Optical imaging of mitochondrial redox state in rodent models with 3-iodothyronamine

Abstract

This study used an optical technique to measure the effects of treating low (10 mg/kg) and high (25 mg/kg) doses of 3-iodothyronamine (T1AM) on the metabolism in the kidney and heart of mice. The ratio of two intrinsic fluorophores in tissue, (NADH/FAD), called the NADH redox ratio (NADH RR), is a marker of the metabolic state of the tissue. A cryofluorescence imaging instrument was used to provide a quantitative assessment of NADH RR in both kidneys and hearts in mice treated with 3-iodothyronamine. We compared those results to corresponding tissues in control mice. In the kidneys of mice treated with a high dose T1AM, the mean values of the maximum projection of NADH RR were 2.6 ± 0.6 compared to 3.20 ± 0.03 in control mice, indicating a 19% (± 0.4) significant increase in oxidative stress (OS) in the high dose-treated kidneys (P=0.047). However, kidneys treated with a low dose of T1AM showed no difference in NADH RR compared to the kidneys of control mice. Furthermore, low versus high dose treatment of T1AM showed different responses in the heart than in the kidneys. The mean value of the maximum projection of NADH RR in the heart changed from 3.0 ± 0.3 to 3.2 ± 0.6 for the low dose and the high dose T1AM-treated mice, respectively, as compared to 2.8 ± 0.7 in control mice. These values correspond to a 9% (±0.5) (P=0.045) and 14% (±0.5) (P=0.008) significant increase in NADH RR in the T1AM-treated hearts, indicating that the high dose T1AM-treated tissues have reduced OS compared to the low dose-treated tissues or the control tissues. These results suggest that while T1AM at a high dose increases oxidative response in kidneys, it has a protective effect in the heart and may exert its effect through alternative pathways at different doses and at tissue specific levels.

3-Iodothyronamine: A High Potency Metabolic Hormone and its Potential for Therapeutic Applications

“…T1AM is also observed to interact with Complex III via antimycin A in mitochondria, decreasing O 2 consumption and increasing H 2 O 2 release in mitochondria of cultured hepatocytes, which may partially explain observed decrease in O 2 consumption in vivo [39]. Most recently, Ghanian et al [4] found that T1AM is able to modulate cellular redox state (NADH/FAD ratio) in mouse tissue-specifically and in a dose specific manner [4]; interestingly this effect was divergent between dosage and tissue type. High dosage (25 mg/kg) induced oxidative stress (OS) in kidneys with no elevation in OS in response to low dosage (10 mg/kg) compared to controls.…”

“…T1AM's capacity to prevent ischemic injury was also countered by glibenclamide, a K + ATP channel blocker, effectively disrupting mitochondrial permeability transition, a proposed aspect of ischemiareperfusion injury [33]. In addition, the chronic application of T1AM at 10 and 25 mg/Kg shows heart protection against oxidative stress [4]. Coupled with the rapid onset of T1AMs effects, its negative inotropic properties may prove an effective acute treatment at the onset of a myocardial infarction to prevent the development of irreversible ischemic damage.…”

“…These alternative responses in different tissue to varying dosages of T1AM suggest there are different receptor expression patterns either through different levels of T1AM target receptor expression or differing isoforms resulting in divergent uptake patterns and/or receptor affinity mediating the differing responses between tissues. Furthermore, this ability to alter cellular redox state may shed additional light on T1AM's with more persistent effects, which would likely modulate cellular function internally beyond its acute membrane receptor mediated signaling; NAD is the substrate required for the function of Sirtuins, a family of enzymes that regulate epigenetic deacetylation and protein ribosalation influencing gene transcription and mitochondrial function (AssadiPorter, unpublished results) [4,38]. T1AM's role in modulating mitochondrial function, with sirtuins being a promising mediator, is the area of research that may be a key to unlock the specific mechanisms by which T1AM is able to alter whole body and cellular metabolism.…”

“…T1AM has become a research area of intense interest due to its rapid induction of hypometabolic effects, largely in opposition to those of TH, and its strong potential for therapeutic applications [2][3][4]. This recent discovery has opened up a new realm of thyroid metabolism research and continues to broaden in scope to encompass a diverse array of physiologic research fields including cardiovascular [5], neurological [6], cellular redox [4], lipid and carbohydrate metabolism [3], sleep [7], and torpidity [8]. Though other thyronamines have been characterized that can produce similar effects, T1AM remains the most promising thyronamine in physiological research due to its…”

The Possible Role of 3-lodothyronamine in Browning of Inguinal White Adipose Tissue in Mice

“…The subchronic T1AM treatment causes ketonuria and a significant loss of body fat indicating a shift in the metabolic pathways from carbohydrate to lipid oxidation. The treatment also triggers lipolytic pattern in rat adipose tissue and modulates mitochondrial FoF1-ATP synthase activity [16][17][18][19][20]. Taken together, these modulations in lipid metabolism provide a balance in energy homeostasis and thus have a great potential in therapeutic applications (especially for treating obesity).…”