RESUMEN
Obesity is characterized by chronic low-grade inflammation that could lead to other health complications, such as cardiovascular disease, diabetes, and various forms of cancer. Emerging evidence has shown that taste perception is altered during the development of obesity. Moreover, suppression of taste receptor or taste signaling molecules potentiate the inflammatory response, and the progression of inflammation attenuates the expression of taste receptors in vivo. Together, these findings suggest a possible interplay between taste signaling and inflammation. This review summarizes the interactions between type 1 (T1Rs) and type 2 taste receptors (T2Rs) and inflammation, as well as the impact of obesity on T1R- and T2R-mediated signaling. Furthermore, we evaluate the possible role that taste receptors play in regulating the inflammatory response during obesity as a therapeutic target to prevent the progression of comorbidities associated with obesity.
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Diabetes Mellitus Tipo 2 , Papilas Gustativas , Humanos , Inflamación , Obesidad/complicaciones , Gusto/fisiología , Percepción del GustoRESUMEN
Eggs are protein-rich, nutrient-dense, and contain bioactive ingredients that have been shown to modify gene expression and impact health. To understand the effects of egg consumption on tissue-specific mRNA and microRNA expression, we examined the role of whole egg consumption (20% protein, w/w) on differentially expressed genes (DEGs) between rat (n = 12) transcriptomes in the prefrontal cortex (PFC), liver, kidney, and visceral adipose tissue (VAT). Principal component analysis with hierarchical clustering was used to examine transcriptome profiles between dietary treatment groups. We performed Gene Ontology and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis as well as genetic network and disease enrichment analysis to examine which metabolic pathways were the most predominantly altered in each tissue. Overall, our data demonstrates that whole egg consumption for 2 weeks modified the expression of 52 genes in the PFC, 22 genes in VAT, and two genes in the liver (adj p < 0.05). Additionally, 16 miRNAs were found to be differentially regulated in the PFC, VAT, and liver, but none survived multiple testing correction. The main pathways influenced by WE consumption were glutathione metabolism in VAT and cholesterol biosynthesis in the PFC. These data highlight key pathways that may be involved in diseases and are impacted by acute consumption of a diet containing whole eggs.
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Nutrigenomic evidence supports the idea that Type 2 Diabetes Mellitus (T2DM) arises due to the interactions between the transcriptome, individual genetic profiles, lifestyle, and diet. Since eggs are a nutrient dense food containing bioactive ingredients that modify gene expression, our goal was to examine the role of whole egg consumption on the transcriptome during T2DM. We analyzed whether whole egg consumption in Zucker Diabetic Fatty (ZDF) rats alters microRNA and mRNA expression across the adipose, liver, kidney, and prefrontal cortex tissue. Male ZDF (fa/fa) rats (n = 12) and their lean controls (fa/+) (n = 12) were obtained at 6 wk of age. Rats had ad libitum access to water and were randomly assigned to a modified semi-purified AIN93G casein-based diet or a whole egg-based diet, both providing 20% protein (w/w). TotalRNA libraries were prepared using QuantSeq 3' mRNA-Seq and Lexogen smallRNA library prep kits and were further sequenced on an Illumina HighSeq3000. Differential gene expression was conducted using DESeq2 in R and Benjamini-Hochberg adjusted P-values controlling for false discovery rate at 5%. We identified 9 microRNAs and 583 genes that were differentially expressed in response to 8 wk of consuming whole egg-based diets. Kyto Encyclopedia of Genes and Genomes/Gene ontology pathway analyses demonstrated that 12 genes in the glutathione metabolism pathway were upregulated in the liver and kidney of ZDF rats fed whole egg. Whole egg consumption primarily altered glutathione pathways such as conjugation, methylation, glucuronidation, and detoxification of reactive oxygen species. These pathways are often negatively affected during T2DM, therefore this data provides unique insight into the nutrigenomic response of dietary whole egg consumption during the progression of T2DM.
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Diabetes Mellitus Tipo 2/genética , Diabetes Mellitus Tipo 2/metabolismo , Huevos , Glutatión/metabolismo , Nutrigenómica , Animales , Diabetes Mellitus Tipo 2/dietoterapia , Huevos/efectos adversos , Perfilación de la Expresión Génica , Masculino , Redes y Vías Metabólicas/genética , MicroARNs/genética , MicroARNs/metabolismo , Ratas , Ratas Zucker , Distribución Tisular , Regulación hacia ArribaRESUMEN
BACKGROUND: Whole egg (WE) consumption has been demonstrated to attenuate body weight (BW) gain and adiposity in genetic animal models of type 2 diabetes (T2D). This finding was accompanied by increased food consumption. OBJECTIVES: This study aimed to examine the effects of long-term WE intake on BW gain, fat distribution, and food intake in a rat model of diet-induced obesity (DIO). METHODS: Male Sprague Dawley rats (n = 24) were obtained at 5 wk of age and were randomly weight-matched across 1 of 4 dietary intervention groups (6 rats per group): a casein-based diet (CAS), a high-fat high-sucrose CAS diet (HFHS CAS), a whole egg-based diet (EGG), or a high-fat high-sucrose EGG diet (HFHS EGG). All diets provided 20% (w/w) protein and were provided for 33 wk. HFHS diets provided â¼61% of kilocalories from fat and 10% from sucrose. Daily weight gain and food intake were recorded, biochemical parameters were measured via ELISA, and epididymal fat pad weights were recorded at the end of the study. RESULTS: At 33 wk, cumulative BW gain in DIO rats fed HFHS EGG resulted in 23% lower weight gain compared with DIO rats fed HFHS CAS (P < 0.0001), but no significant differences in BW gain were observed between the HFHS EGG group and the control EGG and CAS groups (P = 0.71 and P = 0.61, respectively). Relative food intake (grams per kilogram BW) was 23% lower (P < 0.0001) in rats fed HFHS CAS compared with CAS, whereas there was no difference in food intake within the EGG dietary groups. DIO rats fed HFHS EGG exhibited a 22% decrease in epididymal fat weight compared with their counterparts fed the HFHS CAS. CONCLUSIONS: Our data demonstrate that consumption of a WE-based diet reduced BW gain and visceral fat in the DIO rat, similar to our previous findings in a genetic rat model with T2D.
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Glucemia , Dieta , Huevos , Aumento de Peso , Animales , Insulina/sangre , Masculino , Obesidad/sangre , Ratas , Ratas Sprague-Dawley , Triglicéridos/sangreRESUMEN
BACKGROUND: We previously reported that a whole-egg-based diet attenuated weight gain in rats with type 2 diabetes (T2D) and more effectively maintained vitamin D status than an equivalent amount of supplemental cholecalciferol. OBJECTIVES: The objective of this study was to determine the lowest dose of whole egg effective at maintaining vitamin D homeostasis and attenuating the obese phenotype in T2D rats. METHODS: Zucker diabetic fatty (ZDF) rats (n = 40; age 6 wk; prediabetic) and their lean controls (n = 40; age 6 wk) were randomly assigned to a diet containing 20% casein (CAS) or 20%, 10%, 5%, or 2.5% protein from whole egg (20% EGG, 10% EGG, 5% EGG, and 2.5% EGG, respectively). All diets contained 20% total protein (wt:wt). All rats received their respective diets for 8 wk, at a stage of growth and development that translates to adolescence in humans, until 14 wk of age, a point at which ZDF rats exhibit overt T2D. Weight gain was measured 5 d/wk, and circulating 25-hydroxyvitamin D [25(OH)D] was measured by ELISA. Mean values were compared by 2-factor ANOVA. RESULTS: The 20% EGG diet maintained serum 25(OH)D at 30 nmol/L in ZDF rats, whereas the 10%, 5%, and 2.5% EGG diets did not prevent insufficiency, resulting in mean serum 25(OH)D concentrations of 24 nmol/L in ZDF rats. Body weight gain was reduced by 29% (P < 0.001) and 31% (P < 0.001) in ZDF rats consuming 20% and 10% EGG diets, respectively, and by 16% (P = 0.004) and 12% (P = 0.030) in ZDF rats consuming 5% and 2.5% EGG diets, respectively, compared with CAS. CONCLUSIONS: Whole-egg-based diets exerted a dose-dependent response with respect to attenuating weight gain. These data could support dietary recommendations aimed at body weight management in individuals predisposed to obesity and T2D.
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Diabetes Mellitus Tipo 2/sangre , Dieta , Huevos , Obesidad/prevención & control , Alimentación Animal , Animales , Glucemia , Humanos , Distribución Aleatoria , Ratas , Ratas ZuckerRESUMEN
BACKGROUND: The literature regarding the relation between egg consumption and type 2 diabetes (T2D) is inconsistent and there is limited evidence pertaining to the impact of egg consumption on measures of insulin sensitivity. OBJECTIVES: The aim of this study was to investigate the effect of dietary whole egg on metabolic biomarkers of insulin resistance in T2D rats. METHODS: Male Zucker diabetic fatty (ZDF) rats (n = 12; 6 wk of age) and age-matched lean controls (n = 12) were randomly assigned to be fed a casein- or whole egg-based diet. At week 5 of dietary treatment, an insulin tolerance test (ITT) was performed on all rats and blood glucose was measured by glucometer. After 7 wk of dietary treatment, rats were anesthetized and whole blood was collected via a tail vein bleed. Following sedation, the extensor digitorum longus muscle was removed before and after an intraperitoneal insulin injection, and insulin signaling in skeletal muscle was analyzed by Western blot. Serum glucose and insulin were analyzed by ELISA for calculation of the homeostatic model assessment of insulin resistance (HOMA-IR). RESULTS: Mean ITT blood glucose over the course of 60 min was 32% higher in ZDF rats fed the whole egg-based diet than in ZDF rats fed the casein-based diet. Furthermore, whole egg consumption increased fasting blood glucose by 35% in ZDF rats. Insulin-stimulated phosphorylation of key proteins in the insulin signaling pathway did not differ in skeletal muscle of ZDF rats fed casein- and whole egg-based diets. In lean rats, no differences were observed in insulin tolerance, HOMA-IR and skeletal muscle insulin signaling, regardless of experimental dietary treatment. CONCLUSIONS: These data suggest that whole body insulin sensitivity may be impaired by whole egg consumption in T2D rats, although no changes were observed in skeletal muscle insulin signaling that could explain this finding.
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Nephropathy is a well-characterized complication of type 1 diabetes (T1D), resulting in proteinuria and urinary loss of micronutrients. We previously found that a whole egg-based diet maintained vitamin D balance in type 2 diabetic rats despite excessive urinary losses due to nephropathy. The goal of this study was to investigate the impact of whole egg consumption in T1D rats. Sprague-Dawley rats were randomly assigned to T1D or nondiabetic control groups and fed a casein or whole egg-based diet for 32 days. On day 26, two-thirds of the rats received a streptozotocin injection to induce T1D. Whole egg consumption attenuated polyuria, proteinuria, and renal hypertrophy in T1D rats. These data suggest that dietary intervention with whole egg may offer renal protection in T1D.
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Diabetes Mellitus Experimental/complicaciones , Diabetes Mellitus Tipo 1/complicaciones , Nefropatías Diabéticas/prevención & control , Dieta , Huevos , Animales , Hipertrofia/prevención & control , Riñón/patología , Masculino , Poliuria/prevención & control , Proteinuria/prevención & control , Ratas , Ratas Sprague-Dawley , Vitamina D/sangre , Deficiencia de Vitamina D/prevención & controlRESUMEN
Background: Type 2 diabetes (T2D) is characterized by vitamin D insufficiency owing to excessive urinary loss of 25-hydroxycholecalciferol [25(OH)D]. We previously reported that a diet containing dried whole egg, a rich source of vitamin D, was effective at maintaining circulating 25(OH)D concentrations in rats with T2D. Furthermore, whole egg consumption reduced body weight gain in rats with T2D.Objective: This study was conducted to compare whole egg consumption with supplemental cholecalciferol with respect to vitamin D balance, weight gain, and body composition in rats with T2D.Methods: Male Zucker diabetic fatty (ZDF) rats (n = 24) and their lean controls (n = 24) were obtained at 5 wk of age and randomly assigned to 3 treatment groups: a casein-based diet (CAS), a dried whole egg-based diet (WE), or a casein-based diet containing supplemental cholecalciferol (CAS+D) at the same amount of cholecalciferol provided by WE (37.6 µg/kg diet). Rats were fed their respective diets for 8 wk. Weight gain and food intake were measured daily, circulating 25(OH)D concentrations were measured by ELISA, and body composition was analyzed by dual X-ray absorptiometry.Results: Weight gain and percentage of body fat were reduced by â¼20% and 11%, respectively, in ZDF rats fed WE compared with ZDF rats fed CAS or CAS+D. ZDF rats fed CAS had 21% lower serum 25(OH)D concentrations than lean rats fed CAS. In ZDF rats, WE consumption increased serum 25(OH)D concentrations 130% compared with CAS, whereas consumption of CAS+D increased serum 25(OH)D concentrations 35% compared with CAS.Conclusions: Our data suggest that dietary consumption of whole eggs is more effective than supplemental cholecalciferol in maintaining circulating 25(OH)D concentrations in rats with T2D. Moreover, whole egg consumption attenuated weight gain and reduced percentage of body fat in ZDF rats. These data may support new dietary recommendations targeting the prevention of vitamin D insufficiency in T2D.
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Calcifediol/sangre , Colecalciferol/uso terapéutico , Diabetes Mellitus Experimental/complicaciones , Diabetes Mellitus Tipo 2/complicaciones , Huevos , Deficiencia de Vitamina D/prevención & control , Aumento de Peso/efectos de los fármacos , Animales , Colecalciferol/sangre , Diabetes Mellitus Experimental/sangre , Diabetes Mellitus Experimental/dietoterapia , Diabetes Mellitus Tipo 2/sangre , Diabetes Mellitus Tipo 2/dietoterapia , Dieta , Suplementos Dietéticos , Conducta Alimentaria , Masculino , Ratas Zucker , Vitamina D/sangre , Deficiencia de Vitamina D/sangre , Deficiencia de Vitamina D/etiologíaRESUMEN
The worldwide prevalence of diabetes mellitus is expected to reach 439 million by 2030. Diabetes increases the risk for developing secondary complications such as nephropathy and cardiovascular disease, critical factors that dictate the survival rate of diabetes patients. Compelling evidence has indicated that the positive impact of fermentable carbohydrates in obesity-related diabetes is mediated by the production of short-chain fatty acids and the modulation of colonic microbiota. This review summarizes the potential implications of dietary resistant starch, a class of fermentable fiber, in glucose homeostasis and kidney health in obesity-associated diabetes and examines the mechanisms underlying the protective effect of resistant starch. Though extensive clinical studies are still warranted, replacement of simple carbohydrates with resistant starch could be a highly effective alternative dietary strategy to prevent secondary complications resulting from hyperglycemia.
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Diabetes Mellitus/dietoterapia , Fibras de la Dieta , Enfermedades Renales/prevención & control , Almidón , Animales , Dieta , Glucosa/metabolismo , Homeostasis , HumanosRESUMEN
We previously demonstrated that feeding of dietary resistant starch (RS) prior to the induction of diabetes delayed the progression of diabetic nephropathy and maintained vitamin D balance in streptozotocin (STZ)-induced type 1 diabetic (T1D) rats. Here, we examined the impact of RS on kidney function and vitamin D homeostasis following STZ injection. Male Sprague-Dawley rats were administered STZ and fed a standard diet containing cornstarch or 20, 10, or 5% RS for 4 weeks. T1D rats fed 10 and 20% RS, but not 5% RS, gained more weight than cornstarch-fed rats. Yet, renal health and glucose metabolism were not improved by RS. Our data suggest that RS normalized growth patterns in T1D rats after diabetes induction in a dose-dependent manner despite having no effect on blood glucose and vitamin D balances. Future interventions should focus on the preventative strategies with RS in T1D.
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Diabetes Mellitus Experimental/dietoterapia , Riñón/efectos de los fármacos , Almidón/farmacología , Animales , Peso Corporal/efectos de los fármacos , Diabetes Mellitus Experimental/fisiopatología , Diabetes Mellitus Tipo 1/dietoterapia , Hiperglucemia/metabolismo , Interleucina-6/sangre , Riñón/fisiología , Pruebas de Función Renal , Masculino , Ratas Sprague-Dawley , Almidón/química , Estreptozocina , Factor de Necrosis Tumoral alfa/sangre , Vitamina D/sangreRESUMEN
We previously reported that dietary resistant starch (RS) type 2 prevented proteinuria and promoted vitamin D balance in type 2 diabetic (T2D) rats. Here, our primary objective was to identify potential mechanisms that could explain our earlier observations. We hypothesized that RS could promote adiponectin secretion and regulate the renin-angiotensin system activity in the kidney. Lean Zucker rats (n = 5) were fed control diet; Zucker diabetic fatty rats (n = 5/group) were fed either an AIN-93G control diet (DC) or AIN-93G diet containing either 10% RS or 20% RS (HRS) for 6 weeks. Resistant starch had no impact on blood glucose concentrations and hemoglobin A1c percentage, yet circulating adiponectin was 77% higher in HRS-fed rats, compared to DC rats. Adiponectin concentrations strongly correlated with serum 25-hydroxycholecalciferol (r = 0.815; P < .001) and urinary creatinine concentrations (r = 0.818; P < .001) and inversely correlated with proteinuria (r = -0.583; P = .02). Serum angiotensin II concentrations were 44% lower, and expression of the angiotensin II receptor, type 1, was attenuated in RS-fed rats. Moreover, we observed a 14-fold increase in messenger RNA expression of nephrin, which is required for functioning of the renal filtration barrier, in HRS rats. The HRS, but not 10% RS diet, increased circulating 25-hydroxycholecalciferol concentrations and attenuated urinary loss of vitamin D metabolites in Zucker diabetic fatty rats. Taken together, we provide evidence that vitamin D balance in the presence of hyperglycemia is strongly associated with serum adiponectin levels and reduced renal renin-angiotensin system signaling.
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Adiponectina/sangre , Calcifediol/sangre , Diabetes Mellitus Tipo 2/fisiopatología , Carbohidratos de la Dieta/administración & dosificación , Riñón/fisiopatología , Almidón/administración & dosificación , Adiposidad , Angiotensina II/sangre , Animales , Glucemia/análisis , Diabetes Mellitus Tipo 2/sangre , Expresión Génica , Hemoglobina Glucada/análisis , Insulina/sangre , Masculino , Proteínas de la Membrana/genética , Ratas , Ratas Zucker , Sistema Renina-Angiotensina/efectos de los fármacos , Sistema Renina-Angiotensina/fisiología , Transducción de Señal , Almidón/metabolismoRESUMEN
Type 2 diabetes (T2D) is characterized by vitamin D deficiency owing to increased urinary loss of 25-hydroxycholecalciferol (25D). Whole eggs are a rich source of vitamin D, particularly 25D, the circulating form that reflects status. Zucker diabetic (type 2) fatty (ZDF) rats and their lean counterparts were fed casein- or whole egg-based diets for 8 weeks. Whole egg consumption attenuated both hyperglycemia and hypertriglyceridemia, as well as reduced weight gain in ZDF rats compared to casein-fed diabetic rats. Circulating 25D was lower in casein-fed ZDF rats compared to lean controls; however, ZDF rats fed whole egg exhibited the same circulating 25D concentration as casein-fed lean rats. These data suggest that dietary whole egg can attenuate metabolic anomalies, as well as maintain normal circulating 25D concentrations in T2D rats. This finding may support new dietary recommendations targeting vitamin D deficiency prevention in T2D.
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Calcifediol/sangre , Diabetes Mellitus Tipo 2/metabolismo , Huevos/análisis , Animales , Diabetes Mellitus Tipo 2/sangre , Diabetes Mellitus Tipo 2/dietoterapia , Modelos Animales de Enfermedad , Humanos , Masculino , Ratas , Ratas Zucker , Vitamina D/metabolismoRESUMEN
BACKGROUND: Type 2 diabetes (T2D) is the leading cause of nephropathy in the United States. Renal complications of T2D include proteinuria and suboptimal serum 25-hydroxycholecalciferol (25D) concentrations. 25D is the major circulating form of vitamin D and renal reabsorption of the 25D-vitamin D-binding protein (DBP) complex via megalin-mediated endocytosis is believed to determine whether 25D can be activated to 1,25-dihydroxycholecalciferol (1,25D) or returned to circulation. We previously demonstrated that excessive urinary excretion of 25D-DBP and albuminuria occurred in rats with type 1 diabetes (T1D) and T2D. Moreover, feeding rats with T1D high-amylose maize partially resistant to digestion [resistant starch (RS)] prevented excretion of 25D-DBP without significantly affecting hyperglycemia. OBJECTIVE: We used Zucker diabetic fatty (ZDF) rats, a model of obesity-related T2D, to determine whether feeding RS could similarly prevent loss of vitamin D and maintain serum 25D concentrations. METHODS: Lean control Zucker rats (n = 8) were fed a standard semi-purified diet (AIN-93G) and ZDF rats were fed either the AIN-93G diet (n = 8) or the AIN-93G diet in which cornstarch was replaced with RS (550 g/kg diet; 35% resistant to digestion) (n = 8) for 6 wk. RESULTS: RS attenuated hyperglycemia by 41% (P < 0.01) and prevented urinary DBP excretion and albuminuria, which were elevated 3.0- (P < 0.01) and 3.6-fold (P < 0.01), respectively, in control diet-fed ZDF rats. Additionally, urinary excretion of 25D (P = 0.01) and 1,25D (P = 0.03) was higher (89% and 97%, respectively), whereas serum 25D concentrations were 31% lower (P < 0.001) in ZDF rats fed the control diet compared with RS-fed ZDF rats. Histopathologic scoring of the kidney revealed that RS attenuated diabetes-mediated damage by 21% (P = 0.12) despite an â¼50% decrease in megalin protein abundance. CONCLUSIONS: Taken together, these data provide evidence that suggests vitamin D balance can be maintained by dietary RS through nephroprotective actions in T2D, which are independent of vitamin D supplementation and renal expression of megalin.
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Alimentación Animal/análisis , Calcifediol/sangre , Vitamina D/metabolismo , Animales , Carbohidratos de la Dieta/administración & dosificación , Digestión , Regulación de la Expresión Génica/fisiología , Riñón/metabolismo , Masculino , ARN Mensajero/genética , ARN Mensajero/metabolismo , Distribución Aleatoria , Ratas , Ratas Zucker , Vitamina D/orina , Zea mays/química , Zea mays/metabolismoRESUMEN
Megalin and disabled-2 (Dab2) are essential for uptake of the 25-hydroxycholecalciferol (25D3)-vitamin D binding protein (DBP) complex in tissues. In the kidney, this mechanism regulates serum 25D3 levels and production of 1,25-dihydroxycholecalciferol (1,25D3) by CYP27B1 for systemic use. Previously, we showed that mammary epithelial cells expressing CYP27B1 express megalin and Dab2 and internalize DBP by endocytosis, indicating 25D3 was accessible for conversion to 1,25D3 in extra-renal tissues. Moreover, induction of megalin and Dab2 (protein and mRNA abundance) by all-trans-retinoic acid (RA) enhanced DBP uptake. This suggests megalin and Dab2 play a central role in uptake of vitamin D and may predict actions of vitamin D in extra-renal tissues. Here, we characterized megalin and Dab2 expression and uptake of DBP in transformed human prostate and colon epithelial cells. Megalin and Dab2 were expressed in prostate and colon epithelial cells, which was markedly enhanced following treatment with RA. Furthermore, DBP uptake was stimulated by low-dose RA supplementation in LNCaP, PC-3, and Caco-2 cells. Taken together, these are the first studies to our knowledge that have demonstrated modulated expression of megalin and Dab2, as well as an association between increased expression of endocytic proteins with DBP uptake in prostate and colon cells.
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Proteínas Adaptadoras Transductoras de Señales/genética , Proteína 2 Relacionada con Receptor de Lipoproteína de Baja Densidad/genética , Proteínas Supresoras de Tumor/genética , Vitamina D/farmacocinética , Proteínas Adaptadoras Transductoras de Señales/metabolismo , Proteínas Reguladoras de la Apoptosis , Células CACO-2 , Línea Celular Tumoral , Colon/citología , Colon/efectos de los fármacos , Colon/patología , Células Epiteliales/efectos de los fármacos , Células Epiteliales/metabolismo , Humanos , Proteína 2 Relacionada con Receptor de Lipoproteína de Baja Densidad/metabolismo , Masculino , Próstata/citología , Próstata/efectos de los fármacos , Próstata/patología , ARN Mensajero/genética , ARN Mensajero/metabolismo , Tretinoina/farmacología , Proteínas Supresoras de Tumor/metabolismo , Proteína de Unión a Vitamina D/genética , Proteína de Unión a Vitamina D/metabolismoRESUMEN
Diabetes is a rapidly growing epidemic affecting millions of Americans and has been implicated in a number of devastating secondary complications. We previously demonstrated that type 2 diabetic rats exhibit vitamin D deficiency due to aberrant megalin-mediated endocytosis and excessive urinary excretion of 25-hydroxycholecalciferol (25D3) and vitamin D-binding protein (DBP). Here, we examined whether a model of type 1 diabetes [T1D; streptozotocin (STZ)-treated Sprague-Dawley rats] would similarly excrete abnormally high concentrations of 25D3 and DBP due to renal damage and compromised expression of megalin and its endocytic partner, disabled-2 (Dab2). Moreover, we tested whether feeding diabetic rats starch that is resistant to digestion could alleviate these abnormalities. Control (n = 12) rats were fed a standard, semipurified diet (AIN-93G) containing 55% total dietary starch and STZ-treated rats were fed the AIN-93G diet (n = 12) or a diet containing 55% high-amylose maize that is partially resistant to digestion [20% total dietary resistant starch (RS); n = 12] for 2 and 5 wk. The RS diet attenuated weight loss and polyuria in STZ-treated rats. Histology and immunohistochemistry revealed that dietary RS also attenuated the loss of Dab2 expression in renal proximal tubules. Moreover, urinary concentrations of both 25D3 and DBP were elevated â¼10-fold in STZ-treated rats (5 wk post STZ injection), which was virtually prevented by the RS. We also observed a â¼1.5-fold increase in megalin mRNA expression in STZ-treated rats, which was attenuated by feeding rats the RS diet for 2 wk. Taken together, these studies indicate that consumption of low-glycemic carbohydrates can attenuate disruption of vitamin D homeostasis in T1D through the rescue of megalin-mediated endocytosis in the kidney.
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Calcifediol/orina , Diabetes Mellitus Experimental/tratamiento farmacológico , Diabetes Mellitus Tipo 1/tratamiento farmacológico , Dieta , Almidón/administración & dosificación , Proteína de Unión a Vitamina D/orina , Proteínas Adaptadoras del Transporte Vesicular/genética , Proteínas Adaptadoras del Transporte Vesicular/metabolismo , Amilosa/administración & dosificación , Animales , Glucemia/análisis , Glucemia/metabolismo , Carbohidratos de la Dieta/administración & dosificación , Digestión , Homeostasis/efectos de los fármacos , Inmunohistoquímica , Riñón/efectos de los fármacos , Riñón/metabolismo , Proteína 2 Relacionada con Receptor de Lipoproteína de Baja Densidad/genética , Proteína 2 Relacionada con Receptor de Lipoproteína de Baja Densidad/metabolismo , Masculino , ARN Mensajero/genética , ARN Mensajero/metabolismo , Ratas , Ratas Sprague-Dawley , Reacción en Cadena en Tiempo Real de la Polimerasa , Estreptozocina/efectos adversos , Estreptozocina/metabolismo , Zea mays/químicaRESUMEN
The major circulating form of vitamin D, 25-hydroxycholecalciferol (25D3), circulates bound to vitamin D-binding protein (DBP). Prior to activation to 1,25-dihydroxycholecalciferol in the kidney, the 25D3-DBP complex is internalized via receptor-mediated endocytosis, which is absolutely dependent on the membrane receptors megalin and cubilin and the adaptor protein disabled-2 (Dab2). We recently reported that mammary epithelial cells (T-47D) expressing megalin, cubilin, and Dab2 rapidly internalize DBP via endocytosis, whereas cells that do not express all 3 proteins (MCF-7) do not. The objectives of this study were to characterize megalin, cubilin, and Dab2 expression and transport of DBP in human mammary epithelial cells. Using immunoblotting and real-time PCR, we found that megalin, cubilin, and Dab2 were expressed and dose dependently induced by all-trans-retinoic acid (RA) in T-47D human breast cancer cells and that RA-treated T-47D cells exhibited enhanced DBP internalization. These are the first studies to our knowledge to demonstrate that mammary epithelial cells express megalin, cubilin, and Dab2, which are enhanced during differentiation and may explain, at least in part, our finding that receptor-mediated endocytosis of DBP is upregulated in differentiated mammary epithelial cells.
Asunto(s)
Proteínas Adaptadoras Transductoras de Señales/metabolismo , Mama/efectos de los fármacos , Mama/metabolismo , Proteína 2 Relacionada con Receptor de Lipoproteína de Baja Densidad/metabolismo , Receptores de Superficie Celular/metabolismo , Tretinoina/farmacología , Proteína de Unión a Vitamina D/metabolismo , Proteínas Adaptadoras Transductoras de Señales/genética , Proteínas Reguladoras de la Apoptosis , Secuencia de Bases , Mama/citología , Diferenciación Celular , Línea Celular , Cartilla de ADN/genética , Endocitosis/efectos de los fármacos , Endocitosis/fisiología , Células Epiteliales/citología , Células Epiteliales/efectos de los fármacos , Células Epiteliales/metabolismo , Femenino , Expresión Génica/efectos de los fármacos , Humanos , Metabolismo de los Lípidos/efectos de los fármacos , Proteína 2 Relacionada con Receptor de Lipoproteína de Baja Densidad/genética , ARN Mensajero/genética , ARN Mensajero/metabolismo , Receptores de Superficie Celular/genética , Proteínas Supresoras de Tumor , Proteína de Unión a Vitamina D/genéticaRESUMEN
Mice lacking 25-hydroxycholecalciferol [25(OH)D]-1alpha-hydroxylase (CYP27B1) are growth retarded, hypocalcemic, and have poor bone mineralization. We tested whether high dietary cholecalciferol (VD3) could exert effects in the absence of CYP27B1 in vivo. Weanling male wild-type (WT) and CYP27B1 knockout (KO) mice were fed either a 2% calcium (Ca), 20% lactose rescue diet or an AIN93G diet (0.5% Ca, 0.4% phosphorus) containing 1000 (1K, the rodent requirement, 25 microg), 10,000 (10K, 250 microg), or 20,000 (20K, 500 microg) IU VD3/kg diet until 12 wk when blood and tissues were taken. Serum 25(OH)D was >90 nmol/L in the 1K diet group and increased >4-fold in mice fed 10K and 20K diets. The 1K diet impaired growth and caused hypocalcemia in KO mice; the 10K and 20K diets were as effective as the high Ca rescue diet in preventing these outcomes. High VD3 restored expression of vitamin D-regulated genes in intestine (calbindin D(9K)) and kidney (CYP27B1, 24-hydroxylase, calbindin D(9K)) of KO mice. Micro-computed tomography of femora revealed complete recovery of cortical bone in KO mice fed either the rescue or 10K diets but only partial recovery of trabecular bone measures (e.g. 40% lower bone volume, 20% lower trabecular thickness, and 23% increase in trabecular separation). These data show that very high serum 25(OH)D can influence Ca and bone metabolism independent of its conversion to 1,25 dihydroxycholecalciferol. However, neither high dietary Ca nor high dietary VD3 is sufficient to fully recover the phenotype of CYP27B1 KO mice.
Asunto(s)
25-Hidroxivitamina D3 1-alfa-Hidroxilasa/genética , Hipocalcemia/prevención & control , Osteomalacia/prevención & control , Vitamina D/farmacología , Envejecimiento , Animales , Calcio de la Dieta/farmacología , Dieta , Predisposición Genética a la Enfermedad , Ratones , Ratones NoqueadosRESUMEN
The major circulating form of vitamin D is 25-hydroxycholecalciferol [25(OH)D3], which is delivered to target tissues in complex with the serum vitamin D binding protein (DBP). We recently observed that mammary cells can metabolize 25(OH)D3 to 1,25-dihydroxycholecalciferol [1,25(OH)(2)D3], the vitamin D receptor (VDR) ligand, and the objective of our study was to elucidate the mechanisms by which the 25(OH)D3-DBP complex is internalized by mammary cells prior to metabolism. Using fluorescent microscopy and temperature-shift techniques, we found that T-47D breast cancer cells rapidly internalize DBP via endocytosis, which is blunted by receptor-associated protein, a specific inhibitor of megalin-mediated endocytosis. Endocytosis of DBP was associated with activation of VDR by 25(OH)D3 but not 1,25(OH)(2)D3 (as measured by induction of the VDR target gene, CYP24). We also found that megalin and its endocytic partner, cubilin, are coexpressed in normal murine mammary tissue, in nontransformed human mammary epithelial cell lines, and in some established human breast cancer cell lines. To our knowledge, our studies are the first to demonstrate that mammary-derived cells express megalin and cubilin, which contribute to the endocytic uptake of 25(OH)D3-DBP and activation of the VDR pathway.
Asunto(s)
Mama/metabolismo , Calcifediol/farmacología , Endocitosis , Proteína 2 Relacionada con Receptor de Lipoproteína de Baja Densidad/fisiología , Proteína de Unión a Vitamina D/metabolismo , 25-Hidroxivitamina D3 1-alfa-Hidroxilasa/fisiología , Animales , Mama/citología , Línea Celular Tumoral , Femenino , Humanos , Proteína 2 Relacionada con Receptor de Lipoproteína de Baja Densidad/genética , Ratones , Ratones Endogámicos C57BL , Receptores de Calcitriol/fisiología , Receptores de Superficie Celular/genética , Receptores de Superficie Celular/fisiologíaRESUMEN
The hepatic enzyme glycine N-methyltransferase (GNMT) plays a major role in the control of methyl group and homocysteine metabolism. Because disruption of these vital pathways is associated with numerous pathologies, understanding GNMT control is important for evaluating methyl group regulation. Recently, gluconeogenic conditions have been shown to modulate homocysteine metabolism and treatment with glucocorticoids and/or all-trans-retinoic acid (RA)-induced active GNMT protein, thereby leading to methyl group loss. This study was conducted to determine the effect of diabetes, alone and in combination with RA, on GNMT regulation. Diabetes and RA increased GNMT activity 87 and 148%, respectively. Moreover, the induction of GNMT activity by diabetes and RA was reflected in its abundance. Cell culture studies demonstrated that pretreatment with insulin prevented GNMT induction by both RA and dexamethasone. There was a significant decline in homocysteine concentrations in diabetic rats, owing in part to a 38% increase in the abundance of the transsulfuration enzyme cystathionine beta-synthase; treatment of diabetic rats with RA prevented cystathionine beta-synthase induction. A diabetic state also increased the activity of the folate-independent homocysteine remethylation enzyme betaine-homocysteine S-methyltransferase, whereas the activity of the folate-dependent enzyme methionine synthase was diminished 52%. In contrast, RA treatment attenuated the streptozotocin-mediated increase in betaine-homocysteine S-methyltransferase, whereas methionine synthase activity remained diminished. These results indicate that both a diabetic condition and RA treatment have marked effects on the metabolism of methyl groups and homocysteine, a finding that may have significant implications for diabetics and their potential sensitivity to retinoids.
Asunto(s)
Diabetes Mellitus Experimental/metabolismo , Homocisteína/metabolismo , Tretinoina/farmacología , Animales , Cistationina betasintasa/biosíntesis , Glicina N-Metiltransferasa , Homocisteína/sangre , Masculino , Metiltransferasas/biosíntesis , Ratas , Ratas Sprague-Dawley , S-Adenosilhomocisteína/metabolismo , S-Adenosilmetionina/metabolismo , EstreptozocinaRESUMEN
Perturbation of folate and methyl group metabolism is associated with a number of pathological conditions, including cardiovascular disease and neoplastic development. Glycine N-methyltransferase (GNMT) is a key protein that functions to regulate the supply and utilization of methyl groups for S-adenosylmethionine (SAM)-dependent transmethylation reactions. Factors or conditions that have the ability to regulate GNMT and the generation of homocysteine, a product of transmethylation, have important implications in the potential perturbation of methyl group metabolism. We showed that retinoid compounds induce active hepatic GNMT, resulting in compromised transmethylation processes. Because retinoids can stimulate gluconeogenesis, a condition known to alter methyl group and homocysteine metabolism, the current study was undertaken to determine the relationship between all-trans-retinoic acid (RA) and gluconeogenic hormones on these metabolic pathways. Intact adrenal function was not required for RA to induce and activate hepatic GNMT; however, treatment of rats with dexamethasone (DEX) was as effective as RA in inducing GNMT in rat liver. The marked increase in plasma total homocysteine levels observed in adrenalectomized rats was reduced to normal levels by treatment with either RA or DEX, indicating that the transsulfuration and/or remethylation pathways may be enhanced. Moreover, coadministration of RA and DEX had an additive effect on GNMT induction. Similar findings were also observed in a rat hepatoma cell culture model using H4IIE cells. Taken together, these results demonstrate that both RA and DEX independently induce GNMT, thereby having substantial implications for the potential interaction of retinoid administration with diabetes.