Fatty acids differentially regulate insulin resistance through endoplasm reticulum stress-mediated induction of tribbles homologue 3: a potential link between dietary fat composition and the pathophysiological outcomes of obesity

AIMS/HYPOTHESIS

Previous studies have shown that saturated fatty acids cause insulin resistance (IR) that is prevented by unsaturated fatty acids. Tribbles homologue 3 (TRIB3) is a putative endogenous inhibitor of insulin signalling, but its role in insulin signalling is controversial. This study aimed to determine whether fatty acids regulate IR via TRIB3.

METHODS

We treated HepG2 cells with saturated and unsaturated fatty acids and evaluated TRIB3 expression. We then tested whether regulation of TRIB3 occurred through endoplasmic reticulum (ER) stress, and whether modulating TRIB3 and ER stress marker genes was necessary and/or sufficient for regulation of insulin signalling. To test the in vivo significance of this mechanism, we fed mice obesogenic diets with different fatty acid profiles and assessed physiological variables of diabetes, ER stress markers and Trib3 expression in the liver.

RESULTS

Our data show that fatty acids differentially regulate IR through ER stress-mediated induction of TRIB3. Intriguingly, a standard and widely used obesogenic diet high in unsaturated fats failed to induce ER stress, TRIB3 or IR. However, an alternative obesogenic diet with lower unsaturated fat recapitulated the cell studies by causing ER stress, TRIB3 induction and IR.

CONCLUSIONS/INTERPRETATION

This study revealed a novel mechanism linking dietary fat composition to IR. Given the emerging roles for ER stress in non-alcoholic liver disease, we conclude that dietary fat composition rather than total amount may mediate hepatic pathology associated with obesity.

Enhanced tumor cures after Foscan photodynamic therapy combined with the ceramide analog LCL29. Evidence from mouse squamous cell carcinomas for sphingolipids as biomarkers of treatment response

To improve anticancer therapeutic success of photodynamic therapy (PDT), combination treatments represent a viable strategy. Sphingolipid analogs combined with anticancer drugs can enhance tumor response. We have shown that LCL29, a C6-pyridinium ceramide, promotes therapeutic efficacy of Photofrin-PDT in mouse SCCVII squamous cell carcinoma tumors. The long-term effect of the combination PDT + LCL29 is unknown. In this study we used the same model to test the long-term curative potential of Foscan-PDT + LCL29. We show that treatment of SCCVII tumors with the combination led to enhanced long-term tumor cure compared to PDT alone. LCL29 itself did not prevent tumor growth. All treatments triggered early increases in tumor-associated C16-ceramide, C18-ceramide, dihydrosphingosine, and global levels of dihydroceramides. PDT-evoked increases in tumor-associated sphingosine-1-phosphate and dihydrosphingosine-1-phosphate remained elevated or were attenuated after the combination, respectively; in contrast, LCL29 had no effect on these two sphingolipids. Our data demonstrate that adjuvant LCL29 improves PDT long-term therapeutic efficacy, implying translational potential of the combination. Furthermore, our findings indicate that changes in the sphingolipid profile might serve as predictive biomarkers of tumor response to treatments.

Distribution and dynamic changes of sphingolipids in blood in response to platelet activation

BACKGROUND

Sphingolipids are signaling molecules in a range of biological processes. While sphingosine-1-phosphate (S1P) is thought to be abundantly stored in platelets and released upon stimulation, knowledge about the distribution and function of other sphingolipids in blood is lacking.

OBJECTIVES

To analyze the sphingolipid content of blood components with special emphasis on dynamic changes in platelets.

METHODS

Blood components from mice and humans were prepared by gradient centrifugation and analyzed by liquid chromatography-mass spectrometry. Additionally, murine platelets were activated in vitro and in vivo.

RESULTS

Isolated non-activated platelets of mice were devoid of S1P, but instead contained dihydrosphingosine-1-phosphate (dhS1P), along with a high concentration of ceramide. Activation of platelets in vitro led to a loss of dhS1P and an increase in sphingosine, accompanied by a reduction of ceramide content. Platelet activation in vivo led to an immediate and continuous rise of dhS1P in plasma, while S1P remained stable. The sphingolipid distribution of human blood was markedly different from mice. Human platelets contained dhS1P in addition to S1P.

CONCLUSIONS

Mouse platelets contain dhS1P instead of S1P. Platelet activation causes loss of dhS1P and breakdown of ceramide, implying ceramidase activation. Release of dhS1P from activated platelets might be a novel signaling pathway. Finally, the sphingolipid composition of mouse and human blood shows large differences, which must be considered when studying sphingolipid biology.

Modulation of ceramide metabolism enhances viral protein apoptin's cytotoxicity in prostate cancer

Despite local and systemic therapies, the National Cancer Institute estimates that prostate cancer will cause over 30,000 deaths in 2006. This suggests that additional therapeutic approaches are needed. The chicken anemia viral protein Apoptin causes tumor-selective apoptosis in human tumor lines independent of p53 and Bcl-2 status. Tet-regulated expression of Apoptin from an adenoviral vector showed cytotoxicity in DU145, PC-3, and LNCaP tumor cells regardless of expression of p53, Bcl-2, Bcl-xL, Bax, survivin, FLIP(S), XIAP, or CIAP. Apoptin expression caused an increase in the tumor suppressor lipid ceramide, which regulates the cellular stress response. Interestingly, 10 of 15 primary prostate cancers examined by Western blotting overexpressed acid ceramidase (AC), suggesting that ceramide deacylation might serve to negate elevated levels of ceramide, creating a more antiapoptotic phenotype. This was confirmed in AC-overexpressing cells in which we observed decreased sensitivity to apoptosis following treatment with Apoptin. Addition of the AC inhibitor LCL204, in combination with Apoptin, augmented cell killing. This effect was also demonstrated in vivo in that Apoptin and LCL204 cotreatment significantly reduced tumor growth in DU145 xenografts (P<0.05). Taken together, our data demonstrated that Apoptin is a promising therapeutic agent for prostate cancer and that its function is improved when combined with acid ceramidase inhibitors.

The mechanism of bile salt-induced hemolysis

The hemolytic activities of sodium deoxycholate (DChol) and its tauro-conjugate (TDChol) and glyco-conjugate (GDChol) were analysed. 50 % hemolysis occurred in 30 min at pH 7.3, at the concentrations of these detergents equal to 0.044, 0.042 and 0.040 % respectively. These values are below their critical micellar concentrations. Based on its kinetics, this hemolysis is classified as being of permeability type. The detergents increase the permeability of erythrocyte membranes to KCl, and colloid osmotic hemolysis occurs. The minimum of hemolytic activity of the three cholates is at about pH 7.5. A very high increase in hemolytic activity occurs at pHs below 6.8, 6.5 and 6.2 for DChol, TDChol, and GDChol, respectively. These values are close to the pK(a) for DChol (6.2), but much higher than the pK(a) for TDChol (1.9) and GDChol (4.8). It is therefore suggested that the increase in hemolytic activity is not a result of the protonation of the anionic groups of the cholates. At acidification below pH 6, the kinetics of DChol induced hemolysis change to the damage type characterised by nonselective membrane permeability. Such a transition is not observed in TDChol and GDChol induced hemolysis. It is therefore suggested that the change in the type of hemolysis depends on protonation of the anionic group of cholates.

[Choice of correct stabilization in long bone fractures]

The paper presents an algorithm to facilitate the choice of the correct stabilization system in fractures of long bones. The algorithm is based on fracture morphology. The indications and contractions for surgical treatment are discussed.

[Is posttraumatic osteomyelitis of iatrogenic nature?]

A series of 112 patients with posttraumatic osteomyelitis has been reviewed. Analysis of the management revealed, that malpractice contributed to the onset of osteomyelitis in many cases. Since politrauma patients with extensive bone and soft tissue injury are prone to infection errors in management of these patients lead to serious complications. Neglecting of primary immobilization of the open fracture in politrauma patients, incorrect methods of fracture fixation or technical errors at surgery, erroneous soft tissue injury management (complete closure of the wound, neglecting compartment syndrome) and disregarding local antibiotics are among most frequently committed errors. The authors conclude, that in majority of cases posttraumatic osteomyelitis is of iatrogenic nature.

[Chronic bone abscess]

The review of 68 patients with chronic bone abscess as a long-term sequel to ostomyelitis is presented. Antibiotic instillation within abscess cavity is recommended by the authors. Once the drainage is concluded immunotherapy should be introduced to secure long-lasting remission as in 90% of presented cases.

[Principles of treatment for infected pseudarthoses]

Review of literature and own experience of the authors make them conclude, that assessment of extremity blood supply and precise bacteriologic evaluation with establishing the lowest efficient antibiotic concentration is necessary in planning of the treatment. It must include improvement of the blood supply by surgical reconstruction in case of impaired blood flow through great vessels and lumbar sympathectomy if crural arteries are compromised. Correct fixation of the fragments is equally important; the choice of the method depends on bony changes. Frequently, the management must be multi-stage. Improvement of the blood supply must always be included in the first stage. Rational surgical treatment supplemented by contemporary topical antibiotic administration allowed for termination of infection and bony union even in patients who were earlier considered for an amputation.

Two types of haemolytic activity of detergents

The nonionic detergent Triton X-100 at concentrations of about 0.003 to 0.008% causes swelling followed by the haemolysis of erythrocytes suspended in 160 mM KCl. The rate of haemolysis increases with the increase in detergent concentration. Finally all the erythrocytes are haemolysed. The resistance of erythrocytes to this detergent decreases with an increase in temperature. The effect of Triton X-100 is explained by increased membrane permeability to KCl and colloid osmotic haemolysis. The anionic detergent, sodium dodecyl sulfate (SDS), at concentrations of about 0.003 to 0.001% causes the haemolysis of a certain number of erythrocytes. This number increases with an increase in detergent concentration. The resistance of erythrocytes to SDS increases with an increase in temperature. The effect of SDS is explained by direct disruption of membranes by the detergent.

Tobacco smoke chemistry. 2. Alkyl and alkenyl substituted guaiacols found in cigarette smoke condensate

A series of alkyl and alkenyl substituted guaiacols, which comprise a group of biologically and organoleptically active compounds, have been synthesized. Mass spectra and GC retention times for these have been recorded and compared with those obtained for constituents of a weakly acidic fraction of smoke condensate derived from American blend type cigarettes. On the basis of these results, 25 guaiacols have been identified, 18 of which have not been detected in tobacco smoke condensate previously.

Kinetic resolution in the oxidation of iminium ion to lactam catalysed by aldehyde oxidase

A rabbit liver enzyme preparation oxidised racemic iminium ions 1 and 2 to optically active lactams 3 and 4 with enantiomer ratios ER/S = 5.5 and 0.14, respectively.

Diagnosis of insulin secreting tumour by retrograde pancreatography

The case of a 26-year-old male with insulinoma is presented. An insulin secreting tumour was indicated by laboratory data. The tumour was accurately localized by endoscopic retrograde pancreatography, as verified by subsequent surgery.

Diagnostic value of endoscopic retrograde cholangio-pancreatography in biliodigestive anastomoses

Endoscopic retrograde cholangio-pancreatography performed in patients with bilodigestive anastomosis may furnish not only reliable radiograms revealing abnormal morphology of the two duct system but allows also endoscopic investigation of the stoma, which is often of equal diagnostic value in such patients. The size of the anastomosis is of crucial importance in such complications as cholangitis and secondary bile stone formation. In a significant portion of patients with biliodigestive anastomoses, i.e. in 75% of the present patient material, a morphologic abnormality could be demonstrated offering in many if not most cases the possibility of a surgical correction and eventual cure of the symptoms.