Dopamine induces contraction in the proximal, but relaxation in the distal rat isolated small intestine

Pharmacomicrobiomics: a new field contributing to optimizing drug therapy in Parkinson's disease

Gut microbiota, which act as a determinant of pharmacokinetics, have long been overlooked. In recent years, a growing body of evidence indicates that the gut microbiota influence drug metabolism and efficacy. Conversely, drugs also exert a substantial influence on the function and composition of the gut microbiota. Pharmacomicrobiomics, an emerging field focusing on the interplay of drugs and gut microbiota, provides a potential foundation for making certain advances in personalized medicine. Understanding the communication between gut microbiota and antiparkinsonian drugs is critical for precise treatment of Parkinson's disease. Here, we provide a historical overview of the interplay between gut microbiota and antiparkinsonian drugs. Moreover, we discuss potential mechanistic insights into the complex associations between gut microbiota and drug metabolism. In addition, we also draw attention to microbiota-based biomarkers for predicting antiparkinsonian drug efficacy and examine current state-of-the-art knowledge of microbiota-based strategies to optimize drug therapy in Parkinson's disease.

Zonulin levels are associated with cortisol, dopamine, and serotonin levels in irritable bowel syndrome

Increase intestinal permeability is one of the main mechanisms for the development of irritable bowel syndrome (IBS). The role of stress and nutrition factors is considered as key modifiable factors contributing to the development of increase intestinal permeability. Purpose of the study: to evaluate the content of a marker of increased intestinal permeability (zonulin in feces) in relation to dietary habits, levels of anxiety and depression, levels of stress hormones (cortisol in saliva) and neurotransmitters (serotonin in blood serum, dopamine in blood plasma) in patients with IBS. Materials and methods: an open cohort prospective study was conducted with the inclusion of 263 patients with an established diagnosis of IBS. The control group consisted of 40 healthy volunteers. All individuals included in the study were assessed for diet and eating habits, the severity of anxiety and depression, including the level of specific anxiety in relation to gastrointestinal symptoms, and quality of life. In addition, the levels of cortisol in the morning and evening portions of saliva, serum serotonin, plasma dopamine and fecal zonulin were assessed. Results: in patients with IBS, the marker of increased intestinal permeability (zonulin in feces) is closely related to the nature of nutrition, anxiety levels, cortisol and serotonin secretion, and is also associated with the development of abdominal pain, diarrhea, and the severity of the disease.

Eating Habits, Anxiety and Depression in Patients with Irritable Bowel Syndrome: Clinical and Laboratory Comparisons

Aim: to assess the level of stress hormones (cortisol in saliva), neurotransmitters (serotonin in blood serum, dopamine in blood plasma) in relation to eating habits, anxiety and depression levels in patients with IBS.

Materials and methods. An open cohort prospective study was conducted with the inclusion of 263 patients with an established diagnosis of IBS, among them 189 (71.9 %) women and 74 (28.1 %) men. The average age of patients with IBS was 29 [25; 35] years. The control group included 40 healthy volunteers. All individuals included in the study were assessed for diet and eating habits using the WHO CINDI program questionnaire, “Information on Nutrition and Eating Behavior”, the severity of anxiety and depression according to the HADS questionnaire, the level of specific anxiety in relation to gastrointestinal symptoms according to the VSI questionnaire, quality of life according to the IBS-QoL questionnaire. In addition, the enzyme immunoassay method was used to assess the levels of cortisol in the morning and evening portions of saliva, serotonin in the blood serum and dopamine in the blood plasma.

Results. Among patients with IBS there is a statistically significantly higher level of cortisol in the morning and evening portions of saliva (U = 19.5, p < 0.001 and U = 111.5, p < 0.001, respectively), serotonin in blood serum (U = 269.0, p = 0.042) and lower plasma dopamine levels (U = 93.5, p = 0.0002) compared with controls. The mean salivary cortisol level among patients with IBS was 45.39 [29.86; 70.10] ng/ml in the morning and 19.21 [13.98; 23.50] ng/ml in the evening, while in the group of healthy individuals it was 19.0 [16.5; 21.7] and 9.7 [8.5; 10.5] ng/ml, respectively. The average content of serotonin in blood serum in patients with IBS was 188.78 [150.41; 230.32] ng/ml, among healthy individuals — 142.80 [130.52; 154.15] ng/ml. The average content of dopamine in blood plasma in patients with IBS was 28.83 [20.08; 41.54] ng/ml, in healthy individuals — 58.20 [48.15; 66.62] ng/ml.

Conclusion. In patients with IBS the secretion of the stress hormone (cortisol) and neurotransmitters (serotonin, dopamine) is closely related to the nature of nutrition, the level of anxiety and depression, and is also associated with the clinical variant and severity of the course of the disease.

The multiple roles of dopamine receptor activation in the modulation of gastrointestinal motility and mucosal function

Dopamine (DA) is a catecholamine regulatory molecule with potential role in physiology and physiopathology of the intestinal tract. Various cellular sources of DA have been indicated as enteric neurons, immune cells, intestinal flora and gastrointestinal epithelium. Moreover, DA is produced by nutritional tyrosine. All the five DA receptors, actually described, are present throughout the gut. Current knowledge of DA in this area is reviewed, focusing on gastrointestinal function in health and during inflammation. Research on animal models and humans are reported. A major obstacle to understanding the physiologic and/or pharmacological roles of enteric DA is represented by the multiplicity of receptors involved in the responses together with many signalling pathways related to each receptor subtype. It is mandatory to map precisely the distributions of DA receptors, to determine the relevance of a receptor in a specific location in order to explore novel therapies directed to dopaminergic targets that may be useful in the control of intestinal inflammation.

Small intestine neuromuscular dysfunction in a mouse model of dextran sulfate sodium-induced ileitis: Involvement of dopaminergic neurotransmission

AIMS

Anomalies in dopaminergic machinery have been shown in inflammatory bowel disease (IBD) patients and preclinical models of IBD. Thus, we aimed to evaluate the impact of dextran sodium sulfate (DSS)-induced ileitis on enteric dopaminergic pathways.

MATERIALS AND METHODS

Male C57/Bl6 mice (10 ± 2 weeks old) received 2% DSS in drinking water for 5 days and were then switched to regular drinking water for 3 days. To measure ileitis severity inflammatory cytokines (IL-1β, TNFα, IL-6) levels were assessed. Changes in ileal muscle tension were isometrically recorded following: 1) cumulative addition of dopamine on basal tone (0.1-1000 μM); ii) 4-Hz electric field stimulation (EFS) in the presence of 30 μM dopamine with/without 10 μM SCH-23390 (dopamine D1 receptor (D1R) antagonist) or 10 μM sulpiride (D2R antagonist). Immunofluorescence distribution of the neuronal HuC/D protein, glial S100β marker, D1R, and dopamine transporter (DAT) were determined in longitudinal-muscle-myenteric plexus whole-mounts (LMMPs) by confocal microscopy. D1R and D2R mRNA transcripts were evaluated by qRT-PCR.

KEY FINDINGS

DSS caused an inflammatory process in the small intestine associated to dysmotility and altered barrier permeability, as suggested by decreased fecal output and enhanced stool water content. DSS treatment caused a significant increase of DAT and D1R myenteric immunoreactivity as well as of D1R and D2R mRNA levels, accompanied by a significant reduction of dopamine-mediated relaxation, involving primarily D1-like receptors.

SIGNIFICANCE

Mouse ileitis affects enteric dopaminergic neurotransmission mainly involving D1R-mediated responses. These findings provide novel information on the participation of dopaminergic pathways in IBD-mediated neuromuscular dysfunction.

Mapping the Influence of the Gut Microbiota on Small Molecules across the Microbiome Gut Brain Axis

Microbes exert influence across the microbiome-gut-brain axis through neurotransmitter production, induction of host immunomodulators, or the release or induction of other microbial or host molecules. Here, we used mass spectrometry imaging (MSI), a label-free imaging tool, to map molecular changes in the gut and brain in germ-free, antibiotic-treated and control mice. We determined spatial distribution and relative quantification of neurotransmitters and their precursors in response to the microbiome. Using untargeted MSI, we detected a significant change in the levels of four identified small molecules in the brains of germ-free animals compared to controls. However, antibiotic treatment induced no significant changes in these same metabolites in the brain after 1 week of treatment. This work exemplifies the utility of MSI as a tool for the study of known and discovery of novel, mediators of microbiome-gut-brain axis communication.

Parkinson's Disease Medication Alters Small Intestinal Motility and Microbiota Composition in Healthy Rats

Parkinson’s disease (PD) is known to be associated with altered gastrointestinal function and microbiota composition. To date, the effect of PD medication on the gastrointestinal function and microbiota, at the site of drug absorption, the small intestine, has not been studied, although it may represent an important confounder in reported microbiota alterations observed in PD patients. To this end, healthy (non-PD) wild-type Groningen rats were employed and treated with dopamine, pramipexole (in combination with levodopa-carbidopa), or ropinirole (in combination with levodopa-carbidopa) for 14 sequential days. Rats treated with dopamine agonists showed a significant reduction in small intestinal motility and an increase in bacterial overgrowth in the distal small intestine. Notably, significant alterations in microbial taxa were observed between the treated and vehicle groups; analogous to the changes previously reported in human PD versus healthy control microbiota studies. These microbial changes included an increase in Lactobacillus and Bifidobacterium and a decrease in Lachnospiraceae and Prevotellaceae. Markedly, certain Lactobacillus species correlated negatively with levodopa levels in the systemic circulation, potentially affecting the bioavailability of levodopa. Overall, the study highlights a significant effect of PD medication intrinsically on disease-associated comorbidities, including gastrointestinal dysfunction and small intestinal bacterial overgrowth, as well as the gut microbiota composition. The results urge future studies to take into account the influence of PD medication per se when seeking to identify microbiota-related biomarkers for PD.

IMPORTANCE Parkinson’s disease (PD) is the second most common neurodegenerative disorder and is known to be associated with altered gastrointestinal function and microbiota composition. We previously showed that the gut bacteria harboring tyrosine decarboxylase enzymes interfere with levodopa, the main treatment for PD (S. P. van Kessel, A. K. Frye, A. O. El-Gendy, M. Castejon, A. Keshavarzian, G. van Dijk, and S. El Aidy, Nat Commun 10:310, 2019). Although PD medication could be an important confounder in the reported alterations, its effect, apart from the disease itself, on the microbiota composition or the gastrointestinal function at the site of drug absorption, the small intestine, has not been studied. The findings presented here show a significant impact of commonly prescribed PD medication on the small intestinal motility, small intestinal bacterial overgrowth, and microbiota composition, irrespective of the PD. Remarkably, we observed negative associations between bacterial species harboring tyrosine decarboxylase activity and levodopa levels in the systemic circulation, potentially affecting the bioavailability of levodopa. Overall, this study shows that PD medication is an important factor in determining gastrointestinal motility and, in turn, microbiota composition and may, partly, explain the differential abundant taxa previously reported in the cross-sectional PD microbiota human studies. The results urge future studies to take into account the influence of PD medication on gut motility and microbiota composition when seeking to identify microbiota-related biomarkers for PD.

Dopamine Modulates Drosophila Gut Physiology, Providing New Insights for Future Gastrointestinal Pharmacotherapy

Dopamine has a variety of physiological roles in the gastrointestinal tract (GI) through binding to Drosophila dopamine D1-like receptors (DARs) and/or adrenergic receptors and has been confirmed as one of the enteric neurotransmitters. To gain new insights into what could be a potential future promise for GI pharmacology, we used Drosophila as a model organism to investigate the effects of dopamine on intestinal physiology and gut motility. GAL4/UAS system was utilized to knock down specific dopamine receptors using specialized GAL4 driver lines targeting neurons or enterocytes cells to identify which dopamine receptor controls stomach contractions. DARs (Dop1R1 and Dop1R2) were shown by immunohistochemistry to be strongly expressed in all smooth muscles in both larval and adult flies, which could explain the inhibitory effect of dopamine on GI motility. Adult males' gut peristalsis was significantly inhibited by knocking down dopamine receptors Dop1R1, Dop1R2, and Dop2R, but female flies' gut peristalsis was significantly repressed by knocking down only Dop1R1 and Dop1R2. Our findings also showed that dopamine drives PLC-β translocation from the cytoplasm to the plasma membrane in enterocytes for the first time. Overall, these data revealed the role of dopamine in modulating Drosophila gut physiology, offering us new insights for the future gastrointestinal pharmacotherapy of neurodegenerative diseases associated with dopamine deficiency.

Molecular Mechanisms of Microbiota-Mediated Pathology in Irritable Bowel Syndrome

Irritable bowel syndrome (IBS) is one of the most prevalent functional gastrointestinal disorders, and accumulating evidence gained in both preclinical and clinical studies indicate the involvement of enteric microbiota in its pathogenesis. Gut resident microbiota appear to influence brain activity through the enteric nervous system, while their composition and function are affected by the central nervous system. Based on these results, the term “brain–gut–microbiome axis” has been proposed and enteric microbiota have become a potential therapeutic target in IBS cases. However, details regarding the microbe-related pathophysiology of IBS remain elusive. This review summarizes the existing knowledge of molecular mechanisms in the pathogenesis of IBS as well as recent progress related to microbiome-derived neurotransmitters, compounds, metabolites, neuroendocrine factors, and enzymes.

Contributions of Gut Bacteria and Diet to Drug Pharmacokinetics in the Treatment of Parkinson's Disease

Parkinson's disease is the second-most common neurodegenerative disorder worldwide. Besides deciphering the mechanisms that underlie the etiology of the disease, it is important to elucidate the factors that influence the efficacy of the treatment therapeutics. Levodopa, which remains the golden treatment of the disease, is absorbed in the proximal small intestine. A reduction in levodopa absorption, leads to reduction in striatal dopamine levels and, in turn, an "off"-episode. In fact, motor fluctuations represent a major problem during the progression of the disease and alteration between "on" (mobility often with dyskinesia) and "off" (immobility, akinesia) episodes contribute to a decreased quality of life. Dietary amino acids can interfere with the absorption of levodopa from the gut lumen and its transport through the blood brain barrier. In addition, higher abundance of specific gut bacteria that restrict levodopa absorption plays a significant role in motor fluctuations in a subset of Parkinson's disease patients. Here, we review the impact of factors potentially interfering with levodopa absorption, focusing on levodopa transport, diet, and gut bacterial interference with the bioavailability of levodopa.

MitoPark transgenic mouse model recapitulates the gastrointestinal dysfunction and gut-microbiome changes of Parkinson's disease

Gastrointestinal (GI) disturbances are one of the earliest symptoms affecting most patients with Parkinson's disease (PD). In many cases, these symptoms are observed years before motor impairments become apparent. Hence, the molecular and cellular underpinnings that contribute to this early GI dysfunction in PD have actively been explored using a relevant animal model. The MitoPark model is a chronic, progressive mouse model recapitulating several key pathophysiological aspects of PD. However, GI dysfunction and gut microbiome changes have not been categorized in this model. Herein, we show that decreased GI motility was one of the first non-motor symptoms to develop, evident as early as 8 weeks with significantly different transit times from 12 weeks onwards. These symptoms were observed well before motor symptoms developed, thereby paralleling PD progression in humans. At age 24 weeks, we observed increased colon transit time and reduced fecal water content, indicative of constipation. Intestinal inflammation was evidenced with increased expression of iNOS and TNFα in the small and large intestine. Specifically, iNOS was observed mainly in the enteric plexi, indicating enteric glial cell activation. A pronounced loss of tyrosine hydroxylase-positive neurons occurred at 24 weeks both in the mid-brain region as well as the gut, leading to a corresponding decrease in dopamine (DA) production. We also observed decreased DARPP-32 expression in the colon, validating the loss of DAergic neurons in the gut. However, the total number of enteric neurons did not significantly differ between the two groups. Metabolomic gas chromatography-mass spectrometry analysis of fecal samples showed increased sterol, glycerol, and tocopherol production in MitoPark mice compared to age-matched littermate controls at 20 weeks of age while 16 s microbiome sequencing showed a transient temporal increase in the genus Prevotella. Altogether, the data shed more light on the role of the gut dopaminergic system in maintaining intestinal health. Importantly, this model recapitulates the chronology and development of GI dysfunction along with other non-motor symptoms and can become an attractive translational animal model for pre-clinical assessment of the efficacy of new anti-Parkinsonian drugs that can alleviate GI dysfunction in PD.

Effects of apomorphine, a dopamine agonist, on Daphnia magna: Imaging of swimming track density as a novel tool in the assessment of swimming activity

Apomorphine (APO) is a non-selective agonist of dopamine receptor activating D2-like receptors. Although Daphnia has been used in neurotoxicology in toxicity testing, little is known on its behavioural and physiological responses to dopamine receptors ligands. Therefore, the aim of our study was to determine swimming behaviour (swimming track density, speed, turning activity) and physiological parameters such as heart rate, thoracic limb activity and post-abdominal claw movement frequency in daphnids exposed for 1, 2 and 4h to concentrations of 0.3, 3 and 30mg/L of APO. The results showed the most significant decrease of behavioural endpoints such as swimming track density, speed and degree of turning angles of daphnids exposed for 4h to the highest concentrations of APO. The study also showed that a decrease of thoracic limb activity was found after 2 and 4h but only at the highest concentration. Heart rate was not affected by APO which may be a result of a lack of signalling with dopamine receptors in the heart of Daphnia. Therefore, activity of this organ seems to be not a valuable physiological biomarker in the assessment of effects induced by dopamine receptor ligands. The study also showed that our new methodological approach, imaging of swimming track density may be a promising tool for studying the effects of neuroactive substances on locomotor system activity of Daphnia magna.

Postnatal development of the dopaminergic signaling involved in the modulation of intestinal motility in mice

BACKGROUND

Since antidopaminergic drugs are pharmacological agents employed in the management of gastrointestinal motor disorders at all ages, we investigated whether the enteric dopaminergic system may undergo developmental changes after birth.

METHODS

Intestinal mechanical activity was examined in vitro as changes in isometric tension.

RESULTS

In 2-d-old (P2) mice, dopamine induced a contractile effect, decreasing in intensity with age, replaced, at the weaning (day 20), by a relaxant response. Both responses were tetrodotoxin (TTX)-insensitive. In P2, dopaminergic contraction was inhibited by D1-like receptor antagonist and mimicked by D1-like receptor agonist. In 90-d-old (P90) mice, the relaxation was reduced by both D1- and D2-like receptor antagonists, and mimicked by D1- and D2-like receptor agonists. In P2, contraction was antagonized by phospholipase C inhibitor, while in P90 relaxation was antagonized by adenylyl cyclase inhibitor and potentiated by phospholipase C inhibitor. The presence of dopamine receptors was assessed by immunofluorescence. Quantitative real-time polymerase chain reaction (qRT-PCR) revealed a significant increase in D1, D2, and D3 receptor expression in proximal intestine with the age.

CONCLUSION

In mouse small intestine, the response to dopamine undergoes developmental changes shifting from contraction to relaxation at weaning, as the consequence of D2-like receptor recruitment and increased expression of D1 receptors.

P2Y receptor-mediated transient relaxation of rat longitudinal ileum preparations involves phospholipase C activation, intracellular Ca(2+) release and SK channel activation

AIM

Purinergic signaling plays a major role in the enteric nervous system, where it governs gut motility through a number of P2X and P2Y receptors. The aim of this study was to investigate the P2Y receptor-mediated motility in rat longitudinal ileum preparations.

METHODS

Ileum smooth muscle strips were prepared from rats, and fixed in an organ bath. Isometric contraction and relaxation responses of the muscle strips were measured with force transducers. Drugs were applied by adding of stock solutions to the organ bath to yield the individual final concentrations.

RESULTS

Application of the non-hydrolyzable P2 receptor agonists α,β-Me-ATP or 2-Me-S-ADP (10, 100 μmol/L) dose-dependently elicited a transient relaxation response followed by a sustained contraction. The relaxation response was largely blocked by SK channel blockers apamin (500 nmol/L) and UCL1684 (10 μmol/L), PLC inhibitor U73122 (100 μmol/L), IP3 receptor blocker 2-APB (100 μmol/L) or sarcoendoplasmic Ca(2+) ATPase inhibitor thapsigargin (1 μmol/L), but not affected by atropine, NO synthase blocker L-NAME or tetrodotoxin. Furthermore, α,β-Me-ATP-induced relaxation was suppressed by P2Y1 receptor antagonist MRS2179 (50 μmol/L) or P2Y13 receptor antagonist MRS2211 (100 μmol/L), and was abolished by co-application of the two antagonists, whereas 2-Me-S-ADP-induced relaxation was abolished by P2Y6 receptor antagonist MRS2578 (50 μmol/L). In addition, P2Y1 receptor antagonist MRS2500 (1 μmol/L) not only abolished α,β-Me-ATP-induced relaxation, but also suppressed 2-Me-S-ADP-induced relaxation.

CONCLUSION

P2Y receptor agonist-induced transient relaxation of rat ileum smooth muscle strips is mediated predominantly by P2Y1 receptor, but also by P2Y6 and P2Y13 receptors, and involves PLC, IP3, Ca(2+) release and SK channel activation, but is independent of acetylcholine and NO release.

The role of the vagal pathway and gastric dopamine in the gastroparesis of rats after a 6-hydroxydopamine microinjection in the substantia nigra

AIM

Gastroparesis is a common non-motor system symptom of Parkinson's disease (PD). However, the mechanism responsible for the gastric motor abnormality is not clear. We previously reported on the impaired gastric motility in 6-hydroxydopamine (6-OHDA) rats, which were treated with a bilateral microinjection of 6-OHDA in the substantia nigra (SN). We hypothesize that the enhanced dopamine system and reduced acetylcholine (Ach) in gastric tissues might contribute to the delayed gastric emptying observed in PD.

METHODS

A strain gauge force transducer, digital X-ray imaging system, Western blot, immunofluorescence and Radio Immunoassay were used in this study.

RESULTS

Dopaminergic neurones in the SN were greatly reduced following the bilateral microinjection of 6-OHDA. 6-OHDA rats exhibited impaired gastric motility and delayed gastric emptying, accompanied by increased dopamine content and the overexpression of D2 receptors in the stomach. The administration of the D2 receptor antagonist domperidone relieved gastric dysmotility in 6-OHDA rats, but the D1 receptor antagonist SCH23390 failed to do so. Subdiaphragmatic vagotomy prevented the increase in the gastric dopamine content and D2 receptor expression and improved gastric dysmotility in 6-OHDA rats.

CONCLUSION

Dopaminergic deficiency in the SN results in impaired gastric motility, possibly as a result of the enhanced activity of dopamine system and reduced Ach in gastric tissue. The vagus nerve plays an important role in peripheral gastric motility disorder.

In vivo and in vitro evaluation of the effects of domperidone on the gastrointestinal tract of healthy horses

OBJECTIVE

To determine the effects of domperidone on in vivo and in vitro measures of gastrointestinal tract motility and contractility in healthy horses.

SAMPLE

18 adult horses and tissue samples from an additional 26 adult horses.

PROCEDURES

Domperidone or placebo paste was administered to healthy horses in a 2-period crossover study. Gastric emptying was evaluated after oral administration of domperidone paste (1.1 or 5.0 mg/kg) or placebo paste by means of the acetaminophen absorption test in 12 horses. Frequency of defecation, weight of feces produced, fecal moisture, and stomach-to-anus transit time of microspheres were evaluated after administration of domperidone paste (1.1 mg/kg) or placebo paste in 6 horses. The effect of domperidone on smooth muscle contractile activity in samples of duodenum, jejunum, ileum, or colon obtained from 26 horses immediately after euthanasia (for nonsystemic medical problems) was investigated.

RESULTS

Oral administration of 5.0 mg of domperidone/kg increased peak plasma acetaminophen concentration and area under the curve, indicating increased gastric emptying. Administration of 1.1 mg of domperidone/kg had no effect on gastric emptying, transit time, defecation frequency, or amount and moisture of excreted feces. Contractile activities of circular and longitudinal muscle strips from the duodenum, jejunum, ileum, or colon were not altered by domperidone. Dopamine increased contractile activity of longitudinal muscle strips but not that of circular muscle strips from the midjejunum. Domperidone decreased the dopamine-induced contractile activity of midjejunal longitudinal muscle strips.

CONCLUSIONS AND CLINICAL RELEVANCE

The potential beneficial effects of domperidone in horses with ileus need to be evaluated in horses with decreased gastric emptying or adynamic ileus.