A Brief Overview of the Oral Delivery of Insulin as an Alternative to the Parenteral Delivery

The Current and Promising Oral Delivery Methods for Protein- and Peptide-Based Drugs

Drugs based on peptides and proteins (PPs) have been widely used in medicine, beginning with insulin therapy in patients with diabetes mellitus over a century ago. Although the oral route of drug administration is the preferred one by the vast majority of patients and improves compliance, medications of this kind due to their specific chemical structure are typically delivered parenterally, which ensures optimal bioavailability. In order to overcome issues connected with oral absorption of PPs such as their instability depending on digestive enzymes and pH changes in the gastrointestinal (GI) system on the one hand, but also their limited permeability across physiological barriers (mucus and epithelium) on the other hand, scientists have been strenuously searching for novel delivery methods enabling peptide and protein drugs (PPDs) to be administered enterally. These include utilization of different nanoparticles, transport channels, substances enhancing permeation, chemical modifications, hydrogels, microneedles, microemulsion, proteolytic enzyme inhibitors, and cell-penetrating peptides, all of which are extensively discussed in this review. Furthermore, this article highlights oral PP therapeutics both previously used in therapy and currently available on the medical market.

Nanomedicines based on trace elements for intervention of diabetes mellitus

Epidemiology shows that the incidence of diabetes mellitus (DM) is increasing year by year globally. Proper interventions are highly aspired for diabetics to improve the quality of life and prevent development of chronic complications. Trace elements, also known as microelements, are chemical substances that are present in our body in minute amounts. They are necessitated by the body for growth, development and functional metabolism. For the past few years, trace element nanoparticles have aroused considerable interest as a burgeoning form of nanomedicines in antidiabetic applications. These microelement-based nanomedicines can regulate glucose metabolism in several ways, showing great potential for diabetes management. Starting from the pathophysiology of diabetes, the state-of-the-art of diabetes treatment, the physiological roles of trace elements, various emerging trace element nanoparticles specific for diabetes were comprehensively reviewed in this work. Our findings disclose that trace element nanoparticles can fight against diabetes by lowering blood glucose, promoting insulin secretion, alleviating glucose intolerance, improving insulin sensitivity, ameliorating lipid profile, anti-inflammation and anti-oxidant stress, and other mechanisms. In conclusion, trace element nanoparticles can be applied as nanomedicines or dietary modifiers for effective intervention for diabetes.

The promising application of hydrogel microneedles in medical application

OBJECTIVES

Hydrogel microneedles are emerging, and promising microneedles mainly composed of swelling polymers. This review is intended to summarize the preparation materials, formation mechanisms, applications and existing problems of hydrogel microneedles.

METHODS

We collected the literature on the materials, preparation and application of hydrogel microneedles in recent years, and summarized their mechanism and application in drugs delivery.

KEY FINDINGS

Hydrogel microneedles have higher safety and capabilities of controlled drug release, and have been mainly used in tumour and diabetes treatment, as well as clinical monitoring. In recent years, hydrogel microneedles have shown great potential in drug delivery, and have played the role of whitening, anti-inflammatory and promoting healing.

CONCLUSIONS

As an emerging drug delivery idea, hydrogel microneedles for drug delivery has gradually become a research hotspot. This review will provide a systematic vision for the favourable development of hydrogel microneedles and their promising application in medicine, especially drug delivery.

An overview of oral insulin delivery strategies (OIDS)

Despite tremendous efforts, the world continues its fight against the common chronic disease-diabetes. Diabetes is caused by elevated glucose levels in the blood, which can lead to several complications like glaucoma, cataract, kidney failure, diabetic ketoacidosis, heart attack, and stroke. According to recent statistics, China, India, and the US rank at the top three positions with regards to the number of patients affected by diabetes. Ever since its discovery, insulin is one of the major therapeutic molecules that is used to control the disease in the diabetic population, worldwide. The most common route of insulin administration has been the subcutaneous route. However, the limitations associated with this route have motivated global efforts to explore alternative strategies to deliver insulin, including pulmonary, transdermal, nasal, rectal, buccal, and oral routes. Oral insulin delivery is the most convenient and patient-centered route. However, the oral route is also associated with numerous drawbacks that present significant challenges to the scientific fraternity. The human physiological system acts as a formidable barrier to insulin, limiting its bioavailability. The present review covers the major barriers against oral insulin delivery and explains formulation strategies that have been adopted to overcome these barriers. The review focuses on oral insulin delivery strategies (OIDS) for increasing the bioavailability of oral insulin, including nanoparticles, microparticles, nano-in-microparticles, hydrogels, tablets, capsules, intestinal patches, and use of ionic liquids. It also highlights some of the notable recent advancements and clinical trials in oral insulin delivery. This formulation based OIDS may significantly improve patient compliance in the treatment of diabetes.

Emerging Treatment Strategies for Diabetes Mellitus and Associated Complications: An Update

The occurrence of diabetes mellitus (DM) is increasing rapidly at an accelerating rate worldwide. The status of diabetes has changed over the last three generations; whereas before it was deemed a minor disease of older people but currently it is now one of the leading causes of morbidity and mortality among middle-aged and young people. High blood glucose-mediated functional loss, insulin sensitivity, and insulin deficiency lead to chronic disorders such as Type 1 and Type 2 DM. Traditional treatments of DM, such as insulin sensitization and insulin secretion cause undesirable side effects, leading to patient incompliance and lack of treatment. Nanotechnology in diabetes studies has encouraged the development of new modalities for measuring glucose and supplying insulin that hold the potential to improve the quality of life of diabetics. Other therapies, such as β-cells regeneration and gene therapy, in addition to insulin and oral hypoglycemic drugs, are currently used to control diabetes. The present review highlights the nanocarrier-based drug delivery systems and emerging treatment strategies of DM.

In vivo oral insulin delivery via covalent organic frameworks

With diabetes being the 7th leading cause of death worldwide, overcoming issues limiting the oral administration of insulin is of global significance. The development of imine-linked-covalent organic framework (nCOF) nanoparticles for oral insulin delivery to overcome these delivery barriers is herein reported. A gastro-resistant nCOF was prepared from layered nanosheets with insulin loaded between the nanosheet layers. The insulin-loaded nCOF exhibited insulin protection in digestive fluids in vitro as well as glucose-responsive release, and this hyperglycemia-induced release was confirmed in vivo in diabetic rats without noticeable toxic effects. This is strong evidence that nCOF-based oral insulin delivery systems could replace traditional subcutaneous injections easing insulin therapy.

Innovative Mucoadhesive Precursor of Liquid Crystalline System Loading Anti-Gellatinolytic Peptide for Topical Treatment of Oral Cancer

Current researches report an actual benefit of a treatment for oral cancer via inhibition of proteolytic matrix metallopro-teinases (MPP) with a peptide drug, called CTT1. However, peptides present poor oral bioavailability. Topical administration on oral mucosa avoids its passage through the gastrointestinal tract and the first-pass liver metabolism, but the barrier function of the oral mucosa can impair the permeation and retention of CTT1. The objective of this study is to incorporate CTT1 into a mucoadhesive precursor of liquid crystalline system (PLCS) as an interesting strategy for the topical treatment of oral cancer. PLCS consisting of oleic acid, ethoxylated 20 and propoxylated cetyl alcohol 5, polyethyleneimine (P)-associated chitosan (C) dispersion and CTT1 (FPC-CTT1) was developed and characterized by polarized light microscopy (PLM) and small-angle X-ray scattering (SAXS). In vitro permeation and retention across esophageal mucosa, In vitro cytotoxicity towards tongue squamous cell carcinoma cells, and in vivo evaluation of vascular changes using the chick embryo chorioallantoic membrane (CAM) model were performed. PLM and SAXS showed that FPC-CTT1acted as PLCS, because it formed a lamellar liquid crystalline system after the addition of artificial saliva. FPC-CTT1increased approximately 2-fold the flux of permeation and 3-fold the retention of CTT1 on the porcine esophageal mucosa. CTT1 does not affect cell viability. CAM tests showed that FPC preserved the blood vessels and it can be a safe formulation. These findings encourage the use of the FPC-CTT1 for topical treatment of oral cancer.

In vivo testing of mucus-permeating nanoparticles for oral insulin delivery using Caenorhabditis elegans as a model under hyperglycemic conditions

The aim was to evaluate the potential of mucus-permeating nanoparticles for the oral administration of insulin. These nanocarriers, based on the coating of zein nanoparticles with a polymer conjugate containing PEG, displayed a size of 260 nm with a negative surface charge and an insulin payload of 77 μg/mg. In intestinal pig mucus, the diffusivity of these nanoparticles (PPA-NPs) was found to be 20-fold higher than bare nanoparticles (NPs). These results were in line with the biodistribution study in rats, in which NPs remained trapped in the mucus, whereas PPA-NPs were able to cross this layer and reach the epithelium surface. The therapeutic efficacy was evaluated in Caenorhabditis elegans grown under high glucose conditions. In this model, worms treated with insulin-loaded in PPA-NPs displayed a longer lifespan than those treated with insulin free or nanoencapsulated in NPs. This finding was associated with a significant reduction in the formation of reactive oxygen species (ROS) as well as an important decrease in the glucose and fat content in worms. These effects would be related with the mucus-permeating ability of PPA-NPs that would facilitate the passage through the intestinal peritrophic-like dense layer of worms (similar to mucus) and, thus, the absorption of insulin.