Alzheimer disease (AD) is a neurodegenerative disease, induces irreversible destruction of neuronal networks, resulting in permanent functional impairment. The hallmark of AD is presence of amyloid beta plaques and neurofibrially tangles in the cerebral cortex and hippocampus¹. Most of the currently available drugs are used to maintain cognitive function, and delay the symptoms of disease without affecting the underlying disease process. Rasa-Sindoor (RS), an organometallic derivative of mercury, is used in traditional Indian medicine (Ayurveda) for general debility in human. RS has been shown to prevent accumulation of heat shock proteins, suppress apoptosis, and improved physiology in different neurodegenerative disorders in drosophila model². The objective of the present study is to evaluate the effects of RS on memory, and neuronal metabolism in AβPP-PS1 mice model of AD.

All animal experiments were performed under approved protocols by the Institutional Animal Ethics Committee of CCMB. AβPP-PS1 (Tg) and wild type (Wt) mice were divided into four groups: Group (i) WT + Carboxymethyl cellulose (CMC 1%, n=5); (ii) Tg + CMC (n=7); (iii) WT + RS (2 g/kg, i.g., n=5); (iv) Tg + RS (2 g/kg, i.g., n=6). RS was suspended in CMC (1%), and administered orally (2 g/kg) for 30 days in Group (iii) and (iv) mice while those in Group (i) and (ii) received 0.25 ml of CMC. For metabolic measurements, overnight fasted mice were anesthetized using urethane (1.5 g/kg, i.p.) and lateral tail vein was catheterized for infusion of labeled glucose. The body temperature was maintained ~37°C. After 45 min of induction of anesthesia, [1,6-¹³C₂]glucose was administered using a bolus variable infusion protocol³. Blood was collected from orbital sinus just before the end of infusion, and head was frozen in situ in liquid nitrogen. The metabolites were extracted from frozen hippocampal and striatal tissues⁴. Concentration and percentage ¹³C enrichment of amino acids were measured in ¹H-[¹³C]-NMR spectra of tissue extracts acquired at 600 MHz spectrometer⁵. The metabolic rates of glucose oxidation by glutamatergic and GABAergic neurons in different groups were determined from the ¹³C labeling of brain amino acids neurotransmitters from [1,6-¹³C₂]glucose⁶.The memory of the animals was assessed by Morris Water Maze (MWM) test. AβPP-PS1 mice took longer time (81.7±5.7 s) to reach the hidden platform as compared with wild type controls (32.5±6.9 s). The RS treatment in AβPP-PS1 for a month decreased the latency (41.3±13.2 s) very close to control value (32.5±6.9 s) suggesting RS intervention has improved memory in AD mice (Fig. 1). The concentrations of ¹³C labeled glutamate-C4 (p=0.0025), GABA-C2, (p=0.015), glutamine-C4 (p=0.0008) and glutamate-C3 (p=0.009) in hippocampus were found to be significantly lower in AβPP-PS1 mice as compared with age matched controls (Fig. 2, Table 1), suggesting impaired energy metabolism in AD mice. The cerebral metabolic rates of glucose oxidation derived from ¹³C labeled amino acids indicated hypometabolism for glutamatergic and GABAergic neurons in the hippocampus and striatum (Fig. 3). The intervention of RS in AβPP-PS1 mice increased ¹³C labeling of amino acids closer to control value in hippocampus as well as in striatum (Fig. 2, Table 1). Most interestingly, the cerebral metabolic rate of glucose oxidation associated with glutamatergic neurons was found to be improved significantly with RS treatment in AβPP-PS1 mice both in hippocampus (AβPP-PS1+RS: 0.14±0.02 AβPP-PS1+CMC: 0.12±0.02 μmol/g/min, p=0.008) and striatum (AβPP-PS1+RS: 0.16±0.02 AβPP-PS1+CMC: 0.12±0.02 μmol/g/min, p=0.008) (Fig. 3). However, GABAergic metabolic activity was recovered only in the striatum. The partial recovery in cerebral metabolism may due to small treatment period of RS. The longer RS treatment period may further improve the energy metabolism in AD mice. Further studies are needed to understand the mechanism of RS for the improvement of memory and energy metabolism. These data suggest that the traditional Rasa-Sindoor has potential to improve cognitive function and memory in AD. Hence, Rasa-Sindoor in conjunction with AD drugs may be useful for the management of AD.