Effects of inorganic lead in vitro on ion exchanges and respiratory metabolism of rat kidney cortex

Mitochondrial Oxidative Stress Is the General Reason for Apoptosis Induced by Different-Valence Heavy Metals in Cells and Mitochondria

This review analyzes the causes and consequences of apoptosis resulting from oxidative stress that occurs in mitochondria and cells exposed to the toxic effects of different-valence heavy metals (Ag+, Tl+, Hg2+, Cd2+, Pb2+, Al3+, Ga3+, In3+, As3+, Sb3+, Cr6+, and U6+). The problems of the relationship between the integration of these toxic metals into molecular mechanisms with the subsequent development of pathophysiological processes and the appearance of diseases caused by the accumulation of these metals in the body are also addressed in this review. Such apoptosis is characterized by a reduction in cell viability, the activation of caspase-3 and caspase-9, the expression of pro-apoptotic genes (Bax and Bcl-2), and the activation of protein kinases (ERK, JNK, p53, and p38) by mitogens. Moreover, the oxidative stress manifests as the mitochondrial permeability transition pore (MPTP) opening, mitochondrial swelling, an increase in the production of reactive oxygen species (ROS) and H2O2, lipid peroxidation, cytochrome c release, a decline in the inner mitochondrial membrane potential (ΔΨmito), a decrease in ATP synthesis, and reduced glutathione and oxygen consumption as well as cytoplasm and matrix calcium overload due to Ca2+ release from the endoplasmic reticulum (ER). The apoptosis and respiratory dysfunction induced by these metals are discussed regarding their interaction with cellular and mitochondrial thiol groups and Fe2+ metabolism disturbance. Similarities and differences in the toxic effects of Tl+ from those of other heavy metals under review are discussed. Similarities may be due to the increase in the cytoplasmic calcium concentration induced by Tl+ and these metals. One difference discussed is the failure to decrease Tl+ toxicity through metallothionein-dependent mechanisms. Another difference could be the decrease in reduced glutathione in the matrix due to the reversible oxidation of Tl+ to Tl3+ near the centers of ROS generation in the respiratory chain. The latter may explain why thallium toxicity to humans turned out to be higher than the toxicity of mercury, lead, cadmium, copper, and zinc.

Effect of dietary protein on glomerular renin secretion

Previous studies from our and other laboratories demonstrated that dietary protein restriction lowers plasma renin activity by impairing renin release. The effect of protein intake on glomerular renin secretion has not been investigated. Accordingly, we studied male Sprague-Dawley rats weighing 180 to 200 g for 3 weeks that were receiving isocaloric diets that provided either standard 20% protein (SP) or low 6% protein (LP). Renin secretion was measured in the glomeruli isolated from these rats, at baseline and following stimulation with arachidonic acid and isoproterenol. The activity of plasma renin (3.0 +/- 0.5 ng/mL/min on SP v 1.1 +/- 0.1 ng/mL/min on LP) was significantly (P < 0.02) lower on LP intake. In contrast, glomerular renin content (22.9 +/- 0.7 ng/micrograms protein on SP v 32.3 +/- 1.4 ng/micrograms protein on LP) was significantly (P < 0.01) higher on the LP diet. Furthermore, renin secretion (ng/mL/h) from the isolated glomeruli at baseline (3.9 +/- 1.0 on SP v 12.5 +/- 3.0 on LP, P < 0.02), and following incubation with arachidonic acid 10(-5) mol/L (5.9 +/- 1.7 on SP v 19.6 +/- 3.1 on LP, P < 0.005), and isoproterenol 10(-3) mol/L (6.0 +/- 0.5 on SP v 17.3 +/- 3.3 on LP, P < 0.01) was significantly higher on the LP diet. These studies suggest that dietary protein restriction impairs in vivo renin release. In contrast, in vitro glomerular renin release is augmented by protein restriction. The factors modulating in vivo renin release require further characterization.