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

Renal Handling of Albumin-From Early Findings to Current Concepts

Albumin is the main protein of blood plasma, lymph, cerebrospinal and interstitial fluid. The protein participates in a variety of important biological functions, such as maintenance of proper colloidal osmotic pressure, transport of important metabolites and antioxidant action. Synthesis of albumin takes place mainly in the liver, and its catabolism occurs mostly in vascular endothelium of muscle, skin and liver, as well as in the kidney tubular epithelium. Long-lasting investigation in this area has delineated the principal route of its catabolism involving glomerular filtration, tubular endocytic uptake via the multiligand scavenger receptor tandem—megalin and cubilin-amnionless complex, as well as lysosomal degradation to amino acids. However, the research of the last few decades indicates that also additional mechanisms may operate in this process to some extent. Direct uptake of albumin in glomerular podocytes via receptor for crystallizable region of immunoglobulins (neonatal FC receptor) was demonstrated. Additionally, luminal recycling of short peptides into the bloodstream and/or back into tubular lumen or transcytosis of whole molecules was suggested. The article discusses the molecular aspects of these processes and presents the major findings and controversies arising in the light of the research concerning the last decade. Their better characterization is essential for further research into pathophysiology of proteinuric renal failure and development of effective therapeutic strategies.

Numerical Investigations of Hepatic Spheroids Metabolic Reactions in a Perfusion Bioreactor

Miniaturized culture systems of hepatic cells are emerging as a strong tool facilitating studies related to liver diseases and drug discovery. However, the experimental optimization of various parameters involved in the operation of these systems is time-consuming and expensive. Hence, developing numerical tools predicting the function of such systems can significantly reduce the associated cost. In this paper, a perfusion-based three dimensional (3D) bioreactor comprising encapsulated human liver hepatocellular carcinoma (HepG2) spheroids are analyzed. The flow and mass transfer equations for oxygen as well as different metabolites such as albumin, glucose, glutamine, ammonia, and urea were solved in three different domains, i.e., free flow, hydrogel, and spheroid porous media sections. Since the spheroids were encapsulated inside the hydrogel, shear stress imposed on them were found to be less than tolerable thresholds. The predicted cumulative albumin concentration over the 7 days of culture period showed a good agreement with the experimental data. Based on the critical role of oxygen supply to the hepatocytes, a parametric study was performed and the effect of various parameters was investigated. Results illustrated that convection mechanism was the dominant transport mechanism in the main-stream section contrary to the intra spheroids parts where the diffusion was the prevailing transport mechanism. In the hydrogel parts, the rate of diffusion and convection mechanisms were almost identical. As expected, higher perfusion rate would provide high oxygen level for the cells and, smaller spheroids with a diameter of 100 μm were at the low risk of hypoxic conditions due to short diffusive oxygen penetration depth. Numerical results evidenced that spheroids with diameter size >200 μm at low porosities (ε = 0.2-0.3) were at risk of oxygen depletion, especially at locations near the core center. Therefore, these results could be beneficial in preventing hypoxic conditions during in vitro experiments. The presented numerical model provides a numerical platform which can help researchers to design and optimize complex bioreactors and obtain numerical indexes of the main metabolites in a very short time prior to any fabrications. Such numerical indexes can be helpful in certifying the outcomes of forensic investigations.

Aminoacyl-tRNA synthetase deficiencies in search of common themes

Purpose

Pathogenic variations in genes encoding aminoacyl-tRNA synthetases (ARSs) are increasingly associated with human disease. Clinical features of autosomal recessive ARS deficiencies appear very diverse and without apparent logic. We searched for common clinical patterns to improve disease recognition, insight into pathophysiology, and clinical care.

Methods

Symptoms were analyzed in all patients with recessive ARS deficiencies reported in literature, supplemented with unreported patients evaluated in our hospital.

Results

In literature, we identified 107 patients with AARS, DARS, GARS, HARS, IARS, KARS, LARS, MARS, RARS, SARS, VARS, YARS, and QARS deficiencies. Common symptoms (defined as present in ≥4/13 ARS deficiencies) included abnormalities of the central nervous system and/or senses (13/13), failure to thrive, gastrointestinal symptoms, dysmaturity, liver disease, and facial dysmorphisms. Deep phenotyping of 5 additional patients with unreported compound heterozygous pathogenic variations in IARS, LARS, KARS, and QARS extended the common phenotype with lung disease, hypoalbuminemia, anemia, and renal tubulopathy.

Conclusion

We propose a common clinical phenotype for recessive ARS deficiencies, resulting from insufficient aminoacylation activity to meet translational demand in specific organs or periods of life. Assuming residual ARS activity, adequate protein/amino acid supply seems essential instead of the traditional replacement of protein by glucose in patients with metabolic diseases.

Rapid Eye Movement sleep deprivation of rat generates ROS in the hepatocytes and makes them more susceptible to oxidative stress

Background

Rapid Eye Movement sleep deprivation (REMSD) of rats causes inflammation of the liver and apoptotic cell death of neurons and hepatocytes. Studies also suggest that REM sleep deprivation can cause muscle as well as cardiac injury and neurodegenerative diseases.

Objective and methods

The aim of this research was to determine whether REM sleep deprivation of rats would increase the levels of reactive oxygen species (ROS) in the hepatocytes and create oxidative stress in them. We selectively deprived the rats for REM sleep using the standard flower pot method.

Results

We observed that when rats were subjected to REM sleep deprivation, the levels of ROS in their hepatocytes increased ~184.33% compared to large platform control (LPC) group by day 9 of deprivation, but it returned towards normal level (~49.27%) after recovery sleep for 5 days. Nitric oxide synthase (iNOS) gene expression and protein levels as determined by real-time PCR and western blot analysis respectively were found to be elevated in hepatocytes of REM sleep deprived rats as compared to the LPC group. The level of nitric oxide (NO) in the hepatocytes of REMSD rats also increased by ~404.40% as compared to the LPC group but sleep recovery for 5 days normalized the effect (~135.35% compared to LPC group). We used a large platform control group as a reference group to compare with the REM sleep deprived group as the effect on the hepatocytes of both LPC group and cage control groups were not significantly different.

Discussion

We have analyzed the oxidative stress generated in the hepatocytes of rats due to REM sleep deprivation and further consequences of it. REMS deprivation not only increased the levels of ROS in the hepatocytes but also induced iNOS and NO in them. REM sleep deprived hepatocytes became more susceptible to oxidative stresses on further exposures. Furthermore, our study has great pathological and physiological.

Insulin Is Required to Maintain Albumin Expression by Inhibiting Forkhead Box O1 Protein

Diabetes is accompanied by dysregulation of glucose, lipid, and protein metabolism. In recent years, much effort has been spent on understanding how insulin regulates glucose and lipid metabolism, whereas the effect of insulin on protein metabolism has received less attention. In diabetes, hepatic production of serum albumin decreases, and it has been long established that insulin positively controls albumin gene expression. In this study, we used a genetic approach in mice to identify the mechanism by which insulin regulates albumin gene transcription. Albumin expression was decreased significantly in livers with insulin signaling disrupted by ablation of the insulin receptor or Akt. Concomitant deletion of Forkhead Box O1 (Foxo1) in these livers rescued the decreased albumin secretion. Furthermore, activation of Foxo1 in the liver is sufficient to suppress albumin expression. These results suggest that Foxo1 acts as a repressor of albumin expression.

Sandwich-cultured hepatocytes: an in vitro model to evaluate hepatobiliary transporter-based drug interactions and hepatotoxicity

Sandwich-cultured hepatocytes (SCH) are a powerful in vitro tool that can be utilized to study hepatobiliary drug transport, species differences in drug transport, transport protein regulation, drug-drug interactions, and hepatotoxicity. This review provides an up-to-date summary of the SCH model, including a brief history of, and introduction to, the use of SCH, as well as methodology to evaluate hepatobiliary drug disposition. A summary of the literature that has utilized this model to examine the interplay between drug-metabolizing enzymes and transport proteins, drug-drug interactions at the transport level, and hepatotoxicity as a result of altered hepatic transport also is provided.

Defining normal adrenal function testing in the intensive care unit setting: a canine study

OBJECTIVE

To determine whether intensive care medicine therapies and testing influence hypothalamic-pituitary-adrenal test results. It is routine in intensive care medicine to measure hypothalamic-pituitary-adrenal function, commonly utilizing the adrenocorticotropic hormone stimulation test to diagnose absolute or relative adrenal insufficiency.

DESIGN

Prospective, 96-hr animal study.

SETTING

Research laboratory.

SUBJECTS

Twenty-four healthy canines.

INTERVENTIONS

Animals were randomized into two groups--awake and unrestrained or treated with intensive care medicine therapies, including sedation, intubation, and mechanical ventilation. Animals were further randomized to receive dexamethasone (or placebo) or undergo either a total of four or seven adrenocorticotropic hormone stimulation tests over 96 hrs.

MEASUREMENTS AND MAIN RESULTS

Sedation, intubation, and mechanical ventilation transiently increased both basal and postadrenocorticotropic hormone total and free cortisol concentrations >2-fold as compared with baseline for the first 24 hrs (p < or = .05 for both). Performance of seven stimulation tests increased both basal and postadrenocorticotropic hormone total and free cortisol concentrations from baseline by >1.5-fold for the duration of the 96-hr study (p < or = .05). Neither sedation, intubation, and mechanical ventilation nor the performance of more stimulation tests affected delta cortisol measurements (total or free cortisol, p = NS). In contrast, dexamethasone suppressed basal total cortisol concentrations by >2-fold (p < or = .005) at all time points and transiently increased delta total cortisol by approximately 35% during the first 24 hrs of the study (p < or = .05).

CONCLUSIONS

Total and free cortisol measurements--whether pre- or post- adrenocorticotropic hormone or as a calculated delta--were altered by intensive care therapies or frequent adrenocorticotropic hormone stimulation testing with one exception. Delta free cortisol was the only hypothalamic-pituitary-adrenal measurement unaffected by sedation, intubation, and mechanical ventilation, completion of more adrenocorticotropic hormone stimulation tests, or dexamethasone therapy. These findings support the need to determine normal ranges for hypothalamic-pituitary-adrenal testing in subjects receiving intensive care medicine before establishing laboratory criteria for the diagnosis of relative adrenal insufficiency.

Identification of multiple proteins whose synthetic rates are enhanced by high amino acid levels in rat hepatocytes

Amino acids are key regulators of protein synthesis in liver. However, it remains to be determined whether amino acids stimulate synthesis of all or certain specific liver proteins. No techniques are currently available to simultaneously measure synthetic rates of several individual proteins. Here we report studies performed on rat hepatocyte primary cultures in which we used metabolic labeling with [(14)C]leucine, two-dimensional gel electrophoresis (2DGE), and tandem mass spectrometry to identify proteins that showed increased leucine incorporation when high amino acid levels were present in the media. Rat hepatocytes were isolated by in situ collagenase perfusion, cultured in serum-free medium containing insulin, and incubated for 2, 4, and 8 h in media of standard and high amino acid concentrations. SDS-PAGE and 2DGE were performed to separate proteins from cell lysates. Proteins that consistently showed increased synthesis on triplicate cultures, as detected by phosphorimaging of gels, were identified by tandem mass spectrometry. The combination of these approaches enabled the detection of 16 specific liver proteins whose synthetic rates were enhanced by increased amino acid concentration. These proteins are involved in specific functions such as translation initiation, protein folding and modification, oxidative phosphorylation, antioxidant defense, signal transduction, and transport, as well as cell motility and tissue integrity. No quantitative changes for any of these proteins were detected by gel staining, indicating that no detectable changes in protein concentration occurred. In contrast, measurable changes in synthetic rates occurred in 16 proteins. In conclusion, amino acids stimulate the synthesis of several liver proteins with important cellular functions.

Mechanism of negative regulation of rat glutathione S-transferase A2 by the cytokine interleukin 6

A decrease in concentration of some liver proteins, including the detoxification enzyme glutathione S-transferase A2 (rGSTA2), occurs during the acute-phase response. Interleukin 6 (IL-6) with dexamethasone (DEX) decreases transcription of rGSTA2 in rat hepatocytes. The promoter region that mediates suppression of rGSTA2 was localized to 150 bp. These 150 bp were divided and used for electrophoretic mobility-shift assays. Induction of a protein that specifically bound to an oligonucleotide from this region required new protein synthesis and IL-6 with DEX in the culture media. The protein bound to part of the hepatocyte nuclear factor 1 (HNF1) site but was different from and did not displace HNF1. A core sequence, TGATT, was required for binding. The protein also bound to an HNF1 site in the albumin promoter. We hypothesize that IL-6 along with DEX induced a novel protein that decreased transcription of rGSTA2 and possibly albumin by interfering with the transactivating function of HNF1. The protein may be an important negative regulator of transcription during the acute-phase response.

Effects of medium composition on the morphology and function of rat hepatocytes cultured as spheroids and monolayers

Primary hepatocytes cultured as monolayers or as spheroids were studied to compare the effects of four different culture media (Williams' E, Chee's, Sigma Hepatocyte, and HepatoZYME medium). Rat hepatocytes were cultured as conventional monolayers for 3 d or as spheroids for 2 wk. For spheroid formation a method was emplOyed that combined the use of a nonadherent substratum with rotation of cultures. Hepatocyte integrity and morphology were assessed by light and electron microscopy and by reduced glutathione content. Hepatocyte function was measured by albumin secretion and 7-ethoxycoumarin metabolism. Chee's medium was found to be optimal for maintenance of hepatocyte viability and function in monolayers, but it failed to support spheroid formation. For spheroid formation and for the maintenance of spheroid morphology and function, Sigma HM was found to be optimal. These results demonstrate that the medium requirements of hepatocytes differ markedly depending on the culture model employed. Spheroid culture allowed better preservation of morphology and function of hepatocytes compared with conventional monolayer culture. Hepatocytes in spheroids formed bile canaliculi. and expressed an actin distribution resembling that found in hepatocytes in vivo. Albumin secretion was maintained at the same level as that found during the first d in primary culture, and 7-ethoxycoumarin metabolism was maintained over 2 wk in culture at approximately 30% of the levels found in freshly isolated hepatocytes. The improved morphology and function of hepatocyte cultures as spheroids may provide a more appropriate in vitro model for certain applications where the maintenance of liver-specific functions in long-term culture is crucial.

Synthesis of hepatic secretory proteins in normal adults consuming a diet marginally adequate in protein

The plasma concentration and hepatic synthesis rates of albumin, transthyretin, very low-density lipoprotein apolipoprotein B-100 (VLDL-apoB-100), high-density lipoprotein apolipoprotein A-1, fibrinogen, alpha1-antitrypsin, and haptoglobin were measured in six normal adults before and after consuming a protein intake of 0.6 g. kg body wt(-1). day(-1) for 7 days. The synthesis of hepatic proteins was measured from the incorporation of [(2)H(5)]- phenylalanine, following prime/continuous infusion, using plasma VLDL-apoB-100 isotopic enrichment to represent the precursor pool. Synthesis of albumin declined by 50% (P < 0.001) following the lower-protein diet, VLDL-apoB-100 declined by 20% (P < 0.001), and apoA-1 declined by 16% (P < 0.05). By contrast, synthesis increased for fibrinogen (50%, P < 0.05) and haptoglobin (90%, P < 0.001). This pattern of change, with decreased synthesis of nutrient transport proteins and increased formation of acute-phase proteins, suggestive of a low-grade inflammatory response, was accompanied by increased plasma concentration of the inflammatory cytokine interleukin 6 (30%, P < 0.05). The pattern of change in the synthesis of hepatic secretory proteins following 7 days on the low-protein diet may be of functional relevance for lipid transport and the capacity to cope with stress.

Effects of medium composition on the morphology and function of rat hepatocytes cultured as spheroids and monolayers

Primary hepatocytes cultured as monolayers or as spheroids were studied to compare the effects of four different culture media (Williams' E, Chee's, Sigma Hepatocyte, and HepatoZYME medium). Rat hepatocytes were cultured as conventional monolayers for 3 d or as spheroids for 2 wk. For spheroid formation a method was emplOyed that combined the use of a nonadherent substratum with rotation of cultures. Hepatocyte integrity and morphology were assessed by light and electron microscopy and by reduced glutathione content. Hepatocyte function was measured by albumin secretion and 7-ethoxycoumarin metabolism. Chee's medium was found to be optimal for maintenance of hepatocyte viability and function in monolayers, but it failed to support spheroid formation. For spheroid formation and for the maintenance of spheroid morphology and function, Sigma HM was found to be optimal. These results demonstrate that the medium requirements of hepatocytes differ markedly depending on the culture model employed. Spheroid culture allowed better preservation of morphology and function of hepatocytes compared with conventional monolayer culture. Hepatocytes in spheroids formed bile canaliculi. and expressed an actin distribution resembling that found in hepatocytes in vivo. Albumin secretion was maintained at the same level as that found during the first d in primary culture, and 7-ethoxycoumarin metabolism was maintained over 2 wk in culture at approximately 30% of the levels found in freshly isolated hepatocytes. The improved morphology and function of hepatocyte cultures as spheroids may provide a more appropriate in vitro model for certain applications where the maintenance of liver-specific functions in long-term culture is crucial.

Coordinate regulation of tetrahydrobiopterin turnover and phenylalanine hydroxylase activity in rat liver cells

This work had two purposes: (i) to determine in vivo whether liver phenylalanine hydroxylase (PAH) is regulated by its substrates phenylalanine and tetrahydrobiopterin (BH4) as studies with purified enzyme suggest and (ii) to investigate in vivo the relationship between PAH activity and BH4 turnover. We found there are two BH4 pools in hepatocytes, one that is metabolically available (free BH4) and one that is not (bound BH4). Bound BH4 appears bound to PAH; the PAH-BH4 complex has much less catalytic activity and is less readily phenylalanine activated than uncomplexed enzyme. Interconversion of activated and unactivated PAH and bound and free BH4 is driven by phenylalanine; and free BH4 concentration is determined by the state of activation and activity of PAH. In hepatocytes, BH4 and PAH (subunit) concentrations are equal, all intracellular BH4 appears to be available to PAH, and free BH4 turns over rapidly (t1/2 approximately 1 hr). There is no evidence for feedback inhibition of BH4 synthesis; the BH4 synthetic rate appears high when free BH4 concentration is high and low when free BH4 is low. The data provide support in vivo that phenylalanine and BH4 are positive and negative regulators of the activity and activation state of PAH in the proposed manner; they also imply that regulation of BH4 turnover and PAH activity are linked processes, which are both controlled by phenylalanine concentration.

Insulin and glucocorticoid dependence of hepatic gamma-glutamylcysteine synthetase and glutathione synthesis in the rat. Studies in cultured hepatocytes and in vivo

We reported that glucagon and phenylephrine decrease hepatocyte GSH by inhibiting gamma-glutamylcysteine synthetase (GCS), the rate-limiting enzyme in GSH synthesis (Lu, S.C., J. Kuhlenkamp, C. Garcia-Ruiz, and N. Kaplowitz. 1991. J. Clin. Invest. 88:260-269). In contrast, we have found that insulin (In, 1 microgram/ml) and hydrocortisone (HC, 50 nM) increased GSH of cultured hepatocytes up to 50-70% (earliest significant change at 6 h) with either methionine or cystine alone as the sole sulfur amino acid in the medium. The effect of In occurred independent of glucose concentration in the medium. Changes in steady-state cellular cysteine levels, cell volume, GSH efflux, or expression of gamma-glutamyl transpeptidase were excluded as possible mechanisms. Both hormones are known to induce cystine/glutamate transport, but this was excluded as the predominant mechanism since the induction in cystine uptake required a lag period of greater than 6 h, and the increase in cell GSH still occurred when cystine uptake was blocked. Assay of GSH synthesis in extracts of detergent-treated cells revealed that In and HC increased the activity of GCS by 45-65% (earliest significant change at 4 h) but not GSH synthetase. In and HC treatment increased the Vmax of GCS by 31-43% with no change in Km. Both the hormone-mediated increase in cell GSH and GCS activity were blocked with either cycloheximide or actinomycin D. Finally, when studied in vivo, streptozotocin-treated diabetic and adrenalectomized rats exhibited lower hepatic GSH levels and GCS activities than respective controls. Both of these abnormalities were prevented with hormone replacement. Thus, both in vitro and in vivo, In and glucocorticoids are required for normal expression of GCS.