The effect of aging on the immunohistochemistry of apolipoprotein E in the liver

Health benefits of late-onset metformin treatment every other week in mice

Chronic 1% metformin treatment is nephrotoxic in mice, but this dose may nonetheless confer health benefits if given intermittently rather than continuously. Here, we examined the effects of 1% metformin given every-other week (EOW) or two consecutive weeks per month (2WM) on survival of 2-year-old male mice fed standard chow. EOW and 2WM mice had comparable life span compared with control mice. A significant reduction in body weight within the first few weeks of metformin treatment was observed without impact on food consumption and energy expenditure. Moreover, there were differences in the action of metformin on metabolic markers between the EOW and 2WM groups, with EOW metformin conferring greater benefits. Age-associated kidney lesions became more pronounced with metformin, although without pathological consequences. In the liver, metformin treatment led to an overall reduction in steatosis and was accompanied by distinct transcriptomic and metabolomic signatures in response to EOW versus 2WM regimens. Thus, the absence of adverse outcomes associated with chronic, intermittent use of 1% metformin in old mice has clinical translatability into the biology of aging in humans.

Chronic daily exposure to a high dose of metformin (e.g., 1% w/w) shortens lifespan of non-diabetic mice, although in the short term this treatment confers a similar pattern of gene expression and phenotypes consistent with the benefits of caloric restriction. A team of researchers led by Rafael de Cabo at the National Institute on Aging, NIH tested whether a strategy of intermittent 1% metformin treatment in old mice alters the course of aging and avoids toxicity. They found that when metformin was given every-other-week, it significantly improved insulin sensitivity and reduced age-associated liver lesions without having a negative impact on maximum lifespan in male mice. The absence of adverse outcomes associated with the use of 1% metformin in old mice has clinical translatability into the biology of aging in humans.

Hepatoprotective Activity of the Total Saponins from Actinidia valvata Dunn Root against Carbon Tetrachloride-Induced Liver Damage in Mice

The protective activity of the total saponins from Actinidia valvata Dunn root (TSAV) was studied against carbon-tetrachloride- (CCl₄-) induced acute liver injury in mice. Mice were orally administered TSAV (50, 100, and 200 mg/kg) for five days and then given CCl₄. TSAV pretreatment significantly prevented the CCl₄-induced hepatic damage as indicated by the serum marker enzymes (AST, ALT, and ALP). Parallel to these changes, TSAV also prevented CCl₄-induced oxidative stress by inhibiting lipid peroxidation (MDA) and restoring the levels of antioxidant enzymes (SOD, CAT, GR, and GPX), GSH and GSSG. In addition, TSAV attenuated the serum TNF-α and IL-6 levels and inhibited the serum iNOS and NO levels. Liver histopathology indicated that TSAV alleviated CCl₄-induced inflammatory infiltration and focal necrosis. TSAV (200 mg/kg) also significantly decreased Bak, Bax mRNA and Fas, FasL, p53, and NF-κB p65 protein expressions and increased Bcl-2 mRNA and protein expressions. Meanwhile, TSAV significantly downregulated caspase-3 and caspase-8 activities and prevented CCl₄-induced hepatic cell apoptosis. In addition, TSAV exhibited antioxidant activity through scavenging hydroxyl and DPPH free radicals in vitro. These results indicated that TSAV could protect mice against CCl₄-induced acute liver damage possibly through antioxidant, anti-inflammatory activities and regulating apoptotic-related genes.

The influence of old age and poloxamer-407 on the hepatic disposition of diazepam in the isolated perfused rat liver

BACKGROUND AND PURPOSE

The normal liver sinusoidal endothelium is thin and punctuated with fenestrations 50-200 nm in diameter that filter endobiotics and xenobiotics. Defenestration of the liver sinusoidal endothelium in old age and after pre-treatment with poloxamer-407 (P407) has been shown to prevent the transfer of small chylomicrons across the liver sinusoidal endothelium. The aim of this study was to investigate the impact of liver sinusoidal endothelium fenestrations on the hepatic uptake of the highly protein-bound drug diazepam. We hypothesized that defenestration will reduce the hepatic extraction of drugs which are highly bound to albumin.

METHODOLOGY

The isolated perfused rat liver (IPRL) model and multiple indicator dilution technique were used to investigate the effect of fenestrations in the liver sinusoidal endothelium on the hepatic disposition of diazepam in old and young rats, and in young rats treated with P407 or vehicle. A bolus dose of (14)C-diazpeam and non-extracted tracers ((3)H-sucrose and Evans blue) was injected into the portal vein. The single-pass recovery of diazepam and markers and the apparent volume of distribution were determined.

RESULTS

Scanning electron microscopy confirmed reduced porosity of the liver sinusoidal endothelial cells in P407-treated rats and old rats compared to young and control rats. The fractional recovery of diazepam was significantly increased in P407-treated rats compared to controls (0.20 ± 0.16, n = 12, P407; 0.08 ± 0.05, n = 8, controls; p = 0.0029), and in old rats compared to young rats (0.15 ± 0.03, n = 11, old; 0.10 ± 0.02, n = 11, young; p = 0.0004) following a single pass.

CONCLUSION

Defenestration due to age-related pseudocapillarization and treatment with P407 resulted in reduced hepatic extraction of diazepam after a single pass through the IPRL. These results highlight the importance of the liver sinusoidal endothelium in the ultrafiltration of highly protein-bound drugs, and may also provide an additional mechanism for reduced hepatic clearance of diazepam in conditions associated with defenestration.

Age-related pseudocapillarization of the liver sinusoidal endothelium impairs the hepatic clearance of acetaminophen in rats

We investigated the effect of age-related pseudocapillarization of the liver sinusoidal endothelium on the hepatic disposition of acetaminophen. The multiple indicator dilution technique assessed the hepatic disposition of tracer (14)C-acetaminophen and reference markers in isolated perfused livers of young (n = 11) and old (n = 12) rats. Electron microscopy confirmed defenestration of the sinusoidal endothelium in old rats compared with young rats. Acetaminophen recovery following a single pass through the liver was significantly increased in old rats (0.64 ± 0.04, old; 0.59 ± 0.05, young; p < .05). In old age, there was significant reduction of the intercompartmental rate constant k(1) (0.34 ± 0.10 s(-1), old; 0.61 ± 0.38 s(-1), young; p < .05) and the permeability-surface area product for the transfer of acetaminophen across the sinusoidal endothelium (0.034 ± 0.006 mL/s/g, old; 0.048 ± 0.014 mL/s/g, young; p < .005). There was no difference in k(3), the measure of sequestration of acetaminophen that reflects enzyme activity. Age-related pseudocapillarization of the liver sinusoid resulted in increased acetaminophen recovery and decreased transfer of acetaminophen into the liver.

The effect of old age on apolipoprotein E and its receptors in rat liver

Apolipoprotein E (apoE) is associated with aging and some age-related diseases. The majority of apoE is produced by hepatocytes for the receptor-mediated uptake of lipoproteins. Here, the effects of age on the hepatic expression and distribution of apoE and its receptors were determined using immunofluorescence, Western blots, and quantitative PCR in rat liver tissue and isolated hepatocytes. The expression of apoE mRNA and protein was not influenced significantly by aging. Immunofluorescence studies in isolated hepatocytes showed that apoE was more likely to be co-localized with early endosomes, golgi, and microtubules in isolated old hepatocytes. The mRNA expression of the receptor involved in sequestration of apoE, heparan sulfate proteoglycan was reduced in old age, without any significant effect on the expression of either the low-density lipoprotein receptor or low density-lipoprotein receptor-related protein. Old age is associated with changes in hepatic apoE intracellular trafficking and heparan sulfate proteoglycan expression that might contribute to age-related disease.

Effects of hydrogen peroxide and apolipoprotein E isoforms on apolipoprotein E trafficking in HepG2 cells

1. The major source of apolipoprotein E (apoE) is the liver. In the present study, the effects of oxidative stress and apoE isoforms on apoE distribution and trafficking were established using the HepG2 liver tumour cell line. 2. Hydrogen peroxide (0, 25, 250 and 1000 micromol/L) was associated with rapid and concentration-dependent redistribution of apoE into the early endosomal compartment. This redistribution was achieved with a much lower concentration (25 micromol/L) than that needed to induce changes in intracellular apoE mRNA expression, apoE protein levels and markers of oxidative stress (250-1000 micromol/L). 3. Live cell imaging of apoE3-green fluorescent protein revealed a significant decrease in traffic velocity in response to oxidative stress. 4. The E4 isoform was associated with reduced trafficking velocity compared with the E3 isoform under basal conditions. 5. The results indicate that oxidative stress and apoE isoforms influence apoE trafficking and distribution within HepG2 cells. Altered apoE hepatocyte trafficking may provide a mechanistic link between oxidative stress, ageing and some diseases in older people.

The effect of aging on the response of isolated hepatocytes to hydrogen peroxide and tert-butyl hydroperoxide

Aging is associated with increased susceptibility to oxidative stress. To study this in the liver and to elucidate underlying mechanisms, hepatocytes from young (4-6 months) and old (24-26 months) rats were exposed to two oxidants, hydrogen peroxide and tert-butyl hydroperoxide. ATP content and mitochondrial activity were lower in old hepatocytes and decreased further with oxidative stress. Expression of Cu/Zn superoxide dismutase, Mn superoxide dismutase and catalase was not substantially influenced by oxidative stress in young and old hepatocytes, whereas glutathione peroxidase 1 expression was markedly increased only in young hepatocytes. Oxidative stress in young hepatocytes led to increased expression of apoE and movement of apoE to the early endosomes. In old hepatocytes, oxidative stress did not increase apoE expression and apoE was co-localized with early endosomes under control conditions. The results show that old age is associated with impaired hepatocyte responses of mitochondria, ATP, glutathione peroxidase 1 and apoE to oxidative stress.