Cell culture model for acetaminophen-induced hepatocyte death in vivo

Overdose of the popular, and relatively safe, analgesic acetaminophen (N-acetyl-p-aminophenol, APAP, paracetamol) can produce a fatal centrilobular liver injury. APAP-induced cell death was investigated in a differentiated, transforming growth factor alpha (TGFalpha)-overexpressing, hepatocyte cell line and found to occur at concentrations, and over time frames, relevant to clinical overdose situations. Coordinated multiorganellar collapse was evident during APAP-induced cytotoxicity with widespread, yet selective, protein degradation events in vitro. Cellular proteasomal activity was inhibited with APAP treatment but not with the comparatively nonhepatotoxic APAP regioisomer, N-acetyl-m-aminophenol (AMAP). Low concentrations of the proteasome-directed inhibitor MG132 (N-carbobenzoxyl-Leu-Leu-Leucinal) increased chromatin condensation and cellular stress responses preferentially in AMAP-treated cultures, suggesting a contribution of the proteasome in APAP- but not AMAP-mediated cell death. APAP-specific alterations to mitochondria were observed morphologically with evidence of mitochondrial proliferation in vitro. Biochemical alterations to cellular proteolytic events were also found in vivo, including APAP- or AMAP-mediated inhibition of caspase-3 processing. These results indicate that, although retaining some attributes of apoptosis, both APAP- and AMAP-mediated cell death have additional distinctive features consistent with longer term necrosis.

Structure toxicity relationships--how useful are they in predicting toxicities of new drugs?

This chapter provides just a few newer examples of structural moieties found in drugs that have been associated with reactive metabolite formation and toxicities. For a discussion of several other structures in drugs that undergo metabolic activation to reactive intermediates, the reader is directed to previous volumes in this series and other chapters in this book, as well as a previous condensed review (Nelson, 1982). Since that review, some new knowledge allows us to better predict that some structural moieties are more likely than others to form drug reactive metabolites that may be involved in causing toxic effects in humans. For example, most aniline-, thiophene-, and nitroaromatic-containing drugs have had a relatively high incidence of adverse effects, and it would be prudent in the drug discovery process to avoid these substructures if possible. However, as illustrated by the case of olanzapine, these structures may be important for potent activity, and could therefore be beneficial in some cases. The glitazones represent a new class of drugs with a unique thiazolidinedione structure. This raises two important points. First, it demonstrates how limited our knowledge base is in regard to structure toxicity relationships when new structures are introduced. Our approaches must be very empirical and are far from quantitative for the reasons outlined in the introduction. Secondly, the glitazones point out the importance of benefit/risk considerations. This was a new structural class of drugs with a unique spectrum of action that is very beneficial in the treatment of a major disease. Despite some suspected risk of toxicity, based on early trials, troglitazone was approved for use with careful monitoring. This author believes that was the right decision, as was the decision to withdraw the drug when the risk became unacceptable, especially with the introduction of safer alternatives. If this were just another NSAID (e.g., bromfenac), there would be little reason for approval. In summary, as I pointed out previously (Nelson, 1982), with our limited knowledge of structure toxicity relationships, we can only make reasonable judgments as to risk assessment of a new drug in humans, and hope that we neither release a dangerous chemical entity nor, as importantly, abort an effective one.

Mitochondrial aconitase modification, functional inhibition, and evidence for a supramolecular complex of the TCA cycle by the renal toxicant S-(1,1,2,2-tetrafluoroethyl)-L-cysteine

Metabolism of the common industrial gas tetrafluoroethylene in mammals results in the formation of S-(1,1,2,2)-tetrafluoroethyl-L-cysteine (TFEC), which can be bioactivated by a mitochondrial C-S lyase commonly referred to as beta-lyase. The resultant "reactive intermediate", difluorothioacetyl fluoride (DFTAF), is a potent thioalkylating and protein-modifying species. Previously, we have identified mitochondrial HSP70, HSP60, aspartate aminotransferase, and the E2 and E3 subunits of the alpha-ketoglutarate dehydrogenase (alphaKGDH) complex as specific proteins structurally modified during this process. Moreover, functional alterations to the alphaKGDH complex were also detected and implicated in the progression of injury. We report here the identification, by tandem mass spectrometry, and functional characterization of the final remaining major protein species modified by DFTAF, previously designated as P99(unk), as mitochondrial aconitase. Aconitase activity was maximally inhibited by 56.5% in renal homogenates after a 6 h exposure to TFEC. In comparison to alphaKGDH, aconitase inhibition (up to 79%) in a cell culture model for TFEC-mediated cytotoxicity was greater and preceded alphaKGDH inhibition, indicating that aconitase modification may constitute an early event in TFEC-mediated mitochondrial damage and cell death. These findings largely define the initial lesion of TFEC-mediated cell death and also have implications for the modeling of mitochondrial enzymatic architecture and the localization and identity of renal mitochondrial cysteine S-conjugate beta-lyase.

Molecular structure-property relationships for alkenes

Structure-property relationships were obtained for 11 physical and chemical properties (boiling points (bp), melting points (mp), molar refractions (MR), molar volumes (MV), heats of combustion (HCKJ), molar heats of vaporization (HVMOL), flashpoints (FLASHK), second virial coefficients (VIRC2), critical temperatures (Tc), critical pressures (Pc), and viscosities (VISC)) for a data set consisting of 162 C4-C9 monoalkenes. Both molecular connectivity indices and ad hoc descriptors were tested as structural descriptors, and both produced high-quality regression equations for most of the properties. As was observed in an earlier study of alkanes [J. Am. Chem. Soc. 110 (1988) 4186], mp were not well described by either descriptor set. For most properties, the mass/bulk of the molecule was found to be the most important structural feature determining the property, suggesting that dispersion forces play a dominant role in determining those properties influenced by intermolecular interactions. The amount of branching in the molecule and the nature of the double bond environment were also found to be influential features.

A real-time ST-segment monitoring algorithm for implantable devices

Continuous ST-segment monitoring by implantable devices may lead to clarification of the substrate of arrhythmias, clarification of the origin of nonspecific chest pain, and titration or preventative application of established anti-ischemic therapies. Although ST-segment monitoring algorithms are available for surface electrocardiogram, the computational demand of algorithms for implantable devices must be minimized for considerations of device longevity. The new algorithm first locates a fiducial point (FPT) at the dominant peak of each QRS complex. The ST-segment deviation (measured at 2 rate-adaptive delays after FPT, eg, FPT + 96 ms and FPT + 152 ms at 60 BPM) with respect to the isoelectric level (measured at the minimum slope preceding the QRS) is then measured. The following features are also quantified by simple operations: R-R interval, R-wave slope, R-wave amplitude, ST-segment slope, and noise content during the isoelectric segment. Inconsistencies in these features relative to their adaptive normal ranges are used to reject noisy or ectopic beats and sudden morphology changes. Finally, the ST-segment deviation over time is filtered to reject rates of change that are not likely attributable to human ischemia. Performance of the algorithm was evaluated on the European Society of Cardiology ST-T Database, which contains 180 hours of ambulatory electrocardiogram with 250 expert-annotated ischemic episodes. The sensitivity was 79% [74% 84%] (mean [95% CI]) and positive predictivity was 81% [76% 86%]. This performance is statistically equivalent to that of published electrocardiogram algorithms that were validated on the same dataset. Estimates of computational burden suggest that the algorithm could process two channels of electrogram continuously for more than 5 years with current implanted device technology. In conclusion, we have developed an algorithm for ST-segment monitoring that can be implemented in current implantable devices with sensitivity and positive predictivity that are comparable with the state-of-the-art.

Inhibition of macrophage migration inhibitory factor (MIF) tautomerase and biological activities by acetaminophen metabolites

The cytokine macrophage migration inhibitory factor (MIF) has emerged to be an important regulator of the inflammatory response and is critically involved in the development of septic shock, arthritis, and glomerulonephritis. Although the biological activities of MIF are presumed to require a receptor-based mechanism of action, the protein is also a tautomerase and has a catalytically active N-terminal proline that is invariant in structurally homologous bacterial isomerases. This observation raises the possibility that MIF may exert its biological action via an enzymatic reaction. Physiologically relevant substrates for MIF have not been identified, nor have site-directed mutagenesis studies consistently supported the requirement for a functional catalytic site. Small molecule inhibitors of MIF's isomerase activity also have been developed, but none have been shown yet to inhibit MIF biological activity. We report herein that the iminoquinone metabolite of acetaminophen, N-acetyl-p-benzoquinone imine (NAPQI), inhibits both the isomerase and the biological activities of MIF. The reaction between NAPQI and MIF is covalent and produces a NAPQI-modified MIF species with diminished cell binding activity and decreased recognition by anti-MIF mAb. These data are consistent with a model by which the NAPQI reacts with the catalytic Pro-1 of MIF to disrupt the integrity of epitope(s) critical to MIF's biological activity and point to the importance of the catalytic domain, but not the catalytic activity per se, in MIF function. These results also point to a powerful approach for the design of small molecule inhibitors of MIF based on interaction with its catalytic site and constitute an example of a pharmacophore capable of irreversibly inhibiting the action of a proinflammatory cytokine.

Efficacy of 1,3-dichloropropene in soil amended with compost and unamended soil

1,3-Dichloropropene (1,3-D) is a likely alternative soil fumigant for methyl bromide. The objective was to determine root-knot nematode, Meloidogyne incognita, survival in microplots after exposure to 1,3-D for various periods of time in soil that have previously been amended with compost. The treatments were 1,3-D applied broadcast at 112 liters/ha and untreated controls in both compost-amended and unamended soil. Soil samples were collected from each microplot at 6, 24, 48, 72, and 96 hours after fumigation at three depths (0-15, 15-30, and 30-45 cm). One week after fumigation, six tomato seedlings were transplanted into each microplot and root galling was recorded 6 weeks later. Plants grown in fumigated compost-amended soil had more galls than plants from fumigated unamended soil at P </= 0.1. Gall indices from roots in fumigated soil amended with compost were not different from nonfumigated controls. Based on soil bioassays, the number of galls decreased with increasing time after fumigation in both compost-amended and unamended soil at 0-to-15 and 15-to-30 cm depths, but not at 30 to 45 cm deep. Higher soil water content due to the elevated levels of organic matter in the soil at these depths may have interfered with 1,3-D movement, thus reducing its efficacy.

Enhanced acetaminophen hepatotoxicity in transgenic mice overexpressing BCL-2

Mitochondria play an important role in the cell death induced by many drugs, including hepatotoxicity from overdose of the popular analgesic, acetaminophen (APAP). To investigate mitochondrial alterations associated with APAP-induced hepatotoxicity, the subcellular distribution of proapoptotic BAX was determined. Based on the antiapoptotic characteristics of BCL-2, we further hypothesized that if a BAX component was evident then BCL-2 overexpression may be hepatoprotective. Mice, either with a human bcl-2 transgene (-/+) or wild-type mice (WT; -/-), were dosed with 500 or 600 mg/kg (i.p.) APAP or a nonhepatotoxic isomer, N-acetyl-m-aminophenol (AMAP). Immunoblot analyses indicated increased mitochondrial BAX-beta content very early after APAP or AMAP treatment. This was paralleled by disappearance of BAX-alpha from the cytosol of APAP treated animals and, to a lesser extent, with AMAP treatment. Early pathological evidence of APAP-induced zone 3 necrosis was seen in bcl-2 (-/+) mice, which progressed to massive panlobular necrosis with hemorrhage by 24 h. In contrast, WT mice dosed with APAP showed a more typical, and less severe, centrilobular necrosis. AMAP-treated bcl-2 (-/+) mice displayed only early microvesicular steatosis without progression to extensive necrosis. Decreased complex III activity, evident as early as 6 h after treatment, correlated well with plasma enzyme activities at 24 h (AST r(2) = 0.89, ALT r(2) = 0.87) thereby confirming a role for mitochondria in APAP-mediated hepatotoxicity. In conclusion, these data suggest for the first time that BAX may be an early determinant of APAP-mediated hepatotoxicity and that BCL-2 overexpression unexpectedly enhances APAP hepatotoxicity.

Patellar metastasis from a squamous carcinoma of the lung: a case report

Bone is a common site of metastasis from lung cancer. Metastasis to the patella, however, is rare. A 76-year-old man presented with knee pain caused by an isolated patellar metastasis from squamous cell carcinoma of the lung. Treatment was delayed secondary to delay in diagnosis. In cases of bone pain that are unexplained or out of proportion to a traumatic event, more extensive diagnostic studies should be done.

Tophaceous pseudogout: a pitfall in the diagnosis of chondrosarcoma

Tumoral calcium pyrophosphate dihydrate deposition disease (TCPPD, tumoral or tophaceous pseudogout) is a rare nonneoplastic entity which mimics soft-tissue or skeletal malignancy. We present here the fine-needle aspiration cytology findings of a unique case of TCPPD in a 76-yr-old woman, with a large paraischial soft-tissue mass diagnosed as a malignant neoplasm. The difficulty in diagnosing such lesions by fine-needle aspirates is discussed and reviewed in the context of known cases from the literature.

Human aromatase in high yield and purity by perfusion chromatography and its characterization by difference spectroscopy and mass spectrometry

Expression of human cytochrome P450 aromatase (CYP19A1, aromatase) was accomplished at a high level using a baculovirus expression system in an insect cell suspension culture. Using the relatively new chromatographic technique of perfusion chromatography, a very rapid procedure for purification of the protein from solubilized cells was developed. At extraordinary flow rates of between 3 and 9 column volumes per minute, all chromatographic procedures could be performed, including setup, equilibration, and column regeneration steps, in less than 2 h, not including brief dialysis periods. Total yields were 40-52% and resulted in preparations with specific content values of 17.1 nmol aromatase/mg protein. Final purified preparations showed virtually no typical P450 spectra under standard conditions, but displayed full activity with typical enzyme kinetic parameters. These unusual results suggest that standard methods of P450 measurement are inappropriate when applied to aromatase. The findings are fully consistent with those encountered previously for purified preparations from a human placental source and led us to a new aromatase quantification method based on ligand-induced difference spectroscopy. A new HPLC assay is described which rapidly separates heme and apoprotein while measuring total heme content. Matrix-assisted laser desorption ionization time-of-flight mass spectrometry was employed with both glycosylated and deglycosylated forms of the final purified product to confirm its identity as a glycosylated cytochrome P450.

Treatment-induced pathologic necrosis: a predictor of local recurrence and survival in patients receiving neoadjuvant therapy for high-grade extremity soft tissue sarcomas

PURPOSE

To determine whether treatment-induced pathologic necrosis correlates with local recurrence and overall survival in patients who receive neoadjuvant therapy for high-grade extremity soft tissue sarcomas.

PATIENTS AND METHODS

Four hundred ninety-six patients with intermediate- to high-grade extremity soft tissue sarcomas received protocol neoadjuvant therapy. All patients underwent surgical resection after neoadjuvant therapy and had pathologic assessment of tumor necrosis in the resected specimens.

RESULTS

The 5- and 10-year local recurrence rates for patients with > or = 95% pathologic necrosis were significantly lower (6% and 11%, respectively) than the local recurrence rates for patients with less than 95% pathologic necrosis (17% and 23%, respectively). The 5- and 10-year survival rates for the patients with > or = 95% pathologic necrosis were significantly higher (80% and 71%, respectively) than the survival rates for the patients with less than 95% pathologic necrosis (62% and 55%, respectively). Patients with less than 95% pathologic necrosis were 2.51 times more likely to develop a local recurrence and 1.86 times more likely to die of their disease as compared with patients with > or = 95% pathologic necrosis. The percentage of patients who achieved > or /= 95% pathologic necrosis increased to 48% with the addition of ifosfamide as compared with 13% of the patients in all the other protocols combined.

CONCLUSION

Treatment-induced pathologic necrosis is an independent predictor of both local recurrence and overall survival in patients who receive neoadjuvant therapy for high-grade extremity soft tissue sarcomas. A complete pathologic response (> or = 95% pathologic necrosis) correlated with a significantly lower rate of local recurrence and improved overall survival.

Soft tissue echinococcosis: a report of two cases and review of the literature

Echinococcosis (hydatid cyst disease) is a zoonotic infection caused by the parasitic tapeworm Echinococcus. The larval stage of this parasite can implant in many organs of the body, most commonly the liver, and create internal budding cystic masses. Echinococcal cysts also can implant in soft tissues; however, a review of the literature revealed no published case with the patient initially presenting with a soft tissue mass. Two such cases are reported in the current study. Physicians who evaluate soft tissue masses, particularly in patients from Echinococcus-endemic areas, need to include echinococcosis in their differential diagnoses. The current treatment of choice for soft tissue echinococcosis is wide resection combined with perioperative medical therapy.

The innervation of the triangular fibrocartilage complex: nitric acid maceration rediscovered

Injury to the triangular fibrocartilage complex (TFCC) is frequently implicated in the etiology of ulnar-sided wrist pain. This study examines the nervous anatomy of the TFCC using a nitric acid maceration technique and attempts to correlate this information with known tear patterns. Ten fresh frozen cadaveric specimens were studied in detail. Gross dissection of each upper-extremity specimen included removal of all flexor and extensor tendons. After identification and labeling with permanent color of the ulnar nerve, dorsal sensory branch of the ulnar nerve, posterior interosseous nerve, anterior interosseous nerve, and median nerve, an en bloc excision of the distal radioulnar region was performed. Digestion of the soft tissue was performed with nitric acid at sequential concentrations of 50% and 33% for 9 of 10 specimens. The digestion was halted by immersing the specimen in a mixture of 10% formaldehyde and 1% glycerine. After removal of bone, the specimens were fixed in paraffin, sectioned, and stained with hematoxylin and eosin. Nine of the 10 specimens were studied microscopically to determine the contribution of the grossly identified nerves to each zone of the triangular fibrocartilage complex as defined by Palmer's classification of acute TFCC tears. The anterior interosseous, median, and superficial radial nerves did not contribute to the innervation of the TFCC. The intraarticular course of the peripheral nerves could not be defined in the one specimen that was not digested with nitric acid. Nitric acid maceration is a rediscovered technique for identifying the nervous anatomy of soft tissues. The study showed that the triangular fibrocartilage complex is innervated by branches of the posterior interosseous, ulnar, and dorsal sensory ulnar nerves in a fairly consistent manner. Improved treatment of TFCC tears may result from an enhanced understanding of the supporting structures' innervation and mechanical function.

Involvement of human cytochrome P450 2D6 in the bioactivation of acetaminophen

Acetaminophen (APAP), a widely used analgesic and antipyretic agent, can cause acute hepatic necrosis in both humans and experimental animals when consumed in large doses. It is generally accepted that N-acetyl-p-benzoquinone imine (NAPQI) is the toxic, reactive intermediate whose formation from APAP is mediated by cytochrome P450. Several forms of P450 in humans, including 2E1, 1A2, 2A6, 3A4, have been shown to catalyze the oxidation of APAP to NAPQI. We now present evidence which demonstrates that human cytochrome P450 2D6 (CYP2D6) is also involved in the bioactivation of APAP. The formation of NAPQI from APAP by cDNA-expressed CYP2D6 was examined. K(m) and V(max) values were 1.76 mM and 3.02 nmol/min/nmol of P450, respectively, such that the efficiency of CYP2D6 in the conversion of APAP to NAPQI is approximately one-third of that of CYP2E1. The contribution of CYP2D6 to the total formation of NAPQI from APAP (1 mM) in human liver was investigated using quinidine (1 microm) as a CYP2D6-specific inhibitor, and varied from 4.5 to 22.4% among 10 livers, with an average at 12.6%. The correlation between the contribution of CYP2D6 to NAPQI formation in human liver microsomes and the CYP2D6 activity probed by the O-demethylation of dextromethorphan was studied, and found to be strong (r(2) = 0.85), and significant (P <.0001). Our findings indicate that CYP2D6, one of the major P450 isoforms in humans and also one of the pharmacogenetically important isoforms, may contribute significantly to the formation of the cytotoxic metabolite NAPQI, especially in CYP2D6 ultra-rapid and extensive metabolizers and at toxic doses of APAP when plasma APAP concentrations reach 2 mM or more.