Methylene blue, chemically methylthioninium chloride, is a phenothiazinium dye first made in 1876 and still found on the shelves of most biology laboratories. It stains nuclei and bacteria, it changes color as it gains and loses electrons, and those same redox properties have made it a research tool in mitochondrial biology, enzyme pharmacology and neuroscience.
Few compounds have a history as long or as varied. This overview traces methylene blue from the dye industry to modern cell biology, explains the redox chemistry and enzyme interactions behind most of its research uses, summarizes key preclinical studies, and notes what that work does and does not show.
At a glance
- Class: Phenothiazinium dye; redox-active small molecule
- Origin: First synthesized by Heinrich Caro in 1876 as a textile dye
- Structure: 3,7-bis(dimethylamino)phenothiazin-5-ium chloride; C16H18ClN3S; MW 319.9 g/mol; CAS 61-73-4
- Main research areas: mitochondrial electron transfer, monoamine oxidase inhibition, nitric oxide signaling, neuroprotection models, protein aggregation, histological staining
- Regulatory status: An injectable methylene blue drug product is FDA-approved for a specific indication; the capsules sold here are a research reagent only
Structure and origin
Heinrich Caro prepared methylene blue in 1876 while working in the German synthetic dye industry. Within a few years it had become a biological stain: Paul Ehrlich and others used it to color nerve fibers and microorganisms, and Ehrlich’s observation that the dye was taken up selectively by certain cells fed into his ideas about targeted chemicals. In the early 1890s it was tested against malaria parasites, which makes it one of the first synthetic compounds used in medicine. Its three-ring phenothiazine core later served as a starting point for other drug classes, including the phenothiazine antipsychotics.
The molecule is a flat, positively charged aromatic system with two dimethylamino groups. In its oxidized form it is deep blue. When it accepts two electrons and a proton it becomes leucomethylene blue, which is colorless. The two forms interconvert readily under biological conditions, and that reversible redox cycle explains most of what the compound does in experiments.
Mechanism: what the research shows
At low concentrations in cells, methylene blue can accept electrons from NADH and pass them on to cytochrome c, partly bypassing complexes I and III of the mitochondrial electron transport chain. Atamna and colleagues studied this in cultured human fibroblasts and reported increased activity of complex IV and oxygen consumption, along with a slower onset of cellular senescence markers over repeated passages (Atamna et al., 2008).
The compound also inhibits several enzymes. It is a potent, reversible inhibitor of monoamine oxidase A, a finding that Ramsay and colleagues confirmed with purified enzyme and that explains reported serotonin toxicity when it is combined with serotonergic drugs (Ramsay et al., 2007). Azure B, a demethylated metabolite, is an even more potent MAO inhibitor in vitro (Petzer et al., 2012). Methylene blue also inhibits nitric oxide synthase and soluble guanylate cyclase, which places it in the nitric oxide-cGMP pathway. A broad review by Oz and colleagues catalogued these and other actions in the nervous system, including effects on ion channels and neurotransmitter receptors (Oz et al., 2011).
Key areas of study
Mitochondrial biology and cellular aging
The fibroblast work made methylene blue a reference compound for alternative electron transfer in mitochondria. Readouts such as complex IV activity, oxygen consumption, and senescence markers over repeated cell divisions are now used to compare it with related redox cyclers (Atamna et al., 2008).
Monoamine oxidase pharmacology
Enzyme kinetic studies with purified monoamine oxidase showed tight, reversible inhibition of MAO-A (Ramsay et al., 2007), and later work identified azure B as a contributor to the overall inhibitory profile (Petzer et al., 2012). These studies are often cited in drug-interaction research and in the design of phenothiazine derivatives with less MAO activity.
Neuroprotection models
Poteet and colleagues compared methylene blue with several structural derivatives in cultured neuronal cells exposed to oxidative and metabolic stress, relating the degree of protection to the chemical properties of each compound (Poteet et al., 2012). Such derivative studies help separate the redox mechanism from other actions of the parent dye.
Protein aggregation and nervous system pharmacology
In vitro studies have examined methylene blue as an inhibitor of tau aggregation and of other aggregating proteins, and it has been a lead structure for related compounds in that field. The Oz review places this work alongside the compound’s many receptor and channel effects, which complicate attribution of any single outcome to one mechanism (Oz et al., 2011).
What the evidence does not show
Methylene blue acts on many targets at once: mitochondrial electron transfer, MAO-A, nitric oxide signaling, ion channels and protein aggregation. In any given experiment it can be hard to know which action is responsible. Concentration matters a great deal; effects seen at low concentrations in cells can reverse or turn toxic at higher ones, and the compound itself absorbs light and generates reactive oxygen species under illumination. Much of the neuroprotection work is in cultured cells or short-term rodent models. Approval of an injectable drug product for one specific indication does not extend to any other use or form. None of these findings describes the research capsules sold here.
Regulatory status
Methylene blue in injectable form is an FDA-approved prescription drug for the treatment of acquired methemoglobinemia, and methylene blue is on the WHO Model List of Essential Medicines. The capsules sold by Rogue Compounds are a research reagent, not that drug product or any approved drug product, and are not for human use.
Handling and storage in the lab
Methylene blue capsules should be kept sealed at room temperature (20–25°C), away from heat, moisture and light. The dye is photoactive, so storing the pouch closed and out of direct light is especially important.
Sourcing and documentation
Rogue Compounds has methylene blue made in small batches. Every batch is tested by an independent U.S. lab and the batch COA is on the product page and in the COA Library.
View Methylene Blue on Rogue Compounds
References
- Ramsay RR, et al. Methylene blue and serotonin toxicity: inhibition of monoamine oxidase A (MAO A) confirms a theoretical prediction. Br J Pharmacol. 2007;152(6):946-951. PMID 17721552
- Atamna H, et al. Methylene blue delays cellular senescence and enhances key mitochondrial biochemical pathways. FASEB J. 2008;22(3):703-712. PMID 17928358
- Petzer A, et al. Azure B, a metabolite of methylene blue, is a high-potency, reversible inhibitor of monoamine oxidase. Toxicol Appl Pharmacol. 2012;258(3):403-409. PMID 22197611
- Poteet E, et al. Neuroprotective actions of methylene blue and its derivatives. PLoS One. 2012;7(10):e48279. PMID 23118969
- Oz M, Lorke DE, Petroianu GA. Cellular and molecular actions of methylene blue in the nervous system. Med Res Rev. 2011;31(1):93-117. PMID 19760660
Research use only. Rogue Compounds products are sold strictly for laboratory research. They are not for human or veterinary use, and nothing in this article is medical advice. The studies cited here describe published research, not this product or any use of it.