Neuroprotective effect of Decalepis hamiltonii aqueous root extract and purified 2-hydroxy-4-methoxy benzaldehyde on 6-OHDA induced neurotoxicity in Caenorhabditis elegans.

In this study, we investigated the possible neuroprotective efficacy of Decalepis hamiltonii tuber extract against 6-Hydroxy dopamine (6-OHDA) induced neurotoxicity and associated effects in Caenorhabditis elegans. The major component of flavour rich extract from D. hamiltonii is 2-hydroxy-4-methoxy benzaldehyde (2H4MB) which is an isomer of vanillin. We have conducted preliminary experiments with different types of extracts and subsequently DHFE (D. hamiltonii Fresh Tuber Extract) and DHPF (D. hamiltonii purified 2H4MB fraction) were used for further studies. Here we attempted to enumerate the neuroprotective efficacy of the above compounds in worms by evaluating behavioural and mitochondrial function, dopamine content and selective degeneration of dopaminergic neurons in BZ555 strains in comparison with control and 6-OHDA treated organisms. The relative expression levels of selected antioxidant genes involved in defence mechanism like SOD-3, GST-2 and GST-4 were evaluated along with those of CAT-2 and DOP-2 at mRNA level. We observed that both DHPF and DHFE exhibited significant levels of neuroprotective property against 6-OHDA induced neurotoxicity, which was evident in mitochondrial/dopaminergic function and antioxidant defence mechanism.

Alpha-linolenic acid suppresses dopaminergic neurodegeneration induced by 6-OHDA in C. elegans.

Parkinson's disease (PD) is the second most common neurodegenerative disorder characterized by the specific and massive loss of dopamine (DA) containing neurons in the substantia nigra pars compacta (SNpc) and aggregation of protein α-synuclein. There are a few animal studies, which indirectly implicate the neuroprotective action of omega-3 polyunsaturated fatty acids in neurodegenerative diseases. In this study, we exposed Caenorhabditis elegans (both wild type N2, and transgenic strain, UA44) to 6-hydroxydopamine (6-OHDA, the model neurotoxicant) and evaluated the extent of protection offered by alpha-linolenic acid (ALA). Larval stage worms (L1/L2) of N2 and transgenic strains were exposed to 6-OHDA (25 mM) with or without ALA (10, 50 and 100 µM) for 48 h at 20 °C. After 48 h, while the N2 worms were assessed for their responses in terms of locomotion, pharyngeal pumping, lifespan and AChE activity, the transgenic worms were monitored for dopaminergic neuronal degeneration. Worms exposed to 6-OHDA exhibited a significant reduction (48%) in the locomotion rate. Interestingly, supplementation with ALA increased the locomotion rate in 6-OHDA treated worms. A marked decrease (45%) in thrashing was evident in worms exposed to 6-OHDA while thrashing was slightly improved in worms co-exposed to 6-OHDA and higher concentrations of ALA. Interestingly, worms co-exposed to 6-OHDA with ALA (100 µM) exhibited a significant increase in thrashing (66 ± 1.80 thrashes/30s). The pharyngeal pumping rate declined significantly in the case of worms exposed to 6-OHDA (35%). However, the worms co-treated with ALA exhibited significant recovery in pharyngeal pumping. The mean survival for the control worms was 26 days, while the worms exposed to 6-OHDA, showed a marked reduction in survival (21 days). Worms co-exposed to 6-OHDA and ALA showed a concentration-dependent increase in lifespan compared to those exposed to 6-OHDA alone (23, 25 and 26 days respectively). Transgenic worms treated with 6-OHDA showed significant loss of processes of CEP and ADE neurons as evident from visibly marked reduction in GFP expression. Worms co-exposed to 6-OHDA and ALA showed visibly significant reduction in neuronal degeneration in both CEP and ADE. However, worms exposed to 6-OHDA together with ALA showed increased GFP expression within processes of CEP and ADE neurons. Overall, our results demonstrate that ALA significantly suppresses the dopaminergic neurodegeneration and movement disorder induced by 6-OHDA in C. elegans.