Italian version of the Occupational Depression Inventory: Validity, reliability, and associations with health, economic, and work-life characteristics

BACKGROUND

The Occupational Depression Inventory (ODI) reflects a new approach to job-related distress centered on work-attributed depressive symptoms. The instrument was developed with reference to the characterization of major depression found in the Diagnostic and statistical manual of mental disorders, fifth edition. The ODI has been validated in English, French, and Spanish. This study (a) investigated the psychometric and structural properties of the ODI's Italian version and (b) inquired into the nomological network of occupational depression.

METHODS

A convenience sample of 963 employed individuals was recruited in Italy (69.9% female; mean age = 40.433). We notably relied on exploratory structural equation modeling bifactor analysis, common-practice confirmatory factor analysis, and Mokken scale analysis to examine our dataset.

RESULTS

Our analyses indicated that the Italian version of the ODI meets the requirements for essential unidimensionality, thus justifying the use of the instrument's total score. The ODI's reliability was excellent. Measurement invariance held across sexes, age groups, and occupations. Occupational depression was negatively associated with general wellbeing and positively associated with a 12-month history of depressive disorder, current antidepressant intake, 12-month sick leave, 6-month physical assault at work, 6-month verbal abuse at work, lack of money for leisure activities, and financial strain in the household.

CONCLUSIONS

The ODI's Italian version exhibits robust psychometric and structural properties, suggesting that the instrument can be fruitfully used for addressing job-related distress in Italian-speaking populations. Furthermore, the present study relates occupational depression to important health, economic, and work-life characteristics, including past depressive episodes, antidepressant medication, sickness-related absenteeism, workplace violence, and economic stress.

Impaired exocrine pancreatic function in different stages of type 1 diabetes

INTRODUCTION

Aim of this study was to investigate the pancreatic exocrine function in patients with type 1 diabetes (T1D) by multiple non-invasive tests.

RESEARCH DESIGN AND METHODS

The study is a single-center, cross-sectional study of pancreatic exocrine function in adult patients with new-onset or long-standing T1D and healthy controls.

RESULTS

Healthy controls, new-onset T1D, and long-standing T1D were similar for age at the time of the study, gender and body mass index (BMI) categories. Age of onset of T1D patients with long-standing disease was younger than that of patients with new-onset T1D (p<0.001). As expected, the three groups differed for C-peptide and hemoglobin A1c (HbA1c) levels. Lipase activity measured by ¹³C-mixed triglyceride breath test was reduced progressively, although not significantly, from controls to recent-onset T1D and long-standing T1D participants. Fecal elastase-1 was significantly lower in participants with T1D, either new onset or long standing. Pancreatic amylase, lipase, retinol binding protein and prealbumin were significantly different across the groups, with a significant trend toward lower values in long-standing T1D and intermediate values in new-onset T1D, while no differences were observed for total amylase. The markers of impaired exocrine function tests (fecal elastase-1, serum pancreatic amylase and lipase) and of nutritional status (retinol binding protein and prealbumin levels) correlated with the reduction of fasting and urinary C-peptide.

CONCLUSIONS

Our results confirm that exocrine pancreatic impairment is a feature of T1D, with low fecal elastase-1, serum pancreatic amylase and lipase as specific markers, associated with reduced levels of nutritional indexes. Moreover, the evidence of more advanced insufficiency in long-standing disease reflects the chronic nature of this process, and its correlation with the residual β-cell function suggests parallel pathways for the impairment of the endocrine and exocrine pancreatic function.

Awareness about diabetes and pregnancy among diabetes specialists and fellows: The YoSID diabetes and pregnancy project

BACKGROUND AND AIMS

Despite evidence that pregnancy planning improves outcomes, in Italy, as in many other countries worldwide, <50% of women with diabetes prepare their pregnancy. The aim of this study was to document training and knowledge on diabetes and pregnancy (D&P) among diabetes professionals.

METHODS AND RESULTS

We administered an anonymous online questionnaire, focused on diabetes and pregnancy planning, to diabetes team members. Between Nov-2017 and Jul-2018, n = 395 professionals (60% diabetes/endocrinology/internal medicine specialists, 28% fellows) completed the survey. Fifty-nine percent of the specialists, mainly (78%) those completing their fellowship after 2006, reported having received training on D&P during fellowship. Considering specialists reporting training, 43% correctly identified fetal risks of inadequate preconceptional glucose control and 55% maternal risks, 38% identified risks associated with overweight/obesity, and 39% would prescribe hormonal contraception to women with diabetes only if glucose control is good.

CONCLUSIONS

The results of our survey suggest the need to improve training and awareness of professionals in the area of diabetes and pregnancy.

Trends in Factors Affecting Pregnancy Outcomes Among Women With Type 1 or Type 2 Diabetes of Childbearing Age (2004-2017)

AIM

To describe trends in modifiable and non-modifiable unfavorable factors affecting pregnancy outcomes, over time (years 2004-2017), in women with diabetes of childbearing age from an English primary care perspective.

METHODS

We identified women with diabetes aged 16-45 years from the Royal College of General Practitioners (RCGP) Research and Surveillance Centre (RSC) network, an English primary care sentinel database. Repeated annual cross-sectional analyses (2004-2017) assessed the prevalence of unfavorable factors for pregnancy, such as obesity, poor glycaemic control, microalbuminuria, hypertension, use of medications for treating diabetes, and associated comorbidities not recommended for pregnancy.

RESULTS

We identified 3,218 women (61.5% with Type 2 diabetes) in 2004 and 6,657 (65.0% with Type 2 diabetes) in 2017. The proportion of women with ideal glycaemic control for conception (HbA1c<6.5%) increased over time, in patients with Type 1 diabetes from 9.0% (7.1%-11.0%) to 19.1% (17.2%-21.1%), and in those with Type 2 diabetes from 27.2% (24.6%-29.9%) to 35.4% (33.6%-37.1%). The proportion of women with Type 2 diabetes prescribed medications different from insulin and metformin rose from 22.3% (20.5%-24.2%) to 27.3% (26.0%-28.6%).In 2017, 14.0% (12.6%-15.4%) of women with Type 1 and 30.7% (29.3%-32.0%) with Type 2 diabetes were prescribed angiotensin-modulating antihypertensives or statins. We captured at least one unfavorable factor for pregnancy in 50.9% (48.8%-52.9%) of women with Type 1 diabetes and 70.7% (69.3%-72.0%) of women with Type 2 diabetes. Only one third of women with Type 1 diabetes (32.2%, 30.3%-34.0%) and a quarter of those with Type 2 diabetes (23.1%, 21.9%-24.4%) were prescribed hormonal contraception. Contraception was prescribed more frequently to women with unfavorable factors for pregnancy compared to those without, however, the difference was significant only for women with Type 1 diabetes.

CONCLUSIONS

Despite significant improvements in general diabetes care, the majority of women with Type 1 or Type 2 diabetes have unfavorable, although mostly modifiable, factors for the start of pregnancy. Good diabetes care for women of childbearing age should include taking into consideration a possible pregnancy.

Portrait of women with type 1 or type 2 diabetes of childbearing age attending diabetes clinics in Italy: the AMD-Annals initiative

AIM

To describe characteristics relevant in case of an unplanned pregnancy for T1D or T2D women of childbearing age.

METHODS

We analyzed the 2011 AMD-Annals dataset, compiling information from 300 clinics (28,840 T1D patients and 532,651 T2D patients). A risk score of unfavorable conditions for pregnancy included HbA1c > 8.0%; BMI ≥ 35; systolic BP ≥ 140 mmHg or diastolic BP ≥ 90 mmHg; microalbuminuria/proteinuria; use of statins, ACE inhibitors, ARB; use of diabetes drugs other than metformin/insulin.

RESULTS

The proportion of T2D cases increased from 30.8% (95% CI 29.9-32.4) at age 18-30 years to 67.5% (66.6-68.5) at age 36-45 years. The proportion of women with HbA1c < 7.0% was 20.4% (20.0-20.8) in T1D and 43.4% (42.8-43.9) in T2D women. Furthermore, 47.6% (47.0-48.3) of T1D women and 34.5% (33.9-35.0) of T2D women had HbA1c ≥ 8.0%. The prevalence of obesity (BMI ≥ 30) was sevenfold higher among T2D than T1D women [49.9% (49.4-50.5) and 7.4% (7.2-7.5), respectively]. T2D women were more likely to have hypertension or microalbuminuria than T1D women. Almost half of the T2D women were taking drugs not approved during pregnancy. At least one unfavorable condition for starting a pregnancy was present in 51% of T1D women of childbearing age and in 66.7% of T2D women.

CONCLUSIONS

Women with either T1D or T2D of childbearing age in Italy were far from the ideal medical condition for conception. Our data strongly support the need for counseling all women with diabetes about pregnancy planning.

Screening for gestational diabetes in the Lombardy region: A population-based study

AIM

As the treatment of hyperglycaemia during pregnancy with diet or insulin reduces the risk of adverse maternal outcomes and perinatal complications, screening for gestational diabetes mellitus (GDM) is included, albeit to variable extents, in all guidelines of care for pregnant women. The aim of the present investigation was to estimate the proportion of pregnancies screened for GDM in Lombardy between 2007 and 2010, and to identify predictors of screening.

METHODS

A retrospective cross-sectional study using regional healthcare utilization databases of Lombardy was conducted. The study included all residents of Lombardy without pregestational diabetes who delivered between 1 January 2007 and 31 December 2010. The proportion of pregnancies with at least one screening test for GDM was calculated, along with the odds ratios and 95% confidence intervals associated with selected covariates for GDM screening.

RESULTS

Of the 362,818 pregnancies included in the sample, 30% were screened for GDM. The proportion of pregnancies screened increased slightly from 2007 (27%) to 2010 (33%) and with maternal age (from 28% among women<25 years to 32% among those ≥35 years), and varied widely across local health management organizations (HMOs) of residence (range: 20% to 68%). Socioeconomic indicators (education, immigrant status), obstetric history and prepregnancy hypertension were independent predictors of GDM screening.

CONCLUSION

The study finding of a low rate of pregnant women screened for GDM among residents of Lombardy supports the need for programmes to improve training of healthcare professionals, to raise women's awareness of GDM and to eliminate barriers to GDM screening.

Absence of telomere shortening and oxidative DNA damage in the young adult offspring of women with pre-gestational type 1 diabetes

AIMS/HYPOTHESIS

The offspring of mothers with pre-gestational type 1 diabetes (PGDM) may be at increased risk of glucose intolerance and cardiovascular disease in childhood. The underlying causes of these observations, and whether they persist into adulthood, are unknown. The aim of the present study was to test the hypothesis that fetal chromosomal telomere oxidative DNA damage resulting from maternal PGDM programmes the offspring towards a senescent phenotype that is detectable in young adulthood.

METHODS

We studied 21 young adult offspring (age 16-23 years) with a maternal history of PGDM and 23 age- and weight-matched controls with no maternal history of diabetes. All participants underwent anthropometric assessments, a standard 75 g OGTT, measurement of peripheral blood mononuclear cell and skin fibroblast telomere length, fibroblast senescence, cell DNA damage (by determination of 8-oxoguanine levels using flow cytometry), plasma lipoprotein profiles (determined by nuclear magnetic resonance) and plasma levels of soluble adhesion molecules and inflammatory markers.

RESULTS

The groups did not differ significantly with respect to anthropometric measures, glucose tolerance, fasting and 2 h plasma insulin levels during OGTT, estimated peripheral insulin resistance, peripheral blood mononuclear cell or fibroblast telomere length, DNA damage or senescence in vitro, plasma NMR lipoprotein profiles or levels of high-sensitivity C-reactive protein. Plasma concentrations of soluble intercellular adhesion molecule 1 (sICAM-1; p < 0.05) and IL-6 (p = 0.08) were higher in the PGDM offspring.

CONCLUSIONS/INTERPRETATION

Young adult offspring of mothers with PGDM do not differ in terms of glucose tolerance, DNA damage or telomere length from controls of the same weight and BMI. This does not preclude such abnormalities at an earlier age, but there is no evidence of telomere damage as a pre-programming mechanism in the young adults enrolled in this study.

Low density lipoprotein from patients with Type 2 diabetes increases expression of monocyte matrix metalloproteinase and ADAM metalloproteinase genes

Aims

Type 2 diabetes is characterised by increased plasma concentrations of pro-inflammatory cytokines [such as tumour necrosis factor – alpha; TNF-α] and soluble forms of adhesion molecules involved in leukocyte – endothelial interactions. These molecules are synthesised as transmembrane proteins and the plasma soluble forms are generated by ectodomain cleavage from the cell surface by members of the ADAM [adisintegrin and metalloproteinase] proteinase family. We hypothesised that plasma low density lipoprotein [LDL] from subjects with Type 2 diabetes would influence in vitro monocytic ADAM and matrix metalloproteinase [MMP] gene expression differently compared to control LDL.

Methods

We examined relative mRNA expression by real time PCR in a monocytic cell line [THP-1] cultured for 4, 8 and 24 hrs with human plasma LDL derived from subjects with [n = 5] or without [n = 4] Type 2 diabetes. Gene expression for MMP-1 and 9, and ADAM – 8, 15, 17 and 28 was studied.

Results

Type 2 diabetes LDL significantly increased gene expression of MMP – 1 [p < 0.01] MMP – 9 [p < 0.001], and ADAM 17 [p < 0.05], – 28 [p < 0.01] and – 15 [p < 0.01] compared to control LDL. Type 2 diabetes LDL had disparate effects on inhibitors of MMP.

Conclusion

These data suggest that Type 2 diabetes LDL could lead to increased adhesion molecule and TNF alpha cell surface shedding, and vascular plaque instability, by promoting increased expression of ADAM and MMP genes.

Total and excess bed occupancy by age, specialty and insulin use for nearly one million diabetes patients discharged from all English Acute Hospitals

To investigate total diabetes bed occupancy and prolonged inpatient length of stay (LOS) in all English Acute Hospitals, we analysed hospital episode statistics (HES) discharge data for all English Acute Hospitals over 4 years for ICD10 discharge codes of E10 ('insulin-dependent diabetes') or E11 ('non-insulin dependent diabetes') by age-band (18-60, 61-75 and >75 years) and specialties. We matched these data to control discharges without these codes. There were 943,613 diabetes discharges (6,508,668 bed days) and 10,724,414 matched controls. Mean diabetes LOS increased with age for each specialty and both E10 and E11 codes, but excess diabetes LOS decreased with age. Excess diabetes LOS was <1.0 days in most groups and highest (1.2 days) in insulin-dependent surgical patients under 60 years old, where 19.7% of bed days were excess. A similar pattern was seen for 76,570 diabetes inpatients with key cardiac or surgical conditions. Excess bed occupancy due to prolonged mean LOS accounted for 325,033 bed days under general medical and surgical codes. There were 25,525 discharges with diabetic ketoacidosis (126,495 bed days) in these 4 years. Excess diabetes LOS is concentrated in younger age groups. Excess bed occupancy due to prolonged LOS in medical and surgical inpatients is three times greater than bed occupancy due to diabetic ketoacidosis. Strategies to reduce excess diabetes bed occupancy should emphasize reducing inpatient LOS in younger inpatients.

Trends in bed occupancy for inpatients with diabetes before and after the introduction of a diabetes inpatient specialist nurse service

AIMS

To compare diabetes bed occupancy and inpatient length of stay, before and after the introduction of a dedicated diabetes inpatient specialist nurse (DISN) service in a large UK Hospital.

METHODS

We analysed bed occupancy data for medical or surgical inpatients for 6 years (1998-2004 inclusive), with a DISN service in the final 2 years. Excess bed days per diabetes patient were derived from age band, specialty, and seasonally matched data for all inpatients without diabetes. We also analysed the number of inpatients with known diabetes who did not have diabetes recorded as a discharge diagnosis.

RESULTS

There were 14,722 patients with diabetes (9.7% of all inpatients) who accounted for 101 564 occupied bed days (12.4% of total). Of these, 18 161 days (17.8%) were excess compared with matched patients without diabetes, and were concentrated in those < 75 years old. Mean excess bed days per diabetes inpatient under 60 years of age was estimated to be 1.9 days before the DISN appointment, and this was reduced to 1.2 bed days after the appointment (P = 0.03). This is equivalent to 700 bed days saved per year per 1000 inpatients with diabetes under 60 years old, with an identical saving for those aged 61-75 years (P = 0.008), a saving of 1330 diabetes bed days per year by one DISN. Excess diabetes bed occupancy was 167 excess bed days per year per 1000 patients with diabetes in the local population after the DISN appointment. One quarter of the known Type 2 diabetes population were admitted annually, but one quarter of patients had no diagnostic code for diabetes.

CONCLUSIONS

Diabetes excess bed occupancy was concentrated in patients < 75 years old, and this was reduced notably following the introduction of a DISN service.

Monocyte telomere shortening and oxidative DNA damage in type 2 diabetes

OBJECTIVE

Telomeres are DNA sequences necessary for DNA replication, which shorten at cell division at a rate related to levels of oxidative stress. Once shortened to a critical length, cells are triggered into replicative senescence. Type 2 diabetes is associated with oxidative DNA damage, and we hypothesized that telomere shortening would characterize type 2 diabetes.

RESEARCH DESIGN AND METHODS

We studied 21 male type 2 diabetic subjects (mean age 61.2 years, mean HbA(1c) 7.9%) selected to limit confounding effects on telomere length and 29 matched control subjects. Telomere length was measured in peripheral venous monocyte and T-cells (naïve and memory) by fluorescent in situ hybridization and oxidative DNA damage by flow cytometry of oxidized DNA bases. Peripheral insulin resistance (homeostasis model assessment) and high-sensitivity C-reactive protein (hsCRP) were measured.

RESULTS

Mean monocyte telomere length in the diabetic group was highly significantly lower than in control subjects (4.0 [1.1] vs. 5.5 [1.1]; P < 0.0001), without significant differences in lymphocyte telomere length. There was a trend toward increased oxidative DNA damage in all diabetes cell types examined and a significant inverse relationship between oxidative DNA damage and telomere length (r = -0.55; P = 0.018) in the diabetic group. Telomere length was unrelated to plasma CRP concentration or insulin resistance.

CONCLUSIONS

Monocyte telomere shortening in type 2 diabetes could be due to increased oxidative DNA damage to monocyte precursors during cell division. This data suggests that monocytes adhering to vascular endothelium and entering the vessel wall in type 2 diabetes are from a population with shorter telomeres and at increased risk of replicative senescence within vascular plaque.

A mobile screening programme for the cardiovascular and microvascular complications of Type 2 diabetes in primary care

The Diabetes National Service framework (NSF), and the quality payments in the new contract for UK General Practitioners, promote regular screening for diabetes complications. The new contract also includes immediate incentives to meet screening and quality targets, but it will be difficult to meet these targets in primary care. We have developed a mobile 'annual review' programme for patients with Type 2 diabetes managed solely in primary care, that screens for cardiovascular disease, hypertension, retinopathy and neuropathy at the patient's general practice, and gives written foot care, dietary advice and level 1 smoking cessation advice to all patients.

Absence of otoacoustic emissions in insulin-dependent diabetic patients: is there evidence for diabetic cochleopathy?

In order to evaluate cochlear function in Type 1 diabetes mellitus, this study analyses otoacoustic emissions (OAEs) on normal hearing subjects with diabetes and on controls. Patients with Type 1 diabetes (n=60), with a mean age of 31+/-6.23 years, mean disease duration of 17.5+/-8.9 years, and mean HbA1c of 8.1+/-1.8%, of whom 43% had signs of retinopathy and 28% had clinical signs of neuropathy, were studied. All patients underwent an OAE analysis and brainstem-evoked potentials. Fifty-eight normal volunteers were used as controls for the OAE analysis. Seventeen patients (28.3%) had no OAEs in at least one ear and 10% in both ears. The mean intensity of the response was lower in diabetic subjects [7.1+/-4.4 vs. 10.9+/-9.3 dB SPL (sound pressure level)] than in controls. The cochlear impairment was over 5 dB for the 1-kHz frequency, which is the critical level for speech understanding. These findings suggest that cochleopathy can be detected in a relatively high proportion of subjects with Type 1 diabetes in spite of a normal audiometric hearing threshold.

T cell responses to type 1 diabetes related peptides sharing homologous regions

Glutamic acid decarboxylase (GAD) 65 is a major autoantigen in type 1 diabetes. Regions of homology exist between GAD65 (residues 250-273) and the Coxsackie P2-C protein (residues 28-50) and between GAD65 (residues 506-518) and proinsulin (residues 24-36), and each of these has been reported to be a diabetes-associated T cell target. The aim of this study was to determine whether the homologous regions are shared targets of T lymphocyte reactivity in individual patients with type 1 diabetes. T cell proliferation against the corresponding peptide pairs, GAD254-276 and Coxsackie P2-C32-54 and GAD506-518 and proinsulin24-36, were measured in peripheral blood mononuclear cells from 26 patients with newly diagnosed type 1 diabetes and 24 control subjects. Responses with stimulation indices higher than 3 were found against each of the antigens tested in both patients and control subjects, and no differences were observed between groups. A strong positive correlation was found between responses to the corresponding peptide pairs GAD254-276 and Coxsackie P2-C32-54 (r=0.77, P<0.0001), and between responses to the corresponding peptide pairs GAD506-518 and proinsulin24-36 (r=0.66, P<0.0001). However, a similar correlation was also observed between responses to the noncorresponding pairs Coxsackie P2-C32-54 and proinsulin24-36 (r=0.82, P<0.0001), Coxsackie P2-C32-54 and GAD506-518 (r=0.82, P<0.0001), and GAD254-276 and proinsulin24-36 (r=0.83, P<0.0001). Strikingly, increased responses to peptides were found almost exclusively in subjects with high stimulation indices against the recall antigen tetanus toxoid, further suggesting that peripheral blood T cell responses are related to a general subject hyperreactivity. These data suggest that proliferative T cell responses to peptides containing putative autoreactive epitopes of GAD65 and proinsulin are not specific for type 1 diabetes, that correlation between T cell reactivity to peptides is not restricted to those containing homologous regions, and that non-antigen-specific factors are important determinants of in vitro measurements of T cell reactivity.

Insulin receptor antibodies inhibit insulin uptake by the liver: in vivo 123I-insulin scintigraphic scanning and in vitro characterization in autoimmune hypoglycemia

BACKGROUND

Insulin receptor antibodies can induce severe hypoglycemia or insulin resistance in rare autoimmune syndromes. In vitro properties of these antibodies occasionally explain the clinical features of the syndrome, but direct evidence of their in vivo activity is poor. We studied a 58-year-old male with rheumatoid arthritis who presented with hypoglycemic coma.

METHODS AND RESULTS

Antibodies were detected by inhibition of 125I-insulin binding to human insulin receptor-3T3 cells by the patient's serum. By immunofluorescence, they were immunoglobulin G of all four subclasses, immunoprecipitated insulin receptors from biotin-labeled cells, and triggered phosphorylation of the beta subunit of the insulin receptor. Insulin binding on the patient's red blood cells was markedly reduced. A biodistribution study after intravenous 123I-Tyr A14 insulin showed a marked inhibition of tracer uptake by the liver, reaching 10% of the injected dose (controls, mean +/- SD, 21.1 +/- 1.7%; n = 10). Time activity curves generated on the liver and on the heart were parallel, with a T1/2 of 11.5 minutes for both, suggesting that no specific uptake occurred in the liver, where tracer activity represented only the blood pool. Clearance of insulin from the blood was indeed slower than in controls and mainly occurred through the kidneys. Analysis of plasma 123I-insulin immunoreactivity and trichloroacetic acid precipitate showed that insulin degradation did not occur as in normal controls.

CONCLUSIONS

In this patient with hypoglycemic syndrome, insulin receptor antibodies with in vitro insulin-like activity are capable of blocking in vivo the access of insulin to the liver receptor compartment, as directly demonstrated by the markedly altered biodistribution of intravenously injected 123I-insulin.

Cellular and humoral immunity against cow's milk proteins in type 1 diabetes

Cow's milk beta-casein has been proposed as a candidate trigger of autoimmunity associated with type 1 diabetes. In this study, cellular and humoral immunity against beta-casein was compared to that against other major cow's milk proteins in patients with recent onset type 1 diabetes and control subjects. T cell responses were found against alpha-casein, beta-casein, beta-lactoglobulin and bovine serum albumin in both patients with type 1 diabetes (stimulation index: 0.2-22.8, n=23) and control subjects (stimulation index: 0.1-18.2, n=22), with no significant differences between groups. Twelve (52%) patients and nine (41%) control subjects had stimulation indices >3 to at least one protein, including 9 (39%) patients and 4 (18%) control subjects against beta-casein, all but one of these also having elevated responses to alpha-casein. The highest responses (stimulation index >9) were against alpha- and beta-casein in some patients and control subjects who had the HLA DR3 allele. Antibody levels against alpha-casein, beta-casein and beta-lactoglobulin were low in both patients (n=59) and control subjects (n=52). Nevertheless, significantly higher IgG binding to both alpha-casein in ELISA (P=0.02) and beta-casein using ELISA (P=0.02) and RIA (P=0.04) was observed in patients aged <15 years compared to control subjects of similar age. No relationship was found between cellular and humoral immunity against individual antigens. These data show that immune responses to cow's milk are not limited to patients with diabetes and not solely against beta-casein.

Reversal of diabetes in mice by implantation of human fibroblasts genetically engineered to release mature human insulin

Autoimmune destruction of pancreatic beta cells in type I, insulin-dependent diabetes mellitus (IDDM) results in the loss of endogenous insulin secretion, which is incompletely replaced by exogenous insulin administration. The functional restoration provided by allogeneic beta-cell transplantation is limited by adverse effects of immunosuppression. To pursue an insulin replacement therapy based on autologous, engineered human non-beta cells, we generated a retroviral vector encoding a genetically modified human proinsulin, cleavable to insulin in non-beta cells, and a human nonfunctional cell surface marker. Here we report that this vector efficiently transduced primary human cells, inducing the synthesis of a modified proinsulin that was processed and released as mature insulin. This retrovirally derived insulin displayed in vitro biological activity, specifically binding to and phosphorylation of the insulin receptor, comparable to human insulin. In vivo, the transplantation of insulin-producing fibroblasts reverted hyperglycemia in a murine model of diabetes, whereas proinsulin-producing cells were ineffective. These results support the possibility of developing insulin production machinery in human non-beta cells for gene therapy of IDDM.

Autoimmune responses to the beta cell autoantigen, insulin, and the INS VNTR-IDDM2 locus

Type 1 diabetes is associated with autoimmunity to insulin. Genetic susceptibility to type 1 diabetes is polygenic and includes the INS VNTR-IDDM2 locus which may regulate the expression of insulin in pancreas and thymus. In order to determine whether insulin autoimmunity could be attributed to a genetic susceptibility conferred by the INS VNTR-IDDM2 locus, peripheral blood T cell proliferation to human insulin and insulin autoantibodies (IAA) was measured in patients with new onset type 1 diabetes and control subjects. IAA were detected in 21 of 53 patients and in none of 25 control subjects, while T cell responses were low (stimulation index range 0.4-7.2) and similar in both groups. Both antibody and T cell responses were higher in younger subjects and IAA were more prevalent in patients with the HLA-DR4 allele. No relationship was observed between humoral and cellular responses to insulin. No association was found between the INS VNTR-IDDM2-susceptible allele and insulin autoimmunity. Increased T cell responses and IAA were found in patients with either the diabetes-susceptible or the diabetes-protective INS VNTR-IDDM2 locus genotypes, and increased T cell responses were also found in control subjects with either susceptible or protective INS VNTR-IDDM2 locus genotypes. This study confirms that primary T cell proliferative responses to insulin are low and detectable also in control subjects. The detection of T cell proliferation and autoantibodies to insulin in subjects with and without the protective INS VNTR-IDDM2 locus genotypes does not support the hypothesis of an allele-specific capacity for tolerance induction which could determine a susceptibility to develop autoimmunity against the insulin protein and subsequently diabetes.

Two-step islet autoantibody screening for risk assessment of type 1 diabetes in relatives

OBJECTIVE

To examine the performance of islet cell antibodies (ICAs) and antibodies to glutamate decarboxylase (GADA), IA-2 (IA-2 antibody [IA-2A]), and insulin (insulin autoantibody [IAA]), alone and in combination, in assessing type 1 diabetes risk within type 1 diabetic families to identify a practical and effective screening strategy for predicting type 1 diabetes in relatives.

RESEARCH DESIGN AND METHODS

ICA, GADA, IA-2A, and IAA were determined in 806 first-degree relatives participating in a prospective type 1 diabetes family study (median follow-up 6.17 years, range 0.6-8.3). The conferred risk of developing type 1 diabetes within 6 years was evaluated by Kaplan-Meier for each antibody marker, used alone or in combination.

RESULTS

ICAs were detected in 3%, GADA in 5.1%, IA-2A in 2.5%, and IAA in 3.7% of relatives; > or =1 antibody markers were detected in 10.7% of relatives and > or =2 were detected in 1.9% of relatives. The risk of type 1 diabetes at 6 years was 1.5% in relatives with only 1 marker and 24.8% in relatives with > or =2 markers. As a practical and effective strategy for type 1 diabetes risk assessment in relatives, this study indicates a first-step screening based on GADA and IA-2A measurement--which identified 6.5% of relatives, including all who developed the disease, with a 6-year type 1 diabetes risk of 9.0%--followed by a second step based on ICA and IAA measurement in relatives with either GADA or IA-2A, which identified a total of 1.9% of all relatives as having > or =2 markers, and a 6-year risk of 24.8%, including 6 of 7 who developed type 1 diabetes.

CONCLUSIONS

A two-step antibody screening, based first on GADA and IA-2A and then on ICA and IAA measurements in identified individuals, is likely to be a practical, sensitive, and effective strategy for predicting type 1 diabetes in first-degree relatives.

Comparison of a novel micro-assay for insulin autoantibodies with the conventional radiobinding assay

Measurement of insulin autoantibodies (IAA) with a novel micro radiobinding assay which requires only 20 microl of serum was compared with that in a conventional radiobinding assay which uses 600 microl of serum. IAA were measured with both assays in samples from 94 new onset insulin-dependent diabetes mellitus (IDDM) patients, 97 control subjects. and 48 first degree relatives of IDDM patients selected for having IAA in the conventional radiobinding assay. Overall, 227 (95%) of 239 samples tested were concordant. and IAA levels correlated well (r2 = 0.7) between the two assays. Discordant results were obtained in 7 new onset patients, 4 control subjects, and 1 first degree relative, and these had low IAA levels in the respective assays. Sensitivity and specificity in the new onset IDDM patients and control subjects were 69% and 98% for the micro radiobinding assay and 72% and 98% for the conventional radiobinding assay. The use of the micro radiobinding assay should greatly facilitate islet related antibody screening, particularly in children.

Imaging of the buffering effect of insulin antibodies in the autoimmune hypoglycemic syndrome

Insulin autoimmune hypoglycemia is characterized by recurrent hypoglycemia and high levels of immunoreactive insulin in the presence of insulin autoantibodies. The mechanisms inducing hypoglycemia are largely unknown. An [123I]insulin scintigraphic scanning was performed to directly demonstrate the effect of antibodies on insulin biodistribution in one patient with this syndrome both before and after treatment. The patient had insulin autoantibodies IgG3 lambda, which had a single site dissociation constant (Kd = 10(-7) mol/L, by Scatchard analysis), a very fast dissociation rate of immune complexes, and a very rapid association of [125I]insulin. Insulin receptors on red blood cells were down-regulated. The [123I]insulin scintigraphic study imaged the buffering effect of antibodies on insulin bioavailability. [123I]Insulin was not removed from the blood, and no liver or kidney uptake of the hormone occurred. The frequency and severity of hypoglycemic episodes required treatment. Insulin antibody levels decreased and [123I]insulin biodistribution improved after treatment with plasmapheresis and prednisone. Improved hormone bioavailability was further evidenced by the reduction in the hypoglycemic delay after i.v. insulin from 90 min before any treatment to 60 min after plasmapheresis and 30 min after steroid administration. Glucose tolerance was normal after treatment. Plasmapheresis followed by steroid treatment can lower the insulin antibody concentration, abolish severe hypoglycemia, and improve insulin biodistribution and glucose tolerance in insulin autoimmune hypoglycemia.

Low prevalence of islet autoantibodies in patients with gestational diabetes mellitus

OBJECTIVE

To determine the proportion of patients with gestational diabetes mellitus (GDM) who have serological characteristics typical of IDDM.

RESEARCH DESIGN AND METHODS

Islet cell antibodies (ICAs), insulin autoantibodies (IAAs), GAD65, and IA-2 antibodies were measured in 145 pregnant women with GDM, 33 with impaired glucose tolerance (IGT), and in 73 with normal glucose tolerance (NGT). ICAs were measured by indirect immunofluorescence; GAD65 and IA-2 antibodies, by a radio-ligand immunoassay incorporating 35S-labeled recombinant antigen; and IAAs, by a liquid-phase radiobinding assay.

RESULTS

The prevalences of islet autoantibodies were low and not significantly different between groups. ICAs were detected at levels ranging from 5 to 45 Juvenile Diabetes Foundation U in 14 (10%) women with GDM, 2 (6%) women with (GT, and in 4 (5%) women with NGT. IAAs were detected at levels between 3 and 4 SD above the mean in 4 (3%) women with GDM, 0 women with IGT, and in 1 (1%) woman with NGT. None had both ICAs and IAAs. Neither GAD65 nor IA-2 antibodies, which have been detected in the majority of pre-IDDM and IDDM patients, were found in NGT, IGT, or GDM patients.

CONCLUSIONS

Low-titer ICAs and IAAs are not infrequent in pregnant women, but multiple islet autoantibodies and antibodies to GAD65 or IA-2 were not found in GDM. These findings suggest that the serological characteristics of IDDM are rare in GDM.

Insulin antibodies do not preclude optimization of metabolic control in women with IDDM during pregnancy

OBJECTIVE

To evaluate whether the presence of insulin antibodies (IAs) may preclude the optimization of metabolic control during pregnancy and affect outcome in women with IDDM.

RESEARCH DESIGN AND METHODS

IAs were measured by radiobinding assay in 44 women with IDDM referred to the Diabetes and Pregnancy Outpatients' Clinic during 46 pregnancies. Age, duration of IDDM, metabolic control (HbA1c, mean pre- and postprandial capillary blood glucose, frequency of hypo- or hyperglycemia), insulin requirement at 1st and 3rd trimester of pregnancy, BM1, and weight gain were recorded. Neonatal variables such as gestational age, weight, length, and the presence at birth of either hypoglycemia, hypocalcemia, or jaundice requiring phototherapy were also considered.

RESULTS

IAs correlated positively with insulin requirement (P < 0.05) and negatively with HbA1c at term (P < 0.01). Patients with IA levels > or = 40% insulin binding (8 of 46) had a higher insulin requirement and lower preprandial capillary blood glucose at the beginning of pregnancy but not at term (P < 0.005), whereas they had lower HbA1c at term than did patients with low IA levels (P < 0.01). IA levels decreased slightly at term (P = 0.007). IA levels > or = 40% were not associated with a higher rate of hypo- or hyperglycemic episodes or with diabetic complications or thyreopathy. No correlation was found between 1A levels and any of the neonatal variables considered.

CONCLUSIONS

The presence of IAs does not preclude optimization of metabolic control during pregnancy and is compatible with a favourable outcome.

Differential immunogenetic determinants of polyclonal insulin autoimmune syndrome (Hirata's disease) and monoclonal insulin autoimmune syndrome

The insulin autoimmune syndrome (IAS), or Hirata's disease, is characterized by the combination of fasting hypoglycemia, high concentration of total serum immunoreactive insulin, and presence of autoantibodies to native human insulin in serum. Autoantibody production is classified as monoclonal or polyclonal, with the majority of IAS cases classified as polyclonal. Previously, we observed a striking association between the human leukocyte antigen (HLA) class II alleles DRB1*0406/DQA1* 0301/DQB1*0302 and Japanese IAS patients with polyclonal insulin autoantibodies (IAAs) and T-cell recognition of human insulin in the context of DRB1*0406 molecules. Because of such a strong HLA association in IAS, we performed intra- and interethnic studies on IAS-associated DRB1 alleles and searched for the critical amino acid residue(s) for IAS pathogenesis. Glutamate at position 74 in the HLA-DR4 beta 1-chain was presumed to be essential to the production of polyclonal IAA in IAS, whereas alanine at the same position of the HLA-DR beta 1-chain might be important in the production of monoclonal IAA.

In vivo metabolic effects of insulin-like growth factor-I not mediated through the insulin receptor

Patients with mutations affecting insulin receptor function may maintain some degree of metabolic control. The hypothesis has been put forth that in these patients, fuels may be metabolized through pathways (i.e. receptor activation) that become relevant in such abnormal conditions. The aim of our study was to evaluate the metabolic effects of insulin-like growth factor-I (IGF-I) in a 19-yr-old patient with homozygous mutation of the insulin receptor alpha-subunit. Her metabolic and hormonal features were marked hyperglycemia (11-33 mmol/L) and hyperinsulinemia (1000-2000 pmol/L); normal free fatty acids and lactate; low IGF-I; glycerol, alanine, and pyruvate below the normal range; and elevated beta-hydroxybutyrate. Unlike diabetic ketoacidosis, no triglyceride or protein breakdown was present, suggesting a compensatory mechanism, possibly sustained by the insulin concentration acting on IGF-I receptors. Subcutaneous administration of IGF-I (40, 80, and 120 micrograms/kg), although not affecting plasma glucose, resulted in a rapid decrease in free fatty acids and prevented the rise of beta-hydroxybutyrate levels compared to placebo. Therefore, IGF-I can exert direct metabolic effects in vivo, probably through activation of its own receptor, even at a concentration not affecting blood glucose levels. Furthermore, these findings are consistent with the hypothesis that IGF-I receptors may be activated by high insulin levels, providing lipid and protein regulation in patients with nonfunctional insulin receptors.

Heterogeneous IgG subclass distribution of islet cell antibodies

Islet cell antibodies (ICA)-IgG are the serological marker of type 1 diabetes, an organ-specific autoimmune disease. A proportion of patients also have thyro-gastric autoimmunity, implying a broader humoral autoreactivity in these cases. In order to determine whether this is also reflected within islet cell antibodies (ICA) we examined the ICA-IgG subclass distribution in type 1 diabetic patients with or without associated thyro-gastric autoantibodies. ICA-IgG subclasses were detected by two-step indirect immunofluorescence, using monoclonal antibodies against the four IgG subclasses, in sera from 51 patients with type 1 diabetes and detectable ICA; 31 had no other antibodies (group 1) and 20 had at least one associated thyroid and/or gastric autoantibody (group 2). Our results show that ICA are polyclonal and invariably IgG1. In 48% of patients with type 1 diabetes without associated thyro-gastric autoantibodies, ICA were restricted to IgG1 only. Conversely, only 10% of those with thyro-gastric antibodies had ICA-IgG1 only (P < 0.02), and a larger ICA-IgG subclass recruitment was observed in these patients (P = 0.002). These findings provide evidence of heterogeneity within ICA at the IgG subclass level, with a broader clonal recruitment within this specificity in individuals displaying features of multiple organ autoimmunity. These results support the hypothesis of heterogeneity within the pathogenetic process leading to type 1 diabetes.

Substitution of Leu for Pro-193 in the insulin receptor in a patient with a genetic form of severe insulin resistance

Mutations have been identified in the insulin receptor (IR) gene in patients who are insensitive to insulin action. We studied an extremely insulin resistant patient whose insulin binding to Epstein-Barr virus (EBV) transformed lymphocytes was severely reduced. Transmembrane signalling, evaluated as insulin receptor autophosphorylation, was normal. The patient's IR was immunoprecipitated normally by AbP6, a polyclonal antibody directed to the beta subunit. However, there was an approximately 50% decrease in the affinity of IR immunoprecipitation by a monoclonal antibody (MA-10) directed against the alpha subunit. These observations suggested that there were likely to be a mutation in the patient's insulin receptor that caused misfolding of the IR alpha subunit. Analysis of gene structure by Southern blotting experiments did not reveal any major deletion in the IR gene of the proband. Northern blot analysis showed a normal level of expression of IR gene. We applied denaturing gradient gel electrophoresis (DGGE) as well as direct sequence analysis to study the 22 exons of IR gene amplified by polymerase chain reaction (PCR) using the proband's genomic DNA as a template. We identified a new missense mutation substituting leucine (CTG) for proline (CCG) in homozygous state at codon 193 in exon 3. Both parents are heterozygous for the Leu193 mutation. The Leu193 mutation was not detected in any of 75 normal subjects (150 chromosomes), indicating that it is not a common sequence variant of the insulin receptor. In addition, during the course of screening the patient's DNA with perpendicular DGGE, we identified two previously unreported silent substitutions in exon 9.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunoelectron microscopy: a new method for detection of insulin antibodies

The aim of the present study was to set up a sensitive technical alternative to the classical procedures for detection of human insulin antibodies. We developed a method of post-embedding immunoelectron microscopy (IEM) using as the substrate fresh human pancreas, embedded in acrylic resin to maintain its antigenic structure. The antigen was insulin within the mature secretory granule. Serum samples obtained from 10 patients with insulin antibodies detected at various titers by either radio binding assay (RBA) or enzymatic immunoassay (EIA) were incubated for 2 hr at 37 degrees C at dilutions of 1:25, 1:100, 1:400, 1:1600, 1:6400, 1:25,600, and 1:102,400. The electron microscope photographs were analyzed by computerized morphometry and the number of protein A-gold-IgG complexes was calculated per micron2 of insulin granule. IEM results were compared with those obtained with EIA. The specificity of both techniques towards insulin was assessed as the difference between the signals (number of gold particles per micron2 of insulin granule in IEM or optical density > or = 0.193 in EIA) with and without excess insulin. Sensitivity was defined as the detection limit of the assay. In all the 10 sera investigated, IEM was more sensitive, with a 12- to 40-fold lower detection limit than EIA. IEM, with native insulin granules as substrate, is a specific, reproducible, and sensitive method for detection of human serum insulin antibodies. These findings also suggest IEM as a procedure potentially suitable for identifying antigen specificity of autoantibodies circulating at low concentration.

In vivo demonstration of insulin-receptor defect with 123I-labeled insulin and scintigraphic scanning in severe insulin resistance

OBJECTIVE

Insulin-receptor function in humans is usually studied in vitro on readily available cells, e.g., erythrocytes and fibroblasts. Although these cells are not metabolically important targets for insulin action, information derived from them are often taken as representative of other tissues. The aim of this study was to investigate insulin receptors in vitro on erythrocytes and in vivo on one of the main insulin-target organs, the liver.

RESEARCH DESIGN AND METHODS

A 16-yr-old girl affected by severe insulin resistance was identified. Insulin receptor binding was measured on the erythrocytes of the patient and of 6 nondiabetic volunteers. The biodistribution of 123I-labeled insulin was studied in vivo by scintigraphic scanning in the insulin-resistant patient and in 10 nondiabetic volunteers.

RESULTS

Erythrocytes of this patient displayed a markedly reduced [125I]insulin binding. In vivo 123I-insulin biodistribution was characterized by lack of hormone uptake by the liver (4 vs. 21% of the injected dose in control subjects) contrasting with intense accumulation of radioactivity in the kidneys.

CONCLUSIONS

Our studies show that defects of insulin binding can be directly demonstrated in vivo on liver receptors with a noninvasive technique with low radiotoxicity.

An unusual case of recurrent hypoglycaemia: 10-year follow up of a child with insulin auto-immunity

We report the case of a child with hypoglycaemia due to insulin auto-immunity. Insulin auto-immunity is the third most frequent cause of hypoglycaemia in Japan where the first cases were described. The child has been followed for the past 10 years with recurrence of hypoglycaemic symptoms and high titres of insulin antibodies.

Autoantibodies to glutamic acid decarboxylase (GAD) detected by an immuno-trapping enzyme activity assay: relation to insulin-dependent diabetes mellitus and islet cell antibodies

It has recently been proposed that the islet 64,000 Mr protein autoantigen (64K) of insulin-dependent diabetes mellitus (IDDM) is glutamic acid decarboxylase (GAD). We evaluated, by means of a newly developed immunotrapping enzyme activity assay (ITEAA), the prevalence of circulating GAD-autoantibodies (Ab) in a large population of IDDM patients (n = 168), blood donors (n = 87) and non-diabetic autoimmune patients (n = 40). The latter two groups were used as controls. Overall, GAD-Ab were found in 22% of IDDM patients, but in none of the two control groups (P = 0.007). These specificities were invariably associated with islet cell antibodies (ICA) (31.6% in IDDM with ICA vs 0 in IDDM without ICA, P = 0.0001), and this prevalence was higher in sera with high titer ICA (54.5% in IDDM with ICA greater than 80 JDF-units vs 22.6% of IDDM with ICA 5-80 JDF units; P = 0.002). Moreover, GAD-Ab were associated with the female sex (P = 0.002) and the concomitant presence of thyroid and/or gastric antibodies (P = 0.002). No correlation was observed between GAD-Ab and age of the patients, duration of IDDM, or associated non-organ specific antibodies. Our study indicates that GAD-Ab measured by ITEAA are: (1) detected in a proportion of IDDM patients; (2) strongly associated with ICA; (3) preferentially found in IDDM female patients with autoimmune polyendocrine serology; and (4) detected with lower frequency than that reported for 64K-Ab in IDDM.

Polymorphism of insulin antibodies in six patients with insulin-immune hypoglycaemic syndrome

Insulin antibodies in six patients with immune hypoglycaemic syndrome were studied. The antibodies displayed a higher affinity for bovine insulin in two patients, were specific for human insulin in one patient and non-species specific in the other three patients. The predominant IgG subclass of the insulin antibodies was IgG4 in two patients, IgG3 in two and IgG1 in two. In one of these, the other three subclasses were also detectable. Insulin autoantibodies of four patients were homogeneous with regard to light chains (kappa), and those of the other two contained both kappa and gamma light chains. Analysis of insulin immune complex size by fast protein liquid chromatography was possible in three patients and demonstrated immune complexes with elution profile close to that of IgG, although not exactly superimposable to the one obtained with a mouse monoclonal insulin antibody. In two patients, avidity was too low to permit chromatography of the immune complexes, and, moreover, in these two cases insulin antibodies were of the IgG3 isotype and spontaneously formed aggregates independently of insulin binding. We conclude that insulin antibodies of the insulin immune syndrome are polymorphic but different from those generated by insulin therapy.

Is quantitative assessment of insulin-antibodies and autoantibodies feasible?

Nine selected sera were studied using radioimmunoassay and enzyme linked immunosorbent assay; eight contained insulin antibodies and were from Type 1 (insulin-dependent) diabetic patients, one of whom had antibody-mediated insulin resistance, and one contained insulin-autoantibodies and was from an asymptomatic blood donor. Sera were assayed in serial dilution to assess their suitability for use as reference standards. Dilution curves were non-parallel in radioimmunoassay but were parallel in immunosorbent assay. In all sera, insulin antibodies were readily detected in both assays whereas the low avidity insulin autoantibodies were only detected by immunosorbent assay and not at all by radioimmunoassay, suggesting that the assays respond differently to antibodies of different avidity. Avidity was estimated in liquid phase from the dissociation rate of preformed complexes of antibody and 125-iodinated insulin. When high avidity antibodies are used as a reference in radioimmunoassay, lower avidity antibodies are underestimated and vice versa. In contrast, in immunosorbent assay, any serum could be used as a reference regardless of avidity; furthermore competition experiments comparing the highest avidity insulin antibodies, from the insulin-resistant patient, with the insulin autoantibodies from the asymptomatic blood donor yielded near-superimposable curves. We conclude that radioimmunoassay is selective for high avidity antibodies whereas enzyme linked immunosorbent assay is not; computer modelling of the two assays supports this conclusion. In practice immunosorbent assay can be standardized using a reference serum, whereas experimental findings and mathematical considerations preclude the use of a standard serum in radioimmunoassay.

Glycerol-insulin raises circulating insulin antibodies in type I diabetic patients treated with permanently implanted devices

The instability of insulin in the reservoirs of implantable insulin delivery devices has been a major obstacle in implementing this form of therapy. To overcome the problem of precipitation, a glycerol-insulin preparation has been used in large-scale long-term clinical trials. The aim of this study was to evaluate the stability of the glycerol-insulin solution and its effects on circulating insulin antibodies in eight type I diabetic patients who were implanted with an Infusaid pump (Infusaid Corporation, Norwood, MA) and followed for 1 year or more. Total insulin requirement did not change throughout the observation period. Plasma free insulin was higher during treatment with glycerol-insulin than with the standard insulin treatment (P less than .02). Insulin antibodies increased in all patients (P less than .05). High-performance liquid HPLC analysis of insulin samples from the pump reservoirs showed the generation of insulin modification products at a daily rate of 1.84%, reaching 40% to 50% of the total reservoir content 3 weeks after refilling; among these products, high molecular weight species accounted for about 15%. It is concluded that glycerol-insulin is not an adequate insulin preparation for use in implanted devices. Insulin deteriorated in the pump reservoirs, and insulin antibody concentration increased in the treated patients. It is believed that this antibody production is favored by circulating insulin fragments and polymers of insulin generated inside the pump reservoirs.

Advantages and pitfalls of radioimmune and enzyme linked immunosorbent assays of insulin antibodies

Human sera were tested for insulin antibodies by fluid and solid phase assays. Radioimmune titres determined with 125-I Tyr A14 insulin were not correlated with those obtained using insulin coated microplates and enzyme linked immunodetection (n = 60). Several reasons for this lack of correlation were found. Iodine substitution on the A14 residue of insulin may significantly alter the avidity of some insulin antibodies for their ligand; hence, disclosing a heretofore unsuspected pitfall for antibody determination by radioimmunoassay. Specificity for bovine insulin was easily demonstrable in fluid phase by comparing the binding of monoiodinated bovine, porcine and human insulin. By contrast, in solid phase assay, titres obtained with microplates coated with bovine or human insulin were almost equal, regardless of the serum specificity for bovine insulin. This lack of specificity of the solid phase assay is not due to denaturation or unavailability of the bovine specific epitope because: bovine specificity could be demonstrated by competitive assay, after preincubation of the serum with insulin of the different species; and, coating with crosslinked insulin dimers or oligomers instead of monomers did not unmask bovine specificity. It is concluded that radioimmune methods are best suited to study specificity but may be biased by the presence of the radioiodine label whereas solid phase assay detects low avidity antibodies with great efficiency but is less appropriate to study specificity.

Scintigraphic distribution of complexes of antiinsulin antibodies and 123I-insulin. In vivo studies in rats

Clearance of immune complexes made of antiinsulin antibodies and 123I-insulin was studied with scintillation scanning in anesthetized rats. Complexes made with purified guinea pig antiinsulin IgG2 (cytophilic isotype) were rapidly cleared by the liver whereas those made with IgG1 remained in the plasma, as did 123I-labeled IgG1 or IgG2 of control animals. Hepatic clearance of insulin-antiinsulin IgG complexes was not inhibited by either an excess of insulin or decomplementation, thereby ruling out interaction with insulin and C3b receptors. Insulin and guinea pig antiinsulin serum or its purified IgG isotypes formed large aggregates exceeding 5 IgG. Antiinsulin antibodies of diabetics, mostly IgG1 and IgG3 (cytophilic isotypes), formed complexes that either remained in plasma (small aggregates) or were cleared by the liver (large aggregates). In conclusion, clearance of insulin-antiinsulin IgG complexes is probably mediated by Fc gamma receptors on macrophages and requires cytophilic subclass composition and formation of large IgG aggregates.

The effect of alpha-latrotoxin on the neurosecretory PC12 cells differentiated by treatment with nerve growth factor

Neurosecretory PC12 cells differentiated in vitro by prolonged (at least 2 weeks) treatment with nerve growth factor were exposed to alpha-latrotoxin and studied by morphological and biochemical techniques. Cell monolayers or suspensions responded to the toxin with a prompt and massive release of neurotransmitter. The dose dependency (Km approximately 5 X 10(-10)M) and the maximum release effect (approximately 60% of the stored [3H]dopamine released within 8 min) were not appreciably different from the values found in non-differentiated PC12 cells. Moreover, the concentration dependency of the release was found to correspond closely to that of the [125I]alpha-latrotoxin binding to its specific sites (the alpha-latrotoxin receptors). The number of these receptors was over two-fold higher in differentiated than in undifferentiated cells. Since, however, differentiation implies a large increase in cell size and surface area, the receptor density (number/unit area) remained virtually unchanged. By radioautography the alpha-latrotoxin receptors were found to remain diffusely distributed at the entire surface of differentiated cells even when these were allowed to form synapses with myotubes. This situation is at variance with that demonstrated recently at the frog neuromuscular junction, where alpha-latrotoxin receptors are exclusively localized at the nerve terminal plasmalemma. Scanning and transmission electron microscopy revealed that the enlargements of neurites where dense granules are preferentially accumulated--the varicosities and terminals--underwent swelling and extensive disorganization within a few minutes after the application of alpha-latrotoxin, whereas the cell bodies and the tracts of neurites occupied primarily by microtubules were less severely affected. The greater sensitivity of varicosities and terminals with respect to the other parts of the differentiated cells, rather than the consequence of a specific addressing of the toxin to these structures, might be due to their vulnerability by toxin-induced events, such as the uncontrolled activation of ion fluxes.

Ca2+-dependent and -independent release of neurotransmitters from PC12 cells: a role for protein kinase C activation?

The intracellular mechanisms regulating the process of evoked neurotransmitter release were studied in the cloned neurosecretory cell line PC12. Various agents were employed that were known, from previous studies in other systems, to stimulate release in a manner either strictly dependent or independent of the concentration of extracellular Ca2+, [Ca2+]o. Three parameters were investigated in cells suspended in either Ca2+-containing or Ca2+-free Krebs-Ringer media: release of previously accumulated [3H]dopamine; average free cytoplasmic Ca2+ concentration, [Ca2+]i (measured by the quin2 technique); and cell ultrastructure, with special reference to the number and structure of secretion granules. The release induced by the ionophores transporting monovalent cations, X537A and monensin, occurred concomitantly with profound alterations of secretory granule structure (swelling and dissolution of the dense core). These results suggest that the effect of these drugs is due primarily to leakage of dopamine from granules to the cytoplasm and extracellular space. In contrast, the changes induced by other stimulatory drugs used concerned not the structure but the number of secretory granules, indicating that with these drugs stimulation of exocytosis is the phenomenon underlying the increased transmitter release. The release response induced by the Ca2+-ionophore ionomycin was dependent on [Ca2+]o, occurred rapidly, was concomitant with a marked rise of [Ca2+]i, and ceased after 1-2 min even though [Ca2+]i remained elevated for many minutes. 12-O-tetradecanoylphorbol, 13-acetate and diacylglycerol (both of which are known as activators of protein kinase C) induced slow responses almost completely independent of [Ca2+]o and not accompanied by changes of [Ca2+]i. Combination of an activator of protein kinase C with a low concentration of ionomycin failed to modify the [Ca2+]i rise induced by the ionophore, but elicited a marked potentiation of the release response, which was two- to fourfold larger than the sum of the responses elicited separately by either drugs. Thus, activation of protein kinase C seems to play an important role in the regulation of exocytosis in neurosecretory cells, possibly by increasing and maintaining the sensitivity to Ca2+ of the intracellular apparatus regulating granule discharge by exocytosis.

Alpha latrotoxin of black widow spider venom: an interesting neurotoxin and a tool for investigating the process of neurotransmitter release

Alpha latrotoxin, purified from the venom of the black widow spider, is a high Mr (130000) protein devoid of detectable enzymatic activity. When applied to vertebrate nerve terminals (of the central as well as peripheral nervous systems) the toxin elicits massive release of neurotransmitters by stimulating the fusion of synaptic vesicles with the presynaptic membrane (exocytosis). Among non-neuronal systems, only the neurosecretory cell line PC12 is sensitive to alpha latrotoxin; all others investigated so far are insensitive. In order to act, alpha latrotoxin requires the presence of divalent cations in the medium. Ca2+ can be substituted by other divalent cations as Sr2+, Ba2+, Mn2+, Mg2+. However, with the last two the catecholamine release response is reduced in PC12 cells and synaptosomes. A specific, high affinity receptor of alpha latrotoxin exists in preparation sensitive to the toxin. This receptor has been purified and found to be a high Mr, integral membrane protein. In the frog neuromuscular junction the receptor is localized exclusively in the presynaptic membrane. Binding of alpha latrotoxin to the receptor in a Ca2+-containing incubation medium induces membrane depolarization (insensitive to tetrodotoxin), stimulation of Ca2+ influx (insensitive to verapamil) with consequent increase in the cytoplasmic free Ca2+ concentration and stimulation of phosphoinositide breakdown. In Ca2+ free medium depolarization is maintained, but free Ca2+ concentration does not rise after toxin application. In conclusion, alpha latrotoxin seems to act through a dual mechanism. The Ca2+-independent part of this mechanism may be mediated by the activation of protein kinase C, triggered by phosphoinositide metabolism. The relevance of these findings for presynaptic physiology is discussed.