Increased Ghrelin but Low Ghrelin-Reactive Immunoglobulins in a Rat Model of Methotrexate Chemotherapy-Induced Anorexia

Abstract

Background and aimsCancer chemotherapy is commonly accompanied by mucositis, anorexia, weight loss, and anxiety independently from cancer-induced anorexia–cachexia, further aggravating clinical outcome. Ghrelin is a peptide hormone produced in gastric mucosa that reaches the brain to stimulate appetite. In plasma, ghrelin is protected from degradation by ghrelin-reactive immunoglobulins (Ig). To analyze possible involvement of ghrelin in the chemotherapy-induced anorexia and anxiety, gastric ghrelin expression, plasma levels of ghrelin, and ghrelin-reactive IgG were studied in rats treated with methotrexate (MTX).MethodsRats received MTX (2.5 mg/kg, subcutaneously) for three consecutive days and were killed 3 days later, at the peak of anorexia and weight loss. Control rats received phosphate-buffered saline. Preproghrelin mRNA expression in the stomach was analyzed by in situ hybridization. Plasma levels of ghrelin and ghrelin-reactive IgG were measured by immunoenzymatic assays and IgG affinity kinetics by surface plasmon resonance. Anxiety- and depression-like behaviors in MTX-treated anorectic and in control rats were evaluated in the elevated plus-maze and the forced-swim test, respectively.ResultsIn MTX-treated anorectic rats, the number of preproghrelin mRNA-producing cells was found increased (by 51.3%, p < 0.001) as well were plasma concentrations of both ghrelin and des-acyl-ghrelin (by 70.4%, p < 0.05 and 98.3%, p < 0.01, respectively). In contrast, plasma levels of total IgG reactive with ghrelin and des-acyl-ghrelin were drastically decreased (by 87.2 and 88.4%, respectively, both p < 0.001), and affinity kinetics of these IgG were characterized by increased small and big Kd, respectively. MTX-treated rats displayed increased anxiety- but not depression-like behavior.ConclusionMTX-induced anorexia, weight loss, and anxiety are accompanied by increased ghrelin production and by a decrease of ghrelin-reactive IgG levels and affinity binding properties. Such changes of ghrelin-reactive IgG may underlie their decreased ghrelin-transporting capacities compromising ghrelin orexigenic and anxiolytic effects and contributing to chemotherapy-induced loss of appetite.

Ghrelin-Reactive Immunoglobulins in Conditions of Altered Appetite and Energy Balance

“…The review focuses mainly on the data from five papers, all reporting affinity kinetics of ghrelin- and desacyl-ghrelin-reactive IgG. They include a study of patients with hyperphagic obesity and anorexia nervosa (AN) and of ob/ob mice by Takagi et al ( 13 ); two studies by François et al in high-fat diet (HFD)-induced obese mice ( 14 ) and in rats with methotrexate (MTX)-induced anorexia ( 15 ), a study by Lucas et al in obese Zucker rats ( 16 ) as well as a Legrand et al study in mice after chronic food-restriction and activity-based anorexia ( 17 ). In all mentioned studies, the same protocols of IgG plasma extraction and affinity kinetic assay by the surface plasmon resonance were used as was previously described in details ( 18 ).…”

“…Moreover, a study using plasma samples of a large number of healthy male ( n = 562) and female ( n = 636) adolescents also revealed an ubiquitous presence of ghrelin-reactive autoantibodies of both IgG and IgM classes, which mean plasma levels were slightly elevated in girls vs. boys ( 21 ). In rodents, ghrelin-reactive IgG were detected in both rats ( 15 , 19 ) and mice ( 13 , 14 , 17 ). Since the rodents studies were performed only in males, presence of possible sex differences of ghrelin-reactive IgG was not explored.…”

“…Desacyl-ghrelin-reactive IgG are also present in humans ( 13 , 20 ) and rodents ( 15 , 17 ). Although some part of desacyl-ghrelin-reactive IgG may bind to acyl-ghrelin, they should also have distinct paratopes, because levels of desacyl-ghrelin IgG are often higher than of acyl-ghrelin IgG in human plasma ( 13 , 20 ) and also because they have different affinity kinetics properties ( 13 ).…”

“…It is of interest that gastric electrical stimulation activated c-fos production in numerous lymphoid cells of the gastric mucosa surrounding the enteroendocrine ghrelin-synthetizing cells ( 26 ). Strong inhibition of ghrelin-reactive IgG levels in plasma is observed in rats after treatment with MTX, an immunosuppressive agent, which induces intestinal mucositis ( 15 ).…”

The octanoylated energy regulating hormone ghrelin: An expanded view of ghrelin’s biological interactions and avenues for controlling ghrelin signaling

“…Ghrelin-reactive IgG was identified in human plasma by Takagi and co-workers, who proposed these autoantibodies stabilize ghrelin in the plasma by reducing serine ester hydrolysis and peptide degradation ( Figure 2) (Takagi et al, 2013). In addition to protecting ghrelin from enzymatic deacylation, ghrelin autoantibodies are reported to enhance the ability of ghrelin to stimulate appetite (Francois et al, 2016a(Francois et al, , 2016bTakagi et al, 2013). Ghrelin-reactive IgG Figure 2.…”