Mechanisms of synergistic toxicity of the radioprotective agent, WR2721, and 6-hydroxydopamine

WR2721 is a "prodrug" for a radioprotective thiol which has been proposed for adjunctive use as a free radical scavenger in cancer chemotherapy. When used adjunctively with oxygen radical generating chemotherapeutic agents in mice, however, WR2721 produces synergistic toxicity rather than attenuation of the toxic effects of such agents. The present paper discusses potential mechanisms for such synergistic toxicity. The pathway for glutathione synthesis appeared to be inactivated in mice treated with WR2721. The disulfide metabolite of WR2721 was a potent inactivator of gamma-glutamylcysteine synthetase, the rate-limiting enzyme in glutathione synthesis. The inactivation of the enzyme by this compound was similar to that reported for cystamine, a compound known to form a mixed disulfide with a cysteine residue near the glutamic acid binding site of the enzyme. Oxygen radicals not only inactivated the synthetase, as well, but hastened the oxidation of the free thiol metabolite of WR2721 to its corresponding disulfide.     

Amifostine (WR2721) Confers DNA Protection to In Vivo Cisplatin-Treated Murine Peripheral Blood Leukocytes

Amifostine [S-2-3-aminopropil amino ethyl phosphorotioic acid], a modulator agent for antineoplastic drugs involved in free radicals generation has given controversial results in cisplatin treated leukocytes in vitro. We have evaluated the amifostine protection over leukocytes in vivo, using comet assay. Groups of five OF1 male mice were given one of three doses of amifostine (56, 105 and 200 mg/Kg) after a cisplatin single injection (10 mg/Kg). Serum malonyldialdehide levels, catalase and superoxide dismutase activity were also evaluated. Amifostine showed significant DNA protection (p< 0.01) at the two lower doses evaluated. Malonyldildehide decreased in all amifostine treatments with respect to cisplatin while antioxidant enzyme activities remained unchanged. However, DNA migration increased with the highest amifostine dose; in fact highest dose of amifostine did no protect damage caused by cisplatin this result have implications on amifostine treatment schedules in clinical practice.     

Effect of atenolol on cadmium-induced testicular toxicity in male rats

Cadmium-induced stress adversely affects testicular activity and causes sympathetic stimulation. To investigate the effect of atenolol, a β-adrenergic receptor blocker, on testicular androgen synthesis after cadmium treatment, adult Sprague-Dawley strain male rats were given a single sc dose of cadmium chloride 0.45 mg/kg BW. Animals were killed on day 3 after treatment. Adrenal weight, adrenal Δ⁵-3β-hydroxysteroid dehydrogenase (Δ⁵-3β-HSD) activity, serum corticosterone, and brain noradrenaline were increased significantly while testicular Δ⁵-3β-HSD and 17β-HSD activities, serum testosterone, and accessory sex organs weight were decreased. Oral coadministration of atenolol at a dose of 2.0 mg/kg body weight for 3 days resulted in complete protection of adrenal Δ⁵-3β-HSD, testicular Δ⁵-3β-HSD, and 17β-HSD activities, adrenal weight, serum corticosterone, and serum testosterone when compared with cadmium-only group and there were no significant differences in these parameters from the vehicle control values. Simultaneous administration of cadmium and atenolol also protected brain noradrenaline content and reduced the rise of testicular cadmium concentration. All the parameters were similar to control levels in rats treated with atenolol alone. We conclude that atenolol may protect testicular androgen synthesis by inhibiting the action of noradrenaline on testicular Leydig cells and adrenocortical hyperactivity in cadmium-treated rats.     

Protective effect of theaflavins on cadmium-induced testicular toxicity in male rats

Male Sprague–Dawley rats were treated with cadmium (Cd) (0.4 mg/kg body weight, s.c., once a day) and three concentrations of theaflavins (50, 100 or 200 mg/kg body weight, orally, once a day) for five weeks to evaluate the protective role of theaflavins on Cd-induced testicular toxicity. After five weeks, serum sex hormone levels, sperm characteristics, DNA damage, oxidant-antioxidant status, Cd content in several organs were measured. The results showed that a low dose of Cd caused testicular toxicity, which was represented by decreased serum testosterone levels, induction of DNA damage, increased malondialdehyde (MDA) content, Cd accumulation in several organs. Administration of theaflavins led to a dose-dependent alleviation Cd-induced damage in testis, including enhanced serum testosterone levels, improved sperm characteristics and abrogation of DNA damage. Theaflavins may also reduce the production of Cd-induced MDA content, decrease Cd concentration in liver, testis and blood, increase Cd content in urine and feces. These findings suggest the use of theaflavins as a potential therapeutic agent for Cd-induced testicular toxicity.     

Sensitive endpoints for evaluating cadmium-induced acute toxicity in LLC-PK1 cells

Cadmium chloride (CdCl(2)) is a nephrotoxicant that causes damage to the proximal tubular epithelium. In vivo, it increases the permeability of epithelial surfaces, while in vitro, it acts on active trans-epithelial ion transport. The purpose of this study was to investigate CdCl(2) effects on a porcine renal proximal tubular epithelial cell line (LLC-PK1), and, in particular, to identify sensitive endpoints revealing damage both at the epithelial barrier level and at the molecular level. After exposure of the cells to CdCl(2), trans-epithelial resistance (TER) decreased while paracellular permeability (PCP) increased, indicating a structural alteration of the junctional complex. At the molecular level, we observed an increase in protective proteins, such as metallothioneins (MTs) and heat shock proteins (HSP70), starting from 25 microM CdCl(2), together with alterations in cytoskeleton organization. Production of reactive oxygen species (ROS) was also evident, indicating cellular oxidative stress. Our data indicate that CdCl(2) toxicity can be detected at the barrier level and at the molecular level at low concentrations, at which cytotoxicity assays are unable to show any damage. Therefore, these endpoints should prove very useful in studying heavy metal-induced acute toxicity. Exposure of the cells to higher concentrations of CdCl(2) (50 microM) revealed the initiation of apoptosis, mediated by caspase-3.     

Sexual dimorphism of cadmium-induced toxicity in rats: involvement of sex hormones

The toxic effect of cadmium varies with sex in experimental animals. Previous studies have demonstrated that pretreatment of male Fischer 344 (F344) rats with the female sex hormone progesterone markedly enhances the susceptibility to cadmium, suggesting a role for progesterone in the sexual dimorphism of cadmium toxicity. In the present study, we attempted to further elucidate the mechanism for sex differences in cadmium-induced toxicity in F344 rats. A single exposure to cadmium (5.0?mg Cd/kg, sc) was lethal in 10/10 (100?%) female compared with 6/10 (60?%) male rats. Using a lower dose of cadmium (3.0?mg Cd/kg), circulating alanine aminotransferase activity, indicative of hepatotoxicity, was highly elevated in the cadmium treated females but not in males. However, no gender-based differences occurred in the hepatic cadmium accumulation, metallothionein or glutathione levels. When cadmium (5.0?mg Cd/kg) was administered to young rats at 5?weeks of age, the sex-related difference in lethality was minimal. Furthermore, although ovariectomy blocked cadmium-induced lethality, the lethal effects of the metal were restored by pretreatment with progesterone (40?mg/kg, sc, 7 consecutive days) or β-estradiol (200?μg/kg, sc, 7 consecutive days) to ovariectomized rats. These results provide further evidence that female sex hormones such as progesterone and β-estradiol are involved in the sexual dimorphism of cadmium toxicity in rats.     

Antagonism of cocaine, amphetamine, and methamphetamine toxicity

The effect of diazepam, haloperidol, MK-801, and propranolol in antagonizing behavioral symptoms induced by lethal doses of cocaine, amphetamine, and methamphetamine were studied in a rat model. Animals were first pretreated IP with potential antagonists, diazepam (2, 5, and 10 mg/kg), haloperidol (5, 10, and 20 mg/kg), propranolol (5, 10, and 20 mg/kg), MK-801 (0.5, 1.0, and 2.5 mg/kg), and then were challenged IP with cocaine (70 mg/kg) (LD85), d-amphetamine (75 mg/kg) (LD100), and methamphetamine (100 mg/kg) (LD90). Diazepam, at all doses, provided significant protection against cocaine- (p less than or equal to 0.01) and methamphetamine- (p less than or equal to 0.05) induced seizures and produced a dose-dependent effect against amphetamine-induced seizures. MK-801, at all doses, reduced seizures in all groups (p less than or equal to 0.01). Propranolol altered the incidence of methamphetamine-induced seizures. Significant protection against cocaine-induced death was afforded by diazepam (p less than or equal to 0.01) and propranolol (p less than or equal to 0.05). Significant protection against amphetamine-induced death was provided by haloperidol (all doses, p less than or equal to 0.1), MK-801 (all doses, p less than or equal to 0.1), and propranolol (10 and 20 mg/kg, p less than or equal to 0.1). No agent reduced the incidence of methamphetamine- (50 or 100 mg/kg) induced death. The failure of d-amphetamine antagonists to protect against methamphetamine-induced toxicity and death suggest that different mechanisms of toxicity may exist between these drugs.     

Genetic background of resistance to cadmium-induced testicular toxicity in inbred Wistar-Imamichi rats

We have previously reported that inbred Wistar-Imamichi (WI) rats are highly resistant to cadmium (Cd)-induced testicular toxicity compared with inbred Fischer 344 (F344) rats. The present study was to elucidate the genetic background of resistance to Cd-induced testicular toxicity in WI rats. The genetic analysis of susceptibility to Cd-induced testicular toxicity was conducted by using Cd-resistant WI and Cd-sensitive F344 strains as the parental rats and by using the testicular hemoglobin level as the indicator. In the frequency distribution of testicular hemoglobin levels in parental, first filial (F₁) and second filial (F₂) rats treated with Cd at a dose of 2.0 mg/kg, F₁ rats had testicular hemoglobin levels intermediate to WI and F344 rats, and F₂ rats segregated into three groups of low, intermediate, and high phenotypes at the expected ratio. Furthermore, the backcross progeny between WI and F₁ or between F344 and F₁ segregated into two groups with the expected ratio. Based on a simple Mendelian genetic analysis, these segregation patterns lead us to conclude that two codominant alleles at a gene locus are responsible for the susceptibility to Cd-induced testicular toxicity in rats. This is the first report for the genetic analysis of susceptibility to Cd-induced testicular toxicity in inbred rat strains.     

Sulforaphane mitigates cadmium-induced toxicity pattern in human peripheral blood lymphocytes and monocytes

Cadmium (Cd) is a highly toxic and widely distributed heavy metal that induces various diseases in humans through environmental exposure. Therefore, alleviation of Cd-induced toxicity in living organisms is necessary. In this study, we investigated the protective role of sulforaphane on Cd-induced toxicity in human peripheral blood lymphocytes and monocytes. Sulforaphane did not show any major reduction in the viability of lymphocytes and monocytes. However, Cd treatment at a concentration of 50 μM induced around 69% cell death. Treatment of IC₁₀-Cd and 100 μM sulforaphane combination for 24 and 48 h increased viability by 2 and 9% in cells subjected to Cd toxicity, respectively. In addition, IC₂₅ of Cd and 100 μM sulforaphane combination recovered 17–20% of cell viability. Cd induced apoptotic and necrotic cell death. Sulforaphane treatment reduced Cd-induced cell death in lymphocytes and monocytes. Our results clearly indicate that when the cells were treated with Cd + sulforaphane combination, sulforaphane decreased the Cd-induced cytotoxic effect in lymphocytes and monocytes. In addition, sulforaphane concentration plays a major role in the alleviation of Cd-induced toxicity.     

Methotrexate pulmonary toxicity

Methotrexate is a commonly prescribed antineoplastic and immune modulating compound that has gained wide acceptance in the management of rheumatoid arthritis, psoriasis, sarcoidosis and a number of neoplastic disorders. Although generally considered safe and easy to use, methotrexate has been associated with a number of adverse reactions. Pulmonary toxicity has been well-described and may take a variety of forms. Pulmonary infiltrates are the most commonly encountered form of methotrexate pulmonary toxicity and these infiltrates resemble hypersensitivity lung disease. This discussion focuses primarily on low-dose methotrexate pulmonary toxicity and will discuss the diagnosis using clinical, pulmonary function, radiographical and pathological manifestations. Suggestions for clinical monitoring to detect adverse effects are given. In addition, management of pulmonary toxicity through discontinuation of the methotrexate, support and possibly the administration of corticosteroids is discussed.     

Methotrexate pulmonary toxicity

Methotrexate is a commonly prescribed antineoplastic and immune modulating compound that has gained wide acceptance in the management of rheumatoid arthritis, psoriasis, sarcoidosis and a number of neoplastic disorders. Although generally considered safe and easy to use, methotrexate has been associated with a number of adverse reactions. Pulmonary toxicity has been well-described and may take a variety of forms. Pulmonary infiltrates are the most commonly encountered form of methotrexate pulmonary toxicity and these infiltrates resemble hypersensitivity lung disease. This discussion focuses primarily on low-dose methotrexate pulmonary toxicity and will discuss the diagnosis using clinical, pulmonary function, radiographical and pathological manifestations. Suggestions for clinical monitoring to detect adverse effects are given. In addition, management of pulmonary toxicity through discontinuation of the methotrexate, support and possibly the administration of corticosteroids is discussed.     

Amiodarone-induced pulmonary toxicity

AIMS

A number of factors have been hypothesized to increase the risk of amiodarone-induced pulmonary toxicity (AIPT). This study aimed to confirm these risk factors and determine whether a cohort of tertiary hospital patients diagnosed with AIPT demonstrated comparable characteristics.

METHODS

Phase I of this study involved compilation of a database of adverse reactions to amiodarone reported to the Australian and US drug agencies, and identification of risk factors for AIPT using logistic regression analysis. In Phase II, AIPT cases were identified via a retrospective review of medical records of patients discharged from Fremantle Hospital and Health Service, Western Australia (FHHS) between 2000 and 2005 with diagnosed interstitial lung disease. Data were collected regarding these patients’ risk factors for AIPT and compared with those previously identified in Phase I.

RESULTS

A total of 237 cases of AIPT were identified from agency data. Patients aged > 60 years and those on amiodarone for 6–12 months (odds ratio 18.28, 95% confidence interval 6.42, 52.04) were determined to be at the highest risk of AIPT. Australian data also suggested increased risk in patients who had received cumulative doses of 101–150 g. The seven AIPT cases identified among the FHHS patients were all at high risk of AIPT based on their age and duration of amiodarone therapy.

CONCLUSION

Contrary to previous findings, only patient age and the duration of amiodarone therapy were confirmed as significant risk factors for AIPT. Targeted monitoring of these patients may facilitate early identification and management of AIPT.

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

• A number of factors have been hypothesized to increase the risk of amiodarone-induced pulmonary toxicity (AIPT), although there remains some controversy in the literature as to their relative significance.
• This study aimed to clarify this situation to permit better characterization of patients at risk of AIPT and thus guide the development of guidelines for the monitoring for AIPT in patients receiving the drug.

WHAT THIS STUDY ADDS

• Via compilation and analysis of a database of 237 AIPT cases, it was demonstrated that only patient age and duration of therapy significantly affected the risk of AIPT.
• A small cohort of hospital AIPT patients demonstrated these ‘at-risk’ characteristics, suggesting that targeted monitoring of patients aged >60 years and those on amiodarone for 6–12 months may enhance the safety of these patients and minimize their risk of morbidity and mortality secondary to AIPT.

     

Amiodarone-induced pulmonary toxicity

Amiodarone-induced pulmonary toxicity (AIPT) is one of the most serious adverse effects of amiodarone therapy and can be fatal. Therefore, vigilant monitoring is advised. Baseline chest radiograph and pulmonary function tests and follow-up chest films at 3-month intervals are advocated. However, since abnormalities on these two examinations do not always precede symptoms, patient self-reports of respiratory symptoms appear to be the best method for early detection of AIPT.     

Irinotecan-associated pulmonary toxicity

We present the circumstances surrounding a 57-year-old Caucasian man with advanced colorectal cancer who developed relapsing interstitial lung disease following a single exposure to irinotecan (CPT-11). Progressive pulmonary insufficiency and death were reported in the initial Japanese studies, despite institution of empiric steroid therapy for a syndrome similar to that which our patient experienced. As a result, patients with compromised pulmonary function were generally excluded from US clinical trials. Notwithstanding this, cough and dyspnea were reported in approximately 20% of patients in the US studies. As the clinical indications for the use of this agent expand, we describe irinotecan-associated interstitial pneumonitis as a serious potential adverse effect. Patients with pre-existing pulmonary disease may be at higher risk for this complication and clinicians should be alert to this possibility.     

Antagonism of anticholinesterase (DFP) toxicity by donepezil plus scopolamine: a preliminary study

Studies in animals exploring the antagonism of the cholinesterase inhibitors soman and sarin have shown that pretreatment with low doses of the centrally acting cholinesterase inhibitor, physostigmine, alone or in conjunction with the centrally acting anticholinergic agent, scopolamine, is effective against their lethality and toxicity. The current study evaluated the effects of pretreatment with the oral anticholinesterase agent, donepezil (Aricept, 2.0 mg/kg), used to treat Alzheimer's disease, with and without scopolamine in decreasing the hypothermic, hypokinetic, and diarrhea-inducing effects of the irreversible long-acting cholinesterase inhibitor diisopropyl fluorophosphate (DFP, 1.0 mg/kg) in adult Flinders sensitive line (FSL) male rats. Donepezil alone and donepezil plus scopolamine (0.1 mg/kg) to a greater extent antagonized the decrease in temperature, hypoactivity, and induction of diarrhea due to DFP observed at 4 h after its administration. However, donepezil alone induced hypothermia at 1 and 2 h after treatment. Therefore, these preliminary findings are encouraging, but many additional studies are needed to establish the effectiveness of donepezil as a prophylactic agent against irreversible cholinesterase inhibition by DFP.     

Ambroxol and pulmonary toxicity induced by antineoplastic drugs

The authors describe the potential effects of ambroxol on the pulmonary disorders induced by antineoplastic agents (in particular, bleomycin and the nitrosureas). An experimental stage focussed attention on the early modifications occurring in the alveolar surfactant and in the afflux of inflammatory and immune-effector cells following bleomycin-induced lung fibrosis in the rat (by intratracheal instillation). The ambroxol-protected rats showed a slower drop of alveolar lecithins in the first few hours after bleomycin administration and a lower afflux of neutrophils, macrophages and lymphocytes. In the clinical stage, respiratory function was studied in two groups of cancer patients treated with nitrosureas or bleomycin. Preliminary findings indicate a rapid worsening of some functional parameters--maximal expiratory flow at 25% vital capacity, diffusing capacity for carbon monoxide and diffusing capacity/ventilation--in controls, while no such changes occurred in the ambroxol-protected subjects. The possible pathogenetic implications of these results and perspective for future investigations are discussed.