Several members of cucurbitaceae family have been reported to regulate growth of cancer by interfering with STAT3 signaling. In the present study, we investigated the unique role and molecular mechanism of cucurbitacins (Cucs) in reducing symptoms of metabolic syndrome in mice. Cucurbitacin E (CuE) was found to reduce adipogenesis in murine adipocytes. CuE treatment diminished hypertrophy of adipocytes, visceral obesity and lipogenesis gene expression in diet induced mice model of metabolic syndrome (MetS). CuE also ameliorated adipose tissue dysfunction by reducing hyperleptinemia and TNF-alpha levels and enhancing hypoadiponectinemia. Results show that CuE mediated these effects by attenuating Jenus kinase- Signal transducer and activator of transcription 5 (JAK- STAT5) signaling in visceral fat tissue. As a result, CuE treatment also reduced PPAR gamma expression. Glucose uptake enhanced in adipocytes after stimulation with CuE and insulin resistance diminished in mice treated with CuE, as reflected by reduced glucose intolerance and glucose stimulated insulin secretion. CuE restored insulin sensitivity indirectly by inhibiting JAK phosphorylation and improving AMPK activity. Consequently, insulin signaling was up-regulated in mice muscle. As CuE positively regulated adipose tissue function and suppressed visceral obesity, dyslipedemia, hyperglycemia and insulin resistance in mice model of MetS, we suggest that CuE can be used as novel approach to treat metabolic diseases.

Several reports indicate anti-hyperglycemic effects of Syzygium aromaticum. In the present study, we report for the first time that clove extract (SAM) and its compound nigricin (NGC) decreases free fatty acid-mediated insulin resistance in mouse myoblasts. In addition, NGC was able to diminish insulin resistance in a diabetic mouse model. We observed that SAM and its compound NGC exhibited significant antioxidant activity in murine skeletal muscle cells. They also modulated stress signaling by reducing p38 MAP kinase phosphorylation. NGC and SAM treatments enhanced proximal insulin signaling by decreasing serine phosphorylation of insulin receptor substrate-1 (IRS-1) and increasing its tyrosine phosphorylation. SAM and NGC treatments also modified distal insulin signaling by enhancing protein kinase B (PKB) and glycogen synthase kinase-3-beta (GSK-3 beta) phosphorylation in muscle cells. Glucose uptake was enhanced in muscle cells after treatment with SAM and NGC. We observed increased glucose tolerance, glucose-stimulated insulin secretion, decreased insulin resistance, and increased beta cell function in diabetic mice treated with NGC. The results of our study demonstrate that clove extract and its active agent NGC can be potential therapeutic agents for alleviating insulin resistance.

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