Glucose-6-Phosphate Dehydrogenase and NADPH Redox Regulates Cardiac Myocyte L-Type Calcium Channel Activity and Myocardial Contractile Function

Abstract

We recently demonstrated that a 17-ketosteroid, epiandrosterone, attenuates L-type Ca2+ currents (ICa-L) in cardiac myocytes and inhibits myocardial contractility. Because 17-ketosteroids are known to inhibit glucose-6-phosphate dehydrogenase (G6PD), the rate-limiting enzyme in the pentose phosphate pathway, and to reduce intracellular NADPH levels, we hypothesized that inhibition of G6PD could be a novel signaling mechanism which inhibit ICa-L and, therefore, cardiac contractile function. We tested this idea by examining myocardial function in isolated hearts and Ca2+ channel activity in isolated cardiac myocytes. Myocardial function was tested in Langendorff perfused hearts and ICa-L were recorded in the whole-cell patch configuration by applying double pulses from a holding potential of −80 mV and then normalized to the peak amplitudes of control currents. 6-Aminonicotinamide, a competitive inhibitor of G6PD, increased pCO2 and decreased pH. Additionally, 6-aminonicotinamide inhibited G6PD activity, reduced NADPH levels, attenuated peak ICa-L amplitudes, and decreased left ventricular developed pressure and ±dp/dt. Finally, dialyzing NADPH into cells from the patch pipette solution attenuated the suppression of ICa-L by 6-aminonicotinamide. Likewise, in G6PD-deficient mice, G6PD insufficiency in the heart decreased GSH-to-GSSG ratio, superoxide, cholesterol and acetyl CoA. In these mice, M-mode echocardiographic findings showed increased diastolic volume and end-diastolic diameter without changes in the fraction shortening. Taken together, these findings suggest that inhibiting G6PD activity and reducing NADPH levels alters metabolism and leads to inhibition of L-type Ca2+ channel activity. Notably, this pathway may be involved in modulating myocardial contractility under physiological and pathophysiological conditions during which the pentose phosphate pathway-derived NADPH redox is modulated (e.g., ischemia-reperfusion and heart failure).

Regulation of G6PD acetylation by KAT9/SIRT2 modulates NADPH homeostasis and cell survival during oxidative stress

“…Higher expression level of G6PD is associated with breast cancer metastasis and is thought to contribute to tumor cell proliferation by enhanced ribose and NADPH supply (Jiang et al , ; Du et al , ). Moreover, G6PD deficiency, perhaps through decreasing the NADPH‐dependent cholesterol synthesis, may be advantageous against the risk of heart disease in both G6PD‐deficient mouse models and clinical studies (Matsui et al , ; Muntoni, ; Rawat et al , ). Furthermore, decreased G6PD activity may predispose to the occurrence of diabetes and aldosterone‐induced endothelial dysfunction (Leopold et al , ; Zhang et al , ).…”

Vascular smooth muscle cell contractile protein expression is increased through protein kinase G-dependent and -independent pathways by glucose-6-phosphate dehydrogenase inhibition and deficiency

“…Hemizygous (XbY) G6PD-deficient male and female mice and wild-type (XY) control mice (WT) age 12-16 wk were studied. Animals were genotyped as described previously (39). Normally, G6PD-deficient mice do not exhibit any abnormal cardiovascular phenotype and live up to 2-2.5 yr.…”

Low dose exposure to HBCD, CB-153 or TCDD induces histopathological and hormonal effects and changes in brain protein and gene expression in juvenile female BALB/c mice

“…Besides oxidative stress related pathologies, G6PD deficiency was also highlighted to be a primary cause of decreased cholesterol anabolism and fatty acid β-oxidation; both of which are key to processes and functions such as plasma membrane formation, energy metabolism and cell signalling [65]. Fatty acid β-oxidation was recently demonstrated to be a target of HBCD toxicity; it was found to be downregulated in vitro in HepG2 cells and in vivo in livers of juvenile female BALB/c mice after exposure to t-HBCD and α-HBCD, respectively [2,66].…”