Apparent insulin resistance due to abnormal enzymatic insulin degradation: a new mechanism for insulin resistance

Recurrent diabetic ketoacidosis and a brief history of brittle diabetes research: contemporary and past evidence in diabetic ketoacidosis research including mortality, mental health and prevention

Pharmacological, technological and educational approaches have advanced the treatment of Type 1 diabetes in the last four decades and yet diabetic ketoacidosis (DKA) continues to be a leading cause of admission in Type 1 diabetes. This article begins by reviewing the contemporary epidemiological evidence in DKA. It highlights a rise in DKA episodes in the last two decades, with DKA continuing to be the leading cause of death in young people with Type 1 diabetes, and that DKA episodes are a marker for subsequent all-cause mortality. It also summarizes the limited evidence base for DKA prevention and associations with psychopathology. To emphasize the importance of this group with high-risk Type 1 diabetes and the degree to which they have been overlooked in the past two decades, the article summarizes the research literature of recurrent DKA during 1976-1991 when it was extensively investigated as part of the phenomenon of 'brittle diabetes'. This period saw numerous basic science studies investigating the pathophysiology of recurrent DKA. Subsequently, research centres published their experiences of brittle diabetes research participants manipulating their treatment under research conditions. Unfortunately, the driver for this behaviour and whether it was indicative of other people with ketoacidosis was not pursued. In summary, we suggest there has been a stasis in the approach to recurrent DKA prevention, which is likely linked to historical cases of mass sabotage of brittle diabetes research. Further investigation is required to clarify possible psychological characteristics that increase the risk of DKA and thereby targets for DKA prevention.

Extreme subcutaneous insulin resistance: a misunderstood syndrome

Extreme subcutaneous insulin resistance (SIR) is a rare syndrome characterized by severe resistance to subcutaneous insulin with normal intravenous insulin sensitivity. Its pathophysiology is unknown, though an increased insulin degrading activity has been suggested. We report the case of a 35 year-old female patient with type I diabetes since the age of 3. Despite five shots of insulin/day, the patient progressively developed permanent ketosis related to severe acquired SIR with insulin doses as high as 500 U/day. Subcutaneous infusion of insulin and lispro insulin through an external pump did not improve resistance: HbA(1c) levels remained between 14 and 18% (N<6.5%). After numerous ketoacidotic episodes, continuous ambulatory intravenous insulin infusion was attempted through a central port due to a lack of peripheral venous access. HbAlc improved (8.5%) and daily insulin needs decreased to below 40U. However, the treatment had to be discontinued because of thrombosis and infection at different times. Intraperitoneal insulin infusion with an external pump was then proposed. HbAlc improved to 8% during 18 months but several episodes of catheter infection and encapsulation led to its removal. An intraperitoneal pump was surgically implanted, leading to the stabilization of HbA(1c) to around 8%. An insulin degradation assay did not demonstrate any excess of insulin degrading activity in the patient's or controls' subcutaneous tissue; nevertheless, excessive amounts of insulin were found in the patient's derm compared to controls. This case report of acquired SIR raises the question of its treatment and mechanisms. Regarding treatment, intraperitoneal delivery of insulin appears to be the best solution, but the mechanisms underlying SIR still remain unclear.

Lack of pharmacological effect of subcutaneous octreotide in an insulin-dependent diabetic patient: reversal after mixing with aprotinin

Octreotide, a synthetic analogue of somatostatin, may improve metabolic control and reduce GH and glucagon levels in insulin-dependent diabetic patients. We report hereto the case of an insulin-dependent diabetic patient in whom the subcutaneous continuous infusion of octreotide (150 micrograms/daily for six days) resulted ineffective on blood glucose levels, GH and glucagon. However, when octreotide was administered mixed together with aprotinin-an inhibitory of proteolytic enzymes (10,000 I.U. daily), it had lowering effect on blood glucose levels, GH and glucagon. We suggest the possibility that a local subcutaneous enzymatic degradation of octreotide may have occurred and that this degradation was blocked by aprotinin.

Human insulin-degrading enzyme shares structural and functional homologies with E. coli protease III

A proteinase with high affinity for insulin has been proposed to play a role in the cellular processing of this hormone. A complementary DNA (cDNA) coding for this enzyme has been isolated and sequenced. The deduced amino acid sequence of the enzyme contained the sequences of 13 peptides derived from the isolated protein. The cDNA could be transcribed in vitro to yield a synthetic RNA that in cell-free translations produced a protein that coelectrophoresed with the native proteinase and could be immunoprecipitated with monoclonal antibodies to this enzyme. The deduced sequence of this proteinase did not contain the consensus sequences for any of the known classes of proteinases (that is, metallo, cysteine, aspartic, or serine), but it did show homology to an Escherichia coli proteinase (called protease III), which also cleaves insulin and is present in the periplasmic space. Thus, these two proteins may be members of a family of proteases that are involved in intercellular peptide signaling.

Management of diabetes resistant to subcutaneous insulin with intravenous insulin via an implanted infusion pump

Diabetes resistant to conventional subcutaneous insulin injection is a rare complication of insulin-dependent diabetes which poses a major management problem. We report three cases treated for a total of over seven patient years with fully implanted insulin infusion devices. Technical difficulties with the devices and their operation have been substantial but the patients are much improved and hospitalisation has been dramatically reduced. We suggest that implanted insulin pumps are a real treatment option for patients with this unusual syndrome.

Massive insulin resistance apparently due to rapid clearance of circulating insulin

A 23-year-old insulin-dependent diabetic woman demonstrated increasing resistance to insulin administered by all routes, eventually requiring up to 20,000 units per day intravenously. Therapeutic trials of human and chemically modified insulin and of aprotinin were unsuccessful. Inappropriately low plasma free insulin levels (less than 60 mU/liter) during administration of extremely high insulin dosages (300 to 10,000 units per day) suggested that resistance was caused by rapid clearance of circulating insulin. There were several short periods of normal insulin sensitivity with hyperinsulinemia (more than 300 mU/liter) persisting long after intravenous insulin withdrawal, suggesting reentry to the circulation of intact, previously sequestered insulin. For four years, she has been treated with ambulatory continuous intravenous insulin infusion, which has been complicated by septicemia and central venous thrombosis. Her condition remains poorly controlled with documented intravenous insulin requirements of 2 to 20 units/hour.

In search of the subcutaneous-insulin-resistance syndrome

In numerous patients with diabetes mellitus, a defect in the absorption of subcutaneously injected insulin has been suspected as an explanation for diabetic instability. The common clinical characteristic of these patients is poor metabolic control when insulin is injected subcutaneously, but good metabolic control when the insulin is infused intravenously. We have used three approaches to attempt to identify patients with "subcutaneous-insulin resistance." First, we performed a series of studies of subcutaneous-insulin absorption in 16 patients referred to us with a presumptive diagnosis of resistance to subcutaneous insulin; in none of these patients did we detect an abnormal response of blood glucose levels to insulin administered subcutaneously. Plasma free-insulin levels rose normally after injection. Second, we assayed insulin-degrading activity in subcutaneous biopsy specimens obtained from 25 patients throughout North America and Europe who had been diagnosed as resistant to subcutaneous insulin. In none of these patients did the insulin-degrading activity of subcutaneous tissue exceed the mean value (+/- 2 SD) of eight subcutaneous biopsy specimens obtained from control patients with diabetes. Third, we performed studies of tritiated-insulin absorption in three additional diabetic patients and three control patients with nonbrittle diabetes. These studies also suggested normal absorption of insulin. In none of the patients we studied were we able to confirm the clinical diagnosis of subcutaneous-insulin resistance. We therefore conclude that this syndrome is extremely rare and that misdiagnosis is common.

Inhibition of insulin degradation by hepatoma cells after microinjection of monoclonal antibodies to a specific cytosolic protease

Four monoclonal antibodies were identified by their ability to bind to 125I-labeled insulin covalently linked to a cytosolic insulin-degrading enzyme from human erythrocytes. All four antibodies were also found to remove more than 90% of the insulin-degrading activity from erythrocyte extracts. These antibodies were shown to be directed to different sites on the enzyme by mapping studies and by their various properties. Two antibodies recognized the insulin-degrading enzyme from rat liver; one inhibited the erythrocyte enzyme directly; and two recognized the enzyme after gel electrophoresis and transfer to nitrocellulose filters. By this latter procedure and immunoprecipitation from metabolically labeled cells, the enzyme from a variety of tissues was shown to be composed of a single polypeptide chain of apparent Mr 110,000. Finally, these monoclonal antibodies were microinjected into the cytoplasm of a human hepatoma cell line to assess the contribution of this enzyme to insulin degradation in the intact cell. In five separate experiments, preloading of cells with these monoclonal antibodies resulted in an inhibition of insulin degradation of 18-54% (average 39%) and increased the amount of 125I-labeled insulin associated with the cells. In contrast, microinjection of control antibody or an extraneous monoclonal antibody had no effect on insulin degradation or on the amount of insulin associated with the cells. Moreover, the monoclonal antibodies to the insulin-degrading enzyme caused no significant inhibition of degradation of another molecule, low density lipoprotein. Thus, these results support a role for this enzyme in insulin degradation in the intact cell.

Implantable infusion pump management of insulin resistant diabetes mellitus

Diabetes mellitus with resistance to insulin administered subcutaneously or intramuscularly (DRIASM) is a rare and brittle form of Type I diabetes, found predominantly in young females and characterized by inadequate glycemic response to subcutaneous or intramuscular insulin administration. DRIASM leads to frequent ketoacidosis and obligatory hospitalization for administration of intravenous insulin. The use of a totally implantable infusion pump effected dramatic improvement in the treatment of five patients with this difficult form of diabetes. Frequency of clinical ketoacidosis was reduced from 37 episodes per year to 0.4 episodes per year (99%), and average in-hospital days per month were reduced from 20.8 days to 2.2 days (89%) with a mean follow-up period of 14.4 months. Cost savings were approximately +10,000 per patient month. Quality of life was greatly improved for these individuals.

Insulin resistance in total lipodystrophy: evidence for a pre-receptor defect in insulin action

The cause of insulin resistance in lipodystrophic diabetes is unknown but has generally been ascribed to dysfunction at either the receptor or post receptor level. In a 14 year-old girl with total acquired lipodystrophy, subcutaneous and intravenous insulin requirements approximated 600 units daily. However, circulating total and free insulin levels were not increased, and during testing by the euglycemic clamp method, the glucose response to increasing free insulin concentrations was within the range found in eight subjects with insulin-dependent diabetes. Insulin clearance during the euglycemic clamp was 43, 98, 115, and 116 mL/kg/min at each of four insulin infusion rates compared to means of 13, 13, 12, and 11 in the control subjects with diabetes. No detectable degrading activity was present in serum, and serum inhibited insulin degradation normally. Binding of insulin to IgG, IgM, and IgE was not increased, insulin binding to monocytes and erythrocytes was not sufficiently abnormal to account for the the insulin resistance, and insulin receptor increased insulin clearance or accelerated degradation of insulin by tissues.

Characterization of an insulin degrading enzyme from cultured human lymphocytes

An insulin degrading enzyme from cultured human lymphocytes, IM-9 cells, has been purified and characterized. The biochemical, enzymatic and immunological characteristics of this enzyme were all found to be similar to the characteristics of insulin degrading enzymes previously isolated from rat and pig skeletal muscle. Furthermore, this insulin degrading enzyme was found to have no effect on the structure of the insulin receptor nor to be linked to the insulin receptor either on the plasma membrane of cells or when they are shed into the media. The present studies suggest that the IM-9 lymphocytes, which have been extensively used to study the human insulin receptor, may also be a good system for studying human insulin degrading enzymes.

Diabetic ketoacidosis due to insulin resistance treated by haemodialysis

A 14-year-old female patient with insulin resistance is reported in whom it appeared that initially insulin breakdown was unusually rapid. Subsequently there was in addition evidence of reduced insulin sensitivity. The rapidly increasing requirement of insulin (1600 units daily), given by continuous IV infusion, was dramatically reduced by haemodialysis, and was maintained subsequently. We suggest that insulin aggregates which may have blocked insulin receptor sites, causing insulin resistance, were removed by haemodialysis.

Insulin degrading enzyme activity and insulin binding of erythrocytes in normal subjects and Type 2 (non-insulin-dependent) diabetic patients

Specific insulin degrading enzyme activity of erythrocytes was determined in relation to erythrocyte insulin binding in 16 healthy subjects, 14 Type 1 (insulin-dependent) and various groups of Type 2 (non-insulin-dependent) diabetic patients (n = 39). Degrading activity was increased in Type 2 diabetic patients on sulphonylureas, as well as in a subgroup with good metabolic control (p less than 0.001) and in patients with secondary failure to oral therapy (p less than 0.02); degrading activity returned to normal in the latter patients after 1 week of insulin treatment. Highest degrading activity was found in insulin-treated, yet insulin-insensitive patients (daily insulin dose greater than 80 U). Degrading activity was significantly correlated in healthy subjects both with circulating insulin concentrations and maximal specific insulin binding. In contrast, in Type 2 diabetic subjects, degrading activity was inversely correlated with serum insulin with no apparent association with maximal specific insulin binding except in those patients given 1 week of insulin treatment. High erythrocyte insulin degrading enzyme activity might be a common feature in the insulin-insensitive Type 2 diabetic patient and might occur subsequent to some aspect of insulin deficiency at the tissue level.

Subcutaneous aprotinin causes local hyperaemia. A possible mechanism by which aprotinin improves control in some diabetic patients

Local changes in blood flow at the subcutaneous injection site of the proteinase inhibitor aprotinin and its diluent were measured by photoelectric plethysmography. Aprotinin, but not its diluent, caused local hyperaemia in five normal subjects and in five stable and five brittle insulin-dependent diabetic patients, local blood flow increasing by 80%-180%. The duration of the hyperaemic response was shorter in the brittle diabetic patients than in the other two groups, but there was wide individual variation. Aprotinin is known to enhance subcutaneous insulin absorption in normal subjects and in some brittle diabetic patients. The basis for this might be through increasing blood flow near the injection site rather than by inhibition of insulin breakdown.

Diabetes responsive to intravenous but not subcutaneous insulin: effectiveness of aprotinin

Patients with diabetes that is insensitive to subcutaneous insulin but sensitive to intravenous insulin have recently been described. We have studied this phenomenon is five female diabetics (14 to 31 years of age) who required excessive amounts of insulin (2.5 to 30.0 units per kilogram of body weight per day) to avoid recurrent ketoacidosis. Known causes of insulin resistance were excluded. All patients had normal responses to conventional doses of intravenous insulin (0.35 to 0.9 unit per kilogram per day). Four patients required continuous intravenous infusion of insulin for one to six months. When a mixture of aprotinin (a protease inhibitor) and regular porcine insulin was given subcutaneously, conventional doses (0.7 to 1.4 units per kilogram per day) produced euglycemia; plasma levels of free insulin rose, and ketonuria disappeared. Four patients had episodes of spontaneous, severe hypoglycemia before and during aprotinin therapy, necessitating continuous infusion of glucose for two to 14 days. Although no insulin was administered, hyperinsulinemia (50 to 2000 muU of free insulin per milliliter [359 to 14,350 pmol per liter]) was present. These findings suggest excessive degradation or sequestration of insulin at the site of injection.

Insulin degradation by insulin target cells

Recent findings illustrate the complexities associated with the interaction between insulin and its target cells. These results suggest that the processes involved in insulin action and those involved in insulin degradation may have certain steps in common. Both apparently begin when insulin binds to the insulin receptor. The next step is unknown but it ultimately leads to the internalization of the hormone before insulin dissociates from the cell surface. Furthermore, internalization appears to be a requirement for efficient degradation of insulin since the vast majority (perhaps all in certain cells) of the degrading activity is intracellular. Internalization may not be required to produce certain actions of the hormone, however, and the two processes may diverge at the point. It is not clear how insulin enters the target cell other than the process appears to be receptor-mediated. Also, further work is needed to more fully characterize the vesicles that contain internalized insulin. Finally, the actual location of insulin degradation and the enzyme(s) involved need further study, especially to clarify the relative contributions of lysosomes, cytosolic protease, and GIT to physiological insulin destruction. An understanding of the overall process of insulin degradation is required for a complete description of the physiologic disposition of the hormone at the target cell. Moreover, this system has subtle control mechanisms that may have important implications for the management of diabetes and other endocrine and metabolic disorders.

Management of severely brittle diabetes by continuous subcutaneous and intramuscular insulin infusions: evidence for a defect in subcutaneous insulin absorption

Severely brittle diabetes is defined as a rare subtype of insulin-dependent diabetes with wide, fast, unpredictable, and inexplicable swings in blood glucose concentration, often culminating in ketoacidosis or hypoglycaemic coma. To assess the role of inappropriate type, amount, or timing of insulin treatment and the route of administration as a cause of severe brittleness six patients with continuous subcutaneous insulin infusion, which provides a high degree of optimisation of dosage with exogenous insulin in stable diabetics. The glycaemic control achieved during continuous subcutaneous insulin infusion was compared with that during continuous intramuscular insulin infusion. Six patients with non-brittle diabetes were also treated by continuous subcutaneous insulin infusion. These patients achieved the expected improvement in glycaemic control (mean +/- SD plasma glucose concentration 5.1 +/- 2.3 mmol/l (92 +/- 41 mg/100 ml)), but not the patients with brittle diabetes remained uncontrolled with continuous subcutaneous infusion (13.6 +/- 5.8 mmol/1 (245 +/- 105 mg/100 ml) compared with 10.3 +/- 4.1 mmol/l (186 +/- 74 mg/100 ml) during treatment with optimised conventional subcutaneous injections). During continuous intramuscular infusion, however, glycaemic control in five of the patients with brittle diabetes was significantly improved (7.7 +/- 2.6 mmol/l (139 +/- 47 mg/100 ml). The remaining patient with brittle diabetes, previously safely controlled only with continuous intravenous insulin, did not respond to continuous intramuscular infusion. It is concluded that in five of the six patients with brittle diabetes studied here impaired or irregular absorption of insulin from the subcutaneous site played a more important part in their hyperlability than inappropriate injection strategies. This absorption defect was presumably bypassed by the intramuscular route.