Insulin Resistance/Sensitivity Measures as Screening Indicators of Metabolic-Associated Fatty Liver Disease and Liver Fibrosis.

BACKGROUND: Measures of insulin resistance (IR)/sensitivity (IS) are emerging tools to identify metabolic-associated fatty liver disease (MAFLD). However, the comprehensive assessment of the performance of various indicators is limited. Moreover, the utility of measures of IR/IS in detecting liver fibrosis remains unclear. AIMS: To evaluate the predictive ability of seventeen IR/IS and two beta cell function indices to identify MAFLD and liver fibrosis. METHODS: A cross-sectional study was conducted on individuals aged 25-75 years. Transient elastography was used to estimate liver stiffness and controlled attenuation parameter. The following measures were computed: homeostatic model assessment (HOMA/HOMA2) for IR, IS, and beta cell function; QUICKI; Bennett index; glucose/insulin; FIRI; McAuley index; Reynaud index; SPISE index; TyG; TyG-BMI; TyG-WC; TyG-WHtR; TG/HDL; and METS-IR. Subgroup analyses were performed according to age, gender, diabetes status, and body weight. RESULTS: A total of 644 individuals were included in our analysis. MAFLD and significant liver fibrosis were detected in 320 (49.7%) and 80 (12.4%) of the participants, respectively. All measures of IR/IS identified MAFLD and liver fibrosis. However, TyG-WC, TyG-BMI, and TyG-WHtR were the top three indicators that identified MAFLD. Measures that include insulin level in their mathematical calculation, namely, Raynaud index, HOMA-IR, HOMA 2-IR, FIRI, and QUICKI had the best performance in identifying liver fibrosis in the entire population, as well as among the study subgroups. CONCLUSIONS: TyG-WC, TyG-BMI, and TyG-WHtR were the best predictors of MAFLD. Insulin-based measures had better performances in the detection of advanced fibrosis. This was independent of age, gender, obesity, or diabetes status.

Effect of Empagliflozin and Pioglitazone on left ventricular function in patients with type two diabetes and nonalcoholic fatty liver disease without established cardiovascular disease: a randomized single-blind clinical trial.

BACKGROUND: Nonalcoholic fatty liver disease (NAFLD) is a complex metabolic disorder that increases the risk for cardiovascular disease in patients with type 2 diabetes mellitus (T2DM). Global longitudinal strain (GLS) is an indicator of left ventricular (LV) mechanics and can detect subclinical myocardial dysfunction. We compared the effects of pioglitazone and empagliflozin on GLS in patients with T2DM and NAFLD without established atherosclerotic cardiovascular disease. METHODS: This study was a 24-week randomized, single-blind, and parallel-group (1: 1 ratio) clinical trial. Seventy-three participants with T2DM (being treated with metformin) and NAFLD but without established atherosclerotic cardiovascular disease (ASCVD) were randomized to empagliflozin or pioglitazone. Liver steatosis and fibrosis were measured using transient elastography, and GLS was measured by echocardiography. The primary endpoint was the change in GLS from baseline to week 24. Secondary end points include changes in controlled attenuation parameter (CAP) and Liver stiffness measure (LSM). RESULTS: In this study, GLS improved by 1.56 ± 2.34% (P < 0.01) in the pioglitazone group and 1.06 ± 1.83% (P < 0.01) in the empagliflozin group without a significant difference between the two groups (P = 0.31). At baseline, GLS was inversely associated with the severity of liver fibrosis: r = - 0.311, P = 0.007. LSM in the pioglitazone and empagliflozin group [(-0.73 ± 1.59) and (-1.11 ± 1.33)] kpa (P < 0.01) decreased significantly. It was without substantial difference between the two groups (P = 0.26). Empagliflozin and pioglitazone both improved controlled attenuation parameter. The improvement was more critical in the empagliflozin group: -48.22 + 35.02 dB/m vs. -25.67 + 41.50 dB/m, P = 0.01. CONCLUSION: Subclinical cardiac dysfunction is highly important in patients with T2DM and with NAFLD. Empagliflozin and Pioglitazone improve LV mechanics and fibrosis in patients without established ASCVD. This has a prognostic importance on cardiovascular outcomes in high-risk patients with T2DM. Moreover, empagliflozin ameliorates liver steatosis more effectively them pioglitazone. This study can serve as a start point hypothesis for the future. Further studies are needed to explore the concept in larger populations. TRIAL REGISTRATION: This trial was registered in the Iranian Registry of Clinical Trials (IRCT): "A Comparison between the Effect of Empagliflozin and Pioglitazone on Echocardiographic Indices in Patients with Type 2 Diabetes Mellitus and Nonalcoholic Fatty Liver Disease" IRCT20190122042450N5, 29 November 2020. https://www.irct.ir/search/result?query=IRCT20190122042450N5 .

The effect of sodium-glucose co-transporter-2 (SGLT2) inhibitors on blood interleukin-6 concentration: a systematic review and meta-analysis of randomized controlled trials.

BACKGROUND: The low-grade chronic inflammation in diabetes plays an important role in development of cardiovascular and renal complications. Sodium-glucose co-transporter-2 (SGLT2) inhibitors are recognized as protective agents for cardio-renal complications. Interleukin-6 (IL-6) is positively associated with the pathophysiology of metabolic-related pathologies. The aim of this meta-analysis is to investigate the effect of SGLT2 inhibitors on blood IL-6 concentration in randomized controlled trials (RCTs). METHODS: Embase, PubMed, and Scopus were systematically searched up to 1st of November 2023. The eligible studies were RCTs with adult population that had provided blood IL-6 for both control and intervention groups. Cochrane risk-of-bias tool were for study quality assessment. Data were analyzed using random effect model via Stata statistical software. RESULTS: Eighteen studies with a total of 5311 patients were included. Of which 3222 and 2052 patients were in intervention and control arm, respectively. Of the total population, 49.7% were men. The study durations ranged from 8 to 52 weeks. The pooled analysis showed a significant association between the use of SGLT2 inhibitors and lower IL-6 levels (standardized mean difference (SMD) = -1.04, Confidence Interval (CI): -1.48; -0.60, I2 = 96.93%). Dapagliflozin was observed to have a higher IL-6-lowering effect (SMD = -1.30, CI: -1.89; -0.71, I2 = 92.52) than empagliflozin or canagliflozin. Sub-group analysis of control groups (SMD = -0.58 (-1.01, -0.15) and -1.35 (-2.00, -0.70 for the placebo and active control sub-groups, respectively) and duration of interventions (SMD = -0.78 (-1.28, -0.28) and -1.20 (-1.86, -0.55) for study duration of ≤ 12 and > 12 weeks, respectively) did not change the results. Meta-regression analysis showed a significant correlation between the level of HbA1c and IL-6-lowering efficacy of SGLT2 inhibitors. CONCLUSION: IL-6 levels are significantly reduced with the use of SGLT2 inhibitors with HbA1c as the only marker influencing such reductions, and dapagliflozin had the highest potency. The anti-inflammatory effect of SGLT2 inhibitors supports their broader use to address diabetic complications related to inflammatory responses.

Evolution of insulin at the edge of foldability and its medical implications.

Proteins have evolved to be foldable, and yet determinants of foldability may be inapparent once the native state is reached. Insight has emerged from studies of diseases of protein misfolding, exemplified by monogenic diabetes mellitus due to mutations in proinsulin leading to endoplasmic reticulum stress and ß-cell death. Cellular foldability of human proinsulin requires an invariant Phe within a conserved crevice at the receptor-binding surface (position B24). Any substitution, even related aromatic residue TyrB24, impairs insulin biosynthesis and secretion. As a seeming paradox, a monomeric TyrB24 insulin analog exhibits a native-like structure in solution with only a modest decrement in stability. Packing of TyrB24 is similar to that of PheB24, adjoining core cystine B19-A20 to seal the core; the analog also exhibits native self-assembly. Although affinity for the insulin receptor is decreased ∼20-fold, biological activities in cells and rats were within the range of natural variation. Together, our findings suggest that the invariance of PheB24 among vertebrate insulins and insulin-like growth factors reflects an essential role in enabling efficient protein folding, trafficking, and secretion, a function that is inapparent in native structures. In particular, we envision that the para-hydroxyl group of TyrB24 hinders pairing of cystine B19-A20 in an obligatory on-pathway folding intermediate. The absence of genetic variation at B24 and other conserved sites near this disulfide bridge-excluded due to ß-cell dysfunction-suggests that insulin has evolved to the edge of foldability. Nonrobustness of a protein's fitness landscape underlies both a rare monogenic syndrome and "diabesity" as a pandemic disease of civilization.

"Register-shift" insulin analogs uncover constraints of proteotoxicity in protein evolution.

Globular protein sequences encode not only functional structures (the native state) but also protein foldability, i.e. a conformational search that is both efficient and robustly minimizes misfolding. Studies of mutations associated with toxic misfolding have yielded insights into molecular determinants of protein foldability. Of particular interest are residues that are conserved yet dispensable in the native state. Here, we exploited the mutant proinsulin syndrome (a major cause of permanent neonatal-onset diabetes mellitus) to investigate whether toxic misfolding poses an evolutionary constraint. Our experiments focused on an invariant aromatic motif (PheB24-PheB25-TyrB26) with complementary roles in native self-assembly and receptor binding. A novel class of mutations provided evidence that insulin can bind to the insulin receptor (IR) in two different modes, distinguished by a "register shift" in this motif, as visualized by molecular dynamics (MD) simulations. Register-shift variants are active but defective in cellular foldability and exquisitely susceptible to fibrillation in vitro Indeed, expression of the corresponding proinsulin variant induced endoplasmic reticulum stress, a general feature of the mutant proinsulin syndrome. Although not present among vertebrate insulin and insulin-like sequences, a prototypical variant ([GlyB24]insulin) was as potent as WT insulin in a rat model of diabetes. Although in MD simulations the shifted register of receptor engagement is compatible with the structure and allosteric reorganization of the IR-signaling complex, our results suggest that this binding mode is associated with toxic misfolding and so is disallowed in evolution. The implicit threat of proteotoxicity limits sequence variation among vertebrate insulins and insulin-like growth factors.

Study rationale and design of a study of EMPAgliflozin's effects in patients with type 2 diabetes mellitus and Coronary ARtery disease: the EMPA-CARD randomized controlled trial.

BACKGROUND: Recent trials have revealed that sodium-glucose co-transporter 2 inhibitors (SGLT2-i) are effective against hyperglycemia and also reduce micro- and macro-vascular complications in patients with type 2 diabetes mellitus (T2DM). Most of the beneficial cardiovascular effects have been investigated in patients with heart failure and coronary artery disease (CAD). Yet, few human studies have been conducted to investigate the molecular mechanisms underlying these clinically beneficial effects in patients with CAD. Accordingly, the EMPA-CARD trial was designed to focus on the molecular effects of empagliflozin in patients with T2DM and CAD. METHODS: In this multicenter, triple-blind randomized controlled trial, patients with documented known T2DM and CAD will be recruited. They will be randomized on a 1:1 ratio and assigned into two groups of empagliflozin 10 mg/daily and placebo. The primary endpoint is the effect of empagliflozin on changes of plasma interleukin 6 (IL-6) after 26 weeks of treatment. The secondary endpoints will consist of changes in other inflammatory biomarkers (Interleukin 1-beta and high-sensitive C-reactive protein), markers of oxidative stress, platelet function, and glycemic status. DISCUSSION: The EMPA-CARD trial mainly tests the hypothesis that SGLT2 inhibition by empagliflozin may improve inflammatory status measured as reduction in inflammatory biomarkers in patients with T2DM and CAD. The results will provide information about the underlying mechanisms of SGLT2 inhibition that mediate the beneficial effects of this medication on clinical outcomes. TRIAL REGISTRATION: Iranian Registry of Clinical Trials. www.IRCT.ir , Identifier: IRCT20190412043247N2. Registration Date: 6/13/2020. Registration timing: prospective.

Reassessment of an Innovative Insulin Analogue Excludes Protracted Action yet Highlights the Distinction between External and Internal Diselenide Bridges.

Long-acting insulin analogues represent the most prescribed class of therapeutic proteins. An innovative design strategy was recently proposed: diselenide substitution of an external disulfide bridge. This approach exploited the distinctive physicochemical properties of selenocysteine (U). Relative to wild type (WT), Se-insulin[C7UA , C7UB ] was reported to be protected from proteolysis by insulin-degrading enzyme (IDE), predicting prolonged activity. Because of this strategy's novelty and potential clinical importance, we sought to validate these findings and test their therapeutic utility in an animal model of diabetes mellitus. Surprisingly, the analogue did not exhibit enhanced stability, and its susceptibility to cleavage by either IDE or a canonical serine protease (glutamyl endopeptidase Glu-C) was similar to WT. Moreover, the analogue's pharmacodynamic profile in rats was not prolonged relative to a rapid-acting clinical analogue (insulin lispro). Although [C7UA , C7UB ] does not confer protracted action, nonetheless its comparison to internal diselenide bridges promises to provide broad biophysical insight.

Intermittent fasting and 'metabolic switch': Effects on metabolic syndrome, prediabetes and type 2 diabetes.

Various intermittent fasting (IF) dietary plans have gained popularity among obese individuals in recent years as a means of achieving weight loss. However, studies evaluating the effect of IF regimens in people with metabolic syndrome, prediabetes and type 2 diabetes (T2D) are limited. The aim of the present review was to briefly elucidate the biochemical and physiological mechanisms underlying the positive effects of IF, especially the effect of the proposed 'metabolic switch' on metabolism. Next, we examined the efficacy and safety of IF regimens in individuals with metabolic syndrome, prediabetes and T2D. To achieve this, we performed a MEDLINE PubMed search using combinations of various IF terms, including trials in which participants met the additional criteria for metabolic syndrome, prediabetes or T2D. We found four studies in individuals with metabolic syndrome, one study in people with prediabetes, and eight studies in people with T2D evaluating the effects of different IF regimens. The limited available evidence, with small sample sizes and short trial durations, suggests that IF regimens have a similar effectiveness compared with calorie-restriction diets for weight loss and improvement in glycaemic variables. In general, most IF regimens are effective and safe. However, there is an increased risk of hypoglycaemia in patients with T2D who are treated with insulin or sulphonylureas. Moreover, long-term adherence to these regimens appears uncertain. There is a need for large controlled randomized trials to evaluate the efficacy of IF regimens, especially in individuals with metabolic syndrome and prediabetes. If proven to be sustainable and efficacious for prolonged periods, IF could offer a promising approach to improving health at the population level, and would result in multiple public health benefits.

Impaired fasting glucose and major adverse cardiovascular events by hypertension and dyslipidemia status: the Golestan cohort study.

BACKGROUND: Whether pre-diabetes in the absence of hypertension (HTN) or dyslipidemia (DLP) is a risk factor for occurrence of major adverse cardiovascular events (MACE) is not fully established. We investigated the effect of impaired fasting glucose (IFG) alone and in combination with HTN, DLP or both on subsequent occurrence of MACE as well as individual MACE components. METHODS: This longitudinal population-based study included 11,374 inhabitants of Northeastern Iran. The participants were free of any cardiovascular disease at baseline and were followed yearly from 2010 to 2017. Cox proportional hazard models were fitted to measure the hazard of IFG alone or in combination with HTN and DLP on occurrence of MACE as the primary endpoint. RESULTS: Four hundred thirty-seven MACE were recorded during 6.2 ± 0.1 years follow up. IFG alone compared to normal fasting glucose (NFG) was not associated with an increase in occurrence of MACE (HR, 0.87; 95% CI, 0.19-4.02; p, 0.854). However, combination of IFG and HTN (HR, 2.88; 95% CI, 2.04-4.07; p, 0.000) or HTN + DLP (HR, 2.98; 95% CI, 1.89-4.71; p, 0.000) significantly increased the risk for MACE. Moreover, IFG + DM with or without HTN, DLP, or both was also associated with an increase in the incidence of MACE. CONCLUSION: IFG, per se, does not appear to increase hazard of MACE. However, IFG with HTN or HTN + DLP conferred a significant hazard for MACE in an incremental manner. Moreover, IFG without HTN, adjusted for DLP, can be associated with an increase in the risk for CVD- death.

Solution structure of an ultra-stable single-chain insulin analog connects protein dynamics to a novel mechanism of receptor binding.

Domain-minimized insulin receptors (IRs) have enabled crystallographic analysis of insulin-bound "micro-receptors." In such structures, the C-terminal segment of the insulin B chain inserts between conserved IR domains, unmasking an invariant receptor-binding surface that spans both insulin A and B chains. This "open" conformation not only rationalizes the inactivity of single-chain insulin (SCI) analogs (in which the A and B chains are directly linked), but also suggests that connecting (C) domains of sufficient length will bind the IR. Here, we report the high-resolution solution structure and dynamics of such an active SCI. The hormone's closed-to-open transition is foreshadowed by segmental flexibility in the native state as probed by heteronuclear NMR spectroscopy and multiple conformer simulations of crystallographic protomers as described in the companion article. We propose a model of the SCI's IR-bound state based on molecular-dynamics simulations of a micro-receptor complex. In this model, a loop defined by the SCI's B and C domains encircles the C-terminal segment of the IR α-subunit. This binding mode predicts a conformational transition between an ultra-stable closed state (in the free hormone) and an active open state (on receptor binding). Optimization of this switch within an ultra-stable SCI promises to circumvent insulin's complex global cold chain. The analog's biphasic activity, which serendipitously resembles current premixed formulations of soluble insulin and microcrystalline suspension, may be of particular utility in the developing world.

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.

An ultra-stable single-chain insulin analog resists thermal inactivation and exhibits biological signaling duration equivalent to the native protein.

Thermal degradation of insulin complicates its delivery and use. Previous efforts to engineer ultra-stable analogs were confounded by prolonged cellular signaling in vivo, of unclear safety and complicating mealtime therapy. We therefore sought an ultra-stable analog whose potency and duration of action on intravenous bolus injection in diabetic rats are indistinguishable from wild-type (WT) insulin. Here, we describe the structure, function, and stability of such an analog, a 57-residue single-chain insulin (SCI) with multiple acidic substitutions. Cell-based studies revealed native-like signaling properties with negligible mitogenic activity. Its crystal structure, determined as a novel zinc-free hexamer at 2.8 Å, revealed a native insulin fold with incomplete or absent electron density in the C domain; complementary NMR studies are described in the accompanying article. The stability of the analog (ΔGU 5.0(±0.1) kcal/mol at 25 °C) was greater than that of WT insulin (3.3(±0.1) kcal/mol). On gentle agitation, the SCI retained full activity for >140 days at 45 °C and >48 h at 75 °C. These findings indicate that marked resistance to thermal inactivation in vitro is compatible with native duration of activity in vivo Further, whereas WT insulin forms large and heterogeneous aggregates above the standard 0.6 mm pharmaceutical strength, perturbing the pharmacokinetic properties of concentrated formulations, dynamic light scattering, and size-exclusion chromatography revealed only limited SCI self-assembly and aggregation in the concentration range 1-7 mm Such a combination of favorable biophysical and biological properties suggests that SCIs could provide a global therapeutic platform without a cold chain.

Adverse Effects of Glycemia-Lowering Medications in Type 2 Diabetes.

PURPOSE OF REVIEW: Treatment of patients with type 2 diabetes mellitus is focused on preventing the occurrence and delaying the development of macro- and micro-vascular complications. Glycemic control can help prevent these complications, but there is concern about the adverse effects of glycemia-lowering medications. A rational approach is to balance the desired low risk of adverse events against the unwanted higher risk of major complications resulting from suboptimal glucose control. RECENT FINDINGS: Using the above approach, approved glucose-lowering agents have favorable benefit-to-risk profiles for use in most patients with type 2 diabetes. We first briefly review the mechanism of actions and benefits of the different commonly used classes of glycemia-lowering medications and then discuss adverse effects and safety concern associated with their use. Our overall assessment is that if used appropriately, the different classes of glycemia-lowering medications offer beneficial outcomes with relatively modest and, in some instances, preventable adverse events.

DEXAMETHASONE STRESS TEST: A PILOT CLINICAL STUDY FOR IDENTIFICATION OF INDIVIDUALS HIGHLY PRONE TO DEVELOP TYPE 2 DIABETES.

OBJECTIVE: We examined whether the "Dexamethasone Stress Test" exhibits the requisite high predictive ability to identify individuals highly prone to develop type 2 diabetes mellitus (T2DM). METHODS: Seven years ago, we administered an oral glucose tolerance test (OGTT) to 33 individuals without T2DM and repeated the OGTT 24 hours after a single oral dose of 8 mg dexamethasone (Dex); all participants had a first-degree relative with T2DM, and close to half had prediabetes. We calculated receiver operating characteristic (ROC) curves for all parameters derived from the OGTT before and after Dex in individuals who subsequently developed diabetes compared to individuals who did not. RESULTS: At 7 years of follow-up, 9 individuals had developed T2DM, while 24 remained without diabetes. None of the OGTT-derived parameters before administration of Dex had an area under the ROC curve of >0.8. However, 24 hours after Dex, three parameters, including fasting plasma insulin, homeostatic model assessment-insulin resistance, and 2-hour plasma glucose level, exhibited areas under the ROC curves of 0.84, 0.86, and 0.92, respectively. CONCLUSION: The Dexamethasone Stress Test appears to be a good to excellent test in identifying individuals highly prone to develop T2DM. ABBREVIATIONS: AUC = area under the curve; Dex = dexamethasone; HOMA-IR = homeostatic model assessment-insulin resistance; NGT = normal glucose tolerance; OGTT = oral glucose tolerance test; PreDiab = prediabetes; ROC = receiver operating characteristic; T2DM = type 2 diabetes mellitus.

Shifting Paradigms in the Medical Management of Type 2 Diabetes: Reflections on Recent Cardiovascular Outcome Trials.

An important challenge in the management of patients with type 2 diabetes is cardiovascular disease (CVD) prevention. While it is well established that intensive glycemic control prevents the onset and slows the progression of certain microvascular complications, such a strategy utilized in multiple clinical trials over the past few decades has failed to show a similar benefit with regard to cardiovascular events, including mortality. Despite this, a major hope has been the discovery of glucose-lowering medications that simultaneously improve cardiovascular outcomes. Over the past year and a half, four randomized clinical trials (involving empagliflozin, pioglitazone, liraglutide, and semaglutide) have reported important benefits in preventing adverse cardiovascular outcomes in patients with or at risk for type 2 diabetes and established CVD. On the basis of these landmark trials, we propose that a paradigm shift in the management of patients with type 2 diabetes, specifically in those with prior macrovascular disease. A transition from current algorithms based primarily on hemoglobin A1c values to a more comprehensive strategy additionally focused on CVD prevention seems warranted.

Protective hinge in insulin opens to enable its receptor engagement.

Insulin provides a classical model of a globular protein, yet how the hormone changes conformation to engage its receptor has long been enigmatic. Interest has focused on the C-terminal B-chain segment, critical for protective self-assembly in ß cells and receptor binding at target tissues. Insight may be obtained from truncated "microreceptors" that reconstitute the primary hormone-binding site (α-subunit domains L1 and αCT). We demonstrate that, on microreceptor binding, this segment undergoes concerted hinge-like rotation at its B20-B23 ß-turn, coupling reorientation of Phe(B24) to a 60° rotation of the B25-B28 ß-strand away from the hormone core to lie antiparallel to the receptor's L1-ß2 sheet. Opening of this hinge enables conserved nonpolar side chains (Ile(A2), Val(A3), Val(B12), Phe(B24), and Phe(B25)) to engage the receptor. Restraining the hinge by nonstandard mutagenesis preserves native folding but blocks receptor binding, whereas its engineered opening maintains activity at the price of protein instability and nonnative aggregation. Our findings rationalize properties of clinical mutations in the insulin family and provide a previously unidentified foundation for designing therapeutic analogs. We envisage that a switch between free and receptor-bound conformations of insulin evolved as a solution to conflicting structural determinants of biosynthesis and function.

Biophysical optimization of a therapeutic protein by nonstandard mutagenesis: studies of an iodo-insulin derivative.

Insulin provides a model for the therapeutic application of protein engineering. A paradigm in molecular pharmacology was defined by design of rapid-acting insulin analogs for the prandial control of glycemia. Such analogs, a cornerstone of current diabetes regimens, exhibit accelerated subcutaneous absorption due to more rapid disassembly of oligomeric species relative to wild-type insulin. This strategy is limited by a molecular trade-off between accelerated disassembly and enhanced susceptibility to degradation. Here, we demonstrate that this trade-off may be circumvented by nonstandard mutagenesis. Our studies employed Lys(B28), Pro(B29)-insulin ("lispro") as a model prandial analog that is less thermodynamically stable and more susceptible to fibrillation than is wild-type insulin. We have discovered that substitution of an invariant tyrosine adjoining the engineered sites in lispro (Tyr(B26)) by 3-iodo-Tyr (i) augments its thermodynamic stability (ΔΔGu 0.5 ± 0.2 kcal/mol), (ii) delays onset of fibrillation (lag time on gentle agitation at 37 °C was prolonged by 4-fold), (iii) enhances affinity for the insulin receptor (1.5 ± 0.1-fold), and (iv) preserves biological activity in a rat model of diabetes mellitus. (1)H NMR studies suggest that the bulky iodo-substituent packs within a nonpolar interchain crevice. Remarkably, the 3-iodo-Tyr(B26) modification stabilizes an oligomeric form of insulin pertinent to pharmaceutical formulation (the R6 zinc hexamer) but preserves rapid disassembly of the oligomeric form pertinent to subcutaneous absorption (T6 hexamer). By exploiting this allosteric switch, 3-iodo-Tyr(B26)-lispro thus illustrates how a nonstandard amino acid substitution can mitigate the unfavorable biophysical properties of an engineered protein while retaining its advantages.

Aromatic anchor at an invariant hormone-receptor interface: function of insulin residue B24 with application to protein design.

Crystallographic studies of insulin bound to fragments of the insulin receptor have recently defined the topography of the primary hormone-receptor interface. Here, we have investigated the role of Phe(B24), an invariant aromatic anchor at this interface and site of a human mutation causing diabetes mellitus. An extensive set of B24 substitutions has been constructed and tested for effects on receptor binding. Although aromaticity has long been considered a key requirement at this position, Met(B24) was found to confer essentially native affinity and bioactivity. Molecular modeling suggests that this linear side chain can serve as an alternative hydrophobic anchor at the hormone-receptor interface. These findings motivated further substitution of Phe(B24) by cyclohexanylalanine (Cha), which contains a nonplanar aliphatic ring. Contrary to expectations, [Cha(B24)]insulin likewise exhibited high activity. Furthermore, its resistance to fibrillation and the rapid rate of hexamer disassembly, properties of potential therapeutic advantage, were enhanced. The crystal structure of the Cha(B24) analog, determined as an R6 zinc-stabilized hexamer at a resolution of 1.5 Å, closely resembles that of wild-type insulin. The nonplanar aliphatic ring exhibits two chair conformations with partial occupancies, each recapitulating the role of Phe(B24) at the dimer interface. Together, these studies have defined structural requirements of an anchor residue within the B24-binding pocket of the insulin receptor; similar molecular principles are likely to pertain to insulin-related growth factors. Our results highlight in particular the utility of nonaromatic side chains as probes of the B24 pocket and suggest that the nonstandard Cha side chain may have therapeutic utility.

Effects of intensive glycaemic control on ischaemic heart disease: analysis of data from the randomised, controlled ACCORD trial.

BACKGROUND: Hyperglycaemia could substantially increase the risk of ischaemic heart disease in patients with type 2 diabetes. We investigated whether intensive lowering of glucose concentrations affects risk. METHODS: We assessed 10,251 adults aged 40-79 years with established type 2 diabetes, mean glycated haemoglobin A1c (HbA1c) concentration of 67 mmol/mol (8·3%), and risk factors for ischaemic heart disease enrolled in the ACCORD trial. Participants were assigned to intensive or standard therapy (target HbA1c less than 42 or 53-63 mmol/mol [less than 6·0% or 7·0-7·9%], respectively). We assessed fatal or non-fatal myocardial infarction, coronary revascularisation, unstable angina, and new angina during active treatment (mean 3·7 years) plus a further mean 1·2 years. This trial is registered with ClinicalTrials.gov, number NCT00000620. FINDINGS: Myocardial infarction was less frequent in the intensive than in the standard therapy group during active treatment (hazard ratio [HR] 0·80, 95% CI 0·67-0·96; p=0·015) and overall (0·84, 0·72-0·97; p=0·02). Findings were similar for combined myocardial infarction, coronary revascularisation, and unstable angina (active treatment HR 0·89, 95% CI 0·79-0·99, overall 0·87 0·79-0·96) and for coronary revascularisation alone (0·84, 0·75-0·94) and unstable angina alone (0·81, 0·67-0·97) during full follow-up. With lowest achieved HbA1C concentrations included as a time-dependent covariate, all hazards became non-significant. INTERPRETATION: Raised glucose concentration is a modifiable risk factor for ischaemic heart disease in middle-aged people with type 2 diabetes and other cardiovascular risk factors. FUNDING: National Heart, Lung, and Blood Institute, National Institute of Diabetes and Digestive and Kidney Diseases, National Institute on Aging, National Eye Intitute, and Centers for Disease Control and Prevention.

α-Helical element at the hormone-binding surface of the insulin receptor functions as a signaling element to activate its tyrosine kinase.

The primary hormone-binding surface of the insulin receptor spans one face of the N-terminal ß-helix of the α-subunit (the L1 domain) and an α-helix in its C-terminal segment (αCT). Crystallographic analysis of the free ectodomain has defined a contiguous dimer-related motif in which the αCT α-helix packs against L1 ß-strands 2 and 3. To relate structure to function, we exploited expanded genetic-code technology to insert photo-activatable probes at key sites in L1 and αCT. The pattern of αCT-mediated photo-cross-linking within the free and bound receptor is in accord with the crystal structure and prior mutagenesis. Surprisingly, L1 photo-probes in ß-strands 2 and 3, predicted to be shielded by αCT, efficiently cross-link to insulin. Furthermore, anomalous mutations were identified on neighboring surfaces of αCT and insulin that impair hormone-dependent activation of the intracellular receptor tyrosine kinase (contained within the transmembrane ß-subunit) disproportionately to their effects on insulin binding. Taken together, these results suggest that αCT, in addition to its hormone-recognition role, provides a signaling element in the mechanism of receptor activation.