Mechanistic understanding of insulin receptor modulation: Implications for the development of anti-diabetic drugs

Insulin-mimetic peptides in sports drug testing

Because of its influence on carbohydrate metabolism and, at the same time, anti-catabolic effects, the misuse of the peptide hormone insulin and its synthetic analogs is prohibited in sports at all times according to the regulations of the World Anti-Doping Agency (WADA). The biological effects of insulin and its analogs are mediated through binding to the insulin receptor, which was also found to be activated by different peptides structurally largely unrelated to insulin. Such insulin-mimetic peptides or selective-insulin receptor modulators (SIRMs) represent a novel class of potential performance-enhancing agents, which is currently not explicitly mentioned on the WADA Prohibited List. Within this research project, advanced solid-phase extraction (SPE) and liquid chromatography coupled to high-resolution tandem mass spectrometry (LC-HRMS/MS) were employed to develop a fast, reliable, and specific assay for the detection of the insulin-mimetic peptides S597 and S519 from plasma. Method validation demonstrated a detection limit of 0.5 ng/mL and successfully illustrated the applicability of the approach to routine sports drug testing programs. Moreover, sophisticated and comprehensive in vitro metabolism experiments were conducted, and several metabolic degradation products were identified, which will enhance the information generated from future analyses of doping control samples.

Association of glucocorticoid receptor expression with key members of the insulin signaling pathway and heat shock proteins in the bovine ovary

Glucocorticoids (GCs) act through their receptor (GR) as regulators in different biological processes such as reproduction. In the absence of GCs, the GR remains inactive in the cytoplasm by associating with heat shock proteins (HSPs), which act as molecular chaperones, among which the most relevant are HSP90 and HSP70. Cytoplasmic GC-activated GR mediates non-genomic effects, interacting with members of signaling pathways such as PI3K/Akt, which participates in several metabolic processes, including the insulin signaling pathway. The aim of the present study was to evaluate possible associations between the cytoplasmic GR and the main intermediates of the insulin signaling pathway and HSP90 and HSP70 in ovaries of dairy cows. To this end, the protein expression of cytoplasmic GR, key members of the insulin signaling pathway, and HSPs was evaluated in ovarian preovulatory follicles of non-lactating Holstein cows in proestrus. Positive associations were observed between protein expression of GR and HSP90, IRS1, pIRS1, PI3K and pAkt (p < 0.05; β > 0) in granulosa cells of dominant follicles of dairy cows. Instead, in theca cells, no associations were observed between protein expression of GR and members of the insulin signaling pathway or HSPs. These data provide evidence of the possible association between the non-genomic mechanisms of action of the GR and the insulin signaling pathway in the bovine ovary.

A stepwise activation model for the insulin receptor

The binding of insulin to the insulin receptor (IR) triggers a cascade of receptor conformational changes and autophosphorylation, leading to the activation of metabolic and mitogenic pathways. Recent advances in the structural and functional analyses of IR have revealed the conformations of the extracellular domains of the IR in inactive and fully activated states. However, the early activation mechanisms of this receptor remain poorly understood. The structures of partially activated IR in complex with aptamers provide clues for understanding the initial activation mechanism. In this review, we discuss the structural and functional features of IR complexed with various ligands and propose a model to explain the sequential activation mechanism. Moreover, we discuss the structures of IR complexed with biased agonists that selectively activate metabolic pathways and provide insights into the design of selective agonists and their clinical implications.

The Insulin Receptor: An Important Target for the Development of Novel Medicines and Pesticides

The insulin receptor (IR) is a transmembrane protein that is activated by ligands in insulin signaling pathways. The IR has been considered as a novel therapeutic target for clinical intervention, considering the overexpression of its protein and A-isoform in multiple cancers, Alzheimer's disease, and Type 2 diabetes mellitus in humans. Meanwhile, it may also serve as a potential target in pest management due to its multiple physiological influences in insects. In this review, we provide an overview of the structural and molecular biology of the IR, functions of IRs in humans and insects, physiological and nonpeptide small molecule modulators of the IR, and the regulating mechanisms of the IR. Xenobiotic compounds and the corresponding insecticidal chemicals functioning on the IR are also discussed. This review is expected to provide useful information for a better understanding of human IR-related diseases, as well as to facilitate the development of novel small-molecule activators and inhibitors of the IR for use as medicines or pesticides.

Enhancement of bioavailability and bioactivity of diet-derived flavonoids by application of nanotechnology: a review

Flavonoids, which are a class of polyphenols widely existing in food and medicine, have enormous pharmacological effects. The functional properties of flavonoids are mainly distributed to their anti-oxidative, anticancer, and anti-inflammatoryeffects, etc. However, flavonoids' low bioavailability limits their clinical application, which is closely related to their intestinal absorption and metabolism. In addition, because of the short residence time of oral bioactive molecules in the stomach, low permeability and low solubility in the gastrointestinal tract, flavonoids are easy to be decomposed by the external environment and gastrointestinal tract after digestion. To tackle these obstacles, technological approaches like microencapsulation have been developed and applied for the formulation of flavonoid-enriched food products. In the light of these scientific advances, the objective of this review is to establish the structural requirements of flavonoids for appreciable anticancer, anti-inflammatory, and antioxidant effects, and elucidate a comprehensive mechanism that can explain their activity. Furthermore, the novelty in application of nanotechnology for the safe delivery of flavonoids in food matrices is discussed. After a literature on the flavonoids and their health attributes, the encapsulation methods and the coating materials are presented.

Anti-Insulin Receptor Antibodies in the Pathology and Therapy of Diabetes Mellitus

Diabetes mellitus (DM) is recognized as the most common and the world's fastest-growing chronic disease with severe complications leading to increased mortality. Many strategies exist for the management of DM and its control, including treatment with insulin and insulin analogs, oral hypoglycemic therapy such as insulin secretion stimulators and insulin sensitizers, and diet and physical training. Over the years, many types of drugs and molecules with an interesting pharmacological diversity have been developed and proposed for their anti-diabetic potential. Such molecules target diverse key receptors, enzymes, and regulatory/signaling proteins known to be directly or indirectly involved in the pathophysiology of DM. Among them, insulin receptor (IR) is undoubtedly the target of choice for its central role in insulin-mediated glucose homeostasis and its utilization by the major insulin-sensitive tissues such as skeletal muscles, adipose tissue, and the liver. In this review, we focus on the implication of antibodies targeting IR in the pathology of DM as well as the recent advances in the development of IR antibodies as promising anti-diabetic drugs. The challenge still entails development of more powerful, highly selective, and safer anti-diabetic drugs.