RESUMEN
The pathogenesis of Alzheimer's disease (AD) is complex and involves an imbalance between production and clearance of amyloid-ß peptides (Aß), resulting in accumulation of Aß in senile plaques. Hypercholesterolemia is a major risk factor for developing AD, with cholesterol shown to accumulate in senile plaques and increase production of Aß. ABCG4 is a member of the ATP-binding cassette transporters predominantly expressed in the CNS and has been suggested to play a role in cholesterol and Aß efflux from the brain. In this study, we bred Abcg4 knockout (KO) with the APPSwe,Ind (J9) mouse model of AD to test the hypothesis that loss of Abcg4 would exacerbate the AD phenotype. Unexpectedly, no differences were observed in novel object recognition (NOR) and novel object placement (NOP) behavioral tests, or on histologic examinations of brain tissues for senile plaque numbers. Furthermore, clearance of radiolabeled Aß from the brains did not differ between Abcg4 KO and control mice. Metabolic testing by indirect calorimetry, glucose tolerance test (GTT), and insulin tolerance test (ITT) were also mostly similar between groups with only a few mild metabolic differences noted. Overall, these data suggest that the loss of ABCG4 did not exacerbate the AD phenotype.
Asunto(s)
Transportador de Casetes de Unión a ATP, Subfamilia G , Enfermedad de Alzheimer , Animales , Masculino , Ratones , Enfermedad de Alzheimer/metabolismo , Enfermedad de Alzheimer/genética , Enfermedad de Alzheimer/patología , Péptidos beta-Amiloides/metabolismo , Péptidos beta-Amiloides/genética , Precursor de Proteína beta-Amiloide/genética , Precursor de Proteína beta-Amiloide/metabolismo , Transportador de Casetes de Unión a ATP, Subfamilia G/metabolismo , Transportador de Casetes de Unión a ATP, Subfamilia G/genética , Encéfalo/metabolismo , Encéfalo/patología , Ratones Endogámicos C57BL , Placa Amiloide/patologíaRESUMEN
The pathogenesis of Alzheimer's disease (AD) is complex and involves an imbalance between production and clearance of amyloid-ß peptides (Aß), resulting in accumulation of Aß in senile plaques. Hypercholesterolemia is a major risk factor for developing AD, with cholesterol shown to accumulate in senile plaques and increase production of Aß. ABCG4 is a member of the ATP-binding cassette transporters predominantly expressed in the CNS, and has been suggested to play a role in cholesterol and Aß efflux from the brain. In this study, we bred Abcg4 knockout (KO) with the APPSwe,Ind (J9) mouse model of AD to test the hypothesis that loss of Abcg4 would exacerbate the AD phenotype. Unexpectedly, no differences were observed in Novel object recognition (NOR) and Novel object placement (NOP) behavioral tests, or on histologic examinations of brain tissues for senile plaque numbers. Furthermore, clearance of radiolabeled Aß from the brains did not differ between Abcg4 KO and control mice. Metabolic testing by indirect calorimetry, glucose tolerance test (GTT) and insulin tolerance test (ITT), were also mostly similar between groups with only a few mild metabolic differences noted. Overall these data suggest that the loss of ABCG4 did not exacerbate the AD phenotype.
RESUMEN
Fasting is associated with increased susceptibility to hypoglycemia in people with type 1 diabetes, thereby making it a significant health risk. To date, the relationship between fasting and insulin-induced hypoglycemia has not been well characterized, so our objective was to determine whether insulin-independent factors, such as counterregulatory hormone responses, are adversely impacted by fasting in healthy control individuals. Counterregulatory responses to insulin-induced hypoglycemia were measured in 12 healthy people during 2 metabolic studies. During one study, participants ate breakfast and lunch, after which they underwent a 2-hour bout of insulin-induced hypoglycemia (FED). During the other study, participants remained fasted prior to hypoglycemia (FAST). As expected, hepatic glycogen concentrations were lower in FAST, and associated with diminished peak glucagon levels and reduced endogenous glucose production (EGP) during hypoglycemia. Accompanying lower EGP in FAST was a reduction in peripheral glucose utilization, and a resultant reduction in the amount of exogenous glucose required to maintain glycemia. These data suggest that whereas a fasting-induced lowering of glucose utilization could potentially delay the onset of insulin-induced hypoglycemia, subsequent reductions in glucagon levels and EGP are likely to encumber recovery from it. As a result of this diminished metabolic flexibility in response to fasting, susceptibility to hypoglycemia could be enhanced in patients with type 1 diabetes under similar conditions.
Asunto(s)
Diabetes Mellitus Tipo 1 , Hipoglucemia , Humanos , Glucagón , Glucemia/metabolismo , Diabetes Mellitus Tipo 1/tratamiento farmacológico , Diabetes Mellitus Tipo 1/metabolismo , Hipoglucemia/inducido químicamente , Hipoglucemia/metabolismo , Insulina , Glucosa/metabolismo , Ayuno Intermitente , HipoglucemiantesRESUMEN
OBJECTIVE: The objective of this clinical practice guideline is to provide updated and new evidence-based recommendations for the comprehensive care of persons with diabetes mellitus to clinicians, diabetes-care teams, other health care professionals and stakeholders, and individuals with diabetes and their caregivers. METHODS: The American Association of Clinical Endocrinology selected a task force of medical experts and staff who updated and assessed clinical questions and recommendations from the prior 2015 version of this guideline and conducted literature searches for relevant scientific papers published from January 1, 2015, through May 15, 2022. Selected studies from results of literature searches composed the evidence base to update 2015 recommendations as well as to develop new recommendations based on review of clinical evidence, current practice, expertise, and consensus, according to established American Association of Clinical Endocrinology protocol for guideline development. RESULTS: This guideline includes 170 updated and new evidence-based clinical practice recommendations for the comprehensive care of persons with diabetes. Recommendations are divided into four sections: (1) screening, diagnosis, glycemic targets, and glycemic monitoring; (2) comorbidities and complications, including obesity and management with lifestyle, nutrition, and bariatric surgery, hypertension, dyslipidemia, retinopathy, neuropathy, diabetic kidney disease, and cardiovascular disease; (3) management of prediabetes, type 2 diabetes with antihyperglycemic pharmacotherapy and glycemic targets, type 1 diabetes with insulin therapy, hypoglycemia, hospitalized persons, and women with diabetes in pregnancy; (4) education and new topics regarding diabetes and infertility, nutritional supplements, secondary diabetes, social determinants of health, and virtual care, as well as updated recommendations on cancer risk, nonpharmacologic components of pediatric care plans, depression, education and team approach, occupational risk, role of sleep medicine, and vaccinations in persons with diabetes. CONCLUSIONS: This updated clinical practice guideline provides evidence-based recommendations to assist with person-centered, team-based clinical decision-making to improve the care of persons with diabetes mellitus.
Asunto(s)
Diabetes Mellitus Tipo 2 , Dislipidemias , Endocrinología , Niño , Diabetes Mellitus Tipo 2/terapia , Femenino , Humanos , Hipoglucemiantes , Insulina , Embarazo , Estados UnidosRESUMEN
Parenteral nutrition-associated cholestasis (PNAC) significantly limits the safety of intravenous parenteral nutrition (PN). Critically ill infants are highly vulnerable to PNAC-related morbidity and mortality, however the impact of hepatic immaturity on PNAC is poorly understood. We examined developmental differences between fetal/infant and adult livers, and used human induced pluripotent stem cell-derived hepatocyte-like cells (iHLC) to gain insights into the contribution of development to altered sterol metabolism and PNAC. We used RNA-sequencing and computational techniques to compare gene expression patterns in human fetal/infant livers, adult liver, and iHLC. We identified distinct gene expression profiles between the human feta/infant livers compared to adult liver, and close resemblance of iHLC to human developing livers. Compared to adult, both developing livers and iHLC had significant downregulation of xenobiotic, bile acid, and fatty acid metabolism; and lower expression of the sterol metabolizing gene ABCG8. When challenged with stigmasterol, a plant sterol found in intravenous soy lipids, lipid accumulation was significantly higher in iHLC compared to adult-derived HepG2 cells. Our findings provide insights into altered bile acid and lipid metabolizing processes in the immature human liver, and support the use of iHLC as a relevant model system of developing liver to study lipid metabolism and PNAC.
Asunto(s)
Colestasis/dietoterapia , Hepatocitos/citología , Células Madre Pluripotentes Inducidas/citología , Hígado/fisiopatología , Nutrición Parenteral , Femenino , Humanos , Recién Nacido , MasculinoRESUMEN
The enzyme 3ß-hydroxysterol-Δ24 reductase (DHCR24, EC 1.3.1.72) catalyzes the conversion of desmosterol to cholesterol and is obligatory for post-squalene cholesterol synthesis. Genetic loss of this enzyme results in desmosterolosis (MIM #602398), a rare disease that presents with multiple congenital anomalies, features of which overlap with subjects with the Smith-Lemli-Opitz syndrome (another post-squalene cholesterol disorder). Global knockout (KO) of Dhcr24 in mice recapitulates the biochemical phenotype, but pups die within 24 h from a lethal dermopathy, limiting its utility as a disease model. Here, we report a conditional KO mouse model (Dhcr24flx/flx) and validate it by generating a liver-specific KO (Dhcr24flx/flx,Alb-Cre). Dhcr24flx/flx,Alb-Cre mice showed normal growth and fertility, while accumulating significantly elevated levels of desmosterol in plasma and liver. Of interest, despite the loss of cholesterol synthesis in the liver, hepatic architecture, gene expression of sterol synthesis genes, and lipoprotein secretion appeared unchanged. The increased desmosterol content in bile and stool indicated a possible compensatory role of hepatobiliary secretion in maintaining sterol homeostasis. This mouse model should now allow for the study of the effects of postnatal loss of DHCR24, as well as role of tissue-specific loss of this enzyme during development and adulthood.
Asunto(s)
Anomalías Múltiples , Errores Innatos del Metabolismo LipídicoRESUMEN
Smith-Lemli-Opitz Syndrome (SLOS) is a developmental disorder (OMIM #270400) caused by autosomal recessive mutations in the Dhcr7 gene, which encodes the enzyme 3ß-hydroxysterol-Δ7 reductase. SLOS patients present clinically with dysmorphology and neurological, behavioral, and cognitive defects, with characteristically elevated levels of 7-dehydrocholesterol (7-DHC) in all bodily tissues and fluids. Previous mouse models of SLOS have been hampered by postnatal lethality when Dhcr7 is knocked out globally, while a hypomorphic mouse model showed improvement in the biochemical phenotype with aging and did not manifest most other characteristic features of SLOS. We report the generation of a conditional knockout of Dhcr7 (Dhcr7flx/flx), validated by generating a mouse with a liver-specific deletion (Dhcr7L-KO). Phenotypic characterization of liver-specific knockout mice revealed no significant changes in viability, fertility, growth curves, liver architecture, hepatic triglyceride secretion, or parameters of systemic glucose homeostasis. Furthermore, qPCR and RNA-Seq analyses of livers revealed no perturbations in pathways responsible for cholesterol synthesis, either in male or in female Dhcr7L-KO mice, suggesting that hepatic disruption of postsqualene cholesterol synthesis leads to minimal impact on sterol metabolism in the liver. This validated conditional Dhcr7 knockout model may now allow us to systematically explore the pathophysiology of SLOS, by allowing for temporal, cell and tissue-specific loss of DHCR7.
Asunto(s)
Síndrome de Smith-Lemli-OpitzRESUMEN
PURPOSE OF REVIEW: In this review, we summarize the genetics and mechanisms of sitosterolemia and sterol trafficking, and provide an update on the understanding of the prevalence of ABCG5 and ABCG8 variants and their role in human disease. RECENT FINDINGS: Defects in ABCG5/G8 result in the accumulation of xenosterols. It had been previously thought that near total LoF of one of the proteins was required to cause pathology. However, recently there was the first report of a patient with Sitosterolemia who was heterozygous for mutations in both genes. Moreover, large population studies have demonstrated the even simple heterozygous carriers are associated with altered lipid profiles and cardiovascular risk. Broader screening has added to the rapidly growing list of gene variants indicating that the prevalence of ABCG5/G8 variants is higher than previous thought, especially in patients with hypercholesterolemia. SUMMARY: These findings support a strategy of measuring xenosterol levels in patients with hypercholesterolemia to screen for ABCG5/G8 variants, and then tailoring treatment with a sterol absorption inhibitor, like ezetimibe, where indicated. Xenosterol trafficking affects remnant clearance and maybe pathogenically linked to the increased risk of atherosclerosis.
Asunto(s)
Transportador de Casetes de Unión a ATP, Subfamilia G, Miembro 5 , Transportador de Casete de Unión a ATP, Subfamilia G, Miembro 8 , Hipercolesterolemia , Esteroles/farmacocinética , Transportador de Casetes de Unión a ATP, Subfamilia G, Miembro 5/genética , Transportador de Casete de Unión a ATP, Subfamilia G, Miembro 8/genética , Humanos , Hipercolesterolemia/epidemiología , Hipercolesterolemia/genética , Enfermedades Intestinales , Errores Innatos del Metabolismo Lipídico , Lipoproteínas/genética , Fitosteroles/efectos adversosRESUMEN
BACKGROUND: Autosomal dominant familial hypercholesterolemia (ADH; MIM#143890) is one of the most common monogenic disorders characterized by elevated circulatory LDL cholesterol. Initial studies in humans with ADH identified a potential relationship with variants of the gene encoding signal transducing adaptor family member protein 1 (STAP1; MIM#604298). However, subsequent studies have been contradictory. In this study, mice lacking global Stap1 expression (Stap1-/-) were characterized under standard chow and a 42% kcal western diet (WD). METHODS: Mice were studied for changes in different metabolic parameters before and after a 16-week WD regime. Growth curves, body fats, circulatory lipids, parameters of glucose homeostasis, and liver architecture were studied for comparisons. RESULTS: Surprisingly, Stap1-/- mice fed the 16-week WD demonstrated no marked differences in any of the metabolic parameters compared to Stap1+/+ mice. Furthermore, hepatic architecture and cholesterol content in FPLC-isolated lipoprotein fractions also remained comparable to wild-type mice. CONCLUSION: These results strongly suggest that STAP1 does not alter lipid levels, that a western diet did not exacerbate a lipid disorder in Stap1 deficient mice and support the contention that it is not causative for hyperlipidemia in ADH patients. These results support other published studies also questioning the role of this locus in human hypercholesterolemia.
Asunto(s)
Proteínas Adaptadoras Transductoras de Señales/genética , LDL-Colesterol/sangre , Dieta Occidental , Triglicéridos/sangre , Proteínas Adaptadoras Transductoras de Señales/deficiencia , Tejido Adiposo/metabolismo , Animales , Glucemia/metabolismo , Femenino , Expresión Génica , Humanos , Hiperlipoproteinemia Tipo II/genética , Hiperlipoproteinemia Tipo II/metabolismo , Hígado/metabolismo , Masculino , Ratones , Ratones Endogámicos C57BL , Ratones NoqueadosRESUMEN
The elucidation of the molecular basis of the rare disease, sitosterolemia, has revolutionized our mechanistic understanding of how dietary sterols are excreted and how cholesterol is eliminated from the body. Two proteins, ABCG5 and ABCG8, encoded by the sitosterolemia locus, work as obligate dimers to pump sterols out of hepatocytes and enterocytes. ABCG5/ABCG8 are key in regulating whole-body sterol trafficking, by eliminating sterols via the biliary tree as well as the intestinal tract. Importantly, these transporters keep xenosterols from accumulating in the body. The sitosterolemia locus has been genetically associated with lipid levels and downstream atherosclerotic disease, as well as formation of gallstones and the risk of gallbladder cancer. While polymorphic variants raise or lower the risks of these phenotypes, loss of function of this locus leads to more dramatic phenotypes, such as premature atherosclerosis, platelet dysfunction, and thrombocytopenia, and, perhaps, increased endocrine disruption and liver dysfunction. Whether small amounts of xenosterol exposure over a lifetime cause pathology in normal humans with polymorphic variants at the sitosterolemia locus remains largely unexplored. The purpose of this review will be to summarize the current state of knowledge, but also highlight key conceptual and mechanistic issues that remain to be explored.
Asunto(s)
Transportador de Casetes de Unión a ATP, Subfamilia G, Miembro 5/metabolismo , Transportador de Casete de Unión a ATP, Subfamilia G, Miembro 8/metabolismo , Esteroles/metabolismo , Transportador de Casetes de Unión a ATP, Subfamilia G, Miembro 5/química , Transportador de Casetes de Unión a ATP, Subfamilia G, Miembro 5/genética , Transportador de Casete de Unión a ATP, Subfamilia G, Miembro 8/química , Transportador de Casete de Unión a ATP, Subfamilia G, Miembro 8/genética , Animales , HumanosRESUMEN
BACKGROUND: Nemaline myopathy (NEM) is one of the three major forms of congenital myopathy and is characterized by diffuse muscle weakness, hypotonia, respiratory insufficiency, and the presence of nemaline rod structures on muscle biopsy. Mutations in troponin T1 (TNNT1) is 1 of 10 genes known to cause NEM. To date, only homozygous nonsense mutations or compound heterozygous truncating or internal deletion mutations in TNNT1 gene have been identified in NEM. This extended family is of historical importance as some members were reported in the 1960s as initial evidence that NEM is a hereditary disorder. METHODS: Proband and extended family underwent Sanger sequencing for TNNT1. We performed RT-PCR and immunoblot on muscle to assess TNNT1 RNA expression and protein levels in proband and father. RESULTS: We report a novel heterozygous missense mutation of TNNT1 c.311A>T (p.E104V) that segregated in an autosomal dominant fashion in a large family residing in the United States. Extensive sequencing of the other known genes for NEM failed to identify any other mutant alleles. Muscle biopsies revealed a characteristic pattern of nemaline rods and severe myofiber hypotrophy that was almost entirely restricted to the type 1 fiber population. CONCLUSION: This novel mutation alters a residue that is highly conserved among vertebrates. This report highlights not only a family with autosomal dominant inheritance of NEM, but that this novel mutation likely acts via a dominant negative mechanism.
Asunto(s)
Miopatías Nemalínicas/genética , Troponina T/genética , Adolescente , Secuencia de Aminoácidos , Secuencia de Bases , Homocigoto , Humanos , Masculino , Músculo Esquelético/metabolismo , Músculo Esquelético/patología , Mutación Missense , Miopatías Nemalínicas/diagnóstico , Linaje , Polimorfismo de Nucleótido Simple , ARN/química , ARN/aislamiento & purificación , ARN/metabolismo , Empalme del ARN , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Alineación de Secuencia , Análisis de Secuencia de ADNRESUMEN
ABCG4 is an ATP-binding cassette transmembrane protein which has been shown, in vitro, to participate in the cellular efflux of desmosterol and amyloid-ß peptide (Aß). ABCG4 is highly expressed in the brain, but its localization and function at the blood-brain barrier (BBB) level remain unknown. We demonstrate by qRT-PCR and confocal imaging that mouse Abcg4 is expressed in the brain capillary endothelial cells. Modelling studies of the Abcg4 dimer suggested that desmosterol showed thermodynamically favorable binding at the putative sterol-binding site, and this was greater than for cholesterol. Additionally, unbiased docking also showed Aß binding at this site. Using a novel Abcg4-deficient mouse model, we show that Abcg4 was able to export Aß and desmosterol at the BBB level and these processes could be inhibited by probucol and L-thyroxine. Our assay also showed that desmosterol antagonized the export of Aß, presumably as both bind at the sterol-binding site on Abcg4. We show for the first time that Abcg4 may function in vivo to export Aß at the BBB, in a process that can be antagonized by its putative natural ligand, desmosterol (and possibly cholesterol).
Asunto(s)
Transportador de Casetes de Unión a ATP, Subfamilia G/genética , Transportador de Casetes de Unión a ATP, Subfamilia G/metabolismo , Péptidos beta-Amiloides/metabolismo , Barrera Hematoencefálica/metabolismo , Encéfalo/metabolismo , Expresión Génica , Transportador de Casetes de Unión a ATP, Subfamilia G/química , Transportadoras de Casetes de Unión a ATP/genética , Transportadoras de Casetes de Unión a ATP/metabolismo , Péptidos beta-Amiloides/química , Animales , Biomarcadores , Permeabilidad Capilar , Permeabilidad de la Membrana Celular , Desmosterol/metabolismo , Técnica del Anticuerpo Fluorescente , Marcación de Gen , Sitios Genéticos , Ratones , Ratones Noqueados , Modelos Moleculares , Unión Proteica , Conformación Proteica , Multimerización de Proteína , Relación Estructura-ActividadRESUMEN
Sitosterolemia is an autosomal recessive metabolic disease caused by mutations in ABCG5 or ABCG8 genes which encode for the (ATP)-binding cassette (ABC) transporters that are responsible for the trafficking of xenosterols. Liver involvement is not a recognized manifestation of this disease, and cirrhosis has been reported only once in the medical literature. We describe a fatal case of a 21-year old South Asian male who presented with decompensated cirrhosis, and biochemical abnormalities consistent with sitosterolemia. Genetic testing showed a homozygous pathogenic mutation in ABCG5, confirming the diagnosis. Sitosterolemia is a rare, but likely under-recognized condition, and a high degree of suspicion is imperative to make the diagnosis. We propose that sitosterolemia should be included in the differential diagnosis for patients with cryptogenic cirrhosis, especially as there are effective oral therapies to treat this condition. Newly diagnosed sitosterolemia patients should undergo a thorough hepatology evaluation and follow-up to evaluate for the presence, development, and progression of any hepatic involvement.
Asunto(s)
Hipercolesterolemia/complicaciones , Enfermedades Intestinales/complicaciones , Errores Innatos del Metabolismo Lipídico/complicaciones , Cirrosis Hepática/etiología , Fitosteroles/efectos adversos , Transportador de Casetes de Unión a ATP, Subfamilia G, Miembro 5/genética , Anemia Hemolítica/etiología , Anticolesterolemiantes/uso terapéutico , Biopsia , Angiografía Coronaria , Enfermedad de la Arteria Coronaria/etiología , Análisis Mutacional de ADN , Dieta con Restricción de Grasas , Ezetimiba/uso terapéutico , Resultado Fatal , Predisposición Genética a la Enfermedad , Herencia , Homocigoto , Humanos , Hipercolesterolemia/diagnóstico , Hipercolesterolemia/genética , Hipercolesterolemia/terapia , Enfermedades Intestinales/diagnóstico , Enfermedades Intestinales/genética , Enfermedades Intestinales/terapia , Errores Innatos del Metabolismo Lipídico/diagnóstico , Errores Innatos del Metabolismo Lipídico/genética , Errores Innatos del Metabolismo Lipídico/terapia , Lipoproteínas/genética , Cirrosis Hepática/diagnóstico , Masculino , Microscopía Electrónica , Mutación , Linaje , Fenotipo , Fitosteroles/genética , Factores de Riesgo , Resultado del Tratamiento , Xantomatosis/etiología , Adulto JovenRESUMEN
BACKGROUND: Premature and critically ill infants receiving total parenteral nutrition (TPN) are at risk for dyslipidemia, and altered cholesterol levels in early life may contribute to later cardiovascular risk. Data regarding plasma cholesterol response to TPN in young infants are lacking. OBJECTIVE: To determine the changes in plasma cholesterol levels during the first week of life in infants receiving TPN and a comparison group of infants who did not receive TPN during routine care. METHODS: In a prospective, pilot cohort study, 38 neonates (30 TPN vs. 8 No-TPN) underwent serial blood sampling during the first week of life. Gas chromatography-mass spectrometry was used to measure cholesterol in plasma and TPN administered to study participants. RESULTS: Baseline cholesterol level was similar between groups. In contrast to infants who did not receive TPN, cholesterol levels during the first week of life were significantly higher than baseline in infants receiving TPN (maximum cholesterol response 34% vs. 103% change from baseline, No-TPN vs. TPN, respectively, P = .036). After adjusting for cumulative cholesterol received by infants receiving TPN, maximum cholesterol response remained inversely related to gestational age and birth weight (P < .05). CONCLUSION: Plasma cholesterol significantly increases during the first week of life in neonates receiving TPN. A higher cholesterol response was induced by TPN in infants of lower gestational age and birth weight.
Asunto(s)
Colesterol/sangre , Edad Gestacional , Nutrición Parenteral Total/efectos adversos , Femenino , Humanos , Lactante , Recién Nacido , Masculino , Nacimiento Prematuro/sangreRESUMEN
UNLABELLED: The adenosine triphosphate-binding cassette (ABC) sterol transporter, Abcg5/g8, is Lith9 in mice, and two gallstone-associated variants in ABCG5/G8 have been identified in humans. Although ABCG5/G8 plays a critical role in determining hepatic sterol secretion, cholesterol is still secreted to bile in sitosterolemic patients with a defect in either ABCG5 or ABCG8 and in either Abcg5/g8 double- or single-knockout mice. We hypothesize that in the defect of ABCG5/G8, an ABCG5/G8-independent pathway is essential for regulating hepatic secretion of biliary sterols, which is independent of the lithogenic mechanism of the ABCG5/G8 pathway. To elucidate the effect of the ABCG5/G8-independent pathway on cholelithogenesis, we investigated the biliary and gallstone characteristics in male wild-type (WT), ABCG5(-/-)/G8(-/-), and ABCG8 (-/-) mice fed a lithogenic diet or varying amounts of cholesterol, treated with a liver X receptor (LXR) agonist, or injected intravenously with [(3) H]sitostanol- and [(14) C]cholesterol-labeled high-density lipoprotein (HDL). We found that ABCG5(-/-)/G8(-/-) and ABCG8 (-/-) mice displayed the same biliary and gallstone phenotypes. Although both groups of knockout mice showed a significant reduction in hepatic cholesterol output compared to WT mice, they still formed gallstones. The LXR agonist significantly increased biliary cholesterol secretion and gallstones in WT, but not ABCG5(-/-)/G8(-/-) or ABCG8 (-/-), mice. The 6-hour recovery of [(14) C]cholesterol in hepatic bile was significantly lower in both groups of knockout mice than in WT mice and [(3) H]sitostanol was detected in WT, but not ABCG5(-/-)/G8(-/-) or ABCG8 (-/-), mice. CONCLUSIONS: The ABCG5/G8-independent pathway plays an important role in regulating biliary cholesterol secretion, the transport of HDL-derived cholesterol from plasma to bile, and gallstone formation, which works independently of the ABCG5/G8 pathway. Further studies are needed to observe whether this pathway is also operational in humans. (Hepatology 2016;64:853-864).
Asunto(s)
Transportador de Casetes de Unión a ATP, Subfamilia G, Miembro 5/genética , Transportador de Casete de Unión a ATP, Subfamilia G, Miembro 8/genética , Colesterol/metabolismo , Cálculos Biliares/etiología , Lipoproteínas/genética , Animales , Bilis/metabolismo , Ácidos y Sales Biliares/metabolismo , Femenino , Vesícula Biliar/fisiología , Cálculos Biliares/metabolismo , Hidrocarburos Fluorados , Metabolismo de los Lípidos , Masculino , Ratones Endogámicos C57BL , Ratones Noqueados , SulfonamidasRESUMEN
UNLABELLED: The cholesterol synthesis pathway is a ubiquitous cellular biosynthetic pathway that is attenuated therapeutically by statins. Importantly, type I interferon (IFN), a major antiviral mediator, also depresses the cholesterol synthesis pathway. Here we demonstrate that attenuation of cholesterol synthesis decreases gammaherpesvirus replication in primary macrophages in vitro and reactivation from peritoneal exudate cells in vivo. Specifically, the reduced availability of the intermediates required for protein prenylation was responsible for decreased gammaherpesvirus replication in statin-treated primary macrophages. We also demonstrate that statin treatment of a chronically infected host attenuates gammaherpesvirus latency in a route-of-infection-specific manner. Unexpectedly, we found that the antiviral effects of statins are counteracted by type I IFN. Our studies suggest that type I IFN signaling counteracts the antiviral nature of the subdued cholesterol synthesis pathway and offer a novel insight into the utility of statins as antiviral agents. IMPORTANCE: Statins are cholesterol synthesis inhibitors that are therapeutically administered to 12.5% of the U.S. POPULATION: Statins attenuate the replication of diverse viruses in culture; however, this attenuation is not always obvious in an intact animal model. Further, it is not clear whether statins alter parameters of highly prevalent chronic herpesvirus infections. We show that statin treatment attenuated gammaherpesvirus replication in primary immune cells and during chronic infection of an intact host. Further, we demonstrate that type I interferon signaling counteracts the antiviral effects of statins. Considering the fact that type I interferon decreases the activity of the cholesterol synthesis pathway, it is intriguing to speculate that gammaherpesviruses have evolved to usurp the type I interferon pathway to compensate for the decreased cholesterol synthesis activity.
Asunto(s)
Antivirales/farmacología , Colesterol/biosíntesis , Gammaherpesvirinae/inmunología , Infecciones por Herpesviridae/inmunología , Inhibidores de Hidroximetilglutaril-CoA Reductasas/farmacología , Interferón Tipo I/inmunología , Lovastatina/farmacología , Animales , Células Cultivadas , Gammaherpesvirinae/efectos de los fármacos , Infecciones por Herpesviridae/virología , Macrófagos/metabolismo , Macrófagos/virología , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Prenilación de Proteína , Receptor de Interferón alfa y beta/genética , Transducción de Señal , Latencia del Virus/efectos de los fármacos , Replicación Viral/genéticaRESUMEN
Cerebrotendinous Xanthomatosis (CTX) is a treatable inborn error of metabolism caused by recessive variants in CYP27A1. Clinical presentation varies, but typically includes infant-onset chronic diarrhea, juvenile-onset bilateral cataracts, and later-onset tendinous xanthomas and progressive neurological dysfunction. CYP27A1 plays an essential role in side-chain oxidation of cholesterol necessary for the synthesis of the bile acid, chenodeoxycholic acid, and perturbations in this gene that reduce enzyme activity result in elevations of cholestanol. It is commonly held that CTX is exceedingly rare, but epidemiological studies are lacking. In order to provide an accurate incidence estimate of CTX, we studied the ExAC cohort of ~60,000 unrelated adults from global populations to determine the allele frequency of the 57 variants in CYP27A1 reported pathogenic for CTX. In addition, we conducted bioinformatics analyses on these CTX-causing variants and determined a bioinformatics profile to predict variants that may be pathogenic but have not yet been reported in the CTX patient literature. An additional 29 variants were identified that met bioinformatics criteria for being potentially pathogenic. Incidence was estimated based allele frequencies of pathogenic CTX variants plus those determined to be potentially pathogenic. One variant, p.P384L, previously reported in three unrelated CTX families had an allele frequency ≥ 1% in European, Latino and Asian populations. Three additional mutations had a frequency of ≥ 0.1% in Asian populations. CTX disease incidence was calculated excluding the high frequency p.P384L and separately using a genetic paradigm where this high frequency variant only causes classic CTX when paired in trans with a null variant. These calculations place CTX incidence ranging from 1:134,970 to 1:461,358 in Europeans, 1:263,222 to 1:468,624 in Africans, 1:71,677 to 1:148,914 in Americans, 1:64,267 to 1:64,712 in East Asians and 1:36,072 to 1:75,601 in South Asians. This work indicates CTX is under-diagnosed and improved patient screening is needed as early intervention prevents disease progression.
Asunto(s)
Colestanotriol 26-Monooxigenasa/genética , Exoma , Mutación , Xantomatosis Cerebrotendinosa/diagnóstico , Xantomatosis Cerebrotendinosa/epidemiología , Xantomatosis Cerebrotendinosa/genética , África/epidemiología , Alelos , Américas/epidemiología , Asia/epidemiología , Catarata/patología , Ácido Quenodesoxicólico/metabolismo , Colestanol/metabolismo , Colesterol/metabolismo , Enfermedad Crónica , Biología Computacional , Bases de Datos Genéticas , Diarrea/patología , Europa (Continente)/epidemiología , Frecuencia de los Genes , Genes Recesivos , Humanos , Incidencia , Xantomatosis/patología , Xantomatosis Cerebrotendinosa/patologíaRESUMEN
The human diet is naturally varied and contains not only essential nutrients, but also contains molecules that the body actively excludes or minimizes exposure. Among these molecules are xenosterols, of which plant sterols comprise the greatest exposure risk. These sterols comprise approximately 50% of the total sterols we eat, yet we retain <0.5% of these in our bodies. The bulk of this exclusion takes place in the intestine and the heterodimeric transporters ABCG5 and ABCG8 are key to keeping these xenosterols out of our bodies. In normal humans, pharmacological supplementation with plant sterols (and stanols) has been used to lower cholesterol as these impair intestinal absorption/ re-absorption of this molecule; lowering plasma cholesterol has cardiovascular risk benefits. This review challenges whether this intervention is beneficial and may even be harmful. We summarize the evidence involving humans who have genetic disruption of ABCG5/ABCG8 function, from clinical trial data examining plant sterols and cardiovascular risk, from genetic data affecting normal humans and ABCG5/ABCG8 variations to data obtained using animal models. Accumulation of xenosterols in any significant amount is clearly associated with increased toxicity, and data suggest that at even low levels there may be effects. Importantly, there is also a paucity of data showing cardiovascular end-point benefits with plant sterol/stanol supplementation. The summary of evidence highlights not only caution in recommending such strategies to lower plasma cholesterol, but also in investigating how these xenosterols can affect processes ranging from cardiovascular, endocrine, and neurological function.
Asunto(s)
Aterosclerosis/inducido químicamente , Aterosclerosis/genética , Fitosteroles/efectos adversos , Plantas/química , Animales , Ensayos Clínicos como Asunto , Humanos , Hipercolesterolemia/complicaciones , Enfermedades Intestinales/complicaciones , Errores Innatos del Metabolismo Lipídico/complicacionesRESUMEN
BACKGROUND: Phytosterols in soybean oil (SO) lipids likely contribute to parenteral nutrition-associated liver disease (PNALD) in infants. No characterization of phytosterol metabolism has been done in infants receiving SO lipids. METHODS: In a prospective cohort study, 45 neonates (36 SO lipid vs. 9 control) underwent serial blood sample measurements of sitosterol, campesterol, and stigmasterol. Mathematical modeling was used to determine pharmacokinetic parameters of phytosterol metabolism and phytosterol exposure. RESULTS: Compared to controls, SO lipid-exposed infants had significantly higher levels of sitosterol and campesterol (P < 0.01). During SO lipid infusion, sitosterol and campesterol reached half of steady-state plasma levels within 1.5 and 0.8 d, respectively. Steady-state level was highest for sitosterol (1.68 mg/dl), followed by campesterol (0.98 mg/dl), and lowest for stigmasterol (0.01 mg/dl). Infants born < 28 wk gestational age had higher sitosterol steady-state levels (P = 0.03) and higher area under the curve for sitosterol (P = 0.03) during the first 5 d of SO lipid (AUC5) than infants born ≥ 28 wk gestational age. CONCLUSION: Phytosterols in SO lipid accumulate rapidly in neonates. Very preterm infants receiving SO lipid have higher sitosterol exposure, and may have poorly developed mechanisms of eliminating phytosterols that may contribute to their vulnerability to PNALD.
Asunto(s)
Nutrición Parenteral , Fitosteroles/farmacocinética , Femenino , Semivida , Humanos , Recién Nacido , Masculino , Estudios ProspectivosRESUMEN
The discovery and elucidation of the role of the low-density lipoprotein receptor (LDL-R) in familial hypercholesterolemia (FH) ushered in the statin group of drugs. These drugs, in addition to lowering low-density lipoprotein cholesterol (LDL-C), result in a significant reduction in cardiovascular events (CVE) and mortality. Recently, a gain-of-function mutation in another protein, proprotein convertase subtilisin/kexin type 9 (PCSK9), was reported to result in a FH phenotype by promoting degradation of the LDL-R. More importantly, loss-of-function mutations in the same gene resulted in low LDL-C and a reduction in CVE, making this an enticing target for drug development. Numerous strategies have been developed to target PCSK9, the most successful being monoclonal antibodies (mAbs) that bind PCSK9. These mAbs have been shown to reduce LDL-C around 50% as either monotherapy with diet or in combination with statin therapy. In this short perspective, we discuss the biochemistry and biology of PCSK9 in relation to lipid metabolism and the promising studies in humans demonstrating a substantial reduction in LDL-C with relative good short-term safety of PCSK9 mAbs.