Pathobiological Relationship of Excessive Dietary Intake of Choline/L-Carnitine: A TMAO Precursor-Associated Aggravation in Heart Failure in Sarcopenic Patients

The microecological environment of the gastrointestinal tract is altered if there is an imbalance between the gut microbiota phylases, resulting in a variety of diseases. Moreover, progressive age not only slows down physical activity but also reduces the fat metabolism pathway, which may lead to a reduction in the variety of bacterial strains and bacteroidetes’ abundance, promoting firmicutes and proteobacteria growth. As a result, dysbiosis reduces physiological adaptability, boosts inflammatory markers, generates ROS, and induces the destruction of free radical macromolecules, leading to sarcopenia in older patients. Research conducted at various levels indicates that the microbiota of the gut is involved in pathogenesis and can be considered as the causative agent of several cardiovascular diseases. Local and systematic inflammatory reactions are caused in patients with heart failure, as ischemia and edema are caused by splanchnic hypoperfusion and enable both bacterial metabolites and bacteria translocation to enter from an intestinal barrier, which is already weakened, to the blood circulation. Multiple diseases, such as HF, include healthy microbe-derived metabolites. These key findings demonstrate that the gut microbiota modulates the host’s metabolism, either specifically or indirectly, by generating multiple metabolites. Currently, the real procedures that are an analogy to the symptoms in cardiac pathologies, such as cardiac mass dysfunctions and modifications, are investigated at a minimum level in older patients. Thus, the purpose of this review is to summarize the existing knowledge about a particular diet, including trimethylamine, which usually seems to be effective for the improvement of cardiac and skeletal muscle, such as choline and L-carnitine, which may aggravate the HF process in sarcopenic patients.


Introduction
The human intestine microbiota is primarily comprised of four phyla: proteobacteria, firmicutes, actinobacteria, and bacteroidetes [1]. An imbalance between the gut microbiota

Clinical Characteristics of Sarcopenia in Association with Gut Microbiota Diversity
Sarcopenia can be referred to as the gradual loss in mass of skeletal muscle, the loss of its strength, and the loss of functions performed, and it is now considered as the major factor of negative effects of health in the later period of life [12]. In fact, the high pervasiveness of chronic health conditions can be correlated with old age (e.g., inflammatory irritable bowel syndrome, celiac disease, autoimmune disease, colitis, diabetes, cancer, cardiovascular disease, neurodegeneration, and so on), which lead in turn to many negative health events (e.g., illness, loss of freedom, institutionalization, underprivileged quality of life, and mortality) [13][14][15].
The authors established a link between health status, diet, and microbiota. To be more precise, the composition of the microbial population was predominantly influenced by fruit, meat, and vegetable intake. Additionally, a higher proportion of two dominant phyla, namely Firmicutes (64%) and Bacteroidetes (23%), comprise up to 90% of the overall gut microbiota in older people who are living in long-term care facilities [16][17][18]). It has been identified that the level of Staphylococcus spp. and Lactobacillus Reuters, both of which are from phylum firmicutes, is high in obese people. A positive correlation has been established between plasma > C-reactive protein (CRP) and plasma [19,20]. Moreover, older people are primarily affected by a rise in Escherichia (phylum of proteobacteria) abundance [16]. However, it is understood that an increase in gram-negative bacteria such as proteobacteria in their relative abundance is one of the most significant harmful age-changes for the human intestinal microbiota composition, as lipopolysaccharides are secreted by these gram-negative bacteria, through which inflammation can be induced in the intestines [21]. Advancing age can also be characterized by a gastrointestinal microbiota's dysbiosis, which promotes the circulation passage of endotoxin and other microbial products or metabolites via the increased permeability of the intestine [22], thereby highlighting the influential role of gut dysbiosis for deficits in muscle functions associated with age. Sarcopenic patients have increased serum c-reactive protein (CRP) levels, while trials with other inflammatory mediators such as interleukin 6 have not shown consistent results [23].
In addition, the maintenance of sarcopenia is supported by the insufficient nutritional system and aged immune system, which play key roles in stimulating the activation of chronic inflammation [24,25]. In cachexia and sarcopenia, however, mitochondrial and systemic inflammation plays a central role. The proinflammatory role of cytokines (e.g., IL6, IL1β, TNF-α, and TNF-style weak apoptosis inducer (TWEAK)) has previously been reported in inducting muscle catabolism [26] (Figure 1). of chronic inflammation [24,25]. In cachexia and sarcopenia, however, mitochondrial and systemic inflammation plays a central role. The proinflammatory role of cytokines (e.g., IL6, IL1β, TNF-α, and TNF-style weak apoptosis inducer (TWEAK)) has previously been reported in inducting muscle catabolism [26] (Figure 1).

Dietary Intake Choline and L-Carnitine-mediated Aggravation of CVD
Choline/L-carnitine was investigated as an ergogenic aid for improving the training ability of a stable athletic population due to its pivotal role in the oxidation of fatty acids and energy metabolism. Beneficial impacts on acute physical performance, such as increased power production and increased intake of maximum oxygen, were observed in earlier research studies and further studies show the beneficial influence of L-carnitine as a dietary supplementation in the post-exercise recovery process. L-carnitine has been shown to alleviate the injury of muscles and condenses' cellular damage markers, and muscle soreness attenuation is accompanied by free radical formation [27].
Change in the microbiota composition of the gut caused by sarcopenia and heart failure can alter the circulating levels of TMAO. Moreover, it has been identified that hypertension patients experience an alteration in intestinal microbiota diversity. Experiments

Dietary Intake Choline and L-Carnitine-Mediated Aggravation of CVD
Choline/L-carnitine was investigated as an ergogenic aid for improving the training ability of a stable athletic population due to its pivotal role in the oxidation of fatty acids and energy metabolism. Beneficial impacts on acute physical performance, such as increased power production and increased intake of maximum oxygen, were observed in earlier research studies and further studies show the beneficial influence of L-carnitine as a dietary supplementation in the post-exercise recovery process. L-carnitine has been shown to alleviate the injury of muscles and condenses' cellular damage markers, and muscle soreness attenuation is accompanied by free radical formation [27].
Change in the microbiota composition of the gut caused by sarcopenia and heart failure can alter the circulating levels of TMAO. Moreover, it has been identified that hypertension patients experience an alteration in intestinal microbiota diversity. Experiments conducted on rats who were treated with angiotensin II revealed that intestinal biota species were less diverse and when compared to regulated rats, the Firmicutes to Bacteroidetes ratio was increased [44,45]. Moreover, heart failure was considered a chronic systemic inflammatory disorder, which indicates a substantial rise in pro-inflammatory cytokines of plasma; although its origin is still unclear, this unresolved inflammation can be considered as one of the key components of cardiovascular diseases [46,47]. Several occurring signs indicate that the microbiota of the gut produces bioactive metabolites including bile acids, short chains of fatty acids, and TMAO, and might have systemic effects on the host [48]. Microbiotas and their metabolites affect intestinal health and other physiological processes, especially within the circulatory system. Under normal circumstances, most can be considered as healthy and safe bacterial metabolites, but due to the involvement of heart-failure-related cardiovascular pathologic processes, there is a risk of disruption in the balance of the microbiota of the gut as well as a risk of a rise in the level of harmful metabolites; generally, it was shown in studies that TMAO was found to be related with the prognosis of at-risk heart-failure patients. Moreover, Firmicutes, including Enterococcus, Proteobacteria, Anaerococcus, Streptococcus, and Desulfitobacterium including Actinobacteria, Clostridium, Citrobacter, Dseulfovibrio Enterobacter, Escherichia, Proteus, Pseudomonas, and Klebsiella, have been linked with the production of the primary component of TMAO, i.e., TMA [49].
One research study found that eight Firmicute and Proteobacteria species have absorbed more than 60% of the production of choline of TMA, including Escherichia fergusonii, Clostridium asparagiforme, C. hathawayi, C. sporogenes, Edwardsiella tarda Anaerococcus hydrogenalis, Proteus penneri, and Providencia rettgeri [50]. Akkermansia, Prevotella, and Sporobacter are some other gut microbiota that are associated with the higher production of TMAO [51], and atherosclerotic CAD is associated with Ruminococcus gnavus [52]. The growth of CAD may be predicted via different metabolites such as betaine, choline, and TMA. It can be explained, for instance, by considering that TMAOproducing microbes can be reduced by blocking or inhibiting specific microbial metabolic pathways via utilizing pharmacological intervention and probiotics [53]. Furthermore, the increased level of Ruminococcus is due to the high fat and high protein diet [54], and additionally, downregulation of Treg cells is led by TLR4 activation, which is associated with inflammatory responses such as CD4, Pro-inflammatory cytokines, and Th1 and T cells [55,56]. Thus, we explore, from top to bottom, all of the contributing factors associated with CVD.

Pathobiological Interactions in Heart Failure Involving TMAO
Mechanisms of heart failure pathophysiological pathways are quite intricate and include inflammatory reaction, hemodynamics irregularity, cardiac remodeling, neuroendocrine system stimulation, etc. Traditionally, the key causes of heart failure are supposed to be the activation of the pathways of the neuroendocrine system, which include the natriuretic peptide system, renin-angiotensin-aldosterone cascade, and sympathetic nervous system, which lead to a pathologic myocardial remodeling process series including apoptosis, extracellular matrix deposition, myocardial hypertrophy, and resultant fibrosis [57,58]. Hence, neuroendocrine inhibition is the main basis of the strategies of current treatments [59]. Mechanisms driving the development and progression of heart failure are, however, still under consideration. In the conversion of dietary choline into the intermediate trimethylamine (TMA), a requisite role is played by microbiota of the gut and TMAO is formed by the subsequent oxidization of TMA after it enters into the circulatory system by the flavin-containing monooxygenase (FMO) enzyme, which is encoded by the FMO gene present in the kidney, liver, and in many other tissues [60,61]. There is an increase in the permeability of the intestinal barrier via two mechanisms in the condition of heart failure, in which during the initial stage, a decreased inflow of blood to the intestinal endothelium is observed, and via the ischemia of the wall of the intestine, there is an increase in the permeability of the intestinal epithelial barrier [62]. Due to the intestinal wall's congestion and swelling in the advanced stages of heart failure, there is an increase in the permeability of the intestine. Additionally, in the patients identified with chronic heart failure, higher levels of enteropathogenic candida, such as Campylobacter, Shigella, and Salmonella, were observed [63]. This process is directly linked with microbial and microbial metabolite translocation [64,65]. Recent research evidence indicates that chronic inflammation can be caused by both an increase in the permeability and an increase in the disordered microbiota of the intestine, further leading to impaired Nutrients 2021, 13, 3453 6 of 12 cardiac function [62,66]. In addition, studies have shown that there are severe clinical symptoms and worse survival rates associated with patients with heart failure, which are due to the elevated serum levels of multiple cytokines, such as IL-1, IL-6, and the TNF [67][68][69]. This is consistent with findings that both heart failure and sarcopenic patients have an elevated proportion of these bacterial strains of the intestine, indicating shifts in intestinal microbiota, which may influence levels of TMAO by controlling intestinal TMA synthesis. TMAO has recently become a major mediator showing that the microbiota of the gut has a close relationship with several CVDs. Subsequent preclinical experiments explored the evidence concerning that the heart is directly affected by the TMAO, inducing endothelial cell and vascular inflammation, fibrosis and myocardial hypertrophy, and heart mitochondrial dysfunction, thus aggravating the heart-failure process [70][71][72]. In addition, the association of TMAO is established with both the C-reactive protein (CRP) and with endothelial dysfunction in evaluating the increased permeability of the gut, and is closely related to increased LPS endotoxin serum levels [49], leading to the release of calcium and the hyperreactivity of the platelets [73], contributing to the aggravation of heart failure. The several key pathophysiological pathways of TMAO include the following: explicitly and implicitly contributing in heart failure, including through the pathological LV dilation of the mouse-fed TMAO or choline-demonstrated decreased LVEF, and enhanced circulatory BNP volumes, myocardial fibrosis, and lung oedema [31]; TMAO-encouraged myocardial hypertrophy and fibrosis through Smad3 signals [71]; cardiac remodeling attenuated through 3,3-dimethyl-1-butanol via the reduction in the volume of plasma TMAO, which modifies the signals of TGF-β1/Smad3 and p65 NF-kB [74]; TMAO-promoted activated leukocyte recruitment into endothelial cells and induced inflammatory gene expression via the activation of NF-kB signaling [75]; TMAO significantly affected the contractile nature of cardiomyocyte and intracellular calcium-handling in the negative direction [76]; Pyruvates and fatty acid oxidation in cardiac mitochondria is influenced by TMAO [70]; and, last but not least, TMAO stimulated vascular inflammation by triggering the inflammatory NLRP3 induced by inhibiting SIRT3-SOD2-mitochondrial ROS signaling pathway [77]. Moreover, the function of TMAO, as first assessed by Suzuki et al. [78] in acute HF (AHF), was found to be a predicting marker for mortality and mortality/heart failure within a year (Table 1) [79]. Reduces the production of TMA in the gut Mice show beneficial benefits. However, the consequences on people remain unknown.

Meldonium
Reduces the production of TMAO from L-carnitine (GBB conversion to L-carnitine is inhibited) TMAO production from choline cannot be reduced. It may result in a rise in the urine excretion of TMAO in people.

Oral non-absorbent binders
Eliminates TMAO or any of its precursors from the gut A speculative approach. There has not yet been found a chemical capable of removing TMAO specifically.
Additionally, an independent cohort of ambulatory individuals with persistent systolic HF supports our results and provides new insights on the link between the three phosphatidylcholine metabolic isomers, namely TMAO, choline, and betaine, considering echocardiographic determinants and the associations between both renal and inflammatory biomarkers. Numerous noteworthy discoveries have been made. To begin, we found that TMAO had a superior predictive value to choline and betaine in patients with chronic systolic heart failure, regardless of the cardio-renal parameters. Second, rather than LV systolic dysfunction, we found associations between all three metabolites and LV diastolic dysfunction. Thirdly, the very low correlations between TMAO, choline, and betaine in many well-characterized inflammatory biomarkers and in their distinct associations with endothelial dysfunction indicators indicated the existence of a separate pathophysiological mechanism. Notably, the increased TMAO levels seen in individuals with renal insufficiency or diabetes mellitus suggest an underlying metabolic deficiency associated with those disease states rather than a systemic inflammatory response. Nonetheless, the relationship between increased TMAO and both HF severity and adverse outcomes, irrespective of other cardio-renal indices, argues for a possible harmful molecular link between the gut microbiota pathway that generates TMAO and the development and/or progression of HF. Notably, this is a cohort of ambulatory stable heart failure patients with left ventricular systolic dysfunction and with an annualized mortality of 7.1% (considering transplantation as the equivalent of death), which is not dissimilar to that seen in published clinical trials. Taken together, our results validate the clinical relevance of TMAO levels in heart failure and indicate that further research is needed to elucidate the association's molecular underpinnings. However, after tuning for the parameters of renal function, the capacity of the TMAO to independently forecast is lost, likely due to the substantial correlations between the parameters of renal function (approximate glomerular filtration rate and urea) and TMAO. These findings indicate that a higher degree of "backward failure" (congestion associated with scarring or ischemia) rather than "forward failure" (or reduced perfusion) may be linked with the main metabolic deficiency underlying the observed correlations. Consistent with this, correlations between choline and renal function indices were seen for both choline and TMAO, although the link between TMAO and adverse outcomes in individuals persisted even after adjusting for renal function. The purpose of this study was to investigate the connection between (1) the intestinal microbiota-dependent analyte TMAO and its dietary precursors, namely and choline and betaine, and (2) echocardiographic indicators in sarcopenic patients with chronic systolic heart failure [80,81] (Figure 2).

Conclusions
Sarcopenia is common in cases of heart failure, leading to inadequate disease prognosis. While the pathophysiology of muscle wastage is quite complicated in heart failure, multiple pathogenetic mechanisms tend to be shared by sarcopenia and heart failure, and they can benefit from strategies of standard treatment focused on a nutritional, physical, and pharmacological approach. In recent years, several studies have identified a clear correlation between CVDs and the microbiota of the gut. We already know that TMAO, a gut microbiota metabolite, may have fresh perspectives and insights regarding how heart failure is supported by the microbiota of the gut. These findings provide a good opportunity for controlling heart failure via addressing the microbiota of the gut, including through the use of updated probiotics, prebiotics, dietary therapy, and FMT. Moreover, emerging research from different groups and clinical findings reveal the association between the dysfunction of the microbiota of the gut, the TMAO circulation, and the susceptibility of heart failure, indicating a fresh and desirable therapeutic target for HF treatment. Furthermore, excessive intake of a diet such as choline or L-carnitine, which contain intermediate precursor TMA for TMAO, should be carefully used in elderly people who have dysbiosis with muscle disorders. Future research studies are warranted.

Conclusions
Sarcopenia is common in cases of heart failure, leading to inadequate disease prognosis. While the pathophysiology of muscle wastage is quite complicated in heart failure, multiple pathogenetic mechanisms tend to be shared by sarcopenia and heart failure, and they can benefit from strategies of standard treatment focused on a nutritional, physical, and pharmacological approach. In recent years, several studies have identified a clear correlation between CVDs and the microbiota of the gut. We already know that TMAO, a gut microbiota metabolite, may have fresh perspectives and insights regarding how heart failure is supported by the microbiota of the gut. These findings provide a good opportunity for controlling heart failure via addressing the microbiota of the gut, including through the use of updated probiotics, prebiotics, dietary therapy, and FMT. Moreover, emerging research from different groups and clinical findings reveal the association between the dysfunction of the microbiota of the gut, the TMAO circulation, and the susceptibility of heart failure, indicating a fresh and desirable therapeutic target for HF treatment. Furthermore, excessive intake of a diet such as choline or L-carnitine, which contain intermediate precursor TMA for TMAO, should be carefully used in elderly people who have dysbiosis with muscle disorders. Future research studies are warranted.