In our ongoing work searching for new trypanocidal lead compounds from Malaysian plants, two known piperidine alkaloids (+)-spectaline (1) and iso-6-spectaline (2) were isolated from the leaves of Senna spectabilis (sin. Cassia spectabilis). Analysis of the 1H and 13C NMR spectra showed that 1 and 2 presented analytical and spectroscopic data in full agreement with those published in the literature. All compounds were screened in vitro against Trypanosoma brucei rhodesiense in comparison to the standard drug pentamidine. Compound 1 and 2 inhibited growth of T. b. rhodesiense with an IC50 value of 0.41 ± 0.01 μM and 0.71 ± 0.01 μM, without toxic effect on L6 cells with associated a selectivity index of 134.92 and 123.74, respectively. These data show that piperidine alkaloids constitute a class of natural products that feature a broad spectrum of biological activities, and are potential templates for the development of new trypanocidal drugs. To our knowledge, the compounds are being reported for the first time to have inhibitory effects on T. b. rhodesiense. The ultrastructural alterations in the trypanosome induced by 1 and 2, leading to programmed cell death were characterized using electron microscopy. These alterations include wrinkling of the trypanosome surface, formation of autophagic vacuoles, disorganization of kinetoplast, and swelling of the mitochondria. These findings evidence a possible autophagic cell death.
Understanding the mechanism by which the exogenous biomolecule modulates the GLUT-4 signalling cascade along with the information on glucose metabolism is essential for finding solutions to increasing cases of diabetes and metabolic disease. This study aimed at investigating the effect of hamamelitannin on glycogen synthesis in an insulin resistance model using L6 myotubes. Glucose uptake was determined using 2-deoxy-D-[1-3H] glucose and glycogen synthesis were also estimated in L6 myotubes. The expression levels of key genes and proteins involved in the insulin-signaling pathway were determined using real-time PCR and western blot techniques. The cells treated with various concentrations of hamamelitannin (20 µM to 100 µM) for 24 h showed that, the exposure of hamamelitannin was not cytotoxic to L6 myotubes. Further the 2-deoxy-D-[1-3H] glucose uptake assay was carried out in the presence of wortmannin and Genistein inhibitor for studying the GLUT-4 dependent cell surface recruitment. Hamamelitannin exhibited anti-diabetic activity by displaying a significant increase in glucose uptake (125.1%) and glycogen storage (8.7 mM) in a dose-dependent manner. The optimum concentration evincing maximum activity was found to be 100 µm. In addition, the expression of key genes and proteins involved in the insulin signaling pathway was studied to be upregulated by hamamelitannin treatment. Western blot analysis confirmed the translocation of GLUT-4 protein from an intracellular pool to the plasma membrane. Therefore, it can be conceived that hamamelitannin exhibited an insulinomimetic effect by enhancing the glucose uptake and its further conversion into glycogen by regulating glucose metabolism.