Immunological responses to exogenous insulin.

Regardless of purity and origin, therapeutic insulins continue to be immunogenic in humans. However, severe immunological complications occur rarely, and less severe events affect a small minority of patients. Insulin autoantibodies (IAAs) may be detectable in insulin-naive individuals who have a high likelihood of developing type 1 diabetes or in patients who have had viral disorders, have been treated with various drugs, or have autoimmune disorders or paraneoplastic syndromes. This suggests that under certain circumstances, immune tolerance to insulin can be overcome. Factors that can lead to more or less susceptibility to humoral responses to exogenous insulin include the recipient's immune response genes, age, the presence of sufficient circulating autologous insulin, and the site of insulin delivery. Little proof exists, however, that the development of insulin antibodies (IAs) to exogenous insulin therapy affects integrated glucose control, insulin dose requirements, and incidence of hypoglycemia, or contributes to beta-cell failure or to long-term complications of diabetes. Studies in which pregnant women with diabetes were monitored for glycemic control argue against a connection between IAs and fetal risk. Although studies have shown increased levels of immune complexes in patients with diabetic microangiopathic complications, these immune complexes often do not contain insulin or IAs, and insulin administration does not contribute to their formation. The majority of studies have shown no relationship between IAs and diabetic angiopathic complications, including nephropathy, retinopathy, and neuropathy. With the advent of novel insulin formulations and delivery systems, such as insulin pumps and inhaled insulin, examination of these issues is increasingly relevant.

Insulin antibodies with pulmonary delivery of insulin.

BACKGROUND AND METHODS: Delivery of insulin to the deep lung presents unique challenges to the body's mucosal defense system. Pulmonary mucosal defense has the ability to discriminate between self and non-self antigens and has the potential for induction of immunologic tolerance. Published data concerning the immunogenicity of inhaled human insulin in drug trials will be reviewed, and data regarding the possible adverse effects of anti-insulin antibody development will be presented. Examination of the immunologic safety of inhaled human insulin will include discussion of comparator studies, factors affecting immunogenicity, the effects of insulin immunity on glycemic control and pulmonary function, and the relationship of insulin antibodies to dose requirements, pharmacodynamics, and hypoglycemia. CONCLUSIONS: Inhaled human insulin, whether formulated as a powder or liquid, has been shown to be more immunogenic than comparator insulins given by subcutaneous routes; however, adverse effects of antibody formation have not been demonstrated.

Immunogenicity of xenopeptide hormone therapies.

Peptides are a growing class of agents whose therapeutic use originated with non-human treatments such as animal insulins. Xenopeptides continue to be explored for biotherapeutic development using genetic engineering, and through the rich resource of animal and plant polypeptides. One of the major concerns of therapeutic administration of xenopeptides is the potential for untoward immune responses that may lead to loss of drug efficacy or adverse events in recipients. An increased risk of immunogenicity is perceived with xenopeptides, however, human-derived therapies also induce antibody formation that in some cases has been associated with severe clinical sequelae. In this review, antibody responses to xenopeptides are highlighted looking at current hormone therapies used to treat endocrine disorders. Similar to clinical experiences with peptide-based agents in general, antibody responses against xenopeptide hormone therapies in majority of cases have been benign in nature with minimal clinical impact.

Antibody response to inhaled insulin in patients with type 1 or type 2 diabetes. An analysis of initial phase II and III inhaled insulin (Exubera) trials and a two-year extension trial.

OBJECTIVE: To compare antibody responses to inhaled human insulin vs. sc human insulin and to determine whether insulin antibody binding is associated with adverse clinical consequences. RESEARCH DESIGN AND METHODS: Insulin antibody data from initial phase II/III trials were analyzed comparing the efficacy and safety of inhaled insulin with various agents, including sc insulin. Additionally, data from a 24-month extension of the phase III studies were examined. Data were pooled into the following three groups based on insulin treatment status at baseline: patients with type 1 diabetes, and patients with type 2 diabetes using insulin and not using insulin at baseline. Ig class analysis was also performed on randomly selected sera from type 1 patients at the end of the initial trials. RESULTS: In the initial trials, greater insulin antibody binding was observed in patients receiving inhaled insulin vs. sc insulin. The greatest antibody responses to inhaled insulin were observed in patients with type 1 diabetes [nonparametric comparison of medians at the end of the study, 22.0% binding (unadjusted 95% confidence interval: 19.5, 24.5)], and the lowest responses were observed in non-insulin-using patients with type 2 diabetes in which there was no difference in median values at the end of the study. There were no correlations between antibody binding and glycemic control (measured using glycosylated hemoglobin), insulin dose requirements, hypoglycemic events, or pulmonary function (measured by changes in forced expiratory volume in 1 sec and diffusion capacity of carbon monoxide). Antibody responses were IgG in type. Differences in antibody levels observed in patients with type 1 vs. type 2 diabetes were maintained over the 24-month extension trials. Peak antibody levels across all groups were generally observed after 6-12 months of insulin therapy. Inhaled insulin therapy was not associated with a greater incidence of allergy or other hypersensitivity reactions. CONCLUSION: Inhaled insulin was observed to produce a larger antibody response than sc insulin. Insulin antibody binding has not been associated with adverse clinical consequences in trials to date.

Effect of long-term exposure to insulin lispro on the induction of antibody response in patients with type 1 or type 2 diabetes.

OBJECTIVE: To determine the long-term effects of insulin lispro on inducing lispro-specific, insulin-specific, and cross-reactive (reactive with both insulin lispro and human insulin) antibodies. RESEARCH DESIGN AND METHODS: A multinational, multicenter combination of controlled and noncontrolled, open-label studies of 4.5 years' duration was designed to evaluate the long-term immunologic profile of subcutaneously administered insulin lispro. A total of 1,221 patients (men and women; 12-81 years of age) with type 1 or type 2 diabetes were enrolled. Circulating anti-insulin antibodies were measured using radioimmunoassays. RESULTS: Insulin-specific and lispro-specific antibody responses were within the background noise levels of the assays. Significant elevations of antibody were confined to a cross-reactive antibody response. Antibody levels resulting from prior exposure to long- and short-acting insulins changed little after transfer to insulin lispro and remained within or near the baseline levels. De novo exposure to insulin lispro resulted in increases in cross-reactive but not insulin- or lispro-specific antibody levels. Cross-reactive insulin antibodies developed more readily in patients with type 1 diabetes than in those with type 2 diabetes. Long-term antibody responses tended to decrease over time and returned to baseline or near-baseline levels by the end of the long-term studies. No evidence of an anamnestic antibody response could be found in individuals treated intermittently with insulin lispro. CONCLUSIONS: The immunogenic profile of patients treated with insulin lispro was comparable to that of patients treated with recombinant human insulin. Inductions of significant levels of specific or cross-reactive antibodies were not observed in patients who had received insulin previously. No significant antibody-dependent increases in insulin dosage requirements were noted in these patients. The incidence of insulin allergy was not different from that in patients treated with recombinant regular human insulin.

The influence of blood pressure and carbohydrate tolerance on vascular compliance in humans.

We conducted noninvasive measures of vascular compliance and glucose tolerance in 275 normotensive and hypertensive subjects. Of the total, 194 (70.5%) were hypertensive, 73 (26%) diabetic, 7 (2.5%) normotensive and diabetic and 66 (24%) both hypertensive and diabetic, and 74 (27%) normotensive and nondiabetic. In addition, 57 of the nondiabetic subjects had impaired glucose tolerance based on the results of blood glucose levels 2 h after a glucose challenge. For the entire population, large artery compliance was correlated with systolic (P < .001), diastolic (P = .041), and pulse (P < .001) pressures, whereas small artery compliance correlated significantly (P < .001) only with systolic and pulse pressures. Among hypertensives, a significant decrease in large and small vessel compliance was seen, which was reduced further in the case of small vessel compliance by the presence of diabetes. When the population was separated on the basis of glucose tolerance into normal, impaired, and diabetic groups, a progressive reduction (P < .001) in small artery compliance was seen that was independent of age. Similar significant (P < .001) progressive increases in body mass index and systolic pressure were seen with progression of carbohydrate intolerance. These findings confirm the close relationship between elevated blood pressure (BP) and carbohydrate intolerance and indicate that the vascular effects of both are separate, additive, and primarily on small blood vessel compliance. These findings have important implications for the preclinical detection and potential prevention of hypertension, diabetes, and associated vascular disease.

Animal versus plant protein meals in individuals with type 2 diabetes and microalbuminuria: effects on renal, glycemic, and lipid parameters.

OBJECTIVE: To determine, for individuals with type 2 diabetes and microalbuminuria, the effects of 6 weeks of meals containing plant-based protein (PP) versus meals with predominantly animal-based protein (AP) on renal function and secondarily on glycemia, lipid levels, and blood pressure. RESEARCH DESIGN AND METHODS: In a randomized crossover trial, we compared 6 weeks of meals containing only PP with meals containing primarily AP (60% animal, 40% plant) in 17 subjects with type 2 diabetes and microalbuminuria treated with diet and/or oral antidiabetic agents. Protein content was equivalent to the average American diet, and calories provided weight maintenance. Nutrients were equivalent between the two diets. Meals were prepared and packaged by a metabolic kitchen staff and were sent home weekly. At the beginning and end of each 6-week period, subjects were studied for 36 h on a metabolic unit. RESULTS: There were no significant differences between diets for glomerular filtration rate, renal plasma flow, albumin excretion rate, total cholesterol, HDL cholesterol, triglyceride area under the curve (AUC), glucose and insulin AUC, HbA(1c,) blood pressure, or serum amino acids. For both diets, at the end of the treatment periods as compared with baseline, total cholesterol was significantly lower (PP and AP: from 4.75 to 4.34 mmol/l, P < 0.01), HbA(1c) had significantly improved (PP: from 8.1 to 7.5%, P < 0.01; AP: from 7.9 to 7.4%, P < 0.01), and diastolic blood pressure was significantly lower (PP: from 83 to 80 mmHg, P < 0.02; AP: from 82 to 78, P < 0.02). CONCLUSIONS: There is no clear advantage for the recommendation of diets containing only PP rather than diets containing protein that is primarily animal-based for individuals with type 2 diabetes and microalbuminuria. There are, however, potential lipid, glycemic, and blood pressure benefits for following a carefully constructed, weight-maintaining, healthy diet, regardless of protein source.

Effects of age, race, gender, blood pressure, and estrogen on arterial compliance.

BACKGROUND: Although a variety of factors have been shown to influence vascular compliance in humans, few studies have been large enough to adequately assess the effects of age, race, gender, blood pressure (BP), and estrogen therapy. METHODS: As part of a long-term follow-up study, 272 subjects, 50% women, 26% African American, 71% currently hypertensive, ranging in age from 33 to 80 years were studied with noninvasive measures of vascular compliance by pulse wave analysis. RESULTS: A significant age-related decrease in large and small vessel compliance and increase in vascular resistance and impedance was seen in all hypertensive subjects and in normotensive women. The slope of the relationship was significantly steeper for women than for men. No effect of estrogen or race could be observed. In hypertensive subjects, pulse pressure exerted an effect similar to that of age. CONCLUSIONS: Studies of vascular compliance must consider a variety of demographic and physiologic factors including age, gender, and BP. Race and estrogen administration do not appear to contribute to the variables independent of the factors identified.

Long-term follow-up of participants in clinical studies.

We evaluated a multistep protocol to locate and ascertain data from 708 subjects who participated in clinical studies at our medical center up to 27 years ago. The protocol involved computerized and manual chart audits, introductory letters, internet searches, death registries, and a commercial person locator. We were able to ascertain vital status on 596 (84%) of study participants. Moreover, of the 475 persons known to be alive, 426 (90%) returned questionnaires and 275 (58%) completed physical examination and laboratory studies in our Clinical Research Center. The relatively modest cost of the protocol ($53,426) suggests that it is a reasonable strategy to test hypotheses involving long-term outcomes among well-characterized cohorts. The fact that the protocol can be easily implemented in most sites should encourage investigators to use these strategies to conduct similar studies.