Experiments using radiolabeled a-lipoic acid indicate
that the compound is absorbed. When 14C-labeled
lipoic acid was administered to rats, either as an IP
injection or orally, via stomach tube, 80% of the administered
radioactivity was either excreted or found
in the tissues. 64 This was true even in animals whose
intestinal flora had been killed, so it is unlikely that
the animals were absorbing metabolites produced by
bacteria in the gut.
The next question is how much of the ot-lipoic acid
is converted to DHLA intracellularly.
ot-Lipoic acid administered to a variety of cell and
tissue systems appears in the medium as DHLA. 65
However, the intracellular fate was unknown. In a
more recent study, l° lipoic acid was added to the culture
medium for human fibroblasts or Jurkat T-cells,
at concentrations from 1 to 4 mM. The concentrations