In vivo and in vitro acute cardiovascular effects of bimoclomol

The role of heat shock protein 90 in modulating ischemia-reperfusion injury in the kidney

INTRODUCTION

Kidney transplantation is the gold standard treatment for end-stage renal disease. Ischemia-reperfusion injury (IRI) is an unavoidable consequence of the transplantation procedure and is responsible for delayed graft function and poorer long-term outcomes.

AREAS COVERED

Pharmacological induction of heat shock protein (Hsp) expression is an emerging pre-conditioning strategy aimed at reducing IRI following renal transplantation. Hsp90 inhibition up-regulates protective Hsps (especially Hsp70) and potentially down-regulates NF-κB by disruption of the IκB kinase (IKK) complex. However, the clinical application of Hsp90 inhibitors is currently limited by their toxicity profile and the exact mechanism of protection conferred is unknown. Toll-like receptor 4 (TLR4) is a further regulator of NF-κB and recent studies suggest TLR4 plays a dominant role in mediating kidney damage following IRI. The full interaction of Hsps with TLRs is yet to be delineated and whether TLR4 signalling can be targeted by Hsp90 inhibition in IRI remains uncertain.

EXPERT OPINION

Pharmacological pre-conditioning by Hsp90 inhibition involves direct treatment to the kidney donor and/or organ, which aims to reduce injury prior to the onset of ischemia. The major challenges going forward are to establish the exact mechanism of protection offered by these drugs and the investgiation of less toxic analogues that could be safely translated into human studies.

Induction of heat shock proteins may combat insulin resistance

The molecular mechanism responsible for obesity-associated insulin resistance has been partially clarified: increased fatty acid levels in muscle fibers promote diacylglycerol synthesis, which activates certain isoforms of protein kinase C (PKC). This in turn triggers a kinase cascade which activates both IkappaB kinase-beta (IKK-beta) and c-Jun N-terminal kinase (JNK), each of which can phosphorylate a key serine residue in IRS-1, rendering it a poor substrate for the activated insulin receptor. Heat shock proteins Hsp27 and Hsp72 have the potential to prevent the activation of IKK-beta and JNK, respectively; this suggests that induction of heat shock proteins may blunt the adverse impact of fat overexposure on insulin function. Indeed, bimoclomol--a heat shock protein co-inducer being developed for treatment of diabetic neuropathy--and lipoic acid--suspected to be a heat shock protein inducer--have each demonstrated favorable effects on the insulin sensitivity of obese rodents, and parenteral lipoic acid is reported to improve the insulin sensitivity of type 2 diabetics. Moreover, there is reason to believe that heat shock protein induction may have a favorable impact on the microvascular complications of diabetes, and on the increased risk for macrovascular disease associated with diabetes and insulin resistance syndrome. Heat shock protein induction may also have potential for preventing or treating neurodegenerative disorders, controlling inflammation, and possibly even slowing the aging process. The possible complementarity of bimoclomol and lipoic acid for heat shock protein induction should be assessed, and further efforts to identify well-tolerated agents active in this regard are warranted.

Heat shock proteins as emerging therapeutic targets

Chaperones (stress proteins) are essential proteins to help the formation and maintenance of the proper conformation of other proteins and to promote cell survival after a large variety of environmental stresses. Therefore, normal chaperone function is a key factor for endogenous stress adaptation of several tissues. However, altered chaperone function has been associated with the development of several diseases; therefore, modulators of chaperone activities became a new and emerging field of drug development. Inhibition of the 90 kDa heat shock protein (Hsp)90 recently emerged as a very promising tool to combat various forms of cancer. On the other hand, the induction of the 70 kDa Hsp70 has been proved to be an efficient help in the recovery from a large number of diseases, such as, for example, ischemic heart disease, diabetes and neurodegeneration. Development of membrane-interacting drugs to modify specific membrane domains, thereby modulating heat shock response, may be of considerable therapeutic benefit as well. In this review, we give an overview of the therapeutic approaches and list some of the key questions of drug development in this novel and promising therapeutic approach.

Heat Shock Proteins in Cardiovascular Disease

Cells have the capability of defending themselves from various stressors by activating a genetic program with the production of substances known as heat shock proteins and their regulatory partners, the heat shock transcription factors. In this article, heat shock proteins are discussed, including their roles in pathophysiology and as possible pharmacologic targets to treat disease. Multiple investigations have demonstrated an elevation in heat shock proteins in patients with systemic hypertension, coronary artery disease, carotid atherosclerosis, and myocardial infarction and ischemia. As we further understand how to manipulate their expression, we can explore pharmacologic interventions and gene transfection techniques that can safely be used in humans.

Bimoclomol elevates heat shock protein 70 and cytoprotects rat neonatal cardiomyocytes

Bimoclomol is a new compound that improves cell survival under experimental stress conditions partly by increasing intracellular heat shock proteins (HSPs). HSPs, especially HSP70, play a cytoprotective role in the rat heart. Rat neonatal cardiomyocytes were used to determine the ability of bimoclomol to induce HSP70 and affect cell survival across a broad concentration range (0.01-100 microM). Bimoclomol significantly elevated HSP70 levels at concentrations ranging from 0.01 to 10 microM, depending on the time of exposure. Pretreatment with bimoclomol for 24 h significantly increased survival of cells. There was a significant correlation between the increased levels of HSP70 and the increase in cell survival as a result of the treatment with bimoclomol. In conclusion, bimoclomol improved cell survival in rat neonatal cardiomyocytes, in part, by increasing the levels of HSP70. This cytoprotection began at the relatively low concentration of 0.1 microM, which is a concentration that can be achieved clinically.