The role of folate coenzymes in the initiation of protein synthesis

Topical Sulfamylon cream inhibits DNA and protein synthesis in the skin donor site wound

BACKGROUND

Whereas Sulfamylon is effective in treatment of burn wound infection, controversy exists regarding its effect on the healing process.

METHODS

A partial thickness skin donor site wound was created on the back and indwelling catheters were placed in the carotid artery and jugular vein in rabbits under general anesthesia. Sulfamylon cream (8.5%, BERTEK Pharmaceuticals Inc., Morgantown, W Va) was applied on the wound, with either open or occlusive dressing. The control wound was covered with dressings only. On day 7 after injury, stable isotope tracers were infused to determine the fractional synthetic rate (FSR) of DNA, and FSR and fractional breakdown rate (FBR) of protein in the wound.

RESULTS

In the Sulfamylon-open dressing group, the DNA FSR was 1.3 +/- 0.6%/day, the protein FSR was 8.0 +/- 3.5%/day, and the net protein deposition (FSR - FBR) was -0.3 +/- 3.7%/day. These values were lower (P < .01 to .05) than the corresponding values in the control group (DNA FSR: 2.9 +/- 0.9%/day; protein FSR: 20.5 +/- 8.4%/day; net protein deposition: 7.9 +/- 6.0%/day). Sulfamylon cream selectively inhibited DNA FSR from the de novo base synthesis pathway (2.3 +/- 1.2 vs 0.8 +/- 0.5%/day, P < .05 vs control). With the occlusive dressing Sulfamylon cream did not decrease wound DNA FSR due to a stimulation of the base salvage pathway, but still decreased protein FSR (11.5 +/- 5.1%/day, P < .05 vs control). Histologic slides indicated that Sulfamylon cream inhibited re-epithelialization, collagen formation, and angiogenesis in the wound.

CONCLUSIONS

Topical Sulfamylon cream application inhibited DNA and protein synthesis in the wound, which would be expected to retard the healing process.

Trimethoprim action and its analogy with thymine starvation

In a minimal medium, trimethoprim is merely bacteriostatic on the prototroph Escherichia coli 114. The drug was bactericidal when the amino acids methionine and glycine, plus a purine or purine nucleoside, were also present. This response could be reversed completely when thymine and lysine were added to the culture. Methionine, glycine, and the purine are thought to maintain the integrity of the tetrahydrofolate pool under trimethoprim treatment and prevent the thymidylate synthetase reaction. Thus, the organism behaves phenotypically as a thymineless mutant. The mechanisms by which thymine and lysine reverse the bactericidal effect of trimethoprim in a minimal medium containing methionine, glycine, and adenine is discussed.