Creatine kinase, energy reserve, and hypertension: from bench to bedside

Abstract

We hypothesized that human variation in the activity of the ATP regenerating enzyme creatine kinase (CK) activity affects hypertension and cardiovascular disease risk. CK is tightly bound close to ATP-utilizing enzymes including Ca²⁺-ATPase, myosin ATPase, and Na⁺/K⁺-ATPase, where it rapidly regenerates ATP from ADP, H⁺, and phosphocreatine. Thus, relatively high CK was thought to enhance ATP-demanding processes including resistance artery contractility and sodium retention, and reduce ADP-dependent functions. In a series of studies of our group and others, CK was linked to hypertension and bleeding risk. Plasma CK after rest, used as a surrogate measure for tissue CK, was associated with high blood pressure and failure of antihypertensive therapy in case-control and population studies. Importantly, high tissue CK preceded hypertension in animal models and in humans, and human vascular tissue CK gene expression was strongly associated with clinical blood pressure. In line with this, CK inhibition substantially reduced the contractility of human resistance arteries ex vivo. We also presented evidence that plasma CK reduced ADP-dependent platelet aggregation. In subsequent intervention studies, the oral competitive CK inhibitor beta-guanidinopropionic acid (GPA) reduced blood pressure in spontaneously hypertensive rats (SHRs), and a 1-week trial of sub-therapeutic dose GPA in healthy men was uneventful. Thus, based on theoretical concepts, evidence was gathered in laboratory, case-control, and population studies that high CK is associated with hypertension and with bleeding risk, potentially leading to a new mode of cardiovascular risk reduction with CK inhibition.

Keywords: ADP; Creatine kinase (CK); ancestry groups; bleeding; hypertension.

Figure 1

Smooth muscle contraction with high creatine kinase activity. A model of the four-state contractile system of vascular smooth muscle adapted from Brewster (18), based on Murphy (25), and Hai and Murphy (26). Ca²⁺ initiates contraction with activation of MLCK. MLCK phosphorylates myosin light chains to activate myosin ATPase (MA) and the MyosinP-ADP interacts generates tension with actin through an Actin-MyosinP-ADP complex. Shortening occurs through cross bridge cycling. The MyosinP-ADP can be dephosphorylated to form the so-called “latch bridges”, which are slowly cycling cross bridges depending on ADP (27). Controlled exit from the latch bridge occurs by re-phosphorylation of myosin, while dephosphorylation of MyosinP and a decrease in Ca²⁺concentration inactivates the high-tension state. Smooth muscle creatine kinase (CK) activity is relatively low compared to striated muscle (23). With relatively high CK activity, lower ADP levels might hinder the ADP-dependent latch bridge formation and enhance myosin ATPase activity, leading to greater microvascular contractility (18). MLCK, myosin light chain kinase.

Figure 2

SBP by increasing plasma creatine kinase activity. Crude SBP according to resting plasma creatine kinase (CK) tertiles, adapted from Brewster et al. (19). I–III are the first through the third tertile of log plasma CK (IU/L), of a random population sample stratified by ethnicity, with respectively 447, 444 and 452 subjects in each tertile. Values are mean ± 2 (SEM). Similar values were found for DBP, and both SBP and DBP differed significantly among the CK tertiles (P<0.001; Kruskal-Wallis test). SBP, systolic blood pressure.

Figure 3

Plasma creatine kinase activity in normotension and treated hypertension. Values depict significant differences in mean plasma creatine kinase (CK) activity (SE) after rest in a random population sample as assessed with ANOVA (P<0.001) (54). *, in the post-test, CK levels between “normotension” and “controlled hypertension” were not significantly different. ^†‡, CK in “treated”, but “uncontrolled hypertension” was significantly higher than “normotension”, and “treated controlled hypertension” (P<0.001).

Figure 4

Molecular modulators of microvascular contractility. This schematic representation of vascular smooth muscle contraction is based on Brewster et al. (57). Creatine kinase (CK) is tightly bound near Ca²⁺ ATPase and myosin ATPase, and evidence suggests the enzyme is also located near myosin light chain (LC) kinase. Here, CK serves to rapidly regenerate ATP from phosphocreatine (Creatine ~ P) (18-27,57). Nitric oxide (NO) and creatine compete for bioavailable L-Arginine (19,57). Importantly, NO, RhoA/Rho kinase, and calcium-dependent pathways involved in the regulation of vascular contractility, converge on metabolic processes modulated by CK (57). Antihypertensive drugs and vasodilators may enhance NO-dependent pathways, such as in ACE inhibitor (ACE-i) induced NO synthesis, or inhibit CK-dependent pathways. Calcium blockers (CaB) directly antagonize CK dependent processes by reduction of cellular Ca²⁺ uptake and release from the sarcoendoplasmic reticulum (SER), while β-adrenergic agonists inhibit myosin LC kinase. High CK is thought to amplify contractile responses, including of β-adrenergic blockers and the high creatine demand with high CK is thought to compromise nitric oxide synthesis, further enhancing contractility (57). cGMP, guanosine cyclic 3',5'-(monophosphate); MLCP, myosin light chain phosphatase.

Figure 5

Creatine kinase and sodium retention. Renal sodium retention is driven by basolateral Na⁺/K⁺ ATPase (15). Depicted is the kidney distal convoluted tubule. Creatine kinase (CK) is tightly bound near basolateral Na⁺/K⁺ ATPase to regenerate ATP for sodium retention (17,53). Thiazide diuretics may antagonize this effect indirectly as these drugs inhibit luminal Na⁺/Cl⁻-cotransport (53,57).