Antidiabetes and Anti-obesity Activity of Lagerstroemia speciosa

The leaves of Lagerstroemia speciosa (Lythraceae), a Southeast Asian tree more commonly known as banaba, have been traditionally consumed in various forms by Philippinos for treatment of diabetes and kidney related diseases. In the 1990s, the popularity of this herbal medicine began to attract the attention of scientists worldwide. Since then, researchers have conducted numerous in vitro and in vivo studies that consistently confirmed the antidiabetic activity of banaba. Scientists have identified different components of banaba to be responsible for its activity. Using tumor cells as a cell model, corosolic acid was isolated from the methanol extract of banaba and shown to be an active compound. More recently, a different cell model and the focus on the water soluble fraction of the extract led to the discovery of other compounds. The ellagitannin Lagerstroemin was identified as an effective component of the banaba extract responsible for the activity. In a different approach, using 3T3-L1 adipocytes as a cell model and a glucose uptake assay as the functional screening method, Chen et al. showed that the banaba water extract exhibited an insulin-like glucose transport inducing activity. Coupling HPLC fractionation with a glucose uptake assay, gallotannins were identified in the banaba extract as components responsible for the activity, not corosolic acid. Penta-O-galloyl-glucopyranose (PGG) was identified as the most potent gallotannin. A comparison of published data with results obtained for PGG indicates that PGG has a significantly higher glucose transport stimulatory activity than Lagerstroemin. Chen et al. have also shown that PGG exhibits anti-adipogenic properties in addition to stimulating the glucose uptake in adipocytes. The combination of glucose uptake and anti-adipogenesis activity is not found in the current insulin mimetic drugs and may indicate a great therapeutic potential of PGG

Synthesis and Antitumor Activity of Ellagic Acid Peracetate

Ellagic acid (<b>1</b>) was synthesized for the first time from methyl gallate through α-pentagalloylglucose (α-PGG), and ellagic acid peracetate (3,4,3′,4′-tetra-<i>O</i>-acetylellagic acid, <b>2</b>) was derived from <b>1</b> by acetylation. Oral administration of <b>2</b> suppressed melanoma growth significantly in C7BL/6 immunocompetent mice without having any effect on natural killer (NK) cell activity. Comparison of the immunoenhancing activities of <b>1</b> and <b>2</b> indicated that the latter compound increased white blood cell quantities in peripheral blood and immune cells enriched from the bone marrow and liver of mice. Therefore, both the antitumor efficacy and the immunity enhancement by <b>2</b> were greater than those by <b>1</b>. In addition, on oral administration, neither <b>1</b> nor <b>2</b> resulted in whole body, liver, or spleen weight changes of normal, tumor-free mice, indicating that these compounds are potentially nontoxic to mice. It was shown that ellagic acid peracetate (<b>2</b>) inhibits B16 melanoma cell growth in vitro and induces B16 cell apoptosis, corresponding to BCL-2 down-regulation. Collectively, the present data imply that <b>2</b> can suppress tumor growth by enhancing mouse immunity and inducing tumor cell apoptosis without apparent side effects