Adult Liver Enzyme Research Articles

Association of Serum Uric Acid and Liver Enzymes in Adults at Tertiary Level Hospital in Bangladesh

The level of serum uric acid (SUA) has been linked to metabolic syndrome, diabetes, and cardiovascular disease. The purpose of this study was to evaluate the relationship between SUA and serum liver enzymes in a Bangladeshi adult population. This cross-sectional study was conducted among apparently healthy adults aged >18 years, from March 2019 to February 2020 at the Department of Biochemistry, Sir Salimullah Medical College (SSMC), Dhaka. SUA, liver enzymes, lipid profile and other biochemical markers were measured in the collected samples by using standard methods. All statistical analyses were performed by using SPSS version 22.0 software and p<0.05 was considered statistically significant. A total of 140 subjects were selected and blood sample were collected for biochemical analysis. Among them 70 were male and 70 were female. Serum uric acid (SUA), Alanine transaminase (ALT), Aspartate aminotransferase (AST) and Gamma-glutamyl transferase (GGT) levels were significantly (p<0.001) higher in male than female group. Pearson’s correlation analysis showed that there were significant positive correlation between SUA and serum ALT, AST, GGT (p<0.001). However, it also showed significant positive correlation between SUA and total cholesterol (TC), triglycerides (TG), low density lipoprotein cholesterol (LDL-C), while negative correlation was found between SUA and high density lipoprotein cholesterol (HDL-C) (p<0.001). The role of SUA in the prediction of elevated liver enzymes showed area under the ROC Curve (AUC) 0.839 for ALT, 0.848 for AST and 0.809 for GGT respectively. SUA is positively related with ALT, AST, GGT in adults. More prospective studies are needed to clarify the complex relationship between SUA and liver enzymes in the general population. Bangladesh Med J. 2022 Sept; 51(3): 18-27

The impact of food restriction on liver enzyme levels: a systematic review and meta-analysis.

The relationship between food restriction (FR) and liver enzyme levels, such as alanine transferase (ALT), aspartate transferase (AST), and γ-glutamyl transferase (GGT), has not yet been confirmed. A meta-analysis of research articles was conducted to investigate the association of FR and liver enzyme levels. The PubMed, Web of Science, Embase, and Cochrane Library databases were screened for articles published up to April 30, 2022. Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement methodology was used to search for research articles. Publication bias was detected using Begg's test. Finally, 17 trials involving 1982 participants and that reported mean value, mean difference, and standard deviation were identified. Data were described as the weighted mean difference of body mass index, body weight, and standardized mean difference (SMD) of ALT, AST, and GGT. A reduction in ALT level was observed after a FR intervention (total SMD, -0.36, 95% confidence interval [CI], -0.68 to -0.05). GGT levels also were decreased in 4 studies (total SMD, -0.23; 95%CI, -0.33 to -0.14). According to subgroup analysis, serum AST levels decreased in the medium-term (between 5 wk and 6 mo) group (subtotal SMD, -0.48; 95%CI, -0.69 to -0.28). Existing evidence suggests that dietary restriction improves adult liver enzyme levels. The long-term maintenance of healthy liver enzyme levels, particularly in real-world applications, necessitates additional consideration.

Association between Serum Uric Acid and Liver Enzymes in Adults Aged 20 Years and Older in the United States: NHANES 2005-2012.

Although the relationship between serum uric acid (SUA) and nonalcoholic fatty liver disease has been widely reported, the relationship between SUA and liver enzymes has rarely been reported. The purpose of this study was to evaluate the association of SUA levels with alanine aminotransferase (ALT) and aspartate aminotransferase (AST) in populations aged 20 years and older in the United States. We analyzed 7165 individuals aged 20 years and older from the National Health and Nutrition Examination Survey (NHANES) in the United States. Weighted multiple linear regression models were used to analyze the relationship between SUA and ALT and AST. A generalized additive model and a smooth curve fitting were used to observe the linear relationship. SUA was positively correlated with ALT and AST. In addition, the overall increasing trend of ALT and SUA was observed across the SUA quartile groups. In the stratified analysis by sex and race, the SUA levels in male, female, Mexican American, and Non-Hispanic White individuals, and those of another race, were positively correlated with ALT and AST. However, the SUA levels in Non-Hispanic Black individuals had a nonlinear relationship with ALT and AST. In individuals aged 20 years and older in the United States (excluding Non-Hispanic Black individuals), SUA levels were positively associated with ALT and AST. Therefore, with a rise in SUA levels, liver function should be monitored or intervened with in people aged 20 years and older in the United States.

Association between non-nutritive sweetener consumption and liver enzyme levels in adults: a systematic review and meta-analysis of randomized clinical trials.

The use of non-nutritive sweeteners (NNSs) is dramatically increasing in food commodities, and their effects on biochemical parameters have been the subject of great controversy. Liver enzymes as markers of liver injury may be helpful measures of non-alcoholic fatty liver disease (NAFLD), but the outcomes of randomized controlled trials (RCTs) suggest their associations with NNSs are contentious. The current study was designed to provide a GRADE-assessed systematic review and meta-analysis of RCTs studying the consequences of NNS consumption on ALT, AST, and GGT concentrations (ie, the 3 main liver enzymes in adults). Scopus, PubMed, and EMBASE were searched for relevant studies up to April 2021, with no time and language limitations. Two independent researchers extracted information from qualified studies, and a third researcher rechecked it. Of 3212 studies, 10 studies that enrolled a total of 854 volunteers were included. A random-effects or fixed-effects model was utilized to calculate weighted mean differences (WMDs) and 95% confidence intervals (CIs). Heterogeneity between studies was evaluated using Cochran's Q test and quantified using the I2 statistic. The pooled results demonstrated that, compared with control groups, NNS intake led to nonsignificant reductions in ALT (WMD: -.78, 95% CI: -2.14, .57, P = .25) and GGT (WMD: -.21, 95% CI: -1.46, 1.04, P = .74). Also, a small nonsignificant increasing effect on AST level was found (WMD: .02, 95% CI: -1.26, 1.30, P = .97). NNS significantly reduced AST levels in type 2 diabetes patients when subgroup analyses were performed. Also, in trials with ≥24-week intervention or studies that utilized stevioside for intervention, a significant reducing effect on ALT level was observed. The results of this study showed that NNS intake has no significant effect on liver enzyme levels in adults. PROSPERO registration no. CRD42021250067.

Structural Basis for the Diminished Ligand Binding and Catalytic Ability of Human Fetal-Specific CYP3A7.

Cytochrome P450 3A7 (CYP3A7) is a fetal/neonatal liver enzyme that participates in estriol synthesis, clearance of all-trans retinoic acid, and xenobiotic metabolism. Compared to the closely related major drug-metabolizing enzyme in adult liver, CYP3A4, the ligand binding and catalytic capacity of CYP3A7 are substantially reduced. To better understand the structural basis for these functional differences, the 2.15 Å crystal structure of CYP3A7 has been solved. Comparative analysis of CYP3A enzymes shows that decreased structural plasticity rather than the active site microenvironment defines the ligand binding ability of CYP3A7. In particular, a rotameric switch in the gatekeeping amino acid F304 triggers local and long-range rearrangements that transmit to the F-G fragment and alter its interactions with the I-E-D-helical core, resulting in a more rigid structure. Elongation of the β3-β4 strands, H-bond linkage in the substrate channel, and steric constraints in the C-terminal loop further increase the active site rigidity and limit conformational ensemble. Collectively, these structural distinctions lower protein plasticity and change the heme environment, which, in turn, could impede the spin-state transition essential for optimal reactivity and oxidation of substrates.

Body Adiposity, But Not Elements of Objectively Measured Sedentary Behavior or Physical Activity, Is Associated With Circulating Liver Enzymes in Adults With Overweight and Obesity.

ObjectiveWe studied the associations between accelerometer-measured sedentary behavior (SB) and habitual physical activity (PA) as well as markers of body adiposity and other cardiometabolic risk factors with liver enzymes alanine aminotransferase (ALT), aspartate aminotransferase (AST) and γ-glutamyltransferase (GGT).MethodsA total of 144 middle-aged adults (mean age 57 (SD 6.5) years) with overweight or obesity (mean body mass index [BMI] 31.8 [SD 3.9] kg/m2) participated. Different components of SB (sitting, lying) and PA (standing, breaks in SB, daily steps, light PA, moderate-to-vigorous PA and total PA) were measured with validated hip-worn accelerometers for four consecutive weeks (mean 25 days, [SD 4]). Fasting venous blood samples were analysed using standard assays. The associations were examined with Pearson’s partial correlation coefficient test and linear mixed model.ResultsAmong 102 women and 42 men accelerometer measured SB or the elements of PA were not associated with circulating liver enzymes. When adjusted for age and sex, liver enzymes correlated positively with BMI and waist circumference (WC) (ALT r=0.34, p<0.0001, r=0.41, < 0.0001, AST r=0.17, p=0.049, r=0.26, p=0.002, GGT r=0.29, p=0.0005, r=0.32, p < 0.0001, respectively). SB proportion associated positively with BMI (r=0.21, p=0.008) and WC (r=0.27, p=0.001). Components of PA associated negatively with BMI (MVPA r=-0.23, p=0.005, daily steps r=-0.30, p<0.0001 and breaks in sedentary time r=-0.32, p<0.0001), as well as with WC (breaks in SB r=-0.35, p<0.0001, MVPA r=-0.26, p=0.002, daily steps r=-0.31, p<0.0001, standing time r=-0.27, p=0.001). Liver enzymes associated positively with common cardiometabolic markers such as resting heart rate (ALT; β=0.17, p=0.03, AST; β=0.25, p=0.002, GGT; β=0.23, p=0.004) and systolic/diastolic blood pressure (ALT β=0.20, p=0.01, β=0.22, p=0.005, AST (only diastolic) β=0.23, p=0.006, GGT β=0.19, p=0.02, = 0.23, p=0.004, respectively), fasting insulin (ALT β=0.41, p<0.0001, AST β=0.36, p=0.0003, GGT β=0.20, p=0.04) and insulin resistance index (ALT β=0.42, p<0.0001, AST β=0.36, p=0.0003, GGT β=0.21, p=0.03), even after adjustment with BMI.ConclusionsLiver enzymes correlate with body adiposity and appear to cluster with other common cardiometabolic risk factors, even independently of body adiposity. SB and PA appear not to be essential in modulating the levels of circulating liver enzymes.

Effects of resveratrol supplementation on liver enzymes: A systematic review and meta-analysis of randomised controlled trials.

The available evidence regarding the possible effects of resveratrol on liver function is inconsistent. Therefore, the present meta-analysis was performed to investigate the overall effects of resveratrol supplementation on liver enzymes in adults. A systematic and comprehensive search of the online medical databases including PubMed, Scupos, Web of Science and Cochran Library was performed up to February 2020. All RCTs using resveratrol supplements in adults were included in this systematic review and meta-analysis. The overall effect was presented as weighted mean difference (WMD) and 95% confidence interval (CI) in a random-effects meta-analysis model. Finally, 15 randomised trials including 714 participants were selected for the present meta-analysis. Pooled analysis did not show any significant changes in alanine aminotransferase (ALT) (WMD: 0 IU/L, 95% CI: -3.17 to 3.17, P = .99; I2 = 74.2%), aspartate aminotransferase (AST) (WMD: -2.40 IU/L, 95% CI: -5.45 to 0.65, P = .11; I2 = 82.9%), gamma-glutamyl transferase (GGT) (WMD: -1.26 IU/L, 95% CI: -4.64 to 2.13, P = .64; I2 = 23.7%), alkaline phosphatase (ALP) (WMD: 3.80 IU/L, 95% CI: -4.65 to 12.25, P = .37; I2 = 29.9%) and bilirubin (WMD: 0.13 IU/L, 95% CI: -0.43 to 0.17, P = .39; I2 = 8.9%) after supplementation with resveratrol. Overall, in our study, resveratrol does not affect liver enzyme levels significantly, but subgroup analysis indicates that these results may be influenced by resveratrol dose, duration of the study and population status, so future high-quality studies are necessary to get definitive results.

Long-term exposure to ambient fine particulate matter and liver enzymes in adults: a cross-sectional study in Taiwan

ObjectivesAnimal experiments indicate that exposure to particulate matter (PM) can induce hepatotoxic effects but epidemiological evidence is scarce. We aimed to investigate the associations between long-term exposure to PM air...

Prevalence of elevated liver enzymes in adults with type 1 diabetes: A multicentre analysis of the German/Austrian DPV database.

To assess the prevalence of elevated liver enzymes in adults with type 1 diabetes mellitus (T1DM) in routine clinical care and the association with cardiovascular risk profile in the Diabetes-Prospective-Documentation (DPV) network in Germany and Austria. This cross sectional observational study from the DPV registry includes data from 45 519 adults with T1DM at 478 centres up to September 2016. Liver enzyme measurements were available in 9226 (29%) patients at 270 centres and were analysed for increased alanine aminotransferase (ALT; men >50 U/L, women >35U/L) and/or aspartate aminotransferase (AST; men >50 U/L, women >35U/L) and/or gamma-glutamyltransferase (GGT; men >60U/L, women >40 U/L). A subgroup analysis in patients for whom 2 or more ALT measurements were available (n = 2335, 25%) and whose ALT was increased at least twice (men >30 U/L, women >19U/L) was performed. Associations with glycaemic control, cardiovascular risk factors and late complications were investigated with multiple regression analyses. Twenty percent (19.8%, n = 1824) had increased liver enzyme(s) on one or more occasions. Increased liver enzymes were associated with worse glycaemic control and higher BMI (both P < .0001), dyslipidemia (OR, 1.75; 95% CI, 1.54-2.0), hypertension (OR, 1.48; 95% CI: 1.31-1.68), myocardial infarction (OR, 1.49; 95% CI, 1.17-1.91) and end stage renal disease (OR, 1.59; 95% CI, 1.17-2.17). ALT was increased twice in 29% and was associated with worse glycaemic control (P < .0001), higher BMI (P < .0001), hypertension (OR, 1.58; 95% CI, 1.26-1.97) and dyslipidemia (OR, 1.89; 95% CI, 1.51-2.37). In this clinical audit in adults with T1DM, elevated liver enzymes on routine assessment were associated with a less favourable cardiovascular risk profile and with poorer glycaemic control.

Indicators of fetal growth and adult liver enzymes: the Bogalusa Heart Study and the Cardiovascular Risk in Young Finns Study.

Despite the interest in the relationship of fetal exposures to adult cardiovascular disease, few studies have examined indicators of adult fatty liver disease as an outcome. Previous results are inconsistent, and indicate possible variation by sex. Adult liver enzymes [γ-glutamyl transferase (GGT), alanine transaminase (ALT) and aspartase transaminase (AST)] were measured in two cohort studies: the Bogalusa Heart Study (BHS; n=1803) and the Cardiovascular Risk in Young Finns (YF; n=3571) study, which also had ultrasound measures of liver fat (n=2546). Predictors of dichotomized (clinical cut-offs) and continuous (within the reference range) liver enzymes included low birthweight (4000 g), small-for-gestational-age (birthweight 90th percentile), and preterm birth. Multiple logistic and linear regression were conducted, adjusted for medical, behavioral and socioeconomic indicators. Interactions with sex were also examined. In BHS, birth measures were not strongly associated with clinically high levels of liver enzymes, and within the reference range measures of reduced growth were associated with increased AST in women. In the YF study, at least one marker of reduced growth was associated with higher GGT, higher ALT and higher AST (in women). Probable fatty liver on ultrasound was associated with low birthweight (2.41, 1.42-4.09) and preterm birth (2.84, 1.70-4.76). These results suggest a link between birth parameters and adult fatty liver, but encourage consideration of population variation in these relationships.

Daily chocolate consumption is inversely associated with insulin resistance and liver enzymes in the Observation of Cardiovascular Risk Factors in Luxembourg study.

This study examined the association of chocolate consumption with insulin resistance and serum liver enzymes in a national sample of adults in Luxembourg. A random sample of 1153 individuals, aged 18-69 years, was recruited to participate in the cross-sectional Observation of Cardiovascular Risk Factors in Luxembourg study. Chocolate consumption (g/d) was obtained from a semi-quantitative FFQ. Blood glucose and insulin levels were used for the homoeostasis model assessment of insulin resistance (HOMA-IR). Hepatic biomarkers such as serum γ-glutamyl-transpeptidase (γ-GT), serum aspartate transaminase and serum alanine transaminase (ALT) (mg/l) were assessed using standard laboratory assays. Chocolate consumers (81·8 %) were more likely to be younger, physically active, affluent people with higher education levels and fewer chronic co-morbidities. After excluding subjects taking antidiabetic medications, higher chocolate consumption was associated with lower HOMA-IR (β=-0·16, P=0·004), serum insulin levels (β=-0·16, P=0·003) and γ-GT (β=-0·12, P=0·009) and ALT (β=-0·09, P=0·004), after adjustment for age, sex, education, lifestyle and dietary confounding factors, including intakes of fruits and vegetables, alcohol, polyphenol-rich coffee and tea. This study reports an independent inverse relationship between daily chocolate consumption and levels of insulin, HOMA-IR and liver enzymes in adults, suggesting that chocolate consumption may improve liver enzymes and protect against insulin resistance, a well-established risk factor for cardiometabolic disorders. Further observational prospective research and well-designed randomised-controlled studies are needed to confirm this cross-sectional relationship and to comprehend the role and mechanisms that different types of chocolate may play in insulin resistance and cardiometabolic disorders.

Abstract P142: Daily Chocolate Consumption is Inversely Associated with Insulin Resistance and Liver Enzymes in Adults: The Observation of Cardiovascular Risk Factors Study

Introduction: Research into the health effects of cocoa has received much attention over the past few years. Several systematic reviews and meta-analyses of existing studies have generally agreed on a potentially beneficial association between chocolate consumption and risk for cardiometabolic disorders. However, evidence regarding a potential role of chocolate consumption in insulin resistance and hepatic biomarkers, from human epidemiological studies, is lacking. Hypothesis: We assessed the hypothesis that daily chocolate consumption would be inversely associated with insulin resistance and hepatic biomarkers in appraently healthy adults. Methods: A random sample of 1153 individuals, aged 18-69 years, was recruited between 2007 and 2009 to participate in the Observation of Cardiovascular Risk Factors (ORISCAV-LUX) study. Chocolate consumption in g/day was obtained from a semi-quantitative food-frequency questionnaire. Blood glucose and insulin were used for the homeostasis model assessment of insulin resistance (HOMA-IR). Hepatic biomarkers, namely serum γ-glutamyl-transpeptidase (γ-GT), serum Aspartate Transaminase (AST) and serum Alanine Transaminase (ALT) in mg/l were assessed using standard laboratory assays. Results: Chocolate consumers (81.8 %) were more likely to be younger, physically active, affluent people with higher education levels and have fewer chronic comorbidities. After exclusion of subjects taking antidiabetic medications, higher chocolate consumption was associated with lower HOMA-IR (β= -0.16, P=0.004), serum insulin levels (β= -0.16, P=0.003), and liver enzymes, including γGT (β= -0.12, P=0.009) and ALT (β= -0.09, P=0.004) after adjustment for age, sex, education, lifestyle (smoking status and physical activity) and dietary confounding factors, including daily energy intake, consumption of fruit and vegetables, alcohol, as well as polyphenol-rich coffee, and tea. Conclusion: This is the first population-based study reporting an independent inverse relationship between daily chocolate consumption and levels of insulin, HOMA-IR and liver enzymes in adults.. Small dietary changes with respect to chocolate consumption may improve liver enzymes and protect against insulin resistance, a well-established risk factor for cardiometabolic disorders.

Low‐fat dairy reduces inflammatory genes and liver enzymes in adults with metabolic syndrome (40.5)

We evaluated the effect of low‐fat dairy (LFD) intake on plasma inflammatory markers, gene expression of these markers in peripheral blood mononuclear cells (PBMC) and liver enzymes in individuals with metabolic syndrome (MetS). Subjects (13 male, 22 female) with low dairy intake (&lt;1.5 ser/dairy/day) were randomly assigned to receive LFD (296 mL low‐fat milk, 170 g yogurt, 510 g cheese stick, 3 servings of dairy/day) or isocaloric control foods (CON) (42 g granola bar, 177 mL juice) daily for 6‐wk. After a 4‐wk wash‐out, subjects were allocated to the alternate treatment. Participants had lower concentrations of both hepatic alanine aminotransferase (ALT) (p &lt; 0.05) and aspartate aminotransferase (AST) (p&lt; 0.005) as well as lower concentrations of plasma monocyte chemoattractant protein (MPC‐1) (p&lt;0.05) after the LFD period. Gene expression was evaluated in a subset of subjects (n = 17). IL‐1b and IL‐6 were reduced by 46 and 63%, respectively compared to the control period. Protein and gene expression of tumor necrosis factor (TNF)‐alpha was not altered by diet. These results indicate that consumption of three dairy servings per day improve both liver inflammatory markers and systemic inflammation in subjects with MetS.Grant Funding Source: Dairy Council

Nonalcoholic Fatty Liver Disease: Implications for Clinical Practice and Health Promotion

Nonalcoholic fatty liver disease (NAFLD), a condition caused by fatty infiltration of the liver, in the absence of large alcohol consumption, that can result in liver failure. It is the leading cause of elevated liver enzymes in adults and of liver disease in children, and it is increasing in the United States commensurately with obesity. Initially an asymptomatic disease, diagnosis is based on risk factor assessment, laboratory findings, and imaging studies. Prevention and early intervention require lifestyle changes. Prognosis is typically good, especially early in the disease course.

Induced differentiation and maturation of newborn liver cells into functional hepatic tissue in macroporous alginate scaffolds

The present work explores cell cultivation in macroporous alginate scaffolds as a means to reproduce hepatocyte terminal differentiation in vitro. Newborn rat liver cell isolates, consisting of proliferating hepatocytes and progenitors, were seeded at high cell density of 125 x 10(6)/cm(3) within the scaffold and then cultivated for 6 wk in chemically defined medium. Within 3 days, the alginate-seeded cells expressed genes for mature liver enzymes, such as tryptophan oxygenase, secreted a high level of albumin, and performed phase I drug metabolism. The cells formed compacted spheroids, establishing homotypic and heterotypic cell-to-cell interactions. By 6 wk, the spheroids developed into organoids, with an external mature hepatocyte layer covered by a laminin layer encasing inner vimentin-positive cells within a laminin-rich matrix also containing collagen. The hepatocytes presented a distinct apical surface between adjacent cells and a basolateral surface with microvilli facing extracellular matrix deposits. By contrast, viable adherent cells within collagen scaffolds presenting the identical porous structure did not express adult liver enzymes or secrete albumin after 6 wk. This study thus illustrates the benefits of cell cultivation in macroporous alginate scaffolds as an effective promoter for the maturation of newborn liver cells into functional hepatic tissue, capable of maintaining prolonged hepatocellular functions.

Multiple forms of 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase are expressed in perinatal rat liver

Fetal rat liver expresses a 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (PFK-2/Fru-2,6-Pase2) form that differs from the adult liver enzyme in the inhibition by phosphorylation by the adenosine 3',5'-cyclic monophosphate-dependent protein kinase and in the recognition by an antibody specific for the NH2-terminal domain of the adult liver enzyme. Northern blot analysis shows that fetal hepatocytes contain a species of mRNA that is 2.2 kb in size and that exhibits the maximal levels after delivery. PFK-2/Fru-2,6-Pase2 mRNA analysis using a sensitive ribonuclease protection assay reveals the presence of nearly similar amounts of adult liver-specific and skeletal muscle-specific mRNA in fetal liver and hepatocytes during the last days of gestation, as well as a 233-bp protected fragment present in fetal liver. These results were confirmed by polymerase chain reaction using specific oligonucleotide pairs. Primer extension of fetal liver cDNA suggests the presence of two initiation sites of transcription. Analysis of the adult liver PFK-2/Fru-2,6-Pase2 protein during the perinatal transition using a specific antibody shows a marked accumulation of this form immediately after birth.

Induction of ornithine-urea cycle enzymes and nitrogen metabolism and excretion in rainbow trout (Oncorhynchus mykiss) during early life stages

The ornithine&shy;urea cycle (OUC) is present in elasmobranch fish and many terrestrial vertebrates. Recently, a functional OUC has been reported in a few teleost species, suggesting that all teleost fish have the genes for the OUC, but expression is relatively rare. We investigated the possibility that the OUC is expressed during early development in trout as a mechanism for detoxifying ammonia produced from the catabolism of yolk protein. We followed ammonia and urea excretion rates, tissue ammonia and urea levels and OUC enzyme activities in rainbow trout up to 93 days after fertilization. Both ammonia and urea tissue concentrations increased several-fold in the first 40 days after fertilization (embryo stage), peaking at 1.7 mmol N l-1 and 2.5 mmol N l-1, respectively. Ammonia excretion could be detected in 4-day-old embryos, but urea excretion was not initiated until after hatching (day 45). Urea excretion in larval fish (days 42&shy;93) increased several-fold and by day 93 was 14 % of total nitrogen excretion, as found in adult trout. Glutamine synthetase (GSase) and arginase activities were detected in 'whole animal' homogenates just after hatching and the levels of activity increased markedly to day 93. Carbamoyl phosphate synthetase (CPSase) and ornithine transcarbamylase (OTCase) were first detected in 40-day-old embryos; activities peaked between days 53 and 71 and then subsequently decreased. Adult liver enzyme activity for GSase was several-fold lower than in whole larval trout and OTCase and CPSase III (glutamine- and N-acetylglutamate-dependent CPSase catalysing the first step of the OUC) activities were essentially absent in adult liver. We conclude that embryonic and larval trout are primarily ammoniotelic. Urea is synthesized immediately after fertilization, but is not excreted until after the embryo is hatched. The results provide evidence for the presence of the OUC in larval rainbow trout, since four of the OUC enzymes are induced just after hatching and the levels of activity are relatively high compared with those in adult liver tissue. Furthermore, we suggest that all teleosts have retained the OUC genes, which are expressed only during certain stages of development (embryogenesis), and in a few rare species expression is maintained throughout the life cycle to cope with unusual environmental conditions (e.g. alkaline water, air exposure).

Cloning and expression of murine S-adenosylmethionine synthetase

Mice homozygous for chromosomal deletions at or around the albino locus on chromosome 7 express reduced levels of a group of liver genes. Here, we report the isolation and characterization of cDNA and genomic clones encoding one of the affected genes, the mouse adult liver S-adenosylmethionine (AdoMet) synthetase. This enzyme catalyzes the synthesis of AdoMet, which functions in transmethylation and transsulfuration. Mouse AdoMet synthetase cDNA is 3232 base pairs (bp) in length and contains an open reading frame that encodes an enzymatically active polypeptide of 396 amino acids. The mouse AdoMet synthetase shares 98 and 96% amino acid sequence identity with the adult liver enzyme in the rat and human, respectively. AdoMet synthetases possess the consensus ATP-binding motif Gly-X-Gly-X-X-Gly and a putative ATP-binding Lys residue at conserved locations. As an initial step toward understanding the control of AdoMet synthetase gene expression, we characterized the complete transcription unit of this gene. The AdoMet synthetase gene spans approximately 18 kilobases and consists of nine exons ranging from 78 to 1920 bp. The transcription initiation site was demonstrated by rapid amplification of cDNA ends and confirmed by primer extension studies. A putative TATA box is located at -28 to -23 bp upstream of the transcription start site. The cis-acting DNA elements in the 5'-flanking region of the AdoMet synthetase gene that drive chloramphenicol acetyltransferase gene expression in mouse hepatocytes were identified by transient expression assays. The -365 to -2-bp DNA region upstream of the transcription start site of the AdoMet synthetase gene contains promoter elements, and the -518 to -366-bp DNA region might be involved in negative gene regulation.

Expression of hepatic mitochondrial carbonic anhydrase V

We have raised specific (rabbit anti-rat) polyclonal antibodies to hepatic mitochondrial anhydrase V (CA V) and used them to assay the amounts of protein expressed in liver mitochondria isolated form term-foetal, control or diabetic adult rats and in perivenous and periportal rat hepatocytes. The levels of CA V expressed in mitochondria isolated from the livers of adult male and female rats are similar and increase (about 2-fold) in mitochondria from adult diabetic rats when compared to those isolated from the livers of control rats. The level of enzyme in adult liver was higher than in the livers of term-foetal rats. CA V is expressed in both perivenous and periportal hepatocytes, but the level of expression is greater (approx. 40%) in perivenous cells. The implications and significance of these findings are discussed with reference to the roles and properties of the other carbonic anhydrase isoenzymes and the metabolic function of the mitochondrial isoenzyme.

Developmental alterations in hepatic UDP-glucuronosyltransferase: A comparison of the kinetic properties of enzymes from adult sheep and fetal lambs

The kinetic properties of hepatic microsomal UDP-glucuronosyltransferase were studied in sheep in the perinatal period, using acetaminophen as the aglycone. Kinetic analyses indicated that activity at V max was significantly less in fetal microsomes (113, 135 or 141 days) as compared with the adult sheep. However, these differences between fetal and adult animals were not due simply to smaller amounts of UDP-glucuronosyltransferases catalyzing conjugation of acetaminophen in fetuses versus adults. Thus, the kinetic properties of UDP-glucuronosyltransferase(s) were different in fetus and adult. The “fetal” versus “adult” enzyme had a higher affinity for UDP-glucuronic acid, but a poorer affinity for acetaminophen. Furthermore, enzyme in fetal liver (113 days of gestation) was activated about 30% by the allosteric effector UDP- N-acetylglucosamine, whereas enzyme in adult liver was activated by 500%. These differences between fetal and adult enzymes diminished just prior to parturition (141-day fetus). Enzyme in microsomes from the 141-day fetus responded to UDP- N-acetylglucosamine-like enzyme in adult microsomes and had affinities for substrates that were similar to “adult” enzymes. These data indicate that maturation of the system that glucuronidates acetaminophen is a complex process. It may involve the expression in fetuses of a type of UDP-glucuronosyltransferase that is different from that expressed in the adult. An alternative but not mutually exclusive possibility is that maturation of the glucuronidation system involves modification of enzyme function by alteration of the phospholipids in the immediate environment of UDP-glucuronosyltransferase within the microsomal membrane.