A systematic review on drugs for synaptic plasticity in the treatment of dementia

The aim of the present systematic review (SR) was to provide an overview of all published and unpublished clinical trials investigating the safety and efficacy of disease-modifying drugs targeting synaptic plasticity in dementia. Searches on CT.gov and EuCT identified 27 trials (4 phase-1, 1 phase-1/2, 18 phase-2, 1 phase-2/3, 1 phase-3, 1 phase-4, and 1 not reported). Twenty of them completed, and seven are currently active or enrolling. The structured bibliographic searches yielded 3585 records. A total of 12 studies were selected on Levetiracetam, Masitinib, Saracatinib, BI 40930, Bryostatin 1, PF-04447943 and Edonerpic drugs. We used RoB tool for quality analysis of randomized studies. Efficacy was assessed as a primary outcome in all studies except one and the main scale used was ADAS-Cog (7 studies), MMSE and CDR (4 studies). Safety and tolerability were reported in eleven studies. The incidence of SAEs was similar between treatment and placebo. At the moment, only one molecule reached phase-3. This could suggest that research on these drugs is still preliminary. Of all, three studies reported promising results on Levetiracetam, Bryostatin 1 and Masitinib.

Redox-Dependent Modulation of Lipid Synthesis Induced by Oleic Acid in the Human Intestinal Epithelial Cell Line Caco-2

The absorption, remodeling, and delivery of dietary lipids by intestinal cells are part of a complex multi-step process, the dynamics of which is influenced by the lipid composition of the diet and the physiological state of enterocytes. Emerging data indicate that, among the parameters known to modulate the cell functionality, the internal oxidative balance plays a pivotal role. In this study, we analyzed the effects of varying redox equilibria on the way in which the intestinal Caco-2 cell line utilize an otogenous lipid source such as oleic acid. Firstly, we manipulated the intracellular levels of soluble thiols (glutathione), and the amount of cell-associated products of lipid peroxidation, commonly regarded as two critical parameters characterizing the redox profile of the cells. Two different perturbants having opposite effects on the cell's redox profile were used: the pro-oxidizing agent CuSO4 (2.5 and 10 µM) and the antioxidant and thiol supplier N-acetylcysteine (NAC, 2.5 and 5 mM). The influence of these mild but critical manipulations on the incorporation of oleate (50 and 500 µM) into cholesterol, triacylglycerol, end phospholipid was then evaluated. We found that the emerging pro-oxidant condition induced by CuSO4 pre-exposure was associated with a significant up-regulation of phospholipid synthesis, while minor modifications were detected in that of triacylgiycerols. Conversely, when a more reducing state was induced by NAC pre-treatment, there was a significant down-regulation of triacylglycerol synthesis, with minor modifications in that of phospholipids. In addition, the incorporation of oleic acid in the cholesteryl ester fraction appeared to be unmodified under all the redox conditions reported. On the whole, these results indicate that the pre-existing internal redox potential of the enterocytes is a critical factor that is able to differentially modulate lipid synthesis at the Intestinal level. Thus, the adoption of a strategy designed to control/buffer the antioxidant capacity of the gastrointestinal tract could have important consequences for the modulation of lipid balance in the body.

The fatty acid composition of chylomicron remnants influences their propensity to oxidate

BACKGROUND AND AIM

Although the replacement of saturated with unsaturated dietary fat has been advocated as a means of reducing the risk of cardiovascular disease, diets high in polyunsaturated fatty acids (PUFAs) may increase lipid peroxidation, thus contributing to the pathogenesis of atherosclerosis. As the susceptibility of individual fatty acids to oxidation directly depends on their degree of unsaturation, and the oxidative modification of lipoproteins may be an important determinant of atherogenesis, the aim of this study was to evaluate the susceptibility to auto-oxidation and copper-mediated oxidation of chylomicron remnants (CMRs) enriched in n-3 or n-6 PUFA.

METHODS AND RESULTS

The remnants were prepared in vitro from chylomicrons obtained from rats given an oral dose of fish or corn oil, using rat plasma containing lipoprotein lipase. Their propensity to oxidate and the extent of the oxidation were estimated by measuring the formation of conjugated dienes and the detrimental products of lipid peroxidation. The results showed that: 1) the corn oil CMRs contained a relatively high proportion of n-6 PUFA (mainly linoleic acid), whereas the fish oil CMRs contained more n-3 PUFA, mainly eicosapentanoic and docosahexaenoic acids; 2) n-3-rich CMRs have a significantly lower propensity to oxidate than n-6-rich CMRs despite their 50% lower alpha-tocopherol content and 40% higher unsaturation index.

CONCLUSION

Our data indicate that the precise allocation of n-3 PUFA within the lipid core of CMRs may play a pivotal role in lowering the susceptibility to oxidation of fish CMRs by overcoming the effects of unfavourable alpha-tocopherol concentration. Eating n-3 rather than n-6 PUFAs seems to make CMRs more resistant against free radical attack, which may contribute to attenuating their potential atherogenic properties.

Epithelial cells challenged with a Rac-activating E. coli cytotoxin acquire features of professional phagocytes

Activation of Rho, Rac and Cdc42 GTPases by an Escherichia coli cytotoxin (CNF1) has been reported to induce a phagocytic-like activity by epithelial cells in terms of a ruffle-driven capture and ingestion of large material. More recently, it has been reported that treatment with CNF1 induces superoxide anion release by these cells following a phagocytic stimulus. We herein show that in epithelial cells both transfection with the dominant form of Rac (RacV12) and treatment with the Rac-activating epidermal growth factor (EGF) may increase the secretion of superoxide anions on challenge with latex beads. Moreover, exposure to CNF1 induces a significant augmentation of acidic vesicles where the internalized particles were detectable. Our results indicate that (i) Rac is a pivotal GTPase for inducing in epithelial cells superoxide anion generation and (ii) the internalized material travels trough acidic compartments in CNF1-treated epithelial cells. Altogether this suggests a novel role for epithelial cells that, following Rac activation, might share with professional phagocytes the task of eliminating unwanted pathogens.

The internal redox balance of the cells influences the metabolism of lipids of dietary origin by J774 macrophages: implications for foam cell formation

The effects of chylomicron remnants on lipid accumulation in J774 macrophages, and the incorporation of radioactivity from remnant lipids radiolabelled with [3H]oleate into cellular lipids was investigated. After 24 h of incubation with chylomicron remnants, there was considerable accumulation of lipid within the cells as assessed by staining with oil red O, indicating that the particles induce the formation of foam cells. Fatty acids released from the radiolabelled remnant lipids after uptake were found to be incorporated into cellular triacylglycerol (52%), phospholipid (37%) and cholesteryl ester (8%), but at higher remnant concentrations, the proportion used for triacylglycerol formation increased (up to 73%). When the macrophages were shifted into a pro-oxidising or pro-reducing state by incubation (24 h) with CuSO4 (2.5 microM) or N-acetylcysteine (5 mM), respectively, the incorporation of [3H]oleate from remnant lipid into cellular triacylglycerol and phospholipid was increased by 20-30% in the more oxidised as compared with the more reduced cells. These findings indicate that exposure of J774 macrophages to chylomicron remnants leads to the accumulation of lipid within the cells, and that this process is enhanced by pro-oxidising conditions. We conclude, therefore, that both lipids of dietary origin and the redox balance within macrophages may have a significant role in the induction of foam cell formation.

An Escherichia coli cytotoxin increases superoxide anion generation via rac in epithelial cells

Cytotoxic Necrotizing Factor 1 (CNF1) is a protein toxin from Escherichia coli that induces the activation of Rho, Rac, and Cdc42 GTPases, all involved in actin reorganization. Rac plays a further role in oxidase function. In epithelial cells, CNF1 has been reported to induce a phagocytic-like behavior in terms of a ruffle-driven ingestion of large material. We herein show that CNF1-activated epithelial cells may exert additional cell responses typical of professional phagocytes following stimulation, i.e., an increase in oxygen consumption and the generation of superoxide anions. Such effects were triggered by the contact of latex beads with epithelial cells and were significantly augmented by CNF1-induced Rac activation. Altogether our data indicate that Rac, one of the targets of CNF1, plays a pivotal role in these phenomena, suggesting the involvement in epithelial cells of a Rac-dependent NADPH-oxidase complex similar to that employed by professional phagocytes.

Role of pre-existing redox profile of human macrophages on lipid synthesis and cholesteryl ester cycle in presence of native, acetylated and oxidised low density lipoprotein

The importance of the interactions of modified lipids and macrophages in foam cell generation is clear; however, little attention has been paid to the role of intra-macrophagic redox potential as a modulator of their lipid synthesis and metabolism. In this study, the effects of previously induced non-toxic manipulations of intracellular redox balance on lipid synthesis in human monocyte-derived macrophages (HMDM) was evaluated. Cells, pre-treated with 2.5 microM of the pro-oxidising agent CuSO(4) or with 5 mM of the antioxidant and thiol supplier N-acetylcysteine (NAC), were exposed to radiolabelled oleic acid alone or in combination with native low density lipoprotein (LDL) or modified LDL to evaluate the incorporation of radioactivity into cholesteryl ester, triacylglycerols and phospholipids. CuSO(4)-treated macrophages synthesised more lipids than NAC-treated cells in absence of exogenous lipid, and, generally, in the presence of native or acetylated, but oxidised LDL. In addition, the activities of the enzymes involved in cholesteryl ester storage were also influenced by the pro-oxidant condition. The ratio values between acyl-coenzyme A:cholesterol acyl transferase and cholesteryl ester hydrolase activity suggest that in CuSO(4)-treated macrophages the hydrolysis of cholesteryl ester is favoured with respect to esterification. The interaction of HMDM with oxidised LDL showed a significant different pattern in term of lipid synthesis with respect to those induced by native or acetylated LDL, disrespectful of the initial redox profile of the cells. On the whole, these results suggest that the pre-existing internal redox condition is a further parameter able to modulate the effects of native or acetylated LDL-cell interaction, influencing both HMDM lipid synthesis profile and cholesterol storage. Moreover, oxidised LDL represent a carrier of additional factor(s) able per se to introduce perturbation in the synthetic pathway of lipids, which is not influenced by the redox potential of the macrophage.

Oxidation affects the regulation of hepatic lipid synthesis by chylomicron remnants

The effects of native and oxidized chylomicron remnants on lipid synthesis in normal and oxidatively stressed liver cells were investigated using MET murine hepatocytes (MMH cells), a nontransformed mouse hepatocyte cell line that maintains a highly differentiated hepatic phenotype in culture. Lipid synthesis was determined by measuring the incorporation of [(3)H]oleate into cholesteryl ester, triacylglycerol, and phospholipid by the cells. The formation of cholesteryl ester and phospholipid was decreased by chylomicron remnants in a dose-dependent manner, while triacylglycerol synthesis was increased. Exposure of MMH cells to mild oxidative stress by incubation with CuSO(4) (2.5 microM) for 24 h led to significantly increased incorporation of [(3)H]oleate into triacylglycerol and phospholipid, but not cholesteryl ester, in the absence of chylomicron remnants. In the presence of the lipoproteins, however, similar effects to those found in untreated cells were observed. Oxidatively modified chylomicron remnants prepared by incubation with CuSO(4) (10 microM, 18 h, 37 degrees C) did not influence cholesteryl ester or phospholipid synthesis in MMH cells, but had a similar effect to that found with native remnants on triacylglycerol synthesis. These findings show that hepatic lipid metabolism is altered by exposure to mild oxidative stress and by lipids from the diet delivered to the liver in chylomicron remnants, and these effects may play a role in the development of atherosclerosis.

N-acetylcysteine protects epithelial cells against the oxidative imbalance due to Clostridium difficile toxins

Toxins A and B from the anaerobic bacterium Clostridium difficile are the causative agents of the antibiotic-associated pseudomembraneous colitis. At the subcellular level, they inhibit the Rho family GTPases, thus causing alterations of the actin cytoskeleton. The cytoskeletal integrity is also controlled by the redox state of cells. Therefore, we have evaluated whether an oxidative imbalance could be involved in the toxin-induced cytopathic effects. Our results indicate that both toxins induce oxidative stress with a significant depletion of protein SH-groups. These responses and the cytoskeleton-dependent cell retraction and rounding are significantly counteracted by N-acetylcysteine but not by alpha-tocopherol. Our study provides the first evidence that the thiol supplier N-acetylcysteine impairs the cellular intoxication by acting on the cytoskeleton integrity. This also suggests a possible beneficial role for this drug during therapeutic intervention.

In vitro cytotoxic effect of wheat gliadin-derived peptides on the Caco-2 intestinal cell line is associated with intracellular oxidative imbalance: implications for coeliac disease

Coeliac disease (CD) is an inflammatory disorder of the upper small intestine in which gluten acts as an essential factor in its pathogenesis. Although it is generally accepted that cereal protein activation of the immune system is involved in CD progression, a non-immunomediated cytotoxic activity of gliadin-derived peptides on the jejunal/duodenal tract cannot be excluded. In this work, considering that (a) little has been reported about the intracellular metabolic events associated with gliadin toxicity, and (b) an important role for free radicals in a number of gastrointestinal disease has been demonstrated, we investigated the in vitro effects of gliadin-derived peptides on redox metabolism of Caco-2 intestinal cells during a kinetic study in which cells were exposed to peptic-tryptic digest of bread wheat up to 48 h. We found that the antiproliferative effects displayed by gliadin exposure was associated with intracellular oxidative imbalance, characterised by an increased presence of lipid peroxides, an augmented oxidised (GSSG)/reduced (GSH) glutathione ratio and a loss in protein-bound sulfhydryl groups. Significant structural perturbations of the cell plasma membrane were also detected. Additional experiments performed by using the specific GSH-depleting agent buthionine sulfoximine provide evidence that the extent of gliadin-induced cell growth arrest critically depends upon the 'basal' redox profile of the enterocytes. On the whole, these findings seem to suggest that, besides the adoption of a strictly gluten-free diet, the possibility for an adjuvant therapy with antioxidants may be considered for CD patients.

The role of oxidative imbalance in progression to AIDS: effect of the thiol supplier N-acetylcysteine

In this study we investigate the redox profile of HIV+ patients at different stages of disease with regard to immunological parameters, i.e., the number of circulating CD4+ and CD8+ lymphocytes. For this purpose, peripheral blood mononuclear cells (PBMCs) obtained from healthy donors, HIV+ patients in the asymptomatic phase, long-term nonProgressors (LTNPs), and AIDS patients have been considered. Cells have been exposed in vitro to the prooxidizing agent menadione, which is able to induce superoxide anion formation, and the susceptibility of the cells to the induced oxidative stress was estimated. Moreover, the possibility that the susceptibility of the cells to oxidative stress might be reduced by preexposing them to the antioxidizing agent N-acetylcysteine (NAC) has also been analyzed. The results obtained can be summarized as follows: (1) treatment with the prooxidant agent is capable of inducing massive morphological alterations in PBMCs. In particular, a significant correlation was found between the decrease in number of CD4+ lymphocytes in patients at different stages of disease and the susceptibility of their PBMCs to oxidative stress; (2) preincubation with NAC was able to preserve partially the ultrastructural characteristics of PBMCs isolated from HIV+ patients. In particular, a direct relationship was found between the efficacy of NAC protection and CD4 counts; (3) evaluation of the plasma index of peroxidation and the number of circulating CD4 lymphocytes indicates the existence of a positive correlation between "systemic" oxidative imbalance and stage of the disease; and (4) cells from LTNPs display either oxidative susceptibility or oxidative markers similar to those of healthy donor cells. Our study suggests that the redox profile of patients may be considered a predictive marker of AIDS progression and that the acute infection and the asymptomatic phase of the disease may represent a useful period in which the combined use of antiretroviral and antioxidant drugs may be beneficial.

Clostridium difficile toxin B induces apoptosis in intestinal cultured cells

Toxigenic strains of the anaerobic bacterium Clostridium difficile produce at least two large, single-chain protein exotoxins involved in the pathogenesis of antibiotic-associated diarrhea and colitis. Toxin A (CdA) is a cytotoxic enterotoxin, while toxin B (CdB) is a more potent cytotoxin lacking enterotoxic activity. This study dealt with CdB, providing the first evidence that intestinal cells exposed to this toxin exhibit typical features of apoptosis in that a significant proportion of the treated cells displayed nuclear fragmentation and chromatin condensation. In keeping with ultrastructural data, CdB-treated cells showed the typical flow cytometric hallmark of apoptosis consisting of a distinct sub-G1 peak. The CdB-induced apoptotic response was dose and time dependent and not simply due to the actin-disrupting effect of the toxin or to the subsequent impairment of cell anchorage. Rather, the inhibition of proteins belonging to the Rho family due to CdB seems to play a role in the induction of apoptosis in intestinal cells. The origin of cells and the growth rate may also be cofactors relevant to such a response.

Antiproliferative activity of interferon alpha and retinoic acid in SiHa carcinoma cells: the role of cell adhesion

Several lines of evidence have demonstrated that IFNs could be relevant in the treatment of certain neoplastic diseases such as carcinomas. In particular, IFN-alpha, in addition to the anti-proliferative and cytostatic effects, was demonstrated to be capable of inducing cell death by apoptosis both in vivo and in vitro. Numerous protocols have also been proposed which consider the association of IFN-alpha with other drugs. Among these are retinoids, a class of compounds capable of inducing inhibition of cell growth and differentiation. We address the question here by analyzing the role of cell adhesion in susceptibility to IFN-alpha, RA and their combination of a human cell line derived from a squamous carcinoma of the cervix, the Bcl-2-negative SiHa cell line. In this context, cytoskeleton components and several surface molecules playing a role in cell substrate and cell-to-cell relationships have been evaluated. We found that RA treatment is capable of improving stress fiber formation, decreasing cell detachment and increasing cell-adhesion capability. However, no variations in the ability to adhere to specific extracellular-matrix molecules were found in RA-treated cells. No quantitative changes were detected in integrins involved as receptors for extracellular matrix molecules (VLAI-VLA5) or in other cell-adhesion-associated molecules (e.g., CD44). By contrast, 2 important molecules involved in cell-adhesion processes appeared to be up-regulated by RA exposure: focal adhesion kinase and E-cadherin, involved in adhesion plaque formation and cell-to-cell contacts, respectively. Keeping in mind the importance of adhesion properties in the cell-growth pathway, our findings could be of interest in the study of carcinoma-cell proliferation and metastatic potential.

The HIV-1 vpr protein acts as a negative regulator of apoptosis in a human lymphoblastoid T cell line: possible implications for the pathogenesis of AIDS

Although apoptosis is considered one of the major mechanisms of CD4(+) T cell depletion in HIV-infected patients, the virus-infected cells somehow appear to be protected from apoptosis, which generally occurs in bystander cells. Vpr is an auxiliary HIV-1 protein, which, unlike the other regulatory gene products, is present at high copy number in virus particles. We established stable transfectants of CD4+ T Jurkat cells constitutively expressing low levels of vpr. These clones exhibited cell cycle characteristics similar to those of control-transfected cells. Treatment of control clones with apoptotic stimuli (i.e., cycloheximide/tumor necrosis factor alpha (TNF-alpha), anti-Fas antibody, or serum starvation) resulted in a massive cell death by apoptosis. In contrast, all the vpr-expressing clones showed an impressive protection from apoptosis independently of the inducer. Notably, vpr antisense phosphorothioate oligodeoxynucleotides render vpr-expressing cells as susceptible to apoptosis induced by cycloheximide and TNF-alpha as the control clones. Moreover, the constitutive expression of HIV-1 vpr resulted in the upregulation of bcl-2, an oncogene endowed with antiapoptotic activities, and in the downmodulation of bax, a proapoptotic factor of the bcl-2 family. Altogether, these results suggest that low levels of the endogenous vpr protein can interfere with the physiological turnover of T lymphocytes at early stages of virus infection, thus facilitating HIV persistence and, subsequently, viral spread. This might explain why apoptosis mostly occurs in bystander uninfected cells in AIDS patients.

Oxidized low-density lipoproteins affect natural killer cell activity by impairing cytoskeleton function and altering the cytokine network

Several lines of evidence indicate that oxidative imbalance can play an important role in determining an impairment of natural killer (NK) cell activity in a variety of human diseases. Because a specific role for oxidized low-density lipoproteins (LDL) as pro-oxidizing agents has been envisaged, we tested the activity of oxidized LDL (ox-LDL) on NK cell-mediated cytotoxicity, cytokine release, and membrane molecule modulation. Native LDL served as control. Treatment with ox-LDL at noncytotoxic concentrations (0.2 mg/ml) during the NK/target cell (TC) interaction markedly reduced NK cytotoxic activity against U937 tumor cells. This inhibitory activity was also noticed when NK cells were pretreated with ox-LDL. Scanning electron microscopy examination of NK-target cell conjugates failed to reveal any morphological cell damage. In addition, the number of conjugates and the expression of some adhesion molecules (CD11a, CD11b, CD18, CD2, and CD62L) were not modified by ox-LDL. These observations argued against a possible interference of ox-LDL with the binding process leading to the formation of NK/TC conjugates. By contrast, immunocytochemical analyses of cytoskeleton components of NK cells exposed to ox-LDL showed a partial depolymerization and a derangement of the microtubular apparatus. These alterations were accompanied by an evident decrease in their intracellular reduced glutathione content. Owing to the important role played by the microtubular network during the killing process, it is possible to infer that a cytoskeleton alteration underlies the inhibitory activity of ox-LDL on NK cell function. In addition, exposure of mitogen-stimulated peripheral blood mononuclear cells to ox-LDL markedly reduced specific mRNA transcription and release of cytokines relevant for NK cell activity (such as tumor necrosis factor-alpha, interferon gamma, and interleukin 12). These data suggest that the impairment of NK cell activity by ox-LDL likely reflects the concomitant dysregulation of some essential mechanisms of NK cell function.

Age-related variations in hepatic biosynthesis of phosphatidylcholine: a study of choline metabolism with perfused rat liver

This study investigated the age-related increase in phospholipid secretion previously described in perfused rat livers. The hypothesis of this study was that the increased secretion is mainly due to an enhanced hepatic biosynthesis of phosphatidylcholine (PC). Specifically, we evaluated the contribution to this increase of the major hepatic pathway of phosphatidylcholine formation (i.e., the conversion of choline into phosphatidylcholine via cytidine diphosphate [CDP]-choline). The measurements of [3H]choline incorporation into phosphatidylcholine and its precursors in liver and bile throughout the 2-hr duration of the experiments showed significant differences in the amount of newly synthesized labeled PC secreted in the bile produced by adult and young rat livers. However, the present findings do not support the idea that the age-related increase in phosphatidylcholine hepatic secretion was due only to a strong increase in phosphatidylcholine synthesis by via CDP-choline. Conversely, they suggest that future research should be directed towards the mechanisms regulating the diacylglycerol metabolism in the hepatocytes, as the alteration of the splitting ratio of hepatic diacylglycerol flow could lead to an age-related increase in conversion of diacylglycerol into phosphatidylcholine, rather than into triacylglycerol. This, in turn, may decrease the availability of triacylglycerol for hepatic very low density lipoprotein (VLDL) assembly and contribute to altered VLDL synthesis, as previously observed in the aging process.

Interference with cell cycle progression and induction of apoptosis by dideoxynucleoside analogs

The in vitro effect of single or combined doses of zidovudine (AZT) and dideoxycytidine (ddC) on PHA-activated human peripheral blood mononuclear cells (PBMC) proliferative response and lymphoblastoid T cell line CEM cell growth was evaluated. Clinically relevant amounts (0.1, 1 and 10 microM) of AZT, ddC and AZT/ddC combination (10 + 10 microM) inhibited 3H TdR uptake in both cell models in a dose-dependent manner. The inhibitory effect on cell growth was confirmed by counting the amount of viable CEM cells recovered after 24, 48 and 72 h exposure to the drugs. On equimolar basis, ddC was considerably more efficient than AZT although the latter potentiates the activity of the former Flow cytometric analysis of PBMC and CEM cells exposed to the dideoxynucleosides revealed a decrease in the rate of DNA synthesis (rate of passage through the S phase of the cell cycle) and a reduced number of cell generations, the latter assessed by measuring the halving of the fluorescent probe 5-6-carboxyfluorescein diacetate succinimidyl ester by flow cytometry. The analysis of CEM cells recovered after exposure to ddC or AZT/ddC combination (10 + 10 microM), showed that in addition to perturbing cell cycle progression, ddC, and most efficiently the AZT/ddC combination, induced cell death by apoptosis. The latter was manifested as enhanced side scatter and decreased, sub-G1, DNA content by flow cytometry, and as DNA breakdown in nucleosomal fragments by gel electrophoresis. Present findings indicate that clinically relevant concentrations of dideoxynucleosides reduce cell growth by hampering DNA replication and inducing apoptosis.

Oxidized low density lipoproteins impair peripheral blood mononuclear cell proliferation and cytokine production

Oxidized low density lipoproteins (ox-LDL) are known to behave as physiological pro-oxidants leading to the formation of intracellular reactive oxygen species. The presence of these altered lipoproteins in the human plasma has been associated with a number of morbid states, including atherosclerosis and immuno-deficiency. Common features of such pathological conditions seem to be represented by several alterations occurring in the immune system. In this work we analyze the in vitro effects of ox-LDL on both proliferative response and cytokine production of normal human peripheral blood mononuclear cells (PBMC). Our results indicate that ox-LDL significantly inhibit proliferative response and modulate cytokine network interfering both at protein secretion and mRNA synthesis level.

Induction of apoptosis in HT-29 cells infected with SA-11 rotavirus

Rotavirus infection is associated both in vivo and in vitro with a series of subcellular pathological alterations leading to cell lysis. It has been suggested that these modifications can play a key role in the pathogenesis of rotavirus-associated diarrheal disease. We describe the effects of SA-11 rotavirus infection in HT-29 cells, a human enterocyte-like cell line. Cytological analyses suggested that the viral-induced cytopathic process, including chromatin clumping, can be referred to as apoptosis, the cell death pathway alternative to necrosis. A time course of the process was performed to investigate whether rotavirus-associated cell death showed specific injury signs. HT-29-infected cells were analyzed by scanning and transmission electron microscopy and features of apoptosis such as blebbing of the plasma membrane, peripheral condensation of chromatin, and fragmentation of the nucleus were observed. Specific changes occurring in cell-substrate adhesion and in some organelles relevant for viral maturation, i.e., rough endoplasmic reticulum, were detected. These findings indicate a role for apoptosis in the rotavirus infection process and its related cytopathology, and also suggested that specific histological alterations such as derangement of enterocytes are associated with the pathogenesis of rotavirus-induced diarrheal disease and could be a direct consequence of viral-triggered apoptosis.

Retinoic acid and IFN inhibition of cell proliferation is associated with apoptosis in squamous carcinoma cell lines: role of IRF-1 and TGase II-dependent pathways

Both retinoids and IFNs are known to inhibit proliferation of many normal and transformed cells and to have an in vivo antitumor effect against a variety of cancers, including squamous cell carcinoma. Because the combination of IFNs and all-trans retinoic acid (RA) could improve their antitumor effectiveness (depending on the histological origin and state of differentiation of the cells), we compared the activity of RA and/or IFN-alpha 2b with regard to the mechanism of growth inhibition of ME180 and SiHa cell lines, derived from squamous cervix carcinoma at different stages of differentiation. We reported previously that, in the ME180 cell line, the combined treatment significantly increased the growth inhibitory effect of the single agents. Here, we show that the SiHa cell line appears more sensitive to IFN-alpha 2b than the ME180 cell line, and resistant to RA, which does not significantly inhibit SiHa cell growth. Induction of apoptotic cell death clearly occurs and correlates with the inhibition of cell proliferation in both cell lines. It is interesting that the induction of the transcription factor IFN regulatory factor 1 correlates with the subsequent induction of apoptosis, whereas TGase I and II expression does not. In particular, TGase I and II appear differentially expressed in the ME180 and SiHa cell lines; i.e., TGase I is expressed in ME180 and specifically inhibited by RA, whereas TGase II is expressed in SiHa. It is interesting that both IFN-alpha and RA are able to increase TGase II expression and activity in this cell line.

Induction of apoptosis in HT-29 cells infected with SA-11 rotavirus

Rotavirus infection is associated both in vivo and in vitro with a series of subcellular pathological alterations leading to cell lysis. It has been suggested that these modifications can play a key role in the pathogenesis of rotavirus-associated diarrheal disease. We describe the effects of SA-11 rotavirus infection in HT-29 cells, a human enterocyte-like cell line. Cytological analyses suggested that the viral-induced cytopathic process, including chromatin clumping, can be referred to as apoptosis, the cell death pathway alternative to necrosis. A time course of the process was performed to investigate whether rotavirus-associated cell death showed specific injury signs. HT-29-infected cells were analyzed by scanning and transmission electron microscopy and features of apoptosis such as blebbing of the plasma membrane, peripheral condensation of chromatin, and fragmentation of the nucleus were observed. Specific changes occurring in cell-substrate adhesion and in some organelles relevant for viral maturation, i.e., rough endoplasmic reticulum, were detected. These findings indicate a role for apoptosis in the rotavirus infection process and its related cytopathology, and also suggested that specific histological alterations such as derangement of enterocytes are associated with the pathogenesis of rotavirus-induced diarrheal disease and could be a direct consequence of viral-triggered apoptosis.

Tumor necrosis factor alpha is a powerful apoptotic inducer in lymphoid leukemic cells expressing the P-170 glycoprotein

Multidrug resistance (MDR) is a phenomenon by which tumor cells exposed to a single anti-proliferative agent acquire resistance to other structurally and functionally unrelated drugs. The classical form of MDR is caused by a plasma-membrane protein currently named P-glycoprotein or P-170 encoded by the human mdr-1 gene in its functional isoform. In vitro cell lines expressing P-170 usually also present phenotypic and functional alterations. In the present study we report that the cytotoxicity mediated by tumor necrosis factor alpha (TNF alpha) in MDR variants of the human T-lymphoblastoid CEM cell line is associated with apoptosis (programmed cell death). Susceptibility of MDR cells to apoptosis was increased upon cycloheximide + TNF alpha sequential treatment, whereby the impairment of protein synthesis due to the former agent was followed by the effect of cytokine exposure. Massive apoptosis of P-170-positive cells, but not of controls, was also obtained by depletion of nutrients (i.e., serum starvation). In contrast, TNF-alpha exerted a similar apoptotic effect in epithelial (MCF-7) or myeloma (S8226) drug-sensitive/ -resistant cell pairs. However, the MDR variant of myeloma S8226 was more sensitive to the cytostatic effect of TNF alpha than the parental drug-sensitive cell line. These results suggest that the presence of the MDR phenotype may be associated with increased histotype-dependent cell susceptibility to specific, protein-synthesis-independent, apoptotic pathways.

Antioxidant N-acetyl-cysteine increasing cell adhesion capability could facilitate the biocompatibility processes

Cell adhesion plays an important role in several cell processes and functions, including differentiation, proliferation and death. An important role for cell attachment to medical devices in biocompatibility studies has also been hypothesized. In this paper we report that the use of the antioxidant drug N-acetyl-cysteine is capable of increasing the adhesion properties of epithelial cells in culture. This is associated with a modification of specific cytoskeletal element assembly, such as microfilament system molecules. In contrast, no quantitative alterations in the expression of certain surface receptors for extracellular matrix molecules, such as VLA2, VLA3 and VLA6, are found. These data seem to indicate that intracellular oxidative balance, in particular of thiol groups, could play a key role in the cell adhesion properties and that N-acetyl-cysteine treatment, acting as 'thiol supply', could be of importance in several circumstances, including biocompatibility of medical devices.

Age-related changes in lipid secretion of perfused livers from male Wistar rats donors

Male Wistar rats show typical age-related variations in the distribution of high-density lipoprotein subfractions that include an increase in HDL1 and a decrease in HDL2 proportion. The role of liver in these variations was evaluated by studying the lipoprotein and bile secretions from perfused livers of 14 +/- 1 and 3.5 +/- 0.5 month old Wistar rats (adult and young animals, respectively). The lipid content of lipoproteins secreted from adult livers was higher in HDL2 fraction and lower in VLDL fraction. The lipid output did not show significant age-related variations in the case of HDL1 fraction. However, the lipoproteins secreted from adult livers contained a higher proportion of phospholipids, and a lower proportion of triacylglycerols in comparison with lipoproteins secreted by young livers. Therefore, the molar ratio of core to surface lipids was lower in lipoproteins secreted by adult livers. Adult livers showed a reduction in bile flow by about 37% with a significantly higher phospholipid secretion. These findings suggest that both the hepatic metabolism of glycerophospholipids and their repartition between plasma and bile compartments are affected by aging process. In conclusion, present data show that the age-related increase in plasma HDL1 proportion, previously observed in this rat strain in vivo, are not due to a higher liver secretion of these particles. Conversely, liver appears to have a major role in the age-related VLDL increase and in the variations of phospholipid lipoprotein secretion.

Probucol reduces hepatic cholesterol secretion in hyperlipidemic Yoshida rats

In this study, perfused livers from Yoshida rats, either on a normal diet or on a diet with 0.3% probucol, were examined. The analysis of liver lipid content and of bile and lipoprotein secretion changes showed that probucol had a relevant effect on liver lipid biosynthesis. In particular, it reduced the production of triacylglycerols and, to a much greater extent that of cholesterol. In addition, probucol reduced plasma cholesterol concentration by decreasing esterified cholesterol in HDL1 and HDL2 fractions. Furthermore, HDL1 composition of both hepatic neosynthetized and circulating particles was strongly modified by probucol. Finally, probucol did not appear to induce significant differences in lipid bile secretion while phospholipid secretion from perfused livers was increased. These facts suggest that the hypolipidemic action of probucol is not mediated by an increase in bile steroid secretion, but rather by a direct reduction in hepatic lipoprotein cholesterol secretion. This secretion induces a modified plasma profile of HDL particles such that these variations are advantageous in terms of reverse cholesterol transport.

Protective effect of N-acetylcysteine in tumor necrosis factor-alpha-induced apoptosis in U937 cells: the role of mitochondria

The existence of two different pathways for cell death has been postulated. In addition to the passive and traumatic process leading to necrosis, an active program characterized by organelle integrity and called apoptosis has been described. A positive correlation between the apoptotic cell death process and oxidative imbalance has been demonstrated. In fact, the antioxidant N-acetylcysteine (NAC) seems to be capable of impairing the apoptotic program, replenishing intracellular reduced glutathione content in cells exposed to tumor necrosis factor-alpha (TNF) as apoptotic inducer. Moreover, protein synthesis inhibitors such as cycloheximide (CHX) can facilitate apoptotic triggering by TNF, and mitochondrial function was suggested to be essential in the TNF-mediated apoptotic process. With this in mind, a specific analysis using the JC-1 probe, a fluorescent dye which is capable of indicating mitochondrial membrane potential (delta psi m) changes, was carried out. Our results show that TNF exposure is capable of altering the mitochondria and that NAC protection from CHX + TNF-induced apoptosis could be due to a direct effect of the drug on mitochondrial integrity and function.

N-acetyl-cysteine enhances cell adhesion properties of epithelial and lymphoid cells

In this paper, we show that the antioxidant N-acetyl-cysteine (NAC) is capable of enhancing the adhesion properties of the epithelial cell line A431 and of the lymphocytic cells with cytotoxic activity from human peripheral blood: the natural killer (NK) cells. This effect leads to an increased efficiency of A431 cells to form a monolayer and of NK cells to kill their targets. In both cases a specific effect of NAC was found in the distribution of those molecules of the cytoskeleton which are generally involved in cell substrate and cell-to-cell contact region formation, e.g., the actin microfilaments. NAC could thus behave as a drug influencing certain cytoskeleton-dependent cell processes in a non-histotype dependent manner.

The antioxidant N-acetyl-cysteine protects cultured epithelial cells from menadione-induced cytopathology

The effects of the antioxidant N-acetyl-cysteine (NAC) were assessed after short term exposure of A431 epithelial cells. The drug was able to protect, at least partially, the cells from the oxidative stress induced by the quinone menadione. In particular, the oxidizing agent-induced cell rounding and detachment from the substrate were strongly impaired by pre-exposure to the compound. The mechanism of such an effect seems to be ascribable to a target effect of the drug on the adhesion properties of the cells. In fact, a modification of morphological features of NAC-exposed cells and of their ability to adhere to different coated substrates was found. These changes resulted in a significant improvement of the A431 tumor cell adhesion pattern which was associated with a noticeable rearrangement of some cytoskeletal components, mainly of the microfilament system. These data add new importance to the subcellular activity of NAC and seem to indicate that the redox status of the cells, i.e. the intracellular balance between proxidants and antioxidants, could also play a role in their adhesive properties.

3-Aminobenzamide protects cells from UV-B-induced apoptosis by acting on cytoskeleton and substrate adhesion

3-aminobenzamide (3-ABA) is an inhibitor of poly-(ADP-ribose)-polymerase, an enzyme involved in numerous subcellular processes, including cell death. Recently, a target effect of the drug on some cytoskeletal elements has also been described (Malorni et al., Biochem. Biophys. Res. Commun. 202: 915-922, 1994). In this study we evaluated the ability of 3-ABA to interfere with UV-B ray-induced apoptosis in cells selected for their cytoskeletal features and their different capability to adhere to the substrate. Human melanoma (M14) and epithelial (A431) cell lines and murine primary fibroblastic cultures (MFC) were studied. Our results indicate that cytoskeleton is indeed an important cellular target of 3-ABA, which can prevent apoptotic cell death by UV-B through a specific effect on the adhesion properties of the cells. Indeed, an inverse correlation was observed between sensitivity to UV-B-induced apoptosis (M14 > A431 > MFC) and substrate adhesion (MFC > A431 > M14). The potential relevance of these observations to understand the possible relationships among apoptosis, cytoskeletal functions and substrate adhesion is discussed.

Thiol supplier N-acetylcysteine enhances conjugate formation between natural killer cells and K562 or U937 targets but increases the lytic function only against the latter

In this in vitro study, an evaluation of the importance of intracellular oxidative balance on cell-mediated cytotoxicity was performed by analyzing the effects of the antioxidant N-acetylcysteine (NAC), a specific thiol supplier, on natural killer (NK) cell-mediated cytotoxicity. The results obtained indicate that an enhancement of target cell (TC) killing can be detected when a pre-exposure of effector cells (EC) to NAC was performed. However, this effect seems to depend upon the TC type used. In fact, the increase of EC activity was detected against the differentiated U937 TC while no changes were detected by the same effectors against K562 cells. The mechanism of this enhancement seems to be ascribable to an increased ability of NAC-exposed NK cells to form conjugates (binding) which, in turn, appears to be due to a specific effect of NAC on actin microfilaments. A role for NAC as a cytoskeleton thiol-modifier contributing to the activation of effector cells can thus be hypothesized.

Different susceptibilities to cell death induced by t-butylhydroperoxide could depend upon cell histotype-associated growth features

The effects of the oxidizing agent t-butylhydroperoxide (t-BHP) were investigated on three human cell lines of different origin and growth features (A431 epithelial cells, ADF astrocytoma cells and U937 leukemic cells) using electron microscopy and electron paramagnetic resonance spectroscopy. The results indicate that important biophysical and ultrastructural modifications are induced in the plasma and mitochondrial membranes of these cells and that these changes can ultimately lead to cell death. In addition, the cell cytoskeleton also appears to be a target of hydroperoxide-mediated stress. In particular, all three cell types undergo cytoskeletal alterations leading to surface blebbing, a typical characteristic of cell damage. However, the timing and extent of this damage as well as that occurring at the mitochondrial and plasma membrane levels seems to be different: cells with weak (ADF) or absent (U937) cell-to-cell and cell-substrate contacts and a poorly developed cytoskeleton appear to be more susceptible than other cell types (e.g., A431) to t-BHP-mediated injury. These diverse cell susceptibilites to hydroperoxide-mediated oxidative stress could thus depend upon cell histotype-associated growth features.

3-Aminobenzamide induces cytoskeleton rearrangement in M14 melanoma cells

3-aminobenzamide (3-ABA) is an inhibitor of poly-ADP-ribose-polymerase, an enzyme involved in numerous subcellular processes including cell death. With the aim of contributing to clarify the mode of action of the drug, which is still poorly understood, its effects on cultured melanoma cells M14 have been assessed. In particular, an impairment of cell growth accompanied by the formation of long and numerous dendritic-like protrusions has been detected. This finding appears to be due to a specific effect of the drug on some cytoskeletal elements and could be associated with its differentiating capability. This finding, together with previous data from our group--Biochem. Biophys. Res. Commun., (1994) 199, 525-530 and 1250-1255--suggests that cytoskeleton is an important target of 3-ABA.

Changes in plasma dolichol levels, transport, and hepatic delivery during rat liver regeneration

During the proliferative process that follows partial hepatectomy in the rat, the dolichol content increases in both plasma and liver. Its transport in the blood by lipoproteins also changes. The difference in the distribution of dolichols of various chain lengths in plasma and in the liver is further enhanced during liver regeneration. The dolichol released by perfused liver shows a homologue distribution more similar to that observable in blood than in the liver, thus confirming the importance of the liver as a regulatory site for the blood dolichol supply.

Cell death protection by 3-aminobenzamide: impairment of cytoskeleton function in human NK cell-mediated killing

3-aminobenzamide, an inhibitor of the nuclear enzyme poly(ADP-ribose) polymerase, is capable of interfering with the tumor cell lysis induced by specialized cells from the immune system, i.e., natural killer (NK) cells. In this report we suggest that the mechanism by which the drug can exert its protective effects on target cell killing by NK effectors can also be due to its ability to impair cell-to-cell conjugate formation (binding), without affecting either the expression of cell adhesion molecules nor the features of effector-target cell contact. The mechanism of this inhibition seems to be associated with an alteration of cytoskeletal elements involved during conjugate formation, i.e., with the integrity and function of the microfilament system.

Cell death protection by 3-aminobenzamide and other poly(ADP-ribose)polymerase inhibitors: different effects on human natural killer and lymphokine activated killer cell activities

The death of target cells by cytotoxic effector cells is a relevant biological phenomenon, where cells are activated and a very quick apoptotic program occurs. In order to test the hypothesis that the nuclear enzyme poly(ADP-ribose)polymerase (PADPRP) plays a role in such a process, a variety of PADPRP inhibitors such as 3-aminobenzamide, nicotinamide, 4-aminobenzamide and luminol were used. All of them were able to strongly inhibit K562 target cell killing by human effector natural killer cells (NK) in a 4hr 51Cr release assay. PADPRP inhibitors were much less effective in protecting target cells when lymphokine activated killer cells (LAK) were used as effectors. These substances were active only when both target and effector cells were mixed, being ineffective on target or effector cells alone. On the whole, these data indicate that PADPRP is involved in the death of target cells. Moreover, the different sensitivity of NK and LAK activities to PADPRP inhibitors suggests that the molecular mechanisms underlying these two types of cytotoxicity are at least partially different.

Down-modulation of CD4 antigen during programmed cell death in U937 cells

It has been hypothesized that programmed cell death (PCD), an active cell suicide process occurring in place of necrosis, can be associated with the pathogenesis of acquired immunodeficiency syndrome (AIDS). The entry of human immunodeficiency virus (HIV) into competent cells is mediated by the CD4 molecule present on the surface of certain lymphocyte subpopulations as well as on some cultured cell lines, e.g. U937 myelomonocytic cells. The present paper focuses on some specific aspects of PCD induced by the cytokine tumor necrosis factor (TNF). The results obtained indicate that the exposure of U937 cells to cycloheximide facilitates TNF-mediated PCD via a short term cell death program and modifies the expression of CD4 surface molecules. This change in surface antigen expression, manifested by internalization of the CD4 molecule, occurs in cells in which apoptosis has been triggered, but not in cells undergoing necrosis. These results indicate that the progression of cell death could be associated with specific alterations of certain surface molecules and could have a role in the entry of HIV into cells.

N-acetylcysteine inhibits apoptosis and decreases viral particles in HIV-chronically infected U937 cells

Apoptosis or programmed cell death (PCD) is a type of death occurring in various physiological processes. Several data suggest that: (1) apoptosis may play a critical role in AIDS pathogenesis; (2) an increase of endocellular free radical levels can be associated with activation of previously latent HIV virus. Tumor necrosis factor (TNF), a cytokine capable of inducing oxygen free radicals and apoptosis, appears also to be involved in HIV activation. The present findings, which elucidate a relationship between the percentage of apoptotic cells, reduced glutathione (GSH) depletion and an increase of p24 antigenemia, suggest that pretreatment with N-acetylcysteine (NAC) is capable of decreasing the above-mentioned phenomena in HIV-infected U937 cells.

Effects of cholesterol uptake from high-density lipoprotein on bile secretion and 3-hydroxy-3-methylglutaryl-coenzyme A reductase activity in perfused rat liver

Small aliquots of rat high-density lipoproteins (HDL) (388 +/- 67 nmol lipoprotein cholesterol) were labeled with [14C]cholesterol and administered as a bolus to perfused rat livers. Bile and perfusate samples were collected for 2 hours at 30-minute intervals. After perfusion, both the microsomes and lipid extracts were prepared from the livers. Lipid composition was examined in both liver and microsomes, and 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase activity was evaluated in microsomes. Basal values of bile flow, lipid composition, and enzyme activity were evaluated using livers in which perfusion was discontinued before injecting the lipoprotein. In some experiments, the effect of perfusion per se was assessed by infusing saline instead of lipoprotein. After 10 minutes of lipoprotein perfusion, 50% of cholesterol administered was taken up by the perfused liver. During infusion, transient but significant increases in both bile flow and bile steroid secretion were observed. Cholesterol administration, even if rapid, represented less than 0.4% of total liver cholesterol content. However, this was enough to significantly increase the cholesterol to phospholipid (CH/PL) molar ratio in liver microsomes and at the same time decrease HMG-CoA reductase activity. In conclusion, the main response of the perfused liver to HDL cholesterol infusion is a reduced activity of the rate-limiting enzyme in cholesterol biosynthesis, due to the shift in the microsomal CH/PL molar ratio. A small proportion of the infused cholesterol enters bile as cholesterol and bile salts.

Effect of HDL1 infusion on biliary secretion in perfused rat liver

The effects of HDL1 lipoprotein infusion on biliary lipid secretion were studied in the in vitro model of rat perfused liver. A strong increase in bile flow was observed during and after lipoprotein infusion. This caused a significant rise in cholesterol, phospholipid and bile salt secretions. However, only the percentage of cholesterol increased with respect to the other bile lipids. The changes observed in the cholesterol/phospholipid molar ratio values of liver membrane subfractions (i.e., liver plasma membrane, mitochondria plus lysosomes and microsomes) isolated from the perfused rat liver after HDL1 administration were not significant.