Pharmacological Basis for Medical Use of Flaxseed (Linum usitatisimum) in Inflammatory Bowel Disease

Abstract

Inflammatory bowel disease (IBD) comprising of Ulcerative colitis (UC) and Crohn’s disease (CD) is a multifactorial disease with major maneuvering targets being immune dysregulation, microbial homeostasis, and barrier dysfunctioning. Natural products which comprise of multiple bioactive constituents could control multiple targets of a disease simultaneously. Flaxseed has traditionally been used in IBD but its effectiveness has not yet been pharmacologically validated. Hence, it was aimed to explore the pharmacological basis for medicinal use of Flaxseed in IBD. For this purpose, methanolic-aqueous (70:30) extract of Flaxseed (Fs.Cr), was used to test the different parameters of IBD. This was followed by screening of Flaxseed oil for its potential in IBD. Fs.Cr was at first assessed for its effect against acetic acid (AA)-induced colitis model of mice. Colitis was induced under anaesthesia by intrarectal administration of 0.1 ml of 6% AA, and the parameters were assessed after 24 hrs of induction. Fs.Cr reduced the disease activity index (DAI) dose-dependently at 150 mg/kg and 300 mg/kg and macroscopic damage with the highest ulcer index (21.88) for untreated groups, whereas, pre-treatment of animals with Fs.Cr, significantly reduced this ulcer index to 11.68, 7.83 and 6.01 at 150, 300 and 500 mg/kg doses respectively, as compared to untreated group. Hemotoxylin and Eosin stained sections of colon in Fs.Cr treated groups, showed reduction in Neurath scores, where untreated mice had a score of 3.48±0.65 (max score = 4) and Fs.Cr pretreated mice showed a reduction in score to 2.33±0.57 and 1.56±0.5 at 150 mg/kg and 300 mg/kg respectively. Vilaseca score parameters (including ulceration, inflammation and depth of lesion) with untreated groups score being 2.08±0.275 reduced significantly to 1.51±0.2 and 1.08±0.14 at 150 mg/kg and 300 mg/kg doses, respectively. Periodic acid Schiff-alcian blue (PAS-Ab) stains showed an increase in mucin levels and restoration of goblet cells in the treated groups with a score of 1.50±0.25, 2.100±0.25 and 2.3±0.5 with increasing doses of 150 mg/kg, 300 mg/kg and 500 mg/kg respectively, as compared to the untreated mice groups who had the lowest scores (1.2±0.37 out of 3). Anti-inflammatory potential of Fs.Cr was evidently supported by the reduced myeloperoxidase activity with untreated animals exhibiting activity at 400±59.5 mU/ml, which reduced to 150.85±65 mU/ml and 107±13.89mU/ml at at 150 mg/kg and 300 mg/kg doses, respectively. Its effect against oxidative stress was evident by reduced malondialdehyde activity, where untreated mice exhibited 77.25±4 nmol/mg activity, whereas this reduced to 49.66±4.88 nmol/mg and 26.36±2.14 nmol/mg at respective doses of 150 mg/kg and 300 mg/kg. Enhanced antioxidant activity (catalase, superoxide dismutase, glutathione peroxidase and total glutathione) in Fs.Cr groups was significantly higher than both the untreated control as well as sham control, evident at 300 mg/kg and 500 mg/kg doses. Anti-inflammatory effect of Fs.Cr was characterized by its effect on modulation of cytokines. Colons of untreated mice showed elevated levels of IFN- (a pro-inflammatory marker), as compared to sham controls at all the time points (1238±195.2 pg/ml, 859±100.9 pg/ml and 943.2±177.8 pg/ml). Compared to this, the colons of Fs.Cr pretreated mice showed reduced IFN-levels to 605±62.17 pg/ml and 492.7±37.96 pg/ml at 6 hrs for 150 and 300 mg/kg doses with similar reducing trend evident at 12 hrs and 24 hrs. TNF-levels were also elevated in untreated mice colons’ at all time points 194.1±27.36 pg/ml, 110.3±3.39 pg/ml and 142.4±4.93 pg/ml), whereas Fs.Cr pre-treated groups showed a reduction in these levels, with effect evident at 300 mg/kg and 500 mg/kg at all the tested time points. Kinetics of IL-17 levels was studied in AA-induced colitis model for the first time. Untreated groups showed increased IL-17 levels at 6 hrs (233.2±18.41 pg/ml), and sharply decreased levels at 12 hrs (166.1±32.26 pg/ml) and 24 hrs (114.2±16.29 pg/ml). On the contrary, Fs.Cr-treated tissues showed insignificant decline of IL-17 at 6 hrs, but exhibited a dose-dependent increase at 24 hrs with 175.9±31.1 pg/ml at 150 mg/kg dose, 209±29.85 pg/ml for 300 mg/kg dose and 223.8±13.69 pg/ml for 500 mg/kg dose. Hence, it was concluded that Fs.Cr ameliorated the severity of AA-induced colitis model of mice by mucosal protective, anti-inflammatory and antioxidant mechanisms with modulation of multiple cytokines.Diarrhea and spasm are the main manifestation of IBD and hence, Fs.Cr was also assessed for its effectiveness in diarrhoea and spasm along with possible mechanisms. Fs.Cr showed antidiarrheal activity in castor oil-induced diarrhea in mice with mean diarrhoeal score being 35.7±0.81 for untreated mice, whereas, Fs.Cr significantly reduced the diarrhoeal score to 21.6±2.85, 13±2.13 and 11.3±1.35 at 150, 300 and 500 mg/kg doses. Reduced intestinal secretions in mice were evident in Fs.Cr treated groups as compared to untreated groups whose intestinal secretions were increased from 77.35±1.52g (sham control) to 149±5.90 g (untreated), whereas, Fs.Cr pretreated groups showed secretions significantly being reduced to 24.12% (113±5.12 g), 28.09% (107±2.49 g) and 38.8% (91±3.06 g) at respective doses of 150, 300 and 500 mg/kg. Gut motility was increased in untreated controls by administration of castor oil that increased the charcoal meal transit from 45.68±1.96 cm to 68.43±3.95 cm, whereas, Fs.Cr reduced the intestinal motility in mice by 31.66% (46.76±3.46 cm), 46.98% (36.28±3.73 cm; and 56.2% (29.97±4.30 cm); at the respective doses of 150, 300 and 500 mg/kg. The main antispasmodic mechanism of Fs.Cr was mediated by phosphodiesterase enzyme inhibitory activity (PDEI), followed by Ca++ antagonist effect, as Fs.Cr dose-dependently inhibited spontaneous-induced contractions, carbachol (CCh)-induced contractions (at 3 mg/ml) and high K+-induced contractions (at 5 mg/ml), in isolated rabbit jejunum with higher potency against CCh, similar to that of papaverine, while verapamil was more potent against high K+. This was also supported by potentiation of isoprenaline concentration-response curves (CRCs) by pretreatment with low doses of Fs.Cr (0.01 and 0.03 mg/ml). Fs.Cr mediated PDE inhibitory activity via PDE-4 subtype, as pre-treatment of Fs.Cr did not potentiate Rolipram (PDE-4 inhibitor) inhibitory activity against CCh-induced contractions, whereas it potentiated the inhibitory effect of Cilostazol (PDE-3 inhibitor) and zaprinast (PDE-5 inhibitor). Subsequent dose dependent increase in cAMP levels after pre-treatment with 1, 3 and 5 mg/ml of Fs.Cr, similar to papaverine (1 M and 3 M doses), further supported its PDEI effect. Possible presence of Ca++ antagonist like activity was studied because of Fs.Cr’s inhibitory effect against high K+-induced contractions at high doses. Fs.Cr at 0.1 mg/ml and 0.3 mg/ml caused a rightward shift in the Ca++ CRCs with suppression of maximal response, indicating its Ca++ antagonist effect. Hence, Fs.Cr possessed antispasmodic effect mediated through a dual inhibition of PDE enzyme and Ca++ influx. Microbes being the persistent source of immune trigger and inflammation, Fs.Cr was therefore, also studied for its antimicrobial potential in the in vitro assay. Fs.Cr at the dose of 50 μg/ml showed cidal effect against enteropathogenic E. coli (EPEC), Pseudomonas aeruginosa and Bacillus cereus, whereas, a static effect was observed against enterotoxigenic E.coli (ETEC) and enteroaggregative E. coli (EAEC). The cidal activity against methicillin-resistant Staphylococcus aureus was observed at 12.5 mg/ml and at 5 mg/ml against vancomycin-resistant Enterococcus faecalis, along with remarkable 100% kill at 12.5 mg/ml indicating presence of some novel compounds. Interestingly, the HPLC peaks of Fs.Cr resembled with retention times of some synthetic antimicrobial compounds Further to this, Flaxseed oil which is an available edible source was studied for its potential in IBD. Flaxseed oil ameliorated the severity of AA-induced colitis as evident by improved DAI, mortality rate and microscopic damage. The comparison of microscopic damage caused by test materials revealed that Flaxseed oil exhibited a stronger effect on neutrophil infiltration as compared to Fs.Cr, whereas, Fs.Cr produced more pronounced increase on mucin levels indicating possibility for employing different mechanisms to mediate the protective effect. When studied for its potential against diarrhoea and spasm, Flaxseed oil showed a combination of laxative effect at low doses and antidiarrheal effect at high doses. The gut stimulant effect was prominently cholinergic and at lesser level histaminergic. The antispasmodic activity of Flaxseed oil was mediated by K+ channel opening (KCO) mechanism, followed by a weak PDEI activity as it inhibited CCh-induced contraction. Flaxseed oil was more potent and efficacious as bactericidal against enteropathogeni Eschericia.coli (EPEC), enterotoxigenic E.coli (ETEC) and enteroaggregative E.coli (EAEC) which are implicated in IBD, as they killed these microbes at 9 μg/ml and 14 μg/ml, whereas, Fs.Cr was only cidal against EPEC at a concentration 10 times higher than that of Flaxseed oil (100 μg/ml), whereas, it had a static mechanism against ETEC and EAEC. A different mechanism is speculated for Flaxseed oil and Fs.Cr; this is further advocated by difference in HPLC fingerprints of Fs.Cr and Flaxseed oil. Based on the above mentioned findings, it is concluded that Flaxseed extract and oil have potential for targeting multiple etiological aspects of IBD through multiple pathways; thus, indicating that Flaxseed as a whole has the potential to be used as alternate remedy with a known safety profile being edible in nature.