T-lymphocyte requirement for diabetes in RT6-depleted diabetes-resistant BB rats

Lessons on autoimmune diabetes from animal models

T1DM (Type I diabetes mellitus) results from selective destruction of the insulin-producing beta-cells of the pancreas by the immune system, and is characterized by hyperglycaemia and vascular complications arising from suboptimal control of blood glucose levels. The discovery of animal models of T1DM in the late 1970s and early 1980s, particularly the NOD (non-obese diabetic) mouse and the BB (BioBreeding) diabetes-prone rat, had a fundamental impact on our ability to understand the genetics, aetiology and pathogenesis of this disease. NOD and BB diabetes-prone rats spontaneously develop a form of diabetes that closely resembles the human counterpart. Early studies of these animals quickly led to the realization that T1DM is caused by autoreactive T-lymphocytes and revealed that the development of T1DM is controlled by numerous polymorphic genetic elements that are scattered throughout the genome. The development of transgenic and gene-targeting technologies during the 1980s allowed the generation of models of T1DM of reduced genetic and pathogenic complexity, and a more detailed understanding of the immunogenetics of T1DM. In this review, we summarize the contribution of studies in animal models of T1DM to our current understanding of four fundamental aspects of T1DM: (i) the nature of genetic elements affording T1DM susceptibility or resistance; (ii) the mechanisms underlying the development and recruitment of pathogenic autoreactive T-cells; (iii) the identity of islet antigens that contribute to the initiation and/or progression of islet inflammation and beta-cell destruction; and (iv) the design of avenues for therapeutic intervention that are rooted in the knowledge gained from studies of animal models. Development of new animal models will ensure continued progress in these four areas.

Diabetes prone BB rats are severely deficient in natural killer T cells

Diabetes prone (DP) BB rats develop spontaneous autoimmune hyperglycemia. Coisogenic diabetes resistant (DR) BB rats develop diabetes in response to immunological and environmental perturbants, but not spontaneously. Both are used to model human insulin-dependent diabetes mellitus (IDDM). Deficiencies in natural killer (NK) T cells have been implicated in the expression of human IDDM, but little is known of their phenotype or function in the rat. We now report that the phenotype of NK T cells in the rat is alphabetaTcR+ CD8+ CD4-, comparable to the NK T cell phenotype reported for humans, which is alphabetaTcR+ CD4- Valpha24-JalphaQ, and either CD8- or CD8alphaalpha+. We also report that DP- but not DR-BB rats are severely deficient in splenic and intrahepatic NKR-P1+ alphabetaTcR+ (NK T) cells. Because RT6+ T cells are deficient in DP-BB rats, and because depletion of cells expressing RT6 induces IDDM in DR-BB rats, we studied NK T cells for expression of this antigen. We observed that the majority of rat NK T cells express RT6+. In addition, injection of cytotoxic anti-RT6.1 monoclonal antibody depleted splenic and intrahepatic RT6+ NK T cells, T cells, and NK cells, but left intact the RT6- subset of each population. These results suggest that deficiencies in NK T cells may play a role in the susceptibility of DP- and DR-BB rats, respectively, to spontaneous and induced autoimmune IDDM.

Insulin lispro: its role in the treatment of diabetes mellitus

OBJECTIVE

To introduce a rapid-acting human insulin analog, insulin lispro; to review its pharmacology, therapeutics, pharmacokinetics, dosing guidelines, adverse effects, and drug interactions; and to summarize the clinical trials of its efficacy and safety alone and in comparison with regular human insulin in the treatment of diabetes mellitus.

DATA SOURCES

A MEDLINE database search was completed to identify all relevant articles, including reviews; Eli Lilly and Co.; published articles and abstracts; and review chapters from medical textbooks.

STUDY SELECTION

Due to the relatively few citations listed in MEDLINE (12 as of December 1995), most of the studies reported were found from abstracts summarizing the clinical action, adverse effects, or pharmacokinetics of insulin lispro in healthy volunteers or patients with diabetes mellitus. A few of the studies used patients with diabetes mellitus in multicenter, randomized, crossover trials of insulin lispro.

DATA EXTRACTION

All clinical trials that were available prior to submission of this manuscript for publication, including unpublished reports, were reviewed.

DATA SYNTHESIS

The human insulin analog, insulin lispro, which is biosynthetically made by inverting the amino acid sequence of human insulin at B-28 and B-29, is more effective than regular human insulin in improving postprandial glucose control. Subcutaneous injections of insulin lispro result in decreased blood glucose peaks following meals and a potential decreased risk of hypoglycemic episodes, including nighttime hypoglycemia in patients with type 1 diabetes. Insulin lispro in comparison with regular human insulin provides equal or slightly better blood glucose control. When compared with subcutaneous injections of regular human insulin, the peak serum insulin concentration of insulin lispro is three times higher, time to peak is 4.2 times faster, the absorption rate constant is double, and the duration of action is half as long. Insulin lispro is similar to regular human insulin with reference to dose, toxicity, adverse effects, drug interactions, and immunogenicity. When insulin lispro is mixed with human NPH (isophane) or Lente insulins, insulin lispro should be drawn into the syringe first, mixed with the long-acting insulin, and injected immediately after mixing. Patients using insulin lispro perceive an improvement in their well-being and quality of life due to flexible injection times and less frequent hypoglycemic reactions. Insulin lispro is believed to be suitable for patients using insulin infusion pumps.

CONCLUSIONS

Insulin lispro is equipotent to human insulin and has a much more rapid onset and shorter duration of action than human insulin does, which may reduce the risk of hypoglycemia. In addition, insulin lispro improves the dosing convenience for patients with diabetes and provides a more natural control of blood glucose concentrations. Insulin lispro is a useful new agent in the treatment of diabetes mellitus.

Anti-insulin and regulatory anti-idiotypic antibodies use the same germ-line VHIX gene

In humans and in BALB/c mice, immune responses to the hormone insulin use evolutionarily related VHV (human) and VHIX (murine) gene families. To determine if these structural relationships include regulatory elements, BALB/c mice were pretreated with autologous immunoglobulin G (IgG) monoclonal antibodies (mAb) that recognize shared idiotopes on human anti-insulin antibodies and the subsequent immune response to human insulin assessed. One mAb, Id227, was found to augment and accelerate the insulin response by inducing a human idiotype that is expressed on both insulin-binding and non-insulin-binding BALB/c antibodies. Analysis of VH gene utilization by Id227 shows that it expresses a VHIX gene similar to that of anti-insulin mAb 125, but the anti-Id has no anti-insulin activity. Using DNA amplification, four germ-line VHIX genes were isolated from BALB/c liver DNA and sequence analysis shows that the anti-insulin and anti-Id are derived from the same germ-line gene. Consistent with its role as a regulatory idiotype, IgG Id227 entirely preserves germ-line sequence in the complementary determining regions and contains only three mutations in framework regions. These studies show that both structural and regulatory features of immune responses to conserved self antigens extend beyond species boundaries.

Detection of an equilibrium intermediate in the folding of a monomeric insulin analog

To determine the conformational properties of the C-terminal region of the insulin B-chain relative to the helical core of the molecule, we have investigated the fluorescence properties of an insulin analog in which amino acids B28 and B29 have been substituted with a tryptophan and proline residue respectively, ([WB28,PB29]insulin). The biological properties and far-UV circular dichroism (CD) spectrum of the molecule indicate that the conformation is similar to that of native human insulin. Guanidine hydrochloride (GdnHCl)-induced equilibrium denaturation of the analog as monitored by CD intensity at 224 nm indicates a single cooperative transition with a midpoint of 4.9 M GdnHCl. In contrast, when the equilibrium denaturation is observed by steady-state fluorescence emission intensity at 350 nm, two distinct transitions are observed. The first transition accounts for 60% of the observed signal and has a midpoint of 1.5 M GdnHCl. The second transition roughly parallels that observed by CD measurements with an approximate midpoint of 4.5 M GdnHCl. The near-UV CD spectrum, size-exclusion, and ultracentrifugation properties of [WB28,PB29]insulin indicate that this analog does not self-associate in a concentration-dependent manner as does human insulin. Thus, the observed fluorescence changes must be due to specific conformational transitions which occur upon unfolding of the insulin monomer with the product of the first transition representing a stable folding intermediate of this molecule.