1. Introduction
Celiac disease (CD) is an immune-mediated enteropathy that arises in genetically susceptible people after ingestion of dietary gluten per the Oslo definitions [
1]. CD is a common disease recognized in multiple ethnicities and encountered across the globe, with a global estimated prevalence around 1% [
2,
3,
4]. Conversely, non-gluten celiac sensitivity (NGCS) is a term encompassing the symptomatic and immunological manifestations precipitated by gluten- containing food ingestion in those where CD has been previously excluded [
1]. In contrast to CD, people with NCGS lack elevations in celiac-specific antibodies and enteropathy [
2,
5,
6]. Although an exact mechanism is yet to be elucidated, it is hypothesized that the innate but not adaptive immune response may play a part in NCGS [
7,
8]. Both CD and NGCS patients commonly experience gastrointestinal symptoms, ranging from abdominal discomfort to irregular bowel habits, necessitating a meticulous examination of the factors influencing, such as motility abnormalities. Dysmotility in the gastrointestinal (GI) tract has been described in patients with CD and may be linked to the generation of symptoms [
9,
10,
11,
12]. Some of the mechanisms associated with dysmotility in gluten-related disorders include impaired food absorption, low-grade inflammation in the small intestine, dysfunction of the autonomic nervous system, hormonal imbalances, and dysbiosis [
13]. In fact, it has been described that a gluten-free diet (GFD) can reverse motor disturbances in patients with CD, but its effect on NGCS is unknown [
11,
13,
14]. It is important to highlight that the few studies that have assessed motor alterations in the small intestine and colon in patients with CD have used tests such as small intestine manometry and oro-cecal transit [
9,
10,
11,
12,
13,
14].
Until the introduction of the wireless motility capsule (WMC) [SmartPill®, Given Imaging, Yoqneam, Israel], assessing the entire gut transit profile in a single test without radiation had proven challenging. The WMC represents a novel technique capable of measuring the whole gut transit time (WGTT) and regional transit times, including gastric emptying time (GET), small bowel transit time (SBTT), and colonic transit time (CTT) [
16]. The capsule, measuring 26.8 mm in length and 11.7 mm in diameter, is equipped with three sensors for temperature (ranging between 25 and 49°C), pH (ranging between 0.05 and 9.0), and pressure (ranging between 0- and 350-mm Hg) [
17]. As it traverses the gastrointestinal tract, the capsule continuously records various measurements, transmitting data wirelessly and in real-time to a receiver worn by the patient on their waist throughout the study. While numerous studies have explored the utility of WMC in identifying multiregional dysmotility in various conditions (such as diabetes [
18], chronic constipation [
19] and gastroparesis [
20]), no current data is available regarding the GI tract transit profile among patients with celiac CD and other gluten-related disorders, such as NGCS.
While the implementation of a GFD has become a cornerstone in managing CD and NGCS, providing a therapeutic avenue to alleviate symptoms and prevent long-term complications, the specific influence of gluten withdrawal on WGTT warrants a more in-depth investigation. This study seeks to bridge this knowledge gap by employing the WMC, a non-invasive and patient-friendly technology, to monitor real-time transit dynamics in response to dietary modifications.
4. Discussion
In recent times, there has been heightened scrutiny of the management approaches for CD and NGCS particularly with a focus on dietary interventions. A pivotal area of investigation revolves around understanding the impact of a GFD on the gastrointestinal dynamics of individuals grappling with CD and NGCS. In this research we explored the intricate connection between gluten consumption and WGTT by utilizing the state-of-the-art WMC technology.
The WMC provides an office-based, radiation free, standardized testing modality capable of simultaneously measuring gastric emptying time, small bowel transit time, and colon transit time. WMC has demonstrated comparable results with traditional radiolabeled and radiographic motility testing modalities [
17]
. WMC should be considered as an alternative for transit testing in suspected cases of gastroparesis, small bowel dysmotility, and colon transit testing, and considered the test of choice in suspected conditions of multiregional or generalized motility disorders [
17,
18,
19,
20]
.
Our findings are novel in several ways, as we employed precise definitions (Oslo criteria for celiac disease, Salerno criteria for non-gluten celiac sensitivity), innovative technology (WMC), and an ideal therapeutic intervention (gluten-free diet). Through this approach, we demonstrated that gluten induces colonic intestinal dysmotility, especially in patients with CD. Intestinal dysmotility occurs in a variety of disorders in which the gut has lost its ability to coordinate muscular activity because of endogenous or exogenous causes [
9,
13]. Such disorders may be primary or secondary and may manifest symptomatically in a variety of ways, including abdominal distention, recurrent obstruction, abdominal colicky pain, constipation, gastroesophageal reflux disease and recurrent vomiting. In a broad sense, any alteration in the transit of foods and secretions into the digestive tract may be considered an intestinal motility disorder.
Previous studies employing various methods such as mouth-to-cecum transit time, lactulose H
2 breath test, antroduodenal manometry, ultrasound, colonic transit time with radiopaque markers, and
13C-occtanoid breath test have reported motor disturbances in the intestine and colon of patients with celiac disease [
9,
13]. However, these abnormalities have been not appropriately in NGCS.
In our study we found that compared to NGCS, CD exhibited prolonged colonic and intestinal transit times. These results are like those reported by Chiarioni [
15] and Benini [
14], where it is described that patients with celiac disease have a prolonged oro-cecal transit time when compared to a control group. On the other hand, in another study conducted by Bai and colleagues [
26] using radiopaque markers, it was demonstrated that patients with CD have an accelerated colonic transit. The differences between studies may be explained using different methodologies and populations with more severe symptoms (e.g., patients with chronic diarrhea). In our patients with CD, the predominant symptoms were abdominal pain and distension, while only 4 out of 12 experienced diarrhea. Although, the classic presentation of CD is more common in young children, consisting primarily of gastrointestinal symptoms with malabsorption (chronic diarrhea, abdominal pain, distension, and failure to thrive or weight loss), some patients also present with constipation [
27]. In adults, the presentation of CD is often more subtle and can be mistaken for irritable bowel syndrome, as in our cases [
26,
27,
28].
Regarding the evidence of dysmotility in the small intestine, it has been reported that individuals with CD exhibit fasting motor abnormalities, including clustered contractions, giant jejunal contractions, and bursts of non-propagated contractions, observed in both adults and children with CD [
9,
10,
11]. In a further study Bassotti et al. [
12] validated that most of untreated celiac patients displayed distinct motor abnormalities in the upper gut during both fasting and fed periods. Although it is not precisely understood why gluten induces dysmotility, multiple mechanisms have been proposed, including: low-grad inflammation, diminished food absorption, dysfunction of the autonomic nervous system, hormonal imbalances, and dysbiosis [
9,
13].
What is clear, according to our results, is that a GFD has a positive effect on symptoms and reverses dysmotility in patients with CD, especially in the small intestine. Significantly, the frequency, amplitude, and pressure of the small intestine, measured by WMC, improved after the intestine was no longer exposed to gluten. Some previous studies have had examined the impact of a GFD on gastrointestinal motility. As in our study, there is evidence that dysmotility could be reversible with a GFD. For example, Cucciara et al [
11] found that gut dysmotilities (reduction postprandial antral motility index and abnormal fasting and fed motor responses) disappeared in children with CD after GFD. In another study, through the use of the orocecal transit test with lactulose, it was demonstrated that after a GFD period, mouth-to-cecum transit time in patients was significantly reduced compared to prediet transit (134 +/- 8 vs 243 +/- 10 min, P = 0.0001) and did not show statistical difference when compared to that found in controls (P = 0.1) [
15]. Benini et al. [
29] showed that following mucosal recovery, the gastric emptying of a gluten-free meal improves, albeit it remains delayed in comparison to controls. Therefore, it is possible that the improvement in the motor function of the small intestine observed after a gluten-free diet is the result of inflammation resolution.
Non-celiac gluten sensitivity (NGCS) is a clinical entity characterized by the absence of CD and wheat allergy in patients that trigger reproducible symptomatic responses to gluten-containing foods consumption [31]. The absence of a clear definition, coupled with controversies in clinical trials, indicates a limited understanding of the etiopathogenesis and besides gluten other components such as fructans or protein alpha-amylase-trypsin inhibitors. In this population, our study demonstrates for first time that a GFD also has a positive effect on intestinal motility. There is only one previous study that shows that patients with NCGS, diagnosed by gluten-related symptoms and presence of IgG AGA, present with motility alterations that improve in most cases after a GFD [
30]. Although an exact mechanism is yet to be elucidated, it is hypothesized that the innate but not adaptive immune response may play a part in NCGS [
5,
6,
7,
31]. Suggested factors encompass alterations in intestinal permeability, abnormal motility, and gut stimulation. In specific animal models, like mice expressing human leukocyte antigen (HLA)-DQ8 genes, gliadin has been proposed to induce hypercontractility of smooth muscle and dysfunction in cholinergic nerves, all without causing atrophy in the duodenal mucosa [
32,
33]. Studies involving mice indicate that wheat germ agglutinins provoke the release of IL-4 and IL-13, elevate inflammation, disrupt epithelial integrity, and enhance the synthesis of proinflammatory cytokines [
34]. Therefore, just as it is described that inflammation and epithelial alterations are associated with intestinal motor dysfunctions in subjects with CD and that these are reversible, something similar may occur in patients with NGCS. Nevertheless, further investigations are required in this regard.
Although our study is innovative and the findings are thought-provoking, we must acknowledge some limitations. Firstly, it is a study with a small sample size, as conducting intervention studies with a GFD before and after is complex. Nevertheless, it is noteworthy that our patients exhibited good adherence to the treatment throughout the 4 weeks of the study. Another limitation is the absence of a healthy control group, as seen in other similar studies. However, we consider the most relevant statistical comparisons to be the intervention before and after, where each subject served as their own control. Lastly, the study assesses the effect of the GFD for only 4 weeks, and longer-term studies are needed, considering that histological recovery in patients with celiac disease can take 6 to 12 months.