Determination of haptoglobin expression in IL-6 treated HepG2 cells by ELISA and by RNA hybridization--evaluation of a quantitative method to measure IL-6

IL-6-mediated hepatocyte production is the primary source of plasma and urine neutrophil gelatinase-associated lipocalin during acute kidney injury

Neutrophil gelatinase associated lipocalin (NGAL, Lcn2) is the most widely studied biomarker of acute kidney injury (AKI). Previous studies have demonstrated that NGAL is produced by the kidney and released into the urine and plasma. Consequently, NGAL is currently considered a tubule specific injury marker of AKI. However, the utility of NGAL to predict AKI has been variable suggesting that other mechanisms of production are present. IL-6 is a proinflammatory cytokine increased in plasma by two hours of AKI and mediates distant organ effects. Herein, we investigated the role of IL-6 in renal and extra-renal NGAL production. Wild type mice with ischemic AKI had increased plasma IL-6, increased hepatic NGAL mRNA, increased plasma NGAL, and increased urine NGAL; all reduced in IL-6 knockout mice. Intravenous IL-6 in normal mice increased hepatic NGAL mRNA, plasma NGAL and urine NGAL. In mice with hepatocyte specific NGAL deletion (Lcn2hep-/-) and ischemic AKI, hepatic NGAL mRNA was absent, and plasma and urine NGAL were reduced. Since urine NGAL levels appear to be dependent on plasma levels, the renal handling of circulating NGAL was examined using recombinant human NGAL. After intravenous recombinant human NGAL administration to mice, human NGAL in mouse urine was detected by ELISA during proximal tubular dysfunction, but not in pre-renal azotemia. Thus, during AKI, IL-6 mediates hepatic NGAL production, hepatocytes are the primary source of plasma and urine NGAL, and plasma NGAL appears in the urine during proximal tubule dysfunction. Hence, our data change the paradigm by which NGAL should be interpreted as a biomarker of AKI.

Identification of Haptoglobin as a Readout of rhGH Therapy in GH Deficiency

BACKGROUND

GH deficiency (GHD) is characterized by a cluster of cardiovascular risk factors and subtle inflammation. We aimed to demonstrate, through a proteomic approach, molecules directly modulated by GHD and involved in the inflammatory state.

METHODS

Ten children with isolated GHD were studied before and after 1 year of treatment with rhGH and compared with 14 matched controls. A two-dimensional electrophoresis plasma proteomics analysis was performed at baseline and after GH treatment to identify the top molecules modulated by GH. In vitro studies on human hepatoma (HepG2) cells were performed to validate the data.

RESULTS

Twelve of 20 proteomic spots were predicted to be isoforms α and β of haptoglobin (Hp) and confirmed by liquid chromatography tandem mass spectrometry and Western immunoblot analyses. Hp levels were higher in patients with GHD than controls at baseline (P < 0.001) and were reduced following GH treatment (P < 0.01). In HepG2 cells, both GH and IGF-1 were able to downregulate IL-6-induced Hp secretion. Moreover, Hp secretion was restored in pegvisomant-treated HepG2 cells.

CONCLUSIONS

Hp is a molecule acting in the inflammatory state of GHD and a possible biomarker for GH treatment. Nevertheless, the contribution of other factors and the molecular pathways involved in the GH downregulation of Hp remain to be clearly defined.

Targeted antisense modulation of inflammatory cytokine receptors

Antisense technology is potentially a powerful means by which to selectively control gene expression. We have used antisense oligonucleotides to modulate the response of the hepatoma cell line, HepG2, to the inflammatory cytokine, IL-6, by inhibiting the expression of its multifunctional signal transducer, gp130. HepG2 cells respond to IL-6 by upregulating acute phase proteins, such as haptoglobin, by five- to tenfold. Gp130 is central to this response, as the upregulation of haptoglobin is almost completely blocked by the addition of high concentrations ( approximately 100 microg/ml) of a monoclonal antibody to gp 130. Antisense oligodeoxynucleotides complementary to the mRNA encoding gp 130 inhibited the upregulation of haptoglobin by IL-6-stimulated HepG2 cells by about 50%. However, a nonsense sequence also inhibited haptoglobin secretion by about 20%. To improve the specificity and efficiency of action, we targeted the antisense oligonucleotides to HepG2 cells using a conjugate of asialoglycoprotein-poly-L-lysine. The targeted antisense reduced the binding of IL-6 to HepG2 cells, virtually eliminating high affinity binding. In addition, it inhibited haptoglobin upregulation by over 70%. Furthermore, the dose of targeted antisense required for biological effect was reduced by about an order of magnitude as compared with unconjugated antisense. These results demonstrate the potential of antisense oligonucleotides as a means to control the acute phase response as well as the need for a greater understanding of the mechanism and dynamics of antisense molecules as they are developed toward therapeutic application.

Activin A regulates growth and acute phase proteins in the human liver cell line, HepG2

Activin, and its binding protein, follistatin, are up-regulated by mediators of inflammation, and recent studies have demonstrated that activin A can block the activity of the key inflammatory cytokine, interleukin-6 (IL-6). These findings thereby implicate activin and follistatin in the control of the inflammatory cascade. In this study, interactions between interleukin-1beta (IL-1beta), IL-6 and activin were examined the human liver cell line, HepG2, for their effect on cell proliferation and the production of the acute phase proteins, haptoglobin and alpha1-acid glycoprotein (alpha1-AGP). IL-1beta and activin A, but not IL-6, inhibited the proliferation of HepG2 cells. Activin A together with IL-1beta caused a greater inhibition of proliferation than either factor alone, and the inhibitory effects of activin A were blocked by the addition of follistatin to the cultures. Activin A alone inhibited the production of haptoglobin but did not affect alpha1-AGP concentrations. However, activin A suppressed the stimulatory effects of IL-6 on the production of both haptoglobin and alpha1-AGP. Production of follistatin by HepG2 cells was stimulated by activin A, but was inhibited by both IL-1beta and IL-6, indicating a complex regulatory loop is operable to modulate the effects of activin A during inflammation. Taken together, these data suggest that activin A interacts with IL-1beta and IL-6 to regulate and coordinate the production of acute phase proteins during an inflammatory episode.

Alternative assay procedures for cytokines and soluble receptors of the IL-6 family

Human hepatoma cells (HepG2 cells) were transfected with expression vectors for human IL-6 (hIL-6) and rat IL-6R (rIL-6-R). The cell lines were used for testing the biological activity of different IL-6 species, soluble hIL-6R (shIL-6R) and some members of the IL-6 cytokine family by means of an ELISA procedure. The assay is based on induction of the gene expression of the acute phase protein haptoglobin in hepatoma cells and provides an alternative bioassay taking advantage of the hepatocyte stimulatory activity of IL-6 (as opposed to the B9 proliferative assay). A dose-response experiment with IL-6 showed that half-maximal stimulation was achieved with approx. 5 ng/ml of hIL-6 in HepG2 cells and with 5-10 ng/ml muIL-6 in HepG2-rIL-6R cells after 24 h. The same response was achieved with 10 ng/ml shIL-6R in HepG2-IL6 cells. In conclusion, the assay is fast and reliable and might be adopted for other cytokines and receptors with hepatocyte stimulating activity.

In vitro and in vivo production of interleukin-6 induced by muramyl peptides and lipopolysaccharide in normal dogs

Interleukin-6 (IL-6) is a multifactorial cytokine produced by many cells including monocytes and macrophages in the immune-stimulated host. We measured IL-6 activity induced by muramyl dipeptide (MDP) and lipopolysaccharide (LPS) in vitro and by liposome-encapsulated muramyl tripeptide-phosphatidylethanolamine (L-MTP-PE) in vivo in normal dogs. Adherent mononuclear cells were cultured with MDP, LPS, or MDP plus LPS for various time periods. After incubation, culture supernatants were collected and assayed for IL-6 activity. Sera from dogs following L-MTP-PE administration were also evaluated for IL-6 activity. IL-6 activity both in supernatants and sera was measured using a 7TD1 bioassay. Significantly elevated IL-6 activity could be measured as early as 2 hours after mononuclear cells were exposed to MDP, LPS, or MDP plus LPS. IL-6 activity induced by LPS was greater than that induced by MDP, and the combination of MDP and LPS induced the greatest increase in IL-6 activity. Serum IL-6 activity was elevated within 3 to 4 hours post L-MTP-PE administration and subsequently declined to pretreatment level at 24 hours post injection. Neutralization of supernatant and serum IL-6 activity was not achieved with goat or rabbit anti-recombinant human IL-6 polyclonal antibody. This study demonstrates that MDP and LPS, alone and in combination, can induce enhanced IL-6 activity of canine adherent mononuclear cells in vitro, and that intravenous injection of L-MTP-PE is capable of eliciting increased IL-6 activity in vivo in normal dogs. These findings suggest that IL-6 may play an important role in the biologic response observed in canine cancer patients treated with L-MTP-PE.