Methotrexate: studies on cellular metabolism. III.--Effect on the transplasma-membrane redox activity and on ferricyanide-induced proton extrusion by HeLa cells

Can pretreatment serum calcium level predict the efficacy of methotrexate in the treatment of severe plaque psoriasis?

BACKGROUND

The efficacy of methotrexate (MTX) varies in the treatment of psoriasis.

OBJECTIVE

We sought to identify an indicator from routine pretreatment tests to predict MTX efficacy in the treatment of psoriasis.

METHODS

In a retrospective analysis of 77 psoriatic patients, the correlation between MTX efficacy and pretreatment routine test results was analyzed with Spearman correlation. The potential risks were further evaluated with a linear regression model. Receiver operating characteristic analysis was performed to examine the effectiveness of serum total calcium (tCa) to predict the effect of MTX on psoriasis. The highest Youden index was used to determine the cutoff point, with which the positive and negative predictive values were calculated. Synergistic effects of MTX and calcium on keratinocyte growth and psoriasis-like mouse model were also investigated.

RESULTS

The pretreatment tCa level exhibited the closest association with MTX efficacy. The relative psoriasis improvement with tCa was 61.07% (95% confidence interval, 42.85-79.29; P < .001) and better improvements were observed in patients with higher tCa (r = 0.588; P < .002). MTX inhibited keratinocyte growth, which was enhanced synergistically by calcium. In a psoriasis-like mouse model, MTX strongly inhibited epidermis proliferation in the high-calcium group.

LIMITATIONS

One limitation of our study is the relatively small sample size.

CONCLUSION

Pretreatment tCa level has the highest correlation with MTX efficacy, which might be useful in predicting beneficial treatment results in psoriasis. Larger studies are required to confirm our findings.

Mechanism of the antimicrobial drug trimethoprim revisited

We tested the hypothesis that the mechanism of action of the antifolate drug trimethoprim is through accumulation of bacterial dihydrofolate resulting in depletion of tetrahydrofolate coenzymes required for purine and pyrimidine biosynthesis. The folate pool of a strain of Escherichia coli (NCIMB 8879) was prelabeled with the folate biosynthetic precursor [(3)H]-p-aminobenzoic acid before treatment with trimethoprim. Folates in untreated E. coli were present as tetrahydrofolate coenzymes. In trimethoprim-treated cells, however, a rapid transient accumulation of dihydrofolate occurred, followed by complete conversion of all forms of folate to cleaved catabolites (pteridines and para-aminobenzoylglutamate) and the stable nonreduced form of the vitamin, folic acid. Both para-aminobenzoylglutamate and folic acid were present in the cell in the form of polyglutamates. Removal of trimethoprim resulted in the reconversion of the accumulated folic acid to tetrahydrofolate cofactors for subsequent participation in the one-carbon cycle. Whereas irreversible catabolism is probably bactericidal, conversion to folic acid may constitute a bacteriostatic mechanism since, as we show, folic acid can be used by the bacteria and proliferation is resumed once trimethoprim is removed. Thus, the clinical effectiveness of this important drug may depend on the extent to which the processes of either catabolism or folic acid production occur in different bacteria or during different therapeutic regimes.

Methotrexate: pentose cycle and oxidative stress

The effect of methotrexate (MTX) and leucovorin (LCV) on pentose cycle enzymes and the activity of enzymes involved in enzyme defence mechanisms against ROS in HeLa cells, were studied. The effect of MTX was also investigated on the cellular levels of glutathione. MTX inhibited the activity of glucose-6-phosphate and 6-phosphogluconate dehydrogenases. The activities of glutathione reductase and gamma-glutamylcysteine synthetase were also inhibited by the drug. No effect was observed on the activities of catalase, superoxide dismutase or transketolase. LCV had no effect on any of the enzymes studied. MTX decreased the cellular levels of glutathione (70 per cent), while the presence of LCV and glutamine did not interfere with the effect of MTX. The net results appear to show that the biological situation resulting from treatment with MTX leads to a reduction of effectiveness of the antioxidant enzyme defence system.

Effect of methotrexate (MTX) on NAD(P)+ dehydrogenases of HeLa cells: malic enzyme, 2-oxoglutarate and isocitrate dehydrogenases

The effects of methotrexate (MTX) on oxygen uptake by permeabilized HeLa cells were evaluated. MTX did not inhibit state III respiration when the oxidizable substrate was succinate, but when the substrates were 2-oxoglutarate or isocitrate the respiration decreased about 50 per cent at 1.0 mM concentration of the drug. This effect was explained by inhibition of 2-oxoglutarate and isocitrate dehydrogenases by MTX. No effect was observed on succinate dehydrogenase. An evaluation of the effects of MTX on malic enzyme activity as measured by pyruvate plus lactate production in intact cells supplied with malate showed a decrease of about 40 per cent in metabolite production using 0.4 mM MTX. HeLa cell malic enzyme, as observed for other tumour cells, is compartmentalized in mitochondria and cytosol, and is another example of a dehydrogenase inhibited by MTX.

Activation of glycogenolysis by methotrexate. Influence of calcium and inhibitors of hormone action

The influence of Ca2+ and the possible action of hormone blockers on the activation of glycogenolysis by methotrexate were investigated. Methotrexate was inactive on glycogenolysis and oxygen uptake when the liver, depleted of intracellular Ca2+, was perfused with Ca(2+)-free medium. The action of methotrexate in calcium-depleted hepatocytes could be restored by the addition of extracellular Ca2+. When Ca2+ was absent in the extracellular medium, but the intracellular stores were not depleted, methotrexate produced transient and progressively attenuated increases in glycogenolysis and oxygen uptake. Like many agonists, methotrexate produced transient increases in Ca2+ efflux. The action of methotrexate was not blocked by the antagonists of norepinephrine, phenylephrine, isoproterenol, vasopressin and angiotensin II. It was concluded that methotrexate acts through a Ca(2+)-dependent mechanism, which is similar to that of the Ca(2+)-dependent agonists. This action, however, seems not to be receptor mediated.

D-glyceraldehyde-3-phosphate dehydrogenase from HeLa cells--2. Immunological characterization

1. An immunological relationship between GPDH from HeLa cells and those from other phylogenetically different sources was carried out. 2. It was found that HeLa cell anti-GPDH antibody presented an immunological cross-reaction specificity with GPDH from HeLa cells, Caiman sp. muscle and human mammary tumor tissue and a partial one with GPDH from Anas sp. muscle.

D-glyceraldehyde-3-phosphate dehydrogenase from HeLa cells--1. Purification and properties of the enzyme

1. D-GPDH from HeLa cells was isolated and purified. 2. Some basic kinetic constants are reported. 3. Sodium dodecyl polyacrylamide gel electrophoresis gave a single band with a molecular weight of approximately 36 K. 4. ATP and NADH inhibit competitively enzyme activity. 5. Comparative catalytic properties of GPDH from normal and tumor cells were effectuated.

Methotrexate: studies on cellular metabolism. IV. Effect on the mitochondrial oxidation of cytosolic-reducing equivalents in HeLa cells

The effect of methotrexate (MTX) on the mitochondrial oxidation of cytosolic-reducing equivalents in HeLa cells was studied. MTX inhibited (100 per cent) malate dehydrogenase activity, but no effect was observed on that of GOT. MTX (0.5 mM) inhibited (100 per cent) the activity of reconstituted enzymatic system MDH-GOT, probably as a consequence of inhibition of malate dehydrogenase activity. MTX decreased pyruvate production (54 per cent), demonstrating its inhibitory action on the malate-aspartate shuttle. Blockage of the malate-aspartate shuttle by MTX accounts for the decrease in cellular energetic gain. The results obtained are consistent with the view that in HeLa cells, as well as in other tumour cells, the transport of reducing equivalents from cytoplasmic NADH into the respiratory chain of mitochondria is via the malate-aspartate shuttle.