In Vitro Evaluation of Reversible and Time-Dependent Inhibitory Effects of Kalanchoe crenata on CYP2C19 and CYP3A4 Activities

Abstract

Kalanchoe crenata popularly known as “dog’s liver” is used in most African countries for the treatment of chronic diseases such as diabetes, asthma and HIV/AIDS related infections. The evaluation of K. crenata for herb-drug interactions has not been reported. This study therefore aims to evaluate the risk of K. crenata for herb-drug interaction in vitro. Crude methanol and fractions of K. crenata were incubated and preincubated with recombinant human CYP2C19 and CYP3A4. Comparative studies were conducted in both human liver microsomes and recombinant human CYP to ascertain the inhibition profile of the crude extract and the various fractions. The cocktail approach of recombinant human CYPs was conducted to confirm the inhibition potential of the fractions in the presence of other CYPs. The results showed significant time-dependent inhibition of tested samples on CYP3A4 with crude methanol (39KC), fractions 45A, 45B and 45D given IC50 fold decrease of 3.29, 2.26, 1.91 and 1.49, respective. Time dependent kinetic assessment of 39KC and 45D showed KI and kinact values for 39KC as 1.77µg/mL and 0.091 min-1 while that of 45D were 6.45 µg/mL and 0.024 min-1, respectively. Determination of kinact based on IC50 calculations yielded 0.015 and 0.04 min-1 for 39KC and 45D, respectively. Cocktail approach exhibited fold decreases in IC50 for all test fractions on CYP3A4 within the ranges of 2.10 – 4.10. At least one phytoconstituent in the crude methanol extract of Kalanchoe crenata is a reversible and time-dependent inhibitor of CYP3A4.

Critical evaluation of causality assessment of herb–drug interactions in patients

“…In most instances, in vitro and animal studies are conducted to evaluate the effect of herbal extracts and phytochemical constituents on pharmacokinetic and pharmacodynamic properties of probe drugs [16][17][18][19][20][21][22]. However, preclinical investigations often do not correlate with findings in human subjects [23][24][25][26][27].…”

In Vitro Reversible and Time-Dependent CYP450 Inhibition Profiles of Medicinal Herbal Plant Extracts Newbouldia laevis and Cassia abbreviata: Implications for Herb-Drug Interactions

“…Due to the multi-phyto nature of herbals, their bio-availabilities are variable depending on the constituents [24]. Prediction of in vivo HDI using in vitro results [21,23,35,36] gives preliminary information that can caution patients to be wary of combination therapies of herbals with conventional medications and also for pharmaceutical companies and researchers to get baseline information guiding further investigation. For herbal extracts that are already in use, HDI studies allow assessment of risk, helping with the design of in vivo HDI studies and revision of product labels to highlight the risk of co-use of these herbs with conventional medication, as in the case of Saint John′s Wort and the protease inhibitor indinavir [37].…”

“…The natural logarithm of the percentage remaining activity was plotted against the pre-incubation times at each extract concentration to obtain K obs (slope) as employed by Awortwe et al [36]. K obs depicts the rate constant describing the inactivation at each inhibitor (extract) concentration.…”

Inhibitory Effects of Schisandra Lignans on Cytochrome P450s and Uridine 5′-Diphospho-Glucuronosyl Transferases in Human Liver Microsomes

“…We investigated the effect of incubation time on the IC 50 values of six lignans on nine P450s (Table 3). A test compound with an IC 50 fold-shift decrease ≥ 1.5 is considered to be a time-dependent inhibitor as recommended by Awortwe et al [39]. Previous studies have shown that gomisin A, -B, -C, and -N inhibit CYP3A activity in a time-and NADPH-dependent manner when co-incubated with HLMs or rP450s [21,35,36].…”