Decreased SIRT1 expression and LKB1 phosphorylation occur with long-term high-fat diet feeding, in addition to AMPK phosphorylation impairment in the early phase

SUMMARY

AIMS

Energy sensing systems including AMPK and SIRT1 play important roles in the regulation of hepatic gluconeogenesis and fatty acid oxidation. In this study, we investigated how hepatic LKB1-AMPK signaling and SIRT1 expression are altered after 2 or 8 weeks of HFD feeding.

METHODS

The livers of male mice fed a HFD or a standard diet for 2 or 8 weeks were removed. The expression and phosphorylation levels of LKB1, AMPK, ACC and TORC2, and SIRT1 expression levels were examined by immunoblotting.

RESULTS

In mice fed a HFD for 2 weeks, the phosphorylations of AMPKα and ACC were decreased without significant alterations in LKB1 phosphorylation or SIRT1 protein levels, while TORC2 protein levels were increased. In mice fed a HFD for 8 weeks, marked reductions in LKB1 phosphorylation and SIRT1 protein amount were observed in addition to the decreased phosphorylations of AMPKα and ACC.

CONCLUSIONS

The mechanisms underlying impaired energy sensing signaling differ with the duration of HFD feeding. In the early phase of HFD feeding, LKB1 and SIRT1 were not impaired, while in the later phase of HFD feeding, decreased SIRT1 expression and LKB1 phosphorylation may be involved in the development of severe glucose and lipid intolerance.

Valsartan restores inflammatory response by macrophages in adipose and hepatic tissues of LPS-infused mice

Inflammation involving adipose tissue is regarded as one of the major molecular mechanisms underlying obesity-related insulin resistance. Recent studies have suggested a series of angiotensin II receptor blockers (ARBs) to improve insulin resistance or protect against the development of diabetes mellitus. We previously demonstrated that valsartan suppresses the inflammatory response of macrophages. Interestingly, however, this effect did not occur via peroxisome proliferator-activated receptor (PPAR) γ or the AT1a receptor. This suppression appears to secondarily lead to amelioration of insulin resistance and reductions in abnormal gene expressions in adipocytes. In addition to these in vitro findings, we herein demonstrate the in vivo effects of valsartan, using mice constitutively infused with lipopolysaccharide (LPS) for 4 weeks. Oral administration of valsartan to LPS-infused mice normalized the increased expressions of inflammatory cytokines in adipose and liver tissues. These results raise the possibility that valsartan not only contributes to normalization of obesity-related insulin resistance, but is also beneficial for the treatment of other diseases with inflammation related to the metabolic syndrome such as atherosclerosis and non-alcoholic steatohepatitis. Further study is necessary to clarify these issues.

Valsartan, independently of AT1 receptor or PPARγ, suppresses LPS-induced macrophage activation and improves insulin resistance in cocultured adipocytes

Macrophages are integrated into adipose tissues and interact with adipocytes in obese subjects, thereby exacerbating adipose insulin resistance. This study aimed to elucidate the molecular mechanism underlying the insulin-sensitizing effect of the angiotensin II receptor blocker (ARB) valsartan, as demonstrated in clinical studies. Insulin signaling, i.e., insulin receptor substrate-1 and Akt phosphorylations, in 3T3-L1 adipocytes was impaired markedly by treatment with tumor necrosis factor-α (TNFα) or in the culture medium of lipopolysaccharide (LPS)-stimulated RAW 264.7 murine macrophages, and valsartan had no effects on these impairments. However, in contrast, when cocultured with RAW 264.7 cells using a transwell system, the LPS-induced insulin signaling impairment in 3T3-L1 adipocytes showed almost complete normalization with coaddition of valsartan. Furthermore, valsartan strongly suppressed LPS-induced productions of cytokines such as interleukin (IL)-1β, IL-6, and TNFα with nuclear factor-κB activation and c-Jun NH(2)-terminal kinase phosphorylation in RAW 264.7 and primary murine macrophages. Very interestingly, this effect of valsartan was also observed in THP-1 cells treated with angiotensin II type 1 (AT1) siRNA or a peroxisome proliferator-activated receptor-γ (PPARγ) antagonist as well as macrophages from AT1a receptor-knockout mice. We conclude that valsartan suppresses the inflammatory response of macrophages, albeit not via PPARγ or the AT1a receptor. This suppression appears to secondarily improve adipose insulin resistance.

Adipocyte-macrophage interaction may mediate LPS-induced low-grade inflammation: Potential link with metabolic complications

Chronic low-grade infection has been suggested to be associated with metabolic disorder such as diabetes. However, the molecular mechanism underlying this important association is largely unknown. The only clue established so far is that many subjects exhibit elevated levels of C-reactive protein as measured by highly sensitive assay. Here, we hypothesized that adipocyte–macrophage interaction plays a key role in amplifying such low grade infection to the level of influencing metabolic disorders. The presence of macrophages in abdominal adipose tissues was investigated by immunohistochemistry. To see whether molecules associated with acute phase protein, LPS signaling, and persistent recruitment of monocytes, are produced at higher amounts in adipocytes co-cultured with macrophages stimulated with low concentration of LPS (1 ng/ml), we measured serum amyloid A (SAA), LPS binding protein (LBP), soluble CD14 (sCD14), and RANTES levels in culture supernatant of co-cultures. Lastly, we investigated in vivo effect of low-grade LPS infusion on the production of these molecules using obese model mice. The macrophages were certainly identified in abdominal adipose tissues. Investigated molecules, especially LBP, SAA, and RANTES were produced at higher amounts in co-cultures stimulated with LPS compared with the cells without LPS. The ob/ob, and high-fat diet-induced obesity mice produced higher amounts of LBP, SAA, and RANTES one day after LPS infusion (1 ng/ml/g body weight) compared with ob/– and normal-fat fed control mice. Thus, adipocytes and infiltrated macrophages, and their interaction with low endotoxin stimulation appear to play an important role in amplifying and maintaining LPS-induced low-grade inflammation.

Electrochemistry of DNA duplex containing an anthraquinonylmethyl group at the 2'-sugar position

Cyclic voltammetry of oligonucleotide containing an anthraquinonylmethyl group at the 2'-sugar position was carried out for exploiting an electrochemical probe of DNA.

Chlorella vulgaris culture supernatant (CVS) reduces psychological stress-induced apoptosis in thymocytes of mice

A glycoprotein prepared from Chlorella vulgaris culture supernatant (CVS) is a biological response modifier (BRM) which exhibits protective activities against tumor metastasis and 5-fluorouracil-induced immunosuppression. We here show that oral administration of CVS prevented significantly the apoptosis of thymocytes in mice undergoing psychological stress in a communication box. Mice were exposed to the emotional stress for 14 days by witnessing other mice being exposed to foot-shock. The numbers in thymocytes, especially CD4(+)CD8(+) population, were decreased significantly and apoptotic cells, as assessed by Annexin V expression, were reciprocally increased after the exposure to the psychological stress. C. vulgaris culture supernatant (CVS) administration significantly suppressed the increase in serum corticosterone level in the psychologically stressed mice. These results suggest that CVS prevents psychological stress and maintain homeostasis in the face of external environmental changes.

Oral administration of hot water extracts of Chlorella vulgaris reduces IgE production against milk casein in mice

Hot water extract of Chlorella vulgaris (CVE) is a biological response modifier (BRM) which enhances resistance to Listeria monocytogenes through augmentation of helper T cell type 1 (Thl) responses producing gamma-interferon (gammaIFN). We show here that oral administration of CVE in mice suppressed the production of immunoglobulin (Ig)E against casein antigen accompanied by increased gammaIFN and IL-12 mRNA expression. Oral administration of CVE enhanced Thl response to casein in the spleen of casein immunized mice. CVE may be useful for prevention of allergic diseases with a predominant Th2 response.

Enhanced resistance against Escherichia coli infection by subcutaneous administration of the hot-water extract of Chlorella vulgaris in cyclophosphamide-treated mice

The effects of Chlorella vulgaris extract (CVE-A) on the recovery of leukocyte number and the augmentation of resistance to bacterial infection were examined in CDF1 mice made neutropenic by cyclophosphamide (CY). They were treated intraperitoneally with CY (150 mg/kg) on day 0, and were given CVE-A (50 mg/kg) subcutaneously (s.c.) every other day from day 1 to day 13 after CY treatment. CVE-A accelerated the recovery of polymorphonuclear leukocytes (PMN) in the peripheral blood in CY-treated mice. The number of granulocyte/monocyte-progenitor cells (CFU-GM) in the spleen increased rapidly and highly after the administration of CVE-A in CY-treated mice, in contrast to the absence of change due to CVE-A in the number of bone marrow cells in CY-treated mice. Administration of CVE-A in CY-treated mice enhanced the accumulation of PMN in the inflammatory site and the activity of the accumulated leukocyte cells in luminol-dependent chemiluminescence. The mice became highly susceptible to an intraperitoneal infection with E. coli on day 4 after CY treatment, whereas the mice given CVE-A showed an enhanced resistance against E. coli infection, irrespective of the timing of challenge. The bacterial number in CY-treated mice increased explosively after inoculation, resulting in death within 24 h. A progressive elimination of bacteria was observed from 6 h in the peritoneal cavity, spleen and liver of CY-treated mice given CVE-A s.c. These results indicate that CVE-A can be used as a potent stimulant of nonspecific resistance to infection in neutropenic mice.

Serum-free culture of insulin-secreting clonal cells from a hamster insulinoma

We experimented with a wide range of serum-free media to find the best one for culturing insulinoma cells from the Syrian golden hamster, cell line In-R1-I10. Optimum cell growth came with a mixture of equal proportions of Dulbecco's modified Eagle's medium and Ham's F-12, supplemented with 10(-6) M insulin, 10 micrograms/ml transferrin, and 10(-9) M triiodothyronine (what we labeled DF-ITT medium). In addition to testing different varieties of basal media, we also experimented with different concentrations of known stimulants of cell proliferation, including transferrin, ferrous sulfate, insulin, epidermal growth factor, triiodothyronine, hydrocortisone, monoethanolamine, prolactin, proteose peptone, and selenium. Cells cultured in DF-ITT medium grew as well as those in serum-containing medium for 94 consecutive generations. Their insulin secreting capacity was maintained. The substitution of epidermal growth factor (10 ng/ml) for the insulin did not reduce either the growth rate or the insulin secreting capacity of the culture cells.