Impact of aging on cardiac sympathetic innervation measured by <Superscript>123</Superscript>I-mIBG imaging in patients with systolic heart failure

Purpose

Sympathetic nervous system (SNS) hyperactivity is a salient characteristic of chronic heart failure (HF) and contributes to the progression of the disease. Iodine-123 meta-iodobenzylguanidine (¹²³I-mIBG) imaging has been successfully used to assess cardiac SNS activity in HF patients and to predict prognosis. Importantly, SNS hyperactivity characterizes also physiological ageing, and there is conflicting evidence on cardiac ¹²³I-mIBG uptake in healthy elderly subjects compared to adults. However, little data are available on the impact of ageing on cardiac sympathetic nerve activity assessed by ¹²³I-mIBG scintigraphy, in patients with HF.

Methods and results

We studied 180 HF patients (age?=?66.1?±?10.5 years [yrs]), left ventricular ejection fraction (LVEF?=?30.6?±?6.3 %) undergoing cardiac ¹²³I-mIBG imaging. Early and late heart to mediastinum (H/M) ratios and washout rate were calculated in all patients. Demographic, clinical, and echocardiographic data were also collected. Our study population consisted of 53 patients aged >75 years (age?=?77.7?±?4.0 year), 67 patients aged 62–72 years (age?=?67.9?±?3.2 years) and 60 patients aged ≤61 year (age?=?53.9?±?5.6 years). In elderly patients, both early and late H/M ratios were significantly lower compared to younger patients (p?<?0.05). By multivariate analysis, H/M ratios (both early and late) and washout rate were significantly correlated with LVEF and age.

Conclusions

Our data indicate that, in a population of HF patients, there is an independent age-related effect on cardiac SNS innervation assessed by ¹²³I-mIBG imaging. This finding suggests that cardiac ¹²³I-mIBG uptake in patients with HF might be affected by patient age.

     

Species-dependent serum interference in a sandwich ELISA for Apo2L/TRAIL

To support pre-clinical studies of Apo2L/TRAIL in rodents and non-human primates, a sandwich ELISA was developed using two mouse monoclonal anti-Apo2L/TRAIL antibodies. Mouse, rat, cynomolgus monkey, and chimpanzee serum at concentrations of > or =1% were found to interfere with accurate quantitation of Apo2L/TRAIL. Moreover, the characteristics of the serum interference for each species were different. In order to resolve the observed serum effect, studies were performed in which salts, detergents, and blocking proteins were added to the sample diluent, and optimized sample diluents that eliminated serum interference were developed for mouse, cynomolgus monkey, and chimpanzee serum. These buffers consisted of a base assay diluent (PBS/0.5% BSA/0.05% Tween-20/10 ppm ProClin 300) supplemented with: NaCl (mouse serum); NaCl, EDTA, CHAPS, bovine gamma globulin (BGG), and human IgG (cynomolgus monkey serum); and NaCl and EDTA (chimpanzee serum). Full characterization studies were performed for the "buffer" ELISA run in base assay diluent (intended for non-serum samples) as well as the assays optimized for mouse serum and cynomolgus monkey serum. Precision, accuracy, linearity, and specificity were found to be satisfactory. With the availability of a rabbit polyclonal antibody against Apo2L/TRAIL, a new pAb/mAb ELISA was developed. This assay was not only more sensitive by > or =6-fold, but it was also much less subject to serum interference.     

Increased Ca2+ sensitivity and protein expression of SERCA 2a in situations of chronic β3-adrenoceptor deficiency

This study investigated the influence of chronic β₃-adrenoceptor deficiency on myocardial function. Therefore, we investigated Ca²⁺-regulatory proteins, SERCA 2a activity, and myofibrillar and mitochondrial function in hearts of wild-type (WT, n=7) and β₃-adrenoceptor knockout mice (β₃-KNO, n=7). Morphometric heart analysis showed no difference between WT and β₃-KNO. No alterations were observed for the protein expression of the ryanodine receptor or phospholamban. However, in β₃-KNO mice, protein expression of SERCA 2a and phospholamban phosphorylation were significantly increased. These changes were accompanied by an increased SERCA 2a activity in β₃-KNO. Alterations in phospholamban phosphorylation were independent of alterations in β₁/β₂-adrenoceptor distribution and protein expression of G proteins in β₃-KNO. Measurement of myofibrillar Ca²⁺ sensitivity showed no difference in the Ca²⁺/force relation for WT and β₃-KNO. The same seems to hold true for mitochondrial function since the protein expressions of cytochrome c, uncoupling protein 3 and cytochrome c oxidase subunit IV were similar in WT and β₃-KNO. The conclusion is that depression of β₃-adrenergic stimulation may modulate the protein expression of SERCA 2a and phospholamban phosphorylation, thereby improving sarcoplasmic reticulum Ca²⁺ uptake. Thus, β₃-adrenergic depression may be a therapeutic aim in situations of impaired SERCA 2a activity, e.g. for the treatment of heart failure.     

GRK2 as a therapeutic target for heart failure

Introduction: G protein-coupled receptor (GPCR) kinase-2 (GRK2) is a regulator of GPCRs, in particular β-adrenergic receptors (ARs), and as demonstrated by decades of investigation, it has a pivotal role in the development and progression of cardiovascular disease, like heart failure (HF). Indeed elevated levels and activity of this kinase are able to promote the dysfunction of both cardiac and adrenal α- and β-ARs and to dysregulate other protective signaling pathway, such as sphingosine 1-phospate and insulin. Moreover, recent discoveries suggest that GRK2 can signal independently from GPCRs, in a ‘non-canonical’ manner, via interaction with non-GPCR molecule or via its mitochondrial localization.

Areas covered: Based on this premise, GRK2 inhibition or its genetic deletion has been tested in several disparate animal models of cardiovascular disease, showing to protect the heart from adverse remodeling and dysfunction.

Expert opinion: HF is one of the leading cause of death worldwide with enormous health care costs. For this reason, the identification of new therapeutic targets like GRK2 and strategies such as its inhibition represents a new hope in the fight against HF development and progression. Herein, we will update the readers about the ‘state-of-art’ of GRK2 inhibition as a potent therapeutic strategy in HF.     

GABAB receptor phosphorylation regulates KCTD12-induced K current desensitization

GABA_B receptors assemble from GABA_B1 and GABA_B2 subunits. GABA_B2 additionally associates with auxiliary KCTD subunits (named after their K⁺ channel tetramerization-domain). GABA_B receptors couple to heterotrimeric G-proteins and activate inwardly-rectifying K⁺ channels through the βγ subunits released from the G-protein. Receptor-activated K⁺ currents desensitize in the sustained presence of agonist to avoid excessive effects on neuronal activity. Desensitization of K⁺ currents integrates distinct mechanistic underpinnings. GABA_B receptor activity reduces protein kinase-A activity, which reduces phosphorylation of serine-892 in GABA_B2 and promotes receptor degradation. This form of desensitization operates on the time scale of several minutes to hours. A faster form of desensitization is induced by the auxiliary subunit KCTD12, which interferes with channel activation by binding to the G-protein βγ subunits. Here we show that the two mechanisms of desensitization influence each other. Serine-892 phosphorylation in heterologous cells rearranges KCTD12 at the receptor and slows KCTD12-induced desensitization. Likewise, protein kinase-A activation in hippocampal neurons slows fast desensitization of GABA_B receptor-activated K⁺ currents while protein kinase-A inhibition accelerates fast desensitization. Protein kinase-A fails to regulate fast desensitization in KCTD12 knock-out mice or knock-in mice with a serine-892 to alanine mutation, thus demonstrating that serine-892 phosphorylation regulates KCTD12-induced desensitization in vivo. Fast current desensitization is accelerated in hippocampal neurons carrying the serine-892 to alanine mutation, showing that tonic serine-892 phosphorylation normally limits KCTD12-induced desensitization. Tonic serine-892 phosphorylation is in turn promoted by assembly of receptors with KCTD12. This cross-regulation of serine-892 phosphorylation and KCTD12 activity sharpens the response during repeated receptor activation.     

Liver-derived insulin-like growth factor-I is involved in the regulation of blood pressure in mice

IGF-I has been suggested to be of importance for cardiovascular structure and function, but the relative role of locally produced and liver-derived endocrine IGF-I remains unclear. Using the Cre-LoxP recombination system, we have previously created transgenic mice with a liver-specific, inducible IGF-I knockout (LI-IGF-I-/-). To examine the role of liver-derived IGF-I in cardiovascular physiology, liver-derived IGF-I was inactivated at 4 wk of age, resulting in a 79% reduction of serum IGF-I levels. At 4 months of age, systolic blood pressure (BP) was increased in LI-IGF-I-/- mice. Echocardiography showed increased posterior wall thickness in combination with decreased stroke volume and cardiac output, whereas other systolic variables were unchanged, suggesting that these cardiac effects were secondary to increased peripheral resistance. Acute nitric oxide-synthase inhibition increased systolic BP more in LI-IGF-I-/- mice than in control mice. LI-IGF-I-/- mice showed impaired acetylcholine-induced vasorelaxation in mesenteric resistance vessels and increased levels of endothelin-1 mRNA in aorta. Thus, the increased peripheral resistance in LI-IGF-I-/- mice might be attributable to endothelial dysfunction associated with increased expression of endothelin-1 and impaired vasorelaxation of resistance vessels. In conclusion, our findings suggest that liver-derived IGF-I is involved in the regulation of BP in mice.     

The response of gingiva monolayer,spheroid, and ex vivo tissue cultures to collagen membranes and bone substitute

Collagen membranes and bone substitute are popular biomaterials in guided tissue regeneration for treatment of traumatized or diseased periodontal tissue. Development of these biomaterials starts in monolayer cell culture, failing to reflect in vivo tissue organization. Spheroid cultures potentially mimic in vivo tissues in structure and functionality. This study aims to compare gingiva cell (GC) monolayers and spheroids to ex vivo gingiva. Human GC monolayers, spheroids and gingiva ex vivo tissues were cultured on plastic surfaces, collagen membranes or bone substitute. Hematoxylin–eosin (HE) staining, immunohistochemistry for KI67 and caspase 3 (CASP3), resazurin‐based toxicity assays, quantitative polymerase chain reaction for collagen I (COL1A1), vascular endothelial growth factor (VEGF), angiogenin (ANG), interleukin (IL)6 and IL8 and ELISA for COL1A1, VEGF, ANG, IL6 and IL8 were performed in all cultures. Morphology was different in all culture set‐ups. Staining of KI67 was positive in monolayers and staining of CASP3 was positive in spheroids. All culture set‐ups were viable. COL1A1 production was modulated in monolayers and ex vivo tissues at mRNA levels, VEGF in monolayers and ex vivo tissues at mRNA levels and in spheroids at protein levels, ANG in spheroids at mRNA levels and in monolayers and spheroids at protein levels, IL6 in monolayers and spheroids at mRNA levels and in spheroids and ex vivo tissues at protein levels and IL8 in monolayers and ex vivo tissues at mRNA levels. Modulations were surface‐dependent. In conclusion, each culture model is structurally and functionally different. Neither GC monolayers nor spheroids mimicked gingiva ex vivo tissue in all measured aspects.