Variations in the Human Serum Albumin Gene: Molecular and Functional Aspects

HSADab: A comprehensive database for human serum albumin

Human Serum Albumin (HSA), the most abundant protein in human body fluids, plays a crucial role in the transportation, absorption, metabolism, distribution, and excretion of drugs, significantly influencing their therapeutic efficacy. Despite the importance of HSA as a drug target, the available data on its interactions with external agents, such as drug-like molecules and antibodies, are limited, posing challenges for molecular modeling investigations and the development of empirical scoring functions or machine learning predictors for this target. Furthermore, the reported entries in existing databases often contain major inconsistencies due to varied experiments and conditions, raising concerns about data quality. To address these issues, a pioneering database, HSADab, was established through an extensive review of >30,000 scientific publications published between 1987 and 2023. The database encompasses over 5000 affinity data points at multiple temperatures and >130 crystal structures, including both ligand-bound and apo forms. The current HSADab resource (www.hsadab.cn) serves as a reliable foundation for validating molecular simulation protocols, such as traditional virtual screening workflows using docking, end-point, and al-chemical free energy techniques. Additionally, it provides a valuable data source for the implementation of machine learning predictors, including plasma protein binding models and plasma protein-based drug design models.

Computational Study of Molecular Mechanism for the Involvement of Human Serum Albumin in the Renin-Angiotensin-Aldosterone System

Human serum albumin (HSA) is an endogenous inhibitor of angiotensin I-converting enzyme (ACE) and, thus, plays a key role in the renin-angiotensin-aldosterone system (RAAS). However, little is known about the mechanism of interaction between these proteins, and the structure of the HSA-ACE complex has not yet been obtained experimentally. The purpose of the presented work is to apply computer modeling methods to study the interaction of HSA with ACE in order to obtain preliminary details about the mechanism of their interaction. Ten possible HSA-ACE complexes were obtained by the procedure of macromolecular docking. Based on the number of steric and polar contacts between the proteins, three leading complexes were selected, the stabilities of which were then tested by molecular dynamics (MD) simulation. Based on the results of MD simulation, the two most probable conformations of the HSA-ACE complex were selected. The analysis of these conformations revealed that the processes of oxidation of the thiol group of Cys34 of HSA and the binding of albumin to ACE can reciprocally affect each other. Known point mutations in the albumin molecules Glu82Lys, Arg114Gly, Glu505Lys, Glu565Lys and Lys573Glu can also affect the interaction with ACE. According to the result of MD simulation, the known ACE mutations, albeit associated with various diseases, do not affect the HSA-ACE interaction. A comparative analysis was performed of the resulting HSA-ACE complexes with those obtained by AlphaFold 3 as well as with the crystal structure of the HSA and the neonatal Fc receptor (FcRn) complex. It was found that domains DI and DIII of albumin are involved in binding both ACE and FcRn. The obtained results of molecular modeling outline the direction for further study of the mechanisms of HSA-ACE interaction in vitro. Information about these mechanisms will help in the design and improvement of pharmacotherapy aimed at modulation of the physiological activity of ACE.

Incidental detection of hereditary bisalbuminemia in a patient with positive DAT coombs: A case-based review

Bisalbuminemia is a rare, typically benign condition marked by the presence of a bifid albumin band on serum protein electrophoresis. It can either be inherited due to a point mutation or acquired in association with various medical conditions, most commonly diabetes mellitus. Bisalbuminuria, the presence of bifid albumin in urine, may or may not accompany bisalbuminemia. Both conditions are often discovered incidentally during screening for monoclonal gammopathy. Bisalbuminemia and related variants provide insights into albumin's genetic diversity and functional roles, influencing clinical diagnostics and research in human genetics. Understanding these variants aids in distinguishing benign conditions from potential disease states, guiding appropriate clinical management. In this case-based review, we present a case of hereditary bisalbuminemia identified unexpectedly during an investigation of a positive Direct Antiglobulin Test Coombs in an adult female patient. This review aims to highlight the key features of bisalbuminemia, a rare condition that should be recognized by clinicians.

Expression genome-wide association study identifies key regulatory variants enriched with metabolic and immune functions in four porcine tissues

BACKGROUND

Integration of high throughput DNA genotyping and RNA-sequencing data enables the discovery of genomic regions that regulate gene expression, known as expression quantitative trait loci (eQTL). In pigs, efforts to date have been mainly focused on purebred lines for traits with commercial relevance as such growth and meat quality. However, little is known on genetic variants and mechanisms associated with the robustness of an animal, thus its overall health status. Here, the liver, lung, spleen, and muscle transcriptomes of 100 three-way crossbred female finishers were studied, with the aim of identifying novel eQTL regulatory regions and transcription factors (TFs) associated with regulation of porcine metabolism and health-related traits.

RESULTS

An expression genome-wide association study with 535,896 genotypes and the expression of 12,680 genes in liver, 13,310 genes in lung, 12,650 genes in spleen, and 12,595 genes in muscle resulted in 4,293, 10,630, 4,533, and 6,871 eQTL regions for each of these tissues, respectively. Although only a small fraction of the eQTLs were annotated as cis-eQTLs, these presented a higher number of polymorphisms per region and significantly stronger associations with their target gene compared to trans-eQTLs. Between 20 and 115 eQTL hotspots were identified across the four tissues. Interestingly, these were all enriched for immune-related biological processes. In spleen, two TFs were identified: ERF and ZNF45, with key roles in regulation of gene expression.

CONCLUSIONS

This study provides a comprehensive analysis with more than 26,000 eQTL regions identified that are now publicly available. The genomic regions and their variants were mostly associated with tissue-specific regulatory roles. However, some shared regions provide new insights into the complex regulation of genes and their interactions that are involved with important traits related to metabolism and immunity.

Combined bisalbuminemia and Bisalbuminuria: A rare finding on serum and urine electrophoresis

BACKGROUND

Bisalbuminemia and bisalbuminuria are rarely encountered serum and urine albumin anomalies characterized by the presence of a bifid albumin band on serum/urine protein electrophoresis (SPE/UPE) and serum/urine immunofixation electrophoresis (SIFE/UIFE). They are usually detected incidentally while screening for monoclonal gammopathy with a cumulative frequency of 1:1,000---1:10,000.

CASE REPORT

We report two cases of bisalbuminemia in two adult male diabetic patients. The first patient had a history of rheumatoid arthritis and strong clinical suspicion for Sjogren syndrome. The SPEP/UPEP and SIFE/UIFE in this patient showed combined bisalbuminemia and bisalbuminuria. While the second patient had chronic kidney disease due to nephrotic syndrome but showed bisalbuminemia alone.

CONCLUSION

Bisalbuminemia and bisalbuminuria are rare findings with few case reports available in the English literature. These findings may occur secondary to inherited albumin variants or may be acquired. Diabetes mellitus is the medical condition most associated with acquired bisalbuminemia and bisalbuminuria. Although most cases of bisalbuminemia and bisalbuminuria are clinically insignificant, some albumin variants may have altered affinity for steroid hormones (e.g., thyroxine) and/or drugs which potentially could be clinically significant.

Human Serum Albumin: From Molecular Aspects to Biotechnological Applications

Human serum albumin (HSA), the most abundant protein in plasma, is a monomeric multidomain macromolecule that represents the main determinant of plasma oncotic pressure and the principal modulator of fluid distribution between body compartments [...].

Severe hypercholesterolemia in a patient with very low albumin and normal renal function

A 20-year-old male presented with severe elevation in low-density lipoprotein cholesterol (LDL-C). Initial genetic testing for familial hypercholesterolemia was negative. Patient also had low albumin, and further genetic testing showed homozygous variants in the ALB gene, suggesting congenital analbuminemia (CAA) causing severe hyperlipidemia. CAA is an autosomal recessive disorder with incidence of about 1:1,000,000. The gene for albumin is a single autosomal gene, and pathological variants that affect splicing lead to premature stop, nonsense variants, and deletions that result in a defect in albumin synthesis with CAA. CAA can be fatal in the prenatal period and cause infections in early childhood. CAA is tolerated better in adulthood because of compensatory increase in other plasma proteins. Plasma lipoproteins also increase, and CAA can cause gross hyperlipidemia with severe elevations in LDL-C and hypercholesterolemia. Genetic examination of ALB is mandatory to establish the diagnosis. Early diagnosis may be important to initiate lipid-lowering treatments to avoid premature coronary artery disease.

Role of sex hormone-binding globulin in the free hormone hypothesis and the relevance of free testosterone in androgen physiology

According to the free hormone hypothesis, biological activity of a certain hormone is best reflected by free rather than total hormone concentrations. A crucial element in this theory is the presence of binding proteins, which function as gatekeepers for steroid action. For testosterone, tissue exposure is governed by a delicate equilibrium between free and total testosterone which is determined through interaction with the binding proteins sex hormone-binding globulin and albumin. Ageing, genetics and various pathological conditions influence this equilibrium, hereby possibly modulating hormonal exposure to the target tissues. Despite ongoing controversy on the subject, strong evidence from recent in vitro, in vivo and human experiments emphasizes the relevance of free testosterone. Currently, however, clinical possibilities for free hormone diagnostics are limited. Direct immunoassays are inaccurate, while gold standard liquid chromatography with tandem mass spectrometry (LC-MS/MS) coupled equilibrium dialysis is not available for clinical routine. Calculation models for free testosterone, despite intrinsic limitations, provide a suitable alternative, of which the Vermeulen calculator is currently the preferred method. Calculated free testosterone is indeed associated with bone health, frailty and other clinical endpoints. Moreover, the added value of free testosterone in the clinical diagnosis of male hypogonadism is clearly evident. In suspected hypogonadal men in whom borderline low total testosterone and/or altered sex hormone-binding globulin levels are detected, the determination of free testosterone avoids under- and overdiagnosis, facilitating adequate prescription of hormonal replacement therapy. As such, free testosterone should be integrated as a standard biochemical parameter, on top of total testosterone, in the diagnostic workflow of male hypogonadism.