Cleavage of caspases-1, -3, -6, -8 and -9 substrates by proteases in skeletal muscles from mice undergoing cancer cachexia

A prominent feature of several type of cancer is cachexia. This syndrome causes a marked loss of lean body mass and muscle wasting, and appears to be mediated by cytokines and tumour products. There are several proteases and proteolytic pathways that could be responsible for the protein breakdown. In the present study, we investigated whether caspases are involved in the proteolytic process of skeletal muscle catabolism observed in a murine model of cancer cachexia (MAC16), in comparison with a related tumour (MAC13), which does not induce cachexia. Using specific peptide substrates, there was an increase of 54% in the proteolytic activity of caspase-1, 84% of caspase-8, 98% of caspase-3 151% to caspase-6 and 177% of caspase-9, in the gastrocnemius muscle of animals bearing the MAC16 tumour (up to 25% weight loss), in relation to muscle from animals bearing the MAC13 tumour (1-5% weight loss). The dual pattern of 89 kDa and 25 kDa fragmentation of poly (ADP-ribose) polymerase (PARP) occurred in the muscle samples from animals bearing the MAC16 tumour and with a high amount of caspase-like activity. Cytochrome c was present in the cytosolic fractions of gastrocnemius muscles from both groups of animals, suggesting that cytochrome c release from mitochondria may be involved in caspase activation. There was no evidence for DNA fragmentation into a nucleosomal ladder typical of apoptosis in the muscles of either group of mice. This data supports a role for caspases in the catabolic events in muscle involved in the cancer cachexia syndrome.

Effect of oral eicosapentaenoic acid on weight loss in patients with pancreatic cancer

Eicosapentaenoic acid (EPA) has been shown to modulate aspects of the inflammatory response that may contribute to weight loss in cancer. This study aimed to evaluate the acceptability and effects of oral supplementation with high-purity EPA in weight-losing patients with advanced pancreatic cancer. Twenty-six patients were entered into the study. EPA (95% pure) was administered as free acid starting at 1 g/day; the dose was increased to 6 g/day over four weeks, and then a maintenance dose of 6 g/day was administered. Patients were assessed before EPA and at 4, 8, and 12 weeks while receiving EPA, for weight, body composition, hematologic and clinical chemistry variables, acute-phase protein response, and performance status. Overall survival was noted. Supplementation was well tolerated, with only five patients experiencing side effects possibly attributable to the EPA. Before starting EPA, all patients had been losing weight at a median rate of 2 kg/mo. In general, after EPA supplementation, weight was stable. After four weeks of EPA supplementation, patients had a median weight gain of 0.5 kg (p = 0.0009 vs. rate of weight loss at baseline), and this stabilization of weight persisted over the 12-week study period. Total body water as a percentage of body weight remained stable, as did the proportion of patients with an acute-phase protein response, patients' nutritional intake, and performance status. Overall median survival from diagnosis in this study was 203 days. This study suggests that EPA is well tolerated, may stabilize weight in cachectic pancreatic cancer patients, and should be tested as an anticachectic agent in controlled trials.

Loss of skeletal muscle in cancer: biochemical mechanisms

Patients with cancer often undergo a specific loss of skeletal muscle mass, while the visceral protein reserves are preserved. This condition known as cachexia reduces the quality of life and eventually results in death through erosion of the respiratory muscles. Nutritional supplementation or appetite stimulants are unable to restore the loss of lean body mass, since protein catabolism is increased mainly as a result of the activation of the ATP-ubiquitin-dependent proteolytic pathway. Several mediators have been proposed. An enhanced protein degradation is seen in skeletal muscle of mice administered tumour necrosis factor (TNF), which appears to be mediated by oxidative stress. There is some evidence that this may be a direct effect and is associated with an increase in total cellular-ubiquitin-conjugated muscle proteins. Another cytokine, interleukin-6 (IL-6), may play a role in muscle wasting in certain animal tumours, possibly through both lysosomal (cathepsin) and non-lysosomal (proteasome) pathways. A tumour product, proteolysis-inducing factor (PIF) is produced by cachexia-inducing murine and human tumours and initiates muscle protein degradation directly through activation of the proteasome pathway. The action of PIF is blocked by eicosapentaenoic acid (EPA), which has been shown to attenuate the development of cachexia in pancreatic cancer patients. When combined with nutritional supplementation EPA leads to accumulation of lean body mass and prolongs survival. Further knowledge on the biochemical mechanisms of muscle protein catabolism will aid the development of effective therapy for cachexia.

Metabolic abnormalities in cachexia and anorexia

An increased glucose requirement by many solid tumors produces an increased metabolic demand on the liver, resulting in an increased energy expenditure. In addition, several cytokines and tumor catabolic products have been suggested as being responsible for the depletion of adipose tissue and skeletal-muscle mass in cachexia. A sulphated glycoprotein of molecular mass 24 kDa, produced by cachexia-inducing tumors and present in the urine of cancer patients actively losing weight, has been shown to be capable of inducing direct muscle catabolism in vitro and a state of cachexia in vivo, with specific loss of the non-fat carcass mass. In vitro studies have shown the bioactivity of this proteolysis-inducing factor to be attenuated by the polyunsaturated fatty acid, eicosapentaenoic acid. Preliminary clinical studies have shown that eicosapentaenoic acid stabilizes body weight and protein and fat reserves in patients with pancreatic carcinoma. Further trials are required to confirm the efficacy of eicosapentaenoic acid and to determine the anticachectic activity in other types of cancer.

Effect of the specific cyclooxygenase-2 inhibitor meloxicam on tumour growth and cachexia in a murine model

The effects of the cyclooxygenase-2 (COX-2) inhibitor, meloxicam, on tumour growth and cachexia have been determined in 2 established murine adenocarcinomas (MAC). At a dose level of 2.5 and 5.0 mgkg(-1), meloxicam produced pronounced inhibition of the growth of the MAC13 tumour, increasing the tumour volume doubling time from 2 to 5 days. Meloxicam also suppressed growth of the MAC16 tumour, which is generally refractory to standard cytotoxic agents, increasing the tumour volume doubling time from 1.5 to 2.5 days at dose levels of 0.5 and 1.0 mgkg(-1). Cachexia was also effectively attenuated at these dose levels. To investigate whether meloxicam exerted a direct effect on the cachectic process, studies on protein degradation were carried out using C(2)C(12) mouse myoblasts in response to a proteolysis-inducing factor (PIF). PIF produced maximum protein degradation at a concentration of 4.2 nM, and this was effectively attenuated by meloxicam at concentrations greater than 1 microM. This suggests that meloxicam may be capable of directly antagonizing the process of muscle catabolism in cachexia.

Effect of a fluorinated pyrimidine on cachexia and tumour growth in murine cachexia models: relationship with a proteolysis inducing factor

The fluorinated pyrimidine nucleoside, 5'-deoxy-5-fluorouridine (5'-dFUrd) has been shown to effectively attenuate the progress of cachexia in the murine adenocarcinomas MAC16 and colon 26 as well as in the human uterine cervical carcinoma xenograft, Yumoto. Although concomitant inhibition of tumour growth was observed in all three models this was not sufficient to account for the preservation of body weight. An attempt has been made to correlate the anti-cachectic activity of 5'-dFUrd with the presence of a tumour produced proteolysis-inducing factor (PIF), thought to be responsible for the development of cachexia in the MAC16 model. Two variants of colon 26 adenocarcinoma were employed, clone 20 which produces profound cachexia, and clone 5 which produces no change in body weight in recipient animals. Mice bearing the colon 26, clone 20 variant showed evidence for the presence of PIF in tumour, serum and urine, while there was no evidence for the presence of PIF in tumour or body fluids of mice bearing the clone 5 tumours. Treatment of animals bearing the clone 20 variant with 5'-dF Urd led to the disappearance of PIF from the tumour, serum and urine concomitant with the attenuation of the development of cachexia. The human cervical carcinoma, Yumoto, which also induced cachexia in recipiant animals, showed expression of PIF in tumour, serum and urine in control and vehicle-treated mice, but was absent in mice treated with 5'-dFUrd. Thus in these experimental models cachexia appears to be correlated with the presence of PIF.

Effect of the specific cyclooxygenase-2 inhibitor meloxicam on tumour growth and cachexia in a murine model

The effects of the cyclooxygenase-2 (COX-2) inhibitor, meloxicam, on tumour growth and cachexia have been determined in 2 established murine adenocarcinomas (MAC). At a dose level of 2.5 and 5.0 mgkg(-1), meloxicam produced pronounced inhibition of the growth of the MAC13 tumour, increasing the tumour volume doubling time from 2 to 5 days. Meloxicam also suppressed growth of the MAC16 tumour, which is generally refractory to standard cytotoxic agents, increasing the tumour volume doubling time from 1.5 to 2.5 days at dose levels of 0.5 and 1.0 mgkg(-1). Cachexia was also effectively attenuated at these dose levels. To investigate whether meloxicam exerted a direct effect on the cachectic process, studies on protein degradation were carried out using C(2)C(12) mouse myoblasts in response to a proteolysis-inducing factor (PIF). PIF produced maximum protein degradation at a concentration of 4.2 nM, and this was effectively attenuated by meloxicam at concentrations greater than 1 microM. This suggests that meloxicam may be capable of directly antagonizing the process of muscle catabolism in cachexia.

Increased gene expression of brown fat uncoupling protein (UCP)1 and skeletal muscle UCP2 and UCP3 in MAC16-induced cancer cachexia

Weight loss in cancer cachexia is attributable to decreased food intake and/or enhanced energy expenditure. We investigated the roles of the uncoupling proteins (UCPs) UCPI, -2, and -3 in a murine model of cachexia, the MAC16 adenocarcinoma. Weight fell to 24% below that of non-tumor-bearing controls (P < 0.01) 18 days after MAC16 inoculation, with significant reductions in fat-pad mass (-67%; P < 0.01) and muscle mass (-20%; P < 0.01). Food intake was 26-60% lower (P < 0.01) than in controls on days 17-18. Non-tumor-bearing mice, pair-fed to match MAC16-induced hypophagia, showed less weight loss (10% below controls, P < 0.01; 16% above MAC-16, P < 0.01) and smaller decreases in fat-pad mass (21% below controls, P < 0.01). Core temperature in MAC16 mice was significantly lower (-2.4 degrees C, P < 0.01) than in controls, and pair-feeding had no effect. MAC16 mice showed significantly higher UCP1 mRNA levels in brown adipose tissue (BAT) than in controls (+63%, P < 0.01), and pair-feeding had no effect. UCP2 and -3 expression in BAT did not differ significantly between groups. By contrast, UCP2 mRNA levels in skeletal muscle were comparably increased in both MAC16 and pair-fed groups (respectively, 183 and 163% above controls; both, P < 0.05), with no significant difference between these two groups. Similarly, UCP3 mRNA was significantly higher than controls in both MAC16 (+163%, P < 0.05) and pair-fed (+253%, P < 0.01) groups, with no significant difference between the two experimental groups. Overexpression of UCP1 in BAT in MAC16-bearing mice may be an adaptive response to hypothermia, which is apparently induced by tumor products; increased thermogenesis in BAT could increase total energy expenditure and, thus, contribute to tissue wasting. Increased UCP2 and -3 expression in muscle are both attributable to reduced food intake and may be involved in lipid utilization during lipolysis in MAC16-induced cachexia.

Characteristics of patients with pancreatic cancer expressing a novel cancer cachectic factor

BACKGROUND

Recently a novel tumour-derived cachectic factor was identified in the murine MAC16 colonic adenocarcinoma model of cachexia. This factor, provisionally named proteolysis-inducing factor (PIF), was subsequently identified in the urine of weight-losing patients with cancer but not in the urine of weight-stable patients with cancer or weight-losing controls with benign disease. This study determined the nutritional characteristics of patients with pancreatic cancer who excrete PIF in the urine and investigated the relationship between PIF and the acute-phase protein response.

METHODS

PIF was isolated from urine by precipitation and ultrafiltration and was then identified by Western blotting of nitrocellulose membranes using a previously developed monoclonal antibody. Full nutritional assessment of patients was undertaken at the same time as urine collection.

RESULTS

PIF was detected in the urine of 80 per cent of patients (n = 55). These patients had a significantly greater total weight loss and rate of weight loss than patients whose urine did not contain PIF (median 12.5 (range 4-43) kg versus 4.5 (0-14) kg; P < 0.0002). No association was evident between the presence of PIF in patients' urine and serum C-reactive protein (CRP) concentration. Furthermore, the accelerated weight loss associated with PIF expression also appeared to be independent of the acute-phase response. Overall the presence of PIF was not associated with reduced survival, although the previously reported association between raised CRP concentration and poor prognosis was confirmed.

CONCLUSION

PIF is associated with an accelerated rate of weight loss in patients with a tumour of the pancreatic head. This observation appears to be independent of the effect of an increased hepatic acute-phase protein response.

Effect of a cancer cachectic factor on protein synthesis/degradation in murine C2C12 myoblasts: modulation by eicosapentaenoic acid

The effect of a proteolysis inducing factor (PIF) on protein synthesis and degradation and the modulation of this effect by the polyunsaturated fatty acid, eicosapentaenoic acid (EPA), have been examined using a surrogate model system, C2C12 myoblasts in vitro. After 90 min of incubation, PIF produced a significant inhibition of protein synthesis in a dose-dependent manner, with maximal inhibition at a concentration of 4 nM. The effect was attenuated both by treatment with a monoclonal antibody to PIF and by treatment with insulin at physiological concentrations (1 nM) and below (0.1 nM), but not by EPA (50 microM). The inhibitory effect on protein synthesis was transitory and was not seen after prolonged incubation with PIF. An increased rate of protein degradation was observed in C2C12 myoblasts after addition of PIF, which was also maximal at a concentration of PIF of 4 nM. Higher concentrations of PIF did not produce an increase in protein degradation. Unlike the effect on protein synthesis, the enhanced protein degradation was completely abolished by pretreatment with 50 microM EPA, suggesting that the two effects are mediated by different mechanisms. PIF produced an increased release of [3H]arachidonic acid from prelabeled myoblasts with a dose-response curve parallel to that of protein degradation and with a maximum at 4 nM PIF. Release of [3H] arachidonic acid was completely blocked in cells pretreated with 50 microM EPA, suggesting that the effect was related to protein degradation. The [3H]arachidonic acid was rapidly metabolized to prostaglandins E2 and F2alpha and to 5-, 12-, and 15-hydroxyeicosatetraenoic acids (HETEs). Production of all eicosanoids was attenuated in cells pretreated with EPA. Of all of the metabolites, only 15-HETE produced a significant increase in protein degradation in C2C12 myoblasts with a maximal effect at 30 nM and with a bell-shaped dose-response curve similar to that produced by PIF. These results suggest that PIF enhances protein degradation as a result of an increased production of 15-HETE.

The effect of an oral nutritional supplement enriched with fish oil on weight-loss in patients with pancreatic cancer

Previous studies have suggested that administration of oral eicosapentaenoic acid (EPA) will stabilize weight in patients with advanced pancreatic cancer. The aim of the present study was to determine if a combination of EPA with a conventional oral nutritional supplement could produce weight gain in these patients. Twenty patients with unresectable pancreatic adenocarcinoma were asked to consume two cans of a fish oil-enriched nutritional supplement per day in addition to their normal food intake. Each can contained 310 kcal, 16.1 g protein and 1.09 g EPA. Patients were assessed for weight, body composition, dietary intake, resting energy expenditure (REE) and performance status. Patients consumed a median of 1.9 cans day(-1). All patients were losing weight at baseline at a median rate of 2.9 kg month(-1). After administration of the fish oil-enriched supplement, patients had significant weight-gain at both 3 (median 1 kg, P= 0.024) and 7 weeks (median 2 kg, P = 0.033). Dietary intake increased significantly by almost 400 kcal day(-1) (P = 0.002). REE per kg body weight and per kg lean body mass fell significantly. Performance status and appetite were significantly improved at 3 weeks. In contrast to previous studies of oral conventional nutritional supplements in weight-losing cancer patients, this study suggests that an EPA-enriched supplement may reverse cachexia in advanced pancreatic cancer.

Role of a proteolysis-inducing factor (PIF) in cachexia induced by a human melanoma (G361)

Human melanoma, G361, which induces cachexia in nude mice, has been shown to produce a proteolysis-inducing factor (PIF) of Mr 24000, which is immunologically identical to that isolated from a cachexia-inducing murine tumour (MAC16). Biosynthetic labelling of G361 cells using a combination of [35S]sulphate and [6-3H]glucosamine gave a single component of Mr 24000 after affinity chromatography employing a murine monoclonal antibody. The material contained both radiolabels and, after digestion with peptide N-glycosidase F, two fragments were produced of Mr 14000 and 10000 also containing both radiolabels. Digestion with O-glycosidase produced three fragments of Mr 14000, 6000 and 4000, the first two of which contained both radiolabels, while the third only contained 3H. This digestion pattern is the same as that previously observed with PIF from the MAC16 tumour and is commensurate with one N-linked sulphated oligosaccharide chain of Mr 10000, one O-linked sulphated oligosaccharide chain of Mr 6000 and a central polypeptide chain of Mr 4000 with some residual carbohydrate. When PIF from G361 cells was administered to female NMRI mice (20 g) a pronounced depression of body weight (1.36+/-0.36 g; P < 0.0001 from control) was observed over a 24 h period without a decrease in either food or water consumption. Body composition analysis showed a significant decrease in the non-fat carcass mass without a change in carcass fat or body water. This result suggests that depletion of lean body mass in mice bearing G361 melanoma arises from the production of PIF.

Effect of a cachectic factor on carbohydrate metabolism and attenuation by eicosapentaenoic acid

The effect of a proteolysis-inducing factor (PIF), produced by cachexia-inducing tumours on glucose utilization by different tissues and the effect of pretreatment with the polyunsaturated fatty acid eicosapentaenoic acid (EPA), has been determined using the 2-deoxyglucose tracer technique. Mice receiving PIF showed a profound depression of body weight (2.3 g) over a 24-h period, which was completely abolished by pretreatment with a monoclonal antibody to PIF or by 3 days pretreatment with EPA at 500 mg kg(-1). Animals receiving PIF exhibited a marked hypoglycaemia, which was effectively reversed by both antibody and EPA pretreatment. There was an increase in glucose utilization by brain, heart and brown fat, but a decrease by kidney, white fat, diaphragm and gastrocnemius muscle after administration of PIF. Changes in organ glucose consumption were attenuated by either monoclonal antibody, EPA, or both. There was a decrease in 2-deoxyglucose uptake by C2C12 myoblasts in vitro, which was attenuated by EPA. This suggests a direct effect of PIF on glucose uptake by skeletal muscle. These results suggest that in addition to a direct catabolic effect on skeletal muscle PIF has a profound effect on glucose utilization during cachexia.

Catabolism of adipose tissue by a tumour-produced lipid-mobilising factor

Induction of lipolysis in murine white adipocytes by a tumour lipid-mobilising factor (LMF) was associated with stimulation of adenylate cyclase in adipocyte plasma membrane preparations. Induction of lipolysis was attenuated by the adenylate cyclase inhibitor MDL12330A and the protein kinase A inhibitor H8, suggesting that cAMP was the intracellular mediator of induction. The effect of LMF on adenylate cyclase was responsive to GTP, with low concentrations (0.1 microM) causing stimulation and high concentrations (10 microM) causing inhibition, suggesting the involvement of both stimulatory (Gs) and inhibitory (Gi) guanine nucleotide-binding proteins. At a concentration of 10 microM, propranolol noncompetitively reduced the induction of lipolysis by LMF. Thus, lipolysis in white adipose tissue during the process of cancer cachexia is mediated by a tumour factor which stimulates cAMP production, possibly through a beta-adrenergic receptor.

Wasting in cancer

Progressive weight loss is a common feature of many types of cancer and is responsible not only for a poor quality of life and poor response to chemotherapy, but also a shorter survival time than is found in patients with comparable tumors without weight loss. Although anorexia is common, a decreased food intake alone is unable to account for the changes in body composition seen in cancer patients, and increasing nutrient intake is unable to reverse the wasting syndrome. Although energy expenditure is increased in some patients, cachexia can occur even with a normal energy expenditure. Various factors have been investigated as mediators of tissue wasting in cachexia. These include cytokines such as tumor necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6), interferon-gamma (IFN-gamma) and leukemia inhibitory factor (LIF), as well as tumor-derived factors such as lipid mobilizing factor (LMF) and protein mobilizing factor (PMF), which can directly mobilize fatty acids and amino acids from adipose tissue and skeletal muscle respectively. Induction of lipolysis by the cytokines is thought to result from an inhibition of lipoprotein lipase (LPL), although clinical studies provide no evidence for an inhibition of LPL in the adipose tissue of cancer patients. Instead there is an increased expression of hormone sensitive lipase, the enzyme activated by LMF. Protein degradation in cachexia is associated with an increased activity of the ATP-ubiquitin-proteasome pathway. The biological activity of both the LMF and PMF was shown to be attenuated by eicosapentaenoic acid (EPA). Clinical studies show that this polyunsaturated fatty acid is able to stabilize the rate of weight loss and adipose tissue and muscle mass in cachectic patients with unresectable pancreatic cancer. Knowledge of the mechanism of cancer cachexia should lead to the development of new therapeutic agents.

Mechanism of inhibition of a tumor lipid-mobilizing factor by eicosapentaenoic acid

Stimulation of lipolysis or adenylate cyclase activity by either isoprenaline or a tumor-derived lipid-mobilizing factor was effectively attenuated in isolated white adipocytes or in adipocyte plasma membranes pretreated with eicosapentaenoic acid (EPA) dissolved in ethanol or from mice dosed p.o. with EPA (1.25 g/kg). A similar effect was observed with docosahexanoic acid (DHA) that may be partly due to retroconversion to EPA. Stimulation of adenylate cyclase activity by forskolin, which acts directly on the enzyme without the involvement of a receptor, was also decreased in membranes of mice treated with EPA, suggesting a direct interaction between EPA and adenylate cyclase. Pertussis toxin eliminated the inhibition of lipolysis and the stimulation of adenylate cyclase by isoprenaline and lipid-mobilizing factor in the presence of EPA, but not DHA. This suggests that the attenuation of hormonal stimulation of adenylate cyclase by EPA was due, at least in part, to an inhibitory guanine nucleotide-binding protein-mediated inhibition of adenylate cyclase activity. The effect of DHA may be due to a direct inhibition of the cyclase catalytic component. The ability of EPA to preserve fat stores during the process of cachexia seems to arise from the attenuation of the stimulation of adenylate cyclase.

Mechanism of muscle protein degradation induced by a cancer cachectic factor

A proteolysis-inducing factor (PIF) isolated from a cachexia-inducing murine tumour (MAC16) produced a decrease in body weight (1.6 g, P < or = 0.01 compared with control subjects) within 24 h after i.v. administration to non-tumour-bearing mice. Weight loss was associated with significant decreases in the weight of the spleen and soleus and gastrocnemius muscles, with no effect on the weight of the heart or kidney and with an increase in weight of the liver. Protein degradation in isolated soleus muscle was significantly increased in mice bearing the MAC16 tumour. To define which proteolytic pathways contribute to this increase, soleus muscles from mice bearing the MAC16 tumour and non-tumour-bearing animals administered PIF were incubated under conditions that modify different proteolytic systems. In mice bearing the MAC16 tumour, there were increases in both cathepsin B and L, and the Ca2+-dependent lysosomal and ATP-dependent pathways were found to contribute to the increased proteolysis; whereas, in PIF-injected animals, there was activation only of the ATP-dependent pathway. Further studies in mice bearing the MAC16 tumour have provided evidence for increased levels of ubiquitin-conjugated proteins and increased mRNA levels for the 14 kDa ubiquitin carrier protein E2 and the C9 proteasome subunit in gastrocnemius muscle, suggesting activation of the ATP-ubiquitin-dependent proteolytic pathway. A monoclonal antibody to PIF attenuated the enhanced protein degradation in soleus muscle from mice bearing the MAC16 tumour, confirming that PIF is responsible for the loss of skeletal muscle in cachectic mice.

Purification and characterization of a tumor lipid-mobilizing factor

Cancer patients with weight loss showed urinary excretion of a lipid-mobilizing factor (LMF), determined by the ability to stimulate lipolysis in isolated murine epididymal adipocytes. Such bioactivity was not detectable in the urine of cancer patients without weight loss or in normal subjects. The LMF was purified using a combination of ion exchange, exclusion, and hydrophobic interaction chromatographies to give a single component of apparent Mr 43,000, which showed homology in amino acid sequence with human plasma Zn-alpha2-glycoprotein. Both substances showed the same mobility on denaturing and nondenaturing gels and the same chymotrypsin digestion pattern, both stained heavily for carbohydrate, and they showed similar immunoreactivity. Polyclonal antisera to human plasma Zn-alpha2-glycoprotein was also capable of neutralization of the bioactivity of human LMF in vitro. Using competitive PCR to quantify expression of Zn-alpha2-glycoprotein, we found that only those tumors that were capable of producing a decrease in carcass lipid expressed mRNA for Zn-alpha2-glycoprotein. These results provide strong evidence to suggest that tumor production of Zn-alpha2-glycoprotein is responsible for the lipid catabolism seen in cancer patients.

Biological evaluation of a lipid-mobilizing factor isolated from the urine of cancer patients

We have previously shown human lipid-mobilizing factor (LMF) to be homologous with the plasma protein Zn-alpha2-glycoprotein in amino acid sequence, electrophoretic mobility, and immunoreactivity. In this study, both LMF and Zn-alpha2-glycoprotein have been shown to stimulate glycerol release from isolated murine epididymal adipocytes with a comparable dose-response profile. Both LMF and Zn-alpha2-glycoprotein caused a stimulation of adenylate cyclase in murine adipocyte plasma membranes in a GTP-dependent process, with maximum stimulation at 0.1 microM GTP and with saturation at protein concentrations of >5 microg/assay. Administration of LMF to exbreeder male mice over a 89-h period produced a decrease in body weight without a change in food and water intake. Body composition analysis showed a 42% reduction in carcass lipid when compared with controls. Treatment of ob/ob mice with human LMF over a 160-h period also produced a decrease in body weight, with a 19% reduction in carcass fat, without a change in body water or nonfat mass. Serum levels of glycerol and 3-hydroxybutyrate were significantly increased, as was oxygen uptake by interscapular brown adipose tissue, providing evidence of increased lipid mobilization and utilization. Human white adipocytes responded to both LMF and isoprenaline to the same extent, although the maximal response was lower than that for murine white adipocytes. These results suggest that LMF not only has the capacity to induce lipid mobilization and catabolism in mice, but it also has the potential to exert similar effects in cachectic cancer patients.

New cachexic factors

Patients with pancreatic cancer show evidence of cachexia at the time of diagnosis, involving not only loss of adipose tissue, but also lean body mass. The shorter survival time of men than women with non-small cell lung cancer has been attributed to their enhanced rate of weight loss. From studies in animal models, various cytokines have been proposed as mediators of the cachectic process, although evidence from human studies is generally lacking. Only serum levels of IL-6 have been found to correlate with the clinical development of cachexia, but this may be a marker for the process rather than the actual mediator, because the direct administration of this cytokine to experimental animals failed to induce cachexia, despite the induction of an acute-phase response. Ciliary neurotrophic factor, a member of the IL-6 superfamily, has, however, been shown to produce loss of muscle mass in experimental animals, although it failed to exert a direct catabolic effect on muscle in vitro. A sulphated glycoprotein found in the urine of patients with cancer cachexia is capable of directly inducing protein catabolism in skeletal muscle by a process involving an increase in prostaglandin E2. Agents capable of attenuating this effect, e.g. eicosapentaenoic acid and ibuprofen, have been shown to stabilize body weight loss in cachectic cancer patients. This pharmacological approach to the treatment of cachexia appears to be more successful than nutritional manipulation.

Biology of cachexia

About half of all cancer patients show a syndrome of cachexia, characterized by loss of adipose tissue and skeletal muscle mass. Such patients have a decreased survival time, compared with the survival time among patients without weight loss, and loss of total body protein leads to substantial impairment of respiratory muscle function. These changes cannot be fully explained by the accompanying anorexia, and nutritional supplementation alone is unable to reverse the wasting process. Despite a falling caloric intake, patients with cachexia frequently show an elevated resting energy expenditure as a result of increases in Cori cycle (i.e., catalytic conversion of lactic acid to glucose) activity, glucose and triglyceride-fatty acid cycling, and gluconeogenesis. A number of cytokines, including tumor necrosis factor-apha, interleukins 1 and 6, interferon gamma, and leukemia-inhibitory factor, have been proposed as mediators of the cachectic process. However, the results of a number of clinical and laboratory studies suggest that the action of the cytokines alone is unable to explain the complex mechanism of wasting in cancer cachexia. In addition, cachexia has been observed in some xenograft models even without a cytokine involvement, suggesting that other factors may be involved. These probably include catabolic factors, which act directly on skeletal muscle and adipose tissue and the presence of which has been associated with the clinical development of cachexia. A polyunsaturated fatty acid, eicosapentaenoic acid, attenuates the action of such catabolic factors and has been shown to stabilize the process of wasting and resting energy expenditure in patients with pancreatic cancer. Such a pharmacologic approach may provide new insights into the treatment of cachexia.

Structural analysis of a tumor-produced sulfated glycoprotein capable of initiating muscle protein degradation

A material of Mr 24,000 has been isolated from a cachexia-inducing mouse tumor (MAC16) and shown to initiate protein degradation in isolated gastrocnemius muscle. Biological activity was destroyed by preincubation with peptide N-glycosidase F (PNGase F) and endo-alpha-N-acetylgalactosaminidase (O-glycosidase) but not by neuraminidase or trypsin. Antibody reactivity was destroyed by treatment with periodate, indicating carbohydrate moieties to be the antigenic determinants. Antigenic activity was also reduced by treatment with PNGase F and O-glycosidase and was completely destroyed by treatment with chondroitinase ABC but was unaffected by treatment with either trypsin or chymotrypsin, confirming that the N- and O-linked sulfated oligosaccharide chains were both the antigenic and biological determinants. Biosynthetic labeling of MAC16 cells using a combination of [35S]sulfate and [6-3H]GlcN gave a single component of Mr 24,000 containing both radiolabels. Similar material could not be isolated from a cell line (MAC13) originating from a tumor that does not cause cachexia in vivo. Digestion of 3H/35S material with PNGase F produced two fragments of Mr 14,000 and 10,000 containing both radiolabels, and digestion with O-glycosidase produced three fragments of Mr 14,000, 6,000, and 4, 000, the first two contained both radiolabels and the third contained only 3H. Digestion of the fragment of Mr 14,000 released by PNGase F with O-glycosidase also gave fragments of Mr 6,000 and 4, 000. The products from both digestions were acidic as determined by anion exchange chromatography on DEAE-cellulose. The negative charge on the fragment of Mr 4,000 was removed by treatment with alkaline phosphatase. This suggests that the charge originated from phosphate residues, and this has been confirmed by biosynthetic labeling of MAC16 cells with [32P]orthophosphate, where radiolabel was incorporated into material of Mr 24,000 and into the fragment of Mr 4,000 after treatment with O-glycosidase. To determine the size of the polypeptide core MAC16 cells were biosynthetically labeled with L-[2,5-3H]His which after chemical deglycosylation produced a major component of Mr 4,000. These results suggest a model for the Mr 24, 000 material consisting of a central polypeptide chain of Mr 4,000 and with phosphate residues that may be attached to the polypeptide or a short oligosaccharide chain containing GlcN, one O-linked sulfated oligosaccharide chain containing GlcN, and of Mr 6,000 and one N-linked sulfated oligosaccharide chain of Mr 10,000 also containing GlcN. Neither chain was cleaved into disaccharides with chondroitinase ABC, suggesting that the material is a sulfated glycoprotein.