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James Parkinson first described a disease characterized by tremor in 1817. Today, Parkinson’s disease is the second most common neurodegenerative disease, after Alzheimer’s. Parkinson’s disease is characterized by neuronal death in the substantia nigra, which is Latin for ‘black substance,’ as it appears darker than neighboring brain regions due to the high levels of neuromelanin in its dopaminergic neurons.
Dopaminergic neurons are neurons that carry receptors for the neurotransmitter dopamine, which is involved in motor coordination, reward, and habituation. Dopamine is also the neurotransmitter whose action most characterizes drug addiction – hence the term ‘dope.’ In drug addiction, enhanced dopamine transmission causes excitotoxicity of dopaminergic neurons. Failing to downregulate their dopamine receptors, neurons die of over-stimulation. In some ways, dopamine can be thought of an endogenous neurotoxin.
The search for drugs to prevent or repair damage to dopaminergic neurons is important to sufferers of the debilitating disease Parkinson’s, to those who have damaged their brains with recreational drug use, and to the emerging community interested in cognitive enhancement. This article briefly reviews a promising, little-known molecule who’s exceptional regenerative ability on dopaminergic neurons was discovered in recent years.
CARBOLINES IN NATURE
Carbolines are a heterogenous group of naturally occurring pyridoindole compounds. Classified according to their skeleton as alpha, beta, gamma, or delta-carbolines, depending on the location of the nitrogen in their pyridine ring, the beta-carbolines (BCs) are best studied because of the rarity of alpha, gamma, and delta-carbolines in nature. BCs, which can be synthesized from tryptamine and tryptamine-like compounds, are characterized as either tetrahydro-BCs or aromatic BCs.
BCs have been found in fruits, grilled bacon, fish, and sausages. In meats, the formation of BCs is accelerated during charcoal-grilling, where aromatic BCs are found in high quantities. BCs are also found in coffee, tobacco smoke, and alcohol, as well as endogenously in the human body, where they have been detected in milk, urine, blood, and cerebrospinal fluid.
THE TOXICITY OF SOME BETA-CARBOLINES
Many derivatives of BCs resemble 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), the neurotoxin commonly used in academic studies to produce a Parkinsonian-like phenotype in rodent brains. Several BCs, particularly methylated forms such as 2,9-dimethyl-beta-carbolinium ion (2,9-dime-BC+), have proven to be neurotoxic to dopaminergic neurons. Nonmethylated BCs can also be metabolized into neurotoxic forms by the enzymes 2N-methyltransferase and 9N-methyltransferase. Thankfully, the subject of this article, 9-methyl-beta-carboline (9-me-BC), has not been observed to be acted on by 2N-methyltransferase.
THE USES OF BETA-CARBOLINES
BCs of the harman and norharman varieties exhibit heterogenous actions on the nervous system. Some act on the inhibitory GABA receptors, producing antidepressant, anxiolytic, and anti-epileptic effects. Others act on glycine, serotonin, acetylcholine, and dopamine neurotransmitter systems.
They have particularly remarkable potential as a substrate for the dopamine transporter (DAT) and as inhibitors of the monoamine oxidase enzymes (A and B) that degrade monoamine neurotransmitters, such as dopamine, norepinephrine, and serotonin. To prevent the degradation of the hallucinogen N,N-Dimethyltryptamine (DMT) by monoamine oxidase upon its oral consumption, BCs from the harmala plants are included in all preparations of the traditional ayahuasca beverage. In tobacco smoke, harman and norharman BCs exert potent dopaminergic effects.
9-ME-BC’S BIOLOGICAL FUNCTION ON DOPAMINERGIC NEURONS
At high doses (0.25 millimole/kg), 9-methyl-beta-carboline (9-me-BC, the subject of this article), had previously been shown to be neurotoxic in mouse models. However, in 2007 a German team of MDs showed that lower doses of 9-me-BC (0.48 micromole/kg) were neuroprotective in rats in vitro. 9-me-BC is transported into dopaminergic neurons by the dopamine transporter (DAT), after which tyrosine hydroxylase (TH) neurons increase (by 30% at 90 micromole) and protein expression of TH increased by 75%. TH is the rate-limiting enzyme crucial to the synthesis of the neurotransmitter dopamine, and early loss of TH activity is characteristic of the development of Parkinson’s disease.
9-me-BC has been shown to upregulate a variety of neurotrophic and morphogenic factors, including dopaminergic transcription factors engrailed in homeobox 1 (En1), the sonic hedgehog (Shh), nuclear receptor related 1 (Nurr1), wingless-type mouse mammary tumor virus (MMTV) integration site family, member 1 (Wnt1) and member 5a (Wnt5a), and paired-like homeodomain transcription factor 3 (Pitx3). Nurr1 activity is particularly attractive, as Nurr1 is required for the development and maintenance of dopaminergic neurons, and the Nurr1 gene is under-expressed in Parkinson’s disease patients.
9-me-BC increased gene expression of the neurotrophic factors brain derived neurotrophic factor (BDNF), conserved dopamine neurotrophic factor (CDNF), cerebellin 1 (CBLN1), ciliary neurotrophic factor (CNTF), neurotrophin-3, and nerve growth factor (NGF) in astrocyte cell cultures. These factors modulate the health of dopaminergic neurons - CDNF has been shown to regenerate dopaminergic neurons, while CBLN improves the synaptic plasticity and integrity of neurons.
9-me-BC also reduced gene expression of the pro-apoptotic (i.e. enhancing cell death) members of the p53 pathway, death-domain-associated protein Fas, the growth arrest and DNA-damage-inducing protein 45a (GADD45A), and caspase 3. It also increases ATP content of dopaminergic cultures by upregulating nicotinamide adenine dinucleotide dehydrogenase (NADH) activity of the monomeric complex I of mitochondria.
Note that inhibition of the dopamine transporter (DAT) or PKA/C blocks the stimulatory effect of 9-me-BC on dopaminergic neurons, indicating their integral role in its effect.
9-ME-BC AND MONOAMINE OXIDASE
Monoamine oxidase is an enzyme that degrades dopamine in the brain. Monoamine oxidase’s (MAO) two isoforms both deaminate dopamine, while monoamine oxidase A preferentially deaminates norepinephrine and serotonin. Elevated MAO-B has been shown to degrade dopaminergic neurons while the inhibition of MAO-A and MAO-B has been shown to protect neurons from apoptosis. Strikingly, 9-me-BC inhibits both isoforms of MAO.
9-ME-BC AND INFLAMMATION
Inflammatory processes are integral to the degradation of dopaminergic neurons and the use of anti-inflammatory drugs have been associated with reduced incidence of Parkinson’s disease (and Alzheimer’s disease). In addition to its neurotrophic and neuroprotective effects on dopaminergic neurons, 9-me-BC is also anti-inflammatory.
Lipopolysaccharides (LPS), the notorious endotoxins produced by gastrointestinal bacteria, were studied in vitro with dopaminergic neurons to determine whether 9-me-BC could reduce their pro-inflammatory effect. LPS increased gene expression of the inflammatory cytokines and receptors CCL-1, CCL-2, CCL-4, CCL-5, complement factor 3 (C3), CVCL1, , beta 2 microglobulin (b2m),chemokine ligand 10 (CVCL-10), nitric oxide synthase 2 (NOS2), heat shock protein 90-kDa alpha (HSP90AB1), tumor necrosis factor (TNF), Fc receptor of IgE (FCER1G), interleukin 1-beta (IL-1B) and interleukin-18 (IL-18), all of which 9-me-BC sharply inhibited. It is hypothesized that 9-me-BC’s anti-inflammatory properties are mediated by the anti-inflammatory interleukin-10.
9-me-BC’s neuroprotective, neurotrophic, and anti-inflammatory qualities are profound, highly desirable, and rarely found in a single molecule.
Despite its attractiveness to researchers and cognitive enhancement aficionados, research on the molecule appears to have ceased for nearly a decade. In a future episode of The Live Long Podcast, I hope to interview one of the researchers who produced the admirable work on the molecule to learn more about it and determine why research on it has ceased. Nonetheless, the molecule is used in cognitive enhancement communities. If you do use it, be sure to avoid sunlight.
 Rabey, J. M., & Hefti, F. (1990). Neuromelanin synthesis in rat and human substantia nigra. Journal of Neural Transmission-Parkinson's Disease and Dementia Section, 2(1), 1-14.  Quinton, M. S., & Yamamoto, B. K. (2006). Causes and consequences of methamphetamine and MDMA toxicity. The AAPS journal, 8(2), E337-E337.  Rabinovic, A. D., Lewis, D. A., & Hastings, T. G. (2000). Role of oxidative changes in the degeneration of dopamine terminals after injection of neurotoxic levels of dopamine. Neuroscience, 101(1), 67-76.  Susilo, R., & Rommelspacher, H. (1987). Formation of a β-carboline (1, 2, 3, 4-tetrahydro-l-methyl-β-carboline-1-carboxylic acid) following intracerebroventricular injection of tryptamine and pyruvic acid. Naunyn-Schmiedeberg's archives of pharmacology, 335(1), 70-76.  Herraiz, T., & Galisteo, J. (2003). Tetrahydro-β-carboline alkaloids occur in fruits and fruit juices. Activity as antioxidants and radical scavengers. Journal of agricultural and food chemistry, 51(24), 7156-7161.  Gross, G. A., Turesky, R. J., Fay, L. B., Stillwell, W. G., Skipper, P. L., & Tannenbaum, S. R. (1993). Heterocyclic aromatic amine formation in grilled bacon, beef and fish and in grill scrapings. Carcinogenesis, 14(11), 2313-2318.  Herraiz, T., & Chaparro, C. (2006). Analysis of monoamine oxidase enzymatic activity by reversed-phase high performance liquid chromatography and inhibition by β-carboline alkaloids occurring in foods and plants. Journal of Chromatography A, 1120(1-2), 237-243.  Liao, G. Z., Wang, G. Y., Xu, X. L., & Zhou, G. H. (2010). Effect of cooking methods on the formation of heterocyclic aromatic amines in chicken and duck breast. Meat science, 85(1), 149-154.  Herraiz, T., & Chaparro, C. (2005). Human monoamine oxidase is inhibited by tobacco smoke: β-carboline alkaloids act as potent and reversible inhibitors. Biochemical and biophysical research communications, 326(2), 378-386.  Adachi, J., Mizoi, Y., Naito, T., Ogawa, Y., Uetani, Y., & Ninomiya, I. (1991). Identification of tetrahydro-β-carboline-3-carboxylic acid in foodstuffs, human urine and human milk. The Journal of nutrition, 121(5), 646-652.  Honecker, H., Coper, H., Fähndrich, C., & Rommelspacher, H. (1980). Identification of tetrahydronorharmane (tetrahydro-β-carboline) in human blood platelets.  Matsubara, K., Kobayashi, S., Kobayashi, Y., Yamashita, K., Koide, H., Hatta, M., ... & Kimura, K. (1995). beta-Carbolinium cations, endogenous MPPplus analogs, in the lumbar cerebrospinal fluid of patients with Parkinson's disease. Neurology, 45(12), 2240-2245.  Neafsey, E. J., Albores, R., Gearhart, D., Kindel, G., Raikoff, K., Tamayo, F., & Collins, M. A. (1995). Methyl-β-carbolinium analogs of MPP+ cause nigrostriatal toxicity after substantia nigra injections in rats. Brain research, 675(1-2), 279-288.  Collins, M. A., Neafsey, E. J., Matsubara, K., Cobuzzi Jr, R. J., & Rollema, H. (1992). Indole-N-methylated β-carbolinium ions as potential brain-bioactivated neurotoxins. Brain research, 570(1-2), 154-160.  Farzin, D., & Mansouri, N. (2006). Antidepressant-like effect of harmane and other β-carbolines in the mouse forced swim test. European neuropsychopharmacology, 16(5), 324-328.  Stephens, D. N., Schneider, H. H., Kehr, W., Jensen, L. H., Petersen, E., & Honore, T. (1987). Modulation of anxiety by β-carbolines and other benzodiazepine receptor ligands: relationship of pharmacological to biochemical measures of efficacy. Brain research bulletin, 19(3), 309-318.  ARICIOGLU, F., & ALTUNBAS, H. (2003). Harmane Induces Anxiolysis and Antidepressant‐Like Effects in Rats. Annals of the New York Academy of Sciences, 1009(1), 196-201.  Aricioglu, F. E. Y. Z. A., YILLAR, O., KORCEGEZ, E., & BERKMAN, K. (2003). Effect of harmane on the convulsive threshold in epilepsy models in mice. Annals of the New York Academy of Sciences, 1009(1), 190-195.  Chen, X., Cromer, B. A., & Lynch, J. W. (2009). Molecular determinants of β‐carboline inhibition of the glycine receptor. Journal of neurochemistry, 110(5), 1685-1694.  Touiki, K., Rat, P., Molimard, R., Chait, A., & de Beaurepaire, R. (2005). Harmane inhibits serotonergic dorsal raphe neurons in the rat. Psychopharmacology, 182(4), 562-569.  Rook Y, Schmidtke KU, Gaube F et al. Bivalent E-carbolines as potential multitarget anti-Alzheimer agents  Yang, Y. J., Lee, J. J., Jin, C. M., Lim, S. C., & Lee, M. K. (2008). Effects of harman and norharman on dopamine biosynthesis and L-DOPA-induced cytotoxicity in PC12 cells. European journal of pharmacology, 587(1-3), 57-64.  Wernicke, C., Schott, Y., Enzensperger, C., Schulze, G., Lehmann, J., & Rommelspacher, H. (2007). Cytotoxicity of β-carbolines in dopamine transporter expressing cells: Structure–activity relationships. biochemical pharmacology, 74(7), 1065-1077.  Storch, A., Hwang, Y. I., Gearhart, D. A., Beach, J. W., Neafsey, E. J., Collins, M. A., & Schwarz, J. (2004). Dopamine transporter‐mediated cytotoxicity of β‐carbolinium derivatives related to Parkinson's disease: relationship to transporter‐dependent uptake. Journal of neurochemistry, 89(3), 685-694.  Ho, B. T., McIsaac, W. M., Tansey, L. W., & Walker, K. E. (1969). Inhibitors of monoamine oxidase III: 9‐substituted‐β‐carbolines. Journal of pharmaceutical sciences, 58(2), 219-221.  Rommelspacher, H., Meier-Henco, M., Smolka, M., & Kloft, C. (2002). The levels of norharman are high enough after smoking to affect monoamineoxidase B in platelets. European journal of pharmacology, 441(1-2), 115-125.  Simão, A. Y., Gonçalves, J., Caramelo, D., Rosado, T., Barroso, M., Restolho, J., ... & Gallardo, E. (2020). Determination of N, N-dimethyltryptamine and beta-carbolines in plants used to prepare ayahuasca beverages by means of solid-phase extraction and gas-chromatography–mass spectrometry. SN Applied Sciences, 2(3), 1-11.  Lantz, S. M., Cuevas, E., Robinson, B. L., Paule, M. G., Ali, S. F., & Imam, S. Z. (2015). The Role of Harmane and Norharmane in In Vitro Dopaminergic Function. Journal of Drug and Alcohol Research, 4(1), 1-8.  Matsubara, K., Gonda, T., Sawada, H., Uezono, T., Kobayashi, Y., Kawamura, T., ... & Akaike, A. (1998). Endogenously Occurring β‐Carboline Induces Parkinsonism in Nonprimate Animals: A Possible Causative Protoxin in Idiopathic Parkinson's Disease. Journal of neurochemistry, 70(2), 727-735.  Hamann, J., Wernicke, C., Lehmann, J., Reichmann, H., Rommelspacher, H., & Gille, G. (2008). 9-Methyl-β-carboline up-regulates the appearance of differentiated dopaminergic neurones in primary mesencephalic culture. Neurochemistry international, 52(4-5), 688-700.  Polanski, W., Enzensperger, C., Reichmann, H., & Gille, G. (2010). The exceptional properties of 9‐methyl‐β‐carboline: stimulation, protection and regeneration of dopaminergic neurons coupled with anti‐inflammatory effects. Journal of neurochemistry, 113(6), 1659-1675.  Nagatsu, T. (1990). Change of tyrosine hydroxylase in the parkinsonian brain and in the brain of MPTP-treated mice as revealed by homospecific activity. Neurochemical research, 15(4), 425-429.  Simon, H. H., Saueressig, H., Wurst, W., Goulding, M. D., & O'Leary, D. D. (2001). Fate of midbrain dopaminergic neurons controlled by the engrailed genes. Journal of Neuroscience, 21(9), 3126-3134.  Hynes, M., Porter, J. A., Chiang, C., Chang, D., Tessier-Lavigne, M., Beachy, P. A., & Rosenthal, A. (1995). Induction of midbrain dopaminergic neurons by Sonic hedgehog. Neuron, 15(1), 35-44.  Saucedo-Cardenas, O., Quintana-Hau, J. D., Le, W. D., Smidt, M. P., Cox, J. J., De Mayo, F., ... & Conneely, O. M. (1998). Nurr1 is essential for the induction of the dopaminergic phenotype and the survival of ventral mesencephalic late dopaminergic precursor neurons. Proceedings of the National Academy of Sciences, 95(7), 4013-4018.  Prakash, N., Brodski, C., Naserke, T., Puelles, E., Gogoi, R., Hall, A., ... & Martinez, S. (2006). A Wnt1-regulated genetic network controls the identity and fate of midbrain-dopaminergic progenitors in vivo. Development, 133(1), 89-98.  Castelo-Branco, G., Wagner, J., Rodriguez, F. J., Kele, J., Sousa, K., Rawal, N., ... & Arenas, E. (2003). Differential regulation of midbrain dopaminergic neuron development by Wnt-1, Wnt-3a, and Wnt-5a. Proceedings of the National Academy of Sciences, 100(22), 12747-12752.  Maxwell SL, Ho HY, Kuehner E, Zhao S, Li M. Pitx3 regulates tyrosine hydroxylase expression in the substantia nigra and identifies a subgroup of mesencephalic dopaminergic progenitor neurons during mouse development  Kadkhodaei, B., Ito, T., Joodmardi, E., Mattsson, B., Rouillard, C., Carta, M., ... & Chambon, P. (2009). Nurr1 is required for maintenance of maturing and adult midbrain dopamine neurons. Journal of Neuroscience, 29(50), 15923-15932.  Le, W., Pan, T., Huang, M., Xu, P., Xie, W., Zhu, W., ... & Jankovic, J. (2008). Decreased NURR1 gene expression in patients with Parkinson's disease. Journal of the neurological sciences, 273(1-2), 29-33.  Wernicke, C., Hellmann, J., Zięba, B., Kuter, K., Ossowska, K., Frenzel, M., ... & Rommelspacher, H. (2010). 9-Methyl-β-carboline has restorative effects in an animal model of Parkinson’s disease. Pharmacological Reports, 62(1), 35-53.  Keller, S., Reichmann, H., & Gille, G. (2010). 9-Methyl-β-Carboline Inhibits Monoamine Oxidase Activity And Stimulates The Expression Of Growth Factors By Astrocytes: P02. 06. Movement Disorders, 25.  Lindholm, P., Voutilainen, M. H., Laurén, J., Peränen, J., Leppänen, V. M., Andressoo, J. O., ... & Tuominen, R. K. (2007). Novel neurotrophic factor CDNF protects and rescues midbrain dopamine neurons in vivo. Nature, 448(7149), 73-77.  Hirai, H., Pang, Z., Bao, D., Miyazaki, T., Li, L., Miura, E., ... & Morgan, J. I. (2005). Cbln1 is essential for synaptic integrity and plasticity in the cerebellum. Nature neuroscience, 8(11), 1534-1541.  Hamann, J., Wernicke, C., Lehmann, J., Reichmann, H., Rommelspacher, H., & Gille, G. (2008). 9-Methyl-β-carboline up-regulates the appearance of differentiated dopaminergic neurones in primary mesencephalic culture. Neurochemistry international, 52(4-5), 688-700.  Hamann, J., Wernicke, C., Lehmann, J., Reichmann, H., Rommelspacher, H., & Gille, G. (2008). 9-Methyl-β-carboline up-regulates the appearance of differentiated dopaminergic neurones in primary mesencephalic culture. Neurochemistry international, 52(4-5), 688-700.  Polanski W, Enzensperger C, Reichmann H, Gille G. The exceptional properties of 9-methyl-E-carboline: stimulation, protection and regeneration of dopaminergic neurons coupled with anti-inflammatory effects  Bortolato, M., Chen, K., & Shih, J. C. (2008). Monoamine oxidase inactivation: from pathophysiology to therapeutics. Advanced drug delivery reviews, 60(13-14), 1527-1533.  Mallajosyula, J. K., Kaur, D., Chinta, S. J., Rajagopalan, S., Rane, A., Nicholls, D. G., ... & Andersen, J. K. (2008). MAO-B elevation in mouse brain astrocytes results in Parkinson's pathology. PloS one, 3(2), e1616.  Malorni, W., Giammarioli, A. M., Matarrese, P., Pietrangeli, P., Agostinelli, E., Ciaccio, A., ... & Mondovi', B. (1998). Protection against apoptosis by monoamine oxidase A inhibitors. FEBS letters, 426(1), 155-159.  Maruyama, W., Youdim, M. B., & Naoi, M. (2001). Antiapoptotic properties of rasagiline, N-propargylamine-1 (R)-aminoindan, and its optical (S)-isomer, TV1022. ANNALS-NEW YORK ACADEMY OF SCIENCES, 939, 320-329.  Keller, S., Reichmann, H., & Gille, G. (2010). 9-Methyl-β-Carboline Inhibits Monoamine Oxidase Activity And Stimulates The Expression Of Growth Factors By Astrocytes: P02. 06. Movement Disorders, 25.  Gagne, J. J., & Power, M. C. (2010). Anti-inflammatory drugs and risk of Parkinson disease: a meta-analysis. Neurology, 74(12), 995-1002.  Stewart, W. F., Kawas, C., Corrada, M., & Metter, E. J. (1997). Risk of Alzheimer's disease and duration of NSAID use. Neurology, 48(3), 626-632.  Polanski, W., Enzensperger, C., Reichmann, H., & Gille, G. (2010). The exceptional properties of 9‐methyl‐β‐carboline: stimulation, protection and regeneration of dopaminergic neurons coupled with anti‐inflammatory effects. Journal of neurochemistry, 113(6), 1659-1675.  Vignoni, M., Rasse-Suriani, F. A., Butzbach, K., Erra-Balsells, R., Epe, B., & Cabrerizo, F. M. (2013). Mechanisms of DNA damage by photoexcited 9-methyl-β-carbolines. Organic & Biomolecular Chemistry, 11(32), 5300-5309.