Optimization of a mouse model of pancreatic cancer to simulate the human phenotypes of metastasis and cachexia

BACKGROUND

Pancreatic ductal adenocarcinoma (PDAC) presents with a high mortality rate. Two important features of PDAC contribute to this poor outcome. The first is metastasis which occurs in ~ 80% of PDAC patients. The second is cachexia, which compromises treatment tolerance for patients and reduces their quality of life. Although various mouse models of PDAC exist, recapitulating both metastatic and cachectic features have been challenging.

METHODS

Here, we optimize an orthotopic mouse model of PDAC by altering several conditions, including the subcloning of parental murine PDAC cells, implantation site, number of transplanted cells, and age of recipient mice. We perform spatial profiling to compare primary and metastatic immune microenvironments and RNA sequencing to gain insight into the mechanisms of muscle wasting in PDAC-induced cachexia, comparing non-metastatic to metastatic conditions.

RESULTS

These modifications extend the time course of the disease and concurrently increase the rate of metastasis to approximately 70%. Furthermore, reliable cachexia endpoints are achieved in both PDAC mice with and without metastases, which is reminiscent of patients. We also find that cachectic muscles from PDAC mice with metastasis exhibit a similar transcriptional profile to muscles derived from mice and patients without metastasis.

CONCLUSION

Together, this model is likely to be advantageous in both advancing our understanding of the mechanism of PDAC cachexia, as well as in the evaluation of novel therapeutics.

Retrospective study of testosterone deficiency and symptom burden in patients with pancreatic cancer

Background

Pancreatic cancer patients have poor quality of life. Testosterone deficiency is associated with constitutional symptoms and sexual dysfunction which may contribute to poor quality of life. We investigated the prevalence of screening for and presence of testosterone deficiency in male pancreatic cancer patients.

Methods

To determine the frequency of screening for testosterone deficiency in pancreatic cancer patients, our institution's electronic medical record system was queried for male patients diagnosed with a pancreatic mass between 2006 and 2020 and an available testosterone level. In a separate analysis, total testosterone was measured in serum samples from a cohort of 89 male pancreatic ductal adenocarcinoma (PDAC) patients. Low serum testosterone was defined as <300 ng/dL.

Results

One thousand five hundred and sixty-six male patients were identified with a pancreatic mass, and 35 (2.2%) also had a testosterone level. In our analysis cohort, 44 of 89 patients (49.4%) were found to have low serum testosterone. Symptoms consistent with testosterone deficiency were documented for 70% of these patients, with fatigue being the most common. Testosterone level had no significant association with progression-free survival (PFS) (P=0.66) or overall survival (OS) (P=0.95).

Conclusions

Testosterone deficiency is common but rarely assessed in male patients with pancreatic cancer. Further studies are warranted to explore the possibility of testosterone supplementation to improve quality of life in this patient population.

Identification of circulating plasma ceramides as a potential sexually dimorphic biomarker of pancreatic cancer-induced cachexia

Background

Cancer patients who exhibit cachexia lose weight and have low treatment tolerance and poor outcomes compared to cancer patients without weight loss. Despite the clear increased risk for patients, diagnosing cachexia still often relies on self-reported weight loss. A reliable biomarker to identify patients with cancer cachexia would be a valuable tool to improve clinical decision making and identification of patients at risk of adverse outcomes.

Methods

Targeted metabolomics, that included panels of amino acids, tricarboxylic acids, fatty acids, acylcarnitines, and sphingolipids, were conducted on plasma samples from patients with confirmed pancreatic ductal adenocarcinoma (PDAC) with and without cachexia and control patients without cancer (n=10/group, equally divided by sex). Additional patient samples were analyzed (total n=95) and Receiver Operating Characteristic (ROC) analyses were performed to establish if any metabolite could effectively serve as a biomarker of cachexia.

Results

Targeted profiling revealed that cachectic patients had decreased circulating levels of three sphingolipids compared to either non-cachectic PDAC patients or patients without cancer. The ratio of C18-ceramide to C24-ceramide (C18:C24) outperformed a number of other previously proposed biomarkers of cachexia (area under ROC = 0.810). It was notable that some biomarkers, including C18:C24, were only altered in cachectic males.

Conclusions

Our findings identify C18:C24 as a potentially new biomarker of PDAC-induced cachexia that also highlight a previously unappreciated sexual dimorphism in cancer cachexia.

Emerging signaling mediators in the anorexia–cachexia syndrome of cancer

The cachexia syndrome in cancer is characterized by weight loss resulting from the combination of anorexia and atrophy of adipose and skeletal muscle. For decades, inflammatory circulatory factors have been identified to regulate wasting, but inhibitors of these factors have not yielded the same clinical benefit as in animal models. Therefore, additional mediators of cachexia likely regulate this syndrome, and such factors might be more suitable for targeted intervention. We highlight several anorexia-cachexia signaling mediators, including activin A, myostatin, GDF15, and lipocalin-2. We discuss current evidence that these factors associate with cachexia in cancer patients, and summarize translational efforts including essential early-phase clinical trials. We conclude with thoughts on targeted and personalized approaches for future anti-cachexia treatments.

Abstract IA-17: Mechanisms of pancreatic cancer-induced cachexia

Cachexia is a debilitating syndrome that results in severe, involuntary weight loss due to the depletion of skeletal muscle mass. Currently, no effective therapy exists to combat this malignant disorder. For pancreatic cancer, 85% of patients lose on average 14% of their pre-illness weight, and cachexia dramatically limits their ability to tolerate surgery, chemo- or radiotherapy. New therapies will likely evolve from an enhanced understanding of the mechanisms leading to muscle wasting and tumor development. Our laboratory has been examining the role of the NF-κB signaling pathway in tumorigenesis for several decades and that interest led us to discover the connection between NF-κB and muscle wasting in cancer cachexia and more recently in pancreatic cancer. We view the pathway as playing two separate functions in pancreatic cancer-induced cachexia. The first occurs at the level of skeletal muscle, or more preciously in skeletal muscle stem cells. We have found that during cancer progression, skeletal muscle undergoes a type of injury response leading to the activation of resident stem cells to engage in a regeneration program. NF-κB is activated in these stem cells and functions to inhibit regeneration, which contributes to the overall wasting process in cachexia. New data reveal that NF-κB activity in progenitor cells also regulates a local muscle inflammatory environment that might also contribute to skeletal muscle catabolism. The mechanism of this regulation will be discussed in more details. The second function of NF-κB signaling that we are pursuing focuses in the tumor microenvironment of pancreatic cancer. Using orthotopic mouse models of pancreatic cancer, we showed that NF-κB plays a critical role in protecting tumor cells from the surveillance property of anti-tumor macrophages. This occurs through the direct transcriptional regulation of the immunosuppressive cytokine, GDF15. Interestingly, circulating levels of GDF15 are elevated in cachectic patients and recent studies indicate that this cytokine might be an attractive therapeutic target in cancer cachexia. Together, we speculate that NF-κB functions in cancer cachexia by acting in muscle stem cells to block muscle repair, as well as promoting pancreatic cancer through the production of immunosuppressive genes such as GDF15.

Citation Format: Benjamin Pryce, Nivedita Ratnam, Erin E. Talbert, Mary Dilhoff, Carl R. Schmidt, David J. Wang, Denis C. Guttridge. Mechanisms of pancreatic cancer-induced cachexia [abstract]. In: Proceedings of the AACR Virtual Special Conference on Pancreatic Cancer; 2020 Sep 29-30. Philadelphia (PA): AACR; Cancer Res 2020;80(22 Suppl):Abstract nr IA-17.

Prevention of Doxorubicin-Induced Autophagy Attenuates Oxidative Stress and Skeletal Muscle Dysfunction

Clinical use of the chemotherapeutic doxorubicin (DOX) promotes skeletal muscle atrophy and weakness, adversely affecting patient mobility and strength. Although the mechanisms responsible for DOX-induced skeletal muscle dysfunction remain unclear, studies implicate the significant production of reactive oxygen species (ROS) in this pathology. Supraphysiological ROS levels can enhance protein degradation via autophagy, and it is established that DOX upregulates autophagic signaling in skeletal muscle. To determine the precise contribution of accelerated autophagy to DOX-induced skeletal muscle dysfunction, we inhibited autophagy in the soleus via transduction of a dominant negative mutation of the autophagy related 5 (ATG5) protein. Targeted inhibition of autophagy prevented soleus muscle atrophy and contractile dysfunction acutely following DOX administration, which was associated with a reduction in mitochondrial ROS and maintenance of mitochondrial respiratory capacity. These beneficial modifications were potentially the result of enhanced transcription of antioxidant response element-related genes and increased antioxidant capacity. Specifically, our results showed significant upregulation of peroxisome proliferator-activated receptor gamma co-activator 1-alpha, nuclear respiratory factor-1, nuclear factor erythroid-2-related factor-2, nicotinamide-adenine dinucleotide phosphate quinone dehydrogenase-1, and catalase in the soleus with DOX treatment when autophagy was inhibited. These findings establish a significant role of autophagy in the development of oxidative stress and skeletal muscle weakness following DOX administration.

Modeling Human Cancer-induced Cachexia

Cachexia is a wasting syndrome characterized by pronounced skeletal muscle loss. In cancer, cachexia is associated with increased morbidity and mortality and decreased treatment tolerance. Although advances have been made in understanding the mechanisms of cachexia, translating these advances to the clinic has been challenging. One reason for this shortcoming may be the current animal models, which fail to fully recapitulate the etiology of human cancer-induced tissue wasting. Because pancreatic ductal adenocarcinoma (PDA) presents with a high incidence of cachexia, we engineered a mouse model of PDA that we named KPP. KPP mice, similar to PDA patients, progressively lose skeletal and adipose mass as a consequence of their tumors. In addition, KPP muscles exhibit a similar gene ontology as cachectic patients. We envision that the KPP model will be a useful resource for advancing our mechanistic understanding and ability to treat cancer cachexia.

Abstract 354: Accelerated Autophagy is Required for Doxorubicin-induced Oxidative Damage and Cardiomyopathy

Doxorubicin (DOX) is a highly effective chemotherapeutic agent used in the treatment of a broad spectrum of malignancies. However, clinical use of DOX is limited by the risk of severe cardiotoxicity. In patients, the acute onset of cardiomyopathy often precludes chemotherapy treatment, resulting in reduced quality of life and increased morbidity. While the mechanisms by which DOX promotes cardiac dysfunction are not well understood, our previous findings show that intracellular metabolism of DOX elicits mitochondrial reactive oxygen species (ROS) generation, and subsequent activation of the autophagy/lysosomal system. Equally, evidence suggests that elimination of vital cellular organelles and proteins within the cell as a result of pathologically elevated autophagy may in turn stimulate an increase in ROS generation. Therefore, we hypothesize that DOX-induced autophagy promotes cardiac dysfunction as a result of an autophagy-induced increase in oxidative stress in the heart. To prevent elevated activity of the autophagy/lysosomal system, we administered a dominant negative mutation of the autophagy protein ATG5 (rAAV-dnATG5) to female Sprague-Dawley rats via tail vein administration four weeks prior to either DOX (20 mg/kg ip) or saline treatment. Two days following treatment, assessment of cardiac function showed significant alterations to the myocardial performance index and fractional shortening percentage in control, DOX treated animals. These changes corresponded with deficits to mitochondrial respiration, increased mitochondrial ROS emission and increased appearance of autophagic vacuoles within the heart. In contrast, rAAV-dnATG5 administration in DOX treated animals prevented the conjugation of ATG12 to ATG5 thereby reducing autophagosome formation and attenuating cardiac dysfunction. Interestingly, protein expression of the antioxidant enzymes catalase and superoxide dismutase 2 (SOD2) was elevated in these animals, which may account for improved mitochondrial respiration and reduced mitochondrial free radical production. These findings indicate that accelerated autophagy promotes DOX-induced cardiac dysfunction and is an underlying cause of chemotherapy-induced oxidative damage to the heart.

Circulating monocyte chemoattractant protein-1 (MCP-1) is associated with cachexia in treatment-naïve pancreatic cancer patients

BACKGROUND

Cancer-associated wasting, termed cancer cachexia, has a profound effect on the morbidity and mortality of cancer patients but remains difficult to recognize and diagnose. While increases in circulating levels of a number of inflammatory cytokines have been associated with cancer cachexia, these associations were generally made in patients with advanced disease and thus may be associated with disease progression rather than directly with the cachexia syndrome. Thus, we sought to assess potential biomarkers of cancer-induced cachexia in patients with earlier stages of disease.

METHODS

A custom multiplex array was used to measure circulating levels of 25 soluble factors from 70 pancreatic cancer patients undergoing attempted tumour resections. A high-sensitivity multiplex was used for increased sensitivity for nine cytokines.

RESULTS

Resectable pancreatic cancer patients with cachexia had low levels of canonical pro-inflammatory cytokines including interleukin-6 (IL-6), interleukin-1β (IL-1β), interferon-γ (IFN-γ), and tumour necrosis factor (TNF). Even in our more sensitive analysis, these cytokines were not associated with cancer cachexia. Of the 25 circulating factors tested, only monocyte chemoattractant protein-1 (MCP-1) was increased in treatment-naïve cachectic patients compared with weight stable patients and identified as a potential biomarker for cancer cachexia. Although circulating levels of leptin and granulocyte-macrophage colony-stimulating factor (GM-CSF) were found to be decreased in the same cohort of treatment-naïve cachectic patients, these factors were closely associated with body mass index, limiting their utility as cancer cachexia biomarkers.

CONCLUSIONS

Unlike in advanced disease, it is possible that cachexia in patients with resectable pancreatic cancer is not associated with high levels of classical markers of systemic inflammation. However, cachectic, treatment-naïve patients have higher levels of MCP-1, suggesting that MCP-1 may be useful as a biomarker of cancer cachexia.

Crosstalk between autophagy and oxidative stress regulates proteolysis in the diaphragm during mechanical ventilation

Mechanical ventilation (MV) results in the rapid development of ventilator-induced diaphragm dysfunction (VIDD). While the mechanisms responsible for VIDD are not fully understood, recent data reveal that prolonged MV activates autophagy in the diaphragm, which may occur as a result of increased cellular reactive oxygen species (ROS) production. Therefore, we tested the hypothesis that (1) accelerated autophagy is a key contributor to VIDD; and that (2) oxidative stress is required to increase the expression of autophagy genes in the diaphragm. Our findings reveal that targeted inhibition of autophagy in the rat diaphragm prevented MV-induced muscle atrophy and contractile dysfunction. Attenuation of VIDD in these animals occurred as a result of increased diaphragm concentration of the antioxidant catalase and reduced mitochondrial ROS emission, which corresponded to reductions in the activity of calpain and caspase-3. To determine if increased ROS production is required for the upregulation of autophagy biomarkers in the diaphragm, rats that were administered the mitochondrial-targeted peptide SS-31 during MV. Results from this study demonstrated that mitochondrial ROS production in the diaphragm during MV is required for the increased expression of key autophagy genes (i.e. LC3, Atg7, Atg12, Beclin1 and p62), as well as for increased activity of cathepsin L. Together, these data reveal that autophagy is required for VIDD, and that autophagy inhibition reduces MV-induced diaphragm ROS production and prevents a positive feedback loop whereby increased autophagy is stimulated by oxidative stress, resulting in further increases in ROS and autophagy.

NF-κB regulates GDF-15 to suppress macrophage surveillance during early tumor development

Macrophages are attracted to developing tumors and can participate in immune surveillance to eliminate neoplastic cells. In response, neoplastic cells utilize NF-κB to suppress this killing activity, but the mechanisms underlying their self-protection remain unclear. Here, we report that this dynamic interaction between tumor cells and macrophages is integrally linked by a soluble factor identified as growth and differentiation factor 15 (GDF-15). In vitro, tumor-derived GDF-15 signals in macrophages to suppress their proapoptotic activity by inhibiting TNF and nitric oxide (NO) production. In vivo, depletion of GDF-15 in Ras-driven tumor xenografts and in an orthotopic model of pancreatic cancer delayed tumor development. This delay correlated with increased infiltrating antitumor macrophages. Further, production of GDF-15 is directly regulated by NF-κB, and the colocalization of activated NF-κB and GDF-15 in epithelial ducts of human pancreatic adenocarcinoma supports the importance of this observation. Mechanistically, we found that GDF-15 suppresses macrophage activity by inhibiting TGF-β-activated kinase (TAK1) signaling to NF-κB, thereby blocking synthesis of TNF and NO. Based on these results, we propose that the NF-κB/GDF-15 regulatory axis is important for tumor cells in evading macrophage immune surveillance during the early stages of tumorigenesis.

Dual Inhibition of MEK and PI3K/Akt Rescues Cancer Cachexia through both Tumor-Extrinsic and -Intrinsic Activities

Involuntary weight loss, a part of the cachexia syndrome, is a debilitating comorbidity of cancer and currently has no treatment options. Results from a recent clinical trial at our institution showed that biliary tract cancer patients treated with a MEK inhibitor exhibited poor tumor responses but surprisingly gained weight and increased their skeletal muscle mass. This implied that MEK inhibition might be anticachectic. To test this potential effect of MEK inhibition, we utilized the established Colon-26 model of cancer cachexia and the MEK1/2 inhibitor MEK162. Results showed that MEK inhibition effectively prevented muscle wasting. Importantly, MEK162 retained its ability to spare muscle loss even in mice bearing a Colon-26 clone resistant to the MEK inhibitor, demonstrating that the effects of blocking MEK are at least in part independent of the tumor. Because single-agent MEK inhibitors have been limited as a first-line targeted therapy due to compensatory activation of other oncogenic signaling pathways, we combined MEK162 with the PI3K/Akt inhibitor buparlisib. Results showed that this combinatorial treatment significantly reduced tumor growth due to a direct activity on Colon-26 tumor cells in vitro and in vivo, while also preserving skeletal muscle mass. Together, our results suggest that as a monotherapy, MEK inhibition preserves muscle mass, but when combined with a PI3K/Akt inhibitor exhibits potent antitumor activity. Thus, combinatorial therapy might serve as a new approach for the treatment of cancer cachexia. Mol Cancer Ther; 16(2); 344-56. ©2016 AACRSee related article by Kobayashi et al., p. 357.

Blockage of the Ryanodine Receptor via Azumolene Does Not Prevent Mechanical Ventilation-Induced Diaphragm Atrophy

Mechanical ventilation (MV) is a life-saving intervention for patients in respiratory failure. However, prolonged MV causes the rapid development of diaphragm muscle atrophy, and diaphragmatic weakness may contribute to difficult weaning from MV. Therefore, developing a therapeutic countermeasure to protect against MV-induced diaphragmatic atrophy is important. MV-induced diaphragm atrophy is due, at least in part, to increased production of reactive oxygen species (ROS) from diaphragm mitochondria and the activation of key muscle proteases (i.e., calpain and caspase-3). In this regard, leakage of calcium through the ryanodine receptor (RyR1) in diaphragm muscle fibers during MV could result in increased mitochondrial ROS emission, protease activation, and diaphragm atrophy. Therefore, these experiments tested the hypothesis that a pharmacological blockade of the RyR1 in diaphragm fibers with azumolene (AZ) would prevent MV-induced increases in mitochondrial ROS production, protease activation, and diaphragmatic atrophy. Adult female Sprague-Dawley rats underwent 12 hours of full-support MV while receiving either AZ or vehicle. At the end of the experiment, mitochondrial ROS emission, protease activation, and fiber cross-sectional area were determined in diaphragm muscle fibers. Decreases in muscle force production following MV indicate that the diaphragm took up a sufficient quantity of AZ to block calcium release through the RyR1. However, our findings reveal that AZ treatment did not prevent the MV-induced increase in mitochondrial ROS emission or protease activation in the diaphragm. Importantly, AZ treatment did not prevent MV-induced diaphragm fiber atrophy. Thus, pharmacological inhibition of the RyR1 in diaphragm muscle fibers is not sufficient to prevent MV-induced diaphragm atrophy.

Impaired regeneration: A role for the muscle microenvironment in cancer cachexia

While changes in muscle protein synthesis and degradation have long been known to contribute to muscle wasting, a body of literature has arisen which suggests that regulation of the satellite cell and its ensuing regenerative program are impaired in atrophied muscle. Lessons learned from cancer cachexia suggest that this regulation is simply not a consequence, but a contributing factor to the wasting process. In addition to satellite cells, evidence from mouse models of cancer cachexia also suggests that non-satellite progenitor cells from the muscle microenvironment are also involved. This chapter in the series reviews the evidence of dysfunctional muscle repair in multiple wasting conditions. Potential mechanisms for this dysfunctional regeneration are discussed, particularly in the context of cancer cachexia.

AT1 receptor blocker losartan protects against mechanical ventilation-induced diaphragmatic dysfunction

Mechanical ventilation is a life-saving intervention for patients in respiratory failure. Unfortunately, prolonged ventilator support results in diaphragmatic atrophy and contractile dysfunction leading to diaphragm weakness, which is predicted to contribute to problems in weaning patients from the ventilator. While it is established that ventilator-induced oxidative stress is required for the development of ventilator-induced diaphragm weakness, the signaling pathway(s) that trigger oxidant production remain unknown. However, recent evidence reveals that increased plasma levels of angiotensin II (ANG II) result in oxidative stress and atrophy in limb skeletal muscles. Using a well-established animal model of mechanical ventilation, we tested the hypothesis that increased circulating levels of ANG II are required for both ventilator-induced diaphragmatic oxidative stress and diaphragm weakness. Cause and effect was determined by administering an angiotensin-converting enzyme inhibitor (enalapril) to prevent ventilator-induced increases in plasma ANG II levels, and the ANG II type 1 receptor antagonist (losartan) was provided to prevent the activation of ANG II type 1 receptors. Enalapril prevented the increase in plasma ANG II levels but did not protect against ventilator-induced diaphragmatic oxidative stress or diaphragm weakness. In contrast, losartan attenuated both ventilator-induced oxidative stress and diaphragm weakness. These findings indicate that circulating ANG II is not essential for the development of ventilator-induced diaphragm weakness but that activation of ANG II type 1 receptors appears to be a requirement for ventilator-induced diaphragm weakness. Importantly, these experiments provide the first evidence that the Food and Drug Administration-approved drug losartan may have clinical benefits to protect against ventilator-induced diaphragm weakness in humans.

Immobilization-induced activation of key proteolytic systems in skeletal muscles is prevented by a mitochondria-targeted antioxidant

Long periods of skeletal muscle disuse result in muscle fiber atrophy, and mitochondrial production of reactive oxygen species (ROS) appears to be a required signal for the increase in protein degradation that occurs during disuse muscle atrophy. The experiments detailed here demonstrate for the first time in limb muscle that the inactivity-induced increases in E3 ligase expression and autophagy biomarkers result from increases in mitochondrial ROS emission. Treatment of animals with a mitochondrial-targeted antioxidant also prevented the disuse-induced decrease in anabolic signaling (Akt/mammalian target of rapamycin signaling) that is normally associated with prolonged inactivity in skeletal muscles. Additionally, our results confirm previous findings that treatment with a mitochondrial-targeted antioxidant is sufficient to prevent casting-induced skeletal muscle atrophy, mitochondrial dysfunction, and activation of the proteases calpain and caspase-3. Collectively, these data reveal that inactivity-induced increases in mitochondrial ROS emission play a required role in activation of key proteolytic systems and the downregulation of important anabolic signaling molecules in muscle fibers exposed to prolonged inactivity.

Calpain and caspase-3 play required roles in immobilization-induced limb muscle atrophy

Prolonged skeletal muscle inactivity results in a rapid decrease in fiber size, primarily due to accelerated proteolysis. Although several proteases are known to contribute to disuse muscle atrophy, the ubiquitin proteasome system is often considered the most important proteolytic system during many conditions that promote muscle wasting. Emerging evidence suggests that calpain and caspase-3 may also play key roles in inactivity-induced atrophy of respiratory muscles, but it remains unknown if these proteases are essential for disuse atrophy in limb skeletal muscles. Therefore, we tested the hypothesis that activation of both calpain and caspase-3 is required for locomotor muscle atrophy induced by hindlimb immobilization. Seven days of immobilization (i.e., limb casting) promoted significant atrophy in type I muscle fibers of the rat soleus muscle. Independent pharmacological inhibition of calpain or caspase-3 prevented this casting-induced atrophy. Interestingly, inhibition of calpain activity also prevented caspase-3 activation, and, conversely, inhibition of caspase-3 prevented calpain activation. These findings indicate that a regulatory cross talk exists between these proteases and provide the first evidence that the activation of calpain and caspase-3 is required for inactivity-induced limb muscle atrophy.

Hyperthermia induces injury to the intestinal mucosa in the mouse: evidence for an oxidative stress mechanism

Loss of the intestinal barrier is critical to the clinical course of heat illness, but the underlying mechanisms are still poorly understood. We tested the hypothesis that conditions characteristic of mild heatstroke in mice are associated with injury to the epithelial lining of the intestinal tract and comprise a critical component of barrier dysfunction. Anesthetized mice were gavaged with 4 kDa FITC-dextran (FD-4) and exposed to increasing core temperatures, briefly reaching 42.4°C, followed by 30 min recovery. Arterial samples were collected to measure FD-4 concentration in plasma (in vivo gastrointestinal permeability). The small intestines were then removed to measure histological evidence of injury. Hyperthermia resulted in a ≈2.5-fold elevation in plasma FD-4 and was always associated with significant histological evidence of injury to the epithelial lining compared with matched controls, particularly in the duodenum. When isolated intestinal segments from control animals were exposed to ≥41.5°C, marked increases in permeability were observed within 60 min. These changes were associated with release of lactate dehydrogenase, evidence of protein oxidation via carbonyl formation and histological damage. Coincubation with N-acetylcysteine protected in vitro permeability during hyperthermia and reduced histological damage and protein oxidation. Chelation of intracellular Ca(2+) to block tight junction opening during 41.5°C exposure failed to reduce the permeability of in vitro segments. The results demonstrate that hyperthermia exposure in mouse intestine, at temperatures at or below those necessary to induce mild heatstroke, cause rapid and substantial injury to the intestinal lining that may be attributed, in part, to oxidative stress.

Reactive oxygen and nitrogen species as intracellular signals in skeletal muscle

It is well established that contracting skeletal muscles produce free radicals. Given that radicals are known to play a prominent role in the pathogenesis of several diseases, the 1980s-90s dogma was that contraction-induced radical production was detrimental to muscle because of oxidative damage to macromolecules within the fibre. In contrast to this early outlook, it is now clear that both reactive oxygen species (ROS) and reactive nitrogen species (RNS) play important roles in cell signalling pathways involved in muscle adaptation to exercise and the remodelling that occurs in skeletal muscle during periods of prolonged inactivity. This review will highlight two important redox sensitive signalling pathways that contribute to ROS and RNS-induced skeletal muscle adaptation to endurance exercise. We begin with a historical overview of radical production in skeletal muscles followed by a discussion of the intracellular sites for ROS and RNS production in muscle fibres. We will then provide a synopsis of the redox-sensitive NF-B and PGC-1α signalling pathways that contribute to skeletal muscle adaptation in response to exercise training. We will conclude with a discussion of unanswered questions in redox signalling in skeletal muscle in the hope of promoting additional research interest in this field.

Reactive oxygen species are signalling molecules for skeletal muscle adaptation

Increased reactive oxygen species (ROS) production is crucial to the remodelling that occurs in skeletal muscle in response to both exercise training and prolonged periods of disuse. This review discusses the redox-sensitive signalling pathways that are responsible for this ROS-induced skeletal muscle adaptation. We begin with a discussion of the sites of ROS production in skeletal muscle fibres. This is followed by an overview of the putative redox-sensitive signalling pathways that promote skeletal muscle adaptation. Specifically, this discussion highlights redox-sensitive kinases, phosphatases and the transcription factor nuclear factor-κB. We also discuss the evidence that connects redox signalling to skeletal muscle adaptation in response to increased muscular activity (i.e. exercise training) and during prolonged periods of muscular inactivity (i.e. immobilization). In an effort to stimulate further research, we conclude with a discussion of unanswered questions about redox signalling in skeletal muscle.

Mechanical ventilation induces diaphragmatic mitochondrial dysfunction and increased oxidant production

Mechanical ventilation (MV) is a life-saving intervention used in patients with acute respiratory failure. Unfortunately, prolonged MV results in diaphragmatic weakness, which is an important contributor to the failure to wean patients from MV. Our laboratory has previously shown that reactive oxygen species (ROS) play a critical role in mediating diaphragmatic weakness after MV. However, the pathways responsible for MV-induced diaphragmatic ROS production remain unknown. These experiments tested the hypothesis that prolonged MV results in an increase in mitochondrial ROS release, mitochondrial oxidative damage, and mitochondrial dysfunction. To test this hypothesis, adult (3-4 months of age) female Sprague-Dawley rats were assigned to either a control or a 12-h MV group. After treatment, diaphragms were removed and mitochondria were isolated for subsequent respiratory and biochemical measurements. Compared to control, prolonged MV resulted in a lower respiratory control ratio in diaphragmatic mitochondria. Furthermore, diaphragmatic mitochondria from MV animals released higher rates of ROS in both State 3 and State 4 respiration. Prolonged MV was also associated with diaphragmatic mitochondrial oxidative damage as indicated by increased lipid peroxidation and protein oxidation. Finally, our data also reveal that the activities of the electron transport chain complexes II, III, and IV are depressed in mitochondria isolated from diaphragms of MV animals. In conclusion, these results are consistent with the concept that diaphragmatic inactivity promotes an increase in mitochondrial ROS emission, mitochondrial oxidative damage, and mitochondrial respiratory dysfunction.

Calpain-1 is required for hydrogen peroxide-induced myotube atrophy

Recent reports suggest numerous roles for cysteine proteases in the progression of skeletal muscle atrophy due to disuse or disease. Nonetheless, a specific requirement for these proteases in the progression of skeletal muscle atrophy has not been demonstrated. Therefore, this investigation determined whether calpains or caspase-3 is required for oxidant-induced C2C12 myotube atrophy. We demonstrate that exposure to hydrogen peroxide (25 microM H2O2) induces myotube oxidative damage and atrophy, with no evidence of cell death. Twenty-four hours of exposure to H2O2 significantly reduced both myotube diameter and the abundance of numerous proteins, including myosin (-81%), alpha-actinin (-40%), desmin (-79%), talin (-37%), and troponin I (-80%). Myotube atrophy was also characterized by increased cleavage of the cysteine protease substrate alphaII-spectrin following 4 h and 24 h of H2O2 treatment. This degradation was blocked by administration of the protease inhibitor leupeptin (10 microM). Using small interfering RNA transfection of mature myotubes against the specific proteases calpain-1, calpain-2, and caspase-3, we demonstrated that calpain-1 is required for H2O2-induced myotube atrophy. Collectively, our data provide the first evidence for an absolute requirement for calpain-1 in the development of skeletal muscle myotube atrophy in response to oxidant-induced cellular stress.

Teaching nonprofessionals three techniques to modify children's behavior

The relative effectiveness of video-taped lecturing, video-taped modeling or a combination of lecturing and modeling was compared in teaching nonprofessionals to correctly choose the behavioral categories of “praise” (verbal reinforcement), “ignore” (extinction), and “timeout.” All three teaching techniques were significantly more effective in teaching these categories than the no-treatment control group ( ns = 17). While no significant over-all differences were found between the three training methods, the subjects trained with both lecturing and modeling emitted the fewest errors. Furthermore, the no-training control subjects showed a tendency to employ timeout for behaviors which should be reinforced and for behaviors which should be extinguished. Suggestions for future research and possible applications of the modeling procedure were discussed.