Transition states of native and drug-resistant HIV-1 protease are the same

HIV-1 protease is an important target for the treatment of HIV/AIDS. However, drug resistance is a persistent problem and new inhibitors are needed. An approach toward understanding enzyme chemistry, the basis of drug resistance, and the design of powerful inhibitors is to establish the structure of enzymatic transition states. Enzymatic transition structures can be established by matching experimental kinetic isotope effects (KIEs) with theoretical predictions. However, the HIV-1 protease transition state has not been previously resolved using these methods. We have measured primary ¹⁴C and ¹⁵N KIEs and secondary ³H and ¹⁸O KIEs for native and multidrug-resistant HIV-1 protease (I84V). We observed ¹⁴C KIEs (¹⁴V/K) of 1.029 ± 0.003 and 1.025 ± 0.005, ¹⁵N KIEs (¹⁵V/K) of 0.987 ± 0.004 and 0.989 ± 0.003, ¹⁸O KIEs (¹⁸V/K) of 0.999 ± 0.003 and 0.993 ± 0.003, and ³H KIEs (³V/K) KIEs of 0.968 ± 0.001 and 0.976 ± 0.001 for the native and I84V enzyme, respectively. The chemical reaction involves nucleophilic water attack at the carbonyl carbon, proton transfer to the amide nitrogen leaving group, and C-N bond cleavage. A transition structure consistent with the KIE values involves proton transfer from the active site Asp-125 (1.32 Å) with partial hydrogen bond formation to the accepting nitrogen (1.20 Å) and partial bond loss from the carbonyl carbon to the amide leaving group (1.52 Å). The KIEs measured for the native and I84V enzyme indicate nearly identical transition states, implying that a true transition-state analogue should be effective against both enzymes.     

Right ventricular assist device in end-stage pulmonary arterial hypertension: insights from a computational model of the cardiovascular system

BackgroundThe high mortality rate of pulmonary arterial hypertension (PAH) mainly relates to progressive right ventricular (RV) failure. With limited efficacy of medical therapies, mechanical circulatory support for the RV has been considered. However, there is lack of understanding of the hemodynamic effects of mechanical support in this setting.MethodsWe modeled the cardiovascular system, simulated cases of PAH and RV dysfunction and assessed the theoretical effects of a continuous flow micro-pump as an RV assist device (RVAD). RVAD inflow was sourced either from the RV or RA and outflow was to the pulmonary artery. RVAD support was set at various flow rates and additional simulations were carried out in the presence of atrial septostomy (ASD) and tricuspid regurgitation (TR).ResultsRVAD support increased LV filling, thus improving cardiac output and arterial pressure, unloading the RA and RV, while raising pulmonary arterial and capillary pressures in an RVAD flow-dependent manner. These effects diminished with increasing disease severity. The presence of TR did not significantly impact the hemodynamic effects of RVAD support. ASD reduced the efficacy of RVAD support, since right-to-left shunting decreased and ultimately reversed with increasing RVAD support due to the progressive drop in RA pressure.ConclusionsThe results of this theoretical analysis suggest that RVAD support can effectively increase cardiac output and decreases RA pressure with the consequence of increasing pulmonary artery and capillary pressures. Especially in advanced PAH, low RVAD flow rates may mitigate these potentially detrimental effects while effectively increasing systemic hemodynamics.     

Cement pulmonary embolism after percutaneous vertebroplasty and kyphoplasty: An overview

BACKGROUND: Because of the aging of the American population, osteoporotic vertebral fractures are becoming a common problem in the elderly. Minimally invasive percutaneous vertebral augmentation techniques have gained a great deal of importance in relieving the pain associated with these fractures, and are becoming the standard of care. METHODS: These procedures involve the injection of polymethylmethacrylate (PMMA) into the vertebral body. However, these techniques have their complications, and among these, pulmonary embolism is one of the most feared. It is attributable to the passage of cement into the pulmonary vasculature. After encountering a case of PMMA embolism in our practice, we decided to highlight this topic and discuss the incidence, clinical presentation, diagnosis, and treatment of cement pulmonary embolisms.