UNDERSTANDING DRUG-DRUG INTERACTION DUE TO ENZYMATIC INHIBITION USING IN VITRO APPROACHES.
interaction due to enzymatic inhibition is the focus of this research. Two different
projects to address separate questions of drug-drug interaction were carried out
applying the in vitro approaches. In the project 1, we generated a fuller picture on the
in vitro inhibitory effects of the selected anti-tuberculosis drugs on common human
hepatic CYP450 and UGT enzymes in ho... read morepe that these data may provide an in vitro basis for
understanding some clinical DDI observations and practice. Briefly, the comorbidities of
tuberculosis and diseases such as HIV require long-term treatment with multiple
medications. Despite extensively available in vitro and in vivo information on effects
of rifampicin and isoniazid on human CYPs, there is limited published data regarding the
inhibitory effects of other anti-TB drugs on human CYPs and UGTs. The inhibitory effects
of 5 first-line anti-TB drugs (isoniazid, rifampicin, pyrazinamide, ethambutol, and
rifabutin), and the newly approved bedaquiline, were evaluated for 6 common human
hepatic UGT enzymes (UGT1A1, 1A4, 1A6, 1A9, 2B7 and 2B15) in vitro using HLMs.
Pyrazinamide, ethambutol, rifabutin and bedaquiline were also studied for their
inhibitory effects on 8 of the most common human CYP enzymes (CYP1A2, 2B6, 2C8, 2C9,
2C19, 2D6, 2E1 and 3A). Rifabutin was observed in vitro to inhibit different CYPs to
varying degrees, but with all IC50 values exceeding 25 µM. Rifabutin and rifampicin
also inhibited several tested human UGTs. The Ki value for rifabutin on human hepatic
UGT1A4 was 2 μM. In addition, the 6 selected anti-TB drugs produced minimal
inhibition of acetaminophen glucuronidation suggesting that DDI between APAP and the
selected drugs is unlikely. In the project 2, the mechanism of the protective effects of
two flavonoids, namely luteolin and quercetin, on APAP induced hepatotoxicity was
investigated in the in vitro settings using HLMs. Acetaminophen is a common
over-the-counter analgesic and antipyretic. When overdosed, APAP can cause acute hepatic
necrosis. The key mechanism in APAP induced hepatotoxicity is the CYP450 catalyzed
formation of the reactive metabolite, N-acetyl-p-benzoquinone imine which depletes
hepatic glutathione and accumulates to cause excessive cellular oxidative stress. In
this study, we observed that luteolin and quercetin inhibited in vitro most of the
hepatic CYP450 enzyme isoforms including several key isoforms which are responsible to
the formation of NAPQI; both luteolin and quercetin strongly inhibited APAP sulfation.
In addition, although both luteolin and quercetin inhibited individually several UGT
isoforms in vitro, they didn't inhibit the overall APAP glucuronidation. Thus, the
beneficial effects of luteolin and quercetin against APAP induced hepatotoxicity
possibly result from their properties of being able to partially block the CYP-mediated
oxidation and to drive the reaction via APAP
Thesis (M.S.)--Tufts University, 2016.
Submitted to the Dept. of Pharmacology & Experimental Therapeutics.
Advisor: David Greenblatt.
Committee: Jeffrey Blumberg, Awewura Kwara, Louis Shuster, and Theoharis Theoharides.
Keywords: Pharmacology, and Health sciences.read less