Cancer cachexia (CC) is a multifactorial clinical complication in numerous human malignancies. Its incidence in Europe is highest in patients with lung (83/36% inpatients/outpatients, respectively) and gastrointestinal cancers (62/42%). There are currently no therapeutic agents used for treatment of this paraneoplastic syndrome, caused by impaired/reduced nutritional intake, or metabolic disorders with increased catabolism and chronic inflammation. In the mechanisms of CC pathogenesis, in addition to inflammation, the role of insulin resistance, damage to mitochondrial function, oxidative stress, as well as the activation of lipolysis and proteolysis through the ubiquitin-proteasome system and macro-autophagy are emphasized. The main target in CC is skeletal and cardiac muscle, as well as the adipose tissue (AT). The most important role in CRC-associated cachexia is played by pro-inflammatory cytokines, including the tumor necrosis factor α (TNFα), originally known as cachectin, Interleukin (IL)-1, IL-6, and certain chemokines (e.g., IL-8). Heterogeneous CRC cells themselves also produce numerous cytokines (including chemokines), as well as novel factors called “cachexokines”. The tumor microenvironment (TME) contributes to systemic inflammation and increased oxidative stress and fibrosis.
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. Other reports indicate a correlation between elevated SIR, as measured by the high modified Glasgow prognostic score (mGPS), CRP, and neutrophil:lymphocyte ratio (NLR) with a low skeletal-muscle index in patients with primary operable CRC[46]
. In turn, Malietzis et al. reported that host SIR in resectable CRC patients is associated with not only myopenia but also myosteatosis (increased infiltration by inter- and intra-muscular adipose tissue). High neutrophil:lymphocyte ratios (NLR) and low albumin levels were independent predictors of myopenia, with the former being correlated with myosteatosis[47]
. Furthermore, Sirniö et al. noted correlations between serum levels of several amino acids (AAs) (low with glutamine and histidine and high with phenylalanine), SIR markers, and muscle catabolism in patients with CRC. Hence, the authors proposed several SIR indicators, e.g., mGPS, high blood NLR, and high serum levels of CRP, IL-6, and IL-8. Of the 13 cytokines tested, IL-6 most strongly associated with increased phenylalanine and lower histidine levels. The authors suggest that SIR is associated with glutamine consumption and muscle wasting in CRC[44]
. In turn, the studies of Ohmori et al. suggest that only TNF-α, the levels of which were negatively correlated with skeletal-muscle index (SMI) and SDS-soluble myosin light chain 1 (SDS-MYL1), is a good serum muscle-atrophy marker in CRC-associated cachexia[45]
. Other authors confirmed that higher TNF-α concentrations are usually associated with patients with more advanced CRC stages (stage III/IV vs. stage I/II tumors). In turn, patients with the greatest nutritional deficit exhibited higher levels of adipocytokines. However, these TNF-α variations were only significant in CRC vs. control when the nutritional status was evaluated by phase-angle tertiles[48]
. There was also an attempt to evaluate the role of gut barrier disruption, possibly resulting in persistent activation of the host immune response, as a cause of local and systemic inflammatory changes in CRC-associated cachexia. Comparative studies concerned cachectic and weight-stable CRC patients, analyzing the circulating profile and tissue expression of various cytokines (including chemokines), growth and differentiation factors, as well as morphological intestinal changes in CRC-associated cachexia. Mucosal biopsies were derived from the rectosigmoid region, 20 cm from the tumor margin. An increase in serum concentrations of IL-6 and IL-8 was observed, together with elevated tissue expression of IL-7, IL-13, and transforming growth factor β3 (TGF-β3), as well as rich lymphocyte and macrophage infiltration in the colon of CC patients, compared to those of normal body weight. These changes suggest the presence of repair mechanisms in the damaged large intestine, with expanded recruitment of immune cells and higher tissue production of IL-13 and TGF-β3[6]
. Animal models also allowed for the clarification of some of the mechanisms of heart-muscle damage in CRC-associated cachexia involving inflammation. Studies on CD2F1 mice inoculated with C26 cells presented an increase in the production of IL-6, IL-6R, and F4/80 (a marker for macrophages infiltration) in the heart of tumor-bearing vs. non-tumor-bearing mice. Furthermore, increased fibrosis, disrupted myocardial structure, and altered composition of contractile proteins, e.g., troponin I (decreased), myosin heavy-chains isoforms α (decreased), and β (increased), was detected in the cardiac muscle of tumor-bearing mice, resulting in muscle-function impairment[49]
. Inflammatory changes also play a role in metabolic disturbances observed in patients with CRC-associated cachexia. Mice bearing C26 carcinoma represented a well-established murine model of CC resulting in a high systemic level of IL-6[50]
. It was proven that these mice exhibit reduced adipose mass, increased AT lipolysis, and a five-fold increase in FFA plasma levels. These alterations were linked to the activation of IL-6 signaling in WAT through a three-fold increase in phosphorylated STAT3 and high suppressor of cytokine signaling 3 (SOCS3) gene expression levels[51]
. It was also recently reported that the leukemia inhibitory factor (LIF) secreted by the tumor induces changes in the expression of AT, as well as serum levels of IL-6 and leptin, acting in a JAK-dependent manner. This, in turn, results in cachexia-associated adipose wasting as well as anorexia. The authors noted that the use of JAK inhibitors in both in vitro and in vivo models of CC inhibits this process[52]
. Lipolysis is also a typical manifestation of CC. Some of the mechanisms of this process were elucidated, mainly in in vitro models, through the evaluation of the activity of enzymes involved in lipid degradation in cancer cachexia. One example of such is spermidine/Spermine N-1 acetyl transferase (SSAT), an important enzyme in polyamine metabolism, which plays other potential roles, e.g., decreasing lipid accumulation. Its activity is stimulated by a multitude of factors, including those associated with cachexia, such as several cytokines, hormones, and natural substances (reviewed in:[53]
). Constant SSAT activation leads to an increased demand for acetyl-CoA (a cofactor of SSAT), thereby restricting conversion of acetyl-CoA by acetyl-CoA carboxylase (ACC) to malonyl-CoA[54]
. Malonyl-CoA inhibits the rate-limiting step in the β-oxidation of fatty acids and is a substrate in fatty-acid synthesis. A study of the activity of enzymes responsible for increased lipolysis in a mouse model of cancer cachexia (C26) using a cachexigenic clone 20 (c20), and noncachexigenic clone 5 (c5), showed a significant increase in SSAT as well as a decrease in acetyl-CoA carboxylase (ACC) and malonyl-CoA in cachectic mice[55]
. The studies of Chiba et al. confirmed these observations, demonstrating a correlation between malonyl-CoA in the liver and symptoms of CC (c5). In turn, in mice bearing the c5 tumor, the levels of SSAT mRNA did not correlate with the severity of CC manifestations. Hence, malonyl-CoA in the liver, correlating with the weight of fat stores in mice, seems to be a good marker of CC. A decrease in malonyl-CoA resulted in lowered fatty-acid synthesis and accelerated lipolysis via activation of carnitine palmitoyltransferase 1 (CPT-1) and ketogenesis. According to the authors, a decrease in the level of malonyl-CoA activity, playing a major role in CC induction, can be also caused by factors other than SSAT. From the panel of investigated pro-inflammatory (e.g., IL-1β, IL-6, and TNF-α) and anti-inflammatory/immunomodulatory cytokines (e.g., IL-10), only IL-10 had a negative correlation with body weight and the weights of skeletal muscle and storage fat[54]
. In another study, ApcMin/+
mice (carrying a dominant mutation in the APC gene) are a model of colon cachexia directly related to an intestinal tumor burden and subsequent chronic inflammation (with elevated IL-6 levels). These mice were classified as noncachectic (8 weeks of age), precachectic (14 weeks of age), and severely cachectic (20 weeks of age). These studies confirmed the disturbances in hepatic triglyceride metabolism in catechetic mice. Furthermore, a novel role of hepatic glycosylphosphatidylinositol-anchored high-density lipoprotein binding protein 1 (GPIHBP1) was confirmed in hypertriglyceridemia with marked liver steatosis in ApcMin/+
mice. It was also reported that GPIHBP1 is involved in the NF-κB signaling pathway in the liver of cachectic mice. The authors found a decrease in the hepatic uptake of fatty acids and lipolysis, with no differences in fatty-acid β-oxidation[56]
. Clinical studies of CC showed that the increase in serum FFAs (an indicator of enhanced lipolysis) was positively correlated with serum pro-inflammatory cytokine levels (e.g., IL-6 and TNF-α)[38]
. In turn, disorders of lipid metabolism in cachexia (including mechanisms of lipolysis) were described in recent review papers. The involvement of both inflammatory factors, defects in energy utilization, and molecular mechanisms underlying the WAT dysfunction and browning in CC are all highlighted in the mentioned works .The role of direct adipose-cell involvement in the mechanisms of lipolysis in cachexia is described later in the paper. In turn, a brief summary of selected mediator action during systemic inflammatory response associated with CC is presented in
The role of direct adipose-cell involvement in the mechanisms of lipolysis in cachexia is described later in the paper (Section 5.2). In turn, a brief summary of selected mediator action during systemic inflammatory response associated with CC is presented in .Procachectic Mediator | Model of the Study | Target Tissue | Mechanism of Action | Ref. | ||
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TNF-α | Murine C2C12 and primary myoblasts; mouse colon-26 cells (C26); various in vitro and in vivo mouse models of CC; patients with CC | Muscle | (i) catabolic effects; (ii) TNF-α + IFN-γ led to ↓expression of myosin via RNA-dependent mechanism in myotubes and muscle tissue; (iii) UPS pathway contribution | [18] | ||
Adipose; muscle | (i) catabolic effects; (ii) loss of AT and proteolysis, while causing ↓protein, lipid, and glycogen synthesis; (iii) ↓lipoprotein lipase; ↑gluconeogenesis; (iv) ↓protein synthesis via ↓in the active eIF4F complex; (v) serum levels do not correlate with weight loss | [19][15] | ||||
CRC patients with different stages of CC; BALB/c male mice; C26/clone 20 cells | Adipose | was positively linked to FFA in early- but not late-stage CC | [38] | |||
cancer patients with CC; WSC; C | ↑level in CC patients vs. C | [39] | ||||
CRC tissue samples | Muscle | (i) negative correlation with SMI and SDS-MYL1; (ii) positive correlation with HMGB1 | [45] | * | ||
primary operable CRC and control | (i) ↑level was correlated with CRC staging; (ii) patients with the greatest nutritional deficit exhibited ↑levels of adipocytokines | [48] | * | |||
PIF | various mouse models of CC; cancer patients with CC | Muscle | (i) catabolic effect on skeletal muscle; (ii) ↓protein synthesis via ↑phosphorylation of the eIF2 on the alpha-subunit; (iii) its presence is indicative of weight loss; (iv) its presence in the urine of CC patients is indicative of weight loss | [15] | ||
C2C12 mouse myoblasts; MAC16 tumors | Muscle | ↑Ca | +2i | , initiating a signaling cascade that leads to a ↓protein synthesis and ↑ in protein degradation | [20] | |
IL-1 (α and β) |
C2C12 myoblasts, mature C2C12 myotubes model | Muscle | (i) an oxidant and Akt/FOXO-independent mechanism to activate p38 MAPK, ↑NF-κB signaling; (ii) ↑expression of Atrogin 1/MAFbx and MuRF1, and ↓myofibrillar protein in differentiated myotubes; (iii) the direct mechanisms in human CC tissue wasting are not recognized | [27] | ||
IFN-γ | Various in vitro and in vivo mouse models of CC | Adipose; muscle | (i) with TNF-α led to ↓expression of myosin via RNA-dependent mechanism in myotubes and muscle tissue; (ii) UPS pathway contribution; (iii) changes in expression and signaling may be perceived at stages preceding refractory cachexia | [18][28] | ||
cancer patients with CC; WSC; C | positive correlation with plasma FA profile | [39] | ||||
IL-6 | Apc | Min/+ | mice; C2C12 cells | Muscle | (i) ↑muscle wasting; (ii) altered the expression of proteins regulating mitochondrial biogenesis and fusion; (iii) ↓in mitochondrial content during the progression of cachexia; (iv) directly ↑FIS1 expression in muscle cells; (v) ↑indices of ROS in myotubes | [34] |
mature C2C12 myotubes model; in vitro and in vivo mouse model of CC | Muscle | STAT3 activation is a common feature of muscle wasting, muscle fiber atrophy and exacerbated wasting in CC | [30] | |||
Mouse model of CC; C26 cells; human cancerous-tissue samples | Adipose | ↑expression of UPC1 in WAT, which affects the mitochondrial respiration, uncoupling it toward thermogenesis instead of ATP synthesis, which results in ↑lipid mobilization and energy spending in CC | [37] | |||
CRC patients with different stages of CC; BALB/c male mice; C26/clone 20 cells | Adipose | (i) regulating WAT lipolysis in early-stage cachexia and browning in late-stage cachexia; (ii) correlation with serum FFA | [38] | |||
cancer patients with CC; WSC; C | ↑level in CC patients vs. control | [39] | ||||
C26 model of CC | Adipose | (i) ↓AT mass, ↑AT lipolysis, and a 5-fold ↑ in FFA plasma levels; (ii) activation of IL-6 signaling in WAT through a 3-fold ↑ in pSTAT3 and high SOCS3 gene expression levels | [51] | * | ||
CD2F1 mice inoculated with C26 cells and vehicle | Muscle | (i) ↑IL-6, IL-6R, and F4/80 in the heart of tumor-bearing vs. control; (ii) ↑fibrosis, disrupted myocardial structure, and altered composition of contractile proteins | [49] | * | ||
IL-8 | cancer patients with CC; WSC; C | (i) ↑level in CC patients vs. control and in WSC vs. control; (ii) positive correlation with plasma FA profile | [39] |
Legend: ↑, ↓—increase (up-regulation)/decrease expression/level; *—concerns CRC patients/tissues; Akt—serine-threonine protein kinase; AMPK—AMP-activated protein kinase; AT—adipose tissue; C—control; CC—cancer cachexia; (F)FA—(free) fatty acid; FIS1—fission protein 1; FOXO—Forkhead-O; HMGB 1—high mobility group box 1; eIF4E—eukaryotic initiation factor-4E; IL-1, -6, -8—interleukin 1, 6, 8; IFN-γ—interferon gamma; MAPK—AMP-activated protein kinase; MAFbx—muscle atrophy F-box; MAPK—mitogen-activated protein kinase; MuRF1—muscle RING-finger 1; NF-κB—nuclear factor kappa B; PIF—proteolysis-inducing factor; pSTAT3—phosphorylated signal transducer and activator of transcription protein; ROS—reactive oxygen species; SDS-MYL1—SDS-soluble myosin light chain 1; SMI—skeletal-muscle index; SOCS3—suppressor of cytokine signaling 3; TG—triglycerides; TNF-α—tumor necrosis factor α; UPC1—uncoupling protein 1; UPS—ubiquitin-proteasome system; WAT—white adipose tissue; WSC—weight stable cancer.