Validation of antibody-based assays for regulatory peptides: Do it once, get it right, and exploit the under-appreciated benefit of long-term antibody stability

Many submitted manuscripts utilizing antibody-based assays for biologically active peptides frequently neither include nor cite adequate validation data with the risk that the report is adding to the reproducibility crisis in biological research. On the basis of recent experience in re-characterizing in a radioimmunoassay format a polycolonal antibody to gastrin that was first raised nearly five decades ago, it is argued that some antibodies can be stable for very many decades. Researchers concerned about the reproducibility of data using antibodies in assays for regulatory peptides should therefore note that by rigorous validation at an early stage they may not only contribute to the resolution of the reproducibility crisis but also establish a resource that could be useful for very many years.

Abstract 5057: Activation of stroma-derived matrix metalloproteinases (MMPs) in a model of gastric cancer

Gastric cancer is the second commonest cause of cancer-related death worldwide. Within these tumors, it is increasingly recognised that signaling between myofibroblasts, an important stromal cell type, and cancer cells results in proliferation, invasion and metastasis. However, little is known of the range of proteins secreted by stromal cells ie their secretome, or the contribution of proteases in shaping the extracellular milieu ie the cancer degradome.

Using SILAC labeling and combined fractional diagonal chromatography (COFRADIC) we identified and quantified differential abundance and appearance of neo-N-termini (ie cleavage products) in the secretomes of gastric cancer-associated myofibroblasts (CAMs) compared with myofibroblasts from adjacent tissue (ATMs). There was decreased abundance of many proteins in CAM secretomes, but a small sub-set exhibited increased abundance including matrix metalloproteinases (MMP) -1 and -3. Cancer-restricted proteolytic cleavages included cleavage in the prodomains of MMP-1, -2 and -3 consistent with activation. Western blot, enzyme activity and cancer cell migration assays verified significantly increased abundance of active MMP-1, -2 and -3 in CAM media.

To establish the in vivo relevance of these findings we utilized a model in which primary gastric CAMs stimulate growth of MKN45 gastric cancer cells in xenografts in nude mice. MMP activity was imaged by fluorescence molecular tomography (FMT) employing MMPSense750 FAST™, which produces a fluorescent signal following MMP cleavage. CAMs enhanced xenograft growth by 6-fold (mean ± SEM, 29.6±21.1 vs 196.8±32.2 mm3 n=12, p=0.004). Using an experimental design that achieved similar volumes for tumors containing MKN45 cells alone and those containing MKN45+CAM, FMT assessment of tumor-related MMP activity in vivo indicated a two-fold increase in CAM-MKN45 xenografts compared with MKN45 cells alone (0.9±0.4 vs 1.8±0.8 fmol/mm3).

Stromal cell secretomes therefore contribute to the remodelling of the cancer cell microenvironment by activation of MMPs with consequences for cell migration and tumor growth. This system has potential for in vivo screening of anti-cancer therapies directed at the inhibition of stroma-stimulated tumor growth.

Citation Format: Sandhir Kandola, Christopher Holmberg, Bart Ghesquiere, Francis Impens, Kris Gevaert, J. Dinesh Kumar, Nicole Cash, Peter Hegyi, Nikolina Vlatkovic, Timothy Wang, Graham Dockray, Andrea Varro. Activation of stroma-derived matrix metalloproteinases (MMPs) in a model of gastric cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5057. doi:10.1158/1538-7445.AM2013-5057

Gut endocrine secretions and their relevance to satiety

The three major regions of the gastrointestinal tract (stomach, upper small intestine, ileum/colon) are each the source of factors influencing food intake. These can enhance appetite or, conversely, inhibit it. The active factors include hormones, lipid mediators, nutrients and gastric distension. Vagal afferent neurons mediate the effects of some gut signals on the brain, but other gut hormones also act directly on the brain in areas where the blood-brain barrier can be penetrated. Many different interactions between these factors are now emerging. Collectively, this system presents an array of new potential targets in seeking to modify energy intake.

Gastrin: old hormone, new functions

It is exactly a century since the gastric hormone gastrin was first described as a blood-borne regulator of gastric acid secretion. The identities of the main active forms of the hormone (the "classical gastrins") and their cellular and molecular sites of action in regulating acid secretion have all attracted sustained attention. However, recent work on peptides derived from the gastrin precursor that do not stimulate acid secretion ("non-classical gastrins"), together with studies on mice over-expressing the gene, or in which the gastrin gene has been deleted, suggest hitherto unsuspected roles in regulating cell proliferation, migration, and differentiation. Moreover, microarray and proteomic studies have identified previously unsuspected target genes of the classical gastrins. Some of the newer actions have implications for our understanding of the progression to cancer in oesophagus, stomach, pancreas and colon, all of which have recently been linked in one way or another to dysfunctional signalling involving products of the gastrin gene. The present review focuses on recent progress in understanding the biology of both classical and non-classical gastrins.

Helicobacter pylori-associated gastric cancer in INS-GAS mice is gender specific

Previous studies from our group have shown that hypergastrinemia in mice can synergize with Helicobacter felis infection to induce gastric carcinoma. In addition, epidemiological evidence and a recent study with C57BL/6 mice have strongly suggested a link between a high-salt diet during Helicobacter pylori infection and the development of hypergastrinemia and preneoplastic gastric lesions. To address the possible relationship between the two cofactors (gastrin and salt) and whether H. pylori can also lead to gastric cancer in this model, we undertook a longitudinal study involving 86 INS-GAS mice. The mice were fed either a high-salt (7.5%) or basal (0.25%) diet, and half were infected with H. pylori. Necropsies at 5 and 7 months postinfection included histopathological examination, quantitative culturing for bacterial colonization levels, and serology to estimate the magnitude of the Th1 and Th2 systemic inflammatory responses. Lesions consistent with in situ and intramucosal carcinoma were seen in H. pylori-infected male mice only. There was a highly significant main effect for Helicobacter infection status for all fundic and antral lesion parameters (P < 0.0001), as well as significant interactions of infection status with diet for all of the fundic parameters (all P < 0.03), except intestinal metaplasia. In subsequent ANOVAs in which the data were limited to that from infected animals, there was a highly significant main effect for time, diet, and gender (all P < 0.02) on all of the corpus lesion parameters scored (inflammation, atrophy, hyperplasia, metaplasia, and dysplasia/neoplasia). In addition, gender interacted significantly with time (all P < 0.03), and. H. pylori colonization increased quantitatively over the course of the experiment but were independent of either diet or gender. The Th1-associated serum IgG2a responses to H. pylori increased from the time of experimental infection to necropsy at 5 or 7 months and were similar among all experimentally infected mice with no influence of gender (P > 0.10) or dietary salt (P > 0.27). In contrast, the Th2-associated serum IgG1 response to H. pylori was significantly increased in infected male INS-GAS mice on the high-salt diet at 7 months postinfection (P < 0.012). These results show that H. pylori can also accelerate the development of gastric cancer in the INS-GAS mouse model, and the results suggest that salt has less of a procarcinogenic effect in the setting of endogenous hypergastrinemia. The increased Th2-associated humoral response of the infected male mice on the high-salt diet correlated with less severe gastric lesions. In the INS-GAS mouse model, male gastric tissue responded more rapidly and aggressively to H. pylori infection, high-salt diet, and the combination when compared with females; a finding that appears consistent with the greater incidence of gastric carcinoma in men. This study highlights the importance of using both genders to investigate the pathogenesis of H. pylori.

Expression and regulation of cholecystokinin and cholecystokinin receptors in rat nodose and dorsal root ganglia

Cholecystokinin (CCK) is an important satiety factor, acting via the vagus nerve to influence central feeding centers. CCK binding sites have been demonstrated in the vagal sensory nodose ganglion and within the nerve proper. Using in situ hybridization, expression of the CCK(A) and (B) receptors (Rs), as well as of CCK itself, was studied in the normal nodose ganglion (NG), and after vagotomy, starvation and high-fat diet. CCK(A)-R mRNA expression in dorsal root ganglia (DRGs) was also explored. In the NG, 33% of the neuron profiles (NPs) contained CCK(A)-R mRNA and in 9% we observed CCK(B)-R mRNA. CCK mRNA was not found in normal NGs. Peripheral vagotomy decreased the number of CCK(A)-R mRNA-expressing NPs, dramatically increased the number of CCK(B)-R mRNA, and induced CCK mRNA and preproCCK-like immunoreactivity in nodose NPs. No significant differences in the number of NPs labelled for either mRNA species were detected following 48 h food deprivation or in rats fed a high-fat content diet. In DRGs, 10% of the NPs expressed CCK(A)-R mRNA, a number that was not affected by either axotomy or inflammation. This cell population was distinct from neurons expressing calcitonin gene-related peptide mRNA. These results demonstrate that the CCK(A)-R is expressed by both viscero- and somatosensory primary sensory neurons, supporting a role for this receptor as a mediator both of CCK-induced satiety and in sensory processing at the spinal level. The stimulation of CCK and CCK(B)-R gene expression following vagotomy suggests a possible involvement in the response to injury for these molecules.

Cholecystokinin in cortico-striatal neurons in the rat: immunohistochemical studies at the light and electron microscopical level

Using immunohistochemical techniques we have analysed the occurrence of cholecystokinin-like immunoreactivity (CCK-LI) in the cortex and striatum of the rat. In the cortex few CCK-immunoreactive cell bodies, mainly interneurons, could be visualized in normal brains, and a moderately dense network of CCK fibres was also observed. Injections of colchicine into the striatum led to an accumulation, in the surrounding cortex, of CCK-LI in the initial segment of the axon of numerous cells. In addition, with an antibody to pro-CCK several cell bodies, many of which with pyramidal shape, could be visualized. Furthermore, retrograde staining of cortical cells after unilateral injection of wheat germ agglutinin into the striatum revealed bilaterally in the cortex a number of labelled cells that also contained pro-CCK-LI. In the striatum CCK-LI was diffusely distributed in fine fibres as well as in patches of fibres located in the medial aspects. After decortication followed by callosotomy these patches disappeared on the side ipsilateral to the lesion, while the pattern of immunoreactivity of several other peptides in the striatum was unaffected. No change was observed on the contralateral side. Decortication or callosotomy alone did not affect the pattern of CCK-LI. At the ultrastructural level several CCK-immunoreactive terminals could be observed, mostly with clear, densely packed vesicles and straight asymmetric synaptic contacts with small spines, characteristic for terminals of cortical origin. The results are consistent with the presence of a major, partly crossed, CCK-containing cortico-striatal pathway.

A subpopulation of dopaminergic neurons in rat ventral mesencephalon contains both neurotensin and cholecystokinin

The coexistence of the neuropeptides neurotensin and cholecystokinin and the catecholamine-synthesizing enzyme tyrosine hydroxylase within neurons of the ventral mesencephalon was analyzed using an immunofluorescence triple-labeling technique. Virtually all of the neurotensin-positive cell bodies in the ventral tegmental area, medial substantia nigra pars compacta, retrorubral field, and rostral and caudal linear raphe nuclei were found to contain both cholecystokinin and tyrosine hydroxylase immunoreactivities. The degree of colocalization was lower and more variable in other regions including the ventral and central periaqueductal grey matter and dorsal raphe nucleus. It appeared that immunoreactivities for these 3 neuroactive substances were not contained within the same axonal-like fibers and terminals in the ventral midbrain. These results demonstrate that a subpopulation of dopaminergic neurons, which presumably comprise part of the ascending mesotelencephalic system, contains the two peptides neurotensin and cholecystokinin. Thus, the data suggest a morphological basis for some of the reported functional interactions of these 3 putative neurotransmitters/neuromodulators within this system.

Cellular origins of different forms of gastrin. The specific immunocytochemical localization of related peptides

We have localized the antigenic determinants for the main forms of gastrin (big gastrin, G34, and little gastrin, G17) in hog antral mucosa using sequence specific antibodies and an indirect immunofluorescence technique. Populations of monospecific antibodies were obtained after affinity immunoadsorption to remove populations of unwanted specificity. The specificity of the purified antisera was established by direct binding of 125I labeled peptides to antisera at the same dilutions as those used in immunocytochemistry. The results indicate that in hog antral mucosa there is a single population of cells with the antigenic determinants of the C-terminal region of G17 and G34, the N-terminal region of G17, the N-terminal region of G34, and the intact G17 molecule. In duodenum there are cells with only C-terminal reactivity; since gastrin and CCK share a common C-terminal sequence it is concluded that this cell type contains CCK-like peptides rather than gastrin.

The hypothalamic arcuate nucleus-median eminence complex: immunohistochemistry of transmitters, peptides and DARPP-32 with special reference to coexistence in dopamine neurons

In this paper, we describe the results of a series of experiments which have examined the distribution within the arcuate nucleus of the hypothalamus of neurons containing the following immunoreactivities: TH-LI, GAD-LI, NT-LI, GAL-LI, GRF-LI, Met-ENK-LI, Leu-ENK-LI, Met-ENK-7-LI, Met-ENK-8-LI, metorphamide-LI, DYN-LI, NPY-LI, SOM-LI, FMRFamide-LI, and CLIP-LI and ependymal tanycytes containing DARPP-32-LI. Using elution-restaining and double antibody staining techniques we have established numerous patterns of coexistence of these various neurotransmitters and neuropeptides. Thus, neurons containing TH-LI were, in some instances, also found to contain GAD-LI, NT-LI, GAL-LI, GRF-LI, Met-ENK-8-LI, Leu-ENK-LI, or DYN-LI or combinations of these compounds. For example, some TH-IR neurons also contained GAL-LI and GRF-LI, while other TH-IR. neurons were also seen to contain GRF- and NT-LI. These neurons may, in fact, contain even more compounds. NPY-IR neurons and those containing SOM-LI and CLIP-LI were distinct and separate from those containing TH-LI. The distribution of these different neurochemical types of neurons and their patterns of coexistence are summarized in Fig. 34, while the relative distribution patterns of immunoreactive fibres in the median eminence are summarized in Fig. 35.

Evidence for periaqueductal cholecystokinin-substance P neurons projecting to the spinal cord

Using indirect immunofluorescence techniques combined with retrogradely transported fluorescent dyes, cholecystokinin (CCK)-like and substance P immunoreactive cell bodies in the periaqueductal central grey of the rat brain were studied. Data from both adjacent sections and elution-restaining techniques indicated that some of these central grey cells contain both a CCK-like peptide and substance P. Injection of the fluorescent dye, Fast Blue, into the cervical spinal cord indicated that this CCK-substance P cell group is a descending system. These findings provide evidence for two peptides in a single neuron, and the possible functional significance of such an occurrence is discussed.

Immunohistochemical demonstration of peptides, serotonin and dopamine-beta-hydroxylase-like material in the nervous system of the leech Hirudo medicinalis

The central ganglia of the leech, Hirudo medicinalis, were processed for the immunohistochemical localisation of bombesin-, substance P-, cholecystokinin-, vasoactive intestinal polypeptide-, enkephalin-, serotonin- and dopamine-beta-hydroxylase-related substances. To varying extents all of the substances were localised in neuropile processes, and all, with the exception of substance P, were associated with specific perikarya. The most prominent neuropeptides, in terms of the number of immunoreactive neurones, were cholecystokinin and vasoactive intestinal peptide. The dopamine-beta-hydroxylase positive neurones are thought to be octopaminergic, and the serotonin monoclonal antibody revealed positive staining in the Retzius cells. We were unable to demonstrate the coexistence of pairs of substances in any neurones in the leech ganglia.