Failure of exogenous IGF-I to restore normal growth in rats submitted to dietary zinc deprivation

Effect of zinc supplementation on growth hormone-insulin growth factor axis in short Egyptian children with zinc deficiency

Background

The relationship between zinc (Zn) and growth hormone-insulin growth factor (GH-IGF) system and how Zn therapy stimulates growth in children has not been clearly defined in humans. Thus, we aimed to assess GH-IGF axis in short children with Zn deficiency and to investigate the effect of Zn supplementation on these parameters.

Methods

Fifty pre-pubertal Egyptian children with short stature and Zn deficiency were compared to 50 age-, sex-, and pubertal stage- matched controls. All subjects were subjected to history, auxological assessment and measurement of serum Zn, IGF-1, insulin growth factor binding protein-3 (IGFBP-3); and basal and stimulated GH before and 3 months after Zn supplementation (50 mg/day).

Results

After 3 months of Zn supplementation in Zn-deficient patients, there were significant increases in height standard deviation score (SDS, P = 0.033), serum Zn (P < 0.001), IGF-1 (P < 0.01), IGF-1 standard deviation score (SDS,P < 0.01) and IGFBP-3 (P = 0.042). Zn rose in all patients but reached normal ranges in 64 %, IGF-1 levels rose in 60 % but reached normal ranges in 40 % and IGFBP-3 levels rose in 40 % but reached reference ranges in 22 %. Growth velocity (GV) SDS did not differ between cases and controls (p = 0.15) but was higher in GH-deficient patients than non-deficient ones, both having Zn deficiency (p = 0.03).

Conclusion

Serum IGF-1 and IGFBP-3 levels were low in short children with Zn deficiency, and increased after Zn supplementation for 3 months but their levels were still lower than the normal reference ranges in most children; therefore, Zn supplementation may be necessary for longer periods.

Zinc and human health: an update

The importance of micronutrients in health and nutrition is undisputable, and among them, zinc is an essential element whose significance to health is increasingly appreciated and whose deficiency may play an important role in the appearance of diseases. Zinc is one of the most important trace elements in the organism, with three major biological roles, as catalyst, structural, and regulatory ion. Zinc-binding motifs are found in many proteins encoded by the human genome physiologically, and free zinc is mainly regulated at the single-cell level. Zinc has critical effect in homeostasis, in immune function, in oxidative stress, in apoptosis, and in aging, and significant disorders of great public health interest are associated with zinc deficiency. In many chronic diseases, including atherosclerosis, several malignancies, neurological disorders, autoimmune diseases, aging, age-related degenerative diseases, and Wilson's disease, the concurrent zinc deficiency may complicate the clinical features, affect adversely immunological status, increase oxidative stress, and lead to the generation of inflammatory cytokines. In these diseases, oxidative stress and chronic inflammation may play important causative roles. It is therefore important that status of zinc is assessed in any case and zinc deficiency is corrected, since the unique properties of zinc may have significant therapeutic benefits in these diseases. In the present paper, we review the zinc as a multipurpose trace element, its biological role in homeostasis, proliferation and apoptosis and its role in immunity and in chronic diseases, such as cancer, diabetes, depression, Wilson's disease, Alzheimer's disease, and other age-related diseases.

Alteration in the expression of inflammatory parameters as a result of oxidative stress produced by moderate zinc deficiency in rat lung

Suboptimal intake of dietary zinc (Zn) is one of the most common nutritional problems worldwide. Previously, the authors have shown that zinc deficiency (ZD) produces oxidative and nitrosative stress in lung of male rats. The goal of this study is to test the effect of moderate ZD on insulin-like growth factor (IGF)-1, IGF-binding protein (IGFBP)-5, NADH oxidase (NOX)-2, tumor necrosis factor alpha (TNFalpha), as well as the effect of restoring zinc during the refeeding period. Adult male rats were divided into 3 groups: Zn-adequate control group, Zn-deficient group, and Zn-refeeding group. eNOS, metallothionein (MT) II, and NOX-2 was increased in ZD group. The authors observed an increased gene transcription of superoxide dismutase (SOD)-2 and gluthathione peroxidase (GPx)-1 in ZD group, as well as in ZD-refeeding group, but catalase (CAT) transcription did not change in the treated groups. Proinflammatory factors, such as TNFalpha and vascular cell adhesion molecular (VCAM)-1 increased in ZD, whereas it decreased in ZD refeeding. However, peroxisome proliferator-activated receptor gamma (PPARgamma) and IGF-1 gene transcription decreased in ZD, whereas IGFBP-5 decreased in the ZD group. These parameters are associated to alterations in the lung histoarchitecture. The zinc supplementation period is brief (only 10 days), but it is enough to inhibit some proinflammatory factors. Perhaps, zinc deficiency implications must be taken into account in health interventions because inflammation and prooxidant environment are associated with ZD in lung.

The role of zinc in the modulation of neuronal proliferation and apoptosis

Although a requirement of zinc (Zn) for normal brain development is well documented, the extent to which Zn can modulate neuronal proliferation and apoptosis is not clear. Thus, we investigated the role of Zn in the regulation of these two critical events. A low Zn availability leads to decreased cell viability in human neuroblastoma IMR-32 cells and primary cultures of rat cortical neurons. This occurs in part as a consequence of decreased cell proliferation and increased apoptotic cell death. In IMR-32 cells, Zn deficiency led to the inhibition of cell proliferation through the arrest of the cell cycle at the G₀/G₁ phase. Zn deficiency induced apoptosis in both proliferating and quiescent neuronal cells via the intrinsic apoptotic pathway. Reductions in cellular Zn triggered a translocation of the pro-apoptotic protein Bad to the mitochondria, cytochrome c release, and caspase-3 activation. Apoptosis is the resultant of the inhibition of the prosurvival extracellular-signal-regulated kinase, the inhibition of nuclear factor-kappa B, and associated decreased expression of antiapoptotic proteins, and to a direct activation of caspase-3. A deficit of Zn during critical developmental periods can have persistent effects on brain function secondary to a deregulation of neuronal proliferation and apoptosis.

The influence of gestational zinc deficiency on the fetal insulin-like growth factor axis in the rat

The insulin-like growth factor (IGF) axis, a key regulator of embryonic growth and development, is exquisitely sensitive to the nutrient status of the animal. In addition to macronutrient deficiencies, zinc deficiency can impact the IGF axis. Gestational zinc deficiency is teratogenic, resulting in intrauterine growth retardation and structural abnormalities. The aim of this study was to investigate the effects of gestational zinc deficiency on the fetal IGF axis in a rat model. From gestation day (GD) 0.5, dams consumed zinc-deficient (ZD, 0.3 mg zinc/kg) or control (25 mg zinc/kg) diet ad libitum, while a third group of dams consumed the control diet in amounts equivalent to the food intake of the ZD dams (Paired group). On GD 19.5 fetal tissue, blood and amniotic fluid were collected. Fetal growth was significantly reduced by zinc deficiency compared with the Paired and Control groups. Fetuses from the Paired group were smaller compared with the Control, but only ZD fetuses had structural malformations. Amniotic fluid IGF-1 concentrations were significantly lower in the Paired group than in the ZD and Control groups. Plasma of ZD fetuses contained lower levels of IGF binding protein-1 when compared with fetuses in the Paired and Control groups. Fetal liver IGF-1 mRNA levels were lower in the ZD fetuses than in the Paired and Control fetuses. These observations suggest that differences in the fetal IGF axis between ZD and Paired groups contribute to the poor pregnancy outcome and enhanced fetal growth retardation observed with zinc deficiency.

Serum insulin-like growth factor-I and insulin-like growth factor binding protein-3 levels in children with zinc deficiency and the effect of zinc supplementation on these parameters

AIM

To determine the effect of zinc (Zn) therapy on serum insulin-like growth factor-I (IGF-I) and insulin-like growth factor binding protein-3 (IGFBP-3) levels in children with Zn deficiency and growth retardation, but without systemic disease, and to investigate the effect of Zn supplementation on these parameters.

METHODS

Twenty-nine children (11 girls and 18 boys) were included. Blood samples were obtained for serum IGF-I and IGFBP-3 determination before and after 50 mg/day Zn supplementation for two months.

RESULTS

The mean age of the children was 11.0 +/- 3.1 years (range 3.7-16.2 years). Serum IGF-I and IGFBP-3 levels were below the mean values in 28 (96.6%) and all children, respectively. After Zn therapy, serum IGF-I levels were increased in 62% of the children; this increase was statistically significant in 48.3% of the children. Serum IGFBP-3 levels were significantly increased in 10 children. There was a positive correlation between serum Zn level and bone age, and serum IGF-I and IGFBP-3 levels. A positive correlation was present between BMI (r = 0.485, p < 0.001) and serum IGF-I levels before therapy.

CONCLUSION

Serum IGF-I and IGFBP-3 levels were decreased in children with Zn deficiency, and were increased after Zn supplementation. In addition, after Zn supplementation, increment of serum IGF-I levels was found to be higher in children with low BMI than those with normal BMI; therefore, the nutritional status of children may also be important, as well as Zn supplementation. Additionally, the determination of higher variation percentile of serum IGF-I level in prepubertal children compared to pubertal children was an interesting finding and necessitates further investigation.

Zinc increases the effects of essential amino acids-whey protein supplements in frail elderly

Protein undernutrition is frequent in the elderly. It contributes to the development of osteoporosis, possibly via lower IGF-I. Dietary zinc can influence IGF-I production.

OBJECTIVES

To determine the influence of dietary zinc addition on IGF-I and bone turnover responses to essential amino acids-whey (EAA-W) protein supplements in frail elderly.

DESIGN AND SETTING

A daily oral protein supplement was given to hospitalized patients for 4 weeks. On a randomized, double-blind basis, patients received either an additional 30 mg/day of zinc or control.

PARTICIPANTS

Sixty-one hospitalized elderly aged 66.7 to 105.8, with a mini-nutritional assessment score between 17 and 24 were enrolled.

MEASUREMENTS

Activities of daily living; dietary intakes; serum IGF-I, IGF-BP3, CrossLapsTM, osteocalcin and zinc were measured before and after 1, 2 and 4 weeks of protein supplementation.

RESULTS

Serum IGF-I rapidly increased in both groups. Zinc accelerated this increase with changes of +48.2 +/- 14.3 and +22.4 +/- 4.7% (p < .05) by 1 week, in the zinc-supplemented and control groups, respectively. Zinc significantly decreased the serum bone resorption marker CrossLapsTM by already 1 week. Activities of daily living improved by +27.0 +/- 3.1 and +18.3 +/- 4.5% in zinc-supplemented and control groups, respectively.

CONCLUSION

In the elderly, zinc supplementation accelerated the serum IGF-I response to EAA-W protein by 1 week and decreased a biochemical marker of bone resorption.

Zinc deficiency-induced cell death

Zinc deficiency is characterized by an attenuation of growth factor signaling pathways and an amplification of p53 pathways. This outcome is facilitated by hypo-phosphorylation of AKT and ERK secondary to zinc deficiency, which are permissive events to the activation of the intrinsic cell death pathway. Low zinc concentrations provide an environment that is also conducive to the production of reactive oxygen/reactive nitrogen species (ROS/RNS) and caspase activation. Additionally, during zinc deficiency endogenous survival pathways such as NF-kappaB are inhibited in their transactivation potential. The above factors contribute to the irreversible commitment of the zinc deficient cell to death.

A graded model of dietary zinc deficiency: effects on growth, insulin-like growth factor-I, and the glucose/insulin axis in weanling rats

OBJECTIVE

Severe zinc (Zn) deficiency inhibits growth, insulin storage and release. Mild or moderate Zn deficiency may also have profound physiological effects that are not outwardly evident. We examined the effects of graded levels of low Zn intake on growth, insulin-like growth factor-I (IGF-I) and glucose homeostasis in weanling rats.

METHODS

Weanling rats were fed ad libitum for 3 weeks with diets containing different Zn levels: very low Zn, low Zn or mildly low Zn; there was also a control group and an additional group was pair-fed to very low Zn rats. Growth and food intake were recorded. Serum Zn, IGF-I, IGF binding protein-3 (IGFBP-3), serum insulin and glucose, tissue Zn and jejunal sucrase activity were measured. Relative liver IGF-I and IGFBP-3 mRNA levels were quantified.

RESULTS

Serum and tissue Zn were significantly lower in rats fed very low Zn (compared with pair-fed animals and controls) and low Zn (compared with controls). Growth was significantly lower in rats fed very low Zn and pair-fed animals (compared with controls) and in those fed very low Zn (compared with pair-fed animals). Liver IGF-I and IGFBP-3 mRNA levels were higher in low Zn animals compared with controls. Serum IGF-1 and IGFBP-3 levels were not affected by diet. Serum glucose was significantly higher in rats fed very low Zn than in pair-fed animals (191 +/- 28 vs 99 +/- 5 mg/dL, respectively). Sucrase activity was lower in rats fed very low Zn than in pair-fed animals or controls and a linear relationship was observed between serum glucose and insulin (r = 0.65, P < 0.01) in pair-fed animals and controls but not in Zn-deficient groups.

CONCLUSION

Severe Zn deficiency was associated with hyperglycemia and relative hypoinsulinemia. Mild degrees of Zn deficiency also altered glucose metabolism, suggesting that Zn intake may be a sensitive regulator of glucose homeostasis.

The positive effects of zinc on skeletal strength in growing rats

The aim of the present study was to assess the skeletal effects of alimentary zinc depletion and supplementation in an animal model of intact, growing rats. The study was planned as a dose-response study. Thirty-six male Wistar rats, 4 weeks old, were divided into three groups of 12 rats each. The rats had free access to a semisynthetic diet with different amounts of zinc added. Group 1 was given a zinc-free diet containing 2 mg zinc/kg, group 2 was given a normal-zinc diet containing 47 mg zinc/kg; and group 3 was given a zinc-supplemented diet containing 60 mg zinc/kg. All animals were killed 4 weeks after initiation of the experiment and the right femora were removed. The biomechanical effects were measured at the following skeletal sites: femoral diaphysis; femoral neck; and distal femoral metaphysis. In addition, static histomorphometry was performed at the middiaphyseal region. Biomechanical testing revealed a significant zinc-induced increase in bone strength at all sites investigated. It also showed that zinc influenced bone strength in a dose-dependent manner except at the distal metaphysis, where there was no significant difference between the group fed normal-zinc diet and the group fed a hyper-zinc diet. Zinc also improved the rates of growth in the rats. The body weights and length of femora increased dose-dependently. Static histomorphometry showed that zinc exerted its main effect on the periosteal envelope, thereby increasing bone area, tissue area, and axial moment of inertia. We conclude that alimentary zinc supplementation in growing rats induces an increase of bone strength in both the femoral neck and the femoral diaphysis. These results further support the view that zinc has a positive effect on bone metabolism which mimics that of growth hormone (GH) or insulin-like growth factor 1 (IGF-1).

Selenium deficiency-induced growth retardation is associated with an impaired bone metabolism and osteopenia

Although the importance of selenium for bone metabolism is unknown, some clinical conditions such as Kashin-Beck osteoarthropathy have been associated with selenium deficiency. Although selenium deficiency induces growth retardation in rats, it has not been established whether this growth inhibition is associated with changes in bone metabolism. We investigated the effect of selenium deficiency on bone metabolism in growing male rats fed a selenium-deficient diet for two generations (Se-). In Se- rats, erythrocyte glutathione peroxidase activity and plasma selenium concentration were strongly reduced compared with pair-fed selenium-adequate rats (Se+). Weight and tail length were reduced by 31% and 13% in the Se- rats, respectively (p < 0.001). The Se- diet was associated with a 68% reduction of pituitary growth hormone (GH; p = 0.01) and a 50% reduction of plasma insulin-like growth factor I (IGF-I; p < 0.001). Plasma calcium was lower and urinary calcium concentration was greater in Se- rats. This group had a 2-fold increase in parathyroid hormone (PTH) and 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] in plasma. Plasma osteocalcin and urinary deoxypyridoline were reduced by 25% and 57% in the Se- rats (p < 0.001). Selenium deficiency resulted in a 23% and 21% reduction in bone mineral density (BMD) of the femur and tibia (p < 0.001) and this effect persisted after adjustment for weight in a linear regression model. A 43% reduction in trabecular bone volume of the femoral metaphysis (p < 0.001) was found in Se- rats. This experimental study shows that growth retardation induced by selenium deficiency is associated with impaired bone metabolism and osteopenia in second-generation selenium-deficient rats.

Interactions between nutrients and peptide growth factors in intestinal growth, repair, and function

Several lines of evidence demonstrate that general nutritional status, specific nutrients (eg, zinc, glutamine), and certain trophic growth factors (eg, growth hormone, insulin-like growth factor I, keratinocyte growth factor, and glucagon-like peptide-2) have important interactions relevant for intestinal growth and function. Adequate nutritional status is critical for endogenous growth factor synthesis in the gut and other tissues and is an important mediator of organ responsiveness to exogenous growth factor administration. Both endogenously synthesized and exogenously administered growth factors upregulate nutrient uptake and utilization by gut mucosa, skeletal muscle, and other organs. Emerging data from both animal and human studies indicate that combinations of selected growth factors and specific nutrients may improve the growth, adaptation, and repair of the intestinal mucosa. Additional studies to determine basic mechanisms of nutrient-growth factor interactions and the safety and efficacy of treatment with combinations of specific nutrients and recombinant growth factors are needed. Results of these investigations should define new methods for support of the intestinal tract during short bowel syndrome (SBS), catabolic illness, and malnutrition.

Regulation of insulin-like growth factor-I in starvation and injury

Both starvation and sepsis are characterized by growth hormone (GH) insensitivity, which leads to a reduction in circulating insulin-like growth factor (IGF)-I. Because of the anabolic properties of this growth factor, its decline may contribute to the growth arrest and the catabolic reaction observed in starvation and sepsis. This review focuses on the mechanisms responsible for the reduction in circulating IGF-I and impairment of GH responsiveness that occur during starvation and sepsis. A clearer understanding of the complex nature of GH resistance should lead to the development of new therapeutic strategies aimed at restoring the beneficial effects of anabolic agents such as GH and IGF-I.

Inhibition of insulin-like growth factor-I mitogenic action by zinc chelation is associated with a decreased mitogen-activated protein kinase activation in RAT-1 fibroblasts

The mechanisms responsible for the resistance to the anabolic actions of IGF-I induced by zinc deficiency are not understood. We showed that zinc chelation by DTPA (diethylenetriaminepenta-acetic acid) inhibits [3H]thymidine incorporation stimulated by IGF-I in Rat-1 fibroblasts. This inhibition was specific of zinc chelation since it was prevented by the addition of zinc to DTPA. The stimulation of MAPK, which is crucial for the [3H]thymidine incorporation induced by IGF-I in Rat-1 cells, was partially blunted by DTPA. Therefore, the inhibition of the mitogenic action of IGF-I in Rat-1 fibroblasts by DTPA is potentially caused by decreased MAPK activation by IGF-I.