Biomedical subjects

F J Ballard

Publications and source records attributed to F J Ballard.

At least 55 records · Page 3Linked to original sources

PubMed1993

Anabolic effects of insulin-like growth factor-I (IGF-I) and an IGF-I variant in normal female rats.

Administration of IGF-I over a 14-day period to growing female rats via s.c. implanted osmotic pumps led to an increased body weight gain, an improved N retention and a greater food conversion efficiency. The effects were dose-dependent, with the highest daily dose tested, 278 micrograms/day, producing 18-26% increases in these measurements. LR3IGF-I, a variant of human IGF-I that contains an amino terminal extension peptide as well as glutamate-3 replaced by arginine and exhibits very weak binding to IGF-binding proteins, was substantially more potent than the natural growth factor, in the 44 micrograms/day of this peptide produced similar effects to the high IGF-I dose. Organ weight and carcass composition measurements showed that the two IGF peptides generally maintained body proportions at those existing when the experiment began. Muscle protein synthesis and myofibrillar protein breakdown were both slightly increased by IGF treatment, so that the observed improvement in N retention could not be explained through protein accretion rates calculated from these measures. Infusion of human GH at a dose of 213 micrograms/day did not stimulate body growth. This investigation establishes that IGF peptides stimulate the growth of normal growing animals, with IGF-I variants that bind less well to IGF-binding proteins being more active than IGF-I.

Animals↗

PubMed1993

Plasma clearance and tissue distribution of labelled insulin-like growth factor-I (IGF-I) and an analogue LR3IGF-I in pregnant rats.

To determine whether the changes in insulin-like growth factor-binding proteins (IGFBPs) and IGF-I levels during pregnancy in rats affect the clearance of IGFs from the circulation, we have measured pharmacokinetic parameters and the tissue distribution of radiolabelled IGF-I and LR3IGF-I, a potent analogue which has a markedly reduced affinity of binding to the IGFBPs. Intravenous boluses of radiolabelled growth factors were administered to catheterized virgin and age-matched pregnant rats on day 18 of gestation when plasma IGFBPs, in particular IGFBP-3, are dramatically reduced. IGF-I was cleared more rapidly from plasma in pregnant rats compared with the virgins; metabolic clearance rate (MCR) = 2.88 +/- 0.12 (S.E.M.) and 0.90 +/- 0.05 ml/min per kg respectively. Although LR3IGF-I was cleared more rapidly than IGF-I from plasma, similar clearance rates for the analogue were obtained in both pregnant and virgin animals, MCR = 9.19 +/- 0.15 and 9.84 +/- 0.28 ml/min per kg respectively. In virgin rat plasma, labelled IGF-I was mainly associated with the 150 kDa complex, whereas in pregnant rat plasma IGF-I was predominantly associated with lower M(r) IGFBPs (approximately 30-50 kDa). The majority of LR3IGF-I was detected as free peptide. A larger proportion of the tracer was detected as small M(r) breakdown products in plasma from rats under conditions of reduced binding to IGFBPs, e.g. during pregnancy or when LR3IGF-I was the labelled tracer, suggesting greater rates of IGF degradation. More LR3IGF-I tracer was detected in kidneys, ovaries and adrenals of virgin rats and in the ovaries and adrenals of pregnant rats, compared with IGF-I tracer. IGF-I radioactivity was greater than LR3IGF-I in caecum, brain, liver and heart in virgin rats and in kidneys, caecum, brain, liver, heart, placenta, fetus and fetal plasma of the pregnant rats. These results show that the reduction in IGFBP during pregnancy dramatically increased the clearance of IGF-I from the circulation towards that obtained with LR3IGF-I. The observation that less LR3IGF-I was detected in placenta, fetus and fetal plasma compared with IGF-I raises the possibility that the ability to bind IGFBPs during pregnancy may enhance IGF uptake by the conceptus.

Adrenal Glands↗

PubMed1993

Evolution of insulin-like growth factor binding proteins.

In order to understand more about the origins and evolutionary relationships of insulin-like growth factors (IGFs) and their binding proteins (IGFBPs) we have commenced characterization of the IGFBPs in non-mammalian sera. We show by both in vitro labelling with subsequent analytical gel filtration and by ligand blotting that IGFBPs are present in lamprey serum, indicating that the IGFBPs are indeed, very ancient proteins. Furthermore we present evidence that the major serum IGFBP in lamprey is significantly smaller than the high molecular weight IGFBP3 complex in rat serum. In addition, we show that IGFBPs occur widely throughout vertebrates as we detect IGFBPs in ligand blots of serum from marsupials, monotremes, reptiles, birds and turtles.

Animals↗

PubMed1993

Effects of interactions between IGFBPs and IGFs on the plasma clearance and in vivo biological activities of IGFs and IGF analogs.

The relative activities in vivo of IGFs that differ in their association affinities towards IGF binding proteins (IGFBPs) have been examined in a series of comparisons between IGF-I and LR3IGF-I. IGF-I has approximately 1000 fold higher affinity than LR3IGF-I towards IGFBP-3, IGFBP-4, total rat plasma IGFBPs and L6 myoblast BP. In cultured L6 myoblasts the reduced association with IGFBPs gives LR3IGF-I a 5-10 fold greater biological potency. Chronic administration of the peptides over 14 days to normal female rats produces marked increases in body weight, nitrogen retention and food conversion efficiency as well as retention of the carcass composition and fractional weights of the gut, spleen and thymus that are characteristic of the younger age. In the growth measurements LR3IGF-I is 6 fold more potent than IGF-I, thus reflecting the in vitro difference. In a second series of experiments in which the clearance rates of the two peptides were compared, LR3IGF-I was shown to be removed from the plasma much more rapidly than was IGF-I, a difference reflecting the poor association of LR3IGF-I with plasma IGFBPs. The crucial relevance of binding protein association in explaining the difference was confirmed in pregnant rats where IGFBP levels are markedly reduced. In this condition only the clearance of IGF-I was affected to produce a clearance rate almost as rapid as that found with LR3IGF-I. These experiments demonstrate that an IGF variant which associates poorly with IGFBPs is removed more rapidly from the blood and is more potent than IGF-I.

Animals↗

PubMed1992

Insulin-like growth factor-I (IGF-I) and especially IGF-I variants are anabolic in dexamethasone-treated rats.

The administration of insulin-like growth factor-I (IGF-I) via subcutaneously implanted osmotic pumps partially reversed a catabolic state produced by the co-administration of 20 micrograms of dexamethasone/day to 150 g male rats. Marked dose-dependent effects on body weight and nitrogen retention were produced, with the highest IGF-I dose, 695 micrograms/day, giving a 6 g increase in body weight over 7 days, compared with a 19 g loss in the dexamethasone-only group and an 18 g gain in pair-fed controls. Two IGF-I analogues that bind poorly to IGF-binding proteins, the truncated form, des(1-3)IGF-I, and a variant with an N-terminal extension as well as arginine at residue 3, LR3IGF-I, were approx. 2.5-fold more potent than IGF-I. The response with LR3IGF-I was particularly striking because this peptide binds 3-fold less well than IGF-I to the type 1 IGF receptor. The increased potencies of the IGF-I variants may relate to the substantially increased plasma levels of IGF-binding proteins, particularly IGFBP-3, produced by the combined treatment of dexamethasone with IGF-I or the variants. These binding proteins would be expected to decrease the transfer of IGF-I, but not that of the variants, from blood to tissue sites of action. Measurements of muscle protein synthesis at the end of the treatment period and muscle protein breakdown by 3-methylhistidine (3MH) excretion throughout the experiment indicated coordinate anabolic effects of the IGF peptides on both processes. Thus 3MH excretion was decreased at the highest IGF-I dose from 83.5 +/- 4.2 (S.E.M.) mumol/kg per 7 days to 65.1 +/- 2.2, compared with 54.9 +/- 1.2 in the pair-fed controls. Part of this response in 3MH excretion may have reflected a decrease in gut protein breakdown, because IGF-I and especially the IGF analogues increased the gut weight by up to 45%. Notwithstanding the effects on protein synthesis and breakdown, the fractional carcass weights remained low in the IGF-treated groups, although the increase in total carcass weight reflected nitrogen rather than fat gain. The dexamethasone-induced changes in liver, spleen and heart weight were restored towards normal by the IGF treatment. The experiment demonstrates the potential of IGF-I treatment of catabolic states and especially the value of modified forms of growth factors that bind weakly to IGF-binding proteins.

Amino Acid Sequence↗

PubMed1992

Factors in ruminant colostrum that influence cell growth and murine IgE antibody responses.

Bovine colostrum was investigated as a source of biologically active molecules capable of stimulating the growth of mammalian cells in culture and modifying the immune response in a murine model. An extract prepared from bovine colostral whey by cation exchange and reversed-phase chromatography stimulated the growth of L6 rat myoblasts, Balb/c-3T3 mouse fibroblasts and BHK-21 baby hamster kidney cells with equal or greater potency than fetal bovine serum. Fractionation of the bovine colostral extract by gel-permeation chromatography in M-acetic acid identified a number of cell-growth factors for each cell type. Bovine colostral extract was compared with an ovine colostral whey preparation for its ability to modulate IgE antibody responses in mice. Doses of 8 and 4 mg/d of ovine colostral whey or bovine colostral extract specifically suppressed IgE antibody responses, whereas at lower doses suppression did not occur. We conclude that bovine colostrum contains cell-growth factors as well as immunomodulatory factors that are able to regulate the IgE response in a heterologous species.

Animals↗

PubMed1992

Differences in energy metabolism between normal weight 'large-eating' and 'small-eating' women.

Nine 'large-eating' (approximately 12 MJ/d) and nine 'small-eating' (approximately 5.3 MJ/d) women were selected from the population on the basis of diet and activity diaries. At rest and in the post-absorptive state the rate of oxygen consumption (VO2)/kg fat-free mass (FFM) and rate of carbon dioxide production (VCO2)/kg FFM were 9-17% higher (P < 0.05) in the 'large-eaters' than in the 'small-eaters'. As energy expenditure was increased by walking at 2.4, 3.9 and 5.4 km/h the differences between the two experimental groups for both VO2/kg FFM and VCO2/kg FFM were decreased to negligible values, but energy expended on a body-weight basis (MJ/kg per min) remained significantly higher (5-10%) in 'large-eaters'. Oral temperature was also consistently higher (up to 0.5 degrees) in this group both at rest and during sitting, standing and walking activities. Although the average thermic effect of a standardized liquid meal tended to be higher (27%; not significant) in the 'small-eaters', the other results demonstrate that the 'large-eating' females had a markedly higher rate of energy expenditure at rest and during light physical activities.

Adult↗

PubMed1992

Production and characterization of recombinant insulin-like growth factor-I (IGF-I) and potent analogues of IGF-I, with Gly or Arg substituted for Glu3, following their expression in Escherichia coli as fusion proteins.

The development of an efficient expression system for insulin-like growth factor-I (IGF-I) in Escherichia coli as a fusion protein is described. The fusion protein consists of an N-terminal extension made up of the first 46 amino acids of methionyl porcine GH ([Met1]-pGH) followed by the dipeptide Val-Asn. The latter two residues provide a unique hydroxylamine-sensitive link between [Met1]-pGH(1-46) and the N-terminal Gly of IGF-I. Downstream processing of the fusion proteins involved isolation of inclusion bodies, cleavage at the Asn-Gly bond, refolding of the reduced IGF-I peptide and purification to homogeneity. This expression system was also used to produce two variants of IGF-I in which Glu3 was substituted by either Gly or Arg to give [Gly3]-IGF-I and [Arg3]-IGF-I respectively. Production of milligram quantities of IGF-I peptide was readily achieved. The purity of the IGF-I, [Gly3]-IGF-I and [Arg3]-IGF-I was established by high-performance liquid chromatography and N-terminal sequence analysis. [Gly3]-IGF-I and [Arg3]-IGF-I were more potent than IGF-I in biological assays measuring stimulation of protein synthesis and DNA synthesis or inhibition of protein breakdown in rat L6 myoblasts. Both analogues bound very poorly to bovine IGF-binding protein-2 and slightly less well than IGF-I to the type-1 receptor on rat L6 myoblasts. We conclude that reduced binding to IGF-binding proteins rather than increased receptor binding is the likely explanation for the greater biological potency of the analogues compared with IGF-I.

Amino Acid Sequence↗

PubMed1992

Novel recombinant fusion protein analogues of insulin-like growth factor (IGF)-I indicate the relative importance of IGF-binding protein and receptor binding for enhanced biological potency.

An efficient expression system in Escherichia coli for several biologically active insulin-like growth factor-I (IGF-I) fusion peptide analogues is described. These novel IGF-I fusion protein analogues have properties that make them very useful reagents in the investigation of IGF-I action. The analogues comprise an IGF-I sequence and the first 11 amino acids of methionyl porcine growth hormone (pGH) and include [Met1]-pGH(1-11)-Val-Asn-IGF-I, which contains the authentic IGF-I sequence, and two analogues, [Met1]-pGH(1-11)-Val-Asn-[Gly3]-IGF-I and [Met1]-pGH(1-11)-Val-Asn-[Arg3]-IGF-I, where Glu-3 in the human IGF-I sequence has been replaced by Gly or Arg respectively. The three peptides are referred to as Long IGF-I, Long [Gly3]-IGF-I or Long [Arg3]-IGF-I depending on the IGF-I sequence present. Production of the purified fusion peptides was aided by folding the reduced and denatured fusion peptide sequence under conditions that gave very high yields of biologically active product. Introduction of a hydrophobic N-terminal extension peptide appears to facilitate the correct folding of the IGF-I analogues compared with that obtained previously when folding normal-length IGFs. The biological activities of the IGF-I fusion peptides were compared with authentic IGF-I and the truncated analogue, des(1-3)IGF-I. In L6 rat myoblasts, all the analogues were more potent than authentic IGF-I in their abilities to stimulate protein and DNA synthesis and inhibit protein breakdown. In H35 hepatoma cells, where the IGFs act through the insulin receptor, the Long IGF-I analogues maintained a similar potency relative to IGF-I as was observed in the L6 myoblasts. The order of biological potency in cell lines secreting IGF-binding proteins (IGFBPs) into the medium was Long [Arg3]-IGF-I-des(1-3)IGF-I greater than Long [Gly3]-IGF-I greater than Long IGF-I greater than IGF-I. In chicken embryo fibroblasts, a cell line that does not secrete detectable IGFBPs into the medium, Long [Arg3]-IGF-I, was less potent than IGF-I. Investigation of receptor and IGFBP association by these analogues reinforced our previous findings that N-terminal analogues of IGF-I show increased biological potency due to changes in the degree of their IGFBP interactions.

Amino Acid Sequence↗

PubMed1992

Production and characterization of recombinant chicken insulin-like growth factor-I from Escherichia coli.

Recombinant chicken insulin-like growth factor-I (cIGF-I) has been produced in Escherichia coli after first modifying a plasmid that coded for a human IGF-I (hIGF-I) fusion protein, in order to introduce codons for the eight amino acid substitutions. The cIGF-I fusion protein, deposited in bacterial inclusion bodies, was dissolved under reducing conditions, desalted, subjected to anion-exchange chromatography to remove proteinases, refolded and partially purified by reverse-phase high-performance liquid chromatography. The fusion protein was cleaved with hydroxylamine after which cIGF-I was purified to homogeneity by three additional chromatographic steps. Recombinant cIGF-I was equipotent with hIGF-I in cell culture bioassays of protein synthesis and breakdown using rat L6 myoblasts and chick embryo fibroblasts. Binding of radiolabelled cIGF-I and hIGF-I was also equivalent in the two cell lines, as was their binding in ligand blots of chicken, sheep and human plasma. The cross-reactivity of cIGF-I in a polyclonal hIGF-I radioimmunoassay was 60% of that observed with hIGF-I. The availability of recombinant cIGF-I will facilitate investigations into the role of IGF-I in chicken growth and development.

Amino Acid Sequence↗

PubMed1992

Insulin-like growth factor-I and its N-terminal modified analogues induce marked gut growth in dexamethasone-treated rats.

The effects of insulin-like growth factor-I (IGF-I) on the gut of 150 g dexamethasone-treated rats were compared with those of two analogues with reduced affinity for IGF-binding proteins, des(1-3)IGF-I and LR3IGF-I, an N-terminal-extended variant. Administration of IGF-I for 7 days to rats made catabolic by co-treatment with dexamethasone induced a dose-dependent increase in total gut weight, with the highest dose of IGF-I (695 micrograms/day) increasing gut weight by up to 60%, and gut weight as a fraction of body weight by up to 32%. Effects were apparent in all regions of the gut examined, including the stomach, small intestine and colon. Histological and biochemical analyses of the intestine showed that cross-sectional mass, rather than gut length, was increased, and proportional increases in wet weight, protein and DNA content per unit length were measured in both the mucosa and muscularis layers. The rate of duodenal protein synthesis measured on day 7 of treatment was not increased by IGF-I treatment. The IGF-I analogues had qualitatively similar effects to IGF-I, but were consistently severalfold more potent, providing evidence that IGF-binding proteins reduce the biological activity of exogenous IGF-I in the gut. The results indicate that the gut is one of the most sensitive IGF-I target tissues, and that potency in vivo correlates with a reduced interaction with IGF-binding proteins.

Animals↗

PubMed1992

Insulin-like growth factor I and its variant, des(1-3)IGF-I, improve nitrogen balance and food utilization in rats with renal failure.

The growth-promoting effects of IGF-I were examined in rats following partial nephrectomy and compared with the effects of the des(1-3) variant of IGF-I. Four groups of rats were subjected to 5/6 nephrectomy (n = 8 per group) and treated for 7 days with IGF-I (0.9 or 2.2 mg/kg BW/day), des(1-3)IGF-I (0.9 mg/kg/BW/day), or vehicle (0.1 M acetic acid) administered subcutaneously by osmotic pump. A group of vehicle-treated, sham-operated control rats (n = 7) was included. Food utilization was significantly improved in all three peptide-treated groups, by 13-16% compared with the vehicle-treated nephrectomized group. Also, nitrogen balance was enhanced, particularly in the des(1-3)IGF-I group, in which nitrogen excretion was reduced by 24%, with the low- and high-dose IGF-I groups showing 16 and 18% reductions, respectively. Serum urea levels were significantly decreased, by 25%, in the des(1-3)IGF-I group, with 20 and 17% reductions being observed in the low- and high-dose IGF-I groups. Muscle protein degradation was found to be significantly attenuated with des(1-3)IGF-I treatment but was not significantly affected in the two IGF-I-treated groups. While carcass composition was not altered with IGF peptide treatment, absolute mass of protein in the carcass was improved in rats treated with the high dose of IGF-I. These results show that IGF-I or, more particularly, des(1-3)IGF-I may be efficacious in overcoming impaired growth in renal failure.

Animals↗

PubMed1991

Increased weight gain, nitrogen retention and muscle protein synthesis following treatment of diabetic rats with insulin-like growth factor (IGF)-I and des(1-3)IGF-I.

We have examined the effects of infusing recombinant human growth hormone (hGH), insulin-like growth factor-I (IGF-I), the truncated IGF-I analogue, des(1-3)IGF-I, and insulin over a 7-day period in streptozotocin-induced diabetic rats. IGF-I at a dose of 1.05 or 1.08 mg/kg per day in two experiments increased body weight and nitrogen retention above those of vehicle-infused controls to about 30% of the improvement achieved with 25 or 30 units of insulin/kg per day, but only in the second experiment were the differences statistically significant (P less than 0.05). A 2.5-fold higher IGF-I dose, or des(1-3)IGF-I at 1.08 mg/kg per day, gave effects that were approx. 70% of those obtained with insulin. hGH at 1.38 mg/kg per day was not effective. The IGF peptides, unlike insulin, did not ameliorate the diabetic glucosuria. The improvements in nitrogen balance could be accounted for in part by increases in muscle protein synthesis. Muscle protein breakdown, as assessed by 3-methylhistidine excretion, was inhibited by insulin, but not by the IGF peptides. Carcass fat increased substantially following insulin administration. This did not occur with the IGF peptides, suggesting that IGF predominantly stimulates the growth of lean tissue. IGF-I concentrations and IGF-I-binding proteins in plasma were increased by IGF-I, especially at the higher dose, whereas hGH produced only a transient increase in IGF-I. Des(1-3)IGF-I induced binding proteins, but had only a slight effect on measured IGF-I concentrations. We conclude that IGF peptides stimulate muscle protein synthesis and improve nitrogen balance in diabetes without obviously influencing the abnormal carbohydrate metabolism. Moreover, des(1-3)IGF-I is at least as potent as the full-length IGF-I.

Animals↗

PubMed1991

Insulin-like growth factor (IGF)-I and IGF-II binding to an IGF binding protein. An investigation using chemical modification of tyrosine residues as a structural probe for the sites of interaction.

We have investigated insulin-like growth factor (IGF)-I and IGF-II binding to bovine insulin-like growth factor binding protein-2 (bIGFBP-2) using chemical modification to locate sites on the IGF involved in the binding interaction. bIGFBP-2 was incubated with either recombinant human (hIGF-I) or purified ovine (oIGF-II) to form a mixture of bound and free IGF. Sites of interaction between the binding protein and IGF were then probed by iodination of the available tyrosine residues. Subsequently, the mixture of free IGF and IGF.bIGFBP-2 complex was resolved by neutral chromatography, and the IGF component of the complex with bIGFBP-2 was recovered by reverse-phase high performance liquid chromatography at pH 2.1. The tyrosine labeling patterns of the two populations of IGF, one iodinated while free and the other iodinated while associated with binding protein, were determined following endoproteinase Glu-C peptide mapping. Binding of hIGF-I or oIGF-II to bIGFBP-2 resulted in reduced iodination of the tyrosines in both hIGF-I and oIGF-II that are near the carboxyl-terminal, Tyr-60 and Tyr-59, respectively. The reduction in labeling of these tyrosine residues was 2-fold and 6-fold for hIGF-I and oIGF-II, respectively. On the other hand, labeling of the other 2 tyrosines in hIGF-I and oIGF-II was not different between the free and complexed growth factors. From these results we conclude that Tyr-60 and Tyr-59 in the carboxyl-terminal regions of hIGF-I and oIGF-II, respectively, are either directly involved in the binding reaction or lie in a region of the IGF molecule encompassed by the association with bIGFBP-2. Conversely, the labeling pattern of the other tyrosines, Tyr-24 and Tyr-31 in hIGF-I and Tyr-2 and Tyr-27 in oIGF-II, implies that they are not involved in binding to bIGFBP-2. To examine the role of IGF tyrosine residues in the association with bIGFBP-2, we prepared nonradioactive 127I-labeled oIGF-II. In bIGFBP-2 competition binding assays, 127I-labeled oIGF-II was 2.5-fold and 5-fold less potent than native oIGF-II when competing for binding of 125I-labeled IGF-I or IGF-II tracers, respectively. We interpret these results as indicating that at least 1 tyrosine in oIGF-II is involved in binding to bIGFBP-2.

Animals↗

PubMed1991

IGF-I and the truncated analogue des-(1-3)IGF-I enhance growth in rats after gut resection.

Effects of insulin-like growth factor I (IGF-I) administration and that of the truncated analogue des-(1-3)IGF-I have been examined in 170-g rats over a 7-day period after surgery to remove 80% of the jejunum plus ileum. The doses administered via osmotic infusion pumps were 0.96 and 2.4 mg.kg-1.day-1 IGF-I and 0.96 mg.kg-1.day-1 des-(1-3)IGF-I. All groups lost weight on the day after surgery, but over the next 3 days the des-(1-3)IGF-I and high-dose IGF-I groups stabilized better and subsequently gained significantly (P less than 0.05) more weight than the vehicle or low-dose IGF-I groups over the last 3 days. The weight gains (mean +/- SE) for the groups over this last 3-day period were 14.0 +/- 1.7, 14.4 +/- 2.9, 21.9 +/- 1.7, and 20.8 +/- 1.0 g for the vehicle, low-dose IGF-I, high-dose IGF-I, and des-(1-3)IGF-I groups, respectively. The nitrogen balances over the last 3 days for the high-dose IGF-I and des-(1-3)IGF-I groups, at 242 +/- 14 and 217 +/- 13 mg/d, respectively, were significantly (P less than 0.05) more positive than the control group at 153 +/- 21 mg/d. These differences could at least partially be explained by changes in muscle protein breakdown, as assessed by 3-methyl-L-histidine excretion. The kidneys were heavier in all treatment groups and the thymus after administration of des-(1-3)IGF-I.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

IGF-I and its variant, des-(1-3)IGF-I, enhance growth in rats with reduced renal mass.

The efficacy of insulin-like growth factor I (IGF-I) in enhancing growth in animals with reduced renal mass was investigated in subtotally nephrectomized young male rats. Recombinant human IGF-I was administered by osmotic minipumps for 7 days at two doses, 0.9 and 2.2 mg.kg body wt-1. day-1, and the truncated analogue of IGF-I, des-(1-3)IGF-I, was given at a dose of 0.9 mg.kg body wt-1.day-1. The partial nephrectomy procedure resulted in significantly impaired renal function as evidenced by elevated serum urea and creatinine concentrations, reduced creatinine clearance, and increased average daily urine output. Carcass composition was significantly altered in animals with reduced renal mass; water content increased and fat content decreased, while protein content remained unchanged. Carcass composition was not affected by IGF treatment. Body weight gain, food utilization, and nitrogen balance during the treatment period were significantly increased in rats treated with IGF-I at both the lower and higher doses and in those treated with des-(1-3)IGF-I. The improved nitrogen balance in the des-(1-3)IGF-I group could at least partly be explained by a diminished rate of muscle protein breakdown, as indicated by the reduced urinary excretion rate of 3-methylhistidine. Compensatory hypertrophy of the remnant kidney was significantly increased in the group treated with the high dose of IGF-I. These results suggest that IGF-I may have beneficial effects on somatic growth and nitrogen balance in renal insufficiency, with des-(1--3)IGF-I being particularly effective in reducing the rate of muscle protein breakdown.

Animals↗

PubMed1991

Expression, purification and characterization of secreted recombinant human insulin-like growth factor-I (IGF-I) and the potent variant des(1-3) IGF-I in Chinese hamster ovary cells.

Recombinant human insulin-like growth factor-I (hIGF-I) and a biologically potent variant lacking the N-terminal tripeptide (des(1-3)IGF-I) were produced from transfected Chinese hamster ovary cells. The constructs encoding the signal peptide, sequence of the mature peptide and a C-terminal extension peptide were expressed under the control of a Rous sarcoma virus promoter. Successfully transfected clones secreting correctly processed recombinant hIGF-I or des(1-3)IGF-I were selected by their secretion of IGF-I-like activity into the culture medium. The recombinant peptides were purified to homogeneity as assessed by high-performance liquid chromatography and N-terminal sequence analysis. The purified recombinant peptides exhibited biological potencies equivalent to authentic IGF-I and des(1-3)IGF-I respectively.

Amino Acid Sequence↗

PubMed1991

Effects of full-length and truncated insulin-like growth factor-I on nitrogen balance and muscle protein metabolism in nitrogen-restricted rats.

The ability of insulin-like growth factor-I (IGF-I) to protect against losses of body protein during periods of dietary nitrogen restriction has been evaluated in young rats. Recombinant human IGF-I was administered by osmotic pumps at dose rates of 0, 1.2 or 2.9 mg/kg per day over a 7-day period beginning with the transfer of animals from an 18% to a 4% protein diet. A fourth group received the potent truncated IGF-I analogue, des(1-3)IGF-I, at a dose of 1.2 mg/kg per day over a comparable 7-day period. Plasma IGF-I levels were reduced by 60% following nitrogen restriction, a reduction that was partly prevented by IGF-I administration, especially at the higher dose, but not measurably by des(1-3)IGF-I. The major IGF-binding protein circulating in blood, IGFBP-3, demonstrated a similar pattern of change. A significant (P less than 0.05) protection of body weight was achieved in the low dose IGF-I and des(1-3)IGF-I groups, but only after differences in food intake had been eliminated by analysis of covariance. Nitrogen balances were not significantly different unless analysis of covariance was used to adjust for the nitrogen intakes, whereupon all treatment groups showed improved balance, especially the animals treated with the low IGF-I dose and des(1-3)IGF-I (both P less than 0.01). The rate of muscle protein breakdown calculated from the urinary excretion of 3-methyl-histidine was not significantly altered by the treatments, but fell progressively throughout the 7 days. The fractional rate of muscle protein synthesis measured on the final day was increased by 31,26 and 21% respectively by the low and high doses of IGF-I and by des(1-3)IGF-I. Organ weights (g/kg body weight) showed no effects of IGF-I treatment except for 16% increases in the weight of kidneys in the high dose IGF-I and the des(1-3)IGF-I groups. Carcass analyses demonstrated higher water and lower fat contents (all P less than 0.01) in the same groups. These results suggest that exogenous IGF-I and especially des(1-3)IGF-I can partly protect body protein reserves during nitrogen restriction.

Animals↗