Assessing the health risks of benzene: a report on the benzene state-of-the-science workshop.
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Animals↗
Biomedical subjects
R Snyder
Publications and source records attributed to R Snyder.
Metabolism of [14C]phenol in the isolated perfused mouse liver.
A previous report from this laboratory focused on the metabolism of [14C]benzene (BZ) in the isolated, perfused, mouse liver (C. C. Hedli, et al., 1997, Toxicol. Appl. Pharmacol. 146, 60-68). Whereas administration of BZ to mice results in bone marrow depression (R. Snyder et al., 1993, Res. Commun. Chem. Pathol. Pharmacol. 20, 191-194), administration of phenol (P), the major metabolite of BZ, does not. It was, therefore, of interest to determine whether the metabolic fate of P produced during BZ metabolism differed from that of P metabolized in the absence of BZ. Mouse livers were perfused with a solution of [14C]P in both the orthograde (portal vein to central vein) and retrograde (central vein to portal vein) direction to investigate the metabolic zonation of enzymes involved in P hydroxylation and conjugation. Perfusate samples were collected, separated by HPLC, and tested for radioactivity. Unconjugated metabolites were identified by comparing their retention times with nonradiolabeled standards, which were detected by UV absorption. Conjugated metabolites were identified and collected on the basis of radiochromatogram results, hydrolyzed enzymatically, and identified by co-chromatography with unlabeled BZ metabolites. The objective was to compare and quantify the metabolites formed during the perfusion of P in the orthograde and retrograde directions and to compare the orthograde P-perfusion results with the orthograde BZ results reported previously. Regardless of the direction of P perfusion, the major compounds released from the liver were P. phenylgucuronide, phenylsulfate, hydroquinone (HQ), and HQ glucuronide. A comparison of the results of perfusing P in the orthograde versus the retrograde direction showed that more P was recovered unchanged and more HQ was formed during retrograde perfusion. The results suggest that enzymes involved in P hydroxylation are generally closer to the central vein than those involved in conjugation, and that during retrograde perfusion, P metabolism may be limited by the sub-optimal conditions of perfusion. Comparison of the orthograde perfusion studies of P and BZ revealed that a larger percentage of the radioactivity released from the liver was identified as unconjugated HQ after BZ perfusion than after P perfusion. In addition, the amount of radioactivity covalently bound to liver macromolecules was measured after each perfusion and determined to be proportional to the amount of HQ and HQG detected in the perfusate samples.
Animals↗
Genetic influences on electrical seizure threshold.
C57BL/6J (B6) and DBA/2J (D2) mice have been characterized previously as seizure-resistant and seizure-sensitive, respectively, a distinction based primarily upon a differential response to the convulsant effects of various drugs. In the present study, electroconvulsive shock (ECS) was used to assess maximal electroshock threshold (MET) in B6, D2 and hybrid mice. Results revealed that D2 mice have a significantly lower MET compared to B6 mice. There was also a significant gender effect for B6 and F2 mice with females exhibiting a lower MET compared to males. METs for F1 and F2 intercross mice were intermediate between the two parental strains. The difference in variance between F2 and F1 generation mice indicated that about three-quarters of the total variance is due to genetic influence. Taken together, results of this study suggest that the large difference in MET between B6 and D2 mice is a highly heritable trait which may yield to genetic dissection through use of quantitative trait locus mapping.
Animals↗
Scientific update on benzene.
The mechanism of benzene toxicity has been extremely difficult to fully characterize. Much progress has been made in assessing the relative potency of benzene metabolites but specific pathways to leukemia remain to be determined. Metabolite and mechanistic studies will have to focus on aplastic anemia and MDS and separate endpoints. This may serve to clarify the array of metabolite effects and consequent disparate effects. Biomarker research can contribute to the understanding of the toxicity process. The significance of understanding benzene toxicity will also lead to better clinical treatment of aplastic anemia and therapy-related MDS and AML, detection of populations particularly susceptible to benzene toxicity, screening of populations with suspected or unknown exposures, and determination of meaningful values for occupational and individual health risk while effectively monitoring ongoing exposures for early signs of toxicity.
Anemia, Aplastic↗
Benzene metabolism in the isolated perfused mouse liver.
The hematotoxicity of benzene (BZ) requires its hepatic metabolism, the release of metabolites into the circulation, and the access of metabolites to the bone marrow. Although a range of potentially toxic metabolites produced by the liver was identified using subcellular systems and isolated hepatocytes, these models do not allow identification of the metabolites released from the liver with respect to time and flow through the liver. We developed an isolated perfused mouse liver model to evaluate metabolites released following a single-pass of radiolabeled BZ and after recirculation of single-pass metabolites back through the liver. Reversing the path of flow through the liver changes the orientation of hepatic oxidizing and conjugating enzymes with respect to perfusate flow. Comparison of metabolite production following normal (orthograde, portal vein to hepatic vein) perfusion with reversed (retrograde) perfusion permitted an evaluation of the impact of zonal distributions of these enzymes on BZ metabolism. The major metabolites detected by HPLC, irrespective of the direction of perfusion, were free phenol (P), phenylsulfate (PS), and phenylglucuronide (PG), plus lesser amounts of hydroquinone (HQ) and hydroquinone glucuronide (HQG). Recirculation of the products of single pass orthograde perfusion through the liver yielded P conjugates as well as low levels of free and conjugated HQ. No free P was detected after recirculation. Although no qualitative differences between orthograde and retrograde perfusion were observed, the percentage of free P and P conjugates (PS + PG) found as free P was twice as great following orthograde perfusion as compared to retrograde perfusion. These results suggest that regional differences in the zonation of enzymes involved in oxidation and conjugation may play a critical role in hepatic BZ metabolism.
Animals↗
Multi-unit mapping of acoustic stimuli in gerbil inferior colliculus.
Multi-unit peristimulus time (MU-PST) histograms were recorded in the gerbil inferior colliculus (IC) in response to tone burst stimuli. Histograms were collected every 100 microns as the recording electrode was advanced along the tonotopic axis of the central nucleus of the IC. Space/time maps of neural activity were constructed from these data. In most of our sample the pattern of response changed systematically as the stimulating frequency was increased in octave steps. At low frequencies (< 500 Hz) the pattern of response was broadly distributed spatially and phase-locked to the stimulus frequency. At higher frequencies (> 1 kHz) the pattern of response was more localized and showed no evidence of phase locking. The location of the maximum response to tones from 1 to 32 kHz moved ventrally along the tonotopic axis at an approximate rate of 230 microns/stimulus octave. The patterns of response were localized near stimulus threshold and spread over a larger region as level increased. This method of collecting and displaying multi-unit response maps provides an overview of ensemble activity that allows concurrent observation of spatial and temporal variations in activity patterns. The quantitative analysis of components of MU-PST Maps are consistent with trends illustrated with single-unit tuning and level functions. This perspective of IC activity suggests potential processing mechanisms that are congruent with single-unit reconstructions.
Acoustic Stimulation↗
Refsum's disease: long term treatment preserves sensory nerve action potentials and motor function.
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Adult↗
Self-discrepancy theory, standards for body evaluation, and eating disorder symptomatology among college women.
Potential links between personal and sociocultural aspects of body-image concerns and sets of behavioral and emotional symptoms associated with eating disorders were explored within a self-discrepancy theory framework. It was predicted that actual:ideal body-image discrepancies from one's own standpoint would be related to symptoms reflecting feelings like dissatisfaction and actual:ought body-image discrepancies from a societal standpoint would be related to symptoms reflecting feelings like anxiety. The Bodies Questionnaire, Eating Disorder Inventory, and demographic information were completed by 196 undergraduate women volunteers. Results generally supported the predictions, although the effects were small. Perceived body-image discrepancies from sociocultural prescriptions for slimness and appearance are more closely associated with symptoms reflecting failures to achieve these standards than with symptoms reflecting efforts to attain them. In addition, the contribution of personal ideals to bulimic symptomatology and body dissatisfaction includes concerns about body attributes not associated with weight. Possible clinical applications are discussed.
Adolescent↗
Bioprocessing in microgravity: applications of continuous flow electrophoresis to rat anterior pituitary particles.
In this report we describe the results of a continuous flow electrophoresis (CFE) experiment done on STS-65 in which we tested the idea that intracellular growth hormone (GH) particles contained in a cell lysate prepared from cultured rat anterior pituitary cells in microgravity might have different electrophoretic mobilities from those in a synchronous ground control cell lysate. Collectively, the results suggested that CFE processing in microgravity was better than on earth; more sample could be processed/time (6 x) and more variant forms of GH molecules could be resolved as well. We had also hoped to carry out a pituitary cell CFE experiment, but failure of the hardware required that the actual cell electrophoresis trials be done on earth shortly after Shuttle landing. Data from these experiments showed that space-flown cells possessed a higher electrophoretic mobility than ground control cells, thereby offering evidence for the idea that exposure of cultured cells to microgravity can change their net surface charge-density especially when the cells are fed. Collectively, the results from this pituitary cell experiment document the advantage of using coupled cell culture and CFE techniques in the microgravity environment.
Animals↗
Effects of benzene metabolite treatment on granulocytic differentiation and DNA adduct formation in HL-60 cells.
Reactive metabolites of benzene (BZ) play important roles in BZ-induced hematotoxicity. Although reactive metabolites of BZ covalently bind to DNA, the significance of DNA adduct formation in the mechanism of BZ toxicity is not clear. These studies investigated the covalent binding of the BZ metabolites hydroquinone(HQ) and 1,2,4-benzenetriol(BT) using the DNA [32P]postlabeling method and explored the potential relationship between DNA adduct formation and cell differentiation in human promyelocytic leukemia (HL-60) cells, a model system for studying hematopoiesis. Maturation of HL-60 cells to granulocytes, as assessed by light and electron microscopy, was significantly inhibited in cells that were pretreated with HQ or BT prior to inducing differentiation with retinoic acid (RA). The capacity of RA-induced cells to phagocytose sheep red blood cells (RBC) and to reduce nitroblue tetrazolium (NBT), two functional parameters characteristic of mature, differentiated neutrophils, was also inhibited in cells pretreated with HQ or BT. These BZ metabolite treatments induced DNA adduct formation in HQ- but not in BT-treated cells. These results indicate that whereas HQ and BT each block granulocytic differentiation in HL-60 cells, DNA adducts were observed only following HQ treatment. Thus DNA adduct formation may be important in HQ but not in BT toxicity.
Benzene Derivatives↗
Promoter elements that mediate the pH response of PCK mRNA in LLC-PK1-F+ cells.
The onset of metabolic acidosis causes an increased transcription of the renal phosphoenolpyruvate carboxykinase (PCK) gene. When transgenic mice carrying a bovine growth hormone (bGH) gene driven by the -460 to +73 segment of the PCK promoter were made chronically acidotic, the bGH mRNA was increased twofold after 4 days. Confluent and well-differentiated cultures of LLC-PK1-F+ cells exhibit a 2.5-fold increase in PCK mRNA when transferred to acidic media (pH 6.9, 10 mM HCO3-) for 16 h. Confluent cultures transfected with PCK-490 CAT exhibit an increase (3.5-fold) in chloramphenicol acetyltransferase (CAT) activity when shifted to acidic medium for 48 h. Mutation or deletion of the P2 element causes a four- to fivefold decrease in basal CAT activity but does not affect the pH response. In contrast, mutations of the P3(II) element or the CRE-1 cAMP-response element have little effect on basal activity but cause a 50% decrease in the pH response. Other deletions or mutations have little effect on either activity. Thus changes in the activity or levels of the protein(s) in the renal proximal tubule that binds to the P3(II) and CRE-1 elements may mediate increased transcription of the PCK gene during metabolic acidosis.
Animals↗
An overview of benzene metabolism.
Benzene toxicity involves both bone marrow depression and leukemogenesis caused by damage to multiple classes of hematopoietic cells and a variety of hematopoietic cell functions. Study of the relationship between the metabolism and toxicity of benzene indicates that several metabolites of benzene play significant roles in generating benzene toxicity. Benzene is metabolized, primarily in the liver, to a variety of hydroxylated and ring-opened products that are transported to the bone marrow where subsequent secondary metabolism occurs. Two potential mechanisms by which benzene metabolites may damage cellular macromolecules to induce toxicity include the covalent binding of reactive metabolites of benzene and the capacity of benzene metabolites to induce oxidative damage. Although the relative contributions of each of these mechanisms to toxicity remains unestablished, it is clear that different mechanisms contribute to the toxicities associated with different metabolites. As a corollary, it is unlikely that benzene toxicity can be described as the result of the interaction of a single metabolite with a single biological target. Continued investigation of the metabolism of benzene and its metabolites will allow us to determine the specific combination of metabolites as well as the biological target(s) involved in toxicity and will ultimately lead to our understanding of the relationship between the production of benzene metabolites and bone marrow toxicity.
Animals↗
Phase II metabolism of benzene.
The hepatic metabolism of benzene is thought to be a prerequisite for its bony marrow toxicity. However, the complete pattern of benzene metabolites formed in the liver and their role in bone marrow toxicity are not fully understood. Therefore, benzene metabolism was studied in isolated rodent hepatocytes. Rat hepatocytes released benzene-1,2-dihydrodiol, hydroquinone (HQ), catechol (CT), phenol (PH), trans-trans-muconic acid, and a number of phase II metabolites such as PH sulfate and PH glucuronide. Pretreatment of animals with 3-methylcholantrene (3-MC) markedly increased PH glucuronide formation while PH sulfate formation was decreased. Likewise, V79 cells transfected with the 3-MC-inducible rat UGT1.6 cDNA showed a considerable rate of PH and HQ glucuronidation. In addition to inducing glucuronidation of phenols, 3-MC treatment (reported to protect rats from the myelotoxicity of benzene) resulted in a decrease of hepatic CYP2E1. In contrast, pretreatment of rats with the CYP2E1-inducer isopropanol strongly enhanced benzene metabolism and the formation of phenolic metabolites. Mouse hepatocytes formed much higher amounts of HQ than rat hepatocytes and considerable amounts of 1,2,4-trihydroxybenzene (THB) sulfate and HQ sulfate. In conclusion, the protective effect of 3-MC in rats is probably due to a shift from the labile PH sulfate to the more stable PH glucuronide, and to a decrease in hepatic CYP2E1. The higher susceptibility of mice toward benzene may be related to the high rate of formation of the myelotoxic metabolite HQ and the semistable phase II metabolites HQ sulfate and THB sulfate.
Animals↗
Good intentions (Ohio's PAP smear law).
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Female↗
Survival after trauma pneumonectomy: the pathophysiologic balance of shock resuscitation with right heart failure.
Emergency pneumonectomy for trauma has a high mortality. Although exsanguination is a major factor leading to death, mortality remains high even after adequate resuscitation and is thought to be related to pulmonary edema and right heart failure. We present a series of nine patients who underwent pneumonectomy at Harbor-UCLA from penetrating (7) and blunt (2) trauma. Two patients survived; three initially survived the surgery but died postoperatively of hypoxemia and right heart failure; four died intraoperatively (2 from right heart failure and 2 from exsanguination). One survivor required open cardiac massage for asystole. Careful attention to prevent volume overloading before and during trauma pneumonectomy and maintaining a negative fluid balance postoperatively may contribute to survival in these patients.
Adolescent↗
The hematotoxic effects of 6-hydroxy-trans,trans-2,4-hexadienal, a reactive metabolite of trans,trans-muconaldehyde, in CD-1 mice.
6-Hydroxy-trans,trans-2,4-hexadienal (CHO-M-OH) is a metabolite of trans,trans-muconaldehyde (muconaldehyde or MUC), a microsomal hematotoxic ring-opened metabolite of benzene. In the present study, the toxicity of CHO-M-OH was examined. In order to assess potential toxic effects of CHO-M-OH on the maturation of erythroid cells in the bone marrow, 10-week-old male CD-1 mice were administered CHO-M-OH intraperitoneally and 59Fe incorporation into erythrocytes was measured. The uptake of 59Fe by erythroid cells was significantly inhibited at doses of 20, 25, and 30 mg/kg. There was no inhibition of 59Fe incorporation at a dose of 15 mg/kg. In other hematotoxicity studies, bone marrow cellularity, peripheral blood cells, and sulfhydryl contents in bone marrow cells were examined in mice administered CHO-M-OH intraperitoneally. An increase in the white blood cell count was observed in mice treated with 5 mg/kg/day for 16 consecutive days, while bone marrow cellularity and red blood cell parameters were not changed. Administration of 10 mg/kg/day for 16 consecutive days caused a significant decrease in sulfhydryls of bone marrow cells but no changes in bone marrow cellularity and peripheral blood parameters compared with controls. At a dose of 25 mg/kg/day for 4 days, there was a significant decrease in nucleated bone marrow cells. The white blood cell count, mainly lymphocytes, also significantly decreased. Our results indicate that CHO-M-OH is a hematotoxin in mice and conceivably could play a role in benzene toxicity.
Aldehydes↗
Temporal resolution of neurons in cat inferior colliculus to intracochlear electrical stimulation: effects of neonatal deafening and chronic stimulation.
1. Cochlear implants have been available for > 20 yr to profoundly deaf adults who have lost their hearing after acquiring language. The success of these cochlear prostheses has encouraged the application of implants in prelingually deaf children as young as 2 yr old. To further characterize the consequences of chronic intracochlear electrical stimulation (ICES) on the developing auditory system, the temporal-response properties of single neurons in the inferior colliculus (IC) were recorded in deafened anesthetized cats. 2. The neurons were excited by unilateral ICES with the use of a scala tympani stimulating electrode implanted in the left cochlea. The electrodes were modeled after those used in cochlear implant patients. Responses of 443 units were recorded extracellularly in the contralateral (right) IC with the use of tungsten microelectrodes. Recordings were made in three groups of adult animals: neonatally deafened/chronically stimulated animals (192 units), neonatally deafened/unstimulated animals (80 units), and adult-deafened/prior normal-hearing animals (171 units). The neonatally deafened cats were deafened by multiple intramuscular injections of neomycin sulfate and never developed demonstrable hearing. Most of the deafened, chronically stimulated animals were implanted at 6 wk of age and stimulated at suprathreshold levels for 4 h/day for 3-6 mo. The unstimulated animals were implanted as adults at least 2 wk before the acute physiological experiment and were left unstimulated until the acute experiment was conducted. Prior-normal adults were deafened and implanted at least 2 wk before the acute experiment. 3. IC units were isolated with the use of a search stimulus consisting of three cycles of a 100-Hz sinusoid. Most units responded to sinusoidal stimulation with either an onset response or a sustained response. Onset units were the predominant unit found in the external nucleus, whereas sustained units were found almost exclusively in the central nucleus. The temporal resolution of sustained response units was measured with the use of pulse trains of increasing frequency and calculating the discharges/pulse. 4. The range of electrical pulse frequencies to which IC units responded in a temporally synchronized manner was comparable with that produced by acoustic stimulation. The discharge rate/pulse-versus-pulse frequency transfer functions of IC units were uniformly low-pass, although they varied widely in their cutoff frequencies. This variation in pulse response was partially correlated with the unit's response to sinusoids. Most onset neurons responded only to pulse frequencies below 20 pulses per second (pps). Most sustained units responded best to pulse frequencies < 100 pps, and most ceased to respond to pulse frequencies > 300 pps.(ABSTRACT TRUNCATED AT 400 WORDS)
Animals↗