[Normal values and aging of the main enzyme series in serum]

Diagnostic biomarkers of muscle injury and exertional rhabdomyolysis

Early recognition of muscle injury, up to development of exertional rhabdomyolysis (ER), is essential for many clinical and practical reasons, such as planning the suitable period of recovery and deciding an appropriate time for return to exercise. Albeit magnetic resonance imaging (MRI) remains the reference technique for assessing muscle injuries, and ultrasonography (US) may be a complementary approach for easy, inexpensive and fast screening, the potential drawbacks of both techniques may be overcome by some laboratory tests, which may help guiding both diagnostic reasoning and clinical decision making. Current evidence attest that creatine kinase remains the most validated test across the clinical spectrum of muscles injuries, as its measurement may be helpful for screening subjects with suggestive signs and symptoms, its concentration substantially reflects the amount of injured muscle and its kinetics appears suitable, combined with clinics and results of imaging testing, for making decisions on return to exercise. Relatively low cost and widespread availability are additional advantages of this test. In athletes with ER, myoglobin assessment may provide adjunctive useful information, due to high predictive value for development of acute kidney injury. Regarding other historical biomarkers, namely aldolase and lactate dehydrogenase, the kinetics, correlation with injury severity, laboratory standardization and availability make their measurement unsuitable and redundant. Some innovative biomarkers have also been tested in recent years, including fatty acid-binding proteins and carbonic anhydrase III, myosin light chain 3 and muscle micro RNAs. However, their clinical effectiveness, standardization, availability in clinical laboratories and costs are still regarded as major drawbacks.

Phosphohexose isomerase in hypernephroma. Significance as serum tumor marker, comparison to other glycolytic enzymes and isozyme patterns in normal and tumor tissue

In hypernephroma an overall diagnostic sensitivity of 72% and a specificity of 87% was found for the serum tumor marker phosphohexose isomerase (PHI). Both in early stage disease and in well differentiated tumors a sensitivity of about 60% was reached. In contrast the sensitivity of three other glycolytic enzymes tested was found to be less than 20%. Since the cancer induced elevation of PHI activity in the tumor was found to be comparable to those of the other test enzymes, elevated PHI serum activities cannot be attributed to overproportional PHI synthesis and unspecific cell-lysis. In 6 of 10 cases studied differences in the PHI isozyme pattern between the tumor and the normal tissue were found suggesting the occurrence of cancer associated structural alterations of PHI.

[Investigations for pathogenesis of depression of lymphocyte transformation in chronic uremia (author's transl)]

In order to investigate the depressive effect of the hypothetical low molecular weight "uremic toxins" methylguanidine and phenol on lymphocyte transformation these substances were added to lymphocyte cultures with increasing concentrations. 3H-thymidine uptake and LDH-activity in the supernatant culture medium as a parameter of continuous cell destruction were analyzed after incubation for 5 days. Both substances induced in spontaneous as well as in PHA-stimulated cultures dose-dependent depression of 3H-thymidine uptake and simultaneous increase in LDH-activity. Thus the effect of both toxins may be cytotoxic depression of lymphocyte viability. Furthermore in the same arrangement-way higher molecular weight metabolites from urine of healthy and chronic uremic persons were added in increasing concentrations to lymphocyte cultures. The same result: dose-dependent depression of transformation and increase of LDH-activity was slightly diminished by urine metabolites from uremic patients as compared to healthy persons. This may be due to a shift toward non-toxic compounds. But as these metabolites are excreted in 20-30 fold larger quantities in chronic renal insufficiency, an accumulation in the serum and classification as "uremic toxins" can be excluded.