Inherited epithelial transporter disorders-an overview

In the late 1990s, the identification of transporters and transporter-associated genes progressed substantially due to the development of new cloning approaches such as expression cloning and, subsequently, to the implementation of the human genome project. Since then, the role of many transporter genes in human diseases has been elucidated. In this overview, we focus on inherited disorders of epithelial transporters. In particular, we review genetic defects of the genes encoding glucose transporters (SLC2 and SLC5 families) and amino acid transporters (SLC1, SLC3, SLC6 and SLC7 families).

Gain-of-function haplotype in the epithelial calcium channel TRPV6 is a risk factor for renal calcium stone formation

The rate-limiting step of dietary calcium absorption in the intestine requires the brush border calcium entry channel TRPV6. The TRPV6 gene was completely sequenced in 170 renal calcium stone patients. The frequency of an ancestral TRPV6 haplotype consisting of three non-synonymous polymorphisms (C157R, M378V, M681T) was significantly higher (P = 0.039) in calcium stone formers (8.4%; derived = 502, ancestral = 46) compared to non-stone-forming individuals (5.4%; derived = 645, ancestral = 37). Mineral metabolism was investigated on four different calcium regimens: (i) free-choice diet, (ii) low calcium diet, (iii) fasting and (iv) after a 1 g oral calcium load. When patients homozygous for the derived haplotype were compared with heterozygous patients, no differences were found with respect to the plasma concentrations of 1,25-vitamin D, PTH and calcium, and the urinary excretion of calcium. In one stone-forming patient, the ancestral haplotype was found to be homozygous. This patient had absorptive hypercalciuria. We therefore expressed the ancestral protein (157R+378V+681T) in Xenopus oocytes and found a significantly enhanced calcium permeability when tested by a (45)Ca(2+) uptake assay (7.11 +/- 1.93 versus 3.61 +/- 1.01 pmol/min/oocyte for ancestral versus derived haplotype, P < 0.01). These results suggest that the ancestral gain-of-function haplotype in TRPV6 plays a role in calcium stone formation in certain forms of absorptive hypercalciuria.

Mechanisms and regulation of epithelial Ca2+ absorption in health and disease

Ca2+ is essential for numerous physiological functions in our bodies. Therefore, its homeostasis is finely maintained through the coordination of intestinal absorption, renal reabsorption, and bone resorption. The Ca2+-selective epithelial channels TRPV5 and TRPV6 have been identified, and their physiological roles have been revealed: TRPV5 is important in final renal Ca2+ reabsorption, and TRPV6 has a key role in intestinal Ca2+ absorption. The TRPV5 knockout mice exhibit renal leak hypercalciuria and accordingly upregulate their intestinal TRPV6 expression to compensate for their negative Ca2+ balance. In contrast, despite their severe negative Ca2+ balance, TRPV6-null mice do not display any compensatory mechanism, thus resulting in secondary hyperparathyroidism. These results indicate that the genes for TRPV5 and TRPV6 are differentially regulated in human diseases associated with disturbed Ca2+ balance such as hypercalciuria, osteoporosis, and vitamin D-resistant rickets.

Parotid tumors: fine-needle aspiration and/or frozen section

OBJECTIVE: The purpose of this study was to analyze and compare the value of fine-needle aspiration cytology (FNAC) and frozen section (FS) analysis in the assessment of parotid gland tumors. STUDY DESIGN: Chart review and cross-sectional analysis. SUBJECTS AND METHODS: FNAC and FS analysis of 110 parotid tumors, 68 malignancies and 42 benign tumors, were analyzed and compared with the final histopathologic diagnosis. RESULTS: The accuracy, sensitivity, and specificity of FNAC in detecting malignant tumors were 79 percent, 74 percent, and 88 percent, respectively. On FS analysis, the accuracy, sensitivity, and specificity in detecting malignant tumors were 94 percent, 93 percent, and 95 percent, respectively. The histologic tumor type was correctly diagnosed by FNAC and FS in 27 of 42 (64%) and 39 of 42 (93%) benign tumors, respectively, and in 24 of 68 (35%) and 49 of 68 (72%) malignant neoplasms, respectively. CONCLUSION: The current analysis showed a superiority of FS compared with FNAC regarding the diagnosis of malignancy and tumor typing. FNAC alone is not prone to determine the surgical management of parotid malignancies.

A newly developed in vitro model of the human epithelial airway barrier to study the toxic potential of nanoparticles

The potential health effects of inhaled engineered nanoparticles are almost unknown. To avoid and replace toxicity studies with animals, a triple cell co-culture system composed of epithelial cells, macrophages and dendritic cells was established, which simulates the most important barrier functions of the epithelial airway. Using this model, the toxic potential of titanium dioxide was assessed by measuring the production of reactive oxygen species and the release of tumour necrosis factor alpha. The intracellular localisation of titanium dioxide nanoparticles was analyzed by energy filtering transmission electron microscopy. Titanium dioxide nanoparticles were detected as single particles without membranes and in membrane-bound agglomerates. Cells incubated with titanium dioxide particles showed an elevated production of reactive oxygen species but no increase of the release of tumour necrosis factor alpha. Our in vitro model of the epithelial airway barrier offers a valuable tool to study the interaction of particles with lung cells at a nanostructural level and to investigate the toxic potential of nanoparticles.

In vitro models of the human epithelial airway barrier to study the toxic potential of particulate matter

BACKGROUND: Several epidemiological studies show that inhalation of particulate matter may cause increased pulmonary morbidity and mortality. Of particular interest are the ultrafine particles that are particularly toxic. In addition more and more nanoparticles are released into the environment; however, the potential health effects of these nanoparticles are yet unknown. OBJECTIVES: To avoid particle toxicity studies with animals many cell culture models have been developed during the past years. METHODS: This review focuses on the most commonly used in vitro epithelial airway and alveolar models to study particle-cell interactions and particle toxicity and highlights advantages and disadvantages of the different models. RESULTS/CONCLUSION: There are many lung cell culture models but none of these models seems to be perfect. However, they might be a great tool to perform basic research or toxicity tests. The focus here is on 3D and co-culture models, which seem to be more realistic than monocultures.

Prevention of radiochemotherapy-induced toxicity with amifostine in patients with malignant orbital tumors involving the lacrimal gland: a pilot study

BACKGROUND: To use amifostine concurrently with radiochemotherapy (CT-RT) or radiotherapy (RT) alone in order to prevent dry eye syndrome in patients with malignancies located in the fronto-orbital region. METHODS: Five patients (2 males, 3 females) with diagnosed malignancies (Non-Hodgkin B-cell Lymphoma, neuroendocrine carcinoma) involving the lacrimal gland, in which either combined CT-RT or local RT were indicated, were prophylactically treated with amifostine (500 mg sc). Single RT fraction dose, total dose and treatment duration were individually adjusted to the patient's need. Acute and late adverse effects were recorded using the RTOG score. Subjective and objective dry eye assessment was performed for the post-treatment control of lacrimal gland function. RESULTS: All patients have completed CT-RT or RT as indicated. The median total duration of RT was 29 days (range, 23 - 39 days) and the median total RT dose was 40 Gy (range, 36 - 60 Gy). Median lacrimal gland exposure was 35.9 Gy (range, 16.8 - 42.6 Gy). Very good partial or complete tumor remission was achieved in all patients. The treatment was well tolerated without major toxic reactions. Post-treatment control did not reveal in any patient either subjective or objective signs of a dry eye syndrome. CONCLUSION: The addition of amifostine to RT/CT-RT of patients with tumors localized in orbital region was found to be associated with absence of dry eye syndrome.

Bronchial and bronchovascular sleeve resection for treatment of central lung tumors

BACKGROUND: To improve postoperative pulmonary reserve, we have employed parenchyma-sparing resections for central lung tumors irrespective of pulmonary function. The results of lobectomy, pneumonectomy, and sleeve resection were analyzed retrospectively. METHODS: From October 1995 to June 1999, 422 typical lung resections were performed for lung cancer. Of these, 301 were lobectomies (group I), 81 were sleeve resections (group II), and 40 were pneumonectomies (group III). RESULTS: Operative mortality was 2% in group I, 1.2% in group II, and 7.5% in group III (group I and II vs. group III, p<0.03). Mean time of intubation was 1.0+/-4.1 days in group I, 0.9+/-1.3 days in group II, and 3.6+/-11.2 days in group III (groups I and II vs. group III, p<0.01). The incidence of bronchial complications was 1.3% in group I, none in group II, and 7.5% in group III (group I and II vs group III, p<0.001). After 2 years, survival was 64% in group I, 61.9% in group II, and 56.1% in group III (p = NS). Freedom from local disease recurrence was 92.1% in group I, 95.7% in group II, and 90.9% in group III after 2 years (p = NS). CONCLUSIONS: Sleeve resection is a useful surgical option for the treatment of central lung tumors, thus avoiding pneumonectomy with its associated risks. Morbidity, early mortality, long-term survival, and recurrence of disease after sleeve resection are similar to those seen after lobectomy.

The cranial bone window model: studying angiogenesis of primary and secondary bone tumors by intravital microscopy

The successful treatment of primary and secondary bone tumors in a huge number of cases remains one of the major unsolved challenges in modern medicine. Malignant primary bone tumor growth predominantly occurs in younger people, whereas older people predominantly suffer from secondary bone tumors since up to 85% of the most frequently occurring malignant solid tumors, such as lung, mammary, and prostate carcinomas, metastasize into the bone. It is well known that a tumor's course may be altered by its surrounding tissue. For this reason, reported here is the protocol for the surgical preparation of a cranial bone window in mice as well as the method to implant tumors in this bone window for further investigations of angiogenesis and other microcirculatory parameters in orthotopically growing primary or secondary bone tumors using intravital microscopy. Intravital microscopy represents an internationally accepted and sophisticated experimental method to study angiogenesis, microcirculation, and many other parameters in a wide variety of neoplastic and nonneoplastic tissues. Since most physiologic and pathophysiologic processes are active and dynamic events, one of the major strengths of chronic animal models using intravital microscopy is the possibility of monitoring the regions of interest in vivo continuously up to several weeks with high spatial and temporal resolution. In addition, after the termination of experiments, tissue samples can be excised easily and further examined by various in vitro methods such as histology, immunohistochemistry, and molecular biology.

EpCAM-targeted delivery of nanocomplexed siRNA to tumor cells with designed ankyrin repeat proteins

Specific delivery to tumors and efficient cellular uptake of nucleic acids remain major challenges for gene-targeted cancer therapies. Here we report the use of a designed ankyrin repeat protein (DARPin) specific for the epithelial cell adhesion molecule (EpCAM) as a carrier for small interfering RNA (siRNA) complementary to the bcl-2 mRNA. For charge complexation of the siRNA, the DARPin was fused to a truncated human protamine-1 sequence. To increase the cell binding affinity and the amount of siRNA delivered into cells, DARPin dimers were generated and used as fusion proteins with protamine. All proteins expressed well in Escherichia coli in soluble form, yet, to remove tightly bound bacterial nucleic acids, they were purified under denaturing conditions by immobilized metal ion affinity chromatography, followed by refolding. The fusion proteins were capable of complexing four to five siRNA molecules per protamine, and fully retained the binding specificity for EpCAM as shown on MCF-7 breast carcinoma cells. In contrast to unspecific LipofectAMINE transfection, down-regulation of antiapoptotic bcl-2 using fusion protein complexed siRNA was strictly dependent on EpCAM binding and internalization. Inhibition of bcl-2 expression facilitated tumor cell apoptosis as shown by increased sensitivity to the anticancer agent doxorubicin.

A functional model for adult stem cells in epithelial tissues

Tissue turnover, regeneration, and repair take place throughout life. Stem cells are key players in these processes. The characteristics and niches of the stem cell populations in different tissues, and even in related tissues, vary extensively. In this review, stem cell differentiation and stem cell contribution to tissue maintenance and regeneration is compared in the epithelia of the skin, the cornea, the lung, and the intestine. A hierarchical model for adult stem cells is proposed, based on the potency of stem cell subpopulations in a specific tissue. The potency is defined in terms of the maintenance, the repair, and the regeneration of the tissue. The niche supplies cues to maintain the specific stem cell potency.