Correlation of albumin production rates and albumin mRNA levels in livers of normal, diabetic, and insulin-treated diabetic rats

The higher the serum albumin, the better? Findings from the PRACTICE study

AIMS

The relation between hypoalbuminemia and coronary artery disease (CAD) has been established. However, the association of increased albumin level and outcomes of CAD has not been investigated.

METHODS

There were 14 994 CAD patients from the PRACTICE study, which is a large, single center prospective cohort study based on case records and follow-up registry performed in the First Affiliated Hospital of Xinjiang Medical University from Dec. 2016 to Oct. 2021 in the present study. All the 14 994 patients were divided into five categories according albumin levels: <35 g/L group (n = 1 478), 35-40 g/L group (n = 5 007), 40-45 g/L group (n = 6 076), 45-50 g/L group (n = 1 835), and ≥50 g/L group (n = 598).

RESULTS

A total of 448 all-cause deaths(ACD), 333 cardiac deaths (CD), 1 162 MACEs and 1 276 MACCEs were recorded during up to 60-months follow-up period. After adjusting for confounders, we observed a non-linear relation for either MACE or MACCE with the lowest risk at 45 g/L of albumin levels. A threshold value of albumin ≥50 g/L was associated with an increased risk for either MACE (adjusted HR=1.617, 95%CI:1.130-2.315, P = 0.009) or MACCE (adjusted HR= 1.439, 95%CI: 1.007-2.056, P = 0.045) in multivariable Cox regression model. For mortality, we only found decreased (<35 g/L) but not increased albumin level was associated with either ACD (HR=2.744, 95%CI: 1.631-4.617, P<0.001) or CD (HR=2.736, 95%CI: 1.484-5.045, P = 0.001).

CONCLUSIONS

In the present study, a U-shaped curve relation was identified between albumin levels and MACE and MACCE in CAD patients, with the lowest risk at 45 g/L levels.

A novel inflammatory biomarker, high-sensitivity C-reactive protein-to-albumin ratio, is associated with 5-year outcomes in patients with type 2 diabetes who undergo percutaneous coronary intervention

BACKGROUND

Patients with coronary artery disease (CAD) combined with diabetes have a higher risk of cardiovascular events, and high-sensitivity C-reactive protein (hs-CRP)-to-albumin ratio (CAR) is a novel inflammatory biomarker. However, whether the CAR can identify high-risk patients with CAD and type 2 diabetes (T2DM) remains unclear.

METHODS

The present study was based on a prospective and observational cohort with 10,724 individuals who undergo percutaneous coronary intervention (PCI) in Fu Wai Hospital throughout the year 2013 consecutively enrolled. The primary endpoint was all-cause mortality. The secondary endpoint was cardiac mortality. CAR was calculated with the formula: hs-CRP (mg/L)/albumin (g/L). According to the optimal cut-off value of CAR for all-cause mortality, patients were divided into higher CAR (CAR-H) and lower CAR (CAR-L) groups.

RESULTS

A total of 2755 patients with T2DM who underwent PCI and received dual antiplatelet therapy were finally enrolled. During a follow-up of 5 years (interquartile range: 5.0-5.1 years), 126 (4.6%) all-cause mortalities and 74 (2.7%) cardiac mortalities were recorded. In the multivariable Cox model, CAR-H was associated with a higher risk of all-cause mortality (hazard ratio [HR]: 1.634, 95% confidence interval [CI] 1.121-2.380, p = 0.011) and cardiac mortality (HR: 1.733, 95% CI 1.059-2.835, p = 0.029) compared with CAR-L. When comparing the predictive value, CAR was superior to hs-CRP for all-cause mortality (area under the curve [AUC] 0.588 vs. 0.580, p = 0.002) and cardiac mortality (AUC 0.602 vs. 0.593, p = 0.004).

CONCLUSION

In this real-world cohort study, a higher level of CAR was associated with worse 5-year outcomes among diabetic patients with PCI.

Molecular Scale Optimum Hydrophobicity To Establish an Enhanced Probe-Protein Interaction: Near-Infrared Imaging of Albumin Biosynthesis Modulation

Albumin is the most abundant serum protein and shows variation in its synthesis rate in different physiological and pathophysiological conditions. Thus, there might be an association expected between serum albumin concentration and body health. A library of NIR probes engineered with the optimum hydrophobicity has been developed and characterized using spectroscopy techniques and was employed to understand the variation of hepatic albumin synthesis rates on physiological and pathophysiological states. Given the importance of hydrophobicity in rendering an effective interaction of small molecules with biomolecules, strategic structure interaction relationship studies led us toward the development of a potent emissive molecular probe through chemical library development. By exploration of these newly developed molecular probes, our study elegantly showed how a pathophysiological condition like the hyperinsulinemic state significantly downregulates albumin biosynthesis in HepG2 cells using fluorescence microscopy as a tool. An excellent correlation between the albumin transcript level and fluorescence intensity inside the cells has been observed. The key role of hydrophobicity resulting in an effective interaction of the probes with albumin, thus leading to strong optical signals, has been experimentally demonstrated in this report. Also, a siRNA interference technique has been utilized to establish the excellent selectivity of the developed probes with excitation as well as emission in the NIR region. We therefore have established through our experimental findings that suitable cell permeable emissive molecular markers with a high degree of albumin specificity can be used as a good optical tool for studying the effect of hyperinsulinemia on albumin biosynthesis modulation.

Carbohydrate restriction ameliorates nephropathy by reducing oxidative stress and upregulating HIF-1α levels in type-1 diabetic rats

Background

Carbohydrate restricted diet regimen is widely accepted as therapeutic approach for the treatment of kidney disease associated with type-2 diabetes, obesity and hypertensive disorders. The present study tested the influence of carbohydrate-energy restricted diet (CR) on type-1 diabetes induced renal dysfunction, hypoxia and structural alterations against diabetic rat group fed control diet (ad libitium).

Methods

Male wistar rats weighing between 180 and 190 g were subjected to 30% carbohydrate energy restricted diet (CR) and diabetes was induced by administration of streptozotocin (45 mg/kg., i.p). Assessment of renal function was done after 4 weeks by determining the serum levels of creatinine, BUN, proteinuria. Oxidative stress was determined by estimating the reduced glutathione, malonaldehyde levels, catalase activity and extent of renal hypoxia by estimating the HIF-1α levels in kidney tissue homogenates. Histological studies were conducted on kidney sections using hematoxylin and eosin, periodic acid-schiff staining.

Results

Diabetic rats exhibited marked hyperglycemia and renal dysfunction developed in diabetic rats fed control diet (ad libitium) as shown by significantly elevated levels of serum creatinine, BUN and massive proteinuria after 4 weeks period. CR diet treatment in diabetic rats significantly lowered hyperglycemia, reversed the above renal functional abnormalities, reduced oxidative stress and enhanced HIF-1α levels. Furthermore histological examination of kidney sections from CR diet treated diabetic rat group showed absence of glomerular hypertrophy, mesangial expansion and tubular vacoulations.

Conclusion

Our results demonstrated that CR diet treatment in diabetic rats attenuated renal damage by reducing oxidative stress and preventing the development of hypoxia by up-regulating HIF-1α levels.

Higher serum albumin was related with diabetes incidence and the impact of BMI changes: Based on cohort study of 18,384 Chinese male elderly

AIMS

Albumin (ALB) was a useful marker of nutrition and general health status. However, the conclusion about the association between ALB and diabetes was inconsistent, and little information was known about the elderly.

METHODS

A cohort study based on 18,384 army cadres was conducted Beijing, from 2009 to 2013.

RESULTS

The mean age of the total 18,384 participants was 71±14years, and the mean ALB concentration was 44.33±3.94g/L at baseline. Diabetes incident showed an increasing trend according to the four ALB concentration groups, from 2.054% to 2.811% for incident. Cox regression showed that participants with higher ALB concentration were at increased HRs for diabetes incident. The HRs of ALB (per SD) and ALB concentration for diabetes were 1.125 (95% CI: 1.024-1.231) and 1.029 (95% CI: 1.007-1.051) respectively in the adjusted model. Also the HRs were closely related with BMI changes. For those who had a BMI changes<-1.00kg/m², the HRs were lower and not statistically significant, and for those with increasing BMI during an average of 4years' follow-up, the HRs were higher.

CONCLUSION

There was a positive and independent association between baseline ALB concentrations with diabetes incident among Chinese male elderly, and this association was closely related with BMI changes.

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.

Metabolic differences in hepatocytes of obese and lean pigs

There are important differences in terms of metabolic activity, energy utilization and capacity of protein and fat deposition when Iberian and modern pigs are compared. Primary culture of hepatocytes was used to evaluate hepatic function and sensitivity to hormones between breeds without the interference of circulating blood factors. Hepatocytes were isolated from pure Iberian (n=10) and Landrace (n=8) pigs of similar BW (24.5±12.1 and 32.9±6.1 kg BW, respectively), by collagenase perfusion. Monolayers were established in medium containing fetal bovine serum for 1 day and switched to serum-free medium for the remainder of the culture period. Hepatocytes were maintained in William's E supplemented with β-mercaptoethanol (0.1 mM), glutamine (2 mM), antibiotics (gentamicin, penicillin, streptomycin and amphotericin B), dimethyl sulfoxide (1 µg/ml), dexamethasone (10-8 M), insulin (0.173 and 17.3 nM) and glucagon (0.287, 2.87 and 28.7 nM) for 24 to 48 h. Gluconeogenesis (GNG), glycogen degradation, triglycerides (TG) content and esterification, β-hydroxybutyrate (BHB) synthesis, IGF-1 synthesis, albumin and urea synthesis were determined. Iberian pigs had greater capacity of GNG than Landrace (24%, P<0.05), although no difference in glycogen degradation was found (P>0.10). TG content and esterification tended to be lower in hepatocytes from Iberian compared with Landrace pigs (12% and 31%, respectively; 0.10<P<0.05). Furthermore, addition of free fatty acids (CLA or linoleic acid, 0.2 mM) increased TG content (64%, P<0.001) although no difference between fatty acids was found. When free fatty acids were compared, a trend toward increased esterification (41%, P=0.078) was found for CLA. Although glucagon stimulated and insulin inhibited BHB synthesis, no difference between breeds was found (P>0.10). IGF-1 synthesis was diminished in hepatocytes from Iberian compared with Landrace pigs (16%, P<0.05). On the contrary, rate of albumin synthesis was greater in Iberian compared with Landrace pigs (58%, P<0.05). Finally, the capacity of urea synthesis was lower in hepatocytes of Iberian compared with Landrace pigs (37%, P<0.05). When ammonia was added to the media, urea concentration increased (648%, 1108% and 2791% when 0 mM was compared with 2.5, 5 and 10 mM, respectively). Urea synthesis increased on increasing ammonia content (55% and 325% when 0 mM was compared with 5 and 10 mM, respectively; P<0.0001). In conclusion, the genetic background accounts for important differences in protein and energy metabolism pathways found in primary culture of hepatocytes from lean and obese pigs.

Proteomic study reveals downregulation of apolipoprotein A1 in plasma of poorly controlled diabetes: a pilot study

Proteomic approaches aid in gaining a better understanding of the pathophysiology of diabetic complications. In view of this, differential protein expression in diabetic plasma samples was studied by a combination of proteomic and western blot analyses. Diabetic plasma samples were categorized based on glycated haemoglobin levels as controlled diabetes (CD; 7-8%), poorly controlled diabetes (PCD; >8%) and non-diabetic control (ND;<6.4%). Two-dimensional electrophoresis and liquid chromatography‑mass spectrometry revealed differential expression of proteins including upregulation of fibrinogen and haptoglobin and downregulation of vitamin D binding protein, α-1-antitrypsin, transthyretin and apolipoprotein A1 (Apo A1) in diabetic compared with non-diabetic plasma samples. Amongst these proteins, Apo A1 downregulation was prominent in PCD. Downregulation of Apo A1 may serve as an early predictive marker of diabetic complications.

Polysome profiling in liver identifies dynamic regulation of endoplasmic reticulum translatome by obesity and fasting

Obesity-associated metabolic complications are generally considered to emerge from abnormalities in carbohydrate and lipid metabolism, whereas the status of protein metabolism is not well studied. Here, we performed comparative polysome and associated transcriptional profiling analyses to study the dynamics and functional implications of endoplasmic reticulum (ER)–associated protein synthesis in the mouse liver under conditions of obesity and nutrient deprivation. We discovered that ER from livers of obese mice exhibits a general reduction in protein synthesis, and comprehensive analysis of polysome-bound transcripts revealed extensive down-regulation of protein synthesis machinery, mitochondrial components, and bile acid metabolism in the obese translatome. Nutrient availability also plays an important but distinct role in remodeling the hepatic ER translatome in lean and obese mice. Fasting in obese mice partially reversed the overall translatomic differences between lean and obese nonfasted controls, whereas fasting of the lean mice mimicked many of the translatomic changes induced by the development of obesity. The strongest examples of such regulations were the reduction in Cyp7b1 and Slco1a1, molecules involved in bile acid metabolism. Exogenous expression of either gene significantly lowered plasma glucose levels, improved hepatic steatosis, but also caused cholestasis, indicating the fine balance bile acids play in regulating metabolism and health. Together, our work defines dynamic regulation of the liver translatome by obesity and nutrient availability, and it identifies a novel role for bile acid metabolism in the pathogenesis of metabolic abnormalities associated with obesity.

Chronic diseases including obesity and associated metabolic abnormalities have become the greatest threat to human health worldwide. How metabolic organs and organelles adapt to nutritional fluctuations, or fail to do so, remains incompletely understood. To explore these issues, we developed a new platform to explore translational responses in the liver, a critical organ for metabolic homeostasis. In this translatomic platform, we integrated polysome profiling and global analysis of polysome-associated mRNAs to systematically quantify protein synthesis on each transcript in obesity and during fasting. Our analysis demonstrated for the first time that protein synthesis is progressively suppressed in the obese liver and that the overall translatome profile of obese liver markedly resembles that of fasting lean mice, particularly in mitochondrial function and bile metabolism. We also examined the physiological impact of some of these alterations and concluded that aberrant bile acid metabolism in the obese liver represents a novel mechanism contributing to hyperglycemia and continuous weight gain. Together, our work reveals abnormal translational regulation as a novel aspect of obesity that could impact future directions in metabolic disease treatment, and we believe translatome profiling represents a new approach to unravel complex mechanisms regulating cellular function and disease pathology.

Mechanisms and outcomes of drug- and toxicant-induced liver toxicity in diabetes

Increase dincidences of hepatotoxicity have been observed in diabetic patients receiving drug therapies. Neither the mechanisms nor the predisposing factors underlying hepatotoxicity in diabetics are clearly understood. Animal studies designed to examine the mechanisms of diabetes-modulated hepatotoxicity have traditionally focused only on bioactivation/detoxification of drugs and toxicants. It is becoming clear that once injury is initiated, additional events determine the final outcome of liver injury. Foremost among them are two leading mechanisms: first, biochemical mechanisms that lead to progression or regression of injury; and second, whether or not timely and adequate liver tissue repair occurs to mitigate injury and restore liver function. The liver has a remarkable ability to repair and restore its structure and function after physical or chemical-induced damage. The dynamic interaction between biotransformation-based liver injury and compensatory tissue repair plays a pivotal role in determining the ultimate outcome of hepatotoxicity initiated by drugs or toxicants. In this review, mechanisms underlying altered hepatotoxicity in diabetes with emphasis on both altered bioactivation and liver tissue repair are discussed. Animal models of both marked sensitivity (diabetic rats) and equally marked protection (diabetic mice) from drug-induced hepatotoxicity are described. These examples represent a remarkable species difference. Availability of the rodent diabetic models offers a unique opportunity to uncover mechanisms of clinical interest in averting human diabetic sensitivity to drug-induced hepatotoxicities. While the rat diabetic models appear to be suitable, the diabetic mouse models might not be suitable in preclinical testing for potential hepatotoxic effects of drugs or toxicants, because regardless of type 1 or type2 diabetes, mice are resistant to acute drug-or toxicant-induced toxicities.

Diabetic changes in the redox status of the microsomal protein folding machinery

Changes in assisted protein folding are largely unexplored in diabetes. In the present studies, we have identified a reductive shift in the redox status of rat liver microsomes after 4 weeks of streptozotocin-induced diabetes. This change was reflected by a significant increase in the total- and protein-sulfhydryl content, as well as in the free sulfhydryl groups of the major protein disulfide isomerases (PDIs), the 58 kDa PDI and the 57 kDa ERp57 but not other chaperones. A parallel decrease of the protein-disulfide oxidoreductase activity was detected in the microsomal fraction of diabetic livers. The oxidant of PDI, Ero1-Lalpha showed a more oxidized status in diabetic rats. Our results reveal major changes in the redox status of the endoplasmic reticulum and its redox chaperones in diabetic rats, which may contribute to the defective protein secretion of the diabetic liver.

Searching QTL by gene expression: analysis of diabesity

Background

Recent developments in sequence databases provide the opportunity to relate the expression pattern of genes to their genomic position, thus creating a transcriptome map. Quantitative trait loci (QTL) are phenotypically-defined chromosomal regions that contribute to allelically variant biological traits, and by overlaying QTL on the transcriptome, the search for candidate genes becomes extremely focused.

Results

We used our novel data mining tool, ExQuest, to select genes within known diabesity QTL showing enriched expression in primary diabesity affected tissues. We then quantified transcripts in adipose, pancreas, and liver tissue from Tally Ho mice, a multigenic model for Type II diabetes (T2D), and from diabesity-resistant C57BL/6J controls. Analysis of the resulting quantitative PCR data using the Global Pattern Recognition analytical algorithm identified a number of genes whose expression is altered, and thus are novel candidates for diabesity QTL and/or pathways associated with diabesity.

Conclusion

Transcription-based data mining of genes in QTL-limited intervals followed by efficient quantitative PCR methods is an effective strategy for identifying genes that may contribute to complex pathophysiological processes.

Insulin suppresses collagenase stimulatory effect of stratifin in dermal fibroblasts

A delicate balance between synthesis and degradation of extracellular matrix (ECM) by matrix metalloproteinases (MMPs) is an essential feature of tissue remodeling. We have recently demonstrated that keratinocyte releasable stratifin, also known as 14-3-3 sigma protein, plays a critical role in modulating collagenase (MMP-1) mRNA expression in human dermal fibroblasts. In this study, we further characterized the collagenase stimulatory effect of stratifin in dermal fibroblasts and evaluated its effect in the presence and absence of insulin. Our data indicate that stratifin increases the expression of collagenase mRNA more than 20-fold in dermal fibroblasts, grown in either Dulbecco's modified Eagle's medium (DMEM) plus 2% or 10% fetal bovine serum (FBS). Collagenase stimulatory effect of stratifin was completely blocked, when fibroblasts were cultured in test medium consisting of 50% keratinocyte serum-free medium (KSFM) and 50% DMEM. The collagenase suppressive effect of test medium was directly proportional to the volume of KSFM used. As this medium contained insulin, we then evaluated the collagenase stimulatory effect of stratifin in dermal fibroblasts in the presence and absence of insulin. The results revealed that stratifin significantly increased the expression of collagenase mRNA/18S (*p < 0.05, n = 3) ratio, while insulin significantly decreased the expression of collagenase mRNA/18S (*p < 0.05, n = 3) ratio. The insulin inhibitory effect on collagenase mRNA expression was time and dose dependent. The maximal inhibitory effect of insulin was seen at 36 h post treatment. In conclusion, stratifin stimulates the expression of collagenase mRNA expression in dermal fibroblasts and this effect is suppressed by insulin treatment.

Insulin secretion and sensitivity in space flight: diabetogenic effects

Nearly three decades of space flight research have suggested that there are subclinical diabetogenic changes that occur in microgravity. Alterations in insulin secretion, insulin sensitivity, glucose tolerance, and metabolism of protein and amino acids support the hypothesis that insulin plays an essential role in the maintenance of muscle mass in extended-duration space flight. Experiments in flight and after flight and ground-based bedrest studies have associated microgravity and its experimental paradigms with manifestations similar to those of diabetes, physical inactivity, and aging. We propose that these manifestations are characterized best by an etiology that falls into the clinical category of "other" causes of diabetes, including, but not restricted to, genetic beta-cell defects, insulin action defects, diseases of the endocrine pancreas, endocrinopathies, drug or chemically induced diabetes, infections, immune-mediated metabolic alteration, and a host of genetic related diseases. We present data showing alterations in tumor necrosis factor-alpha production, insulin secretion, and amino acid metabolism in pancreatic islets of Langerhans cultured in a ground-based cell culture bioreactor that mimics some of the effects of microgravity. Taken together, space flight research, ground-based studies, and bioreactor studies of pancreatic islets of Langerhans support the hypothesis that the pancreas is unable to overcome peripheral insulin resistance and amino acid dysregulation during space flight. We propose that measures of insulin secretion and insulin action will be necessary to design effective countermeasures against muscle loss, and we advance the "disposition index" as an essential model to be used in the clinical management of space flight-induced muscle loss.

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 [(2)H(5)]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/microg total RNA, 2.9+/-0.8 ng/microg total RNA (NS) and 4.7+/-1.8 ng/microg 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.

Cell density-dependent regulation of hepatic development by a gp130-independent pathway

We previously demonstrated that oncostatin M (OSM) promotes hepatic development in concert with glucocorticoid. The livers from mice deficient for gp130, a signaling subunit of the OSM receptor, displayed reduced expression of hepatic differentiation marker and defective glycogenic function. However, these phenotypes were not completely abolished in gp130(-/-) mice, suggesting that there is an alternative pathway regulating hepatic development in vivo. To test this possibility, we cultured gp130(-/-) fetal hepatic cells and investigated a signal that induces hepatic differentiation. When hepatocytes were forced to interact with each other by inoculating cells at high densities, hepatic differentiation was induced even in the absence of gp130. Moreover, cells stimulated with OSM and/or cultured at a high density possess many other metabolic functions. These observations suggest that fetal hepatic cells acquire multiple characteristics of differentiated hepatocytes in response to the signals generated by cell-cell contacts as well as by OSM.

Metabolic flux analysis of postburn hepatic hypermetabolism

The hepatic response to severe injury is characterized by a marked upregulation of glucose, fatty acid, and amino acid turnover, which, if persistent, predisposes the patient to progressive organ dysfunction. To study the effect of injury on liver intermediary metabolism, metabolic flux analysis was applied to isolated perfused livers of burned and sham-burned rats. Intracellular fluxes were calculated using metabolite measurements and a stoichiometric balance model. Significant flux increases were found for multiple pathways, including mitochondrial electron transport, the TCA and urea cycles, gluconeogenesis, and pentose phosphate pathway (PPP). The burn-induced increase in gluconeogenesis did not significantly increase glucose output. Instead, glucose-6-phosphate was diverted into the PPP. These changes were paralleled by increases in glucose-6-phosphate dehydrogenase (G6PDH) and glutathione reductase (GR) activities. Given that G6PDH and GR are the most significant NADPH producers and consumers in the liver, respectively, and that GR is responsible for recycling the free radical scavenger glutathione, these data are consistent with the notion that hepatic metabolic changes are in part due to the induction of liver antioxidant defenses.

Relationship of triglyceride accumulation to insulin clearance and hormonal responsiveness in bovine hepatocytes

The accumulation of triglycerides in the liver has been associated with reduced hepatic function; however, direct evidence that fat accumulation causes decreased liver function is lacking. Hepatocyte monolayers isolated from ruminating calves with an initial low triglyceride concentration were either loaded or not loaded with triglycerides by incubation with 1.5 or 0 mM exogenous nonesterified fatty acids from 12 to 48 h after plating. Basal rates of synthesis of albumin and protein were not affected by triglycerides in the cell. Inclusion of insulin and glucagon from 12 to 72 h after plating increased rates of albumin and protein synthesis. Hepatocytes loaded with triglycerides were less sensitive to the hormonal stimulation of albumin and protein synthesis than were normal hepatocytes. Insulin clearance rates were also lower in hepatocytes loaded with triglycerides than in normal hepatocytes. Decreased insulin clearance and hormonal control of protein synthesis could contribute to the etiology of metabolic disorders that are associated with periparturient fatty liver in dairy cows.

Pancreatic islet transplantation improves body composition, decreases energy intake and normalizes energy efficiency in previously diabetic female rats

We investigated the weight gain, body composition, and feed efficiency of female Wistar Furth rats (170 +/- 1 g) made diabetic with streptozotocin (55 mg/kg intravenously), then infused intraportally with 3519 +/- 838 (150 mu equivalent units) syngeneic pancreatic islets of Langerhans. After islet transplants (5-6 wk), nutritional energetics were evaluated in transplanted rats (Transplant), and also in 3- and 9-wk diabetic (Diab-3, 9) and control rats treated with sham infusions and similar surgical manipulations (Sham-3, 9). Diabetic rats demonstrated marked hyperphagia, which was corrected by islet transplantation (577 +/- 53 vs. 266 +/- 19 kJ/d; P < 0.0001) and was not different than sham control rats (285 +/- 24 kJ/d; P > 0.05). Three weeks of diabetes resulted in a lower protein (Diab-3, 24.8 +/- 2.6 g vs. Sham-3, 30.9 +/- 1.0 g) and fat content (1.9 +/- 0.8 g vs. 11.6 +/- 1.7 g) in the rats' carcasses. However, 6 wk after islet transplantation, rats receiving islets (Transplant) were not different than control rats (Sham-9) (31.9 +/- 1.7 g vs. 33.3 +/- 1.9 g protein and 15.4 +/- 3.0 g vs. 15.1 +/- 3.2 g fat). Three weeks of diabetes resulted in a lesser energy efficiency compared with Sham rats (2.7 +/- 2.0 vs. 7.1 +/- 1.9 kJ gained/100 kJ ingested); islet-transplanted rats were not different than Sham-9 rats (4.9 +/- 2.3 vs. 4.7 +/- 1.4 kJ gained/100 kJ ingested). These data illustrate that islet transplantation in previously diabetic female rats improves growth with proportional gains in body protein and fat mass. This is modulated in part by a reduced food intake and an energy efficiency that is improved relative to controls. These studies offer an optimistic outlook for the continued development of more physiological insulin delivery strategies that preclude the nutritional complications associated with exogenous insulin administration.

Streptozotocin-induced diabetes lowers retinol-binding protein and transthyretin concentrations in rats

Retinol-binding protein (RBP) and transthyretin (TTR) in the plasma, liver and kidney, retinol in plasma, and total vitamin A in the liver were measured in rats 6 weeks after diabetes mellitus had been induced by streptozotocin (STZ). The diabetic rats gained 83% less weight despite consuming 45% more feed than the non-diabetic controls. Plasma and kidney concentrations of RBP and TTR were significantly lower in diabetic than in the non-diabetic control rats. Unlike the retinol carrier proteins, plasma albumin concentrations remained unaffected. Plasma concentrations of retinol were decreased while its hepatic levels increased in the diabetic animals. The depressed circulatory levels of retinol may reflect an altered metabolism of its transport proteins.

Molecular biological analysis of the effects of ginsenoside-Rb2 on albumin mRNA in streptozotocin-induced diabetic rats

The mechanisms of the mRNA synthesis-promoting action of ginsenoside-Rb2, were investigated at the gene level. Rot analysis suggested that the previously reported increase in RNA polymerase activity as a result of administration of ginsenoside-Rb2 might be because of its effect on a specific gene. In this regard, albumin mRNA, which is expressed specifically in the liver, was assayed by northern blot hybridization using albumin cDNA in normal rats, diabetic control rats and diabetic rats given ginsenoside-Rb2. When the level of albumin mRNA in normal rats was set at 100, the level was reduced markedly to 32 in diabetic control rats. In contrast, in diabetic rats given ginsenoside-Rb2 the level was 0.54, significantly higher (69%) than that in diabetic rats given no ginsenoside-Rb2. In addition, poly(A)+RNA was purified from total RNA and subjected to hybridization, and poly(A)+RNA bands with different charges were measured by densitometry. The results of the measurement revealed changes dependent on the charge, and this was confirmed by autoradiography. We found no significant difference in the transcription activity of albumin mRNA, however, it showed only a tendency to increase. This suggests that ginsenoside-Rb2 has some effect on post-transcriptional regulation of the stability of mRNA itself. The results of Rot analysis suggest that ginsenoside-Rb2 affects a specific gene alone.

Islet transplantation reverses carcass protein loss in diabetic rats without inducing disproportionate fat accumulation

The Diabetes Control and Complications Trial demonstrated that intensive insulin therapy (IIT) improves many secondary complications of insulin-dependent diabetes mellitus. However, weight gain in IIT is associated with increased body fat, and no improvement in lean body mass. In the present study we investigated the effects of experimental diabetes on changes in body composition and probed the benefit of glycaemic control achieved through islet transplantation. Male Wistar Furth rats (weight 273 +/- 9 g) made diabetic for 2 weeks with streptozotocin (55 mg/kg) were infused intraportally with 3265 +/- 692 (150 microns islet equivalent units) syngeneic islets of Langerhans. Body composition was evaluated by proximate analysis in carcasses of transplant rats (Trans), and also in rats made diabetic for 2 or 7 weeks (Db-2, Db-7) and in 2- and 7-week sham controls (Sham-2, Sham-7). Fed plasma glucose levels were 7.3 +/- 1.1, 28.2 +/- 2.4, 26.8 +/- 3.9, 7.5 +/- 1.0 and 7.0 +/- 0.1 mm/l, respectively, and neither glucose tolerance nor fasting plasma insulin differed between control vs transplant rats (p > 0.05). Two weeks of diabetes resulted in a body weight 82% of that of controls (240 +/- 5 vs 292 +/- 8 g, p < 0.05) and 5 subsequent weeks of diabetes further suppressed growth by an additional 12% (p < 0.05). Five weeks following islet transplantation, islet-transplant rats had regained lost weight and were not significantly different from control animals (274 +/- 19 vs 291 +/- 21 g, p > 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Hormonal regulation of albumin gene expression in primary cultures of rat hepatocytes

When primary cultures of rat hepatocytes were placed in a chemically defined serum-free medium containing a combination of insulin, glucagon, and dexamethasone, the synthesis of albumin and total protein and the cellular content of RNA and DNA were maintained at constant values for 8 days. Despite the constant rate of albumin synthesis, secretion of the protein increased more than twofold during the initial 4 days in culture and was then maintained at a value similar to that observed in vivo through day 8. This observation suggested an initial defect in albumin secretion that was corrected with time in culture. Deprivation of insulin between days 2 and 5 resulted in a decline in albumin secretion to approximately 40% of the control value. The decline in albumin secretion was accompanied by proportional decreases in albumin synthesis, albumin mRNA, and albumin gene transcription. Return of insulin-deprived cells to complete medium on day 5 restored albumin synthesis and secretion as well as albumin mRNA to control values by day 8. Deprivation of either glucagon or dexamethasone also resulted in reduced albumin synthesis and secretion accompanied by proportional decreases in albumin mRNA and gene transcription. However, the magnitude of the changes in these parameters was less with glucagon or dexamethasone deprivation compared with insulin deprivation. Return of glucagon- or dexamethasone-deprived cells to complete medium on day 5 restored albumin synthesis and secretion as well as albumin mRNA to control values by day 8.(ABSTRACT TRUNCATED AT 250 WORDS)

Albumin and transferrin synthesis are increased in H4 cells by serum from analbuminemic or nephrotic rats

The hepatic synthesis of several proteins, including both albumin and transferrin is increased in the nephrotic syndrome. While active suppression of albumin synthesis by lymphokines has been described, it has been assumed that augmentation of albumin synthesis is governed by a physical factor, plasma oncotic pressure (pi), and that this regulation is by a direct effect of pi on hepatocytes. The mechanisms have not been defined. Furthermore, experiments relying on suppression of protein synthesis may only test non-specific inhibitory effects of the experimental intervention. We tested an alternative hypothesis that a serum factor(s) present in hypooncotic states stimulates albumin synthesis. We incubated an immortalized cell line derived from rat hepatocytes (H4 cells) with serum from Nagase analbuminemic rats (NAR) and rats with passive Heymann nephritis (HN), a model of the nephrotic syndrome. Synthesis (incorporation of [35S]methionine) into both albumin and transferrin was increased significantly. The stimulatory effect of these sera was not extinguished by addition of rat or human albumin to the medium prior to or during incubation, even when pi in the incubation medium was increased to normal plasma levels by added albumin. Incorporation of [35S]methionine into albumin was 7841 +/- 394 cpm/mg cell protein using 10% NAR serum in the presence of human albumin (medium pi 26.1 +/- 0.17) versus 5149 +/- 420 cpm incorporation (P < 0.05) in the presence of control serum and in the absence of added albumin (medium pi 2.06 +/- 0.26 mm Hg, P < 0.001). The stimulatory activity was preserved following heating of serum for one hour at 60 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of a flooding dose of leucine in stimulating incorporation of constantly infused valine into albumin

Recently, we demonstrated increased incorporation of [13C]valine tracer into muscle protein after administration of a flooding dose of L-leucine. We have now investigated the possibility of a similar effect on albumin synthesis in the same group of volunteers. We gave L-[1-13C]leucine (20 atom%, 0.05 g/kg) during the final 90 min of a 7.5-h primed constant infusion of L-[1-13C]valine (99 atom%, 1.5 mg/kg prime constant infusion of 1.5 mg.kg-1.h-1) in healthy male volunteers in the postabsorptive state. Blood samples, taken at 0.5- to 1-h intervals during the constant infusion and at 5- to 30-min intervals during the application of the flooding dose, were analyzed for the concentration and 13C enrichment of leucine, valine, and their ketoacids. Albumin was isolated and hydrolyzed, and the enrichments of incorporated valine and leucine were compared with the mean enrichment of various possible precursor pools to calculate the apparent rate of albumin protein synthesis according to the standard procedures. During constant infusion of [13C]valine tracer the rate of albumin synthesis (measured using alpha-ketoisovalerate labeling as a surrogate for the true precursor) was 0.250 +/- 0.041%h (SD), a value identical to that routinely obtained using constant leucine tracer infusion and alpha-ketoisocaproate labeling. During the application of the flooding dose of leucine, the rate of incorporation of tracer [13C]valine into albumin increased by 73% to 0.433 +/- 0.129%/h (P < 0.05); the apparent protein synthetic rate calculated from the incorporation of leucine applied during the flood was 0.402 +/- 0.057 (P < 0.001). These results raise further doubts about the validity of the flooding dose method for the measurement of rates of human protein synthesis.

Cis-regulation of the L-type pyruvate kinase gene promoter by glucose, insulin and cyclic AMP

The glucose/insulin response element of the L-pyruvate kinase gene is a perfect palindrome located from nt -168 to -144 with respect to the cap site. This element (L4) is partially homologous to MLTF binding sites. Its full efficiency requires cooperation with a contiguous binding site for HNF4, termed L3 and located from nt -145 to -125. In the presence of the L4 element contiguous to L3, cyclic AMP inhibits activity of the L-PK promoter while in its absence, or when the normal L4-L3 contiguity is modified, cyclic AMP behaves as a transcriptional activator that does not seem to be sequence-specific. Therefore, we propose that the mechanism of inhibition of the L-PK gene by cyclic AMP requires precise interactions between the nucleoprotein complex built up at sites L4 and L3 and other components of the L-PK transcription initiation complex.

Regulation of gene expression by insulin

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Differential effects of insulin deficiency on albumin and fibrinogen synthesis in humans

Insulin deficiency decreases tissue protein synthesis, albumin mRNA concentration, and albumin synthesis in rats. In contrast, insulin deficiency does not change, or, paradoxically, increases estimates of whole body protein synthesis in humans. To determine if such estimates of whole body protein synthesis could obscure potential differential effects of insulin on the synthetic rates of individual proteins, we determined whole body protein synthesis and albumin and fibrinogen fractional synthetic rates using 5-h simultaneous infusions of [14C]leucine and [13C]bicarbonate, in six type 1 diabetics during a continuous i.v. insulin infusion (to maintain euglycemia) and after short-term insulin withdrawal (12 +/- 2 h). Insulin withdrawal increased (P less than 0.03) whole body proteolysis by approximately 35% and leucine oxidation by approximately 100%, but did not change 13CO2 recovery from NaH13CO3 or estimates of whole body protein synthesis (P = 0.21). Insulin deficiency was associated with a 29% decrease (P less than 0.03) in the albumin fractional synthetic rate but a 50% increase (P less than 0.03) in that of fibrinogen. These data provide strong evidence that albumin synthesis in humans is an insulin-sensitive process, a conclusion consistent with observations in rats. The increase in fibrinogen synthesis during insulin deficiency most likely reflects an acute phase protein response due to metabolic stress. These data suggest that the absence of changes in whole body protein synthesis after insulin withdrawal is the result of the summation of differential effects of insulin deficiency on the synthesis of specific body proteins.

Effect of diabetes and insulin treatment of diabetic rats on total RNA, poly(A)+ RNA, and mRNA in skeletal muscle

We have assessed the time course of alterations in several biochemical parameters and expression of specific mRNAs in gastrocnemius muscle following both the induction of diabetes and the administration of insulin to diabetic rats. Muscle mass, total RNA, and total protein were reduced, whereas poly(A)+ RNA relative to total RNA was increased following the induction of diabetes. All the above parameters, with the exception of poly(A)+ RNA, were reciprocally and rapidly altered following administration of insulin to 3-day diabetic animals. These changes suggest that during the induction of diabetes 1) total cellular protein is reduced at a rate that is less than the reduction in gastrocnemius mass, whereas RNA is reduced at a rate 1.5 times the reduction in tissue mass, and 2) poly(A)+ RNA is elevated relative to total RNA. After insulin administration, there appears to be coordinate synthesis of both poly(A)+ RNA and ribosomal RNA, assuming 85% of total RNA is ribosomal. Therefore, we conclude that poly(A)+ RNA is more stable than ribosomal RNA during diabetes, whereas the amounts of poly(A)+ RNA and ribosomal RNA are increased at the same rates following insulin administration to diabetic animals. Analysis of expression of specific gene products over the same time course, as assessed by in vitro translation of total RNA followed by two-dimensional gel analysis, suggests that there are a few mRNAs that are very rapidly altered in response to insulin administration. The mRNAs that are altered demonstrate variable temporal patterns of either repression or full or transient expression. These rapid, but limited, alterations in gene expression may prove important in the development of the defects that occur in skeletal muscle in response to diabetes.

Transcriptional regulation of rat liver protein disulphide-isomerase gene by insulin and in diabetes

The mRNA encoding for rat protein disulphide-isomerase (PDI) increases 3-fold in the liver of diabetic rats and is accompanied by similar changes at the protein level. Long treatment (for 3 days) of diabetic rats with insulin reverses this effect of diabetes both at the mRNA and protein levels. The higher expression of rat PDI mRNA in diabetes is due to an increase in the transcriptional rate of the gene, and insulin treatment of diabetic animals produces within 30 min a decrease in the level of transcription of PDI gene, as judged by nuclear run-on transcription experiments performed in vivo. These results clearly show a role for insulin in the regulation of transcription of the gene encoding this multifunctional protein in rat liver.

Effects of streptozotocin diabetes in the rat on blood levels of ten specific plasma proteins and on their net biosynthesis by the isolated perfused liver

Adult male Sprague-Dawley rats with streptozotocin-induced diabetes (6 to 8 wk duration), treated or untreated with insulin, were studied with two aims: (a) to ascertain whether protracted diabetes in the rat is associated with changes in circulating plasma protein levels analogous to those reported in human diabetic patients with clinical evidence of complications; (b) to evaluate the effects of experimental diabetes on the net cumulative biosynthesis of 10 specific plasma proteins by the isolated liver, perfused for 24 hr. Samples of liver donor plasma and samples of perfusate were analyzed by single radial immunodiffusion or by rocket immunoelectrophoresis for albumin, alpha 1-macroglobulin and the acute phase glycoproteins: fibrinogen, alpha 1-acid glycoprotein (Darcy), alpha 1-acid glycoprotein (Kawasaki), haptoglobin, alpha 2-(acute phase) globulin, hemopexin, C3-complement and ceruloplasmin. Diabetes (6 to 8 wk), untreated with insulin, resulted in significantly increased liver donor plasma levels of alpha 1-acid glycoprotein (Darcy) and alpha 1-acid glycoprotein (Kawasaki); plasma levels of hemopexin and of C3 decreased to 75% and 30% of normal, respectively. Insulin treatment of diabetic liver donors for 6 to 8 wk prevented the increase in alpha 1-acid glycoprotein (Darcy) and alpha 1-acid glycoprotein (Kawasaki) and minimized the decrease in C3 to 75% of normal. Perfused livers from untreated diabetic rats (6 to 8 wk) showed slightly decreased cumulative synthesis and secretion of alpha 1-acid glycoprotein (Darcy); however, synthesis of albumin was reduced to 35% of normal and that of eight glycoproteins ranged from 25% of normal (fibrinogen) to 12% of normal (C3). The striking in vitro induction of increased synthesis of acute-phase proteins by cortisol plus insulin in the isolated perfused normal liver was in contrast to the severely attenuated induction in perfused livers of untreated diabetic rats, which ranges from 50% of normal for alpha 1-acid glycoprotein (Darcy) to 5% of normal (C3). Severely negative perfusate nitrogen balance and impaired glucose utilization by perfused untreated diabetic livers contrasted with positive nitrogen balance and good glucose utilization of normal livers in response to insulin plus cortisol. The plasma protein synthetic capacity and the in vitro response to insulin plus cortisol of perfused livers from insulin-treated diabetic rats were normal for seven of the proteins but moderately decreased for albumin, haptoglobin and C3.

Regulation by dimethylsulfoxide, insulin, and corticosteroids of hepatitis B virus replication in a transfected human hepatoma cell line

A human hepatoblastoma cell clone E4 was obtained by transfection of HepG2 cells with a plasmid DNA containing four tandem copies of hepatitis B virus (HBV) genome. Analysis of both intracellular and extracellular viral DNA revealed that this clone exhibited the main steps of the replication process previously found in normal hepatocyte primary cultures experimentally infected in vitro. Indeed, relaxed-circular, covalently closed circular, and single-stranded forms of viral DNA were identified in the cells together with complete virions and immature cores in the medium. Furthermore, the ability of these secreted particles to infect normal human hepatocyte cultures was established. These E4 cells were used to evaluate the effect of various soluble factors on HBV replication. Corticosteroids and, to a greater extent, dimethylsulfoxide (DMSO) increased intracellular viral DNA, whereas insulin reduced it dramatically. Parallel changes in the amounts of viral DNA secreted in the medium were observed. Measurement of the albumin secretion rate indicated that cellular and viral activities could be regulated, at least in part, in a coordinated manner.

Insulin effects on apolipoprotein B production by normal, diabetic and treated-diabetic rat liver and cultured rat hepatocytes

1. The effect of insulin on apolipoprotein (apo B) secretion was studied in 24 h recirculating liver perfusions of isolated normal, diabetic and insulin-treated diabetic rats. In single perfusions from each group apo B accumulated in the media in a linear fashion. 2 In perfusions of normal rat livers, when the medium contained insulin plus cortisol, apo B production was significantly inhibited (by 35.8%), demonstrating a hormone effect on apo B secretion. 3. In perfusions of diabetic-rat livers, apo B production was decreased to 11.8% of normal when the medium contained no hormones, and was not significantly changed by the addition of insulin plus cortisol to the medium, suggesting that the hormone effect on apo B secretion is missing in long-term hypoinsulinaemic states. 4. Treatment of diabetic rats with daily insulin injection restored apo B production and restored the effect of insulin plus cortisol in the medium to inhibit apo B secretion during perfusion. 5. Parallel studies of apo B secretion with insulin alone, cortisol alone and insulin plus cortisol in the medium were performed in primary cultures of hepatocytes to compare results from liver perfusions. 6. Apo B secretion by hepatocytes from normal, diabetic and treated-diabetic rats was inhibited (by 36.8%, 57.1% and 57.9% respectively) when insulin alone was added to the medium. 7. Insulin plus cortisol inhibited apo B secretion by hepatocytes from normal and treated diabetic rats (by 30.2% and 47.2% respectively), but failed to inhibit apo B secretion by hepatocytes from diabetic rats.

Albumin metabolism in the nephrotic syndrome: the effect of dietary protein intake

The nephrotic syndrome is characterized by increased urinary excretion of albumin and other serum proteins, accompanied by hypoproteinemia and edema formation. Nephrotic patients have lower serum albumin concentrations than do patients undergoing continuous ambulatory peritoneal dialysis when albumin and protein losses are the same in both groups, suggesting that nephrotic patients may not maximally adapt to loss of protein. The fractional rate of albumin catabolism is increased in nephrotic patients, possibly as a result of increased albumin catabolism by the kidney, but the absolute albumin catabolic rate is decreased in nephrotic patients. The rate of albumin synthesis may be increased, but not sufficiently to maintain normal serum albumin concentration or albumin pools. Augmentation of dietary protein in nephrotic rats directly stimulates albumin synthesis by increasing albumin mRNA content in the liver, but also causes an increase in glomerular permeability to macromolecules so that much if not all of the excess albumin synthesized is lost in the urine. When dietary protein is restricted, the rate of albumin synthesis is not increased either in nephrotic patients or in rats, despite severe hypoalbuminemia. Although dietary protein supplementation may lead to positive nitrogen balance, dietary protein supplementation alone does not cause an increase in serum albumin concentration or body albumin pools, and may instead cause further albumin pool depletion because of changes induced in glomerular permselectivity. The use of angiotensin-converting enzyme inhibitors may blunt the increased albuminuria caused by dietary protein supplementation and allow albumin stores to be increased.