The gut microbiota as a key regulator of visceral pain

Photobiomodulation of the microbiome: implications for metabolic and inflammatory diseases

The human microbiome is intimately associated with human health, with a role in obesity, metabolic diseases such as type 2 diabetes, and divergent diseases such as cardiovascular and neurodegenerative diseases. The microbiome can be changed by diet, probiotics, and faecal transplants, which has flow-on effects to health outcomes. Photobiomodulation has a therapeutic effect on inflammation and neurological disorders (amongst others) and has been reported to influence metabolic disorders and obesity. The aim of this study was to examine the possibility that PBM could influence the microbiome of mice. Mice had their abdomen irradiated with red (660 nm) or infrared (808 nm) low-level laser, either as single or multiple doses, over a 2-week period. Genomic DNA extracted from faecal pellets was pyrosequenced for the 16S rRNA gene. There was a significant (p < 0.05) difference in microbial diversity between PBM- and sham-treated mice. One genus of bacterium (Allobaculum) significantly increased (p < 0.001) after infrared (but not red light) PBM by day 14. Despite being a preliminary trial with small experimental numbers, we have demonstrated for the first time that PBM can alter microbiome diversity in healthy mice and increase numbers of Allobaculum, a bacterium associated with a healthy microbiome. This change is most probably a result of PBMt affecting the host, which in turn influenced the microbiome. If this is confirmed in humans, the possibility exists for PBMt to be used as an adjunct therapy in treatment of obesity and other lifestyle-related disorders, as well as cardiovascular and neurodegenerative diseases. The clinical implications of altering the microbiome using PBM warrants further investigation.

Reversal of visceral hypersensitivity in rat by Menthacarin® , a proprietary combination of essential oils from peppermint and caraway, coincides with mycobiome modulation

BACKGROUND

Irritable bowel syndrome (IBS) is a common gastrointestinal disorder associated with altered gastrointestinal microflora and increased nociception to colonic distension. This visceral hypersensitivity can be reversed in our rat maternal separation model by fungicides. Menthacarin^® is a proprietary combination of essential oils from Mentha x piperita L. and Carum carvi. Because these oils exhibit antifungal and antibacterial properties, we investigated whether Menthacarin^® can reverse existing visceral hypersensitivity in maternally separated rats.

METHODS

In non-handled and maternally separated rats, we used the visceromotor responses to colorectal distension as measure for visceral sensitivity. We evaluated this response before and 24 hours after water-avoidance stress and after 7 days treatment with Menthacarin^® or control. The pre- and post-treatment mycobiome and microbiome were characterized by sequencing of fungal internal transcribed spacer 1 (ITS-1) and bacterial 16s rDNA regions. In vitro antifungal and antimicrobial properties of Menthacarin^® were studied with radial diffusion assay.

KEY RESULTS

Menthacarin^® inhibited in vitro growth of yeast and bacteria. Water-avoidance caused visceral hypersensitivity in maternally separated rats, and this was reversed by treatment. Multivariate analyses of ITS-1 and 16S high throughput data showed that maternal separation, induced changes in the myco- and microbiome. Menthacarin^® treatment of non-handled and maternally separated rats shifted the mycobiomes to more similar compositions.

CONCLUSIONS & INFERENCES

The development of visceral hypersensitivity in maternally separated rats and the Menthacarin^® -mediated reversal of hypersensitivity is associated with changes in the mycobiome. Therefore, Menthacarin^® may be a safe and effective treatment option that should be tested for IBS.

Theories of pain, up to Descartes and after neuromatrix: what role do they have to develop future paradigms?

The article represents a synthesis of literature about antique, medieval and modern pain theories. In short there are described the most relevant theories about nociception and pain. Chronologically there are presented the discoveries in physiology, anatomy, histology and other methods and investigations of pain. There is discussed the character of past pain theories and its influence on elaboration of the new ones. There was elaborated the hypothesis about the neuromatrix theory and impact of human microbiota on pain perception or other comorbidities with psychological and pain component.

Wheezing and infantile colic are associated with neonatal antibiotic treatment

BACKGROUND

Cohort studies have suggested that early-life antibiotic treatment is associated with increased risk of atopy. We determined whether antibiotic treatment already in the first week of life increases the risk of atopic and non-atopic disorders.

METHODS

The INCA study is a prospective observational birth cohort study of 436 term infants, with follow-up of 1 year; 151 neonates received broad-spectrum antibiotics for suspected neonatal infection (AB+), vs a healthy untreated control group (N = 285; AB-). In the first year, parents recorded daily (non-) allergic symptoms. At 1 year, doctors' diagnoses were registered and a blood sample was taken (n = 205).

RESULTS

Incidence of wheezing in the first year was higher in AB+ than AB- (41.0% vs 30.5%, P = .026; aOR 1.56 [95%CI 0.99-2.46, P = .06]). Infantile colics were more prevalent in AB+ compared to AB- (21.9% and 14.4% P = .048), and antibiotic treatment was an independent risk factor for infantile colics (aOR 1.66 (95%CI 1.00-2.77) P = .05). Allergic sensitization (Phadiatop >0.70kUA/L) showed a trend toward a higher risk in AB+ (aOR 3.26 (95%CI 0.95-11.13) P = .06). Incidence of eczema, infections, and GP visits in the first year were similar in AB+ and AB-.

CONCLUSION

Antibiotic treatment in the first week of life is associated with an increased risk of wheezing and infantile colics. This study may provide a rationale for early cessation of antibiotics in neonates without proven or probable infection.

Fecal Microbiota Transplantation Is Effective in Relieving Visceral Hypersensitivity in a Postinfectious Model

AIM

To investigate the effect of fecal microbiota transplantation on visceral hypersensitivity compared with Bifidobacterium longum.

METHODS

Mice visceral hypersensitivity was induced by Trichinella spiralis. After 8 weeks, they were divided into three groups (controls, Bifidobacterium longum, and fecal microbiota transplantation) and were daily treated by gavage with 0.2 ml PBS, Bifidobacterium longum HB55020, or fecal microbiota for 7 days. Visceral hypersensitivity was tested with abdominal withdrawal reflex. Permeability of colon epithelium was assessed with Ussing chamber.

RESULTS

After administration of Bifidobacterium longum, compared with mice in postinfectious group, mice had higher pain threshold (p < 0.05). After administration of fecal microbiota, compared with mice in postinfectious group, mice had higher pain threshold (p < 0.05). Fecal microbiota transplantation was as effective as Bifidobacterium in relieving visceral hypersensitivity. Administration of Bifidobacterium longum or fecal microbiota transplantation improved colon epithelium permeability. Expression of occluding-1 was increased.

CONCLUSION

Manipulation of microbiota is effective in relieving visceral hypersensitivity. Fecal microbiota transplantation is as effective as Bifidobacterium longum administration.

Tackling Pain Associated with Rheumatoid Arthritis: Proton-Sensing Receptors

Rheumatoid arthritis (RA), characterized by chronic inflammation of synovial joints, is often associated with ongoing pain and increased pain sensitivity. Chronic pain that comes with RA turns independent, essentially becoming its own disease. It could partly explain that a significant number (50%) of RA patients fail to respond to current RA therapies that focus mainly on suppression of joint inflammation. The acute phase of pain seems to associate with joint inflammation in early RA. In established RA, the chronic phase of pain could be linked to inflammatory components of neuron-immune interactions and noninflammatory components. Accumulating evidence suggests that the initial inflammation and autoimmunity in RA (preclinical RA) begin outside of the joint and may originate at mucosal sites and alterations in the composition of microbiota located at mucosal sites could be essential for mucosal inflammation, triggering joint inflammation. Fibroblast-like synoviocytes in the inflamed joint respond to cytokines to release acidic components, lowering pH in synovial fluid. Extracellular proton binds to proton-sensing ion channels, and G-protein-coupled receptors in joint nociceptive fibers may contribute to sensory transduction and release of neurotransmitters, leading to pain and hyperalgesia. Activation of peripheral sensory neurons or nociceptors further modulates inflammation, resulting in neuroinflammation or neurogenic inflammation. Peripheral and central nerves work with non-neuronal cells (such as immune cells, glial cells) in concert to contribute to the chronic phase of RA-associated pain. This review will discuss actions of proton-sensing receptors on neurons or non-neuronal cells that modulate RA pathology and associated chronic pain, and it will be beneficial for the development of future therapeutic treatments.

Neurobehavioural effects of Lactobacillus rhamnosus GG alone and in combination with prebiotics polydextrose and galactooligosaccharide in male rats exposed to early-life stress

Early life is a period of significant brain development when the brain is at its most plastic and vulnerable. Stressful episodes during this window of development have long-lasting effects on the central nervous system. Rodent maternal separation (MS) is a reliable model of early-life stress and induces alterations in both physiology and behaviour. Intriguingly, the gut microbiota of MS offspring differ from that of non-separated offspring, suggesting a mechanistic role for the microbiota-gut-brain axis. Hence, we tested whether dietary factors known to affect the gut microbiota alter the neurobehavioural effects of MS. The impact of consuming diet containing prebiotics polydextrose (PDX) and galactooligosaccharide (GOS) alone or in combination with live bacteria Lactobacillus rhamnosus GG (LGG) from weaning onwards in rats subjected to early-life MS was assessed. Adult offspring were assessed for anxiety-like behaviour in the open field test, spatial memory using the Morris water maze, and reactivity to restraint stress. Brains were examined via PCR for changes in mRNA gene expression. Here, we demonstrate that diets containing a combination of PDX/GOS and LGG attenuates the effects of early-life MS on anxiety-like behaviour and hippocampal-dependent learning with changes to hippocampal mRNA expression of genes related to stress circuitry, anxiety and learning.

Adherent-Invasive E. coli enhances colonic hypersensitivity and P2X receptors expression during post-infectious period

Irritable Bowel Syndrome (IBS) and Inflammatory Bowel Disease (IBD) are related gastrointestinal disorders characterized by abdominal pain associated with colonic hypersensitivity (CHS). Studies in humans have reported an abnormal colonization of Adherent-Invasive E. coli (AIEC) in the ileum of Crohn's disease (CD) patients associated with overexpression of the bacterial colonizing receptor CEACAM6. The aim of the present study was to investigate whether AIEC reference strain LF82 could induce intestinal impairment during infectious and/or post-infectious periods and subsequently the development of CHS. Transgenic mice overexpressing human CEACAM6 protein (TG) and their wild-type littermates were gavaged by CD-associated AIEC bacteria (reference strain LF82) or PBS for 3 d. Colonic hypersensitivity was assessed by colorectal distension (CRD) test during infectious (D4) and post-infectious periods (D21). Several markers of intestinal inflammation were monitored and the colonic expression of purinergic P2X receptors was quantified. At D4, an increased visceromotor response (VMR) to the CRD test was observed in TG mice infected with CD-associated AIEC LF82 in comparison with non-infected TG mice and persisted in a subgroup of infected animals at D21 after bacteria clearance. Increased VMR was associated with low-grade intestinal inflammation, increased intestinal permeability and expression of P2X 3, 4 and 7. This study shows that certain susceptible hosts infected with CD-associated AIEC bacteria can develop persistent CHS associated with low-grade inflammation and increased P2X receptors expression. Thus, CD-associated AIEC infection in CEACAM6 transgenic mice could be used as a novel post-infectious mouse model mimicking quiescent IBD with IBS-like symptoms such as visceral pain.

Maternal late pregnancy anxiety and stress is associated with children's health: a longitudinal study

AIM

Maternal prenatal anxiety and stress (PNS) have been positively associated to physical health prob lems in offspring in the first year of life. Whether these associations are transient, persistent, or even progressive over time, is as yet unknown. The goal of this study is to investigate associations between late pregnancy PNS and child health from 18 months to age 6.

METHODS

Mothers were recruited in late pregnancy, and had uncomplicated, singleton pregnancies without physical health problems. Around week 37 of pregnancy, mothers reported on their PNS by means of questionnaires, and provided saliva for determination of circadian cortisol concentrations. Children's illnesses in the preceding year were assessed using maternal reports at 30, 48, 60, and 72 months. Antibiotic use was obtained from medical records between one and six years. Multilevel models (N¼174) showed a positive relation between maternal prenatal general and pregnancy-specific anxiety during late pregnancy and offspring respiratory illnesses and symptoms. Interaction effects with time indicated that more PNS was related to more respiratory illnesses until toddlerhood, but not later in life. Furthermore, maternal prenatal cortisol concentrations were related to child digestive illnesses. A steeper maternal cortisol decline over the day was related to more child digestive illnesses, until around three years of age. Finally, children of mothers who suffered more from daily hassles during pregnancy received more antibiotics between one and six years of age. PNS was not related to general and skin illnesses.

CONCLUSION

Summarizing, this study showed that late pregnancy anxiety and cortisol was associated with children's respiratory and digestive illnesses till the age of 3.0-3.5 years. Additionally, more daily hassles were related to more prescribed antibiotics between one and six years. These findings point in the direction of possible effects of PNS persisting beyond the first year of life and into toddlerhood, but disappearing at older ages.

Microbiota regulates visceral pain in the mouse

The perception of visceral pain is a complex process involving the spinal cord and higher order brain structures. Increasing evidence implicates the gut microbiota as a key regulator of brain and behavior, yet it remains to be determined if gut bacteria play a role in visceral sensitivity. We used germ-free mice (GF) to assess visceral sensitivity, spinal cord gene expression and pain-related brain structures. GF mice displayed visceral hypersensitivity accompanied by increases in Toll-like receptor and cytokine gene expression in the spinal cord, which were normalized by postnatal colonization with microbiota from conventionally colonized (CC). In GF mice, the volumes of the anterior cingulate cortex (ACC) and periaqueductal grey, areas involved in pain processing, were decreased and enlarged, respectively, and dendritic changes in the ACC were evident. These findings indicate that the gut microbiota is required for the normal visceral pain sensation.

DOI:http://dx.doi.org/10.7554/eLife.25887.001

The human gut is home to over 100 trillion microbes collectively known as the gut microbiota. These microbes help us to digest food and absorb the nutrients effectively. A diverse and stable community of gut microbes is believed to be important for good health. Recently, it has also become clear that the microbiota can also influence the brain and how we behave. For example, many studies suggest that gut microbiota can alter how an individual perceives pain, but it is not clear how this works.

Rodents are often used in experiments as models of human biology. One of the most frequently used rodent models in studies of gut microbes is the “germ-free” mouse. These mice grow up in laboratory environments that are completely free of microbes, making it possible to study how having no gut microbes affects the health and behaviour of the mice. Luczynski, Tramullas et al. used germ-free mice to study how the gut microbiota influences an animal’s sensitivity to pain.

The experiments show that, compared to mice with normal gut microbiota, the germ-free mice were more sensitive to pain from internal organs especially the gut. These mice also produced larger amounts of specific proteins involved in immune responses, which contributed to the animal’s increased sensitivity to pain. Allowing the germ-free mice to be colonised with gut microbes could reverse these changes.

The experiments also show that the germ-free mice had changes in the size of two areas of the brain involved in sensing pain: an area called the anterior cingulate cortex was smaller, while the periaqueductal grey region was enlarged. There were also differences in individual nerve cells within the anterior cingulate cortex compared to normal mice.

The findings of Luczynski, Tramullas et al. reinforce the idea that the gut microbiota is involved in the sensation of pain from internal organs, and show that hypersensitivity to this form of pain can be reversed later in life by colonising the gut with microbes. Continuing to study the impact of microbes on this type of pain could aid the development of new therapies for the treatment of pain disorders in humans.

DOI:http://dx.doi.org/10.7554/eLife.25887.002