Drug metabolism in the intestine or intestinal first-pass metabolism can cause low bioavailability of some oral drugs, which depends on the contents of relevant enzymes in the gastrointestinal lumen and epithelium as well as bacterial enzymes (1, 2). Probiotics can modulate gut microbiota and regulate immune responses, benefiting patients with intestinal diseases, diabetes, tumors and obesity (3). Probiotics have been widely used in humans and animals, and probiotics may alter the expression of intestinal drug-metabolizing enzymes (DMEs) to change the bioavailability of some oral drugs. However, the effect of probiotics on the expression of intestinal DMEs and their mechanisms have not been clarified. Accordingly, it is important to understand the effect and mechanisms of probiotics on the expression of intestinal DMEs.
Mammalian cytochrome P450s (CYP450s) are crucial for the oxidative metabolism of xenobiotics, including therapeutic drugs, environmental carcinogens and toxins(4). CYP3A4, one of the DMEs in humans, can metabolize > 50% of clinical drugs (5). Pigs have a high similarity in physiology and anatomy to humans and become an important animal model for evaluating new drugs (6, 7). Porcine CYP3A29 accounts for 30% of total CYP proteins and the major CYP3A activity in pig liver microsomes (8). Pig CYP3A29 and human CYP3A4 have similar tissue distribution, pharmacokinetic characteristics and regulatory mechanisms, and pig CYP3A29 is a suitable model for research of human CYP3A4 (9, 10).
The nuclear receptors (NRs), such as retinoid X receptor alpha (RXR-α), pregnane X receptor (PXR), vitamin D receptor (VDR) and the constitutive androstane receptor (CAR), are important for regulating the expression of CYP450s(11). The RXR-α can directly interact with PXR, VDR or CAR to form heterodimers and bind to the CYP450s gene promoter to regulate their expression(12). For example, the VDR/RXR-α heterodimer can bind to the CLEM4-ER6 motif to regulate the expression of CYP3A4(13), and the CAR/RXRα and PXR/RXR-α heterodimers can interact with pER6 and dXREM to regulate the expression of CYP3A4, respectively (14, 15). Our previous study has shown that the PXR/RXR-α can bind to the CYP3A29 promoter to induce its expression in porcine liver HepLi cells (16). Apparently, RXR-α expression is critical for the expression of CYP3A in the digestive system.
The nuclear factor-kappa B (NF-κB) signaling is crucial for inflammation, immunity, cell proliferation and apoptosis(17). It can regulate the expression of CYP450s by directly binding to the CYP450 promoters, or indirectly regulate the expression of NRs (11, 16, 18). In addition, the NF-κB can also enhance the activity of CYP450 at the post-transcriptional level by stabilizing CYP450 proteins (19). Interestingly, previous studies have revealed that some probiotics can inhibit the NF-κB activity (20, 21). However, whether and how probiotics could modulate the expression of CYP450s, such as CYP3A29 in pig intestinal tissues, have not been clarified.
Toll-like receptors (TLRs) act as a type of pattern recognition receptors (PRR) in the innate immune system and TLRs can recognize microbial components to initiate immune responses. TLR2 can directly interact with TLR1 or TLR6 to form a heterodimer and recognize conserved molecular patterns (such as peptidoglycan, lipoteichoic acid, etc.) on the cell wall of Gram-positive bacteria(22, 23). Engagement of TLR2 by the cell wall components of some probiotics can up-regulate the expression of some NF-κB inhibitors, such as A20 (tumor necrosis factor-α-induced protein 3), IRAK-M and Tollip, to inhibit inflammation(20, 21). Actually, A20 is a deubiquitinating enzyme and can inhibit the NF-kB activation (24). Our previous study indicates that Enterococcus faecium HDRsEf1 enhances the expression of occluding, the intestinal tight junction protein, by activating the TLR2 (25). Accordingly, we hypothesize that HDRsEf1 can modulate the expression of CYP3A29 in pig intestinal tissues by modulating the NB-κB signaling.
In this study, we explored the effect of HDRsEf1 on CYP3A29 expression and potential mechanisms in pig intestinal tissues and epithelial IPEC-J2 cells. We found that HDRsEf1 decreased the expression of CYP3A29 in pig intestinal tissues by activating the TLR2 to up-regulate A20 expression, inhibiting the NF-κB activation to attenuate RXR-α expression.