Enema ion compositions for enhancing colorectal drug delivery

Tenofovir Douche as HIV Preexposure Prophylaxis for Receptive Anal Intercourse: Safety, Acceptability, Pharmacokinetics, and Pharmacodynamics (DREAM 01)

BACKGROUND

Despite highly effective HIV preexposure prophylaxis (PrEP) options, no options provide on-demand, nonsystemic, behaviorally congruent PrEP that many desire. A tenofovir-medicated rectal douche before receptive anal intercourse may provide this option.

METHODS

Three tenofovir rectal douches-220 mg iso-osmolar product A, 660 mg iso-osmolar product B, and 660 mg hypo-osmolar product C-were studied in 21 HIV-negative men who have sex with men. We sampled blood and colorectal tissue to assess safety, acceptability, pharmacokinetics, and pharmacodynamics.

RESULTS

The douches had high acceptability without toxicity. Median plasma tenofovir peak concentrations for all products were several-fold below trough concentrations associated with oral tenofovir disoproxil fumarate (TDF). Median colon tissue mucosal mononuclear cell (MMC) tenofovir-diphosphate concentrations exceeded target concentrations from 1 hour through 3 to 7 days after dosing. For 6-7 days after a single product C dose, MMC tenofovir-diphosphate exceeded concentrations expected with steady-state oral TDF 300 mg on-demand 2-1-1 dosing. Compared to predrug baseline, HIV replication after ex vivo colon tissue HIV challenge demonstrated a concentration-response relationship with 1.9 log10 maximal effect.

CONCLUSIONS

All 3 tenofovir douches achieved tissue tenofovir-diphosphate concentrations and colorectal antiviral effect exceeding oral TDF and with lower systemic tenofovir. Tenofovir douches may provide a single-dose, on-demand, behaviorally congruent PrEP option, and warrant continued development. Clinical Trials Registration . NCT02750540.

Hydrogels for Mucosal Drug Delivery

Mucosal tissues are often a desirable site of drug action to treat disease and engage the immune system. However, systemically administered drugs suffer from limited bioavailability in mucosal tissues where technologies to enable direct, local delivery to these sites would prove useful. In this Spotlight on Applications article, we discuss hydrogels as an attractive means for local delivery of therapeutics to address a range of conditions affecting the eye, nose, oral cavity, gastrointestinal, urinary bladder, and vaginal tracts. Considering the barriers to effective mucosal delivery, we provide an overview of the key parameters in the use of hydrogels for these applications. Finally, we highlight recent work demonstrating their use for inflammatory and infectious diseases affecting these tissues.

Colonic drug delivery: Formulating the next generation of colon-targeted therapeutics

Colonic drug delivery can facilitate access to unique therapeutic targets and has the potential to enhance drug bioavailability whilst reducing off-target effects. Delivering drugs to the colon requires considered formulation development, as both oral and rectal dosage forms can encounter challenges if the colon's distinct physiological environment is not appreciated. As the therapeutic opportunities surrounding colonic drug delivery multiply, the success of novel pharmaceuticals lies in their design. This review provides a modern insight into the key parameters determining the effective design and development of colon-targeted medicines. Influential physiological features governing the release, dissolution, stability, and absorption of drugs in the colon are first discussed, followed by an overview of the most reliable colon-targeted formulation strategies. Finally, the most appropriate in vitro, in vivo, and in silico preclinical investigations are presented, with the goal of inspiring strategic development of new colon-targeted therapeutics.

Advances and future perspectives in epithelial drug delivery

Epithelial surfaces protect exposed tissues in the body against intrusion of foreign materials, including xenobiotics, pollen and microbiota. The relative permeability of the various epithelia reflects their extent of exposure to the external environment and is in the ranking: intestinal≈ nasal ≥ bronchial ≥ tracheal > vaginal ≥ rectal > blood-perilymph barrier (otic), corneal > buccal > skin. Each epithelium also varies in their morphology, biochemistry, physiology, immunology and external fluid in line with their function. Each epithelium is also used as drug delivery sites to treat local conditions and, in some cases, for systemic delivery. The associated delivery systems have had to evolve to enable the delivery of larger drugs and biologicals, such as peptides, proteins, antibodies and biologicals and now include a range of physical, chemical, electrical, light, sound and other enhancement technologies. In addition, the quality-by-design approach to product regulation and the growth of generic products have also fostered advancement in epithelial drug delivery systems.

Toxicity of phosphate enemas - an updated review

INTRODUCTION

Enemas containing phosphate are widely prescribed and may cause important adverse effects. A systemic review published in 2007 reported the literature on the adverse effects of phosphate enemas from January 1957 to March 2007 and identified 12 deaths. These were thought due to electrolyte disturbances, heart failure and kidney injury. These data raised concerns about the use of phosphate enemas in routine practice. Newer osmotic-based enema alternatives are now available that do not contain absorbable ions. We sought to review the literature since this review and evaluate the latest data on the toxicity of phosphate-containing enemas. To gain a fuller picture we included case series and larger studies as well as case reports.

OBJECTIVES

To review the toxicity of phosphate enemas, particularly with respect to acute metabolic consequences and their associated clinical features. To identify risk factors for metabolic toxicity and consider whether phosphate enemas should be relatively contra-indicated in specific patient groups.

METHODS

A systematic literature review was conducted in PubMed, Google Scholar, and Cochrane Reviews (2005-2021) using the search terms 'phosphate enema or sodium phosphate enema' or 'phosphate-based enema' or (phosphate AND enema) or (Fleet AND enema) or 'sodium phosphate laxatives' or 'sodium phosphate catharsis' or 'sodium phosphate cathartic'. Relevant papers were read, and data were extracted.

RESULTS

The searches identified 489 papers of which 25 were relevant: seven papers were case reports or small case series of metabolic abnormalities from the use of phosphate enemas in nine children, six were case reports on 16 adults. Nine papers were large case series or clinical studies that included data on systemic metabolic effects, of varying size from 24 healthy volunteers to a cohort of 70,499 patients. Case reports identified seven adult deaths but none in children. Children most often presented with decreased consciousness (6/9), and tetany (4/9). In adults overall only five cases had clinical features reported, hypotension was seen in four and QT prolongation in two. Treatment was generally symptomatic, with intravenous fluid and calcium salts for electrolyte changes and hypocalcaemia, and vasopressors for severe hypotension. Haemodialysis was used in three children and peritoneal dialysis in one, all of whom survived. In adults, haemodialysis did not prevent death in two of four cases in whom it was used. Common factors underlying toxicity were inappropriately high phosphate dose, or enema retention, both resulting in greater absorption of phosphate. Associated pre-disposing conditions included Hirschsprung disease in children and co-morbidity and renal impairment (2/5) in older adults. Absolute reported changes in serum phosphate or calcium were not accurate indicators of outcome. Larger case series and clinical trials confirm an acute effect of phosphate enemas on serum phosphate, which was related to both dose and retention time. These effects were not seen with non-phosphate preparations. In these cases series, adverse events were rarely reported.

CONCLUSION

Phosphate enemas are potentially toxic, particularly in young children with Hirschsprung disease and in the elderly with co-morbidity. Raised awareness of the risk of phosphate enemas is still required. Other less toxic enema preparations are available and should be considered in patients at extremes of age. If phosphate enemas are the only clinical option careful monitoring of biochemical sequelae should be undertaken.

Untangling Mucosal Drug Delivery: Engineering, Designing, and Testing Nanoparticles to Overcome the Mucus Barrier

Mucus is a complex viscoelastic gel and acts as a barrier covering much of the soft tissue in the human body. High vascularization and accessibility have motivated drug delivery to various mucosal surfaces; however, these benefits are hindered by the mucus layer. To overcome the mucus barrier, many nanomedicines have been developed, with the goal of improving the efficacy and bioavailability of drug payloads. Two major nanoparticle-based strategies have emerged to facilitate mucosal drug delivery, namely, mucoadhesion and mucopenetration. Generally, mucoadhesive nanoparticles promote interactions with mucus for immobilization and sustained drug release, whereas mucopenetrating nanoparticles diffuse through the mucus and enhance drug uptake. The choice of strategy depends on many factors pertaining to the structural and compositional characteristics of the target mucus and mucosa. While there have been promising results in preclinical studies, mucus-nanoparticle interactions remain poorly understood, thus limiting effective clinical translation. This article reviews nanomedicines designed with mucoadhesive or mucopenetrating properties for mucosal delivery, explores the influence of site-dependent physiological variation among mucosal surfaces on efficacy, transport, and bioavailability, and discusses the techniques and models used to investigate mucus-nanoparticle interactions. The effects of non-homeostatic perturbations on protein corona formation, mucus composition, and nanoparticle performance are discussed in the context of mucosal delivery. The complexity of the mucosal barrier necessitates consideration of the interplay between nanoparticle design, tissue-specific differences in mucus structure and composition, and homeostatic or disease-related changes to the mucus barrier to develop effective nanomedicines for mucosal delivery.

Preclinical evaluation of a hypotonic docetaxel nanosuspension formulation for intravesical treatment of non-muscle-invasive bladder cancer

Intravesical chemotherapy is a key approach for treating refractory non-muscle-invasive bladder cancer (NMIBC). However, the effectiveness of intravesical chemotherapy is limited by bladder tissue penetration and retention. Here, we describe the development of a docetaxel nanosuspension that, when paired with a low osmolality (hypotonic) vehicle, demonstrates increased uptake by the bladder urothelium with minimal systemic exposure. We compare the bladder residence time and efficacy in an immune-competent rat model of NMIBC to the clinical comparator, solubilized docetaxel (generic Taxotere) diluted for intravesical administration. We found that only the intravesical docetaxel nanosuspension significantly decreased cell proliferation compared to untreated tumor tissues. The results presented here suggest that the combination of nanoparticle-based chemotherapy and a hypotonic vehicle can provide more efficacious local drug delivery to bladder tissue for improved treatment of refractory NMIBC.

Prevalence and Correlates of Rectal Douching and Enema Use Among Black Sexual Minority Men and Black Transwomen in the Deep South

HIV/STI disparities are highest among Black sexual minority men (BSMM) and Black transwomen (BTW) in the Deep South. Exploring the prevalence and correlates of rectal douching and enema use could provide insights into risk factors and HIV/STI prevention opportunities among these groups. This study explored the prevalence and correlates of rectal douching and enema using Poisson regression models among 375 BSMM and BTW in Jackson, MS, and Atlanta GA. Approximately 95% reported their gender as male/man; 5.6% self-identified as transwomen. Most reported being single (73.1%) and were unemployed (56.0%); 36.1% were previously diagnosed with HIV. In multivariable models, BSMM and BTW who reported that their typical sexual position during anal sex was "bottom" (aPR = 2.39, 95% CI = 1.48, 3.84) or "versatile" (aPR = 2.46, 95% CI = 1.44, 4.17) had a higher prevalence of rectal douching and enema use than those who reported "top." Deeper understanding of the contexts of rectal douching, enema use, and sexual positioning practices is needed.

Physiological and Pharmaceutical Considerations for Rectal Drug Formulations

Although the oral route is the most convenient route for drug administration, there are a number of circumstances where this is not possible from either a clinical or pharmaceutical perspective. In these cases, the rectal route may represent a practical alternative and can be used to administer drugs for both local and systemic actions. The environment in the rectum is considered relatively constant and stable and has low enzymatic activity in comparison to other sections of the gastrointestinal tract. In addition, drugs can partially bypass the liver following systemic absorption, which reduces the hepatic first-pass effect. Therefore, rectal drug delivery can provide significant local and systemic levels for various drugs, despite the relatively small surface area of the rectal mucosa. Further development and optimization of rectal drug formulations have led to improvements in drug bioavailability, formulation retention, and drug release kinetics. However, despite the pharmaceutical advances in rectal drug delivery, very few of them have translated to the clinical phase. This review will address the physiological and pharmaceutical considerations influencing rectal drug delivery as well as the conventional and novel drug delivery approaches. The translational challenges and development aspects of novel formulations will also be discussed.

Feasibility Study for the Rectal Route of Administration for Gentamicin Evaluated in the Neonatal Minipig Model

Neonatal infections are a major cause of newborn mortality in low- and middle-income countries, particularly in areas without access to inpatient care. To address this, the World Health Organization developed guidelines for delivering simplified antibiotic regimens (oral amoxicillin and intramuscular gentamicin) in outpatient settings to young infants with suspected serious bacterial infection when referral is not feasible. However, there are still limitations to access, as the regimen requires a health care provider trained in giving intramuscular injections to infants. To provide a needle-free, simplified alternate to intramuscular delivery, PATH investigated the feasibility of the rectal administration of gentamicin. Potential formulations were screened by in vitro testing, and 2 liquid enema formulations and a cocoa butter suppository were developed and evaluated in a preclinical study of the rectal uptake of gentamicin in a neonatal minipig model. Sera samples from the control group, dosed by intramuscular injection, resulted in expected sera concentrations of gentamicin, but no gentamicin was detected in the sera of groups rectally dosed with the test formulations. The results of this study did not provide evidence to support the therapeutic feasibility of rectally absorbed gentamicin.

Engineering the Mucus Barrier

Mucus selectively controls the transport of molecules, particulate matter, and microorganisms to the underlying epithelial layer. It may be desirable to weaken the mucus barrier to enable effective delivery of drug carriers. Alternatively, the mucus barrier can be strengthened to prevent epithelial interaction with pathogenic microbes or other exogenous materials. The dynamic mucus layer can undergo changes in structure (e.g., pore size) and/or composition (e.g., protein concentrations, mucin glycosylation) in response to stimuli that occur naturally or are purposely administered, thus altering its barrier function. This review outlines mechanisms by which mucus provides a selective barrier and methods to engineer the mucus layer from the perspective of strengthening or weakening its barrier properties. In addition, we discuss strategic design of drug carriers and dosing formulation properties for efficient delivery across the mucus barrier.

Rectal Douching Practices Associated with Anal Intercourse: Implications for the Development of a Behaviorally Congruent HIV-Prevention Rectal Microbicide Douche

Tenofovir administration via rectal douching results in higher rectal-mucosa drug concentration than oral administration. Many who engage in receptive anal intercourse (RAI) use cleansing rectal douches. To inform development of a behaviorally-congruent tenofovir douche, 4751 individuals ≥ 18 years-old, born male, from all US states/territories, who engaged in anal intercourse responded to an online survey. Of those who reported RAI in the prior 3 months, 80% douched beforehand, 82% within 1 h, mean 2.9 consecutive applications; 27% douched afterwards, 83% within 1 h, mean 1.7 consecutive applications. Among multidose users, 78% applied doses within 2 min, and 76% retained liquid < 1 min. Most used tap water (89%) in an enema bottle (50%) or rubber bulb (43%), and douched for cleanliness (97%), to avoid smelling bad (65%), and to enhance pleasure (24%). 98% reported high likelihood of using an HIV-prevention douche. An ideal product will protect within a user's typical number of applications, within 1 h, and be dissolvable in tap water.

Pharmaceutical Vehicles for Vaginal and Rectal Administration of Anti-HIV Microbicide Nanosystems

Prevention strategies play a key role in the fight against HIV/AIDS. Vaginal and rectal microbicides hold great promise in tackling sexual transmission of HIV-1, but effective and safe products are yet to be approved and made available to those in need. While most efforts have been placed in finding and testing suitable active drug candidates to be used in microbicide development, the last decade also saw considerable advances in the design of adequate carrier systems and formulations that could lead to products presenting enhanced performance in protecting from infection. One strategy demonstrating great potential encompasses the use of nanosystems, either with intrinsic antiviral activity or acting as carriers for promising microbicide drug candidates. Polymeric nanoparticles, in particular, have been shown to be able to enhance mucosal distribution and retention of promising antiretroviral compounds. One important aspect in the development of nanotechnology-based microbicides relates to the design of pharmaceutical vehicles that allow not only convenient vaginal and/or rectal administration, but also preserve or even enhance the performance of nanosystems. In this manuscript, we revise relevant work concerning the selection of vaginal/rectal dosage forms and vehicle formulation development for the administration of microbicide nanosystems. We also pinpoint major gaps in the field and provide pertinent hints for future work.

High-molecular-weight polymers from dietary fiber drive aggregation of particulates in the murine small intestine

The lumen of the small intestine (SI) is filled with particulates: microbes, therapeutic particles, and food granules. The structure of this particulate suspension could impact uptake of drugs and nutrients and the function of microorganisms; however, little is understood about how this suspension is re-structured as it transits the gut. Here, we demonstrate that particles spontaneously aggregate in SI luminal fluid ex vivo. We find that mucins and immunoglobulins are not required for aggregation. Instead, aggregation can be controlled using polymers from dietary fiber in a manner that is qualitatively consistent with polymer-induced depletion interactions, which do not require specific chemical interactions. Furthermore, we find that aggregation is tunable; by feeding mice dietary fibers of different molecular weights, we can control aggregation in SI luminal fluid. This work suggests that the molecular weight and concentration of dietary polymers play an underappreciated role in shaping the physicochemical environment of the gut.

Editorial note: This article has been through an editorial process in which the authors decide how to respond to the issues raised during peer review. The Reviewing Editor's assessment is that all the issues have been addressed (see decision letter).

Colorectal distribution and retention of polymeric nanoparticles following incorporation into a thermosensitive enema

The incorporation of nanoparticles into a thermosensitive enema enhances colorectal distribution and retention.

Mucus-penetrating budesonide nanosuspension enema for local treatment of inflammatory bowel disease

Inflammatory bowel disease (IBD) is a chronic inflammatory gastrointestinal disorder that affects more than 1 million individuals in the USA. Local therapy with enema formulations, such as micronized budesonide (Entocort®), is a common strategy for treating patients with distally active IBD. However, we hypothesize that micronized particulates are too large to effectively penetrate colorectal mucus, limiting the extent of drug delivery to affected tissues prior to clearance. Here, we describe the development of a budesonide nanosuspension (NS) with the appropriate surface coating and size to enhance penetration of colorectal mucus and ulcerated colorectal tissues. We demonstrate that model fluorescent polystyrene (PS) particles ∼200 nm in size with a muco-inert Pluronic F127 coating provide enhanced mucosal distribution and tissue penetration in mice with trinitrobenzenesulfonic acid (TNBS)-induced IBD compared to model 2 μm PS particles coated with polyvinylpyrollidone (PVP), the stabilizer used in the clinical micronized budesonide formulation. We then used a wet-milling process to develop a budesonide NS formulation with a muco-inert Pluronic F127 coating (particle size ∼230 nm), as well as a budesonide microsuspension (MS) stabilized with PVP (particle size ∼2 μm). Using an acute TNBS mouse model of IBD, we show that daily budesonide NS enema treatment resulted in a significant reduction in the macroscopic (decreased colon weight) and microscopic (histology score) symptoms of IBD compared to untreated controls or mice treated daily with the budesonide MS enema. Further, we show that the budesonide NS enema treated mice had a significantly reduced number of inflammatory macrophages and IL-β producing CD11b + cells in colon tissue compared to untreated controls or mice treated with the budesonide MS enema. We conclude that the nano-size and muco-inert coating allowed for enhanced local delivery of budesonide, and thus, a more significant impact on local colorectal tissue inflammation.

Rectal administration of metronidazole with and without rectal evacuation prior to use in horses

In a randomized crossover design study, 10 adult horses were administered crushed metronidazole tablets rectally at 20 mg/kg. Horses' rectums were either evacuated (E) or not evacuated (NE) of manure prior to the administration of the drug. Serum samples were taken over 24 hr and plasma concentrations were determined via high pressure liquid chromatography. At 15 min post-administration, group E had a significantly higher plasma concentration (p = 0.027), but there were no concentration differences at any other time points. There was large variability in relative bioavailability in the NE group, with a median of 86.7%. Based on our results, there is no advantage to manually evacuating a horse's rectum prior to rectal administration of metronidazole. Further study at higher dosages as well as examination of clinical efficacy is warranted.

Surface modification with polyethylene glycol enhances colorectal distribution and retention of nanoparticles

Dense surface modification with short chain polyethylene glycol (PEG) has been previously demonstrated as favoring the transport of nanoparticles (NPs) across mucus. However, the ability of such approach to influence the distribution and retention of NPs along the length of the colorectum after rectal delivery has not been previously established. Herein, the distribution and retention of poly(lactic-co-glycolic acid) NPs modified with PEG in a non-covalent fashion are reckoned in a mouse model. Despite overall rapid depletion, both PEG-modified and non-modified NPs are able to reach the middle segment of the colon. PEG-modified NPs are able to enhance retention up to at least two hours post-administration, contrasting with nearly residual levels observed for non-modified NPs after 15 min. The ability of PEG-modified NPs to putatively cross mucus also appears to promote association with tissues. Overall, the work provides significant insights as to the behavior of NPs in the colorectum, which could be valuable for the development of rectal nanomedicines. It further reinforces the potential usefulness of PEG-modified NPs as mucus-penetrating carriers for mucosal drug delivery.

Co association of mucus modulating agents and nanoparticles for mucosal drug delivery

Nanoparticulate drug delivery systems (nDDS) offer a variety of options when it comes to routes of administration. One possible path is crossing mucosal barriers, such as in the airways and in the GI tract, for systemic distribution or local treatment. The main challenge with this administration route is that the size and surface properties of the nanoparticles, as opposed to small molecular drugs, very often results in mucosal capture, immobilization and removal, which in turn results in a very low bioavailability. Strategies to overcome this challenge do exist, like surface 'stealth' modification with PEG. Here we review an alternative or supplemental strategy, co-association of mucus modulating agents with the nDDS to improve bioavailability, where the nDDS may be surface modified or unmodified. This contribution presents some examples on how possible co-association systems may be achieved, using currently marketed mucolytic drugs, alternative formulations or novel agents.

Hypo-osmolar Formulation of Tenofovir (TFV) Enema Promotes Uptake and Metabolism of TFV in Tissues, Leading to Prevention of SHIV/SIV Infection

Oral preexposure prophylaxis (PrEP) has been approved for prophylaxis of HIV-1 transmission but is associated with high costs and issues of adherence. Protection from anal transmission of HIV using topical microbicides and methods congruent with sexual behavior offers the promise of improved adherence. We compared the pharmacokinetics (PK) and ex vivo efficacy of iso-osmolar (IOsm) and hypo-osmolar (HOsm) rectal enema formulations of tenofovir (TFV) in rhesus macaques. Single-dose PK of IOsm or HOsm high-dose (5.28 mg/ml) and low-dose (1.76 mg/ml) formulations of TFV enemas were evaluated for systemic uptake in blood, colorectal biopsy specimens, and rectal CD4⁺ T cells. Markedly higher TFV concentrations were observed in plasma and tissues after administration of the HOsm high-dose formulation than with all other formulations tested. TFV and TFV diphosphate (TFV-DP) concentrations in tissue correlated for the HOsm high-dose formulation, demonstrating rapid uptake and transformation of TFV to TFV-DP in tissues. TFV-DP amounts in tissues collected at 1 and 24 h were 7 times and 5 times higher, respectively (P < 0.01), than the ones collected in tissues with the IOsm formulation. The HOsm high-dose formulation prevented infection in ex vivo challenges of rectal tissues collected at 1, 24, and 72 h after the intrarectal dosing, whereas the same TFV dose formulated as an IOsm enema was less effective.

Hyperosmolal vaginal lubricants markedly reduce epithelial barrier properties in a three-dimensional vaginal epithelium model

Most of the widely used vaginal lubricants in the U.S. and Europe are strongly hyperosmolal, formulated with high concentrations of glycerol, propylene glycol, polyquaternary compounds or other ingredients that make these lubricants 4 to 30 times the osmolality of healthy vaginal fluid. Hyperosmolal formulations have been shown to cause marked toxicity to human colorectal epithelia in vivo, and significantly increase vaginal transmission of genital herpes infections in the mouse/HSV model. They also cause toxicity to explants of vaginal epithelia, to cultured vaginal epithelial cells, and increase susceptibility to HIV in target cells in cell cultures. Here, we report that the osmolality of healthy vaginal fluid is 370 ± 40 mOsm/Kg in women with Nugent scores 0–3, and that a well-characterized three-dimensional human vaginal epithelium tissue model demonstrated that vaginal lubricants with osmolality greater than 4 times that of vaginal fluid (>1500 mOsm/Kg) markedly reduce epithelial barrier properties and showed damage in tissue structure. Four out of four such lubricants caused disruption in the parabasal and basal layers of cells as observed by histological analysis and reduced barrier integrity as measured by trans-epithelial electrical resistance (TEER). No epithelial damage to these layers was observed for hypo- and iso-osmolal lubricants with osmolality of <400 mOsm/Kg. The results confirm extensive reports of safety concerns of hyperosmolal lubricants and suggest the usefulness of reconstructed in vitro vaginal tissue models for assessing safety of lubricants in the absence of direct clinical tests in humans.

Local enema treatment to inhibit FOLH1/GCPII as a novel therapy for inflammatory bowel disease

Here we evaluate the potential for local administration of a small molecule FOLH1/GCPII inhibitor 2-phosphonomethyl pentanedioic acid (2-PMPA) as a novel treatment for inflammatory bowel disease (IBD). We found that FOLH1/GCPII enzyme activity was increased in the colorectal tissues of mice with TNBS-induced colitis, and confirmed that 2-PMPA inhibited FOLH1/GCPII enzyme activity ex vivo. In order to maximize local enema delivery of 2-PMPA, we studied the effect of vehicle tonicity on the absorption of 2-PMPA in the colon. Local administration of 2-PMPA in a hypotonic enema vehicle resulted in increased colorectal tissue absorption at 30min compared to 2-PMPA administered in an isotonic enema vehicle. Furthermore, local delivery of 2-PMPA in hypotonic enema vehicle resulted in prolonged drug concentrations for at least 24h with minimal systemic exposure. Finally, daily treatment with the hypotonic 2-PMPA enema ameliorated macroscopic and microscopic symptoms of IBD in the TNBS-induced colitis mouse model, indicating the potential of FOLH1/GCPII inhibitors for the local treatment of IBD.

Multicompartmental Pharmacokinetic Model of Tenofovir Delivery to the Rectal Mucosa by an Enema

Rectal enemas that contain prophylactic levels of anti-HIV microbicides such as tenofovir have emerged as a promising dosage form to prevent sexually transmitted HIV infections. The enema vehicle is promising due to its likely ability to deliver a large amount of drug along the length of the rectal canal. Computational models of microbicide drug delivery by enemas can help their design process by determining key factors governing drug transport and, more specifically, the time history and degree of protection. They can also inform interpretations of experimental pharmacokinetic measures such as drug concentrations in biopsies. The present work begins rectal microbicide PK modeling, for enema vehicles. Results here show that a paramount factor in drug transport is the time of enema retention; direct connectivity between enema fluid and the fluid within rectal crypts is also important. Computations of the percentage of stromal volume protected by a single enema dose indicate that even with only a minute of enema retention, protection of 100% can be achieved after around 14 minutes post dose. Concentrations in biopsies are dependent on biopsy thickness; and control and/or knowledge of thickness could improve accuracy and decrease variability in biopsy measurements. Results here provide evidence that enemas are a promising dosage form for rectal microbicide delivery, and offer insights into their rational design.

Polymers in the gut compress the colonic mucus hydrogel

Colonic mucus is a key biological hydrogel that protects the gut from infection and physical damage and mediates host-microbe interactions and drug delivery. However, little is known about how its structure is influenced by materials it comes into contact with regularly. For example, the gut abounds in polymers such as dietary fibers or administered therapeutics, yet whether such polymers interact with the mucus hydrogel, and if so, how, remains unclear. Although several biological processes have been identified as potential regulators of mucus structure, the polymeric composition of the gut environment has been ignored. Here, we demonstrate that gut polymers do in fact regulate mucus hydrogel structure, and that polymer-mucus interactions can be described using a thermodynamic model based on Flory-Huggins solution theory. We found that both dietary and therapeutic polymers dramatically compressed murine colonic mucus ex vivo and in vivo. This behavior depended strongly on both polymer concentration and molecular weight, in agreement with the predictions of our thermodynamic model. Moreover, exposure to polymer-rich luminal fluid from germ-free mice strongly compressed the mucus hydrogel, whereas exposure to luminal fluid from specific-pathogen-free mice-whose microbiota degrade gut polymers-did not; this suggests that gut microbes modulate mucus structure by degrading polymers. These findings highlight the role of mucus as a responsive biomaterial, and reveal a mechanism of mucus restructuring that must be integrated into the design and interpretation of studies involving therapeutic polymers, dietary fibers, and fiber-degrading gut microbes.

Barriers to inhaled gene therapy of obstructive lung diseases: A review

Knowledge of genetic origins of obstructive lung diseases has made inhaled gene therapy an attractive alternative to the current standards of care that are limited to managing disease symptoms. Initial lung gene therapy clinical trials occurred in the early 1990s following the discovery of the genetic defect responsible for cystic fibrosis (CF), a monogenic disorder. However, despite over two decades of intensive effort, gene therapy has yet to help patients with CF or any other obstructive lung disease. The slow progress is due in part to poor understanding of the biological barriers to inhaled gene therapy. Encouragingly, clinical trials have shown that inhaled gene therapy with various viral vectors and non-viral gene vectors is well tolerated by patients, and continued research has provided valuable lessons and resources that may lead to future success of this therapeutic strategy. In this review, we first introduce representative obstructive lung diseases and examine limitations of currently available therapeutic options. We then review key components for successful execution of inhaled gene therapy, including gene delivery systems, primary physiological barriers and strategies to overcome them, and advances in preclinical disease models with which the most promising systems may be identified for human clinical trials.

Nanoparticles coated with high molecular weight PEG penetrate mucus and provide uniform vaginal and colorectal distribution in vivo

AIM

We previously reported that nanoparticles (NPs) coated with 10 kDa PEG were mucoadhesive. Here, we demonstrate that by increasing the surface density, PEG with molecular weight (MW) as high as 40 kDa can be used as a mucoinert NP surface coating.

MATERIALS & METHODS

We compared two sets of reaction conditions for coating model polystyrene NPs with 10 kDa PEG and used optimized conditions to coat NPs with PEG as high as 40 kDa in MW. We then characterized NP transport in human cervicovaginal mucus ex vivo. We further administered PEG-coated NPs to the mouse cervicovaginal tract and colorectum to assess mucosal distribution in vivo.

RESULTS & CONCLUSION

We demonstrate here that PEG with MW as high as 40 kDa can be densely grafted to the surface of NP to prevent interactions with mucus. NP coated with 10-40 kDa PEG rapidly diffused through human cervicovaginal mucus ex vivo, and uniformly lined the mouse colorectal and vaginal epithelium in vivo.