Inflammatory reactions after vascular prosthesis implantation: a comparison of gelatin-sealed and unsealed Dacron prostheses

Despite widespread use of the gelatin-sealed knitted Dacron prosthesis (GDP) in clinical practice owing to its zero porosity, the biological impacts of this graft are still controversial. We conducted a randomized controlled study on 50 patients undergoing abdominal aortic aneurysm repair to evaluate the inflammatory reaction to GDP (n = 25) and unsealed knitted Dacron prostheses (UDP, n = 25). There were no significant differences in the mean age, size of the aneurysm, operative time, blood loss, or transfusion requirements between the GDP and UDP groups. During the first 7 postoperative days (PODs), slight fever and leukocytosis were noticed in both groups. Significant differences in maximum body temperature, leukocyte count, and plasma C-reactive protein concentration were observed between the GDP and UDP groups on POD 14:37.2 +/- 0.5 degrees C vs 36.9 +/- 0.3 degrees C (P = 0.019), 8,151 +/- 1,788/microliters vs 6,914 +/- 1,501/microliters (P = 0.015), and 32.6 +/- 27.5 mg/l vs 19.0 +/- 15.8 mg/l (P = 0.048), respectively. By POD 21, however, there were no detectable differences in these variables. Thus, we concluded that GDP caused an inflammatory reaction in the 2nd week after implantation, but ultimately there were no significant differences from UDP by the 3rd week.

Inhibition of glutamine synthetase reduces ammonia-induced astrocyte swelling in rat

Astrocyte hypertrophy and swelling occur in a variety of pathophysiological conditions, including diseases associated with hyperammonemia. Ammonia is rapidly incorporated into glutamine by glutamine synthetase localized in astrocytes. We tested the hypotheses that (1) 6 h of hyperammonemia (500-600 microM) is adequate for producing astrocyte enlargement, and (2) astrocyte enlargement is attenuated by inhibition of glutamine synthetase with methionine sulfoximine. Pentobarbital-anesthetized rats received an intravenous infusion of either sodium or ammonium acetate after intraperitoneal pretreatment with vehicle, methionine sulfoximine (0.8 mmol/kg) or buthionine sulfoximine (4 mmol/kg), an analogue that does not inhibit glutamine synthetase. Hyperammonemia produced enlarged cortical astrocytes characterized by (1) decreased electron density of cytoplasmic matrix in perikaryon, processes and perivascular endfeet, (2) increased circumference of nuclear membrane, (3) increased numbers of mitochondria and rough and smooth endoplasmic reticulum in perikarya and large processes, and (4) less compact bundles of intermediate filaments. Pretreatment with methionine sulfoximine, but not buthionine sulfoximine, attenuated the decrease in cytoplasmic density and the increase in nuclear circumference; most perivascular endfeet remained as dense as occurred with sodium acetate infusion. However, increased numbers of organelles in expanded perikarya and large processes occurred after methionine sulfoximine treatment with and without ammonium acetate infusion. In separate groups of rats, hyperammonemia produced an increase in cortical tissue water content which was inhibited by methionine sulfoximine, but not buthionine sulfoximine. We conclude that clinically-relevant levels of hyperammonemia can cause astrocyte enlargement within 6 h in vivo characterized by both watery cytoplasm and increased organelles indicative of a cellular metabolic stress and altered astrocyte function. The watery cytoplasm component of astrocyte enlargement depends on glutamine synthesis rather than on ammonium ions per se, and is possibly caused by the osmotic effect accumulated glutamine.

Two thromboxane A2 receptor isoforms in human platelets. Opposite coupling to adenylyl cyclase with different sensitivity to Arg60 to Leu mutation

Thromboxane A2 (TXA2) receptor is a key molecule in hemostasis as its abnormality leads to bleeding disorders. Two isoforms of the human TXA2 receptor have been cloned; one from placenta and the other from endothelium, here referred to as TXR alpha and TXR beta, respectively. These isoforms differ only in their carboxyl-terminal tails. We report that both isoforms are present in human platelets. The two isoforms expressed in cultured cells show similar ligand binding characteristics and phospholipase C (PLC) activation but oppositely regulate adenylyl cyclase activity; TXR alpha activates adenylyl cyclase, while TXR beta inhibits it. The Arg60 to Leu mutant of TXR alpha, which has been shown to impair PLC activation (Hirata, T., A. Kakizuka, F. Ushikubi, I. Fuse, M. Okuma, and S. Narumiya. 1994. J. Clin. Invest. 94: 1662-1667), also impairs adenylyl cyclase stimulation, whereas that of TXR beta retains its activity to inhibit adenylyl cyclase. These findings suggest that the pathway linked to adenylyl cyclase inhibition might be involved in some of the TXA2-induced platelet responses such as shape change and phospholipase A2 activation which remain unaffected in the patients with this mutation.

Positional cues that are strictly localized in the telencephalon induce preferential growth of mitral cell axons

In mice, mitral cells are the major efferent neurons of the main olfactory bulb and elongate axons into a very narrow part of the telencephalon to form a fiber bundle referred to as the lateral olfactory tract (LOT). To clarify the mechanisms responsible for guidance of mitral cell axons along this particular pathway, we co-cultured mouse embryo main olfactory bulbs with the telencephalons, and analyzed the pathways taken by mitral cell axons. Ingrowth of mitral cell axons into the telencephalon was observed in those co-cultures in which the olfactory bulbs had been exactly combined to their normal pathway (the LOT position) of the telencephalon. The axons grew preferentially along the LOT position, and formed a LOT-like fiber bundle. When the olfactory bulbs were grafted at positions apart from their normal pathway, however, no mitral cell axons grew into the telencephalon. Neocortical fragments combined with the telencephalon projected fibers into the telencephalon in random directions. These results suggest that the LOT position of the telencephalon offers a guiding pathway for mitral cell axons and that guiding cues for mitral cell axons are extremely localized.

Surgical treatment for invasive thymoma, especially when the superior vena cava is invaded

BACKGROUND

We analyzed the operative outcome of extensive surgery for invasive thymoma, especially in those with thymomas invading the superior vena cava, the left innominate vein, or both.

METHODS

We treated 41 patients with invasive thymoma, including 34 stage III, 5 stage IVa, and 2 stage IVb thymomas. Thirty-eight patients received radiotherapy preoperatively or postoperatively. In 12 patients with invasion of the superior vena cava or innominate vein, we performed angioplasty, reconstruction, or both.

RESULTS

The overall 5-year survival rate was 77% and the 10-year survival rate was 59%. In the stage III group, there was a significant difference between those with complete and those with incomplete resection. Ten of 12 patients who had angioplasty with or without reconstruction of the superior vena cava or innominate vein survived without recurrence of the tumors.

CONCLUSION

Angioplasty and vascular reconstruction are recommended because successful treatment for invasive thymomas depends on complete resection of the tumors.

Cervical discitis associated with spinal epidural abscess caused by methicillin-resistant staphylococcus aureus

A 53-year-old male developed fever, nuchalgia, shoulder pain, and sore throat after a partial sigmoidectomy. He suffered sudden onset of quadriplegia about 5 days later. Magnetic resonance (MR) imaging indicated the characteristic appearance of C5-6 intervertebral disc herniation. However, anterior discectomy showed that he had cervical discitis associated with spinal epidural abscess. Continuous pus drainage from the abscess and vigorous antibiotic therapy were undertaken after surgery. He improved and could walk with assistance. MR imaging with gadolinium can be useful in diagnosing pyogenic spinal infection (epidural abscess, osteomyelitis, and discitis), but care should be taken in MR image interpretation since spinal epidural abscess associated with discitis may mimic disc herniation. Axial MR images are important to distinguish this rare disease from other cervical disorders.

Molecular characterization of a dominantly inherited bleeding disorder with impaired platelet responses to thromboxane A2

Thromboxane A2 (TXA2) is a major arachidonic acid metabolite of platelets and induces platelet functions by binding to specific receptors on the membrane. We have found patients with hemostatic defects due to impaired platelet responses to TXA2, and molecular characterization of the patients has been carried out. Platelets from these two unrelated patients showed impaired aggregation responses to TXA2 and its analogues despite the normal response to thrombin. Although the patients' platelets exhibited normal binding activities to TXA2 analogues, they showed decreased GTPase activity and second messenger formation when stimulated by STA2, a stable TXA2 agonist. To understand the molecular basis of this abnormality, we determined the cDNA sequence of the TXA2 receptor by reverse transcription-polymerase chain reaction (RT-PCR) from the patient's platelet RNA, and identified a single amino acid substitution (Arg60 for Leu) in the first cytoplasmic loop of the receptor. This mutation was found in both isoforms of the platelet TXA2 receptor which we have recently found: TXR alpha with the same structure as the placental TXA2 receptor and TXR beta with the same structure as the endothelial TXA2 receptor, and was detected exclusively in affected members of two unrelated families with the disorder. The mutant TXR alpha and TXR beta expressed in COS-m6 cells showed decreased agonist-induced phospholipase C activation despite their normal ligand binding affinities. These results suggest that the Arg60 for Leu mutation is responsible for the disorder and imply a critical role for the first cytoplasmic loop in the interaction of the TXA2 receptor with the G protein.

Electrophysiological effects of MS-551 in humans: a class III antiarrhythmic agent

To investigate the clinical effects of MS-551, a Class III antiarrhythmic agent, 11 patients underwent electrophysiological study. MS-551 was given intravenously as an initial dose of 0.2 or 0.3 mg/kg for 5 minutes followed by the continuous infusion at 0.2 or 0.3 mg/kg for 30 minutes, respectively, in all patients. The rate corrected QT interval increased significantly from 3 minutes after the beginning of MS-551 infusion. The sinus heart rate decreased significantly by 8% at 10 minutes after the drug administration (P < 0.025). Mean PR and QRS intervals, and blood pressure were not significantly affected by the drug. Mean PA, AH, and HV intervals during sinus rhythm were also not affected. The effective refractory periods (ERPs) of the atrium and ventricle were significantly prolonged by 13% from 202 +/- 24 ms to 231 +/- 26 ms (P < 0.0005), and by 7% from 238 +/- 11 ms to 257 +/- 13 ms (P < 0.002), respectively, by MS-551. The ERP of the atrioventricular node and sinoatrial nodal recovery time were not changed significantly by the drug. This is a report of the effects of MS-551 in humans. This agent could be useful for treatment of tachyarrhythmias by prolongation of ERPs of the atrium and ventricle without significant variations of blood pressure and intracardiac conduction times. It is noteworthy that MS-551 slightly but significantly decreased heart rate.

Thyrotropin-producing pituitary adenoma discovered as a pituitary incidentaloma

A 46-year-old woman with incidentally discovered thyrotropin (TSH)-producing pituitary adenoma showed endocrine data which was consistent with TSH-producing pituitary tumor. However, she showed only slight hyperthyroidism and the oversecretion and autonomous secretion of TSH from the tumor seemed to be limited from the results of several endocrine examinations. Immunohistochemical examination revealed that not only TSH-beta and TSH-alpha but also prolactin and growth hormone synthesizing cells were present in the tumor tissue. Pituitary-transcription activator 1 (Pit-1) immunoreactivity was also detected in the adenoma cell nuclei. It was conceivable that the presented TSH-producing adenoma clinically located close to the non-functioning adenoma and Pit-1 may have played an important role in the multidirectional differentiation or development of this tumor.

Evaluation of cases with combined bronchoplasty and pulmonary arterioplasty for the treatment of lung cancer

Bronchoplasty and pulmonary angioplasty(PA-plasty) have been performed in recent years for lung cancer invading the bronchus and pulmonary artery. We evaluated the results and complications in patients who underwent such operations. There were 23 cases of bronchoplasty performed between 1988 and October 1993. Of these 23 cases, 9 underwent PA-plasty with bronchoplasty. There were 8 males and 1 female (mean 65.6 year-old). There were 8 patients with primary lung cancer(sq 5, ad 1, la 1, and sm 1) and 1 with metastatic lung tumor of colon cancer. One patient was in p-stage II, 6 in p-stage III, and 1 in p-stage IV. Seven patients underwent right upper lobectomy, 1 did the right upper and middle bilobectomy, and 1 did a left upper lobectomy. Bronchoplasty was performed using sleeve resection in 8 patients, and a wedge resection in 1 patient. PA-plasty was performed using sleeve resection and end to end anastomosis in 2 cases, and using side wall resection and plasty in 7 patients after clamp. Of 9 patients in whom both broncho- and PA-plasty were performed, there was one with the resected bronchial stump of cancer-positive. Total resection of the cancer was possible in the remaining 8 patients. Postoperative complications included 2 pneumonia, 2 empyema, and 1 each, acute cardiac failure, pulmonary thrombus, and chylothorax. The patients with empyema required re-operation using omentopexy or thoracoplasty. Long-term results showed that 2 patients died because of recurrence. Another patient died of respiratory failure. The remaining 6 patients were alive without any evidence of cancer. Pneumonectomy was avoided and the combination of PA-plasty and bronchoplasty was performed instead. However, the incidence of postoperative complications was high, indicating that utmost care must be exercised in the postoperative management of these patients.

Acute spontaneous hemorrhagic degeneration of the thyroid nodule with subacute thyroiditis-like symptoms and laboratory findings

Seventeen consecutive patients (3 men and 14 women, aged 14-75 years) with a hemorrhagic degeneration of the thyroid nodule, which was confirmed by both ultrasonography and either reddish or brown fluid evacuated by fine-needle aspiration, were classified as either acute type with an episode of abrupt painful swelling of the thyroid (n = 4), or chronic type in which a painless thyroid nodule was incidentally found (n = 13). One of the four acute type patients demonstrated subacute thyroiditis-like symptoms and laboratory findings including transient painful thyrotoxicosis associated with high serum levels of thyroid hormones and thyroglobulin (Tg), a suppressed serum TSH level, a low thyroidal radioactive iodine uptake (RAIU), and accelerated erythrocyte sedimentation rate (ESR). In the other three acute type patients the serum level of Tg increased markedly, the serum thyroid hormones level increased in one, the thyroidal RAIU was low in two, and the ESR was accelerated in one. In the thirteen chronic type patients, the serum levels of the thyroid hormones and the thyroidal RAIU were within the normal range, and few inflammatory signs were observed. These findings suggest that acute hemorrhagic degeneration of the thyroid nodule may thus cause transient subacute thyroiditis-like symptoms and laboratory findings.

In vitro and in vivo activities of the benzoxazinorifamycin KRM-1648 against Mycobacterium tuberculosis

The in vitro and in vivo activities of a new benzoxazinorifamycin, KRM-1648 (KRM), against Mycobacterium tuberculosis were studied. The MIC at which 50% of the isolates are inhibited (MIC50) and the MIC90 of KRM for 30 fresh isolates of M. tuberculosis measured by the BACTEC 460 TB System were 0.016 and 2 micrograms/ml, respectively. These values were much lower than those for rifampin (RMP), which were 4 and >128 micrograms/ml, respectively, and considerably lower than those for rifabutin (RBT), which were 0.125 and 8 micrograms/ml, respectively. A correlational analysis of the MICs of these drugs for the clinical isolates revealed the presence of cross-resistance of the organisms to KRM and either RMP or RBT although the MICs of KRM were distributed over a much lower range than were those of the other two drugs. KRM and RMP at concentrations of 1 to 10 micrograms/ml almost completely inhibited the bacterial growth of RMP-sensitive strains (H37Rv, Kurono, and Fujii) of M. tuberculosis phagocytosed in macrophage-derived J774.1 cells. KRM was more active than RMP in inhibiting the growth of the RMP-resistant (MIC = 8 micrograms/ml) Kurata strain but failed to show such an effect against the RMP-resistant (MIC >128 micrograms/ml) Watanabe stain. When KRM was given to M. tuberculosis-infected mice at dosages of 5 to 20 mg/kg of body weight by gavage, one daily six times per week from day 1 after infection, it was much more efficacious than RMP against infections induced in mice by the RMP-sensitive Kurono strain, as measured by a reduction of rates of mortality, a reduction of the frequency and extent of gross lung lesions, histopathological changes in lung tissues, and a decrease in the bacterial loads in the lungs and spleens of infected mice. KRM also displayed significant therapeutic efficacy against infection induced by the RMP-resistant Kurata strain, while neither KRM nor RMP was efficacious against infection by the RMP-resistant Watanabe strain. In the case of infection with the Kurono strain, the efficacy of the drugs in prolonging the time of survival was in the order KRM, RBT, RMP. KRM was much more efficacious than RMP, when given at 1- to 4-week intervals. These findings suggest that KRM may be useful for the clinical treatment of tuberculosis contracted through RMP-sensitive strains, even when it is administered at long intervals.

[Thoracoscopic debridement for acute empyema]

Thoracoscopic debridement for acute empyema was successfully performed in three patients who were refractory to closed drainage, irrigation and antibiotic therapy. In two patients anaerobic organisms were isolated from the pus. None of the patients had bronchopleural fistula. All patients were relieved of fever promptly after surgery. Operative invasion was minimal, and postoperative lung function was well maintained one month after the operation. If empyema is in the fibrinopurulent phase and does not respond to pleural drainage, thoracoscopic debridement may be indicated before more aggressive therapy.

Rejection and expression of thioredoxin in transplanted canine lung

Thioredoxin (TRX) production has been shown to be induced by a variety of stresses. In this study, we examined TRX expression in lung tissues after canine lung transplantation to determine whether it could be induced by allogenic stimulations and could be used to diagnose early rejection. Thirty-five adult mongrel dogs were used in all. In group A, 24 dogs underwent allotransplantation of the left lung with no immunosuppressant and were sacrificed at various times; 5 were sacrificed on postoperative day (POD) 1; 5 on POD 2; 7 on POD 3; and 7 on POD 5. In group B, 5 donor right lungs were used for negative control. In group C, 3 dogs underwent autotransplantation. In group D, 8 dogs underwent allotransplantation of the left lung with optimal immunosuppression and were sacrificed at POD 28. Lung tissues were stained with anti-TRX antibody, and the TRX high-producer (TRXh) cells in a randomly chosen field were counted as the index of TRX expression. In group A, the number of TRXh cells were as follows: 1.68 +/- 1.14 in grade 0; 4.87 +/- 1.07 in grade 1; 10.42 +/- 4.24 in grade 2; 27.34 +/- 17.96 in grade 3; and 50.90 +/- 17.36 in grade 4. In group B, the number of TRXh cells was 1.82 +/- 1.01. There was a significant difference between each rejection grade in group A and group B (p < 0.01), and we could observe TRXh cells in the early stage of rejection. These results suggest that analysis of TRXh cells in lung tissues may be useful in the early diagnosis of rejection.

Preservation of cerebral blood flow responses to hypoxia and arterial pressure alterations in hyperammonemic rats

Acute hyperammonemia causes cerebral edema, elevated intracranial pressure and loss of cerebral blood flow (CBF) responsivity to CO2. Inhibition of glutamine synthetase prevents these abnormalities. If the loss of CO2 responsivity is secondary to the mechanical effects of edema, one would anticipate loss of responsivity to other physiological stimuli, such as hypoxia and changes in mean arterial blood pressure (MABP). To test this possibility, pentobarbital-anesthetized rats were subjected to either hypoxic hypoxia (PaO2 approximately 30 mm Hg), hemorrhagic hypotension (MABP approximately 70 and 50 mm Hg), or phenylephrine-induced hypertension (MABP approximately 125 and 145 mm Hg). CBF was measured with radiolabeled microspheres. Experimental groups received intravenous ammonium acetate (approximately 50 mumol min-1 kg-1) for 6 h to increase plasma ammonia to 500-600 microM. Control groups received sodium acetate plus HCl to prevent metabolic alkalosis. The increase in CBF during 10 min of hypoxia after 6 h of ammonium acetate infusion (84 +/- 19 to 259 +/- 52 ml min-1 100 g-1) was similar to that after sodium acetate infusion (105 +/- 20 to 265 +/- 76 ml min-1 100 g-1). Cortical glutamine concentration was elevated equivalently in hyperammonemic rats subjected to normoxia only or to 10 min of hypoxia. With severe hypotension, CBF was unchanged in both the ammonium (80 +/- 20 to 76 +/- 24 ml min-1 100 g-1) and the sodium (80 +/- 14 to 73 +/- 16 ml min-1 100 g-1) acetate groups. With moderate hypertension, CBF was unchanged. With the most severe hypertension, significant increases in CBF occurred in both groups, but there was no difference between groups. We conclude that hypoxic and autoregulatory responses are intact during acute hyperammonemia. The previously observed loss of CO2 responsivity is not the result of a generalized vasoparalysis to all physiological stimuli.

Blood flow rate in jejunal ischemia-reperfusion injury

We examined changes in the blood flow rate in the course of jejunal ischemic injury using a laser Doppler flowmeter. For this purpose, we designed a sensor holding system, which involved the fixation of the sensor to the jejunum and allowed their movements to be synchronized. When the jejunum was reperfused after 10 min of ischemia, the blood flow rate markedly increased and then gradually decreased to the initial level. A 30-min period of ischemia produced the slowest recovery of the blood flow rate. This system could be useful for monitoring the blood flow rate in different anatomical regions.

Surgical treatment of small cell carcinoma of the lung: advantage of preoperative chemotherapy

To assess the effect of chemotherapy on postoperative survival of patients with small cell lung carcinoma (SCLC), 46 patients who underwent surgery at Kyoto University between 1976 and 1991 were retrospectively reviewed. Seventeen patients (37.0%) received chemotherapy prior to as well as after surgery (neoadjuvant therapy group), 23 (50.5%) received chemotherapy only after surgery (adjuvant therapy group), and the other six received no chemotherapy (non-chemotherapy group). The 5-year survival rate of patients with c-Stage I or II disease in the neoadjuvant therapy group was as high as 80.0%, which seemed to be higher, although with no statistical significance, than that in the adjuvant therapy group (37.7%, P = 0.10). The 5-year survival rate of patients with c-Stage III (IIIa or IIIb) disease in the neoadjuvant therapy group, although not satisfactory (10.0%), was significantly higher than that in the adjuvant therapy group (0.0%, P = 0.04). No patients in the non-chemotherapy group had survived 5 years. Moreover, multivariate analysis showed that failure to employ preoperative chemotherapy was the strongest prognostic factor causing a poor prognosis (P = 0.01). On the other hand, eight (30.8%) out of 26 patients with c-Stage I or II disease postoperatively proved to have mediastinal lymph node involvement (pN2-3), and two (7.7%) proved to have intrapulmonary metastasis (PM). Considering the advantage of preoperative chemotherapy and the discrepancy between c- and p-stage, sufficient chemotherapy prior to surgery should be employed, and may realize a good prognosis in patients with c-Stage I or II disease. In contrast, patients with c-Stage III disease are not appropriate as candidates for surgery even if preoperative chemotherapy is performed.

Expression of the adult T-cell leukemia-derived factor, human thioredoxin, in the allotransplanted canine lung

The relationship between the expression of adult T-cell leukemia-derived factor, human thioredoxin (ADF/TRX), and rejection in transplanted canine lungs was investigated in this study. Of a total 27 adult mongrel dogs, 24 underwent allotransplantation of the left lung with no immunosuppressant and the other three underwent autotransplantation of the left lung. Of the allotransplanted dogs, five were killed on postoperative day (POD) 1, five on POD 2, seven on POD 3, and seven on POD 5, while all three autotransplanted dogs were killed on POD 5. Histological examination was performed on the 24 allotransplanted left lungs (group A), 12 autologous right lungs (group B), and bilateral lungs of the three autotransplanted dogs (group C). The lung tissue was stained with anti-ADF antibody, and the high-ADF-producing cells (ADFh cells) in a randomly chosen field were counted as an index of ADF expression. As the signs of rejection in the group A lungs became more severe with time, the ADFh cells increased in number: 1.68 +/- 1.15, 6.08 +/- 3.44, 14.03 +/- 6.09, and 47.74 +/- 18.89, on PODs 1, 2, 3, and 5, respectively. However, the number of ADFh cells in the group B and group C lungs did not become significantly different from that on POD 1 in group A. These results suggested that ADF/TRX expression may be useful for the early diagnosis of rejection of transplanted lungs.

Patent ductus venosus associated with a hyperintense globus pallidum on T1-weighted magnetic resonance imaging and pulmonary hypertension

We report the case of a 13-year-old Japanese boy with a patent ductus venosus. He experienced mild disorientation and hallucination at age 8 years. Hyperammonaemia was discovered at age 12 years. Brain MRI demonstrated multiple intracranial hyperintense lesions, mainly in the globus pallidum, which suggested portosystemic encephalopathy. Patent ductus venosus was demonstrated by abdominal ultrasonography and angiography. Cardiopulmonary investigation revealed pulmonary hypertension. An intracranial hyperintense lesion observed on T1-weighted MRI may be an initial clue for discovering a patent ductus venosus in asymptomatic patients.

CONCLUSION

When patent ductus venosus is disclosed, pulmonary hypertension should be sought, as in cases with other portosystemic shunts.

Characterization of the binding site for cyclothialidine on the B subunit of DNA gyrase

The mechanism of inhibition of DNA gyrase by cyclothialidine, a novel gyrase inhibitor isolated from Streptomyces filipinensis NR0484, has been studied further by using [14C]benzoylcyclothialidine and a reconstituted Escherichia coli gyrase system consisting of the A subunit, the B subunit and relaxed ColE1 DNA. The mechanism of inhibition was also studied with the 43-kDa N-terminal fragment of the B subunit. The [14C]benzoylcyclothialidine could bind to the B subunit alone but not to the A subunit nor to the plasmid DNA alone. Furthermore, the compound also bound to the 43-kDa N-terminal fragment of the B subunit. Scatchard analysis of [14C]benzoylcyclothialidine binding to DNA gyrase showed that the binding affinity of the compound increased, depending on the assembly of the gyrase (A2B2). DNA complex. This suggests that the binding site of cyclothialidine on the B subunit or its vicinity causes a conformational change during the assembly of the gyrase.DNA complex (increase in affinity: B-->A2B2-->A2B2.DNA). Furthermore, displacement curves of [14C]benzoylcyclothialidine binding by nonlabeled cyclothialidine, ATP analogues, and coumarin antibiotics indicated that cyclothialidine, coumarins, and ATP share a common (or overlapping) site of action on the B subunit of DNA gyrase; however, the microenvironment of the binding sites may differ.