These observations suggest that lactate-associated increase in the diameter of C2C12 myotubes is induced via activation of GRP81-mediated MEK/ERK pathway. Extracellular lactate might have a positive effect on skeletal muscle size.

Osteopenia is a recognized complication of diabetes mellitus in humans and experimental animals. We recently found that tetracyclines prevent osteopenia in the streptozotocin-induced diabetic rat and that this effect was associated with a restoration of defective osteoblast morphology (Golub et al., 1990). The present study extends these initial ultrastructural observations by assessing osteoblast function in the untreated and tetracycline-treated diabetic rats. After a 3-week protocol, non-diabetic control and diabetic rats, including those orally administered a tetracycline, minocycline (MC), or a non-antimicrobial tetracycline analog (CMT), were perfusion-fixed with an aldehyde mixture; the humeri were dissected and processed for ultracytochemical localization of alkaline phosphatase (ALPase) and Ca-ATPase activities. Some rats from each experimental group received an intravenous injection of 3H-proline as a radioprecursor of procollagen, and the humeri were processed for light microscopic autoradiography. In addition, the osteoid volume in each experimental group was quantitatively examined by morphometric analysis of electron micrographs. During the diabetic state, active cuboidal osteoblasts in the endosteum of control rats were replaced by flattened bone-lining cells that contained few cytoplasmic organelles for protein synthesis (Golgi-RER system), and active transport (mitochondria). Treating diabetic rats with MC, and even more so with CMT, appeared to "restore" osteoblast structure. During diabetes, bone-lining cells incorporated little 3H-proline or secreted little labeled protein and produced only a very thin osteoid layer. Tetracycline administration to the diabetics increased both the incorporation of 3H-proline by osteoblasts and their secretion of labeled protein toward the osteoid matrix, in a pattern similar to that seen in the non-diabetic controls.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of lactate on muscle mass and regeneration were investigated using mouse skeletal muscle tissue and cultured C2C12 cells. Male C57BL/6J mice were randomly divided into (1) control, (2) lactate (1 mol/L in distilled water, 8.9 mL/g body weight)-administered, (3) cardio toxin (CTX)-injected (CX), and (4) lactate-administered after CTX-injection (LX) groups. CTX was injected into right tibialis anterior (TA) muscle before the oral administration of sodium lactate (five days/week for two weeks) to the mice. Oral lactate administration increased the muscle weight and fiber cross-sectional area, and the population of Pax7-positive nuclei in mouse TA skeletal muscle. Oral administration of lactate also facilitated the recovery process of CTX-associated injured mouse TA muscle mass accompanied with a transient increase in the population of Pax7-positive nuclei. Mouse myoblast-derived C2C12 cells were differentiated for five days to form myotubes with or without lactate administration. C2C12 myotube formation with an increase in protein content, fiber diameter, length, and myo-nuclei was stimulated by lactate. These observations suggest that lactate may be a potential molecule to stimulate muscle hypertrophy and regeneration of mouse skeletal muscle via the activation of muscle satellite cells.

Diabetes induces osteopenia, which is characterized by a deficiency of osteoid and decreased activity of osteoblasts. We recently found that tetracyclines prevent the loss of osteoid and bone matrix and the degeneration of osteoblasts in diabetic rats by a mechanism independent of their antimicrobial efficacy. However, bone remodeling requires the activity of osteoclasts as well as osteoblasts. To determine the in vivo effects of tetracycline on osteoclasts in long bones, either a tetracycline (minocycline, TC) or its chemically modified non-antibiotic analogue (CMT), 4-de-dimethylaminotetracycline, was administrated daily to streptozotocin-induced diabetic rats by oral intubation. After 21 days, the rats were perfusion-fixed with a mixture of formaldehyde and glutaraldehyde, and the humeri were dissected and processed for ultracytochemical demonstration of acid trimetaphosphatase (ACPase) activity. In untreated non-diabetic (control) rats, the osteoclasts at the zone of provisional ossification exhibited abundant mitochondria and cisterns of rough endoplasmic reticulum (RER) throughout the cytoplasm, prominent stacks of Golgi membranes, and lysosomes in the perinuclear cytoplasm, and numerous various pale vacuoles in the cytoplasmic area adjacent to well-developed ruffled border. Intense ACPase activity was observed in the Golgi saccules, lysosomes, pale vacuoles, and the extracellular canals of ruffled border. The reaction products were also noted along the resorbing bone surfaces associated with the osteoclast ruffled border. The osteoclasts in the untreated diabetic rats showed a cytoplasmic organization similar to that of the non-diabetic control rats, but showed little or no ruffled border which was replaced by a broad clear zone in some of these cells. However, most of the osteoclasts on bone matrix in the diabetics were devoid of both a ruffled border and a clear zone. ACPase activity was detected in the osteoclast cytoplasm of diabetic rat, as in the controls, but to a much lesser extent along the broad clear zone facing the resorbing bone surfaces. The osteoclasts in TC-treated diabetic rats possessed both a clear zone and a small ruffled border. However, in some cases, they lacked both structures reminiscent of the untreated diabetic cells. The osteoclasts of CMT-treated diabetic rats exhibited structural and enzymatic features essentially identical to those of the non-diabetic control rats. These results suggest that the diabetes-induced osteopenia results, at least in part, from degeneration of osteoclasts (as well as atrophic osteoblasts) and that tetracyclines may be effective in preventing these abnormalities by a mechanism not dependent on the drugs' antimicrobial properties.

Simple and efficient methods were developed for sp 2-sp 3 and sp 3-sp 3 CC bond-activation reactions of 2-substituted 1,3-diketones. 3-Substituted 3-bromopentane-2,4-diones were deacylated in the presence of an aromatic compound and a silica gel supported Brønsted acid containing sulfonic groups. The carbocation formed by cleavage of the sp 3-sp 3 CC bond of the dione alkylated the aromatic compound.