BACKGROUND : The essential amino acid tryptophan cannot be synthesised in the body and must be acquired
through dietary intake. Oxidation of tryptophan, due to immune induction of the enzyme indoleamine 2,3-
dioxygenase (IDO), is considered to be the main cause of tryptophan depletion in HIV infection and AIDS.
We examined plasma tryptophan levels in a low-income sub-Saharan HIV-infected population and compared it to
that of developed countries. Tryptophan levels were further examined in context of the general nutritional and
METHODS : This cross-sectional study included 105 HIV-positive patients recruited from the Kalafong Hospital in
Pretoria, South Africa, and 60 HIV-negative controls.
RESULTS : Patient tryptophan levels were in general markedly lower than those reported for developed countries. In
contrast to reports from developed countries that showed tryptophan levels on average to be 18.8 % lower than
their control values, tryptophan levels in our study were 44.1 % lower than our controls (24.4 ± 4.1 vs. 43.6 ±
11.9 μmol/l; p < 0.001). Tryptophan levels correlated with both CD4 counts (r = 0.341; p = 0.004) and with proinflammatory
activity as indicated by neopterin levels (r = −0.399; p = 0.0001). Nutritional indicators such as albumin
and haemoglobin correlated positively with tryptophan and negatively with the pro-inflammatory indicators
neopterin, interleukin 6 and C-reactive protein. The most probable causes of the lower tryptophan levels seen in
our population are food insecurity and higher levels of inflammatory activity.
CONCLUSIONS : We contend that inflammation-induced tryptophan depletion forms part of a much wider effect of
pro-inflammatory activity on the nutritional profile of HIV-infected patients.