystathionine gamma-synthesis with O-acetyl-L-homoserine and L-cysteine as substrates but not beta-synthesis with DL-homocysteine and L-serine (or O-acetyl-L-serine). The amounts of synthesized enzymes metabolizing sulfur-containing amino acids were estimated by determining their catalytic activities in cell extracts. The syntheses of cystathionine beta-lyase (EC 4.4.1.8) and O-acetyl-L-serine sulfhydrylase (EC 4.2.99.8) were markedly repressed by L-methionine supplemented to the medium. L-Cysteine and glutathione, both at 0.5 mM, added to the medium as the sole sulfur source repressed the synthesis of O-acetylserine sulfhydrylase by 55 and 73%, respectively, confirming that this enzyme functions as a cysteine synthase. Methionine employed at 1 to 5 mM in the same way derepressed the synthesis of O-acetylserine sulfhydrylase 2.1- to 2.5-fold. A method for assaying a low concentration of sulfide (0.01 to 0.05 mM) liberated from homocysteine by determining cysteine synthesized with it in the presence of excess amounts of O-acetylserine and a purified preparation of the sulfhydrylase was established. The extract of cells catalyzed the homocysteine gamma-lyase reaction, with a specific activity of 5 to 7 nmol/min/mg of protein, but not the methionine gamma-lyase reaction. These results suggested that cysteine was also synthesized under the conditions employed by the catalysis of O-acetylserine sulfhydrylase using sulfur of homocysteine derived from methionine. Methionine inhibited O-acetylserine sulfhydrylase markedly. The effects of sulfur sources added to the medium on the synthesis of O-acetylhomoserine sulfhydrylase and the inhibition of the enzyme activity by methionine were mostly understood by assuming that the organism has two proteins having O-acetylhomoserine sulfhydrylase activity, one of which is cystathionine gamma-synthase. Although it has been reported that homocysteine is directly synthesized in T. thermophilus HB27 by the catalysis of O-acetylhomoserine sulfhydrylase on the basis of genetic studies (T. Kosuge, D. Gao, and T. Hoshino, J. Biosci. Bioeng. 90:271-279, 2000), the results obtained in this study for the behaviors of related enzymes indicate that sulfur is first incorporated into cysteine and then transferred to homocysteine via cystathionine in T. thermophilus HB8.

Different binding sites for the neuropeptide Y Y1 antagonists 1229U91 and J-104870 on human Y1 receptors

The peptidic Y1 antagonist 1229U91 and the non-peptidic antagonist J-104870 have high binding affinities for the human Y1 receptor. These Y1 antagonists show anorexigenic effects on NPY-induced feeding in rats, although they have completely different structures and molecular sizes. To identify the binding sites of these ligands, we substituted amino acid residues of the human Y1 receptor with alanine and examined the abilities of the mutant receptors to bind the radio-labeled ligands. Alanine substitutions, F98A, D104A, T125A, D200A, D205A, L215A, Q219A, L279A, F282A, F286A, W288A and H298A, in the human Y1 receptor lost their affinity for the peptide agonist PYY, but not for 1229U91 and J-104870, while L303A and F173A lost affinity for 1229U91 and J-104870, respectively. N283A retained its affinity for 1229U91, but not for PYY and J-104870. Y47A and N299A retained their affinity for J-104870, but not for PYY and 1229U91. W163A and D287A showed no affinity for any of the three ligands. Taken together, these data indicate that the binding sites of 1229U91 are widely located in the shallow region of the transmembrane (TM) domain of the receptor, especially TM1, TM6 and TM7. In contrast, J-104870 recognized the pocket formed by TM4, TM5 and TM6, based on the molecular modeling of the Y1 receptor and J-104870 complex. In conclusion, 1229U91 and J-104870 have high affinities for Y1 receptors using basically different binding sites. D287 of the common binding site in the TM6 domain could be crucial for the binding of Y1 antagonists.

Role of ceramide during cisplatin-induced apoptosis in C6 glioma cells

Cisplatin is commonly used for the treatment of malignant brain tumors. However, the mechanisms of cell death by cisplatin are not fully understood. Therefore, the present study was designed to elucidate the apoptotic signaling pathway(s) activated by cisplatin in a C6 rat glioma cell line. C6 cells were treated with various concentrations of cisplatin (0.2-10 microg/ml) for 24-72 h. At 10 microg/ml cisplatin, over 90% of the cells became dead at 72 h. Apoptotic death was confirmed by condensation and fragmentation of nuclei, and DNA laddering. Even in cells treated with 1.5 microg/ml cisplatin, typical apoptotic cells were observed at 72 h. The intracellular level of ceramide, measured Escherichia coli diacylglycerol kinase markedly increased during 24-72 h after the addition of 10 microg/ml cisplatin. The activity of caspase-3(-like) proteases increased and reached a peak at 48 h. Inhibitors of caspases reduced the number of apoptotic cells. Pretreatment of C6 cells with glutathione or N-acetyl-cysteine, which are known to block the activation of neutral magnesium-dependent sphingomyelinase, inhibited ceramide formation, leading to suppression of both activation of caspase-3(-like) proteases and apoptosis by cisplatin. In contrast, pretreatment of the cells with N-oleoylethanolamine (OE), a ceramidase inhibitor, potentiated apoptosis induced by cisplatin. Furthermore, OE enhanced sensitivity of the cisplatin-resistant cells to cisplatin. These results suggest that ceramide is closely implicated in apoptosis of glioma cells by cisplatin through activation of caspase-3(-like) proteases.

Racemic and asymmetric Diels-Alder reactions of 1-(2-oxazolidinon-3-yl)-3-siloxy-1,3-butadienes

Achiral and chiral 1-(2-oxazolidinon-3-yl)-3-siloxy-1,3-butadienes were prepared from readily available starting materials. Although more stable than the parent 1-amino-3-siloxy dienes, the 1-(2-oxazolidinon-3-yl)-3-siloxy-1,3-butadienes are still very reactive in Diels-Alder reactions, somewhat more than 1,3-dialkoxy-1, 3-butadienes (e.g., Danishefsky's diene). The cycloadditions of the achiral and chiral dienes with several different dienophiles were examined. The reactions proceeded in good yield, with modest to high endo selectivity. The chiral dienes exhibited excellent facial selectivity in cycloadditions with alpha-substituted acroleins, maleic anhydride and N-phenylmaleimide. Upon reduction and hydrolysis of the cycloadducts, substituted cyclohexenones were obtained with ee's ranging from 22% to >98%.

A mutant Escherichia coli tyrosyl-tRNA synthetase utilizes the unnatural amino acid azatyrosine more efficiently than tyrosine

Alloproteins, proteins that contain unnatural amino acids, have immense potential in biotechnology and medicine. Although various approaches for alloprotein production exist, there is no satisfactory method to produce large quantities of alloproteins containing unnatural amino acids in specific positions. The tyrosine analogue azatyrosine, l-beta-(5-hydroxy-2-pyridyl)-alanine, can convert the ras-transformed phenotype to normal phenotype, presumably by its incorporation into cellular proteins. This provided the stimulus for isolation of a mutant tyrosyl-tRNA synthetase (TyrRS) capable of charging azatyrosine to tRNA. A plasmid library of randomly mutated Escherichia coli tyrS (encoding TyrRS) was made by polymerase chain reaction techniques. The desired TyrRS mutants were selected by screening for in vivo azatyrosine incorporation of E. coli cells transformed with the mutant tyrS plasmids. One of the clones thus isolated, R-6-A-7, showed a 17-fold higher in vivo activity for azatyrosine incorporation than wild-type TyrRS. The mutant tyrS gene contained a single point mutation resulting in replacement of phenylalanine by serine at position 130 in the protein. Structural modeling revealed that position 130 is located close to Asp(182), which directly interacts with tyrosyladenylate. Kinetic analysis of aminoacyl-tRNA formation by the wild-type and mutated F130S TyrRS enzymes showed that the specificity for azatyrosine, measured by the ratios of k(cat)/K(m) for tyrosine and the analogue, increased from 17 to 36 as a result of the F130S mutation. Thus, the high discrimination against azatyrosine is significantly reduced in the mutant enzyme. These results suggest that utilization of F130S TyrRS for in vivo protein biosynthesis may lead to efficient production of azatyrosine-containing alloproteins.