Evolving views on the first two ligands of the angiotensin II type 2 receptor. From putative antagonists to potential agonists?

The renin-angiotensin system is one of the most complex regulatory systems that controls multiple organ functions. One of its key components, angiotensin II (Ang II), stimulates two G-protein coupled class A receptors: the Ang II type 1 (AT1) receptor and the Ang II type 2 (AT2) receptor. While stimulation of the AT1 receptor causes G-protein-dependent signaling and arrestin recruitment, the AT2 receptor seems to have a constitutively active-like conformation and appears to act via G-protein-dependent and -independent pathways. Overstimulation of the AT1 receptor may lead to unwanted effects like inflammation and fibrosis. In contrast, stimulation of the AT2 receptor leads to opposite effects thus restoring the balance. However, the role of the AT2 receptor has become controversial due to beneficial effects of putative AT2 receptor antagonists. The two first synthetic AT2 receptor-selective ligands, peptide CGP42112 and small molecule PD123319, were initially both considered antagonists. CGP42112 was subsequently considered a partial agonist and it was recently demonstrated to be a full agonist. Based on the search-term PD123319 in Pubmed, 1652 studies have investigated putative AT2 receptor antagonist PD123319. Here, we put forward literature that shows beneficial effects of PD123319 alone, even at doses too low for antagonist efficacy. These beneficial effects appear compatible with agonist-like activity via the AT2 receptor. Taken together, a more consistent image of a therapeutic role of stimulated AT2 receptor emerges which may clarify current controversies.</p

Evolving views on the first two ligands of the angiotensin II type 2 receptor. From putative antagonists to potential agonists?

The renin-angiotensin system is one of the most complex regulatory systems that controls multiple organ functions. One of its key components, angiotensin II (Ang II), stimulates two G-protein coupled class A receptors: the Ang II type 1 (AT1) receptor and the Ang II type 2 (AT2) receptor. While stimulation of the AT1 receptor causes G-protein-dependent signaling and arrestin recruitment, the AT2 receptor seems to have a constitutively active-like conformation and appears to act via G-protein-dependent and -independent pathways. Overstimulation of the AT1 receptor may lead to unwanted effects like inflammation and fibrosis. In contrast, stimulation of the AT2 receptor leads to opposite effects thus restoring the balance. However, the role of the AT2 receptor has become controversial due to beneficial effects of putative AT2 receptor antagonists. The two first synthetic AT2 receptor-selective ligands, peptide CGP42112 and small molecule PD123319, were initially both considered antagonists. CGP42112 was subsequently considered a partial agonist and it was recently demonstrated to be a full agonist. Based on the search-term PD123319 in Pubmed, 1652 studies have investigated putative AT2 receptor antagonist PD123319. Here, we put forward literature that shows beneficial effects of PD123319 alone, even at doses too low for antagonist efficacy. These beneficial effects appear compatible with agonist-like activity via the AT2 receptor. Taken together, a more consistent image of a therapeutic role of stimulated AT2 receptor emerges which may clarify current controversies.</p

LP2, the first lanthipeptide GPCR agonist in a human pharmacokinetics and safety study

Introduction of a lanthionine into a peptide may enhance target affinity, target specificity and proteolytic resistance. This manuscript reports preclinical safety studies and the first-in-human study with the lanthipeptide AT 2R agonist LP2, a structural analog of cAng-(1–7), whose N-terminus was protected against aminopeptidases by the presence of a D-lysine. None of the preclinical studies, including an in vitro multitarget panel, behavioral, respiratory and cardiovascular measurements, genotoxicity and toxicity studies in rat and dog, posed any safety concern. Due to lack of toxicity the maximum tolerated dose was not reached neither in rat nor in dog. In the human dose escalation study, healthy male volunteers received a single 1 mL subcutaneous injection (0.001 mg, 0.01 mg or 0.1 mg) of LP2 or matching placebo. In contrast to angiotensin II which has a T 1/2 in plasma of < 1 min, LP2 has a T 1/2 of approximately 2.1–2.6 hours. The fraction of the dose excreted unchanged in urine ranged from 84.73 ± 10.4 % at a dose of 0.001 mg to 66.4 ± 3.9 % at 0.1 mg. There were no deaths, serious adverse events or subject withdrawals as a result of an adverse event. The incidence of adverse events was 16.7 %; each was mild in severity. One adverse event, peripheral coldness, was considered to be possibly related to LP2 at 0.001 mg LP2. None of the results was considered to pose a clinically relevant safety concern. This study supports the potential for the therapeutic use of lanthipeptides

Efficacy of lanthionine-stabilized angiotensin-(1-7) in type I and type II diabetes mouse models

Native angiotensin-(1-7) exerts many therapeutic effects. However, it is rapidly degraded by ACE and other peptidases. This drawback is largely eliminated for lanthionine-stabilized angiotensin-(1-7), termed cAng-(1-7), which is fully resistant to ACE and has strongly increased resistance to other peptidases. Goal of the present study was to test whether cAng-(1-7) has therapeutic activity in diabetes mouse models: in a multiple low dose streptozotocin-induced model of type I diabetes and / or in a db/db model of type II diabetes. In the type I diabetes model cAng-(1-7) caused in an increase in the insulin level of 133% in week 4 (p < 0.001) compared to vehicle, and in the type II diabetes model an increase of 55% of the insulin level in week 8 (p < 0.05) compared to vehicle. cAng-(1-7) reduced blood glucose levels in the type I model by 37% at day 22 (p < 0.001) and in the type II diabetes model by 17% at day 63 of treatment (p < 0.001) and in an oral glucose tolerance test in a type II diabetes model, by 17% at week 4 (p < 0.01). cAng-(1-7) also caused a reduction of glycated hemoglobin levels in the type II diabetes model of 21% in week 6 (p < 0,001). These data are consistent with therapeutic potential of cAng-(1-7) in type I and II diabetes

AT2 receptor agonist LP2 restores respiratory function in a rat model of bleomycin-induced lung remodelling

This study aimed to evaluate the prophylactic and therapeutic potential of angiotensin II type 2 receptor peptide agonist LP2 in bleomycin-induced airway and cardiac remodeling in rats. Male Wistar rats were intratracheally instillated with bleomycin. Animals of a prophylactic arm received LP2 from day 0 at intraperitoneal doses of 1, 3 or 10μg/kg/d, whereas animals from a therapeutic arm received this LP2 treatment from day 7. On day 28 direct lung mechanics were determined and cardiac and lung tissues were collected and (histo)morphologically assessed. Prophylactic LP2 at 1µg/kg/d with bleomycin, versus bleomycin alone, significantly improved the airway pressure responses at fixed inflation of 4ml (p&lt;0.05) and 7ml volume (p&lt;0.05), static compliance (p&lt;0.01), inspiratory capacity (p&lt;0.05), lung tolerance of increased volume (p&lt;0.0001), right to left ventricular hypertrophy (p&lt;0.05). Therapeutic regime showed a similar trend as the prophylactic arm but was less effective, mostly lacking significance. However, and importantly, therapeutic LP2 at 1µg/kg/d significantly decreased mRNA expression of collagen 1A1 (p&lt;0.01), of Connective Tissue Growth Factor 1 (p&lt;0.05) and of Tissue MetalloPeptidase inhibitor 1 (p&lt;0.05). In conclusion, a very low dose of 1µg/kg/d LP2 has capacity to counter bleomycin-induced impairment of lung functioning and consequent cardiac remodeling.</p

Cyclic angiotensin-(1-7) contributes to rehabilitation of animal performance in a rat model of cerebral stroke

Peptidase-resistant, lanthionine-stabilized angiotensin-(1-7), termed cAng-(1-7), has shown therapeutic efficacy in animal models of cardiovascular, metabolic, kidney and pulmonary disease. Goal of the present study was testing the capacity of subcutaneously administered cAng-(1-7) to induce rehabilitation of animal performance in the transient middle cerebral artery occlusion rat model of cerebral stroke. 24 h after ischemic stroke induction, cAng-(1-7) was administered for 28 days at a dose of 500 μg/kg/day, either daily via subcutaneous injection or continuously via an alzet pump. Both ways of administration of cAng-(1-7) were equally effective. Measurements were continued until day 50. Compared to vehicle, cAng-(1-7) clearly demonstrated significantly increased capillary density (p < 0.01) in the affected hemisphere and improved motor and somatosensory functioning. The modified neurological severity score (p < 0.001 at days 15 and 50), stepping test (p < 0.001 at days 36–50), forelimb placement test (p < 0.001 at day 50), body swing test (p < 0.001 at days 43 and 50) all demonstrated that cAng-(1-7) caused significantly improved animal performance. Taken together the data convincingly indicate rehabilitating capacity of subcutaneously injected cAng-(1-7) in cerebral ischemic stroke