The molecular link between beta- and gamma-secretase activity on the amyloid beta precursor protein.

Alzheimer's disease (AD) is characterized by an accumulation in the brain of amyloid beta peptides (Abeta). The production of Abeta requires two sequential cleavages induced by beta- and gamma-secretases on the beta-amyloid precursor protein (APP). Altered activity of these secretases is involved in the pathogenesis of AD. The expression and activity of beta-secretase (BACE1) is augmented in the brain in late-onset sporadic AD. Mutant presenilin 1 (PS1), the major genetic defect of early-onset familial AD (FAD), alters the activity of gamma-secretase, leading to increased production of Abeta42. Here we review the role of oxidative stress as a molecular link between the beta- and the gamma-secretase activities, and provide a mechanistic explanation of the pathogenesis of sporadic late-onset AD. We also discuss evidence for a role of the same mechanism in the pathogenesis of familial AD carrying PS1 mutations.

Dehydroepiandrosterone reduces expression and activity of BACE in NT2 neurons exposed to oxidative stress.

Recently, we showed that oxidative stress activates the expression and activity of the beta-site AbetaPP-cleaving enzyme (BACE), an aspartyl protease responsible for the beta-secretase cleavage of AbetaPP. The identification of compounds able to prevent the induction of this event is an important goal of therapeutic strategies for Alzheimer's disease (AD). Dehydroepiandrosterone (DHEA) is an adrenal steroid that improves a variety of functions in the central nervous system. Moreover, a series of evidence suggests that DHEA displays antioxidant properties in different experimental models. In the present paper we show that pretreatment with DHEA is able to rescue the increase of mRNA expression, protein levels, and activity of BACE, produced by oxidative stress in NT2 neurons. BACE, being the enzyme that initiates the production of Abeta, is a drug target for AD. Our results imply that DHEA administration may slow down the AD pathological process, lowering Abeta accumulation.

H2O2 and 4-hydroxynonenal mediate amyloid beta-induced neuronal apoptosis by activating JNKs and p38MAPK.

Amyloid beta peptides (Abeta) may be neurotoxic during the progression of Alzheimer's disease by eliciting oxidative stress. Exposure of neuronally differentiated SK-N-BE cells to Abeta(25-35) fragment as well as to full-length Abeta(1-40) and Abeta(1-42) induces early and time-dependent generation of oxidative stress that has been evaluated by carefully monitoring generation of hydrogen peroxide (H(2)O(2)), 4-hydroxynonenal (HNE), thiobarbituric acid reactive substances (TBARS), and fluorescent chromolipids. Abeta treatment also results in the activation of c-Jun aminoterminal kinases (JNKs) and p38(MAPK) and is followed by characteristic nuclear changes of apoptosis as evaluated by DAPI staining and TUNEL technique. To reproduce the relationships between oxidative stress and Abeta apoptosis we found that only the simultaneous administration of HNE and H(2)O(2), at concentrations similar to those generated within the first 3 h of Abeta exposure, can fully mimic Abeta-dependent activation of JNKs and p38(MAPK) and occurrence of apoptosis. Antioxidants such as alpha-tocopherol and N-acetylcysteine prevent completely either neuronal apoptosis or activation of JNKs and p38(MAPK) elicited by Abeta or by simultaneous HNE and H(2)O(2) addition. Finally, direct evidence that activation of these kinases is required for cell death induced by Abeta has been obtained by pretreating cell with specific inhibitors of JNKs and p38(MAPK). These results suggest the existence of a sequence of events in Abeta-induced apoptosis involving simultaneous generation of HNE and H(2)O(2) and oxidative stress-dependent activation of JNKs and p38(MAPK).

Oxidative stress and eicosanoids in the kidneys of hyperglycemic rats treated with dehydroepiandrosterone.

Oxidative stress plays a crucial role in the pathogenesis of chronic diabetic complications. Normoglycemic and streptozotocin-diabetic rats were treated with dehydroepiandrosterone (DHEA) (4 mg/d per rat) for 3 weeks. At the end of treatment, hydroxynonenal, hydroperoxyeicosatetraenoic acids and antioxidant levels, as well as Na/K-ATPase activity and membrane fatty acids composition were evaluated in kidney homogenates. Chronic hyperglycemia caused a marked increase of both hydroxynonenal and lipoxygenase pathway products and a drop in both GSH levels and membrane Na/K-ATPase activity. DHEA treatment restored the antioxidant levels to close to the control value and considerably reduced hydroxynonenal and hydroperoxyeicosatetraenoic acid levels. Moreover, DHEA counteracted the detrimental effect of hyperglycemia on membrane function: the drop of Na/K-ATPase activity in diabetic animals was significantly inhibited by DHEA treatment. These results show that DHEA reduces oxidative stress and the consequent increase of lipoxygenase pathway products induced by experimental diabetes in rat kidney; they also suggest that, by reducing the inflammatory response to oxidative stress, DHEA treatment might delay the progression of diabetic kidney disease.

Dehydroepiandrosterone prevents oxidative injury induced by transient ischemia/reperfusion in the brain of diabetic rats.

Both chronic hyperglycemia and ischemia/reperfusion (IR) cause an imbalance in the oxidative state of tissues. Normoglycemic and streptozotocin (STZ)-diabetic rats were subjected to bilateral carotid artery occlusion for 30 min followed by reperfusion for 60 min. Rats had either been treated with dehydroepiandrosterone (DHEA) for 7, 14, or 21 days (2 or 4 mg/day per rat) or left untreated. Oxidative state, antioxidant balance, and membrane integrity were evaluated in isolated synaptosomes. IR increased the levels of reactive species and worsened the synaptic function, affecting membrane Na/K-ATPase activity and lactate dehydrogenase release in all rats. The oxidative imbalance was much severer when transient IR was induced in STZ-diabetic rats. DHEA treatment restored H2O2, hydroxyl radical, and reactive oxygen species to close to control levels in normoglycemic rats and significantly reduced the level of all reactive species in STZ-diabetic rats. Moreover, DHEA treatment counteracted the detrimental effect of IR on membrane integrity and function: the increase of lactate dehydrogenase release and the drop in Na/K-ATPase activity were significantly prevented in both normoglycemic and STZ-diabetic rats. The results confirm that DHEA, an adrenal steroid that is synthesized de novo by brain neurons and astrocytes, possesses a multitargeted antioxidant effect. They also show that DHEA treatment is effective in preventing both derangement of the oxidative state and neuronal damage induced by IR in experimental diabetes.

Dehydroepiandrosterone prevents lipid peroxidation and cell growth inhibition induced by high glucose concentration in cultured rat mesangial cells.

The oxidative stress induced by high glucose concentration contributes to tissue damage associated with diabetes, including renal injury. Dehydroepiandrosterone (DHEA), the major secretory product of the human adrenal gland, has been shown to possess a multi-targeted antioxidant activity which is also effective against lipid peroxidation induced by high glucose. In this study we evaluated the effect of DHEA on the growth impairment which high glucose concentration induces in cultured rat mesangial cells. Primary cultures of rat mesangial cells were grown for 10 days in media containing either normal (i.e. 5.6 mmol/l) or high (i.e. 30 mmol/l) concentrations of glucose, without or with DHEA at different concentrations. The impairment of cell growth induced by high glucose was reversed by 100 nmol/l and 500 nmol/l DHEA, which had no effect on mesangial cells cultured in media containing glucose at the normal physiological concentration (5.6 mmol/l). In high-glucose cultured mesangial cells, DHEA also attenuated the lipid peroxidation, as measured by thiobarbituric acid reactive substances (TBARS) generation and 4-hydroxynonenal (HNE) concentration, and preserved the cellular content of reduced glutathione as well as the membrane Na+/K+ ATPase activity. The data further support the protective effect of DHEA against oxidative damage induced by high glucose concentrations, and bring into focus its possible effectiveness in preventing chronic complications of diabetes.

NT2 neurons, a classical model for Alzheimer's disease, are highly susceptible to oxidative stress.

We have tested undifferentiated NT2 cells as well as differentiated NT2 neurons (NT2N) for vulnerability to oxidative stress, lipid composition and antioxidant pattern. NT2N, but not NT2 cells, are highly susceptible to oxidative stress elicited by different classic pro-oxidant stimuli. In particular, NT2N cells undergo a high level of oxidative decomposition of omega-3 and omega-6 polyunsaturated fatty acids (PUFA) of membrane phospholipids, as evaluated by monitoring generation of thiobarbituric reactive substances, 4-hydroxynonenal (HNE) and chromolipid fluorescent adducts. NT2N cells exhibit low levels of natural antioxidants such as glutathione (GSH) and alpha-tocopherol and of antioxidant enzymatic activities such as Se-dependent GSH peroxidase and catalase. Accordingly, a direct correlation between lipid peroxidation and irreversible cell damage is suggested by prevention of NT2N cell death by alpha-tocopherol.

Oxidative derangement in rat synaptosomes induced by hyperglycaemia: restorative effect of dehydroepiandrosterone treatment.

Central nervous system damage in diabetes is caused by both cerebral atherosclerosis and the detrimental effect of chronic hyperglycaemia on nervous tissue. Hyperglycaemia is the primer of a series of cascade reactions causing overproduction of free radicals. There is increasing evidence that these reactive molecules contribute to neuronal tissue damage. Dehydroepiandrosterone (DHEA) has been reported to possess antioxidant properties. This study evaluates the oxidative status in the synaptosomal fraction isolated from the brain of streptozotocin-treated rats and the antioxidant effect of DHEA treatment on diabetic rats. Hydroxyl radical generation, hydrogen peroxide content, and the level of the reactive oxygen species was increased (P<0.05) in synaptosomes isolated from streptozotocin-treated rats. The derangement of the oxidative status was confirmed by a low level of reduced glutathione and alpha-tocopherol. DHEA treatment (4 mg per day for 3 weeks, per os) protected the synaptosomes against oxidative damage: synaptosomes from diabetic DHEA-treated rats showed a significant decrease in reactive species (P<0.05) and in the formation of end products of lipid peroxidation, evaluated in terms of fluorescent chromolipid (P<0.01). Moreover, DHEA treatment restored the unsaturated fatty acid content of the membrane and the reduced glutathione and alpha-tocopherol levels to normal levels and restored membrane NaK-ATPase activity close to control levels. The results demonstrate that DHEA supplementation greatly reduces oxidative damage in synaptosomes isolated from diabetic rats and suggest that this neurosteroid may participate in protecting the integrity of synaptic membranes against hyperglycaemia-induced damage.

Protective effect of dehydroepiandrosterone against lipid peroxidation in a human liver cell line.

OBJECTIVE: Dehydroepiandrosterone (DHEA) is a widely studied steroid hormone with multi-functional properties. Reports suggest that some of the many activities of DHEA are due to its protective effect against lipid peroxidation. Nevertheless, the antioxidant properties of DHEA are still the subject of debate. The aim was to evaluate whether its two opposed effects on lipid peroxidation reported in the literature may be dependent on schedule and doses used. METHODS: Chang liver cells, a line derived from normal human liver, were grown in media containing either no steroids (control) or DHEA at concentrations ranging from 0.1 micromol/l to 50 micromol/l. At specific times, cultures were halted and cells received a pro-oxidant stimulus (cumene (CuOOH) 0.5 mmol/l), at which time cell viability (by trypan blue staining and lactate dehydrogenase (LDH) release) and thiobarbituric acid reactive substances (TBARS) concentration (spectrophotometrical assay) were evaluated. RESULTS: At concentrations ranging from 0.1 micromol/l to 1 micromol/l, DHEA protects Chang liver cells against lipid peroxidation and/or death induced by cumene. This effect disappears if the concentration is increased to 10 micromol/l; at higher concentrations (50 micromol/l) a pro-oxidant/cytotoxic effect of DHEA appears. CONCLUSIONS: DHEA exhibits two opposed effects on lipid peroxidation; depending on its concentration it acts either to limit or to induce oxidative stress. The threshold concentration at which the pro-oxidant activity of DHEA prevails is not far in excess of that having an antioxidant effect. Either effect of DHEA on lipid peroxidation is only evident after a 'lag-phase'.

Dehydroepiandrosterone protects tissues of streptozotocin-treated rats against oxidative stress.

Chronic hyperglycemia in diabetes determines the overproduction of free radicals, and evidence is increasing that these contribute to the development of diabetic complications. It has recently been reported that dehydroepiandrosterone possesses antioxidant properties; this study evaluates whether, administered daily for three weeks per os, it may provide antioxidant protection in tissues of rats with streptozotocin-induced diabetes. Lipid peroxidation was evaluated on liver, brain and kidney homogenates from diabetic animals, measuring both steady-state concentrations of thiobarbituric acid reactive substances and fluorescent chromolipids. Hyperglycemic rats had higher thiobarbituric acid reactive substances formation and fluorescent chromolipids levels than controls. Dehydroepiandrosterone-treatment (4 mg/day for 3 weeks) protected tissues against lipid peroxidation: liver, kidney and brain homogenates from dehydroepiandrosterone-treated animals showed a significant decrease of both thiobarbituric acid reactive substances and fluorescent chromolipids formation. The effect of dehydroepiandrosterone on the cellular antioxidant defenses was also investigated, as impaired antioxidant enzyme activities were considered proof of oxygen-dependent toxicity. In kidney and liver homogenates, dehydroepiandrosterone treatment restored to near-control values the cytosolic level of reduced glutathione, as well as the enzymatic activities of superoxide-dismutase, glutathione-peroxidase, catalase. In the brain, only an increase of catalase activity was evident (p < .05), which reverted with dehydroepiandrosterone treatment. The results demonstrate that DHEA treatment clearly reduces oxidative stress products in the tissues of streptozotocin-treated rats.

Liver AP-1 activation due to carbon tetrachloride is potentiated by 1,2-dibromoethane but is inhibited by alpha-tocopherol or gadolinium chloride.

Experimental acute intoxication by prooxidant haloalkanes produces marked stimulation of hepatic lipid peroxidation and cytolysis, which is followed by tissue regeneration. Our aim was to clarify the role of oxidative imbalance in the activation of the redox-sensitive transcription factor, activator protein-1 (AP-1), which is involved in tissue repair. Rats were poisoned with a very low concentration of carbon tetrachloride, given alone or in combination with another hepatotoxin, 1,2-dibromoethane, to provide varying extents of oxidative damage. The level of AP-1-DNA binding was analyzed by electrophoretic mobility shift assay on liver extracts, obtained from rats killed 6 h after poisoning. Stimulation of lipid peroxidation and AP-1 upregulation were already established when the hepatic damage due to carbon tetrachloride +/-1,2-dibromoethane was beginning to appear. Rat supplementation with the antioxidant vitamin E completely inhibited AP-1 upregulation, thus supporting a causative role of membrane lipid oxidation in the observed modulation of the transcription factor. Moreover, activation of Kupffer cells appears to be a crucial step in the increased AP-1 binding to DNA, the latter being largely prevented by gadolinium chloride, a macrophage-specific inhibitor.

Dehydroepiandrosterone protects bovine retinal capillary pericytes against glucose toxicity.

Pericyte loss is an early feature of diabetic retinopathy and represents a key step in the progression of this disease. This study aimed to evaluate the effect of dehydroepiandro-sterone (DHEA) on glucose toxicity in retinal capillary pericytes. Bovine retinal pericytes (BRP) were cultured in a high glucose concentration, with or without DHEA. After 4 days of incubation the number of BRP was significantly reduced by the high glucose concentration. The addition of DHEA to the medium reversed the adverse effect of high glucose: BRP proliferation partially recovered in the presence of 10 nmol/l DHEA, and completely recovered in the presence of DHEA at concentrations equal to or greater than 100 nmol/l. At physiological glucose concentrations, DHEA had no effect on BRP growth. Data show that DHEA, at concentrations similar to those found in human plasma, protects BRP against glucose toxicity. This effect seems specific for DHEA, since its metabolites, 5-en-androstene-3 beta, 17 beta-diol, dihydrotestosterone and estradiol did not alter BRP growth in normal or high glucose media. Various pieces of evidence link the antioxidant properties of DHEA to its protective effect on glucose-induced toxicity in BRP.

Dehydroepiandrosterone inhibits the growth of DMBA-induced rat mammary carcinoma via the androgen receptor.

Dehydroepiandrosterone (DHEA) exerts opposite effects on the growth of mammary carcinoma. A stimulatory effect is observed in absence of estrogens, due to interaction of DHEA metabolite(s) with the estrogen receptor (ER); by contrast, in presence of estrogens DHEA inhibits tumor growth. The mechanism underlying the latter DHEA effect, which might be related to activation of the androgen receptor (AR), is poorly understood. Focusing on this point, we measured over a 20 days period the areas of DMBA-induced mammary tumors in rats given DHEA and/or the anti-androgen flutamide (FLU). Results show that DHEA inhibitory effect on the growth of mammary carcinoma is no longer observed when the ARs are blocked by FLU. Data are consistent with an involvement of ARs in the inhibitory effect of DHEA.

Oxygen free radical scavenger properties of dehydroepiandrosterone.

The microsomes from dehydroepiandrosterone (DHEA)-supplemented animals are good hydroxyl radical scavengers, as demonstrated through electron spin resonance and deoxyribose degradation. The ability of DHEA-supplemented microsomes to react with superoxide radical was also demonstrated through the inhibition of nitroblue-tetrazolium reduction determined by superoxide radicals produced in a hypoxanthine-xanthine oxidase system. DHEA-enriched microsomes, obtained from acutely DHEA-treated rats, become resistant to iron-dependent lipid peroxidation triggered by H2O2/FeSO4 and ascorbate/FeSO4. The direct addition of DHEA to microsomes from untreated rats failed to prevent iron-dependent lipid peroxidation, even if the microsomes were preincubated with DHEA for up to 15 min, indicating that in vivo transformation is required before antioxidant action can be exerted.

Protective effect of dehydroepiandrosterone against copper-induced lipid peroxidation in the rat.

This study investigates the effectiveness and multitargeted activity of dehydroepiandrosterone (DHEA) as antioxidant in vivo. A single dose of DHEA was given IP to male rats. Liver and brain microsomes, and plasma low density lipoprotein (LDL), were isolated from rats sacrificed 17 h later. Liver and brain microsomes were challenged with CuSO(4) and, as index of lipid peroxidation, the production of thiobarbituric acid reactive substances (TBARS) was measaured. Also, plasma low-density lipoprotein (LDL) were challenged with copper and the time course of lipid peroxidation was evaluated following the formation of conjugated dienes. The onset of TBARS generation induced by copper was marked delayed in both liver and brain microsomes from DHEA-treated animals. Also, the resistance of LDL to oxidation, expressed by the duration of the lag-phase of the kinetic curve, was significantly enhanced in DHEA-treated rats. Results indicate that in vivo DHEA supplementation makes subcellular fractions isolated from different tissues and plasma constituents (LDL) more resistant to lipid peroxidation triggered by copper. The antioxidant effect on plasma LDL might be of special relevance to the proposed antiatherogenic activity of DHEA. Moreover, multitargeted antioxidant activity of DHEA might protect tissues from oxygen radicals damage.

Dehydroepiandrosterone administration prevents the oxidative damage induced by acute hyperglycemia in rats.

Free radical overproduction contributes to tissue damage induced by acute hyperglycemia. Dehydroepiandrosterone, which has recently been found to have antioxidant properties, was administered i.p. to rats at different doses (10, 50 or 100 mg/kg body weight) 3 h before treatment with dextrose (5 g/kg). Lipid peroxidation was evaluated on liver, brain and kidney homogenates, measuring both steady-state concentrations of thiobarbituric acid reactive substances, and fluorescent chromolipids, evaluated as hydroxynonenal adducts. Formation of thiobarbituric acid reactive substances was significantly higher in hyperglycemic than in normoglycemic animals. Three hours (but not 1 h) dehydroepiandrosterone-pretreatment protected tissues against lipid peroxidation induced by dextrose; both thiobarbituric acid reactive substances and hydroxynonenal adducts in liver, kidney and brain homogenates were significantly lower in dehydroepiandrosterone-pretreated animals. Dehydroepiandrosterone did not modify the cytosolic level of antioxidants, such as alpha-tocopherol or glutathione, nor the activities of glutathione peroxidase, reductase or transferase. The results of this study indicate that the 'in vivo' administration of dehydroepiandrosterone increases tissue resistance to lipid peroxidation triggered by acute hyperglycemia.

In vivo potentiation of 1,2-dibromoethane hepatotoxicity by ethanol through inactivation of glutathione-s-transferase.

In the rat, a single ethanol (EtOH) pretreatment (2.5 g/kg b.w., per os) was able to strongly enhance the cytotoxicity of 1,2-dibromoethane (DBE)(87 mg/kg b.w., per os). The principal metabolic routes of DBE involve both oxidative and conjugative transformations. Microsomal cytochrome P450 content and dimethyl nitrosamine demethylase activity were not changed, while a significant loss of cytosolic total GSH-transferase was observed in rats killed 6 h after EtOH pretreatment. Pretreatment with methylpyrazole, an inhibitor of alcohol-dehydrogenase prevented the effects provoked by ethanol. The major EtOH metabolite, acetaldehyde. seemed thus to play a fundamental role in the mechanism responsible for the potentiation of DBE toxicity mediated by EtOH. To further support this hypothesis, disulfiram (75 mg/kg b.w.), an inhibitor of aldehyde dehydrogenase, was given i.p. to rats. When DBE was administered to disulfiram- and EtOH-pretreated rats, a marked increase of liver cytolysis was shown and cytosolic GSH-transferase activity was further inhibited if compared to that induced by EtOH treatment alone. The results are consistent with the hypothesis that EtOH given to rats increases DBE liver toxicity because its major metabolite, acetaldehyde, reduces the DBE conjugates to GSH transferase, with consequent shift of DBE metabolism to the oxidative route and accumulation of reactive oxidative intermediates no longer effectively conjugated with GSH.

Acetaldehyde involvement in ethanol-induced potentiation of rat hepatocyte damage due to the carcinogen 1,2-dibromoethane.

Previous experiments with hepatocytes isolated from ethanol-treated rats showed that alcohol potentiates the toxic action of 1,2-dibromoethane (DBE) by inhibiting its metabolism via glutathione-S-transferase. The aim of this study was to investigate whether acetaldehyde, the main product of ethanol metabolism, may be responsible for such inactivation. By pretreatment with 4-methylpyrazole, an inhibitor of acetaldehyde formation, the ethanol inactivation of glutathione transferase was actually prevented. As a consequence of this protective action, 4-methylpyrazole also prevented the high basal lipid peroxidation and the potentiated DBE toxicity observed in hepatocytes from ethanol-dosed animals. Finally, the inactivation of glutathione-S-transferase by concentrations of acetaldehyde likely to occur in the ethanol-intoxicated animal was confirmed in an in vitro model by direct aldehyde addition to hepatocyte suspensions.

Growth inhibition of DMBA-induced rat mammary carcinomas by the antiandrogen flutamide.

Antiandrogens have sporadically been reported to exert antitumor activities in both pre- and post-menopausal breast cancer. To explore the possibility of using the pure antiandrogen flutamide (FLU) in breast cancer therapy, rats bearing DMBA-induced mammary tumors were treated with FLU, dihydrotestosterone (DHT), or FLU plus DHT. FLU was administered orally, at doses comparable to those used in the treatment of prostate cancer patients. FLU-treated animals had a significantly smaller average tumor area than controls from day 11 up to the end of the experiment (day 20). A similar reduction of tumor growth was observed in rats given DHT and in those treated with DHT plus FLU. Plasma levels of LH, FSH, P, 17-OH P, E2 and DHEA measured at the end of experiment did not differ between treated animals and controls. Results demonstrate that the antiandrogen FLU and the full androgen DHT exert similar inhibitory effects on the growth of dimethylbenz(a)anthracene (DMBA)-induced rat mammary tumors. Moreover, data show that plasma steroids levels are unaffected by FLU treatment. This finding rules out any antitumor effect dependent on the reduction of adrenal and gonadal steroidosynthesis, and makes it appear more likely that androgen receptors are involved in the antiproliferative effect of FLU.

Prevention of carbon tetrachloride-induced lipid peroxidation in liver microsomes from dehydroepiandrosterone-pretreated rats.

Dehydroepiandrosterone (DHEA), a lipid soluble steroid, administered to rats (100 mg/kg b.wt) by a single intraperitoneal injection, increases to twice its normal level in the liver microsomes. Microsomes so enriched become resistant to lipid peroxidation induced by incubation with carbon tetrachloride in the presence of a NADPH-regenerating system: also the lipid peroxidation-dependent inactivation of glucose-6-phosphatase and gamma-glutamyl transpetidase due to the haloalkane are prevented. Noteworthy, the liver microsomal drug-metabolizing enzymes and in particular the catalytic activity of cytochrome P450IIE1, responsible for the CCl4-activation, are not impaired by the supplementation with the steroid. Consistently, in DHEA-pretreated microsomes the protein covalent binding of the trichloromethyl radical (CCl3 degrees), is similar to that of not supplemented microsomes treated with CCl4. It thus seems likely that DHEA protects liver microsomes from oxidative damage induced by carbon tetrachloride through its own antioxidant properties rather than inhibiting the metabolism of the toxin.