Probing Receptor Specificity by Sampling the Conformational Space of the Insulin-like Growth Factor II C-domain

Insulin and insulin-like growth factors I and II are closely related protein hormones. Their distinct evolution has resulted in different yet overlapping biological functions with insulin becoming a key regulator of metabolism, whereas insulin-like growth factors (IGF)-I/II are major growth factors. Insulin and IGFs cross-bind with different affinities to closely related insulin receptor isoforms A and B (IR-A and IR-B) and insulin-like growth factor type I receptor (IGF-1R). Identification of structural determinants in IGFs and insulin that trigger their specific signaling pathways is of increasing importance in designing receptor-specific analogs with potential therapeutic applications. Here, we developed a straightforward protocol for production of recombinant IGF-II and prepared six IGF-II analogs with IGF-I-like mutations. All modified molecules exhibit significantly reduced affinity toward IR-A, particularly the analogs with a Pro-Gln insertion in the C-domain. Moreover, one of the analogs has enhanced binding affinity for IGF-1R due to a synergistic effect of the Pro-Gln insertion and S29N point mutation. Consequently, this analog has almost a 10-fold higher IGF-1R/IR-A binding specificity in comparison with native IGF-II. The established IGF-II purification protocol allowed for cost-effective isotope labeling required for a detailed NMR structural characterization of IGF-II analogs that revealed a link between the altered binding behavior of selected analogs and conformational rearrangement of their C-domains

Pharmacokinetics and pharmacodynamics of insulin analogs in special populations with type 2 diabetes mellitus

Candis M Morello1,21Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California San Diego, 2School of Pharmacy, University of California San Francisco, Veterans Affairs San Diego Healthcare System, San Diego, CA, USAIntroduction: The goal of insulin therapy in patients with either type 1 diabetes mellitus (T1DM) or type 2 diabetes mellitus (T2DM) is to match as closely as possible normal physiologic insulin secretion to control fasting and postprandial plasma glucose. Modifications of the insulin molecule have resulted in two long-acting insulin analogs (glargine and detemir) and three rapid-acting insulins (aspart, lispro, and glulisine) with improved pharmacokinetic/pharmacodynamic (PK/PD) profiles. These agents can be used together in basal-bolus therapy to more closely mimic physiologic insulin secretion patterns.Methods: This study reviews effects of the multiple demographic and clinical parameters in the insulin analogs glargine, detemir, lispro, aspart, and glulisine in patients with T2DM. A search was conducted on PubMed for each major topic considered (effects of injection site, age, race/ethnicity, obesity, renal or hepatic dysfunction, pregnancy, exercise, drug interactions) using the topic words and name of each type of insulin analog. Information was also obtained from the prescribing information for each insulin analog.Results: The PK/PD profiles for insulin analogs may be influenced by many variables including age, weight, and hepatic and renal function. However, these variables do not have equivalent effects on all long-acting or rapid-acting insulin analogs.Conclusion: Rapid-acting and long-acting insulin analogs represent major advances in treatment for patients with T2DM who require insulin therapy. However, there are potentially important PK and PD differences between the two long-acting agents and among the three rapid-acting insulin analogs, which should be considered when designing treatment regimens for special patient groups.Keywords: insulin analogs, type 2 diabetes mellitus, pharmacodynamics, pharmacokinetic

Insulin glulisine in the management of diabetes

Insulin glulisine is appealing in principle, but the advantages of this drug over the other rapid-acting insulin analogs are still relatively unknown. The frequency of hypoglycemia, convenience in the timing of administration, and improvements in terms of HbA1c seem similar among the rapid-acting insulin analogs, including insulin glulisine. Only properly randomized long-term clinical studies with insulin glulisine will reveal the true value of this novel insulin analog

Synthesis and Characterization of Insulin Receptor Partial Agonists as a Route to Improved Diabetes Therapy

Thesis (Ph.D.) - Indiana University, Biochemistry, 2015Insulin-dependent diabetes requires the daily administration of insulin to regulate blood glucose. Unfortunately, insulin possesses a narrow therapeutic index which represents a risk for overdose and life-threatening hypoglycemia. This research investigates the synthesis and biological characterization of insulin-based analogs that activate the insulin receptor with high potency, but varying degrees of maximal activity. These analogs are dimeric peptides that consist of native insulin and a covalently bound insulin receptor antagonist. Structure-activity analysis revealed a key amino acid within the antagonist, and mutations at this single position control the maximal activity of the heterodimer. These analogs may represent a route to a safer insulin therapy, through selection of an optimized analog that has diminished activity relative to the native hormone

Discriminative Insulin Antagonism of Stimulatory Effects of Various cAMP Analogs on Adipocyte Lipolysis and Hepatocyte Glycogenolysis

Although insulin effectively blocked hormone-stimulated glycerol output in adipocytes or phosphorylase activation in hepatocytes, the inhibitory effect of insulin on cAMP analog-stimulated cells depended on the cAMP analog used. Of the 20 analogs tested in adipocytes and 13 tested in hepatocytes, the effects of about half of them were effectively blocked by insulin, whereas the effects of many of them were not inhibited at all. In order to approach the explanation for this discriminative insulin action, the inhibitory effects of insulin on the responses to the analogs in the intact cells were correlated with the in vitro cAMP analog specificity for the hepatocyte cAMP-dependent protein kinase isozymes and the low K(m), hormone-sensitive phosphodiesterases from both cell types. No correlation was found between insulin resistance of analog-stimulated hepatocyte phosphorylase and the concentration of analog required in vitro for half-maximal activation of either type I or type II cAMP-dependent protein kinase from hepatocytes. However, a good correlation was found between insulin resistance of cAMP analog-stimulated responses and the analog I50 values for the phosphodiesterase from both cell types. Using a new method capable of measuring hydrolysis at low analog concentrations, several of those analogs which had relatively low, but not high, phosphodiesterase I50 values were shown to be directly hydrolyzed by the low K(m) adipocyte phosphodiesterase. The insulin inhibition of cell responses when stimulated by hydrolyzable analogs, but not by poorly hydrolyzable analogs, is best explained by insulin stimulation of the low K(m) phosphodiesterases from both cell types

Structure-based stabilization of insulin as a therapeutic protein assembly via enhanced aromatic-aromatic interactions

Key contributions to protein structure and stability are provided by weakly polar interactions, which arise from asymmetric electronic distributions within amino acids and peptide bonds. Of particular interest are aromatic side chains whose directional π-systems commonly stabilize protein interiors and interfaces. Here, we consider aromatic-aromatic interactions within a model protein assembly: the dimer interface of insulin. Semi-classical simulations of aromatic-aromatic interactions at this interface suggested that substitution of residue TyrB26 by Trp would preserve native structure while enhancing dimerization (and hence hexamer stability). The crystal structure of a [TrpB26]insulin analog (determined as a T3Rf3 zinc hexamer at a resolution of 2.25 Å) was observed to be essentially identical to that of WT insulin. Remarkably and yet in general accordance with theoretical expectations, spectroscopic studies demonstrated a 150-fold increase in the in vitro lifetime of the variant hexamer, a critical pharmacokinetic parameter influencing design of long-acting formulations. Functional studies in diabetic rats indeed revealed prolonged action following subcutaneous injection. The potency of the TrpB26-modified analog was equal to or greater than an unmodified control. Thus, exploiting a general quantum-chemical feature of protein structure and stability, our results exemplify a mechanism-based approach to the optimization of a therapeutic protein assembly

Insulin based analogs HLVEALYLV and LVEALYLV to inhibit the formation of amyloid fibrils in beta cells

Human islet amyloid polypetide (hIAPP) is a 37 amino acid peptide, co-secreted along with insulin in the islets of Langerhans of pancreatic beta cells. Aggregation of hIAPP fibrils is believed to be toxic to beta cells and responsible for beta cell dysfunction and death associated with type 2 diabetes. Insulin has been found to act against the actions of hIAPP. The internal sequence of insulin, HLVEALYLV, recognizes and binds the 10-19 region of hIAPP. Since insulin reportedly blocks the formation of amyloid fibers, insulin analogs may protect cell membranes from damage. In an effort to study this effect, truncated analogs of insulin, namely HLVEALYLV and LVEALYLV, were synthesized and tested in the presence of hIAPP. Carboxyfluorescein-encapsulating vesicles that mimic the $-cell were created using a 7:3 ratio of the lipids 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and 1,2-dioleoyl-sn-glycero-3- (phospho-L-serine) (DOPS), respectively, and the percent leakage of fluorescent dye from the vesicles in the presence of the peptides was calculated as compared to a 100% Triton-X detergent-treated control. The activity of the truncated analogs was compared to that of insulin under the same conditions. Whereas insulin was somewhat protective of the effects of hIAPP, the shorter analogs were found to increase the damage caused by hIAPP rather than reducing it, possibly by co-aggregating with the hIAPP

An analog of glibenclamide selectively enhances autophagic degradation of misfolded α1-antitrypsin Z

The classical form of α1-antitrypsin deficiency (ATD) is characterized by intracellular accumulation of the misfolded variant α1-antitrypsin Z (ATZ) and severe liver disease in some of the affected individuals. In this study, we investigated the possibility of discovering novel therapeutic agents that would reduce ATZ accumulation by interrogating a C. elegans model of ATD with high-content genome-wide RNAi screening and computational systems pharmacology strategies. The RNAi screening was utilized to identify genes that modify the intracellular accumulation of ATZ and a novel computational pipeline was developed to make high confidence predictions on repurposable drugs. This approach identified glibenclamide (GLB), a sulfonylurea drug that has been used broadly in clinical medicine as an oral hypoglycemic agent. Here we show that GLB promotes autophagic degradation of misfolded ATZ in mammalian cell line models of ATD. Furthermore, an analog of GLB reduces hepatic ATZ accumulation and hepatic fibrosis in a mouse model in vivo without affecting blood glucose or insulin levels. These results provide support for a drug discovery strategy using simple organisms as human disease models combined with genetic and computational screening methods. They also show that GLB and/or at least one of its analogs can be immediately tested to arrest the progression of human ATD liver disease.</div

Vascular effects of rapid-acting insulin analogs in the diabetic patient: a review

The insulin analogs lispro, aspart, and glulisine are the only commercially available rapid-acting insulins to treat diabetes. We review the evidence for treating hyperglycemia, using insulin, and specifically using rapid-acting analogs in diabetic individuals, on the prevention of vascular events. We review the beneficial effects of insulin on the vascular system, which include vasodilation and anti-inflammatory actions. The effects of treating hyperglycemia and intensive blood glucose control on vascular outcomes are reviewed

Minimizing hypoglycemia while maintaining glycemic control in diabetes

In the accompanying Perspective, Cryer identifies a number of different areas where therapeutic interventions have the potential to reduce hypoglycemia without compromising glycemic control. Some approaches provide well defined clinical benefits, a few offer dramatic reductions in hypoglycemia but remain out of reach for most people while others, although promising have yet to be properly evaluated. (Table 1) In this Perspective, I examine the evidence which underpins these interventions. It is beyond the scope of this article to review the data for each potential intervention in detail but the reader is directed to the appropriate source where appropriate. The Perspective focuses on treatment of Type 1 diabetes as most of the potential specific therapies have been evaluated in this group although I have commented in relation to recent trials of intensive therapy in Type 2 diabetes