FREE AMINO ACIDS IN BLOOD. IV ATeE 
When the free amino acid pools are not reduced to such a marked extent, the cysteine— 
cystine level (as cysteic acid) may be increased in kidney, and glutathione may be 
increased in spleen and bone marrow at the peak of the peripheral blood cell response. 
Taurine levels of plasma, blood cells, and tissues always fell in both man and the 
rabbit after nitrogen mustard. The glutamine level is decreased in both species. 
Nitrogen mustard is thought by some to act on nucleic acids as a cross-linking 
agent. This was postulated because mustards with 2 reactive groups are much more 
effective than those with one reactive group. The reaction with nucleic acids 77 vivo 
does not appear to have been demonstrated in animals. It is our feeling that a highly 
reactive substance like nitrogen mustard that decomposes in water within a few 
minutes, disappears from the blood within minutes after intravenous injection, and 
shows such strong reactivity toward many functional groups when tested 7u vitro is 
unlikely to affect a single substance or enzyme system. On the other hand, it seems 
most probable that wide effects on enzymes and small molecules may be observed 
and that the particular sensitivity of certain functional groups related to their position 
or availability for interaction with nitrogen mustard may bring about or emphasize 
a reaction that might be thought to be less important on the basis of reactions ob- 
served in a test tube. 
WEISBERGER AND HEINLE*! have shown that cysteine administered to rabbits 
prior to intravenous injection of mustard exerts a marked protective effect. Leukocyte 
counts do not fall to the low levels observed with mustard alone. GOLDENTHAL et al.3” 
have observed the formation of a mustard-cysteine derivative both 7m vitro and in 
vivo and they suggest that the sparing effect of cysteine is due to direct interaction 
of cysteine with nitrogen mustard. This is a very attractive hypothesis in view of 
the actual formation of a reaction product of the two compounds and its excretion 
in the urine of mice. A direct interaction is indicated also by the observation that 
cysteine protects against the effects of mustard if injected before, but not after the 
injection of the drug. 
The marked changes in the levels of the sulfur compounds in blood and tissues in 
the present studies indicate marked effects on the metabolism of sulfur compounds. 
The very small amounts of mustard required to produce marked changes in humans 
make it apparent that the major effects of nitrogen mustard must be at the enzyme 
level. Many of the changes observed could be due to inhibition of activity of sulfhy- 
dryl dependent enzymes. The protective effect of cysteine is in keeping with this 
concept. Regardless of the mechanism, the marked fall in free amino acids of cells 
indicates marked changes in permeability with a decrease in the ability of cells to 
concentrate free amino acids. The increased levels of glutamic and aspartic acids 
may be explained by increased transamination of amino acids with a-ketoglutarate 
and oxalacetate from increased protein catabolism as a result of cell damage and 
death caused by nitrogen mustard. 
Chlorambucil produced a marked fall in free amino acids of plasma and cells as 
noted for nitrogen mustard. This drug has not been studied as extensively as nitrogen 
mustard, but the free amino acid changes suggest that some of the 7m vivo interactions 
may be the same for both compounds . 
The effects of phenylhydrazine ‘are quite different from those produced by both 
chlorambucil and nitrogen mustard since blood free amino acids are increased greatly 
by phenylhydrazine. The increase is even greater than the increase in free amino 
References p. 447/448 
