Effect of Orally Ingested Water Containing H2-Filled Ultrafine Bubbles (UFBs) on Ethanol-Induced Oxidative Stress in Rats.

Ultrafine bubbles (UFBs), which are bubbles with diameters of less than 1 µm, are widely recognized for their ability to exist stably in liquid as a result of the effects of Brownian motion. In this study, we focused on hydrogen, known for its antioxidant potential, and explored the function of H2-filled UFBs, which encapsulate hydrogen, to determine their potential use as oral carriers for the delivery bioactive gases to living organisms. To this end, rats were orally administered ethanol to induce hepatic oxidative stress, and the effects of drinking H2-filled UFBs (H2 NanoGAS®) water for two weeks were evaluated to assess the reduction of oxidative stress. Continuous alcohol consumption was found to significantly increase the blood lipid peroxidation levels in the control group, confirming the induction of oxidative stress. An increase in blood lipid peroxidation was significantly inhibited by the consumption of concentrated H2 NanoGAS® (C-HN) water. Furthermore, the measurement of mitochondrial activity in the liver revealed that drinking H2 NanoGAS® water helped to maintain at a normal level and/or boosted the functional activity of the electron transport system in mitochondria affected by ethanol intake. To our knowledge, this study is the first to provide evidence for the use of orally ingested UFBs as carriers for the delivery gases to tissues, thereby exerting their physiological activity in the body. Our findings highlight the potential for the application of UFBs to various physiologically active gases and their utilization in the medical field in the future.

Evaluation of Function and Features of Human Induced Pluripotent Stem Cell-Derived Small Intestinal Epithelial Cells for Analyzing Peptide Drug Intestinal Absorption Profiles.

Caco-2 cell monolayers are widely employed as an in vitro model of the intestinal barrier, capable of accurately predicting the absorption of conventional small-molecule drugs. However, this model may not be applicable to all drugs, and the accuracy of absorption prediction is typically poor for high molecular weight drugs. Recently, human induced pluripotent stem (iPS) cell-derived small intestinal epithelial cells (hiPSC-SIECs), exhibiting properties similar to those of the small intestine when compared with Caco-2 cells, have been developed and are considered a novel candidate model for in vitro evaluation of intestinal drug permeability. Therefore, we evaluated the utility of human hiPSC-SIECs as a new in vitro model to predict the intestinal absorption of middle-molecular weight drugs and peptide drugs. Firstly, we showed that the hiPSC-SIEC monolayer allowed faster transport of peptide drugs (insulin and glucagon-like peptide-1) than the Caco- 2 cell monolayer. Second, we revealed that hiPSC-SIECs require divalent cations (Mg2+ and Ca2+) to maintain barrier integrity. Third, we demonstrated that experimental conditions established for Caco-2 cells are not persistently applicable to hiPSC-SICEs when analyzing absorption enhancers. Comprehensively clarifying the features of hiPSC-SICEs is essential to establish a new in vitro evaluation model.

In Vivo Proof of Biological Safety and Physiological Effects of Orally Ingested Water Containing H2-Filled Ultrafine Bubbles (UFBs).

Owing to their unique physicochemical properties and diverse biological effects, ultrafine bubbles (UFBs) have recently been expected to be utilized for industrial and biological purposes. Thus, this study investigated the biological safety of UFBs in water for living beings in drinking the water with a view to future use in health sciences. In this study, we used H2-filled UFBs (NanoGAS®) that can hold hydrogen in the aqueous phase for a long time. Mice were randomly assigned to one of three groups: those receiving NanoGAS® water, reverse osmosis water, or natural mineral water, and they ingested it ad libitum for one month or three months. As a result, subchronic drinking of NanoGAS® water does not affect either the common blood biochemical parameters or the health of the organs and mucosal membranes. Our results, for the first time, scientifically demonstrated the biological safety of H2-filled UFBs water for subchronic oral consumption.

Reconstructing the concept of empathy: an analysis of Japanese doctors' narratives of their experiences with illness.

The ability of doctors to empathise with patients is a crucial concern in establishing humanistic medicine. Therefore, the cultivation of this ability has been discussed extensively in medical education. One theory suggests that the experience of patienthood can increase empathy among doctors. This theory is supported by previous research that published doctors' illness narratives. However, the concept of empathy has been ambiguously defined in academic fields, including medicine; therefore, analysing how doctors experience 'empathy' in their interactions with patients is difficult. Our research question is how doctors who became patients describe the relationship between their illness experiences and the interactions with patients after their illness. To this end, this paper initially tracks the debates on 'empathy' in medicine and other disciplines, to develop a lens for analysing doctors' illness narratives. Next, we conduct a narrative analysis of illness stories from 18 Japanese medical doctors who became patients. Our analysis supports the traditional idea that an illness can enable a doctor to become more empathetic. However, this is overly simplistic; how doctors experience and subsequently process their illness is more complex. Moreover, this notion can disregard doctors' suffering in these circumstances, and fail to represent the often-lengthy process of mastering 'empathy' based on their experiences. Therefore, our analysis deconstructed the concept of 'empathy', showing that it can appear in various ways. Further research is required to elucidate how empathy is cultivated during the process of transformation of doctors' illnesses, focusing on their communities and practices.

Evaluation of Bactericidal Effects of H2- and O3-filled Ultrafine Bubbles Water.

Ultrafine bubbles (UFBs) are gaining attention in diverse industries as a new type of material with specific physical properties. Bactericidal activity has been reported as one of the unique properties of UFB water; however, the bactericidal activities of UFBs related to the gas type remain unclear. In particular, the bactericidal effect of hydrogen (H2) -filled UFB water has not been verified. Therefore, this study aimed to evaluate the bactericidal effects of H2- or ozone (O3) -filled UFB water using a bacterial suspension test. The results of this study clearly showed that H2- or O3-filled UFB water had strong bactericidal activity. Exposure of Escherichia coli for 6 h and Staphylococcus aureus for 3 h reduced the survival rate of those bacteria by >90%. This finding suggests that both O3 gas- and H2-filled UFBs are novel environmentally friendly disinfectants that can be employed to avoid the use of chemicals.

Patient experience (PX) among individuals with disabilities in Japan: a mixed-methods study.

BACKGROUND: People with disabilities (PWDs) tend to be disadvantaged in terms of receiving preventive medicine and medical checkups. About 7.6% of the Japanese population is estimated to have a disability. Although patient experience (PX) is an effective measure of patient-centeredness, little is known about the PX of PWDs. The present study aimed to compare the PX of PWDs with those of the non-disabled both quantitatively and qualitatively. METHODS: The present study involved a questionnaire survey and a free-response question on the survey form. The quantitative part of the study involved a comparison of JPCAT scores between PWDs and non-disabled participants. JPCAT is composed of five primary care principles: First contact, Longitudinality, Coordination, Comprehensiveness (service provided and service available), and Community orientation. Descriptive statistics were used to assess age, sex, years of education, self-rated health status, and type of disability (for PWDs). Multivariable analysis was performed using a linear regression model to detect differences between PWDs and non-disabled participants in total and domain-specific JPCAT scores. The model included the following confounding variables: age, sex, years of education, and self-rated health status. The qualitative part of the study involved a thematic analysis of answers to the free-response question. RESULTS: Data from 338 participants (169 PWDs and 169 non-disabled participants) were analyzed (response rate of 36% for PWDs). After adjusting for age, sex, years of education, and self-rated health status, PWD scores were significantly lower than those of non-disabled participants for the Longitudinality, Community Orientation, and Comprehensiveness (services available) domains of the JPCAT. Qualitative analysis yielded six themes, each of which was further divided to have Disability-Specific and General themes. CONCLUSIONS: JPCAT scores in PWDs were significantly lower than those of non-disabled participants for the Longitudinality, Community Orientation, and Comprehensiveness (services available) domains. Qualitative analysis revealed that PWDs shared several themes with non-disabled participants, but also to face unique challenges due to disabilities, such as the lack of a health care provider familiar with disabilities and the insurance transition at age 65, a unique feature of the Japanese health care system. TRIAL REGISTRATION: The study was a non-interventional, observational research trial, and thus registration was not required.

Therapeutic effects of anti-amyloid ß antibody after intravenous injection and efficient nose-to-brain delivery in Alzheimer's disease mouse model.

Antibody drugs that target amyloid ß (Aß) are considered possible treatments for Alzheimer's disease; however, most have been dropped from clinical trials. We hypothesized that administration route for antiAß antibody (AntiAß) might affect its therapeutic potential and thus compared delivery of antibodies to the brain and their effect on cognitive dysfunction and amyloid disposition via intravenous (i.v.) and intranasal routes with and without the cell-penetrating peptide, L-penetratin. We demonstrated that intranasal administration with L-penetratin more efficiently delivered human immunoglobulin G (IgG), a model molecule for AntiAß, to the brain compared with i.v. injection. We found that multiple intranasal treatments with Alexa 594-labeled AntiAß (A594-AntiAß) with L-penetratin significantly improved learning by mice with aged amyloid precursor protein (APP) knock-in (App KI mice). Further, intranasal administration of A594-AntiAß increased the amount of soluble Aß (1-42) in the brain, suggesting suppression of Aß aggregation in insoluble form and involvement of activated microglia in Aß clearance. Thus, administration route may be critical for efficient delivery of AntiAß to the brain, and the nose-to-brain delivery with L-penetratin can maximize its therapeutic efficacy.

Investigation of the Transport Pathways Associated with Enhanced Brain Delivery of Peptide Drugs by Intranasal Coadministration with Penetratin.

We previously found that coadministering peptides and proteins with the cell-penetrating peptide L-penetratin intranasally significantly increased transport to the brain and enhanced pharmacological effects. The present study aimed to clarify the mechanisms of nose-to-brain drug delivery enhancement by L-penetratin coadministration. First, we compared the concentrations of Exendin-4 in plasma and brain after intranasal and subcutaneous administration and suggested that coadministration with L-penetratin facilitated the direct nose-to-brain transport of Exendin-4. Second, we demonstrated that L-penetratin did not stimulate the transport of Cy7-labeled Exendin-4 and insulin through the trigeminal nerves but shifted their distribution to the olfactory mucosal pathway. Third, we investigated the distribution of insulin into the deeper regions of the brain after delivery via the olfactory pathway and suggested that insulin had entered the olfactory bulb, bottom part of the brain, and perivascular space through the cerebrospinal fluid and had diffused throughout the brain. We further demonstrated that intranasally delivered insulin with L-penetratin specifically accumulated on the hippocampus neuronal cells. Thus, this study suggested that administrating peptide drugs intranasally with L-penetratin allows direct transport to the olfactory bulb, bottom part of the brain, and perivascular space of the cerebral artery. This technique also potentially allows targeting of specific brain areas.

The Effects of Andrographolide on the Enhancement of Chondrogenesis and Osteogenesis in Human Suprapatellar Fat Pad Derived Mesenchymal Stem Cells.

Andrographolide is a labdane diterpenoid herb, which is isolated from the leaves of Andrographis paniculata, and widely used for its potential medical properties. However, there are no reports on the effects of andrographolide on the human suprapatellar fat pad of osteoarthritis patients. In the present study, our goal was to evaluate the innovative effects of andrographolide on viability and Tri-lineage differentiation of human mesenchymal stem cells from suprapatellar fat pad tissues. The results revealed that andrographolide had no cytotoxic effects when the concentration was less than 12.5 µM. Interestingly, andrographolide had significantly enhanced, dose dependent, osteogenesis and chondrogenesis as evidenced by a significantly intensified stain for Alizarin Red S, Toluidine Blue and Alcian Blue. Moreover, andrographolide can upregulate the expression of genes related to osteogenic and chondrogenic differentiation, including Runx2, OPN, Sox9, and Aggrecan in mesenchymal stem cells from human suprapatellar fat pad tissues. In contrast, andrographolide suppressed adipogenic differentiation as evidenced by significantly diminished Oil Red O staining and expression levels for adipogenic-specific genes for PPAR-γ2 and LPL. These findings confirm that andrographolide can specifically enhance osteogenesis and chondrogenesis of mesenchymal stem cells from human suprapatellar fat pad tissues. It has potential as a therapeutic agent derived from natural sources for regenerative medicine.

Comparative study of commercial protocols for high recovery of high-purity mesenchymal stem cell-derived extracellular vesicle isolation and their efficient labeling with fluorescent dyes.

The extracellular vesicles (EVs) derived from mesenchymal stem cells (MSCs) can be used as carriers for therapeutic molecules and drugs to target disordered tissues. This aimed to compare the protocols used for isolation of MSC-derived EVs by comparing EV collection conditions and three commercial purification kits. We also determined appropriate fluorescent dyes for labeling EVs. MSC-derived EVs were efficiently secreted during cell growth and highly purified by the phosphatidyl serine-based affinity kit. Although the EV membrane was more efficiently labeled with the fluorescent dye PKH67 compared to other probes, the efficiency was not enough to accurately analyze the endothelial cellular uptake of EVs. Results verified the easy protocol for isolating and fluorescently labeling EVs with commercial reagents and kits, but meanwhile, further modification of the protocol is required in order to scale up the amount of EVs derived from MSCs using fluorescent probes.

The in vitro and in vivo study of novel formulation of andrographolide PLGA nanoparticle embedded into gelatin-based hydrogel to prolong delivery and extend residence time in joint.

Andrographolide (AG), a well-known traditional medicinal plant in Southeast Asia, is widely used for treatment of many chronic diseases. Interestingly, AG has been reported to have inhibitory effects on osteoclast function and anti-inflammatory properties. Because of these therapeutic properties, this study aimed to develop and optimize the formulation of AG using PLGA nanocarriers and gelatin-based hydrogel to prolong the retention time in the joint. We investigated the in vitro release pattern of the AG nanoparticles formulation which prepared by emulsion solvent evaporation method and embedded into gelatin-based hydrogel. The result showed that the AG loaded ester terminated end group PLGA polymer gradually released AG from the PLGA nanoparticles when compared with AG solution. Importantly, the combined use of gelatin-based hydrogel with AG from the PLGA nanoparticles significantly delayed the AG release more than 1 month. Furthermore, we selected the DiR fluorescence dye to represents AG and monitored the retention time by IVIS imaging. The optimal formulation was administered as intra-articular drug delivery systems in in vivo study. The results successfully displayed a long-term sustained release for implantation (≈2 months) and injection (≥2 months) providing a novel strategy for the local management of osteoarthritis disease.

The Intestinal Efflux Transporter Inhibition Activity of Xanthones from Mangosteen Pericarp: An In Silico, In Vitro and Ex Vivo Approach.

The capacity of α-mangostin (α-MG) and ß-mangostin (ß-MG) from mangosteen pericarp on P-glycoprotein (Pgp) in silico, in vitro, and ex vivo was investigated in this study. Screening with the ADMET Predictor™ program predicted the two compounds to be both a Pgp inhibitor and Pgp substrate. The compounds tended to interact with Pgp and inhibit Pgp ATPase activity. Additionally, bidirectional transport on Caco-2 cell monolayers demonstrated a significantly lower efflux ratio than that of the control (α-(44.68) and ß-(46.08) MG versus the control (66.26); p < 0.05) indicating an inhibitory effect on Pgp activity. Test compounds additionally revealed a downregulation of MDR1 mRNA expression. Moreover, an ex vivo absorptive transport in everted mouse ileum confirmed the previous results that α-MG had a Pgp affinity inhibitor, leading to an increase in absorption of the Pgp substrate in the serosal side. In conclusion, α- and ß-MG have the capability to inhibit Pgp and they also alter Pgp expression, which makes them possible candidates for reducing multidrug resistance. Additionally, they influence the bioavailability and transport of Pgp substrate drugs.

Evaluation of Cell-Penetrating Peptides as Versatile, Effective Absorption Enhancers: Relation to Molecular Weight and Inherent Epithelial Drug Permeability.

PURPOSE: The poor permeability of new drug candidates across intestinal epithelial membranes complicates their development in oral form. This study investigated the potential of cell-penetrating peptides (CPPs) to improve the intestinal permeation and absorption of low-permeable low-molecular-weight (low-MW) drugs. METHODS: The in vitro epithelial permeation of six different drugs (metformin, risedronate, zanamivir, methotrexate [MTX], tacrolimus, and vincristine [VCR]) across Caco-2 cell monolayers was examined in the presence and absence of L- or D-penetratin, and the correlation between permeation enhancement efficiency and the properties of tested drugs was analyzed. In addition, a rat closed ileal loop absorption study was conducted to determine the in vivo effects of penetratin. RESULTS: MTX and VCR efficiently permeated Caco-2 monolayers in the presence of L- and D-penetratin, suggesting that CPPs enhanced the epithelial permeation of drugs with relatively high molecular weight and resultant limited intrinsic permeability. The in vivo rat closed ileal loop absorption study revealed the stimulatory effect of L- and D-penetratin on the intestinal absorption of MTX and VCR. CONCLUSIONS: CPPs are useful as oral absorption enhancers for low-permeable drugs.

Effects of intestinal luminal contents and the importance of microfold cells on the ability of cell-penetrating peptides to enhance epithelial permeation of insulin.

We previously reported that oral and intestinal absorption of insulin in rats and mice is significantly enhanced in vivo by coadministration with cell-penetrating peptides (CPPs). To evaluate the clinical use of CPPs as absorption enhancers, it is imperative to clarify the mechanisms associated with the permeation-stimulatory effect of CPPs in vitro. The confirmation experiment revealed a discrepancy between in vivo and in vitro effects of CPPs, such as D-octaarginine (D-R8) and L-penetratin, on epithelial permeation of insulin. The present study was designed to determine the factors that work in vivo but are deficient in an in vitro system consisting of Caco-2 cells. The effects of D-R8 and L-penetratin on permeation of insulin through the Caco-2 cell monolayer were partially boosted in fasted-state simulated intestinal fluid (FaSSIF). Contrary to expectation, the effects of CPPs on cellular uptake of insulin and the binding ratio of CPPs to insulin analyzed by surface plasmon resonance in normal buffer and FaSSIF were similar. Also, the effects of CPPs, especially D-R8, on cellular uptake of insulin, were stronger in Caco-2 cell monolayers with microfold cell (M cell)-like properties. These results suggested a key role of intestinal lipids and M cells in the stimulatory effect of CPPs on net epithelial permeation of insulin in vivo.

Systemic and brain delivery of leptin via intranasal coadministration with cell-penetrating peptides and its therapeutic potential for obesity.

Leptin is an endogenous hormone that regulates the appetite, energy metabolism, and glucose intake in the central nervous system (CNS) and is a potential therapeutic agent for obesity. In the normal healthy condition, peripherally secreted leptin is transported across the blood-brain barrier (BBB) to the target brain site, in particular the hypothalamus. However, it was reported that the progression of obesity causes diminished permeation of leptin across the BBB. The present study therefore aimed to effectively deliver leptin to the brain via intranasal coadministration with penetratin, an amphipathic cell-penetrating peptide (CPP), for potential treatment and prevention of obesity. The single administration study with normal rats demonstrated that leptin coadministered with L-penetratin was efficiently absorbed into the systemic circulation and accumulated in the anterior part of brain. Furthermore, chronic delivery of leptin via repeated intranasal coadministrations with L-penetratin suppressed the appetite and the body weight increase of the rats and lowered their plasma triglyceride levels. Analysis of brain samples after repeated administration suggested that Stat3 phosphorylation via leptin receptor stimulation potentially contributed to the therapeutic effect of leptin in the CNS. Thus, the present study suggests that intranasal coadministration with CPPs will become a promising strategy for delivering leptin to treat and prevent the progression of obesity.

Doctors' experience of becoming patients and its influence on their medical practice: A literature review.

PURPOSE: Doctors' illness experiences can deeply influence not only their perceptions of illness and roles but also their medical practice. Researchers and doctors have sought to understand what happens when doctors become patients. However, currently, literature reviews focused exclusively on their illness experiences are lacking. This review examines academic literature and combines it with illness narratives (i.e., pathographies) written by doctors to elucidate the unknown about doctors' experiences and its subsequent influence on medical practice. METHODS: An electronic search of the databases Academic Search Complete, Google Scholar, PubMed, ProQuest, and Ichushi-Web was conducted using relevant keywords. The literature reviewed included studies that described doctors' illness experiences or doctors' perspectives on their experiences of being patients. RESULTS: Previous studies showed that doctors' disease prognoses are generally better than or similar to those of patients belonging to the general population. However, doctors' documented illness experiences are multi-dimensional and have several common themes. These include the concept of the 'medical self' (behaving as a doctor despite being a patient) and 'role reversal' (the doctor adjusting to the patient role). The other elements of their experiences include barriers to health care, self-treatment and self-doctoring, presenteeism, and 'wounded healers' (those who can heal others using the wisdom from their illness experiences). Most previous literature has omitted the sociocultural and historical dispositions of doctors and their biomedical perspectives of their own afflictions, even though these strongly impact their illness experiences. CONCLUSION: Further research that re-contextualises the meaning of illness for doctors is necessary.

Optimization of the method for analyzing endocytosis of fluorescently tagged molecules: Impact of incubation in the cell culture medium and cell surface wash with glycine-hydrochloric acid buffer.

To obtain the therapeutic effect of biological medicines, such as proteins and nucleic acids, these medicines must achieve their intracellular target, such as the cytoplasm, and pass through biological membrane barriers. Endocytosis is an attractive route for the intracellular delivery of such drugs, and various endocytosis inhibitors have been used as tools to study the involvement of endocytosis in the cell internalization of delivery carriers. However, the specificity of these inhibitors has been insufficiently studied, and our preliminary tests could not detect the expected effect of the well-known endocytosis inhibitors. Therefore, the present study aimed to optimize the experimental conditions to precisely analyze cellular internalization via endocytosis. We first found that incubation of model molecules, such as transferrin (Tf) and cholera toxin subunit B (CTB), in cell culture medium (DMEM) could efficiently induce their internalization to HeLa cells compared to that in transport buffer (HBSS). Moreover, we clarified that cell surface wash with glycine-hydrochloric acid buffer before confocal microscopy and flow cytometry strengthened the intracellular fluorescence of Tf, CTB, and dextran tagged with fluorescent probes possibly via the neutralization of endosomal pH. Even under the optimized condition, however, the specificity of endocytosis inhibitors was disputable. The present study suggested the importance of the optimization of the study design with endocytosis inhibitors in analyzing cellular internalization.

Effective nose-to-brain delivery of exendin-4 via coadministration with cell-penetrating peptides for improving progressive cognitive dysfunction.

In a recent study, we demonstrated the potential of a cell-penetrating peptide (CPP) penetratin to deliver the peptide drug insulin to the brain via nasal administration, and its pharmacological effect on the mild cognitive dysfunction in senescence-accelerated mouse (SAMP8). However, the therapeutic potential of intranasal insulin administration was attenuated when applied to the aged SAMP8 with severe cognitive dysfunction. The present study, therefore, aimed to overcome the difficulty in treating severe cognitive dysfunction using insulin by investigating potential alternatives, glucagon-like peptide-1 (GLP-1) receptor agonists such as exendin-4. Examination using normal ddY mice demonstrated that the distribution of exendin-4 throughout the brain was dramatically increased by intranasal coadministration with the L-form of penetratin. The activation of hippocampal insulin signaling after the simultaneous nose-to-brain delivery of exendin-4 and an adequate level of insulin were confirmed by analyzing the phosphorylation of Akt. Furthermore, spatial learning ability, evaluated in the Morris water maze test after daily administration of exendin-4 with L-penetratin and supplemental insulin for 4 weeks, suggested therapeutic efficacy against severe cognitive dysfunction. The present study suggests that nose-to-brain delivery of exendin-4 with supplemental insulin, mediated by CPP coadministration, shows promise for the treatment of progressive cognitive dysfunction in SAMP8.

Hydrophobic Amino Acid Tryptophan Shows Promise as a Potential Absorption Enhancer for Oral Delivery of Biopharmaceuticals.

Cell-penetrating peptides (CPPs) have great potential to efficiently deliver drug cargos across cell membranes without cytotoxicity. Cationic arginine and hydrophobic tryptophan have been reported to be key component amino acids for cellular internalization of CPPs. We recently found that l-arginine could increase the oral delivery of insulin in its single amino acid form. Therefore, in the present study, we evaluated the ability of another key amino acid, tryptophan, to enhance the intestinal absorption of biopharmaceuticals. We demonstrated that co-administration with l-tryptophan significantly facilitated the oral and intestinal absorption of the peptide drug insulin administered to rats. Furthermore, l-tryptophan exhibited the ability to greatly enhance the intestinal absorption of other peptide drugs such as glucagon-like peptide-1 (GLP-1), its analog Exendin-4 and macromolecular hydrophilic dextrans with molecular weights ranging from 4000 to 70,000 g/mol. However, no intermolecular interaction between insulin and l-tryptophan was observed and no toxic alterations to epithelial cellular integrity-such as changes to cell membranes, cell viability, or paracellular tight junctions-were found. This suggests that yet to be discovered inherent biological mechanisms are involved in the stimulation of insulin absorption by co-administration with l-tryptophan. These results are the first to demonstrate the significant potential of using the single amino acid l-tryptophan as an effective and versatile bioavailability enhancer for the oral delivery of biopharmaceuticals.