Posttranslational processing of secretory component in the rat jejunum by a brush border metalloprotease.

Secretory component (SC) is a glycoprotein that mediates the transcellular transport of polymeric immunoglobulins into external secretions. SC is synthesized and inserted into the plasma membrane of epithelial cells and hepatocytes as a transmembrane protein, where it serves as a receptor for polymeric immunoglobulins. SC is posttranslationally cleaved to a soluble protein before secretion into external fluids. In the rat jejunum, we observed that the molecular weights of both the major membrane and soluble forms of SC were 10,000-20,000 smaller than the comparable hepatic forms of the glycoprotein. We therefore set out to determine the reason for the differences in size of SC between these two tissues. The smaller size of jejunal SC was not due to the action of pancreatic proteases or differential glycosylation but was due to proteolysis by a jejunal brush border protease. The protease was characterized as a metalloprotease, with a pH optimum of approximately 5. It is present in jejunal, ileal, and renal tubular brush borders as an integral membrane constituent. When the protease was inhibited in vivo, conversion of jejunal secretory component to the smaller size was partially prevented. Thus, in the rat jejunum, SC undergoes two posttranslational proteolytic events: conversion of membrane secretory component to the soluble form and conversion of soluble SC to a smaller size by a previously undescribed brush border protease.

Paraneoplastic myopathy: response to intravenous immunoglobulin.

Necrotizing myopathy is an unusual and severe form of paraneoplastic myopathy in which inflammation is minimal or absent. We report two cases of necrotizing myopathy which demonstrated significant response to intravenous immunoglobulin (IVIG) (one in spite of tumor progression). A third case represents the first association of anti-signal recognition particle (anti-SRP) syndrome with large-cell lung cancer. These cases highlight the role of histopathologic diagnosis in directing the treatment of paraneoplastic myopathy, and the role for IVIG in treatment of the syndrome.

Insulin-like growth factor I receptor prevents apoptosis and enhances neuroblastoma tumorigenesis.

Autocrine stimulation of the type I insulin-like growth factor receptor (IGF-IR) by IGF-II is one mechanism that allows cancer cells to maintain unregulated growth and to resist programmed cell death (PCD). SH-SY5Y and SHEP cells are cloned human neuroblastoma (NBL) lines originating from a single primary tumor. SH-SY5Y cells, which express abundant cell surface IGF-IR and produce IGF-II, exhibit serum independent growth and resist PCD due to hypoxia and hyperosmolar conditions. In contrast, SHEP cells, which produce no IGF-II and express five-fold fewer IGF-IRs, die in serum-free media or following exposure to metabolic stressors. To better understand the roles of IGF-IR and its ligand, IGF-II, in NBL carcinogenesis, we stably transfected SHEP cells with either IGF-II or IGF-IR. Unregulated expression of IGF-II did not alter the growth characteristics of SHEP/human IGF-II transfectants. In contrast, overexpression of IGF-IR allowed SHEP/IGF-IR transfectants to survive in media supplemented only by IGF-II. IGF-IR abundance correlated in a graded fashion with resistance to PCD in response to three different death-inducing paradigms: mitogen withdrawal, hyperosmolar metabolic stress, and treatment with etoposide. Our results suggest that adjuvant therapy aimed at reducing IGF-IR abundance may enhance chemotherapy-coupled apoptosis in the treatment of NBL.

Increased prevalence of impaired glucose tolerance in patients with painful sensory neuropathy.

OBJECTIVE: To characterize a cohort of patients with neuropathy and impaired glucose tolerance (IGT) but no other identifiable cause of neuropathy. Of patients with diabetes, 10% have peripheral neuropathy at the time of their diagnosis, suggesting that axonal injury may occur early in the course of glucose intolerance. The American Diabetes Association (ADA) revised diagnostic criteria to recognize IGT (a serum glucose between 140 and 200 mg/dl in a 2-h oral glucose tolerance test [OGTT]) as a risk factor for cardiovascular disease independent of development of diabetes. RESEARCH DESIGN AND METHODS: Using revised ADA criteria for diabetes and IGT, we prospectively evaluated 107 sequential patients with idiopathic neuropathy. RESULTS: A total of 13 of the 107 patients had diabetes, whereas 36 (34%) had IGT, nearly three times the prevalence in age-matched control subjects (P < 0.01). OGTT was often elevated, whereas both fasting plasma glucose and HbA(1c) were normal. Comparing patients with diabetes, IGT, or normal OGTT, age and BMI were similar. However, painful sensory symptoms were more common in patients with IGT and diabetes, and family history of neuropathy was significantly more common in normoglycemic patients. Electrodiagnostic findings of axonal injury were less severe in patients with IGT and were more likely to be confined to sensory fibers than in patients with diabetes. CONCLUSIONS: Our results suggest that IGT may cause or contribute to small-fiber neuropathy, which is similar in phenotype to the painful sensory neuropathy commonly encountered in diabetes. Two-hour OGTT is more sensitive than other measures of glucose handling in screening these patients.

Dexamethasone inhibits insulin-like growth factor signaling and potentiates myoblast apoptosis.

In the critically ill, glucocorticoids induce myopathy, combining profound protein catabolism and mild myotubular death. Insulin-like growth factors (IGFs) inhibit muscle catabolism through activation of phosphatidylinositol 3-kinase (PI3K). Using rat L6 myoblasts, we show that IGF-I also acts through PI3K to inhibit apoptosis induced by hyperosmolar metabolic stress with 300 mM mannitol. We find that the glucocorticoid dexamethasone inhibits this antiapoptotic effect of IGF-I by impairing PI3K signaling. Dexamethasone induces overexpression of the PI3K subunit p85alpha, which, in turn, competes with the complete PI3K heterodimer for binding at insulin receptor substrate-1, inhibiting PI3K activation. Dexamethasone blocks IGF-I-induced phosphorylation of Akt, a PI3K-dependent process. Increased cellular p85alpha abundance, induced by either 10 microM dexamethasone or transient transfection with a plasmid coding for p85alpha, significantly inhibits IGF-I rescue from apoptosis induced by mannitol, as indicated by both loss of cell viability and increased activity of caspase-3 by fluorogenic assay. Conversely, constitutively active PI3K inhibits death induced by mannitol, even in the presence of dexamethasone. These findings may have particular relevance in the pathogenesis of acute steroid myopathy in critical illness, in which catabolic glucocorticoid effects combine with acute metabolic stressors, including sepsis, fasting, and chemical denervation.

Epidermal nerve innervation in impaired glucose tolerance and diabetes-associated neuropathy.

The authors describe skin biopsy findings in patients with peripheral neuropathy associated with diabetes and impaired glucose tolerance (IGT). Six patients with IGT, eight with early diabetes-associated neuropathy, and five controls were recruited. Most subjects underwent nerve conduction studies (NCS) and quantitative sensory tests (QST). Skin biopsy was abnormal in all neuropathy subjects and correlated poorly with NCS. Neuropathy associated with IGT primarily affects small fibers and is similar to early diabetes-associated neuropathy.

The use of "clinic room" presentation as an educational tool in the ambulatory care setting.

OBJECTIVE: To evaluate the utility of "clinic room" case presentation in the ambulatory care setting. BACKGROUND: Neurology is increasingly an outpatient specialty. The transition from ward to clinic presents challenges for student and resident education. Interaction between attending physician and trainee is limited by busy patient schedules. New educational strategies must be developed to address the particular challenges of the outpatient clinic. One strategy to increase the quality and length of attending-trainee interaction is case presentation in the patient's presence. METHODS: The authors randomized 100 patients seen in an academic neuromuscular clinic to presentation in a conference room or clinic room. In the latter, all interaction between the trainee and attending occurred in the patient's presence. The attending recorded the time spent with the trainee and patient. The patient was asked to complete a survey and provide certain demographic information. RESULTS: The two groups were similar demographically. Time spent by the attending physician was similar between the two settings. Although there was no difference in patient satisfaction, those randomized to clinic room presentation were significantly more likely (p < 0.002) to feel their questions were answered adequately. There were trends toward these patients feeling less embarrassed, feeling that they were treated respectfully, and feeling that adequate time was spent with them. CONCLUSIONS: Although clinic room presentation does not save attending time, it allows for a more dynamic and intensive interaction among teacher, student, and patient.

Changes in excitability of motor cortical circuitry in primary restless legs syndrome.

OBJECTIVE: To investigate the excitability of segmental and suprasegmental systems in patients with primary restless legs syndrome (pRLS) by measuring the cortical silent period (C-SP) and the peripheral silent period (P-SP). BACKGROUND: There is some evidence that RLS may be the motor manifestation of normal CNS periodicity that becomes disinhibited under certain conditions. The mechanism of this disinhibition is unclear. DESIGN/METHODS: Ten patients with pRLS and 10 normal age-matched subjects were studied. The mixed nerve P-SP produced by electrical stimulation of the median and common peroneal nerves was recorded during maximal contraction of the abductor pollicis brevis (APB) and tibialis anterior (TA) muscles. The C-SP produced by a single magnetic shock to motor cortex at 150% of resting threshold was also measured during maximal contraction of the APB and TA muscles. The average of 5 to 10 trials at each site was obtained and compared using Student's t-test. RESULTS: Resting central motor threshold was not significantly different between pRLS patients and the control group. The average duration of the C-SP was shorter in the APB (74.5+/-37.7 versus 129.56+/-35.95 msec, p<0.05) and TA (66.81+/-25.63 versus 136.1+/-40.35 msec, p<0.05) in patients with pRLS. The P-SP duration, however, was not significantly different between two groups in either limb. CONCLUSION: The supraspinal inhibitory system is impaired in pRLS.

Effects of serum and insulin-like growth factors on human neuroblastoma cell growth.

Insulin-like growth factors (IGF-I and IGF-II) are mitogenic polypeptides expressed in both developing and adult tissues. To examine the effects of IGFs on neuronal growth, we used SH-SY5Y neuroblastoma cells as an in vitro model of nervous system development. In the current study, we found that either IGF-I (0.1 to 10 nM), insulin (0.1 to 5 micrograms/ml) or calf serum (0.1 to 3%) increased SH-SY5Y proliferation over a 3 day period in a dose dependent manner. In each case, treatment with anti-IGF-I receptor antibodies blocked cell proliferation. IGF-II mRNA levels correlated with SH-SY5Y cell density; subconfluent cells expressed high levels of IGF-II mRNA while low levels of IGF-II mRNA were present in confluent cells. Similarly, serum deprivation increased IGF-I receptor mRNA by 4-fold. Collectively, these results support the concept that an IGF/IGF-I receptor system at least partially mediates SH-SY5Y cell proliferation and suggests the importance of IGFs in regulating neuronal growth.

IGF receptor function and regulation in autocrine human neuroblastoma cell growth.

Insulin-like growth factor-II (IGF-II) and its receptors (type I and II IGF receptors) are expressed in the nervous system in a tissue and developmentally specific manner. We have previously shown that SH-SY5Y human neuroblastoma cells synthesize and secrete high levels of IGF-II, and respond to it with increased neuritic outgrowth, DNA synthesis, and cell proliferation. SH-SY5Y cells also produce type I IGF and IGF-II/M6P receptors; however, it is not known whether these receptors mediate the observed growth promoting effects of IGF-II. In this study, we assayed the role of type I IGF receptor and IGF-II/M6P receptor expression in mediating autocrine IGF-II induced growth. Using anti-receptor antibodies, we found that IGF-II stimulates cell proliferation via the type I IGF receptor but not via the IGF-II/M6P receptor. By Northern analysis, we detected increased mRNA expression of both receptors, with more dramatic changes in type I IGF receptor expression. Collectively, our results indicate a role for the type I IGF receptor in mediating IGF-II induced autocrine neuroblastoma cell growth.

Measures of small-fiber neuropathy in HIV infection.

INTRODUCTION: Noninvasive methods are needed to detect distal sensory polyneuropathy in HIV-infected persons on antiretroviral therapy (ART). METHODS: Quantitative sudomotor axon reflex test (QSART) and Utah Early Neuropathy Scale (UENS), small-fiber sensitive measures, were assessed in subjects with and without clinical neuropathy. Pain was assessed by visual analog scale (VAS). RESULTS: Twenty-two subjects had symptoms and signs of neuropathy, 19 had neither, and all were receiving ART. Median sweat volume (µL) was lower at all testing sites in those with neuropathy compared to those without (p<0.01 for all). UENS and VAS (mm) were higher in neuropathy subjects (p<0.05 for each). Lower sweat volume at all sites correlated with higher pin UENS subscore, total UENS, and VAS (p<0.05 for all). In multivariable analyses adjusting for age, CD4⁺ T cells, sex, and use of "d-drug" ART, QSART and UENS remained associated (p=0.003). CONCLUSION: QSART and UENS have not been previously studied in this patient population and may identify small-fiber neuropathy in HIV-infected, ART-treated persons.

Assessing autonomic dysfunction in early diabetic neuropathy: the Survey of Autonomic Symptoms.

OBJECTIVE: Autonomic symptoms may occur frequently in diabetic and other neuropathies. There is a need to develop a simple instrument to measure autonomic symptoms in subjects with neuropathy and to test the validity of the instrument. METHODS: The Survey of Autonomic Symptoms (SAS) consists of 11 items in women and 12 in men. Each item is rated by an impact score ranging from 1 (least severe) to 5 (most severe). The SAS was tested in observational studies and compared to a previously validated autonomic scale, the Autonomic Symptom Profile (ASP), and to a series of autonomic tests. RESULTS: The SAS was tested in 30 healthy controls and 62 subjects with neuropathy and impaired glucose tolerance or newly diagnosed diabetes. An increased SAS score was associated with the previously validated ASP (rank order correlation=0.68; p<0.0001) and with quantitative measures of autonomic function: a reduced quantitative sudomotor axon reflex test sweat volume (0.31; p<0.05) and an abnormal 30:15 ratio (0.53; p<0.01). The SAS shows a high sensitivity and specificity (area under the receiver operating characteristic curve 0.828) that compares favorably with the ASP. The SAS scale domains had a good internal consistency and reliability (Cronbach α=0.76). The SAS symptom score was increased in neuropathy (95% confidence interval [CI] 2.99-4.14) compared to control (95% CI 0.58-1.69; p<0.0001) subjects. CONCLUSIONS: The SAS is a new, valid, easily administered instrument to measure autonomic symptoms in early diabetic neuropathy and would be of value in assessing neuropathic autonomic symptoms in clinical trials and epidemiologic studies.

Insulin-like growth factor-I in muscle metabolism and myotherapies.

The critical anabolic and trophic role of signaling by insulin-like growth factors (IGF) I and II via the type-I IGF receptor (IGF-IR) is reviewed throughout the life of skeletal myocytes. The proliferative effects of IGF-IR stimulation, both during embryogenesis and during satellite cell proliferation following denervation or muscle injury, are mediated primarily through activation of mitogen-activated protein kinases. Signaling through phosphatidylinositol 3-kinase is essential to muscle protein synthesis and glucose uptake and may contribute to the observed resilience of mature muscle to programmed cell death. Degeneration or inhibition of the GH--IGF-I axis by aging, cachexia, sepsis, diabetes, drugs, and disuse all enhance muscle catabolism, and opposition of these effects by IGF-I may form the basis of effective myotherapy.

Type I insulin-like growth factor receptor activation regulates apoptotic proteins.

Activation of the type I insulin-like growth factor receptor (IGF-IR) blocks osmotic mediated programmed cell death (PCD) in neurons. We speculated that IGF-IR activation could afford neuroprotection either by effecting the negative regulators of the death pathway, Bcl-2 and Bcl-xL, or by altering activity of the ced-3/ICE-like proteases. Here we report that osmotic stress decreases total neuronal Bcl-2 by 4-fold and that hyperosmotic PCD correlates with proteolytic processing of neuronal ced-3/ICE-like proteases. IGF-IR activation maintains normal Bcl-2 levels, and signaling via the IGF-IR:phosphatidylinositol 3-kinase pathway prevents ICE/LAP-3 and Yama/CPP32 processing. Finally, increased neuronal IGF-IR expression enhances the negative death regulator Bcl-xL. We suggest that IGF-IR signaling exerts its short-term inhibitory effects upon PCD "upstream" of both Bcl proteins and ced-3/ICE-like proteases, while chronic increased IGF-IR expression may modulate susceptibility to death signals by mediating the negative death regulator, Bcl-xL.

Painful sensory polyneuropathy associated with impaired glucose tolerance.

We examined records of 121 patients coded as idiopathic polyneuropathy, extracting neuropathy symptoms, electromyographic data, and diagnostic blood work. Of 89 patients screened for glucose handling, 28 demonstrated frank diabetes mellitus. Of the remaining 61 patients, 15 (25%) had impaired glucose tolerance (IGT) by American Diabetes Association criteria (serum glucose 140--200 mg/dl 2 h after a 75-g glucose load). Excluding those with diabetes mellitus, 35% of patients with neuropathic pain had IGT, more than twice the prevalence found in large, unselected population studies. No other common etiology of polyneuropathy was identified. Two-hour oral glucose tolerance test results were often abnormal, whereas fasting glucose or hemoglobin A1c was normal. Bias due to referral pattern, body weight, or genetics might affect the comparison of our polyneuropathy cohort with a broader, population-based control. However, our results corroborate an association between IGT and painful sensory polyneuropathy and link these patients syndromically to the typical painful polyneuropathy of diabetes mellitus.