In vitro effects of rooibos herbal tea (Aspalathus linearis) against methamphetamine on the mouse blood brain barrier
Methamphetamine (MA), also known as ‘Tik’, has detrimental short- and long-term psychological and morphological effects on the central nervous system (CNS). The lipophilic nature of MA allows it to cross the blood-brain barrier (BBB) which normally plays a protective role in limiting solute exchange (including narcotics) into the neuronal tissue. Numerous studies have indicated that MA not only crosses the BBB but is implicated in distorting its crucial role in that it increases the permeability of the endothelial cells and thereby compromises its core homeostatic function. The speculated mechanism by which MA elicits its effects involves elevated ROS production which may be reversed by antioxidant treatment. Rooibos herbal tea (Aspalathus linearis) which is well documented for its antioxidative properties and ROS scavenging abilities may therefore be the ideal candidate to reverse the harmful ROS-induced effects of MA. The aim of the study was to investigate the in vitro ameliorating potential of fermented rooibos (Rf) against the MA-induced effects on mouse brain endothelial (bEnd5) cells by utilizing various assays (trypan blue exclusion and XTT viability assays) and physiological parameters (cell numbers, viability, monolayer permeability and cell cycle phases) over a period of 96 hrs. Statistical analysis was performed using the Wilcoxon rank sum test with P<0.05 denoted as significant. Once-off exposure to physiological MA concentrations and Rf resulted in % viability similar to controls by 96 hrs with suppression observed only when the cells were exposed to daily MA (0.1-1000 μM) (P≤0.0063). Exposure to supraphysiological concentrations (≥100 μM) of MA greatly suppressed viability (P≤0.0463). Both daily and once-off treatment to the combinations initially resulted in increased viability however by 96 hrs was similar to- or exceeding the controls (P≤0.0180). MA exposure also resulted in decreased live cell numbers (P≤0.0339) with no effect when exposed to Rf by 96 hrs. The combinations resulted in cell numbers comparable to controls. Dose-dependent increases in electrical resistance were observed in response to singular MA and Rf treatment with lower MA concentrations displaying significant decreases (P≤0.0064). Similar trends were observed with combinations however greater resistance was observed. Increased G1-phase populations (P≤0.0495) in response to singular MA and Rf exposure was noted followed by decreased S-phase fractions (P≤0.0356). While MA decreased G2-M phase cells (P≤0.0498) it was unaffected by Rf. In contrast, the combination of MA and Rf decreased events in the G1-phase (P≤0.0483), with an increased S-phase population (P≤0.0415). In conclusion, the single compounds displayed mirroring effects, decreasing the cells’ permeability and causing G1-phase arrest. The modulatory effects of Rf in combination with MA was illustrated with the restoration of viability and live cell numbers comparable to that of controls, and a more restrictive monolayer as well as reversal of the G1-phase arrest. Findings suggest that Rf may reverse the adverse effects of MA on the BBB.