Biologic and clinical importance of proinsulin

Insulin Resistance and Bone Metabolism Markers in Women with Polycystic Ovary Syndrome: A Cross-Sectional Study on Females from the Islamic University Medical Center

Background and Objectives: polycystic ovarian syndrome (PCOS) prevails in females in the 18–40-year-old age group and varies from 5–20% depending on the demographic and diagnostic standards. It is unknown how long passes between the onset of a specific symptom and the appearance of the disease. The three most significant characteristics of PCOS include irregular menstruation, a polycystic ovarian shape found by pelvic ultrasound, and hyperandrogenism, which could possibly delay menarche. This study’s objective was to assess insulin resistance and bone bio-markers’ metabolism-involved characteristics of females with PCOS. Materials and Methods: We present a cross-sectional study carried out on 100 female patients suffering from PCOS and 100 healthy female subjects as a control living in Saudi Arabia in the Al-Madinah Al-Munawara Region between May 2021 and March 2022. The age of the studied groups ranges from 20–40 years, and patients were categorized into three groups; group I (control, n = 100), group IIa (overweight or obese females with PCOS, n = 70), and group IIb (non-obese females with PCOS, n = 30). The diagnosis of PCOS was carried out as per Rotterdam criteria as recommended for adolescent and adult subjects. All the groups were subjected to physical examination, and anthropometric measures, biochemical parameters, endocrine activity, and clinical parameters were determined. The data obtained were computerized and analyzed statistically using the SPSS program for range, mean, and standard deviation. ANOVA test with post hoc Tukey test was applied to assess the pattern and variation among the test and control groups. Results: In the present study, age, waist circumstances, systolic blood pressure, and diastolic blood pressure were reported enhanced in the PCOS over the control group. Additionally, anthropometric measures were reported slightly upregulated in group IIa over group IIb (p < 0.001). Biochemical parameters including glucose, insulin incidence, and lipids were reported higher in the PCOS over the control group, where group IIa showed slightly increased values compared to group IIb (p < 0.001). On the contrary, PTH, Ca+2, and 25(OH)D levels were reported lower in the PCOS over the control group. However, in the control groups, a slight variation was reported as higher in group IIa compared to group II. In the study, PTH and 25(OH)D were found associated with bone metabolism; a lower level of PTH and 25 (OH) D is linked with a decline in bone density. Conclusions: Lower serum levels of PINP and osteocalcin along with the 25(OH)D were associated with the PCOS compared to the control group, imposing a higher risk of the syndrome. On the contrary, an elevated level of NTx in groups IIa and IIb over the control group was associated with insulin resistance and bone metabolism.

Circulating obesity-driven biomarkers are associated with risk of clear cell renal cell carcinoma: a two-stage, case-control study

Obesity is one of modifiable risk factors for clear cell renal cell cancer (ccRCC). We aim to identify the association between obesity-driven biomarkers and ccRCC risk. This is a retrospective, two-phase, case-control study involving 682 cases and 733 controls. Obesity-driven biomarkers [gastric inhibitory polypeptide (GIP), C-peptide, insulin, resistin, adipsin, peptide YY, pancreatic polypeptide, interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), plasminogen activator inhibitor-1, monocyte chemoattractant protein 1, lipocalin2, leptin, adiponectin] were measured using the Milliplex method. Multivariate logistic regression was used to assess the associations between biomarkers and ccRCC risk. Results revealed that GIP, C-peptide, IL-6 and TNF-α levels were consistently distinct between cases and controls. These markers were significantly associated with ccRCC risk in both phases (except C-peptide). In the combined population, compared with individuals with low levels of the biomarkers, individuals with high level of GIP [odds ratio (OR) = 0.52, 95% confidence interval (CI): 0.40-0.67] had lower risk, whereas individuals with high levels of C-peptide (OR = 1.46, 95% CI: 1.15-1.87), IL-6 (OR = 2.20, 95% CI: 1.50-3.22), TNF-α (OR = 1.90, 95% CI: 1.49-2.43) had significantly higher risk. Stratified analysis showed consistent associations with ccRCC risk in most subgroups (P < 0.05). The risk score based on the IL-6, TNF-α and GIP was positively associated with ccRCC risk in a dose-response manner (P for trend = 2.18E-13). Data from The Cancer Genome Atlas indicate that insulin signaling, IL-6 signaling and TNF-α signaling were enhanced in tumors. Collectively, our study demonstrates the integrative effect of insulin resistance and inflammation in ccRCC development, which may elucidate the basis of association between obesity and carcinogenesis. Further confirmation in prospective cohort studies are warranted for clinical applications in prevention and precision medicine of ccRCC.

The Prohormone Proinsulin as a Neuroprotective Factor: Past History and Future Prospects

Proinsulin was first identified as the primary translation product of the insulin gene in Donald Steiner’s laboratory in 1967, and was the first prohormone to be isolated and sequenced. While its role as an insulin precursor has been extensively studied in the field of endocrinology, the bioactivity of the proinsulin molecule itself has received much less attention. Insulin binds to isoforms A and B of the insulin receptor (IR) with high affinity. Proinsulin, in contrast, binds with high affinity only to IR-A, which is present in the nervous system, among other tissues and elicits antiapoptotic and neuroprotective effects in the developing and postnatal nervous system. Proinsulin specifically exerts neuroprotection in the degenerating retina in mouse and rat models of retinitis pigmentosa (RP), delaying photoreceptor and vision loss after local administration in the eye or systemic (intramuscular) administration of an adeno-associated viral (AAV) vector that induces constitutive proinsulin release. AAV-mediated proinsulin expression also decreases the expression of neuroinflammation markers in the hippocampus and sustains cognitive performance in a mouse model of precocious brain senescence. We have therefore proposed that proinsulin should be considered a functionally distinct member of the insulin superfamily. Here, we briefly review the legacy of Steiner’s research, the neural expression of proinsulin, and the tissue expression patterns and functional characteristics of IR-A. We discuss the neuroprotective activity of proinsulin and its potential as a therapeutic tool in neurodegenerative conditions of the central nervous system, particularly in retinal dystrophies.

Lower Plasma Ghrelin Levels are Found in Women with Diabetes-Complicated Pregnancies

OBJECTIVE

To evaluate the associations of glycemic control and gestational age with ghrelin and proinsulin levels in cord blood and mothers' peripheral blood during pregnancy.

METHODS

This is a cross-sectional comparative study of twenty-four pregnant women with gestational diabetes (GD), 18 with type 2 diabetes mellitus (T2DM), and 36 without diabetes, as well as their neonates. Levels of proinsulin, ghrelin, and glycated hemoglobin A1c (HbA1c) were measured from maternal blood during the last week before caesarian delivery and in neonatal umbilical cord blood samples.

RESULTS

Mothers with GD and T2DM had significantly lower ghrelin levels compared to the healthy mothers (p<0.001). Maternal proinsulin was lower in women with GD than in women without diabetes (p<0.001). Proinsulin was significantly elevated in the neonates of women with GD and in women with HbA1c ≥6.5% (p<0.001). However, maternal ghrelin levels were higher (p=0.031) and neonate proinsulin levels lower in the pre-term offspring of mothers with GD (p=0.033). There was a negative correlation between HbA1c levels and birth weight (r=-0.407, p<0.001).

CONCLUSION

Ghrelin levels were lower in pregnant women with diabetes, although pre-term birth appeared to reverse this trend in GD. Proinsulin levels were also low in pregnant women with diabetes and even lower in pre-term vs. at-term births. Both ghrelin and proinsulin levels were lower in pregnant women with diabetes and HbA1c of <6.5%. Thus, ghrelin participates in the adaptation to the caloric imbalance of diabetic pregnancy and may play a similar role in pregnancy-related complications, since high ghrelin concentrations may be necessary for normal fetal development.

Novel diabetes mellitus treatment: mature canine insulin production by canine striated muscle through gene therapy

Muscle-targeted gene therapy using insulin genes has the potential to provide an inexpensive, low maintenance alternative or adjunctive treatment method for canine diabetes mellitus. A canine skeletal muscle cell line was established through primary culture, as well as through transdifferentiation of canine fibroblasts after infection with a myo-differentiation gene containing adenovirus vector. A novel mutant furin-cleavable canine preproinsulin gene insert (cppI4) was designed and created through de novo gene synthesis. Various cell lines, including the generated canine muscle cell line, were transfected with nonviral plasmids containing cppI4. Insulin and desmin immunostaining were used to prove insulin production by muscle cells and specific canine insulin ELISA to prove mature insulin secretion into the medium. The canine myoblast cultures proved positive on desmin immunostaining. All cells tolerated transfection with cppI4-containing plasmid, and double immunostaining for insulin and desmin proved present in the canine cells. Canine insulin ELISA assessment of medium of cppI4-transfected murine myoblasts and canine myoblast and fibroblast mixture proved presence of mature fully processed canine insulin, 24 and 48 h after transfection. The present study provides proof of principle that canine muscle cells can be induced to produce and secrete canine insulin on transfection with nonviral plasmid DNA containing a novel mutant canine preproinsulin gene that produces furin-cleavable canine preproinsulin. This technology could be developed to provide an alternative canine diabetes mellitus treatment option or to provide a constant source for background insulin, as well as C-peptide, alongside current treatment options.

Clinical features and morphological characterization of 10 patients with noninsulinoma pancreatogenous hypoglycaemia syndrome (NIPHS)

OBJECTIVE

Noninsulinoma pancreatogenous hypoglycaemia syndrome (NIPHS), characterized by postprandial neuroglycopaenia, negative prolonged fasts and negative perioperative localization studies for insulinoma, but positive selective arterial calcium stimulation tests and nesidioblastosis in the gradient-guided resected pancreas, is a rare hypoglycaemic disorder of undetermined aetiology. We analysed the clinical, morphological and immunohistological features to further clarify the aetiology and pathogenesis of this rare disease.

PATIENTS

Ten consecutive patients with NIPHS (nine men and one woman, aged 29-78 years) were included in the study. Six of the 10 received a gradient-guided subtotal (70%) or distal (50%) pancreatectomy. In the remaining four patients, diazoxide treatment was initiated and the precise mechanism of its action was assessed by meal tests.

RESULTS

All of the patients showed a combination of postprandial neuroglycopaenia, negative prolonged fasts (except one patient) and negative localization studies for insulinoma, but positive calcium stimulation tests and nesidioblastosis in the gradient-guided resected pancreas. Immunohistological studies of the resected pancreatic tissues revealed neither an increased rate of proliferation of beta-cells nor an abnormal synthesis and/or processing of either proinsulin or amylin. Evidence of overexpression of the two pancreatic differentiation factors, PDX-1 and Nkx-6.1, as well as the calcium sensing receptor (CaSR) was absent. Nevertheless, abnormal expression of islet neogenesis-associated protein (INGAP), a human cytokine expressed only in the presence of islet neogenesis, in ducts and/or islets, was identified in three of the five patients studied. All of the six patients who received a surgical operation were relieved of further neuroglycopaenic attacks, but one patient who received a subtotal pancreatectomy developed diabetes. In the remaining four patients who received diazoxide treatment, hypoglycaemic episodes were satisfactorily controlled with an attenuated response of beta-cell peptides to meal stimulation.

CONCLUSIONS

Our results strengthen the existence of this unique clinical hypoglycaemic syndrome from beta-cell hyperfunction as well as the value of the selective arterial calcium stimulation test in its correct diagnosis and localization. The mechanisms underlying beta-cell hyperfunction and release of insulin to calcium, however, remain poorly characterized. Nevertheless, in a subset of patients with NIPHS, there exists some, as yet undefined, pancreatic humoral/paracrine factor(s) other than proinsulin, amylin, PDX-1, Nkx-6.1 and possibly glucagon-like peptide-1 (GLP-1) that are capable of inducing the INGAP gene and, if activated, will initiate ductal proliferation and islet neogenesis. As for the treatment, we recommend that diazoxide be tried first in each patient and, should it fail, a gradient-guided subtotal or distal pancreatectomy be attempted.

Proinsulin in development: New roles for an ancient prohormone

In postnatal organisms, insulin is well known as an essential anabolic hormone responsible for maintaining glucose homeostasis. Its biosynthesis by the pancreatic beta cell has been considered a model of tissue-specific gene expression. However, proinsulin mRNA and protein have been found in embryonic stages before the formation of the pancreatic primordium, and later, in extrapancreatic tissues including the nervous system. Phylogenetic studies have also confirmed that production of insulin-like peptides antecedes the morphogenesis of a pancreas, and that these peptides contribute to normal development. In recent years, other roles for insulin distinct from its metabolic function have emerged also in vertebrates. During embryonic development, insulin acts as a survival factor and is involved in early morphogenesis. These findings are consistent with the observation that, at these stages, the proinsulin gene product remains as the precursor form, proinsulin. Independent of its low metabolic activity, proinsulin stimulates proliferation in developing neuroretina, as well as cell survival and cardiogenesis in early embryos. Insulin/proinsulin levels are finely regulated during development, since an excess of the protein interferes with correct morphogenesis and is deleterious for the embryo. This fine-tuned regulation is achieved by the expression of alternative embryonic proinsulin transcripts that have diminished translational activity.

Feasibility of Standardization of Serum C-Peptide Immunoassays with Isotope-Dilution Liquid Chromatography–Tandem Mass Spectrometry

Background: Serum C-peptide concentrations reflect pancreatic function in different clinical and diagnostic settings; however, the utility of C-peptide testing is limited by the lack of standardized commercial immunoassays. Standardization can best be done by split-sample comparison with a hierarchically higher reference measurement procedure with a set of native sera. For serum peptides, isotope-dilution liquid chromatography–mass spectrometry (ID-LC/MS) is recommended as a reference measurement procedure.

Methods: We evaluated the analytical performance characteristics of an ID-LC/tandem MS procedure for measurement of serum C-peptide after a 2-step solid-phase extraction. To investigate the feasibility of this procedure for use in standardization, we also performed a method comparison with 3 representative commercial assays.

Results: The ID-LC/tandem MS procedure showed maximum within-run, between-run, and total CVs on dedicated sera (C-peptide concentrations, 1.6 and 4.0 μg/L) of 2.1%, 2.5%, and 2.9%, respectively; an accuracy of 94.6%–104.1%; a minimum trueness of 98.1% (95% confidence interval, 96.2%–100.0%), and limits of quantification and detection of 0.15 and 0.03 μg/L, respectively. Deming linear regression analysis of the method-comparison data showed that the immunoassays correlated well with ID-MS and were specific, but lacked intercomparability and trueness. We propose that the deficiencies can be resolved by recalibration on the basis of the method comparison.

Conclusions: The ID-LC/tandem MS procedure is suitable for specific and accurate measurement of basal and stimulated serum concentrations of proinsulin C-peptide fragment 33–63 and is suitable for use in standardization of C-peptide immunoassays.

Upstream AUGs in embryonic proinsulin mRNA control its low translation level

Proinsulin is expressed prior to development of the pancreas and promotes cell survival. Here we study the mechanism affecting the translation efficiency of a specific embryonic proinsulin mRNA. This transcript shares the coding region with the pancreatic form, but presents a 32 nt extended leader region. Translation of proinsulin is markedly reduced by the presence of two upstream AUGs within the 5' extension of the embryonic mRNA. This attenuation is lost when the two upstream AUGs are mutated to AAG, leading to translational efficiency similar to that of the pancreatic mRNA. The upstream AUGs are recognized as initiator codons, because expression of upstream ORF is detectable from the embryonic transcript, but not from the mutated or the pancreatic mRNAs. Strict regulation of proinsulin biosynthesis appears to be necessary, since exogenous proinsulin added to embryos in ovo decreased apoptosis and generated abnormal developmental traits. A novel mechanism for low level proinsulin expression thus relies on upstream AUGs within a specific form of embryonic proinsulin mRNA, emphasizing its importance as a tightly regulated developmental signal.

Intra-arterial calcium stimulation test for detection of insulinomas: detection rate, responses of pancreatic peptides, and its relationship to differentiation of tumor cells

The selective intra-arterial calcium stimulation test has greatly facilitated the precise regionalization of insulinomas smaller than 2 cm, which noninvasive techniques (ultrasound [US], computed tomography [CT], magnetic resonance imaging [MRI]) often fail to localize. This study examined not only the role of the test in the localization of insulinomas, but also the responsiveness of 3 beta-cell peptides (insulin, C peptide, and proinsulin) and their relationship to the degree of differentiation of the tumor cells, using percentage decrease of both proinsulin/insulin (P/I) and proinsulin/C peptide (P/C) ratios after stimulation as indices. Ten consecutive surgically proven insulinoma patients each received an injection of calcium into the arteries supplying the pancreas after standard selective angiography and beta-cell peptide levels were measured in samples taken from the right hepatic vein before and 30, 60, 90, 120, and 180 seconds after each injection prior to operation. After surgery, the expressions of the calcium sensing receptor (CaSR) on the resected tumors were assessed by immunohistochemistry. Intra-arterial calcium stimulation with sampling either for insulin or for C peptide correctly predicted the site of insulinoma in 8 of 9 patients or in 7 of 8 patients if the 2 big malignant insulinomas were excluded; thus, the detection rate of this test was 89% and 88%, respectively. Calcium administration stimulated a marked and prompt release of insulin and C peptide simultaneously. Both peaked within 30 to 60 seconds, then declined gradually thereafter, remaining above the baseline at 180 seconds. The magnitude of increase correlated well with the corresponding percentage decrease of P/I and P/C ratios. The response of proinsulin was much less. Immunohistochemistry demonstrated variable membraneous staining for CaSR in normal pancreatic islets and in about 9% of the total normal beta cells, whereas staining in tumor cells was only minimally detectable. We conclude that selective intra-arterial calcium stimulation with hepatic venous sampling either for insulin or for C peptide is a highly sensitive method for the preoperative localization of small insulinomas. Calcium injection stimulates a brisk response of insulin, C peptide, and proinsulin simultaneously and the magnitude of increase of both insulin and C peptide appears to be correlated well with the degree of differentiation of the tumor cells. The exact mechanism by which calcium provokes the release of beta-cell peptides is less clear and whether the CaSR is involved in the mechanism of its action requires further study.

Insulin, proinsulin and insulin resistance status in relation to lipid profiles among school children in Taiwan-The Taipei Children Heart Study

PURPOSE

Evidence suggests that there may be a metabolic syndrome characterized by hyperinsulinemia or insulin resistance associated with increased cardiovascular disease risk. The purpose of this study is to evaluate insulin, proinsulin or insulin resistance to determine which is the best parameter to predict lipid profiles among children in Taiwan.

METHODS

After multi-stage sampling, we randomly included 852 school children (415 boys and 437 girls) with a mean age of 13 yr in this study. We measured insulin and intact proinsulin levels by RIA (<0.2% cross-reactivity) and estimated insulin resistance index (IRI) using the homeostatic model assessment (HOMA) method. We used standard methods to measure atherosclerotic lipid profiles including total cholesterol (CHOL), triglyceride (TG), HDL-C, apolipoprotein A (ApoA), apolipoprotein B (ApoB), and lipoprotein[a] and calculated LDL-C and TCHR (total cholesterol to HDL-C ratio) levels.

RESULTS

Girls had higher CHOL, LDL-C, ApoA and ApoB levels than boys (p < 0.001). There was no significant difference in insulin, proinsulin and IRI status between boys and girls. Among boys, insulin, proinsulin and IRI were positively correlated with TG, ApoB and TCHR and negatively related to HDL-C. Among girls, these associations were attenuated and became insignificantly for TCHR and HDL-C. After adjusting for potential confounders, IRI and insulin were still positively associated with TG and ApoB levels and negatively associated with HDL-C in boys. However, in girls, proinsulin and insulin were positively associated with TG only. Finally, in the stepwise regression analyses, IRI was a better predictor of TG, HDL-C, and ApoB than insulin or proinsulin in boys. However, in girls, proinsulin was a stronger predictor than insulin or IRI for TG and TCHR.

CONCLUSION

From this study, we found that IRI (in boys) and proinsulin (in girls) levels are generally more significant and stronger parameters than insulin for predicting lipid profiles among children in Taiwan.

Naked plasmid-mediated gene transfer to skeletal muscle ameliorates diabetes mellitus

BACKGROUND

The ability of tissues to take up naked plasmid DNA in vivo suggests an approach for reconstituting systemic metabolic deficiencies without the disadvantages of viral vectors and lipid-DNA complexes. Plasmid-mediated gene transfer into skeletal muscle was investigated as a means of providing a therapeutic source of insulin.

METHODS

Four plasmid constructs, each bearing a mouse furin cDNA transgene and rat proinsulin cDNA (modified for processing by furin) driven by four different promoters were injected into the calf muscles of male Balb/c mice. Insulin and C-peptide concentrations were measured by radio-immunoassays having minimal crossreactivity for proinsulin and partially processed proinsulin.

RESULTS

Intramuscular insulin concentrations increased by up to 3.6-fold over controls seven days after single injections of CMV, beta-actin, hsp70 and myoglobin promoter constructs. The optimal dose for most constructs was 100 micrograms plasmid DNA. Intramuscular plasmid injection into streptozotocin-induced diabetic Balb/c mice raised plasma insulin and C-peptide concentrations, and reduced hyperglycaemia. Two injections (100 micrograms plasmid DNA each) caused higher plasma insulin concentrations and significantly reduced hyperglycemia in diabetic mice than a single injection. Best results were obtained when plasmid injections preceded induction of diabetes by 14 days.

CONCLUSIONS

Skeletal muscle is a potentially useful platform for ectopic secretion of insulin using naked plasmid as a gene transfer vector. Injection at two sites 14 days before the onset of severe hyperglycemia is optimal. This approach could protect Type I diabetics from fatal ketoacidosis and enhance the action of agents that sensitize tissues to insulin in type II diabetes.

Insulinoma with hyperproinsulinemia during hypoglycemia and loss of expression of vacuolar-type H(+)-ATPase (V-ATPase) in the tumor tissue

Hypoglycemia with a low serum immunoreactive insulin (IRI) level and serum immunoreactive C-peptide (IRC) level was found in a 74-yr-old female. Although a fasting test induced hypoglycemia, the responses of IRI and IRC during the fasting test, and the results of a glucose tolerance test, glucagon test, and secretin test did not indicate the presence of an insulinoma. However, the serum proinsulin level before the fasting test was 130.5 pmol/L (N: 3.0-10.0 pmol/L), and this high level was maintained throughout the test. Soon after surgical enucleation of the tumor, the patient's blood glucose levels increased. Postoperatively, the hypoglycemic status resolved, and the serum proinsulin levels returned to normal (2.8 pmol/L). Histopathological studies revealed a typical insulinoma. Immunohistochemical studies by the recently developed method for vacuolar-type H+ (V-ATPase), which is responsible for acidification of the intracellular compartments in eukaryotic cells, showed that normal islets stained positive, but not the tumor. This finding indicates that the insulin-secretory granules in the insulinoma cells existed in a microenvironment in which V-ATPase activity had been lost. This suggests that the reduced activity of V-ATPase on the endomembrane of the insulin-secretory granules in insulinomas may result in loss of the acidic microenvironment and impaired conversion of proinsulin by converting enzymes.

Low levels of sex hormone-binding globulin and hyperproinsulinemia as markers of increased pancreatic beta-cell demand in men

Low levels of sex hormone-binding globulin (SHBG) are considered to be an indirect index of hyperinsulinemia, predicting the later onset of diabetes mellitus type 2. In the insulin resistance state and in the presence of an increased pancreatic beta-cell demand (e.g. obesity) both absolute and relative increases in proinsulin secretion occur. In the present study we investigated the correlation between SHBG and pancreatic beta-cell secretion in men with different body compositions. Eighteen young men (30.0 +/- 2.4 years) with normal glucose tolerance and body mass indexes (BMI) ranging from 22.6 to 43.2 kg/m2 were submitted to an oral glucose tolerance test (75 g) and baseline and 120-min blood samples were used to determine insulin, proinsulin and C-peptide by specific immunoassays. Baseline SHBG values were significantly correlated with baseline insulin (r = -0.58, P < 0.05), proinsulin (r = -0.47, P < 0.05), C-peptide (r = -0.55, P < 0.05) and also with proinsulin at 120 min after glucose load (r = -0.58, P < 0.05). Stepwise regression analysis revealed that proinsulin values at 120 min were the strongest predictor of SHBG (r = -0.58, P < 0.05). When subjects were divided into obese (BMI > 28 kg/m2, N = 8) and nonobese (BMI < or = 25 kg/m2, N = 10) groups, significantly lower levels of SHBG were found in the obese subjects. The obese group had significantly higher baseline proinsulin, C-peptide and 120-min proinsulin and insulin levels. For the first time using a specific assay for insulin determination, a strong inverse correlation between insulinemia and SHBG levels was confirmed. The finding of a strong negative correlation between SHBG levels and pancreatic beta-cell secretion, mainly for the 120-min post-glucose load proinsulin levels, reinforces the concept that low SHBG levels are a suitable marker of increased pancreatic beta-cell demand.

Insulin resistance with altered secretory kinetics and reduced proinsulin in cystic fibrosis patients

BACKGROUND

Impaired glucose tolerance and secondary diabetes are frequent in older patients with cystic fibrosis (CF), associated with increased frequency of infections and reduced life expectancy. Studies on the pathophysiology of islet cell secretion in CF are a prerequisite for a scientifically based therapeutic approach.

METHODS

Oral glucose tolerance tests were performed in 71 patients (14.2 +/- 0.5 years; mean +/- SE) and 56 control subjects (16.5 +/- 0.9 years). Glucose, insulin, C-peptide, and proinsulin were measured every 30 min.

RESULTS

Glucose tolerance in CF patients was classified as normal (NGT, n = 48), impaired (IGT, n = 14), or diabetic (DM, n = 9). Even in CF patients with NGT, blood glucose was significantly elevated at 30, 60, and 90 min of the test. Surprisingly, the secretory responses of insulin and C-peptide were not reduced in CF patients with IGT or DM compared with both healthy controls or CF patients with normal glucose tolerance. However, peak insulin concentration was reached at 90 min in CF-IGT or CF-DM patients compared with 30 min in controls. The ratio of glucose to insulin, an indicator of insulin resistance, increased in CF patients with progression of carbohydrate intolerance. Proinsulin was significantly reduced in all CF patients compared with controls (p < 0.001; Wilcoxon's rank sum test).

CONCLUSIONS

In CF patients with impaired glucose tolerance or diabetes, integrated insulin release is not diminished, indicating that insulin resistance is likely to contribute to hyperglycemia in CF patients with IGT or DM. Reduced proinsulin levels in CF patients are compatible either with enhanced conversion of proinsulin to insulin in compensation for reduced beta-cell mass, or enhanced clearance of proinsulin.

Development of an isotope dilution assay for precise determination of insulin, C-peptide, and proinsulin levels in non-diabetic and type II diabetic individuals with comparison to immunoassay

We describe the application of a stable isotope dilution assay (IDA) to determine precise insulin, C-peptide, and proinsulin levels in blood by extraction from serum and quantitation by mass spectrometry using analogues of each target protein labeled with stable isotopes. Insulin and C-peptide levels were also determined by immunoassay, which gave consistently higher results than by IDA, the relative difference being larger at low concentrations. Insulin, C-peptide, and proinsulin levels were all shown by IDA to be higher in type II diabetics than in non-diabetics, with mean values rising from 22 (+/- 2) to 92 (+/- 8), 335 (+/- 11) to 821 (+/- 24), and 6 (+/- 1) to 37 (+/- 3) pM, respectively. Interestingly, the ratio between IDA and immunoassay values for insulin levels increased from 1.3 in non-diabetics to 1.7 in type II diabetics. The ratio between proinsulin and insulin levels by IDA increased from 0.24 in non-diabetics to 0.36 in type II diabetics, whereas the ratio between C-peptide and insulin levels by IDA decreased from 17.6 to 10.7. This disproportionate change in protein levels between different types of individuals has implications for the metabolism of insulin in the diabetics studied (type II) and suggests that C-peptide levels are not always a reliable guide as to pancreatic insulin secretion. In addition, levels of the 33-residue C-peptide (partially trimmed form) were shown to be less than 10% that of the fully trimmed 31-residue C-peptide levels, and we tested IDA in a clinical context by two post-pancreatic graft studies. IDA was shown to give direct, positive identification of the target protein with unrivaled accuracy, avoiding many of the problems associated with present methodology for protein determination.

Gastrointestinal endocrine tumours. Insulinoma

Fundamental to establishing a diagnosis of insulinoma is first to consider the diagnosis when presented with the constellation of symptoms and signs that indicate hypoglycaemia. Prominent and most convincing are manifestations of neuroglycopenia. Although hypoglycaemia can be caused by a number of disorders, the combination of hypoglycaemia and endogenous hyperinsulinaemia is diagnostic of insulinoma. Our criteria now include a glucose level of 40 mg/dl with a concomitant insulin level of 6 microU/ml, a C-peptide level exceeding 200 pmol/l, and negative screen for sulphonlyurea. Ancillary diagnostic tests or the use of insulin surrogates may offer helpful confirmation. Localization is still evolving, but in our hands pre-operative ultrasound is the best and only pre-operative test that we obtain in the usual situation. Expertise and experience with other modalities at other institutions offer reasonable but more costly alternatives. Intraoperative ultrasonography provides significant benefit in both tumour localization and delineating important related anatomy. Insulinomas are virtually all located in the pancreas; 90% are benign, single, and are generally firmer than surrounding normal pancreas. Extensive exposure may be required to identify and remove safely the tumour. Enucleation is our preferred technique, but distal pancreatectomy for tumours in the body or tail is an excellent method as well. Pancreatoduodenectomy is rarely necessary. Complications most commonly relate to leak of pancreatic secretions, causing pseudocyst, abscess, or fistula. except in MEN 1 syndrome, excision of a benign insulinoma equates with disease cure, and patients are often extraordinarily grateful as the change in their lives may be profound.

Immunoluminometric assay (ILMA) for intact human proinsulin and its conversion intermediates

We describe an immunoluminometric assay (ILMA) for determination of intact proinsulin and its conversion intermediates. 32,33-split and 65,66-split proinsulin, in human serum. After incubation of the serum samples with the IgG fraction of a guinea pig antiserum against human insulin coated to the surface of polystyrene beads, a sandwich complex was formed using a monoclonal antibody against human C-peptide labelled with acridinium ester as second antibody, yielding a detection limit of 0.11 pmol/l. Mean proinsulin concentration in the serum of 38 healthy fasting subjects was 7.3 pmol/l (S.D. +/- 5 pmol/l, median 5 pmol/l, 95th percentile 15 pmol/l); maximum serum proinsulin after oral glucose stimulation never exceeded 40 pmol/l. Eighteen of 20 patients with confirmed insulinoma had proinsulin concentrations over 50 pmol/l (mean 261 pmol/l, S.D. +/- 248 pmol/l, median 170 pmol/l, 95th percentile 663 pmol/l); serum proinsulin in two patients with completely enucleated B-cell adenoma declined to normal values after surgery.

Autocrine/paracrine role of insulin-related growth factors in neurogenesis: local expression and effects on cell proliferation and differentiation in retina

Early neurogenesis progresses by an initial massive proliferation of neuroepithelial cells followed by a sequential differentiation of the various mature neural cell types. The regulation of these processes by growth factors is poorly understood. We intend to understand, in a well-defined biological system, the embryonic chicken retina, the role of the insulin-related growth factors in neurogenesis. We demonstrate the local presence of signaling elements together with a biological response to the factors. Neuroretina at days 6-8 of embryonic development (E6-E8) expressed proinsulin/insulin and insulin-like growth factor I (IGF-I) mRNAs as well as insulin receptor and IGF type I receptor mRNAs. In parallel with this in vivo gene expression, E5 cultured neuroretinas synthesized and released to the medium a metabolically radiolabeled immunoprecipitable insulin-related peptide. Furthermore, insulin-related immunoreactive material with a HPLC mobility close to that of proinsulin was found in the E6-E8 vitreous humor. Exogenous chicken IGF-I, human insulin, and human proinsulin added to E6 cultured neuroretinas showed relatively close potencies stimulating proliferation, as determined by [methyl-3H]thymidine incorporation, with a plateau reached at 10(-8) M. These factors also stimulated neuronal differentiation, indicated by the expression of the neuron-specific antigen G4. Thus, insulin-related growth factors, interestingly including proinsulin, are present in the developing chicken retina and appear to play an autocrine/paracrine stimulatory role in the progression of neurogenesis.

The low birth weight hypothesis as a plausible explanation for the black/white differences in hypertension, non-insulin-dependent diabetes, and end-stage renal disease

It is well known that black Americans have a higher risk for low birth weight (LBW) than white Americans. In addition, blacks are at a higher risk for hypertension (HT), non-insulin dependent diabetes mellitus (NIDDM), and end-stage renal disease (ESRD), particularly ESRD attributed to HT (ESRD-HT) and NIDDM (ESRD-NIDDM). It has been shown that LBW is associated with postpartum anatomic and functional alterations in the kidney and pancreas as well as with progressive renal damage in animals and increased risk for HT and NIDDM during adulthood in humans. Based on these empirical findings, it is here proposed that a greater risk of HT, NIDDM, and ESRD, particularly ESRD-HT and ESRD-NIDDM, in black Americans during adulthood may be partly related to their higher risk of LBW. However, LBW is proposed here as a component factor rather than a sufficient cause or a necessary factor for the development of these diseases. The ultimate contribution of LBW to the black/white disparities regarding HT, NIDDM, and ESRD may depend not only on the black/white differences in LBW but also on the race-specific prevalences of other component factors, both environmental/behavioral and genetic, that may or may not require the presence of LBW to cause each of these diseases.

Circulating proinsulin-like molecules

An improved understanding of the characteristics of proinsulin and its intermediate conversion products has resulted from the use of novel assays for distinguishing these molecules from insulin. Use of such assays may help clarify the role of insulin deficiency in non-insulin-dependent diabetes mellitus (NIDDM). Levels of proinsulin-like molecules are elevated in subjects who have NIDDM or impaired glucose tolerance. However, the observation that hyperproinsulinemia may occur in individuals without hyperglycemia suggests that elevated proinsulin levels may be a manifestation of beta-cell dysfunction rather than of increased demand on the beta cell. Although the metabolic effects of proinsulin-like molecules have yet to be elucidated, some studies indicate that the effect of these molecules on hepatocytes is greater than that on other insulin-sensitive cells. A potential therapeutic role of proinsulin in NIDDM thus has been envisioned, in that suppression of hepatic glucose output might reduce the risk of hypoglycemia caused by increased peripheral glucose uptake. Clinical study of proinsulin has been discontinued, however, owing to the finding of an association between use of human proinsulin and cardiovascular adverse events in one study. In NIDDM subjects, associations have been reported between elevated des 31,32 proinsulin concentrations and such cardiovascular risk factors as elevated blood pressure, increased serum triglyceride and total cholesterol values, and elevated plasminogen-activator inhibitor levels, suggesting a role of proinsulin in cardiovascular risk. Epidemiologic data, however, indicate that elevated levels of proinsulin-like molecules are related to low birth weight and that low birth weight is associated with increased risk of cardiovascular events, suggesting that inadequate intrauterine nutrition may be the common antecedent of augmented proinsulin levels and cardiovascular risk.

Molecular determinants of insulin action

Insulin elicits an array of biologic responses. Insulin exerts a regulatory role in almost all cells of the body and is the primary hormone responsible for signaling the storage and utilization of basic nutrients. On the molecular level, the actions of insulin are initiated by binding of insulin to the insulin receptor. Interaction of the alpha and beta subunits of the receptor results in tyrosine kinase activity, which is integral to the initiation of cascades of phosphorylation/dephosphorylation reactions that mediate a large number of the actions of insulin. Insulin-receptor substrate 1 may be central to phosphorylation reactions through a role in serine and threonine kinase activity. Insulin action may also involve the generation of low-molecular-weight mediators capable of modulating intracellular enzymes. The regulation of glucose transport is a primary feature of the physiologic role of insulin and is performed by a family of glucose-transporter proteins with different characteristics. One mechanism by which insulin exerts its effect on glucose transport is the stimulation of the translocation of the glucose transporter to the plasma membrane. Degradation of insulin occurs through diverse mechanisms at numerous sites in the body. Reversal of the insulin signal at the cellular level may be accomplished by a class of enzymes termed phosphotyrosine phosphatases, which may play a role in certain pathophysiologic states. Important roles for insulin-receptor kinase, glucose transporters, insulin-receptor substrate 1, and various intracellular enzymes in the actions of insulin have been demonstrated; nonetheless, the formulation of potential therapeutic strategies directed at particular stages of the insulin action cascade will require further elucidation of its components.

Generation and characterization of an antiserum directed against neurohypophyseal prohormones

Abstract An antiserum to neurohypophyseal prohormones was generated by immunization of rabbits with a synthetic peptide fragment bridging the prohormone cleavage site between the vasopressin (AVP) and human AVP-neurophysin sequences of pro-pressophysin. Polyclonal antibodies directed against this peptide cross-reacted with intact human pro-pressophysin (ED(50) of 260fmol), but not with either of the final products of enzymatic processing, AVP and human AVP-neurophysin. Gel electrophoresis and Western immunoblotting of pituitary or hypothalamic extracts from multiple species including mouse, cow and man identified a protein band of molecular weight consistent with intact pro-pressophysin; in hypothalamic extracts from normally-hydrated rats no protein bands were stained, but in extracts from Brattleboro rats a faint band in the area of pro-oxyphysin was identified. Immunohistochemical studies using the antiserum demonstrated the presence of only very small amounts of immunoreactive prohormone in a few widely scattered cells in the hypothalami of normally-hydrated rats. However, after 5 days of solute loading with 2% NaCl as drinking solution, staining for intact prohormone was prominent in the supraoptic and paraventricular nuclei of the hypothalamus. Combined immunoperoxidase-immunofluorescence labeling for prohormone and either AVP-neurophysin or oxytocin-neurophysin revealed prohormone staining in both types of magnocellular neurons in rat hypothalami. These studies suggest that during states of accelerated synthesis and secretion of neurohypophyseal hormones some accumulation of intact prohormone occurs in both AVP and oxytocin magnocellular neurons.

Demonstration of an endocrine signaling circuit for insulin in the sponge Geodia cydonium

The existence of an insulin-mediated cell-to-cell signaling in the sponge Geodia cydonium is demonstrated in this study by molecular biological and immunological techniques. The sequence of a sponge cDNA clone encoding preproinsulin was analyzed for the first time and determined to comprise a high homology to human preproinsulin (60-80% homology). The predicted polypeptide of preproinsulin from sponge contains two disulfide bridges which link the A- to the B-chain. The intra-A chain disulfide bridge is absent. Applying immunological and electron microscopical techniques it is shown that insulin is produced in specialized cells (spherulous cells). Experimental evidence is presented which indicates that the sponge preproinsulin (predicted Mr 11,850) is processed to insulin (Mr 5600; B-chain, Mr 3700 and A-chain, Mr 1900). Plasma membranes of sponge cells are shown to be provided with an insulin-binding receptor composed of two molecules (Mr 104,000 and Mr 98,000). Heterologous insulin (from bovine pancreas) was found to stimulate gene expression in G. cydonium cells. It is concluded that sponges are provided with an endocrine signaling circuit: signaling cells (spherulous cells), hormone (insulin), and hormone receptor bearing target cells which respond to the hormone stimulus.

Insulin-resistant diabetes due to a point mutation that prevents insulin proreceptor processing

A point mutation in the human insulin receptor gene in a patient with type A insulin resistance alters the amino acid sequence within the tetrabasic processing site of the proreceptor molecule from Arg-Lys-Arg-Arg to Arg-Lys-Arg-Ser. Epstein-Barr virus-transformed lymphocytes from this patient synthesize an insulin receptor precursor that is normally glycosylated and inserted into the plasma membrane but is not cleaved to mature alpha and beta subunits. Insulin binding to these cells is severely reduced but can be increased about fivefold by gentle treatment with trypsin, accompanied by the appearance of normal alpha subunits. These results indicate that proteolysis of the proreceptor is necessary for its normal full insulin-binding sensitivity and signal-transducing activity and that a cellular protease that is more stringent in its specificity than trypsin is required to process the receptor precursor.

Secretion of N-terminal fragment of gamma-human atrial natriuretic polypeptide

To elucidate the posttranslational processing of gamma-human atrial natriuretic polypeptide (human atrial natriuretic factor-[1-126]), which is a prohormone of alpha-human atrial natriuretic polypeptide (human atrial natriuretic factor-[99-126]), and the secretion of gamma-human atrial natriuretic polypeptide-derived peptides from the heart, we established a radioimmunoassay specific for the N-terminal sequence of gamma-human atrial natriuretic polypeptide, gamma-human atrial natriuretic polypeptide-(1-25), as well as a radioimmunoassay for alpha-human atrial natriuretic polypeptide. With the aid of the radioimmunoassays for gamma-human atrial natriuretic polypeptide-(1-25) and for alpha-human atrial natriuretic polypeptide, we detected 290 +/- 35.6 pg/ml of gamma-human atrial natriuretic polypeptide-(1-25)-like immunoreactivity in plasma from healthy humans, while the simultaneously determined plasma alpha-human atrial natriuretic polypeptide-like immunoreactivity level was 20.9 +/- 2.8 pg/ml. Correlation between the two values was significant. High performance gel permeation chromatographic analysis revealed that the plasma gamma-human atrial natriuretic polypeptide-(1-25)-like immunoreactivity was composed of a component (molecular weight, 10,000) without alpha-human atrial natriuretic polypeptide-like immunoreactivity, while the plasma alpha-human atrial natriuretic polypeptide-like immunoreactivity was composed of alpha-human atrial natriuretic polypeptide with a molecular weight of 3000. In patients with heart diseases, the plasma gamma-human atrial natriuretic polypeptide-(1-25)-like immunoreactivity level showed a concomitant and graded increase, with the plasma alpha-human atrial natriuretic polypeptide-like immunoreactivity level in agreement with the severity of the disease. There were significant positive correlations between the two immunoreactivity levels and right or left atrial pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Insulin Wakayama: familial mutant insulin syndrome in Japan

We describe a family from Japan displaying the mutant insulin syndrome with hyperinsulinaemia and an increased insulin: C-peptide molar ratio. Serum insulin isolated from several family members showed reduced in vitro biological activity, and analysis by high performance liquid chromatography revealed a peak co-eluting with human insulin and a second species of increased hydrophobicity co-migrating with the previously reported Insulin Wakayama. The insulin genes from the propositus were cloned and sequenced, revealing one normal allele; the second allele, encoding a leucine for valine amino acid substitution at position 3 of the insulin A chain, was similar to that previously described for Insulin Wakayama. Synthesized [LeuA3] insulin showed 0.14% of receptor binding activity on rat adipocytes and a 10-fold prolonged half-life in a somatostatin-infused dog compared with human insulin. The finding of the same mutant gene in two unrelated Japanese families suggests that Insulin Wakayama may be discovered in additional Japanese families with hyperinsulinaemia and/or diabetes.

Basal and glucose- and arginine-stimulated serum concentrations of insulin, C-peptide, and glucagon in hyperthyroid patients

The effect of oral glucose and arginine infusion on plasma glucose, glucagon, serum insulin, and C-peptide concentrations was evaluated in 16 patients with hyperthyroid Graves' disease and in ten euthyroid age- and sex-matched normal subjects. Basal plasma glucose concentrations were significantly higher in the hyperthyroid patients, but the plasma glucose response following glucose and arginine administration was similar in the two groups. The insulin response was similar in the hyperthyroid and normal subjects after glucose administration and significantly lower during arginine infusion in the hyperthyroid patients. The serum C-peptide response to both glucose and arginine administration was markedly blunted in the hyperthyroid patients, and the plasma glucagon response to arginine infusion was decreased. These results suggest that pancreatic beta and alpha cell secretory function is impaired in hyperthyroidism as assessed by C-peptide and glucagon secretion following oral glucose administration and arginine infusion. The apparent discrepancy between C-peptide and insulin secretion in the hyperthyroid patients following glucose administration might be due to diminished hepatic extraction of insulin or enhanced metabolism of C-peptide.

Diabetes due to secretion of a structurally abnormal insulin (insulin Wakayama). Clinical and functional characteristics of [LeuA3] insulin

We have identified a non-insulin-dependent diabetic patient with fasting hyperinsulinemia (90 microU/ml), an elevated insulin:C-peptide molar ratio (1.68; normal, 0.05-0.20), normal insulin counterregulatory hormone levels, and an adequate response to exogenously administered insulin. Insulin-binding antibodies were absent from serum, erythrocyte insulin receptor binding was normal, and greater than 90% of circulating immunoreactive insulin coeluted with 125I-labeled insulin on gel filtration. The patient's insulin diluted in parallel with a human standard in the insulin radioimmunoassay, confirming close molecular similarity. The patient's insulin was purified from serum and shown to possess both reduced binding and ability to stimulate glucose uptake and oxidation in vitro. Analysis of the patient's insulin by high-performance liquid chromatography (HPLC) revealed two products: 7.3% of insulin immunoreactivity coeluted with the human standard, while the remaining 92.7% eluted as a single peak with increased hydrophobicity. Family studies confirmed the presence of hyperinsulinemia in four of five relatives in three generations, with secretion of an abnormal insulin documented by HPLC in the three tested. Leukocyte DNA was harvested from the propositus and the insulin gene cloned. One allele was normal, but the other displayed a thymine for guanine substitution at nucleotide position 1298 from the putative cap site, resulting in a leucine for valine substitution at position 3 of the insulin A chain. Insulin Wakayama is therefore identified as [LeuA3] insulin.

Rat platelets activate high molecular weight atrial natriuretic peptides in vitro

Evidence suggests that the more biologically active low molecular weight forms (less than 10,000) of rat atrial natriuretic peptides are proteolytically derived from a less active precursor of higher molecular weight. Conversion and activation could occur within the myocyte as well as during circulation. The present study found that in vitro rat blood and platelets were capable of converting the high molecular weight atrial natriuretic peptides (greater than 10,000) to low molecular weight atrial natriuretic peptides within minutes and that enhanced biological activity attended the conversion. Rat high molecular weight peptides were partially purified by gel filtration, lyophilized, and reconstituted in Krebs-Ringer bicarbonate buffer. One milliliter of fresh rat blood was incubated with the high molecular weight peptides at 37 degrees C for 2 minutes. After centrifugation, the supernatant was fractionated on Sephadex G-75. Natriuretic activity was determined by bioassay in anesthetized rats. In contrast to the results following incubation of high molecular weight peptides in Krebs-Ringer bicarbonate buffer alone, which showed that 95% of the natriuretic activity remained in the high molecular weight peptide region, the natriuretic activity of the blood-treated high molecular weight peptides eluted almost exclusively in the low molecular weight peptide region, which indicates conversion. Blood was separated into plasma, erythrocytes, lymphocytes, and platelets. Conversion of high to low molecular weight peptides occurred only after incubation with platelets. Compared with control high molecular weight peptides, rat platelet-treated high molecular weight peptides had significantly greater activity in relaxing histamine-contracted rabbit aortic smooth muscle (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Biochemical and clinical implications of proinsulin conversion intermediates

Since a complete map of insulin-related peptides in humans requires consideration of proinsulin, Arg32/Glu33-split proinsulin, Arg65/Gly66-split proinsulin, des-Arg31,Arg32-proinsulin, des-Lys64, Arg65-proinsulin, and insulin, we applied high performance liquid chromatography coupled with radioimmunoassay to investigate the formation of proinsulin conversion intermediates in vitro and in vivo. Kinetic analysis of proinsulin processing by a mixture of trypsin and carboxypeptidase B (to stimulate in vivo processes) revealed (a) a rapid decline in proinsulin concommitant with formation of conversion intermediates, (b) formation of des-Arg31, Arg32-proinsulin and des-Lys64,Arg65-proinsulin in the ratio 3.3:1 at steady state, and (c) complete conversion of the precursor to insulin during extended incubation. Studies on normal human pancreas identified a similar ratio of des-Arg31,Arg32-proinsulin to des-Lys64,Arg65-proinsulin (approximately 3:1), whereas two insulinomas contained sizable amounts of des-Arg31,Arg32-proinsulin, but barely detectable amounts of des-Lys64,Arg65-proinsulin. None of the tissues contained measurable quantities of Arg32/Glu33- or Arg65/Gly66-split proinsulin. Analysis of plasma from three diabetic subjects managed by the intravenous infusion of human proinsulin revealed less than 1% processing of the circulating precursor to conversion intermediates and no processing of the precursor to human insulin. Nevertheless, analysis of plasma from the same subjects managed by the subcutaneous infusion of proinsulin revealed 4-11% processing of the precursor to intermediates that had the properties of des-Arg31,Arg32-proinsulin and Arg65/Gly66-split proinsulin. We conclude that (a) processing of proinsulin to insulin in vivo as in vitro likely occurs by preferential cleavage at the Arg32-Glu33 peptide bond in proinsulin, (b) proinsulin is inefficiently processed in the vascular compartment, and (c) subcutaneous administration of the precursor can result in the formation of conversion intermediates with the potential for contributing to biological activity.

Hypoglycemia: causes, neurological manifestations, and outcome

During a 12-month prospective study there were 125 visits to the Harlem Hospital Emergency Room for symptomatic hypoglycemia. Sixty-five patients had obtundation, stupor, or coma; 38 had confusion or bizarre behavior; 10 were dizzy or tremulous; 9 had had seizures; and 3 had suffered sudden hemiparesis. Diabetes mellitus, alcoholism, and sepsis, alone or in combination, accounted for 90% of predisposing conditions; others included fasting, terminal cancer, gastroenteritis, insulin abuse, and myxedema. Average blood glucose levels were lower among comatose than among obtunded patients, but overlap was considerable, and overall there was little correlation among cause, blood glucose levels, and symptoms. Although mortality was 11%, only one death was attributable to hypoglycemia per se, and only four survivors had focal neurological residua.