ABSTRACT
The in vitro anti-proliferative activity of MA (5,7-dihydroxy-8-(3-methylbut-2-enyl)-6-(3-methyl-1-oxobutyl)-4-phenyl[1]2H-[1]benzopyran-2-one)on a variety of cancer cells was previously demonstrated. This work strives to understand the mechanisms by which MA exerts this biological activity. Thereafter, the binding of MA to calf thymus DNA was studied by monitoring the change in the UV-visible absorbance of MA. It was found that, the response of MA to binding with calf thymus DNA is characterised by an increase in the AS/AL ratio of the absorbance of the longest wavelength absorption band to the shortest one, and the appearance of a new band at about 377 nm assigned to S0âS1 transition, which is red shifted as compared to free MA. From the bands ratio, the binding constant is found to be 4.3x105 M-1, indicating strong binding. The deduced binding free energy, enthalpy and entropy are -7.7 kcal/mol, -10.89 ± 0.28 kcal/mol and -54.46 ± 4 J/K, respectively, indicating that MA binds to DNA by a non-bonding Van der Waals type interactions and hydrogen bonds. Further study with classical molecular dynamics shows that MA binds to DNA by intercalation, where it is positioned between two AT base pairs. Unlike isolated MA, TDDFT calculations on ten images extracted from the MD trajectory show that, the frontier molecular orbitals of the complex are distributed over the DNA and MA. This indicates a strong stacking interaction and then explains the hypochromism and the red shift of the S0âS1 transition. The present work demonstrates the potency of MA as antitumor compound and as absorbance-based molecular probe.Communicated by Ramaswamy H. Sarma.
ABSTRACT
BACKGROUND: Spirulina platensis produced in Nomayos (Cameroon) is used as a dietary supplement. S. platensis is known as a neutraceutical with many beneficial effects on humans like lipid-lowering action. This study aims to investigate the mechanism of hypolipidemic action of aqueous extract of Spirulina platensis (S. platensis) through the toxicological studies. METHODS: In this study, we included two month old Wistar rats, weighing between 180 and 200 g. Aqueous S. platensis was extracted and prepared using standard methods. The rats received a supplementation of S. platensis at 5000 mg/Kg of body weight as single dose in acute toxicity whereas different doses (250, 500, 1000 mg / kg body weight) were administered in subacute toxicity compared to control. Acute and subacute toxicities were determined according to the guidelines 420 (14 days) and 407 (28 days) of the Organization for Economic Cooperation and Development (OECD) respectively. Biochemical parameters such as urea, creatinine, total and direct bilirubin, lipid profile and transaminases; and histopathological analysis of the liver and kidneys were used to evaluate the toxicity of S. platensis on these Wistar rats. Plasmatic hydroxymethyl glutaryl coenzyme A reductase (HMG CoA reductase) and lecithine cholesterol acyl transferase (LCAT) were performed to explain the lipid-lowering action of S. platensis. Histopathological analysis of the liver and kidneys was performed. RESULTS: Our results show a decrease in total cholesterol for male rats (from 84 to 74 mg/dl) when the dose of S. platensis increased; this reduction of the total cholesterol level in male rats was significant at 500 mg/kg. There was also a significant inhibition of HMG CoA reductase in a dose dependent manner between 25 and 84.5 fold compared to the control in both male and female groups. At the dose of 250 mg/kg bw, the level of LCAT was higher compared with other groups and control, but the difference was not statistically significant. A slight inflammation in the liver and the mesangial hyperplasia of the renal glomeruli was revealed by the histopathological investigation in subacute toxicity. CONCLUSION: Spirulina platensis from Cameroon appears to have little toxic effects and may demonstrate hypolipidemic activity through the activation of LCAT.
