Metallothionein induction in cultured rat hepatocytes by arthritic rat serum, activated macrophages, interleukin-6, interleukin-11 and leukaemia inhibitory factor

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Abstract
Potential mediators of hepatic metallothionein (MT) synthesis in adjuvant-induced arthritis were investigated in cultured rat hepatocytes. Sera from arthritic rats (14 d post-adjuvant treatment) in the presence of Zn (50 µmol/L) + dexamethasone (Dex; 1 µmol/L) increased metallothionein (MT) accumulation by 34% above that obtained with control rat serum with Zn + Dex. Endogenous IL-6 activity in serum from arthritic rats was 93 ± 49 U/mL and was undetectable in control rat serum. The activities of TNF, IL-1 and corticosterone concentrations were the same in control and arthritic rats. The accumulation of MT in hepatocytes in the presence of Zn (10 µmol/L) + Dex (1 µmol/L) was enhanced 29% and 49% by media from lipopolysaccharide (LPS)-stimulated peritoneal macrophage (PMM) and Kupffer cell cultures (KCM), respectively. The response with PMM and KCM was quantitatively the same as that with interleukin-6 (IL-6). Analysis of PMM and KCM showed activities of 1,000–10,000 U/mL for IL-6, 100–1000 U/mL for TNF and <10,000 U/mL for IL-1, the latter detected only in PMM. LPS alone enhanced the accumulation of MT above Zn + Dex in a dose dependent manner. A significant LPS response was obtained at 5 mg/L with a maximal stimulation above Zn + Dex of 38% at 10 mg/L. This direct stimulation of MT by LPS was not part of the response observed with PMM and KCM where the final LPS concentration in culture was only 0.1 mg/L. Other cytokines capable of synergy with Zn + Dex on MT synthesis were investigated. Interleukin-11 (IL-11) increased the Zn + Dex induction in a dose dependent manner with maximal stimulation at 100 U/mL of 40%. A small stimulation of 12% above Zn + Dex was obtained with leukaemia inhibitory factor (LIF) at concentrations greater than 100 U/mL. No enhancement of the Zn + Dex response was obtained with interleukin-3 (1000 U/mL), interleukin-4 (10 µg/L), platelet activating factor (5 nmol/L) or granulocyte-colony stimulating factor (5 µg/L). Neither IL-11 nor LIF enhanced the response obtained with Zn + Dex + IL-6. The results demonstrate that mediators present in arthritic rat serum and in LPS-stimulated PMM and KCM cause a quantitatively similar response on MT accumulation as IL-6. IL-11 and to a lesser extent LIF, are also potential mediators of MT synthesis in inflammation.