Functional ablation of sensory neurons impairs healing of acute gastric mucosal damage in rats

Influence of Comorbidities: Neuropathy, Vasculopathy, and Diabetes on Healing Response Quality

SIGNIFICANCE

Prolonged and nonhealing connective tissue injuries are often seen associated with common diseases, such as metabolic disorders, obesity, hypertension, arteriosclerosis, neuropathy, and diabetes mellitus and these influences result in considerable burden on society via the health care system, the economy, and quality of life for patients.

RECENT ADVANCES

Emerging findings have established important new links in our understanding of effective connective tissue healing. Thereby, the function of the nervous system, vascular supply, and metabolic state of the patient can be directly linked to the quality of the connective tissue healing process.

CRITICAL ISSUES

As some of these conditions are also more common in individuals as they age, and aging can also impact healing effectiveness, such complications will have an emerging significant impact as the demographics of many societies change with expanding percentages of the populations >60-65 years of age.

FUTURE DIRECTIONS

Comorbidities have to be early identified in patients with acute wounds or planned surgery. Necessary interactions between physicians with different subspecialties have to be initiated to optimize wound healing potentials.

Denervation affects regenerative responses in MRL/MpJ and repair in C57BL/6 ear wounds

The MRL/MpJ mouse displays the rare ability amongst mammals to heal injured ear tissue without scarring. Numerous studies have shown that the formation of a blastema-like structure leads to subsequent tissue regeneration in this model, indicating many parallels with amphibian limb regeneration and mammalian embryogenesis. We have recently shown that the MRL/MpJ mouse also possesses an enhanced capacity for peripheral nerve regeneration within the ear wound. Indeed, nerves are vital for the initial phase of blastema formation in the amphibian limb. In this study we investigated the capacity for wound regeneration in a denervated ear. The left ears of MRL/MpJ mice and C57BL/6 (a control strain known to have a poorer regenerative capacity) were surgically denervated at the base via an incision and nerve transection, immediately followed by a 2-mm ear punch wound. Immunohistochemical analysis showed a lack of neurofilament expression in the denervated ear wound. Histology revealed that denervation prevented blastema formation and chrondrogenesis, and also severely hindered normal healing, with disrupted re-epithelialisation, increasing wound size and progressive necrosis towards the ear tip. Denervation of the ear obliterated the regenerative capacity of the MRL/MpJ mouse, and also had a severe negative effect on the ear wound repair mechanisms of the C57BL/6 strain. These data suggest that innervation may be important not only for regeneration but also for normal wound repair processes.

The effect of stochastic electrical noise on hard-to-heal wounds

OBJECTIVE

To evaluate the effect of electrical stochastic noise stimulation on hard-to-heal wounds.

METHOD

This open-label observational case series aimed to evaluate the effect of the Bioelectrical Signal Therapy (BST) device on the treatment of hard-to-heal (recalcitrant) wounds. The study group comprised nine patients (three males and six females), with a total of 11 ulcers that had not healed (ulcer duration range: 18 months to 20 years) despite being treated with other standard methods. Ulcer aetiologies were: EPUAP grade IV pressure ulcers (n=6) and grade III pressure ulcer (n=1), vasculitic ulcer (n=1), post-actinic lesion (n=1), ischaemic (n=1) and post-surgical lesion (n=1). The median patient age was 75. Treatment was delivered for 30 minutes, three times a day for 60 days.

RESULTS

Four patients (five ulcers) closed completely. Ulcers in three patients reduced in size with signs of epithelialisation. No improvement was observed in one patient (who had paraplegia). One patient stopped treatment due to skin irritation at electrode sites. No other adverse effects were observed and all of the treated patients defined the treatment as painless.

CONCLUSION

Stochastic white noise applied to hard-to-heal ulcers for 60 consecutive days reduced the wound surface area by an overall mean closure rate of 82.5% (SD=25.2%). This open-label observational case series provides preliminary indication of the possible role of stochastic resonance in wound healing.

DECLARATION OF INTEREST

This study was supported by Vivisol (Italy), a distributor of Lifewave's BST.

Morphine-induced early delays in wound closure: involvement of sensory neuropeptides and modification of neurokinin receptor expression

Dose-limiting side effects of centrally acting opioid drugs have led to the use of topical opioids to reduce the pain associated with chronic cutaneous wounds. However, previous studies indicate that topical morphine application impairs wound healing. This study was designed to elucidate the mechanisms by which morphine delays wound closure. Rats were depleted of sensory neuropeptides by treatment with capsaicin, and full-thickness 4-mm diameter wounds were excised from the intrascapular region. Wounds were treated topically twice daily with 5mM morphine sulfate, 1mM substance P, 1mM neurokinin A, or 5mM morphine combined with 1mM substance P or neurokinin A and wound areas assessed. During closure, wound tissue was taken 1, 3, 5, and 8 days post-wounding from control and morphine-treated rats and immunostained for neurokinin receptors and markers for macrophages, myofibroblasts, and vasculature. Results obtained from capsaicin-treated animals demonstrated a significant delay in the early stages of wound contraction that was reversed by neuropeptide application. Treatment of capsaicin-treated rats with topical morphine did not further delay wound closure, suggesting that topical opioids impair wound closure via the inhibition of peripheral neuropeptide release into the healing wound. Morphine application altered neurokinin-1 and neurokinin-2 receptor expression in inflammatory and parenchymal cells essential for wound healing in a cell-specific manner, demonstrating a direct effect of morphine on neurokinin receptor regulation within an array of cells involved in wound healing. These data provide evidence indicating a potentially detrimental effect of topical morphine application on the dynamic wound healing process.

Temporal effects of topical morphine application on cutaneous wound healing

BACKGROUND

Studies have shown that topical administration of exogenous opioid drugs impairs wound healing by inhibiting the peripheral release of neuropeptides, thereby inhibiting neurogenic inflammation. This delay is immediate and peaks during the first days of wound closure. This study examined the effects of topical morphine treatment in a cutaneous wound healing model in the rat.

METHODS

Full-thickness 4-mm-diameter wounds were placed on the periscapular region of rats that subsequently received twice-daily topical applications of IntraSite Gel (Smith+Nephew, Hull, United Kingdom) alone or gel infused with 5 mm morphine sulfate on days 0-3 or 4-10 postwounding or throughout the time course. Wound tissue was taken on days 1, 3, 5, 8, and 18 postwounding and immunostained for myofibroblast and macrophage markers or stained with hematoxylin and eosin.

RESULTS

Delays in wound closure observed during morphine application on days 0-3 postwounding mimicked those seen in wounds treated with morphine throughout the entire healing process. However, no significant delays in closure were seen in wounds treated with morphine beginning on day 4 postwounding. Treatment of wounds with morphine significantly reduced the number of myofibroblasts and macrophages in the closing wound. In addition, morphine application resulted in decreases in skin thickness and an increase in residual scar tissue in healed skin.

CONCLUSIONS

These findings demonstrate the time-dependent and persistent nature of the detrimental effects of topical morphine on cutaneous wound healing. The data identify specific limitations that could be ameliorated to optimize topical opioid administration as an analgesic therapeutic strategy in the treatment of painful cutaneous wounds.

Delay of cutaneous wound closure by morphine via local blockade of peripheral tachykinin release

Topically applied morphine is routinely used to alleviate pain in cutaneous wounds such as burns and pressure sores. Evidence suggests the topical administration of exogenous opioid drugs may impair wound closure. This study examined the effects of topical morphine on a standardized model of cutaneous wound healing in the rat. Full-thickness 4mm diameter circular skin flaps were excised from the intrascapular region of male Sprague-Dawley rats. IntraSite Gel infused with either morphine-sulfate, neurokinin-1 (NK-1) or neurokinin-2 (NK-2) receptor antagonists, substance P (SP), neurokinin A (NKA), SP+morphine-sulfate, or NKA+morphine-sulfate was applied to the wound twice daily. Results demonstrated a significant overall delay in the time course of wound contraction in morphine-treated animals when compared with gel-only treated controls. The delay in wound contraction seen in morphine-treated animals increased in a concentration-dependent manner. Topical application of NK-1 or NK-2 receptor antagonists mimicked the effects of morphine in delaying wound closure, suggesting topical opioids impair wound closure via the inhibition of SP and NKA release peripherally into the healing wound. Additionally, no significant delays in closure were seen in rats receiving morphine combined with SP or NKA, demonstrating the ability of each neuropeptide to attenuate the effects of morphine in delaying wound closure and restore normal wound closure rates. The combination of SP or NKA and morphine-sulfate for wound therapy may provide local analgesia while maintaining normal closure rates.

Capsaicin and gastric ulcers

In recent years, infection of the stomach with the organism Helicobacter Pylori has been found to be the main cause of gastric ulcers, one of the common ailments afflicting humans. Excessive acid secretion in the stomach, reduction in gastric mucosal blood flow, constant intake of non-steroid anti-inflammatory drugs (NSAIDS), ethanol, smoking, stress etc. are also considered responsible for ulcer formation. The prevalent notion among sections of population in this country and perhaps in others is that "red pepper" popularly known as "Chilli," a common spice consumed in excessive amounts leads to "gastric ulcers" in view of its irritant and likely acid secreting nature. Persons with ulcers are advised either to limit or avoid its use. However, investigations carried out in recent years have revealed that chilli or its active principle "capsaicin" is not the cause for ulcer formation but a "benefactor." Capsaicin does not stimulate but inhibits acid secretion, stimulates alkali, mucus secretions and particularly gastric mucosal blood flow which help in prevention and healing of ulcers. Capsaicin acts by stimulating afferent neurons in the stomach and signals for protection against injury causing agents. Epidemiologic surveys in Singapore have shown that gastric ulcers are three times more common in the "Chinese" than among Malaysians and Indians who are in the habit of consuming more chillis. Ulcers are common among people who are in the habit of taking NSAIDS and are infected with the organism "Helicobacter Pylori," responsible for excessive acid secretion and erosion of the mucosal layer. Eradication of the bacteria by antibiotic treatment and avoiding the NSAIDS eliminates ulcers and restores normal acid secretion.

Wound Healing in Denervated Tissue

Sacral and trochanteric pressure sores in patients with plegias, and foot ulceration in patients with diabetic neuropathy, are similar because these wounds occur in tissues that do not have normal innervation. While it is recognized that insensitive tissue increases the likelihood of ulceration and recurrence of ulceration, this review attempts to answer the question, Is wound healing impaired in denervated tissue? A review of the scientific literature of the past 35 years demonstrates that all phases of wound healing are impaired in denervated tissue, and these mechanisms are different from those related to one of the underlying diseases, diabetes. Understanding the value of innervation, a goal of wound healing should be to seek strategies that provide reinnervation to these at-risk tissues.

Role of capsaicin-sensitive afferent nerves in different models of gastric inflammation in rats

Capsaicin-sensitive afferent nerves are described as being protective against gastric inflammation; their destruction leads to an exacerbation of inflammatory processes. However, these nerves have been shown to exert a pro-inflammatory action on stress-induced gastritis in rats. Our study aimed to investigate the role of capsaicin-sensitive afferent nerves in different experimental models of gastritis in rats. Functional ablation of sensory nerves was achieved by systemic capsaicin treatment (100 mg/kg). Gastritis was induced by mild (iodoacetamide, diquat, surgical duodeno-gastric reflux [DGR]) and strong (70% ethanol, indomethacin) inflammatory agents. Antagonists of the CGRP1 and NK1 receptors, hCGRP8-37 and SR140333, were administered in rats treated with iodoacetamide and ethanol. Macroscopic damage scores (MDS), myeloperoxidase (MPO) activity and malondialdehyde (MDA) concentration were evaluated after sacrifice. Macroscopic lesions appeared only in ethanol and indomethacin gastritis and were enhanced by capsaicin treatment. Gastric MPO activity was significantly increased by all agents compared to controls. Capsaicin treatment did not have any effect on MPO activity in indomethacin-treated rats or in rats submitted to surgery for duodeno-gastric reflux. However, it abolished the increase in MPO induced by iodoacetamide and diquat, and significantly enhanced that induced by ethanol. hCGRP8-37 and SR140333 abolished the increase in MPO activity and MDA concentration in iodoacetamide treated rats. In ethanol-treated rats, SR140333 diminished MPO activity. These results indicate that, depending upon the nature and duration of the experimental inflammation, capsaicin-sensitive afferent nerves may act differently to control gastric inflammatory processes, suggesting the involvement of a neurogenic component in some forms of gastric inflammation.

Innervation of the gastric mucosa

A plethora of neuronal messengers ("classical" transmitters, gaseous messengers, amino acid transmitters, and neuropeptides) are capable of mediating or modulating gastric functions. Accordingly, the stomach is richly innervated. Gastric nerves are either intrinsic to the gastric wall, i.e., they have their cell bodies in the intramural ganglia and thus belong to the enteric nervous system, or they reach the stomach from outside, originating in the brainstem, in sympathetic ganglia, or in sensory ganglia. Topographically, the nerve fibers in the stomach reach all layers from the most superficial portions of the gastric glands to the outer smooth muscle layer. This wide distribution implies that virtually all different cell types may be reached by neuronal messengers. Within the gastric mucosa endocrine and paracrine cells (e.g., gastrin cells, ECL cells, somatostatin cells), exocrine cells (parietal cells, chief cells, mucous cells), smooth muscle cells, and stromal cells are regulated by neuronal messengers. The sensory innervation, responding to capsaicin, plays an important role in mucosal protection, and in ulcer healing. Presumably also other nerves are involved and a plasticity in the neuropeptide expression has been demonstrated at the margin of gastric ulcers. Taken together, available data indicate a complex interplay between hormones, paracrine messengers and neuronal messengers, growth factors and cytokines in the regulation of gastric mucosal activities such as secretion, local blood flow, growth, and restitution after damage.

Neural emergency system in the stomach

The maintenance of gastric mucosal integrity depends on the rapid alarm of protective mechanisms in the face of pending injury. Afferent neurons of extrinsic origin constitute an emergency system that is called into operation when the gastric mucosa is endangered by acid and other noxious chemicals. The function of these chemoceptive afferents can be manipulated selectively and explored with the excitotoxin capsaicin. Most of the homeostatic actions of capsaicin-sensitive afferents are brought about by peptides released from their peripheral endings in the gastric wall. When stimulated, chemoceptive afferents enhance gastric blood flow and activate hyperemia-dependent and hyperemia-independent mechanisms of protection and repair. In the rodent stomach, these local regulatory roles of sensory neurons are mediated by calcitonin gene-related peptide acting via calcitonin gene-related peptide 1 receptors and neurokinin A acting via neurokinin 2 receptors, with both peptides using nitric oxide as their common messenger. In addition, capsaicin-sensitive neurons form the afferent arc of autonomic reflexes that control secretory and motor functions of the stomach. The pathophysiological potential of the neural emergency system is best portrayed by the gastric hyperemic response to acid backdiffusion, which is signaled by afferent nerve fibers. This mechanism limits damage to the surface of the mucosa and creates favorable conditions for rapid restitution and healing of the wounded mucosa.

Capsaicin and the stomach. A review of experimental and clinical data

Capsaicin, the pungent principle of hot pepper, because of its ability to excite and later defunctionalize a subset of primary afferent neurons, has been extensively used as a probe to elucidate the function of these sensory neurons in a number of physiological processes. In the rat stomach, experimental data provided clear evidence that capsaicin-sensitive (CS) sensory nerves are involved in a local defense mechanism against gastric ulcer. Stimulation of CS sensory nerves with low intragastric concentrations of capsaicin protected the rat gastric mucosa against injury produced by different ulcerogenic agents. High local desensitizing concentrations of capsaicin or systemic neurotoxic doses of the agent markedly enhanced the susceptibility of the rat gastric mucosa to later noxious challenge. Resiniferatoxin, a potent analogue of capsaicin possesses an acute gastroprotective effect similar to that of capsaicin in the stomach. The gastroprotective effect of capsaicin-type agents involves an enhancement of the microcirculation effected through the release of mediator peptides from the sensory nerve terminals with calcitonin gene-related peptide being the most likely candidate implicated. They do not depend on vagal efferent or sympathetic neurons or involve prostanoids. The gastric mucosal protective effect of prostacyclin is retained after systemic or topical capsaicin desensitization. Capsaicin-sensitive fibers are involved in the repair mechanisms of the gastric mucosa. A protective role for CS sensory nerves has also been demonstrated in the colon. In most studies, capsaicin given into the stomach of rats or cats inhibited gastric acid secretion. In humans, although recent studies provide evidence in favor of a beneficial effect of capsaicin on the gastric mucosa, an exact concentration-related assessment of the effect of the agent is still lacking.

A protective role for calcitonin gene-related peptide in water-immersion stress-induced gastric ulcers in rats

This study investigated the role of endogenous and exogenous calcitonin gene-related peptide (CGRP) in water immersion stress (WIS)-induced gastric ulcers in rats. WIS produced gastric ulcers which were inversely correlated to the decrease in CGRP-like immunoreactivity observed in the whole thickness of the corpus stomach but not in its mucosal layers. Systemic administration of CGRP (100 micrograms kg-1 s.c.) produced a significant decrease in lesion index of WIS-ulcers and this protection was inhibited by functional ablation of afferent neurons induced by capsaicin pretreatment (100 mg kg-1 s.c. in two days, a week before the experiments). These findings suggest that sensory endogenous CGRP plays a defensive role in WIS-ulcers.