Dual and pan-peroxisome proliferator-activated receptors (PPAR) co-agonism: the bezafibrate lessons

There are three peroxisome proliferator-activated receptors (PPARs) subtypes which are commonly designated PPAR alpha, PPAR gamma and PPAR beta/delta. PPAR alpha activation increases high density lipoprotein (HDL) cholesterol synthesis, stimulates "reverse" cholesterol transport and reduces triglycerides. PPAR gamma activation results in insulin sensitization and antidiabetic action. Until recently, the biological role of PPAR beta/delta remained unclear. However, treatment of obese animals by specific PPAR delta agonists results in normalization of metabolic parameters and reduction of adiposity. Combined treatments with PPAR gamma and alpha agonists may potentially improve insulin resistance and alleviate atherogenic dyslipidemia, whereas PPAR delta properties may prevent the development of overweight which typically accompanies "pure" PPAR gamma ligands. The new generation of dual-action PPARs – the glitazars, which target PPAR-gamma and PPAR-alpha (like muraglitazar and tesaglitazar) are on deck in late-stage clinical trials and may be effective in reducing cardiovascular risk, but their long-term clinical effects are still unknown. A number of glitazars have presented problems at a late stage of clinical trials because of serious side-effects (including ragaglitazar and farglitazar). The old and well known lipid-lowering fibric acid derivative bezafibrate is the first clinically tested pan – (alpha, beta/delta, gamma) PPAR activator. It is the only pan-PPAR activator with more than a quarter of a century of therapeutic experience with a good safety profile. Therefore, bezafibrate could be considered (indeed, as a "post hoc" understanding) as an "archetype" of a clinically tested pan-PPAR ligand. Bezafibrate leads to considerable raising of HDL cholesterol and reduces triglycerides, improves insulin sensitivity and reduces blood glucose level, significantly lowering the incidence of cardiovascular events and new diabetes in patients with features of metabolic syndrome. Clinical evidences obtained from bezafibrate-based studies strongly support the concept of pan-PPAR therapeutic approach to conditions which comprise the metabolic syndrome. However, from a biochemical point of view, bezafibrate is a PPAR ligand with a relatively low potency. More powerful new compounds with pan-PPAR activity and proven long-term safety should be highly effective in a clinical setting of patients with coexisting relevant lipid and glucose metabolism disorders.     

Independent influence of insulin, catecholamines, and thyroid hormones on metabolic syndrome

The objective of this study was to examine whether metabolic syndrome, defined according to adult treatment panel III criteria, is associated with insulin, catecholamines, and thyroid hormones, independently of age and gender. A cohort of 651 euthyroid overweight and obese patients, 440 women and 211 men, aged 18-68 years, were examined. Central fat accumulation (indirectly measured by waist circumference), fasting thyroid-stimulating hormone (TSH), FT(3), FT(4), insulin, glucose, and lipid (cholesterol, HDL-cholesterol, and triglyceride) serum concentrations, 24-h urinary catecholamines, and the level of insulin resistance (estimated by homeostasis model assessment for insulin resistance (HOMA(IR))) were measured. Patients with metabolic syndrome showed higher insulin (P < 0.001) and FT(3) (P < 0.001) serum levels and higher 24-h urinary noradrenaline (P < 0.001) than subjects without this syndrome. The number of metabolic syndrome parameters was directly associated with insulin (P < 0.001) and FT(3) (P < 0.05) serum levels, and with 24-h urinary noradrenaline (P < 0.001) in the whole population. When a multiple regression analysis was performed with the metabolic syndrome as the dependent variable, and age, gender, and insulin, and TSH, FT(3), FT(4) serum levels, and 24-h urinary noradrenaline and adrenaline as independent variables, the metabolic syndrome maintained an independent positive association with age (P < 0.001), male sex (P < 0.001), insulin (P < 0.001), and 24-h urinary noradrenaline (P < 0.001). In conclusion, this study suggests that insulin and noradrenaline cooperate independently to the development of the metabolic syndrome.     

The effects of K-111, a new insulin-sensitizer, on metabolic syndrome in obese prediabetic rhesus monkeys.

K-111, formerly BM 17.0744, (2,2-dichloro-12-(4-chlorophenyl)-dodecanoic acid) is a new insulin-sensitizer with peroxisome proliferator-activated receptor (PPAR) alpha activity but without PPAR gamma activity. We determined the efficacy of K-111 in non-human primates in increasing insulin-stimulated glucose uptake and improving metabolic syndrome, assessing the general health-related effects. Six adult male obese normoglycemic prediabetic and insulin-resistant rhesus monkeys were studied on vehicle and following K-111 treatment (four-week chronic dosing each of 3 doses: 1, 3, and 10 mg/kg/d) with assessment of changes in substrate, hormone, and blood pressure measurements and alterations in insulin sensitivity using the euglycemic, hyperinsulinemic clamp technique. K-111 led to significantly decreased body weight and improved hyperinsulinemia, insulin sensitivity, hypertriglyceridemia, and HDL-cholesterol levels without adipogenesis or significant effects on fasting glucose, 24-hour urine glucose excretion, systolic or diastolic blood pressure, plasma fibrinogen, total cholesterol, or chemistry and hematology profile. These benefits are similar to the health-improving effects of calorie restriction, providing preliminary evidence that K-111 has excellent potential as a calorie-restriction mimetic agent. These results indicate the necessity of future study of K-111 for metabolic syndrome in humans, and suggest potential in reducing the risks of diabetes and cardiovascular disease.     

Metabolic effect of telmisartan and losartan in hypertensive patients with metabolic syndrome

Background

Metabolic syndrome is a cluster of common cardiovascular risk factors that includes hypertension and insulin resistance. Hypertension and diabetes mellitus are frequent comorbidities and, like metabolic syndrome, increase the risk of cardiovascular events. Telmisartan, an antihypertensive agent with evidence of partial peroxisome proliferator-activated receptor activity-gamma (PPARγ) activity, may improve insulin sensitivity and lipid profile in patients with metabolic syndrome.

Methods

In a double-blind, parallel-group, randomized study, patients with World Health Organization criteria for metabolic syndrome received once-daily doses of telmisartan (80 mg, n = 20) or losartan (50 mg, n = 20) for 3 months. At baseline and end of treatment, fasting and postprandial plasma glucose, insulin sensitivity, glycosylated haemoglobin (HBA_1c) and 24-hour mean systolic and diastolic blood pressures were determined.

Results

Telmisartan, but not losartan, significantly (p < 0.05) reduced free plasma glucose, free plasma insulin, homeostasis model assessment of insulin resistance and HbA_ic. Following treatment, plasma glucose and insulin were reduced during the oral glucose tolerance test by telmisartan, but not by losartan. Telmisartan also significantly reduced 24-hour mean systolic blood pressure (p < 0.05) and diastolic blood pressure (p < 0.05) compared with losartan.

Conclusion

As well as providing superior 24-hour blood pressure control, telmisartan, unlike losartan, displayed insulin-sensitizing activity, which may be explained by its partial PPARγ activity.     

PPAR家族及其与代谢综合征的关系

过氧化物酶体增殖物激活受体(peroxisome proliferator-activated receptors,PPARs)是配体激活的转录因子核受体超家族成员之一。目前已知有三种亚型：PPARα、-β／δ和-γ。它们在脂肪生成、脂质代谢、胰岛素敏感性、炎症和血压调节中起着关键作用,因而近年来倍受关注。越来越多的研究表明,PPARs与代谢综合征,包括胰岛素抵抗、糖耐量受损、2型糖尿病、肥胖、高脂血症、高血压病、动脉粥样硬化和蛋白尿之间存在因果关系。重要的是,PPARα的激动剂如贝丁酸类降脂药(Fibrate)和PPARγ的激动剂如噻唑烷二酮(Thiazolidinedione,TZD)均已被证实有改善代谢综合征的作用。此外,三种PPAR亚型在2型糖尿病及糖尿病肾病的发展中均有重要作用。不断增加的证据提示,PPARs有可能成为代谢综合征及其相关并发症的潜在治疗靶点。本文将就PPARs的生物学活性、配体选择性和生理学功能作一综述,并对其在代谢综合征发病机制中的作用和PPAR配体对2型糖尿病的治疗效用进行重点讨论。     

Emerging roles of PPARdelta in metabolism

PPARdelta differs from the other two PPAR isotypes (alpha and gamma) by its more wide-spread tissue-specific expression pattern, its involvement in developmental processes and its profound impact on muscle and heart fat metabolism. Activation of PPARdelta modulates inflammatory responses of macrophages and is linked to altered lipoprotein metabolism, most importantly a significant raise of HDL cholesterol. PPARdelta activation in the liver decreases hepatic glucose output, thereby contributing to improved glucose tolerance and insulin sensitivity. Several studies have shown that PPARdelta polymorphisms are associated with plasma lipid levels, body mass index and the risk for diabetes and coronary heart disease. These findings support that high affinity PPARdelta agonists may be promising drugs of the future to treat the metabolic syndrome which is an expanding overweight-related health threat characterized by insulin resistance, hyperglycemia, dyslipidemia, hypertension, and accelerated atherosclerosis.     

Safety issues and prospects for future generations of PPAR modulators

Because of their wide range of actions on glucose homeostasis, lipid metabolism and vascular inflammation, peroxisome proliferator-activated receptors (PPARs) are promising targets for the development of new drugs for the treatment of metabolic disorders such as diabetes, dyslipidemia and atherosclerosis. In clinical practice, PPARalpha agonists, such as the already available fibrates, improve dyslipidemia, while PPARgamma agonists, such as thiazolidinediones, improve insulin resistance and diabetes. The complementary action of simultaneous activation of each PPAR in patients suffering from metabolic syndrome and type 2 diabetes has led to new pharmacological strategies focused on the development of agonists targeting more than one receptor such as the dual PPARalpha/gamma agonists. However, despite the proven benefits of targeting PPARs, safety concerns have recently led to late stage development failures of various PPAR agonists including novel specific PPARgamma agonists and dual PPARalpha/gamma agonists. These safety concerns include potential carcinogenicity in rodents, signs of myopathy and rhabdomyolysis, increase in plasma creatinine and homocysteine, weight gain, fluid retention, peripheral edema and potential increased risk of cardiac failure. Although the discontinued compounds shared common side effects, the reason for discontinuation was always compound specific and the toxicological or adverse effects which have motivated the discontinuation could be either due to the activation of PPARgamma, PPARalpha or both (class effect) or due to a PPAR unrelated effect. Thus, the risk evaluation of each adverse effect should be viewed on a case by case basis considering both the PPAR profile of the drug, its absorption/distribution profile, the nature of the side effect and the putative PPAR-related mechanism of action. This review mainly focuses on the preclinical and clinical adverse events of PPAR agonists that could be of concern when considering the development of new PPAR agonists. The selective modulation of PPAR activities is a promising approach to develop new drugs with preserved efficacy but diminished adverse effects.     

Design and synthesis of substituted phenylpropanoic acid derivatives as human peroxisome proliferator-activated receptor alpha/delta dual agonists

A series of phenylpropanoic acids was prepared as candidate dual agonists of peroxisome proliferator-activated receptors (PPAR) alpha and delta. Structure-activity relationship studies indicated that the shape of the linker moiety and the nature of the substituent at the distal benzene ring play key roles in determining the potency and selectivity of PPAR subtype transactivation. Optically active alpha-ethylphenylpropanoic acid derivatives were identified as potent human PPAR alpha and delta dual agonists with potential for the treatment of metabolic syndrome.     

Uric Acid nephrolithiasis: recent progress and future directions

The prevalence of urolithiasis has been increasing for the past few decades in industrialized nations. Uric acid calculi account for a significant percentage of urinary stones. Certain risk factors may be involved in the pathogenesis of uric acid nephrolithiasis, including hyperuricosuria, low urinary volume, and persistently low urinary pH. Patients with medical conditions that promote profound hyperuricosuria are at high risk of developing uric acid calculi. These conditions include chronic diarrheal states; myeloproliferative disorders; insulin resistance, including diabetes mellitus; and monogenic metabolic disorders, such as Lesch-Nyhan syndrome. Computed tomography can provide a definitive diagnosis. Except in cases in which there is severe obstruction, progressive azotemia, serious infection, or unremitting pain, the initial treatment of patients with uric acid nephrolithiasis should be medical dissolution therapy because this approach is successful in the majority of cases. A thorough review of the epidemiology and pathophysiology of uric acid nephrolithiasis is crucial for the diagnosis, treatment, and prevention of stones in patients with this condition.     

4,4-Dimethyl-1,2,3,4-tetrahydroquinoline-based PPARα/γ agonists. Part. II: Synthesis and pharmacological evaluation of oxime and acidic head group structural variations

Type-2 diabetes (T2D) is a complex metabolic disease characterized by insulin resistance in the liver and peripheral tissues accompanied by a deficiency in pancreatic β-cells. Since their discovery, three subtypes of peroxisome proliferator activated receptors have been identified, namely PPARα, PPARγ and PPARβ/(δ). In this study, we were interested in designing novel PPARγ selective agonists and/or dual PPARα/γ agonists. Based on the typical topology of synthetic PPAR agonists, we focused our design approach on using 4,4-dimethyl-1,2,3,4-tetrahydroquinoline as a novel cyclic scaffold with oxime and acidic head group structural variations.     

Identification of novel PPARα/γ dual agonists by virtual screening,ADMET prediction and molecular dynamics simulations

PPARα and PPARγ have been the most widely studied Peroxisome proliferator-activated receptor (PPAR) subtypes due to their important roles in regulating glucose, lipids, and cholesterol metabolism. By combining the lowering serum triglyceride levels benefit of PPARα agonists (such as fibrates) with the glycemic advantages of the PPARγ agonists (such as TZD), the dual PPAR agonists approach can both improve the metabolic effects and minimize the side effects caused by either agent alone, and hence, has become a promising strategy for designing effective drugs against type-2 diabetes. In this study, by means of virtual screening, ADMET prediction and molecular dynamics (MD) simulations techniques, one compound-ASN15761007 with high binding score, low toxicity were gained. It was observed by MD simulations that ASN15761007 not only possessed the same function as AZ242 did in activating PPARα and BRL did in activating PPARγ, but also had more favorable conformation for binding to the two receptors. Our results provided an approach to rapidly produce novel PPARα/γ dual agonists which might be a potential lead compound to develop against insulin resistance and hyperlipidemia.     

The role of peroxisome proliferator activated receptors in metabolic balance disturbances under stress

Some aspects of peroxisome proliferator activated receptors (PPAR) involvement in regulation of stress-dependent biological processes leading to insulin resistance, lipid imbalance, hypertension and inflammation are reviewed. Analysis of literature data clearly shows the main role of PPAR in stress signal transduction following to metabolic disbalance development under prolonged stress conditions. The interplay of three PPAR isoforms functional activity with metabolic process disturbances during stress is under special emphasis. Taking into account experimental data described in literature we suggest that PPAR activation under acute stress is an adaptive response while stable PPAR hyperexpression under prolonged stress can cause insulin resistance, hypertension, and visceral obesity. The strategy of PPAR using as pharmacological targets in metabolic syndrome correction is under consideration.     

Glomerular filtration rate and blood pressure monitoring in awake baboons

Minimally invasive techniques were used to collect urine with an external catheter together with automated intermittent monitoring of arterial blood pressure in awake male baboons. Using endogenous creatinine, 24-hour creatinine clearances were measured for 2 to 3 consecutive days in four intact and in four uninephrectomized baboons. Despite large differences in urinary volume and sodium excretion, reproducibility of 24-hour creatinine clearances was within 15% in 15 of 19 studies obtained from 6 of 8 animals. Arterial blood pressure was monitored intermittently at 30 to 60 minute intervals over 24 hours with a Dinamap monitor and recorder. Mean blood pressure averaged 71 +/- 4.4 to 89 +/- 5.5 mm Hg in different animals. Blood pressure tended to be lower at night than during the day. In separate studies using 15 to 60 minute urine collection periods, inulin clearance was compared in awake and in anesthetized animals with endogenous or exogenous creatinine clearance measured simultaneously. The clearance of creatinine systematically exceeded the clearance of inulin, even in intact animals with a normal serum creatinine. The creatinine-to-inulin clearance ratio averaged 1.16 +/- 0.03 at a serum concentration of 0.7 to 0.8 mg/dl; 1.27 +/- 0.03 at a serum creatinine of 1.0 to 1.1 mg/dl and 1.56 +/- 0.04 at a serum creatinine greater than 10 mg/dl. All values exceed unity significantly (p less than 0.001). Thus, renal function, including inulin clearance, can be measured in awake baboons. Duplicate or triplicate 24-hour urine collections are needed to assess the reliability of creatinine excretion. However, creatinine clearance overestimates glomerular filtration rate, as it does in humans.     

Difference in 24-Hour Urine Composition between Diabetic and Non-Diabetic Adults without Nephrolithiasis

Background

Diabetic patients are more likely to develop kidney stones than the general population. The underlying mechanisms for this disparity remain to be elucidated. Little is known about the relationship between urine composition and diabetes mellitus in non-stone-forming individuals. We sought to examine the differences in the 24-hour (24-h) urine composition between diabetic and non-diabetic adults who were not stone formers.

Methods

A convenience sample of 538 individuals without a history of nephrolithiasis, gout, hyperparathyroidism, or gastroenteric diseases participated in this study. The 24-h urine profiles of 115 diabetic adults were compared with those of 423 non-diabetic adults. Diabetes was defined by self-reported physician diagnosis or medication use. All participants were non-stone formers confirmed by urinary tract ultrasonography. Participants provided a fasting blood sample and a single 24-h urine collection for stone risk analysis. Student’s t-test was used to compare mean urinary values. Linear regression models were adjusted for age, gender, body mass index, hypertension, fasting serum glucose, serum total cholesterol, estimated creatinine clearance rate and urinary factors.

Results

Univariable analysis showed that the diabetic participants had significantly higher 24-h urine volumes and lower urine calcium and magnesium excretions than non-diabetic participants (all P < 0.05). After multivariate adjustment, no significant differences in 24-h urine composition were observed between diabetic and non-diabetic participants except for a slightly increased 24-h urine volume in diabetic participants (all P > 0.05). The main limitation of this study is that the convenience samples and self-reported data may have been sources of bias.

Conclusion

Our data showed that there were no differences in 24-h urine composition between diabetic and non-diabetic adults who are not stone formers. The reason for it might be the improved glycemic control in diabetic individuals in our study. Therefore, a tighter glycemic control might reduce stone formation in diabetic adults.     

几种天然产物对高尿酸血症大鼠血清尿酸水平的影响初探

目的:探讨几种天然产物对高尿酸血症大鼠血清尿酸水平及尿酸排泄的影响.方法:对wistar大鼠灌胃氧嗪酸钾和酵母膏,制作高尿酸血症大鼠动物模型.灌胃给药褐藻糖胶、柠檬酸钾和东哥阿里提取物,2周后采血并进行代谢实验,检测血清尿酸、尿素氮,24小时尿液体积、pH值、尿酸浓度及总量,分析三种活性物质对机体尿酸水平、尿酸排泄、肾脏功能的影响.结果:三种物质均可显著降低高尿酸血症模型大鼠的血清尿酸水平,其中东哥阿里提取物组的24小时排泄尿酸总量较模型组显著降低,褐藻糖胶对实验大鼠的血清尿素氮水平升高有抑制作用.结论:三种活性物质对高尿酸血症大鼠血清尿酸浓度有降低作用,其中褐藻糖胶对肾脏功能有保护作用,从而保证尿酸的顺利排泄,而东哥阿里在降低血尿酸水平的同时,24小时尿液中排泄的尿酸总量也显著低于模型对照组,其机制可能与抑制尿酸生成有关.     

Single-mouse urine collection and pH monitoring system.

A glass cage with minimal surface area was designed and used to house mice for 24-hour urine collections. An experiment was performed with a radio-labeled compound excreted in the urine to assess the collection efficiency of the cage. In this experiment 74.2 +/- 6.5% of the excreted radioactivity was recovered in the urine, with 25.8 +/- 6.5% found adhering to the cage surfaces. When a flow-through pH electrode, meter, and recorder were attached, the system provided a continuous pH versus time urination record.     

The renin-angiotensin system: a target of and contributor to dyslipidemias, altered glucose homeostasis, and hypertension of the metabolic syndrome

The renin-angiotensin system (RAS) is an important therapeutic target in the treatment of hypertension. Obesity has emerged as a primary contributor to essential hypertension in the United States and clusters with other metabolic disorders (hyperglycemia, hypertension, high triglycerides, low HDL cholesterol) defined within the metabolic syndrome. In addition to hypertension, RAS blockade may also serve as an effective treatment strategy to control impaired glucose and insulin tolerance and dyslipidemias in patients with the metabolic syndrome. Hyperglycemia, insulin resistance, and/or specific cholesterol metabolites have been demonstrated to activate components required for the synthesis [angiotensinogen, renin, angiotensin-converting enzyme (ACE)], degradation (ACE2), or responsiveness (angiotensin II type 1 receptors, Mas receptors) to angiotensin peptides in cell types (e.g., pancreatic islet cells, adipocytes, macrophages) that mediate specific disorders of the metabolic syndrome. An activated local RAS in these cell types may contribute to dysregulated function by promoting oxidative stress, apoptosis, and inflammation. This review will discuss data demonstrating the regulation of components of the RAS by cholesterol and its metabolites, glucose, and/or insulin in cell types implicated in disorders of the metabolic syndrome. In addition, we discuss data supporting a role for an activated local RAS in dyslipidemias and glucose intolerance/insulin resistance and the development of hypertension in the metabolic syndrome. Identification of an activated RAS as a common thread contributing to several disorders of the metabolic syndrome makes the use of angiotensin receptor blockers and ACE inhibitors an intriguing and novel option for multisymptom treatment.     

Effect of Beer Ingestion on the Plasma Concentrations and Urinary Excretion of Purine Bases: One-Month Study

To investigate the effect of long-term beer ingestion on the plasma concentrations and urinary excretion of purine bases, 5 healthy males participated in the present study, during which they ingested beer every evening for 30 days. Blood and 24-hour urine samples were collected in the morning one day before and 14 and 30 days after the initiation of the beer ingestion. During the beer ingestion period, the plasma concentration and the urinary excretion of uric acid were increased significantly, while uric acid clearance was not decreased. Further, purine ingestion was not significantly different throughout the study. These results suggest that production of uric acid by ethanol ingestion was the main contributor to the increased plasma uric acid. Therefore, patients with gout should be encouraged to avoid drinking large amounts of beer on a daily basis.