Spirocercosis in dogs is characterized by oesophageal nodules that readily undergo neoplastic transformation, but the pathogenesis of this neoplastic transformation is poorly understood. Vitamin D has putative anti-proliferative, pro-differentiating, immunomodulatory and anti-neoplastic effects through gene modulation. Hypovitaminosis D is associated with the development of many human neoplasias.
The objective of this study was to measure and compare vitamin D status assessed by serum 25-hydroxyvitamin D [25(OH)D] and 1,25-dihydroxyvitamin D [1,25(OH)2D] concentrations in non-neoplastic (n=25) and neoplastic (n=26) spirocercosis dogs and healthy dogs (n=24). We hypothesized that hypovitaminosis D was present in Spirocerca lupi-infected dogs; that lower concentrations were present in the neoplastic form of the disease; and finally that hypovitaminosis D could be a potential risk factor for neoplastic transformation.
From 119 dogs presenting to our hospital over a three year period, 51 dogs were selected and further divided into a non-neoplastic or a neoplastic group, based on histopathology of the nodules, macroscopic endoscopic appearance, computed tomography findings, response to therapy, and/or a combination of these findings. Dogs were excluded if they were less than 1 year of age, had concurrent diseases, had received corticosteroids in the previous 6 months or if they were treated prophylactically for spirocercosis. Serum 25(OH)D and 1,25-dihydroxyvitamin D (1,25(OH)2D) concentrations were measured by high-performance liquid chromatography. Spirocercosis dogs appetites were recorded as normal or abnormal (inappetence or anorexia) and the absolute number of dogs with normal and abnormal appetites were compared between the spirocercosis groups and to the 25(OH)D concentrations. The influence of age and serum albumin on serum 25(OH)D concentrations were also evaluated. The interaction and significance of sex and spay neuter status, body weight and appetite (independent variables) with serum 25(OH)D concentrations (dependent variable) were assessed. Statistical significance was set at p<0.05. Serum 25(OH)D and 1,25(OH)2D concentrations were significantly different among all groups (Kruskal-Wallis test, p<0.001). Dunn s multiple comparison test showed that median 25(OH)D concentrations were significantly lower in the neoplastic group [30.7 nmol/l (range 14.7-62.2)] compared to the non-neoplastic [52.7 nmol/l (range 19.1-129.7, (p<0.05)] and the healthy groups [74.6 nmol/l (range 37.4-130.5, p<0.001)]. Median 25(OH)D concentrations were significantly lower in the non-neoplastic spirocercosis group compared to the healthy group (p<0.05). Dunn s multiple comparison test also showed that median 1,25(OH)2D concentrations were significantly lower in the neoplastic group (56.5 pmol/l (range 18-130)] compared to the healthy group [94.5 pmol/l (range 46-142, p<0.001)]. No significant difference in the median 1,25(OH)2D concentrations were detected between the neoplastic and the non-neoplastic spirocercosis [70 pmol/l (range 34-127), p>0.05] groups and between the non-neoplastic spirocercosis group compared to the healthy group (p>0.05). Neoplastic and non-neoplastic spirocercosis dogs had similar appetite classification (Fisher´s Exact test, p=1.0). Mann-Whitney U test showed that in the neoplastic spirocercosis groups the median 25(OH)D (p=0.087) and 1,25(OH)2D (p=0.94) concentrations were not significantly different between dogs with normal and abnormal appetites. In the non-neoplastic spirocercosis groups, the median 25(OH)D (p=0.125) and 1,25(OH)2D (p=0.08) concentrations were also not significantly different between dogs with normal and abnormal appetites. Analysis of covariance (ANCOVA) demonstrated a significant difference in serum 25(OH)D concentrations among the three groups of dogs independent of either albumin or age (p<0.05). No statistical significance was detected for breed (p=0.84), sex (p=0.32) and spay neuter status (p=0.58) among the three groups, using the Chi-square test. Median body weight compared among the groups was not statistically significant (Kruskal-Wallis test, p=0.27). Multivariable linear regression analysis demonstrated that all independent variables (sex and spay neuter status, body weight, appetite) were independent of each other, and that there was no linear relationship between serum 25(OH)D concentration and either body weight (p=0.08, r=0.24) nor appetite (p=0.16, r=-0.49). Neutered and female dogs had higher serum 25(OH)D concentrations than intact and male dogs.
Hypovitaminosis D is present in dogs with spirocercosis and is lower in the neoplastic dogs compared to non-neoplastic spirocercosis and healthy dogs. Further studies are warranted to determine the potential therapeutic use of vitamin D in spirocercosis and explore the role of hypovitaminosis D in the pathogenesis of malignant transformation. Additional studies focusing on the calcium-regulatory role of vitamin D is also warranted.
Dissertation (MMedVet)--University of Pretoria, 2013.