Differential effects of ethanol on spectral binding and inhibition of cytochrome P450 3A4 with eight protease inhibitors antiretroviral drugs.

CYTOCHROME P450 3A4 (CYP3A4) is the most abundant CYP enzyme in the liver, which is responsible to metabolize approximately 50% of the marketed drugs including antiretroviral agents non-nucleoside reverse transcriptase inhibitors (NNRTIs) and protease inhibitors (PIs) (Anzenbacher and Anzenbacherova, 2002). In addition to substrates, several NNRTIs and PIs act as CYP3A4 inducers, inhibitors, or both (Acosta, 2002; Eagling et al., 1997; Granfors et al., 2006; Walubo, 2007; Xu and Desai, 2009). As highly active antiretroviral therapy (HAART) regimens consist of multiple drugs, especially NNRTIs and PIs, there are several reports of drug–drug interactions as a result of CYP3A4 induction or inhibition (Pal and Mitra, 2006; Walubo, 2007), for example, ritonavir is present in most of the HAART regimens, because it is an extremely potent inhibitor of CYP3A4. Thus, ritonavir leads to increased bioavailability of NNRTIs and PIs because of their decreased metabolism by CYP3A4 (Acosta, 2002; Xu and Desai, 2009). Saquinavir is the first PI that was used for the treatment of HIV-1 infection approximately 25 years ago (Roberts et al., 1992). Subsequently, several other PIs: ritonavir, indinavir, nelfinavir, amprenavir, fosamprenavir, atazanavir, tipranavir, lopinavir, and darunavir were developed and prescribed over the past 2 decades (De Clercq, 2009a,b). In the past 15 years, there has been a clear trend of reduced prescription of indinavir, nelfinavir, and saquinavir, mainly because of the toxicities of the drugs or drug metabolites, as well as drug–drug interactions (Jimenez-Nacher et al., 2008). On the other hand, the prescription of atazanavir, fosamprenavir, darunavir, lopinavir, and tipranavir has increased since their first use. Fosamprenavir is a prodrug, which is eventually converted into active drug amprenavir. In the past couple of years, fosamprenavir/ritonavir (Arvieux and Tribut, 2005), atazanavir/ritonavir (Croom et al., 2009), darunavir/ritonavir (McKeage et al., 2009; Rittweger and Arasteh, 2007), and lopinavir/ritonavir (Croxtall and Perry, 2010) are gaining significant attention because of the reduced risk of adverse reactions and their ability to cross blood–brain barrier. Ethanol is known to interact with many medications, including PIs, through CYP3A4 induction leading to altered drug metabolism and toxicity in the liver (Flexner et al., 2002; Fraser, 1997; Weathermon and Crabb, 1999). Recently, we have shown that ethanol also induces CYP3A4 in monocyte-derived macrophage (Jin et al., 2011), which is one of the HIV-1 replication sites and therefore target of PIs (Gavegnano and Schinazi, 2009). Thus, individuals who consume ethanol and take PI drugs are at high risk of deleterious ethanol–PIs interaction. Although CYP3A4 induction by alcohol is well documented (Flexner et al., 2002; Fraser, 1997; Weathermon and Crabb, 1999), there is no report on ethanol–CYP3A4 physical interaction and its impact on PIs–CYP3A4 interaction. Recently, based on spectral binding and inhibition studies, we have shown that ethanol binds to the active site of CYP3A4 and facilitates the binding of nelfinavir with CYP3A4 (Kumar et al., 2010). As PIs have different physicochemical properties, such as size, shape, polarity, and hydrophobicity, it is logical to anticipate that alcohol will show differential CYP3A4–PIs interactions. This hypothesis was tested by studying spectral binding and inhibition of CYP3A4 with different PIs (amprenavir, atazanavir, darunavir, indinavir, lopinavir, ritonavir, saquinavir, and tipranavir) currently available for clinical use.