Cytomegalovirus infection is a risk factor for venous thromboembolism in ANCA-associated vasculitis

BACKGROUND

Venous thromboembolism (VTE) is a common complication in patients with anti-neutrophil cytoplasm antibody (ANCA)-associated vasculitides (AAV) and confers significant morbidity and mortality. Both acute and past cytomegalovirus (CMV) infection have been identified as risk factors for VTE in immunocompetent and immunosuppressed individuals. Here, we examine whether past exposure to CMV is a risk factor for VTE amongst patients with AAV.

METHODS

We retrospectively analysed outcomes of patients with a new diagnosis of AAV from a UK cohort. All confirmed cases of VTE where CMV IgG serology was available were recorded. Retrospective collection of the same data for patients at a North American centre was used as a validation cohort.

RESULTS

VTE was common with 12% of patients from the study cohort (total 259 patients) developing an event during the median follow-up period of 8.5 years of which 60% occurred within the first 12 months following diagnosis. Sixteen percent of CMV seropositive patients developed a VTE compared with 5% of patients who were seronegative (p = 0.007) and CMV seropositivity remained an independent predictor of VTE in multivariable analysis (HR 2.96 [1.094-8.011] p = 0.033). CMV seropositivity at diagnosis was confirmed as a significant risk factor for VTE in the American validation cohort (p = 0.032).

CONCLUSIONS

VTE is common in patients with AAV, especially within the first year of diagnosis. Past infection with CMV is an independent risk factor associated with VTE in AAV.

Hyaline cartilage differentiation of fibroblasts in regeneration and regenerative medicine

Amputation injuries in mammals are typically non-regenerative; however, joint regeneration is stimulated by BMP9 treatment, indicating the presence of latent articular chondrocyte progenitor cells. BMP9 induces a battery of chondrogenic genes in vivo, and a similar response is observed in cultures of amputation wound cells. Extended cultures of BMP9-treated cells results in differentiation of hyaline cartilage, and single cell RNAseq analysis identified wound fibroblasts as BMP9 responsive. This culture model was used to identify a BMP9-responsive adult fibroblast cell line and a culture strategy was developed to engineer hyaline cartilage for engraftment into an acutely damaged joint. Transplanted hyaline cartilage survived engraftment and maintained a hyaline cartilage phenotype, but did not form mature articular cartilage. In addition, individual hypertrophic chondrocytes were identified in some samples, indicating that the acute joint injury site can promote osteogenic progression of engrafted hyaline cartilage. The findings identify fibroblasts as a cell source for engineering articular cartilage and establish a novel experimental strategy that bridges the gap between regeneration biology and regenerative medicine.

Summary:In vivo articular cartilage regeneration serves as a model to develop novel approaches for engineering cartilage to repair damaged joints and identifies fibroblasts as a BMP9-inducible chondroprogenitor.

Caring for Families Separated by Changing Immigration Policies and Enforcement: A Cultural Psychiatry Perspective

Recent changes in U.S. immigration policies and enforcement have precipitated a 300% rise in arrests and planned deportations. Although some family members face deportation, other family members may have state-sanctioned status. Such mixed status puts hundreds of thousands of families at risk of forced separation and associated mental health problems. Building on cross-cultural work with refugee families and other groups and on work with families separated by parental incarceration, the authors provide recommendations to guide clinicians working with families who are separated or who fear separation. Mental health problems among separated families can in part be addressed through identifying the origins of distress, elucidating family structures and roles, strengthening communication practices, linking with legal and economic resources, and facilitating decision making through distress reduction.

Lenalidomide for refractory cutaneous manifestations of pediatric systemic lupus erythematosus

Objective Cutaneous manifestations of pediatric systemic lupus erythematosus cause significant morbidity. Lenalidomide, a thalidomide analogue, has shown promise treating cutaneous lupus erythematosus in adults. Our objective was to evaluate lenalidomide's efficacy and safety in treating refractory cutaneous manifestations of pediatric systemic lupus erythematosus. Methods We performed a retrospective chart review of 10 adolescents who received lenalidomide for recalcitrant cutaneous lupus erythematosus. Information was gathered at drug initiation and 6-month follow-up. The Wilcoxon matched-pairs signed-rank test was used to assess change in quantitative parameters of disease activity. Results Nine subjects were girls and six were African-American. Indications for lenalidomide treatment included alopecia, nasal and oral ulcers, extensive malar rash, discoid lesions, bullous lesions, panniculitis, cutaneous vasculitis, and Raynaud's phenomenon with digital ulcerations. Within 6 months, all patients demonstrated complete or near resolution based on physician report. Prednisone dose decreased from a mean 23.5 mg (SD± 13.3) to 12.25 mg (SD± 9.2) ( P= 0.008). Sedimentation rate decreased from a mean 29 mm/hour (SD± 31.5) to 17 mm/hour (SD± 18.1) ( P= 0.004). Lenalidomide was well tolerated. Conclusion Lenalidomide is an effective and safe treatment for a spectrum of dermatological conditions in pediatric systemic lupus erythematosus. Its use may allow a reduction in prednisone dose and decreased disfigurement. Prospective study is needed to clarify lenalidomide's role in treating cutaneous manifestations of systemic lupus erythematosus.

Hydrogen-release mechanisms in the breakdown of thin SiO2 films

The mechanism of hydrogen release from the anode Si/SiO(2) interface that triggers defect generation and finally the dielectric breakdown of the oxide in metal-oxide-semiconductor structures is investigated. Extensive experimental charge-to-breakdown statistics are used to derive the defect generation efficiency as a function of gate voltage and oxide thickness in wide ranges. The presented results provide strong support to single-electron assisted Si-H bond breakage and discard multiple electron induced incoherent vibrational heating mechanisms.

Preventing mediastinal shift after pneumonectomy impairs regenerative alveolar tissue growth

To examine the effects of mechanical lung strain on regenerative growth of alveolar septal tissue after pneumonectomy (PNX), we replaced the right lungs of adult dogs with a custom-shaped inflatable silicone prosthesis. The prosthesis was either inflated (Inf) to maintain the mediastinum at the midline or deflated to allow mediastinal shift. The animals were euthanized approximately 15 mo later, and the lungs were fixed at a constant distending pressure. With the Inf prostheses, lung expansion, alveolar septal tissue volumes, surface areas, and diffusing capacity of the tissue-plasma barrier were significantly lower than with the deflated prostheses; the expected post-PNX tissue responses were impaired by 30-60%. Capillary blood volume was significantly higher with Inf prostheses, consistent with microvascular congestion. Measurements in the Inf group remained consistently and significantly higher than those expected for a normal left lung, indicating persistence of partial compensation. In one dog, delayed deflation of the prosthesis 9-10 mo after PNX led to vigorous lung expansion and septal tissue growth, particularly of type II epithelial cells. We conclude that mechanical lung strain is a major signal for regenerative lung growth; however, other signals are also implicated, accounting for a significant fraction of the compensatory response to PNX.

Adaptation of respiratory muscle perfusion during exercise to chronically elevated ventilatory work

Pneumonectomy (PNX) leads to chronic asymmetric ventilatory loading of respiratory muscles (RM). We measured RM energy requirements during exercise from RM blood flow (Q) using a fluorescent microsphere technique in dogs that had undergone right PNX as adults (adult R-PNX) or as puppies (puppy R-PNX), compared with dogs subjected to right thoracotomy without PNX as puppies (Sham) and to left PNX as adults (adult L-PNX). Ventilatory work (W) was measured during exercise. RM weight was determined post mortem. After adult and puppy R-PNX, the right hemidiaphragm becomes grossly distorted, but W and right costal muscle mass increased only after adult R-PNX. After adult L-PNX, the diaphragm was undistorted; W and left hemidiaphragm RM Q were elevated, but muscle mass did not increase. Mass of parasternal muscle did not increase after adult R-PNX, despite increased Q. Thus muscle mass increased only in response to the combination of chronic stretch and dynamic loading. There was a dorsal-to-ventral gradient of increasing Q within the diaphragm, but the distribution was unaffected by anatomic distortion, hypertrophy, or workload, suggesting a fixed pattern of neural activation. The diaphragm and parasternals were the primary muscles compensating for the asymmetric loading from PNX.

Preventing mediastinal shift after pneumonectomy does not abolish physiological compensation

To determine the role of mediastinal shift after pneumonectomy (PNX) on compensatory responses, we performed right PNX in adult dogs and replaced the resected lung with a custom-shaped inflatable silicone prosthesis. Prosthesis was inflated (Inf) to prevent mediastinal shift, or deflated (Def), allowing mediastinal shift to occur. Thoracic, lung air, and tissue volumes were measured by computerized tomography scan. Lung diffusing capacities for carbon monoxide (DL(CO)) and its components, membrane diffusing capacity for carbon monoxide (Dm(CO)) and capillary blood volume (Vc), were measured at rest and during exercise by a rebreathing technique. In the Inf group, lung air volume was significantly smaller than in Def group; however, the lung became elongated and expanded by 20% via caudal displacement of the left hemidiaphragm. Consequently, rib cage volume was similar, but total thoracic volume was higher in the Inf group. Extravascular septal tissue volume was not different between groups. At a given pulmonary blood flow, DL(CO) and Dm(CO) were significantly lower in the Inf group, but Vc was similar. In one dog, delayed mediastinal shift occurred 9 mo after PNX; both lung volume and DL(CO) progressively increased over the subsequent 3 mo. We conclude that preventing mediastinal shift after PNX impairs recruitment of diffusing capacity but does not abolish expansion of the remaining lung or the compensatory increase in extravascular septal tissue volume.

Phase I study of AG 331, a novel thymidylate synthase inhibitor, in patients with refractory solid tumors

PURPOSE

This was a phase I study of AG 331 to determine systemic tolerance and pharmacokinetics following single and multiple escalating intravenous doses.

METHODS

The study was an open-label phase I trial that was divided into two components. In phase IA (single dose), six dose levels from 12.5 to 225 mg/m2 were administered to 18 patients (3 at each dose level) and serial blood samples were collected for 72 h. Upon achieving satisfactory pharmacologic parameters, the multiple dosing component (phase IB) was initiated. Six dose levels from 50 to 800 mg/m2 per day were administered for 5 consecutive days to 18 patients. Pre- and postdose blood samples were obtained on days 1-4 and serial blood samples were collected over 24 h following dose 5. Nonhematologic and hepatic toxicities were assessed, serum AG 331 concentrations were measured and pharmacokinetic parameters determined.

RESULTS

Other than fatigue, no severe toxicities were encountered in phase IA. Liver toxicity was manifested by elevations in transaminase first noted at multiple doses of 200 mg/m2 per day for 5 days. Fever and malaise but no myelosuppression were noted. The mean terminal t1/2 following single doses was significantly shorter than the t1/2 following multiple dosing (6.8 vs 9.9 h) and clearance was significantly faster following single doses than following multiple dosing (81.7 vs 30.4 l/h), but no significant difference in Vd was noted.

CONCLUSIONS

The dose-related toxicity profile precludes further clinical development at this time. The pharmacokinetics of AG 331 following single and multiple doses showed significant differences.

Initial clinical trial and pharmacokinetics of Thymitaq (AG337) by 10-day continuous infusion in patients with advanced solid tumors

PURPOSE

To establish the maximum tolerated dose (MTD), dose-limiting and other major toxicities and the major pharmacokinetic parameters of a 10-day infusion of the nonclassical antifolate Thymitaq.

METHODS

The drug was given by 10-day infusion via a portable pump. The starting dose was 286 mg/m2 per day with escalation to 572 and 716 mg/m2 per day. Thymitaq in plasma was assayed by a validated isocratic reverse-phase HPLC assay with detection at 273 nm.

RESULTS

The dose of 716 mg/m2 per day x 10 was considered too high as none of three patients completed a 10-day infusion and two of three developed grade IV myelotoxicity. At 572 mg/m2 per day three of four patients completed a 10-day infusion. Dose-limiting myelosuppression was seen in one of four but owing to a high incidence of thrombotic phenomena, no further patients were added.

CONCLUSION

Continuous 10-day infusions of Thymitaq should be limited to low doses until further studies can be done.

High-performance liquid chromatographic method for the determination of nelfinavir, a novel HIV-1 protease inhibitor, in human plasma

Nelfinavir mesylate, a potent and orally bioavailable inhibitor of HIV-1 protease (Ki=2 nM), has undergone Phase III clinical evaluation in a large population of HIV-positive patients. A high-performance liquid chromatography analytical method was developed to determine the pharmacokinetic parameters of the free base, nelfinavir, in these human subjects. The method involved the extraction of nelfinavir and an internal standard, 6,7-dimethyl-2,3-di-(2-pyridyl)quinoxaline, from 250 microl of human plasma with a mixture of ethyl acetate-acetonitrile (90:10, v/v). The analysis was via ultraviolet detection at 220 nm using a reversed-phase C18 analytical column and a mobile phase consisting of 25 mM monobasic sodium phosphate buffer (adjusted to pH 3.4 with phosphoric acid)-acetonitrile (58:42, v/v) that resolved the drug and internal standard peaks from non-specific substances in human plasma. The method was validated under Good Laboratory Practice (GLP) conditions for specificity, inter- and intra-assay precision and accuracy, absolute recovery and stability. The mean recovery ranged from 92.4 to 83.0% for nelfinavir and was 95.7% for the internal standard. The method was linear over a concentration range of 0.0300 microg/ml to 10 microg/ml, with a minimum quantifiable level of 0.0500 microg/ml for nelfinavir.

In vivo assessment of changes in air and tissue volumes after pneumonectomy

We examined the progression and topographical distribution of postpneumonectomy volume changes in immature foxhounds undergoing right pneumonectomy (R-Pnx, n = 5) or sham pneumonectomy (Sham, n = 6) at 2 mo of age and subsequently raised to maturity. Volumes of lung air (Vair) and tissue (Vti) were estimated by computerized tomography (CT) scan at 7, 22, and 52 wk after surgery at a transpulmonary pressure of 20 cmH2O. Estimates of Vti by CT scan included both septal tissue as well as nonseptal tissue (small- and medium-sized airways and blood vessels); these were compared with estimates of septal Vti by an acetylene rebreathing (Rb) method. We found significant correlations between these techniques (Vair(CT) = 0.83 Vair(Rb) + 275, R = 0.97; Vti(CT) = 1.62 Vti(Rb) - 30, R = 0.81). Extravascular septal Vti returned to normal 7 wk after R-Pnx and remained normal up to maturity. Nonseptal Vti remained significantly below normal. The greatest increase in Vti occurred in the midlung region just cephalad and caudal to the heart. After an early period of accelerated tissue growth after R-Pnx, the rate of septal tissue growth matched that of somatic growth, whereas nonseptal tissue growth lagged behind. Compensatory growth of the remaining left lung was not associated with selective alterations in thoracic development.

Source of error on A-aDO2 calculated from blood stored in plastic and glass syringes

We studied the effects of time delay on blood gases, pH, and base excess in blood stored in glass and plastic syringes on ice and the effects of resulting errors on calculated alveolar-to-arterial PO2 difference (A-aDO2). Matched samples of dog whole blood were tonometered with gas mixtures of 5% CO2-12% )2-83% N2 (mixture A), 10% CO2-5% O2-85% N2 (mixture B), and 2.88% CO2-4% O2-93.12% N2 (mixture C). Tonometered blood samples were transferred to 5-ml glass (5G), 5-ml plastic (5P), and 3-ml plastic (3P) syringes and stored on ice. Blood gases were measured every 1 h up to 6 h. In 5G, PO2 progressively decreased in blood tonometered with mixture A but rose in blood tonometered with mixtures B and C. O2 saturation progressively fell in all cases. In 5G, blood PCO2 progressively rose regardless of which gas mixture was used, and pH as well as base excess progressively fell. The rise in PO2 was faster in plastic than in glass syringes, and O2 saturation always rose in plastic syringes. Differences between storage in plastic and glass syringes on PO2 change were greatest when initial blood PO2 was highest (mixture A). At the highest PO2, O2 exchange was faster in 3P than in 5P. The rise of PCo2 was just as fast in plastic as in glass syringes, but in both the rise in PCO2 was faster at a higher initial PCO2 (mixture B) than in lower initial PCO2 (mixtures B and C). Rates of PO2 and PCO2 change in matched samples were significantly faster in 3P than in 5P. Errors due to rises in PCO2 and PO2 cause additive errors in calculated A-aDO2, and when blood is stored in plastic syringes for > 1 h significant errors result. Errors are greater in normoxic blood, in which estimated A-aDO2 decreased by > 10 Torr after 6 h on ice in plastic syringes, than in hypoxic blood.

Phase I trial of the thymidylate synthase inhibitor AG331 as a 5-day continuous infusion

AG331 (N6-[4-(morpholinosulfonyl)benzyl]-N6-methyl-2, 6-diaminobenz-[c,d]-indole glucuronate) is a lipophilic thymidylate synthase inhibitor with activity in solid tumor models. On the basis of preclinical data supporting regimens of frequent drug administration, we performed a Phase I trial of AG331 as a 5-day continuous infusion repeated every 3 weeks. Twenty-nine patients were entered at doses ranging from 25 to 1000 mg/m2/day. The major side effects were mild to moderate fatigue, nausea, vomiting, diarrhea, and fever. At doses >/=400 mg/m2, acute reversible elevation of bilirubin, aspartate aminotransferase, alanine aminotransferase, and gamma-glutamyltranspeptidase was observed. All patients who received >/=600 mg/m2/day experienced elevated alanine aminotransferase. Elevated liver function tests were evident by day 3 of the infusion and had resolved by day 8 in the majority. This toxicity was dose limiting at 1000 mg/m2/day, at which dose two of two patients developed grade 4 reversible hyperbilirubinemia in addition to the enzyme elevations. Serum and urine samples were analyzed by a novel high-pressure liquid chromatography method for the determination of the pharmacokinetics of AG331. Over the 50-1000 mg/m2/day dose range, mean total clearance ranged from 11.6 to 30.0 liters/h/m2, and volume of distribution at steady state ranged from 279.5 to 758.7 liters/m2. These parameters were dose independent over the dose range tested. The harmonic mean terminal half-life of AG331 was 20.2 h. Less than 5% of an AG331 dose is eliminated unchanged in the urine. Both the administered dose and exposure to the drug were related to the changes in bilirubin and aminotransferase blood levels. Evidence for inhibition of thymidylate synthase was obtained at doses ranging from 100 to 1000 mg/m2 in seven patients; plasma deoxyuridine concentrations at end-infusion were 1.8-3.8-fold higher than pretreatment values. Because of the nature of toxicity on this schedule, more extensive Phase II evaluation is not recommended, although an AG331 dose of 800 mg/m2/day for 5 days is tolerable. Exploration of less frequent dose administration is under way.

Temporal course of gas exchange and mechanical compensation after right pneumonectomy in immature dogs

To determine the temporal progression and magnitude of functional compensation in immature dogs raised to maturity after extensive lung resection, we performed right pneumonectomy (R-Pnx) or right thoracotomy without pneumonectomy (Sham) in matched foxhounds at 2 mo of age. At 4, 8, 20, 40, and 60 wk after surgery, static transpulmonary pressure-lung volume relationships were determined. Lung diffusing capacity, membrane diffusing capacity, pulmonary capillary blood volume, pulmonary blood flow, septal lung tissue volume, and lung volumes were measured simultaneously by a rebreathing technique. During maturation, total lung capacity, lung volume at a given distending pressure, and compliance were lower in the R-Pnx group than in the Sham group (P < 0.05). Pulmonary viscous resistance at maturity was elevated after R-Pnx. There were no significant differences in total lung diffusing capacity, membrane diffusing capacity, pulmonary capillary blood volume, pulmonary blood flow, and septal lung tissue volume between groups. Compensation of alveolar-capillary gas exchange was complete by 4-8 wk after R-Pnx, but compensation of mechanical properties remained incomplete throughout maturation. Relative magnitude of compensation after R-Pnx was greater in immature dogs than in adult dogs studied previously by similar techniques.

Role of hematocrit in the recruitment of pulmonary diffusing capacity: comparison of human and dog

In dogs, maximal O2 uptake (VO2max) per kilogram of body weight is two- to threefold that in humans; the difference cannot be explained solely by differences in structural features between species. We compared the functional recruitment of pulmonary diffusing capacity (DLCO) during exercise in dogs with that in humans to determine whether pulmonary gas exchange is matched to VO2max or the size of the lungs and to define the potential role of exercise-induced polycythemia in producing the superior aerobic capacity of the dogs. We compared the relationships of DLCO, membrane diffusing capacity (DMCO), and pulmonary capillary blood volume (Vc) with respect to pulmonary blood flow (Qc) by a rebreathing method during steady-state exercise in adult male human subjects and in conditioned adult male foxhounds. The slopes and intercepts of the relationships of DLCO and DMCO to Qc are significantly greater in dogs than in humans; the slopes of the relationship of Vc to Qc are similar. In dogs diffusive pulmonary gas transport is matched to the higher VO2max. The enhanced recruitment of DLCO and DMCO in dogs during exercise could potentially be explained entirely by the exercise-induced polycythemia, which is seen in dogs but not in humans.

High-performance liquid chromatographic method for the determination of a novel thymidylate synthase inhibitor, AG 331, in human serum

AG 331 is a novel thymidylate synthase inhibitor currently in Phase I clinical trial. To determine the pharmacokinetic parameters of AG 3331 in human subjects, a suitable analytical method was developed using high-performance liquid chromatography. Serum and urine samples were prepared using both solid-phase extraction and solvent extraction. Either 4,4'-diaminodiphenyl sulfone or benz[cd]indole-2(1H)-one were used as internal standards for the method. A reversed-phase C18 analytical column completely resolved the drug and internal standard peaks from non-specific substances present in biological matrix. The method was validated for precision, accuracy, and reproducibility in serum and was linear over a concentration range of 50-2000 ng/ml, with a limit of detection of 20.0 ng/ml and a quantifiable limit of 50 ng/ml.

Toxicity of the 1-methyl-4-phenyl-2,3-dihydropyridinium and 1-methyl-4-phenylpyridinium species in primary cultures of mouse astrocytes

The biochemical and toxic effects of the two monoamine oxidase-generated metabolites of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine were investigated using primary cultures of mouse astrocytes. After the addition of equimolar concentrations (25 microM) of these metabolites, namely 1-methyl-4-phenyl-2,3-dihydropyridinium (MPDP+) ion or 1-methyl-4-phenylpyridinium (MPP+) ion, similar levels of MPP+ accumulated within the astrocytes. Both MPDP+ and MPP+ caused cytotoxicity which was preceded by increased glucose utilization and lactate accumulation. The metabolites were equipotent in producing a rapid decrease in cellular ATP which correlated well with the intracellular accumulation of MPP+ and the loss of cell viability. When astrocytes were incubated in glucose-free medium, both ATP depletion and loss of viability occurred more rapidly. Formation of MPP+ from MPDP+ was not affected by the presence of astrocytes, because MPP+ concentrations increased over time at the same rate regardless of the presence or absence of cells. In contrast to pretreatment of cells with monoamine oxidase inhibitors before addition of MPTP, pretreatment of astrocytes with deprenyl and clorgyline had no effect on intracellular levels of MPP+ after exposure to MPDP+ or MPP+ and did not protect against ATP depletion or cytotoxicity. These results indicate that 1) MPP+ and MPDP+ cause similar metabolic changes leading to cell death probably via ATP depletion; (2) intracellular levels of MPP+ are directly correlated to cytotoxicity; and (3) MPDP+ toxicity is also correlated to intracellular MPP+ accumulation, further confirming that MPP+ rather than MPDP+ is responsible for cell damage.

Toxicity of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine in primary cultures of mouse astrocytes

The conversion of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to its toxic 1-methyl-4-phenylpyridinium (MPP+) metabolite catalyzed by monoamine oxidase (MAO) type B is likely to occur within glial cells in the central nervous system. In this study, primary cultures of mouse astrocytes were used to assess the biochemical and toxic consequences of exposure to MPTP. MPTP caused a concentration-dependent loss of cell viability. This effect was probably due to the intracellular generation of MPP+, because cytotoxicity was prevented by preincubation of astrocytes in the presence of MAO inhibitors. After addition of 250 microM MPTP, loss of cell viability was preceded by an increased rate of glucose utilization and lactate accumulation, and by depletion of ATP. The ratio between the rates of lactate production (0.37 mM/hr) and glucose consumption (0.2 mM/hr) was 1.85, indicating that most of the glucose present in the medium was stoichiometrically converted to lactate via glycolysis. A remarkable correlation was found between ATP depletion and cytotoxicity caused by MPTP, and, when astrocytes were incubated in glucose-free medium, both ATP depletion and loss of viability occurred more rapidly. Finally, even after exposure for several days, astrocyte death could be prevented by washing MPTP from the incubation medium, suggesting that MPP(+)-induced mitochondrial damage may be reversible. We conclude that prolonged exposure of astrocytes to MPTP may result in loss of viability via the MAO-dependent generation of MPP+ and the ability of this toxic metabolite to impair mitochondrial function.(ABSTRACT TRUNCATED AT 250 WORDS)

Production and disposition of 1-methyl-4-phenylpyridinium in primary cultures of mouse astrocytes

Dopaminergic neurons are a primary target for 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) neurotoxicity. However, the conversion of MPTP to its neurotoxic 1-methyl-4-phenylpyridinium metabolite (MPP+) is likely to occur in astrocytes via the monoamine oxidase (MAO)-dependent formation of the 1-methyl-4-phenyl-2,3-dihydropyridinium intermediate (MPDP+). The main purpose of this study was to characterize the molecular mechanism(s) by which MPP+, once generated by astrocytes, may reach the extracellular space to become available for the active accumulation into dopaminergic neurons. Primary cultures of mouse astrocytes were used as an in vitro model system. After the addition of MPTP, levels of MPP+ were found to increase at constant rates both intracellularly and extracellularly at time points when no sign of cytotoxicity was evident. In contrast, MPDP+ levels remained quite stable during 4 days of incubation in the presence of MPTP. Finally, when astrocytes were allowed to accumulate MPP+ by pretreatment with either MPTP or MPP+ and then were incubated in fresh medium not containing MPTP or MPP+, intracellular levels of MPP+ rapidly declined and corresponding amounts of this compound were found in the incubation medium. Results of this study are compatible with the following conclusions: 1) the MPP+ accumulated in the extracellular compartment during incubations with MPTP is not released from astrocytes as a consequence of its own cytotoxic effects; 2) MPP+ can be formed extracellularly presumably via autoxidation of MPDP+ after this latter compound has been generated within astrocytes and has crossed astrocyte membranes; and 3) despite its charged chemical structure, MPP+ can cross the plasma membrane toward the extracellular space after being formed within astrocytes.

Biotransformation of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine in primary cultures of mouse astrocytes

Astrocytes are likely to be a main locus for the metabolic bioactivation of the neurotoxicant 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). In this study, a detailed analysis of MPTP metabolism was conducted in primary cultures of mouse astrocytes. A constant rate of conversion of 1.22 nmol/mg of protein per hr was observed when astrocyte cultures were incubated in the presence of 250 microM MPTP for 4 days. Three metabolites were detected as products of this conversion: 1-methyl-4-phenyl-2,3-dihydropyridinium ion (MPDP+), 1-methyl-4-phenylpyridinium ion (MPP+) and MPTP N-oxide. Production of MPP+ and MPTP N-oxide occurred at constant rates of 0.68 and 0.43 nmol/mg of protein per hr, respectively, whereas the level of MPDP+ remained quite stable and relatively low throughout the time of incubation. Both clorgyline, an inhibitor of monoamine oxidase (MAO) type A, and deprenyl, a MAO B inhibitor, blocked MPTP conversion to MPDP+ and MPP+; quantitative analysis of the effects of these two inhibitors revealed that MAO A and MAO B contribute to a similar extent to MPP+ production in astrocyte cultures. MAO inhibition did not result in an increased production of MPTP N-oxide and, in fact, the level of this metabolite was reduced markedly in the presence of 100 microM clorgyline. Formation of MPTP N-oxide was probably dependent upon the activity of the flavin-containing monooxygenase because: 1) it was blocked completely by thiobenzamide, a competitive substrate for this microsomal enzyme and 2) it was increased in the presence of n-octylamine, a known positive effector for flavin-containing monooxygenase.(ABSTRACT TRUNCATED AT 250 WORDS)

Relationships between the mitochondrial transmembrane potential, ATP concentration, and cytotoxicity in isolated rat hepatocytes

The relationships between mitochondrial transmembrane potential, ATP concentration, and cytotoxicity were evaluated after exposure of isolated rat hepatocytes to different mitochondrial poisons. Both the neurotoxicant 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and its fully oxidized metabolite, the 1-methyl-4-phenylpyridinium (MPP+) ion, caused a concentration- and time-dependent depolarization of mitochondrial membranes which followed ATP depletion and preceded cytotoxicity. The effect of MPTP, but not that of MPP+, was prevented by deprenyl, an inhibitor of MPTP conversion to MPP+ via monoamine oxidase type B. Addition of fructose to the hepatocyte incubations treated with either MPTP or MPP+ counteracted the loss of mitochondrial transmembrane potential. Fructose was also effective in protecting against the mitochondrial membrane depolarization as well as ATP depletion and cytotoxicity induced by antimycin. A, carbonyl cyanide p-trifluoromethoxyphenyl hydrazone, and valinomycin. Data confirm the key role played by MPP(+)-induced mitochondrial damage in MPTP toxicity and indicate that (i) ATP produced via the glycolytic pathway can be utilized by hepatocytes to maintain mitochondrial electrochemical gradient, and (ii) a loss of mitochondrial membrane potential may occur only when supplies of ATP are depleted.

1-methyl-4-phenylpyridinium (MPP+) analogs: in vivo neurotoxicity and inhibition of striatal synaptosomal dopamine uptake

The ability of various 1-methyl-4-phenylpyridinium (MPP+) analogs to inhibit the uptake of tritium labeled dopamine and MPP+ by synaptosomes prepared from neostriata of male C57 Black mice was measured and compared with their dopaminergic neurotoxic potential which was estimated by an in vivo intracerebral microdialysis technique. The correlation observed between these two properties suggests that nerve terminal uptake is an important step in the expression of the nigrostriatal toxicity of structural analogs of MPP+. The uptake inhibition and neurotoxic properties of this series of compounds appear to be highly structurally sensitive and suggest that few nitrogenous bases will be potent 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-type neurotoxins.

The effect of diethyldithiocarbamate on the biodisposition of MPTP: an explanation for enhanced neurotoxicity

Diethyldithiocarbamate (DDC) has been reported to exacerbate the neurotoxic effects of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in mice. In this study, the effects of DDC on the biotransformation and distribution of MPTP and 1-methyl-4-phenylpyridinium ion (MPP+, the putative toxic metabolite of MPTP) were investigated. When DDC was administered prior to a standardized dosage of MPTP, the initial concentrations of MPTP in striatum, ventral mesencephalon and frontal cortex were markedly increased when compared to animals given MPTP alone. The pre-administration of DDC also produced increased concentrations of MPP+ in these regions at all time points studied. Further, the rate of disappearance of MPP+ from brain was significantly less in DDC pretreated animals, when compared to animals given MPTP alone. In vitro studies, using either brain homogenates or partially purified MAO-B, showed that DDC enhanced the biotransformation of MPTP. These results suggest that DDC enhances MPTP-induced neurotoxicity by increasing brain concentrations of MPP+. Factors contributing to this increase appear to include greater delivery of MPTP to the central nervous system (CNS), increased biotransformation of MPTP to MPP+ via MAO, and possibly reduced clearance of MPP+ from the brain.

Cation-exchange high-performance liquid chromatography assay for the nigrostriatal toxicant 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine and its monoamine oxidase B generated metabolites in brain tissues

This paper describes a sensitive (1 pmol/mg tissue) and selective bioanalytical method for the quantitative estimation of the nigrostriatal toxicant 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and its monoamine oxidase B generated metabolites, the 1-methyl-4-phenyl-2,3-dihydropyridinium species MPDP+ and the 1-methyl-4-phenylpyridinium species MPP+. The method is based on initial separation of the analytes after treatment of brain tissue homogenates with 5% trichloroacetic acid. The soluble fraction is analyzed directly by cation-exchange high-performance liquid chromatography employing a diode array UV detector. Results obtained with this assay have provided the first evidence for the presence of MPDP+ in the mouse brain following intravenous administration of MPTP.

Interactions of the 1-methyl-4-phenyl-2,3-dihydropyridinium species with synthetic dopamine-melanin

This paper describes interactions between the 1-methyl-4-phenyl-2,3-dihydropyridinium (MPDP+) metabolite of the nigrostriatal toxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) with synthetic dopamine-melanin, a polymeric pigment which is similar to the neuromelanin found in the nigrostriatal cell bodies of humans and primates. Although MPTP and its 1-methyl-4-phenylpyridinium (MPP+) metabolite bind to the synthetic pigment at physiological pH, both compounds are recovered quantitatively upon treatment with acid. Unlike MPTP and MPP+, MPDP+ proved to be unstable in the presence of synthetic dopamine-melanin which promoted its conversion to the fully oxidized pyridinium product MPP+. The possible biological significance of this interaction is discussed.