Novel DNA Aptamer for CYP24A1 Inhibition with Enhanced Antiproliferative Activity in Cancer Cells

Overexpression of the vitamin D3-inactivating enzyme CYP24A1 (cytochrome P450 family 24 subfamily and hereafter referred to as CYP24) can cause chronic kidney diseases, osteoporosis, and several types of cancers. Therefore, CYP24 inhibition has been considered a potential therapeutic approach. Vitamin D3 mimetics and small molecule inhibitors have been shown to be effective, but nonspecific binding, drug resistance, and potential toxicity limit their effectiveness. We have identified a novel 70-nt DNA aptamer-based inhibitor of CYP24 by utilizing the competition-based aptamer selection strategy, taking CYP24 as the positive target protein and CYP27B1 (the enzyme catalyzing active vitamin D3 production) as the countertarget protein. One of the identified aptamers, Apt-7, showed a 5.8-fold higher binding affinity with CYP24 than the similar competitor CYP27B1. Interestingly, Apt-7 selectively inhibited CYP24 (the relative CYP24 activity decreased by 39.1 ± 3% and showed almost no inhibition of CYP27B1). Furthermore, Apt-7 showed cellular internalization in CYP24-overexpressing A549 lung adenocarcinoma cells via endocytosis and induced endogenous CYP24 inhibition-based antiproliferative activity in cancer cells. We also employed high-speed atomic force microscopy experiments and molecular docking simulations to provide a single-molecule explanation of the aptamer-based CYP24 inhibition mechanism. The novel aptamer identified in this study presents an opportunity to generate a new probe for the recognition and inhibition of CYP24 for biomedical research and could assist in the diagnosis and treatment of cancer.

Macrocyclic Peptide-Conjugated Tip for Fast and Selective Molecular Recognition Imaging by High-Speed Atomic Force Microscopy

Fast and selective recognition of molecules at the nanometer scale without labeling is a much desired but still challenging goal to achieve. Here, we show the use of high-speed atomic force microscopy (HS-AFM) for real-time and real-space recognition of unlabeled membrane receptors using tips conjugated with small synthetic macrocyclic peptides. The single-molecule recognition method is validated by experiments on the human hepatocyte growth factor receptor (hMET), which selectively binds to the macrocyclic peptide aMD4. By testing and comparing aMD4 synthesized with linkers of different lengths and rigidities, we maximize the interaction between the functionalized tip and hMET added to both a mica surface and supported lipid bilayers. Phase contrast imaging by HS-AFM enables us to discriminate nonlabeled hMET against the murine MET homologue, which does not bind to aMD4. Moreover, using ligands and linkers of small size, we achieve minimal deterioration of the spatial resolution in simultaneous topographic imaging. The versatility of macrocyclic peptides in detecting unlimited types of membrane receptors with high selectivity and the fast imaging by HS-AFM broaden the range of future applications of this method for molecular recognition without labeling.

[Gastroesophageal reflux and ventilation with continuous positive pressure. Experimental study]

Gastroesophageal reflux (GER) often occurs in babies receiving respiratory assistance for neonatal distress. The authors examined the lower esophageal sphincter and the thoracic and abdominal pressure conditions in rats under progressively higher continuous positive airway pressure (CPAP) to test the efficacy of the antireflux barrier under such conditions. Intrathoracic and intraabdominal pressures were recorded within the esophagus and within the inferior vena cava in 10 anesthesized 250-g male rats. Pull-through techniques were used for lower esophageal sphincter pressure (LESP) and length (LESL) studies, and the length of the intraabdominal segment of the esophagus (LIASE) was also determined. Measurements were performed in baseline conditions and at CPAP levels of 0, 1, 3, 5 and 7 cm H2O. The respiratory effort progressively increased with prolonged expiration and decreased frequency. LESP and LESL did not change significantly, but the antireflux barrier was weakened by a progressive shortening of LIASE. Successive CPAP increases led to increasingly negative thoracic pressures during inspiration, and increasingly positive abdominal pressure during expiration yielded progressively greater transdiaphragmatic pressure gradients. The authors suggest that CPAP weakens the antireflux barrier and, at the same time, increases the gastroesophageal pressure gradient, thus increasing the risk of GER. Although transpolation of experimental data to the clinical setting is always hazardous, the authors believe this issue should be investigates in infants.

[The defense against infection in the short bowel syndrome]

The high risk of infection in the short-bowel syndrome (SBS) may be due to malnutrition, lost of lymphoid bowel structures or both. Total parenteral nutrition (TPN) may alleviate the malnutrition, but we do not know what will happen with immune response in SBS with good nutritional state. We have studied the cellular immunity (lymphocytic subsets T4 and T8 and T4/T8 ratio) and the humoral one (IgG, IgM, IgA and B lymphocytes) in blood, spleen and mesenteric lymph nodes, in 12 wistar rats with 80% bowel resection, 6 of them with oral feeding and 6 with TPN, and 6 control rats, during 7 days. The weight increased and the total protein, albumin and prealbumin levels were the same in all groups. There was not difference between the resected groups. No difference was observed in the rate of immunoglobulins and the resected groups showed significatively lower figures than the control group in T4, B lymphocytes and T4/T8 ratio in blood, T4 and T8 in mesenteric nodes and in T4 and T4/T8 ratio in the spleen. These results suggest that the resection of large amounts of bowel could produce a fall in the immune response even when adequate nutritional state is preserved.

[Duodenogastric reflux: values in normal children and in children with gastroesophageal reflux]

Duodenogastric reflux (DGR) is a natural event, occurring occasionally and whose pathological significance is not well known. The accuracy of 24-hour gastric pH-metry for the DGR diagnosis has been tested in adults but not in children. For this purpose we measured the area under curve (AUC) at pH 4, 6 and 7 and the percentage of total time above pH 4 (%pH4), 6 (%pH6) and 7 (%pH7), excluding the 2-hours post-prandial period in 88 children suspected of having gastroesophageal reflux (GER). Forty were considered normal whereas 40 had acid GER and 8 with GER. In the control group %pH4 was 9.68 +/- 14.1, %pH6 3.4 +/- 8.7 and %pH7 1.0 +/- 2.4. The values for AUC were 101 +/- 112.8, 16.5 +/- 22.3 and 3.3 +/- 6.1 pH unit/min, respectively. Comparable results were found in the acid GER group. On the other hand alkaline refluxes had higher figures for all parameters: %pH4 22.1 +/- 13.9, %pH6 12 +/- 13 y %pH7 7 +/- 12, AUC at pH 4,406.5 +/- 410, 136.1 +/- 194 at pH6 and 48.2 +/- 85.1 at pH7 (p < 0.05). Because of the large dispersion of values in the control group we selected the 95 percentile, as the upper limit of normal values instead of the mean +/- SD. Therefore the upper limit were 27 for %pH4, 9 for %pH6 and 3.8 for %pH7. The AUC, 316, 64 and 16 pH/min, respectively. These results prove that DGR in children is a very common event and confirm that DGR definitely contributes to alkaline GER.

[Alkaline gastroesophageal reflux. Diagnosis by double-channel pH measurement]

Alkaline gastroesophageal reflux (AGER) has been documented in adult subjects, but few in pediatrics. 24-hours double pH-monitoring was performed in 40 nonrefluxers (control group) and 69 gastroesophageal reflux (RGE) children to quantify AGER. Esophageal phmetric variables were measured at 4 and 7 levels; gastric variables were measured at 4. Forty cases were classified into acid GER, 15 into acid alkaline GER (mixed), 8 into AGER, and 6, with clinical, manometric or endoscopic evidence of GER into "silent" GER. The acid and mixed GER groups had longer periods of acid exposure in esophagus than control, AGER and "silent" GER groups. All groups had long periods of pH > 7 in esophagus. In conclusion, the double gastroesophageal pH monitoring, by verifying the source of alkaline reflux into the esophagus had advantage of better quantifying alkaline reflux over single pH monitoring. AGER might be more frequent in pediatrics than adults.