Tumor inoculation site affects the development of cancer cachexia and muscle wasting

The phenotype and severity of cancer cachexia differ among tumor types and metastatic site in individual patients. In this study, we evaluated if differences in tumor microenvironment would affect the development of cancer cachexia in a murine model, and demonstrated that body weight, adipose tissue and gastrocnemius muscle decreased in tumor‐bearing mice. Interestingly, a reduction in heart weight was observed in the intraperitoneal tumor group but not in the subcutaneous group. We evaluated 23 circulating cytokines and members of the TGF‐β family, and found that levels of IL‐6, TNF‐α and activin A increased in both groups of tumor‐bearing mice. Eotaxin and G‐CSF levels in the intraperitoneal tumor group were higher than in the subcutaneous group. Atrogin 1 and MuRF1 mRNA expressions in the gastrocnemius muscle increased significantly in both groups of tumor‐bearing mice, however, in the myocardium, expression of these mRNAs increased in the intraperitoneal group but not in subcutaneous group. Based on these results, we believe that differences in microenvironment where tumor cells develop can affect the progression and phenotype of cancer cachexia through alterations in various circulating factors derived from the tumor microenvironment.     

Rosiglitazone delayed weight loss and anorexia while attenuating adipose depletion in mice with cancer cachexia

Cachexia is characterized by severe weight loss, including adipose and muscle wasting, and occurs in a large percentage of cancer patients. Insulin resistance contributes to dysregulated metabolism in cachexia and occurs prior to weight loss in mice with colon-26 tumor-induced cachexia. Therefore, we hypothesized that the insulin sensitizer, rosiglitazone, would attenuate the loss of adipose and muscle to result in improved outcomes for mice with late-stage cachexia. Male CD2F1 mice were inoculated with colon-26 adenocarcinoma cells or vehicle. Treatments included vehicle, rosiglitazone (10 mg/kg body weight/day) or rosiglitazone plus pair-feeding to food intake of vehicle-treated mice with tumors. Rosiglitazone delayed weight loss onset by 2 d over the 16 d duration of this aggressive tumor model. This finding was associated, in part, with increased food intake. In addition, adipose mass, adipocyte cross-sectional area and inflammation were improved with rosiglitazone. However, at the time of necropsy 16 d after tumor inoculation rosiglitazone had no effect on retention of muscle mass, strength or proteolysis in late-stage cachexia. We did not measure stamina or endurance in this study. In early-stage cachexia, rosiglitazone normalized PDK4 and PPAR-delta mRNA in quadriceps muscle and rescued the decrease in insulin-stimulated glucose disappearance in mice with tumors. Rosiglitazone may delay weight loss onset by decreasing tumor-induced markers of metabolic change in early-stage cachexia. These changes predict for modest improvement in adipose, but no improvement in muscle strength in late-stage cachexia.     

Inhibition of the renin–angiotensin system improves physiological outcomes in mice with mild or severe cancer cachexia

Cancer cachexia describes the progressive skeletal muscle wasting and weakness associated with many cancers. Cachexia reduces mobility and quality of life and accounts for 20–30% of all cancer‐related deaths. Activation of the renin–angiotensin system causes skeletal muscle wasting and weakness. We tested the hypothesis that treatment with the angiotensin converting enzyme (ACE) inhibitor, perindopril, would enhance whole body and skeletal muscle function in cachectic mice bearing Colon‐26 (C‐26) tumors. CD2F1 mice received a subcutaneous injection of phosphate buffered saline or C‐26 tumor cells inducing either a mild or severe cachexia. The following day, one cohort of C‐26 mice began receiving perindopril in their drinking water (4 mg kg^?1 day^?1) for 21 days. In mild and severe cachexia, perindopril increased measures of whole body function (grip strength and rotarod) and reduced fatigue in isolated contracting diaphragm muscle strips (p < 0.05). In severely cachectic mice, perindopril reduced tumor growth, improved locomotor activity and reduced fatigue of tibialis anterior muscles in situ (p < 0.05), which was associated with increased oxidative enzyme capacity (succinate deyhydrogenase, p < 0.05). Perindopril attenuated the increase in MuRF‐1 and IL‐6 mRNA expression and enhanced Akt phosphorylation in severely cachectic mice but neither body nor muscle mass was increased. These findings support the therapeutic potential of ACE inhibition for enhancing whole body function and reducing fatigue of respiratory muscles in early and late stage cancer cachexia and should be confirmed in future clinical trials. Since ACE inhibition alone did not enhance body or muscle mass, co‐treatment with an anabolic agent may be required to address these aspects of cancer cachexia.     

Chronic Exendin-4 Treatment Prevents the Development of Cancer Cachexia Symptoms in Male Rats Bearing the Yoshida Sarcoma

Cancer cachexia is the syndrome of weight loss, loss of appetite, and wasting of skeletal muscle and adipose tissue experienced by many individuals with cancer. Currently, few effective treatment and prevention strategies are available for these patients, due in part to a poor understanding of the mechanisms contributing to cachexia. Insulin resistance has been associated with cancer cachexia in epidemiological, human, and animal research. The present experiment was designed to examine the ability of Exendin-4, a GLP-1 agonist and insulin sensitizing agent, to prevent the development of cachexia symptoms in male Sprague Dawley rats bearing the Yoshida sarcoma. Following tumor implantation or sham surgery, rats were treated daily with saline or Exendin-4 (3 μg/kg body weight/day) and were monitored for tumor growth and cachexia symptoms for 21–23 days. As a result of large variability in treatment effects, data were analyzed separately for animals with large and small tumors. Exendin-4 treatment reduced tumor growth and prevented the development of cancer cachexia symptoms in animals with small, but not large, tumors. In addition, insulin levels were preserved in Exendin-4-treated tumor-bearing animals. The results of this experiment demonstrate a novel preventative therapy for cancer cachexia and a novel use of Exendin-4. Further research is necessary to determine the mechanisms through which Exendin-4 exerts these potent effects.     

Epigallocatechin-3-gallate effectively attenuates skeletal muscle atrophy caused by cancer cachexia

Cachexia, also known as wasting syndrome notably with skeletal muscle atrophy, costs nearly one-third of all cancer deaths in man. (-)-Epigallocatechin-3-gallate (EGCG), the principal polyphenolic component in green tea, is a potent preventive against cachexia as well as cancers. However, how EGCG counteracts cachexia-provoked muscle wasting is unclear. EGCG was demonstrated to be able to retard tumor progression as well as to prevent body weight from loss, because EGCG attenuates skeletal muscle leukocytic infiltration and down-regulates tumor-induced NF-κB and E3-ligases in muscle. In mice, the dosages optimized against cachexia were determined to be 0.2 mg/mouse/day for prevention and to be 0.6 mg/mouse/day for treatment. Anti-cachexia effects were assessed using the LLC tumor model. Mice with the same body weight were divided into groups, including control, tumor bearing, and tumor-bearing but receiving water or EGCG in both prevention and treatment experiments. RT-PCR was used to assess mRNA expressions of NF-κB, MuRF 1, and MAFbx. The intracellular NF-κB, MuRF 1 and MAFbx were determined and quantified by immunofluorescence and Western blotting, respectively. Our results conclude EGCG regulates the expressions of NF-κB as well as downstream mediators, MuRF 1 and MAFbx, so EGCG may be an appropriate agent to be included in ensemble therapeutics of the tumor-induced muscle atrophy.     

Establishment and characterization of cachexia-inducing and -non-inducing clones of murine colon 26 carcinoma

To investigate the mechanism causing cachexia and its association with shorter patient survival, we cloned weight-loss-inducing and -non-inducing sublines of murine colon 26 carcinoma (colon 26). One clone, clone 20, induced substantial weight loss, wasting of adipose tissue and muscle, and hypogly-cemia in mice with a minimum tumor burden of 0.3 g (2 g per 100 g body weight). Clone-20-bearing mice had a median survival of 24.5 days with average tumor weight of 0.4 g. In contrast, clone 5 induced neither severe weight loss, wasting of adipose tissue and muscle, nor hypoglycemia; clone-5-bearing mice survived for a median of 70 days with average tumor weight of 12 g. These results clearly indicate that shorter survival is associated with the degree of cachexia and is independent of tumor size. Using this pair of colon 26 clones, we examined mediators of cachexia. Neither TNFα, IL-1α nor IFNγ was detected in the serum of mice bearing either clone, while IL-6 was detected in mice bearing both clones by ELISA and a bioassay. Administration of anti-IL-6 monoclonal antibody (MAb) partially but significantly suppressed cachexia induction in clone-20-bearing mice. These results point to the involvement of IL-6 in experimental cachexia. However, our finding of the presence of IL-6 in the serum of mice bearing clone 5, which does not induce weight loss, clearly indicates that IL-6 is not solely responsible for the induction of cachexia. © 1995 Wiley-Liss, Inc.     

Experimental cancer cachexia induced by transplantable colon 26 adenocarcinoma in mice

The present study investigates a tumor model for cachectic mice. Among various murine transplantable tumors, used for assessing cytostatics, we identified colon 26 adenocarcinoma (colon 26) as capable of causing cachexia. Fifteen days after inoculation, the tumor grew to about 6% of the body weight causing substantial carcass weight loss of 3.4 g (14.5% of the carcass weight). When the tumor size was 2.7 g at 3 weeks after the inoculation, the carcass weight was 12 g less than the age-matched control. The tumor continued to grow while the mice maintained this weight, surviving for an average of 45 days. This extensive weight loss was essentially the wasting of adipose and muscle tissues. Hypoglycemia and hypercorticism occurred during the time of the weight loss. In addition, the colon 26 caused disorders of hepatic functions: the concentration of acute phase proteins in serum increased; the number of hepatic glucocorticoid-cytosol receptors decreased; and activities of hepatic catalase and drug-metabolizing enzymes decreased. On the other hand, noncachectic mice with Meth A fibrosarcoma gained weight, which was somewhat less than the control, and had neither hypoglycemia nor hypercorticism, although some mild disorders of hepatic functions were found. Mice bearing colon 26 is an appropriate model for elucidating the mechanism that causes cachexia.     

Adipose tissue lipolysis and energy metabolism in early cancer cachexia in mice

Cancer cachexia is a progressive metabolic disorder that results in depletion of adipose tissue and skeletal muscle. A growing body of literature suggests that maintaining adipose tissue mass in cachexia may improve quality-of-life and survival outcomes. Studies of lipid metabolism in cachexia, however, have generally focused on later stages of the disorder when severe loss of adipose tissue has already occurred. Here, we investigated lipid metabolism in adipose, liver and muscle tissues during early stage cachexia – before severe fat loss – in the colon-26 murine model of cachexia. White adipose tissue mass in cachectic mice was moderately reduced (34–42%) and weight loss was less than 10% of initial body weight in this study of early cachexia. In white adipose depots of cachectic mice, we found evidence of enhanced protein kinase A - activated lipolysis which coincided with elevated total energy expenditure and increased expression of markers of brown (but not white) adipose tissue thermogenesis and the acute phase response. Total lipids in liver and muscle were unchanged in early cachexia while markers of fatty oxidation were increased. Many of these initial metabolic responses contrast with reports of lipid metabolism in later stages of cachexia. Our observations suggest intervention studies to preserve fat mass in cachexia should be tailored to the stage of cachexia. Our observations also highlight a need for studies that delineate the contribution of cachexia stage and animal model to altered lipid metabolism in cancer cachexia and identify those that most closely mimic the human condition.     

L-carnitine ameliorates cancer cachexia in mice by regulating the expression and activity of carnitine palmityl transferase

Cancer cachexia is characterized by progressive weight loss with the depletion of adipose tissue and skeletal muscle. Impaired fatty acid oxidation mainly resulting from the decrease of carnitine palmitoyltransferase I and II activities in the liver is an important factor that contributes to cancer cachexia . Although recent studies suggest a potential application of L-carnitine in treatment of cancer cachexia, the underlying mechanisms are unknown. In the present study, we aim to assess the effects of L-carnitine on the activity and expression of CPT I and II in the liver of cachectic cancer mice. Our results show that the inoculation of colon-26 adenocarcinoma cells into mice led to cancer cachexia characterized by notable decreases in food intake, gastrocnemius muscle and epididymus fat weight. In addition, the mRNA level and activity of liver carnitine palmitoyltransferase (CPT) I and II, and serum levels of free carnitine and acetylcarnitine were markedly decreased in cachectic mice, accompanied by marked increases in serum levels of tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6). A continuous oral treatment with L-carnitine at 18 mg/kg per day increased dietary uptake, gastrocnemius muscle weight and epididymus fat weight, increased blood glucose and serum albumin levels, and decreased total cholesterol level in cancer cachectic mice, but did not affect tumor growth. These effects of L-carnitine on cancer cachexia mice were accompanied by the upregulation of mRNA level of CPT I and II and increased enzyme activity of CPT I in the liver, as well as the downregulation of serum TNF-α and IL-6 levels. Moreover, free carnitine levels were negatively correlated with serum TNF-α or IL-6 level. These results indicate that L-carnitine ameliorates cancer cachexia by regulating serum TNF-α and IL-6 levels and modulating the expression and activity of CPT in the liver.     

Antitumor activity of indomethacin in mice bearing advanced colon 26 carcinoma compared with those with early transplants

The antitumor activity of indomethacin (IND) was investigated in mice bearing advanced colon 26 adenocarcinoma compared with its early transplants. Treatment with 0.001% IND in drinking water retarded the growth of tumor when commenced at Day 1 after the tumor inoculation. The suppression of the tumor growth by IND continued up to 4 to 5 weeks as long as the size of the tumor remained small. On the other hand, IND given to mice bearing a large burden of the tumor at 2 weeks after the inoculation had facilitated the tumor growth. IND reduced tumor-associated PGE2 production in mice bearing either small or large burdens of the tumors. These results indicate that the antitumor activity of IND depends on tumor size and therefore is not simply associated with the reduction of PGE2 levels. We found that colon 26 caused changes in parameters reported for tumor cachexia, such as weight loss, wasting of muscle and adipose tissues and hypoglycemia, when it grew to around 1 g at 2-3 weeks after the tumor inoculation. IND given to the mice with large burdens of colon 26 alleviated the cachexia of the mice, resulting in the increase of the survival time even though the growth of the tumor had been facilitated. It is possible that IND affects the tumor growth and survival by reversing tumor-induced disorders in homeostasis.     

Experimental study of the effect of IL-6 on cancer cachexia

Several cytokines, including IL-1, TNF, LIF and IL-6 have recently been proposed as cachexia inducers. We experimentally examined the participation of cytokines, particularly, IL-6, in cancer cachexia using the human digestive cancer cell lines MKN 28, MKN 45, MKN 74, Kato-III, OCUM-2M (gastric cancer), SW1990, Panc-1 (pancreatic cancer), and OCUG (gallbladder cancer). A high level of IL-6 was detected in the OCUG culture medium. Nude mice bearing OCUG tumor had reduced body weight even when the tumor was relatively small. Loss of both muscle and adipose tissue, anemia, hypoglycemia, and a high serum level of human IL-6 were observed in these mice. However, body weight recovered rapidly to the level of that of nontumor-bearing mice after resection of OCUG tumor. Antihuman IL-6 but not anti-murine IL-6 receptor antibodies significantly suppressed the development of cachexia as measured by various indicators of cachexia including loss of both muscle and adipose tissue, anemia and hypoglycemia, as well as weight loss. These results suggest that OCUG-bearing mice exhibited cancer cachexia mediated by IL-6, and that of OCUG cell line might be useful as a human digestive cancer cachexia model.     

Exosomal circRNA derived from gastric tumor promotes white adipose browning by targeting the miR-133/PRDM16 pathway

Cancer-related cachexia is a metabolic syndrome characterized by a wasting disorder of adipose and skeletal muscle and is accompanied by body weight loss and systemic inflammation. The treatment options for cancer cachexia are limited, and the molecular mechanism remains poorly understood. Circular RNAs (circRNAs) are a novel family of endogenous noncoding RNAs that have been proposed to regulate gene expression in mammals. Exosomes are small vesicles derived from cells, and recent studies have shown that circRNAs are stable in exosomes. However, little is known about the biological role of circRNAs in exosomes. In our study, we showed that circRNAs in plasma exosomes have specific expression features in gastric cancer (GC), and ciRS-133 is linked with the browning of white adipose tissue (WAT) in GC patients. Exosomes derived from GC cells deliver ciRS-133 into preadipocytes, promoting the differentiation of preadipocytes into brown-like cells by activating PRDM16 and suppressing miR-133. Moreover, knockdown of ciRS-133 reduced cancer cachexia in tumor-implanted mice, decreasing oxygen consumption and heat production. Thus, exosome-delivered circRNAs are involved in WAT browning and play a key role in cancer-associated cachexia.     

Anticachectic effects of the natural herb Coptidis rhizoma and berberine on mice bearing colon 26/clone 20 adenocarcinoma

We previously showed that the natural herb Coptidis rhizoma has an anticachectic effect in nude mice bearing human esophageal cancer cells. We further investigated this phenomenon by examining the anticachectic effect of C. rhizoma in syngeneic mice bearing colon 26/clone 20 carcinoma cells, which cause IL-6-related cachexia after cell injection. We evaluated nutritional parameters such as serum glucose level and wasting of adipose tissue and muscle in tumor-bearing and non-tumor-bearing mice treated with C. rhizoma (CR) supplement or a normal diet. IL-6 levels in those mice were quantified by ELISA and real-time RT-PCR. CR supplementation significantly attenuated weight loss in tumor-bearing mice without changing food intake or tumor growth. Furthermore, these mice maintained good nutritional status. IL-6 mRNA levels in tumors and spleens and IL-6 protein levels in tumors and sera were significantly lower in tumor-bearing mice treated with CR supplement than in those treated with a normal diet. CR supplementation did not affect food intake, body weight, nutritional parameters and IL-6 levels in non-tumor-bearing mice. An in vitro study showed that C. rhizoma and its major component, berberine, inhibited IL-1-induced IL-6 mRNA expression in a dose-dependent manner in colon 26/clone 20 cells. Our results showed that C. rhizoma exerts an anticachectic effect on colon 26/clone 20-transplanted mice and that its effect is associated with tumor IL-6 production. We also suggest that its effect might be due to berberine.     

Attenuation of muscle atrophy in a murine model of cachexia by inhibition of the dsRNA-dependent protein kinase

Atrophy of skeletal muscle is due to a depression in protein synthesis and an increase in degradation. Studies in vitro have suggested that activation of the dsRNA-dependent protein kinase (PKR) may be responsible for these changes in protein synthesis and degradation. In order to evaluate whether this is also applicable to cancer cachexia the action of a PKR inhibitor on the development of cachexia has been studied in mice bearing the MAC16 tumour. Treatment of animals with the PKR inhibitor (5 mg kg(-1)) significantly reduced levels of phospho-PKR in muscle down to that found in non-tumour-bearing mice, and effectively attenuated the depression of body weight, with increased muscle mass, and also inhibited tumour growth. There was an increase in protein synthesis in skeletal muscle, which paralleled a decrease in eukaryotic initiation factor 2alpha phosphorylation. Protein degradation rates in skeletal muscle were also significantly decreased, as was proteasome activity levels and expression. Myosin levels were increased up to values found in non-tumour-bearing animals. Proteasome expression correlated with a decreased nuclear accumulation of nuclear factor-kappaB (NF-kappaB). The PKR inhibitor also significantly inhibited tumour growth, although this appeared to be a separate event from the effect on muscle wasting. These results suggest that inhibition of the autophosphorylation of PKR may represent an appropriate target for the attenuation of muscle atrophy in cancer cachexia.     

Muscle atrophy in experimental cancer cachexia: Is the IGF‐1 signaling pathway involved?

Skeletal muscle wasting, one of the main features of cancer cachexia, is associated with marked protein hypercatabolism, and has suggested to depend also on impaired IGF‐1 signal transduction pathway. To investigate this point, the state of activation of the IGF‐1 system has been evaluated both in rats bearing the AH‐130 hepatoma and in mice transplanted with the C26 colon adenocarcinoma. In the skeletal muscle of tumor hosts, the levels of phosphorylated (active) Akt, one of the most relevant kinases involved in the IGF‐1 signaling pathway, were comparable to controls, or even increased. Accordingly, downstream targets such as GSK3β, p70^S6K and FoxO1 were hyperphosphorylated, while the levels of phosphorylated eIF2α were markedly reduced with respect to controls. In the attempt to force the metabolic balance toward anabolism, IGF‐1 was hyperexpressed by gene transfer in the tibialis muscle of the C26 hosts. In healthy animals, IGF‐1 overexpression markedly increased both fiber and muscle size. As a positive control, IGF‐1 was also overexpressed in the muscle of aged mice. In IGF‐1 hyperexpressing muscles the fiber cross‐sectional area definitely increased in both young and aged animals, while, by contrast, loss of muscle mass or reduction of fiber size in mice bearing the C26 tumor were not modified. These results demonstrate that muscle wasting in tumor‐bearing animals is not associated with downregulation of molecules involved in the anabolic response, and appears inconsistent, at least, with reduced activity of the IGF‐1 signaling pathway.     

Evidence for cardiac atrophic remodeling in cancer-induced cachexia in mice

Cachexia is a common complication in cancer patients, which dramatically reduces quality of life and survival. In contrast to the well-studied feature of skeletal muscle loss, alterations in cardiac muscle are unclear. Recently, we reported that heart contractile function was significantly impaired in mice with colon-26 (C26) tumors, a widely used rodent model of cancer cachexia. In the present study, we investigated the potential underlying mechanisms for decreased heart function, specifically related to cardiac remodeling and atrophy. In cachectic mice bearing C26 tumors compared to mice without tumors, there was a gene expression pattern for cardiac remodeling, including increased BNP and c-fos, decreased PPARα and its responsive gene CPT1β, and a switch from 'adult' isoforms (MHCα, GLUT4) to 'fetal' isoforms (MHCβ and GLUT1). Echocardiography identified a decreased cardiac wall thickness. RT-PCR and Western blotting revealed a decreased amount of cardiac myofibrillar proteins MHC and troponin I, induced expression of E-3 ligases (MuRF-1 and Atrogin-1) and increased protein ubiquitination, providing evidence for cardiac atrophy in mice with cancer cachexia. Regulatory signaling pathways mediating these changes may include p44/42 MAPK. Together, these data provide evidence that pathways leading to cardiac remodeling and atrophy occur in mice with C26 cachexia.     

Peptide‐2 from mouse myostatin precursor protein alleviates muscle wasting in cancer‐associated cachexia

Cancer cachexia, characterized by continuous muscle wasting, is a key determinant of cancer‐related death; however, there are few medical treatments to combat it. Myostatin (MSTN)/growth differentiation factor 8 (GDF‐8), which is a member of the transforming growth factor‐β family, is secreted in an inactivated form noncovalently bound to the prodomain, negatively regulating the skeletal muscle mass. Therefore, inhibition of MSTN signaling is expected to serve as a therapeutic target for intractable muscle wasting diseases. Here, we evaluated the inhibitory effect of peptide‐2, an inhibitory core of mouse MSTN prodomain, on MSTN signaling. Peptide‐2 selectively suppressed the MSTN signal, although it had no effect on the activin signal. In contrast, peptide‐2 slightly inhibited the GDF‐11 signaling pathway, which is strongly related to the MSTN signaling pathway. Furthermore, we found that the i.m. injection of peptide‐2 to tumor‐implanted C57BL/6 mice alleviated muscle wasting in cancer cachexia. Although peptide‐2 was unable to improve the loss of heart weight and fat mass when cancer cachexia model mice were injected with it, peptide‐2 increased the gastrocnemius muscle weight and muscle cross‐sectional area resulted in the enhanced grip strength in cancer cachexia mice. Consequently, the model mice treated with peptide‐2 could survive longer than those that did not undergo this treatment. Our results suggest that peptide‐2 might be a novel therapeutic candidate to suppress muscle wasting in cancer cachexia.     

Elevated circulating adiponectin and elevated insulin sensitivity in adiponectin transgenic mice are not associated with reduced susceptibility to colon carcinogenesis

Obesity, particularly visceral adiposity, is an established risk factor for colorectal cancer (CRC) and this is thought to result, at least in part, from insulin resistance and chronic hyperinsulinemia that may be mediated by adipokines. Serum levels of adiponectin, the most abundant protein secreted from adipocytes, are decreased in obesity and are inversely associated with insulin resistance and hyperinsulinemia. The objective of this study was to determine whether elevated circulating adiponectin plays a role in colon carcinogenesis using adiponectin transgenic (AdTg) mice that have 2–3‐fold elevated circulating adiponectin but similar body weights as wildtype (WT) littermates used as controls. Eight‐week old male and female AdTg and WT mice were treated with 4 weekly injections of the colon‐specific carcinogen azoxymethane (AOM). One week following the last dose of AOM, all mice were placed on a high‐fat diet and killed 24 weeks later, at 36 weeks of age, for the analysis of colon tumors. Glucose tolerance tests (GTT) were performed by injecting 2g/kg dextrose or 1.25–1.5 g/kg dextrose into all 12‐week and 32–35‐week‐old mice respectively, and measuring blood from the tail vein 15, 30, 60 and 120 min following glucose administration. There were no significant differences in colon tumor incidence, number or size between AdTg and WT mice of either sex. AdTg mice of both sexes displayed resistance to diet‐induced decreases in insulin sensitivity. Our results show that constitutively elevated levels of circulating adiponectin in AdTg mice do not confer protection against the development of colon tumors. © 2008 Wiley‐Liss, Inc.