Intraoperative rupture in the surgical treatment of patients with intracranial aneurysms.

Intraoperative rerupture (IOR) during clipping of cerebral aneurysms is a difficult complication of microneurosurgery. The aim of this study was to evaluate the incidence of IOR and analyze the strategies for controlling profound hemorrhage. A total of 165 patients with unruptured intracranial aneurysms and 46 patients with subarachnoid hemorrhage (SAH) treated surgically between April 2010 and March 2011, were reviewed. The data were collected with regard to age, sex, presence of symptoms, confounding factors and strategy for controlling intraoperative hemorrhage was analyzed in terms of location of aneurysms, timing of rupture and severity of IOR. 211 patients with 228 aneurysms were treated in this series. There were a total of six IORs which represented an IOR rate of 2.84% per patient and 2.63% per aneurysm. The highest ruptures rates occurred in patients with internal carotid artery aneurysms (25%). Surgeries in the group with ruptured aneurysms had a much higher rate of IOR compared with surgeries in the group with unruptured aneurysms. Of the six IOR aneurysms, one occurred during predissection, four during microdissection and one during clipping. One was major IOR, three were moderate and two were minor. Intraoperative rupture of an intracranial aneurysm can be potentially devastating in vascular neurosurgery. Aneurysm location, presence of SAH and surgical experience of the operating surgeon seem to be important factors affecting the incidence of IOR.

Development of an oncolytic HSV vector fully retargeted specifically to cellular EpCAM for virus entry and cell-to-cell spread.

Oncolytic herpes simplex virus (HSV) vectors have attracted increasing attention as novel anti-cancer agents. HSV entry is triggered by the binding of glycoprotein D (gD) to its receptors, such as herpesvirus entry mediator or nectin-1. We have recently reported the construction of a fully retargeted HSV platform that incorporates single-chain antibodies (scFv) into gD to mediate entry exclusively via tumor-associated antigens. In this study, we created an scFv directed against epithelial cell adhesion molecule (EpCAM), a recognized carcinoma-associated antigen, and inserted it into the retargeted HSV platform that is ablated for gD recognition of its canonical receptors and contains the entry-enhancing mutations in gB we previously identified. We observed that both initial entry and subsequent cell-to-cell spread of the retargeted virus were stringently dependent on cellular EpCAM expression. Interestingly, the retargeted virus developed larger plaques on some of the human tumor lines tested than the control virus bearing wild-type gD. Intratumoral injection of the retargeted virus revealed antitumor activity in a mouse xenograft model. These observations illustrate the versatility of our retargeted HSV platform as it allows expansion of the oncolytic virus toolbox for the treatment of diverse cancers.

Use of a Latent Topic Model for Characteristic Extraction from Health Checkup Questionnaire Data.

OBJECTIVES: When patients complete questionnaires during health checkups, many of their responses are subjective, making topic extraction difficult. Therefore, the purpose of this study was to develop a model capable of extracting appropriate topics from subjective data in questionnaires conducted during health checkups. METHODS: We employed a latent topic model to group the lifestyle habits of the study participants and represented their responses to items on health checkup questionnaires as a probability model. For the probability model, we used latent Dirichlet allocation to extract 30 topics from the questionnaires. According to the model parameters, a total of 4381 study participants were then divided into groups based on these topics. Results from laboratory tests, including blood glucose level, triglycerides, and estimated glomerular filtration rate, were compared between each group, and these results were then compared with those obtained by hierarchical clustering. RESULTS: If a significant (p < 0.05) difference was observed in any of the laboratory measurements between groups, it was considered to indicate a questionnaire response pattern corresponding to the value of the test result. A comparison between the latent topic model and hierarchical clustering grouping revealed that, in the latent topic model method, a small group of participants who reported having subjective signs of urinary disorder were allocated to a single group. CONCLUSIONS: The latent topic model is useful for extracting characteristics from a small number of groups from questionnaires with a large number of items. These results show that, in addition to chief complaints and history of past illness, questionnaire data obtained during medical checkups can serve as useful judgment criteria for assessing the conditions of patients.

Surgical treatment of patients with unruptured intracranial aneurysms.

We present our experience with elective microsurgical clipping of unruptured intracranial aneurysms (UIA) and analyze this management. A total of 150 patients with UIA were reviewed and data were collected with regard to age, sex, presence of symptoms, location and size of the aneurysms, surgical complications and postoperative 1 year outcomes. Aneurysm size was assessed either by three-dimensional CT angiography or digital subtraction angiogram. Glasgow Outcome Scale was used to assess clinical outcomes. One hundred and fifty patients with 165 aneurysms were treated in this series. The mean size of the UIA was 5.6mm. Eighty aneurysms (48.5%) were less than 5mm in size, and 73 (44.2%) were from 5 to 10mm. Ten (6.1%) of the aneurysms were large and two (1.2%) were giant. One hundred and forty-three were asymptomatic and seven were symptomatic before surgery. The outcome was good in 147 patients (98%), and only three patients (2%) had a treatment-related unfavorable outcome. Five patients experienced transient neurological deficits and one patient experienced permanent neurological deficits. Overall 98.7% of the treated aneurysms were satisfactorily obliterated. Wound complications were seen only in three patients. In conclusion, UIA pose a significant challenge for neurosurgeons, where a delicate balance between benefits and possible risks must be weighed. If the requisite expertise is available, they can be treated surgically with low morbidity and a good outcome at specialized neurovascular centers.

Prediction model for glucose metabolism based on lipid metabolism.

OBJECTIVES: We developed a robust, long-term clinical prediction model to predict conditions leading to early diabetes using laboratory values other than blood glucose and insulin levels. Our model protects against missing data and noise that occur during long-term analysis. METHODS: RESULTS of a 75-g oral glucose tolerance test (OGTT) were divided into three groups: diabetes, impaired glucose tolerance (IGT), and normal (n = 114, 235, and 325, respectively). For glucose metabolic and lipid metabolic parameters, near 30-day mean values and 10-year integrated values were compared. The relation between high-density lipoprotein cholesterol (HDL-C) and variations in HbA1c was analyzed in 158 patients. We also constructed a state space model consisting of an observation model (HDL-C and HbA1c) and an internal model (disorders of lipid metabolism and glucose metabolism) and applied this model to 116 cases. RESULTS: The root mean square error between the observed HbA1c and predicted HbA1c was 0.25. CONCLUSIONS: In the observation model, HDL-C levels were useful for prediction of increases in HbA1c. Even with numerous missing values over time, as occurs in clinical practice, clinically valid predictions can be made using this state space model.

Intraoperative near-infrared indocyanine green-videoangiography (ICG-VA) and graphic analysis of fluorescence intensity in cerebral aneurysm surgery.

We present our preliminary experience with intraoperative near-infrared indocyanine green-videoangiography (ICG-VA) and analysis of blood flow dynamics using fluorescence intensity assessment in cerebral aneurysm clipping surgery. Thirty-nine patients with 43 intracranial aneurysms underwent microsurgical clipping. Intraoperative ICG-VA was performed before and after clip application. An infrared fluorescence module integrated into a surgical microscope was used to visualize fluorescence in the surgical field and we recorded the emitted fluorescent light. An integrated analytical visualization tool simultaneously analyzed the video sequence and converted it into an intensity diagram, which allowed an objective evaluation of the results rather than the subjective assessment of fluorescence using ICG-VA. Overall, ICG-VA was performed 137 times. Incomplete clipping was detected in four patients, which allowed suitable adjustment to completely obliterate the aneurysm. In 12 patients, perforators arising close to, or from, the aneurysmal neck were identified in the surgical field. In three patients, the ICG-VA intensity diagram provided valuable information leading to modification of the primary surgical maneuver. ICG-VA provides high resolution images allowing real-time assessment of the blood flow in the parent artery and arterial branches, including the perforators. The intensity diagram is useful for providing a more objective record of the hemodynamics than the traditional ICG-VA, which relies more on subjective assessment and may allow interobserver variability. We conclude that ICG-VA, combined with the intensity diagram, can reduce the morbidity and complications associated with aneurysm clipping and improve patient outcomes.

The application of intraoperative near-infrared indocyanine green videoangiography and analysis of fluorescence intensity in cerebrovascular surgery.

OBJECTIVE: To evaluate the usefulness and limitations of the intraoperative near-infrared (NIR) indocyanine green videoangiography (ICG-VA) and analysis of fluorescence intensity in cerebrovascular surgery. METHODS: Forty-eight patients received ICG-VA during various surgical procedures from May 2010 to August 2010. Included among them were 45 cases of cerebral aneurysms and 3 cases of cerebral arteriovenous malformations (AVMs). The infrared fluorescence module integrated into the surgical microscope was used to visualize fluorescent areas in the surgical field. An integrated analytical visualization tool constantly analyzed the fluorescence video sequence and generated it in the form of an intensity diagram for objective interpretation. RESULTS: Overall, the procedure of ICG VA was done 158 times in 48 patients. There was no adverse effect of ICG dye. In cerebral aneurysm cases, the images obtained were of high resolution. In 4 cases, incomplete clipping was detected by ICG-VA and allowed suitable adjustment to completely obliterate the aneurysm. In 3 aneurysm cases, the intensity diagram of ICG VA provided valuable information. ICG-VA identified the feeding arteries, the draining veins, and nidus in all 3 AVM cases, which was confirmed by an immediate analysis of fluorescence intensity. CONCLUSIONS: ICG-VA provides high resolution images allowing real-time assessment of the blood flow in surgical field. The intensity analysis function, in addition, is a useful adjunct to improve the accuracy of the clipping and decrease the complication rates in cerebral aneurysm cases. In cerebral AVM cases, with the help of color map and intensity diagram function, the superficial feeders, drainers, and nidus can be identified easily.

Retrograde suction decompression assisted clipping of large and giant cerebral aneurysms: our experience.

OBJECTIVE: The aim of this study was to present our experience with retrograde suction decompression in clipping of large and giant cerebral aneurysms and analyze its advantages and pitfalls. METHODS: A retrospective analysis of 27 patients with large and giant intracranial aneurysms treated by suction decompression assisted clipping between November 2005 and February 2010 was done. The surgical technique and the outcome of patients were reviewed. RESULTS: All aneurysms were successfully clipped, and postoperative 3-D CTA or DSA revealed no major branch occlusion or residual aneurysm. There was no surgical mortality in both giant and large aneurysm groups. CONCLUSION: Retrograde suction decompression is a successful adjunct to clipping of large and giant cerebral aneurysms.

Preliminary evaluation of the role of surgical microscope-integrated intraoperative FLOW 800 colored indocyanine fluorescence angiography in arteriovenous malformation surgery.

OBJECTIVE: To discuss the role of FLOW 800 innovative software for analytical color visualization and objective evaluation of fluorescence videos obtained by microscope-integrated intraoperative indocyanine green (ICG) fluorescence angiography in arteriovenous malformations (AVM) surgery. MATERIALS AND METHODS: Microscope-integrated intraoperative FLOW 800 was used and evaluated in three consecutive AVM surgeries over a period of two months. The role of FLOW 800 to distinguish feeding arteries from arterialized veins and other arteries was evaluated. Its advantages and limitations over conventional intraoperative ICG angiography were evaluated. RESULTS: This software was found to be useful in identifying arterial feeders, arterialized veins and other arteries in all the three patients and it gives additional information on the status of AVM before and after clipping suspected feeders which is sometimes difficult to interpret on conventional ICG angiography. CONCLUSION: Flow 800 is a reliable and useful addition to microscope-integrated color ICG video angiography. Although its role is limited in deep-seated AVMs, if properly dissected and exposed it can give useful information which can be easily interpretable and reproducible.

A classification of unruptured middle cerebral artery bifurcation aneurysms that can help in choice of clipping technique.

Middle cerebral artery (MCA) aneurysms comprise 20-25% of all intracranial aneurysms. The majority of middle cerebral artery aneurysms are treated by microsurgical clipping. Most of the classifications of aneurysms at present are based on size, location or pathology which are effective for the description but are less useful in preoperative planning and also in deciding on the technique or type of clip application. The aim of our study was to examine the morphological features of unruptured MCA bifurcation aneurysms which influence the techniques of clipping of these aneurysms and to attempt to subclassify unruptured middle cerebral artery aneurysms based on their preoperative 3D CTA and intraoperative characteristics so as to help in the intraoperative choice of technique and clip application, respectively. Preoperative 3D CT angiography and intraoperative images along with the record of technique and type of clips used for 141 unruptured MCA aneurysms operated at our center were studied retrospectively. Unruptured MCA bifurcation aneurysms could be subclassified into 5 types based on the similarities in their morphological features which influenced the techniques of clipping as recorded from their preoperative 3D CTA and intraoperative view. These types and the distinctive feature of each type are described. The various techniques of clipping are discussed based on these subgroups. The groups outlined make possible the establishment of a common technical approach to clipping within the groups. This classification, based on preoperative 3D CTA and intraoperative morphological features of the aneurysm and parent vessels, helps in the intraoperative choice of technique and type of clip application to tackle these lesions.

CYP3A4 and CYP2D6 inhibitory activities of Indonesian medicinal plants.

Thirty samples of Indonesian medicinal plants were analyzed for their capacity to inhibit in vitro metabolism by human cytochrome P450 3A4 (CYP3A4) and CYP2D6 with a radiometric assay. The MeOH-soluble fractions of 25 samples, prepared from water extracts, demonstrated inhibitory activity more than 50% on the metabolism mediated by CYP3A4, and 21 samples on the metabolism mediated by CYP2D6. Among the MeOH-soluble fractions, Piper nigrum leaf showed the highest inhibitory activity against CYP3A4 (91.7%), and Punica granatum against CYP2D6 (98.1%). The water extracts of which MeOH-soluble fraction showed inhibitory activity more than 70% were fractionated with EtOAc. From the EtOAc-soluble fractions, Curcuma heyneana (67.0%), Pi. cubeba (75.0%), Pi. nigrum fruit (84.0%), Pi. nigrum leaf (85.8%), and Zingiber aromaticum (75.3%) demonstrated inhibitory activity more than 50% on the metabolism mediated by CYP3A4, but only Pi. nigrum fruit (72.8%) and Pi. nigrum leaf (69.1%) showed strong inhibitory activity against CYP2D6. For samples that showed more than 70% inhibition, their IC(50) values were determined. The most potent inhibitory activity against CYP3A4 (IC(50) value of 25 microg/ml) was found for the extract of Pi. nigrum leaf, while that of Catharanthus roseus showed the most potent inhibitory effect against CYP2D6 (IC(50) value of 11 microg/ml). These results should indicate once more the possibility of potential medicinal plant-drug interactions.

Combined anterior and posterior instrumentation in severe fracture-dislocation of the lower cervical spine with help of navigation: a case report.

The authors report a case of severe fracture-dislocation of C6-C7 with dural and spinal cord damage causing quadriplegia. The patient was treated surgically with circumferential stabilisation. Intense spinal instrumentation with pedicle screw fixation in addition to anterior decompression and plate fixation was essential for restoring the original vertebral column. This technique of internal fixation provided a more rigid anchor, however the risk to the neurovascular structures could not be completely eliminated. Therefore, the combined anterior and posterior stabilisation assisted with a navigation system was a safer and reasonable surgical treatment for this patient with severe cervical injuries.

(S)-preferential detoxification of 4-hydroxy-2(E)-nonenal enantiomers by hepatic glutathione S-transferase isoforms in guinea-pigs and rats.

In guinea-pig liver cytosol, racemic 4-hydroxy-2(E)-nonenal (HNE), a reactive and highly toxic product released from biomembranes by lipid peroxidation, was detoxified (S)-preferentially by GSH conjugation mediated by glutathione S-transferases (GSTs) and (R)-preferentially by NAD(+)-dependent oxidation mediated by aldehyde dehydrogenase (ALDH). The GST-mediated detoxification of the HNE enantiomers proceeded at much higher rates than that mediated by ALDH in guinea-pig liver cytosol. All the major guinea-pig GSTs, A1-1, M1-1, M1-2 and M1-3*, isolated from guinea-pig liver cytosol also catalysed the (S)-preferential conjugation of the HNE enantiomers. The liver and other major tissues of guinea-pigs had no immunologically detectable level of a putative GSTA4-4 orthologue, which exists as a minor GST protein in rat, mouse and human livers and exhibits extremely high catalytic activity towards HNE. All the hepatic rat GSTs, A1-1(2), A1-3, A4-4, M1-1, M1-2 and M2-2, also catalysed the (S)-preferential conjugation of HNE enantiomers.

Giant basilar bifurcation aneurysm presenting as a third ventricular mass with unilateral obstructive hydrocephalus: case report.

We report a rare case of a non-ruptured basilar bifurcation aneurysm presenting as a third ventricular mass producing unilateral obstructive hydrocephalus. This is the first reported case of its kind. A 70 year old woman presented with a giant basilar bifurcation aneurysm in which the aneurysm protruded into the third ventricle as a mass causing unilateral left hydrocephalus. The patient gradually became disoriented and developed a right hemiparesis and global aphasia. The right vertebral artery was occluded by placing coils intravascularly followed by an endoscopic septostomy. The patient's neurological state dramatically improved immediately. One month after the septostomy, however, the aneurysm ruptured and the patient eventually died. Treatment of the hydrocephalus only was selected instead of direct surgery or an intravascular procedure on the aneurysm, which eventually ruptured. The mechanisms for the unilateral hydrocephalus and the rupture of the aneurysm are described. The treatment strategy for these lesions is also discussed.

Surgical resection of cerebral arteriovenous malformation combined with pre-operative embolisation.

To assess the importance of pre-operative embolisation, 27 cases of cerebral artriovenous malformation (AVM) treated in this institute between July 1994 and October 1998 were analysed. The patients' ages ranged from 3 to 70 years (average 36.9) with a follow-up period of 1-41 months (average 19.2). The patient presented with haemorrhage in 21 cases and seizure in five. In 21 of 27 cases, surgical resection of a nidus was performed, gamma knife therapy was applied in three and conservative therapy was chosen in three. Of 21 cases treated surgically, total removal was achieved in 19 cases and a residual nidus was seen in one (a large basal ganglia AVM). In the remaining case, postoperative angiography was not available. Pre-operative embolisation followed by surgical resection of the nidus was performed in seven cases in which there was a large AVM. A volume index was calculated to indicate the size of the nidus using X x Y x Z, where X is the maximum diameter (cm) of the nidus on the lateral angiogram, Y is the diameter (cm) perpendicular to X and Z is the maximum diameter (cm) on the anteroposter or angiogram. The index averaged 45.9 for the cases in which pre-operative embolisation was performed, while it was 5.6 in the cases without embolisation. Pre-operative embolisation was performed to reduce the nidus flow as much as possible, to prevent overload to the surrounding structures. At surgery, the nidus was resected from the surrounding tissue and care was taken not to enter the nidus. Postoperatively, the systolic blood pressure was maintained at 90-100 mmHg for several days in the intensive care unit. The results were excellent in 15 cases, good in three (hemiparesis due to the initial haemorrhage remained in all three), fair in one (a patient with a severe subarachnoid haemorrhage). Two patients died (acute pulmonary oedema and severe meningitis). Minor postoperative bleeding or oozing was seen in three cases. In conclusion, reducing the shunt flow through a nidus in a step-wise fashion with pre-operative embolisation of a large AVM seems to be quite helpful in preventing postoperative haemodynamic overload to the surrounding brain. It is also important not to enter the nidus when it is removed at surgery. This helps to prevent intraoperative and/or postoperative bleeding, and led to successful total removal of the nidus with a good postoperative course.

Anatomical variants in the floor of the third ventricle; implications for endoscopic third ventriculostomy.

Longstanding hydrocephalus and raised intracranial pressure can lead to unusual anatomical variants in the floor of the third ventricle, which may be important when performing endoscopic third ventriculostomy. Two middle aged patients with symptomatic longstanding hydrocephalus had scans that showed ventricular hydrocephalus, an empty sella, and a dilated infundibular recess which herniated into the sella turcica. Endoscopic third ventriculostomy confirmed that instead of the tuber cinerum and infundibular recess, the anterior inferior floor of the third ventricle was hanging down ventral to the pons into the sellar floor. Third ventriculostomy to the prepontine cistern was made on the dorsal wall of the dilated infundibular recess to the area surrounded by the dorsum sellae, the basilar artery trunk, and the left superior cerebellar artery, with good symptomatic control. Association of the empty sella and persistence of the infundibular recess must be carefully evaluated by MRI before attempting endoscopic third ventriculostomy. Herniation of the anterior inferior floor of the third ventricle into the empty sella can lead to loss of anatomical landmarks that require special attention during third ventriculostomy.

Xlim-1 and LIM domain binding protein 1 cooperate with various transcription factors in the regulation of the goosecoid promoter.

The homeobox genes Xlim-1 and goosecoid (gsc) are coexpressed in the Spemann organizer and later in the prechordal plate that acts as head organizer. Based on our previous finding that gsc is a possible target gene for Xlim-1, we studied the regulation of gsc transcription by Xlim-1 and other regulatory genes expressed at gastrula stages, by using gsc-luciferase reporter constructs injected into animal explants. A 492-bp upstream region of the gsc promoter responds to Xlim-1/3m, an activated form of Xlim-1, and to a combination of wild-type Xlim-1 and Ldb1, a LIM domain binding protein, supporting the view that gsc is a direct target of Xlim-1. Footprint and electrophoretic mobility shift assays with GST-homeodomain fusion proteins and embryo extracts overexpressing FLAG-tagged full-length proteins showed that the Xlim-1 homeodomain or Xlim-1/Ldb1 complex recognize several TAATXY core elements in the 492-bp upstream region, where XY is TA, TG, CA, or GG. Some of these elements are also bound by the ventral factor PV.1, whereas a TAATCT element did not bind Xlim-1 or PV.1 but did bind the anterior factors Otx2 and Gsc. These proteins modulate the activity of the gsc reporter in animal caps: Otx2 activates the reporter synergistically with Xlim-1 plus Ldb1, whereas Gsc and PV.1 strongly repress reporter activity. We show further, using animal cap assays, that the endogenous gsc gene was synergistically activated by Xlim-1, Ldb1, and Otx2 and that the endogenous otx2 gene was activated by Xlim-1/3m, and this activation was suppressed by the posterior factor Xbra. Based on these data, we propose a model for gene interactions in the specification of dorsoventral and anteroposterior differences in the mesoderm during gastrulation.

Non-ruptured large dorsal internal carotid artery aneurysm presenting with temporal quadrantanopsia.

A 63-year-old woman presenting with temporal lower quadrantanopsia of the right eye was found to have a large dorsal internal carotid artery aneurysm. Large dorsal aneurysms of the internal carotid artery are rare. Lateral compression of the optic nerve by the aneurysm might damage the optic nerve at the medial side of the right optic foramen. Direct clipping surgery was performed uneventfully. Since the dome of the aneurysm was buried in the frontal lobe and also attached to the anterior skull base, a careful approach to the aneurysm with removal of the anterior clinoid process and drilling into the planum sphenoidale around the aneurysm dome was needed. The surgical strategy is discussed.

4-Hydroxy-2(E)-nonenal enantiomers: (S)-selective inactivation of glyceraldehyde-3-phosphate dehydrogenase and detoxification by rat glutathione S-transferase A4-4.

The glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase was irreversibly and (S)-selectively inactivated by the enantiomers of racemic 4-hydroxy-2(E)-nonenal (HNE), a reactive product released from biomembranes by lipid peroxidation in cells. Rates of the enzyme inactivations were 1.7, 3.0, and 6.0 M(-1).s(-1) for (R)-, racemic and (S)-HNEs respectively. In rat liver cytosol the HNE was detoxified 2.5-fold more (S)-selectively by GSH conjugation and 2. 4-fold more (R)-selectively by NADH-dependent reduction mediated by alcohol dehydrogenase (ADH) than the opposite enantiomers. However, in the cytosol the GSH conjugation of (R)-HNE proceeded at a much higher rate than did its ADH-mediated reduction. The minor glutathione S-transferase (GST) isoform, A4-4, in the rat (r) liver had a major role in the cytosolic (S)-selective GSH conjugation. The catalytic efficiency, k(cat)/K(m), of purified rGSTA4-4 was 4-fold higher for (S)-HNE than for (R)-HNE; the K(m) was 3-fold higher for (R)-HNE than for (S)-HNE. (S)-HNE was preferentially detoxified to (R)-HNE by rGSTA4-4 when racemic HNE was used as a substrate.

Mechanism-based inactivation of human dihydropyrimidine dehydrogenase by (E)-5-(2-bromovinyl)uracil in the presence of NADPH.

Purified recombinant human dihydropyrimidine dehydrogenase (hDPD) was incubated with (14)C-labeled (E)-5-(2-bromovinyl)uracil ([(14)C]BVU) in the presence of NADPH to investigate a possible mechanism in the 18 patient deaths caused by interactions of 5-fluorouracil prodrugs with the new oral antiviral drug, sorivudine. BVU is formed from sorivudine by gut flora and absorbed through intestinal membrane. hDPD, a rate-limiting enzyme for the catabolism of 5-fluorouracil and endogenous pyrimidines in the human, was NADPH dependently radiolabeled and inactivated by [(14)C]BVU. Two radioactive tryptic fragments, I and II, isolated from radiolabeled hDPD were found by complete amino acid sequencing to originate from a common regional amino acid sequence located at positions 656 (Lys) to 678 (Arg) for I and positions 657 (Ser) to 678 (Arg) for II. However, only Cys(671), which should be present in the peptides, was not identified by amino acid sequencing. Mass spectrometric analysis of the tryptic fragments indicated that the sulfhydryl group of Cys(671) in the hDPD was modified with 5, 6-dihydro-5-(2-bromoethylydenyl)uracil (BEDU), a putative allyl bromide type of reactive molecule, to form a sulfide bond with loss of hydrogen bromide. The Cys(671) sulfide bearing the debrominated BEDU had a 5,6-dihydrouracil ring highly strained by the exocyclic double bond at the 5-position, so that it underwent facile hydrolytic ring fission with alkali and heated acid treatments. A new proposal is also made for the amino acid sequence of the pyrimidine-binding domain, including Cys(671), of DPD in the human and other species.