Changes In Albumin Synthesis Research Articles

ENHANCED ALBUMIN SYNTHESIS IN SEVERELY BURNED ADULTS

Albumin plays an important role in maintaining physiological homeostasis. Although decreased albumin concentration has been well described as an acute-phase response following injury, it is unclear whether the decrease is due to compromised synthesis of albumin, dilution, or imbalance between synthesis and breakdown rates, particularly after injury. We investigated changes in albumin synthesis in severely burned patients using stable isotope infusion techniques. Five patients (29 ± 3 years; 80 ± 7 kg) with burn of 48% ± 4% total body surface area (TBSA) were enrolled and studied in the ICU at the Burn Unit of the US Army Institute of Surgical Research. Five age- and sex-matched healthy volunteers (33 ± 5 years; 81 ± 6 kg) were included as controls. On the study day (13 ± 3 days after burn), a primed constant infusion (4 h) of stable isotope d5-phenlylalanine and d3-ketoisocaproic acid was given. Hourly arterial blood samples were drawn during the infusion to determine albumin synthesis rates, using gas chromatography-mass spectrometry analysis. Burned patients had higher heart and respiration rates. Plasma total protein in burn patients (4.5 ± 0.3 g · dL-1) was lower compared with controls (6.8 ± 0.2 g · dL-1). Plasma albumin concentration in burn patients (1.1 ± 0.1 g · dL-1) was also lower compared with controls (3.8 ± 0.1 g · dL-1; both P < 0.05). Albumin synthesis rate in burn patients (4.6 ± 0.2 mg · kg-1 · h-1) was enhanced compared with controls (2.2 ± 0.2 mg · kg-1 · h-1; P < 0.05). Despite the decrease in albumin concentration, albumin synthesis was enhanced in severely burned patients during the flow phase.

WHAT'S NEW IN SHOCK, OCTOBER 2010?

WHAT'S NEW IN SHOCK, OCTOBER 2010?

INFLIXIMAB IMPROVES ALBUMIN SYNTHESIS RATE IN PEDIATRIC CROHN'S DISEASE

Background: Children with Crohn's disease frequently have disturbances in growth. Serum albumin levels are found to be below normal in many children with active Crohn's disease. Tumor necrosis factor-alpha (TNF-α) may contribute to growth disturbance and decreases in serum albumin levels. Although infliximab, a TNF-α antibody, is an effective therapy for Crohn's disease in children, there are no data regarding its effects on albumin synthesis. Aim: To characterize changes in albumin synthesis following the initial dose of infliximab in children with Crohn's disease. Methods: Children with active Crohn's disease scheduled for their initial dose of infliximab underwent outpatient metabolic assessment immediately before and two weeks following infliximab infusion. Using the stable isotope [d5] phenylalanine, albumin enrichment was measured, and rates of fractional and absolute albumin synthesis were calculated. Measurements were made in both the fasting and parenterally fed states. Pre- and post- infliximab measurements were compared using the paired t-test. Results: Eleven children completed the study. Their mean age was 14.8 yr, mean serum albumin was 3.6 g/dL, and mean PCDAI score was 21 before infliximab therapy. In response to infliximab, during fasting, there was no change in fractional albumin synthesis rate (9.0%/d to 9.1%/d) (p = 0.93), and no change in absolute albumin synthesis rate (142.3 mg/kg/d to 142.6 mg/kg/d) (p = 0.88). During parenteral nutrition infusion, however, the fractional albumin synthesis rate increased from 10.3%/d to 12.7%/d (p = 0.06), and the absolute albumin synthesis rate increased from 171.0 mg/kg/d to 212.3 mg/kg/d (p = 0.05). Conclusions: Although no significant difference in fasting albumin synthesis rates were observed following infliximab therapy in children with Crohn's disease, fractional albumin synthesis and absolute albumin synthesis increased by 24% in the parenterally fed state. Infliximab may have an important effect on hepatic synthetic function, with subsequent positive effects on healing and growth.

Inflammation and reduced albumin synthesis associated with stable decline in serum albumin in hemodialysis patients

The concentration of albumin in serum is maintained by its rates of synthesis, catabolism, and distribution between vascular and extravascular compartments. Albumin synthesis is suppressed when there is inflammation or inadequate protein intake. This study was conducted to establish whether a decline in serum albumin of >0.3 g/dL was accompanied by a change in albumin synthesis and if so whether these changes were associated with increased levels of acute phase proteins and/or with a decrease in equilibrated normalized protein catabolic rate (enPCR). Seventy-nine patients in the National Institutes of Health (NIH)-sponsored HEMO Study had baseline measurements of albumin synthesis (measured kinetically as the disappearance of [125]I human serum albumin), the serum concentrations of albumin, transferrin, C-reactive protein (CRP), alpha1 acid glycoprotein (alpha1AG), ceruloplasmin, interleukin-6 (IL-6), plus monthly measurements of enPCR. The plasma levels of all proteins and enPCR were measured regularly over 2 years or until serum albumin decreased by >0.3 g/dL on two sequential measurements. Albumin synthesis was measured a second time when serum albumin declined by >0.3 g/dL or after 2 years. Fifty-nine patients [21 with a significant decrease in serum albumin (decliners) and 38 with stable values of serum albumin] had albumin synthesis measured twice. A decline in albumin concentration and synthesis was associated with an increase in alpha1AG when data from all patients were analyzed as a group. In decliners, albumin synthesis decreased significantly but was unchanged in stable. Likewise, in decliners, IL-6, CRP, alpha1AG, and ceruloplasmin increased significantly but were unchanged in stable. enPCR was unchanged in both groups and was not associated with either changes in albumin level or synthesis in the whole group. A decrease in serum albumin of >0.3 g/dL that persists for a period of 6 weeks is associated a decrease in albumin synthesis. This response is associated with evidence of activation of the acute phase response (inflammation) but not with changes in enPCR. In well-dialyzed patients, inflammation is the principal cause of a decrease in serum albumin while protein intake plays an insignificant role.

Stimulation of human albumin synthesis and gene expression by growth hormone treatment

Background and aims: In this study the effects of acute (5 h) and short-term (5 days) GH treatment on albumin synthesis rates in man were investigated and related to changes in the availability of hepatic albumin mRNA.Methods: 30 patients undergoing elective laparoscopic cholecystectomy were randomized into controls (n=10) or GH-treatment (12 U/dose) for 5 h or 5 days (n=10 in each group). Albumin mRNA levels (in liver biopsy specimens) were measured employing a quantitative polymerase chain reaction assay developed specifically for this purpose, whereas albumin synthesis was measured using [2H5]phenylalanine.Results:The fractional synthesis rate of albumin was 6.0±0.9 %/day in the control group and 8.0±1.8 %/day and 8.3±1.7 %/day in the GH-treated groups, respectively (P<0.05 vs controls in both cases). The corresponding values for the concentration of albumin mRNA were 2.6±1.1 ng/μg total RNA, 2.9±0.8 ng/μg total RNA (NS) and 4.7±1.8 ng/μg total RNA in the ‘GH 5’ group (P<0.01 vs controls). The changes in albumin synthesis were only partly explained by the differences in hepatic albumin mRNA levels (r=0.5, P<0.01).Conclusion: These results suggest that GH may induce a quick, gene expression-independent increase in albumin synthesis, which is sustained by a later-occurring increase in albumin gene expression.

Translational and pretranslational regulation of protein synthesis by amino acid availability in primary cultures of rat hepatocytes

Protein synthesis is Inhibited in both rat liver and isolated rat bepatocytes following deprivation of single essential amino acids. The aim of the present study was to define the time course of changes in peptide-chain initiation, albumin synthesis, and albumin mRNA following histiäine deprivation and the reversal of these changes in response to readdition of the deprived amino acid. A further aim was to ascertain whether there was an accommodation of the inhibition of initiation following long-term amino acid deprivation. Primary cultures of rat bepatocytes were maintained in serum-free medium containing either all ammo acids (complete medium) or all except histidine. Synthesis of total protein was reduced to 34% of control values following 48 hr of histidine deprivation and was restored to control values within 1 hr of addition of complete medium to prised cells. These changes in protein synthesis were due to translational regulation involving initiation. No accommodation of the inhibition was observed following long-term deprivation of histidine as has been observed under other conditions of cellular stress. The synthesis of albs was reduced to a greater extent than that of total protein, and required 72 br to recover to control values following return to complete medium. These changes in albumin synthesis were due to a combination of altered initiation and a mechanism involves pretranslatioul regulation as evidenced by corresponding alterations in albinnin mRNA. The ruts show that amino acid availability controls protein synthesis in fiver cells through both translational and pretranslational mechanisms.

Hepatic Protein and Amino-Acid Metabolism in Poultry

Two subjects are discussed: first, the regulation of hepatic protein synthesis; and second, the intermediary metabolism of methionine, particularly with respect to the role of 2-hydroxy-4-(methylthio)-butanoic acid (HMB, Alimer®). In the first section, the regulation of albumin synthesis is reviewed in terms of molecular events associated with the changes in albumin synthesis during fasting and refeeding. The effect of infection or of inflammatory stress on both albumin and total protein synthesis in the liver is also discussed. In the second part, research results are presented which indicate that HMB is a naturally occurring compound in methionine intermediary metabolism. The HMB synthesis by chick liver enzymes is demonstrated, and its role in normal avian methionine metabolism is discussed.

Fate and biological action of human recombinant interleukin 1β in the rat in vivo

The plasma half life of recombinant human interleukin 1 beta (rhIL 1 beta) was determined in rats by measuring the disappearance of the radioactivity of 125I-labeled rhIL 1 beta from the circulation. The plasma clearance showed a biphasic behavior: an initial fast disappearance (half life of about 3 min) was followed by a second slower one (half life of about 4 h). Twenty minutes after a single-dose injection of 125I-labeled rhIL 1 beta most of the radioactivity was concentrated in kidneys, liver and intestine. rhIL 1 beta induced the synthesis of alpha 1-acid glycoprotein (AGP), alpha 1-cysteine proteinase inhibitor (CPI) and beta-fibrinogen mRNA in liver. Half maximal stimulation was elicited by approximately 3000 U of rhIL 1 beta per animal. The mRNA changes for AGP and CPI were followed by corresponding protein increases in serum. Twenty hours after rhIL 1 beta injection, serum AGP rose from 0.7 to 2.5 mg/ml. CPI increased from 0.3 to 1.9 mg/ml 25 h after administration of rhIL 1 beta. Within 20 h after rhIL 1 beta injection, albumin serum concentration showed a strong decrease, preceded by a reduction in hepatic albumin mRNA levels. Neither changes in albumin synthesis nor degradation can explain this decrease suggesting that other mechanisms such as increased transvascular permeability are involved.

Molecular aspects of age-related changes in albumin synthesis in female WAG/Rij rats

The rate of albumin gene transcription and the level of albumin RNA sequences in liver nuclei of rats of various ages were determined to investigate the regulation of age-related changes in levels of cytoplasmic albumin mRNA in rat liver. No change was observed with age in both the rate of albumin gene transcription and the amount of nuclear albumin RNA sequences, which suggests that the increase in cytoplasmic albumin mRNA content in the rat liver with age is caused by a decreased turnover of this messenger. The length of poly(A)-tails of rat liver cytoplasmic RNA with age was also examined. Although no change with age was observed in the poly(A)-tail length sedimenting at the peak fraction, a shift towards shorter poly(A)-tails was found with age in the overall poly(A)-tail length distribution.

Regulation of albumin synthesis by hormones and amino acids in primary cultures of rat hepatocytes.

Culture conditions necessary for optimizing albumin secretion were studied in rat hepatocytes maintained in a chemically defined, serum-free medium. Amino acid analysis of the culture medium, which was based on a 1:1 mixture of Ham's F12:Dulbecco's modified Eagle's medium (unsupplemented medium), revealed that certain essential amino acids were depleted from this medium over a 24-h incubation. Rates of albumin secretion were significantly higher and better maintained when the medium was supplemented with additional amino acids (supplemented medium). Moreover, selective removal of an essential amino acid resulted in an immediate decrease in total protein and albumin synthesis and after 48 h a further selective decrease in albumin synthesis. Linear rates of albumin secretion were observed over a wide variety of experimental conditions, but secretion was not strictly proportional to cell number. Maximal rates of secretion were obtained at plating densities of 2-3 X 10(6) cells/60 mm culture dish. Albumin secretion also increased with time in culture reaching a maximum on days 3 and 4. When added singly, either insulin or dexamethasone increased rates of albumin secretion in a dose-dependent manner, but both hormones and an adequate supply of amino acids were necessary for maximal rates of secretion as well as long-term maintenance of the hepatocytes (greater than 3-4 days). In the presence of dexamethasone the dose-response curve for insulin was shifted toward physiological insulin concentrations. Changes in rates of albumin secretion in response to added hormones in supplemented media were found to parallel changes in albumin synthesis and relative amounts of albumin mRNA. Changes in gene transcription were probably involved.

Time course of changes in albumin synthesis and mRNA in diabetic and insulin-treated diabetic rats.

Albumin synthesis in rat liver in vivo decreased from 12.7 to 2.2% of total protein synthesis during the first 3 days after the induction of diabetes and then remained relatively constant at this depressed rate for another 3 days. Insulin treatment begun on the 3rd day after the induction of diabetes restored albumin synthesis to control values within 3 days. Hybridization of total polyadenylate-containing RNA with a specific albumin cDNA probe revealed a close correspondence between the relative abundance of albumin mRNA and the relative rate of albumin synthesis after induction of diabetes and in response to insulin treatment. The apparent half-life of albumin mRNA, based on the rate of change of the message from one steady-state level to another, was approximately 22 h in both diabetic and insulin-treated diabetic rats. Diabetes of 3-day duration had no effect on the average sizes of total and albumin-synthesizing polysomes or on the ribosomal half-transit time for total protein and albumin. However, the number of albumin-synthesizing polysomes decreased as a result of diabetes to approximately one-third the number found in control livers. Taken together the results indicate that albumin synthesis was regulated by the availability of albumin mRNA and not by alterations in degradation, sequestration, or translation of message.

Changes in the sequence content of albumin mRNA and in its translational activity in the rat liver with age

To investigate the regulation of age-related changes in albumin synthesis in the rat liver, total postnuclear RNA and polyribosomes, both membrane-bound and free, were prepared from livers of rats of different ages. By the use of a specific complementary DNA probe, the albumin mRNA sequence content was quantitated in these RNA fractions. These studies showed a specific increase in albumin mRNA sequence content in total postnuclear RNA and membrane-bound polyribosomes at between 12 and 24 months of age. Between 24 and 36 months of age, the increase in the amount of albumin mRNA in these two fractions was due only to an increase in liver weight. The increase in albumin mRNA sequence content was not found in the poly(A) + fraction but in the RNA extracted from the void of oligo(dT)-cellulose column chromatography. The isolated polyribosomes were translated in a cell-free system to assess age-related changes in total protein and albumin synthesis due to translational control. No changes with age were found in the translational capacity of membrane-bound and free polyribosomes per RNA unit. Immunoprecipitation of the synthesized albumin in the translation products revealed that albumin synthesis in the cell-free system is not increased proportionally with the elevated albumin mRNA level between 12 and 24 months of age. This indicates that albumin mRNAs present in the livers of old rats are biologically less active than those found in younger animals.

Serum stimulation of plasma protein synthesis in culture is selective and rapidly reversible

Primary hepatocyte monolayers, derived from chick embryos, can be cultured from the onset in a completely chemically defined medium, free of added hormones. The liver cells synthesize and secrete a wide spectrum of plasma proteins for several days in this serum-free environment. Addition of fetal bovine serum elicits a 3–5-fold increase in the production of certain plasma proteins: fibrinogen, albumin, and the α 1- globulin M. This effect of serum is selective; transferrin and plasminogen syntheses are enhanced less than 1.5-fold. Significant stimulation is observed with 0.1% fetal bovine serum, and half-maximal values for individual plasma proteins are obtained with concentrations ranging between 0.4 and 1%. The stimulatory activity of serum shows no developmental or species specificity. Plasma is as active as serum derived from the same blood sample. The hepatocytes respond rapidly to serum, significant changes in albumin synthesis occurring less than 1 h after serum addition or removal. The effect of short exposure is fully reversible. These results establish the capacity of low concentrations of serum to stimulate plasma protein synthesis and underscore the importance of studying the effects of hormones and other factors under serum-free conditions. The findings suggest that, in addition to the classical hormones, ubiquitous but as yet uncharacterized serum components play a role in controlling this major hepatic function.

Effect of fibrinogenolytic products D and E on fibrinogen and albumin synthesis in the rat.

Previous studies are in conflict over the effect of infusing mixed fibrinogen-fibrin degradation products on fibrinogen synthesis, as determined by changes in fibrinogen concentration or by incorporation of labeled amino acids into fibrinogen. We have injected purified homologous fragments D1 and E into rats and measured their fibrinogen and albumin synthetic rates by the [14C]carbonate technique, a method that provides quantitative estimates of hepatic secretory protein synthesis. Fibrinogen fractional synthetic rates were increased 2.5 times in animals injected with fragment D1, compared with saline-injected controls. No increase were observed in fragment E-injected animals. Neither fragment produced changes in albumin synthesis. Fragment D increased plasma fibrinogen concentration, but did not raise plasma haptoglobin levels. These results suggest that fragment D is a regulator of fibrinogen synthesis.

Alcohol-induced depression of albumin synthesis: reversal by tryptophan.

The influence of alcohol on albumin synthesis was studied in the isolated perfused rabbit liver. Carbonate-(14)C was used to label the intracellular arginine pool which serves as the precursor of both the carbon of urea and the guanido carbon of arginine in albumin. The control group synthesized albumin at a rate of 33 mg/100 g of wet liver weight during 2.5 hr of perfusion. When alcohol, 220 mg/100 ml, was added to the perfusate, albumin synthesis decreased to between 7 and 11 mg, less than one-third the control rate. The addition of 10 mM tryptophan to perfusates containing alcohol prevented most of the inhibitory effects and albumin synthesis increased to average 24 mg. Further, the addition of alcohol to the perfusate decreased the hepatic protein/DNA ratio from 70 to 54 and the RNA/DNA ratio from 2.3 to 1.8, changes equivalent to those seen after a 24 hr fast. The addition of tryptophan to the perfusate prevented these findings in both instances. Endoplasmic membrane-bound polysomes were examined for aggregation. Alcohol decreased the quantity of heavier aggregates. Reaggregation occurred when tryptophan was added but quantitative changes in albumin synthesis could not be related to the degree of reaggregation.