Identification of potent agonists acting at an endogenous atypical beta3-adrenoceptor state that modulate lipolysis in rodent fat cells

Standard Curves Are Necessary to Determine Pharmacological Properties for Ligands in Functional Assays Using Competition Binding Technologies

Homogeneous functional assays that utilize competition binding technology are widely used for determining pharmacological properties such as intrinsic activity and potency. One example is time-resolved fluorescence resonance energy transfer (TR-FRET) 3',5'-cyclic adenosine monophosphate (cAMP) assays, where labeled cAMP (tracer) and a labeled anti-cAMP antibody bind together to produce a TR-FRET signal when the two constituents are proximal to each other. This signal is disrupted when unlabeled and cellularly generated cAMP competes with the tracer cAMP for binding to the labeled antibody. It is important that the resulting assay signal, usually expressed as a TR-FRET ratio, be transformed to cAMP concentration using a cAMP standard curve. However, examples are still generated in the literature wherein investigators have used the ratiometric signal (not transformed using a standard curve) to determine values for intrinsic activity and potency of ligands. Untransformed raw data often produce reasonable looking sigmoidal concentration response curves, perhaps tempting investigators to use the raw data instead of the transformed data for applying pharmacological models. In this article, we describe the correct procedure for determining the potency and intrinsic activity of ligands that result in changes in cAMP levels using a lysate dilution assay of GLP-1 (7-36)-mediated TR-FRET cAMP accumulation and simulated data. We also highlight how the inappropriate use of raw signal data can dramatically affect interpretation of intrinsic activity and potency of ligands, and how this can adversely affect drug discovery programs. These findings apply not only to cAMP functional assays but also to other functional cellular signaling assays that utilize competition binding technologies.

Interaction of p-synephrine on the pharmacodynamics and pharmacokinetics of gliclazide in animal models

Background

Type 2 diabetes is frequently seen in patients suffering from obesity. p-synephrine and gliclazide are widely used medicines for the treatment of obesity and diabetes, respectively.

Objectives

The present study was undertaken to determine the potential for interactions between p-synephrine and gliclazide, based on the relationship between obesity and diabetes.

Methods

Influence of p-synephrine on the activity of gliclazide was determined by conducting single and multiple dose interaction studies in animal models. Blood samples collected at pre-determined time intervals from experimental animals were used for the estimation of glucose and insulin levels. The insulin resistance and β-cell function were determined by homeostasis model assessment. Additionally, serum gliclazide levels in rabbits were analyzed by high-performance liquid chromatography (HPLC).

Results

Gliclazide alone showed peak reduction in blood glucose levels at 2 and 8 h after administration in rats and after 3 h in rabbits. The activity of gliclazide was not altered by a single dose treatment with p-synephrine. However, in multiple dose interaction studies, samples from all the time points analyzed showed significant changes in percent blood glucose reduction ranging from 19.73 to 44.18% in normal rats, 23.76–46.43% in diabetic rats and 16.36–38.34% in normal rabbits. The homeostasis model assessment parameters were also significantly altered in multiple dose interaction studies. The pharmacokinetics of gliclazide was not altered by either single or multiple dose p-synephrine treatments in rabbits.

Conclusion

The effect of multiple dose p-synephrine treatments upon gliclazide appeared to be pharmacodynamic in nature, indicating the need for periodic monitoring of glucose levels and dose adjustment as necessary when this combination is prescribed to obese patients.

Antilipolytic effects of 1,8-naphthyridine derivatives β-adrenoceptor antagonists in rat white adipocytes

The rat fat cell β-adrenoceptors were investigated by studying the effects of new 1,8-naphthyridine derivatives synthesized starting from 7-amino-2-chloro-3-phenyl-1,8-naphthyridine on lipolysis induced by isoprenaline, and alprenolol. Lipolysis induced by isoprenaline agonist was competitively antagonized by the 1,8-naphthyridine analogue with a 7-hydroxy-2-(4'-methoxybenzylamine)-6-nitro-3-phenyl substituent designated as 3. In contrast, 10, 50, and 100 μm of 7-methoxy and 7-ethoxy derivatives did not modify the concentration-response curve of isoprenaline. A rightward shift of the curve was, however, observed with 50 μm of a 7-methoxy-2-(4'-methoxybenzylamine)-6-amino-3-phenyl substituent designated as 10. The selective β₁ -AR antagonist, 7-hydroxy-4-morpholinomethyl-2-piperazino-1,8-naphthyridine slightly reduced isoprenaline-induced lipolysis only at high doses. Alprenolol-mediated lipolytic effect was antagonized by derivative 3, 10 and the selective β₃ -AR antagonist SR 59,230A, but resistant to the selective β₁ -AR antagonist 7-hydroxy-4-morpholinomethyl-2-piperazino-1,8-naphthyridine. The results provide preliminary pharmacological evidence for the antilipolytic effect of the newly synthesized 1,8-naphthyridine derivatives on rat fat cells. The analogues designated as 3 and 10 were the most potent antagonists of this series.

Physiological functions and pharmacological and toxicological effects of p-octopamine

p-Octopamine occurs naturally in plants, invertebrates and animals with diverse functions and effects. This review summarizes the chemistry, metabolism, receptor binding characteristics, known physiological functions, and pharmacological and toxicological effects of p-octopamine. Databases used included PubMed and Google Scholar Advanced. p-Octopamine binds to neuroreceptors in insects that are not present in humans, while exhibiting poor binding to α-1, α-2, β-1, and β-2 adrenergic receptors in mammalian systems. p-Octopamine modestly binds to β-3 adrenergic receptors and may therefore promote lipolysis and weight loss. p-Octopamine is produced in brain and nerve tissues of mammals and is present and can be measured in the blood of normal human subjects. p-Octopamine is considered to be a CNS stimulant in spite of the fact that it binds poorly to adrenergic receptors. Variations occur in blood levels in association with neurological and hepatic diseases. Its precise role in normal neurophysiology is unclear. No human studies have been reported that demonstrate adverse cardiovascular effects following oral administration. No human studies have examined the effects of p-octopamine on athletic performance or weight loss and weight management. A need exists for both animal and human safety and efficacy studies involving oral administration of p-octopamine.

A review of the receptor-binding properties of p-synephrine as related to its pharmacological effects

Bitter orange (Citrus aurantium) extract and its primary protoalkaloid p-synephrine are used widely in weight loss/weight management and sports performance products. Because of structural similarities, the pharmacological effects of p-synephrine are widely assumed to be similar to those of ephedrine, m-synephrine (phenylephrine), and endogenous amine neurotransmitters as norepinephrine and epinephrine. However, small structural changes result in the receptor binding characteristics of these amines that are markedly different, providing a plausible explanation for the paucity of adverse effects associated with the wide-spread consumption of p-synephrine in the form of dietary supplements as well as in various Citrus foods and juices. This paper summarizes the adrenoreceptor binding characteristics of p-synephrine relative to m-synephrine, norepinephrine, and other amines as related to the observed pharmacological effects.

The safety of Citrus aurantium (bitter orange) and its primary protoalkaloid p-synephrine

Citrus aurantium (bitter orange) extract and its principal protoalkaloidal constituent p-synephrine are widely used in weight loss and weight management as well as in sports performance products. However, questions are raised frequently regarding the safety of these ingredients. The potential inherent dangers associated with the use of products containing C. aurantium extract are frequently touted, while conversely, millions of doses of dietary supplements have been consumed by possibly millions of individuals in recent years. Furthermore, millions of people consume on a daily basis various juices and food products from Citrus species that contain p-synephrine. This review summarizes current information regarding the safety of C. aurantium (bitter orange) extract and p-synephrine based on human, animal and in vitro assessments as well as receptor binding and mechanistic studies. The data indicate that based on current knowledge, the use of bitter orange extract and p-synephrine appears to be exceedingly safe with no serious adverse effects being directly attributable to these ingredients.