Cotinine as a Sentinel of Canine Exposure to Tobacco Smoke

Simple Summary Smoking is a global health problem, recognized as being responsible for increased risk for many diseases. Pets cohabiting with smoking owners may be exposed to tobacco by inhalation, absorption, or ingesting residual smoke particles. Cotinine is a product of the endogenous metabolism of nicotine, and it is used as a biomarker of environmental cigarette smoke exposure in humans. In particular, cotinine in biofluids (blood, saliva, and urine) and hair provides information on short- and long-term smoke exposure, respectively. Despite the considerable evidence of the harmful effects of active and passive tobacco smoke, few studies have explored the relationship between secondhand smoke exposure and cotinine in dogs. This study aimed to measure cotinine concentration in the serum and hair of dogs that were exposed to the owner's tobacco smoke and to compare it with that of unexposed dogs. Moreover, the influence of exposure intensity (number of cigarettes), age, weight, and sex on cotinine concentration was explored. Cotinine was significantly higher in exposed than unexposed dogs in serum and fur. A sex difference in the concentration of cotinine was also evidenced. These results confirmed the role of cotinine as a sentinel of cigarette smoke exposure in dogs with a different sex sensibility. The adverse health effects of both active and passive tobacco smoke have been well-known in humans for a long time. It is presumable that even pets, which intimately share the owner's lifestyle, may be exposed to the same risks. This study aimed to detect and quantify cotinine (a metabolite of nicotine) in the serum and hair of dogs using a specific commercial ELISA immunoassay kit. A total of 32 dogs, 16 exposed and 16 unexposed to the owner's smoke, were enrolled. The cotinine concentration was higher in the exposed than the unexposed group in both matrices (p < 0.001), with greater values in serum than in hair (p < 0.001). Exposed bitches had higher hair cotinine than male dogs (p < 0.001). Conversely, serum and fur cotinine concentrations were lower in female than male dogs of the unexposed group (p < 0.01). The exposure intensity, age, and weight of the dogs did not affect cotinine concentrations. A cut-off value of 2.78 ng/mL and 1.13 ng/mL cotinine concentration in serum and fur, respectively, was estimated to distinguish between the exposed and unexposed dogs. Cotinine was confirmed as a valuable marker of passive smoking also in dogs. Although owners do not perceive secondhand smoke as a risk for their dogs, greater awareness should be advisable, especially in pregnant animals.