Role of probiotic extracellular vesicles in inter-kingdom communication and current technical limitations in advancing their therapeutic utility

Abstract

Diverse functions of probiotic extracellular vesicles (EVs) have been extensively studied over the past decade, proposing their role in inter-kingdom communication. Studies have explored their therapeutic role in pathophysiological processes ranging from cancer, immunoregulation, and ulcerative colitis to stress-induced depression. These studies have highlighted the significant and novel potential of probiotic EVs for therapeutic applications, offering immense promise in addressing several unmet clinical needs. Additionally, probiotic EVs are being explored as vehicles for targeted delivery approaches. However, the realization of clinical utility of probiotic EVs is hindered by several knowledge gaps, pitfalls, limitations, and challenges, which impede their wider acceptance by the scientific community. Among these, limited knowledge of EV biogenesis, markers and regulators in bacteria, variations in cargo due to culture conditions or EV isolation method, and lack of proper understanding of gut uptake and demonstration of in vivo effect are some important issues. This review aims to summarize the diverse roles of probiotic EVs in health and disease conditions. More importantly, it discusses the significant knowledge gaps and limitations that stand in the way of the therapeutic utility of probiotic EVs. Furthermore, the importance of addressing these gaps and limitations with technical advances such as rigorous omics has been discussed.

Keywords: Extracellular vesicles; bacterial extracellular vesicles; inter-kingdom communication; membrane vesicles; outer membrane vesicles; probiotic extracellular vesicles; species crosstalk.

Figure 1

Implicated beneficial effects of probiotic extracellular vesicles in pathophysiological conditions. Schematic representation of the implicated roles that probiotic-derived EVs play in a plethora of pathophysiological processes. Several studies so far have demonstrated the potential of probiotic EVs in modulating the immune system and alleviating pathological conditions such as IBD, diabetes, and ulcerative colitis. The suggested health benefits of probiotic EVs range from improving gut health to inducing chemosensitivity and apoptosis in resistant cancer cells. Their role in several other diseases such as asthma, metabolic disorders including diabetes and obesity and their antimicrobial properties have been investigated in several studies. Table 1 provides a detailed summary of studies where the role of probiotic EVs in pathophysiology and disease alleviation has been suggested. IBD: Inflammatory bowel disease; EVs: extracellular vesicles; HIV: human immunodeficiency virus.

Figure 2

Immune regulatory effects of probiotic EVs. Schematic diagram depicting the various immunomodulatory roles of probiotic EVs, including alteration to cytokine release, activation of immune cells, surface interactions, and changes to antibody production. Table 1 provides a comprehensive summary of the literature suggesting a functional role for probiotic EVs in the immune setting. EVs: Extracellular vesicles; IgA: immunoglobulin A; TRL: toll-like receptor; LPS: lipopolysaccharide; NF-κβ: nuclear factor kappa β.

Figure 3

Current challenges and technical limitations hindering the therapeutic utility of probiotic EVs. Schematic illustration to depict challenges and limitations facing the utility of probiotic EVs in clinical applications. Several technical constraints such as EV cargo and yield variations due to different isolation methods, the presence of secretory factors and contaminants in the preparation, and the use of inappropriate preclinical models to study the effect and variation in phenotype based on the route of administration could prevent a detailed understanding and widespread acceptance of the role of probiotic EVs in pathophysiology. Additionally, current technical limitations prevent a better understanding of the EV cargo component responsible for the observed phenotypes. The annotated bibliography is shown in the Supplementary Materials. EVs: Extracellular vesicles.

Figure 4

Omics approaches to thoroughly characterize probiotic bacterial EV cargo could aid in the identification of conserved cargo and lead to the identification of EV-enriched proteins conserved between strains and species. Venn diagrams depicting common and unique cargo in EVs of various species and strains of probiotic bacteria. Venn diagrams were generated using FunRich software (version 3.1.4)^[129]. EVs: Extracellular vesicles.