Autotaxin-LPA signaling contributes to obesity-induced insulin resistance in muscle and impairs mitochondrial metabolism.

Autotaxin (ATX) is an adipokine that generates the bioactive lipid, lysophosphatidic acid (LPA). ATX-LPA signaling has been implicated in diet-induced obesity and systemic insulin resistance. However, it remains unclear whether the ATX-LPA pathway influences insulin function and energy metabolism in target tissues, particularly skeletal muscle, the major site of insulin-stimulated glucose disposal. The objective of this study was to test whether the ATX-LPA pathway impacts tissue insulin signaling and mitochondrial metabolism in skeletal muscle during obesity. Male mice with heterozygous ATX deficiency (ATX+/-) were protected from obesity, systemic insulin resistance, and cardiomyocyte dysfunction following high-fat high-sucrose (HFHS) feeding. HFHS-fed ATX+/- mice also had improved insulin-stimulated AKT phosphorylation in white adipose tissue, liver, heart, and skeletal muscle. Preserved insulin-stimulated glucose transport in muscle from HFHS-fed ATX+/- mice was associated with improved mitochondrial pyruvate oxidation in the absence of changes in fat oxidation and ectopic lipid accumulation. Similarly, incubation with LPA decreased insulin-stimulated AKT phosphorylation and mitochondrial energy metabolism in C2C12 myotubes at baseline and following palmitate-induced insulin resistance. Taken together, our results suggest that the ATX-LPA pathway contributes to obesity-induced insulin resistance in metabolically relevant tissues. Our data also suggest that LPA directly impairs skeletal muscle insulin signaling and mitochondrial function.

Loss of protein association causes cardiolipin degradation in Barth syndrome.

Cardiolipin is a specific mitochondrial phospholipid that has a high affinity for proteins and that stabilizes the assembly of supercomplexes involved in oxidative phosphorylation. We found that sequestration of cardiolipin in protein complexes is critical to protect it from degradation. The turnover of cardiolipin is slower by almost an order of magnitude than the turnover of other phospholipids. However, in subjects with Barth syndrome, cardiolipin is rapidly degraded via the intermediate monolyso-cardiolipin. Treatments that induce supercomplex assembly decrease the turnover of cardiolipin and the concentration of monolyso-cardiolipin, whereas dissociation of supercomplexes has the opposite effect. Our data suggest that cardiolipin is uniquely protected from normal lipid turnover by its association with proteins, but this association is compromised in subjects with Barth syndrome, leading cardiolipin to become unstable, which in turn causes the accumulation of monolyso-cardiolipin.

Lipid metabolism and signaling in cardiac lipotoxicity.

The heart balances uptake, metabolism and oxidation of fatty acids (FAs) to maintain ATP production, membrane biosynthesis and lipid signaling. Under conditions where FA uptake outpaces FA oxidation and FA sequestration as triacylglycerols in lipid droplets, toxic FA metabolites such as ceramides, diacylglycerols, long-chain acyl-CoAs, and acylcarnitines can accumulate in cardiomyocytes and cause cardiomyopathy. Moreover, studies using mutant mice have shown that dysregulation of enzymes involved in triacylglycerol, phospholipid, and sphingolipid metabolism in the heart can lead to the excess deposition of toxic lipid species that adversely affect cardiomyocyte function. This review summarizes our current understanding of lipid uptake, metabolism and signaling pathways that have been implicated in the development of lipotoxic cardiomyopathy under conditions including obesity, diabetes, aging, and myocardial ischemia-reperfusion. This article is part of a Special Issue entitled: Heart Lipid Metabolism edited by G.D. Lopaschuk.

Membrane curvature modulation of protein activity determined by NMR.

In addition to specific intermolecular interactions, biological processes at membranes are also modulated by the physical properties of the membrane. One of these properties is membrane curvature. NMR methods are useful for studying how membrane curvature affects the binding and insertion of proteins into membranes as well as how proteins can affect membrane curvature properties. In many cases these interactions result in a marked change in protein activity. We have reviewed examples from a range of systems having varied mechanisms by which membrane curvature is linked to protein activity. Among the examples discussed are antimicrobial peptides, proteins affecting membrane fusion, rhodopsin, protein kinase C, phospholipase C-delta1, phosphatidylinositol-3 kinase-related kinases and tafazzin.

The phosphatidylinositol synthase-catalyzed formation of phosphatidylinositol does not exhibit acyl chain specificity.

Phosphatidylinositol (PI) and its phosphorylated forms are required for many critical cellular processes. PI is highly enriched at its sn-1 and sn-2 positions, the major species being 1-stearoyl-2-arachidonoyl PI (18:0/20:4 PI). This enrichment is achieved in part through enzymatic acyl chain specificity in PI synthesis. Here we characterize the acyl chain specificity of phosphatidylinositol synthase (PIS), which is involved in the terminal step of PI synthesis. Unlike several other enzymes involved in PI synthesis, PIS appears to exhibit no acyl chain specificity toward its substrates. Thus, enrichment of newly formed PI occurs prior to the terminal synthesis step.

Enrichment of phosphatidylinositols with specific acyl chains.

There are six major species of phospholipids in eukaryotes, each of which plays unique structural and functional roles. One species, phosphatidylinositol (PI) only contributes about 2-10% of the total phospholipid pool. However, they are critical factors in the regulation of several fundamental processes such as in membrane dynamics and signal transduction pathways. Although numerous acyl species exist, PI species are enriched with one specific acyl chain composition at both sn-1 and sn-2 positions. Recent work has identified several enzymes that act on lipids to lead to the formation or interconversion of PI species that exhibit acyl chain specificity. These enzymes contribute to this lipid's enrichment with specific acyl chains. The nature of the acyl chains on signaling lipids has been shown to contribute to their specificity. Here we review some of the critical functions of PI and the multiple pathways in which PI can be produced and metabolized. We also discuss a common motif that may confer arachidonoyl specificity to several of the enzymes involved. This article is part of a Special Issue entitled: Membrane Structure and Function: Relevance in the Cell's Physiology, Pathology and Therapy.

Distinct properties of the two isoforms of CDP-diacylglycerol synthase.

CDP-diacylglycerol synthases (CDS) are critical enzymes that catalyze the formation of CDP-diacylglycerol (CDP-DAG) from phosphatidic acid (PA). Here we show in vitro that the two isoforms of human CDS, CDS1 and CDS2, show different acyl chain specificities for its lipid substrate. CDS2 is selective for the acyl chains at the sn-1 and sn-2 positions, the most preferred species being 1-stearoyl-2-arachidonoyl-sn-phosphatidic acid. CDS1, conversely, shows no particular substrate specificity, displaying similar activities for almost all substrates tested. Additionally, we show that inhibition of CDS2 by phosphatidylinositol is also acyl chain-dependent, with the strongest inhibition seen with the 1-stearoyl-2-arachidonoyl species. CDS1 shows no acyl chain-dependent inhibition. Both CDS1 and CDS2 are inhibited by their anionic phospholipid end products, with phosphatidylinositol-(4,5)-bisphosphate showing the strongest inhibition. Our results indicate that CDS1 and CDS2 could create different CDP-DAG pools that may serve to enrich different phospholipid species with specific acyl chains.

Recurrent chylothorax as a consequence of esophageal stent.

Incidence of chylothorax post-esophageal stenting has not been reported. We present a 40-year-old female with metastatic breast cancer who presented with dyspnea. She was recently hospitalized for dysphagia secondary to a mediastinal mass requiring an esophageal stent. CT chest now reported large bilateral pleural effusions. A benign chylothorax was drained from the right side. After persistent high-output drainage, a review of her CT chest revealed thoracic duct impingement by the esophageal stent. The stent was retracted proximally, and pleural fluid output subsequently decreased. Repeat fluid analysis revealed a transudative effusion. This is the first reported case of esophageal stenting causing reversible chylothorax.

Endobronchial blood-patch: A novel technique for a persistent pleural air leak.

Introduction: Patients with severe COVID-19 Pneumonia requiring prolonged mechanical ventilation have an increased incidence of pneumothorax. Mechanically ventilated patients who are critically ill and develop a persistent air leak from pneumothorax are poor candidates for surgical repair. As the persistent air leak can be a significant barrier to vent-weaning and clinical stability, these patients present a unique clinical challenge. Clinical case: A 65-year-old male intubated and on prolonged mechanical ventilation for severe COVID-19 Pneumonia developed a pneumothorax complicated by a persistent alveolar-pleural fistula with a persistent air-leak. Given his critical state with ongoing pressor requirements and elevated vent requirements, surgical repair was not an option. A bedside bronchoscopy occlusion study with isolation of the air leak, and subsequent autologous endobronchial blood-patch repair with thrombin was performed with rapid and definitive resolution of the air leak. The patient progressed favorably, ultimately being weaned from the ventilator, decannulated, and walking out of the hospital. Conclusion: In critically ill ventilated patients with pneumothorax complicated by a persistent air-leak, bedside endobronchial evaluation and blood-patch repair is a feasible approach to management.

Fast tracking in cardiac surgery: is it safe?

BACKGROUND: While fast track clinical pathways have been demonstrated to reduce resource utilization in patients undergoing cardiac surgery, it remains unclear as to whether they adversely affect post-operative outcomes. The purpose of this study was to determine the impact of fast tracking on post-operative outcomes following cardiac surgery. METHODS: In a retrospective study, all patients undergoing first-time, on-pump, non-emergent coronary artery bypass grafting, valve, or coronary artery bypass grafting + valve at a single centre between 2010 and 2017 were included. Patients were considered to have been fast tracked if they were extubated and transferred from intensive care to a step-down unit on the same day as their procedure. The risk-adjusted effect of fast tracking on a 30-day composite of all-cause mortality, stroke, renal failure, infection, atrial fibrillation, and readmission to hospital was determined. Furthermore, propensity score matching was used to match fasting track patients in a 1-to-1 manner with their nearest "neighbor" in the control group and subsequently compared in terms of 30-day post-operative outcomes. RESULTS: 3252 patients formed the final study population (fast track: n = 245; control: n = 3007). Patients who were fast tracked experienced reduced time to initial extubation (4.3 vs. 5.6 h, p < 0.0001) and lower median initial intensive care unit length of stay (7.8 vs. 20.4 h, p < 0.0001). Fast tracked patients experienced lower 30-day rates of the composite outcome (42.4% vs. 51.5%, p = 0.008). However, following propensity score matching, fast tracked patients experienced similar 30-day rates of the composite outcome as the control group (42.4% vs. 44.5%, p = 0.72). After risk adjustment using multivariable regression modeling, fast tracking was predictive of an improved 30-day composite outcome (OR 0.75, 95% CI 0.57-0.98, p = 0.03). CONCLUSION: Fast track clinical pathways was associated with reduced intensive care unit, overall length of stay and similar 30-day post-operative outcomes. These results suggest that fast tracking appropriate patients may reduce resource utilization, while maintaining patient safety.

Staged versus concurrent native nephrectomy and renal transplantation in patients with autosomal dominant polycystic kidney disease: A systematic review.

BACKGROUND: Patients with Autosomal Dominant Polycystic Kidney Disease (ADPKD) frequently undergo native nephrectomy before transplantation. The nephrectomy may be a staged procedure or undertaken simultaneously with transplantation. When performed simultaneously, the transplant procedure is more prolonged, involves a larger operative field and incision. There is also a concern of a greater risk of graft loss with simultaneous nephrectomy and transplantation. Moreover, staged surgery may allow nephrectomy to be performed before immunosuppression introduction via a smaller incision or involving a minimally invasive approach. However, staged nephrectomy may require a period of dialysis not otherwise necessary if a transplant and nephrectomy were simultaneous. Moreover, only a single procedure is needed, implying the avoidance of a prior nephrectomy and its attendant morbidity in a patient with chronic renal insufficiency. To account for these issues, this study aims to compare the cumulative morbidity of two-staged procedures versus a single simultaneous approach in term of morbidity and graft outcomes. OBJECTIVES: This study aims to systematically review the literature to determine whether a staged or simultaneous approach to native nephrectomy in ADPKD is the optimal approach in terms of morbidity and graft outcomes. METHODS: A literature search of MEDLINE and EMBASE was conducted to identify published systematic reviews, randomized control trials, case-controlled studies and case studies. Data comparing outcomes of staged and simultaneous nephrectomy for patients undergoing kidney transplantation was extracted and analyzed. The main outcomes analyzed were length of hospitalization, blood loss, operative time, other early postoperative complications and risk of graft thrombosis. Meta-analysis was conducted where appropriate. RESULTS: Seven retrospective cohort studies were included in the review. There was a total of 385 patients included in the analysis, of whom 273 patients underwent simultaneous native nephrectomy and kidney transplantation. Meta-analysis showed an increased cumulative operative time in staged procedures (RR 1.86；95% CI 0.43-3.29 p = 0.01) and increased risk of blood transfusions (RR 2.69; 95% CI 1.92-3.46 p < 0.00001). For the transplant procedure, there were no significant difference in the length of stay (RR 1.03; 95% CI -2.01-4.14 p = 0.52), major postoperative complications (RR 0.02; 95% CI -0.15-0.10 p = 0.74) and vascular thromboses (RR 1.42 95% CI 0.23-8.59 p = 0.7). CONCLUSION: The results suggest that staged nephrectomy followed by kidney transplantation is associated with a longer cumulative operative time and increased cumulative risk of blood transfusions. There is no evidence to suggest that performing a simultaneous nephrectomy and kidney transplant procedure increases the perioperative mortality rate, major postoperative complication rates or risk of vascular thrombosis.

Whey peptides exacerbate body weight gain and perturb systemic glucose and tissue lipid metabolism in male high-fat fed mice.

Consumption of milk-derived whey proteins has been demonstrated to have insulin-sensitizing effects in mice and humans, in part through the generation of bioactive whey peptides. While whey peptides can prevent insulin resistance in vitro, it is unclear whether consumption of whey peptides can prevent obesity-induced metabolic dysfunction in vivo. We sought to determine whether whey peptides consumption can protect from high fat (HF) diet-induced obesity and dysregulation of glucose homeostasis. Male C57BL/6J mice were fed either a low or HF diet for 13 weeks. HF diet fed mice were provided drinking water with no addition (control), undigested whey protein isolate (WPI, 1 mg ml-1) or whey protein hydrolysate (WPH, 1 mg ml-1) throughout the diet regimen. Mice consuming WPH gained more body weight and were more glucose intolerant compared to those consuming WPI or water only. Despite increased body weight gain, perigonadal adipose tissue weight and lipid accumulation were unchanged. However, excess lipids accumulated ectopically in the liver and skeletal muscle in mice consuming WPH, which was associated with elevated inflammatory markers systemically and in adipose tissue, liver, and skeletal muscle. In skeletal muscle, mitochondrial fat oxidation and electron transport chain proteins were decreased with WPH consumption, indicative of mitochondrial dysfunction. Taken together, our results demonstrate that WPH, but not WPI, exacerbates HF-induced body weight gain and impairs glucose homeostasis, which is accompanied by increased inflammation, ectopic fat accumulation and mitochondrial dysfunction. Thus, our results argue against the use of dietary whey peptide supplementation as a preventative option against HF diet-induced metabolic dysfunction.

Comparison of the effect of single vs dual antiplatelet agents on post-operative haemorrhage after renal transplantation: A systematic review and meta-analysis.

OBJECTIVES: A significant proportion of renal transplant patients have cardiovascular comorbidities for which they receive treatment with antiplatelet agents. The aim of this study was to systematically review the current literature reporting perioperative outcomes for patients receiving dual antiplatelet therapy compared to single antiplatelet therapy at the time of kidney transplantation with particular reference to the risks of postoperative haemorrhage. MATERIALS AND METHODS: Embase, Medline and Cochrane databases were utilized to identify articles reporting outcomes of renal transplant recipients on single antiplatelet therapy and dual antiplatelet therapy. These outcomes were compared using a random effects model meta-analysis where appropriate. RESULTS: Six articles were incorporated in the analysis, including 130 receiving dual antiplatelet therapy, and 781 in the single antiplatelet therapy group. There was a significantly higher risk of post-operative haemorrhagic events in the dual antiplatelet therapy group compared to the single antiplatelet therapy group (RR 1.58, 95% CI 1.19-2.09, p = 0.001). Post-operative cardiovascular event rates were similar between both groups in individual studies, although this could not be quantitatively analysed. CONCLUSIONS: The use of dual antiplatelet therapy was associated with a higher risk of post-operative haemorrhage compared to the use of single antiplatelet therapy without increased rates of surgical intervention. However, the use of dual antiplatelet therapy may provide protection from cardiovascular events in an inherently higher risk patient group.

Modulators of cancer cell invasiveness.

Cell invasiveness is essential for cancer metastasis. Many proteins, and more recently also non-coding RNAs, particularly microRNAs (miRNAs), have been reported to affect the cell invasiveness of various cancers. There is an apparent gap between the high number of these macromolecules and the low number of signaling pathways experimentally verified to control cancer invasiveness. We have brought together these various proteins and RNAs because we could not find any publication that filled this important gap. We have noted 589 proteins, 28 miRNAs, and 1 long non-coding RNA that are reported to modulate invasiveness in cells of various cancers. Interestingly, 44 proteins enhance invasiveness in cells of some cancers, but suppress it in cells of others. Almost all of the proteins that show experimentally verified activation/inhibition effects on, or binding interactions with, each other are linked together in a single network, in a "hub-and-spoke" architecture. The accumulated data show trends that point to anticipated future results and highlight gaps in what is known about invasiveness signaling. Identification of cancer invasiveness signaling networks is important for combination and personalized targeted therapies of cancers.

Whey Peptides Stimulate Differentiation and Lipid Metabolism in Adipocytes and Ameliorate Lipotoxicity-Induced Insulin Resistance in Muscle Cells.

Deregulation of lipid metabolism and insulin function in muscle and adipose tissue are hallmarks of systemic insulin resistance, which can progress to type 2 diabetes. While previous studies suggested that milk proteins influence systemic glucose homeostasis and insulin function, it remains unclear whether bioactive peptides generated from whey alter lipid metabolism and its accumulation in muscle and adipose tissue. Therefore, we incubated murine 3T3-L1 preadipocytes and C2C12 myotubes with a whey peptide mixture produced through pepsin-pancreatin digestion, mimicking peptides generated in the gut from whey protein hydrolysis, and examined its effect on indicators of lipid metabolism and insulin sensitivity. Whey peptides, particularly those derived from bovine serum albumin (BSA), promoted 3T3-L1 adipocyte differentiation and triacylglycerol (TG) accumulation in accordance with peroxisome proliferator-activated receptor γ (PPARγ) upregulation. Whey/BSA peptides also increased lipolysis and mitochondrial fat oxidation in adipocytes, which was associated with the upregulation of peroxisome proliferator-activated receptor δ (PPARδ). In C2C12 myotubes, whey but not BSA peptides ameliorated palmitate-induced insulin resistance, which was associated with reduced inflammation and diacylglycerol accumulation, and increased sequestration of fatty acids in the TG pool. Taken together, our study suggests that whey peptides generated via pepsin-pancreatin digestion profoundly alter lipid metabolism and accumulation in adipocytes and skeletal myotubes.

Renal Transplant Artery Autologous Saphenous Vein Graft Aneurysms: Late Presentation and the Need for Recall and Surveillance.

Autologous saphenous vein grafts are occasionally used in renal transplant recipients, particularly in living donors with short donor vessels or after donor vessel injury during allograft procurement. Autologous saphenous vein graft aneurysm formation is described as a late complication following the use of this conduit in renal transplant. We report a case of a 45-year-old woman who developed an autologous saphenous vein graft aneurysm 21 years after her living donor transplant, which was successfully managed with explantation of the graft, cold perfusion ex situ, and resection of the aneurysm, which was followed by reconstruction using deceased donor iliac vessels. The graft was then successfully reimplanted. Based on this experience and after a review of the literature related to autologous saphenous vein graft aneurysms in renal transplant, we recommend that surveillance for this particular complication should be considered no later than 10 years after implant of an autologous saphenous vein graft when used as an arterial conduit.

Prophylactic Wound Drainage in Renal Transplantation: A Systematic Review.

BACKGROUND: Adult kidney transplantation is most commonly into an extraperitoneal potential space, and surgically placed drains are used routinely in many centers. There is limited evidence of clinical benefit for prophylactic drainage in other major abdominal and vascular surgery. Transplantation is, however, a unique setting combining organ dysfunction and immunosuppression, and the risks and benefits of prophylactic drain placement are not known. This study attempts to examine existing literature to determine whether prophylactic intraoperative drains have an impact on the likelihood of perigraft fluid collections and other wound-related complications following kidney transplantation. METHODS: A literature search of MEDLINE and EMBASE was conducted to identify published comparative studies, including recipients receiving prophylactic drains to recipients in whom drains were omitted. The main outcomes were the incidence of peritransplant fluid collections and wound-related complications. Meta-analysis was performed on these data. RESULTS: Four retrospective cohort studies were deemed eligible for quantitative analysis and 1 additional conference abstract was included in qualitative discussion. A total of 1640 patients, 1023 with drains and 617 without, were included in the meta-analysis. There was a lower rate of peritransplant collections associated with the drain group (RR 0.62; 95% confidence interval, 0.42-0.90). There was no significant difference in the incidence of wound-related complications between the groups (RR 0.85; 95% confidence interval, 0.34-2.11). CONCLUSIONS: These data associate a higher rate of peritransplant fluid collections with omission of prophylactic drainage, without a difference in the incidence of wound-related complications. Further research is required to definitively determine the impact of drains in this patient group.

Lysophosphatidic Acid Signaling in Obesity and Insulin Resistance.

Although simple in structure, lysophosphatidic acid (LPA) is a potent bioactive lipid that profoundly influences cellular signaling and function upon binding to G protein-coupled receptors (LPA1-6). The majority of circulating LPA is produced by the secreted enzyme autotaxin (ATX). Alterations in LPA signaling, in conjunction with changes in autotaxin (ATX) expression and activity, have been implicated in metabolic and inflammatory disorders including obesity, insulin resistance, and cardiovascular disease. This review summarizes our current understanding of the sources and metabolism of LPA with focus on the influence of diet on circulating LPA. Furthermore, we explore how the ATX-LPA pathway impacts obesity and obesity-associated disorders, including impaired glucose homeostasis, insulin resistance, and cardiovascular disease.

Autotaxin Is Regulated by Glucose and Insulin in Adipocytes.

Autotaxin (ATX) is an adipokine that generates the bioactive lipid, lysophosphatidic acid. Despite recent studies implicating adipose-derived ATX in metabolic disorders including obesity and insulin resistance, the nutritional and hormonal regulation of ATX in adipocytes remains unclear. The current study examined the regulation of ATX in adipocytes by glucose and insulin and the role of ATX in adipocyte metabolism. Induction of insulin resistance in adipocytes with high glucose and insulin concentrations increased ATX secretion, whereas coincubation with the insulin sensitizer, rosiglitazone, prevented this response. Moreover, glucose independently increased ATX messenger RNA (mRNA), protein, and activity in a time- and concentration-dependent manner. Glucose also acutely upregulated secreted ATX activity in subcutaneous adipose tissue explants. Insulin elicited a biphasic response. Acute insulin stimulation increased ATX activity in a PI3Kinase-dependent and mTORC1-independent manner, whereas chronic insulin stimulation decreased ATX mRNA, protein, and activity. To examine the metabolic role of ATX in 3T3-L1 adipocytes, we incubated cells with the ATX inhibitor, PF-8380, for 24 hours. Whereas ATX inhibition increased the expression of peroxisome proliferator-activated receptor-γ and its downstream targets, insulin signaling and mitochondrial respiration were unaffected. However, ATX inhibition enhanced mitochondrial H2O2 production. Taken together, this study suggests that ATX secretion from adipocytes is differentially regulated by glucose and insulin. This study also suggests that inhibition of autocrine/paracrine ATX-lysophosphatidic acid signaling does not influence insulin signaling or mitochondrial respiration, but increases reactive oxygen species production in adipocytes.