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    • All HFD fed groups in

    2022-08-15

    All HFD fed groups in our study, having significantly higher levels of EE (heat production) is consistent with previous studies [91], where a significant increase in EE was observed within just one week of HFD feeding [81]. It is hypothesized that this phenomenon is due to the increased body mass and amount of oxygen necessary to facilitate normal cellular/tissue function in addition to higher monensin required to catabolize the 45% high-fat diet vs. the 13.4% fat in the NC diet. However, the increase in EE of the HFD groups is not sufficient to create energy balance resulting in an accumulation of body weight and fat mass. Though calorically (45% fat) similar to the HFD, EE levels in OM3 fed mice remained intermediate to NC and HFD fed mice, yet EE levels were still significantly higher than the NC fed WT group. Previous studies have also shown an OM3 rich diet increases EE levels by enhancing thermogenesis via activating GPR120 [23,92]. Male [Tg(CAT)±] and Bob-Cat mice also displayed significantly higher activity (XAMB) levels compared to WT mice fed NC or high-fat (HFD or OM3) diets. Furthermore, when provided HFD or OM3 diet, the WT mice had the lowest activity levels, not reaching above 3000 counts per 2 h. These results indicate that overexpression of catalase might be increasing the activity levels within the male gender. Previous reports have suggested that in rodent models, a high caloric diet can decrease XAMB counts of physical activity by up to 28% [81]. It is also possible that the increased body weight and fat mass may have been a secondary factor in the hypo-activity. Interestingly, the effect was not as severe in groups overexpressing catalase; again, an indication of the beneficial effect of antioxidant overexpression coupled with an OM3 diet. This is of great importance since evidences in human obesity studies have shown that HFD promotes a more sedentary, less physically active lifestyle in addition to alterations in sleep/wake cycles [93]. Alterations in redox balance (as seen within the catalase overexpressing mice), such as by OM3 dietary interventions, might improve metabolic imbalance and circadian rhythm abnormalities in obese humans. Eight weeks of dietary intervention altered the circulating metabolic profile in the catalase overexpressing mice. As seen in other studies, and expected with increased fat mass, mice fed a HFD had the highest levels of TC [94]. The only exception was the female [Tg(CAT)±] mice fed HFD which had similar TC levels to all mouse groups fed NC and OM3 diet. This female group also had significantly higher levels of activity (XAMB counts) which might have influenced the lowering of cholesterol levels [95]. In contrast to the HFD, and as previously documented [24], mice provided an OM3 diet did not alter TC and the levels remained similar to that seen in NC fed mice groups. HDL levels were highest among the groups fed HFD in both genders, but among OM3 fed mice, there was a higher ratio of HDL:TC compared to the HFD groups. Furthermore, among the OM3 fed mice groups, Bob-Cat males and females had the highest levels of HDL making their HDL:TC ratio the highest among all mice groups thus showing the significance of the regulatory interaction between overexpression of antioxidant catalase and feeding OM3 diet on lipid profile. There have been previous studies conducted in the leptin deficient, Ob/Ob mice (parent group of the Bob-Cat mice model) showing increases in HDL level [96,97]. It has been postulated that although typically in human obesity, HDL levels are substantially lower, the decrease in functional leptin in the obese, Ob/Ob mice may be playing a role in the higher HDL (being the major lipoprotein in rodents) levels [97]. Since Bob-Cats are heterozygous for the Ob gene, it is plausible that leptin is playing a role in modulating HDL levels. Surprisingly, male Bob-Cats had the highest TG levels. A similar effect, although to a lower degree, was also seen in the NC and OM3 fed female Bob-Cats and the other female genotypes on similar diet. In general, the mice provided OM3 diet had lower plasma TG levels, which was expected as the result of a higher intake of OM3 fatty acids [16,23]. Bob-Cat mice, compared to the other genotypes, also had increased levels of plasma ketones in all groups (except the HFD males), and those provided an OM3 diet had the highest ketone levels independent of gender. Generally, high ketone levels are classically associated with metabolic dysfunction and diabetes [[98], [99], [100], [101]], but more recent studies have shown that lower carbohydrate diets provoking ketosis cause an inverse correlation between circulating ketones and plasma glucose levels, thus suggesting higher levels of ketones are associated with more favorable effects on glycemic control [102]. Other studies have now recognized ketones as imperative signaling molecules promoting metabolic function and regulating appetite [56,103]. These studies further solidify the beneficial effects of OM3 diet coupled with antioxidant catalase overexpression on metabolic parameters.