The Role of Early Intubation in Status Epilepticus with Out-of-Hospital Onset: A Large Prospective Observational Study

Background: this study aimed to evaluate the role of early airway management and intubation in status epilepticus (SE) with out-of-hospital onset. Methods: We included all patients with out-of-hospital SE onset referred to the emergency department of the Academic Hospital of Modena between 2013 and 2021. Patients were compared according to out-of-hospital airway management (intubation versus non-intubation) and a propensity score was performed for clinical variables unevenly distributed between the two groups. Results: We evaluated 711 patients with SE. A total of 397 patients with out-of-hospital SE onset were eventually included; of these, 20.4% (81/397) were intubated before arrival at the hospital. No difference was found in the clinical characteristics of patients after propensity score matching. The 30-day mortality in the propensity group was 19.4% (14/72), and no difference was found between intubated (7/36, 19.4%) and non-intubated (7/36, 19.4%) patients. No difference was found in SE cessation. Compared to non-intubated patients, those who underwent out-of-hospital intubation had a higher risk of progression to refractory or super-refractory SE, greater worsening of mRS values between hospital discharge and admission, and lower probability of returning to baseline condition at 30 days after SE onset. Conclusions: Early intubation for out-of-hospital SE onset is not associated with improved patient survival even after balancing for possible confounders. Further studies should evaluate the timing of intubation and its association with first-line treatments for SE and their efficacy. In addition, they should focus on the settings and the exact reasons leading to intubation to better inform early management of SE with out-of-hospital onset.

Electrographic seizure duration and inter-seizure intervals in focal status epilepticus

OBJECTIVE

To characterize the duration of seizures and inter-seizure intervals in focal status epilepticus (SE).

METHODS

We reviewed consecutive scalp EEG recordings from adult patients who were admitted for a first episode of focal status epilepticus. We identified electrographic seizure duration and inter-seizure intervals in the first diagnostic pretreatment EEG. We also reviewed isolated focal self-limiting seizures in epilepsy patients, as a comparison group for seizure duration.

RESULTS

We recorded 307 focal seizures in 100 consecutive focal SE episodes, with a median seizure duration of 107 s (IQR: 54-186), and 134 isolated focal self-limiting seizures in 42 epilepsy patients, with a median duration of 59 s (IQR: 30-90; p < .001). The only clinical feature of SE that significantly increased seizure duration was acute symptomatic etiology. In SE, 15% and 7% of seizures lasted longer than 300 and 600 s, respectively (t1 of the actual definition for tonic-clonic and focal SE), while only 1% of self-limiting seizures lasted longer than 300 s, and none lasted longer than 600 s. The analysis of inter-seizure intervals in SE with multiple seizures showed that 50% of the inter-seizure periods were shorter than 60 s, and 95% were shorter than 540 s (9 min). Patients who had an increase in seizure duration (last versus first) of at least 1.4 times showed an increased 30-day mortality.

SIGNIFICANCE

Focal seizures within a SE episode showed a wide range of duration, partly overlapping with the duration of focal self-limiting seizures but with a longer median duration. Inter-seizure intervals within an episode of SE were shorter than 1 min in 50% of the seizures and never lasted more than 10 min. Finally, an increase in seizure duration could represent an "electrophysiological biomarker" of a more severe SE episode, which may require more aggressive and rapid treatment.

Neuro-glial degeneration in Status Epilepticus: Exploring the role of serum levels of Neurofilament light chains and S100B as prognostic biomarkers for short-term functional outcome

BACKGROUND

The last ILAE definition of Status Epilepticus (SE) highlights that the persistence of the epileptic activity per se could determine irreversible brain damages that could be responsible for long-term consequences. The measurement of neuro-glial injury biomarkers could help in the identification of those patients who will eventually develop short- and long-term consequences of SE. At present none of the already studied biomarkers has been validated to be used in everyday clinical practice. In this study, we explore the role of NfL and S100B as a prognostic biomarkers to identify patients who will develop short-term disability after an episode of SE.

METHODS

This is a retrospective assessment of the serum levels of both NfL and S100B in a cohort of 87 adult patients with SE prospectively collected in our SE registry (Modena Status Epilepticus Registry - MoSER -) at Baggiovara Civil Hospital (Modena, Italy). All samples were acquired during SE within 72 hours of SE diagnosis. The comparison groups were: healthy controls (HC, n = 27) and patients with epilepsy (PWE, n = 30). Demographic, clinical, and therapeutical information and thirty-days follow-up information regarding disability development were acquired for every included patient and analyzed in relation to NfL and S100B values.

RESULTS

Serum levels of NfL were significantly higher in SE compared to those of PWE (median 7.35 pg/ml, IQR 6.4, p < 0.001) and HC (median 6.57 pg/ml, IQR 9.1, p < 0.001); S100B serum levels were higher in SE (median 0.11 ug/L, IQR 0.18) compared to PWE (median 0.03 ug/L, IQR 0.03, p < 0.001) and HC (median 0.02 ug/L, IQR 0.008, p < 0.001). However, only NfL serum levels were found to be an independent predictor of 30 days functional outcome whereas S100B levels did not.

CONCLUSIONS

Our results suggest that NfL measurement in serum during SE could help predict the short-term functional outcome. This paper was presented at the 8th London-Innsbruck Colloquium on Status Epilepticus and Acute Seizures held in September 2022.

Predicting the progression to super-refractory status epilepticus: A machine-learning study

AIM

Super-refractory status epilepticus (SRSE) is a status epilepticus (SE) that continues or recurs ≥24 h after the onset of anesthesia. We aimed to identify the predictors of progression to SRSE and the risk of 30-day mortality in patients with SRSE by using a machine learning technique.

METHODS

We reviewed consecutive SE episodes in patients aged ≥14 years at Baggiovara Civil Hospital (Modena, Italy) from 2013 to 2021. A classification and regression tree analysis was performed to develop a predictive model of progression to SRSE in SE patients. In SRSE patients, a multivariate analysis was conducted to identify predictors of 30-day mortality.

RESULTS

We included 705 patients, 16% of whom (113/705) progressed to SRSE. Acute symptomatic hypoxic etiology and age ≤ 68.5 years predicted the highest risk (87.1%) of progression to SRSE. Etiology other than acute symptomatic hypoxic and absence of NCSE predicted the lowest risk (3.6%) of progression to SRSE. The predictive model was accurate in 96.1% of patients not evolving to SRSE and in 48.7% of those evolving to SRSE. Among patients with SRSE, 46.9% (53/113) died within 30 days compared to 25.2% (149/592) of patients without SRSE (p < 0.001). Among patients with SRSE, older age was associated with increased 30-day mortality (odds ratio 1.075; 95% confidence interval: 1.031-1.112; p = 0.001).

CONCLUSIONS

Acute symptomatic hypoxic etiology and younger age are major predictors of progression to SRSE. In patients with SRSE, older age is associated with increased risk of short-term mortality.

Ictal apnea: A prospective monocentric study in patients with epilepsy

BACKGROUND AND PURPOSE

Ictal respiratory disturbances have increasingly been reported, in both generalized and focal seizures, especially involving the temporal lobe. Recognition of ictal breathing impairment has gained importance for the risk of sudden unexpected death in epilepsy (SUDEP). The aim of this study was to evaluate the incidence of ictal apnea (IA) and related hypoxemia during seizures.

METHODS

We collected and analyzed electroclinical data from consecutive patients undergoing long-term video-electroencephalographic (video-EEG) monitoring with cardiorespiratory polygraphy. Patients were recruited at the epilepsy monitoring unit of the Civil Hospital of Baggiovara, Modena Academic Hospital, from April 2020 to February 2022.

RESULTS

A total of 552 seizures were recorded in 63 patients. IA was observed in 57 of 552 (10.3%) seizures in 16 of 63 (25.4%) patients. Thirteen (81.2%) patients had focal seizures, and 11 of 16 patients showing IA had a diagnosis of temporal lobe epilepsy; two had a diagnosis of frontal lobe epilepsy and three of epileptic encephalopathy. Apnea agnosia was reported in all seizure types. Hypoxemia was observed in 25 of 57 (43.9%) seizures with IA, and the severity of hypoxemia was related to apnea duration. Apnea duration was significantly associated with epilepsy of unknown etiology (magnetic resonance imaging negative) and with older age at epilepsy onset (p &lt; 0.001).

CONCLUSIONS

Ictal respiratory changes are a frequent clinical phenomenon, more likely to occur in focal epilepsies, although detected even in patients with epileptic encephalopathy. Our findings emphasize the need for respiratory polygraphy during long-term video-EEG monitoring for diagnostic and prognostic purposes, as well as in relation to the potential link of ictal apnea with the SUDEP risk.

Retrospective External Validation of the Status Epilepticus Severity Score (STESS) to Predict In-hospital Mortality in Adults with Nonhypoxic Status Epilepticus: A Machine Learning Analysis

BACKGROUND

The objective of this study was to validate the value of the Status Epilepticus Severity Score (STESS) in the prediction of the risk of in-hospital mortality in patients with nonhypoxic status epilepticus (SE) using a machine learning analysis.

METHODS

We included consecutive patients with nonhypoxic SE (aged ≥ 16 years) admitted from 2013 to 2021 at the Modena Academic Hospital. A decision tree analysis was performed using in-hospital mortality as a dependent variable and the STESS predictors as input variables. We evaluated the accuracy of STESS in predicting in-hospital mortality using the area under the receiver operating characteristic curve (AUROC) with 95% confidence interval (CI).

RESULTS

Among 629 patients with SE, the in-hospital mortality rate was 23.4% (147 of 629). The median STESS in the entire cohort was 2.9 (SD 1.6); it was lower in surviving compared with deceased patients (2.7, SD 1.5 versus 3.9, SD 1.6; p < 0.001). Of deceased patients, 82.3% (121 of 147) had scores of 3-6, whereas 17.7% (26 of 147) had scores of 0-2 (p < 0.001). STESS was accurate in predicting mortality, with an AUROC of 0.688 (95% CI 0.641-0.734) only slightly reduced after bootstrap resampling. The most significant predictor was the seizure type, followed by age and level of consciousness at SE onset. Nonconvulsive SE in coma and age ≥ 65 years predicted a higher risk of mortality, whereas generalized convulsive SE and age < 65 years were associated with a lower risk of death. The decision tree analysis using STESS variables correctly classified 90% of survivors and 34% of nonsurvivors after the SE, with an overall risk of error of 23.1%.

CONCLUSIONS

This validation study using a machine learning system showed that STESS is a valuable prognostic tool. The score appears particularly accurate and effective in identifying patients who are alive at discharge (high negative predictive value), whereas it has a lower predictive value for in-hospital mortality.

Machine learning validation through decision tree analysis of the Epidemiology-Based Mortality Score in Status Epilepticus

OBJECTIVE

This study was undertaken to validate the accuracy of the Epidemiology-Based Mortality Score in Status Epilepticus (EMSE) in predicting the risk of death at 30 days in a large cohort of patients with status epilepticus (SE) using a machine learning system.

METHODS

We included consecutive patients with SE admitted from 2013 to 2021 at Modena Academic Hospital. A decision tree analysis was performed using the 30-day mortality as a dependent variable and the EMSE predictors as input variables. We evaluated the accuracy of EMSE in predicting 30-day mortality using the area under the receiver operating characteristic curve (AUC ROC), with 95% confidence interval (CI). We performed a subgroup analysis on nonhypoxic SE.

RESULTS

A total of 698 patients with SE were included, with a 30-day mortality of 28.9% (202/698). The mean EMSE value in the entire population was 57.1 (SD = 36.3); it was lower in surviving compared to deceased patients (47.1, SD = 31.7 vs. 81.9, SD = 34.8; p < .001). The EMSE was accurate in predicting 30-day mortality, with an AUC ROC of .782 (95% CI = .747-.816). Etiology was the most relevant predictor, followed by age, electroencephalogram (EEG), and EMSE comorbidity group B. The decision tree analysis using EMSE variables correctly predicted the risk of mortality in 77.9% of cases; the prediction was accurate in 85.7% of surviving and in 58.9% of deceased patients within 30 days after SE. In nonhypoxic SE, the most relevant predictor was age, followed by EEG, and EMSE comorbidity group B; the prediction was correct in 78.9% of all cases (89.6% in survivors and 46.1% in nonsurvivors).

SIGNIFICANCE

This validation study using a machine learning analysis shows that the EMSE is a valuable prognostic tool, and appears particularly accurate and effective in identifying patients with 30-day survival, whereas its performance in predicting 30-day mortality is lower and needs to be further improved.

Amygdala subnuclear volumes in temporal lobe epilepsy with hippocampal sclerosis and in non-lesional patients

Together with hippocampus, the amygdala is important in the epileptogenic network of patients with temporal lobe epilepsy. Recently, an increase in amygdala volumes (i.e. amygdala enlargement) has been proposed as morphological biomarker of a subtype of temporal lobe epilepsy patients without MRI abnormalities, although other data suggest that this finding might be unspecific and not exclusive to temporal lobe epilepsy. In these studies, the amygdala is treated as a single entity, while instead it is composed of different nuclei, each with peculiar function and connection. By adopting a recently developed methodology of amygdala’s subnuclei parcellation based of high-resolution T₁-weighted image, this study aims to map specific amygdalar subnuclei participation in temporal lobe epilepsy due to hippocampal sclerosis (n = 24) and non-lesional temporal lobe epilepsy (n = 24) with respect to patients with focal extratemporal lobe epilepsies (n = 20) and healthy controls (n = 30). The volumes of amygdala subnuclei were compared between groups adopting multivariate analyses of covariance and correlated with clinical variables. Additionally, a logistic regression analysis on the nuclei resulting statistically different across groups was performed. Compared with other populations, temporal lobe epilepsy with hippocampal sclerosis showed a significant atrophy of the whole amygdala (p_Bonferroni = 0.040), particularly the basolateral complex (p_Bonferroni = 0.033), while the non-lesional temporal lobe epilepsy group demonstrated an isolated hypertrophy of the medial nucleus (p_Bonferroni = 0.012). In both scenarios, the involved amygdala was ipsilateral to the epileptic focus. The medial nucleus demonstrated a volume increase even in extratemporal lobe epilepsies although contralateral to the seizure onset hemisphere (p_Bonferroni = 0.037). Non-lesional patients with psychiatric comorbidities showed a larger ipsilateral lateral nucleus compared with those without psychiatric disorders. This exploratory study corroborates the involvement of the amygdala in temporal lobe epilepsy, particularly in mesial temporal lobe epilepsy and suggests a different amygdala subnuclei engagement depending on the aetiology and lateralization of epilepsy. Furthermore, the logistic regression analysis indicated that the basolateral complex and the medial nucleus of amygdala can be helpful to differentiate temporal lobe epilepsy with hippocampal sclerosis and with MRI negative, respectively, versus controls with a consequent potential clinical yield. Finally, the present results contribute to the literature about the amygdala enlargement in temporal lobe epilepsy, suggesting that the increased volume of amygdala can be regarded as epilepsy-related structural changes common across different syndromes whose meaning should be clarified.

Out-of-hospital versus in-hospital status epilepticus: the role of etiology and comorbidities

Background and purpose

Our objectives were to identify differences in clinical characteristics between patients with out‐of‐hospital and in‐hospital status epilepticus (SE) onset, and to evaluate the influence of SE onset setting on 30‐day mortality and SE cessation.

Methods

We included consecutive patients with SE admitted from 2013–2021 at Modena Academic Hospital. A propensity score was obtained with clinical variables unevenly distributed between the two groups.

Results

Seven hundred eleven patients were included; 55.8% (397/711) with out‐of‐hospital and 44.2% (314/711) with in‐hospital onset. Patients with in‐hospital SE onset were older and had a higher frequency of comorbidities, acute and/or potentially fatal etiologies, impaired consciousness before treatment, and nonconvulsive or myoclonic SE. No difference was found in SE cessation between the groups. Patients with in‐hospital SE had higher 30‐day mortality (127/314, 62.9% vs. 75/397, 37.1%; p < 0.001). In‐hospital onset was an independent risk factor for 30‐day mortality (adjusted odds ratio = 1.720; 95% confidence interval = 1.107–2.674; p = 0.016). In the propensity group (n = 244), no difference was found in 30‐day mortality and SE cessation between out‐of‐hospital and in‐hospital SE onset groups (36/122, 29.5% vs. 34/122, 27.9%; p = 0.888; and 47/122, 38.5% vs. 39/122; 32%; p = 0.347, respectively).

Conclusions

In‐hospital SE is associated with higher 30‐day mortality without difference in SE cessation. The two groups differ considerably for age, acute and possibly fatal etiologies, comorbidities, and SE semiology. The patient location at SE onset is an important prognostic predictor. However, the increased mortality is probably unrelated to the setting of SE onset and reflects intrinsic prognostic predictors.

Case Report: Ictal Central Apnea as First and Overlooked Symptom in Temporal Lobe Seizures

Ictal respiratory changes have been mainly described following generalized tonic-clonic seizures and recently considered to be a biomarker to assess the risk of sudden unexplained death in epilepsy (SUDEP). Nonetheless, modification of respiratory pattern can be related also to focal seizures, especially arising from the temporal lobe. Changes in cardiac function such as tachycardia or bradycardia could be often associated. We report a short case series of four patients with temporal lobe epilepsy admitted to our Epilepsy Monitoring Unit (EMU) presenting with an ictal central apnea as the first clinical manifestation of their seizures. None of these patients was aware of the occurrence of respiratory arrest. Age at onset ranged from 15 to 29 years. One patient had seizures with prolonged central apnea accompanied by a significant decrease in oxygen saturation. Neuroimaging in two patients showed alterations of mesial temporal lobe structures, including the amygdala. Recent neurophysiological studies supported the existence of a cortical network involving the limbic system that modulates downstream brainstem respiratory centers. Monitoring for respiratory changes and oxygen saturation in focal seizures is warranted for their potential value in identifying the epileptogenic zone and for a better understanding of ictal respiratory changes that could potentially define a subgroup of patients with high risk of seizure-related autonomic changes.

Cortical and thalamic hyper-perfusion in non-convulsive status epilepticus. Relationship between perfusion CT patterns and Salzburg EEG criteria

INTRODUCTION

Status epilepticus (SE) is a neurological emergency and in particular nonconvulsive SE (NCSE) represents a diagnostic challenge. To improve clinical decision-making, cerebral perfusion-computed tomography (PCT) has been shown as a helpful tool to support the diagnosis of focal NCSE.

MATERIALS AND METHODS

This is a monocentric retrospective study. Among the 602 cases of SE observed between September 2013 and April 2020 we included 21 patients that were studied with PCT. The perfusion maps were first visually analysed then a quantitative analysis (by regions of interest, ROI) was obtained. For each patient, the diagnostic EEG was reviewed and classified in accordance to the Salzburg Criteria for NCSE (SCC) as definite (D-NCSE) and possible (P-NCSE). Finally, we analysed the relationship between PCT and EEG patterns.

RESULTS

Hyper-perfusion was observed in 18 patients (86%), while in the remaining 3 (14%) a normo-perfused pattern was present. Hyper-perfusion was observed in 14 of the D-NCSE group (88%) and in the two patients with a P-NCSE (100%). No one among the patients with a P-NCSE had a thalamic hyper-perfusion, while among the 6 patients with continuous sustained epileptiform discharges > 2.5 Hz (pattern 1 of SCC), 4 (67%) showed cortical plus thalamic hyper-perfusion.

CONCLUSIONS

PCT could facilitate the differential diagnosis and speed-up the diagnostic process of NCSE in emergency situations. Finding cortical multi-lobar hyper-perfusion, especially if present together with homolateral thalamic hyper-perfusion in a patient with an acute-onset of motor/sensory/language deficits is highly suggestive for the presence of NCSE and is particularly related to continuous/sustained ictal patterns.

New onset status epilepticus in influenza associated encephalopathy: The presenting manifestation of genetic generalized epilepsy

We hereby present a case of a young woman with no history of seizures or epilepsy who experienced a de novo generalized Non Convulsive Status Epilepticus (NCSE) followed by encephalopathy lasting for several days during influenza B infection. Influenza can have a broad spectrum of presentation ranging from an uncomplicated illness to many serious conditions as is the case of influenza associated encephalitis/encephalopathy (IAE). In this context however, it is possible to observe seizures and/or status epilepticus as the presenting manifestation of a genetic generalized epilepsy.

Intravenous brivaracetam in status epilepticus: A multicentric retrospective study in Italy

PURPOSE

to evaluate the use, effectiveness, and adverse events of intravenous brivaracetam (BRV) in status epilepticus (SE).

METHODS

a retrospective multicentric study involving 24 Italian neurology units was performed from March 2018 to June 2020. A shared case report form was used across participating centres to limit biases of retrospective data collection. Diagnosis and classification of SE followed the 2015 ILAE proposal. We considered a trial with BRV a success when it was the last administered drug prior the clinical and/or EEG resolution of seizures, and the SE did not recur during hospital observation. In addition, we considered cases with early response, defined as SE resolved within 6 h after BRV administration.

RESULTS

56 patients were included (mean age 62 years; 57 % male). A previous diagnosis of epilepsy was present in 21 (38 %). Regarding SE etiology classification 46 % were acute symptomatic, 18 % remote and 16 % progressive symptomatic. SE episodes with prominent motor features were the majority (80 %). BRV was administered as first drug after benzodiazepine failure in 21 % episodes, while it was used as the second or the third (or more) drug in the 38 % and 38 % of episodes respectively. The median loading dose was 100 mg (range 50-300 mg). BRV was effective in 32 cases (57 %). An early response was documented in 22 patients (39 % of the whole sample). The use of the BRV within 6 h from SE onset was independently associated to an early SE resolution (OR 32; 95 % CI 3.39-202; p = 0.002). No severe treatment emergent adverse events were observed.

CONCLUSION

BRV proved to be useful and safe for the treatment of SE. Time to seizures resolution appears shorter when it is administered in the early phases of SE.

Occurrence of septic shock in a patient submitted to emergency cerclage following a negative amniocentesis: report of a case

BACKGROUND

Second trimester emergency cerclage is an option for pregnant women presenting bulging fetal membranes. Despite a significant prolongation of pregnancy might be achieved, serious fetal and maternal events have been reported. Exclusion of infections through preprocedure amniocentesis has been proposed.

METHODS

A 37-year-old woman, gravida 4 para 1, was admitted at 21 weeks of gestation to our University Hospital due to bulging fetal membranes. An amniocentesis was performed in order to exclude an actual amniotic infection. Our Microbiology Department found a negative amniotic culture for bacteria and Mycoplasma and a normal glucose and interleukin-6 level, so a cervical cerclage was performed. The patient was discharged home on oral erythromycin.

RESULTS

After 48 h, the patient complained of hyperpyrexia, shivers and reduced fetal movements. Ultrasound at admission showed absent cardiac activity and after cerclage removal a non-viable fetus was delivered vaginally. Piperacillin and tazobactam were started, but the clinical course of the patient deteriorated and she developed a cold septic shock and was submitted to hysterectomy and transferred to the ICU of our hospital.

CONCLUSION

This report heralds that even after negative amniocentesis, a life-threatening infection may not be excluded in women candidate for emergency cerclage due to bulging fetal membranes.

Protective activity of plicatin B against human LDL oxidation induced in metal ion-dependent and -independent processes. Experimental and theoretical studies

Oxidation of low-density lipoproteins (LDL) is thought to be a major factor in the pathophysiology of atherosclerosis. Natural antioxidants have been shown to protect LDL from oxidation and to inhibit atherogenic developments in animals. Structurally related prenylated pterocarpans, erybraedin C and bitucarpin A, and the prenylchalcone plicatin B were examined for their ability to inhibit LDL oxidation in vitro. The kinetic profile of peroxidation is characterized by the lag time of oxidation (t(lag)), the maximal rate of oxidation (V(max)) and the maximal accumulation of oxidation products (OD(max)). Specific variation of the set of kinetic parameters by antioxidants may provide important information about the mechanism of inhibitory action of a given compound. At equimolar concentrations (1 microM) the prenylated derivatives tested were found to inhibit 1 microM copper sulphate-induced oxidation of LDL (50 microg protein/ml) in accordance with the following order of activity: plicatin B>erybraedin Cbitucarpin A. Structural aspects, such as hydrogen-donating substituents, their number and arrangement in the aromatic ring moieties, and the prenyl and methoxy substituents, were investigated in order to explain the findings obtained. It is well known that the antioxidant activity of flavonoids is believed to be caused by a combination of transition metal chelation and free-radical-scavenging activities. To investigate these differences we comparatively studied the protective mechanism of plicatin B in copper-dependent or -independent LDL oxidation. The latter was mediated by 2,2'-azo-bis-(2-amidinopropane) dihydrochloride (ABAP). We measured the formation of conjugated dienes (OD(234 nm)). Plicatin B (0.2-1.5 microM) delayed the Cu(2+) (1 microM) promoted oxidation as conjugate diene formation (t(lag)) of the LDL by 45.2-123.5 min and reduced V(max) by 0.46-0.29 microM/min. In the ABAP (0.2mM) promoted LDL oxidation t(lag) increased by 67.2-110.2 min through plicatin B (0.5-2.5 microM). In experiments in which Cu(2+) concentrations increased (0.5 - 3 microM) and the amount of plicatin B (1 microM) was maintained constant, a significant decrease in t(lag) and an increase in V(max) was observed. In this study plicatin B appeared to exhibit a mixed mechanism, interfering with the formation of the radicals by chelating copper involved in the initiation/propagation reaction, but also by scavenging free hydroperoxyl radicals resulting from ABAP thermolysis. In addition, theoretical analysis indicated that plicatin B preferentially established the chelating complex with Cu(2+), because its affinity value is notably higher (by a factor of 5) than that for Cu(+).

Anti-clastogenic activity of two structurally related pterocarpans purified from Bituminaria bituminosa in cultured human lymphocytes

Plant-derived isoflavones are currently receiving much attention because of their phyto-estrogenic, antioxidant, anti-mutagenic, and anti-tumor activities. In this study we have evaluated the clastogenic and anti-clastogenic activities in human lymphocytes of two structurally related pterocarpans, iso-flavonoid derivatives, termed erybraedin C and bitucarpin A, recently purified from Bituminaria bituminosa and chemically characterized. Mitomycin C (MMC) and the radio-mimetic bleomycin (BL) were used as reference clastogens. The end point studied was micronucleus formation. The results obtained in this study indicate that erybraedin C and bitucarpin A, when assayed alone, do not affect either the mitotic index or the cell-proliferation index of human lymphocytes. Interestingly, both compounds appear to be non-clastogenic in the range of concentrations used. In contrast, both substances seem to affect significantly the clastogenic effects induced by BL and MMC. A 1-h pre-exposition of the cell culture to erybraedin C was necessary to display its anti-clastogenic potential against BL, whereas bitucarpin A was inactive in this respect, with a structure-activity relationship. In contrast, the clastogenic activity of MMC was significantly reduced by both erybraedin C and bitucarpin A, using either a pre-incubation schedule or simultaneous treatment. These results suggest that the protective effects displayed by the two anti-clastogenic compounds against MMC could be due to the induction or inhibition of cellular reductive metabolic enzymes.

Uracil salvage pathway in PC12 cells

The salvage anabolism of uracil to pyrimidine ribonucleosides and ribonucleotides was investigated in PC12 cells. Pyrimidine base phosphoribosyl transferase is absent in PC12 cells. As a consequence any uracil or cytosine salvage must be a 5-phosphoribosyl 1-pyrophosphate-independent process. When PC12 cell extracts were incubated with ribose 1-phosphate, ATP and uracil they can readily catalyze the synthesis of uracil nucleotides, through a salvage pathway in which the ribose moiety of ribose 1-phosphate is transferred to uracil via uridine phosphorylase (acting anabolically), with subsequent uridine phosphorylation. This pathway is similar to that previously described by us in rat liver and brain extracts (Cappiello et al., Biochim. Biophys. Acta 1425 (1998) 273; Mascia et al., Biochim. Biophys. Acta 1472 (1999) 93). We show using intact PC12 cells that they can readily take up uracil from the external medium. The analysis of intracellular metabolites reveals that uracil taken up is salvaged into uracil nucleotides, with uridine as an intermediate. We propose that the ribose 1-phosphate-dependent uracil salvage shown by our in vitro studies, using tissues or cellular extracts, might also be operative in intact cells. Our results must be taken into consideration for the comprehension of novel chemotherapeutics' influence on pyrimidine neuronal metabolism.

Role of the phosphorolysis of deoxyadenosine in the cytotoxic effect of the combination of deoxyadenosine and deoxycoformycin on a human colon carcinoma cell line (LoVo)

In LoVo cells, phosphorolytic activity acting on deoxyadenosine plays a major role in the resistance to the cytotoxic effect of the combination of deoxynucleoside with deoxycoformycin. In fact, the observed dependence of toxicity on cell density appears to be related to the metabolic conversion of deoxyadenosine into adenine. The phosphorylation of the deoxynucleoside, which represents the first step towards the formation of the cytotoxic agent dATP, proceeds at a significantly lower rate as compared to the phosphorolysis of deoxyadenosine. The analysis of the levels of deoxyadenosine and its derivatives in the incubation media reveals that the rates of disappearance of deoxyadenosine and of formation of adenine increase in concert with the reduction of the effect on cell survival.

Cytokinesis-block micronucleus assay in primary human liver fibroblasts exposed to griseofulvin and mitomycin C

Primary liver fibroblasts were applied in a cytokinesis-block micronucleus assay in combination with fluorescence in situ hybridization (FISH) using two protocols. In protocol A (Prot. A), cytochalasin B (Cyt B) was added at the end of the treatment time directly to the medium containing the standard compounds, whereas in protocol B (Prot. B) the chemical-containing medium was removed and fresh medium with Cyt B was added. The study was performed using the aneugen griseofulvin (GF) and the clastogen mitomycin C (MMC) as standard compounds. With both protocols GF induced a significant increase in MN frequency over controls in a dose-related manner at the lower concentrations tested (7.5 and 15 microg/ml). At the highest dose (30 microg/ml) the aneugen effect was substantially reduced. MN induction obtained with Prot. A was significantly higher ( approximately 3-fold) than with Prot. B at the most effective concentration. The aneugen effect induced by GF did not change when different cell densities were used, but again with Prot. A we obtained the highest effect. MN induced by MMC showed a dose- and time-dependent increase in both protocols. In contrast to GF, the greater clastogenic response induced by MMC in human liver fibroblasts was obtained with Prot. B, approximately 3-fold higher than Prot. A at the most effective concentration and approximately 2-fold with 24 h treatment at 0.17 microg/ml MMC. With GF, the FISH data in human liver fibroblasts (80% C+MN) were fairly consistent with those obtained in the rodent cell lines. In human whole blood cultures, the same dose used in our experiment produced a relatively higher percentage of C+MN. FISH analysis showed that MMC induced mainly MN containing acentric fragments rather than whole chromosomes. In conclusion we have demostrated that chemically induced genetic effects are strongly dependent on the cell culture employed, treatment schedule and intra- and post-treatment experimental conditions.

6-thioguanine resistance in a human colon carcinoma cell line with unaltered levels of hypoxanthine guanine phosphoribosyltransferase activity

Cell populations resistant to high doses (30 microM) of 6-thioguanine (6-TG, 6-TG(r) cells) were selected from a human colon carcinoma cell line, LoVo. This cell line, which lacks hMSH2, a component of the human mismatch binding heterodimer hMutSalpha, is resistant to low doses of 6-TG. The level of activity of hypoxanthine-guanine phosphoribosyltransferase, the enzyme responsible for the phosphoribosylation of the thiopurine, was comparable to that expressed in the parental cells. No significant difference was found in the levels of enzyme activities involved in the conversion of 6-TG or its derivatives into non-toxic compounds. In contrast, a significant difference was found in the uptake kinetics of 6-TG in the 2 cell types. Net uptake of 6-TG ceased after 100-sec incubation in the 6-TG(r) cells, while it appeared to continue throughout the 10-min incubation in the wild-type cells. As a consequence, after 10-min incubation, the total amount of 6-TG taken up by the parental LoVo cells was approximately 3 times higher than that present in the 6-TG(r) cells.

Deoxyadenosine metabolism in a human colon-carcinoma cell line (LoVo) in relation to its cytotoxic effect in combination with deoxycoformycin

We have assessed the intracellular metabolism of 2'-deoxyadenosine in a human colon-carcinoma cell line (LoVo), both in the absence and in the presence of deoxycoformycin, the powerful inhibitor of adenosine deaminase. The combination of 2'-deoxyadenosine and deoxycoformycin has been reported to inhibit the growth of LoVo cells in culture. In this paper we demonstrate that the observed toxic effect is strictly dependent on cell density. In the absence of deoxycoformycin, 2'-deoxyadenosine is primarily deaminated to 2'-deoxyinosine and then converted into hypoxanthine. In the presence of the inhibitor, the deoxynucleoside, in addition to a phosphorylation process, undergoes phosphorolytic cleavage giving rise to adenine. The conversion of 2'-deoxyadenosine to adenine might represent a protective device, emerging when the activity of adenosine deaminase is reduced or inhibited. There is much evidence to indicate that the enzyme catalyzing this process may be distinct from methylthioadenosine phosphorylase and S-adenosyl homocysteine hydrolase, which are the enzymes reported to be responsible for the formation of adenine from 2'-deoxyadenosine in mammals.

Establishment and characterization of a new mammary adenocarcinoma cell line derived from MMTV neu transgenic mice

A new murine cell line, named MG1361, was established from mammary adenocarcinomas arising in a MMTV-neu transgenic mouse lineage where breast tumors develop in 100% of females, due to the overexpression of the activated rat neu oncogene in the mammary gland. The MG1361 cell line shows an epithelial-like morphology, has a poor plating efficiency, low clonogenic capacity, and a doubling time of 23.8 hours. Karyotype and flow cytometry analysis revealed a hypotetraploid number of chromosomes, whereas cell cycle analysis showed 31.2% of cells to be in the G1 phase, 21.4% in S and 47.4% in G2 + M. This cell line maintains a high level of neu expression in vitro. The MG1361 cell line was tumorigenic when inoculated in immunodeficient (nude) mice and the derived tumors showed the same histological features as the primary tumors from which they were isolated. MG1361 cells were positive for specific ER and PgR binding which was competed by tamoxifen, making this cell line useful for the evaluation of endocrine therapy. Moreover, they were sensitive to etoposide treatment, suggesting that they could be a model for the study of chemotherapy-induced apoptosis. As the tumors arising in MMTV-neu transgenic mice have many features in common with human mammary adenocarcinomas (Sacco et al., Gene Therapy 1995; 2: 493-497), this cell line can be utilized to perform basic studies on the role of the neu oncogene in the maintenance of the transformed phenotype, and to test novel protocols of therapeutic strategies.

Structure-activity relationship in the induction of chromosomal aberrations and spindle disturbances in Chinese hamster epithelial liver cells by regioisomeric phenanthrene quinones

Four regioisomeric phenanthrene (PH) quinones (Q) were investigated for their ability to induce chromosomal damage and spindle disturbances. PH 1,4-Q and PH 1,2-Q induced structural as well as numerical chromosomal aberrations, whereas the isomers PH 9,10-Q and PH 3,4-Q were virtually inactive in this respect, However, all four compounds enhanced the frequency of c-mitoses.

Development and validation of alternative metabolic systems for mutagenicity testing in short-term assays

We present here the results obtained within the framework of an EU funded project aimed to develop and validate alternative metabolic activating systems to be used in short-term mutagenicity assays, in order to reduce the use of laboratory animals for toxicology testing. The activating systems studied were established cell lines (Hep G2, CHEL), genetically engineered V79 cell lines expressing specific rat cytochromes P450, erythrocyte-derived systems, CYP-mimetic chemical systems and plant homogenates. The metabolically competent cell lines were used as indicator cells for genotoxic effects as well as for the preparation of external activating systems using other indicator cells. The following endpoints were used: micronuclei, chromosomal aberrations and sister chromatid exchanges, mutations at the hprt locus, gene mutations in bacteria (Ames test), unscheduled DNA synthesis and DNA breaks detected in the comet assay. All metabolic systems employed activated some promutagens. With some of them, promutagens belonging to many different classes of chemicals were activated to genotoxicants, including carcinogens negative in liver S9-mediated assays. In other cases, the use of the new activating systems allowed the detection of mutagens at much lower substrate concentrations than in liver S9-mediated assays. Therefore, the alternative metabolizing systems, which do not require the use of laboratory animals, have a substantial potential in in vitro toxicology, in the basic genotoxicity testing as well as in the elucidation of activation mechanisms. However, since the data basis is much smaller for the new systems than for the activating systems produced from subcellular liver preparations, the overlapping use of both systems is recommended for the present and near future. For example, liver S9 preparations may be used with some indicator systems (e.g., bacterial mutagenicity), and metabolically competent mammalian cell lines may be used with other indicator systems (e.g., a cytogenetic endpoint) in a battery of basic tests.

Induction of chromosomal aberrations and spindle disturbances in Chinese hamster epithelial liver cells in culture by pyrene and benzo[a]pyrene quinones

Regioisomers of pyrene and benzo[a]pyrene quinones were tested for their ability to induce structural and numerical aberrations and spindle disturbance in Chinese hamster epithelial liver (CHEL) cells in culture. All quinones tested were clastogenic. Pyrene-1,8-quinone (P-1,8-Q) and benzo[a]pyrene-3,6-quinone (BP-3,6-Q) induced strikingly high levels of triradials. In addition, dicentrics and ring chromosomes were very common in BP-3,6-Q-treated cultures. Isomers of these compounds, pyrene-1,6-quinone (P-1,6-Q) and benzo[a]pyrene-1,6-quinone (BP-1,6-Q), induced unobtrusive patterns of chromosomal aberrations. We suspect that the P-1,8-Q and BP-3,6-Q moieties bound to the DNA were still reactive, and formed crosslinks and/or underwent redox cycling leading to high local concentrations of reactive oxygen species. In addition, P-1,8-Q and BP-3,6-Q induced c-mitoses, hyperdiploidies and polyploidies, in particular endoreduplications. These effects were not seen with the other two test compounds, or they were only detected at the highest concentrations used, which were strongly cytotoxic (c-mitoses with P-1,6-Q, polyploidies with BP-1,6-Q).

Purine enzyme profile in human colon-carcinoma cell lines and differential sensitivity to deoxycoformycin and 2'-deoxyadenosine in combination

Different cell lines, 2 from human colon carcinoma (LoVo and HT29) and 1 from Chinese hamster ovary (CHO K-I), were examined to assess the effect of deoxycoformycin (dCF), an inhibitor of adenosine deaminase (ADA), and 2'-deoxyadenosine (dAdo) on their growth. When used alone, neither dCF or dAdo were cytotoxic for the 3 cell lines, while their combination caused inhibition of cell growth, with the following sensitivity: CHO K-I > LoVo > HT29. We studied the pattern of enzymatic activities involved in the metabolism of dAdo in the 3 cell lines. The phosphorylation of dAdo by adenosine kinase appears to play a central role in the toxicity of the deoxynucleoside in combination with dCF. In fact, CHO K-I cells, which are the most sensitive, possess the highest level of this enzyme. Moreover, the cytotoxic effect was almost completely reversed in the 3 cell lines when inhibitors of adenosine kinase, such as 5'-amino-5'-deoxyadenosine and iodotubercidine, were added to the culture medium together with dCF and dAdo. In addition, baby hamster kidney (BHK) adenosine-kinase-deficient (AK-) cells were highly resistant to this treatment. Uptake inhibition of dAdo using dipyridamole also caused reversal of the toxicity. The AMP and deoxyAMP dephosphorylating activities, much lower in the CHO K-I cells, also appear to play a central role in the toxicity of dAdo when adenosine deaminase is inhibited. However, our data suggest that other factors may modulate the toxic effect, such as S-adenosyl-homocysteine-hydrolase inhibition by dAdo at high concentrations.

3-isobutyl-1-methylxanthine inhibits the mutagenic activity of 7,12-dimethylbenz[a]anthracene in epithelial liver cells in culture

The mutagenic activity of 7,12-dimethylbenz[a]anthracene in epithelial liver cells (CHEL) in culture was unaffected by the enhancement of intracellular cAMP induced to different extents and with different mechanisms by forskolin and 3-isobutyl-1-methylxanthine. However, the latter compound exerted antimutagenic effects (> 60%), which may be tentatively ascribed to inhibition of the inducible monooxygenase isoform(s) responsible for the specific biotransformation of 7,12-dimethylbenz[a]anthracene to highly mutagenic metabolites in CHEL cells.

Cytosolic 5'-nucleotidase/nucleoside phosphotransferase: a nucleoside analog activating enzyme?

Nucleoside phosphotransferase acting on inosine and deoxyinosine has been partially purified from cultured Chinese hamster lung fibroblasts (V79). The activity is associated with a cytosolic 5'-nucleotidase acting on IMP and deoxyIMP. The transfer of the phosphate group from IMP to inosine catalyzed by this enzyme was activated by ATP and 2,3-bisphosphoglycerate. Inosine, deoxyinosine, guanosine, deoxyguanosine, and the nucleoside analogs 2',3'-dideoxyinosine and 8-azaguanosine are substrates, while adenosine and deoxyadenosine are not. IMP, deoxyIMP, GMP, and deoxyGMP are the best phosphate donors. The cytosolic 5'-nucleotidase/phosphotransferase substrate, 8-azaguanosine, was found to be very toxic for cultured fibroblasts (LD50 = 0.32 microM). Mutants resistant to either 8-azaguanosine and the correspondent base 8-azaguanine were isolated and characterized. Our results indicated that the 8-azaguanosine-resistant cells were lacking both cytosolic 5'-nucleotidase and hypoxanthine-guanine phosphoribosyltransferase, while 8-azaguanine resistant cells were lacking only the latter enzyme. Despite this observation, both mutants displayed 8-azaguanosine resistance, thus indicating that cytosolic 5'-nucleotidase is not essential for the activation of this nucleoside analog.

Clastogenic effects of the dithiocarbamate fungicides thiram and ziram in Chinese hamster cell lines cultured in vitro

We report here the results obtained using the dithiocarbamate fungicides thiram and ziram to investigate the induction of chromosomal aberrations (CAs) in Chinese hamster ovary (CHO) cells both in the absence and presence of S9 metabolism, and in a Chinese hamster epithelial liver (CHEL) cells which retain metabolic competence to activate different classes of promutagens/procarcinogens. Both thiram and ziram proved to be strong chromosome breaking agents in the CHEL cells and CHO cells in the presence of S9 metabolism. These findings suggest that thiram and ziram require metabolic conversion to become genetically active, and corroborate the evidence that CHEL cells are suitable to activate and detect a broad spectrum of chemical procarcinogens including these two pesticides.

Application of an epithelial liver cell line, metabolically competent, for mutation studies of promutagens

Recently numerous attempts have been made to reduce the use of vertebrate animals in laboratory experiments to evaluate general and acute toxicity, mutagenesis and teratogenesis of new drugs or chemicals. One common approach is to use established, proliferating cell lines that preserve differentiated functions such as the competence to metabolize xenobiotics. To this end a continuous Chinese hamster epithelial liver cell line (CHEL cells) was established, cultured as used for mutagenesis studies. Structurally different promutagens, such as 7,12-dimethylbenz[a]anthracene (7,12-DMBA), benzo[a]pyrene (B(a)P), aflatoxin B1 (AB1) and cyclophosphamide (CP), were used in order to check and validate the test system. anti-Chrysene-1,2-diol 3,4-epoxide (CDE) and mitomycin C (MMC) were taken as representatives of direct mutagens. The genetic change induced by the mutagens was quantified by measuring mutation frequencies at the HGPRT locus. Several parameters, such as mutant expression time for each chemical, cell density for selection of mutants and enzymatic characterization for HGPRT phenotype, were examined to establish the optimal assay conditions. All promutagens analyzed significantly affected either the cloning efficiency and/or the mutant frequency of CHEL cells after 24 h of exposure. In addition, various enzyme activities involved in the metabolism of the promutagens were determined in CHEL cells, under the experimental conditions of chemical exposure used in the mutagenesis assay. The enzyme activities were compared with those found in uninduced Chinese hamster liver.

High sensitivity of Chinese hamster epithelial liver cells to toxic analogues of purines

The resistance of Chinese hamster epithelial liver cells (CHEL) and Chinese hamster fibroblasts (V79) towards toxic purine analogues has been determined. The liver cells are more sensitive than fibroblasts to 6-thioguanine (6-TG), 8-azaguanine (8-AZ) and 2,6-diaminopurine (DAP). The hypoxanthine-guanine (HGPRT) and adenine phosphoribosyl transferase (APRT) activities of extracts of CHEL cells were lower than those of corresponding extracts of V79. The level of 5'-nucleotidase was about 5-fold higher in the epithelial cells. It appears that HGPRT and APRT activities of extracts of liver epithelial cells are masked or reduced by 5'-nucleotidase activity and other inhibitors. The significance of these findings is discussed.

8-azaguanosine-5'-monophosphate synthesis via nucleoside kinase in cultured Chinese hamster lung fibroblasts

Cultured chinese hamster lung fibroblasts, and a variant clone selected for resistance to 8-azaguanine, that lacks hypoxanthine-guanine phosphoribosyl transferase (EC 2.4.2.8), have been tested for the ability to convert 8-azaguanine into 8-azaguanosine-5'-monophosphate via purine nucleoside phosphorylase and nucleoside kinase. Purine nucleoside phosphorylase of both cell types is able to synthesize 8-azaguanosine from 8-azaguanine with the same efficiency. Wild type cells possess a nucleoside kinase activity acting on 8-azaguanosine, but this activity is considerably lower in the cells displaying resistance to the base analog. Our lines of evidence demonstrate that purine nucleoside phosphorylase and nucleoside kinase constitute a possible way of synthesis of the cytotoxic mononucleotide of 8-azaguanine, and, in fact, cells selected for resistance to the base analog show an impairement in the nucleoside kinase activity.

Alpha-5-phosphoribosyl-1-pyrophosphate-independent salvage of purines in cultured Chinese hamster lung fibroblasts

A variant clone of cultured chinese hamster lung fibroblasts (V79), selected for resistance to 8-azaguanine (V79 azagrst), although lacking hypoxanthine-guanine phosphoribosyltransferase (EC 2.4.2.8), is able to convert hypoxanthine into IMP via purine-nucleoside phosphorylase (EC 2.4.2.1) and nucleoside kinase. In addition to the phosphoribosylation pathway, we also present evidence for the occurrence of a kinase-mediated pathway of recovery of hypoxanthine in the wild-type cells. The lower rate of formation of IMP in the V79 azagrst cells, apparently correlated with the phosphorylation of the nucleoside, suggests possible differences in the catalytic and/or regulatory properties of nucleoside kinase in the two cell lines. This fact might be of particular relevance in evaluating the mechanisms of resistance to purine analogs displayed by several cell types.

Induction of sister-chromatid exchanges by procarcinogens in metabolically competent Chinese hamster epithelial liver cells

An epithelial cell strain has been established from the livers of male Chinese hamsters (CHEL cells). These cells, which proliferate in culture and retain their metabolic enzymatic activities during several subcultures, were used in a sister-chromatid exchange assay to evaluate the effectiveness of polycyclic aromatic hydrocarbons (PAHs), aflatoxin B1 (AFB1) and cyclophosphamide (CP). The results obtained demonstrate that CHEL cells are metabolically competent to activate different classes of procarcinogens into biologically active metabolites. Moreover, they showed a selective capacity to discriminate chemical carcinogens from noncarcinogens. Thus, the CHEL cell system appears to be a promising alternative to the short-term tests that include cell-free rodent liver homogenate to evaluate new promutagens and/or procarcinogens.

Characterization of an epithelial, nearly diploid liver cell strain, from Chinese hamster, able to activate promutagens

Epithelial liver cells of the Chinese hamster (CHEL cells) were propagated in culture for 35 passages. At favourable cell densities, the population doubling time in normal medium, was 20 h. L-Tyrosine amino transferase activity was retained at a measurable level, but its enhancement by dexamethasone was detected solely in cells of early passages. Pyruvate kinase was strongly activated by fructose-1,6-biphosphate at low substrate concentrations. These enzymatic properties suggest that the CHEL cells are derived from a sub-population of parenchymal hepatocytes or from cells closely related to parenchymal hepatocytes. With a lag period of a few hours, CHEL cultures metabolized benzo[a]pyrene. In cell homogenates the various monooxygenase activities investigated were below the detection limits. However, other xenobiotic-metabolizing activities, such as cytochrome P-450 reductase, glutathione transferase and UDP-glucuronosyl-transferase were high, with levels comparable to those observed in freshly isolated rat parenchymal cells. Epoxide hydrolase activity was also detected, but was lower than in the liver. The CHEL cells were able to activate benzo[a]pyrene, 7,12-dimethylbenz[a]anthracene and aflatoxin B1 to mutagens, as shown in a co-culture assay with V79 cells, in which acquisition of resistance to 6-thioguanine was studied. At early passages, the CHEL cells had a near diploid set of chromosomes. Then, gradually the frequency of cells with slight changes in the number of chromosomes and the frequency of tetraploids were increased. During the observation period (up to passage 20) the modal number of chromosomes shifted from 22 to 23. No gross morphological changes in the cultures were noticed during the 20 passages.(ABSTRACT TRUNCATED AT 250 WORDS)

A benzo[a]pyrene metabolite-DNA adduct occurring in the activating cell but not in exogenous DNA

[3H]Benzo[a]pyrene (BP) and salmon sperm DNA were incubated with hepatocytes from 5,6-benzo-flavone-treated rats. The cellular DNA and the exogenously added DNA were separately isolated, hydrolyzed and chromatographed on a Sephadex LH-20 column. The extracellular DNA yielded 3 peaks of radioactivity in the chromatographic eluate. The cellular DNA contained an additional peak suggesting the formation of a DNA adduct from a metabolite that does not leave the cell.

Structure activity relationship of epoxides: different mutagenicity of the two diastereoisomeric 3-bromo-1,2-epoxycyclohexanes

The mutagenic activities in V79 Chinese hamster cells and the alkylating abilities towards nicotinamide of the two diastereisomeric cis and trans-3-bromo-1,2-epoxycyclohexanes were measured and compared with those of unsubstituted 1,2-epoxycyclohexane and bromocyclohexane. trans-3-Bromo-1,2-epoxycyclohexane exhibited a mutagenic activity 2.5 times higher than that of its cis diastereoisomer, but very similar to that of the parent unbrominated epoxide, whereas the electrophilic reactivities towards nicotinamide were very similar for the three epoxides tested. Bromocyclohexane showed the highest toxicity, but no alkylating ability. The presence of an epoxide hydrolase activity in the V79 Chinese hamster cells used in the mutagenesis tests has been demonstrated using safrole oxide as the substrate, cis-3-Bromo-1,2-epoxycyclohexane, but not its trans diastereoisomer, is hydrolyzed by the enzyme present in microsomal preparations from the V79 cells. The results indicate that for the cycloaliphatic compounds examined: (1) the introduction of a bromide substituent at the carbon adjacent to the oxirane ring does not cause an increase in mutagenicity, (2) the relative stereochemical configuration at the above carbon does affect the biological activity and (3) the significantly different mutagenicity of the two diastereoisomeric 3-bromo-1,2-epoxycyclohexanes is not attributable to a different electrophilic reactivity, but could be related to some specific interaction with detoxifying enzymes present in the V79 Chinese hamster cells used in the biological experiments.

Metabolism of vinylcyclooctane and partition ratio between epoxide formation and cytochrome P-450 destruction

Vinylcyclooctane (VCO), which binds to the active site of cytochrome P-450 (P-450) giving a type I difference spectrum, has been found to form the corresponding epoxide as the main metabolite on treatment with liver microsomal monooxygenase obtained from phenobarbital-treated or untreated mice. During this metabolic process about 40% of the microsomal P-450 isozymes are destroyed, but the remainder still demethylates aminopyrine. Approx. 180 molecules of VCO are turned over and 132 of epoxyethylcyclooctane (EECO) are formed for each destructive event.

Dinemorphan N-demethylation by mouse liver microsomes

Dinemorphan, an antitussive drug, is N-demethylated in vitro by mouse liver microsomes with biphasic kinetics showing two apparent Km and Vmax. Moreover, dinemorphan N-demethylation is inhibited by CO, SKF-525A, metyrapone and it is specifically catalyzed by a phenobarbital-inducible form of cytochrome P-450.

The reaction of 3,4-epoxy-1-butene with deoxyguanosine and DNA in vitro: synthesis and characterization of the main adducts

The reaction of guanosine with 3,4-epoxy-1-butene in acetic acid gives two main products of N-7 alkylation. After acidic hydrolysis the two aglycones have been isolated by h.p.l.c. and shown to be the regioisomeric 7-(2-hydroxy-3-buten-1-yl) guanine (I) and 7-(1-hydroxy-3-buten-2-yl) guanine (II), arising through nucleophilic attack by N-7 of the purine at the two oxirane carbons of 3,4-epoxy-1-butene. Spectral characteristics of both compounds are presented, including u.v., 1H-n.m.r. and mass spectra. Deoxyguanosine reacts with 3,4-epoxy-1-butene in 50% methanol-water at 37 degrees C to give the N-7 alkylated deoxynucleosides corresponding to I and II in a 59:41 ratio. The reaction rate depends on the nucleoside concentration, with second order rate constants at 37 degrees C of 1.6 X 10(-2) and 1.1 X 10(-2) h-1 M-1 for the formation of the two deoxynucleoside adduct corresponding to I and II, respectively. The same two compounds I and II in a similar (54:46) ratio have been identified after acidic or thermal hydrolysis of DNA which had been reacted with 3,4-epoxy-1-butene under similar conditions. The half life for the spontaneous depurination of I and II in the adducted DNA under physiological conditions (37 degrees C, pH 7.2) is 50 h.

Metabolism of 1,3-cyclohexadiene by isolated rat liver cells

The metabolism of 1,3-cyclohexadiene by hepatocytes from phenobarbital induced rat has been investigated. Parenchymal cells were obtained by liver perfusion with a hyaluronidase-collagenase mixture. The addition of the diene to a suspension of hepatocytes gave rise to a type I difference spectrum indicating the formation of an enzyme-substrate complex with cytochrome P-450. The subsequent metabolic pathway of 1,3-cyclohexadiene has been shown to involve, as the first step, the formation of 1,2-epoxy-3-cyclohexene, which is rapidly hydrolyzed to trans-3-cyclohexene-1,2-diol and trans-2-cyclohexene-1,4-diol by a non-enzymatic process. The monoepoxide could not be detected in the incubation medium because of its high reactivity. Therefore, kinetic parameters of the epoxidation reaction were determined by following the rate of production of the diols. When incubated with hepatocytes, trans-3-cyclohexene-1,2-diol, the main product of 1,3-cyclohexadiene metabolism, elicited a reverse type I spectrum, indicating that this compound is not a good substrate for the monooxygenase system.

Loss of hepatic monooxygenase activities, glutathione, and 'green pigment' formation after the administration of vinyl-cyclooctane to mice

Vinylcyclooctane, when administered to mice at 500 mg/kg, produced reduction of microsomal cytochrome P-450, heme, aminopyrine-N-demethylase and ethoxycoumarin-O-deethylase activities with respect to control values; furthermore the hepatic reduced glutathione level was depleted suggesting that glutathione is involved in the vinylcyclooctane metabolism. The reduction of cytochrome P-450 and monooxygenase activities was accompanied by the formation of abnormal 'green pigments'.

Mutagenicity of 3 structurally related epoxides, with defined stereochemical configuration, in Saccharomyces cerevisiae and in V79 Chinese hamster cells

3 structurally related epoxides, 3,4-epoxycyclohexene, trans-1,2,3,4-diepoxycyclohexane and trans-3,4-epoxycyclohexane-r-1,trans-2-diol (anti isomer) were tested for their ability to induce both point mutation, mitotic gene conversion and recombination in a diploid strain (D7) of the yeast Saccharomyces cerevisiae, with and without a mammalian microsomal activation system, and the formation of 6-thioguanine-resistant mutants in V79 hamster cells. Genetic effects were related to the alkylating properties of the epoxides, as measured by alkylation of 4-(p-nitrobenzyl)pyridine (NBP). Of the 3 epoxides, only 3,4-epoxycyclohexene, characterized by the highest reactivity towards NBP, induced all genetic effects in both test systems. A marginal activity was shown by trans-1,2,3,4-diepoxycyclohexane only in the yeast. The lack of genetic activity of the anti isomer of 3,4-epoxycyclohexane-1,2-diol, in spite of the formal similarity of its functional groups with those present in mutagenic polycyclic arene epoxydiols, was attributed to the dramatic reduction of lipophilicity of the molecule.