Fibrinolytic treatment of acute arterial occlusion distal to the wrist in two cases.

Distal arterial occlusion in the hand threatens the viability of the digits and is difficult to treat. This study reports two cases in which fibrinolytic agents were used successfully to restore circulation in the digital arteries.

[Stents in dialysis vascular access--do they promise improved high quality prolonged access use].

UNLABELLED: The life expectancy of dialysis patients depends, to a large extent, on blood access which provides uninterrupted and efficient treatment. Dialysis access created by a direct anastomosis between artery and vein usually allows normal dialysis for many years. Blood access by a bridge graft between artery and vein functions for a much shorter time and occludes chiefly because of endothelial hyperplasia at the graft vein anastomosis. This type of fistula is created when the veins of the patient are small. During the last few years the dialysis population is increasingly composed of adult and elderly patients suffering from diabetes mellitus, hypertension, dyslipidemias and atheromatous vascular disease so that a relatively large proportion of dialysis accesses are created using a bridge graft. Since we currently do not have the knowledge of how to arrest or delay the processes which lead to access occlusion, attempts are made to implement prophylactic strategies, find stenoses and dilate them before the access fails. Up to date, controlled trials have not succeeded in proving that this method prolongs access use. These trials did not describe the use of stents following dilatation. MATERIALS AND METHODS: Between July 2002 and May 2005, 238 angiographies were performed on blood accesses including 179 angioplasties of stenoses. In sixteen patients a stent was deployed during the angioplasty. RESULTS: In ten patients dialysis was performed using the same access up to the end of the study period, an average of 43 months from the creation of the access. Three patients died with a functioning access and in three the access occluded during the period of followup. DISCUSSION: This study shows that the use of stents following angioplasty of dialysis access stenoses can improve the duration of use of accesses created through grafts.

Effects of fenofibrate on lipid parameters in obese rhesus monkeys.

Fenofibrate is a member of the fibrate class of hypolipidemic agents used clinically to treat hypertriglyceridemia and mixed hyperlipidemia. The fibrates were developed primarily on the basis of their cholesterol and triglyceride lowering in rodents. Fibrates have historically been ineffective at lowering triglycerides in experimentally-induced dyslipidemia in nonhuman primate models. The spontaneously obese rhesus monkey is a well-recognized animal model for the study of human obesity and type 2 diabetes, and many of these monkeys exhibit naturally occurring lipid abnormalities, including elevated triglycerides and low HDL cholesterol (HDL-C), similar to patients with type 2 diabetes. To explore whether the obese rhesus model was predictive of the lipid lowering effects of fibrates, we evaluated fenofibrate in six hypertriglyceridemic, hyperinsulinemic, nondiabetic animals in a 20-week, dose-escalating study. The study consisted of a 4-week baseline period, two treatment periods of 10 mg/kg twice daily (b.i.d) for 4 weeks and 30 mg/kg b.i.d. for 8 weeks, and a 4-week washout period. Fenofibrate (30 mg/kg b.i.d) decreased serum triglycerides 55% and LDL-C 27%, whereas HDL-C increased 35%. Apolipoproteins B-100 and C-III levels were also reduced 70% and 29%, respectively. Food intake, body weight, and plasma glucose were not affected throughout the study. Interestingly, plasma insulin levels decreased 40% during the 30 mg/kg treatment period, suggesting improvement in insulin sensitivity. These results support the use of obese rhesus monkey as an excellent animal model for studying the effects of novel hypolipidemic agents, particularly agents that impact serum triglycerides and HDL-C.

4-Hydroxytamoxifen binds to and deactivates the estrogen-related receptor gamma.

The estrogen-related receptors (ERR alpha, ERR beta, and ERR gamma) form a family of orphan nuclear receptors that share significant amino acid identity with the estrogen receptors, but for which physiologic roles remain largely unknown. By using a peptide sensor assay, we have identified the stilbenes diethylstilbestrol (DES), tamoxifen (TAM), and 4-hydroxytamoxifen (4-OHT) as high-affinity ligands for ERR gamma. In direct binding assays, 4-OHT had a K(d) value of 35 nM, and both DES and TAM displaced radiolabeled 4-OHT with K(i) values of 870 nM. In cell-based assays, 4-OHT binding caused a dissociation of the complex between ERR gamma and the steroid receptor coactivator-1, and led to an inhibition of the constitutive transcriptional activity of ERR gamma. ERR alpha did not bind 4-OHT, but replacing a single amino acid predicted to be in the ERR alpha ligand-binding pocket with the corresponding ERR gamma residue allowed high-affinity 4-OHT binding. These results demonstrate the existence of high-affinity ligands for the ERR family of orphan receptors, and identify 4-OHT as a molecule that can regulate the transcriptional activity of ERR gamma.

Acute thrombosis of an aortic aneurysm.

The natural history of abdominal aortic aneurysms is to enlarge gradually. Associated complications are rupture, peripheral embolization and infection.1-5 Complete occlusion of an abdominal aortic aneurysm by thrombus is extremely rare and constitutes a surgical emergency, with an estimated mortality of 50%.1-5 We report a case of a patient with this very uncommon complication of abdominal aortic aneurysm and review the literature discussing its optimal identification and management.

Orphan nuclear receptors: from new ligand discovery technologies to novel signaling pathways.

Members of the nuclear receptor superfamily of ligand-regulated transcription factors play critical roles in multiple aspects of development, cellular differentiation and homeostasis. The ligand-dependent transcriptional effects of nuclear receptors are, in part, mediated by interactions with a group of proteins collectively known as transcriptional coactivators. Receptor agonists promote coactivator binding and receptor antagonists suppress coactivator binding. Recently, biochemical assays that detect ligand-binding based on coactivator recruitment have been developed for several 'orphan' nuclear receptors, i.e., receptors for which no bona fide endogenous ligands are known. We review how these assays have been used to identify naturally occurring and synthetic ligands for the liver X receptor, farnesoid X receptor and estrogen receptor-related receptor subfamilies of orphans, the use of these ligands in the discovery of novel biological signaling pathways and the potential clinical implications of these findings.

Isolated femoral profundoplasty using endarterectomised superficial femoral artery for limb salvage in the elderly.

BACKGROUND: The deep femoral artery provides the primary blood supply to the thigh, and in addition serves as the major collateral channel for bypassing the obstructed superficial femoral artery. The purpose of isolated profundoplasty is to relieve a significant stenosis and improve perfusion of the ischaemic leg. METHODS: Twenty-seven patients with critical limb ischaemia underwent isolated profundoplasty in the Vascular Unit of Meir General Hospital, using endarterectomised superficial femoral artery (ESFA) as an arterial patch. Nineteen patients were men. The average age was 72 (65-79). The presenting symptoms: rest pain: 18 (67%), ischaemic foot ulcer: 7 (28%), pedal gangrene: 2 (7%). Selection criteria for isolated profundoplasty: 1) > 50%: stenosis of arteria profunda femoris lumen. 2) Adequate profunda: popliteal collateral system. 3) Adequate arterial inflow: common femoral artery. RESULTS: There was no operative mortality or immediate operative failure. All 27 limbs were improved: relief of rest pain, healing of ischaemic ulcers and good healing after minor amputations (transphalangeal, transmetatarsal). Follow-up period ranged from 12 to 45 months (mean 30 months) and was based on clinical investigation + ankle/brachial Doppler measurements. All patients remained asymptomatic with improvement of limb function--either to the present or until their death. CONCLUSIONS: In view of our favourable experience, we feel that isolated profundoplasty still has a place in vascular surgery practice--when limb revascularization in elderly patients considered at high risk is dangerous and when there is impossible below knee vascular reconstruction. We recommend the use of ESFA as a patch for long segment profundoplasty--with all advantages of an autogenous material.

The PPARs and PXRs: nuclear xenobiotic receptors that define novel hormone signaling pathways.

Traditional pharmacologic approaches had identified several classes of xenobiotics that elicited characteristic biological effects in vivo but that lacked defined molecular mechanisms of action. Among these xenobiotics were the peroxisome proliferators, the thiazolidinediones (TZDs), and a set of compounds that induced the expression of cytochrome P450 (CYP) 3A genes and promoted the metabolism of other xenobiotics. All three classes of xenobiotics are now known to exert their actions through activation of orphan members of the nuclear receptor family of ligand-activated transcription factors. Peroxisome proliferators are a diverse group of amphipathic acids that include the fibrate class of triglyceride- and cholesterol-lowering drugs. TZDs sensitize tissues such as skeletal muscle, liver, and adipose to the actions of insulin and lower glucose and lipid levels in type 2 diabetics. The peroxisome proliferators and TZDs are now known to mediate their effects through the peroxisome proliferator-activated receptors (PPARs) alpha and gamma, respectively. The activities of these compounds established the PPARs as key regulators of glucose and lipid homeostasis. We and others have recently shown that various naturally occurring fatty acids and eicosanoids serve as PPAR ligands, suggesting a novel regulatory mechanism whereby dietary lipids and their metabolites can regulate gene transcription and impact overall energy balance. The third class of xenobiotics we have studied induces the expression of CYP3A genes, mono-oxygenases responsible for the metabolism of natural steroids as well as a variety of xenobiotics, including > 60% of all drugs. We have recently shown that compounds that induce CYP3A gene expression do so through activation of novel orphan receptors, termed the pregnane X receptors (PXRs). Many of the PXR activators are widely used drugs such as dexamethasone, lovastatin, and rifampicin, whose induction of CYP3A levels causes them to promote the metabolism of other drugs, often with adverse consequences. Thus, the finding that the PXRs regulate CYP3A gene expression provides a basis for the efficient identification and elimination of candidate drugs that will interact with other medicines. Searches for natural ligands have revealed that the PXRs are activated by C21 steroids, including pregnenolone and progesterone, suggesting that these orphan receptors define a novel steroid hormone signaling pathway. In sum, work from our laboratories and others has demonstrated that peroxisome proliferators, TZDs, and inducers of CYP3A gene expression exert their biological actions through the activation of orphan nuclear receptors. These findings provide insights into new endocrine signaling pathways and have important implications for the discovery of safer and more efficacious drugs for the treatment of a variety of diseases.

A novel N-aryl tyrosine activator of peroxisome proliferator-activated receptor-gamma reverses the diabetic phenotype of the Zucker diabetic fatty rat.

The discovery that peroxisome proliferator-activated receptor (PPAR)-gamma was the molecular target of the thiazolidinedione class of antidiabetic agents suggested a key role for PPAR-gamma in the regulation of carbohydrate and lipid metabolism. Through the use of high-throughput biochemical assays, GW1929, a novel N-aryl tyrosine activator of human PPAR-gamma, was identified. Chronic oral administration of GW1929 or troglitazone to Zucker diabetic fatty (ZDF) rats resulted in dose-dependent decreases in daily glucose, free fatty acid, and triglyceride exposure compared with pretreatment values, as well as significant decreases in glycosylated hemoglobin. Whole body insulin sensitivity, as determined by the euglycemic-hyperinsulinemic clamp technique, was significantly increased in treated animals. Comparison of the magnitude of glucose lowering as a function of serum drug concentrations showed that GW1929 was 2 orders of magnitude more potent than troglitazone in vivo. These data were consistent with the relative in vitro potencies of GW1929 and troglitazone. Isolated perfused pancreas studies performed at the end of the study confirmed that pancreata from vehicle-treated rats showed no increase in insulin secretion in response to a step change in glucose from 3 to 10 mmol/l. In contrast, pancreata from animals treated with GW1929 showed a first- and second-phase insulin secretion pattern. Consistent with the functional data from the perfusion experiments, animals treated with the PPAR-gamma agonist had more normal islet architecture with preserved insulin staining compared with vehicle-treated ZDF rats. This is the first demonstration of in vivo efficacy of a novel nonthiazolidinedione identified as a high-affinity ligand for human PPAR-gamma. The increased potency of GW1929 compared with troglitazone both in vitro and in vivo may translate into improved clinical efficacy when used as monotherapy in type 2 diabetic patients. In addition, the significant improvement in daily meal tolerance may impact cardiovascular risk factor management in these patients.

A peroxisome proliferator-activated receptor gamma ligand inhibits adipocyte differentiation.

The peroxisome proliferator-activated receptors (PPARs) are nuclear hormone receptors that regulate glucose and lipid homeostasis. The PPARgamma subtype plays a central role in the regulation of adipogenesis and is the molecular target for the 2, 4-thiazolidinedione class of antidiabetic drugs. Structural studies have revealed that agonist ligands activate the PPARs through direct interactions with the C-terminal region of the ligand-binding domain, which includes the activation function 2 helix. GW0072 was identified as a high-affinity PPARgamma ligand that was a weak partial agonist of PPARgamma transactivation. X-ray crystallography revealed that GW0072 occupied the ligand-binding pocket by using different epitopes than the known PPAR agonists and did not interact with the activation function 2 helix. In cell culture, GW0072 was a potent antagonist of adipocyte differentiation. These results establish an approach to the design of PPAR ligands with modified biological activities.

Bile acids: natural ligands for an orphan nuclear receptor.

Bile acids regulate the transcription of genes that control cholesterol homeostasis through molecular mechanisms that are poorly understood. Physiological concentrations of free and conjugated chenodeoxycholic acid, lithocholic acid, and deoxycholic acid activated the farnesoid X receptor (FXR; NR1H4), an orphan nuclear receptor. As ligands, these bile acids and their conjugates modulated interaction of FXR with a peptide derived from steroid receptor coactivator 1. These results provide evidence for a nuclear bile acid signaling pathway that may regulate cholesterol homeostasis.

Orphan nuclear receptors: shifting endocrinology into reverse.

Steroid and thyroid hormones and vitamin A metabolites (retinoids) regulate the expression of complex gene programs by binding to members of the nuclear receptor family of ligand-activated transcription factors. The nuclear receptor family also includes many "orphan" members that currently lack known ligands but that represent candidate receptors for new hormones. Recently, natural and synthetic ligands have been identified for several orphan receptors and used to dissect their biological roles. This "reverse endocrinology" strategy has resulted in the discovery of unanticipated nuclear signaling pathways for retinoids, fatty acids, eicosanoids, and steroids with important physiological and pharmacological ramifications.

Molecular recognition of fatty acids by peroxisome proliferator-activated receptors.

The peroxisome proliferator-activated receptors (PPARs) are nuclear receptors for fatty acids (FAs) that regulate glucose and lipid homeostasis. We report the crystal structure of the PPAR delta ligand-binding domain (LBD) bound to either the FA eicosapentaenoic acid (EPA) or the synthetic fibrate GW2433. The carboxylic acids of EPA and GW2433 interact directly with the activation function 2 (AF-2) helix. The hydrophobic tail of EPA adopts two distinct conformations within the large hydrophobic cavity. GW2433 occupies essentially the same space as EPA bound in both conformations. These structures provide molecular insight into the propensity for PPARs to interact with a variety of synthetic and natural compounds, including FAs that vary in both chain length and degree of saturation.

N-(2-Benzoylphenyl)-L-tyrosine PPARgamma agonists. 1. Discovery of a novel series of potent antihyperglycemic and antihyperlipidemic agents.

We have identified a novel series of antidiabetic N-(2-benzoylphenyl)-L-tyrosine derivatives which are potent, selective PPARgamma agonists. Through the use of in vitro PPARgamma binding and functional assays (2S)-3-(4-(benzyloxy)phenyl)-2-((1-methyl-3-oxo-3-phenylpropenyl)+ ++amin o)propionic acid (2) was identified as a structurally novel PPARgamma agonist. Structure-activity relationships identified the 2-aminobenzophenone moiety as a suitable isostere for the chemically labile enaminone moiety in compound 2, affording 2-((2-benzoylphenyl)amino)-3-(4-(benzyloxy)phenyl)propionic acid (9). Replacement of the benzyl group in 9 with substituents known to confer in vivo potency in the thiazolidinedione (TZD) class of antidiabetic agents provided a dramatic increase in the in vitro functional potency and affinity at PPARgamma, affording a series of potent and selective PPARgamma agonists exemplified by (2S)-((2-benzoylphenyl)amino)-3-¿4-[2-(methylpyridin-2-ylamino+ ++)ethoxy ]phenyl¿propionic acid (18), 3-¿4-[2-(benzoxazol-2-ylmethylamino)ethoxy]phenyl¿-(2S)-((2- benzoylph enyl)amino)propanoic acid (19), and (2S)-((2-benzoylphenyl)amino)-3-¿4-[2-(5-methyl-2-phenyloxazol-4-y l)e thoxy]phenyl¿propanoic acid (20). Compounds 18 and 20 show potent antihyperglycemic and antihyperlipidemic activity when given orally in two rodent models of type 2 diabetes. In addition, these analogues are readily prepared in chiral nonracemic fashion from L-tyrosine and do not show a propensity to undergo racemization in vitro. The increased potency of these PPARgamma agonists relative to troglitazone may translate into superior clinical efficacy for the treatment of type 2 diabetes.

Subclavian artery aneurysms. A report of 2 cases and a review of the literature.

True aneurysm of the subclavian artery is extremely rare and atherosclerosis is the most common cause. Syphilis, tuberculosis, and cystic medial necrosis are less often the cause. Their exact prevalence in the general population is unknown. These aneurysms can rupture, thrombose, embolize or cause symptoms by local compression. In reviewing the literature the great latency of the disease, high complication rate at presentation and the significant incidence, concomitant aneurysms elsewhere are emphasized. Duplex scanning followed by angiography should be performed in order to establish the diagnosis and to plan the operation. Elective surgical treatment is associated with little risk to the patient and avoids the need for emergency operations. Two cases of surgically treated true subclavian aneurysms are presented with review of the English language literature on the subject.

The human orphan nuclear receptor PXR is activated by compounds that regulate CYP3A4 gene expression and cause drug interactions.

The cytochrome P-450 monooxygenase 3A4 (CYP3A4) is responsible for the oxidative metabolism of a wide variety of xenobiotics including an estimated 60% of all clinically used drugs. Although expression of the CYP3A4 gene is known to be induced in response to a variety of compounds, the mechanism underlying this induction, which represents a basis for drug interactions in patients, has remained unclear. We report the identification of a human (h) orphan nuclear receptor, termed the pregnane X receptor (PXR), that binds to a response element in the CYP3A4 promoter and is activated by a range of drugs known to induce CYP3A4 expression. Comparison of hPXR with the recently cloned mouse PXR reveals marked differences in their activation by certain drugs, which may account in part for the species-specific effects of compounds on CYP3A gene expression. These findings provide a molecular explanation for the ability of disparate chemicals to induce CYP3A4 levels and, furthermore, provide a basis for developing in vitro assays to aid in predicting whether drugs will interact in humans.