Introduction

Referred pain is a painful sensation in an area of ​​the body that is distant from the actual source of pain. The physiological cause of this condition is the activation of somatic sensory cells in the spinal cord due to strong signals carried by visceral afferent nerve fibers to the same level of the spinal cord. The location of the pain is predictable based on the location of the visceral injury [1].

Cardiac visceral pain is associated with the somatic segments T1-5 on the left, gastric pain is associated with the epigastric and posterior sternal regions, and hepatic and pancreatic pain is associated with the epigastric region. Gallbladder pain often radiates to the area below the right scapula [2].

Somatic pathways innervated by the visceral afferent nerves of the small intestine affect the peri-umbilical region, and lesions in the colon cause radiating pain in the subumbilical region.

Acute abdominal pain: Distinguishing features: Acute abdominal pain may be due to a serious intra-abdominal process, such as appendicitis or intestinal obstruction, or it may be of extra-intestinal origin, such as lower lobe pneumonia or biliary tract stones. Not all attacks of acute abdominal pain require emergency intervention [3].

Appendicitis should be ruled out as soon as possible. The evaluation should be effective, sufficiently focused, and rapid.

Only a small number of children presenting with acute abdominal pain truly require emergency surgery. Patients who require surgery should be separated from those who can be managed conservatively. Importance of the microbiota:

 Hormonal, Neurotransmitter, and Hypothalamic-Pituitary-Adrenal Axis Effects on Sleep

The neuroendocrine regulation of sleep involves a broad spectrum of hormones that modulate the architecture and quality of sleep. Melatonin, synthesized in the pineal gland, is a pivotal regulator of circadian rhythms that synchronizes the sleep-wake cycle with dark signaling. It acts via MT1 and MT2 receptors to influence sleep onset and duration. Adenosine also plays a role as an endogenous neuromodulator in increasing sleep pressure through its accumulation during wakefulness and binding to A1 and A2A receptors for the inhibition of wake-promoting neurotransmitters. The interaction between excitatory (such as glutamate) and inhibitory (GABA) neurotransmitters influences sleep dynamics [4].

GABAergic activity is crucial in the initiation and maintenance of sleep by inhibiting the neural circuits involved in wakefulness. In contrast, monoamines such as norepinephrine and serotonin, although typically associated with states of wakefulness, have subtle roles in sleep regulation, for example, with serotonergic activity modulating slow-wave sleep [5] (SWS) and rapid eye movement [6] (REM) cycles. Proliferative or proliferative-related hormones (such as estrogen and prolactin) can have a significant impact on sleep patterns, particularly in relation to stress responses and proliferative cycles [5-7].

The HPA axis plays a central role in the stress response and has important implications for sleep regulation. Activation of this axis leads to the release of corticotropin-releasing hormone (CRH) from the hypothalamus, stimulation of adrenocorticotropic hormone (ACTH) from the pituitary, and consequent release of glucocorticoids from the adrenal cortex [8].

Glucocorticoids, particularly cortisol, have complex effects on sleep, typically delaying sleep onset and reducing SWS through their effects on the central nervous system. Chronic activation of the HPA axis, as seen in chronic stress conditions, can lead to disruption of the sleep-wake cycle and contribute to the development and maintenance of insomnia. The inhibitory feedback of the HPA axis by cortisol is essential; however, disruption of this feedback loop [7], which is often observed in psychiatric disorders such as depression and anxiety, exacerbates sleep disturbances (Figure 1).

Figure 1. Contribution of the Gut Microbiome to Drug

Demographic and Lifestyle Effects on Sleep

Demographic factors, including age, gender, and employment status, influence sleep patterns and quality. Age-related changes in sleep architecture, such as decreased SWS and increased sleep fragmentation, have been well documented. These changes are attributed, in part, to changes in circadian rhythms and decreased sleep pressure. Gender differences in sleep are also notable [9].

Women generally report more sleep disturbances, which may be related to hormonal fluctuations during the menstrual cycle, pregnancy, and menopause. Occupational factors, particularly those involving irregular hours or night shifts, disrupt circadian rhythms and are associated with increased prevalence of sleep disturbances, impaired cognitive function, and a higher risk of chronic diseases.

 Food Intake, Hunger, and Satiety: Metabolic Effects on Sleep

The relationship between food intake and sleep is increasingly recognized as bidirectional. Hormones involved in the regulation of hunger and satiety, such as leptin, ghrelin, and insulin, not only affect energy balance, but also affect sleep architecture. Leptin, an anorectic hormone, promotes sleep, while ghrelin, an appetite-stimulating hormone, is associated with increased wakefulness. Dietary patterns and specific nutrients also play an important role in sleep regulation [10].

For example, diets high in fat and sugar are associated with poorer sleep quality, while diets high in fiber and low-fat proteins are associated with better sleep outcomes. Meal timing, especially eating late at night, can disrupt day-night rhythms and negatively affect sleep.

 Circadian Rhythms: Molecular Mechanisms and Sleep

Regulation Circadian rhythms are approximately 24-hour endogenous cycles that regulate various physiological processes, including the sleep-wake cycle. These rhythms are driven by a set of core clock genes [1], including PER, BMAL1, CLOCK, and CRY, which generate oscillations through transcriptional-translational feedback loops. The suprachiasmatic nucleus (SCN) of the hypothalamus acts as a master and central clock [8] and synchronizes environmental clocks [9] in various tissues such as the liver, heart, adipose tissue, gastrointestinal tract, etc. Disturbances in circadian rhythms, whether due to genetic mutations or environmental factors such as exposure to light or behavioral patterns such as shift work, can lead to internal clock dissynchrony. This imbalance is associated with various sleep disorders, including delayed sleep phase disorder [10], as well as broader health issues such as metabolic syndrome and mood disorders [11].

Gut Microbiota and Sleep

Now that we have provided a general overview of the importance of sleep and the factors that influence it, and if you recall our previous article on how the brain and gut microbiota interact, you might guess that there are clear pathways that could mediate between sleep and gut microbial activity, such as inflammation, the vagus nerve, bacterial metabolism, and the HPA axis [12].

But there is also other compelling evidence that reinforces the need for such a connection. Various studies have reported that gut bacteria follow a circadian rhythm, similar to our sleep-wake cycle. In mice and humans, some bacterial species change in number throughout the day, or some bacteria are more active during the day and others at night. Thus, rhythmic fluctuations in the gut microbiota include both demographic and functional rhythms. For example, in mice, bacteria such as Clostridiales [11] and Lactobacilli [12] change their abundance according to a 24-hour cycle, and in humans, bacteria such as Parabacteroids [13] and Roseophoria [14] also show diurnal fluctuations. Other reports also indicate changes in the activity of Enterobacter aerogenes [15] on a daily basis and changes in the abundance of Mucospirillum schadlerii [16] between light and dark periods. It has also been reported that in mice, gut bacteria focus on energy use and cellular growth when active (usually at night) and on energy conservation when resting (during the day).

A variety of factors, such as genetic variations, diet, and exposure to light, can disrupt these daily rhythms. Different foods can affect how and when gut bacteria change. For example, bacteria that utilize carbohydrates may respond differently to changes in dietary patterns. Microbial rhythms are closely linked to the circadian rhythms of their hosts. These bacterial daily patterns are influenced by melatonin and temperature, which also regulate our internal clock (Figure 2).

Disruptions in host circadian clock genes, such as Clock mutations, can affect microbial rhythms, even if the host behavior is normal. Notably, it has been shown that meal timing can restore healthy bacterial rhythms in mice with Clock mutations, indicating that meal timing is an important factor in regulating gut bacteria that operates independently of the host's internal clock. It is important to note that fluctuations in gut bacteria affect digestion, energy balance, and metabolism. Bacterial metabolites that are produced rhythmically can affect circadian rhythms and host metabolism [16]. For example, dietary choline is converted by gut bacteria to trimethylamine and then to trimethylamine N-oxide (TMAO) [17], which may affect the expression of circadian clock genes.

Figure 2. Targeting the gut microbiome to control drug pharmacomicrobiomics

Based on the above findings, it can be concluded that one of the challenges of studies focused on microbiota is the sampling time, because there is a possibility that the number of bacteria may vary at different times. In a study of two individuals who had an 8- and 10-hour flight with jet lag [18], fecal samples were taken under three conditions: before the flight, one day before the flight (during jet lag), and two weeks after the flight (recovery), and transplanted into germ-free mice, and then the mice's weight gain and blood sugar were measured.

Analysis of human feces showed that jet lag induced changes in Firmicutes abundance [19], which returned to pre-jet lag levels after recovery. It was also observed that after fecal transplantation into mice, the weight gain trend was significantly higher in mice that had received jet lag fecal samples than in the other two groups. Similarly, in this study, it was observed that after consuming dietary glucose, blood glucose levels in germ-free mice colonized [20] with fecal microbiota from a jet lag sample were significantly higher than in the group colonized with a pre-jet lag sample, while this metabolic change was not observed in the recipient group after recovery.

On the other hand, studies show that insufficient sleep is associated with weight gain and obesity. Studies consistently show that short sleep is linked to obesity, type 2 diabetes, and metabolic syndrome (a group of conditions that increase the risk of heart disease, stroke, and diabetes). Experiments in which people are kept awake for 24 to 120 hours show changes in body functions associated with metabolic diseases. Both sleep restriction and disruption of sleep patterns, as well as circadian rhythm dissonance (when your internal clock is out of sync), affect metabolism.

These changes in sleep position are considered a type of physiological stress, which, like psychological stress, may lead to the activation of the stress response in the body and affect the intestinal microbiota. In addition to changes in the composition and diversity of bacteria (dysbiosis), they lead to inflammation and subsequent damage to the intestinal barrier [21], and by increasing intestinal permeability, they create conditions for systemic and widespread inflammation and even the translocation of harmful bacteria to other areas. All of these things can lead to metabolic problems. So this pathway may explain why and how shift work and poor sleep are linked to fatigue and metabolic problems.

In another study in 2021, researchers found that sleep deprivation [22] can cause dysbiosis. In this study, it was observed that despite no changes in the microbial composition of the gastrointestinal tract after 24 hours of sleep deprivation, if the deprivation process continues for up to 48 hours, this situation leads to significant changes in the diversity of intestinal bacteria, and we witness a decrease in the number of some bacteria such as Butyricococcus butyricimonas, Alistipes, Intestinmonas and Lactobacillus and an increase in the number of Streptococcus bacteria, which returned to their pre-sleep state after two weeks of recovery. Wang and colleagues showed in another study in 2023 that the protective and improving effects of melatonin on memory, inflammation, and neural tissue in a sleep deprivation model could be mediated by the gut microbiota.

These findings are consistent with findings from sleep deprivation studies that show learning and memory impairment, inflammation, and mood changes, and suggest that the gut microbiota is an important mediator in creating these conditions. Therefore, based on the evidence and arguments, it can be expected that the gut microbiota can be considered as an important target in the study of sleep-related mechanisms and related diseases, and also create a change in the theoretical frameworks focused on therapeutic strategies.

Therefore, research has also been conducted to investigate the potential of microbiota-focused therapeutic interventions for the treatment of sleep-related disorders. It has been shown that consuming probiotics such as Lactobacillus and Bifidobacterium reduces stress and improves sleep quality by preventing the growth of harmful bacteria such as Enterobacteriaceae, regulating the intestinal microbial balance, and suppressing the inflammatory response [23].

Also, administration of galacto-oligosaccharides and fructo-oligosaccharides as prebiotics in mice model of sleep deprivation has been able to reduce symptoms of nocturnal anxiety in mice by regulating inflammation and synchronizing the day-night rhythm, and also reduce inflammation caused by sleep deprivation.

It has also been shown in human samples with insomnia that fecal microbiota transplantation increases Lactobacillus and Bifidobacterium and restores the disrupted balance in the microbiota of these patients. Accordingly, recent studies have opened new windows into sleep and its related disorders, which can help us improve the quality of one of the most important physiological processes, the disorders related to which have, according to statistics, a market worth 20 billion dollars and have been growing in the last decade. Targeting microbiota in the treatment of sleep disorders and investigating the impact of gut microbiota on the pathophysiology of these disorders, such as narcolepsy and sleep apnea, is an emerging field that urgently requires continued research to expand our understanding of this fascinating relationship.

Distribution

The process of drug distribution is important because it determines how much of a drug reaches the active sites, and thus affects the effectiveness and toxicity of the drug. The drug is transported from the site of absorption to other tissues in the body, including brain, fat, and muscle tissue. Several factors can play a role in this process, including blood flow, lipophilicity, molecular size, and how the drug interacts with blood components such as plasma proteins [24].

This mechanism is important because it determines how much of a drug reaches the active sites, and thus affects the effectiveness and toxicity of the drug. The drug is transported from the site of absorption to various tissues in the body, including brain, fat, and muscle tissue. Several factors can play a role in this process, including blood flow, lipophilicity, molecular size, and how the drug interacts with blood components such as plasma proteins. In addition, there are anatomical barriers in some organs, such as the blood-brain barrier, which prevent some drugs from entering brain tissue. Drugs with specific properties, such as high lipophilicity, small size, and low molecular weight, are more likely to cross the blood-brain barrier.

Food and Herbal Interactions

Although foods and herbal products that inhibit or induce P-gp and CYP3A4 appear to have kinetic interactions with NOACs, none of these interactions have been confirmed by human or in vivo studies. Limited evidence suggests that rivaroxaban bioavailability is improved when taken with food. Therefore, it is recommended that rivaroxaban be taken with food when used for stroke prevention. The drug should be taken with food, especially at doses of 15 and 20 mg [25].

In this case, the area under the curve (AUC) increases by at least 39% and the bioavailability of the drug reaches almost 100%. Other drugs in this class do not interact with food. It is worth noting that the concomitant use of PPIs and H2 blockers leads to a decrease in the bioavailability of dabigatran, but this interaction does not affect the clinical efficacy of the drug. Other NOACs do not interact with any of the antacids.

Clinical studies indicate that administration of the crushed form of the drug via nasogastric tube does not alter the bioavailability of apixaban, rivaroxaban, and edoxaban. While dabigatran capsules should not be opened. Because this leads to a significant increase in the bioavailability of the drug. Regarding herbal products, it should be noted that several major limitations are particularly relevant to the assessment of NOAC interactions with herbal drugs.

Among these interactions, we can mention the possibility of multiple putative pharmacokinetic and pharmacodynamics pathways for interaction, unknown mechanisms of drug interaction, and inherent variability in the composition of herbs. Thus, it is difficult to provide firm recommendations on the safety of using these products. In some patients with other risk factors, NOAC blood levels may be considered. On the other hand, although there is no evidence from clinical studies, grapefruit appears to affect the bioavailability of rivaroxaban. Another example is catechu, a known inducer of P-gp and CYP3A4.

Plasma levels of NOACs that are substrates of P-gp and CYP3A4 (rivaroxaban and apixaban) are expected to be decreased when coadministered with this product, potentially increasing the risk of stroke. Therefore, caution is advised when catechu is coadministered with apixaban or edoxaban. Some sources have recommended that rivaroxaban and dabigatran should be avoided with catechu (Figure 3).

Figure 3. Drug–gut microbiota interactions: implications for neuropharmacology

Pharmacodynamic interactions

In addition to pharmacokinetic interactions, concomitant administration of NOACs with other anticoagulants, platelet inhibitors such as aspirin, clopidogrel, ticlopidine, prasugrel, and ticagrelor, and nonsteroidal anti-inflammatory drugs (NSAIDS) can increase the risk of bleeding. Among herbal products, turmeric extract products may also interact with NOACs, especially apixaban. Before co-administering these drugs, the patient's clinical condition should be carefully evaluated and the risk of this complication should be weighed against the benefits of treatment [26].

It should be noted that if NOACs are co-administered with a dual antiplatelet drug regimen, the patient needs active measures to prevent bleeding. In these situations, the dose of the NOAC drug, as well as the duration of taking other antiplatelet drugs, should be adjusted in consultation with a cardiologist. According to recent research, half of the drugs used harm intestinal bacteria.

On October 23, 2019, a groundbreaking presentation at UEG Week 2019 in Barcelona revealed that the gut microbiome is at risk of damage whenever we take one or more of 18 common classes of drugs. This damage can range from changes in the ratios of beneficial and potentially harmful species to changes in the cellular metabolism of the bacteria themselves, with consequences including increased risk of obesity, gut infections and microbiome-related diseases.

In addition, drugs from eight other classes induce genes that lead to increased antibiotic resistance in those treated. The researchers examined the effects of taking 41 classes of drugs by examining more than 1,880 stool samples from three groups: a cohort from the general population, a group with inflammatory bowel disease (IBD) and a third group without IBD as healthy controls. The researchers looked at the effects of taking a single drug and then multiple drugs taken simultaneously. They analyzed the differences in gut microbiota composition and cellular metabolism caused by the drug compared to people who did not use the drug [27].

Microbiota and learning and memory

The gut microbiota can even be a factor in learning and memory. Studies show that the gut microbiota also affects spatial memory in mice. Mice treated with ampicillin have impaired spatial memory. Rats treated with ampicillin perform poorly on object recognition memory tests. It is predicted that the gut microbiota in humans also affects memory and learning. Bifid bacterium breve, Lactobacillus fermentum and Bifid bacterium longum enhance memory as a probiotic treatment. The gut microbiota affects the amygdala of the brain, altering emotions, increasing memory and learning with emotion, social behavior and anxiety. The amygdala is part of the limbic system of the brain that plays an important role in learning, especially learning with emotion, understanding emotions, responding to pain, happiness and fear. The gut microbiota can alter learning and memory by affecting the hippocampus of the brain. Recently, it has been suggested that the gut microbiota regulates hippocampal neurogenesis. Studies on germ-free mice show that the gut microbiota can induce the expression of many hippocampal miRNAs and mRNAs [28].

How do gut microbes help regulate cholesterol and fat metabolism?

The role of bile acids and gut microbiota in the digestion of dietary fats Bile acids are produced in the liver from cholesterol and released in the small intestine to help digest dietary fats after a meal. Most bile acids are reabsorbed and recycled, while some are converted by gut bacteria into secondary bile acids. Some bacteria, such as Lactobacillus and Clostridium difficile species, can modify bile acids in a variety of ways.

These modified bile acids affect metabolic processes by regulating cholesterol levels, fat digestion, and glucose metabolism. For example, some modified bile acids, such as deoxycholic acid (DCA), activate a liver receptor that reduces bile acid production, which could be a key regulator of metabolic health. Recent research in mice has uncovered a novel host-microbiota partnership that helps regulate bile acid production and fat metabolism.

The scientists identified a compound called bile acids-methylcystine (BA-MYC), which is produced by the host's gut microbes. BA-MYC reduces the activity of the liver receptor, leading to increased bile acid production. The findings suggest a strong connection between the host liver and the gut microbiota, which helps regulate bile acid production in response to diet and, in turn, metabolic balance.

Conclusion

There are many projects trying to decode the human genome by sequencing all of the human genes. The microbiome is undergoing intensive efforts to uncover all of its genetic information. The body’s microbes are so small that, despite their large number of cells, they only make up about 2 to 3 percent of the total body weight of a human. The microbial samples found in the mouth and feces are very diverse. In contrast, samples from sites such as the vagina show a relatively simple microbiome. This study demonstrates the great diversity of the human microbiome among a large group of healthy Westerners, but raises questions for further research. By determining the phenotype of a patient’s gut microbiota, it is possible to develop unique therapeutic and clinical approaches. Using microbes to fight microbes? Many studies have examined the effectiveness of gut supplements and targeted microbiome therapies to protect the body from disease or even fight disease directly. In other words, researchers say that microorganisms should be used directly as medicine and destroy a specific group of gut microbes.

According to doctors, “beneficial” microbes, such as probiotics and prebiotics, can be directly increased in order to defeat or neutralize pathogens. Of course, they also point out that not all patients’ bodies react the same to these methods; therefore, it is necessary to determine whether this method is beneficial or detrimental to the patient.