Caracterização química estrutural e avaliação do efeito neuroprotetor de polissacarídeos sulfatados da alga marinha Asparagopsis Armata Harvey em modelo de doença de Parkinson em ratos

Abstract

Parkinson's Disease (PD) is characterized by the degeneration of dopaminergic neurons located in the substantia nigra pars compacta (SNpc), which leads to a series of motor and non-motor symptoms. Levodopa remains the primary medication used in current therapy. However, continuous use has resulted in side effects such as tolerance and motor fluctuations. The search for new therapeutic sources, such as seaweeds, has increased in recent years due to their richness in natural compounds. Asparagopsis armata Harvey is a Portuguese Rhodophyta marine alga that possesses various bioactive compounds, including sulfated polysaccharides (PS). These polysaccharides have generated significant interest in research

due to their wide range of biological activities, such as anticoagulant, antioxidant, anti- inflammatory, immunomodulatory, and neuroprotective effects. Thus, the aim of this study

was to characterize the chemical structure of sulfated polysaccharides from A. armata Harvey (PST-Aa) and investigate their neuroprotective effects in a rat model of PD induced by 6- hydroxydopamine (6-OHDA). For this purpose, 5 g of dried algae were subjected to enzymatic extraction (6 h; 60oC) using papain, with a yield of 13.64% for PST-Aa. The chemical analysis of the soluble carbohydrate and free sulfate contents of PST-Aa showed a yield of 53.20% and 30.29%, respectively, while no protein content was detected in PST-Aa. The molar mass of PST-Aa, estimated by 0.5% agarose gel electrophoresis, was 332.7 kDa. The results of the structural characterization of PST-Aa using Fourier Transform Infrared Spectroscopy (FT-IR) and Nuclear Magnetic Resonance (NMR) techniques demonstrated that

PST-Aa presented structures composed of hybrid galactans composed of 3-β-D- galactopyranose-(1→4)-α-D/L-galactopyranose. For the evaluation of the neuroprotective

effect of PST-Aa, albino Wistar rats, aged 6-9 weeks (250-290 g), were used. They were lesioned in the right striatum with 6-OHDA through stereotaxic surgery. After 24 hours, the animals were treated once daily by gavage for 14 days with doses of PST-Aa at 0.3 mg/kg and 3.0 mg/kg. On the 14th day, 1 hour after the last day of treatment, the animals were subjected to behavioral tests. The neuroprotective effects assessed through the open-field test showed that PST-Aa at doses of 0.3 mg/kg and 3.0 mg/kg increased the number of crossings by 32.92% and 21.47%, and the number of rearing by 83.25% and 100.5%, respectively. The grooming activity was reduced by doses of 0.3 mg/kg and 3.0 mg/kg by 57.28% and 53.47%, respectively, and the time spent motionless was reduced by 40.69% and 59.72%, respectively. The cylinder test demonstrated that animals treated with doses of 0.3 mg/kg and 3.0 mg/kg showed increased activity with the ipsilateral paw at (41.34±3.74) and (32.11±4.61), and with both paws at (21.73±2.86) and (32.34±2.47), respectively. The apomorphine test showed that

the dose of 3.0 mg/kg was able to reduce the number of contralateral rotations by 61% compared to the 6-OHDA group. On the 15 day, the animals were decapitated, and their brains (including the ipsilateral and contralateral striatum, hippocampus, and prefrontal cortex) were removed. The results demonstrated that PST-Aa at a dose of 3.0 mg/kg showed anti-nitrosative effects in the region of the ipsilateral striatum (24.09±4.78). PST-Aa reduced lipid peroxidation in the hippocampus region at doses of 0.3 mg/kg (26.98±0.68) and 3.0 mg/kg (27.65±1.37), and exhibited antioxidant effects by elevating GSH levels in the contralateral striatum region at doses of 0.3 mg/kg (334.7±15.13) and 3.0 mg/kg (306.8±7.44). Thus, PST-Aa suggests new promising sources in the treatment of neurodegenerative disorders.