Immunohistochemical localization of albumin and in situ hybridization of albumin mRNA

Hepatocytes actively involved in albumin synthesis were identified by immunohistochemical method. In sections of perioidate-lysine-2 per cent (w/v) paraformaldehyde fixed normal rat liver, albumin was detected in all hepatocytes. At the ultrastructural level, albumin was localized in the rough endoplasmic reticulum and in Golgi complexes located near the nucleus in only a small subpopulation of hepatocytes, while all other hepatocytes contained albumin only in Golgi complexes located near the bile canaliculi. Stimulation of albumin synthesis by puromycin aminonucleoside-induced nephrosis resulted in an altered intracellular distribution of albumin at the light microscopic level. When examined at the ultrastructural level, albumin was localized in the rough endoplasmic reticulum as well as in Golgi complexes located near the nucleus in nearly all these hepatocytes. Hepatocytes with the potential to synthesize albumin were identified by in situ hybridization of albumin mRNA. In sections of 0.1 per cent (v/v) glutaraldehyde perfusion fixed normal rat liver, albumin mRNA was detected in the cytoplasm of only a few hepatocytes scattered throughout the lobule. Following stimulation of albumin synthesis by the induction of nephrosis, albumin mRNA was detected in the cytoplasm of the hepatocytes. The source of albumin in those hepatocytes which lacked albumin mRNA was identified in analbuminemic rats injected with rat albumin. At 6 h post injection, the light microscopic distribution of albumin in the liver of these animals was virtually indistinguishable from that in normal rat liver. At the ultrastructural level, injected albumin was localized in lysosomes and in Golgi complexes located near the bile canaliculi.     

Lymphocyte surface receptors and albumin

Albumin was shown to be hidden component of mouse B and T lymphocyte plasma membranes. It was readily radiolabeled from within the plasma membrane by a lipophilic, photoactivated reagent (125I-iodonaphthylazide) but not from the cell exterior by lactoperoxidase-catalyzed iodination; it was not detected by immunofluorescence on intact cells. The function of this cryptic lymphocyte membrane albumin is unknown at present. This cryptic albumin component was discovered during immunoprecipitation experiments using anti-Ig reagents. It is considered of general methodologic significance that many antisera, both native and rigorously Ig-absorbed (both positively and negatively), contained such contaminating activity. The possibility is raised that such contaminating activity may be involved in some reported findings of albumin-size "Ig-like heavy chains" in both the B and T lymphocyte lineages.     

Generation time and albumin evolution

The albumins of long-generation animals such as man and chimpanzee are shown to be no less evolved immunologically than those of some short generation time rodents such as rat, mouse, and hamster. This finding casts very serious doubt on certain assumptions concerning the times of divergence of these species made by DNA hybridization workers. As these assumptions have led them to conclude that generation time is a key factor controlling the rate of genomic or DNA evolution, this latter conclusion is also made suspect. The molecular clock concept—that it is absolute time which determines the amount of protein and DNA evolution—is, on the other hand, strengthened.This research was supported by NSF grants GB-20750 to the author and GB-13119 to Dr. A. C. Wilson.     

Glycated albumin and diabetes mellitus

Background

Diabetes is a growing worldwide problem that is strongly associated with atherosclerosis. Screening and intervention for diabetes in the earliest stages are advocated for the prevention of diabetic complications and cardiovascular disease.

Scope of review

This review gives a background of and discusses the potential clinical utility of glycated albumin (GA) in diabetes.

Major conclusions

GA is a ketoamine formed via a non-enzymatic glycation reaction of serum albumin and it reflects mean glycemia over two to three weeks. GA can be used for patients with anemia or hemoglobinopathies for whom the clinically measured hemoglobin A1c level may be inaccurate. Because both serum and plasma samples can be used, GA can be analyzed from the same samples as common biological markers. GA is a useful marker for the screening of diabetes in a medical evaluation. It can be also used to determine the effectiveness of treatment before initiating or changing medications for diabetic patients. GA is potentially an atherogenic protein in the development of diabetic atherosclerosis.

General significance

GA measurement is useful as part of a routine examination to screen for both diabetes and atherosclerosis. This article is part of a Special Issue entitled Serum Albumin.     

Estrogen dramatically decreases albumin mRNA levels and albumin synthesis in Xenopus laevis liver

The levels of albumin mRNA in Xenopus laevis liver were measured at various times after injection of estradiol using two different methods involving hybridization of cloned albumin cDNA to total liver RNA. The absolute levels of albumin mRNA fell by more than 95% during the first 4 days following estrogen treatment, then slowly returned to normal levels over the following 12 days. Albumin synthesis paralleled the albumin mRNA levels during the first 8 days after injection; but, 16 and 32 days after injection, albumin synthesis again decreased while albumin mRNA remained at normal levels. The time courses of the effects of estrogen on albumin and vitellogenin mRNA levels were different. Whereas albumin mRNA levels were minimal 4 days after estradiol injection, vitellogenin mRNA levels were maximal 8 days after injection.     

Interaction of ergosterol with bovine serum albumin and human serum albumin by spectroscopic analysis

This study was designed to examine the interactions of ergosterol with bovine serum albumin (BSA) and human serum albumin (HSA) under physiological conditions with the drug concentrations in the range of 2.99-105.88?μM and the concentration of proteins was fixed at 5.0?μM. The analysis of emission spectra quenching at different temperatures revealed that the quenching mechanism of HSA/BSA by ergosterol was the static quenching. The number of binding sites n and the binding constants K were obtained at various temperatures. The distance r between ergosterol and HSA/BSA was evaluated according to F?ster non-radioactive energy transfer theory. The results of synchronous fluorescence, 3D fluorescence, FT-IR, CD and UV-Vis absorption spectra showed that the conformations of HSA/BSA altered in the presence of ergosterol. The thermodynamic parameters, free energy change (ΔG), enthalpy change (ΔH) and entropy change (ΔS) for BSA-ergosterol and HSA-ergosterol systems were calculated by the van't Hoff equation and discussed. Besides, with the aid of three site markers (for example, phenylbutazone, ibuprofen and digitoxin), we have reported that ergosterol primarily binds to the tryptophan residues of BSA/HSA within site I (subdomain II A).     

Bilirubin binding properties of pigeon serum albumin and its comparison with human serum albumin

Binding of bilirubin (BR) to pigeon serum albumin (PgSA) was studied by absorption, fluorescence and CD spectroscopy and results were compared with those obtained with human serum albumin (HSA). PgSA was found to be structurally similar to HSA as judged by near- and far-UV CD spectra. However, PgSA lacks tryptophan. Binding of BR to PgSA showed relatively weaker interaction compared to HSA in terms of binding affinity, induced red shift in the absorption spectrum of BR and CD spectral characteristics of BR-albumin complexes. Photoirradiation results of BR-albumin complexes also showed PgSA-bound BR more labile compared to HSA-bound BR.     

Renal cortical albumin gene induction and urinary albumin excretion in response to acute kidney injury

This study evaluated the potential utility of albuminuria as a "biomarker" of acute kidney injury (AKI) and tested whether AKI induces renal expression of the normally silent albumin gene. Urine albumin concentrations were measured in mice with five different AKI models (maleate, ischemia-reperfusion, rhabdomyolysis, endotoxemia, ureteral obstruction). Albumin gene induction in renal cortex, and in antimycin A-injured cultured proximal tubular cells, was assessed (mRNA levels; RNA polymerase II binding to the albumin gene). Albumin's clinical performance as an AKI biomarker was also tested (29 APACHE II-matched intensive care unit patients with and without AKI). Results were contrasted to those obtained for neutrophil gelatinase-associated lipocalin (NGAL), an established "AKI biomarker" gene. The experimental and clinical assessments indicated albumin's equivalence to NGAL as an AKI biomarker (greater specificity in experimental AKI; slightly better receiver-operating curve in humans). Furthermore, experimental AKI markedly induced the albumin gene (mRNA/RNA polymerase II binding increases; comparable to those seen for NGAL). Albumin gene activation in patients with AKI was suggested by fivefold increases in RNA polymerase II binding to urinary fragments of the albumin gene (vs. AKI controls). Experimental AKI also increased renal cortical mRNA levels for α-fetoprotein (albumin's embryonic equivalent). A correlate in patients was increased urinary α-fetoprotein excretion. We conclude that AKI can unmask, in the kidney, the normally silent renal albumin and α-fetoprotein genes. In addition, the urinary protein data independently indicate that albuminuria, and perhaps α-fetoprotein, have substantial utility as biomarkers of acute tubular injury.