Postprandial physiology and the pathogenesis of type 2 diabetes mellitus

High-Resolution PTP1B Inhibition Profiling Combined with HPLC-HRMS-SPE-NMR for Identification of PTP1B Inhibitors from Miconia albicans

Protein tyrosine phosphatase 1B (PTP1B) is an intracellular enzyme responsible for deactivation of the insulin receptor, and consequently acts as a negative regulator of insulin signal transduction. In recent years, PTP1B has become an important target for controlling insulin resistance and type 2 diabetes. In the present study, the ethyl acetate extract of leaves of Miconia albicans (IC₅₀ = 4.92 µg/mL) was assessed by high-resolution PTP1B inhibition profiling combined with HPLC-HRMS-SPE-NMR for identification of antidiabetic compounds. This disclosed eleven PTP1B inhibitors, including five polyphenolics: 1-O-(E)-caffeoyl-4,6-di-O-galloyl-β-d-glucopyranose (2), myricetin 3-O-α-l-rhamnopyranoside (3), quercetin 3-O-(2″-galloyl)-α-l-rhamnopyranoside (5), mearnsetin 3-O-α-l-rhamnopyranoside (6), and kaempferol 3-O-α-l-arabinopyranoside (8) as well as eight triterpenoids: maslinic acid (13), 3-epi-sumaresinolic acid (14), sumaresinolic acid (15), 3-O-cis-p-coumaroyl maslinic acid (16), 3-O-trans-p-coumaroyl maslinic acid (17), 3-O-trans-p-coumaroyl 2α-hydroxydulcioic acid (18), oleanolic acid (19), and ursolic acid (20). These results support the use of M. albicans as a traditional medicine with antidiabetic properties and its potential as a source of PTP1B inhibitors.

Effect and potential mechanism of action of sea cucumber saponins on postprandial blood glucose in mice

Postprandial blood glucose control is the major goal in the treatment of diabetes. Here, we investigated the effect of sea cucumber saponins (SCSs) on postprandial blood glucose levels. SCS inhibited yeast as well as rat intestinal α-glucosidase activity in a dose-dependent manner and showed better inhibition of yeast α-glucosidases compared to the positive control. Further studies were performed using ICR mice treated with SCS and starch or SCS alone by oral gavage. Unexpectedly, SCS increased postprandial blood glucose levels a short time (1 h) after oral gavage. The serum corticosterone (CORT) level showed a consistent correlation with glucose levels. In vitro experiments confirmed that SCS treatment increased the secretion of CORT in the Y1 adrenal cell line. Overall, these studies demonstrated that SCS gavage could inhibit α-glucosidase activity but cannot attenuate postprandial blood glucose level within short time periods. The underlying mechanisms are probably related to increased serum CORT levels.

Intranasal insulin: from nose to brain

BACKGROUND

Intranasal insulin has proven useful to control hyperglycemia in diabetics but its mechanism of action has not been well defined. We attempted to understand several aspects of human insulin metabolism by measurement of and interaction of insulin and its associated moieties in nasal mucus, saliva and blood plasma under various physiological and pathological conditions.

METHODS

Insulin, insulin receptors, insulin-like growth factor 1 (IGF1) and insulin-like growth receptor 3 (IGFR3) were measured in nasal mucus, saliva and blood plasma in normal subjects, in thin and obese subjects and in diabetics under fasting and fed conditions.

RESULTS

There are complex relationships among each of these moieties in each biological fluid. Insulin and its associated moieties are present in both nasal mucus and saliva. These moieties in nasal mucus and saliva report on physiological and pathological changes in glucose metabolism as do these moieties in plasma. Indeed, insulin and its associated moieties in nasal mucus may offer specific data on how insulin enters the brain and thereby play essential roles in control of insulin metabolism.

INTERPRETATION

These data support the concept that insulin is synthesized not only in parotid glands but also in nasal serous glands. They also support the concept that insulin enters the brain following intranasal administration either 1) by direct entry through the cribriform plate, along the olfactory nerves and into brain parenchyma, 2) by entry through specific receptors in blood-brain barrier and thereby into the brain or 3) some combination of 1) and 2). Conversely, data also show that insulin introduced directly into the brain is secreted out of brain into the peripheral circulation. Data in this study demonstrate for the first time that insulin and its associated moieties are present not only in saliva but also in nasal mucus. How these complex relationships among nasal mucus, saliva and plasma occur are unclear but results demonstrate these relationships play separate yet interrelated roles in physiology and pathology of human insulin metabolism.