Tetrahydrocannabinol (THC), the major psychoactive component of marijuana, is a cannabinoid agonist that exerts its effects by activating at least two specific receptors (CB1 and CB2) that belong to the seven transmembrane G-protein coupled receptor (GPCR) family. Both CB1 and CB2 mRNA and proteins are present in the heart. THC treatment was beneficial against hypoxia in neonatal cardiomyocytes in vitro. We also observed a neuroprotective effect of an ultra low dose of THC when applied to mice before brain insults. The present study was aimed to test and characterize the cardioprotective effects of a very low dose (0.002mg/kg) of THC which is 3-4 orders of magnitude lower than the conventional doses, administered before myocardial infarction in mice in vivo. Three regimens of THC administration were tested: single THC application 2h or 48h before the induction of infarct, or 3 weeks continuous treatment before MI. All protocols of THC administration were found to be beneficial. In the case of THC treatment 2h before MI, fractional shortening was elevated (37±4% vs. 42±1%, p<0.04), troponin T leakage to the blood was reduced (14±3ng/ml vs. 10±4ng/ml, p<0.008), infarct size decreased (29±4% vs. 23±4%, p<0.02), and the accumulation of neutrophils to the infarct area declined (36±10cells/field vs. 19±4cells/field, p<0.007) in THC- compared to vehicle-pretreated mice, 24h after MI. ERK1/2 phosphorylation following infarct was also inhibited by pre-treatment with THC (p<0.01).
Conclusion: A single ultra low dose of THC before ischemia is a safe and effective treatment that reduces myocardial ischemic damage.
Copyright © 2013 Elsevier Inc. All rights reserved.
- Tetrahydrocannabiol (THC);
Figures and tables from this article:
- Fig. 1. Echocardiographic studies 24 h after MI of vehicle- and THC (0.002 mg/kg, i.p.) – treated mice. The figure demonstrates left ventricular end systolic diameter (ESD) and left ventricular end diastolic diameter (EDD) of sham and infarcted hearts with the 2 h vehicle or THC pretreatment (A and B). Fractional shortening (FS) of sham and infarcted hearts were compared with THC pretreated mice (C). Heart rates of the four groups are also presented (D). Values represent mean ± SD, n = 3 mice in each sham group, n = 12 mice in each MI group. #p < 0.05 sham vs. MI, *p < 0.01 vehicle vs. THC (t test).
- Fig. 2. The effect of 2 h pretreatment with THC on cardiac damage caused by 24 h of LAD ligation: Infarct size was determined by scanning the images of mice heart ventricular sections stained with triphenyl tetrazolium chloride. Representative images of vehicle pretreated (left) and THC pretreated (2 h) mice (right) are shown and relative area of injury (indicated by arrow) was calculated as percentage of total left ventricle area of the section. n = 8–10 hearts in each group, *p < 0.01(t test) (A). Measurements of troponin T in vehicle pretreated and THC pretreated mice. The release of troponin T serum was measured 24 h post LAD ligation, n = 7–8 in sham groups, n = 10–14 hearts in MI groups. #p < 0.001 sham vs. MI, *p < 0.04 (t test) vehicle vs. THC (B). Values represent mean ± SD.
- Fig. 3. The inflammatory response after THC pretreatment (2 h): Hematoxylin and Eosin staining, magnification × 100, showed massive cardiac damage (long arrow) and leukocyte infiltration (short arrow) to the hearts 24 h post MI compared to sham operated mice. The cardiac damage and leukocyte infiltration were reduced by THC pretreatment (A-D). Immunohistochemistry for neutrophils with rat anti-mouse neutrophil antibody (MCA771GA), magnification ×200, showed neutrophil infiltration (indicated by arrows) in MI groups that was reduced by THC pretreatment (2 h pre MI) (E-H). Quantification of immunohistochemistry staining for neutrophils by counting 5 randomly selected fields/slide (n = 3/group in sham groups and n = 6/group in MI groups). Significant neutrophil infiltration was observed in vehicle-pretreated mice hearts 24 h post MI, compared to the sham groups. Mice pretreated with THC showed significantly lower neutrophil infiltration. #p < 0.005 sham vs. MI, *p < 0.01 (t test) MI vs. MI mice pretreated (2 h pre MI) with THC (I). Cytokine expression of TNF-α in the serum 24 h after sham or MI operation (n = 4/group) was measured with ELISA, TNF-α level in the serum increased in mice 24 h post MI, compared to the sham groups; 2 h pretreatment with THC reduced TNF-α secretion 24 h post MI (J). Data are expressed as mean ± SD.
- Fig. 4. Extracellular signal-regulated kinase (ERK) activity: The levels of phosphorylated (P)-ERK and total (T)-ERK in the left ventricle were determined by densitometric analysis of Western blots. C57BL mice were subjected to either sham operation (control) or LAD ligation (MI) and sacrificed 24 h later (n = 7 each). P-ERK was significantly elevated in the infarcted mice (p < 0.02, t-test) while there was no effect on total ERK, resulting in a significant increase of 250% in ERK activity (P/T-ERK; p < 0.04) (A). C57BL mice were injected with vehicle (n = 7) or 0.002 mg/kg THC (n = 8) 2 h before MI and the levels of P-ERK and T-ERK in their left ventricles 24 h after the insult were determined by densitometric analysis of Western blots. Pretreatment with THC induced a significant reduction in P-ERK levels in the left ventricles of the infarcted mice (p < 0.01, t test) without affecting T-ERK levels. Thus, a significant reduction of 78% in ERK activity was found in THC-injected compared to vehicle-injected infarcted mice (*p < 0.01) (B). Data are expressed as mean ± SD.
- Fig. 5. Cardioprotection by THC (0.002 mg/kg, i.p.) applied 48 h before MI: Cardioprotection was studied 24 h after MI in vehicle or in THC pretreated mice. These studies demonstrated increased fractional shortening (FS) in THC-pretreated compared to vehicle-pretreated mice (n = 7–12, *p < 0.001, t test) (A); reduced infarct size (indicated by arrow) in mice pretreated with THC(right) compared to vehicle (left) pretreated mice (n = 7–12, *p < 0.001, t test) (B); reduced neutrophil infiltration to the infarcted area (n = 6, *p < 0.03, t test) (C); and decreased TNF-α levels in the serum 24 h after MI (n = 4/group, not significant) (D). Values represent mean ± SD.
- Fig. 6. Cardioprotection by continuous pretreatment with THC (0.002 mg/kg, i.p.) Mice were treated with vehicle or THC for 3 weeks (3 injections per week) before MI. Cardioprotection was assessed 24 h after MI. These studies demonstrated increased fractional shortening (FS) in THC-pretreated compared to vehicle-pretreated mice (n = 11–12, *p < 0.004, t test) (A); reduced infarct size (indicated by arrow) in mice pretreated with THC (right) compared to vehicle (left) pretreated mice (n = 11–12, *p < 0.03, t test) (B); reduced neutrophil infiltration to the infarcted area (n = 6, *p < 0.05, t test) (C); and decreased TNF-α levels in the serum 24 h after MI (n = 6/group) (*p = 0.05, t test) (D). Values represent mean ± SD.
Copyright © 2013 Elsevier Inc. All rights reserved.