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D R Clemmons

Publications and source records attributed to D R Clemmons.

At least 55 records · Page 3Linked to original sources
PubMed1998

Role for cyclic adenosine monophosphate in modulating insulin-like growth factor binding protein secretion by muscle cells.

The modulation of insulin-like growth factor-binding protein (IGFBP) secretion is an important variable affecting muscle cell metabolism, proliferation, and differentiation. We have previously shown that secretion of IGFBP-4 and IGFBP-5 by L6 and BC3H-1 muscle cells was stimulated by treatment with either insulin, IGF-I, or IGF-II. Herein, these cells were used to further identify mechanisms involved in controlling IGFBP secretion. Agents that elevate intracellular cAMP concentrations (dcAMP, forskolin, isoproterenol, and prostaglandin [PGE1]) increase secretion of IGFBP-4 and IGFBP-5 from L6 cells. Similar increases in IGFBP secretion were found by treatment with either insulin, IGF-I, or dcAMP. The effects of dcAMP and either insulin or IGF-I were additive, but the effects of insulin and IGF-I were not additive. These results suggest that insulin/IGF-I and dcAMP are acting via distinct mechanisms to stimulate IGFBP secretion. Indomethacin, which blocks endogenous prostaglandin synthesis, and progesterone, which decreases intracellular cAMP levels, decreased IGFBP-4 and IGFBP-5 secretion. IGFBP-5 secretion by BC3H-1 cells was increased by either insulin or IGF-I. Agents which elevate intracellular cAMP concentrations did not increase IGFBP-5 secretion. Additionally, these agents were not synergistic with either insulin or IGF-I. However, indomethacin and progesterone depressed IGFBP-5 secretion by BC3H-1 cells. In summary, there appear to be at least two intracellular signaling mechanisms controlling IGFBP-4 and IGFBP-5 secretion by L6 and BC3H-1 muscle cells. IGFBP secretion by L6 cells is stimulated by both insulin/IGF-I and cAMP-dependent pathways, whereas IGFBP-5 secretion by BC3H-1 cells is stimulated only by the insulin/IGF pathway. IGFBP secretion by both cell lines can be decreased by agents which depress cAMP levels. Our results suggest that two divergent but synergistic pathways modulate IGFBP production and these mechanisms can potentially modulate IGF activity during muscle cell proliferation and differentiation.

1-Methyl-3-isobutylxanthine↗
PubMed1998

The secretion of insulin-like growth factor I, prolactin and insulin-like growth factor binding protein 1 by the decidua as predictors of human fetal growth.

To determine if in vitro secretion of the decidual peptides insulin-like growth factor I (IGF-I), prolactin or insulin-like growth factor binding protein 1 (IGFBP-1) correlates with infant birthweight in uncomplicated, term human pregnancies, decidua from 45 pregnancies with normally distributed birthweights was cultured in defined medium for 24 h. IGF-I, prolactin and IGFBP-1 concentrations in the culture medium were measured by radioimmunoassay. Neither infant birthweight nor a normalized measure of infant birthweight (birthweight z-score) correlated with the quantity of IGF-I, prolactin or IGFBP-1 secreted by the decidua from that pregnancy. There were no differences in any of the peptide hormones assayed when the pregnancies were grouped by infant sex. IGF-I and prolactin secretion by individual decidual samples correlated positively. IGF-I and IGFBP-1 secretion also correlated positively in individual samples. A previously identified correlation between decidual IGF-I secretion and infant birthweight among a group of normal and growth restricted (IUGR) pregnancies was not confirmed in the current study. These data indicate that the decrease in decidual IGF-I and prolactin secretion seen in IUGR pregnancies is not the hormone profile of the low birthweight end of a normal population, but a distinct endocrine profile.

Amniotic Fluid↗
PubMed1998

Binding of insulin-like growth factor (IGF)-binding protein-5 to smooth-muscle cell extracellular matrix is a major determinant of the cellular response to IGF-I.

Insulin-like growth factor-binding protein-5 (IGFBP-5) has been shown to bind to fibroblast extracellular matrix (ECM). Extracellular matrix binding of IGFBP-5 leads to a decrease in its affinity for insulin-like growth factor-I (IGF-I), which allows IGF-I to better equilibrate with IGF receptors. When the amount of IGFBP-5 that is bound to ECM is increased by exogenous addition, IGF-I's effect on fibroblast growth is enhanced. In this study we identified the specific basic residues in IGFBP-5 that mediate its binding to porcine smooth-muscle cell (pSMC) ECM. An IGFBP-5 mutant containing alterations of basic residues at positions 211, 214, 217, and 218 had the greatest reduction in ECM binding, although three other mutants, R214A, R207A/K211N, and K202A/R206N/R207A, also had major decreases. In contrast, three other mutants, R201A/K202N/R206N/R208A, and K217N/R218A and K211N, had only minimal reductions in ECM binding. This suggested that residues R207 and R214 were the most important for binding, whereas alterations in K211 and R218, which align near them, had minimal effects. To determine the effect of a reduction in ECM binding on the cellular replication response to IGF-I, pSMCs were transfected with the mutant cDNAs that encoded the forms of IGFBPs with the greatest changes in ECM binding. The ECM content of IGFBP-5 from cultures expressing the K211N, R214A, R217A/R218A, and K202A/R206N/R207A mutants was reduced by 79.6 and 71.7%, respectively, compared with cells expressing the wild-type protein. In contrast, abundance of the R201A/K202N/R206N/R208A mutant was reduced by only 14%. Cells expressing the two mutants with reduced ECM binding had decreased DNA synthesis responses to IGF-I, but the cells expressing the R201A/K202N/R206N/R208A mutant responded well to IGF-I. The findings suggest that specific basic amino acids at positions 207 and 214 mediate the binding of IGFBP-5 to pSMC/ECM. Smooth-muscle cells that constitutively express the mutants that bind weakly to ECM are less responsive to IGF-I, suggesting that ECM binding of IGFBP-5 is an important variable that determines cellular responsiveness.

Animals↗
PubMed1998

Effect of glucose on insulin-like growth factor binding protein-4 proteolysis.

The role of hyperglycemia in diabetic changes of the insulin-like growth factors (IGFs) and their binding proteins (IGFBPs) has not been clearly established. We therefore determined whether glucose modulates IGFBP synthesis and stability in vitro. Porcine vascular smooth muscle cells (pSMC) cultured in low glucose (pSMC-L) had 2.1-fold more IGFBP-4 in the conditioned medium compared with pSMC cultured in high glucose (pSMC-H) (P < 0.01). In contrast, IGFBP-2 levels remained constant. Although pSMC-H and pSMC-L cultures expressed similar levels of IGFBP-4 messenger RNA, in vitro protease assays demonstrated an increase in IGFBP-4 proteolysis in pSMC-H conditioned medium compared with pSMC-L conditioned medium (P < 0.01). The protease had properties similar to a previously characterized IGFBP-4 protease. The addition of 20 mM mannitol to pSMC-L cultures did not decrease IGFBP-4 levels, suggesting that the difference in IGFBP-4 proteolysis was not osmotically induced. The change was not due to selection bias, because cultures that were initially isolated from aortic explants in high and low glucose still exhibited the glucose-dependent difference in IGFBP-4 proteolytic activity. The results suggest that high glucose acts on pSMC to induce a change in IGFBP-4 proteolytic activity, which results in increased IGF-I availability to its receptors thereby enhancing the SMC proliferative response.

Animals↗
PubMed1998

A protease-resistant form of insulin-like growth factor (IGF) binding protein 4 inhibits IGF-1 actions.

Smooth muscle cells (SMC) secrete a serine protease that cleaves insulin-like growth factor (IGF) binding protein (IGFBP)-4 into fragments that have low affinity for IGF-1. When IGFBP-4 is added to monolayer cultures of cell types that do not secrete this protease, IGF-1 stimulation of DNA synthesis is significantly inhibited. In contrast, if cell types that secrete this protease are used, IGFBP-4 is a much less potent inhibitor. These studies were conducted to determine whether proteolysis of IGFBP-4 accounted for its reduced capacity to inhibit IGF-1-stimulated DNA synthesis. The cleavage site in IGFBP-4 that the SMC protease uses was determined to be lysine120, histidine121. A protease-resistant mutant form of IGFBP-4 was prepared, expressed, purified, and tested for biologic activity using porcine SMC cultures. Addition of the protease-resistant mutant resulted in inhibition of DNA and cell migration responses to IGF-1. The inhibition was concentration dependent and was maximal when 500 ng/ml (20 nM) of the mutant was added with 20 ng/ml (2.8 nM) of IGF-1. When the mutant was added in the absence of IGF-1, it had no activity. The results show that cleavage of IGFBP-4 at lysine120, histidine121 results in inactivation of the ability of IGFBP-4 to bind to IGF-1. Creation of a mutant form of IGFBP-4 that was not cleaved by the protease resulted in inhibition of IGF-1-stimulated actions. The results suggest that IGFBP-4 can act as a potent inhibitor of the anabolic effects of IGF-1 and that the variables that regulate protease activity may indirectly regulate IGF-1 actions.

Animals↗
PubMed1998

Insulin-like growth factor-binding protein-5 is cleaved by physiological concentrations of thrombin.

Insulin-like growth factor (IGF)-binding protein-5 (IGFBP-5) is cleaved by a serine protease that is secreted by fibroblasts and porcine smooth muscle cells (pSMC) in culture. To investigate whether other serine proteases could cleave this substrate at physiologically relevant concentrations, we determined the proteolytic effects of thrombin on IGFBP-5. Human alpha-thrombin (0.0008 NIH U/ml) cleaved IGFBP-5 into 24-, 23-, and 20-kDa non-IGF-I-binding fragments. Cleavage occurred at a physiologically relevant thrombin concentration. The effect was specific for IGFBP-5, as other forms of IGFBPs, e.g. IGFBP-1, IGFBP-2, and IGFBP-4 were not cleaved by thrombin. Although IGFBP-3 was cleaved by thrombin, this effect required a 50-fold greater thrombin concentration. [35S]Methionine labeling followed by immunoprecipitation confirmed that IGFBP-5 that was constitutively synthesized by pSMC cultures was also degraded by thrombin into 24-, 23-, and 20-kDa fragments. The binding of IGF-I to IGFBP-5 partially inhibited IGFBP-5 degradation by thrombin, and an IGF analog that does not bind to IGFBP-5 had no effect. Thrombin did not account for the serine protease activity that had been shown previously to be present in pSMC-conditioned medium. This was proven by showing that 1) no immunoreactive thrombin could be detected in the pSMC-conditioned medium; 2) the IGFBP-5 fragments that were generated by thrombin showed three cleavage sites (Arg192-Ala193, Arg156-Ile157, and Lys120-His121), whereas the serine protease in conditioned medium cleaves IGFBP-5 at a different site; and 3) hirudin had no effect on IGFBP-5 cleavage by the protease in pSMC medium; however, it inhibited IGFBP-5 degradation by thrombin. To determine the physiological significance of IGFBP-5 cleavage, the effect of an IGFBP-5 mutant that is resistant to cleavage by the pSMC protease and has been shown to inhibit IGF-I actions in pSMC was determined. This mutant inhibited IGF-I-stimulated DNA synthesis, but if thrombin was added simultaneously, IGF-I was fully active. In summary, physiological concentrations of thrombin degrade IGFBP-5. Degradation can be blocked by hirudin and is partially inhibited by IGF-I binding. Generation of active thrombin in vessel walls may be a physiologically relevant mechanism for controlling IGF-I bioactivity.

Animals↗
PubMed1998

MK-677, an orally active growth hormone secretagogue, reverses diet-induced catabolism.

The reversal of diet-induced negative nitrogen balance by GH suggests a possible therapeutic role for GH treatment in catabolic patients. A double-blind, randomized, placebo-controlled, two-period cross-over study was designed to investigate whether MK-677, an orally active nonpeptide mimic of GH-releasing peptide, can reverse diet-induced protein catabolism. Eight healthy volunteers (ages 24-39 yr) were calorically restricted (18 kcal/kg.day) for two 14-day periods. During the last 7 days of each diet period, subjects received either oral MK-677 25 mg or placebo once daily. There was a 14- to 21-day washout interval between periods. During the first week of caloric restriction (i.e. diet alone), daily nitrogen losses were similar for both treatment groups (mean +/- SE; MK-677 group -2.67 +/- 0.40 g/day vs. placebo group -2.83 +/- 0.26 g/day). During the second week (diet and study drug), mean daily nitrogen balance was 0.31 +/- 0.21 g/day in the MK-677 treatment group compared with -1.48 +/- 0.21 g/day in the placebo group (P < 0.01). MK-677 improved nitrogen balance integrated over the 7 days of treatment; area under the curve day 8-14 nitrogen balance response was +2.69 +/- 5.0 (SE) for MK-677 and -8.97 +/- 5.26 g.day for placebo (P < 0.001). MK-677 produced a peak GH response of 55.9 +/- 31.7 micrograms/L after single dose (day 1 of treatment) and 22.6 +/- 9.3 micrograms/L after a week of dosing compared with placebo treatment peak GH values of approximately 9 (treatment day 1) and approximately 7 micrograms/L (treatment day 7). Following the initial 7-day caloric restriction, insulin-like growth factor-I (IGF-I) declined from 232 +/- 25 to 186 +/- 19 ng/mL in the MK-677 group and from 236 +/- 19 to 174 +/- 23 ng/mL in the placebo group. Mean IGF-I concentration increased significantly during MK-677 to 264 +/- 31 ng/mL (mean for the last 5 days of treatment) compared with 188 +/- 19 ng/mL with placebo (P < 0.01). No significant difference in IGF binding protein-2 was found between the MK-677 and placebo treatments. However, the mean in IGF binding protein-3 for the last 5 days of MK-677 treatment was also significantly increased to 3273 +/- 330 ng/mL (mean +/- SE) compared with placebo 2604 +/- 253 ng/mL (P < 0.01). Neither the serum cortisol nor the PRL response was significantly greater after 7 days of MK-677 dosing compared with 7 days of placebo. MK-677 (25 mg) was generally well tolerated and without clinically significant adverse experiences. In conclusion, MK-677 reverses diet-induced nitrogen wasting, suggesting that if these short-term anabolic effects are maintained in patients who are catabolic because of certain acute or chronic disease states, it may be useful in treating catabolic conditions.

Adult↗
PubMed1997

Protease-resistant form of insulin-like growth factor-binding protein 5 is an inhibitor of insulin-like growth factor-I actions on porcine smooth muscle cells in culture.

IGFs are pleiotrophic mitogens for porcine smooth muscle cells (pSMC) in culture. The effects of IGFs on cells are modulated by various insulin-like growth factor-binding proteins (IGFBP). IGFBP-5 is synthesized by pSMC and binds to the extracellular matrix. However, IGFBP-5 is also secreted into conditioned medium of cultured cells and is cleaved into fragments by a concomitantly produced protease. These fragments have reduced affinity for the IGFs and cleavage makes it difficult to assess the role of intact IGFBP-5. To study the consequence of accumulation of intact IGFBP-5 in medium, we determined the cleavage site in IGFBP-5 and prepared a protease resistant mutant. Amino acid sequencing of purified IGFBP-5 fragments suggested Arg138-Arg139 as the primary cleavage site. Arg138-Arg139-->Asn138-Asn139 mutations were introduced to create protease-resistant IGFBP-5, which has the same affinity for IGF-I as the native protein. This mutant IGFBP-5 remained intact even after 24 h of incubation and it inhibited several IGF-I actions when added to pSMC culture medium. The mutant IGFBP-5 (500 ng/ml) decreased IGF-I stimulated cellular DNA synthesis by 84%, protein synthesis by 77%, and it inhibited IGF-I stimulated migration of pSMC by 77%. It also inhibited IGF-I stimulation of IRS-1 phosphorylation. In contrast, the same amount of native IGFBP-5 did not inhibit IGF-I actions. The significance of inhibitory effects of the protease resistant IGFBP-5 was further demonstrated in pSMC transfected with mutant or native IGFBP-5 cDNAs. The mutant IGFBP-5 accumulated in culture medium of transfected cells, while native IGFBP-5 was degraded into fragments, PSMC overexpressing the mutant IGFBP-5 also responded poorly to IGF-I compared with mock transfected cells. IGF-I (5 ng/ml) increased [35S]methionine incorporation into control cells by 36% above the basal level, but it did not significantly change (4%) in pSMC cultures that were producing the mutant IGFBP-5. In conclusion, the accumulation of protease-resistant IGFBP-5 in the medium was inhibitory to IGF-I actions on pSMC. This suggests that proteolysis can prevent IGFBP-5 from acting as an inhibitor of IGF-I-stimulated effects and that it serves as an important mechanism for regulating cellular responsiveness to IGF-I.

Amino Acid Sequence↗
PubMed1997

Retinoic acid inhibits cell growth in HPV negative cervical carcinoma cells by induction of insulin-like growth factor binding protein-5 (IGFBP-5) secretion.

Retinoids have been demonstrated to inhibit epithelial cell growth and differentiation. We examined the anti-proliferative effects of retinoic acid (RA) in an HPV positive and negative cervical carcinoma cell line. Our findings indicate that HPV-negative C33A cervical carcinoma cells are more sensitive to the growth inhibitory activity of retinoic acid (RA) than are HPV-positive CaSki cervical carcinoma cells. However, conditioned medium from RA-treated C33A cells displayed strong growth inhibitory activity in both C33A and CaSki cells. Since RA has been shown to modulate the expression of insulin-like growth factor binding proteins (IGFBPs) in many cells, we examined RA regulated expression of IGFBPs in medium isolated from RA treated C33A cells. IGFBP-5 was detectable in medium from C33A cells exposed to RA, and addition of purified exogenous IGFBP-5 resulted in growth inhibition of C33A cells. These results indicate that RA exerts it's anti-neoplastic effect in HPV negative cervical carcinoma cells via the overproduction of IGFBP-5.

Antineoplastic Agents↗
PubMed1997

Use of lanthanum to accurately quantify insulin-like growth factor binding to proteins on cell surfaces.

Insulin-like growth factor binding proteins (IGFBPs) are found both associated with cells and in extracellular fluids. Cell-associated IGFBPs increase [125I]-IGF binding to cell monolayers, whereas extracellular (soluble, released) IGFBPs decrease binding. In the current study, we show that either IGFBP-3 or IGFBP-5 are the major forms of IGFBP released from monolayers of human GM10 fibroblasts, T98G glioblastoma cells and forskolin-treated bovine MDBK cells. IGFBPs represent the most abundant [125I]-IGF-I binding site on GM10 and T98G cell monolayers, but 4-17% of the total cell-associated IGFBPs are released from the cell monolayer at 8 degrees C during their quantification. Most of the IGFBPs (> 70%) are released from MDBK cells. Quantitative estimates of [125I]-IGF binding to the cell monolayers are altered because of the ability of the released IGFBPs to reduce the amount of radiolabeled ligand that is available to bind to the cell surface. Lanthanum (La3+) depresses IGFBP release from all three cell types (> 80% for GM10 and T98G cells and > 65% for MDBK cells). The effect was cation specific, noted with La3+ or Zn2+ but not with either Mn2+, Sr2+ or Se3+. The effect was also IGFBP specific; La3+ markedly depressed the release of IGFBP-3 and IGFBP-5, but had less of an effect on IGFBP-2 and IGFBP-4. Concomitant with a decrease in IGFBP-3 and IGFBP-5 release, La3+ caused an increase in [125I]-IGF-I binding to cell-associated IGFBPs and type I IGF receptors. The released soluble IGFBPs have a three- to 20-fold greater affinity (Ka) for [125I]-IGF-I compared to cell-associated IGFBPs. La3+ did not alter the affinity constants of cell-associated IGFBPs. In summary, we have identified a means to prevent loss of IGFBPs from cell monolayers during binding assays. This procedure will be useful in accurately quantifying the levels of IGFBPs on cell monolayers and in determining the role of cell-associated IGFBPs in controlling IGF activity. Retention of cell-associated low affinity IGFBPs may be important in controlling the size of the pericellular IGF pool and in regulating IGF-I access to the type IIGF receptor.

Cell Line↗
PubMed1997

Insulin-like growth factor binding proteins and their role in controlling IGF actions.

The insulin-like growth factor binding proteins (IGFBPs) are a family of six proteins that bind to insulin-like growth factor-I and -II with very high affinity. Because their affinity constants are between two- and 50-fold greater than the IGF-I receptor, they control the distribution of the IGFs among soluble IGFBPs in interstitial fluids, IGFBPs bound to cell surfaces or extracellular matrix (ECM) and cell surface receptors. Although there are six forms of insulin-like growth factor binding proteins, most interstitial fluids contain only three or four forms, and usually only one or two predominate. The proteins differ significantly in their biochemical characteristics, and this accounts for many of the differences that have been observed in their biological actions. Several different types of protease cleave these binding proteins. Proteolytic cleavage generally inactivates the binding proteins or reduces their ability to bind to IGF-I or -II substantially. Several cell types have been shown to secrete these proteases; therefore, the factors that regulate protease activity can control binding protein actions indirectly. Other post-translational modifications, such as glycosylation and phosphorylation, have been shown to alter IGF binding protein activity. While binding protein actions have been studied extensively in vitro, many of the in vivo activities of these proteins remain to be defined.

Amino Acid Sequence↗
PubMed1997

Insulin-like growth factor binding protein-5 binds to plasminogen activator inhibitor-I.

Insulin-like growth factor binding protein-5 (IGFBP-5) has been shown to bind to the extracellular matrix (ECM) of both fibroblasts and smooth muscle cells. The ECM-IGFBP-5 interaction is mediated in part by binding to heparan sulfate containing proteoglycans. Because proteoglycans may not be the only components of ECM that bind to IGFBP-5, we have determined its ability to bind to other ECM proteins. When a partially purified mixture of the proteins that were present in fibroblast conditioned medium was purified by IGFBP-5 affinity chromatography, a 55-kDa protein was eluted. Amino acid sequencing of the amino terminal 28 amino acids showed that it was human plasminogen activator inhibitor-1 (PAI-1). To determine if this interaction was specific, purified human PAI-1 was incubated with IGFBP-5 and the IGFBP-5/PAI-1 complex immunoprecipitated with anti-PAI-1 antiserum. When the precipitate was analyzed by immunoblotting using anti-IGFBP-5 antiserum, the intensity of the IGFBP-5 band was substantially increased compared with controls that did not contain human PAI-1. A synthetic IGFBP-5 peptide that contained the amino acid sequence between positions 201 and 218 inhibited IGFBP-5/PAI-1 interaction. Coincubation of IGFBP-5 mutants that contained substitutions for specific basic residues located between positions 201 and 218 with PAI-1 indicated that some of these amino acids were important for binding. Two mutants that contained neutral substitutions for specific basic amino acids within the glycosaminoglycan binding domain had reduced binding to PAI-1. In contrast, three other mutants that also had substitutions for charged residues in the same region had no reduction in binding. Heparin and heparan sulfate inhibited the IGFBP-5/PAI-1 interaction; however, several other glycosaminoglycans had no effect. PAI-1 was determined to be an important ECM component for binding because approximately 27% of total ECM binding could be inhibited with anti-PAI-1 antiserum. Competitive binding studies with unlabeled IGFBP-5 showed that the dissociation constant of PAI-1 for IGFBP-5 was 9.1 x 10(-8) M. In summary, IGFBP-5 binds specifically to plasminogen activator inhibitor-1. Because this is present in the extracellular matrix of several cell types, it may be one of the important binding components of ECM. PAI-1 binding partially protects IGFBP-5 from proteolysis, suggesting that it is one of the ECM components that is involved in mediating this effect.

Animals↗
PubMed1997

Use of insulin-like growth factor I (IGF-I) and IGF-binding protein measurements to monitor feeding of premature infants.

To determine whether peptides of the insulin-like growth factor (IGF) system might be useful indicators of nutritional adequacy in premature infants, we studied 50 premature (25-34 weeks gestation) infants prospectively to define the relationship between nutrient intake and serum concentrations of IGF-I, IGF-binding protein-2 (IGFBP-2), and IGFBP-3. Each infant was monitored for at least 2 weeks. Nutrient intake was quantified from daily logs; weight was determined daily, and measurements of IGF-I, IGFBP-2, and IGFBP-3 in serum were made twice weekly. Serum IGF-I correlated strongly with length of gestation, increasing 4.03 +/- 0.95 ng/mL for each additional week of gestation (P < 0.0001) and 0.36 +/- 0.07 ng/mL day each day since birth (P < 0.0001). A higher intake of calories increased IGF-I by 0.07 +/- 0.01 ng/mL for each calorie per kg ingested over the previous 3 days (P < 0.0001). IGF-I increased quadratically as protein intake increased. For each change of 1% in calories as protein squared, IGF-I increased 0.36 +/- 0.11 ng/mL (P < 0.0001). Serum IGFBP-3 concentrations also correlated with length of gestation, increasing 25.06 +/- 11.83 micrograms/L.wk (P = 0.035) and 4.14 +/- 1.33 micrograms/.day since birth (P = 0.003). Unlike IGF-I, variation in the amount of protein supplied did not change IGFBP-3. As calorie intake increased, IGFBP-3 increased by 0.54 +/- 0.17 microgram/L for each calorie per kg consumed over the previous 3 days (P = 0.0015). In contrast to IGF-I and IGFBP-3, IGFBP-2 declined as the length of gestation increased (56.12 +/- 16.92 ng/mL.week; P = 0.001) and with each additional day of life (7.57 +/- 2.44 ng/mL.day; P = 0.003). Dietary protein, the predominant regulator of IGFBP-2, caused a decrease of 33.22 +/- 9.00 ng/mL with each percent increase in dietary calories as protein (P < 0.0003). Calorie intake had less effect on IGFBP-2 than protein intake. These results indicate that each of the three peptides studied is regulated in premature infants by nutritional intake, and that their regulatory patterns are qualitatively similar to those observed in older individuals. Measurements of these peptides in premature infants may be useful indicators of nutritional status and adequacy of nutrient intake.

Humans↗
PubMed1997

Cellular distribution of insulin-like growth factor binding protein mRNAs and peptides during rat lung development.

A role for IGF binding proteins (IGFBPs) in lung development is suggested by the identification of IGFBPs in lung tissue and production of IGFBPs by fetal lung cells in culture. To characterize the expression of IGFBPs during lung development in the rat in vivo (16 days gestation through adulthood), the expression of IGFBP mRNAs (IGFBP-1 to IGFBP-6) was examined by Northern analysis and in situ hybridization, and IGFBP peptides (IGFBP-2, IGFBP-3, and IGFBP-5) were localized by immunohistochemistry. IGFBP-1 mRNA was not detectable. IGFBP-2 mRNA (1.8 kb) was expressed in both fetal and postnatal life with peak expression during the fetal pseudoglandular stage. IGFBP-2 mRNA was localized mainly to airway epithelium. IGFBP-3 mRNA (2.4 kb) was maximally expressed postnatally in the saccular stage of lung development; it was identified in airway epithelium and interstitium in the fetal lung, but predominantly in airway epithelium after birth. IGFBP-4 (2.6 kb) and IGFBP-5 (6.0 kb) mRNA levels were maximal after birth, from 3 to 21 days postnatal (saccular and alveolar stage). IGFBP-4 mRNA was localized primarily to the interstitium and blood vessels early in development, but was abundant in airway epithelium in the adult. IGFBP-5 mRNA was most abundant in the airway epithelium. IGFBP-3, IGFBP-4, IGFBP-5, and to a lesser extent IGFBP-6 were localized to the large cartilaginous airways in the adult. IGFBP-2, IGFBP-3, and IGFBP-5 peptides were distributed more widely than their respective mRNAs, with a temporal pattern of immunoreactivity following that of their mRNAs. Maximal staining was noted in airway epithelium for IGFBP-2 in the newborn, for IGFBP-3 in the saccular stage (newborn to 3 days postnatal), and for IGFBP-5 in the alveolar stage (5 to 21 days postnatal). Our studies demonstrate that IGFBP-2, IGFBP-3, IGFBP-4, and IGFBP-5 are synthesized and distributed in spatially and temporally different patterns in the developing lung. The widespread distribution of IGFBP immunoreactivity compared with their respective mRNAs suggests that IGFBPs are important paracrine factors in the regulation of IGF action in the developing lung.

Animals↗