The effect of mesalamine and nicotine in the treatment of inflammatory bowel disease

Nicotine Evoked Currents in Human Primary Sensory Neurons

Sensory neuron nicotinic acetylcholine receptors (nAChRs) contribute to pain associated with tissue injury. However, there are marked differences between rats and mice with respect to both the properties and distribution of nAChR currents in sensory neurons. Because both species are used to understand pain signaling in humans, we sought to determine whether the currents present in either species was reflective of those present in human sensory neurons. Neurons from the L4/L5 dorsal root ganglia were obtained from adult male and female organ donors. Nicotine evoked currents were detected in 40 of 47 neurons (85%). In contrast with the naïve mouse, in which almost all nAChR currents are transient, or the rat, in which both mouse-like transient and more slowly activating and inactivating currents are detected, all the currents in human DRG neurons were slow, but slower than those in the rat. Currents were blocked by the nAChR antagonists mecamylamine (30 µmol/L), but not by the TRPA1 selective antagonist HC-030031 (10 µmol/L). Single cell polymerase chain reaction analysis of nicotinic receptor subunit expression in human DRG neurons are consistent with functional data indicating that receptor expression is detected 85 ± 2.1% of neurons assessed (n = 48, from 4 donors). The most prevalent coexpression pattern was α3/β2 (95 ± 4% of neurons with subunits), but α7 subunits were detected in 70 ± 3.4% of neurons. These results suggest that there are not only species differences in the sensory neuron distribution of nAChR currents between rodent and human, but that the subunit composition of the channel underlying human nAChR currents may be different from those in the mouse or rat. PERSPECTIVE: The properties and distribution of nicotine evoked currents in human sensory neurons were markedly different from those previously observed in mice and rats. These observations add additional support to the suggestion that human sensory neurons may be an essential screening tool for those considering moving novel therapeutics targeting primary afferents into clinical trials.

Nicotine can skew the characterization of the macrophage type-1 (MPhi1) phenotype differentiated with granulocyte-macrophage colony-stimulating factor to the MPhi2 phenotype

Macrophages (MPhis) exhibit functional heterogeneity and plasticity in the local microenvironment. Recently, it was reported that MPhis can be divided into proinflammatory MPhis (MPhi1) and anti-inflammatory MPhis (MPhi2) based on their polarized functional properties. Here, we report that nicotine, the major ingredient of cigarette smoke, can modulate the characteristics of MPhi1. Granulocyte-macrophage colony-stimulating factor-driven MPhi1 with nicotine (Ni-MPhi1) showed the phenotypic characteristics of MPhi2. Like MPhi2, Ni-MPhi1 exhibited antigen-uptake activities. Ni-MPhi1 suppressed IL-12, but maintained IL-10 and produced high amounts of MCP-1 upon lipopolysaccharide stimulation compared with MPhi1. Moreover, we observed strong proliferative responses of T cells to lipopolysaccharide-stimulated MPhi1, whereas Ni-MPhi1 reduced T cell proliferation and inhibited IFN-gamma production by T cells. These results suggest that nicotine can change the functional characteristics of MPhi and skew the MPhi1 phenotype to MPhi2. We propose that nicotine is a potent regulator that modulates immune responses in microenvironments.

Hypothesis about mechanisms through which nicotine might exert its effect on the interdependence of inflammation and gut barrier function in ulcerative colitis

Ulcerative colitis (UC) is characterized by impairment of the epithelial barrier and the formation of ulcer-type lesions, which result in local leaks and generalized alterations of mucosal tight junctions. Ultimately, this results in increased basal permeability. Although disruption of the epithelial barrier in the gut is a hallmark of inflammatory bowel disease and intestinal infections, it remains unclear whether barrier breakdown is an initiating event of UC or rather a consequence of an underlying inflammation, evidenced by increased production of proinflammatory cytokines. UC is less common in smokers, suggesting that the nicotine in cigarettes may ameliorate disease severity. The mechanism behind this therapeutic effect is still not fully understood, and indeed it remains unclear if nicotine is the true protective agent in cigarettes. Nicotine is metabolized in the body into a variety of metabolites and can also be degraded to form various breakdown products. It is possible these metabolites or degradation products may be the true protective or curative agents. A greater understanding of the pharmacodynamics and kinetics of nicotine in relation to the immune system and enhanced knowledge of gut permeability defects in UC are required to establish the exact protective nature of nicotine and its metabolites in UC. This review suggests possible hypotheses for the protective mechanism of nicotine in UC, highlighting the relationship between gut permeability and inflammation, and indicates where in the pathogenesis of the disease nicotine may mediate its effect.

Neuronal nicotinic receptors: from structure to pathology

Neuronal nicotinic receptors (NAChRs) form a heterogeneous family of ion channels that are differently expressed in many regions of the central nervous system (CNS) and peripheral nervous system. These different receptor subtypes, which have characteristic pharmacological and biophysical properties, have a pentameric structure consisting of the homomeric or heteromeric combination of 12 different subunits (alpha2-alpha10, beta2-beta4). By responding to the endogenous neurotransmitter acetylcholine, NAChRs contribute to a wide range of brain activities and influence a number of physiological functions. Furthermore, it is becoming evident that the perturbation of cholinergic nicotinic neurotransmission can lead to various diseases involving nAChR dysfunction during development, adulthood and ageing. In recent years, it has been discovered that NAChRs are present in a number of non-neuronal cells where they play a significant functional role and are the pathogenetic targets in several diseases. NAChRs are also the target of natural ligands and toxins including nicotine (Nic), the most widespread drug of abuse. This review will attempt to survey the major achievements reached in the study of the structure and function of NAChRs by examining their regional and cellular localisation and the molecular basis of their functional diversity mainly in pharmacological and biochemical terms. The recent availability of mice with the genetic ablation of single or double nicotinic subunits or point mutations have shed light on the role of nAChRs in major physiological functions, and we will here discuss recent data relating to their behavioural phenotypes. Finally, the role of NAChRs in disease will be considered in some details.

Transport mechanisms of nicotine across the human intestinal epithelial cell line Caco-2

Ulcerative colitis is a disease more commonly seen in nonsmokers. Because nicotine was postulated to be a beneficial component of tobacco smoke for ulcerative colitis, various formulations of nicotine have been developed to improve the local bioavailability within the gastrointestinal tissue. In the present study, to characterize the disposition of nicotine in the intestines, we investigated intestinal nicotine transport using Caco-2 cells. Nicotine was predominantly transported across Caco-2 cell monolayers in a unidirectional mode, corresponding to intestinal secretion, by pH-dependent specific transport systems. The specific uptake systems appear to be distinct from organic cation transporters and the transport system for tertiary amines, in terms of its substrate specificity and the pattern of the interaction. These transport systems could play a role in the intestinal accumulation of nicotine from plasma and could also be responsible for the topical delivery of nicotine for ulcerative colitis therapy. These findings could provide useful information for the design of effective nicotine delivery.

Inflammatory bowel disease

Till about 3 decades ago, inflammatory bowel disease (IBD) was considered as non-existent in our country. However, since that time several reports of IBD, mainly ulcerative colitis have been published. More recently, Crohn's disease is also being reported from the country. This trend of UC appearing first in a population followed by CD also appears to be true in other developing nations. A substantial increase in the rates of CD over UC in the last few decades is reported from developed nations as well. Of the other epidemiological factors, an increased risk of CD and lower risk of UC in smokers is established in adults. However, it appears that smoking increases the risk of IBD in children. The etiology of IBD remains elusive. Within the triad of genetics, immunity and antigen responsible for the development of IBD, maximum advances have been made in the field of immune aberrations and this is being exploited to treat the disease. It is well established that IBD results from a disordered immune system in the gut, in response to an unidentified antigen in a predisposed individual. The immune response is enhanced and revolves around antigen-presenting cells, CD 4 T-lymphocytes and tumor necrosis factor alpha. CD results from an enhanced Th1 activity. The pathogenesis of UC is less clear but appears to be humoral. Advances in diagnostics include the availability of serology, ultrasound and nuclear scans, none of which have been tried in our setting where infectious diseases and tuberculosis is rampant. Growth failure and the importance of nutrition in IBD, especially CD, cannot be underemphasized. In many situations nutritional interventions have been used solely as a form of therapy for CD. Newer steroid molecules with minimal systemic effects are also being considered. Other treatment options highlighted are the use of immunosuppressive agents, biologic agents and role of surgery.

Inflammatory bowel disease

Although ulcerative colitis and Crohn's disease are relatively uncommon disorders, most primary care practices include a number of individuals with these diagnoses. Much of the initial evaluation and long-term care of these patients is managed or coordinated by their primary care physicians. A familiarity with current principles of diagnosis and treatment is essential. Ulcerative colitis and Crohn's disease are related, immunologically mediated disorders of unknown cause. Both are characterized by chronic relapsing courses, frequent need for surgical intervention, and increased colorectal cancer risk. Significant differences are seen between these two inflammatory bowel disease syndromes, in their histopathologic features, clinical manifestations, and response to treatment. This review focuses on the colorectal manifestations of inflammatory bowel disease, emphasizing clinical presentation, approach to diagnosis, medical and surgical management, and long-term prognosis.

Clinical economics review: medical management of inflammatory bowel disease

Inflammatory bowel diseases, although they are uncommon and rarely fatal, typically present during the period of economically productive adult life. Patients may require extensive therapeutic intervention as a result of the chronic, relapsing nature of the diseases. Their medical management includes oral and topical 5-amino salicylic acid derivatives and corticosteroids, as well as antibiotics and immunosuppressive therapies. Assessing the cost-effectiveness of rival treatments requires valid, reliable global assessments of outcome which consider quality of life, as well as the usual clinical end-points. Macro-economic studies of the overall impact of inflammatory bowel disease on health care systems have so far been largely confined to North America, where the total annual US costs, both direct and indirect, incurred by the estimated 380 000-480 000 sufferers has been put at around US2bn. Drugs were estimated to account for only 10% of total costs, whereas surgery and hospitalization account for approximately half. Studies from Europe suggest that the proportion of patients with Crohn's disease and ulcerative colitis who are capable of full time work is 75% and 90%, respectively. However, whilst only a minority of inflammatory bowel disease patients suffer chronic ill health and their life expectancy is normal, obtaining life assurance may be problematic, suggesting a misconception that inflammatory bowel disease frequently results in a major impact on an individual's economic productivity.