Intestinal delivery in a long-chain fatty acid formulation enables lymphatic transport and systemic exposure of orlistat

Inquiry lipaseoring the mechanism of pancreatic lipase inhibition by isovitexin based on multispectral method and enzyme inhibition assay

Isovitexin is a main natural flavonoid component in various plants. Currently, the inhibitory effect of isovitexin on pancreatic lipase (PL) and its mechanism have not been elucidated yet. In the present study, we investigated the inhibitory effect of isovitexin on PL, as well as its interaction mechanism, using enzyme inhibition methods, spectroscopic analysis, and molecular simulations. Results showed that isovitexin possessed significant PL inhibitory activity, with IC50 values of 0.26 ± 0.02 mM. The interaction between isovitexin and PL was dominated by static quenching, and mainly through hydrogen bonding and hydrophobic interaction forces. Analysis of fluorescence spectroscopy confirmed that isovitexin binding altered the conformation of the PL. Circular dichroism (CD) spectrum indicated that isovitexin altered the secondary structure of PL by decreasing the α-helix content and increasing the β-fold content. Molecular simulations further characterize the conformational changes produced by the interaction between isovitexin with PL. The performed study may provide a new insight into the inhibitory mechanism of isovitexin as a novel PL inhibitor.

Lymphatic Uptake of a Highly Lipophilic Protease Inhibitor Prodrug from a Lipid-Based Formulation is Limited by Instability in the Intestine

Dabigatran etexilate (DABE) is a lipophilic double alkyl ester prodrug of dabigatran (DAB) which is a serine protease inhibitor used clinically as an anticoagulant. Recently, translocation of serine protease enzymes, including trypsin, from the gut into the mesenteric lymph and then blood has been associated with organ failure in acute and critical illnesses (ACIs). Delivery of DABE into mesenteric lymph may thus be an effective strategy to prevent organ failure in ACIs. Most drugs access the mesenteric lymph in low quantities following oral administration, as they are rapidly transported away from the intestine via the blood. Here, we examine the potential to deliver DABE into the mesenteric lymph by promoting association with lymph lipid transport pathways via co-administration with a lipid-based formulation (LBF). A series of self-emulsifying LBFs were designed and tested in vitro for their potential to form stable DABE loaded emulsions and keep DABE solubilised and stable over time in simulated gastrointestinal conditions. The LBFs were found to form fine emulsions with a droplet size of 214 ± 30 nm and DABE was stable in the formulation. The stability of DABE in vitro in simulated intestinal conditions, plasma and lymph samples was also evaluated to ensure stability in collected samples and to evaluate whether the prodrug is likely to release active DAB. Ultimately, a highly uniform and stable self-emulsifying Type III A LBF of DABE was chosen for progression into in vivo studies in male Sprague Dawley rats to confirm the lymphatic uptake and plasma pharmacokinetics. Both in vitro and in vivo in plasma and lymph, DABE was rapidly converted to an intermediate and DAB. The main species present in vivo in both plasma and lymph was DAB and mass transport of DABE and DAB in lymph was minimal (∼0.5 % of dose). Importantly, the concentration of DABE in lymph was substantially (20-176 fold) higher than in plasma, supporting that if the prodrug were stable and did not convert to DAB in the intestine, it would be lymphatically transported. Future studies will therefore focus on optimizing the design of the prodrug and formulation to improve stability during absorption and further promote lymphatic uptake.

Development of lipophilic ester prodrugs of dolutegravir for intestinal lymphatic transport

The establishment of latent cellular and anatomical viral reservoirs is a major obstacle to achieving a cure for people infected by HIV. Mesenteric lymph nodes (MLNs) are one of the most important anatomical reservoirs of HIV. Suboptimal levels of antiretroviral (ARVs) drugs in these difficult-to-penetrate viral reservoirs is one of the limitations of current antiretroviral therapy (ART) regimens. This study aimed to design and assess highly lipophilic ester prodrugs of dolutegravir (DTG) formulated with long-chain triglyceride (LCT) for delivery of DTG to the viral reservoir in mesenteric lymph and MLNs. A number of alkyl ester prodrugs of DTG were designed based on the predicted affinity to chylomicrons (CM), and the six most promising prodrugs were selected and synthesised. The synthesised prodrugs were further assessed for their intestinal lymphatic transport potential and biotransformation in biorelevant media in vitro and ex vivo. DTG and the most promising prodrug (prodrug 5) were then assessed in pharmacokinetic and biodistribution studies in rats. Although oral administration of 5 mg/kg of unmodified DTG (an allometrically scaled dose from humans) with or without lipids achieved concentrations above protein binding-adjusted IC90 (PA-IC90) (64 ng/mL) in most tissues, the drug was not selectively targeted to MLNs. The combination of lipophilic ester prodrug and LCT-based formulation approach improved the targeting selectivity of DTG to MLNs 4.8-fold compared to unmodified DTG. However, systemic exposure to DTG was limited, most likely due to poor intestinal absorption of the prodrug following oral administration. In vitro lipolysis showed a good correlation between micellar solubilisation of the prodrug and systemic exposure to DTG in rats in vivo. Thus, it is prudent to include in vitro lipolysis in the early assessment of orally administered drugs and prodrugs in lipidic formulations, even when intestinal lymphatic transport is involved in the absorption pathway. Further studies are needed to clarify the underlying mechanisms of low systemic bioavailability of DTG following oral administration of the prodrug and potential ways to overcome this limitation.

Mechanisms of Nanoparticle Transport across Intestinal Tissue: An Oral Delivery Perspective

Oral drug administration has been a popular choice due to patient compliance and limited clinical resources. Orally delivered drugs must circumvent the harsh gastrointestinal (GI) environment to effectively enter the systemic circulation. The GI tract has a number of structural and physiological barriers that limit drug bioavailability including mucus, the tightly regulated epithelial layer, immune cells, and associated vasculature. Nanoparticles have been used to enhance oral bioavailability of drugs, as they can act as a shield to the harsh GI environment and prevent early degradation while also increasing uptake and transport of drugs across the intestinal epithelium. Evidence suggests that different nanoparticle formulations may be transported via different intracellular mechanisms to cross the intestinal epithelium. Despite the existence of a significant body of work on intestinal transport of nanoparticles, many key questions remain: What causes the poor bioavailability of the oral drugs? What factors contribute to the ability of a nanoparticle to cross different intestinal barriers? Do nanoparticle properties such as size and charge influence the type of endocytic pathways taken? In this Review, we summarize the different components of intestinal barriers and the types of nanoparticles developed for oral delivery. In particular, we focus on the various intracellular pathways used in nanoparticle internalization and nanoparticle or cargo translocation across the epithelium. Understanding the gut barrier, nanoparticle characteristics, and transport pathways may lead to the development of more therapeutically useful nanoparticles as drug carriers.

Targeting Lymphatics for Nanoparticle Drug Delivery

The lymphatics transport material from peripheral tissues to lymph nodes, where immune responses are formed, before being transported into systemic circulation. With key roles in transport and fluid homeostasis, lymphatic dysregulation is linked to diseases, including lymphedema. Fluid within the interstitium passes into initial lymphatic vessels where a valve system prevents fluid backflow. Additionally, lymphatic endothelial cells produce key chemokines, such as CCL21, that direct the migration of dendritic cells and lymphocytes. As a result, lymphatics are an attractive delivery route for transporting immune modulatory treatments to lymph nodes where immunotherapies are potentiated in addition to being an alternative method of reaching systemic circulation. In this review, we discuss the physiology of lymphatic vessels and mechanisms used in the transport of materials from peripheral tissues to lymph nodes. We then summarize nanomaterial-based strategies to take advantage of lymphatic transport functions for delivering therapeutics to lymph nodes or systemic circulation. We also describe opportunities for targeting lymphatic endothelial cells to modulate transport and immune functions.

Triglyceride-Mimetic Prodrugs of Buprenorphine Enhance Oral Bioavailability via Promotion of Lymphatic Transport

Buprenorphine (BUP) is a potent opioid analgesic that is widely used for severe pain management and opioid replacement therapy. The oral bioavailability of BUP, however, is significantly limited by first-pass metabolism. Previous studies have shown that triglyceride (TG) mimetic prodrugs of the steroid hormone testosterone circumvent first-pass metabolism by directing drug transport through the intestinal lymphatics, bypassing the liver. The current study expanded this prodrug strategy to BUP. Here different self-immolative (SI) linkers were evaluated to conjugate BUP to the 2 position of the TG backbone via the phenol group on BUP. The SI linkers were designed to promote drug release in plasma. Lipolysis of the prodrug in the intestinal tract was examined via incubation with simulated intestinal fluid (SIF), and potential for parent drug liberation in the systemic circulation was evaluated via incubation in rat plasma. Lymphatic transport and bioavailability studies were subsequently conducted in mesenteric lymph duct or carotid artery-cannulated rats, respectively. TG prodrug derivatives were efficiently transported into the lymphatics (up to 45% of the dose in anaesthetised rats, vs. less than 0.1% for BUP). Incorporation of the SI linkers facilitated BUP release from the prodrugs in the plasma and in concert with high lymphatic transport led to a marked enhancement in oral bioavailability (up to 22-fold) compared to BUP alone. These data suggest the potential to develop an orally bioavailable BUP product which may have advantages with respect to patient preference when compared to current sublingual, transdermal patch or parenteral formulations.

Drug delivery to the intestinal lymph by oral formulations

Oral drug delivery systems (DDS) targeting lymphocytes in intestinal lymphatic vessels, ducts, and nodes are useful for treating diverse diseases. The intestinal lymph harbors numerous lymphocyte subsets, and DDS containing lipids such as triglycerides and fatty acids can deliver drugs to the lymph through the chylomicron pathway. DDS are efficient, thus allowing the administration of reduced drug doses, which mitigate systemic adverse effects. Here we review orally administered lipid formulations comprising oil solutions, suspensions, micro/nanoemulsions, self-micro/nano emulsifying DDS, liposomes, micelles, solid lipid nanoparticles, and nanostructured lipid carriers for targeting drugs to the lymph. We first describe the structures of lymphatic vessels and lymph nodes and the oral absorption of lipids and drugs into the intestinal lymph. We next summarize the effects of the properties and amounts of lipids and drugs delivered into the lymph and lymphocytes, as well as their effects on drug delivery ratios of lymph to blood. Finally, we describe lymphatic DDS containing saquinavir, tacrolimus, and methotrexate, and their potency that reduce drug concentrations in blood, which are associated with systemic adverse effects.

Targeting the Gut Mucosal Immune System Using Nanomaterials

The gastrointestinal (GI) tract is one the biggest mucosal surface in the body and one of the primary targets for the delivery of therapeutics, including immunotherapies. GI diseases, including, e.g., inflammatory bowel disease and intestinal infections such as cholera, pose a significant public health burden and are on the rise. Many of these diseases involve inflammatory processes that can be targeted by immune modulatory therapeutics. However, nonspecific targeting of inflammation systemically can lead to significant side effects. This can be avoided by locally targeting therapeutics to the GI tract and its mucosal immune system. In this review, we discuss nanomaterial-based strategies targeting the GI mucosal immune system, including gut-associated lymphoid tissues, tissue resident immune cells, as well as GI lymph nodes, to modulate GI inflammation and disease outcomes, as well as take advantage of some of the primary mechanisms of GI immunity such as oral tolerance.