Calcium Channel Blockers Activate the Interleukin-6 Gene Via the Transcription Factors NF-IL6 and NF-κB in Primary Human Vascular Smooth Muscle Cells
To the Editor:
We read with interest the recent study by Eickelberg et al1 concerning the activation of the interleukin-6 (IL-6) gene via the transcription factors NF-IL6 and NF-κB by calcium channel blockers (CCBs) in human vascular smooth muscle cells (VSMCs). CCBs reduce the severity of experimentally induced atherosclerosis, and some clinical trials suggest that they retard or impede the progression of atherosclerosis in humans. We previously reported that IL-6 stimulates the proliferation of VSMCs.2 Thus, the study by Eickelberg et al suggests that CCBs promote atherogenesis by inducing IL-6. However, Eickelberg et al cite the study by Lotz and Guerne.3 In this study, IL-6 induced the expression of the tissue inhibitor of metalloproteinase-1 (TIMP-1), an endogenous inhibitor of matrix metalloproteinases (MMPs), in human connective tissue cells. Eickelberg et al1 proposed that the local induction of IL-6 in the arterial vessel wall by CCBs essentially reduced atherosclerotic progression by inducing the expression of tissue TIMPs.
CCBs also have direct effects on the expression of MMPs and TIMPs. Indeed, Eickelberg et al4 themselves previously reported that CCBs modulated directly MMP-2 activity and inhibited TIMP-2 expression in human VSMCs. We also observed that amlodipine and diltiazem increased MMP-1 and MMP-2 activity in human vascular endothelial cells (unpublished observation). Thus, we cannot agree with their premise that CCBs prevent atherogenesis by inducing TIMPs via IL-6 expression.
In addition, both positive and negative effects of CCBs on IL-6 expression have been reported in various kinds of cells.5 We investigated the effects of the CCBs diltiazem, nifedipine, and amlodipine on IL-6 production by human VSMCs. IL-6 levels in the culture medium of VSMCs were measured by ELISA. The addition of angiotensin II (10-7 mol/L) for 24 hours increased IL-6 production by VSMCs, and all 3 subclasses of CCBs significantly prevented the angiotensin II–induced secretion of IL-6, which is contrary to the observation by Eickelberg et al.
- Copyright © 2000 by American Heart Association
Eickelberg O, Roth M, Mussmann R, et al. Calcium channel blockers activate the interleukin-6 gene via the transcription factors NF-IL6 and NF-κB in primary human vascular smooth muscle cells. Circulation. 1999;99:2276–2282.
Ikeda U, Ikeda M, Oohara T, et al. Interleukin 6 stimulates growth of vascular smooth muscle cells in a PDGF-dependent manner. Am J Physiol. 1991;260:H1713–H1717.
Lotz M, Guerne PA. Interleukin-6 induces the synthesis of tissue inhibitor of metalloproteinases-1/erythroid potentiating activity (TIMP-1/EPA). J Biol Chem. 1991;266:2017–2020.
Roth M, Eickelberg O, Köhler E, et al. Ca2+ channel blockers modulate metabolism of collagens within the extracellular matrix. Proc Natl Acad Sci USA. 1996;93:5478–5482.
We greatly appreciate the comments of Dr Ikeda and coworkers on our article about interleukin-6 (IL-6) gene activation by calcium channel blockers (CCBs).R1 Their concern addresses the possible in vivo mechanisms for our data, specifically the actual impact of increased IL-6 levels under CCB treatment during the progression of atherosclerosis. IL-6 has dual effects on cellular proliferation; it can act as a growth inhibitor or promoter in the same cell type, depending on culture conditions. To date, data on the effect of exogenous IL-6 on vascular smooth muscle cell (VSMC) proliferation remain controversial. Although Ikeda et alR2 described increased proliferation in response to IL-6, other studies found no increased proliferation under conditions of significantly increased IL-6 biolevels in a culture media of VSMCs.R3 Moreover, Ikeda et alR4 found an inhibition of cell proliferation by IL-6 in a similar cell type, the rat mesangial cell. In this respect, we continuously investigated our cell cultures for the effects of IL-6 on cell proliferation, but we did not observe any mitogenic effect of recombinant human IL-6 (data unpublished). Therefore, we disagree with the conclusion by Ikeda et al that “CCBs promote atherogenesis by inducing IL-6.” However, we are well aware of the fact that such diverse data can be due to different culture conditions and the sources from which VSMCs are generated.
Many studies have addressed the effects of CCBs on IL-6 production. Both positive and negative effects have been described, as Ikeda et al point out. Interestingly, however, fewer studies have addressed the single effect of CCBs alone on IL-6 production, without pretreatment with, for example, angiotensin II.
Regarding the possibility the involvement of tissue inhibitors of metalloprotinases (TIMP), it is well known that TIMP-1 and TIMP-2 are distinct isoforms contributing to the homeostasis of the extracellular matrix. Both genes have distinct promoter structures and, therefore, are differently regulated by a specific stimulus. We have previously reported on the ability of transforming growth factor-β to upregulate TIMP-1 but downregulate TIMP-2.R5 It would, thus, be intriguing to assess the overall effect of CCBs on matrix formation in an in vivo study.
Eickelberg O, Roth M, Mussmann R, et al. Calcium channel blockers activate the interleukin-6 gene via the transcription factors NF-IL6 and NF-(B in primary human vascular smooth muscle cells. Circulation. 1998;99:2276–2282.
Ikeda U, Ikeda M, Oohara T, et al. Interleukin-6 stimulates growth of vascular smooth muscle cells in a PDGF-dependent manner. Am J Physiol. 1991;260:H1713–H1717.
Loppnow H, Bil R, Hirt S, et al. Platelet-derived interleukin-1 induces cytokine production, but not proliferation of human vascular smooth muscle cells. Blood. 1998;91:134–141.
Eickelberg O, Koehler E, Reichenberger F, et al. Extracellular matrix deposition by primary human lung fibroblasts in response to TGFβ1 and TGFβ3. Am J Physiol. 1999;276:L814–L824.