Hypoxia-Induced Changes in L-Cysteine Metabolism and Antioxidative Processes in Melanoma Cells

This study was performed on human primary (WM115) and metastatic (WM266-4) melanoma cell lines developed from the same individual. The expression of proteins involved in L-cysteine metabolism (sulfurtransferases, and cystathionine β-synthase) and antioxidative processes (thioredoxin, thioredoxin reductase-1, glutathione peroxidase, superoxide dismutase 1) as well as the level of sufane sulfur, and cell proliferation under hypoxic conditions were investigated. Hypoxia in WM115 and WM266-4 cells was confirmed by induced expression of carbonic anhydrase IX and 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 4 by the RT-PCR and Western blot methods. It was shown that, under hypoxic conditions the inhibition of WM115 and WM266-4 melanoma cell proliferation was associated with decreased expression of thioredoxin reductase-1 and cystathionine β-synthase. These two enzymes may be important therapeutic targets in the treatment of melanoma. Interestingly, it was also found that in normoxia the expression and activity of 3-mercaptopyruvate sulfurtransferase in metastatic WM266-4 melanoma cells was significantly higher than in primary melanoma WM115 cells.

Sulfurtransferases and Cystathionine Beta-Synthase Expression in Different Human Leukemia Cell Lines

The studies concerned the expression of sulfurtransferases and cystathionine beta-synthase in six human leukemia cell lines: B cell acute lymphoblastic leukemia-B-ALL (REH cells), T cell acute lymphoblastic leukemia-T-ALL (DND-41 and MOLT-4 cells), acute myeloid leukemia—AML (MV4-11 and MOLM-14 cells), and chronic myeloid leukemia—CML (K562 cells). Reverse transcription-polymerase chain reaction (RT-PCR) and Western blot analysis were performed to determine the expression of thiosulfate sulfurtransferase, 3-mercaptopyruvate sulfurtransferase, gamma-cystathionase, and cystathionine beta-synthase on the mRNA and protein level. Interestingly, we found significant differences in the mRNA and protein levels of sulfurtransferases and cystathionine beta-synthase in the studied leukemia cells. The obtained results may contribute to elucidating the significance of the differences between the studied cells in the field of sulfur compound metabolism and finding new promising ways to inhibit the proliferation of various types of leukemic cells by modulating the activity of sulfurtransferases, cystathionine beta-synthase, and, consequently, the change of intracellular level of sulfane sulfur as well as H₂S and reactive oxygen species production.

Sulfur Administration in Fe-S Cluster Homeostasis

Mitochondria are the key organelles of Fe–S cluster synthesis. They contain the enzyme cysteine desulfurase, a scaffold protein, iron and electron donors, and specific chaperons all required for the formation of Fe–S clusters. The newly formed cluster can be utilized by mitochondrial Fe–S protein synthesis or undergo further transformation. Mitochondrial Fe–S cluster biogenesis components are required in the cytosolic iron–sulfur cluster assembly machinery for cytosolic and nuclear cluster supplies. Clusters that are the key components of Fe–S proteins are vulnerable and prone to degradation whenever exposed to oxidative stress. However, once degraded, the Fe–S cluster can be resynthesized or repaired. It has been proposed that sulfurtransferases, rhodanese, and 3-mercaptopyruvate sulfurtransferase, responsible for sulfur transfer from donor to nucleophilic acceptor, are involved in the Fe–S cluster formation, maturation, or reconstitution. In the present paper, we attempt to sum up our knowledge on the involvement of sulfurtransferases not only in sulfur administration but also in the Fe–S cluster formation in mammals and yeasts, and on reconstitution-damaged cluster or restoration of enzyme’s attenuated activity.

Combination of ERK2 and STAT3 Inhibitors Promotes Anticancer Effects on Acute Lymphoblastic Leukemia Cells

BACKGROUND/AIM

Deregulated activation of signaling through the RAS/RAF/mitogen-activated protein kinase/extracellular signal-regulated kinase (RAS/RAF/MEK/ERK) and signal transducer and activator of transcription (STAT) pathways is involved in numerous hematological malignancies, making it an attractive therapeutic target. This study aimed to assess the effect of the combination of ERK2 inhibitor VX-11e and STAT3 inhibitor STA-21 on acute lymphoblastic leukemia cell lines REH and MOLT-4.

MATERIALS AND METHODS

REH and MOLT-4 cell lines were cultured with each drug alone and in combination. Cell viability, ERK activity, cell cycle distribution, apoptosis and oxidative stress induction were assessed by flow cytometry. Protein levels of STAT3, phospho-STAT3, protein tyrosine phosphatase 4A3 (PTP4A3), survivin, p53 and p21 were determined by western blotting.

RESULTS

VX-11e in combination with STA-21 significantly inhibited cell viability, induced G₀/G₁ cell-cycle arrest, enhanced production of reactive oxygen species, and induced apoptosis. These effects were associated with an increased level of p21 protein in REH cells and with reduced levels of phopho-STAT3, survivin and PTP4A3 proteins in MOLT-4 cells.

CONCLUSION

Our findings provide a rationale for combined inhibition of RAS/RAF/MEK/ERK and STAT3 pathways in order to enhance anticancer effects against acute lymphoblastic leukemia cells.

Identification of Taurine-Responsive Genes in Murine Liver Using the Cdo1-Null Mouse Model

The cysteine dioxygenase (Cdo1)-null mouse is unable to synthesize hypotaurine and taurine by the cysteine/cysteine sulfinate pathway and has very low taurine levels in all tissues. The lack of taurine is associated with a lack of taurine conjugation of bile acids, a dramatic increase in the total and unconjugated hepatic bile acid pools, and an increase in betaine and other molecules that serve as organic osmolytes. We used the Cdo1-mouse model to determine the effects of taurine deficiency on expression of proteins involved in sulfur amino acid and bile acid metabolism. We identified cysteine sulfinic acid decarboxylase (Csad), betaine:homocysteine methytransferase (Bhmt), cholesterol 7α-hydroxylase (Cyp7a1), and cytochrome P450 3A11 (Cyp3a11) as genes whose hepatic expression is strongly regulated in response to taurine depletion in the Cdo1-null mouse. Dietary taurine supplementation of Cdo1-null mice restored hepatic levels of these four proteins and their respective mRNAs to wild-type levels, whereas dietary taurine supplementation had no effect on abundance of these proteins or mRNAs in wild-type mice.

Cystathionine Promotes the Proliferation of Human Astrocytoma U373 Cells

BACKGROUND/AIM

In certain cancers, accumulation of cystathionine has been observed. The present study investigated the effect of cystathionine on astrocytoma (U373) cell proliferation, the activity of γ-cystathionase (CTH) and changes in thiols levels.

MATERIALS AND METHODS

The methods used in the study included cytotoxicity assay, crystal violet staining method, CTH activity assay and reverse phase-high performance liquid chromatography (RP-HPLC).

RESULTS

The addition of cystathionine to the culture medium resulted in an increase of cystathionine level in U373 cells after 24 h of culture. Reduction of intracellular cystathionine level after 48 and 72 h of culture was associated with increased L-cysteine and L-cystine levels and stimulation of cell proliferation. Interestingly, a decrease in intracellular L-cysteine and L-cystine levels during the first hours of culture was observed.

CONCLUSION

Elevated levels of cystathionine resulted in increased U373 cell proliferation by increasing the L-cysteine levels and GSH/GSSG ratio (especially after 72 h of the culture), but not with a simultaneous increase in the levels of total glutathione.

New aspects of antiproliferative activity of 4-hydroxybenzyl isothiocyanate, a natural H2S-donor

The effect of 4-hydroxybenzyl isothiocyanate (HBITC), a natural H₂S-donor from white mustard seeds (Sinapis alba), on the proliferation of human neuroblastoma (SH-SY5Y) and glioblastoma (U87MG) cells was studied and some aspects of the mechanism of its activity were suggested. The inhibition of both SH-SY5Y and U87MG cell proliferation was associated with an increase in the thiosulfate level, the number of cells with the inactive form of Bcl-2 protein, and with a decrease of mitochondrial membrane potential. Interestingly, HBITC results in downregulation of p53 protein and upregulation of p21 protein levels in SH-SY5Y cells. In the presence of elevated levels of H₂S and thiosulfate, the sulfhydryl groups of p53 protein as well as Bcl-2 protein could be modified via HBITC-induced S-sulfuration or by oxidative stress. It seems that the induction of p21 protein level is mediated in SH-SY5Y cells by p53-independent mechanisms. In addition, HBITC-treatment caused downregulation of the level of mitochondrial rhodanese and 3-mercaptopyruvate sulfurtransferase, and consequently increased the level of the reactive oxygen species in SH-SY5Y cells.

Colonic hydrogen sulfide produces portal hypertension and systemic hypotension in rats

Hydrogen sulfide, a toxic gas, at low concentrations is also a biological mediator in animals. In the colon, hydrogen sulfide is produced by intestinal tissues and gut sulfur bacteria. Gut-derived molecules undergo liver metabolism. Portal hypertension is one of the most common complications contributing to the high mortality in liver cirrhosis. We hypothesized that the colon-derived hydrogen sulfide may affect portal blood pressure. Sprague-Dawley rats were maintained either on tap water (controls) or on water solution of thioacetamide to produce liver cirrhosis (CRH-R). Hemodynamics were measured after administration of either saline or Na₂S, a hydrogen sulfide donor, into (1) the colon, (2) the portal vein, or (3) the femoral vein. Expression of enzymes involved in hydrogen sulfide metabolism was measured by RT-PCR. CRH-R showed a significantly higher portal blood pressure but a lower arterial blood pressure than controls. Saline did not affect hemodynamic parameters. In controls, intracolonic hydrogen sulfide decreased arterial blood pressure and portal blood flow but increased portal blood pressure. Similarly, hydrogen sulfide administered into the portal vein decreased arterial blood pressure but increased portal blood pressure. In contrast, hydrogen sulfide administered into the systemic vein decreased both arterial and portal blood pressures. CRH-R showed significantly greater responses to hydrogen sulfide than controls. CRH-R had a significantly higher liver concentration of hydrogen sulfide but lower expression of rhodanese, an enzyme converting hydrogen sulfide to sulfate. In conclusion, colon-administered hydrogen sulfide increases portal blood pressure while decreasing the systemic arterial blood pressure. The response to hydrogen sulfide is more pronounced in cirrhotic rats which show reduced hydrogen sulfide liver metabolism. Therefore, colon-derived hydrogen sulfide may be involved in the regulation of portal blood pressure, and may contribute to portal hypertension. Impact statement Accumulating evidence suggests that gut-derived molecules affect the control of the circulatory system. Mechanisms controlling liver circulation have been profoundly studied; however, the effects of gut bacteria-derived molecules on portal blood pressure have not been established. In the colon, hydrogen sulfide is produced by intestinal tissues and gut sulfur bacteria. We found that colon-administered hydrogen sulfide increases portal blood pressure while decreasing the systemic arterial blood pressure. The hemodynamic response to hydrogen sulfide was more pronounced in cirrhotic rats which showed reduced hydrogen sulfide liver metabolism, i.e. lower expression of rhodanese, an enzyme converting hydrogen sulfide to sulfate. We propose that colon-derived hydrogen sulfide may affect the regulation of portal and arterial blood pressures and may be involved in portal hypertension.

A possible mechanism of inhibition of U87MG and SH-SY5Y cancer cell proliferation by diallyl trisulfide and other aspects of its activity

The study was conducted to elucidate the mechanism of antiproliferative and antioxidative action of diallyl trisulfide (DATS), a garlic-derived organosulfur compound. Changes in the l-cysteine desulfuration, and the levels of cystathionine and non-protein thiols in DATS-treated human glioblastoma (U87MG) and neuroblastoma (SH-SY5Y) cells were investigated. The inhibition of proliferation of the investigated cells by DATS was correlated with an increase in the inactivated form of Bcl-2. In U87MG cells, an increased level of sulfane sulfur and an increased activity of 3-mercaptopyruvate sulfurtransferase (MPST) and rhodanese, the enzymes involved in sulfane sulfur generation and transfer, suggest that DATS can function as a donor of sulfane sulfur atom, transferred by sulfurtransferases, to sulfhydryl groups of cysteine residues of Bcl-2 and in this way lower the level of active form of Bcl-2 by S-sulfuration. Diallyl trisulfide antioxidative effects result from an increased level of cystathionine, a precursor of cysteine, and an increased glutathione level. MPST and rhodanese, the level of which is increased in the presence of DATS, can serve as antioxidant proteins.

Na2S, a fast-releasing H2S donor, given as suppository lowers blood pressure in rats

BACKGROUND

Hydrogen sulfide (H₂S) is involved in blood pressure control. The available slow-releasing H₂S-donors are poorly soluble in water and their ability to release H₂S in biologically relevant amounts under physiological conditions is questionable. Therefore, new slow-releasing donors or new experimental approaches to fast-releasing H₂S donors are needed.

METHODS

Hemodynamics and ECG were recorded in male, anesthetized Wistar Kyoto rats (WKY) and in Spontaneously hypertensive rats (SHR) at baseline and after: 1) intravenous (iv) infusion of vehicle or Na₂S; 2) administration of vehicle suppositories or Na₂S suppositories.

RESULTS

Intravenously administered vehicle and vehicle suppositories did not affect mean arterial blood pressure (MABP) and heart rate (HR). Na₂S administered iv caused a significant, but transient (2-5min) decrease in MABP. Na₂S suppositories produced a dose-dependent hypotensive response that lasted ∼45min in WKY and ∼75-80min in SHR. It was accompanied by a decrease in HR in WKY, and an increase in HR in SHR. Na₂S suppositories did not produce a significant change in corrected QT, an indicator of cardiotoxicity. Na₂S suppositories increased blood level of thiosulfates, products of H₂S oxidation.

CONCLUSIONS

Na₂S administered in suppositories exerts a prolonged hypotensive effect in rats, with no apparent cardiotoxic effect. SHR and WKY differ in hemodynamic response to the H₂S donor. Suppository formulation of fast-releasing H₂S donors may be useful in research, if a reference slow-releasing H₂S donor is not available.

Downregulation of hepatic betaine:homocysteine methyltransferase (BHMT) expression in taurine-deficient mice is reversed by taurine supplementation in vivo

The cysteine dioxygenase (Cdo1)-null and the cysteine sulfinic acid decarboxylase (Csad)-null mouse are not able to synthesize hypotaurine/taurine by the cysteine/cysteine sulfinate pathway and have very low tissue taurine levels. These mice provide excellent models for studying the effects of taurine on biological processes. Using these mouse models, we identified betaine:homocysteine methyltransferase (BHMT) as a protein whose in vivo expression is robustly regulated by taurine. BHMT levels are low in liver of both Cdo1-null and Csad-null mice, but are restored to wild-type levels by dietary taurine supplementation. A lack of BHMT activity was indicated by an increase in the hepatic betaine level. In contrast to observations in liver of Cdo1-null and Csad-null mice, BHMT was not affected by taurine supplementation of primary hepatocytes from these mice. Likewise, CSAD abundance was not affected by taurine supplementation of primary hepatocytes, although it was robustly upregulated in liver of Cdo1-null and Csad-null mice and lowered to wild-type levels by dietary taurine supplementation. The mechanism by which taurine status affects hepatic CSAD and BHMT expression appears to be complex and to require factors outside of hepatocytes. Within the liver, mRNA abundance for both CSAD and BHMT was upregulated in parallel with protein levels, indicating regulation of BHMT and CSAD mRNA synthesis or degradation.

Propargylglycine inhibits hypotaurine/taurine synthesis and elevates cystathionine and homocysteine concentrations in primary mouse hepatocytes

Our investigation showed that hepatocytes isolated from cysteine dioxygenase knockout mice (Cdo1^−/−) had lower levels of hypotaurine and taurine than Cdo1^+/+ hepatocytes. Interestingly, hypotaurine accumulates in cultured wild-type hepatocytes. dl-propargylglycine (PPG, inhibitor of cystathionine γ-lyase and H₂S production) dramatically decreased both taurine and hypotaurine levels in wild-type hepatocytes compared to untreated cells. Addition of 2 mM PPG resulted in the decrease of the intracellular taurine levels: from 10.25 ± 5.00 observed in control, to 2.53 ± 0.68 nmol/mg protein (24 h of culture) and from 17.06 ± 9.40 to 2.43 ± 0.26 nmol/mg protein (control vs. PPG; 48 h). Addition of PPG reduced also intracellular hypotaurine levels: from 7.46 ± 3.55 to 0.31 ± 0.12 nmol/mg protein (control vs. PPG; 24 h) and from 4.54 ± 3.20 to 0.42 ± 0.11 nmol/mg protein (control vs. PPG; 48 h). The similar effects of PPG on hypotaurine and taurine levels were observed in culture medium. PPG blocked hypotaurine/taurine synthesis in wild-type hepatocytes, suggesting that it strongly inhibits cysteinesulfinate decarboxylase (pyridoxal 5′-phosphate-dependent enzyme) as well as cystathionine γ-lyase. In the presence of PPG, intracellular and medium cystathionine levels for both wild-type and Cdo1^−/− cells were increased. Addition of homocysteine or methionine resulted in higher intracellular concentrations of homocysteine, which is a cosubstrate for cystathionine β-synthase (CBS). It seems that PPG increases CBS-mediated desulfhydration by enhancing homocysteine levels in hepatocytes. There were no overall effects of PPG or genotype on intracellular or medium glutathione levels.

Primary hepatocytes from mice lacking cysteine dioxygenase show increased cysteine concentrations and higher rates of metabolism of cysteine to hydrogen sulfide and thiosulfate

The oxidation of cysteine in mammalian cells occurs by two routes: a highly regulated direct oxidation pathway in which the first step is catalyzed by cysteine dioxygenase (CDO) and by desulfhydration-oxidation pathways in which the sulfur is released in a reduced oxidation state. To assess the effect of a lack of CDO on production of hydrogen sulfide (H2S) and thiosulfate (an intermediate in the oxidation of H2S to sulfate) and to explore the roles of both cystathionine γ-lyase (CTH) and cystathionine β-synthase (CBS) in cysteine desulfhydration by liver, we investigated the metabolism of cysteine in hepatocytes isolated from Cdo1-null and wild-type mice. Hepatocytes from Cdo1-null mice produced more H2S and thiosulfate than did hepatocytes from wild-type mice. The greater flux of cysteine through the cysteine desulfhydration reactions catalyzed by CTH and CBS in hepatocytes from Cdo1-null mice appeared to be the consequence of their higher cysteine levels, which were due to the lack of CDO and hence lack of catabolism of cysteine by the cysteinesulfinate-dependent pathways. Both CBS and CTH appeared to contribute substantially to cysteine desulfhydration, with estimates of 56 % by CBS and 44 % by CTH in hepatocytes from wild-type mice, and 63 % by CBS and 37 % by CTH in hepatocytes from Cdo1-null mice.

Effect of histone deacetylase inhibitors trichostatin A and valproic acid on etoposide-induced apoptosis in leukemia cells

BACKGROUND

Histone deacetylase inhibitors (HDACi) have been extensively studied as potential candidates for treatment of various malignancies, including leukemia, since they not only induce growth inhibition, cell cycle arrest and apoptosis of cancer cells, but can also increase the sensitivity of cancer cells to chemotherapeutic drugs. The aim of this study was to investigate the effect of two HDACi, trichostatin A (TSA) and valproic acid (VPA), on etoposide-induced apoptosis in human leukemia cell lines.

MATERIALS AND METHODS

Viability, apoptosis rate, caspase activity, mitochondrial membrane potential and expression of BCL2 mRNA were assessed in HL60 and U937 cell lines treated with 250 nM TSA or 1.25 mM VPA alone or followed by 5 μM etoposide.

RESULTS

Preincubation of HL60 cells with TSA or VPA significantly potentiated etoposide-induced cytotoxicity and apoptosis, which was associated with activation of caspases and loss of mitochondrial membrane potential. Similar effects were not observed in U937 cells. Expression of BCL2 mRNA was strongly down-regulated after treatment of cells with HDACi alone but did not show additive effect with etoposide.

CONCLUSION

Combination of HDACi with etoposide can have a synergistic effect on increased apoptosis in leukemia cells but this effect depends on the cancer cell type and other factors such as the concentration of drugs and the administration schedule.

The expression and activity of cystathionine-γ-lyase and 3-mercaptopyruvate sulfurtransferase in human neoplastic cell lines

The expression and activity of cystathionine γ-lyase (CST) and 3-mercaptopyruvate sulfurtransferase (MPST) were investigated in the human neoplastic cells lines: astrocytoma U373, neuroblastoma SH-SY5Y, melanoma A375, and melanoma WM35. Gene expression analysis demonstrated that the investigated neoplastic cells showed the expression of MPST and what is particularly interesting, the expression of CST. The presence of CST in these cells was confirmed using RT-PCR and western blot analysis. However, in U373 cells, a very low activity of CST was detected. In all the investigated cell lines, the activity of MPST was higher than that of CST, which suggests that in these cells, the main pathway of sulfane sulfur formation is the MPST-catalyzed reaction. RP-HPLC analysis showed a large disparity between the level of cystathionine and GSH in the investigated neoplastic cells. In SH-SY5Y cells, the low level of GSH and low GSH/GSSG ratio corresponded with the highest CST activity. Further investigations could aim at verifying whether the stimulation of CST, at the level of protein or gene expression, could change the proliferation of neoplastic cells.

Menadione effect on l-cysteine desulfuration in U373 cells

The non-cytotoxic concentration (20 microM) of menadione (2-methyl-1,4-naphthoquinone), after 1 h of incubation, leads to loss of the activity of rhodanese by 33%, 3-mercaptopyruvate sulfurtransferase by 20%, as well as the level of sulfane sulfur by about 23% and glutathione by 12%, in the culture of U373 cells, in comparison with the control culture. Reactive oxygen species generated by menadione oxidize sulfhydryl groups in active centers of the investigated enzymes, inhibiting them and saving cysteine for glutathione synthesis. A decreased sulfane sulfur level can be correlated with an oxidative stress.

N-acetyl-L-cysteine as a source of sulfane sulfur in astrocytoma and astrocyte cultures: correlations with cell proliferation

N-acetyl-L-cysteine (NAC), a precursor of L-cysteine, not only elevates the level of glutathione in both astrocytoma and astrocyte cultures, but also affects the cellular level of sulfane sulfur. Astrocytoma cells were investigated using the stable U373 human cell line. In the U373 cells, N-acetyl-L-cysteine, depending on the concentration in the culture medium and culture duration, either elevated or diminished the level of sulfane sulfur, and this was respectively accompanied by decreased or increased cellular proliferation. In murine astrocytes, in turn, NAC was capable of lowering the level of sulfane sulfur and in this way decreased cellular proliferation. It seems that normal (astrocyte) and transformed (astrocytoma) cells differed in their reaction to NAC in the culture medium. The effect of N-acetyl-L-cysteine on astrocytoma cells was advantageous in that it inhibited their proliferation through the elevation of the level of sulfane sulfur.

Menadione effect on l-cysteine desulfuration in U373 cells

The non-cytotoxic concentration (20 microM) of menadione (2-methyl-1,4-naphthoquinone), after 1 h of incubation, leads to loss of the activity of rhodanese by 33%, 3-mercaptopyruvate sulfurtransferase by 20%, as well as the level of sulfane sulfur by about 23% and glutathione by 12%, in the culture of U373 cells, in comparison with the control culture. Reactive oxygen species generated by menadione oxidize sulfhydryl groups in active centers of the investigated enzymes, inhibiting them and saving cysteine for glutathione synthesis. A decreased sulfane sulfur level can be correlated with an oxidative stress.

Rhodanese in mouse brain: regional differences and their metabolic implications

Our results concern the regional localization of rhodanese in the mouse brain. A histoenzymatic examination was undertaken in telencephalon, diencephalon, mesencephalon, and rhombencephalon. The sites of rhodanese activity are revealed as punctuate, granular, dark dots, small in some regions such as hippocampus or bigger in others, and as long, thread-like particles especially, abundant in the region of the telencephalon in the astroglia cells and in the region of the mesencephalon in the hippocampus. There were sites with a high density of the histochemical test products, for example, the ependymoma of the forth cerebral ventricle, choroid plexus, and nerve ducts. These findings support the detoxifying role of rhodanese in brain regions.