Characterization of two types of mitochondrial creatine kinase isolated from normal human cardiac muscle and brain tissue

Increased activity of serum mitochondrial isoenzyme of creatine kinase in hepatocellular carcinoma patients predominantly with recurrence

BACKGROUND & AIMS

Mitochondrial isoenzyme of creatine kinase (MtCK) is reportedly highly expressed in hepatocellular carcinoma (HCC). Clinical relevance of serum MtCK activity in patients with HCC was assessed using a novel immuno-inhibition method.

METHODS

Among patients with cirrhosis caused by hepatitis B or C virus, 147 patients with HCC (12 with the first occurrence and 135 with recurrence) and 92 patients without HCC were enrolled.

RESULTS

Serum MtCK activity was higher in cirrhotic patients with HCC than in those without HCC or healthy subjects. Elevated serum MtCK activity in HCC patients decreased after radiofrequency ablation. In case of prediction of HCC, MtCK had a sensitivity of 62.6% and a specificity of 70.7% at a cut-off point of 8.0 U/L, with an area under the receiver operating curve of 0.722 vs. 0.713 for alpha-fetoprotein (AFP) and 0.764 for des-gamma-carboxy prothrombin (DCP). Among the HCC patients, serum MtCK activity was elevated in 52.9% individuals with serum AFP level < 20 ng/ml and 63.2% individuals with serum DCP level < 40 mAu/ml. Even in patients with a single HCC ≤ 2 cm, the sensitivity of serum MtCK activity for the prediction of HCC was 64.4%, which was comparable to the overall sensitivity. This increased activity was due to an increase in ubiquitous MtCK, not sarcomeric MtCK, and the enhanced mRNA expression of ubiquitous MtCK was observed in cell lines originating from HCCs in contrast to healthy liver tissues.

CONCLUSIONS

Serum MtCK activity merits consideration as a novel marker for HCC to be further tested as for its diagnostic and prognostic power.

Increase in serum mitochondrial creatine kinase levels induced by tenofovir administration

Recently, 2 monoclonal antibodies that specifically inhibit mitochondrial creatine kinase (MtCK) activity have been developed. In this study, we measured the serum MtCK activity in HIV-1-infected individuals (n = 100) by employing a novel method using these antibodies. The mean serum MtCK activity in 44 patients treated with highly active antiretroviral therapy (HAART) including tenofovir disoproxil fumarate (TDF) was 16.0 IU/L. The MtCK activity was significantly higher in patients receiving TDF than in those receiving HAART without TDF (3.4 IU/L) or in naïve patients (6.9 IU/L) (Tukey-Kramer test, p < 0.0001 and p = 0.0029, respectively). The serum MtCK activity reached a plateau at 1 month after the initiation of TDF administration and decreased upon discontinuation. It showed no significant correlation with the trough plasma TDF concentration, serum creatinine level, or red blood cell count. The activity was elevated in 75% of the patients receiving TDF, and this elevation was specific to TDF; it was not observed with other anti-HIV drugs. In addition, our report emphasizes the careful interpretation of creatine kinase-MB (CK-MB) test results in patients receiving TDF because MtCK in serum could cause false-positive results on a conventional CK-MB test, which does not include MtCK-specific inhibitory antibodies.

Proteomic analysis of specific brain proteins in aged SAMP8 mice treated with alpha-lipoic acid: implications for aging and age-related neurodegenerative disorders

Free radical-mediated damage to neuronal membrane components has been implicated in the etiology of Alzheimer's disease (AD) and aging. The senescence accelerated prone mouse strain 8 (SAMP8) exhibits age-related deterioration in memory and learning along with increased oxidative markers. Therefore, SAMP8 is a suitable model to study brain aging and, since aging is the major risk factor for AD and SAMP8 exhibits many of the biochemical findings of AD, perhaps as a model for and the early phase of AD. Our previous studies reported higher oxidative stress markers in brains of 12-month-old SAMP8 mice when compared to that of 4-month-old SAMP8 mice. Further, we have previously shown that injecting the mice with alpha-lipoic acid (LA) reversed brain lipid peroxidation, protein oxidation, as well as the learning and memory impairments in SAMP8 mice. Recently, we reported the use of proteomics to identify proteins that are expressed differently and/or modified oxidatively in aged SAMP8 brains. In order to understand how LA reverses the learning and memory deficits of aged SAMP8 mice, in the current study, we used proteomics to compare the expression levels and specific carbonyl levels of proteins in brains from 12-month-old SAMP8 mice treated or not treated with LA. We found that the expressions of the three brain proteins (neurofilament triplet L protein, alpha-enolase, and ubiquitous mitochondrial creatine kinase) were increased significantly and that the specific carbonyl levels of the three brain proteins (lactate dehydrogenase B, dihydropyrimidinase-like protein 2, and alpha-enolase) were significantly decreased in the aged SAMP8 mice treated with LA. These findings suggest that the improved learning and memory observed in LA-injected SAMP8 mice may be related to the restoration of the normal condition of specific proteins in aged SAMP8 mouse brain. Moreover, our current study implicates neurofilament triplet L protein, alpha-enolase, ubiquitous mitochondrial creatine kinase, lactate dehydrogenase B, and dihydropyrimidinase-like protein 2 in process associated with learning and memory of SAMP8 mice.

Mitochondrial creatine kinase with atypical pI values detected in serum of a patient with ovarian hepatoid yolk sac tumor

Atypical mitochondrial creatine kinase (creatine N-phosphotransferase, CK, EC 2.7.3.2) was detected in the serum of a patient with carcinoma of germ cell origin, probably hepatoid yolk sac tumor. The pI of the oligomeric atypical mitochondrial CK (Mi-CK) was found at the acidic side compared to that of the typical ubiquitous Mi-CK (uMi-CK), while the molecular size of the atypical Mi-CK was similar to that of the typical uMi-CK. The pIs of the oligomeric and the dimeric atypical Mi-CKs became the same as those of the typical uMi-CK upon treatment with 2-mercaptoethanol. Therefore, the atypical Mi-CK was suggested to be an oxidized form of uMi-CK, and the oxidation might have occurred in the mitochondria because the oligomeric atypical Mi-CK had atypical pIs. The physicochemical characteristics of the oxidized uMi-CK were similar to those of the typical uMi-CK.