Oral branched-chain amino acid granules improve structure and function of human serum albumin in cirrhotic patients

Impaired Cholesterol Efflux Capacity rather than Low HDL-C Reflects Oxidative Stress under Acute Myocardial Infarction

AIMS

Acute myocardial infarction (AMI) causes irreversible damage to cardiomyocytes due to the discontinuation of oxygen supply and leads to systemic oxidative stress. It has been reported that high-density lipoprotein (HDL) particles have antioxidant capacity, and reduced antioxidant capacity is associated with decreased cholesterol efflux capacity (CEC). The purpose of this study was to clarify the usefulness of CEC measurement in patients with AMI.

METHODS

We investigated the association between CEC and oxidative stress status in a case-control study. This study included 193 AMI cases and 445 age- and sex-matched controls. We examined the associations of CEC with HDL-cholesterol (HDL-C) and oxidized human serum albumin (HSA), an index of systemic oxidative stress status, and the effect of aldehyde dehydrogenase 2 (ALDH2) rs671 polymorphism, which has been reported to affect HDL-C level and risk for MI, on these associations.

RESULTS

Both bivariable and multivariable analyses showed that CEC was positively correlated with HDL-C levels in both AMI cases and controls, with a weaker correlation in AMI cases than in controls. In AMI cases, oxidized HSA levels were associated with CEC in both bivariable and multivariable analyses, but not with HDL-C. These associations did not differ among the ALDH2 genotypes.

CONCLUSIONS

CEC, but not HDL-C level, reflects systemic oxidative stress status in patients with AMI. CEC measurement for patients with AMI may be useful in that it provides information on systemic oxidative stress status as well as atherosclerosis risk.

The Thiol Group Reactivity and the Antioxidant Property of Human Serum Albumin Are Controlled by the Joint Action of Fatty Acids and Glucose Binding

The binding of ubiquitous serum ligands (free fatty acids) to human serum albumin (HSA) or its glycation can affect thiol group reactivity, thus influencing its antioxidant activity. The effects of stearic acid (SA) and glucose binding on HSA structural changes and thiol group content and reactivity were monitored by fluoroscopy and the Ellman method during a 14-day incubation in molar ratios to HSA that mimic pathophysiological conditions. Upon incubation with 5 mM glucose, HSA glycation was the same as HSA without it, in three different HSA:SA molar ratios (HSA:SA-1:1-2-4). The protective effect of SA on the antioxidant property of HSA under different glucose regimes (5-10-20 mM) was significantly affected by molar ratios of HSA:SA. Thiol reactivity was fully restored with 5-20 mM glucose at a 1:1 HSA:SA ratio, while the highest thiol content recovery was in pathological glucose regimes at a 1:1 HSA:SA ratio. The SA affinity for HSA increased significantly (1.5- and 1.3-fold, p < 0.01) with 5 and 10 mM glucose compared to the control. These results deepen the knowledge about the possible regulation of the antioxidant role of HSA in diabetes and other pathophysiological conditions and enable the design of future HSA-drug studies which, in turn, is important for clinicians when designing information-based treatments.

Current vision on diagnosis and comprehensive care in hepatic encephalopathy

The first clinical guidelines on hepatic encephalopathy were published in 2009. Almost 14 years since that first publication, numerous advances in the field of diagnosis, treatment, and special condition care have been made. Therefore, as an initiative of the Asociación Mexicana de Gastroenterología A.C., we present a current view of those aspects. The manuscript described herein was formulated by 24 experts that participated in six working groups, analyzing, discussing, and summarizing the following topics: Definition of hepatic encephalopathy; recommended classifications; epidemiologic panorama, worldwide and in Mexico; diagnostic tools; conditions that merit a differential diagnosis; treatment; and primary and secondary prophylaxis. Likewise, these guidelines emphasize the management of certain special conditions, such as hepatic encephalopathy in acute liver failure and acute-on-chronic liver failure, as well as specific care in patients with hepatic encephalopathy, such as the use of medications and types of sedation, describing those that are permitted or recommended, and those that are not.

Association Between the Redox State of Human Serum Albumin and Exercise Capacity in Patients With Cardiac Disease

The redox state of human serum albumin (HSA) is reported to be an oxidative stress biomarker; however, its clinical use in cardiac disease has not yet been examined. This study aimed to investigate the relation between the redox state of HSA and exercise capacity, which is a robust prognostic factor, in patients with cardiovascular disease. This cross-sectional study included outpatients with cardiac disease. Exercise capacity was assessed by peak oxygen consumption (peakVO₂) measured using symptom-limited cardiopulmonary exercise testing. The high-performance liquid chromatography postcolumn bromocresol green method was used to part HSA into human nonmercaptalbumin (oxidized form) and human mercaptalbumin (HMA, reduced form). The fraction of human mercaptalbumin found in HSA (f[HMA]) was calculated as an indicator of the redox state of HSA. The association between peakVO₂ and f(HMA) was examined using the Spearman correlation coefficient and multivariate linear regression analysis. A total of 70 patients were included (median age 76 years; 44 men; median peakVO₂ 15.5 ml/kg/min). The f(HMA) was positively correlated with peakVO₂ (r = 0.38, p <0.01). Even after controlling for potential confounders, this association remained in the multivariate linear regression analysis (standardized beta = 0.24, p <0.05). We found a positive association between f(HMA) and peakVO₂, independent of potential confounders in patients with cardiac disease, suggesting that f(HMA) may be a novel biomarker related to exercise capacity in cardiac disease. Longitudinal studies are required to further examine the prognostic capability of f(HMA), the responsiveness to clinical intervention, and the association between f(HMA) and cardiac disease.

Effect of dietary branched chain amino acids on liver related mortality: Results from a large cohort of North American patients with advanced HCV infection

Branched chain amino acids (BCAA) supplementation may reduce the incidence of liver failure and hepatocellular carcinoma in patients with cirrhosis. We aimed to determine whether long-term dietary intake of BCAA is associated with liver-related mortality in a well-characterized cohort of North American patients with advanced fibrosis or compensated cirrhosis. We performed a retrospective cohort study using extended follow-up data from the Hepatitis C Antiviral Long-term Treatment against Cirrhosis (HALT-C) Trial. The analysis included 656 patients who completed two Food Frequency Questionnaires. The primary exposure was BCAA intake measured in grams (g) per 1000 kilocalories (kcal) of energy intake (range 3.0-34.8 g/1000 kcal). During a median follow-up of 5.0 years, the incidence of liver-related death or transplantation was not significantly different among the four quartiles of BCAA intake before and after adjustment of confounders (AHR 1.02, 95% CI 0.81-1.27, P-value for trend = 0.89). There remains no association when BCAA was modeled as a ratio of BCAA to total protein intake or as absolute BCAA intake. Finally, BCAA intake was not associated with the risk of hepatocellular carcinoma, encephalopathy or clinical hepatic decompensation. We concluded that dietary BCAA intake was not associated with liver-related outcomes in HCV-infected patients with advanced fibrosis or compensated cirrhosis. The precise effect of BCAA in patients with liver disease warrants further study.

Predictive Ability of Visit-to-Visit Variability of HbA1c Measurements for the Development of Diabetic Kidney Disease: A Retrospective Longitudinal Observational Study

AIMS

This study is aimed at clarifying the relationship between visit-to-visit variability of glycated hemoglobin (HbA1c) and the risk of diabetic kidney disease (DKD) and to identifying the most useful index of visit-to-visit variability of HbA1c.

METHODS

This clinic-based retrospective longitudinal study included 699 Japanese type 2 diabetes mellitus patients. Visit-to-visit variability of HbA1c was calculated as the internal standard deviation of HbA1c (HbA1c-SD), the coefficient of variation of HbA1c (HbA1c-CV), the HbA1c change score (HbA1c-HVS), and the area under the HbA1c curve (HbA1c-AUC) with 3-year serial HbA1c measurement data, and the associations between these indices and the development/progression of DKD were examined.

RESULTS

Cox proportional hazards models showed that the HbA1c-SD and HbA1c-AUC were associated with the incidence of microalbuminuria, independently of the HbA1c level. These results were verified and replicated in propensity score (PS) matching and bootstrap analyses. Moreover, the HbA1c-SD and HbA1c-AUC were also associated with oxidized human serum albumin (HSA), an oxidative stress marker.

CONCLUSIONS

Visit-to-visit variability of HbA1c was an independent risk factor of microalbuminuria in association with oxidative stress among type 2 diabetes mellitus patients. HbA1c-AUC, a novel index of HbA1c variability, may be a potent prognostic indicator in predicting the risk of microalbuminuria.

Advanced oxidation protein products contribute to chronic kidney disease-induced muscle atrophy by inducing oxidative stress via CD36/NADPH oxidase pathway

BACKGROUND

Sarcopenia with chronic kidney disease (CKD) progression is associated with life prognosis. Oxidative stress has attracted interest as a trigger for causing CKD-related muscular atrophy. Advanced oxidation protein products (AOPPs), a uraemic toxin, are known to increase oxidative stress. However, the role of AOPPs on CKD-induced muscle atrophy remains unclear.

METHODS

In a retrospective case-control clinical study, we evaluated the relationship between serum AOPPs levels and muscle strength in haemodialysis patients with sarcopenia (n = 26, mean age ± SEM: 78.5 ± 1.4 years for male patients; n = 22, mean age ± SEM: 79.1 ± 1.5 for female patients), pre-sarcopenia (n = 12, mean age ± SEM: 73.8 ± 2.0 years for male patients; n = 4, mean age ± SEM: 74.3 ± 4.1 for female patients) or without sarcopenia (n = 12, mean age ± SEM: 71.3 ± 1.6 years for male patients; n = 7, mean age ± SEM: 77.7 ± 1.6 for female ). The molecular mechanism responsible for the AOPPs-induced muscle atrophy was investigated by using 5/6-nephrectomized CKD mice, AOPPs-overloaded mice, and C2C12 mouse myoblast cells.

RESULTS

The haemodialysis patients with sarcopenia showed higher serum AOPPs levels as compared with the patients without sarcopenia. The serum AOPPs levels showed a negative correlation with grip strength (P < 0.01 for male patients, P < 0.01 for female patients) and skeletal muscle index (P < 0.01 for male patients). Serum AOPPs levels showed a positive correlation with cysteinylated albumin (Cys-albumin), a marker of oxidative stress (r2  = 0.398, P < 0.01). In the gastrocnemius of CKD mice, muscle AOPPs levels were also increased, and it showed a positive correlation with atrogin-1 (r2  = 0.538, P < 0.01) and myostatin expression (r2  = 0.421, P < 0.05), but a negative correlation with PGC-1α expression (r2  = 0.405, P < 0.05). Using C2C12 cells, AOPPs increased atrogin-1 and myostatin expression through the production of reactive oxygen species via CD36/NADPH oxidase pathway, and decreased myotube formation. AOPPs also induced mitochondrial dysfunction. In the AOPPs-overloaded mice showed that decreasing running time and hanging time accompanied by increasing AOPPs levels and decreasing cross-sectional area in gastrocnemius.

CONCLUSIONS

Advanced oxidation protein products contribute to CKD-induced sarcopenia, suggesting that AOPPs or its downstream signalling pathway could be a therapeutic target for the treatment of CKD-induced sarcopenia. Serum AOPPs or Cys-albumin levels could be a new diagnostic marker for sarcopenia in CKD.

Effect of Cinacalcet on the Redox Status of Albumin in Secondary Hyperparathyroidism Patients Receiving Hemodialysis

Chronic kidney disease (CKD) patients with secondary hyperparathyroidism (SHPT) have an increased risk of cardiovascular disease (CVD). Cinacalcet is a calcimimetic that permits impaired endothelial functions to be recovered via inhibiting parathyroid hormone (PTH) production in SHPT patients. However, the underlying mechanism for its action remains unknown. The purpose of this study was to examine the effect of cinacalcet on the redox state of human serum albumin (HSA), a reliable marker for assessing endothelial oxidative damage in SHPT patients who were receiving hemodialysis. Cinacalcet was administered to six SHPT patients for a period of 8 weeks. After 4 weeks of treatment, cinacalcet significantly decreased the oxidized albumin ratio which is a ratio of reduced and oxidized forms of HSA via increasing reduced form of HSA. Moreover, the radical scavenging abilities of HSA that was isolated from SHPT patients were increased by cinacalcet, suggesting the recovery of the impaired vascular anti-oxidant ability. Interestingly, the oxidized albumin ratio in SHPT patients was significantly higher than that in hemodialysis patients. In addition, the changes of intact PTH levels were significantly correlated with the oxidized albumin ratio. It therefore appears that PTH may induce oxidative stress in SHPT patients. In fact, an active analogue of PTH increased the production of reactive oxygen species in human endothelial cells. Thus, cinacalcet exhibits anti-oxidative activity through its pharmacological action. Additionally, cinacalcet itself showed radical scavenging activity. In conclusion, cinacalcet improves the redox status of HSA by inhibiting PTH production and partially by its radical scavenging action.

Human Nonmercaptalbumin Is a New Biomarker of Motor Function

The ratio of human nonmercaptalbumin (HNA) and reduced albumin (HMA) may be a new marker for oxidative stress. Locomotive syndrome (LS) is reduced mobility due to impairment of locomotive organs. We investigated whether the HNA/HMA ratio could be a new biomarker of LS. This study included 306 subjects (mean age 64.24 ± 10.4 years) who underwent LS tests, grip strength, walking speed, and tests for HNA and HMA. Oxidative stress was measured by the ratio of HMA (f(HMA) = (HMA/(HMA + HNA) × 100)), and the subjects were divided into normal (N group; f[HMA] ≥ 70%) and low (L group; f[HMA] < 70%) groups. There were 124 non-elderly (<65 years) and 182 elderly subjects (≥65 years). There were no significant differences in LS, grip strength, and walking speed between the L and N groups in the non-elderly subjects. However, significant differences were found in the elderly subjects. In logistic regression analysis, there was an association between f(HMA) and the LS severity at older ages. LS in the elderly is associated with a decline in HMA and, thus, an increase in oxidative stress. Thus, f(HMA) is a new biomarker of LS.

Efficacy of rifaximin, a poorly absorbed rifamycin antimicrobial agent, for hepatic encephalopathy in Japanese patients

AIM

Rifaximin is recommended as treatment for hepatic encephalopathy (HE) that targets intestinal bacterial flora. Although combined use with synthetic disaccharides is the standard of care worldwide, the therapeutic effects of rifaximin for overt encephalopathy (OHE) in Japanese patients have not been examined sufficiently. We examined the therapeutic effects of rifaximin for OHE in Japanese patients.

METHODS

A total of 76 patients who developed OHE of West Haven grade II or higher at least once within the 12 months before starting rifaximin were included. Blood ammonia levels and the incidence of OHE during the 12 months before and after starting rifaximin therapy were compared in a before-and-after study. Rifaximin efficacy and predictors of efficacy were also examined.

RESULTS

Post-treatment blood ammonia levels were significantly lower than pretreatment levels. The mean annual number of OHE incidents and intravenous branched-chain amino acid preparations used per patient were significantly lower after starting rifaximin therapy (2.51 vs. 0.76 times/year, p < 0.001; and 71.9 vs. 20.7 preparations/year, p = 0.003, respectively). The cumulative incidence of hospitalizations associated with HE significantly decreased after rifaximin therapy (hazard ratio 0.187; p < 0.001). The efficacy rate, defined as the proportion of patients without OHE during the administration of rifaximin for 1 year after starting rifaximin therapy, was 65.8%. Serum albumin ≥2.7 g/dl was an independent predictor of efficacy.

CONCLUSION

Rifaximin was associated with decreased blood ammonia levels, lower incidence of OHE, and fewer hospitalizations in Japanese patients with HE. In addition, serum albumin level was an important predictor on efficacy of rifaximin.

Serum Albumin Redox States: More Than Oxidative Stress Biomarker

Serum albumin is the most abundant circulating protein in mammals including humans. It has three isoforms according to the redox state of the free cysteine residue at position 34, named as mercaptalbumin (reduced albumin), non-mercaptalbumin-1 and -2 (oxidized albumin), respectively. The serum albumin redox state has long been viewed as a biomarker of systemic oxidative stress, as the redox state shifts to a more oxidized state in response to the severity of the pathological condition in various diseases such as liver diseases and renal failures. However, recent ex vivo studies revealed oxidized albumin per se could aggravate the pathological conditions. Furthermore, the possibility of the serum albumin redox state as a sensitive protein nutrition biomarker has also been demonstrated in a series of animal studies. A paradigm shift is thus ongoing in the research field of the serum albumin. This article provides an updated overview of analytical techniques for serum albumin redox state and its association with human health, focusing on recent findings.

Association between serum albumin and cognitive dysfunction in hepatic encephalopathy: An exploratory data analysis

Background and Aim

Because covert hepatic encephalopathy (CHE) has been shown to affect the prognosis of cirrhotic patients, early diagnosis of hepatic encephalopathy (HE) is a prerequisite for the preservation of patients' quality of life and for prophylaxis of overt HE. The aim of this study was to identify a clinical parameter to predict impairment of cognitive function in cirrhotic patients with early‐stage HE.

Methods

We investigated the data from 172 patients with cirrhotic or idiopathic portosystemic shunt (PSS) in phase II/III trials of rifaximin in Japan. Classification and regression trees (CARTs) were constructed to identify clinical profiles related to cognitive dysfunction as indicated by the prolongation of time required for the Number Connection Test (NCT‐B).

Results

CART analysis detected age 65 years as the variable for the initial split, and serum albumin level was selected as the variable for the second split among patients aged ≤65 years. In 27 cirrhotic patients aged ≤65 years without PSS, receiver operating characteristic curve analysis revealed that the optimal albumin level cutoff point was 3.05 g/dL, and the area under the curve was 0.80 for the prolongation of NCT‐B time, which was higher than that of the branched‐chain amino acids‐to‐tyrosine ratio (0.46), the prothrombin time–international normalized ratio (PT‐INR) (0.68), serum ammonia (0.61), and total bilirubin (0.69).

Conclusions

Lower serum albumin level as a clinical biomarker associated with impaired cognitive function may be available as a screening examination for early‐stage HE in cirrhotic patients aged ≤65 years without PSS before undergoing neuropsychological tests.

Important Unresolved Questions in the Management of Hepatic Encephalopathy: An ISHEN Consensus

Management of hepatic encephalopathy (HE) remains challenging from a medical and psychosocial perspective. Members of the International Society for Hepatic Encephalopathy and Nitrogen Metabolism recognized 5 key unresolved questions in HE management focused on (i) driving, (ii) ammonia levels in clinical practice, (iii) testing strategies for covert or minimal HE, (iv) therapeutic options, and (v) nutrition and patient-reported outcomes. The consensus document addresses these topical issues with a succinct review of the literature and statements that critically evaluate the current science and practice, laying the groundwork for future investigations.

Changes in redox state of albumin before and after kidney transplantation in patients with end-stage renal disease

OBJECTIVES

Cardiovascular disease is one of the major causes of death in patients with end-stage kidney disease who have undergone kidney transplantation. Since the complication of cardiovascular disease in patients with chronic kidney disease is strongly linked to oxidative stress, understanding the oxidative stress condition after kidney transplantation would be of great importance for the prevention of cardiovascular disease. This study examined whether improvement of renal function after kidney transplantation has an impact on the redox state of the Cys34 residue of albumin that reflects the level of oxidative stress in blood.

DESIGN & METHODS

We enrolled 23 patients with end-stage renal failure who received kidney transplantation. All patients were followed for 180 days after transplantation. The fractions of albumin isoforms were determined by the electrospray ionization time-of-flight mass spectrometry (ESI-TOFMS) method.

RESULTS

Serum creatinine decreased significantly immediately after kidney transplantation, suggesting successful transplantations. The ESI-TOFMS method identified three albumin isoforms cysteinylated at the Cys34 residue (Cys-Cys34-albumin) and the three corresponding albumin isoforms without Cys34 cysteinylation. The fraction of total Cys-Cys34-albumin decreased transiently after kidney transplantation, and was followed by an elevation at day 7 and gradual decrease thereafter until day 180. Meanwhile, reduced albumin concentration did not change until day 14 after kidney transplantation, then showed a significant increase compared to pre-transplant level at day 30 and remained stably elevated until day 180.

CONCLUSIONS

Actual reduced albumin levels were found to exceed pre-transplant levels on or after day 30 following kidney transplantation unlike immediate restoration of renal function. Renal function was recovered immediately following kidney transplantation, but reduced albumen concentration increased above the pre-transplant levels only from day 30 after transplantation.

The DsbA-L gene is associated with respiratory function of the elderly via its adiponectin multimeric or antioxidant properties

Oxidative stress and inflammation play a key role in the age-related decline in the respiratory function. Adipokine in relation to the metabolic and inflammatory systems is attracting growing interest in the field of respiratory dysfunction. The present clinical and experimental studies investigated the role of the disulfide bond-forming oxidoreductase A-like protein (DsbA-L) gene, which has antioxidant and adiponectin multimeric (i.e. activation) properties, on the respiratory function of the elderly. We performed a retrospective longitudinal genotype-phenotype relationship analysis of 318 Japanese relatively elderly participants (mean age ± standard deviation: 67.0 ± 5.8 years) during a health screening program and an in vitro DsbA-L knock-down evaluation using 16HBE14o-cells, a commonly evaluated human airway epithelial cell line. The DsbA-L rs1917760 polymorphism was associated with a reduction in the ratio of forced expiratory volume in 1 second (FEV1)/forced vital capacity (FVC) and %FEV1 and with the elevation of the prevalence of FEV1/FVC < 70%. We also confirmed that the polymorphism was associated with a decreased respiratory function in relation to a decrease in the ratio of high-molecular-weight adiponectin/total adiponectin (as a marker of adiponectin multimerization) and an increase in the oxidized human serum albumin (as an oxidative stress marker). Furthermore, we clarified that DsbA-L knock-down induced oxidative stress and up-regulated the mucus production in human airway epithelial cells. These findings suggest that the DsbA-L gene may play a role in protecting the respiratory function of the elderly, possibly via increased systemic adiponectin functions secreted from adipocytes or through systemic and/or local pulmonary antioxidant properties.

Melinjo seed extract increases adiponectin multimerization in physiological and pathological conditions

Melinjo seed extract (MSE) contains large amounts of polyphenols, including dimers of trans-resveratrol (e.g. gnetin C, L, gnemonoside A, B and D), and has been shown to potentially improve obesity. However, there is no clinical evidence regarding the anti-obesity effects of MSE, and its mechanisms are also unclear. We investigated the hypothesis that MSE supplementation increases the adiponectin (APN) multimerization via the up-regulation of disulfide bond A oxidoreductase-like protein (DsbA-L) under either or both physiological and obese conditions. To investigate the effect of MSE on the physiological condition, 42 healthy young volunteers were enrolled in a randomized, double-blind placebo-controlled clinical trial for 14 days. The participants were randomly assigned to the MSE 150 mg/day, MSE 300 mg/day or placebo groups. Furthermore, in order to investigate the effect of MSE on APN levels under obese conditions, we administered MSE powder (500 or 1000 mg/kg/day) to control-diet- or high-fat-diet (HFD)-fed C57BL/6 mice for 4 weeks. All participants completed the clinical trial. The administration of MSE 300 mg/day was associated with an increase in the ratio of HMW/total APN in relation to the genes regulating APN multimerization, including DsbA-L. Furthermore, this effect of MSE was more pronounced in carriers of the DsbA-L rs191776 G/T or T/T genotype than in others. In addition, the administration of MSE to HFD mice suppressed their metabolic abnormalities (i.e. weight gain, increased blood glucose level and fat mass accumulation) and increased the levels of total and HMW APN in serum and the mRNA levels of ADIPOQ and DsbA-L in adipose tissue. The present study suggests that MSE may exert beneficial effects via APN multimerization in relation to the induction of DsbA-L under both physiological and obese conditions.

A More Oxidized Plasma Albumin Redox State and Lower Plasma HDL Particle Number Reflect Low-Protein Diet Ingestion in Adult Rats

BACKGROUND

Plasma albumin (ALB) redox state reflects protein nutritional status, but how it differs from other protein nutrition biomarkers remains to be fully elucidated.

OBJECTIVE

This study aimed to delineate the characteristics of plasma ALB redox state as a protein nutrition biomarker.

METHODS

Adult male Wistar rats were maintained on an AIN-93 M [14% casein, control (CT)] diet or an AIN-93 M-based 5% casein [low protein (LP)] diet ad libitum for 4 wk. Plasma samples were repeatedly obtained from the same rats at weeks 0-4, ALB redox state was determined by HPLC, and the concentrations of conventional protein nutrition biomarkers, ALB and transthyretin (TTR), were compared between the groups by Student t test. Body mass, relative muscle masses, plasma proteome, and plasma lipids at week 4 were also compared.

RESULTS

Plasma ALB redox state shifted to a more oxidized state in the LP diet group compared with the CT diet group at weeks 1-4. The LP diet group also showed significantly lower plasma ALB concentrations at weeks 1 and 2 (13% and 11% lower, respectively) and significantly lower TTR concentration at week 1 (21% lower) compared with the CT diet group, but these concentrations did not differ significantly at weeks 3 and 4. After 4 wk, body mass and relative soleus and gastrocnemius muscle masses did not differ, but the relative plantaris muscle mass tended to be 4% lower (1.75 compared with 1.68 g/kg body mass) in the LP diet group compared with the CT group (P = 0.06). The LP diet group also had a significantly lower HDL particle number than the CT group (30% lower).

CONCLUSIONS

A more oxidized plasma ALB redox state and lower plasma HDL particle number reflect LP diet ingestion in adult rats, which did not exhibit changes of plasma ALB and TTR concentrations.

Association between redox state of human serum albumin and exercise capacity in older women: A cross-sectional study

AIM

Oxidative stress plays a key role in declining exercise capacity, which is one of the major health problems in old age. The redox state of human serum albumin (HSA) has been considered a biomarker reflecting oxidative stress; however, its relationship to exercise capacity in older people remains to be examined. We aimed to examine the redox state of HSA as a potential biomarker of exercise capacity in community-dwelling older women.

METHODS

We analyzed 125 women aged ≥75 years. Exercise capacity was evaluated using 6-min walk distance (6MWD). The redox state of HSA was analyzed using the high-performance liquid chromatography post-column bromocresol green reaction method. The fraction of human mercaptalbumin in HSA (f[HMA]) was considered the redox state of HSA. Pearson's correlation coefficient (r) or Spearman's correlation coefficient (ρ) was used to assess correlations between 6MWD, f(HMA) and HSA. The association between 6MWD and f(HMA) was further examined using multivariate linear regression analysis adjusted for age, diabetes mellitus, renal function, number of medications, HSA and knee extensor isometric strength.

RESULTS

The 6MWD was significantly correlated with f(HMA; ρ = 0.44, P < 0.001), but not with HSA (r = 0.05, P = 0.562). The f(HMA) was not significantly correlated with HSA (ρ = 0.03, P = 0.769). Multivariate linear regression analysis showed that f(HMA) was independently associated with 6MWD (standardized β = 0.27, P = 0.004).

CONCLUSIONS

The findings of this study suggest that f(HMA) might serve as a novel biomarker for exercise capacity in community-dwelling older women. Geriatr Gerontol Int 2019; ••: ••-••.

Impaired albumin function: a novel potential indicator for liver function damage?

Albumin is the most abundant plasma protein and albumin infusion is commonly used. Conventionally, the biologic and therapeutic effects of albumin have been thought to be due to its oncotic properties. However, albumin has a variety of biologic functions, including molecular transport, anti-oxidation, anti-inflammation, endothelial stabilisation, anti-thrombotic effects, and the adjustment of capillary permeability. Despite this, the functions of albumin have not been thoroughly investigated. Recent studies have shown non-alcoholic fatty liver disease (NAFLD), viral hepatitis, cirrhosis, and liver failure to be associated with impairments in albumin function, which are associated with impairments in liver function and disease prognosis. Post-translational modifications of albumin cause structural modifications that affect protein function. Recently, the concentration of albumin associated with normal function, the 'efficient albumin concentration', has been attracting more interest. In addition, although many biologic markers, including albumin concentration, are widely used for the assessment of early liver dysfunction in patients with liver diseases, the predictive values are unsatisfactory. However, clinical evidence has suggested that albumin function may represent a novel biomarker of early impairment in liver function. In this review, we summarise the factors affecting albumin function and discuss the clinical significance of impairments in albumin function in various liver diseases.Key messagesThe importance of albumin depends not only on its concentration, but also on its various physiological functions.Impaired albumin function has been reported in a variety of liver diseases, and is associated with disease severity and prognosis, thereby proposing the concept of 'effective albumin concentration'.Albumin dysfunction occurs earlier than other conventional indicators, and albumin dysfunction may be a new biomarker of early impairment in liver function.Many exogenous and endogenous factors lead to post-translational modifications of albumin, which alters the three-dimensional structure of albumin, resulting in a decrease in its biological activity.

Plasma Albumin Redox State Is Responsive to the Amino Acid Balance of Dietary Proteins in Rats Fed a Low Protein Diet

We recently reported that plasma albumin redox state, which correlates with albumin synthesis rate, could be associated with the quality of dietary protein. Aiming to elucidate the association between them, plasma albumin redox state was investigated in rats fed various kinds of AIN-93G-based low protein diets. Plasma albumin redox state was shifted to a more oxidized state in rats fed 3% casein (CN) diet than those fed 3% whey protein or 3% wheat gluten diet, while supplementing 3% CN diet with cystine reversed it to a more reduced state, indicating that cystine would complement the shortage of cysteine in CN, thereby increasing albumin synthesis rate. Supplementation with glutathione, a cysteine-containing antioxidative tripeptide, normalized hepatic glutathione redox state modulated by ingestion of 3% CN diet, but it only reversed the oxidized shift of plasma albumin redox state to an extent similar to cystine alone or the constituting amino acid mixture of glutathione (i.e., glutamic acid, cystine, and glycine), indicating that glutathione would primarily serve as a source of cysteine rather than exert its antioxidative activity. Plasma albumin would thus be influenced by amino acid balance in dietary proteins, and it could be useful as a biomarker that contributes to prevention of protein under-nutriton, caused by not only insufficient protein intake but also ingestion of poor-quality protein.

Increased Ratio of Non-mercaptalbumin-1 Among Total Plasma Albumin Demonstrates Potential Protein Undernutrition in Adult Rats

The redox state of plasma albumin shifts in response to dietary protein intake in growing rats, and the shift is more sensitive than that of plasma albumin level, a classical marker of protein nutritional status. While it has been suggested that plasma albumin redox state could be useful as a novel marker of protein nutritional status, the above animal model is highly sensitive to dietary protein intake and the observation may not be extrapolated widely to humans. This study aimed to investigate whether albumin redox state also reflects protein nutritional status in adult rats, which have a lower dietary protein requirement and are less responsive to protein intake. Male adult rats were placed on AIN-93M diet (14% casein), or AIN-93M-based low protein diets (10 or 5% casein) ad libitum for 24 weeks. Whereas there was no significant difference in body weight between the groups at the end of the experimental period, the 5% casein diet group had the smallest gastrocnemius muscle weight among the groups, which was significantly lower than that of the 10% casein diet group. Plasma albumin level was also lower in the 5% casein diet group compared with the other groups, but the differences were limited and inconsistent during the experimental period. Among the albumin redox isoforms such as mercaptalbumin, non-mercaptalbumin-1, and non-mercaptalbumin-2, the ratio of non-mercaptalbumin-1 among total albumin was significantly higher in the 5% casein diet group, and the increase remained constant throughout the experimental period. Increased non-mercaptalbumin-1 ratio would thus demonstrate the presence of potential protein undernutrition in adult rats, as manifested only by a decreased gain in a specific type of skeletal muscle; non-mercaptalbumin-1 among total albumin ratio could be useful as a robust marker of protein nutritional status, contributing to prevention of protein undernutrition-related diseases such as frailty and sarcopenia.

Modeling of the Weight Status and Risk of Nonalcoholic Fatty Liver Disease in Elderly Individuals: The Potential Impact of the Disulfide Bond-Forming Oxidoreductase A-Like Protein (DsbA-L) Polymorphism on the Weight Status

Nonalcoholic fatty liver disease (NAFLD) is closely associated with obesity. Disulfide bond‐forming oxidoreductase A‐like protein (DsbA‐L) is known to be a key molecule in protection against obesity and obesity‐induced inflammation. In the present study, we used a modeling and simulation approach in an attempt to develop body mass index (BMI) and BMI‐based NAFLD prediction models incorporating the DsbA‐L polymorphism to predict the BMI and NAFLD in 341 elderly subjects. A nonlinear mixed‐effect model best represented the sigmoidal relationship between the BMI and the logit function of the probability of NAFLD prevalence. The final models for BMI and NAFLD showed that DsbA‐L rs1917760 polymorphism, age, and gender were associated with the BMI, whereas gender, patatin‐like phospholipase 3 rs738409 polymorphism, HbA1c, and high‐density and low‐density lipoprotein cholesterol levels were associated with the risk of NAFLD. This information may aid in the genetic‐based prevention of obesity and NAFLD in the general elderly population.

Potential Role of Amino Acid/Protein Nutrition and Exercise in Serum Albumin Redox State

Albumin is the major protein in the serum of mammals. It is synthesized exclusively in the liver, before being secreted into the circulation. Similar to skeletal muscle protein, albumin synthesis is stimulated by dietary amino acids and proteins as well as exercise. Albumin has three isoforms based on the redox states of the free cysteine residue at position 34. The redox state of serum albumin has long been extensively investigated in terms of oxidative stress-related chronic diseases, with the redox state of serum albumin having been regarded as a marker of systemic oxidative stress. However, according to recent animal studies, the redox state of serum albumin is modulated by albumin turnover and may also reflect amino acid/protein nutritional status. Furthermore, as the redox state of serum albumin is modulated by exercise training, measuring the pre- and post-exercise redox states of serum albumin in athletes may be useful in assessing amino acid/protein nutritional status and exercise-induced oxidative stress, which are closely associated with skeletal muscle adaptive responses. This article extensively reviews serum albumin and the redox state of albumin in the context of amino acid/protein nutritional status and exercise training.