Disulfide activated protein kinase G Ialpha as a new therapeutic target in sepsis

Sepsis, often referred to as blood poisoning, occurs when bacteria get into the blood stream. This is a very common disease and when it occurs the chances of survival are rather poor. Major issues in sepsis are that the patients' blood pressure becomes very low and their blood vessels become leaky. Together this causes a lot of harm and many of the bodies organs are not supplied with enough blood and so they become injured. Recently we identified a new pathway that lowers blood pressure and promotes vessel leakiness in healthy people, and have now we have found this is over-stimulated during sepsis resulting in organ damage. In these studies we hope to develop and test new drugs that prevent this pathway being actuated during sepsis. Such therapies are predicted to prevent organ damage and ultimately enhance patient survival during sepsis.

Sepsis is a common and often deadly medical condition that exerts an enormous burden on healthcare systems. Previously we showed that PKGIalpha can be activated by oxidative stress independently of the classical NO-cGMP activation pathway. This alternate activation pathway involves oxidants inducing a disulfide bond between the kinases two subunits. This pathway is also relevant to sepsis, consistent with it being a time of oxidative stress that drives formation of the disulfide. This explains in part the hypotension that occurs during sepsis and partly accounts for the associated organ injury as a result of their under-perfusion. Based on the literature and pilot data presented in this application, we think that PKGIalpha oxidation can also directly damage tissue (independently of hypotension and tissue under-perfusion) by inducing apoptosis. These studies proposed here are aimed at defining the relative contributions of these two pathways to injury during sepsis. In addition, as disulfide PKGIalpha formation underlies the damage caused by both these pathways (i.e. both by hypotension as well as apoptosis), we think pharmacological interventions that blocked oxidation would be protective. Consequently, we plan on developing and testing a number of drugs for their ability to prevent PKGIalpha oxidation and limit tissue damage during sepsis.

Sepsis is a common and often deadly medical condition that exerts an enormous burden on healthcare systems and society. Current therapeutic strategies of administering antibiotics (to combat the underlying infection) or vasopressor (to elevate blood pressure) are often ineffective, with a high risk (approximately 25%) of mortality. In recent years much attention has been paid to the idea that injury during sepsis is driven by over-production of nitric oxide to detrimentally lower blood pressure by activating soluble Guanylate Cyclase and then protein kinase G (PKG). However, clinical trials preventing nitric oxide production during sepsis were ineffective and in fact increased mortality. Clearly our current understanding of the disease is lacking. By better understanding the mechanisms that underlie the dysfunction that occurs in sepsis we improve our chances of implementing or designing rational therapeutic strategies. Our previous work identified an important new way of activating PKG independently of the nitric oxide pathway, involving it becoming oxidised to form an interprotein disulfide. Sepsis is well-known as a time of oxidative stress and so PKG oxidation was anticipated to occur. Indeed, we found PKG oxidative activation would significantly explain the hypotension that occurs during sepsis. Indeed, we found sepsis induces PKG oxidation and this was associated with murine hypotension and organ damage in vivo. In contrast a Cys42Ser PKG knock-in mouse that cannot be activated by disulfide oxidation was resistant in part to sepsis-induced hypotension and ensuing organ damage. However, we now know that additional PKG oxidation signals to tissue apoptosis, and here we will define the contribution of this mechanism to damage during sepsis independently of the role of hypotension. It is evident from our findings so far that PKG oxidation causes damaging hypotension and likely also apoptosis. We hope to identify and test drugs that will prevent PKG oxidation as these should be protective and provide resistance to injury during sepsis - in the same way the knock-in mouse that cannot be oxidised to disulfide is protected. Overall we have identified a potentially important new mechanism that may be injurious during sepsis, and we propose studies that may lead to therapies that help treat this major healthcare problem.