D cutoffs have been suggested [36]. It has been shown that atenolol-modulated changes in lipids involve more than simply a general adrenergic-mediated alteration in lipolysis rate [37]. In cultured vascular smooth muscle cells, atenolol induced a 61 increase in NAD+/NADH ratio and a similar increase in the level of NADH-cytochrome b5 reductase [38]. This protein is involved in desaturation and elongation of fatty acids [39], as well as cholesterol biosynthesis [40], suggesting that some of the observed changes could be caused by this enzyme. The metabolite with the largest percent change was the ketone body 3-hydroxybutyric acid, the concentration of which was reduced by 33.3 in Caucasian individuals (p = 0.000050, Q = 0.0080) upon atenolol treatment but was not significantly altered in African Americans (Table 4). Such a change could result from either decreased production or increased utilization of 3hydroxybutyric acid, which is produced from acetyl-CoA as a result of ketogenesis, mitochondrial free fatty acid b-oxidation (breakdown), which occurs mostly in the liver [41]. This production typically occurs during 
periods of low Epigenetics glucose levels, when carbohydrate availability has been reduced. A concentration change may reflect an alteration in the balance of energy usage between carbohydrates and lipids. Note however that glucose undergoes only a slight but significant increase (Table 2), suggesting the 3-hydroxybutyric acid reduction could be the direct result of the reduction in plasma free fatty acids upon atenolol treatment.Racial differences in Atenolol treatmentDifferences in drug response between racial groups is increasingly recognized as an important aspect of pharmacometabolomics and, more Epigenetic Reader Domain generally, personalized health care [42?4]. Atenolol monotherapy is significantly less effective for blood pressure lowering in patients of African origin than for Caucasian patients [45]. While racial differences in plasma renin activity associate with these differences in antihypertensive response, more detailed understanding of the genetic or biochemical factors that underpin these differences in response is needed. While there is not a clear biochemical mechanism to explain the metabolic differences observed in response to atenolol in Caucasians compared to African Americans, there are differences in lipid metabolism that may relate to specific mechanisms. African Americans have on average higher plasma concentrations of arachidonic acid compared with Caucasians, resulting from genetic variants (SNP rs174537) in the fatty acid desaturase enzyme (FADS gene cluster) that converts linoleic acid to arachidonic acid [46]. For example, experiments on human adipose tissue have shown that the basal lipolysis rate is approximately 50 lower in obese African American women than in Caucasian women and that this may be due to differences in hormone-sensitive lipase enzyme levels [47]. The degree ofmetabolic inflexibility, which relates to the ability of an individual to switch substrate usage under different metabolic conditions, is different in African American compared with Caucasian women. Caucasians had higher rates of fat oxidation with lower rates of carbohydrate oxidation during a high fat diet in comparison with a low fat diet, whereas African Americans showed no difference [48]. There are known racial differences in the blood pressure response to atenolol between African American and Caucasian patients [49?1]. Although physiological diff.D cutoffs have been suggested [36]. It has been shown that atenolol-modulated changes in lipids involve more than simply a general adrenergic-mediated alteration in lipolysis rate [37]. In cultured vascular smooth muscle cells, atenolol induced a 61 increase in NAD+/NADH ratio and a similar increase in the level of NADH-cytochrome b5 reductase [38]. This protein is involved in desaturation and elongation of fatty acids [39], as well as cholesterol biosynthesis [40], suggesting that some of the observed changes could be caused by this enzyme. The metabolite with the largest percent change was the ketone body 3-hydroxybutyric acid, the concentration of which was reduced by 33.3 in Caucasian individuals (p = 0.000050, Q = 0.0080) upon atenolol treatment but was not significantly altered in African Americans (Table 4). Such a change could result from either decreased production or increased utilization of 3hydroxybutyric acid, which is produced from acetyl-CoA as a result of ketogenesis, mitochondrial free fatty acid b-oxidation (breakdown), which occurs mostly in the liver [41]. This production typically occurs during periods of low glucose levels, when carbohydrate availability has been reduced. A concentration change may reflect an alteration in the balance of energy usage between carbohydrates and lipids. Note however that glucose undergoes only a slight but significant increase (Table 2), suggesting the 3-hydroxybutyric acid reduction could be the direct result of the reduction in plasma free fatty acids upon atenolol treatment.Racial differences in Atenolol treatmentDifferences in drug response between racial groups is increasingly recognized as an important aspect of pharmacometabolomics and, more generally, personalized health care [42?4]. Atenolol monotherapy is significantly less effective for blood pressure lowering in patients of African origin than for Caucasian patients [45]. While racial differences in plasma renin activity associate with these differences in antihypertensive response, more detailed understanding of the genetic or biochemical factors that underpin these differences in response is needed. While there is not a clear biochemical mechanism to explain the metabolic differences observed in response to atenolol in Caucasians compared to African Americans, there are differences in lipid metabolism that may relate to specific mechanisms. African Americans have on average higher 
plasma concentrations of arachidonic acid compared with Caucasians, resulting from genetic variants (SNP rs174537) in the fatty acid desaturase enzyme (FADS gene cluster) that converts linoleic acid to arachidonic acid [46]. For example, experiments on human adipose tissue have shown that the basal lipolysis rate is approximately 50 lower in obese African American women than in Caucasian women and that this may be due to differences in hormone-sensitive lipase enzyme levels [47]. The degree ofmetabolic inflexibility, which relates to the ability of an individual to switch substrate usage under different metabolic conditions, is different in African American compared with Caucasian women. Caucasians had higher rates of fat oxidation with lower rates of carbohydrate oxidation during a high fat diet in comparison with a low fat diet, whereas African Americans showed no difference [48]. There are known racial differences in the blood pressure response to atenolol between African American and Caucasian patients [49?1]. Although physiological diff.