ISSLS prize in basic science 2021: a novel inducible system to regulate transgene expression of TIMP1.

PURPOSE: Inflammatory and oxidative stress upregulates matrix metalloproteinase (MMP) activity, leading to intervertebral disc degeneration (IDD). Gene therapy using human tissue inhibitor of metalloproteinase 1 (hTIMP1) has effectively treated IDD in animal models. However, persistent unregulated transgene expression may have negative side effects. We developed a recombinant adeno-associated viral (AAV) gene vector, AAV-NFκB-hTIMP1, that only expresses the hTIMP1 transgene under conditions of stress. METHODS: Rabbit disc cells were transfected or transduced with AAV-CMV-hTIMP1, which constitutively expresses hTIMP1, or AAV-NFκB-hTIMP1. Disc cells were selectively treated with IL-1ß. NFκB activation was verified by nuclear translocation. hTIMP1 mRNA and protein expression were measured by RT-PCR and ELISA, respectively. MMP activity was measured by following cleavage of a fluorogenic substrate. RESULTS: IL-1ß stimulation activated NFκB demonstrating that IL-1ß was a surrogate for inflammatory stress. Stimulating AAV-NFκB-hTIMP1 cells with IL-1ß increased hTIMP1 expression compared to unstimulated cells. AAV-CMV-hTIMP1 cells demonstrated high levels of hTIMP1 expression regardless of IL-1ß stimulation. hTIMP1 expression was comparable between IL-1ß stimulated AAV-NFκB-hTIMP1 cells and AAV-CMV-hTIMP1 cells. MMP activity was decreased in AAV-NFκB-hTIMP1 cells compared to baseline levels or cells exposed to IL-1ß. CONCLUSION: AAV-NFκB-hTIMP1 is a novel inducible transgene delivery system. NFκB regulatory elements ensure that hTIMP1 expression occurs only with inflammation, which is central to IDD development. Unlike previous inducible systems, the AAV-NFκB-hTIMP1 construct is dependent on endogenous factors, which minimizes potential side effects caused by constitutive transgene overexpression. It also prevents the unnecessary production of transgene products in cells that do not require therapy.

Cardiogenic shock complicating peripartum cardiomyopathy: Importance of early left ventricular unloading and bromocriptine therapy.

INTRODUCTION: Acute peripartum cardiomyopathy complicated by cardiogenic shock is a rare but life-threatening disease. A prolactin fragment is considered causal for the pathogenesis of peripartum cardiomyopathy. This analysis sought to investigate the role of early percutaneous mechanical circulatory support with micro-axial flow-pumps and/or veno-arterial extracorporeal membrane oxygenation in combination with the prolactin inhibitor bromocriptine in refractory cardiogenic shock complicating peripartum cardiomyopathy. METHODS AND RESULTS: In this single-centre analysis, five peripartum cardiomyopathy patients with refractory cardiogenic shock received mechanical circulatory support with either Impella CP microaxial pump only (n=2) or in combination with veno-arterial extracorporeal membrane oxygenation (n=3) in the setting of biventricular failure. All patients were mechanically ventilated. In all cases mechanical circulatory support was combined with bromocriptine therapy and early administration of levosimendan. All patients survived the acute phase of refractory cardiogenic shock. Mechanical circulatory support using a micro-axial pump allowed to significantly reduce catecholamine dosage. Remarkably, early left ventricular support with micro-axial flow-pumps resulted in myocardial recovery whereas delayed Impella (mechanical circulatory support) implantation was associated with poor left ventricular recovery. CONCLUSION: Mechanical circulatory support in patients with refractory cardiogenic shock complicating peripartum cardiomyopathy was associated with a 30-day survival of 100% and a favourable outcome. Notably, early left ventricular unloading combined with bromocriptine therapy was associated with left ventricular recovery. Therefore, an immediate transfer to a tertiary hospital experienced in mechanical circulatory support in combination with bromocriptine treatment seems indispensable for successful treatment of peripartum cardiomyopathy complicated by cardiogenic shock.

Bioabsorbable interbody magnesium-polymer cage: degradation kinetics, biomechanical stiffness, and histological findings from an ovine cervical spine fusion model.

STUDY DESIGN: An experimental study using a sheep cervical spine interbody fusion model. OBJECTIVE: First, to compare anterior cervical discectomy and fusion of an experimental bioabsorbable cage consisting of a magnesium alloy and a polymer (poly-ε-caprolactone, PCL) with an autologous tricortical iliac crest bone graft. Second, to determine the degradation kinetics of the cage, assess the 2 fusion devices for biomechanical stability, and determine their histological characteristics. SUMMARY OF BACKGROUND DATA: Bioabsorbable cages are not routinely used in spine surgery at present, due to some undesirable effects such as cracks and foreign body reactions. This study involved the manufacture of a bioabsorbable cage from a magnesium alloy and the polymer PCL, which was then used as a device for anterior cervical discectomy and fusion in a sheep cervical spine fusion model. METHODS: Twenty-four sheep had anterior cervical discectomy and fusion of C3-C4 and C5-C6 with an experimental bioabsorbable cage consisting of the magnesium alloy AZ31, which was infiltrated and covered with PCL at 1 level and with an autologous tricortical iliac crest bone graft at a second level. The sheep were divided into 4 groups. After 3, 6, 12, or 24 weeks postimplantation, the animals were killed and the cervical spines were harvested. The intervertebral spaces with the cage were investigated using µ-computed tomographic images to calculate degradation kinetics. Stiffness of all monosegments was determined through biomechanical testing. Histological analysis was performed to evaluate fusion status and to detect any foreign body reactions. The results from both implants were compared. RESULTS: The magnesium-PCL cage showed nonlinear degradation over time. Both implants demonstrated time-dependent increases in stability, with a significantly greater stiffness of the bone graft after 24 weeks in all directions of motion. Histologically, the cage showed no signs of fusion with progressive encapsulation over time. CONCLUSION: In comparison with the bone graft, the bioabsorbable cage showed inferior stiffness and fusion properties. Thus, further component modifications are necessary. LEVEL OF EVIDENCE: N/A.