9-ME-BC

9-Me-BC is the usual abbreviation for 9-methyl-beta-carboline (9-methyl-β-carboline), the small molecule 9-methyl-9H-pyrido[3,4-b]indole. It belongs to the beta-carbolines, tricyclic pyridoindoles that include norharmane, the unsubstituted β-carboline, and harmane, 1-methyl-β-carboline. Norharmane and harmane form in the body and occur in fried meat and fish, coffee, alcoholic drinks and tobacco smoke (Pfau and Skog, 2004). 9-Me-BC is norharmane with a methyl group on the indole nitrogen at position 9.

Because β-carbolines had mostly been studied as possible neurotoxins, Gabriele Gille's group at the Technical University of Dresden described 9-Me-BC in 2008 as the first β-carboline found to protect dopaminergic neurons and promote their differentiation in culture (Hamann et al., 2008).

Formula, molecular weight, CAS number, aliases and structure are from PubChem CID 164979.

Published work on 9-Me-BC falls into six areas. Each summary below states the model used. The evidence is cell, enzyme and animal data from a small number of groups. The protective neuron findings and all of the rat studies come from linked, German-led laboratories that share authors.

Independent groups in Japan and the United States reported toxic effects instead: loss of dopaminergic neurons in mice given 9-Me-BC (Matsubara et al., 1998) and complex I inhibition in mouse brain mitochondria and neuronal cells (Chattopadhyay et al., 2019). PubMed indexes no study in which people received 9-Me-BC (searched October 2026).

Dopaminergic neurons in midbrain culture

In primary mesencephalic (midbrain) cultures, 9-Me-BC lowered lactate dehydrogenase release, the number of propidium iodide-stained cells and caspase-3 activity, raised ATP content and increased the number of differentiated dopaminergic neurons, with higher expression of genes for dopaminergic differentiation such as Nurr1 and Pitx3 and of markers including Th and Dat.

It was anti-proliferative in human SH-SY5Y neuroblastoma cells (Hamann et al., 2008). A follow-up reported that tyrosine hydroxylase (TH) expression rose in neurons already expressing dopa decarboxylase, along with TH-relevant transcription factors, and that neurite outgrowth of TH-positive neurons increased (Polanski et al., 2010). Models: primary midbrain cultures and a human neuroblastoma line.

Toxin models and a toxic relative

In the same culture system, 9-Me-BC protected TH-positive neurons from lipopolysaccharide and from the 2,9-dimethyl-β-carbolinium ion. Added after chronic rotenone exposure, it was followed by regeneration of TH-positive neurons, and it reduced microglial proliferation and α-synuclein protein (Polanski et al., 2010).

The 2,9-dimethyl ion is what forms when a methyl group is added at position 2 of 9-Me-BC, as shown in assays with a bovine brain enzyme activity (Gearhart et al., 1997) and purified phenylethanolamine N-methyltransferase (Gearhart et al., 2002), and it killed dopaminergic neurons preferentially in mouse midbrain cultures (Hamann et al., 2006).

In rats pretreated for 28 days with the toxin MPP+, 9-Me-BC delivered for 14 days into the left cerebral ventricle reversed the fall in left striatal dopamine, returned nigral TH-positive cell counts to normal values, raised striatal mitochondrial complex I activity by about 80 percent and induced neurotrophic factor genes including BDNF (Wernicke et al., 2010).

In contrast, in mice given 9-Me-BC itself for 7 days, brain levels of the 2,9-dimethyl ion reached 14 times those after norharmane, nigral TH-positive cells fell to 66 percent of control values and the animals showed bradykinesia (Matsubara et al., 1998). In a study of three such compounds including 9-Me-BC, complex I activity and respiration in mouse brain mitochondria were significantly affected in normal mice but not in mice lacking the Cyp2d6 gene locus (Chattopadhyay et al., 2019). Models: midbrain cultures, enzyme assays, rats, mice and a mouse neuronal cell line.

Hippocampus and spatial learning in rats

Rats given 9-Me-BC for 10 days, but not for 5 days, showed better spatial learning in a radial maze, higher dopamine levels in the hippocampal formation, and longer, more complex dendritic trees with more spines on granule neurons of the dentate gyrus (Gruss et al., 2012). In a separate mouse study, 9-Me-BC given for 7 days was followed by bradykinesia with reduced locomotor activity (Matsubara et al., 1998). PubMed indexes no other study of 9-Me-BC on learning. Models: rats and mice.

Astrocytes and monoamine oxidase

In mouse midbrain cultures, 9-Me-BC raised TH-positive neuron numbers by up to 33 percent at 90 µM, but at 150 µM it halved them in cultures depleted of astrocytes. In cortical astrocytes it did not raise a cell-damage marker at 10 to 150 µM, reduced proliferation at 90 and 150 µM, and raised expression of neurotrophic factor genes such as artemin and Bdnf.

With human enzymes it inhibited MAO-A with an IC50 of 1 µM and MAO-B with an IC50 of 15.5 µM (Keller et al., 2020). In human mitochondria, it inhibited the MAO-B-driven oxidation of MPTP to toxic pyridinium products with an IC50 of 7.3 µM, close to norharmane at 9.9 µM (Herraiz and Guillén, 2011). Models: mouse cell cultures, human enzymes and human mitochondria.

Light-activated DNA damage

β-Carbolines, 9-methyl derivatives in particular, are efficient photosensitizers. Under ultraviolet A (UVA) excitation at physiological pH, 9-methyl-norharmane and two related 9-methyl-β-carbolines damaged DNA mainly by oxidizing purine bases, far in excess of oxidized pyrimidines, strand breaks and sites of base loss, and also generated cyclobutane pyrimidine dimers (Vignoni et al., 2013).

A comparison of N-methyl-β-carbolines found N9-substituted members the most efficient photosensitizers, and the compounds appeared to accumulate mainly in the mitochondria of HeLa cells (Denofrio et al., 2020). Models: DNA under UVA light and a human cell line. PubMed indexes no animal or human phototoxicity study of 9-Me-BC.

Antiviral screening in cell culture

Of 21 β-carbolines screened against herpes simplex virus type 1 (HSV-1), 11 had antiviral activity at non-cytotoxic concentrations, and 9-methyl-norharmane was one of three that fully prevented virus-driven cell damage, with a half-maximal effective concentration of 4.9 µM and a selectivity index of 88.8. The three were not virucidal and did not block attachment or entry; they acted at later stages of infection, delaying or suppressing viral protein expression, and also inhibited HSV-2 (Gonzalez et al., 2018). Model: virus-infected cell cultures.