Targeting opioid signaling in Crohn's disease: new therapeutic pathways

Role of the δ-Opioid Receptor in 2 Murine Models of Colitis

Crohn disease and ulcerative colitis, collectively referred to as inflammatory bowel disease (IBD), are chronic inflammatory disorders of the gastrointestinal tract. Currently, the etiology of IBD is unknown, and immunosuppressive therapies have become the standard of care to reduce the inflammation; however, these agents only induce remission 50% of the time in patients and can have serious side effects. Recently, endogenous opioids and opioid receptors have been shown to play a role in the mediation of inflammation. In addition, opioid receptor blockade with a nonselective antagonist, naltrexone, has been shown to reduce colitis in both murine models and human subjects. The goal of the current study was to determine if the antiinflammatory effects of naltrexone are mediated through the delta (δ) opioid receptor. Male C57BL/6NCrl (6 to 8 wk.; n = 110) and female BALB/cAnNCrl (6-8 wk.; n = 91) mice were studied using 2 animal models of chemically induced colitis: dextran sodium sulfate (DSS) and 2, 4, 6-trinitrobenzenesulfonic acid (TNBS). The selective δ-receptor antagonists naltrindole and 7-benzylidenenaltrexone were administered to examine the role of the δ-opioid receptor in colonic inflammation. The quantitative measurement of colitis activity, colon weight and length, Hct, WBC count, and gross and microscopic aberrations were analyzed. Administration of naltrexone in the DSS colitis model significantly improved overall disease activity indices on day 5 of therapy. The use of δ-antagonists and naltrexone had limited to no effect on TNBS colitis. Similar findings were obtained by using the DSS colitis model. Based on the current findings, the authors conclude that naltrexone therapy has limited effect on the improvement of colitis in 2 murine models; however, the δ-opioid receptor was not responsible for mediating the effects.

Involvement of central opioid receptors in protective effects of methadone on experimental colitis in rats

PURPOSE

There are several lines of evidence on the protective roles of opioids in gastrointestinal inflammatory conditions. This study aims to distinguish the central and peripheral roles of methadone, a non-selective opioid receptor agonist, in an acute model of ulcerative colitis in male rats.

METHODS

Ulcerative colitis was induced by intrarectal administration of acetic acid 4%. Methadone was injected subcutaneously (s.c.), 5 and 10 mg/kg, and intracerebroventricular (i.c.v.), 50 and 300 ng/rat. Opioid antagonists were employed. Methylnaltrexone (MNTX; 5 mg/kg, i.p.), a peripherally acting opioid receptor antagonist, and naltrexone (NTX; 5 mg/kg, i.p. and 10 ng/rat, i.c.v.), a peripherally and centrally acting opioid receptor antagonist were injected before methadone (10 mg/kg, s.c. and or 300 ng/rat, i.c.v.) administration. NTX (5 mg/kg, i.p. and 10 ng/rat, i.c.v.) were administered 30 min prior to administration of methadone (10 mg/kg, s.c. and 300 ng/rat, i.c.v.), respectively. MNTX (5 mg/kg, i.p.) was injected 30 min prior to methadone (10 mg/kg, s.c.). Seventy-two hours following colitis induction, macroscopic and microscopic mucosal lesions, and the colonic levels of tumor necrosis factor-alpha (TNF-α) and interleukin-1β (IL-1β) were determined.

RESULTS

Methadone (300 ng/rat, i.c.v.) and Methadone (5 and 10 mg/kg, s.c.) improved the macroscopic and microscopic scores through opioid receptors. Also, a significant reduction in TNF-α and IL-1β was observed. Peripherally and centrally injected NTX significantly reversed methadone 10 mg/kg s.c. anti-inflammatory effects while MNTX could not completely reverse this effect. Moreover, centrally administered methadone (300 ng/rat) showed the anti-inflammatory effect which was reversed by central administration of NTX (10 ng/rat).

CONCLUSIONS

The opioid receptors mainly the central opioid receptors may mediate the protective actions of methadone on the experimental model of inflammatory bowel disease in rat.

The Effect of Low-Dose Naltrexone on Medication in Inflammatory Bowel Disease: A Quasi Experimental Before-and-After Prescription Database Study

BACKGROUND AND AIMS

Low-dose naltrexone [LDN] is a controversial off-label treatment used by many Crohn's disease [CD] and ulcerative colitis [UC] patients. A small number of preliminary studies indicate that LDN might be beneficial in CD, but evidence is too scarce to demonstrate efficacy. We sought to examine whether initiation of LDN therapy by patients with inflammatory bowel disease [IBD] was followed by changes in dispensing of relevant medication.

METHODS

We performed a quasi-experimental before-and-after study following a sudden increase in LDN use in the Norwegian population in 2013. IBD patients were identified from among all the patients who had at least one LDN prescription recorded in the Norwegian Prescription Database [NorPD] in 2013. Drug dispensing 2 years before and after the first LDN prescription was compared.

RESULTS

We identified 582 IBD patients who had received LDN. Of the 256 patients who became persistent LDN users, there were reductions in the number of users for [i] all examined drugs [-12%], [ii] intestinal anti-inflammatory agents [-17%], [iii] other immunosuppressants [-29%], [iv] intestinal corticosteroids [-32%] and [v] aminosalicylates [-17%]. In subgroups of identified CD and UC patients, there were significant reductions in the number of users of intestinal corticosteroids [CD: -44%, UC: -53%] and systemic corticosteroids [UC: -24%]. No significant differences in cumulative defined daily doses were observed.

CONCLUSIONS

Our findings imply that the initiation of LDN in IBD is followed by reduced dispensing of several drugs considered essential in the treatment of CD and UC.

Low dose naltrexone for induction of remission in Crohn's disease

BACKGROUND

Crohn's disease is a transmural, relapsing inflammatory condition afflicting the digestive tract. Opioid signalling, long known to affect secretion and motility in the gut, has been implicated in the inflammatory cascade of Crohn's disease. Low dose naltrexone, an opioid antagonist, has garnered interest as a potential therapy.

OBJECTIVES

The primary objective was to evaluate the efficacy and safety of low dose naltrexone for induction of remission in Crohn's disease.

SEARCH METHODS

A systematic search of MEDLINE, Embase, PubMed, CENTRAL, and the Cochrane IBD Group Specialized Register was performed from inception to 15 January 2018 to identify relevant studies. Abstracts from major gastroenterology conferences including Digestive Disease Week and United European Gastroenterology Week and reference lists from retrieved articles were also screened.

SELECTION CRITERIA

Randomized controlled trials of low dose naltrexone (LDN) for treatment of active Crohn's disease were included.

DATA COLLECTION AND ANALYSIS

Data were analyzed on an intention-to-treat basis using Review Manager (RevMan 5.3.5). The primary outcome was induction of clinical remission defined by a Crohn's disease activity index (CDAI) of < 150 or a pediatric Crohn's disease activity index (PCDAI) of < 10. Secondary outcomes included clinical response (70- or 100-point decrease in CDAI from baseline), endoscopic remission or response, quality of life, and adverse events as defined by the included studies. Risk ratios (RR) and 95% confidence intervals (CI) were calculated for dichotomous outcomes. The methodological quality of included studies was evaluated using the Cochrane risk of bias tool. The overall quality of the evidence supporting the primary outcome and selected secondary outcomes was assessed using the GRADE criteria.

MAIN RESULTS

Two studies were identified (46 participants). One study assessed the efficacy and safety of 12 weeks of LDN (4.5 mg/day) treatment compared to placebo in adult patients (N = 34). The other study assessed eight weeks of LDN (0.1 mg/kg, maximum 4.5 mg/day) treatment compared to placebo in pediatric patients (N = 12). The primary purpose of the pediatric study was to assess safety and tolerability. Both studies were rated as having a low risk of bias. The study in adult patients reported that 30% (5/18) of LDN treated patients achieved clinical remission at 12 weeks compared to 18% (3/16) of placebo patients, a difference that was not statistically significant (RR 1.48, 95% CI 0.42 to 5.24). The study in children reported that 25% of LDN treated patients achieved clinical remission (PCDAI < 10) compared to none of the patients in the placebo group, although it was unclear if this result was for the randomized placebo-controlled trial or for the open label extension study. In the adult study 70-point clinical response rates were significantly higher in those treated with LDN than placebo. Eighty-three per cent (15/18) of LDN patients had a 70-point clinical response at week 12 compared to 38% (6/16) of placebo patients (RR 2.22, 95% CI 1.14 to 4.32). The effect of LDN on the proportion of adult patients who achieved a 100-point clinical response was uncertain. Sixty-one per cent (11/18) of LDN patients achieved a 100-point clinical response compared to 31% (5/16) of placebo patients (RR 1.96, 95% CI 0.87 to 4.42). The proportion of patients who achieved endoscopic response (CDEIS decline > 5 from baseline) was significantly higher in the LDN group compared to placebo. Seventy-two per cent (13/18) of LDN patients achieved an endoscopic response compared to 25% (4/16) of placebo patients (RR 2.89; 95% CI 1.18 to 7.08). However, there was no statistically significant difference in the proportion of patients who achieved endoscopic remission. Endoscopic remission (CDEIS < 3) was achieved in 22% (4/18) of the LDN group compared to 0% (0/16) of the placebo group (RR 8.05; 95% CI 0.47 to 138.87). Pooled data from both studies show no statistically significant differences in withdrawals due to adverse events or specific adverse events including sleep disturbance, unusual dreams, headache, decreased appetite, nausea and fatigue. No serious adverse events were reported in either study. GRADE analyses rated the overall quality of the evidence for the primary and secondary outcomes (i.e. clinical remission, clinical response, endoscopic response, and adverse events) as low due to serious imprecision (sparse data).

AUTHORS' CONCLUSIONS

Currently, there is insufficient evidence to allow any firm conclusions regarding the efficacy and safety of LDN used to treat patients with active Crohn's disease. Data from one small study suggests that LDN may provide a benefit in terms of clinical and endoscopic response in adult patients with active Crohn's disease. Data from two small studies suggest that LDN does not increase the rate of specific adverse events relative to placebo. However, these results need to be interpreted with caution as they are based on very small numbers of patients and the overall quality of the evidence was rated as low due to serious imprecision. Further randomized controlled trials are required to assess the efficacy and safety of LDN therapy in active Crohn's disease in both adults and children.

Low-dose Naltrexone for the treatment of sarcoidosis

Systemic therapy is administered to 50% of patients and the need for long-term use of therapy is quite variable (1,2). Prednisone is often administered for many months with risk for multiple side effects, immunomodulators as steroid sparing agents have a delayed onset of action and have risks for infection and malignancies, and infliximab increases the risk for infection (1). In light of these issues, alternative options for therapy are desirable. We made a comparison between sarcoidosis and Crohn's disease in that in each disease there is unregulated lymphocyte activity, a common unique pathological finding of non-caseating granulomas, and a similar approach to medical therapy (3,4). Low dose naltrexone (LDN) has been utilized for many conditions (5). Efficacy has been documented in Crohn's disease with randomized controlled studies showing mucosal healing and histologic improvement (6-7). LDN is compounded in 1/10^th to 1/20^th the dose used for the FDA-approved indications of narcotic and alcohol dependence (8). Neuropeptides (e.g., enkephalins and endorphins) are present in the gastrointestinal tract and endocrine cells and modulate immune responses (9). Up-regulation of met-enkephelin and opioid receptors can be induced by a rebound effect by short-acting LDN (10). Higher levels of endogenous opioids and receptors inhibit cell proliferation which suppress T and B lymphocyte responses (11,12) and decrease production of pro-inflammatory interleukins-6 and -12 (13). In light of the Crohn's disease LDN literature and similar experiences with other inflammatory conditions in our clinic (14,15), LDN was administered to a sarcoidosis patient with severe fatigue, sarcoid rash, and marked radiographic evidence of gastrointestinal involvement. (Sarcoidosis Vasc Diffuse Lung Dis 2017; 34: 184-187).

Low dose naltrexone for induction of remission in Crohn's disease

BACKGROUND

Crohn's disease is a transmural, relapsing inflammatory condition afflicting the digestive tract. Opioid signalling, long known to affect secretion and motility in the gut, has been implicated in the inflammatory cascade of Crohn's disease. Low dose naltrexone, an opioid antagonist, has garnered interest as a potential therapy.

OBJECTIVES

The primary objective was to evaluate the efficacy and safety of low dose naltrexone for induction of remission in Crohn's disease.

SEARCH METHODS

A systematic search of MEDLINE, EMBASE, CENTRAL, and the Cochrane Inflammatory Bowel Disease and Functional Bowel Disorders Review Group Specialized Register was performed from inception to February 2013 to identify relevant studies. Abstracts from major gastroenterology conferences including Digestive Disease Week and United European Gastroenterology Week and reference lists from retrieved articles were also reviewed.

SELECTION CRITERIA

Randomized controlled trials of low dose naltrexone (LDN) for treatment of active Crohn's disease were included.

DATA COLLECTION AND ANALYSIS

Data were analyzed on an intention-to-treat basis using Review Manager (RevMan 5.2). The primary outcome was induction of clinical remission defined by a Crohn's disease activity index (CDAI) of < 150 or a pediatric Crohn's disease activity index (PCDAI) of < 10. Secondary outcomes included clinical response (70- or 100-point decrease in CDAI from baseline), endoscopic remission or response, quality of life, and adverse events as defined by the included studies. Risk ratios (RR) and 95% confidence intervals (CI) were calculated for dichotomous outcomes. The methodological quality of included studies was evaluated using the Cochrane risk of bias tool. The overall quality of the evidence supporting the primary outcome and selected secondary outcomes was assessed using the GRADE criteria.

MAIN RESULTS

Two studies were identified (46 participants). One study assessed the efficacy and safety of 12 weeks of LDN (4.5 mg/day) treatment compared to placebo in adult patients (N = 34). The other study assessed eight weeks of LDN (0.1 mg/kg, maximum 4.5 mg/day) treatment compared to placebo in pediatric patients (N = 12). The primary purpose of the pediatric study was to assess safety and tolerability. Both studies were rated as having a low risk of bias. The study in adult patients reported that 30% (5/18) of LDN treated patients achieved clinical remission at 12 weeks compared to 18% (3/16) of placebo patients, a difference that was not statistically significant (RR 1.48, 95% CI 0.42 to 5.24). The study in children reported that 25% of LDN treated patients achieved clinical remission (PCDAI < 10) compared to none of the patients in the placebo group, although it was unclear if this result was for the randomized placebo-controlled trial or for the open label extension study. In the adult study 70-point clinical response rates were significantly higher in those treated with LDN than placebo. Eighty-three per cent (15/18) of LDN patients had a 70-point clinical response at week 12 compared to 38% (6/16) of placebo patients (RR 2.22, 95% CI 1.14 to 4.32). The effect of LDN on the proportion of adult patients who achieved a 100-point clinical response was uncertain. Sixty-one per cent (11/18) of LDN patients achieved a 100-point clinical response compared to 31% (5/16) of placebo patients (RR 1.96, 95% CI 0.87 to 4.42). The proportion of patients who achieved endoscopic response (CDEIS decline > 5 from baseline) was significantly higher in the LDN group compared to placebo. Seventy-two per cent (13/18) of LDN patients achieved an endoscopic response compared to 25% (4/16) of placebo patients (RR 2.89; 95% CI 1.18 to 7.08). However, there was no statistically significant difference in the proportion of patients who achieved endoscopic remission. Endoscopic remission (CDEIS < 3) was achieved in 22% (4/18) of the LDN group compared to 0% (0/16) of the placebo group (RR 8.05; 95% CI 0.47 to 138.87). Pooled data from both studies show no statistically significant differences in withdrawals due to adverse events or specific adverse events including sleep disturbance, unusual dreams, headache, decreased appetite, nausea and fatigue. No serious adverse events were reported in either study. GRADE analyses rated the overall quality of the evidence for the primary and secondary outcomes (i.e. clinical remission, clinical response, endoscopic response, and adverse events) as low due to serious imprecision (sparse data).

AUTHORS' CONCLUSIONS

Currently, there is insufficient evidence to allow any firm conclusions regarding the efficacy and safety of LDN used to treat patients with active Crohn's disease. Data from one small study suggests that LDN may provide a benefit in terms of clinical and endoscopic response in adult patients with active Crohn's disease. Data from two small studies suggest that LDN does not increase the rate of specific adverse events relative to placebo. However, these results need to be interpreted with caution as they are based on very small numbers of patients and the overall quality of the evidence was rated as low due to serious imprecision. Further randomized controlled trials are required to assess the efficacy and safety of LDN therapy in active Crohn's disease in both adults and children. One study is currently ongoing (NCT01810185).