Exploring psychotherapeutic issues and agents in clinical practice
Methylene blue (methylthioninium chloride) is an old drug with a storied history and a remarkable diversity of medical applications, reflected in the fact that there were more than 11,000 entries for “methylene blue” in PubMed by 2010, not including studies published in the era before PubMed (Schirmer, Adler, Pickhardt, & Mandelkow, 2011). Today, there are more than 15,000 entries in PubMed.
Methylene blue is a cationic thiazine dye long used for biological staining in histology, bacteriology, and hematology (Kristiansen, 1989). When ingested, it causes a blue discoloration of the skin, mucous membranes, and urine. Methylene blue was the first synthetic drug used in medicine, having been used to treat malaria more than one century ago, and there has been renewed interest in using it against malaria in recent years (Coulibaly et al., 2009). Methylene blue also was one of the first drugs used for the treatment of patients with psychosis at the end of the 19th century, and it was the lead drug in the serendipitous development of phenothiazine antipsychotic drugs in the mid-20th century. During the 1980s, methylene blue was studied in bipolar disorder (Narsapur & Naylor, 1983). More recently, it has been investigated in dementia and related neurodegenerative disorders (Wischik et al., 2015).
Prescription combination products containing methylene blue (e.g., Urelle®) are approved by the U.S. Food and Drug Administration (FDA) with an indication for the treatment of urinary tract irritation symptoms. Methylene blue (ProvayBlue®) is currently approved by the FDA as an orphan drug to treat acquired methemoglobinemia, but is also used off-label for the treatment of congenital methemoglobinemia. Other off-label uses of methylene blue include use as a clinical dye in therapeutic and diagnostic applications (e.g., parathyroid imaging, sentinel lymph node biopsy), and for treatment of hypotension (associated with shock or cardiac surgery), ifosfamide-induced encephalopathy, and cyanide poisoning.
How a stain can be used as a therapy for the brain is a fascinating and instructive story of a chemical that played a central role in the first development and use of synthetic drugs as chemotherapeutic agents to treat medical and neuropsychiatric disorders. I will describe the early history of methylene blue in this month's column, before turning to its specific use in psychiatry next month.
Discovery of Organic Dyes and Methylene Blue
The bark of the cinchona tree had been used to treat malaria as early as the 1600s, and the anti-malarial drug quinine was first extracted and isolated from the bark in 1820 (Achan et al., 2011). In an effort to develop a method for synthesizing quinine, which was expensive to produce from bark, an 18-year-old Englishman, W.H. Perkin (1838–1907), serendipitously created the dye aniline purple (mauve or mauveine). Perkin was a chemistry student of and a laboratory assistant to August Wilhelm Hofmann (1818–1892), but Perkin's interest in chemistry was so strong that he worked evenings and vacations in a makeshift laboratory in his family's home (Read, 1957). Perkin's discovery of mauveine occurred while working in his home laboratory during his Easter vacation of 1856.
The desirability of artificially synthesizing quinine was Hofmann's idea, but Perkin himself realized the industrial importance of his dye creation. Until the mid-1800s, most dyes were derived from materials found in nature, and the discovery of aniline purple was the first fully synthetic dye. Within months of his discovery, Perkin decided to leave school and Hofmann's laboratory to pursue commercial development of mauveine. He obtained a patent for mauveine in August 1856, and his father, using the family's savings, built a manufacturing factory. By the end of 1857, the new dyestuff “aniline purple” was being supplied in large quantities to a silk dyehouse in London. Perkin's discovery spurred a wider interest in the industrial development of other synthetic dyes (Brightman, 1956).
Methylene blue was first synthesized as an aniline-based dye for cotton staining by the German chemist Heinreich Caro (1834–1911) in 1876 (Oz, Lorke, Hasan, & Petroianu, 2011), although its chemical structure would not be elucidated until 9 years later (Ohlow & Moosmann, 2011). Another German chemist, Heinrich August Bernthsen (1855–1931), first synthesized the drug thiodiphenylamine (phenothiazine) in 1883 while working on the development of dyes derived from aniline. Phenothiazine has a characteristic central tricyclic ring structure, and this drug represents the structural parent compound for many other drugs, including what would later become known as the phenothiazine group of antipsychotic drugs. Bernthsen determined in 1885 that methylene blue had a phenothiazine chemical structure (Ohlow & Moosmann, 2011). Mere differences in the side chains attached to the central tricyclic structure distinguish phenothiazine, methylene blue, and related drugs.
Staining and Chemical Properties of Methylene Blue
The German physician Paul Ehrlich (1854–1915) had an intense interest in chemistry that formed the foundation for his pioneering discoveries and achievements in hematology, immunology, pharmacology, and chemotherapy (Valent et al., 2016). His cousin, Karl Weigert (1845–1904), was a noted pathologist who first introduced the use of aniline dyes in histology and bacterial diagnostics (Buchwalow, Boecker, & Tiemann, 2015). As a teenager, Ehrlich was fascinated by the process of staining microscopic tissue sections prepared by his cousin. Ehrlich's 1878 medical school doctoral thesis, “Contributions to the Theory and Practice of Histological Staining,” compared the problem of histological staining with the dyeing of textiles, arguing that both processes are the result of a chemical reaction (Schwartz, 2004). Ehrlich's dissertation led to further studies in which he developed a stain in 1880 that incorporated methylene blue, allowing him to differentiate among different types of blood cells (Krafts, Hempelmann, & Skorska-Stania, 2012). In 1885, Ehrlich published a paper on the staining of the tuberculous bacilli, which included a description of his theory of the affinity of tissues for various chemical compounds, a concept he called “the side-chain theory” (Kristiansen, 1989). According to the side-chain theory, the interaction between synthetic compounds and tissues was chemical in nature, involving a chemical reaction. In other words, the biological effect of any substance depends on the chemical constitution of the substance and cell.
Ehrlich used methylene blue to stain living tissue by injecting it in live animals and then examining the intensity of staining of various organs (Kristiansen, 1989). He conducted similar experiments using other dyes and in different animal species. Through these comparative studies, which he published in 1886, Ehrlich determined that methylene blue had a high affinity for brain and nerve tissue. For this reason, methylene blue has been used routinely for the staining of neuronal structures in clinical and histological studies. The affinity of methylene blue for nervous tissue also is relevant for why it has been used in neuropsychiatric disorders. Ehrlich suggested methylene blue had a selective affinity for nervous tissue because of the redox-cycling properties of this drug that he had first observed in 1885 (Ohlow & Moosmann, 2011).
Methylthioninium (MT) is a redox molecule, which exists in equilibrium between a reduced (leucomethylthioninium) and oxidized (MT+) form, depending on environmental conditions (Baddeley et al., 2015). Methylene blue is the chloride form of MT (methylthioninium chloride). As a chloride salt, methylene blue is stabilized in its MT+ form. Redox refers to a chemical reduction–oxygenation reaction, which involves the transfer of electrons. A molecule that is oxidized loses electrons, whereas a molecule that is reduced gains electrons. The reduced form of methylene blue (leucoMB) is colorless, but when exposed to oxygen it becomes a blue cation. The conversion between reduced and oxidized states of methylene blue (redox-cycling) occurs rapidly and spontaneously. A glucose solution of methylene blue in an airtight jar will be colorless; upon opening the jar the solution turns blue by exposure to oxygen. Closing the jar, the solution will turn colorless again. Ehrlich suggested that neuronal structures showed a high affinity for leucoMB. In his experiments, he demonstrated this phenomenon by exposing nervous tissue sections stained with leucoMB to air or iron chloride, which resulted in the return of a blue color (Oz et al., 2011).
The redox-cycling properties of methylene blue are why this drug is used for the treatment of methemoglobinemia, which is characterized by a poor oxygen carrying form of hemoglobin that causes patients to have the symptom of cyanosis (i.e., a blue discoloration). Curiously, treatment with methylene blue, which ordinarily causes blue discoloration of the skin, mucous membranes, and urine, gives these blue patients a healthier pink color (Trost, 1982).
Methylene Blue and the Development of Anti-Malarial Therapies
In 1887, the Polish pathologist Czeslaw Checinski discovered that a combination of methylene blue and the chemical eosin could selectively stain for plasmodium parasites (i.e., the organism causing malaria) in blood smears (Krafts et al., 2012). As a corollary of his side-chain theory, Ehrlich originated the novel idea that if pathogens (i.e., bacteria or parasites) could be preferentially stained by methylene blue, then such staining might indicate a specific harmful effect on the pathogen (Schirmer et al., 2011). If so, a dye could be used as a drug to kill the pathogen without harming other tissues. In 1891, Ehrlich discovered that methylene blue had this effect against the malarial organism and successfully treated two patients with malaria.
As a fully synthetic compound, methylene blue could be produced on a larger scale than quinine, and it was used to some extent as an alternative anti-malarial therapy. Because methylene blue was not as effective as quinine, many related compounds were synthesized and tested by scientists at Bayer I.G. Farbenindustrie A.G., a German chemical company. Bayer patented this group of drugs in Germany in 1939, and the same patents were granted in the United States to the Winthrop Chemical Company under a cartel arrangement between Bayer and Winthrop. One of these drugs was quinacrine, which was derived from methylene blue and introduced in the 1930s as a drug with improved anti-malarial properties (Korth, May, Cohen, & Prusiner, 2001). Quinacrine was widely used through the end of World War II. The drug resochin was developed through a simple modification of quinacrine by a chemist at Bayer in 1934 (Krafts et al., 2012).
Resochin was initially tested against bird malaria in 1935, and then in 1935 or 1936 at a psychiatric clinic in Germany in four patients with neurosyphilis who were deliberately infected with malaria (Coatney, 1963). Why were these psychiatric patients infected with malaria? The incidence of neurosyphilis (i.e., general paresis of the insane), which is characterized by psychosis, paralysis, and dementia, increased significantly during the 19th and early 20th centuries, and these patients represented a significant proportion of asylum populations. The arsenic drug arsphenamine (Compound 606; Salvarsan®) had been synthesized in Ehrlich's laboratory in 1907, and his group announced their experimental and clinical findings on this drug's effectiveness against syphilis in 1910 (Schwartz, 2004). They also developed the related, but less toxic, compound neoarsphenamine (Neosalvarsan®) in 1912. Although these drugs became standard therapies for treating syphilis until penicillin was introduced in the 1940s, they were relatively ineffective against neurosyphilis. Based on the potentially curative effect of fevers in the treatment of psychosis, deliberate inoculation with malaria was used to treat neurosyphilis by causing high and prolonged fevers (Tsay, 2013). After inducing the fever in this way, anti-syphilitic and anti-malarial drugs (e.g., quinine, methylene blue) were administered. Malarial therapy for treatment of neurosyphilis was used from 1917 until the mid-1940s, and the psychiatrist Julius Wagner-Jauregg was awarded a Nobel Prize in 1927 for his central role in developing this therapy (Tsay, 2013).
Resochin was shelved and seemingly forgotten after the individual who tested it in the four patients with neurosyphilis reported the drug as being as effective as quinacrine, but that it was too toxic for practical use in humans (Coatney, 1963). During World War II, there was critical interest in stimulating the production of quinacrine and developing other anti-malarial drugs because Japan had severely restricted the world's supply of quinine following Pearl Harbor. As a result, the American government asked Winthrop to synthesize and test all patented compounds it shared with Bayer. One of these drugs, designated as SN-7618, was found to have superior efficacy and tolerability compared to quinacrine in human trials involving more than 5,000 individuals conducted during 1944–1945. This drug also did not cause blue discoloration of the skin, eyes, or urine, which was an unpopular effect of methylene blue and quinacrine. As it turns out, resochin and SN-7618 are the same drug. The apparent toxicity of resochin based on experience with only four patients who had neurosyphilis and malaria was related to the high dosage used. The therapeutic dose of SN-7618 in a larger group of individuals with malaria was much lower than the dose-causing toxicity. SN-7618 was given the name chloroquine in 1946, and it became a first-line therapy for malaria for many years.
The history of methylene blue from its discovery as a dye to its use as a stain and then its therapeutic application in medicine should illustrate for nurses and physicians the importance of careful observation, being familiar with concepts outside of their range of practice, and the role of serendipity in advancing clinical science. In next month's column, I will describe the role of methylene blue in the development and use of phenothiazine antipsychotic drugs, studies on its use in bipolar disorder, and its investigation in dementia and related neurodegenerative disorders.
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