Influence of Probiotics in Prevention and Treatment of Patients Who Undergo Chemotherapy or/and Radiotherapy and Suffer from Mucositis, Diarrhoea, Constipation, Nausea and Vomiting

The administration of probiotics to patients treated with chemo- and/or radiotherapy is assumed to be beneficial. The aim of this study was to evaluate the effects of probiotic intake on the severity of selected gastrointestinal side effects of chemotherapy and radiotherapy. The searched databases included PubMed, Web of Science, and Scopus from which twenty-one studies were included. Most of them concerned diarrhoea, however, two of the studies examined constipation, another two nausea and vomiting, and eight of the included studies regarded mucositis. The total number of patients equalled 2621. The time of the conducted therapy, the administered species, neoplasm pathology, and adjuvant therapy varied. The outcome was assessed by gathering information about the statistical significance of the improvements. An enhancement was observed in thirteen studies, where probiotics had a significant impact on each of the included chemo- and/or radiotherapy side effects. However, the heterogeneity of the assessed data makes it impossible to state a firm conclusion.


Introduction
Huge progress made in the treatment of cancer is not accompanied by the development of methods to prevent the unpleasant side effects of therapy [1,2]. According to the American Society of Clinical Oncology (ASCO) and the European Society for Medical Oncology (ESMO) guidelines [3][4][5], the most commonly chosen therapeutic options are radiotherapy and chemotherapy, as a monotherapy or as an adjuvant therapy with surgical intervention. The cells of the gastrointestinal epithelium are mainly affected by the cytotoxic effect of these therapeutic agents [6]. Therefore, the side effects related to chemotherapy or radiotherapy directly influence the digestive system. Usually, patients suffer from mucositis, diarrhoea, constipation, nausea, and vomiting [7]. Alleviation of them is crucial to the improvement of patients' comfort as they strongly influence therapy results [2,8]. It was suggested that probiotic administration may help to achieve this goal [9], particularly as they have shown a protective effect on epithelial cells [10]. The bacteria in the genus Lactobacillus are the most frequently studied and are considered to be possibly related to the reduction of undesirable effects [9][10][11][12]. Additionally, research on Bifidobacterium strains indicates promising outcomes for oncological patients [11,13]. However, there is limited available data on the effectiveness of probiotics, especially when it comes to constipation, mucositis, nausea, and vomiting.
The aim of this study was to evaluate the effects of probiotic intake on the severity of chemotherapy and radiotherapy selected gastrointestinal side effects.

Search Strategy, Inclusion, and Exclusion Criteria
From September 2020 to December 2021, the following databases were searched and reviewed in order to identify interventional studies that investigate the influence of probiotics on chemotherapy-and/or radiotherapy-induced mucositis, diarrhoea, constipation, nausea, and vomiting: PUBMED (MEDLINE), SCOPUS, and WEB OF SCIENCE. The review was registered on the PROSPERO database (ID: CRD42021248256).
The search was limited to studies concerning humans and published in English. Original articles were included. No restrictions regarding the date of the publication or kind of neoplasm were used. Administering probiotics orally was a required inclusion criterion. Taking into account the study design, the following articles were included: randomised, double-blind, placebo-controlled study (RDBPC) (10), randomised controlled study (RCT) (9), and non-randomised controlled study (NRS) (2). The articles with lowquality or incomplete data that could not be fully obtained from the authors were excluded.
The search strategy included the following index terms: #1 probiotics OR probiotic OR probiotic bacterium OR probiotic microflora OR probiotic flora; #2 mucositides OR mucositis OR inflammation of mucosa OR mucous membranes inflammation OR mucous membrane inflammation OR mucosal inflammation OR mucosal lesions OR diarrheas OR diarrhoea OR diarrhea OR obstruction OR constipation OR dyschezia OR colonic inertia OR nausea OR emesis OR vomiting OR CINV OR breakthrough CINV OR anticipatory CINV; #3 Neoplasms OR Neoplasms OR Neoplasia OR Neoplasias OR Neoplasm OR Tumors OR Tumor OR Malignant Neoplasms OR Malignant Neoplasm.

Data Extraction and Analysis
Three different teams separately reviewed the databases in order to identify articles that fulfilled the inclusion criteria. Each team consisted of two independent researchers. Firstly, titles and abstracts were screened by every researcher independently. Secondly, a detailed assessment of the full texts was conducted by each team in order to select eligible articles. Lastly, the selected studies were jointly evaluated by all researchers, who decided on the inclusion or exclusion of a study.
Included studies were appraised in order to derive the title, main author, publication year, study name and design, countries involved, total number of patients, age, sex, and type of neoplastic disease and its staging. From the medical interventions, the following information was obtained: species included in the probiotic, method of probiotic administration, dosage, and duration of treatment. Moreover, the occurrence of adverse effects related to probiotics was assessed. The implemented treatment details about both chemoand radiotherapy and any additional therapies were extracted.
The following definitions of selected gastrointestinal side effects were used in the data interpretation of the single studies. Diarrhoea is defined as loose or semisolid discharge, which appears at least three times per day or more often than usual [14]. The assessment of diarrhoea comprises grades according to the National Cancer Institute Common Toxicity Criteria (NCI CTC) 2.0, NCI CTC 3.0, the Common Terminology Criteria for Adverse Events (CTCAE) 4.0, CTCAE 4.1, or the World Health Organisation's (WHO) duration, frequency, and consistency degrees according to the Bristol scale, and abdominal discomfort occurrence and administration of antidiarrheal medications. Constipation is described as less than three bowel movements per week associated with other symptoms such as hard stools, bloating, distention, abdominal discomfort, excessive straining, a feeling of anorectal blockage, and incomplete defecation [15]. Constipation characteristics include the duration, frequency, and the Wexner score, which describes faecal incontinence. Nausea is a subjective feeling, which might precede vomiting [16]. Vomiting is an expeditious removal of gastric contents through the mouth [16]. For nausea and vomiting, information on the duration and grade according to CTCAE 3.0 was selected. Mucositis is defined as the erythema and ulceration of the gastrointestinal tract [17]. Concerning mucositis, the following data were extracted: grade according to the NCI CTC, time to onset, time to resolution or healing, and the administration of additional nutrition.

Search Results
The flow chart of the database searches is shown in Figure 1. A total of 1346 articles were selected as a result of the screening of the studies' titles. The assessment of the studies' abstracts led to the exclusion of 1191 papers. Another 122 positions were removed after consultations due to insufficient data about probiotics used during intervention. Finally, the full texts of 33 articles were carefully examined, with 12 studies being eliminated for incomplete information about changes in the condition of patients during probiotic intake as well as for no possible contact with the authors. A total of 21 papers met the inclusion criteria and were involved in the qualitative synthesis.
clude the duration, frequency, and the Wexner score, which describes faecal incont Nausea is a subjective feeling, which might precede vomiting [16]. Vomiting is an e tious removal of gastric contents through the mouth [16]. For nausea and vomiting mation on the duration and grade according to CTCAE 3.0 was selected. Mucositi fined as the erythema and ulceration of the gastrointestinal tract [17]. Concerning m tis, the following data were extracted: grade according to the NCI CTC, time to onse to resolution or healing, and the administration of additional nutrition.

Search Results
The flow chart of the database searches is shown in Figure 1. A total of 1346 were selected as a result of the screening of the studies' titles. The assessment of th ies' abstracts led to the exclusion of 1191 papers. Another 122 positions were re after consultations due to insufficient data about probiotics used during intervent nally, the full texts of 33 articles were carefully examined, with 12 studies being elim for incomplete information about changes in the condition of patients during pr intake as well as for no possible contact with the authors. A total of 21 papers m inclusion criteria and were involved in the qualitative synthesis.

Effects of Interventions
A summary of the outcomes is presented in Tables 3-6. The conditions of the patients who qualified for the study and control groups were compared in four categories: diarrhoea, constipation, nausea and vomiting, and mucositis. The outcomes were described as improvements or non-significant results. Improvement means at least one significant outcome. The studies regarded different parameters in order to assess the significance of the differences between the study and control groups.
In studies that analysed constipation [36,38] as well as nausea and vomiting [37,38], probiotic therapy has been recognised as a factor that could have a beneficial impact. Receiving probiotics was accompanied by lower scores in the Wexner classification [36] and a shorter duration of constipation [38] (Table 4). However, only the results regarding the duration of constipation were significant [38]. Additionally, significant improvements in stool character and frequency were observed in [36]. A reduction in the duration of vomiting [38] and the nausea grade according to CTCAE 3.0 [37] in the study groups compared to the control groups was regarded as significant.
In most of the studies that focused on mucositis, an alleviation of symptoms following probiotic intake was reported [20,25,27,37]. The results regarding the differences in mucositis between the study and control groups varied widely. No significant differences in probiotic treatments were observed in two out of six studies [30,34]. The severity of mucositis was significantly lower in two studies [20,25,27]. The toxicity of the treatment, regarded as mouth erythema or ulcers, was also significantly alleviated in [37]. In one study [30], enteral nutrition was applied in the study group, which is considered to be a determinant for an improvement in mucositis. Also, parenteral nutrition was administered and a Ryle's tube was inserted when needed [20]. The requirement for parenteral nutrition or a Ryle's tube was significantly lower for the study group [20].     1 Significantly better outcomes in the study group in at least one parameter (α = 0.05); 2 Markedly: stool returned to normal and the frequency to once a day after treatment; 3 Effective: stool character improved and the frequency became more than 3 times per week after treatment; 4 Invalid: no improvement in frequency and character of stool after treatment.  1 Significantly better outcomes in the study group in at least one parameter (α = 0.05); 2 CTCAE-Common Terminology Criteria for Adverse Events.

Discussion
According to the collected data, the influence of probiotics on the severity of chemoand/or radiotherapy side effects may not be established. Furthermore, relevant uncertainties regarding the administration of probiotics also occur.
There were no incidences of adverse effects confirmed as a result of the administration of probiotics. Nevertheless, it needs to be mentioned that patients undergoing chemoand/or radiotherapy are at greater risk of adverse effects induced by probiotics than the healthy population. Therefore, it is highly recommended to observe patients who receive probiotics [39]. There are cases of bacteraemia caused by Lactobacillus strains (such as L. GG, L. casei strains, L. acidophilus strains), Bacillus species (B. subtilis), and Bifidobacterium species (B. breve) [39]. The development of abscesses after L. rhamnosus [39] and L. GG [40] administration as well as endocarditis caused by L. GG and L. rhamnosus [40] were also reported. The safety of probiotics administered to patients suffering from neoplasms is not established [39][40][41].
Concerning the administration of probiotics, the variety of the chosen species needs to be taken into account as a factor that influences the outcome. Similarly, the dosage of probiotics and the duration of the treatment differed. To our knowledge, there are no recommendations regarding both dosage and time of intervention while undergoing chemoand/or radiotherapy. Nonetheless, in most of the included studies treatment started on the first day of chemo-and/or radiotherapy [19,20,23,[25][26][27][28][29][30][31]36]. Only in four studies were probiotics administered at least 7 days prior to the beginning of therapy [18,21,32,35]. It is possible that therapies could diminish the protective effects of probiotics due to the limitations of their prophylactic possibilities, which could be overcome by administering probiotics one month prior to therapy [9]. Moreover, the influence of probiotic administration on the microbiome should be considered as an observation of the differences between the placebo and control groups [25]. Additionally, there is a possibility that probiotic administration could be helpful in balancing gut dysbiosis during cancer treatment [27].
It is assessed that changes to the human microbiome as a result of treatment [42] have a huge impact on the development of digestive system-related chemo-and/or radiotherapy side effects. Anti-cancer therapy can lead to a reduction in gut bacteria diversity and, more importantly, to a decrease in bacteria that limit inflammation and increase bacteria associated with mucositis [43]. Furthermore, the polyamine transport deficiencies associated with the increased risk of cytotoxic T cell antigen 4 (CTLA-4) blockade-induced colitis may be caused by this disruption to the ecological network balance in the gastrointestinal tract [44]. Probiotic intake greatly corrects the composition of the microbiome [45], which could be beneficial for a reduction in side effects. Another mechanism resulting in disorders in the gastrointestinal tract is the activation of transcription factors, particularly nuclear factor-κB (NF-κB) and the subsequent upregulation of pro-inflammatory cytokines and inflammatory mediators [46]. B. bifidum, B. longum, B. longum subsp. infantis, and L. rhamnosus may have the potential to reduce tumour necrosis factor α (TNF-α) and interleukin 1β (IL-1β) concentrations [47], whereas a decrease in NF-κB, interleukin 6 (IL-6), and TNF-α is observed during L. delbruekii and L. fermentum administration [48]. The main mechanism with which the therapy fights cancer cells is the induction of apoptosis. However, it also applies to other cells, especially those that undergo rapid proliferation such as gastrointestinal epithelial cells [49]. B. lactis reduces apoptosis and improves cellular renewal by encouraging proliferation among intestinal cells [50]. L. rhamnosus GG and a few other strains are also known to have similar properties [51]. An important role in the initial phase of the mucositis process is attributed to the generation of reactive oxygen species [52]. The administration of Escherichia coli successfully prevents lipid peroxidation and the decline of mucosal glutathione [53]. Also, multistrain probiotic VSL#3 (L. plantarum, L. acidophilus, L. casei, L. delbrueckii subsp. bulgaricus; B. infantis, B. breve, B. longum, S. salivarius subsp. thermophilus) is known to have a positive effect on the extent of glutathione and additionally can reduce the expression of inducible nitric oxide synthase, protein nitrosylation, and malondialdehyde levels in rats [54]. This leads to a highly antioxidative effect. The growth of intestinal permeability above the average is another component of mucosal impairment. It is followed by an increased risk of the expansion of pathogens and a general loss of intestinal functions [55]. Tight junctions (TJ), which consist of occludin, claudin, and the zonula occludens (ZO) family of proteins, among others, are sealing the space between the epithelial cells and regulating their permeability. Escherichia coli intake is leading to increased expression of ZO-2 protein and a redistribution of ZO-2 from the cytosol to the cell boundaries. Furthermore, B. infantis Y1 produces substances that lead to increased ZO-1 expression [56] and the administration of B. infantis Y1 and L. plantarum increases occluding protein expression [56]. This provides a protective effect against chemically induced destruction of the epithelial barrier [56].
The effectiveness of probiotics during chemo-and/or radiotherapy-induced diarrhoea was observed in most of the included studies [19,21,23,28,[31][32][33]37,38] despite some variances, which appears consistent with the conclusions of other studies [9,41,[57][58][59][60][61]. Nevertheless, patients were suffering from different neoplasms and, therefore, therapy might have been focused on only one region of the body. Regarding abdominal and pelvic neoplasms, which occurred in most of the studies [18,19,[21][22][23][24]26,28,29,[31][32][33][34], it is well-established that probiotics have a beneficial influence [9,41,[58][59][60]. However, the impact of probiotics on diarrhoea observed during therapy for both central nervous system neoplasms [37] and white blood cell neoplasms [35,38] is not properly described. Therefore, significant improvements in these two areas [35,38] should be made. What is more, the type of implemented therapy might have had an impact on the effectiveness of probiotics as it is firmly associated with neoplasm pathology. Moreover, the administration of probiotics might even be unrecommended for the treatment of diarrhoea during both chemo-and radiotherapy and for the prevention of diarrhoea during chemotherapy due to inconclusive data [61]. In contrast, in one of the included studies, the implementation of probiotics during individual chemotherapy treatment was found to be beneficial [38]. Similarly, the administration of probiotics during radiotherapy treatment was found to be effective [32]. Due to the diversity of the results, it is essential to conduct further research.
A positive impact on the condition of patients with mucositis after chemo-and/or radiotherapy that was reported in enrolled studies [20,25,27,37] confirms previous findings in the literature [62]. It is worth emphasizing that the results might have been strongly influenced by the composition of the probiotics. In most of the studies, the administered probiotics included Lactobcillus [20,25,27]. However, different species were considered in every study: L. brevis [20], L. lactis [25], L. plantarum, L. rhamnosus, and L. acidophilus [27]. What is more, Sharma et al. [20] reported the beneficial influence of the intake of only L. brevis, which correlates fairly well with [11] and further supports the concept that the bacteria from this family play a major role in alleviating inflammation. However, other species, such as B. adolescensis [33], which are considered beneficial for inflammation [62], were used in selected papers. Lactobacillus and Bifidobacterium were the most commonly used types of bacteria in articles, and they presented improvements in other ailments (diarrhoea, nausea and vomiting, constipation) [19,21,23,31,33,36] as well. This indicates the advantageous results of such a combination. However, different species were used in these studies. Moreover, radiotherapy induces changes in the intestinal microbiome, which might be balanced during probiotic administration [25].
There was little research related to constipation, however B. tetragenous viable was previously proven to be beneficial for constipation [36]. Our study provides further evidence for the effectiveness of probiotics during chemo-and/or radiotherapy. A decrease in the duration of constipation [38] and less severe ailments [36] were noted through the use of compositions containing L. acidophilus, B. infantis [36], and L. rhamnosus [38].
For the treatment of nausea and vomiting, traditional antiemetics are mainly used [63]. Our results offer evidence for the legitimacy of using probiotics for this purpose [37,38].
The most remarkable result to emerge from the data is that probiotics might be effective in treating a wide variety of ailments caused by radio-and/or chemotherapy. According to available knowledge, probiotics inhibit inflammation, maintain intestinal permeability, eliminate pathogenic bacteria, inhibit cell apoptosis, prevent oxidative damage, and maintain mucous barriers [64], which allows them to act comprehensively in preventing and curing the side effects of radio-and/or chemotherapy that are related to the digestive system.

Limitations
This study has distinct limitations. Firstly, not all the results were considered significant [18,22,24,26,30,34,35], which might indicate the positive effects of probiotics. Therefore, the outcomes of these studies were not able to evince the conclusion and have limited the number of studies taken into account. Secondly, insufficient data concerning constipation [36,38] and nausea and vomiting [37,38] were found. The limited description of these adverse effects prevented a thorough analysis. Moreover, it was impossible to generalise the research findings due to the heterogeneity of data. This prevented a firm conclusion and decreased the relevance of the outcomes of this review, which therefore must be interpreted with caution and the number of limitations should be considered. Regarding the involved studies, several limitations also occurred. Probiotics were administered in varying schedules, amounts, and dosages. The time of day when the probiotics were administered and the presence of meals before or after administration could have had an additional impact on the outcomes. Unfortunately, there are no regulations regarding this application. Additionally, probiotics are often prepared without following pharmaceutical standards, which could have caused insufficient responses [65]. Certainly, the additional intake of medication could also have had an impact on the outcomes, especially antiemetics, antidiarrheals, and analgesics, which could have influenced the responses to the interventions. Nevertheless, it is impossible to guarantee a drug-free trial that also considers the adverse effects of chemoand/or radiotherapy.
In order to avoid the listed obstacles, it is necessary to provide well-designed trials and to ensure a detailed description of all regarded side effects. Moreover, the accurate assessment of live organisms included in probiotics should be assured.

Conclusions
The administration of probiotics has a positive influence on the condition of patients receiving chemotherapy and/or radiotherapy. The intake of probiotics leads to the alleviation of side effects such as diarrhoea, constipation, nausea, vomiting, and mucositis. Further research into the exact dosage, composition, timing of administration and safety of probiotics are needed.

Conflicts of Interest:
The authors declare no conflict of interest.