Gut bacteria and bitter taste receptor genes show surprising links to endometriosis pain.
Study: Connecting gut microbiome composition to symptom severity and host genetics in endometriosis. Image Credit: People Business/Finance / Shutterstock.com
In a recent study published in Frontiers in Microbiology, researchers investigated the associations between gut microbiome alterations, host genetic variation, and clinical symptom severity in women with endometriosis.
Why endometriosis pain doesn't always match disease severity
Endometriosis is defined as an estrogen-dependent, chronic inflammatory gynecological disorder that affects 10-15% of women of reproductive age worldwide. Endometriosis is clinically characterized by the ectopic proliferation of endometrial tissue outside the uterus. This proliferation frequently affects pelvic organs, including the ovaries, bladder, and bowel.
The condition has been previously associated with a broad spectrum of debilitating symptoms, particularly chronic pelvic pain, dyspareunia (pain during intercourse), dyschezia (painful bowel movements), and dysmenorrhea. Infertility may affect up to 50% of women with endometriosis.
Previous research has identified a disconnect between anatomical disease stage and pain burden. Patients with advanced stage IV disease may experience minimal symptoms, whereas those with earlier stage (I-II) lesions may report severe, refractory pain.
Emerging evidence suggests that gut microbiota dysbiosis may promote systemic inflammation and alter estrogen metabolism, potentially through bacterial enzymes such as beta-glucuronidase. The microbial changes associated with individual symptoms, and how they interact with host genetics, remain poorly understood.
How researchers investigated the gut microbiome and endometriosis
The present case-only study aimed to address this knowledge gap and inform future endometriosis interventions by evaluating 50 adult women of European genetic ancestry with surgically and histologically confirmed endometriosis at the IRCCS Burlo Garofolo Hospital in Trieste, Italy.
Participants' disease severity was classified using the revised American Society for Reproductive Medicine (rASRM) guidelines. Most participants (74%) had advanced (stage III-IV) disease, while the remaining 26% had earlier-stage (I-II) endometriosis.
Symptom severity across eight clinical pain domains was evaluated on a 0–10 Numerical Rating Scale (NRS), with intense pain represented by scores of 5.0 or higher. Moreover, 16S rRNA gene sequencing (V3 region) of distal rectal swabs was used to characterize participants' gut microbiome profiles. Bacterial composition was subsequently estimated using the DADA2 package.
Researchers analyzed genomic DNA from participants' peripheral blood samples, examining 12 selected single-nucleotide polymorphisms (SNPs) in four candidate bitter taste receptor genes (TAS2R3, TAS2R4, TAS2R5, and TAS2R14) associated with signaling in ovarian follicle cells.
The researchers used statistical methods to group participants by gut microbial profiles and examine relationships with symptoms and genetic variation. Analyses accounted for participants' age, body mass index (BMI), hormonal therapy, and sequencing depth. The authors applied Bonferroni corrections to account for multiple comparisons.
Menstrual pain linked to fewer beneficial gut bacteria
Anatomical disease stage was not significantly associated with pain intensity, consistent with previous research showing that symptom burden does not necessarily reflect disease stage.
Gut microbial community analysis classified patients into three distinct clusters: a Bacteroides-dominant community (C1), a Prevotella-dominant community (C2), and an Escherichia-Shigella-dominant cluster (C3). The Prevotella-dominant cluster had lower microbial diversity than the Bacteroides-dominant cluster, while the Escherichia-Shigella cluster showed a distinct bacterial profile. These differences may reflect variation in gut microbial communities among women with endometriosis.
Differences in gut microbial composition, measured through beta diversity (which compares bacterial communities between individuals), were associated with both dysmenorrhea and anatomical disease stage, even though disease stage was not significantly associated with pain severity.
Multivariable linear regression identified significant associations between dysmenorrhea and lower relative abundances of short-chain fatty acid (SCFA)-producing taxa within the order Lachnospirales. Women reporting dysmenorrhea had lower relative abundances of several butyrate-producing bacterial genera, including Faecalibacterium, Blautia, and Roseburia.
Higher relative abundance of Prevotella_9 was positively associated with dysuria (painful urination), while the genital dysbiosis-linked genus Mobiluncus was positively associated with infertility among participants. Only seven women in the study had an endometriosis-related infertility diagnosis, limiting the strength of this finding.
Higher premenstrual pain severity was associated with lower relative abundances of Burkholderiales and Sutterellaceae, whereas greater postmenstrual pain severity was associated with a lower relative abundance of Bifidobacteriaceae.
Could bitter taste receptor genes influence gut bacteria?
Host genetic analyses revealed that genetic polymorphisms across all four candidate genes (TAS2R3, TAS2R4, TAS2R5, and TAS2R14) were significantly associated with measures of microbial alpha diversity, which describes the diversity of bacteria within an individual sample.
Nine single-nucleotide polymorphisms within TAS2R14 were also associated with beta diversity, suggesting that extra-oral taste receptors may play a role in host-microbiome interactions. The study found no significant associations between the selected genetic variants and individual bacterial taxa.
The researchers acknowledged several limitations, including the small sample size and absence of a healthy control group. Menstrual cycle timing was not standardized, and dietary differences may have influenced microbial composition. The observational design also prevents conclusions about whether the microbial changes directly contribute to endometriosis symptoms.
Could targeting gut bacteria help manage endometriosis?
The present study identified associations between gut microbial composition, endometriosis symptoms, and genetic variation in bitter taste receptors. These relationships may help explain why symptom severity varies among women with the condition, independently of anatomical disease stage.
Further research could examine microbiota-targeted interventions, including personalized dietary approaches and prebiotic or probiotic supplementation. Larger studies are needed to confirm these associations and determine whether such interventions can reduce pain or improve reproductive outcomes.
Online approach helped patients manage anxiety after chest pain