The associations between serum adiponectin, leptin, C-reactive protein, insulin, and serum long-chain omega-3 fatty acids in Labrador Retrievers

A Systematic Review and Meta-Analysis of Serum Adiponectin Measurements in the Framework of Dog Obesity

Simple Summary

Adiponectin is a molecule with biological activity that is closely linked with obesity and obesity-related problems. Despite some literature publications, there is a lack of consensus about how adiponectin changes in canine obesity. Therefore, a meta-analysis is performed here to assess the global performance of adiponectin concentrations in terms of obesity in dogs. After considering 20 different studies, including a total sample size of 366 dogs with obesity and 349 normal weight dogs, the meta-analysis indicates that adiponectin in serum is lower in obese dogs compared with normal weight dogs and increases after weight loss programs.

Abstract

Adiponectin is an abundant plasma protein that is closely related to obesity and obesity-related pathologies. The molecule can be found in three different isoforms, each with different biological activities. Studies on canine obesity have suggested that adiponectin concentrations are decreased in obesity; however, no canine meta-analyses have been performed that feature all the required data. The aim of this study is to perform a systematic review and meta-analysis of studies that pertain to total and high molecular weight (HMW) adiponectin in relation to canine obesity. From 20 different studies, a total of 366 dogs with obesity and 349 normal weight dogs are included in the meta-analysis. Client-owned dogs were most represented, accounting for 54.3% of the dogs used, while experimental dogs enrolled in the studies made up the remaining 45.7%. The concentrations of total adiponectin in dogs with obesity were significantly lower compared with normal weight dogs. Additionally, adiponectin concentrations were significantly higher in dogs after a successful weight loss protocol compared to the start of the protocol and were significantly lower in dogs after gaining weight. In conclusion, although caution should be taken due to the relatively low number of studies that exist and the high heterogeneity between them, this meta-analysis indicates that adiponectin is decreased in obese dogs.

Relationships between expression levels of genes related to adipogenesis and adipocyte function in dogs

There are three kinds of adipocytes; white adipocytes accumulate excess energy as fat, whereas brown/beige adipocytes dissipate energy through expression of uncoupling protein 1 (UCP1). Obesity, a feature of excess accumulation of white adipocytes in a body, is one of the risk factors for onset of various diseases in dogs. As the first step to explore adipose genes related to dog obesity, we examined relationships among mRNA levels of putative molecules related to adipogenesis and function of adipocytes in fat of hospitalized dogs. Gonadal adipose tissues were collected from a total of 29 dogs, and the gene expression levels were examined by quantitative RT-PCR analysis. The multicollinearity analysis revealed that body condition score (BCS), which reflects adiposity, did not correlate with expression levels of any genes but correlated with age of dog. Bone morphogenetic protein (BMP) pathway stimulates not only commitment of mesenchymal stem cells to white adipocyte-lineage cells but also brown/beige adipogenesis. Some relationships between expression levels of BMP receptors were significant; especially, expression levels of activin receptor-like kinase (Alk) 3 (a BMP type I receptor) positively related to those of Alk2 (another BMP type I receptor), activin receptor type II (ActRII) A (a type II receptor to transmit BMP signal), ActRIIB (another type II receptor to transmit BMP signal) and BMP receptor type 2 (Bmpr2). PR domain containing 16 (Prdm16) expression levels strongly correlated with expression levels of ActRIIB. Although PRDM16 is known to stimulate brown/beige adipogenesis, expression levels of Ucp1 did not correlate with those of Prdm16. On the other hand, expression levels of Ucp1 correlated with those of Alk6. The present study suggests close relationships among adipose expressions of BMP signal components, and the relationships of expression levels of BMP receptor and those of Prdm16 or Ucp1 in dogs. Further studies using more dogs with various BCS potentially lead to identification of adipose factors to relate with adiposity in dogs.