Endocrine cells in tumour-bearing lungs

Neuron-Specific Enolase in Non-Neoplastic Lung Diseases, a Marker of Hypoxemia?

Neuron-specific enolase (NSE) is a glycolytic enzyme localized within neuronal and neuroendocrine tissues. Serum NSE is widely used as a marker of neuroendocrine tumors. Moderate serum NSE elevation has been reported in some patients with benign lung diseases. We decided to investigate whether the elevation of serum NSE in non-neoplastic lung diseases is connected with hypoxemia and to what extent the recovery of sufficient ventilation with a respirator may influence NSE concentrations. Serum NSE was estimated by means of radioimmunoassay in 83 patients with various non-neoplastic lung diseases. Serum NSE exceeding 12.5 μg/L was significantly more frequent in patients with marked hypoxemia (PaO2<6.67 kPa; p=0.03) than in others. The median NSE value in the group of patients without respiratory failure (Ro) was 7.2 μg/L (10% >12.5 μg/L), in the group of patients with respiratory failure not requiring mechanical ventilation (Rf) it was 8.5 μg/L (24%>12.5 μg/L), and in the group of patients with respiratory failure requiring mechanical ventilation (Rfv) 13.1 μg/L (60%>12.5 μg/L). The differences between the Rfv group and the other two groups (Rf and Ro) were significant (p=0.049 and p=0.0004, respectively). During successful mechanical ventilation elevated serum NSE decreased to values below the cutoff in 8/10 patients. We conclude that serum NSE elevation is a frequent event in patients with terminal hypoxemia in the course of benign lung diseases. Normalization of serum NSE is observed in the majority of patients during the first week of mechanical ventilation.

Wild-type and splice-variant secretin receptors in lung cancer: overexpression in carcinoid tumors and peritumoral lung tissue

Gastrointestinal peptide hormone receptors, like somatostatin receptors, are often overexpressed in human cancer, allowing receptor-targeted tumor imaging and therapy. A novel candidate for these applications is the secretin receptor recently identified in pancreatic and cholangiocellular carcinomas. In the present study, secretin receptors were assessed in a non-gastrointestinal tissue, the human lung. Non-small-cell lung cancers (n=26), small-cell lung cancers (n=10), bronchopulmonary carcinoid tumors (n=29), and non-neoplastic lung (n=46) were investigated for secretin receptor protein expression with in vitro receptor autoradiography, using (125)I-[Tyr(10)] rat secretin and for secretin receptor transcripts with RT-PCR. Secretin receptor protein expression was found in 62% of bronchopulmonary carcinoids in moderate to high density, in 12% of non-small cell lung cancers in low density, but not in small cell lung cancers. In tumors found to be secretin receptor positive by autoradiography, RT-PCR revealed transcripts for the wild-type secretin receptor and for novel secretin receptor splice variants. In the non-neoplastic lung, secretin receptor protein expression was observed in low density along the alveolar septa in direct tumor vicinity in cases of acute inflammation, but not in histologically normal lung. In the autoradiographically positive peritumoral lung, RT-PCR showed transcripts for the wild-type secretin receptor and for a secretin receptor spliceoform different from those occurring in lung and gut tumors. In conclusion, secretin receptors are new markers for bronchopulmonary carcinoid tumors, and represent the molecular basis for an in vivo targeting of carcinoid tumors for diagnosis and therapy. Furthermore, secretin receptors may play a role in peritumoral lung pathophysiology. Secretin receptor mis-splicing specifically occurs in tumor and non-tumor lung pathology.

Functional facets of the pulmonary neuroendocrine system

Pulmonary neuroendocrine cells (PNECs) have been around for 60 years in the scientific literature, although phylogenetically they are ancient. Their traditionally ascribed functions include chemoreception and regulation of lung maturation and growth. There is recent evidence that neuroendocrine (NE) differentiation in the lung is regulated by genes and pathways that are conserved in the development of the nervous system from Drosophila to humans (such as achaete-scute homolog-1), or implicated in the carcinogenesis of the nervous or NE system (such as the retinoblastoma tumor suppressor gene). In addition, complex neural networks are in place to regulate chemosensory and other functions. Even solitary PNECs appear to be innervated. For the first time ever, we have mouse models for lung NE carcinomas, including the most common and virulent small cell lung carcinoma. Moreover, PNECs may be important for inflammatory responses, and pivotal for lung stem cell niches. These discoveries signify an exciting new era for PNECs and are likely to have therapeutic and diagnostic applications.

Pulmonary neuroendocrine cell system in pediatric and adult lung disease

In humans lungs affected by naturally occurring pulmonary disease, the pulmonary neuroendocrine cell system, which is normally arranged in a sparse but even distribution throughout the respiratory tract, increases in size. It is likely that the stimulus for this is pulmonary injury and that its purpose is the paracrine regulation of the restoration of pulmonary tissues to their normal state, an hypothesis supported by studies of animal lungs subjected to experimental injury as well as of the development of human and animal lungs in utero. Initially, this increase involves the development of interrupted rows of neuroendocrine cells. In the later stages, however, development of more disorderly intraepithelial aggregates can occur and the small, locally invasive neuroendocrine cell lesions known as tumourlets may occasionally result. Both of these latter structures often contain secretory products not found in the neuroendocrine cells of normal human lungs, probably indicating a derangement of what appears to be a fundamentally physiological response. It is likely that, in some circumstances, this disorderly change may contribute to pulmonary disease as well as being the result of it.