José H. Martínez‐Liarte

Melanocyte stimulating hormone activation of tyrosinase in B16 mouse melanoma cells Evidence for a differential induction of two distinct isoenzymes

Tyrosinase induction in murine malignant melanocytes by αMSH is well known, but its molecular basis has not been characterized. Treatment of B16 melanoma cells with theophylline or αMSH mediates a larger induction of tyrosine hydroxylase than of dopa oxidase activity in total cell extracts, and in the melanosomal and microsomal fractions. No evidence for the modulation of a tyrosinase effector was found. SDS‐PAGE and specific activity stain demonstrated two forms of tyrosinase, with different degrees of induction by theophylline. These results agree with the recent proposal that two tyrosinases, encoded by different genes, are present in murine melanocytes.

Serum tyrosine hydroxylase activity is increased in melanoma patients. An ROC curve analysis

We have studied the serum tyrosine hydroxylase activity of tyrosinase, the key enzyme in the melanogenesis via, as a possible diagnostic factor or marker for detection, prognosis and follow-up of patients with melanoma. This activity was determined in 30 melanoma patients (MP) and in 30 healthy persons (HP) by using a radiometric method. We found mean values of 10.8+/-3.0 and 7.65+/-2.32 mU/l for serum tyrosine hydroxylase activity in MP and HP, respectively. A very significant increase in serum tyrosine hydroxylase activity was observed in MP in comparison to the enzymatic activity in HP (P < 0.00001). Although these data seem very conclusive, we wanted to know whether this test could discriminate adequately between MP and HP. In order to reach this aim, a complete statistical study was performed by using receiver operating characteristic (ROC) curve analysis. The cut-off value obtained was 8.47 mU/l. According to our results and after analytical treatment of the data, we can confirm that evaluation of tyrosine hydroxylase activity in serum could be a quick and reliable diagnostic method for detection, prognosis and follow-up in melanoma patients.

Whole blood glutathione peroxidase activity in melanoma patients

We have studied whole blood glutathione peroxidase activity as a possible diagnostic factor or marker for detection and diagnosis of patients with melanoma. This activity was determined in 40 melanoma patients (MP) and in 40 healthy persons (HP) using an enzymatic method. We found a mean value of 17.90+/-6.82 units/ml in MP and 27.07+/-14.35 units/ml in HP. A very significant decrease in whole blood glutathione peroxidase activity was observed in MP in comparison to the enzymatic activity in HP (P = 0.0005). In order to check whether this test could discriminate between MP and HP, a complete statistical Receiver Operating Characteristic (ROC) curve analysis was performed. The cut-off value was 14.26 units/ml. The area under the curve was 0.737. According to these results, the test could discriminate adequately between both groups. However, the high specificity and low sensitivity values associated with that cut-off value would make this test a very valuable tool for confirming the detection, rather than for primary screening.