Similar hormonal changes in sera from scorbutic and fasted (vitamin C-supplemented) guinea pigs, including decreased IGF-I and appearance of an IGF-I reversible mitogenic inhibitor

Dietary Vitamin C and Age-Induced Lipid and Hormonal Metabolic Changes in a Humanized Mouse Model Not Synthesizing Vitamin C and Producing Lipoprotein(a) [Gulo (-/-); Lp(a)+]

The lack of ability to produce vitamin C innately and the ability to synthesize human lipoprotein(a) (Lp(a)) are two unique metabolic features present in humans, compared with most other animal species. The Gulo (-/-) and Lp(a)+ mouse model displays these two features and is therefore suitable for the study of metabolic aspects relevant to human metabolism. It is a well-known fact that vitamin C is essential in collagen synthesis, and in maintaining extracellular matrix integrity, as well as being a powerful antioxidant and cofactor in many metabolic pathways, which makes it a critically important micronutrient for health and healthy aging. In this study, we investigated the effects of a long-term intake of high and low doses of vitamin C on age-related metabolic lipid and hormonal changes in young (eight to nine months), mid-aged (one year), and old (two years) Gulo (-/-) and Lp(a)+ mice. We observed that chronic vitamin C deficiency resulted in a less healthy metabolic lipid profile, impaired serum insulin-like growth factor (IGF-1), and sex-hormones secretion, all of which can accelerate the development of various pathological conditions in the aging process. The most susceptible to the negative impact of vitamin C deficiency were the young (eight to nine months) and old (two years) mice. Our study conducted in this humanized mouse model indicates that sustained adequate vitamin C intake is essential in maintaining a healthier metabolic profile, important in preventing age-related pathologies throughout the aging process.

Relation of insulin-like growth factor (IGF) I and IGF-binding protein 3 concentrations with intakes of fruit, vegetables, and antioxidants

BACKGROUND

Fruit, vegetable, and antioxidant intakes may reduce the risk of several insulin-like growth factor (IGF)-related chronic diseases, such as certain types of cancers and cardiovascular diseases.

OBJECTIVE

This study investigated whether intakes of fruit, vegetables, and antioxidants (beta-carotene, lycopene, and vitamin C) are associated with plasma IGF-I and IGF-binding protein 3 (IGFBP-3) concentrations.

DESIGN

Plasma IGF-I and IGFBP-3 concentrations were measured in 1542 healthy women by enzyme-linked immunosorbent assay. A self-administered semiquantitative food-frequency questionnaire was used to estimate mean daily dietary intakes of fruit, vegetables, and antioxidants over the year preceding blood sampling. Multivariate analyses were performed by using generalized linear models to evaluate the association of quintiles of daily intakes with concentrations of growth factors.

RESULTS

A higher intake of citrus fruit was associated with higher concentrations of IGF-I (215 ng/mL for quintile 5 compared with 205 ng/mL for quintile 1; P for trend = 0.04) and with lower concentrations of IGFBP-3 (4803 ng/mL for quintile 5 compared with 4960 ng/mL for quintile 1; P for trend = 0.04). Higher dietary vitamin C intake was associated with higher concentrations of IGF-I (214 ng/mL for quintile 5 compared with 204 ng/mL for quintile 1; P for trend = 0.02) and lower concentrations of IGFBP-3 (4813 ng/mL for quintile 5 compared with 4953 ng/mL for quintile 1; P for trend = 0.03). Total intake of fruit and vegetables and intakes of other botanical fruit and vegetable subgroups, beta-carotene, and lycopene were not related to either IGF-I or IGFBP-3 concentrations.

CONCLUSION

Women with higher intakes of citrus fruit or dietary vitamin C tend to have higher plasma concentrations of IGF-I and lower plasma concentrations of IGFBP-3.

Modulation of the growth hormone-insulin-like growth factor (GH-IGF) axis by pharmaceutical, nutraceutical and environmental xenobiotics: an emerging role for xenobiotic-metabolizing enzymes and the transcription factors regulating their expression. A review

The growth hormone-insulin-like growth factor (GH-IGF) axis has gained considerable focus over recent years. One cause of this increased interest is due to a correlation of age-related decline in plasma GH/IGF levels with age-related degenerative processes, and it has led to the prescribing of GH replacement therapy by some practitioners. On the other hand, however, research has also focused on the pro-carcinogenic effects of high GH-IGF levels, providing strong impetus for finding regimes that reduce its activity. Whereas the effects of GH/IGF activity on the action of xenobiotic-metabolizing enzyme systems is reasonably well appreciated, the effects of xenobiotic exposure on the GH-IGF axis has not received substantial review. Relevant xenobiotics are derived from pharmaceutical, nutraceutical and environmental exposure, and many of the mechanisms involved are highly complex in nature, not easily predictable from existing in vitro tests and do not always predict well from in vivo animal models. After a review of the human and animal in vivo and in vitro literature, a framework for considering the different levels of direct and indirect modulation by xenobiotics is developed herein, and areas that still require further investigation are highlighted, i.e. the actions of common endocrine disruptors such as pesticides and phytoestrogens, as well as the role of xenobiotic-metabolizing enzymes and the transcription factors regulating their expression. It is anticipated that a fuller appreciation of the existing human paradigms for GH-IGF axis modulation gained through this review may help explain some of the variation in levels of plasma IGF-1 and its binding proteins in the population, aid in the prescription of particular dietary regimens to certain individuals such as those with particular medical conditions, guide the direction of long-term drug/nutraceutical safety trials, and stimulate ideas for future research. It also serves to warn athletes that using compounds touted as performance enhancing because they promote short-term GH release could in fact be detrimental to performance in the long-run.

Metalloproteinases, insulin-like growth factor-I and its binding proteins in aortic aneurysm

Abdominal aortic aneurysm is accompanied by the impairment of collagen metabolism in arterial wall. Metalloproteinases and collagen-stimulating factors play an important role in the maintenance of balance between collagen biosynthesis and degradation in tissues. Insulin-like growth factor-I (IGF-I) plays a major role in the stimulation of collagen biosynthesis. Its activity and bioavailability to target cells are modulated by IGF binding proteins (IGFBPs). The potential role of these factors in the mechanism of collagen metabolism deregulation in aortic aneurysm is the purpose of this study. Therefore, we have compared the content of collagen, gelatinolytic activity, IGF-I, IGFBP-1 and IGFBP-3 in normal human aorta and aortic aneurysm. The content of hydroxyproline (representing collagen content) in the proteins of aortic aneurysm was found to be similar to that found in normal aorta. Taking into account that some of the hydroxyproline may be derived from collagen degradation products (CDPs), they were separated and hydroxyproline was determined. It has been found that CDP-derived hydroxyproline content in aortic aneurysm was increased as compared with normal aorta, suggesting an increased collagen degradation. In contrast, zymography showed a decrease of collagenolytic activity in aortic aneurysm tissue, but an increase in mural thrombus, compared to respective controls. IGF-I concentration in aortic aneurysm was decreased, while the concentrations of BP-1 and BP-3 were both increased compared to control. The data suggest that increased collagen degradation in aortic aneurysm is due to the increase in collagenolytic activity in mural thrombus accompanying aneurysm tissue. It suggests that the mural thrombus may play a critical role in the pathogenesis of abdominal aortic aneurysm.

Proline analogue of melphalan as a prodrug susceptible to the action of prolidase in breast cancer MDA-MB 231 cells

Proline analogue of melphalan (Mel-pro) was synthesized as a prodrug susceptible to the action of ubiquitously distributed, cytosolic imidodipeptidase-prolidase [E.C.3.4.13.9]. Conjugation of melphalan (Mel) with proline (Pro) through imido-bond resulted in formation of a good substrate for prolidase. Cytosolic location of prolidase in neoplastic cell suggests that proline analogue of melphalan (Mel-pro) may serve as a prolidase convertible prodrug. We have compared several aspects of pharmacologic actions of Mel and Mel-pro in estrogen-independent breast cancer MDA-MB 231 cells. It has been found that Mel-pro is more effectively transported into the MDA-MB 231 cells, evokes higher cytotoxicity, similar inhibitory effect on DNA synthesis, lower inhibitory effect on collagen biosynthesis and reduces IGF-I receptor and MAPkinase expression in MDA-MB 231 cells, compared to Mel. The results suggest that targeting of prolidase as a Mel-pro-converting enzyme may serve as a potential strategy in pharmacotherapy of breast cancer.

Expression of IGF-binding protein-1 phosphoisoforms in fasted rat skin and its role in regulation of collagen biosynthesis

Insulin-like growth factor-I (IGF-I) is an important stimulator of collagen and glycosaminoglycan (GAG) biosynthesis in tissues. IGF-I activity is modulated by a family of IGF-binding proteins (IGFBPs) with different IGF-I binding affinities. At least IGFBP-1 and IGFBP-2 are known as inhibitors of IGF functions. Some IGFBPs (IGFBP-1, IGFBP-3 and IGFBP-5) may undergo phosphorylation that dramatically increase their affinity for IGF. During fasting of animals there is a significant decrease of the collagen and GAG content of the skin, accompanied by a reduction of plasma IGF-I levels. However, in previous studies we showed that in the skin of fasted rats IGF-I as well as IGFBP-1 and IGFBP-2 expressions were not different, compared to control rat skin, although collagen content was significantly decreased. In the present study we show that fasted rat skin contains similar amounts of IGF-I, IGFBP-3 and IGFBP-1, although extract from fasted rat skin induced inhibition of collagen biosynthesis in cultured fibroblasts, compared to control rat skin extract. Western immunoblot analysis of control and fasted rat skin extracts, using anti-phosphoserine antibodies for immunoprecipitated IGFBP-1 and IGFBP-3, revealed that both proteins are present in phosphorylated form. Although no differences were found in the expression of phosphorylated IGFBP-3 between control and fasted rat skins, that of phosphorylated IGFBP-1 in fasted rat skin extract was higher than in control one. We suggest that there is an increased level of IGFBP-1 phosphoisoform in fasted rat skin, associated with increased affinity for IGF-I. The increase of phosphorylated IGFBP-1 in fasted rat skin tissue may augment IGF-I binding affinity for IGF and decrease its bioavailability for receptor interaction. This mechanism may prevent IGF-I dependent stimulation of fibroblasts to produce extracellular matrix components. The specific expression of IGFBPs and their phosphoisoforms in tissues may play an important role in regulation of IGF-I action during physiologic and pathologic responses.

Serum and tissue level of insulin-like growth factor-I (IGF-I) and IGF-I binding proteins as an index of pancreatitis and pancreatic cancer

Previously we have found deregulation of collagen metabolism in human pancreatitis and pancreatic cancer tissues. Insulin-like growth factor-I (IGF-I) is known to stimulate collagen biosynthesis through interaction with IGF-I receptor. IGF-I binding proteins (BPs) regulate the activity of IGF-I. We investigated whether serum and tissue IGF-I and IGF-BPs as well as tissue IGF-I receptor expression may reflect disturbances of collagen metabolism in patients with pancreatitis and pancreatic cancer. In pancreatitis tissue, a significant increase in IGF-I and IGFBP-3 content was accompanied by a distinct increase in IGF-I receptor expression, compared to control pancreas tissue. In contrast, serum from patients with pancreatitis did not show significant increases in IGF-I and IGFBP-3 levels, however, significant increases in IGFBP-1 level (2.5 fold). Moreover, a distinct decrease in radioactive IGF-binding to the BPs, compared to control serum, was found. Pancreatic cancer tissue and serum of patients with pancreatic cancer showed significant increases in IGF-I, IGFBP-3 and IGFBP-1 content, accompanied by dramatic increases in IGF-I tissue receptor expression, compared to controls. In serum of patients with pancreatic cancer distinct increases in radioactive IGF-binding to 46 kDa BP, compared to control serum, were observed. The data suggest that disturbances in tissue collagen metabolism during pancreatic diseases may result from deregulation of IGF-I homeostasis and that elevated serum levels of IGF-I, IGFBP-3 and IGFBP-1 may serve as markers of pancreatic cancer.

An expression of IGF-binding proteins in normal and pre-eclamptic human umbilical cord serum and tissues

Pre-eclampsia, is the most common, pregnancy-associated pathological syndrome accompanied by a significant increase in collagen and sulphated glycosaminoglycans (GAGs) contents in the umbilical cord arteries (UCAs). Insulin-like growth factor-I (IGF-I) is expressed in most foetal tissues and it is involved in anabolic effects. It stimulates protein (mainly collagen) and GAG biosynthesis, cell proliferation and differentiation. Previously, we have found that pre-eclampsia is associated with an increase of IGF-I concentration in the umbilical cord blood. A family of IGF-I-binding proteins (BPs) modulates the activity of IGF-I. We demonstrated qualitative differences between BPs of normal and pre-eclamptic human umbilical cord (UC) serum and UC-tissues (UCA-wall and Wharton's jelly) by Western immunoblot analysis. All examined sera and tissues contained BP-1 and BP-5 as well lower molecular weight materials. The BP-2 was recovered from both control and pre-eclamptic sera, while it was not detected in the UC-tissues. Instead, lower molecular weight forms of BP-2 were found as judged by the anti-BP-2 antibody. The BP-3 was detected in sera, UCA and Wharton's jelly. The most distinct expression of BP-3 was found in the UCA. The pre-eclamptic UCA and Wharton's jelly contained additional BP-3-reactive material of lower molecular weight. The BP-4 was strongly expressed in pre-eclamptic UC-serum and the expression was decreased in pre-eclamptic UC-tissues, compared to respective controls. Ligand binding assay revealed that most of IGF-I was bound to 46 kDa region (typical for BP-3) in both control and pre-eclamptic sera and tissues. However, distinctly less IGF-I was bound in pre-eclamptic serum, distinctly more in pre-eclamptic UCA and no differences were found in pre-eclamptic Wharton's jelly, compared to controls. We demonstrated that both normal and pre-eclamptic UC-sera and tissues are able to degrade 46 kDa IGF-I-BP. The degradation may result in a decrease of IGF-I binding, contributing to increase in free IGF-I that may stimulate the cells to produce extracellular matrix (ECM) components. The specific BPs and their proteolytic modification in UC tissues may be important modulators of IGF-I action during foetal development.

The potential mechanism for glutamine-induced collagen biosynthesis in cultured human skin fibroblasts

Although glutamine (Gln) is known as an important stimulator of collagen biosynthesis in collagen-producing cells, the mechanism and endpoints by which it regulate the process remain largely unknown. Intermediates of Gln interconversion: glutamate (Glu) and pyrroline-5-carboxylate (P5C) stimulate collagen biosynthesis in cultured cells but evoke different maxima of collagen biosynthesis stimulating activity at different times of incubation. P5C was found to be the most potent stimulator of collagen biosynthesis after 6 h of incubation (approx. three-fold increase); after 12 h, it induced increase in collagen biosynthesis to 260%, while at 24 h, the process was decreased to approximately 80% of control values. Glu induced increase in collagen biosynthesis to approximately 180%, 400% and 120% of control values, after 6, 12 and 24 h, respectively, suggesting that after 12 h of incubation, Glu was the most potent stimulator of collagen biosynthesis. Glu was also the most potent stimulator of type I procollagen expression at this time. After 6, 12 and 24 h incubation, Gln induced collagen biosynthesis to approximately 112, 115 and 230% of control values, respectively. Since prolidase is known to be involved in collagen metabolism, the enzyme activity assay was performed in fibroblasts cultured in the presence of Gln, Glu and P5C. While Gln and Glu required 24 h for maximal stimulation of prolidase activity, P5C induced it after 6-12 h. The data suggest that P5C induced collagen biosynthesis and prolidase activity in a shorter time than Gln and Glu. We considered that P5C directly stimulates the processes, while Gln acts through its intermediate-P5C. Reduction of P5C to proline is coupled to the conversion of glucose-6-phosphate (G6P) to 6-phospho-gluconate, catalyzed by G6P dehydrogenase. We have found that dehydroepiandrosterone (DHEA), a potent inhibitor of G6P dehydrogenase, inhibited a stimulatory effect of P5C on collagen synthesis, expression of type I collagen and prolidase activity. Our results postulate a potential mechanism of glutamine-induced collagen biosynthesis through its intermediate - P5C. P5C-dependent activation of nucleotide biosynthesis, prolidase activity and P5C conversion into proline may contribute to the stimulation of collagen biosynthesis.

Inhibition of collagen biosynthesis and increases in low molecular weight IGF-I binding proteins in the skin of fasted rats

Insulin-like growth factor-I (IGF-I) is an important stimulator of collagen biosynthesis and prolidase activity in connective tissue cells. The disturbances in skin collagen metabolism (reflected by significant decrease in skin collagen content, collagen biosynthesis and prolidase activity) in fasted rats were accompanied by decrease in serum IGF-I level. Fasted rat serum was found to contain about 58% of IGF-I (101.6 +/- 15.4 ng/ml) as compared to control rat serum (175.7 +/- 19.8 ng/ml), while the skin of control and fasted rats contained similar concentrations of IGF-I (about 77 ng/g tissue). The insulin-like growth factor binding proteins (IGFBPs) of sera and tissue extracts (known to regulate IGF-I activity) were analysed by ligand blotting. In the serum of control rats one IGFBP band of about 46 kDa (corresponding to the acid-dissociated IGFBP-3) was detected. In the serum of fasted rats the 46 kDa IGFBP was not observed, however, an other IGFBP of about 30 kDa (corresponding to low molecular weight IGFBPs, e.g. IGFBP-1 or IGFBP-2) was found. The intensity of IGF-I binding to the 30 kDa IGFBP was much higher than that of IGFBP-3, found in control rat serum. Control and fasted rat skin contained similar IGFBPs, however their IGF-I binding abilities were much lower, compared to their serum counterparts. It was found that 46 kDa and 30 kDa proteins, observed in ligand blotting represent IGFBP-3 and IGFBP-1 or IGFBP-2. respectively as demonstrated by western immunoblot analysis. An increase in IGF-binding to 30 kDa IGFBP-1 and/or IGFBP-2 (known as an inhibitors of IGF-dependent functions) in the skin of fasted rats may explain the mechanism of reduced collagen biosynthesis and deposition in tissues during fasting.

Preeclampsia is associated with alterations in insulin-like growth factor (IGF)-1 and IGF-binding proteins in Wharton's jelly of the umbilical cord

Wharton's jelly is abundant in extracellular matrix, which is known as a storage site to concentrate and stabilise growth factors in the vicinity of cells. It was previously found that Wharton's jelly contains significant amounts of insulin-like growth factor (IGF)-1 and IGF-binding proteins (BPs). IGF-1 is a stimulator of biosynthetics of collagen and sulphated glycosaminoglycans. Preeclampsia (edema, proteinuria, hypertension (EPH)-gestosis) is accompanied by an accumulation of sulphated glycosaminoglycans in Wharton's jelly. IGF-1 and BPs may play an important role in such a remodelling of this tissue. It was decided to evaluate the alterations in amounts of IGF-1 and BPs in Wharton's jelly of newborns delivered by mothers with preeclampsia. Studies were performed on Wharton's jelly of 10 controls and 10 newborns delivered by mothers with preeclampsia (edema, proteinuria > 500 mg/l, arterial pressure: systolic > 140 mm Hg, diastolic > 90 mmHg). Radioimmunological techniques were employed to determine IGF-1 and IGF-BPs (BP-1 and BP-3). It was found that preeclampsia is associated with a decrease in IGF-1 and IGF-BP-1 in Wharton's jelly. A slight increase in IGF-BP-3 was found. Ligand blotting demonstrated that BP-3 (not BP-1) is a main component of Wharton's jelly, which binds IGF-1. Heparin drastically inhibited the binding of IGF-1 by BP-3. It is known from our previous studies that preeclampsia is associated with an increase in the amount of sulphated glycosaminoglycans (heparin, heparan sulphate, dermatan sulphate) in Wharton's jelly. This may be a factor, which prevents the binding of IGF-1 by BPs and facilitates the binding of IGF-1 to cells, stimulating them to produce sulphated glycosaminoglycans in Wharton's jelly.

Pre-eclampsia-induced alterations in IGF-I of human umbilical cord

BACKGROUND

Extracellular matrix (ECM)-components serve as a storage site to concentrate and stabilise growth factors in the vicinity of cells. Human umbilical cord (UC) tissues contain significant amounts of IGF-I and IGF-binding proteins (BPs). IGF-I is known as a stimulator of collagen and sulphated glycosaminoglycans (GAGs) biosynthesis. Pre-eclampsia, the most common pregnancy associated syndrome, is accompanied by an accumulation of collagen and sulphated glycosaminoglycans in the UC. One may expect that IGF-I and BPs play an important role in such a remodelling of the UC tissue. For this reason it was decided to evaluate the alterations in amounts of IGF-I and BPs in UC serum and in the UC arterial wall of newborns delivered by mothers with pre-eclampsia.

MATERIALS AND METHODS

Studies were performed on the UCs of 12 control and 12 investigated newborns, delivered by mothers with pre-eclampsia (edema, proteinuria > 500 mg l-1, arterial pressure: systolic > 140 mmHg, diastolic > 100 mmHg). Radioimmunological techniques were employed to determine IGF-I and IGF-BPs (BP-1 and BP-3).

RESULTS

It was found that pre-eclampsia is associated with an increase of IGF-I concentration in the UC serum and with simultaneous decrease of its content in the umbilical cord artery (UCA). The decrease of IGF-I content in the UCA wall was accompanied by an increase of BP-3 and BP-1 in this tissue. The increase in BPs content in the UCA wall was not associated with an enhancement of IGF binding by extracts from the homogenates of arterial wall. Heparin drastically decreased the binding of IGF-I by BP-3.

CONCLUSIONS

Pre-eclampsia is associated with an increase of IGF-I-concentration in the umbilical cord blood and an elevation of BPs contents in the UCA wall. Despite a high concentration of binding proteins, IGF-I is not accumulated in this tissue. High amounts of sulphated GAGs in the UCA wall may be a factor that prevents the binding of IGF-I by BPs. Free IGF-I can easily bind to cell receptors and stimulate the cells to produce collagen and sulphated GAGs in the arterial wall.

An accumulation of IGF-I and IGF-binding proteins in human umbilical cord

It is known that extracellular matrix components (ECM) may serve as a storage site to concentrate and stabilize growth factors in the vicinity of cells. IGF-I is expressed in most fetal tissues and it is involved in anabolic effects on protein and sulphated glycosaminoglycans biosynthesis, cell proliferation and differentiation. We demonstrated that human umbilical cord (UC) tissues contain large amounts of IGF-I and IGF-I-binding proteins (BP-3 and BP-1). Particularly Wharton's jelly appears to be an abundant reservoir of IGF-I and BPs. Relatively low amount of cells and large amounts of collagen and glycosaminoglycans in UC tissues (especially in Wharton's jelly) suggest that IGF-I may play a major role in stimulation of these cells to produce ECM components. The specific BPs in these tissues may be important modulators of IGF-I action during fetal development.

Differential effect of fasting on IGF-BPs in serum of young and adult rats and its implication to impaired skin GAG content

During fasting or aging of animals there is a decreased content of skin glycosaminoglycans (GAGs). It has been found that the skin of adult rats contains about 60% of GAGs found in the skin of young animals. Fasting of both groups of animals (young and adult) resulted in decrease of GAG content. However, GAG content in the skin of fasted young rats decreased by 30% and in fasted adult rats by 15% only, compared to fed animals, respectively. The mechanism for the phenomena is not known. We considered insulin-like growth factor-I (IGF-I) as a potential candidate involved in regulation of GAG biosynthesis in both experimental models of animals. Adult rat sera were found to contain about 75% of IGF-I recovered from young rat sera. Fasting of both groups of animals resulted in dramatic decrease in serum IGF-I levels to about 50% of initial values. Since IGF-I activity and IGF-I serum half-life depends on the level of specific IGF-binding proteins (IGFBPs) we determined (i) relationship between main groups of IGFBPs, namely high molecular weight binding proteins (HMWBPs) and low molecular weight binding proteins (LMWBPs) and (ii) the amounts of IGF-I bound to respective proteins in the sera of all experimental animals. Control young rat serum was found to contain about 90% of HMWBPs and about 10% of LMWBPs as determined by ligand binding assay. In contrast, control adult rat serum contained about 60% of HMWBPs and about 40% of LMWBPs. Fasting of both groups of animals resulted in significant increase in serum levels of LMWBPs. Control young rat serum was found to contain about 8% IGF-I bound to LMWBPs while serum of control adult rats contained 18% IGF-I bound to these proteins. In sera of fasted young animals however, about 75% of the bound IGF-I was recovered from LMWBPs (about 60% of total serum IGF-I) while in sera of fasted adult animals only about 56% of the bound IGF-I was recovered from LMWBPs (about 50% of total serum IGF-I). Evidence was provided that during fasting of both groups of animals there is a significant decrease in serum BP-3 and dramatic increase in serum BP-1 concentrations, compared to respective controls. However, the concentration of BP-1 in serum of fasted young rats was increased by about 60 fold while in serum of fasted adult rats only by about 10 fold, compared to respective control animals. Negative correlation between skin GAG content and LMWBPs derived IGF-I during fasting of young (r = -0.943, p < 0.001) and adult ( r = -0.571, p < 0.01) rats was found. The data presented suggest that the effects of aging and fasting on decreased skin GAG content may be due to induction of LMWBPs that are known to (i) inhibit IGF-I dependent function and (ii) increase clearance of IGF-I from circulation. However, the effects of fasting are distinct in respect to young and adult rats suggesting that mechanisms involved in regulation of IGF-I bioactivity during aging are more complex that during fasting.

Potential role of pyrroline 5-carboxylate in regulation of collagen biosynthesis in cultured human skin fibroblasts

Although insulin-like growth factor-I (IGF-I) is known as an important stimulator of collagen biosynthesis in collagen-producing cells, the mechanism and endpoints by which it regulate the process remain largely unknown. Serum of acutely fasted rats contained reduced amount of IGF-I (72+/-16 ng/ml) and showed about 75% reduced ability to stimulate collagen and DNA synthesis in confluent human skin fibroblasts in comparison to the effect of control rat serum (IGF-I, 168+/-19 ng/ml). An addition of IGF-I (at least 40 ng/ml) to fasted rat serum restored its mitogenic activity but could not restore its ability to stimulate collagen biosynthesis to control values during 24 h of incubation. However, when the cells were incubated in fasted rat serum supplemented with 40 ng/ml of IGF-I for 48 h, collagen biosynthesis was restored to control values. It suggests that the stimulatory role of IGF-I in collagen biosynthesis undergo indirectly. We considered pyrroline-5-carboxylate (P5C) as a candidate to play a direct role in this process. Since IGF-I and P5C are known to be decreased in serum of fasted rats it seems that the action of IGF-I on collagen biosynthesis may involve participation of P5C. We have found that serum of fasted rats (showing low level of P5C) supplemented with 1 mmol/l P5C induced collagen biosynthesis in confluent human skin fibroblasts during 24 h to control values. Supporting evidence comes from the experiment showing stimulatory action of P5C on collagen biosynthesis in fibroblasts cultured in serum-free medium. Our results postulate potential role of P5C in regulation of collagen biosynthesis and indicate participation of this molecule in the pathway of IGF-I action in this process.

Insulin-like growth factor I-dependent regulation of prolidase activity in cultured human skin fibroblasts

Prolidase [E.C.3.4.13.9] is a cytosolic exopeptidase that catalyses the hydrolysis of C-terminal proline containing dipeptides or tripeptides. The enzyme plays an important role in the recycling of proline for collagen synthesis. Increase in enzyme activity is correlated with increased rates of collagen turnover but the mechanism and endpoints by which this enzyme is regulated remain largely unknown. We have found that insulin-like growth factor-I (IGF-I), potent stimulator of collagen biosynthesis, induces prolidase activity in cultured human skin fibroblasts. Supporting evidence comes from the following observations: (1) Serum of fasted rats, (IGF-I, 72 +/- 16 ng/ml) showed about 50% reduced ability to stimulate prolidase activity and collagen biosynthesis in confluent fibroblasts in comparison to the effect of control rat serum (IGF-I, 168 +/- 29). (2) An addition of IGF-I (100 ng/ml) to fasted rat serum restored its ability to stimulate prolidase activity and collagen biosynthesis to control values. (3) In confluent human skin fibroblasts, cultured for 48 h with serum free medium prolidase activity was decreased to 50% of control cells, cultured in the presence of normal rat serum. Supplementation of serum free medium with EGF, PDGF and IGF-I (factors that can replace growth promoting activity of serum) stimulated prolidase activity to control values while the medium deprived IGF-I had no such effect. (4) The relative differences in prolidase activity due to specific treatment of confluent cells with above growth factors were accompanied by parallel differences in the amount of the enzyme protein recovered from these cells as shown by western immunoblot analysis. Thus we conclude that prolidase activity is regulated by IGF-I in confluent fibroblasts.

Phosphorylation of rat insulin-like growth factor binding protein-1 does not affect its biological properties

Insulin-like growth factors (IGFs) I and II stimulate growth and expression of specific genes through binding to cell membrane receptors. IGF binding proteins also bind IGF-I with higher affinity than the receptor. They are found in the circulation and tissues and can modulate IGF actions. Human IGFBP-1 is phosphorylated on serine residues, which increases its affinity for IGF-I. An acidic, presumably phosphorylated, form of human IGFBP-1 inhibits IGF-I-stimulated DNA synthesis in cultured cells, while a less acidic, unphosphorylated form potentiates this function. Phosphorylation of human IGFBP-3, however, does not affect its affinity for IGF-I. Previously we found that multiple forms of rat IGFBP-1 are obtained by anion-exchange chromatography, raising the possibility that it also is phosphorylated, which led us to examine its properties. Phosphopeptide analysis of 32P-labeled, immunoprecipitated rat IGFBP-1 synthesized by H-4-II-EC3 rat hepatoma cells indicated that it is phosphorylated on two sites that were deduced to be ser107 and ser132 in the central nonconserved domain. Dephosphorylation of purified phosphorylated rat IGFBP-1 did not affect its affinity for IGF-I or its specific binding activity, and the dephosphorylated form inhibited DNA synthesis in 3T3 cells. Incubation of cells labeled with radioactive proline in the presence of monensin and brefeldin A, which inhibit secretion at different sites, led to intracellular accumulation of the least phosphorylated form of rat IGFBP-1, but prevented further phosphorylation. The results suggested that phosphorylation occurs at two sites in cells, the cis-Golgi and the trans-Golgi network. In summary, these studies have shown that rat IGFBP-1 is phosphorylated on two sites by reactions that occur in different secretory organelles and that similar to human IGFBP-3, but unlike human IGFBP-1, phosphorylation does not affect its affinity for IGF-I.

Fibroblast chemotaxis and prolidase activity modulation by insulin-like growth factor II and mannose 6-phosphate

Chemotactic locomotion of fibroblasts requires extensive degradation of extracellular matrix components. The degradation is provided by a variety of proteases, including lysosomal enzymes. The process is regulated by cytokines. The present study shows that mannose 6-phosphate and insulin-like growth factor II (IGF-II) enhance fibroblast chemotaxis toward platelet-derived growth factor (PDGF). It is suggested that lysosomal enzymes (bearing mannose 6-phosphate molecules) are involved in chemotactic activity of the cells. The suggestion is supported by the observation that alpha-mannosidase and cathepsin D inhibitor-pepstatin are very potent inhibitors of fibroblast chemotaxis. Simultaneously, mannose 6-phosphate stimulates extracellular collagen degradation. The final step in collagen degradation is catalyzed by the cytosolic enzyme-prolidase. It has been found that mannose 6-phosphate stimulates also fibroblast prolidase activity with concomitant increase in lysosomal enzymes activity. The present study demonstrates that the prolidase activity in fibroblasts may reflect the chemotactic activity of the cells and suggests that the mechanism of cell locomotion may involve lysosomal enzyme targeting, probably through IGF-II/mannose 6-phosphate receptor.

Decrease in the glycosaminoglycan content in the skin of diabetic rats. The role of IGF-I, IGF-binding proteins and proteolytic activity

The results of our previous studies demonstrated that acute streptozotocin-induced diabetes in rats evoked a decrease in skin collagen content with little effect on glycosaminoglycans (GAG) content. In our present study we employed the model of chronic diabetes in order to check its effect on skin GAG content. It was found that the skin of diabetic rats showed a significant decrease in almost all the investigated GAGs by 50-70%. The decrease in heparan sulfate content was slight and statistically insignificant. We sought to determine whether the insulin-like growth factor-I (IGF-I) and IGF-binding proteins (IGF-BPs) levels are altered in animals with experimental diabetes and might contribute to the decrease in tissue GAG content. Circulating IGF-I level was found to be reduced in animals with diabetes and significant changes in serum IGF-BPs were observed. The amount of high molecular weight binding proteins (HMW-BPs) was decreased and the content of low molecular weight binding proteins (LMW-BPs), known as IGF-I inactivating substances, markedly increased. Furthermore, diabetic rats demonstrated an increase of skin proteolytic activity. We conclude that the decrease of GAG content in the skin of diabetic rats is a result of three co-existing phenomena: decreased circulating IGF-I level, increased plasma content of LMW-BPs and increased proteolytic activity of the skin.

Insulin-like growth factor (IGF) binding proteins and their mRNAs in connective tissues of fasted guinea-pigs

Fasting (with vitamin C-supplementation) and vitamin C-deficiency in guinea-pigs are associated with decreased collagen gene expression in connective tissues. Recently we presented evidence that circulating insulin-like growth factor binding protein (IGFBP)-1 and-2 that are induced during both nutritional deficiencies may be responsible for this inhibition by interfering with IGF-I action. The present objective was to determine whether circulating IGFBPs are accumulated in bone, skin and cartilage during fasting, which would support an endocrine role for them. IGFBP-1 mRNA was not detected in any of the connective tissues. The protein, as measured by ligand blotting, was not present in tissues of normal animals but accumulated early during fasting in all of the tissues. Bone and cartilage from normal animals contained IGFBP-2 and its mRNA, but only in bone did their levels increase during fasting. IGFBP-3 mRNA was not detected in connective tissues from normal or fasted guinea-pigs. Little or no IGFBP-3 was detected in normal tissue extracts, but protein accumulated during fasting and presumably was derived from the circulation. IGF-I and-II mRNAs were expressed in bone and cartilage but in skin, only IGF-II mRNA was detected. Affinity cross-linking revealed that in skin, IGFBP-3 contained relatively few unoccupied IGF-I binding sites compared to IGFBP-1 while in bone and cartilage, only IGFBP-1 contained unoccupied binding sites. IGFBP-1, acting by endocrine action, is probably the major factor responsible for inhibition of IGF-I-dependent collagen gene expression during fasting.

1,25-Dihydroxyvitamin D3 and osteocalcin in maternal and fetal guinea pigs

Maternal and fetal 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) and osteocalcin were measured in guinea pigs, to examine their potential use as animal models for fetal bone development and calcium homeostasis. Measurements were performed on days 42, 57 and 63 of gestation. Maternal serum total 1,25(OH)2D3 concentrations were increased only at the end of gestation (day 63). However, because the vitamin D binding protein (DBP) and albumin levels were decreased by 35-50% from day 42 onwards, the unbound 1,25(OH)2D3, calculated as the 1,25(OH)2D3/DBP molar ratio, was increased before day 63. Osteocalcin concentrations during gestation were 50-54% of levels found in nongravid animals. Fetal serum total 1,25(OH)2D3 concentrations were 20% of those in maternal guinea pigs. Since DBP levels were only 9-15% of maternal levels, the unbound 1,25(OH)2D3 was consistently higher in fetuses, from day 42 onwards. There was a rise in total and unbound 1,25(OH)2D3 between days 57 and 63 of fetal life. Osteocalcin concentrations were higher in fetal than in adult guinea pigs, and reached peak values on day 57 (1023 micrograms/l, i.e. 4.2 times higher than in adult female guinea pigs). Fetuses of guinea pigs that had received a restricted food supply for 14 days (days 49-63) had normal 1,25(OH)2D3 concentrations, but decreased osteocalcin concentrations compared with normal fetuses. The data obtained in fetal guinea pigs are comparable with those found in human fetuses, and suggest that the guinea pig may be a suitable model for studies on fetal bone and mineral development.

Circulating insulin-like growth factor binding proteins (IGFBPs) 1 and 2 induced in vitamin C-deficient or fasted guinea pigs inhibit IGF-I action in cultured cells

Collagen gene expression and proteoglycan synthesis are decreased in vitamin C-deficient guinea pigs losing weight and in fasted guinea pigs receiving ascorbate. Sera from such guinea pigs contain an insulin-like growth factor (IGF)-I-reversible inhibitor of collagen, proteoglycan and DNA synthesis and elevated levels of 29 and 35-kDa IGF binding proteins (IGFBPs). We now have identified the induced proteins as IGFBPs 1 and 2 and investigated their role as inhibitors. Guinea pig sera were treated with antibodies to IGFBPs 1 and 2 and antibody-IGFBP complexes were removed by passage through a Protein A-Sepharose column. Inhibitor content of fasted and scorbutic sera, and Protein A pass-through fractions derived from them, was assessed by their level of stimulation of DNA and collagen synthesis in 3T3 cells, compared to analogously treated normal guinea pig serum. Removal of IGFBP-1 from scorbutic serum reversed inhibition of collagen and DNA synthesis by more than half but removal of IGFBP-2 was less effective. Removal of both IGFBPs reversed inhibition almost completely. Similar results were obtained with fasted guinea pig serum. Conversely, purified rat IGFBPs 1 and 2 inhibited DNA and collagen synthesis in cells cultured in normal guinea pig serum or IGF-I-stimulated DNA synthesis, with IGFBP-1 being more potent. Thus, IGFBP-1 and, to a lesser extent IGFBP-2, cause inhibition of IGF-I action by sera from fasted and scorbutic guinea pigs and may inhibit collagen gene expression in vivo.

Similar, but not identical, modulation of expression of extracellular matrix components during in vitro and in vivo aging of human skin fibroblasts

Regulation of the synthesis of procollagen and other extracellular matrix components was examined in human skin fibroblasts obtained from donors of various ages, from fetal to 80 years old (in vivo aged), and in fetal fibroblasts at varying passage levels (in vitro aged). Growth rates and saturation densities of fibroblasts decreased with increasing age of the donor and after passage 20 of fetal fibroblasts. The rates of collagen and proteoglycan synthesis also decreased during both types of aging to about 10-25% of the rate in early passage fetal fibroblasts, whereas the synthesis of total noncollagenous proteins was not greatly affected. Decreased collagen synthesis in both types of aging was correlated with lower steady-state levels of mRNAs for the two subunits of type I procollagen mRNA, although their regulation was not coordinate. Type III collagen mRNA levels also declined in both types of aging. The concentration of fibronectin mRNA also decreased during in vitro aging but more rapidly than the collagen mRNAs, whereas in fibroblasts from 51-80-year-old donors, it was similar to or higher than in early passage fetal fibroblasts. This study suggests that the decreased synthesis of procollagen and proteoglycans in in vivo aged fibroblasts represents changes that are responsible for intrinsic degenerative changes that occur in human skin during aging. Furthermore, although in vitro and in vivo aging were similar in many respects, they were not equivalent, as evidenced by the differences in regulation of fibronectin expression.

Scorbutic and fasted guinea pig sera contain an insulin-like growth factor I-reversible inhibitor of proteoglycan and collagen synthesis in chick embryo chondrocytes and adult human skin fibroblasts

Chick embryo chondrocytes cultured in sera from scorbutic and fasted guinea pigs exhibited decreases in collagen and proteoglycan production to about 30-50% of control values (I. Oyamada et al., 1988, Biochem. Biophys. Res. Commun. 152, 1490-1496). Here we show by pulse-chase labeling experiments that in the chondrocyte system, as in the cartilage of scorbutic and fasted guinea pigs, decreased incorporation of precursor into collagen was due to decreased synthesis rather than to increased degradation. There was a concomitant decrease in type II procollagen mRNA to about 32% of the control level. As in scorbutic cartilage, proteoglycan synthesis by chondrocytes in scorbutic serum was blocked at the stage of glycosaminoglycan chain initiation. Scorbutic and fasted guinea pig sera also caused a 50-60% decrease in the rates of collagen and proteoglycan synthesis in adult human skin fibroblasts, which synthesize mainly type I collagen. Decreased matrix synthesis in both cell types resulted from the presence of an inhibitor in scorbutic and fasted sera. Elevated cortisol levels in these sera were not responsible for inhibition, as determined by the addition of dexamethasone to chondrocytes cultured in normal serum. Insulin-like growth factor I (IGF-I, 300-350 ng/ml) reversed the inhibition of extracellular matrix synthesis by scorbutic and fasted guinea pig sera in both cell types and prevented the decrease in type II procollagen mRNA in chondrocytes. Therefore, in addition to its established role in proteoglycan metabolism, IGF-I also regulates the synthesis of several collagen types. An increase in the circulating inhibitor of IGF-I action thus could lead to the negative regulation of collagen and cartilage proteoglycan synthesis that occurs in ascorbate-deficient and fasted guinea pigs.