Increased Insulin Availability Research Articles

In-vitro Antioxidant and DPP-IV Enzyme Assay of Ethyl Acetate Extract of Enicostemma littorale

Background: Pharmacological treatments for diabetes are based on increasing insulin availability and improving insulin sensitivity. Today, glucagon-like peptide 1 (GLP-1) -based therapies aim to control glucose through DPP-4 inhibitors. DPP-4 is a transmembrane glycoprotein belonging to the prolyl oligopeptidase family, with the specificity of eliminating the X-Pro or X-Ala dipeptides from the N-terminal end of the polypeptides. The effect of GLP-1 in stimulating the release of glucose-dependent insulin from pancreatic islets inhibits inappropriate glucagon release after meals and slow gastric emptying promotes intestinal permeability.
 Study Design: The current study investigated the inhibitory activity of DPP-4 along with the antioxidant activity of Enicostemma littorale extract. 
 Place and Duration of Study: The present study was conducted at Anurag University, Hyderabad between June-2021 to Sept-2021.
 Methodology: The extracts tested for a range of activities such as hydroxyl radical scavenging activity test, In-vitro DPP-IV enzyme test activity test, DPPH free radical scavenging.
 Results: The extract shows dose-dependent DPPH and hydrogen peroxide radical scavenging activity. In in-vitro DPP-IV enzyme assay activity, Enicostemma littorale ethyl acetate extract showed greater inhibitory activity of DPP-IV compared to vildagliptin with IC50 values ​​of 165.64μg/ml, respectively. Vildagliptin, based on the reference standard for DPP-IV inhibitor activity, has an IC50 value of 57.44 μg/ml. According to the in-vitro analysis, the Enicostemma littorale extract has a strong inhibitory activity of DPP-IV.
 Conclusion: We concluded that the Enicostemma littorale will be a better source for further development as new antidiabetic drugs. To the best of our knowledge, there is no report and study on the bark part of this species.

The Role of DPP-4 Inhibitors in the Treatment Algorithm of Type 2 Diabetes Mellitus: When to Select, What to Expect.

Type 2 diabetes mellitus is a growing global public health problem, the prevalence of which is projected to increase in the succeeding decades. It is potentially associated with many complications, affecting multiple organs and causing a huge burden to the society. Due to its multi-factorial pathophysiology, its treatment is varied and based upon a multitude of pharmacologic agents aiming to tackle the many aspects of the disease pathophysiology (increasing insulin availability [either through direct insulin administration or through agents that promote insulin secretion], improving sensitivity to insulin, delaying the delivery and absorption of carbohydrates from the gastrointestinal tract, or increasing urinary glucose excretion). DPP-4 (dipeptidyl peptidase-4) inhibitors (or “gliptins”) represent a class of oral anti-hyperglycemic agents that inhibit the enzyme DPP-4, thus augmenting the biological activity of the “incretin” hormones (glucagon-like peptide-1 [GLP-1] and glucose-dependent insulinotropic polypeptide [GIP]) and restoring many of the pathophysiological problems of diabetes. They have already been used over more than a decade in the treatment of the disease. The current manuscript will review the mechanism of action, therapeutic utility, and the role of DPP-4 inhibitors for the treatment of type 2 diabetes mellitus.

INHIBITORY POTENCY OF WITHANIA SOMNIFERA EXTRACTS AGAINST DPP-4: AN IN VITRO EVALUATION

Background: Pharmacologic treatments for type 2 diabetes are based upon increasing insulin availability and improving sensitivity to insulin. Nowadays, glucagon like peptide-1 (GLP-1) based therapies aims at glucose control through DPP-4 inhibitors. DPP-4 is a transmembrane glycoprotein belongs to prolyl oligopeptidase family, with the specificity of removing X-Pro or X-Ala dipeptides from the N-terminus of polypeptides. GLP-1 effect by stimulating glucose-dependent insulin release from the pancreatic islets, inhibit inappropriate post-meal glucagon release and slow gastric emptying promoting leaky gut. The current study investigated DPP-4 inhibitory activity of catechin, isolated from Withania somnifera (WS), for ethnopharmacological treatment of type 2 diabetes and aimed to increase availability of GLP-1and sensitivity to insulin.
 Materials and Methods: Young and matured fresh roots, leaves, and fruits of WS plant extract were considered and were systematically evaluated for DPP-4 inhibitory activity using in vitro method, enzyme kinetics, phytochemical analysis, RP-HPLC, LCMS and 1H and 13C NMR method and structure-activity relationship (SAR) studies.
 Results: In this study, methanol (100% and 80%) extracts of WS matured root exhibited maximum DPP-4 inhibitory activity when compared to other extracts. The maximum DPP-4 inhibitory activity was found in 100% methanol extract of matured root. Phytobioactive was purified by RP-HPLC. The compound purified was found to be flavonoid and was characterized (LCMS, 1H and 13C NMR studies), identified as catechin. Auxiliary, molecular docking was performed using Ligand Fit method using PatchDock package. The study revealed the binding affinity of catechin with DPP-4 to be -6.601 kcal/mol with 13 hydrogen interactions with the receptor and was very similar to the standard potent blockers withaferin A and others (cuscohygrine, scopoletin, sitoindoside IV, tropine), further confirming its hyperglycemic potency.
 Conclusion: The study reveals that, 100% methanol extract of WS matured roots contains the compound- catechin, which exhibits DPP-4 inhibitory activity resulting in increased level of bioactive GLP-1 and GIP. In this background, we concluded that the WS will be a better source for further development as new antidiabetic drugs.

Increasing Insulin Availability Does Not Augment Postprandial Muscle Protein Synthesis Rates in Healthy Young and Older Men.

Skeletal muscle protein synthesis is highly responsive to food intake. It has been suggested that the postprandial increase in circulating insulin modulates the muscle protein synthetic response to feeding. The objective of the study was to investigate whether a greater postprandial rise in circulating insulin level increases amino acid uptake in muscle and augments postprandial muscle protein synthesis rates. Forty-eight healthy young (age 22 ± 1 y; body mass index 22.0 ± 0.3 kg/m2) and older males (age 68 ± 1 y; body mass index 26.3 ± 0.4 kg/m2) ingested 20 g intrinsically L-[1-13C]-leucine- and L-[1-13C]-phenylalanine-labeled casein protein with or without local insulin infusion. Primed continuous infusions of L-[1-13C]-leucine and L-[ring-2H5]-phenylalanine were applied, with arterial and venous blood samples and muscle biopsies being collected during a 5-hour postprandial period. Insulin administration did not increase overall leg blood flow (P = .509) but increased amino acid uptake over the leg in both young and older subjects (P = .003). The greater amino acid uptake over the leg did not further increase postprandial muscle protein synthesis rates (0.050% ± 0.006% and 0.037% ± 0.004% per hour vs 0.044% ± 0.004% and 0.037% ± 0.002% per hour in the insulin-stimulated vs control condition in the young and older groups, respectively; P = .804) and did not affect postprandial deposition of dietary protein-derived amino acids in de novo muscle protein (P = .872). Greater postprandial plasma insulin availability stimulates amino acid uptake over the leg but does not further augment postprandial muscle protein synthesis rates or stimulate the postprandial deposition of protein derived amino acids into de novo muscle protein in healthy young and older men.

GLUCOMANNAN AND GLUCOMANNAN PLUS SPIRULINA-ENRICHED SQUID-SURIMI ADDED TO HIGH SATURATED DIET AFFECT GLYCEMIA, PLASMA AND ADIPOSE LEPTIN AND ADIPONECTIN LEVELS IN GROWING FA/FA RATS.

Type 2 diabetes is a very prevalent chronic disease. Among dietary factors for its prevention and treatment, interest has grown in satiating fibre (konjac glucomannan) and spirulina. Our previous studies suggest that glucomannan itself and/or in conjunction to spirulina displayed hypolipemic and antioxidant effects when incorporated to squid surimi as functional ingredients. The present study aims to determine whether glucomannan- enriched or glucomannan plus spirulina-enriched squid-surimi improve plasma glucose and insulin levels in Zucker fa/fa rats fed a high saturated fat diet. Twenty four growing rats, divided into three groups, were given modified AIN-93M diets for seven weeks: 30% squid-surimi control diet (C), 30% glucomannan-enriched squid-surimi diet (G) and 30% glucomannan plus spirulina-enriched squid-surimi diet (GS). All rats became hyperglycemics and hyperinsulinemics, but G and GS diets induced significantly lower glucose levels (20%; p < 0.05) but did not modify insulinemia with respect to C diet. GS animals showed higher HOMA-D (p < 0.05) than C ones suggesting increased insulin availability. Plasma leptin and adiponectin decreased in G and GS vs. C group (p < 0.05). Adipose adiponectin increased significantly in G and GS vs. C rats (16-20 times, p < 0.01). Leptin in adipose tissue was higher in GS vs. G group (p < 0.05). In conclusion, both glucomannan-diets were able to reduce hyperglycemia and increase adipose tissue adiponectin levels in fa/fa rats, suggesting an anti-hypertrophic and insulin-sensitizing adipokine effect in this tissue. Spirulina inclusion increased insulin availability. Although results are promising, the utility of consuming glucomannan surimis as part of usual diets demands future studies.

Blunting of insulin inhibition of proteolysis in legs of older subjects may contribute to age-related sarcopenia

BackgroundReduced postprandial muscle proteolysis is mainly due to increased insulin availability. Whether rates of proteolysis in response to low physiologic doses of insulin are affected by aging is unknown. ObjectivesWe tested the hypothesis that suppression of leg protein breakdown (LPB) by insulin is blunted in older subjects, together with blunted activation of Akt–protein kinase B (PKB). DesignGroups of 8 young [mean (±SD) age: 24.5 ± 1.8 y] and older (65.0 ± 1.3 y) participants were studied during euglycemic (5 mmol/L), isoaminoacidemic (blood leucine ≈ 120 ¼mol/L) clamp procedures at plasma insulin concentrations of ≈5 and ≈15 ¼IU/mL for 1.5 h. Leg amino acid balance, whole-leg protein turnover (as dilution of amino acid tracers), and muscle protein synthesis were measured with d5-phenylalanine and [1,2-13C2]leucine. The kinase activity of muscle Akt-PKB and the extent of phosphorylation of signaling proteins associated with the mTOR (mammalian target of rapamycin) pathway were measured before and after the clamp procedures. ResultsBasal LPB rates were not different between groups (66 ± 11 compared with 51 ± 10 nmol leucine · 100 mL leg−1 · min−1 and 30 ± 5 compared with 24 ± 4 nmol phenylalanine · 100 mL leg−1 · min−1 in young and older groups, respectively). However, although insulin at ≈15 ¼IU/mL lowered LPB by 47% in the young subjects (P < 0.05) and abolished the negative leg amino acid balance, this caused only a 12% fall (P > 0.05) in the older group. Akt-PKB activity mirrored decreases in LPB. No differences were seen in muscle protein synthesis or associated anabolic signaling phosphoproteins. ConclusionsAt moderate availability, the effect of insulin on LPB is diminished in older human beings, and this effect may be mediated through blunted Akt-PKB activation.

Anabolic signaling deficits underlie amino acid resistance of wasting, aging muscle

The nature of the deficit underlying age-related muscle wasting remains controversial. To test whether it could be due to a poor anabolic response to dietary amino acids, we measured the rates of myofibrillar and sarcoplasmic muscle protein synthesis (MPS) in 44 healthy young and old men, of similar body build, after ingesting different amounts of essential amino acids (EAA). Basal rates of MPS were indistinguishable, but the elderly showed less anabolic sensitivity and responsiveness of MPS to EAA, possibly due to decreased intramuscular expression, and activation (phosphorylation) after EAA, of amino acid sensing/signaling proteins (mammalian target of rapamycin, mTOR; p70 S6 kinase, or p70(S6k); eukaryotic initiation factor [eIF]4BP-1; and eIF2B). The effects were independent of insulin signaling since plasma insulin was clamped at basal values. Associated with the anabolic deficits were marked increases in NFkappaB, the inflammation-associated transcription factor. These results demonstrate first, EAA stimulate MPS independently of increased insulin availability; second, in the elderly, a deficit in MPS in the basal state is unlikely; and third, the decreased sensitivity and responsiveness of MPS to EAA, associated with decrements in the expression and activation of components of anabolic signaling pathways, are probably major contributors to the failure of muscle maintenance in the elderly. Countermeasures to maximize muscle maintenance should target these deficits.

Obesity and the polycystic ovary syndrome.

The polycystic ovary syndrome (PCOS) is a condition characterized by hyperandrogenism and chronic oligo-anovulation. However, many features of the metabolic syndrome are inconsistently present in the majority of women with PCOS. Approximately 50% of PCOS women are overweight or obese and most of them have the abdominal phenotype. Obesity may play a pathogenetic role in the development of the syndrome in susceptible individuals. In fact, insulin possesses true gonadotrophic function and an increased insulin availability at the level of ovarian tissue may favour excess androgen synthesis. Obesity, particularly the abdominal phenotype, may be partly responsible for insulin resistance and associated hyperinsulinemia in women with PCOS. Therefore, obesity-related hyperinsulinemia may play a key role in favouring hyperandrogenism in these women. Other factors such as increased estrogen production rate, increased activity of the opioid system and of the hypothalamic-pituitary-adrenal axis, decreased sex hormone binding globulin synthesis and, possibly, high dietary lipid intake, may be additional mechanisms by which obesity favours the development of hyperandrogenism in PCOS. Irrespective of the pathogenetic mechanism involved, obese PCOS women have more severe hyperandrogenism and related clinical features (such as hirsutism, menstrual abnormalities and anovulation) than normal-weight PCOS women. This picture tends to be more pronounced in obese PCOS women with the abdominal phenotype. Body weight loss is associated with beneficial effects on hormones, metabolism and clinical features. A further clinical and endocrinological improvement can also be achieved by adding insulin-sensitizing agents and/or antiandrogens to weight reduction programmes. These obviously emphasize the role of obesity in the pathophysiology of PCOS.

Glucose-dependent insulinotropic hormone potentiates the hypoglycemic effect of glibenclamide in healthy volunteers: evidence for an effect on insulin extraction.

Glucose-dependent insulinotropic hormone (GIP) is an intestinal hormone considered to be an important mediator of the incretin effect, i.e. the augmented insulin release observed in response to orally, compared with iv, administered glucose, despite isoglycemic glucose profiles. Stimulation of beta-cell secretion of insulin by GIP is seen both in vitro and in vivo at permissive extracellular glucose concentrations (> 6 mmol/L). It has also been claimed that part of the incretin effect is due to decreased insulin extraction. We now show that an infusion of GIP in healthy volunteers in whom blood glucose levels were maintained at 5 mmol/L, increased glibenclamide-stimulated levels of plasma insulin without significantly changing the C peptide profile. The increased plasma insulin levels necessitated extra glucose infusion to maintain euglycemia, demonstrating the biological significance of the elevated insulin levels. Infusion of GIP alone caused neither glucose changes nor elevation of C peptide or insulin levels. Hence, our results show that at a blood glucose concentration of 5 mmol/L, GIP augments the increase in plasma insulin levels stimulated by glibenclamide, possibly acting through a mechanism involving decreased insulin extraction in the liver or peripheral tissues, thus increasing insulin availability.

A rational approach to drug therapy of type 2 diabetes mellitus.

Several new pharmacological agents have recently been developed to optimise the management of type 2 (non-insulin-dependent) diabetes mellitus. The aim of this article is to briefly review the various therapeutic agents available for management of patients with type 2 diabetes mellitus and to suggest a potential approach to drug selection. There are three general therapeutic modalities relevant to diabetes care. The first modality is lifestyle adjustments aimed at improving endogenous insulin sensitivity or insulin effect. This can be achieved by increased physical activity and bodyweight reduction with diet and behavioural modification, and the use of pharmacological agents or surgery. This first modality is not discussed in depth in this article. The second modality involves increasing insulin availability by the administration of exogenous insulin, insulin analogues, sulphonylureas and the new insulin secretagogue, repaglinide. The most frequently encountered adverse effect of these agents is hypoglycaemia. Bodyweight gain can also be a concern, especially in patients who are obese. The association between hyperinsulinaemia and premature atherosclerosis is still a debatable question. The third modality consists of agents such as biguanides and thiazolidinediones which enhance insulin sensitivity, or agents that decrease insulin requirements like the alpha-glucosidase inhibitors. Type 2 diabetes mellitus is a heterogeneous disease with multiple underlying pathophysiological processes. Therapy should be individualised based on the degree of hyperglycaemia, hyperinsulinaemia or insulin deficiency. In addition, several factors have to be considered when prescribing a specific therapeutic agent. These factors include efficacy, safety, affordability and ease of administration.

REDUCING LITTER SIZE BY ABLATION ENHANCES GROWTH AND INSULIN SECRETION IN THE FETAL RAT

Fetal growth is inversely related to litter size. Little is known about the mechanisms responsible for this or its potential consequences in the newborn. To address this, we developed a fetal ablation model in the rat. After anesthetizing the mother on day 15 (term 21.5 days), we ligated selected arteries in the secondary cascade of uterine vessels. This ablates individual fetuses, Ablation (A) reduced fetal number compared to controls (C) (5±2 v 8±3) and accelerated fetal growth (Birthweight 5.34±.05 v 5.01±.09 g, p<.01). A pups had increased liver mass .289±.005 v .254±.005 g, p<.001) but similar liver/body ratios compared to C suggesting symmetrical growth enhancement. To some extent accelerated growth was mediated by insulin, a critical growth stimulating hormone, since plasma insulin conc were significantly elevated in A v C newborns (112.2± 14.2 v 67.0±10.1 uU/ml, p<.001). A pups developed hypoglycemia at 0 and 20 minutes of life (20 min 78.2±2.6 v 91.0±4.8 mg/dl, p<.01). This resulted from a carryover of fetal hyperinsulinism (20 min 211.2±16.0 v 52.5±19.0 uU/ml, p<.01) since plasma glucagon conc did not differ (20 min 736.7±80.0 v 655.0±99.0 pg/ml) and hepatic glycogen cone remained elevated in A pups (20 min 71.4±3.2 v 52.08±6.4 mg/g liver, p<.01). Restricting litter size may enhance blood flow to the remaining fetuses thereby enhancing metabolic fuel supply, fetal growth, and hepatic glycogen deposition. Increased insulin availability may mediate these changes and also cause neonatal hypoglycemia.

CCK, endogenous insulin condition and satiety in free-fed rats

Cholecystokinin (CCK) has been shown to elicit insulin secretion and increased insulin availability has been shown to correlate with increased satiety attributed to reduced size of spontaneously occurring meals. The present experiment, however, clearly showed that CCK was effective in suppressing food ingestion in free-fed rats independent of the animal's level of insulin. Rats were tested with 1, 2 and 4 μg/kg of CCK-octapeptide (Sincalide, Squibb) during a baseline (pancreatic-normal) period, an insulin-poor state (streptozotocin diabetic) and an insulin clamped condition (diabetic treated by a minipump). CCK produced a highly significant ( p<0.01) reduction of food intake compared to saline, control injections regardless of the insulin conditions of the animals. Higher doses of CCK were more effective than lower doses during all three periods of study. CCK and hyperinsulinemia function independently if they produce satiety or reductions in food intake.