Clinical problems in renovascular disease and the role of nuclear medicine

Targeted design of a recombinant tracer for SPECT renal imaging

Rationale: A robust radiopharmaceutical has high uptake in the target and low retention in non-target tissues. However, traditional tracers for renal imaging that chemically chelate ^99mTc are excreted through the renal route with transient resident time in the kidney. Following a rational design approach, we constructed a protein-based radiotracer, designated PBT-Fc, to sequentially bind tubular neonatal Fc-receptor and subsequently proximal tubular basement membrane for its targeted sequestration in kidney parenchyma. In this process, the tracer participates in physiologic glomerular filtration and tubular reabsorption while escaping lysosomal catabolism and urinary clearance. Methods: To specifically target renal receptors in navigating the urinary passage in the kidney, we produced a recombinant fusion protein with two separate functional parts: a polybasic PBT segment derived from human Vascular Endothelial Growth Factor and Fc segment of IgG1. The chimeric fusion of PBT-Fc was labeled with radionuclide ^99mTc and tested in rodent models of kidney diseases. Planar scintigraphy and single-photon emission computerized tomography (SPECT) were performed to evaluate renal-specificity of the tracer. Results: When injected in mouse and rat, following a brief 10 - 15 min dynamic redistribution phase in circulation, ~ 95% of the [^99mTc]-PBT-Fc signal was concentrated in the kidney and lasted for hours without urinary loss or surrounding tissue activities. Long-lasting tracer signals in the kidney cortex in conjunction with SPECT greatly augmented the image quality in detecting pathological lesions in a variety of disease models, including ischemic acute kidney injury, drug-induced renal toxicity, and chronic kidney disease from renin-angiotensin system (RAS) overactivation. Conclusion: Exclusive renal retention of the recombinant radiotracer greatly facilitated static-phase signal acquisition by SPECT and achieved submillimeter spatial resolution of kidney alternations in glomerular and tubular disease models.

The SNMMI and EANM practice guideline for renal scintigraphy in adults

PURPOSE

The Society of Nuclear Medicine and Molecular Imaging (SNMMI) is an international scientific and professional organization founded in 1954 to promote the science, technology, and practical application of nuclear medicine. The European Association of Nuclear Medicine (EANM) is a professional nonprofit medical association that facilitates communication worldwide between individuals pursuing clinical and research excellence in nuclear medicine. The EANM was founded in 1985. SNMMI and EANM members are physicians, technologists, and scientists specializing in the research and practice of nuclear medicine.

METHODS

The SNMMI and EANM will periodically define new guidelines for nuclear medicine practice to help advance the science of nuclear medicine and to improve the quality of service to patients throughout the world. Existing practice guidelines will be reviewed for revision or renewal, as appropriate, on their fifth anniversary, or sooner, if indicated.

CONCLUSION

Each practice guideline, representing a policy statement by the SNMMI/EANM, has undergone a thorough consensus process in which it has been subjected to extensive review. The SNMMI and EANM recognize that the safe and effective use of diagnostic nuclear medicine imaging requires specific training, skills, and techniques, as described in each document. Reproduction or modification of the published practice guideline by entities not providing these services is not authorized.

The Succinate Receptor GPR91 Is Involved in Pressure Overload-Induced Ventricular Hypertrophy

Background

Pulmonary arterial hypertension is characterized by increased pressure overload that leads to right ventricular hypertrophy (RVH). GPR91 is a formerly orphan G-protein-coupled receptor (GPCR) that has been characterized as a receptor for succinate; however, its role in RVH remains unknown.

Methods and Results

We investigated the role of succinate-GPR91 signaling in a pulmonary arterial banding (PAB) model of RVH induced by pressure overload in SD rats. GPR91 was shown to be located in cardiomyocytes. In the sham and PAB rats, succinate treatment further aggravated RVH, up-regulated RVH-associated genes and increased p-Akt/t-Akt levels in vivo. In vitro, succinate treatment up-regulated the levels of the hypertrophic gene marker anp and p-Akt/t-Akt in cardiomyocytes. All these effects were inhibited by the PI3K antagonist wortmannin both in vivo and in vitro. Finally, we noted that the GPR91-PI3K/Akt axis was also up-regulated compared to that in human RVH.

Conclusions

Our findings indicate that succinate-GPR91 signaling may be involved in RVH via PI3K/Akt signaling in vivo and in vitro. Therefore, GPR91 may be a novel therapeutic target for treating pressure overload-induced RVH.

Mesenchymal stem cells and chronic renal artery stenosis

Renal artery stenosis is the main cause of renovascular hypertension and results in ischemic nephropathy characterized by inflammation, oxidative stress, microvascular loss, and fibrosis with consequent functional failure. Considering the limited number of strategies that effectively control renovascular hypertension and restore renal function, we propose that cell therapy may be a promising option based on the regenerative and immunosuppressive properties of stem cells. This review addresses the effects of mesenchymal stem cells (MSC) in an experimental animal model of renovascular hypertension known as 2 kidney-1 clip (2K-1C). Significant benefits of MSC treatment have been observed on blood pressure and renal structure of the stenotic kidney. The mechanisms involved are discussed.

Where and when device therapy may be useful in the management of drug-resistant hypertension

Device therapy for the treatment of uncontrolled and resistant hypertension has evolved significantly over the past several decades. Both renal artery disease and sympathetic hyperactivity have been linked to resistant hypertension. This manuscript will review the current evidence base supporting device therapy (e.g., renal artery revascularization, sympathetic nervous system modulation) for resistant hypertension.

Management of Renal Arterial Disease

Severe atherosclerotic renal artery stenosis can manifest as treatment-resistant hypertension, ischemic nephropathy and/or cardiac disturbance syndromes of recurrent flash pulmonary edema and refractory angina. Renal artery revascularization can dramatically impact patient outcome. However, patient selection for revascularization can be challenging. Renal artery stenting is most commonly used for renal revascularization and is a safe procedure when performed in carefully selected patients. This review addresses the pathophysiology of renal artery stenosis and the data supporting revascularization in such patients.