Combining Lovastatin and Minocycline for the Treatment of Fragile X Syndrome: Results From the LovaMiX Clinical Trial

Results from a Double-Blind, Randomized, Placebo-Controlled, Single-Dose, Crossover Trial of Lovastatin or Minocycline in Fragile X Syndrome

Introduction: Treatment studies in FMR1 knockout rodent models have found that minocycline and lovastatin each improve synaptic, neurological, and behavioral functioning, and open-label chronic dosing studies in human patients with fragile X syndrome (FXS) have demonstrated modest clinical improvements. Findings from blinded studies are mixed, and there is a limited understanding of electrophysiological target engagement that would facilitate cross-species translational studies. Smaller-scale, acute (e.g., single-dose) drug studies may speed treatment identification by detecting subtle electrophysiological and behavioral changes. Materials and Methods: Twenty-nine participants with FXS (31% female) ages 15-45 years completed a randomized, double-blind, crossover study in which they received a single oral dose of 40 mg of lovastatin, 270 mg of minocycline, or placebo, with a 2-week washout period between dosing visits. Participants completed a comprehensive neuropsychological battery and three EEG paradigms (resting state; auditory chirp; auditory habituation) before and 4 hours after dosing. Results: No serious adverse events were reported, and both drugs were well-tolerated. Compared with placebo, there were no overall treatment effects for any outcomes, including EEG, but several modest drug responses varied as a function of sex and age. Lovastatin treatment was associated with improved spatial awareness in older participants and females compared with minocycline and placebo. Discussion: We show that single-dose drug studies are highly feasible in FXS and that patients with FXS can complete a range of EEG and behavioral tasks, many of which have been shown to be reliable and may therefore be sensitive to subtle drug target engagement. Conclusions: Acute single doses of lovastatin or minocycline did not lead to changes in electrophysiological or performance-based measures. This may be due to the limited effects of these drugs in human patients or limited acute effects relative to chronic dosing. However, the study design was further validated for use in neurodevelopmental populations.

Emerging autism and Fragile X syndrome treatments

The limitations of current symptom-focused treatments drive the urgent need for effective therapies for autism and Fragile X syndrome (FXS). Currently, no approved pharmacological interventions target the core symptoms of these disorders. Advances in understanding the underlying biology of autism and FXS make this an important time to explore novel options. Indeed, several treatments have recently been tested in clinical trials, with promising results in treating core symptoms of autism and FXS. We focus on emerging interventions, such as gut microbiome therapies, anti-inflammatory approaches, bumetanide, phosphodiesterase 4D inhibitors, and endocannabinoid modulators. We also discuss factors, such as disorder heterogeneity, which may have contributed to poor efficacy in previously failed late-phase trials and impact recent trials, emphasizing the need for personalized treatment approaches.

Understanding pathophysiology in fragile X syndrome: a comprehensive review

Fragile X syndrome (FXS) is the leading hereditary cause of intellectual disability and the most commonly associated genetic cause of autism. Historically, research into its pathophysiology has focused predominantly on neurons; however, emerging evidence suggests involvement of additional cell types and systems. The objective of this study was to review and synthesize current evidence regarding the pathophysiology of Fragile X syndrome. A comprehensive literature review was conducted using databases such as PubMed and Google Scholar, employing MeSH terms including "Fragile X Syndrome," "FMR1 gene," and "FMRP." Studies on both human and animal models, from inception to 2022, published in recognized journals were included. The evidence supports those neurons, glial cells, stem cells, the immune system, and lipid metabolism pathways contribute to the pathophysiology of Fragile X syndrome. Further research is necessary to explore these fields independently and to elucidate their interactions.

Astrocytes in fragile X syndrome

Astrocytes have an important role in neuronal maturation and synapse function in the brain. The interplay between astrocytes and neurons is found to be altered in many neurodevelopmental disorders, including fragile X syndrome (FXS) that is the most common inherited cause of intellectual disability and autism spectrum disorder. Transcriptional, functional, and metabolic alterations in Fmr1 knockout mouse astrocytes, human FXS stem cell-derived astrocytes as well as in in vivo models suggest autonomous effects of astrocytes in the neurobiology of FXS. Abnormalities associated with FXS astrocytes include differentiation of central nervous system cell populations, maturation and regulation of synapses, and synaptic glutamate balance. Recently, FXS-specific changes were found more widely in astrocyte functioning, such as regulation of inflammatory pathways and maintenance of lipid homeostasis. Changes of FXS astrocytes impact the brain homeostasis and function both during development and in the adult brain and offer opportunities for novel types of approaches for intervention.

Minocycline improves autism-related behaviors by modulating microglia polarization in a mouse model of autism

Autism spectrum disorder (ASD) is a heterogeneous neurodevelopmental disorder with few pharmacological treatments. Minocycline, a tetracycline derivative that inhibits microglial activation, has been well-identified with anti-inflammatory properties and neuroprotective effects. A growing body of research suggests that ASD is associated with neuroinflammation, abnormal neurotransmitter levels, and neurogenesis. Thus, we hypothesized that minocycline could improve autism-related behaviors by inhibiting microglia activation and altering neuroinflammation. To verify our hypothesis, we used a mouse model of autism, BTBR T + Itpr3tf/J (BTBR). As expected, minocycline administration rescued the sociability and repetitive, stereotyped behaviors of BTBR mice while having no effect in C57BL/6J mice. We also found that minocycline improved neurogenesis and inhibited microglia activation in the hippocampus of BTBR mice. In addition, minocycline treatment inhibited Erk1/2 phosphorylation in the hippocampus of BTBR mice. Our findings show that minocycline administration alleviates ASD-like behaviors in BTBR mice and improves neurogenesis, suggesting that minocycline supplementation might be a potential strategy for improving ASD symptoms.

Neurodevelopment and early pharmacological interventions in Fragile X Syndrome

Fragile X Syndrome (FXS) is a neurodevelopmental disorder and the leading monogenic cause of autism and intellectual disability. For years, several efforts have been made to develop an effective therapeutic approach to phenotypically rescue patients from the disorder, with some even advancing to late phases of clinical trials. Unfortunately, none of these attempts have completely succeeded, bringing urgency to further expand and refocus research on FXS therapeutics. FXS arises at early stages of postnatal development due to the mutation and transcriptional silencing of the Fragile X Messenger Ribonucleoprotein 1 gene (FMR1) and consequent loss of the Fragile X Messenger Ribonucleoprotein (FMRP) expression. Importantly, FMRP expression is critical for the normal adult nervous system function, particularly during specific windows of embryogenic and early postnatal development. Cellular proliferation, migration, morphology, axonal guidance, synapse formation, and in general, neuronal network establishment and maturation are abnormally regulated in FXS, underlying the cognitive and behavioral phenotypes of the disorder. In this review, we highlight the relevance of therapeutically intervening during critical time points of development, such as early postnatal periods in infants and young children and discuss past and current clinical trials in FXS and their potential to specifically target those periods. We also discuss potential benefits, limitations, and disadvantages of these pharmacological tools based on preclinical and clinical research.

An iPSC-derived astrocyte model of fragile X syndrome exhibits dysregulated cholesterol homeostasis

Cholesterol is an essential membrane structural component and steroid hormone precursor, and is involved in numerous signaling processes. Astrocytes regulate brain cholesterol homeostasis and they supply cholesterol to the needs of neurons. ATP-binding cassette transporter A1 (ABCA1) is the main cholesterol efflux transporter in astrocytes. Here we show dysregulated cholesterol homeostasis in astrocytes generated from human induced pluripotent stem cells (iPSCs) derived from males with fragile X syndrome (FXS), which is the most common cause of inherited intellectual disability. ABCA1 levels are reduced in FXS human and mouse astrocytes when compared with controls. Accumulation of cholesterol associates with increased desmosterol and polyunsaturated phospholipids in the lipidome of FXS mouse astrocytes. Abnormal astrocytic responses to cytokine exposure together with altered anti-inflammatory and cytokine profiles of human FXS astrocyte secretome suggest contribution of inflammatory factors to altered cholesterol homeostasis. Our results demonstrate changes of astrocytic lipid metabolism, which can critically regulate membrane properties and affect cholesterol transport in FXS astrocytes, providing target for therapy in FXS.

New Animal Models for Understanding FMRP Functions and FXS Pathology

Fragile X encompasses a range of genetic conditions, all of which result as a function of changes within the FMR1 gene and abnormal production and/or expression of the FMR1 gene products. Individuals with Fragile X syndrome (FXS), the most common heritable form of intellectual disability, have a full-mutation sequence (>200 CGG repeats) which brings about transcriptional silencing of FMR1 and loss of FMR protein (FMRP). Despite considerable progress in our understanding of FXS, safe, effective, and reliable treatments that either prevent or reduce the severity of the FXS phenotype have not been approved. While current FXS animal models contribute their own unique understanding to the molecular, cellular, physiological, and behavioral deficits associated with FXS, no single animal model is able to fully recreate the FXS phenotype. This review will describe the status and rationale in the development, validation, and utility of three emerging animal model systems for FXS, namely the nonhuman primate (NHP), Mongolian gerbil, and chicken. These developing animal models will provide a sophisticated resource in which the deficits in complex functions of perception, action, and cognition in the human disorder are accurately reflected and aid in the successful translation of novel therapeutics and interventions to the clinic setting.