Exploring Probiotic Loaded Gastroprotective Microgel Strategy for Gut Health and Ulcer Therapy

The worldwide epidemiology of gastric ulcers and Inflammatory bowel diseases (IBD), including ulcerative colitis and Crohns disease can be taken as one of the most significant threats to the well-being of individuals and the healthcare systems in general. Being triggered by infection with Helicobacter pylori or widespread use of non-steroidal anti-inflammatory drugs (NSAIDs), gastrointestinal ulcers present themselves in the form of painful ulcers in the stomach mucosa, causing bleeding, perforation, or complications of various kinds. IBD, in its turn, is a condition that is marked by chronic, relapsing gastrointestinal tract inflammation, which leads to its debilitating symptoms such as severe diarrhea, abdominal pain, and weight loss. The pathogenesis of these diseases is complicated and characterized by a combination of genetic factors, immune system malfunctions, environmental factors, and most importantly, microbiota dysfunction- the enormous system of microorganisms that live in our intestines. This microbial imbalance or dysbiosis is not only becoming more and more accepted as a result, but a powerful pathogenesis of diseases, providing a vicious circle of inflammation and barrier dysfunction. These diseases are so widespread that millions of people are already infected, and their quality of life and economic performance have become greatly affected, which is why there is a pressing and ongoing necessity of effective and sustainable treatment programs [1].

The traditional therapeutic options, although they deliver the necessary levels of symptom control and remission development, are highly limited in nature negatively affecting long-term care of the patients. In gastric ulcers, the first-line therapies are normally proton pump inhibitors (PPIs) to reduce gastric acid and the use of antibiotics to eliminate H. pylori. In the case of IBD, the most common therapies are those that are anti-inflammatory, such as aminosalicylates, acute flares with corticosteroids, and more advanced immunomodulators or biologics that are designed to exert influence on individual inflammatory pathways [2]. These methods are however usually marred by some problematic side effects, such as long term use of PPI has been linked to higher risks of infections, deficiencies of nutrients, and bone fractures, whereas corticosteroids may cause weight gain, diabetes, and osteoporosis. More essentially, such treatments often do not help in treating the underlying root causes, especially dysbiosis, and are characterized by a high proportion of disease recurrence following discontinuation. Ironically, though, certain traditional treatments may cause microbial imbalance by themselves. Ulcer treatment requires broad-spectrum antibiotics which in turn, wipe off both the pathology and the good bacteria indiscriminately further disrupting the gut ecosystem. Likewise, potent immunosuppressives are capable of modifying the capability of the host to control its microbial flora. This is a therapeutic contradiction: the same medication that is employed to suppress inflammation can actually contribute to maintaining the dysbiotic condition that supports it, which is a major missing link in our treatment repertoire of producing lasting, comprehensive gastrointestinal health [3-5].

In this regard, probiotics: live microorganisms, which have a health benefit when taken in sufficient quantities, have become a promising adjunct in therapy that has the potential to balance fundamental pathological mechanisms. They are not intended to have a direct antimicrobial or immunosuppressive effect, but rather a multi-faceted and restorative effect on the disease basis. The intestinal epithelial barrier performance can also be improved with probiotic strains (including some species of Lactobacillus and Bifidobacterium) that are able to drive the synthesis of tight junction proteins which essentially seal a permeable gut [6]. Their competition has the effect of exclusion of the pathogens in a competitive way of sharing adhesion sites and nutritional resources. Moreover, they alter the immune response of the host, facilitating the transition towards anti-inflammatory cytokine states (e.g. raising IL-10) and suppressing pro-inflammatory cues (e.g. down-regulation of TNF-α). Most importantly, they are able to generate positive metabolites such as short-chain fatty acids (e.g., butyrate), which can act as a source of energy to colonocytes and have a strong anti-inflammatory impact. Probiotics seek to counter dysbiosis and inflammation by having a direct effect on the gut microbial community to reestablish a healthy and resilient microbiota. This comprehensive action mechanism makes them the best candidates of long-term management, which could lead to the minimization of use of conventional drugs and their side effects [7].

Although such a great therapeutic potential exists, biotic and technological challenges have been an insurmountable barrier to the successful delivery of probiotics to their target sites of action within the gastrointestinal tract. Much of the ingested probiotic organisms cannot withstand the harsh and acidic conditions of the stomach which may have a pH of 1.5 or less. The ones that escape the gastric transit are then met in the duodenum by bile salts and pancreatic enzymes which further destroy their population [8]. Therefore, a very small portion of the administered dose gets to the small and large intestines in their active and metadata forms, seriously reducing their therapeutic effects. This implies that it requires the administration of very high doses to become clinically effective, which is not cost-effective and guaranteed. Additionally, some probiotic strains exhibit a transient colonizing property that is, they do not permanently settle in the gut and their effect fades away soon after discontinuation of their use [9]. The clinical translation and overall therapeutic efficacy of probiotics significantly have been impeded by these delivery challenges, posing a desperate requirement of a delivery mechanism that has the potential to shield the fragile biological objects as their gastrointestinal systems navigate their environment [10].

It is precisely the fact that microencapsulation technology is aimed at overcoming these delivery barriers to convert probiotics into a form that is no longer vulnerable but rather is shielded, targeted, and sustained-release therapeutic delivery systems. Microencapsulation is essentially the process of entrapment of living probiotic cells within a protective shell or matrix, usually made of biocompatible, edible polymers including alginate, chitosan, whey protein or resistant starches. The main role of this microscopic shield is to give a physical and chemical protection against the high acidity and bile salts in the stomach which is extremely acidic strongly enhancing the survival rate of the bacteria [11]. It has been demonstrated that microencapsulation is capable of enhancing viability of probiotics following simulated gastric digestion by many orders of magnitude compared to non-encapsulated cells. In addition to protection, more sophisticated microencapsulation can be developed to be released specifically. The payload can be specifically targeted to the ileum and colon- the main disease sites in IBD and important interaction zones of the microbes by choosing polymers that are resistant to stomach acid but degrade at higher pH of the intestines or are digested through enzymes specific to the colon. This localized delivery reduces waste and localizes the maximum therapeutic effect. Lastly, microencapsulation enables sustained-release profile, which is a great benefit compared to bolus release of free probiotics [12]. The released encapsulated cells are slower in being released as the polymer shell degrades or fills up in the intestinal environment. Such long-term release may aid in preserving a larger and more consistent population of useful bacteria in the gut in the longer term, which may increase their capacity to colonize and give them a greater treatment window. This action is especially useful when it comes to chronic diseases such as IBD, in which the perpetual rehabilitation of the intestinal ecosystem is preferable. Overall, the problem of microencapsulation will deal with the inherent Achilles heel of probiotic therapy [13]. This technology means that the full clinical potential of probiotics can be unlocked through the synergistic provision of gastrointestinal insult protection, specific intestinal location targeting and sustained delivery. It is a complex integration of microbiology and material science, which seeks to change the way we administer live biotherapeutics in order to effectively and permanently treat debilitating gastric and inflammatory bowel diseases and, in this way, change the treatment paradigm of these diseases to not focusing on symptom suppression but ecological restoration of the gut microbiome [14-16].

Fig: 1 Emerging microbiome-directed therapies in inflammatory bowel disease: beyond diet modification and FMT

2. Design rationale and engineering of probiotic microgels

The careful selection of the fundamental biological agent the probiotic strain itself is the principle step in the fabrication of an efficient microencapsulated probiotic treatment. This is not any random selection but one that depends basically on the pathophysiology of the desired target condition and the intended mechanistic action. To protect the gastric health and antimicrobial activity against H. pylori, Lactobacillus (e.g., L. reuteri, L. casei) are often selected due to their survival in the acidic environment of the stomach, the production of antimicrobial agents such as bacteriocins, and competition with H. pylori regarding available adhesion sites. In the case of inflammatory bowel diseases, there is an expansion of the choice, to encompass a consortium directed at immune modulation and restoration of a barrier [17]. The species of Bifidobacterium (e.g., B. longum, B. infantis, etc.) are outstanding due to their capability to generate butyrate and strengthen the gut barrier. One of the most relevant and clinically proven strains is Escherichia coli Nissle 1917, a non-pathogenic probiotic that is proven to be effective in keeping ulcerative colitis in remission, which occurs with the help of pathogen exclusion mechanisms, microcin secretion, and tight junction reinforcement. Most recently, there is interest in the next-generation probiotics such as Akkermansia muciniphila. It is a bacterium that degrades mucus that has an inverted relationship with IBD and metabolic disorders, strengthens the mucus layer, enhances gut integrity of barriers, and regulates immune response. Its rigid anaerobic style, however, poses a daunting challenge of encapsulation and delivery and necessitates technologies that can preserve an oxygen-free microenvironment. In this way, the intrinsic characteristics of the strain such as sensitivity to acid, oxygen, bile, the adhesion properties of the strain and its metabolic activities will directly govern the design specifications of the microencapsulation system, which will host it [18].

The choice of microgel matrix material is an important engineering choice, which dictates the performance of the capsule, that is, a balance between protection, release, and biocompatibility. These polymers create the physical and chemical protection of the probiotic. Alginate is a natural polysaccharide derived out of seaweed, and it is still a cornerstone material because of its biocompatibility, low cost, and softer gelation procedure, through cross-linking with divalent cations such as calcium [19]. It is pH-sensitive and does not dissolve at pH 7.6, that is, at the intestinal level, but at pH 4.5, that is, at the stomach level, it does not dissolve, thus it is targeted to be released. Also, it is capable of staying longer at the intestinal mucosa because of its natural mucoadhesive properties. An alternative is the protein-based gelatin and its photocross-linkable product, gelatin methacryloyl (GelMA). These are biodegradable, facilitate cell adhesion and proliferation and can be enzymatically broken down by colonic proteases enabling colon-specific release. This is why GelMA is a great candidate to entrap the delicate strains such as Akkermansia muciniphila inside of a porous yet supportive 3D scaffold [20]. One cationic chitin-derived polysaccharide, chitosan, is valued due to its high mucoadhesive characteristics - owing to electrostatic interaction with negatively charged mucosal surfaces - and inherent antimicrobial qualities, which can serve to provide an extra protective layer against pathogenic conditions to the probiotic encased within it. Hyaluronic acid is a bioactive polymer and a major component of the extracellular matrix that has the potential to target CD44 receptors that are frequently overexpressed on inflamed intestinal epithelial cells in IBD, providing the potential of active targeting. Lastly, cellulose derivatives such as carboxymethyl cellulose (CMC) tend to be employed as modifiers in order to increase viscosity, mechanical stability of gels, or as a coating material to create an additional barrier to diffusion. The strategic combination of these polymers in the composite matrices can be used to customize microgels to certain strains and disease targets, as in the table, optimizing the trade-off between robust protection and efficient, site-specific release [21-25].

Beyond the simple world of spherical beads, more complicated encapsulation architectures are currently being developed to handle even more complicated therapeutic issues. Among the revolutionary ones is the creation of single-bacterium microgels, or precision encapsulation. The method includes a process whereby the individual probiotic cells are encased in an ultra-thin nano-sized hydrogel shell usually with a substance such as CMC or alginate mixed with protective coating. This design optimizes the ratio of surface to volume to come into contact with the gut environment and offers a consistent and accurate dosage [26]. It does not solve the problem of bacterial aggregation and enables each cell to be equally covered, which can result in significantly higher survival rates and more predictable therapeutic outcomes. Multi-layer coatings are used to protect further especially against the hostile upper GI tract. These are used as a hierarchical armor. One of the earliest applications is an example of a triple-coat of proanthocyanidins (antioxidant plant compounds), mucin (a gut glycoprotein), and phosphatidylcholine (a phospholipid). The proanthocyanidin layer offers a sacrificial antioxidant protection against the presence of reactive oxygen species in inflamed guts; the mucin layer increases biocompatibility and mucoadhesion, camouflaging the probiotic as a native gut particle; and the outer phosphatidylcholine layer withstands attack by bile salts. It is a more complex design that has the potential to enhance the viability of probiotics in simulated gastrointestinal fluids by more than 100-fold that of unencapsulated cells [27]. Last, the combination therapy is at the nano-in-micro. In this design, not only live probiotics are confined in a larger microgel particle (the micro) but also nano-carriers (the nano) with therapeutic drugs (e.g. anti-inflammatory spices such as curcumin or 5-ASA) or prebiotics. This enables synergistic, co-localized application of a variety of therapeutic interventions: the probiotic recovers the microbial ecology, the drug suppressed acute inflammation and the prebiotic promotes the growth of desirable bacteria. Such a multi-pronged approach in one delivery vehicle replicates the complexity of pathology of diseases and provides an effective, combined treatment approach [28-30].

The practicality of these microencapsulation designs depends upon advanced fabrication methods, and each is advantageous in a different way, with regard to particle size, uniformity, scalability, and compatibility with live cells. The most common and simplest technique of algae-based systems is ionic gelation [31]. It is based on the ability to extrude a drop of probiotic-polymer mixture into a hardening bath using calcium ions and create gel beads. It is soft but yields relatively wide size distribution beads in millimeters. Both internal and external emulsification techniques are employed to form smaller particles that have a size of microns. These are used whereby a probiotic-polymer aqueous solution is placed in an immiscible oil phase agitated to create a water-in-oil emulsion. Induction of gelation in the droplets is then induced, and commonly through the addition of cross-linkers by use of the oil phase or temperature variation [32]. This technique enables a better level of control on size but involves the removal of oil residues. Spray-drying is a continuous process, at the industrial scale, in which a probiotic-polymer suspension is atomized to a hot air chamber, leading to a rapid evaporation of water and the creation of dry and powdered microparticles. Although it is efficient and scalable, probiotics are susceptible to high temperatures and shear forces, which require protection formulations and cryoprotectants to be robust. Microfluidic methods are the most important in the case of the greatest control and production of other superior architectures such as single-cell microgels or intricate core-shell architectures [33]. An example, gas-shearing microfluidics, applies a specific flow rate of gases in order to shear monodisperse droplets of the probiotic-polymer solution at a junction and suspended droplets are immediately gelled. This technology makes it possible to create highly uniform particles of tunable sizes in the tens to hundreds of microns and is ideally applicable to making the multi-layered or nano-in-micro systems mentioned described. The selection of fabrication method therefore represents a trade off between the particle specifications, the throughput, the cost and above all preservation of the probiotic viability thus leading the transformation between the beautiful laboratory designs to practical clinical and commercial products [34].

3. Mechanisms of gastroprotection and therapeutic action

The therapeutic activity of microencapsulated probiotics depends on their programmed capacity to first pass translocation to the pathogenic lesion site and second, conduct a multi-pronged biological repair program. The obstacle most intricate and the first one is the mighty gastric acid barrier and enzyme degradation in the upper gastrointestinal tract. Probiotics that are not under protection are soon killed by the low-pH environment in the stomach. Microencapsulation is a crucial physical protective effect; the polymer skeleton is a diffusion barrier that regulates the pH of the interior and prevents the hydrogen ions and pepsin to actively assault the cells of the bacteria [35]. Even more robust protection is provided by advanced architectures, e.g., multi-layer coatings that have acid-resistant lipids like phosphatidylcholine or antioxidant-containing plant polyphenol layers. This allows a much increased viable payload to be obtained to the duodenum - studies have shown improvements of many orders of magnitude. Moreover, through the application of pH-sensitive polymers such as alginate or Eudragit which are stable at the stomach but soluble at neutral intestinal pH, the system is able to deliver targets. This spatial containment means that the probiotics do not get wasted in the stomach rather; they are released straight in the small intestine and colon where they are required to fight against inflammation and ulceration [36-38]. After entering the intestinal tract a second engineered property, namely mucoadhesion, is involved in order to have as much therapeutic contact time as possible. Such polymers as chitosan, alginate, and hyaluronic acid have natural mucoadhesive characteristics and are non-covalent in interactions (electrostatic, hydrogen bonds, hydrophobic interactions) with the mucin coating the epithelium. This adhesion is essential in such situations as gastric ulcers or IBD when therapeutics can be rapidly transported by the gastric or diarrhea system and washed away. It increases the retention time of the microgels on the ulcerated or inflamed locations forming a localized sustained release depot of probiotics [39]. An unceasing drip-feed of useful bacteria can in this way be persistently used to manage the local microenvironment which is much more efficient than the temporary passage of unencapsulated cells. This is because of the targeted-release of the agent coupled with the mucoadhesion so that the therapeutic agents can be localized at the precise location of where the pathology is and this increases the potency as well as allowing lower effectiveness doses [40].

First, probiotics are released and have a direct contribution to the restoration of mucosal barriers. Their action is to induce the goblet cells to produce more mucus resulting in physically thicker and stronger protective mucus layer studies involving microencapsulated formulations have shown that it is increased by 5.63- folds of the thickness of the mucus [41]. At the same time, they increase the expression of epithelial tight junction proteins (e.g., occludin, ZO-1), which cover the "leaky gut" and decrease intestinal permeability. Second, they have a strong anti-inflammatory effect, mediating the effect on the host immune response. They inhibit the release of pro-inflammatory cytokines (such as TNF-a, IL-6 and IL- 1b ) and enhance the release of anti-inflammatory cytokines (such as IL-10 and TGF-b1). This cytokine action is the key to the solution of inflammation in gastric as well as IBD cases [42-44]. Third, probiotics fight oxidative stress which is a major cause of tissue destruction in ulcers and colitis. Some of these strains have inherent antioxidant enzymes, and microencapsulation may further augment this by including antioxidant material in the shell to produce systems with an exponentially higher (e.g. 26.47x) reactive oxygen species (ROS) scavenging capacity. The fourth mechanism is the underlying one: microbiota modulation. The probiotics administered to the patient also compete with the pathogenic and opportunistic bacteria (pathobionts) to prevent adhesion niche and resources [45]. They also generate metabolites such as short-chain fatty acids (e.g. butyrate) that provide a hostile environment to the pathogens and support, however, the beneficial native species. The possible precision of microbial ecology engineering is found in innovative strategies, e.g. microgels that can release tungsten to target sulfate-reducing bacteria. Such restoration of the gut microbiome to a eubiotic form is essential to remission in the long term. Fifth, most probiotic strains offer direct pathogen inhibition. In the case of H. pylori-related ulcers, strains such as L. reuteri contain bacteriocins and organic acids that have the ability to destabilize and annihilate pathogen biofilms, and microencapsulated forms have been found to work at concentrations 2-fold lower than the minimum inhibitory concentration (MIC) in planktonic cells [46].

In addition to these mechanisms, there is a capping therapeutic effect of spurring epithelial repair and angiogenesis. The healed inflammation and the re-established microbial balance provide a pro-healing microenvironment [47]. Probiotic metabolites, especially butyrate, are the major energy source of colonocytes in stimulating the proliferation and differentiation of the epithelial cells to heal the ulcerated surfaces. Moreover, they induce the expression of growth factors such as vascular endothelial growth factor (VEGF) that promotes the development of new blood vessels (angiogenesis) in the damaged submucosal tissues. This increased vascularization increases blood flow to the wound, increasing tissue regeneration, and improving normal mucosal structure. Therefore, microencapsulated probiotic systems are complex, bioreactive therapeutic, that cover the complex pathophysiology of gastrointestinal ulcers and inflammatory diseases in their entirety; in other words, starting with initial shielding, through to the ultimate remodelling of the tissue.

4. Application in Specific Gastric and Intestinal Pathologies

Its elementary engineering principles are confirmed by the substantial preclinical success of microencapsulated biotherapeutics application in the gamut of gastroduodenal and intestinal diseases. The protective and restorative properties of such systems are obviously demonstrated in models of NSAID induced and ethanol induced gastric ulcers. As an example, co-encapsulated microbeads of alginate with diterpene phytol have been found to substantially decrease gastric acidity, ulcer index, and the markers of the oxidative stress. Cytoprotective effects are immediate due to buffering acid and creating a temporary physical shield over the mucosa with the alginate matrix itself whereas anti-inflammatory and antioxidant effects are long-term owing to the sustained release of phytol and amplified the production of mucosal defensive factors. In the same vein, microcapsules of myrtle essential oil utilise the antimicrobial and wound-healing effects of the oil, and the encapsulation enables the volatile oil to arrive in the stomach intact with the desired effects of significantly reducing the size of lesions and histopathological scores. These papers emphasize the role of microencapsulation in the conversion of bioactive substances into ulcer-targeted, stable therapeutic agents [48]. In the case of ulcers related to Helicobacter pylori, cytoprotection is not the only issue, but localized antimicrobial activity against inert biofilms. In this case, high-level mucoadhesive microgel systems will be developed to be dual-targeted. One of such is a microgel loaded with resveratrol and antimicrobial nanoparticles (a RESV-MNP system). The mucoadhesive polymer, which in many cases is chitosan-based, guarantees sustained retention in the gastric mucosa, at which point the H. pylori colonizes. This enables controlled, localized delivery of the antimicrobial payload to destabilize and eliminate the pathogenic biofilm and the probiotic/resveratrol component to reduce inflammation and protect the gastric epithelium at the same time. This multi-mechanistic, synergistic strategy results in much higher eradication rates than systemic antibiotic programs alone and it results in the least amount of collateral damage to the commensal microbiota, overcoming the severe drawbacks of systemic antibiotic therapy [49].

In the case of the Inflammatory Bowel Disease (IBD) supported by ulcerative colitis and Crohn’s disease, the most advanced microencapsulation systems are being implemented to control the complex, relapsing character of the disease. An outstanding instance is of self-adaptive microgels in next-generation probiotics. Systems such as gelatin methacryloyl (GelMA)-based porous microgel (Akkermansia muciniphila (AKK)-encapsulated Akkermansia muciniphila (AKK)-based Akkermansia muciniphila (AKK)-based Akkermansia muciniphila (AKK)-based Akkermansia muciniphila (AKK)-based Akkermansia muciniphila (AKK)-based Akkermansia muciniphila (AKK)- The gel matrix is degraded selectively by the process of matrix metalloproteinases (MMPs) that are excessively produced in inflamed intestinal tissue. This enzyme-directed release guarantees that the sensitive A. muciniphila is released at the location of maximum inflammation and immediately it can act to strengthen the mucus layer and reduce endotoxemia and induce regulatory immune responses thereby facilitating mucosal recovery and homeostasis of the microbiota [50].

Fig: 2 Mechanism of action gastric and intestinal pathologies