L: -carnitine fumarate and isovaleryl-L: -carnitine fumarate accelerate the recovery of bone volume/total volume ratio after experimetally induced osteoporosis in pregnant mice

Anabolic skeletal agents have recently broadened the therapeutic options for osteoporosis by directly stimulating bone formation and improving bone turnover, bone density, bone size, and bone microarchitecture. We recently demonstrated that two new L: -carnitine derivatives, L: -carnitine fumarate (LC) and isovaleryl-L: -carnitine fumarate (Iso-V-LC), stimulated osteoblast proliferation and differentiation. We here investigated, by histomorphometry in a mouse model of osteoporosis, the impact of these compounds on the repair of trabecular bone and the osteoblast involvement in this process. Fifty-nine inbred adult female CD1 mice in pregnancy were assigned to four treatment groups: (1) controls, mice fed a standard normocalcemic pre- and postpartal diet; (2) Hypo, mice fed a low-calcium isocaloric prepartal diet and a standard postpartal diet; (3) LC, mice fed a group 2-type diet supplemented post-partum with LC; (4) Iso-V-LC, mice fed a group 2-type diet supplemented post-partum with Iso-V-LC. Bone volume/total volume ratio (BV/TV), bone perimeter, osteoblast surface/bone surface, and osteoblast number/bone surface were measured from sections of L3 and L4 vertebral bodies obtained from animals killed on the day of delivery (controls and Hypo) and on days 7, 14, and 21 after delivery (all groups). BV/TV and all osteoblast-based indexes were significantly higher in LC and Iso-V-LC than in Hypo mice at each time point, and Iso-V-LC at the end of the treatment attained levels observed in controls. In conclusion, Iso-V-LC and, to a lesser extent, LC accelerated the recovery of normal BV/TV level after a hypocalcemic diet.

Respiratory complex I in brain development and genetic disease

A study is presented on the expression and activity of complex I, as well as of other complexes of the respiratory chain, in the course of brain development and inherited encephalopathies. Investigations on mouse hippocampal cells show that differentiation of these cells both in vivo and in cell cultures is associated with the expression of a functional complex I, whose activity markedly increases with respect to that of complexes III and IV. Data are presented on genetic defects of complex I in six children with inborn encephalopathy associated with isolated deficiency of the complex. Mutations have been identified in nuclear and mitochondrial genes coding for subunits of the complex. Different mutations were found in the nuclear NDUFS4 gene coding for the 18 kD (IP, AQDQ) subunit of complex I. All the NDUFS4 mutations resulted in impairment of the assembly of a functional complex. The observations presented provide evidence showing a critical role of complex I in differentiation and functional activity of brain cells.

Pathological mutations of the human NDUFS4 gene of the 18-kDa (AQDQ) subunit of complex I affect the expression of the protein and the assembly and function of the complex

Presented is a study of the impact on the structure and function of human complex I of three different homozygous mutations in the NDUFS4 gene coding for the 18-kDa subunit of respiratory complex I, inherited by autosomal recessive mode in three children affected by a fatal neurological Leigh-like syndrome. The mutations consisted, respectively, of a AAGTC duplication at position 466-470 of the coding sequence, a single base deletion at position 289/290, and a G44A nonsense mutation in the first exon of the gene. All three mutations were found to be associated with a defect of the assembly of a functional complex in the inner mitochondrial membrane. In all the mutations, in addition to destruction of the carboxyl-terminal segment of the 18-kDa subunit, the amino-terminal segment of the protein was also missing. In the mutation that was expected to produce a truncated subunit, the disappearance of the protein was associated with an almost complete disappearance of the NDUFS4 transcript. These observations show the essential role of the NDUFS4 gene in the structure and function of complex I and give insight into the pathogenic mechanism of NDUFS4 gene mutations in a severe defect of complex I.

Expression and subcellular distribution of Bcl-2 and BAX proteins in serum-starved human keratinocytes and mouth carcinoma epidermoid cultures

Squamous cell carcinoma (SSC) is the most frequent malignant tumor of the oral cavity. Aberration of programmed cell death is thought to participate in cancer. Using specific antibodies a study of the expression and subcellular distribution of Bcl-2, BAX, caspase-3 and cytochrome c in normal human keratinocytes and mouth carcinoma slowly (HN) and rapidly growing (KB) cells has been carried out. In carcinoma cells depressed expression of BAX, presence in the cytosol of procaspase-3 and absence in this fraction of cytochrome c have been found. PGE2 treatment prevented cell growth depression induced by pro-apoptotic serum starvation both in control and carcinoma cell cultures. It is also shown that PGE2 promoted both in keratinocytes and KB cells expression of Bcl-2, which was accompanied in the first case by increase in its mitochondrial level. These results indicate that in carcinoma cells there is an apparent down regulation of the apoptotic cascade as compared to normal keratinocytes. Thus the possibility that down regulation of apoptosis is associated with promotion of tumor development in the oral mucosa cells seems to be supported by these observations.

The NADH: ubiquinone oxidoreductase (complex I) of the mammalian respiratory chain and the cAMP cascade

Recent work has revealed cAMP-dependent phosphorylation of the 18-kDa IP subunit of the mammalian complex I of the respiratory chain, encoded by the nuclear NDUFS4 gene (chromosome 5). Phosphorylation of this protein has been shown to take place in fibroblast cultures in vivo, as well as in isolated mitochondria, which in addition to the cytosol also contain, in the inner-membrane matrix fraction, a cAMP-dependent protein kinase. Mitochondria appear to have a Ca2+-inhibited phosphatase, which dephosphorylates the 18-kDa phosphoprotein. In fibroblast and myoblast cultures cAMP-dependent phosphorylation of the 18-kDa protein is associated with potent stimulation of complex I and overall respiratory activity with NAD-linked substrates. Mutations in the human NDUFS4 gene have been found, which in the homozygous state are associated with deficiency of complex I and fatal neurological syndrome. In one case consisting of a 5 bp duplication, which destroyed the phosphorylation site, cAMP-dependent activation of complex I was abolished in the patient's fibroblast cultures. In another case consisting of a nonsense mutation, leading to termination of the protein after only 14 residues of the putative mitochondria targeting peptide, a defect in the assembly of complex I was found in fibroblast cultures.

Complex I and the cAMP cascade in human physiopathology

A cAMP-dependent protein kinase (PKA) is localized in mammalian mitochondria with the catalytic site at the matrix side of the membrane where it phosphorylates a number of proteins. One of these is the 18 kDa(IP) subunit of the mammalian complex I of the respiratory chain, encoded by the nuclear NDUFS4 gene. Mitochondria have a Ca(2+)-inhibited phosphatase, which dephosphorylates the 18 kDa phosphoprotein of complex I. In fibroblast and myoblast cultures cAMP-dependent phosphorylation of the 18 kDa protein is associated with stimulation of complex I and overall respiratory activity with NAD-linked substrates. Mutations in the human NDUFS4 gene have been found, which in the homozygous state are associated with deficiency of complex I and fatal neurological syndrome.

A nonsense mutation in the NDUFS4 gene encoding the 18 kDa (AQDQ) subunit of complex I abolishes assembly and activity of the complex in a patient with Leigh-like syndrome

Sequence analysis of mitochondrial and nuclear candidate genes of complex I in children with deficiency of this complex and exhibiting Leigh-like syndrome has revealed, in one of them, a novel mutation in the NDUFS4 gene encoding the 18 kDa subunit. Phosphorylation of this subunit by cAMP-dependent protein kinase has previously been found to activate the complex. The present mutation consists of a homozygous G-->A transition at nucleotide position +44 of the coding sequence of the gene, resulting in the change of a tryptophan codon to a stop codon. Such mutation causes premature termination of the protein after only 14 amino acids of the putative mitochondrial targeting peptide. Fibroblast cultures from the patient exhibited severe reduction of the rotenone-sensitive NADH-->UQ oxidoreductase activity of complex I, which was insensitive to cAMP stimulation. Two-dimensional electrophoresis showed the absence of detectable normally assembled complex I in the inner mitochondrial membrane. These findings show that the expression of the NDUFS4 gene is essential for the assembly of a functional complex I.

Mutation in the NDUFS4 gene of complex I abolishes cAMP-dependent activation of the complex in a child with fatal neurological syndrome

Evidence is presented showing that in a patient with fatal neurological syndrome, the homozygous 5 bp duplication in the cDNA of the NDUFS4 18 kDa subunit of complex I abolishes cAMP-dependent phosphorylation of this protein and activation of the complex. These findings show for the first time that human complex I is regulated via phosphorylation of the subunit encoded by the NDUFS4 gene.

Comparison of oxidative phosphorylation in the anastomosis of the small and large bowel. An experimental study in the rabbit

Dehiscence of anastomosis in the large bowel (LB) is more frequent compared with that in the small bowel (SB). The pathophysiological mechanisms underlying the phenomenon are well known. The goal of this study is to demonstrate the different oxidative phosphorylation roles in the response of the anastomosed SB and LB. In 45 male rabbits under general anaesthesia, the ileum and colon were transected always on the same side and an end-to-end anastomosis was constructed using single-layer inverting interrupted 5-0 Ethilon sutures. Tracts containing bowel anastomoses were collected at 3, 12 and 24 h and 3, 7 and 21 days after the operation and compared with non-anastomosed bowel. Respiratory rates with different substrates, enzymatic activities, respiratory complex structures and cytochrome contents were measured in smooth muscle purified mitochondria. Mitochondrial respiration showed significant differences in the LB versus anastomosed SB: respiratory rates were markedly reduced in the LB (residual activity: 25 vs. 95% of the SB). Detailed analysis of other mitochondrial parameters confirmed a better tolerance of the ileum to anastomosis. From these preliminary studies we can consider two different aerobic thresholds for either the large or the small rabbit intestine, the latter being oxygen dependent. This can explain the mitochondrial sufferance of anastomosis in the LB whose prevalent aerobic metabolism can be more easily affected by different noxae if compared with the tendency to glycolytic metabolism of the small intestine.

cAMP-dependent phosphorylation of the nuclear encoded 18-kDa (IP) subunit of respiratory complex I and activation of the complex in serum-starved mouse fibroblast cultures

A study is presented on the in vivo effect of elevated cAMP levels induced by cholera toxin on the phosphorylation of subunits of the mitochondrial respiratory complexes and their activities in Balb/c 3T3 mouse fibroblast cultures. Treatment of serum-starved fibroblasts with cholera toxin promoted serine phosphorylation in the 18-kDa subunit of complex I. Phosphorylation of the 18-kDa subunit, in response to cholera toxin treatment of fibroblasts, was accompanied by a 2-3-fold enhancement of the rotenone-sensitive endogenous respiration of fibroblasts, of the rotenone-sensitive NADH oxidase, and of the NADH:ubiquinone oxidoreductase activity of complex I. Direct exposure of fibroblasts to dibutyryl cAMP resulted in an equally potent stimulation of the NADH:ubiquinone oxidoreductase activity. Stimulation of complex I activity and respiration with NAD-linked substrates were also observed upon short incubation of isolated fibroblast mitoplasts with dibutyryl cAMP and ATP, which also promoted phosphorylation of the 18-kDa subunit. These observations document an extension of cAMP-mediated intracellular signal transduction to the regulation of cellular respiration.

Respiratory activity and growth of human skin derma fibroblasts

A study has been made on the speed of growth and respiratory activity of fibroblast cultures from control derma, cheloid (hypertrophic) scar and stabilized scar taken from human skin. The speed of growth and the efficiency of plaque formation of fibroblasts from cheloid scar were greater in comparison with those of fibroblasts from stabilized scar and were stimulated by the addition to the culture medium of the exudate from post-traumatic ulcer. Measurement of the contents of cytochromes showed a decrease in the content of cytochromes b562 and c + c1 in the fibroblast culture from both cheloid and stabilized scar as compared to the fibroblast culture from control derma. Cytochrome aa3 content did not show significant difference among the three types of fibroblast cultures. The respiratory activities supported by pyruvate plus malate, succinate or ascorbate plus N,N,N',N'-tetramethyl-p-phenylenediamine did not show, however, significant difference among the three fibroblast cultures. These observations show that the speed of growth of skin fibroblasts does not depend on the overall respiratory capacity. The exudate stimulated the activity of cytochrome c oxidase in fibroblasts from control derma, and cheloid scar. This effect and the accompanying stimulation of fibroblast growth might be correlated with the balance of oxygen free radicals.

Ageing is associated in females with a decline in the content and activity on the b-c1 complex in skeletal muscle mitochondria

The activity of cytochrome-c oxidase [E.C. 1.9.3.1] and b-c1 complex [E.C. 1.10.2.2] and the content of cytochromes b, c + c1 and a + a3 in human skeletal muscle mitochondria from orthopaedic patients (108 women and 68 males), of age ranging between 10 and 50 years, have been analyzed. The activity of cytochrome c-oxidase declines with age both in females and males. The activity of b-c1 complex, which in young females is significantly higher than in young males, declines sharply in females, but not in males, with ageing. These results reveal that the content of active b-c1 complex in muscle mitochondria is specifically controlled by female sex hormones.

Decline with age of the respiratory chain activity in human skeletal muscle

Mitochondrial respiratory systems have been screened in 63 orthopaedic patients of age ranging between 17 and 91 years. The results show a statistically significant definite decrease with ageing of mitochondrial respiratory activity with pyruvate plus malate, succinate and ascorbate plus TMPD. This pattern is associated with an equally significant decrease with age of the enzymatic activity of complex I, II and IV. No significant decrease with age is, on the contrary, observed in the mitochondrial content of cytochromes a+a3, and c+c1. Preliminary Western blot analysis indicates an altered polypeptide pattern in cytochrome c oxidase. This study provides evidence for a decline with age of mitochondrial respiratory activity in human skeletal muscle, affecting complex I, II and IV.