Sutimlimab in Cold Agglutinin Disease

BACKGROUND

Cold agglutinin disease is a rare autoimmune hemolytic anemia characterized by hemolysis that is caused by activation of the classic complement pathway. Sutimlimab, a humanized monoclonal antibody, selectively targets the C1s protein, a C1 complex serine protease responsible for activating this pathway.

METHODS

We conducted a 26-week multicenter, open-label, single-group study to assess the efficacy and safety of intravenous sutimlimab in patients with cold agglutinin disease and a recent history of transfusion. The composite primary end point was a normalization of the hemoglobin level to 12 g or more per deciliter or an increase in the hemoglobin level of 2 g or more per deciliter from baseline, without red-cell transfusion or medications prohibited by the protocol.

RESULTS

A total of 24 patients were enrolled and received at least one dose of sutimlimab; 13 patients (54%) met the criteria for the composite primary end point. The least-squares mean increase in hemoglobin level was 2.6 g per deciliter at the time of treatment assessment (weeks 23, 25, and 26). A mean hemoglobin level of more than 11 g per deciliter was maintained in patients from week 3 through the end of the study period. The mean bilirubin levels normalized by week 3. A total of 17 patients (71%) did not receive a transfusion from week 5 through week 26. Clinically meaningful reductions in fatigue were observed by week 1 and were maintained throughout the study. Activity in the classic complement pathway was rapidly inhibited, as assessed by a functional assay. Increased hemoglobin levels, reduced bilirubin levels, and reduced fatigue coincided with inhibition of the classic complement pathway. At least one adverse event occurred during the treatment period in 22 patients (92%). Seven patients (29%) had at least one serious adverse event, none of which were determined by the investigators to be related to sutimlimab. No meningococcal infections occurred.

CONCLUSIONS

In patients with cold agglutinin disease who received sutimlimab, selective upstream inhibition of activity in the classic complement pathway rapidly halted hemolysis, increased hemoglobin levels, and reduced fatigue. (Funded by Sanofi; CARDINAL ClinicalTrials.gov number, NCT03347396.).

BIVV001 Fusion Protein as Factor VIII Replacement Therapy for Hemophilia A

BACKGROUND

Factor VIII replacement products have improved the care of patients with hemophilia A, but the short half-life of these products affects the patients' quality of life. The half-life of recombinant factor VIII ranges from 15 to 19 hours because of the von Willebrand factor chaperone effect. BIVV001 (rFVIIIFc-VWF-XTEN) is a novel fusion protein designed to overcome this half-life ceiling and maintain high sustained factor VIII activity levels. Data are lacking on the safety and pharmacokinetics of single-dose BIVV001.

METHODS

In this phase 1-2a open-label trial, we consecutively assigned 16 previously treated men (18 to 65 years of age) with severe hemophilia A (factor VIII activity, <1%) to receive a single intravenous injection of recombinant factor VIII at a dose of 25 IU per kilogram of body weight (lower-dose group) or 65 IU per kilogram (higher-dose group). This injection was followed by a washout period of at least 3 days. The patients then received a single intravenous injection of BIVV001 at the same corresponding dose of either 25 IU or 65 IU per kilogram. Adverse events and pharmacokinetic measurements were assessed.

RESULTS

No inhibitors to factor VIII were detected and no hypersensitivity or anaphylaxis events were reported up to 28 days after the injection of single-dose BIVV001. The geometric mean half-life of BIVV001 was three to four times as long as that of recombinant factor VIII (37.6 hours vs. 9.1 hours in the lower-dose group and 42.5 vs. 13.2 hours in the higher-dose group); the area under the curve (AUC) for product exposure was six to seven times as great in the two dose groups (4470 hours vs. 638 hours × IU per deciliter in the lower-dose group and 12,800 hours vs. 1960 hours × IU per deciliter in the higher-dose group). After the injection of BIVV001 in the higher-dose group, the mean factor VIII level was in the normal range (≥51%) for 4 days and 17% at day 7, which suggested the possibility of a weekly interval between treatments.

CONCLUSIONS

In a small, early-phase study involving men with severe hemophilia A, a single intravenous injection of BIVV001 resulted in high sustained factor VIII activity levels, with a half-life that was up to four times the half-life associated with recombinant factor VIII, an increase that could signal a new class of factor VIII replacement therapy with a weekly treatment interval. No safety concerns were reported during the 28-day period after administration. (Funded by Sanofi and Sobi; ClinicalTrials.gov number, NCT03205163.).

Long-term safety and sustained efficacy for up to 5 years of treatment with recombinant factor IX Fc fusion protein in subjects with haemophilia B: Results from the B-YOND extension study

INTRODUCTION

Recombinant factor IX Fc fusion protein (rFIXFc) has demonstrated efficacy for treatment of haemophilia B in the Phase 3 B-LONG and Kids B-LONG studies. However, long-term rFIXFc safety and efficacy data have not yet been reported.

AIM

To report long-term rFIXFc safety and efficacy in subjects with haemophilia B.

METHODS

B-YOND (NCT01425723) was an open-label extension for eligibl previously treated subjects who completed B-LONG or Kids B-LONG. Subjects received ≥1 treatment regimen: weekly prophylaxis (WP), individualized interval prophylaxis (IP), modified prophylaxis or episodic treatment. Subjects could switch regimens at any time. The primary endpoint was inhibitor development.

RESULTS

Ninety-three subjects from B-LONG and 27 from Kids B-LONG (aged 3-63 years) were enrolled. Most subjects received WP (B-LONG: n = 51; Kids B-LONG: n = 23). For subjects from B-LONG, median (range) treatment duration was 4.0 (0.3-5.4) years and median (range) number of exposure days (EDs) was 146 (8-462) EDs. Corresponding values for paediatric subjects were 2.6 (0.2-3.9) years and 132 (50-256) EDs. No inhibitors were observed (0 per 1000 subject-years; 95% confidence interval, 0-8.9) and the overall rFIXFc safety profile was consistent with prior studies. Annualized bleed rates remained low and extended-dosing intervals were maintained for most subjects. Median dosing interval for the IP group was approximately 14 days for adults and adolescents (n = 31) and 10 days for paediatric subjects (n = 5).

CONCLUSIONS

B-YOND results confirm the long-term (up to 5 years, with cumulative duration up to 6.5 years) well-characterized safety and efficacy of rFIXFc treatment for haemophilia B.

Recombinant factor VIII Fc fusion protein for the treatment of severe haemophilia A: Final results from the ASPIRE extension study

Introduction

The efficacy and safety of recombinant factor VIII Fc fusion protein (rFVIIIFc) as an extended half‐life treatment for severe haemophilia A were demonstrated in the Phase 3 A‐LONG and Kids A‐LONG studies. Eligible subjects who completed A‐LONG and Kids A‐LONG could enrol in ASPIRE (NCT01454739), an open‐label extension study.

Aim

To report the long‐term safety and efficacy of rFVIIIFc in subjects with severe haemophilia A who enrolled in ASPIRE.

Methods

Previously treated subjects received one or more of the following regimens: individualized prophylaxis (IP), weekly prophylaxis, modified prophylaxis or episodic treatment. Subjects could switch treatment regimen at any time. The primary endpoint was inhibitor development.

Results

A total of 150 subjects from A‐LONG and 61 subjects from Kids A‐LONG enrolled in ASPIRE. Most subjects received the IP regimen (A‐LONG: n = 110; Kids A‐LONG: n = 59). Median (range) treatment duration in ASPIRE for subjects from A‐LONG and Kids A‐LONG was 3.9 (0.1‐5.3) years and 3.2 (0.3‐3.9) years, respectively. No inhibitors were observed (0 per 1000 subject‐years; 95% confidence interval, 0‐5.2) and the overall rFVIIIFc safety profile was consistent with prior studies. For subjects on the IP regimen, annualized bleed rates (ABR) remained low (median overall ABR for adults and adolescents was <1.0) and extended‐dosing intervals were maintained (median of 3.5 days) for the majority of subjects in ASPIRE.

Conclusion

ASPIRE results, which include up to 5 years of follow‐up data, confirm earlier reports on the consistent and well‐characterized safety and efficacy of rFVIIIFc treatment for severe haemophilia A.

Measuring cone density in a Japanese macaque (Macaca fuscata) model of age-related macular degeneration with commercially available adaptive optics

The aim of this study was to assess the feasibility of using a commercially available high-resolution adaptive optics (AO) camera to image the cone mosaic in Japanese macaques (Macaca fuscata) with dominantly inherited drusen. The macaques examined develop drusen closely resembling those seen in humans with age-related macular degeneration (AMD). For each animal, we acquired and processed images from the AO camera, montaged the results into a composite image, applied custom cone-counting software to detect individual cone photoreceptors, and created a cone density map of the macular region. We conclude that flood-illuminated AO provides a promising method of visualizing the cone mosaic in nonhuman primates. Future studies will quantify the longitudinal change in the cone mosaic and its relationship to the severity of drusen in these animals.

C1qTNF–related protein-1 (CTRP-1): a vascular wall protein that inhibits collagen-induced platelet aggregation by blocking VWF binding to collagen

CTRP-1 is a novel member of the C1qTNF–related protein family containing family characteristic collagen and TNF-like domains and shows marked expression in vascular wall tissue. We observed that recombinant human CTRP-1 specifically bound to fibrillar collagen and blocked collagen-induced platelet aggregation. CTRP-1 completely or partially prevented VWF and GPVI-Fc4 binding to collagen, respectively. However, GPVI-Fc4 failed to compete for the binding of CTRP-1 to collagen. CTRP-1 had no effects on α2β1 integrin I–domain binding to collagen. Using whole human blood under flow at low and high shear rates, CTRP-1 prevented platelets from accumulating on a collagen-coated surface but had no effects on “platelet-rolling” on a surface coated with VWF. These data suggest that CTRP-1 prevents collagen-induced platelet aggregation by specific blockade of VWF binding to collagen. By using the Folts vascular injury model in nonhuman primates (Macaca fascicularis), we were able to demonstrate that CTRP-1 can prevent platelet thrombosis in vivo. This effect was achieved in the absence of changes in activated-clotting time (ACT) and template cut bleeding times, suggesting that CTRP-1 has promising antiplatelet thrombotic activity and most likely acts by pacifying the thrombogenic site of vascular injury.

ACRP30, a new hormone controlling fat and glucose metabolism

Adipocyte complement-related protein of 30 kDa (ACRP30) is a secreted serum protein expressed exclusively in differentiated adipocytes. Recent studies have indicated that its expression and serum levels are reduced in humans and animals with obesity and insulin resistance. Metabolic studies have demonstrated a role for ACRP30 in the regulation of glucose and lipid homeostasis. This review will describe the current literature on the biochemistry of ACRP30 and its physiological functions. We will also discuss issues that are relevant to the directions of future research.

Proteolytic cleavage product of 30-kDa adipocyte complement-related protein increases fatty acid oxidation in muscle and causes weight loss in mice

Adipocyte complement-related protein (30 kDa) (Acrp30), a secreted protein of unknown function, is exclusively expressed in differentiated adipocytes; its mRNA is decreased in obese humans and mice. Here we describe novel pharmacological properties of the protease-generated globular head domain of Acrp30 (gAcrp30). Acute treatment of mice with gAcrp30 significantly decreased the elevated levels of plasma free fatty acids caused either by administration of a high fat test meal or by i.v. injection of Intralipid. This effect of gAcrp30 was caused, at least in part, by an acute increase in fatty acid oxidation by muscle. As a result, daily administration of a very low dose of gAcrp30 to mice consuming a high-fat/sucrose diet caused profound and sustainable weight reduction without affecting food intake. Thus, gAcrp30 is a novel pharmacological compound that controls energy homeostasis and exerts its effect primarily at the peripheral level.

Effect of aging on aortic expression of the vascular cell adhesion molecule-1 and atherosclerosis in murine models of atherosclerosis

Although age is a strong risk factor for atherosclerosis, it is unclear whether age may directly influence the process of atherogenesis. We, therefore, performed several studies in young (2-4 months old), mature (10-14 months old), and old (20-22 months old) mice to determine if the rate of aortic lesion formation increases with age, and whether this is related to increases in oxidative stress or vascular cell adhesion molecule (VCAM-1) expression in the aortic wall. In chow-fed low-density lipoprotein receptor-deficient (LDLR-/-) mice, plasma total cholesterol levels increased with age (250 +/- 52 mg/dl in young, 276 +/- 58 in mature, and 314 +/- 101 mg/dl in old mice). In contrast, the extent of atherosclerosis rose more rapidly, increasing from 3.6 +/- 2.7% of the aortic surface in mature mice to 18.2 +/- 8% in old mice. Plasma and tissue levels of antioxidant enzymes and molecules, as well as plasma thiobarbituric acid reactive substances and low-density lipoprotein susceptibility to oxidation, did not change with age. In a second study, VCAM-1 expression in the aortic arch and the extent of atherosclerosis in the aortic origin were significantly greater in old LDLR-/- mice than in young LDLR-/- mice. Additionally, after 1 month of a high-fat diet, which induced equally elevated plasma cholesterol levels in both young and old LDLR-/- mice, VCAM-1 expression and aortic lesion formation were still greater in old mice. The extent of atherosclerosis correlated well (r = .65,p <.01) with the expression of VCAM-1 in the aortic origin. In a final study, we measured VCAM-1 expression and atherosclerosis in young, mature, and old C57BL/6 mice, which have low plasma cholesterol levels (< or =100 mg/dl) when fed a standard chow diet. Although plasma cholesterol levels did not increase with age, old C57BL/6 mice had significantly more VCAM-1 expression in the aortic arch than did young mice. However, no lesions were observed in the aortic origin in either group. These data demonstrate that plasma cholesterol levels and VCAM-1 expression increase with age and suggest that this may contribute to the increased rate of atherosclerotic lesion formation in LDLR-/- mice. Importantly, the age-dependent increase in VCAM-1 expression does not appear to be related to plasma cholesterol levels. This study also suggests that in the absence of elevated plasma cholesterol, an increased expression of VCAM-1 alone is not sufficient for lesion formation.

Inhibition of VCAM-1 expression in the arterial wall is shared by structurally different antioxidants that reduce early atherosclerosis in NZW rabbits

We previously established that probucol decreases basal expression of VCAM-1 in the aorta of WHHL rabbits and inhibits the up-regulation of VCAM-1 expression that normally accompanies atherogenesis. To determine whether this effect is shared by other antioxidants in vivo, we now investigated whether a structurally unrelated antioxidant, vitamin E, also inhibits arterial VCAM-1 expression and whether the degree of VCAM-1 inhibition correlates with the reduction of atherosclerosis or the antioxidant protection of LDL. Atherogenesis and VCAM-1 mRNA and protein were determined in four groups of NZW rabbits (n = 6;-8) fed 0.5% cholesterol alone or supplemented with 0.1% vitamin E, a low dose (0.04;-0.075%) of probucol yielding the same degree of antioxidant protection of plasma LDL as vitamin E, or a high dose (0.5%) of probucol, and in normocholesterolemic rabbits. After 81 days, extensive atherosclerosis and a greater than 4-fold up-regulation of VCAM-1 mRNA was seen in rabbits on high cholesterol diet, mostly in the intima. Treatment with vitamin E, high-dose probucol, and low-dose probucol significantly decreased VCAM-1 mRNA by 49.0, 74.9, and 57. 5%, respectively, and reduced atherosclerosis in adjacent segments of the thoracic aorta to a similar degree as reported by previous studies. Immunocytochemistry confirmed that lesions of antioxidant-treated animals also contained less VCAM-1 protein. Neither the degree of VCAM-1 inhibition nor the extent of atherosclerosis correlated with the degree of antioxidant protection of plasma LDL.In summary, treatment with structurally unrelated antioxidants conveyed different degrees of antioxidant protection to plasma LDL but significantly reduced VCAM-1 expression in vivo and inhibited atherogenesis. This is consistent with the assumption that antiatherogenic effects of antioxidants may in part be mediated by interference with oxidation-dependent intracellular signaling.

Measurement of gene expression in the vascular wall by reverse transcription-polymerase chain reaction (rt-PCR) analysis

The developments of the polymerase chain reaction (PCR) analysis (1-3) and quantitative PCR by Gilliland (4) has provided researchers with a unique tool to analyze the expression of various genes in very small amounts of tissue samples. The sensitivity of PCR allows measurement of the expression level of any known gene in a biological sample, in this case, arterial wall tissue. This is achieved by determining the amount of mRNA coding for the target gene product present in the sample. Because PCR requires very little mRNA, a pool of mRNA can be studied for the expression of several genes and can also be used in more specialized PCR-based methods discussed in other chapters (see Chapters 7 - l0 ). This represents a major advantage over other methods, such as in situ hybridization, RNAase protection, and Northern blot analysis. Although in situ hybridization provides information about the localization of gene expression, it cannot give quantitative results, and the large amounts of mRNA required for Northern blot analysis prevents the analysis of small tissue samples. Thus, the main advantages of PCR are its sensitivity, the possibility of obtaining quantitative results, and the ability to analyze a number of genes using the same RNA sample. However, PCR analysis does not offer localization of gene expression, and although quantitative results are obtained, additional studies, in particular the analysis of protein expression, should be performed.

Effect of probucol on LDL oxidation and atherosclerosis in LDL receptor-deficient mice

Probucol is a powerful inhibitor of atherosclerosis in a number of animal models. However, it is unknown whether this is due to the strong antioxidant protection of low density lipoprotein (LDL), to antioxidant effects in the artery wall, or to cellular effects not shared by other antioxidants. To investigate whether murine models are suitable to study the antiatherogenic mechanisms of probucol, three experiments following different protocols were carried out in 135 male and female LDL receptor-deficient (LDLR-/-) mice. Treatment groups received a high (0.5%) or low (0.025%) dose of probucol, or low-dose probucol plus a high dose (0.1%) of vitamin E for periods ranging from 6 to 26 weeks. In all experiments, probucol strongly protected LDL against ex vivo oxidation (lag times exceeding 1400 min in 0.5% probucol-treated mice). Treatment with 0.5% probucol significantly lowered both HDL-cholesterol and plasma apolipoprotein (apo)A-I concentrations. In all three experiments, treatment with 0.5% probucol consistently increased the size of lesions in the aortic origin, from 1.3-fold (n.s.) to 2.9-fold (P < 0.05) in female mice and from 3.6- to 3.7-fold in males (P < 0.001). Even treatment with 0.025% probucol increased atherosclerosis 1.6-fold in male mice (P < 0.01). Addition of the high dose of vitamin E did not attenuate the pro-atherogenic effect of 0.025% probucol. In conclusion, probucol not only failed to decrease but actively increased atherogenesis in LDLR-/- mice in a dose-dependent manner, even though it provided a very strong antioxidant protection of LDL. This suggests that the reduction of atherosclerosis observed in other animal models is due to intracellular effects of probucol not found in mice, to differences in the metabolism of probucol, and/or to an overriding atherogenic effect of the decrease in HDL in murine models.

Extent of antioxidant protection of plasma LDL is not a predictor of the antiatherogenic effect of antioxidants

Oxidation of LDL plays all important role in atherogenesis. The lag-time in the formation of conjugated dienes provides a sensitive measure of the resistance of plasma LDL to oxidation and is widely assumed to be an indicator of atherogenic risk. To test this assumption, we investigated whether different antioxidants yielding similar lag-times result in similar reduction of atherosclerosis. A 6-months intervention study was carried out in three groups of 10 LDL receptor-deficient rabbits each. Because previous studies indicated that antioxidants that reduce atherosclerosis resulted in very long lag-times, the first group was treated with an antioxidant combination containing 1,000 IU vitamin E, 0.05% probucol analogue (BM15.0639), and 0.025% probucol. The lag-times achieved throughout the intervention period by this combination (952 +/- 39 min) were matched in a second group (829 +/- 46 min) treated with a variable dose of probucol (0.0575-0.11%, average 0.091%). A third, untreated group served as a control. Plasma cholesterol levels of all groups were matched. Even though both treatments yielded similar antioxidant protection of plasma LDL, 0.091% probucol reduced aortic atherosclerosis by 51.7% compared to the untreated group (P < 0.005), whereas the antioxidant combination failed to reduce lesion formation. Thus, the lag-time is clearly not correlated with the antiatherogenic efficacy of different antioxidants. However, a weak correlation was found within the group treated with probucol only. Our results suggest that the degree of antioxidant protection of plasma LDL may not be a good indicator of the atherogenic risk, in general, and that probucol reduces atherogenesis by mechanisms not shared by all antioxidants.

Effect of probucol treatment on gene expression of VCAM-1, MCP-1, and M-CSF in the aortic wall of LDL receptor-deficient rabbits during early atherogenesis

Probucol is a potent inhibitor of atherosclerosis in animal models. However, the mechanism of its antiatherogenic effect is not known. To investigate the effects of probucol on gene expression of VCAM-1, MCP-1, and M-CSF in vivo during the early stages of atherogenesis, we determined gene expression in 12 control WHHL rabbits and 12 WHHL rabbits fed 1% probucol from age 3 weeks. Three animals from each group were killed at 6, 9, 12, and 18 weeks of age. Two intimal/medial segments of the thoracic aorta, each comprising the orifices of a pair of intercostal arteries, were analyzed by semiquantitative RT-PCR using GAPDH as an internal standard. A third segment located between these two segments was studied by immunocytochemistry. A basal level of VCAM-1 gene expression was observed in lesion-free aortas of both treated and untreated WHHL rabbits (and in normal NZW aortas). Immunocytochemistry showed some VCAM-1 protein in normal arteries and confirmed that VCAM-1 protein expression generally correlated with gene expression. In the untreated WHHL rabbits, a marked upregulation of VCAM-1 expression was observed at 18 weeks. To correlate gene expression with intimal monocyte/macrophages in each animal, the macrophage area was determined by morphometry of immunostained sections. In addition, a scoring system of lesions was used. VCAM-1 expression showed a highly significant correlation with the extent of intimal macrophage presence (P < .001). A lesser degree of correlation between gene expression and macrophage accumulation was also seen for MCP-1. In contrast, M-CSF expression remained constant over the entire study period and showed no correlation with the intimal macrophage accumulation. Probucol treatment completely prevented lesion formation in all animals up to 18 weeks of age. Probucol reduced the level of basal VCAM-1 expression and prevented its upregulation. MCP-1 expression was not affected by probucol treatment, whereas M-CSF expression was significantly lowered by probucol. Our results support the idea that VCAM-1 plays an important role in early atherogenesis and suggest that the antiatherogenic effect of probucol may in part be due to a downregulation of VCAM-1. Reduction of the basal level of M-CSF gene expression by probucol treatment may also contribute to its ability to inhibit atherogenesis.

Effect of vitamin E on atherogenesis in LDL receptor-deficient rabbits

Vitamin E has been postulated to be antiatherogenic because of its antioxidative potency. However, intervention studies published to date have yielded conflicting results. To assess the antiatherogenic effect of vitamin E, two groups of 10 Watanabe heritable hyperlipidemic (WHHL) rabbits each were fed chow pellets containing D-alpha-tocopherol-acetate at either 40 mg/kg (control group) or 1000 mg/kg (vitamin E group) for 28 weeks. Plasma vitamin E levels in the vitamin E group increased five-fold over those controls (475.5 mumol/l vs. 95.9 mumol/l). The average total plasma cholesterol during the treatment period was not significantly affected by vitamin E (control, 950 +/- 113 mg/dl; vitamin E, 884 +/- 90 mg/dl). Vitamin E treatment had no significant effects on body weights, lipoprotein profiles, or HDL levels. The protection of plasma LDL against oxidation was determined by ex vivo by measuring the lag time in the formation of conjugated dienes in a standardized Cu22+(-)containing system. Lag time in the vitamin E-treated group increased four-fold over that in controls (404 vs. 123 min). The extent of atherosclerosis determined at the end of the study was not significantly different in the two groups (control group, 59.2 +/- 6.0%; vitamin E group, 50.6 +/- 6.2%, P = 0.33). Analysis of the correlation between vitamin E levels and extent of lesions also failed to indicate an antiatherosclerotic effect of vitamin E treatment. We previously reported that an analogue of probucol that provided antioxidative protection similar to that provided by vitamin E failed to prevent atherogenesis in WHHL-rabbits. In contrast probucol conveyed a much greater degree of antioxidant protection and effectively reduced atherosclerosis in rabbits. The results of the present study therefore support the hypothesis that a threshold level of antioxidative protection of LDL may be required to inhibit atherosclerosis.

A comparison of the antiatherogenic effects of probucol and of a structural analogue of probucol in low density lipoprotein receptor-deficient rabbits

The efficacies of probucol and a close structural analogue as antioxidants in the prevention of atherogenesis in LDL receptor-deficient rabbits were compared. The antioxidant potency of the analogue in vitro was equal to that of probucol. Its biological availability was much greater: almost comparable concentrations in total plasma were achieved by feeding 1% probucol (wt/wt) and 0.05% analogue (wt/wt). Total plasma concentrations were comparable, but the concentration of probucol within the LDL fraction was about twice that of the analogue. Probucol slowed lesion progression by almost 50%, confirming earlier reports; the analogue, however, showed no detectable inhibitory effect on atherogenesis. Resistance of LDL to oxidation was measured at the end of the study by incubating it with Cu2+ and measuring the rate of diene conjugation. Probucol prolonged diene conjugation lag time from the control value of 130 min to values > 1,000 min. The analogue approximately tripled the lag time (mean, 410 min) and yet failed to slow the atherogenic process. The results suggest that LDL resistance to oxidation must reach some threshold level before there is significant protection against atherogenesis. However, probucol has additional biological effects, possibly not shared by the analogue, that could contribute to its antiatherogenic potential.

Evidence for a concerted reaction between lipid hydroperoxides and polypeptides

The events accompanying oxidative modification of low density lipoprotein (LDL) are multiple and complex, and the precise mechanisms remain to be determined. In the present studies, we examined a simple system in which we first prepared large amounts of lipid hydroperoxides (from linoleic acid or from phospholipids containing linoleic acid) by using soybean lipoxygenase (linoleate:oxygen oxidoreductase, EC 1.13.11.12). Linoleoyl hydroperoxide was then incubated with polypeptides in the absence of metal ions. We observed the generation of fluorescent products with a spectrum like that of oxidized LDL. The generation of fluorescent products from incubation of polypeptides with linoleoyl hydroperoxide was manyfold greater than that generated on incubation with preformed 4-hydroxynonenal at the same concentration. Superoxide dismutase (superoxide: superoxide oxidoreductase, EC 1.15.1.1) had no effect on the generation of fluorescent products. Incubation of linoleoyl hydroperoxide with cytochrome c (cyt c) under the same conditions led to progressive reduction of cyt c at a rate determined by the initial linoleoyl hydroperoxide concentration. This reduction was not significantly inhibited by probucol but was inhibited, although never completely, by superoxide dismutase. Even at 100 micrograms/ml, superoxide dismutase inhibited by only 65%. From these results, we are led to suggest a concerted reaction between the peroxy radical and free amino groups of polypeptides or phosphatidylethanolamine to generate fluorescent adducts. During oxidation of LDL or of cell membranes, this mechanism may occur side by side with the conventional Schiff base mechanism.

Aminoguanidine inhibits oxidative modification of low density lipoprotein protein and the subsequent increase in uptake by macrophage scavenger receptors

Aminoguanidine decreases the formation of advanced glycosylation end products that occurs during chronic hyperglycemia. Presumably this occurs because early glycosylation products preferentially bind to aminoguanidine rather than to lysine groups of adjacent proteins. Because oxidative modification of low density lipoprotein (LDL) also involves derivatization of lysine residues of apolipoprotein (apo) B by reactive aldehydes formed during the decomposition of oxidized fatty acids, we postulated that aminoguanidine might also inhibit the oxidatively induced modification of LDL protein. To test this hypothesis we oxidized LDL by incubation with Cu2+ or with endothelial cells in the absence or presence of aminoguanidine. Aminoguanidine prevented apo B lysine modification, as measured by fluorescence spectroscopy, and inhibited in a dose-dependent manner the oxidatively induced increase in subsequent macrophage uptake. At concentrations that inhibited apo B modification (5-10 mM), aminoguanidine increased the lag time in diene conjugation but did not affect the plateau value reached. These data indicate that aminoguanidine inhibits oxidative modification of LDL protein in large part by binding reactive aldehydes formed during lipid peroxidation and preventing their subsequent conjugation to apo B. Thus, aminoguanidine (and related compounds) may be of dual benefit in inhibiting atherosclerosis, both by inhibiting formation of advanced glycosylation end products and by inhibiting the modification of LDL apo B that makes it a ligand for scavenger receptors.