Lipid metabolism in cachectic tumor-bearing rats at different stages of tumor growth

Lipid traits and lipid-lowering drug target genes and risk of melanoma: a mendelian randomization study

Our study aimed to investigate the role of lipids in melanoma risk and the effect of lipid-lowering drug targets on melanoma. Using Mendelian Randomization analysis, we examined the genetic agents of nine lipid-lowering drugs and their association with melanoma risk. We found that genetically proxied inhibition of HMGCR, ABCG5/ABCG8, and ANGPTL3 was associated with a reduced risk of melanoma. On the other hand, inhibition of LPL and Apo-B100 was significantly associated with an increased risk of melanoma. Sensitivity analyses did not reveal any statistical evidence of bias from pleiotropy or genetic confounding. We did not find a robust association between lipid traits NPC1L1, PCSK9, APOC3 inhibition, and melanoma risk. These findings were validated using two independent lipid datasets. Our analysis also revealed that HMGCR, ANGPTL3, and ABCG5/ABCG8 inhibitors reduced melanoma risk independent of their effects on lipids. This suggests that these targets may have potential for melanoma prevention or treatment. In conclusion, our study provides evidence for a causal role of lipids in melanoma risk and highlights specific lipid-lowering drug targets that may be effective in reducing the risk of melanoma. These findings contribute to the understanding of the underlying mechanisms of melanoma development and provide potential avenues for further research and therapeutic interventions.

Metabolic Biomarkers for the Early Detection of Cancer Cachexia

Background: Cancer cachexia is a severe metabolic disorder characterized by progressive weight loss along with a dramatic loss in skeletal muscle and adipose tissue. Like cancer, cachexia progresses in stages starting with pre-cachexia to cachexia and finally to refractory cachexia. In the refractory stage, patients are no longer responsive to therapy and management of weight loss is no longer possible. It is therefore critical to detect cachexia as early as possible. In this study we applied a metabolomics approach to search for early biomarkers of cachexia.

Methods: Multi-platform metabolomics analyses were applied to the murine Colon-26 (C26) model of cachexia. Tumor bearing mice (n = 5) were sacrificed every other day over the 14-day time course and control mice (n = 5) were sacrificed every fourth day starting at day 2. Linear regression modeling of the data yielded metabolic trajectories that were compared with the trajectories of body weight and skeletal muscle loss to look for early biomarkers of cachexia.

Results: Weight loss in the tumor-bearing mice became significant at day 9 as did the loss of tibialis muscle. The loss of muscle in the gastrocnemius and quadriceps was significant at day 7. Reductions in amino acids were among the earliest metabolic biomarkers of cachexia. The earliest change was in methionine at day 4. Significant alterations in acylcarnitines and lipoproteins were also detected several days prior to weight loss.

Conclusion: The results of this study demonstrate that metabolic alterations appear well in advance of observable weight loss. The earliest and most significant alterations were found in amino acids and lipoproteins. Validation of these results in other models of cachexia and in clinical studies will pave the way for a clinical diagnostic panel for the early detection of cachexia. Such a panel would provide a tremendous advance in cachectic patient management and in the design of clinical trials for new therapeutic interventions.

The role of triglyceride lipases in cancer associated cachexia

Cancer associated cachexia (CAC) is a complex multiorgan syndrome frequently associated with various forms of cancer. Affected patients suffer from a dramatic loss of skeletal muscle and adipose tissue. Most cases are accompanied by anorexia, and nutritional supplements are not sufficient to stop or reverse its course. CAC impairs many forms of therapeutic interventions and accounts for 15-20% of all deaths of cancer patients. Recently, several studies have recognized the importance of lipid metabolism and triglyceride hydrolysis as a major metabolic pathway involved in the initiation and/or progression of CAC. In this review, we explore the contributions of the triglyceride lipases to CAC and discuss various factors modulating lipase activity.

Increased lipoprotein lipase activity in non-small cell lung cancer tissue predicts shorter patient survival

BACKGROUND AND AIMS

Cumulative evidence suggests the involvement of lipoprotein lipase (LPL) in tumor progression. We tested the hypothesis that increased LPL activity in resectable non-small cell lung cancer (NSCLC) tissue and the increased LPL gene expression in the surrounding non-cancer lung tissue found in our previous study are predictors of patient survival.

METHODS

Forty two consecutive patients with resected NSCLC were enrolled in the study. Paired samples of lung cancer tissue and adjacent non-cancer lung tissue were collected from resected specimens for baseline LPL activity and gene expression estimation. During a 4-year follow-up, 21 patients died due to tumor progression. One patient died due to a non-cancer reason and was not included in Cox regression analysis.

RESULTS

High LPL activity in cancer tissue (relative to the adjacent non-cancer lung tissue) predicted shorter survival, independently of standard prognostic factors (p=0.003). High gene expression in the non-cancer lung tissue surrounding the tumor had no predictive value.

CONCLUSIONS

Our study further underlines the involvement of cancer tissue LPL activity in tumor progression.

Lipoprotein lipase activity and gene expression in lung cancer and in adjacent noncancer lung tissue

The authors tested the hypothesis that lipoprotein lipase (LPL) gene expression and enzyme activity are increased in lung cancer tissue, as compared to adjacent, apparently healthy, lung tissue. Paired samples of lung cancer tissue and adjacent noncancer lung tissue were collected from 42 patients with resectable non-small cell lung cancer. LPL activity was higher in cancer tissue (1.9-fold median difference, P < .0001); however, LPL gene expression was higher in noncancer tissue (3.8-fold median difference, P < .0001). The higher LPL activity in lung cancer tissue provides a possible mechanism for increasing the supply of lipid nutrients to the tumor, necessary for tumor growth.

The effect of glutamine and dihydroxyacetone supplementation on food intake, weight gain, and postprandial glycogen synthesis in female Zucker rats

OBJECTIVE

We sought to test the hypothesis that increasing postprandial hepatic glycogen synthesis rate would decrease food intake and growth rate in obese Zucker rats.

DESIGN

Supplements of glutamine, with and without dihydroxyacetone (DHA), which have previously been shown to stimulate hepatic glycogen synthesis, were administered in the diet of obese Zucker rats for periods of 1 and 3 wk.

MEASUREMENTS

Food intake and body weight were monitored throughout the experiments. At the end of the feeding period the rats were fed a test meal and injected with (3)H(2)O to measure in vivo rates of glycogen and lipid synthesis. Final plasma glucose and triacylglycerol and hepatic glycogen content were also determined. Carcass fat and water contents were also measured in the 3-wk study.

RESULTS

Dietary glutamine had no effect on food intake, weight gain, or body composition. Addition of DHA caused a reduction in food intake and weight gain and a stimulation of in vivo hepatic glycogen synthesis after 1 wk, but these changes were abolished by the end of 3 wk. Hepatic lipogenesis in vivo was increased by DHA treatment for 1 and 3 wk.

CONCLUSIONS

Stimulation of hepatic glycogen synthesis by DHA treatment was associated with a reduction in food intake. However, the effect of DHA on glycogen synthesis and food intake disappeared after 3 wk of supplementation.

Effect of diet supplementation with glutamine, dihydroxyacetone, and leucine on food intake, weight gain, and postprandial glycogen metabolism of rats

OBJECTIVE

We tested the hypothesis that increasing the rate of postprandial hepatic glycogen synthesis would decrease food intake and growth rate in normal rats.

METHODS

Diets supplemented with glutamine, glutamine plus dihydroxyacetone, and glutamine plus dihydroxyacetone plus leucine were administered to male Sprague-Dawley rats for 1 wk. These are combinations that have been shown to stimulate hepatic glycogen synthesis in vitro. Food intake and body weight were monitored throughout the experiment. At the end of the feeding period, rats were fed a test meal and injected with 3H2O to measure in vivo rates of glycogen and lipid synthesis. Positional analysis of the 3H incorporated into glycogen was used to determine the proportion of glycogen synthesized via pyruvate. Final levels of plasma glucose and triacylglycerol and hepatic glycogen were also measured.

RESULTS

Dietary glutamine increased hepatic glycogen synthesis. Addition of dihydroxyacetone, with or without additional leucine, caused an additional increase in hepatic glycogen synthesis and increased the proportion of glycogen synthesized via pyruvate. Lipogenesis was not altered in the liver or adipose tissue. None of the dietary treatments had any effect on food intake, but the diets that contained dihydroxyacetone decreased the rate of weight gain.

CONCLUSIONS

Increasing glycogen synthesis had no effect on food intake. Increasing the proportion of glycogen synthesized by the indirect pathway through pyruvate was associated with a decrease in weight gain.

Regulation of fatty acid synthase expression in breast cancer by sterol regulatory element binding protein-1c

Activation of fatty acid synthase (FAS) expression and fatty acid synthesis is a common event in human breast cancer. Sterol regulatory element binding proteins (SREBPs) are a family of transcription factors that regulate genes involved in lipid metabolism, including FAS. SREBP-1c expression is induced in liver and adipose tissue by insulin and by fasting/refeeding and is critical for nutritional regulation of lipogenic gene expression. In contrast, upregulation of fatty acid metabolism during in vitro transformation of human mammary epithelial cells and in breast cancer cells was driven by increased MAP kinase and PI 3-kinase signaling, which increased SREBP-1 levels. SREBP-1a was more abundant than SREBP-1c in many proliferative tissues and cultured cells and was thus a candidate to regulate lipogenesis for support of membrane synthesis during cell growth. We now show that SREBP-1c and FAS mRNA were both increased by H-ras transformation of MCF-10a breast epithelial cells and were both reduced by exposure of MCF-7 breast cancer cells to the MAP kinase inhibitor, PD98059, or the PI 3-kinase inhibitor, wortmannin, while SREBP-1a and SREBP-2 showed less variation. Similarly, the mRNA levels for FAS and SREBP-1c in a panel of primary human breast cancer samples showed much greater increases than did those for SREBP-1a and SREBP-2 and were significantly correlated with each other, suggesting coordinate regulation of SREBP-1c and FAS in clinical breast cancer. We conclude that regulation of FAS expression in breast cancer is achieved through modulation of SREBP-1c, similar to the regulation in liver and adipose tissue, although the upstream regulation of liopgenesis differs in these tissues.

Expression of apoptosis regulatory proteins in the skeletal muscle of tumor-bearing rabbits

We reported finding that apoptosis occurred in skeletal muscle in the early stage after implantation. In the present study, we investigated expression of the apoptosis-related proteins Bax and Bcl-2 to determine the mechanism of the apoptosis. In the early stage of tumor bearing, 20 days after implantation, lean body mass (LBM) was reduced by 5.06 +/- 1.10% in the tumor-bearing group, compared with an increase of 4.96 +/- 1.26% in the control group. The apoptotic index (AI) of the skeletal muscle in the tumor-bearing group increased to 40.5 +/- 3.20% but was 0% in the control group, and Bax expression was strongly positive in 5 of the 10 rabbits in the tumor-bearing group, and significantly stronger than in the control group (P = 0.0002). In the late stage of tumor bearing, 40 days after implantation, the AI had declined to 0.93 +/- 0.96% in the tumor-bearing group, but was still 0% in the control group. Bax expression was rarely detected in either the tumor-bearing group or the control group, and there was no significant difference between the two groups (P = 0.706). No significant changes in Bcl-2 were observed in either group. The above results showed that apoptosis via Bax played a role in muscle wasting associated with progression of the malignant tumor. However, the apoptosis and expression of Bax were seen only in the early stage, within 20 days after implantation, not in the late stage. This suggested that the muscle wasting in the early stage might be caused by a different mechanism from that in the late stage.

Cachexia in experimental models

Cachexia refers to a state of severe malnutrition characterized by anorexia, weight loss, and muscle wasting. Although it is most commonly considered in the context of cancer, it may occur as a consequence of a variety of chronic diseases. Cachexia appears to differ from "semistarvation" in that there is evidence of metabolic changes that are different from the normal response to reduce food intake. Animal models are useful in the study of cachexia because they allow homogeneous groups of subjects, free from confounding influences, to be studied. Accurate control of diet is possible, and pair-fed controls can be used to allow specific investigation of the metabolic component. However, the model must show features that are appropriate for the disease being studied. In the case of cancer this means using a model in which cachexia occurs without too high a tumor burden or growth rate or too severe a reduction in food intake. Studies in the author's laboratory have used a transplantable Leydig cell tumor in Fischer rats. Food intake decreases by 20-40% and energy expenditure is greater than that of pair-fed controls. One mechanism that may be responsible for this relates to the postprandial metabolism of carbohydrate, since after a test meal there appears to be a greater rate of hepatic glycogen synthesis via the indirect pathway in tumor-bearing rats than in controls. The indirect pathway involves gluconeogenic enzymes, and studies using a variety of different tracers and enzyme inhibitors suggest that amino acids are important precursors. An increased rate of hepatic glycogen synthesis also appears to be maintained for a longer time after the meal in tumor-bearing rats, and this may act to delay the onset of the next meal, thereby explaining the decreased meal frequency that has been observed.

Metabolic and morphologic characteristics of adipose tissue associated with the growth of malignant tumors

Changes in total body fat and the metabolic and morphologic characteristics of adipose tissue were sequentially investigated in individual rabbits implanted with VX2 tumors to elucidate the pathology of the fat reduction in animals with malignant tumors as compared with that of diet-restricted rabbits. Lipogenesis in normal, VX2-implanted, and diet-restricted rabbit groups on day 40 after the start of the experiments was 19.1 +/- 2.9, 13.3 +/- 3.5, and 41.7 +/- 6.0 x 10(5) cpm/g/h, respectively, and glycerol liberation by their adipose tissue was 199 +/- 21, 528 +/- 94, and 301 +/- 45 nmol/g/h, respectively. In addition, apoptotic cells were noted in the adipose tissue of VX2-implanted rabbits on days 20-30 after implantation, but not in diet-restricted rabbits. The results showed clear differences between the total body fat reduction profiles of VX2-implanted rabbits and diet-restricted rabbits, suggesting a characteristic lipid metabolism with enhanced lipolysis and diminished lipogenesis in VX2-implanted rabbits. The results strongly suggest that adipocyte apoptosis might be involved in these phenomena.

Isolation, characterization, and distribution of a 24-kDa proteoglycan in the urine of cachectic cancer and AIDS patients

Substantial weight loss in individuals with AIDS or cancer is associated with a poor prognosis and increased mortality. We have isolated and partially characterized a proteoglycan (named azaftig) from the urine of a cancer patient experiencing weight loss. Furthermore, we have raised a polyclonal antibody to azaftig in rabbits and developed a procedure to measure the level of this proteoglycan in urine by Western blot. We report the presence of azaftig in the urine of cancer and AIDS patients experiencing weight loss, but not in the control or weight-stable subjects. The azaftig-like immunoreactivity was present in 69.2% (9/13) of patients with weight loss, but only in 27.0% (3/11) of weight-stable cancer or AIDS patients and none of the control subjects (n = 8).

Glycogen synthesis in tumor-bearing rats after ingestion of a high-glycerol meal

Tumor-bearing rats have a high rate of postprandial hepatic glycogen synthesis by the indirect pathway that involves gluconeogenesis. This study was designed to investigate the role of glycerol as a precursor for postprandial glycogen synthesis in tumor-bearing rats. Rats bearing a Leydig cell tumor and freely fed controls were fasted overnight, then fed a 16-kJ meal with or without 50 mg of glycerol by gavage. [U-14C]glycerol (1 microCi) was also administered intragastrically, and 7 mCi of 3H2O were injected intraperitoneally. The rats were killed one hour later, and the specific activities at different positions within the glycogen glucose residues in the liver were measured. Increasing the glycerol content of the meal had no significant effect on the overall incorporation of 3H into liver glycogen or on the proportion of glycogen synthesized via pyruvate in tumor-bearing or control rats. There was no difference between tumor-bearing and control rats in the amount of glycerol incorporated into glycogen, although this was increased by the high-glycerol meal. Thus glycerol appeared to make a small contribution to postprandial glycogen synthesis in tumor-bearing and control rats.

The effect of meal size on postprandial carbohydrate metabolism in normal and tumor-bearing rats

Doubling the size of a meal causes less than a two-fold increase in the thermic effect of feeding. One possible reason for this is that larger meals may be associated with a change in the pathway of postprandial hepatic glycogen synthesis from the indirect pathway, involving gluconeogenesis, to the more energetically efficient direct pathway. We have therefore investigated the effect of meal size on the relative contributions of those two pathways both in normal rats and in tumor-bearing rats, which have previously been shown to utilize the indirect pathway to a greater extent. Rats bearing a transplantable Leydig cell tumor and freely fed controls were fasted overnight and given a test meal amounting to 12 or 24 kJ of their normal diet. They were then injected with 3H2O and 14C-glycerol and killed one hour later. The total amount of 3H incorporated into liver glycogen was not affected by meal size, although it was greater in tumor-bearing rats than controls. Analysis of the 3H labelling at different positions in the glycogen glucose residues showed that the proportion of glycogen synthesized via pyruvate, which tended to be greater in tumor-bearing rats, was significantly reduced by increasing the size of the meal. Glycogen synthesis from glycerol was not affected by either meal size or tumor growth. Increasing the size of the meal increased the rate of fatty acid synthesis in both the liver and the epididymal fat pad, but not the tumor. Thus increasing the size of the meal appeared to increase the proportion of glycogen synthesized by the direct pathway from glucose in both tumor-bearing and control animals.

Suppression of carcass weight loss in cachexia in rats bearing Leydig cell tumor by the novel compound NO-1886, a lipoprotein lipase activator

The Leydig cell tumor has been reported to produce tumor necrosis factor (TNF) and induce cachexia in rats. TNF is thought to reduce lipoprotein lipase (LPL) activity, decrease fat deposits, induce emaciation, and worsen cachexia. Therefore, we thought emaciation might be prevented and thus cachexia improved by increasing LPL activity. We administered NO-1886, a lipoprotein lipase activator, to rats bearing Leydig cell tumor and observed its effect on improving the cachexia induced by the tumor. In Leydig cell tumor-bearing rats, the emaciation progressed after tumor inoculation and the general condition worsened daily. Plasma levels of total protein, albumin, and glucose, which are biological parameters of malnutrition, were found to decrease soon after tumor inoculation in tumor-bearing rats. In contrast, rats given NO-1886 showed less malnutrition than tumor-bearing rats. LPL activity of rat adipose tissue was decreased, the weight of adipose tissue was decreased, carcass weight was reduced, and food consumption was decreased after Leydig cell tumor inoculation. NO-1886 increased adipose tissue LPL activity and suppressed the decrease in the weight of adipose tissue, carcass weight, and food consumption due to cachexia without influencing tumor growth. The present results suggest that the novel compound NO-1886 may suppress carcass weight loss in rats bearing Leydig cell tumor by suppressing the decrease in food consumption and LPL activity.

Effect of acute acipimox administration on the rates of lipid and glycogen synthesis in cachectic tumor-bearing rats

Increased energy expenditure in cancer cachexia may be associated with increased postprandial glycogen synthesis via an indirect pathway involving gluconeogenesis. The possible beneficial effect of acipimox, a nicotinic acid analogue that suppresses lipolysis and may also inhibit gluconeogenesis, were therefore examined. Rats bearing a transplantable Leydig cell tumor and freely fed controls were fasted overnight, then given a test meal with or without 10 mg of acipimox. The meal included 200 mg of [1-13C]glucose, and the rats were injected simultaneously with 7 mCi of 3H2O and 1 microCi of [14C]glycerol. The rats were killed one hour later. The rate of incorporation of 3H2O into hepatic glycogen was increased in the tumor-bearing rats and suppressed by acipimox. Positional analysis of the tritium incorporated into glycogen indicated that a greater proportion of the glycogen was synthesized via pyruvate in the tumor-bearing rats. Acipimox tended to reduce this proportion, although the effect was not statistically significant. Neither tumor growth nor acipimox significantly affected the proportion of 13C incorporated into different positions in the glycogen glucose. Glycogen synthesis from glycerol tended to decrease when lipolysis was suppressed by acipimox, although the statistical significance of this effect was marginal. Fatty acid synthesis in liver and adipose tissue was reduced in tumor-bearing rats, but acipimox had no effect. It is concluded that acipimox does suppress gluconeogenesis and glycogenesis in the postprandial state, but it does not normalize all the metabolic abnormalities observed in cancer cachexia.

Alterations in postprandial glycogen and lipid synthesis in cachectic tumor-bearing rats

Alterations in the postprandial metabolism of glucose were investigated in groups of tumor-bearing rats and freely fed controls and in groups of normal rats whose food intake had been restricted to match that of the tumor-bearing rats. A standard mixed meal was administered by gavage, and the rate of incorporation of 3H from 3H2O into hepatic glycogen and into saponifiable lipids in the liver and adipose tissue was measured at intervals up to three hours after the meal. In tumor-bearing rats, the rate of glycogen synthesis rose by more than twice as much as normal after the meal, while the normal rise in rates of fatty acid synthesis was suppressed. In contrast, in the rats whose food intake had been restricted, the postprandial rise in hepatic glycogenesis was suppressed and the rates of postprandial lipogenesis in liver and adipose tissue were increased. Thus the changes that were observed in the tumor-bearing animals did not represent a normal response to reduced food intake. Increased postprandial glycogenesis in tumor-bearing rats is likely to be associated with increased gluconeogenesis, thereby increasing energy expenditure. The prolonged high rate of hepatic glycogen synthesis may also delay the initiation of the next meal and thus contribute to the decrease in food intake in cancer cachexia.