A randomized phase 2 study on demeclocycline in patients with mild-to-moderate COVID-19

Tetracyclines exhibit anti-viral, anti-inflammatory, and immunomodulatory activities via various mechanisms. The present study investigated the efficacy and safety of demeclocycline in patients hospitalized with mild-to-moderate COVID-19 via an open-label, multicenter, parallel-group, randomized controlled phase 2 trial. Primary and secondary outcomes included changes from baseline (day 1, before the study treatment) in lymphocytes, cytokines, and SARS-CoV-2 RNA on day 8. Seven, seven, and six patients in the control, demeclocycline 150 mg daily, and demeclocycline 300 mg daily groups, respectively, were included in the modified intention-to-treat population that was followed until day 29. A significant change of 191.3/μL in the number of CD4+ T cells from day 1 to day 8 was observed in the demeclocycline 150 mg group (95% CI 5.1/μL-377.6/μL) (p = 0.023), whereas that in the control group was 47.8/μL (95% CI - 151.2/μL to 246.8/μL), which was not significant (p = 0.271). The change rates of CD4+ T cells negatively correlated with those of IL-6 in the demeclocycline-treated groups (R = - 0.807, p = 0.009). All treatment-emergent adverse events were of mild-to-moderate severity. The present results indicate that the treatment of mild-to-moderate COVID-19 patients with demeclocycline elicits immune responses conducive to recovery from COVID-19 with good tolerability.Trial registration: This study was registered with the Japan Registry of Clinical Trials (Trial registration number: jRCTs051200049; Date of the first registration: 26/08/2020).

Neuroprotective Effects of a Novel Demeclocycline Derivative Lacking Antibiotic Activity: From a Hit to a Promising Lead Compound

The antibiotic tetracycline demeclocycline (DMC) was recently reported to rescue α-synuclein (α-Syn) fibril-induced pathology. However, the antimicrobial activity of DMC precludes its potential use in long-term neuroprotective treatments. Here, we synthesized a doubly reduced DMC (DDMC) derivative with residual antibiotic activity and improved neuroprotective effects. The molecule was obtained by removal the dimethylamino substituent at position 4 and the reduction of the hydroxyl group at position 12a on ring A of DMC. The modifications strongly diminished its antibiotic activity against Gram-positive and Gram-negative bacteria. Moreover, this compound preserved the low toxicity of DMC in dopaminergic cell lines while improving its ability to interfere with α-Syn amyloid-like aggregation, showing the highest effectiveness of all tetracyclines tested. Likewise, DDMC demonstrated the ability to reduce seeding induced by the exogenous addition of α-Syn preformed fibrils (α-Syn_PFF) in biophysical assays and in a SH-SY5Y-α-Syn-tRFP cell model. In addition, DDMC rendered α-Syn_PFF less inflammogenic. Our results suggest that DDMC may be a promising drug candidate for hit-to-lead development and preclinical studies in Parkinson's disease and other synucleinopathies.

Cortical bone histomorphometry of the iliac crest in normal black and white South African adults

Fragility fracture rates in South African blacks (B) are lower than in whites (W). Since bone strength in many parts of the skeleton depends mainly on cortical bone, we examined iliac crest cortical bone from 97 B (49 male, 48 female) aged 22-80 and 111 W (60 male, 51 female) aged 21-84 histomorphometrically for differences between B and W and effects of age. B had thicker (P = 0.02) and less porous (P = 0.0007) cortices, fewer haversian (H) osteons (P < 0.0001), and greater endocortical (Ec) wall thickness (P < 0.0001). B also had thicker H (P = 0.0005) and Ec osteoid seams (P < 0.0001); greater Ec osteoid surface (P = 0.0005), Ec mineral apposition rate (P < 0.0001), and Ec bone formation rate (P = 0.038); and lower H (P = 0.0002) and Ec eroded surfaces (P = 0.029). Some of the differences were already present in subjects aged 21-30 years. Although cortical structure deteriorated with age in B and W, after age 40 Ec wall thickness declined only in W. Greater Ec mineral apposition and bone formation rates, i.e., greater osteoblast efficiency at the cellular and tissue levels, suggest better Ec bone preservation that may contribute to lower fragility fracture rates in B.

Differences in osteocyte density and bone histomorphometry between men and women and between healthy and osteoporotic subjects

Bone defects related to osteoporosis develop with increasing age and differ between males and females. It is currently thought that the bone remodeling process is supervised by osteocytes in a strain-dependent manner. We have shown an altered response of osteocytes from osteoporotic patients to mechanical loading, and osteocyte density is reduced in osteoporotic patients, which might relate to imperfect bone remodeling, leading to lack of bone mass and strength. Hence, information on osteocyte density will contribute to a better understanding of bone biology in males and females and to the assessment of osteoporosis. Osteocyte density as well as conventional histomorphometric parameters of trabecular bone were determined in cancellous iliac crest bone of healthy postmenopausal women and men and of osteoporotic women and men. Osteocyte density was higher in healthy females than in healthy males and lower in osteoporotic females than in healthy females. Bone mass was reduced in osteoporotic patients, both male and female. In females, trabecular number was reduced, whereas in males, trabecular thickness was reduced and eroded surface was increased. There were no correlations between the parameter groups bone architecture, bone formation, bone resorption, and osteocyte density. These results are consistent with impaired osteoblast function in osteoporotic patients and with a different mechanism of bone loss between men and women, in which osteocyte density might play a role. The reduced osteocyte numbers in female osteoporotic patients might relate to imperfect bone remodeling leading to lack of bone mass and strength.

Effects of growth hormone and testosterone on cortical bone formation and bone density in aged orchiectomized rats

Osteoporosis in men is a disease that is increasing in incidence, and with an increasing elderly population it poses a serious health problem. Since both testosterone (T) and growth hormone (GH) have an anabolic effect on bone and both decrease with aging, we were prompted to test whether the administration of these hormones in combination would increase bone mass in orchiectomized (orx) senile rats more than administration of either agent alone. Twenty-month-old male Wistar rats were divided into five groups with seven animals each: (a) age-matched intact control, (b) orx, (c) orx+GH (2.5 mg/kg/day), (d) orx+T [10 mg/kg, subcutaneous (s.c.), injection given twice a week], and (e) orx+GH+T. Testosterone and GH were given subcutaneously for 4 weeks. Bone histomorphometry of the tibial shaft showed that the orx group had lower cortical bone area than the intact control group. The decrease in cortical bone area was due to increased intracortical porosis as well as decreased periosteal bone formation rate (BFR). Administration of T to the orx animals prevented the development of the porosis and the decrease in periosteal BFR. The bone mineral content (BMC) and bone mineral density (BMD) of the femur as tested by dual-energy X-ray absorptiometry were significantly higher in the orx+T than in the orx group and were not significantly different from that of the intact control group. Administration of GH to the orx rats increased periosteal BFR significantly; however, the BMC and BMD measured were not increased significantly in comparison to the orx group. When GH and T were combined in treatment, the cortical bone area, periosteal BFR, and femoral BMD were all significantly higher than that of the orx and even higher than the intact control rats. Two-way analysis of variance shows that the individual effect of GH and T treatment on the periosteal BFR and cortical bone area was significant. The effect of T, but not GH, on femoral BMC and BMD was also significant; however, there is no synergistic interaction between the two treatments. Four weeks of orx with or without GH or T administration had no significant effect on tibial metaphyseal cancellous bone volume. In conclusion, this short-term study suggests that the combined intervention of GH and T in androgen-deficient aged male rats may have an independent effect in preventing osteopenia. The significant effect of GH+T may be attributed to the prevention of intracortical porosis, and an increase in periosteal bone formation and cortical bone mass.

POSSIBLE RELATIONSHIP BETWEEN TETRACYCLINE STABILITY AND EFFECT ON FOETAL SKELETON

A possible relationship between stability of a tetracycline and persistence in the foetal skeleton is discussed; it seems that the greater the stability of a tetracycline, the more it may interfere with bone-forming processes. Therefore, assuming that limited instability does not impair antibiotic potency in vivo, the use of a low-stability tetracycline seems to be a safer form of treatment in order to avoid undesired effects on the foetal skeleton.

Quantitative assessment of dentin bridge formation following pulp-capping in miniature swine

A quantitative assessment of dentin bridges was conducted on sections prepared from teeth capped with four pulp-capping agents (Bioglass, Life, Demineralized Dentin Matrix, and Teflon) in a micro-swine model. The degree of mineralization of the dentin bridges relative to the adjacent primary dentin was measured using a computer-based image analysis of microradiographs prepared from the sections. The rate of formation of the dentin bridge was measured from fluorescent bands formed in the same sections by a Demeclocycline dentin marker. There were no statistically significant differences in the relative mineral densities of the dentin bridges and the rate of dentin bridge formation under the four pulp-capping agents. These findings support the suggestion that components of the extracellular matrix rather than pulp-capping agents may be important in the formation and mineralization of dentin bridges in repairing dental pulps.

Distribution of bone remodeling units in the otic capsule of the rabbit. A semiquantitative morphometric study

Distribution of bone remodeling units (BRU) in relation to the perilymphatic space was studied in undecalcified temporal bones from adult rabbits labeled in vivo with bone-seeking fluorochromes. Based on recordings of focal bone formation, relative densities of BRUs inside concentric tissue zones around the inner ear spaces were estimated. Zonal densities of BRUs were found to decline towards the perilymphatic space, lending further support to the existence of a local inner ear mechanism in control of capsular bone tissue dynamics. The possible nature of this mechanism is considered briefly with special reference to inner ear electromechanic activity.

Multiple miliary osteoma cutis

We describe the clinical, radiographic, histologic, and metabolic features of an unusual case of multiple miliary osteoma cutis in an otherwise healthy 57-year-old woman. Although the pathogenesis of this rarely reported entity is not fully understood, the novel application of a dynamic bone study revealed a high rate of internal bone remodeling within the lesion. This finding prompted a brief therapeutic trial of a diphosphonate, not previously reported in the treatment of this condition.

Difference in label length between demethylchlortetracycline and oxytetracycline: implications for the interpretation of bone histomorphometric data

We measured the individual lengths of fluorescent labels on the three subdivisions of the endosteal envelope in iliac bone biopsy specimens produced by the administration of both oxytetracycline and demethylchlortetracycline. Fifty-one healthy subjects and 53 patients with postmenopausal osteoporosis were labeled in the stated order, and 8 osteopenic patients were labeled in the reverse order. Whatever the order of administration, the demethylchlortetracycline label was longer than the oxytetracycline label. We conclude: (1) the difference in label lengths reflects a difference between the two compounds in some intrinsic property, whether physical, chemical, or pharmacokinetic. (2) If the calculation of extent of mineralizing surface is based on the mean length of the two labels, a suitable correction should be applied to the shorter label; alternatively, the length of the longer label alone should be used. (3) Unlabeled osteoid not due to label escape probably results from slow terminal mineralization after cessation of matrix synthesis during which too few tetracycline molecules are incorporated to exceed the threshold for visible fluorescence, rather than from the temporary interruption of mineralization followed by its resumption.

Relationship between toluidine blue-stained calcification fronts and tetracycline-labeled surfaces in normal human iliac crest biopsies

The relationship between toluidine blue-stained calcification fronts and tetracycline labeling was examined in iliac crest biopsies from 56 normal subjects aged 19-80 years, all of whom had received double tetracycline labeling. Sections were quantitated using an eye-piece graticule and all values were expressed as a percentage of osteoid surface. Values for double plus single tetracycline-labeled surfaces were lower than those obtained for toluidine blue-stained calcification fronts in 66% of subjects, although the difference between the two measurements was not statistically significant. Values obtained for calcification fronts demonstrated by toluidine blue staining were significantly greater than those obtained for single, double, and double plus half single tetracycline-labeled surfaces. No significant correlation could be demonstrated between toluidine blue-stained calcification and tetracycline-labeled surfaces. In conclusion, the fraction of osteoid bearing a tetracycline label differed from that showing a toluidine blue-stained calcification front and no correlation could be demonstrated between the two measurements. These differences may arise from methodological problems associated with their demonstration and identification; alternatively their lack of similarity might reflect uptake of stain and tetracycline at different sites within the calcification front. Which of the two parameters most accurately represents the active mineralizing surface is unknown.

Tetracycline double-labelling in post-traumatic osteopenia in man

Biopsy specimens were taken from parts of earlier fractured bones in seven patients with post-traumatic osteopenia and one healthy volunteer, who were all administered a double dose of tetracycline for the purpose of prelabelling. In the volunteer, specimens were taken from both the proximal tibia epiphysis and the iliac crest. The fraction of labelled surfaces and the rate of apposition were calculated. The results were also compared with normative data from the iliac crest. At least in the first year after fracture, post-traumatic osteopenia appears to be a condition with an increased appositional activity.

Inhibition of cortical and trabecular bone formation in the long bones of immobilized monkeys

The acute effects of immobilization on cortical and trabecular bone formation were studied in juvenile male rhesus monkeys (Macaca mulatta). Four animals were immobilized for two weeks by application of total body casts. Two control monkeys were housed in separate metabolic cages under similar environmental and dietary conditions. Tetracycline derivatives were administered on three separate occasions to label sites of bone formation. The tetracycline-labeling frequency and mineral apposition rate of osteons and trabecular bone surfaces in the humerus and femur were determined. The inhibition of bone formation induced by immobilization was more pronounced in trabecular bone. Immobilized monkeys exhibited a moderate, but statistically nonsignificant, reduction in the percentage of osteons forming bone. Conversely, the dramatic decline in the percentage of trabecular surfaces undergoing bone formation in immobilized monkeys was found to be highly significant. The diminished rate of mineral apposition in osteons suggested that osteoblastic activity was impaired in cortical bone during immobilization. The mineral apposition rate in trabecular bone could not be determined reliably due to minimal tetracycline deposition, which indicated that osteoblastic activity and/or recruitment almost ceased in the metaphyseal tissue of immobilized monkeys.

Role of complement and polymorphonuclear cells in demethylchlortetracycline-induced phototoxicity in guinea pigs. Inhibition by decomplementation in vivo

In this study, demethylchlortetracycline was used as a prototype of exogenous phototoxic substances. In vitro, exposure of serum containing demethylchlortetracycline to ultraviolet-A irradiation resulted in the diminution of total complement hemolytic activity and C4, C2, C3, and C5 activities. In addition, chemotactic activity for human polymorphonuclear cells was generated, which was thermostable and antigenically related to human C5 but not human C3. In vivo, phototoxic lesions were induced in guinea pigs upon intradermal injections of demethylchlortetracycline solution, followed by ultraviolet-A irradiation. On a scale of 0-3+, the animals developed a maximal response of 2.5 at 20 h. This clinical response was associated with cellular infiltrate in the dermis, consisting of 29 +/- 2% of neutrophils at 24 h. The participation of the polymorphonuclear cells was evaluated in guinea pigs rendered neutropenic by treatment with cyclophosphamide. In these guinea pigs, demethylchlortetracycline and ultraviolet-A induced a maximal response of 0.75 +/- 0.5, which was associated histologically with 1.2 +/- 0.5% neutrophils in the dermis. The role of complement in this process was studied in guinea pigs congenitally deficient in C4, and in guinea pigs decomplemented by treatment with cobra venom factor. In contrast to normal guinea pigs, C4-deficient animals exhibited a maximal reaction of 0.83 +/- 0.16 at 6 h, which subsided within 24 h. Cobra venom factor-treated guinea pigs developed a maximal response of 0.5 at 0.5 and at 6 h. These clinical changes were associated with the development of an increased vascular permeability, as demonstrated by studies using guinea pigs injected intravenously with Evans blue solution. In animals with a normal complement system, there was intense localized bluing at the sites of phototoxic lesion. In contrast, only minimal bluing was observed in decomplemented guinea pigs. These data indicate that a normal number of polymorphonuclear cells and an intact complement system are required for the full development of demethylchlortetracycline-induced phototoxic lesions.

A correlation analysis between bone formation rate and bioelectric potentials in rabbit tibia

The origin of the bioelectric potentials in unstressed living bones is still an open question. Blood-flow in vessels, stationary potentials on peripheral nerves, muscle injury potentials, and viability of bone cells are claimed to be possible sites of origin of the electric potentials recorded on bone surface. The present data show that the topographic quantitative distribution of tetracycline labeling at sequential levels of rabbit tibia and the distribution pattern of the bioelectric potentials in this bone are significantly superimposable. This coincidence of bone formation rates and bioelectric potentials seems to support the view that the latter are in some way linked with the laying down of new bone.

Effect of spaceflight on periosteal bone formation in rats

Male Wistar rats were placed in orbit for 18.5 days aboard the Soviet COSMOS 1129 biological satellite. Tetracycline was administered before and after spaceflight to label areas of bone formation. An inhibition of periosteal bone formation occurred during spaceflight in the tibial and humeral diaphyses, but this defect was corrected during the postflight period. The increased extent of arrest lines at these skeletal sites suggested that periosteal bone formation may have even ceased during spaceflight. The rib exhibited a small but nonsignificant decrease in periosteal bone formation. Endosteal bone resorption was not affected markedly by spaceflight conditions. The observed inhibition of periosteal bone formation may be a result of mechanical unloading, but endocrine factors cannot be ruled out.

Effects on intact femora of dogs of the application and removal of metal plates. A metabolic and structural study comparing stiffer and more flexible plates

Studies of flexible plates made of plastic have shown that less osteoporosis develops beneath them than beneath rigid metal plates. However, to date plastic plates of appropriate physical properties and biocompatibility are not available for use in humans. To determine if a similar beneficial effect could be obtained using metal plates, the effects of thick chromium cobalt plates were contrasted in experiments in dogs with the effects of thinner plates of similar design made of titanium, 6-aluminum, 4-vandium. A significant reduction in the osteoporosis was obtained by use of the more flexible plates. Following plate application a delayed, massive, transient stimulus to bone formation occurred endosteally, periosteally, and intracortically. Despite this, a substantial decrease in bone mass occurred, primarily mediated by endosteal bone resorption. Intracortical porosity played little or no role in net bone loss. The major effects subsided by six months. Recovery after plate removal was predominantly the result of endosteal new-bone formation.

Mandibular condylectomy in the guinea pig: quantitative triple fluorochrome study

Different-colored fluorochromes were administered sequentially to guinea pigs and the rate of bone formation measured in their condylectomized control contralateral hemimandibles. The values for labeled bone for condylectomized hemimandibles were lower than for the control contralateral hemimandibles of the same guinea pig. The differences in values of condylectomized and control contralateral sides for DCTC- and total surface area-labeled bone were statistically significant, but were not statistically significant for DCAF- and hematoporphyrin-labeled bone. There was partial regeneration of the condylar process. Although the condylectomized area was nearly normal in shape, its size and proportions were different from those of the contralateral hemimandibles that were not operated on. The greatest differences were noted in the length, height, and the distances measured between the inferior alveolar foramen and the mental foramen and the posterior border of the condyle.

Determination of growth rates by tetracycline labeling in young guinea pig mandibles

Tetracycline-labeled regions of undecalcified sections of the mandibles of 22 young male guinea pigs were measured with a planimeter to assess bone-forming activity. There were statistically significant age-associated differences and differential growth in various regions.

Aspects of the epimerization of certain tetracycline derivatives

The epimerization of several tetracycline derivatives was examined at several pH values using varying conditions of temperature and buffer strength. Rate coefficients for the epimerization of tetracycline and demethylchlortetracycline are reported and factors associated with the epimerization of chlortetracycline and oxytetracycline are discussed. Under the conditions used calcium had no effect on the rate of epimerization and copper promoted degradation other than epimerization.