ATGL-catalyzed lipolysis regulates SIRT1 to control PGC-1α/PPAR-α signaling

Sirtuin 1 (SIRT1), an NAD(+)-dependent protein deacetylase, regulates a host of target proteins, including peroxisome proliferator-activated receptor (PPAR)-γ coactivator-1α (PGC-1α), a transcriptional coregulator that binds to numerous transcription factors in response to deacetylation to promote mitochondrial biogenesis and oxidative metabolism. Our laboratory and others have shown that adipose triglyceride lipase (ATGL) increases the activity of the nuclear receptor PPAR-α, a PGC-1α binding partner, to promote fatty acid oxidation. Fatty acids bind and activate PPAR-α; therefore, it has been presumed that fatty acids derived from ATGL-catalyzed lipolysis act as PPAR-α ligands. We provide an alternate mechanism that links ATGL to PPAR-α signaling. We show that SIRT1 deacetylase activity is positively regulated by ATGL to promote PGC-1α signaling. In addition, ATGL mediates the effects of β-adrenergic signaling on SIRT1 activity, and PGC-1α and PPAR-α target gene expression independent of changes in NAD(+). Moreover, SIRT1 is required for the induction of PGC-1α/PPAR-α target genes and oxidative metabolism in response to increased ATGL-mediated lipolysis. Taken together, this work identifies SIRT1 as a critical node that links β-adrenergic signaling and lipolysis to changes in the transcriptional regulation of oxidative metabolism.

Hepatic ATGL mediates PPAR-α signaling and fatty acid channeling through an L-FABP independent mechanism

Adipose TG lipase (ATGL) catalyzes the rate-limiting step in TG hydrolysis in most tissues. We have shown that hepatic ATGL preferentially channels hydrolyzed FAs to β-oxidation and induces PPAR-α signaling. Previous studies have suggested that liver FA binding protein (L-FABP) transports FAs from lipid droplets to the nucleus for ligand delivery and to the mitochondria for β-oxidation. To determine if L-FABP is involved in ATGL-mediated FA channeling, we used adenovirus-mediated suppression or overexpression of hepatic ATGL in either WT or L-FABP KO mice. Hepatic ATGL knockdown increased liver weight and TG content of overnight fasted mice regardless of genotype. L-FABP deletion did not impair the effects of ATGL overexpression on the oxidation of hydrolyzed FAs in primary hepatocyte cultures or on serum β-hydroxybutyrate concentrations in vivo. Moreover, L-FABP deletion did not influence the effects of ATGL knockdown or overexpression on PPAR-α target gene expression. Taken together, we conclude that L-FABP is not required to channel ATGL-hydrolyzed FAs to mitochondria for β-oxidation or the nucleus for PPAR-α regulation.

Hepatic ATGL knockdown uncouples glucose intolerance from liver TAG accumulation

Adipose triglyceride lipase (ATGL) is the predominant triacylglycerol (TAG) hydrolase in mammals; however, the tissue-specific effects of ATGL outside of adipose tissue have not been well characterized. Hence, we tested the contribution of hepatic ATGL on mediating glucose tolerance and insulin action. Glucose or insulin tolerance tests and insulin signaling were performed in C57BL/6 mice administered control (nongene specific shRNA) or Atgl shRNA adenoviruses. Glucose and lipid metabolism assays were conducted in primary hepatocytes isolated from mice transduced with control or Atgl shRNA adenoviruses. Knocking down hepatic ATGL completely abrogated the increase in serum insulin following either 1 or 12 wk of feeding a high-fat (HF) diet despite higher hepatic TAG content. Glucose tolerance tests demonstrated that ATGL knockdown normalized glucose tolerance in HF-diet-fed mice. The observed improvements in glucose tolerance were present despite unaltered hepatic insulin signaling and increased liver TAG. Mice with suppressed hepatic ATGL had reduced hepatic glucose production in vivo, and hepatocytes isolated from Atgl shRNA-treated mice displayed a 26% decrease in glucose production and a 38% increase in glucose oxidation compared to control cells. Taken together, these data suggest that hepatic ATGL knockdown enhances glucose tolerance by increasing hepatic glucose utilization and uncouples impairments in insulin action from hepatic TAG accumulation.

Palmitoleate induces hepatic steatosis but suppresses liver inflammatory response in mice

The interaction between fat deposition and inflammation during obesity contributes to the development of non-alcoholic fatty liver disease (NAFLD). The present study examined the effects of palmitoleate, a monounsaturated fatty acid (16∶1n7), on liver metabolic and inflammatory responses, and investigated the mechanisms by which palmitoleate increases hepatocyte fatty acid synthase (FAS) expression. Male wild-type C57BL/6J mice were supplemented with palmitoleate and subjected to the assays to analyze hepatic steatosis and liver inflammatory response. Additionally, mouse primary hepatocytes were treated with palmitoleate and used to analyze fat deposition, the inflammatory response, and sterol regulatory element-binding protein 1c (SREBP1c) activation. Compared with controls, palmitoleate supplementation increased the circulating levels of palmitoleate and improved systemic insulin sensitivity. Locally, hepatic fat deposition and SREBP1c and FAS expression were significantly increased in palmitoleate-supplemented mice. These pro-lipogenic events were accompanied by improvement of liver insulin signaling. In addition, palmitoleate supplementation reduced the numbers of macrophages/Kupffer cells in livers of the treated mice. Consistently, supplementation of palmitoleate decreased the phosphorylation of nuclear factor kappa B (NF-κB, p65) and the expression of proinflammatory cytokines. These results were recapitulated in primary mouse hepatocytes. In terms of regulating FAS expression, treatment of palmitoleate increased the transcription activity of SREBP1c and enhanced the binding of SREBP1c to FAS promoter. Palmitoleate also decreased the phosphorylation of NF-κB p65 and the expression of proinflammatory cytokines in cultured macrophages. Together, these results suggest that palmitoleate acts through dissociating liver inflammatory response from hepatic steatosis to play a unique role in NAFLD.

Targeted overexpression of inducible 6-phosphofructo-2-kinase in adipose tissue increases fat deposition but protects against diet-induced insulin resistance and inflammatory responses

Increasing evidence demonstrates the dissociation of fat deposition, the inflammatory response, and insulin resistance in the development of obesity-related metabolic diseases. As a regulatory enzyme of glycolysis, inducible 6-phosphofructo-2-kinase (iPFK2, encoded by PFKFB3) protects against diet-induced adipose tissue inflammatory response and systemic insulin resistance independently of adiposity. Using aP2-PFKFB3 transgenic (Tg) mice, we explored the ability of targeted adipocyte PFKFB3/iPFK2 overexpression to modulate diet-induced inflammatory responses and insulin resistance arising from fat deposition in both adipose and liver tissues. Compared with wild-type littermates (controls) on a high fat diet (HFD), Tg mice exhibited increased adiposity, decreased adipose inflammatory response, and improved insulin sensitivity. In a parallel pattern, HFD-fed Tg mice showed increased hepatic steatosis, decreased liver inflammatory response, and improved liver insulin sensitivity compared with controls. In both adipose and liver tissues, increased fat deposition was associated with lipid profile alterations characterized by an increase in palmitoleate. Additionally, plasma lipid profiles also displayed an increase in palmitoleate in HFD-Tg mice compared with controls. In cultured 3T3-L1 adipocytes, overexpression of PFKFB3/iPFK2 recapitulated metabolic and inflammatory changes observed in adipose tissue of Tg mice. Upon treatment with conditioned medium from iPFK2-overexpressing adipocytes, mouse primary hepatocytes displayed metabolic and inflammatory responses that were similar to those observed in livers of Tg mice. Together, these data demonstrate a unique role for PFKFB3/iPFK2 in adipocytes with regard to diet-induced inflammatory responses in both adipose and liver tissues.

Adipose triglyceride lipase is a major hepatic lipase that regulates triacylglycerol turnover and fatty acid signaling and partitioning

Despite advances in our understanding of the ways in which nutrient oversupply and triacylglycerol (TAG) anabolism contribute to hepatic steatosis, little is known about the lipases responsible for regulating hepatic TAG turnover. Recent studies have identified adipose triglyceride lipase (ATGL) as a major lipase in adipose tissue, although its role in the liver is largely unknown. Thus, we tested the contribution of ATGL to hepatic lipid metabolism and signaling. Adenovirus-mediated knockdown of hepatic ATGL resulted in steatosis in mice and decreased hydrolysis of TAG in primary hepatocyte cultures and in vitro assays. In addition to altering TAG hydrolysis, ATGL was shown to play a significant role in partitioning hydrolyzed fatty acids between metabolic pathways. Although ATGL gain and loss of function did not alter hepatic TAG secretion, fatty acid oxidation was increased by ATGL overexpression and decreased by ATGL knockdown. The effects on fatty acid oxidation coincided with decreased expression of peroxisome proliferator-activated receptor α (PPAR-α) and its target genes in mice with suppressed hepatic ATGL expression. However, PPAR-α agonism was unable to normalize the effects of ATGL knockdown on PPAR-α target gene expression, and this suggests that ATGL influences PPAR-α activity independently of ligand-induced activation.

CONCLUSION

Taken together, these data show that ATGL is a major hepatic TAG lipase that plays an integral role in fatty acid partitioning and signaling to control energy metabolism.

Influence of storage conditions and type of plasticizers on ethylcellulose and acrylate films formed from aqueous dispersions

PURPOSE

To investigate the influence of storage conditions and types of plasticizers on the properties and stability of ethylcellulose and polymethacrylate films and to elucidate the mechanism for the changes observed.

METHODS

Films were prepared from Surelease, Aquacoat and Eudragit L 30D dispersions by the casting method. The effects of different plasticizers on the morphology, transparency, mechanical property and water vapour permeability of the prepared films were studied. The film samples were exposed to storage conditions of 30 degrees C and 50 or 75 %RH. Samples were removed at pre-determined time intervals for mechanical testing and analysis of plasticizer content in the films.

RESULTS

It was found that films prepared from aqueous ethylcellulose dispersions were relatively weaker and more brittle than acrylate films. Acrylate films did not show any significant change in mechanical property when stored at high humidity. However, the properties of ethylcellulose films stored at high humidity varied depending on the type of plasticizers present.

CONCLUSIONS

The changes in mechanical property of ethylcellulose films on storage were mainly attributed to the loss of plasticizers during storage, causing further coalescence of ethylcellulose films and to a smaller extent, reduction in moisture content of the film.

Oral intake and serum levels of ascorbic acid in continuous ambulatory peritoneal dialysis patients

Oral intake of ascorbic acid is essential for optimum health in human beings. Continuous ambulatory peritoneal dialysis (CAPD) patients have an increased need for ascorbic acid, because of increased loss through dialysate, reduced intake owing to nausea and loss of appetite, and increased oxidative stress. However, optimum intake is still controversial. We studied 50 clinically stable patients to determine the relationship between oral ascorbic acid intake and serum ascorbic acid (SAA) level. Total oral intake ranged from 28 mg daily to 412 mg daily. Only one patient had an oral intake of ascorbic acid below 60 mg per day. The SAA levels ranged from 1 mg/L to 36.17 mg/L. Although a strong correlation existed between intake and SAA (p < 0.001, R2 = 0.47), the variation in SAA at any given intake level was wide. Of the studied patients, 62% had an SAA < 8.7 mg/L, 40% had an SAA < 5.1 mg/L (below the level in a healthy population), and 12% had a level below 2 mg/L (scorbutic). None of the patients demonstrated clinical manifestations of scurvy. Our results show that, in CAPD patients, ascorbic acid deficiency can be reliably detected only with SAA measurements, and oral intake may influence SAA level. To maintain ascorbic acid in the normal range for healthy adults, daily oral intake needs to be increased above the U.S. recommended dietary allowance to 80-140 mg.

Pressure ulcers--randomised controlled trial comparing hydrocolloid and saline gauze dressings

An open comparative randomised study comparing the performance of hydrocolloid dressings (DuoDERM CGF) to saline gauze dressings in the treatment of pressure ulcers was done to evaluate the overall dressing performance, wound healing and cost effectiveness. Thirty-four subjects were enrolled at the University Hospital, Kuala Lumpur over a 643 days period. Inclusion criteria were Stage II or III pressure ulcers, at least 18 years of age and written informed consent. Only one pressure ulcer per subject was enrolled in the study. Patients with infected pressure ulcers, diabetes mellitus, an immuno-compromised status and known sensitivity to the study dressings were excluded. Subjects who met the enrollment criteria were randomised to one of the two dressing regimes. They were expected to participate in the study for a maximum of eight weeks or until the pressure ulcer healed, which ever occurred first. Overall subject age averaged 58 years and the mean duration of pressure ulcer existence was about 1 month. Twenty-one of the thirty-four ulcers enrolled were stage II and thirteen were stage III. The majority of the ulcers (88%) were located in the sacral area and seventeen subjects (50%) were incontinent. In the evaluation of dressing performance in terms of adherence to wound bed, exudate handling ability, overall comfort and pain during dressing removal; all favoured the hydrocolloid dressing by a statistically significant margin (p < 0.001). Subjects assigned the hydrocolloid dressing experienced a mean 34% reduction from their baseline surface area measurement compared to a mean 9% increase by subjects assigned gauze dressings. This was not statistically significant (p = 0.2318). In cost evaluation of the study products, there was no statistical significance in the total cost of wound management per subject. When only labour time and cost was evaluated, there was a statistically significant advantage towards hydrocolloid dressings.