J Mol Cell Cardiol
24, 775-780 (1992)
Paradoxical
Elkt of Cerium on Collagen in Cardiac Fibroblasts
K. Shivakumar*, Division
of Cardiomyopathy,
R. Rem&a
Nair
Synthesis
and M. S. Valiathan
Sree Chitra Tirunal Institutefor Medical Sciences and Technology, Ttivandrum 695 011, India
(Received 29 April 1991, accepted in revisedform 10 March 1992) K. SHIVAKUMAR, R. RENUKA NAIR AND M. S. VALIATHAN. Paradoxical Effect of Cerium on Collagen Synthesis. Journal ofMolecular and Cellular Cardiology (1992) 24, 777-782. The present study examined the effect of cerium on collagen synthesis in cultured cardiac fibroblasts and explants. At 100n~, a concentration comparable with that found in the cardiac tissue of patients with endomyocardial fibrosis, the element was found to enhance the incorporation of tritiated proline into collagen and non-collagen proteins while at 10~~. it had an inhibitory effect. Cerium was found to have no effect on rates of DNA synthesis in fibroblasts at 10011~. However, at this concentration, the element markedly enhanced the incorporation of tritiated uridine into RNA, suggesting that cerium may act at the level of transcription to stimulate collagen and non-collagen protein syntheses. The stimulatory action of very low levels of cerium on collagen synthesis may contribute to the accumulation of collagen seen in endomyocardial fibrosis. KEY WORDS:
Cerium;
Collagen
synthesis;
Transcription;
Introduction A recent hypothesis on the causation of endomyocardial fibrosis (EMF), a restrictive cardiomyopathy, envisages a pathogenic role for low levels of cerium (Ce) in conjunction with Mg deficiency in the cardiac tissue (Valiathan et al., 1989; Valiathan and Kartha, 1990). The speculation is based upon the observation that cardiac tissues of patients with EMF have elevated levels of Ce and depressed levels of Mg, compared to the control. While several biochemical processes are known to be dependent on Mg and could be affected in Mg deficiency (Grubbs and Maguire, 1987), the significance of low tissue levels of Ce remains unclear. As excessive collagen accumulation in the endomyocardium is central to the pathophysiology of EMF, the present study was undertaken to determine whether Ce has an effect on collagen synthesis at levels comparable with those in the cardiac tissue of the patients. It was found that at lOOnM, a concentration comparable with that in question, the element enhances incorporation of tritiated proline into collagen and non-collagen proteins in neonatal rat heart explants while at *To whom 002s2828/92/070777
all correspondence
should
+ 06 f03.00/0
Endomyocardial
fibrosis.
concentrations >~OPM, it is inhibitory. At lOOnM, the element was found to have a similar stimulatdry effect on cardiac fibroblasts in culture. Further, at this concentration, Ce was also found to markedly increase the rate of incorporation of tritiated uridine into RNA, suggesting an effect on transcription. These data show that the lanthanide is biologically active at such low levels and are consistent with a stimulatory effect of very low levels of Ce on collagen synthesis which may contribute to the accumulation of collagen observed in EMF.
Materials
and Methods
Medium 199, MEM (410-1100) and fetal bovine serum were obtained from Gibco Laboratories, Grand Island, New York. Cerous chloride, penicillin, gentamycin, protease-free purified collagenase, N-ethylmaleimide and other fine chemicals were obtained from Sigma Chemical Company, St. Louis, MO, USA [3H]-proline (sp.activity 1500 mCi/mmol), [‘HI-thymidine (sp.activity 6800 mCi/mmol), and [3H]-uridine (sp.activity
be addressed. @ 1992 Academic
Press Limited
K.
776
Shivakumar
16000 mCi/mmole) were supplied by Bhabha Atomic Research Centre, India. Commercial tissue culture plates were purchased from Nunc, Denmark.
Measurement
of collagen synthesis in cardiac explants
et al.
changed to MEM (410-1100) (untainirlg sodium ascorbate at 50pglml. Cells \~t‘r
24, 775-780 (1992)
Paradoxical
Elkt of Cerium on Collagen in Cardiac Fibroblasts
K. Shivakumar*, Division
of Cardiomyopathy,
R. Rem&a
Nair
Synthesis
and M. S. Valiathan
Sree Chitra Tirunal Institutefor Medical Sciences and Technology, Ttivandrum 695 011, India
(Received 29 April 1991, accepted in revisedform 10 March 1992) K. SHIVAKUMAR, R. RENUKA NAIR AND M. S. VALIATHAN. Paradoxical Effect of Cerium on Collagen Synthesis. Journal ofMolecular and Cellular Cardiology (1992) 24, 777-782. The present study examined the effect of cerium on collagen synthesis in cultured cardiac fibroblasts and explants. At 100n~, a concentration comparable with that found in the cardiac tissue of patients with endomyocardial fibrosis, the element was found to enhance the incorporation of tritiated proline into collagen and non-collagen proteins while at 10~~. it had an inhibitory effect. Cerium was found to have no effect on rates of DNA synthesis in fibroblasts at 10011~. However, at this concentration, the element markedly enhanced the incorporation of tritiated uridine into RNA, suggesting that cerium may act at the level of transcription to stimulate collagen and non-collagen protein syntheses. The stimulatory action of very low levels of cerium on collagen synthesis may contribute to the accumulation of collagen seen in endomyocardial fibrosis. KEY WORDS:
Cerium;
Collagen
synthesis;
Transcription;
Introduction A recent hypothesis on the causation of endomyocardial fibrosis (EMF), a restrictive cardiomyopathy, envisages a pathogenic role for low levels of cerium (Ce) in conjunction with Mg deficiency in the cardiac tissue (Valiathan et al., 1989; Valiathan and Kartha, 1990). The speculation is based upon the observation that cardiac tissues of patients with EMF have elevated levels of Ce and depressed levels of Mg, compared to the control. While several biochemical processes are known to be dependent on Mg and could be affected in Mg deficiency (Grubbs and Maguire, 1987), the significance of low tissue levels of Ce remains unclear. As excessive collagen accumulation in the endomyocardium is central to the pathophysiology of EMF, the present study was undertaken to determine whether Ce has an effect on collagen synthesis at levels comparable with those in the cardiac tissue of the patients. It was found that at lOOnM, a concentration comparable with that in question, the element enhances incorporation of tritiated proline into collagen and non-collagen proteins in neonatal rat heart explants while at *To whom 002s2828/92/070777
all correspondence
should
+ 06 f03.00/0
Endomyocardial
fibrosis.
concentrations >~OPM, it is inhibitory. At lOOnM, the element was found to have a similar stimulatdry effect on cardiac fibroblasts in culture. Further, at this concentration, Ce was also found to markedly increase the rate of incorporation of tritiated uridine into RNA, suggesting an effect on transcription. These data show that the lanthanide is biologically active at such low levels and are consistent with a stimulatory effect of very low levels of Ce on collagen synthesis which may contribute to the accumulation of collagen observed in EMF.
Materials
and Methods
Medium 199, MEM (410-1100) and fetal bovine serum were obtained from Gibco Laboratories, Grand Island, New York. Cerous chloride, penicillin, gentamycin, protease-free purified collagenase, N-ethylmaleimide and other fine chemicals were obtained from Sigma Chemical Company, St. Louis, MO, USA [3H]-proline (sp.activity 1500 mCi/mmol), [‘HI-thymidine (sp.activity 6800 mCi/mmol), and [3H]-uridine (sp.activity
be addressed. @ 1992 Academic
Press Limited
K.
776
Shivakumar
16000 mCi/mmole) were supplied by Bhabha Atomic Research Centre, India. Commercial tissue culture plates were purchased from Nunc, Denmark.
Measurement
of collagen synthesis in cardiac explants
et al.
changed to MEM (410-1100) (untainirlg sodium ascorbate at 50pglml. Cells \~t‘r
