Cannabinoids ameliorate pain and reduce disease pathology in cerulein-induced acute pancreatitis

Abstract

Background & aims: The functional involvement of the endocannabinoid system in modulation of pancreatic inflammation, such as acute pancreatitis, has not been studied to date. Moreover, the therapeutic potential of cannabinoids in pancreatitis has not been addressed.

Methods: We quantified endocannabinoid levels and expression of cannabinoid receptors 1 and 2 (CB1 and CB2) in pancreas biopsies from patients and mice with acute pancreatitis. Functional studies were performed in mice using pharmacological interventions. Histological examination, serological, and molecular analyses (lipase, myeloperoxidase, cytokines, and chemokines) were performed to assess disease pathology and inflammation. Pain resulting from pancreatitis was studied as abdominal hypersensitivity to punctate von Frey stimuli. Behavioral analyses in the open-field, light-dark, and catalepsy tests were performed to judge cannabinoid-induced central side effects.

Results: Patients with acute pancreatitis showed an up-regulation of cannabinoid receptors and elevated levels of endocannabinoids in the pancreas. HU210, a synthetic agonist at CB1 and CB2, abolished abdominal pain associated with pancreatitis and also reduced inflammation and decreased tissue pathology in mice without producing central, adverse effects. Antagonists at CB1- and CB2-receptors were effective in reversing HU210-induced antinociception, whereas a combination of CB1- and CB2-antagonists was required to block the anti-inflammatory effects of HU210 in pancreatitis.

Conclusions: In humans, acute pancreatitis is associated with up-regulation of ligands as well as receptors of the endocannabinoid system in the pancreas. Furthermore, our results suggest a therapeutic potential for cannabinoids in abolishing pain associated with acute pancreatitis and in partially reducing inflammation and disease pathology in the absence of adverse side effects.

Figure 1

Induction of the endocannabinoid system in acute pancreatitis. Immunohistochemical detection of CB1 and CB2 is shown in human pancreas (A–C and G–I) or mouse pancreas (D–F and J–L) derived either from control subjects (A, D, G, and J) or subjects with acute pancreatitis (B and C, E and F, H and I, K and L). (C, F, I and L) Areas of necrosis within human and mouse acute pancreatitis are indicated by dotted lines. In normal human pancreas (A) CB1-immunoreactivity in acinar cells (▶; magnified in inset C), ducts (→), and nerves (magnified in insets), was weak but strong in acute pancreatitis (B, C). (D–F) Similarly, pancreas demonstrated increased immunoreactivity for CB1 after induction of acute pancreatitis with cerulein (E, F) over normal mouse pancreas (D). Intense CB1 immunostaining is observed on acinar cell necrosis (dotted arrow; F). (G–I) Moderate staining for CB2 is seen in normal human pancreas (G) with a slight increase in acute pancreatitis (H, I) in acinar cells (▶; magnified in inset I), ducts (→), and nerves (magnified in insets). Upon induction of acute pancreatitis in mice, there is a pronounced increase in CB2 immunoreactivity over expression levels in normal mouse pancreas (J–L). This is particularly present within acinar cell necrosis (dotted arrow; L). Original magnification: 40x (A and B, D and E, G and H, J and K) or 80x (F and L; insets in A–C and G–I) objective. (M, N) Immunoblot analysis of pancreas samples derived from acute pancreatitis (lanes 1–3) and control human donors (lanes 4–6) with antibodies recognizing CB1 (M) or CB2 (N). (▶) indicates anti-CB1 (at approximately 128 kDa) and anti-CB2-immunoreactive bands (at 38 and 26 kDa), which were abolished by preadsorption with the respective blocking peptide (lower lanes). Anti-ERK2 was used as an equal loading control. (O) In humans, pancreatic concentrations of the endocannabinoid anandamide (AEA) are higher in acute pancreatitis (black bars) than in normal pancreas (white bars; P < .05), whereas levels of combined 1- plus 2-arachidonoylglycerol (1 - AG + 2 - AG) are unchanged.

Figure 2

Levels of serological, molecular, and inflammatory markers in acute pancreatitis and effects of CB1/CB2 antagonists. (A) Levels of serum lipase, pancreatic MPO, and the pancreatic wet weight/dry weight ratio are increased in mice following cerulein-induced pancreatitis (black bars) over control animals (white bars; * P < .05). (B) Pancreatic levels of IL-6 protein and KC1 mRNA (normalized to GAPDH expression levels) rise significantly following induction of acute pancreatitis. Treatment with cannabinoid receptor antagonists AM251 or AM630 either alone or in combination did not change levels of these parameters, except pancreatic KC1 mRNA expression (P < .05). * and ^# represent P < .05 as compared with the saline group or the cerulein group, respectively. (*) Mann–Whitney U test. (^#) Analysis of variance followed by post hoc Bonferroni’s multiple comparison test. n.s. = statistically not significant.

Figure 3

Analysis of abdominal pain thresholds to graded pressure applied via von Frey filaments in saline- or cerulein-treated mice. Y-axes show frequency of withdrawals to von Frey filaments over 10 applications. (A) Cerulein-induced pancreatitis leads to hyperalgesia (increased response frequency to a force of 0.02g to 0.16g) and allodynia (increased response frequency to 0.008g) over saline-injected mice (control). (B–D) AM251, AM630, and a combination of both increase response thresholds significantly at some filament forces. Data are shown as mean ± SEM. *P < .05; analysis of variance with post hoc Bonferroni’s multiple comparison test.

Figure 4

Nature and receptor mechanisms of effects of a cannabinoid agonist (HU210) on serological, molecular, and inflammatory markers in acute pancreatitis. Subcutaneous treatment with HU210 (0.05 mg/kg intraperitoneally) led to decreased serum lipase (P = .015), pancreatic MPO levels, and pancreatic IL-6 levels (P = .001 and P = .02, respectively; A, B), which was reversed completely by a combination of AM251 and AM630 (^#P < .05). Pancreatic edema (as judged by wet weight/dry weight ratio) was significantly reduced by HU210 (P = .007) with a tendency toward reversal by CB receptor antagonists (P > .05). Data are shown as mean ± SEM. *^,#P < .05; Mann–Whitney U test. (*) analysis of variance with post hoc Bonferroni’s multiple comparison test (^#).

Figure 5

Nature and receptor mechanisms of effects of a cannabinoid agonist (HU210) on abdominal pain thresholds to graded pressure applied via von Frey filaments in cerulein- or saline-treated mice. Y-axes show frequency of withdrawals to von Frey filaments over 10 applications. (A) HU210 (0.05 mg/kg intraperitoneally) completely reversed cerulein-induced hyperalgesia (increased response frequency to a force of 0.02g to 0.16g) and allodynia (increased response frequency to 0.008g) and produced analgesia. (B) In control mice (saline-injected), HU210 treatment did not affect nociceptive responses by itself. (C–E) Pretreatment with AM251, with AM630, or a combination of both blocked HU210-induced analgesia in cerulein-injected mice. Data are shown as mean ± SEM. *P < .05; analysis of variance with post-hoc Bonferroni’s multiple comparison test.

Figure 6

Effects of HU210 (0.05 mg/kg intraperitoneally) on locomotor activity, anxiety, and grooming in mice with acute pancreatitis. (A) In the open-field test, the numbers of rearings (vertical activity, A), of grid crosses (horizontal activity, A), and of time in inner rows (center time, A) is not affected by HU210. (B) HU210 treatment does not affect the frequency of grooming in the open-field test and time spent in the dark chamber in the light-dark test for evaluation of anxiety. Co-administration of AM251 or AM630 has no significant effects in any of the previously mentioned tests. (C) HU210 (0.05 mg/kg) did not induce freezing behavior in the ring catalepsy test.