John Nash and the Organization of Stroke Care.

The concept of Nash equilibrium, developed by John Forbes Nash Jr, states that an equilibrium in noncooperative games is reached when each player takes the best action for himself or herself, taking into account the actions of the other players. We apply this concept to the provision of endovascular thrombectomy in the treatment of acute ischemic stroke and suggest that collaboration among hospitals in a health care jurisdiction could result in practices such as shared call pools for neurointervention teams, leading to better patient care through streamlined systems.

Effects of locally-delivered human macrophage products and estrogen on murine inflammatory bone resorption.

The objective of this study was to use an in vivo model of periodontitis (mouse calvaria) to quantify the effects of local release of secreted human macrophage products, 17beta-estradiol (E2), and proinflammatory lipopolysaccharide (LPS) on histologic bone resorption. Human THP-1 monocytes (106) were converted to macrophage phenotype by 500 ng/ml phorbol 12-myristate- 13-acetate (PMA) and treated as follows: no stimulation or Escherichia coli LPS (10 microg/ml) alone or in combination with a physiologic dose of E2 (100 pg/ml) for 24 h in RPMI/10% FBS, washed extensively, then incubated for 24 h in serum-free media. Supernatant products were concentrated and incorporated into a 4% (w/v) methylcellulose gel. Separate gels were incorporated with the following: LPS (500 microg/animal) alone, high dose of E2 (10 ng/animal) alone, a combination of LPS + E2, or gel only (controls). Loaded or control gels were placed into a polylactic acid occlusive dome, inserted subcutaneously over the calvaria of mature ovariectomized ICR Swiss mice (8 mice x 7 groups x 2 times [5/14 days] = 112 animals), then calvaria were evaluated histologically. Macrophage stimulation with LPS alone, but not LPS in combination with E2, produced supernatants which upregulated osteoclast numbers in the suture area compared to gel controls at 5 days (p = 0.009). The addition of LPS directly to the local delivery gels significantly upregulated osteoclasts in endosteal surfaces compared to gel controls at 5 days (p = 0.024) and at 14 days (p = 0.025). The addition of E2 to LPS down-regulated resorption to a level not different from gel controls at 14 days. This in vivo model appears effective in studying inflammatory bone resorption, which may be inhibited by E2 directly or through its influence on secreted macrophage products.

Synthesis and solution properties of deferoxamine amides.

The poor membrane permeability and oral bioavailability of the iron chelating agent deferoxamine (DFO) mesylate result from the low octanol/water partition coefficient and high aqueous solubility. With the ultimate aim to improve biomembrane permeability while retaining the iron-binding ability of DFO, a series of more lipophilic amides were prepared by reacting the terminal primary amino group with fatty and aromatic acid chlorides or anhydrides. Octanol/water partition coefficients and equilibrium solubilities of these analogs in solvents, chosen to delineate physicochemical interactions, were determined as a function of temperature. Solid-state properties were evaluated by calorimetry. All DFO amide derivatives had higher melting points, indicating that derivatives formed strong intermolecular interactions in the solid phase. Formamidation of the primary amine of deferoxamine resulted in a 200-fold increase in the octanol/water partition coefficient and reduced aqueous solubility at least 2000-fold compared with the parent molecule. The partition coefficient increased and aqueous solubility decreased 2-fold with the addition of each methylene group in the homologous series of aliphatic amides. Solubilities of the derivatives in water-saturated octanol and hexane showed irregular profiles as a function of increasing aliphatic chain length that were attributed to intermolecular packing in the solid state. The temperature dependence of the partition coefficients was interpreted to indicate that interfacial transfer of the deferoxamine amides was, in part, affected by an apparent diminished ability to form energetically favorable interactions in the water-saturated organic phase.

Identification of a yellow impurity in aged samples of aqueous butamben suspension: evidence for the oxidative degradation of poly(ethylene glycol).

Butamben (butyl p-aminobenzoate) has been formulated to provide long-acting treatment for chronic pain. The suspension, which contains poly(ethylene glycol) and polysorbate 80, was found to yellow under ambient conditions if not adequately protected from oxygen. The impurity responsible for the color was isolated and identified on the basis of nuclear magnetic resonance spectroscopy and mass spectrometry. The compound is an oxalamidine, which is formally the condensation product of oxalic acid with four equivalents of butamben, and may be formed by the reaction of butamben with an oxidation product of poly(ethylene glycol).

Rapid and early export of Phaeocystis antarctica blooms in the Ross Sea, Antarctica.

The Southern Ocean is very important for the potential sequestration of carbon dioxide in the oceans and is expected to be vulnerable to changes in carbon export forced by anthropogenic climate warming. Annual phytoplankton blooms in seasonal ice zones are highly productive and are thought to contribute significantly to pCO2 drawdown in the Southern Ocean. Diatoms are assumed to be the most important phytoplankton class with respect to export production in the Southern Ocean; however, the colonial prymnesiophyte Phaeocystis antarctica regularly forms huge blooms in seasonal ice zones and coastal Antarctic waters. There is little evidence regarding the fate of carbon produced by P. antarctica in the Southern Ocean, although remineralization in the upper water column has been proposed to be the main pathway in polar waters. Here we present evidence for early and rapid carbon export from P. antarctica blooms to deep water and sediments in the Ross Sea. Carbon sequestration from P. antarctica blooms may influence the carbon cycle in the Southern Ocean, especially if projected climatic changes lead to an alteration in the structure of the phytoplankton community.

A bioresorbable, polylactide reservoir for diffusional and osmotically controlled drug delivery.

The purpose of this study was to design and characterize a zero-order bioresorbable reservoir delivery system (BRDS) for diffusional or osmotically controlled delivery of model drugs including macromolecules. The BRDS was manufactured by casting hollow cylindrical poly (lactic acid) (PLA): polyethylene glycol (PEG) membranes (10 x 1.6 mm) on a stainless steel mold. Physical properties of the PLA:PEG membranes were characterized by solid-state thermal analysis. After filling with drug (5 fluorouracil [5FU] or fluorescein isothiocyanate [FITC]-dextran:mannitol, 5:95 wt/wt mixture) and sealing with viscous PLA solution, cumulative in vitro dissolution studies were performed and drug release monitored by ultraviolet (UV) or florescence spectroscopy. Statistical analysis was performed using Minitab (Version 12). Differential scanning calorimetry thermograms of PLA:PEG membranes dried at 25 degrees C lacked the crystallization exotherms, dual endothermal melting peaks, and endothermal glass transition observed in PLA membranes dried at -25 degrees C. In vitro release studies demonstrated zero-order release of 5FU for up to 6 weeks from BRDS manufactured with 50% wt/wt PEG (drying temperature, 25 degrees C). The release of FITC dextrans of molecular weights 4400, 42 000, 148 000, and 464 000 followed zero-order kinetics that were independent of the dextran molecular weight. When monitored under different concentrations of urea in the dissolution medium, the release rate of FITC dextran 42 000 showed a linear correlation with the calculated osmotic gradient(DeltaPi). This study concludes that PEG inclusion at 25 degrees C enables manufacture of uniform, cylindrical PLA membranes of controlled permeability. The absence of molecular weight effects and a linear dependence of FITC-dextran release rate on DeltaPi confirm that the BRDS can be modified to release model macromolecules by an osmotically controlled mechanism.

In vitro properties of an in situ forming gel for the parenteral delivery of macromolecular drugs.

The purpose of this research was to (i) formulate a solution of a water-insoluble interpolymeric complex (IPC) containing poly(methacrylic acid) (PMA), 15 kDa, and poly(ethylene glycol) (PEG), 20 kDa, in a biocompatible cosolvent system; (ii) demonstrate that the IPC solution can transform into a gel, in situ, at physiological pH; and (iii) determine the ability of the gel to entrap, protect, and control the release of macromolecular drugs such as proteins and oligonucleotides. Ternary phase diagrams were prepared to identify cosolvent composition containing N-methylpyrrolidone (NMP), ethanol, and water that dissolve the IPC. IPC solutions (40, 50, or 60% w/v) each containing 1 mg of either model proteins, fluorescein isothiocyanate (FITC)-insulin and FITC-albumin, or 24-mer phosphorothioate oligonucleotides, were placed in containers that were immersed in buffer, pH 7.4. Aliquots of the buffer were sampled periodically and analyzed for the macromolecular content. In addition, in vitro bioactivity of another model protein, alpha-amylase, contained in the IPC solution was also determined. The studies demonstrated that a cosolvent containing 1:1:2 ratio of NMP/ethanol/water was most suitable for dissolving the IPC. Concentrations > 30% w/v IPC were required to form the gel, however, those mixtures containing > 60% w/v IPC could not be easily injected via 18-22 gauge needle. The gel can entrap and control the release of the model macromolecules for up to 6 days, in vitro. In addition, the gel can maintain the bioactivity of the protein, alpha-amylase, for 6 days. Therefore, an IPC gel can entrap, protect, and control the release of macromolecular drugs over a period of 6 days, in vitro, and therefore can be considered for in vivo investigation.

Embolization of meningohypophyseal and inferolateral branches of the cavernous internal carotid artery.

BACKGROUND AND PURPOSE: Despite the continued improvements in endovascular techniques this decade, few dedicated studies addressing the feasibility of such procedures or their efficacy relative to risk have been conducted. The purpose of this study was to use current endovascular techniques to assess the feasibility, effectiveness, and safety of direct selective catheterization and embolization of the small branches of the cavernous segment of the internal carotid artery. METHODS: We retrospectively reviewed the findings in 10 patients with lesions (five meningiomas and five arteriovenous malformations) primarily or partly supplied by branches of the meningohypophyseal trunk or inferolateral trunk who had undergone endovascular embolization of the feeding arteries during the period from 1991 to 1997. In each case, the artery was selectively catheterized with a microcatheter/microguidewire system and embolized with polyvinyl alcohol particles (n = 5), n-butyl cyanoacrylate tissue adhesive (n = 4), or both (n = 1). RESULTS: In all 10 patients, the feeding artery from the meningohypophyseal trunk (eight patients) or inferolateral trunk (three patients; one patient with both) was successfully catheterized and embolized. In nine patients, embolization resulted in complete obliteration of the vascular territory; in the remaining patient, blood supply was decreased by an estimated 80%. No immediate or delayed complications occurred. CONCLUSION: Advances in microcatheter and microguidewire technology allow more efficient and safer selective catheterization and embolization of branches of the cavernous segment of the internal carotid artery than in the recent past. Meticulous technique and detailed knowledge of the vascular anatomy of the cavernous sinus region are necessary to maximize lesion devascularization and to minimize the risk of stroke, cranial nerve palsies, and blindness.

A slow release calcium delivery system for the study of reparative dentine formation.

Several liquid, semi-solid and solid delivery systems were formulated and tested to devise a method of reproducibly administering accurate micro-doses of calcium into a 700 microns diameter cavity in a rat maxillary incisor tooth, in the absence of hydroxyl ions. Development of this delivery system was necessary to facilitate studies of the mechanisms of pulpal repair and odontoblast differentiation. The principal requirements for the delivery system were that it should be easily administered into a small pulp exposure in the rat incisor and that a greater than 1000-fold range in calcium ion concentrations could be incorporated and delivered for a period of 2-3 days, preferably in an acidic environment to minimize the effect of non-specific nucleation under alkaline conditions. Poly- (ethylene) glycol microspheres were found to be an ideal vehicle. Under the in vitro dissolution conditions used, complete release of all calcium salts occurred within 12-15 hours, except for the very water-insoluble calcium stearate. It was anticipated that the release of calcium ions would be significantly more prolonged in vivo because of the physical constraints of the prepared cavity as well as the restricted access to fluid flow.

In vitro characterization of poly(ethylene) glycol calcium citrate microspheres as a delivery system for the study of reparative dentinogenesis.

The characterization of poly(ethylene) glycol calcium citrate microspheres is described. The calcium content and content uniformity of microspheres, prepared at five concentrations ranging from 46.56 micrograms/g to 81.49 mg/g, were determined by spectroscopy. Under sink conditions first-order in vitro dissolution kinetics were observed. Granules containing approximately 80 mg Ca++/g PEG gave an in vitro calcium release over a 3-day period similar to that of a calcium hydroxide product, Pulpdent.

Functional consequences of mutations in the transmembrane domain and the carboxy-terminus of the murine AE1 anion exchanger.

We have characterized mouse AE1-mediated 36Cl- influx and surface AE1 polypeptide expression in Xenopus oocytes injected with cRNA encoding two classes of loss-of-function mutants. The first arose spontaneously. Chimeric mutants constructed with a functional AE1 cDNA localized the site of spontaneous mutation to the transmembrane domain, and DNA sequencing revealed two missense mutations encoding the double-mutant polypeptide V728F/M7301. Each mutation individually produced only partial loss of AE1 transport activity, and coexpression of the individual mutants did not restore full activity. The functional changes produced by the mutations correlated with reduced fractional accumulation of polypeptides at the oocyte surface. The V728F/M7301 polypeptide expressed in mammalian cells displayed complete endoH resistance and rapid degradation. We also examined the effect on AE1 function of engineered removal of its hydrophilic carboxy-terminus. Both delta(c)890 and the internal deletion delta(c)890-917 were functionally inactive in Xenopus oocytes. Lack of transport activity correlated with lack of detectable polypeptide accumulation at the oocyte surface. Coexpression with wt AE1 of some, but not all, of these AE1 mutants partially suppressed wt AE1-mediated 36Cl- uptake. In contrast, coexpression with wt AE1 of soluble N-terminal AE1 fragments was not inhibitory.

At-lexical, articulatory interference in silent reading: the "upstream" tongue-twister effect.

In two experiments, we investigated the interpretation and boundary conditions of the tongue-twister (TT) effect in silent reading. Previously, McCutchen, Bell, France, and Perfetti (1991) observed a TT effect when students made semantic acceptability judgments on sentences, but not when they made lexical decisions on lists of words. Using similar methodology in Experiment 1, along with two changes (using "better" TTs and longer word lists), we observed a TT effect in a lexical decision task. In Experiment 2, a memory span task revealed that students recalled fewer words from TT lists than from control lists. These results suggest that the basic mechanism of the TT effect may be articulatory, rather than working-memory, interference that occurs during lexical access and resurfaces post-lexically, inhibiting efforts to maintain the temporal order of several words.

Evaluation of properties of apigenin and [G-3H]apigenin and analytic method development.

This study provides baseline data and analytical methods to assist in the evaluation of apigenin, a plant flavonoid with promising chemopreventive activity against skin cancer. Apigenin was freely soluble in dimethylsulfoxide (> 100 mg/mL), but it had low solubility (0.00135-1.63 mg/mL) in all the other solvents and surfactants tested, especially in highly hydrophilic or nonpolar solvents. The partition coefficient (log K) calculated from the solubility ratio of apigenin in n-octanol and water was 2.87. Apigenin strongly absorbed UV light, with three maximum absorption wavelengths at 212, 269, and 337 nm (epsilon = 29,800, 19,020, and 18,930 M-1 cm-1, respectively). Using quercetin as the internal standard, a reversed-phase HPLC method was developed to quantitatively analyze apigenin in epidermal cells obtained from SENCAR mice. Apigenin was labeled at position 6, 8, 3', and 5' with tritium by a platinum-catalyzed proton-tritium exchange as confirmed indirectly by 1H NMR analysis of the deuterated apigenin. The tritium label was stable in aqueous environments, especially under acidic and neutral conditions, so [G-3H]apigenin was considered suitable for subsequent absorption and metabolic studies.

Response to intracrevicular controlled delivery of 25% tetracycline from poly(lactide/glycolide) film strips in SPT patients.

Controlled local delivery of antibiotics has been shown to reduce periodontopathic micro-organisms with minimal side-effects. Clinical studies in our laboratory have shown that 25% tetracycline HCl delivered from poly(D,L-lactide/glycolide) film strips (25 TTC-PLGA) released therapeutic concentrations of tetracycline for 10 days. The present pilot study compared the intracrevicular delivery of 25% tetracycline HCl incorporated in these biodegradable film strips to scaling and root planing (SRP) in 10 adult periodontitis patients, who in spite of therapy and regular supportive periodontal treatment (SPT), continued to possess 5 bleeding periodontal pockets at least 5 mm deep. Sites were randomly selected to receive the following treatments: (1) 25 TTC-PLGA, (2) control strips without TTC (PLGA), (3) SRP, and (4) untreated control. Film-strip retention was augmented with a suture/cement technique, followed by strip removal after 2 weeks. Clinical parameters and subgingival bacterial morphotypes (darkfield analysis) were evaluated over time (0, 2.4, 8, 12, 26 weeks). Results indicated that, compared to baseline, 25 TTC-PLGA film strips caused significant (p < or = 0.01): (1) probing depth reduction for 26 weeks, (2) a clinical attachment level gain for 12 weeks, (3) lower %s of spirochetes for 4 weeks and motile rods for 8 weeks (p < or = 0.05), and (4) an accompanying increase in cocci for 4 weeks. In the scaled and root planed sites, probing depth was the only finding that demonstrated a significant change from baseline (p < or = 0.01). Controls and PLGA showed isolated reductions in probing depth and % of motile organisms. From these findings, applications of intracrevicular 25 TTC-PLGA, when compared to scaling and root planing, appears to have an enhanced antibacterial effect and a similar clinical effect in SPT patients. The results of this study indicate further investigation of 25 TTC-PLGA film strips should be undertaken using more subjects and sophisticated microbiological and clinical measurements.

Porcine brain microvascular endothelial cells support the in vitro expansion of human primitive hematopoietic bone marrow progenitor cells with a high replating potential: requirement for cell-to-cell interactions and colony-stimulating factors.

Primary autologous as well as allogeneic and xenogeneic stroma will support human stem cell proliferation and differentiation for several months. In the present study, we investigated the capacity of porcine microvascular endothelial cells (PMVECs) together with combinations of cytokines (granulocyte-macrophage colony-stimulating factor [GM-CSF] + stem factor [SCF], interleukin-3 [IL-3] + SCF + IL-6, and GM-CSF + IL-3 + SCF + IL-6) to support the expansion and development of purified human CD34+ bone marrow cells. In short-term cultures (7 days), the greatest expansion of nonadherent hematopoietic cells and clonogenic progenitors was seen with CD34+ cells in direct contact with PMVEC monolayers (PMVEC contact), followed by PMVEC noncontact and liquid suspension cultures, respectively. Maximal expansion of nonadherent cells (42-fold) and total CD34+ cells (12.6-fold) occurred in PMVEC contact cultures treated with GM-CSF + IL-3 + SCF + IL-6, with similar increases in the number of granulocyte-macrophage colony-forming units (CFU-GM), CFU-mix, erythroid burst-forming units (BFU-E), CFU-blast and CFU-megakaryocyte (CFU-Mk) progenitor cells. Moreover, the number of CD34+ CD38- and CD34+ CD38+ cells increased 148.1-fold and 8.0-fold, respectively. Replating studies show that cells from day 7 dispersed blast cell colonies generated on cytokine-treated PMVEC monolayers have a high replating potential for multilineage progenitor cells. In long-term PMVEC contact cultures, CD34+ cells seeded onto PMVEC monolayers with GM-CSF + IL-3 + SCF + IL-6 showed a total calculated expansion of over 5,000,000-fold of nonadherent cells over 35 days in culture. Maximal clonogenic cell production was observed at day 28, with 6,353-fold for total CFC and comparable increases for CFU-GM, CFU-mix, CFU-blast, BFU-E, and CFU-Mk. The total number of CD34+ cells increased 2,584-fold at day 28. Furthermore, the extended growth kinetics of these cultures indicates that these phenotypically primitive progenitor cells are also functionally expanded on PMVEC monolayers. These results support the hypothesis that direct contact with a PMVEC monolayer supports the initial expansion of hematopoietic progenitor cells with a high replating potential and, possibly, a more primitive phenotype (CD34+, CD34+/CD38-).

Expression of the mouse testis-determining gene Sry in male preimplantation embryos.

The testis-determining factor in the mouse is encoded by the Sry gene on the Y chromosome. Transcripts of this gene have been shown previously to be present in the genital ridge at the beginning of gonadal differentiation (11.5 days post coitum) and in adult testis. In this study, RNA transcripts of the Sry gene are also detected in male blastocyst-stage embryos (3.5 days post coitum) at approximately 40-100 copies per cell, long before overt sex differentiation. These results indicate that preimplantation mouse embryos have sexually dimorphic gene expression at least with respect to Sry transcripts. In addition, at least some of the Sry RNA transcripts in blastocysts are circular, as has been reported for Sry transcripts from adult testis. The appearance of Sry transcripts in blastocysts at this level raises the possibility that sex determination begins earlier during embryonic development than previously thought.

Intravenous manganese-mesoporphyrin as a magnetic resonance imaging contrast agent: an experimental model using VX-2 carcinoma in rabbits.

RATIONALE AND OBJECTIVES: We investigated the potential of manganese (III) mesoporphyrin (Mn-mesoporphyrin) as a hepatobiliary contrast agent for magnetic resonance (MR) imaging in rabbits given VX-2 carcinoma liver implants. METHODS: Rabbits given VX-2 carcinoma liver implants (n = 8) were imaged before and after the intravenous (i.v.) administration of 0.04 mmol/kg Mn-mesoporphyrin. MR images were correlated with gross-specimen cross-sections. The distribution of Mn in various tissues following i.v. administration of 0.04 mmol/kg Mn-mesoporphyrin was determined using atomic absorption analysis. A standard panel of serum chemistries was followed over 7 days in six rabbits following this same dose of Mn-mesoporphyrin and compared with chemistries from two control rabbits. RESULTS: I.v. administration of 0.04 mmol/kg (25 mg/kg) Mn-mesoporphyrin resulted in improvement of tumor-to-liver contrast, with enhancement of normal liver (99.7 +/- 14.7%) and the gallbladder (442 +/- 116%), but not VX-2 tumor tissue (14.8 +/- 13.9%), (n = 8, p = .05). Analysis of tissue Mn levels 100 min after i.v. Mn-mesoporphyrin injection demonstrated preferential distribution of Mn to normal liver tissue (57.8 +/- 15.3 micrograms Mn/g) compared with VX-2 tumor (4.28 +/- 1.48 micrograms Mn/g). No significant change was found in the serum chemistries of six normal rabbits over a 7-day period after the i.v. administration of 0.04 mmol/kg Mn-mesoporphyrin. CONCLUSION: I.v. Mn-mesoporphyrin improved lesion-to-liver contrast because of preferential distribution of Mn-mesoporphyrin to normal liver parenchyma and bile.

Shelf-lives and factors affecting the stability of morphine sulphate and meperidine (pethidine) hydrochloride in plastic syringes for use in patient-controlled analgesic devices.

Published reports regarding the stability of morphine are at variance, especially in syringes used in patient-controlled analgesia (PCA) devices. In addition to the effects of container type and vehicle, reasons for this variation include the effect of excipients temperature and light during storage. Furthermore, the literature varies regarding the mechanisms of decomposition for morphine. To our knowledge, the stability of meperidine (pethidine) stored in plastic syringes has not been reported. The purposes of this study were to investigate the stability of morphine sulphate (1 and 5 mg/ml) and meperidine hydrochloride (5 and 10 mg/ml) in plastic syringes for use in PCA devices for a duration of 12 weeks, and evaluate the influence of light (240 foot-candles), temperature (-20, 4 and 23 degrees C), diluent (5% dextrose or normal saline), and drug concentration on the stability of these narcotic analgesics. Samples were taken bi-weekly for solutions protected from light and weekly for solutions exposed to light. Morphine sulphate and meperidine hydrochloride concentrations were quantified using independent, stability-indicating, high performance liquid chromatographic assays. The within-day and between-day coefficients of variation for these assays were < or = 4% over each of the concentration ranges studied. Under the conditions of this study, it is proposed that although decomposition of morphine to its main product, pseudomorphine, can be interpreted using first-order kinetics, consecutive (to form the N-oxide) and parallel mechanisms (to form apomorphine) exist. Morphine solutions were more stable in normal saline than in 5% dextrose. Shelf-life data indicate that morphine is stable for at least 6 weeks when protected from light.(ABSTRACT TRUNCATED AT 250 WORDS)

Oxidative stress-induced apoptosis prevented by Trolox.

The ability of oxidative stress to induce apoptosis (programmed cell death), and the effect of Trolox, a water soluble vitamin E analog, on this induction were studied in vitro in mouse thymocytes. Cells were exposed to oxidative stress by treating them with 0.5-10 microM hydrogen peroxide (H2O2) for 10 min, in phosphate-buffered saline supplemented with 0.1 mM ferrous sulfate. Cells were resuspended in RPMI 1640 medium with 10% serum and incubated at 37 degrees C under 5% CO2 in air. Electron microscopic studies revealed morphological changes characteristic of apoptosis in H2O2-treated cells. H2O2 treatment fragmented the DNA in a manner typical of apoptotic cells, producing a ladder pattern of 200 base pair increments upon agarose gel electrophoresis. The percentage of DNA fragmentation (determined fluorometrically) increased with increasing doses of H2O2 and postexposure incubation times. Pre- or posttreatment of cells with Trolox reduced H2O2-induced DNA fragmentation to control levels and below. The results indicate that oxidative stress induces apoptosis in thymocytes, and this induction can be prevented by Trolox, a powerful inhibitor of membrane damage.