Sensitive determination of D-lactic acid and L-lactic acid in urine by high-performance liquid chromatography-tandem mass spectrometry

D-lactic acid in urine originates mainly from bacterial production in the intestinal tract. Increased D-lactate excretion as observed in patients affected by short bowel syndrome or necrotizing enterocolitis reflects D-lactic overproduction. Therefore, there is a need for a reliable and sensitive method able to detect D-lactic acid even at subclinical elevation levels. A new and highly sensitive method for the simultaneous determination of L- and D-lactic acid by a two-step procedure has been developed. This method is based on the concentration of lactic acid enantiomers from urine by supported liquid extraction followed by high-performance liquid chromatography-tandem mass spectrometry. The separation was achieved by the use of an Astec Chirobiotic™ R chiral column under isocratic conditions. The calibration curves were linear over the ranges of 2-400 and 0.5-100 µmol/L respectively for L- and D-lactic acid. The limit of detection of D-lactic acid was 0.125 µmol/L and its limit of quantification was 0.5 µmol/L. The overall accuracy and precision were well within 10% of the nominal values. The developed method is suitable for production of reference values in children and could be applied for accurate routine analysis.

Characterization of the expression and activation of the epidermal growth factor receptor in squamous cell carcinoma of the skin

BACKGROUND

Locally advanced skin cancers including squamous cell carcinoma (SCC) of the skin are increasing in incidence. Patients are often elderly with significant comorbidities and therapy can be difficult. New targeted therapies, such as treatment directed at the epidermal growth factor receptor (EGFR), may be effective and less toxic in these patients. However, before designing appropriate clinical trials it is necessary to characterize the expression and activation of targets such as the EGFR to evaluate the rationale of using EGFR inhibitors (EGFRIs) in the treatment of this type of cancer.

OBJECTIVES

To characterize the expression and activation by phosphorylation of EGFR in SCC of the skin by quantitative Western blotting using the LiCor immunofluorescence detection system with validation by immunohistochemistry. Secondary objectives were to evaluate downstream targets of EGFR expression and activation in SCC of the skin and to examine the associations between EGFR, pathological features and clinical behaviour of these tumours.

METHODS

Twenty-one mainly locally advanced skin SCCs collected in our institution and stored in our tissue bank over a 4-year period were used for the study.

RESULTS

Nine of 21 (43%) tumours expressed EGFR above background. Of those nine, five expressed phosphorylated EGFR. There was no correlation with downstream activation of canonical signalling pathways, pathological features or clinical behaviour.

CONCLUSIONS

EGFR is expressed in a minority of tumours and then is not always activated. These results show that, before designing a trial with a targeted agent such as an EGFRI in SCC of the skin, it is important to verify the presence of the appropriate target to maximize the best outcome.

Differential regulation by calcium reveals distinct signaling requirements for the activation of Akt and p70S6k

Activation of the phosphatidylinositol 3-kinase (PI3K) plays an important role in the mitogenic response of many cell types. Recently, two serine/threonine kinases Akt and p70(S6k) have been identified as physiological targets of PI3K. Observations that expression of activated forms of Akt led to the activation of p70(S6k) implied Akt might mediate mitogenic signaling through activation of p70(S6k). To clarify the relationship between signaling through these two kinases, we have examined their regulation by various mitogenic stimuli. In this study we have focused on the role of calcium in the regulation of each kinase in Balb/c-3T3 fibroblasts. Depletion of intracellular calcium stores by EGTA pretreatment has no effect on growth factor-induced Akt activation but completely abolishes p70(S6k) stimulation. Increase of intracellular calcium induced by ionomycin or thapsigargin results in a full activation of p70(S6k), whereas little or no activation of Akt is observed. Furthermore, although PI3K in anti-phosphotyrosine immunoprecipitates is only very weakly activated by ionomycin, the calcium-induced stimulation of p70(S6k) is completely inhibited by the specific PI3K inhibitor wortmannin. We conclude Akt and p70(S6k) lie on separate signaling pathways. Activation of signaling to Akt is insufficient for the activation of p70(S6k), which can be achieved independently of Akt. p70(S6k) requires a separate calcium-dependent and wortmannin-sensitive process that is likely to be independent of type IA PI3K family members.

Effect of heat stress on glucose kinetics during exercise

To identify the mechanism underlying the exaggerated hyperglycemia during exercise in the heat, six trained men were studied during 40 min of cycling exercise at a workload requiring 65% peak pulmonary oxygen uptake (VO2peak) on two occasions at least 1 wk apart. On one occasion, the ambient temperature was 20 degrees C [control (Con)], whereas on the other, it was 40 degrees C [high temperature (HT)]. Rates of glucose appearance and disappearance were measured by using a primed continuous infusion of [6,6-2H]glucose No differences in oxygen uptake during exercise were observed between trials. After 40 min of exercise, heart rate, rectal temperature, respiratory exchange ratio, and plasma lactate were all higher in HT compared with Con (P < 0.05). Plasma glucose levels were similar at rest (Con, 4.54 +/- 0.19 mmol/l; HT, 4.81 +/- 0.19 mmol/l) but increased to a greater extent during exercise in HT (6.96 +/- 0.16) compared with Con (5.45 +/- 0.18; P < 0.05). This was the result of a higher glucose rate of appearance in HT during the last 30 min of exercise. In contrast, the glucose rate of disappearance and metabolic clearance rate were not different at any time point during exercise. Plasma catecholamines were higher after 10 and 40 min of exercise in HT compared with Con (P < 0.05), whereas plasma glucagon, cortisol, and growth hormone were higher in HT after 40 min. These results indicate that the hyperglycemia observed during exercise in the heat is caused by an increase in liver glucose output without any change in whole body utilization.