Chemotherapeutics-Induced Intestinal Mucositis: Pathophysiology and Potential Treatment Strategies

Nonpharmacological approaches for improving gut resilience to chemotherapy

PURPOSE OF REVIEW

Mucositis of the gastrointestinal tract is a debilitating side effect of chemotherapy that negatively influences treatment tolerance and patient life quality. This review will evaluate the recent literature on nonpharmacological strategies that have the potential to improve chemotherapy-induced mucositis (CIM).

RECENT FINDINGS

Alternatives to pharmacological approaches have shown great promise in preventing CIM. Natural products, including curcumin, ginseng, quercetin, and patchouli all show potential in mitigating CIM. In addition, dietary patterns, such as the elemental diet, high fiber diet, and diets high in amino acids have documented benefits in preventing CIM. Perhaps the greatest advancement coming to this arena in recent years is in the field of probiotics. Indeed, research on single species as well as probiotic mixtures show potential in reducing CIM insofar as probiotics are now being suggested for treatment of CIM by governing bodies. Although behavioral interventions including psychological interventions and exercise interventions have shown promise in reducing cancer therapy-related side effects, more work in this domain is warranted and particularly in the context of CIM.

SUMMARY

Alternatives to pharmacological approaches show great potential for use in prevention and treatment of CIM and should be further developed for use in the clinic.

Paraprobiotics and Postbiotics of Lactobacillus delbrueckii CIDCA 133 Mitigate 5-FU-Induced Intestinal Inflammation

Intestinal mucositis is a commonly reported side effect in oncology practice. Probiotics are considered an excellent alternative therapeutic approach to this debilitating condition; however, there are safety questions regarding the viable consumption of probiotics in clinical practice due to the risks of systemic infections, especially in immune-compromised patients. The use of heat-killed or cell-free supernatants derived from probiotic strains has been evaluated to minimize these adverse effects. Thus, this work evaluated the anti-inflammatory properties of paraprobiotics (heat-killed) and postbiotics (cell-free supernatant) of the probiotic Lactobacillus delbrueckii CIDCA 133 strain in a mouse model of 5-Fluorouracil drug-induced mucositis. Administration of paraprobiotics and postbiotics reduced the neutrophil cells infiltrating into the small intestinal mucosa and ameliorated the intestinal epithelium architecture damaged by 5-FU. These ameliorative effects were associated with a downregulation of inflammatory markers (Tlr2, Nfkb1, Il12, Il17a, Il1b, Tnf), and upregulation of immunoregulatory Il10 cytokine and the epithelial barrier markers Ocln, Cldn1, 2, 5, Hp and Muc2. Thus, heat-killed L. delbrueckii CIDCA 133 and supernatants derived from this strain were shown to be effective in reducing 5-FU-induced inflammatory damage, demonstrating them to be an alternative approach to the problems arising from the use of live beneficial microorganisms in clinical practice.

Mechanisms of Chemotherapy-Induced Neurotoxicity

Since the first clinical trials conducted after World War II, chemotherapeutic drugs have been extensively used in the clinic as the main cancer treatment either alone or as an adjuvant therapy before and after surgery. Although the use of chemotherapeutic drugs improved the survival of cancer patients, these drugs are notorious for causing many severe side effects that significantly reduce the efficacy of anti-cancer treatment and patients’ quality of life. Many widely used chemotherapy drugs including platinum-based agents, taxanes, vinca alkaloids, proteasome inhibitors, and thalidomide analogs may cause direct and indirect neurotoxicity. In this review we discuss the main effects of chemotherapy on the peripheral and central nervous systems, including neuropathic pain, chemobrain, enteric neuropathy, as well as nausea and emesis. Understanding mechanisms involved in chemotherapy-induced neurotoxicity is crucial for the development of drugs that can protect the nervous system, reduce symptoms experienced by millions of patients, and improve the outcome of the treatment and patients’ quality of life.

Protective Effects of Melatonin and Misoprostol against Experimentally Induced Increases in Intestinal Permeability in Rats

Intestinal mucosal barrier dysfunction caused by disease and/or chemotherapy lacks an effective treatment, which highlights a strong medical need. Our group has previously demonstrated the potential of melatonin and misoprostol to treat increases in intestinal mucosal permeability induced by 15-min luminal exposure to a surfactant, sodium dodecyl sulfate (SDS). However, it is not known which luminal melatonin and misoprostol concentrations are effective, and whether they are effective for a longer SDS exposure time. The objective of this single-pass intestinal perfusion study in rats was to investigate the concentration-dependent effect of melatonin and misoprostol on an increase in intestinal permeability induced by 60-min luminal SDS exposure. The cytoprotective effect was investigated by evaluating the intestinal clearance of ⁵¹Cr-labeled EDTA in response to luminal SDS as well as a histological evaluation of the exposed tissue. Melatonin at both 10 and 100 µM reduced SDS-induced increase in permeability by 50%. Misoprostol at 1 and 10 µM reduced the permeability by 50 and 75%, respectively. Combination of the two drugs at their respective highest concentrations had no additive protective effect. These in vivo results support further investigations of melatonin and misoprostol for oral treatments of a dysfunctional intestinal barrier.

Effects of Multispecies Probiotic on Intestinal Microbiota and Mucosal Barrier Function of Neonatal Calves Infected With E. coli K99

Altered gut microbiota are implicated in inflammatory neonatal calf diarrhea caused by E. coli K99. Beneficial probiotics are used to modulate gut microbiota. However, factors that mediate host-microbe interactions remain unclear. We evaluated the effects of a combination of multispecies probiotics (MSP) on growth, intestinal epithelial development, intestinal immune function and microbiota of neonatal calves infected with E. coli K99. Twelve newborn calves were randomly assigned as follows: C (control, without MSP); D (E. coli O78:K99 + gentamycin); and P (E. coli O78:K99 + supplemental MSP). All groups were studied for 21 d. MSP supplementation significantly (i) changed fungal Chao1 and Shannon indices of the intestine compared with group D; (ii) reduced the relative abundance of Bacteroides and Actinobacteria, while increasing Bifidobacteria, Ascomycetes, and Saccharomyces, compared with groups C and D; (iii) improved duodenal and jejunal mucosal SIgA and total Short Chain Fatty Acids (SCFA) concentrations compared with group D; (iv) increased relative ZO-1 and occludin mRNA expression in jejunal mucosa compared with group D; and (v) enhanced intestinal energy metabolism and defense mechanisms of calves by reducing HSP90 expression in E. coli K99, thereby alleviating the inflammatory response and promoting recovery of mucosal function. Our research may provide direct theoretical support for future applications of MSP in ruminant production.

Chemotherapeutics Combined with Luminal Irritants: Effects on Small-Intestinal Mannitol Permeability and Villus Length in Rats

Chemotherapy causes intestinal mucositis, which includes villous atrophy and altered mucosal barrier function. However, there is an uncertainty regarding how the reduced small-intestinal surface area affects the mucosal permeability of the small marker probe mannitol (MW 188), and how the mucosa responds to luminal irritants after chemotherapy. The aims in this study were to determine (i) the relationship between chemotherapy-induced villus atrophy and the intestinal permeability of mannitol and (ii) how the mucosa regulate this permeability in response to luminal ethanol and sodium dodecyl sulfate (SDS). This was investigated by treating rats with a single intraperitoneal dose of doxorubicin, irinotecan, or 5-fluorouracil. After 72 h, jejunum was single-pass perfused and mannitol permeability determined at baseline and after 15 min luminal exposure to 15% ethanol or 5 mg/mL SDS. Tissue samples for morphological analyses were sampled from the perfused segment. All three chemotherapeutics caused a similar 30% reduction in villus length. Mannitol permeability increased with irinotecan (1.3-fold) and 5-fluorouracil (2.5-fold) and was reduced with doxorubicin (0.5-fold), suggesting that it is not epithelial surface area alone that regulates intestinal permeability to mannitol. There was no additional increase in mannitol permeability induced by luminal ethanol or SDS in the chemotherapy-treated rats compared to controls, which may be related to the relatively high basal permeability of mannitol compared to other common low-permeability probes. We therefore suggest that future studies should focus on elucidating the complex interplay between chemotherapy in combination with luminal irritants on the intestinal permeability of other probes.

Chemotherapy induced gastrointestinal toxicities

Chemotherapy-induced gastrointestinal dysfunction is a common occurrence associated with many different classes of chemotherapeutic agents. Gastrointestinal toxicity includes mucositis, diarrhea, and constipation, and can often be a dose-limiting complication, induce cessation of treatment and could be life threatening. The gastrointestinal epithelium is rich in rapidly dividing cells and hence is a prime target for chemotherapeutic drugs. The incidence of gastrointestinal toxicity, including diarrhea and mucositis, is extremely high for a wide array of chemotherapeutic and radiation regimens. In fact, 60%-100% of patients on high-dose chemotherapy suffer from gastrointestinal side effects. Unfortunately, treatment options are limited, and therapy is often restricted to palliative care. Therefore, there is a great unmet therapeutic need for preventing and treating chemotherapy-induced gastrointestinal toxicities in the clinic. In this review, we discuss our current understanding of the mechanisms underlying chemotherapy-induced diarrhea and mucositis, and emerging mechanisms involving the enteric nervous system, smooth muscle cells and enteric immune cells. Recent evidence has also implicated gut dysbiosis in the pathogenesis of not only chemotherapy-induced mucositis and diarrhea, but also chemotherapy-induced peripheral neuropathy. Oxidative stress induced by chemotherapeutic agents results in post-translational modification of ion channels altering neuronal excitability. Thus, investigating how chemotherapy-induced changes in the gut- microbiome axis may lead to gut-related toxicities will be critical in the discovery of new drug targets for mitigating adverse gastrointestinal effects associated with chemotherapy treatment.

Glucagon-Like Peptide-1 Is Associated With Systemic Inflammation in Pediatric Patients Treated With Hematopoietic Stem Cell Transplantation

Patients undergoing allogeneic hematopoietic stem cell transplantation (HSCT) are challenged with severe side effects, which are propagated by mucosal barrier disruption, and the related microbial translocation and systemic inflammation. Glucagon-like peptide-1 (GLP-1), a well-known incretin hormone, possesses anti-inflammatory properties and promotes regeneration of damaged intestinal epithelium in animal studies. We hypothesized that the immense inter-individual variation in the degree of mucosal damage and systemic inflammation, seen after HSCT is influenced by endogenous GLP-1 and could be related to acute post-transplant complications. In this prospective study we measured serial weekly fasting plasma GLP-1, along with C-reactive protein (CRP), and citrulline in 82 pediatric patients during allogeneic HSCT together with a fasting plasma GLP-1 in sex- and age-matched healthy controls. Overall, GLP-1 levels were increased in the patients during the course of HSCT compared with the controls, but tended to decrease post-transplant, most pronounced in patients receiving high-intensity conditioning regimen. The increase in CRP seen in the early post-transplant phase was significantly lower from day +8 to +13 in patients with GLP-1 above the upper quartile (>10 pmol/L) at day 0 (all P ≤ 0.03). Similar findings were seen for peak CRP levels after adjusting for type of conditioning (-47.0%; 95% CI, -8.1 - -69.4%, P = 0.02). Citrulline declined significantly following the transplantation illustrating a decrease in viable enterocytes, most evident in patients receiving high-intensity conditioning regimen. GLP-1 levels at day 0 associated with the recovery rate of citrulline from day 0 to +21 (34 percentage points (pp)/GLP-1 doubling; 95% CI, 10 - 58pp; P = 0. 008) and day 0 to day +90 (48 pp/GLP-1 doubling; 95% CI, 17 - 79pp; P = 0. 004), also after adjustment for type of conditioning. This translated into a reduced risk of acute graft-versus-host disease (aGvHD) in patients with highest day 0 GLP-1 levels (>10 pmol/L) (cause-specific HR: 0.3; 95% CI, 0.2 - 0.9, P = 0.02). In conclusion, this study strongly suggests that GLP-1 influences regeneration of injured epithelial barriers and ameliorates inflammatory responses in the early post-transplant phase.

Melatonin-Activated Receptor Signaling Pathways Mediate Protective Effects on Surfactant-Induced Increase in Jejunal Mucosal Permeability in Rats

A well-functional intestinal mucosal barrier can be compromised as a result of various diseases, chemotherapy, radiation, and chemical exposures including surfactants. Currently, there are no approved drugs targeting a dysfunctional intestinal barrier, which emphasizes a significant medical need. One candidate drug reported to regulate intestinal mucosal permeability is melatonin. However, it is still unclear if its effect is primarily receptor mediated or antioxidative, and if it is associated with enteric neural pathways. The aim of this rat intestinal perfusion study was to investigate the mechanisms of melatonin and nicotinic acetylcholine receptors on the increase in intestinal mucosal clearance of 51Cr-labeled ethylenediaminetetraacetate induced by 15 min luminal exposure to the anionic surfactant, sodium dodecyl sulfate. Our results show that melatonin abolished the surfactant-induced increase in intestinal permeability and that this effect was inhibited by luzindole, a melatonin receptor antagonist. In addition, mecamylamine, an antagonist of nicotinic acetylcholine receptors, reduced the surfactant-induced increase in mucosal permeability, using a signaling pathway not influenced by melatonin receptor activation. In conclusion, our results support melatonin as a potentially potent candidate for the oral treatment of a compromised intestinal mucosal barrier, and that its protective effect is primarily receptor-mediated.