Comparison of Effects of Diet on Mammary Cancer: Efficacy of Various Preventive Agents and Metabolomic Changes of Different Diets and Agents

Abstract

To determine the effects of diet, rats were placed on a standard diet (4% fat) or on a modified Western (highfat diet, HFD) diet (21% fat) at 43 days of age (DOA) and administered methylnitrosourea (MNU) at 50 DOA. Rats were administered effective (tamoxifen, vorozole, and Targretin) or ineffective (metformin and Lipitor) chemopreventive agents either by daily gavage or in the diet beginning at 57 DOA and continuing until sacrifice (190 DOA). Latency period of the tumors was determined by palpation, and multiplicity and cancer weights per rat were determined at final sacrifice. Rats on the HFD versus standard diet had: (i) a 6% increase in final body weights; (ii) significant decreases in tumor latency; and (iii) significant increases in final tumor multiplicity and average tumor weight. Tamoxifen, vorozole, and Targretin were highly effective preventive agents, whereas Lipitor and metformin were ineffective in rats on either diet. Serum was collected at 78 DOA and at sacrifice (190 DOA), and metabolomics were determined to identify the metabolite changes due to diets and effective agents. Rats given the HFD had increased levels of saturated free fatty acids (including myristate) and decreased levels of 2-aminooctanoate. Furthermore, rats on the HFD diet had increased levels of 2-aminobutyrate and decreases in glycine markers previously identified as indicators of prediabetes. Targretin increased long-chain glycophospholipids (e.g., oleyl-linoleoyl-glycerophosphocholine) and decreased primary bile acids (e.g., taurocholate). Tamoxifen increased palmitoyl-linoleoyl-glycophosphocholine and decreased stearoyl-arachidonyl glycophosphocholine. Finally, increased levels of methylated nucleotides (5-methylcytidine) and decreased levels of urea cycle metabolites (N-acetylcitrulline) were associated with the presence of mammary cancers.

Pharmacometabolomic Pathway Response of Effective Anticancer Agents on Different Diets in Rats with Induced Mammary Tumors

“…On day 57, either control vehicle, or the preventive agents Tgt or Tmx, were started and continued until the end of the study. Blood samples were obtained at day 78 (T1) and day 190 (T2) for both control and treated rats; metabolomic analysis of those samples was done at Metabolon as previously described [10].…”

“…Anticancer protection agents, Tgt and Tmx, yielded strong positive results (reduced tumor multiplicity and weights, as well as increased tumor latency) not only in the rats on CD but also in rats on HFD. Serum metabolites associated with diets and Tgt and Tmx treatments were also examined briefly by metabolomics analysis [10]. Here, we systematically reviewed metabolic changes related to diets and drug treatments with the aim to identify specific metabolites as biomarkers for the physiological or pharmacological effect of a given agent at an effective preventive dose in the animal model.…”

“…Regardless of time points or drugs, there were 68 metabolites altered in abundance consistently by feeding different diets (Figure 5A), and the altered metabolites may be directly related to the composition of the diets. For example, higher levels of some long/medium chain fatty acid, branched fatty acids in rats fed with HFD might be related to the high fat content in the HFD, while rats fed with CD had higher levels of genistein, daidzein, and equol might be related to the high soy content in the CD [10]. This is consistent with the results of the pathway analysis which showed that the food component/plant pathway was altered due to the different diets.…”

“…Thus, targretin (Tgt), tamoxifen (Tmx), and vorozole (aromatase inhibitor) were all clearly and similarly positive in rats on either diet whereas metformin and Lipitor gave negative results on either diet. We employed the MNU-rat model because it is perhaps the most standard ER+ model of breast cancer and was employed in the development of SERMs (tamoxifen, raloxifene, toremifene) and aromatase inhibitors (letrozole, vorozole), which are indeed the standard prevention and treatment modalities for ER+ breast cancer in humans [10]. The study was initially undertaken to determine whether the Western Diet, which might be considered a “more relevant” diet for comparison to humans, gave similar results with various prevention/therapeutic agents.…”

“…The study was initially undertaken to determine whether the Western Diet, which might be considered a “more relevant” diet for comparison to humans, gave similar results with various prevention/therapeutic agents. The metabolomics was also performed to identify potential pharmacodynamic biomarker candidates with various agents [10].…”