Relevance of laser irradiance threshold in the induction of alkaline phosphatase in human osteoblast cultures.

Induction of matrix synthesis by low-level laser has been demonstrated extensively. However, the question of dose- or power intensity-dependency is under-investigated. To address this issue we chose human osteoblast cell cultures and measured their alkaline phosphatase (ALP) activity after laser irradiation. The cell cultures were irradiated periodically by 690 nm radiation via optical transmission fiber-based laser needles, reaching into the culture dishes. The osteoblasts showed no induction of ALP activity when we used a single laser needle stimulation with a laser irradiance of 51 mW/cm(2), an increase of approximately 43% at 102 mW/cm(2) irradiance (two needles per well) and a ninefold increase at 204 mW/cm(2) irradiance (four needles per well), leaving the temperature of the culture medium unaffected. We concluded that the osteoblastic response in ALP activity to a laser stimulus shows a logarithmic relationship, with a distinct threshold, rather than a linear dose-dependency. Secondly, the laser irradiance, rather than the dose, is relevant for the impact of the laser.

Diabetic nephropathy and anaemia.

Anaemia is a frequent complication of diabetic nephropathy. It has only recently been recognised that in diabetic patients anaemia is seen not only in preterminal renal failure, but also frequently in patients with only minor derangement of renal function. At any level of glomerular filtration rate (GFR) anaemia is more frequent and severe in diabetic compared to nondiabetic patients. A major cause of anaemia is an inappropriate response of erythropoietin to anaemia. Additional factors are iron deficiency and iatrogenic factors, e.g. ACE inhibitor treatment. When serum creatinine is still normal, the erythropoietin concentration is predictive of more rapid loss of glomerular function. When serum creatinine is elevated, the haemoglobin values are predictive of the rate of progression. It is currently under investigation whether reversal of anaemia attenuates the rate of progression. Because most of the late complications of diabetes (retinopathy, neuropathy, heart disease, peripheral arterial disease) involve ischaemic tissue damage, it would be intuitively plausible that treatment with human recombinant erythropoietin should be beneficial, but definite evidence for this hypothesis is currently not available.

Effects of all-trans retinoic acid on renin-angiotensin system in rats with experimental nephritis.

We previously demonstrated that all-trans retinoic acid (RA) preserves glomerular structure and function in anti-Thy1.1 nephritis (Wagner J, Dechow C, Morath C, Lehrke I, Amann K, Floege J, and Ritz E. J Am Soc Nephrol 11: 1479-1489, 2000). Because the renin-angiotensin system (RAS) contributes to renal damage, we 1) studied retinoid-specific effects on its components and 2) compared the effects of all-trans-RA with those of the AT(1)-receptor blocker candesartan. Rats were pretreated for 3 days before injection of the OX-7 antibody and continued with treatment with either vehicle or daily injections of 10 mg/kg all-trans-RA only (study 1) or 10 mg/kg body wt all-trans-RA, 1 mg/kg candesartan, or both (study 2) for an additional 7 days. The blood pressure increase observed in anti-Thy1.1 nephritic rats was equally normalized by all-trans-RA and candesartan (P < 0.05). In nephritic rats, mRNAs of angiotensinogen and angiotensin-converting enzyme (ACE) in the kidney were unchanged, but renin mRNA was lower (P < 0.01). Renal and glomerular AT(1)-receptor gene and protein expression levels were higher in anti-Thy1.1 nephritic rats (P < 0.05). In the renal cortex of nephritic rats, pretreatment with all-trans-RA significantly reduced mRNAs of all the examined RAS components, but in the glomeruli it increased ACE gene and protein expression (P < 0.01). In nephritic rats, candesartan reduced the number of glomerular cells and mitoses (P < 0.05) less efficiently than all-trans-RA (P < 0.01). Both substances reduced cellular proliferation (proliferating cell nuclear antigen) significantly (P < 0.05). No additive effects were noted when both compounds were combined. In conclusion, all-trans-RA influences the renal RAS in anti-Thy1.1 nephritis by decreasing ANG II synthesis and receptor expression. The beneficial effect of retinoids may be explained, at least in part, by reduction of RAS activity.

Retinoids inhibit the actions of angiotensin II on vascular smooth muscle cells.

Retinoids are derivatives of vitamin A and powerful inhibitors of cell proliferation and inflammation. Angiotensin II (Ang II) contributes to vascular lesions by promoting cell growth of vascular smooth muscle cells (VSMCs). Therefore, we examined whether retinoids interfere with the proproliferative actions of Ang II in VSMCs via AT(1) receptor-dependent or activator protein-1 (AP-1)-dependent mechanisms. VSMCs express retinoid receptor proteins, ie, retinoic acid receptor (RAR) alpha and retinoid X receptor (RXR) alpha. Long-term exposure to 1 micromol/L all-trans retinoic acid (RA) dose-dependently inhibited Ang II-induced cell proliferation (P<0.005) as well as DNA and protein synthesis (P<0.001). All-trans RA blocked Ang II stimulation of transforming growth factor-beta(1) mRNA (P<0.005). All-trans RA inhibition of vascular VSMC growth was mediated both via RAR- and RXR-dependent pathways, as shown by receptor-specific synthetic retinoids. Transfection experiments revealed that inhibition of AP-1-dependent gene transcription is one mechanism by which all-trans RA inhibits Ang II action. RARalpha cotransfection enhanced the anti-AP-1 effects of all-trans RA dose-dependently. AP-1 activity was similarly inhibited by cotransfection with either RARalpha or RXRalpha. Ang II-induced gene expression of c-fos was abrogated by all-trans RA treatment (P<0.005). In VSMCs, all-trans RA downregulated AT(1) receptor mRNA (P<0.01) and reduced B(max) (P<0.001). All-trans RA repressed Ang II-stimulated AT(1) receptor promoter activity. The all-trans RA inhibitory effect was abolished when the AP-1 consensus site on the AT(1) receptor promoter was deleted. Our findings demonstrate that retinoids are potent inhibitors of the actions of Ang II on VSMCs. The findings support the notion that retinoids may interfere with proliferative vascular disease.