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    • Lean mass is representative of the muscle

    2021-12-02

    Lean mass is representative of the muscle tissue mass equivalent of all the body parts containing water, excluding fat, bone minerals, and such substances which do not contribute to the NMR signal, such as hair, claws, etc. (ECHO-MRI (Houston, TX) user's manual). It was interesting that in the Bob-Cat male groups, we observed an increase in lean mass at 4 weeks and decrease at 8 weeks independent of diet. Other studies have shown similar fluctuations in lean mass as the body begins to adapt to alterations in diet or food/caloric intake [79]. At the 4 week time point, the body likely had not completely adjusted to the diet, however at around the 8 week time point, a complete response to the dietary intervention had occurred. In addition to lean mass, other studies have also seen similar fluctuations in bone mass in density [80]. Nonetheless, it is unclear why only Bob-Cat male mice behaved as such compared to the other genotypes. One can only speculate that it might be a response to the differences in redox regulation in these novel mice model. CLAMS assessment of Benzoylmesaconitine metabolism (energy intake vs. energy expenditure) showed differences between the genotypes tested on various diets. The three day CLAMS measurement of FI supported the earlier observation of lower weekly food intake by the HFD and OM3 fed groups despite the genotype [72]. In addition, it was observed that HFD and OM3 feeding altered the eating patterns (circadian rhythm) in WT mice compared to those fed NC. This is consistent with other studies that showed HFD feeding alters the quantity, time of day, and how much chow is consumed during each visit to the food hopper [[81], [82], [83]]. However, this diet effect (HFD or OM3) on eating patterns was not altered in either gender of the [Tg(CAT)±] and Bob-Cat mice, which followed similar circadian rhythm patterns of eating as that seen in mice provided NC diet. This observation suggested that catalase overexpression (i.e. redox balance) may be shifting the paradigm of a high-fat diet altering circadian rhythm and patterns of food intake. This speculation is further supported by our previously published observations where the secretion of key adipokines that modulate hypothalamic appetite regulation was altered in mice overexpressing catalase [43]. In addition to measurement of FI, the CLAMS analysis also provided insights into the differences in RER and EE in the various genotypes and diet interventions. We observed a significant increase in RER as well as CHO oxidation (hence lower fat oxidation) in the NC fed male mice overexpressing catalase compared to their WT groups fed NC. This might be attributed to the increased expression of human catalase gene, since other studies have shown changes in energy metabolism as a result of increased antioxidant catalase [41,43] in addition to alterations in substrate utilization as a result of differences in genetics [84]. In contrast, all groups on a high-fat diet intervention (lard or fish oil), had a lower RER and levels of CHO oxidation (higher fat oxidation) which has been reported in numerous other studies as a result of higher fat % available to be oxidized from the HFD provided to the animals [[85], [86], [87]]. The ability of OM3 diet to lower the RER and increase fat oxidation within the male mice groups overexpressing catalase and female Bob-Cats vs. the Bob-Cat mice fed NC may have contributed to the observed decrease in their body weights compared to their littermates that overexpress catalase fed NC or HFD. On the contrary, male mice overexpressing catalase provided an OM3 diet, had significantly lower fat oxidation compared to WT mice provided a NC diet. This may be a beneficial outcome from the intake of OM3 fatty acids termed “metabolic flexibility;” a newer concept describing the body's ability to match fuel oxidation to fuel availability [88]. We believe this may have been acquired in our mouse model through intake of the OM3 diet during the 8 week study period. Another plausible reason for the lower levels of fat oxidation observed may be due to “altered metabolic partitioning” of fatty acids where there is a reduction in oxidation and increased re-esterification of particular fatty acids dependent on their structure [89]. This would also provide reasoning as to why the same effect was not seen in the HFD fed mice overexpressing catalase. In comparison to males, fat oxidation trended to be elevated in females (kcal/h/g) even though all were provided the same type of diet and the quantity consumed by females was not higher than what was consumed by males. Even more interesting was the opposite effects of CHO vs. fat oxidation seen in male and female Bob-Cat mice groups provided an OM3 diet. We believe this was a result of sexual dimorphism [90].