Phytomodulatory proteins promote inhibition of hepatic glucose production and favor glycemic control via the AMPK pathway.

ABSTRACT

Phytomodulatory proteins from the latex of the medicinal plant Calotropis procera has been shown to be implicated in many pharmacological properties. However there is no current information about their activity on glucose metabolism, although the latex is used in folk medicine for treating diabetes. In this study the phytomodulatory proteins (LP) from C. procera latex were assessed on glycemic homeostasis. Control animals received a single intravenous dose (5 mg/kg) of LP or saline solution (CTL). Four hours after treatment, the animals were euthanized and their livers were excised for analysis by western blot and RT-PCR AMP-activated protein kinase (AMPK), phosphoenolpyruvate carboxykinase (PEPCK) and tumor necrosis factor alpha (TNF-α). In vivo tests of intraperitoneal tolerance to insulin, glucose and pyruvate were also performed, and the effect of LP administration on fed glycemia was studied followed by blood analysis to determine serum insulin levels. Treatment with LP reduced glycemia two hours after glucose administration (LP 87.2 ± 3.70 mg/dL versus CTL 115.6 ± 8.73 mg/dL). However, there was no change in insulin secretion (CTL 14.16 ± 0.68 mUI/mL and LP 14.96 ± 0.55 mUI/mL). LP improved the insulin sensitivity, represented by a superior glucose decay constant during an insulin tolerance test (kITT) (4.17 ± 0.94%/min) compared to the CTL group (0.82 ± 0.72%/min), and also improved glucose tolerance at 30 min (105.2 ± 12.4 mg/dL versus 154.2 ± 18.51 mg/dL), while it decreased hepatic glucose production at 15 and 30 min (LP 75.5 ± 9.31 and 52.5 ± 12.05 mg/dL compared to the CTL 79.0 ± 3.02 and 84.5 ± 7.49 mg/dL). Furthermore, there was a significant inhibition of gene expression of PEPCK (LP 0.66 ± 0.06 UA and CTL 1.14 ± 0.22 UA) and an increase of phosphorylated AMPK (LP 1.342 ± 0.21 UA versus CTL 0.402 ± 0.09 UA). These findings confirm the effect of LP on glycemic control and suggest LP may be useful in diabetes treatment. However, the pharmacological mechanism of LP in PEPCK modulation still needs more clarification.