Enhydrin Regulates Postprandial Hyperglycemia in Diabetic Rats by Inhibition of α-Glucosidase Activity

During the last few years, numerous attempts were made to identify effective α-glucosidase inhibitors from natural sources in order to develop new alternatives for diabetes management. Smallanthus sonchifolius (yacon) leaves were found to be effective in controlling postprandial hyperglycemia. Enhydrin, a constituent of yacon leaves, was noted for its significant hypoglycemic properties in diabetic rats. These properties were also demonstrated for yacon leaves decoction, which is rich in phenolic compounds such as chlorogenic acid and its derivatives. The purpose of the present study was to evaluate the potential of yacon leaves decoction and the isolated compound enhydrin to inhibit α-glucosidase enzyme, a possible mechanism of the above antihyperglycemic effect. In vitro assays showed that both 10% decoction and enhydrin significantly inhibited the activity of the yeast α-glucosidase enzyme in a dose-dependent manner, IC₅₀ values being 50.40 and 134.17 μg/ml, respectively. In vivo experiments showed a rapid decrease in the hyperglycemic peak after sucrose load (2 g/kg body weight) in normal rats treated with the 10% decoction (140 mg/kg) and enhydrin (0.8 mg/kg). Both treatments caused a significant decrease in blood glucose levels in diabetic rats after sucrose load compared to diabetic control. These results suggest that both products assayed could be effective in the management of postprandial hyperglycemia through inhibition of α-glucosidase in the small intestine.

Changes in the expression of small intestine extracellular matrix proteins in streptozotocin-induced diabetic rats

Diabetes mellitus is characterized by anatomical and functional alterations of the intestinal tract. However, the aetiology of these disturbances remains unclear. The aim of the present work was to investigate the effects of diabetes on the expression of laminin-1 and fibronectin in the small intestine of Streptozotocin (STZ)-induced diabetic rats. The Western immunoblotting of the extracts from the small intestine revealed that experimental diabetes resulted in a marked increase in the intensity of the bands corresponding to laminin-1 and fibronectin. Immunohistochemical studies demonstrated a strong labelling to these two extracellular matrix (ECM) proteins in the small intestine of diabetic rats, mainly localized in the smooth muscle layer. These results occur together with a thickening of the basement membrane (BM) of the smooth muscle cells, demonstrated by transmission electron microscopy (TEM). We propose that the accumulation of ECM proteins in the smooth muscle layer may be an effect mediated by hyperglycaemia, since insulin treatment of diabetic rats reversed this accumulation. These results could provide information on the potential role of the ECM in the intestine, an organ which is known to exhibit important alterations in diabetes.

Effect of gap junction uncoupling in full-grown Bufo arenarum ovarian follicles: participation of cAMP in meiotic arrest

The aim of the present study was to determine the presence of the connexins Cx43, Cx32 and Cx26 in Bufo arenarum ovarian follicles during the breeding season as well as to analyse the possible alterations in the meiotic process when connexins are blocked by specific antibodies. Western blot analysis revealed that the Cx43 and Cx32 proteins were present but not Cx26. We demonstrated that the anti-Cx43 and anti-Cx32 antibodies produced the uncoupling of the gap junctions. When these junctions are blocked the maturation process is triggered in the oocytes. We determined that dbcAMP exerts an inhibitory effect on the maturation induced by the uncoupling of the gap junctions when the oocytes are injected or pretreated with this metabolite. We propose the idea that cAMP is the regulatory molecule in meiotic arrest in this amphibian species.

Participation of the GM1 ganglioside in the gastrulation of anuran amphibian Bufo arenarum

In the present paper we established the ganglioside composition of the blastula and gastrula stages of the anuran amphibian Bufo arenarum, two relevant stages characterized by dynamic changes in morphology and cellular rearrangements. Densitometric studies evidenced that GD1a and GT1b were the more abundant gangliosides of the blastula embryos whereas GM1 and GM2 were the predominant species in gastrula embryos. Analysis of ganglioside abundance indicates that the "a" and "b" synthesis pathways perform similar biosynthetic activities in the blastula stage, in contrast to the gastrula stage in which a marked predominance of the "a" pathway occurred. The spatio-temporal expression of GM1 and of polygangliotetraosyl ceramides (pGTC) was investigated by wholemount immunocytochemistry using cholera toxin B subunit (CTB) and an affinity purified human anti-GM1 antibody. The pGTC were detected as GM1 after treatment with neuraminidase. Blastomeres from the inner surface of the blastocoelic roof (BCR) of blastula embryos were GM1 and pGTC positive. At midgastrula stage, embryos showed an increased labeling on the inner surface of BCR. To establish whether the GM1 ganglioside was involved in the gastrulation processes, CTB, anti-GM1 antibodies and anti-GM1 Fab' fragments were microinjected into the blastocoel cavity of blastula embryos. Treatment with the probes blocked gastrulation. Scanning electron microscopy analysis of blocked embryos revealed that mesodermal cell migration, radial interdigitation, and convergent extension movements were affected. The blocking of gastrulation was correlated with the absence of fibronectin and EP3/EP4 on the inner surface of blastocoelic roof of CTB- or anti-GM1 treated embryos. Results show that the GM1 ganglioside is differentially expressed by embryonic cells and participates in the morphogenetic processes of amphibian gastrulation. J. Exp. Zool. 286:457-472, 2000.

Evidence for the presence and participation of 85-75 KDa extracellular matrix components in cell interactions of Bufo arenarum gastrulation

We studied the presence and distribution of the extracellular materials (ECM), obtained by mild embryonic dissociation through nondenaturing and denaturing PAGE, immunoblotting and immunocytochemical wholemount in the gastrulation of anuran amphibian Bufo arenarum. The SDS-PAGE, under reducing conditions, revealed the protein profile of the ECM which comprised six bands. The Western immunoblotting effected with antibodies against fibronectins (FN) of Xenopus laevis, Ambystoma mexicanum and Bufo arenarum revealed that the 210 and 190 KDa bands (EP1-EP2) present in the ECM were identified as FN. Polyclonal antibodies against the 85-75 KDa polypeptides (EP3-EP4) were obtained and used throughout this study. The distribution of FN and EP3-EP4 was comparatively studied in the blastocoelic roof (BCR) of stage 10.5 Bufo arenarum, Xenopus laevis and Ambystoma mexicanum embryos. In the anurans, FN appeared as a network of fine fibrils apparently oriented at random, while in Ambystoma, FN appeared as a complex anastomosing network of oriented fibrils. EP3-EP4 were found in Bufo and in Xenopus both in the intercellular contact zones and in the cellular periphery. No linear arrangements of these proteins were observed. Few, if any, EP3-EP4 were found on the BCR of Ambystoma mexicanum. At stage 11, EP3-EP4, which showed a dramatic increase at the chordomesoderm-neuroectoderm junction in Bufo arenarum embryos, appeared as an amorphous material. For the purpose of analyzing the role of EP3-EP4 during Bufo arenarum gastrulation, anti-EP3-EP4 antibodies and anti-EP3-EP4 Fab fragments were microinjected into the blastocoel cavity of stage 9 embryos, an event that cause severe alterations in the gastrulation process. Convergent extension of the dorsal marginal zone and the epiboly of the BCR were the most strongly affected events. Results show that EP3-EP4 are required for normal Bufo arenarum gastrulation.

Amphibian Bufo arenarum vitronectin-like protein: its localization during oogenesis

In the present study, we analyzed the localization of vitronectin-like protein in oocytes during oogenesis as well as in the serum and liver tissue of the amphibian Bufo arenarum. Vitronectin-like protein was purified from serum by heparin-affinity chromatography and showed to have the two biological properties in common with most animal vitronectins (VN): heparin binding activity and an RGD-dependent cell-spreading activity. SDS-PAGE of vitronectin-like protein revealed that it consists of two bands of 64 kDa and 72 kDa, while immunoblotting analyses showed that this protein strongly cross-reacts with two monoclonal antibodies against human VN. No immunofluorescent staining of vitronectin-like protein was observed in previtellogenic oocytes (stages I and II). In vitellogenic oocytes (stages III, IV and V) fluorescence was observed in the cortical cytoplasm localized in yolk platelets, extending concomitantly with the vitellogenic process. When we examined the yolk platelet formation pathway by immunoelectron microscopy, gold particles indicated that vitronectin-like protein was located on the yolk platelet precursors: multivesicular bodies and primordial yolk platelets. Gold particles also were seen sparsely distributed in all oocyte investing layers. The mean serum vitronectin-like protein concentration in amphibian animals was 127.8 +/- 11.6 micrograms/ml in adult males and 181.5 +/- 14.3 micrograms/ml in adult females. Serum vitronectin-like protein of males and females was susceptible to hormonal stimulation (17-beta estradiol). These results suggest that vitronectin-like protein is stored in the yolk platelets and may be involved in the later events of amphibian development.