Luminal contents from the gut of colicky infants induce visceral hypersensitivity in mice

Microbiome contributions to pain: a review of the preclinical literature

ABSTRACT

Over the past 2 decades, the microbiome has received increasing attention for the role that it plays in health and disease. Historically, the gut microbiome was of particular interest to pain scientists studying nociplastic visceral pain conditions given the anatomical juxtaposition of these microorganisms and the neuroimmune networks that drive pain in such diseases. More recently, microbiomes both inside and across the surface of the body have been recognized for driving sensory symptoms in a broader set of diseases. Microbiomes have never been a more popular topic in pain research, but to date, there has not been a systematic review of the preclinical microbiome pain literature. In this article, we identified all animal studies in which both the microbiome was manipulated and pain behaviors were measured. Our analysis included 303 unique experiments across 97 articles. Microbiome manipulation methods and behavioral outcomes were recorded for each experiment so that field-wide trends could be quantified and reported. This review specifically details the animal species, injury models, behavior measures, and microbiome manipulations used in preclinical pain research. From this analysis, we were also able to conclude how manipulations of the microbiome alter pain thresholds in naïve animals and persistent pain intensity and duration in cutaneous and visceral pain models. This review summarizes by identifying existing gaps in the literature and providing recommendations for how to best plan, implement, and interpret data collected in preclinical microbiome pain experiments.

A proof of concept infant-microbiota associated rat model for studying the role of gut microbiota and alleviation potential of Cutibacterium avidum in infant colic

Establishing the relationship between gut microbiota and host health has become a main target of research in the last decade. Human gut microbiota-associated animal models represent one alternative to human research, allowing for intervention studies to investigate causality. Recent cohort and in vitro studies proposed an altered gut microbiota and lactate metabolism with excessive H₂ production as the main causes of infant colic. To evaluate H₂ production by infant gut microbiota and to test modulation of gut colonizer lactose- and lactate-utilizer non-H₂-producer, Cutibacterium avidum P279, we established and validated a gnotobiotic model using young germ-free rats inoculated with fecal slurries from infants younger than 3 months. Here, we show that infant microbiota-associated (IMA) rats inoculated with fresh feces from healthy (n = 2) and colic infants (n = 2) and fed infant formula acquired and maintained similar quantitative and qualitative fecal microbiota composition compared to the individual donor’s profile. We observed that IMA rats excreted high levels of H₂, which were linked to a high abundance of lactate-utilizer H₂-producer Veillonella. Supplementation of C. avidum P279 to colic IMA rats reduced H₂ levels compared to animals receiving a placebo. Taken together, we report high H₂ production by infant gut microbiota, which might be a contributing factor for infant colic, and suggest the potential of C. avidum P279 in reducing the abdominal H₂ production, bloating, and pain associated with excessive crying in colic infants.

Human milk oligosaccharides alleviate stress-induced visceral hypersensitivity and associated microbiota dysbiosis

Pain-related functional gastrointestinal disorders (FGIDs) are characterized by visceral hypersensitivity (VHS) associated with alterations in the microbiota-gut-brain axis. Since human milk oligosaccharides (HMOs) modulate microbiota, gut and brain, we investigated whether HMOs impact VHS, and explored the role of gut microbiota. To induce VHS, C57BL/6JRj mice received hourly water avoidance stress (WAS) sessions for 10 d, or antibiotics (ATB) for 12 d. Challenged and unchallenged (Sham) animals were fed AIN93M diet (Cont) or AIN93M containing 1% of a 6-HMO mix (HMO6). VHS was assessed by monitoring the visceromotor response to colorectal distension. Fecal microbiome was analyzed by shotgun metagenomics. The effect of HMO6 sub-blends on VHS and nociceptive pathways was further tested using the WAS model. In mice fed Cont, WAS and ATB increased the visceromotor response to distension. HMO6 decreased WAS-mediated electromyographic rise at most distension volumes and overall Area Under Curve (AUC=6.12±0.50 in WAS/HMO6 vs. 9.46±0.50 in WAS/Cont; P<.0001). In contrast, VHS in ATB animals was not improved by HMO6. In WAS, HMO6 promoted most microbiota taxa and several functional pathways associated with low VHS and decreased those associated with high VHS. Among the sub-blends, 2'FL+DFL and LNT+6'SL reduced visceromotor response close to Sham/Cont values and modulated serotoninergic and CGRPα-related pathways. This research further substantiates the capacity of HMOs to modulate the microbiota-gut-brain communication and identifies mitigation of abdominal pain as a new HMO benefit. Ultimately, our findings suggest the value of specific HMO blends to alleviate pain associated FGIDs such as infantile colic or Irritable Bowel Syndrome.

Shedding light on excessive crying in babies

BACKGROUND

Excessive and inconsolable crying behavior in otherwise healthy infants (a condition called infant colic (IC)) is very distressing to parents, may lead to maternal depression, and in extreme cases, may result in shaken baby syndrome. Despite the high prevalence of this condition (20% of healthy infants), the underlying neural mechanisms of IC are still unknown.

METHODS

By employing the latest magnetic resonance imaging (MRI) techniques in newborns, we prospectively investigated whether newborns' early brain responses to a sensory stimulus (smell) is associated with a subsequent crying behavior.

RESULTS

In our sample population of 21 healthy breastfed newborns, those who developed IC at 6 weeks exhibited brain activation and functional connectivity in primary and secondary olfactory brain areas that were distinct from those in babies that did not develop IC. Different activation in brain regions known to be involved in sensory integration was also observed in colicky babies. These responses measured shortly after birth were highly correlated with the mean crying time at 6 weeks of age.

CONCLUSIONS

Our results offer novel insights into IC pathophysiology by demonstrating that, shortly after birth, the central nervous system of babies developing IC has already greater reactivity to sensory stimuli than that of their noncolicky peers.

IMPACT

Shortly after birth, the central nervous system of colicky infants has a greater sensitivity to olfactory stimuli than that of their noncolicky peers. This early sensitivity explains as much as 48% of their subsequent crying behavior at 6 weeks of life. Brain activation patterns to olfactory stimuli in colicky infants include not only primary olfactory areas but also brain regions involved in pain processing, emotional valence attribution, and self-regulation. This study links earlier findings in fields as diverse as gastroenterology and behavioral psychology and has the potential of helping healthcare professionals to define strategies to advise families.

Supernatants of intestinal luminal contents from mice fed high-fat diet impair intestinal motility by injuring enteric neurons and smooth muscle cells

BACKGROUND

Damage to enteric neurons and impaired gastrointestinal muscle contractions cause motility disorders in 70% of diabetic patients. It is thought that enteric neuropathy and dysmotility occur before overt diabetes, but triggers of these abnormalities are not fully known. We tested the hypothesis that intestinal contents of mice with and without high-fat diet- (HFD-) induced diabetic conditions contain molecules that impair gastrointestinal movements by damaging neurons and disrupting muscle contractions.

METHODS

Small and large intestinal segments were collected from healthy, standard chow diet (SCD) fed mice. Filtrates of ileocecal contents (ileocecal supernatants; ICS) from HFD or SCD mice were perfused through them. Cultured intact intestinal muscularis externa preparations were used to determine whether ICS and their fractions obtained by solid-phase extraction (SPE) and SPE subfractions collected by high-performance liquid chromatography (HPLC) disrupt muscle contractions by injuring neurons and smooth muscle cells.

KEY RESULTS

ICS from HFD mice reduced intestinal motility, but those from SCD mice had no effect. ICS, aqueous SPE fractions and two out of twenty HPLC subfractions of aqueous SPE fractions from HFD mice blocked muscle contractions, caused a loss of nitrergic myenteric neurons through inflammation, and reduced smooth muscle excitability. Lipopolysaccharide and palmitate caused a loss of nitrergic myenteric neurons but did not affect muscle contractions.

CONCLUSIONS & INFERENCES

Unknown molecules in intestinal contents of HFD mice trigger enteric neuropathy and dysmotility. Further studies are required to identify the toxic molecules and their mechanisms of action.

Infantile Colic Treated With Bifidobacterium longum CECT7894 and Pediococcus pentosaceus CECT8330: A Randomized, Double-Blind, Placebo-Controlled Trial

Background: Colic is a common condition in infants <4 months of age. Attempts to treat infantile colic with probiotics have shown variable efficacy and overall low evidence of success. In this work, we tested the hypothesis that oral administration of Bifidobacterium longum CECT7894 (KABP042) and Pediococcus pentosaceus CECT8330 (KABP041) mix (1 × 10⁹ colony forming units) would improve the symptoms of infantile colic. Methods: A total of 112 exclusively breastfed or mixed fed infants aged <2 months and meeting the ROME IV criteria for infantile colic were recruited. The infants were randomized in a double-blind, placebo-controlled trial to receive orally administered probiotics (intervention group, IG, n = 48) or placebo (placebo group, PG, n = 42) daily for 21 days. Results: Infants in the IG had significantly shorter crying time (p < 0.001) on day 7 [IG vs. PG, median (25-75th percentile): 38 (3.5-40.5) vs. 62 (40-108) min/day], day 14 [IG vs. PG: 20 (0-40) vs. 50 (30-75) min/day], and day 21 [IG vs. PG: 14 (0-33) vs. 40 (28-62) min/day]. Higher responder ratio and fewer crying/fussing episodes on days 7, 14, and 21 and better stool consistency on day 21 were observed in the IG (p < 0.01) as compared to the PG. Conversely, no significant effects on stool frequency or quality of life were observed. Conclusions: In summary, daily oral administration of B. longum CECT7894 (KABP042) and P. pentosaceus CECT8330 (KABP041) was an effective treatment for shortening crying time due to infantile colic and for improving fecal consistency. This trial was registered retrospectively in December 2019 with a trial number of ISRCTN92431452.

Vitamin D supplementation in pregnancy and early infancy in relation to gut microbiota composition and C. difficile colonization: implications for viral respiratory infections

In Canada and the US, the infant diet is supplemented with vitamin D via supplement drops or formula. Pregnant and nursing mothers often take vitamin D supplements. Since little is known about the impact of this supplementation on infant gut microbiota, we undertook a study to determine the association between maternal and infant vitamin D supplementation, infant gut microbiota composition and Clostridioides difficile colonization in 1,157 mother-infant pairs of the CHILD (Canadian Healthy Infant Longitudinal Development) Cohort Study over 2009-2012. Logistic and MaAsLin regression were employed to assess associations between vitamin D supplementation, and C. difficile colonization, or other gut microbiota, respectively. Sixty-five percent of infants received a vitamin D supplement. Among all infants, infant vitamin D supplementation was associated with a lower abundance of genus Megamonas (q = 0.01) in gut microbiota. Among those exclusively breastfed, maternal prenatal supplementation was associated with lower abundance of Bilophila (q = 0.01) and of Lachnospiraceae (q = 0.02) but higher abundance of Haemophilus (q = 0.02). There were no differences in microbiota composition with vitamin D supplementation among partially and not breastfed infants. Neither infant nor maternal vitamin D supplementation were associated with C. difficile colonization, after adjusting for breastfeeding status and other factors. However, maternal consumption of vitamin-D fortified milk reduced the likelihood of C. difficile colonization in infants (adjustedOR: 0.40, 95% CI: 0.19-0.82). The impact of this compositional difference on later childhood health, especially defense against viral respiratory infection, may go beyond the expected effects of vitamin D supplements and remains to be ascertained.

The Effect of Probiotics on Symptoms, Gut Microbiota and Inflammatory Markers in Infantile Colic: A Systematic Review, Meta-Analysis and Meta-Regression of Randomized Controlled Trials

Immaturity in digestive-tract motor function and altered intestinal microbiome may play roles in pathogenesis of infantile colic. We assessed the impact of probiotic therapy on crying duration day, in newborns experiencing colic attacks. The PubMed, Embase, Cinnahl, Web of Science databases, and a clinical trials registry (ClinicalTrials.gov) were searched from inception until 12/02/2020. Random-effects meta-analyses were used to derive standardized mean differences/differences in means and risk ratios. We included 16 studies, which involved 1319 newborns aged up to 6 months. Lactobacillus reuteri strain DSM17938 was administered predominantly (n = 10). Probiotic intervention reduced the duration of crying (standardized mean difference = -2.012, 95% confidence interval: -2.763 to -1.261, z = -5.25, p < 0.0001). The probability of at least a 50% reduction in crying duration was at least 1.98 times higher in the intervention group than in controls (Z = 4.80, p < 0.0001). The effects of the intervention were not significantly affected by the risk of bias assessment, percentage of breastfed infants, and duration of the study. In 11 studies, data concerning gut microbiota composition and function and/or immunological markers were given. Probiotics significantly shortened the crying duration, but a causal relationship between the modulatory effect of probiotics on microbiota and the immune system has not been confirmed.

Microbiota: a novel regulator of pain

Among the various regulators of the nervous system, the gut microbiota has been recently described to have the potential to modulate neuronal cells activation. While bacteria-derived products can induce aversive responses and influence pain perception, recent work suggests that "abnormal" microbiota is associated with neurological diseases such as Alzheimer's, Parkinson's disease or autism spectrum disorder (ASD). Here we review how the gut microbiota modulates afferent sensory neurons function and pain, highlighting the role of the microbiota/gut/brain axis in the control of behaviors and neurological diseases. We outline the changes in gut microbiota, known as dysbiosis, and their influence on painful gastrointestinal disorders. Furthermore, both direct host/microbiota interaction that implicates activation of "pain-sensing" neurons by metabolites, or indirect communication via immune activation is discussed. Finally, treatment options targeting the gut microbiota, including pre- or probiotics, will be proposed. Further studies on microbiota/nervous system interaction should lead to the identification of novel microbial ligands and host receptor-targeted drugs, which could ultimately improve chronic pain management and well-being.

Infant Colic Represents Gut Inflammation and Dysbiosis

OBJECTIVE

To dissect potential confounding effects of breast milk and formula feeding on crying + fussing, fecal calprotectin, and gut microbiota in babies with colic. We hypothesized that infant colic is associated with gut inflammation linked to intestinal dysbiosis.

STUDY DESIGN

A nested case-control design of 3 of our studies was used to analyze clinical and laboratory data at presentation, comparing babies with colic with controls. All investigators other than the biostatistician were blinded during data analysis. Subjects were recruited based on their age and crying + fussy time. We screened 65 infants, 37 with colic, as defined by Barr diary (crying + fussing time >3 hours daily), who were compared with 28 noncolicky infants.

RESULTS

Fecal calprotectin was elevated in babies with colic. For each mode of infant feeding (breast milk, formula, or breast + formula), infants' fecal calprotectin was higher in babies with colic. Infants with colic had similar levels of fecal alpha diversity (richness) when compared with controls, and alpha diversity was lower in breast-fed babies. Beta diversity at the phylum level revealed significant differences in microbial population. A phylum difference resulted from reduced Actinobacteria (95% of which are Bifidobacilli) in babies with colic. Species significantly associated with colic were Acinetobacter and Lactobacillus iners.

CONCLUSIONS

Colic is linked with gut inflammation (as determined by fecal calprotectin) and dysbiosis, independent of mode of feeding, with fewer Bifidobacilli.

TRIAL REGISTRATION

Clinicaltrials.gov: NCT01279265 and NCT01849991.

Why do babies cry?

Persistent, inconsolable crying in young infants is common, distressing but usually benign. This selective review examines perceptions and perceived origins of this phenomenon in babies where serious pathology has been excluded. Adult brains have evolved to become hypersensitive to infant cries. Babies respond to parental stress by crying more, thus setting up a vicious cycle. Most treatments appear to work largely through a placebo effect. The imperative for healthcare professionals is to reduce parental anxiety by offering reassurance and support.

Recent advances in understanding and managing infantile colic

A newborn brings joy to the family. Crying belongs to the spectrum of normal behaviour of young infants. However, although it occurs in about 20% of all infants, unsoothable and persistent crying in young infants distresses the family, although it is usually benign. The aetiology of infantile colic remains unknown, although an unbalanced gastro-intestinal microbiome, increased intestinal permeability, and chronic inflammation are involved, as well as behavioural factors, including over- and under-stimulation. It is a challenge for healthcare professionals to decide when organic disease needs to be excluded. Parental stress is a reason for babies to cry more, inducing a vicious cycle. Therefore, parental reassurance with explanatory guidance is the cornerstone of management. The placebo effect is estimated to be as high as 50%. If an intervention is felt to be necessary to offer further support to the baby and family, it is important to choose the options for which there is some efficacy without adverse effects. There is evidence that some specific probiotic strains such as Lactobacillus reuteri DSM 19378, especially in breastfed infants, are effective. However, there are also promising data for some synbiotics and/or killed or tyndallized bacteria, as well as substances decreasing intestinal permeability. Formula management with extensive and/or partial hydrolysates may also bring relief. But, above all, offering parental support remains imperative.

Infant colic: mechanisms and management

Infant colic is a commonly reported phenomenon of excessive crying in infancy with an enigmatic and distressing character. Despite its frequent occurrence, little agreement has been reached on the definition, pathogenesis or the optimal management strategy for infant colic. This Review aims to delineate the definitional entanglement with the Rome IV criteria, which were published in 2016, as the leading, most recent diagnostic criteria. Moreover, neurogenic, gastrointestinal, microbial and psychosocial factors that might contribute to the pathophysiology of infant colic are explored. This Review underlines that a comprehensive medical history and physical examination in the absence of alarm symptoms serve as guidance for the clinician to a positive diagnosis. It also highlights that an important aspect of the management of infant colic is parental education and reassurance. Management strategies, including behavioural, dietary, pharmacological and alternative interventions, are also discussed. Owing to a lack of large, high-quality randomized controlled trials, none of these therapies are strongly recommended. Finally, the behavioural and somatic sequelae of infant colic into childhood are summarized.