Aldehyde Dehydrogenase 2 Preserves Mitochondrial Function in the Ischemic Heart: A Redox-dependent Mechanism for AMPK Activation by Thioredoxin-1.

ABSTRACT: Aldehyde dehydrogenase 2 (ALDH2) protects the ischemic heart by activating adenosine 5'-monophosphate-activated protein kinase (AMPK) signaling. However, the molecular mechanisms linking ALDH2 and AMPK signaling are not fully understood. This study aimed to explore the potential mechanisms linking ALDH2 and AMPK in myocardial ischemic injury. An ischemic model was established by ligating the left anterior descending coronary artery in rats. The overexpression or knockdown of ALDH2 in H9c2 cells treated with oxygen-glucose deprivation was obtained through lentivirus infection. Transferase-mediated dUTP nick-end labeling was used to evaluate apoptosis in an ischemic rat model and oxygen-glucose deprivation cells. ALDH2 activity, mitochondrial oxidative stress markers, adenosine triphosphate, respiratory control ratio, and cell viability in H9c2 cells were evaluated using a biological kit and 3-(4,5-dimethylthiazol-2-yl)-2,5 diphenyl tetrazolium bromide. Protein expression of ALDH2 , 4-hydroxynonenal, thioredoxin-1 (Trx-1), and AMPK-proliferator-activated receptor gamma coactivator-1 alpha (PGC-1α) signaling pathway was detected through Western blotting. ALDH2 activation reduced ischemic-induced myocardial infarct size and apoptosis. ALDH2 protected mitochondrial function by enhancing mitochondrial respiratory control ratio and adenosine triphosphate production, alleviated mitochondrial oxidative stress, and suppressed myocardial apoptosis. Moreover, ALDH2 attenuated ischemia-induced oxidative stress and maintained Trx-1 levels by reducing 4-hydroxynonenal, thereby promoting AMPK-PGC-1α signaling activation. Inhibiting Trx-1 or AMPK abolished the cardioprotective effect of ALDH2 on ischemia. ALDH2 alleviates myocardial injury through increased mitochondrial biogenesis and reduced oxidative stress, and these effects were achieved through Trx1-mediating AMPK-PGC1-α signaling activation.

Aged Garlic Extract Prevents Alcohol-Induced Cytotoxicity through Induction of Aldehyde Dehydrogenase 2 in the Liver of Mice.

SCOPE: Acetaldehyde is a highly toxic primary metabolite of ethanol, and converts to nontoxic acetic acid by aldehyde dehydrogenase (ALDH). Accumulation of acetaldehyde causes significant damage to human body. Aged garlic extract (AGE) is a functional food material and possesses various health beneficial effects. This study investigates whether AGE contributes to acetaldehyde detoxification through ALDH induction and its underlying mechanism. METHODS AND RESULTS: C57BL/6J mice are orally administrated 10-1000 mg kg-1 body weight (BW) of AGE for 1 week before ethanol administration. AGE suppresses ethanol-caused accumulation of acetaldehyde level in the plasma through inducing mitochondrial ALDH2 but not cytosolic ALDH1A1. AGE also induces antioxidant enzymes, heme oxygenase-1, and NAD(P)H:quinone oxidoreductase 1, resulting in prevention of lipid peroxidation in the liver. In HepG2 cells, AGE prevents ethanol- and acetaldehyde-caused cytotoxicity. AGE induces mitochondrial ALDH2 through activating nuclear factor-erythroid 2-related factor 2 (Nrf2). AGE inhibits protein degradation of Nrf2 and enhances protein degradation of kelch-like ECH-associated protein 1. Furthermore, S-allyl cysteine and S-allyl mercaptocysteine as the bioactive compounds in AGE also induce ALDH2 and Nrf2. CONCLUSION: AGE prevents acetaldehyde-induced hepatotoxicity through enhancing acetaldehyde detoxification through Nrf2-dependent induction of mitochondrial ALDH2.

[Antitumor Effect of Dihydroartemisinin on Diffuse Large B-Cell Lymphoma].

OBJECTIVE: To investigate the potential antitumor effect and its mechanism of dihydroartemisinin (DHA) on diffuse large B-cell lymphoma (DLBCL). METHODS: OCI-Ly7 cells were respectively treated with different concentrations of DHA (0, 12.5, 25, 50 and 100 µmol/L) , CCK-8 was used to detect the cells viability. Subsequently, OCI-Ly7 cells were divided into 5 groups : DHA 0,25,50,100 µmol / L and DHA (100 µmol / L) + Colivelin (STAT3 activator). Aldehyde dehydrogenase (ALDH) positive cells were sorted by flow cytometry, the sphere-forming ability of stem cells was detected. Transwell assay and scratch test were used to analyze the invasion and migration of cells. Western blot was used to detect the expression of migration and invasion-related proteins, as well as the phosphorylation levels of Janus kinase 2 (JAK2) and signal transducer and activator of transcription 3(STAT3). RESULTS: DHA induced obvious cytotoxicity to OCI-Ly7 cells. Compared with the control group, the stem cell-like properties, invasion and migration of OCI-Ly7 were significantly inhibited in DHA 50 µmol/L group and 100 µmol/L group, while the phosphorylation levels of JAK2 and STAT3 were significantly reduced. There was no significant difference in DHA 25 µmol/L group compared with the control group. Treated with Colivelin, the inhibition of DHA on OCI-Ly7 stem cell-like properties, invasion and migration was significantly reversed, and the expression of p-STAT3 was significantly up-regulated. CONCLUSION: DHA has antitumor effect on DLBCL, and its mechanism may be through inhibiting the activation of JAK2/STAT3 pathway to inhibit the stem cell-like properties, invasion and migration of DLBCL cells.

Phosphodiesterase 4 mRNA Level Suppression is Important for Extract of Black Carrot to Protect Against Hepatic Injury Induced by Ethanol.

Excessive alcohol use often results in alcoholic liver disease (ALD). An early change in the liver due to excessive drinking is hepatic steatosis, which may ultimately progress to hepatitis, liver fibrosis, cirrhosis, and liver cancer. Among these debilitating processes, hepatic steatosis is reversible with the appropriate treatment. Therefore, it is important to find treatments and foods that reverse hepatic steatosis. Black carrot has antioxidant and anti-inflammatory effects. In this study, we examined the effectiveness of black carrot extract (BCE) on hepatic steatosis in in vivo and in vitro ethanol-induced liver injury models. For the in vivo experiments, serum aminotransferase activities enhanced by ethanol- and carbon tetrachloride were significantly suppressed by the BCE diet. Furthermore, morphological changes in the liver hepatic steatosis and fibrosis were observed in the in vivo ethanol-induced liver injury model, however, BCE feeding resulted in the recovery to an almost normal liver morphology. In the in vitro experiments, ethanol treatment induced reactive oxygen species (ROS) levels in hepatocytes at 9 h. Conversely, ROS production was suppressed to control levels and hepatic steatosis was suppressed when hepatocyte culture with ethanol were treated with BCE. Furthermore, we investigated enzyme activities, enzyme protein levels, and messenger RNA levels of alcohol dehydrogenase (ADH), cytochrome p450 2E1 (CYP2E1), and aldehyde dehydrogenase (ALDH) using enzyme assays, western blot, and quantitative reverse transcription-polymerase chain reaction analyses. We found that the activities of ADH, CYP2E1, and ALDH were regulated through the cAMP-PKA pathway at different levels, namely, translational, posttranslational, and transcriptional levels, respectively. The most interesting finding of this study is that BCE increases cAMP levels by suppressing the Pde4b mRNA and PDE4b protein levels in ethanol-treated hepatocytes, suggesting that BCE may prevent ALD.

Disulfiram and dithiocarbamate analogues demonstrate promising antischistosomal effects.

Schistosomiasis is a neglected tropical disease with more than 200 million new infections per year. It is caused by parasites of the genus Schistosoma and can lead to death if left untreated. Currently, only two drugs are available to combat schistosomiasis: praziquantel and, to a limited extent, oxamniquine. However, the intensive use of these two drugs leads to an increased probability of the emergence of resistance. Thus, the search for new active substances and their targeted development are mandatory. In this study the substance class of "dithiocarbamates" and their potential as antischistosomal agents is highlighted. These compounds are derived from the basic structure of the human aldehyde dehydrogenase inhibitor disulfiram (tetraethylthiuram disulfide, DSF) and its metabolites. Our compounds revealed promising activity (in vitro) against adults of Schistosoma mansoni, such as the reduction of egg production, pairing stability, vitality, and motility. Moreover, tegument damage as well as gut dilatations or even the death of the parasite were observed. We performed detailed structure-activity relationship studies on both sides of the dithiocarbamate core leading to a library of approximately 300 derivatives (116 derivatives shown here). Starting with 100 µm we improved antischistosomal activity down to 25 µm by substitution of the single bonded sulfur atom for example with different benzyl moieties and integration of the two residues on the nitrogen atom into a cyclic structure like piperazine. Its derivatization at the 4-nitrogen with a sulfonyl group or an acyl group led to the most active derivatives of this study which were active at 10 µm. In light of this SAR study, we identified 17 derivatives that significantly reduced motility and induced several other phenotypes at 25 µm, and importantly five of them have antischistosomal activity also at 10 µm. These derivatives were found to be non-cytotoxic in two human cell lines at 100 µm. Therefore, dithiocarbamates seem to be interesting new candidates for further antischistosomal drug development.

Verteporfin synergizes the efficacy of anti-PD-1 in cholangiocarcinoma.

BACKGROUND: Cholangiocarcinoma (CCA) is one of the primary hepatobiliary malignant neoplasms with only 10% of 5-year survival rate. Promising immunotherapy with the blockade of immune checkpoints has no clear benefit in CCA. The inhibition of YAP1 signaling by verteporfin has shown encouraging results by inhibiting cell proliferation and inducing apoptosis. This study aimed to evaluate the potential benefit of the combination of verteporfin and anti-programmed cell death 1 (PD-1) in CCA mouse model. METHODS: We assessed the cytotoxicity of verteporfin in human CCA cell lines in vitro, including both intrahepatic CCA and extrahepatic CCA cells. We examined the in vitro effect of verteporfin on cell proliferation, apoptosis, and stemness. We evaluated the in vivo efficacy of verteporfin, anti-PD-1, and a combination of both in subcutaneous CCA mouse model. RESULTS: Our study showed that verteporfin reduced tumor cell growth and enhanced apoptosis of human CCA tumor cells in vitro in a dose-dependent fashion. Nevertheless, verteporfin impaired stemness evidenced by reduced spheroid formation and colony formation, decreased numbers of cells with aldehyde dehydrogenase activity and positive cancer stem cell markers (all P < 0.05). The combination of verteporfin and anti-PD-1 reduced tumor burden in CCA subcutaneous SB1 tumor model compared to either agent alone. CONCLUSIONS: Verteporfin exhibits antitumor effects in both intrahepatic and extrahepatic CCA cell lines and the combination with anti-PD-1 inhibited tumor growth.

Protective effect of aldehyde dehydrogenase 2 against rat corneal dysfunction caused by streptozotocin-induced type I diabetes.

Aldehyde dehydrogenase 2 plays a pivotal role in detoxifying aldehydes, and our previous study revealed that aldehyde dehydrogenase 2 could alleviate diabetic retinopathy-associated damage. We aimed to characterize the potential role of aldehyde dehydrogenase 2 in diabetic keratopathy. Twenty-four rats with streptozotocin-induced (60 mg/kg, single intraperitoneal injection) type 1 diabetes mellitus (T1DM) were divided the T1DM group and the T1DM + Alda1 (an activator of aldehyde dehydrogenase 2) group (5 mg/kg/d, intraperitoneal injection, 1/2/3 months), while an additional 12 healthy rats served as the control group. Corneal morphology was examined in vivo and in vitro at one, two, and three months after T1DM induction. Additionally, serum inflammatory factors were measured by ELISA, and the expression of corneal vascular endothelial growth factor A (VEGF-A) and aldehyde dehydrogenase 2 was measured by immunofluorescence staining. Corneal cell death was evaluated by terminal-deoxynucleotidyl transferase-mediated nick end labeling (TUNEL) staining. Slit lamp analysis showed that the area of corneal epithelial cell injury in the T1DM + Alda1 group was significantly smaller than that in the T1DM group at one and two months after T1DM induction (all P < 0.05). OCT analysis and HE staining showed that the central corneal thickness (indication of corneal edema) and the epithelial keratinization level in the T1DM + Alda1 group was evidently decreased compared with those in the T1DM group (all P < 0.05). The serum inflammatory factors interleukin-1 and interleukin-6 were significantly upregulated in the T1DM group compared with the T1DM + Alda1 group at three months after T1DM induction (all P < 0.05), while there were no differences in SOD or TNF-α levels among all groups. Furthermore, corneal VEGF-A expression and corneal cell death in the T1DM + Alda1 group were dramatically reduced compared to those in the T1DM group (all P < 0.05). In conclusion, the aldehyde dehydrogenase 2 agonist Alda1 attenuated rat corneal dysfunction induced by T1DM by alleviating corneal edema, decreasing corneal cell death, and downregulating corneal VEGF-A expression.

Development of 2,5-dihydro-4H-pyrazolo[3,4-d]pyrimidin-4-one inhibitors of aldehyde dehydrogenase 1A (ALDH1A) as potential adjuncts to ovarian cancer chemotherapy.

There is strong evidence that inhibition of one or more Aldehyde Dehydrogenase 1A (ALDH1A) isoforms may be beneficial in chemotherapy-resistant ovarian cancer and other tumor types. While many previous efforts have focused on development of ALDH1A1 selective inhibitors, the most deadly ovarian cancer subtype, high-grade serous (HGSOC), exhibits elevated expression of ALDH1A3. Herein, we report continued development of pan-ALDH1A inhibitors to assess whether broad spectrum ALDH1A inhibition is an effective adjunct to chemotherapy in this critical tumor subtype. Optimization of the CM39 scaffold, aided by metabolite ID and several new ALDH1A1 crystal structures, led to improved biochemical potencies, improved cellular ALDH inhibition in HGSOC cell lines, and substantial improvements in microsomal stability culminating in orally bioavailable compounds. We demonstrate that two compounds 68 and 69 are able to synergize with chemotherapy in a resistant cell line and patient-derived HGSOC tumor spheroids, indicating their suitability for future in vivo proof of concept experiments.

Randomized, double-blind pilot study of transendocardial injection of autologous aldehyde dehydrogenase-bright stem cells in patients with ischemic heart failure.

BACKGROUND: The optimal type of stem cell for use in patients with ischemic heart disease has not been determined. A primitive population of bone marrow-derived hematopoietic cells has been isolated by the presence of the enzyme aldehyde dehydrogenase and comprises a multilineage mix of stem and progenitor cells. Aldehyde dehydrogenase-bright (ALDH(br)) cells have shown promise in promoting angiogenesis and providing perfusion benefits in preclinical ischemia studies. We hypothesize that ALDH(br) cells may be beneficial in treating ischemic heart disease and thus conducted the first randomized, controlled, double-blind study to assess the safety of the transendocardial injection of autologous ALDH(br) cells isolated from the bone marrow in patients with advanced ischemic heart failure. METHODS: Aldehyde dehydrogenase-bright cells were isolated from patients' bone marrow on the basis of the expression of a functional (aldehyde dehydrogenase) marker. We enrolled 20 patients (treatment, n = 10; control, n = 10). Safety (primary end point) and efficacy (secondary end point) were assessed at 6 months. RESULTS: No major adverse cardiovascular or cerebrovascular events occurred in ALDH(br)-treated patients in the periprocedural period (up to 1 month); electromechanical mapping-related ventricular tachycardia (n = 2) and fibrillation (n = 1) occurred in control patients. Aldehyde dehydrogenase-bright-treated patients showed a significant decrease in left ventricular end-systolic volume at 6 months (P = .04) and a trend toward improved maximal oxygen consumption. The single photon emission computed tomography delta analysis showed a trend toward significant improvement in reversibility in cell-treated patients (P = .053). CONCLUSIONS: We provide preliminary evidence that treatment with the novel cell population, ALDH(br) cells, is safe and may provide perfusion and functional benefits in patients with chronic myocardial ischemia.

Combinatorial human progenitor cell transplantation optimizes islet regeneration through secretion of paracrine factors.

Transplanted human bone marrow (BM) and umbilical cord blood (UCB) progenitor cells activate islet-regenerative or revascularization programs depending on the progenitor subtypes administered. Using purification of multiple progenitor subtypes based on a conserved stem cell function, high aldehyde dehydrogenase (ALDH) activity (ALDH(hi)), we have recently shown that transplantation of BM-derived ALDH(hi) progenitors improved systemic hyperglycemia and augmented insulin secretion by increasing islet-associated proliferation and vascularization, without increasing islet number. Conversely, transplantation of culture-expanded multipotent-stromal cells (MSCs) derived from BM ALDH(hi) cells augmented total beta cell mass via formation of beta cell clusters associated with the ductal epithelium, without sustained islet vascularization. To identify paracrine effectors produced by islet-regenerative MSCs, culture-expanded BM ALDH(hi) MSCs were transplanted into streptozotocin-treated nonobese diabetic/severe combine immune deficient (SCID) mice and segregated into islet-regenerative versus nonregenerative cohorts based on hyperglycemia reduction, and subsequently compared for differential production of mRNA and secreted proteins. Regenerative MSCs showed increased expression of matrix metalloproteases, epidermal growth factor receptor (EGFR)-activating ligands, and downstream effectors of Wnt signaling. Regenerative MSC supernatant also contained increased levels of pro-angiogenic versus pro-inflammatory cytokines, and augmented the expansion of ductal epithelial but not beta cells in vitro. Conversely, co-culture with UCB ALDH(hi) cells induced beta cell but not ductal epithelial cell proliferation. Sequential transplantation of MSCs followed by UCB ALDH(hi) cells improved hyperglycemia and glucose tolerance by increasing beta cell mass associated with the ductal epithelium and by augmenting intra-islet capillary densities. Thus, combinatorial human progenitor cell transplantation stimulated both islet-regenerative and revascularization programs. Understanding the progenitor-specific pathways that modulate islet-regenerative and revascularization processes may provide new approaches for diabetes therapy.

Mechanism of cell death induced by spermine and amine oxidase in mouse melanoma cells.

Polyamines such as spermine, spermidine and putrescine are necessary for cell proliferation and are detected at higher concentrations in most tumor tissues, compared to normal tissues. The amine oxidase enzymes can generate cytotoxic products such as hydrogen peroxide and aldehydes from these polyamines. This study investigates the mechanisms of cell death in B16-F0 mouse melanoma tumor cells exposed to bovine serum amine oxidase and exogenous spermine. The bovine serum amine oxidase/spermine enzymatic system induced inhibition of cell proliferation in B16-F0 melanoma cells and cell death by both apoptotic and necrotic processes. Bovine serum amine oxidase or spermine, alone, did not induce cytotoxicity or cell death by apoptosis, indicating that the enzymatic reaction products were responsible. Catalase and NAD-dependent aldehyde dehydrogenase, inhibitors of hydrogen peroxide and aldehydes, respectively, decreased cell death by apoptosis and necrosis. This further confirms that the cytotoxic products are responsible for causing cell death. Use of inhibitors of different caspases showed that melanoma cells were sensitive to processes involving caspase-3 and -9, but were insensitive to caspase-6. Bovine serum amine oxidase in the presence of spermine could be useful as a promising new tool for anticancer treatment by the selective generation of toxic compounds from polyamines in tumors.

Alcohol flushing, alcohol and aldehyde dehydrogenase genotypes, and risk for esophageal squamous cell carcinoma in Japanese men.

Alcohol flushing after light drinking is triggered mainly by severe acetaldehydemia in individuals possessing inactive aldehyde dehydrogenase (ALDH)-2. Inactive ALDH2 encoded by ALDH2*1/2*2 and the low-activity form of alcohol dehydrogenase (ADH)-2 encoded by ADH2*1/2*1 enhance the risk for esophageal cancer in Japanese light to heavy drinkers, a significant association that emphasizes the importance of screening tests for inactive ALDH2 based on alcohol flushing. The objectives of the present report were (a). to evaluate the reliability of a simple questionnaire that asks about both current and past flushing for detecting inactive ALDH2 and (b). to predict cancer risk based on flushing in a case-control manner. The study subjects consisted of 233 Japanese men with esophageal squamous cell carcinoma and 610 cancer-free Japanese men. When current or former flushing individuals were considered to have inactive ALDH2, the sensitivity and specificity of the test were 84.8% and 82.3%, respectively, for the cases and 90.1% and 88.0%, respectively, for the controls. To clarify the characteristics of men who had genetically inactive ALDH2 but did not report alcohol flushing, we analyzed individuals possessing the ALDH2*1/2*2 genotype and found that those who also had ADH2*1/2*1 (both cases and controls) tended not to report current flushing, and those who did not report current flushing (controls only) tended to be heavier drinkers. As compared with overall never or rare drinking, the cancer risks for light (1-8.9 units/week; 1 unit = 22 g of ethanol), moderate (9-17.9 units/week), and heavy (18+ units/week) drinkers with current or former flushing (odds ratio = 6.69, 42.66, and 72.86, respectively) significantly exceeded the risks for those who had never flushed (odds ratio = 1.27, 10.12, and 15.61, respectively), even after adjustment for age, smoking, and diet. The flushing questionnaire may be used in large-scale epidemiological studies as a surrogate marker of ALDH2 genotype to predict individual cancer risk.

Genetic polymorphisms of tobacco- and alcohol-related metabolizing enzymes and the risk of hepatocellular carcinoma.

The effect of genetic polymorphisms for glutathione S-transferase ( GST) M1, GSTT1, GSTP1-1( GSTP1), cytochrome P450 2E1 ( CYP2E1) and aldehyde dehydrogenase 2 ( ALDH2) on the risk of hepatocellular carcinoma (HCC) was observed in 78 Japanese patients with HCC and 138 non-cancer hospital controls. We found a positive association between cumulative amounts of alcohol consumption (>/=600,000 ml in a lifetime) and the risk of HCC (OR=4.52, 95% CI 2.39-8.55). However, cigarette smoking was not significantly related to the risk of HCC (OR=1.23, 95% CI 0.57-2.68). The allelic frequencies of GSTM1, GSTT1, GSTP1, CYP2E1and ALDH2of HCC patients were not significantly different from those of controls when odds ratios were only adjusted for age and gender except for any 2 alleles of ALDH2in drinkers (OR=2.53, 95% CI 1.21-5.31). However, the frequency of any C2 alleles of CYP2E1and any 2 alleles of ALDH2were significantly higher than those of controls (OR=5.77, 95% CI 1.24-27.39, OR=9.77, 95% CI 1.63-58.60) when covariates including viremia were selected by using stepwise logistic regression analysis. We conclude that habitual alcohol drinking is likely to lead to an increased risk of HCC, and any C2alleles of CYP2E1as well as any two alleles of ALDH2were also associated with an increased risk of HCC.

Population distribution of aldehyde dehydrogenase-2 genetic polymorphism: implications for risk assessment.

The role of genetic polymorphisms in modulating xenobiotic metabolism and susceptibility to cancer and other health effects has been suggested in numerous studies. However, risk assessments have generally not used this information to characterize population variability or adjust risks for susceptible subgroups. This paper focuses upon the aldehyde dehydrogenase-2 (ALDH2) system because it exemplifies the pivotal role genetic polymorphisms can play in determining enzyme function and susceptibility. Allelic variants in ALDH2 cause decreased ability to clear acetaldehyde and other aldehyde substrates, with homozygous variants (ALDH2*2/2) having no activity and heterozygotes (ALDH2*1/2) having intermediate activity relative to the predominant wild type (ALDH2*1/1). These polymorphisms are associated with increased buildup of acetaldehyde following ethanol ingestion and increased immediate symptoms (flushing syndrome) and long-term cancer risks. We have used Monte Carlo simulation to characterize the population distribution of ALDH2 allelic variants and inter-individual variability in aldehyde internal dose. The nonfunctional allele is rare in most populations, but is common in Asians such that 40% are heterozygotes and 5% are homozygote variants. The ratio of the 95th or 99th percentiles of the Asian population compared to the median of the U.S. population is 14- to 26-fold, a variability factor that is larger than the default pharmacokinetic uncertainty factor (3.2-fold) commonly used in risk assessment. Approaches are described for using ALDH2 population distributions in physiologically based pharmacokinetic-Monte Carlo refinements of risk assessments for xenobiotics which are metabolized to aldehyde intermediates (e.g., ethanol, toluene, ethylene glycol monomethyl ether).

Heat enhancement of cytotoxicity induced by oxidation products of spermine in Chinese hamster ovary cells.

This study investigates the potential of using polyamines as thermosensitizers, in the presence of bovine serum amine oxidase (BSAO), as a new anticancer strategy. The effect of hyperthermia on cytotoxicity of spermine oxidized by purified bovine serum amine oxidase was investigated in Chinese hamster ovary cells. Several different spermine concentrations were employed in the presence of BSAO at 37 degrees and 42 degrees. Cytotoxicity was considerably enhanced at 42 degrees. Heat also increased the individual cytotoxicity of both exogenous H2O2 and the exogenous aldehyde acrolein. Thus, both of these species could contribute to the thermal enhancement of cytotoxicity caused by BSAO and spermine. The effect of temperature was especially marked in the presence of exogenous catalase. This cytotoxicity cannot be accounted for by H2O2 and was attributed to aldehyde(s). The involvement of aldehyde(s) in cytotoxicity at 42 degrees was also confirmed by the complete inhibition of cytotoxicity with both exogenous aldehyde dehydrogenase and exogenous catalase. A particularly interesting finding, in the presence of exogenous catalase, was that conditions of BSAO and spermine (< or = 50 microM) which were non-toxic at 37 degrees became cytotoxic at 42 degrees. This suggests that spermine-derived aldehyde(s), that were non-toxic at 37 degrees, contributed to cytotoxicity at 42 degrees and resemble thermosensitizers. The thermosensitizing activity of aldehyde(s) produced in the BSAO-catalysed oxidation of spermine has potential value for improving the therapeutic effects of hyperthermia and could be considered for future application in cancer therapy. Polyamines are present at elevated levels in tumour cells and have been considered as heat sensitizers. By delivering BSAO into tumour cells, toxic oxidation products of polyamines could be produced in situ for selective killing of tumour cells.

Metabolism and cytotoxicity of trans,trans-muconaldehyde and its derivatives: potential markers of benzene ring cleavage reactions.

trans,trans-Muconaldehyde (MA) has been proposed to be a myelotoxic metabolite of benzene, although it has not been isolated from benzene administration in vivo. Since the reactivity and further metabolism of MA may preclude its isolation, we have examined the metabolism of MA by: (a) mixtures of yeast alcohol and aldehyde dehydrogenases, (b) mouse liver cytosol, and (c) isolated rat hepatocytes. In all three systems, MA was metabolized rapidly and the major stable end-product of metabolism was the hydroxy/acid (OH/COOH) derivative of MA. The major route of metabolism involved initial reduction to the hydroxy/aldehyde (OH/CHO) derivative. trans,trans-Muconic acid (COOH/COOH), which is used as a marker of benzene ring cleavage reactions in vivo, was also formed from MA albeit to a much lesser extent compared to the OH/COOH. The thiol reactivity, metabolism, and cytotoxicity of MA and its different redox forms (i.e., OH/OH, OH/CHO, COOH/CHO, COOH/COOH, OH/COOH) were also investigated. MA was found to react most rapidly with reduced glutathione (GSH) in a cell-free system and was also the most cytotoxic to rat hepatocytes. Apart from MA, only the OH/CHO demonstrated GSH-reactivity and cytotoxicity. The OH/CHO was a major initial metabolite in all three systems and, thus, could represent a less reactive but more diffusible derivative of MA. These studies define the metabolism and cytotoxicity of MA and its redox derivatives and suggest that the OH/COOH metabolite of MA may have relevance as a marker of ring cleavage reactions of benzene in vivo.

Glutathione and antioxidants protect microsomes against lipid peroxidation and enzyme inactivation.

The study investigated the relationship between lipid peroxidation and enzyme inactivation in rat hepatic microsomes and whether prior inactivation of aldehyde dehydrogenase (ALDH) exacerbated inactivation of other enzymes. In microsomes incubated with 2.5 microM iron as ferric sulfate and 50 microM ascorbate, ALDH, glucose-6-phosphatase (G6Pase) and cytochrome P450 (Cyt-P450) levels decreased rapidly and concurrently with increased levels of thiobarbituric acid-reactive substances. Microsomal glutathione S-transferase and nicotinamide adenine dinucleotide phosphate-cytochrome c reductase were little affected during 1 hr of incubation. Addition of reduced glutathione partially protected and N,N'-diphenyl-p-phenylenediamine and butylated hydroxytoluene completely protected microsomes against inactivation of ALDH, G6Pase and Cyt-P450, as well as lipid peroxidation induced by iron and ascorbate. ALDH was more susceptible than G6Pase to inactivation by iron and ascorbate, and was thus an excellent marker for oxidative stress. Inhibition of ALDH by cyanamide injection of rats exacerbated the inactivation of G6Pase in microsomes incubated with 0.1 mM, but not 25 microM 4-hydroxynonenal (4-HN). 4-HN did not stimulate lipid peroxidation. Thus, 4-HN may play a minor role in microsomal enzyme inactivation. In contrast, lipid peroxyl radicals play an important role in microsomal enzyme inactivation, as evidenced by the prevention of both lipid peroxidation and enzyme inactivation by chain-breaking antioxidants.

Metabolic and cellular basis of 2-butoxyethanol-induced hemolytic anemia in rats and assessment of human risk in vitro.

Recent work in this laboratory indicated that 2-butoxyethanol (BE) causes acute hemolytic anemia in rats, and activation of BE to butoxyacetic acid (BAA), presumably through the intermediate 2-butoxyacetaldehyde (BAL), is a prerequisite for development of hematotoxicity. In the present studies, the effects of BE and its metabolites, BAL and BAA, on erythrocytes from rats and humans were investigated in vitro. Incubation of BE (up to 10 mM) with blood from male F344 rats caused no hemolysis and resulted in no metabolic alteration of BE. Further, addition of alcohol and aldehyde dehydrogenases, with their co-factors, to the incubation mixture failed to alter BE or its effect. At 20 mM, BE caused significant (P less than or equal to 0.05) hemolysis of rat erythrocytes accompanied by a significant (P less than or equal to 0.05) decrease in hematocrit (HCT). In contrast, incubation of BAL or BAA with rat blood caused time- and concentration-dependent swelling of red blood cells followed by hemolysis; however, BAA was significantly more efficacious than BAL. Addition of aldehyde dehydrogenase and its co-factors significantly (P less than or equal to 0.05) potentiated the effect of BAL on rat erythrocytes. Further in vitro investigation of the cellular mechanisms involved in the hemolytic effect revealed that incubation of rat blood with BAA or BAL caused a time- and concentration-dependent decrease in blood ATP concentration. As observed with the hemolytic effects, the decrease in blood ATP was significantly (P less than or equal to 0.05) greater with BAA than with BAl and was not induced by BE. Further, BAA caused no significant changes in the concentration of reduced glutathione and glucose-6-phosphate dehydrogenase in rat erythrocytes. Assessment of human sensitivity by incubation of human blood with BAA showed minimal swelling or hemolysis of erythrocytes with minimal decline in blood ATP levels at BAA concentrations several-fold higher than required to cause complete hemolysis of rat erythrocytes. In summary, the current studies confirm that the hemolytic effect of BE can be attributed primarily to its metabolite BAA, that hemolysis of rat erythrocytes by BAA or BAL is preceded by swelling and ATP depletion, suggesting that the erythrocyte membrane is the most likely target, and, finally, that human erythrocytes are comparatively insensitive to the hemolytic effects of BAA in vitro.

Isotope effects and their implications for the covalent binding of inhaled [3H]- and [14C]formaldehyde in the rat nasal mucosa.

DNA-protein crosslinks were formed in the nasal respiratory mucosa of Fischer-344 rats exposed for 3 hr to selected concentrations of [3H]- and [14C]formaldehyde (3HCHO and H14CHO) (M. Casanova and H. d'A. Heck (1987). Toxicol. Appl. Pharmacol. 89, 105-121). In rats depleted of glutathione (GSH) and exposed to 10 ppm of 3HCHO and H14CHO, the 3H/14C ratio of the fraction of the DNA that was crosslinked to proteins was significantly (39 +/- 6%) higher than that of the inhaled gas. This suggests an isotope effect, either on the formation of DNA-protein crosslinks by labeled HCHO or on the oxidation of labeled HCHO catalyzed by formaldehyde (FDH) or aldehyde dehydrogenase (AldDH). The possibility of an isotope effect on the formation of crosslinks was investigated using rat hepatic nuclei incubated with [3H]- and [14C]formaldehyde (0.1 mM, 37 degrees C). A small (3.4 +/- 0.9%) isotope effect was detected on this reaction, which slightly favored 3HCHO over H14CHO in binding to DNA. The magnitude of this isotope effect cannot account for the high isotope ratio observed in the crosslinked DNA in vivo. The possibility of an isotope effect on the oxidation of 3HCHO and H14CHO catalyzed by FDH was investigated using homogenates of the rat nasal mucosa incubated with [3H]- and [14C]formaldehyde at total formaldehyde concentrations ranging from 0.1 to 11 microM, NAD+ (1 mM), GSH (15 mM), and pyrazole (1 mM). The experiments showed that 3HCHO is oxidized significantly more slowly than H14CHO under these conditions (Vmax/Km (H14CHO) divided by Vmax/Km (3HCHO) = 1.82 +/- 0.11). A similar isotope effect was observed in the absence of GSH, presumably due to the oxidation of 3HCHO and H14CHO catalyzed by AldDH. These results suggest that the residual (unoxidized) formaldehyde present in the nasal mucosa of rats exposed to [3H]- and [14C]formaldehyde may be "enriched" in 3HCHO relative to H14CHO, which can bind to DNA resulting in an isotope ratio higher than that of the inhaled gas. The isotope effect on the oxidation of 3HCHO and H14CHO suggests that previous estimates of the amount of HCHO covalently bound to nasal mucosal DNA (M. Casanova-Schmitz, T. B. Starr, and H. d'A. Heck (1984). Toxicol. Appl. Pharmacol. 76, 26-44) may have been too large, especially at low airborne concentrations and that the shape of the concentration-response curve for DNA-protein crosslinking is more nonlinear than reported previously.