INTRODUCTION (996 words)
Parkinson’s disease (PD) is a progressive, age-associated
neurodegenerative disorder characterized by a depletion of dopamine in
the striatum due to the loss of dopaminergic neurons of the substantia
nigra compacta (SNc; Fahn et al., 2004; Olanow et al., 2004). L-DOPA
(3,4-dihydroxyphenyl-L-alanine) is considered the most effective and
well-tolerated noninvasive therapy for the treatment of PD motor
symptoms. However, over time this effect decreases and more than 75% of
L-DOPA-treated PD patients develop incapacitating abnormal involuntary
movements (AIMs) referred to as L-DOPA-induced dyskinesia (LID) (Aquino
and Fox, 2015; Cenci et al., 2020; Cenci and Olanow, 2017; Espay et al.,
2018; Fahn et al., 2004; Olanow et al., 2004). As such, there has been a
number of studies conducted to try and find alternative therapies that
do not result in the pro-dyskinetic side effects or can reduce the
dyskinetic signs.
The mechanisms involved in the pathogenesis of LID are complex and are
not entirely understood. In the nigrostriatal circuitry, there are
several alterations associated with LID manifestation, for example, the
expression of specific genes (ERK1/2 extracellular signal-regulated
kinase 1/2; DARP32 dopamine- and cAMP-regulated neuronal phosphoprotein;
Fos, Finkel–Biskis–Jinkins osteosarcoma) (Cenci et al., 2007; Cenci,
2014; Cenci and Crossman 2018; You et al., 2018), and altered synaptic
plasticity (Cenci et al., 2007, 2020; Cenci, 2014) with modifications in
the long-term potentiation of the cortico-striatal pathway (Borgkvist et
al., 2018; Calabresi et al., 2015; Picconi et al., 2011; 2003).
Pre-clinical and clinical evidence has emerged to support the use of a
number of compounds to treat LID. Amantadine (the non-selective
N-methyl-D-aspartate receptor antagonist - Blanchet et al., 1998;
Lundblad et al., 2002) is the only compound with robust evidence of
anti-dyskinetic effects in patients. However, its therapeutic success is
limited (Bortolanza et al., 2015; Cenci et al., 2020; 2014).
Various neural pathways such as the serotonin, acetylcholine,
γ-aminobutyric acid, nitric oxide, or cannabinoid interact with
dopaminergic pathways have been proposed as possible pharmacological
targets for LID suppression (Dos-Santos-Pereira et al., 2016; Espadas et
al., 2020; Huot et al., 2013; Johnston et al., 2018; Vijayakumar and
Jankovic, 2016). In rodent PD models, neuroinflammation has been
reported to be associated with the development and onset of LID (Barnun
et al., 2008; Boi et al., 2019 Bortolanza et al., 2015 a, b; Munoz et
al., 2014; Mulas et al., 2016; for review see Del Bel et al., 2016;
Carta et al., 2017). In pre-clinical studies, pharmacological based
therapy with anti-inflammatory compounds as corticosterone (Barnum et
al., 2008), cannabidiol (dos-Santos-Pereira et al., 2016, Espadas et
al., 2020), nitric oxide synthase inhibitor (Bortolanza et al., 2016;
Padovan-Neto et al., 2009, 2015; Solís et al., 2015), thalidomide (Boi
et al., 2019; Mulas et al., 2016), or IRC-82451 a multitargeting
molecule (Aron-Badin et al., 2013), reduced the severity of dyskinesia
and was associated with a reduction in inflammation. Amantadine may also
be somewhat beneficial by inhibiting the inflammatory activation of
microglia (Kim et al., 2012).
Recently, it was hypothesized that the striatum in LID, evolves from the
combination of dopaminergic terminals degeneration, inadequate dopamine
presence following the administration of L-DOPA and excessive glutamate
concentration (Barcia et al., 2003; McGeer et al., 2003; Picconi et al.,
2011; 2003; Tansey et al., 2007). In vivo brain imaging of
patients with PD reveals an association between widespread microglial
activation and the pathological process (Bartels et al., 2007; Gerhard
et al., 2006; Ouchi et al., 2005). Inflammatory reaction in the basal
ganglia of both parkinsonian rats and patients with PD that have a
history of dyskinesia also revealed angiogenesis, vascular endothelial
growth factor up-regulation and altered brain-blood barrier properties
(Janelidze et al., 2015; Lerner et al., 2017; Ohlin et al., 2011, 2012).
Furthermore, long after the neurotoxin, 6-hydroxydopamine (6-OHDA) has
been cleared from the brain the striatum of lesioned rats receiving
L-DOPA treatment displayed sustained neuroinflammation and
neurodegeneration (Bortolanza et al., 2015a and b; Muñoz et al., 2014;
Spinnewyn et al., 2011; Teema et al., 2016). Therefore, targeting
neuroinflammation might be a pharmacological strategy to limit LID (Del
Bel et al., 2016; Huot et al., 2013;).
Tetracycline antibiotics are increasingly being used, largely due to
their anti-inflammatory features (Bortolanza et al., 2018; Reglodi et
al., 2017). The second-generation tetracycline antibiotic, doxycycline
(6-deoxy-5-hydroxytetracycline, a Food and Drug Administration approved
compound), protects dopaminergic neurons from degeneration induced by
6-OHDA (Lazzarini et al., 2013),
1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP, Du et al. 2001; Wu
et al. 2003) and lipopolysaccharide (LPS, Zhang et al., 2015). This
neuroprotective effect seems to be associated with its anti-inflammatory
properties (Lazzarini et al., 2013; Stoilova et al., 2013). At a
clinical level, the therapeutic rationale for targeting inflammation in
PD is supported by the observation of the reduced incidence of PD in
patients using tetracycline for rosacea treatment (Egeberg et al.,
2016). Moreover, these rosacea patients did not present any prominent
side effects related to the antimicrobial activity (Gompels et al. 2006;
Langevitz et al. 1992; NINDS NET-PD Investigators 2006; Payne et al.
2011; Smith et al. 2011). Although it is unclear what drives increased
inflammation in patients with PD, tetracycline and analog compounds have
emerged as a potential treatment for PD and other neurodegenerative
disorders (Johnston et al., 2019; Socias et al., 2018).
Due to the well-known anti-inflammatory effects of doxycycline, we
hypothesized that this drug might reduce LID displayed inflammatory
processes and, as a result, alleviate the expression of LID. In
addition, to avoid side effects, such as bacterial resistance, COL-3
(CMT-3,6-demethyl-6-deoxy-4-de[dimethylamino]-tetracycline formerly
known as incyclinide) a chemically modified tetracycline (Edan et al.,
2013; Liu et al., 2001) might be efficacious in the treatment of LID.
In the present study, we examined the potential effect of doxycycline
and COL-3 to modify LID induced by chronic L-DOPA treatment in 6-OHDA
lesioned rats. We analyzed whether doxycycline and/or COL-3 given once
dyskinesia was already present decreased dyskinetic signals and also
whether the co-administration of doxycycline with L-DOPA from day one
inhibited the appearance of LID. Using an immunohistochemistry analysis,
we examined dopamine depleted striatum changes due to L-DOPA and
doxycycline treatment.