Ultrafast-acting insulins: state of the art

Optimal coverage of prandial insulin requirements remains an elusive goal. The invention of rapid-acting insulin analogs (RAIAs) was a big step forward in reducing postprandial glycemic excursions in patients with diabetes in comparison with using regular human insulin; however, even with these, the physiological situation cannot be adequately mimicked. Developing ultrafast-acting insulins (UFIs)-showing an even more rapid onset of action and a shorter duration of action after subcutaneous (SC) administration-is another step forward in achieving this goal. The need for UFIs has been gradually recognized over the years, and subsequently, a number of different approaches to cover this need are in clinical development. A rapid increase in circulating insulin levels can be achieved by different measures: modification of the primary structure of insulin molecule (as we know from RAIAs), addition of excipients that enhance the appearance in the monomeric state post-injection, or addition of enzymes that enable more free spreading of the insulin molecules in the SC tissue. Other measures to increase the insulin absorption rate increase the local blood flow nearby the insulin depot in the SC tissue, injecting the insulin intradermally or applying via another route, e.g., the lung. The development of these approaches is in different stages, from quite early stages to nearing market authorization. In time, daily practice will show if the introduction of UFIs will fulfill their clinical promise. In this review, the basic idea for UFIs will be presented and the different approaches will be briefly characterized.     

Insulin Pump Therapy: What Is the Evidence for Using Different Types of Boluses for Coverage of Prandial Insulin Requirements?

Bolus infusion of insulin along with a meal is a standard procedure with continuous subcutaneous insulin infusion. Modern insulin pumps allow applying this bolus in four different ways: infusion of the total dose at once or splitting the dose into two boluses, infusion of a part of the bolus in the usual manner plus infusion of the other part over a prolonged period of time (with a higher infusion rate than the basal rate), or infusion of the total dose in the form of an elevated basal rate. Depending on the composition of the given meal and its glycemic index, this is an attempt to match the circulating insulin levels to the rate of glucose absorption from the gut in order to minimize postprandial glycemic excursions. However, in the framework of evidence-based medicine, the benefits of this approach should be proven in appropriately designed clinical studies. Performance of meal-related studies requires careful attention to many aspects in order to allow meaningful evaluation of a given intervention (i.e., type of bolus). Critical evaluation of the clinical experimental studies and the one clinical study published about the impact of different types of boluses on postprandial metabolic control revealed fundamental shortcomings in study design and performance in these studies. Insufficient establishment of comparable preprandial glycemia and insulinemia on the different study days within and between the patients studied is one key aspect. Therefore, the recommendation made in most of these studies (i.e., use of dual-wave bolus) has to be accepted with care, until we have better evidence.     

Reduction of postprandial glycemic excursions in patients with type 1 diabetes: a novel human insulin formulation versus a rapid-acting insulin analog and regular human insulin

Background:

Evaluation of postprandial glycemic excursions in patients with type 1 diabetes with three prandial insulins: VIAject™ (Linjeta™), an ultra-fast insulin (UFI); insulin lispro (LIS); and regular human insulin (RHI).

Methods:

After stabilization of preprandial glycemia, 18 patients received a subcutaneous injection with an individualized insulin dose prior to a meal.

Results:

Injection of UFI resulted in a more rapid insulin absorption than with either LIS or RHI (time to half-maximal insulin levels: 13.1 ± 5.2 vs 25.4 ± 7.6 and 38.4 ± 19.5 min; p = .001 vs LIS and p < .001 vs RHI, LIS vs. RHI p < .001). Maximal postprandial glycemia was lower with UFI (0–180 min; 157 ± 30 mg/dl; p = .002 vs RHI) and LIS (170 ± 42 mg/dl; p = .668 vs RHI) than after RHI (191 ± 46 mg/dl; RHI vs LIS p = .008). The difference between maximum and minimum glycemia was smaller with UFI (70 ± 17 mg/dl) than with either RHI (91 ± 33 mg/dl; p = .007 vs UFI) or LIS (89 ± 18 mg/dl; p = .011 vs UFI). Also, the area under the blood glucose profile was lower with UFI than with RHI (0–180 min; 21.8 ± 5.8 vs 28.4 ± 7.6 g·min/dl; p < .001).

Conclusions:

The rapid absorption of UFI results in a reduction of postprandial glycemic excursions.     

Absorption kinetics and action profiles of mixtures of short-and intermediate-acting insulins

Summary The effects of mixing short- and intermediate-acting insulins (lente and NPH) on plasma insulin levels and action profiles, assessed by the euglycaemic clamp technique, were studied in 10 volunteers. Four protocols were used: (1) comparison between two semi-synthetic human soluble insulins in seven subjects (0.22 IU/kg); (2) assessment of insulin levels and action profiles of lente insulin in six subjects and of NPH insulin in five subjects (0.33 IU/kg); (3) comparison between mixtures of soluble with lente insulin and soluble with NPH insulin, administered immediately after mixing, in eight subjects (0.55IU/kg, 40% short-acting); (4) same mixtures, administered 2 days after preparation, in seven subjects. No differences in insulin levels and action profiles during the first 4 h after injection were found between both short-acting insulins and the soluble + NPH insulin mixtures. After the administration of NPH insulin, plasma insulin levels rose slightly faster in comparison with lente insulin, with no significant differences between the action profiles for either insulin. Onset of action was delayed after soluble + lente insulin, both when administered immediately after mixing and to a greater extent when stored for 2 days before administration. After the latter procedure, the onset of action was markedly retarded and only slightly faster than after lente insulin alone.We conclude, therefore, that mixing soluble with NPH insulin in a ratio of 2:3 does not affect the absorption kinetics of soluble insulin, whereas the onset of action is delayed when soluble is combined in the syringe with lente insulin, even when administered immediately after mixing.     

A review of a family of ultra-rapid-acting insulins: formulation development

This review summarizes the clinical development of a family of ultra-rapid-acting recombinant human insulin formulations. These formulations use ethylenediaminetetraacetic acid (EDTA) to chelate zinc and thereby destabilize insulin hexamers. In addition, insulin monomer surface charges are chemically masked with citrate to prevent reaggregation. The first phase 1 trials were performed using BIOD-090, an acidic 25 unit U/ml insulin formulation, which contained disodium-EDTA (NaEDTA). When compared with regular human insulin (RHI) and/or insulin lispro in multiple phase 1 studies, BIOD-090 consistently showed more rapid absorption and/or onset of action. A standard meal challenge study also demonstrated improved postprandial glucose profiles associated with BIOD-090. However, increased patient exposure in larger phase 3 trials showed that this formulation was associated with an increased incidence of local injection site reactions, most commonly pain. A next generation formulation, BIOD-100, contained the same excipients as a standard insulin concentration of 100 U/ml. BIOD-100 maintained an ultra-rapid action profile and was associated with modest but significantly improved toleration when compared with BIOD-090. In order to further improve toleration, the hypothesis that NaEDTA contributed to discomfort by chelating endogenous calcium was tested by either substituting calcium-EDTA for NaEDTA or by adding calcium chloride to the NaEDTA formulation. These calcium formulations essentially eliminated the excess discomfort associated with BIOD-090 but were associated with less optimal pharmacokinetic profiles in humans. Recent efforts have succeeded in developing ultra-rapid-acting human insulin formulations with acceptable injection site toleration by optimizing concentrations of calcium (BIOD-125) and with the use of magnesium sulfate to mitigate discomfort (BIOD-123). Similar formulation technology has also been shown to accelerate absorption of insulin analogs in animal models.     

Effect of storage temperature of insulin on pharmacokinetics and pharmacodynamics of insulin mixtures injected subcutaneously in subjects with Type 1 (insulin-dependent) diabetes mellitus

Summary These studies were undertaken to assess the influence of storage temperature of insulin vials on pharmacokinetics and pharmacodynamics of a mixture of lente insulin (Monotard HM) and regular insulin (Actrapid HM) injected subcutaneously. Seven subjects with Type 1 (insulin-dependent) diabetes mellitus were studied twice after overnight normalization of plasma glucose. A mixture of lente insulin (0.22 U/kg) and regular insulin (0.11 U/kg) was prepared from insulin vials kept either refrigerated (4 °C) or at room temperature (18 °C) and injected subcutaneoulsy (abdomen). Euglycaemia was maintained for the following 16 h by glucose infusion at variable rate. With refrigerated insulin, the plasma free insulin peak was greater (53±5 versus 45±6 mU/l) and occurred earlier (2.5±0.2 versus 6±0.3 h), and the glucose infusion rate showed a greater (16.5±1.2 versus 14.5±0.9 mol·kg^–1·min^–1) and earlier peak (3.2±0.2 versus 6±0.4 h) as compared to that occurring with the non-refrigerated insulin (p<0.05). However, 6 h after insulin injection, both plasma free insulin and glucose infusion rate were 30% lower with the mixture of refrigerated as compared to that of non-refrigerated insulin (p<0.05). In contrast, when NPH-insulin (Protaphane HM) was mixed with regular insulin and injected in 4 out of the 7 diabetic patients, the storage temperature of insulin vials had no effect on the pharmacokinetics and pharmacodynamics of the mixture. Thus, the storage temperature of insulin vials profoundly influences the effects of the mixture lente/regular insulin, but does not affect the pharmacokinetics and pharmacodynamics of the mixture NPH/regular insulin.     

Immunogenicity of recombinant DNA human insulin

Summary We postulated that human insulin of recombinant DNA origin would be a poor immunogen and might prove to be less immunogenic than purified pork insulin. Results are reported for 100 diabetic subjects not previously treated with insulin. Individuals completed the first 12 months of a clinical trial of human insulin of recombinant DNA origin. These patients are contrasted with 121 similar individuals who are taking part in a trial of purified pork insulin. Prior to therapy, species-specific binding of ¹²⁵I human insulin and pork insulins and insulin bound to antibody were undetectable in all individuals. In patients treated with human insulin of recombinant DNA origin, binding of ¹²⁵I human insulin increased to 10±1.2% at 12 months versus increases in binding of ¹²⁵I pork insulin in pork insulin-treated patients to 12.6±1.4% (NS). Mean percentages of species-specific binding tended to reach a plateau in the human insulin-treated group but continued to increase in the pork insulin group (p<0.001). Median bound values were nil throughout in patients treated with human insulin, but increased to 52 mU/l in the pork insulin group with significantly less bound insulin seen in the former group at all visits (p<0.001). The percentage of individuals who remained antibody free at 12 months, as indicated by bound insulin, was 56% in the human insulin-treated patients and 40% in the patients treated with pork insulin (p<0.01). In 11 out of 55 individuals who initially developed detectable insulin antibodies while being treated with human insulin, bound insulin levels later became undectable compared with three out of 77 individuals in the pork insulin-treatment group (p<0.005). Human insulin of recombinant DNA origin is less immunogenic than purified pork insulin. Level of antibodies in patients treated with human insulin of recombinant DNA origin reached a plateau after 6 months and antibody levels often tended subsequently to decrease below detection limits.     

Isoimmunization of man by recrystallized human insulin

Summary Ten non-diabetic psychiatric patients, who had not previously been treated with insulin, underwent insulin coma therapy by recrystallized, non-monocomponent human insulin in neutral solution. The treatment was given for 1–3 months, in maximum doses of 96–196 units daily. Several patients formed insulin antibodies. The cause of the antibody formation is discussed. The presence of small quantities of the a-fraction in the insulin is assumed to be of importance in the insulin antibody formation.

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Isoimmunisation des Menschen mit rekristallisiertem menschlichen Insulin

Zusammenfassung Zehn nicht-diabetische psychiatrische Patienten, die vorher nicht mit Insulin behandelt worden waren, wurden einer Insulinkomatherapie mit einem nicht-monokomponentartigen Humaninsulin in neutraler Lösung unterzogen. Die Behandlung wurde 1–3 Monate lang mit Maximaldosen von 96–196 E täglich durchgeführt. Mehrere Patienten erzeugten Insulinantikörper. Die Ursache der Antikörperentstehung wird diskutiert. Die Anwesenheit kleiner Mengen der a-Fraktion des Insulins könnte für die Insulinantikörperbildung von Bedeutung sein.

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Isoimmunisation de l'homme par de l'insuline humaine recristallisée

Résumé Dix patients non-diabétiques, atteints de maladie psychiatrique, n'ayant pas été traités auparavant par l'insuline, ont subi une thérapeutique par coma insulinique avec de l'insuline humaine contenant plusieurs fractions, recristallisée et mise en solution neutre. Le traitement a été administré pendant 1–3 mois, à des doses maximales de 96–196 unités par jour. Plusieurs patients ont élaboré des anticorps anti-insuline. La cause de la formation d'anticorps est discutée. La présence de petites quantités de la fraction-a dans l'insuline semble avoir une importance dans la formation des anticorps anti-insuline.

     

Biosimilar Insulins: Basic Considerations

Until now most of the insulin used in developed countries has been manufactured and distributed by a small number of multinational companies. Beyond the established insulin manufacturers, a number of new players have developed insulin manufacturing capacities based on modern biotechnological methods. Because the patents for many of the approved insulin formulations have expired or are going to expire soon, these not yet established companies are increasingly interested in seeking market approval for their insulin products as biosimilar insulins (BI) in highly regulated markets like the EU and the United States. Differences in the manufacturing process (none of the insulin manufacturing procedures are 100% identical) can lead to insulins that to some extent may differ from the originator insulin. The key questions are if subtle differences in the structure of the insulins, purity, and so on are clinically relevant and may result in different biological effects. The aim of this article is to introduce and discuss basic aspects that may be of relevance with regard to BI.     

Binding of human,porcine and bovine insulin to insulin receptors from human brain,muscle and adipocytes and to expressed recombinant alternatively spliced insulin receptor isoforms

Summary Previous studies have suggested that human and porcine insulin exert identical effects on blood glucose and counter-regulatory hormones but elicit different neurophysiological reactions. A major goal of the present study was to investigate whether this could be caused by different relative affinities of the insulins from different species to insulin receptors from the brain compared to other tissues. Insulin receptors isolated from human brain, muscle or adipocytes as well as from cultured cells over-expressing either of the human insulin receptor isoforms (exon 11– or exon 11 + ) were immobilized to microwells coated with monoclonal anti-insulin receptor antibody. Subsequently the binding of human, porcine and bovine insulin was measured. While the receptors derived from the different tissues had different affinities for insulin, there were no tissue-specific differences in the relative binding of the insulins of the three species. The insulins of the three species were also not different with regard to their binding to the receptor isoforms. Finally, in human brain homogenates no differences in the degradation rates for human, porcine and bovine insulin were detected. Thus, our data do not support the hypothesis that different neurophysiological reactions during hypoglycaemia due to human or porcine insulin are caused by differences of the binding of the insulins to human brain insulin receptors or their degradation in the human brain. [Diabetologia (1995) 38: 757–763] Received: 18 July 1994 and in revised form: 6 December 1994     

Clinical Use and Evaluation of Insulin Pens

Insulin pens are more accurate and easier to teach than other methods of insulin delivery. They also do not suffer from the risk of mismatch of insulin concentration and type of insulin syringe. The ISO standard used to test insulin pens, however, needs to be updated to reflect their clinical use.     

Biosimilar Insulins: How Similar is Similar?

Biosimilar insulins (BIs) are viewed as commercially attractive products by a number of companies. In order to obtain approval in the European Union or the United States, where there is not a single BI currently on the market, a manufacturer needs to demonstrate that a given BI has a safety and efficacy profile that is similar to that of the "original" insulin formulation that is already on the market. As trivial as this may appear at first glance, it is not trivial at all for a good number of reasons that will be discussed in this commentary. As with protein manufacturing, modifications in the structure of the insulin molecule can take place (which can have serious consequences for the biological effects induced), so a rigid and careful assessment is absolutely necessary. The example of Marvel's failed application with the European Medicines Agency provides insights into the regulatory and clinical challenges surrounding the matter of BI. Although a challenging BI approval process might be regarded as a hurdle to keep companies out of certain markets, it is fair to say that the potential safety and efficacy issues surrounding BI are substantial and relevant and do warrant a careful and evidence-driven approval process.     

Pharmacokinetics of continuous subcutaneous insulin infusion

Summary One of the reasons for the variability of blood glucose regulation in Type 1 (insulin-dependent) diabetic patients is the huge variation in subcutaneous absorption of intermediate-acting insulin. We have investigated the variation in insulin absorption during continuous subcutaneous insulin infusion in eight such patients. The content of insulin in the subcutaneous tissue was measured using ¹²⁵I-labelled insulin. The concentration of free serum insulin and blood glucose was followed from 1 h before and from 7 h after breakfast on two consecutive days. The amount of insulin absorbed during 24 h differed in all cases by less than 3% from the daily insulin dose given by the pumps. Mean insulin absorption rates and mean free insulin concentration showed peak values 30–90 min after meal bolus injections; this was sufficient to maintain near-normal blood glucose. Mean free serum insulin correlated strongly with disappearance of insulin from the subcutaneous tissue (r=0.98). From the insulin absorption rates and free insulin concentrations during basal constant insulin infusion, the half-time of serum insulin was calculated as 6 min. Compared with the known large variability in the absorption of intermediate-acting insulin, continuous subcutaneous insulin infusion offers a precise and reproducible way of insulin administration resulting in post-prandial serum insulin peaks sufficient to maintain near-normal blood glucose levels. The half-time of serum insulin during subcutaneous infusion corresponds to values for intravenous infusion given in the literature, indicating that local degradation of insulin in subcutaneous tissue is of minor importance.     

Allergy reactions to insulin: effects of continuous subcutaneous insulin infusion and insulin analogues

The purification of animal insulin preparations and the use of human recombinant insulin have markedly reduced the incidence but not completely suppressed the occurrence of insulin allergy manifestations. Advances in technologies concerning the mode of delivery of insulin, i.e. continuous subcutaneous insulin infusion (CSII), and the use of insulin analogues, resulting from the alteration in the amino acid sequence of the native insulin molecule, may influence the immunogenicity and antigenicity of native insulin. Instead of increasing allergy reactions, CSII has been reported to represent a successful alternative treatment in diabetic patients presenting local or generalized allergy to insulin or other components (zinc, protamine) of conventional treatment. Most recent reports concern CSII-treated patients using short-acting insulin analogues (essentially insulin lispro), although the precise role of these insulin analogues remains unclear as allergy to them has also been described. Finally, data on antigenicity and immunogenicity of long-acting insulin analogues (glargine, detemir), which may mimic the basal insulin delivery with CSII, remain scarce at present.     

Oral Insulin and Buccal Insulin: A Critical Reappraisal

Despite the availability of modern insulin injection devices with needles that are so sharp and thin that practically no injection pain takes place, it is still the dream of patients with diabetes to, for example, swallow a tablet with insulin. This is not associated with any pain and would allow more discretion. Therefore, availability of oral insulin would not only ease insulin therapy, it would certainly increase compliance. However, despite numerous attempts to develop such a “tablet” in the past 85 years, still no oral insulin is commercially available. Buccal insulin is currently in the last stages of clinical development by one company and might become available in the United States and Europe in the coming years (it is already on the market in some other countries). The aim of this review is to critically describe the different approaches that are currently under development. Optimal coverage of prandial insulin requirements is the aim with both routes of insulin administration (at least with most approaches). The speed of onset of metabolic effect seen with some oral insulin approaches is rapid, but absorption appears to be lower when the tablet is taken immediately prior to a meal. With all approaches, considerable amounts of insulin have to be applied in order to induce therapeutically relevant increases in the metabolic effect because of the low relative biopotency of buccal insulin. Unfortunately, the number of publications about clinical–experimental and clinical studies is surprisingly low. In addition, there is no study published in which the variability of the metabolic effect induced (with and without a meal) was studied adequately. In summary, after the failure of inhaled insulin, oral insulin and buccal insulin are hot candidates to come to the market as the next alternative routes of insulin administration.     

An examination of the role of insulin dimerisation and negative cooperativity using the biological properties of the despentapeptide and deshexapeptide insulins

Summary The C-terminus of the insulin B chain is essential for dimerisation and expression of negative cooperativity. In order to evaluate the possible physiological role of these phenomena, we have studied the properties in vivo and in vitro of despentapeptide insulin (B 26–30 deleted), derived from beef insulin, and deshexapeptide insulin (B25–30 deleted), derived from pork insulin. These materials do not dimerise and have 15% and 0% retention of negative cooperativity respectively. Lipogenesis potencies in rat adipocytes were: despentapeptide insulin 19.9±0.3%; deshexapeptide insulin 19.9±1.5%. Binding potencies in adipocytes were: despentapeptide insulin 22.6±7.8%; deshexapeptide insulin 13.2±3.3%. Metabolic clearance rates were reduced compared to insulin (insulin = 19.1±0.9; despentapeptide insulin = 9.7±0.8; deshexapeptide insulin = 6.4±0.6ml·min^–1·kg^–1 at plasma concentration 0.5 nmol/l). Hypoglycaemic potencies were reduced for both analogues (40% and 30%) when calculated on the basis of plasma concentration although both analogues and insulin were equally effective at lowering plasma glucose concentration in equimolar doses. Plasma half-disappearance time was prolonged (despentapeptide insulin=7.3±0.5; deshexapeptide insulin=9.1±0.2 min). Both analogues were full agonists and conformed to the general relationship between in vitro and in vivo properties seen with a wide range of modified insulins. They resemble other analogues with modifications which reduce receptor affinity without impairing dimerisation or negative cooperativity. The results do not support a physiological role for dimerisation or negative cooperativity.     

Low subcutaneous degradation and slow absorption of insulin in insulin-dependent diabetic patients during continuous subcutaneous insulin infusion at basal rate

Summary As information on the absorption kinetics and local degradation of infused insulin is relevant to programming strategies for continuous subcutaneous insulin infusion, we examined the time relationship of systemic insulin appearance and quantitated subcutaneous degradation during a near-basal rate of continuous subcutaneous insulin infusion in five insulin-dependent diabetic patients. Plasma free insulin was monitored for 8 h during and 3 h after a subcutaneous (abdominal wall) infusion of neutral insulin at 2.4 U/h. An identical intravenous infusion (2–4 h) was given on a separate occasion. Plateau levels of free insulin were not significantly different during the subcutaneous (37±8 mU/l) and intravenous (40±7 mU/l) infusions. Fitting of the free insulin data to our two-pool model of the subcutaneous space gave a mean estimate of 9.2 units insulin (= 3.8 h infusion) for the subcutaneous depot after 8 h. Model estimates of systemic insulin appearance, as a percentage of subcutaneous infusion rate, were 59% and 93% after 4 and 8 h respectively, and 76% 2 h after cessation of infusion. In insulin-dependent diabetic patients subcutaneous degradation of infused insulin is negligible but local accumulation in the subcutaneous space is considerable. The delay in absorption has important clinical implications for interruption and resumption of continuous subcutaneous insulin infusion and also for programming of variable basal rates.