Lipoprotein(a) levels in a global population with established atherosclerotic cardiovascular disease

OBJECTIVE

Lipoprotein(a) (Lp(a)) is an important genetically determined risk factor for atherosclerotic vascular disease (ASCVD). With the development of Lp(a)-lowering therapies, this study sought to characterise patterns of Lp(a) levels in a global ASCVD population and identify racial, ethnic, regional and gender differences.

METHODS

A multicentre cross-sectional epidemiological study to estimate the prevalence of elevated Lp(a) in patients with a history of myocardial infarction, ischaemic stroke or peripheral artery disease conducted at 949 sites in 48 countries in North America, Europe, Asia, South America, South Africa and Australia between April 2019 and July 2021. Low-density lipoprotein cholesterol (LDL-C) and Lp(a) levels were measured either as mass (mg/dL) or molar concentration (nmol/L).

RESULTS

Of 48 135 enrolled patients, 13.9% had prior measurements of Lp(a). Mean age was 62.6 (SD 10.1) years and 25.9% were female. Median Lp(a) was 18.0 mg/dL (IQR 7.9-57.1) or 42.0 nmol/L (IQR 15.0-155.4). Median LDL-C was 77 mg/dL (IQR 58.4-101.0). Lp(a) in women was higher, 22.8 (IQR 9.0-73.0) mg/dL, than in men, 17.0 (IQR 7.1-52.2) mg/dL, p<0.001. Black patients had Lp(a) levels approximately threefold higher than white, Hispanic or Asian patients. Younger patients also had higher levels. 27.9% of patients had Lp(a) levels >50 mg/dL, 20.7% had levels >70 mg/dL, 12.9% were >90 mg/dL and 26.0% of patients exceeded 150 nmol/L.

CONCLUSIONS

Globally, Lp(a) is measured in a small minority of patients with ASCVD and is highest in black, younger and female patients. More than 25% of patients had levels exceeding the established threshold for increased cardiovascular risk, approximately 50 mg/dL or 125 nmol/L.

TRIAL REGISTRATION NUMBER

Residual inflammatory risk associated with interleukin-18 and interleukin-6 after successful interleukin-1β inhibition with canakinumab: further rationale for the development of targeted anti-cytokine therapies for the treatment of atherothrombosis

AIMS

The Canakinumab Antiinflammatory Thrombosis Outcomes Study (CANTOS) established that targeting inflammation with interleukin-1β (IL-1β) inhibition can significantly reduce cardiovascular (CV) event rates in the absence of any beneficial effects on cholesterol. Yet, CANTOS participants treated with both high-intensity statins and canakinumab remain at considerable risk for recurrent CV events. Both interleukin-18 (IL-18, which like IL-1β requires the NLRP3 inflammasome for activation) and interleukin-6 (IL-6, a pro-inflammatory cytokine downstream of IL-1) may contribute to the recurrent events that occur even on canakinumab therapy, and thus represent novel targets for treating atherothrombosis.

METHODS AND RESULTS

Plasma samples from 4848 stable post-myocardial infarction patients who were assigned to active IL-1β inhibition or placebo within CANTOS underwent measurement of IL-18 and IL-6 both before and after initiation of canakinumab using validated ELISA. All participants were followed over a median 3.7-year period (maximum 5 years) for recurrent major adverse cardiovascular events (MACE) and for all-cause mortality. Compared to placebo, canakinumab significantly reduced IL-6 levels in a dose-dependent manner yielding placebo-subtracted median percent reductions in IL-6 at 3 months of 24.8%, 36.3%, and 43.2% for the 50, 150, and 300 mg doses, respectively (all P-values <0.001). By contrast, no dose of canakinumab significantly altered IL-18 levels measured at 3 months (all effects <1%, all P-values > 0.05). Yet, despite these differential plasma effects, either baseline and on-treatment levels of IL-18 or IL-6 associated with rates of future CV events. For example, for MACE, each tertile increase in IL-18 measured 3 months after canakinumab initiation associated with a 15% increase in risk [95% confidence interval (CI) 3-29%, P = 0.016], while each tertile increase in IL-6 measured 3 months after canakinumab initiation associated with a 42% increase in risk (95% CI 26-59%, P < 0.0001). Similar effects were observed for MACE-plus, CV death, all-cause mortality, and the for the combination endpoint of all vascular events inclusive of revascularization procedures and hospitalization for congestive heart failure. In baseline as well as on-treatment analyses, risks were highest among those with the highest levels of both IL-18 and IL-6.

CONCLUSION

There remains substantial residual inflammatory risk related to both IL-18 and IL-6 after IL-1β inhibition with canakinumab These data support further pharmacologic development of therapies for atherothrombosis that target IL-18 or IL-6 signalling, or that can simultaneously inhibit both IL-1β and IL-18 (such as NLRP3 inflammasome inhibitors).

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov NCT01327846.

Effects of Interleukin-1β Inhibition on Incident Hip and Knee Replacement : Exploratory Analyses From a Randomized, Double-Blind, Placebo-Controlled Trial

BACKGROUND

Osteoarthritis is a common inflammatory disorder with no disease-modifying therapies. Whether inhibition of interleukin-1β (IL-1β) can reduce the consequences of large joint osteoarthritis is unclear.

OBJECTIVE

To determine whether IL-1β inhibition with canakinumab reduces incident total hip or knee replacement (THR/TKR).

DESIGN

Exploratory analysis of a randomized trial. (ClinicalTrials.gov: NCT01327846).

SETTING

1091 clinical sites in 39 countries.

PARTICIPANTS

10 061 CANTOS (Canakinumab Anti-inflammatory Thrombosis Outcomes Study) participants.

INTERVENTION

Random allocation to placebo or canakinumab (50, 150, or 300 mg) subcutaneously once every 3 months.

MEASUREMENTS

The primary and secondary outcomes were time to first incident THR/TKR and time to first occurrence of an osteoarthritis-related adverse event (AE). Data were obtained through blinded ascertainment of trial clinical and safety databases.

RESULTS

Median follow-up was 3.7 years. For the individual canakinumab dose groups, compared with placebo, hazard ratios (HRs) for incident THR/TKR during follow-up were 0.60 (95% CI, 0.38 to 0.95) for the 50-mg group, 0.53 (CI, 0.33 to 0.84) for the 150-mg group, and 0.60 (CI, 0.38 to 0.93) for the 300-mg group. Thus, in the pooled canakinumab groups, compared with the placebo group, incidence rates for THR/TKR were 0.31 and 0.54 events per 100 person-years (HR, 0.58 [CI, 0.42 to 0.80]; P = 0.001), respectively. The HR for the secondary end point of osteoarthritis-related AEs was 0.73 (CI, 0.61 to 0.87). Similar findings were observed in analyses restricted to participants with a history of osteoarthritis.

LIMITATION

Because the parent trial was not designed to examine the efficacy of IL-1β inhibitors in osteoarthritis, information on structural joint outcomes was not collected.

CONCLUSION

Findings from this exploratory analysis of a randomized controlled trial support further investigation of IL-1β inhibition for treatment of large joint osteoarthritis.

PRIMARY FUNDING SOURCE

Novartis Pharmaceuticals.

Effects of Interleukin-1β Inhibition on Incident Anemia: Exploratory Analyses From a Randomized Trial

BACKGROUND

Inflammatory cytokines, such as interleukin (IL)-1β, alter iron homeostasis and erythropoiesis, resulting in anemia, but whether inhibition of IL-1β can reverse these effects is unclear.

OBJECTIVE

To determine whether IL-1β inhibition with canakinumab reduces incident anemia and improves hemoglobin levels among those with prevalent anemia.

DESIGN

Exploratory analysis of a randomized controlled trial. (ClinicalTrials.gov: NCT01327846).

SETTING

Many clinical sites in 39 countries.

PARTICIPANTS

8683 CANTOS (Canakinumab Anti-inflammatory Thrombosis Outcomes Study) participants without anemia at trial entry and 1303 with prevalent anemia at trial entry.

INTERVENTION

Random assignment to receive placebo or canakinumab (50, 150, or 300 mg) subcutaneously once every 3 months.

MEASUREMENTS

Primary outcome was incident anemia (hemoglobin level <130 g/L in men or <120 g/L in women).

RESULTS

Anemia incidence increased with rising baseline levels of high-sensitivity C-reactive protein (hsCRP), and both hsCRP and IL-6 decreased among participants receiving canakinumab compared with the placebo group. During a median follow-up of 3.7 years, participants without baseline anemia who received canakinumab at any dosage had significantly less incident anemia than those who received placebo (hazard ratio, 0.84 [95% CI, 0.77 to 0.93]; P < 0.001). Compared with placebo, the greatest benefits of IL-1β inhibition on incident anemia were observed among participants with the most robust anti-inflammatory response, an effect corroborated in formal mediation analyses. Among those with baseline anemia, canakinumab increased mean hemoglobin levels by 11.3 g/L (P < 0.001) compared with placebo after 2 years of treatment. Canakinumab increased the risk for infection and was associated with mild cases of thrombocytopenia and neutropenia, none of which was grade 3 or higher.

LIMITATION

CANTOS was not designed to assess the cause of anemia in individual trial participants.

CONCLUSION

These exploratory analyses of randomized trial data provide proof of principle that inflammation inhibition, at least through the IL-1β/IL-6 signaling pathway, reduces the incidence of anemia and improves hemoglobin levels in patients with anemia.

PRIMARY FUNDING SOURCE

Novartis Pharmaceuticals.

Effects of Interleukin-1β Inhibition on Blood Pressure, Incident Hypertension, and Residual Inflammatory Risk: A Secondary Analysis of CANTOS

Supplemental Digital Content is available in the text.

While hypertension and inflammation are physiologically inter-related, the effect of therapies that specifically target inflammation on blood pressure is uncertain. The recent CANTOS (Canakinumab Anti-inflammatory Thrombosis Outcomes Study) afforded the opportunity to test whether IL (interleukin)-1β inhibition would reduce blood pressure, prevent incident hypertension, and modify relationships between hypertension and cardiovascular events. CANTOS randomized 10 061 patients with prior myocardial infarction and hsCRP (high sensitivity C-reactive protein) ≥2 mg/L to canakinumab 50 mg, 150 mg, 300 mg, or placebo. A total of 9549 trial participants had blood pressure recordings during follow-up; of these, 80% had a preexisting diagnosis of hypertension. In patients without baseline hypertension, rates of incident hypertension were 23.4, 26.6, and 28.1 per 100-person years for the lowest to highest baseline tertiles of hsCRP (P>0.2). In all participants random allocation to canakinumab did not reduce blood pressure (P>0.2) or incident hypertension during the follow-up period (hazard ratio, 0.96 [0.85–1.08], P>0.2). IL-1β inhibition with canakinumab reduces major adverse cardiovascular event rates. These analyses suggest that the mechanisms underlying this benefit are not related to changes in blood pressure or incident hypertension.

Anti-Inflammatory Therapy With Canakinumab for the Prevention of Hospitalization for Heart Failure

BACKGROUND

Subclinical inflammation is associated with an increased risk of heart failure and with adverse prognosis in patients with established heart failure. Yet, treatments specifically directed at reducing inflammation in patients with heart failure have not yet shown improved clinical outcomes. We tested the hypothesis that the interleukin-1β inhibitor canakinumab would prevent hospitalization for heart failure (HHF) and the composite of HHF or heart failure-related mortality.

METHODS

We randomized 10 061 patients with prior myocardial infarction and high-sensitivity C-reactive protein ≥2 mg/L to canakinumab 50, 150, or 300 mg or placebo, given subcutaneously once every 3 months. In total, 2173 (22%) reported a history of heart failure at baseline. We tested the hypothesis that canakinumab prevents prospectively collected HHF events and the composite of HHF or heart failure-related mortality.

RESULTS

A total of 385 patients had an HHF event during a median follow-up of 3.7 years. Patients who had HHF were older, had higher body mass index, and were more likely to have diabetes mellitus, hypertension, and prior coronary bypass surgery. As anticipated, median (quartile 1, 3) baseline concentrations of high-sensitivity C-reactive protein were higher among those who had HHF during follow-up than those who did not (5.7 [3.5, 9.9] mg/L versus 4.2 [2.8, 6.9] mg/L, respectively; P<0.0001). The unadjusted hazard ratios for HHF with each dose of canakinumab compared with placebo were 1.04 (95% CI, 0.79-1.36) for 50 mg, 0.86 (95% CI, 0.65-1.13) for 150 mg, and 0.76 (95% CI, 0.57-1.01) for 300 mg ( P for trend=0.025). The composite of HHF or heart failure-related mortality was also reduced by canakinumab, with unadjusted hazard ratios of 1.00 (95% CI, 0.78-1.29) for 50 mg, 0.88 (95% CI, 0.68-1.13) for 150 mg, and 0.78 (95% CI, 0.60-1.02) for 300 mg ( P for trend=0.042).

CONCLUSIONS

These randomized double-blind placebo-controlled data suggest that therapy with canakinumab, an interleukin-1β inhibitor, is related to a dose-dependent reduction in HHF and the composite of HHF or heart failure-related mortality in a population of patients with prior myocardial infarction and elevations in high-sensitivity C-reactive protein.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov . Unique identifier: NCT01327846.

Modulation of the interleukin-6 signalling pathway and incidence rates of atherosclerotic events and all-cause mortality: analyses from the Canakinumab Anti-Inflammatory Thrombosis Outcomes Study (CANTOS)

Aims

Canakinumab, a monoclonal antibody targeting interleukin (IL)-1β, reduces rates of recurrent cardiovascular events without lowering lipids. It is uncertain, however, to what extent these beneficial cardiovascular outcomes are mediated through interleukin-6 (IL-6) signalling, an issue with substantial pathophysiologic consequences and therapeutic implications.

Methods and results

A total of 4833 stable atherosclerosis patients in the Canakinumab Anti-Inflammatory Thrombosis Outcomes Study (CANTOS) had IL-6 levels measured before randomization and after treatment with placebo or one of three doses of canakinumab (50 mg, 150 mg, or 300 mg) given subcutaneously once every 3 months. Participants were followed for up to 5 years (median follow-up 3.7 years). Compared with those allocated to placebo, CANTOS participants receiving canakinumab who achieved on-treatment IL-6 levels below the study median value of 1.65 ng/L experienced a 32% reduction in major adverse cardiovascular events [MACE, multivariable adjusted hazard ratio (HRadj) 0.68, 95% confidence interval (CI) 0.56-0.82; P < 0.0001], a 30% reduction in MACE plus the additional endpoint of hospitalization for unstable angina requiring urgent revascularization (MACE+, HRadj 0.70, 95% CI 0.59-0.84; P < 0.0001), a 52% reduction in cardiovascular mortality (HRadj 0.48, 95% CI 0.34-0.68; P < 0.0001), and a 48% reduction in all-cause mortality (HRadj 0.52, 95% CI 0.40-0.68; P < 0.0001) with prolonged treatment. In contrast, those with on-treatment IL-6 levels equal to or above 1.65 ng/L after taking the first dose of canakinumab had no significant benefit for any of these endpoints. These differential findings based on the magnitude of IL-6 response were seen in analyses alternatively based on tertiles of on-treatment IL-6 levels, and in analyses using a statistical inference approach to estimate the effect of treatment among individuals who would achieve a targeted IL-6 level.

Conclusion

CANTOS provides proof of concept evidence in humans that modulation of the IL-6 signalling pathway, at least with canakinumab, associates with reduced cardiovascular event rates, independent of lipid lowering.

Clinical trial registration

ClinicalTrials.gov NCT01327846.

2417Elevated interleukin-6 and interleukin-18 concentrations predict residual inflammatory risk both before and after interleukin-1beta inhibition with canakinumab

Background

The Canakinumab Antiinflammatory Thrombosis Outcomes Study (CANTOS) established that targeting inflammation with interleukin-1b (IL-1b) inhibition can significantly reduce cardiovascular event rates in the absence of beneficial effects on cholesterol. Yet, CANTOS participants treated with both statins and canakinumab remain at considerable risk. Both interleukin-6 (IL-6, a central signaling cytokine) or interleukin-18 (IL-18, which like IL-1b requires the NLRP3 inflammasome for activation) may contribute to the recurrent events that occur even on canakinumab therapy, and thus represent novel targets for treating atherothrombosis.

Purpose

To assess the impact of canakinumab therapy on plasma levels of IL-6 and IL-18, and to assess the potential contributions of IL-6 and IL-18 to residual inflammatory risk both before and after treatment with canakinumab.

Methods

Plasma samples from 3,381 stable post-myocardial infarction patients assigned to active IL-1b inhibition within CANTOS underwent measurement of IL-6 and IL-18 both before and after initiation of canakinumab. All participants were followed over a 3.7 year period for major adverse cardiovascular events (MACE) and all-cause mortality.

Results

When compared to placebo, canakinumab significantly reduced IL-6 levels in a dose-dependent manner yielding placebo-subtracted median percent reductions in IL-6 at 3 months of 24.8, 36.3, and 43.2 percent for the 50mg, 150mg, and 300mg doses, respectively (all p-values <0.001). In marked contrast, no dose of canakinumab significantly altered IL-18 levels measured at 3 months (all effects less than 1 percent, all p-values >0.05). Yet, despite these differential plasma effects, both baseline and on-treatment levels of IL-6 and IL-18 associated with rates of future cardiovascular events and with all-cause mortality. For example, for MACE, each tertile increase in IL-6 measured 3 months after canakinumab initiation associated with a 42 percent increase in risk (95% CI 26–59%, P<0.0001) while each tertile increase in IL-18 measured 3 months after canakinumab initiation associated with a 15 percent increase in risk (95% CI 3–29% P=0.015). Similar effects were observed for MACE-plus, cardiovascular death, and all-cause mortality.

Conclusions

These randomized trial biomarker analyses from CANTOS demonstrate that interleukin-1b inhibition with canakinumab significantly reduces plasma levels of IL-6 but not IL-18, yet that there remains substantial residual inflammatory risk related to both IL-6 and IL-18. As such, our data support further pharmacologic development of potential anti-cytokine therapies for atherothrombosis that simultaneously inhibit IL-1b and IL-18 (such as NLRP3 inhibitors) as well as agents that directly target IL-6 signaling.

Acknowledgement/Funding

Novartis

Inhibition of Interleukin-1β by Canakinumab and Cardiovascular Outcomes in Patients With Chronic Kidney Disease

BACKGROUND

Inflammation contributes to chronic kidney disease (CKD), in part mediated through activation of interleukin (IL)-1β by the NLRP3 inflammasome within the kidney. This process also likely contributes to the accelerated atherosclerosis associated with nephropathy.

OBJECTIVES

The authors hypothesized that canakinumab, a human monoclonal antibody targeting IL-1β, might reduce cardiovascular event rates and improve renal function among post-myocardial infarction patients with CKD.

METHODS

Stable post-myocardial infarction patients with high-sensitivity C-reactive protein (hsCRP) ≥ 2mg/l were randomly allocated to placebo or to 1 of 3 doses of canakinumab (50, 150, or 300 mg) given subcutaneously once every 3 months. Participants were followed for incident myocardial infarction, stroke, hospitalization for unstable angina requiring urgent revascularization, cardiovascular death, or death from any cause over a median follow-up period of 3.7 years (maximum 5 years). All patients additionally had serial monitoring of estimated glomerular filtration rate (eGFR), creatinine, the urine albumin to creatinine ratio (uACR), and were monitored for adverse renal and urinary events.

RESULTS

Of 10,061 participants, 1,875 (18.6%) had baseline eGFR <60 ml/min/1.73 m². These moderate CKD patients had higher incidence rates for major adverse vascular events compared with those with eGFR ≥60 ml/min/1.73 m² (6.92 vs. 4.13 per 100 person-years; p < 0.0001). Random allocation to canakinumab reduced the risk of major adverse cardiovascular events among those with CKD (hazard ratio: 0.82; 95% confidence interval: 0.68 to 1.00; p = 0.05) with the largest cardiovascular benefits accruing among those who achieved on-treatment hsCRP levels below 2 mg/l measured after taking the first dose (hazard ratio: 0.68; 95% confidence interval: 0.53 to 0.86; p = 0.0015). Comparable effects were observed among those with baseline albuminuria or diabetes. Canakinumab had neither clinically meaningful benefits nor substantive harms with respect to serial measures of eGFR, creatinine, the uACR, or reported adverse renal events during trial follow-up.

CONCLUSIONS

IL-1β inhibition with canakinumab reduces major adverse cardiovascular event rates among high-risk atherosclerosis patients with CKD, particularly among those with a robust anti-inflammatory response to initial treatment. These cardiovascular benefits accrued with no adverse clinical renal events. (Canakinumab Anti-inflammatory Thrombosis Outcomes Study [CANTOS]; NCT01327846).

New strategies for the development of lipid-lowering therapies to reduce cardiovascular risk

The very high occurrence of cardiovascular events presents a major public health issue, because treatment remains suboptimal. Lowering LDL cholesterol (LDL-C) with statins or ezetimibe in combination with a statin reduces major adverse cardiovascular events. The cardiovascular risk reduction in relation to the absolute LDL-C reduction is linear for most interventions without evidence of attenuation or increase in risk at low LDL-C levels. Opportunities for innovation in dyslipidaemia treatment should address the substantial risk of lipid-associated cardiovascular events among patients optimally treated per guidelines but who cannot achieve LDL-C goals and who could benefit from additional LDL-C-lowering therapy or experience side effects of statins. Fresh approaches are needed to identify promising drug targets early and develop them efficiently. The Cardiovascular Round Table of the European Society of Cardiology (ESC) convened a workshop to discuss new lipid-lowering strategies for cardiovascular risk reduction. Opportunities to improve treatment approaches and the efficient study of new therapies were explored. Circulating biomarkers may not be fully reliable proxy indicators of the relationship between treatment effect and clinical outcome. Mendelian randomization studies may better inform development strategies and refine treatment targets before Phase 3. Trials should match the drug to appropriate lipid and patient profile, and guidelines may move towards a precision-based approach to individual patient management. Stakeholder collaboration is needed to ensure continued innovation and better international coordination of both regulatory aspects and guidelines. It should be noted that risk may also be addressed through increased attention to other risk factors such as smoking, hypertension, overweight, and inactivity.

Relationship of Interleukin-1β Blockade With Incident Gout and Serum Uric Acid Levels: Exploratory Analysis of a Randomized Controlled Trial

BACKGROUND

Although studies have shown that interleukin-1β (IL-1β) inhibitors can shorten gout attacks, whether they can prevent gout attacks is unclear.

OBJECTIVE

To examine the relationship among canakinumab, a monoclonal antibody targeting IL-1β; serum uric acid levels; and the incidence of gout attacks.

DESIGN

Secondary exploratory analysis of a randomized controlled trial. (ClinicalTrials.gov: NCT01327846).

SETTING

Many clinical sites in 39 countries.

PARTICIPANTS

10 059 patients with a prior myocardial infarction and a high-sensitivity C-reactive protein (hsCRP) level of at least 19.1 nmol/L.

INTERVENTION

Random allocation to canakinumab (50 mg, 150 mg, or 300 mg) versus placebo, administered subcutaneously every 3 months.

MEASUREMENTS

Rates of gout attacks were compared across patients with different baseline concentrations of serum uric acid (≤404.5 µmol/L, 404.6 to 535.3 µmol/L, and ≥535.4 µmol/L) and in different intervention groups in Cox proportional hazards regression models.

RESULTS

The median baseline concentration of serum uric acid was 362.9 µmol/L (interquartile range, 309.3 to 428.3 µmol/L), and median follow-up was 3.7 years. Among participants receiving placebo, incidence rates of gout attacks for serum uric acid concentrations of 404.5 µmol/L or lower, 404.6 to 535.3 µmol/L, and 535.4 µmol/L or higher were 0.28, 1.36, and 5.94, respectively, per 100 person-years. Canakinumab did not affect serum uric acid levels over time yet significantly reduced rates of gout attacks at all baseline concentrations of serum uric acid: Hazard ratios were 0.40 (95% CI, 0.22 to 0.73) for concentrations of 404.5 µmol/L or lower, 0.48 (CI, 0.31 to 0.74) for those between 404.6 and 535.3 µmol/L, and 0.45 (CI, 0.28 to 0.72) for those of 535.4 µmol/L or higher.

LIMITATION

No adjudication of gout attacks.

CONCLUSION

Quarterly canakinumab administration was associated with significantly reduced risk for gout attacks without any change in serum uric acid levels. These data have relevance for the development of agents for gout that target the IL-1β pathway of innate immunity.

PRIMARY FUNDING SOURCE

Novartis.

Anti-Inflammatory Therapy With Canakinumab for the Prevention and Management of Diabetes

BACKGROUND

Subclinical inflammation mediated in part by interleukin (IL)-1β participates in peripheral insulin resistance and impaired pancreatic insulin secretion.

OBJECTIVES

The authors tested the hypothesis that the IL-1β inhibitor canakinumab reduces incident diabetes.

METHODS

The authors randomized 10,061 patients with prior myocardial infarction and high-sensitivity C-reactive protein (hsCRP) ≥2 mg/l to placebo or canakinumab at doses of 50 mg, 150 mg, or 300 mg subcutaneously once every 3 months. The authors tested the effects of canakinumab on major cardiovascular events in patients with and without diabetes at baseline, and evaluated as a pre-specified analysis whether canakinumab would reduce the risk of adjudicated cases of new-onset type 2 diabetes among those with protocol-defined pre-diabetes at trial entry. The authors also evaluated the effect of canakinumab on fasting plasma glucose and glycosylated hemoglobin (HbA_1c) in patients with and without established diabetes.

RESULTS

Of the participants, 4,057 (40.3%) had baseline diabetes, 4,960 (49.3%) had pre-diabetes, and 1,044 (10.4%) had normal glucose levels. Among those without diabetes, increasing tertiles of hsCRP at baseline associated with an increased risk of developing diabetes during the median follow-up period of 3.7 years (incidence rates 3.2, 4.1, and 4.4 per 100 person-years; p = 0.003). Canakinumab 150 mg as compared with placebo had similar magnitude effects on major cardiovascular event rates among those with diabetes (hazard ratio [HR]: 0.85; 95% confidence interval [CI]: 0.70 to 1.03), pre-diabetes (HR: 0.86; 95% CI: 0.70 to 1.06), and normoglycemia (HR: 0.81; 95% CI: 0.49 to 1.35). Despite large reductions in hsCRP and IL-6, canakinumab did not reduce the incidence of new-onset diabetes, with rates per 100 person-years in the placebo, 50 mg, 150 mg, and 300 mg canakinumab groups of 4.2, 4.2, 4.4, and 4.1, respectively (log-rank p = 0.84). The HR comparing all canakinumab doses to placebo was 1.02 (95% CI: 0.87 to 1.19; p = 0.82). Canakinumab reduced HbA_1c during the first 6 to 9 months of treatment, but no consistent long-term benefits on HbA_1c or fasting plasma glucose were observed.

CONCLUSIONS

Although IL-1β inhibition with canakinumab had similar effects on major cardiovascular events among those with and without diabetes, treatment over a median period of 3.7 years did not reduce incident diabetes. (Canakinumab Anti-inflammatory Thrombosis Outcomes Study [CANTOS]; NCT01327846).

Relationship of C-reactive protein reduction to cardiovascular event reduction following treatment with canakinumab: a secondary analysis from the CANTOS randomised controlled trial

BACKGROUND

Canakinumab, a monoclonal antibody targeting interleukin-1β, reduces inflammation and cardiovascular event rates with no effect on lipid concentrations. However, it is uncertain which patient groups benefit the most from treatment and whether reductions in the inflammatory biomarker high-sensitivity C-reactive protein (hsCRP) correlate with clinical benefits for individual patients.

METHODS

The Canakinumab Anti-Inflammatory Thrombosis Outcomes Study (CANTOS) used computer-generated codes to randomly allocate 10 061 men and women with a history of myocardial infarction to placebo or one of three doses of canakinumab (50 mg, 150 mg, or 300 mg) given subcutaneously once every 3 months. In a prespecified secondary analysis designed to address the relationship of hsCRP reduction to event reduction in CANTOS, we evaluated the effects of canakinumab on rates of major adverse cardiovascular events, cardiovascular mortality, and all-cause mortality according to on-treatment concentrations of hsCRP. We used multivariable modelling to adjust for baseline factors associated with achieved hsCRP and multiple sensitivity analyses to address the magnitude of residual confounding. The median follow-up was 3·7 years. The trial is registered with ClinicalTrials.gov, number NCT01327846.

FINDINGS

Baseline clinical characteristics did not define patient groups with greater or lesser cardiovascular benefits when treated with canakinumab. However, trial participants allocated to canakinumab who achieved hsCRP concentrations less than 2 mg/L had a 25% reduction in major adverse cardiovascular events (multivariable adjusted hazard ratio [HR^adj]=0·75, 95% CI 0·66-0·85, p<0·0001), whereas no significant benefit was observed among those with on-treatment hsCRP concentrations of 2 mg/L or above (HR^adj=0·90, 0·79-1·02, p=0·11). For those treated with canakinumab who achieved on-treatment hsCRP concentrations less than 2 mg/L, cardiovascular mortality (HR^adj=0·69, 95% CI 0·56-0·85, p=0·0004) and all-cause mortality (HR^adj=0·69, 0·58-0·81, p<0·0001) were both reduced by 31%, whereas no significant reduction in these endpoints was observed among those treated with canakinumab who achieved hsCRP concentrations of 2 mg/L or above. Similar differential effects were found in analyses of the trial prespecified secondary cardiovascular endpoint (which additionally included hospitalisation for unstable angina requiring unplanned revascularisation) and in sensitivity analyses alternatively based on median reductions in hsCRP, on 50% or greater reductions in hsCRP, on the median percent reduction in hsCRP, in dose-specific analyses, and in analyses using a causal inference approach to estimate the effect of treatment among individuals who would achieve a targeted hsCRP concentration.

INTERPRETATION

The magnitude of hsCRP reduction following a single dose of canakinumab might provide a simple clinical method to identify individuals most likely to accrue the largest benefit from continued treatment. These data further suggest that lower is better for inflammation reduction with canakinumab.

FUNDING

Novartis Pharmaceuticals.

Effect of interleukin-1β inhibition with canakinumab on incident lung cancer in patients with atherosclerosis: exploratory results from a randomised, double-blind, placebo-controlled trial

BACKGROUND

Inflammation in the tumour microenvironment mediated by interleukin 1β is hypothesised to have a major role in cancer invasiveness, progression, and metastases. We did an additional analysis in the Canakinumab Anti-inflammatory Thrombosis Outcomes Study (CANTOS), a randomised trial of the role of interleukin-1β inhibition in atherosclerosis, with the aim of establishing whether inhibition of a major product of the Nod-like receptor protein 3 (NLRP3) inflammasome with canakinumab might alter cancer incidence.

METHODS

We did a randomised, double-blind, placebo-controlled trial of canakinumab in 10 061 patients with atherosclerosis who had had a myocardial infarction, were free of previously diagnosed cancer, and had concentrations of high-sensitivity C-reactive protein (hsCRP) of 2 mg/L or greater. To assess dose-response effects, patients were randomly assigned by computer-generated codes to three canakinumab doses (50 mg, 150 mg, and 300 mg, subcutaneously every 3 months) or placebo. Participants were followed up for incident cancer diagnoses, which were adjudicated by an oncology endpoint committee masked to drug or dose allocation. Analysis was by intention to treat. The trial is registered with ClinicalTrials.gov, NCT01327846. The trial is closed (the last patient visit was in June, 2017).

FINDINGS

Baseline concentrations of hsCRP (median 6·0 mg/L vs 4·2 mg/L; p<0·0001) and interleukin 6 (3·2 vs 2·6 ng/L; p<0·0001) were significantly higher among participants subsequently diagnosed with lung cancer than among those not diagnosed with cancer. During median follow-up of 3·7 years, compared with placebo, canakinumab was associated with dose-dependent reductions in concentrations of hsCRP of 26-41% and of interleukin 6 of 25-43% (p<0·0001 for all comparisons). Total cancer mortality (n=196) was significantly lower in the pooled canakinumab group than in the placebo group (p=0·0007 for trend across groups), but was significantly lower than placebo only in the 300 mg group individually (hazard ratio [HR] 0·49 [95% CI 0·31-0·75]; p=0·0009). Incident lung cancer (n=129) was significantly less frequent in the 150 mg (HR 0·61 [95% CI 0·39-0·97]; p=0·034) and 300 mg groups (HR 0·33 [95% CI 0·18-0·59]; p<0·0001; p<0·0001 for trend across groups). Lung cancer mortality was significantly less common in the canakinumab 300 mg group than in the placebo group (HR 0·23 [95% CI 0·10-0·54]; p=0·0002) and in the pooled canakinumab population than in the placebo group (p=0·0002 for trend across groups). Fatal infections or sepsis were significantly more common in the canakinumab groups than in the placebo group. All-cause mortality did not differ significantly between the canakinumab and placebo groups (HR 0·94 [95% CI 0·83-1·06]; p=0·31).

INTERPRETATION

Our hypothesis-generating data suggest the possibility that anti-inflammatory therapy with canakinumab targeting the interleukin-1β innate immunity pathway could significantly reduce incident lung cancer and lung cancer mortality. Replication of these data in formal settings of cancer screening and treatment is required.

FUNDING

Novartis Pharmaceuticals.

Antiinflammatory Therapy with Canakinumab for Atherosclerotic Disease

BACKGROUND

Experimental and clinical data suggest that reducing inflammation without affecting lipid levels may reduce the risk of cardiovascular disease. Yet, the inflammatory hypothesis of atherothrombosis has remained unproved.

METHODS

We conducted a randomized, double-blind trial of canakinumab, a therapeutic monoclonal antibody targeting interleukin-1β, involving 10,061 patients with previous myocardial infarction and a high-sensitivity C-reactive protein level of 2 mg or more per liter. The trial compared three doses of canakinumab (50 mg, 150 mg, and 300 mg, administered subcutaneously every 3 months) with placebo. The primary efficacy end point was nonfatal myocardial infarction, nonfatal stroke, or cardiovascular death.

RESULTS

At 48 months, the median reduction from baseline in the high-sensitivity C-reactive protein level was 26 percentage points greater in the group that received the 50-mg dose of canakinumab, 37 percentage points greater in the 150-mg group, and 41 percentage points greater in the 300-mg group than in the placebo group. Canakinumab did not reduce lipid levels from baseline. At a median follow-up of 3.7 years, the incidence rate for the primary end point was 4.50 events per 100 person-years in the placebo group, 4.11 events per 100 person-years in the 50-mg group, 3.86 events per 100 person-years in the 150-mg group, and 3.90 events per 100 person-years in the 300-mg group. The hazard ratios as compared with placebo were as follows: in the 50-mg group, 0.93 (95% confidence interval [CI], 0.80 to 1.07; P=0.30); in the 150-mg group, 0.85 (95% CI, 0.74 to 0.98; P=0.021); and in the 300-mg group, 0.86 (95% CI, 0.75 to 0.99; P=0.031). The 150-mg dose, but not the other doses, met the prespecified multiplicity-adjusted threshold for statistical significance for the primary end point and the secondary end point that additionally included hospitalization for unstable angina that led to urgent revascularization (hazard ratio vs. placebo, 0.83; 95% CI, 0.73 to 0.95; P=0.005). Canakinumab was associated with a higher incidence of fatal infection than was placebo. There was no significant difference in all-cause mortality (hazard ratio for all canakinumab doses vs. placebo, 0.94; 95% CI, 0.83 to 1.06; P=0.31).

CONCLUSIONS

Antiinflammatory therapy targeting the interleukin-1β innate immunity pathway with canakinumab at a dose of 150 mg every 3 months led to a significantly lower rate of recurrent cardiovascular events than placebo, independent of lipid-level lowering. (Funded by Novartis; CANTOS ClinicalTrials.gov number, NCT01327846 .).

Pharmacokinetic and pharmacodynamic characteristics of single-dose Canakinumab in patients with type 2 diabetes mellitus

PURPOSE

Interleukin (IL)-1β, an inflammatory molecule, contributes to the development of atherothrombosis and worsening of islet β-cell function. Canakinumab, a human monoclonal antibody, targets IL-1β-dependent inflammation and reduces the vascular inflammatory biomarker, high-sensitivity C-reactive protein (hsCRP), and other inflammatory cardiovascular biomarkers. Here, we aimed to assess the pharmacokinetic (PK) and pharmacodynamic characteristics, including the effect on hsCRP, of canakinumab in patients with type 2 diabetes mellitus (T2DM) after a 2-hour single-dose intravenous infusion.

METHODS

This multicenter, randomized, double-blind, placebo-controlled, dose-escalation study was conducted in patients with T2DM (diagnosed ≥6 months before screening) on a stable daily dose of metformin. Patients were randomly assigned to receive a single intravenous dose of canakinumab 0.03, 0.1, 0.3, 1.5, or 10 mg/kg or placebo. The study was initially designed with 1 small cohort (15 patients, 0.3 mg/kg) on a stable dose of metformin ≥500 mg/d for an initial tolerability evaluation; all other patients were on a stable dose of ≥850 mg/d of metformin. The PK profile was assessed at 0 and 2 hours and at days 2, 14, 28, 56, 84, and 168. Changes in hsCRP and hemoglobin (Hb) A1c levels were assessed at weeks 4, 8, 12, and 24.

FINDINGS

Of the 231 enrolled patients, 222 completed the study. Median hsCRP values at screening ranged from 1.8 to 3.2 mg/L, and the median daily dose of metformin ranged from 1000 to 2000 mg. Exposure to canakinumab was dose proportional. The mean half-life ranged from 17 to 26 days, and mean systemic clearance ranged from 0.094 to 0.128 mL/h/kg. Dose-related reductions in hsCRP were significantly greater with canakinumab compared with those with placebo at week 4 (-0.2 mg/L, -0.5 mg/L, -1.5 mg/L, and -1.7 mg/L with the 0.1-, 0.3-, 1.5-, and 10-mg/kg doses, respectively; all, P < 0.05). Significant reductions in hsCRP were maintained up to week 12 with the 2 highest doses of canakinumab (-0.8 mg/L with 1.5 mg/kg and -1.3 mg/L with 10 mg/kg; both, P < 0.05). A placebo-adjusted decrease in HbA1c of 0.31% at week 12 was reported with canakinumab 10 mg/kg (P = 0.038), and a reduction of 0.23% at week 4 was found with canakinumab 1.5 mg/kg (P = 0.011).

IMPLICATIONS

The findings from this study suggest that IL-1β blockade after single-dose administration of canakinumab at 1.5 and 10 mg/kg provided sustained suppression of hsCRP levels for 12 weeks in patients with T2DM. ClinicalTrials.gov identifier: NCT00900146.

Effects of Interleukin-1β Inhibition With Canakinumab on Hemoglobin A1c, Lipids, C-Reactive Protein, Interleukin-6, and Fibrinogen

Background—

To test formally the inflammatory hypothesis of atherothrombosis, an agent is needed that reduces inflammatory biomarkers such as C-reactive protein, interleukin-6, and fibrinogen but that does not have major effects on lipid pathways associated with disease progression.

Methods and Results—

We conducted a double-blind, multinational phase IIb trial of 556 men and women with well-controlled diabetes mellitus and high cardiovascular risk who were randomly allocated to subcutaneous placebo or to subcutaneous canakinumab at doses of 5, 15, 50, or 150 mg monthly and followed over 4 months. Compared with placebo, canakinumab had modest but nonsignificant effects on the change in hemoglobin A1c, glucose, and insulin levels. No effects were seen for low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, or non–high-density lipoprotein cholesterol, although triglyceride levels increased ≈10% in the 50-mg ( P =0.02) and 150-mg ( P =0.03) groups. By contrast, the median reductions in C-reactive protein at 4 months were 36.4%, 53.0%, 64.6%, and 58.7% for the 5-, 15-, 50-, and 150-mg canakinumab doses, respectively, compared with 4.7% for placebo (all P values ≤0.02). Similarly, the median reductions in interleukin-6 at 4 months across the canakinumab dose range tested were 23.9%, 32.5%, 47.9%, and 44.5%, respectively, compared with 2.9% for placebo (all P ≤0.008), and the median reductions in fibrinogen at 4 months were 4.9%, 11.7%, 18.5%, and 14.8%, respectively, compared with 0.4% for placebo (all P values ≤0.0001). Effects were observed in women and men. Clinical adverse events were similar in the canakinumab and placebo groups.

Conclusions—

Canakinumab, a human monoclonal antibody that neutralizes interleukin-1β, significantly reduces inflammation without major effect on low-density lipoprotein cholesterol or high-density lipoprotein cholesterol. These phase II trial data support the use of canakinumab as a potential therapeutic method to test directly the inflammatory hypothesis of atherosclerosis.

Clinical Trial Registration—

URL: http://www.clinicaltrials.gov . Unique identifier: NCT00900146.

Effect of anti-IL-1β antibody (canakinumab) on insulin secretion rates in impaired glucose tolerance or type 2 diabetes: results of a randomized, placebo-controlled trial

AIMS

Evaluate anti-interleukin-1β (IL-1β) antibody, canakinumab, in patients with type 2 diabetes and impaired glucose tolerance (IGT) in whom hyperglycaemia may trigger IL-1β-associated inflammation leading to suppressed insulin secretion and β-cell dysfunction.

METHODS

This 4-week, parallel-group study randomized 190 patients with type 2 diabetes 2 : 1, canakinumab versus placebo, into the following treatment arms: metformin monotherapy, metformin + sulfonylurea, metformin + sulfonylurea + thiazolidinedione or insulin ± metformin. IGT population (n = 54) was randomized 1 : 1, canakinumab versus placebo. Primary efficacy assessment was change from baseline in insulin secretion rate (ISR) relative to glucose 0-2 h.

RESULTS

Mean changes from baseline to week 4 in ISR relative to glucose at 0-2 h or other time points were not statistically significant for canakinumab versus placebo across groups. ISR (relative to glucose) at 0-0.5 h (first-phase insulin secretion) numerically favoured canakinumab versus placebo in insulin-treated patients {difference in mean change from baseline [point estimate (PE)] 3.81 pmol/min/m(2)/mmol/l; p = 0.0525} and in the IGT group (PE 3.92 pmol/min/m(2)/mmol/l; p = 0.1729). Mean change from baseline in fasting plasma glucose favoured canakinumab in the type 2 diabetes/metformin group and the IGT group; however, differences were not statistically significant. Mean change from baseline in peak insulin level and insulin AUC 0-4 h were statistically significantly higher in the canakinumab group in IGT patients. Canakinumab was well tolerated and consistent with known safety experience.

CONCLUSIONS

The trend towards improving ISR relative to glucose 0-0.5 h in patients treated with insulin supports the hypothesis that insulin secretion can be improved by blocking IL-1β.

Interleukin-1β inhibition and the prevention of recurrent cardiovascular events: rationale and design of the Canakinumab Anti-inflammatory Thrombosis Outcomes Study (CANTOS)

BACKGROUND

Inflammation contributes to all phases of the atherothrombotic process, and patients with elevated inflammatory biomarkers such as high-sensitivity C-reactive protein (hsCRP) have increased vascular risk. Yet, it remains unknown whether direct inhibition of inflammation will reduce cardiovascular event rates.

DESIGN

The CANTOS will evaluate whether interleukin-1β (IL-1β) inhibition as compared with placebo can reduce rates of recurrent myocardial infarction, stroke, and cardiovascular death among stable patients with coronary artery disease who remain at high vascular risk due to persistent elevations of hsCRP (>2 mg/L) despite contemporary secondary prevention strategies. Canakinumab is a human monoclonal antibody that selectively neutralizes IL-1β, a proinflammatory cytokine that plays multiple roles in the atherothrombotic process and that undergoes activation by the nucleotide-binding leucine-rich repeat-containing pyrin receptor 3 inflammasome, a process promoted by cholesterol crystals. Canakinumab significantly reduces systemic C-reactive protein and other inflammatory biomarker levels, is generally well tolerated, and is currently indicated for the treatment of inherited IL-1β driven inflammatory diseases such as the Muckle-Wells syndrome. In a multinational collaborative effort using an event-driven intention-to-treat protocol, CANTOS will randomly allocate 17,200 stable postmyocardial infarction patients with persistent elevation of hsCRP to either placebo or to canakinumab at doses of 50, 150, or 300 mg every 3 months, administered subcutaneously. All participants will be followed up over an estimated period of up to 4 years for the trial primary end point (nonfatal myocardial infarction, nonfatal stroke, cardiovascular death) as well as for other vascular events, total mortality, adverse events, and specific clinical end points associated with inflammation including new onset diabetes, venous thrombosis, and atrial fibrillation.

SUMMARY

If positive, CANTOS would confirm the inflammatory hypothesis of atherothrombosis and provide a novel cytokine-based therapy for the secondary prevention of cardiovascular disease and new-onset diabetes.

Inhibition of CETP by Torcetrapib Attenuates the Atherogenicity of Postprandial TG-Rich Lipoproteins in Type IIB Hyperlipidemia

Objective— The purpose of this study was to evaluate the impact of torcetrapib on atherogenic TG-rich lipoprotein subfractions in the postprandial phase in Type IIB hyperlipidemia.

Methods and Results— The quantitative and qualitative features of the postprandial profile of TG-rich lipoproteins were determined at baseline, after treatment for 6 weeks with 10 mg/d atorvastatin, and subsequently with an atorvastatin/torcetrapib combination (10/60 mg/d) in Type IIB patients (n=18). After ingestion of a standardized mixed meal, TG-rich lipoprotein subfractions were evaluated over 8 hours after each experimental period. On a background of atorvastatin, torcetrapib significantly attenuated the incremental postprandial area under the curve (iAUC 0 to 8 hours) for VLDL-1 (−40%), and the AUC 0 to 8 hours for VLDL-2 (-53%), with minor effect on chylomicron iAUC (−24%); concomitantly, the CE/TG ratio in both VLDL-1 and VLDL-2 was significantly reduced (−27% to −42%). Such reduction was attributable to torcetrapib-mediated attenuation of postprandial CE transfer to Chylomicrons (−17%) and VLDL-1 (−33%). Marked reduction in postprandial VLDL-1 levels was associated with apoE enrichment.

Conclusions— On a background of atorvastatin, torcetrapib attenuated the quantitative and qualitative features of the atherogenic postprandial profile of chylomicrons, VLDL-1 and VLDL-2. Such changes reflect the sum of torcetrapib-mediated effects on TG-rich lipoprotein production, intravascular remodeling, and catabolism.

Hepatic lipase and HDL metabolism

Hepatic lipase is a lipolytic enzyme that has been suggested to have a role in HDL metabolism. Evidence suggests that HDL-cholesterol level is at least partly regulated by hepatic lipase level. Recent studies have shown that hepatic lipase not only hydrolyzes triglyceride and phospholipid in HDL, but also stimulates HDL cholesterol ester uptake by hepatocytes. Therefore, hepatic lipase, together with lipid transfer proteins, determines both HDL-cholesterol level and its function in reverse cholesterol transport. These conclusions are based on observations from in-vitro model substrate studies, cell culture studies, transgenic animal studies, and clinical studies. At present time, it is not known whether hepatic lipase action increases or decreases risk of developing atherosclerosis.

Biosynthetic conversion of phosphatidylglycerol to sn-1:sn-1' bis(monoacylglycerol) phosphate in a macrophage-like cell line

Bis(monoacylglycerol) phosphate has a unique stereoconfiguration of sn-glycero-1-phospho-1'-sn-glycerol and is synthesized from exogenous phosphatidylglycerol by macrophages. Previous work by our laboratory showed that the macrophage-like cell line RAW 264.7 synthesizes sn-glycero-1-phospho-1'-sn-glycerol bis(monoacylglycerol) phosphate. Here we describe studies using RAW 264.7 cells that examine the biosynthetic pathway by which bis(monoacylglycerol) phosphate is formed. Experiments were conducted using precursors that were specifically radiolabeled on the glycerol backbone in order to examine the stereoconfiguration of the intermediates and products formed in intact RAW 264.7 cells. The results of our studies indicate that a complex series of reactions are involved in the synthesis of bis(monoacylglycerol) phosphate. In this proposed pathway phosphatidylglycerol is hydrolyzed to form 1-acyllysophosphatidylglycerol which is then acylated on the headgroup glycerol to form the sn-glycero-1-phospho-1'-sn-glycerol enantiomer of bis(monoacylglycerol) phosphate. The sn-glycero-1-phospho-1'-sn-glycerol enantiomer of bis(monoacylglycerol) phosphate is then thought to undergo a stereoconversion that proceeds via the required removal of the acyl group at the sn-1 position. The resulting sn-glycero-1-phospho-1'-sn-glycerol enantiomer of lysophosphatidylglycerol with the acyl moiety on the original headgroup glycerol is then acylated to form sn-glycero-1-phospho-1'-sn-glycerol bis(monoacylglycerol) phosphate.

Lipoprotein lipase domain function

Human lipoprotein lipase (LPL) monomer consists of two domains, a larger NH2-terminal domain that contains catalytic residues and a smaller COOH-terminal domain that modulates substrate specificity and is a major determinant of heparin binding. Analyses of NH2-terminal domain function were performed after site-directed mutagenesis of the putative active-site serine residue, while COOH-terminal domain function was assessed following reaction with a monoclonal antibody. The native enzyme and mutant LPL in which serine 132 was replaced with alanine, cysteine, or glycine were transiently expressed in COS-7 cells. Mutant proteins were synthesized and secreted at levels comparable to native LPL; however, none of the mutants retained enzymatic activity. The mutant with alanine replacing serine 132 was purified and shown to be inactive with both esterase and lipase substrates; however, binding to a 1,2-didodecanoyl-sn-glycero-3-phosphatidylcholine monolayer was comparable to native LPL. These results are consistent with a catalytic, and not a lipid binding, role for serine 132. To investigate the function of the smaller COOH-terminal domain, LPL lipolytic and esterolytic activities as well as heparin binding properties were determined after reaction with a monoclonal antibody specific for this domain. Lipolytic activity was inhibited by the monoclonal antibody, whereas esterolytic activity was only marginally affected, indicating that the LPL COOH-terminal domain is required for lipolysis, perhaps by promoting interaction with insoluble substrates. Also, the affinity of antibody-reacted LPL for heparin was not significantly different from that of LPL alone, suggesting that (i) the heparin-binding site is physically distinct from the COOH-terminal domain region required for lipolysis and (ii) binding of antibody did not cause dimer dissociation. A model is proposed for the two LPL domains fulfilling different roles in the lipolytic process.

Regulation of rat hepatic lipase by the composition of monomolecular films of lipid

The regulation of hepatic lipase (HL) by the lipid composition of monomolecular substrate films was examined using a monolayer technique at constant surface pressure. HL-catalyzed hydrolysis of triacylglycerol, a poor substrate for HL in pure monomolecular films, was activated by diradylglycerol and its phosphorylated derivatives in mixed films containing 10 mol % triacylglycerol. When triacylglycerol was progressively diluted with dialkylglycerol, triacylglycerol hydrolysis by HL was maximal between 90 and 98 mol % dialkylglycerol. The best activators, dialkylphosphatidic acid and dialkylphosphatidylethanolamine, increased triacylglycerol hydrolysis 13-14-fold, and the enhancement of HL-catalyzed triacylglycerol hydrolysis by the activator lipids was inversely related to the average mean molecular area of the mixed films. The hydrolysis of 5 mol % triacylglycerol in mixed films that also contained phosphatidylcholine and 0-20 mol % cholesterol was inhibited approximately 80% when the concentration of cholesterol was 10-13 mol %. Interestingly, between 15 and 17 mol % cholesterol the hydrolysis rate was restored to about 50% of the uninhibited rate, but at 20 mol % cholesterol this value decreased back to 80% inhibition of hydrolysis. The hydrolysis of phosphatidylethanolamine in mixed films with 0-20 mol % cholesterol decreased approximately 30% in films containing 10-12 mol % cholesterol. However, at 15 mol % cholesterol the hydrolysis rate was restored to the same level observed for a pure phosphatidylethanolamine film. This enhancement of HL activity occurred at about the same cholesterol concentration as the restoration of triacylglycerol hydrolysis observed for the triacylglycerol/phosphatidylcholine/cholesterol films.(ABSTRACT TRUNCATED AT 250 WORDS)

Action of lysosomal phospholipase A1 on bis(monoacylglycerol)phosphate

Bis(monoacylglycerol)phosphate (BMP) in macrophages is known to rapidly turn over its acyl moiety(s) located at primary positions of the glycerols, yet the glycerols and phosphate remain stable within the BMP molecule. Here we examine whether the phospholipase A1 isolated from rat-liver lysosomes is capable of deacylating BMP. By comparison with the precursor of BMP, phosphatidylglycerol, BMP is a very poor substrate for the phospholipase A1. We conclude, therefore, that a direct deacylation of the acyl groups at the primary alcohol level of the glycerol probably does not occur, but postulate that transacylations may occur to account for the removal of the acyl moiety.

Role of apolipoprotein E in hepatic lipase catalyzed hydrolysis of phospholipid in high-density lipoproteins

We reported earlier that hepatic lipase (HL)-catalyzed hydrolysis of phospholipid monolayers is activated by apolipoprotein (apo) E [Thuren et al. (1991b) J. Biol. Chem. 266, 4853-4861]. On the basis of these studies, it was postulated that apoE-rich high-density lipoproteins (HDL) were preferred substrates for HL. In the present study, we tested this hypothesis, as well as further characterizing the activation of HL hydrolysis of phospholipid by apoE. The apoE-rich HDL, referred to as HDL-I, were isolated by heparin-Sepharose chromatography, and the phospholipid hydrolysis by HL was compared to an apoE-poor HDL, designated HDL-II. The hydrolysis of HDL-I phosphatidylcholine was approximately 3-fold higher than HDL-II, supporting the hypothesis that HL preferably hydrolyzes the phospholipids in apoE-rich HDL. In order to gain additional insight into the nature of the activation, we used phospholipid monolayers as model systems. Comparison of the ability of the two thrombolytic fragments of apoE (22 kDa, residues 1-191; 12 kDa, residues 192-299) revealed that only the 12-kDa fragment was capable of activating the hydrolysis of phospholipid by HL (1.75-fold). However, activation was less than with the intact protein (2.8-fold for apoE3), suggesting that the intact protein was required for full activation. The fact that the 12-kDa fragment, which represents a major lipid region of the protein, did activate HL suggests that activation occurs at the lipid-water interface.(ABSTRACT TRUNCATED AT 250 WORDS)

A continuous fluorometric assay for phospholipase C from Clostridium perfringens

A fluorescent assay for Clostridium perfringens phospholipase C is described using 1-palmitoyl-2-[6(pyren-1-yl)hexanoyl]-sn-glycero-3- phospho-N-(trinitrophenyl)aminoethanol (PPHTE) as the substrate. This method is based on the decrease of the quenching of pyrene monomer fluorescence when phospholipase C hydrolyzes PPHTE into pyrenediglyceride and phospho(trinitrophenyl)-aminoethanol. The hydrolysis of egg lecithin/PPHTE (25:1 molar ratio) substrate by C. perfringens phospholipase C was linear with time for at least 2 min. Optimal conditions for the hydrolysis by phospholipase C were 50 mM Tris-HCl pH 7.0-30 mM CaCl2/63 microM egg lecithin and 2.5 microM PPHTE. The Km and Vmax values for the hydrolysis of egg lecithin/PPHTE vesicles were 28 microM and 280 pmol min-1, respectively. The detection limit of the assay was 40 microU of C. perfringens phospholipase C. When diglyceride was included into egg lecithin/PPHTE vesicles up to 30 mol% the reaction velocity increased 13-fold. Higher molar proportions of diglyceride were inhibitory. When the hydrolysis of mixtures of different naturally occurring phospholipids and PPHTE was studied egg lecithin was found to be the best substrate. When dipalmitoylphospholipids with different polar head groups were used the reaction velocity decreased in the order egg lecithin greater than or equal to dipalmitoylphosphatidylserine greater than dipalmitoylphosphatidic acid greater than dipalmitoylphosphatidylcholine greater than dipalmitoylphosphatidylglycerol.

Activation of hepatic lipase catalyzed phosphatidylcholine hydrolysis by apolipoprotein E

The effect of apolipoproteins A-I, A-II, C-II, C-III and E on the hydrolysis of phosphatidylcholine and triacylglycerol by hepatic lipase was studied. Hepatic lipase catalyzed phospholipid hydrolysis was 1.8-fold activated by apolipoprotein E while the other apolipoproteins did not affect the hydrolysis by this enzyme. Triacylglycerol hydrolysis by hepatic lipase was 1.5-fold activated by apolipoprotein E while the other apolipoproteins inhibited hepatic lipase. These results suggest that lipoproteins containing apolipoprotein E may be preferred substrates for hepatic lipase.

Glycerol reorientation during the conversion of phosphatidylglycerol to bis(monoacylglycerol)phosphate in macrophage-like RAW 264.7 cells

Bis(monoacylglycero)phosphate (BMP) has the unique stereoconfiguration of 3-acyl-sn-glycero-1-phosphoryl-1'-sn-[3'-acylglycerol] (Brotherus, J., Renkonen, O., Herrmann, J., and Fischer, W. (1974) Chem. Phys. Lipids 13, 178-182) which differs from other known mammalian phospholipids that have the sn-glycero-3-phosphoryl configuration. This stereochemistry may contribute to its physiologic function. Here we describe studies using the macrophage-like cell line RAW 264.7 designed to determined how this unique stereoconfiguration occurs. These studies show that the stereoconfiguration of BMP produced from exogenous phosphatidylglycerol (PG) by RAW 264.7 cells has the expected stereoconfiguration of 3-acyl-sn-glycero-1-phosphoryl-1'-sn-[3'-acylglycerol]. Experiments using diacyl-sn-[2-3H]glycero-3-phosphoryl-sn-1'-[2-3H]glycerol demonstrate that this unique stereoconfiguration is not produced due to an oxidation/reduction mechanism involving the sn-2-glycerol carbon. When dioleoyl-sn-[1-14C]glycero-3-phosphoryl-rac-glycerol was converted to 14C-labeled BMP, the 14C label was found esterified to the phosphate moiety. These results suggest that a stereospecific enzyme is capable of reorienting the radiolabeled glycerol backbone of this PG substrate, effectively changing the stereochemistry of the lipid. We also show that this enzyme is stereoselective with regard to the base glycerol moiety of the substrate PG used. Finally, we propose a new pathway for the synthesis of BMP from PG.

Hydrolysis of neutral lipid substrates by rat hepatic lipase

Rat hepatic lipase, an enzyme whose involvement in the catabolism of lipoproteins remains poorly defined, has both neutral lipid and phospholipid hydrolyzing activity. We determined the substrate specificity of hepatic lipase for 1-oleoyl-sn-glycerol, 1,2-dioleoyl-sn-glycerol, and 1,3-dioleoyl-sn-glycerol in the Triton X-100 mixed micellar state, and compared these results to those obtained previously in our laboratory for the phospholipid substrates phosphatidic acid (PA), phosphatidylethanolamine (PE), and phosphatidylcholine (PC). Vmax values were determined by diluting the substrate concentration in the surface of the micelle by Triton X-100. The Vmax values obtained were 144 mumol/min/mg for 1-oleoyl-sn-glycerol, 163 mumol/min/mg for 1,2-dioleoyl-sn-glycerol, and 145 mumol/min/mg for 1,3-dioleoyl-sn-glycerol. These values were higher than those obtained earlier for phospholipids which were 67 mumol/min/mg for PA, 50 mumol/min/mg for PE and 4 mumol/min/mg for PC. In addition, the mole fraction of lipid substrate at half maximal velocity (K) in the surface dilution plot was lower for the neutral lipid substrates as compared to those obtained for the phospholipid substrates. When the hydrolysis of 1,3-dioleoyl-sn-glycerol mixed micelles was studied as a function of time, cleavage at the sn-1 and sn-3 positions occurred at the same rate, suggesting that hepatic lipase is not stereoselective with respect to 1,3-diacyl-sn-glycerol substrates.(ABSTRACT TRUNCATED AT 250 WORDS)

Hepatic lipase hydrolysis of lipid monolayers. Regulation by apolipoproteins

A monolayer technique was used to study the substrate specificity of hepatic lipase (HL) and the effect of surface pressure and apolipoproteins on hydrolysis of lipid monolayers by this enzyme. HL hydrolyzed readily phosphatidylethanolamine monolayers. Pure trioctanoylglycerol was found to be a poor substrate but when progressively diluted with nonhydrolyzable 1,2-didodecanoylphosphatidylcholine hydrolysis of triacylglycerol by HL reached maximum at a molar ratio of 1:1 triacylglycerol to phosphatidylcholine. The activation of triacylglycerol hydrolysis was not due to altered penetration of HL. The surface pressure optimum of HL for the hydrolysis of phosphatidylethanolamine monolayers was broad between 12.5 and 25 mN/m. When apolipoprotein E was injected beneath the monolayer of phosphatidylethanolamine prior to enzyme addition, a 3-fold activation of HL was observed at surface pressures equal to or below 15 mN/m. Below surface pressures of 20 mN/m apolipoprotein E did not affect the penetration of HL into the lipid-water interface. Apolipoprotein E slightly activated the hydrolysis of triacylglycerol by HL at 10 mN/m. At a high surface pressure of 25 mN/m all apolipoproteins tested (apolipoproteins A-I, A-II, C-I, C-II, C-III, and E) inhibited the penetration into and HL activity on phosphatidylethanolamine At 18.5 mN/m all apolipoproteins except apolipoprotein E inhibited the hydrolysis of triacylglycerol in the triacylglycerol:phosphatidylcholine mixed film. Based on these results we present a hypothesis that phospholipid present in apolipoprotein E-rich high density lipoprotein-1 and triacylglycerol in intermediate density lipoprotein would be preferred substrates for HL.

Hydrolysis of lipid mixtures by rat hepatic lipase

The hydrolysis of phospholipid mixtures by purified rat hepatic lipase, also known as hepatic triglyceride lipase, was studied in a Triton X-100/lipid mixed micellar system. Column chromatography of the mixed micelles showed elution of Triton X-100 and binary lipid mixtures of phosphatidic acid, phosphatidylcholine, phosphatidylethanolamine and phosphatidylserine as a single peak. This indicated that the mixed micelles were homogenous and contained all components in the designated molar ratios. The molar ratio of Triton X-100 to lipid was kept constant at 4 to 1. Labeling one lipid with 3H and the other lipid with 14C enabled us to determine the hydrolysis of both components of these binary lipid mixed micelles. We found that the hydrolysis of phosphatidylcholine was activated by the inclusion of small amounts of phosphatidic acid (2.5-fold), phosphatidylethanolamine (1.5-fold) or phosphatidylserine (1.4-fold). The maximal activation of phosphatidylcholine hydrolysis was observed when 5 mol% of phosphatidylethanolamine, 7.5 mol% phosphatidic acid or 5 mol% phosphatidylserine was added to Triton X-100 mixed micelles. The hydrolysis of phosphatidic acid was activated 30%, and that of phosphatidylserine was inhibited 30% when the molar proportion of phosphatidylcholine was less than 50 mol%. The hydrolysis of phosphatidylethanolamine was slightly activated when the mol% of phosphatidylcholine was below 5. The hydrolysis of phosphatidylserine was inhibited by phosphatidylethanolamine when the mol% of the latter was 50 or less whereas phosphatidylethanolamine hydrolysis was not affected by phosphatidylserine. Under the conditions used sphingomyelin and cholesterol did not have a significant effect on the hydrolysis of the phospholipids studied. In agreement with our previous study (Kucera et al. (1988) J. Biol. Chem. 263, 1920-1928) these studies show that the phospholipid polar head group is an important factor which influences the action of hepatic lipase and that the interfacial properties of the substrate play a role in the expression of the activity of this enzyme. The molar ratios of phosphatidic acid, phosphatidylethanolamine and phosphatidylserine which activated phosphatidylcholine hydrolysis correspond closely to the molar ratios of these lipids found in the surface lipid film of lipoproteins e.g., high density lipoproteins.(ABSTRACT TRUNCATED AT 400 WORDS)

Increased serum phospholipase A2 activity in schizophrenia: a replication study

Phospholipase A2 (PLA2) is a key enzyme in the metabolism of phospholipids. Because a disordered phospholipid metabolism has frequently been reported in schizophrenia, we investigated the PLA2 activity in serum from 14 drug-free paranoid schizophrenic patients, 20 healthy controls, and 8 nonschizophrenic psychiatric patients. Schizophrenics showed significantly higher PLA2 activity than healthy controls and nonschizophrenic patients. The increment in schizophrenics was not due to increased concentration of pancreatic secretory PLA2, as concerning pancreatic PLA2 no differences were found among the 3 proband groups. The present findings confirm the results of our previous study and suggest that increased serum PLA2 activity might reflect an increment in the intracellular enzyme activity in schizophrenia. In the brain the activation of intracellular PLA2 results in changes in neuronal activity due to alterations in receptor sensitivity and in neurotransmitter metabolism. The possibility that such PLA2-induced mechanisms are involved in the pathogenesis of schizophrenia should be investigated in further experiments.

Hydrolysis of supported pyrenephospholipid monolayers by phospholipase A2

Hydrolysis by pancreatic and snake venom (Crotalus atrox) phospholipase A2 of fluorescent monolayers of pyrene-labelled phosphatidylglycerol on solid support was studied. We used a fluorescence microscope equipped with video camera, video recorder and an image analyzer to monitor changes in fluorescence. Decrease in pyrene excimer emission was evident when pyrene phosphatidylglycerol monolayers transferred onto quartz glass slides (at a surface pressure of 15 mN m-1) were subjected to enzymatic hydrolysis. Snake venom phospholipase A2 could hydrolyze the monolayers almost completely while pancreatic phospholipase A2 could cause only 50% decrease in fluorescence intensity. EDTA totally inhibited the action of both A2 phospholipases. When monolayers were transferred onto solid supports at a surface pressure of 31 mN m-1 C. atrox phospholipase A2 could still exert activity whereas porcine pancreatic phospholipase A2 was inactive.

Pancreatic and catalytic phospholipase A2 in relation to pregnancy, labor and fetal outcome

The serum pancreatic and catalytic phospholipase A2 level (PLA2) in human pregnancy is normal, and the increase of pancreatic enzyme before delivery is small. In patients with pruritus associated with obstetric hepatosis maternal serum had a slightly lower pancreatic PLA2 level if the cholic acid level was higher. Umbilical cord blood has twice as much pancreatic PLA2 as maternal blood. If the enzyme concentration was very high, pregnancies were postterm and the newborns had low Apgar scores. Amniotic fluid contains these enzymes, but there is no change in the enzymes during the course of pregnancy. The amount of pancreatic enzyme was not reflected in catalytic activity. A very high PLA2 activity was observed in 1 patient with suspected amniotic fluid embolism and in the meconium, but low in the first urine of neonates.

Human pancreatic phospholipase A2 in acute necrotizing pancreatitis

The activity and the content of phospholipase A2 (PLA2), a potential 'toxin' in pancreatitis, were determined separately by respective methods in pancreatic tissue resected from 22 patients treated for acute necrotizing pancreatitis. Correspondent enzyme assays were analyzed in the serum of 6 last patients. In cases with total necrosis in the tissue resected, the pancreatic PLA2 activity, but not the content, was almost totally lost. Serum PLA2 activity slightly decreased within the extension of pancreatic necrosis. The timing of sampling, number of positive Ranson signs or the course of the disease had no influence on the tissue PLA2 results. Serum PLA2 activity showed a correlation with tissue PLA2 activity.

Phospholipase A2 assay using an intramolecularly quenched pyrene-labeled phospholipid analog as a substrate

A phospholipid analog 1-palmitoyl-2-6(pyren-1-yl)hexanoyl-sn-glycero-3-phospho-N- (trinitrophenyl)aminoethanol (PPHTE) in which pyrene fluorescence is intramolecularly quenched by the trinitrophenyl group was used as a substrate for pancreatic phospholipase A2. Upon phospholipase A2 catalyzed hydrolysis of this molecule pyrene monomer fluorescence emission intensity increased as a result of the transfer of the pyrene fatty acid to the aqueous phase. Optimal conditions for phospholipase A2 hydrolysis of PPHTE were similar to those observed earlier for other pyrenephospholipids (T. Thuren, J. A. Virtanen, R. Verger, and P. K. J. Kinnunen (1987) Biochim. Biophys. Acta 917, 411-417). Although differential scanning calorimetry revealed no thermal phase transitions for PPHTE between +5 and +60 degrees C the Arrhenius plot of the enzymatic hydrolysis of the lipid showed a discontinuity at 30 degrees C. The molecular origin of this discontinuity remains at present unknown. To study the effects of dimyristoylphosphatidylcholine (DMPC) phase transition at 23.9 degrees C on phospholipase A2 reaction PPHTE was mixed with DMPC in a molar ratio of 1:200 in small unilamellar vesicles. The hydrolysis of DMPC-PPHTE vesicles was measured by following the increase in pyrene monomer fluorescence emission due to phospholipase A2 action on PPHTE. Below the phase transition of DMPC the enzymatic reaction exhibited a hyperbolic behavior. At the transition as well as at slightly higher temperatures a lag period was observed. The longest lag period was approximately 20 min. Above 26 degrees C no lag time could be observed. However, the reaction rates were slower than below the phase transition temperature.(ABSTRACT TRUNCATED AT 250 WORDS)

A model for the molecular mechanism of interfacial activation of phospholipase A2 supporting the substrate theory

Changes occurring in the activity of porcine pancreatic phospholipase A2 upon formation of mixed micelles of sodium cholate and the fluorescent phosphocholines 1,2-di[6-(pyren-1-yl)butanoyl]-sn-glycero-3-phosphocholine or 1-[6-(pyren-1-yl)butanoyl]-2-[6-(pyren-1-yl)hexanoyl]- sn-glycero-3- phosphocholine were studied. A 2-fold enhancement was observed in the activity of phospholipase A2 towards both pyrene phospholipids upon exceeding the critical micellar concentration of the system. Changes in the pyrene excimer/monomer fluorescence emission intensity ratio coincide with the enhancement of phospholipase A2 activity at the critical micellar concentration. Due to the different effects of micellization on the alignment of the pyrene in the two fluorescent probes conformational changes could be assessed. A model describing possible conformations of these pyrene phospholipid molecules below and above the critical micellar concentration is presented and correlated with the interfacial activation of phospholipase A2.

Control of the action of phospholipases A by "vertical compression" of the substrate monolayer

Monolayers of rac-1,2-didodecanoyl-sn-glycero-3-phosphoglycerol at an air-water interface were "vertically compressed" by substituting an alkylated glass plate for air while maintaining a constant surface pressure of 15 mN m-1. At this surface pressure the overlaying of the lipid film by the alkylated surface resulted in an average increase of 16 A2/molecule in the mean molecular area of those phospholipid molecules residing at the interface between water and the alkylated glass. Subsequently, the activities of phospholipases A1 and A2 toward the monolayers were measured both in the presence and in the absence of the support. While phospholipase A1 activity was increased 4-fold by the support, the activity of phospholipase A2 was reduced to 15% of the activity measured in the absence of the alkylated surface. These findings indicate that such a "vertical compression" of the monolayer is likely to induce a conformational change in the phospholipid molecules, which in turn would cause the above reciprocal changes in the activities of phospholipases A1 and A2. A molecular model accounting to these findings is presented.

Triggering of the activity of phospholipase A2 by an electric field

In this paper we show that the action of phospholipase A2 can be triggered by applying an electric field across a 1,2-didodecanoyl-sn-3-phosphoglycerol monolayer residing between an alkylated silicon surface and water. When the silicon wafer served as a cathode, rapid activation of porcine pancreatic phospholipase was observed and did depend on the magnitude of the applied potential. The degree of activation was different for the pancreatic phospholipase A2 and snake and bee venom enzymes. Maximally, a 7-fold activation of pancreatic phospholipase A2 was observed when the applied potential was 75 V. The effective field over the lipid film could be estimated to be approximately 25-175 mV, i.e., in the range of membrane potentials found in cells. On the basis of these results, we suggest that changes in membrane potential might be an important factor in the regulation of the action of intracellular phospholipases A2 in vivo.