[Effects of histamine on proliferation, apoptosis and differentiation of human keratinocytes]

To investigate the effects of histamine on the proliferation, apoptosis and differentiation of human keratinocytes (HKC) and the mechanisms.

The effect of histamine on the growth of HKC in vitro was examined by MTT assay and trypan blue exclusion assay. Cell cycle analysis and early apoptosis analysis by double staining with Annexin V-FITC and PI were carried out by flow cytometry. DNA ladder assay was performed for the detection of cell apoptosis. HKC free calcium concentration ([Ca(2+)](i)) was measured by laser scanning confocal microscopy in combination with calcium fluorescence probe Fluo-3/AM. HKC differentiation markers keratin 10 (K10) and involucrin was detected by streptavidinbiotin complex immunocytochemical assay.

Histamine at high concentration inhibited the proliferation of HKC with cell viability ratio of 65.6% at 1 x 10(-4) mol/L, while histamine at low concentrations promoted proliferation of HKC with the cell viability ratio of 130.7% at 1 x 10(-8) mol/L. Histamine at 1 x 10(-4) mol/L altered cell cycle distribution of HKC with an increase in G0/G1-phase cell population to 30.97%, a decrease in S-phase population to 73.81% and inhibition of G1/S switching. Histamine at 1 x 10(-4) mol/L induced obvious apoptosis of HKC with early apoptosis ratio of 18.64% as compared with the control (5.60%, P<0.05). Histamine 1 x 10(-4) mol/L induced an increase of HKC [Ca(2+)](i) up to 58.9% and cimetidine (an H(2) receptor antagonist) decreased HKC [Ca(2+)](i) down to 25.4%. Histamine at this concentration down-regulated the expressions of K10 and involucrin of HKC but these changes were not significantly different from those of the control (P>0.05).

Histamine at high concentrations inhibits cell cycle progress of HKC, mediates cell apoptosis and induces the increase of [Ca(2+)](i), which might be a partial explanation for growth arrest of HKC elicited by histamine. Histamine may regulate epidermal tissue turnover under physiological conditions, whereas under pathological circumstances of the skin as in trauma and inflammation, histamine at high concentrations may inhibit the regeneration of epidermis and the differentiation of HKC.