Biomedical subjects
Friedrich C Luft
Publications and source records attributed to Friedrich C Luft.
Autosomal-dominant hypertension with type E brachydactyly is caused by rearrangement on the short arm of chromosome 12.
We are studying a Turkish family with autosomal-dominant hypertension and brachydactyly; affected persons die of stroke before 50 years of age. With interphase fluorescence in situ hybridization, we found a chromosome 12p deletion, reinsertion, and inversion in affected persons. This finding suggested that the hypertension could be caused by one or more of 3 genes, the ATP-dependent potassium channel Kir6.1, its regulator the sulfonyl urea receptor SUR2, and the phosphodiesterase PDE3A. We further studied 6 affected and 4 nonaffected persons. Buttocks biopsies were done, small vessels were tested on a myograph, and mRNA was extracted. We performed forearm blood flow studies with intrabrachial artery diazoxide, isoproterenol, and milrinone infusions. Systemic pharmacological testing was done with intravenous diazoxide, nitroprusside, and isoproterenol. PDE3A mRNA was high in vessels from 3 affected subjects, but not high in 3 others. The vessels responded similarly to forskolin, with or without glibenclamide, and to cromakalim. However, there was a suggestion that the dilatation after milrinone might be exaggerated. The forearm infusion studies showed no differences in the responses to diazoxide, isoproterenol, or milrinone. Systemically, affected persons showed a greater blood pressure response to diazoxide and nitroprusside, and a greater heart rate response to isoproterenol than nonaffected persons. The results shed doubt on Kir6.1 and SUR2. The differences in PDE3A expression and responses may be the result of hypertension rather than the cause. Although our 3 candidate genes are no longer likely, the rearrangement we describe greatly enhances the perspectives of this project.
Validation of fluorescence-labeled artificial nonhuman sequences for single-strand conformation polymorphism mutation detection in familial hypercholesterolemia.
We developed a two-in-one, polymerase chain reaction (PCR)-based method with a specific amplification step and a universal amplification step in one tube to screen for the presence of DNA variations. The method relies on fluorescence-labeled artificial nonhuman sequences for mutation detection. To document utility, we applied this method as a high-throughput capillary single-strand conformation polymorphism screening system to identify 30 mutations in the low-density lipoprotein receptor gene. The sensitivity of mutant allele detection compared to wild-type allele detection was 93%. We conclude that the "two-in-one PCR" is sensitive, simple, and cost effective.
Matrix metalloproteinases and their regulators are cardiovascular therapeutic targets.
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Adrenergic responsiveness of adipose tissue lipolysis in autonomic failure.
The sympathetic nervous system mobilizes lipids from adipose tissue through stimulation of beta-adrenergic receptors. The increase in lipid supply augments lipid oxidation. Patients with autonomic failure provide a unique opportunity to further elucidate the role of the adrenergic system in adipose tissue metabolism. In 4 patients with severe pure autonomic failure (PAF), in 3 multiple system atrophy patients (MSA), and in 16 healthy young controls, we inserted a microdialysis catheter in abdominal adipose tissue. The catheter was perfused with incremental concentrations of the nonselective beta-adrenoreceptor agonist isoproterenol. Dialysate glucose, lactate, and glycerol were measured to assess glucose supply, glycolysis, and lipolysis, respectively. Basal dialysate glycerol concentrations were 84 +/- 28 microM in PAF and 130 +/- 64 microM in MSA patients. The increase in dialysate glycerol with isoproterenol was identical in PAF and in MSA patients. We found an almost complete overlap in dialysate glycerol concentrations during isoproterenol stimulation between PAF and MSA patients and healthy young control subjects. Our findings suggest that adipose tissue metabolism is remarkably well preserved in patients with chronic sympathetic denervation, both at rest and during local adrenergic stimulation. We propose that beta-adrenoreceptor upregulation is compensated by a desensitization of post receptor mechanisms or by an upregulation of antilipolytic pathways.
Influence of St John's wort on catecholamine turnover and cardiovascular regulation in humans.
BACKGROUND: St John's wort (Hypericum perforatum) is a popular over-the-counter antidepressant. Its antidepressive effect has been attributed in part to inhibition of monoamine transporters and monoamine oxidase, on the basis of in vitro studies. METHODS: In a double-blind, randomized, placebo-controlled, crossover study, 16 healthy subjects (11 men and 5 women; mean age, 31 +/- 5 years) ingested either St John's wort (300 mg three times daily) or placebo for 7 days. Imipramine treatment (50 mg three times daily) in 7 subjects served as a positive control. After treatment, physiologic and biochemical tests included cardiovascular reflex testing, graded head-up tilt testing, and plasma catecholamine determinations. RESULTS: St John's wort had no effect on blood pressure, heart rate, heart rate variability, or blood pressure variability, regardless of the test condition. St John's wort had no effect on plasma concentrations of norepinephrine and its main metabolite, dihydroxyphenylglycol, whereas plasma dihydroxyphenylacetic acid (DOPAC; the main metabolite of dopamine) concentrations increased in every subject (1661 +/- 924 pg/mL versus 1110 +/- 322 pg/mL with placebo, P=.04). In contrast, imipramine increased resting blood pressure (124 +/- 10 mmHg/71 +/- 5 mmHg versus 110 +/- 8 mmHg/61 +/- 6 mmHg with placebo, P=.005 for systolic values and P=.003 for diastolic values) and heart rate (74 +/- 7 beats/min versus 62 +/- 6 beats/min with placebo, P=.005) and elicited a marked orthostatic tachycardia (increase in heart rate of 43 +/- 17 beats/min versus 26 +/- 8 beats/min with placebo, P=.006). CONCLUSIONS: Our findings challenge the concept that St John's wort elicits a major change in norepinephrine uptake or monoamine oxidase activity in vivo. The consistent increase in plasma DOPAC concentrations might suggest a novel mode of action or an inhibitory effect on dopamine beta-hydroxylase that should be followed up. We propose that a combination of physiologic and biochemical profiling may help better define the mode of action and potential side effects of herbal remedies.
Insulin resistance in healthy prepubertal twins.
OBJECTIVES: To evaluate insulin sensitivity (S(I)) in prepubertal twins and to examine the relation to reduced birth weight, prematurity, and peroxisome proliferator-activated receptor-gamma (PPAR gamma) polymorphism. STUDY DESIGN: Fifty twins (birth weight SDS, -0.7 +/- 0.2; gestation, 33.5 +/- 0.5 weeks; and body mass index SDS, -0.04 +/- 0.2) were studied at 8.2 +/- 0.3 years. S(I) was measured by Bergman's minimal model from a 90 minutes frequently sampled intravenous glucose test. Twenty control children (height SDS, -1.7 +/- 0.3; birth weight SDS, -0.3 +/- 0.2; and gestation of 39.2 +/- 0.7 weeks) were also evaluated at 7.0 +/- 0.4 years. The PPAR gamma T-variant polymorphism was evaluated in 41 twins. Values are expressed as mean +/- SEM, or 95% confidence intervals. RESULTS: S(I) was reduced in twins compared with control subjects, (12.7 [11-15] versus 23.0 [16.8-31.4] 10(-4) min(-1) microU/mL, respectively, P=.005). The reduction in S(I) was independent of prematurity and birth weight and zygosity (P<.0001). There was no difference in S(I), even in twin pairs with >20% difference in birth weight (P=.9). The PPAR gamma heterozygote T-variant polymorphism was present in 7 of 41, with a further reduction in S(I) (P=.03) and a later gestation (P=.03). These twins also had increased fat mass (P=.02) but with similar fat free mass (P=.14). CONCLUSIONS: Twin children, independent of prematurity or birth weight, had a marked reduction in S(I). To use twins as a model to study the fetal origins of adult diseases for glucose homeostasis is not valid.
A peroxisome proliferator-activated receptor-alpha activator induces renal CYP2C23 activity and protects from angiotensin II-induced renal injury.
Cytochrome P450 (CYP)-dependent arachidonic acid (AA) metabolites are involved in the regulation of renal vascular tone and salt excretion. The epoxygenation product 11,12-epoxyeicosatrienoic acid (EET) is anti-inflammatory and inhibits nuclear factor-kappa B activation. We tested the hypothesis that the peroxisome proliferator-activated receptor-alpha-activator fenofibrate (Feno) induces CYP isoforms, AA hydroxylation, and epoxygenation activity, and protects against inflammatory organ damage. Double-transgenic rats (dTGRs) overexpressing human renin and angiotensinogen genes were treated with Feno. Feno normalized blood pressure, albuminuria, reduced nuclear factor-kappa B activity, and renal leukocyte infiltration. Renal epoxygenase activity was lower in dTGRs compared to nontransgenic rats. Feno strongly induced renal CYP2C23 protein and AA-epoxygenase activity under pathological and nonpathological conditions. In both cases, CYP2C23 was the major isoform responsible for 11,12-EET formation. Moreover, we describe a novel CYP2C23-dependent pathway leading to hydroxy-EETs (HEETs), which may serve as endogenous peroxisome proliferator-activated receptor-alpha activators. The capacity to produce HEETs via CYP2C23-dependent epoxygenation of 20-HETE and CYP4A-dependent hydroxylation of EETs was reduced in dTGR kidneys and induced by Feno. These results demonstrate that Feno protects against angiotensin II-induced renal damage and acts as inducer of CYP2C23-mediated epoxygenase activities. We propose that CYP-dependent EET/HEET production may serve as an anti-inflammatory control mechanism.
Present status of genetic mechanisms in hypertension.
Studies on Mendelian hypertension have provided great insight into mechanisms causing hypertension. Mineralocorticoid synthesis and degradation, the mineralocorticoid receptor, sodium channel resorptive mechanisms, and regulation of the thiazide-sensitive sodium-chloride cotransporter have been shown to cause hypertension. Aberrant regulation of peripheral vascular resistance and circulatory regulation have not yet been proved but have been strongly implicated in Mendelian hypertension with brachydactyly. Hypertension as a complex genetic trait has proved more difficult because many genes are involved and the genes have much smaller effects. Association studies, linkage analyses, single nucleotide polymorphism analyses, synteny in animal models, and gene expression studies are the current tools and steady progress is being made.
AT1 receptor agonistic antibodies, hypertension, and preeclampsia.
Immunologic mechanisms and putatively circulating mediators of preeclampsia are not a new idea, but are nevertheless compelling. Here we review studies relating to the role of agonistic antibodies that bind the second extracellular loop of the angiotensin II (AII) AT1 receptor in the pathogenesis as well as a pathologic phenotype of this disorder, focusing on observations in our laboratory. These agonistic autoantibodies (AT1-AA) appear with the development of preeclampsia and mostly are gone by 6 weeks after delivery. We have purified AT1-AA and have shown that they belong to the immunoglobulin (Ig)G3 subclass. We have shown their specificity by Western blotting, colocalization, and coimmunoprecipitation experiments. AT1-AA induce signaling in vascular cells and trophoblasts including activating protein-1 (AP-1) and nuclear factor kappa B (NF-kappaBeta) activation. The signaling results in tissue factor production and reactive oxygen species generation, both of which have been implicated in preeclampsia. AT1-AA also signal via the calcineurin-nuclear factor of activated T cells and contribute to plasminogen activator inhibitor-1 (PAI-1) production and decreased trophoblast invasion. The role of AT1-AA in preeclampsia and other severe hypertensive conditions has not yet been proven with certainty. However, we believe the findings are compelling and warrant further study.
Regulation of glucose transporter SGLT1 by ubiquitin ligase Nedd4-2 and kinases SGK1, SGK3, and PKB.
OBJECTIVE: Serum- and glucocorticoid-inducible kinase 1 (SGK1) inhibits the ubiquitin ligase neuronal cell expressed developmentally downregulated 4-2 (Nedd4-2), which retards the retrieval of the epithelial Na+ channel ENaC. Accordingly, SGK1 enhances ENaC abundance in the cell membrane. The significance of this effect is shown by an association of an E8CC/CT;I6CC polymorphism in the SGK1 gene with increased blood pressure. However, strong expression of SGK1 in enterocytes not expressing ENaC points to further functions of SGK1. This study was performed to test for regulation of Na+-coupled glucose transporter 1 (SGLT1) by Nedd4-2, SGK1, and/or the related kinases SGK3 and PKB. Additional studies searched for an association of the SGK1 gene with BMI. RESEARCH METHODS AND PROCEDURES: mRNA encoding SGLT1, wild-type Nedd4-2, inactive (C938S)Nedd4-2, wild type SGK1, constitutively active (S422D)SGK1 or inactive (K127N)SGK1, wild-type SGK3, and constitutively active (T308DS473D)PKB or inactive (T308AS473A)PKB were injected into Xenopus oocytes, and glucose transport was quantified from glucose-induced current (I(glc)). BMI was determined in individuals with or without the E8CC/CT;I6CC polymorphism. RESULTS: I(glc) was significantly decreased by coexpression of Nedd4-2 but not of (C938S)Nedd4-2. Coexpression of SGK1, (S422D)SGK1, SGK3, or (T308DS473D)PKB, but not of (K127N)SGK1 or (T308AS473A)PKB, enhanced I(glc) and reversed the effect of Nedd4-2. SGK1 and SGK3 phosphorylated Nedd4-2. Deletion of the SGK/PKB phosphorylation sites in Nedd4-2 blunted the kinase effects. BMI was significantly (p < 0.008) greater in individuals with the E8CC/CT;I6CC polymorphism than in individuals without. DISCUSSION: Overactivity of SGK1 may lead not only to excessive ENaC activity and hypertension but also to enhanced SGLT1 activity and obesity.
Regulation of 11beta-HSD genes in human adipose tissue: influence of central obesity and weight loss.
OBJECTIVES: The activity of adipose 11beta-hydroxysteroid dehydrogenase (11beta-HSD) 1 is increased in obese subjects, and animal data suggest that increased cortisol formation in adipose tissue contributes to the development of the metabolic syndrome. The aim of this study was to determine whether up-regulation of human adipose 11beta-HSD1 in obesity can also be found at the gene expression level. RESEARCH METHODS AND PROCEDURES: 11beta-HSD gene expression in subcutaneous adipose tissue biopsies of 70 postmenopausal women was studied by real-time reverse-transcription polymerase chain reaction. The influence of weight reduction and in vitro effects of several modulators of adipocyte gene expression on 11beta-HSD genes in human adipocytes were also studied. RESULTS: The 11beta-HSD1 gene was highly expressed in human adipose tissue. 11beta-HSD2 mRNA was also detectable at lower levels. Adipose 11beta-HSD1 gene expression was increased by two-fold and was positively correlated with waist circumference and homeostasis model assessment index of insulin resistance. 11beta-HSD2 gene expression was reduced by half in obese women. Weight reduction did not change gene expression levels of 11beta-HSD1 or 11beta-HSD2. Cortisol increased 11beta-HSD1 gene expression in isolated human adipocytes in vitro, whereas estradiol, triiodothyronine, angiotensin II, and pioglitazone had no influence. DISCUSSION: Our data suggest that increased expression of the 11beta-HSD1 gene is associated with metabolic abnormalities in obese women and that increased expression of this gene may contribute to the previously reported increased local conversion of cortisone to cortisol in adipose tissue of obese individuals.
Growth arrest specific protein 6/Axl signaling in human inflammatory renal diseases.
BACKGROUND: Growth arrest-specific gene 6 (Gas6) and its binding partner, the receptor tyrosine kinase Axl, are important mediators in experimental nephritis. The authors tested whether the Gas6/Axl signaling pathway participates in human renal diseases. METHODS: The authors compared 26 human renal specimens from patients with IgA nephritis, acute diffuse immune complex glomerulonephritis, acute lupus nephritis, antineutrophil cytoplasmic antibody--associated glomerulonephritis, acute transplant rejection, and normal renal tissue. Because reactive oxygen species are pivotal in inflammation, the authors tested whether the Axl/Gas6 expression is influenced by NADPH oxidase in vitro. RESULTS: Gas6 and Axl immunofluorescence was barely detectable in normal kidney. However, in disease Axl was copiously expressed in the small vessel media, glomeruli, distal tubules, and collecting ducts. Similarly, Gas6 was upregulated in the small vessel intima and media, all segments of the renal tubules, the brush border, and glomeruli. Gas6 and Axl upregulation was a prominent but nonspecific finding in these renal diseases. Cultured rat vascular smooth muscle cells and immortalized human mesangial cells were stimulated with angiotensin (Ang) II (1 x 10(-7) mol/L) for 6 or 18 hours. Confocal microscopy and Western blot showed Ang II-dependent Gas6 and Axl expression. An antisense probe against the p22 phox unit of NADPH-oxidase suppressed Ang II-induced Gas6 and Axl expression. In addition, in p47 phox knockout cells Ang II-induced Gas6 and Axl expression were blocked. CONCLUSION: GAS6/Axl signaling is involved in human renal disease. The Ang II-induced Gas6 and Axl expression may be dependent on NADPH-oxidase. Gas6 and Axl are important signaling molecules in human renal disease and may be potential therapeutic targets.
A woman with postoperative hyponatremia related to desmopressin acetate.
A patient was referred to the intensive care unit with sudden delirium and a serum sodium level of 111 mEq/L (mmol/L). A computerized tomographic scan revealed marked cerebral edema. Laboratory values were highly consistent with the action of the antidiuretic hormone. She had received desmopressin acetate (DDAVP) for 4 days preoperatively and postoperatively for putative van Willebrand's disease. Hyponatremia as a sequel to DDAVP treatment is an unusual complication and the medication is generally safe. However, our patient nevertheless teaches that vigilance equals avoidance.
Hard times with hard water.
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Blue acid blues.
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The phosphorus connection--a puzzling business.
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