Mitochondrial activity of orbicularis oris muscle in unilateral cleft lip patients

Abstract

To better evaluate the role of a possible mitochondrial alteration in the pathogenesis of cleft lip, we obtained and examined 38 orbicularis oris muscle specimens taken from the cleft margin of both cleft and noncleft sides of 10 unilateral cleft lip infants at the time of primary closure. Part of each sample was frozen in liquid nitrogen/cooled isopentane, while the remainder was fixed in 2.5% glutaraldehyde, postfixed in osmium tetroxide, and embedded in Araldyte resin. Ten-micrometer-thick sections were obtained from the frozen samples and stained for histologic (Gomori trichrome) and histochemical (adenosine triphosphatase, nicotinamide adenine dinucleotide-tetrazolium reductase, cytochrome c-oxidase, succinate dehydrogenase) techniques. Ultra-thin sections (70 to 100 nm) of the resin-embedded specimens were stained with uranyl acetate and lead cytrate and were examined with a Zeiss 109 transmission electron microscope operating at 80 kV. Muscular fiber-type ratio was found to be 19.2 percent type 1 and 80.8 percent type 2 fibers on the cleft side and 26.3 percent type 1 and 73.7 percent type 2 fibers on the noncleft side. We detected aspecific structural alterations, such as variations in the fiber size without fiber group atrophy or fiber-type grouping with the ATPase reaction, in all biopsies. Although Gomori trichrome revealed a dark staining and red granularity of the fibers, suggesting an increase in mitochondria activity, no ragged-red fibers or cytochrome c-oxidase-negative/succinate dehydrogenase-positive fibers were found. At the ultrastructural level, the mitochondrial morphology was always preserved, without inclusions or variations in size and/or shape. On the other hand, we invariably noticed an increase of the number of mitochondria, associated with abnormal glycogen deposits, in some areas of every specimen. Both of these two latter findings were regularly localized at the periphery of the sarcolemma, resembling the so-called lobulated fibers, an aspecific sign of muscular flogosis. Our findings, although excluding an inherent metabolic myopathy of orbicularis oris muscle in unilateral cleft lip patients, evinced both an increased oxidative metabolism and a generic inflammatory condition of that muscle, the nature of which must still be defined.