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P J O'Brien

Publications and source records attributed to P J O'Brien.

At least 73 records · Page 4Linked to original sources
PubMed1997

Locking intramedullary nailing with and without reaming for open fractures of the tibial shaft. A prospective, randomized study.

Ninety-one patients who had ninety-four open fractures of the tibial shaft were randomized into two treatment groups. Fifty fractures (nine type-I, eighteen type-II, sixteen type-IIIA, and seven type-IIIB fractures, according to the classification of Gustilo et al.) were treated with nailing after reaming, and forty-four fractures (five type-I, sixteen type-II, nineteen type-IIIA, and four type-IIIB fractures) were treated with nailing without reaming. The average diameter of the nail was 11.5 millimeters (range, nine to fourteen millimeters) in the group treated with reaming and 9.2 millimeters (range, eight to ten millimeters) in the group treated without reaming. Follow-up information was adequate for forty-five patients (forty-seven fractures) who had been managed with reaming and forty patients (forty-one fractures) who had been managed without reaming. No clinically important differences were found between the two groups with regard to the technical aspects of the procedure or the rate of early postoperative complications. The average time to union was thirty weeks (range, thirteen to seventy-two weeks) in the group treated with reaming and twenty-nine weeks (range, thirteen to fifty weeks) in the group treated without reaming. Four (9 per cent) of the fractures treated with reaming and five (12 per cent) of the fractures treated without reaming did not unite (p = 0.73). There were two infections in the group treated with reaming and one in the group treated without reaming. Significantly more screws broke in the group treated without reaming (twelve; 29 per cent) than in the group treated with reaming (four; 9 per cent) (p = 0.014). There was no difference between the two groups with regard to the frequency of broken nails (two nails that had been inserted after reaming broke, compared with one that had been inserted without reaming). The functional outcome, in terms of pain in the knee, range of motion, return to work, and recreational activity, did not differ significantly between the groups. We concluded that the clinical and radiographic results of nailing after reaming are similar to those of nailing without reaming for fixation of open fractures of the tibial shaft, although more screws broke when reaming had not been done.

Adolescent↗
PubMed1997

Interlocking intramedullary nailing with and without reaming for the treatment of closed fractures of the tibial shaft. A prospective, randomized study.

One hundred and fifty-two patients who had 154 closed fractures of the shaft of the tibia were prospectively randomized to management with interlocking intramedullary nailing either with or without reaming. Thirteen patients who had been randomized to treatment without reaming were switched to the group that had reaming because of technical reasons; these patients were excluded from the analysis of the results. An additional five patients were lost to follow-up. Thus, seventy-two patients (seventy-three fractures) who had been managed with nailing with reaming and sixty-three patients (sixty-three fractures) who had been managed with nailing without reaming were available for follow-up at an average of twelve months (range, three to thirty-three months) postoperatively. The two groups were similar with regard to demographics and the configurations of the fractures. The average total duration of the procedures performed without reaming was eleven minutes shorter than that of the procedures done with reaming (p = 0.0013). The duration of fluoroscopy was not significantly different between the two groups (p = 0.35, Mann-Whitney test). The average estimated blood loss was identical for the two groups. Seventy fractures (96 per cent) that were treated with nailing with reaming and fifty-six (89 per cent) that were treated with nailing without reaming united without the need for an additional operation (p = 0.19). Because of the small sample size, the study has insufficient power (34.7 per cent) to detect this difference if it is real. There was only one deep infection, which developed after nailing without reaming. The nail fractured after one procedure with reaming. A screw fractured after two procedures with reaming and after ten without reaming (p = 0.012); multiple screws fractured after three procedures in the latter group. Malunion occurred after three nailing procedures with reaming and after two without reaming. Four malunions were of very proximal fractures and one was of a very distal fracture. Seventeen screws and twenty-four nails were removed after nailing with reaming, and twenty screws and nineteen nails were removed after nailing without reaming; neither of these prevalences was significantly different between the two groups (p = 0.27 and 0.89; chi-square test). We concluded that there are no major advantages to nailing without reaming as compared with nailing with reaming for the treatment of closed fractures of the shaft of the tibia. There was a higher prevalence of delayed union and breakage of screws after nailing without reaming.

Adult↗
PubMed1997

Deficiencies of myocardial troponin-T and creatine kinase MB isoenzyme in dogs with idiopathic dilated cardiomyopathy.

OBJECTIVE: To test the hypothesis that the derangement of myocardial energy homeostasis characteristic of idiopathic dilated cardiomyopathy (IDCM) of Doberman Pinschers was attributable to deficiency of creatine kinase (CK) isoenzyme MB relative to CK isoenzyme MM and troponin-T (Tn-T). ANIMALS: 9 Doberman Pinschers with advanced congestive heart failure attributable to IDCM and 9 mixed-breed dogs without cardiac disease (controls). PROCEDURE: Myocardial myofibrillar CK-MM, mitochondrial CK, and cytosolic CK-MB activities were determined in comparison with the concentration of cardiac-specific, myofibrillar protein Tn-T. Myocardial biopsy specimens were obtained after euthanasia and were ultrafrozen. Isoenzymes of CK were separated electrophoretically, and their activity was determined, using a coupled-enzyme, kinetic, fluorescent assay and densitometry. Troponin-T content was determined by immunoassay. RESULTS: Myofibrillar CK-MM and mitochondrial CK activities and Tn-T content were 25% lower in the dogs with IDCM than in controls, whereas cytosolic CK-MB activity was 50% lower. CONCLUSION: Deficiency of CK-MB activity is a component of and may have a central role in the energy deficiency characteristic of failing myocardium in IDCM of Doberman Pinschers. A side-product of this study was the observation that, in dogs, CK-MB activity and Tn-T content of myocardium are sufficiently high to be candidate serum markers for active cardiac injury.

Animals↗
PubMed1997

Enhancement of calcium cycling by atrial sarcoplasmic reticulum after cardiopulmonary bypass and cardioplegia during open heart surgery.

We studied myocardial Ca2+ cycling during cardiopulmonary bypass and cold-blood cardioplegia (CPB/CBC) in patients with coronary heart disease undergoing coronary artery bypass grafting. Right atrial biopsies were taken from 13 patients before and after CPB/CBC: after pericardiotomy, immediately after aortic cross-clamp removal, and following termination of CPB/CBC. Changes in ionized Ca2+ concentration (nM) were monitored with indo 1 during Ca2+ uptake and Ca2+ release by sarcoplasmic reticulum in a medium containing 1% homogenized myocardium. Ryanodine inhibition was used to estimate Ca2+ release channel activity. With CPB/CBC, the initial Ca2+ concentration of reaction media increased 33%, (962 +/- 150 to 1262 +/- 106 nM; mean +/- SD). Ca2+ cycling increased asymmetrically, 108% for Ca2+ uptake (3.91 +/- 1.32 to 8.15 +/- 3.17 nM/s), 197% for Ca2+ release (0.90 +/- 0.80 to 2.73 +/- 1.13 nM/s), and 68% for the ratio of Ca(2+)-release to Ca(2+)-uptake activities (0.22 +/- 0.14 to 0.37 +/- 0.13). The dissociation constant of the Ca2+ pump for Ca2+ was unaltered by CPB/CBC (289 +/- 76 nM). During the time period that was studied post-bypass, Ca(2+)-pump activity remained increased, although the Ca(2+)-channel activity returned to pre-bypass values (all p < 0.05). We conclude that CPB/CBC produces increased myocardial Ca2+ load, twofold increased Ca2+ uptake, and threefold increased Ca2+ release by sarcoplasmic reticulum.

Calcium↗
PubMed1997

Cardiac troponin T is a sensitive, specific biomarker of cardiac injury in laboratory animals.

A reliable serum assay that can discriminate between cardiac and skeletal muscle injury is not available for diagnostic use in laboratory animals. We tested and supported the hypotheses that serum cardiac troponin T (cTnT) was widely applicable in laboratory animals as a biomarker of cardiac injury arising from various causes; that it increased in proportion to severity of cardiac injury; and that it was more cardiospecific than creatine kinase (CK) or lactate dehydrogenase (LD) isozyme activities. In canine and rat models of myocardial infarction, cTnT concentration increased 1,000- to 10,000-fold and was highly correlated with infarct size within 3 h of injury. Serum CK and LD isozymes were substantially less effective biomarkers and, in contrast to cTnT, were ineffective markers in the presence of moderate skeletal muscle injury, with resulting serum CK activity > 5,000 U/L. Using these animal models, and mouse and ferret models, we also showed cTnT to be an effective biomarker in doxorubicin cardiotoxicosis, traumatic injury, ischemia, and cardiac puncture. Reference range serum concentrations for all species were at the detection limit of the assay, except those for mice, in which they were slightly increased, possibly because mice were used to generate assay monoclonal antibodies. We conclude that cTnT is a powerful biomarker in laboratory animals for the sensitive and specific detection of cardiac injury arising from various causes.

Animals↗
PubMed1997

Differential reactivity of cardiac and skeletal muscle from various species in a cardiac troponin I immunoassay.

To identify a blood test that can differentiate cardiac from skeletal muscle injury in animals, we compared tissue reactivities for various species with the use of an immunoassay for human cardiac troponin I (cTnI). Tissue reactivity varied as a function of the homology of tissue troponin with human cTnI. Cardiac reactivity in large mammals was equivalent to cTnI, 9.8 +/- 0.6 mg/g, and was 2-fold, 10-fold, and 100-fold greater than in small mammals, birds, and fish, respectively. Skeletal muscle reactivity was equivalent to cTnI, 5.1 +/- 0.6 micrograms/g, in all species except fish, in which it was 50% lower. The ratio of reactivities of cardiac and skeletal muscle was: 1800 in large mammals, 1100 in small mammals, 230 in birds, and 43 in fish. We conclude that cTnI is a powerful candidate in mammals, a possible candidate in birds, but unlikely to be of use in fish as a sensitive and tissue-selective diagnostic test for cardiac injury.

Animals↗
PubMed1996

Involvement of nitric oxide in nitroprusside-induced hepatocyte cytotoxicity.

Sodium nitroprusside (SNP) cytotoxicity towards rat hepatocytes was accompanied by peroxynitrite formation, lipid peroxidation, inhibition of glycolysis, cyanide (CN) release, partial inhibition of hepatocyte respiration, and ATP depletion. Antioxidants and desferoxamine prevented both cytotoxicity and lipid peroxidation induced by SNP. The CN antidote thiosulfate or the CN trapping agents dihydroxyacetone and glyceraldehyde increased SNP metabolism, SNP-induced peroxynitrite formation, cytotoxicity, and lipid peroxidation. On the other hand, addition of non-toxic concentrations of CN to hepatocytes prevented SNP metabolism and SNP-induced lipid peroxidation and cytotoxicity. SNP depleted hepatocyte GSH immediately upon addition, and GSH-depleted hepatocytes were more susceptible to SNP. The results of this study suggest that nitric oxide rather than CN mediates SNP cytotoxicity in isolated cells.

Animals↗
PubMed1996

Antidotal effect of dihydroxyacetone against cyanide toxicity in vivo.

Potassium cyanide (CN) intoxication in mice was found to be effectively antagonized by dihydroxyacetone (DHA), particularly if administered in combination with another CN antidote, sodium thiosulfate. Cyanide-induced convulsions were also prevented by DHA treatment, either alone or in combination with thiosulfate. Injection (i.p.) of DHA (2 g/kg) 2 min after or 10 min before CN (s.c.) increased LD50 values of CN(8.7 mg/kg) by factors of 2.1 and 3.0, respectively. Treatment with a combination of DHA and thiosulfate after CN increased the LD50 by a factor of 2.4. Pretreatment with a combination of DHA and thiosulfate (1 g/kg) increased the LD50 of CN to 83 mg/kg. Administration of alpha-ketoglutarate (2.0 g/kg), but not pyruvate, 2 min after CN increased the LD50 of CN by a factor of 1.6. Brain, heart and liver cytochrome oxidase activities were also measured following in vivo CN treatment with and without DHA. Pretreatment with DHA prevented the inhibition of cytochrome oxidase activity by CN and treatment with DHA after CN accelerated the recovery of cytochrome oxidase activity, especially in brain and heart homogenates. DHA is a physiological agent and, therefore, could prove to be a safe and effective antidote for CN, particularly in cases of fire smoke inhalation in which a combination of CN and carbon monoxide is present. In these cases the normally used antidote, sodium nitrite, to induce methemoglobin so as to trap the CN, is contraindicated because some of the oxygen-carrying capacity of the blood will have already been diminished by carbon monoxide.

Animals↗
PubMed1996

The prevention of CCl4-induced liver necrosis in mice by naturally occurring methylenedioxybenzenes.

Methylenedioxybenzenes (MDBs) and structurally related alkenylbenzenes were compared for their effectiveness in preventing carbon tetrachloride (CCl4)-induced liver necrosis in mice. Pretreatment with isosafrole, safrole, dihydrosafrole, and benzodioxole at dosages as low as 10 mg/kg significantly prevented the increase in plasma transaminase levels and histochemical changes associated with CCl4-induced liver necrosis, whereas piperonyl butoxide (PBO), eugenol, isoeugenol, sesamol, and curcumin did not prevent CCl4 hepatotoxicity even at 200 mg/kg. However, isosafrole was only partly hepatoprotective if administered 10 min after the toxicant. Liver microsomes isolated 1 hr after isosafrole but not after PBO administration had a markedly decreased CYP2E1 activity. Isosafrole, safrole, dihydrosafrole, and benzodioxole in vitro also inhibited CYP2E1-dependent metabolism more effectively than eugenol and isoeugenol, whereas PBO did not inhibit CYP2E1 activity. The protective effects of isosafrole, safrole, and benzodioxole were therefore predominantly attributed to their ability to inactivate CYP2E1, the major isozyme involved in CCl4 bioactivation. The marked potentiation of CCl4 hepatotoxicity in CYP2E1-induced mice was also completely prevented by isosafrole but not PBO pretreatment, supporting the hypothesis that CYP2E1 inhibition by isosafrole contributes to its hepatoprotective effect against CCl4. Isosafrole and safrole also prevented bromotrichloromethane (BrCCl3)-induced hepatocyte cytotoxicity, whereas PBO was ineffective.

Animals↗
PubMed1996

The involvement of cytochrome P450 peroxidase in the metabolic bioactivation of cumene hydroperoxide by isolated rat hepatocytes.

Organic hydroperoxides are believed to be primarily detoxified in cells by the GSH peroxidase/GSSG reductase system and activated to cytotoxic radical species by non-heme iron. However, organic hydroperoxides seem to be bioactivated by cytochrome P450 (P450) in isolated hepatocytes as various P450 (particularly P450 2E1) inhibitors inhibited cumene hydroperoxide (CumOOH) metabolism and attenuated subsequent cytotoxic effects including antimycin A-resistant respiration, lipid peroxidation, iron mobilization, ATP depletion, and cell membrane disruption. CumOOH metabolism was also faster in P450 1A-induced hepatocytes and was inhibited by the P450 1A inhibitor alpha-naphthoflavone. The ferric chelator deferoxamine also prevented cytotoxicity even after CumOOH had been metabolized but had no effect on CumOOH metabolism. This emphasizes the toxicological significance of the iron released following hydroperoxide metabolic activation by cytochrome P450. The radical trap, 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO), had no effect on CumOOH metabolism but prevented CumOOH-induced antimycin A-resistant respiration, lipid peroxidation, iron mobilization, and loss of membrane integrity. These results suggest that CumOOH is metabolically activated by some P450 enzymes (e.g., P450 2E1) in hepatocytes to form reactive radical metabolites or oxidants that cause lipid peroxidation and cytotoxicity.

Animals↗
PubMed1996

Reamed nailing of open tibial fractures: does the antibiotic bead pouch reduce the deep infection rate?

Eighty-one open tibial fractures were treated by reamed intramedullary nailing. There were 38 type II, 23 type IIIa and 20 type IIIb injuries. At the end of the nailing procedure the first 26 fractures (15 type II, five type IIIa, and six type IIIb) had antibiotic prophylaxis and delayed closure of the open wound. The subsequent 55 fractures (23 type II, 18 type IIIa, and 14 type IIIb) had identical management but in addition had an antibiotic bead pouch inserted into the open wound following debridement. Three amputations were performed: one (3.8%) in the group treated without a bead pouch and two (3.6%) in the bead pouch group in patients with grade IIIb fractures and severe crushing injuries. Of the remainder, there were four deep infections (16%) in the 25 fractures treated prior to the use of the bead pouch and two (4%) deep infections in the 53 fractures following introduction of the bead pouch. Addition of the bead pouch to the wound management protocol was associated with a worthwhile reduction of deep infection.

Adolescent↗
PubMed1996

Range of motion and complications after postburn heterotopic bone excision about the elbow.

OBJECTIVE: To review the results of surgical management of heterotopic ossification about the elbow in burned patients. DESIGN: Retrospective analysis with long-term patient follow-up. MATERIALS AND METHODS: Eleven patients with 16 elbows requiring surgery were admitted between January 1, 1982 and December 31, 1993. A posterior approach to the elbow with release of the encased ulnar nerve +/- anterior transposition and transolecranon osteotomy to access extensive bone formation in the olecranon fossa was employed. Eight patients (11 elbows) were available for long-term follow-up conducted at mean 50 +/- 13 months after surgery. Long-term follow-up consisted of measurement of range of elbow motion, as well as clinical assessment of ulnar nerve function. MAIN RESULTS: For the 11 elbows examined postoperatively, the mean range of motion preoperatively in flexion-extension was 11 degrees +/- 5 degrees compared to 89 degrees +/- 12 degrees postoperatively (p < 0.001). Three patients with poor long-term results had ankylosis of the joint preoperatively. Of four patients with ulnar nerve paresis preoperatively, none had ulnar nerve dysfunction at follow-up. Of 16 elbows operated on, four (25%) had postoperative complications. Two suffered soft-tissue breakdown with hardware exposure requiring abdominal flap closure, one early failure of olecranon fixation, and one late infected hardware. CONCLUSIONS: Surgery for both limited range of motion as well as ulnar nerve compression is effective in cases of heterotopic ossification about the elbows of burned patients. Early operative intervention is indicated in progressive disease, particularly ulnar nerve palsy, if soft-tissue quality is adequate. Complications with 25% of elbows suggest that use of olecranon osteotomy for joint access may warrant review.

Adult↗
PubMed1996

The involvement of cytochrome P4502E1 in 2-bromoethanol-induced hepatocyte cytotoxicity.

The cytotoxicity of 2-bromoethanol towards hepatocytes isolated from rats was concentration-dependent (EC(50)100 mu M, 2 hr). Bromoacetaldehyde was more toxic (EC(50)60 mu M, 2 hr) and bromoacetic acid was less toxic (EC(50)150 mu M, 2 hr). Glutathione (GSH) depletion occurred before cytotoxicity ensued and GSH depleted hepatocytes were more susceptible to 2-bromoethanol. Lipid peroxidation increased steadily 1 hr after 2-bromoethanol addition and antioxidants, iron chelators or hypoxia prevented 2-bromoethanol induced lipid peroxidation and cell lysis. Alcohol dehydrogenase inhibitors, methyl pyrazole or dimethyl sulfoxide only partly prevented 2-bromoethanol induced GSH depletion, lipid peroxidation and cytotoxicity. However, cytochrome P4502E1 (CYP2E1) inhibitors/substrates were more effective at preventing 2-bromoethanol-induced GSH depletion, lipid peroxidation and cytotoxicity suggesting that 2-bromoethanol is mostly metabolically activated by CYP2E1. Also, hepatocytes isolated from CYP2E1 induced rats were more susceptible to 2-bromoethanol and hepatocytes isolated from rats pretreated with carbon disulfide to inactivate CYP2E1 were more resistant to 2-bromoethanol treatment. Formation of S-(formylmethyl)glutathione during 2-bromoethanol metabolism by microsomal mixed function oxidase in the presence of GSH was also prevented by cytochrome P4502E1 inhibitors/substrates or by Anti-Rat CYP2E1. Furthermore, aldehyde dehydrogenase inhibitors-cyanamide or chloral hydrate increased 2-bromoethanol dependent hepatocyte susceptibility. This suggests that 2-bromoethanol is preferably metabolised by CYP2E1 dependent monoxygenase to form 2-bromoacetaldehyde which causes cell lysis as a result of GSH depletion and lipid peroxidation.

1-Propanol↗
PubMed1996

Chemical carcinogenesis, mutagenesis, and teratogenesis.

An international symposium entitled Chemical Carcinogenesis, Mutagenesis and Teratogenesis: a Tribute to James and Elizabeth Miller was held in Toronto, Ont., July 19, 1994. This symposium theme was discussed in the presence of James Miller, 79 years young, who with his wife, Elizabeth Miller (1920-1987), are considered to be the pioneers of this medical and environmental toxicology research field. It is generally believed that the susceptibility of an individual to chemical carcinogenesis or teratogenesis varies considerably depending upon their genetic makeup, diet, lifestyle, and their environmental exposure. One goal of the research discussed at this symposium was an examination of the role of the enzymes involved in the metabolic activation and detoxification of carcinogens and teratogens. The interindividual variabilities in the levels and activity of these enzymes could contribute to the susceptibility of the individual to chemical carcinogens or teratogens. At the symposium evidence was presented indicating that theta-class glutathione (GSH) S-transferase levels activate dihalomethanes and could therefore initiate the carcinogenic response to butadiene and 1,2-dibromo-3-chloropropane. The dramatic genetic polymorphism of this class of GSH S-transferase could thereby contribute to the individual's susceptibility to these carcinogens. Similarly, the GSH S-transferase and GSH levels in the embryo and yolk sac that are determined during organogenesis could also be important factors in determining the susceptibility of the embryo to teratogens. The levels of cytochrome P450 1A2, aromatic amine N-acetyltransferases, and sulfotransferases could also determine the susceptibility of the individual to carcinogenic arylamines. Accordingly, an Ames tester strain was described that was genetically engineered so as to express both aromatic amine N-acetyltransferase and human cytochrome P450 1A2. This should prove useful for predicting which arylamines are likely to be carcinogenic to humans. Nonsteroidal anti-inflammatory drugs may also prove useful in inhibiting the cytochrome P450s that activate the nitrosamines found in tobacco smoke suspected to cause lung cancer. Finally, the sulfotransferase isoforms involved in the metabolic activation of carcinogenic arylamines were identified.

Biotransformation↗
PubMed1996

Effect of a high omega-3 fatty acid diet on cardiac contractile performance in Oncorhynchus mykiss.

OBJECTIVE: Omega-3 fatty acids have been implicated in the amelioration of cardiovascular disease in humans. Since these fatty acids are found in salmonid fish and are known to be essential for all salmonids, this study was undertaken to determine the effect of a high dietary intake of omega-3 fatty acids on the function of trout myocardium. METHODS: Rainbow trout (Oncorhynchus mykiss) from a single stock population were divided into two groups and fed either a diet high in omega-3 fatty acids (i.e. 4.0%) or low in omega-3 fatty acids (i.e. 2.1%) for 3 months. Heart function was studied at the whole heart and isolated muscle level. RESULTS: In whole heart preparations, peak developed pressures in freely ejecting hearts from salmonids fed the high omega-3 fatty acid diet were significantly greater than the hearts from salmonids fed the low omega-3 fatty acid diet (21 +/- 1.5 vs. 11.5 +/- 0.9 mmHg respectively, P < 0.05). These data correlated with results from isolated muscle preparations of myocardium from fish fed high and low omega-3 fatty acid diets (4.12 +/- 0.32 vs. 3.08 +/- 0.28 mN/mm2 respectively, P < 0.05). The calcium uptake rate of heart homogenates from fish fed the high omega-3 diet was slower and sarcoplasmic reticulum Ca2+ ATPase activity was lower. The myofilament force-calcium relationship in myocardium from trout fed the low omega-3 diet was shifted leftward on the calcium axis to lower intracellular calcium concentrations (delta 0.4 pCa units) compared to mammalian myocardium. This resulted in greater activation at lower intracellular calcium concentrations. However, trouts fed diets high in omega-3 fatty acids had [Ca2+] required for half maximal activation more similar to what has been reported for mammalian myocardium (delta 0.1 pCa unit). Furthermore, the myofilaments of trout hearts appear to show less cooperativity (Hill coefficient approximately 1) than has been found in mammalian myocardium (Hill coefficient > or = 2). CONCLUSIONS: Our experimental results demonstrate for the first time that dietary omega-3 fatty acid content affects myocardial force of contraction by affecting calcium metabolism and myofilament calcium-activation.

Actin Cytoskeleton↗
PubMed1996

Cytotoxic mechanisms of anti-tumour quinones in parental and resistant lymphoblasts.

The group I aziridinylquinone anti-cancer agents mitomycin C, diaziquone or trenimon were much more cytotoxic to DT-diaphorase-enriched L5178Y/HBM10 lymphoblasts than parental L5178Y cells and caused little oxygen activation. Furthermore, inactivation of cellular DT-diaphorase prevented cytotoxicity whereas catalase did not affect cytotoxicity. This suggests that DT-diaphorase activated these agents and the hydroquinone formed mediated DNA alkylation, crosslinking and cytotoxicity. The group II quinone agents phenanthrenequinone, 2-amino-1, 4-naphthoquinoneimine or naphthazarin were also more cytotoxic to L5178Y/HBM10 cells than parental cells and caused considerable oxygen activation. Inactivation of DT-diaphorase, however, prevented both oxygen activation and cytotoxicity. Furthermore added catalase decreased cytotoxicity, whereas catalase inactivation enhanced cytotoxicity. This suggests that DT-diaphorase activated these agents and the hydroquinone formed caused extensive oxygen activation sufficient to cause DNA oxidative damage and cytotoxicity. The group III quinone agents menadione, 2,3-dimethoxy-1,4-naphthoquinone and 2,6-dimethoxy-benzoquinone, on the other hand, were more cytotoxic to the parental cells than L5178Y/HBM10 cells and caused less oxygen activation than group II agents. Furthermore, inactivation of DT-diaphorase enhanced cytotoxicity and prevented oxygen activation than group II agents. Oxygen activation was therefore also attributed to hydroquinone autoxidation. However catalase did not affect cytotoxicity towards parental cells. This suggests that DT-diaphorase detoxified group III quinones and that cytotoxicity may involve DNA oxidative damage by the semiquinone radicals.

Animals↗
PubMed1996

2-Chloroacetaldehyde-induced cerebral glutathione depletion and neurotoxicity.

2-Chloroacetaldehyde (CAA) formed during the metabolism of the anti-cancer drug ifosfamide (IP) has been implicated in ifosfamide-related neurotoxicity during chemotherapy but the neurotoxic mechanisms are unknown. We have found that IP (900 mg kg-1, p.o.) caused lethargy and mild hind limb paralysis after 6 h. Neurotoxicity and IP-induced mortality was markedly enhanced in mice pretreated with either phenobarbital or dexamethasone to induce cytochrome P4503A. Cerebral glutathione (GSH) levels were also markedly depleted in these pretreated mice. 2-Chloroethanol (92 mg kg-1, i.p.) (CE) also caused a 50% reduction in cerebral GSH 6 h after administration to mice. At this time maximum lethargy and unresponsiveness to touch was apparent in CE-treated mice. Severe hind limb paralysis developed and death ensued 12-18 h later. Prior depletion of cerebral GSH with 2-cyclohexene-1-one greatly accelerated the onset of CE-induced neurotoxicity suggesting that cerebral GSH status is an important determinant of CE-induced neurotoxicity. Furthermore, pretreatment with N-acetylcysteine delayed both CE-induced neurotoxicity and cerebral GSH depletion. Induction of cerebral but not hepatic CYP2E1 by ethanol before CE challenge also potentiated CE-induced cerebral GSH depletion and neurotoxicity. Hepatic GSH depletion was unaffected suggesting that CE-induced paralysis is dependent on a cerebral but not a hepatic CYP2E1 catalysed oxidation of CE to CAA. Ethanol was neuroprotective even if given 60 min after CE and prevented further cerebral GSH depletion. 4-Methylpyrazole, a CYP2E1 and alcohol dehydrogenase inhibitor, prevented both CE-induced hepatic and cerebral GSH depletion and paralysis. This suggests that the neurotoxicity associated with IP chemotherapy involves activation of chloroethanol by cerebral CYP2E1 to chloroacetaldehyde which mediates cerebral GSH depletion. Neurotoxicity may be prevented by restoring cerebral GSH status and/or by preventing activation of CE by CYP2E1 with ethanol.

Acetaldehyde↗