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Cannabidiol attenuates cardiac dysfunction, oxidative stress, fibrosis, inflammatory and cell death signaling pathways in diabetic cardiomyopathy Address correspondence to: Pál Pacher M.D., Marijuana use and heart-attack risk were correlated in a large human study, Stanford scientists and their collaborators found. A molecule in soybeans may counteract these effects.

Cannabidiol attenuates cardiac dysfunction, oxidative stress, fibrosis, inflammatory and cell death signaling pathways in diabetic cardiomyopathy

Address correspondence to: Pál Pacher M.D., Ph.D., F.A.P.S., F.A.H.A.; Chief, Section on Oxidative Stress Tissue Injury, Laboratory of Physiological Studies, National Institutes of Health/NIAAA, 5625 Fishers Lane, MSC-9413, Bethesda, Maryland 20892-9413, USA. Phone: (301)443-4830; Fax: (301)480-0257; [email protected]

Prof. Mechoulam is a consultant for GW Pharmaceuticals, UK. GW not involved in this publication and is unaware of it.

Associated Data

Abstract

Objectives

In this study, we have investigated the effects of cannabidiol (CBD) on myocardial dysfunction, inflammation, oxidative/nitrosative stress, cell death and interrelated signaling pathways, using a mouse model of type I diabetic cardiomyopathy and primary human cardiomyocytes exposed to high glucose.

Background

CBD, the most abundant nonpsychoactive constituent of Cannabis sativa (marijuana) plant, exerts antiinflammatory effects in various disease models and alleviates pain and spasticity associated with multiple sclerosis in humans.

Methods

Left ventricular function was measured by pressure-volume system. Oxidative stress, cell death and fibrosis markers were evaluated by molecular biology/biochemical techniques, electron spin resonance spectroscopy and flow cytometry.

Results

Diabetic cardiomyopathy was characterized by declined diastolic and systolic myocardial performance associated with increased oxidative-nitrosative stress, NF-κB and MAPK (JNK and p-38, p38α) activation, enhanced expression of adhesion molecules (ICAM-1, VCAM-1), TNF-α, markers of fibrosis (TGF-β, CTGF, fibronectin, collagen-1, MMP-2 and MMP-9), enhanced cell death (caspase 3/7 and PARP activity, chromatin fragmentation and TUNEL) and diminished Akt phosphorylation. Remarkably, CBD attenuated myocardial dysfunction, cardiac fibrosis, oxidative/nitrosative stress, inflammation, cell death, and interrelated signaling pathways. Furthermore, CBD also attenuated the high glucose-induced increased reactive oxygen species generation, NF-κB activation and cell death in primary human cardiomyocytes.

Conclusions

Collectively, these results coupled with the excellent safety and tolerability profile of cannabidiol in humans, strongly suggest that it may have great therapeutic potential in the treatment of diabetic complications, and perhaps other cardiovascular disorders, by attenuating oxidative/nitrosative stress, inflammation, cell death and fibrosis.

Introduction

Cardiovascular complications are the leading cause of morbidity and mortality in diabetic patients. Diabetic cardiomyopathy characterized by myocardial left ventricular dysfunction (both diastolic and later systolic one), independent of atherosclerosis and coronary artery disease, has been well documented in both humans and animals (1-3). The mechanism of diabetic cardiac dysfunction is complex and involves increased oxidative/nitrosative stress (4-7), activation of various downstream transcription factors, pro-inflammatory and cell death pathways such as NF-κB (8,9), poly(ADP-ribose) polymerase (PARP) (10), and MAPKs (11,12), inactivation of pro-survival pathways such as Akt (13), eventually culminating in cell death (14), changes in the composition of extracellular matrix with enhanced cardiac fibrosis and increased inflammation (15).

Various components of Cannabis sativa (marijuana) plant, termed cannabinoids (e.g. the most characterized active ingredient, the delta 9-tetrahydrocannabinol (THC)), exert potent analgesic effects through the activation of classic CB1 receptors located in the central nervous system and anti-inflammatory properties through the activation of CB2 cannabinoid receptors on immune cells (16). However, the major limitation of the therapeutic utility of THC is the development of centrally mediated CB1-depend psychoactive effects (16). Furthermore, CB1 receptor activation in the cardiovascular system by endocannabinoids may also contribute to the pathophysiology of multiple cardiovascular diseases including heart failure and atherosclerosis (17). In contrast to THC, cannabidiol (CBD), the most abundant cannabinoid of Cannabis sativa, which has been approved for the treatment of inflammation, pain and spasticity associated with multiple sclerosis in humans since 2005 in Canada (18), does not bind to these receptors (19), therefore it is devoid of psychoactive properties and has no potential to cause adverse cardiac toxicity (20). Importantly, CBD is well tolerated without side effects when chronically administered to humans (21,22). A previous study has demonstrated cardiac protection by CBD in myocardial ischemic reperfusion injury (23); therefore, we have investigated the potential protective effects of CBD in diabetic hearts and in primary human cardiomyocytes exposed to high glucose. Our findings underscore the potential of CBD for the prevention/treatment of diabetic complications.

Materials and Methods

Animals and treatment

All the animal protocols conformed to the National Institutes of Health (NIH) guidelines and were approved by the Institutional Animal Care and use Committee of NIAAA/NIH. Diabetes was induced in 8-12 weeks C57/BL6J mice weighing 23-25g (male, Jackson Laboratories, Bar Harbor, ME) by intraperitoneal (I.P.) injection of streptozotocin (STZ, Sigma, St. Louis, MO) at the dose of 50 mg/kg dissolved in 100 mM citrate buffer pH 4.5 for 5 consecutive days. After one week, blood glucose levels were measured using Ascensia Coutour Glucometer (Bayer HealthCare, NY) by mandibular puncture blood sampling. Mice which had blood sugar values >250 mg/dl were used for the study. In the first set of experiments 1 week diabetic mice were treated with cannabidiol (CBD; 1, 10 or 20 mg/kg I.P) or vehicle for 11 weeks (Suppl.Fig.1). In another set of experiments, 8 weeks diabetic mice were treated with CBD or vehicle for 4 weeks (Suppl.Fig.2). CBD was isolated as described earlier (24). The corresponding control groups were treated with either vehicle or CBD alone for the same duration. All the animals were provided with food and water ad libitum.

Hemodynamic measurements in mice

Left ventricular performance was measured in mice anesthetized with 2% isoflurane as previously described (25) (26).

Determination of SOD activity, MDA, GSH, GSSG, 4-HNE, protein carbonyl content

SOD activities and reduced/oxidized glutathione (GSH, GSSG), malondialdehyde (MDA), 4-HNE, protein carbonyl levels in the myocardial tissues were determined as described in the appendix.

Determination of myocardial ROS by electron paramagnetic resonance spectrometer (EPR) is described in the appendix.

Reverse transcription and real time PCR

Preparation of samples and reverse transcription and real time PCR experiments from heart tissues and the primers are described in the appendix and Suppl. Table1.

Determination of PARP, caspase 3/7 activities, chromatin fragmentation, TUNEL and 3-nitrotyrosine (3-NT) content

PARP and caspase 3/7 activities, chromatin fragmentation, TUNEL, and 3-nitrotyrosine (3-NT) content in the heart homogenates and/or human cardiomyocyte extracts are described in the appendix.

Western immunoblot analysis

Sample preparations, Western immunoblot analysis and sources of antibodies are described in the appendix.

Immunohistochemistry

The immunohistochemistry/staining from frozen or formalin-fixed myocardial tissues (nitrotyrosine, TUNEL, Sirius red) is described in the appendix.

Cell culture studies

Human cardiomyocytes (HCM) along with the culture medium were purchased from ScienCell Research Laboratories (Carlsbad, CA) and were maintained and treated as described in the appendix.

Simultaneous determination of cytosolic and mitochondrial ROS generation and apoptosis by flow cytometry

Mitochondrial superoxide/ROS generation and cell death were determined as described (27) and detailed in the appendix.

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Statistical analysis

Results are expressed as mean±SEM. Statistical comparisons were made by one way ANOVA followed by Newman-Keuls post-hoc analysis using GraphPad Prism 5 software (San Diego, CA). When heterogeneity of variance was present, ANOVA was performed after logarithmic transformation of the data. Probability values of P

Results

Blood glucose levels, pancreas insulin content and body weights

Diabetic animals exhibited increased blood glucose levels (Suppl. Figs.1A&2A) with the decrease in the body weight (Suppl. Fig.1D). Diabetic animals also had increased glycosylated hemoglobin (HbA1c) levels with concomitant decline in the pancreas insulin content (Suppl. Fig. 1B/2B). CBD or vehicle treatment (1, 10 or 20 mg/kg I.P) for 11 or 4 weeks, did not significantly alter the body weight/blood glucose level/pancreas insulin content neither in control nor in diabetic animals (Suppl. Figs.1& 2).

CBD treatment attenuates diabetes-induced hemodynamic alterations

12 weeks of established diabetes was associated with impaired diastolic and systolic left ventricular function, which was largely attenuated by the treatment with CBD for 11 weeks (starting 1 week after the establishment of diabetes)( Fig.1 ). CBD treatment also improved the diabetes-induced myocardial dysfunction when it was given for 4 weeks in 8 weeks diabetic mice (Suppl.Fig.3.).

A) Representative pressure–volume (P–V) loops at different preloads after inferior vena cava occlusion, showing differences in the end-systolic and end-diastolic P–V relations (ESPVR and EDPVR) in control and diabetic mice treated with vehicle or cannabidiol (CBD). The shift of P-V loops right and changed slope of ESPVR and EDPVR in diabetic mice indicates decreased systolic and diastolic functions, which were less pronounced in diabetic mice treated with CBD (20 mg/kg/day) for 11 weeks. B) 12 weeks of diabetes was associated with decrease in left ventricular systolic pressure (LVSP), maximum first derivative of ventricular pressure with respect to time (+dP/dt), stroke work, ejection fraction, cardiac output, and load-independent indexes of contractility (preload-recruitable stroke work (PRSW), dP/dt–end-diastolic volume relation (dP/dt-EDV), and end-systolic pressure–volume relation (Emax), respectively), and an increase in left ventricular end-diastolic pressure (LVEDP) and prolongation of relaxation time constants (τ Weiss and Glantz), which were largely attenuated by CBD treatment (20 mg/kg/day I.P.) for 11 weeks. Results are mean±SEM of 8-11/group. *P

CBD treatment attenuates diabetes-induced myocardial oxidative stress

There was increased accumulation of lipid peroxides ( Fig.2A,B ), protein carbonyls ( Fig.2C ), ROS generation ( Fig.2D ), expression of mRNA of various ROS generating NADPH oxidases (p22phox,p67phox, gp91phox; Fig.2E ) with concordant decrease of GSH/GSSG ratio ( Fig.2F ) and attenuated activity of the superoxide eliminating enzyme, the superoxide dismutase (SOD) ( Fig.2G ) in hearts of diabetic mice. These changes were attenuated when mice were treated with CBD for 11 weeks during the course of the diabetes ( Fig.2A-G ).

Oxidative stress in the myocardial tissues were determined by measuring (A) MDA, (B) 4-HNE, (C) protein carbonyls content and (D) ROS levels by EPR as described in the Methods section and the (E) NADPH oxidase subunits mRNA expression by real time RT-PCR (F) endogenous antioxidants (GSH) content and (G) SOD activity. *PD], n=6-9/group.

CBD treatment attenuates diabetes-induced myocardial NF-κB activation and inflammation

As shown in ( Fig.3A ) there was a marked IκB-α degradation in the cytosol of diabetic hearts, with increased phosphorylation of IκB-α leading to release of active p65NF-κB, which subsequently translocates to the nucleus to induce the inflammatory and apoptotic gene expressions ( Fig.3B ). Gel shift assay also confirmed the NF-κB activation in diabetic hearts ( Fig.3C ). CBD treatment of diabetic mice inhibited the IκB-α and subsequent p65NF-κB nuclear translocation ( Fig.3A-C ). CBD treatment also inhibited the NF-κB-dependent mRNA and/or protein expression of adhesion molecules ICAM-1 and VCAM-1 ( Fig.3D,F ) and pro-inflammatory cytokine TNF-α ( Fig.3E,G ) respectively in the diabetic myocardial tissues.

(A) Western blot analysis demonstrates IκB-α expression and its phosphorylation in the cytosolic fraction and (B) the nuclear translocation of p65NF-κB in the nuclear fraction of the heart tissue homogenates. (C) Shows the gel shift assay demonstrating NF-κB activation. (D) Shows the mRNA expression of ICAM-1/VCAM-1 (E) TNF-α in the respective groups as indicated (F) Shows the western blot analysis for the protein expression of ICAM-1/VCAM-1 and (G) TNF-α protein in the myocardial tissues. *P

CBD treatments attenuates diabetes-induced nitrosative/nitrative stress

There was significant increase in inducible nitric oxide synthase (iNOS) expression ( Fig.4A ) and 3-nitrotyrosine (3-NT) accumulation ( Fig.4B-E ) in hearts of diabetic mice compared to vehicle or CBD alone treated mice. CBD treatment attenuated the diabetes-induced iNOS expression and 3-NT accumulation (marker of nitrosative/nitrative stress) ( Fig.4B-E ).

(A) iNOS expression was determined by Western immunoblot in the heart tissues (B) 3-NT levels in the heart samples were quantitatively determined by ELISA with indicated CBD concentration (mg/kg body weight) respectively. (C) Representative gel indicating the nitrated proteins analyzed by immunoprecipitation with 3-NT specific antibody (D) shows the representative images for the histochemical staining for 3-NT levels in the formalin-fixed myocardial tissues. (E) Depicts the immunofluorescence staining for 3-NT from frozen sections as described in methods. *P

CBD treatment attenuates diabetes-induced mitogen activated protein kinases (MAPKs) activation and apoptosis

There was marked increase in the p38MAPK ( Fig.5A ) and JNK ( Fig.5B ) activation in the myocardial tissues of diabetic mice. In addition, there was marked activation p38αMAPK ( Fig.5C ) and slightly diminished p38βMAPK ( Fig.5C ) in the diabetic myocardium. There was also activation of MAPKAPK-2 in the diabetic heart ( Fig.5D ). CBD treatment for 11 weeks significantly mitigated p38MAPK/JNK/p38αMAPK/MAPKAPK-2 activation, while it was not effective in restoring the p38βMAPK levels. In addition, Akt activation was also significantly hampered in the diabetic myocardium, which was attenuated with CBD treatment ( Fig.5E ). In diabetic myocardium there was marked increase in caspase 3 cleavage, caspase 3/7 activity ( Fig.6A,B ), chromatin fragmentation and PARP activity ( Figs.6C,D ), and enhanced apoptosis ( Fig.6E and Fig.7 ); all these changes in diabetes were attenuated by CBD treatment.

Western blot analysis shows the (A) p38MAPK (B) JNK (C) p38α/βMAPK (D) MAPKAPK-2 and (E) Akt activation in the myocardial tissues. P

(A) Western blot analysis for the caspase 3 and (B) caspase 3/7 activity (C) chromatin fragmentation and (D) PARP activation and (E) quantitative TUNEL assay was performed as described in Methods. *P

Shown are the representative TUNEL images in the diabetic myocardium and mice that were treated with CBD for 11 weeks. For details see the supplemental methods.

CBD treatment attenuates diabetes-associated myocardial fibrosis

Real time RT-PCR analysis revealed significant increases in the pro-fibrotic gene expressions ( Fig.8A ) and in collagen deposition ( Fig.8B ) in diabetic hearts, and these were attenuated by CBD ( Fig.8 ).

CBD post-treatment following the establishment of diabetic cardiomyopathy attenuates diabetes-induced myocardial oxidative/nitrosative stress, cell death and fibrosis

Remarkably, CBD 20 (mg/kg) treatment also attenuated the diabetes-induced increased myocardial nitrative stress, cell death (Suppl.Fig.4) and fibrosis (Suppl.Fig.5) when it was given for 4 weeks in 8 weeks diabetic mice.

CBD treatment attenuates high glucose (HG)-induced cytosolic and mitochondrial ROS generation and 3-NT formation in human cardiomyocytes (HCM)

HG treatment of HCM for 48 hrs markedly increased cytosolic (Suppl.Fig.6A) and mitochondrial (Suppl.Fig.6B) ROS/superoxide generation compared to cells treated with either D-glucose 5 mM, L-glucose 30 mM, or CBD (4μM) alone for the same duration. CBD markedly attenuated the HG-induced increased ROS generation (Suppl. Fig.6A,B) and 3-NT accumulation in HCM (Suppl. Fig.6C).

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CBD mitigates HG-induced NF-κB activation and apoptosis in HCM

HG treatment induced NF-κB activation (Suppl.Fig.7A,B) and increased apoptosis and PARP-dependent cell death in cardiomyocytes (Suppl.Fig.8A,B); the anti-apoptotic activity of CBD was mediated, at least in part, via its ability to modulate Akt activity (Suppl. Fig.8A).

Discussion

Accumulating evidence suggests that increased oxidative/nitrosative stress coupled with activation of various downstream pro-inflammatory and cell death pathways play pivotal role in the development of complex biochemical, mechanical and structural alterations associated with diabetic cardiomyopathy (11,14,15) (3,4,6,12). However, in spite of the accumulating knowledge obtained during the past decades, the treatment of diabetic cardiomyopathy still remains poor and largely symptomatic (1,2).

Cannabidiol, a nonpsychoactive component of marijuana, has been shown to exert anti-inflammatory and antioxidant effects both in vitro and in various preclinical models of neurodegeneration and inflammatory disorders, independent from classical CB1 and CB2 receptors (20). Furthermore, CBD has recently been reported to lower the incidence of diabetes in non-obese diabetic mice (28) and to preserve the blood-retinal barrier in experimental diabetes (29).

In the present study, we have evaluated the effects of CBD treatment (for 11 weeks administered after the destruction of pancreatic beta cells and development of frank type 1 diabetes, as well as in 8 weeks diabetic animals for 4 weeks) on myocardial dysfunction, inflammation, oxidative/nitrosative stress, cell death and interrelated signaling pathways, using a mouse model of type I diabetic cardiomyopathy or primary human cardiomyocytes exposed to high glucose. Since significant cardiac dysfunction in this model starts to develop from 4 weeks of established diabetes (4,10) with gradually increasing fibrosis thereafter (12,15) (peaking around 8 weeks of established diabetes), in the first treatment protocol (Suppl.Fig.1A.) we aimed to study if CBD treatment can prevent the development of characteristic alterations of type I diabetic cardiomyopathy, in the second (Suppl.Fig.2A) if it is able to reverse these changes once they already developed.

Consistently with previous reports, diabetic cardiomyopathy was characterized by declined diastolic and systolic myocardial performance associated with enhanced myocardial expression of NADPH oxidase isoforms p22 phox , p67 phox , gp91 phox , attenuated antioxidant defense (decreased glutathione content and SOD activity) coupled with increased myocardial reactive oxygen species generation and lipid peroxidation (4,6,10,12,15). The high glucose-induced ROS generation besides inducing lipid peroxidation may also initiate activation of various stress signaling pathways (e.g. jun Nterminal kinase and p38 MAPK). Our results are also in agreement with previous studies demonstrating enhanced activation of p38 MAPK and its downstream effector (p38 MAPKAPK-2) in diabetic cardiomyopathy models and demonstrating that pharmacological inhibition of p38 MAPK signaling attenuates the expression of cardiac inflammatory markers, such as TNF-α, IL-1β, and IL-6, and collagen content associated with diabetic cardiomyopathy (11,12). Likewise, with recent evidence supporting an emerging role of p38α activation in diabetic cardiomyopathy (12), in addition to its already established role in mediating cell death during myocardial ischemic-reperfusion injury. The high glucose induced-ROS generation also impairs important pro-survival signaling pathways such as Akt in diabetic hearts (13), activates pro-inflammatory and cell death pathways such as NF-κB (8,9) and nuclear enzyme poly(ADP)-ribose polymerase 1(10), which in turn regulate expression of important pro-inflammatory cytokines, cell adhesion molecules and iNOS. The latter results in increased nitrosative/nitrative stress, which is also implicated in cardiovascular complications of diabetes (5). A recent study has also suggested that the NF-κB activation may induce increased oxidative stress and contributes to mitochondrial and cardiac dysfunction in type II diabetes(9). Importantly, the oxidative-nitrosative stress, stress signaling and inflammatory pathways in diabetic cardiomyopathy are closely interrelated eventually promoting the development myocardial fibrosis (3,9,11,15,30).

CBD treatment (Suppl.Fig.1.) was able to attenuate the oxidative-nitrosative stress (decreased the myocardial ROS generation and expression of p22 phox , p67 phox , gp91 phox , restored glutathione content and SOD activity, decreased 3-NT formation) and alterations of the above mentioned pro-survival (Akt) and stress signaling (p38, p38α, JNK) pathways in diabetic hearts. It also attenuated the NF-κB activation, expression of iNOS, TNFα, and ICAM-1, cell death and fibrosis in diabetic myocardium, and improved the associated characteristic functional alterations. Importantly, CBD treatment was able to attenuate/reverse (though to a lesser extent) some of the above mentioned diabetes-induced myocardial biochemical and functional changes following the establishment of diabetic cardiomyopathy with fibrosis (Suppl.Figs.2-5). CBD also attenuated the high glucose-induced increased reactive oxygen and nitrogen species generation, NF-κB activation and cell death in primary human cardiomyocytes (Suppl.Figs.6-8).

The above mentioned beneficial effects of CBD could be explain in part by its potent antioxidant properties, which was first suggested by the Nobel Prize winner Dr. Julius Axelrod (31). In Axelrod’s study CBD was more protective against glutamateinduced neurotoxicity than any of the well-know antioxidants (e.g. ascorbate or α-tocopherol), indicating additional cytoprotective effects of CBD beyond its potent antioxidant properties (31). Indeed, our recent results suggest that CBD may exert potent effects on key pro-inflammatory pathways such as NF-κB and on pro-survival signaling such as Akt in vivo, which is most likely not related to its antioxidant effect. This is also supported by observations that CBD decreases inflammation in models in which conventional antioxidants are not very effective (e.g. in arthritis (20,32)), as well as by recent studies demonstrating that CBD is a potent inhibitor of bacterial lipopolysaccharide-activated NF-κB proinflammatory pathway in microglia cells(33). These results are also in support of the emerging role of the inflammation in the development and progression of diabetic cardiomyopathy (9,11,15,30).

Collectively, our results strongly suggest that CBD may have tremendous therapeutic potential in the treatment of diabetic cardiovascular and other complications by attenuating diabetes-induced oxidative/nitrosative stress, inflammation, cell death and fibrotic pathways.

Marijuana linked to heart disease; supplement may mitigate risk, study reports

Marijuana use and heart-attack risk were correlated in a large human study, Stanford scientists and their collaborators found. A molecule in soybeans may counteract these effects.

April 29, 2022 – By Krista Conger

People who smoke marijuana more than once a month have an increased risk of heart attack and heart disease, Stanford researchers and their colleagues have found.
Dmytro Tyshchenko/Shutterstock.com

People who use marijuana have an increased risk of heart disease and heart attack, according to a large study led by researchers at Stanford Medicine.

The study also showed that the psychoactive component of the drug, known as THC, causes inflammation in endothelial cells that line the interior of blood vessels, as well as atherosclerosis in laboratory mice.

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The inflammation and atherosclerosis can be blocked by a small molecule called genistein that occurs naturally in soy and fava beans, the researchers found. Because genistein has limited brain penetration, it doesn’t inhibit THC’s ability to stimulate appetite, dull pain and tamp down nausea — characteristics vital to medicinal marijuana users.

“As more states legalize the recreational use of marijuana, users need to be aware that it could have cardiovascular side effects,” said Joseph Wu, MD, PhD, professor of cardiovascular medicine and of radiology, and the director of the Stanford Cardiovascular Institute. “But genistein works quite well to mitigate marijuana-induced damage of the endothelial vessels without blocking the effects marijuana has on the central nervous system, and it could be a way for medical marijuana users to protect themselves from a cardiovascular standpoint.”

In part because THC, or tetrahydrocannabinol, is a controlled substance in the United States and therefore strictly regulated in medical research, the investigators cautioned that the long-term health effects of regular use remain largely unclear.

“Marijuana has a significantly adverse effect on the cardiovascular system,” said instructor of medicine Mark Chandy, MD, PhD. “As more states legalize marijuana use, I expect we will begin to see a rise in heart attacks and strokes in the coming years. Our studies of human cells and mice clearly outline how THC exposure initiates a damaging molecular cascade in the blood vessels. It’s not a benign drug.”

Wu, who holds the Simon H. Stertzer, MD, Professorship, is the senior author of the study, which will be published online April 29 in Cell. Chandy shares lead authorship with former postdoctoral scholar Tzu-Tang Wei, PhD, and instructor Masataka Nishiga, MD.

THC and inflammation

The researchers analyzed the genetic and medical data of about 500,000 people ages 40-69. The data was from the UK Biobank. Nearly 35,000 participants reported smoking cannabis; of those, about 11,000 smoked more than once a month. The more-than-monthly smokers were significantly more likely than others in the study to have a heart attack after controlling for other factors including age, body mass index and sex. The researchers found that frequent marijuana smokers were also more likely than nonusers to have their first heart attack before the age of 50 — an unusual medical event called a premature heart attack that increases a person’s lifelong risk of subsequent heart attack, heart failure and life-threatening arrhythmias that can cause sudden death.

Inflammation of the blood vessels is a primary hallmark of atherosclerosis — the thickening of the vessel wall due to the buildup of plaques made up of fats, cholesterol and other substances — which can lead to heart attack. The researchers found that the levels of inflammatory molecules in the blood of volunteers who smoked a marijuana cigarette increased significantly over the subsequent three hours. They further showed that THC promotes inflammation and hallmarks of atherosclerosis in human endothelial cells grown in the laboratory. Finally, laboratory mice bred to have high cholesterol levels and fed a high-fat diet developed significantly larger atherosclerosis plaques when injected with THC at levels comparable to smoking one marijuana cigarette per day than did control animals.

THC binds to a receptor called CB1 on cells in the human brain, heart and vasculature system. The receptor recognizes naturally occurring cannabinoids, or endocannabinoids, which regulate mood, pain perception, immune function and metabolism. But frequent marijuana use causes inappropriate activation of CB1, which can cause inflammation and atherosclerosis, and it is associated with obesity, cancer and diabetes. Researchers have been trying to develop molecules called antagonists to block CB1’s function in conditions in which the receptor is overactive, like obesity, but until now the use of the antagonists has been thwarted by psychiatric side effects including mood disorders and anxiety arising from their activity in the brain.

Search for CB1 antagonists

The researchers used machine-learning techniques to screen a large database of protein structures and identify molecules structurally similar to previously identified CB1 antagonists that could block THC’s inflammatory and atherosclerotic properties without causing psychiatric side effects. They found that genistein, a naturally occurring molecule in soybeans, binds to CB1 but has poor brain penetration. When they added the genistein molecule to THC-treated human endothelial cells or gave it to the THC-injected mice with high cholesterol, they found genistein blocked the drug’s deleterious effects and did not block the psychoactive effects of THC on the brain.

As more states legalize the recreational use of marijuana, users need to be aware that it could have cardiovascular side effects.

“We didn’t see any blocking of the normal painkilling or sedating effects of THC in the mice that contribute to marijuana’s potentially useful medicinal properties,” Chandy said. “So genistein is potentially a safer drug than previous CB1 antagonists. It is already used as a nutritional supplement, and 99% of it stays outside the brain, so it shouldn’t cause these particular adverse side effects.”

The researchers hope to conduct clinical trials to learn whether genistein can reduce the risk of cardiovascular disease in marijuana users. They’d also like to extend their studies to include CBD — another cannabinoid in marijuana that does not have the psychoactive effects of THC.

“There’s a growing public perception that marijuana is harmless or even beneficial,” Wu said, comparing the legalization of marijuana use to vaping, which was first marketed as a safe way to stop smoking but has since been shown to cause lung damage and lead to increased tobacco use. “Marijuana clearly has important medicinal uses, but recreational users should think carefully about excessive use.”

Other Stanford authors of the study are graduate student Angela Zhang; postdoctoral scholars Kaavya Krishna Kumar, PhD, Dilip Thomas, PhD, Amit Manhas, PhD, and Johanne Marie Justesen, PhD; instructors of cardiovascular medicine Siyeon Rhee, PhD, and Chun Liu, PhD; cardiovascular fellow Ian Chen, MD, PhD; former postdoctoral scholars Saereh Khanamiri, PhD, and Hung-Ta Wo, MD; life sciences researcher Johnson Yang, former graduate student Frederick Seidl, PhD; Noah Burns, PhD, associate professor of chemistry; Nazish Sayed, MD, PhD, assistant professor of vascular surgery; Manuel Rivas, PhD, assistant professor of biomedical data science; and Brian Kobilka, PhD, professor of molecular and cellular physiology.

Researchers from National Taiwan University, the University of Copenhagen, Academia Sinica, the University of Colorado School of Medicine and UC-San Francisco also contributed to the work.

The research was supported by the Stanford Cardiovascular Institute, the American Heart Association, the Steven M. Gootter Foundation, the Taiwan Ministry of Science and Technology, the Royal College of Physicians and Surgeons, the Leducq Foundation, and the Tobacco-Related Disease Research Program.

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