Analbuminemia: three cases resulting from different point mutations in the albumin gene

Plasma Protein-Mediated Uptake and Contradictions to the Free Drug Hypothesis: A Critical Review

According to the free drug hypothesis (FDH), only free, unbound drug is available to interact with biological targets. This hypothesis is the fundamental principle that continues to explain the vast majority of all pharmacokinetic and pharmacodynamic processes. Under the FDH, the free drug concentration at the target site is considered the driver of pharmacodynamic activity and pharmacokinetic processes. However, deviations from the FDH are observed in hepatic uptake and clearance predictions, where observed unbound intrinsic hepatic clearance (CL_int,u) is larger than expected. Such deviations are commonly observed when plasma proteins are present and form the basis of the so-called plasma protein-mediated uptake effect (PMUE). This review will discuss the basis of plasma protein binding as it pertains to hepatic clearance based on the FDH, as well as several hypotheses that may explain the underlying mechanisms of PMUE. Notably, some, but not all, potential mechanisms remained aligned with the FDH. Finally, we will outline possible experimental strategies to elucidate PMUE mechanisms. Understanding the mechanisms of PMUE and its potential contribution to clearance underprediction is vital to improving the drug development process.

Why Do the Mechanistic Actions of Albumin Not Translate Into Tangible Clinical Benefits?

Albumin has only reduced crude mortality in one randomized controlled trial conducted to date. This raises the question as to why potentially beneficial oncotic and pleiotropic properties of albumin do not consistently translate into clinically important outcomes. Four postulated explanations are provided as to why the theoretical advantages of albumin are not apparent in clinical trials: diminished oncotic action due to leakage of albumin from the intravascular compartment, modification of the pleiotropic properties of albumin both in vitro and in vivo, the ability of other plasma proteins to take over the major functions of albumin, and possible adverse effects.

Very Low Vitamin D in a Patient With a Novel Pathogenic Variant in the GC Gene That Encodes Vitamin D-Binding Protein

Circulating plasma vitamin D metabolites are highly bound to vitamin D-binding protein (DBP), also known as group-specific component or Gc-globulin. DBP, encoded by the GC gene, is a member of the albumin family of globular serum transport proteins. We previously described a homozygous GC gene deletion in a patient with apparent severe vitamin D deficiency, fragility fractures, and ankylosing spondylitis. Here, we report an unrelated patient free of fractures or rheumatologic disease, but with very low 25-hydroxyvitamin D and 1,25-hydroxyvitamin D, as well as undetectable DBP measured by liquid chromatography–tandem mass spectrometry. A whole gene deletion was excluded by microarray, and Sanger sequencing of GC revealed a homozygous pathogenic variant affecting a canonical splice site (c0.702-1G > A). These findings indicate that loss of function variants in GC that eliminate DBP, and severely reduced total circulating vitamin D levels, do not necessarily result in significant metabolic bone disease. Together with our previous report, these cases support the free-hormone hypothesis, and suggest free vitamin D metabolites may serve as preferable indicators of bone and mineral metabolism, particularly when clinical suspicion of DBP deficiency is high.

Impact of Interindividual Differences in Plasma Fraction Unbound on the Pharmacokinetics of a Novel Syk Kinase Inhibitor in Beagle Dogs

Inconsistencies in pharmacokinetic parameters between individual animals in preclinical studies are a common occurrence. Often such differences between animals are simply accepted as experimental variability rather than as indications of specific differences in animal phenotype that could lead to a different interpretation of the data. The fraction unbound in plasma is one factor influencing pharmacokinetic parameters and is typically determined using pooled plasma from multiple animals, making the assumption that there is limited population variance. However, this assumption is not often tested and may not hold true if there are polymorphisms affecting binding or variation in the concentrations of individual plasma proteins that could give rise to different fraction unbound phenotypes in individual animals. During profiling of a novel Syk inhibitor, AZ8399, striking interindividual differences in total plasma clearance and volume of distribution were observed between dogs consistent with differences in fraction unbound between animals. Determination of the fraction unbound showed a ∼5-fold difference in fraction unbound between the animals in the study. Broader analysis of individual dogs across a colony demonstrated a correlation between individual animal fraction unbound with total plasma clearance and volume of distribution. The concentrations of the common drug-binding proteins albumin and α1-acid glycoprotein in plasma were determined, and α1-acid glycoprotein levels were found to correlate with fraction unbound. Finally, single-nucleotide polymorphisms were identified at c.502 and c.522 of exon 5 of the dog α1-acid glycoprotein gene that may be correlated to the α1-acid glycoprotein concentration phenotype observed. SIGNIFICANCE STATEMENT: The current work demonstrates the potential for significant interindividual differences in plasma fraction unbound in beagle dogs and goes on to examine the underlying cause for the compound described. The findings suggest that the application of a population mean value of fraction unbound generated from a pooled sample may not always be appropriate and could introduce significant errors in scaling of in vitro clearance values, PBPK understanding, and interpretation of PKPD or toxicokinetic data in the context of unbound concentrations.

Recurrent Hypoglycemia in a Case of Congenital Analbuminemia

In congenital analbuminemia (CAA), mutations in the albumin gene result in a severe deficiency or absence of plasma albumin. Only about 90 cases have been reported to date, but the specific features of glucose and lipid metabolism in congenital analbuminemia have only been studied in a rat model of analbuminemia. We report the case of a female patient hospitalized for a streptococcal skin infection who showed recurrent hypoglycemia. A diagnosis of CAA was confirmed by mutation analysis and by the detection of a single base variation in the ALB gene. Hypoglycemia was first documented after a fasting period during acute illness. Recurrent hypoglycemia persisted despite good general condition and normal nutrition during antimicrobial therapy with moxifloxacin. Several contributing factors causing this hypoglycemia can be discussed. Individuals with CAA are prone to adverse drug effects caused by changes in drug-protein binding properties. It is unclear if specific changes of glucose and lipid metabolism in CAA constitute a risk factor for hypoglycemia.

Diagnosis, Phenotype, and Molecular Genetics of Congenital Analbuminemia

Congenital analbuminemia (CAA) is an inherited, autosomal recessive disorder with an incidence of 1:1,000,000 live birth. Affected individuals have a strongly decreased concentration, or complete absence, of serum albumin. The trait is usually detected by serum protein electrophoresis and immunochemistry techniques. However, due to the existence of other conditions in which the albumin concentrations are very low or null, analysis of the albumin (ALB) gene is necessary for the molecular diagnosis. CAA can lead to serious consequences in the prenatal period, because it can cause miscarriages and preterm birth, which often is due to oligohydramnios and placental abnormalities. Neonatally and in early childhood the trait is a risk factor that can lead to death, mainly from fluid retention and infections in the lower respiratory tract. By contrast, CAA is better tolerated in adulthood. Clinically, in addition to the low level of albumin, the patients almost always have hyperlipidemia, but they usually also have mild oedema, reduced blood pressure and fatigue. The fairly mild symptoms in adulthood are due to compensatory increment of other plasma proteins. The condition is rare; clinically, only about 90 cases have been detected worldwide. Among these, 53 have been studied by sequence analysis of the ALB gene, allowing the identification of 27 different loss of function (LoF) pathogenic variants. These include a variant in the start codon, frame-shift/insertions, frame-shift/deletions, nonsense variants, and variants affecting splicing. Most are unique, peculiar for each affected family, but one, a frame-shift deletion called Kayseri, has been found to cause about one third of the known cases allowing to presume a founder effect. This review provides an overview of the literature about CAA, about supportive and additional physiological and pharmacological information obtained from albumin-deficient mouse and rat models and a complete and up-to-date dataset of the pathogenic variants identified in the ALB gene.

Hypoalbuminemia and Clinical Outcomes: What is the Mechanism behind the Relationship?

Albumin has a number of important physiologic functions, which include maintaining oncotic pressure, transporting various agents (fatty acids, bile acids, cholesterol, metal ions, and drugs), scavenging free oxygen radicals, acting as an antioxidant, and exerting an antiplatelet effect. Hypoalbuminemia in adults, defined by an intravascular albumin level of <3.5 g/dL, is associated with poor postoperative outcomes in patients undergoing surgical intervention. Although the relationship of hypoalbuminemia and poor surgical outcome has been known for many years, the pathophysiology behind the relationship is unclear. Three theoretical constructs might explain this relationship. First, albumin might serve as a nutritional marker, such that hypoalbuminemia represents poor nutritional status in patients who go on to experience poor postoperative outcomes. Second, albumin has its own pharmacologic characteristics as an antioxidant or transporter, and therefore, the lack of albumin might result in a deficiency of those functions, resulting in poor postoperative outcomes. Or third, albumin is known to be a negative acute phase protein, and as such hypoalbuminemia might represent an increased inflammatory status of the patient, potentially leading to poor outcomes. A thorough review of the literature reveals the fallacy of these arguments and fails to show a direct cause and effect between low albumin levels per se and adverse outcomes. Interventions designed solely to correct preoperative hypoalbuminemia, in particular intravenous albumin infusion, do little to change the patient's course of hospitalization. While surgeons may use albumin levels on admission for their prognostic value, they should avoid therapeutic strategies whose main endpoint is correction of this abnormality.

Hepatic FcRn regulates albumin homeostasis and susceptibility to liver injury

The neonatal crystallizable fragment receptor (FcRn) is responsible for maintaining the long half-life and high levels of the two most abundant circulating proteins, albumin and IgG. In the latter case, the protective mechanism derives from FcRn binding to IgG in the weakly acidic environment contained within endosomes of hematopoietic and parenchymal cells, whereupon IgG is diverted from degradation in lysosomes and is recycled. The cellular location and mechanism by which FcRn protects albumin are partially understood. Here we demonstrate that mice with global or liver-specific FcRn deletion exhibit hypoalbuminemia, albumin loss into the bile, and increased albumin levels in the hepatocyte. In vitro models with polarized cells illustrate that FcRn mediates basal recycling and bidirectional transcytosis of albumin and uniquely determines the physiologic release of newly synthesized albumin into the basal milieu. These properties allow hepatic FcRn to mediate albumin delivery and maintenance in the circulation, but they also enhance sensitivity to the albumin-bound hepatotoxin, acetaminophen (APAP). As such, global or liver-specific deletion of FcRn results in resistance to APAP-induced liver injury through increased albumin loss into the bile and increased intracellular albumin scavenging of reactive oxygen species. Further, protection from injury is achieved by pharmacologic blockade of FcRn-albumin interactions with monoclonal antibodies or peptide mimetics, which cause hypoalbuminemia, biliary loss of albumin, and increased intracellular accumulation of albumin in the hepatocyte. Together, these studies demonstrate that the main function of hepatic FcRn is to direct albumin into the circulation, thereby also increasing hepatocyte sensitivity to toxicity.

Pregnancy in a patient with congenital analbuminaemia

Congenital analbuminaemia is a rare autosomal recessive disorder that is characterised by a severe reduction or total absence of serum albumin. This condition has implications for therapeutics as a large proportion of commonly used drugs are plasma protein bound where albumin is the primary component of plasma protein. This is the first case report of pregnancy in a patient with congenital analbuminaemia in the medical literature. In the absence of drug dosage guidelines for patients with congenital analbuminaemia, a list of drugs which may be required for this patient during pregnancy, delivery and/or emergency situations were compiled by a multidisciplinary team. Our patient suffered from polyhydramnios during her pregnancy which was successfully managed with albumin transfusions and had a normal vaginal delivery with no complications in the intrapartum or postpartum period. The management and unique challenges of pregnancy in a patient with congenital analbuminaemia are discussed.

Human serum albumin homeostasis: a new look at the roles of synthesis, catabolism, renal and gastrointestinal excretion, and the clinical value of serum albumin measurements

Serum albumin concentration (CP) is a remarkably strong prognostic indicator of morbidity and mortality in both sick and seemingly healthy subjects. Surprisingly, the specifics of the pathophysiology underlying the relationship between CP and ill-health are poorly understood. This review provides a summary that is not previously available in the literature, concerning how synthesis, catabolism, and renal and gastrointestinal clearance of albumin interact to bring about albumin homeostasis, with a focus on the clinical factors that influence this homeostasis. In normal humans, the albumin turnover time of about 25 days reflects a liver albumin synthesis rate of about 10.5 g/day balanced by renal (≈6%), gastrointestinal (≈10%), and catabolic (≈84%) clearances. The acute development of hypoalbuminemia with sepsis or trauma results from increased albumin capillary permeability leading to redistribution of albumin from the vascular to interstitial space. The best understood mechanism of chronic hypoalbuminemia is the decreased albumin synthesis observed in liver disease. Decreased albumin production also accounts for hypoalbuminemia observed with a low-protein and normal caloric diet. However, a calorie- and protein-deficient diet does not reduce albumin synthesis and is not associated with hypoalbuminemia, and CP is not a useful marker of malnutrition. In most disease states other than liver disease, albumin synthesis is normal or increased, and hypoalbuminemia reflects an enhanced rate of albumin turnover resulting either from an increased rate of catabolism (a poorly understood phenomenon) or enhanced loss of albumin into the urine (nephrosis) or intestine (protein-losing enteropathy). The latter may occur with subtle intestinal pathology and hence may be more prevalent than commonly appreciated. Clinically, reduced CP appears to be a result rather than a cause of ill-health, and therapy designed to increase CP has limited benefit. The ubiquitous occurrence of hypoalbuminemia in disease states limits the diagnostic utility of the CP measurement.

Are predictions of cancer response to targeted drugs, based on effects in unrelated tissues, the ‘Black Swan’ events?

Adverse effects of targeted drugs on normal tissues can predict the cancer response. Rash correlates with efficacy of erlotinib, cetuximab and gefitinib and onset of arterial hypertension with response to bevacizumab, sunitinib, axitinib and sorafenib, possible examples of ‘Black Swan’ events, unexpected scientific observations, as described by Karl Popper in 1935. The proposition is that our patients have individual intrinsic variants of cell growth control, important for tumor response and adverse effects on tumor-unrelated tissue. This means that the lack of predictive side effects in healthy tissue is linked with poor results of tumor therapy when tumor resistance is caused by mechanisms that protect all cells of that patient from the targeted drug effects.

Congenital analbuminaemia: molecular defects and biochemical and clinical aspects

BACKGROUND

DNA and mRNA sequencing of the coding regions of the human albumin gene (ALB) and of its intron/exon junctions has revealed twenty-one different molecular defects causing congenital analbuminaemia (CAA).

SCOPE OF REVIEW

To describe the mutations in molecular terms and to present the current knowledge about the most important biochemical and clinical effects of CAA.

MAJOR CONCLUSIONS

CAA is rare, but its frequency seems to be significantly higher in restricted and minimally admixed populations. The condition affects especially the lipid metabolism but apart from a possible increased risk for atherosclerotic complications, it is generally associated with mild clinical symptoms in adults. By contrast, several reports indicate that analbuminaemic individuals may be at risk during the perinatal and childhood periods, in which they seem to show increased morbidity and mortality. The twenty-one causative defects include seven nonsense mutations, seven changes affecting splicing, five frame-shift/deletions, one frame-shift/insertion and one mutation in the start codon. These results indicate that the trait is an allelic heterogeneous disorder caused by homozygous (nineteen cases) or compound heterozygous (single case) inheritance of defects. Most mutations are unique, but one, named Kayseri, is responsible for about half of the known cases.

GENERAL SIGNIFICANCE

Study of the defects in the ALB resulting in CAA allows the identification of "hot spot" regions and contributes to understanding the molecular mechanism underlying the trait. Such studies could also give molecular information about different aspects of ALB regulation and shed light on the regulatory mechanisms involved in the synthesis of the protein. This article is part of a Special Issue entitled Serum Albumin.

Perinatal and childhood morbidity and mortality in congenital analbuminemia

Albumin, a serum transport protein, provides 80% of colloid osmotic pressure. Congenital analbuminemia (CAA) is an autosomal recessive disorder characterized by absence of serum albumin. Fifty cases of CAA have been reported throughout the world; however, little is known about its clinical impact. Most reported cases have few clinical signs and symptoms. Twelve local cases from the northwestern central plains region in Saskatchewan were identified and reviewed to ascertain morbidity and mortality related with CAA. All the cases are from two remote First Nations communities. Cases had frequent hospital admissions and recurrent respiratory tract infections. Placental abnormalities included hydropic placentas, placental infarcts and microcalcifications. One-half of the cases were born preterm and one-quarter were small for their gestational age. There were three mortalities in the case series. The present case series suggests increased morbidity and mortality during infancy in patients with CAA. The long-term risks of CAA in this population are unknown and a longitudinal study is recommended.

A novel splicing mutation causes analbuminemia in a Portuguese boy

Analbuminemia is a rare autosomal recessive disorder manifested by the absence or severe reduction of circulating serum albumin in homozygous or compound heterozygous subjects. It is an allelic heterogeneous defect, caused by a variety of mutations within the albumin gene. The analbuminemic condition was suspected in a Portuguese boy who presented with low albumin level (about 3.8 g/L) and a significant hypercholesterolemia, but with no clinical findings. The albumin gene was screened by single strand conformational polymorphism and heteroduplex analysis and submitted to direct DNA sequencing. The proband was found to be homozygous for a previously unreported G>A change at position c.1289+1, the first base of intron 10, which inactivates the strongly conserved GT dinucleotide at the 5' splice site consensus sequence of the intron. The effect of this mutation was evaluated by examining the cDNA obtained by RT-PCR from the albumin mRNA extracted from proband's leukocytes. The splicing defect results in the skipping of the preceding exon. The subsequent reading frame-shift in exon 11 produces a premature stop codon located 33 codons downstream the 5' end of the exon. This extensive cDNA alteration is responsible for the analbuminemic trait. Both parents were found to be heterozygous for the same mutation. DNA and cDNA sequence analysis established the diagnosis of congenital analbuminemia in the proband. The effects of the so far identified splice-site mutations in the albumin gene are discussed.

Human serum albumin: from bench to bedside

Human serum albumin (HSA), the most abundant protein in plasma, is a monomeric multi-domain macromolecule, representing the main determinant of plasma oncotic pressure and the main modulator of fluid distribution between body compartments. HSA displays an extraordinary ligand binding capacity, providing a depot and carrier for many endogenous and exogenous compounds. Indeed, HSA represents the main carrier for fatty acids, affects pharmacokinetics of many drugs, provides the metabolic modification of some ligands, renders potential toxins harmless, accounts for most of the anti-oxidant capacity of human plasma, and displays (pseudo-)enzymatic properties. HSA is a valuable biomarker of many diseases, including cancer, rheumatoid arthritis, ischemia, post-menopausal obesity, severe acute graft-versus-host disease, and diseases that need monitoring of the glycemic control. Moreover, HSA is widely used clinically to treat several diseases, including hypovolemia, shock, burns, surgical blood loss, trauma, hemorrhage, cardiopulmonary bypass, acute respiratory distress syndrome, hemodialysis, acute liver failure, chronic liver disease, nutrition support, resuscitation, and hypoalbuminemia. Recently, biotechnological applications of HSA, including implantable biomaterials, surgical adhesives and sealants, biochromatography, ligand trapping, and fusion proteins, have been reported. Here, genetic, biochemical, biomedical, and biotechnological aspects of HSA are reviewed.

Pulmonary vascular heterogeneity and the Starling hypothesis

It has generally been assumed that movement of fluid between the pulmonary microvasculature and surrounding tissues is governed by a "Starling" balance of hydrostatic and protein osmotic forces similar to that which prevails in the extremities. However, both recent and older observations suggest that the lungs are more resistant to edema formation than most other organs. Several structural aspects of the lung may account for protection of the airspaces from edema formation. The pulmonary microvasculature, which comprises >70% of the pulmonary circulatory bed, appears to be less permeable to fluid and electrolytes than the endothelium of the pulmonary arteries and veins and other microvascular exchange areas. This arrangement may help explain why early edema is confined to the perivascular and peribronchial regions and why lymphatics do not reach the alveoli. Unlike the peripheral vasculature, which is compressed by edema formation, the extra-alveolar vessels remain tethered open by airway distention, even when interstitial pressures rise above those in the vessels. This may also facilitate return of proteins to the circulation. Ultrafiltration of plasma may lower local protein concentrations in the interstitium, thereby slowing further edema formation. Transendothelial reabsorption of fluid may also be altered by vesicular transport.

Congenital analbuminemia with acute glomerulonephritis: a diagnostic challenge

Congenital analbuminemia is a rare autosomal recessive disease in which albumin is not synthesized. Patients with this disorder generally have minimal symptoms despite complete absence of the most abundant serum protein. We report a family in which the proband presented with acute glomerulonephritis and was found to have underlying congenital analbuminemia. Consequently, the patient's two older sisters were diagnosed with the same condition. Sequencing of the human serum albumin gene was performed, and a homozygous mutation in exon 3 was found in all three patients. Together with these three patients of Arab ethnicity, this mutation, known as Kayseri, is the most frequently described mutation in congenital analbuminemia. This article discusses clinical features and diagnostic challenges of this disorder, particularly in this case, where concomitant renal disease was present.

Mutations and polymorphisms of the gene of the major human blood protein, serum albumin

We have tabulated the 77 currently known mutations of the familiar human blood protein, serum albumin (ALB). A total of 65 mutations result in bisalbuminemia. Physiological and structural effects of these mutations are included where observed. Most of the changes are benign. The majority of them were detected upon clinical electrophoretic studies, as a result of a point mutation of a charged amino acid residue. Three were discovered by their strong binding of thyroxine or triiodothyronine. A total of 12 of the tabulated mutations result in analbuminemia, defined as a serum albumin concentration of <1 g/L. These were generally detected upon finding a low albumin concentration in patients with mild edema, and involve either splicing errors negating translation or premature stop codons producing truncated albumin molecules. A total of nine mutations, five of those with analbuminemia and four resulting in variants modified near the C-terminal end, cause frameshifts. Allotypes from three of the point mutations become N-glycosylated and one C-terminal frameshift mutation shows O-glycosylation.

A boy with congenital analbuminemia and steroid-sensitive idiopathic nephrotic syndrome: an experiment of nature

In this paper, a boy is reported with the association of congenital analbuminemia (CAA) and steroid-sensitive idiopathic nephrotic syndrome (INS), two conditions resulting independently in reduced colloid oncotic pressure. The unique occurrence helps confirm earlier reports that albumin is not the exclusive factor responsible for maintaining colloid oncotic pressure.

Analbuminemia in a Swedish male is caused by the Kayseri mutation (c228_229delAT)

BACKGROUND

Analbuminemia is a rare autosomal recessive disorder manifested by the absence, or severe reduction, of circulating serum albumin. Here we report the first case of hereditary analbuminemia in the ethnic Swedish population, and we define the molecular defect that causes the analbuminemic trait.

METHODS

Total DNA, extracted from peripheral blood samples from the analbuminemic proband and his parents, was PCR-amplified using oligonucleotide primers designed to amplify the 14 exons, the exon-intron splice junctions, and the 5' and 3' untranslated regions of the albumin gene. The products were screened for mutations by single-strand conformation polymorphism and heteroduplex analyses. The latter allowed the identification of the abnormal fragment, which was then sequenced.

RESULTS

The analbuminemic trait of the proband was caused by a homozygous AT deletion at nucleotides c. 228-229, the 91st and 92nd bases of exon 3. This defect, previously identified as Kayseri mutation [M. Galliano, M. Campagnoli, A. Rossi, et al. Molecular diagnosis of analbuminemia: a novel mutation identified in two Amerindian and two Turkish families. Clin Chem 2002;48: 844-849.], produces a frameshift leading to a premature stop, two codons downstream.

CONCLUSIONS

The Kayseri mutation appears to be the most common cause of analbuminemia in humans, and is found in individuals belonging to geographically distant, and apparently unrelated ethnic groups.

Analbuminemia Produced by a Novel Splicing Mutation

Analbuminemia is a rare autosomal recessive disorder manifested by the absence or severe reduction of circulating human serum albumin in homozygous or compound heterozygous individuals. It is an allelic heterogeneous defect, caused by a variety of mutations within the albumin gene. The analbuminemic condition was diagnosed in a Turkish female infant on the basis of low albumin concentration (∼9.0 g/L). The albumin gene was screened by single-strand conformation polymorphism and heteroduplex analysis and submitted to direct sequencing. The proband was found to be homozygous for a T→C transition at nucleotide 13381, the 2nd base of intron 11. The effect of this previously unreported mutation, which inactivates the strongly conserved GT dinucleotide at the 5′ splice site consensus sequence of intron 11, was evaluated by examining the cDNA obtained by reverse transcription-PCR from the albumin mRNA extracted from the proband leukocytes. This analysis revealed that the mutation, named Bartin for the geographical origin of the patient’s family, results in the skipping of exon 11. The subsequent frameshift within exon 12 originates a premature stop codon located 5 codons downstream at position 411. The predicted translation product would consist of 410 amino acids. This novel extensive cDNA alteration is responsible for the analbuminemic trait.

Active focal segmental glomerulosclerosis is associated with massive oxidation of plasma albumin

The basic mechanism for idiopathic FSGS still is obscure. Indirect evidence in humans and generation of FSGS by oxidants in experimental models suggest a role of free radicals. In vitro studies demonstrate a main role of plasma albumin as antioxidant, its modification representing a chemical marker of oxidative stress. With the use of complementary liquid chromatography electron spray ionization tandem mass spectrometry (LC-ESI-MS/MS) and biochemical methods, plasma albumin was characterized in 34 patients with FSGS; 18 had received a renal transplant, and 17 had IgM mesangial deposition. Patients with FSGS that was in remission or without recurrence after transplantation had normal plasma albumin, and the same occurred in patients with primary and secondary nephrites and with chronic renal failure. In contrast, patients with active FSGS or with posttransplantation recurrence had oxidized plasma albumin. This finding was based on the characterization of albumin Cys 34 with an mass-to-charge ratio of 511.71 in triple charge that was consistent with the formation of a cysteic acid carrying a sulfonic group (alb-SO(3)(-)). The exact mass of albumin was increased accordingly (+48 Da) for incorporation of three oxygen radicals. Direct titration of the free sulfhydryl group 34 of plasma albumin and electrophoretic titration curves confirmed loss of free sulfhydryl group and formation of a fast-moving isoform in all cases with disease activity. This is the first demonstration of in vivo plasma albumin oxidation that was obtained with an adequate structural approach. Albumin oxidation seems to be specific for FSGS, suggesting some pathogenetic implications. Free radical involvement in FSGS may lead to specific therapeutic interventions.

Signaling Mechanisms Regulating Endothelial Permeability

The microvascular endothelial cell monolayer localized at the critical interface between the blood and vessel wall has the vital functions of regulating tissue fluid balance and supplying the essential nutrients needed for the survival of the organism. The endothelial cell is an exquisite “sensor” that responds to diverse signals generated in the blood, subendothelium, and interacting cells. The endothelial cell is able to dynamically regulate its paracellular and transcellular pathways for transport of plasma proteins, solutes, and liquid. The semipermeable characteristic of the endothelium (which distinguishes it from the epithelium) is crucial for establishing the transendothelial protein gradient (the colloid osmotic gradient) required for tissue fluid homeostasis. Interendothelial junctions comprise a complex array of proteins in series with the extracellular matrix constituents and serve to limit the transport of albumin and other plasma proteins by the paracellular pathway. This pathway is highly regulated by the activation of specific extrinsic and intrinsic signaling pathways. Recent evidence has also highlighted the importance of the heretofore enigmatic transcellular pathway in mediating albumin transport via transcytosis. Caveolae, the vesicular carriers filled with receptor-bound and unbound free solutes, have been shown to shuttle between the vascular and extravascular spaces depositing their contents outside the cell. This review summarizes and analyzes the recent data from genetic, physiological, cellular, and morphological studies that have addressed the signaling mechanisms involved in the regulation of both the paracellular and transcellular transport pathways.

Analbuminemia in a Slovak Romany (gypsy) family: case report and mutational analysis

BACKGROUND

Analbuminemia is a rare autosomal recessive disorder manifested by the absence, or severe reduction, of circulating serum albumin. Here we report three new cases of hereditary analbuminemia, fortuitously detected in three Slovak Romany children, members of the same family, and define the molecular defect that causes the analbuminemic trait.

METHODS

Total DNA, extracted from peripheral blood samples from six members of the family, was PCR-amplified using oligonucleotide primers designed to amplify the 14 exons of the human albumin gene and the flanking intron regions. The products were screened for mutations by single-strand conformation polymorphism (SSCP) and heteroduplex analyses (HA). HA allowed the identification of the abnormal fragment, which was then sequenced.

RESULTS

In the 3 patients the analbuminemic trait was caused by the same mutation, an AT deletion at nucleotides 2430-31, the 91 th and 92 th bases of exon 3. This defect, previously identified as Kayseri mutation, produces a frameshift leading to a premature stop, two codons downstream. The predicted translation product would consist of 54 amino acid residues. The parents were found to be heterozygous for the mutation.

CONCLUSIONS

Our results confirm that the combination of SSCP and HA represents a powerful tool to study the molecular defects causing analbuminemia in humans.

Analbuminemia in a Swiss family is caused by a C → T transition at nucleotide 4446 of the albumin gene

OBJECTIVE

To define the molecular defect that causes analbuminemia in an apparently healthy boy, son of non-consanguineous Swiss parents.

DESIGN AND METHODS

Total DNA, extracted from peripheral blood samples from the proband and from both parents, was PCR-amplified using oligonucleotide primers designed to amplify the 14 exons of the human albumin gene and the flanking intron regions. The products were screened for mutations by single-strand conformation polymorphism (SSCP) and heteroduplex analyses (HA) either directly or after digestion with restriction enzymes. The combination of these methods identified the abnormal fragment, which was then sequenced.

RESULTS

DNA sequence analysis identified in the homozygous proband a C --> T transition at nucleotide 4446. The mutation changes the codon CGA for Arg 114 to a stop codon TGA, resulting in premature termination and is therefore responsible for the analbuminemic trait. The same mutation has been previously reported to cause analbuminemia in an American female. The putative protein product would have a length of 113 residues. The parents were found to be heterozygous for the mutation.

CONCLUSIONS

Gel-based mutation detection and DNA sequencing confirmed the diagnosis of congenital analbuminemia in the proband. Our results show that the combination of SSCP and HA represents a powerful tool to study the molecular defects causing analbuminemia in humans.

Congenital analbuminaemia: biochemical and clinical implications. A case report and literature review

Congenital analbuminaemia was diagnosed in a small-for-gestational-age neonate presenting with placental and body oedema, an unusual presentation of this rare autosomal recessive disorder. A review of 39 reported cases in the literature shows that the clinical symptoms are always remarkably mild and that the diagnosis is rarely made in infancy. The absence of albumin appears to be partly counterbalanced by high levels of non-albumin proteins and circulatory adaptations. However, congenital analbuminemia can have important complications: lipodystrophy and hypercholesterolaemia, possibly leading to atherosclerosis. Other possible complications reported in literature are hypercoagulability, osteoporosis, respiratory tract infections, intrauterine growth retardation and intrauterine death. Moreover, albumin-binding drugs should be used with caution.

CONCLUSION

Congenital analbuminaemia is a rare disorder with remarkably mild signs and symptoms at all ages. Although often thought to be innocent, this disorder may have important clinical complications.

The albumin controversy

There are relatively few studies of albumin use in neonates and children, with most showing no consistent benefit compared with the use of crystalloid solutions. Certainly, albumin treatment is not indicated for treatment of hypoalbuminemia alone. Studies also show that albumin is not indicated in neonates for the initial treatment of hypotension, respiratory distress, or partial exchange transfusions. In adults, albumin is not considered to be the initial therapy for hypovolemia, burn injury, or nutritional supplementation. Based on the evidence, albumin should be used rarely in the neonatal ICU. Albumin may be indicated in the treatment of hypovolemia only after crystalloid infusion has failed. In patients with acute hemorrhagic shock, albumin may be used with crystalloids when blood products are not available immediately. Inpatients with acute or continuing losses of albumin and normal capillary permeability and lymphatic function, such as during persistent thoracostomy tube or surgical site drainage, albumin supplementation will prevent the development of hypoalbuminemia, and possibly edema formation. This has not been studied systematically, however. In patients with hypoalbuminemia and increased capillary permeability, albumin supplementation often leads to greater albumin leakage across the capillary membrane, contributing to edema formation without improvement in outcome. As the disease process improves and capillary permeability normalizes, albumin supplementation may accelerate recovery, but long-term benefits of albumin treatment usually cannot be demonstrated. These patients will recover whether or not albumin is administered.

Microarray reality checks in the context of a complex disease

A problem in analyzing microarray-based gene expression data is the separation of genes causally involved in a disease from innocent bystander genes, whose expression levels have been secondarily altered by primary changes elsewhere. To investigate this issue systematically in the context of a class of complex human diseases, we have compared microarray-based gene expression data with non-microarray-based clinical and biological data about the schizophrenias to ask whether these two approaches prioritize the same genes. We find that genes whose expression changes are deemed to be of importance from microarrays are rarely those classified as of importance from clinical, in situ, molecular, single-nucleotide polymorphism (SNP) association, knockout and drug perturbation data. This disparity is not limited to the schizophrenias but characterizes other human disease data sets. It also extends to biological validation of microarray data in model organisms, in which genome-wide phenotypic data have been systematically compared with microarray data. In addition, different bioinformatic protocols applied to the same microarray data yield quite different gene sets and thus make clinical decisions less straightforward. We discuss how progress may be improved in the clinical area by the assignment of high-quality phenotypic values to each member of a microarray-assigned gene set.

Albumin infusion for low serum albumin in preterm newborn infants

BACKGROUND

Intravenous albumin infusion to treat hypoalbuminaemia is used in intensive care nurseries. Hypoalbuminaemia occurs in a number of clinical situations including prematurity, the acutely unwell infant, respiratory distress syndrome (RDS), chronic lung disease (CLD), necrotising enterocolitis (NEC), intracranial haemorrhage, hydrops fetalis and oedema. Fluid overload is a potential side effect of albumin administration. Albumin is a blood product and therefore carries the potential risk of infection and adverse reactions. Albumin is also a scarce and expensive resource.

OBJECTIVES

The primary objective was to assess whether albumin infusions, in preterm neonates with low serum albumin, reduces mortality and morbidity. A secondary objective was to assess whether albumin infusion is associated with significant side effects.

SEARCH STRATEGY

Searches were made of MEDLINE from 1966 to April 2004, CINAHL from 1982 to April 2004 and the current Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library issue 1, 2004). Previous reviews (including cross references) and abstracts were also searched.

SELECTION CRITERIA

All randomised controlled trials in which individual patients were allocated to albumin infusion versus control were included. Cross-over studies were excluded. Quasi randomised trials were excluded. Participants were preterm infants who had hypoalbuminaemia. Types of interventions included albumin infusion versus placebo (e.g. crystalloid) or no treatment.

DATA COLLECTION AND ANALYSIS

The reviewers worked independently to search for trials for inclusion and to assess methodological quality. Studies were assessed using the following key criteria: blinding of randomisation, blinding of intervention, completeness of follow up and blinding of outcome measurement.

MAIN RESULTS

Only two small studies were found for inclusion in this review and only one reported clinically relevant outcomes - it found no significant differences for our primary outcome measure of death (RR 1.5 [95% confidence interval 0.3 - 7.43]) or secondary outcome measures of intraventricular haemorrhage, patent ductus arteriosus, necrotising enterocolitis, bronchopulmonary dysplasia, duration of mechanical ventilation and duration of oxygen therapy.

REVIEWERS' CONCLUSIONS

There is a lack of evidence from randomised trials to determine whether the routine use of albumin infusion, in preterm neonates with low serum albumin, reduces mortality or morbidity, and no evidence to assess whether albumin infusion is associated with significant side effects. There is a need for good quality, double-blind randomised controlled trials to assess the safety and efficacy of albumin infusions in preterm neonates with low serum albumin.

An outline of inherited disorders of the thyroid hormone generating system

To date, various genetic defects impairing the biosynthesis of thyroid hormone have been identified. These congenital heterogeneous disorders result from mutations of genes involved in many steps of thyroid hormone synthesis, storage, secretion, delivery, or utilization. In contrast to thyroid dyshormonogenesis, the elucidation of the underlying etiology of most cases of thyroid dysgenesis is much less understood. It is suggested that genetic factors might play a role in some cases of thyroid dysgenesis and the best candidate genes involved are those encoding transcription factors known to play a role in the embryonic development of the thyroid gland. Moreover, discordance for thyroid dysgenesis is the rule for monozygotic twins as recently reported and this may result from epigenetic phenomena, early somatic mutations, or postzygotic events. In the final part of this review the molecular defects involved in proteins that transport thyroid hormone in the circulation are described: thyroxine-binding globulin (TBG), transtiretin and albumin, that may be associated with altered thyroid function tests and other pathologic conditions such as amyloidotic polyneuropathy.

Albumin activates the AKT signaling pathway and protects B-chronic lymphocytic leukemia cells from chlorambucil- and radiation-induced apoptosis

Activation of the phosphatidylinositol 3- kinase/AKT pathway antagonizes apoptosis in diverse cellular systems. We previously showed that human plasma activated AKT and potently blocked the ability of chlorambucil or gamma radiation to induce apoptosis of B-chronic lymphocytic leukemia (CLL) cells. Here we report experiments that identify albumin as the major component of plasma that blocks CLL cell killing by chlorambucil or radiation. Intact plasma depleted of albumin by chromatography on Cibacron blue-Sepharose or plasma from a subject with analbuminemia failed either to activate AKT or to protect CLL cells from chlorambucil-induced apoptosis. Both functions were restored by re-addition of albumin. The protective action of albumin as well as AKT activation was compromised by the binding of lipids. Fluorescence-activated cell sorter (FACScan) analysis demonstrated the uptake of fluoresceinated albumin by CLL cells. Accumulation of albumin in intracellular vesicles was also shown by confocal microscopy. Indirect inhibition of AKT activation by the phosphatidylinositol 3-kinase inhibitor LY294002 reversed the blockade of chlorambucil-induced killing by plasma albumin. The data suggest that activation of AKT consequent to binding of albumin by CLL cells blocks chlorambucil- and radiation-induced apoptosis. Strategies designed to block albumin-induced antiapoptotic signaling may, therefore, be of value in enhancing cytotoxic drug action on CLL cells.

Ouabain as a mammalian hormone

Endogenous ouabain changes rapidly in humans and dogs upon physical exercise and is under the control of epinephrine and angiotensin II. Hence, the steroid acts as a rapidly acting hormone. A search for a specific binding globulin for cardiac glycosides in bovine plasma resulted in the identification of the d allotype of the micro chain of IgM whose hydrophobic surfaces interact with cardiotonic steroids and cholesterol. Such IgM complexes might be involved in the hepatic elimination of cardiotonic steroids. Thus, differences in the signaling cascade starting at Na(+),K(+)-ATPase must explain any differences in the action of ouabain and digoxin in the genesis of arterial hypertension.

Idiopathic hypoalbuminemia explained by reduced synthesis rate and an increased catabolic rate

OBJECTIVE

To determine the contribution of albumin synthetic and catabolic rates to steady state levels in a patient with idiopathic hypoalbuminemia.

METHODS

Using L-[1-(13)C] valine, both FSR (fractional synthesis rate) as well as FCR (fractional catabolic rate) were studied. Human albumin cDNA analysis and determination of the exact albumin mass by electrospray mass spectrometry were performed.

RESULTS

Compared with controls, plasma albumin concentration in the patient was reduced (6.7 vs. 37.0 +/- 2.6 g/L). Albumin FSR (= FCR in steady state) was increased compared to controls. The ASR (absolute synthesis rate) of albumin was decreased based on the enrichment in plasma valine and KIV, but estimated to be normal based on VLDL apoB100 at plateau compared to controls. Direct estimation of albumin FCR rejected the latter. No mutation was found in the transcribed region of albumin gene. The exact mass of albumin (66.493 Da) was not different from controls.

CONCLUSION

The hypoalbuminemia was a result of accelerated clearance of albumin from plasma in addition to defective albumin synthesis. This study also shows that the chosen method of the precursor pool could lead to misinterpretation of data in hepatic protein synthesis.

Molecular Diagnosis of Analbuminemia: A Novel Mutation Identified in Two Amerindian and Two Turkish Families

Background: Analbuminemia is a rare autosomal recessive disorder in which individuals have little or no circulating albumin, usually the most abundant plasma protein. We describe a new mutation associated with analbuminemia.

Methods: We studied four apparently unrelated patients who had congenital analbuminemia: two of Amerindian and two of Turkish origin. The 14 exons and the flanking intron sequences of the albumin gene were amplified by PCR and screened for mutations by single-strand conformational polymorphism and heteroduplex analysis. The mutated DNA fragments were sequenced directly.

Results: In all four cases, analbuminemia was caused by the same mutation, an AT deletion at nucleotides 2430–2431, the 91st and 92nd bases of exon 3. This novel defect, named Kayseri, produces a frameshift leading to a premature stop two codons downstream. The predicted translation product would consist of 54 amino acid residues.

Conclusions: The AT deletion at nucleotides 2430–2431 is a novel mutation associated with analbuminemia.