Development of beta 3-adrenoceptor agonists for the treatment of obesity and diabetes--an update.
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Beta 3-adrenoceptor (beta 3-AR) agonists were found to have remarkable anti-obesity and anti-diabetic effects in rodents shortly after their discovery in the early 1980s. Despite these promising qualities, several pharmaceutical problems and theoretical concerns have slowed the development of these products as therapeutic agents in humans during the last 15 years. To date, the pharmaceutical industry has not been successful in developing a beta 3-AR agonist for use in the treatment of human obesity and type 2 diabetes. Pharmaceutical problems in this area concern important differences between rodent and human beta 3-AR and the difficulty in finding a compound with sufficient bioavailability that is a highly selective and full agonist at the human receptor. Some of these problems seem to have been solved with the cloning of the human beta 3-AR, which has made it possible to develop novel compounds directly and specifically against the human receptor. However, several theoretical concerns still remain. These include the major question as to whether the number of biologically active beta 3-ARs in adult humans is sufficient to produce relevant metabolic effects and, if so, whether their long-term stimulation is safe and free of unwarranted side effects. In addition, the mechanisms of action of beta 3-AR agonists remain poorly understood. Recent studies using CL 316,243, a highly selective beta 3-adrenergic compound, have provided new insights into the potential mechanisms of action of these drugs in rodents as well as the first evidence that treatment with a highly selective beta 3-AR agonist exerts relevant metabolic effects in humans. It appears that chronic beta 3-adrenergic stimulation in white adipose tissue increases the expression of newly discovered mitochondrial uncoupling proteins (UCP 2 and 3) and a "reawakening" of dormant brown adipocytes. In addition, beta 3-ARs may be present in skeletal muscle where ectopic expression of UCP-1 has been reported. If these findings are confirmed, tissues other than brown fat may play an important role in mediating beta 3-adrenergic effects on thermogenesis and substrate oxidation. In humans, treatment with CL 316,243 for 8 weeks, in spite of limited bioavailability, induced marked plasma concentration-dependent increases in insulin sensitivity, lipolysis, and fat oxidation in lean volunteers, without causing beta 1-, or beta 2-mediated side effects. These results clearly indicate that favourable metabolic effects can be achieved by selective beta 3-AR stimulation in humans. The compounds of the next generation currently emerging from preclinical development are full agonists at the human beta 3-AR. These agents have demonstrated promising results in non-human primates. It will be interesting to see whether their efficacy in clinical trials is superior to that achieved with previous (rodent) beta 3-AR agonists and, if so, whether their effects will eventually translate into weight loss and improved metabolic control that could facilitate their use as effective drugs for the treatment of obesity and Type 2 diabetes in humans. (+info)
Orlistat, a lipase inhibitor, for weight maintenance after conventional dieting: a 1-y study.
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BACKGROUND: Long-term maintenance of weight loss remains a therapeutic challenge in obesity treatment. OBJECTIVE: This multicenter, double-blind, placebo-controlled study was designed to test the hypothesis that orlistat, a gastrointestinal lipase inhibitor, is significantly more effective than a placebo in preventing weight regain. DESIGN: Obese subjects who lost > or = 8% of their initial body weight during a 6-mo lead-in of a prescribed hypoenergetic diet (4180-kJ/d deficit) with no adjunctive pharmacotherapy were randomly assigned to receive placebo, 30 mg orlistat, 60 mg orlistat, or 120 mg orlistat 3 times daily for 1 y in combination with a maintenance diet to help prevent weight regain. Of 1313 recruited subjects [body mass index (in kg/m2): 28-43], 729 subjects lost > or =8% of their initial body weight during the 6-mo weight-loss lead-in period and were enrolled in the double-blind phase. RESULTS: After 1 y, subjects treated with 120 mg orlistat 3 times daily regained less weight than did placebo-treated subjects (32.8 +/- 4.5% compared with 58.7 +/- 5.8% regain of lost weight; P < 0.001). Moreover, more subjects in the 120-mg orlistat group than in the placebo group regained < or = 25% of lost weight (47.5% of subjects compared with 29.9%). In addition, orlistat treatment (120 mg 3 times daily) was associated with significantly greater reductions in total and LDL-cholesterol concentrations than was placebo (P < 0.001). CONCLUSION: The use of orlistat during periods of attempted weight maintenance minimizes weight readjustment and facilitates long-term improvement in obesity-related disease risk factors. (+info)
The effect of moxonidine on feeding and body fat in obese Zucker rats: role of hypothalamic NPY neurones.
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The antihypertensive agent moxonidine, an imidazoline Ii-receptor agonist, also induces hypophagia and lowers body weight in the obese spontaneously hypertensive rat, but the central mediation of this action and the neuronal pathways that moxonidine may interact with are not known. We studied whether moxonidine has anti-obesity effects in the genetically-obese and insulin-resistant fa/fa Zucker rat, and whether these are mediated through inhibition of the hypothalamic neuropeptide Y (NPY) neurones. Lean and obese Zucker rats were given moxonidine (3 mg kg(-1) day(-1)) or saline by gavage for 21 days. Moxonidine decreased food intake throughout by 20% in obese rats (P<0.001) and by 8% in lean rats (P<0.001), and reduced weight gain that final body weight was 15% lower in obese (P<0.001) and 7% lower in lean (P<0.01) rats than their untreated controls. Plasma insulin and leptin levels were decreased in moxonidine-treated obese rats (P<0.01 and P<0.05), but unchanged in treated lean rats. Uncoupling protein-1 gene expression in brown adipose tissue was stimulated by 40-50% (P< or =0.05) in both obese and lean animals given moxonidine. Obese animals given moxonidine showed a 37% reduction in hypothalamic NPY mRNA levels (P = 0.01), together with significantly increased NPY concentrations in the paraventricular nucleus (P<0.05), but no changes in the arcuate nucleus or other nuclei; this is consistent with reduced NPY synthesis in the arcuate nucleus and blocked release of NPY in the paraventricular nucleus. In lean animals, moxonidine did not affect NPY levels or NPY mRNA. The hypophagic, thermogenic and anti-obesity effects of moxonidine in obese Zucker rats may be partly due to inhibition of the NPY neurones, whose inappropriate overactivity may underlie obesity in this model. (+info)
Review article: malnutrition and maltreatment--a comment on orlistat for the treatment of obesity.
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The prevalence of obesity has doubled in the last 10 years and is now reaching epidemic proportions. There is a significant comorbidity and financial cost associated with this disorder. Orlistat is an intestinal lipase inhibitor that is approved for the treatment of obesity. Recent randomized, double-blind, placebo-controlled trials have demonstrated the benefit of orlistat used in conjunction with a hypocaloric (low-fat) diet in facilitating weight reduction and the long-term maintenance of this weight loss. Patients treated with orlistat lost a greater amount of initial body weight compared to those who received placebo. After 24 months of treatment, weight loss of more than 5% was maintained in a greater number of those treated with orlistat. This was associated with significant reductions in cardiovascular risk factors (cholesterol, LDL cholesterol, LDL:HDL cholesterol ratio). The main adverse events are related to fat malabsorption, with potential losses of fat-soluble vitamins and other compounds. Orlistat as a treatment for obesity, when prescribed within present guidelines, can aid modest weight loss in about one-third of patients. More importantly, it can assist in the maintenance of weight loss with major medical benefits for these patients. (+info)
Orlistat. No hurry....
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Treatments for obesity are disappointing. None has yet shown an effect on morbidity and mortality. Nondrug treatments are poorly assessed. Stable long-term weight loss necessitates long-term management. Orlistat (Xenical, Hoffman-La Roche), a gastrointestinal lipase inhibitor, is indicated, in combination with a low-calorie diet, for management of obesity. The assessment file is bulky and methodologically sound, at least in terms of the weight loss end point. During medium-term trials (12 to 24 months), orlistat administered at a dose of 120 mg three times daily and combined with dietary intervention had a moderate positive effect on body weight (-3.5 kg on average). No longer-term trials have been done. It is unknown whether this drug affects morbidity and mortality linked to obesity. In clinical trials, patients treated with orlistat had an increased frequency of breast cancer. This potential risk is currently being assessed in a specific trial. Gastrointestinal adverse effects are frequent. Treatment is costly. (+info)
Drug therapy for obesity.
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Obesity is a common health problem in the United States, and effective treatment is challenging. Obesity is associated with an increased mortality rate and risk factors such as hypertension, hyperlipidemia and diabetes mellitus. Numerous treatments are available for obesity. Behavioral therapy, surgery and pharmacologic treatment have been used with varying degrees of success. Older anorectic agents have significant side effects and limited benefit, and some have even been withdrawn from the U.S. market because of a possible association with cardiovascular complications. The safety of newer agents must be extensively evaluated before widespread use is recommended. Therefore, behavioral therapy, including regular exercise and the development of healthy eating habits, continues to be the best treatment for long-term weight loss. (+info)
Urothelial carcinoma associated with the use of a Chinese herb (Aristolochia fangchi)
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BACKGROUND: Chinese-herb nephropathy is a progressive form of renal fibrosis that develops in some patients who take weight-reducing pills containing Chinese herbs. Because of a manufacturing error, one of the herbs in these pills (Stephania tetrandra) was inadvertently replaced by Aristolochia fangchi, which is nephrotoxic and carcinogenic. METHODS: The diagnosis of a neoplastic lesion in the native urinary tract of a renal-transplant recipient who had Chinese-herb nephropathy prompted us to propose regular cystoscopic examinations and the prophylactic removal of the native kidneys and ureters in all our patients with end-stage Chinese-herb nephropathy who were being treated with either transplantation or dialysis. Surgical specimens were examined histologically and analyzed for the presence of DNA adducts formed by aristolochic acid. All prescriptions written for Chinese-herb weight-reducing compounds during the period of exposure (1990 to 1992) in these patients were obtained, and the cumulative doses were calculated. RESULTS: Among 39 patients who agreed to undergo prophylactic surgery, there were 18 cases of urothelial carcinoma (prevalence, 46 percent; 95 percent confidence interval, 29 to 62 percent): 17 cases of carcinoma of the ureter, renal pelvis, or both and 1 papillary bladder tumor. Nineteen of the remaining patients had mild-to-moderate urothelial dysplasia, and two had normal urothelium. All tissue samples analyzed contained aristolochic acid-related DNA adducts. The cumulative dose of aristolochia was a significant risk factor for urothelial carcinoma, with total doses of more than 200 g associated with a higher risk of urothelial carcinoma. CONCLUSIONS: The prevalence of urothelial carcinoma among patients with end-stage Chinese-herb nephropathy (caused by aristolochia species) is a high. (+info)
Detection of impaired intestinal absorption of long-chain fatty acids: validation studies of a novel test in a rat model of fat malabsorption.
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BACKGROUND: Classic fat balance studies detect fat malabsorption but do not discriminate between the potential causes of malabsorption, such as impaired intestinal lipolysis or reduced uptake of fatty acids. OBJECTIVE: We aimed to validate a novel test for the specific, sensitive detection of impaired intestinal uptake of long-chain unesterified fatty acids in an appropriate rat model of fat malabsorption. DESIGN: The absorption and appearance in plasma of [(13)C]palmitic acid were determined in control rats and in rats with fat malabsorption due either to chronic bile deficiency (permanent bile diversion) or to oral administration of the lipase inhibitor orlistat (200 mg/kg diet). [(13)C]Palmitic acid results were compared with the percentage absorption of ingested dietary fat determined by fat balance. RESULTS: Between 1 and 6 h after intraduodenal administration, plasma [(13)C]palmitate concentrations in control rats were 4-10-fold higher than in bile-deficient rats (P < 0.05) but were not significantly different between orlistat-supplemented rats and their controls. In control and bile-deficient rats, plasma [(13)C]palmitate concentrations allowed complete discrimination between normal (>92%) and reduced (<92%) fat absorption, whereas the percentage absorption of [(13)C]palmitate over 48 h appeared to be highly correlated with the percentage absorption of ingested dietary fat (r = 0.89, P < 0.001). CONCLUSIONS: The [(13)C]palmitic acid absorption test detects impaired intestinal absorption of long-chain fatty acids selectively and sensitively in a rat model of fat malabsorption due to bile deficiency. Our data strongly support the use of the [(13)C]palmitic acid absorption test for the diagnosis of clinical fat malabsorption syndromes. (+info)