Targeted renal therapies through microbubbles and ultrasound

Folate receptor-targeted antioxidant therapy ameliorates renal ischemia-reperfusion injury

Antioxidant therapy can protect against ischemic injury, but the inability to selectively target the kidney would require extremely high doses to achieve effective local concentrations of drug. Here, we developed a directed therapeutic that specifically targets an antioxidant to renal proximal tubule cells via the folate receptor. Because a local increase in superoxide contributes to renal ischemic injury, we created the folate-antioxidant conjugate 4-hydroxy-Tempo (tempol)-folate to target folate receptors, which are highly expressed in the proximal tubule. Dihydroethidium high-performance liquid chromatography demonstrated that conjugated tempol retained its efficacy to scavenge superoxide in proximal tubule cells. In a mouse model of renal ischemia-reperfusion injury, tempol-folate reduced renal superoxide levels more effectively than tempol alone. Furthermore, electron spin resonance revealed the successful targeting of the tempol-folate conjugate to the kidney and other tissues expressing folate receptors. Administration of tempol-folate protected the renal function of mice after ischemia-reperfusion injury and inhibited infiltration of macrophages. In conclusion, kidney-specific targeting of an antioxidant has therapeutic potential to prevent renal ischemic injury. Conjugation of other pharmaceuticals to folate may also facilitate the development of treatments for other kidney diseases.

A pilot study to assess markers of renal damage in the rodent kidney after exposure to 7 MHz ultrasound pulse sequences designed to cause microbubble translation and disruption

Acoustic radiation force has been proposed as a mechanism to enhance microbubble concentration for therapeutic and molecular imaging applications. It is hypothesized that once microbubbles are localized, bursting them with acoustic pressure could result in local drug delivery. It is known that low-frequency, high-amplitude acoustic energy combined with cavitation nuclei can result in bioeffects. However, little is known about the bioeffects potential of acoustic parameters involved in radiation force and microbubble destruction pulse sequences applied at higher frequencies. In this pilot study, rat kidneys are exposed to high-duty cycle, low-amplitude pulse sequences known to cause substantial bubble translation due to radiation force, as well as high-amplitude short pulse sequences known to cause microbubble destruction. Both studies are performed at 7 MHz on a clinical ultrasound system, and implemented in three-dimensions (3-D) for entire kidney exposure. Analysis of biomarkers of renal injury and renal histopathology indicate that there was no significant renal damage due to these ultrasound parameters in conjunction with microbubbles within the study group.

Molecular properties of lysozyme-microbubbles: towards the protein and nucleic acid delivery

Microbubbles (MBs) have specific acoustic properties that make them useful as contrast agents in ultrasound imaging. The use of the MBs in clinical practice led to the development of more sensitive imaging techniques both in cardiology and radiology. Protein-MBs are typically obtained by dispersing a gas phase in the protein solution and the protein deposited/cross-linked on the gas-liquid interface stabilizes the gas core. Innovative applications of protein-MBs prompt the investigation on the properties of MBs obtained using different proteins that are able to confer them specific properties and functionality. Recently, we have synthesized stable air-filled lysozyme-MBs (LysMBs) using high-intensity ultrasound-induced emulsification of a partly reduced lysozyme in aqueous solutions. The stability of LysMBs suspension allows for post-synthetic modification of MBs surface. In the present work, the protein folded state and the biodegradability property of LysMBs were investigated by limited proteolysis. Moreover, LysMBs were coated and functionalized with a number of biomacromolecules (proteins, polysaccharides, nucleic acids). Remarkably, LysMBs show a high DNA-binding ability and protective effects of the nucleic acids from nucleases and, further, the ability to transform the bacteria cells. These results highlight on the possibility of using LysMBs for delivery of proteins and nucleic acids in prophylactic and therapeutic applications.

Leveraging the power of ultrasound for therapeutic design and optimization

Contrast agent-enhanced ultrasound can facilitate personalized therapeutic strategies by providing the technology to measure local blood flow rate, to selectively image receptors on the vascular endothelium, and to enhance localized drug delivery. Ultrasound contrast agents are micron-diameter encapsulated bubbles that circulate within the vascular compartment and can be selectively imaged with ultrasound. Microbubble transport-based estimates of local blood flow can quantify changes resulting from anti-angiogenic therapies and facilitate differentiation of angiogenic mechanisms. Microbubbles that are conjugated with targeting ligands attach to endothelial surface receptors that are upregulated in disease, providing high signal-to-noise ratio images of pathological vasculature. In addition to imaging applications, microbubbles can be used to enhance localized gene and drug delivery, either by changing membrane and vascular permeability or by carrying and locally releasing cargo. Our goal in this review is to provide an overview of the use of contrast-enhanced ultrasound methodologies in the design and evaluation of therapeutic strategies with emphases on quantitative blood flow mapping, molecular imaging, and enhanced drug delivery.

Antifibrotic treatment and other new strategies for improving renal outcomes

Diabetic nephropathy (DN) is clinically characterized by proteinuria and hypertension. Investigations suggest that matrix accumulation and inflammatory processes contribute to the pathological features of this progressive disease. This chapter reviews novel targeted approaches to the treatment of DN, with the goal of slowing the progression and improving renal function. Many studies support the use of agents that block the renin-angiotensin-aldosterone system in DN. Novel, oral agents that are promising in early clinical studies are agents such as pirfenidone and bardoxolone as they are associated with early improvement in renal function in patients with advanced diabetic kidney disease. Additionally, strategies that inhibit inflammatory cytokines, chemokines, adhesion molecules and mediators of the innate immune response may provide novel targets for the treatment of DN. Larger clinical studies are eagerly awaited to determine if new agents that specifically block kidney fibrosis and inflammation will delay, arrest and possibly reverse progressive renal failure.