Prolylcarboxypeptidase (PRCP) as a new target for obesity treatment

Detection of QTL controlling feed efficiency and excretion in chickens fed a wheat-based diet

Background

Improving feed efficiency is a major goal in poultry production in order to reduce production costs, increase the possibility of using alternative feedstuffs and decrease the volume of manure. However, in spite of their economic and environmental impact, very few quantitative trait loci (QTL) have been reported on these traits. Thus, we undertook the detection of QTL on 820 meat-type chickens from a F2 cross between D− and D+ lines that were divergently selected on low or high digestive efficiency at 3 weeks of age. Birds were measured for growth between 0 and 23 days, feed intake and feed conversion ratio between 9 and 23 days, breast and abdominal fat yields at 23 days, and the anatomy of their digestive tract (density, relative weight and length of the duodenum, jejunum, ileum, and ratio of proventriculus to gizzard weight) was examined. To evaluate excretion traits, fresh and dry weight, water content, pH, nitrogen to phosphorus ratio from 0 to 23 days, and pH of gizzard and jejunum contents at 23 days were measured. A set of 3379 single nucleotide polymorphisms distributed on 28 Gallus gallus (GGA) autosomes, the Z chromosome and one unassigned linkage group was used for QTL detection.

Results

Using the QTLMap software developed for linkage analyses by interval mapping, we detected 16 QTL for feed intake, 13 for feed efficiency, 49 for anatomy-related traits, seven for growth, six for body composition and ten for excretion. Nine of these QTL were genome-wide significant (four for feed intake on GGA1, one for feed efficiency on GGA2, and four for anatomy on GGA1, 2, 3 and 4). GGA16, 19, and 26 carried many QTL for different types of traits that co-localize at the same position.

Conclusions

This study identified several QTL regions that are involved in the control of digestive efficiency in chicken. Further studies are needed to identify the genes that underlie these effects, and to validate these in other commercial populations and for different breeding environments.

Electronic supplementary material

The online version of this article (doi:10.1186/s12711-015-0156-y) contains supplementary material, which is available to authorized users.

The brain melanocortin system, sympathetic control, and obesity hypertension

Excess weight gain is the most significant, preventable cause of increased blood pressure (BP) in patients with primary (essential) hypertension and increases the risk for cardiovascular and renal diseases. In this review, we discuss the role of the brain melanocortin system in causing increased sympathetic activity in obesity and other forms of hypertension. In addition, we highlight potential mechanisms by which the brain melanocortin system modulates metabolic and cardiovascular functions.

Pyrazoles as non-classical bioisosteres in prolylcarboxypeptidase (PrCP) inhibitors

Bioisosteres are integral components of modern pharmaceutical research that allow structural optimization to maximize in vivo efficacy and minimize adverse effects by selectively modifying pharmacodynamic, pharmacokinetic and physicochemical properties. A recent medicinal chemistry campaign focused on identifying small molecule inhibitors of prolylcarboxypeptidase (PrCP) initiated an investigation into the use of pyrazoles as bioisosteres for amides. The results indicate that pyrazoles are suitable bioisosteric replacements of amide functional groups. The study is an example of managing bioisosteric replacement by incorporating subsequent structural modifications to maintain potency against the selected target. A heuristic model for an embedded pharmacophore is also described.

A digestive prolyl carboxypeptidase in Tenebrio molitor larvae

Prolyl carboxypeptidase (PRCP) is a lysosomal proline specific serine peptidase that also plays a vital role in the regulation of physiological processes in mammals. In this report, we isolate and characterize the first PRCP in an insect. PRCP was purified from the anterior midgut of larvae of a stored product pest, Tenebrio molitor, using a three-step chromatography strategy, and it was determined that the purified enzyme was a dimer. The cDNA of PRCP was cloned and sequenced, and the predicted protein was identical to the proteomic sequences of the purified enzyme. The substrate specificity and kinetic parameters of the enzyme were determined. The T. molitor PRCP participates in the hydrolysis of the insect's major dietary proteins, gliadins, and is the first PRCP to be ascribed a digestive function. Our collective data suggest that the evolutionary enrichment of the digestive peptidase complex in insects with an area of acidic to neutral pH in the midgut is a result of the incorporation of lysosomal peptidases, including PRCP.

Prolyl carboxypeptidase and its inhibitors in metabolism

Proopiomelanocortin (POMC)-expressing neurons in the hypothalamus integrate a variety of central and peripheral metabolic inputs, and regulate energy homeostasis by controlling energy expenditure and food intake. To accomplish this, a precise balance of production and degradation of α-melanocyte-stimulating hormone (α-MSH), an anorexigenic neuropeptide and product of the POMC gene, in the hypothalamus, is crucial. Prolyl carboxypeptidase (PRCP) is a key enzyme that degrades α-MSH to an inactive form unable to inhibit food intake. Because it represents a new therapeutic target for the treatment of metabolic disorders, such as obesity and diabetes, efforts have been made to generate potent, brain-penetrant PRCP inhibitors. Here, we discuss the role of PRCP on energy metabolism and the development of PRCP inhibitors.

Angiotensin II type 2 receptor-stimulated activation of plasma prekallikrein and bradykinin release: role of SHP-1

ANG II type 2 receptors (AT(2)R) elicit cardioprotective effects in part by stimulating the release of kinins; however, the mechanism(s) responsible have not been fully explored. We demonstrated previously that overexpression of AT(2)R increased expression of prolylcarboxypeptidase (PRCP; a plasma prekallikrein activator) and release of bradykinin by mouse coronary artery endothelial cells (ECs). In the present study we hypothesized that the AT(2)R-stimulated increase in PRCP is mediated by the tyrosine phosphatase SHP-1, which in turn activates the PRCP-dependent prekallikrein-kallikrein pathway and releases bradykinin. We found that activation of AT(2)R using the specific agonist CGP42112A increased SHP-1 activity in ECs, which was blocked by the AT(2)R antagonist PD123319. Activation of AT(2)R also enhanced conversion of plasma prekallikrein to kallikrein, and this effect was blunted by a small interfering RNA (siRNA) to SHP-1 and abolished by the tyrosine phosphatase inhibitor sodium orthovanadate. Treating cells with a siRNA to PRCP also blunted AT(2)R-stimulated prekallikrein activation and bradykinin release. Furthermore, blocking plasma kallikrein with soybean trypsin inhibitor (SBTI) abolished AT(2)R-stimulated bradykinin release. These findings support our hypothesis that stimulation of AT(2)R activates a PRCP-dependent plasma prekallikrein pathway, releasing bradykinin. Activation of SHP-1 may also play an important role in AT(2)R-induced PRCP activation.

A new class of prolylcarboxypeptidase inhibitors, part 2: the aminocyclopentanes

A series of potent inhibitors of prolylcarboxypeptidase (PrCP) was developed by modifying a lead structure that was discovered by high-throughput screening. The tert-butyl pyrrolidine was replaced by an aminocyclopentane to reduce the metabolic liabilities of the original lead. The compounds demonstrated sub-nanomolar in vitro IC(50) values, minimal activity shifts in pure plasma and improved pharmacokinetics. Complete ex vivo plasma target engagement was achieved with low brain exposure at the 20 h time point following p.o. dosing in a mouse. The results indicate that the aminocyclopentanes are useful tools for studying the therapeutic potential of peripheral (non-CNS) PrCP inhibition.

A new class of prolylcarboxypeptidase inhibitors, part 1: discovery and evaluation

A new structural class of potent prolylcarboxypeptidase (PrCP) inhibitors was discovered by high-throughput screening. The series possesses a tractable SAR profile with sub-nanomolar in vitro IC(50) values. Compared to prior inhibitors, the new series demonstrated minimal activity shifts in pure plasma and complete ex vivo plasma target engagement in mouse plasma at the 20 h post-dose time point (po). In addition, the in vivo level of CNS and non-CNS drug exposure was measured.

Discovery of aminoheterocycles as potent and brain penetrant prolylcarboxypeptidase inhibitors

Efforts were dedicated to develop potent and brain penetrant prolylcarboxypeptidase (PrCP) inhibitors by replacing the amide group of original leads 1 and 2 with heterocycles. Aminopyrimidines including compound 32a were identified to display good PrCP inhibitory activity (32a, IC(50)=43 nM) and impressive ability to penetrate brain in mice (brain/plasma ratio: 1.4).

Influence of a novel inhibitor (UM8190) of prolylcarboxypeptidase (PRCP) on appetite and thrombosis

Preclinical pharmacological characterization of a novel inhibitor (UM8190) of prolylcarboxypeptidase (PRCP) was investigated. We synthesized and evaluated a library of proline-based analogs as prospective recombinant PRCP (rPRCP) inhibitors and inhibitors of PRCP-dependent prekallikrein (PK) activation on human pulmonary artery endothelial cells (HPAEC). Among the newly synthesized compounds, UM8190 was further characterized in vivo using methods that encompassed a mouse carotid artery thrombosis model and animal model of food consumption. (S)-N-dodecyl-1-((S)-pyrrolidine-2-carbonyl) pyrrolidine-2-carboxamide [Compound 3 (UM8190)] was selected for further evaluation from the initial assessment of its PRCP inhibitory action (K(i)= 43 μM) coupled with its ability to block PRCP-dependent PK activation on HPAEC (K(i)= 34 μM). UM8190 demonstrated excellent selectivity against a panel of carboxypeptidases and serine proteases and blocked bradykinin (BK) generation and BK-induced permeability by 100%, suggesting that it may be useful in preventing the local production of large amounts of BK. Furthermore, UM8190 showed an anorexigenic effect when systemically administered to fasted mice, reducing food intake in a dose- and time-dependent manner. In a mouse carotid artery thrombosis model, it also demonstrated an antithrombotic effect. UM8190 is a selective PRCP inhibitor and it may represent a new anorexigenic, and antithrombotic drug, that works by inhibiting PRCP-mediated mechanisms.

Discovery of a new class of potent prolylcarboxypeptidase inhibitors derived from alanine

Efforts to modify the central proline portion of lead compound 4 lead to the discovery of novel prolylcarboxypeptidase (PrCP) inhibitors. Especially, replacement with alanine afforded compound 19 displaying more potent human and mouse PrCP inhibitory activity than 4 and an overall comparable profile.

The discovery of non-benzimidazole and brain-penetrant prolylcarboxypeptidase inhibitors

Novel prolylcarboxypeptidase (PrCP) inhibitors with nanomolar IC(50) values were prepared by replacing the previously described dichlorobenzimidazole-substituted pyrrolidine amides with a variety of substituted benzylamine amides. In contrast to prior series, the compounds demonstrated minimal inhibition shift in whole serum and minimal recognition by P-glycoprotein (P-gp) efflux transporters. The compounds were also cell permeable and demonstrated in vivo brain exposure. The in vivo effect of compound (S)-6e on weight loss in an established diet-induced obesity (eDIO) mouse model was studied.