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Aquaporin-3 (AQP3) plays an important role in maintaining the normal water content of the skin. Previously, we revealed that the expression of cutaneous AQP3 increased following oral administration of Gypsum fibrosum (main component: CaSO₄) to mice. The purpose of this study is to elucidate the mechanism by which Gypsum fibrosum increases the expression of cutaneous AQP3 in a keratinocyte cell line. Gypsum fibrosum or CaSO₄ was added to keratinocytes, and the expression level of AQP3, the Ca concentration, the activity of protein kinase C (PKC), and the degrees of phosphorylation of both extracellular signal-regulated kinase (ERK) and cAMP response element binding protein (CREB) were measured. The mRNA and protein expression levels of AQP3 increased significantly 6 h-post addition of Gypsum fibrosum. In keratinocytes treated with Gypsum fibrosum, increases in the concentration of intracellular Ca, PKC activity, and the phosphorylation of ERK and CREB were observed. Pre-treatment with GF109203X, a PKC inhibitor, suppressed the mRNA expression levels of AQP3. Similarly to treatment with Gypsum fibrosum, the addition of CaSO₄ led to the same observations in keratinocytes. It is hypothesized that Gypsum fibrosum causes an increase in the intracellular Ca concentration, PKC activity, and the phosphorylation levels of ERK and CREB, resulting in increased AQP3 expression in keratinocytes. In addition, it is possible that the effect of Gypsum fibrosum is attributable to CaSO₄, based on the results demonstrating that the mechanisms of action of Gypsum fibrosum and CaSO₄ were nearly identical.

Ethnopharmacological relevance We have previously reported that Byakkokaninjinto improves cutaneous pruritus by increasing the expression level of aquaporin-3 (AQP3). In this study, we examined the effect of Gypsum fibrosum (main component: CaSO 4 ), which is the main component of Byakkokaninjinto, on the cutaneous AQP3 expression level. Materials and methods KKAy mice were given a diet containing 0.3% Gypsum fibrosum extract, or a diet containing 0.3% CaSO 4 for 4 weeks. The urine volume, plasma glucose levels, cutaneous AQP3 protein expression, and the Ca 2+ content were measured. Results The 24-h urine volumes and the plasma glucose levels in the Gypsum fibrosum extract group were not significantly different from those in the control group. In the Gypsum fibrosum extract group, the cutaneous AQP3 protein levels increased significantly, by approximately 3.2-fold, compared to the control group. The cutaneous Ca 2+ content in the control group was approximately 35 μg/g. In the Gypsum fibrosum extract group, the Ca 2+ content increased to approximately 51 μg/g, which was significant compared to the control group. In the CaSO 4 group, an increase in the AQP3 protein expression levels and Ca 2+ content were observed; the extent of these increases were similar to those in the Gypsum fibrosum extract group. Conclusions The results of this study suggest that Gypsum fibrosum plays an important role in the increased levels of cutaneous AQP3 expression enhanced by Byakkokaninjinto. The results also indicate that the increase in AQP3 caused by Gypsum fibrosum is attributable to an increase in the cutaneous Ca 2+ content from its main component, CaSO 4 .

Aquaporin-3 (AQP3) plays an important role in maintaining the normal water content of the skin. Previously, we revealed that the expression of cutaneous AQP3 increased following oral administration of Gypsum fibrosum (main component: CaSO₄) to mice. The purpose of this study is to elucidate the mechanism by which Gypsum fibrosum increases the expression of cutaneous AQP3 in a keratinocyte cell line. Gypsum fibrosum or CaSO₄ was added to keratinocytes, and the expression level of AQP3, the Ca concentration, the activity of protein kinase C (PKC), and the degrees of phosphorylation of both extracellular signal-regulated kinase (ERK) and cAMP response element binding protein (CREB) were measured. The mRNA and protein expression levels of AQP3 increased significantly 6 h-post addition of Gypsum fibrosum. In keratinocytes treated with Gypsum fibrosum, increases in the concentration of intracellular Ca, PKC activity, and the phosphorylation of ERK and CREB were observed. Pre-treatment with GF109203X, a PKC inhibitor, suppressed the mRNA expression levels of AQP3. Similarly to treatment with Gypsum fibrosum, the addition of CaSO₄ led to the same observations in keratinocytes. It is hypothesized that Gypsum fibrosum causes an increase in the intracellular Ca concentration, PKC activity, and the phosphorylation levels of ERK and CREB, resulting in increased AQP3 expression in keratinocytes. In addition, it is possible that the effect of Gypsum fibrosum is attributable to CaSO₄, based on the results demonstrating that the mechanisms of action of Gypsum fibrosum and CaSO₄ were nearly identical.

Enhanced expression of renal aquaporin-2 (AQP2) has been reported when polyuria occurs in diabetic animal models. The purpose of this study was to clarify the possibility that increased AQP2 expression in the kidneys play a role as a compensatory mechanism to alleviate diabetic dehydration. Lithium carbonate (Li₂CO₃), which decreases the renal expression of AQPs, was administered to streptozotocin (STZ)-induced model mice of type I diabetes mellitus (STZ mice), to investigate the relationship between urine volume and renal AQP expression. Plasma glucose and urine glucose levels were similar between STZ mice given feed containing Li₂CO₃ for 10 d and un-treated STZ mice. Urine volume increased to 70 ml/d for the Li₂CO₃-treated STZ mice, compared to 36 ml/d for un-treated STZ mice. No changes were observed in creatinine clearance or the mRNA expression levels of sodium myo-inositol transporter and taurine transporter, which are genes associated with the regulation of osmotic pressure in the kidney, in the Li₂CO₃-treated STZ mice relative to un-treated STZ mice. Protein expression levels of AQP2 and aquaporin-3 (AQP3) of the renal inner medulla were significantly decreased in the Li₂CO₃-treated STZ mice, compared to levels in the STZ group. This study revealed that the decreased expression levels of AQP2 and AQP3 in the kidney increased the urine volume in mice without a change in urinary osmotic pressure. The results of this study suggest that the increased renal AQP2 and AQP3 expression, in the setting of polyuria, physiologically serves as a compensatory mechanism to alleviate dehydration in diabetes mellitus.