Complementary
HPLC, in silico toxicity, and molecular docking studies for
investigation of the potential influences of gastric acidity and nitrite
content on paracetamol safety
ABSTRACT
This study was initiated for investigating the possible gastro-transformations
that may affect the integrity and safety of the most commonly administered
analgesic and antipyretic, paracetamol (PCM). Revisiting the safety of
PCM has been accomplished by complementary HPLC, in silico toxicity prediction,
and molecular docking approaches. The potential influences of the gastric-nitrite
content on the chemistry of PCM were monitored via a simple and sensitive
HPLC-UV method utilizing methanol: 0.05 M NaH2PO4.2H2O (40: 60, v/v) pH 2.5 as the mobile phase and a C18 column. This study revealed the likely transformation of PCM to three
products which have been efficiently separated by the proposed HPLC method
and identified by LC-ESI+/MS as 3-nitroparacetamol (P1), 5-nitro-3,3′-diparacetamol
(P2), and 3,3′-diparacetamol (P3). The same products were also detected
under the WHO-recommended standard test to evaluate the vulnerability of
drugs to interaction with nitrite. The principle mechanism probably involves
the in situ conversion of nitrite to the radical form NO2 that induces subsequent PCM radical formation, nitration, and dimerization.
In silico toxicity prediction showed that P1 and P2 are mutagenic while
P3 has a reproductive toxicity and P1 has acute rat toxicity 2 folds greater
than PCM itself. P2 and P3 were also predicted to have androgenic toxicity
by competing with testosterone for the androgen receptors and blocking
the transmission of natural hormonal signal. The binding mode of the two
compounds to the androgenic receptors has been explored via molecular docking
study. Our results revealed the liability of PCM to generate three potentially
toxic products under the influence of gastric acidity and nitrite. This
encourages the co-administration of ascorbic acid with PCM to inhibit these
gastro-transformation reactions.