Exploring psychotherapeutic issues and agents in clinical practice
In last month's column (Howland, 2016c), I described the early history of methylene blue, a drug synthesized in 1876 as a dye in the textile industry, but subsequently used for biologic staining in histology, bacteriology, and hematology. Beyond its use as a biologic stain, methylene blue has a remarkably diverse assortment of medical applications. The German physician Paul Ehrlich (1854–1915) was an astute clinician and experimentalist who pioneered many of the early clinical applications of methylene blue, including its use as the first synthetic drug for treating malaria. More importantly, however, Ehrlich was instrumental in ascertaining the unique physiochemical properties of methylene blue, especially its redox-cycling properties and its selective affinity for the nervous system. This selective affinity was a key observation that led to its use in treating psychotic disorders, foreshadowing its role in the later development of phenothiazine antipsychotic drugs. Selective affinity for the nervous system also explains why this drug came to be investigated in dementia. The redox-cycling properties suggested its use in treating bipolar disorder. In this month's column, I will describe the evolutionary use of methylene blue in these neuropsychiatric disorders.
Methylene Blue and the Development of Phenothiazine Antipsychotic Drugs
The drug thiodiphenylamine (phenothiazine) was synthesized in 1883, and methylene blue was found to have a phenothiazine chemical structure 2 years later (Howland, 2016c). Phenothiazine has a characteristic central tricyclic ring structure, and this drug represents the structural parent compound for what later became known as the group of phenothiazine antipsychotic drugs (Ohlow & Moosmann, 2011). Mere differences in the side chains attached to the central ring structure distinguish methylene blue, phenothiazine, promethazine (Phenergan®), chlorpromazine (Thorazine®), thioridazine (Mellaril®), and fluphenazine (Prolixin®). Because of the public health significance of malaria, as well as restrictions on the supply of quinine and the unpopularity of quinacrine, the known anti-malarial properties of methylene blue prompted American chemists during the 1940s to synthesize and test other phenothiazine derivative drugs that might be effective as alternative therapies to quinine and quinacrine, but none of these drugs showed anti-malarial activity (Frankenburg & Baldessarini, 2008; López-Muñoz et al., 2005).
During the 1940s, French chemists also investigated the anti-malarial potential of phenothiazine derivative drugs, apparently unaware of the negative findings from American researchers (Frankenburg & Baldessarini, 2008). French researchers similarly concluded that these phenothiazine drugs had little anti-malarial activity, but they continued to investigate their anti-histamine properties and potential therapeutic use for preventing surgical shock. Promethazine, introduced in 1947 for treating allergies and also used in Parkinson's disease, was one such drug developed and marketed for its antihistamine properties (López-Muñoz et al., 2005).
Chlorpromazine, another phenothiazine drug synthesized in 1950, was tested in animals and humans for its central nervous system and anti-shock effects. Chlorpromazine not only was effective at preventing surgical shock, but patients receiving the drug felt calmer and more relaxed before an operation. The calming effect of chlorpromazine observed by the French army surgeon Henri-Marie Laborit (1914–1995) led him to suggest to his psychiatric colleagues to try this drug in patients with psychosis. Chlorpromazine was first administered to an extremely agitated patient with mania in January 1952, and this patient was able to be discharged from the hospital weeks later. This case was published in March 1952, the first published report of the use of chlorpromazine in psychiatry (López-Muñoz et al., 2005). During the following months of 1952, additional reports were published describing the successful use of chlorpromazine in psychiatric patients with agitation, excitation, mania, and psychosis. Chlorpromazine was commercialized in France in 1952, and its clinical use subsequently spread throughout Europe and North America during the 1950s (López-Muñoz et al., 2005).
Methylene Blue and the Treatment of Psychoses
Although chlorpromazine is heralded as the first phenothiazine drug used in psychiatry (in 1952), this is not entirely accurate. Because of its sedative–hypnotic effects, the phenothiazine drug promethazine had been tested in patients with psychosis 2 years earlier. A report of 24 patients with manic-depressive psychosis treated with promethazine was published in 1950, but the un-impressive findings in this obscure paper apparently did not generate attention (López-Muñoz et al., 2005).
Even earlier than chlorpromazine and promethazine was the phenothiazine methylene blue. Paul Ehrlich and his pathologist colleague Paul Guttmann (1834–1893) reported on the use of methylene blue to treat malaria in two patients in 1891, ostensibly representing the first ever use of a synthetic drug in medicine (Howland, 2016c). In 1890, however, Ehrlich and a German psychiatrist, Arthur Leppmann (1854–1921), had described the use of methylene blue as an analgesic (Kristiansen, 1989). Ehrlich was stimulated to investigate the effect of methylene blue on pain because he had found that this drug had such a striking affinity for the nervous system. Ehrlich and Leppmann reported that methylene blue markedly alleviated pain in neuralgic and rheumatic diseases of the muscles, joints, and tendons. It is notable that methylene blue injections have recently been investigated in controlled studies of low-back pain (Farrokhi, Lotfi, Masoudi, & Gholami, 2016; Peng, Pang, Wu, Zhao, & Song, 2010).
In their 1890 paper, Ehrlich and Leppmann discussed whether methylene blue may have an effect on mental diseases, but they decided against testing this use (Kristiansen, 1989). Seemingly aware of the report by Ehrlich and Leppmann, an Italian physician, Pietro Bodoni of the University of Genoa, used methylene blue in 14 agitated patients with psychosis, and he described a rapid calming effect in a paper published in 1899 (Bodoni, 1899). Bodoni (1899) also noted that other physicians in Genoa had been using methylene blue for the same reason. In 1938, William Allexsaht described the use of methylene blue in five patients with catatonic psychoses, and he justified its use based on the known oxidative cellular effects of this drug (Allexsaht, 1938). More recent preclinical studies using animal models of psychosis demonstrated that methylene blue has antipsychotic drug-like effects (Klamer, Engel, & Svensson, 2004). In an open-label study of eight patients with schizophrenia, methylene blue had a modest, but statistically significant, effect on reducing psychopathology when it was added to ongoing antipsychotic drug therapy (Deutsch et al., 1997).
No additional clinical studies of methylene blue for schizophrenia have been conducted and none are listed on the clinicaltrials.gov website. However, one of the accepted off-label clinical uses of methylene blue is for the treatment of ifosfamide-induced encephalopathy (Pelgrims et al., 2000). Ifosfamide is an alkylating agent used to treat solid tumors, and it can cause an adverse neuropsychiatric syndrome characterized by symptoms ranging from somnolence or agitation to confusion, hallucinations, or coma.
Neurochemical Effects of Methylene Blue and the Treatment of Mood Disorders
With the introduction of chlorpromazine in the 1950s, there was obvious interest at that time in identifying other chlorpromazine-like drugs for the treatment of schizophrenia. A Swiss psychiatrist, Roland Kuhn (1912–2005), suggested to scientists at the Swiss pharmaceutical company Geigy that one of their compounds (known as G 22,355) be tested because this drug seemed to have the closest structural resemblance to chlorpromazine (Ban, 2006). Kuhn's studies of G 22,355 found little benefit in schizophrenia, but he noted serendipitously that some of these patients became hypomanic and some who were depressed seemed to have improved moods (Brown & Rosdolsky, 2015). Subsequent studies of G 22,355 were conducted in patients with depression, confirming the drug's antidepressant effect, and the findings were published in 1957. Later that year, the drug was released for clinical use with the generic name imipramine and the brand name Tofranil®. Imipramine has a central tricyclic ring structure that resembles, but is not the same as, the phenothiazine central ring structure found in methylene blue.
Also in 1957, the clinical antidepressant effect of the monoamine oxidase inhibitor (MAOI) drug iproniazid was reported (Ban, 2006). Iproniazid was synthesized in 1951 for the treatment of tuberculosis, but the drug was noted to cause euphoria and hyperactivity in some patients. This serendipitous observation led to the successful clinical trials of iproniazid in patients with depression. Other tricyclic and MAOI antidepressant drugs were subsequently developed, and studies of the mechanism of action of these drugs contributed to what has been called the monoamine hypothesis of depression (Hirschfeld, 2000).
Based on the redox-cycling properties of methylene blue first described by Ehrlich in 1885 (Howland, 2016c) and the use of this drug in patients with psychosis described by Bodoni in 1899, methylene blue was investigated in several studies of patients with bipolar disorder. An open-label study of methylene blue reported improvement in 14 of 24 patients with bipolar disorder (Narsapur & Naylor, 1983). In a 2-year double-blind crossover study, two doses of methylene blue (300 mg and 15 mg) were compared in 31 patients with bipolar depression (Naylor, Martin, Hopwood, & Watson, 1986). All patients were taking lithium and 17 completed the 2-year trial. The 300-mg dose was significantly more effective at reducing depression than the 15-mg dose. Methylene blue was not associated with changes in manic symptoms. A randomized placebo-controlled 3-week trial in 28 patients with bipolar depression demonstrated significant benefit for methylene blue 15 mg per day compared to placebo (Naylor, Smith, & Connelly, 1987). Methylene blue does not seem to worsen mania and may help with manic symptoms (Naylor, Smith, & Connelly, 1988). Recently, Alda et al. (2016) reported that high-dose methylene blue (195 mg per day versus 15 mg per day, each given for 3 months in random order) significantly reduced depression and anxiety symptoms without triggering hypomania or mania in a randomized double-blind crossover study of patients with bipolar disorder treated with lamotrigine (Lamictal®).
In addition to these clinical studies, anxiolytic and antidepressant-like effects have been demonstrated for methylene blue in preclinical animal models (Harvey et al., 2010; Oz, Lorke, Hasan, & Petroianu, 2011). Beyond redox-cycling, other neurochemical properties of methylene blue (and its metabolites) may explain the possible antidepressant effects of this drug. Methylene blue is excreted in the urine as a mixture of methylene blue, leucoMB, and several demethylated metabolites (i.e., azure B and azure A). LeucoMB is the reduced form of methylene blue (Howland, 2016c). These metabolites, in particular azure B, have active pharmacological effects contributing to the therapeutic effects of methylene blue (Petzer, Harvey, Wegener, & Petzer, 2012; Schirmer, Adler, Pickhardt, & Mandelkow, 2011).
Studies have shown that methylene blue inhibits the activity of the enzymes monoamine oxidase (MAO), nitric oxide synthase, and guanylyl cyclase, and it increases the release of neurotransmitters, such as serotonin and norepinephrine. The MAOI effect of methylene blue was demonstrated as long ago as 1937 (Oz et al., 2011). The enzyme MAO occurs in the body in two subtypes: type A (MAO-A) and type B (MAO-B) (Howland, 2006). Methylene blue and azure B may be selective reversible inhibitors of MAO-A (Harvey et al., 2010; Petzer et al., 2012). Moclobemide (Aurorix®) is a reversible inhibitor of MAO-A demonstrated to be effective in controlled treatment studies of chronic depressive disorders (Griffiths, Ravindran, Merali, & Anisman, 2000), which are associated with significant morbidity and functional impairment (Howland, 1993; Howland & Thase, 1993; Howland et al., 2008). Consistent with its MAOI properties, methylene blue is known to cause serotonin syndrome (Ng & Cameron, 2010). The U.S. Food and Drug Administration labeling for products comprising methylene blue contain a warning about the risk of combining these products with serotonergic drugs.
No additional clinical studies of methylene blue for unipolar depression or bipolar disorder have been conducted, and no clinical studies are listed on the clinicaltrials.gov website. Based on the findings from preclinical investigations and the bipolar disorder clinical studies, methylene blue deserves further study in the treatment of mood disorders. A relevant analogy is experience with atypical antipsychotic drugs. These drugs were first developed for use in treating schizophrenia, but were later found to have beneficial mood stabilizing and then antidepressant effects (Howland, 2010; Howland, 2016a). Methylene blue may be viewed in the same way.
Methylene Blue and Neurodegenerative Disorders
Alzheimer's disease is characterized by the pathological presence of amyloid-beta deposits (senile plaques) and neurofibrillary tangles. Neurofibrillary tangles contain paired helical filaments comprising truncated fragments of protein tau. Neuronal cell death in Alzheimer's disease preferentially affects cholinergic neurons, leading to a marked reduction in cholinergic function. During the 1980s, the psychiatrist Claude Wischik used electron microscopy to study protein tau, and he observed that the dye alcian blue used in electron microscopy caused tau filaments to dissolve (Gura, 2008). Because methylene blue was similar to alcian blue and had been used clinically in bipolar disorder and for urinary tract infections, further preclinical laboratory investigations of tau protein were conducted using methylene blue and other phenothiazine drugs. Methylene blue was found to selectively inhibit tau aggregation, facilitating the proteolytic degradation of tau filaments (Wischik, Edwards, Lai, Roth, & Harrington, 1996). Methylene blue also reduces amyloid-beta levels (Medina, Caccamo, & Oddo, 2011) and increases cholinergic transmission (Oz et al., 2011). Other neurochemical and cellular effects of methylene blue have been identified that justify its investigation in dementia and other neurodegenerative disorders (Oz, Lorke, & Petroianu, 2009).
Based on the tau protein laboratory findings, an exploratory randomized placebo-controlled Phase 2 study of methylthioninium (MT) was conducted in 321 patients with mild-moderate Alzheimer's disease (Wischik et al., 2015). The chloride form of MT (methylthioninium chloride; MTC) is methylene blue (Howland, 2016c). Study participants received one of three doses of MT or placebo for 24 weeks. Effect of treatment on regional cerebral blood flow (rCBF) was assessed in 135 patients using SPECT brain scans conducted before and after 24 weeks. After 24 weeks, patients entered sequential 6- and 12-month blinded extension phases where they all received MT (patients treated with placebo were switched to active drug during the extension phases). At 24 weeks, there was a significant benefit found for the middle 138 mg per day dose of MT at preventing cognitive decline compared to placebo, but no apparent benefit from the 69-mg or 228-mg doses. A significant treatment effect also was seen with the 138-mg dose on rCBF. With continued treatment with active drug for 12 months, benefit was seen with the 138-mg dose (Wischik et al., 2015).
As a redox molecule (see discussion by Howland [2016c]), MT has a complex pharmacokinetic profile that influences its dissolution, absorption, and disposition (Baddeley et al., 2015). This property may explain why a dose-response relationship was not found in the Phase 2 study of MT (Wischik et al., 2015). For this reason, a novel chemical entity (LMTX; TRx0237) was synthesized, in which the reduced form of MT (leucoMT; LMT) is available and stable in an oxygen environment. TRx0237 is being investigated in studies of Alzheimer's disease and frontotemporal dementia (NCT01689246; NCT01626391; NCT01689233; NCT01626378; NCT02245568; all on the clinicaltrials.gov website).
Recently, the first results from one of these TRx0237 Phase 3 studies (NCT01689246) were released at the 2016 Alzheimer's Association International Conference in Toronto, Canada on July 27, 2016. In this 15-month study, 891 patients with mild-moderate Alzheimer's disease were randomized to receive double-blind treatment with one of three TRx0237 doses: 250 mg per day, 150 mg per day, or 8 mg per day. The 8 mg per day dose was used as a control (having no expected benefit). Approved medications for treating dementia were being taken by 85% of participants and the mean age of patients was 71. Among all participants, there was no clear benefit for either dose compared to control. However, among those 15% of participants who were not taking other dementia medications, TRx0237 was found to have a statistically significant benefit on the cognitive and functional outcomes as well as having a positive effect on brain atrophy as measured by magnetic resonance imaging (MRI).
Also recently, the effect of a single dose of methylene blue versus placebo on cognitive function during brain functional MRI (fMRI) was assessed in a study of 26 healthy individuals (Rodriguez et al., 2016). Compared to placebo, methylene blue was found to modulate fMRI activity during sustained attention and working memory tasks and it enhanced memory retrieval. These findings support further investigation of the effect of methylene blue on cognition in individuals during healthy aging as well as in patients who have mild cognitive impairment or may otherwise be at risk for dementia.
Depression, anxiety disorder, bipolar disorder, and schizophrenia are associated with cognitive dysfunction and an increased risk for dementia (Zilkens, Bruce, Duke, Spilbury, & Semmens, 2014). Various psychotropic drugs have been shown to activate or regulate intracellular neurotrophic and neuroprotective processes that promote neurogenesis, and these drugs are protective in models of neurodegenerative diseases (Howland, 2016b). Methylene blue seems to have similar virtues (Oz et al., 2009). However, in the recent bipolar study by Alda et al. (2016) described above, methylene blue had no apparent effect on cognitive function. Methylene blue is currently being investigated for its effect on cognition and functional connectivity in healthy aging, mild cognitive impairment, and Alzheimer's disease (NCT02380573 on the clinicaltrials.gov website). However, given the discrepant outcomes reported for the Phase 2 and Phase 3 studies described above, an issue that will need to be considered is whether methylene blue and reduced forms of methylene blue (i.e., leucoMB or leucoMT) have important neurobiological differences that meaningfully influence their clinical effect on cognition or neurodegeneration.
Methylene blue is a truly unique chemical entity with a plethora of scientific and clinical uses. It was the first synthetic drug ever used in medicine, having been used to treat clinical pain syndromes, malaria, and psychotic disorders more than one century ago. Investigations of methylene blue were instrumental in the serendipitous development of phenothiazine antipsychotic drugs. It has been studied in bipolar disorder and deserves further investigation for the treatment of unipolar and bipolar disorders. More recently, methylene blue has been the subject of preclinical and clinical investigations for cognitive dysfunction, dementia, and other neurodegenerative disorders. The history of methylene blue, from its discovery as a dye to its use as a stain and then its therapeutic application in medicine, serves as an important example of how the use of a drug can evolve over time—through clinical need, careful observation and serendipity, and the integration of concepts across different scientific and clinical disciplines.
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