Plasma enterobacterial ClpB levels and ClpB- and α-MSH-reactive immunoglobulins in lung cancer patients with and without anorexia

Objectives: Anorexia represents a common and debilitating clinical problem in patients with several forms of cancer, in particular lung cancer, but its mechanisms are not completely understood. Recently, the caseinolytic-protease-B (ClpB) homologue protein, produced by common gut bacteria, such as Escherichia coli, was identified as an antigen-mimetic of α-melanocyte-stimulating hormone (α-MSH), an anorexigenic neuropeptide. ClpB was previously detected in human plasma and displayed satietogenic properties; however, its possible relevance to cancer anorexia has not yet been investigated.

Methods: To address this question, we analyzed plasma ClpB concentrations as well as levels and affinities of anti-ClpB and α-MSH-reactive antibodies in patients with lung cancer with and without anorexia as compared with body mass index-matched healthy controls with normal appetite.

Results: We found that plasma ClpB concentrations were significantly lower in non-anorexic patients with cancer than those of the control group (P = 0.028). In contrast, patients with cancer and anorexia had lower levels of anti-ClpB immunoglobulins (Ig)M (P < 0.0001) and of both α-MSH IgM and IgG (P < 0.05) with respect to controls. Moreover, in patients with cancer and anorexia, anti-ClpB IgG showed a trend of lower affinities compared with non-anorexic patients (P = 0.05).

Conclusions: Taken together, the results revealed a reduced humoral immune response to ClpB in patients with cancer and anorexia, which may lead to an enhanced satietogenic effect of this enterobacterial protein contributing to the mechanisms of reduced appetite.

Keywords: Autoantibodies; Cancer anorexia; Caseinolytic peptidase B; Gut microbiota; α-MSH.