Role of Prebiotics and Probiotics in Improving Muscle Mass

1. Health benefits of FOS

2. Background Background - - Proteins for building Muscle Mass Proteins for building Muscle Mass It is already known that amino acids (building blocks of proteins) are essential for muscle mass building and tissue repair. Of the amino acids, the branch chain amino acids (BCAAs; leucine, isoleucine and valine) are typically not oxidized in the liver but in skeletal muscle for muscle building. Thus the availability of BCAAs is important as they regulate the rate of protein synthesis and degradation in skeletal muscle and other organs. The BCAAs and aromatic amino acid (as phenylalaline, tryptophan, tyrosine among others) bind to the same carrier proteins to be transported to brain, ratio of which in the brain may influence the synthesis of specific neurotransmitters, thus influence the behavior of the individual (Skeie et al 1990; Fernstrom, 2005). Thus, the availability of all essential amino acids, importantly BCAAs, is vital for improved muscle health (Monirujjaman and Ferdouse, 2014). Prebiotics and Probiotics Improve the Gut Barrier Functions Prebiotics and Probiotics Improve the Gut Barrier Functions Prebiotics are defined as “a non-digestible food ingredient by the gastro intestinal tract but fermented in colon and beneficially affect the host by selectively stimulating the growth and/or activity of one or a limited number of bacteria (particularly Lactobacilli Bifidobacteria spp.) in the colon (Singh et al. 2017), and thus improves host health” (Gibson and Roberfroid, 1995) by yielding beneficial metabolites such as short chain fatty acids (SCFAs - acetate, propionate, and butyrate). These SCFAs play a role for various health support and body functions (such as inhibit liver cholesterol synthesis, providing energy source for colonic cells, inhibit the fatty acid synthesis in liver, etc.) (Wong et al. 2006). Prebiotic or a synbiotic (prebiotics and probiotics) supplementation may positively alter the gut microbiota. Prebiotics act as energy to probiotics in the colon and support their growth among other beneficial function as improvement of the gut/epithelial barrier functions by providing energy source to the intestinal epithelial cells (Krishna Rao and Samak, 2013; Chambers et al. 2018). Any dysfunction of the gut/epithelial barrier, may contribute to intestinal inflammation by allowing host immune system access to luminal antigens and microbes (Nighot et al. 2015). Thus it is important to protect the intestinal membranes from disruption which may be compromised during intestinal diseases (Salim et al. 2011; McGuckin et al. 2009). SCFAs protect intestinal barrier function by up - regulating tight junction protein claudin-1 or facilitating tight junction assembly (Wang et al 2012; Peng et al 2009). In a recent in vitro experiment (Feng et al. 2018), effect of SCFAs on intestinal barrier function was studied using the Caco-2 model by exposing to acetate, butyrate and propionate. Clearly, the study showed that SCFAs contribute to the formation of intestinal barrier at proper concentration, and ameliorate the disruption of intestinal barrier by suppressing NLRP3 inflammasome (promotes the maturation and secretion of pro-inflammatory cytokines Interleukin 1β and Interleukin 18; Martinon et al. 2002) and inhibition of ROS production (ROS – reactive oxygen species result in cell structure damage; Belikov et al 2015). Thus it may be concluded that an intake of prebiotics (with/out probiotics) may support improvement of the gut barrier function, and support prevention of infections. `Page 1 1 of 6 6

3. Gut barrier functions and its relation with Muscle Mass Gut barrier functions and its relation with Muscle Mass The gut barrier modulates the transfer of molecules as nutrients, electrolytes, water, toxins, microbes and microbial byproducts, from the intestinal lumen to the mucosa. As a consequence, the gut barrier may affect energy balance, fat homeostasis. Figure possible mechanisms worsening of nutritional state at the gut barrier level. Other deprivation or restriction are also associated with alterations at the level of epithelial gut barrier, gut-associated lymphoid tissue (GALT), gut microbiota and enteric nervous system (ENS) and protein energy wasting which closely interact with each other. Thus with such a proposed mechanism, the overall health of an individual maybe compromised (Genton et al. 2015). regulation, 1, highlights underlying water the the way around, food Picca et al. (2018) proposed a model on the role of gut microbiota and control of muscle wasting. The imbalanced gut microbiota contributes to host inflammation leading to impairment of mitochondrial quality. This may further lead to the release of mitochondrial damage-associated molecular patterns (DAMPs), such as mitochondrial DNA and ATP. The subsequent recruitment of local macrophages may maintain a persistent inflammatory situation by alerting circulating immune cell and mounting a systemic response through the activation of mitochondrial DNA-induced inflammatory pathways. Cytokines (influence immune response), chemokines, nitric oxide (NO), and ROS, released in the circulation by inflammatory cells, can induce further mitochondrial damage, thereby establishing a vicious circle and eventually contributing to muscle wasting (Picca et al. 2018). Overall, it may be concluded that with an unhealthy possibilities are that there would be disruption in the gut barrier functions leading to compromised nutrient availability. importantly, this will also lead to exposure to microbes to the internal systems. These unhealthy microbes may affect the energy output from the cells, including the muscle cells. Thus, it is important to not only maintain a microbiome, it is also important to provide better nutrition to the healthy bacteria which can be successfully come prebiotic fibers. microbiota, More the unhealthy healthy gut from the `Page 2 2 of 6 6

4. The Gut The Gut- -Muscle Axis Muscle Axis It is well documented that gut microbiota induces variety of host responses within the intestinal mucosa and thereby controls the gut’s barrier, immune and endocrine functions. Gut microbes also influence the metabolism of host cells in tissues outside the intestine and modulate energy homeostasis and systemic inflammation (Delzenne and Cani, 2011). Animal studies have demonstrated that germ free mice are protected from diet induced obesity by two mechanisms that result in increased muscle fatty acid catabolism (Backhed et al 2007). In the muscle of germ free mice, the AMP-activated protein kinase activity (regulator of cellular energy homeostasis) is increased. With its increase, there is an increase in the muscular activity of CPT-1 (responsible for the fatty acid oxidation in the mitochondria). Further in the germ free mice, there are elevated fasting induced adipocyte factor, leading to increased expression of PGC–1α (regulates genes involved in energy metabolism) (Figure 3 (1)). In humans, endurance exercise has been shown to activate the PGC- 1α gene in human skeletal muscle (Pilegaard et al. 2003). This means that with an unhealthy gut microbiota, energy output from the microbiota is compromised; thus making it important to provide a healthy microbiome in individuals. Second pathway (Figure 3 (2)) is the effect of gut microbiota on amino acid bio-availability. amino acid (particularly of lysine) can be contributed to by the microbial fermentation in the gut. Further, microbiota Essential requirement gut produces various metabolites which can reach the muscle, such as conjugated linoleic acids, acetate and bile acids (Delzenne and Cani, 2011). Bile acids increase energy expenditure in human skeletal muscle cells by promoting intracellular thyroid hormone activation via TGR5 (a G-protein-coupled receptor for bile acids; Watanabe et al., 2006). Moreover, bile acids also activate the nuclear farnesoid X receptor and thereby protect against muscle fat deposition (Cipriani et al. 2010). In addition, through the fat regulation pathway, gut metabolites indirectly influence the muscle mass management (Bindels et al. 2013). `Page 3 3 of 6 6

5. Table 1: Summarized role of microbiota influencing the physio Table 1: Summarized role of microbiota influencing the physio- -pathology of distant organs, with a specific focus on the gut gut- -muscle axis (Adopted muscle axis (Adopted from from Ticinesi Ticinesi et al et al 2018) 2018) pathology of distant organs, with a specific focus on the putative putative X Release of bacterial toxins into circulation Reduced gut mucosa permeability Production of metabolites with endocrine function Possible Mediators Lipopolysaccharide and other species-specific toxins Bacteria or their components penetrating circulation Short-chain fatty acids (acetate, propionate, butyrate) Relevance for the skeletal muscle Stimulation of chronic inflammation and immune system activation Stimulation of chronic inflammation and immune system activation 1. Promotion of insulin sensitivity 2. Promotion of muscle anabolism and adipose tissue catabolism 3. Modulation of inflammation 4. Stimulation of mitochondrial biogenesis 5. Reduction of myocyte apoptosis Availability of substrates for protein synthesis Modulation of dietary amino acid bioavailability Synthesis of substances with nutritive significance for the host None 1. Folate, riboflavin, vitamin B12, glycine betaine Stimulation of anabolism and insulin-growth factor-1 synthesis Prevention of oxidative stress and endothelial damage Improvement of redox reactions DNA synthesis, methylation and repair Improved mitochondrial biogenesis and muscle strength 2. 3. 4. Transformation of dietary nutrients into metabolically active mediators Modulation of autonomic nervous system function Urolithins derived by ellagitannins (most known example) Unknown None known Available literature on Prebiotic/Probiotics and Mechanism of action on muscle physiology Recent researches are suggesting that gut microbes also influence the metabolism of host cells in tissues outside the intestine and modulate energy homeostasis and systemic inflammation (Delzenne and Cani, 2011). In an animal study, supplementation of inulin-type fructans prebiotics has shown its influences on body weight composition, with a switch from fat mass to muscle mass (Cani et al., 2009). Likewise, the probiotic (Lactobacillus spp) supplementation of had shown the association with improved exercise performance. The mechanism of action was proposed as Lactobacillus bacteria produce lactic acid, which could facilitate the production of butyrate by lactate-utilizing bacteria that first producing acetylCoA from lactate (Duncan et al. 2004). In the so - called classical pathway, the enzymes phosphortransbutyrylase and butyrate kinase convert b utyryl- CoA to butyrate and coenzyme A with the concomitant formation of ATP. These factors could potentially influence the muscle physiology. Summary Prebiotics are acts as fuel source for gut microbes and thereby healthy gut micro flora. Thereby the Improved gut microbial load leads to improved gut metabolites productions such as SCFA and thus improved gut barrier functions. Consequently, the improved gut barrier functions helps for the improved nutrient absorption, down regulate the fat metabolism, improvement of the fat free mass, involving in energy balance and increase the amino acid availability. Available evidences suggest that 6 synbiotics such as inulin / fructo-oligosaccharide and lactobacillus spp combination may be beneficial on reducing the muscle wasting. In conclusion, gut microbiota modulation might potentially constitute a future therapeutic target in the management of muscle wasting, total body fat percentage reduction, partial energy balance. However, the molecular mechanisms involved gutmicrobiota-muscle mass must be established more. Further the current available data is with animal studies and therefore data in human studies are warranted. `Page 4 4 of 6 6

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