Antagonistic reactions of arginine and lysine against formaldehyde and their relation to cell proliferation, apoptosis, folate cycle and photosynthesis.

1H, 13C NMR, ESMS and MS/MS investigations proved that there is an antagonism in the spontaneous reaction of formaldehyde with L-lysine and L-arginine. L-Arginine can only be hydroxymethylated on the guanidino group in a very fast reaction forming mono-, di-, and trihydroxymethyl arginines (HMA). L-Lysine can be methylated on the epsilon-amino group forming mono-, di-, and trimethyl lysine on physiological pH. Hydroxymethyl arginines are relative stable, isolable products, and can also be formed in biological systems, especially in plants. Significant amounts of hydroxymethyl arginines were identified in the aqueous extract of lyophilized kohlrabi, which can be formed in photosynthesis during CO2 fixation. 14C-Formaldehyde formed in a short-term (10, 30 sec) 14CO2 fixation reaction in Zea mays L. (early maturity variety: Szegedi TC 277) was captured by L-arginine, which occurs in leaves in large amount. Formaldehyde formed during photosynthesis can react not only with the arginine, but with ribulose-1,5-diphosphate present in leaves. In model reactions formaldehyde can react with the 'ene diole' group of ribulose-1,5-diphosphate in the absence of Rubisco enzyme, which is a similar reaction to the addition of formaldehyde to L-ascorbic acid. Hydroxymethyl arginines (HMA) are endogenous formaldehyde carrier molecules transferring the bound formaldehyde to thymidylate synthase enzyme system incorporating it into the folate cycle. HMA can also carry the bound formaldehyde to the cells especially to the tumorous cells (HT29 adenocarcinoma), and cause significant inhibition of cell proliferation and causes apoptosis.

Prognostic significance of the thymidylate biosynthetic enzymes in human colorectal tumors.

The aim of the present study was to determine the relative intratumoral activity of two pyrimidine biosynthetic enzymes, i.e. thymidylate synthase (TS) and thymidine kinase (TK), in human colorectal cancers to compare their possible relationship with demographic and pathologic characteristics of the patients and their tumors, and moreover to evaluate their predictive significance regarding 5-fluorouracil (5-FU) sensitivity and the overall survival of patients, respectively. TS and TK levels were significantly increased in the tumor compared to peritumoral tissue. However, no significant relationship between TS/TK activity and demographic features of the patients or pathologic characteristics of their tumors could be demonstrated. Kaplan-Meier analysis showed that the overall survival of patients with low TS activity was significantly longer (p < 0.012) compared to those with high TS activity. Such a difference could not be demonstrated between patients with high or low TK activity; however, combined evaluation of the two parameters proved that TK may contribute to the more precise assessment of disease prognosis, and it may further influence treatment decisions, i.e. the selection of patients for adjuvant therapy with 5-FU and folinic acid. Multivariate analysis showed that among the variables tested, beside Dukes' stage, TS and TK activities were significant prognostic factors for the overall survival of colorectal cancer patients.