The aromatic beta-carbolines norharman and harman have been implicated
in a number of human diseases including Parkinson's disease, tremor,
addiction and cancer. It has been shown that these compounds are normal
body constituents formed endogenously but external sources have been
identified. Here, we summarise literature data on levels of norharman
and harman in fried meat and fish, meat extracts, alcoholic drinks, and
coffee brews. Other sources include edible and medicinal plants but
tobacco smoke has been identified as a major source. Exposure levels
from these different dietary sources are estimated to a maximum of 4
microg norharman per kg body weight (bw) per day and 1 microg harman per
kg bw per day.
beta carboline
Exposure via tobacco smoke depends on smoking habits and type of
cigarettes but can be estimated to 1.1 microg/kg bw for norharman and
0.6 microg/kg bw for harman per package of cigarettes smoked. Studies on
toxicokinetics indicate that inhalative exposure leads to a rapid
increase in plasma levels and high bioavailability of norharman and
harman. Oral bioavailability is lower but there are indications that
sublingual absorption may increase dietary uptake of beta-carbolines.
Endogenous formation can be estimated to be 50-100 ng/kg bw per day for
norharman and about 20 ng/kg bw per day for harman but these rates may
increase with high intake of precursors. Biomarker studies on plasma
levels of beta-carbolines reported on elevated levels of norharman,
harman or both in diseased patients, alcoholics and following tobacco
smoking or consumption of beta-carboline-containing food. Cigarette
smoking has been identified as major influence but dietary exposure may
contribute to exposure.
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