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Methionine is an essential amino acid and methyl donor for most transmethylation reactions in mammals. The product of transmethylation reactions is homocysteine, which is associated with enhanced risk for CVD. The aim of this study was to analyse metabolic and vascular functional consequences of a methionine-enriched diet in rats. The dose of methionine was chosen to reflect the range of over-nutrition in man. We quantified plasma levels of homocysteine, asymmetrical dimethylarginine and adenosine, determined methionine and its metabolites in tissues and blood plasma and assessed relaxation of mesenteric arteries toward acetylcholine and sodium nitroprusside. A methionine-enriched diet for 4 weeks elevated homocysteine levels in plasma 2-fold and in spleen by 70 %. The level ofS-adenosylhomocysteine was increased in liver only, while methionine andS-adenosylmethionine were unchanged in all organs studied. Plasma adenosine and asymmetrical dimethylarginine levels were unchanged, as were vessel relaxations. A 2-fold elevation of plasma homocysteine, which is assigned a risk indicator for cardiovascular events, did not impair mesenteric artery vasodilatation during 4 weeks of a methionine-rich diet. Furthermore, asymmetrical dimethylarginine and adenosine, which have been shown to be changed in more severe degrees of hyperhomocysteinaemia, remained unaltered.

We showed that human osteoprogenitor cells produced adenosine and expressed ecto-5?-nucleotidase and all four adenosine receptor subtypes. Adenosine stimulated IL-6 but inhibited osteoprotegerin secretion, suggesting that adenosine is a newly described regulator of progenitor cell function. Introduction: Maintaining skeletal homeostasis relies on there being a balance between bone formation and resorption; an imbalance between these processes can lead to diseases such as osteoporosis and rheumatoid arthritis. Recent reports showed that locally produced ATP, acting through P2 receptors, has pronounced effects on bone formation. However, ATP can be enzymatically cleaved to adenosine that has little or no activity at P2 receptors but mediates its action through the P1 family of receptors. We studied whether adenosine may also have an important role in controlling bone cell differentiation and function. Materials and Methods: Extracellular adenosine levels were analyzed by high-performance liquid chromatography in HCC1 and bone marrow stromal (BMS) cells. Ecto-5?-nucleotidase (CD73) expression and activity was determined by RT-PCR, immunocytochemistry, and the cleavage of etheno-AMP to ethenoadenosine. Adenosine receptor expression and activity were determined by RT-PCR and cAMP measurements. The effects of adenosine receptor agonists on IL-6, osteoprotegerin (OPG), and RANKL expression were determined by ELISA and QRT-PCR. Results: HCC1 and BMS cells produce adenosine and express CD73 and all four adenosine receptor subtypes. The A2b receptor was shown to be functionally dominant in HCC1 cells, as determined by cAMP production and in its stimulation of IL-6 secretion. Adenosine receptor agonism also inhibited OPG secretion and OPG but not RANKL mRNA expression. Conclusions: Our findings show that HCC1 and primary BMS cells produce adenosine, express CD73 and all four adenosine receptor subtypes. In HCC1 cells, adenosine has a potent stimulatory action on IL-6 secretion but an inhibitory action on OPG expression. These data show for the first time that adenosine may be an important regulator of progenitor cell differentiation and hence an important local contributor to the regulation of bone formation and resorption.

Nutritional factors can elevate the concentration of homocysteine in plasma, which is regarded as a risk indicator for cardiovascular events and other degenerative diseases. Although alimentary methionine is believed to be the main source for plasma homocysteine, the literature is lacking information about the homocysteine content of daily food. In this paper, the total homocysteine content of some commercially available food items such as tuna, swine liver, roquefort cheese, coffee, beer and white bread was measured by RP-HPLC with fluorescence detection after pre-column derivatization with a thiol-specific sulfonylbenzofuran, namely 7-benzo-2-oxa-1,3-diazole-4-sulfonic acid (SBD-F). With the exception of coffee, all examined food contained homocysteine in amounts between 30 and 950 μg per kg, which was 2,000–10,000-fold compared to the methionine content of the respective food. Based on a hypothetical daily consumption of the investigated foods, a maximum daily intake of homocysteine ranging from 400 to 700 μg or 3–5 μmol could be estimated. Compared to plasma homocysteine levels of 6–9 μmol/l, we conclude that the amount of alimentary homocysteine has only a very slight significant impact on the plasma homocysteine level even if complete resorption of the thiol compound is assumed.

BACKGROUND: It is unclear whether improved metabolism or a “lipid sink” effect of lipid infusion is responsible for the positive effects in local anesthetic-induced myocardial depression. METHODS: We used an isolated rat heart, constant-pressure perfused, nonrecirculating Langendorff preparation and exposed hearts to 5 g/mL l-bupivacaine and 9 L/mL lipid emulsion. Hearts were freeze-clamped and energy was charge measured by HPLC. In a second experiment the effects of pacing hearts was evaluated. The effects of lipid addition on local anesthetic concentrations in Krebs–Henseleit buffer and human plasma were examined by using a mass spectrometer. RESULTS: With spontaneously beating hearts l-bupivacaine led to a significant decrease in heart rate (to 74% 7% of baseline), dP/dt (69% 7%), systolic pressure (78% 6%), coronary flow (61% 8%), and to an increase in PR (177% 52%) and QRS intervals (166% 36%). Lipid infusion exerted a positive inotropic effect, significantly augmenting dP/dt and systolic pressure back to 94% 11% and 102% 16% of baseline in l-bupivacaine-treated hearts. Heart rate, coronary flow, PR, and QRS intervals remained unchanged after lipid intervention. Lipid infusion in paced hearts had a significant effect on dP/dt, systolic pressure, and Mvo2. Neither l-bupivacaine nor lipids had an effect on energy charge. A lipid concentration of 500 L/mL plasma was necessary to effect changes in the plasma concentration of local anesthetics. CONCLUSION: Lipid application in l-bupivacaine-induced cardiac depression had a significant positive inotropic effect, which we would attribute to a direct inotropic effect. However, in an isolated heart model, indirect, local anesthetic plasma-binding effect of lipids cannot be excluded. (Anesth Analg 2007;104:186‐92)

Objective: Due to limited resources, improvement of preservation solutions is still of great importance in cardiac transplant surgery. New additives with antioxidant properties were tested with respect to coronary function of isolated rat hearts. Methods: Bretschneider HTK solution containing none or an antioxidant additive (deferoxamine, trolox or LK 616) was used for 8 h cold cardioplegia. After reperfusion with KrebsHenseleit buffer (KHB), we assessed vascular dilator capacity (bradykinin, adenosine triphosphate, reactive hyperemia), myocardial function (left ventricular developed pressure,heart rate, oxygen consumption) and release of biochemical markers (aspartate aminotransferase, creatine kinase, lactate dehydrogenase, troponin, adenosine). Results: Bradykinin- and adenosine triphosphate-induced vasodilations were largely reduced in hearts stored 8 h in traditional HTK as compared to unstored controls. Storage in HTK + LK 616 significantly improved bradykinininduced vasodilation. Vasodilation toward ATP was best preserved in hearts stored in HTK + deferoxamine. Deferoxamine and trolox, both improved reactive hyperaemic response during reperfusion. Left ventricular pressure development was significantly reduced after 8 h cardioplegia, but no difference existed between different cardioplegia groups. Release of biochemical markers of tissue injury was similar in all cardioplegia groups. After storage in HTK + LK 616 (100 mM), however, heart marker release was slightly augmented as compared to HTK. Conclusions: Despite similar myocardial function and marker release, coronary vascular function after cardioplegic storage may profit by addition of iron chelators (or antioxidants) to traditional HTK solution. # 2007 European Association for Cardio-Thoracic Surgery. Published by Elsevier B.V. All rights reserved.

Adenosine metabolism and transport were evaluated in the isolated perfused mouse heart and compared with the well-established model of isolated perfused guinea pig heart. Coronary venous release of adenosine under well-oxygenated conditions in the mouse exceeds that in the guinea pig threefold when related to tissue mass. Total myocardial adenosine production rate under this condition was approximately 2 nmol/min per gramme and similar in both species. Coronary resistance vessels of mice are highly sensitive to exogenous adenosine, and the threshold for adenosine-induced vasodilation is approximately 30 nmol/l. Adenosine membrane transport was largely insensitive to nitrobenzyl-thioinosine (NBTI) in mouse heart, which is in contrast to guinea pig and several other species. This indicates the dominance of NBTI-insensitive transporters in mouse heart. For future studies, the assessment of cytosolic and extracellular adenosine metabolism and its relationship with coronary flow will require the use of more effective membrane transport blockers.