Albumin Deficiency Reduces Hepatic Steatosis and Improves Glucose Metabolism in a Mouse Model of Diet-Induced Obesity

Metabolic responses to albumin deficiency differ distinctly between partial and full ablation of albumin expression in mice

It had been observed that homozygous albumin knockout mice (Alb-/-) exhibit low plasma free fatty acid (FFA) concentration and improved blood glucose regulation. However, it was not yet known to what extent heterozygous albumin knockout (Alb+/-) mice would display a similar phenotype. Alb-/-, Alb+/-, and wild-type (WT) female mice were studied on a low-fat diet (LFD) or high-fat diet (HFD). On both diets, decreased plasma FFA concentration, and improved glucose tolerance test were observed in Alb-/-, but not in Alb+/-, compared to WT. Plasma adiponectin concentration showed greater elevation in Alb-/- than Alb+/-. Consistent with that, adiponectin gene expression was significantly higher in Alb-/- mice than in Alb+/- and WT mice. A dose-dependent response was observed for hepatic Acadl gene expression showing higher Acadl gene expression in Alb-/- mice than in Alb+/- and WT mice. In conclusion, although female Alb+/- mice exhibited some slight differences from WT mice (e.g., increased plasma adiponectin and hepatic Acadl gene expression), Alb+/- mice did not exhibit improved glucoregulation in comparison to WT mice, indicating that a minor suppression of albumin expression is not sufficient to improve glucoregulation. Furthermore, it is now clear that although the response of female mice to HFD might be unique from how males generally respond, still the complete albumin deficiency in Alb-/- mice and the associated FFA reduction is capable of improving glucoregulation in females on this diet. The present results have implications for the role of albumin and FFA in the regulation of metabolism.

Risk of hepatic steatosis with the preoperative treatment of pancreatic cancer and the short-term postoperative outcomes

PURPOSE

We investigated whether the preoperative treatment of patients with pancreatic cancer is a risk factor for hepatic steatosis (HS), and whether preoperative HS affects the short-term postoperative outcomes.

METHODS

Patients who underwent radical surgery for pancreatic cancer between 2010 and 2023 were enrolled. The patients' medical records were reviewed. Albumin and carbohydrate antigen 19-9 were measured before and after chemotherapy in the patients who received preoperative chemotherapy. A logistic regression univariate analysis was performed to analyze the factors associated with new-onset HS.

RESULTS

A total of 230 patients who underwent surgery were included. HS was observed on the date of surgery in 11 (10%) and two (2%) patients with and without preoperative chemotherapy, respectively. Female sex, initially borderline resectable or unresectable disease, history of cholangitis, presence of PEI, long-term (≥ 3 months) biliary drainage, preoperative chemotherapy, and serum albumin ≥ 3.9 mg/dl before chemotherapy were identified as risk factors for HS. The incidence of postoperative morbidity did not differ between the patients with and without preoperative steatosis.

CONCLUSIONS

Preoperative chemotherapy, a history of cholangitis, the presence of PEI, and ≥ 3 months' duration of biliary drainage were risk factors for the development of HS before surgery for pancreatic cancer. However, preoperative HS did not affect the short-term postoperative outcomes.

Albumin is an important factor in the control of serum free fatty acid flux in both male and female mice

Albumin knockout (Alb-/-) mice exhibit a low plasma free fatty acid (FFA) concentration, but it was not known if the suppressed concentration reflects a lower rate of appearance (Ra) of FFA in the circulation (i.e., lower FFA flux) or if the absence of albumin alters the relationship between FFA flux and concentration. For understanding the role of albumin in FFA transport through the bloodstream, it is not sufficient to rely on FFA concentration data alone. Therefore, we developed a method to study FFA kinetics in Alb-/- mice. Using an albumin-free formulation of [U-13C]palmitate tracer, serum FFA kinetics were tested in Alb-/- and wild-type (WT) mice. Results indicate that the flux of FFA in serum of Alb-/- mice was significantly lower than in WT mice (P < 0.05), while albumin deficiency did not alter the relationship between FFA flux and concentration. Next, to test if suppressed lipolysis might have also been involved in the suppressed FFA kinetics, gene expression of a lipolytic enzyme (adipose triglyceride lipase, Atgl) and a marker of lipolysis (phosphorylation of hormone-sensitive lipase, p-HSL) were measured in adipose tissue. In contrast to the low FFA flux in Alb-/-, both Atgl gene expression and p-HSL protein were significantly higher in adipose tissue of Alb-/- than in WT mice (P < 0.05). Thus, the low FFA flux in Alb-/- appeared to be driven by the absence of albumin's FFA binding functions rather than through regulation of lipolysis, indicating that albumin is an important factor in determining the flux of FFA in circulation.NEW & NOTEWORTHY To improve understanding of the albumin protein's function in vivo, we tested plasma free fatty acid kinetics in albumin knockout mice compared with wild-type mice. Using a new tracer formulation strategy, it was discovered that the appearance rate of free fatty acids in serum is lower in albumin knockout mice than in wild-type mice. The results indicate that albumin is a major controller of free fatty acid kinetics.

Performance evaluation of different albumin assays for the detection of analbuminemia

Analbuminemia is characterized by the near absence of albumin in the plasma. Different methods are available for measuring albumin levels, but they do not necessarily agree with one another. It is a concern that analbuminemic samples could be falsely characterized due to the incorrect estimation of albumin. The objective of the work was to evaluate the performance of different assays in detecting analbuminemia. Albumin knockout (Alb-/-) mouse plasma was used to test the suitability of different albumin assays for their ability to properly characterize extreme albumin deficiency. Bromocresol green (BCG), bromocresol purple (BCP), enzyme-linked immunosorbent assay (ELISA), liquid chromatography-tandem mass spectrometry (LC-MS/MS), and gel electrophoresis were tested. The LC-MS/MS assay exhibited broad coverage of the amino acid sequence of albumin and indicated 8,400-fold lower (P<0.0001) albumin expression in Alb-/- than wildtype (WT), demonstrating its suitability for identifying extreme albumin deficiency. ELISA estimated albumin at 1.5±0.1 g/dL in WT and was below the detection limit in all Alb-/- samples. Gel electrophoresis yielded consistent results with LC-MS/MS and ELISA. The BCG assay overestimated albumin with apparently appreciable albumin concentrations in Alb-/- mice, yet the assay still indicated a significant difference between genotypes (Alb-/-, 1.2±0.05 g/dL, WT, 3.7±0.1 g/dL, P<0.0001). BCP drastically overestimated albumin and could not successfully identify the known analbuminemic phenotype of Alb-/- mice. By using Alb-/- plasma as a reference material and LC-MS/MS as a reference method, ELISA and gel electrophoresis appear appropriate for identifying analbuminemia, while BCG and BCP are not suitable. It is concluded that dye-binding assays should be avoided when extreme hypoalbuminemia or analbuminemia is suspected.

Combining albumin deficiency and acute exercise reduces hepatic lipid droplet size in mice

Hepatic lipid droplets (LDs) are implicated in ectopic lipid accumulation. The core of LDs, triacylglycerol (TAG), is synthesized from the esterification of fatty acids to a glycerol-3-phosphate (G-3-P) backbone. Albumin transports plasma free fatty acids, and previously albumin knockout (Alb^-/-) mice were shown to exhibit lower hepatic TAG levels than wildtype (WT). Exercise is a beneficial strategy to alter hepatic metabolism, but its impacts on reducing hepatic lipids are far from satisfactory. The aim of this study was to investigate the combined effect of albumin deficiency and acute exercise on hepatic LDs. Eight-week-old male Alb^-/- and WT mice were divided into sedentary and exercise groups. Exercised mice performed a 30-min high-intensity exercise bout. Results showed that sedentary Alb^-/- mice had smaller hepatic LDs (P < 0.0001), associated with mitochondria, while WT mice exhibited larger LDs, surrounded by glycogen granules. Following acute exercise, hepatic LDs in Alb^-/- mice reduced by 40% in size, while in WT increased by 14% (P < 0.0001). The maintenance of WT hepatic LDs was associated with elevated G-3-P level (P < 0.05), potentially derived from glycogen (R = -0.32, %change in glycogen versus LD content, P < 0.05). The reduction in Alb^-/- mice LDs after exercise was possibly due to their low glycogen level. In conclusion, Alb^-/- mice exhibited an enhanced capacity for reducing hepatic LD size and content in response to exercise. These findings suggest that modulating albumin's functions combined with exercise could be a potential strategy to reduce ectopic lipid deposition in the liver.