Effectiveness of Fragment C Domain of Tetanus Toxin and Pramipexole in an Animal Model of Parkinson’s Disease

BSS-4, a diosgenin analogue, reduces carrageenan-induced paw inflammation in rat

Inflammation is an adaptive response that ensures the survival of the organism in the face of injuries or trauma primarily via the immune system. However, overactivation of this process can be detrimental to the point of fatality. To overcome this overactivation, immunosuppressant agents such as steroids and non-steroidal anti-inflammatory drugs (NSAIDs) are used. Given the limitations of these drugs, including their side effects, an urgent need for development of potent and safer anti-inflammatory drugs is evident. Diosgenin, a steroidal saponin (a glycoside found in plants) and its analog, BSS-4 are gaining ground in this respect. Our objective in this study was to determine the effectiveness of BSS-4 in an established model of inflammation and provide clues on its mechanism of action. Carrageenan (Carr)-induced paw edema was used to evaluate the effectiveness of two doses of BSS-4 (0.5 and 1 mg/kg administered intraperitoneally) in adult male Wistar rats. Plantar edema was induced by subcutaneous injection of 50 µL of carrageenan (1 %) into the plantar aponeurosis of the right paw. Inflammatory cytokine markers, tumor necrosis factor-alpha (TNF-α), and interleukin-1 beta (IL-1β) were quantified in this paw region using immunohistochemical assays. BSS-4 at 0.5 mg/kg dose, significantly reduced the paw edema up to three hours after administration. Concomitantly, TNF-α and IL-1β immunostaining were significantly reduced. BSS-4 also preserved the tissue architecture as assessed by hematoxylin and eosin (H&E) staining. These results indicate that BSS-4 can impart potent anti-inflammatory effects as well as reductions in TNF-α and IL-1β in an inflammatory rat model.

Pramipexole decreases allodynia and hyperalgesia via NF-κB in astrocytes in rats with Parkinson's disease

Pain is one of the principal non-motor symptoms of Parkinson's disease (PD), negatively impacting the patient's quality of life. This study aimed to demonstrate whether an effective dose of pramipexole (PPX) can modulate the NF-κB/p-p65 activation in glial cells (astrocytes and microglia) and diminish the hypersensitivity (allodynia and hyperalgesia) in male Wistar rats with PD. For this, 2 μl of 6-hydroxydopamine (6-OHDA, 8 μg/μL/0.2 μl/min) was administered unilaterally in the Substantia Nigra of the Pars Compacta (SNpc) to establish a PD model rat. Motor behavioral tests were used to validate the PD model, and von Frey filaments were used to evaluate allodynia and hyperalgesia. Immunohistochemical and immunofluorescence were used to analyze the level of tyrosine hydroxylase in SNpc and striatum as well as the expression of GFAP, Iba-1, NF-κB/p-65 in the L4-L6 spinal cord dorsal horn. Unilateral 6-OHDA-lesion reduces motor capacity and produces long-term allodynia and hyperalgesia in both hind paws. L4-L6 spinal cord dorsal horn astrocytes and microglia were active in these 6-OHDA-lesioned rats. Moreover, PPX (1 and 3 mg/Kg, i.p./10 days, n = 10 per group) inhibited the bilateral mechanical hypersensitivity, and PPX (3 mg/Kg/i.p./10 days) reduced 6-OHDA-induced astrocyte and microglia activation, as well as reduced NF-κB/p-p65 expression only in astrocytes of dorsal horn spinal cord in the L5-L6. These findings suggest that PPX could alleviate pain by decreasing the activation of microglia and astrocytes through the NF-κB/p-p65 pathway in the dorsal horn spinal cord. Therefore, PPX could be considered an optional tool for improving pain hypersensitivity in PD patients.

Neurotrophic fragments as therapeutic alternatives to ameliorate brain aging

Aging is a global phenomenon and a complex biological process of all living beings that introduces various changes. During this physiological process, the brain is the most affected organ due to changes in its structural and chemical functions, such as changes in plasticity and decrease in the number, diameter, length, and branching of dendrites and dendritic spines. Likewise, it presents a great reduction in volume resulting from the contraction of the gray matter. Consequently, aging can affect not only cognitive functions, including learning and memory, but also the quality of life of older people. As a result of the phenomena, various molecules with notable neuroprotective capacity have been proposed, which provide a therapeutic alternative for people under conditions of aging or some neurodegenerative diseases. It is important to indicate that in recent years the use of molecules with neurotrophic activity has shown interesting results when evaluated in in vivo models. This review aims to describe the neurotrophic potential of molecules such as resveratrol (3,5,4'-trihydroxystilbene), neurotrophins (brain-derived neurotrophic factor), and neurotrophic-type compounds such as the terminal carboxyl domain of the heavy chain of tetanus toxin, cerebrolysin, neuropeptide-12, and rapamycin. Most of these molecules have been evaluated by our research group. Studies suggest that these molecules exert an important therapeutic potential, restoring brain function in aging conditions or models of neurodegenerative diseases. Hence, our interest is in describing the current scientific evidence that supports the therapeutic potential of these molecules with active neurotrophic.

The C-terminal domain of the heavy chain of tetanus toxin prevents the oxidative and nitrosative stress induced by acute toxicity of 1-methyl-4-phenylpyridinium, a rat model of Parkinson's disease

The recombinant carboxyl-terminal domain of the heavy chain of tetanus toxin (Hc-TeTx) exerts neuroprotective and neurorestorative effects on the dopaminergic system of animal models of Parkinson's disease (PD). The present study aimed to determine the effect of the Hc-TeTx fragment on the markers of oxidative stress and nitrosative stress generated by the acute toxicity of 1-methyl-4-phenylpyridinium (MPP⁺). For this purpose, the Hc-TeTx fragment was administered once a day in three 20 μg/kg consecutive injections into the grastrocnemius muscle of the rats, with an intra-striatal unilateral injection of 1 μL of MPP⁺ [10 μg/mL] then administered in order to cause a dopaminergic lesion. The results obtained show that the rats treated with Hc-TeTx plus MPP⁺ presented an increase in the expression of tyrosine hydroxylase (TH), a significantly greater decrease in the levels of the markers of oxidative stress, nitrosative stress, and neurodegeneration than that observed for the group injured with only MPP⁺. Moreover, it was observed that total superoxide dismutase (SOD) and copper/zinc SOD activity increased with the administration of Hc-TeTx. Finally, immunoreactivity levels were observed to decrease for the levels of 3-nitrotyrosine and the glial fibrillary acidic protein in the ipsilateral striatum of the rats treated with Hc-TeTx plus MPP⁺, in contrast with those lesioned with MPP⁺ alone. Our results demonstrate that the recombinant Hc-TeTx fragment may be a potent antioxidant and, therefore, could be suggested as a therapeutic tool against the dopaminergic neuronal impairment observed in the early stages of PD.

The Chronic Oral Administration of Clobenzorex or Amphetamine Decreases Motor Behavior and Induces Glial Activation in the Striatum Without Dopaminergic Degeneration

Described as amphetamine-like due to their structural and stimulant similarities, clobenzorex is one of the five most-commonly used drugs in Mexico for the treatment of obesity. Various studies have shown that amphetamines induce dopaminergic neurotoxicity and neuroinflammation in the striatum, symptoms which are associated with motor damage. For this reason, the present study aimed to evaluate the effect of chronic clobenzorex administration on motor behaviors, TH immunoreactivity, gliosis, and the neurodegenerative process in the striatum and substantia nigra pars compacta (SNpc). The present research was conducted on three experimental groups of male Wistar rats: the vehicle group, the amphetamine group (2 mg/kg), and the clobenzorex group (30 mg/kg). All groups were subject to oral administration every 24 h for 31 days. Motor activity and motor coordination were evaluated in the open field test and the beam walking test, respectively. The animals were euthanized after the last day of treatment to enable the extraction of their brains for the evaluation of tyrosine hydroxylase (TH) levels, the immunoreactivity of the glial cells, and the neurodegeneration of both the striatum and SNpc via amino-cupric-silver stain. The results obtained show that amphetamine and clobenzorex administration decrease motor activity and motor coordination in the beam walking test and cause increased gliosis in the striatum, while no significant changes were observed in terms of immunoreactivity to TH and neurodegeneration in both the striatum and SNpc. These results suggest that the chronic administration of clobenzorex may decrease motor function in a manner similar to amphetamine, via the neuroadaptive and non-neurotoxic changes caused to the striatum under this administration scheme.

Synergistic antiallodynic and antihyperalgesic interaction between L-DOPA and celecoxib in parkinsonian rats is mediated by NO-cGMP-ATP-sensitive K+ channel

Pain is a usual and troublesome non-motor symptom of Parkinson's disease, with a prevalence of 29-82%. Therefore, it's vital to find pharmacological treatments for managing PD-associated pain symptoms, to improve patients' quality of life. For this reason, we tested the possible synergy between L-DOPA and celecoxib in decreasing allodynia and hyperalgesia induced by unilateral lesioning with 6-OHDA into the SNpc in rats. We also tested whether the antiallodynic and antihyperalgesic effect induced by combination of L-DOPA and celecoxib is mediated by the NO-cGMP-ATP-sensitive K⁺ channel pathway. Tactile allodynia and mechanical hyperalgesia were evaluated using von Frey filament. Isobolographic analyses were employed to define the nature of the drug interaction using a fixed dose ratio (0.5: 0.5). We found that acute and sub-acute (10-day) treatment with a single dose of L-DOPA (3-25 mg/kg, i. p.) or celecoxib (2.5-20 mg/kg, i. p.) induced a dose-dependent antiallodynic and antihyperalgesic effect in parkinsonian rats. Isobolographic analysis revealed that the ED₅₀ values obtained by L-DOPA + celecoxib combination was significantly less than calculated additive values, indicating that co-administration of L-DOPA with celecoxib produces synergistic interactions in its antiallodynic and antihyperalgesic effect in animals with nigrostriatal lesions. Moreover, the antiallodynic and antihyperalgesic effects induced by L-DOPA + celecoxib combination were blocked by intrathecal pre-treatment with L-NAME, ODQ, and glibenclamide. Taken together, the data suggest that L-DOPA + celecoxib combination produces an antiallodynic and antihyperalgesic synergistic interaction at the systemic level, and these effects are mediated, at the central level, through activation of the NO-cGMP-ATP-sensitive K⁺ channel pathway.

An update on the use of non-ergot dopamine agonists for the treatment of Parkinson's disease

INTRODUCTION

Long-term treatment of Parkinson's disease (PD) with levodopa is hampered by motor complications related to the inability of residual nigrostriatal neurons to convert levodopa to dopamine (DA) and use it appropriately. This generated a tendency to postpone levodopa, favoring the initial use of DA agonists, which directly stimulate striatal dopaminergic receptors. Use of DA agonists, however, is associated with multiple side effects and their efficacy is limited by suboptimal bioavailability.

AREAS COVERED

This paper reviewed the latest preclinical and clinical findings on the efficacy and adverse effects of non-ergot DA agonists, discussing the present and future of this class of compounds in PD therapy.

EXPERT OPINION

The latest findings confirm the effectiveness of DA agonists as initial treatment or adjunctive therapy to levodopa in advanced PD, but a more conservative approach to their use is emerging, due to the complexity and repercussions of their side effects. As various factors may increase the individual risk to side effects, assessing such risk and calibrating the use of DA agonists accordingly may become extremely important in the clinical management of PD, as well as the availability of new DA agonists with better profiles of safety and efficacy.

Antidepressant effects of C-Terminal domain of the heavy chain of tetanus toxin in a rat model of depression

The C-terminal domain of the heavy chain of tetanus toxin (Hc-TeTx) may be of therapeutic potential in motor impairments associated with Parkinson disease (PD). Since depression is a common co-morbid condition with PD, we undertook this study to determine whether Hc-TeTx might also show antidepressant-like properties and whether central brain-derived neurotrophic factor (BDNF) and/or tumor necrosis factor (TNF)-alpha are also affected by it. Adult male Wistar-Kyoto rats, a putative animal model of depression, were treated with various doses of Hc-TeTx (0, 20, 40 and 60 μg/kg, IM) and their performance in the open field locomotor activity (OFLA) as well as in the forced swim test (FST) was evaluated at 24 h, one week and two weeks after the single injection. A separate group of rats were injected with 60 μg/kg Hc-TeTx and sacrificed 24 h later for neurochemical evaluations. Hc-TeTx resulted in a dose-dependent decrease in immobility score after 24 h, whereas OFLA was not affected. Concomitant with the 24 h behavioral effects, the levels of hippocampal and frontal cortical BDNF were significantly increased, whereas the levels of TNF-alpha in both these areas were significantly decreased. The decrease in immobility scores following higher doses of Hc-TeTx were still evident after one week, but not 2 weeks of rest. These results indicate long lasting antidepressant effects of a single Hc-TeTx dose and suggest potential utility of Hc-TeTx in PD-depression co-morbidity.

Differential Effects of LPS and 6-OHDA on Microglia's Morphology in Rats: Implications for Inflammatory Model of Parkinson's Disease

Parkinson's disease (PD) is an idiopathic and progressive neurodegenerative disease characterized by the loss of ~ 80% of dopaminergic neurons in substantia nigra pars compacta (SNpc). Because activation of the innate cellular immune response, mediated by microglia, has been linked to the neurodegeneration in PD, in the present study, we evaluated the effects of lipopolysaccharide (LPS) and 6-hydroxydopamine (6-OHDA) on microglia's morphology, reflective of their activity, as well as tyrosine hydroxylase (TH)-positive neurons in SNpc and motor behavior. Adult male Wistar rats were stereotactically injected with LPS or 6-OHDA into the left dorsolateral striatum. Control groups received appropriate vehicle. The morphological changes of microglial cells and neurotoxic effects were examined at 1, 7, and 14 post-injection days. Both LPS and 6-OHDA caused activation and morphological changes in microglial cells as well as loss of dopaminergic neurons in SNpc. These effects were maximal at 14 days post-injection where motor impairments were also evident. However, our findings indicate that 6-OHDA causes a low degree of microglia activation compared to LPS. Hence, it may be concluded that LPS model of PD might be a better representation of inflammatory involvement in this devastating disease.