Aggregation of Monomeric Ferritin-Insulin Occupied Receptor Sites on Liver Plasma Membranes Caused by Anti-Insulin Antibody

Abstract

Anti-insulin antibody enhanced ¹²⁵I-insulin binding to liver plasma membranes. Ultrastructural studies revealed that monomeric ferritin-insulin occupied receptors on liver membranes were observed as predominantly single receptors and that increasing concentrations of ferritin-insulin did not alter the distribution patterns. Anti-insulin antibody caused a marked shift in the organizational pattern of insulin receptors from predominantly single receptors to small aggregates of 2–6 receptors.     

Prolactin and Growth Hormone Binding in Mammary and Liver Tissue of Lactating Cows

Abstract

A radioligand/receptor binding assay was developed using homologous hormones to distinguish between bovine growth hormone (bGH) and bovine prolactin (bPRL) receptors in liver and mammary tissue of lactating cows. Mammary and liver tissues were homogenized in 0.3 M sucrose and centrifuged at 100,000 x g over a 1.3 M sucrose density gradient. Membranes from the 0.3 - 1.3 M sucrose interface were incubated with 1 ng of iodinated bGH or bPRL for 20 h at 22°C in the presence of increasing concentrations of native bGH or bPRL. High affinity receptor binding sites were found for bPRL in liver and mammary tissue membranes (Ka=3.2 and 1.3 × 10⁸ 1/mol with 34 and 63 fmol receptors/mg liver and mammary membrane protein, respectively) and for bGH only in liver tissue (Ka=1.8 × 10⁹ 1/mol, 18 fmol receptors/mg membrane protein). Receptor number estimates were 3 and 11 times higher in mammary and liver tissue using a heterologous hGH system indicating that heterologous systems may overestimate the number of receptors in bovine tissue. The absence of demonstratable bGH receptors in lactating bovine mammary tissue supports in vitro results of others with isolated mammary tissue indicating that the positive effect of bGH on milk production in intact cows is via an indirect mechanism.     

Modeling of Sequestration and Down Regulation in Cells Containing Beta2-Adrenergic Receptors

Abstract

Desensitization of G-protein coupled receptors following agonist occupancy is accompanied by two temporally distinguishable cellular trafficking phenomena of the receptors referred to as sequestration and down regulation. For the β₂-adrenergic receptor, sequestration occurs within minutes of agonist binding and results in a reversible internalization and loss of cell surface receptor binding. With longer occupancy, greater than 1 hour, down regulation results in a variable loss of the complement of cellular receptors. Here we compare the two methods that have been used to monitor these receptor changes, competition of whole cell hydrophobic ligand binding (¹²⁵I-pindolol) with a hydrophilic ligand (CGP-12177) and now cytometry quantification of immunologically tagged β₂-adrenergic receptor. While both methods give reliable results, we show that because of a 1:500 partitioning of the hydrophilic ligand into cells, slightly different conditions should be used to assess basally or agonist stimulated sequestered receptor levels. Using a sequestration defective β₂-adrenergic receptor mutant we demonstrate that even though sequestration and down regulation behave as independent processes, sequestration can significantly affect the rate at which receptors are lost by the down regulatory process by removing receptors from the pool of down regulating receptors. A mathematical model expressing these relationships is provided.     

Receptor Interactions of Abbott-81988, A Highly Potent,Non-Peptide Angiotensin-II Antagonist Selective for Type-1 Receptors

Abstract

Abbott-81988 (A-81988) was selected from a series of related compounds as a highly potent and selective antagonist of angiotensin receptors. In the rabbit aorta, A-81988 exhibited a _pA₂ of 10.12 (± 0.08) vs. angiotensin-II, for type 1 receptors (AT₁), and the antagonism appeared competitive. These results agreed with radioligand assays in which A-81988 inhibited the binding of [¹²⁵l]-Sar¹ –lle⁸—Angiotensin-II to rat liver membranes with a _pK_I of 9.12 (± 0.63). A-81988 was selective for AT₁ receptors based on its lack of activity at other sites, such as aortic α 1 receptors. Moreover, A-81988 lacked affinity for AT₂ receptors of bovine cerebellar membranes or for α or β adrenergic receptors in binding assays. A-81988 lowered blood pressure significantly in vivo in renal artery-ligated rats at doses of 0.3 mg/kg administered either i.v. or p.o. The compound was rapidly and almost completely absorbed from the duodenum of anesthetized rats and demonstrated very low first-pass metabolism in the rat liver. These properties of selectivity toward and potency for antagonizing AT₁ receptors, activity in lowering blood pressure in experimental animals, and favorable pharmacokinetic properties indicate that A-81988 should be a useful antihypertensive agent in man.     

Methods for Quantitative Detection of Antibody-induced Complement Activation on Red Blood Cells

Antibodies against red blood cells (RBCs) can lead to complement activation resulting in an accelerated clearance via complement receptors in the liver (extravascular hemolysis) or leading to intravascular lysis of RBCs. Alloantibodies (e.g. ABO) or autoantibodies to RBC antigens (as seen in autoimmune hemolytic anemia, AIHA) leading to complement activation are potentially harmful and can be - especially when leading to intravascular lysis - fatal¹. Currently, complement activation due to (auto)-antibodies on RBCs is assessed in vitro by using the Coombs test reflecting complement deposition on RBC or by a nonquantitative hemolytic assay reflecting RBC lysis^1-4. However, to assess the efficacy of complement inhibitors, it is mandatory to have quantitative techniques. Here we describe two such techniques. First, an assay to detect C3 and C4 deposition on red blood cells that is induced by antibodies in patient serum is presented. For this, FACS analysis is used with fluorescently labeled anti-C3 or anti-C4 antibodies. Next, a quantitative hemolytic assay is described. In this assay, complement-mediated hemolysis induced by patient serum is measured making use of spectrophotometric detection of the released hemoglobin. Both of these assays are very reproducible and quantitative, facilitating studies of antibody-induced complement activation.     

Three pentraxins C-reactive protein,serum amyloid p component and pentraxin 3 mediate complement activation using Collectin CL-P1

BackgroundPentraxins (PTXs) are a superfamily of multifunctional conserved proteins involved in acute-phase responses. Recently, we have shown that collectin placenta 1 (CL-P1) and C-reactive protein (CRP) mediated complement activation and failed to form terminal complement complex (TCC) in normal serum conditions because of complement factor H inhibition.MethodsWe used CL-P1 expressing CHO/ldlA7 cells to study the interaction with PTXs. Soluble type CL-P1 was used in an ELISA assay for the binding, C3 and TCC deposition experiments. Furthermore, we used our previously established CL-P1 expressing HEK293 cells for the C3 fragment and TCC deposition assay.ResultsWe demonstrated that CL-P1 also bound serum amyloid p component (SAP) and pentraxin 3 (PTX3) to activate the classical pathway and the alternative pathway using factor B. CRP and PTX3 further amplified complement deposition by properdin. We found that CRP and PTX3 recruit CFH, whereas SAP recruits C4 binding protein on CL-P1 expressing cell surfaces to prevent the formation of TCC in normal serum conditions. In addition, depletion of CFH, C4BP and complement factor I (CFI) failed to prevent TCC formation both in ELISA and cell experiments. Furthermore, soluble complement receptor 1, an inhibitor of all complement pathways prevents PTX induced TCC formation.ConclusionOur current study hypothesizes that the interaction of pentraxins with CL-P1 is involved in complement activation.General significanceCL-P1 might generally inhibit PTX induced complement activation and host damage to protect self-tissues.     

Suppression of Receptors for Prolactin and Estrogen in Rat Liver Due to Treatment with the Growth Hormone Analogue Produced by the Tapeworm Spirometra Mansonoides

Abstract

Somatogenic hormones play an important role in regulation of receptors for prolactin (PRL) and estrogen. Plerocercoids of the tapeworm, S. mansonoides produce a factor which mimics some, but not all of the actions reported for GH. Intact female rats were subjected to a constant infusion of plerocercoid growth factor (PGF) via a subcutaneous infection for two weeks to determine if PGF influences receptors for PRL, GH or estradiol. The rate of weight gain in the PGF-treated rats was accelerated in spite of a marked reduction in serum GH. Partially-purified PGF specifically displaced [¹²⁵I]hGH from rat liver receptors but microsomes prepared from rats treated with PGF specifically bound significantly less [¹²⁵I]hGH than microsomes from control rats. The reduction in [¹²⁵I]hGH binding was not due to occupancy or to a change in affinity but to a suppression in receptor concentration. Scatchard analysis of [³H]estradiol binding in rat liver cytosols shows a 50% reduction in receptor concentration in the PGF-treated group. Specific binding of [³H]estradiol in anterior pituitary was also suppressed by PGF treatment.     

Evidence of alterations in the expression of orphan receptors GPR26 and GPR39 due to the etiology of the metabolic syndrome

Aims: Metabolic syndrome (MS) is composed of several metabolic abnormalities that increase the risk of cardiovascular diseases and diabetes. Although there are treatments for the components of MS, this pathology maintains a high mortality, suggesting that there are other mechanisms in which orphan receptors such as GPR26 and GPR39 may be involved. For this reason, the aim of this work was to evaluate the expression of GPR26 and GPR39 orphan receptors in two models of MS (diet and genetics).

Materials and methods: We used male Wistar rats, which received 70% fructose in drinking water for 9 weeks, and obese Zucker rats. We measured weight, blood pressure, glucose, triglycerides, total cholesterol, HDL cholesterol, LDL cholesterol to determine the MS and the expression of the orphan receptors GPR26 and GPR39 in brain, heart, aorta, liver, and kidney by RT-PCR.

Results: The analysis of the expression of the orphan receptors GPR26 and GPR39 showed that the receptors are expressed in some tissues, but the expression of the GPR26 tends to decrease in the heart and aorta, whereas in the brain, no changes were observed, this receptor is not expressed in the liver and kidney of both strains. The expression of GPR39 isoforms depends on the tissue and MS model.

Conclusions: We conclude that the orphan receptors GPR26, GPR39v1, and GPR39v2 are expressed in different tissues and their profile expression is dependent on the etiology of the MS.     

Liposome recognition by resident and newly recruited murine liver macrophages

The evidence in this communication indicate that, unlike resident Kupffer cells, newly recruited liver macrophages (following monocyte migration from the blood to the liver) use complement receptors to recognize and internalize stearylamine-incorporated liposomes. Within two weeks of hepatic residency complement receptors no longer participate in liposome recognition and uptake.     

Collectin CL-P1 utilizes C-reactive protein for complement activation

BackgroundC-reactive protein (CRP) is a plasma pentraxin family protein that is massively induced as part of the innate immune response to infection and tissue injury. CRP and other pentraxin proteins can activate a complement pathway through C1q, collectins, or on microbe surfaces. It has been found that a lectin-like oxidized LDL receptor 1 (LOX-1), which is an endothelial scavenger receptor (SR) having a C-type lectin-like domain, interacts with CRP to activate the complement pathway using C1q. However it remains elusive whether other lectins or SRs are involved in CRP-mediated complement activation and the downstream effect of the complement activation is also unknown.MethodsWe prepared CHO/ldlA7 cells expressing collectin placenta-1 (CL-P1) and studied the interaction of CRP with cells. We further used ELISA for testing binding between proteins. We tested for C3 fragment deposition and terminal complement complex (TCC) formation on HEK293 cells expressing CL-P1.ResultsHere, we demonstrated that CL-P1 bound CRP in a charge dependent manner and the interaction of CRP with CL-P1 mediated a classical complement activation pathway through C1q and additionally drove an amplification pathway using properdin. However, CRP also recruits complement factor H (CFH) on CL-P1 expressing cell surfaces, to inhibit the formation of a terminal complement complex in normal complement serum conditions.General SignificanceThe interaction of collectin CL-P1 with CFH might be key for preventing attack on “self” as a result of complement activation induced by the CL-P1 and CRP interaction.     

Glycosylation in viral hepatitis

BackgroundThe interaction between hepatitis viruses and host cells is regulated by glycans exposed on the surfaces of human and viruses cells. As the biosynthesis and degradation of human glycoproteins take place at the highest level in the liver, the changes in glycosylation of serum proteins may potentially be useful in the diagnosis of liver pathology. On the other hand, specific alterations in viruses envelope glycans could cause large changes in the entry process of hepatitis viruses into a host cells.Scope of reviewUnique alterations in glycosylation of specific proteins can be detected in HBV and HCV infected patients especially with confirmed fibrosis/cirrhosis. On the other hand, viral envelope proteins that bind to host cells are glycosylated. These glycosylated proteins play a key role in recognition, binding and penetration of the host cells. In this review we summarized the knowledge about significance of glycosylation for viral and host factors.Major conclusionsGlycosylation changes in single serum glycoproteins are noticed in the sera of patients with viral hepatitis. However, a more specific biomarker for the diagnosis of chronic hepatitis than that of a single glycosylated molecule is systemic investigation of complete set of glycan structures (N-glycome). Glycans play important roles in the viral biology cycle especially as a connecting element with host receptors.General significanceThe interaction between virus glycoproteins and cellular receptors, which are also glycoproteins, determines the possibility of virus penetration into host cells. Therefore these glycans can be the targets for the developing of novel treatment strategies of viral hepatitis.     

超声结合血清学指标对自身免疫性肝病相关肝硬化的预测价值

摘要 目的：本研究旨在结合二维剪切波弹性成像（2D-SWE）技术、超声特征及血清学指标构建自身免疫性肝病（AILD）相关肝硬化的预测模型并评估该模型的预测效能。方法：收集2019年 月至2022年5月于福建医科大学孟超肝胆医院行肝脏活检确诊为AILD,并行肝胆脾超声、2D-SWE及相关血清学检查的患者。根据病理结果,分为肝硬化组与非肝硬化组。通过多因素logistic回归分析筛选出AILD相关肝硬化的独立风险因素,构建AILD相关肝硬化的列线图模型（AILDC）。采用Bootstrap法对模型进行内部验证,绘制ROC曲线,校准曲线及临床决策曲线评估模型的区分度、校准度及临床净获益。结果：共纳入AILD255例,肝硬化组共45例。logistic回归分析结果显示：肝硬度（OR:1.322,95%CI:1.186-1.474）,脾脏厚度＞4 cm（OR:5.154,95%CI: 1.943-13.674）,补体C4（OR:0.001,95%CI:0.000-0.674 ）,高尔基体-73（OR:1.014,95%CI: 1.002-1.027 ）均是AILD肝硬化独立预测指标。AILDC的最佳截断值为80,敏感度84.4%,特异度78.6%;曲线下面积（Area under curve, AUC）0.866。AILD肝硬度的最佳截断值为10 Kpa,敏感度为71.1%,特异度为85.2%,AUC为0.803。相较于其它无创指标,AILDC具有更高的净重新分类指数、综合判别改善指数及临床决策曲线。结论：AILDC具有较好的预测效能,优于其他无创指标,适于在临床中运用并进一步推广。     

THE INFLUENCE OF COUMESTROL,ZEARALENONE, AND GENISTEIN ADMINISTRATION ON INSULIN RECEPTORS AND INSULIN SECRETION IN OVARIECTOMIZED RATS

ABSTRACT

The influence of phytoestrogens (genistein and coumestrol) and mycoestrogen (zearalenone) on insulin secretion, liver insulin receptors and some aspects of lipid and carbohydrate metabolism were investigated in this study. Ovariectomized rats were injected s.c. with the above mentioned compounds in the amount of 1?mg for three days. Coumestrol and zearalenone caused a significant increase in uterus weight, similar to the effects observed after estrone action, while this effect was not observed after the genistein injection. Blood insulin level was not changed after phyto- or mycoestrogen treatment. However, coumestrol and genistein significantly decreased the binding capacity of liver insulin receptors. These changes corresponded with alterations in glucose and free fatty acids profiles in blood, as well as with glycogen content in liver. The effects observed after genistein and coumestrol injections differed from those noticed in rats treated with zearalenone or estrone. On the basis of these results we conclude that metabolic effects of high doses of coumestrol and genistein in ovariectomized rats are partly mediated by changes in insulin sensitivity of the liver and that the action of plant estrogens on metabolism is, at least to the some degree, independent of their estrogen activity.     

Proinflammatory and Antiinflammatory Attributes of Fetu Iν-A: A Novel Hepatokine Modulating Cardiovascular and Glycemic Outcomes in Metabolic Syndrome

ObjectiveFetuin-A is a novel hepatokine. The number of biologic roles attributed to fetuin-A has increased exponentially in the past decade. The objective of this review is to discuss the pathophysiology of fetuin-A action, its proinflammatory and antiinflammatory attributes in different biological systems throughout the body, and pharmacologic interventions that modulate fetuin-A levels.MethodsPubMed, Medline, and Embase search for articles published to July 2014, using the terms “alpha-2-hs-glycoprotein” [MeSH Terms] OR “alpha-2-hs-glyco-protein” [All Fields] OR “fetuin a” [All Fields].ResultsFetuin-A is the endogenous ligand for Toll-like receptor-4 activation, for lipid-induced insulin resistance. Fetuin-A has inverse interaction with adiponectin. Increased fetuin-A is a risk factor for diabetes and fatty liver disease in normoglycemia and prediabetes. Fetuin-A is a negative acute-phase reactant in sepsis and endotoxemia, promotes wound healing, and is neuroprotec-tive in Alzheimer’s disease. Decreased fetuin-A predicts increased disease activity in obstructive lung disease, Crohn’s disease, and ulcerative colitis. Both elevated and reduced fetuin-A may be linked with increased cardiovascular events.ConclusionFetuin-A is a pleotropic molecule with diverse (sometimes even contradictory) effects in different systems, brought about by interaction with a variety of receptors, including the insulin, transforming growth factor-β, and a plethora of Toll-like receptors. As a proinflammatory molecule, fetuin-A contributes to insulin resistance and is an important link between liver, adipose tissue, and muscles. Fetuin-A is neuroprotective and plays an important antiinflammatory role in sepsis and autoimmune disorders. Pharmacologic options are limited in modulating serum fetuin-A, but salsalates, curcumin, and vitamin D are promising agents of the future. (Endocr Pract. 2014;20:1345-1351)     

Calcitonin-Secreting Pancreatic Neuroendocrine Tumors: A Case Report and Review of the Literature

ObjectiveWe report the presentation and novel therapy of a calcitonin-secreting pancreatic neuroendocrine tumor (PNET) and review the literature on this unusual neoplasm.Methods:We cite the history of a 38-year-old male who presented with fatigue, weight loss, and diarrhea and was found to have a pancreatic head mass on cross-sectional imaging, as well as liver metastases.Results:The patient’s laboratory evaluation was notable for a >100-fold elevation of the peptide hormone calcitonin in serum. As calcitonin is typically secreted by thyroid C-cells, hypercalcitoninemia is considered a marker for medullary thyroid cancer (MTC) or C-cell hyperplasia, but it may be present in several physiologic or pathologic conditions or may be ectopically secreted in rare PNETs. An octreotide scan confirmed the presence of somatostatin (SST) receptors on the pancreatic mass and liver metastases, leading to the diagnosis of a calcitonin-secreting PNET. We initiated treatment with long-acting SST analogs and peptide receptor radionuclide therapy (⁹⁰Yttrium-DOTATOC) and achieved disease regression while maintaining a high quality of life.Conclusion:Functional PNETs that secrete calcitonin are exceedingly rare, but they are important to consider in the differential diagnosis of nonthyroid-mediated hypercalcitonemia or pancreatic tumors that present with diarrhea, as the management differs markedly from both MTC and other pancreatic malignancies. (Endocr Pract. 2014;20:e140-e144)     

Associations between manganese exposure and multiple immunological parameters in manganese-exposed workers healthy cohort

BackgroundManganese (Mn) ions play a crucial role in the immune response. The immunotoxicity of Mn is rarely reported compared with the neurotoxicity of Mn.ObjectivesThe purpose of this study was to investigate the associations between chronic Mn exposure and immunological parameters in occupational Mn-exposed workers.MethodsA total of 538 workers were selected from the follow-up of manganese-exposed workers healthy cohort (MEWHC) in 2017. We divided the workers into the low-exposure group and the high-exposure group by the cutoff of the manganese-time weighted average (Mn-TWA) setting at 0.15 mg/m³. We examined serum immunological parameters by the immunoturbidimetric method and leukocyte counts and ratios in blood routine. Then we used the generalized linear model analyses and spline analyses to explore the associations between external exposure of Mn and multiple immunological parameters adjusted for variables. Based on the epidemiological analyses, we used Elisa (enzyme-linked immune sorbent assay) to detect plasma complement C3 of Mn-exposed rats.ResultsIn male workers, the mean value of complement C3 was 1.20 ± 0.16 g/L in the high-exposure group, which was significantly lower as compared to the low-exposure group (1.25 ± 0.18 g/L, P = 0.023). The generalize linear models’ analyses showed that complement C3 value had a significantly negative association with external exposure of Mn included adjustment for variables (β = -0.04, P = 0.035). Moreover, in male rats, the high-exposure group also had a lower level of complement C3 compared with the low-exposure group (P < 0.001). None significant association was observed in immunological parameters among female workers and rats (all P > 0.05).ConclusionsMn exposure from inhalable dust was associated with decreased complement C3 among occupationally Mn-exposed male individuals but not in female workers, which was further confirmed by the rat model. Further research into the possible mechanism of C3 reduction is needed in the future.     

In vivo and in vitro effect of androstene derivatives as 5α-reductase type 1 enzyme inhibitors

The aim of these studies was to synthesize twelve ester derivatives of dehydroepiandrosterone with therapeutic potential. The effect of 1–12 was demonstrated in the flank organs of gonadectomized hamsters treated with testosterone and the synthesized steroids. In vitro studies were carried out determining the IC₅₀ values for the inhibition of the activity of 5α-reductase type 1 and 2, which are present in rat liver and human prostate respectively. The binding of 1–12 to the androgen receptors (AR) was determined using rat’s prostate cytosol. Steroids 1–12 containing different substituents in the phenyl group of the ester moiety in C-3 reduced the flank organs and inhibited the activity of 5α-R type 1; however only steroids 1 and 2 inhibited 5α-R type 2. 1–12 did not bind to the AR. The modification of one atom of the substituents in the phenyl group of the ester moiety in C-3 changed their biological potency (IC₅₀).     

Use of Receptor Affinity Chromatography in Purification of the Growth Hormone-Like Factor Produced by Plerocercoids of the Tapeworm Spirometra Mansonoides

Abstract

The plerocercoid stage of the tapeworm Spirometra mansonoides produces a functional analog of human growth hormone (hGH). Among the similarities between plerocercoid growth factor (PGF) and hGH is competition for the same receptors on rabbit liver membranes. To take advantage of this characteristic in a purification scheme for PGF, rabbit liver microsomes were solubilized in Triton X-100 and the hGH receptors were purified over an hGH affinity column. The purified receptors from six rabbit livers were coupled to Affi-Gel-10 to create a receptor affinity column which was used to purify PGF. Chromatography of crude PGF over the receptor column resulted in a 1044 fold increase in specific activity. SDS-PAGE in the presence of 2-mercaptoethanol showed that the affinity-purified PGF contained three protein bands with apparent M_rs of 27.5 K, 22 K, and 16.7 K. Injections of the partially-purified PGF into hypophysectomized rats produced a dose-dependent growth response and 400 ng eq of PGF each day for 10 days stimulated a growth response not significantly different from that produced by 250 μg of bovine GH each day. Receptor affinity chromatography was an effective method to purify small amounts of PGF in a single step with negligible loss of biological activity.     

Epstein-Barr virus (EBV) receptors, complement receptors, and EBV infectibility of different lymphocyte fractions of human peripheral blood. II. Epstein-Barr virus studies.

In B-cell fractions isolated from human peripheral blood, the frequency of surface immunoglobulin-positive and of complement receptor-positive cells showed a good correlation with the frequency of EBV-binding cells, as detected by membrane fluorescence or by a quantitative bioassay for infectious virus in the absorbed supernatant fluid. There was a close relationship between all three parameters mentioned, the frequency of EBNA-positive cells 2 or 3 days after the infection, and the stimulation of cellular DNA synthesis. So-called O-cell fractions remaining after the removal of nylon adherent and E-rosetting cells contained a certain frequency of complement receptor-positive cells and absorbed EBV to a limited extent, but did not respond to EBV infection with EBNA induction or stimulation of DNA synthesis. None of the T-cell fractions absorbed EBV to a detectable extent. This includes the T_ea+ fraction that contained a certain proportion of complement receptor-positive cells. It is concluded that the previously demonstrated relationship between EBV receptors and complement receptors on B-lymphoblastoid lines also holds for peripheral B lymphocytes. In these cells, virus absorption is followed by an intracellular infectious process, signaled by the appearance of EBNA and cellular DNA synthesis. O cells carry complement receptors and absorb EBV to a certain extent, but do not respond with EBNA synthesis or DNA stimulation, presumably due to intracellular restrictions. T cells do not bind EBV, and the complement receptors present on some cells of the T_ea+ fraction do not function as EBV receptors.     

Lipid accumulation impairs lysosomal acid lipase activity in hepatocytes: Evidence in NAFLD patients and cell cultures

AimsIt has been hypothesized that the activity of lysosomal acid lipase (LAL), a key enzyme involved in lipid metabolism, is involved in the NAFLD phenotype. To clarify the role of LAL in NAFLD, we studied 164 consecutive patients with biopsy-proven NAFLD and fat-loaded HepG2 cells.MethodsLAL activity was measured (i) on dried blood spots (DBS) from NAFLD patients and dyslipidemic subjects without fatty liver and (ii) on liver biopsies from NAFLD patients. LAL activity and expression were evaluated in HepG2 cells cultured in the presence of free fatty acids (FAs), with or without a PPAR-alpha agonist.ResultsLAL activity was significantly reduced in patients with NAFLD compared to dyslipidemic subjects. LAL activity measured in liver biopsies from NAFLD patients was highly correlated to that measured on DBS and was independent of LAL expression in the liver. In a fully adjusted model, LAL activity on DBS was associated only with platelets and, when normalized by platelet count, it did not differ according to fibrosis stage. In vitro, FA loading of HepG2 fully replicated the impairment of LAL activity observed in NALFD patients. In these cells, the activation of PPAR-alpha receptors prevented and corrected FA-induced LAL impairment, by stimulating FA oxidation and LAL expression.ConclusionsLAL activity is reduced in NAFLD patients, independently from disease progression. In vitro, impaired LAL activity induced by FA loading was rescued by PPAR-alpha activation. These data suggest that the pharmacological modulation of LAL should be explored in the management of NAFLD patients.