Aldose reductase activity and glucose-related opacities in incubated lenses from dogs and cats

Detemir improves diabetic regulation in poorly controlled diabetic dogs with concurrent diseases

OBJECTIVE

This study evaluated the use of detemir for treating diabetic dogs with comorbidities that were poorly controlled with intermediate-acting insulins.

ANIMALS

7 insulin-treated diabetic dogs.

PROCEDURES

Retrospective pilot study. Dogs were treated with detemir for at least 3 months, and glycemia was assessed by the owners at home initially 2 to 4 times daily for 6 to 8 weeks and twice daily thereafter. Clinical evaluations occurred on days 7 to 14, day 30, and then every 60 to 90 days, and dosage adjustments of detemir occurred as needed to control glycemia.

RESULTS

The mean, peak, nadir, morning, and evening preinsulin daily blood glucose concentrations were significantly lower after dosing with detemir for 1, 3, or 6 months and during the last month of treatment compared to the final month of treatment with intermediate-acting insulin. Intermediate-acting insulins resulted in significantly worse glycemic control than detemir in all 3 categories of control. The odds of a biochemical hypoglycemic measurement with detemir were not significantly different compared to intermediate-acting insulins. Clinical hypoglycemia did not occur following detemir treatment. When insulin was withheld because of low morning preinsulin blood glucose concentration < 6.7 mmol/L (≤ 120 mg/dL) and dogs were fed, mean blood glucose concentration was significantly higher 1 hour later. Glucose concentrations were also significantly higher 12 hours later on days when insulin was withheld in the morning or evening for either 1 or 12 hours.

CLINICAL RELEVANCE

Detemir is useful in diabetic dogs with other comorbidities and can be considered an alternative treatment in poorly controlled diabetic dogs.

Retrospective Study of Long-Term Outcome of Phacoemulsification in 22 Feline Eyes with Presumed Congenital/Juvenile Cataracts (2007-2020)

The objective of this study was to determine the complication risk and prevalence after phacoemulsification in cats with presumed congenital/inherited cataracts. Twelve client-owned cats were included in the study. This retrospective study spanned 13 yr and involved 22 eyes. The median age at the time of surgery was 15 mo (range: 4.5-168 mo of age). Recorded complications were 3 eyes developed postoperative ocular hypertension, 1 eye developed glaucoma, 7 eyes developed feline herpes virus-1 signs, and 7 eyes developed postoperative uveitis >2 wk after surgery. No eyes had developed intraocular sarcomas at the time of their last exam. All eyes remained visual at last follow-up (range: 0.5-121 mo). Success was defined as a comfortable and visual eye without intraocular neoplasia, glaucoma, a partial or complete retinal detachment, or uveitis that occurred >2 wk after surgery or persisted longer than 2 wk. Twenty-one out of 22 eyes had a successful outcome. In this study, cats with presumed congenital/juvenile cataracts who underwent phacoemulsification had an excellent outcome.

A possible follow-up method for diabetic heart failure patients

INTRODUCTION

Plasma osmolarity is maintained through various mechanisms. The osmolarity of the aqueous humor around the crystalline lens is correlated with plasma osmolarity. A vacuole can be formed in the lens upon changes in osmolarity. The sodium-glucose cotransporter 2 inhibitors (SGLT2i) are new in the treatment of heart failure. They can cause osmotic diuresis but do not affect plasma osmolarity.

OBJECTIVE

It is unclear if the presence or absence of lens vacuole changes can monitor diabetic heart failure and SGLT2i treatment efficacy.

METHODS

Web of Science, PubMed and Scopus databases were searched for relevant articles about osmolarity, diabetes, transient receptor potential vanilloid channel, diabetic heart failure, lens vacuoles up to May 2021.

MAIN MESSAGE

The effect of SGLT2i on osmosis underlies its benefit to heart failure, but this in turn affects many other mechanisms. Failure to experience osmolarity changes will reduce the negative changes in terms of heart failure affected by osmolarity. A practical observable method is needed.

CONCLUSIONS

There is a possibility of using lens vacuoles in the follow-up of diabetic heart failure patients.

Evaluation of diabetes mellitus regulation in dogs treated with ophthalmic preparations of prednisolone acetate versus diclofenac sodium

OBJECTIVE

To evaluate and compare regulation of diabetes mellitus (DM) in dogs with cataracts and well-controlled DM that received an ophthalmic preparation of prednisolone acetate versus diclofenac sodium.

ANIMALS

22 client-owned dogs with cataracts and well-controlled DM.

PROCEDURES

A prospective, randomized, double-masked, experimental study was conducted. On days 0 and 32, serum fructosamine concentrations (SFCs), clinical scores, and body weights were determined. Dogs were assigned to receive a topically administered ophthalmic preparation of either prednisolone acetate 1% or diclofenac sodium 0.1% in each eye 4 times daily for 28 days. Data analysis was conducted with generalized linear mixed models.

RESULTS

Findings indicated no meaningful differences in SFCs, clinical scores, or body weights between the treatment groups on days 0 or 32. Clinical score on day 0 was positively associated with SFC, as indicated by the corresponding rate of change such that each 1 -unit increase in clinical score was associated with an approximately 45.6 ± 9.4 μmol/L increase in SFC. In addition, the least squares mean ± SEM SFC was higher in spayed females (539.20 ± 19.23 μmol/L; n = 12) than in castrated males (458.83 ± 23.70 μmol/L; 8) but did not substantially differ between sexually intact males (446.27 ± 49.72 μmol/L; 2) and spayed females or castrated males regardless of the treatment group assigned.

CONCLUSIONS AND CLINICAL RELEVANCE

Findings indicated no evidence for any differential effect on DM regulation (assessed on the basis of SFCs, clinical scores, and body weights) in dogs treated topically with an ophthalmic preparation of prednisolone versus an ophthalmic preparation of diclofenac. Additional research investigating plasma concentrations of topically applied ophthalmic glucocorticoid medications is warranted. (Am J Vet Res 2019;80:1129-1135).

Canine Diabetes Mellitus Associated Ocular Disease

Diabetes mellitus (DM) is a commonly encountered disease in companion animal veterinary practice. Ocular complications in dogs with DM are thought to be common but there are no reports of the overall incidence of DM-associated ocular disease. Some complications, such as cataracts and ocular surface disease, can lead to vision loss and significant morbidity among DM patients, therefore early recognition and intervention are essential for successful outcomes. The purpose of this article is to provide a review of several currently known or suspected ocular diseases associated with DM.

Diabetic phenotype of transgenic pigs introduced by dominant-negative mutant hepatocyte nuclear factor 1α

AIM

The present study aimed to identify the characteristics of genetically modified pigs carrying a mutant human gene as a research model for diabetes and its complications.

METHODS

We developed a transgenic cloned pig (founder, male) carrying a mutant gene, i.e., human HNF-1α (P291fsinsC), which is responsible for maturity-onset diabetes of the young type 3. Transgenic progeny obtained via the artificial insemination of wild type (WT) sows with the cryopreserved sperm derived from the founder pig was pathologically examined.

RESULTS

The transgenic progeny maintained a high blood glucose level (>200mg/dL). Additionally, the oral glucose tolerance test results showed that the recovery of blood glucose levels in the transgenic progeny was significantly delayed compared with that in the WT semi-siblings. Hypoplasia of the islets of Langerhans was confirmed by the histopathological image of the pancreas, based on the hyperglycemia noted in the progeny being ascribed to decreased insulin secretion. Retinal hemorrhage and cotton-wool spots, i.e., findings consistent with non-proliferative diabetic retinopathy, were detected, and these progressed over time. The histopathological image of the renal glomeruli showed a nodular lesion that is characteristic of diabetic nephropathy in humans.

CONCLUSIONS

These data demonstrated that the genetically modified pig that we developed is a promising model for research on diabetes and its complications.

Effect of Oral Alpha Lipoic Acid in Preventing the Genesis of Canine Diabetic Cataract: A Preliminary Study

Blinding cataract is a significant effect of canine diabetes with 75% of animals affected two years after diagnosis. Lens opacification occurs primarily through the generation of sorbitol, a sugar alcohol, through the action of aldose reductase (AR). The osmotic effect of sorbitol draws water into the lens, causing opacification. Inhibition of AR should thus prevent the generation of cataracts. A topical AR inhibitor has been shown to have this effect, as has the commercially available neutraceutical OcuGLO, containing the AR inhibitor alpha lipoic acid (ALA) together with other plant-based antioxidants. Here a comparison is made between the number of diabetic dogs developing cataracts when given oral ALA alone and those given a mix containing ascorbic acid and tocopherol. Animals given ALA developed significantly fewer lens opacities than those given conventional antioxidants. Cataracts which formed occurred at a significantly greater duration after the commencement of treatment than those on the antioxidant mix. Although this is a small study conducted over a short period, the significant benefit of ALA in diabetic dogs is a reason to evaluate these effects in larger trials. As AR is involved in diabetic retinopathy and neuropathy, this enzyme inhibitor may be worthy of evaluation in preventing these conditions in human diabetics also.

Update on animal models of diabetic retinopathy: from molecular approaches to mice and higher mammals

Diabetic retinopathy (DR) is the most common microvascular complication of diabetes and one of the major causes of blindness worldwide. The pathogenesis of DR has been investigated using several animal models of diabetes. These models have been generated by pharmacological induction, feeding a galactose diet, and spontaneously by selective inbreeding or genetic modification. Among the available animal models, rodents have been studied most extensively owing to their short generation time and the inherited hyperglycemia and/or obesity that affect certain strains. In particular, mice have proven useful for studying DR and evaluating novel therapies because of their amenability to genetic manipulation. Mouse models suitable for replicating the early, non-proliferative stages of the retinopathy have been characterized, but no animal model has yet been found to demonstrate all of the vascular and neural complications that are associated with the advanced, proliferative stages of DR that occur in humans. In this review, we summarize commonly used animal models of DR, and briefly outline the in vivo imaging techniques used for characterization of DR in these models. Through highlighting the ocular pathological findings, clinical implications, advantages and disadvantages of these models, we provide essential information for planning experimental studies of DR that will lead to new strategies for its prevention and treatment.

Monitoring methods for dogs and cats with diabetes mellitus

Effective monitoring is essential for the management of dogs and cats with diabetes mellitus. However, methods for evaluating glycemic control must be tailored to meet both the needs of the patient and the expectations of the owner. This article discusses the philosophies that drive blood glucose monitoring in veterinary diabetics and review common practices. The advantages and limitations of the various options are presented.

Topical KINOSTAT™ ameliorates the clinical development and progression of cataracts in dogs with diabetes mellitus

OBJECTIVE

To determine whether topical administration of the aldose reductase inhibitor Kinostat™ can ameliorate the onset or progression of cataracts in dogs with naturally occurring diabetes mellitus (DM).

MATERIALS AND METHODS

A randomized, prospective, double-masked placebo control pilot study was conducted with 40 dogs newly diagnosed with DM with no or minimal lens changes. Twenty-eight dogs received Kinostat™ and 12 dogs received placebo.

PROCEDURES

Owners administered the agent into both eyes three times daily for 1 year and compliance was monitored with log sheets. Complete ophthalmic examinations were performed on dilated eyes at the time of enrollment and 1, 2, 3, 6, and 12 months into treatment. Cataract severity was assessed on a scale of 0-3. At 12 months, full bloodwork, including HbA1C and blood Kinostat™ levels were performed.

RESULTS

After 12 months of treatment, the cataract score in the placebo group significantly increased with seven dogs (14 eyes) developing mature cataracts, two dogs (4 eyes) developing cortical opacities, and one dog (2 eyes) developing equatorial vacuoles with mild punctate cortical opacities. In contrast, the cataract score in the Kinostat™ treated dogs was significantly less with seven developing anterior equatorial vacuoles, two developing incipient anterior cortical cataracts, and four developing mature cataracts. In fact, the cataract scores of the Kinostat™ group at 12 months did not significantly increase from the score at the time of enrollment. The HbA1C values between the two groups after 12 months of treatment were similar, and no blood levels of Kinostat™ were found in any enrolled dog.

CONCLUSION

The onset and/or progression of cataracts in dogs with DM can be significantly delayed by topical administration of Kinostat™.

Are the available experimental models of type 2 diabetes appropriate for a gender perspective?

Several experimental models have so far been developed to improve our knowledge of the pathogenetic mechanisms of type 2 diabetes mellitus (T2D), to determine the possible pharmacological targets of this disease and to better evaluate diabetes-associated complications, e.g. the cardiovascular disease. In particular, the study of T2D gained the attention of several groups working with different animal species: rodents, cats or pigs, as well as other non-human primate species. Each of these species provided useful and different clues. However, T2D has to be considered as a gender-associated disease: sex differences play in fact a key role in the onset as well as in the progression of the disease and a higher mortality for cardiovascular diseases is detected in diabetic women with respect to men. The results obtained from all the available animal models appear to only partially address this issue so that the search for more precise information in this respect appears to be mandatory. In this review we summarize these concepts and literature in the field and propose a reappraisal of the various animal models for a study of T2D that would take into consideration a gender perspective.

Advanced glycation end products and sorbitol in blood from differently compensated diabetic dogs

Canine diabetes mellitus (DM) is a common metabolic disorder with long term complications, most of which are caused by glycosylation of structural proteins, decreases in antioxidant concentrations, altered osmotic balance and hypoxia due to impaired oxygen transport. Previous studies have demonstrated that under hyperglycemic conditions canine erythrocytes undergo swelling, probably due to activation of the polyol pathway. The present work aimed to assess the plasma concentration of advanced glycation end (AGE) products, stable Amadori-products generated by non-enzymatic glycosylation of proteins and the intracellular concentration of sorbitol, produced by the activation of polyol pathway in 34 blood samples from diabetic dogs and in 14 controls. AGE products were significantly higher (p<0.01) in plasma from diabetic dogs compared with control animals. The sorbitol concentration in erythrocytes was also significantly higher in diabetic dogs and, in particular, in poorly compensated animals and in dogs with ketonuria. In five cases that were analysed before and after clinical improvement, sorbitol concentration was found to correlate with improvement. These results suggest that non-specific glycosylation is increased and that the polyol pathway is activated in diabetic dogs in a manner that is proportionate to the severity of disease. Moreover, the concentration of AGE products and sorbitol may be useful for monitoring the onset of diabetic complications and assessing the most appropriate therapeutic approaches for management of canine DM.

Age-dependent retinal capillary pericyte degeneration in galactose-fed dogs

The galactose-fed beagle develops diabetes-like microvascular changes that are histologically and clinically similar in appearance to all stages of human diabetic retinopathy. This animal model is extremely useful for evaluating drugs for the treatment of diabetic retinopathy; however, the time required to develop the various retinal lesions (24-72 months for background to the proliferative stage) may be considered prohibitive. Retinal vascular changes begin with an initial degeneration of capillary pericytes, which has been linked to the aldose reductase catalyzed formation of galactitol. Because aldose reductase-linked sugar cataract formation is known to be age dependent, with the onset and severity of cataract higher in younger diabetic and galactose-fed animals, retinal capillary changes in the eyes of initially 2- versus 9-month-old beagles fed a diet containing 30% galactose were compared. Eyes were enucleated after 36 months of galactose feeding, the intact retinal capillaries were isolated by trypsin digestion, and defined retinal regions were evaluated by computer image analysis. Nicotinamide adenine dinucleotide phosphate-dependent reductase activity, using DL-glyceraldehyde and D-xylose as substrates, was also compared in the lenses and whole retinas of eyes from the 2- and 9-month-old beagles. Significantly (P<or=0.05) increased pericyte degeneration, expressed as either the number of pericytes/mm capillary length or the ratio of endothelial cells versus pericytes (E/P ratio) was observed in the retinas of the younger dogs. The number of microaneurysms per eye was also significantly increased in the younger dogs, but no difference in acellular capillary areas was observed. This correlates with a threefold higher level of reductase activity in the retinas of the 2-month-old dogs. Because retinal capillary pericyte destruction is age dependent similar to the formation of sugar cataracts, the use of younger dogs may shorten the time period required for evaluating the efficacy of drugs for diabetic retinopathy in this animal model.

Effects of topical administration of an aldose reductase inhibitor on cataract formation in dogs fed a diet high in galactose

OBJECTIVE

To determine effects of a topical formulation of an aldose reductase inhibitor (ARI) on the development of sugar cataracts in dogs fed a diet high in galactose. Animals-Ten 6-month old Beagles.

PROCEDURES

Dogs were fed a diet containing 30% galactose, and after 16 weeks, 6 dogs were treated topically with a proprietary ARI formulation and 4 dogs were treated with a placebo. Cataract formation was monitored by means of slit-lamp biomicroscopy and fundus photography. Dogs were euthanized after 10 weeks of treatment, and lenses were evaluated for degree of opacity, myo-inositol and galactitol concentrations, and concentration of the ARI.

RESULTS

All dogs developed bilateral cortical opacities dense enough to result in a decrease in the tapetal reflex after being fed the galactose-containing diet for 16 weeks. Administration of the ARI arrested further development of cataract formation. In contrast, cataracts in the vehicle-treated dogs progressed over the 10-week period to the mature stage. Evaluation of the isolated lenses after 26 weeks of galactose feeding indicated that lenses from treated dogs were significantly less optically dense than lenses from control dogs. Lenticular myo-inositol concentration was significantly higher in the treated than in the control dogs.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that topical application of a proprietary ARI formulation may arrest or reverse the development of sugar cataracts in dogs fed a diet high in galactose. This suggests that this ARI formulation may be beneficial in maintaining or improving functional vision in diabetic dogs with early lens opacities.

Is active glucose transport present in bovine ciliary body epithelium?

Hyperglycemia is a major risk factor for diabetic cataract formation. Effective regulation of glucose transport by the ciliary body epithelium (CBE) is pivotal to normal glycemic control in the anterior eye, which in turn affects the glucose level of the crystalline lens. The present study aimed to characterize the glucose transport mechanisms across the bovine blood-aqueous barrier (BAB) represented by the CBE. With an Ussing-type chamber, the glucose transport kinetics were measured and characterized in the presence and absence of various glucose transporter inhibitors. The saturation characteristics of the CBE to glucose were estimated from an Eadie-Hofstee plot. The mRNA expression of glucose transporters in specific regions of the bovine CBE was assessed using RT-PCR. The trans-CBE glucose flux was found to be sensitive to the glucose transporter inhibitors cytochalasin B, phloretin, and phlorizin. The transport system had a kinetic constant of 5.3 mM and a maximum velocity of 349.5 nmol.h(-1).cm(-2). Gene expression for GLUT1, GLUT3, GLUT4, GLUT5, and SGLT2 was observed in both the pars plana and pars plicata regions of the bovine CBE. This study demonstrates that glucose transport across the bovine CBE is primarily passive in nature. However, the novel findings of 1) the presence of a phlorizin-sensitive glucose flux and 2) gene expression for SGLT2 mean that a potential role for active glucose transport cannot be ruled out. The elucidation of the exact function of SGLT2 in the bovine CBE may shed important light on the glucose transport and physiology of the BAB and inform future studies of glycemic control in relation to diabetic cataract formation.

Canine cataracts, diabetes mellitus and spontaneous lens capsule rupture: a retrospective study of 18 dogs

OBJECTIVE

To describe the clinical presentation and surgical outcome of diabetic canine patients with cataracts and preoperative spontaneous lens capsule rupture.

ANIMALS STUDIED

A total of 20 dogs and 40 eyes were included in the retrospective evaluation. The patients' ages ranged from 5 to 14 years (mean 8.5 years).

RESULTS

All dogs had clinical diabetes mellitus, with the duration since diagnosis ranging from 30 to 240 days (mean 123 days). Cataracts were bilateral and noted to have been present for 14-112 days (mean 39 days). Of the 40 eyes affected with cataracts, 30 had a spontaneous rupture of the lens capsule prior to surgery. The capsular rupture was diagnosed on clinical examination in 28/30 eyes and was noted intraoperatively in 2/30. The location of the capsular rupture was equatorial in 29/30 and posterior in 1/30 eyes. Surgery was performed in 38/40 eyes, with one case lost to follow-up without surgical intervention. Prior to surgery, routine diagnostic ophthalmic examination, ocular ultrasound, electroretinography, and systemic evaluation were performed in all dogs. Surgical procedures included phacoemulsification in 28/40 eyes, with IOL placement performed in 20/28 eyes. Intrascleral prosthesis placement or enucleation was performed in 8/40 and 2/40 eyes, respectively, due to a significantly reduced ERG or secondary glaucoma.

CONCLUSIONS

The duration of clinical follow-up (19/20 dogs) ranged from 1 to 36 months (mean 12.9 months). All eyes that had cataract surgery with or without IOL placement were sighted at the time of the last follow-up examination. Spontaneous lens capsule rupture associated with diabetes mellitus, cataract and rapid lens intumescence occurs in the dog. Early surgical intervention, prior to secondary complications of glaucoma and loss of retinal function, is associated with a favorable outcome.

Prevalence of feline cataract: results of a cross-sectional study of 2000 normal animals, 50 cats with diabetes and one hundred cats following dehydrational crises

OBJECTIVE

In this study 2000 normal cats, 50 cats with diabetes and 100 cats with a history of dehydrational crises were examined ophthalmoscopically to determine presence of cataract.

MATERIALS AND METHODS

The cats examined were predominantly from veterinary hospital populations but also from re-homing facilities and breeding catteries. Prevalence of cataract was determined for different age groups (year cohorts). The age at which prevalence of cataract was 50% (C(50)) was determined indirectly from a fitted prevalence curve as previously described. C(50) was determined for animals of different genders and different breeds as well as for those with diabetes and histories of dehydrational episodes related to chronic renal failure, chronic vomiting or chronic diarrhea.

RESULTS

The mean +/- standard deviation of C(50) for all normal cats in the study was 12.7 +/- 3.4 years. All cats over 17.5 years were affected by some degree of lens opacity. C(50) for cats with diabetes was 5.6 +/- 1.9 years (significantly different from normal cats at P < 0.0001). For cats with a history of dehydrational crises C(50) was 9.9 +/- 2.5 (difference from normal cats nearing statistical significance at P = 0.06).

CONCLUSIONS

The study yields novel findings regarding the prevalence of age-related cataract in normal cats together with cats with diabetes and history of previous dehydrational episodes in which prevalence of cataract is increased.

Feline Models of Type 2 Diabetes Mellitus

Feline diabetes mellitus (FDM) closely resembles human type 2 diabetes mellitus (T2DM) in many respects including clinical, physiological, and pathological features of the disease. These features include age of onset of FDM in middle age, association with obesity, residual but declining insulin secretion, development of islet amyloid deposits, loss of approximately 50% of beta-cell mass, and development of complications in several organ systems including peripheral polyneuropathy and retinopathy. Many of the pathological aspects of the disease are also experimentally inducible, facilitating study of the pathogenesis of these lesions. Physiological aspects of FDM and obesity are also well studied in the cat and provide an excellent basis for comparative studies of human T2DM. The relatively short generation time of cats along with breed predispositions to development of FDM may allow for more rapid screening and identification of genetic markers for diabetes susceptibility. FDM, in both spontaneous and inducible forms, therefore provides a good animal model of human T2DM and may provide additional insights into the pathogenesis of this important condition.

Ocular manifestations of systemic disease in cats

Systemic feline diseases (parasitic, bacterial, fungal, viral, neoplastic, metabolic, vascular, and immune-mediated) are often associated with ocular symptoms. An ocular examination is an important diagnostic tool and should be part of any physical examination. Conversely, cats afflicted with systemic disease require periodic ocular examinations for prognostic information and to prevent vision threatening complications. Typical feline systemic diseases encountered by the practicing clinician are presented with their commonly associated ocular signs.

Feline Lens Disorders

The lens is the second most powerful structure for refraction in the eye, and is important in the fine-focusing ability in individual species. Specific disorders of the feline lens are frequent in clinical practice and include: congenital anomalies, nuclear sclerosis, cataracts, lens subluxations and luxations, intraocular sarcomas, and anterior lens displacement associated with aqueous misdirection glaucoma. Clinical signs and current therapeutic options are discussed for the general practitioner. A close working relationship with the regional veterinary ophthalmologist is advised.