Intracellular carbonic anhydrase activity sensitizes cancer cell pH signaling to dynamic changes in CO2 partial pressure.

Carbonic anhydrase (CA) enzymes catalyze the chemical equilibration among CO2, HCO3(-) and H(+). Intracellular CA (CAi) isoforms are present in certain types of cancer, and growing evidence suggests that low levels correlate with disease severity. However, their physiological role remains unclear. Cancer cell CAi activity, measured as cytoplasmic CO2 hydration rate (kf), ranged from high in colorectal HCT116 (∼2 s(-1)), bladder RT112 and colorectal HT29, moderate in fibrosarcoma HT1080 to negligible (i.e. spontaneous kf = 0.18 s(-1)) in cervical HeLa and breast MDA-MB-468 cells. CAi activity in cells correlated with CAII immunoreactivity and enzymatic activity in membrane-free lysates, suggesting that soluble CAII is an important intracellular isoform. CAi catalysis was not obligatory for supporting acid extrusion by H(+) efflux or HCO3(-) influx, nor for maintaining intracellular pH (pHi) uniformity. However, in the absence of CAi activity, acid loading from a highly alkaline pHi was rate-limited by HCO3(-) supply from spontaneous CO2 hydration. In solid tumors, time-dependence of blood flow can result in fluctuations of CO2 partial pressure (pCO2) that disturb cytoplasmic CO2-HCO3(-)-H(+) equilibrium. In cancer cells with high CAi activity, extracellular pCO2 fluctuations evoked faster and larger pHi oscillations. Functionally, these resulted in larger pH-dependent intracellular [Ca(2+)] oscillations and stronger inhibition of the mTORC1 pathway reported by S6 kinase phosphorylation. In contrast, the pHi of cells with low CAi activity was less responsive to pCO2 fluctuations. Such low pass filtering would "buffer" cancer cell pHi from non-steady-state extracellular pCO2. Thus, CAi activity determines the coupling between pCO2 (a function of tumor perfusion) and pHi (a potent modulator of cancer cell physiology).

A Case of Small Bowel Obstruction and Enterocutaneous Fistulation Resulting from a Mesenteric Haematoma following Blunt Abdominal Trauma.

A 23-year-old male with a history of previous abdominal surgery was involved in a road traffic accident. He was discharged after initial assessment but represented several days with small bowel obstruction secondary to a mesenteric haematoma. He underwent resection and recovered well but represented later on the day of discharge with a leaking surgical wound consistent with an enterocutaneous fistula. This was managed conservatively and closed spontaneously after ten days. This case serves to highlight that adhesions from previous surgery can tether the small bowel causing mesenteric injury following blunt-force trauma. It also demonstrates that postoperative ileus can result in an enterocutaneous fistula that has the appearance of an anastomotic breakdown but which resolves more rapidly.

What Evidence Underlies Clinical Practice in Paediatric Surgery? A Systematic Review Assessing Choice of Study Design.

OBJECTIVE: Identify every paediatric surgical article published in 1998 and every paediatric surgical article published in 2013, and determine which study designs were used and whether they were appropriate for robustly assessing interventions in surgical conditions. METHODS: A systematic review was conducted according to a pre-specified protocol (CRD42014007629), using EMBASE and Medline. Non-English language studies were excluded. Studies were included if meeting population criteria and either condition or intervention criteria. POPULATION: Children under the age of 18, or adults who underwent intervention for a condition managed by paediatric surgeons when they were under 18 years of age. CONDITION: One managed by general paediatric surgeons. INTERVENTION: Used for treatment of a condition managed by general paediatric surgeons. MAIN OUTCOME MEASURE: Studies were classified according to whether the IDEAL collaboration recommended their design for assessing surgical interventions or not. Change in proportions between 1998 and 2013 was calculated. RESULTS: 1581 paediatric surgical articles were published in 1998, and 3453 in 2013. The most commonly used design, accounting for 45% of studies in 1998 and 46.8% in 2013, was the retrospective case series. Only 1.8% of studies were RCTs in 1998, and 1.9% in 2013. Overall, in 1998, 9.8% of studies used a recommended design. In 2013, 11.9% used a recommended design (proportion increase 2.3%, 95% confidence interval 0.5% increase to 4% increase, p = 0.017). CONCLUSIONS AND RELEVANCE: A low proportion of published paediatric surgical manuscripts utilise a design that is recommended for assessing surgical interventions. RCTs represent fewer than 1 in 50 studies. In 2013, 88.1% of studies used a less robust design, suggesting the need for a new way of approaching paediatric surgical research.