Insulin like growth factor-1 and insulin like growth factor binding proteins in the cerebrospinal fluid and serum from patients with Alzheimer's disease

Insulin like growth factor-1 (IGF-1) is ubiquitously expressed growth factor that has profound effects on the growth and differentiation of many cell types and tissues, including cells of the central nervous system (CNS). IGF-1 is produced by a wide variety of cells and is found in many biological fluids including cerebrospinal fluid (CSF). IGF-1 plays important role during CNS development and repair. IGF-1 has broad range neuroprotective effects and is a therapeutic candidate for Huntington's disease (HD). IGF-1 protects striatal neurons from the toxicity of mutated Huntington in vitro and improves neuronal survival in vivo in a phenotypic model of HD. Alzheimer's disease (AD) is an age-dependent dementia characterized by progressive loss of cognitive functions and by characteristic pathological changes in the brain: the formation of aggregates extracellularly by beta-amyloid (AB) peptide and intracellularly by tau proteins. Since cerebrospinal fluid (CSF) is in contact with the extracellular space of the brain, biochemical brain modifications could be reflected in the CSF. IGFs in circulation and other physiological fluids are associated with a group of high-affinity binding proteins insulin like growth factor binding proteins (IGFBPs) that specifically bind and modulate their bioactivity at the cellular level. The aim of this study was to determine the level of CSF and serum IGF-1 and IGFBPs concentrations in the patients with AD. CSF was obtained by lumbar puncture. The presence of IGF-1 and IGFBPs in the CSF and serum samples was confirmed by Western blot using anti-IGF-1 and IGFBPs antibodies. Using enzyme linked immunosorbent assay (ELISA), it was shown that the concentration of CSF and serum IGF-1 and IGFBPs in the patients with AD is higher than in normal control. The data from this study indicate that IGF-1 is a constant component of human CSF. It is also concluded that high levels of CSF IGF-1 may be partly related to AD pathophysiology.

Insulin-like growth factor binding proteins in cerebrospinal fluid during human development and aging

We analyzed samples of insulin-like growth factor binding proteins (IGFBPs) in human cerebrospinal fluid (CSF) in neurologically normal patients from one day after birth to age 76 years. CSF samples were separated on SDS-PAGE and then transferred to nitrocellulose membranes where IGFBPs were detected by Western ligand blot using [(125)I]-IGF-II, confirming other reports where we found the presence of IGFBP-2, 3, 4, 5. The 34 kDa IGFBP-2 was present in all samples, and progressively decreased with age. A broad 28- to 30-kDa IGFBP band, having the appearance of IGFBP-5, was triphasic: faint during infancy, barely detectable at 6 months, but intense in adult and aged individuals. The 24-kDa IGFBP-4 band was only seen in neonatal CSF samples, while the IGFBP-3 doublet gradually increased during aging. Thus, these present results show that IGFBP-2, 3, 4 and 5 in CSF are developmentally regulated, suggesting roles for these molecules in the development of the nervous system.

Characterization of human insulin-like growth factor-binding proteins by two-dimensional polyacrylamide gel electrophoresis and Western ligand blot analysis

The insulin-like growth factor (IGF)-binding proteins (IGFBPs) from adult human serum, amniotic fluid, and cerebrospinal fluid were analyzed by a modified two-dimensional gel electrophoresis followed by Western ligand blotting. The samples were subjected to immobilized pH gradient isoelectric focusing in the first dimension, followed by nondenaturing SDS-PAGE in the second dimension and autoradiography after ligand blotting with [125I]IGF-I or [125I]IGF-II. The identity of the binding proteins was confirmed by immunoblotting and immunoprecipitation with specific antibodies. Using this method, all six human high affinity IGFBPs could be clearly separated from each other according to their molecular mass and isoelectric points (pI). All IGFBPs exhibited a variety of specific pI isoforms, which presumably represent posttranslational modifications. In adult human serum, glycosylated IGFBP-3 is found as a broad band of spots with molecular masses of 41 and 45 kDa and a pI in the range of 4.8-8.2. The two IGFBP-3 bands could be reduced to a single 36-kDa band after deglycosylation (pI 6-9). Furthermore, the specific spots for IGFBP-2 (33 kDa; pI 6.2-7.1) and deglycosylated IGFBP-4 (24 kDa; pI 6.3, 6.5, and 6.8) were found with their expected molecular masses. Additionally, the diffuse bands around 30 kDa, found in one-dimensional Western ligand blotting, could be clearly separated into distinct groups of specific spots representing IGFBP-1 (30 kDa; pI 4.0-4.8), IGFBP-6 (30 kDa; pI 4.8-5.8), glycosylated IGFBP-4 (29 kDa; pI 6.1 and 6.3), and IGFBP-5 (30/31 kDa; pI 6.4-8). As expected, IGFBP-6 was visible only when IGF-II was used as radioligand. In conclusion, two-dimensional gel electrophoresis followed by Western ligand blotting allows identification of all six high affinity IGFBPs with their isoforms on the basis of their characteristic molecular masses and pI, especially in the range of 30 kDa. This technique can be rapidly performed with small amounts of complex biological fluids and is a powerful tool for the detection and analysis of posttranslational modifications of IGFBPs.

Insulin-like growth factor binding proteins (IGFBPs) and IGFBP-related protein 1-levels in cerebrospinal fluid of children with acute lymphoblastic leukemia

Abnormalities in insulin-like growth factor binding proteins (IGFBPs) have been reported in the cerebrospinal fluid (CSF) of children with acute leukemia. In the present study, we have further characterized the IGFBPs in whole CSF prospectively in 11 children with acute B-lineage lymphoblastic leukemia (ALL) undergoing chemotherapy. Western ligand blots Western immunoblots using a new anti-IGFBP-6 and a new IGFBP-rP1 (related protein-1 antibody and immunoassays (Diagnostic Systems Laboratories, Inc., Webster, TX) were used to characterize and measure IGFBP-6, IGFBP-2, IGFBP-3, and IGFBP-rP1 in children with ALL at diagnosis, and with treatment. Comparisons at baseline were made with 11 children with meningitis and 11 children with febrile convulsions (controls). The mean (+/- SE) CSF IGFBP-6 in ALL patients, 56 (+/- 7) ng/mL, was significantly lower than in meningitis, 97 (+/- 17) ng/mL; and in controls, 123 (+/- 24) ng/mL (P < 0.05, t test). In contrast, CSF IGFBP-3 was elevated in ALL patients, 29 (+/- 9) ng/mL; compared with meningitis, 11 (+/- 1) ng/mL; and controls, 10 (+/- 1) ng/mL (P < 0.05, t test); and IGFBP-2 did not differ among the three groups (47-59 ng/mL, P > 0.05). CSF IGFBP-6 remained very low in the patients with ALL, at 4 and 36 weeks of treatment; whereas IGFBP-3 decreased to control levels, and IGFBP-2 did not change significantly. At baseline, Western ligand blots and Western immunoblots identified a 25- to 28-kDa broad band as IGFBP-6 and a 30-kDa band as IGFBP-2 and showed that there was almost no intact IGFBP-3 in CSF. IGFBP-rP1 was also present in the CSF and was elevated in patients with ALL, compared with the 2 control groups. In conclusion, at diagnosis, IGFBP-rP1 and fragments of IGFBP-3 are elevated, and IGFBP-6 is significantly decreased, in the CSF of ALL children; and IGFBP-6 remained low, with treatment, up to 36 weeks. The role of the IGFBPs and IGFBP-rPs in central nervous system acute leukemia remain to be further elucidated.

Distinct sites of insulin-like growth factor (IGF)-II expression and localization in lesioned rat brain: possible roles of IGF binding proteins (IGFBPs) in the mediation of IGF-II activity

Although expression of the IGF-II has been demonstrated within the central nervous system (CNS), past studies have failed to reveal its precise roles or responses subsequent to a traumatic injury. To demonstrate that IGF-II, IGFBP, and IGF receptor (-R) expression alters in response to a penetrating CNS injury, we used the techniques of ribonuclease protection assay, in situ hybridization, immunohistochemistry, Western blotting, and RIA. Under normal physiology, IGF-II expression is restricted to the mesenchymal support structures of the brain, including the choroid plexus, where its expression is coincident with that of IGFBP-2. Between 1-7 days post lesion (dpl), in the acute phase following a penetrant wound to the CNS, IGF-II and IGF-IIR protein, but not messenger RNA, were colocalized, with IGF-I, IGF-IR, and IGFBP-1, -2, -3, and -6, to neurons, macrophages, astrocytes, and microglia within the damaged tissue. Within the cerebrospinal fluid (CSF), levels of IGF-II peptide increased to peak at 7 dpl. IGFBP-2, -3, and -6 were also observed within the CSF, with IGFBP-2 predominating and exhibiting an increase in binding efficiency from 7-10 dpl. In the chronic phase of injury (7-14 dpl), an increase in both IGF-II, IGF-IIR and IGFBP-5 messenger RNA and protein was observed specifically and focally in the marginal astrocytes forming the limiting glial membrane of the wound. Thus, our evidence suggests that there are two mechanisms of action for IGF-II within the injured rat brain. During the acute phase, the secretion of IGF-II from the choroid plexus into the CSF is up-regulated, resulting in increased transport of the peptide to the wound. In the CSF, transported IGF-II is complexed to IGFBP-2 and essentially demonstrates an endocrine mode of action with a balance of locally produced IGFBPs modulating its bioactivity in the wound. Later in the wounding response, levels of IGF-II decline in the CSF and the wound neuropil, possibly with the aid of increased IGFBP-5 levels that may help to locally sequester and down-regulate IGF-II activity. Hence, in the chronic phase of the injury response, IGF-II reasserts itself to a predominantly autocrine/paracrine role restricted to the mesenchymal support structures, including the glia limitans, which may help reestablish and maintain tissue homeostasis.

Displacement of insulin-like growth factors from their binding proteins as a potential treatment for stroke

Insulin-like growth factors I and II (IGF-I and IGF-II) play an important role in normal growth and brain development and protect brain cells from several forms of injury. The effects of IGFs are mediated by type-I and type-II receptors and modulated by potentially six specific binding proteins that form high-affinity complexes with IGFs in blood and cerebrospinal fluid (CSF) and under most circumstances inactivate them. Because brain injury is commonly associated with increases in IGFs and their associated binding proteins, we hypothesized that displacement of this large "pool" of endogenous IGF from the binding proteins would elevate "free" IGF levels to elicit neuroprotective effects comparable to those produced by administration of exogenous IGF. A human IGF-I analog [(Leu24, 59, 60, Ala31)hIGF-I] with high affinity to IGF-binding proteins (Ki = 0.3-3.9 nM) and no biological activity at the IGF receptors (Ki = >10,000 nM) increased the levels of "free, bioavailable" IGF-I in the CSF. Intracerebroventricular administration of this analog up to 1h after an ischemic insult to the rat brain had a potent neuroprotective action comparable to IGF-I. This novel strategy for increasing "free" IGF levels in the brain may be useful for the treatment of stroke and other neurodegenerative diseases.