Toxicity of chemically generated nitric oxide towards pancreatic islet cells can be prevented by nicotinamide.

Previous studies have indicated that nitric oxide is involved in the lysis of pancreatic islet cells by inflammatory macrophages. Here we show that the incubation of islet cells with chemical NO-donors leads to cell lysis in a concentration and time dependent way. Islet cell death could be prevented by nicotinamide and 3-aminobenzamide, which are known to inhibit ADP-ribosylation, while several scavengers of oxygen radicals, N-acetylcysteine, dihydrolipoic acid, dimethylthiourea and citiolone, provided no protection.     

A new model of primary human adipocytes reveals reduced early insulin signalling in type 2 diabetes.

The aim of this study was to establish a diabetic model of primary human adipocytes for investigating potential defects in early insulin signalling. Specimens of human subcutaneous adipose tissue were obtained during orthopaedic surgical procedures. Preadipocytes were isolated and differentiated to adipocytes. Western blot analysis and immunoprecipitation were performed to determine protein content of IRS-1, IRS-2, p85, phosphorylation of IRS-1, IRS-2, Akt and MAPK as well as association between p85 and IRS-1/IRS-2. In addition to short-term insulin stimulation, the effect of hyperinsulinaemia was investigated by treating cells with insulin over a period of 36 hours. We found a significantly reduced basal expression of IRS-1 (54 +/- 15%) in adipocytes from type 2 diabetic subjects compared to controls with a further significant reduction in expression after long-term treatment (30 +/- 12%) compared to short-term treatment. IRS-2 expression also showed a significant reduction under hyperinsulinaemic conditions (20 +/- 2%) in diabetics vs. controls. Furthermore, long-term treatment with insulin in diabetic adipocytes led to a significant reduction in the phosphorylation of IRS-1(68 +/- 11%), IRS-2 (82 +/- 11%), Akt (42 +/- 2%), and MAPK (92 +/- 12%) and in the subsequent association between p85 to IRS-1 and IRS-2 (100 +/- 16% and 96 +/- 12%) in comparison to controls. Investigating glucose uptake diabetic adipocytes revealed a significant reduction of 90 +/- 2%. In this study, we were able to establish a new diabetic model of primary human adipocytes. A defect in early insulin signalling in type 2 diabetic patients under hyperinsulinaemic conditions was determined. These results might help to give further insights in early insulin action; additionally, this human model represents a useful target for the study of new therapeutic approaches.     

Association of humoral immunity to human Hsp60 with the IL-6 gene polymorphism C-174G in patients with type 2 diabetes and controls.

The relationship between humoral immunity to hsp60 and type 2 diabetes along with other relevant metabolic, inflammatory and immunogenetic variables was studied in 76 non-diabetic and 74 diabetic persons aged 55-74 years selected from the population-based KORA Survey 2000. Antibodies to human hsp60 were measured in serum samples by ELISA. Hsp60 antibodies were detected in all but two individuals in a considerable range of titres (22-1,856 AU/ml). There was no significant association to age and sex, or to key clinical or metabolic parameters (BMI, WHR, HbA1c, total cholesterol, LDL cholesterol, HDL cholesterol, systolic and diastolic blood pressure, albumin, uric acid) or immunological parameters (CRP, IL-6, sIL-6R, TNFalpha, sTNFalpha R60, sTNFalpha R80). Analysis of antibody-positive individuals revealed an association between hsp60 antibodies and diabetes at borderline significance (p = 0.047), which was lost when the two antibody-negative individuals were included. Genetic analyses indicated that this association was significant in carriers of the C allele of the IL-6 promoter region polymorphism at nucleotide -174 (p = 0.02), but not in GG genotype carriers. We conclude that humoral immunity to human hsp60 may be enhanced in those diabetic patients carrying the -174C allele of the IL-6 gene. This finding may contribute to an understanding of the relationship between the -174C allele and increased risk of atherosclerosis.     

Terrestrial carbon balance in a drier world: the effects of water availability in southwestern North America

Global modeling efforts indicate semiarid regions dominate the increasing trend and interannual variation of net CO₂ exchange with the atmosphere, mainly driven by water availability. Many semiarid regions are expected to undergo climatic drying, but the impacts on net CO₂ exchange are poorly understood due to limited semiarid flux observations. Here we evaluated 121 site‐years of annual eddy covariance measurements of net and gross CO₂ exchange (photosynthesis and respiration), precipitation, and evapotranspiration (ET) in 21 semiarid North American ecosystems with an observed range of 100 – 1000 mm in annual precipitation and records of 4–9 years each. In addition to evaluating spatial relationships among CO₂ and water fluxes across sites, we separately quantified site‐level temporal relationships, representing sensitivity to interannual variation. Across the climatic and ecological gradient, photosynthesis showed a saturating spatial relationship to precipitation, whereas the photosynthesis–ET relationship was linear, suggesting ET was a better proxy for water available to drive CO₂ exchanges after hydrologic losses. Both photosynthesis and respiration showed similar site‐level sensitivity to interannual changes in ET among the 21 ecosystems. Furthermore, these temporal relationships were not different from the spatial relationships of long‐term mean CO₂ exchanges with climatic ET. Consequently, a hypothetical 100‐mm change in ET, whether short term or long term, was predicted to alter net ecosystem production (NEP) by 64 gCm^?2 yr^?1. Most of the unexplained NEP variability was related to persistent, site‐specific function, suggesting prioritization of research on slow‐changing controls. Common temporal and spatial sensitivity to water availability increases our confidence that site‐level responses to interannual weather can be extrapolated for prediction of CO₂ exchanges over decadal and longer timescales relevant to societal response to climate change.     

Transport constraints on water use by the Great Basin shrub, Artemisia tridentata

As soil and plant water status decline, decreases in hydraulic conductance can limit a plant's ability to maintain gas exchange. We investigated hydraulic limitations for Artemisia tridentata during summer drought. Water use was quantified by measurements of soil and plant water potential ( Ψ ), transpiration and leaf area. Hydraulic transport capacity was quantified by vulnerability to water stress-induced cavitation for root and stem xylem, and moisture release characteristics for soil. These data were used to predict the maximum possible steady-state transpiration rate ( E _crit) and minimum leaf xylem pressure ( Ψ _crit). Transpiration and leaf area declined by ~ 80 and 50%, respectively, as soil Ψ decreased to –2·6 MPa during drought. Leaf-specific hydraulic conductance also decreased by 70%, with most of the decline predicted in the rhizosphere and root system. Root conductance was projected to be the most limiting, decreasing to zero to cause hydraulic failure if E _crit was exceeded. The basis for this prediction was that roots were more vulnerable to xylem cavitation than stems (99% cavitation at –4·0 versus –7·8 MPa, respectively). The decline in water use during drought was necessary to maintain E and Ψ within the limits defined by E _crit and Ψ _crit.     

Proteolytic activity in the yolk sac membrane of quail eggs.

Extraembryonal degradation of yolk protein is necessary to provide the avian embryo with required free amino acids during early embryogenesis. Screening of proteolytic activity in different compartments of quail eggs revealed an increasing activity in the yolk sac membrane during the first week of embryogenesis. In this tissue, the occurrence of cathepsin B, a lysosomal cysteine proteinase, and cathepsin D, a lysosomal aspartic proteinase, has been described recently (Gerhartz et al., Comp Biochem Physiol, 118B:159-166, 1997). Determination of cathepsin B-like and cathepsin D-like proteolytic activity in the yolk sac membrane indicated a significant correlation between growth of the yolk sac membrane and proteolytic activity, shown by an almost constant specific activity. Both proteinases could be localized in the endodermal cells, which are in direct contact to the yolk. The concentration of proteinases in the endodermal cells appears to be almost unaltered in the investigated early stage of quail development, whereas the amount of endodermal cells increases rapidly, seen by a complicated folding of the yolk sac membrane. In the same cells quail cystatin, a potent inhibitor of quail cathepsin B (Ki 0.6 nM), has been localized at day 8 of embryonic development. Approximately at this stage of development, the quail embryo stops metabolizing yolk. In conclusion, it is strongly indicated that the amount of available free amino acids, produced by proteolytic degradation and supporting embryonic growth, is regulated by the growth of the yolk sac membrane.