Direct Effects of Minoxidil on Epidermal Cells in Culture

Abstract

Minoxidil, a potent antihypertensive agent, induces generalized hypertrichosis when administered systemically, or localized hair regrowth when applied topically to sites of severe alopecia areata. The pharmacologic mechanisms by which minoxidil stimulates hair growth are unknown. This study was designed to examine whether minoxidil has direct effects on neonatal murine epidermal cells in culture. In the presence of minoxidil, cultures showed a marked dose-dependent second peak of DNA synthesis 8-10 days after culture initiation. In addition, two morphologically distinct cell types appeared. Indirect immunofluorescence staining with keratin-specific antibody revealed cytoplasmic keratin fibers, suggesting the epidermal origin of these cells. Our experiments demonstrate that minoxidil can affect epidermal cells in culture by altering their growth pattern and phenotypic appearance.

Biphasic Effects of Minoxidil on the Proliferation and Differentiation of Normal Human Keratinocytes

“…We also found that high doses of Mi noxidil (1 mM ) has pro-differentiative prop erties, and similar results were described by Bernd et al [ 18] on HaCat keratinocytes with 1.2 mM Minoxidil. No effects on NHK differ entiation were observed with lower doses of Minoxidil, either by us or by others [14,17,18]. However, we showed that millimolar concentrations of Minoxidil are partially cy totoxic, in agreement with other reports [13][14][15]17], rendering this pro-differentiative ef fect difficult to interpret.…”

“…No effects on NHK differ entiation were observed with lower doses of Minoxidil, either by us or by others [14,17,18]. However, we showed that millimolar concentrations of Minoxidil are partially cy totoxic, in agreement with other reports [13][14][15]17], rendering this pro-differentiative ef fect difficult to interpret. On an other hand, such high concentrations are poorly relevant to in vivo data (maximal plasmatic levels of Minoxidil after systemic administration of hair growth-promoting doses: 0.775 \iM), but we cannot exclude an accumulation of drug in some compartments of the follicle, especially the hair shaft rich in keratins and melanin [42].…”

“…Baden and Kubilus [ 14] reported that Minoxidil-treated epidermal NHK (100 pA/, in high-calcium, serum-containing medium) survived longer than controls and could be passaged successfully for longer peri ods after confluency, thus concluding to the inhibition of keratinocyte senescence by Mi noxidil. (NB: a similar technical approach gave similar results and conclusions on mu rine neonatal epidermal keratinocytes, as re ported by Cohen et al [17].) Along the same lines.…”

“…Two independent studies [12,17] using murine primary epidermal cell cultures plated at high density in high-calcium, serum-con taining medium showed a burst in DNA syn thesis (increase in 3H-thymidine incorpora tion) after 7-8 days of culture in the presence of 50 \iM Minoxidil. The authors concluded that Minoxidil maintains the proliferative ac tivity of differentiating epidermal keratino cyte cultures, but the possibility cannot be excluded that Minoxidil interferes with thy midine metabolism (shunt of the salvage Skin Pharmacol 1997; 10:206-220pathway or reduction in thymidine catabo lism) [30], thus increasing the -'H-thymidine incorporation without stimulating prolifera tive growth.…”

“…The authors concluded that Minoxidil maintains the proliferative ac tivity of differentiating epidermal keratino cyte cultures, but the possibility cannot be excluded that Minoxidil interferes with thy midine metabolism (shunt of the salvage Skin Pharmacol 1997; 10:206-220pathway or reduction in thymidine catabo lism) [30], thus increasing the -'H-thymidine incorporation without stimulating prolifera tive growth. Furthermore, one of these au thors [17] mentioned the appearance of nu merous multinucleated cells in Minoxidiltreated cultures, raising the possibility that the observed burst in DNA synthesis does not necessarily reflect cell proliferation. A ^-th y midine incorporation technique was also em ployed by O'Keefe and Payne [16] on epider mal NHK from foreskins grown in low-cal cium, serum-free medium: after 1 day of treatment.…”