Recombinant human macrophage colony-stimulating factor reduces plasma cholesterol and carrageenan granuloma foam cell formation in Watanabe heritable hyperlipidemic rabbits

Low level of serum HDL-cholesterol with increased sIL-2R predicts a poor clinical outcome for patients with malignant lymphoma and adult T-cell leukemia-lymphoma

Low concentrations of high-density lipoprotein cholesterol (HDL-C) have been reported in patients with hematological malignancies. However, the proof of decreased HDL-C in hematological malignancies and its association with clinical outcomes remain unclear. We analyzed 140 Japanese patients with malignant lymphoma (ML) and adult T-cell leukemia-lymphoma (ATLL). HDL-C, LDL-C and soluble interleukin-2 receptor (sIL-2R) were measured. Treatment decisions were determined with established protocols. HDL-C was 0.98 ± 0.45 mmol/l in patients and 1.51 ± 0.35 mmol/l in controls (P < 0.001). LDL-C was lower in patients than in controls (2.76 ± 0.96, 3.16 ± 0.76 mmol/l, respectively, P < 0.001). HDL-C was the lowest in ATLL (0.81 ± 0.37 mmol/l), modest in non-Hodgkin lymphoma (1.09 ± 0.42 mmol/l) and the highest in Hodgkin's disease (1.14 ± 0.68 mmol/l), (P = 0.0019). Inverse correlation was found between HDL-C and sIL-2R (r = -0.6584, P < 0.001). Categorized patients into 3 subgroups according to HDL-C (<0.52, 0.52-1.02 and ≥1.03 mmol/l), sIL-2R were the highest (median, 36,675; IQR, 17,180-92,600 U/mL) in patients with HDL-C < 0.52 mmol/l, modest (2386, 1324-8340) in HDL-C 0.52-1.02 mmol/l and the lowest (761, 450-1596) in HDL-C ≥ 1.03 mmol/l (P < 0.001). In Cox regression model, the lowest HDL-C levels, <0.52 mmol/l, were associated with poorer clinical outcome and the hazard ratio was 5.73 (95%CI, 3.09-10.50; P < 0.001). In Kaplan-Meier analysis according to HDL-C tertiles (<0.78, 0.78-1.10 and ≥1.11 mmol/l), patients with lowest HDL-C tertile showed inferior overall survival with a median follow-up of 23 months (P < 0.001). We concluded that cytokine-induced low levels of HDL-C in patients with ML and ATLL has independent prognostic significance, and suggesting an early indicator of poorer outcome.

Receptor-independent fluid-phase pinocytosis mechanisms for induction of foam cell formation with native low-density lipoprotein particles

PURPOSE OF REVIEW

Because early findings indicated that native low-density lipoprotein (LDL) did not substantially increase macrophage cholesterol content during in-vitro incubations, investigators presumed that LDL must be modified in some way to trigger its uptake by the macrophage. The purpose of this review is to discuss recent findings showing that native unmodified LDL can induce massive macrophage cholesterol accumulation mimicking macrophage foam cell formation that occurs within atherosclerotic plaques.

RECENT FINDINGS

Macrophages that show high rates of fluid-phase pinocytosis also show similar high rates of uptake of native unmodified LDL through nonreceptor mediated uptake within both macropinosomes and micropinosomes. Nonsaturable fluid-phase uptake of LDL by macrophages converts the macrophages into foam cells. Different macrophage phenotypes demonstrate either constitutive fluid-phase pinocytosis or inducible fluid-phase pinocytosis. Fluid-phase pinocytosis has been demonstrated by macrophages within mouse atherosclerotic plaques indicating that this pathway contributes to plaque macrophage cholesterol accumulation.

SUMMARY

Contrary to what has been believed previously, macrophages can take up large amounts of native unmodified LDL by receptor-independent, fluid-phase pinocytosis converting these macrophages into foam cells. Thus, targeting macrophage fluid-phase pinocytosis should be considered when investigating strategies to limit macrophage cholesterol accumulation in atherosclerotic plaques.

Macrophage-specific overexpression of human matrix metalloproteinase-12 in transgenic rabbits

Increased matrix metalloproteinase-12 (MMP-12) has been implicated in atherosclerosis and many other inflammatory processes. To define MMP-12 functions in vivo, we generated transgenic rabbits that expressed human (h) MMP-12 gene under the control of a macrophage-specific promoter, the human scavenger receptor promoter. Two transgenic founder rabbits were found to have hMMP-12 transgene integration by Southern blot analysis. hMMP-12 mRNA was expressed in peritoneal and alveolar macrophages, and in tissues enriched in macrophages in transgenic rabbits. High levels of hMMP-12 protein were detected in the conditioned media of cultured peritoneal and alveolar macrophages from transgenic rabbits. Zymography showed that hMMP-12 secreted from macrophages possessed enzymatic activity toward beta-casein. To evaluate the expression of hMMP-12 in inflammatory sites, we used carrageenan-induced granulomas as an in vivo model for tissue macrophages and foam cells. Granuloma size in transgenic rabbits was significantly increased compared to that in control rabbits, and histological examination revealed that granulomas of transgenic rabbits were enriched in macrophages associated with increased hMMP-12 expression. We believe that this transgenic rabbit model with increased expression of hMMP-12 may become a useful model for further mechanistic studies of MMP-12 in inflammatory diseases and cancer invasion; it is also an ideal model for testing the in vivo action of MMP-12 inhibitors.

Effect of polysaccharide Krestin on the up-regulation of macrophage colony-stimulating factor gene expression in protecting mouse peritoneal macrophages from oxidative injury

Oxidative injury caused by oxidatively modified low density lipoprotein (Ox-LDL) plays an important role in the transformation of macrophages into foam cells and atherogenesis. Treatments to protect macrophages from oxidative injury will be effective in treating atherosclerosis. A macrophage-specific growth factor, macrophage colony-stimulating factor (M-CSF), was reported to be able to prevent the progression of atherosclerosis in Watanabe heritable hypercholesterolemic (WHHL) rabbits. A protein-bound polysaccharide, polysaccharide Krestin (PSK), was also proven to have effects in preventing atherosclerosis in our previous work. We proposed that, both M-CSF and PSK could protect macrophages from oxidative injury, and the effects of PSK were associated with its capability of inducing M-CSF expression. In our present results, M-CSF could alleviate the Ox-LDL- or tert-butyl hydroperoxide (tbOOH)-induced injury to mouse peritoneal macrophages, and PSK exhibited some similar effects. PSK treatment could induce M-CSF gene expression and secretion in mouse peritoneal macrophages. Furthermore actinomycin D and cycloheximide could attenuate that induction. We concluded that, maybe PSK exerted its effects on macrophages partly through the transcriptional induction of M-CSF in the cells.

GM-CSF: a strong arteriogenic factor acting by amplification of monocyte function

We investigated the role of the colony stimulating factor for monocytes (GM-CSF) to test the hypothesis whether prolongation of the monocyte's life cycle will support arteriogenesis (rapid growth of preexisting collateral arteries). This appeared logical in view of our discovery that circulating monocytes play an important part in the positive remodeling of small preexisting arterioles into arteries to compensate for arterial occlusions (arteriogenesis) and especially following our findings that MCP-1 markedly increases the speed of arteriogenesis. The continuous infusion of GM-CSF for 7 days into the proximal stump of the acutely occluded femoral artery of rabbits by osmotic minipump produced indeed a marked arteriogenic response as demonstrated by an increase (2-fold) in number and size of collateral arteries on postmortem angiograms and by the increase of maximal blood flow during vasodilation measured in vivo by blood pump perfusion of the hindquarter (5-fold). When GM-CSF and MCP-1 were simultaneously infused the effects on arteriogenesis were additive on angiograms as well as on conductance. GM-CSF was also able to widen the time window of MCP-1 activity: MCP-1 treatment alone was ineffective when given after the third week following occlusion. When administered together with GM-CSF about 80% of normal maximal conductance of the artery that was replaced by collaterals were achieved, a result that was not reached before by any other experimental treatment. Experiments with cells isolated from treated animals showed that monocyte apoptosis was markedly reduced. In addition we hypothesize that GM-CSF may aid in releasing pluripotent monocyte (stem-) cells from the bone marrow into the circulation. In contrast to MCP-1, GM-CSF showed no activity on monocyte transmigration through- and also no influence on monocyte adhesion to cultured endothelial cells. In conclusion we have discovered a new function of the hemopoietic stem cell factor GM-CSF, which is also a powerful arteriogenic peptide that acts via prolongation of the life cycle of monocytes/macrophages.

Postmenopausal changes in serum cytokine levels and hormone replacement therapy

OBJECTIVE

Our purpose was to investigate the effect of hormone replacement therapy on the postmenopausal changes in serum cytokine levels.

STUDY DESIGN

Fifteen cytokines were measured by an enzyme-linked immunosorbent assay in 97 untreated and hormone replacement-treated women. Thirteen women were examined before and during hormone replacement therapy.

RESULTS

Serum concentrations of macrophage colony-stimulating factor were significantly (P < .05) lower during the early postmenopausal period (< or = 10 years) than the values in premenopause and the elevated levels in the late postmenopausal period (< or = 30 years). A significant increase in tumor necrosis factor alpha and a decline in transforming growth factor beta1 were found in late postmenopausal women. Serum levels of macrophage colony-stimulating factor in women receiving hormone replacement therapy were significantly higher than those in untreated postmenopausal women. Furthermore, hormone replacement therapy induced a significant (P < .01) increase in serum levels of macrophage colony-stimulating factor, whereas serum levels of other cytokines were not affected.

CONCLUSION

It is well documented that macrophage colony-stimulating factor lowers serum cholesterol concentrations and prevents atherosclerosis. Inducing the production of macrophage colony-stimulating factor is a possible additional mechanism of hormone replacement therapy in mediating the antiatherogenic effect.

Macrophage colony-stimulating factor reduces tert-butyl hydroperoxide induced oxidative injury to monocytes/macrophages

The transformation of macrophages into foam cells is an important event in the development of atherosclerosis, and the oxidative injury caused by oxidized low density lipoprotein (Ox-LDL) plays an essential role in that process. It has been proved that macrophage colony-stimulating factor (M-CSF) could prevent the progression of atherosclerosis in Watanabe heritable hypercholesterolemic (WHHL) rabbits. We proposed that the anti-atherogenic effect of M-CSF was partly associated with its protective effect on monocyte-derived macrophages from Ox-LDL induced oxidative injury. In order to prove this, we investigated the effect of M-CSF on the oxidative injury caused by tert-butyl hydroperoxide (tbOOH) to mouse peritoneal macrophages and U937/J774 cell lines. The results showed that M-CSF could protect mouse peritoneal macrophages from oxidative injury (presented by cell morphology and cell survival rate); L929 cell-conditioned medium (L929-CM) had the same effect as M-CSF; and anti-M-CSF monoclonal antibody could mostly block the protective effect of L929-CM on macrophages. L929-CM was proved to be also able to decrease the impact of plasma membrane fluidity in U937 and J774 cells treated with tbOOH. Incubation with tbOOH caused DNA fragmentation in U937 cells. The presence of L929-CM greatly reduced the number of apoptotic U937 cells characterized by DNA fragmentation. From these results, we concluded that M-CSF could protect monocytes/macrophages from oxidative injury. It may be one of the mechanisms which explain the anti-atherogenic effect of exogenous M-CSF in WHHL rabbits.

Heterozygous osteopetrotic (op) mutation reduces atherosclerosis in LDL receptor- deficient mice

Previous studies of osteopetrotic (op) mice lacking macrophage colony-stimulating factor (M-CSF) have revealed an inhibition of atherosclerosis development in the apolipoprotein E (apo E)-deficient model and in a diet-induced model. Using LDL receptor-deficient mice, we now show that atheroma development depends on M-CSF concentration, as not only did homozygous osteopetrotic (op/op) mice have dramatically reduced lesions (approximately 0.3% of control lesion size) but heterozygous (op/+) mice had lesions < 1% of controls. Mice heterozygous for the op mutation (op/+) had plasma levels of M-CSF about half those in controls (+/+). The finding that an approximately 2-fold reduction in M-CSF expression reduced lesion size approximately 100-fold suggests the requirement for a threshold level of M-CSF. The effect of M-CSF on atherosclerosis did not appear to be mediated either by changes in plasma lipoprotein levels or alterations in the number of circulating monocytes, since both op/op and op/+ mice exhibited higher levels of atherogenic lipoprotein particles and (op/+) mice showed a near normal number of circulating monocytes. LDL receptor-null littermates of genotypes from op/op, op/+, to +/+ showed monocyte differentials of approximately 4.5, 8, and 10%, respectively. Taken together, these results suggest that the effects of M-CSF on atherogenesis may not be mediated by expression of M-CSF systemically or by modulation of the number of circulating monocytes. These studies support the conclusion that M-CSF participates critically in fatty streak formation and progression to a complex fibrous lesion.

Transient Thrombocytopenia Produced by Administration of Macrophage Colony-Stimulating Factor: Investigations of the Mechanism

Administration of macrophage colony-stimulating factor (M-CSF) to mice (2 to 8 mg/kg/d × 5d) produced dose-dependent thrombocytopenia, which reached its nadir on days 4 to 5, followed by rapid recovery. Surprisingly, when administration of M-CSF was prolonged, the thrombocytopenia completely resolved, despite continued treatment. Splenectomy did not prevent the thrombocytopenia. Readministration of M-CSF after various intervals continued to produce the thrombocytopenic effect, even after 35 days. Measurements of Meg-CFC and megakaryocyte ploidy during the periods of M-CSF treatment and recovery of normal platelet levels showed no evidence of bone marrow suppression. Platelet survival was markedly decreased after 5 days of M-CSF (at the platelet count nadir) and after 9 days of continued M-CSF treatment, when the platelet count had returned to normal. Platelets from M-CSF–treated donors demonstrated normal survival when transfused into normal recipients. We concluded that thrombocytopenia produced by M-CSF was not due to suppression of thrombopoiesis, but to increased activity of the monocyte/macrophage system, which caused shortened platelet survival, and that subsequently, increased platelet production compensated for ongoing platelet destruction and resulted in normal platelet levels.

Transient Thrombocytopenia Produced by Administration of Macrophage Colony-Stimulating Factor: Investigations of the Mechanism

Administration of macrophage colony-stimulating factor (M-CSF) to mice (2 to 8 mg/kg/d × 5d) produced dose-dependent thrombocytopenia, which reached its nadir on days 4 to 5, followed by rapid recovery. Surprisingly, when administration of M-CSF was prolonged, the thrombocytopenia completely resolved, despite continued treatment. Splenectomy did not prevent the thrombocytopenia. Readministration of M-CSF after various intervals continued to produce the thrombocytopenic effect, even after 35 days. Measurements of Meg-CFC and megakaryocyte ploidy during the periods of M-CSF treatment and recovery of normal platelet levels showed no evidence of bone marrow suppression. Platelet survival was markedly decreased after 5 days of M-CSF (at the platelet count nadir) and after 9 days of continued M-CSF treatment, when the platelet count had returned to normal. Platelets from M-CSF–treated donors demonstrated normal survival when transfused into normal recipients. We concluded that thrombocytopenia produced by M-CSF was not due to suppression of thrombopoiesis, but to increased activity of the monocyte/macrophage system, which caused shortened platelet survival, and that subsequently, increased platelet production compensated for ongoing platelet destruction and resulted in normal platelet levels.

Immunoreactive macrophage colony-stimulating factor is increased in atherosclerotic lesions of Watanabe heritable hyperlipidemic rabbits after recombinant human macrophage colony-stimulating factor therapy

Infiltration of monocytes into arteries is an early event in the pathogenesis of atherosclerosis. This recruitment is interpreted as enhancing lesion development, but it could also be a host response limiting lipid accumulation. The ability of macrophages to limit cholesterol uptake, however, can be reduced by the impaired mobility and metabolic activity associated with foam cell development. As lesions enlarge, foam cells die and become the nidus for the necrotic core. Treatments to improve viability might improve foam cell function and promote regression. Macrophage colony-stimulating factor (M-CSF) is vital to monocyte/macrophage differentiation, proliferation, and activation. We found that foam cells of Watanabe heritable hyperlipidemic (WHHL) rabbits had faint staining for M-CSF. Treatment of rabbits with recombinant human M-CSF (rhM-CSF) increased M-CSF staining, which correlated with reduced cholesterol content of these foam cells.

Immunological mechanisms in atherosclerosis

Immunological mechanisms seem to be potent modulators of the atherosclerotic process. The presence of substantial numbers of T-lymphocytes in the lesion and local and circulating autoantibodies to plaque components suggests that a specific immune response is operating. Focal expression of adhesion molecules and local secretion of chemoattractants could mediate the recruitment of inflammatory cells to the lesion. Local cytokine and growth factor networks may operate later, controlling cell migration and proliferation. Although it is still important to realize the complexity of these mechanisms, the ongoing characterization of the molecular mechanisms in atherogenesis may lead to new strategies for intervention with the disease process.

Decreased atherosclerosis in mice deficient in both macrophage colony-stimulating factor (op) and apolipoprotein E

To develop a murine model system to test the role of monocyte-derived macrophage in atherosclerosis, the osteopetrotic (op) mutation in the macrophage colony-stimulating factor gene was bred onto the apolipoprotein E (apoE)-deficient background. The doubly mutant (op/apoE-deficient) mice fed a low-fat chow diet had significantly smaller proximal aortic lesions at an earlier stage of progression than their apoE-deficient control littermates. These lesions in the doubly mutant mice were composed of macrophage foam cells. The op/apoE-deficient mice also had decreased body weights, decreased blood monocyte differentials, and increased mean cholesterol levels of approximately 1300 mg/dl. Statistical analysis determined that atherosclerosis lesion area was significantly affected by the op genotype and gender. The confounding variables of body weight, plasma cholesterol, and monocyte differential, which were all affected by op genotype, had no significant additional effect on lesion area once they were adjusted for the effects of op genotype and gender. Unexpectedly, there was a significant inverse correlation between plasma cholesterol and lesion area, implying that each may be the result of a common effect of macrophage colony-stimulating factor levels. The data support the hypothesis that macrophage colony-stimulating factor and its effects on macrophage development and function play a key role in atherogenesis.

A phase I study of anti-GD3 ganglioside monoclonal antibody R24 and recombinant human macrophage-colony stimulating factor in patients with metastatic melanoma

BACKGROUND

Macrophages activated by macrophage-colony stimulating factor (M-CSF) are potent immune effector cells and can mediate both in vitro cytotoxicity and antitumor effects in vivo. A Phase I trial combining M-CSF with R24, a mouse monoclonal antibody against GD3 ganglioside that has been shown to localize to melanoma tumors, induce inflammation at tumor sites, and result in major tumor responses in some patients with melanoma was performed.

METHODS

Nineteen patients with metastatic melanoma received a 14-day continuous intravenous infusion of 80 micrograms/kg/day of recombinant human M-CSF. R24 was administered daily by intravenous infusion on days 6-10 at doses of 1, 3, 10, 30, and 50 micrograms/m2/day.

RESULTS

All patients developed pruritus and urticaria; 13 patients developed transient thrombocytopenia less than 100,000/mm3. The maximum tolerated dose was not reached. All patients developed a monocytosis characterized by increased expression of the antigen HLA-DR and decreased expression of CD14, a phenotype reported to represent a subpopulation of monocytes active in mediating antibody-directed cellular cytotoxicity. Other biologic effects of treatment included marked but transient decreases in total cholesterol, low density lipoprotein, and high density lipoprotein. Three patients experienced tumor regression in breast, liver, and lymph node metastases and received a second course of therapy. Six of the 19 patients, one of whom received no further therapy, survived more than 2 years and 4 of these patients remain alive 24 to 37 months after treatment. Of the six patients with liver metastases, three (50%) survived more than 2.5 years and one remains alive at 37+ months.

CONCLUSIONS

Combination therapy with R24 and M-CSF resulted in both clinical and biologic effects that warrant further investigation of this combination.

Induction of sustained expression of proto-oncogene c-fms by platelet-derived growth factor, epidermal growth factor, and basic fibroblast growth factor, and its suppression by interferon-gamma and macrophage colony-stimulating factor in human aortic medial smooth muscle cells

Vascular medial smooth muscle cells migrate, proliferate and transform to foam cells in the process of atherosclerosis. We have reported that the intimal smooth muscle cells express proto-oncogene c-fms, a characteristic gene of monocyte-macrophages, which is not normally expressed in medial smooth muscle cells. In the present study, we demonstrated that combinations of platelet-derived growth factor (PDGF)-BB and either epidermal growth factor (EGF) or fibroblast growth factor (FGF) induced high expression of c-fms in normal human medial smooth muscle cells to the level of intimal smooth muscle cells or monocyte-derived macrophages, whereas c-fms expression by PDGF-BB alone was 1/10 and both EGF and FGF had no independent effect on c-fms expression. By contrast, interferon (IFN)-gamma and macrophage colony-stimulating factor (M-CSF) suppressed the induction of c-fms expression. These results indicate that multiple growth factors and cytokines may play a role in the phenotypic transformation of medial smooth muscle cells to intimal smooth muscle cells in atherosclerotic lesions by altering c-fms expression.