Minocycline as Treatment for Psychiatric and Neurological Conditions: A Systematic Review and Meta-Analysis

Psilocybin for dementia prevention? The potential role of psilocybin to alter mechanisms associated with major depression and neurodegenerative diseases

Major depression is an established risk factor for subsequent dementia, and depression in late life may also represent a prodromal state of dementia. Considering current challenges in the clinical development of disease modifying therapies for dementia, the focus of research is shifting towards prevention and modification of risk factors to alter the neurodegenerative disease trajectory. Understanding mechanistic commonalities underlying affective symptoms and cognitive decline may reveal biomarkers to aid early identification of those at risk of progressing to dementia during the preclinical phase of disease, thus allowing for timely intervention. Adult hippocampal neurogenesis (AHN) is a phenomenon that describes the birth of new neurons in the dentate gyrus throughout life and it is associated with spatial learning, memory and mood regulation. Microglia are innate immune system macrophages in the central nervous system that carefully regulate AHN via multiple mechanisms. Disruption in AHN is associated with both dementia and major depression and microgliosis is a hallmark of several neurodegenerative diseases. Emerging evidence suggests that psychedelics promote neuroplasticity, including neurogenesis, and may also be immunomodulatory. In this context, psilocybin, a serotonergic agonist with rapid-acting antidepressant properties has the potential to ameliorate intersecting pathophysiological processes relevant for both major depression and neurodegenerative diseases. In this narrative review, we focus on the evidence base for the effects of psilocybin on adult hippocampal neurogenesis and microglial form and function; which may suggest that psilocybin has the potential to modulate multiple mechanisms of action, and may have implications in altering the progression from major depression to dementia in those at risk.

Drug repurposing for neurodegenerative diseases

Neurodegenerative diseases (NDDs) are neuronal problems that include the brain and spinal cord and result in loss of sensory and motor dysfunction. Common NDDs include Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), Multiple Sclerosis (MS), and Amyotrophic Lateral Sclerosis (ALS) etc. The occurrence of these diseases increases with age and is one of the challenging problems among elderly people. Though, several scientific research has demonstrated the key pathologies associated with NDDs still the underlying mechanisms and molecular details are not well understood and need to be explored and this poses a lack of effective treatments for NDDs. Several lines of evidence have shown that NDDs have a high prevalence and affect more than a billion individuals globally but still, researchers need to work forward in identifying the best therapeutic target for NDDs. Thus, several researchers are working in the directions to find potential therapeutic targets to alter the disease pathology and treat the diseases. Several steps have been taken to identify the early detection of the disease and drug repurposing for effective treatment of NDDs. Moreover, it is logical that current medications are being evaluated for their efficacy in treating such disorders; therefore, drug repurposing would be an efficient, safe, and cost-effective way in finding out better medication. In the current manuscript we discussed the utilization of drugs that have been repurposed for the treatment of AD, PD, HD, MS, and ALS.

Evidence that minocycline treatment confounds the interpretation of neurofilament as a biomarker

Neurofilament light (NfL) concentration in cerebrospinal fluid (CSF) and blood serves as an important biomarker in neurology drug development. Changes in NfL are generally assumed to reflect changes in neuronal damage, while little is known about the clearance of NfL from biofluids. We observed an NfL increase of 3.5-fold in plasma and 5.7-fold in CSF in an asymptomatic individual at risk for genetic prion disease following 6 weeks' treatment with oral minocycline for a dermatologic indication. Other biomarkers remained normal, and proteomic analysis of CSF revealed that the spike was exquisitely specific to neurofilaments. NfL dropped nearly to normal levels 5 weeks after minocycline cessation, and the individual remained free of disease 2 years later. Plasma NfL in dermatology patients was not elevated above normal controls. Dramatically high plasma NfL (>500 pg/mL) was variably observed in some hospitalized individuals receiving minocycline. In mice, treatment with minocycline resulted in variable increases of 1.3- to 4.0-fold in plasma NfL, with complete washout 2 weeks after cessation. In neuron-microglia co-cultures, minocycline increased NfL concentration in conditioned media by 3.0-fold without any visually obvious impact on neuronal health. We hypothesize that minocycline does not cause or exacerbate neuronal damage, but instead impacts the clearance of NfL from biofluids, a potential confounder for interpretation of this biomarker.

Network-based drug repurposing for schizophrenia

Despite recent progress, the challenges in drug discovery for schizophrenia persist. However, computational drug repurposing has gained popularity as it leverages the wealth of expanding biomedical databases. Network analyses provide a comprehensive understanding of transcription factor (TF) regulatory effects through gene regulatory networks, which capture the interactions between TFs and target genes by integrating various lines of evidence. Using the PANDA algorithm, we examined the topological variances in TF-gene regulatory networks between individuals with schizophrenia and healthy controls. This algorithm incorporates binding motifs, protein interactions, and gene co-expression data. To identify these differences, we subtracted the edge weights of the healthy control network from those of the schizophrenia network. The resulting differential network was then analysed using the CLUEreg tool in the GRAND database. This tool employs differential network signatures to identify drugs that potentially target the gene signature associated with the disease. Our analysis utilised a large RNA-seq dataset comprising 532 post-mortem brain samples from the CommonMind project. We constructed co-expression gene regulatory networks for both schizophrenia cases and healthy control subjects, incorporating 15,831 genes and 413 overlapping TFs. Through drug repurposing, we identified 18 promising candidates for repurposing as potential treatments for schizophrenia. The analysis of TF-gene regulatory networks revealed that the TFs in schizophrenia predominantly regulate pathways associated with energy metabolism, immune response, cell adhesion, and thyroid hormone signalling. These pathways represent significant targets for therapeutic intervention. The identified drug repurposing candidates likely act through TF-targeted pathways. These promising candidates, particularly those with preclinical evidence such as rimonabant and kaempferol, warrant further investigation into their potential mechanisms of action and efficacy in alleviating the symptoms of schizophrenia.

Minocycline as a prospective therapeutic agent for cancer and non-cancer diseases: a scoping review

Minocycline is an FDA-approved secondary-generation tetracycline antibiotic. It is a synthetic antibiotic having many biological effects, such as antioxidant, anti-inflammatory, anti-cancer, and neuroprotective functions. This study discusses the pharmacological mechanisms of preventive and therapeutic effects of minocycline. Specifically, it provides a comprehensive overview of the molecular pathways by which minocycline acts on the different cancers, including ovarian, breast, glioma, colorectal, liver, pancreatic, lung, prostate, melanoma, head and neck, leukemia, and non-cancer diseases such as Alzheimer's disease, Parkinson, schizophrenia, multiple sclerosis, Huntington, polycystic ovary syndrome, and coronavirus disease 19. Minocycline may be a potential medication for these disorders due to its strong blood-brain barrier penetrance. It is also widely accepted as a specific medication, has a well-known side-effect characteristic, is reasonably priced, making it appropriate for continuous use in managing diseases, and has been demonstrated as an oral approach because it is effectively absorbed and accomplished almost all of the body's parts.

Association between doxycycline use and long-term functioning in patients with schizophrenia

IMPORTANCE AND OBJECTIVE

The brain-penetrant tetracycline antibiotics, minocycline and doxycycline, have been proposed as potential candidate drugs for treatment of schizophrenia, based on preclinical studies and clinical trials. A potential long-term beneficial effect of these antibiotics for schizophrenia patients has not been investigated. This study was designed to determine if redemption of doxycycline prescription in schizophrenia is associated with decreased incidence of disability pension, a proxy for long-term functioning.

DESIGN

We performed a population-based cohort study with data from schizophrenia patients available through the Danish registers. Survival analysis models with time-varying covariates were constructed to assess incidence rate ratios (IRR) of disability pension after exposure to doxycycline or a non-brain penetrant tetracycline, defined as at least one filled prescription. The analysis was adjusted for age, sex, calendar year, parental psychiatric status and educational level.

RESULTS

We used data from 11,157 individuals with schizophrenia (4,945 female and 6,212 male; average age 22.4 years old, standard deviation (std) 4.50). 718 of these were exposed to brain-penetrant doxycycline, and 1,498 individuals redeemed a prescription of one or more of the non-brain-penetrant tetracyclines. The average years at risk per person in this cohort was 4.9, and 2,901 individuals received disability pension in the follow-up period. There was a significantly lower incidence rate of disability pension in schizophrenia patients who had redeemed doxycycline compared to patients who did not redeem a prescription of any tetracycline antibiotics (Incidence rate ratio (IRR) 0.68; 95 % CI 0.56, 0.83). There was also a significant lower rate of disability pension in schizophrenia patients who redeemed doxycycline compared to individuals who redeemed a prescription of one of the non-brain penetrant tetracycline antibiotics (IRR 0.69 95 % CI 0.55, 0.87).

CONCLUSIONS

In this observational study, doxycycline exposure is associated with a reduced incidence of disability pension. These data support further studies on the potential long term neuroprotective effects of doxycycline and level of functioning in schizophrenia patients.

Emerging drugs for the treatment of irritability associated with autism spectrum disorder

INTRODUCTION

Autism spectrum disorder (ASD) is an early-onset disorder with a prevalence of 1% among children and reported disability-adjusted life years of 4.31 million. Irritability is a challenging behavior associated with ASD, for which medication development has lagged. More specifically, pharmacotherapy effectiveness may be limited against high adverse effects (considering side effect profiles and patient medication sensitivity); thus, the possible benefits of pharmacological interventions must be balanced against potential adverse events in each patient.

AREAS COVERED

After reviewing the neuropathophysiology of ASD-associated irritability, the benefits and tolerability of emerging medications in its treatment based on randomized controlled trials were detailed in light of mechanisms and targets of action.

EXPERT OPINION

Succeeding risperidone and aripiprazole, monotherapy with memantine may be beneficial. In addition, N-acetylcysteine, galantamine, sulforaphane, celecoxib, palmitoylethanolamide, pentoxifylline, simvastatin, minocycline, amantadine, pregnenolone, prednisolone, riluzole, propentofylline, pioglitazone, and topiramate, all adjunct to risperidone, and clonidine and methylphenidate outperformed placebo. These effects were through glutamatergic, γ-aminobutyric acidergic, inflammatory, oxidative, cholinergic, dopaminergic, and serotonergic systems. All medications were reported to be safe and tolerable. Considering sample size, follow-up, and effect size, further studies are necessary. Along with drug development, repositioning and combining existing drugs supported by the mechanism of action is recommended.

GABAergic and inflammatory changes in the frontal cortex following neonatal PCP plus isolation rearing, as a dual-hit neurodevelopmental model for schizophrenia

The pathogenesis of schizophrenia begins in early neurodevelopment and leads to excitatory-inhibitory imbalance. It is therefore essential that preclinical models used to understand disease, select drug targets and evaluate novel therapeutics encompass similar neurochemical deficits. One approach to improved preclinical modelling incorporates dual-hit neurodevelopmental insults, like neonatal administration of phencyclidine (PCP, to disrupt development of glutamatergic circuitry) then post-weaning isolation (Iso, to mimic adolescent social stress). We recently showed that male Lister-hooded rats exposed to PCP-Iso exhibit reduced hippocampal expression of the GABA interneuron marker calbindin. The current study expanded on this by investigating changes to additional populations of GABAergic interneurons in frontal cortical and hippocampal tissue from the same animals (by immunohistochemistry) as well as levels of GABA itself (via ELISA). Because inflammatory changes are also implicated in schizophrenia, we performed additional immunohistochemical evaluations of Iba-1 positive microglia as well as ELISA analysis of IL-6 in the same brain regions. Single-hit isolation-reared and dual-hit PCP-Iso rats both showed reduced parvalbumin immunoreactivity in the prelimbic/infralimbic region of the frontal cortex. However, this was more widespread in PCP-Iso, extending to the medial/ventral and lateral/dorsolateral orbitofrontal cortices. Loss of GABAergic markers was accompanied by increased microglial activation in the medial/ventral orbitofrontal cortices of PCP-Iso, together with frontal cortical IL-6 elevations not seen following single-hit isolation rearing. These findings enhance the face validity of PCP-Iso, and we advocate the use of this preclinical model for future evaluation of novel therapeutics-especially those designed to normalise excitatory-inhibitory imbalance or reduce neuroinflammation.

Between Dysbiosis, Maternal Immune Activation and Autism: Is There a Common Pathway?

Autism spectrum disorder (ASD) is a neuropsychiatric condition characterized by impaired social interactions and repetitive stereotyped behaviors. Growing evidence highlights an important role of the gut-brain-microbiome axis in the pathogenesis of ASD. Research indicates an abnormal composition of the gut microbiome and the potential involvement of bacterial molecules in neuroinflammation and brain development disruptions. Concurrently, attention is directed towards the role of short-chain fatty acids (SCFAs) and impaired intestinal tightness. This comprehensive review emphasizes the potential impact of maternal gut microbiota changes on the development of autism in children, especially considering maternal immune activation (MIA). The following paper evaluates the impact of the birth route on the colonization of the child with bacteria in the first weeks of life. Furthermore, it explores the role of pro-inflammatory cytokines, such as IL-6 and IL-17a and mother's obesity as potentially environmental factors of ASD. The purpose of this review is to advance our understanding of ASD pathogenesis, while also searching for the positive implications of the latest therapies, such as probiotics, prebiotics or fecal microbiota transplantation, targeting the gut microbiota and reducing inflammation. This review aims to provide valuable insights that could instruct future studies and treatments for individuals affected by ASD.

Targeting inflammatory signaling in obsessive compulsive disorder: a promising approach

Obsessive-compulsive disorder (OCD) is a neuropsychiatric disorder. Approximately, around 2% to 3% percent of the general population experience symptoms of OCD over the course of their lifetime. OCD can lead to economic burden, poor quality of life, and disability. The characteristic features exhibited generally in OCD are continuous intrusive thoughts and periodic ritualized behaviours. Variations in genes, pathological function of Cortico-Striato-Thalamo-Cortical (CSTC) circuits and dysregulation in the synaptic conduction have been the major factors involved in the pathological progression of OCD. However, the basic mechanisms still largely unknown. Current therapies for OCD largely target monoaminergic neurotransmitters (NTs) in specific dopaminergic and serotonergic circuits. However, such therapies have limited efficacy and tolerability. Drug resistance has been one of the important reasons reported to critically influence the effectiveness of the available drugs. Inflammation has been a crucial factor which is believed to have a significant importance in OCD progression. A significant number of proinflammatory cytokines have been reportedly amplified in patients with OCD. Mechanisms of drug treatment involve attenuation of the symptoms via modulation of inflammatory signalling pathways, modification in brain structure, and synaptic plasticity. Hence, targeting inflammatory signaling may be considered as a suitable approach in the treatment of OCD. The present review focuses mainly on the significant findings from the animal and human studies conducted in this area, that targets inflammatory signaling in neurological conditions. In addition, it also focusses on the therapeutic approaches that target OCD via modification of the inflammatory signaling pathways.

Repurposing of pexidartinib for microglia depletion and renewal

Pexidartinib (PLX3397) is a small molecule receptor tyrosine kinase inhibitor of colony stimulating factor 1 receptor (CSF1R) with moderate selectivity over other members of the platelet derived growth factor receptor family. It is approved for treatment of tenosynovial giant cell tumors (TGCT). CSF1R is highly expressed by microglia, which are macrophages of the central nervous system (CNS) that defend the CNS against injury and pathogens and contribute to synapse development and plasticity. Challenged by pathogens, apoptotic cells, debris, or inflammatory molecules they adopt a responsive state to propagate the inflammation and eventually return to a homeostatic state. The phenotypic switch may fail, and disease-associated microglia contribute to the pathophysiology in neurodegenerative or neuropsychiatric diseases or long-lasting detrimental brain inflammation after brain, spinal cord or nerve injury or ischemia/hemorrhage. Microglia also contribute to the growth permissive tumor microenvironment of glioblastoma (GBM). In rodents, continuous treatment for 1-2 weeks via pexidartinib food pellets leads to a depletion of microglia and subsequent repopulation from the remaining fraction, which is aided by peripheral monocytes that search empty niches for engraftment. The putative therapeutic benefit of such microglia depletion or forced renewal has been assessed in almost any rodent model of CNS disease or injury or GBM with heterogeneous outcomes, but a tendency of partial beneficial effects. So far, microglia monitoring e.g. via positron emission imaging is not standard of care for patients receiving Pexidartinib (e.g. for TGCT), so that the depletion and repopulation efficiency in humans is still largely unknown. Considering the virtuous functions of microglia, continuous depletion is likely no therapeutic option but short-lasting transient partial depletion to stimulate microglia renewal or replace microglia in genetic disease in combination with e.g. stem cell transplantation or as part of a multimodal concept in treatment of glioblastoma appears feasible. The present review provides an overview of the preclinical evidence pro and contra microglia depletion as a therapeutic approach.

Depression and the Aberrant Intestinal Microbiome

Depression is one of the most common mental health disorders affecting adults in the United States. The current treatment is the combination of pharmacotherapy and psychotherapy. Recently, the evidence linking gut microbiome dysregulation to the development of depression has grown. The pathophysiology is currently poorly understood, although leading hypotheses include involvement of the hypothalamic-pituitary-adrenal axis, a bidirectional relationship between the gut microbiome and the central nervous system, and production of signaling molecules by the gut microbiome. Available and emerging treatments of the aberrant microbiome include antidepressants, antibiotics, diet modification, probiotics, and fecal microbiota transplant. This article explores the interconnectivity of gut microbiota and depression and treatments targeted toward the gut, reviews the gastroenterologist's potential role in managing gut dysbiosis in patients with depression, and highlights research topics to be addressed to create evidence-based guidelines.

From Animal Models to Clinical Trials: The Potential of Antimicrobials in Multiple Sclerosis Treatment

Multiple sclerosis (MS) is a chronic, autoimmune, demyelinating disease of the central nervous system (CNS). Microbes, including bacteria and certain viruses, particularly Epstein-Barr virus (EBV), have been linked to the pathogenesis of MS. While there is currently no cure for MS, antibiotics and antivirals have been studied as potential treatment options due to their immunomodulatory ability that results in the regulation of the immune process. The current issue addressed in this systematic review is the effect of antimicrobials, including antibiotics, antivirals, and antiparasitic agents in animals and humans. We performed a comprehensive search of PubMed, Google Scholar, and Scopus for articles on antimicrobials in experimental autoimmune encephalomyelitis animal models of MS, as well as in people with MS (pwMS). In animal models, antibiotics tested included beta-lactams, minocycline, rapamycin, macrolides, and doxycycline. Antivirals included acyclovir, valacyclovir, and ganciclovir. Hydroxychloroquine was the only antiparasitic that was tested. In pwMS, we identified a total of 24 studies, 17 of them relevant to antibiotics, 6 to antivirals, and 1 relevant to antiparasitic hydroxychloroquine. While the effect of antimicrobials in animal models was promising, only minocycline and hydroxychloroquine improved outcome measures in pwMS. No favorable effect of the antivirals in humans has been observed yet. The number and size of clinical trials testing antimicrobials have been limited. Large, multicenter, well-designed studies are needed to further evaluate the effect of antimicrobials in MS.

Minocycline in depression not responding to first-line therapy: A systematic review and meta-analysis

BACKGROUND

Major depressive disorder is often resistant to first-line treatment, with around 30% failing to respond to traditional therapy. Treatment-resistant depression results in prolonged hospitalization and healthcare costs. Anti-inflammatory drugs have shown promising results in depression not responding to initial therapy. Minocycline has anti-inflammatory properties and crosses the blood-brain barrier. It has demonstrated varied results in several randomized controlled trials (RCTs).

METHODS

We assessed the efficacy of minocycline compared to placebo in depression not responding to one first-line antidepressant via a systematic review and meta-analysis. We performed a comprehensive literature search across PubMed, Cochrane, and Scopus for RCTs. We visualized the results using forest plots and drapery plots. We assessed and explored heterogeneity using I2, prediction interval, and meta-regression. Then, we rated the certainty of the evidence.

RESULTS

Four RCTs revealed a non-significant difference in depression severity [-3.93; 95% CI: -16.14 to 8.28], rate of response [1.15; 0.33-4.01], and rate of remission [0.94; 0.44-2.01]. However, the reduction in depression severity is significant at a trend of P < .1. The high between-study heterogeneity (I2 = 78%) for depression severity could be answered by meta-regression (P = .02) for the duration of therapy.

CONCLUSION

There is no significant difference with minocycline compared to placebo for depression not responding to first-line antidepressant therapy. However, the treatment response varies with treatment duration and patients' neuroinflammatory state. Thus, larger and longer RCTs, especially in diverse disease subgroups, are needed for further insight. This is needed to allow greater precision medicine in depression and avoid elevated healthcare expenditure associated with hit-and-trial regimens.

REGISTRATION

CRD42023398476 (PROSPERO).