Reduced body fat and increased hepatic lipid synthesis in mice bearing interleukin-6-secreting tumor

Persistence on subcutaneous tocilizumab as monotherapy or in combination with synthetic disease-modifying anti-rheumatic drugs in rheumatoid arthritis patients in Greece (EMBRACE study): a multicenter, post-marketing, non-interventional, observational trial

INTRODUCTION

Rheumatoid arthritis (RA) is a systemic, inflammatory disease affecting multiple organs and causing physical disability over time.

OBJECTIVE

The primary objective was to evaluate treatment persistence to subcutaneous tocilizumab (TCZ-SC). Additionally, treatment effects on persistence and their associations with clinical and patient-reported outcomes were assessed.

METHOD

We performed a multicenter, non-interventional, 52-week observational study on 222 patients with moderate or severe RA. Clinical outcomes were evaluated by using disease activity score for 28 joints (DAS28) and European League Against Rheumatism (EULAR) response, and patients' perceptions were evaluated by using Health Assessment Questionnaire (HAQ), Visual Analog Scale (VAS) for pain, and patient global assessment (PtGA) of disease activity. Safety was assessed throughout the study.

RESULTS

The mean age of the overall cohort was 62.2 ± 12.3 years, and 83.8% were females. Persistence to TCZ-SC was 89.6% at week 24 and 85.1% at week 52 in the overall cohort with slightly increased persistence in the combination group. At week 52, changes from the baseline were - 2.68 in DAS28, - 0.76 in HAQ, - 43.21 in VAS pain, and - 41.66 in PtGA (p < 0.0001 for all). Moderate and good EULAR response was achieved in 83.2% of patients. Non-serious and serious adverse events occurred in 18.5% and 3.2% of the participants, respectively.

CONCLUSIONS

The current study confirms the favorable safety and effectiveness of TCZ-SC as well as its acceptability by RA patients in Greece, with sustained high persistence rates up to 52 weeks. TCZ-SC offers a sustainable treatment response in RA. Key Points • Based upon clinical and patient-reported outcomes, TCZ-SC is a highly effective and safe treatment modality in patients with moderate-to-severe RA. • Persistence to TCZ-SC was high throughout the study, both as monotherapy and in combination with csDMARDs. • TCZ-SC is effective both as monotherapy and when used in combination with other csDMARDs regardless of the line of treatment.

Inflammaging as a target for healthy ageing

Life expectancy has been on the rise for the past few decades, but healthy life expectancy has not kept pace, leading to a global burden of age-associated disorders. Advancing age is accompanied by a chronic increase in basal systemic inflammation, termed inflammaging, contributing towards an increased risk of developing chronic diseases in old age. This article reviews the recent literature to formulate hypotheses regarding how age-associated inflammaging plays a crucial role in driving chronic diseases and ill health in older adults. Here, we discuss how non-pharmacological intervention strategies (diet, nutraceutical supplements, phytochemicals, physical activity, microbiome-based therapies) targeting inflammaging restore health in older adults. We also consider alternative existing pharmacological interventions (Caloric restriction mimetics, p38 mitogen-activated protein kinase inhibitors) and explore novel targets (senolytics) aimed at combating inflammaging and optimising the ageing process to increase healthy lifespan.

Elevated metabolic rate and skeletal muscle oxidative metabolism contribute to the reduced susceptibility of NF-κB p50 null mice to obesity

Mice with a deletion of the p50 subunit of the proinflammatory nuclear factor kappa B pathway (NF-κB p50) have reduced weight compared to wild-type control mice. However, the physiological underpinning of this phenotype remains unknown. This study addressed this issue. Compared to littermate controls, lean male p50 null mice (p50-/- ) had an increased metabolic rate (~20%) that was associated with increased skeletal muscle (SkM, ~35%), but not liver, oxidative metabolism. These metabolic alterations were accompanied by decreases in adiposity, and tissue and plasma triglyceride levels (all ~30%). Notably, there was a marked decrease in skeletal muscle, but not liver, DGAT2 gene expression (~70%), but a surprising reduction in muscle PPARα and CPT1 (both ~20%) gene expression. Exposure to a high-fat diet accentuated the diminished adiposity of p50-/- mice despite elevated caloric intake, whereas plasma triglycerides and free fatty acids (both ~30%), and liver (~40%) and SkM (~50%) triglyceride accumulation were again reduced compared to WT. Although SkM cytokine expression (IL-6 and TNFα, each ~100%) were increased in p50-/- mice, neither cytokine acutely increased SkM oxidative metabolism. We conclude that the reduced susceptibility to diet-induced obesity and dyslipidemia in p50-/- mice results from an increase in metabolic rate, which is associated with elevated skeletal muscle oxidative metabolism and decreased DGAT2 expression.

Role of heparanase on hepatic uptake of intestinal derived lipoprotein and fatty streak formation in mice

Background

Heparanase modulates the level of heparan sulfate proteoglycans (HSPGs) which have an important role in multiple cellular processes. Recent studies indicate that HSPGs have an important function in hepatic lipoprotein handling and processes involving removal of lipoprotein particles.

Principal Findings

To determine the effects of decreased HSPGs chain length on lipoprotein metabolism and atherosclerosis, transgenic mice over-expressing the human heparanase gene were studied.

Hepatic lipid uptake in hpa-Tg mice were evaluated by giving transgenic mice oral fat loads and labeled retinol. Sections of aorta from mice over-expressing heparanase (hpa-Tg) and controls (C57/BL6) fed an atherogenic diet were examined for evidence of atherosclerosis. Heparanase over-expression results in reduced hepatic clearance of postprandial lipoproteins and higher levels of fasting and postprandial serum triglycerides. Heparanase over-expression also induces formation of fatty streaks in the aorta. The mean lesion cross-sectional area in heparanase over-expressing mice was almost 6 times higher when compared to control mice (23,984 µm²±5,922 vs. 4,189 µm²±1,130, p<0.001).

Conclusions

Over-expression of heparanase demonstrates the importance of HSPGs for the uptake of intestinal derived lipoproteins and its role in the formation of fatty streaks.

Polymorphism in the IL6 promoter region is associated with the risk factors and markers of subclinical atherosclerosis in men: The Cardiovascular Risk in Young Finns Study

OBJECTIVE

Inflammatory factors modify the risk of coronary heart disease. Promoter region genetic polymorphism of inflammatory cytokine interleukin-6 (IL6 -174 G>C) is associated with the variation of IL-6 production. We investigated whether IL6 -174 G>C associates with the risk factors of atherosclerosis and carotid artery compliance (CAC) in young subjects.

METHODS AND RESULTS

As part of the Cardiovascular Risk in Young Finns Study, we performed carotid artery ultrasound examinations, IL6 -174 G>C genotyping and coronary heart disease risk factor determination for 2228 subjects aged 24-39 years. In men CAC was higher for IL6 -174 GG (2.10+/-0.65) than for GC (2.00+/-0.68) or CC (1.95+/-0.63, %/10mmHg, mean+/-S.D., p=0.0221). A similar association was observed for HDL cholesterol (GG 1.22+/-0.29, GC 1.15+/-0.27 and CC 1.14+/-0.28mmol/L, p=0.0015) and apolipoprotein A1 (apoA1) (GG 1.44+/-0.21, GC 1.40+/-0.20, CC 1.38+/-0.21mmol/L, p=0.0118). The opposite genotype effect was present in systolic (GG 127+/-13.1, GC 129+/-13.1, CC 130+/-14.3mmHg, p=0.0382) and diastolic blood pressure (GG 73.8+/-9.14, GC 75.1+/-8.68, CC 75.9+/-9.70mmHg, p=0.0374). The genetic effect size for these parameters was not significant in women.

CONCLUSIONS

IL6 -174 allele G homozygozity associates with beneficial profile of early predictors of atherosclerosis such as high CAC, HDL-C and apoA1 as well as low systolic and diastolic blood pressure in men.

Direct evidence of lipid translocation between adipocytes and prostate cancer cells with imaging FTIR microspectroscopy

Various epidemiological studies show a positive correlation between high intake of dietary FAs and metastatic prostate cancer (CaP). Moreover, CaP metastasizes to the bone marrow, which harbors a rich source of lipids stored within adipocytes. Here, we use Fourier transform infrared (FTIR) microspectroscopy to study adipocyte biochemistry and to demonstrate that PC-3 cells uptake isotopically labeled FA [deuterated palmitic acid (D(31)-PA)] from an adipocyte. Using this vibrational spectroscopic technique, we detected subcellular locations in a single adipocyte enriched with D(31)-PA using the upsilon(as+s)(C-D)(2+3) (D(31)-PA): upsilon(as+s)(C-H)(2+3) (lipid hydrocarbon) signal. In addition, larger adipocytes were found to consist of a higher percentage of D(31)-PA of the total lipid found within the adipocyte. Following background subtraction, the upsilon(as)(C-D)(2+3) signal illuminated starved PC-3 cells cocultured with D(31)-PA-loaded adipocytes, indicating translocation of the labeled FA. This study demonstrates lipid-specific translocation between adipocytes and tumor cells and the use of FTIR microspectroscopy to characterize various biomolecular features of a single adipocyte without the requirement for cell isolation and lipid extraction.

Long-Term Change in Cholesterol in Relation to Inflammation-Sensitive Plasma Proteins: A Longitudinal Study

PURPOSE

The nature of the relationship between inflammation and elevated serum lipid levels is incompletely understood. This longitudinal study explores whether elevated levels of inflammation-sensitive plasma proteins (ISPs) are a risk factor for developing increased cholesterol and triglyceride levels.

METHODS

Five ISPs (fibrinogen, orosomucoid, alpha1-antitrypsin, haptoglobin, and ceruloplasmin) were measured in a population-based cohort of nondiabetic healthy men aged 38 to 50 years at baseline. Subjects were reexamined after a mean of 6.2 years. The development of hypercholesterolemia (cholesterol>or=6.5 mmol/L [>or=251 mg/dL]) and hypertriglyceridemia (triglycerides>or=2.3 mmol/L [>or=204 mg/dL]) during follow-up was studied in relation to the number of elevated levels of ISPs (i.e., in the top quartile).

RESULTS

Of men with initially normal cholesterol levels (<6.5 mmol/L; n=2224), proportions of men with no, one, two, and three or more elevated ISP levels at baseline who developed hypercholesterolemia were 12%, 13%, 16%, and 20%, respectively (p for trend=0.0002). This relationship remained significant after adjustments for cholesterol level at baseline and other confounding factors. The relationship between ISP levels and future hypertriglyceridemia was attenuated and nonsignificant after adjustments for confounding factors.

CONCLUSION

In apparently healthy men with initially normal cholesterol levels, elevated ISP levels are a risk factor for development of hypercholesterolemia.

Interleukin-6 gene polymorphism -174G/C influences plasma lipid levels in women

Elevated levels of the pro-inflammatory cytokine interleukin-6 (IL-6) have been associated with cardiovascular risk factors. The objective of this study was to investigate potential associations between the promoter polymorphism IL-6 -174G/C and the following indices of metabolism: BMI, waist-to-hip ratio, and plasma levels of IL-6, cholesterol, low-density lipoprotein, triglycerides, high-density lipoprotein, leptin, and C-reactive protein in 252 42-year-old women and 245 51-year-old men. Subgroups were also studied 5 years later. The CC genotype of the IL-6 polymorphism was associated with lower levels of cholesterol and low-density lipoprotein (p < 0.001) in women. This finding was replicated in the follow-up, when a significant association between the CC genotype and low triglycerides was also observed. The association between the C allele and lipid pattern found in women was not found in men, where on the contrary, C carriers tended to display elevated triglycerides. IL-6 genotype was not associated with IL-6 plasma levels in either sample. The results suggest different effects of the IL-6 polymorphism on metabolic indices in women and men. None of the associations between IL-6 genotype and lipid pattern seemed to result from an effect of the polymorphism on IL-6 plasma levels.

Impact of interleukin-1 and interleukin-6 in murine primary schistosomiasis

BACKGROUND

Immunization with schistosome antigens invariably elicits a plethora of cytokines and, hence, it is reasonable to assume that these cytokines influence host responses to challenge lung-stage larvae and, consequently, the adult worm burden, and may be responsible for the erratic data generally observed in protection studies against schistosome infection.

METHODS

Schistosoma mansoni-infected mice were administered with recombinant interleukin (IL)-1beta or IL-6 to evaluate the impact of cytokines in host responses to lung-stage schistosomula, and subsequent effects on adult worm parameters. Plasma lipid levels were assayed by colorimetric enzymatic tests and antibody responses by ELISA. Cytokine profile in peripheral blood mononuclear cells was evaluated by RT-PCR.

RESULTS

S. mansoni infection elicited, at the time of parasite residency in the lung, significant increase in free fatty acids (FA) and decrease in cholesterol plasma levels in C57BL/6 and CD1 mice, and stimulation of mRNA expression for cytokines of T helper type (Th) 2 in BALB/c, Th1 in C57BL/6, and Th1/Th2 in CD1 mice. However, no specific antibody production was evident in any mouse strain. In BALB/c mice, exogenous IL-1beta-related plasma free FA level significant increase, stimulation of expression of IL-1 and IL-12 mRNA, and considerable increase in percent of specific antibody-producing mice were associated with significant reduction in adult worm burden and egg load. In contrast, exogenous IL-1beta elicited decrease in free FA plasma levels, and down-regulation of cytokines' mRNA expression in C57BL/6 and CD1 mice, changes associated with aggravation of the worm burden. Likewise, exogenous IL-6 failed to stimulate increase in plasma free FA levels or percent of antibody-producing mice except in BALB/c mice, effects that were protective for the host in BALB/c and for the parasite in C57BL/6 and CD1 mice.

CONCLUSION

These findings were discussed in relation to the erratic data of protection experiments with schistosome subunit antigens in different mouse strains.

Hypothalamic integration of immune function and metabolism

The immune and neuroendocrine systems are closely involved in the regulation of metabolism at peripheral and central hypothalamic levels. In both physiological (meals) and pathological (infections, traumas and tumors) conditions immune cells are activated responding with the release of cytokines and other immune mediators (afferent signals). In the hypothalamus (central integration), cytokines influence metabolism by acting on nucleus involved in feeding and homeostasis regulation leading to the acute phase response (efferent signals) aimed to maintain the body integrity. Peripheral administration of cytokines, inoculation of tumor and induction of infection alter, by means of cytokine action, the normal pattern of food intake affecting meal size and meal number suggesting that cytokines acted differentially on specific hypothalamic neurons. The effect of cytokines-related cancer anorexia is also exerted peripherally. Increase plasma concentrations of insulin and free tryptophan and decrease gastric emptying and d-xylose absorption. In addition, in obesity an increase in interleukin (IL)-1 and IL-6 occurs in mesenteric fat tissue, which together with an increase in corticosterone, is associated with hyperglycemia, dyslipidemias and insulin resistance of obesity-related metabolic syndrome. These changes in circulating nutrients and hormones are sensed by hypothalamic neurons that influence food intake and metabolism. In anorectic tumor-bearing rats, we detected upregulation of IL-1beta and IL-1 receptor mRNA levels in the hypothalamus, a negative correlation between IL-1 concentration in cerebro-spinal fluid and food intake and high levels of hypothalamic serotonin, and these differences disappeared after tumor removal. Moreover, there is an interaction between serotonin and IL-1 in the development of cancer anorexia as well as an increase in hypothalamic dopamine and serotonin production. Immunohistochemical studies have shown a decrease in neuropeptide Y (NPY) and dopamine (DA) and an increase in serotonin concentration in tumor-bearing rats, in first- and second-order hypothalamic nuclei, while tumor resection reverted these changes and normalized food intake, suggesting negative regulation of NPY and DA systems by cytokines during anorexia, probably mediated by serotonin that appears to play a pivotal role in the regulation of food intake in cancer. Among the different forms of therapy, nutritional manipulation of diet in tumor-bearing state has been investigated. Supplementation of tumor bearing rats with omega-3 fatty acid vs. control diet delayed the appearance of tumor, reduced tumor-growth rate and volume, negated onset of anorexia, increased body weight, decreased cytokines production and increased expression of NPY and decreased alpha-melanocyte-stimulating hormone (alpha-MSH) in hypothalamic nuclei. These data suggest that omega-3 fatty acid suppressed pro-inflammatory cytokines production and improved food intake by normalizing hypothalamic food intake-related peptides and point to the possibility of a therapeutic use of these fatty acids. The sum of these data support the concept that immune cell-derived cytokines are closely related with the regulation of metabolism and have both central and peripheral actions, inducing anorexia via hypothalamic anorectic factors, including serotonin and dopamine, and inhibiting NPY leading to a reduction in food intake and body weight, emphasizing the interconnection of the immune and neuroendocrine systems in regulating metabolism during infectious process, cachexia and obesity.

Interleukin-6 and new strategies for the treatment of cancer, hyperproliferative diseases and paraneoplastic syndromes

Interleukin-6 (IL-6) is a pleiomorphic cytokine whose growth factor properties play an important role in the development and progression of many types of cancer. IL-6 is produced in response to a variety of stimuli, and is required for the development of T and B lymphocytes to effector cells. In certain neoplasias, such as multiple myeloma, IL-6 is both produced and required for survival by the cancer cell itself. In other neoplasias, IL-6 may come from tissue surrounding the tumour. Thus, therapeutic strategies aimed at inhibiting the production, expression or action of IL-6 would be quite beneficial in the treatment of cancer. Moreover, IL-6 is a pathophysiological factor in several hyperproliferative diseases and the paraneoplastic syndromes that often accompany cancer, such as cachexia and osteoporosis; thus, anti-IL-6 therapy would be useful in treating these entities as well. This expert opinion acquaints the reader with IL-6, its physiological responses, the cancer types with which it is associated, and discusses the current state of therapy aimed at inhibiting it.

Antisense oligonucleotide reduction of DGAT2 expression improves hepatic steatosis and hyperlipidemia in obese mice

In this study, we investigated the role of acyl-coenzyme A:diacylglycerol acyltransferase 2 (DGAT2) in glucose and lipid metabolism in obese mice by reducing its expression in liver and fat with an optimized antisense oligonucleotide (ASO). High-fat diet-induced obese (DIO) C57BL/6J mice and ob/ob mice were treated with DGAT2 ASO, control ASO, or saline. DGAT2 ASO treatment reduced DGAT2 messenger RNA (mRNA) levels by more than 75% in both liver and fat but did not change DGAT1 mRNA levels in either of these tissues, which resulted in decreased DGAT activity in liver but not in fat. DGAT2 ASO treatment did not cause significant changes in body weight, adiposity, metabolic rate, insulin sensitivity, or skin microstructure. However, DGAT2 ASO treatment caused a marked reduction in hepatic triglyceride content and improved hepatic steatosis in both models, which was consistent with a dramatic decrease in triglyceride synthesis and an increase in fatty acid oxidation observed in primary mouse hepatocytes treated with DGAT2 ASO. In addition, the treatment lowered hepatic triglyceride secretion rate and plasma triglyceride levels, and improved plasma lipoprotein profile in DIO mice. The positive effects of the DGAT2 ASO were accompanied by a reduction in the mRNA levels of several hepatic lipogenic genes, including SCD1, FAS, ACC1, ACC2, ATP-citrate lyase, glycerol kinase, and HMG-CoA reductase. In conclusion, reduction of DGAT2 expression in obese animals can reduce hepatic lipogenesis and hepatic steatosis as well as attenuate hyperlipidemia, thereby leading to an improvement in metabolic syndrome.

Physical activity and modulation of systemic low-level inflammation

It has been recognized for some time that cardiovascular disease and type 2 diabetes are, to a major extent, inflammatory disorders associated with an environment characterized by a sedentary lifestyle together with abundant intakes of calories. Systemic low-level inflammation is suggested to be a cause as well as consequence of pathological processes with local tumor necrosis factor alpha production as an important biological driver. It is hypothesized that physical inactivity contributes to an enhanced proinflammatory burden independently of obesity, as regular muscle contractions mediate signals with myokines/cytokines as important messengers, which suppress proinflammatory activity at distant sites as well as within skeletal muscle. Muscle-derived interleukin (IL)-6 is considered to possess a central role in anti-inflammatory activities and health beneficial effects in relation to physical exercise. It is discussed how this fits the consistent observation that enhanced plasma levels of IL-6 represent a strong risk marker in chronic disorders associated with systemic low-level inflammation and all-cause mortality.

Evaluation of an in vitro model of hepatic inflammatory response by gene expression profiling

The body's response to biochemical stress involves coordinated changes in the expression of several sets of genes that regulate its return to homeostasis. Although several cell culture systems have been utilized for studying such complex physiological events in vitro, their assessment has been limited to biochemical assays on individual genes and proteins, limiting interpretation of the results in a systems context. Advances in genomics provide an opportunity to provide a more comprehensive assessment. In this study, we have used DNA microarrays to profile gene expression dynamics during interleukin 6-stimulated inflammation in hepatocytes maintained in a stable, collagen double-gel in vitro model system. The observed expression profile was also compared with that obtained from rat liver tissue after burn injury to determine the extent and nature of responses captured by the in vitro system. Our results indicate that several aspects of the in vivo hepatic inflammatory response can be captured by the in vitro system at the molecular systems level. Statistical analysis of the mRNA profiles was also used to characterize the temporal response in each model system and demonstrate similar behavior. A small panel of molecules involved in the hepatic acute-phase response was also profiled, using quantitative kinetic polymerase chain reaction, to confirm these observations. These results indicate the utility of the stable hepatocyte culture system for expression profiling of inflammatory states and for providing insights into the interplay of changes in gene expression during complex physiological states.

Interaction of fish oil and conjugated linoleic acid in affecting hepatic activity of lipogenic enzymes and gene expression in liver and adipose tissue

The interaction of dietary fish oil and conjugated linoleic acid (CLA) in affecting the activity of hepatic lipogenic enzymes and gene expression in liver and adipose tissue was examined in mice. A diet containing 1.0% CLA, mainly composed of 9cis,11trans- and 10trans,12cis-octadecadienoic acids at equivalent amounts, greatly decreased adipose tissue weight and serum concentrations of leptin and adiponectin and was accompanied by a downregulation of the expression of various adipocyte-abundant genes in epididymal adipose tissue. However, CLA increased the serum insulin concentration fourfold, and it caused hepatomegaly, with huge increases in the triacylglycerol level and the activity and mRNA levels of hepatic lipogenic enzymes. Different amounts (1.5, 3, and 6%) of fish oil added to CLA-containing diets dose-dependently downregulated parameters of lipogenesis and were accompanied by a parallel decrease in the triacylglycerol level in the liver. The supplementation of CLA-containing diets with fish oil was also associated with an increase in fat pad mass and mRNA levels of many adipocyte-abundant genes in epididymal adipose tissue along with a normalization of serum concentrations of leptin and adiponectin in a dose-dependent manner. However, in mice fed a diet containing 1.5% fish oil and CLA in whom fat pad mass was still low and comparable to that in the animals fed CLA alone, the serum insulin concentration greatly exceeded (twofold) the value observed in mice fed CLA alone, indicating an aggravation of insulin resistance. This hyperinsulinemia was ameliorated with increasing amounts of fish oil in the diets. Apparently, many of the physiological effects of CLA can be reversed by fish oil.

Elevated levels of tumor necrosis factor alpha and mortality in centenarians

BACKGROUND

Aging is accompanied by low-grade inflammation. Tumor necrosis factor (TNF) alpha initiates the cytokine cascade, and high levels are associated with dementia and atherosclerosis in persons aged 100 years. We hypothesized that TNF-alpha was also a prognostic marker for all-cause mortality in these persons.

METHODS

We enrolled 126 subjects at or around the time of their 100th birthday. Plasma levels of TNF-alpha, interleukin (IL)-6, IL-8, and C-reactive protein were measured at baseline, and we determined the associations between the markers of inflammation and mortality during the subsequent 5 years.

RESULTS

Only 9 subjects were alive after 5 years. Elevated levels of TNF-alpha were associated with mortality in both men and women (hazard ratio = 1.34 per SD of 2.81 pg/mL; 95% confidence interval: 1.12 to 1.60, P = 0.001). Levels of IL-6 and IL-8 did not affect survival; levels of C-reactive protein were not associated with mortality when levels of TNF-alpha were included in the analysis. Dementia and cardiovascular diseases represented the major causes of comorbid conditions at baseline. TNF-alpha was still associated with mortality in multivariate models that included these parameters as confounders.

CONCLUSION

TNF-alpha was an independent prognostic marker for mortality in persons aged 100 years, suggesting that it has specific biological effects and is a marker of frailty in the very elderly.

Massive liver growth in mice induced by systemic interleukin 6 administration

The multifunctional cytokine interleukin 6 (IL-6) is expressed in a wide variety of disease states and pathologic processes. Mice deficient in IL-6 display abnormal and delayed liver regeneration and repair. Currently, IL-6 is thought to influence liver growth indirectly by priming hepatocytes to respond to growth factors such as hepatocyte growth factor (HGF) by inducing expression of HGF and by inhibiting hepatocyte apoptosis, as distinct from the direct mitotic effects of IL-6 on myeloid and other cell types. Here, we show that systemic administration of IL-6 using CHO cell tumors in nude mice results in dramatic hepatomegaly and hepatocyte hyperplasia in the absence of liver injury. Liver mass and liver to body mass ratios increased to 2 to 3 times normal because of proliferation of hepatocytes. Liver growth was associated with high levels of serum IL-6 and with activation of the IL-6-signaling pathway, including increased expression of IL-6 receptor-alpha/gp80, activation of the signal transducer and activator of transcription-3 (STAT-3), and mitogen-activated protein kinase (MAPK/ERK)-signaling pathways and induction of downstream target genes, including c-myc. HGF receptor and transforming growth factor alpha (TGF-alpha)/epidermal growth factor (EGF) receptor activation were decreased in hypertrophied livers, suggesting that IL-6-induced liver growth was independent of these known hepatocyte mitotic pathways. In conclusion, we suggest that IL-6 may function as a direct hepatic mitogen in vivo and, furthermore, that IL-6 warrants closer examination as a potent liver growth factor with potential clinical utility for increasing liver mass following injury.

Acute interleukin-6 administration does not impair muscle glucose uptake or whole-body glucose disposal in healthy humans

The cytokine interleukin (IL)-6 has recently been linked with type 2 diabetes mellitus and has been suggested to affect glucose metabolism. To determine whether acute IL-6 administration affects whole-body glucose kinetics or muscle glucose uptake, 18 healthy young men were assigned to one of three groups receiving a high dose of recombinant human IL-6 (HiIL-6; n = 6), a low dose of IL-6 (LoIL-6; n = 6) or saline (Con; n = 6) infused into one femoral artery for 3 h. The stable isotope [6,6-2H2] glucose was infused into a forearm vein throughout the 3 h infusion period and for a further 3 h after the cessation of infusion (recovery) to determine endogenous glucose production and whole-body glucose disposal. Infusion with HiIL-6 and LoIL-6 resulted in a marked (P < 0.05) increase in systemic IL-6 concentration throughout the 3 h of infusion (mean arterial plasma [IL-6]s of 319 and 143 pg ml-1 for HiIL-6 and LoIL-6, respectively), followed by a rapid decline (P < 0.05) during the recovery period. Subjects experienced clinical symptoms such as shivering and discomfort during HiIL-6 administration, but were asymptomatic during LoIL-6 administration. In addition, only HiIL-6 elevated (P < 0.05) plasma adrenaline (epinephrine). IL-6 infusion, irrespective of dose, did not result in any changes to endogenous glucose production, whole-body glucose disposal or leg- glucose uptake. These data demonstrate that acute IL-6 administration does not impair whole-body glucose disposal, net leg-glucose uptake, or increase endogenous glucose production at rest in healthy young humans.

Predicting death from tumour necrosis factor-alpha and interleukin-6 in 80-year-old people

Ageing is associated with low-grade inflammation and markers such as IL-6 possess prognostic value. Tumour necrosis-alpha (TNF-alpha) initiates the inflammatory cascade and has been linked to several age-associated disorders. It remains, however, unknown if TNF-alpha is associated with mortality in old populations. The aim of the present study was to investigate if serum levels of TNF-alpha were associated with all-cause mortality independently of interleukin (IL)-6 in a prospective study of 333 relatively healthy 80-year-old people. A Cox regression model was used to explore effects of TNF-alpha and IL-6 on survival in the following 6 years. A total of 133 participants died during this follow-up period. TNF-alpha was associated with mortality in men, but not in women, whereas low-grade elevations in IL-6 were associated strongly with mortality in both sexes. TNF-alpha explained only 7% of the variability in IL-6 and effects of the two cytokines were independent of each other as well as of other traditional risk factors for death [smoking, blood pressure, physical exercise, total cholesterol, co-morbidity, body mass index (BMI) and intake of anti-inflammatory drugs]. These findings indicate that at least in old populations chronic elevated levels of TNF-alpha and IL-6 have different biological functions that trigger age-associated pathology and cause mortality.

Age-related inflammatory cytokines and disease

Aging is associated with chronic low-grade increases in circulating levels of inflammatory markers. A wide range of environmental factors, including smoking, infections, and obesity, genetic factors, and the declining function of sex hormones may contribute to systemic low-grade inflammatory activity in older individuals. Age-associated disease may exacerbate this phenomenon. The multifunctional cytokines TNF-alpha and IL-6 have been associated with morbidity and mortality in the elderly. Evidence supports the direct role of TNF-alpha in the pathogeneses of atherosclerosis, type 2 DM, and AD in older individuals. Age-related increases in systemic levels of TNF-alpha could provide a unifying basis for these disorders. Furthermore, TNF-alpha induces a catabolic state that causes frailty. Circulating levels of IL-6 seem to be a strong risk factor for frailty in the elderly, which could reflect its association with increased production of TNF-alpha. IL-6 also may be a risk factor for thromboembolic complications. In healthy, elderly populations, high circulating levels of TNF-alpha and IL-6 predict mortality, independent of comorbidity, indicating that TNF-alpha and IL-6 cause morbidity and mortality. In cohorts of frail, older individuals, TNF-alpha and IL-6 also act as disease markers. Circulating levels of TNF-alpha seem to be the best predictor of mortality in frail, elderly populations with a high mortality rate, whereas IL-6 seems to be the strongest risk marker in healthy, elderly populations. This finding could reflect that in relatively healthy old populations the increase in circulating levels of IL-6 represent a systemic response to local proinflammatory activities; however, when age-related inflammatory diseases progress, levels of TNF-alpha increase in the circulation and become gradually a stronger risk marker than IL-6. In conclusion low-grade elevations in levels of circulating cytokines are strong independent risk factors of morbidity and mortality in the elderly, and lifestyle factors and comorbidities may modulate these levels. Exercise and dietary interventions may be possible strategies to decrease inflammatory activity and improve the health status of the elderly.

Peripheral mechanisms involved with catabolism

PURPOSE OF REVIEW

This review summarizes recent developments concerning the mechanisms of skeletal muscle and adipose tissue breakdown, which are a hallmark of cachexia during many diseases. Current knowledge on the hypermetabolism which often contributes to cachexia is also considered.

RECENT FINDINGS

Recent studies have identified interactions between Ca2+, proinflammatory cytokines (in particular tumor necrosis factor-alpha) and the activation of transcription factors (e.g. nuclear factor-kappaB) in the stimulation of major proteolytic pathways in cachexia. Progress has also been made in explaining the inhibiting effects of several drugs on protein breakdown. Advances in our understanding of the mechanisms of adipose tissue catabolism in cachexia include demonstrations that (1) tumor necrosis factor-alpha, in addition to its direct lipolytic effect, promotes adipose tissue breakdown by inhibiting adipocyte differentiation and increasing adipocyte apoptosis, (2) interleukin-6 has a lipolytic effect, and (3) chemokines are expressed by adipocytes and interact with tumor necrosis factor-alpha to cause lipolysis. Concerning the hypermetabolism in cachexia, new evidence supports previous theories that uncoupling protein-2 and 3 are primarily involved in the generation of reactive oxygen species and in the control of fatty acid flux across the mitochondrial membrane, respectively. Furthermore, the cytokine-induced transcriptional coactivator-1 for the peroxysome proliferator-activated receptor-gamma was recently identified as a contributor to hypermetabolism.

SUMMARY

These new insights into major catabolic pathways during cachexia provide a focus for future studies in this area and may help to develop promising therapeutic approaches.

Intracerebroventricular interleukin-6 treatment decreases body fat in rats

Recently we found that interleukin-6 (IL-6) knockout mice develop mature-onset obesity and that a single intracerebroventricular (ICV) injection of IL-6 increases energy expenditure. In the present study we investigated if chronic ICV treatment with IL-6 can suppress body fat mass. IL-6 was injected ICV daily for two weeks to rats fed a high-fat diet. IL-6 treatment but not saline treatment decreased body weight by 8.4% and decreased the relative weights of mesenteric and retroperitoneal fat pads. Consistent with this, circulating leptin levels were decreased by 40% after IL-6 treatment but not after saline treatment. Average food intake per day was decreased in the IL-6 treated group compared to the saline treated rats. IL-6 treatment did not change hepatic expression of the acute-phase protein haptoglobin, serum levels of insulin or insulin-like growth factor-I, or the weights of the heart, liver, kidneys, adrenals, and spleen. We conclude that centrally administered IL-6 can decrease body fat in rats without causing acute-phase reaction.