Studying the heterogeneous pathogenesis of canine diabetes: Observational characterization of an island population

Evaluation of serum vitamin D metabolites, phagocytosis, and biomarkers of inflammation in dogs with naturally occurring diabetes mellitus

Naturally occurring diabetes mellitus (NODM) is one of the most common endocrine disorders in dogs and its etiology closely resembles type 1 diabetes mellitus (T1DM) in people. Human patients with T1DM commonly have cellular derangements consistent with inflammation, impaired immune function, and hypovitaminosis D. There is little information available regarding inflammatory biomarkers, immune function, and vitamin D status in diabetic dogs. Therefore, our objectives were to assess inflammatory biomarkers, vitamin D metabolites, and phagocytic capacity in diabetic dogs and determine whether associations exist with these variables and the level of clinical control or vitamin D metabolites. This was a prospective case-control study that included 20 otherwise healthy diabetic dogs (clinically controlled, n = 10; uncontrolled, n = 10) and 20 non-diabetic, healthy, age (± 2 years), breed, and sex matched controls. Complete blood count, biochemical panel, urinalysis, and fructosamine were performed at a single commercial reference laboratory. Basal plasma tumor necrosis factor (TNF)-α, interleukin (IL)-6, IL-8, and IL-10 were measured using a canine-specific multiplex bead-based assay. Serum C-reactive protein (CRP) was measured using a commercially available ELISA kit. Serum 25-hydroxyvitamin (OH)D3 and 24,25-dihydroxyvitamin (OH)2D3 were measured with HPLC. Phagocytosis of opsonized-Escherichia coli (E. coli) was evaluated with flow cytometry. Diabetic dogs had higher serum CRP concentrations than controls (p = 0.02). Plasma IL-8 concentrations were higher in diabetic dogs with uncontrolled clinical disease compared to controls (p = 0.02). Diabetic dogs had a lower percentage of leukocytes that phagocytized opsonized-E. coli (p = 0.02), but an increased number of bacteria phagocytized per cell (p < 0.001) compared to controls. No between-group differences were identified in vitamin D metabolites, nor were associations found between vitamin D and any variables. Fructosamine had a positive association with serum CRP concentration (rho = 0.35, p = 0.03) and number of bacteria phagocytized per cell (rho = 0.45, p = 0.004) in our cohort (n = 40). Like people with T1DM, diabetic dogs have a proinflammatory phenotype and phagocytic dysregulation that may be correlated with glycemic control.

Ex Vivo Immune Function and Modulatory Effects of Calcitriol in Dogs with Naturally Occurring Diabetes Mellitus

Human patients with type 1 diabetes mellitus (T1DM) are susceptible to several long-term complications that are related to glycemic control and immune dysregulation. Immune function remains relatively unexplored in dogs with naturally occurring diabetes mellitus (NODM). Calcitriol improves various aspects of immune function in a variety of species, but its effect in diabetic dogs remains unexplored. Therefore, the objectives of this study were to (i) evaluate immune function in dogs with NODM and determine if differences exist based on the level of clinical control and (ii) assess the immunomodulatory effects of calcitriol. Twenty diabetic dogs (clinically controlled, n = ten, not controlled, n = ten) and 20 non-diabetic, healthy control dogs were included in this prospective, case-control study. Whole blood was incubated with calcitriol (10-7 M) or negative control, after which the samples were divided for phagocytosis and leukocyte cytokine response experiments. The phagocytosis of opsonized Escherichia coli (E. coli) was evaluated with flow cytometry. The samples for leukocyte cytokine response evaluations were stimulated with lipopolysaccharide (LPS), lipoteichoic acid (LTA), or phosphate buffer solution (PBS; negative control), and tumor necrosis factor (TNF)-α, interleukin (IL)-6, IL-8, and IL-10 were measured in supernatant using a canine-specific multiplex bead-based assay. The leukocytes from diabetic dogs produced higher concentrations of IL-10 (p = 0.01), IL-6 (p < 0.0001), and IL-8 (p < 0.0001) than the control dogs while controlling for the intervention and stimulant. Calcitriol decreased the supernatant concentrations of TNF-α (p < 0.001) and IL-8 (p = 0.04) with concomitant increases in IL-6 (p = 0.005). Diabetic dogs had a lower percentage of leukocytes undergoing phagocytosis (p < 0.0001) but a higher number of bacteria phagocytized per cell (p = 0.001) when compared to the control dogs. Calcitriol had no effect on phagocytic capacity. Lastly, the status of clinical control in diabetic dogs did not yield differences in immune function. These results support that dogs with NODM exhibit immune dysregulation and warrant additional investigation.

Development of a requirement for exogenous insulin treatment in dogs with hyperglycemia

BACKGROUND

It has been suggested that overt diabetes mellitus in dogs be defined based on a persistent fasting blood glucose concentration (BGC) >144 mg/dL.

OBJECTIVE

Determine the number of dogs with randomly identified hyperglycemia without insulin-treated diabetes mellitus (ITDM) that later develop a need for exogenous insulin treatment.

ANIMALS

A total of 1318 dogs examined at a university teaching hospital without ITDM and with randomly identified hyperglycemia.

METHODS

Retrospective longitudinal study. Hyperglycemia was defined as randomly identified BGC above >112 mg/dL, moderate hyperglycemia as BGC >144 mg/dL but <200 mg/dL and pronounced hyperglycemia as BGC ≥200 mg/dL. Dogs were defined as having ITDM if they were treated with insulin. Follow-up was attempted 7 to 12 years after hyperglycemia was documented to determine if over time dogs developed a need for exogenous insulin treatment.

RESULTS

Twenty-nine of 824 dogs (3.5%) with hyperglycemia and follow-up information developed ITDM, including 3/824 dogs (0.4%) with moderate hyperglycemia, and 2/824 dogs (0.2%) with pronounced hyperglycemia. Most dogs with hyperglycemia that developed ITDM (24/29, 83%) had BGC ≤144 mg/dL. Among dogs that eventually developed a need for exogenous insulin treatment, no association was found between the degree of hyperglycemia and the time interval between documentation of hyperglycemia and diagnosis of ITDM. Logistic regression determined that BGC is not significantly associated with ITDM.

CONCLUSIONS AND CLINICAL IMPORTANCE

Most dogs with randomly identified hyperglycemia did not develop a need for exogenous insulin treatment. Other criteria could be required to augment the definition of overt DM in non-insulin treated dogs.

Spontaneous remission and relapse of diabetes mellitus in a male dog

An 8-year-old male neutered Miniature Schnauzer was diagnosed with diabetes mellitus based on fasting hyperglycemia and glucosuria after a 2-week history of polydipsia and periuria, in line with the Agreeing Language in Veterinary Endocrinology consensus definition. Treatment of insulin and dietary management was initiated. The insulin dose was gradually reduced and eventually discontinued over the next year based on spot blood glucose concentrations that revealed euglycemia or hypoglycemia. After discontinuation, the dog remained free of clinical signs for 1 year until it was again presented for polyuria/polydipsia with fasting hyperglycemia and glucosuria. Insulin therapy was resumed and continued for the remainder of the dog's life. Although diabetic remission often occurs in cats and humans, the presumed etiopathogenesis of pancreatic beta cell loss makes remission rare in dogs, except for cases occurring with diestrus or pregnancy. This case demonstrates that diabetic remission is possible in dogs, even in cases without an identifiable reversible trigger.

Association between Hyperglycemia and Canine Serum Pancreatic Lipase Immunoreactivity Concentration in Diabetic Dogs

It has been reported that hypertriglyceridemia can partially mediate between diabetes mellitus (DM) and pancreatitis in dogs, implying that another mediator, such as chronic hyperglycemia, might exist. Therefore, this study aimed to evaluate the relationship between hyperglycemia and serum canine pancreatic lipase immunoreactivity (cPLI) concentration in diabetic dogs. This retrospective cohort study included 26 client-owned diabetic dogs, divided according to their serum fructosamine levels (<500 μmol/L = well-controlled DM group; ≥500 μmol/L = untreated or poorly controlled DM group). Five of the 26 DM dogs (19.2%) had serum cPLI concentrations consistent with pancreatitis, among which two showed ultrasonographic evidence of pancreatitis without clinical signs. The serum cPLI concentrations (median [interquartile range]) were significantly higher in the untreated or poorly controlled group (520 μg/L [179.76-1000 μg/L]) than in the well-controlled group (77 μg/L [32.22-244.6 μg/L], P = 0.0147). The serum fructosamine concentration was positively correlated with the serum cPLI concentration (r = 0.4816; P = 0.0127). Multivariate analysis revealed serum triglyceride and fructosamine concentrations were associated with the serum cPLI concentration. In conclusion, this study suggests that chronic hyperglycemia may induce pancreatic inflammation in diabetic dogs; however, the clinical significance of increased cPLI concentration is unknown.

Evaluation of Candida spp. and Other Fungi in Feces from Dogs with Naturally Occurring Diabetes Mellitus

Simple Summary

Diabetes mellitus is a common endocrine disorder in dogs that is similar to type 1 diabetes mellitus (T1DM) in humans. Candida spp. is a common non-pathogenic fungi that is identified more commonly and in higher amounts in humans with T1DM, including the gastrointestinal tract. This change to the distribution of microorganisms that inhabit the intestine has potential to affect glycemic control and even spread to other organs and cause severe illness. There are no studies that have investigated whether diabetic dogs, like humans, have alterations to the intestinal mycobiome. Therefore, our study sought to determine whether differences exist in the types of fungi cultured from feces in diabetic dogs and non-diabetic healthy control dogs. In addition, we wanted to find out if there were variables associated with fungi colonization. Diabetic dogs had more quantitative fungal growth than controls and females were more likely to yield growth than males. Diabetic dogs were also more likely to have Candida spp. colonized from feces. Glycemic control was also seemingly associated with growth of Candida spp. in diabetic dogs. Our results indicate that the intestinal mycobiome is altered in diabetic dogs with increased prevalence of Candida spp. and quantitative growth of fungi.

Abstract

Diabetes mellitus is a common endocrinopathy in dogs and in most cases is analogous to type 1 diabetes mellitus (T1DM) in humans. Candida spp. is a common commensal fungi with higher prevalence and magnitude of growth in humans with T1DM. There is currently no published information about the fungal microbiome in diabetic dogs. Therefore, the objectives of this study were to (i) determine whether diabetic dogs were more likely to have Candida spp. or other types of fungi from feces compared to non-diabetic controls, and (ii) identify variables associated with fungi colonization. Fourteen diabetic dogs and 14 age, sex, and breed matched non-diabetic healthy control dogs were included in this prospective case–control study. Matrix assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) was used for fungal identification. Diabetic dogs had greater quantitative fungal growth compared to controls (p = 0.004). Moreover, female dogs were more likely to have fungi colonization than males (p = 0.02). All instances of Candida spp. and Aspergillus spp. colonization were exclusively identified in diabetic dogs. Serum fructosamine concentration was higher in diabetic dogs with fecal colonization of Candida spp. compared to diabetic dogs without growth (p = 0.03). Our results indicate that the fungal microbiome in feces is altered in diabetic dogs, which seem to favor an increased prevalence of Candida spp. and higher quantitative fungal growth. Moreover, female sex and glycemic control could affect the intestinal mycobiome.

Studying the heterogeneous pathogenesis of canine diabetes: Observational characterization of an island population

BACKGROUND

Canine diabetes mellitus has mostly been studied in northern European, Australian and American populations, whereas other regions have received less attention.

OBJECTIVES

We evaluated the epidemiological, clinical and histopathological features of diabetic dogs in Gran Canaria, Spain.

METHODS

Prevalence and incidence were estimated. Clinical features were analysed, and serum and genomic DNA were obtained. Dogs with presumed idiopathic or immune-mediated diabetes, were DLA-typed and antibodies against GAD65 and IA-2 were assessed. Pancreases from ten diabetic dogs were examined and compared with pancreases from non-diabetic dogs.

RESULTS AND CONCLUSIONS

Twenty-nine diabetic dogs were identified in a population of 5,213 (prevalence: 0.56%; incidence: 0.37%). Most were female (79%) and sexually intact (87% of females, 83% of males). Diabetes secondary to dioestrus (55.2%) and insulin-deficient diabetes (20.7%) were the most frequent types. Antibodies against GAD65 and IA-2 were identified in two out of five cases and DLA-genotyping revealed novel haplotypes. Breed distribution differed between diabetic and non-diabetic dogs. Reduced number of pancreatic islets and β-cell mass were observed, with vacuolation of islet cells and ductal epithelium. In this population, where neutering is not standard practice, diabetes secondary to dioestrus is the most frequent diabetes subtype. Genetic susceptibility also differed from previous studies. These results support the heterogeneous pathogenesis of canine diabetes.