Review Article - (2023) Volume 15, Issue 3
The gut and placental microbiome have emerged as key determinants of human health and well-being, with their beneficial effects extending well beyond the confines of the digestive and reproductive systems. Recent advances in microbial research have revealed that these microbial communities play crucial roles in nutrient absorption, immune modulation, and even neurobehavioral processes. By regulating the host-microbe interaction and maintaining a balance between commensal and pathogenic bacteria, the gut microbiome is vital for maintaining optimal health and preventing a host of chronic diseases. Dietary fiber plays a critical role in promoting a diverse and healthy gut microbiome, which confers many health benefits to the host. This review article delves into the different functions that gut microbiota can potentially perform in shaping our health status and the implications of gut microbiome disturbances on human health in the form of various gastrointestinal as well as extra-intestinal diseases. Furthermore, we shed light on current scientific investigations that have widened our grasp of the human microbiome, specifically cutting-edge molecular sequencing technology, and analytical approaches. A more nuanced comprehension of this intricate concept harbors diagnostic and therapeutic implications for various pathogenic pathways linked to inflammatory and neoplastic diseases.
Gut microbiota • Short-chain fatty acids • Microbiota-accessible carbohydrates • Obesity • Diabetes •Asthma • Autism spectrum disorder • Alzheimer’s disease • Metagenomics analysis
Microbiotas are the symbiotic organisms of thousands of species that are abundantly present inside and outside the human body, coexisting harmoniously while performing multiple functions that are crucial for optimal physiological processes and well-being. The gut microbiota has been shown to influence various aspects of human physiology, including metabolism, immunity, and brain function. These microorganisms include bacteria, fungi, and viruses, and interestingly, their population in the human body surpasses that of human cells [1]. The human microbiome comprises approximately 10 trillion-100 trillion symbiotic microbial cells present in each individual, making the number of microbial cells in our body more than that of human cells. The human gut alone accommodates up to 1,000 species of microbiota that perform diverse functions [2]. Microbiomics is an expanding discipline that involves investigating these organisms, their roles, and their effects on the human body.
Beginning in the 1680s, when Antonie van Leeuwenhoek compared his oral and fecal flora, research on the diversity of the human microbiome began. He observed the considerable variations in microorganisms between these two habitats as well as between samples from people in healthy and diseased stages in both of these locations [3, 4]. Research into the remarkable differences between microorganisms in various anatomical locations, and the differences between their roles in health and disease, dates back to the earliest days of microbiology. However, recent cutting-edge breakthroughs in technology have enabled us to utilize powerful molecular tools to investigate the underlying reasons behind these distinctions and even manipulate the transformations between states. It is not the observation of these evident contrasts that is groundbreaking today, but rather the ability to elucidate the mechanisms that give rise to them. The mutual evolution of vertebrates and their associated microbial communities, spanning over hundreds of millions of years, has resulted in a distinct microbial consortium that thrives in the gut's stable, nutrient-rich, and warm surroundings. While archaea, eukaryotes, and viruses are also present in the gut, albeit in smaller quantities and should not be overlooked, bacteria comprise the bulk of the biomass and diversity within the human gut and in all other ecosystems that are interconnected with human beings [5-7].
While there are some microorganisms that are pathogenic, it is worth noting that both symbiotic and pathogenic microbiota coexist. There is a complex interplay between symbiotic and pathogenic microorganisms within the human body. The vast majority of the microbiome comprises of beneficial and symbiotic microorganisms that provide advantages to both the host and the microbiota. However, symbiosis can occur due to certain infectious diseases, poor diets, or prolonged usage of antibiotics or other antibiotic-like drugs. This can render an individual more susceptible to a range of diseases, varying in severity from mild to severe [8-11].
One of the most widely scrutinized topics pertaining to the human microbiome is the gut. This manuscript furnishes comprehensive details about the gut microbiome, its diversity, and its influence on human well-being and pathological conditions. It also explores the placental microbiome, its potential role in neonatal gut colonization, the development of the microbiota from infancy through early childhood, and the impact of various factors, such as birth mode and diet.
Fiber, fatty acids, and the gut microbiota: How they shape our health
The gut microbiome is a complex and diverse community of microorganisms that plays a critical role in the regulation of digestion, immunity, and other important bodily processes throughout life. It is an amalgamation of diverse and fluctuating microorganisms which vary according to numerous factors including age, sex, race, ethnicity, gender, and lifestyle choices such as the use of alcohol, smoking, and physical activity, as well as geographical location and medications [12].
Research has shown that an imbalance in the gut microbiota can have negative effects on health, contributing to the development of various diseases, including obesity, diabetes, and inflammatory bowel disease. On the other hand, a healthy gut microbiome can help prevent these diseases and promote overall well-being. Studies have also highlighted the impact of various factors on the gut microbiome, including diet, antibiotic use, age,and environmental factors such as sanitation. For example, a study published in Nature Microbiology found that the gut microbiota of individuals in developed countries is less diverse than those in less developed areas due to factors such as increased hygiene practices and a more processed diet [13-15].
Hippocrates studied the gastrointestinal properties of coarse wheat versus refined wheat in 430 BC, while J.H. Kellogg wrote numerous articles on the benefits of bran in the 1920s, asserting that it boosts stool weight, facilitates laxation, and prevents illnesses [16]. The 1930s saw extensive research on dietary fiber, however, afterward it was neglected until the 1970s. Diet significantly influences the types of bacteria that exist in the colon, in addition to environmental factors, medication use, and genetics from the family[ 17,18].
Role of Short-Chain Fatty Acids (SCFA)
The microbiota in the colon digests the fiber, producing short-chain fatty acids that contribute to shaping the gut environment, influencing the physiology of the colon, and eventually serving as an energy source for host cells. By playing an important role in different host-signaling mechanisms, these fatty acids have enormous potential for promoting a healthy body [26, 27]. Microbial degradation of dietary fiber in the gut is a complex process, including the role of different microbial populations in breaking down and fermenting different types of fiber. Since dietary fiber can only be broken down and fermented by enzymes from microbiota living in the colon that eventually release SCFAs, the pH of the colon becomes more acidic, creating an environment favorable for a specific type of microbiota that can survive in the acidic conditions[28]. While some harmful bacteria cannot survive in this acidic pH, there are numerous benefits of SCFA, including stimulating immune cell activity and maintaining normal blood levels of glucose and cholesterol [29]. Numerous studies have discussed the potential for dietary interventions targeting SCFA production to improve metabolic health [30-32].
The crucial role of gut microbiome in maintaining optimal health from the beginning
The gut microbiome holds sway over the human physique from the moment of birth and persistently influences vital bodily functions such as the digestive, immune, and central nervous systems [33-35]. The placenta was once thought to be sterile, but recent studies have shown that it harbors a diverse microbiome that can impact fetal development. Despite its manifold metabolic and immunological regulating functions, the placental microbiome's compositional and functional diversity remains relatively underexplored. Impactful research has nonetheless evinced a correlation between placental microbiota and antenatal infection history, maternal weight gain, and the altered placental membrane microbiome seen in preterm birth, which remains a significant cause of neonatal morbidity and mortality [36-41] .The early microbial composition of neonates is significantly influenced by both delivery method and gestational age. The mode of delivery, whether vaginal or caesarean, plays a crucial role in determining the initial contact between the fetal body and the microbiome, with the former more closely resembling the maternal flora. Interestingly, infants delivered by cesarean section exhibit a gut flora composition that is less similar to their mothers compared to those delivered vaginally [42-44].
From the moment of birth, a newborn is surrounded by microorganisms, and as the child grows, the gut microbiota begins to colonize [45-47]. The adult gut microbiome, which is influenced by important factors such as an increase in the abundance of Bacteroidetes, elevated fecal SCFA levels, enrichment of genes related to carbohydrate utilization, vitamin biosynthesis, and xenobiotic degradation, is reliant on oral feeding. The composition of the microbiota is significantly influenced by prolonged nursing, which is crucial for the structure and function development of the microbiome [48-50] . Breast milk is rich in chemicals that play a vital role in promoting the growth of Bifidobacteria and Bacteroides [51, 52]. Despite being able to digest lactose, the infant's small intestine lacks the glycoside hydrolases and intestinal membrane transporters needed to break down the human milk oligosaccharides. As a result, milk glycans can increase the number of bacteria in the gut microbiota that break down complex carbohydrates [53]. The introduction of solid food and the cessation of breastfeeding results in a shift in their composition to an adult-like microbiota [54-56]. Variations in the microbial community during the first months are driven by factors such as sanitary conditions or antibiotic use. [57-59] The mechanisms linking these and other important factors to the construction of the microbiota are still being investigated.
Factors that impact gut microbiota and disease
The gut microbiome is impacted by a variety of factors, including stomach pH, bile acids, digestive enzymes, and antimicrobial proteins in the duodenum, among others. Other major variables can also affect microbial colonization further downstream, such as chemical parameters like pH, oxygen concentrations, mucus, and antibodies, as well as anatomical abnormalities related to gut receptors, immune cells, and nerve cells. These factors can ultimately influence gut peristalsis and transit times, playing an essential role in the alteration of the microbiome and host relationship [60-62].For instance, Sonnenburg, E.D. et al describe in their article how a dietdeficient in Microbiota-Accessible Carbohydrates (MACs) can affect thecomposition and function of the gut microbiota and ultimately alter thehost-microbe relationship [63]. Consequently, the gut microbiome has emerged as a significant factor in various metabolic and immune diseases.
Gastrointestinal diseases and diseases of the hepatobiliary system, including intestinal bowel diseases, celiac disease, irritable bowel syndrome, colorectal cancer, chronic liver diseases, and pancreatic disorders, have been linked to the gut microbiota [64, 65]. Various extra-intestinal disorders, such as obesity and obesity-related disorders like type 2 diabetes and non-alcoholic fatty liver disease, have also been linked to the gut microbiome, mainly due to its effects on glucose regulation and correlation with insulin resistance [66-70]. Ley R. E. discussed in their article the role of microbiota in energy metabolism, particularly in the context of obesity. The author also describes the potential mechanisms by which gut microbiota may contribute to the development of obesity, including increased energy harvest and storage, altered gut hormone signaling, and inflammation [71].
Extraintestinal pathology due to gut microbiota dysbiosis
Respiratory Conditions: Susceptibility for development of asthma has been noted in neonates and infants who have correlations with gut microbiome dysbiosis, including microbial depletion and fungal overgrowth. In their infancy, these neonates’ fecal metabolic profile exhibited a deficiency of omega-3 fatty acids and prostaglandin precursors [72]. Numerous researchers have shared profound insights regarding the interplay between environmental pollution, gut microbiota, and allergic bronchitis/asthma [73, 74]. Multiple studies have revealed that the administration of vancomycin was connected to a reduction in gut microbial diversity, altered metabolic profiles, intensified Th2 responses, and an elevated likelihood of allergic bronchitis [75]. The provision of SCFAs has been revealed to alleviate alveolar inflammation, primarily attributed to reduced T cell activity, specifically a decrease in IL-4-producing CD4+ T cells and decreased circulating IgE levels [76].
CNS diseases and Behavioral problems: The gut microbiota has been revealed to act as a mediator of biochemical signaling in the gut-brain axis, demonstrating an association with disrupted gut microbial homeostasis [77]. Disordered microbial flora have exhibited significantly elevated concentrations of SCFAs and ammonia, the metabolites of which may harbor a neurotoxic influence leading to various CNS disorders [78, 79]. The microbial composition of the gut has been found to be intricately linked to Autism Spectrum Disorder (ASD) and other neurodevelopmental conditions characterized by aberrant behavior, cognitive impairment, and mental distress [80-84]. Presently, many researchers are investigating the relationship between the gut microbiota and stroke pathogenesis, Alzheimer's disease, as well as novel therapeutic opportunities for addressing these conditions with the prism of the gut microbiome [85, 86].
Cardiac conditions: Recent studies have brought to light the fact that the gut microbiota is capable of influencing the entire host body. Over the past two decades, there has been a substantial amount of research dedicated to comprehending the evolution of gut microbiota and its implications for risk factors associated with cardiovascular diseases [87]. Substantive evidence has further validated the causal impact of the gut microbiota on Cardiovascular Disease (CVD). Notably, studies on gut microbiota transplantation, gut microbiota-dependent pathways, and downstream metabolites have demonstrated their ability to influence host metabolism and the onset of CVD. For instance, Trimethylamine N-Oxide (TMAO), a met organismal metabolite produced following the consumption of dietary nutrients prevalent in a Western-style diet, and more recently, Phenyl Acetyl Glutamine (PAG), a phenylalanine-derived metabolite, are examples of gut microbiota-dependent metabolites. Elevated levels of these metabolites in the bloodstream have been linked to increased CVD risk in large-scale clinical studies [88-90].
Revolutionizing microbiome research: The power of molecular analysis
The swift advancements in high-throughput molecular methods have facilitated in-depth analysis of the microbiota's genetic and functional diversity, enabling us to comprehend the species present, their relationships with each other, the expressed genes, and the ongoing metabolic activities [91, 92]. With the advent of cutting-edge platforms such as Illumina, 454 Roche, Pac Bio, and Oxford Nano pores, we can now perform metagenomics, metatranscriptomics, met proteomics, and met metabolomics, allowing us to explore biological signatures related to specific environments [93-97].
Metagenomic analysis of gut microbiota involves sequencing the DNA of all the microorganisms present in a given sample and then using bioinformatics tools to identify and characterize the microbial community. This approach has revealed the tremendous diversity of the gut microbiota and has led to the discovery of numerous novel microbial species and genes. Metagenomic analysis has also been used to investigate the role of the gut microbiota in various diseases, including inflammatory bowel disease, colorectal cancer, and metabolic disorders [98-100]. The continual improvement of sequencing techniques and analytical approaches enhances our understanding of the human microbiome, including its definition and constituents. Furthermore, by gaining a better understanding of the gut microbiota and its functions, we may be able to develop new strategies for preventing and treating these diseases.
Studies are ongoing to explore the critical importance of the gut microbiome, the various ways in which the gut microbiome influences human health, and potential therapies to manipulate the microbiome to treat diseases. In the meantime, it is important to prioritize a healthy lifestyle to support the health of our gut microbiome and our overall well-being.
The swift progression of sequencing methods and analytical techniques is augmenting our capacity to understand the human microbiome, as well as our conception of the microbiome and its elements. Therefore, we believe that there is ground for cautious sanguinity that further innovations in sequencing technology and comprehension of the microbiome will present thrilling opportunities for utilizing the microbiota for personalized medicine.
The author declares that he has no financial or personal relationship which may have inappropriately influenced him in writing this article.
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Citation: Saxena, R., Yakyomovych, O. Gut Microbiome, A Link between Nutrition, Physiology, and Pathology: Insights into Current Status and Future Directions. Int. J. Collab. Res. Intern. Med. Public Health. 2023, 15 (3),1-5
Received: 21-Mar-2023, Manuscript No. IJCRIMPH-23-91030; Editor assigned: 23-Mar-2023, Pre QC No. IJCRIMPH-23-91030 (PQ); Reviewed: 26-Mar-2023, QC No. IJCRIMPH-23-91030 (Q); Revised: 27-Mar-2023, Manuscript No. IJCRIMPH-23-91030 (R); Published: 29-Mar-2023, DOI: 10.35248/ 1840-4529.23.15(3).1-4
Copyright: ©2023 Saxena, R. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
