Inhibition of doxorubicin-initiated membrane damage by N-acetylcysteine: possible mediation by a thiol-dependent, cytosolic inhibitor of lipid peroxidation

Effects of histidine and N-acetylcysteine on doxorubicin-induced cardiomyopathy in rats

The amino acids histidine and n-acetylcysteine have many biological activities such as antioxidant effect. The present study investigated the effects of histidine and n-acetylcysteine on the heart lesions induced by doxorubicin (DOX) in rats. Forty-eight male Wistar rats were divided into two major groups treated intraperitoneally (i.p.) with normal saline and 4 mg/kg of DOX, respectively. Each group was further divided into four subgroups that were treated with separate and combined i.p. injections of histidine and n-acetylcysteine (NAC) at a same dose of 40 mg/kg. Electrocardiography (ECG) was recorded using lead II. The heart lesions were evaluated by light microscopy. Serum levels of creatine phosphokinase and lactate dehydrogenase and heart tissue malondialdehyde levels were measured. Histidine and especially NAC at a same dose of 40 mg/kg recovered ECG changes, improved heart lesions and prevented biochemical changes induced by DOX. Co-administration of histidine and NAC showed better responses when compared with them used alone. The results of the present study showed protective effects for histidine and NAC on the heart. Reduction in free radical-induced toxic effects may be involved in cardioprotective properties of histidine and NAC.

The chemistry and biological activities of N-acetylcysteine

BACKGROUND

N-acetylcysteine (NAC) has been in clinical practice for several decades. It has been used as a mucolytic agent and for the treatment of numerous disorders including paracetamol intoxication, doxorubicin cardiotoxicity, ischemia-reperfusion cardiac injury, acute respiratory distress syndrome, bronchitis, chemotherapy-induced toxicity, HIV/AIDS, heavy metal toxicity and psychiatric disorders.

SCOPE OF REVIEW

The mechanisms underlying the therapeutic and clinical applications of NAC are complex and still unclear. The present review is focused on the chemistry of NAC and its interactions and functions at the organ, tissue and cellular levels in an attempt to bridge the gap between its recognized biological activities and chemistry.

MAJOR CONCLUSIONS

The antioxidative activity of NAC as of other thiols can be attributed to its fast reactions with OH, NO2, CO3(-) and thiyl radicals as well as to restitution of impaired targets in vital cellular components. NAC reacts relatively slowly with superoxide, hydrogen-peroxide and peroxynitrite, which cast some doubt on the importance of these reactions under physiological conditions. The uniqueness of NAC is most probably due to efficient reduction of disulfide bonds in proteins thus altering their structures and disrupting their ligand bonding, competition with larger reducing molecules in sterically less accessible spaces, and serving as a precursor of cysteine for GSH synthesis.

GENERAL SIGNIFICANCE

The outlined reactions only partially explain the diverse biological effects of NAC, and further studies are required for determining its ability to cross the cell membrane and the blood-brain barrier as well as elucidating its reactions with components of cell signaling pathways.

Evaluation of ambrein and epicoprostanol for their antioxidant properties: Protection against adriamycin-induced free radical toxicity

Ambrein and epicoprostanol were evaluated for their antioxidant potential in vitro by chemiluminescence (CL), as well as in vivo using lipid peroxides and glutathione levels as indicators in liver tissue of rats treated with adriamycin (doxorubicin) a well known free radicals producing drug. In the in vitro test, the inhibition in CL by ambrein was dose dependent. Both the high concentrations of ambrein (20-40 microg/ml) inhibited CL response significantly (P<0.05 and P<0.01, respectively) when compared to control. Similarly two low concentrations (5-20 microg/ml) of epicoprostanol inhibited CL significantly (P<0.001 and P<0.01, respectively) in comparison of DMSO control. The high concentration (40 microg/ml) of epicoprostanol behaved exceptionally and caused an increase in CL response that was more than control and significantly (P<0.001) higher than both the low concentrations. In the in vivo studies adriamycin treatment significantly (P<0.05) increased malondialdehyde (MDA) and decreased non-protein sulfhydryl (NP-SH) contents in the liver tissue of mice after 5 days treatment. Ambrein (25 and 50 mg/kg) treatment as a solo therapy at both the dose levels significantly (P<0.001) decreased MDA contents in the liver tissue. On the other hand, in the combined treatment the high dose effectively prevented any rise in MDA contents and it remained around the levels of ambrein alone. In the same experiment, adriamycin declined NP-SH contents significantly (P<0.001). Ambrein alone at both the dose levels caused a decline (P<0.01) in NP-SH contents when compared to adriamycin group. But in the combined treatment this decline in NP-SH was significantly (P<0.05) different from adriamycin alone. In the experiments dealing with epicoprostanol, adriamycin treatment increased MDA contents significantly (P<0.05) that declined significantly (P<0.001) with epicoprostanol (10- or 20mg/kg) treatment. In the same experiment co-treatment with adriamycin prevented any rise in MDA contents significantly (P<0.001) as it was observed in adriamycin alone group. Although, this treatment failed to prevent any decline in NP-SH contents either alone or in combination with adriamycin. Epicoprostanol itself had the comparative declining effect on the contents of NP-SH as seen in adriamycin group. From the results of our experiments it seems that ambrein at all concentrations behaves like antioxidant in in vitro studies but the same time it decreased NP-SH contents in vivo accompanied by a decline in MDA contents. Whereas, epicoprostanol at two low concentrations had a decline in CL indicating a possible antioxidant potential but the high concentration increased CL showing a tendency towards oxidant prospective. However, in animal studies it has shown a clear protection against adriamycin induced free radical damage.

FK506 and a nonimmunosuppressant derivative reduce axonal and myelin damage in experimental autoimmune encephalomyelitis: neuroimmunophilin ligand-mediated neuroprotection in a model of multiple sclerosis

Multiple sclerosis (MS) is an inflammatory disease of the central nervous system (CNS) in which demyelination and axonal loss result in permanent neurologic disability. We examined the neuroprotective property of the immunosuppressant FK506 (tacrolimus), FK1706 (a nonimmunosuppressant FK506 derivative) and cyclosporin A (CsA) in a chronic relapsing experimental autoimmune encephalomyelitis (EAE) model of MS. Female SJL/J mice were immunized by subcutaneous (s.c.) injection with proteolipid protein 139-151 peptide in complete Freund's adjuvant. At the onset of paralysis, 12-14 days after immunization, mice received daily s.c. injections of FK506 (0.2, 1, and 5 mg/kg), FK1706 (5 mg/kg), CsA (2, 10, and 50 mg/kg), saline or vehicle (30% dimethylsulfoxide) for 30 days. FK506 (at a dose of 5 mg/kg) reduced the severity of the initial disease and suppressed relapses. FK1706 did not significantly alter the clinical course and CsA (at a dose of 50 mg/kg) lessened the severity of the initial episode of EAE but did not alter relapses. In the thoracic spinal cord, FK506 (5 mg/kg), FK1706 (5 mg/kg), and CsA (50 mg/kg) significantly (P < 0.001) reduced the extent of damage in the dorsal, lateral, and ventral white matter by a mean of up to 95, 68, and 30%, respectively. A nonimmunosuppressant dose of FK506 (0.2 mg/kg) also significantly (P < 0.001) reduced the extent of damage in the spinal cord by a mean of up to 45%. Other dosages of these compounds were ineffective. FK506 markedly protects against demyelination and axonal loss in this MS model through immunosuppression and neuroprotection.

N-acetylcysteine in chronic blepharitis

PURPOSE

To investigate the effects of N-acetylcysteine (NAC) in chronic posterior blepharitis.

METHODS

This was a prospective randomized, controlled study that included 79 eyes of 40 patients with chronic posterior blepharitis. Routine ophthalmologic examination, Schirmer-1 test, fluorescein break-up time (FBUT), and mucous fern tests were carried out during the first visit of all patients. A topical steroid, topical antibiotic, and artificial tears were started in 36 eyes of 18 patients. The therapy group (43 eyes of 22 patients) was administered three daily doses of 100 mg oral NAC. All patients were examined weekly for 1 to 4 months (average, 24 +/- 0.7). A Schirmer-1 test and FBUT were administered at every visit, but mucous fern tests were administered every two weeks. The results of the first and last Schirmer-1 tests, FBUT, and mucous fern test were compared between the therapy and control groups. Student's t and Mann-Whitney U tests were used for statistical analysis.

RESULTS

FBUT was significantly increased (p < 0.0001), and the mucous fern pattern was also significantly improved (p = 0.0096) in the therapy group.

CONCLUSION

NAC is thought to increase FBUT and improve mucous fern pattern by blocking lipid peroxidation in chronic blepharitis.

Cytoprotection by metallothionein against gastroduodenal mucosal injury caused by ethanol in mice

Metallothionein (MT) is a small, cysteine-rich protein that can act as a free radical scavenger at least in vitro. To test the hypothesis that MT participates in gastroduodenal cytoprotection, we studied sensitivity to gastroduodenal mucosal injury caused by ethanol in MT-null mice that have null mutations in MT-I and MT-II genes. MT-null mice and wild-type mice were orally treated with ethanol (60% or 99.5%, 0.2 ml/mouse). The macroscopic gastric lesion indices were significantly higher in MT-null mice than in wild-type mice 90 minutes after ethanol treatment. Histopathological examination in ethanol-treated MT-null mice showed vacuolar degeneration, necrosis of the epithelial cells, and hemorrhage throughout the tunica mucosa. Moreover, the duodenum also showed morphologic changes, including marked degeneration and coagulative necrosis of the entire villi, desquamation of the degenerated epithelial cells, and hemorrhage. In contrast, histopathologic changes were less prominent in the wild-type mice treated with ethanol. MT was not detected either in the stomach or duodenum of MT-null mice, whereas gastric and duodenal zinc contents were not significantly different between MT-null mice and wild-type mice. These results provide direct evidence that intrinsic MT plays a cytoprotective role in gastroduodenal mucosal injury caused by ethanol.

Characterization and purification of a lipoxygenase inhibitor in human epidermoid carcinoma A431 cells

A lipoxygenase inhibitor in the cytosolic fraction of human epidermoid carcinoma A431 cells was characterized and purified. The cytosolic inhibitor lost the inhibitory activity upon heating at 75 degrees C for 15 min or pretreating with 1 mg/ml trypsin at 37 degrees C for 60 min. Cytosol, after dialysis, lost the inhibitory activity but its inhibitory activity recovered when 1 mM GSH was added to the dialysate. The inhibitory activity of cytosol was also abolished by treatment either with 1 mM iodoacetate at 4 degrees C for 1 h or with 0.5 mM H2O2. The pI of the inhibitor was approx. 7.0. In addition to 12-lipoxygenase, the inhibitor inhibited the activities of 5-lipoxygenase and fatty acid cyclo-oxygenase in a cell-free system. The inhibitor was purified by a series of column chromatographies using CM Sephadex C-50, Sephadex G-100 SF and Mono P columns. A major 22 kDa protein was obtained that was distinct from selenium-dependent glutathione peroxidase.

Overexpression of metallothionein in the heart of transgenic mice suppresses doxorubicin cardiotoxicity

Metallothionein (MT) may provide protection against doxorubicin-induced heart damage. To test this hypothesis, a heart-specific promoter was used to drive the expression of human MT-IIa gene in transgenic mice. Four healthy transgenic mouse lines were produced. Cardiac MT was constitutively overexpressed from 10- to 130-fold higher than normal. The MT concentration was not altered in liver, kidneys, lungs, or skeletal muscles. Other antioxidant components including glutathione, glutathione peroxidase, glutathione reductase, catalase, and superoxide dismutase were not altered in the MT-overexpressing heart. Mice (7-wk-old) from transgenic lines expressing MT activity 10- or 130-fold higher than normal and from nontransgenic controls were treated intraperitoneally with doxorubicin at a single dose of 20 mg/kg, and were killed on the 4th day after treatment. As compared to normal controls, transgenic mice exhibited a significant resistance to in vivo doxorubicin-induced cardiac morphological changes, and the increase in serum creatine phosphokinase activity. Atria isolated from transgenic mice and treated with doxorubicin in tissue bath was also more resistant to functional damage induced by this drug. The results provide direct evidence for the role of MT in cardioprotection against doxorubicin toxicity.

Suppression of doxorubicin cardiotoxicity by overexpression of catalase in the heart of transgenic mice

Weak antioxidant capacity, particularly low catalase activity in the heart, may be a factor responsible for the high sensitivity of this organ to doxorubicin-induced oxidative damage. To test this hypothesis, a heart-specific promoter was used to drive the expression of murine catalase cDNA in transgenic mice. Fifteen healthy transgenic mouse lines were produced. Cardiac catalase activity was constitutively overexpressed in both atrium and ventricule, ranging from 2- to 630-fold higher than normal. This enzyme activity was not altered in liver, kidneys, lungs, and skeletal muscles. Other antioxidant components, including glutathione, glutathione peroxidase, glutathione reductase, metallothionein, and superoxide dismutase, were not altered in the catalase-overexpressing heart. Mice (7 weeks old) from several transgenic lines and from nontransgenic controls were treated intraperitoneally with doxorubicin at a single dose of 20 mg/kg and sacrificed on the 4th day after treatment. As compared to normal controls, transgenic lines expressing catalase activity 60- or 100-fold higher than normal exhibited a significant resistance to doxorubicin-induced cardiac lipid peroxidation, elevation of serum creatine phosphokinase, and functional changes in the isolated atrium. Interestingly, 200-fold or greater elevation of catalase activity did not provide protection. The results provide direct evidence for the role of catalase in doxorubicin cardiotoxic responses.

Inhibition of doxorubicin-induced membrane damage by thiol compounds: toxicologic implications of a glutathione-dependent microsomal factor

The hypothesis was tested that glutathione exerts its protective actions against doxorubicin-induced oxidative stress through an enzyme-dependent mechanism. Glutathione at biological concentrations decreased doxorubicin-dependent rat hepatic microsomal lipid peroxidation, whereas N-acetylcysteine had no effect. Glutathione was utilized during this inhibition at a rate dependent on the concentration of both doxorubicin and the sulfhydryl. Increasing glutathione concentrations resulted in significant increases in utilization. N-acetylcysteine was also oxidized in the microsomal system; however, the rate of oxidation was not enhanced by doxorubicin. If bovine cardiac microsomes were substituted for the hepatic microsomes, no lipid peroxidation was detected in the presence of doxorubicin, yet significant utilization of glutathione was detected. Microsomes isolated from tocopherol-deficient rats utilized less glutathione in the presence of doxorubicin, and there was no inhibition of doxorubicin-dependent lipid peroxidation. These findings support the conclusion that glutathione inhibits hepatic microsomal lipid peroxidation initiated by the redox-cycling of doxorubicin. Inhibition of doxorubicin-dependent lipid peroxidation appears to be enzyme-mediated and to require tocopherol. A similar mechanism for protection against doxorubicin appears to be present in heart microsomal membranes.

Dexrazoxane in the prevention of doxorubicin-induced cardiotoxicity

OBJECTIVE

To review doxorubicin-induced cardiotoxicity and to evaluate the use of dexrazoxane in its prevention.

DATA SOURCES

All animal and human reports involving doxorubicin-induced cardiac adverse effects were searched using MEDLINE combined with a fan search of relevant papers.

DATA EXTRACTION

Animal, in vitro cellular, and human data are thoroughly reviewed with particular emphasis on doxorubicin-induced cardiotoxicity, including clinical manifestations, risk factors, and mechanisms of toxicity. The role of dexrazoxane in the prevention of doxorubicin-induced cardiotoxicity is reviewed, including mechanism of effect, animal data, and human trials.

DATA SYNTHESIS

Anthracyclines are associated with a cumulative, dose-dependent, irreversible cardiomyopathy that can lead to congestive heart failure and death. The incidence of cardiotoxicity rises sharply at a total lifetime dose of more than 550 mg/m2. Through its semiquinone metabolite, doxorubicin appears to generate superoxide anion and superhydroxide free radicals with iron as a cofactor. Because of poor myocardial concentrations of superoxide dismutase, catalase, and glutathione peroxidase, these free radicals cause extensive lipid peroxidation and mitochondrial destruction.

CONCLUSIONS

Dexrazoxane is hydrolyzed to its active form intracellularly and binds iron to prevent the formation of superhydroxide radicals, thus preventing mitochondrial destruction. The effect of dexrazoxane on the prevention of doxorubicin-induced cardiotoxicity is impressive in both animal and human studies. Further research is needed to clearly demonstrate the effect dexrazoxane has on the antitumor effects of combination chemotherapy while defining optimal dosing strategies to minimize myelosuppression and maximize cardioprotection.

In-vivo and in-vitro mitochondrial membrane damages induced in mice by adriamycin and derivatives

A major limitation to a prolonged use of adriamycin (ADM) during a clinical treatment is its dose-dependent cardiotoxicity. This toxicity has been related to a general disturbance of the inner mitochondrial membrane structure and its essential biological functions, associated to the production of free radicals by the anthracyclines. 4'-Epiadriamycin (4'-epiADM), 4'-deoxyadriamycin (4'-deoxyADM), 4'-deoxy-4'-iodoadriamycin (4'-deoxy-4'-iodoADM) and 4'-demethoxydaunorubicin (4-demethoxyDNR) are ADM and daunorubicin (DNR) derivatives differing from their parent compounds by minor structural modifications. They are nevertheless documented as less cardiotoxic. Our purpose was to establish whether mitochondrial membrane damages induced in vivo in mice heart by those compounds are correlated with the free radical formation. Heart mitochondria of treated mice were isolated 48 h after a single drug injection in order to measure the acute mitochondrial toxicity. Enzymatic activities of complex I-III and complex IV of the mitochondrial respiratory chain, mitochondrial membrane fluidity and lipid peroxidation were measured. None of the ADM and DNR derivatives displayed a significant acute mitochondrial toxicity. A mitochondrial toxicity was however detected for 4-deoxyADM and 4-demethoxyDNR when drugs were given chronically, but it was strongly reduced as compared with ADM and DNR. Electron transfer between NADH and cytochrome c, formation of superoxide radicals and lipid peroxidation were measured in vitro for the various drugs. Comparison of the in-vivo and in-vitro results provides evidence that free radical production explains only partly the in-vivo toxicities.

Comparison of adriamycin and derivatives uptake into large unilamellar lipid vesicles in response to a membrane potential

The uptake of adriamycin (ADM) and several derivatives into large unilamellar vesicles (LUV) displaying a transmembrane potential and having a lipid composition close to that of the inner mitochondrial membrane has been measured. Drug association to neutral liposomes, made of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) (70:30, w/w) was shown to be potential-dependent: in the absence of potential, accumulation of drug was almost undetectable, whereas between 11 and 50 nmol of drug/mumol phospholipid, depending on the anthracycline used, was associated to LUV exhibiting a membrane potential after 1 h incubation. Association of drugs to LUV with a lipid composition closer to that of the inner mitochondrial (cardiolipin, CL, 20%; PC 50%; PE, 30%, w/w) and displaying a membrane potential is higher than with neutral vesicles (between 40 and 76 nmol of anthracycline/mumol phospholipid after 1 h incubation). Since it is known that ADM and derivatives have a high affinity for CL, a fraction of the associated drug may bind to CL on the outer side of the vesicles. This was confirmed by the fact that, in the absence of potential, between 40 and 56 nmol of anthracycline/mumol phospholipid was still associated to LUV containing CL. In order to discriminate between drug adsorbed at the surface of the LUV and drug accumulated inside the LUV, an anthracycline fluorescence quencher (I-) was used. It was shown on neutral LUV displaying a membrane potential, that between 55 and 81% of the associated drug is actually entrapped inside the vesicles, inaccessible to the quencher. These percentages decreased to between 41 and 68%, respectively, in the presence of LUV containing CL and exhibiting a membrane potential, whereas for LUV of the same composition but displaying no membrane potential almost all the associated drug is adsorbed on the outer face of the LUV, accessible to the quencher, and likely bound to CL. This study brings evidence that antitumour anthracyclines despite important structural homologies do not accumulate to the same extent into vesicles mimicking the lipid composition and the membrane potential of mitoplasts. This ability to reach the matrix compartment of mitochondria could partly explain the differences of cardiotoxicities associated to anthracyclines with closely related molecular structure.

Elevation of glutathione levels in bovine pulmonary artery endothelial cells by N-acetylcysteine

N-Acetylcysteine (NAC), a cysteine derivative with chemoprotective and radioprotective effects, was found to elevate bovine pulmonary artery endothelial cell (EC) glutathione after in vitro incubation. The elevation in glutathione was associated with enhanced uptake of radioactivity of cystine from the medium. Because cystine in medium was converted rapidly to cysteine and cysteinyl-NAC in the presence of NAC and given that cysteine has a higher affinity for uptake by EC than cystine, we conclude that the enhanced uptake of radioactivity was in the form of cysteine and at least part of the stimulatory effect of NAC on EC glutathione was due to a formation of cysteine by a mixed disulfide reaction of NAC with cystine similar to that previously reported for Chinese hamster ovarian cells (R. D. Issels et al. 1988. Biochem. Pharmacol. 37:881-888). However, NAC was more effective than cysteine in elevating cellular glutathione at equimolar concentrations, and at higher concentrations of NAC an elevation of EC glutathione occurred even in the absence of cystine in the medium through a currently unknown mechanism. Thus, at least two mechanisms are operative in the elevation of endothelial cellular glutathione by NAC. NAC may be a useful compound for elevating glutathione of the pulmonary vasculature for protection against oxidant stress.

NADPH- and adriamycin-dependent microsomal release of iron and lipid peroxidation

In a previous study (Minotti, G., 1989, Arch. Biochem. Biophys. 268, 398-403) NADPH-supplemented microsomes were found to reduce adriamycin (ADR) to semiquinone free radical (ADR-.), which in turn autoxidized at the expense of oxygen to regenerate ADR and form O2-. Redox cycling of ADR was paralleled by reductive release of membrane-bound nonheme iron, as evidenced by mobilization of bathophenanthroline-chelatable Fe2+. In the present study, iron release was found to increase with concentration of ADR in a superoxide dismutase- and catalase-insensitive manner. This suggested that membrane-bound iron was reduced by ADR-. with negligible contribution by O2-. or interference by its dismutation product H2O2. Following release from microsomes, Fe2+ was reconverted to Fe3+ via two distinct mechanisms: (i) catalase-inhibitable oxidation by H2O2 and (ii) catalase-insensitive autoxidation at the expense of oxygen, which occurred upon chelation by ADR and increased with the ADR:Fe2+ molar ratio. Malondialdehyde formation, indicative of membrane lipid peroxidation, was observed when approximately 50% of Fe2+ was converted to Fe3+. This occurred in presence of catalase and low concentrations of ADR, which prevented Fe2+ oxidation and favored only partial Fe2+ autoxidation, respectively. Lipid peroxidation was inhibited by superoxide dismutase via increased formation of H2O2 from O2-. and excessive Fe2+ oxidation. Lipid peroxidation was also inhibited by high concentrations of ADR, which favored maximum Fe2+ release but also caused excessive Fe2+ autoxidation via formation of very high ADR:Fe2+ molar ratios. These results highlighted multiple and diverging effects of ADR, O2-., and H2O2 on iron release, iron (auto-)oxidation and lipid peroxidation. Stimulation of malondialdehyde formation by catalase suggested that lipid peroxidation was not promoted by reaction of Fe2+ with H2O2 and formation of hydroxyl radical. The requirement for both Fe2+ and Fe3+ was indicative of initiation by some type of Fe2+/Fe3+ complex.