Phillip D. K. Lee

Insulin-like growth factor binding protein-1: recent findings and new directions.

Abstract In 1988, insulin-like growth factor-binding protein-1 (IGFBP-1) became the first characterized member of a group of structurally related soluble proteins which specifically bind and modulate the actions of the IGFs. Since then, a wealth of information has accumulated regarding the physiology of this dynamic serum protein. In this review, we update our 1993 summary (Lee PDK et al. Proc Soc Exp Biol Med 204:4-29) of the status of IGFBP-1 research. The IGFBP-1 protein sequence contains 12 N-terminal and 6 C-terminal cysteine residues which are conserved in other mammalian IGFBP-1 sequences and amongst other IGFBPs; both of the cysteine-rich regions are required for optimal IGF binding. The nonconserved IGFBP-1 midregion may act as both a hinge which defines ligand binding characteristics and as a specific target for protease activity. Integrin-binding and phosphorylation sites within the IGFBP-1 sequence have functional significance in vitro, but their physiologic relevance in vivo have not been defined. The human IGFBP-1 and IGFBP-3 genes are contiguous and located in close proximity to the homeobox A (HOXA) gene cluster on chromosome 7. The other IGFBP genes, located on chromosomes 2, 12, and 17, are also associated with HOX clusters, suggesting evolutionary linkage of the IGFBP and HOX gene families. Similarities between the hlGFBP-1 and phosphoenolpyruvate kinase (PEPCK) promoters, including regions conferring insulin, glucocorticoid, and cyclic adenosine-monophosphate responses, are consistent with our previous hypothesis that IGFBP-1 is involved in regulation of glucose metabolism. The tissue-specific patterns of IGFBP-1 gene expression in liver, kidney, decidua, and ovary may be due to stimulation of IGFBP-1 transcription by hepatic nuclear factor 1 (HNF1) proteins. Clinical and basic studies of IGFBP-1 physiology have been aided by several recently developed assay methods. Numerous investigations have confirmed that insulin, via inhibition of IGFBP-1 transcription, is the primary determinant of IGFBP-1 expression both in vitro and in viva IGF-I and IGF-II also have specific inhibitory effects on IGFBP-1 expression. Glucocorticoids and cAMP stimulate IGFBP-1 transcription, but these effects are observed only in conditions of low or absent insulin effect. Other stimulants of IGFBP-1 expression include thyroid hormones and epidermal growth factor. Phorbol ester stimulation of IGFBP-1 expression can supersede the effects of insulin in vitro; however, the mechanism and in vivo correlates of this effect have not been determined. Cytokines and, perhaps, growth hormones may affect IGFBP-1 expression, perhaps by altering the regulatory actions of insulin; this effect may have important clinical relevance. IGFBP-1 expression is upregulated in liver and (nonhuman) kidney during postinjury regeneration. The IGF-inhibitory actions of IGFBP-1 has been confirmed by numerous in vitro studies and several in vivo animal investigations, including administration of recombinant IGFBP-1 and IGFBP-1 transgenic models. IGFBP-1 has been shown to inhibit somatic linear growth, weight gain, tissue growth, and glucose metabolism. Moreover, IGFBP-1 appears to be a primary determinant of free IGF-I levels in serum. Excess levels of IGFBP-1 may contribute to growth failure in intrauterine growth restriction and in pediatric chronic renal failure, while low IGFBP-1 levels are associated with obesity and with cardiovascular risk factors in insulin resistance syndromes. Serum IGFBP-1 measurements may be useful biochemical marker in these pathologic conditions. IGFBP-1 is expressed in decidualized stromal cells of the uterine endometrium and in ovarian granulosa cells. IGFBP-1, together with IGFs, insulin, ovarian steroids, cytokines, and other factors, is involved in a complex system which regulates menstrual cycles, ovulation, decidualization, blastocyst implantation, and fetal growth. Models for the role of IGFBP-1 in female reproductive physiology are presented, and evidence for pathophysiologic roles in pre-eclampsia, polycystic ovarian syndrome, and uterine malignancy are reviewed. Very recent data indicates that IGFBP-1 undergoes regulated expression in human osteoblasts. Limited information also suggests that IGFBP-1 may be present in peripheral neurons, and that serum IGFBP-1 may increase during exercise and in critical ilIness. In summary, two major roles for IGFBP-1 in normal physiology can be constructed from current data: (i) As an “endocrine” factor, IGFBP-1 regulates the bio-availability of serum IGF-I, thereby modulating IGF-mediated tissue metabolism. The dominant regulation of IGFBP-1 expression by meal-related changes in hepatic insulin concentrations provides a dynamic link to substrate availability. (ii) As an autocrine/paracrine factor, IGFBP-1 appears to play a crucial role in the female reproductive system and, in particular, the sequence of events leading from ovulation to implantation to successful fetal outcome. Future investigations will further delineate the manner in which IGFBP-1 participates in these and other physiologic processes, and the mechanisms by which IGFBP-1 may be involved in clinical pathophysiology.

Regulation and Function of Insulin-Like Growth Factor-Binding Protein-1:

Abstract Insulin-like growth factor-binding protein (IGFBP)-1 is one of six structurally homologous proteins that specifically bind and modulate the mitogenic and metabolic actions of insulin-like growth factor (IGF)-I and IGF-II. Of the six IGFBP, IGFBP-1 is the only one that displays rapid dynamic regulation in vivo, with serum levels varying 10-fold or more in relation to meals. The complementary cDNA for IGFBP-1 was first reported in 1988. The predicted 234-amino acid sequence has a molecular mass of 25.3 kDa. The N-terminal and C-terminal regions are highly homologous among rat, human, and bovine sequences, and contain 18 conserved cysteines which are postulated to provide a framework for ligand binding. The 65-residue midregion is less homologous and does not contain cysteines, but does include a Pro-Glu-Ser-Thr (PEST) domain that is typical of rapidly metabolized proteins. The gene for IGFBP-1 has been localized to human chromosome region 7p12-p14, where it is contiguous with the gene for IGFBP-3. IGFBP-1 mRNA and protein expression have been identified in human liver and uterine decidua, and in nonhuman kidney. In vitro and in vivo studies indicate that insulin is the primary regulator of IGFBP-1 expression in these tissues, and that the primary effect of insulin is rapid inhibition of transcription. On the other hand, cortisol, glucagon, and cAMP stimulate IGFBP-1 production. Limited data also show a potent stimulatory effect of phorbol esters. A detailed review of IGFBP-1 levels and physiology in vivo and in vitro is presented. The function of IGFBP-1 is not completely defined. However, several studies demonstrate that IGFBP-1 inhibits IGF binding to cell surface receptors and thereby inhibits IGF-mediated mitogenic and cell metabolic actions. Furthermore, IGFBP-1 regulation by insulin and glucoregulatory hormones in vitro and limited in vivo data are consistent with a role for IGFBP-1 in glucose counterregulation.

Relation of body fat indexes to vitamin D status and deficiency among obese adolescents

BACKGROUNDnData on the relation between vitamin D status and body fat indexes in adolescence are lacking.nnnOBJECTIVEnThe objective was to identify factors associated with vitamin D status and deficiency in obese adolescents to further evaluate the relation of body fat indexes to vitamin D status and deficiency.nnnDESIGNnData from 58 obese adolescents were obtained. Visceral adipose tissue (VAT) was measured by computed tomography. Dual-energy X-ray absorptiometry was used to measure total bone mineral content, bone mineral density, body fat mass (FM), and lean mass. Relative measures of body fat were calculated. Blood tests included measurements of 25-hydroxyvitamin D [25(OH)D], parathyroid hormone (PTH), osteocalcin, type I collagen C-telopeptide, hormones, and metabolic factors. Vitamin D deficiency was defined as 25(OH)D < 20 ng/mL. PTH elevation was defined as PTH > 65 ng/mL.nnnRESULTSnThe mean (+/-SD) age of the adolescents was 14.9 +/- 1.4 y; 38 (66%) were female, and 8 (14%) were black. The mean (+/-SD) body mass index (in kg/m(2)) was 36 +/- 5, FM was 40.0 +/- 5.5%, and VAT was 12.4 +/- 4.3%. Seventeen of the adolescents were vitamin D deficient, but none had elevated PTH concentrations. Bone mineral content and bone mineral density were within 2 SDs of national standards. In a multivariate analysis, 25(OH)D decreased by 0.46 +/- 0.22 ng/mL per 1% increment in FM (beta +/- SE, P = 0.05), whereas PTH decreased by 0.78 +/- 0.29 pg/mL per 1% increment in VAT (P = 0.01).nnnCONCLUSIONSnTo the best of our knowledge, our results show for the first time that obese adolescents with 25(OH)D deficiency, but without elevated PTH concentrations, have a bone mass within the range of national standards (+/-2 SD). The findings provide initial evidence that the distribution of fat may be associated with vitamin D status, but this relation may be dependent on metabolic factors. This study was registered at www.clinicaltrials.gov as NCT00209482, NCT00120146.

Management of Prader-Willi syndrome

Diagnosis and Genetics.- Clinical Findings and Natural History of Prader-Willi Syndrome.- Diagnostic Criteria for Prader-Willi Syndrome.- Molecular Genetic Findings in Prader-Willi Syndrome.- Laboratory Testing for Prader-Willi Syndrome.- Medical Physiology and Treatment.- Medical Considerations in Prader-Willi Syndrome.- Gastrointestinal System, Obesity, and Body Composition.- Growth Hormone and Prader-Willi Syndrome.- Multidisciplinary Management.- Neurodevelopmental and Neuropsychological Aspects of Prader-Willi Syndrome.- Speech and Language Disorders Associated with Prader-Willi Syndrome.- Motor and Developmental Interventions.- Educational Considerations for Children with Prader-Willi Syndrome.- Tools for Psychological and Behavioral Management.- Educational and Social Issues for Adolescents with Prader-Willi Syndrome.- Transition from Adolescence to Young Adulthood: The Special Case of Prader-Willi Syndrome.- Vocational Training for People with Prader-Willi Syndrome.- Residential Care for Adults with Prader-Willi Syndrome.- Inpatient Crisis Intervention for Persons with Prader-Willi Syndrome.- Social Work Interventions: Advocacy and Support for Families.- A National Approach to Crisis Intervention and Advocacy.- Advocacy Issues: School Discipline and Expulsion.- Advocacy Issues: Sexuality.

Metformin extended release treatment of adolescent obesity: A 48-week randomized, double-blind, placebo-controlled trial with 48-week follow-up

BACKGROUNDnMetformin has been proffered as a therapy for adolescent obesity, although long-term controlled studies have not been reported.nnnOBJECTIVEnTo test the hypothesis that 48 weeks of daily metformin hydrochloride extended release (XR) therapy will reduce body mass index (BMI) in obese adolescents, as compared with placebo.nnnDESIGNnMulticenter, randomized, double-blind, placebo-controlled clinical trial.nnnSETTINGnThe 6 centers of the Glaser Pediatric Research Network from October 2003 to August 2007.nnnPARTICIPANTSnObese (BMI > or = 95th percentile) adolescents (aged 13-18 years) were randomly assigned to the intervention (n = 39) or placebo groups. Intervention Following a 1-month run-in period, subjects following a lifestyle intervention program were randomized 1:1 to 48 weeks treatment with metformin hydrochloride XR, 2000 mg once daily, or an identical placebo. Subjects were monitored for an additional 48 weeks. Main Outcome Measure Change in BMI, adjusted for site, sex, race, ethnicity, and age and metformin vs placebo.nnnRESULTSnAfter 48 weeks, mean (SE) adjusted BMI increased 0.2 (0.5) in the placebo group and decreased 0.9 (0.5) in the metformin XR group (P = .03). This difference persisted for 12 to 24 weeks after cessation of treatment. No significant effects of metformin on body composition, abdominal fat, or insulin indices were observed.nnnCONCLUSIONnMetformin XR caused a small but statistically significant decrease in BMI when added to a lifestyle intervention program.nnnTRIAL REGISTRATIONnclinicaltrials.gov Identifiers: NCT00209482 and NCT00120146.

IGF binding proteins in growth-retarded children with chronic renal failure

ABSTRACT: Changes in the normal hormonal regulation of linear growth which lead to growth failure in children with chronic renal failure (CRF) are not well understood. Previous studies indicate that serum levels of growth hormone and IGF-I and II are normal or elevated in this population; and that serum levels of poorly defined inhibitors of IGF action are increased. Using a recently developed RIA for the 25-kD IGF-binding protein (IGF-BP25), we report significant elevations of this protein in children with CRF when compared to age- and sex-matched controls. IGF-BP25 levels correlate positively with IGF-binding activity in both populations, indicating that the RIA reflects levels of bioactive protein. Although the variation of serum IGF-BP25 with chronologic age and IGF levels are preserved in CRF, the quantitative interrelationships are disrupted. Levels of the 53-kD IGF-binding protein, an IGFbinding protein derived from the high mol wt IGF complex, were also found to be elevated in the CRF population and, unlike in the control population, did not vary with age or IGF levels. IGF-BP25 has been shown to inhibit IGF mitogenic action in vitro. Our finding of elevated levels of IGF-BP25 in children with CRF suggests that this protein may play a role in the growth retardation of pediatric chronic renal failure. The significance of the elevated IGFBP53 levels in CRF remains uncertain.

IGF-I, IGF-II, free IGF-I and IGFBP-1, -2 and -3 levels in venous cord blood: relationship to birthweight, length and gestational age in healthy newborns.

Abstract The insulin‐like growth factors (IGF‐I and IGF‐II) and their binding proteins (IGFBPs) have been implicated in regulating fetal growth and development. The aim of this study was to determine whether fetal IGFs correlate with auxologic data at birth and/or gestational age. Venous cord blood was obtained from 138 healthy newborns immediately after birth and clinical data were recorded using a standardized data sheet. For the determination of IGF‐I and IGF‐II, IGFBP‐blocked radioimmunoassays were used. A coated‐tube immunoradiometric assay was applied for the measurement of free IGF‐I. IGFBP‐1, ‐2, and ‐3 were measured using specific radioimmunoassays. IGF‐I levels were 61 ± 21 ng ml‐1, median 61 ng ml‐1, range 19‐114ng ml‐1: IGF‐II levels were 466 ± 80ng ml‐1, median 457 ng ml‐1, range 311–701 ng ml‐1; free IGF‐I levels were 2.4 ± 1.8ng ml‐1, median 1.8 ng ml‐1, range 0.4–7.8ng ml‐1. The concentration of IGFBP‐1 was 144± 110 ng ml‐1, median 113 ng ml‐1, range 20–626 ng ml‐1; that of IGFBP‐2 was 1165 ± 455ng ml‐1, median 1119ng ml‐1, range 440–3466 ng ml‐1. IGFBP‐3 levels were 1272 ± 280 ng ml‐1, median 1272ng ml‐1, range 600–1966 ng ml‐1. IGF‐I levels correlated significantly with IGFBP‐3 levels (r= 0.71). birthweight (r= 0.48) and birth length (r= 0.37). There were significant inverse correlations between IGF‐I and both IGFBP‐I (r= ‐ 0.45) and IGFBP‐2 (r= ‐ 0.62). Although free IGF‐I levels correlated (r= 0.71) with total IGF‐I, only marginally significant correlations were found between free IGF‐I and birthweight (r= 0.25). According to multiple regression analysis free IGF‐I levels were only dependent upon total IGF‐I, IGFBP‐2 and IGFBP‐1, whereas IGFBP‐3 levels did not contribute to the variance of free IGF‐1 concentrations in venous cord blood. There was no significant correlation between IGF‐II and auxologic data at birth. When IGF‐I and IGFBP‐3 levels were analysed with respect to gestational age a biphasic pattern with maxima at 270 d was observed. IGFBP‐2 exhibited a reversed pattern with a minimum at 265 d of gestation. In conclusion, these data suggest that IGF‐I and the IGFBPs, but not IGF‐II, play a role in the regulation of late fetal growth and development.

Design and function of a closed, recirculating seawater system with denitrification for the culture of black tiger shrimp broodstock

A closed, recirculating seawater system with a denitrification process was designed for the culture of black tiger shrimp broodstock. The system comprised a circular rearing tank (9 m3 volume), a nitrifying biofilter (6 m3 volume) and denitrification process. The denitrification process comprised a deoxygenation column, a bacterial substrate column (143 L volume) and a re-aeration column connected to the biofilter. The experimental period was 81 weeks, consisting of 3 sequential trials using different substrates, bacterial inoculates and carbon sources: Trial 1- porous plastic balls for substrate, mangrove soil for inoculant and ethanol for the carbon source; Trial 2- crushed oyster shell for substrate, a strain of laboratory cultured bacteria for inoculant and ethanol for the carbon source; and Trial 3- crushed oyster shell for the substrate, no inoculant and methanol for the carbon source. The nitrifying biofilter controlled ammonium-N and nitrite-N within acceptable ranges ( 160 to <25 mg l−1) without the need for bacterial inoculation.

Growth Hormone Treatment of Adults with Prader-Willi Syndrome and Growth Hormone Deficiency Improves Lean Body Mass, Fractional Body Fat, and Serum Triiodothyronine without Glucose Impairment: Results from the United States Multicenter Trial

CONTEXTnGH replacement in Prader-Willi syndrome (PWS) children has well-defined benefits and risks and is used extensively worldwide. Its use in PWS adults has been limited by documentation of benefits and risks, as determined by larger multisite studies.nnnOBJECTIVESnOur objective was to evaluate the effectiveness and safety of GH in GH-deficient genotype-positive PWS adults.nnnDESIGNnWe conducted a 12-month open-label multicenter trial with 6-month dose-optimization and 6-month stable treatment periods.nnnSETTINGnThe study was conducted at outpatient treatment facilities at four U.S. academic medical centers.nnnPATIENTSnLean and obese PWS adults with diverse cognitive skills, behavioral traits, and living arrangements were recruited from clinical populations.nnnINTERVENTIONnHuman recombinant GH (Genotropin) was initiated at 0.2 mg/d with monthly 0.2-mg increments to a maximum 1.0 mg/d, as tolerated.nnnMAIN OUTCOMES MEASURESnLean body mass and percent fat were measured by dual-energy x-ray absorptiometry.nnnRESULTSnLean body mass increased from 42.65 +/- 2.25 (se) to 45.47 +/- 2.31 kg (P < or = 0.0001), and percent fat decreased from 42.84 +/- 1.12 to 39.95 +/- 1.34% (P = 0.025) at a median final dose of 0.6 mg/d in 30 study subjects who completed 6-12 months of GH. Mean fasting glucose of 85.3 +/- 3.4 mg/dl, hemoglobin A1c of 5.5 +/- 0.2%, fasting insulin of 5.3 +/- 0.6 microU/ml, area under the curve for insulin of 60.4 +/- 7.5 microU/ml, and homeostasis model assessment of insulin resistance of 1.1 +/- 0.2 were normal at baseline in 38 study initiators, including five diabetics, and remained in normal range. Total T(3) increased 26.7% from 127.0 +/- 7.8 to 150.5 +/- 7.8 ng/dl (P = 0.021) with normalization in all subjects, including six (20%) with baseline T(3) values at least 2 sd below the mean. Mildly progressive ankle edema was the most serious treatment-emergent adverse event (five patients).nnnCONCLUSIONSnThis multicenter study demonstrates that GH improves body composition, normalizes T(3), and is well tolerated without glucose impairment in PWS genotype adults.

Efficacy of insulin-like growth factor I levels in predicting the response to provocative growth hormone testing.

ABSTRACT: Clinical testing of growth hormone (GH) sufficiency is a controversial area in endocrinology. Due to the episodic nature of endogenous GH secretion, diagnosis of GH deficiency has been defined as a failure to achieve normal GH levels in response to at least two stimuli. This testing is associated with significant patient morbidity and cost. We analyzed our experience over a 4-y period to determine whether clinical or biochemical variables could be used to predict the results of a specific GH testing procedure. Of 180 cases analyzed (67% male, mean age 8.89 ± 4.39 y, range neonate-16 y), eight cases had incomplete GH testing results. Of the remaining 172, 19 were GH deficient (GH level <7 ng/mL). Younger age, higher body mass index and a greater degree of bone age delay were characteristic of the GH-deficient population; however, none of these variables alone was of diagnostic utility. Serum IGF-I level was below the normal range for 81% of the GH deficient and 47% of the GH-sufficient children; and was the only single variable that provided a reasonable between-group distinction. Discriminant analysis resulted in development of a new variable, based on IGF-I z scores, chronologic age, degree of bone age delay, and body mass index, which would have allowed exclusion of GH deficiency without provocative testing for 58% of the GH sufficient population, whereas permitting the diagnosis of GH deficiency for all GH-deficient subjects. Our data are dependent on the IGF-I assay method and the clinical definition for GH deficiency; therefore, the calculated predictive values are not applicable to all clinical populations. However, our data provide a new perspective on the integration of IGF-I levels and clinical information in predicting GH sufficiency.