An investigation of the mechanism of hepatotoxicity of the antitumour agent N-methylformamide in mice

Modulation of the oxidative damage, inflammation, and apoptosis-related genes by dicinnamoyl-L-tartaric acid in liver cancer

Cancer cells can become resistant to existing treatments over time, so it is important to develop new treatments that target different pathways to stay ahead of this resistance. Many cancer treatments have severe side effects that can be debilitating and even life-threatening. Developing drugs that can effectively treat cancer while minimizing the risks of these side effects is essential for improving the quality of life of cancer patients. The study was designed to explore whether the combination of dicinnamoyl-L-tartaric (CLT) and sorafenib ((SOR), an anti-cancer drug)) could be used to treat hepatocellular carcinoma (HCC) in the animal model and to assess whether this combination would lead to changes in certain biomarkers associated with the tumour. In this study, 120 male mice were divided into 8 groups of 15 mice each. A number of biochemical parameters were measured, including liver functions, oxidative stress (malondialdehyde, (MDA); nitric oxide (NO)), and antioxidative activity (superoxide dismutase (SOD), and glutathione peroxidase (GPx)). Furthermore, the hepatic expressions of Bax, Beclin1, TNF-α, IL1β, and BCl-2 genes were evaluated by qRT-PCR. The combination of SOR and CLT was found to reduce the levels of liver enzymes, such as AST, ALT, ALP, and GGT, and reduce the pathological changes caused by DAB and PB. The upregulation of TNF-α, IL1β, and Bcl-2 genes suggests that the CLT was able to initiate an inflammatory response to combat the tumor, while the downregulation of the Bax and Beclin1 genes indicates that the CLT was able to reduce the risk of apoptosis in the liver. Furthermore, the combination therapy led to increased expression of cytokines, resulting in an enhanced anti-tumor effect.

Purification, crystallization and anticancer activity evaluation of the compound alternariol methyl ether from endophytic fungi Alternaria alternata

AIMS

Medicinal plant-associated endophytic fungi are important sources of precious bioactive compounds, contributing more than 80% of the natural drugs for various ailments. The present study was aimed at evaluating the anticancer activity of the crystallized compound alternariol methyl ether (AME) against hepatocellular carcinoma (HCC) both in vitro and in vivo from an endophytic fungus residing in the medicinal plant Vitex negundo.

METHODS AND RESULTS

The secondary metabolites from the endophytic fungus Alternaria alternata MGTMMP031 were isolated. Purification and characterization of the compound was performed and the potential compound was identified as AME. The crystal structure of AME was unambiguously confirmed by X-ray analysis. AME has been checked for its antibacterial and anticancer properties which showed its effectiveness against various bacteria and demonstrated marked anti-proliferative activity against the human HCC cells (HUH-7) both in vitro and in vivo. Mode of actions included cell cycle arrest, reducing the level of markers enzymes of liver cancer and preventing tumour growth.

CONCLUSIONS

Alternariol methyl ether acts as a potential therapeutic target against HCC. The compound was isolated and the crystal structure was obtained for the first time from the endophytic fungus A. alternata MGTMMP031. In the present study, the crystallized structure of AME was obtained by slow evaporation technique. It can be concluded that AME acts as a potential therapeutic target against HCC.

SIGNIFICANCE AND IMPACT OF THE STUDY

Endophytic fungi residing in the medicinal plants have strong biological significance and bioactive compounds from these fungi provide better therapeutic targets against diseases.

Cytoskeleton-dependent surface blebbing induced by the polar solvent N-methylformamide

In vivo and in vitro studies performed on the polar solvent N-methylformamide (NMF), as well as on its association with chemotherapeutic agents or X rays, have clearly demonstrated that this compound is capable of inducing changes in biological characteristics of tumor cells, e.g., cell differentiation. However, the mechanism of action of NMF is far from being elucidated. Hence, in order to better clarify such a mechanism an in vitro study was carried out by using mouse fibroblasts in primary culture (MEF) and human melanoma cultured cells (M14). Results obtained by immunocytochemical and ultrastructural methods with doses of NMF ranging from 0.1 to 7% are reported here. As a general rule, a different sensitivity (in terms of cytopathologic changes induced by NMF) was found between the cell types considered. In fact, melanoma cells appeared to be highly susceptible to the action of the drug, undergoing severe morphological modifications represented mainly by a reversible dose and time-dependent cell rounding and surface blebbing. In contrast, NMF-induced injury in MEF cells was characterized mainly by a simple retraction of the cell body. A cytochemical analysis of the expression of certain membrane antigens (e.g., glycoproteins, epidermal growth factor receptor, B2 microglobulin) in NMF-treated M14 cells undergoing blebbing was also carried out. A randomly distributed labeling of such molecules was observed. Accordingly, freeze-fracturing electron microscopic analysis also displayed a random distribution of intramembrane particles over the plasma membrane. When subcellular changes induced by the drug were investigated, a remarkable modification of cytoskeletal components was detected in both cell types. In particular, cross-linked actin microfilament bundles were easily observed in NMF-exposed MEF cells. Finally, when different experimental conditions which perturb calcium ion homeostasis or restore protein thiol group reduced state were analyzed, a noticeable impairment of the blebbing phenomenon was observed. Thus, a target effect of NMF on the microfilament system, probably leading, in turn, to several subcellular changes and cell surface blebbing, can be hypothesized. Such a cytoskeletal element-dependent cytopathology appears to be related to changes of the oxidized state of such molecules as well as to calcium ion perturbations.

Different effects of sequential combinations of N-methylformamide with 5-fluorouracil on human colon carcinoma cells growing in nude mice

The effects of the combination of N-methylformamide (NMF) with 5-fluorouracil (5-FU) on tumor growth and morphological features of human colon carcinoma cells (HT29) implanted in nude mice were assessed. Both agents were administered i.p. at tolerable doses: 5-FU at 19 mg/kg for 5 days and NMF at 200 mg/kg for 12 days. Four main schedules were tested: 5-FU alone, NMF alone, NMF followed by 5-FU and 5-FU followed by NMF. The last sequence was the most effective, as compared with the other treatment regimens. In particular, the 5-FU----NMF combination induced a tumor inhibition of about 75% at the end of the treatments (17th day) versus an inhibition of 23%-43% in the other schedules. Morphological observations, carried out by light and electron microscopy, indicated a possible relationship between the presence of structural changes and tumor growth inhibition. The results of this study renew interest in the use of NMF in sequential combination confirming sequence as a critical factor for the optimal combination of NMF and 5-FU.

Differences between rodents and humans in the metabolic toxification of N,N-dimethylformamide

The widely used industrial solvent N,N-dimethylformamide (DMF) causes liver damage in occupationally exposed persons and is suspected of involvement in the generation of certain occupational malignancies. Here the extent of the biotransformation of DMF to three urinary metabolites has been compared in humans and rodents. The metabolites, which were quantified by gas chromatography (GC) are N-(hydroxymethyl)-N-methylformamide (HMMF), which yielded N-methylformamide on GC analysis, a species which decomposed to formamide on GC analysis, and N-acetyl-S-(N-methylcarbamoyl) cysteine (AMCC), measured after derivatization with ethanol to give ethyl N-methylcarbamate. Ten volunteers who absorbed between 28 and 60 mumol/kg DMF during an 8-hr exposure to DMF in the air at 60 mg/m3 excreted in the urine within 72 hr between 16.1 and 48.7% of the dose as HMMF, between 8.3 and 23.9% as formamide, and between 9.7 and 22.8% as AMCC. AMCC, together with HMMF, was also detected in the urine of workers after occupational exposure to DMF. The portion of the dose (0.1, 0.7, or 7.0 mmol/kg given ip) which was metabolized in mice, rats, or hamsters to HMMF varied between 8.4 and 47.3% of the dose; between 7.9 and 37.5% were excreted as formamide and only between 1.1 and 5.2%, as AMCC. The results suggest that there is a quantitative difference between the metabolic pathway of DMF to AMCC in humans and rodents. It is argued that the hepatotoxic potential of DMF may be linked to the extent of its metabolic conversion to AMCC.

Cytotoxicity and metabolism of the hepatotoxin N-methylformamide and related formamides in mouse hepatocytes

Some N-alkylformamides such as N-methylformamide (NMF) possess hepatotoxic properties in vivo. To study the mechanism of this toxicity, suspensions of mouse hepatocytes were tested as an in vitro model system suitable for the study of the relationship between (i) the toxic potential of formamides, (ii) their metabolism to N-alkylcarbamoylating species, and (iii) their ability to deplete hepatic glutathione pools. The effects of NMF were compared with those of its analogs N-ethylformamide (NEF), N,N-dimethylformamide (DMF), formamide (F), N-methylacetamide (NMA), and N-methyldeuteroformamide ([2H]NMF). Only NEF and [2H]NMF share with NMF the ability to cause liver damage in vivo in mice. Hepatocellular toxicity was determined by measuring LDH leakage into the extracellular medium; metabolism to N-alkylcarbamoylating species was measured by GLC after derivatization with propanol to form propyl N-alkylcarbamate; glutathione concentrations were determined spectrophotometrically. Of the formamide analogs studied, only NMF and NEF caused cytotoxicity, being apparently equipotent. NMF, NEF, and [2H]NMF gave rise to the formation of detectable levels of N-alkylcarbamoylating metabolites and depleted glutathione pools. Toxicity, metabolism, and glutathione depletion were dependent on NMF concentration. [2H]NMF was markedly less cytotoxic than NMF, yielding only 35% of the amount of N-methylcarbamoylating metabolite compared to NMF and caused less depletion of glutathione than did NMF. These results parallel closely the in vivo hepatotoxic potential of NMF and its analogs, their metabolism to urinary S-(N-alkylcarbamoyl)mercapturates and their ability to deplete hepatic glutathione in mice. The results provide support for the contention that metabolism is involved with formamide-induced hepatotoxicity and suggest that suspensions of isolated mouse hepatocytes are an appropriate in vitro model for the further study of the mechanism by which formamides cause toxicity.

Comparative hepatotoxicity and metabolism of N-methylformamide in rats and mice

N-methylformamide (NMF) produced dose-dependent zone 3 haemorrhagic necrosis in mice; the threshold dose was 100-200 mg/kg. In rats a dose of 1000 mg/kg caused hepatic damage in some animals and slight elevations of plasma transaminases. A species difference in susceptibility to NMF-induced hepatotoxicity is clearly indicated. NMF depleted liver non-protein sulphydryl (NPSH) in a dose-dependent manner in mice, but not in rats. Depletion of liver glutathione by buthionine sulphoximine or diethylmaleate potentiated the hepatotoxicity of NMF in mice. [14C]-methyl NMF was metabolised by mice and rats and a number of urinary metabolites including an N-acetylcysteine conjugate, methylamine and N-hydroxymethylformamide were detected. There were no qualitative differences in the metabolites between rats and mice but mice metabolised NMF much faster and more extensively than rats.

Vitamin E protection against chemical-induced cell injury. I. Maintenance of cellular protein thiols as a cytoprotective mechanism

Vitamin E protection against chemical-induced toxicity to isolated hepatocytes was examined during an imbalance in the thiol redox system. Intracellular reduced glutathione (GSH) was depleted by two chemicals of distinct mechanisms of action: adriamycin, a cancer chemotherapeutic agent that undergoes redox cycling, producing reactive oxygen species that consume GSH, and ethacrynic acid, a direct depleter of GSH. The experimental system used both nonstressed vitamin E-adequate isolated rat hepatocytes and compromised hepatocytes subjected to physiologically induced stress, generated by incubation in calcium-free medium. At doses whereby intracellular GSH was near total depletion, cell injury induced by either chemical was found to follow the depletion of cellular alpha-tocopherol, regardless of the status of the GSH redox system. Changes in protein thiol contents of the cells closely paralleled the changes in alpha-tocopherol contents throughout the incubation period. Supplementation of the calcium-depleted hepatocytes with alpha-tocopheryl succinate (25 microM) markedly elevated their alpha-tocopherol content and prevented the toxicities of both drugs. The prevention of cell injury and the elevation in alpha-tocopherol contents were both associated with a prevention of the loss in cellular protein thiols in the near total absence of intracellular GSH. The mechanism of protection by vitamin E against chemical-induced toxicity to hepatocytes may therefore be an alpha-tocopherol-dependent maintenance of cellular protein thiols.

Hepatotoxicity of N-methylformamide in mice--II. Covalent binding of metabolites of [14C]-labelled N-methylformamide to hepatic proteins

Incubation of the hepatotoxin N-methylformamide (NMF) labelled either in the methyl group (OHCNH14CH3) or the formyl group (OH14CNHCH3) with mouse hepatic microsomes in the presence of NADPH, but not in its absence, led to covalent binding of metabolites to microsomal proteins. When [14C]NMF was injected into BALB/c mice radioactivity was found to be associated with liver and, to a much lesser extent, with kidney proteins. Association of radioactivity derived from OHCNH14CH3 with hepatic proteins was higher in BALB/c mice than in CBA/CA mice and in these it was higher than in BDF1 mice. Association of label derived from either isotopomer was significantly reduced but not abolished by pretreatment of mice with cycloheximide suggesting both covalent binding and metabolic incorporation of NMF metabolites. Depletion of hepatic glutathione by pretreatment of mice with buthionine sulfoximine or diethyl maleate prior to administration of OH14CNHCH3 enhanced the association of label with hepatic proteins measured 1 hr after drug injection. Covalent binding of [14C]NMF to hepatic microsomes in vitro was abolished in the presence of glutathione. It is argued that the generation of the toxic lesion and the association of NMF metabolites with hepatic proteins may be causally related even though certain mechanistic and enzymatic details of this link remain obscure.

Hepatotoxicity of N-methylformamide in mice--I. Relationship to glutathione status

In order to investigate the link between hepatotoxicity caused by N-methylformamide (NMF) and its ability to deplete hepatic glutathione experiments were conducted in three strains of mouse which differ in their susceptibility towards NMF-induced liver damage. NMF toxicity was measured by changes in plasma levels of sorbitol dehydrogenase and alanine and aspartate transaminases. In BALB/c mice, the most susceptible strain, a hepatotoxic dose of NMF (200 mg/kg) caused a depletion of hepatic glutathione to 21% of control levels 2 hr after drug administration. In CBA/CA and BDF1 mice the same dose of NMF depleted glutathione to 53% of control levels and did not cause hepatotoxicity. In BALB/c mice depletion of hepatic glutathione by pretreatment with buthionine sulfoximine decreased the hepatotoxic dose threshold of NMF from 150 mg/kg to 100 mg/kg. Conversely, pretreatment of mice with cysteine or N-acetylcysteine protected against both glutathione depletion and NMF-induced hepatotoxicity. The results are in accordance with the suggestion that the hepatotoxicity of NMF is associated with its metabolism to an intermediate which reacts with glutathione.

The influence of sodium ascorbate, menadione sodium bisulfite or pyridoxal hydrochloride on the toxic and antineoplastic action of N-methylformamide in P 388 leukemia or M 5076 sarcoma in mice

The toxicity of daily subcutaneously applied 500 mg/kg N-methylformamide (NMF) during a period of 8 days in female CD-mice was ameliorated when 100 mg/kg sodium ascorbate, 60 mg/kg menadione bisulfite or 80 mg/kg pyridoxal hydrochloride were applied simultaneously. The comparison of the daily s.c. application of 360 mg/kg NMF with the intermittent s.c. injection of 720 mg/kg NMF with an interval of 48 h in P 388 leukemia showed that the daily application of NMF induced an increase of life span of 82% whereas the intermittent schedule effected a 142% increase of life span. The simultaneous combination of 360 mg/kg NMF with 60 mg/kg sodium ascorbate applied daily caused a 133% increase of life span and the simultaneous combination of 360 mg/kg NMF with 30 mg/kg menadione sodium bisulfite lead to a 126% increase of life span. The combined daily s.c. application of 360 mg/kg NMF with 30 mg/kg pyridoxal hydrochloride induced only a minimal difference compared to the daily application of 360 mg/kg NMF alone. The combination of 720 mg/kg NMF with 120 mg/kg sodium ascorbate applied in intervals of 48 h showed a 164% increase of life span. In advanced M 5076 sarcoma the daily s.c. application of 360 mg/kg NMF effected a 82% increase of life span and the combination of 360 mg/kg NMF with 60 mg/kg sodium ascorbate effected a 135% increase of life span.

The effects of diethyldithiocarbamate on the hepatotoxic action and antitumor activity of N-methylformamide in mice

The oral administration of diethyldithiocarbamate (DTC) prevented hepatic necrosis induced by N-methylformamide (NMF) in ddY-strain mice, in more susceptible BALB/c mice and in diethylmaleate-treated mice in which NMP-hepatotoxicity was potentiated, as evidenced by suppression of increases of plasma glutamic pyruvic transaminase activity and liver calcium content or by histological observations. Early depletion of liver glutathione following NMF administration was also prevented by DTC. DTC markedly delayed the in vivo metabolism of NMF as indicated by a prolonged retention of plasma and liver NMF levels and an enhancement of urinary excretion of NMF. These observations support a bioactivation mechanism for NMF hepatotoxicity, and the hepatoprotective action of DTC may be due to an inhibition of the metabolic activation of NMF. Hepatotoxic manifestations after repeated administration of NMF also tended to be ameliorated by simultaneous treatment with DTC. Cotreatment with DTC, however, decreased the antitumor activity of NMF against Ehrlich ascites tumors, and Sarcoma 180. This also implies the involvement of a bioactivation mechanism in the antitumor action of NMF, but further studies are necessary to confirm this point. The possible therapeutic value of DTC as a hepatoprotector may be diminished by the suppression of the antitumor activity of NMF.

The antitumour effect and toxicity of cis-platinum and N-methylformamide in combination

N-Methylformamide (NMF), currently undergoing phase II clinical evaluation for the treatment of cancer, and the established antitumour agent cis-platinum (CDDP) have nonoverlapping toxicities, with the exception of gastrointestinal side effects. The major target organs for the toxicities of the compounds are the liver (NMF) and the kidney (CDDP). Furthermore, NMF is nonleukopenic. In view of this, and of recent evidence that NMF enhances the cytotoxic effect of CDDP in vitro the activity of NMF and CDDP against the M5076 sarcoma implanted in mice was investigated, together with the various toxicities in mice and rats. The antitumour effect of NMF in combination with CDDP was additive, but NMF did not alter the leukopenia produced by CDDP in the tumour-bearing mice. CDDP produced only a minimal increase in the hepatotoxicity of NMF in mice, and NMF did not augment the nephrotoxicity of CDDP in rats (except for a small effect on calcium excretion). The results support suggestions that clinical evaluation of combination chemotherapy with NMF and CDDP is warranted.

Biological effects of acetamide, formamide, and their monomethyl and dimethyl derivatives

The industrial use of certain acetamides and formamides (particularly DMAC and DMF) for their solvent properties has resulted in rather extensive examination of their biological properties. Both DMAC and DMF are rapidly absorbed through biological membranes and are metabolized by demethylation first to monomethyl derivatives and then to the parent acetamide or formamide. Relatively high single doses to various species following oral, dermal, i.p., i.v., or inhalation exposures generally are required to produce mortality. The liver is the primary target following acute high level exposure, but massive doses can also produce damage to other organs and tissues. Repeated sublethal treatment by various routes also shows the liver to be the target organ with the degree of damage being proportional to the amount absorbed. With MMF, the potential usefulness as a cancer chemotherapeutic agent needs to be measured against the hepatotoxic effects produced in man. Acetamides and formamides are generally inactive in mutagenicity tests. Mammalian test systems do not appear to be genetically sensitive and DMF has been recommended for use as the vehicle in microbial assays designed to test for genetic activity of hard-to-dissolve chemicals. Embryotoxicity can be demonstrated at high doses; doses which generally show toxicity to the maternal animals. Structural abnormalities in sensitive species such as the rabbit are produced following exposure at near-lethal levels. The spectrum of abnormalities seen is broad and fails to show any time or site specificity in terms of developing organs/organ systems. Inhalation exposures to DMAC and DMF at levels producing some maternal toxicity in rats have produced no teratogenic response and only slight evidence of embryotoxicity. Long-term feeding of relatively high levels of acetamide produces liver cancer in rats. DMAC and DMF appear to be noncarcinogenic. The environmental toxicity of these chemicals is low. Liver damage can be produced by overexposure to these chemicals in man. Airborne concentrations need to be controlled and care should be taken to avoid excessive liquid contact as the chemicals are absorbed through the skin. A relationship exists between the amount of DMAC or DMF absorbed and the amount of MMAC or MMF excreted in the urine so that biomonitoring of the urinary metabolites can indicate situations in which total exposures, both dermal and inhalation, are excessive. An interaction between DMF and ethanol occurs such that signs, including severe facial flushing, appear when DMF-exposed individuals consume alcoholic beverages.

N-Methylformamide (NSC 3051): a potential candidate for combination chemotherapy

N-Methylformamide (NMF) was found to be non-toxic to the bone marrow as reflected in the absence of leukopenia in mice, even when the marrow had been compromised by prior administration of cyclophosphamide. Thus recovery from the leukopenic nadir after 160 mg/kg of cyclophosphamide was unaffected by 200 mg/kg X 10 of NMF. This combination, given to animals bearing the M5076 sarcoma, proved to have an additive antitumour effect as measured by tumour growth delay and was superior to the antitumour effect of two doses of cyclophosphamide, a regime which prolonged the leukopenia. Furthermore, the hepatotoxicity of NMF was not augmented by the addition of cyclophosphamide. When hepatotoxicity was induced in BALB/c mice bearing the NMF-resistant ADJ/PC6A plasmacytoma, cyclophosphamide fully maintained its antitumour effect. The results show NMF to be a highly specific antiproliferative agent with potential for use in the therapy of patients with a compromised bone marrow and/or in combination chemotherapy.

Investigation of the mechanism of hepatotoxicity of N-methylformamide in mice: effects on calcium sequestration in hepatic microsomes and mitochondria and on hepatic plasma membrane potential

N-Methylformamide is an antitumour drug with hepatotoxic properties. Three potential targets for hepatocellular toxic lesions caused by N-methylformamide were investigated: the mitochondrial and microsomal Ca2+ pumps and the functional integrity of the plasma membrane. The administration of N-methylformamide to mice caused a dramatic decrease in the ability of the liver mitochondria to sequester [45Ca2+]. This effect was dose-dependent and was not caused by dimethylformamide, N-hydroxymethylformamide or formamide. The microsomal Ca2+ pump was not affected by N-methylformamide. Incubations of isolated mitochondria with N-methylformamide for 1 hr also led to the inhibition of the Ca2+ sequestration. Incubation of isolated mouse hepatocytes with N-methylformamide did not cause changes in plasma membrane potential as measured using the lipophilic cation triphenylmethylphosphonium. Of the three targets studied, the mitochondrial Ca2+ pump may be the one through which N-methylformamide triggers the events leading ultimately to hepatic necrosis.

In vivo metabolism of dimethylformamide and relationship to toxicity in the male rat

After in vivo administration of dimethylformamide (DMF) to male rats, about 50% of the dose is excreted in urine as N-hydroxymethyl-N-methylformamide (DMF-OH) and about 4% as N-methylformamide (NMF). NMF is not a product of DMF-OH biotransformation but is directly formed from DMF. Comparison of the acute toxicity of DMF, DMF-OH and NMF shows that NMF is more toxic than DMF-OH, which is itself more toxic than DMF. This study explains the different toxicity profile of DMF and NMF which until recently was believed to represent the main metabolite of DMF.

Reversal by L-cysteine of the growth inhibitory and glutathione-depleting effects of N-methylformamide and N,N-dimethylformamide

N-Methylformamide and N,N-dimethylformamide, which can induce differentiation in selected malignant cell lines, are known to increase doubling times, inhibit clonigenicity in agar, and to effect responses against particular human colon carcinomas in vivo. At concentrations which inhibit growth and clonigenicity, N-methylformamide (170 mM) and N,N-dimethylformamide (103 mM) deplete total intracellular glutathione levels of DLD-1 Clone A human colon carcinoma cells in a dose and time dependent manner. In the presence of 0.5 mM 1-cysteine, both the growth and glutathione levels of polar-solvent treated DLD-1 Clone A cells are restored. 1-Cysteine also reverses the inhibition of clonigenicity mediated by NMF. The mechanism of action of N-methylformamide and N,N-dimethylformamide against this cell line, at least in vitro, is therefore related to its effects on cysteine/glutathione metabolism. Furthermore, this evidence suggests that glutathione plays a key role in regulating the growth of these cells.