The leaves of green plants as well as a cyanobacterium, a red alga, and fungi contain insulin-like antigens

The in vivo Tetrahymena thermophila extracellular glucose drop assay for characterization of mammalian insulin activity

Insulin activity is generally determined by an in vivo rabbit blood glucose drop assay in research and industriel laboratories. The humane experimental techniques imply the use of alternative invertebrate organisms in place of animals, known as replacement rule of the 3Rs. In this study, we report an alternative in vivo extracellular glucose drop assay using unicellular invertebrate Tetrahymena thermophila to replace the use of rabbit and mouse. This assay has four major steps; growing cells, starving cells, treatment of cells and measurement of glucose drop. In this assay, 0.2 mg/ml of human, porcine and bovine insulins dropped extracellular glucose level to 16%, 14% and 12%, respectively in ten minutes. In addition, mammalian insulins respectively increased the cell area about 19%, 15%, and 16% at 6th hour with statistically significant effect on the cell growth, but not in the cell viability. The results showed that the in vivo Tetrahymena thermophila extracellular glucose drop assay could be used as an alternative assay to replace the mouse or the rabbit insulin blood glucose drop assay.

Anti-diabetic potential of peptides: Future prospects as therapeutic agents

Diabetes mellitus is a metabolic disorder in which the glucose level in blood exceeds beyond the normal level. Persistent hyperglycemia leads to diabetes late complication and obviously account for a large number of morbidity and mortality worldwide. Numerous therapeutic options are available for the treatment of diabetes including insulin for type I and oral tablets for type II, but its effective management is still a dream. To date, several options are under investigation in various research laboratories for efficacious and safer agents. Of them, peptides are currently amongst the most widely investigated potential therapeutic agents whose design and optimal uses are under development. A number of natural and synthetic peptides have so far been found with outstanding antidiabetic effect mediated through diverse mechanisms. The applications of new emerging techniques and drug delivery systems further offer opportunities to achieve the desired target outcomes. Some outstanding peptides in preclinical and clinical studies with better efficacy and safety profile have already been identified. Further detail studies on these peptides may therefore lead to significant clinically useful antidiabetic agents.

Histochemistry and immunolocalisation of glucokinin in antidiabetic plants used in traditional Mexican medicine

Mexico is a megadiverse country that has 3,600 to 4,000 species of medicinal plants, of which approximately 800 are used to treat conditions related to diabetes mellitus (DM). DM is a chronic degenerative disease of energy metabolism that exists as two types: type 1 (DM1) and type 2 (DM2). DM is considered a public health problem that affects 7% of the Mexican population older than 20 years. DM is clinically controlled with hypoglycaemic drugs, alpha-glucosidase inhibitors, insulin secretion stimulants or the direct application of insulin. The hypoglycaemic effectiveness of specific molecules has been determined only for some medicinal plants in Mexico used to treat DM2. The presence of molecules called glucokinins, wich are similar to animal insulin molecules, has been reported in some plant species; glucokinins act as both growth factors and regulators of glucose metabolism in plants. Therefore, we hypothesized that the hypoglycaemic effectiveness of some of the popularly used species for the control of DM could be due to the presence of glucokinin, as reported for Bauhinia variegata. The goal of this work was to use histochemistry to detect, the accumulation of protein that is immunocytochemically compatible with glucokinin in slide sections of hypoglycaemic species used as remedies for DM2. The top fourteen most used medicinal plants in Mexico were selected for study via microscopic sections. Proteins were histochemically detected using naphthol blue black and Johansen's quadruple stain, and the immunocytochemical correspondence of the proteins with glucokinin was investigated using an insulin antibody. All species studied reacted positively to proteins and glucokinin in the same structures. The presence of glucokinin in these structures and the corresponding hypoglycaemic effects are discussed in the contex of the actions of other compounds.

Elucidation of hypoglycemic action and toxicity studies of insulin-like protein from Costus igneus

We have reported earlier, an orally active insulin-like protein (ILP) from Costus igneus having potent hypoglycemic property in STZ-induced diabetic Swiss mice. The blood glucose level was reduced significantly within two hours after feeding ILP orally in an oral glucose tolerance test. The present study elucidates the mechanism underlying the hypoglycemic action of ILP. Mechanism of action of ILP was studied in differentiated L6 myotubes. 2-NBDG uptake stimulated by ILP was studied in differentiated L6 myotubes under normoglycemic, hyperglycemic and induced insulin resistant conditions. ILP treatment significantly increased 2-NBDG uptake in differentiated L6 myotubes. The levels of insulin signaling molecules IRS-1 and GLUT-4 were assessed in ILP treated L6 myotubes by immunoblot analysis of cytoplasmic and plasma membrane fractions respectively. Immunoblot analysis revealed an increase in cytoplasmic IRS-1 with a concomitant increase in GLUT-4 translocation to the plasma membrane in a time dependent manner. Toxicity studies of ILP were performed on normal as well as diabetic Swiss albino mice. ILP did not show any toxicity in the acute and sub-chronic toxicity studies in normal as well as diabetic Swiss albino mice. Mass spectrometry was carried out to identify ILP. MALDI TOF/TOF MS analysis of ILP revealed sequence homology with the predicted protein from Physcomitrella patens. Our study reveals that ILP acts via insulin signaling pathway and can be used as oral insulin mimetic.

Orally active hypoglycemic protein from Costus igneus N. E. Br.: an in vitro and in vivo study

Plants have been used for the treatment of diabetes since time immemorial. In the present study, insulin-like protein (ILP) is purified from Costus igneus belonging to family Costaceae from Western ghats of India. The ILP showed cross reactivity with murine anti-insulin antibodies hence was purified by affinity chromatography using anti-insulin antibodies. The characterization of ILP showed that it is structurally different from insulin but functionally similar. The ILP showed a hypoglycemic activity in an in vitro assay with insulin responsive cell line RIN 5f. Interestingly ILP showed significant decrease in blood glucose level when administered orally in oral glucose tolerance test. This was compared to insulin a positive control given intraperitoneally in streptozotocine induced diabetic mice. There was no toxic effect seen on animals after administrating the ILP. Therefore we conclude that the ILP purified in the present study from C. igneus is a novel protein having hypoglycemic activity.

In Silico Pharmaco-Gene-Informatic Identification of Insulin-Like Proteins in Plants

This chapter presents an extension of the authors’ earlier work, where they showed that nucleotide/amino acid sequences related to insulin occurred in the plant kingdom. It was believed that plants did not have, nor did they need insulin, a protein hormone considered to be restricted to the animal kingdom. In the current study, the human insulin sequence was initially obtained from UniProt/SwissProt (accession no. P01308). Plant genome sequences were obtained from NCBI PubMed (Bauhinia purpurea [Gi|229412], Vigna unguiculata [P83770], and Canavalia ensiformis [Gi|7438602]. Scores were obtained from ProtFun 2.2 [http://www.cbs.dtu.dk/services/ProtFun/]. At the next stage, functions of insulin and glucokinin (insulin like proteins in plants) were predicted by the Protein Function Prediction database (http://dragon.bio.purdue.edu/pfp/index.html), followed by functional site prediction from the ELM database (http://elm.eu.org/). ProtFun predicted the following functions: human insulin (Cell envelope), Jack bean (Energy metabolism), Bauhinia purpurea(Translation). The amino acid Glycine at 32 positions was most highly conserved. Present predictions advocate the use of these sequences (QHLCGS motif) as targets for probing the other plants with lesser homology. In summary our in silico studies have suggested that Bauhinia purpurea (Purple orchid tree-BP), Vigna unguiculata (Cow pea-CP) and Canavalia ensiformis (Jack bean-JB) have conserved the important regions of the human insulin protein.

SCREENING OF PHOTOSYNTHETIC O2 -EVOLVING PROKARYOTES FOR AN INSULIN-LIKE ANTIGEN(1)

Diabetes mellitus (DM), a metabolic disorder, is becoming a major health problem worldwide. Insulin is the single hope for management of type 1 diabetes, but it is not always available or suitable. For finding additional bioresources, the present study was performed. ELISA-based preliminary screening of cyanobacterial biomass using antihuman insulin antibody have detected an insulin-like antigen in Spirulina platensis S-5, Spirulina NCCU-482, and Spirulina NCCU-483. Their similarity with insulin-like antigen was further confirmed by electrophoretic mobility using bovine insulin as marker.

Isolation and intracellular localization of insulin-like proteins from leaves of Bauhinia variegata

Evidence based on immunological cross-reactivity and anti-diabetic properties has suggested the presence of insulin-like peptides in plants. The objective of the present study was to investigate the presence of insulin-like proteins in the leaves of Bauhinia variegata ("pata-de-vaca", "mororó"), a plant widely utilized in popular medicine as an anti-diabetic agent. We show that an insulin-like protein was present in the leaves of this plant. A chloroplast protein with a molecular mass similar to that of bovine insulin was extracted from 2-mm thick 15% SDS-PAGE gels and fractionated with a 2 x 24 cm Sephadex G-50 column. The activity of this insulin-like protein (0.48 mg/mL) on serum glucose levels of four-week-old Swiss albino (CF1) diabetic mice was similar to that of commercial swine insulin used as control. Further characterization of this molecule by reverse-phase hydrophobic HPLC chromatographic analysis as well as its antidiabetic activity on alloxan-induced mice showed that it has insulin-like properties. Immunolocalization of the insulin-like protein in the leaves of B. variegata was performed by transmission electron microscopy using a polyclonal anti-insulin human antibody. Localization in the leaf blades revealed that the insulin-like protein is present mainly in chloroplasts where it is also found associated with crystals which may be calcium oxalate. The presence of an insulin-like protein in chloroplasts may indicate its involvement in carbohydrate metabolism. This finding has strengthened our previous results and suggests that insulin-signaling pathways have been conserved through evolution.

Effect of an aqueous extract of Scoparia dulcis on blood glucose, plasma insulin and some polyol pathway enzymes in experimental rat diabetes

The effects of an aqueous extract of the plant Scoparia dulcis (200 mg/kg) on the polyol pathway and lipid peroxidation were examined in the liver of streptozotocin adult diabetic male albino Wistar rats. The diabetic control rats (N = 6) presented a significant increase in blood glucose, sorbitol dehydrogenase, glycosylated hemoglobin and lipid peroxidation markers such as thiobarbituric acid reactive substances (TBARS) and hydroperoxides, and a significant decrease in plasma insulin and antioxidant enzymes such as glutathione peroxidase (GPx), glutathione-S-transferase (GST) and reduced glutathione (GSH) compared to normal rats (N = 6). Scoparia dulcis plant extract (SPEt, 200 mg kg-1 day-1) and glibenclamide (600 microg kg-1 day-1), a reference drug, were administered by gavage for 6 weeks to diabetic rats (N = 6 for each group) and significantly reduced blood glucose, sorbitol dehydrogenase, glycosylated hemoglobin, TBARS, and hydroperoxides, and significantly increased plasma insulin, GPx, GST and GSH activities in liver. The effect of the SPEt was compared with that of glibenclamide. The effect of the extract may have been due to the decreased influx of glucose into the polyol pathway leading to increased activities of antioxidant enzymes and plasma insulin and decreased activity of sorbitol dehydrogenase. These results indicate that the SPEt was effective in attenuating hyperglycemia in rats and their susceptibility to oxygen free radicals.

A protein with amino acid sequence homology to bovine insulin is present in the legume Vigna unguiculata (cowpea)

Since the discovery of bovine insulin in plants, much effort has been devoted to the characterization of these proteins and elucidation of their functions. We report here the isolation of a protein with similar molecular mass and same amino acid sequence to bovine insulin from developing fruits of cowpea (Vigna unguiculata) genotype Epace 10. Insulin was measured by ELISA using an anti-human insulin antibody and was detected both in empty pods and seed coats but not in the embryo. The highest concentrations (about 0.5 ng/micro g of protein) of the protein were detected in seed coats at 16 and 18 days after pollination, and the values were 1.6 to 4.0 times higher than those found for isolated pods tested on any day. N-terminal amino acid sequencing of insulin was performed on the protein purified by C4-HPLC. The significance of the presence of insulin in these plant tissues is not fully understood but we speculate that it may be involved in the transport of carbohydrate to the fruit.

Plant insulin or glucokinin: a conflicting issue

The presence of insulin in plants is not accepted by the scientific community in general. In this review we discuss this paradigm and retrieve information that strongly suggests that insulin is indeed found in plants. We present results, which indicate that a protein molecule with the same amino acid sequence as bovine insulin is expressed in leguminous plants. Additionally, we provide evidence that proteins associated with insulin signalling pathways in vertebrates are also found in association with insulin-like molecules in plants.