Topical naltrexone increases aquaporin 5 production in the lacrimal gland and restores tear production in diabetic rats

Diabetes mellitus is a prevalent disease that is often accompanied by ocular surface abnormalities including delayed epithelial wound healing and decreased corneal sensitivity. The impact of diabetes on the lacrimal functional unit (LFU) and the structures responsible for maintaining tear homeostasis, is not completely known. It has been shown that the Opioid Growth Factor Receptor (OGFr), and its ligand, Opioid Growth Factor (OGF), is dysregulated in the ocular surface of diabetic rats leading to overproduction of the inhibitory growth peptide OGF. The opioid antagonist naltrexone hydrochloride (NTX) blocks the OGF-OGFr pathway, and complete blockade following systemic or topical treatment with NTX restores the rate of re-epithelialization of corneal epithelial wounds, normalizes corneal sensitivity, and reverses dry eye in diabetic animal models. These effects occur rapidly and within days of initiating treatment. The present study was designed to understand mechanisms related to the fast reversal (<5 days) of dry eye by NTX in type 1 diabetes (T1D) by investigating dysregulation of the LFU. The approach involved examination of the morphology of the LFU before and after NTX treatment. Male and female adult Sprague-Dawley rats were rendered hyperglycemic with streptozotocin, and after 6 weeks rats were considered to be a T1D model. Rats received topical NTX twice daily to one eye for 10 days. During the period of treatment, tear production and corneal sensitivity were recorded. On day 11, animals were euthanized and orbital tissues including conjunctiva, eyelids, and lacrimal glands, were removed and processed for histologic examination including immunohistochemistry. Male and female T1D rats had significantly decreased tear production and corneal insensitivity, significantly decreased number and size of lacrimal gland acini, decreased expression of aquaporin-5 (AQP5) protein and decreased goblet cell size. Thus, 10 days of NTX treatment restored tear production and corneal sensitivity to normal values, increased AQP5 expression, and restored the surface area of goblet cells to normal. NTX had no effect on the number of lacrimal gland acini or the number of conjunctival goblet cells. In summary, blockade of the OGF-OGFr pathway with NTX reversed corneal and lacrimal gland complications and restored some components of tear homeostasis confirming the efficacy of topical NTX as a treatment for ocular defects in diabetes.

Safety study of topical naltrexone therapy for diabetic skin wounds is confirmed in Göttingen mini-pigs

This study was conducted to determine the safety of topical naltrexone treatment in Göttingen swine. Efficacy of topical naltrexone was performed previously in Sprague-Dawley rats. In this study, 25 male and female mini-pigs received topical naltrexone once daily for 30 days. The gel at doses of 1%, 2%, and 10% naltrexone was applied at a dose volume of 0.01 ml/cm2 to an area of unbroken skin encompassing 10% of the animal's surface. Body and food consumption, skin and organ morphology, and clinical signs, including blood analyses were taken periodically. Naltrexone levels in serum were measured at the time of death. No adverse observations were made in the cutaneous skin, autopsied organs, or biochemical parameters. The no-observed adverse effect level (NOAEL) was considered to be 2% topical application daily. The conclusions from the veterinarians and researchers are that topical naltrexone at 1% or 2% can be used safely in clinical efficacy studies.

Acute Low Dose Naltrexone Increases β-Endorphin and Promotes Neuronal Recovery Following Hypoxia-Ischemic Stroke in Type-2 Diabetic Mice

Diabetic patients experience significant mortality and poor recovery following ischemic stroke. Our clinical and basic science studies demonstrate an overall immune suppression in the periphery of diabetic stroke patients, as well as within the central nervous system (CNS) of type-2 diabetic mice following hypoxia-ischemia (HI). Low doses of naltrexone (LDN) improved clinical outcomes in many autoimmune diseases by acting on opioid receptors to release β-endorphin which in turn balances inflammatory cytokines and modulates the opioid growth factor (OGF)-opioid growth factor receptor (OGFr) pathway. We hypothesized that in our model of diabetic mice, LDN treatment will induce the release of β-endorphin and improve CNS response by promoting neuronal recovery post HI. To test this hypothesis, we induced HI in 10 week old male db/db and db/ + mice, collected tissue at 24 and 72 h post HI, and measured OGF levels in plasma and brain tissue. The infarct size and number of OGF + neurons in the motor cortex, caudate and hippocampus (CA3) were measured. Following HI, db/db mice had significant increases in brain OGF expression, increased infarct size and neurological deficits, and loss of OGFr + neurons in several different brain regions. In the second experiment, we injected LDN (1 mg/kg) intraperitoneally into db/db and db/ + mice at 4, 24, and 48 h post HI, and collected brain tissue and blood at 72 h. Acute LDN treatment increased β-endorphin and OGF levels in plasma and promoted neuronal recovery in db/db mice compared to phosphate buffer saline (PBS)-treated diabetic mice suggesting a protective or regenerative effect of LDN.

Opioid growth factor receptor: Anatomical distribution and receptor colocalization in neurons of the adult mouse brain

The opioid growth factor (OGF) is an endogenous peptide that binds to the nuclear-associated receptor (OGFr), and plays a significant role in the proliferation of developing, renewing, and healing tissues. The receptor is widely expressed in a variety of organs, however its distribution in the brain remains unknown. In this study, we investigated the distribution of OGFr in different brain regions of male heterozygous (-/+ Lepr ^db/J), non -diabetic mice and determined the localization of the receptor in three major brain cell types, astrocytes, microglia, and neurons. Immunofluorescence imaging revealed that the highest number of OGFr was in hippocampal CA3 subregion followed by primary motor cortex, hippocampal CA2, thalamus, caudate and hypothalamus in a descending order. Double immunostaining revealed receptor colocalization with neurons and little or no colocalization in microglia and astrocytes. The highest percentage of OGFr positive neurons was identified in the CA3. Hippocampal CA3 neurons play an important role in memory processing, learning and behavior, and motor cortex neurons are important for muscle movement. However, the significance of the OGFr receptor in these brain regions and its relevance in diseased conditions are not known. Our findings provide a basis for understanding the cellular target and interaction of the OGF- OGFr pathway in neurodegenerative diseases such as Alzheimer's, Parkinson's, and stroke where hippocampus and cortex have an important role. This foundational data may also be useful in drug discovery to modulate OGFr by opioid receptor antagonist in various CNS diseases.

Elevated Opioid Growth Factor Alters the Limbus in Type 1 Diabetic Rats

Ocular surface complications occur in more than 50% of individuals diagnosed with diabetes. The financial and health-related burden of diabetes is increasing annually. Several major ocular complications associated with diabetes involve the limbus. The vascular limbus, adjacent to the avascular cornea, is the source of circulating growth factors, elevated glucose, and cytokines for the cornea. The Opioid Growth Factor (OGF) - Opioid OGF Receptor (OGFr) axis is comprised of its effector peptide, OGF, [Met⁵]-enkephalin and the nuclear-associated receptor, OGFr, and has been demonstrated to be dysfunctional in diabetes with elevated serum and tissue levels of the inhibitory growth factor OGF recorded in corneal tissue. Little is known regarding the impact of OGF-OGFr axis dysregulation in diabetes on the functioning of the limbus constituents in support of corneal homeostasis. Adult male and female Sprague-Dawley rats were rendered hyperglycemic through intraperitoneal injections of streptozotocin (T1D); a subset of T1D rats received topical naltrexone (NTX) applied to the cornea and limbus daily for 8 weeks. At 4 and/or 8 weeks of hyperglycemia, different cohorts of animals were euthanized, eyes removed and processed for assessment of limbal morphology, expression of OGF, OGFr, cytokeratin 15, a marker for limbal cells, and Ki-67, a marker of proliferation. Limbal epithelial morphology (cell diameter, packing density) was altered in T1D male and female rats. OGF and OGFr were overexpressed in the limbus and CK15 expression was decreased, relative to normal control rats of the same sex. Blockade of the OGF- OGFr axis with NTX reversed limbal epithelial cell defects, and reduced OGF limbal tissue levels to those recorded in non-diabetic rats. In summary, OGF-OGFr axis dysregulation was observed in the limbus of T1D rats, contributing to the altered limbal morphology and delayed corneal surface healing observed in diabetic animals.

Sex Differences in Diabetic Ocular Surface Complications and Dysregulation of the OGF-OGFr Pathway

Background

Diabetes is a chronic disorder that affects more than 500 million individuals worldwide. It is a life-long disease with complications that attack nearly all other systems within the body. Although there is a slight increase in the prevalence of diabetes in males, ocular surface complications are equally present in males and females.

Aim

This review provides a discussion on preclinical studies related to the dysregulation of a biological pathway that appears to be causally related to diabetic ocular surface complications including dry eye, delayed corneal epithelial healing, and decreased corneal sensitivity. Most basic science and clinical studies focus on male sex in animal models in order to avoid confounders related to hormonal cycling. However, with approximately 10.2% of all women in the US aged 18-44 being diagnosed with diabetes and nearly 4% additional women having undiagnosed disease, it is prudent to examine the onset of these dysregulations also in females and to note any sex-related differences in the timing of onset or severity of ocular surface complications.

Summary

Data from several well-controlled investigations have documented that female rats with type 1 diabetes develop ocular surface complications before male rats. In part, this finding may be due to the increase in the inhibitory peptide Opioid Growth Factor (OGF) that occurs within 2 weeks of the induction of hyperglycemia in female animals in comparison to the changes in OGF levels in male rats which occur at 4 weeks. It was noted that estrogen levels drop within weeks of induction of hyperglycemia and could serve as another marker for the onset of disease activity and/or its complications. Finally, insulin does not appear to protect against early changes in OGF levels or estrogen secretion in diabetic female rats, setting the stage for a distinction in the disease profile of diabetes between males and females. These data encourage further studies on both sexes in order to establish a complete understanding of the underlying pathologies associated with complications associated with diabetes.

Timing of treatment with an endogenous opioid alters immune response and spinal cord pathology in female mice with experimental autoimmune encephalomyelitis

Multiple sclerosis (MS) is a progressive disease of the central nervous system (CNS) that primarily affects women during the second or third decade of life. The mechanism is hypothesized to involve unregulated peripheral inflammation resulting in blood-brain barrier damage, and eventual axonal damage and demyelination. Based on this understanding, the animal model of MS, experimental autoimmune encephalomyelitis (EAE), often is utilized to study lymphocyte activation. Therapeutic paradigms of exogenous opioid growth factor (OGF) or low-dose naltrexone (LDN) treatment can modulate EAE, but little is reported regarding OGF or LDN effects on peripheral inflammation, microglia activation, and/or macrophage proliferation. Moreover, little is known about differential responses to LDN or OGF relative to the duration and timing of treatment. Utilizing a female mouse model of EAE, two treatment regimens were established to investigate differences between prophylactic treatment and traditional therapy initiated at the time of disease presentation. Prophylactic OGF or LDN treatment delayed the onset of behavior, suppressed neutrophil replication, and curtailed lymphocyte proliferation which ultimately improved behavioral outcome. Traditional therapy with OGF or LDN reversed behavioral deficits, restored OGF and IL-17 serum levels, and inhibited microglial activation within 8 days. Reduced serum OGF levels in untreated EAE mice correlated with increased microglia activation within lumbar spinal cords. Both treatment regimens of OGF or LDN reduced activated microglia, whereas only prophylactic treatment prevented CNS macrophage aggregation. These data demonstrate that the timing of LDN or OGF treatment initiation alters outcomes and can prevent or reverse behavioral deficits, cytokine activation, and spinal cord pathology.

Ocular surface complications in diabetes: The interrelationship between insulin and enkephalin

Diabetes is a multi-faceted disorder with increasing prevalence and rising healthcare costs. The burden of diabetes is increased because of associated complications affecting nearly all organs including the eye. The underlying pathophysiology for the onset of these ocular surface disorders is not well known. Enkephalins are endogenous opioids that originate in the brain and have numerous actions in the human body. Opioid growth factor (OGF), chemically termed [Met5]-enkephalin, binds to a novel, nuclear-associated receptor and mediates cellular homeostasis. Serum OGF levels are elevated in diabetic individuals and rodent models of diabetes. Sustained blockade of the OGF receptor (OGFr) with opioid receptor antagonists, such as naltrexone (NTX), reverses many complications of diabetes in the animal model, including delayed cutaneous wound healing, dry eye, altered corneal surface sensitivity, and keratopathy. The increased enkephalin levels observed in diabetes suggest a relationship between endogenous opioid peptides and the pathophysiology of diabetes. It is common for diabetic patients to undergo insulin therapy to restore normal blood glucose levels. However, this restoration does not alter OGF serum levels nor ameliorate ocular surface complications in the animal model of diabetes. Moreover, sex differences in the prevalence of diabetes, response to insulin therapy, and abnormalities in the OGF-OGFr axis have been reported. This review highlights current knowledge on the dysregulation of the OGF-OGFr pathway and possible relationships of insulin and enkephalins to the development of ocular surface defects in diabetes. It proposes that this dysregulation is a fundamental mechanism for the pathobiology of diabetic complications.

Blockade of OGFr delays the onset and reduces the severity of diabetic ocular surface complications

The opioid growth factor (OGF)-OGF receptor (OGFr) pathway is present in the ocular surface and functions to maintain homeostasis of the epithelium. The OGF-OGFr pathway has been reported to be dysregulated in diabetic individuals and animal models, and is reflected in elevations of the inhibitory growth factor, OGF, chemically termed [Met5]-enkephalin. Recently, our laboratory reported elevated levels of OGF and OGFr in the serum and corneal epithelium of type 1 diabetic rats, suggesting that dysregulation of the OGF-OGFr axis may lead to dry eye, abnormal corneal surface sensitivity, and delayed re-epithelialization. Blockade of OGF-OGFr pathway using naltrexone, a potent opioid receptor antagonist, reverses dry eye symptoms and restores corneal surface sensitivity in diabetic rats when used as a therapy. Based on the evidence that both OGF and OGFr are elevated in type 1 diabetic rats, this study examined whether systemic or topical naltrexone treatment initiated at the time of induction of hyperglycemia could protect against the development of diabetic ocular surface complications. Diabetic male Sprague-Dawley rats treated systemically or topically with naltrexone had a delayed onset of dry eye and altered corneal surface sensitivity, and an improved healing rate for corneal wounds, that were comparable to non-diabetic rats. Serum levels of OGF were normal for rats receiving systemic naltrexone, and OGF tissue levels were normal for type 1 diabetic rats receiving twice daily naltrexone drops. OGFr levels remained elevated. These data support the role of the OGF-OGFr axis in regulation of ocular surface complications, and suggest that naltrexone therapy may be beneficial for pre-diabetic and early diabetic individuals.

β-endorphin and opioid growth factor as biomarkers of physical ability in multiple sclerosis

BACKGROUND

Multiple sclerosis (MS) is an autoimmune-mediated degenerative disorder with increased peripheral inflammation disrupting the blood brain barrier. With increasing MS-related healthcare costs, the requirement to validate minimally invasive biomarkers has become imperative.

METHODS

Relapsing-remitting MS patients on disease modifying therapies were consented at the Penn State Health MS Clinic to provide blood samples for analyses of serum cytokines and endogenous opioid peptides, as well as to complete the MSQOL-54 survey.

RESULTS

Serum OGF levels in MS patients on glatiramer acetate (mean = 326 pg/ml), dimethyl fumarate (mean = 193.3 pg/ml) and natalizumab (mean = 393.4 pg/ml) were significantly elevated (p < 0.01) compared to healthy controls (mean = 98.46 pg/ml). Individuals with elevated OGF levels also had increased levels of TNFα (r = 0.78) and IL-17A (r = 0.81). Only patients treated with glatiramer acetate had significant (p < 0.01) elevations in serum β-endorphin levels. Analyses of MS-QoL 54 data showed no significant differences in physical or mental composite scores between treatment groups. However, serum levels of β-endorphin had a direct correlation with physical health composite score (r = 0.70) in all treatments. Serum vitamin D levels had an indirect relationship with 25-foot walk test times (r = 0.47).

CONCLUSION

Both regression and cohort data suggest that serum levels of OGF, β-endorphin, and vitamin D are potential biomarkers for physical disease status in MS.

Dysregulation of the OGF-OGFr pathway and associated diabetic complications

BACKGROUND

Diabetes is a worldwide epidemic with more than 550 million individuals expected to be diagnosed with the disease by 2030. Complications associated with diabetes affect nearly all systems, but more than 54% of diabetic individuals have ocular surface disorders including keratopathy, dry eye or altered corneal surface sensitivity, and nearly 70% experience slow healing foot ulcers which if left untreated, can lead to amputation. There is new information regarding the underlying pathophysiology associated with these complications, as well as potential treatment.

AIM

This commentary assembles data on preclinical studies showing that corneal surface complications such as dry eye and sensitivity, as well as delayed epithelial wound healing in the cornea and skin in diabetic rats and mice, correlate with a dysregulation of the opioid growth factor (OGF)-opioid growth factor receptor (OGFr) regulatory axis. The peptide in this pathway, OGF, chemically termed [Met⁵]-enkephalin, is elevated in the serum of humans and animals with either type 1 or type 2 diabetes. The cause for this finding is unknown. However, there are studies that demonstrate that blockade of the interactions between OGF (or elevated levels of OGF) and its receptor can reverse and, in some cases, prevent the onset of diabetic corneal complications. Clinicians and healthcare workers need to recognize this fundamental pathophysiology leading to diabetic complications.

SUMMARY

Dysfunction of the OGF-OGFr growth regulatory system plays a role in the development of ocular surface complications and delayed cutaneous wound healing complications in multiple animal models of both Type 1 and Type 2 diabetes. Modulation of this system may hold promise for reversing or even preventing these diabetic complications in humans. Moreover, monitoring serum levels of OGF should be investigated as an indicator of the development of these and other diabetic complications.

[Met5]-enkephalin preserves diffusion metrics in EAE mice

Multiple sclerosis is a chronic progressive neurological disorder that has few distinctive biomarkers associated with disease progression or response to therapy. This research investigated whether non-invasive imaging correlated with animal behavior and morphological indicators of disease in response to serum levels of [Met⁵]-enkephalin. Using the experimental autoimmune encephalomyelitis (EAE) model, adult female C57BL/6 J mice were randomized to receive daily injections of 0.1 mg/kg naltrexone (NTX) (= low dose naltrexone, LDN), 10 mg/kg Opioid Growth Factor (OGF) (chemically termed [Met⁵]-enkephalin) or saline beginning at the time of disease induction. Daily composite behavior scores were recorded over a 30-day period based on tail tone, gait, righting reflex, and limb strength. Prior to disease onset (day 7), and at peak disease (day 18), mice were imaged and tissues (blood and spinal cord) collected at day 30 for serum analyses of OGF and morphology. Serum OGF levels of EAE mice treated with saline were significantly reduced from baseline and from normal mice. Longitudinal cohort data demonstrated an increase in fractional anisotropy in all cohorts by day 18. There was a significant decrease in radial diffusivity in the saline group seen at day 18 whereas the axial diffusivity was not altered amongst treatment groups. Treatment with OGF or LDN resulted in mean diffusivity rates that were comparable to baseline (normal) levels at days 7 and 18. Luxol fast blue staining of the lumbar spinal cords demonstrated a 16 % reduction in myelin staining in saline treated EAE animals when compared to OGF and LDN treated EAE mice. Immunohistochemistry with Olig2 (pan-oligodendrocyte marker) and myelin basic protein (MBP) revealed that OGF and LDN treatment restored the area (%) of MBP and number of oligodendrocytes to that of normal spinal cord (∼75 %). Saline treated EAE mice had more demyelination and fewer oligodendrocytes than normal mice. Collectively, these data suggest that a panel of biomarkers including imaging, serum biomarker levels, and behavior correlate with progression of disease, and may begin to validate use of specific non-invasive markers for MS.

Dysregulation of the OGF-OGFr pathway correlates with elevated serum OGF and ocular surface complications in the diabetic rat

IMPACT STATEMENT

This research extends our knowledge about the presence and role of the OGF-OGFr regulatory axis in type 1 diabetes (T1D) and demonstrates specific targets within the pathway that are dysregulated. Serum levels of OGF, an inhibitory growth factor, are significantly elevated in male T1D rats, and OGFr serum values are increased in T1D. The onset of elevated OGF corresponds to the onset of ocular surface complications including dry eye, delayed corneal epithelial repair, and abnormal corneal surface sensitivity in T1D. Systemic insulin does not protect against elevated OGF levels or the onset of dry eye and sensitivity. These data are the first to associate some ocular surface defects in T1D with alterations in the OGF-OGFr pathway.

Naltrexone as a Novel Therapeutic for Diabetic Corneal Complications

Diabetes is a widespread autoimmune disorder that affects nearly 10% of the adult population in the United States. In addition to the primary disease, there are numerous complications associated with inflammation including abnormalities of the heart, visual system, and peripheral nervous system. More than half of the individuals with diabetes will have one or more ocular related complications such as dry eye disease (DED), keratopathy, or retinopathy. Research over the last 3 decades has focused on the role of the opioid growth factor - opioid growth factor receptor (OGF-OGFr) axis as a regulatory system that maintains homeostasis in corneal epithelialization and tear secretion. In diabetes, OGF appears to be dysregulated resulting in decreased cell replication and increased corneal surface sensitivity. Utilization of naltrexone as a topical therapeutic to block the OGF-OGFr axis results in reversal of dry eye and restoration of corneal sensitivity and rates of corneal re-epithelialization. Naltrexone treatment at dosages that are substantially lower than systemically approved doses appear to be safe and effective therapy for corneal surface abnormalities associated with diabetes.

Blockade of the OGF-OGFr pathway in diabetic bone

Purpose: This research investigated the presence and integrity of the opioid growth factor (OGF)-opioid growth factor receptor (OGFr) regulatory pathway in type 1 diabetic (T1D) rats, and investigated whether modulation of this axis by naltrexone (NTX) altered the composition of normal bone or fractured femurs. Materials and Methods: Diabetes was induced by streptozotocin; controls rats received buffer. Hyperglycemic animals were subjected to femur osteotomy, with randomized cohorts receiving either topical NTX or sterile saline in calcium carbonate. In experiment 2, hyperglycemic rats were injected daily for 3 weeks with either 30 mg/kg NTX or sterile saline. Expression levels of OGF and OGFr were measured by immunohistochemistry, bone composition was assessed by histomorphometry, and bone integrity was evaluated by µCT and 3-point bending. Results: Relative to normoglycemic bones, OGF and OGFr expression levels were increased 95% and 84%, respectively, in T1D bone; serum levels of OGF in T1D rats were elevated 23%. Hyperglycemia decreased the strength (26%), osteocalcin expression (17%), and number of proliferative (Ki67+) cells (32%) in intact femur. Topical NTX treatment of fractured femurs reduced the percentage of granulation tissue and increased cartilage. Systemic NTX treatment of diabetic rats increased strength by 21% and energy absorbed by105% in bone relative to measurements in saline-treated diabetic rats. Conclusions: The OGF-OGFr pathway appears to be dysregulated in the bone of T1D rats. Topical NTX treatment of T1D fractured bone accelerated some aspects of delayed diabetic fracture repair, and systemic NTX protected against some elements of compromised bone composition.

Efficacy and safety of a novel naltrexone treatment for dry eye in type 1 diabetes

Background

Dry eye disease (DED) is a prevalent complication of diabetes and presents as reduced tear production and/or increased corneal surface sensitivity often with secondary ocular surface changes. This study examined the safety and efficacy of a proprietary new eye drop formulation for topical treatment of DED.

Methods

Type 1 diabetes (T1D) was established in male Sprague-Dawley rats to study the efficacy and safety of the investigational compound that contained 20 μg/ml of naltrexone (NTX). Tear production was measured by the Schirmer’s 1 test, and ocular surface sensitivity was measured using an aesthesiometer. Diabetic rats received twice daily applications of a single drop (~ 0.02 ml) of the proprietary formulation (NTX-001) or vehicle onto one eye. For comparison, some diabetic rats received eye drops containing NTX in sterile Vigamox®. Safety was monitored by assessment of ocular histopathology in naïve male rats and naïve male rabbits receiving twice daily treatment of two drops for 30 days.

Results

Dry eye in T1D rats was reversed within hours of a single treatment of NTX-001, and over a period of 10 days NTX-001 restored corneal sensitivity and reversed dry eye relative to values measured in diabetic rats receiving vehicle. In comparison to NTX dissolved in Vigamox®, the proprietary NTX-001 was more effective at reversing dry eye. Safety studies in naïve rats and rabbits revealed no visible ocular pathology after 30 days of treatment.

Conclusions

An investigational new eye drop containing 20 μg/ml NTX effectively reversed tear film deficits and restored corneal surface sensitivity in diabetic animals without causing toxic side effects.

Intermittent blockade of OGFr and treatment of autoimmune disorders

IMPACT STATEMENT

This mini-review presents information on the intermittent blockade of the opioid growth factor (OGF)-OGF receptor (OGFr) axis by low-dose naltrexone (LDN), and the role of enkephalin (i.e. OGF) in autoimmune disorders, specifically multiple sclerosis, Crohn's, and fibromyalgia. Clinical reports on subjects taking LDN have documented reduced fatigue, few side-effects, and improved overall health. Preclinical studies on mice with experimental autoimmune encephalomyelitis (EAE), the animal model of multiple sclerosis, revealed that immunization for EAE reduces serum OGF. Intermittent OGFr blockade with LDN restores serum enkephalin levels that correlate with reduced behavioral and pathological signs of EAE; LDN also increases enkephalin levels in naïve mice. The interplay between LDN, and the onset and treatment of autoimmune diseases, chronic pain, and other addictive behaviors requires further investigation, but highlights a central role for enkephalins and intermittent blockade of the OGF-OGFr pathway in pathogenesis and treatment of these disorders.

Featured Article: Modulation of the OGF-OGFr pathway alters cytokine profiles in experimental autoimmune encephalomyelitis and multiple sclerosis

The endogenous neuropeptide opioid growth factor, chemically termed [Met⁵]-enkephalin, has growth inhibitory and immunomodulatory properties. Opioid growth factor is distributed widely throughout most tissues, is autocrine and paracrine produced, and interacts at the nuclear-associated receptor, OGFr. Serum levels of opioid growth factor are decreased in patients with multiple sclerosis and in animals with experimental autoimmune encephalomyelitis suggesting that the OGF-OGFr pathway becomes dysregulated in this disease. This study begins to assess other cytokines that are altered following opioid growth factor or low-dose naltrexone modulation of the OGF-OGFr axis in mice with experimental autoimmune encephalomyelitis using serum samples collected in mice treated for 10 or 20 days and assayed by a multiplex cytokine assay for inflammatory markers. Cytokines of interest were validated in mice at six days following immunization for experimental autoimmune encephalomyelitis. In addition, selected cytokines were validated with serum from MS patients treated with low-dose naltrexone alone or low-dose naltrexone in combination with glatiramer acetate (Copaxone®). Experimental autoimmune encephalomyelitis mice had elevated levels of 7 of 10 cytokines. Treatment with opioid growth factor or low-dose naltrexone resulted in elevated expression levels of the IL-6 cytokine, and significantly reduced IL-10 values, relative to saline-treated experimental autoimmune encephalomyelitis mice. TNF-γ values were increased in experimental autoimmune encephalomyelitis mice relative to normal, but were not altered by opioid growth factor or low-dose naltrexone. IFN-γ levels were reduced in opioid growth factor- or low-dose naltrexone-treated experimental autoimmune encephalomyelitis mice relative to saline-treated mice at 10 days, and elevated relative to normal values at 20 days. Validation studies revealed that within six days of immunization, opioid growth factor or low-dose naltrexone modulated IL-6 and IL-10 cytokine expression. Validation in human serum revealed markedly reduced IL-6 cytokine levels in MS patients taking low-dose naltrexone relative to standard care. In summary, modulation of the OGF-OGFr pathway regulates some inflammatory cytokines, and together with opioid growth factor serum levels, may begin to form a panel of valid biomarkers to monitor progression of multiple sclerosis and response to therapy. Impact statement Modulation of the opioid growth factor (OGF)-OGF receptor (OGFr) alters inflammatory cytokine expression in multiple sclerosis and experimental autoimmune encephalomyelitis (EAE). Multiplex cytokine assays demonstrated that mice with chronic EAE and treated with either OGF or low-dose naltrexone (LDN) had decreased expression of interferon-gamma (IFN-γ), tumor necrosis factor-alpha (TNF-α), and the anti-inflammatory cytokine IL-10 within 10 days or treatment, as well as increased serum expression of the pro-inflammatory cytokine IL-6, relative to immunized mice receiving saline. Multiplex data were validated using ELISA kits and serum from MS patients treated with LDN and revealed decreased in IL-6 levels in patients taking LDN relative to standard care alone. These data, along with serum levels of OGF, begin to formulate a selective biomarker profile for MS that is easily measured and effective at monitoring disease progression and response to therapy.

Topical Naltrexone Is a Safe and Effective Alternative to Standard Treatment of Diabetic Wounds

Objective: Diabetes affects more than 29 million individuals in the United States, resulting in healthcare costs approaching $245 billion. Approximately 15% of these individuals will develop a chronic, non-healing foot ulcer (diabetic foot ulcer [DFU]) that, if untreated, may lead to amputation. The current treatments for DFU are expensive, have significant side-effects, and often result in non-compliance. A new topical treatment is described that accelerates cutaneous wound repair and is disease modifying by targeting underlying aberrant diabetic pathways. Approach: The efficacy of naltrexone (NTX), an opioid receptor antagonist, and Regranex^® was compared in preclinical studies using type 1 diabetic rats. Dorsal cutaneous wounds were treated topically with 0.03% NTX, Regranex, or moisturizing cream alone. Wound closure, DNA synthesis, and cytokine production were monitored. Results: Wound closure rates with topical NTX in type 1 diabetic rats were comparable to Regranex. Topical NTX accelerated DNA synthesis, as measured by BrdU incorporation, increased mast cells, and enhanced expression of platelet-derived growth factor (PDGF) and vascular endothelial growth factor (VEGF), a marker for angiogenesis. Regranex had little effect on DNA synthesis, mast cells, and VEGF expression relative to vehicle-treated wounds, and it only temporarily increased PDGF expression. Fibroblast growth factor expression was not altered by either treatment. Innovation: Topical application of 0.03% NTX cream accelerates diabetic wound closure. Conclusion: Blockade of the opioid growth factor (OGF)-OGF receptor (OGFr) axis utilizing 0.03% NTX cream is comparable to standard care in preclinical studies, and it provides a safe, inexpensive, and effective alternative for treatment of diabetic wounds.

Featured Article: Serum [Met5]-enkephalin levels are reduced in multiple sclerosis and restored by low-dose naltrexone

Low-dose naltrexone is a widely used off-label therapeutic prescribed for a variety of immune-related disorders. The mechanism underlying low-dose naltrexone's efficacy for fatigue, Crohn's disease, fibromyalgia, and multiple sclerosis is, in part, intermittent blockade of opioid receptors followed by upregulation of endogenous opioids. Short, intermittent blockade by naltrexone specifically blocks the opioid growth factor receptor resulting in biofeedback events that increase production of the endogenous opioid growth factor (OGF) (chemically termed [Met5]-enkephalin) facilitating interactions between opioid growth factor and opioid growth factor receptor that ultimately, result in inhibited cell proliferation. Preclinical studies have reported that enkephalin levels are deficient in animal models of experimental autoimmune encephalomyelitis, a mouse model of multiple sclerosis. Our hypothesis is that serum enkephalin levels are diminished in humans with multiple sclerosis and experimental autoimmune encephalomyelitis mice, and that change in serum opioid growth factor levels may serve as a reasonable candidate biomarker for the onset of experimental autoimmune encephalomyelitis and response to therapy. To address this, we designed a two-part study to measure endogenous opioids in multiple sclerosis patients, and to investigate the temporal pattern of decline in serum enkephalin concentrations in mice with chronic progressive experimental autoimmune encephalomyelitis and treated with low-dose naltrexone. For comparison, we investigated whether low-dose naltrexone exposure in normal mice also resulted in altered enkephalin levels. In both animal models, we monitored tactile and heat sensitivity, as well as differential white blood cell counts as indicators of inflammation. Serum [Met5]-enkephalin levels were lower in humans with multiple sclerosis relative to non-multiple sclerosis patients, and low-dose naltrexone restored their levels. In experimental autoimmune encephalomyelitis mice, [Met5]-enkephalin levels were depressed prior to the appearance of clinical disease, and were restored with low-dose naltrexone treatment. Low-dose naltrexone therapy had no effect on serum [Met5]-enkephalin or β-endorphin in normal mice. Thus, [Met5]-enkephalin (i.e. opioid growth factor) may be a reasonable candidate biomarker for multiple sclerosis, and may signal new pathways for treatment of autoimmune disorders. Impact statement This report presents human and animal data identifying a novel biomarker for the onset and progression of multiple sclerosis (MS). Humans diagnosed with MS have reduced serum levels of OGF (i.e. [Met5]-enkephalin) relative to non-MS neurologic patients, and low-dose naltrexone (LDN) therapy restored their enkephalin levels. Serum OGF levels were reduced in mice immunized with MOG35-55 prior to any clinical behavioral sign of experimental autoimmune encephalomyelitis, and LDN therapy restored their serum OGF levels. β-endorphin concentrations were not altered by LDN in humans or mice. Thus, blood levels of OGF may serve as a new, selective biomarker for the progression of MS, as well as response to therapy.

Selective opioid growth factor receptor antagonists based on a stilbene isostere

As part of an ongoing drug development effort aimed at selective opioid receptor ligands based on the pawhuskin natural products we have synthesized a small set of amide isosteres. These amides were centered on lead compounds which are selective antagonists for the delta and kappa opioid receptors. The amide isomers revealed here show dramatically different activity from the parent stilbene compounds. Three of the isomers synthesized showed antagonist activity for the opioid growth factor (OGF)/opioid growth factor receptor (OGFR) axis which is involved in cellular and organ growth control. This cellular signaling mechanism is targeted by "low-dose" naltrexone therapy which is being tested clinically for multiple sclerosis, Crohn's disease, cancer, and wound healing disorders. The compounds described here are the first selective small molecule ligands for the OGF/OGFR system and will serve as important leads and probes for further study.

Long-term treatment with low dose naltrexone maintains stable health in patients with multiple sclerosis

Introduction

A retrospective study was conducted on patients at Penn State Hershey Medical Center diagnosed with relapsing–remitting multiple sclerosis between 2006 and 2015.

Methodology

Laboratory and clinical data collected over this 10-year period were reviewed. Two cohorts of patients were established based on their relapsing–remitting multiple sclerosis therapy at the time of their first visit to Penn State. One group of patients (n = 23) was initially prescribed low dose naltrexone at the time first seen at Hershey. This group was offered low dose naltrexone because of symptoms of fatigue or refusal to take an available disease-modifying therapy. The second group of patients (n = 31) was treated with the glatiramer acetate (Copaxone) and offered low dose naltrexone as an adjunct therapy to their disease-modifying therapy.

Results

Patient data from visits after 1–50 months post-diagnosis were evaluated in a retrospective manner. Data obtained from patient charts included clinical laboratory values from standard blood tests, timed 25-foot walking trials, and changes in magnetic resonance imaging reports. Statistical analyses between the groups and for each patient over time indicated no significant differences in clinical laboratory values, timed walking, or changes in magnetic resonance imaging.

Conclusion

These data suggest that the apparently non-toxic, inexpensive, biotherapeutic is safe and if taken alone did not result in an exacerbation of disease symptoms.

Featured Article: Nuclear export of opioid growth factor receptor is CRM1 dependent

Opioid growth factor receptor (OGFr) facilitates growth inhibition in the presence of its specific ligand opioid growth factor (OGF), chemically termed [Met(5)]-enkephalin. The function of the OGF-OGFr axis requires the receptor to translocate to the nucleus. However, the mechanism of nuclear export of OGFr is unknown. In this study, endogenous OGFr, as well as exogenously expressed OGFr-EGFP, demonstrated significant nuclear accumulation in response to leptomycin B (LMB), an inhibitor of CRM1-dependent nuclear export, suggesting that OGFr is exported in a CRM1-dependent manner. One consensus sequence for a nuclear export signal (NES) was identified. Mutation of the associated leucines, L217 L220 L223 and L225, to alanine resulted in decreased nuclear accumulation. NES-EGFP responded to LMB, indicating that this sequence is capable of functioning as an export signal in isolation. To determine why the sequence functions differently in isolation than as a full length protein, the localization of subNES was evaluated in the presence and absence of MG132, a potent inhibitor of proteosomal degradation. MG132 had no effect of subNES localization. The role of tandem repeats located at the C-terminus of OGFr was examined for their role in nuclear trafficking. Six of seven tandem repeats were removed to form deltaTR. DeltaTR localized exclusively to the nucleus indicating that the tandem repeats may contribute to the localization of the receptor. Similar to the loss of cellular proliferation activity (i.e. inhibition) recorded with subNES, deltaTR also demonstrated a significant loss of inhibitory activity indicating that the repeats may be integral to receptor function. These experiments reveal that OGFr contains one functional NES, L217 L220 L223 and L225 and can be exported from the nucleus in a CRM1-dependent manner.

Topical Application of Naltrexone to the Ocular Surface of Healthy Volunteers: A Tolerability Study

PURPOSE

A short-term, randomized double-masked study was conducted to test the tolerability of topical application of naltrexone to the corneal surface.

METHODS

Healthy human volunteers were recruited at the Penn State Hershey Medical Center between 2010 and 2013. Study groups of 4 subjects were established to receive escalating dosages of naltrexone; within each group, 1 subject received placebo. Four drops of 4 different dosages of naltrexone dissolved in commercial moxifloxacin solution were administered over a 24-h period of time; 1 group of subjects received only 1 drop. The naltrexone dosages tested were 1 × 10(-6) M (1 drop), 1 × 10(-6) M (4 drops), 5 × 10(-6) M (4 drops), 1 × 10(-5) M (4 drops), and 5 × 10(-5) M (4 drops). Drops were administered over a 24-h period. Consenting subjects had complete eye examinations, including visual acuity (ETDRS), external and slit-lamp examinations, corneal sensitivity, pachymetry, corneal topography, endothelial specular microscopy, Schirmer testing with anesthetic, and fundus photography, before receiving naltrexone. Individuals were reexamined at 24 h and 7 days following naltrexone or placebo application.

RESULTS

Twenty subjects were recruited for the study; 62% were male, 90% were Caucasian; and 19 subjects completed the study. No significant differences were noted in ocular health between left (treated) and right (untreated) eyes of subjects receiving naltrexone or placebo. No significant adverse events were reported.

CONCLUSIONS

Topical naltrexone was well tolerated in healthy human subjects after 1 or 4 eye drops of naltrexone at dosages up to 50 μM administered over a 24-h treatment period and observed for 1 week.

Opioid growth factor and low-dose naltrexone impair central nervous system infiltration by CD4 + T lymphocytes in established experimental autoimmune encephalomyelitis, a model of multiple sclerosis

Multiple sclerosis (MS) is an autoimmune disease of the central nervous system (CNS), characterized by infiltrating myelin-reactive T lymphocytes and demyelinating lesions. Experimental autoimmune encephalomyelitis (EAE) is the animal model widely utilized to study MS. EAE is mediated by CD4(+) T cells and can be induced in EAE-susceptible mice through immunization with a myelin antigen, such as proteolipid protein 139-151 (PLP139-151) in SJL mice. In this PLP-induced EAE model, autoreactive CD4(+) T cells migrate from peripheral tissues into the CNS where they are reactivated resulting in CNS damage. Th1 and Th17 cells produce the pro-inflammatory cytokines IFNγ and IL-17, respectively, that have been shown to have pathogenic roles in EAE and MS. Anti-inflammatory Th2, IL-4 secreting cells, have been indicated to inhibit EAE exacerbation. However, given the inflammatory environment of EAE, Th2 effector cells are outnumbered by Th1/Th17 cells. Regulatory CD4(+) T cells suppress immune reactions and have been demonstrated to be dysfunctional in MS patients. Opioid growth factor (OGF), chemically termed [Met(5)]-enkephalin, is a negative growth factor that interacts with the OGF receptor. The OGF-OGFr axis can be activated through exogenous administration of OGF or a low dosage of naltrexone (LDN), an opioid antagonist. We have previously demonstrated that modulation of the OGF-OGFr axis results in alleviation from relapse-remitting EAE, and that CNS-infiltrating CD3(+) T cells are diminished with exogenous OGF or intermittent blockade with LDN administration. In this paper, we aimed to determine whether OGF or LDN alter the Th effector responses of CD4(+) T lymphocytes within the CNS in established EAE. We report in these studies that the numbers of CD4(+) T lymphocytes in the CNS of EAE mice are decreased following treatment with OGF for five days but not LDN. However, modulation of the OGF-OGFr axis did not result in changes to CD4(+) Th effector cell responses in the CNS of EAE mice.

Endogenous opioid inhibition of proliferation of T and B cell subpopulations in response to immunization for experimental autoimmune encephalomyelitis

BACKGROUND

Experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis, is induced by immunization of mice with myelin oligodendrocytic glycoprotein (MOG35-55) injections, and after 9 days, mice develop behavioral signs of chronic progressive EAE. Proliferation of T and B cells located in peripheral lymph tissues such as spleen and inguinal lymph nodes of C57BL/6J mice are stimulated. The opioid growth factor-opioid growth factor receptor (OGF-OGFr) axis has been shown to effectively limit progression of chronic EAE when mice are treated at the time of induction or at time of established disease. In addition to repressed behavioral profiles, spinal cord neuropathology is diminished in mice treated with OGF or low dosages of naltrexone (LDN). However, there is little or no information on peripheral lymphocyte dynamics following immunization of mice with MOG antigen and treatment with OGF or LDN.

METHODS

Six-week old female mice were immunized with MOG35-55 and were injected intraperitoneally with OGF or a low dosage of naltrexone (LDN) beginning at the time of immunization; saline-injected immunized mice served as controls. Normal mice received saline for all injections. Periodically over a 2 week period, spleens and inguinal lymph nodes were removed, total lymphocytes counted, and subpopulations of CD4+ and CD8+ specific T-cells, as well as B lymphocytes, were determined by flow cytometry. On day 15 of treatment, lumbar spinal cord tissue was removed; CNS lymphocytes isolated, and assayed for Th1, Th2, and Th17 markers by flow cytometry.

RESULTS

Exogenous OGF or endogenous OGF following LDN suppressed T and B lymphocyte proliferation in the spleen and inguinal lymph nodes of MOG-immunized mice. Suppression of peripheral immune cell CD4+ and CD8+ T cell proliferation at 5 and 12 days correlated with reductions in clinical behavior. EAE mice treated with OGF for 15 days displayed elevated Th1 and Th17 cells; no subpopulations of Th2-specific T cells were noted.

CONCLUSIONS

OGF or LDN repress proliferation of CD4+ and CD8+T cells and B220+ B lymphocytes in the spleen and lymph nodes of immunized mice within a week of immunization. These data provide novel mechanistic pathways underlying the efficacy of OGF and LDN therapy for MS.

Improved clinical behavior of established relapsing-remitting experimental autoimmune encephalomyelitis following treatment with endogenous opioids: implications for the treatment of multiple sclerosis

Relapse-remitting multiple sclerosis is a chronic disease of the CNS that affects 350,000 individuals in the U.S., reducing the quality of life and often resulting in paralysis. Most current therapies do not target the underlying pathophysiology of multiple sclerosis (MS). This study examined the therapeutic efficacy of an endogenous peptide (opioid growth factor, OGF) known to inhibit cell replication in a receptor-mediated manner, utilizing a mouse model of relapse-remitting experimental autoimmune encephalomyelitis (RR-EAE). RR-EAE was induced by immunization of SJL/J mice with proteolipid protein. Two days following establishment of clinical disease, treatment with OGF (10mg/kg) or saline was initiated and mice were observed on a daily basis. OGF treated mice had markedly reduced clinical signs of disease over the course of 40 days. OGF treatment increased the incidence and lengthened the time of remissions relative to saline-treated mice with RR-EAE. OGF therapy also reduced relapses, and facilitated extended periods of mild disease. Neuropathological examination of lumbar spinal cord after 40 days of treatment revealed decreased numbers of Iba-1 and CD3+ reactive cells, suggesting that OGF inhibited proliferation of microglia/macrophages and T lymphocytes, as well as decreasing the number of proliferating activated astrocytes (Ki-67 and GFAP dual labeled sections). Peptide treatment for 40 days diminished levels of demyelination in comparison to saline-treated mice with RR-EAE. These data are the first to demonstrate that exposure to OGF initiated at the time of established disease can reverse the course of RR-EAE and reduce neuropathological deficits.

Featured Article: Selective blockade of the OGF–OGFr pathway by naltrexone accelerates fibroblast proliferation and wound healing

Naltrexone (NTX) is an opioid receptor antagonist that acts at classical and non-classical opioid receptors including the opioid growth factor receptor (OGFr). Animal models of type 1 and type 2 diabetes, as well as normal rodents, have shown that topical NTX enhances the healing rates of corneal epithelium and full-thickness cutaneous wounds. The mechanism of this general opioid antagonist on growth, and in particular the specific receptor pathway involved, is not understood. Tissue culture studies using NIH 3T3 fibroblasts and primary rat auricular fibroblasts were established to evaluate growth following opioid receptor antagonist treatment. Treatment of cells with CTOP, naltrindole, or nalmefene, selective antagonists for mu, delta, and kappa opioid receptors, respectively, did not accelerate cell replication. Addition of the classical opioid receptor peptides DAMGO, DPDPE, or EKC did not alter cell growth, suggesting that the classical opioid receptors were not involved in cutaneous wound healing. However, NTX (10−6 M) increased the growth of NIH 3T3 fibroblasts in culture over a 96-h period, and the specific ligand OGF decreased cell growth, supporting that the OGF-OGFr axis is tonically active and constitutively expressed in fibroblasts, the primary cell type in granulation tissue of the skin. Transfection of NIH 3T3 cells with OGFr siRNA reduced receptor protein; subsequent treatment with NTX did not accelerate cell proliferation. These data indicate that blockade of the OGFr pathway enhances proliferation of fibroblasts in vitro, and in a primary culture of auricular fibroblasts, suggesting that the effect of NTX on growth is mediated through the OGF-OGFr axis. Finally, antagonists for classical opioid receptors as well as NTX were topically applied to cutaneous wounds in type 1 diabetic rats; only NTX accelerated wound closure. These studies indicate that the mechanistic pathway underlying the effects of NTX to enhance cutaneous wound closure in diabetic and nondiabetic subjects is specific blockade of the OGF–OGFr regulatory axis.

Topical Naltrexone as Treatment for Type 2 Diabetic Cutaneous Wounds

Objective: Type 2 diabetes (T2D) is associated with impaired cutaneous wound healing and can result in ulceration, infection, and/or amputation. More than 25 million people in the United States have T2D and are vulnerable to epithelial-related complications. Current therapies are limited in their efficacy. New treatments for full-thickness cutaneous wounds that focus on underlying diabetic pathways are needed. Approach: Topical application of the opioid receptor antagonist naltrexone (NTX) dissolved in cream reverses delayed wound closure in type 1 diabetic rat by the acceleration of reepithelialization and enhancement of angiogenesis and remodeling. NTX blocks the opioid growth factor (OGF)-OGF receptor (OGFr) axis and upregulates DNA synthesis and cell proliferation. To investigate whether NTX is an effective therapy for T2D wound closure, genetically obese mice (db/db) and normal C57Bl/6J mice received full-thickness cutaneous wounds. Wounds (5 mm in diameter) were treated topically three times daily with 10-5 M NTX or sterile saline dissolved in cream and photographed every 2 days. Results: Wounds in db/db mice treated with saline were 11-92% larger than those in normal mice throughout the 2-week observation. Topical NTX therapy in T2D mice reduced the residual wound size by 13-30% between days 8 and 14 relative to diabetic mice receiving saline. Reepithelialization and DNA synthesis, as analyzed by epithelial thickness and BrdU labeling indexes, respectively, were accelerated in NTX-treated wounds. Innovation and Conclusion: These data suggest that the OGF-OGFr axis plays a role in epithelial-related complications of T2D and that blockade of this pathway by NTX may be an effective treatment for wound repair.

Opioid growth factor and the treatment of human pancreatic cancer: A review

Opioid growth factor (OGF), chemically termed [Met⁵]-enkephalin, and its receptor, OGF receptor (OGFr), form a biological axis that tonically regulates cell proliferation by delaying the G₁/S interface of the cell cycle under homeostatic conditions or in neoplasia. Modulation of the OGF-OGFr pathway mediates the course of pancreatic cancer, with exogenous OGF or upregulation of OGFr repressing growth of human pancreatic cancer cells in culture and in nude mice. OGF therapy alone or in combination with standard chemotherapies such as gemcitabine and 5-fluorouracil results in enhanced inhibition of DNA synthesis and tumor growth. Molecular manipulation of OGFr confirms that the receptor is specific for OGF’s inhibitory action. Preclinical studies have warranted Phase I and Phase II clinical trials using OGF infusions as a treatment for patients with advanced, unresectable pancreatic cancers. OGF, an endogenous neuropeptide, is a safe, non-toxic, and effective biotherapy that utilizes the OGF-OGFr axis to mediate pancreatic tumor progression.

Novel treatment for triple-negative breast and ovarian cancer: endogenous opioid suppression of women's cancers

Breast and ovarian cancers are responsible for more than 500,000 female deaths worldwide each year. Fifteen percent of the 230,000 women in the USA diagnosed with breast cancer in 2013 will have triple-negative breast cancer, a disease with few options for treatment, and a twofold greater mortality risk than other breast cancers. The OGF-OGF receptor pathway is present in these cancers, and regulates cell proliferation during homeostasis and disease. OGF is a tonically active peptide that inhibits DNA synthesis by upregulation of cyclin-dependent inhibitory kinases, without disrupting cell migration, differentiation or apoptosis. OGF receptor is a determinant in the proliferation of triple-negative breast cancer and ovarian cancer, and can be genetically modified to alter neoplastic cell replication in vitro and in nude mice. Preclinical studies warrant the use of OGF alone, or in combination, for treatment of triple-negative breast and ovarian cancer patients.

Opioid growth factor - opioid growth factor receptor axis inhibits proliferation of triple negative breast cancer

Triple negative breast cancer (TNBC) represents approximately 15% of the newly diagnosed cancers worldwide and is characterized by tissue lacking in estrogen, progesterone and human epidermal growth factor receptors. TNBC disproportionately affects younger women and women of colour, and new treatments are needed. The opioid growth factor (OGF) - opioid growth factor receptor (OGFr) axis is a determinant of cell proliferation in neoplasia, and OGF is an endogenously produced pentapeptide that inhibits cell replication by interacting with OGFr and upregulating cyclin-dependent inhibitory kinase pathways thus reducing DNA synthesis. In these studies we investigated the presence and function of the OGF-OGFr axis in two human TNBC cell lines, as well as in breast cancer cell lines containing hormonal receptors. TNBC cell lines MDA-MD-231 and BT-20, as well as human breast cancer cells SK-BR-3 and MCF-7, were examined for the presence of pentapeptide and receptors, as well as their response to OGF. Specificity of peptide and receptor was confirmed by antibody neutralization and molecular studies to knockdown classical receptor protein. The requirement for protein transcription and translation and RNA transcription were investigated. Growth of TNBC cells in the presence of OGF and standard of care chemotherapeutic agent paclitaxel was evaluated to determine both efficacy and protective effects against toxicity. OGF treatment inhibited TNBC cells in a dosage related, receptor mediated, and reversible manner. OGF was the specific endogenous opioid to inhibit cell proliferation, and this was mediated by p21 cyclin dependent inhibitory kinase pathways, and required protein and RNA synthesis. OGFr was the specific receptor involved; both peptide and receptor were detected in all four cell lines. OGF treatment inhibited growth of all cancer cell lines evaluated, and reduced cell death in cultures exposed to paclitaxel. The OGF-OGFr axis is present and functioning in TNBC cell lines, and provides a novel biological pathway as potential therapy.

Topical treatment with the opioid antagonist naltrexone accelerates the remodeling phase of full-thickness wound healing in type 1 diabetic rats

Wound repair involves a series of overlapping phases that include inflammation, proliferation, and tissue remodeling, with the latter phase requiring months for proper healing. Delays in any of these processes can result in infection, chronic ulceration, and possible amputation. Diabetes is a major risk factor for improper wound repair, and impaired wound healing is a major complication for more than 26 million people in the US diagnosed with diabetes. Previous studies have demonstrated that the opioid antagonist naltrexone (NTX) dissolved in moisturizing cream reverses delays in wound closure in streptozotocin-induced type 1 diabetic (T1D) rats. NTX accelerated DNA synthesis and increased the number of epithelial and mast cells, as well as new blood vessel formation. In this study, remodeling was evaluated in T1D rats up to eight weeks after initial wounding. Twenty days following wounding, diabetic rats treated with vehicle had elevated numbers of MMP-2+ fibroblasts, suggesting delayed healing processes; birefringence of granulation tissue stained with Sirius red revealed diminished collagen formation and maturation. Wound tissue from NTX-treated T1D rats had comparable numbers of MMP-2+ fibroblasts to control specimens, as well as accelerated maturation of granulation tissue. The integrity of wounded skin was evaluated by tensile strength measurements. T1D resulted in delayed wound healing, and wounded skin that displayed reduced tensile strength relative to normal rats. Topical NTX applied to wounds in T1D rats resulted in enhanced collagen formation and maturation over a 60-day period of time. Moreover, the force required to tear skin of NTX-treated T1D rats was elevated relative to the force necessary to tear the skin of vehicle-treated T1D rats, and comparable to that for normal rats. These data reveal that complications in wound healing associated with T1D involve the novel OGF-OGFr pathway, and that topical NTX is an effective treatment to enhance wound healing.

Ocular surface abnormalities related to type 2 diabetes are reversed by the opioid antagonist naltrexone

BACKGROUND

Ocular surface complications of type 2 diabetes are associated with reductions in tear production, increased corneal surface sensitivity, and delayed corneal re-epithelialization. This study examined the efficacy of topical application of the opioid antagonist naltrexone (NTX) in reversing these diabetic-related ocular surface complications in mice.

METHODS

The genetic db/db mouse model of type 2 diabetes, along with C57Bl/6 wild-type mice were investigated. Tear production was assessed by phenol red impregnated threads, and ocular surface sensitivity was measured using Von Frey filaments. Centrally located, circular corneal abrasions were created in mice and residual epithelial defects measured by fluorescein photography. Animals in each group received topical applications of drops of 10(-5) M NTX in sterile Vigamox (Vigamox, Alcon Laboratories, Fort Worth, Texas, USA) or sterile Vigamox alone, and tear production, corneal sensitivity, and reepithelialization were monitored.

RESULTS

In comparison to diabetic mice receiving vehicle only, db/db mice treated with one drop of NTX demonstrated a marked reversal in dry eye and ocular surface hypersensitivity within 1 h of one drop of NTX. Reversal of the complications in db/db mice usually lasted for 48-90 h. Corneal epithelial repair in db/db mice was enhanced following a regimen of three drops of NTX daily such that by 72 h, residual wounds were one third the size in db/db mice receiving NTX relative to diabetic mice receiving vehicle. Application of Vigamox alone had no effect. No adverse effects of NTX administration were noted in the cornea.

CONCLUSIONS

This is the first report of the efficacy of topical NTX in reversing corneal surface complications in type 2 diabetic mice.

Topical naltrexone accelerates full-thickness wound closure in type 1 diabetic rats by stimulating angiogenesis

Delays in wound healing often result in infection, chronic ulceration, and possible amputation of extremities. Impaired wound healing is a major complication of the 23 million people in the USA with diabetes, and financial and medical burdens are demanding new treatments for wound healing. Previous studies have demonstrated that topical application of the opioid antagonist naltrexone (NTX) dissolved in moisturizing cream reverses delays in wound closure in rats with streptozotocin-induced type 1 diabetes. A target of NTX's action is DNA synthesis and cell proliferation. In this study, granulation tissue was evaluated to ascertain the specific cellular targets that were impaired in diabetic wounds, as well as those that were enhanced following NTX application. Mast cell number as well as the number of new blood vessels immunoreactive to fibroblast growth factor-2 (FGF-2), vascular endothelial growth factor (VEGF), and alpha smooth muscle actin (α-SMA) antibodies were recorded at 3, 5, 8, 10, 15, and 20 days following creation of full-thickness dorsal cutaneous wounds in normal and type 1 diabetic rats. Diabetic rats displayed delays in wound closure as well as a reduction in the number of mast cells responding to the injury, and delays in the spatial and temporal expression of FGF-2, VEGF, and α-SMA in capillaries. Topical NTX accelerated the rate of wound closure and stimulated expression of angiogenic factors within granulation tissue of diabetic rats relative to control animals receiving saline in moisturizing cream. These data support observations that a novel biological pathway is impaired under diabetic conditions and can be modulated by topical NTX to enhance proliferative events in wound healing.

Targeting the opioid growth factor: Opioid growth factor receptor axis for treatment of human ovarian cancer

The opioid growth factor (OGF) – opioid growth factor receptor (OGFr) axis is a biological pathway that is present in human ovarian cancer cells and tissues. OGF, chemically termed [Met5]-enkephalin, is an endogenous opioid peptide that interfaces with OGFr to delay cells moving through the cell cycle by upregulation of cyclin-dependent inhibitory kinase pathways. OGF inhibitory activity is dose dependent, receptor mediated, reversible, protein and RNA dependent, but not related to apoptosis or necrosis. The OGF-OGFr axis can be targeted for treatment of human ovarian cancer by (i) administration of exogenous OGF, (ii) genetic manipulation to over-express OGFr and (iii) use of low dosages of naltrexone, an opioid antagonist, which stimulates production of OGF and OGFr for subsequent interaction following blockade of the receptor. The OGF-OGFr axis may be a feasible target for treatment of cancer of the ovary (i) in a prophylactic fashion, (ii) following cytoreduction or (iii) in conjunction with standard chemotherapy for additive effectiveness. In summary, preclinical data support the transition of these novel therapies for treatment of human ovarian cancer from the bench to bedside to provide additional targets for treatment of this devastating disease.

Opioid growth factor arrests the progression of clinical disease and spinal cord pathology in established experimental autoimmune encephalomyelitis

An endogenous neuropeptide, opioid growth factor (OGF), chemically termed [Met(5)]-enkephalin, arrested the progression of established disease in a mouse model of multiple sclerosis (MS) called experimental autoimmune encephalomyelitis (EAE). This study treated mice who demonstrated 2 consecutive days of behavioral decline following injections of myelin oligodendrocyte glycoprotein (MOG) with daily injections of OGF (10mg/kg) or saline (0.1ml) for 40 days. Within 6 days of OGF treatment, mice initially demonstrating clinical signs of EAE had significant reductions (45% reduction) in their behavioral scores relative to EAE mice receiving saline. Behavior was attenuated for the entire 40-day period with mice receiving OGF showing only limp tails and wobbly gait in comparison to saline-treated EAE mice who displayed paralysis of one or more limbs. Neuropathological studies revealed that OGF treatment initiated after the appearance of disease reduced the number of activated astrocytes and damaged neurons, decreased demyelination, and inhibited T cell proliferation. These results demonstrate that OGF can halt the progression of established EAE, return aberrant pain sensitivity to normal levels, inhibit proliferation of T cells and astrocytes, and prevent further spinal cord pathology. The data extend our observations that OGF given at the time of disease induction prevented disease onset, reduced the severity of clinical signs of disease, and reversed neurological deficits in a non-toxic manner. Our data substantiate the role of the OGF-OGFr axis in EAE and support the use of OGF as a biotherapy for MS.

The opioid growth factor-opioid growth factor receptor axis: homeostatic regulator of cell proliferation and its implications for health and disease

The opioid growth factor (OGF), chemically termed [Met(5)]-enkephalin, is an endogenous opioid peptide that interacts with the OGF receptor (OGFr) to delay the G(1)/S interface of the cell cycle by modulating cyclin-dependent inhibitory kinase (CKI) pathways. The OGF-OGFr axis is a tonically active, inhibitory pathway that is an important regulator during homeostasis and re-epithelialization, and plays a role in the onset and progression of autoimmune diseases and cancer. Modulation of the OGF-OGFr axis can be accomplished by a variety of pharmacological and molecular approaches including use of intermittent or continuous exposure to the opioid antagonist naltrexone, genetic manipulation of OGFr expression, and antibody neutralization of OGF. Clinically, OGF is a biological therapy that has potential application for treatment of cancer. Currently, naltrexone at low dosages is being evaluated for treatment of autoimmune diseases such as Crohn's and multiple sclerosis. High dosages of naltrexone are effective in reversing dry eye and accelerating the repair of corneal abrasions in normal and diabetic rats; these studies are under investigation in the clinical setting. Naltrexone also enhances full-thickness wound closure in animal models of Type 1 or Type 2 diabetes, and translation of this knowledge to the clinic is planned. In summary, understanding the OGF-OGFr axis as a homeostatic regulator of proliferation has substantial implications for maintaining human health and treatment of disease.

Spontaneous episodic decreased tear secretion in rats is related to opioidergic signaling pathways

PURPOSE

To elucidate the factors in tear production, this study examined the role of endogenous opioids and opioid receptors in spontaneous episodic reduced tear volume.

METHODS

A model of spontaneous episodic decreases in the quantity of tears was characterized in otherwise normal Sprague-Dawley rats using Schirmer's test. A single eye drop of 10(-5) M naltrexone (NTX), 10(-5) M [Met(5)]-enkephalin, or sterile vehicle was administered to one eye. Tear secretion, corneal sensitivity, and corneal morphology were examined in both eyes.

RESULTS

At any given time period, otherwise normal rats were found to have Schirmer test scores with a bimodal distribution (6.5 mm or less, or 7.0 mm or greater). Decreased tear production was detected in male and female rats aged 4 to 24 weeks at least once per animal. The episodes of reduced tear volume ranged from 1 to 7 days. No changes in corneal sensitivity or corneal morphology were observed in any rat. One drop of NTX given to rats with a decrease in tear volume raised levels of tears to scores of 7.0 mm or greater within 1 hour, and increased tear production persisted for at least 48 hours. NTX had no effect on rats with Schirmer scores of 7.0 mm or higher. Topical application of [Met(5)]-enkephalin depressed tear secretion from baseline scores of 9.8 ± 0.6 mm to as low as 4.5 ± 0.7 mm.

CONCLUSIONS

Normal rats experience fluctuations in tear production that can be modulated by opioidergic signaling pathways.

Targeted overexpression of OGFr in epithelium of transgenic mice suppresses cell proliferation and impairs full-thickness wound closure

The opioid growth factor (OGF) and its receptor, OGFr, play a regulatory role in cell proliferation, and maintain homeostasis through a tonically active negative feedback mechanism. To directly evaluate the repercussion of increased OGFr expression and consequent gain-of-function in epithelium, bovine keratin 5 promoter elements were used to direct the expression of OGFr to skin in a tetracycline-regulated manner. Three founder lines overexpressing OGFr (OGFrTG/K5-tTA) were established. Evidence for increased OGFr in the epithelium included a three-fold increase in OGFr binding activity, as well as significant increases in OGFr protein, as monitored by semiquantitative immunohistochemistry. DNA synthesis in target epithelium, including cornea, tongue, and skin of transgenic mice was decreased 41% to 80% from wild-type littermates; the liver, a nonepithelial organ, was not altered. Decreased DNA synthesis in corneal epithelium induced by transgenic expression of OGFr was further reduced by treatment with exogenous OGF but reversed by exposure to the opioid antagonist, naloxone. The number of cell layers in both epidermis and cornea of OGFrTG/K5-tTA animals was reduced nearly 45% from wild-type mice. Full-thickness wounds in mice overexpressing OGFr healed 37% to 75% slower than wild-type littermates. These data demonstrate for the first time that stable genetic amplification of OGFr downregulates homeostatic cell proliferation, as well as pathophysiological processes with respect to wound repair. These mice also can serve as a valuable model to dissect the mechanism of OGF-OGFr action and may be important in understanding the etiology, pathogenesis, and treatment of epithelium-related diseases.

Under-expression of the opioid growth factor receptor promotes progression of human ovarian cancer

The opioid growth factor (OGF) and its receptor, OGFr, serve as a tonically active inhibitory axis regulating the proliferation of human ovarian cancer cells. In the present study, we have investigated the repercussion on the progression of this deadly neoplasia when cells are engineered to molecularly under-express OGFr. shRNA constructs were used to knockdown OGFr in SKOV-3 cells; two clonal cell lines were examined. OGFr protein expression was decreased up to 73% in clones compared with wild-type (WT) and empty vector (EV) controls. OGFr-binding assays of clones revealed 50–55% decreases in binding capacity compared with control cells; binding affinity was comparable in all groups. Cell number in clones was increased 33–132%, and doubling times decreased 29–35%, compared with WT and EV cultures. Addition of exogenous OGF or naltrexone did not affect cell number in cultures with silenced OGFr. DNA synthesis of clonal cell lines was increased 136–146% from the WT and EV groups; no changes were noted in cell survival. Nude mice injected subcutaneously with cells under-expressing OGFr had an increased tumor incidence, decreased latency to tumor formation, increased tumor volume and decreased OGFr expression in tumors compared with WT and EV controls. OGF treatment in mice with WT or EV tumors, but not OGFr under-expressing tumors, inhibited tumor volume and weight. Collectively, these data demonstrate the critical nature of the OGF–OGFr axis as a determinant of the progression of human ovarian cancer, and suggest that attenuation of this system has an important bearing on the survival of these patients.