The inhibitory effects in vitro of phenothiazines and other drugs on lipid-peroxidation systems in rat liver microsomes, and their relationship to the liver necrosis produced by carbon tetrachloride

Synthesis and Spectroscopic Characterization of Selected Phenothiazines and Phenazines Rationalized Based on DFT Calculation

Two unique structures were isolated from the phosphorylation reaction of 10H-phenothiazine. The 5,5-dimethyl-2-(10H-phenothiazin-10-yl)-1,3,2-dioxaphosphinane 2-oxide (2a) illustrates the product of N-phosphorylation of phenothiazine. Moreover, a potential product of 2a instability, a thiophosphoric acid 2b, was successfully isolated and structurally characterized. Molecule 2a, similarly to sulfoxide derivative 3, possesses interesting phosphorescence properties due to the presence of d-pπ bonds. The X-ray, NMR, and DFT computational studies indicate that compound 2a exhibits an anomeric effect. Additionally, the syntheses of selected symmetrical and unsymmetrical pyridine-embedded phenazines were elaborated. To compare the influence of phosphorus and sulfur atoms on the structural characteristics of 10H-phenothiazine derivatives, the high-quality crystals of (4a,12a-dihydro-12H-benzo[5,6][1,4]thiazino[2,3-b]quinoxalin-12-yl)(phenyl)methanone (1) and selected phenazines 5,12-diisopropyl-3,10-dimethyldipyrido[3,2-a:3′,2′-h]phenazine (5) and 5-isopropyl-N,N,3-trimethylpyrido[3,2-a]phenazin-10-amine (6a) were obtained. The structures of molecules 1, 2a, 2-mercapto-5,5-dimethyl-1,3,2-dioxaphosphinane 2-oxide (2b), 3,7-dinitro-10H-phenothiazine 5-oxide (3), 5 and 6a were determined by single-crystal X-ray diffraction measurements.

An Air-Stable, Neutral Phenothiazinyl Radical with Substantial Radical Stabilization Energy

The vital effect of radical states on the pharmacological activity of phenothiazine-based drugs has long been speculated. Whereas cationic radicals of N-substituted phenothiazines show high stability, the respective neutral radicals of N-unsubstituted phenothiazines have never been isolated. Herein, the 1,9-diamino-3,7-di-tert-butyl-N1 ,N9 -bis(2,6-diisopropylphenyl)-10H-phenothiazin-10-yl radical (SQH2 . ) is described as the first air-stable, neutral phenothiazinyl free radical. The crystalline dark-blue species is characterized by means of EPR and UV/Vis/near-IR spectroscopy, as well as cyclic voltammetry, spectro-electrochemical analysis, single-crystal XRD, and computational studies. The SQH2 . radical stands out from other aminyl radicals by an impressive radical stabilization energy and its parent amine has one of the weakest N-H bond dissociation energies ever determined. In addition to serving as open-shell reference in medicinal chemistry, its tridentate binding pocket or hydrogen-bond-donor ability might enable manifold uses as a redox-active ligand or proton-coupled electron-transfer reagent.

Drugs Repurposed as Antiferroptosis Agents Suppress Organ Damage, Including AKI, by Functioning as Lipid Peroxyl Radical Scavengers

BACKGROUND

Ferroptosis, nonapoptotic cell death mediated by free radical reactions and driven by the oxidative degradation of lipids, is a therapeutic target because of its role in organ damage, including AKI. Ferroptosis-causing radicals that are targeted by ferroptosis suppressors have not been unequivocally identified. Because certain cytochrome P450 substrate drugs can prevent lipid peroxidation via obscure mechanisms, we evaluated their antiferroptotic potential and used them to identify ferroptosis-causing radicals.

METHODS

Using a cell-based assay, we screened cytochrome P450 substrate compounds to identify drugs with antiferroptotic activity and investigated the underlying mechanism. To evaluate radical-scavenging activity, we used electron paramagnetic resonance-spin trapping methods and a fluorescence probe for lipid radicals, NBD-Pen, that we had developed. We then assessed the therapeutic potency of these drugs in mouse models of cisplatin-induced AKI and LPS/galactosamine-induced liver injury.

RESULTS

We identified various US Food and Drug Administration-approved drugs and hormones that have antiferroptotic properties, including rifampicin, promethazine, omeprazole, indole-3-carbinol, carvedilol, propranolol, estradiol, and thyroid hormones. The antiferroptotic drug effects were closely associated with the scavenging of lipid peroxyl radicals but not significantly related to interactions with other radicals. The elevated lipid peroxyl radical levels were associated with ferroptosis onset, and known ferroptosis suppressors, such as ferrostatin-1, also functioned as lipid peroxyl radical scavengers. The drugs exerted antiferroptotic activities in various cell types, including tubules, podocytes, and renal fibroblasts. Moreover, in mice, the drugs ameliorated AKI and liver injury, with suppression of tissue lipid peroxidation and decreased cell death.

CONCLUSIONS

Although elevated lipid peroxyl radical levels can trigger ferroptosis onset, some drugs that scavenge lipid peroxyl radicals can help control ferroptosis-related disorders, including AKI.

AMPK activation induced by promethazine increases NOXA expression and Beclin-1 phosphorylation and drives autophagy-associated apoptosis in chronic myeloid leukemia

Relapse and drug resistance is still major challenges in the treatment of leukemia. Promethazine, an antihistaminic phenothiazine derivative, has been used to prevent chemotherapy-induced emesis, although there is no report about its antitumor potential. Thus, we evaluated the promethazine cytotoxicity against several leukemia cells and the underlying mechanisms were investigated. Promethazine exhibited potent and selective cytotoxicity against all leukemia cell types in vitro at clinically relevant concentrations. Philadelphia positive chronic myeloid leukemia (CML) K562 cells were the most sensitive cell line. The cytotoxicity of promethazine in these cells was triggered by the activation of AMPK and inhibition of PI3K/AKT/mTOR pathway. The subsequent downstream effects were NOXA increase, MCL-1 decrease, and Beclin-1 activation, resulting in autophagy-associated apoptosis. These data highlight targeting autophagy may represent an interesting strategy in CML therapy, and also the antitumor potential of promethazine by acting in AMPK and PI3K/AKT/mTOR signaling pathways. Since this drug is currently used with relative low side effects, its repurposing may represent a new therapeutic opportunity for leukemia treatment.

Antioxidant activity of newly synthesized 2,7-diazaphenothiazines

A series of 19 derivatives of 2,7-diazaphenothiazine was synthesized and evaluated for their antioxidant activity bearing in mind the structural similarity with "classical" phenothiazines several of which are considered powerful antioxidants. Among the new derivatives that inhibited in vitro Fe(2+)/ascorbate-induced lipid peroxidation of rat liver microsomal membranes, several exhibited significant antioxidant activity with IC(50 )values in the range of 64-125 microM. Although N-substitution led to a variable degree of antioxidant activity, the latter appears to correlate with the lipophilicity (expressed as clogP values) of the substituted derivatives. Reduced lipophilicity may also explain the relatively lower protection offered by these derivatives against lipid peroxidation when compared to their "classical" phenothiazine counterparts. Thus, modification of the phenothiazine structure by a substitution of two benzene rings with pyridine rings to form this new type of azaphenothiazines does not enhance antioxidant activity, although it retains it.

Biochemical studies of transient intermediates in relation to chemical carcinogenesis

Many chemical carcinogens must be metabolized to chemically reactive transient species before they can exert their full toxic action on mammalian cells. In general, this metabolic activation is performed by NADPH-dependent enzymes in the endoplasmic reticulum; the NADPH-cytochrome P-450 electron-transport chain is very important in this respect. Biochemical studies on the chemical reactivities of such transient intermediates require the application of various fast-reaction and free-radical techniques: the use of such techniques is illustrated by reference to the metabolism of carbon tetrachloride. CCl4 is metabolized by liver endoplasmic reticulum in the presence of NADPH to a highly reactive product, probably CCl3; this activation of CCl4 results in covalent binding of CCl3 and lipid peroxidation. The steady-state concentration of CCl3 is too low to be measured directly by e.s.r. spectroscopy but radical species can be accumulated with spin-trap techniques. The CCl3 radical can be generated by pulse radiolysis and the ensuing reactions with biologically important neighbouring species can be followed in the microsecond range by kinetic spectroscopy. The results point to the high reactivity of CCl3 and its restriction to a microenvironment within the endoplasmic reticulum. Highly reactive electrophilic radicals (e.g. CCl3) can initiate lipid peroxidation in biomembranes and this is associated with changes in polyunsaturated fatty acids and in membrane fluidity. The results are discussed in relation to carcinogen activation, to free-radical-mediated reactions in biomembranes, and to the general thesis that the production of reactive aldehydes by lipid peroxidation may act as a 'coarse control' of cell division.

Effect of Solanum trilobatum on hepatic drug metabolising enzymes during diethylnitrosamine-induced hepatocarcinogenesis promoted by Phenobarbital in rat

The present study was aimed to investigate the chemopreventive effects of Solanum trilobatum (ST) extract against diethylnitrosamine (DEN)-induced hepatocarcinogenesis promoted by Phenobarbital (PB) in Wistar rats. Hepatocarcinogenesis was initiated by a single intraperitoneal injection of DEN (200 mg/kg b.w.) and promoted with PB (0.05%) in basal diet. The experimental study extended for periods of 13 and 26 weeks. Alcoholic extract of ST was orally administered for the entire experimental period after initiation along with commencement of promotion. The chemopreventive effect of ST was assessed from the incidence of nodules, drug metabolizing phase I components such as contents of cytochrome P450, cytochrome b(5), activities of NADPH cytochrome c reductase, NADH - cytochrome b(5) reductase and phase II components such as levels of glutathione, activities of UDP-glucuronyl transferase, glutathione S-transferase and gamma-glutamyl transpeptidase in the liver. Lipid peroxidation at basal and prooxidants-induced (NADPH + ADP + Fe and Ascorbate + Fe) states was assessed in the microsomes. Animals administered with ST extract evidenced significant inhibition of tumor nodular incidence in DEN + PB + ST animals compared to DEN + PB animals, with favorable alterations in the hepatic drug-metabolizing phase I and phase II components. Administration of ST inhibited basal and pro-oxidant-induced lipid peroxidation. The present result suggests the probable mediation of chemoprevention by ST against DEN-induced carcinogenesis by the modulation of drug metabolizing components in the liver of treated animals.

T cell survival/proliferation reconstitution by trifluoperazine in human immunodeficiency virus-1 infection

Recent findings support an indirect relationship between T cell depletion in HIV-1 infection and the rate of virus replication with implications for treatment strategies. We have initiated a new approach to recover immune function through the use of novel chemical agents. A cationic amphiphilic drug that binds to Ca(2+)-calmodulin at high concentrations, [10-[3-(4-methyl-1-piperazinyl)-propyl]-2- (trifluoromethyl)-(10)H-phenothiazine dihydrochloride] [denoted trifluroperazine dihydrochloride (Tfp); molecular weight 480.43] TFP was found at low concentrations (10(-6) to 10(-10) M) to help T cells from AIDS patients to restore proliferation in vitro. Here we show that the Tfp molecule can restore the cell survival of T lymphocytes from PBMCs derived from HIV-1-infected patients in vitro. Tfp enhances T cell proliferation and Th-cell responses by selectively inhibiting cell mortality and apoptosis. The restored antigen-specific response is associated with the synthesis of IL-2 and gamma-interferon. Even though this drug does not possess any detectable antiviral effect, it might be considered as a potential therapeutic agent in HIV-infected patients, to correct immune defects. Besides antiviral compounds, these data may facilitate immune reconstitution in patients with HIV infection and other immunosuppressive diseases.

Mechanism of inhibition of tumor necrosis factor production by chlorpromazine and its derivatives in mice

In previous work, we reported that chlorpromazine inhibits tumor necrosis factor (TNF) production in endotoxin lipopolysaccharide-treated mice, and protects against lipopolysaccharide toxicity. Chlorpromazine is used as an antipsychotic and has several effects on the central nervous system. It acts on different neurotransmitter receptors and has other biochemical activities some of which, like inhibition of phospholipase A2, might be responsible for the inhibitory effect on TNF production. To investigate the role of these actions in the inhibition of TNF production by chlorpromazine, we have synthesized some chlorpromazine derivatives that do not have central activities. Some of these analogs have lost their affinity for various receptors and their phospholipase A2 inhibitory activity, but still inhibit TNF production. No correlation was found between TNF inhibition and the ability to inhibit nitric oxide (NO) synthase, whereas a good correlation was evident between TNF inhibition and antioxidant activity.

Protective effect of safranine on the mitochondrial damage induced by Fe(II)citrate: comparative study with trifluoperazine

In this study, we show that safranine at the concentrations usually employed as a probe of mitochondrial membrane potential significantly protects against the oxidative damage of mitochondria induced by Fe(II)citrate. The effect of safranine was illustrated by experiments showing that this dye strongly inhibits both production of thiobarbituric acid-reactive substances and membrane potential decrease when energized mitochondria were exposed to Fe(II)citrate in the presence of Ca2+ ions. Similar results were obtained with the lipophylic compound trifluoperazine. It is proposed that, like trifluoperazine, safranine decreases the rate of lipid peroxidation due to its insertion in the membrane altering the physical state of the lipid phase.

Preclinical evaluation of the ribosome-inactivating proteins PAP-1, PAP-S and RTA in mice

In a preclinical mouse model the plant ribosome-inactivating proteins (RIPs) pokeweed antiviral proteins PAP-1, and PAP-S and ricin A-chain (RTA) induced a pathological elevation of serum concentrations of glutamate pyruvate transaminase (GPT) and blood urea nitrogen (BUN) and had a significant immunosuppressive effect on B- and T-lymphocytes. The present analysis and comparison of the biodistribution and systemic/organ toxicity associated with RIP injection suggest a possible in vivo mechanism of action of PAP-1 and PAP-S and identify several limitations in the clinical use of these two toxins and RTA. When administered intravenously, PAP-1 and PAP-S consistently accumulated in kidneys and induced histologically documented damage to kidney and liver, with a LD50 of 3.3 mg/kg and 1.6 mg/kg for PAP-1 and PAP-S, respectively. In mice injected with PAP-S after chlorpromazine (CPZ) administration, GPT levels returned to normal between 24 and 72 h after toxin injection, while the BUN levels remained elevated. Mortality of the animals was delayed but all mice eventually succumbed. All the three toxins inhibited the expansion of anti-sheep red blood cells (SRBC) antibody-forming cells and the production of anti-SRBC antibody levels, although PAP-S showed the most potent activity. Despite the immunosuppressive activity, all toxins were highly immunogenic.

Chlorpromazine protection against Ca(2+)-dependent and oxidative cell injury. Limitations due to depressed mitochondrial function

Chlorpromazine (CPZ), a phenothiazine, demonstrated both cytoprotective and toxic effects on cardiomyocytes. CPZ markedly reduced cytotoxicity caused by two toxic challenges, each with a distinct cytotoxic mechanism. Lethal cell injury was induced in cultured neonatal cardiomyocytes by either: (1) ionomycin, a Ca2+ ionophore that caused Ca(2+)-dependent cell injury; or (2) ethacrynic acid (EA), a glutathione (GSH) depletor that killed cells primarily via peroxidative damage. Pretreatment with 50 microM CPZ reduced the extent of ionomycin-induced cell death, as measured by lactate dehydrogenase (LDH) leakage, but enhanced the loss of intracellular ATP and collapsed the mitochondrial transmembrane potential (delta psi). In EA-treated cultures, 50 microM CPZ also lowered LDH leakage and diminished the peroxidative damage responsible for the cytotoxicity, but again enhanced the loss of intracellular ATP and collapsed the delta psi. CPZ protection was incomplete and limited to a narrow concentration range that was essentially identical for both toxic challenges. Maximum protection was observed with 50 microM CPZ, yet the amount of residual damage was similar to the degree of injury caused by a mitochondrial uncoupler, carbonylcyanide-m-chlorophenylhydrazone alone. In the absence of either challenge, 50 microM CPZ did not affect cellular energy status or kill the cells, but a higher concentration of CPZ (150 microM) did deenergize unchallenged cardiomyocytes. These data demonstrate that CPZ can reduce cytotoxicity caused by either Ca(2+)-dependent events or oxidative stress. However, even at an optimally protective level, CPZ in combination with either ionomycin or EA deenergized the cells, although neither toxic challenge nor 50 microM CPZ alone seriously affected delta psi. It would appear that intracellular perturbations induced by either challenge promote a depression of mitochondrial function by CPZ, which limits the protective action of the drug. Since both of the challenges used contain toxicologic features exhibited by a wide variety of toxic insults, results of this study have both mechanistic and clinical implications.

Protective effect of trifluoperazine on the mitochondrial damage induced by Ca2+ plus prooxidants

Isolated rat liver mitochondria undergo extensive swelling and disruption of membrane potential when they accumulate Ca2+ in the presence of a prooxidant such as diamide or t-butylhydroperoxide. The phenothiazinic drug trifluoperazine, at concentrations (15-35 microM) which do not inhibit respiration or the influx of Ca2+ into mitochondria, significantly protected mitochondria against the deleterious effects of Ca2+ plus a prooxidant. In contrast, at concentrations higher than 100 microM the drug potentiated these deleterious effects of Ca2+ and prooxidants and had a damaging effect per se on the inner mitochondrial membrane. It is proposed that the protection conferred by the drug is mediated by changes in membrane protein structure that decrease the production of protein thiol cross-linkings which occur when mitochondria accumulate calcium under oxidant stress conditions.

A phenothiazine derivative reduces rat brain damage after global or focal ischemia

BACKGROUND AND PURPOSE

We previously reported that 2-(10H-phenothiazin-2-yloxy)-N,N-dimethylethanamine hydrochloride is a potent inhibitor of iron-dependent lipid peroxidation in vitro and can protect primary cultures of rat hippocampal neurons from hydrogen peroxide-induced toxicity. Because oxidants may play an important role in mediating postischemic tissue injury, we evaluated this agent in two rat models of transient cerebral ischemia.

METHODS

In a model of global forebrain ischemia, 23 male Wistar rats were subjected to 10 minutes of four-vessel occlusion followed by 72 hours of reperfusion. The rats received three intraperitoneal injections of either vehicle (2% aqueous acacia) or test agent (40 mg/kg). In a model of focal stroke, 19 spontaneously hypertensive rats were subjected to 2 hours of tandem middle cerebral and ipsilateral common carotid artery occlusion followed by 24 hours of reperfusion. The rats received three intraperitoneal injections of either vehicle (2% aqueous acacia) or test agent (40 mg/kg).

RESULTS

In the global model, the phenothiazine significantly protected the CA1 layer of the hippocampus, with a reduction in mean damage score from 2.1 +/- 0.3 for control rats to 1.0 +/- 0.4 for treated rats (p less than 0.05). In the transient focal stroke model, the compound reduced cortical infarct volume from 130.1 +/- 10.3 mm3 for control rats to 95.2 +/- 24.5 mm3 for treated rats (p less than 0.02).

CONCLUSIONS

Although the primary mechanism responsible for the protective effect is unclear at the present time, our study is consistent with the hypothesis that oxidant-mediated lipid peroxidation may be involved in the pathophysiology of postischemic brain injury.

Phenothiazines inhibit copper and endothelial cell-induced peroxidation of low density lipoprotein. A comparative study with probucol, butylated hydroxytoluene and vitamin E

The effect of two phenothiazines, chlorpromazine (CPZ) and trifluoperazine (TFP) on the copper and endothelial cell-induced peroxidation of low density lipoprotein (LDL) has been studied and compared to that of drugs previously shown to protect LDL against peroxidation: probucol (PBC) and butylated hydroxytoluene (BHT). Incubation with CPZ or TFP inhibited in a dose-dependent manner LDL peroxidation induced either by copper ions or by cultured endothelial cells. Both the electrophoretic mobility and the thiobarbituric reactive substance content of LDL returned to almost normal values in the presence of 50 microM CPZ or TFP. The two studied phenothiazines also strongly inhibited the hydrolysis of LDL phosphatidylcholine which accompanies copper or endothelial cell-induced peroxidation of the particle. CPZ and TFP were as effective as PBC and BHT in inhibiting the LDL peroxidation. Whereas copper or endothelial cell-oxidized LDL were recognized and rapidly catabolized by mouse peritoneal macrophages, CPZ- or TFP-, as well as PBC- or BHT-treated LDL were not. Moreover, it was found that, in contrast to vitamin E, neither CPZ nor PBC reacted with model peroxy radicals formed by gamma irradiation of aerated ethanol. The possible mechanisms underlying this protective effect of phenothiazines against LDL oxidative modification are discussed.

Activation of chlorpromazine by the myeloperoxidase system of the human neutrophil

The univalent oxidation of chlorpromazine (CPZ) by the myeloperoxidase (MPO-H2O2) system led to the formation of a cation free radical (CPZ+) which was observed optically at 527 nm. CPZ protected MPO against loss of catalytic activity when co-oxidized in a MPO-Cl(-)-H2O2 system. Due to the stability of CPZ+ either further oxidation, or reduction back to the mother compound, become important mechanisms for disappearance of the free radical. Thus, the rate of formation and decay of CPZ+ were higher in the presence of Cl- than in its absence, since the radical can also be oxidized further by hypochlorous acid (HOCl), which is formed in the MPO-Cl(-)-H2O2 system. Decay of CPZ+ can also be due to electron acceptance from ascorbic acid or oxygenated haemoglobin (HbO2), resulting in regeneration of CPZ. When CPZ+ was generated in the MPO-H2O2 system, addition of HbO2 resulted in a sudden decrease in CPZ+ absorbance at 527 nm and a concomitant formation of metHb. When HbO2 was not added, the decay of CPZ+ was much slower. CPZ (in the absence of the MPO system) also stimulated the oxidation of HbO2 in the presence of 20 microM H2O2, but this reaction was considerably slower than when CPZ+ (generated by the MPO system) was allowed to react directly with HbO2. These results suggest that HbO2 was oxidized by CPZ+. To study the effect of CPZ intermediates, thyroglobulin (TG) was used as a model polypeptide. Chlorinated oxidants formed in the MPO system (in the absence of CPZ) induced TG peptide bond splitting. In contrast, CPZ metabolites generated by the MPO system (in the absence of Cl-) induced polymerization of TG, as revealed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE).

Biochemical mechanism of metallothionein--carbon tetrachloride interaction in vitro

To elucidate the mechanism underlying the protective effect of metallothionein (MT) against carbon tetrachloride (CCl4) toxicity, in vitro experiments were carried out to study the interaction of metallothionein and CCl4. Results from this study showed that incubation of Cd,Zn-MT with CCl4 in the presence of hepatic microsomes and NADPH resulted in a time-dependent depletion of MT thiols with a concurrent reduction in the metal-binding sites of the protein. Moreover, this reaction also released Zn and Cd from MT. Results from experiments conducted to determine whether or not the CCl4-induced decrease in MT-thiol content was due to the scavenging of CCl4 metabolite(s) showed that the trichloromethyl radical, chloroform and phosgene as well as the products of CCl4-induced microsomal lipid peroxidation were not directly involved. Although covalent binding of 14CCl4 to MT was detected following incubation in the presence of a microsomal bioactivation system, it did not account for the CCl4-induced loss of MT thiol groups for the following reasons: (i) prior oxidation of sulfhydryl groups of MT by hydrogen peroxide did not alter the binding; and (ii) anaerobiosis did not alter the extent of covalent binding but obliterated the inhibitory effect of CCl4 on MT thiol content. Measurement of the thiol content of CCl4-treated MT after treatment with 1,4-dithiothreitol revealed that all the thiol groups that were lost subsequent to CCl4 treatment could be regenerated. These data suggest that CCl4-linked oxidation of MT, rather than the covalent binding of 14CCl4 metabolite(s), may be responsible for the CCl4-induced loss of metal binding sites of MT with the concurrent release of Zn and Cd. However, the precise role of the metal released during the oxidation of MT in CCl4 toxicity remains to be defined.

Studies on the hyperplasia ('regeneration') of the rat liver following partial hepatectomy. Changes in lipid peroxidation and general biochemical aspects

Using the experimental model of partial hepatectomy in the rat, we have examined the relationship between cell division and lipid peroxidation activity. In rats entrained to a regime of 12 h light/12 h dark and with a fixed 8 h feeding period in the dark phase, partial hepatectomy is followed by a rapid regeneration of liver mass with cycles of synchronized cell division at 24 h intervals. The latter phenomenon is indicated in this study by pulses of thymidine kinase activity having maxima at 24 h, 48 h and 72 h after partial hepatectomy. Microsomes prepared from regenerating livers show changes in lipid peroxidation activity (induced by NADPH/ADP/iron or by ascorbate/iron), which is significantly decreased relative to that in microsomes from sham-operated controls, again at 24 h, 48 h and 72 h after the operation. This phenomenon has been investigated with regard to possible underlying changes in the content of microsomal fatty acids, the microsomal enzymes NADPH:cytochrome c reductase and cytochrome P-450, and the physiological microsomal antioxidant alpha-tocopherol. The cycles of decreased lipid peroxidation activity are apparently due, at least in part, to changes in microsomal alpha-tocopherol content that are closely associated in time with thymidine kinase activity.

Promethazine inhibits the formation of aldehydic products of lipid peroxidation but not covalent binding resulting from the exposure of rat liver fractions to CCl4

Promethazine is known to have protective activity in relation to CCl4-induced liver necrosis. This hepatoprotective property has been investigated with regard to the free radical scavenging and antioxidant properties of promethazine using isolated hepatocytes and microsomal suspensions. CCl4 is activated in both systems to free radical metabolites that bind covalently to lipid and protein, and initiate lipid peroxidation. A large number of carbonyl products is produced during CCl4-induced lipid peroxidation; promethazine strongly inhibits the production of all classes of carbonyl compounds in both microsomal suspensions and isolated hepatocytes. In contrast, promethazine is a very weak inhibitor of the covalent binding of metabolites of CCl4. We conclude that promethazine acts by scavenging the trichloromethylperoxyl radical and lipid peroxyl radicals, and is a weak scavenger of the trichloromethyl radical. These data, when considered together with the hepatoprotective effects of promethazine, suggest that lipid peroxidation is of relatively more importance than covalent binding in the pathogenesis of CCl4-induced liver necrosis.

Nonesterified fatty acids inhibit iron-dependent lipid peroxidation

The effect of various fatty acids on lipid peroxidation of liver microsomes induced by different methods in vitro was studied using oxygen uptake and malonaldehyde (MDA) production. It was observed that fatty acids with a single double bond are effective inhibitors of peroxidation. Stereo and positional isomers of oleic acid were equally effective as oleic acid. There was an absolute requirement for a free carboxyl group, since methyl esters of fatty acids and long-chain saturated and unsaturated hydrocarbons could not inhibit peroxidation. Saturated fatty acids with a chain length of 12-16 carbon atoms showed inhibition, whereas more than 18 carbon atoms reduced the inhibitory capacity. Fatty acids of lower chain length such as capric and caprylic acids did not show inhibition. Fatty acid inhibition was partially reversed by increasing the concentration of iron in the system. Peroxidation induced by methods which were independent of iron was not inhibited by fatty acids. It was observed that intestinal microsomes which were resistant to peroxidation due to the presence of nonesterified fatty acids in their membrane lipids were able to peroxidise by methods which do not require iron. These results suggest that certain fatty acids inhibit peroxidation by chelating available free iron. In addition, they may also be involved in competing with the esterified fatty acids in the membrane lipids which are the substrates for peroxidation.

An investigation of the novel anti-inflammatory agents ONO-3144 and MK-447. Studies on their potential antioxidant activity

Oxygen-derived free radicals have been implicated as contributors to inflammatory disorders and it has been suggested that certain anti-inflammatory drugs act by scavenging free radicals. In this paper we have studied the free radical scavenging activity of two such experimental anti-inflammatory drugs MK-447 and ONO-3144. Using the technique of pulse radiolysis we have been able to obtain rate constants for the reactions of these compounds with specific free radicals including OH and O2-. We have also investigated the antioxidant capacity of these compounds using rat liver microsomal lipid peroxidation systems. It is suggested that this approach yielding quantitative data concerning defined free radical species will lead to a better understanding of the role of radical scavenging in anti-inflammatory activity.

Lipid peroxidation in purified plasma membrane fractions of rat liver in relation to the hepatoxicity of carbon tetrachloride

Preparations of rat liver sinusoidal plasma membrane have been tested for their ability to metabolize the hepatotoxin carbon tetrachloride (CCl4) to reactive free radicals in vitro and compared in this respect with standard preparations of rat liver microsomes. The sinusoidal plasma membranes were relatively free of endoplasmic reticulum-associated activities such as the enzymes of the cytochrome P450 system and glucose-6-phosphatase. CCl4 metabolism was measured as (i) covalent binding of [14C]-CCl4 to membrane protein, (ii) electron spin resonance spin-trapping of CCl3. radicals and (iii) CCl4-induced lipid peroxidation. By all of these tests, purified sinusoidal plasma membranes were found unable to metabolize CCl4. The fatty acid composition of the plasma membranes was almost identical to that of the microsomal preparation and both membrane fractions exhibited similar rates of the lipid peroxidation that was stimulated non-enzymically by gamma-radiation or incubation with ascorbate and iron. The absence of CCl4-induced lipid peroxidation in the plasma membranes seems to be due, therefore, to an absence of CCl4 activation rather than an inherent resistance to lipid peroxidation. We conclude that damage to the hepatocyte plasma membrane during CCl4 intoxication is not due to a significant local activation of CCl4 to CCl3. within that membrane.

Studies on lipid peroxidation in normal and tumour tissues. The Yoshida rat liver tumour

Reduced rates of lipid peroxidation have been observed in Yoshida hepatoma cells and microsomes when compared with appropriate control tissue (normal rat liver) under the same pro-oxidant conditions. The pro-oxidant conditions used were incubation with NADPH+ADP+iron or ascorbate+iron or exposure to gamma-irradiation. As previously shown with the Novikoff hepatoma, the relative concentrations of alpha-tocopherol and polyunsaturated fatty acids are important in conferring resistance to lipid peroxidation in the Yoshida hepatoma. Furthermore, NADPH-cytochrome c reductase and the NADPH-cytochrome P-450 electron transport chain, which are involved in the initiation and propagation of certain types of lipid peroxidation, are found at very much reduced levels in the Yoshida hepatoma. The relative importance of these aberrations are discussed.

Antioxidant action and photosensitizing effects of three different chlorpromazines

Chlorpromazine inhibits by about 60% the lipid peroxidation stimulated by Fe2+/ascorbate in liposomes and the lipid peroxidation stimulated by cumene hydroperoxide in microsomes. Under the same conditions, two new synthetic derivatives of chlorpromazine, i.e., a N-benzoyloxymethylchlorpromazine and a N-pivaloyloxymethylchlorpromazine, induce no more than a 20% inhibition. On the other hand, when the different chlorpromazines are entrapped in liposomes and subsequently irradiated with near-UV light, they act as photosensitizing agents giving rise to lipid peroxidation. The latter is quite extensive in the presence of chlorpromazine or N-pivaloyloxymethylchlorpromazine, whereas it is drastically lower in the presence of N-benzoyloxymethylchlopromazine. The N-benzoyloxymethylchlorpromazine molecule, despite its low photodynamic effect, retains its neuroleptic properties. The possible mechanisms of the antioxidant and prooxidant actions of these compounds are discussed.

Decrease of serum malondialdehyde in patients treated with chlorpromazine

Malondialdehyde determination in serum from schizophrenic patients before and after treatment with chlorpromazine showed that, after treatment, patients had significantly lower values than before. The antioxidant properties of chlorpromazine can be related to its effect on the level of serum lipid peroxides and possibly to its neuroleptic action.

Effects of carbon tetrachloride on the liver of chickens. Early biochemical and ultrastructural alterations in the absence of detectable lipid peroxidation

Administration of CCl4 i.p. to Leghorn chickens did not promote lipid peroxidation of liver microsomal lipids, as evidenced by either increased diene conjugation or by decreased arachidonic acid content. The hepatotoxin did not produce liver necrosis 24 h after dosing, but decreased the cytochrome P-450 content, and aminopyrine N-demethylase and glucose 6 phosphatase activities at 1, 3, 6 and 24 h. CCl4 administration produced dilation of the rough endoplasmic reticulum and detachment of ribosomes from their membranes. These observations suggest that lipid peroxidation is not the key event in the production of these biochemical and ultrastructural alterations, elicited by CCl4.

Effects of alpha-tocopherol on carbon tetrachloride metabolism in rat liver microsomes

alpha-tocopherol is the major lipid-soluble radical-scavenging antioxidant in rat liver. It has long been used as a putative protective agent in CCl4 induced liver injury but with variable results. We have used alpha-tocopherol loaded rat liver microsomes to study the effect of this vitamin on CCl4 metabolism in vitro. As expected, alpha-tocopherol inhibits CCl4-dependent microsomal lipid peroxidation and, at a very high concentration, will inhibit the covalent binding of CCl3 to microsomal protein by up to 50%. No inhibitory effect was observed towards CCl3 production as measured by the electron spin resonance technique of spin-trapping but this apparent discrepancy may represent a limitation of the technique. The high levels required to inhibit covalent binding probably preclude the likelihood of alpha-tocopherol significantly affecting that phenomenon at endogenous concentrations but may be relevant to other experiments employing high doses of alpha-tocopherol as an experimental hepatoprotective agent.

Lipid peroxidation in regenerating rat liver

Rats entrained to a strictly regulated lighting and feeding schedule have been subjected to partial hepatectomy or a sham operation. In the partially hepatectomised animals the period of liver regeneration is characterised by regular bursts of thymidine kinase activity. Liver microsomes from rats, at times corresponding to maximum thymidine kinase activity, have much reduced rates of lipid peroxidation compared to control preparations: this is due in part to increased levels of lipid-soluble antioxidant at times of maximal DNA synthesis. This temporal relationship between thymidine kinase and lipid peroxidation is consistent with the view that lipid peroxidation is decreased prior to cell division.

Studies on lipid peroxidation in normal and tumour tissues. The Novikoff rat liver tumour

A study has been made of the factors that contribute to the decreased rates of lipid peroxidation under different pro-oxidant conditions in intact Novikoff tumour cells, and in microsomal suspensions prepared from Novikoff tumour cells, compared with isolated normal rat hepatocytes and microsomal suspensions prepared from normal rat liver. The pro-oxidant conditions were the addition of either NADPH, NADPH + ADP + iron, NADPH + CCl4 or ascorbate+iron to the experimental systems used, or exposure to gamma-radiation. Contributory factors to the lower rates of lipid peroxidation observed include: a significant decrease in the polyunsaturated fatty acid content of Novikoff cells or Novikoff microsomes; the decreases are especially marked for the C20:4 and C22:6 fatty acids; a very marked reduction in NADPH-cytochrome c reductase; and no detectable content of cytochrome P-450. Another, and in our opinion critical, contribution to the diminished rate of lipid peroxidation in the tumour material is the substantial increase in alpha-tocopherol relative both to total lipid and to methylene-interrupted double bonds in fatty acids. Moreover, the alpha-tocopherol is the major contributor to lipid-soluble chain-breaking antioxidant in lipid extracts of normal liver and of Novikoff tumour material.

Inhibition of ethanol induced hepatic vitamin A depletion by administration of N,N'-diphenyl-p-phenylene-diamine (DPPD)

The administration of ethanol as 36% of the total calories in a nutritionally adequate liquid diet for three weeks to male Wistar rats caused a 36% decrease in hepatic vitamin A levels (P less than 0.001) when compared with glucose pair-fed control rats, without affecting serum levels of the vitamin. Simultaneous administration of a synthetic antioxidant, DPPD (N,N'-diphenyl-p-phenylene-diamine) to ethanol-fed rats caused a 73% decrease in the extent of the ethanol induced hepatic vitamin A depletion (P less than 0.001). DPPD administration did not affect weight gain, dietary (and hence ethanol) intake or serum ethanol and vitamin A levels in ethanol-fed rats, nor did it affect hepatic or serum vitamin A levels in pair-fed controls. Increased hepatic catabolism of retinoic acid due to induction of cytochrome P450 by ethanol has been suggested as a mechanism of depletion. In the current study, DPPD administration to ethanol-fed rats did not reverse the ethanol induced increase in microsomal cytochrome P450 concentrations or aniline hydroxylase activity. These findings indicate that the ethanol induced hepatic vitamin A depletion can be largely dissociated from the induction of cytochrome P450. In view of the potent free radical scavenging activity of vitamin A, and the protective effect of DPPD against ethanol induced hepatic loss of the vitamin, this study suggests that increased free radical generation and direct peroxidation of vitamin A may be an important mechanism by which ethanol induced hepatic vitamin A depletion occurs in the rat.

Inhibitory effects of ebselen on lipid peroxidation in rat liver microsomes

The effects of ebselen(2-phenyl-1,2-benzoisoselenazol-3(2H)-one), a synthetic seleno-organic compound with glutathione peroxidase-like activity were investigated on lipid peroxidation in rat liver microsomes. Ebselen inhibited malondialdehyde production coupled to the lipid peroxidation stimulated by either ADP-iron-ascorbate or CCl4. The inhibitory activity of ebselen on each system was strongly increased by a 5-min preincubation with liver microsomes; the IC50 values against ADP-Fe-ascorbate-stimulated and CCl4-stimulated lipid peroxidation were 1.6 microM and 70 microM respectively. Ebselen also inhibited the endogenous lipid peroxidation with a NADPH-generating system, but it slightly stimulated the endogenous activity of ADP-Fe-ascorbate-stimulated lipid peroxidation (without a NADPH-generating system). Furthermore, ebselen inhibited oxygen uptake coupled to the lipid peroxidation by ADP-Fe-ascorbate and NADPH-ADP-iron; the IC50 values were 2.5 microM and 20.3 microM respectively. Ebselen also prolonged the lag-time of onset of ADP-Fe-ascorbate-stimulated lipid peroxidation significantly, but not that observed with NADPH-ADP-Fe-stimulated lipid peroxidation. These findings suggest that ebselen penetrates into the membrane lipid and acts as an effective antioxidant, and that there may be some differences between the modes of inhibitory action on the several types of lipid peroxidation.

Enzyme leakage due to change of membrane permeability of primary cultured rat hepatocytes treated with various hepatotoxins and its prevention by glycyrrhizin

Various hepatotoxins were added to the medium of primary cultures of adult rat hepatocytes and the release of the cytosolic enzymes lactic dehydrogenase, glutamic-oxaloacetic and glutamic-pyruvic aminotransferases were measured 24 h later. CCl4 at low concentrations caused dose-dependent release of soluble enzymes into medium without appreciable cytolysis of the hepatocytes. Mitochondrial enzymes were not released under these conditions. At 5 mM CCl4, both soluble and mitochondrial glutamic-oxaloacetic aminotransferase were found in the culture medium. Glycyrrhizin, a triterpenoid glycoside of licorice roots, prevented the enzyme release caused by CCl4.

Low rate of NADPH/ADP-iron dependent lipid peroxidation in hepatic microsomes of DBA/2 mice

Hepatic microsomal lipid peroxidation has been studied in 4 inbred strains of mice: C57BL/6, BALB/c, AKR and DBA/2. The rates of lipid peroxidation stimulated in vitro by carbon tetrachloride, ascorbate-iron and cumene hydroperoxide were similar in all 4 strains. Lipid peroxidation induced by NADPH/ADP-iron, however, proceeded at a substantially lower rate in the hepatic microsomes of DBA/2 mice. It is suggested that this low rate of enzymic iron-induced lipid peroxidation is a factor that may be involved in the resistance of this strain of mice to experimental hepatic porphyria induced by polyhalogenated aromatic hydrocarbons.

The effect of the administration of cobaltic protoporphyrin IX on drug metabolism, carbon tetrachloride activation and lipid peroxidation in rat liver microsomes

The effects of cobaltic protoporphyrin IX (CPP) administration on hepatic microsomal drug metabolism, carbon tetrachloride activation and lipid peroxidation have been investigated using male Wistar rats. CPP (125 mumol/kg, 72 h before sacrifice) profoundly decreased the levels of hepatic microsomal heme, particularly cytochrome P-450. Consequently, the associated mixed-function oxidase systems were equally strongly depressed. An unexpected finding was that CPP administration also greatly decreased the activity of NADPH/cytochrome c reductase, a result not generally found with the administration of the more widely used cytochrome P-450 depleting agents, cobaltous chloride. Activation of carbon tetrachloride, measured as covalent binding of [14C] CCl4, spin-trapping of CCl3 and CCl4-stimulated lipid peroxidation, was much lower in liver microsomes from CPP-treated rats. Other microsomal lipid peroxidation systems, utilising cumene hydroperoxide or NADPH/ADP-Fe2+, were also depressed in parallel with the decrease in microsomal enzyme activities.

Inhibition of lipid peroxidation in muscle homogenates by phospholipase A2 inhibitors

Chloropromazine, mepacrine, tetracaine, dibucaine, chloroquine, and procaine have been shown to inhibit the iron- and ascorbate-induced lipid peroxidation of skeletal-muscle homogenates in vitro. These compounds are known to be inhibitors of phospholipase activity, but they were also found to be effective in blocking free-radical-mediated damage to lipids in denatured homogenates, to linoleate suspensions, and to glutamic acid solutions where phospholipase activity was not a relevant factor. The inhibitory action did not appear to be related to any iron-binding activity of the compounds.

Effects of chlorpromazine on the activities of antioxidant enzymes and lipid peroxidation in the various regions of aging rat brain

In this work, the effect of chronic intraperitoneal administration of chlorpromazine (5 and 10 mg/kg) on the antioxidant enzymes superoxide dismutase (SOD), catalase (CA), glutathione reductase (GR), and glutathione peroxidase (GP); lipid peroxidation; and lipofuscin accumulation in the brains of rats ages 6, 9, and 12 months was studied. Chlorpromazine increased the activities of SOD, GR, and GP in particulate fraction from cerebrum, cerebellum, and brain stem in a dose-dependent manner. While GR and SOD associated with soluble fraction increased, GP associated with soluble fraction was not affected. CA did not change after chlorpromazine administration in any regions of the brain of rats from all age groups. Chlorpromazine, thus, had a somewhat different action on antioxidant enzymes in different subcellular fractions. Chlorpromazine inhibited lipid peroxidation, both in vivo and in vitro, and it also inhibited accumulation of lipid peroxidation fluorescent products (lipofuscin), which was studied histochemically and biochemically as well. The data indicate that chlorpromazine inhibition of lipid peroxidation and of accumulation of lipofuscin can result from elevation of the activity of brain antioxidant enzymes.

Separation and characterization of the aldehydic products of lipid peroxidation stimulated by ADP-Fe2+ in rat liver microsomes

1. Methods using t.l.c. and high-pressure liquid chromatography (h.p.l.c.) have been used to separate the complex variety of substances possessing a carbonyl function that are produced during lipid peroxidation. 2. The major type of lipid peroxidation studied was the ADP-Fe2+-stimulated peroxidation of rat liver microsomal phospholipids. Preliminary separation of the polar and non-polar products was achieved by t.l.c.: further separation and identification of individual components was performed by h.p.l.c. Estimations were performed on microsomal pellets and the supernatant mixture after incubation of microsomes for 30 min at 37 degrees C. 3. The polar fraction was larger than the non-polar fraction when expressed as nmol of carbonyl groups/g of liver. In the non-polar supernatant fraction the major contributors were n-alkanals (31% of the total), alpha-dicarbonyl compounds (22%) and 4-hydroxyalkenals (37%) with the extraction method used. 4. Major individual contributors to the non-polar fraction were found to be propanal, 4-hydroxynonenal, hexanal and oct-2-enal. Other components identified include butanal, pent-2-enal, hex-2-enal, hept-2-enal, 4-hydroxyoctenal and 4-hydroxyundecenal. The polar carbonyl fraction was less complex than the non-polar fraction, although the identities of the individual components have not yet been established. 5. Since these carbonyl compounds do not react significantly in the thiobarbituric acid reaction, which largely demonstrates the presence of malonaldehyde, it is concluded that considerable amounts of biologically reactive carbonyl derivatives are released in lipid peroxidation and yet may not be picked up by the thiobarbituric acid reaction.

The role of lipid peroxidation in CCl4-induced damage to liver microsomal enzymes: comparative studies in vitro using microsomes and isolated liver cells

The question as to whether CCl4 decreases the activities of glucose-6-phosphatase and cytochrome P-450 in liver endoplasmic reticulum mainly through its action in stimulating lipid peroxidation has been investigated using Promethazine to block lipid peroxidation. The investigation, moreover, has compared the effects of CCl4, with and without Promethazine, on isolated rat hepatocytes with corresponding effects on rat liver microsomal suspensions. Our data give no support for the view that products of lipid peroxidation are the main cause of the decrease in cytochrome P-450 observed in CCl4-intoxication. However, our present results are consistent with lipid peroxidation being a major contributory factor to the decrease in glucose-6-phosphatase activity observed in CCl4-induced liver injury.

Free radical initiation in proteins and amino acids by ionizing and ultraviolet radiations and lipid oxidation--part III: free radical transfer from oxidizing lipids

Parallels and similarities in chemical and functional damage to proteins by ionizing and uv radiations and oxidizing lipids have been recognized for some time. However, only recently have oxidizing lipids been shown directly by electron spin resonance to be radiomimetic also in their capacity for protein free radical production. Free radicals play a key role in the transformation of energy to molecular and cellular damage. It is thus of critical importance to elucidate the general mechanisms of free radical formation and reactions in proteins in order to understand protein involvement in various pathological conditions and in food deterioration. Accordingly, this review is a detailed comparison of gamma-radiation, UV radiation, and lipid oxidation for what is presently known concerning (1) the specific modes of energy deposition and free radical formation, (2) the free radicals formed in proteins and amino acids, and (3) the typical damage correlating with these radicals.

Lipid peroxidation of the microsomal fraction and extracted microsomal lipids from DAB-induced hepatomas

NADPH- and ascorbic acid-induced microsomal lipid peroxidation was almost absent in subcutaneously implanted DAB-induced hepatomas D23, D30 and D192A, and present at greatly reduced levels in DAB-induced primary hepatomas when compared with normal liver controls. Fatty acid analysis of the microsomal lipid from passaged tumours demonstrated adequate levels of substrate in the phospholipid fractions to support lipid peroxidation. Lipid extracted from hepatoma microsomal fractions was shown to undergo ascorbic acid-induced lipid peroxidation, but to a lesser extent that the corresponding liver extract. This may be partially explained by a decrease in the phospholipid content of hepatoma microsomal membranes. However, phospholipid extracted from microsomal fractions of hepatoma and liver supported lipid peroxidation to a similar extent. The possible role of the non-lipid component of the membrane in the process of lipid peroxidation is discussed.

Effects of tricresylphosphate on esterase activity of rat serum and tissues

The effect of tricresylphosphate (TCP) was studied in vitro and in vivo on the rat liver and brain enzymes acetylcholinesterase (ACC), butyrylcholinesterase (CHE), arylesterase (ARE), aliesterase (ALI), and the microsomal nicotinamide-adenine dinucleotide phosphate oxidase (NADPH2-oxidase) system. The results show that, in the male rat, TCP given intraperitoneally induces an increase in liver microsomal ARE AND NADPH2-oxidase and a decrease in ALI and cholinesterase; no activation of ARE and NADPH2-oxidase is observed in female rats.