Glutathione monoethyl ester can selectively protect liver from high dose BCNU or cyclophosphamide

A Critical Analysis of Experimental Animal Models of Sinusoidal Obstruction Syndrome

Given the high mortality rate and clinical impact associated with sinusoidal obstruction syndrome (SOS), many studies have attempted to better characterize the disease and potential treatment strategies. However, the unpredictability of SOS onset represents a major obstacle when developing reproducible and controlled clinical trials in humans. Similarly, although in vitro studies have elucidated many of the molecular and cellular mechanisms of SOS, they often lack clinical relevance and translatability, highlighting the importance of experimental in vivo research. Animal models have greatly varied in the approach used to induce SOS in accordance with the numerous causes of human disease. Thus far, the most common and prevalent model is the monocrotaline-induced model in rats, which has served as the basis for both new diagnostic and treatment studies and has been revised over the last 20 years to optimize its use. Furthermore, radiotherapy, oxaliplatin-based chemotherapy, and even hematopoietic stem cell transplantation have been recently used to better replicate human SOS in animals. Nevertheless, because of the novelty of such research, further studies should be conducted to better understand the reproducibility and applicability of these newer models. Thus, this review seeks to summarize the methods and results of experimental in vivo models of SOS and compare the efficacy of these various adaptations.

Interventions for prophylaxis of hepatic veno-occlusive disease in people undergoing haematopoietic stem cell transplantation

BACKGROUND

Hepatic veno-occlusive disease (VOD) is a severe complication after haematopoietic stem cell transplantation (HSCT). Different drugs with different mechanisms of action have been tried in HSCT recipients to prevent hepatic VOD. However, it is uncertain whether high-quality evidence exists to support any prophylactic therapy.

OBJECTIVES

We aimed to determine the effects of various prophylactic therapies on the incidence of hepatic VOD, overall survival, mortality, quality of life (QOL), and the safety of these therapies in people undergoing HSCT.

SEARCH METHODS

We searched the Cochrane Central Registe of Controlled Trials (CENTRAL), MEDLINE, EMBASE, conference proceedings of three international haematology-oncology societies and two trial registries in January 2015, together with reference checking, citation searching and contact with study authors to identify additional studies.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) comparing prophylactic therapies with placebo or no treatment, or comparing different therapies for hepatic VOD in people undergoing HSCT.

DATA COLLECTION AND ANALYSIS

We used standard methodological procedures expected by Cochrane.

MAIN RESULTS

We included 14 RCTs. Four trials (612 participants) compared ursodeoxycholic acid with or without additional treatment versus placebo or no treatment or same additional treatment. Two trials (259 participants) compared heparin with no treatment. Two trials (106 participants) compared low molecular weight heparin (LMWH) with placebo or no treatment. One trial (360 participants) compared defibrotide with no treatment. One trial (34 participants) compared glutamine with placebo. Two trials (383 participants) compared fresh frozen plasma (FFP) with or without additional treatment versus no treatment or same additional treatment. One trial (30 participants) compared antithrombin III with heparin versus heparin. One trial compared heparin (47 participants) with LMWH (46 participants) and prostaglandin E1 (PGE1) (47 participants). No trial investigated the effects of danaparoid. The RCTs included participants of both genders with wide age range and disease spectrum undergoing autologous or allogeneic HSCT. Funding was provided by government sources (two studies), research fund (one study), pharmaceutical companies that manufactured defibrotide and ursodeoxycholic acid (two studies), or unclear source (nine studies). All RCTs had high risk of bias because of lack of blinding of participants and study personnel, or other risks of bias (mainly differences in baseline characteristics of comparison groups).Results showed that ursodeoxycholic acid may reduce the incidence of hepatic VOD (risk ratio (RR) 0.60, 95% confidence interval (CI) 0.40 to 0.88; number needed to treat for an additional beneficial outcome (NNTB) 15, 95% CI 7 to 50, low quality of evidence), but there was no evidence of difference in overall survival (hazard ratio (HR) 0.83, 95% CI 0.59 to 1.18, low quality of evidence). It may reduce all-cause mortality (RR 0.70, 95% CI 0.50 to 0.99; NNTB 17, 95% CI 8 to 431, low quality of evidence) and mortality due to hepatic VOD (RR 0.27, 95% CI 0.09 to 0.87; NNTB 34, 95% CI 16 to 220, very low quality of evidence). There was no evidence of difference in the incidence of hepatic VOD between treatment and control groups for heparin (RR 0.47, 95% CI 0.18 to 1.26, very low quality of evidence), LMWH (RR 0.27, 95% CI 0.06 to 1.18, very low quality of evidence), defibrotide (RR 0.62, 95% CI 0.38 to 1.02, low quality of evidence), glutamine (no hepatic VOD in either group, very low quality of evidence), FFP (RR 0.66, 95% CI 0.20 to 2.17, very low quality of evidence), antithrombin III (RR 0.13, 95% CI 0.01 to 2.15, very low quality of evidence), between heparin and LMWH (RR 1.96, 95% CI 0.80 to 4.77, very low quality of evidence), between heparin and PGE1 (RR 1.20, 95% CI 0.58 to 2.50, very low quality of evidence), and between LMWH and PGE1 (RR 0.61, 95% CI 0.24 to 1.55, very low quality of evidence). There was no evidence of difference in survival between treatment and control groups for heparin (92.6% vs. 88.7%) and defibrotide (HR 1.04, 95% CI 0.54 to 2.02, low quality of evidence). There were no data on survival for trials of LMWH, glutamine, FFP, antithrombin III, between heparin and LMWH, between heparin and PGE1, and between LMWH and PGE1. There were no data on quality of life (QoL) for any trials. Eleven trials reported adverse events. There was no evidence of difference in the frequency of adverse events between treatment and control groups except for one trial showing that defibrotide resulted in more adverse events compared with no treatment (RR 18.79, 95% CI 1.10 to 320.45). These adverse events included coagulopathy, gastrointestinal disorders, haemorrhage and microangiopathy. The quality of evidence was low or very low due to bias of study design, and inconsistent and imprecise results.

AUTHORS' CONCLUSIONS

There is low or very low quality evidence that ursodeoxycholic acid may reduce the incidence of hepatic VOD, all-cause mortality and mortality due to VOD in HSCT recipients. However, the optimal regimen is not well-defined. There is insufficient evidence to support the use of heparin, LMWH, defibrotide, glutamine, FFP, antithrombin III, and PGE1. Further high-quality RCTs are needed.

Use of defibrotide in the treatment and prevention of veno-occlusive disease

Hepatic veno-occlusive disease (VOD) is one of the most important complications of high-dose chemotherapy and stem cell transplantation. VOD is a clinical syndrome characterized by jaundice, hepatic enlargement and fluid retention typically seen by day +30 after transplantation. Severe VOD is complicated by multiorgan failure and a high mortality rate approaching 100%. Defibrotide (DF) is a novel agent with both antithrombotic and fibrinolytic properties that has emerged as an effective therapy for severe VOD. In Phase II studies, treatment of severe VOD has resulted in complete responses of 30-60% and survival past day 100 ranging between 32-50%. A Phase III, historically controlled study of DF for treatment of severe VOD has recently been completed and results are awaited with interest. In addition, DF may be effective prophylaxis for VOD in high-risk patients. This review will focus on a summary of the pharmacology of DF and the clinical evidence for its use in VOD.

Dactinomycin-induced Hepatic Sinusoidal Obstruction Syndrome Responding to Treatment with N-acetylcysteine

Hepatic sinusoidal obstruction syndrome is commonly described in pediatric oncology as a complication of chemotherapy. It has also been occasionally reported in adult cancer patients. Treatment is largely supportive with fluid restriction. A 16-month-old girl with stage II Wilms tumor receiving post-nephrectomy chemotherapy with dactinomycin and vincristine developed hepatic sinusoidal obstruction syndrome with painful hepatomegaly, ascites with significant weight gain, grossly deranged liver function, severe thrombocytopenia, and reversal of blood flow in the portal vein on Doppler sonography. Treatment with N-acetylcysteine was followed by complete resolution of clinical signs and amelioration of laboratory abnormalities within 72 hours of treatment. N-acetylcysteine is a safe and probably an effective treatment for dactinomycin-induced hepatic sinusoidal obstructive syndrome.

Preclinical studies in support of defibrotide for the treatment of multiple myeloma and other neoplasias

PURPOSE OF THE STUDY

Defibrotide, an orally bioavailable polydisperse oligonucleotide, has promising activity in hepatic veno-occlusive disease, a stem cell transplantation-related toxicity characterized by microangiopathy. The antithrombotic properties of defibrotide and its minimal hemorrhagic risk could serve for treatment of cancer-associated thrombotic complications. Given its cytoprotective effect on endothelium, we investigated whether defibrotide protects tumor cells from cytotoxic antitumor agents. Further, given its antiadhesive properties, we evaluated whether defibrotide modulates the protection conferred to multiple myeloma cells by bone marrow stromal cells.

METHODS-RESULTS

Defibrotide lacks significant single-agent in vitro cytotoxicity on multiple myeloma or solid tumor cells and does not attenuate their in vitro response to dexamethasone, bortezomib, immunomodulatory thalidomide derivatives, and conventional chemotherapeutics, including melphalan and cyclophosphamide. Importantly, defibrotide enhances in vivo chemosensitivity of multiple myeloma and mammary carcinoma xenografts in animal models. In cocultures of multiple myeloma cells with bone marrow stromal cells in vitro, defibrotide enhances the multiple myeloma cell sensitivity to melphalan and dexamethasone, and decreases multiple myeloma-bone marrow stromal cell adhesion and its sequelae, including nuclear factor-kappaB activation in multiple myeloma and bone marrow stromal cells, and associated cytokine production. Moreover, defibrotide inhibits expression and/or function of key mediators of multiple myeloma interaction with bone marrow stromal cell and endothelium, including heparanase, angiogenic cytokines, and adhesion molecules.

CONCLUSION

Defibrotide's in vivo chemosensitizing properties and lack of direct in vitro activity against tumor cells suggest that it favorably modulates antitumor interactions between bone marrow stromal cells and endothelia in the tumor microenvironment. These data support clinical studies of defibrotide in combination with conventional and novel therapies to potentially improve patient outcome in multiple myeloma and other malignancies.

Veno-occlusive disease of the liver after high-dose cytoreductive therapy with busulfan and melphalan for autologous blood stem cell transplantation in multiple myeloma patients

Veno-occlusive disease of the liver (VOD) is a potentially severe complication of high-dose cytoreductive therapy (HDT) used for stem cell transplantation (SCT). This complication is uncommon after HDT for autologous SCT (ASCT) in patients with multiple myeloma (MM). The Spanish Myeloma Group/PETHEMA conducted a study (MM2000) for patients with newly diagnosed MM consisting of induction with alternating VBMCP/VBAD chemotherapy followed by intensification with busulfan/melphalan (Bu/MEL) with a second high-dose therapy procedure in patients not achieving at least near-complete remission with the first procedure. After 2 years of the trial, a number of episodes resembling classical VOD but with a late onset were recognized. Consequently, the protocol was modified, and Bu/MEL was replaced by melphalan 200 mg/m(2) (MEL-200). Three years later, after a total of 734 patients had undergone first autologous SCT, the incidence and characteristics of VOD episodes were analyzed in the whole series. Nineteen cases of VOD (8%) were observed among the first 240 patients receiving Bu/MEL, whereas only 2 (0.4%) were observed among the 494 patients treated with MEL-200 (P < .0001). VOD manifestations in the Bu/MEL group appeared at a median of 29 days (range, 3-57 days) after ASCT. Mortality directly attributable to VOD was 2% in the Bu/MEL group and 0.2% in the MEL-200 group (P = .026). This high incidence of severe VOD probably had a multifactorial origin (busulfan followed by melphalan and previous use of BCNU). This observation should be kept in mind when designing future trials for the treatment of MM.

Use of prophylactic anticoagulation and the risk of hepatic veno-occlusive disease in patients undergoing hematopoietic stem cell transplantation: a systematic review and meta-analysis

Hepatic veno-occlusive disease is a serious regimen-related toxicity in patients undergoing hematopoietic stem cell transplantation. We performed a systematic review and meta-analysis of the literature on the effect of anticoagulation in preventing veno-occlusive disease. Several databases and online journals were searched for randomized controlled trials and cohort studies. Twelve studies (2782 patients) were eligible. Anticoagulation prophylaxis was associated with a statistically nonsignificant decrease in risk of veno-occlusive disease (pooled relative risk (RR), 0.90; 95% confidence interval (CI), 0.62-1.29). Results of one of three randomized controlled trials may have been affected by delayed introduction of anticoagulation. A second trial enrolled patients who received conventional chemoradiotherapy for early-stage disease (RR, 0.18; 95% CI, 0.04-0.78). The third trial was a pilot study with a small sample size (RR, 0.74; 95% CI, 0.53-1.04). Significant heterogeneity and methodologic weaknesses preclude drawing a meaningful conclusion from the pooled analysis. Despite some limitations, results of two of three eligible randomized controlled trials suggest that prophylactic anticoagulation may help prevent veno-occlusive disease. However, a large randomized controlled trial is needed for confirmation. Additionally, in future studies, owing to the wide spectrum of severity of veno-occlusive disease, outcomes such as 100-day mortality should strongly be considered.

Hepatotoxicity of Chemotherapy

The selection of an antineoplastic regimen for an oncology patient is based first on the availability of effective drugs and then on a balancing of potential treatment-related toxicities with the patient's clinical condition and associated comorbidities. Liver function abnormalities are commonly observed in this patient population and identifying their etiology is often difficult. Immunosuppression, paraneoplastic phenomena, infectious diseases, metastases, and poly-pharmacy may cloud the picture. While criteria for standardizing liver injury have been established, dose modifications often rely on empiric clinical judgment. Therefore, a comprehensive understanding of hepatotoxic manifestations for the most common chemotherapeutic agents is essential. We herein review the hepatotoxicity of commonly used antineoplastic agents and regimens.

Hepatic veno-occlusive disease: pathogenesis, diagnosis and treatment

Hepatic veno-occlusive disease (VOD) is one of the most serious complications following hematopoietic stem cell transplantation (SCT) and is associated with a very high mortality in its severe form. This review outlines the pathogenesis and clinical features of VOD, with an emphasis on endothelial cell injury and risk factors. The current status and future directions of research for both prophylaxis and treatment are also discussed.

Modulation of rat erythrocyte antioxidant defense system by buthionine sulfoximine and its reversal by glutathione monoester therapy

The protective effects of glutathione monoester (GME) on buthionine sulfoximine (BSO)-induced glutathione (GSH) depletion and its sequel were evaluated in rat erythrocyte/erythrocyte membrane. Animals were divided into three groups (n=6 in each): control, BSO and BSO+GME group. Administration of BSO, at a concentration of 4 mmol/kg bw, to the albino rats resulted in depletion of blood GSH level to about 59%. GSH was elevated several folds in the GME group as compared to the control (P<0.05) and BSO (P<0.001) groups. Decreased concentration of vitamin E was found in the erythrocyte membrane isolated from BSO-administered animals. Antioxidant enzymes, catalase (CAT), superoxide dismutase (SOD) and glutathione peroxidase (GPX) were also found to be altered due to BSO-induced GSH depletion in blood erythrocytes. The SOD and CAT activities in BSO group were significantly lower (P<0.001) than the other groups. Lipid peroxidation index and malondialdehyde (MDA) levels in erythrocytes and their membranes were increased to about 45% and 40%, respectively. The activities of Ca2+ ATPase, Mg2+ ATPase and Na+K+ ATPase were lower than those of control group (P<0.05), whereas the activities of these enzymes were found to be restored to normal followed by GME therapy (P<0.05). Cholesterol, phospholipid and C/P ratio and some of the phospholipid classes like phosphatidylcholine (PC), lysophosphatidylcholine (LPC) and sphingomyelin were significantly (P<0.05) altered in the erythrocyte membranes of BSO-administered rats compared with those of control group. These parameters were restored to control group levels in GME-treated group. Oxidative stress may play a major role in the BSO-mediated gamma glutamyl cysteine synthetase (gamma-GCS) inhibition and hence the depletion of GSH. In conclusion, our findings have shown that antioxidant status decreased and lipid peroxidation increased in BSO-treated rats. GME potentiates the RBC and blood antioxidant defense mechanisms and decreases lipid peroxidation.

Veno-occlusive disease: cytokines, genetics, and haemostasis

Hepatic veno-occlusive disease (VOD) is a major cause of morbidity and mortality following high dose cytotoxic therapy for stem cell transplantation (SCT). Pre-existing liver damage, SCT-related therapy, and genetic polymorphisms all appear to increase the risk of developing VOD. Studies of biological markers during SCT suggest that cytokines, haemostasis, and hepatic drug metabolism via the glutathione pathway are all involved in the pathogenesis of VOD. Until recently, treatment options were limited and experimental therapies directed at the pathogenesis of the disease were mostly unsuccessful. However, Defibrotide, a relatively new agent that has modulatory effects on vascular endothelium, cytokine release, and haemostasis, has been used with some success in the management and prophylaxis of VOD. In the future, a better understanding of genetic polymorphisms and biological markers which may be important in the pathogenesis of VOD, may enable us to predict which patients are most likely to be affected.

Hepatic veno-occlusive disease (sinusoidal obstruction syndrome) after hematopoietic stem cell transplantation

Hepatic veno-occlusive disease (VOD), increasingly referred to as sinusoidal obstruction syndrome, is a well-recognized complication of hematopoietic stem cell transplantation and contributes to considerable morbidity and mortality. In the Western Hemisphere, VOD, classified as a conditioning-related toxicity, is most commonly caused by stem cell transplantation. VOD has been described after all types of stem cell transplantation, irrespective of the stem cell source, type of conditioning therapy, or underlying disease. Recognition of this disease in the posttransplantation setting remains a challenge in the absence of specific diagnostic features because many other more common conditions can mimic it. Limited therapeutic or preventive strategies are currently available for the management of VOD. In this review, we provide a comprehensive account of the pathophysiology of this disease as we understand it today, risk factors for its development, and the current state of knowledge regarding preventive and therapeutic options.

Cyclophosphamide metabolism, liver toxicity, and mortality following hematopoietic stem cell transplantation

Liver toxicity caused by high-dose myeloablative therapy leads to significant morbidity after hematopoietic cell transplantation. We examined the hypothesis that liver toxicity after cyclophosphamide and total body irradiation is related to cyclophosphamide through its metabolism to toxins. Cyclophosphamide was infused at 60 mg/kg over 1 to 2 hours on each of 2 consecutive days, followed by total body irradiation. Plasma was analyzed for cyclophosphamide and its major metabolites. Liver toxicity was scored by the development of sinusoidal obstruction syndrome (veno-occlusive disease) and by total serum bilirubin levels. The hazards of liver toxicity, nonrelapse mortality, tumor relapse, and survival were calculated using regression analysis that included exposure to cyclophosphamide metabolites (as the area under the curve). Of 147 patients, 23 (16%) developed moderate or severe sinusoidal obstruction syndrome. The median peak serum bilirubin level through day 20 was 2.6 mg/dL (range, 0.5-41.1 mg/dL). Metabolism of cyclophosphamide was highly variable, particularly for the metabolite o-carboxyethyl-phosphoramide mustard, whose area under the curve varied 16-fold. Exposure to this metabolite was statistically significantly related to sinusoidal obstruction syndrome, bilirubin elevation, nonrelapse mortality, and survival, after adjusting for age and irradiation dose. Patients in the highest quartile of o-carboxyethyl-phosphoramide mustard exposure had a 5.9-fold higher risk for nonrelapse mortality than did patients in the lowest quartile. Engraftment and tumor relapse were not statistically significantly related to cyclophosphamide metabolite exposure. Increased exposure to toxic metabolites of cyclophosphamide leads to increased liver toxicity and nonrelapse mortality and lower overall survival after hematopoietic cell transplantation.

Oxidative stress and inflammation contribute to lung toxicity after a common breast cancer chemotherapy regimen

Delayed pulmonary toxicity syndrome after high-dose chemotherapy (HDC) and autologous hematopoietic support occurs in up to 64% of women with advanced-stage breast cancer. Using a similar, but nonmyeloablative, HDC treatment regimen in mice, we found both immediate and persistent lung injury, coincident with marked decreases in lung tissue glutathione reductase activity and accompanied by increases in lung oxidized glutathione, bronchoalveolar lavage (BAL) lipid peroxidation, and BAL total cell counts. Most interestingly, at 6 wk, BAL total cell counts had increased fourfold, with lymphocyte cell counts increasing >11-fold. A single supplemental dose of glutathione prevented early lung injury at 48 h but showed no lung-protective effects at 6 wk, whereas single doses of other thiol-sparing agents (Ethyol and glutathione monoethyl ester) showed no benefit. These data suggest that this HDC regimen results in acute and persistent lung toxicity, induced in part by oxidative stress, that culminates with an acute lung cellular inflammatory response. Continuous glutathione supplementation and/or attenuation of the delayed pulmonary inflammatory response may prove beneficial in preventing lung toxicity after the use of these chemotherapeutic agents.

Regulation of glutathione redox status in lung and liver by conditioning regimens and keratinocyte growth factor in murine allogeneic bone marrow transplantation

BACKGROUND

Reactive oxygen species (ROS) and glutathione (GSH) depletion contribute to organ injury after bone marrow transplantation (BMT). Keratinocyte growth factor (KGF) ameliorates graft-versus-host disease (GVHD)-associated organ injury in murine BMT models.

METHODS

B10.BR mice received total body irradiation (TBI; day -1) +/- cyclophosphamide (Cy; 120 mg/kg/day i.p., days -3 and -2), then were transplanted on day 0 with C57BL/6 bone marrow + spleen cells as a source of GVHD-causing T cells. KGF (5 mg/kg/day subcutaneously [s.c.]) or saline was given on days -6, -5, and -4. Lung and liver GSH and oxidized GSH disulfide (GSSG) levels were measured on days 0 and 5 and glutathione redox potential (Eh) calculated. Organ malondialdehyde (MDA) was determined on day 5 as an index of ROS-mediated lipid peroxidation.

RESULTS

In lung, TBI+BMT oxidized GSH Eh and increased MDA. Cy further oxidized lung GSH Eh. In liver, neither BMT regimen altered GSH redox status or MDA. KGF prevented the decrease in lung GSH after TBI+Cy and decreased lung MDA after both TBI and TBI+Cy. KGF increased liver GSH levels and GSH Eh after TBI and GSH Eh after TBI+Cy.

CONCLUSIONS

In murine allogeneic BMT, TBI oxidizes the lung GSH redox pool and Cy exacerbates this response by 5 days post-BMT. In contrast, liver GSH redox status is maintained under these experimental conditions. KGF treatment attenuates the Cy-induced decrease in lung GSH, decreases post-BMT lung lipid peroxidation, and improves liver GSH redox indices. KGF may have a therapeutic role to prevent or attenuate GSH depletion and ROS-mediated organ injury in BMT.

Hepatotoxicity of chemotherapy

After assessment of tumor histology, the next important factor to consider in the selection of a chemotherapy regime is organ function. Patients who are to receive chemotherapy require careful assessment of liver function prior to treatment to determine which drugs may not be appropriate, and which drug doses should be modified. Following therapy abnormalities of liver function tests may be due to the therapy rather than to progressive disease, and this distinction is of critical importance. Furthermore, not all abnormalities in liver function are due to the tumor or its treatment, and other processes, such as hepatitis, must be kept in mind. This article reviews the hepatic toxicity of chemotherapeutic agents, and suggests dose modifications based upon liver function abnormalities. Emphasis is placed on agents known to be hepatotoxic, and those agents with hepatic metabolism.

Dietary antioxidants during cancer chemotherapy: impact on chemotherapeutic effectiveness and development of side effects

Several studies suggest that dietary supplementation with antioxidants can influence the response to chemotherapy as well as the development of adverse side effects that results from treatment with antineoplastic agents. Administration of antineoplastic agents results in oxidative stress, i.e., the production of free radicals and other reactive oxygen species (ROS). Oxidative stress reduces the rate of cell proliferation, and that occurring during chemotherapy may interfere with the cytotoxic effects of antineoplastic drugs, which depend on rapid proliferation of cancer cells for optimal activity. Antioxidants detoxify ROS and may enhance the anticancer effects of chemotherapy. For some supplements, activities beyond their antioxidant properties, such as inhibition of topoisomerase II or protein tyrosine kinases, may also contribute. ROS cause or contribute to certain side effects that are common to many anticancer drugs, such as gastrointestinal toxicity and mutagenesis. ROS also contribute to side effects that occur only with individual agents, such as doxorubicin-induced cardiotoxicity, cisplatin-induced nephrotoxicity, and bleomycin-induced pulmonary fibrosis. Antioxidants can reduce or prevent many of these side effects, and for some supplements the protective effect results from activities other than their antioxidant properties. Certain side effects, however, such as alopecia and myelosuppression, are not prevented by antioxidants, and agents that interfere with these side effects may also interfere with the anticancer effects of chemotherapy.

Veno-occlusive disease of the liver after allogeneic bone marrow transplantation for severe aplastic anemia

There are few reports about the occurrence of hepatic VOD after BMT for severe aplastic anemia (SAA). We prospectively studied 17 patients with SAA after allogeneic BMT for the occurrence and severity of VOD. Plasma levels of protein C, protein S, antithrombin III, vWF, t-PA and PAI-1 were determined before preparative chemotherapy, on the day of marrow infusion, and on days 7, 14 and 21. VOD occurred in seven patients (41.2%) at a median of day 1 (range, day -2 to 15). Five had mild, and two moderate VOD. Platelet transfusion requirements were higher in the patients with VOD. The plasma levels of natural anticoagulants such as protein C, free protein S and antithrombin III decreased significantly on day 0 from the baseline levels. Plasma levels of t-PA, PAI-1 and vWF increased significantly in the early post-transplant period compared to the baseline levels. The mean plasma levels of t-PA on day 7 (P = 0.016) and PAI-1 on days 0 and 7 (P = 0.016, 0.032) were higher in the patients with VOD. In summary, we observed hypercoagulability and a high incidence of VOD after allogeneic BMT for SAA. Levels of t-PA and PAI-1 were significantly higher in the patients with VOD after BMT.

Regulation of redox glutathione levels and gene transcription in lung inflammation: therapeutic approaches

Glutathione (L-gamma-glutamyl-L-cysteinylglycine, GSH), is a vital intra- and extracellular protective antioxidant. Glutathione is synthesized from its constituent amino acids by the sequential action of gamma-glutamylcysteine synthetase (gamma-GCS) and GSH synthetase. The rate-limiting enzyme in GSH synthesis is gamma-GCS. Gamma-GCS expression is modulated by oxidants, phenolic antioxidants, and inflammatory and anti-inflammatory agents in various mammalian cells. The intracellular GSH redox homeostasis is strictly regulated to govern cell metabolism and protect cells against oxidative stress. Growing evidence has suggested that cellular oxidative processes have a fundamental role in inflammation through the activation of stress kinases (JNK, MAPK, p38) and redox-sensitive transcription factors such as NF-kappaB and AP-1, which differentially regulate the genes for proinflammatory mediators and protective antioxidant genes such as gamma-GCS, Mn-SOD, and heme oxygenase-1. The critical balance between the induction of proinflammatory mediators and antioxidant genes and the regulation of the levels of GSH in response to oxidative stress at the site of inflammation is not known. Knowledge of the mechanisms of redox GSH regulation and gene transcription in inflammation could lead to the development of novel therapies based on the pharmacological manipulation of the production of this important antioxidant in inflammation and injury. This FORUM article features the role of GSH levels in the regulation of transcription factors, whose activation and DNA binding leads to proinflammatory and antioxidant gene transcription. The potential role of thiol antioxidants as a therapeutic approach in inflammatory lung diseases is also discussed.

Does early treatment with high-dose methylprednisolone alter the course of hepatic regimen-related toxicity?

Hepatic regimen-related toxicity (RRT) is a serious complication of stem cell transplantation. Cytokine activation may be involved in the pathogenesis. Corticosteroids are potent inhibitors of cytokine production, and, therefore could play a role in the treatment of hepatic RRT. Between January 1994 and June 1998, 28 of 782 consecutive transplant patients (3.6%) developed hepatic RRT (20 veno-occlusive disease (VOD) and eight liver dysfunction of uncertain etiology (LDUE) as defined by Seattle criteria), and were treated with high-dose methylprednisolone (MP, 500 mg/m2 i.v. every 12 h for six doses), initiated upon increase in serum total bilirubin to > or =4 mg/dl. Other causes of liver dysfunction were excluded. Response to therapy with high-dose MP was defined as reduction in total bilirubin by 50% within 10 days of initiation of MP. Overall, 17 patients (61%) responded to treatment (12 patients with VOD, five patients with LDUE). The bilirubin in responding patients decreased from a mean of 8.6 mg/dl (range, 4-17.9) at the start of MP to 4.1 mg/dl (range, 0.5-17.9) 10 days later. There were no statistically significant differences between responders and non-responders in the day treatment with high-dose MP was initiated (P = 0.38), total serum bilirubin (P = 0.17) and percent weight gain at the time high-dose MP was started (P = 0.10) or the calculated probability of fatal outcome from VOD (18% for responders, 23% for non-responders; P = 0.30). A lower pre-transplant DLCOc was observed among non-responders (P = 0.04). At 100 days post-transplant, hepatic RRT resolved in all 13 survivors who responded to high-dose MP, and in one non-responding patient. No serious toxicities due to high-dose MP were observed. We conclude that resolution of hepatic RRT occurred in the majority of patients treated with high-dose MP in this study; however, randomized controlled trials are required to determine the efficacy of high-dose MP for treatment of hepatic RRT.

Lung glutathione and oxidative stress: implications in cigarette smoke-induced airway disease

Glutathione (GSH), a ubiquitous tripeptide thiol, is a vital intra- and extracellular protective antioxidant in the lungs. The rate-limiting enzyme in GSH synthesis is gamma-glutamylcysteine synthetase (gamma-GCS). The promoter (5'-flanking) region of the human gamma-GCS heavy and light subunits are regulated by activator protein-1 and antioxidant response elements. Both GSH and gamma-GCS expression are modulated by oxidants, phenolic antioxidants, and inflammatory and anti-inflammatory agents in lung cells. gamma-GCS is regulated at both the transcriptional and posttranscriptional levels. GSH plays a key role in maintaining oxidant-induced lung epithelial cell function and also in the control of proinflammatory processes. Alterations in alveolar and lung GSH metabolism are widely recognized as a central feature of many inflammatory lung diseases including chronic obstructive pulmonary disease (COPD). Cigarette smoking, the major factor in the pathogenesis of COPD, increases GSH in the lung epithelial lining fluid of chronic smokers, whereas in acute smoking, the levels are depleted. These changes in GSH may result from altered gene expression of gamma-GCS in the lungs. The mechanism of regulation of GSH in the epithelial lining fluid in the lungs of smokers and patients with COPD is not known. Knowledge of the mechanisms of GSH regulation in the lungs could lead to the development of novel therapies based on the pharmacological or genetic manipulation of the production of this important antioxidant in lung inflammation and injury. This review outlines 1) the regulation of cellular GSH levels and gamma-GCS expression under oxidative stress and 2) the evidence for lung oxidant stress and the potential role of GSH in the pathogenesis of COPD.

Characterization of a reproducible rat model of hepatic veno-occlusive disease

Lack of a reproducible animal model has hampered progress in understanding hepatic veno-occlusive disease (HVOD). This article characterizes a reproducible model of HVOD. Rats gavaged with monocrotaline, 160 mg/kg, were killed between days 1 and 10. Sections were evaluated by light microscopy with a standardized scoring system, by immunoperoxidase staining with ED-1 (monocytes, macrophages) and ED-2 (Kupffer cells) antibodies, and by transmission (TEM) and scanning electron microscopy (SEM). On days 1 and 2, the earliest manifestations were progressive injury to the sinusoidal wall with loss of sinusoidal lining cells, sinusoidal hemorrhage, and mild damage to central vein (CV) endothelium. On days 3 through 5 ("early HVOD"), there was centrilobular coagulative necrosis, severe injury to sinusoids, severe sinusoidal hemorrhage, and severe CV endothelial damage; inflammation with ED-1-positive cells was most marked on these days. Days 6 and 7 ("late HVOD") were characterized by subendothelial and advential fibrosis of CVs, damage of the CV endothelium with subendothelial hemorrhage, and some restoration of the sinusoidal wall. Between days 8 and 10, sections showed interindividual variation ranging from mild, residual fibrosis to severe, late HVOD. From days 1 through 10, ED-2-positive cells were decreased in number, and the number of ED-1-positive cells was increased. Sinusoidal damage is the earliest change in HVOD. Coagulative necrosis follows sinusoidal injury and resolves with improvement in sinusoidal endothelial cell (SEC) morphology. Moderate-to-severe CV fibrosis occurs after reappearance of sinusoidal lining cells and resolution of hepatocyte necrosis. The inflammatory response within the lobule and CVs is a result of recruitment of monocytes, whereas Kupffer cells are decreased in number.

Toxicity of fotemustine in rat hepatocytes and mechanism-based protection against it

Fotemustine is a relatively novel DNA-alkylating 2-chloroethyl-substituted N-nitrosourea (CENU) drug, clinically used for the treatment of disseminated malignant melanoma in different visceral and non-visceral tissues. Thrombocytopenia has been observed in patients treated with fotemustine and liver and renal toxicities as well. In this study, firstly the metabolism of fotemustine was investigated in vitro and secondly the undesired cytotoxicity of fotemustine as well as different ways of protection against it. In rat hepatocytes, chosen as a model system, fotemustine was shown to cause lactate dehydrogenase (LDH) leakage, glutathione (GSH) depletion, GSSG-formation and lipid peroxidation (LPO). A reactive metabolite, DEP-isocyanate, is most likely responsible for these undesired cytotoxic effects. Based on the observed cytotoxicity mechanisms, chemoprotection with several sulfhydryl-containing nucleophiles and antioxidants was investigated. The sulfhydryl nucleophiles; GSH, N-acetyl-L-cysteine (NAC) and glutathione isopropylester (GSH-IP) protected almost completely against fotemustine-induced LDH-leakage and LPO. NAC and GSH protected partly against fotemustine-induced GSH-depletion. The antioxidant, vitamin E protected completely against fotemustine-induced LPO, but only partly against fotemustine-induced LDH-leakage and not against GSH-depletion. Ebselen, a peroxidase-mimetic organoselenium compound, did not show protective effects against the cytotoxicity of fotemustine, possibly because GSH is required for the bioactivation of ebselen. It is concluded that co-administration of sulfhydryl nucleophiles, in particular NAC and GSH-IP, possibly in combination with antioxidants, such as vitamin E, are effective against the toxicity of fotemustine in vitro. It might, therefore, be worthwhile to investigate the cytoprotective potency of these agents against undesired toxicities of fotemustine in vivo as well.

Glutathione protection against gentamicin ototoxicity depends on nutritional status

This study demonstrates that gentamicin ototoxicity depends on dietary factors and correlates with tissue glutathione levels. After 15 days of gentamicin injections (100 mg/kg/day s.c.) guinea pigs on a regular protein diet (18.5% protein) had an average hearing loss of 9 dB at 3 kHz, 31 dB at 8 kHz and 42 dB at 18 kHz. Guinea pigs on a 7% protein diet showed an increased hearing loss of 52 dB at 3 kHz, 63 dB at 8 kHz and 74 dB at 18 kHz. Supplementing the low protein diet with either essential or sulfur-containing amino acids did not protect against gentamicin ototoxicity. Glutathione levels in the cochlear sensory epithelium were decreased in animals on a low protein diet and could be restored to normal by oral administration of glutathione monoethyl ester (1.2 g/kg/day) in combination with vitamin C (100 mg/kg/day). Glutathione supplementation significantly reduced the magnitude of hearing loss in the low protein diet group at all frequencies (43 dB reduction at 3 kHz, 27 dB reduction at 8 kHz and 21 dB reduction at 18 kHz). In animals on a full protein diet, dietary glutathione neither increased cochlear glutathione levels nor attenuated hearing loss. Serum gentamicin levels did not differ between animals on the various diets with or without glutathione supplement. These results suggest that gentamicin toxicity and detoxifying mechanisms are affected by the metabolic state of the animal and the glutathione content of the tissue. Thus, compounds that could potentially protect against gentamicin ototoxicity may be more correctly assessed in animal models of deficient nutritional states in which endogenous detoxifying mechanisms are compromised. This animal model might also be more realistically related to the clinical situation of a critically ill patient receiving gentamicin treatment.

Comparison of the delivery of reduced glutathione into P388D1 cells by reduced glutathione and its mono- and diethyl ester derivatives

The effect of reduced glutathione, reduced glutathione monoethyl ester and reduced glutathione diethyl ester on the cellular concentration of reduced glutathione and cysteine in P388D1 macrophages in vitro, and the cellular and extracellular de-esterification of reduced glutathione esters, was investigated. At 1 mM reduced glutathione derivative, only reduced glutathione diester markedly increased the cellular concentration of reduced glutathione. There was little delivery of reduced glutathione monoethyl ester into the cells. Reduced glutathione, and monoethyl and diethyl ester derivatives all increased the cellular concentration of cysteine; reduced glutathione diethyl ester also increased the cellular concentration of gamma-glutamylcysteine. Reduced glutathione diethyl ester also increased the cellular concentration of gamma-glutamylcysteine. Reduced glutathione esters were de-esterified intracellularly where the diester was rapidly converted to the monoester. The diester was also converted to the monoester extracellularly by interaction with cell surface esterases and by a much slower spontaneous hydrolysis. This indicates that the diester of reduced glutathione was a much more effective vehicle for delivery of reduced glutathione into cells than the monoester. Reduced glutathione diester also increased the cellular concentrations of cysteine and gamma-glutamylcysteine, suggesting that de novo synthesis of reduced glutathione was also stimulated.

Use of vitamin E and glutamine in the successful treatment of severe veno-occlusive disease following bone marrow transplantation

Veno-occlusive disease of the liver is a common complication following the administration of conditioning regimens to patients undergoing bone marrow transplantation. Free-radical damage to the liver is believed to be the cause of the hepatic outflow occlusion, and maintenance of adequate antioxidant stores of glutathione and vitamin E may be a means of counteracting the hepatotoxicity. We report the case of a 44-year-old woman who developed severe veno-occlusive disease after bone marrow transplantation and was treated with vitamin E, the major antioxidant of the cell membrane, and glutamine, a precursor of glutathione. The administration of this therapy was associated with reversal of the clinical and biochemical signs of severe hepatic dysfunction.

Cytotoxicity of antitumor platinum complexes with L-buthionine-(R,S)-sulfoximine and/or etanidazole in human carcinoma cell lines sensitive and resistant to cisplatin

Human 2008 ovarian carcinoma cells and the C13 CDDP-resistant subline and human MCF-7 breast carcinoma cells and the MCF-7/CDDP CDDP-resistant subline were exposed to L-buthionine-(S,R)-sulfoximine (50 microM) for 48 h prior to and during exposure for 1 h to the antitumor platinum complexes, cis-diamminedichloroplatinum(II), carboplatin or D,L-tetraplatin and/or to etanidazole (1 mM) for 2 h prior to and during exposure for 1 to the antitumor platinum complexes. These modulators alone did not significantly alter the cytotoxicity of CDDP toward either parental line. A twofold enhancement in cytotoxicity was observed with carboplatin in the 2008 cells and with D,L-tetraplatin in both parental lines with the single modulators. The modulator combination (buthionine sulfoximine/etanidazole) was very effective along with D,L-tetraplatin in both the MCF-7 parent and MCF-7/CDDP cell lines where at the higher platinum complex concentrations there was 1.5 to 3 logs increased killing of cells by the drug plus the modulators compared with the drug alone. Similarly, when C13 cells were exposed to CDDP (100 microM) or D,L-tetraplatin (100 microM) along with buthionine sulfoximine and etanidazole there was a 2-log increase in cell killing compared with exposure to the platinum complex alone. Treatment of each of the four cell lines with buthionine sulfoximine decreased both the non-protein and total sulfhydryl content of the cells. Treatment with the combination of modulators did not produce a further decrease in cellular sulfhydryl content compared with buthionine sulfoximine alone. The total sulfhydryl content in MCF-7 cells and 2008 cells exposed to buthionine sulfoximine and etanidazole was 58% and 31% of normal and the total sulfhydryl content of MCF-7/CDDP cells and C13 cells treated the same way was 54% and 23% of normal, respectively. DNA alkaline elution was used to assess the impact of exposure to the modulators, buthionine sulfoximine and etanidazole, alone and in combination on the cross linking of DNA by the antitumor platinum complexes in the MCF-7 and MCF-7/CDDP cell lines. Overall, the increases in DNA cross linking factors were greater in the MCF-7 cells than in the MCF-7/CDDP cells. These results indicate a possible clinical potential for this modulator combination.

Significance of glutathione in lung disease and implications for therapy

Glutathione is a tripeptide that contains an important thiol (sulfhydryl) group within the central cysteine amino acid. Glutathione is involved in numerous vital processes where the reducing potential of the thiol is used. Several lung disorders are believed to be characterized by an increase in alveolar oxidant burden, potentially depleting alveolar and lung glutathione. Low glutathione has been linked to abnormalities in the lung surfactant system and the interaction between glutathione and antiproteases in the epithelial lining fluid of patients. Normal levels of intracellular glutathione may exert a critical negative control on the elaboration of proinflammatory cytokines. The increase of intracellular reactive oxygen species is believed to correlate with the activation of NF-kappa B, a transcription activator linked to the elaboration of several cytokines. There is now sufficient data to strongly implicate free radical injury in the genesis and maintenance of several lung disorders in humans. This information is substantial and will help the development of clinical studies examining a variety of inflammatory lung disorders.

Elevated doses of carmustine and mitomycin C, with lonidamine enhancement and autologous bone marrow transplantation in the treatment of advanced colorectal cancer: results from a pilot study

10 patients with advanced colorectal cancer were treated with elevated doses of carmustine and mitomycin C. The regimen was potentiated by lonidamine and supported by autologous bone marrow transplantation. The results of this pilot study were encouraging, with a response rate of 50% and a significantly better survival for responders versus non-responders. No appreciable toxicity of the therapy was observed. This aspect, together with the simplicity of the procedure, calls for further investigations to confirm the good therapeutic index of the treatment.

Hepatic veno-occlusive disease after bone marrow transplant

Hepatic veno-occlusive disease (VOD) is a non-thrombotic obliteration of the lumina of small intrahepatic veins. VOD has been reported after exposure to a wide variety of pathogens. It has been suggested that the chemoradiotherapy used as the conditioning regimen for bone marrow transplant (BMT) is now the main cause of this disease. However, the pathogenesis of VOD after BMT is probably multifactorial. Endothelial injury of sinusoids and small hepatic veins is considered to be the initial event in genesis of VOD. This injury is followed by deposition of fibrin-related aggregates in the subendothelial zone. These aggregates, and the intramural entrapment of fluid and cellular debris, occlude progressively the hepatic venous outflow and generate a postsinusoidal intrahepatic hypertension. Clinically, VOD is characterized by jaundice, weight gain, ascites, painful hepatomegaly and platelet refractoriness developing early post transplant, although other posttransplant liver disturbances can produce a similar syndrome. VOD diagnosis is usually established by applying the clinical criteria proposed by the Seattle and Baltimore groups. When clinical diagnosis of VOD is uncertain, a transjugular liver study including a transvenous biopsy and measurement of the gradient between wedged and free hepatic venous pressure, is recommended in order to establish an accurate diagnosis. According to the literature data, the incidence of VOD ranges from 0 to 70% and its mortality from 20 to 50%. This very wide range is attributable to the different incidence of risk factors in the different series and to the differences in applying the diagnostic criteria.(ABSTRACT TRUNCATED AT 250 WORDS)

Development of a model of melphalan-induced gastrointestinal toxicity in mice

The tolerated dose of melphalan is limited by bone marrow suppression; when this complication is ameliorated by bone marrow transplantation, the dose-limiting toxicity becomes gastrointestinal mucositis. No intervention to date has been successful in modulating this life-threatening complication of melphalan. We conducted studies to develop a murine model of melphalan-induced gastrointestinal toxicity to facilitate the preclinical identification of effective strategies for reducing this toxicity. Melphalan given at the 90% lethal dosage produced severe gastrointestinal mucositis and mortality (13 of 23 treated mice). Syngeneic bone marrow transplantation, effective in preventing the myeloablation produced by total-body irradiation, was ineffective in preventing melphalan-induced mortality (16 of 23 treated mice), indicating that gastrointestinal mucositis was the dose-limiting toxicity. On the basis of the results of previous studies, which revealed that depletion of glutathione enhances the antineoplastic activity of melphalan and that glutathione is required for murine intestinal function, we attempted to modulate melphalan-induced gastrointestinal toxicity by the administration of glutathione (8-10 mmol/kg given in 1 ml sterile water by gavage at 12-h intervals for 4-8 doses). Glutathione therapy failed to produce a significant increase in mucosal glutathione content in animals treated with melphalan plus glutathione gavage as compared with those receiving melphalan alone (P > 0.05), and histologic mucosal injury secondary to melphalan was not reduced. The administration of glutathione in the presence or absence of concomitant bone marrow transplantation did not decrease melphalan-induced mortality (melphalan alone, 16/26 deaths; melphalan plus glutathione, 14/25 deaths; melphalan plus glutathione plus bone marrow transplantation, 20/26 deaths). Studies using a reduced melphalan dose (50% lethal dosage) produced similar results, with no survival benefit being seen following glutathione administration. Our studies suggest that melphalan-induced mucositis can be studied in a mouse model in which this complication is dose-limiting. Although glutathione administration at the dose and schedules initially studied is not effective in reducing this damage, other therapeutic strategies such as the use of alternative glutathione regimens or other thiols can be effectively studied in this system.

Elevation of mouse kidney thiol content following administration of glutathione

We have found that kidney glutathione and cysteine content in C3H mice can be increased by intraperitoneal administration of either glutathione (GSH) or glutathione disulfide (GSSG). Kidney thiol content is maximal 20-60 min after administration of 1000 mg/kg glutathione and returns to normal values by 2 h. The same time-course of thiol perturbation was observed when acivicin, an inhibitor of gamma-glutamyl transpeptidase, was administered 15 min prior to GSSG administration. The increase in kidney thiols after GSSG administration appears to saturate, with little additional increase as the administered dose is increased above 750 mg/kg. There was no significant change in liver GSH or cysteine after GSSG administration. We suggest that glutathione administration may provide a strategy for selective radioprotection or chemoprotection of specialized cells which can effectively utilize systemic GSH precursors.

Time course for the elevation of glutathione in numerous organs of L1210-bearing CDF1 mice given the L-cysteine prodrug, RibCys

RibCys, a thiazolidine prodrug of L-cysteine synthesized by the condensation of the sulfhydryl-containing amino acid with the aldose monosaccharide D-ribose, successfully elevated glutathione (GSH) levels in numerous organs of tumor-bearing CDF1 mice. GSH content was assayed 1,2,4,8 and 16 h after RibCys administration (8 mmol/kg, i.p.); various organs achieved maximal GSH content at different time points. GSH in the liver was elevated 1.5-fold compared to untreated controls at the 16-h time point. Kidney GSH also was maximal at 16 h and achieved 1.6-times control values. GSH in muscle achieved 2.5 times the levels in control animals, while the bladder was elevated 2.1-fold, and the heart 1.8-fold. Other tissues tested (spleen, pancreas, lung) showed a 1.1- to 1.2-fold increase in GSH content. GSH in implanted L1210 tumors was also elevated only 1.2-fold. These data suggest the possibility of protecting organs other than the liver from toxic insults that require the intervention of GSH for detoxication and may allow such protection without compromising the utility of chemotherapy.

Glutathione deficiency produced by inhibition of its synthesis, and its reversal; applications in research and therapy

Glutathione, which is synthesized within cells, is a component of a pathway that uses NADPH to provide cells with their reducing milieu. This is essential for (a) maintenance of the thiols of proteins (and other compounds) and of antioxidants (e.g. ascorbate, alpha-tocopherol), (b) reduction of ribonucleotides to form the deoxyribonucleotide precursors of DNA, and (c) protection against oxidative damage, free radical damage, and other types of toxicity. Glutathione interacts with a wide variety of drugs. Despite its many and varied cellular functions, it is possible to achieve therapeutically useful modulations of glutathione metabolism. This article emphasizes an approach in which the synthesis of glutathione is selectively inhibited in vivo leading to glutathione deficiency. This is achieved through use of transition-state inactivators of gamma-glutamylcysteine synthetase, the enzyme that catalyzes the first and rate-limiting step of glutathione synthesis. The effects of marked glutathione deficiency, thus produced in the absence of applied stress, include cellular damage associated with severe mitochondrial degeneration in a number of tissues. Such glutathione deficiency is not prevented or reversed by giving glutathione. The cellular utilization of GSH involves its extracellular degradation, uptake of products, and intracellular synthesis of GSH. This is a normal pathway by which cysteine moieties are taken up by cells. Glutathione deficiency induced by inhibition of its synthesis may be prevented or reversed by administration of glutathione esters which, in contrast to glutathione, are readily transported into cells and hydrolyzed to form glutathione intracellularly. Research derived from this model has led to several potentially useful therapeutic approaches, one of which is currently in clinical trial. Thus, certain tumors, including those that exhibit resistance to several drugs and to radiation, are sensitized to these modalities by selective inhibition of glutathione synthesis. An alternative interpretation is suggested which is based on the concept that some resistant tumors have high capacity for glutathione synthesis and that such increased capacity may be as significant or more significant in promoting the resistance of some tumors than the cellular levels of glutathione. Therapeutic approaches are proposed in which normal cells may be selectively protected against toxic antitumor agents and radiation by cysteine- and glutathione-delivery compounds. Current studies suggest that research on other modulations of glutathione metabolism and transport would be of interest.

L-cysteine prodrug protects against cyclophosphamide urotoxicity without compromising therapeutic activity

2(R,S)-D-ribo-(1',2',3',4'-Tetrahydroxybutyl)-thiazolidine-4(R)-ca rboxylic acid (RibCys) is a prodrug of L-cysteine that releases the sulfhydryl amino acid after nonenzymatic ring opening and hydrolysis. The L-cysteine then elevates glutathione (GSH) levels by stimulating its biosynthesis. RibCys was investigated for its ability to protect CDF1 mice from the potent urotoxicity of cyclophosphamide (CTX) without compromising the therapeutic utility of the drug. RibCys induced a significant reduction in weight loss of the animals and in bladder inflammation at 48 h after CTX administration; however, bladder tissue remained inflamed as compared with that in controls. Bladder histology also showed some pathological changes in the presence of RibCys. In contrast, all parameters of toxicity (body weight loss, bladder inflammation, and pathological abnormalities) had been virtually reversed by day 21 after administration. In tests against L1210 leukemia, RibCys did not interfere with CTX anticancer activity. From these preliminary studies, RibCys appears to be a likely candidate for protecting against long-term CTX toxicity, perhaps reversing the original damage caused by a very high dose, without compromising the therapeutic utility of the alkylating agent.

Cellular glutathione as a protective agent against 4-hydroperoxycyclophosphamide cytotoxicity in K-562 cells

Exposure of cells of the K-562 erythroleukemia cell line to 4-hydroperoxycyclophosphamide (4-HC), an analog of activated cyclophosphamide, causes a concentration-dependent inhibition of in vitro colony formation by these cells. For investigation of the role of glutathione (GSH) in the metabolism of 4-HC, GSH levels of K-562 cells were modulated by exposing the cells to buthionine sulfoximine (BSO), a specific inhibitor of GSH synthesis, and/or to GSH ethyl esters. Both the mono- and diethyl esters of GSH were synthesized in our laboratories and their identities were determined by chromatographic methods and fast-atom-bombardment mass spectrometry. An HPLC method including electrochemical detection used for thiol determination was applied for the measurement of GSH esters. Incubation of the cells with BSO depleted GSH levels to approximately 11% of control values and potentiated the cytotoxicity of 4-HC. By contrast, exposure to GSH esters approximately doubled GSH levels and protected the cells against the toxicity of 4-HC. Moreover, when cellular GSH levels were first depleted by BSO exposure and then replenished by incubation with GSH esters, the BSO-associated potentiation of 4-HC cytotoxicity was abolished. The work described herein extends the application of an HPLC method used for thiol determination to the measurement of GSH ethyl esters. In addition, it established that GSH acts as a competitive protecting agent against the in vitro toxicity of 4-HC in the K-562 cell line.

1,2-dithiol-3-thione and dithioester analogues: potential radioprotectors

Several 1,2-dithiol-3-thione and dithioester compounds were assayed for radioprotective capabilities in EMT6 cells in vitro. The 1,2-dithiol-3-thiones were generally more cytotoxic than the dithioesters and in some instances were more cytotoxic toward hypoxic cells than toward normally oxygenated cells. When the drugs were present at a concentration of 500 microM for 1 h prior to and during radiation delivery, the 5-(2-thienyl)-1,2-dithiol-3-thione produced a radiation protection factor (RPF) of 2.7 at 1 log of cell kill. The 4-methyl analogue of this same compound was, however, much less effective, producing a RPF of only 1.2. The 4-ethoxycarbonyl analogue was moderately active, producing a RPF of 1.7. The 4-methyl-5-(2-pyrazinyl)-1,2-dithiol-3-thione (Oltipraz) was least effective, yielding a RPF of only 1.1. Of the dithioesters tested, methyl 3-pyrrolidino-2-phenylpropene dithiocarboxylate produced a RPF of 2.6, methyl 3-piperidino-2-phenylpropenedithiocarboxylate a RPF of 2.7, and the corresponding 3-morpholino and 3-thiomorpholino derivatives RPF values of 2.7 and 2.9, respectively. The iodide salt of 4-ethoxycarbonyl-5-(2-thienyl)-1,2-dithiol-3-thione produced a RPF of 2.6 Methyl 3-cyclohexylamino-2-phenylpropenedithiocarboxylate was equally effective (RPF = 2.6). Finally, methyl 3-morpholino-3-thienyl-2-methylpropenedithiocarboxylate and methyl 3-morpholino-3-(2-pyrazinyl)-2-methylpropenedithiocarboxylate were less effective, producing RPF values of 2.0 and 1.6, respectively. These results demonstrate that several of these compounds are highly effective radioprotectors. In vitro and in vivo studies testing their efficacy are underway.

Glutathione is required for intestinal function

Glutathione (GSH) deficiency produced in mice by giving buthionine sulfoximine leads to severe degeneration of the epithelial cells of the jejunum and colon. This is prevented by giving GSH monoester (orally or i.p.) and also by giving GSH (orally, but not i.p.). The i.p. administration leads to high plasma levels of GSH but does not appreciably increase GSH levels in intestinal mucosa or pancreas. These and previous studies on lens, lung, lymphocytes, liver, heart, and skeletal muscle indicate that there is very little, if any, transport of intact GSH from plasma to these tissues. Cells can use extracellular GSH by a pathway involving its cleavage, uptake of products and intracellular GSH synthesis. Epithelial cells of the gastrointestinal tract may use this pathway and can also take up lumenal GSH (which arises partly from the bile) by a mechanism(s) that may involve transport of dipeptides or of GSH. It is suggested that biliary GSH normally functions in the protection of intestinal mucosa. Administration of GSH may be protective of the gastrointestinal epithelium and may also serve as a good source of cysteine moieties for intracellular GSH synthesis in the gastrointestinal tract and in other tissues. Administration of GSH delivery agents such as GSH esters is more effective than administration of GSH in increasing cellular and mitochondrial levels of GSH.