Effect of aging on liver regeneration in rats

Three Dimensional Bioprinting for Hepatic Tissue Engineering: From In Vitro Models to Clinical Applications

Fabrication of functional organs is the holy grail of tissue engineering and the possibilities of repairing a partial or complete liver to treat chronic liver disorders are discussed in this review. Liver is the largest gland in the human body and plays a responsible role in majority of metabolic function and processes. Chronic liver disease is one of the leading causes of death globally and the current treatment strategy of organ transplantation holds its own demerits. Hence there is a need to develop an in vitro liver model that mimics the native microenvironment. The developed model should be a reliable to understand the pathogenesis, screen drugs and assist to repair and replace the damaged liver. The three-dimensional bioprinting is a promising technology that recreates in vivo alike in vitro model for transplantation, which is the goal of tissue engineers. The technology has great potential due to its precise control and its ability to homogeneously distribute cells on all layers in a complex structure. This review gives an overview of liver tissue engineering with a special focus on 3D bioprinting and bioinks for liver disease modelling and drug screening.

Metabolic Rewiring by Human Placenta-Derived Mesenchymal Stem Cell Therapy Promotes Rejuvenation in Aged Female Rats

Aging is a degenerative process involving cell function deterioration, leading to altered metabolic pathways, increased metabolite diversity, and dysregulated metabolism. Previously, we reported that human placenta-derived mesenchymal stem cells (hPD-MSCs) have therapeutic effects on ovarian aging. This study aimed to identify hPD-MSC therapy-induced responses at the metabolite and protein levels and serum biomarker(s) of aging and/or rejuvenation. We observed weight loss after hPD-MSC therapy. Importantly, insulin-like growth factor-I (IGF-I), known prolongs healthy life spans, were markedly elevated in serum. Capillary electrophoresis-time-of-flight mass spectrometry (CE-TOF/MS) analysis identified 176 metabolites, among which the levels of 3-hydroxybutyric acid, glycocholic acid, and taurine, which are associated with health and longevity, were enhanced after hPD-MSC stimulation. Furthermore, after hPD-MSC therapy, the levels of vitamin B6 and its metabolite pyridoxal 5′-phosphate were markedly increased in the serum and liver, respectively. Interestingly, hPD-MSC therapy promoted serotonin production due to increased vitamin B6 metabolism rates. Increased liver serotonin levels after multiple-injection therapy altered the expression of mRNAs and proteins associated with hepatocyte proliferation and mitochondrial biogenesis. Changes in metabolites in circulation after hPD-MSC therapy can be used to identify biomarker(s) of aging and/or rejuvenation. In addition, serotonin is a valuable therapeutic target for reversing aging-associated liver degeneration.

Acetylsalicylic acid (Aspirin®) and liver regeneration: experimental study in rats

OBJECTIVE

to evaluate the influence of acetylsalicylic acid (ASA) on cell proliferation after partial hepatectomy in rats.

METHODS

40 male Wistar rats were separated into four groups of ten rats each. Groups 1 and 2 (controls): undergoing 30% partial hepatectomy and, after one day (group 1) and seven days (group 2), to euthanasia; daily administration of 0.9% saline solution (1mL per 200g of body weight). Groups 3 and 4 (experimental): undergoing 30% partial hepatectomy and, after one day (group 3) and seven days (group 4), to euthanasia; daily administration of ASA (40mg/mL, 1mL per 200g of body weight). The absolute number of cells stained with PCNA was counted in photomicrographs, in five fields, and it was calculated the mean of positive cells per animal and per group.

RESULTS

the final mean of PCNA+ cells per group was: in group 1, 17.57 ± 6.77; in group 2, 19.31 ± 5.30; in group 3, 27.46 ± 11.55; and, in group 4, 12.40 ± 5.23. There was no significant difference at the two evaluation times in the control group (p=0.491), but there was in the experimental group (p=0.020), with a lower number of PCNA+ cells on the seventh day. The comparison between the two groups, on the first day, showed more PCNA+ cells in the livers of the animals that received ASA (p=0.047), and on the seventh day the number was lower in the experimental group (p=0.007).

CONCLUSION

ASA induced greater hepatocyte proliferation.

Liver regeneration: biological and pathological mechanisms and implications

The liver is the only solid organ that uses regenerative mechanisms to ensure that the liver-to-bodyweight ratio is always at 100% of what is required for body homeostasis. Other solid organs (such as the lungs, kidneys and pancreas) adjust to tissue loss but do not return to 100% of normal. The current state of knowledge of the regenerative pathways that underlie this 'hepatostat' will be presented in this Review. Liver regeneration from acute injury is always beneficial and has been extensively studied. Experimental models that involve partial hepatectomy or chemical injury have revealed extracellular and intracellular signalling pathways that are used to return the liver to equivalent size and weight to those prior to injury. On the other hand, chronic loss of hepatocytes, which can occur in chronic liver disease of any aetiology, often has adverse consequences, including fibrosis, cirrhosis and liver neoplasia. The regenerative activities of hepatocytes and cholangiocytes are typically characterized by phenotypic fidelity. However, when regeneration of one of the two cell types fails, hepatocytes and cholangiocytes function as facultative stem cells and transdifferentiate into each other to restore normal liver structure. Liver recolonization models have demonstrated that hepatocytes have an unlimited regenerative capacity. However, in normal liver, cell turnover is very slow. All zones of the resting liver lobules have been equally implicated in the maintenance of hepatocyte and cholangiocyte populations in normal liver.

Impaired integrin α5 /β1 -mediated hepatocyte growth factor release by stellate cells of the aged liver

Hepatic blood flow and sinusoidal endothelial fenestration decrease during aging. Consequently, fluid mechanical forces are reduced in the space of Disse where hepatic stellate cells (HSC) have their niche. We provide evidence that integrin α₅ /β₁ is an important mechanosensor in HSC involved in shear stress-induced release of hepatocyte growth factor (HGF), an essential inductor of liver regeneration which is impaired during aging. The expression of the integrin subunits α₅ and β₁ decreases in liver and HSC from aged rats. CRISPR/Cas9-mediated integrin α₅ and β₁ knockouts in isolated HSC lead to lowered HGF release and impaired cellular adhesion. Fluid mechanical forces increase integrin α₅ and laminin gene expression whereas integrin β₁ remains unaffected. In the aged liver, laminin β2 and γ1 protein chains as components of laminin-521 are lowered. The integrin α₅ knockout in HSC reduces laminin expression via mechanosensory mechanisms. Culture of HSC on nanostructured surfaces functionalized with laminin-521 enhances Hgf expression in HSC, demonstrating that these ECM proteins are critically involved in HSC function. During aging, HSC acquire a senescence-associated secretory phenotype and lower their growth factor expression essential for tissue repair. Our findings suggest that impaired mechanosensing via integrin α₅ /β₁ in HSC contributes to age-related reduction of ECM and HGF release that could affect liver regeneration.

Oxidative Stress Parameters in the Liver of Growing Male Rats Receiving Various Alcoholic Beverages

Typical alcohol consumption begins in the adolescence period, increasing the risk of alcoholic liver disease (ALD) in adolescents and young adults, and while the pathophysiology of ALD is still not completely understood, it is believed that oxidative stress may be the major contributor that initiates and promotes the progression of liver damage. The aim of the present study was to assess the influence of alcohol consumption on the markers of oxidative stress and liver inflammation in the animal model of prolonged alcohol consumption in adolescents using various alcoholic beverages. In a homogenic group of 24 male Wistar rats (4 groups—6 animals per group), since 30th day of life, in order to mimic the alcohol consumption since adolescence, animals received (1) no alcoholic beverage (control group), (2) ethanol solution, (3) red wine, or (4) beer (experimental groups) for 6 weeks. Afterwards, the activities of alcohol dehydrogenase (ADH), alanine aminotransferase (ALT), and aspartate aminotransferase (AST), as well as levels of cytochrome P450-2E1 (CYP2E1), thiobarbituric acid-reactive substances (TBARS), protein carbonyl groups, tumor necrosis factor-α (TNF-α), and interleukine-10 (IL-10) were measured in liver homogenates. The difference between studied groups was observed for CYP2E1 and protein carbonyl groups levels (increased levels for animals receiving beer compared with control group), as well as for ALT activity (decreased activity for animals receiving beer compared with other experimental groups) (p < 0.05). The results suggested that some components of beer, other than ethanol, are responsible for its influence on the markers of oxidative stress and liver inflammation observed in the animal model of prolonged alcohol consumption in adolescents. Taking this into account, beer consumption in adolescents, which is a serious public health issue, should be assessed in further studies to broaden the knowledge of the progression of liver damage caused by alcohol consumption in this group.

Influence of Telomere Length in Hepatocytes on Liver Regeneration after Partial Hepatectomy in Rats

BACKGROUND

The aim of this study was to investigate telomere length in hepatocytes as a biomarker for liver regeneration after partial hepatectomy (PH) in rats.

MATERIALS AND METHODS

Sixty male Wistar rats underwent a 70% PH. One-month-old rats were assigned to group Y (n = 30) and 4-month-old rats were assigned to group O (n = 30). The rats were euthanized, and their livers were then harvested at postoperative day (POD) 1, 2, 3, 4, or 7. Telomere lengths and established parameters for liver regeneration (residual liver weight and levels of proliferating cell nuclear antigen [PCNA], Ki67, and interleukin [IL]-6) were measured.

RESULTS

We observed a significant increase in residual liver weight in group Y compared to that in group O (p = 0.001). The levels of Ki67 (p = 0.016), PCNA (p < 0.0001), and IL-6 (p < 0.001) were significantly higher in group Y. Furthermore, the rats in group Y had significantly earlier peak values of Ki67 and PCNA. Telomeres were significantly longer at the time of PH in group Y (p = 0.001). We showed a correlation between telomere length at the day of PH and liver regeneration. Animals with longer telomeres at the time of PH had better liver regeneration (p = 0.015). In group Y, animals with increased liver regeneration (median cut-off: > 122%) did not show any significant difference in telomere length (p = 0.587) compared to rats with regular regeneration (< 122%). However, in the older animals, rats with increased regeneration had significantly longer telomeres (p = 0.019) than rats with regular regeneration.

CONCLUSION

Telomere length in rat hepatocytes depends on age, and animals with long telomeres had earlier and better regeneration of healthy liver tissue than rats with short telomeres. Our data confirms that telomere length in rat hepatocytes could be used as a possible predictive marker for liver regeneration, and could help to identify older individuals with a high capacity for hepatic regeneration.

Stereological assessment of sexual dimorphism in the rat liver reveals differences in hepatocytes and Kupffer cells but not hepatic stellate cells

There is long-standing evidence that male and female rat livers differ in enzyme activity. More recently, differences in gene expression profiling have also been found to exist; however, it is still unclear whether there is morphological expression of male/female differences in the normal liver. Such differences could help to explain features seen at the pathological level, such as the greater regenerative potential generally attributed to the female liver. In this paper, hepatocytes (HEP), Kupffer cells (KC) and hepatic stellate cells (HSC) of male and female rats were examined to investigate hypothesised differences in number, volume and spatial co-localisation of these cell types. Immunohistochemistry and design-based stereology were used to estimate total numbers, numbers per gram and mean cell volumes. The position of HSC within lobules (periportal vs. centrilobular) and their spatial proximity to KC was also assessed. In addition, flow cytometry was used to investigate the liver ploidy. In the case of HEP and KC, differences in the measured cell parameters were observed between male and female specimens; however, no such differences were detected for HSC. Female samples contained a higher number of HEP per gram, with more binucleate cells. The HEP nuclei were smaller in females, which was coincident with more abundant diploid particles in these animals. The female liver also had a greater number of KC per gram, with a lower percentage of KC in the vicinity of HSC compared with males. In this study, we document hitherto unknown morphological sexual dimorphism in the rat liver, namely in HEP and KC. These differences may account for the higher regenerative potential of the female liver and lend weight to the argument for considering the rat liver as a sexually dimorphic organ.

Aging and regeneration in vertebrates

Aging is marked by changes that affect organs and resident stem cell function. Shorting of telomeres, DNA damage, oxidative stress, deregulation of genes and proteins, impaired cell-cell communication, and an altered systemic environment cause the eventual demise of cells. At the same time, reparative activities also decline. It is intriguing to correlate aging with the decline of regenerative abilities. Animal models with strong regenerative capabilities imply that aging processes might not be affecting regeneration. In this review, we selectively present age-dependent changes in stem/progenitor cells that are vital for tissue homeostasis and repair. In addition, the aging effect on regeneration following injury in organs such as lung, skeletal muscle, heart, nervous system, cochlear hair, lens, and liver are discussed. These tissues are also known for diseases such as heart attack, stroke, cognitive impairment, cataract, and hearing loss that occur mostly during aging in humans. Conclusively, vertebrate regeneration declines with age with the loss of stem/progenitor cell function. Future studies on improving the function of stem cells, along with studies in fish and amphibians where regeneration does not decline with age, will undoubtedly provide insights into both processes.

Impact of age on liver regeneration response to injury after partial hepatectomy in a rat model

BACKGROUND

Liver resection is a feasible treatment for multiple liver diseases. There is no evidence about the impact of age on liver regeneration.

OBJECTIVE

To assess the effect of age on liver regeneration in an experimental in vivo animal model of 70%-partial hepatectomy.

METHODS

Forty young (Y) and old (O) Wistar male rats (n = 80) were distributed into four groups [controls (C), sham operated (SO), hepatectomy 6 h (H6), and 48 h (H48)]. Different morphometric and biochemical factors, oxidative and nitrosative stress, lipid peroxidation, cytokines kinetics, and histopathologic tissular parameters were determined.

RESULTS

Early postoperative mortality was higher in aged rats (P = 0.049). Morphometric determinations, liver regeneration index, and total volume weight were favorable to young rats. Serum transaminase levels were higher in aged rats. Parameters of necrosis (measured by histopathologic injury [HI: 0-I-II-III]), regeneration (measured by bromodeoxyuridine-BrdU incorporation) and apoptosis (determined by the TDT-mediated dUTP nick end labeling-TUNEL) were well-synchronized in young rats. Parameters of oxidative stress such as reduced (GSH), oxidized (GSSG) glutathione and lipid peroxidation (measured by hepatic malondialdehyde -MDA-) were lower in young animals throughout the studied period. Nitrosative stress measured by nitric oxide (NO) end-products was higher in late stages in resected old rats. Pro-inflammatory cytokines (TNF- α) reached higher and earlier levels in aged rats while pro-regenerative cytokines (IL-6) were significantly higher in early stages for young rats and in late stages for aged rats. The levels of TGF-β were higher in young rats.

CONCLUSION

Liver regeneration is delayed and reduced in aged animals submitted to liver resection.

Liver regeneration and aging: a current perspective

Many organ systems exhibit significant age-related deficits, but, based on studies in old rodents and elderly humans, the liver appears to be relatively protected from such changes. A remarkable feature of the liver is its capacity to regenerate its mass following partial hepatectomy. Reports suggests that aging compromises the liver's regenerative capacity, both in the rate and to the extent the organ's original volume is restored. There has been modest definitive information as to which cellular and molecular mechanisms regulating hepatic regeneration are affected by aging. Changes in hepatic sensitivity to growth factors, for example, epidermal growth factor (EGF), appear to influence regeneration in old animals. Studies have demonstrated (a) a 60% decline in EGF binding to hepatocyte plasma membranes, (b) reduced expression of the hepatic high affinity EGF receptor and (c) a block between G1 and S-phases of the cell cycle in old rats following EGF stimulation. Recent studies suggest that reduced phosphorylation and dimerization of the EGF receptor, critical steps in the activation of the extracellular signal-regulated kinase pathway and subsequent cell proliferation are responsible. Other studies have demonstrated that aging affects the upregulation of a Forkhead Box transcription factor, FoxM1B, which is essential for growth hormone-stimulated liver regeneration in hepatectomized mice. Aging appears to compromise liver regeneration by influencing several pathways, the result of which is a reduction in the rate of regeneration, but not in the capacity to restore the organ to its original volume.

Regeneração do fígado após hepatectomia parcial em ratos submetidos à hipertensão portal pós-hepática

RACIONAL: O fígado adulto normal é quiescente e apenas uma pequena porcentagem das suas células é submetida à divisão celular em qualquer tempo, mas pode rapidamente iniciar a proliferação celular em resposta a um estímulo. Este processo pode ser desencadeado através da hepatectomia parcial. OBJETIVOS: Avaliar o efeito da hipertensão portal provocada pela oclusão parcial da drenagem venosa hepática sobre a regeneração do fígado remanescente de ratos submetidos à hepatectomia parcial. MÉTODOS: Foram realizadas hepatectomias a dois terços em 50 ratos Wistar machos adultos. Os animais foram divididos em cinco grupos: um grupo controle e quatro grupos de estudo que foram submetidos a diferentes graus de plicatura da veia cava inferior supra-hepática. Após 240 horas do estímulo para regeneração realizou-se nova laparotomia com aferição das pressões portal e de veia cava inferior, além de biópsia hepática. Analisaram-se os fragmentos por imunoistoquímica para os marcadores Ki-67 e fator de von Willebrand. A deposição de colágeno foi avaliada pela coloração tricrômico de Masson e a função hepática através de marcadores sorológicos. RESULTADOS: A proliferação celular nos animais submetidos à hepatectomia parcial e hipertensão portal de diversos graus persistiu mais elevada quando comparada ao grupo controle. O índice de proliferação para Ki-67 estava mais elevado nos grupos submetidos à elevação da pressão portal. A expressão do fator de von Willebrand estava acentuadamente elevada após a hepatectomia parcial nos grupos com maior grau de hipertensão portal. Houve pouco depósito de colágeno no tecido hepático nos animais dos quatro grupos com plicatura parcial da veia cava inferior supra-hepática, porém a deposição foi mais intensa nos grupos com níveis de pressão portal menores. CONCLUSÕES: Ratos submetidos à hepatectomia parcial a 70% e hipertensão portal, após 240 horas, apresentam: 1. atraso no processo regenerativo diretamente proporcional aos níveis pressóricos no sistema porta; 2. após dez dias, persiste a proliferação de hepatócitos proporcionalmente mais intensa quanto maior a elevação da pressão no sistema porta, porém níveis extremos de pressão portal inibem a proliferação, e, no estímulo para regeneração do fígado, demonstrou-se atraso da angiogênese influenciado pelos valores de pressão portal; 3. hipertensão portal extrema promove elevação da expressão de fator VIII, o que sugere capilarização dos sinusóides; 4. quanto mais elevados os níveis de pressão portal, menor será a quantidade de colágeno depositada, podendo-se inferir que o aumento da pressão portal ocasiona atraso na restauração da matriz extracelular; 5. a análise da função hepática evidenciou que a hepatectomia parcial a 70%, após dez dias, não interferiu com a fisiologia hepática, a qual permaneceu dentro dos limites da normalidade, mas com a hipertensão portal pode haver comprometimento funcional do fígado remanescente durante o processo regenerativo.

Advances in the regulation of liver regeneration

Liver regeneration is known to be a process involving highly organized and ordered tissue growth triggered by the loss of liver tissue, and remains a fascinating topic. A large number of genes are involved in this process, and there exists a sequence of stages that results in liver regeneration, while at the same time inhibitors control the size of the regenerated liver. The initiation step is characterized by priming of quiescent hepatocytes by factors such as TNF-α, IL-6 and nitric oxide. The proliferation step is the step during which hepatocytes enter into the cell cycle's G1 phase and are stimulated by complete mitogens including HGF, TGF-α and EGF. Hepatic stimulator substance, glucagon, insulin, TNF-α, IL-1 and IL-6 have also been implicated in regulating the regeneration process. Inhibitors and stop signals of hepatic regeneration are not well known and only limited information is available. Furthermore, the effects of other factors such as VEGF, PDGF, hypothyroidism, proliferating cell nuclear antigen, heat shock proteins, ischemic-reperfusion injury, steatosis and granulocyte colony-stimulating factor on liver regeneration are also systematically reviewed in this article. A tissue engineering approach using isolated hepatocytes for in vitro tissue generation and heterotopic transplantation of liver cells has been established. The use of stem cells might also be very attractive to overcome the limitation of donor liver tissue. Liver-specific differentiation of embryonic, fetal or adult stem cells is currently under investigation.

Ageing, telomeres, senescence, and liver injury

Populations in developed countries continue to grow older and an understanding of the ageing process to allow healthy ageing carries important medical implications. Older individuals are more susceptible to most acquired liver disorders and more vulnerable to the consequences of liver disease. Accordingly, age is a critical determinant of outcome for hepatitis C virus infection and liver transplantation. In this review we describe changes in the ageing liver and discuss mechanisms of senescence at the cellular level. In particular, we focus on mechanisms by which inflammation, oxidative stress, and oncogenic stress accelerate cellular senescence. In the setting of chronic hepatic injury and inflammation, cellular senescence functions as an essential stress-response mechanism to limit the proliferation of damaged cells and reduce the risk of malignancy, but this benefit is achieved at the expense of senescence-related organ dysfunction. The dual role of cell senescence in chronic liver disease will make this an intriguing but challenging area for future clinical interventions.

Imunossupressão com tacrolimus favorece a regeneração hepática induzida por hepatectomia ampla em ratos

OBJETIVO: Avaliar em dois momentos distintos da regeneração hepática a influência do Tacrolimus sobre o fenômeno da regeneração hepática desencadeada pela ressecção de 70% do parênquima hepático em ratos plenamente desenvolvidos. MÉTODOS: Utilizaram-se 40 ratos Wistar com peso médio de 510,08 g ± 11.66 g distribuidos aleatoriamente em dois grupos de 20, cada grupo subdividido em dois subgrupos conforme o dia da morte após a hepatectomia. De acordo com o grupo os animais receberam por gavagem solução aquosa de Tacrolimus 0,1 mg/kg/dia ou solução salina no mesmo volume. Após três dias de pré-terapia todos foram submetidos à hepatectomia de 70% pela ressecção dos lobos hepáticos mediano e lateral esquerdo que foram pesados para posterior cálculo da regeneração hepática pela fórmula de Kwon. Vinte e quatro horas ou sete dias após a hepatectomia, 10 animais de cada grupo foram mortos, os fígados remanescentes (regenerados) foram pesados e amostrados para realização de índice mitótico por hematoxilina-eosina e estudo imunoistoquímico com os marcadores PCNA e Ki-67. RESULTADOS: Os animais que receberam tacrolimus mostraram índice maior de regeneração hepática, atingindo significância estatística quando comparado ao subgrupo de animais mantidos com placebo quando analisados pelos parâmetros: fórmula de Kwon, índice mitótico e marcador PCNA. A tendência para o marcador Ki-67 foi idêntica aos outros parâmetros mas não alcançou significância estatística. CONCLUSÃO: A imunossupressão com tacrolimus possui efeito estimulatório no processo de regeneração hepática desencadeado pela hepatectomia 70% em ratos Wistar adultos, plenamente desenvolvidos.

Imunossupressão com tacrolimus favorece a regeneração hepática induzida por hepatectomia extensa em ratos

RACIONAL: A regeneração hepática representa o resultado de respostas fisiológicas que ocorrem após perdas de parênquima, como consequência de agressões tóxico-medicamentosas, infecciosas, traumáticas ou cirúrgicas. OBJETIVO: Avaliar, em dois momentos distintos da regeneração hepática, a influência do tacrolimus sobre o fenômeno da regeneração hepática desencadeada pela ressecção de 70% do parênquima hepático em ratos plenamente desenvolvidos. MÉTODO: Utilizaram-se 40 ratos Wistar com peso médio de 510,08 g ± 11.66 g divididos aleatoriamente em dois grupos de 20 (Estudo e Controle), cada grupo subdividido em dois subgrupos conforme o dia da morte após a hepatectomia (24 horas e 7 dias). De acordo com o grupo os animais receberam por gavagem, diariamente, iniciando três dias antes da hepatectomia e prolongando-se por todo o período de observação, solução aquosa de tacrolimus 0,1 mg/kg/dia ou solução salina no mesmo volume. Após três dias de pré-terapia todos foram submetidos à hepatectomia de 70% pela ressecção dos lobos hepáticos mediano e lateral esquerdo que foram pesados para posterior cálculo da regeneração hepática pela fórmula de Kwon. Vinte e quatro horas ou sete dias após a hepatectomia, 10 animais de cada grupo foram mortos, os fígados remanescentes (regenerados) foram pesados e amostrados para realização de índice mitótico por hematoxilina-eosina e estudo imunoistoquímico com os marcadores PCNA e Ki-67. RESULTADOS: Os animais que receberam tacrolimus mostraram índice maior de regeneração hepática, atingindo significância estatística quando comparado ao subgrupo de animais mantidos com placebo quando analisados pelos parâmetros: fórmula de Kwon, índice mitótico e marcador PCNA. A tendência para o marcador Ki-67 foi idêntica aos outros parâmetros, mas não alcançou significância estatística. CONCLUSÕES: A imunossupressão com tacrolimus possui efeito estimulante no processo de regeneração hepática desencadeado pela hepatectomia 70% em ratos Wistar adultos, plenamente desenvolvidos.

Decline and compensation in aging brain and cognition: promises and constraints. Preface

Age-related cognitive declines are common and inevitable, but life trajectories of brain and cognitive functions are variable and plastic. To identify the mechanisms of decline, the prospects for improvement, and the constraints on the remedial approaches, the contributors of this special issuer examine several diverse areas of cognitive and brain aging: from structural and metabolic brain aging to genetics, and from age-sensitive cognitive domains to those that resist aging. In spite of such thematic diversity, several common threads are clear. To achieve better compensation for age-related changes in cognition, we need to understand their brain substrates, telling cognitively relevant from epiphenomenal. We also need to understand the sources of profound individual variability in aging trajectories, and to learn to tailor interventions to specific individual profiles of decline.

Influence of age on susceptibility to Pseudomonas aeruginosa exotoxin A-induced hepatotoxicity in Long-Evans rats

Epidemiological investigations suggest that increased age is associated with susceptibility to infection. Pseudomonas aeruginosa (P. aeruginosa) infection and associated exotoxin A (PEA) toxicity have been reported in hospitalized elderly patients and young children with cystic fibrosis. The present study investigated age-related differences in PEA-induced hepatotoxicity in post weaning (PW, 3 weeks), young adult (YA, 12 weeks), and mature adult (MA, 60-64 weeks) rats. PEA (20 microg/kg) was injected intraveneously and mortality, clinical chemistry, hepatic histopathology, TUNEL (Terminal deoxynucleotidyl transferase-mediated dUTP nick end-labelling) and PCNA (Proliferating cell nuclear antigen) staining, and serum cytokine levels were assessed at specific time points, up to 72 hr post-exposure (HPE). Mortality in MA rats was 100% at less than 48 HPE. Serum ALT levels in MA rats were approximately 5-fold greater than levels in PW and YA rats at 36 HPE. MA rat liver histological sections showed diffuse hepatocellular necrosis. In contrast, hepatocellular apoptosis, demonstrable by the TUNEL method, was noted simply in the periportal and midzonal regions from 36 to 48 HPE. Increased morphological mitoses and PCNA-positive hepatocytes were seen in PW and YA rats at 72 HPE. These parameters were correlated with age-dependent significant increases in TNF-alpha, IL-2, IL-6, and IL-18 levels. These data suggest that inflammatory cytokines play an important role in age-related differences in PEA-induced hepatotoxicity. Moreover, these cytokines might correlate with different patterns histopathologic features at various ages.

The survival paradox of elderly patients after major liver resections

OBJECTIVE

The objective of this study is to assess the outcome of liver resections in the elderly in a matched control analysis.

PATIENTS AND METHODS

From a prospective single center database of 628 patients, 132 patients were aged 60 years or over and underwent a primary major liver resection. Of these patients, 93 could be matched one-to-one with a control patient, aged less than 60 years, with the same diagnosis and the same type of liver resection. The mean age difference was 16.7 years.

RESULTS

Patients over 60 years of age had a significantly higher American Society of Anaesthesiologists (ASA) grade. All other demographics and operative characteristics were not different. In-hospital mortality and morbidity were higher in the patients over 60 years of age (11% versus 2%, p = 0.017 and 47% versus 31%, p = 0.024). One-, 3-, and 5-year survival rates in the patients over 60 years of age were 81%, 58%, and 42%, respectively, compared to 90%, 59%, and 42% in the control patients (p = 0.558). Unified model Cox regression analysis showed that resection margin status (hazard ratio 2.51) and ASA grade (hazard ratio 2.26), and not age, were determining factors for survival.

CONCLUSION

This finding underlines the important fact that in patient selection for major liver resections, ASA grade is more important than patient age.

Aging and induced senescence as factors in the pathogenesis of lung emphysema

Classically, the development of emphysema in chronic obstructive pulmonary disease is believed to involve inflammation induced by cigarette smoke and leukocyte activation, including oxidant-antioxidant and protease-antiprotease imbalances. While there is substantial evidence for this, additional aspects have been suggested by a number of clinical and experimental observations. Smokers exhibit signs of premature aging, particularly obvious in the skin. The link between aging and chronic disease is well-known, e.g., for the brain and musculoskeletal or cardiovascular system, as well as the clinical link between malnutrition and emphysema, and the experimental link to caloric restriction. Interestingly, this intervention also increases lifespan, in parallel with alterations in metabolism, oxidant burden and endocrine signaling. Of special interest is the observation that, even in the absence of an inflammatory environment, lung fibroblasts from patients with emphysema show persistent alterations, possibly based on epigenetic mechanisms. The importance of these mechanisms for cellular reprogramming and response patterns, individual risk profile and therapeutic options is becoming increasingly recognized. The same applies to cellular senescence. Recent findings from patients and experimental models open novel views into the arena of gene-environment interactions, including the role of systemic alterations, cellular stress, telomeres, CDK inhibitors such as p16, p21, pRb, PI3K, mTOR, FOXO transcription factors, histone modifications, and sirtuins. This article aims to outline this emerging picture and to stimulate the identification of challenging questions. Such insights also bear implications for the long-term course of the disease in relation to existing or future therapies and the exploration of potential lung regeneration.

Experimental models of hepatectomy and liver regeneration using newborn and weaning rats

OBJECTIVES

Liver regeneration is a complex process that has not been completely elucidated. The model most frequently used to study this phenomenon is 70% hepatectomy in adult rats; however, no papers have examined this effect in developing animals. The aims of the present study were: 1) to standardize two models of partial hepatectomy and liver regeneration in newborn suckling and weaning rats, and 2) to study the evolution of remnant liver weight and histological changes of hepatic parenchyma on the days that follow partial hepatectomy.

METHODS

Fifty newborn and forty-four weaning rats underwent 70% hepatectomy. After a midline incision, compression on both sides of the upper abdomen was performed to exteriorize the right medial, left medial and left lateral hepatic lobes, which were tied inferiorly and resected en bloc. The animals were sacrificed on days 0 (just after hepatectomy), 1, 2, 3, 4 and 7 after the operation. Body and liver weight were determined, and hepatic parenchyma was submitted to histological analysis.

RESULTS

Mortality rates of the newborn and weaning groups were 30% and 0%, respectively. There was a significant decrease in liver mass soon after partial hepatectomy, which completely recovered on the seventh day in both groups. Newborn rat regenerating liver showed marked steatosis on the second day. In the weaning rat liver, mitotic figures were observed earlier, and their amount was greater than in the newborn.

CONCLUSIONS

Suckling and weaning rat models of partial hepatectomy are feasible and can be used for studies of liver regeneration. Although similar, the process of hepatic regeneration in developing animals is different from adults.

Age-related subproteomic analysis of mouse liver and kidney peroxisomes

BACKGROUND

Despite major recent advances in the understanding of peroxisomal functions and how peroxisomes arise, only scant information is available regarding this organelle in cellular aging. The aim of this study was to characterize the changes in the protein expression profile of aged versus young liver and kidney peroxisome-enriched fractions from mouse and to suggest possible mechanisms underlying peroxisomal aging. Peroxisome-enriched fractions from 10 weeks, 18 months and 24 months C57bl/6J mice were analyzed by quantitative proteomics.

RESULTS

Peroxisomal proteins were enriched by differential and density gradient centrifugation and proteins were separated by two-dimensional electrophoresis (2-DE), quantified and identified by mass spectrometry (MS). In total, sixty-five proteins were identified in both tissues. Among them, 14 proteins were differentially expressed in liver and 21 proteins in kidney. The eight proteins differentially expressed in both tissues were involved in beta-oxidation, alpha-oxidation, isoprenoid biosynthesis, amino acid metabolism, and stress response. Quantitative proteomics, clustering methods, and prediction of transcription factors, all indicated that there is a decline in protein expression at 18 months and a recovery at 24 months.

CONCLUSION

These results indicate that some peroxisomal proteins show a tissue-specific functional response to aging. This response is probably dependent on their differential regeneration capacity. The differentially expressed proteins could lead several cellular effects: such as alteration of fatty acid metabolism that could alert membrane protein functions, increase of the oxidative stress and contribute to decline in bile salt synthesis. The ability to detect age-related variations in the peroxisomal proteome can help in the search for reliable and valid aging biomarkers.

Mechanisms of aging and liver functions

BACKGROUND/AIMS

Morphofunctional studies suggest that the liver, compared with other organs, ages fairly well. Its success is ascribable to its lasting ability to regenerate, even if the potential of the cells to replicate progressively declines with age. The aim of this study was to analyze some aspects of the early phases of liver regeneration, its capacity to mount a stress response, and the inflammatory response in the early stage of an acute injury.

METHODS

Rats aged 2, 6, 12 and 19 months received a single intraperitoneal injection of CCl(4), and morphological, biochemical and molecular evaluations were done 2 and 24 h later.

RESULTS

AST and ALT, starting at age 12 months, were significantly higher than in the younger rats after CCl(4). Histological modifications were already detectable after 2 h in rats aged 12 and 19 months, thereafter becoming more diffuse and marked, whereas they become evident only 24 h after the intoxication in rats aged 2 and 6 months. Albumin, c-fos, c-myc, hepatocyte growth factor, transforming growth factor-alpha and HSP70 mRNA levels decreased 24 h after CCl(4 )starting at age 12 months. Mast cell density was higher in the young rats than the old ones.

CONCLUSION

Our results point to: (a) a basically preserved regenerative response of the aged liver, although somehow weaker and slower, with reduced ability to counteract agents inducing cell necrosis; (b) a decrease in the HSP70 response suggesting a reduction in homeostatic capacity, and (c) a lower inflammatory response during aging.