Do patients with small intestinal neuroendocrine tumors (SI-NETs) develop hyperkeratosis and skin fibrosis secondary to chronic hyperserotoninemia?

Abstract

Background: Small intestinal neuroendocrine tumors (SI-NETs) are considered to be lowprevalent, slow-growing tumors with an incidence of approximately 50 new cases per year in Norway. The SI-NETs are associated with a high morbidity due to the effects of the hormones produced by the tumor. The clinical picture is characterized by flushing, diarrhea and bronchoconstriction, and is in later stages of the disease associated with valvular heart fibrosis. Several studies also indicate a correlation between elevated serum levels of serotonin produced by the tumor and fibrotic, scleroderma-like lesions in SI-NET patients. The mechanism behind these hyperkeratotic skin changes remains largely unknown.

Aims: The long-term purpose of this project is to study the mechanisms behind the fibrotic skin lesions that some patients with SI-NETs experience. The aim of the current project is evaluation of suitable methods for investigation of these skin changes.

Methods: Nine SI-NET patients with characteristic symptomatology and biochemically proven hyperserotoninemia and an age and sex adjusted control group (n=10) were included in the study. Three punch biopsies of the skin from the upper gluteal region and two blood samples were collected from each subject. In addition, skin biopsies were collected from 11 Sprague Dawley rats, whereof six had been given serotonin injections and the remaining five were healthy controls. RNA was isolated from the human and rat skin biopsies, and the gene expression was assessed using microarray (human) and RNA sequencing (rat). Serial sections were made from the human skin biopsies for histological and immunohistological analysis and for in situ hybridization. Radioimmunoassay was used to determine the chromogranin A (CgA) levels of the human serum samples.

Results: The RNA sequencing showed that 340 genes had a significantly differentiated expression. As expected, many of these genes are known to be involved in pathways associated with fibrosis and inflammation. The protocols for immunohistochemistry and in situ hybridization were largely successful with correspondent results. The RIA analysis showed that 8 of 9 patients had elevated levels of CgA on the time of blood sample collection.

Discussion: The hypothesis of this thesis has been that a high serum level of serotonin can influence the skin through activation of specific receptor molecules leading to hyperkeratosis and fibrotic skin lesions. Analyses from the sequencing show that genes involved in pathways associated with fibrosis and inflammation are significantly differentially expressed. As serotonin is associated with the same pathways, this is an expected result. In further research we hope to find candidate genes from the genetical data provided by the RNA sequencing and microarray analysis. The objective is to investigate these genes using immunohistochemistry (IHC) and in situ hybridization (ISH).