Feasibility of xeno-transplantation

Exploiting nature's rich source of proteasome inhibitors as starting points in drug development

Cancer is the No. 2 cause of death in the Western world and one of the most expensive diseases to treat. Thus, it is not surprising, that every major pharmaceutical and biotechnology company has a blockbuster oncology product. In 2003, Millennium Pharmaceuticals entered the race with Velcade®, a first-in-class proteasome inhibitor that has been approved by the FDA for treatment of multiple myeloma and its sales have passed the billion dollar mark. Velcade®'s extremely toxic boronic acid pharmacophore, however, contributes to a number of severe side effects. Nevertheless, the launching of this product has validated the proteasome as a target in fighting cancer and further proteasome inhibitors have entered the market as anti-cancer drugs. Additionally, proteasome inhibitors have found application as crop protection agents, anti-parasitics, immunosuppressives, as well as in new therapies for muscular dystrophies and inflammation. Many of these compounds are based on microbial metabolites. In this review, we emphasize the important role of the structural elucidation of the various unique binding mechanisms of these compounds that have been optimized throughout evolution to target the proteasome. Based on this knowledge, medicinal chemists have further optimized these natural products, resulting in potential drugs with reduced off-target activities.

A new bioartificial pancreas utilizing amphiphilic membranes for the immunoisolation of porcine islets: a pilot study in the canine

We have developed a replaceable bioartificial pancreas to treat diabetes utilizing a unique cocontinous amphiphilic conetwork membrane created for macroencapsulation and immunoisolation of porcine islet cells (PICs). The membrane is assembled from hydrophilic poly(N,N-dimethyl acrylamide) and hydrophobic/oxyphilic polydimethylsiloxane chains cross-linked with hydrophobic/oxyphilic polymethylhydrosiloxane chains. Our hypothesis is that this membrane allows the survival of xenotransplanted PICs in the absence of prevascularization or immunosuppression because of its extraordinarily high-oxygen permeability and small hydrophilic channel dimensions (3-4 nm). The key components are a 5-10 microm thick semipermeable amphiphilic conetwork membrane reinforced with an electrospun nanomat of polydimethylsiloxane-containing polyurethane, and a laser-perforated nitinol scaffold to provide geometric stability. Devices were loaded with PICs and tested for their ability to maintain islet viability without prevascularization, prevent rejection, and reverse hyperglycemia in three pancreatectomized dogs without immunosuppression. Tissue tolerance was good and there was no systemic toxicity. The bioartificial pancreas protected PICs from toxic environments in vitro and in vivo. Islets remained viable for up to 3 weeks without signs of rejection. Neovascularization was observed. Hyperglycemia was not reversed, most likely because of insufficient islet mass. Further studies to determine long-term islet viability and correction of hyperglycemia are warranted.

Poly (ADP) ribose polymerase inhibition improves rat cardiac allograft survival

BACKGROUND

Heart transplantation is an accepted treatment modality for end-stage heart failure. However, acute cellular rejection (ACR) continues to be a morbid complication. Recently a novel mechanism of inflammatory allograft injury has been characterized which involves overactivation of the nuclear enzyme poly (ADP-ribose) polymerase (PARP). In the present studies, we compared the efficacy of INO-1001, a novel, potent PARP inhibitor, in limiting ACR with and without adjuvant low-dose cyclosporine (CSA).

METHODS

Heterotopic heart transplantation was performed utilizing Brown-Norway strains as donors and Lewis rats as recipients. Groups received daily intraperitoneal injections of: vehicle, low-dose CSA, low-dose INO-1001, high-dose INO-1001, and low-dose CSA combined with high-dose INO-1001. Additional animals were sacrificed on postoperative Day 5 for histologic assessments of allograft inflammation, including immunohistochemistry for nitrotyrosine and poly (ADP-ribose) (the product of PARP) staining.

RESULTS

PARP inhibition significantly prolonged allograft survival relative to vehicle controls. The combination of low-dose CSA and INO-1001 resulted in a marked increase in allograft survival and significant reductions in allograft rejection scores. This was associated with decreased nitrotyrosine and PAR staining in transplanted cardiac allografts.

CONCLUSIONS

Pharmacologic inhibition of INO-1001 prolongs allograft survival in a dose-dependent fashion in a rodent model of heart transplantation. PARP inhibitors may permit reductions in the dose of CSA needed for adequate immunosuppression after heart transplantation.

New technologies for organ replacement and augmentation

The most common causes of disability and death are diseases of the heart, lungs, liver, kidneys, and pancreas, many of which are potentially treated by organ transplantation. The effect of organ dysfunction and failure will likely grow over time, and patients will increasingly expect "safer" transplants, in particular in cases of "preemptive transplantation." New technologies are being developed in part because of the limited availability of organs, and include transplantation with stem cells, tissue engineering, cloning, and xenotransplantation, which some researchers believe promise ready solutions. Although exciting, none of these approaches alone is likely to address the need for organ replacement. We propose that a melding of these new technologies adapted to the distinct challenges and imperatives of the various organs may address this daunting challenge.

Organization of the newborn piglets vagal motor complex: insights into integrated autonomic control mechanisms

Pediatric disorders frequently exhibit dysregulation of sympatho-vagal activity, and impaired control of cardiovascular vagal networks. Factors influencing the maturation of vagal networks are of special interest because they normally protect the heart and circulation, facilitate digestion, and preserve visceral metabolism. At present, scant literature exists regarding the development of vagal innervation of the heart. This study in neonatal swine, Sus scrofa, mapped the normal anatomy of vagal motor cell groups, with special focus on the origins of cardiomotor neurons. Right cardiac nerve branches, or the right thoracic vagal trunk were resected, inserted into capillary glass vials filled with 2% FluoroGold (FG) tracer solutions, and sealed to prevent leakage (false positives). Dorsal and ventral vagal complexes were identified on cross-sectioned tissues incubated in a well-characterized specific FG antibody. Thoracic and abdominal vagal motoneurons were cytologically heterogeneous, and predominantly medium-sized, polygonal cell bodies. Discrete longitudinal cell columns were observed, as well as organized arrays of elongate spindle-shaped cells in formation. Long axes and dendrites appeared to orient toward incoming peripheral sensory and central afferents, and were juxtaposed to cerebral microvasculature. The piglets' dorsal vagal complex is: (i) thick and long, comparable to ruminants, in contrast to much shorter lengths in non-ruminants, and (ii) the chief source of vagal motoneurons, forming discrete, topographically organized parasympathetic cell groups with distinct dendritic arbors. The cardiac motor subnucleus is localized to a highly restricted areal subunit of nucleus ambiguus' external formation in the vicinity of the obex. On the other hand, dorsal cardiac vagal motoneurons were few in number and diffusely distributed. Dorsal vagal motoneurons of neonatal swine likely projected primarily to the enteric nervous system, exerting excitatory influence over gastrointestinal activity.

Secreted Immunomodulatory Viral Proteins as Novel Biotherapeutics

Many viruses have learned to evade or subvert the host antiviral immune responses by encoding and expressing immunomodulatory proteins that protect the virus from attack by elements of the innate and acquired immune systems. Some of these viral anti-immune regulators are expressed as secreted proteins that engage specific host immune targets in the extracellular environment, where they exhibit potent anti-immune properties. We review here viral immunomodulatory proteins that have been tested as anti-inflammatory reagents in animal models of disease caused by excessive inflammation or hyperactivated immune pathways. The potential for such viral molecules for the development of novel drugs to treat immune-based or inflammatory disorders is discussed.