Opioid receptors are widely distributed in the human body and are crucially involved in numerous physiological processes. These include pain signaling in the central and the peripheral nervous system, reproduction, growth, respiration, and immunological response. Opioid receptors additionally play a major role in the gastrointestinal (GI) tract in physiological and pathophysiological conditions. This review discusses the physiology and pharmacology of the opioid system in the GI tract. We additionally focus on GI disorders and malfunctions, where pathophysiology involves the endogenous opioid system, such as opioid-induced bowel dysfunction, opioid-induced constipation or abdominal pain. Based on recent reports in the field of pharmacology and medicinal chemistry, we will also discuss the opportunities of targeting the opioid system, suggesting future treatment options for functional disorders and inflammatory states of the GI tract.

Lactoferrin (LF), a glycoprotein found in mucosal secretions, is characterized by a wide range of functions, including immunomodulatory and anti-inflammatory activities. Moreover, several investigations confirmed that LF displays high effectiveness against multiple bacteria and viruses and may be regarded as a potential inhibitor of enveloped viruses, such as presently prevailing SARS-CoV-2. In our review, we discuss available studies about LF functions and bioavailability of different LF forms in in vitro and in vivo models. Moreover, we characterize the potential benefits and side effects of LF use; we also briefly summarize the latest clinical trials examining LF application. Finally, we point potential role of LF in inflammatory bowel disease and indicate its use as a marker for disease severity.

Opinion statement Inflammatory bowel diseases (IBD) are a group of chronic inflammatory gastrointestinal (GI) disorders, mainly represented by Crohn's disease and ulcerative colitis. Although the etiology of IBD is not fully understood, there is substantial evidence that immunologic, genetic, and environmental factors are the main contributors in IBD pathogenesis. Conventional therapies for IBD include anti-inflammatory and immunosuppressive drugs, such as 5-aminosalicylic acid, corticosteroids, antibiotics, and biologicals, such as anti-TNFα antibodies. However, because of low efficacy and high risk of side effects, there is a clear need for the development of novel and efficient pharmacologic strategies in IBD treatment. Among various complementary and alternative medicine (CAM) approaches, which are used for the treatment of gastrointestinal (GI) disorders, traditional Chinese medicine (TCM) is one of the most developed and diversified. TCM encompasses methods and therapies that emerged over centuries and is based mostly on ethnic wisdom and observations transmitted from generation to generation. In the recent years, the efficacy of TCM as treatment of IBD has been extensively characterized in preclinical and clinical studies, which resulted in a significant number of research reports. Moreover, the popularity of TCM among patients with IBD has rapidly increased not only in Asia, but also in the Western hemisphere.

Constipation is one of the major gastrointestinal disorders diagnosed in clinical practice in Western countries. Almost 20% of population suffer from this disorder, which means constipation is a substantial utilization of healthcare. Pathophysiology of constipation is complex and multifactorial, where aspects like disturbance in colonic transit, genetic predisposition, lifestyle habits, psychological distress, and many others need to be taken into consideration. Diagnosis of constipation is troublesome and requires thorough accurate examination. A nonpharmacological approach, education of the patient about the importance of lifestyle changes like diet and sport activity state, are the first line of therapy. In case of ineffective treatment, pharmacological treatments such as laxatives, secretagogues, serotonergic agonists, and many other medications should be induced. If pharmacologic treatment fails, the definitive solution for constipation might be surgical approach. Commonness of this disorder, costs of medical care and decrease in quality life cause constipation is a serious issue for many specialists. The aim of this review is to present current knowledge of chronic constipation and management of this disorder.

Polyunsaturated fatty acids (PUFAs) are bioactive lipids which modulate inflammation and immunity. They gained recognition in nutritional therapy and are recommended dietary supplements. There is a growing body of evidence suggesting the usefulness of PUFAs in active therapy of various gastrointestinal (GI) diseases. In this review we briefly cover the systematics of PUFAs and their metabolites, and elaborate on their possible use in inflammatory bowel disease (IBD), functional gastrointestinal disorders (FGIDs) with focus on irritable bowel syndrome (IBS), and colorectal cancer (CRC). Each section describes the latest findings from in vitro and in vivo studies, with reports of clinical interventions when available.