Co. Enwonwu et al., Increased plasma levels of histidine and histamine in falciparum malaria: relevance to severity of infection, J NEURAL TR, 107(11), 2000, pp. 1273-1287
Severe falciparum malaria, with its associated hyperpyrexia, distorts plasm
a levels of large neutral amino acids (NAA) and consequently, brain uptake
of individual NAA. Since brain levels of NAA determine cerebral synthesis o
f monoamines (serotonin, histamine, catecholamines), we measured plasma con
centrations of NAA, and also plasma histamine (Hm) in children with falcipa
rum malaria and in uninfected controls. Malaria elicited a marked (P < 0.02
5) increase in plasma histidine (His) with a 5-fold significant (P < 0.001)
elevation in histamine, as well as a 2.5-fold increase (P < 0.005) in plas
ma phenylalanine (Phe), with no changes in the other NAA. Using kinetic par
ameters of NAA transport at human blood-brain barrier (BBB), we showed that
malaria significantly altered calculated brain uptake of His (+30%), Phe (
+96%), Trp (-30%) and Ile (-27%), with no change in the other NAA, compared
with controls. Our data suggested enhanced cerebral synthesis of Hm with i
mpaired production of serotonin and the catecholamines in the patients, and
therefore, the need to evaluate the encephalopathy in severe malaria withi
n the context of abnormalities in metabolism of Hm and other monoamines res
ulting from imbalance in plasma levels of the large neutral amino acids. Of
clinical relevance also is the impaired inactivation of increased brain Hm
by antimalarials such as the widely used aminoisoquinolines leading to ele
vated brain levels of imidazole-4-acetic acid (IAA), a potent inducer of a
sleep-like state often accompanied by seizures, analgesia, decreased blood
pressure and other effects.