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Biomedical subjects

David G Le Couteur

Publications and source records attributed to David G Le Couteur.

At least 19 recordsLinked to original sources
PubMed2007

Caloric restriction reduces age-related pseudocapillarization of the hepatic sinusoid.

Age-related changes in the hepatic sinusoid, called pseudocapillarization, may contribute to the pathogenesis of dyslipidemia. Caloric restriction (CR) is a powerful model for the study of aging because it extends lifespan. We assessed the effects of CR on the hepatic sinusoid to determine whether pseudocapillarization is preventable and hence a target for the prevention of age-related dyslipidemia. Livers from young (6 months) and old (24 months) CR and ad libitum fed (AL) F344 rats were examined using electron microscopy and immunohistochemistry. In old age, there was increased thickness of the liver sinusoidal endothelium and reduced endothelial fenestration porosity. In old CR rats, endothelial thickness was less and fenestration porosity was greater than in old AL rats. Immunohistochemistry showed that CR prevented age-related decrease in caveolin-1 expression and increase in peri-sinusoidal collagen IV staining, but did not alter the age-related increase of von Willebrand's factor. CR reduces age-related pseudocapillarization of the hepatic sinusoid and correlates with changes in caveolin-1 expression.

Aging↗
PubMed2006

Marked changes of the hepatic sinusoid in a transgenic mouse model of acute immune-mediated hepatitis.

BACKGROUND/AIMS: The liver sinusoidal endothelial cell (LSEC) is increasingly recognized as having an important role in hepatic immunity. However, the responses of LSECs and the hepatic sinusoid in immune-mediated hepatitis are poorly described. METHODS: We studied a transgenic mouse model of acute immune-mediated hepatitis: Met-Kb mice injected with T cells from Des-TCR mice. RESULTS: Hepatitis was characterized by lymphocyte infiltrates causing severe but transient liver damage. There were marked changes in the ultrastructure of the LSEC five days after injection of the T cells that coincided with the peak of the hepatitis. The porosity of fenestrations in the LSEC decreased and the endothelium became thickened. LSECs appeared to be markedly activated. These changes were associated with narrowing of the space of Disse, loss of hepatocellular microvilli and deposition of basal lamina. Lymphocytes were seen passing through fenestrations. Loss of fenestration in the LSEC prevented hepatitis induced by a second injection of lymphocytes on day 5. CONCLUSIONS: Structural changes in the LSEC occur during the peak of a mouse model of immune-mediated hepatitis. These changes were associated with attenuation of subsequent liver damage, suggesting that they may influence immunological responses mediated by LSECs or the passage of lymphocytes through LSEC fenestrations.

Acute Disease↗
PubMed2006

Hyperlipidemia and surfactants: the liver sieve is a link.

Poloxamer 407 is a ubiquitous synthetic surfactant that causes massive hyperlipidemia and atherosclerosis in the rodent. The initial step in hepatic metabolism of lipoproteins is their transfer through 100-200 nm pores (fenestrations) in the liver sinusoidal endothelial cell, prior to receptor-mediated uptake. The 'liver sieve hypothesis' emphasizes the role of these fenestrations in the regulation of lipoprotein disposition. Here we show that P407 causes dramatic defenestration of the liver sinusoidal endothelium in vivo. By 24h after intraperitoneal administration in mice, fenestrations were reduced by approximately 80% coincident with a 10-fold increase in plasma lipids. Moreover impulse-response experiments in the perfused rat liver showed that P407 prevented the passage of small chylomicrons across the liver sinusoidal endothelium. Defenestration was also induced acutely with P407 in isolated liver sinusoidal endothelial cells, indicating this is a direct effect of P407 on fenestrations. The results establish the role of the porosity of the liver sinusoidal endothelial cell as a pivotal yet relatively unrecognised mechanism for hyperlipidemia. Furthermore, the results establish an intriguing mechanism for surfactant-induced hyperlipidemia. Thus the liver sieve is a new and untapped target for the treatment and prevention of hyperlipidemia.

Animals↗
PubMed2006

T lymphocytes interact with hepatocytes through fenestrations in murine liver sinusoidal endothelial cells.

The liver has an established ability to induce tolerance. Recent evidence indicates that this unique property might be related to its distinctive architecture allowing T cells to be activated in situ independently of lymphoid tissues. Unlike lymph node-activated T cells, liver-activated T cells are short-lived, a mechanism that might contribute to the "liver tolerance effect." Although the potential role of hepatocytes as tolerogenic antigen-presenting cells has been demonstrated, the question as to whether these cells are able to interact with CD8(+) T cells in physiological settings remains controversial. Contradicting the immunological dogma stating that naïve T lymphocytes are prevented from interacting with parenchymal cells within non-lymphoid organs by an impenetrable endothelial barrier, we show here that the unique morphology of the liver sinusoidal endothelial cell (LSEC) permits interactions between lymphocytes and hepatocytes. Using electron microscopy, we demonstrate that liver resident lymphocytes as well as circulating naïve CD8(+) T cells make direct contact with hepatocytes through cytoplasmic extensions penetrating the endothelial fenestrations that perforate the LSECs. Furthermore, the expression of molecules required for primary T cell activation, MHC class I and ICAM-1, is polarized on hepatocytes to the perisinusoidal cell membrane, thus maximizing the opportunity for interactions with circulating lymphocytes. In conclusion, this study has identified, at the ultrastructural level, a unique type of interaction between naïve T lymphocytes and liver parenchymal cells in vivo. These results hold implications for the pathogenesis of viral hepatitis in which hepatocytes may represent the main antigen-presenting cell, and for the development of immune tolerance as lymphocytes pass through the liver.

Animals↗
PubMed2005

Hepatic pseudocapillarization in aged mice.

Age-related changes in the hepatic sinusoid of the rat, human and baboons called pseudocapillarization have been discovered and are important because they are considered to be implicated in the pathogenesis of some age-related diseases. In this study, we investigated whether similar changes occur in the livers of old mice. Livers of young (3-4 months) and old (20-24 months) mice were perfusion-fixed and studied using electron microscopy and immunohistochemistry. The thickness of the sinusoidal endothelium was increased in old mice (154+/-4 versus 244+/-8 nm, P<0.001). There was a reduction in fenestrations within the endothelium (porosity decreased from 4.1+/-0.3 to 2.2+/-0.2%, P<0.001). There was perisinusoidal staining with Sirius red in old mice, however, expression of laminin and von Willebrands factor was similar in young and old mice. Novel perisinusoidal fat-engorged stellate cells were found extensively in the old mice. This study confirmed that pseudocapillarization is a widespread aging change in the liver, now documented in several species including the mouse. Mice are an appropriate animal model for studying aging and the hepatic sinusoid.

Aging↗
PubMed2005

Age-related changes in the hepatic sinusoidal endothelium impede lipoprotein transfer in the rat.

The mechanisms for the association of old age with post-prandial hyperlipidemia and atherosclerosis are not well understood. Post-prandial hyperlipidemia has emerged as a significant risk for atherosclerosis. The liver is the central organ for lipoprotein metabolism. The initial step in the hepatic uptake of post-prandial lipoproteins is their transfer from the hepatic sinusoidal capillary lumen across the hepatic sinusoidal endothelium into the space of Disse. Here, they access hepatocytes for receptor-mediated uptake. We proposed that fenestrations (pores) within the hepatic sinusoidal endothelium filter lipoproteins on the basis of size. Recently we discovered age-related changes in the sinusoidal endothelium (pseudocapillarization), including reduction in the porosity of the endothelium. Using the impulse response technique in perfused rat livers, we found that aging is associated with impaired hepatic transendothelial transfer of chylomicrons with diameters smaller than those of fenestrations. In conclusion, age-related pseudocapillarization of the hepatic sinusoidal endothelium provides a novel mechanism for the association of old age with impaired hepatic lipoprotein metabolism and with atherosclerosis.

Aging↗
PubMed2005

Progressive familial intrahepatic cholestasis: genetic disorders of biliary transporters.

Progressive familial intrahepatic cholestasis types 1, 2 and 3 are childhood diseases of the liver. Benign recurrent intrahepatic cholestasis is predominantly an adult form with similar clinical symptoms that spontaneously resolve. These genetic disorders have significantly helped to unravel the basic mechanisms of the canalicular bile transport processes. Progressive familial intrahepatic cholestasis type 1 involves a gene also linked to benign recurrent intrahepatic cholestasis. The gene codes for an aminophospholipid translocase protein that maintains the integrity of the membrane. How a mutation in this protein causes cholestasis is unknown but is thought to involve the enterohepatic recirculation of bile acids. Progressive familial intrahepatic cholestasis types 2 and 3 involve the canalicular bile salt export pump and a phospholipid translocase, respectively, both of which are fundamental to bile secretion. This review covers the clinical manifestations, genetics, treatment and mechanism of each disease.

ATP-Binding Cassette Transporters↗
PubMed2005

Atypical antipsychotic medications and risk of falls in residents of aged care facilities.

OBJECTIVES: To determine whether use of atypical antipsychotics (olanzapine and risperidone) is associated with lower risk of falls than use of typical antipsychotics. DESIGN: Prospective cohort study with 1-month follow-up. SETTING: Residential aged care facilities in Sydney, Australia. PARTICIPANTS: Two thousand five people aged 65 to 104 (mean age 86). MEASUREMENTS: Medication use at baseline was collected from medical records. Data on potential confounders were collected at interview and physical examination and from medical records. The outcome was accidental falls (one or more). RESULTS: One thousand one hundred seven subjects (55%) used at least one type of psychotropic medication, with 289 (14%) using an antipsychotic. There were 82 olanzapine users, 38 risperidone users, and 181 users of typical antipsychotics. Eleven percent of subjects (n=226) had at least one fall during follow-up. After adjusting for a comprehensive range of falls risk factors, hazard ratios (HRs) for falls were 1.35 (95% confidence interval (CI)=0.87-2.09) for typical antipsychotics, 1.32 (95% CI=0.57-3.06) for risperidone, and 1.74 (95% CI=1.04-2.90) for olanzapine. Antidepressants were also associated with falls (adjusted HR=1.45, 95% CI=1.09-1.93). CONCLUSION: Despite fewer extrapyramidal side effects, atypical antipsychotic medications are not associated with fewer falls than the older, more-established antipsychotics.

Accidental Falls↗
PubMed2005

The hepatic sinusoid in aging and cirrhosis: effects on hepatic substrate disposition and drug clearance.

The fenestrated sinusoidal endothelium ('liver sieve') and space of Disse in the healthy liver do not impede the transfer of most substrates, including drugs and oxygen, from the sinusoidal lumen to the hepatocyte. Plasma components transfer freely in both directions through the endothelial fenestrations and into the space of Disse. The endothelium is attenuated, there is no basement membrane and there is minimum collagen in the space of Disse, thus minimising any barriers to substrate diffusion. Both cirrhosis and aging are associated with marked structural changes in the sinusoidal endothelium and space of Disse that are likely to influence bulk plasma transfer into the space of Disse, and diffusion through the endothelium and space of Disse. These changes, termed capillarisation and pseudocapillarisation in cirrhosis and aging, respectively, impede the transfer of various substrates. Capillarisation is associated with exclusion of albumin, protein-bound drugs and macromolecules from the space of Disse, and the progressive transformation of flow-limited to barrier-limited distribution of some substrates. There is evidence that the sinusoidal changes in cirrhosis and aging contribute to hepatocyte hypoxia, thus providing a mechanism for the apparent differential reduction of oxygen-dependent phase I metabolic pathways in these conditions. Structural change and subsequent dysfunction of the liver sieve warrant consideration as a significant factor in the impairment of overall substrate handling and hepatic drug metabolism in cirrhosis and aging.

Aging↗
PubMed2004

The effects of oxidative stress on the liver sieve.

BACKGROUND/AIMS: Oxidative stress is implicated in the pathogenesis of age-related and disease-associated changes in the hepatic sinusoid. We studied the effects of oxidative stress on the morphology of the liver, focusing specifically on the hepatic sinusoidal endothelium (the 'liver sieve'). METHODS: The effects of tert-butyl hydroperoxide on the intact liver and isolated sinusoidal endothelial cells were assessed by electron microscopy, immunohistochemistry and biochemical analysis. RESULTS: Immunohistochemistry revealed a dose-dependent increase in peri-sinusoidal 3-nitrotyrosine staining, particularly in the regions adjacent to the portal triads. Electron microscopy showed dose-dependent formation of large intracellular gaps in the sinusoidal endothelium with reduction in the diameter of the remaining endothelial fenestrations. Activated Kupffer cells extending processes through the fenestrations to contact hepatocytes were noted. Biochemical analysis of total liver tissue showed no significant changes in malondialdehyde content but a decrease in the ratio of GSH to GSSG. tert-Butyl hydroperoxide administered directly onto isolated liver sinusoidal endothelial cells was associated with similar gap formation, indicating a direct effect on the endothelial cells by tert-butyl hydroperoxide. CONCLUSIONS: Oxidative stress selectively damages hepatic sinusoidal endothelial cells. This has implications for those processes associated with changes in the sinusoidal endothelium such as ageing, cirrhosis and exposure to hepatotoxins.

Animals↗
PubMed2004

The hepatic pharmacokinetics of doxorubicin and liposomal doxorubicin.

To determine the role of the hepatic sinusoidal endothelium in the hepatic disposition of liposomal doxorubicin, we compared the hepatic pharmacokinetics of doxorubicin hydrochloride and the pegylated, liposomal formulation of doxorubicin (Caelyx). The multiple indicator-dilution technique and electron microscopy were used to study the disposition of doxorubicin and liposomal doxorubicin in the rat liver. Doxorubicin had a volume of distribution 1.56 +/- 0.45 times greater than that of the extracellular marker, sucrose, whereas liposomal doxorubicin had a volume of distribution 0.56 +/- 0.30 times smaller than that of sucrose (P < 0.001). The recovery of doxorubicin was less than that of liposomal doxorubicin (70 +/- 24% versus 94 +/- 17%, P < 0.05). The disposition of liposomal doxorubicin was found to be flow-limited, whereas a permeability-limited sequestration model fitted doxorubicin. The transfer of doxorubicin across the hepatocyte membrane was symmetrical (permeability - surface area product for influx 0.02 +/- 0.01 ml s/g versus 0.03 +/- 0.02 ml s/g for efflux) and consistent with diffusion. Electron microscopy confirmed that liposomes were restricted entirely to the sinusoidal lumen and none were seen in the extracellular space of Disse. Liposomal doxorubicin is restricted to the sinusoidal lumen, presumably secondary to steric exclusion by fenestrations in the sinusoidal endothelium. This provides the mechanism for the longer half-life and reduced hepatic extraction of liposomal doxorubicin compared with doxorubicin. The sinusoidal endothelium and fenestrations within the sinusoidal endothelium have an important role in hepatic pharmacology and are important considerations when designing liposomal preparations.

Animals↗
PubMed2004

Aging biology and geriatric clinical pharmacology.

Population aging evokes doomsday economic and sociological prognostication, despite a minority of older people suffering significant dependency and the potential for advances in therapeutics of age-related disease and primary aging. Biological aging processes are linked mechanistically to altered drug handling, altered physiological reserve, and pharmacodynamic responses. Parenteral loading doses need only be adjusted for body weight as volumes of distribution are little changed, whereas oral loading doses in some cases may require reduction to account for age-related increases in bioavailability. Age-related reduction of hepatic blood flow and hepatocyte mass and primary aging changes in hepatic sinusoidal endothelium with effects on drug transfer and oxygen delivery reduce hepatic drug clearance. Primary renal aging is evident, although renal clearance reduction in older people is predominantly disease-related and is poorly estimated by standard methods. The geriatric dosing axiom, "start low and go slow" is based on pharmacokinetic considerations and concern for adverse drug reactions, not from clinical trial data. In the absence of generalizable dosage guidelines, individualization via effect titration is required. Altered pharmacodynamics are well documented in the cardiovascular system, with changes in the autonomic system, autacoid receptors, drug receptors, and endothelial function to modify baseline cardiovascular tone and responses to stimuli such as postural change and feeding. Adverse drug reactions and polypharmacy represent major linkages to avoidable morbidity and mortality. This, combined with a deficient therapeutic evidence base, suggests that extrapolation of risk-benefit ratios from younger adults to geriatric populations is not necessarily valid. Even so, therapeutic advances generally may convert healthy longevity from an asset of fortunate individuals into a general social benefit.

Aged↗
PubMed2004

Prescribing in older people.

BACKGROUND: Prescribing medications to older people is difficult due to comorbidity, limited evidence for efficacy, increased risk of adverse drug reactions, polypharmacy, and altered pharmacokinetics. OBJECTIVE: This article describes the principles underlying clinical geriatric pharmacology including approaches to evaluating the evidence for risk and benefit, and adjusting dose for age related pharmacokinetic changes. DISCUSSION: The challenge for the general practitioner is to balance an incomplete evidence base for efficacy in frail, older people against the problems related to adverse drug reactions without denying older people potentially valuable pharmacotherapeutic interventions.

Aged↗