Protective Effects of Ascorbic Acid in Mouse Model of Depression

Abstract

Major Depressive Disorder (MDD), an intricate neuropsychiatric disorder is marked by diminished mood, low energy, no motivation, anhedonia and self-harm or suicidal thoughts in severe cases. Endoplasmic reticulum (ER) dysfunction, impaired neurogenesis, mitochondrial dysfunction and oxidative stress are implicated in the pathophysiology of MDD. Adverse side effects of the available treatments i.e., Selective Serotonin Reuptake Inhibitors (SSRIs) have been reported including serotonin syndrome, nausea, confusion and dizziness. Ascorbic acid (AA), a potent antioxidant and anti-inflammatory compound has shown antidepressant activity as reported in many studies. The present research sought to explore the neuroprotective advantages of ascorbic acid when compared to the conventional drug fluoxetine (FXT) in a mouse model of clinical depression induced by Unpredictable Chronic Mild Stress (UCMS). The mice were distributed into 8 groups (n=6 each). The 9-week long procedure for the UCMS led to a deteriorated coat of mice (p<0.001 for week 4 and p<0.0001 from week 5 to 9). A three-week treatment of AA and FXT displayed a significantly lower coat score exhibiting substantial improvement in the coat state. Behavioral assessment was conducted through Sucrose Splash Test (SST), Novelty Suppressed Feeding test (NSFT), Tail Suspension Test (TST), Y maze test and Forced Swim Test (FST). A significant reduction (p<0.001) in anhedonia was indicated by increased grooming time (189.5±19.67s) in SST task by UCMS+AA group. While the combination group (FXT+ AA) also exhibited the similar increase in grooming time (195.5±15.31) (p < 0.001). The results also indicated the potential ameliorative effect of AA on behavioral despair or depression like behavior and helplessness, assessed through TST. Antidepressant effects of AA were also eminent in FST indicated by significantly delayed latency to immobility. However, a non-significant reduction in xvii latency to immobility was observed in UCMS+FXT+AA (14.83±5.30s) group (p<0.05). Similarly, anxiety-like behavior was assessed through NSFT where increased latency to eat food was evident in UCMS group. A mild trend (p>0.05) showing anxiety like behavior was observed in the UCMS group (185±65.8) In addition, UCMS group exhibited a decrease in percentage of spontaneous alterations, total time period spent in the novel arm and percentage of entries in novel arm in Y-maze test (p>0.05 for each), while treatment with AA and FXT increased the percentage spontaneous alterations and time spent in the novel arm indicating that AA and FXT can improve spatial learning and memory. Moreover, the treatment with AA significantly restored the neuronal cell count in the hippocampal dentate gyrus (27.5±1.04) in the UCMS exposed group which was substantially deteriorated. The combinational treatment of FXT and AA also displayed significantly increased neuronal density (24±1.08) as compared to UCMS group (8.75±1.01). The results of qRT-PCR showed the decreased hippocampal expression of NeuN in UCMS group (p<0.05) in contrast to the control group, however it was substantially normalized by FXT, and AA. In contrast to the control group, the mRNA expression of activating transcription factor 6 (ATF6), was significantly increased (p<0.0001) in UCMS group that is evocative of the higher cellular ER stress. A slight normalization of ATF6 levels in UCMS+AA group (p>0.05) was observed whereas FXT (p<0.0001) substantially recovered the aberrant expression. Protein protein interaction was also assessed for ATF6, NeuN with FXT and AA using molecular docking. The analysis revealed that ATF6 and NeuN can interact with both FXT and AA with comparable binding energies. In conclusion, these findings support that the potent neuroprotective, antidepressant and antianxiety effects of ascorbic acid make it an effective alternative and adjuvant treatment approach for MDD