LONG-TERM EFFECTS OF MORPHINE ON MESANGIAL CELL-PROLIFERATION AND MATRIX SYNTHESIS

Since focal glomerulosclerosis is the predominant glomerular lesion in heroin nephropathy and since mesangial expansion is considered to be a precursor of glomerulosclerosis, we have evaluated the effect of opiates on mesangial cell (MC) proliferation and matrix synthesis. We showed, using a fluorometric assay, that MC are not capable of metabolizing heroin to its active metabolite morphine. Cells exposed to morphine (10(-5) M or 10(-4) M) in prolonged cultures either continuously (Group A) or intermittently (Group B) showed enhanced incorporation of [H-3]thymidine when compared to control cells (control, 88600 +/- 26303 cpm/well vs. morphine 10(-4) M -Group A, 321203 +/- 52867, P < 0.001; control vs. morphine 10(-4) M-Group B, 223126 +/- 46866 cpm/well, P < 0.01; control, 107593 +/- 42284 cpm/well vs. morphine 10(-5) M - Group A, 267108 +/- 41866 cpm/well, P < 0.001; control vs. morphine 10(-5) M - Group B, 202317 +/- 24325 cpm/well, P < 0.05). However, MC incubated with a lower concentration of morphine (10(-6) M) enhanced DNA synthesis when exposed intermittently only (control, 107593 +/- 42284 cpm/well vs. Group B, 219164 +/- 15552 cpm/well, P < 0.05). This growth stimulating effect of morphine (10(-6) M and 10(-5) M) was also observed at earlier time points, that is, one- and one-and-a-half-week old cultures. However, in one-week-old cultures, morphine in a higher concentration (10(-4) M) showed a suppressive effect (P < 0.05) on MC proliferation (morphine, 3620 +/- 220 cpm/well vs. control, 4668 +/- 410 cpm/well). This effect not only subsided by one and a half weeks but morphine (10(-4) M) treated cells enhanced MC proliferation. An opioid antagonist, naloxone attenuated the effect of morphine in one and half week old cultures. Morphine at 10(-6) M to 10(-4) M concentrations enhanced incorporation of [H-3]proline in the extracellular proline pool (a component of mesangial matrix) when compared to control (control, 309661 +/- 3992 vs. morphine 10(-4) M, 363104 +/- 10539 cpm/well, P < 0.05 or morphine 10(-5) M, 397954 +/- 31008 cpm/well, P < 0.001 or morphine 10(-6) M, 384630 +/- 26369 cpm/well, P < 0.01). In addition, MC incubated with morphine (10(-6) M and 10(-4) M) also enhanced (P < 0.001) synthesis of laminin. MC incubated with morphine (10(-5) M or 10(-4), 12 weeks) had a greater number of hillocks (foci of cell proliferation and aggregated matrix) when compared with untreated cells. Morphine treated MC synthesized a decreased amount of PGE2 (129 +/- 48 pg/mg protein, P < 0.02) when compared to PGE2 production by untreated cells (493 +/- 123 pg/mg protein). Morphine pretreated MC when stimulated with arginine vasopressin (AVP, 10(-6) M) also produced a lesser amount of PGE2 (214 +/- 51 pg/mg protein, P < 0.05) when compared to PGE2 production by control cells under stimulation with AVP (1393 +/- 451 pg/mg protein). Our results suggest that morphine may be playing a direct role in mesangial expansion in opiate addicts.