Serum proteins and plasma free amino acids in severe malnutrition

The role of upstream open reading frames in translation regulation in the apicomplexan parasites Plasmodium falciparum and Toxoplasma gondii

During their complex life cycles, the Apicomplexan parasites Plasmodium falciparum and Toxoplasma gondii employ several layers of regulation of their gene expression. One such layer is mediated at the level of translation through upstream open reading frames (uORFs). As uORFs are found in the upstream regions of a majority of transcripts in both the parasites, it is essential that their roles in translational regulation be appreciated to a greater extent. This review provides a comprehensive summary of studies that show uORF-mediated gene regulation in these parasites and highlights examples of clinically and physiologically relevant genes, including var2csa in P. falciparum, and ApiAT1 in T. gondii, that exhibit uORF-mediated regulation. In addition to these examples, several studies that use bioinformatics, transcriptomics, proteomics and ribosome profiling also indicate the possibility of widespread translational regulation by uORFs. Further analysis of these genome-wide datasets, taking into account uORFs associated with each gene, will reveal novel genes involved in key biological pathways such as cell-cycle progression, stress-response and pathogenicity. The cumulative evidence from studies presented in this review suggests that uORFs will play crucial roles in regulating gene expression during clinical disease caused by these important human pathogens.

Linking nutrient sensing and gene expression in Plasmodium falciparum blood-stage parasites

Malaria is one of the most life-threatening infectious diseases worldwide, caused by infection of humans with parasites of the genus Plasmodium. The complex life cycle of Plasmodium parasites is shared between two hosts, with infection of multiple cell types, and the parasite needs to adapt for survival and transmission through significantly different metabolic environments. Within the blood-stage alone, parasites encounter changing levels of key nutrients, including sugars, amino acids, and lipids, due to differences in host dietary nutrition, cellular tropism, and pathogenesis. In this review, we consider the mechanisms that the most lethal of malaria parasites, Plasmodium falciparum, uses to sense nutrient levels and elicit changes in gene expression during blood-stage infections. These changes are brought about by several metabolic intermediates and their corresponding sensor proteins. Sensing of distinct nutritional signals can drive P. falciparum to alter the key blood-stage processes of proliferation, antigenic variation, and transmission.

Molecular Target Validation of Aspartate Transcarbamoylase from Plasmodium falciparum by Torin 2

Malaria is a tropical disease that kills about half a million people around the world annually. Enzymatic reactions within pyrimidine biosynthesis have been proven to be essential for Plasmodium proliferation. Here we report on the essentiality of the second enzymatic step of the pyrimidine biosynthesis pathway, catalyzed by aspartate transcarbamoylase (ATC). Crystallization experiments using a double mutant ofPlasmodium falciparum ATC (PfATC) revealed the importance of the mutated residues for enzyme catalysis. Subsequently, this mutant was employed in protein interference assays (PIAs), which resulted in inhibition of parasite proliferation when parasites transfected with the double mutant were cultivated in medium lacking an excess of nutrients, including aspartate. Addition of 5 or 10 mg/L of aspartate to the minimal medium restored the parasites' normal growth rate. In vitro and whole-cell assays in the presence of the compound Torin 2 showed inhibition of specific activity and parasite growth, respectively. In silico analyses revealed the potential binding mode of Torin 2 to PfATC. Furthermore, a transgenic ATC-overexpressing cell line exhibited a 10-fold increased tolerance to Torin 2 compared with control cultures. Taken together, our results confirm the antimalarial activity of Torin 2, suggesting PfATC as a target of this drug and a promising target for the development of novel antimalarials.

The response of Plasmodium falciparum to isoleucine withdrawal is dependent on the stage of progression through the intraerythrocytic cell cycle

Background

A previous study reported that the malaria parasite Plasmodium falciparum enters an altered growth state upon extracellular withdrawal of the essential amino acid isoleucine. Parasites slowed transit through the cell cycle when deprived of isoleucine prior to the onset of S-phase.

Methods

This project was undertaken to study at higher resolution, how isoleucine withdrawal affects parasite growth. Parasites were followed at regular intervals across an extended isoleucine deprivation time course across the cell cycle using flow cytometry.

Results

These experiments revealed that isoleucine-deprived parasites never exit the cell cycle, but instead continuously grow at a markedly reduced pace. Moreover, slow growth occurs only if isoleucine is removed prior to the onset of schizogony. After S-phase commenced, the parasite is insensitive to isoleucine depletion and transits through the cell cycle at the normal pace.

Conclusions

The markedly different response of the parasite to isoleucine withdrawal before or after the onset of DNA replication is reminiscent of the nutrient-dependent G1 cell cycle checkpoints described in other organisms.

Correlates of Gut Function in Children Hospitalized for Severe Acute Malnutrition, a Cross-sectional Study in Uganda

OBJECTIVE

Children with severe acute malnutrition (SAM) may have impaired intestinal function, which can result in malabsorption, diarrhoea, and poor growth. This study evaluated the gut function of children with SAM using fecal and blood biomarkers and assessed their correlates.

METHODS

A cross-sectional study, nested in a randomized trial (www.isrctn.com, ISRCTN 16454889), was conducted at Mulago hospital, Uganda among subgroups of 400 children with complicated SAM and 30 community controls. Gut function was evaluated by 5 biomarkers: plasma citrulline, fecal myeloperoxidase and fecal neopterin, bacterially derived 16S rRNA gene and internal transcribed Spacer region (ITS) specific for Candida spp. in blood.

RESULTS

Compared with controls, children with SAM had lower median plasma citrulline (5.14 vs 27.4 μmol/L, P < 0.001), higher median fecal myeloperoxidase (18083 vs 7482 ng/mL, P = 0.001), and fecal neopterin (541 vs 210 nmol/L, P < 0.001). A higher blood concentration of 16S rRNA gene copy numbers was observed among children with SAM (95 vs 28 copies/μl, P = 0.05), whereas there was no difference in the blood concentration of Candida-specific ITS fragment.Among those with SAM, plasma citrulline was lower in children with edema, diarrhoea, dermatosis, and plasma C-reactive protein (CRP) >10 mg/L. Fecal neopterin was positively correlated with symptoms of fever and cough whereas it was negatively correlated with mid-upper arm circumference (MUAC), weight-for-height z score (WHZ), edema, and dermatosis.

CONCLUSIONS

Children with complicated SAM seem to have impaired gut function characterized by reduced enterocyte mass, intestinal inflammation, and increased bacterial translocation.

IGFBP-1 hyperphosphorylation in response to leucine deprivation is mediated by the AAR pathway

Insulin-like growth factor-1 (IGF-I) is the key regulator of fetal growth. IGF-I bioavailability is markedly diminished by IGF binding protein-1 (IGFBP-1) phosphorylation. Leucine deprivation strongly induces IGFBP-1 hyperphosphorylation, and plays an important role in fetal growth restriction (FGR). FGR is characterized by decreased amino acid availability, which activates the amino acid response (AAR) and inhibits the mechanistic target of rapamycin (mTOR) pathway. We investigated the role of AAR and mTOR in mediating IGFBP-1 secretion and phosphorylation in HepG2 cells in leucine deprivation. mTOR inhibition (rapamycin or raptor + rictor siRNA), or activation (DEPTOR siRNA) demonstrated a role of mTOR in leucine deprivation-induced IGFBP-1 secretion but not phosphorylation. When the AAR was blocked (U0126, or ERK/GCN2 siRNA), both IGFBP-1 secretion and hyperphosphorylation (pSer101/pSer119/pSer169) due to leucine deprivation were prevented. CK2 inhibition by TBB also attenuated IGFBP-1 phosphorylation in leucine deprivation. These results suggest that the AAR and mTOR independently regulate IGFBP-1 secretion and phosphorylation in response to decreased amino acid availability.

Oedema in kwashiorkor is caused by hypoalbuminaemia

It has been argued that the oedema of kwashiorkor is not caused by hypoalbuminaemia because the oedema disappears with dietary treatment before the plasma albumin concentration rises. Reanalysis of this evidence and a review of the literature demonstrates that this was a mistaken conclusion and that the oedema is linked to hypoalbuminaemia. This misconception has influenced the recommendations for treating children with severe acute malnutrition. There are close pathophysiological parallels between kwashiorkor and Finnish congenital nephrotic syndrome (CNS) pre-nephrectomy; both develop protein-energy malnutrition and hypoalbuminaemia, which predisposes them to intravascular hypovolaemia with consequent sodium and water retention, and makes them highly vulnerable to develop hypovolaemic shock with diarrhoea. In CNS this is successfully treated with intravenous albumin boluses. By contrast, the WHO advise the cautious administration of hypotonic intravenous fluids in kwashiorkor with shock, which has about a 50% mortality. It is time to trial intravenous bolus albumin for the treatment of children with kwashiorkor and shock.

Plasmodium falciparum responds to amino acid starvation by entering into a hibernatory state

The human malaria parasite Plasmodium falciparum is auxotrophic for most amino acids. Its amino acid needs are met largely through the degradation of host erythrocyte hemoglobin; however the parasite must acquire isoleucine exogenously, because this amino acid is not present in adult human hemoglobin. We report that when isoleucine is withdrawn from the culture medium of intraerythrocytic P. falciparum, the parasite slows its metabolism and progresses through its developmental cycle at a reduced rate. Isoleucine-starved parasites remain viable for 72 h and resume rapid growth upon resupplementation. Protein degradation during starvation is important for maintenance of this hibernatory state. Microarray analysis of starved parasites revealed a 60% decrease in the rate of progression through the normal transcriptional program but no other apparent stress response. Plasmodium parasites do not possess a TOR nutrient-sensing pathway and have only a rudimentary amino acid starvation-sensing eukaryotic initiation factor 2α (eIF2α) stress response. Isoleucine deprivation results in GCN2-mediated phosphorylation of eIF2α, but kinase-knockout clones still are able to hibernate and recover, indicating that this pathway does not directly promote survival during isoleucine starvation. We conclude that P. falciparum, in the absence of canonical eukaryotic nutrient stress-response pathways, can cope with an inconsistent bloodstream amino acid supply by hibernating and waiting for more nutrient to be provided.

Mechanisms of pH control in the midgut of Lutzomyia longipalpis: roles for ingested molecules and hormones

Control of the midgut pH in Lutzomyia longipalpis enables the insect's digestive system to deal with different types of diet. Phlebotomines must be able to suddenly change from a condition adequate to process a sugar diet to one required to digest blood. Prior to blood ingestion, the pH in the midgut is maintained at ∼6 via an efficient mechanism. In the abdominal midgut, alkalization to a pH of ∼8 occurs as a consequence of the loss of CO(2) from blood (CO(2) volatilization) and by a second mechanism that is not yet characterized. The present study aimed to characterize the primary stimuli, present in the blood, that are responsible for shutting down the mechanism that maintains a pH of 6 and switching on that responsible for alkalization. Our results show that any ingested protein could induce alkalization. Free amino acids, at the concentrations found in blood, were ineffective at inducing alkalization, although higher concentrations of amino acids were able to induce alkalization. Aqueous extracts of midgut tissue containing putative hormones from intestinal endocrine cells slightly alkalized the midgut lumen when applied to dissected intestines, as did hemolymph collected from blood-fed females. Serotonin, a hormone that is possibly released in the hemolymph after hematophagy commences, was ineffective at promoting alkalization. The carbonic anhydrase (CA) enzyme seems to be involved in alkalizing the midgut, as co-ingestion of acetazolamide (a CA inhibitor) with proteins impaired alkalization efficiency. A general model of alkalization control is presented.

Molecular mechanisms involved in the adaptation to amino acid limitation in mammals

In mammals, metabolic adaptations are required to cope with episodes of protein deprivation and malnutrition. Consequently, mammals have to adjust physiological functions involved in the adaptation to amino acid availability. Part of this regulation involves the modulation of the expression of numerous genes. In particular, it has been shown that amino acids by themselves can modify the expression of target genes. This review describes the regulation of amino acids homeostasis and the their role as signal molecules. The recent advances in the understanding of the molecular mechanisms involved in the control of mammalian gene expression in response to amino acid limitation will be described.

Identification of a novel amino acid response pathway triggering ATF2 phosphorylation in mammals

It has been well established that amino acid availability can control gene expression. Previous studies have shown that amino acid depletion induces transcription of the ATF3 (activation transcription factor 3) gene through an amino acid response element (AARE) located in its promoter. This event requires phosphorylation of activating transcription factor 2 (ATF2), a constitutive AARE-bound factor. To identify the signaling cascade leading to phosphorylation of ATF2 in response to amino acid starvation, we used an individual gene knockdown approach by small interfering RNA transfection. We identified the mitogen-activated protein kinase (MAPK) module MEKK1/MKK7/JNK2 as the pathway responsible for ATF2 phosphorylation on the threonine 69 (Thr69) and Thr71 residues. Then, we progressed backwards up the signal transduction pathway and showed that the GTPase Rac1/Cdc42 and the protein Galpha12 control the MAPK module, ATF2 phosphorylation, and AARE-dependent transcription. Taken together, our data reveal a new signaling pathway activated by amino acid starvation leading to ATF2 phosphorylation and subsequently positively affecting the transcription of amino acid-regulated genes.

Amino acid limitation regulates the expression of genes involved in several specific biological processes through GCN2-dependent and GCN2-independent pathways

Evidence has accumulated that amino acids play an important role in controlling gene expression. Nevertheless, two components of the amino acid control of gene expression are not yet completely understood in mammals: (a) the target genes and biological processes regulated by amino acid availability, and (b) the signaling pathways that mediate the amino acid response. Using large-scale analysis of gene expression, the objective of this study was to gain a better understanding of the control of gene expression by amino acid limitation. We found that a 6 h period of leucine starvation regulated the expression of a specific set of genes: 420 genes were up-regulated by more than 1.8-fold and 311 genes were down-regulated. These genes were involved in the control of several biological processes, such as amino acid metabolism, lipid metabolism and signal regulation. Using GCN2-/- cells and rapamycin treatment, we checked for the role of mGCN2 and mTORC1 kinases in this regulation. We found that (a) the GCN2 pathway was the major, but not unique, signaling pathway involved in the up- and down-regulation of gene expression in response to amino acid starvation, and (b) that rapamycin regulates the expression of a set of genes that only partially overlaps with the set of genes regulated by leucine starvation.

Plasmodium falciparum ensures its amino acid supply with multiple acquisition pathways and redundant proteolytic enzyme systems

Degradation of host hemoglobin by the human malaria parasite Plasmodium falciparum is a massive metabolic process. What role this degradation plays and whether it is essential for parasite survival have not been established, nor have the roles of the various degradative enzymes been clearly defined. We report that P. falciparum can grow in medium containing a single amino acid (isoleucine, the only amino acid missing from human hemoglobin). In this medium, growth of hemoglobin-degrading enzyme gene knockout lines (missing falcipain-2 and plasmepsins alone or in combination) is impaired. Blockade of plasmepsins with the potent inhibitor pepstatin A has a minimal effect on WT parasite growth but kills falcipain-2 knockout parasites at low concentrations and is even more potent on falcipain-2, plasmepsin I and IV triple knockout parasites. We conclude that: (i) hemoglobin degradation is necessary for parasite survival; (ii) hemoglobin degradation is sufficient to supply most of the parasite's amino acid requirements; (iii) external amino acid acquisition and hemoglobin digestion are partially redundant nutrient pathways; (iv) hemoglobin degradation uses dual protease families with overlapping function; and (v) hemoglobin-degrading plasmepsins are not promising drug targets.

Induction of IGFBP-1 expression by amino acid deprivation of HepG2 human hepatoma cells involves both a transcriptional activation and an mRNA stabilization due to its 3'UTR

A dramatic overexpression of IGFBP-1 is responsible for growth inhibition, in response to a low-protein diet feeding. It has been demonstrated that a fall in the amino acid concentration was directly responsible for IGFBP-1 induction. In this report, we sought to determine the mechanism by which amino acid limitation upregulates IGFBP-1 expression. Our results show that both transcriptional activation and mRNA stabilization are involved. We also demonstrate that (i) the mGCN2/ATF4 pathway is not involved in this regulation and (ii) the 3'UTR of IGFBP-1 mRNA is responsible for its destabilization and regulates its stability in response to amino acid starvation.

Amino acids as regulators of gene expression: molecular mechanisms

Regulation of gene expression by nutrients in mammals is an important mechanism allowing them to adapt their physiological functions according to the supply of nutrient in the diet. It has been shown recently that amino acids are able to regulate by themselves the expression of numerous genes. CHOP, asparagine synthetase, and IGFBP-1 regulation following AA starvation will be described in this review with special interest in the molecular mechanisms involved.

Induction of CHOP expression by amino acid limitation requires both ATF4 expression and ATF2 phosphorylation

The CHOP gene is transcriptionally induced by amino acid starvation. We have previously identified a genomic cis-acting element (amino acid response element (AARE)) involved in the transcriptional activation of the human CHOP gene by leucine starvation and shown that it binds the activating transcription factor 2 (ATF2). The present study was designed to identify other transcription factors capable of binding to the CHOP AARE and to establish their role with regard to induction of the gene by amino acid deprivation. Electrophoretic mobility shift assay and transient transfection experiments show that several transcription factors that belong to the C/EBP or ATF families bind the AARE sequence and activate transcription. Among all these transcription factors, only ATF4 and ATF2 are involved in the amino acid control of CHOP expression. We show that inhibition of ATF2 or ATF4 expression impairs the transcriptional activation of CHOP by amino acid starvation. The transacting capacity of ATF4 depends on its expression level and that of ATF2 on its phosphorylation state. In response to leucine starvation, ATF4 expression and ATF2 phosphorylation are increased. However, induction of ATF4 expression by the endoplasmic reticulum stress pathway does not fully activate the AARE-dependent transcription. Taken together our results demonstrate that at least two pathways, one leading to ATF4 induction and one leading to ATF2 phosphorylation, are necessary to induce CHOP expression by amino acid starvation. This work was extended to the regulation of other amino acid regulated genes and suggests that ATF4 and ATF2 are key components of the amino acid control of gene expression.

Recent advances in the understanding of amino acid regulation of gene expression

In mammals, the impact of nutrients on gene expression has become an important area of research. Because amino acids have multiple and important functions, their homeostasis has to be finely maintained. However, amino acidemia can be affected by certain nutritional conditions or various forms of stress. Consequently, mammals must adjust several of the physiological functions involved in the adaptation to amino acid availability by regulating expression of numerous genes. It has been shown that amino acids alone can modify the expression of target genes. However, understanding of amino acid-dependent control of gene expression has just started to emerge. This review focuses on recent advances in the understanding of mechanisms involved in the amino acid control of gene expression.

Recent advances on molecular mechanisms involved in amino acid control of gene expression

In mammals, the impact of nutrients on gene expression has become an important area of research. Because amino acids have multiple and important functions, their homeostasis has to be finely maintained. However, amino acidaemia can be affected by certain nutritional conditions or various forms of aggression. It follows that mammals have to adjust several of their physiological functions involved in the adaptation to amino acid availability by regulating the expression of numerous genes. It has been shown that amino acids by themselves can modify the expression of target genes. However, the current understanding of amino acid-dependent control of gene expression has just started to emerge. This review focuses on the recent advances on mechanisms involved in the amino acids control of gene expression. Several examples discussed in this paper demonstrate that amino acids regulate gene expression at the level of transcription, messenger RNA stability and translation.

Amino acid regulation of gene expression

The impact of nutrients on gene expression in mammals has become an important area of research. Nevertheless, the current understanding of the amino acid-dependent control of gene expression is limited. Because amino acids have multiple and important functions, their homoeostasis has to be finely maintained. However, amino-acidaemia can be affected by certain nutritional conditions or various forms of stress. It follows that mammals have to adjust several of their physiological functions involved in the adaptation to amino acid availability by regulating the expression of numerous genes. The aim of the present review is to examine the role of amino acids in regulating mammalian gene expression and protein turnover. It has been reported that some genes involved in the control of growth or amino acid metabolism are regulated by amino acid availability. For instance, limitation of several amino acids greatly increases the expression of the genes encoding insulin-like growth factor binding protein-1, CHOP (C/EBP homologous protein, where C/EBP is CCAAT/enhancer binding protein) and asparagine synthetase. Elevated mRNA levels result from both an increase in the rate of transcription and an increase in mRNA stability. Several observations suggest that the amino acid regulation of gene expression observed in mammalian cells and the general control process described in yeast share common features. Moreover, amino acid response elements have been characterized in the promoters of the CHOP and asparagine synthetase genes. Taken together, the results discussed in the present review demonstrate that amino acids, by themselves, can, in concert with hormones, play an important role in the control of gene expression.

Amino acids control mammalian gene transcription: activating transcription factor 2 is essential for the amino acid responsiveness of the CHOP promoter

In mammals, plasma concentration of amino acids is affected by nutritional or pathological conditions. It has been well established that nutrients, and particularly amino acids, are involved in the control of gene expression. Here we examined the molecular mechanisms involved in the regulation of CHOP (a CCAAT/enhancer-binding protein [C/EBP]-related gene) expression upon amino acid limitation. We have previously shown that regulation of CHOP mRNA expression by amino acid concentration has both transcriptional and posttranscriptional components. We report the analysis of cis- and trans-acting elements involved in the transcriptional activation of the human CHOP gene by leucine starvation. Using a transient expression assay, we show that a cis-positive element is essential for amino acid regulation of the CHOP promoter. This sequence is the first described that can regulate a basal promoter in response to starvation for several individual amino acids and therefore can be called an amino acid response element (AARE). In addition, we show that the CHOP AARE is related to C/EBP and ATF/CRE binding sites and binds in vitro the activating transcription factor 2 (ATF-2) in starved and unstarved conditions. Using ATF-2-deficient mouse embryonic fibroblasts and an ATF-2-dominant negative mutant, we demonstrate that expression of this transcription factor is essential for the transcriptional activation of CHOP by leucine starvation. Altogether, these results suggest that ATF-2 may be a member of a cascade of molecular events by which the cellular concentration of amino acids can regulate mammalian gene expression.

Amino acid limitation regulates gene expression

In mammals, the plasma concentration of amino acids is affected by nutritional or pathological conditions. For example, an alteration in the amino acid profile has been reported when there is a deficiency of any one or more of the essential amino acids, a dietary imbalance of amino acids, or an insufficient intake of protein. We examined the role of amino acid limitation in regulating mammalian gene expression. Depletion of arginine, cystine and all essential amino acids leads to induction of insulin-like growth factor-binding protein-1 (IGFBP-1) mRNA and protein expression in a dose-dependent manner. Moreover, exposure of HepG2 cells to amino acids at a concentration reproducing the amino acid concentration found in portal blood of rats fed on a low-protein diet leads to a significantly higher (P < 0.0002) expression of IGFBP-1. Using CCAAT/enhancer-binding protein homologous protein (CHOP) induction by leucine deprivation as a model, we have characterized the molecular mechanisms involved in the regulation of gene expression by amino acids. We have shown that leucine limitation leads to induction of CHOP mRNA and protein. Elevated mRNA levels result from both an increase in the rate of CHOP transcription and an increase in mRNA stability. We have characterized two elements of the CHOP gene that are essential to the transcriptional activation produced by an amino acid limitation. These findings demonstrate that an amino acid limitation, as occurs during dietary protein deficiency, can induce gene expression. Thus, amino acids by themselves can play, in concert with hormones, an important role in the control of gene expression.

Amino acid regulation of gene expression

In mammals, the plasma concentration of amino acids is affected by nutritional or pathological conditions. For example, an amino acid profile alteration has been reported as a result of a deficiency of any one of the essential amino acids, a dietary imbalance of amino acids or an insufficient intake of protein. Amino acid availability regulates the expression of several genes involved in the regulation of growth, cellular function or amino acid metabolism. A limitation of several amino acids strongly increases the expression of insulin-like growth factor binding protein CHOP and asparagine synthetase genes. Elevated messenger RNA levels result from both an increase in the rate of transcription and an increase in messenger RNA stability. DNA amino acid response elements have been characterized in the promoter of CHOP and asparagine synthetase genes. The underlying mechanisms of gene regulation by amino acid limitation are not yet completely understood. The results discussed in this review demonstrate that amino acids by themselves can play, in concert with hormones, an important role in the control of gene expression.

Amino acid limitation regulates CHOP expression through a specific pathway independent of the unfolded protein response

The gene encoding CHOP (C/EBP-homologous protein) is transcriptionally activated by many stimuli and by amino acid deprivation. CHOP induction was considered to be due to an accumulation of unfolded protein into the ER (unfolded protein response (UPR)). We investigate the role of the UPR in the induction of CHOP by amino acid deprivation and show that this induction is not correlated with BiP expression (an UPR marker). Moreover, amino acid deprivation and UPR inducers regulate the CHOP promoter activity using distinct cis elements. We conclude that amino acid deprivation does not activate the UPR and regulates CHOP expression through a pathway that is independent of the UPR.

Physiological concentration of amino acids regulates insulin-like-growth-factor-binding protein 1 expression

Protein undernutrition is characterized by growth failure in young growing animals. Current evidence suggests that biosynthesis of insulin-like growth factor (IGF)-I and IGF-binding protein 1 (IGFBP-1) are key control points for nutritional regulation of growth. Here we examined the role of amino acid limitation in regulating the IGFBP-1 expression in the hepatic cell line. Our data show that leucine limitation strongly induces IGFBP-1 without affecting IGF-I and IGF-II expression in human HepG2 cells and in isolated rat hepatocytes. Depletion of arginine, cystine and all essential amino acids leads to induction of IGFBP-1 mRNA and protein expression in a dose-dependent manner. IGFBP-1 expression is significantly induced by leucine concentration in the range of that observed in the blood of rats fed a low-protein diet or in humans affected by kwashiorkor. Moreover, treatment of HepG2 cells with amino acids at a concentration reproducing the amino acid concentration found in portal blood of rats fed a low-protein diet leads to a significantly higher expression of IGFBP-1. These data represent the first demonstration that an amino acid limitation, as occurs during dietary protein deficiency, induces IGFBP-1 expression in hepatic cells. Therefore, amino acids by themselves can play, in concert with hormones, an important role in the control of gene expression.

Effect of recombinant human erythropoietin on insulin, amino acid, and lipid metabolism in uremia

OBJECTIVE

To determine whether anemia is important in the pathogenesis of metabolic abnormalities in insulin, amino acid, and lipid metabolism in uremia.

METHODS

Twelve adolescents (15 +/- 1 years of age) undergoing long-term dialysis were studied before and after correction of their anemia by human recombinant erythropoietin at a mean interval of 6 months. Six patients received hemodialysis, and six received continuous-cycling peritoneal dialysis. Insulin sensitivity was measured by the euglycemic clamp technique and insulin secretion by the hyperglycemic clamp technique in these patients.

RESULTS

Hematocrit increased from 0.219 +/- 0.006 to 0.344 +/- 0.007 (p <0.01). Ferritin concentration did not change significantly (11,252 +/- 356 mg/dl to 785 +/- 226 mg/dl). Serum iron concentration decreased from 134 +/- 13 mg/dl to 83 +/- 11 mg/dl, and percentage saturation decreased from 56 +/- 4 to 41 +/- 5 (p <0.05 in both cases). There were no significant changes in weight, height, blood pressure, caloric intake, triceps skinfold thickness, or arm muscular area. There were also no significant changes in serum calcium, phosphate, bicarbonate, albumin, creatinine, or blood urea nitrogen concentration. Insulin sensitivity increased by 33% (p <0.01), but insulin secretion did not change significantly. Insulin sensitivity during the euglycemic clamp studies in patients before erythropoietin therapy was lower (145 +/- 10 mg/m2 per minute; p <0.01) than published normal values (201 +/- 12 mg/m2 per minute) and was normal after erythropoietin therapy (193 +/- 11 mg/m2 per minute). Insulin secretion was low in patients before erythropoietin therapy (44 +/- 8 microU/ml) compared with published normal values (68 +/- 6 microU/ml) and did not change after erythropoietin therapy (46 +/- 4 microU/ml). Plasma concentrations of branched-chain amino acids and lipids in the patients were compared with values from eight healthy adolescents. Plasma concentrations of valine, leucine, and isoleucine were low before treatment and were normal after 6 months of erythropoietin therapy. Plasma concentrations of triglycerides, total cholesterol, and low-density lipoprotein cholesterol were all high before treatment and were normal after treatment of anemia.

CONCLUSIONS

Treatment of anemia by erythropoietin reversed insulin resistance as well as amino acid and lipid abnormalities in adolescents undergoing dialysis.

A comparison of fasting serum amino acid profiles of young and elderly subjects

The fasting serum amino acid profile in 37 healthy young women and men (30-35 years) was compared with the fasting profile in 30 institutionalized elderly women and men (80-89 years), an ambulatory, self-fed senior-residence group. Levels of serum lysine, leucine, methionine, valine, and total essential amino acids were significantly lower in the older group than in the younger group; however, citrulline and hydroxyproline were significantly higher in the older group compared to the younger group. Histidine, threonine, tryptophan, and the ratio of tryptophan to large neutral amino acids (isoleucine, leucine, phenylalanine, tyrosine, and valine) were also generally lower in the older group than in the younger group, while the difference due to age was more pronounced in the females compared to males. The essential/nonessential amino acid ratio was lower in females compared to males.

Plasma and erythrocyte amino acid concentrations in anorexia nervosa

Plasma and erythrocyte amino acid concentrations in seven female patients in the acute stage of anorexia nervosa were compared with values in the same subjects after refeeding, and with normal controls. We also compared these values with literature values from patients with protein-calorie malnutrition and prolonged starvation in an attempt to identify a biological indicator of severity and prognosis. Our data indicate: (1) Routine laboratory analyses that reflect protein status do not differentiate normal subjects from patients with anorexia nervosa. (2) The plasma aminogram in the acute stage of anorexia nervosa differs from normal, and differs from values reported for both protein malnutrition and prolonged starvation. (3) The Whitehead ratio clearly separates the acutely ill anorectic state from the treated state and from normal controls. (4) Both erythrocyte and plasma amino acid concentrations differ from normal in anorexia nervosa, but changes in erythrocyte concentrations are more obvious. (5) Erythrocyte glycine concentrations are unique, in that values were persistently elevated at all stages of illness in anorexia nervosa. (6) Erythrocyte-to-plasma amino acid ratios do not provide a biological index of severity and prognosis for patients with anorexia nervosa, in contrast to data reported for individuals with protein malnutrition.

Plasma amino acids in preterm infants after a feed of human milk or formula

Prefeeding and sequential postprandial plasma amino acid concentrations were measured in 31 healthy preterm infants with gestational ages between 33 and 37 weeks at the ages of 4 to 12 days, to characterize changes after quantitatively and qualitatively different protein loads. All infants had previously been fed with human milk. The infants received a normal feed of pooled human milk (true protein 0.8 gm/dl) or of adapted or nonadapted milk formula (protein 1.5 gm/dl) from a bottle. The concentrations of all essential and several nonessential amino acids, including arginine and ornithine, rose sharply in plasma. Glycine decreased, and alanine increased slowly. Postprandial alterations in plasma total amino acids seemed to reflect the protein content of the different milks. In preterm infants, fed at three- to four-hour intervals, plasma amino acid concentrations fluctuate continuously. Thus in long-term studies and in screening, samples should be taken immediately before feeds. Postprandial plasma amino acid measurements may prove to be a useful means for testing the infant's ability to handle the protein or individual amino acid loads in various feeds.

Plasma amino acids in term neonates after a feed of human milk or formula. I. Total amino acids and glycine/valine ratios as reflectors of protein intake

Human milk and formulas with different quantities and qualities of protein were compared by measuring sequential postprandial changes in total amino acids and glycine/valine ratios in plasma of 23 healthy term neonates who had previously been breast-fed ad libitum. At the mean age of 5.5 days the infants received from a bottle 1/36 of their body weight of banked human milk (true protein 0.8 g/100 ml), or formula (1.5 g/100 ml of protein, whey-to-casein ratio 60 : 40 (adapted) or 18 : 82 (non-adapted), or 3.0 g/ml of protein, 60 : 40) after a 3.5-4 hour fast. After the feed, the sum of plasma free amino acids rose and the glycine/valine ratio fell, these changes being significant as soon as 30 min after the start of feeding and maximal at 30 min after human milk but at 60 min after the formulas. Both values returned to prefeeding levels, after human milk in 2-3 hours and after the two 1.5 g/100 ml formulas in about 4 hours, but after the 3 g/100 ml formula were still notably altered at 3.5 hours. The postprandial changes measured seemed to reflect dietary protein intake, and to be unaffected by protein quality (adapted vs. non-adapted formulas). The results show that in studies of plasma amino acids in young infants sampling times should be standardized exactly with respect to type of previous feeding and duration of fasting.

Prolonged hyperalimentation in catabolic chronic dialysis therapy patients

Plasma concentrations of 25 essential (EAA) and nonessential (NEAA) amino acids were measured pre- and postdialysis in 46 chronic hemodialysis therapy (CDT) patients. Sixteen of these patients with prior weight loss of 14.5 +/- 2.37 pounds in 24 months were administered a GAA solution (EAA + NEAA + glucose) for 20 weeks during each dialysis. Eight of these patients (group 1) responded with improved appetite and weight gain; the remaining eight patients (group 2) with clinically advanced metabolic bone disease continued to lose weight. Five other patients (group 14), biochemically similar to group 1 but with shorter prior dialysis experience, who received EAA (plus glucose) hyperalimentation (including oral I-histidine), experienced weight gain similar to group 1 but displayed significantly different plasma aminograms indicating a deficit of NEAA. When EAA and glucose hyperalimentation was administered without histidine (1 patient) no weight gain occurred and aminograms differed significantly from other groups. Plasma aminograms of 25 weight-stable, nonhyperalimented CDT patients were obtained for comparison. Results indicate GAA hyperalimentation can promote weight gain in catabolic CDT patients with inadequate prior nutritional intake (as in groups 1 and 14) but cannot reverse weight loss when the primary clinical setting is advanced metabolic bone disease and myopathy due to hyperparathyroidism (group 2). Hyperalimentation with glucose and an amino acid solution specifically tailored to the needs of CDT patients may improve results. Plasma phosphoethanolamine levels, normal for weight-stable and elevated in catabolic CDT patients, suggest a possible role for phosphoethanolamine as a marker for catabolism.

The cord serum free amino acid levels in appropriate and small for gestational age newborn infants of mothers without clinical malnutrition in Abidjan

The cord serum amino acid levels were determined in nine small for gestational age and fourteen appropriate for gestational age newborn infants of Abidjan, Ivory Coast. Small for gestational age newborns had a significantly lower total amount of amino acids, but the characteristic deviation of the individual concentrations and the high glycine/valine ratio seen in experimental and clinical protein deficiency were not found.

The problem of human protein requirements: some kinetic and metabolic considerations

Estimated human protein requirements have been substantially lowered by FAO/WHO expert committees over the past two decades. The estimates and methods of calculation are considered in the light of the kinetics of response to protein intake, body protein turnover, amino acid flows in the body, and the concept of nitrogen (N) steady state. Whereas traditional methods of estimation have assumed an essentially linear (first order) response of N retention to absorbed N, animal studies show that response to graded protein intakes obeys saturation kinetics. Corrections for protein quality have also assumed a linear relation between response and supply of limiting amino acid, while animal experiments indicate that this response likewise follows saturation kinetics. Evidence is lacking that the present minimum protein standards for humans can support acceptable internal nitrogen steady states at any age above infancy or foster normal growth in the child. New research approaches to determination of protein requirements are suggested , including study of the kinetics of human response to graded protein intakes and graded variations of quality; development of indicators of nitrogen steady state and correlation with clinical status; and determination of optimum protein-energy ratios by age and sex.

Plasma amino acids in children and adolescents on hemodialysis

Fasting plasma amino acid concentrations were measured in 16 children on regular hemodialysis for renal failure. Reductions compared to normal were found in valine, leucine, isoleucine, lysine, histidine, tyrosine, and serine; and increases were found in glycine, citruline, proline, and 1- and 3-methylhistidine. Acute reductions in amino acid concentrations occurred in response to i.v. glucose, similar to those reported in normal adults, but plasma alanine, which was raised only in those with poor glucose tolerance, fell to normal and did not vary in those with normal glucose tolerance. No correlations were found with growth, but the plasma glycine concentration was highest in those patients with poorest energy intakes. Plasma alanine concentrations correlated with raised triglyceride concentrations. It is suggested that many of the abnormalities are due to the excessive utilization of protein for energy because of impaired availability of conventional energy sources in uremia.

A study of the age of onset, diet and the importance of infection in the pattern of severe protein-energy malnutrition in Ibadan, Nigeria

1. Fifty unselected consecutive cases of protein-energy malnutrition (PEM) presenting at the General Out-patient Clinic of the University College Hospital, Ibadan were classified as marasmus (twenty), kwashiorkor (nineteen) marasmic-kwashiorkor (seven) and undernutrition (four) according to the Wellcome Classification of PEM (Lancet, 1970; Waterlow, 1972).

2. The mean age of the children with marasmus (22.4 months) and of the children with kwashiorkor (25.4 months) were not significantly different. The children with marasmickwashiorkor (27.8 months) were significantly older than the children with marasmus.

3. The deficits in weight- and length-for-age were similar to values previously reported (Waterlow, 1972) even though the children with marasmus tended to be older and the children with kwashiorkor younger than has been reported. Values obtained for the deficit in length-for-age suggested that the children with marasmus had been undernourished from birth whereas the children with kwashiorkor had apparently grown normally until they were 10 months old. It is possible that the history of growth in the first year of life influences the final form of PEM in these two groups of children.

4. Forty-nine of the fifty children had been breast-fed for at least 9 months and nine children had been breast-fed for 2 years. Of the twenty children with marasmus nine were still receiving some breast milk. The diets fed to weaned children with marasmus and to children with kwashiorkor were identical and consisted solely of a maize-starch gruel with no supplementation of protein or vitamins. The similarity in the dietary histories of the two main groups of children suggests some uncertainty concerning a specific role for protein deficiency in the development of kwashiorkor.

5. All the children had had similar infections. The most common of these were measles (morbilli) (40% of all cases) and gastrointestinal infections. However the children with marasmus had a history of chronic diarrhoea whereas the children with kwashiorkor had had more acute diarrhoea.

6. The similar dietary histories but dissimilar histories of infection given by the mothers of the children with marasmus as opposed to those with kwashiorkor suggest that recurrent diarrhoea was at least partially responsible for the chronic undernutrition in the group of children with marasmus. Furthermore although the weaning diets were inadequate the final deterioration in nutritional status was precipitated by gastroenteritis, often following measles.

Serum albumin and transferrin in protein-energy malnutrition: Their use in the assessment of marginal undernutrition and the prognosis of severe undernutrition

1. Deficits in weight- and length-for-age, and serum albumin and transferrin concentrations were determined for children who were either marginally undernourished (twenty-five children) or suffering from either marasmus (thirty-two children) or kwashiorkor (twenty-six children) defined according to the Wellcome Classification (Waterlow, 1972). The measurements were also made in eight children with kwashiorkor after the loss of oedema, and in sixteen children who were recovering from either marasmus or kwashiorkor.

2. The mean concentration of serum albumin was similar for children from the ‘under-nourished’ group and from the group with marasmus, but was significantly reduced in those with kwashiorkor.

3. The concentration of serum transferrin was significantly reduced in both the group of children with marasmus and those with kwashiorkor. The serum transferrin concentration was significantly lower in children with kwashiorkor when compared with the level in those with marasmus.

4. Seventeen children (seven with kwashiorkor and ten with marasmus) died. These children were neither lighter nor shorter than the severely malnourished children who survived. The concentration of serum albumin was not lower in the children who died than in those who survived.

5. In contrast to the results for serum albumin concentrations, the children who died had significantly lower levels of serum transferrin than those who survived.

6. There was a significant linear relationship between serum transferrin concentrations and the deficits in length-for-age (P< 0·05) and weight-for-length (P< 0·001) in the marginally undernourished children. The deficit in weight-for-length was also linearly related to the serum transferrin concentrations (P< 0·001) in children recovering from severe malnutrition.

7. It is suggested that the measurement of serum transferrin concentrations provides an index of severity in severely malnourished children, and should prove useful in field assessments of nutritional status.