Hydroxychloroquine antiparkinsonian potential: Nurr1 modulation versus autophagy inhibition

Hydroxychloroquine attenuated motor impairment and oxidative stress in a rat 6-hydroxydopamine model of Parkinson's disease

PURPOSE

Parkinson's disease (PD) is associated with the destruction of dopaminergic neurons in the substantia nigra (SN). Hydroxychloroquine (HCQ) has the capability to cross the blood-brain barrier and promote a neuroprotective potential. This study evaluated the effects of HCQ on the 6-hydroxydopamine (6-OHDA)-induced PD model in rats.

METHODS

Wistar rats were randomly divided into sham, PD, PD + levodopa and PD + HCQ groups. The PD model was induced by a stereotactic administration of 6-OHDA into the left SN pars compacta (SNpc) and confirmed by rotation and the Murprogo's tests. HCQ (100 mg/kg, p.o.) and levodopa (12 mg/kg, p.o.) were administered once a day for 21 days. Three weeks after surgery, the behavioral tests were performed. Brain lipid peroxidation index (MDA), glutathione peroxidase activity (GPx), total antioxidant capacity (TAC) levels and α-synuclein protein expression in the SN were also measured.

RESULTS

The behavioral tests demonstrated that induction of PD increased the muscle rigidity and the number of rotations, which were reversed by HCQ treatment. Also, induction of PD was associated with an increase in α-synuclein protein levels and MDA and decreased TAC levels and GPx activity. However, HCQ decreased α-synuclein and MDA levels while increased TAC levels and GPx activity. In addition, histopathological data showed that HCQ protects dopaminergic neurons against 6-OHDA-induced toxicity.

CONCLUSION

According to the results, HCQ has a beneficial effect in improving PD-related pathophysiology, in part, by mitigating oxidative stress and protecting the dopaminergic neurons in the SN.

Novel trajectories of the NK1R antagonist aprepitant in rotenone-induced Parkinsonism-like symptoms in rats: Involvement of ERK5/KLF4/p62/Nrf2 signaling axis

Regulation of the interplay between autophagy and oxidative stress is vital in maintaining neuronal homeostasis during neurotoxicity. The interesting involvement of NK1 receptor (NK1R) in neurodegeneration has highlighted the value of investigating the neuroprotective effect of aprepitant (Aprep), an NK1R antagonist in Parkinson's disease (PD). This study was conducted to disclose Aprep's ability to modulate extracellular signal-regulated kinase 5/Krüppel-like factor 4 (ERK5/KLF4) cue as molecular signaling implicated in regulating autophagy and redox signaling in response to rotenone neurotoxicity. Rotenone (1.5 mg/kg) was administered on alternate days, and rats were given Aprep simultaneously with or without PD98059, an ERK inhibitor, for 21 days. Aprep ameliorated motor deficits as verified by restored histological features, and intact neurons count in SN and striata along with tyrosine hydroxylase immunoreactivity in SN. The molecular signaling of Aprep was illustrated by the expression of KLF4 following the phosphorylation of its upstream target, ERK5. Nuclear factor erythroid 2-related factor 2 (Nrf2) was up-regulated, shifting the oxidant/antioxidant balance towards the antioxidant side, as evidenced by elevated GSH and suppressed MDA levels. In parallel, Aprep noticeably reduced phosphorylated α-synuclein aggregates due to autophagy induction as emphasized by marked LC3II/LC3I elevation and p62 level reduction. These effects were diminished upon PD98059 pre-administration. In conclusion, Aprep showed neuroprotective effects against rotenone-induced PD, which may be partially attributed to the activation of the ERK5/KLF4 signaling pathway. It modulated p62-mediated autophagy and Nrf2 axis which act cooperatively to counter rotenone-associated neurotoxicity pointing to Aprep's prospect as a curious candidate in PD research.

PTPA variants and impaired PP2A activity in early-onset parkinsonism with intellectual disability

The protein phosphatase 2A complex (PP2A), the major Ser/Thr phosphatase in the brain, is involved in a number of signalling pathways and functions, including the regulation of crucial proteins for neurodegeneration, such as alpha-synuclein, tau and LRRK2. Here, we report the identification of variants in the PTPA/PPP2R4 gene, encoding a major PP2A activator, in two families with early-onset parkinsonism and intellectual disability. We carried out clinical studies and genetic analyses, including genome-wide linkage analysis, whole-exome sequencing, and Sanger sequencing of candidate variants. We next performed functional studies on the disease-associated variants in cultured cells and knock-down of ptpa in Drosophila melanogaster. We first identified a homozygous PTPA variant, c.893T>G (p.Met298Arg), in patients from a South African family with early-onset parkinsonism and intellectual disability. Screening of a large series of additional families yielded a second homozygous variant, c.512C>A (p.Ala171Asp), in a Libyan family with a similar phenotype. Both variants co-segregate with disease in the respective families. The affected subjects display juvenile-onset parkinsonism and intellectual disability. The motor symptoms were responsive to treatment with levodopa and deep brain stimulation of the subthalamic nucleus. In overexpression studies, both the PTPA p.Ala171Asp and p.Met298Arg variants were associated with decreased PTPA RNA stability and decreased PTPA protein levels; the p.Ala171Asp variant additionally displayed decreased PTPA protein stability. Crucially, expression of both variants was associated with decreased PP2A complex levels and impaired PP2A phosphatase activation. PTPA orthologue knock-down in Drosophila neurons induced a significant impairment of locomotion in the climbing test. This defect was age-dependent and fully reversed by L-DOPA treatment. We conclude that bi-allelic missense PTPA variants associated with impaired activation of the PP2A phosphatase cause autosomal recessive early-onset parkinsonism with intellectual disability. Our findings might also provide new insights for understanding the role of the PP2A complex in the pathogenesis of more common forms of neurodegeneration.

Association of COVID-19 with Comorbidities: An Update

Coronavirus disease (COVID-19) is caused by severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) which was identified in Wuhan, China in December 2019 and jeopardized human lives. It spreads at an unprecedented rate worldwide, with serious and still-unfolding health conditions and economic ramifications. Based on the clinical investigations, the severity of COVID-19 appears to be highly variable, ranging from mild to severe infections including the death of an infected individual. To add to this, patients with comorbid conditions such as age or concomitant illnesses are significant predictors of the disease's severity and progression. SARS-CoV-2 enters inside the host cells through ACE2 (angiotensin converting enzyme2) receptor expression; therefore, comorbidities associated with higher ACE2 expression may enhance the virus entry and the severity of COVID-19 infection. It has already been recognized that age-related comorbidities such as Parkinson's disease, cancer, diabetes, and cardiovascular diseases may lead to life-threatening illnesses in COVID-19-infected patients. COVID-19 infection results in the excessive release of cytokines, called "cytokine storm", which causes the worsening of comorbid disease conditions. Different mechanisms of COVID-19 infections leading to intensive care unit (ICU) admissions or deaths have been hypothesized. This review provides insights into the relationship between various comorbidities and COVID-19 infection. We further discuss the potential pathophysiological correlation between COVID-19 disease and comorbidities with the medical interventions for comorbid patients. Toward the end, different therapeutic options have been discussed for COVID-19-infected comorbid patients.

Neuroprotective role of chloroquine via modulation of autophagy and neuroinflammation in MPTP-induced Parkinson's disease

Parkinson's disease (PD) is a neuro-motor ailment that strikes adults in their older life and results in both motor and non-motor impairments. In neuronal and glial cells, PD has recently been linked to a dysregulated autophagic system and cerebral inflammation. Chloroquine (CQ), an anti-malarial drug, has been demonstrated to suppress autophagy in a variety of diseases, including cerebral ischemia, Alzheimer's disease (AD), and Traumatic brain injury (TBI), while its involvement in PD is still unclear. BALB/c mice were randomly allocated to one of four groups: 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP), CQ treatment with or without MPTP, or control. The CQ treatment group received CQ (intraperitoneally, 8 mg/kg body weight) after 1 h of MPTP induction on day 1, and it lasted for 7 days. CQ therapy preserves dopamine levels stable, inhibits tyrosine hydroxylase (TH) positive dopaminergic cell death, and lowers oxidative stress. CQ reduces the behavioural, motor, and cognitive deficits caused by MPTP after injury. Furthermore, CQ therapy slowed aberrant neuronal autophagy (microtubule-associated protein-1 light chain 3B; LC3B & Beclin1) and lowered expression levels of the inflammatory cytokines interleukin 1 (IL-1β) and tumour necrosis factor (TNF-α) in the mice brain. In addition, CQ's antioxidant and anti-inflammatory effects were also tested in MPTP-mediated cell death in PC12 cells, demonstrating that CQ has a neurorestorative impact by successfully rescuing MPTP-induced ROS generation and cell loss. Our findings show that CQ's can help to prevent dopaminergic degeneration and improve neurological function after MPTP intoxication by lowering the harmful effects of neuronal autophagy and cerebral inflammation.

Advances in NURR1-Regulated Neuroinflammation Associated with Parkinson's Disease

Neuroinflammation plays a crucial role in the progression of neurodegenerative disorders, particularly Parkinson's disease (PD). Glial cell activation and subsequent adaptive immune involvement are neuroinflammatory features in familial and idiopathic PD, resulting in the death of dopaminergic neuron cells. An oxidative stress response, inflammatory mediator production, and immune cell recruitment and activation are all hallmarks of this activation, leading to chronic neuroinflammation and progressive neurodegeneration. Several studies in PD patients' cerebrospinal fluid and peripheral blood revealed alterations in inflammatory markers and immune cell populations that may lead to or exacerbate neuroinflammation and perpetuate the neurodegenerative process. Most of the genes causing PD are also expressed in astrocytes and microglia, converting their neuroprotective role into a pathogenic one and contributing to disease onset and progression. Nuclear receptor-related transcription factor 1 (NURR1) regulates gene expression linked to dopaminergic neuron genesis and functional maintenance. In addition to playing a key role in developing and maintaining neurotransmitter phenotypes in dopaminergic neurons, NURR1 agonists have been shown to reverse behavioral and histological abnormalities in animal PD models. NURR1 protects dopaminergic neurons from inflammation-induced degeneration, specifically attenuating neuronal death by suppressing the expression of inflammatory genes in microglia and astrocytes. This narrative review highlights the inflammatory changes in PD and the advances in NURR1-regulated neuroinflammation associated with PD. Further, we present new evidence that targeting this inflammation with a variety of potential NURR1 target therapy medications can effectively slow the progression of chronic neuroinflammation-induced PD.

Crosstalk between PI3K/AKT/KLF4 signaling and microglia M1/M2 polarization as a novel mechanistic approach towards flibanserin repositioning in parkinson's disease

Balancing microglia M1/M2 polarization has been shown as a prospective therapeutic strategy for Parkinson's disease (PD). Various vital signaling pathways are likely to govern the microglial phenotype. The implication of 5HT1A receptors in neurodegenerative disorders has raised interest in exploring the repositioning of flibanserin (Flib), a 5HT1A agonist, as an effective neuroprotective agent for PD. Therefore, this study was designed to assess the ability of Flib to modulate microglia phenotype switching from M1 to M2 via PI3K/AKT downstream targets in a rotenone model of PD. Rats received rotenone (1.5 mg/kg) every other day and were concurrently treated with Flib (40 mg/kg/day) with or without wortmannin (15 μg/kg/day), a PI3K inhibitor, for 21 days. Flib improved the motor perturbations induced by rotenone, as confirmed by the reversion of histopathological damage and tyrosine hydroxylase immunohistochemical alterations in both the striata and substantia nigra. The molecular signaling of Flib was elaborated by inducing striatal AKT phosphorylation and the expression of its substantial target, KLF4. Flib induced STAT6 phosphorylation to promote M2 polarization as demonstrated by the increased CD163⁺⁺ microglial count with striatal arginase activity. In parallel, it markedly inhibited M1 activation as evidenced by the reduction in CD86⁺⁺ microglia count with striatal proinflammatory mediators, IL-1β and iNOS. The pre-administration of wortmannin mostly negated Flib's neuroprotective effects. In conclusion, Flib AKT/ KLF4-dependently amended M1/M2 microglial imbalance to exert a promising neuroprotective effect, highlighting its potential as a revolutionary candidate for conquering PD.

A Nurr1 ligand C-DIM12 attenuates brain inflammation and improves functional recovery after intracerebral hemorrhage in mice

We have previously reported that amodiaquine, a compound that binds to the ligand-binding domain of a nuclear receptor Nurr1, attenuates inflammatory responses and neurological deficits after intracerebral hemorrhage (ICH) in mice. 1,1-Bis(3'-indolyl)-1-(p-chlorophenyl)methane (C-DIM12) is another Nurr1 ligand that recognizes a domain of Nurr1 different from the ligand-binding domain. In the present study, mice were treated daily with C-DIM12 (50 or 100 mg/kg, p.o.) or amodiaquine (40 mg/kg, i.p.), or twice daily with 1400 W (20 mg/kg, i.p.), an inducible nitric oxide synthase (iNOS) inhibitor, from 3 h after ICH induction by microinjection of collagenase into the striatum. C-DIM12 improved the recovery of neurological function and prevented neuron loss in the hematoma, while suppressed activation of microglia/macrophages and expression of inflammatory mediators interleukin-6 and CC chemokine ligand 2. In addition, C-DIM12 as well as amodiaquine preserved axonal structures in the internal capsule and axonal transport function. We also found that C-DIM12 and amodiaquine suppressed the increases of iNOS mRNA expression after ICH. Moreover, 1400 W improved neurological function and prevented neuron loss, activation of microglia/macrophages and axonal transport dysfunction. These results suggest that suppression of iNOS induction contributes to several features of the therapeutic effects of Nurr1 ligands.

Disease-Modifying Antirheumatic Drugs and Risk of Parkinson Disease: Nested Case-Control Study of People With Rheumatoid Arthritis

BACKGROUND

Epidemiological studies have suggested a link between rheumatoid arthritis and Parkinson's disease (PD). Disease-modifying anti-rheumatic drugs (DMARDs) might explain this association.

OBJECTIVE

To evaluate the association between DMARDs and risk of PD in persons with rheumatoid arthritis.

METHODS

Nested nationwide case-control study was conducted within the Finnish Parkinson's disease (FINPARK) cohort that includes 22,189 Finnish persons with clinically verified PD diagnosed in 1996-2015. The cases had recorded diagnosis of PD in the Special Reimbursement Register and had no exclusion diagnoses whose symptoms may be confused with PD within two years of PD diagnosis. This study included cases with PD diagnosed during 1999-2015 and rheumatoid arthritis diagnosed >3 years before PD. Rheumatoid arthritis was identified using Finnish Care Register for Health Care and Special Reimbursement Register. Cases were matched with up to seven control persons by age, sex, duration of rheumatoid arthritis and region. DMARDs were categorised into five classes and data on purchased prescriptions was identified from the Prescription Register since 1995. Associations were studied with conditional logistic regression adjusted for confounders.

RESULTS

Altogether 315 cases with PD and 1,571 matched controls were included. Majority (> 60%) were women and median duration of rheumatoid arthritis on matching date was 11.6 years for controls and 12.6 years for cases. Use of DMARDs was not associated with risk of PD with three-year lag period applied between exposure and outcome, except chloroquine/hydroxychloroquine which associated with decreased risk (adjusted odds ratio 0.74; 95% confidence interval 0.56-0.97). Other DMARDs, including sulfasalazine, methotrexate, gold preparations and immunosuppressants, were not associated with PD.

DISCUSSION

Our results suggest that the lower risk of PD in people with rheumatoid arthritis is not explained by DMARD use as these drugs in general did not modify the risk of PD among persons with rheumatoid arthritis. Association between chloroquine/hydroxychloroquine and lower risk of PD as well as the possible underlying mechanisms should be further investigated.

CLASSIFICATION OF EVIDENCE

This study provides Class II evidence that in individuals with rheumatoid arthritis using DMARDs, only chloroquine/hydroxychloroquine was associated with a potentially decreased risk of developing PD (adjusted OR 0.74, 95% CI 0.56-0.97).

Hydroxychloroquine improves motor function and affords neuroprotection without inhibition of inflammation and autophagy in mice after intracerebral hemorrhage

We examined the effect of an immunomodulator hydroxychloroquine, also known as a Nurr1 ligand and an autophagy inhibitor, on a mouse model of intracerebral hemorrhage (ICH). Daily administration of hydroxychloroquine (100 mg/kg, i.p.) from 3 h after induction of ICH alleviated neurological deficits of mice, increased the number of surviving neurons in the hematoma and prevented fragmentation of axon structures in the internal capsule. Unexpectedly, hydroxychloroquine did not inhibit either upregulation of pro-inflammatory mediators or autophagic responses in the brain. Hence, hydroxychloroquine may produce therapeutic effects on ICH primarily via neuroprotection including preservation of the axon tract integrity.

Copolymer Involving 2-Hydroxyethyl Methacrylate and 2-Chloroquinyl Methacrylate: Synthesis, Characterization and In Vitro 2-Hydroxychloroquine Delivery Application

The Poly(2-chloroquinyl methacrylate-co-2-hydroxyethyl methacrylate) (CQMA-co-HEMA) drug carrier system was prepared with different compositions through a free-radical copolymerization route involving 2-chloroquinyl methacrylate (CQMA) and 2-hydroxyethyl methacrylate) (HEMA) using azobisisobutyronitrile as the initiator. 2-Chloroquinyl methacrylate monomer (CQMA) was synthesized from 2-hydroxychloroquine (HCQ) and methacryloyl chloride by an esterification reaction using triethylenetetramine as the catalyst. The structure of the CQMA and CQMA-co-HEMA copolymers was confirmed by a CHN elementary analysis, Fourier transform infra-red (FTIR) and nuclear magnetic resonance (NMR) analysis. The absence of residual aggregates of HCQ or HCQMA particles in the copolymers prepared was confirmed by a differential scanning calorimeter (DSC) and XR-diffraction (XRD) analyses. The gingival epithelial cancer cell line (Ca9-22) toxicity examined by a lactate dehydrogenase (LDH) assay revealed that the grafting of HCQ onto PHEMA slightly affected (4.2-9.5%) the viability of the polymer carrier. The cell adhesion and growth on the CQMA-co-HEMA drug carrier specimens carried out by the (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) (MTT) assay revealed the best performance with the specimen containing 3.96 wt% HCQ. The diffusion of HCQ through the polymer matrix obeyed the Fickian model. The solubility of HCQ in different media was improved, in which more than 5.22 times of the solubility of HCQ powder in water was obtained. According to Belzer, the in vitro HCQ dynamic release revealed the best performance with the drug carrier system containing 4.70 wt% CQMA.

Quantitative Immunohistochemistry to Measure Regional Expression of Nurr1 in the Brain and the Effect of the Nurr1 Heterozygous Genotype

The transcription factor Nurr1 is a member of the steroid hormone nuclear receptor superfamily. Ablation of Nurr1 expression arrests mesencephalic dopamine neuron differentiation while attenuation of Nurr1 in the subiculum and hippocampus impairs learning and memory. Additionally, reduced Nurr1 expression has been reported in patients with Parkinson's disease and Alzheimer's disease. In order to better understand the overall function of Nurr1 in the brain, quantitative immunohistochemistry was used to measure cellular Nurr1 protein expression, across Nurr1 immunoreactive neuronal populations. Additionally, neuronal Nurr1 expression levels were compared between different brain regions in wild-type mice (+/+) and Nurr1 heterozygous mice (+/-). Regional Nurr1 protein was also investigated at various time points after a seizure induced by pentylenetetrazol (PTZ). Nurr1 protein is expressed in various regions throughout the brain, however, a wide range of Nurr1 expression levels were observed among various neuronal populations. Neurons in the parietal and temporal cortex (secondary somatosensory, insular, auditory, and temporal association cortex) had the highest relative Nurr1 expression (100%) followed closely by the claustrum/dorsal endopiriform cortex (85%) and then subiculum (76%). Lower Nurr1 protein levels were found in neurons in the substantia nigra pars compacta and ventral tegmental area (39%) followed by CA1 (25%) and CA3 (19%) of the hippocampus. Additionally, in the parietal and temporal cortex, two distinct populations of high and medium Nurr1 expressing neurons were observed. Comparisons between +/- and +/+ mice revealed Nurr1 protein was reduced in +/- mice by 27% in the parietal/temporal cortex, 49% in the claustrum/dorsal endopiriform cortex, 25% in the subiculum, 33% in substantia nigra pars compacta, 22% in ventral tegmental area, and 21% in CA1 region of the hippocampus. Based on these data, regional mechanisms appear to exist which can compensate for a loss of a Nurr1 allele. Following a single PTZ-induced seizure, Nurr1 protein in the dentate gyrus peaked around 2 h and returned to baseline by 8 h. Since altered Nurr1 expression has been implicated in neurologic disorders and Nurr1 agonists have showed protective effects, understanding regional protein expression of Nurr1, therefore, is necessary to understand how changes in Nurr1 expression can alter brain function.

Potent synthetic and endogenous ligands for the adopted orphan nuclear receptor Nurr1

Until recently, Nurr1 (NR4A2) was known as an orphan nuclear receptor without a canonical ligand-binding domain, featuring instead a narrow and tight cavity for small molecular ligands to bind. In-depth characterization of its ligand-binding pocket revealed that it is highly dynamic, with its structural conformation changing more than twice on the microsecond-to-millisecond timescale. This observation suggests the possibility that certain ligands are able to squeeze into this narrow space, inducing a conformational change to create an accessible cavity. The cocrystallographic structure of Nurr1 bound to endogenous ligands such as prostaglandin E1/A1 and 5,6-dihydroxyindole contributed to clarifying the crucial roles of Nurr1 and opening new avenues for therapeutic interventions for neurodegenerative and/or inflammatory diseases related to Nurr1. This review introduces novel endogenous and synthetic Nurr1 agonists and discusses their potential effects in Nurr1-related diseases.

The nuclear receptor 4A family members: mediators in human disease and autophagy

The Nuclear receptor 4A (NR4A) subfamily, which belongs to the nuclear receptor (NR) superfamily, has three members: NR4A1 (Nur77), NR4A2 (Nurr1) and NR4A3 (Nor1). They are gene regulators with broad involvement in various signaling pathways and human disease responses, including autophagy. Here, we provide a concise overview of the current understanding of the role of the NR4A subfamily members in human diseases and review the research into their regulation of cell autophagy. A deeper understanding of these mechanisms has potential to improve drug development processes and disease therapy.

Anti-SARS-CoV-2 Potential of Artemisinins In Vitro

The discovery of novel drug candidates with anti-severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) potential is critical for the control of the global COVID-19 pandemic. Artemisinin, an old antimalarial drug derived from Chinese herbs, has saved millions of lives. Artemisinins are a cluster of artemisinin-related drugs developed for the treatment of malaria and have been reported to have multiple pharmacological activities, including anticancer, antiviral, and immune modulation. Considering the reported broad-spectrum antiviral potential of artemisinins, researchers are interested in whether they could be used to combat COVID-19. We systematically evaluated the anti-SARS-CoV-2 activities of nine artemisinin-related compounds in vitro and carried out a time-of-drug-addition assay to explore their antiviral mode of action. Finally, a pharmacokinetic prediction model was established to predict the therapeutic potential of selected compounds against COVID-19. Arteannuin B showed the highest anti-SARS-CoV-2 potential with an EC50 of 10.28 ± 1.12 μM. Artesunate and dihydroartemisinin showed similar EC50 values of 12.98 ± 5.30 μM and 13.31 ± 1.24 μM, respectively, which could be clinically achieved in plasma after intravenous administration. Interestingly, although an EC50 of 23.17 ± 3.22 μM was not prominent among the tested compounds, lumefantrine showed therapeutic promise due to high plasma and lung drug concentrations after multiple dosing. Further mode of action analysis revealed that arteannuin B and lumefantrine acted at the post-entry step of SARS-CoV-2 infection. This research highlights the anti-SARS-CoV-2 potential of artemisinins and provides leading candidates for anti-SARS-CoV-2 drug research and development.

Hydroxychloroquine in rheumatic autoimmune disorders and beyond

Initially used as antimalarial drugs, hydroxychloroquine (HCQ) and, to a lesser extent, chloroquine (CQ) are currently being used to treat several diseases. Due to its cost‐effectiveness, safety and efficacy, HCQ is especially used in rheumatic autoimmune disorders (RADs), such as systemic lupus erythematosus, primary Sjögren's syndrome and rheumatoid arthritis. Despite this widespread use in the clinic, HCQ molecular modes of action are still not completely understood. By influencing several cellular pathways through different mechanisms, CQ and HCQ inhibit multiple endolysosomal functions, including autophagy, as well as endosomal Toll‐like receptor activation and calcium signalling. These effects alter several aspects of the immune system with the synergistic consequence of reducing pro‐inflammatory cytokine production and release, one of the most marked symptoms of RADs. Here, we review the current knowledge on the molecular modes of action of these drugs and the circumstances under which they trigger side effects. This is of particular importance as the therapeutic use of HCQ is expanding beyond the treatment of malaria and RADs.