Effects of Trypanothione on the Biological Activity of Irradiated Transforming DNA

Abstract

Held et al. (1984a,b) demonstrated previously that glutathione (GSH), a negatively charged thiol, is significantly less efficient in the hydrogen atom donation repair reaction with radicals induced by radiation in transforming DNA (t-DNA) than are other thiol compounds. Fahey et al. (1991a,b) postulated that the charge on thiols can influence their ability to radioprotect DNA. GSH, which is excluded from the vicinity of DNA due to its negative charge, is less protective than neutral or positively charged thiols. We have investigated this phenomenon further with trypanothione, the conjugate of glutathione and spermidine, N1,N8-bis (L-gamma-glutamyl-L-hemicystinyl-glycyl)-spermidine. Trypanothione exists in aerobic solution largely as the disulphide (T(S)2) but is maintained in the cell in the reduced form (T(SH)2) by means of an NADPH-dependent flavo-enzyme, trypanothione reductase (TR). Experimental data show that T(S)2 in the presence of TR radioprotects t-DNA in the absence of oxygen much better than GSH or spermidine alone or in combination. Little radioprotection by T(S)2 is seen when TR is not present. The results obtained with reduced trypanothione at low concentrations suggest that radioprotection of t-DNA in hypoxia occurs predominantly by H atom donation and slightly by .OH radical scavenging, and the protection is greater than that by GSH or spermidine because the polyamine moiety in trypanothione allows a greater concentration of GSH near the DNA molecule.

Phenotype of recombinant Leishmania donovani and Trypanosoma cruzi which over‐express trypanothione reductase

“…The action of these drugs could result from the formation of highly reactive radicals which then lead to damage to DNA, membrane lipids and other essential cellular components. In this context, the finding that T(SH), is a much better radioprotectant than GSH [43] may be significant.…”

Cloning and Characterization of the Two Enzymes Responsible for Trypanothione Biosynthesis in Crithidia fasciculata

“…The function of glutathionylspermidine in E. coli is unknown, but, since it only accumulates in stationary phase cells, it has been proposed that it might be involved in the regulation of intracellular levels of the precursors, spermidine and glutathione (21). Also, because of its net positive charge at physiological pH, glutathionylspermidine may be more effective at protecting DNA against radical-or oxidant-induced damage than negatively charged glutathione, as has been proposed for trypanothione (36). E. coli GSS has been shown to possess an amidase activity, permitting it to both synthesize and break down glutathionylspermidine (23).…”

Low-Molecular-Weight Thiols in Thiol–Disulfide Exchange

“…In addition to providing reducing equivalents to oxidoreductases, T(SH) 2 can also efficiently scavenge hydrogen peroxide, peroxynitrite and radiation-induced radicals (10,16,96). T(SH) 2 maintains the redox homeostasis by passing electrons to peroxidases via intermediate shuffle molecules, which can either be tryparedoxin, ascorbate, or even glutathione (17).…”