Assessment of cholesteryl ester transfer protein inhibitors for interaction with proteins involved in the immune response to infection

Abstract

to identify agents for raising the levels of HDL. To date, the most potent means for raising plasma HDL has been through the use of cholesteryl ester transfer protein (CETP) inhibitors. Both torcetrapib ( 1, 2 ) and anacetrapib ( 3 ) have demonstrated 2-fold elevations in human trials. However, the development of these new lipid-modulating drugs suffered a major setback in December 2006 with the termination of the phase 3 trials of torcetrapib due to an excess in overall mortality and adverse cardiovascular events ( 4, 5 ). The largest of these trials, the Investigation of Lipid Level Management to Understand Its Impact in Atherosclerotic Events (ILLUMINATE), involved 15,067 patients at high cardiovascular risk. At study termination, 93 deaths had occurred in the torcetrapib/atorvastatin group compared with 59 in atorvastatin group. Of the 34 excess deaths in the torcetrapib group, 14 were cardiovascular-related whereas 20 were noncardiovascular-related. Although the occurence of new infections during the trial was similar for the torcetrapib versus the atorvastatin group (182 versus 177), there were nine deaths from infection in the former group versus zero for the latter.That nearly half of the noncardiovascular excess in mortality for the ILLUMINATE trial was associated with infection raises the question as to whether torcetrapib, apart from its intended effect on CETP, might have interfered with the function of two other proteins in the same family of lipid binding proteins, both of which play important roles in antibacterial defense ( 6 ). The fi rst of these, lipopolysaccharide binding protein (LBP), is an acute phase Abstract The CETP inhibitor, torcetrapib, was prematurely terminated from phase 3 clinical trials due to an increase in cardiovascular and noncardiovascular mortality. Because nearly half of the latter deaths involved patients with infection, we have tested torcetrapib and other CETPIs to see if they interfere with lipopolysaccharide binding protein (LBP) or bactericidal/permeability increasing protein (BPI). No effect of these potent CETPIs on LPS binding to either protein was detected. Purifi ed CETP itself bound weakly to LPS with a Kd у 25 uM compared with 0.8 and 0.5 nM for LBP and BPI, respectively, and this binding was not blocked by torcetrapib. In whole blood, LPS induced tumor necrosis factor-␣ normally in the presence of torcetrapib. Furthermore, LPS had no effect on CETP activity. We conclude that the sepsis-related mortality of the ILLUMI-NATE trial was unlikely due to a direct effect of torcetrapib on LBP or BPI function, nor to inhibition of an interaction of CETP with LPS. Instead, we speculate that the negative outcome seen for patients with infections might be related to the changes in plasma lipoprotein composition and metabolism, or alternatively to the known off-target effects of torcetrapib, such as aldosterone elevation, which may have aggravated the effects of sepsis. In order to reduce the incidence of cardiovascular disease beyond that achieved through the use of sta...

HDL in Infectious Diseases and Sepsis

“…The picture however is more complicated, and not only HDL quantity but also HDL quality/composition is critical. For instance, the increase in sepsis-related mortality of the ILLUMINATE trial observed in the torcetrapib (a cholesteryl ester transfer protein inhibitor, increasing HDL-C levels) arm (Barter et al 2007) was unlikely due to a direct effect of torcetrapib on LBP or bactericidal/permeability increasing protein function nor to inhibition of an interaction of CETP with LPS (Clark et al 2010). It is rather possible that changes in plasma lipoprotein composition despite increased HDL levels, or the known off-target effects of torcetrapib, such as aldosterone elevation, could have aggravated the effects of sepsis (Clark et al 2010).…”

“…For instance, the increase in sepsis-related mortality of the ILLUMINATE trial observed in the torcetrapib (a cholesteryl ester transfer protein inhibitor, increasing HDL-C levels) arm (Barter et al 2007) was unlikely due to a direct effect of torcetrapib on LBP or bactericidal/permeability increasing protein function nor to inhibition of an interaction of CETP with LPS (Clark et al 2010). It is rather possible that changes in plasma lipoprotein composition despite increased HDL levels, or the known off-target effects of torcetrapib, such as aldosterone elevation, could have aggravated the effects of sepsis (Clark et al 2010). Apolipoprotein mimetic peptides represent an emerging area of HDL therapy; the most effective apoA-I mimetic peptide is 4F, which has been shown to improve HDL quality/function (Sherman et al 2010;White et al 2009).…”

Surface Polysaccharide Mutants Reveal that Absence of O Antigen Reduces Biofilm Formation of Actinobacillus pleuropneumoniae

“…5). In comparison to other LPS studies in the SPR literature, our assays were performed using a stringent flow rate (i.e., 25 l/min, like that used by Bahl et al [58]) and avoided the use of complicating carrier proteins, such as BSA, in the running buffer (59). Like the high-affinity interaction reported by Bahl et al (58) that mapped specific LPS-binding hot spots on hemoglobin, the slow dissociation kinetics that we observed suggest that the PGA-LPS interaction is not weak (e.g., there was no immediate return of the SPR signal to the baseline at 70 to 120 s in Fig.…”

Counterpoint: Cholesteryl Ester Transfer Protein Antagonism by Drugs—A Poor Choice

“…After lipopolysaccharide inoculation, tumor necrosis factor ␣ and interleukin-6 concentrations increase in the plasma of transgenic mice to a far lower extent than in wild-type mice, with consequent improved survival. This first report demonstrating a potential role for CETP in the firstline defense against an exacerbated production of proinflammatory mediators was recently criticized, however, because it reported only in vitro findings (14 ).…”