CBD Deep ScienceCannabinoids Working at the Cellular Level
In 2012, French scientists reported the presence of cannabinoid receptors on the membranes of mitochondria, the energy-generating organelle within cells. This discovery laid the groundwork for subsequent investigations into the role of the endocannabinoid system in regulating mitochondrial activity, which is critical to how cells function. Defects in mitochondria have been linked to a wide range of neurodegenerative, autoimmune and metabolic disorders.
A growing body of scientific data indicates that cannabidiol (CBD) can affect mitochondria, both directly and indirectly. It turns out that many of the biological pathways that involve mitochondria — including energy homeostasis, neurotransmitter release, and oxidative stress are modulated by endogenous and exogenous cannabinoids.
But research on cannabinoids often seems to be riddled with contradictions. Cannabinoids are notorious (in science and lived experience) for exerting opposite effects in different situations. How is CBD able to balance physiological excess as well as a deficiency? Why does a small dose of hemp oil stimulate while a large dose tends to sedate? Examining the role of mitochondria sheds light on these questions and other perplexing aspects of the endocannabinoid system.
What are mitochondria?
Mitochondria are universal energy adaptors that exist in the cells of every multicellular organism, including humans. The number of mitochondria in an individual cell can vary greatly depending on the organism and tissue type. (All human cells, except for red blood cells, contain mitochondria.) One of the main functions of mitochondria is to take high-energy molecules – such as sugars and amino acids – and convert them into a form of energy, called adenosine triphosphate (ATP), which the cell can use. For the cell, ATP is like a battery.
The process of extracting small bits of energy from high-energy molecules can be quite dangerous. Imagine trying to power a car by simply lighting the fuel tank on fire. A cell can’t handle the microscopic equivalent of an explosion, so the cell must use finesse to harness this energy. Individual electrons are extracted from high-energy molecules by a process known as cellular respiration and their energy is gradually released.
This gradual release of individual electrons allows the cell to synthesize ATP from its precursors, adenosine diphosphate (ADP) and inorganic phosphate (Pi). The cleavage of ATP back into ADP and Pi releases a small amount of energy, which powers the proteins that allow each cell to function and communicate. ATP is the main energy source for the majority of cellular functions. While commonly referred to as the cell’s powerhouse, mitochondria are also involved in other metabolism-related functions, but the goal is always the same; homeostasis the maintenance of a stable internal environment despite external fluctuations.
Originally, mitochondria were separate from other cells. At some point, one-and- a-half to two billion years ago, a cell engulfed an evolutionary precursor to a mitochondrion. But instead of digesting the mitochondrion, the two living entities formed a symbiotic relationship. The host cell would provide nutrients and a safe place for the mitochondrion to exist, and the mitochondrion would perform the dangerous process of cellular respiration, giving the host a more useable form of energy. The result was so evolutionarily fundamental that this symbiotic relationship preceded the occurrence of multicellular organisms. All plants, animals and fungi are endowed with mitochondria.
This theory of how two different self-organized living systems began to collaborate symbiotically is supported by the fact that mitochondria have retained their own genome that is separate from the host cell’s DNA. Mitochondria and the host cell replicate independently; they also have separate cellular membranes. Two other organelles are thought to have developed in a similar way: the chloroplast, which enables photosynthesis in plants, and the nucleus, which holds the cellular DNA and acts as a kind of coordinator of the cell.
Mitochondrial diseases can be caused by inherited mutations in mitochondrial DNA or defects in the nuclear genes that encode proteins that regulate mitochondrial division and DNA replication. Mitochondrial disorders can also develop due to the adverse effects of drugs, infections, environmental toxins or unhealthy lifestyle habits. Mitochondrial diseases are most severe when the defective mitochondria are present in muscle, brain or nerve tissue, as these cells require more energy.
Free Radicals & Phytocannabinoids
Although mitochondria allow energy to be accessed at a measured pace in relatively small quantities, the process of cellular respiration, whereby cells extract energy from nutrients, still can be damaging. High-energy electrons offload their energy in a multitude of complicated steps until the lower-energy electron is finally released onto an oxygen molecule. Ideally, the oxygen molecule will interact with hydrogen and form water, which is very stable.
But sometimes the ionized oxygen, called superoxide, can escape, resulting in oxidative stress. Similarly, other unstable molecules like peroxide and hydrogen peroxide can form and escape. These unstable, renegade molecules are called reactive oxygen species (ROS) or free radicals. Free radicals cause damage by interacting with DNA, cell membranes, proteins, or other organelles.
By effectively neutralizing free radicals and mitigating oxidative stress, antioxidants confer a broad range of therapeutic benefits. CBD is a potent antioxidant, according to the U.S. government, which filed a patent on the antioxidant and neuroprotective properties of cannabinoids based on research from 1998.
Autophagy & Apoptosis
Oxidative stress is a natural byproduct of mitochondrial activity. The creation of oxidative stress is necessary for obtaining energy and sustaining cellular function. Inevitably this will take its toll on an organism. But oxidative damage can be repaired to a certain extent through an adaptive process known as autophagy, whereby faulty cell parts – misfolded or aggregated proteins, dysfunctional mitochondria, etc. – are removed and replaced by newer, better- working components. Cell survival is dependent on this ongoing regenerative mechanism.
Oxidative stress is not exclusively bad. At low levels, reactive oxygen species act as signaling molecules. Damaged neurons can shed their worn-down mitochondria, which neighboring cells interpret as an SOS. Immune cells in the brain, called astrocytes, respond by donating some of their own mitochondria to the impaired neurons. Lung cells can also secrete healthy mitochondria for damaged cells to use.
Low levels of oxidative stress may stimulate a necessary cellular housecleaning, but high levels of oxidative stress are an indication that something is going wrong in the cell. Too much oxidative stress is a signal for the cell to destroy itself in a regulated way, a process called apoptosis. It’s as if there’s a tipping point when oxidative damage exceeds the capacity of a cell to repair itself, so the cell pivots from survival mode and commits suicide for the betterment of the team. The fate of a cell – whether survival via autophagy or death via apoptosis – is contingent on the kind of stress it encounters and its duration.
While oxidative stress in moderation can be used by the cell, the dysregulation of oxidative stress results in illness. Disruption of the delicate interplay between autophagy and apoptosis allows free radicals and damaged cells to accumulate, which can lead to a wide range of pathologies. Mitochondrial dysfunction is involved in virtually all disease, especially age-related neurodegeneration. Since neurons use a tremendous amount of energy to transmit information throughout the body, they require highly active mitochondria, which means greater oxidative damage. This slowly leads to a loss of functioning and symptoms of age-related decline.
According to a 2016 report in Philosophical Transactions of the Royal Society (London), “Cannabinoids as regulators of mitochondrial activity, as antioxidants and as modulators of clearance processes protect neurons on the molecular level… Neuroinflammatory processes contributing to the progression of normal brain aging and to the pathogenesis of neurodegenerative diseases are suppressed by cannabinoids, suggesting that they may also influence the aging process on the system level.”
Ageing, neurodegeneration, and metabolic disorders are all linked to mitochondrial activity — or lack thereof. But how do cannabinoids improve cognitive function? How do they interact with mitochondria?
Mechanisms of action — receptors and membranes
There are three major ways that plant and endogenous cannabinoids can directly modulate mitochondrial function:
Activating CB1 receptors on the mitochondria
Read More About Mitochondrial CB1 Receptors
Embedded in cell membranes, cannabinoid CB1 receptors are the most prevalent G-coupled protein receptors to populate the human brain and central nervous system. An estimated fifteen percent of all CB1 receptors in neurons exist on the mitochondria. In certain kinds of muscle tissue, half of the CB1 receptors are localized on the mitochondria. In order to directly activate a mitochondrial CB1 receptor must penetrate the outer cellular membrane and be chaperoned through the cell’s interior. Mitochondrial CB1 receptors are not structurally distinct from the prolific CB1 receptors that wrap around the cell’s outer surface, but their effects can be quite different. (Light switches may look the same from room to room, but they are connected to different circuitry throughout the house, and so turning the switch on or off in different places causes different outcomes.) Preclinical science suggests that activation of mitochondrial CB1 receptors usually decreases mitochondrial activity. This can protect the cell from oxidative stress and prevent apoptosis, but paradoxically it can also cause cell death in some conditions.
Perturbing the mitochondrial membrane
Read More About Membrane Pertubation
The membrane of mitochondria is primarily made of lipids, such as fatty acids and cholesterol. As in the outer cellular membrane, the relative concentration of short and long chain fats, saturated and unsaturated fats, and cholesterol influences many aspects of the mitochondrial membrane. Lipophilic compounds like endocannabinoids and plant cannabinoids can also meld into the mitochondrial membrane, changing its fluidity and permeability. Mitochondria harness the energy of electrons by using proteins imbedded in the mitochondrial membrane; alteration of membrane fluidity can inhibit the mitochondria’s ability to produce energy and allow free radicals to more easily escape into the cell. Stephanie Seneff, a senior research scientist at MIT, reports that Monsanto’s Roundup herbicide interferes with ATP production by adversely affecting mitochondrial membrane permeability.
Binding to other (non-cannabinoid) receptors on the mitochondria’s surface
Read More About Non-cannabinoid Receptors
Cannabidiol does not directly activate mitochondrial CB1 receptors. Instead, CBD binds to different receptors, including the sodium-calcium exchanger (NCX), on the mitochondria’s surface. Binding to NCX opens an ion channel, and ions, such as electrically charged calcium atoms, flow from high concentrations to low concentrations. Different levels of calcium ions have different effects. In conditions of low cellular stress, characterized by low intracellular calcium surrounding the mitochondria, CBD will increase stress by allowing calcium to flow out of the mitochondria. But in high stress conditions, characterized by copious intracellular calcium, CBD will do the exact opposite, allowing the flow of calcium from outside to inside the mitochondria (where calcium is stored) by opening NCX. The bidirectional calcium flow regulated by NCX is one of the mechanisms whereby CBD facilitates cellular homeostasis and neuroprotection.
CBD, Calcium Channels & Homeostasis
Cannabinoids are well known among scientists for their trickster-like ability to exert opposite effects in different situations. In mitochondria, cannabinoid activity is even more complicated. At low-stress conditions, cannabinoids often increase mitochondrial activity and cellular respiration, triggering an autophagic cellular repair. Cannabinoids will also buffer high-stress conditions and protect cells by decreasing mitochondrial activity. The dependence on stress is actually trimodular: Plant cannabinoids can also induce apoptosis under similar conditions.
The ebb and flow of calcium and stress, autophagy and cell death, the restoration of homeostasis on a cellular level are all regulated by CBD. A report by British researchers in the Journal of Neuroscience (2009) noted that “under pathological conditions involving mitochondrial dysfunction and calcium [Ca(2+)] dysregulation, CBD may prove beneficial in preventing apoptotic signaling via restoration of calcium homeostasis.”
Examining CBD’s effect on mitochondria sheds light on how Cannabidiol can protect against brain injury by regulating fluctuations in intracellular calcium. A November 2016 study in the European Journal of Pharmacology found that an “imbalance of sodium and calcium homeostasis trigger[s] pathophysiologic processes in cerebral ischemia, which accelerate neuronal brain death.” Ceaseless regeneration. Cannabinoids promote neuroplasticity and mediate homeostasis through various bidirectional pathways.
Biphasic dose-responses often occur when a compound influences a cell through multiple channels. With respect to mitochondrial function, the biphasic effects of cannabinoids depend on cellular conditions as well as dosage. Membrane fluidity and permeability are also modulated by other epigenetic factors, including different levels of cholesterol and dietary fats.
The actions of CBD in the mitochondria highlight some of the ways that the endocannabinoid system regulates cellular repair and renewal. Our body’s default state is one of ceaseless regeneration. Continual turnover on a cellular level is the fulcrum of health, the dynamic underpinning of homeostasis. In times of illness, regenerative processes are overcome by dysfunction and degradation. Cannabinoids and other membrane-penetrating antioxidants can enhance mitochondrial function and restore physiological balance.
One measure of stress in a cell is the concentration of cytosolic calcium (calcium in the intracellular space). Calcium is an important secondary messenger inside of a cell; it modulates the activity and inhibition of various proteins and influences many cellular signals, including apoptosis. On a cellular level, calcium is primarily stored inside the mitochondria and another organelle, endoplasmic reticulum.
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