Phenytoin-induced DNA synthesis and inositol 1,4,5-trisphosphate formation in L-929 fibroblasts

Phenytoin alters transcript levels of hormone-sensitive lipase in muscle from horses with hyperkalemic periodic paralysis

In equine hyperkalemic periodic paralysis (HyperPP), there is evidence suggesting that the primary defect in the sodium channel is associated with a secondary alteration in triacylglycerol-associated fatty acid metabolism (TAFAM) in skeletal muscle. Furthermore, TAFAM may be involved in the therapeutic action of phenytoin. The effects of phenytoin treatment on the transcript levels of three key proteins in TAFAM, hormone sensitive lipase (HSL), carnitine palmitoyltransferase (CPT), and fatty acid binding protein (FABP), were examined. These transcripts were quantitated by competitive reverse transcription polymerase chain reaction in undifferentiated and differentiated primary cultures of equine skeletal muscle from control, heterozygous HyperPP, and homozygous-affected HyperPP horses. There was a 10-fold lower level of HSL transcript in both undifferentiated and differentiated cultures from homozygous-affected horses than from horses of the other genotypes. Phenytoin selectively increased the HSL transcript in homozygous-affected differentiated cultures to levels similar to those of the other genotypes. The levels of CPT and FABP transcripts were unaffected by genotype, differentiation, and phenytoin treatment. These results suggest that the primary defect in HyperPP may secondarily decrease HSL transcript levels and that the therapeutic action of phenytoin may include regulation of mRNA transcripts in skeletal muscle.

Effect of 5-(p-hydroxyphenyl)-5-phenylhydantoin (p-HPPH) enantiomers, major metabolites of phenytoin, on the occurrence of chronic-gingival hyperplasia: in vivo and in vitro study

The purpose of this study was to assess the possible role of the (R)- and (S)- enantiomers of the phenytoin metabolite p-HPPH in the pathogenesis of gingival hyperplasia (GH). About 98% of circulating p-HPPH is in the (S)-form. There were significant differences between patients with and without GH in (R)-p-HPPH level (0.055 vs 0.042 microgram.ml-1), both enantiomer/racemate level ratios, and R/S enantiomeric ratio (0.0313 vs 0.0232); an increase in serum (R)-p-HPPH level was observed in patients with GH. In separate experiments, the effect of p-HPPH enantiomers on the proliferation of the normal human dermal fibroblast was studied. The in vitro study showed that (R)-p-HPPH selectively stimulated fibroblast growth. The results suggest that the least abundant metabolite, (R)-p-HPPH, is the most toxic with respect to gingival hyperplasia.

Influence of the extracellular matrix on fibroblast responsiveness to phenytoin using in vitro wound healing models

Recent reports indicate that the topical administration of phenytoin to cutaneous wounds can promote repair. However, isolated skin cells (keratinocytes and fibroblasts) in vitro have varied in their response to phenytoin, giving rise to apparently contradictory results. We have examined how the structure of the extracellular matrix in which human dermal fibroblasts are grown in vitro can influence the response of these cells to phenytoin. The results indicate that, when fibroblasts are embedded within freely-contracting, relaxed, types I collagen matrices, they are insensitive to phenytoin treatment. However, if fibroblasts are grown in collagen matrices which are nonretracting and under tension, phenytoin (5-50 micrograms/ml) significantly (P < 0.01) stimulates cell proliferation, and inhibits collagenase activity in a dose- and time-dependent manner. The fact that the effects of phenytoin on dermal fibroblasts are biphasic and influenced by the surrounding matrix may help to explain why in vitro investigations with phenytoin give rise to inconsistent data. It also suggests that the matrix alterations which accompany wound healing may modulate the effects of phenytoin on dermal fibroblasts.

Clinical assessment of gingival size among patients treated with diltiazem

Gingival overgrowth induced by nifedipine has been extensively reported. This finding, however, does not apply to gingival size changes caused by other calcium antagonists such as diltiazem. We studied the gingiva of 13 subjects with ischemic cardiopathy who had been treated with diltiazem and established two control groups: (1) a healthy group of 12 patients and (2) a group of 10 patients with ischemic cardiopathy and concomitant treatment similar to that applied to the diltiazem group except that they had not been administered any type of calcium antagonists. The size of the gingiva around the six anterior teeth was measured on plaster models of the upper and lower jaws. Significantly higher scores of the size of the gingiva were found when patients treated with diltiazem were compared with the patients in the other two groups (p < 0.05) gingiva were found when patients treated with diltiazem were compared with the patients in the other two groups (p < 0.05) and also when interproximal (p < 0.05) and vestibular (p < 0.05) sites were considered. We did not observe any significant difference in the plaque index of each group (p < 0.05); only bleeding after probing was found statistically different between the diltiazem and the nondiltiazem groups.

Phenytoin increases gene expression for platelet-derived growth factor B chain in macrophages and monocytes

The mechanism by which phenytoin (PHT) induces gingival overgrowth remains unclear. We hypothesized that PHT increases macrophage production of platelet-derived growth factor (PDGF), an important cytokine in connective tissue growth and repair, and that excessive production PDGF in gingiva could lead to redundant growth. To test the hypothesis, rat peritoneal macrophages and human blood monocytes were cultured in the presence of PHT (5 to 20 micrograms/ml medium) or an equal volume of its solvent for 3 days and tested for expression of PDGF-B mRNA by in situ hybridization. Approximately 300 cells/culture well were examined (3 wells/drug level) for positive indication of PDGF-B mRNA. Data were compared by chi square test. All levels of PHT in both cell types induced a 2- to 8-fold increase in PDGF-B mRNA positive cells, significant in all cases at P < 0.001. Northern blot analysis of RNA from similarly cultured rat macrophages confirmed these findings. Cells treated with 10 micrograms PHT/ml medium or solvent revealed 2.2 +/- 0.3 and 1.0 +/- 0.2 (mean +/- SEM) arbitrary units PDGF mRNA respectively (t tests, P < 0.05). Additionally, rat macrophages were cultured in presence of 5 micrograms PHT/medium or its solvent and medium was analyzed for PDGF secretion by radioimmunoassay. Mean values (+/- SEM) were 1.28 +/- 0.49 and 0.78 +/- 0.07 ng/mg protein respectively (t test, P < 0.05). These data showed that PHT augmented the expression of c-sis, the gene for PDGF-B, and offered a possible explanation for PHT-induced gingival overgrowth.