The association between the incidence of painful bladder syndrome (SVD) and irritable bowel syndrome (IBS) is recorded in a significant percentage of patients (40% to 60%).
In this sense, it has been postulated that the cross communication between the visceral organs, bladder-large intestine (colon), would be due to a mechanism of peripheral sensitization , to the arrival of sensory afferents to the same location in the dorsal root ganglion. , the spinal cord or the processing area in the brain, or to the increase in the permeability of their respective epithelia to signaling molecules.
Accordingly, both clinical conditions are more common in women and, according to various studies, could be controlled by linaclotide. This drug is a 14 amino acid peptide, agonist of guanylate clicklase C (transmembrane receptor located on the luminal surface of the epithelial cell), which increases the secretion of cGMP (cyclic guanosine monophosphate) in the intestinal submucosa, by inducing the activation of the enzyme, due to its similar structure to the hormones uroguanylin and guanylin.
In this way, linaclotide, through the action of cGMP, inhibits peripheral sensitization at the level of nociceptors in the colon. In this sense, the analgesic capacity of the drug has been demonstrated in an animal model of cross communication between visceral organs, of hyperactivity of bladder afferents induced by colitis, in which linaclotide inhibits the activity of sensory fibers coming from the bladder in the dorsal root ganglion.
| It should be noted that, in medical practice, linaclotide is prescribed in the control of chronic idiopathic constipation and IBS with a predominance of constipation (IBS-C). |
The pharmacological activity observed in animal models consists of an increase in intestinal transit and fluid secretion, caused by the activation of the cGMP- and CFTR-dependent protein kinase II (cystic fibrosis transmembrane conductance regulator) signaling cascade, which It is mediated by cGMP.
Both IBS and SVD are clinical conditions in which the patient manifests pain; In the former, they experience chronic abdominal pain in conjunction with altered bowel habits (diarrhea, constipation, or both) and, in SVD, pain is perceived when filling the bladder in combination with the immediate and repeated need to urinate.
The objective of the present work was to determine the action of linaclotide in a murine model of hyperalgesia in the colon and urinary bladder, induced by the application of protamine sulfate (SP) in the latter.
| Methods |
In the present work, Sprague-Dawley rats (n = 68 ovariectomized females, 220 g to 250 g) were used, to which linaclotide was administered orally at a daily dose of 3 ug/kg (prepared in saline) or saline solution (drug control group), for a period of one week. On day 6, urine was removed from the bladder in order to apply an infusion of SP (400 ul solution [1 mg of the drug/ml]) transurethrally.
This solution was kept in the organ for a period of 10 min, after which its emptying was induced by pressure on the lower abdomen and three washes were performed with saline solution administered through the transurethral catheter. Likewise, a control group was separated from the procedure, in which said catheter was applied without performing the SP infusion.
On the day after this treatment, the animals from the different groups were sacrificed and the bladder and colon were removed, with the aim of studying the permeability of their tissues, by determining the conductance and transepithelial electrical resistance (RET). ) in the electrophysiological assay.
In this assay, colon and bladder tissues were placed in modified Ussing and perfusion chambers for biopsies, respectively, in the presence of oxygenated Krebs solution, at 37°C. On the other hand, in animals belonging to the different analysis groups, the sensitivity of the bladder and colon was evaluated.
Bladder sensitivity was studied by applying graduated pressure (forces of 0.16 g to 15 g) exerted by the Von Frey filaments in the upper area of the pubic region, so that it was determined that the animals responded to the stimulus if licking, jumping, or acute abdominal retraction was observed.
Sensitivity in the colon was determined by the number of abdominal contractions, which constituted the visceromotor behavioral response induced by colorectal isobaric distension, caused by pressures graded from 0 to 60 mmHg (the pressure was exerted by means of a 5 cm balloon placed in the colon).
The animals subjected to this experiment were sacrificed and the thoracolumbar (T10-L1) and lumbosacral (L6-S1) regions of the spinal cord were removed for immunohistochemical evaluation of pERK expression, after fixation, cryoprotection and cutting of the tissue in 10 µm sections. The antibody used was anti-phospho-p44/42 MAPK (Erk1/2) (Thr202/ Tyr204) at a concentration of 1:400. Chromogenic detection was carried out using the Betazoid DAB chromogen kit .
One- and two-way ANOVA, Bonferroni and Tukey tests were used in the statistical analysis. A value of p < 0.05 was considered statistically significant.
| Results |
Linaclotide counteracted increased sensitivity in the colon and bladder
Based on observations, linaclotide, administered at clinically relevant doses, was effective in reducing the increased sensitivity in the bladder and colon caused by SP infusion into the bladder, to levels equivalent to those observed in animals. who did not receive said infusion.
In this way, the drug significantly decreased the number of abdominal contractions recorded in response to the pressure exerted by a balloon placed in the colon, compared to what was observed in the animals that received saline solution (F [6, 72] = 12.24).
In agreement, abdominal retraction reached the levels observed in animals that did not receive SP, in response to the forces exerted (1 g to 15 g) (said retraction occurred when applying forces > 4 g and, a lower retraction was recorded, when faced with stimuli of higher intensity (8 and 15 g).
It is worth noting that colorectal distension induced the expression of pERK in neurons in the thoracolumbar region of the spinal cord, and linaclotide decreased the number of neurons positive for said phosphorylated protein (the drug did not affect pERK labeling in the lumbosacral region). Furthermore, although linaclotide was effective in counteracting increased sensitivity in the colon and bladder, its therapeutic action was observed only in controlling colonic permeability.
In this sense, the significant increase in colonic permeability caused by the administration of SP in the bladder, verified in the increase in conductance (F [2, 39] = 22.1) and the reduction of RET (F [2, 39] = 22.1) 39] = 25.83), was inhibited by linaclotide; this was manifested by a decrease in conductance and an increase in RET (F [2, 39] = 8.002 and 0.506, respectively).
However, linaclotide failed to reduce bladder permeability, in which conductance and RET values were recorded that did not present statistical significance, compared to what was observed in animals that consumed saline solution.
| Discussion |
Linaclotide, through activation of guanylate cyclase C, modulates cross-talk between the bladder and colon
Linaclotide counteracted the increased sensitivity in the colon and bladder, caused by an infusion of SP in the latter, showing the analgesic capacity of linaclotide in the context of cross-communication between both organs.
However, this drug was effective in reducing the increase in mucosal permeability only in the colon, which would allow a decrease in visceral sensitivity and, therefore, in the number of pERK-positive neurons in the thoracolumbar region of the colon. spinal cord, which was observed in animals treated with linaclotide.
It is important to mention that, according to previous observations, the presence of shared clinical features between SVD and IBS is due to the existence of an intercommunication between organs of the different systems, which underlies alterations in their permeability and in the magnitude of the response to stimuli (peripheral sensitization of nociceptors), increased activity in neurons in the corresponding regions of the spinal cord and, in certain cases, central sensitization processes.
| Conclusion |
Linaclotide, through the activation of guanylate cyclase C, modulates the cross-communication between the bladder and the colon, an observation that allows us to postulate that the therapeutic capacity of the drug is not limited to the control of IBS-C but has a potential effect on the SVD, which should be evaluated in additional clinical trials.
SIIC- Ibero-American Society of Scientific Information
