A randomised, placebo controlled clinical trial of the aldose reductase inhibitor CT-112 as management of corneal epithelial disorders in diabetic patients

Diabetic Corneal Neuropathy: Pathogenic Mechanisms and Therapeutic Strategies

Diabetes mellitus (DM) is a major global public health problem that can cause complications such as diabetic retinopathy, diabetic neuropathy, and diabetic nephropathy. Besides the reporting of reduction in corneal nerve density and decrease in corneal sensitivity in diabetic patients, there may be a subsequent result in delayed corneal wound healing and increased corneal infections. Despite being a potential cause of blindness, these corneal nerve changes have not gained enough attention. It has been proposed that corneal nerve changes may be an indicator for diabetic neuropathy, which can provide a window for early diagnosis and treatment. In this review, the authors aimed to give an overview of the relationship between corneal nerves and diabetic neuropathy as well as the underlying pathophysiological mechanisms of corneal nerve fiber changes caused by DM for improved prediction and prevention of diabetic neuropathy. In addition, the authors summarized current and novel therapeutic methods for delayed corneal wound healing, nerve protection and regeneration in the diabetic cornea.

Physiological and Pathological Roles of Aldose Reductase

Aldose reductase (AR) is an aldo-keto reductase that catalyzes the first step in the polyol pathway which converts glucose to sorbitol. Under normal glucose homeostasis the pathway represents a minor route of glucose metabolism that operates in parallel with glycolysis. However, during hyperglycemia the flux of glucose via the polyol pathway increases significantly, leading to excessive formation of sorbitol. The polyol pathway-driven accumulation of osmotically active sorbitol has been implicated in the development of secondary diabetic complications such as retinopathy, nephropathy, and neuropathy. Based on the notion that inhibition of AR could prevent these complications a range of AR inhibitors have been developed and tested; however, their clinical efficacy has been found to be marginal at best. Moreover, recent work has shown that AR participates in the detoxification of aldehydes that are derived from lipid peroxidation and their glutathione conjugates. Although in some contexts this antioxidant function of AR helps protect against tissue injury and dysfunction, the metabolic transformation of the glutathione conjugates of lipid peroxidation-derived aldehydes could also lead to the generation of reactive metabolites that can stimulate mitogenic or inflammatory signaling events. Thus, inhibition of AR could have both salutary and injurious outcomes. Nevertheless, accumulating evidence suggests that inhibition of AR could modify the effects of cardiovascular disease, asthma, neuropathy, sepsis, and cancer; therefore, additional work is required to selectively target AR inhibitors to specific disease states. Despite past challenges, we opine that a more gainful consideration of therapeutic modulation of AR activity awaits clearer identification of the specific role(s) of the AR enzyme in health and disease.

Therapeutic Ophthalmic Lenses: A Review

An increasing incidence of eye diseases has been registered in the last decades in developed countries due to the ageing of population, changes in lifestyle, environmental factors, and the presence of concomitant medical conditions. The increase of public awareness on ocular conditions leads to an early diagnosis and treatment, as well as an increased demand for more effective and minimally invasive solutions for the treatment of both the anterior and posterior segments of the eye. Despite being the most common route of ophthalmic drug administration, eye drops are associated with compliance issues, drug wastage by lacrimation, and low bioavailability due to the ocular barriers. In order to overcome these problems, the design of drug-eluting ophthalmic lenses constitutes a non-invasive and patient-friendly approach for the sustained drug delivery to the eye. Several examples of therapeutic contact lenses and intraocular lenses have been developed, by means of different strategies of drug loading, leading to promising results. This review aims to report the recent advances in the development of therapeutic ophthalmic lenses for the treatment and/or prophylaxis of eye pathologies (i.e., glaucoma, cataract, corneal diseases, or posterior segment diseases) and it gives an overview of the future perspectives and challenges in the field.

Diabetic keratopathy: Insights and challenges

Ocular complications from diabetes mellitus are common. Diabetic keratopathy, the most frequent clinical condition affecting the human cornea, is a potentially sight-threatening condition caused mostly by epithelial disturbances that are of clinical and research attention because of their severity. Diabetic keratopathy exhibits several clinical manifestations, including persistent corneal epithelial erosion, superficial punctate keratopathy, delayed epithelial regeneration, and decreased corneal sensitivity, that may lead to compromised visual acuity or permanent vision loss. The limited amount of clinical studies makes it difficult to fully understand the pathobiology of diabetic keratopathy. Effective therapeutic approaches are elusive. We summarize the clinical manifestations of diabetic keratopathy and discuss available treatments and up-to-date research studies in an attempt to provide a thorough overview of the disorder.

Influence of diabetes mellitus on anterior segment of the eye

Diabetes mellitus (DM) has been emerging as one of the most serious health problems worldwide. Ocular complications of DM are currently one of the major causes of blindness in developed countries, among which diabetic retinopathy is relatively well studied and understood. However, although ocular surface complications of DM are common, diabetic complications of anterior segment of the eye, such as, cornea, conjunctiva, and lacrimal glands, are often overlooked. DM is associated with progressive damage to corneal nerves and epithelial cells, which increases the risk of anterior segment disorders including dry eye disease, corneal erosion, persistent epithelial defects, and even sight-threatening corneal ulcer. In this review, the authors will discuss the association of DM with disorders of anterior segment of the eye. Studies indicating the value of corneal nerve assessment as a sensitive, noninvasive, and repeatable biomarker for diabetic neuropathy will also be introduced. In addition, treatment modalities of anterior segment disorders associated with DM is discussed. The studies introduced in this review suggest that early and periodic screening of the anterior segment of the eye, as well as the retina, is important for the optimal treatment of DM.

Novel quinazolinone-based 2,4-thiazolidinedione-3-acetic acid derivatives as potent aldose reductase inhibitors

Aim: Targeting aldose reductase enzyme with 2,4-thiazolidinedione-3-acetic acid derivatives having a bulky hydrophobic 3-arylquinazolinone residue. Materials & methods: All the target compounds were structurally characterized by different spectroscopic methods and microanalysis, their aldose reductase inhibitory activities were evaluated, and binding modes were studied by molecular modeling. Results: All the synthesized compounds proved to inhibit the target enzyme potently, exhibiting IC50 values in the nanomolar/low nanomolar range. Compound 5i (IC50 = 2.56 nM), the most active of the whole series, turned out to be almost 70-fold more active than the only marketed aldose reductase inhibitor epalrestat. Conclusion: This work represents a promising matrix for developing new potential therapeutic candidates for prevention of diabetic complications through targeting aldose reductase enzyme.

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Diabetic complications in the cornea

Diabetic corneal alterations, such as delayed epithelial wound healing, edema, recurrent erosions, neuropathy/loss of sensitivity, and tear film changes are frequent but underdiagnosed complications of both type 1 (insulin-dependent) and type 2 (non-insulin-dependent) diabetes mellitus. The disease affects corneal epithelium, corneal nerves, tear film, and to a lesser extent, endothelium, and also conjunctiva. These abnormalities may appear or become exacerbated following trauma, as well as various surgeries including retinal, cataract or refractive. The focus of the review is on mechanisms of diabetic corneal abnormalities, available animal, tissue and organ culture models, and emerging treatments. Changes of basement membrane structure and wound healing rates, the role of various proteinases, advanced glycation end products (AGEs), abnormal growth and motility factors (including opioid, epidermal, and hepatocyte growth factors) are analyzed. Experimental therapeutics under development, including topical naltrexone, insulin, inhibitors of aldose reductase, and AGEs, as well as emerging gene and cell therapies are discussed in detail.

Cornea and its changes in diabetes mellitus: the review

Diabetes mellitus (DM) is the most common endocrine disease, which makes it a priority among health and social problems. Ocular manifestations in diabetes often lead to patient disability. This review presents an analysis of morphological, experimental and clinical studies of the cornea in patients with diabetes mellitus, including original research, reviews and monographs of Russian and foreign authors from recent years. In addition, modern methods of corneal disease diagnosis are reviewed. Clinical and morphological changes in the diabetic cornea are discussed and early diabetic changes in all structural layers are indicated. The importance of changes to nerve fibres in diabetes is discussed and the correlation between the density of nerve fibres in the cornea and the density of epidermal nerve fibres is shown.

Bioactivity Focus of α-Cyano-4-hydroxycinnamic acid (CHCA) Leads to Effective Multifunctional Aldose Reductase Inhibitors

Bioactivity focus on α-cyano-4-hydroxycinnamic acid (CHCA) scaffold results in a small library of novel multifunctional aldose reductase (ALR2) inhibitors. All the entities displayed good to excellent inhibition with IC50 72-405 nM. (R,E)-N-(3-(2-acetamido-3-(benzyloxy)propanamido)propyl)-2-cyano-3-(4-hydroxy phenyl)acrylamide (5f) was confirmed as the most active inhibitor (IC50 72.7 ± 1.6 nM), and the best antioxidant. 5f bound to ALR2 with new mode without affecting the aldehyde reductase (ALR1) activity, implicating high selectivity to ALR2. 5f was demonstrated as both an effective ALR2 inhibitor (ARI) and antioxidant in a chick embryo model of hyperglycemia. It attenuated hyperglycemia-induced incidence of neural tube defects (NTD) and death rate, and significantly improved the body weight and morphology of the embryos. 5f restored the expression of paired box type 3 transcription factor (Pax3), and reduced the hyperglycemia-induced increase of ALR2 activity, sorbitol accumulation, and the generation of ROS and MDA to normal levels. All the evidences support that 5f may be a potential agent to treat diabetic complications.

Extracellular matrix, gap junctions, and retinal vascular homeostasis in diabetic retinopathy

The vascular basement membrane (BM) contains extracellular matrix (ECM) proteins that assemble in a highly organized manner to form a supportive substratum for cell attachment facilitating myriad functions that are vital to cell survival and overall retinal homeostasis. The BM provides a microenvironment in which bidirectional signaling through integrins regulates cell attachment, turnover, and functionality. In diabetic retinopathy, the BM undergoes profound structural and functional changes, and recent studies have brought to light the implications of such changes. Thickened vascular BM in the retinal capillaries actively participate in the development and progression of characteristic changes associated with diabetic retinopathy. High glucose (HG)-induced compromised cell-cell communication via gap junctions (GJ) in retinal vascular cells may disrupt homeostasis in the retinal microenvironment. In this review, the role of altered ECM synthesis, compromised GJ activity, and disturbed retinal homeostasis in the development of retinal vascular lesions in diabetic retinopathy are discussed.

Aldose reductase inhibitor counteracts the enhanced expression of matrix metalloproteinase-10 and improves corneal wound healing in galactose-fed rats

PURPOSE

We investigated the effect of an aldose reductase inhibitor (ARI) and the role of matrix metalloproteinase (MMP)-10 on recovery after corneal epithelium removal in a rat diabetic keratopathy model.

METHODS

Three-week-old Sprague-Dawley rats were fed the following diets for 6 weeks: normal MF chow (MF), 50% galactose (Gal), and 50% Gal containing 0.01% ARI (Gal +ARI). The corneal epithelium was removed using n-heptanol, and the area of epithelial defects was photographed and measured every 24 h. Real-time reverse transcriptase PCR, western blotting, and immunohistochemistry were used to determine the expression profile of MMP-10 and integrin α3.

RESULTS

Compared to the MF control group, the amount of galactitol in the Gal group increased approximately 200-fold, which was reduced to sevenfold by ARI treatment. The area of corneal erosion in the Gal group was significantly larger than in the MF group at 72 h and thereafter (p<0.01, unpaired t test). The expression level of MMP-10 was enhanced at both the protein and mRNA levels by exposure to a high concentration of Gal, while integrin α3 expression decreased at the protein level but remained unchanged at the mRNA level. Delayed epithelial wound healing and alterations in the expression levels of MMP-10 and integrin α3 were normalized by ARI. The corneal erosion closure rate was significantly decreased with topical recombinant MMP-10.

CONCLUSIONS

These studies confirm that the increased expression of MMP-10 induced by Gal feeding is counteracted by ARI treatment and suggest a role of MMP-10 in modulating corneal epithelial wound healing.

Understanding the role of aldose reductase in ocular inflammation

Aldose reductase, although identified initially as a glucose-reducing enzyme via polyol pathway, is believed to be an important component of antioxidant defense system as well as a key mediator of oxidative stress-induced molecular signaling. The dual role played by AR has made it a very important enzyme for the regulation of not only the cellular redox state by detoxifying the reactive lipid-aldehydes generated by lipid peroxidation which is crucial in the cellular homeostasis, but also in the regulation of molecular signaling cascade that may regulate oxidative stress-induced cytotoxic events. Search for the new molecular targets to restrain the oxidative stress-induced inflammation has resulted in the identification of AR as an unanticipated mediator of oxidative stress-induced signaling. Although, in last one decade or so AR has been implicated in various inflammation-related diseases conditions ranging from diabetes, sepsis, cancer, cardiovascular and ocular inflammation, however, a critical evaluation of the clinical efficacy of AR inhibitors awaits a better understanding of the role of AR in regulating inflammation, especially in ocular inflammation.

Adenovirus-driven overexpression of proteinases in organ-cultured normal human corneas leads to diabetic-like changes

Our previous data suggested the involvement of matrix metalloproteinase-10 (MMP-10) and cathepsin F (CTSF) in the basement membrane and integrin changes occurring in diabetic corneas. These markers were now examined in normal human organ-cultured corneas upon recombinant adenovirus (rAV)-driven transduction of MMP-10 and CTSF genes. Fifteen pairs of normal autopsy human corneas were used. One cornea of each pair was transduced with rAV expressing either CTSF or MMP-10 genes. 1-2 x 10(8) plaque forming units of rAV per cornea were added to cultures for 48 h with or without sildenafil citrate. The fellow cornea of each pair received control rAV with vector alone. After 6-10 days additional incubation without rAV, corneas were analyzed by Western blot or immunohistochemistry, or tested for healing of 5-mm circular epithelial wounds caused by topical application of n-heptanol. Sildenafil significantly increased epithelial transduction efficiency, apparently by stimulation of rAV endocytosis through caveolae. Corneas transduced with CTSF or MMP-10 genes or their combination had increased epithelial immunostaining of respective proteins compared to fellow control corneas. Staining for diabetic markers integrin alpha(3)beta(1), nidogen-1, nidogen-2, and laminin gamma2 chain became weaker and irregular upon proteinase transduction. Expression of phosphorylated Akt was decreased in proteinase-transduced corneas. Joint overexpression of both proteinases led to significantly slower corneal wound healing that became similar to that observed in diabetic corneas. The data suggest that MMP-10 and CTSF may be responsible for abnormal marker patterns and impaired wound healing in diabetic corneas. Inhibition of these proteinases in diabetic corneas may alleviate diabetic keratopathy symptoms.

Naltrexone and insulin are independently effective but not additive in accelerating corneal epithelial healing in type I diabetic rats

Patients with diabetes are at increased risk for developing corneal disorders, termed diabetic keratopathy. Treatments for diabetic keratopathy are limited. Preclinical studies have demonstrated that topical administration of either naltrexone (NTX) or insulin (INS) accelerates corneal re-epithelialization in type I diabetic rats. This study determined whether the combination of NTX and INS would have additive effect(s) on the re-epithelialization of corneal abrasions in diabetic male Sprague-Dawley rats beyond either agent alone. Type 1 diabetes (DB) (glucose levels>400mg/dl) was induced with streptozotocin; glycemic levels were not controlled with INS. Eight weeks after induction of diabetes, a 5mm diameter circular abrasion was created in the center of the cornea in one eye of each rat. Eye drops (0.05ml) of INS [1U ( approximately 6nM)] and NTX (10(-5)M) in Vigamox were administered separately 4 times daily for 7 days (NTX/INS); DB control rats received drops of sterile vehicle (DB SV) 4 times daily. Two other groups of rats were given only NTX (DB NTX) or only INS (DB INS). Re-epithelialization was monitored by fluorescein staining, and images were recorded with a CCD camera. Areal measurements were made using Optimas software, and the percentage of epithelial defect over a 40h period was calculated. Twenty-four hour after formation of an abrasion ( approximately 21.7+/-0.4mm(2)area), corneal wounds in DB rats treated with NTX, INS, or NTX/INS were significantly smaller (p<0.001) than those in DB SV rats, with reductions in the size of the defect ranging from 24 to 84%. DB rats treated with NTX or INS alone also were observed to have reductions in wound size of 22 and 29%, respectively, from subjects in the DB SV group at 16h. At 16h both the DB NTX and DB INS groups had defects that were 13 and 27%, respectively, smaller than those for the DB NTX/INS group, and at 40h the DB INS animals had 78% smaller corneal wounds than in the DB NTX/INS group. Therefore, the DB NTX/INS group exhibited some slight delays in wound repair compared to the DB NTX and DB INS groups. Topical application of NTX and/or INS to the cornea had no effect on non-invasive measures that included ocular morphology, intraocular pressure, or corneal thickness. These data demonstrate that although NTX or INS accelerates wound healing, concomitant application of NTX and INS to corneal abrasions in diabetic animals does not have an additive effect on re-epithelialization.

Topically Applied Naltrexone Restores Corneal Reepithelialization in Diabetic Rats

PURPOSE

Complications of diabetes include an increased risk of delayed corneal epithelial wound healing. This study examined the efficacy of naltrexone (NTX), an opioid antagonist, by topical application in facilitating the repair of such lesions.

METHODS

NTX, in concentrations of 10(-4), 10(-5), or 10(-6) M, was administered topically 4 times per day for 7 days to the abraded eye of type 1 diabetic rats (DB), DB animals receiving insulin and normoglycemic (DB-IN), and nondiabetic (Normal) rats, beginning 8 weeks following the onset of diabetes.

RESULTS

In comparison to DB animals receiving sterile vehicle (SV), DB-NTX rats had 25%-83% smaller defects, a reduction of 24 h (approximately 33%) in closure time, and 20%-42% faster healing rates. DB rats receiving 10(-4) and 10(-5) M NTX were equal to, or surpassed, Normal animals in all parameters of wound closure. NTX also enhanced wound repair in DB-IN and Normal animals relative to their respective SV group. No adverse effects of NTX administration on a variety of noninvasive or invasive measures were discerned.

CONCLUSIONS

Topically applied NTX is not only feasible, but also effective over a one hundredfold dosage for accelerating corneal wound healing in diabetic subjects.

Morphologic alterations of both the stromal and subbasal nerves in the corneas of patients with diabetes

PURPOSE

To evaluate the subbasal and the stromal nerves of the corneas of patients with type 2 diabetes with in vivo confocal microscopy and to compare them with those of nondiabetic patients.

METHODS

Thirty-five corneas of patients with type 2 diabetes and 24 corneas of age-matched control subjects were included in the study. Patients with diabetes were further classified with respect to the stage of retinopathy. Subbasal and stromal nerve plexus morphology and thickness were evaluated with in vivo confocal microscopy. Subbasal long nerve fiber (LNF) and total nerve branch (NB) densities were calculated.

RESULTS

The mean stromal nerve thickness was significantly higher in patients with diabetes (8.99 +/- 2.32 microm) than that of the control subjects (5.69 +/- 1.49 microm; Mann-Whitney U test; P < 0.001). The proportion of curved stromal nerves in patients with diabetes (45.7%) was also higher than that of normal subjects (20.8%; chi(2), P = 0.05). Subbasal LNF and NB densities were found to significantly lower in the corneas of patients with diabetes (28.3 +/- 10.4 and 39.7 +/- 13.2 nerve/mm(2), respectively) than those of the control subjects (34.1 +/- 5.7 and 58.5 +/- 12.4 nerve/mm(2), respectively; Mann-Whitney, P = 0.012 and P < 0.001). In addition, the subbasal nerve plexus of patients with diabetes appeared significantly thicker and more tortuous than those of the control subjects (Mann-Whitney, P = 0.002 and P = 0.001).

CONCLUSION

Both stromal and subbasal nerves appear abnormal in the corneas of patients with diabetes. Patients with proliferative diabetic retinopathy show more pronounced nerve alterations than patients who do not have diabetic retinopathy.